Review on effect of different type of dyes on advanced oxidation processes (AOPs) for textile color removal

A Review of Plant-Mediated ZnO Nanoparticles for Photodegradation and Antibacterial Applications

This review focuses on the synthesis of plant-mediated zinc oxide nanoparticles (ZnO NPs) and their applications for antibacterial and photocatalytic degradation of dyes, thereby addressing the need for sustainable and eco-friendly methods for the preparation of NPs. Driven by the significant rise in antibiotic resistance and environmental pollution from dye pollution, there is a need for more effective antibacterial agents and photocatalysts. Therefore, this review explores the synthesis of plant-mediated ZnO NPs, and the influence of reaction parameters such as pH, annealing temperature, plant extract concentration, etc. Additionally, it also looks at the application of plant-mediated ZnO NPs for antibacterial and photodegradation of dyes, focusing on the influence of the properties of the plant-mediated ZnO NPs such as size, shape, and bandgap on the antibacterial and photocatalytic activity. The findings suggest that properties such as shape and size are influenced by reaction parameters and these properties also influence the antibacterial and photocatalytic activity of plant-mediated ZnO NPs. This review concludes that plant-mediated ZnO NPs have the potential to advance green and sustainable materials in antibacterial and photocatalysis applications.

Critical review on electrooxidation and chemical reduction of azo dyes: Economic approach

Effective degradation technologies have been extensively investigated and used to remove azo dyes from wastewater for decades. However, no review dealing with both electrooxidation and chemical reduction of azo dyes from an economic and, therefore, application-relevant perspective has been found in the current literature. A novelty of this review article consists not only in the brief summarization and comparison of both methods but mainly in the evaluation of their economic side. Based on the literature survey of the last 15 years, the costs of treatment approaches published in individual research articles have been summarized, and the missing data have been calculated. A broad spectrum of advanced electrode materials and catalysts have been developed and tested for the treatment, specifically aiming to enhance the degradation performance. An outline of the global prices of electrode materials, reducing agents, and basic chemicals is involved. All additional costs are described in depth in this review. The advantages and disadvantages of respective methods are discussed. It was revealed that effective and cheap treatment approaches can be found even in advanced degradation methods. Based on the collected data, electrooxidation methods offer, on average, 30 times cheaper treatment of aqueous solutions. Concerning chemical reduction, only ZVI provided high removal of azo dyes at prices <100 $ per kg of azo dye. The factors affecting total prices should also be considered. Therefore, the basic diagram of the decision-making process is proposed. In the conclusion, challenges, future perspectives, and critical findings are described.

Polydopamine coating for enhanced electrostatic adsorption of methylene blue by multiwalled carbon nanotubes in alkaline environments

The removal of dye molecules in alkaline environments is an issue that should receive increased attention. In this study, the interaction mechanism between polydopamine-modified multiwalled carbon nanotubes (P-MWCNTs) and multiwalled carbon nanotubes (MWCNTs) with the cationic dye methylene blue (MB) in alkaline environments was explained in depth by adsorption, spectroscopy, and density functional theory (DFT). The mechanism of action and dominant forces between the adsorbent and adsorbate were analyzed graphically by introducing energy decomposition analysis (EDA) and an independent gradient model (IGM) into the DFT calculations. In addition, the force distribution was investigated through an isosurface. Moreover, batch adsorption studies were conducted to evaluate the performance of MWCNTs and P-MWCNTs for MB removal in alkaline environments. The maximum MB adsorption capacities of the MWCNTs and P-MWCNTs in solution were 113.3 mg‧g-1 and 230.4 mg‧g-1, respectively, at pH 9. The IGM and EDA showed that the better adsorption capacity of the P-MWCNTs originated from the enhancement of the electrostatic effect by the proton dissociation of polydopamine. Moreover, the adsorption of MB by MWCNTs and P-MWCNTs in alkaline environments was governed by dispersion and electrostatic effects, respectively. Through this study, it is hoped that progress will be made in the use of DFT to explore the mechanism of adsorbent-adsorbate interactions.

Facile synthesis of double-cross-linked alginate-based hydrogel: Characterization and use in a context of circular economy for cationic dye removal

Hydrogels based on natural polysaccharides have received special attention in the last decade due to their interesting features, such as availability, biocompatibility, biodegradability and safety. Such characteristics may make them sustainable and eco-friendly materials for water and wastewater treatment, meeting the concept of circular economy. In this study, a novel double-cross-linked alginate-based hydrogel has been successfully synthesized using epichlorhydrin and sodium trimetaphosphate (STMP) as cross-linker agents and then used for the removal of methylene blue (MB) dye under different operating conditions. The obtained hydrogel was deeply characterized by using various analytical techniques, namely Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and differential scanning calorimetry. Experimental results showed that the synthesized double cross-linked hydrogel with relatively high STMP concentration (0.26 M) has promising structural and textural properties. This material exhibited excellent removal ability towards MB with a maximum adsorption capacity of about 992 mg/g for an initial pH of 10. The kinetic and isotherm modeling study revealed that the pseudo-second-order and Freundlich models fitted well the measured adsorption experimental data. The MB adsorption process onto the synthesized hydrogel is exothermic, feasible and spontaneous. It mainly includes electrostatic interaction and hydrogen bonds. These findings suggest that double-cross-linked alginate-based hydrogel can be considered as an attractive and potential adsorbent for an effective cationic dye removal from aqueous environments. The use of such a green adsorbent for the treatment of organic-pollutants-rich industrial wastewaters promotes sustainability and circular economy concepts.

Synthesis of magnetic biochar composite using Vateria indica fruits through in-situ one-pot hydro-carbonization for Fenton-like catalytic dye degradation

The present study reports the synthesis, characterization, and application of sustainable magnetic biochar composite. The inedible fruits of Vateria indica, a powerful ayurvedic plant were hydrothermally transformed into magnetic biochar (BC-Fe3O4) in a single step and characterized by several sophisticated techniques. FESEM analysis portrayed fibrous irregular mesh-like biochar with surface clustered Fe3O4 nanoparticles, while the incidence of carbon, oxygen, and iron in the elemental analysis by EDS established magnetic biochar formation. Numerous peaks consistent with planes of (220), (311), (400), (422), (511), (440), and (120) also substantiated the occurrence of magnetite nanoparticles and biochar respectively, as analyzed by XRD. XPS analysis showed signals at 285.65 eV, 533.28 eV, 711.08 eV, and 724.68 eV corroborating a strong C-O bond, O1s orbit, Fe2+, and Fe3+ respectively. BC-Fe3O4 was superparamagnetic with saturation magnetization of 4.74 emu/g, as per VSM studies, while its specific surface area, pore volume, and pore diameter were 5.74 m2/g, 0.029 cm3/g, and 20.86 nm respectively. The Fenton-like degradation of methylene blue (5.0-25.0 ppm) was accomplished by synthesized BC-Fe3O4, in the presence of H2O2. Within 180 min, almost complete degradation was achieved, with first-order kinetics having rate constants between 0.0299 and 0.0167 min-1. Stability and recyclability studies performed over 7 cycles exhibited unaltered degradation between 93.98 and 97.59%. This study exhibits the exceptional characteristics and degradation capabilities of BC-Fe3O4 synthesized from a sustainable plant biomass.

Supercritical fluid technology as a sustainable alternative method for textile dyeing: An approach on waste, energy, and CO2 emission reduction

The clothing industry is considered one of the most polluting industries on the planet due to the high consumption of water, energy, chemicals/dyes, and high generation of solid waste and effluents. Faced with environmental concerns, the textile ennoblement sector is the most critical of the textile production chain, especially the traditional dyeing processes. As an alternative to current problems, dyeing with supercritical CO2 (scCO2) has been presented as a clean and efficient process for a sustainable textile future. Supercritical fluid dyeing (SFD) has shown a growing interest due to its significant impact on environmental preservation and social, economic, and financial gains. The main SFD benefits include economy and reuse of non-adsorbed dyes; reduction of process time and energy expenditure; capture of atmospheric CO2 (greenhouse gas); use and recycling of CO2 in SFD; generation of carbon credits; water-free process; effluent-free process; reduction of CO2 emission and auxiliary chemicals. Despite being still a non-scalable and evolving technology, SFD is the future of dyeing. This review presented a comprehensive overview of the environmental impacts caused by traditional processes and confronted the advantages of SFD. The SFD technique was introduced, along with its latest advances and future perspectives. Financial and environmental gains were also discussed.

Decolorization and degradation of crystal violet dye by electron beam radiation: Performance, degradation pathways, and synergetic effect with peroxymonosulfate

Ionizing radiation (mainly including gamma ray and electron beam) technology provides a more efficient and ecological option for dye-containing wastewater treatment, which is supported by its successful achievements in industrial-scale applications. However, the degradation pathway of triphenylmethane dyes by radiation technology is still unclear. In this study, crystal violet (CV) was selected as representative cationic triphenylmethane dye, the decolorization and degradation performance by electron beam radiation technology was systematically evaluated. The results showed that CV can be efficiently decolorized and mineralized by radiation, and its degradation kinetics followed the first-order kinetic model. The effect of inorganic anions and chelating agents commonly existed in dye-containing wastewater on CV decolorization and total organic carbon (TOC) removal was explored. Quenching experiments, density functional theory (DFT) calculation and high performance liquid chromatography mass spectrometry (HPLC-MS) analysis were employed to reveal CV decolorization and degradation mechanism and pathway, which mainly included N-demethylation, triphenylmethane chromophore cleavage, ring-opening of aromatic products and further oxidation to carboxylic acid, and mineralization to CO2 and H2O. Additionally, electron beam radiation/PMS process was explored to decrease the absorbed dose required for decolorization and degradation, and the synergetic effect of radiation with PMS was elucidated. More importantly, the findings of this study would provide the support for treating actual dyeing wastewater by electron beam radiation technology.

Efficient adsorption of rhodamine B using synthesized Mg-Al hydrotalcite/ sodium carboxymethylcellulose/ sodium alginate hydrogel spheres: Performance and mechanistic analysis

In this study, the sodium dodecyl sulfate intercalated modified magnesium-aluminum hydrotalcite/sodium alginate/sodium carboxymethylcellulose (modified LDHs/SA/CMC) composite gel spheres were synthesized and their efficacies in adsorbing the cationic dye rhodamine B (RhB) from aqueous solutions were evaluated. The effects of adsorption time, pH and temperature on the adsorption of RhB by spheres were investigated. Remarkably, the modified LDHs/SA/CMC gel spheres achieved adsorption equilibrium after 600 min at 25 °C, and the removal rate of RhB at 60 mg/L reached 91.49 % with the maximum adsorption capacity of 59.64 mg/g. The gel spheres maintained over 80 % efficacy across four adsorption cycles. Kinetic and isotherm analyses revealed that the adsorption of RhB conformed to the secondary kinetic model and the Langmuir isotherm, indicating a spontaneous and exothermic nature of the adsorption process. The adsorption mechanisms of modified LDHs/SA/CMC gel spheres on RhB dyes include electrostatic adsorption, hydrogen bonding and hydrophobic interactions. In conclusion, modified LDHs/SA/CMC gel sphere is a green, simple, recyclable and efficient adsorbent, which is expected to be widely used for the treatment of cationic dye wastewater.

Microorganism-mediated bioremediation of dyes from contaminated soil: Mechanisms, recent advances, and future perspectives

Many methods have been proposed for the remediation of dye-contaminated soils, a widespread form of environment pollution. Bioremediation, it is hoped, can combine ecological benefits with efficiency of dye decontamination. We review the types and sources of dye contaminants; their possible effects on plant, animal, and human health; and emerging strategies for microbial bioremediation. Challenges, limitations, recommendations for future research, and prospects for large-scale commercialization of microbial bioremediation are discussed.

Decolorization and degradation of various dyes and dye-containing wastewater treatment by electron beam radiation technology: An overview

The treatment of dye-containing wastewater generated from textile industries is still a challenge, and various technologies, including physical, chemical and biological ones have been used. In recent years, the ionizing radiation (usually including gamma ray generated by radionuclide, such as 60Co and 137Cs, and electron beam generated by electron accelerator) technology has received increasing attention for degrading refractory or toxic organic pollutants in wastewater because of its unique advantages, such as no chemical additives, fast reaction rate, strong degradation capacity, high efficiency, flexibility, controllability. Compared to the conventional wastewater treatment processes, ionizing radiation technology, as a disruptive wastewater treatment technology, is more efficient for the decolorization and degradation of dyes and the treatment of dye-containing wastewater. In this paper, the recent advances in the treatment of dye-containing wastewater by ionizing radiation, in particular by electron beam (EB) radiation were summarized and analyzed, focusing on the decolorization and degradation of various dyes. Firstly, the formation of various reactive species induced by radiation and their interactions with dye molecules, as well as the influencing factors on the removal efficiency of dyes were discussed. Secondly, the researches on the treating dye-containing wastewater by electron beam radiation technology were systematically reviewed. Then, the decolorization and degradation mechanisms by electron beam radiation were further discussed in detail. And the integrated processes that would contribute to the advancement of this technology in practical applications were examined. More importantly, the recent advances of electron beam radiation technology from laboratory to application were reviewed, especially successful operation of dye-containing wastewater treatment facilities in China. And eventually, current challenges, future research directions, and outlooks of electron beam radiation technology were proposed for further advancing this technology for the sustainable development of water resources.

Comparison of Dye Adsorption of Chitosan and Polyethylenimine Modified Bentonite Clays: Optimization, Isotherm, and Kinetic Studies

The aim of this study was to compare the effect of modifying calcium bentonite (Bent-Ca) clay with two cationic polymers, chitosan (Chi) and polyethylenimine (PEI), on the removal of remazol black B (RB-B) dye from an aqueous solution. The samples were characterized by using scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy. The fractional factorial design of 2(6-1) was applied to investigate the effects of pH, temperature, amount of adsorbent, initial dye concentration, contact time, and shaking rate on the adsorption process. To further optimize RB-B removal from an aqueous solution, a Box-Behnken design with three factors and a response surface methodology was used. The optimum conditions were a pH of 3.77, a temperature of 40.45 °C, and an initial RB-B concentration of 77.27 mg L-1 for Bent-Ca-Chi, whereas for Bent-Ca-PEI, the optimum conditions were a pH of 5.53, a temperature of 41.06 °C, and an initial dye concentration of 238.89 mg L-1. To understand the adsorption behavior, the Langmuir and Freundlich isotherms were fitted to the experimental data. It was found that the Langmuir isotherm model matched well with the dye adsorption by Bent-Ca-Chi and Bent-Ca-PEI. The kinetics study was performed using three kinetic models: pseudo-first-order, pseudo-second-order, and intraparticle diffusion models. Among these models, the RB-B dye kinetics were best represented by the pseudo-second-order model equation for the adsorbents.

Decoration of 0D Bi3NbO7 nanoparticles onto 2D BiOIO3 nanosheets as visible-light responsive S-scheme photocatalyst for photo-oxidation of antibiotics in wastewater

In this work, a new S-type hybrid composed of 2D BiOIO3 and 0D Bi3NbO7 was proposed and hybridized by a facile self-assembly strategy. The developed nanomaterials were characterized and identified by a series of sophisticated analyses, like XRD, SEM, EIS, XPS, PL, UPS, EDS, BET, M-S, TEM, HRTEM, and DRS. The photocatalytic behavior of BiOIO3/Bi3NbO7 was examined and optimized against amoxicillin (AMX) and other types of antibiotics under a variety of environmental conditions, such as visible light (150 W LED), direct sunlight, pH (3-11), catalyst dosages (20-80 mg), humic acid (0-24 mg/L), AMX concentration (10-40 mg/L), and different inorganic ions (0.05 M). The optimized BiOIO3/Bi3NbO7 hybrid attained exceptional AMX degradation activity (96.5%) under visible light (60 min), with a reaction constant of up to 0.04559 min-1, exceeding bare BiOIO3 and Bi3NbO7 by 5.57 and 5.3 folds, respectively. The obtained BiOIO3/Bi3NbO7 hybrid unclosed expanded light utilization behavior compared with neat catalysts, which originates from the powerful incorporation between BiOIO3 and Bi3NbO7 in the S-type system. The radical investigations confirmed the superiority of BiOIO3/Bi3NbO7 in generating both •OH and •O2- during the photoreaction. The novel Bi3NbO7-based heterojunction afforded robust photostability in five treatment cycles and simple charge transfer activity in the S-type route, boosting the photo-mechanism for antibiotic degradation in an efficient manner. The building of the S-scheme heterojunction between BiOIO3 and Bi3NbO7 stimulates the utilization of holes by the recombination process and promotes the overall stability of the composite. Our study introduces a new class of semiconductor heterojunctions that may contribute to the development potential of the photocatalysis sector in wastewater treatment.

Novel Magnetic MnFe2O4-Decorated Graphite-Like Porous Biochar as a Heterogeneous Catalyst for Activation of Peroxydisulfate Toward Degradation of Rhodamine B

A magnetic MnFe2O4-modified graphite-like porous biochar composite (MnFe2O4/KFS800) was synthesized by the hydrothermal method, and its catalytic activity was evaluated in the activation of peroxydisulfate toward degradation of Rhodamine B. After characterization by SEM, XRD, and the BET method, the specific surface area and total pore volume of the MnFe2O4/KFS800 catalyst reached 121 m2/g and 0.263 m3/g, and exhibited plate-like morphology with good crystallinity. The degradation rate of Rhodamine B by the obtained composite was more than 91.1% when the initial concentration of RhB was 10 mg/L, the dosage of MnFe2O4/KFS800 was 0.2 g/L, and the initial pH was 6.7. Then the anti-interference ability of the obtained composite was studied, and it was found that there was a little effect on the degradation of Rhodamine B with the presence of humic acid. Finally, quenching test, EPR research, and XPS analysis were conducted to reveal the catalytic mechanism, and possible mechanism was a synergistic behavior of free radicals (SO4•-, •OH, O2•-) and nonfree radicals (1O2), and trace amounts of uncarbonized bagasse was also involved in the formation of free radicals.

Catalytic Ozonation of Reactive Black 5 in Aqueous Solution Using Iron-Loaded Dead Leaf Ash for Wastewater Remediation

In the current study, iron-loaded dead leaf ash (Fe-DLA) was used as a novel catalyst in the heterogeneous catalytic ozonation process (HCOP) for textile wastewater containing Reactive Black 5 (RB-5). The research demonstrates a significant boost in removal efficiency, reaching 98.76% with 1.0 g/min O3 and 0.5 g/L catalyst dose, by investigating key variables such as pH, ozone and catalyst doses, initial concentration, and the presence of scavengers in 1 L wastewater. The addition of tert-butyl alcohol (TBA) reduced RB-5 elimination, indicating the involvement of OH radicals. Catalyst reusability decreased slightly (2.05% in the second run; 4.35% in the third), which was attributed to iron leaching. A comparison of single ozonation (Fe-DLA) adsorption and catalytic ozonation processes (Fe-DLA/O3) revealed that the combined process improved dye degradation by 25%, with removal rates ranking as Fe-DLA adsorption O3 Fe-DLA/O3, with an impressive 76.44% COD removal. These results strongly support RB-5 removal using Fe-DLA and HCOP at a basic pH, highlighting the catalyst's utility in practical wastewater treatment.

Biochar obtained from alkaline earth metal-treated mushroom residue: Thermal behavior and methyl orange adsorption capability

To achieve the resource utilization of edible fungi residue and obtain efficient adsorbents for treating dyeing wastewater, biochars were prepared from mushroom residue (MR) with the introduction of alkaline-earth metals (AEMs) and used for methyl orange (MO) wastewater treatment. The thermal behavior of the AEM-treated MR was analyzed using thermogravimetric analysis. The physicochemical properties of the biochars obtained from AEM-treated MR (MRCs) were characterized using Fourier transform infrared spectroscopy, laser particle size analyzer, N2 adsorption/desorption, and scanning electron microscopy. The adsorption performance of MRCs on MO was also investigated. The involvement of AEMs was found to obviously move the main pyrolysis zone of MR to a low temperature region and reduce the temperature corresponding to the maximum weight loss rate and activation energy, which is highly dependent on the concentration of AEMs, the anion and cationic species of the AEMs. Moreover, the addition of AEMs resulted in a decrease in oxygen-containing functional groups (-OH, CO, or C-O), a weakening of surface negative charges, an enhancement in aromatic functional groups, and an increase in specific surface area of the MRCs. The adsorption performance of MO on MRCs was significantly improved with the introduction of AEMs as well. Among them, MR pre-treated with 5 mmol/g MgCl2 (MR-MgCl2-5) shows the lowest temperature corresponding to the maximum weight loss rate and the lowest activation energy of 278.52 °C and 4.28 kJ/mol, respectively. The biochar prepared from MR-MgCl2-5 under 400 °C (MR-MgCl2-5-400C) has the weakest surface negative charge and the highest adsorption capacity for MO. The adsorption isotherms, adsorption kinetics, and thermodynamic analysis results showed that the adsorption of MO on MR-MgCl2-5-400C was a spontaneous, chemically dominant monolayer adsorption, with a theoretical maximum adsorption capacity of 81.30 mg/g. This study suggests that AEMs treatment, especially with 5 mmol/g MgCl2, can readily transform edible fungi residue into a low-cost, high-efficient dyeing wastewater adsorbent.

Photocatalyst of manganese ferrite and reduced graphene oxide supported on activated carbon from cow bone for wastewater treatment

The present research aimed to evaluate the photocatalytic activity of manganese ferrite (M) and reduced graphene oxide (G) supported on pulverized activated carbon from cow bone waste (PAC-MG). PAC-MG was characterized by different instrumental techniques. The efficiency of PAC-MG was evaluated using solar irradiation under different conditions of photocatalyst concentration, H2O2 concentration, and pH ranges for the discoloration of methylene blue dye (MB). The synergy between the nanomaterials potentiated the photocatalytic activity, reaching 85.5% of MB discoloration when using 0.25 g L-1 of catalyst at neutral pH with no oxidant needed. Furthermore, PAC-MG demonstrated excellent stability in 6 consecutive cycles. Finally, it is expected that the present study can add value to industrial waste and contribute to the development of novel water and wastewater treatment methods, ensuring water quality for human consumption and the environment.

Chitosan-based magnetic bioadsorbent beads from eucalyptus sawdust waste for the Direct Violet-51 dye remediation: Eco-friendly strategy and statistical optimization

In the present study, a new application was proposed for the eucalyptus sawdust waste, which is an environmental passive. Three adsorbent materials composed of chitosan (CS), sawdust (CSW), and magnetic beads (CSWF) were developed and used for the Direct Violet-51 remediation. The adsorption testes were optimized based on the variation of the adsorption parameters: (i) pH (2-12), (ii) contact time (5-60 min), (iii) initial dye concentration (10-60 mg L-1), (iv) adsorbent mass (10-100 mg) in 10 mL. The optimized conditions of the adsorption essays showed that the three synthesized adsorbents completely removed the dye from the aqueous medium, but under different experimental conditions. As the main findings in this study, we can highlight the excellent performance of CSW adsorbent material, which promoted maximum removal efficiency of Direct Violet-51 at neutral pH, which is of great importance for the industrial processes. On the other hand, CS and CSWF adsorbent materials exhibited a maximum adsorption efficiency at pH 2. Furthermore, the adsorbent materials were applied in the dye remediation in environmental water samples from the tap water, Marcela dam, and Poxim River, they did not suffer any major matrix interference, whose removal efficiency values varied between 99.8 and 100, 70.7-100, and 98.8-99.5 % for the CS, CSW, and CSWF, respectively. Finally, besides being materials produced from the waste, they can be reused more times, fitting into the concept of circular economy.

New insights on the preparation of amine covalent organic polymer and its adsorption properties

Dye pollution is becoming increasingly severe. This study used the Schiff base reaction to synthesize a polyaromatic ring covalent organic polymer material with amide bonds and high electronegativity named SLEL-9 to adsorb Methylene Blue (MB) and Rhodamine B (RhB). SLEL-9 was characterized by Fourier transform infra-red spectra, X-ray photoelectron spectra, Brunauer-Emmett-Teller (BET), zeta potential analysis, and other techniques. It was found that SLEL-9 material contains C-C, CN, C-N, and CO. SLEL-9 had a zeta potential of about -45 mV under neutral conditions, which proved that the material had been synthesized successfully. The BET and Langmuir surface areas of SLEL-9 were 35.187 m2 g-1 and 56.419 m2 g-1, respectively. The adsorptions of SLEL-9 on low concentration (10 mg L-1) Methylene Blue and Rhodamine B reached equilibrium within 48 h. The results showed that SLEL-9's adsorption of dye molecules are more consistent with pseudo-second-order kinetic and Langmuir isotherm model. The adsorption experiments showed that the adsorption process is a spontaneous endothermic reaction, mainly chemisorption. The maximum adsorption capacity of SLEL-9 for MB and RhB were 132.45 mg g-1 and 101.94 mg g-1. In addition, this study investigated to determine the optimal reaction parameters. The primary mechanisms of SLEL-9 adsorption of two dyes are n→π* interaction, π-π EDA interaction and electrostatic attraction. Selective adsorb ability experiment results showed that SLEL-9 could selectively adsorb MB and RhB to a certain extent. Finally, it was found that SLEL-9 can maintain over 70% adsorption capacity after five reuses and can maintain stability after soaking in different pH water and organic solvents for 120 h. SLEL-9 proved to be a promising organic covalent polymer adsorption material for the removal of Methylene Blue and Rhodamine B in water.

Sponge-like biodegradable polypyrrole-modified biopolymers for selective adsorption of basic red 46 and crystal violet dyes from single and binary component systems

Recently, several researchers have been trying to reduce the ecological effects of water pollution by considering the use of biodegradable materials that prevent the generation of secondary pollution in our environment and enable water reuse. Here, new biodegradable hydrogels based on alginate (Alg), gelatin (Gel) and polypyrrole (PPy) were successfully implemented to remove two known highly toxic cationic dyes from wastewater. The design process was performed in two steps: in-situ polymerization of polypyrrole within the Alg/Gel mixture, followed by hydrogel formation. Biocomposites showed promising efficacy for the removal of both basic red 46 (BR46) and crystal violet (CV) dyes from real and demineralized water samples. However, Alg-Gel-PPy hydrogel showed better selectivity for BR46 than for CV as compared to the pristine Alg-Gel hydrogel. Adsorption of both pollutants on biocomposite hydrogel beads followed the Langmuir isotherm and pseudo-second order kinetic models. Besides, the highest adsorption capacities (125 mg g-1 for BR46 and 88.5 mg g-1 for CV) were obtained for the Alg-Gel-PPy hydrogel, compared with those determined for PPy-free hydrogel (103.09 mg g-1 for BR46 and 86.96 mg g-1 for CV) and remained at a satisfactory level for five adsorption-desorption cycles. Finally, the obtained hydrogels showed excellent biodegradability by natural soil microorganisms, with 91 % decomposition.

Enhanced Redox Cycle of Rod-Shaped MIL-88A/SnFe2O4@MXene Sheets for Fenton-like Degradation of Congo Red: Optimization and Mechanism

This study intended to fabricate a novel Fenton-like catalyst by supporting the rod-like MIL-88A and the magnetic tin ferrite nanoparticles (SnFe2O4) on the MXene sheets (MIL-88A/SnFe2O4@MXene). The well fabrication and determination of the MIL-88A/SnFe2O4@MXene properties were investigated using SEM, XPS, VSM, Zeta potential, XRD, and FTIR tools. The Fenton-like degradation reaction of CR by MIL-88A/SnFe2O4@MXene was thoroughly studied to identify the optimal proportions of the catalyst components, the impact of CR and H2O2 concentrations, as well as the effect of raising the temperature and the pH medium of the catalytic system and the catalyst dosage. Kinetics studies were executed to analyze the decomposition of CR and H2O2 using First-order and Second-order models. Furthermore, the degradation mechanism was proposed based on the scavenging test that proceeded in the presence of chloroform and t-butanol, in addition to the XPS analysis that clarified the participation of the containing metal species: Fe, Sn, and Ti, and the formation of a continual redox cycle. The obtained intermediates during the CR degradation were defined by GC-MS. A recyclability test was performed on MIL-88A/SnFe2O4@MXene during five runs of the Fenton-like degradation of CR molecules. Finally, the novel MIL-88A/SnFe2O4@MXene Fenton-like catalyst could be recommended as a propitious heterogeneous catalyst with a continuous redox cycle and a recyclability merit.

Is natural better? An ecotoxicity study of anthraquinone dyes

The concept of sustainability has gained prominence in recent years, enhancing the need to develop products that are less harmful to the environment. Dyes are used by various industrial sectors and have a lot of market value; they are used on a large scale mainly by the textile industry that uses large volumes of water and is one of the main contributors to the contamination of water bodies. Some natural compounds, especially anthraquinones are re-emerging as possible alternatives to synthetic dyes, some of which are known for their toxic and/or mutagenic effects. The BioColour project (https://biocolour.fi/) which is interested in promoting the development of new alternative molecules to synthetic dyes, provided us highly purified anthraquinone dyes dermocybin and dermorubin (>98% purity) extracted from a specie of fungus Cortinarius sanguineus. Dyes were tested for their acute and chronic toxicity using different aquatic organisms. Dermorubin was not toxic to any of the organisms tested for the highest test concentration of 1 mg L-1 and it was the most promising dye. Dermocybin was toxic to Daphnia similis (EC50 = 0.51 mg L-1), Ceriodaphnia dubia (IC10 = 0.13 mg L-1) and Danio rerio embryos (extrapolated LC50 = 2.44 mg L-1). A safety limit, i.e, predicted no-effect concentration (PNEC) of 0.0026 mg L-1 was derived based on the toxicity of dermocybin. The PNEC value can be used to provide hazard information for future application in commercial dyeing processes. Then, we compared the toxicity of dermocybin and dermorubin with ecotoxicity data available in the literature on other anthraquinone dyes of natural and synthetic origin. Some natural dyes can be as toxic as synthetic ones, or more toxic when chronic effects are considered. Despite natural dyes being used since centuries past, there are few ecotoxicological studies available. This study is designed to help develop a more comprehensive understanding of their toxicological properties.

Biochar-Based Single-Atom Catalyst with Fe-N3O-C Configuration for Efficient Degradation of Organic Dyes by Peroxymonosulfate Activation

Iron single-atom catalysts (Fe SACs) hold great promise for peroxymonosulfate (PMS) activation and degradation of organic pollutants in wastewater. However, insights into crucial catalytic sites and activation mechanisms of biochar-based Fe SACs for PMS remain a challenge. Herein, cotton stalk-derived biochar-based Fe SACs (Fe SACs-BC) with an asymmetric Fe-N/O-C configuration were prepared, and their PMS activation and acid orange 7 (AO7) degradation mechanisms were investigated. The results showed that the removal efficiency of the Fe SACs-BC catalyst with Fe-N3O-C configuration for AO7 and other five investigated organic dyes reached 95-99% within 15 min. The EPR spectrums, quenching experiments, electrochemical analysis, masking experiments, XPS, and theoretical calculations indicated that degradations of organic dyes were dominated by singlet oxygen, which was generated by direct PMS conversion at the electron-deficient carbon and iron sites in the Fe-N3O-C configuration. The Fe SACs-BC/PMS exhibited high removal efficiency and strong tolerance in different water matrices with a wide pH range, various coexisting anions and interfering substances, showing great potential and applicability for efficient treatment of actual textile wastewaters.

Nanoparticles of the Perovskite-Structure CaTiO3 System: The Synthesis, Characterization, and Evaluation of Its Photocatalytic Capacity to Degrade Emerging Pollutants

In this research work, the photocatalytic capacity shown by the nanoparticles of the CaTiO3 system was evaluated to degrade two pollutants of emerging concern, namely methyl orange (MO)-considered an organic contaminating substance of the textile industry that is non-biodegradable when dissolved in water-and levofloxacin (LVF), an antibiotic widely used in the treatment of infectious diseases that is released mostly to the environment in its original chemical form. The synthesis process used to obtain these powders was the polymeric precursor method (Pechini), at a temperature of 700 °C for 6 h. The characterization of the obtained oxide nanoparticles of interest revealed the presence of a majority perovskite-type phase with an orthorhombic Pbnm structure and a minority rutile-type TiO2 phase, with a P42/mnm structure and a primary particle size <100nm. The adsorption-desorption isotherms of the synthesized solids had H3-type hysteresis loops, characteristic of mesoporous solids, with a BET surface area of 10.01m2/g. The Raman and FTIR spectroscopy results made it possible to identify the characteristic vibrations of the synthesized system and the characteristic deformations of the perovskite structure, reiterating the results obtained from the XRD analysis. Furthermore, a bandgap energy of ~3.4eV and characteristic emissions in the violet (437 nm/2.8 eV) and orange (611 nm/2.03 eV) were determined for excitation lengths of 250 nm and 325 nm, respectively, showing that these systems have a strong emission in the visible light region and allowing their use in photocatalytic activity to be potentialized. The powders obtained were studied for their photocatalytic capacity to degrade methyl orange (MO) and levofloxacin (LVF), dissolved in water. To quantify the coloring concentration, UV-visible spectroscopy was used considering the variation in the intensity of the characteristic of the greatest absorption, which correlated with the change in the concentration of the contaminant in the solution. The results showed that after irradiation with ultraviolet light, the degradation of the contaminants MO and LVF was 79.4% and 98.1% with concentrations of 5 g/L and 10 g/L, respectively.

The colorful world of sulfonephthaleins: Current applications in analytical chemistry for "old but gold" molecules

Sulfonephthaleins represent one of the most common and widely employed reactive dyes in analytical chemistry, thanks to their stability, low-cost, well-visible colors, reactivity and possibilities of chemical modification. Despite being first proposed in 1916, nowadays, these molecules play a fundamental role in biological and medical applications, environmental analyses, food quality monitoring and other fields, with a particular focus on low-cost and disposable devices or methods for practical applications. Since up to our knowledge, no reviews or book chapters focused explicitly on sulfonephthaleins have ever been published, in this review, we will briefly describe sulfonephthaleins history, their acid-base properties will be discussed, and the most recent applications in different fields will be presented, focusing on the last ten years literature (2014-2023). Finally, safety and environmental issues will be briefly discussed, despite being quite controversial.

Cationic and anionic cross-assisted synergistic photocatalytic removal of binary organic dye mixture using Ni-doped perovskite oxide

Organic dyes present in industrial wastewater are the major contributor to water pollution, which harm human health and the environment. Photocatalytic dye degradation is an effective strategy for water remediation by converting these organic dyes waste into non-harmful by-products. Therefore, in this study, Ni-doped LaFeO3 (NLFO) perovskite nanoparticles were extensively explored for photocatalytic degradation of cationic and anionic dyes and their mixture. The NLFO nanoparticles were successfully synthesized by surfactant assisted hydrothermal method under controlled Ni doping. The X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) revealed the variation in size (40-70 nm) of orthorhombic crystalline LFO nanoparticles with Ni doping and hence the size of microspheres (0.78. to 1.78 μm). The kinetic studies revealed that the LaFe0·6Ni0·4O3 performed well by providing degradation efficiency of 99.2% in 210 min, 99.1% in 100 min, and 98.4% in 70 min for Crystal Violet (CV), Congo Red (CR), and their mixture with rate constant of 0.019, 0.039, and 0.055 min-1 respectively. The radical scavenger tests indicated the synergetic contributions of O2- and •OH- active radicals in faster degradation of CV and CR dye mixture. The stepwise fragmentation of dye molecule during the photocatalytic degradation identified from the LCMS indicates the degradation of CV dye through de-alkylation and benzene ring breaking, whereas azo bond cleavage and oxidation lead to low molecular weight intermediates for CR dye, which all together helped to degrade their dye mixture (50 mg L-1 and 100 mg L-1) in significantly lesser time (70 min). Overall, the Ni-doped LFO microsphere consisting of nanoparticles acts as a superior catalyst for the more efficient and faster degradation of binary dye mixture.

Degradation of xanthene-based dyes by photoactivated persulfate: experimental and computational studies

Dyes are naked-eye detectable even at low concentration levels and can cause environmental damage when released into aquatic effluents; therefore, methods for removing the residual color from the aquatic media are always a current issue. In this paper, degradation of three xanthene dyes, Rhodamine B, Eosin Y, and Sodium Fluorescein, using photoactivated persulfate was evaluated at pH 3.0 and 11.0. The dyes' degradation followed a pseudo-first-order reaction. Although the solution is completely decolorized in 40 min at pH 3.0, achieving 75% mineralization requires a longer reaction time of 180 min. Furthermore, GC-MS analyses indicate that degradation products are mainly low-molecular weight acids, CO2 and H2O. Experiments carried out in dark and under UV irradiation showed substantial contribution of radical (SO4•- and HO•) and non-radical pathways to dye degradation in both pH. Additionally, to get more insights into the degradation pathways, HOMO-LUMO energy gaps of the dyes were calculated by DFT using MPW1PW91/MidiXo level of theory and, in general, the lower the bandgap, the faster the degradation. Fukui functions revealed that the preferential sites to radical attack were the xanthene or the benzoate portion depending on the pH, wherein attack to the xanthene ring provided better kinetic and mineralization results.

Immobilized laccase: an effective biocatalyst for industrial dye degradation from wastewater

Environmental concerns due to the release of industrial wastewater contaminated with dyes are becoming more and more intense with the increasing industrialization. Decolorization of industrial effluents has become the top priority due to the continuous demand for color-free discharge into the receiving water bodies. Different dye removal techniques have been developed, among which biodegradation by laccase enzyme is competitive. Laccase, as a green catalyst, has a high catalytic activity, generates less toxic by-products, and has been extensively researched in the field of remediation of dyes. However, laccase's significant catalytic activity could only be achieved after an effective immobilization step. Immobilization helps strengthen and stabilize the protein structure of laccase, thus enhancing its functional properties. Additionally, the reusability of immobilized laccase makes it an attractive alternative to traditional dye degradation technologies and in the realistic applications of water treatment, compared with free laccase. This review has elucidated different methods and the carriers used to immobilize laccase. Furthermore, the role of immobilized laccase in dye remediation and the prospects have been discussed.

Kinetics and mechanism study of dyes degradation in electric field-promoting catalytic wet air oxidation process

Wet air oxidation (WAO) is a clean and eco-friendly technology for dyes removal, but the high operating temperature and pressure limit its practical application. In the present work, an electric field-promoting (EF-promoting) catalytic WAO process is developed to degrade dyes under room condition. The oxidation kinetics of four different types of dyes and their degradation pathways are studied. A kinetic model is constructed by including the exogenous electric field into the Langmuir-Hinshelwood-Hougen-Watson (LHHW) mechanism framework, and quantitative structure-activity relationship (QSAR) analysis is conducted to correlate the kinetic parameters to the physicochemical properties of the dyes. A negative linear relationship is found between the adsorption equilibrium constants of the dyes and their first ionization energies, and their surface reaction rate constants are positively linearly associated to E_sum (E_LUMO + E_HOMO). The degradation pathways of the different dyes are proposed according to the degradation intermediates and the activities of the atoms within the dye molecules. The heteroatoms N and S, and the atom C connecting the aromatic rings are identified as the susceptible sites upon the electrophilic attack of O₂. Bond cleavage at these sites gives rise to aromatic fragments which are eventually mineralized via carboxyl acids. The results of this work is helpful for guiding the design and operation of the EF-promoting catalytic WAO process into the treatment of various dye wastewaters.

Adsorption and Photodegradation of Lanasol Yellow 4G in Aqueous Solution by Natural Zeolite Treated by CO2-Laser Radiation

Natural zeolite is a widely used material with excellent environmental cleaning performance, especially in water and wastewater treatment. Natural zeolite (Z_ini) calcined by CO₂-laser radiation (ZL) was tested as a catalyst for the photodegradation and the adsorption of industrial azo dye Lanasol Yellow 4G (LY4G) in water. Morphology, chemical structure, and surface composition of Z_ini and ZL were analyzed by XRD, SEM, EDS, and XPS. UV/Visible spectrophotometry was used to evaluate the photocatalytic activity of Z_ini and ZL. The photocatalytic activity of the studied zeolites was associated with the presence of Fe oxides in their composition. Laser-treated natural zeolite showed higher efficiency as a photocatalyst compared to untreated natural zeolite.

Ultrasonic-assisted photocatalytic degradation of various organic contaminants using ZnO supported on a natural polymer of sporopollenin

Water resource pollution by organic contaminants is an environmental issue of increasing concern. Here, sporopollenin/zinc oxide (SP/ZnO) was used as an environmentally friendly and durable catalyst for sonophotocatalytic treatment of three organic compounds: direct blue 25 (DB 25), levofloxacin (LEV), and dimethylphtalate (DMPh). The resulting catalyst had a 2.65 eV bandgap value and 9.81 m²/g surface area. The crystalline structure and functional groups of SP/ZnO were confirmed by X-ray diffraction (XRD) and Fourier transforms infrared spectroscopy (FTIR) analyses. After 120 min of the sonophotocatalysis, the degradation efficiencies of DB 25, LEV, and DMPh by SP/ZnO were 86.41, 75.88, and 62.54%, respectively, which were higher than that of the other investigated processes. The role of reactive oxygen species were investigated using various scavengers, enhancers, photoluminescence, and o-phenylenediamine. Owing to its stability, the catalyst exhibited good reusability after four consecutive cycles. In addition, the high integrity of the catalyst was confirmed by scanning electron microscopy (SEM), XRD, and FTIR analyses. After four consecutive examinations, the leaching of zinc in the aqueous phase was < 3 mg/L. Moreover, gas chromatography-mass spectrometry (GC-MS) analyses indicated that the contaminants were initially converted into cyclic compounds and then into aliphatic compounds, including carboxylic acids and animated products. Thus, this study synthesized an environmentally friendly and reusable SP/ZnO composite for the degradation of various organic pollutants using a sonophotocatalytic process.

Efficient microbial cellulose/Fe3O4 nanocomposite for photocatalytic degradation by advanced oxidation process of textile dyes

Fenton-type advanced oxidative processes (AOP) have been employed to treat textile dyes in aqueous solution and industrial effluent. The work focused on assisting the limitations still presented by the Fenton process regarding the use of suspended iron catalysts. Soon, a nanocomposite of bacterial cellulose (BC) and magnetite (Fe₃O₄) was developed. It has proven to be superior to those available in the literature, exhibiting purely catalytic properties and high reusability. Its successful production was verified through analytical characterization, while its catalytic potential was investigated in the treatment of different textile matrices. In initial tests, the photo-Fenton process irradiated and catalyzed by sunlight and BC/Fe₃O₄ discolored 92.19% of an aqueous mixture of four textile dyes. To improve the efficiency, the design of experiments technique evaluated the influence of the variables pH, [H₂O₂], and the number of BC/Fe₃O₄ membranes. 99.82% of degradation was obtained under optimized conditions using pH 5, 150 mg L^-1 of H₂O₂, and 11 composite membranes. Reaction kinetics followed a pseudo-first-order model, effectively reducing the organic matter (COD = 83.24% and BOD = 88.13%). The composite showed low iron leaching (1.60 ± 0.08 mg L^-1) and high stability. It was recovered and reused for 15 consecutive cycles, keeping the treatment efficiency at over 90%. As for the industrial wastewater, the photo-Fenton/sunlight/BC/Fe₃O₄ system showed better results when combined with the physical-chemical coagulation/flocculation process previously used in the industry's WWTP. Together they reduced COD by 77.77%, also meeting the color standards (DFZ scale) for the wavelengths of 476 nm (<3 m^-1), 525 nm (<5 m^-1), and 620 nm (<7 m^-1). Thus, the results obtained demonstrated that employing the BC/Fe₃O₄ composite as an iron catalyst is a suitable alternative to materials employed in suspension. This is mainly due to the high catalytic activity and power of reuse, which will reduce treatment costs.

Efficient removal of methylene blue from water using magnetic Alyssum homolocarpum seed gum-based matrix

In this study, we fabricated magnetic Fe₃O₄ nanoparticles conjugated with anionic hydroxypropyl starch-graft-acrylic acid (Fe3O4@AHSG) for the efficient removal of methylene blue (MB) dye from aqueous solutions. The synthesized nanoconjugates were characterized using various techniques. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) analysis revealed that the particles exhibited homogeneously distributed nanosized spherical shapes with a mean diameter of 41.72 ± 6.81 nm. The EDX analysis confirmed the absence of impurities, with the Fe₃O₄ particles comprising 64.76 % iron and 35.24 % atomic oxygen. Dynamic light scattering (DLS) measurements showed a monodisperse particle system with a mean hydrodynamic size of 135.4 nm (polydispersity index, PI = 0.530) for the Fe₃O₄ nanoparticles and 163.6 nm (PI = 0.498) for the Fe3O4@AHSG adsorbent. Vibrating sample magnetometer (VSM) analysis indicated superparamagnetic behavior for both Fe₃O₄ and Fe₃O₄@AHSG, with higher saturation magnetization (Ms) observed for Fe₃O₄. The dye adsorption studies demonstrated that the adsorbed dye capacity increased with increasing initial MB concentration and adsorbent dose. The pH of the dye solution significantly influenced the adsorption, with the highest adsorption observed at basic pH values. The presence of NaCl reduced the adsorption capacity due to increased ionic strength. Thermodynamic analysis indicated the thermodynamically favorable and spontaneous nature of the adsorption process. Kinetic studies revealed that the pseudo-second-order model provided the best fit to the experimental data, suggesting chemisorption as the rate-limiting step. Overall, Fe₃O₄@AHSG nanoconjugates exhibited excellent adsorption capacity and could be a promising material for effective removal of MB dye from wastewater.

Waste iron as a robust and ecological catalyst for decomposition industrial dyes under UV irradiation

In an era of increasing environmental awareness, it is very important to work towards eliminating or at least reducing as many harmful industrial substances as possible. However, the implementation of green chemistry methods for wastewater treatment can be difficult especially due to complexity, the high cost of reagents, and the required long process time. This paper focuses on using waste iron (WI) to remove two kinds of amaranth dye commonly used in industry. To enhance the process, UV irradiation and hydrogen peroxide were used. The novelty of the research was the use of efficient and reusable WI as a heterogeneous catalyst in the process. WI material characteristics was done before and after the process using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray fluorescence (XRF). Zeta potential, size characterization, circularity, and direct band gap were also determined. As a result of treatment complete decolorization of both dyes was achieved, as well as 99% absorbance removal after 15-min process time. The total organic carbon (TOC) decrease after 60-min process time was in the range from 86.6 to 89.8%. Modified pseudo-second-order reaction reflects obtained results of treatment efficiency. Treatment results, confirmed by WI material characterization, indicate satisfactory stability of the catalyst and good oxidation capacity.

In situ preparation of TiO2/f-MWCNT catalyst using Pluronic F127 assisted sol-gel process for sonocatalytic degradation of methylene blue

In this study, titanium dioxide- Pluronics @F127/functionalized -multi walled carbon nanotubes (TiO₂-F127f-/MWCNT) nanocatalysts were prepared, characterized, and used in methylene blue (MB) degradation under ultrasonic conditions. The characterization studies were performed using TEM, SEM, and XRD analyses to reveal the morphological and chemical properties of TiO₂-F127/MWCNT nanocatalysts. To detect the optimum parameters for MB degradation using TiO₂-F127/f-MWCNT nanocatalysts, several experimental parameters were conducted at various conditions such as different temperatures, pH, catalyst amount, hydrogen peroxide (H₂O₂) concentration, and various reaction contents. Transmission electron microscopy (TEM) analyses showed that TiO₂-F127/f-MWCNT nanocatalysts consisted of a homogenous structure and have a 12.23 nm particle size. The crystalline particle size of TiO₂-F127/MWCNT nanocatalysts was found to be 13.31 nm. Scanning electron microscope (SEM) analyses revealed the surface structure of TiO₂-F127/f-MWCNT nanocatalysts turned to be modified after TiO₂ loaded on MWCNT. Under the optimum conditions; pH: 4, MB concentration: 25 mg/L, H₂O₂ concentration: 30 mol/L, reaction time: and catalyst dose: 24 mg/L, chemical oxygen demand (COD) removal efficiency reached a maximum of 92%. To detect the radical effectiveness, three scavenger solvents were tested. Reuse experiments revealed that TiO₂-F127/f-MWCNT nanocatalysts retained 84.2% catalytical activity after 5 cycles. Gas chromatography-mass spectrometry (GC-MS) was successfully used to identify the generated intermediates. In addition, the GC-MS was successfully used to identify produced intermediates. Based on the experimental results, it has been suggested that •OH radicals are the main active species responsible for the degradation reaction in the presence of the TiO₂-F127/f-MWCNT nanocatalysts.

Application of xanthan gum as coagulant-aid for decolorization of synthetic Congo red wastewater

In recent years, utilization of polysaccharides as natural coagulant and coagulant-aid has become a topic of interest, due to the nature of biopolymers that are renewable, biodegradable, and non-toxic. In this study, Congo red, as a model dye substance, was treated using polyaluminium chloride (PAC) as the main coagulant and xanthan gum as the coagulant aid. For this purpose, the effect of pH (3-9), xanthan gum dose (0.5-4 mg/L), and the initial concentration of Congo red dye (50-100 mg/L) to the dye removal and sludge volume were investigated. The outcome of this investigation indicates that the best pH for Congo red coagulation occurred at pH 3, due to the charge neutralization mechanism. The addition of coagulant-aid dose increases the %-removal and sludge volume until reaching the best coagulant-aid dose of 2 mg/L that results in a %-removal value of 93.81% and a sludge volume of 23.5 mL/L. Further addition of xanthan gum reduced the %-removal and sludge volume due to the inter-polymer force causing more difficult floc formation. The best initial concentration of dye occurred at a Congo red concentration of 50 mg/L, with a %-removal value of 93.81% with PAC (15 mg/L) and xanthan gum (2 mg/L) coagulants. This value is considerably higher than PAC and xanthan gum only which amounts to 81.16 and 7.18%, respectively. Based on these results, it is apparent that xanthan gum can positively contribute to dye coagulation while reducing the use of harmful inorganic coagulant.

Antibacterial Activity of Solvothermal Obtained ZnO Nanoparticles with Different Morphology and Photocatalytic Activity against a Dye Mixture: Methylene Blue, Rhodamine B and Methyl Orange

In this paper, we report the synthesis of ZnO nanoparticles (NPs) by forced solvolysis of Zn(CH3COO)2·2H2O in alcohols with a different number of –OH groups. We study the influence of alcohol type (n-butanol, ethylene glycol and glycerin) on the size, morphology, and properties of the obtained ZnO NPs. The smallest polyhedral ZnO NPs (<30 nm) were obtained in n-butanol, while in ethylene glycol the NPs measured on average 44 nm and were rounded. Polycrystalline particles of 120 nm were obtained in glycerin only after water refluxing. In addition, here, we report the photocatalytic activity, against a dye mixture, of three model pollutants: methyl orange (MO), methylene blue (MB), and rhodamine B (RhB), a model closer to real situations where water is polluted with many chemicals. All samples exhibited good photocatalytic activity against the dye mixture, with degradation efficiency reaching 99.99%. The sample with smallest nanoparticles maintained a high efficiency >90%, over five catalytic cycles. Antibacterial tests were conducted against Gram-negative strains Salmonella enterica serovar Typhimurium, Pseudomonas aeruginosa, and Escherichia coli, and Gram-positive strains Enterococcus faecalis, Bacillus subtilis, Staphylococcus aureus, and Bacillus cereus. The ZnO samples presented strong inhibition of planktonic growth for all tested strains, indicating that they can be used for antibacterial applications, such as water purification.

Magnetic seeds promoted high-density sulfonic acid-based hydrochar derived from sugar-rich wastewater for removal of methylene blue

Methylene blue (MB) removal from dyeing wastewater using low-cost bio-derived adsorbent is a significant and challenging field. Herein, magnetic sugar hydrochar (MGHC) precursors derived from sugar-rich wastewater with small particle size and rich oxygen-containing functional groups (OCFGs) are prepared from sugar-rich aqueous solution via Fe salt-modified hydrothermal procedure. The role of Fe₃O₄ nanoparticles formed during the sugar carbonization is to provide numerous magnetic seeds to generate MGHC with core-shell structure, which reduces the particle size of hydrochar. This increases the amount of OCFGs on the surface of MGHC for bonding the sulfonic acid groups. Therefore, sulfonic acid-modified MGHC-SA shows the rapid MB adsorption rate and excellent adsorption capacity. The highest MB capacity is 869.6 mg/g at pH = 11.0 and 298 K. Additionally, the MGHC-SA can be easily recovery by magnet. And the stability of MGHC-SA was also evaluated, no degradation of adsorption performance was observed, even the adsorbent was regenerated 10 times. This study puts forward a promising way to acquire functional groups rich and easy recovery hydrochar from sugar wastewater for MB removal.

MgO-La2O3 mixed metal oxides heterostructure catalysts for photodegradation of dyes pollutant: synthesis, characterization and artificial intelligence modelling

In the present work, we prepared MgO-La₂O₃-mixed-metal oxides (MMO) as efficient photocatalysts for degradation of organic pollutants. First, a series of MgAl-%La-CO₃-layered double hydroxide (LDH) precursors with different contents of La (5, 10, and 20 wt%) were synthesized by the co-precipitation process and then calcined at 600 °C. The prepared materials were characterized by XRD, SEM-EDX, FTIR, TGA, ICP, and UV-vis diffuse reflectance spectroscopy. XRD indicated that MgO, La₂O₃, and MgAl₂O₄ phases were found to coexist in the calcined materials. Also, XRD confirms the orthorhombic-tetragonal phases of MgO-La₂O₃. The samples exhibited a small band gap of 3.0-3.22 eV based on DRS. The photocatalytic activity of the catalysts was assessed for the degradation of two dyes, namely, tartrazine (TZ) and patent blue (PB) as model organic pollutants in aqueous mediums under UV-visible light. Detailed photocatalytic tests that focused on the impacts of dopant amount of La, catalyst dose, initial pH of the solution, irradiation time, dye concentration, and reuse were carried out and discussed in this research. The experimental findings reveal that the highest photocatalytic activity was achieved with the MgO-La₂O₃-10% MMO with photocatalysts with a degradation efficiency of 97.4% and 93.87% for TZ and PB, respectively, within 150 min of irradiation. The addition of La to the sample was responsible for its highest photocatalytic activity. Response surface methodology (RSM) and gradient boosting regressor (GBR), as artificial intelligence techniques, were employed to assess individual and interactive influences of initial dye concentration, catalyst dose, initial pH, and irradiation time on the degradation performance. The GBR technique predicts the degradation efficiency results with R² = 0.98 for both TZ and PB. Moreover, ANOVA analysis employing CCD-RSM reveals a high agreement between the quadratic model predictions and the experimental results for TZ and PB (R² = 0.9327 and Adj-R² = 0.8699, R² = 0.9574 and Adj-R² = 0.8704, respectively). Optimization outcomes indicated that maximum degradation efficiency was attained under the following optimum conditions: catalyst dose 0.3 g/L, initial dye concentration 20 mg/L, pH 4, and reaction time 150 min. On the whole, this study confirms that the proposed artificial intelligence (AI) techniques constituted reliable and robust computer techniques for monitoring and modeling the photodegradation of organic pollutants from aqueous mediums by MgO-La₂O₃-MMO heterostructure catalysts.

Study on the ozonation degradation of methylene blue enhanced by microchannel and ultrasound

Azo dye-containing wastewater poses serious risks of environmental pollution because it is generally biologically toxic and resistant to conventional wastewater treatment methods. A novel degradation system integrating ozone, microchannel, and ultrasound was designed to effectively degrade azo dye-contaminated wastewater. The effects of discharge voltage of dielectric barrier discharge (DBD) reactor, liquid flow rate, microchannel width, ultrasonic power, initial pH, and reaction temperature on methylene blue (MB) decolorization were studied. A maximum MB decolorization efficiency of 92.7% was obtained in the ozone/microchannel/ultrasound (O₃/MC/US) system with 14 min of treatment. In addition, the 14-min decolorization efficiency and TOC removal efficiency obtained in O₃/MC/US system were increased by 12.6 and 6.5%, respectively, compared to those obtained in the pure O₃ system. Based on the results of scavenging experiments, the combined effects of microchannel and ultrasound were proved to improve the contribution rate of hydroxyl radicals, thus improving the decolorization efficiency. The present work clearly illustrates that ozonation degradation can be effectively enhanced by microchannel and ultrasound, and also provides a feasible method for the treatment of organic wastewater.

A Comprehensive Review on Adsorption, Photocatalytic and Chemical Degradation of Dyes and Nitro-Compounds over Different Kinds of Porous and Composite Materials

Dye and nitro-compound pollution has become a significant issue worldwide. The adsorption and degradation of dyes and nitro-compounds have recently become important areas of study. Different methods, such as precipitation, flocculation, ultra-filtration, ion exchange, coagulation, and electro-catalytic degradation have been adopted for the adsorption and degradation of these organic pollutants. Apart from these methods, adsorption, photocatalytic degradation, and chemical degradation are considered the most economical and efficient to control water pollution from dyes and nitro-compounds. In this review, different kinds of dyes and nitro-compounds, and their adverse effects on aquatic organisms and human beings, were summarized in depth. This review article covers the comprehensive analysis of the adsorption of dyes over different materials (porous polymer, carbon-based materials, clay-based materials, layer double hydroxides, metal-organic frameworks, and biosorbents). The mechanism and kinetics of dye adsorption were the central parts of this study. The structures of all the materials mentioned above were discussed, along with their main functional groups responsible for dye adsorption. Removal and degradation methods, such as adsorption, photocatalytic degradation, and chemical degradation of dyes and nitro-compounds were also the main aim of this review article, as well as the materials used for such degradation. The mechanisms of photocatalytic and chemical degradation were also explained comprehensively. Different factors responsible for adsorption, photocatalytic degradation, and chemical degradation were also highlighted. Advantages and disadvantages, as well as economic cost, were also discussed briefly. This review will be beneficial for the reader as it covers all aspects of dye adsorption and the degradation of dyes and nitro-compounds. Future aspects and shortcomings were also part of this review article. There are several review articles on all these topics, but such a comprehensive study has not been performed so far in the literature.

La2CoO4+δ perovskite-mediated peroxymonosulfate activation for the efficient degradation of bisphenol A

Sulfate radical-based technology has been considered as an efficient technology to remove pharmaceuticals and personal care products (PPCPs) with heterogeneous metal-mediated catalysts for the activation of peroxymonosulfate (PMS). In this study, La₂CoO_4+δ perovskite with Ruddlesden-Popper type structure was synthesised by the sol-gel method, which was employed in PMS activation. Different characteriazation technologies were applied for the characterization of La₂CoO_4+δ , such as SEM-EDX, XRD, and XPS technologies. A common organic compound, bisphenol A (BPA), is used as a target contaminant, and the effect impactors were fully investigated and explained. The results showed that when the dosage of La₂CoO_4+δ was 0.5 g L^-1 and the concentration of PMS was 1.0 mM in neutral pH solution, about 91.1% degradation efficiency was achieved within 25 minutes. Quenching experiments were introduced in the system to verify the catalytic mechanism of PMS for the BPA degradation, proving the existence of superoxide, hydroxyl radicals and sulfate radicals, which are responsible for the catalytic degradation of BPA. Moreover, the reusability and stability of the catalyst were also conducted which showed good stability during the reaction. This work would improve the applications of A₂BO₄-type perovskites for activating PMS to degrade BPA.

Piezo-Enhanced Photocatalytic Activity of the Electrospun Fibrous Magnetic PVDF/BiFeO3 Membrane

Creating stimulus-sensitive smart catalysts capable of decomposing organic dyes with high efficiency is a critical task in ecology. Combining the advantages of photoactive piezoelectric nanomaterials and ferroelectric polymers can effectively solve this problem by collecting mechanical vibrations and light energy. Using the electrospinning method, we synthesized hybrid polymer-inorganic nanocomposite fiber membranes based on polyvinylidene fluoride (PVDF) and bismuth ferrite (BFO). The samples were studied by scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), total transmittance and diffuse reflectance, X-ray photoelectron spectroscopy (XPS), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), vibrating-sample magnetometer (VSM), and piezopotential measurements. It has been demonstrated that the addition of BFO leads to an increase in the proportion of the polar phase from 86.5% to 96.1% due to the surface ion-dipole interaction. It is shown that the composite exhibits anisotropy of magnetic properties depending on the orientation of the magnetic field. The results of piezo-photocatalytic experiments showed that under the combined action of ultrasonic treatment and irradiation with both visible and UV light, the reaction rate increased in comparison with photolysis, sonolysis, and piezocatalysis. Moreover, for PVDF/BFO, which does not exhibit photocatalytic activity, under the combined action of light and ultrasound, the reaction rate increases by about 3× under UV irradiation and by about 6× under visible light irradiation. This behavior is explained by the piezoelectric potential and the narrowing of the band gap of the composite due to mechanical stress caused by the ultrasound.

Influence of the Alcohols on the ZnO Synthesis and Its Properties: The Photocatalytic and Antimicrobial Activities

Zinc oxide (ZnO) nanomaterials are used in various health-related applications, from antimicrobial textiles to wound dressing composites and from sunscreens to antimicrobial packaging. Purity, surface defects, size, and morphology of the nanoparticles are the main factors that influence the antimicrobial properties. In this study, we are comparing the properties of the ZnO nanoparticles obtained by solvolysis using a series of alcohols: primary from methanol to 1-hexanol, secondary (2-propanol and 2-butanol), and tertiary (tert-butanol). While the synthesis of ZnO nanoparticles is successfully accomplished in all primary alcohols, the use of secondary or tertiary alcohols does not lead to ZnO as final product, underlining the importance of the used solvent. The shape of the obtained nanoparticles depends on the alcohol used, from quasi-spherical to rods, and consequently, different properties are reported, including photocatalytic and antimicrobial activities. In the photocatalytic study, the ZnO obtained in 1-butanol exhibited the best performance against methylene blue (MB) dye solution, attaining a degradation efficiency of 98.24%. The comparative study among a series of usual model dyes revealed that triarylmethane dyes are less susceptible to photo-degradation. The obtained ZnO nanoparticles present a strong antimicrobial activity on a broad range of microorganisms (bacterial and fungal strains), the size and shape being the important factors. This permits further tailoring for use in medical applications.

Application of biochar activated persulfate in the treatment of typical azo pigment wastewater

With the increase of the azo pigment wastewater, it is necessary to seek an efficient and sustainable treatment method to address issues of damaging water ecosystems and human health. In this work, organic representing azo dye Acid Orange 7 (AO7), heavy metal representing hexavalent chromium (Cr(VI)), and inorganic representing ammonia nitrogen (NH₄⁺-N) were selected to roughly simulate the azo pigment wastewater. The simultaneous decontamination of multi-target pollutants by 700 °C pyrolyzed peanut shell biochar (BC) with persulfate (PDS) was evaluated. The results showed that AO7, Cr(VI) and NH₄⁺-N could finally reach 100%, 85% and 30% removal ratios separately in the BC/PDS/mixed pollutants system under certain basic conditions. Functional groups (hydroxyl groups (C-OH) and carboxylic ester/lactone groups (O-C=O)) were found by XPS as competing sites for adsorption and activation and were gradually consumed as the reaction proceeded. Combining a series of experiments results and EPR analysis, it was found that AO7 removal worked best and it relied on both the radical pathway (including SO₄^•-, •OH, O₂^-•, but not ¹O₂) and adsorption. Cr(VI) was mainly adsorbed and reduced by BC surface to form Cr(OH)₃ and Cr₂O₃, and the remaining part could be reduced by O₂^-•, followed by •OH. NH₄⁺-N was removed primarily by the radical same as AO7. Meanwhile, the three target pollutants have a co-competitive mechanism. Specifically, they competed for radicals and adsorption sites simultaneously, while the presence of AO7 and NH₄⁺-N would consume the generated oxidizing radicals and further promote the removal of Cr(VI). The fixed-bed reactor simulated the continuous treatment of wastewater. Various anions (chloride (Cl^-), nitrate (NO₃^-), carbonate (CO₃^2-), and hydrogen phosphate (HPO₄^2-)) interfered differently with the pollutant removal. These findings demonstrate a new dimension of BC potential for decontamination of azo pigment wastewater.

Synthesis of BiOI@NH2-MIL125(Ti)/Zeolite as a novel MOF and advanced hybrid oxidation process application in benzene removal from polluted air stream

One of the popular process in volatile organic compounds removal in gas phase is advanced oxidation process. We in this research, synthesized BiOI@NH2-MIL125(Ti)/Zeolite nanocomposite as a novel nanocomposite to degradation of benzene in hybrid advanced oxidation process. The nanocomposite synthesized via solvothermal method. The effect of airflow, ozone gas concentration, hydrogen peroxide concentration, relative humidity and initial benzene concentration are the main parameters in the UV/O3/H2O2/ nanocomposite hybrid process that were studied. The characterization by XRD, FT-IR, FESEM, EDS element mapping, TEM, BET, and UV-vis spectra indicated that nanocomposite were well synthesized. Optimal operating conditions of the process were determined at air flow of 0.1 l/min, ozone concentration of 0.3 mg/min, hydrogen peroxide concentration of 150 ppm, relative humidity of 45 ± 3% and benzene concentration of 50 ppmv. Under these conditions, more than 99% of benzene was degraded. The synergistic effect coefficient of the mechanisms is 1.53. The nanocomposite had good stability in the hybrid process and remained above 99% efficiency up to 5 times. The ozone concentration residual the system was reported to be negligible (0.013 mg/min). The CO and CO2 emissions in the hybrid process was higher than other processes, which indicates better mineralization in the hybrid process. Formaldehyde, octane, noonan, phenol, decanoic acid were reported as the main by-products. The results indicated that UV/O3/H2O2/ nanocomposite hybrid process has fantastic efficiency in the degradation of benzene as one of the indicators of VOCs.

Rapid degradation of organic pollutants by Fe3O4@PDA/Ag catalyst in advanced oxidation process

Over the past decades, the development of novel catalysts on the degradation of organic pollutants has attracted increasing attention. In this work, we synthesized silver decorated magnetic nanoparticles (Fe₃O₄@PDA/Ag NPs) to activate H₂O₂ for organic pollutants removal via advanced oxidation processes (AOPs). The catalyst was prepared through in-situ reduction of AgNO₃ by the polydopamine (PDA) layer on Fe₃O₄ NPs. Chemiluminescence results obtained from luminol/H₂O₂ system revealed that the catalyst exhibited excellent catalytic effect on the decomposition of H₂O₂ into reactive oxygen species (ROS) and superoxide radical (O₂^-) was mainly responsible for the oxidative degradation. Importantly, the fast evolution frequency of oxygen gas bubbles produced in the reaction of Ag NPs and H₂O₂ could generate vigorous fluid convection and autonomous motion of catalyst when H₂O₂ concentration reached 1%. Additionally, the catalyst can suspend in solution for several minutes. Therefore, by coupling the vigorous motion with slow sedimentation velocity, the catalyst can realize rapid degradation of organic pollutants without external mixing force. The Fe₃O₄@PDA/Ag NPs catalysts not only showed a high removal efficiency of malachite green, but also can be applied for the degradation of other dyes, making it to be a promise candidate for environmental remediation. With the merits of excellent catalytic effect, fast degradation speed, and simplicity of operation, the prepared catalysts exhibits great potential in the practical field.

Facile synthesis of multifunctional C@Fe3O4-MoO3-rGO ternary composite and its versatile roles as sonoadsorbent to ameliorate triphenylmethane textile dye and as potential electrode for supercapacitor applications

The toxic wastewater effluents from textile dyes have been a significant environmental threat worldwide in recent decades. Against this backdrop, this study investigates the performance of C@Fe₃O₄-MoO₃-rGO as a sonoadsorbent to ameliorate crystal violet (CV) dye from the aqua matrix and further explores its potential as an electrode in supercapacitor applications. The phase purity, crystal structure, surface morphology, thermal stability and magnetic behaviour characteristics of the composite were studied using various characterisation techniques such as powder X-ray diffraction (XRD), Raman Spectroscopy, Fourier transform infrared spectroscopy (FTIR), Field emission scanning electron microscopy (FESEM), High-resolution transmission electron microscopy (HRTEM), Thermogravimetric analysis (TGA) and Vibrating-sample magnetometry (VSM). From the Langmuir isotherm model, the synthesised sonoadsorbent exhibited a maximum adsorption capacity of 1664.26 mg/g for crystal violet, which is remarkably high. Further, to its inherited magnetic characteristics, the composite can be easily separated from the solution by using an external magnet. Furthermore, the working electrode was synthesised with 80% active material, 10% carbon black, and 10% polyvinylidene difluoride to investigate its suitability in supercapacitor applications. The C@Fe₃O₄-MoO₃-rGO composite exhibited an excellent capacitance value of 180.36 F/g with commendable cycling stability, making it suitable as a potential cathode material for the next generation supercapacitors.

Ecological Approaches to Textile Dyeing: A Review

Conventional dyeing processes currently practiced in the textile industry have a great environmental impact, mainly in relation to the quantity and pollution of water, use of toxic chemicals, atmospheric emissions, and high energy consumption. This study aims to discuss the relationship between the variables that involve conventional dyeing processes and environmental issues. It presents the mapping of the materials and emerging technologies for ecological coloration, specifically for the pretreatment and dyeing stages. Regarding pretreatment, it discusses biochemical (enzymes) and physical treatment (ultraviolet radiation, plasma, and ozone technology) approaches. With respect to the dyeing processes, it addresses ecological materials (natural dyes) and emerging technologies (such as plasma, supercritical CO2, AirDye®, ultrasonic, microwave, Nano-DyeTM, and electrochemical). Given the importance of ecological coloration, this study provides important reflections on the urgency of resolving issues related to barriers and economic viability in the implementation of the alternatives presented and demonstrates the need to develop educational projects to prepare fashion and textile professionals.