An overview of nanomaterials applied for removing dyes from wastewater

Advances in agar-based composites: A comprehensive review

This review article explores the developments and applications in agar-based composites (ABCs), emphasizing various constituents such as metals, clay/ceramic, graphene, and polymers across diversified fields like wastewater treatment, drug delivery, food packaging, the energy sector, biomedical engineering, bioplastics, agriculture, and cosmetics. The focus is on agar as a sustainable and versatile biodegradable polysaccharide, highlighting research that has advanced the technology of ABCs. A bibliometric analysis is conducted using the Web of Science database, covering publications from January 2020 to March 2024, processed through VOSviewer Software Version 1.6.2. This analysis assesses evolving trends and scopes in the literature, visualizing co-words and themes that underscore the growing importance and potential of ABCs in various applications. This review paper contributes by showcasing the existing state-of-the-art knowledge and motivating further development in this promising field.

A comprehensive review on removal of pollutants from wastewater through microbial nanobiotechnology -based solutions

Increasing wastewater pollution owing to the briskly rising human population, rapid industrialization, and fast urbanization has necessitated highly efficient wastewater treatment technologies. Although several methods of wastewater treatments are in practice, expensiveness, use of noxious chemicals, generation of unsafe by-products, and longer time consumption restrain their use to a great extent. Over the last few decades, nanotechnological wastewater treatment approaches have received widespread recognition globally. Microbially fabricated nanoparticles reduce the utilization of reducing, capping, and stabilizing agents, and exhibit higher adsorptive and catalytic efficiency than chemically synthesized nanomaterials. The present review comprehensively summarizes the applications of microbial nanotechnology in the removal of a wide range of noxious wastewater pollutants. Moreover, prospects and challenges associated with the integration of nanotechnology with other biological treatment technologies including algal-membrane bioreactor, aerobic digestion, microbial fuel cells, and microbial nanofiber webs have also been briefly discussed.

Support based metal incorporated layered nanomaterials for photocatalytic degradation of organic pollutants

An effective approach to producing sophisticated miniaturized and nanoscale materials involves arranging nanomaterials into layered hierarchical frameworks. Nanostructured layered materials are constructed to possess isolated propagation assets, massive surface areas, and envisioned amenities, making them suitable for a variety of established and novel applications. The utilization of various techniques to create nanostructures adorned with metal nanoparticles provides a secure alternative or reinforcement for the existing physicochemical methods. Supported metal nanoparticles are preferred due to their ease of recovery and usage. Researchers have extensively studied the catalytic properties of noble metal nanoparticles using various selective oxidation and hydrogenation procedures. Despite the numerous advantages of metal-based nanoparticles (NPs), their catalytic potential remains incompletely explored. This article examines metal-based nanomaterials that are supported by layers, and provides an analysis of their manufacturing, procedures, and synthesis. This study incorporates both 2D and 3D layered nanomaterials because of their distinctive layered architectures. This review focuses on the most common metal-supported nanocomposites and methodologies used for photocatalytic degradation of organic dyes employing layered nanomaterials. The comprehensive examination of biological and ecological cleaning and treatment techniques discussed in this article has paved the way for the exploration of cutting-edge technologies that can contribute to the establishment of a sustainable future.

Carboxymethyl cellulose assisted morphology controlled synthesis of Mn3O4 nanostructures for adsorptive removal of malachite green from water

The physicochemical properties of manganese oxides and their different applications mainly depend upon their crystallite size, morphology, phase structure, and surface properties, which are again dependent on the preparation methods. So, a simple, cost-effective, and versatile synthesis method for such materials is highly desirable. Intending to accomplish this, herein we report the synthesis of Mn3O4 nanostructures by alkaline hydrolysis of the corresponding metal ions in an aqueous medium. The addition of a biodegradable polymer, sodium salt of carboxymethyl cellulose (Na-CMC) assisted the development of specific morphology, which is tunable by varying the concentration of the biopolymer. The spectroscopic, microscopic, and diffractometric analyses of the synthesized Mn3O4 nanostructures confirm that this particular simple technique is very effective in controlling the morphology of the formed nanostructures. These Mn3O4 nanostructures exhibit excellent adsorption capacity in the removal of malachite green (MG) from its aqueous solution under ambient conditions. The adsorption process is exothermic following pseudo-second-order kinetics with a maximum dye adsorption capacity of 489.68 mg g-1 according to the Sips isotherm model. The Mn3O4 nanostructures can be reused for up to five cycles of dye adsorption without significant loss of their adsorption performance.

Kinetics and adsorption isotherms studies for the effective removal of Evans blue dye from an aqueous solution utilizing forsterite nanoparticles

In the present day, water treatment has emerged as a significant global concern, particularly due to the proliferation of pollution sources. The utilization of dyes, such as Evans blue, in several industries is among the most significant contributors to these pollutants. Forsterite nanoparticles were synthesized by the sol-gel technique and calcined at different temperatures to determine the optimum temperature at which pure nanoforsterite was obtained. Then, it was analyzed using X-ray diffraction (XRD), atomic force microscope (AFM), transmission electron microscope (TEM), Brunauer-Emmett-Teller (BET) , contact angle, and zero-point charge. The adsorption capability of forsterite nanoparticles (Nps) was evaluated by a batch adsorption experimental method to remove Evans blue dye (EBD). Parameters such as agitation speed, dosage of forsterite Nps, pH, and contact time were considered at ambient temperature. At pH = 3, dose of Nps = 1 g/L, and 600 rpm within 10 min, the results indicated a removal rate of around 100%. Furthermore, it was shown that the material may be employed for 3 cycles with a removal rate of 90%. Multiple kinetic and isotherm models, including Langmuir, Temkin, and Freundlich models, were used to analyze the results and clarify the mechanism of the adsorption phenomena. The findings from the isotherm and kinetic studies indicated that the system conforms to Langmuir and pseudo-second-order, respectively.

The usability of green deep eutectic solvents in hollow fiber Liquid-Phase microextraction for the simultaneous extraction of analytes of different Natures: A comprehensive study

In the current study, a wide range of deep eutectic solvents (DESs) with different properties (hydrophilic, hydrophobic, ionic, and nonionic) were prepared in the initial phase. Subsequently, an assessment was conducted to evaluate some characteristics of the produced DESs, including their stability at room temperature and their capacity to extract three distinct types of analytes (anionic, cationic, and non-ionic) simultaneously through hollow fiber-liquid phase microextraction (HF-LPME) technique. To carry out the extraction procedure, the prepared DESs were inserted into the pores (as supported liquid membrane (SLM)) and lumen of hollow fiber membrane (HF) to apply two-phase and three-phase HF-LPME techniques. After a thorough evaluation, the three-phase HF-LPME technique (HF(3)-LPME) was chosen by using a mixture of menthol/TBAB-based hydrophobic DES (DES-35) as SLM and the mixture of malic acid/citric acid/water-based hydrophilic DES (DES-2) as an extraction solvent in the lumen of HF. All factors affecting the extraction recovery (including pH, extraction time, extraction temperature, stirring speed, and salt effect) were optimized utilizing the one-variable-at-a-time (OVAT) methodology. After applying the extraction procedure, all extracted samples were analyzed using the UV-Vis spectrometer and results were recorded at different wavelengths including 655 nm for Methylene blue, 550 nm for Amaranth, and 375 nm for Quercetin. The calibration graphs showed linearity in the range of 20.0-1500 µg/L, with a limit of detection of 6.2-15.1 µg/L and correlation coefficients higher than 0.9913 for the studied analytes. Moreover, the intra-day RSD, inter-day RSD, preconcentration factor (PF), enrichment factors (EF), and extraction recoveries (ER%) were obtained in the range of 3.1-4.8, 3.8-6.7, 125, 102.9-111.4, and 82.3-89.1 %, respectively. The use of the selected DES in the HF-LPME methodology resulted in an ecologically friendly strategy, as evidenced by the use of green metrics from the SPMS tool. The proposed strategy is also considered environmentally friendly due to its use of minimal solvents, waste reduction, and low energy consumption. The proposed technique effectively and simultaneously extractedmethylene blue, amaranth, and quercetin analytes in different real samples.

Zn-Al layered double hydroxide supported on waste cow dung-derived biochar as a highly efficient adsorbent for anionic dye removal from contaminated water

In this study, Zn-Al-SO42- LDH-functionalized biochar was fabricated using the co-precipitation method. The biochar was synthesized from waste cow dung using a low-temperature pyrolysis process (300 °C). The materials were fully characterized by TGA, FTIR, EDS, SEM, and XRD analysis. Then, a comparative study was performed to investigate the adsorption capacity of the materials against an anionic dye (i.e., methyl orange (MO)). The LDH-functionalized biochar demonstrated high adsorption capacity (400 mg/g in 120 min, at pH 5) compared to the raw biochar (212 mg/g in 120 min, at pH 5). The effect of various adsorption parameters (e.g., pH of the dye solution, temperature, initial concentration, adsorbent dosage, and contact time) was investigated. The adsorption of MO on LDH-functionalized biochar followed the Freundlich isotherm and pseudo-second-order kinetics, while the raw biochar followed the Langmuir isotherm and pseudo-second-order kinetics. The thermodynamic data indicated the endothermic nature of adsorption and an increase in the degree of randomness during adsorption. The enhanced adsorption capacity of the Zn-Al LDH-functionalized char was attributed to the synergistic effect of the surface adsorption into the porous biochar matrix, interlayer adsorption, and ion exchange capacity of the LDHs. Therefore, modification of waste cow dung-derived biochar with Zn-Al LDH can be a promising approach to fabricate a highly efficient adsorbent for toxic dyes from wastewater.

Advancements in enzyme immobilization on magnetic nanomaterials: toward sustainable industrial applications

Enzymes are widely used in biofuels, food, and pharmaceuticals. The immobilization of enzymes on solid supports, particularly magnetic nanomaterials, enhances their stability and catalytic activity. Magnetic nanomaterials are chosen for their versatility, large surface area, and superparamagnetic properties, which allow for easy separation and reuse in industrial processes. Researchers focus on the synthesis of appropriate nanomaterials tailored for specific purposes. Immobilization protocols are predefined and adapted to both enzymes and support requirements for optimal efficiency. This review provides a detailed exploration of the application of magnetic nanomaterials in enzyme immobilization protocols. It covers methods, challenges, advantages, and future perspectives, starting with general aspects of magnetic nanomaterials, their synthesis, and applications as matrices for solid enzyme stabilization. The discussion then delves into existing enzymatic immobilization methods on magnetic nanomaterials, highlighting advantages, challenges, and potential applications. Further sections explore the industrial use of various enzymes immobilized on these materials, the development of enzyme-based bioreactors, and prospects for these biocatalysts. In summary, this review provides a concise comparison of the use of magnetic nanomaterials for enzyme stabilization, highlighting potential industrial applications and contributing to manufacturing optimization.

Synthesis of Composite Sorbents with Chitosan and Varied Silica Phases for the Adsorption of Anionic Dyes

In this work, various types of silica materials were used for the synthesis of chitosan-silica composites. The composites were obtained using the chitosan (Ch) immobilization process from an aqueous solution on various silica phases, i.e., amorphous diatomite (ChAD), crystalline diatomite (ChCD), mesoporous silica MCM-41 (ChMCM), and mesoporous silica SBA-15 (ChSBA). Textural, structural, morphological, and surface properties of the materials were determined by using various measurement techniques, i.e., low-temperature adsorption/desorption isotherms of nitrogen, X-ray diffraction (XRD), small-angle X-ray scattering (SAXS), potentiometric titration, high-resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The adsorption properties towards various anionic dyes, i.e., acid red 88 (AR88), acid orange 8 (AO8), and orange G (OG), were evaluated based on kinetic and equilibrium measurements. The ChSBA, ChAD, and ChMCM composites were characterized by relatively high adsorption capacities (am) for AR88, with values equal to 0.78, 0.71, and 0.69 mmol/g, respectively. These composites were also distinguished by the rapid AR88 adsorption rate, with the values of half-time parameter t0.5 equal to 0.35, 2.84, and 1.53 min, respectively. The adsorption equilibrium and kinetic data were analyzed by applying the generalized Langmuir isotherm and the multi-exponential equation (m-exp), respectively. An interaction mechanism between the dyes and the obtained materials was proposed.

Enhanced photocatalytic degradation of Rhodamine B using gold nanoparticles decorated on BaTiO3 with surface plasmon resonance enhancement

This study focused on synthesizing and applying gold nanoparticle (Au NP) decorated barium titanate (BaTiO3) nanoparticles for photocatalytic purposes. BaTiO3 NPs were synthesized using a facile hydrothermal method. Various techniques were employed to characterize the structure and morphological characteristics of the prepared materials. The photocatalytic degradation of Rhodamine B over the Au NPs-modified BaTiO3 photocatalysts was studied. Trapping experiments were conducted using different scavengers to elucidate the degradation mechanism and the involvement of photogenerated species. The incorporation of an appropriate amount of Au NPs into the composites resulted in a significant improvement in photocatalytic activity, attributed to the combined effect of Schottky junction at the interface and the surface plasmon resonance of Au NPs.

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.

A comparison of endosulfan removal by photocatalysis process under UV-A and visible light irradiation: optimization, degradation byproducts and reuse

In this study, the removal efficiency of endosulfan as a persistent organic pollutant and formation of its metabolites were investigated using Ag/TiO2/Fe3O4 photocatalyst under visible and UV-A light. Light intensity, catalyst amount, initial endosulfan concentration, initial pH and time were determined as controllable factors for Taguchi experimental design. The highest removal efficiencies of endosulfan were achieved as 86.14% and 85.46% for visible and UV-A light sources, respectively. According to the greatest best criterion, the level at which the highest S/N ratio was obtained for each parameter was accepted as the optimum value. As a result of the validation experiments, 94.2% and 91.9% efficiency were obtained for visible and UV-A light, respectively. The metabolite formations of endosulfan (endosulfan sulfate, ether, and lactone) remained below 7% in all experiments on a concentration basis. In the reuse experiments of the magnetically recovered photocatalyst, high removal efficiency of around 80% was obtained after four cycles. The removal efficiencies were found to be 86.7% and 84.8%, for real samples taken from the drinking water treatment plant inlet and the spring water network injected with endosulfan under optimal photocatalysis experimental conditions, respectively. It has been shown that nitrate and sulfate anions, which are in significant concentrations in raw water samples, have very little effects on endosulfan removal. The overall results showed that the Ag/TiO2/Fe3O4 photocatalyst was produced successfully, the catalyst was highly effective in the mineralization of endosulfan in synthetic and real water samples under UV and visible light, and effective yields could be obtained even with reuse.

Supplementary information

The online version contains supplementary material available at 10.1007/s40201-023-00864-z.

Treatment of landfill leachate using photocatalytic based advanced oxidation process - a critical review

Landfill leachate is a discrete volumetric component of municipal solid waste; hence, researchers and professionals are more concerned about it because of its obscurity. Innovative treatment and emerging technologies are being scrutinized to address the treatment of landfill leachate challenges. The leading target of this review was to examine the possibility of removing recalcitrant organic pollutants from landfill leachate by photocatalytic-based advanced oxidation processes. A summary of the systematic applicability of conventional treatment for landfill leachate is provided, with a focus on physico-chemical and biological processes. The biological treatment, such as aerobic and anaerobic digestion, is an excellent technique for treating highly concentrated organic pollutants in the wastewater. However, Leachate can scarcely be treated using conventional techniques since it is enriched with refractory organics and inorganic ions. It is clear from the literature review that none of the available combinations of physico-chemical and biological treatments are entirely relevant for the removal of recalcitrant organic pollutants from leachate. Recently, the photo-assisted TiO2/ZnO oxidation has shown an excessively potential and feasible way to treat landfill leachate. TiO2/ZnO photocatalysis is currently developing to treat recalcitrant organic pollutants from landfill leachate. The effect of operating parameters reveals that pH and temperature affect the reaction rate. The addition of oxidant H2O2 to the TiO2/ZnO suspension suggests that TiO2 leads to an increase in the rate of reaction when compared to ZnO. Photocatalytic remediation technique of landfill leachate would support the goal of environmental sustainability by greatly enhancing the effectiveness of treated leachate reutilization. In this review, the selection of the best photocatalytic treatment for leachate based on its systematic relevance and potential conditions, characteristics, cost-effectiveness, essential controlling, discharge limit, long-term environmental effects, and its future study perspectives are emphasized and discussed.

Biosynthesis of silver nanoparticles using tea leaf extract (camellia sinensis) for photocatalyst and antibacterial effect

Silver nanoparticles (C. AgNPs) are synthesized by the biological reduction method using extracts from green tea leaves (Camellia Sinensis) collected from tea hills at an altitude of 100 m above the ground. The chemicals present in the tea leaf extract act as reducing agents used to reduce Ag+ ions to silver atoms to form C. AgNPs in the solution. In this work, we optimized the C. AgNPs synthesis process by investigating the influence of reaction parameters such as concentration of tea leaf extract (1 ppm-50 ppm), reaction temperature (30 °C-60 °C), reaction time (5 min-100 min), and reaction rate (400 rpm-800 rpm) through absorption UV-Vis spectroscopy, TEM transmission electron microscopy, and spectroscopy X-ray. Organic compounds in tea leaf extract are detected by NMR measurement. The functional groups on the C. AgNPs are shown on the Fourier transform infrared (FTIR) spectrum. The C. AgNPs are used to degrade MB dye at 10 ppm concentration based on the photocatalytic effect using a 6500 K white light source. The C. AgNPs have also been studied for their antibacterial activity on two bacteria, Pseudomonas aeruginosa (P.A) and Staphylococcus aureus (S.A), while a positive control is Ampicillin 50 mg/ml and a negative control is H2O. The results reveal that the C. AgNPs with diameters in the range of 25 nm-55 nm degrade 10 ppm MB dye after 1 h with photodegradation efficiency up to 96 %. The antibacterial ability of C. AgNPs against both bacteria is good, even superior to that of Ampicillin. Furthermore, the particle synthesis efficiency and therefore the antibacterial activity as well as the photodegradation effect of C. AgNPs are higher than previously reported. At the same time, using green tea leaf extract to synthesize C. AgNPs creates environmentally friendly products. These useful behaviors are the potential to increase the scope and applicability of C. AgNPs, especially for biomedical applications in the near future.

Photocatalytic Degradation Studies of Organic Dyes over Novel Cu/Ni Loaded Reduced Graphene Oxide Hybrid Nanocomposite: Adsorption, Kinetics and Thermodynamic Studies

Nowadays, for environmental remediation, photocatalytic process involving graphene-based semiconductors is considered a very promising oxidation process for water treatment. In the present study, nanocomposite (Cu/Ni/rGO) has been synthesized by Dypsis lutescens leaf extract. Characterization of the sample was carried out by UV-visible spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). Different parameters like contact time, nanocatalyst amount, dye concentration, effect of temperature. and pH factor were optimized to examine the maximum removal efficiency for dyes rhodamine B and alizarine R with and without visible light source. In both cases, i.e., with or without light, maximum removal was observed at 20 mg of nanocatalyst for 5 ppm concentration of both dyes at 45 °C temperature and pH 10 for rhodamine B and pH 4 for alizarine R, respectively with a 20 min contact time. Maximum removal of dyes 93% rhodamine B and 91% alizarine R were observed under a tungsten lamp as compared to without a tungsten lamp, i.e., 78% of RhB and 75% of AR from mixture solution of these dyes. To assess the rate of reaction, spontaneity, and nature of reaction thermodynamics, kinetics and adsorption isotherms were studied. Thermodynamic values indicated that both dyes depicted endothermic and spontaneous degradation processes. Isotherm data fitted best to a Freundlich isotherm, while results of kinetic studies of both dyes followed the pseudo 2nd order kinetic equation. In the end, scavenging radical studies concluded that hydroxyl radicals were the main active specie involved in the photocatalytic degradation process, and regeneration experiments resulted that Cu/Ni/rGO nanocomposites were re-utilized for about four times.

Bio-fabricated bismuth-based materials for removal of emerging environmental contaminants from wastewater

Although rapid industrialization has made life easier for humans, several associated issues are emerging and harming the environment. Wastewater is regarded as one of the key problems of the 21st century due to its massive production every year and requires immediate attention from all stakeholders to protect the environment. Since the introduction of nanotechnology, bismuth-based nanomaterials have been used in variety of applications. Various techniques, such as hydrothermal, solvo-thermal and biosynthesis, have been reported for synthesizing these materials, etc. Among these, biosynthesis is eco-friendly, cost-effective, and less toxic than conventional chemical methods. The prime focuses of this review are to elaborate biosynthesis of bismuth-based nanomaterials via bio-synthetic agents such as plant, bacteria and fungi and their application in wastewater treatment as anti-pathogen/photocatalyst for pollutant degradation. Besides this, future perspectives have been presented for the upcoming research in this field, along with concluding remarks.

Preparation of Fe2(MoO4)3/graphene/Ti nanocomposite electrode for visible-light photoelectrocatalytic degradation of organic pollutants

The massive emission of organic pollutants, specially organic dyes into water poses a serious threat to the environment and human health. Photoelectrocatalysis (PEC) has been regarded as an efficient, promising and green technology for organic pollution degradation and mineralization. Herein, Fe₂(MoO₄)₃/graphene/Ti nanocomposite was synthesized and applied as a superior photoanode in a visible-light PEC process for degradation and mineralization of an organic pollutant. First, the Fe₂(MoO₄)₃ was synthesized by the microemulsion-mediated method. Then, Fe₂(MoO₄)₃ and graphene particles were simultaneously immobilized on a titanium plate by the electrodeposition technique. The prepared electrode was characterized by XRD, DRS, FTIR and FESEM analyses. The ability of the nanocomposite was investigated in the Reactive Orange 29 (RO29) pollutant degradation by the PEC. The Taguchi method was used for the visible-light PEC experiments design. The efficiency of RO29 degradation was enhanced with increasing bias potential, number of Fe₂(MoO₄)₃/graphene/Ti electrodes, visible-light power and Na₂SO₄ (electrolyte) concentration. The pH of the solution was the most influential variable in the visible-light PEC process. Furthermore, the performance of the visible-light PEC was compared with photolysis, sorption, visible-light photocatalysis and electrosorption processes. The obtained results confirm the synergistic effect of these processes on RO29 degradation by the visible-light PEC.

Novel synthesis of siligraphene/tungstates (g-SiC/AWO) with promoted transportation of photogenerated charge carriers via direct Z-scheme heterojunctions

We developed here the efficient photocatalysts for the removal of high concentrations of tetracycline under visible light by immobilizing the AWO (A = Ag, Bi, Na) nanocrystals on the surface of siligraphene (g-SiC) nanosheets. The g-SiC/AWO composites was synthesized by magnesiothermic synthesis of g-SiC and sonochemical immobilization of tungstates. These new heterojunctions of g-SiC/tungstates show superior photocatalytic activities in the degradation of high concentrations of tetracycline and 97, 98, and 94% of tetracycline were removed by using low amounts of g-SiC/Ag₂WO₄, g-SiC/Bi₂WO₆, and g-SiC/Na₂WO₄ catalysts, respectively. Based on band structures, the band gaps reduce and the photocatalytic activities were extremely enhanced due to the shortening of electron transfer distance through the Z-scheme mechanism. Also, the graphenic structure of g-SiC is another parameter that was effective in improving photocatalytic performance by increasing the electron transfer and decreasing the rate of electron-hole recombination. Furthermore, the π back-bonding of g-SiC with metal atoms increases the electron-hole separation to enhance the photocatalytic activity. Interestingly, g-SiC composites (g-SiC/AWO) showed much higher photocatalytic properties compared to graphene composites (gr/AWO) and can remove the tetracycline even at dark by producing the oxygenated radicals via adsorption of oxygen on the positive charge of Si atoms in siligraphene structure.

Photocatalytic degradation of Reactive Black dye using ZnO-CeO2 nanocomposites

This study presents the photocatalytic efficiency of ZnO-CeO₂ nanocomposites for the degradation of a model Reactive Black (RB) dye. Nano-CeO₂ was synthesized using cerium nitrate precursor solution via chemical precipitation. Synthesized nano-CeO₂ was mixed with ZnO nanoparticles in different mass ratios to obtain ZnO-CeO₂ heterojunction photocatalyst. The morphology of the nanocomposites was examined using transmission electron microscope (TEM). X-ray diffraction patterns of the CeO₂ corresponded well with (1 1 1) plane of cubic-phase CeO₂. The band gap of the ZnO-CeO₂ nanocatalyst synthesized was determined to be 3.08 eV, which was lower than that of the pristine CeO₂ and ZnO powders, respectively. The results indicate that 1:1 wt. ratio ZnO-CeO₂ nanocomposite provides about 85% RB degradation within 90 min under UV light under alkaline pH conditions. Degradation rate of RB dye achieved with ZnO-CeO₂ nanocomposite was almost 1.5 times greater than that obtained with pristine ZnO. Increasing CeO₂ ratio beyond 1:1 wt. ratio did not significantly increase RB degradation. The results demonstrate that addition of CeO₂ to ZnO results in lowering its band gap energy and aids charge carrier separation resulting in enhanced oxidation of RB dye under UV light.

Micro-mechanism insights into the adsorption of anionic dyes using quaternary ammonium-functionalised chitosan aerogels

The development of adsorbents with outstanding adsorption capacities, wide versatility, and excellent recyclability for the removal of organic dyes remains a challenge. In this study, a quaternised chitosan-based aerogel (QCSA) was fabricated via a facile method to effectively treat concomitant anionic dyes. Porous QCSA with high hydrophilicity, nontoxicity, excellent thermal stability, and sustainability exhibits adsorption properties superior to most previously reported adsorbents. The equilibrium adsorption capacities for Congo red, Sunset yellow, and Methyl orange were 1259.6, 550.2, and 607.5 mg/g, respectively. Notably, the spent QCSA exhibits excellent cyclic performance. The multilayer adsorption, external-internal mass transfer resistance, and adsorption on the active site models were employed to enable a more accurate description of the dynamic characteristics, confirming that double-layer chemisorption was the dominant process. A quantitative analysis of the electrostatic potential and the independent gradient model further verified that electrostatic interactions, hydrogen bonding, and van der Waals forces led to the highly efficient adsorption of dye molecules. Therefore, the eco-friendly and recyclable QCSA is a promising adsorbent for trapping anionic dyes from aquatic systems.

Photocatalytic degradation of dyes by novel electrospun nanofibers: A review

Textile industry is a significant contributor of wastewater, which contains pollutants including dye and other chemical substances. The release of thousands of tons of dye used in textile processing and finishing into natural streams and aquatic bodies present dire harm to the environment. In response to environmental concerns, a number of research have been done using low-cost technology to produce absorbents that can remove dyes from water bodies. Distinct techniques such as adsorption, enzymatic and photocatalytic degradation, etc. have been employed to remove dyes. In the last few decades, photocatalysis, a simple and green strategy, has emerged as the most valuable and recent principle that deals with wastewater treatment, using uniquely fabricated nanomaterials. Among them, rapid and versatile electrospinning methods have been used for the construction of a large surface area, hierarchical and reusable nanofibers for environmental remediation. As a flexible and fast fabrication method, reviewing the use of electrospun photocatalytic nanofibers, influential parameters in electrospinning and their effectiveness in the generation of oxidizing agents are a promising platform for the fabrication of novel nanomaterials in photocatalytic degradation of dyes. This review discusses techniques for dye removal, electrospun nanofibers, their fabrication and application in photocatalysis; mechanism of photocatalytic degradation, and challenges and suggested remedies for electrospun nanofibers in photocatalysis.

Insights on applications of bentonite clays for the removal of dyes and heavy metals from wastewater: a review

In recent decades, increased industrial, agricultural, and domestic activities have resulted in the release of various pollutants into the aquatic systems, which require a reliable and environmentally friendly method to remove them. Adsorption is one of the most cost-effective and sustainable wastewater treatment techniques. A plethora of low-cost bio-based adsorbents have been developed worldwide so far to supplant activated carbon and its high processing costs. Bentonite clays (BCs), whether in natural or modified form, have gained enormous potential in wastewater treatment and have been used successfully as a novel and cost-effective bio-sorbent for removing organic and inorganic pollutants from the liquid suspension. It has become a sustainable solution for wastewater treatment due to its variety of surface and structural properties, superior chemical stability, high capacity for cation exchange, elevated surface area due to its layered structure, non-toxicity, abundance, low cost, and high adsorption capacity compared to other clays. This review encompasses comprehensive literature about various modification techniques and adsorption mechanisms of BCs concerning dyes and heavy metal removal from wastewater. A critical overview of different parameters for optimizing adsorption capacity and regeneration via the desorption technique has also been presented here. Finally, a conclusion has been drawn with some future research recommendations based on technological challenges encountered in industrializing these materials.

Copper Nanoparticles Decorated Alginate/Cobalt-Doped Cerium Oxide Composite Beads for Catalytic Reduction and Photodegradation of Organic Dyes

Cobalt-doped cerium oxide (Co-CeO₂) was synthesized and wrapped inside alginate (Alg) hydrogel beads (Alg/Co-CeO₂). Further, copper nanoparticles (Cu) were grown on Alg/Co-CeO₂ beads. Cu decorated Alg/Co-CeO₂ composite beads (Cu@Alg/Co-CeO₂) were tested as a catalyst for the solar-assisted photodegradation and NaBH₄-assisted reduction of organic pollutants. Among different dyes, Cu@Alg/Co-CeO₂ was found to be the best catalyst for the photodegradation of acridine orange (ArO) under solar light and efficient in reducing methyl orange (MO) with the aid of NaBH₄. Cu@Alg/Co-CeO₂ decolorized ArO up to 75% in 5 h under solar light, while 97% of MO was reduced in 11 min. The decolorization efficiency of Cu@Alg/Co-CeO₂ was further optimized by varying different parameters. Thus, the designed catalyst provides a promising way for efficient oxidation and reduction of pollutants from industrial effluents.

Fe-C-based materials: synthesis modulation for the remediation of environmental pollutants-a review

Presently, the rapid pace in the discovery of emerging aquatic pollutants is increasing the demand for the remediation and treatment of our natural resources. Regarding this, nanotechnology is being considered the potential solution for contaminated water remediation with techniques such as filtration, adsorption, catalysis, and desalination. For this purpose, zerovalent iron (ZVI) is being widely used in the remediation of environmental pollutants due to its large specific surface area and high reactivity. However, ZVI is easy to agglomerate and oxidize, limiting its application in the real environment. Therefore, the present study was designed to discuss the preparation and characterization methods of ZVI composite materials, factors affecting adsorption, the removal effect, and adsorption mechanism of different pollutants by Fe-C materials because the optimization and modification of nano-zero-valent iron is a hot research topic nowadays in this field. Moreover, this paper does also analyze the possibility of the practical application prospects of the team's technology for preparing iron-carbon materials. Thus, this information will be helpful for the development and application of Fe-C-based technologies for water and soil remediation and the prediction of the future research direction of Fe-C composite materials.

Template Method for Synthesizing Hierarchically Porous MIL-101(Cr) for Efficient Removal of Large Molecular Dye

As one of the most important prototypical chromium-based MOFs, MIL-101(Cr) is well-studied and widely employed in various scientific fields. However, due to its small capture window sizes and curved internal apertures, its application in large molecular removal is quite limited, and given its high stability and high synthetic temperature (>200 °C), it is difficult to achieve hierarchically porous MIL-101(Cr). In our study, hierarchically porous MIL-101(Cr) involving a high macro-/meso-/micropores ratio was designed and synthesized using acetic acid as an additive and silicon dioxide (SiO2) nanoparticles as a template. The optimal hierarchically porous MIL-101(Cr) (A-4) possessed a high specific surface area (2693 m2 g−1) and an abundant macro-/mesoporous structure with the addition of SiO2 of 200 mg. Compared with the control sample (A-0) with a less macro-/mesoporous structure, A-4 showed good adsorption properties for both coomassie brilliant blue R-250 (CBB, 82.1 mg g−1) and methylene blue (MB, 34.3 mg g−1) dyes, which were 1.36 times and 9.37 times higher than those of A-0. Moreover, A-4 also had good recyclability, and the removal rate of CBB was still higher than 85% after five cycles of adsorption.

A comprehensive review on sustainable greener nanoparticles for efficient dye degradation

The effluents released from textile industries mainly consist of dyes, metals and other pollutants. Dyes often are discharged in wastewater streams causing adverse effect on the environment. To eliminate these harmful dyes, various techniques are emerging out of which nanotechnology is the most reliable and safer. Nanotechnology offers convincing applications in case of environmental and economic concerns. The bio-synthesis of nanoparticles has several advantages over conventional methods and approach towards environment concern as well. Biological method of nanoparticles synthesis is concluded to be the most promising and efficient in action. Bio-synthesised nanoparticles could be used for treatment and decolourisation of dyes in an efficient manner. This review comprises the study of number of bio-synthesised nanoparticles utilised for degradation of various dyes present as pollutants in wastewater. Bio-synthesised nanoparticles such as gold, silver, iron, cobalt, zinc, titanium and molybdenum used for degradation of various dyes have been discussed in this review.

Nanomaterials: An alternative source for biodegradation of toxic dyes

Environment contamination is a colossal worriment across the world, owing to its detrimental and negative impact on health and ecological systems. Dyes are one of the synthetic organic chemicals that are utilised in a variety of fields, including textiles. As a result, throughout one's production and subsequently in fibre colouring, these are becoming frequent industry-contributed contaminants. Increasing globalisation of international market has presented a problem to textile sector in terms of consistency and production. Textile processors' primary concern, as the highly competitive environment and environmental standards grow more severe is about being mindful of the grade of goods and even non-toxicity of their production processes. There seems to be an immediate necessity to look for methods and technologies which are useful in removing dye colours. Even though each has benefits and weaknesses, many physical, chemical, and biological approaches were explored and used with the application being dependent on the effluent properties, technical feasibility, and cost. Several remediation technologies are already developed, but they seem to be ineffective at removing dyes completely. There is a fast growth of nanoparticles applications in the past few years which has opened up newer, innovating, highly efficient, and low-cost dyes remediation systems. Nanomaterials with large surface areas change surface characteristics and distinctive electron conducting capabilities which make them ideal candidate for the treatment of wastewater that contains dyes. In this review, we have highlighted not only the role of nanotechnology in dye remediation processes but also different types of nanomaterials that can be used for the remediation of dyes.

Hexavalent chromium removal from aqueous solutions using biogenic iron nanoparticles: Kinetics and equilibrium study

Green mediated biosynthesis of iron oxide nanoparticles utilising Rosa indica flower petal extracts (RIFP-FeONPs) was used in this investigation. The RIFP-FeONPs were evaluated by the UV-Visible Spectroscopy, FTIR, SEM, EDX, XRD, Zeta potentials, and DLS, and been engaged than for the elimination of Cr (VI) from the contaminated environments. At 269 nm, the RIFP-FeONPs surface plasmon vibration bands were observed, which attributed to the Fe³⁺. XRD patterns of RIFP-FeONPs depicted the intense diffraction peak of face-centered cubic (fcc) iron at a 2θ value of 45.33° from the (311) lattice plane indisputably revealed that the particles are constituted of pure iron. The fabricated nanomaterials are spherical and polydisperse with a diameter of 70-120 nm, and various agglomeration clusters are attributable to intermolecular interaction. Zeta potential measurement and particle size distribution of RIFP-FeONPs showed a mean average size of 115.5 ± 29 nm and a polydispersity index (PDI) of 0.420. The study aims to analyse the appropriateness of RIFP-FeONPs for removing hexavalent chromium from the aqueous environment and the application of adsorption isotherm and statistical models in the experiment. The sorption of Cr (VI) on RIFP-FeONPs was observed to fit well with the isothermal models (R² = 0.98). The linear correlation between processing parameters and time demonstrated that the adsorption efficiency of Cr (VI) well correlated with the pseudo-first order kinetic model and isothermal adsorption with the Langmuir and Freundlich isothermal models, so that the RIFP-FeONPs could be a prospective nanosorbent for hexavalent chromium removal from industrial waste.

Dye Removal Ability of Pure and Doped Graphitic Carbon Nitride

Background:

Rapid escalation in textile, paper, pesticides, pharmaceuticals and several other chemical based manufacturing industries due to amplification in human requirements have proportionately contributed to the extreme contamination of water ecosystem, resulted from the discharge of toxic pollutants from industries. Effluents from textile industries are comprised of coloured dyes like Rhodamine B, Methyl Orange, Methylene Blue and phenolic compounds which deserve special mention owing to their non-biodegradable, carcinogenic and severe detrimental nature. Urgent needs to ameliorate this fast declining environmental situation are of immense necessity in current scenario.

Objectives:

Objectives: In this regard, graphitic carbon nitride (GCN) is a distinguished material for water purification-based applications because of its exclusive characteristics making it highly prospective for degradation of toxic dyes from water by catalysis and adsorption techniques. GCN has been a material of conspicuous interest in recent times owing to its two dimensional sheets like structure with favourable surface area, and cost-effective synthesis approaches along with high production yield. This article presents a detail study of different aspects of GCN as a material of potential for water purification. Through extensive literature survey it has been shown that GCN is an effective material to be used in the fields of application. Several effective procedures like catalysis or adsorption for removal of dyes from water have been discussed with their basic science behind.

Conclusions:

This systematic effort shows that GCN can be considered to be one of the most efficient water purifier with further advantages arising from its easy and cost effective large scale synthesis.

Recent Developments in the Application of Bio-Waste-Derived Adsorbents for the Removal of Methylene Blue from Wastewater: A Review

Over the last few years, various industries have released wastewater containing high concentrations of dyes straight into the ecological system, which has become a major environmental problem (i.e., soil, groundwater, surface water pollution, etc.). The rapid growth of textile industries has created an alarming situation in which further deterioration to the environment has been caused due to substances being left in treated wastewater, including dyes. The application of activated carbon has recently been demonstrated to be a highly efficient technology in terms of removing methylene blue (MB) from wastewater. Agricultural waste, as well as animal-based and wood products, are excellent sources of bio-waste for MB remediation since they are extremely efficient, have high sorption capacities, and are renewable sources. Despite the fact that commercial activated carbon is a favored adsorbent for dye elimination, its extensive application is restricted because of its comparatively high cost, which has prompted researchers to investigate alternative sources of adsorbents that are non-conventional and more economical. The goal of this review article was to critically evaluate the accessible information on the characteristics of bio-waste-derived adsorbents for MB's removal, as well as related parameters influencing the performance of this process. The review also highlighted the processing methods developed in previous studies. Regeneration processes, economic challenges, and the valorization of post-sorption materials were also discussed. This review is beneficial in terms of understanding recent advances in the status of biowaste-derived adsorbents, highlighting the accelerating need for the development of low-cost adsorbents and functioning as a precursor for large-scale system optimization.

A RGO aerogel/TiO2/MoS2 composite photocatalyst for the removal of organic dyes by the cooperative action of adsorption and photocatalysis

A composite consisting of reduced graphene oxide aerogel/titanium dioxide/molybdenum disulfide (abbreviated as RGO aerogel/TiO₂/MoS₂) was developed for the removal of organic dyes from solution cooperatively by adsorption and photocatalytic degradation mechanisms. The composite was successfully synthesized by stepwise layered assembly integration, including sol-gel and physical vapor deposition (PVD) methods. The resulting multi-component composite material featured a high specific surface area (255.441 m²/g) containing a myriad of negatively charged carboxylate functional groups on the surface of the composite, which enabled the composite material to demonstrate a high removal efficiency of cationic dyes, such as rhodamine B, from solution. In addition, the composite featured optimal optical and photocatalytic properties for facilitating efficient photodegradation of the dye molecules, including a large absorbance in the visible light region and a fast transfer of photogenerated electron-hole pairs. Moreover, electron paramagnetic resonance (EPR) analysis and reactive oxygen species scavenging experiments confirmed that superoxide radicals (O₂^•-), holes (h⁺), and hydroxyl radicals (^•OH) were involved in photocatalytic degradation of the organic dyes.

Toward efficient dye degradation and the bactericidal behavior of Mo-doped La2O3 nanostructures

In this study, different concentrations (0, 0.02, 0.04, and 0.06 wt%) of Mo doped onto La2O3 nanostructures were synthesized using a one-pot co-precipitation process. The aim was to study the ability of Mo-doped La2O3 samples to degrade toxic methylene blue dye in different pH media. The bactericidal potential of synthesized samples was also investigated. The structural properties of prepared samples were examined by XRD. The observed XRD spectrum of La2O3 showed a cubic and hexagonal structure, while no change was recorded in Mo-doped La2O3 samples. Doping with Mo improved the crystallinity of the samples. UV-Vis spectrophotometry and density functional theory calculations were used to assess the optical characteristics of Mo-La2O3. The band gap energy was reduced while the absorption spectra showed prominent peaks due to Mo doping. The HR-TEM results revealed the rod-like morphology of La2O3. The rod-like network appeared to become dense upon doping. A significant degradation of MB was confirmed with Mo; furthermore, the bactericidal activities against S. aureus and E. coli were measured as 5.05 mm and 5.45 mm inhibition zones, respectively, after doping with a high concentration (6%) of Mo.

Degradation of Reactive Brilliant Red X-3B by Photo-Fenton-like Process: Effects of Water Chemistry Factors and Degradation Mechanism

Azo dye wastewater belongs to the highly concentrated organic wastewater, which is difficult to be treated by traditional biological processes. The oxidation efficiency of a single physicochemical method is not considerable. Recent research indicated that the advanced oxidation processes (AOPs) based on the highly reactive hydroxyl radical (∙OH) became one of the preferred methods in dealing with such dye wastewater. In this paper, the typical azo dye, reactive brilliant red X-3B, was employed as the target pollutant, and the transition metal Mn and hydrogen peroxide as the catalysts. A photo-Fenton-like process, UV/Mn2+-H2O2 system, was established, which enables a combination of various technologies to improve azo dye degradation efficiency while reducing disposal costs. The results indicated that the UV/Mn2+-H2O2 system had the synergism of Mn2+/H2O2 and UV/H2O2, which was 2.6 times greater than the sum of the two individual effects. And the degradation of X-3B reached the optimum under the conditions of 0.59 mmol/L of the Mn2+, 10 mmol/L of the H2O2, pH = 6 and a high level of DO. The ∙OH, generated from chem-catalytic and photocatalytic decomposition of H2O2, played the predominant role in the decolorization of X-3B and mineralization of its intermediates. The ∙OH tended to attack and break the chromophore group, resulting in the rapid decolorization of X-3B. The azo bond in X-3B was easy to be decomposed in the form of N2, while the triazinyl group was recalcitrant for ring opening. The degradation process of the UV/Mn2+-H2O2 system preferred to be conducted at an acidic condition and appropriate concentrations of Mn2+ and H2O2. The alkaline condition would decrease the utilization of H2O2, and excessive H2O2 would also quench the ∙OH.

Advances in Amine-Surface Functionalization of Inorganic Adsorbents for Water Treatment and Antimicrobial Activities: A Review

In the last decade, adsorption has exhibited promising and effective outcomes as a treatment technique for wastewater contaminated with many types of pollutants such as heavy metals, dyes, pharmaceuticals, and bacteria. To achieve such effectiveness, a number of potential adsorbents have been synthesized and applied for water remediation and antimicrobial activities. Among these inorganic adsorbents (INAD), activated carbon, silica, metal oxide, metal nanoparticles, metal-organic fibers, and graphene oxide have been evaluated. In recent years, significant efforts have been made in the development of highly efficient adsorbent materials for gas and liquid phases. For gas capture and water decontamination, the most popular and known functionalization strategy is the chemical grafting of amine, due to its low cost, ecofriendliness, and effectiveness. In this context, various amines such as 3-aminopropyltriethoxysilane (APTES), diethanolamine (DEA), dendrimer-based polyamidoamine (PAMAM), branched polyethyleneimine (PEI), and others are employed for the surface modification of INADs to constitute a large panel of resource and low-cost materials usable as an alternative to conventional treatments aimed at removing organic and inorganic pollutants and pathogenic bacteria. Amine-grafted INAD has long been considered as a promising approach for the adsorption of both inorganic and organic pollutants. The goal of this review is to provide an overview of surface modifications through amine grafting and their adsorption behavior under diverse conditions. Amine grafting strategies are investigated in terms of the effects of the solvent, temperature, and the concentration precursor. The literature survey presented in this work provides evidence of the significant potential of amine-grafted INAD to remove not only various contaminants separately from polluted water, but also to remove pollutant mixtures and bacteria.

Elimination of rhodamine B from textile wastewater using nanoparticle photocatalysts: A review for sustainable approaches

Rhodamine B (RhB) dye used in the textile industries is associated with carcinogenic and neurotoxic effects with a high potential to cause a variety of human diseases. Semiconductor photocatalysts synthesised through agriculture waste extracts exhibited high efficiency for RhB removal. The current review aimed to explore the efficiency and mechanism of RhB degradation using different photocatalysts that have been used in recent years, as well as the effect of various factors on the removal process. Zinc oxide nanoparticles (ZnO NPs) synthesised from plant extract is the most effective for the RhB degradation with the efficiency reaching 100% after 210 min. The photocatalysis process depends on the pH because pH changes the balance of water dissociation, which impacts the formation of hydroxyl radicals and the surface load of the catalyst. Analysis using Jupyter Notebook revealed a strong correlation between the concentration of ZnO NPs and the photocatalysis efficiency (R = 0.72). These findings reveal that man-sized photocatalysts have a high potential for removing RhB from the wastewater.

Role of Nanofibers in Encapsulation of the Whole Cell

In the field of biomaterial research, the electrospinning device is now used to manufacture nanofibers that can be used to encapsulate whole microorganisms such as bacterial cells, funguses, viruses, and even spores. The nanofiber encapsulated cells will have greater significance in the coming future because of their wide variety of applications in various fields. Nanofibers act as microorganism reservoir systems that enhance their properties such as viability, controlled release of products, biomedical applications, and bioremediation. The effect of electrostatic forces on a droplet of liquid polymer or polymer solution is based on electrospinning. Electrospun nanofibers act as ideal native extracellular matrices for microorganisms and have also had a tremendous advantage in drug delivery systems where modern research is still underway. During electrospinning, nearly all microorganisms may be inserted into a polymer matrix that forms a composite nanofiber. The evolution in electrospinning technique over the past few decades has become promising. New ideas have been generated to enhance the techniques and improve the overall applications and properties of nanofibers. This technique has been transformed by the advent of the electrospinning machine. The electrospun nanofibers can be chemically characterized by a wide variety of procedures such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and Fourier-transform infrared spectroscopy (FTIR). Electrospinning has various applications, for example, in wastewater treatment, tissue engineering, food industry, drug delivery, agriculture, and cosmetics. Nanofiber encapsulation of microorganisms increased the shelf life of the microorganisms; the cells remain viable for months. It also helps in the control release of bacterial products. The present review demonstrates the role of nanofiber in the encapsulation of the whole cell.

Recent advances in dye and metal ion removal using efficient adsorbents and novel nano-based materials: an overview

Excessive levels of dyes and heavy metals in water sources have long been a source of concern, posing significant environmental and public health threats. However, adsorption is a feasible technique for removing dye contaminants and heavy metals from water due to its high efficiency, cost-effectiveness, and easy operation. Numerous researchers in batch studies extensively evaluated various adsorbents such as natural materials, and agriculture-derived and industrial wastes; however, large-scale application is still missing. Nanotechnology is a novel approach that has arisen as one of the most versatile and cost-effective ways for dye and heavy metal removal. Its promotion on large-scale applications to investigate technological, fiscal, and environmental aspects for wastewater decontamination is particularly important. This review critically reviews wastewater treatment techniques, emphasizing the adsorption process and highlighting the most effective parameters: solution pH, adsorbent dosage, adsorbent particle size, initial concentration, contact time, and temperature. In addition, a comprehensive, up-to-date list of potentially effective low-cost adsorbents and nano-sorbents for the removal of dyes and heavy metals has been compiled. Finally, the challenges towards the practical application of the adsorption process based on various adsorbents have been drawn from the literature reviewed, and our suggested future perspectives are proposed.

A Novel N-Doped Nanoporous Bio-Graphene Synthesized from Pistacia lentiscus Gum and Its Nanocomposite with WO3 Nanoparticles: Visible-Light-Driven Photocatalytic Activity

This paper reports the synthesis of a new nitrogen-doped porous bio-graphene (NPBG) with a specific biomorphic structure, using Pistacia lentiscus as a natural carbon source containing nitrogen that also acts as a bio-template. The obtained NPBG demonstrated the unique feature of doped nitrogen with a 3D nanoporous structure. Next, a WO₃/N-doped porous bio-graphene nanocomposite (WO₃/NPBG-NC) was synthesized, and the products were characterized using XPS, SEM, TEM, FT-IR, EDX, XRD, and Raman analyses. The presence of nitrogen doped in the structure of the bio-graphene (BG) was confirmed to be pyridinic-N and pyrrolic-N with N1 peaks at 398.3 eV and 400.5 eV, respectively. The photocatalytic degradation of the anionic azo dyes and drugs was investigated, and the results indicated that the obtained NPBG with a high surface area (151.98 m²/g), unique electronic properties, and modified surface improved the adsorption and photocatalytic properties in combination with WO₃ nanoparticles (WO₃-NPs) as an effective visible-light-driven photocatalyst. The synthesized WO₃/NPBG-NC with a surface area of 226.92 m²/g displayed lower bandgap and higher electron transfer compared with blank WO₃-NPs, leading to an increase in the photocatalytic performance through the enhancement of the separation of charge and a reduction in the recombination rate. At the optimum conditions of 0.015 g of the nanocomposite, a contact time of 15 min, and 100 mg/L of dyes, the removal percentages were 100%, 99.8%, and 98% for methyl red (MR), Congo red (CR), and methyl orange (MO), respectively. In the case of the drugs, 99% and 87% of tetracycline and acetaminophen, respectively, at a concentration of 10 mg/L, were removed after 20 min.

Appraisal of Chitosan-Gum Arabic-Coated Bipolymeric Nanocarriers for Efficient Dye Removal and Eradication of the Plant Pathogen Botrytis cinerea

The treatment of textile wastewater comprising many dyes as contaminants endures an essential task for environmental remediation. In addition, combating antifungal multidrug resistance (MDR) is an intimidating task, specifically owing to the limited options of alternative drugs with multitarget drug mechanisms. Incorporating natural polymeric biomaterials for drug delivery provides desirable properties for drug molecules, effectively eradicating MDR fungal growth. The current study fabricated the bipolymeric drug delivery system using chitosan-gum arabic-coated liposome 5ID nanoparticles (CS-GA-5ID-LP-NPs). This study focused on improving the solubility and sustained release profile of 5I-1H-indole (5ID). These NPs were characterized and tested mechanically as a dye adsorbent as well as their antifungal potencies against the plant pathogen, Botrytis cinerea. CS-GA-5ID-LP-NPs showed 71.23% congo red dye removal compared to crystal violet and phenol red from water and effectively had an antifungal effect on B. cinerea at 25 μg/mL MIC concentrations. The mechanism of the inhibition of B. cinerea via CS-GA-5ID-LP-NPs was attributed to stabilized microtubule polymerization in silico and in vitro. This study opens a new avenue for designing polymeric NPs as adsorbents and antifungal agents for environmental and agriculture remediation.

Enhanced degradation of reactive brilliant red X-3B by photocatalysis integrated with micro-electrolysis

The microwave electrodeless lamp UV photocatalysis (MWUV) integrated with iron carbon micro-electrolysis (ME) was applied to degrade reactive brilliant red X-3B. In the present study, the removal rate of X-3B by MWUV/ME was 95%, which was significantly higher than 56% of MWUV and 62% of ME system. The experiment results demonstrated a synergistic effect in MWUV/ME system, wherein the ME system played an important role in color removal and the formation of ·OH in photocatalysis contributed most for the mineralization of X-3B and its intermediates. The removal efficiency of TOC was 32%, 7.5%, and 59.5% under MWUV, ME, and MWUV/ME processes at the end of the reaction, respectively. The Fe³⁺ existed in the system was an enhancer of producing ·OH via self-generation of ·OH by UV irradiation or improving the separation of electron-hole in photocatalysis by capturing the electrons. Therefore, the combined treatment of MWUV and ME system has the potential of synergistic effect compared to the separate process. Lowering the initial solution pH and increasing the iron filing dosage and dissolved oxygen were beneficial for the enhancement of degradation efficiency. The inorganic anions showed a diversity influencing the degradation of X-3B. NO₃^-, CO₃^2-, and SO₄^2- (at higher concentration) promoted the degradation reaction, while Cl^- had non-significant effect.

Advanced Oxidation Processes Coupled with Nanomaterials for Water Treatment

Water quality management will be a priority issue in the near future. Indeed, due to scarcity and/or contamination of the water, regulatory frameworks will be increasingly strict to reduce environmental impacts of wastewater and to allow water to be reused. Moreover, drinking water quality standards must be improved in order to account for the emerging pollutants that are being detected in tap water. These tasks can only be achieved if new improved and sustainable water treatment technologies are developed. Nanomaterials are improving the ongoing research on advanced oxidation processes (AOPs). This work reviews the most important AOPs, namely: persulfate, chlorine and NH₂Cl based processes, UV/H₂O₂, Fenton processes, ozone, and heterogeneous photocatalytic processes. A critical review of the current coupling of nanomaterials to some of these AOPs is presented. Besides the active role of the nanomaterials in the degradation of water contaminants/pollutants in the AOPs, the relevance of their adsorbent/absorbent function in these processes is also discussed.

Sorptive removal of methylene blue from water by magnetic multi-walled carbon nanotube composites

In the present study, five magnetic multi-walled carbon nanotubes (MMWCNTs) with different diameters were prepared and their performance on the sorptive removal of methylene blue (MB) from water was investigated. Transmission electron microscope, scanning electron microscope, Fourier transform infrared spectrometer, X-ray diffraction, and vibrating sample magnetometer confirm that the surface of these MMWCNTs has been decorated by Fe₃O₄ nanoparticles, which renders the MMWCNTs superparamagnetic. Thus, these MMWCNTs can be easily separated from water after the adsorption. During the adsorption process, pH slightly affected the removal efficiency of MB and the adsorption performed better under weak alkaline conditions. Adsorption kinetics followed the pseudo-second-order kinetic model well, and the Dubinin-Radushkevich model fitted the isotherms best. The maximum adsorption capacity for MB reached 204.2 mg/g, and the values decreased with increasing diameters of MMWCNTs due to decreasing specific surface areas. The thermodynamics parameters indicated the spontaneous and exothermic nature of the adsorption. The reusability test showed that MMWCNTs could be used for 6 cycles without significant loss of the adsorption capacity. And common ions (K⁺, Na⁺, Ca²⁺ and Al³⁺) and SDS in water did not show greatly effects on the removal efficiency of MB. Hence, MMWCNTs prepared in this study could be promising adsorbents for dyes removal from wastewater.