Conducting PANI stimulated ZnO system for visible light photocatalytic degradation of coloured dyes

Textile azo dye, Sudan Black B, inducing hepatotoxicity demonstrated in in vivo zebrafish larval model

Environmental pollution, particularly from textile industry effluents, raises concerns globally. The aim of this study is to investigate the hepatotoxicity of Sudan Black B (SBB), a commonly used textile azo dye, on embryonic zebrafish. SBB exposure led to concentration-dependent mortality, reaching 100% at 0.8 mM, accompanied by growth retardation and diverse malformations in zebrafish. Biochemical marker analysis indicated adaptive responses to SBB, including increased SOD, CAT, NO, and LDH, alongside decreased GSH levels. Liver morphology analysis unveiled significant alterations, impacting metabolism and detoxification. Also, glucose level was declined and lipid level elevated in SBB-exposed in vivo zebrafish. Inflammatory gene expressions (TNF-α, IL-10, and INOS) showcased a complex regulatory interplay, suggesting an organismal attempt to counteract pro-inflammatory states during SBB exposure. The increased apoptosis revealed a robust hepatic cellular response due to SBB, aligning with observed liver tissue damage and inflammatory events. This multidimensional study highlights the intricate web of responses due to SBB exposure, which is emphasizing the need for comprehensive understanding and targeted mitigation strategies. The findings bear the implications for both aquatic ecosystems and potentially parallels to human health, underscoring the imperative for sustained research in this critical domain.

Hues of risk: investigating genotoxicity and environmental impacts of azo textile dyes

The textile industry, with its extensive use of dyes and chemicals, stands out as a significant source of water pollution. Exposure to certain textile dyes, such as azo dyes and their breakdown products like aromatic amines, has been associated with health concerns like skin sensitization, allergic reactions, and even cancer in humans. Annually, the worldwide production of synthetic dyes approximates 7 × 107 tons, of which the textile industry accounts for over 10,000 tons. Inefficient dyeing procedures result in the discharge of 15-50% of azo dyes, which do not adequately bind to fibers, into wastewater. This review delves into the genotoxic impact of azo dyes, prevalent in the textile industry, on aquatic ecosystems and human health. Examining different families of textile dye which contain azo group in their structure such as Sudan I and Sudan III Sudan IV, Basic Red 51, Basic Violet 14, Disperse Yellow 7, Congo Red, Acid Red 26, and Acid Blue 113 reveals their carcinogenic potential, which may affect both industrial workers and aquatic life. Genotoxic and carcinogenic characteristics, chromosomal abnormalities, induced physiological and neurobehavioral changes, and disruptions to spermatogenesis are evident, underscoring the harmful effects of these dyes. The review calls for comprehensive investigations into the toxic profile of azo dyes, providing essential insights to safeguard the aquatic ecosystem and human well-being. The importance of effective effluent treatment systems is underscored to mitigate adverse impacts on agricultural lands, water resources, and the environment, particularly in regions heavily reliant on wastewater irrigation for food production.

Enhanced mitigation of acidic and basic dyes by ZnO based nano-photocatalysis: current applications and future perspectives

Dye wastewater possess immense toxicity with carcinogenic properties and they persist in environment owing to their stability and resistance to chemical and photochemical changes. The bio degradability of dye-contaminated wastewater is low due to its complex molecular structure. Nano-photocatalysts based on zinc oxide are reported as one of the effective metal oxides for dye remediation due to their photostability, enhanced UV and visible absorption capabilities in an affordable manner. An electron-hole pair forms when electrons in the valence band of ZnO nano-photocatalyst transfer into the conduction band by absorbing UV light. The review article presents a detailed review on ZnO applications for treating acidic and basic dyes along with the dye degradation performance based on operating conditions and photocatalytic kinetic models. Several acidic and basic dyes have been shown to degrade efficiently using ZnO and its nanocomposites. Higher removal percentages for crystal violet was reported at pH 12 by ZnO/Graphene oxide catalyst under 400 nm UV light, whereas acidic dye Rhodamine B at a pH of 5.8 was degraded to 100% by pristine ZnO. The mechanism of action of ZnO nanocatalysts in degrading the dye contamination are reported and the research gaps to make these agents in environmental remediation on real time operations are discussed.

A colorimetric sensing platform with smartphone for organophosphorus pesticides detection based on PANI-MnO2 nanozyme

Organophosphorus pesticides (OPs) are of great concern due to its potential harms on human health and the environment. Herein, a budget-friendly, rapid and convenient colorimetric sensing platform is developed for detection of OPs in the environmental and food samples. The sensing element, PANI-MnO2 nanozyme with excellent oxidase mimetic activity is synthesized at room temperature, which is able to directly oxidize 3,3,5,5-tetramethylbenzidine (TMB) to generate blue colored oxidized TMB (OxTMB) within 2 min. Ascorbic acid (AA) can inhibit the oxidization reaction of TMB, consequently causing the blue color fading. Ascorbic acid 2-phosphate (AAP) could be hydrolyzed to produce AA by alkaline phosphatase (ALP). In the presence of OPs can effectively decrease ALP activity, resulting in the recovery of catalytic activity of PANI-MnO2. Therefore, sensitive and selective OPs detection is achieved. Under the optimal conditions, excellent detection performance in term of glyphosate as a model is achieved with a linear range from 0.50 to 50 μM, the detection limit is 0.39 μM (S/N = 3). The utility of method is further improved by combining a portable smartphone platform with a color picking application. The colorimetric platform achieves instrument-free detection of OPs and overcomes the uneven color distribution of traditional paper-based chip, providing an alternative strategy for the qualitative discernment and semi-quantitative analysis of OPs on-site.

A Statistical Physics Approach to Understanding the Adsorption of Methylene Blue onto Cobalt Oxide Nanoparticles

The production of cobalt oxide nanoparticles and their use in the adsorption of methylene blue (MB) from solution is described in the paper. The X-ray diffraction patterns show that the synthesized cobalt oxide nanoparticles have a crystalline cubic structure. The study of the adsorption of methylene blue onto the cobalt oxide nanoparticles involved determining the contact time and initial concentration of the adsorption of MB on the adsorbent. The kinetics of adsorption were analyzed using two kinetic models (pseudo-first order and pseudo-second order), and the pseudo-second-order model was found to be the most appropriate for describing the behavior of the adsorption. This study indicates that the MLTS (monolayer with the same number of molecules per site) model is the most suitable model for describing methylene blue/cobalt oxide systems, and the parameter values help to further understand the adsorption process with the steric parameters. Indicating that methylene blue is horizontally adsorbed onto the surface of the cobalt oxide, which is bonded to two different receptor sites. Regarding the temperature effect, it was found that the adsorption capacity increased, with the experimental value ranging from 313.7 to 405.3 mg g-1, while the MLTS predicted 313.32 and 408.16 mg g-1. From the thermodynamic functions, high entropy was found around 280 mg L-1 concentration. For all concentrations and temperatures examined, the Gibbs free energy and enthalpy of adsorption were found to be negative and positive, respectively, suggesting that the system is spontaneous and endothermic. According to this study's findings, methylene blue adsorption onto cobalt oxide nanoparticles happens via the creation of a monolayer, in which the same amount of molecules are adsorbed at two distinct locations. The findings shed light on the methylene blue adsorption process onto cobalt oxide nanoparticles, which have a variety of uses, including the remediation of wastewater.

ZnO nanostructured matrix as nexus catalysts for the removal of emerging pollutants

Water pollution stands as a pressing global environmental concern, elevating the significance of innovative, dependable, and sustainable solutions. This study represents an extensive review of the use of photocatalytic zinc oxide nanoparticles (ZnO NPs) for the removal of emerging pollutants from water and wastewater. The study examines ZnO NPs' different preparation methods, including physical, chemical, and green synthesis, and emphasizes on advantages, disadvantages, preparation factors, and investigation methods for the structural and morphological properties. ZnO NPs demonstrate remarkable properties as photocatalysts; however, their small dimensions pose an issue, leading to potential post-use environmental losses. A strategy to overcome this challenge is scaling up ZnO NP matrices for enhanced stability and efficiency. The paper introduces novel ZnO NP composites, by incorporating supports like carbon and clay that serve as photocatalysts in the removal of emerging pollutants from water and wastewater. In essence, this research underscores the urgency of finding innovative, efficient, and eco-friendly solutions for the removal of emerging pollutants from wastewater and highlights the high removal efficiencies obtained when using ZnO NPs obtained from green synthesis as a photocatalyst. Future research should be developed on the cost-benefit analysis regarding the preparation methods, treatment processes, and value-added product regeneration efficiency.

Mechanistic view of MoS2 confined chitosan-polyaniline hybrid composite for the photo-oxidation of cationic dyes

In this article, we describe the formulation of polyaniline-chitosan/MoS2 (PANI-CS @MoS2) blended composite and evaluated its efficiency to degrade the dye molecules Rhodamine B (RhB) and Malachite Green (MG) under visible light. In the photocatalytic mechanism, the CS acts as an electron carrier and binding agent during the oxidation reaction to decrease the recombination of electrons and holes generated by the irradiation of light. FTIR, XPS, XRD, TG, Zeta Potential, UV, SEM, AFM and TEM were used to characterize the PANI-CS@MoS2 composite after it had been synthesized. For the degradation analysis, 30 mg/L concentrations of 50 mL MG and RhB dye solutions were used. The recommended dosage of the composite was 100 mg. For MG and RhB dyes, the colour removal rates were 96.2 % and 91.5 %, respectively, under exposure to visible light and at the pH ranges of 8-11. After being exposed to visible light for 60 min, the whole decay process was accomplished. The photocatalyst offers great extensibility up to five iterations. The Langmuir-Hinshelwood kinetic model governs the rate of dye molecules degradation. The result of the study revealed that the PANI-CS@MoS2 composite matrix perhaps be a trustworthy and practical substrate for the efficient refinement of dye-deteriorated water⁠⁠⁠⁠⁠⁠⁠.

Electrochemical monitoring of congo red degradation using strontium titanate-doped biochar nanohybrids derived photocatalytic plates

Present investigation demonstrates the development and characterization of strontium titanate (SrTiO₃) doped biochar nanohybrid photocatalysts. Biochar nanohybrid was synthesized using an ultrasonic-assisted dispersion technique, which involved dispersing SrTiO₃ nanoparticles into activated biochar at a weight ratio of 1:2 (w/w) under ambient conditions. The development of the biochar nanohybrid was verified through a comprehensive analysis of their spectral, microstructural, thermal, electrical, and electrochemical properties. The scanning electron microscopy analysis reveals a surface-associated multiphase morphology of the biochar nanohybrid, attributed to the uniform distribution of SrTiO₃ within the activated biochar matrix. Biochar nanohybrid exhibited a reduced optical band gap of 2.77 eV, accompanied by a crystallite size of 32.45. Thermogravimetric analysis revealed the thermal stability of the biochar nanohybrid, as evidenced by a char residue of 70.83% at 1000 °C. The working electrodes derived from biochar nanohybrid have exhibited ohmic behavior and displayed a significantly enhanced DC conductivity (mS/cm) of 1.13, surpassing that of activated biochar (0.53) and SrTiO₃ (0.62) at 100 V. The developed biochar nanohybrid were employed for the degradation of congo red dye by exposing the dye solution to photocatalytic plates. These photocatalytic plates were prepared by coating biochar nanohybrid onto glass plates using epoxy-based reactive binders for secure binding. The photodegradation of congo red was evaluated through cyclic voltammetric analysis in a 0.1 M KCl solution at pH 8.0, resulting in an impressive 99.95% photocatalytic efficiency in degrading a congo red solution (50 mg/L). This study presents a novel approach for the fabrication of biochar nanohybrid-derived photocatalytic plates, offering high photocatalytic efficiency for the degradation of congo red dye.

Cost-effective one-spot hydrothermal synthesis of graphene oxide nanoparticles for wastewater remediation: AI-enhanced approach for transition metal oxides

This investigation presents a cost-efficient hydrothermal synthesis technique for producing graphene oxide nanoparticles (GO-NPs) that exhibit promising potential in wastewater treatment. The synthesis process involves a facile and expandable hydrothermal reactor that can be regulated using an AI-empowered methodology. The generated GO-NPs were characterised using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, Raman spectroscopy, and transmission electron microscopy (TEM), confirming their successful synthesis and high quality. The high degree of crystallinity observed in the GO-NPs can be attributed to the favourable reaction conditions facilitated by the hydrothermal synthesis. The TEM analysis showed that the GO-NPs had a homogeneous dispersion pattern and a consistent size distribution of approximately 10 nm. Carboxylation was employed to functionalize the GO-NPs, enhancing their reactivity towards diverse contaminants present in wastewater. The remediation potential of the GO-NPs for transition metal oxides, which are frequently found in wastewater, was assessed. The GO-NPs exhibited notable efficacy in remediating the transition metal oxides that were subjected to testing. The heightened efficacy of remediation can be attributed to the substantial surface area and elevated reactivity of the GO-NPs, in addition to their functionalization using carboxylic groups. The cost-effective and efficient synthesis method, coupled with the high remediation potential of the GO-NPs, makes them a highly promising contender for employment in wastewater remediation applications. The use of AI in regulating the hydrothermal synthesis procedure enables accurate manipulation of the reaction parameters, thereby augmenting the quality and uniformity of the resultant GO-NPs. The proposed method exhibits scalability potential for large-scale production of GO-NPs, presenting a viable remedy for the challenges associated with wastewater remediation.

Degradation of methylene blue using a novel gas-liquid hybrid DDBD reactor: Performance and pathways

A novel gas-liquid hybrid double dielectric barrier discharge (DDBD) reactor with coaxial cylinder configuration was developed for the degradation of methylene blue (MB) in this study. In this DDBD reactor, the reactive species generation occurred in the gas-phase discharge, directly in the liquid, and in the mixture of the working gas bubbles and the liquid, which could effectively increase the contact area between the active substance and MB molecules/intermediates, resulting in an excellent MB degradation efficiency and mineralization (COD and TOC). The electrostatic field simulation analysis by Comsol was carried out to determine the appropriate structural parameters of the DDBD reactor. The effect of discharge voltage, air flow rate, pH, and initial concentration on MB degradation was evaluated. Besides, major oxide species, ·OH, the dissolved O₃ and H₂O₂ generated in this DDBD reactor were determined. Moreover, major MB degradation intermediates were identified by LC-MS, based on which, possible degradation pathways of MB were proposed.

Functional impacts of polyaniline in composite matrix of photocatalysts: an instrumental overview

The challenges associated with photocatalysts including their agglomeration, electron-hole recombination and limited optoelectronic reactivity to visible light during the photocatalysis of dye-laden effluent make it necessary to fabricate versatile polymeric composite photocatalysts, and in this case the incredibly reactive conducting polyaniline can be employed. The selection of polyaniline among the conducting polymers is based on its proficient functional impacts in composite blends and proficient synergism with other nanomaterials, especially semiconductor catalysts, resulting in a high photocatalytic performance for the degradation of dyes. However, the impacts of PANI in the composite matrix, which result in the desired photocatalytic activities, can only be assessed using multiple characterization techniques, involving both microscopic and spectroscopic assessment. The characterization results play a significant role in the detection of possible points of agglomeration, surface tunability and improved reactivity during the fabrication of composites, which are necessary to improve their performance in the photocatalysis of dyes. Accordingly, studies revealed the functional impacts of polyaniline in composites including morphological transformation, improved surface functionality, reduction in agglomeration and lowered bandgap potential employing different characterization techniques. In this review, we present the most proficient fabrication techniques based on the in situ approach to achieve improved functional and reactive features and efficiencies of 93, 95, 96, 98.6 and 99% for composites in dye photocatalysis.

Engineering S-scheme CuO/ZnO heterojunctions sonochemically for eradicating RhB dye from wastewater under solar radiation

In this research, S-scheme heterojunctions composed of different concentrations of CuO and ZnO nanoparticles are fabricated for eradicating rhodamine B dye under solar radiation. ZnO nanoparticles are designed through a facile sol-gel route employing Triton X-100. Spherical CuO nanoparticles of 15.2 nm and 1.5 eV band gap energy are deposited on ZnO nanoparticles in an ultrasonic bath of 300 W intensity. The physicochemical performance of the photocatalyst is explored by HRTEM, SAED, BET, XRD, DRS and PL. The in situ homogeneous growth of spherical CuO nanoparticles on ZnO active centers shifts the photocatalytic response to the deep visible region and enhances the efficiency of charge carrier separation and transportation. Among all heterojunctions, ZnCu10 containing 10 wt% CuO displays the best photocatalytic rate for expelling 93% of RhB dye within 240 min, which is twenty-fold higher than that of pristine ZnO and CuO. Reactive oxygen species are the predominant species in degrading the dye pollutant on the heterojunction surface, as shown from scrubber trapping experiments and PL spectrum of terephthalic acid. Coupling ZnO as an oxidative photocatalyst and CuO as a reductive photocatalyst generates an efficient S-scheme heterojunction with strong redox power in destructing various organic pollutants.

In situ doping lignin-derived carbon quantum dots on magnetic hydrotalcite for enhanced degradation of Congo Red over a wide pH range and simultaneous removal of heavy metal ions

A new N, S-CQDs@Fe₃O₄@HTC composite was prepared by loading N, S carbon quantum dots (N, S-CQDs) derived from lignin on magnetic hydrotalcite (HTC) via an in-situ growth method. The characterization results showed that the catalyst had a mesoporous structure. These pores facilitate the diffusion and mass transfer of pollutant molecules inside the catalyst, allowing them to approach the active site smoothly. The catalyst performed well in the UV degradation of Congo red (CR) over a wide pH range (3-11), with efficiencies over 95.43 % in all cases. Even at a high NaCl content (100 g/L), the catalyst showed extraordinary CR degradation (99.30 %). ESR analysis and free radical quenching experiments demonstrated that OH and O₂^- were the main active species governing CR degradation. Besides, the composite had outstanding removal efficiency for Cu²⁺ (99.90 %) and Cd²⁺ (85.08 %) simultaneously due to the electrostatic attraction between the HTC and metal ions. Moreover, the N, S-CQDs@Fe₃O₄@HTC had excellent stability and recyclability during five cycles, making it free of secondary contamination. This work provides a new environment-friendly catalyst for the simultaneous removal of multiple pollutants and a waste-to-waste strategy for the value-added utilization of lignin.

Synthesis and comparative study of the structural and optical properties of binary ZnO-based composites for environmental applications

The development of photoactive systems to solve serious environmental problems is a key objective of researchers and remains a real challenge. Herein, n-p heterojunction ZnO-based composites were developed to achieve better photocatalytic performance in methylene blue (MB) degradation under natural solar irradiation. The hydrothermal technique was used to synthesize zinc oxide (ZnO)/metal oxide (MO) composites, with a molar ratio of 1 : 1 (MO = Mn₃O₄; Fe₃O₄; CuO; NiO). Various characterization techniques were used for the analysis of the structural, morphological and optical properties. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDX) Diffuse Reflectance Spectroscopy analysis (DRS), and Diffuse Reflectance Spectroscopy analysis (DRS) validated the presence of two phases for each sample, excluding any impurities. Indeed, the ZnO structure was not affected by the coupling with MO, confirming that MO was well dispersed on the surface of the ZnO crystalline lattice for each composite. Eventually, the photocatalytic performance evaluation test of the synthesized photocatalysts was carried out on aqueous MB solution. According to the results, the ZnO/Fe₃O₄ nano-catalyst showed the best photodegradation efficiency. This result suggests that the formation of Fe₃O₄/ZnO as a p/n heterojunction reduces the recombination of photo-generated electron/hole pairs and broadens the solar spectral response range, resulting in significant photocatalytic efficiency. Meanwhile, the possible mechanism for degradation of the MB was discussed.

Photodegradation of dye using Polythiophene/ZnO nanocomposite: A computational approach

Incorporating nanostructured photocatalysts in polymers is a strategic way to obtain novel water purification systems. Here, we present density functional theory (DFT) study of Polythiophene/Zinc oxide (PTh/ZnO) nanocomposite with high photocatalytic performance and stability which exhibits superior degradation of alizarine dye under the visible light condition with interaction energy of -149.55 kcal/mol between conducting polymer (PTh) and metal oxide, with PTh sponsoring more number of electrons to the conduction band of ZnO. The electrical and optical properties of optimized geometries of PTh/ZnO nanocomposite were studied by frontier molecular orbital analysis, natural bond orbital (NBO) charge simulation, natural electronic configuration, and UV-vis absorption spectra. The modulation of the energy band gap (∽ 2.60 eV) and exciton binding energy (∽ 0.36 eV) causes visible light absorption and hence enhances the photodegradation activity of PTh/ZnO. NBO analysis evidences the electron accepting behavior of ZnO in the composites as it withdraws electron cloud density of about 0.14e from the polymer unit.

Improvement of Floxin photocatalytic degradability in the presence of sulfite: Performance, kinetic, degradation pathway, energy consumption and total cost of system

In this study, photocatalytic degradability of Floxin antibiotic by UV/ZnO/sulfite (UZS) advanced oxidation process was evaluated. The degradation rate of Floxin antibiotic by UV/ZnO (UZ) and UV alone processes were 30% and 15%, respectively, within 5 min. It was observed sulfite has a synergistic effect on the performance of UZ, as the complete destruction of Floxin was achieved when sulfite was introduced into the photocatalytic medium. The complete degradation of Floxin by UZS was obtained at pH of 12.0, sulfite/ZnO molar ratio of 1:3 after 5 min of reaction. According to kinetic studies, the observed rate of Floxin degradation (r_obs (mg L^-1 min)) by UZS was 63 and 25 times that of UV alone and UZS, respectively. The values of energy consumption and the total cost for UV alone, UZ and UZS processes were estimated to be (50 kWh m^-3 and 1.4 $ m^-3), (20 kWh m^-3 and 0.98 $ m^-3) and (0.78 kWh m^-3 and 0.82 $ m^-3), respectively.

Morphology and Photocatalytic Activity of Zinc Oxide Reinforced Polymer Composites: A Mini Review

There is an approximately 3% of fresh water available globally for utilization, while the rest of the water is not available for usage, leaving billions of people with less water. Less water availability means that the majority of water consists of pollutants either in ground water or drinking water, which in turn may have a negative impact on the environment and people. Various methods such as plasma technology, flocculation, neutralization, and disinfection have been utilized for wastewater treatment. The wastewater treatment methods have been found to be selective in terms of the removal of other pollutants, as a result, the majority of them are unable to remove pollutants such as antibiotics at a trace level. In order to ensure that there is a complete removal of pollutants from water, there is a need for the development of alternative wastewater treatment methods. The use of solar light by photocatalysis is an alternative method for the degradation of toxic pollutants. Different photocatalysts such as zinc oxide (ZnO), titanium dioxide (TiO2), and silver (Ag) have been used in the process of photocatalysis. However, the above photocatalysts were found to have drawbacks such as agglomeration at higher contents and health problems during transportation. To solve the above problem, the nanoparticles were immobilized in various matrices such as polymers and ceramics, with polymers being preferred because of low cost, chemical inertness, and high durability. The current review discusses various methods for the preparation of ZnO and its synergy with other nanoparticles incorporated in various polymer matrices. Because it is known that the preparation method(s) affects the morphology, the morphology and the photocatalytic activity of various ZnO/polymer composites and hybrid systems of ZnO/other nanoparticles/polymer composites are discussed in depth.

Photocatalytic dye degradation using nickel ferrite spinel and its nanocomposite

Coloured wastewater is a major issue of today for human health and ecology. Among all available processes such as physical, chemical, biological and electrochemical methods, photocatalysis can be a promising solution because of its ability to degrade colour-causing compounds completely by converting them into simpler molecules (H₂O, CO₂) depending on dye structure. In this work, NiFe₂O₄ was synthesized by the co-precipitation method. Furthermore, the composites of NiFe₂O₄ with TiO₂ were synthesized by varying amounts of TiO₂. The spinel and composites were characterized by XRD, ZETA analysis and UV-DRS. Their photocatalytic activities were investigated using the photocatalytic degradation of reactive turquoise blue 21 (RB 21) dye as model pollutants under sunlight. The increased absorption of the visible light and the enhanced separation of the electron-hole pairs due to the relative energy band positions in NiFe₂O₄ and TiO₂ are considered as the main advantages. Our results showed that NiFe₂O₄-based nanocomposites could be used as an effective and magnetic retrievable photocatalyst.

Synthesis, characterization, antimicrobial and photocatalytic properties of nano-silver-doped flax fibers

In the present study, the nano-silver-doped flax fibers (NAgDFF) are prepared in two steps. In the first step, oxidation of the flax fibers is performed by potassium periodate to form dialdehyde cellulose (DAC) and the second step is the reduction of silver ions by DAC. A series of characterization techniques of the photocatalyst NAgDFF was carried out using scanning electron microscopy, Fourier transform infrared spectroscopy, N2 adsorption isotherm, thermogravimetric analysis and energy-dispersive X-ray spectroscopy. The dye degradation potential of NAgDFF for methylene blue (MB), crystal violet (CV) and brilliant green (BG) (individually or mixture) was investigated using batch and column tests. The degradation efficiency was studied under optimized conditions such as pH (5.0), dye initial concentrations (100 ppm for MB and BG, and 150 ppm for CV), contact time (3.0 h), photocatalyst NAgDFF dose (0.08 g) and temperature (25° C). The maximum degradation efficiency of NAgDFF for MB, CV and BG is 64.75, 94.98 and 63.87 (mg/g), respectively. The kinetic studies show that the experimental data match well with the pseudo-second-order kinetic model. Furthermore, equilibrium isotherm data were analyzed according to Langmuir, Freundlich and Dubinin–Radushkevich equations. The thermodynamic parameters for the adsorption processes of cationic dyes on the NAgDFF fibers were also calculated; the negative value of ΔG° indicated the spontaneous nature of sorption. NAgDFF fibers were successfully applied for photodegradation of the investigated cationic dyes from different samples. The study was extended to investigate the biological activity of newly synthesized NAgDFF against various microorganisms.

Preparation and Photodegradation Properties of Carbon-Nanofiber-Based Catalysts

In this study, an iron oxide/carbon nanofibers (Fe2O3/CNFs) composite was prepared by a combination of electrospinning and hydrothermal methods. The characterization of Fe2O3/CNFs was achieved via scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). It is shown that when the hydrothermal reaction time was 180 °C and the reaction time was 1 h, the Fe2O3 nanoparticle size was about 90 nm with uniform distribution. The photodegradation performance applied to decolorize methyl orange (MO) was investigated by forming a heterogeneous Fenton catalytic system with hydrogen peroxide. The reaction conditions for the degradation of MO were optimized with the decolorization rate up to more than 99% within 1 h, which can decompose the dyes in water effectively. The degradation process of MO by Fenton oxidation was analyzed by a UV-visible NIR spectrophotometer, and the reaction mechanism was speculated as well.

An innovative S-scheme AgCl/MIL-100(Fe) heterojunction for visible-light-driven degradation of sulfamethazine and mechanism insight

The development of high efficient photocatalysts for antibiotics contamination in water remains a severe challenge. In this study, a novel step-scheme (S-scheme) photocatalytic heterojunction nanocomposites were fabricated from integrating AgCl nanoparticles on the MIL-100(Fe) octahedron surface through facile multi-stage stirring strategy. The S-scheme heterojunction structure in AgCl/MIL-100(Fe) (AM) nanocomposite provided a more rational utilization of electrons (e^-) and holes (h⁺), accelerated the carrier transport at the junction interface, and enhanced the overall photocatalytic performance of nanomaterials. The visible-light-driven photocatalysts were used to degrade sulfamethazine (SMZ) which attained a high removal efficiency (99.9%). The reaction mechanisms of SMZ degradation in the AM photocatalytic system were explored by electron spin resonance (ESR) and active species capture experiments, which superoxide radical (•O₂^-), hydroxyl radical (•OH), and h⁺ performed as major roles. More importantly, the SMZ degradation pathway and toxicity assessment were proposed. There were four main pathways of SMZ degradation, including the processes of oxidation, hydroxylation, denitrification, and desulfonation. The toxicity of the final products in each pathway was lower than that of the parent according to the toxicity evaluation results. Therefore, this work might provide new insights into the environmentally-friendly photocatalytic processes of S-scheme AM nanocomposites for the efficient degradation of antibiotics pollutants.

Role of polyaniline in accomplishing a sustainable environment: recent trends in polyaniline for eradicating hazardous pollutants

Attaining a sustainable environment has become a prime area of research interest, as it is an utmost necessity for a healthy life. Hence, ample studies have been carried out in adopting different processes and utilizing various materials to attain the goal. Herein, we present an exclusive discussion on one such material, i.e., polyaniline (PANI) and its derivatives. Being an intrinsic conducting type, it has grabbed more attention due to its durability in different doped/un-doped states, promptness in structural alteration, and solution processability. This review presents an exhaustive discussion on published reports showing utilization of PANI and its derivative in various forms like pure and composites, for cleaning the environment through adsorption, photodegradation, etc., and the various methods adopted in order to achieve an optimum operating condition to obtain the maximum outcome. In addition to these merits and demerits, various technical challenges faced with materials have been also presented. Therefore, it is expected that this piece of work, presenting the exhaustive discussion on PANI and; its derivatives would help to develop a better understanding of this excellent conducting polymer PANI and provide a state of art on the role of this material for attaining sustainable surroundings for the living beings.

Synthesis of PVDF membrane loaded with wrinkled Au NPs for sensitive detection of R6G

A novel SERS membrane is synthesized by combining metal lattice and surface enhanced Raman scattering (SERS) technology. Since R6G is a carcinogenic and harmful pollutant, and traditional detection methods have many drawbacks and have research value, this paper selects R6G as the detection target. The SERS substrates are synthesized by loading Au nanoparticles (Au NPs) on the surface of polyvinylidene fluoride (PVDF) membrane. The Au NPs are synthesized through a controllable hydrothermal method. The synthesized AuNPs are covered by some gold particles, forming a fold pattern. Finally, the synthesized structure is immobilized on the surface of the PVDF membrane by the phase inversion method. It is suggested that the prepared Au NPs@PVDF membrane exhibits adjustable cavity structure, strong plasmon coupling, tunable magnetic plasmon resonance, prominent SERS performances. The prepared Au NPs@PVDF membrane showed sensitive SERS activity, good mechanical strength and reusability, expanding the application field of SERS detection. Overall, this study establishes a novel technique for the synthesis of SERS membrane with excellent SERS property and expands the application field of SERS detection.

Designing NAZO@BC electrodes for enhanced elimination of hydrophilic organic pollutants in heterogeneous electro-Fenton system: Insights into the detoxification mediated by 1O2 and •OH

Hydrophilic organic pollutants (HLOPs) in effluents of wastewater treatment plants are more prevalent than hydrophobic counterparts, therefore development of upstream processes that can effectively enhance the removal of HLOPs can substantially enhance overall treatment performance. To bridge this gap, 3D electrodes made of biochar-supported Al-ZnO nanoparticles (NAZO@BC) applied in heterogeneous electro-Fenton (EF) system, abbreviated as NBE-EF system, is rationally designed for enhanced elimination of HLOPs in wastewater. Our analysis indicates the NBE-EF system results in an efficient THM elimination, 42.4 times greater than that of conventional EF system. MoS₂ as an efficient cocatalyst plays an important role in the conversion from Fe(III) to Fe(II). Singlet oxygen (¹O₂) and hydroxyl radical (•OH) are identified as the primary reactive oxygen species (ROS) in the NBE-EF system. NAZO@BC electrodes could concentrate HLOPs on their surface and degrade it effectively, achieving also a self-cleaning effect. Effective elimination of four HLOPs, i.e., thiamethoxam (THM), dinotefuran (DIN), nitenpyram (NIT), and acetamiprid (ACE), demonstrated the high degradation performance of the NBE-EF system, even at neutral and alkaline conditions. This study provides a new approach for enhanced elimination of HLOPs in wastewater treatment and mechanical insights into degradation pathways and toxicity attenuation.

500 Methylene blue removal with carbon-cage adsorbent produced by hydrazinium azide and comparison of its performance with graphene quantum dot composite

Water pollution, which is an increasing global concern, is one of the significant environmental problems which damage economic growth and the health of billions of people. Therefore, many companies and investigators make an effort to prepare a reusable and cost-effective filter to overcome the problem of water shortages. In this study, we have investigated two adsorbents with high adsorption capacity: a graphene quantum dot-based composite and a carbon-cage adsorbent prepared only with graphite and hydrazinium azide that are expanded through an electrical heater. Both adsorbents were able to remove almost 100% of the methylene blue dye, which is widely used in the textile industry. Adsorption rates and morphology of adsorbents were analyzed with XRD, SEM, EDS, TGA and UV spectrometry measurements.

Facile Synthesis, Characterization, and Photocatalytic Activity of Hydrothermally Grown Cu2+-Doped ZnO–SnS Nanocomposites for MB Dye Degradation

The morphology, chemical composition, and doping process of metal oxides and sulfides play a significant role in their photocatalytic performance under solar light illumination. We synthesized Cu2+-doped ZnO–SnS nanocomposites at 220 °C for 10 h, using hydrothermal methods. These nanocomposites were structurally, morphologically, and optically characterized using various techniques, including powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-visible absorption spectroscopy. Their photocatalytic activity (PCA) on methylene blue (MB) pollutant dye was examined under 150 W solar light illumination. Mixed-phase abundances with hexagonal ZnO and orthorhombic SnS structures were observed. TEM micrographs showed changes in morphology from spherical to nano-flake structures with an increasing doping concentration. XPS indicated the chemical states of the constituent elements in the nanocomposites. UV-visible absorption spectroscopy showed a decrease in the bandgap with an increasing doping concentration. Strong PCA was observed due to the separation of charge carriers, a change in bandgap, and a high light absorption ability under solar light irradiation. The measured photodegradation efficiency of the MB dye was approximately 97% after 2 h. The movement of the charge carriers and the bandgap alignment of the synthesized composites are briefly discussed.

An Overview of Polymer-Supported Catalysts for Wastewater Treatment through Light-Driven Processes

In recent years, alarm has been raised due to the presence of chemical contaminants of emerging concern (CECs) in water. This concern is due to the risks associated with their exposure, even in small amounts. These complex compounds cannot be removed or degraded by existing technologies in wastewater treatment plants. Therefore, advanced oxidation processes have been studied, with the objective of developing a technology capable of complementing the conventional water treatment plants. Heterogenous photocatalysis stands out for being a cost-effective and environmentally friendly process. However, its most common form (with suspended catalytic particles) requires time-consuming and costly downstream processes. Therefore, the heterogeneous photocatalysis process with a supported catalyst is preferable. Among the available supports, polymeric ones stand out due to their favorable characteristics, such as their transparency, flexibility and stability. This is a relatively novel process; therefore, there are still some gaps in the scientific knowledge. Thus, this review article aims to gather the existing information about this process and verify which questions are still to be answered.

Enhanced Solar Photocatalytic Activity of Thermally Stable I:ZnO/Glass Beads for Reduction of Cr(VI) in Tannery Effluent

Chromium (VI) in tannery effluent is one of the major environmental concerns for the environmentalists due to the hazardous nature of Cr(VI) ions. To reduce Cr(VI) to Cr(III) as an innocuous moiety, pure and I-doped ZnO was grafted over the etched surface of glass beads by successive ionic layer adsorption and reaction (SILAR). Powdered, pure, and I-doped ZnO scrapped from the surface of glass beads was characterized for crystallinity, morphology, and elemental composition by XRD, SEM, TEM, and EDX. The optical properties of both photocatalysts revealed that owing to optimized iodine doping of ZnO, reduction in the bandgap was observed from 3.3 to 2.9 eV. The crystalline nano-bricks of I:ZnO adhered to glass beads were investigated to have remarkable capability to harvest sunlight in comparison to intrinsic ZnO nanodiscs. The thermal stability of I:ZnO was also found to be much improved due to doping of ZnO. The photocatalytic activities of ZnO/GB and I:ZnO/GB were compared by extent of reduction of Cr(VI) under direct natural sunlight (600–650 KWh/m2). The disappearance of absorbance peaks associated with Cr(VI) after treatment with I:ZnO/GB confirmed higher photocatalytic activity of I:ZnO/GB. The reaction parameters of solar photocatalytic reduction, i.e., initial pH (5–9), initial concentration of Cr(VI) (10–50 ppm), and solar irradiation time (1–5 h) were optimized using response surface methodology. The solar photocatalytic reduction of Cr(VI) to Cr(III) present in real tannery effluent was examined to be 87 and 98%, respectively, by employing ZnO/GB and I:ZnO/GB as solar photocatalysts. The extent of reduction was also confirmed by complexation of Cr(VI) and Cr(III) present in treated and untreated tannery waste with 1, 5-diphenylcarbazide. The results of AAS and UV/vis spectroscopy for the decrease in concentration of Cr also supported the evidence of higher efficiency of I:ZnO/GB for reduction of Cr(VI) in tannery effluent. Reusability of the fabricated photocatalyst was assessed for eight cycles, and magnificent extent of reduction of Cr(VI) indicated its high efficiency. Conclusively, I:ZnO/GB is a potential and cost-effective candidate for Cr(VI) reduction in tannery effluent under natural sunlight.

MXene-based hybrid composites as photocatalyst for the mitigation of pharmaceuticals

Environmental contamination is a burning issue and has gained global attention in the present era. Pharmaceuticals are emerging contaminants affecting the natural environment worldwide owing to their extensive consumption particularly in developing countries where self-medication is a common practice. These pharmaceuticals or their degraded active metabolites enter water bodies via different channels and are continuous threat to the whole ecological system. There is a dire need to find efficient approaches for their removal from all environmental matrices. Photocatalysis is one of the most effective and simple approach, however, finding a suitable photocatalyst is a challenging task. Recently, MXenes (two-dimensional transition metal carbides/nitrides), a relatively new material has attracted increasing interest as photocatalysts due to their exceptional properties, such as large surface area, appreciable safety, huge interlayer spacing, thermal conductivity, and environmental flexibility. This review describes the recent advancements of MXene-based composites and their photocatalytic potential for the elimination of pharmaceuticals. Furthermore, present limitations and future research requirements are recommended to attain more benefits of MXene-based composites for the purification of wastewater.

Adsorption of Congo red and tetracycline onto water treatment sludge biochar: characterisation, kinetic, equilibrium and thermodynamic study

In this study, readily available inexpensive water treatment sludge (WTS) was used to prepare adsorbent for the removal of Congo red (CR) and tetracycline (TC) from aqueous solutions. The structural characteristics and adsorption properties of WTS biochar were characterised via scanning electron microscope, energy dispersive X-ray spectroscopy, Brunauer-Emmett-Teller and Fourier Transform infrared spectroscopy. In batch experiments, the adsorption factors, kinetics, isothermal curves and thermodynamics of the adsorption properties were investigated. The optimum preparation condition of WTS biochar was 400 °C for 4 h under O₂-limited pyrolysis, which exhibited increased specific surface area and pore structures. The best adsorption was observed when the pH of the CR and TC solutions was 7 and 4, respectively. The adsorption process followed the pseudo-second-order model, indicating that the main control step was the chemical adsorption process. Isotherm data were best described by the Langmuir model, and the maximum adsorption capacities for CR and TC were 116.4 and 58.5 mg·g^-1, respectively. Thermodynamic parameters revealed that the adsorption process was spontaneous and endothermic. According to the analysis, the adsorption mechanism of CR could be attributed to electrostatic attraction, π-π conjugation and hydrogen bonding, whereas that of TC was potentially associated with cation exchange, complex precipitation, π-π conjugation and hydrogen bonding.

Electroconductive Polyaniline–Ag-ZnO Green Nanocomposite Material

Metal-conducting polyaniline (PANI)-based nanocomposite materials have attracted attention in various applications due to their synergism of electrical, mechanical, and optical properties of the initial components. Herein, metal-PANI nanocomposites, including silver nanoparticle-polyaniline (AgNP-PANI), zinc oxide nanoparticle-polyaniline (ZnONP-PANI), and silver-zinc oxide nanoparticle-polyaniline (Ag–ZnONP-PANI), were prepared using the two processes. Nanocomposite-based electrode platforms were prepared by depositing AgNPs, ZnONPs, or Ag–ZnONPs on a PANI modified glass carbon electrode (GCE) in the presence of 1-ethyl-3-(3-dimethyl aminopropyl) carbodiimide/N-Hydroxysuccinimide (EDC/NHS, 1:2) as coupling agents. The incorporation of AgNPs, ZnONPs, and Ag–ZnONPs onto PANI was confirmed by UV-Vis spectrophotometry, which showed five absorbance bands at 216 nm, 412 nm, 464 nm, 550 nm, and 831 nm (i.e., transition of π-π*, π-polaron band transition, polaron-π* electronic transition, and AgNPs). The FTIR characteristic signatures of the nanocomposite materials exhibited stretching arising from C–H aromatic, C–O, and C–N stretching mode for benzenoid rings, and =C–H plane bending vibration formed during protonation. The CV voltammograms of the nanocomposite materials showed a quasi-reversible behavior with increased redox current response. Notably, AgNP–PANI–GCE electrode showed the highest conductivity, which was attributed the high conductivity of silver. The increase in peak currents exhibited by the composites shows that AgNPs and ZnONPs improve the electrical properties of PANI, and they could be potential candidates for electrochemical applications.

Visible-Light-Driven Photocatalytic Inactivation of Bacteria, Bacteriophages, and Their Mixtures Using ZnO-Coated HDPE Beads as Floating Photocatalyst

Semiconductor materials used as photocatalysts are considered among the most effective ways to treat biologically polluted water. Certainly, efficiency depends on the selection of photocatalyst and its substrate, as well as the possibility of its application in a broader spectrum of light. In this study, a reactive magnetron sputtering technique was applied for the immobilisation of ZnO photocatalyst on the surface of HDPE beads, which were selected as the buoyant substrates for enhanced photocatalytic performance and easier recovery from the treated water. Moreover, the study compared the effect on the inactivation of the microorganism between ZnO-coated HDPE beads without Ni and with Ni underlayer. Crystal structure, surface morphology, and chemical bonds of as-deposited ZnO films were investigated by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, respectively. Visible-light-induced photocatalytic treatment was performed on the Gram-negative and Gram-positive bacteria and bacteriophages PRD1, T4, and their mixture. Higher bacteria inactivation efficiency was obtained using the ZnO photocatalyst with Ni underlayer for the treatment of S. Typhimurium and M. Luteus mixtures. As for infectivity of bacteriophages, T4 alone and in the mixture with PRD1 were more affected by the produced photocatalyst, compared with PRD1.

A systematic review on iron-based nanoparticle-mediated clean-up of textile dyes: challenges and prospects of scale-up technologies

The projected increase of the global textile industry to USD1002.84 billion in 2027 indicates a simultaneous increase in water pollution due to textile dye-rich voluminous effluents highlighting the requirement of source clean-up. This review analyzes the colossal amount of literature on lab-scale nanoremediation technologies involving iron-based nanoparticles and the mechanistic aspects. However, not many studies are in place with regard to execution because there are several bottlenecks in the scale-up of the technology. This review attempts to identify the limitations of scale-up by focusing on each step of nanoremediation from synthesis of iron-based nanoparticles to their applications. The most prominent appears to be the low economic viability of physico-chemical synthesis of nanoparticles, lack of appropriate toxicity studies of iron-based nanoparticles, and dearth of studies on field applications. It is recommended that above studies should be made not only on lab scale but also on field samples preferably utilizing microbial products based green synthesized iron-based nanoparticles and conducting toxicity studies. Besides, immobilization of the nanoparticles on renewable material greatly enhances the sustainability and economic value of the process. Furthermore, since the chemical composition of dye-rich effluents varies among industries, effluent specific optimization of process parameters and kinetics thereof is also a major prerequisite for scale-up. The value of this review lies in the fact that it brings, for the first time, a comprehensive and critical systematization of various aspects needing attention in order to scale-up such effective nanoremediation processes.

Conducting polymers/zinc oxide-based photocatalysts for environmental remediation: a review

The accessibility to clean water is essential for humans, yet nearly 250 million people die yearly due to contamination by cholera, dysentery, arsenicosis, hepatitis A, polio, typhoid fever, schistosomiasis, malaria, and lead poisoning, according to the World Health Organization. Therefore, advanced materials and techniques are needed to remove contaminants. Here, we review nanohybrids combining conducting polymers and zinc oxide for the photocatalytic purification of waters, with focus on in situ polymerization, template synthesis, sol-gel method, and mixing of semiconductors. Advantages include less corrosion of zinc oxide, less charge recombination and more visible light absorption, up to 53%.

Recent advances in structural modifications of photo-catalysts for organic pollutants degradation - A comprehensive review

Over the last few years, industrial and anthropogenic activities have increased the presence of organic pollutants such as dyes, herbicides, pesticides, analgesics, and antibiotics in the water that adversely affect human health and the environment worldwide. Photocatalytic treatment is considered a promising, economical, effective, and sustainable process that utilizes light energy to degrade the pollutants in water. However, certain drawbacks like rapid recombination and low migration capability of photogenerated electrons and holes have restricted the use of photo-catalysts in industries. Hence, despite the abundance of lab-scale research, the technology is still not much commercialized in the mainstream. Several structural modifications in the photo-catalysts have been adopted to enhance the pollutant degradation performance to overcome the same. In this context, the present review article outlines the different advanced heterostructures synthesized to date for improved degradation of three major organic pollutants: antibiotics, dyes, and pesticides. Moreover, the article also emphasizes the degradation kinetics of photo-catalysts and the publication trend in the past decade along with the roadblocks preventing the transfer of technology from the laboratory to industry and new age photo-catalysts for the profitable implications in industrial sectors.

Floating Carbon-Doped TiO2 Photocatalyst with Metallic Underlayers Investigation for Polluted Water Treatment under Visible-Light Irradiation

In the current study, we analysed the influence of metallic underlayers on carbon-doped TiO2 films for RhB decomposition and Salmonella typhimurium inactivation under visible-light irradiation. All the experiments were divided into two parts. First, layered M/C-doped-TiO2 film structures (M = Ni, Nb, Cu) were prepared by magnetron sputtering technique on borosilicate glass substrates in the two-step deposition process. The influence of metal underlayer on the formation of the carbon-doped TiO2 films was characterised by X-ray diffractometer, scanning electron microscope, and atomic force microscope. The comparison between the visible-light assisted photocatalytic activity of M/C-doped TiO2 structures was performed by the photocatalytic bleaching tests of Rhodamine B dye aqueous solution. The best photocatalytic performance was observed for Ni/C-doped-TiO2 film combination. During the second part of the study, the Ni/C-doped-TiO2 film combination was deposited on high-density polyethylene beads which were selected as a floating substrate. The morphology and surface chemical analyses of the floating photocatalyst were performed. The viability and membrane permeability of Salmonella typhimurium were tested in cycling experiments under UV-B and visible-light irradiation. Three consecutive photocatalytic treatments of fresh bacteria suspensions with the same set of floating photocatalyst showed promising results, as after the third 1 h-long treatment bacteria viability was still reduced by 90% and 50% for UV-B and visible-light irradiation, respectively. The membrane permeability and ethidium fluorescence results suggest that Ni underlayer might have direct and indirect effect on the bacteria inactivation process. Additionally, relatively low loss of the photocatalyst efficiency suggests that floating C-doped TiO2 photocatalyst with the Ni underlayer might be seen as the possible solution for the used photocatalyst recovery issue.

Designing a novel visible-light-driven heterostructure Ni-ZnO/S-g-C3N4 photocatalyst for coloured pollutant degradation

In this study, photocorrosion of ZnO is inhibited by doping Ni in the ZnO nanostructure and electron-hole recombination was solved by forming a heterostructure with S-g-C₃N₄. Ni is doped into ZnO NPs from 0 to 10% (w/w). Among the Ni-decorated ZnO NPs, 4% Ni-doped ZnO NPs (4NZO) showed the best performance. So, 4% Ni-ZnO was used to form heterostructure NCs with S-g-C₃N₄. NZO NPs were formed by the wet co-precipitation route by varying the weight percentage of Ni (0-10% w/w). Methylene blue (MB) was used as a model dye for photocatalytic studies. For the preparation of the 4NZO-x-SCN nanocomposite, 4NZO NPs were formed in situ in the presence of various concentrations of S-g-C₃N₄ (10-50% (w/w)) by using the coprecipitation route. The electron spin resonance (ESR) and radical scavenger studies showed that O₂ ^- and OH free radicals were the main reactive species that were responsible for MB photodegradation.