Photoelectrocatalytic decolorization and degradation of textile effluent using ZnO thin films

Review on sterilization techniques, and the application potential of phage lyase and lyase immobilization in fighting drug-resistant bacteria

Many human health problems and property losses caused by pathogenic contamination cannot be underestimated. Bactericidal techniques have been extensively studied to address this issue of public health and economy. Bacterial resistance develops as a result of the extensive use of single or multiple but persistent usage of sterilizing drugs, and the emergence of super-resistant bacteria brings new challenges. Therefore, it is crucial to control pathogen contamination by applying innovative and effective sterilization techniques. As organisms that exist in nature and can specifically kill bacteria, phages have become the focus as an alternative to antibacterial agents. Furthermore, phage-encoded lyases are proteins that play important roles in phage sterilization. The in vitro sterilization of phage lyase has been developed as a novel biosterilization technique to reduce bacterial resistance and is more environmentally friendly than conventional sterilization treatments. For the shortcomings of enzyme applications, this review discusses the enzyme immobilization methods and the application potential of immobilized lyases for sterilization. Although some techniques provide effective solutions, immobilized lyase sterilization technology has been proven to be a more effective innovation for efficient pathogen killing and reducing bacterial resistance. We hope that this review can provide new insights for the development of sterilization techniques.

Progress in Promising Semiconductor Materials for Efficient Photoelectrocatalytic Hydrogen Production

Photoelectrocatalytic (PEC) water decomposition provides a promising method for converting solar energy into green hydrogen energy. Indeed, significant advances and improvements have been made in various fundamental aspects for cutting-edge applications, such as water splitting and hydrogen production. However, the fairly low PEC efficiency of water decomposition by a semiconductor photoelectrode and photocorrosion seriously restrict the practical application of photoelectrochemistry. In this review, the mechanisms of PEC water decomposition are first introduced to provide a solid understanding of the PEC process and ensure that this review is accessible to a wide range of readers. Afterwards, notable achievements to date are outlined, and unique approaches involving promising semiconductor materials for efficient PEC hydrogen production, including metal oxide, sulfide, and graphite-phase carbon nitride, are described. Finally, four strategies which can effectively improve the hydrogen production rate-morphological control, doping, heterojunction, and surface modification-are discussed.

Fabrication of copper molybdate nanoflower combined polymeric graphitic carbon nitride heterojunction for water depollution: Synergistic photocatalytic performance and mechanism insight

In the scope, developed a novel copper molybdate decorated polymeric graphitic carbon nitride (CuMoO4@g-C3N4 or CMC) heterojunction nanocomposite in an easy solvothermal environment for the first time. The synthesized CMC improved the photocatalytic degradation of an antibiotic drug [ciprofloxacin (CIP)] and organic dye [Rhodamine B (RhB)]. Consequently, the CMC demonstrates a marvelous crystalline nature with ∼26 nm size, as obtained from XRD analysis. Besides, the surface morphology studies confirm the large-scale construction of flower-like CMC with a typical size of 10-15 nm. The CMC showed efficient catalytic activity for both the pollutants, achieving the degradation of 98% for RhB and 97% for CIP in 35 and 60 min, respectively. The reaction parameters including the concentration of pollutants, catalyst dosages, and scavengers are optimized for the best photocatalytic results. Notably, the trapping tests showed that the •OH and O2•- radicals are the primary oxidative species liable for the photocatalytic process. The recyclability test of the photocatalyst infers that the photocatalyst is highly stable up to the fifth recycle. Our work affords an efficient and ideal path to constructing the new g-C3N4-based architected photocatalyst for toxic wastewater treatment in the near future.

Next-generation ultrafiltration membranes: A review of material design, properties, recent progress, and challenges

Membrane technology utilizing ultrafiltration (UF) processes has emerged as the most widely used and cost-effective simple process in many industrial applications. The industries like textiles and petroleum refining are promptly required membrane based UF processes to alleviate the potential environmental threat caused by the generation of various wastewater. At the same time, major limitations such as material selection as well as fouling behavior challenge the overall performance of UF membranes, particularly in wastewater treatment. Therefore, a complete discussion on material design with structural property relation and separation performance of UF membranes is always exciting. This state-of-the-art review has exclusively focused on the development of UF membranes, the material design, properties, progress in separation processes, and critical challenges. So far, most of the review articles have examined the UF membrane processes through a selected track of paving typical materials and their limited applications. In contrast, in this review, we have exclusively aimed at comprehensive research from material selection and fabrication methods to all the possible applications of UF membranes, giving more attention and theoretical understanding to the complete development of high-performance UF systems. We have discussed the methodical engineering behind the development of UF membranes regardless of their materials and fabrication mechanisms. Identifying the utility of UF membrane systems in various applications, as well as their mode of separation processes, has been well discussed. Overall, the current review conveys the knowledge of the present-day significance of UF membranes together with their future prospective opportunities whilst overcoming known difficulties in many potential applications.

Lignin-Mediated Silver Nanoparticle Synthesis for Photocatalytic Degradation of Reactive Yellow 4G and In Vitro Assessment of Antioxidant, Antidiabetic, and Antibacterial Activities

This study explored the potential of abundantly available sodium lignosulfonate (LS) as a reducer and fabricating agent in preparing silver nanoparticles (LS–Ag NPs). The operational conditions were optimized to make the synthesis process simpler, rapid, and eco-friendly. The prepared LS–Ag NPs were analyzed via UV–Vis spectroscopy, X-ray diffraction spectroscopy, Fourier transform infrared spectroscopy, and high-resolution transmission electron microscopy. Results demonstrated that LS–Ag NPs were of crystalline structure, capped with LS constituents, and spherical in shape with a size of approximately 20 nm. Under optimized conditions, LS–Ag NPs exhibited significant photocatalytic activity in Reactive Yellow 4G degradation. The effects of photocatalyst (LS–Ag NPs) dosage, dye concentration, and its reusability for dye degradation were studied to make the process practically applicable in textile wastewater treatment. Additionally, the synthesized LS–Ag NPs displayed significant free radical scavenging against 2-diphenyl-1-picrylhydrazyl (DPPH) with an IC₅₀ value of (50.2 ± 0.70 µg/mL) and also exhibited antidiabetic activity in terms of inhibition in the activity of carbohydrate-degrading marker enzyme α-glucosidase with an IC₅₀ value of (58.1 ± 0.65 µg/mL). LS–Ag NPs showed substantial antibacterial potential against pathogenic strains, namely E. coli and S. aureus. In conclusion, LS–Ag NPs can be a reliable and eco-friendly material for their possible application in the treatment of dye-containing wastewater and have a great perspective in the biomedical and pharmaceutical sectors.

Towards a higher photostability of ZnO photo-electrocatalysts in the degradation of organics by using MMO substrates

In this work, it is proposed a novel strategy to increase the photostability of the ZnO photoelectrocatalyst under prolonged light irradiation, without the addition or deposition of metals and/or semiconductor oxides during their synthesis. This strategy is based on the use of a mixed metal oxide (MMO-Ru_0.3Ti_0.7O₂) coating as the substrate for the electrodeposition of ZnO. To assess it, the electrodeposition of ZnO films on Ti and Ti/MMO substrates and the photoelectrocatalytic activity of these materials for the degradation of the herbicide clopyralid were studied. The results showed that the substrate directly influenced the photo-stability of the ZnO film. Under the incidence of UV light and polarization, the novel Ti/MMO/ZnO electrode showed greater photocurrent stability as compared to Ti/ZnO, which is a very important outcome because the behavior of these electrodes was similar when compared in terms of the degradation of clopyralid. Single electrolysis was not able to degrade efficiently clopyralid at the different potentials studied. However, the irradiation of UV light on the polarized surface of the Ti/ZnO and Ti/MMO/ZnO electrodes increased markedly the degradation rate of clopyralid. A synergistic effect was observed between light and electrode polarization, since the rate of degradation of clopyralid was twice as high in photoelectrocatalysis (PhEC) than in photocatalysis (PhC) and different intermediates were formed. From these results, mechanisms of degradation of clopyralid for the PhC and PhEC systems with the Ti/ZnO and Ti/MMO/ZnO electrodes were presented. Therefore, the Ti/MMO/ZnO electrode could be a cheap and simple alternative to be applied in the efficient photodegradation of organic pollutants, presenting the great advantage of having a facile synthesis and high capacity to work at relatively low potentials.

Photo-electrocatalytic degradation of cyclic volatile methyl siloxane by ZnO-coated aluminum anode: Optimal parameters, kinetics, and reaction pathways

Cyclic volatile methylsiloxanes (cVMSs) are widely used in industrial processes and consumer products, which have been reported to be potentially toxic to human health due to their persistence and bioaccumulation. In this study, a novel photo-catalytic zinc oxide (ZnO)-coated aluminum (ZnO@Al) anode was prepared by a facile hydrothermal epitaxial process for the purpose of degrading cVMSs in practical wastewater. Morphological data and compositional analysis showed a compact coating layer that had the characteristic peaks of ZnO. To optimize the degradation process, central composite design combined with response surface methodology was applied to acquire the optimum parameters of cVMSs removal, and results indicated the cVMSs removal efficiency was approximately 63.3% at the conditions of current density = 17.3 mA/cm², initial pH of electrolyte = 7.8, plate distance = 18 mm, UV intensity = 90 W, and reaction time = 80 min. Furthermore, the photo-electrocatalytic degradation of cVMSs obeys the pseudo-first order kinetic reaction, and the anode exhibited high durability as the attenuation of cVMSs removal efficiency was <6% after four times reuse. It was also observed that with the application period of the anode was extended, the electroflocculation reaction gradually occurred. The FT-IR of the generated flocs and the total ion gas chromatograms mass spectrometer analysis unraveled the methyl groups in Si-CH₃ could be easily attacked by hydroxyl radicals to form the intermediates of monohydroxy substituted products (m/z = 298, 372, and 446) and eventually short-chain carboxylic acids, alkyl radical and silicate. The effective removal of cVMSs by photo-electrocatalytic process using ZnO@Al anode provide significant implication in treatment of practical wastewater.

Semiconductor Electrode Materials Applied in Photoelectrocatalytic Wastewater Treatment—an Overview

Industrial sources of environmental pollution generate huge amounts of industrial wastewater containing various recalcitrant organic and inorganic pollutants that are hazardous to the environment. On the other hand, industrial wastewater can be regarded as a prospective source of fresh water, energy, and valuable raw materials. Conventional sewage treatment systems are often not efficient enough for the complete degradation of pollutants and they are characterized by high energy consumption. Moreover, the chemical energy that is stored in the wastewater is wasted. A solution to these problems is an application of photoelectrocatalytic treatment methods, especially when they are coupled with energy generation. The paper presents a general overview of the semiconductor materials applied as photoelectrodes in the treatment of various pollutants. The fundamentals of photoelectrocatalytic reactions and the mechanism of pollutants treatment as well as parameters affecting the treatment process are presented. Examples of different semiconductor photoelectrodes that are applied in treatment processes are described in order to present the strengths and weaknesses of the photoelectrocatalytic treatment of industrial wastewater. This overview is an addition to the existing knowledge with a particular focus on the main experimental conditions employed in the photoelectrocatalytic degradation of various pollutants with the application of semiconductor photoelectrodes.

Sequential photocatalysis and biological treatment for the enhanced degradation of the persistent azo dye methyl red

A combination of photocatalysis and biodegradation is a promising approach for the removal of xenobiotic organic compounds from wastewater, since photocatalysis cleaves the molecules into simpler intermediates that are later mineralized by microorganisms. Sequential photocatalytic and biological treatment (SPABT) consisting of ZnO as a photocatalyst and a microbial consortium (Galactomyces geotrichum and Brevibaccilus laterosporus) enhanced the degradation of a model textile dye, methyl red (MR). SPABT completely decolorized 500 mg MR/L within 4 h. Biotreatment alone required 6 h for 100% decolorization. A maximum of 70% decolorization was achieved with the photocatalytic treatment but reductions in COD and toxicity were not adequate. Significant elevated activities of enzymes, including azo reductase, laccase and veratryl alcohol oxidase, were observed in the microbial consortium after exposure of MR. The degradation pathway and products of MR varied with treatment applied. The persistent azo bond was cleaved by following photocatalytic treatment with the microbial biotreatment. Tests with Sorghum vulgare and Phaseolus mungo indicated the products obtained by SPABT were non-phytotoxic.

Photoelectrocatalytic decolorization of azo dyes with nano-composite oxide layers of ZnO nanorods decorated with Ag nanoparticles

Photoelectrocatalysis provides an excellent frame for the application of photocatalytic nanostructured materials on easy recoverable supports. This study reports the two-step synthesis of hierarchically nanostructured ZnO/Ag composite photoelectrodes. Wurtzite ZnO was selectively electronucleated as spheroidal seeds on fluor doped tin oxide substrates and nanodecorated with Ag nanoclusters under electrochemical control. Hierarchically organized nanorods were selectively chemically grown on the plane (002) perpendicular to the substrate from ZnO/Ag seeds. Solutions emulating dye effluents with the usual contents of 0.1 M of NaCl and a model azo dye (Methyl Orange) were decolorized using ZnO/Ag nanorods in different treatments. Photocatalysis attained discrete decolorizations of 8% whereas photoelectrocatalysis completely decolorized solutions after 60 min. The influence of the metal/semiconductor interface (ZnO/Ag) as introduced Schottky barrier is studied demonstrating a four-fold enhancement on decolorization kinetics respect bare ZnO nanorods. The influence of the seed growth control on the final photoelectrocatalytic response is reported to control the hierarchical organization of nanorods. This resulted in different decolorization kinetics as result of the differences on the efficient use of the delivered photons conditioned by the photoelectrode structure.

Photocatalytic activity of CuO/Cu(OH)2 nanostructures in the degradation of Reactive Green 19A and textile effluent, phytotoxicity studies and their biogenic properties (antibacterial and anticancer)

In this study, CuO/Cu(OH)₂ (denoted as CuONs) nanostructures were synthesized relying to a cheap and rapid chemical co-precipitation method using copper sulfate and liquid ammonia as precursors. Results obtained from X-ray diffraction, and field emission scanning electron microscopy analysis revealed the crystalline nature of synthesized CuONs. Fourier transform infrared spectroscopy and energy dispersive spectroscopy studies showed interactions between copper and oxygen atoms. Synthesized CuONs showed the size in the range of 20-30 nm using high resolution transmission electron microscopy analysis. The photocatalytic degradation performance of Reactive Green 19A (RG19A) dye using CuONs was evaluated. The results showed that CuONs exhibited 98% degradation efficiency after 12 h and also complete mineralization in form of reducing chemical oxygen demand (COD) (84%) and total organic carbon (TOC) (80%). The nanocatalyst was recovered from the dye containing solution and its catalytic activity can be reused up to four times efficiently. CuONs was also able to decolorize actual textile effluent (80% in terms of the American Dye Manufacturers' Institute (ADMI) value) with significant reductions in COD (72%) and TOC (69%). Phytotoxicity studies revealed that the degradation products of RG19A and textile effluent were scarcely toxic in nature, thereby increasing the applicability of CuONs for the treatment of textile wastewater. Additionally, the CuONs showed a maximum antibacterial effect against human pathogens which also displayed synergistic antibacterial potential related to commercial antibiotics. Moreover, CuONs displayed strong antioxidant activity in terms of ABTS (2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (IC₅₀: 51 μg/mL) and DPPH (1,1-diphenyl-2-picrylhydrazyl) (IC₅₀: 60 μg/mL) radical scavenging. The CuONs exhibited dose dependent response against tumor rat C6 cell line (IC₅₀: 60 μg/mL) and may serve as anticancer agents.

A review on the sustainability of textile industries wastewater with and without treatment methodologies

The textile industry in India plays a vital role in the economic growth of the nation. The growth of the textile industry not only impacts the economy of a country but also influences the global economy and mutual exchange of technology between the countries. However, the textile industry also generates an enormous quantity of waste as waste sludge, fibers and chemically polluted waters. The chemically polluted textile wastewater degrades the quality of the soil and water when it mixes with these natural resources and its dependent habitats and environment. Owing to the existing problem of solid and liquid waste, textile industries are facing major problems in environment pollution. Therefore, researchers and the textile industries are focusing on the reduction of textile wastewater and the formulation of alternative efficient treatment techniques without hampering the environment. Hence, the present literature survey mainly concentrates on the various wastewater treatment techniques and their advantages. Moreover, the focus of the study was to describe the methods for the reduction of environmental waste and effective utilization of recycled water with zero wastewater management techniques. The alternative methods for the reduction of textile waste are also covered in this investigation. Finally, this paper also suggests utilization of solid wastes after treatment of wastewater in other sectors like construction for the preparation of low-grade tiles and or bricks by replacing the cement normally used in their manufacturing.

Remediation of water and wastewater by using engineered nanomaterials: A review

Nanotechnology is currently a fast-rising socioeconomic and political knowledge-based technology owing to the unique characteristics of its engineered nanomaterials. This branch of technology is useful for water and wastewater remediation. Many scientists and researchers have been conducting different studies and experiments on the applications of engineered nanomaterials at the local to international level. This review mainly aims to provide a current overview of existing knowledge on engineered nanomaterials and their applications in water and wastewater remediation. Furthermore, the present risks and challenges of nanotechnology are examined.

Abatement of organic pollutants using fly ash based adsorbents

The presence of organic pollutants in the environment is of major concern because of their toxicity, bio-accumulating tendency, threat to human life and the environment. It is a well-known fact that, these pollutants can damage nerves, liver, and bones and could also block functional groups of essential enzymes. Conventional methods for removing dissolved pollutants include chemical precipitation, chemical oxidation or reduction, filtration, ion-exchange, electrochemical treatment, application of membrane technology, evaporation recovery and biological treatment. Although all the pollutant treatment techniques can be employed, they have their inherent advantages and limitations. Among all these methods, adsorption process is considered better than other methods because of convenience, easy operation and simplicity of design. A fundamentally important characteristic of good adsorbents is their high porosity and consequent larger surface area with more specific adsorption sites. This paper presents a review of adsorption of different pollutants using activated carbon prepared from fly ash sources and the attendant environmental implications. Also, the ways of overcoming barriers to fly ash utilization together with regeneration studies are also discussed.

Rapid methyl orange degradation using porous ZnO spheres photocatalyst

Porous zinc oxide (ZnO) spheres were synthesized by facile low temperature solution route. The as-synthesized porous ZnO spheres were characterized in detail in terms of their morphological, structural, optical and photocatalytic properties using field-emission scanning electron microscopy (FESEM, equipped with energy dispersive spectroscopy (EDS)), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), X-ray diffractometer (XRD), UV-visible spectroscopy and Raman-scattering measurements. Nitrogen adsorption-desorption analysis was performed to determine pore size distribution from the adsorption isotherm curves using the Barrett-Joyner-Halenda (BJH) method. Morphological and structural characterizations showed porous nature of ZnO spheres with high surface area, good crystallinity, wurtzite hexagonal phase and good optical features. Next, ZnO spheres were studied as photocatalyst for photodegradation of harmful dye, methyl orange (MO). Under ultraviolet light irradiation, the decrease in MO dye concentration was monitored by UV-visible spectroscopy at different time intervals until the dye was completely degraded to colorless end product. Rapid MO dye decomposition was observed with a degradation rate of ~96.3% within the initial 120min, which is attributed to the porous nature, large specific surface area (114.6m(2)g(-1)), narrow pore size distribution (~2.5 to 25nm) evaluated from N2 adsorption-desorption isotherms analysis and excellent electron accepting features of the engineered porous ZnO spheres.

Photocatalytic Membrane Reactor for the Removal of C.I. Disperse Red 73

After the dyeing process, part of the dyes used to color textile materials are not fixed into the substrate and are discharged into wastewater as residual dyes. In this study, a heterogeneous photocatalytic process combined with microfiltration has been investigated for the removal of C.I. Disperse Red 73 from synthetic textile effluents. The titanium dioxide (TiO₂) Aeroxide P25 was selected as photocatalyst. The photocatalytic treatment achieved between 60% and 90% of dye degradation and up to 98% chemical oxygen demand (COD) removal. The influence of different parameters on photocatalytic degradation was studied: pH, initial photocatalyst loading, and dye concentration. The best conditions for dye degradation were pH 4, an initial dye concentration of 50 mg·L⁻¹, and a TiO₂ loading of 2 g·L⁻¹. The photocatalytic membrane treatment provided a high quality permeate, which can be reused.

Remediation of textile effluents by membrane based treatment techniques: a state of the art review

The textile industries hold an important position in the global industrial arena because of their undeniable contributions to basic human needs satisfaction and to the world economy. These industries are however major consumers of water, dyes and other toxic chemicals. The effluents generated from each processing step comprise substantial quantities of unutilized resources. The effluents if discharged without prior treatment become potential sources of pollution due to their several deleterious effects on the environment. The treatment of heterogeneous textile effluents therefore demands the application of environmentally benign technology with appreciable quality water reclamation potential. These features can be observed in various innovative membrane based techniques. The present review paper thus elucidates the contributions of membrane technology towards textile effluent treatment and unexhausted raw materials recovery. The reuse possibilities of water recovered through membrane based techniques, such as ultrafiltration and nanofiltration in primary dye houses or auxiliary rinse vats have also been explored. Advantages and bottlenecks, such as membrane fouling associated with each of these techniques have also been highlighted. Additionally, several pragmatic models simulating transport mechanism across membranes have been documented. Finally, various accounts dealing with techno-economic evaluation of these membrane based textile wastewater treatment processes have been provided.

Electrochemical advanced oxidation processes: today and tomorrow. A review

In recent years, new advanced oxidation processes based on the electrochemical technology, the so-called electrochemical advanced oxidation processes (EAOPs), have been developed for the prevention and remediation of environmental pollution, especially focusing on water streams. These methods are based on the electrochemical generation of a very powerful oxidizing agent, such as the hydroxyl radical ((•)OH) in solution, which is then able to destroy organics up to their mineralization. EAOPs include heterogeneous processes like anodic oxidation and photoelectrocatalysis methods, in which (•)OH are generated at the anode surface either electrochemically or photochemically, and homogeneous processes like electro-Fenton, photoelectro-Fenton, and sonoelectrolysis, in which (•)OH are produced in the bulk solution. This paper presents a general overview of the application of EAOPs on the removal of aqueous organic pollutants, first reviewing the most recent works and then looking to the future. A global perspective on the fundamentals and experimental setups is offered, and laboratory-scale and pilot-scale experiments are examined and discussed.

Application of magnetic chitosan composites for the removal of toxic metal and dyes from aqueous solutions

Magnetic chitosan composites (MCCs) are a novel material that exhibits good sorption behavior toward various toxic pollutants in aqueous solution. These magnetic composites have a fast adsorption rate and high adsorption efficiency, efficient to remove various pollutants and they are easy to recover and reuse. These features highlight the suitability of MCCs for the treatment of water polluted with metal and organic materials. This review outlines the preparation of MCCs as well as methods to characterize these materials using FTIR, XRD, TGA and other microscopy-based techniques. Additionally, an overview of recent developments and applications of MCCs for metal and organic pollutant removal is discussed in detail. Based on current research and existing materials, some new and futuristic approaches in this fascinating area are also discussed. The main objective of this review is to provide up-to-date information about the most important features of MCCs and to show their advantages as adsorbents in the treatment of polluted aqueous solutions.