A review of graphene-TiO2 and graphene-ZnO nanocomposite photocatalysts for wastewater treatment

A novel green preparation of zinc oxide nanoparticles with Hibiscus sabdariffa L.: photocatalytic performance, evaluation of antioxidant and antibacterial activity

This study investigates the eco-friendly synthesis of zinc oxide nanoparticles (ZnO NPs) utilizing an aqueous solution of Hibiscus sabdariffa L. flower extract, which is acts as reducing agent as well as capping agent. The Fourier transform infrared spectroscopy (FTIR) results revealed the presence of flavonoids and phenols in the plant extract, indicating that they were the major agents capable of reducing zinc nitrate salt. According to our x-ray diffraction (XRD) results, ZnO-NPs exhibit a particular phase wurtzite structure. The ZnO-NPs are spherical in shape and have an average size of 15 nm, according to the measurements of electron microscope (SEM) and transmission electron microscope (TEM) measurements. Energy dispersion (EDX) analysis demonstrates that the NPs are mainly composed of zinc and oxygen. The zeta potential of these nanoparticles shows that they are very stable. The antibacterial activity of ZnO-NPs was tested using agar dilutions with a variety of gram-positive and gram-negative microorganisms. According to the research results, ZnO-NPs can be established as an extremely specific antibacterial agent for a wide variety of organisms to prevent bacterial growth. Furthermore, the antioxidant properties of ZnO-NPs were determined using the 2,2 diphenyl-1-picrylhydrazyl hydrate (DPPH) radical scavenging approach, and the IC50 value of 38 μg/mL was measured for ZnO-NPs. Furthermore, the biosynthesized ZnO-NPs showed significant catalytic performance of methyl orange (MO) under UV irradiation. Overall, ZnO-NPs in their produced state have excellent potential in biomedical and wastewater treatment applications. Radical scavengers were used to evaluate the role of radicals in the reaction mechanism.

A review on existing and emerging approaches for textile wastewater treatments: challenges and future perspectives

This comprehensive review explores the complex environment of textile wastewater treatment technologies, highlighting both well-established and emerging techniques. Textile wastewater poses a significant environmental challenge, containing diverse contaminants and chemicals. The review presents a detailed examination of conventional treatments such as coagulation, flocculation, and biological processes, highlighting their effectiveness and limitations. In textile industry, various textile operations such as sizing, de-sizing, dyeing, bleaching, and mercerization consume large quantities of water generating effluent high in color, chemical oxygen demand, and solids. The dyes, mordants, and variety of other chemicals used in textile processing lead to effluent variable in characteristics. Furthermore, it explores innovative and emerging techniques, including advanced oxidation processes, membrane filtration, and nanotechnology-based solutions. Future perspectives in textile wastewater treatment are discussed in-depth, emphasizing the importance of interdisciplinary research, technological advancements, and the integration of circular economy principles. Numerous dyes used in the textile industry have been shown to have mutagenic, cytotoxic, and ecotoxic potential in studies. Therefore, it is necessary to assess the methods used to remediate textile waste water. Major topics including the chemical composition of textile waste water, the chemistry of the dye molecules, the selection of a treatment technique, the benefits and drawbacks of the various treatment options, and the cost of operation are also addressed. Overall, this review offers a valuable resource for researchers and industry professionals working in the textile industry, pointing towards a more sustainable and environmentally responsible future.

Novel smart fiber/metal/chitosan composite as a filter for self-detoxifying photocatalytic wastewater remediation and biomedical applications

Wastewater treatment remains the most significant delinquent issue world-wide. Generally, wastewater treatment involves filtration followed by acidified de-emulsification through photocatalytic reduction. The aim of the present study is to reduce the use of nanoparticles in wastewater treatment and also to find an appropriate alternative to replace cotton fiber filters used in water treatment plant. The cotton fiber filters are highly prone to bacterial film development leading to bactericidal degradation of the fibers. We developed a ZnO-chitosan nanocomposite coated fiber for wastewater treatment to enhance its photocatalytic activity under acidic condition. The fiber showed high degree of photocatalytic degradation activity, reducing rhodamine B dye, chemical oxygen demand and chromium levels in the synthetic wastewater to 37, 79 and 51% respectively under highly acidic condition. Additionally, ZnO-chitosan nanocomposite did not cause mortality on Danio rerio embryo after 72 h incubation. The ZnO-chitosan nanocomposite coated fiber showed strong antibacterial activity against Escherichia coli and Staphylococcus aureus with a reduction of 96% and 99% respectively. This study demonstrated the potential of a novel smart fiber in wastewater treatment and biomedical applications.

A review on pollutants remediation competence of nanocomposites on contaminated water

Clean freshwater has been required for drinking, sanitation, agricultural activities, and industry, as well as for the development and maintenance of the eco - systems on which all livelihoods rely. Water contamination is currently a significant concern for researchers all over the world; hence it is essential that somehow this issue is resolved as soon as possible. It is now recognised as one of the most important research areas in the world. Current wastewater treatment techniques degrade a wide range of wastewaters efficiently; however, such methods have some limitations. Recently, nanotechnology has emerged as a wonderful solution, and researchers are conducting research in this water remediation field with a variety of potential applications. The pollutants remediation capability of nanocomposites as adsorbents, photocatalysts, magnetic separation, and so on for contaminant removal from contaminated water has been examined in this study. This study has spotlighted the most significant nanocomposites invention reported to date for contaminated and effluent remediation, as well as a research gap as well as possible future perspectives.

Remediation competence of nanoparticles amalgamated biochar (nanobiochar/nanocomposite) on pollutants: A review

Advanced biochar blended nanoparticles substances, such as nano biochar or nanocomposites, have provided long-term solutions to a wide range of modern-day problems. Biochar blended nano-composites can be created to create better composite materials that combine the benefits of biochar and nanoparticles. Such materials have been typically improved with active functional groups, porous structure, active surface area, catalytic deterioration ability, as well as easy recovery or separation of pollutants. Such biochar-basednanocomposites have good adsorption properties for a variety of pollutants in various form of polluted medium (soil and water contamination). Catalytic nanoparticle encapsulated biochar, can perform concurrently the adsorption (by biochar) as well as catalytic degradation (nanoparticles) functions for pollutants removal from polluted sites. In this review, the advanced and practically feasible techniques involved in the biochar blended nanoparticles-based nanocomposites have been discussed with environmental applications. Furthermore, the mechanisms involved in this composite material in remediation, as well as the advantages and disadvantages of biochar blended nanoparticles-based nanocomposites, were discussed, and future directions for study in this field were suggested.

Next-generation graphene oxide additives composite membranes for emerging organic micropollutants removal: Separation, adsorption and degradation

In the past two decades, membrane technology has attracted considerable interest as a viable and promising method for water purification. Emerging organic micropollutants (EOMPs) in wastewater have trace, persistent, highly variable quantities and types, develop hazardous intermediates and are diffusible. These primary issues affect EOMPs polluted wastewater on an industrial scale differently than in a lab, challenging membranes-based EOMP removal. Graphene oxide (GO) promises state-of-the-art membrane synthesis technologies and use in EOMPs removal systems due to its superior physicochemical, mechanical, and electrical qualities and high oxygen content. This critical review highlights the recent advancements in the synthesis of next-generation GO membranes with diverse membrane substrates such as ceramic, polyethersulfone (PES), and polyvinylidene fluoride (PVDF). The EOMPs removal efficiencies of GO membranes in filtration, adsorption (incorporated with metal, nanomaterial in biodegradable polymer and biomimetic membranes), and degradation (in catalytic, photo-Fenton, photocatalytic and electrocatalytic membranes) and corresponding removal mechanisms of different EOMPs are also depicted. GO-assisted water treatment strategies were further assessed by various influencing factors, including applied water flow mode and membrane properties (e.g., permeability, hydrophily, mechanical stability, and fouling). GO additive membranes showed better permeability, hydrophilicity, high water flux, and fouling resistance than pristine membranes. Likewise, degradation combined with filtration is two times more effective than alone, while crossflow mode improves the photocatalytic degradation performance of the system. GO integration in polymer membranes enhances their stability, facilitates photocatalytic processes, and gravity-driven GO membranes enable filtration of pollutants at low pressure, making membrane filtration more inexpensive. However, simultaneous removal of multiple contaminants with contrasting characteristics and variable efficiencies in different systems demands further optimization in GO-mediated membranes. This review concludes with identifying future critical research directions to promote research for determining the GO-assisted OMPs removal membrane technology nexus and maximizing this technique for industrial application.

Graphene-based TiO2 composites for photocatalysis & environmental remediation: synthesis and progress

Photoactive nanomaterials constitute an emerging field in nanotechnology, finding an extensive array of applications spanning diverse areas, including electronics and photovoltaic devices, solar fuel cells, wastewater treatment, etc. Titanium dioxide (TiO₂), in its thin-film form, has been exhaustively surveyed as potential photocatalysts for environmental remediation owing to its innocuousness, stability, and photocatalytic characteristics when subjected to ultraviolet (UV) irradiation. However, TiO₂ has some shortcomings associated with a large bandgap value of around 3.2 eV, making it less efficient in the visible spectral range. TiO₂ is often consolidated with various carbon nanomaterials to overcome this limitation and enhance its efficiency. Graphene, a 2-dimensional allotrope of carbon with a bandgap tuned between 0 and 0.25 eV, exhibits unique properties, making it an attractive candidate to augment the photoactivity of semiconductor (SC) oxides. Encapsulating graphene oxide onto TiO₂ nanospheres demonstrates intensified photocatalytic properties and exceptional recyclability for the degeneration of certain dyes, including Rhodamine B. This review encompasses various techniques to synthesize graphene-based TiO₂ photoactive composites, emphasizing graphene capsulized hollow titania nanospheres, nanofibers, core/shell, and reduced graphene oxide-TiO₂-based nanocomposites. It also consolidates the application of the aforestated nanocomposites for the disintegration of various synthetic dyes, proving efficacious for water decontamination and degradation of chemicals and pharmaceuticals. Furthermore, graphene-based TiO₂ nanocomposites used as lithium (Li)-ion batteries manifesting substantial electrochemical performance and solar fuel cells for energy production are discussed here.

Biophotocatalytic Reduction of CO2 in Anaerobic Biogas Produced from Wastewater Treatment Using an Integrated System

This study presents the bio-photocatalytic upgrading of biogas utilising carbon dioxide (CO2) as a potential option for beginning fossil fuel depletion and the associated environmental risks in the pursuit of sustainable development. Herein, magnetite photocatalyst (Fe-TiO2) was employed with an integrated anaerobic-photomagnetic system for the decontamination of municipality wastewater for biogas production. The Fe-TiO2 photocatalyst used, manufactured via a co-precipitation technique, had a specific surface area of 62.73 m2/g, micropore volume of 0.017 cm3/g and pore size of 1.337 nm. The results showed that using the ultraviolet-visible (UV-Vis) photomagnetic system as a post-treatment to the anaerobic digestion (AD) process was very effective with over 85% reduction in colour, chemical oxygen demand (COD) and turbidity. With an organic loading rate (OLR) of 0.394 kg COD/L·d and hydraulic retention time (HTR) of 21 days, a 92% degradation of the organic content (1.64 kgCOD/L) was attained. This maximised the bioenergy production to 5.52 kWh/m3 with over 10% excess energy to offset the energy demand of the UV-Vis lamp. Assuming 33% of the bioenergy produced was used as electricity to power the UV-Vis lamp, the CO2 emission reduction was 1.74 kg CO2 e/m3, with good potential for environmental conservation.

Super-hydrophobic and photocatalytic antimicrobial activity of iodine-doped ZnO nanoarray films

Iodine(i) doped ZnO nanoarray films (ZnO/I-X) were prepared on a silicon wafer by the in itu growth method.

Sonochemical preparation and characterization of Sm-doped GO/KSrPO4 nanocomposite photocatalyst for degradation of methylene blue dye

The present work pertains to synthesis of Sm-doped GO/KSrPO4 (GO/KSrPO4 :Sm) nanocomposite using ultrasound-assisted method. Successful decoration of graphene oxide sheets with the KSrPO4 :Sm3+ phosphor was confirmed using analysis techniques including SEM, EDS, UV/visible spectrometry, XRD, and FTIR of the prepared GO/KSrPO4 :Sm nanocomposite. Further, photocatalytic activity of this nanocomposite material was studied by examining degradation of methylene blue (MB) dye from water. The effects of several parameters like concentration of Sm3+ in KSrPO4 :Sm3+ phosphor within the GO/KSrPO4 :Sm nanocomposite photocatalyst, photocatalyst loading, initial dye concentration, pH, and preparation method were evaluated. At a higher concentration of Sm3+ in the photocatalyst (1 mol.%), higher photocatalyst loading (1.5 mg/ml), lesser dye concentration (20 mg/L), and higher pH (11.4), the GO/KSrPO4 :Sm nanocomposite photocatalyst prepared using ultrasound-assisted method showed higher dye removal compared to other conditions. A maximum of 83.35% removal of MB dye was achieved by the use of ultrasonically prepared GO/KSrPO4 :Sm nanocomposite photocatalyst having a concentration of 1 mol.% of Sm3+ in the KSrPO4 :Sm3+ phosphor at a loading of 1.5 mg/ml, initial dye concentration of 20 mg/L, and a pH of 11.4. Rate constant for MB dye degradation using the GO/KSrPO4:Sm nanocomposite photocatalyst synthesized by ultrasonic-assisted method was found to be 0.0053 min-1 . PRACTITIONER POINTS: GO/KSrPO4 :Sm nanocomposite photocatalyst prepared by ultrasonic-assisted method. Higher Sm3+ doping in nanocomposite with the use of ultrasound assisted method showed better performance of photocatalyst. A maximum removal of 83.35% of methylene blue dye was achieved.