Recent developments of metal oxide based heterostructures for photocatalytic applications towards environmental remediation

Advancement of metal oxide nanomaterials on agri-food fronts

The application of metal oxide nanomaterials (MOx NMs) in the agrifood industry offers innovative solutions that can facilitate a paradigm shift in a sector that is currently facing challenges in meeting the growing requirements for food production, while safeguarding the environment from the impacts of current agriculture practices. This review comprehensively illustrates recent advancements and applications of MOx for sustainable practices in the food and agricultural industries and environmental preservation. Relevant published data point out that MOx NMs can be tailored for specific properties, enabling advanced design concepts with improved features for various applications in the agrifood industry. Applications include nano-agrochemical formulation, control of food quality through nanosensors, and smart food packaging. Furthermore, recent research suggests MOx's vital role in addressing environmental challenges by removing toxic elements from contaminated soil and water. This mitigates the environmental effects of widespread agrichemical use and creates a more favorable environment for plant growth. The review also discusses potential barriers, particularly regarding MOx toxicity and risk evaluation. Fundamental concerns about possible adverse effects on human health and the environment must be addressed to establish an appropriate regulatory framework for nano metal oxide-based food and agricultural products.

Strong thickness dependence in thin film photocatalytic heterojunctions: the ZnO-Bi2O3 case study

Semiconductor heterojunctions are an effective way to achieve efficient photocatalysts, as they can provide an adequate redox potential with visible light excitation. Several works have reported synergistic effects with nanoparticle semiconductor materials. The question is still open for thin film heterojunctions formed by stacked layers, as photocatalysis is considered a surface phenomenon. To investigate if the internal layer really affects or modifies the photocatalytic properties of the external material, we analyze the thin film heterojunction with ZnO and Bi2O3 semiconductors deposited by spray pyrolysis in two configurations: substrate/ZnO/Bi2O3 and substrate/Bi2O3/ZnO. Microstructural analysis was performed to verify the formation of the physical junction of the materials and discard new ternary phases. The photocatalytic activity was analyzed as a function of the thickness of the layers under blue light irradiation. We determined the conduction and valence bands positions, the carrier concentrations, mobilities, Fermi levels, etc. that allowed us to distinguish two reaction mechanisms depending on the configuration. There is a strong compromise between the order and thickness of the layers with the photocatalytic activity. The internal electric field produced in the interface defines the route of the photogenerated charges, and therefore the photocatalytic response. Thus, well-designed thin film heterojunctions can indeed improve the photocatalytic activity of the surface layer.

Fabrication of Tungsten Oxide Nanowalls through HFCVD for Improved Electrochemical Detection of Methylamine

In this study, well-defined tungsten oxide (WO3) nanowall (NW) thin films were synthesized via a controlled hot filament chemical vapor deposition (HFCVD) technique and applied for electrochemical detection of methylamine toxic substances. Herein, for the thin-film growth by HFCVD, the temperature of tungsten (W) wire was held constant at ~1450 °C and gasification was performed by heating of W wire using varied substrate temperatures ranging from 350 °C to 450 °C. At an optimized growth temperature of 400 °C, well-defined and extremely dense WO3 nanowall-like structures were developed on a Si substrate. Structural, crystallographic, and compositional characterizations confirmed that the deposited WO3 thin films possessed monoclinic crystal structures of high crystal quality. For electrochemical sensing applications, WO3 NW thin film was used as an electrode, and cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were measured with a wide concentration range of 20 μM~1 mM of methylamine. The fabricated electrochemical sensor achieved a sensitivity of ~183.65 μA mM-1 cm-2, a limit of detection (LOD) of ~20 μM and a quick response time of 10 s. Thus, the fabricated electrochemical sensor exhibited promising detection of methylamine with considerable stability and reproducibility.

Ultrasound for the degradation of endocrine disrupting compounds in aqueous solution: A review on mechanisms, influence of operating parameters and cost estimation

Availability of drinking water is one of the basic humanitarian goals but remains as a grand challenge that the world is facing today. Currently, water bodies are contaminated not only with conventional pollutants but also with numerous recalcitrant pollutants, such as PPCPs, endocrine disrupting compounds, etc. These emerging pollutants require special attention because of their toxicity to living organisms, bio-resistant and can sustain even after primary and secondary treatments of wastewater. Among different treatment technologies, sonolysis is found to be an innovative and promising technique for the treatment of emerging pollutants present in aqueous solution. Sonolysis is the use of ultrasound to enhance or alter chemical reactions by the formation of free radicals and shock waves which ultimately helps in degradation of pollutants. This review summarizes several studies in the sonochemical literature, including mechanisms of sonochemical process, physical and chemical effects of ultrasound, and the influence of several process variables such as ultrasound frequency, power density, temperature and pH of the medium on degradation performance for endocrine disrupting compounds. In addition, this review highlighted techno-economic perspectives focusing on the total cost required for translating the ultrasound-based processes on a large scale. Overall, the objective of this study is to exhibit a critical review of information available in the literature to encourage and promote future research on sonolysis for the degradation of Endocrine Disrupting Compounds (EDCs).

Advanced oxidation process for the treatment of industrial wastewater: A review on strategies, mechanisms, bottlenecks and prospects

Due to its complex and, often, highly contaminated nature, treating industrial wastewater poses a significant environmental problem. Many of the persistent pollutants found in industrial effluents cannot be effectively removed by conventional treatment procedures. Advanced Oxidation Processes (AOPs) have emerged as a promising solution, offering versatile and effective means of pollutant removal and mineralization. This comprehensive review explores the application of various AOP strategies in industrial wastewater treatment, focusing on their mechanisms and effectiveness. Ozonation (O3): Ozonation, leveraging ozone (O3), represents a well-established AOP for industrial waste water treatment. Ozone's formidable oxidative potential enables the breakdown of a broad spectrum of organic and inorganic contaminants. This paper provides an in-depth examination of ozone reactions, practical applications, and considerations involved in implementing ozonation. UV/Hydrogen Peroxide (UV/H2O2): The combination of ultraviolet (UV) light and hydrogen peroxide (H2O2) has gained prominence as an AOP due to its ability to generate hydroxyl radicals (ȮH), highly efficient in pollutant degradation. The review explores factors influencing the efficiency of UV/H2O2 processes, including H2O2 dosage and UV radiation intensity. Fenton and Photo-Fenton Processes: Fenton's reagent and Photo-Fenton processes employ iron ions and hydrogen peroxide to generate hydroxyl radicals for pollutant oxidation. The paper delves into the mechanisms, catalyst selection, and the role of photoactivation in enhancing degradation rates within the context of industrial wastewater treatment. Electrochemical Advanced Oxidation Processes (EAOPs): EAOPs encompass a range of techniques, such as electro-Fenton and anodic oxidation, which employ electrode reactions to produce ȮH radicals. This review explores the electrochemical principles, electrode materials, and operational parameters critical for optimizing EAOPs in industrial wastewater treatment. TiO2 Photocatalysis (UV/TiO2): Titanium dioxide (TiO2) photocatalysis, driven by UV light, is examined for its potential in industrial wastewater treatment. The review investigates TiO2 catalyst properties, reaction mechanisms, and the influence of parameters like catalyst loading and UV intensity on pollutant removal. Sonolysis (Ultrasonic Irradiation): High-frequency ultrasound-induced sonolysis represents a unique AOP, generating ȮH radicals during the formation and collapse of cavitation bubbles. This paper delves into the physics of cavitation, sonolytic reactions, and optimization strategies for industrial wastewater treatment. This review offers a critical assessment of the applicability, advantages, and limitations of these AOP strategies in addressing the diverse challenges posed by industrial wastewater. It emphasizes the importance of selecting AOPs tailored to the specific characteristics of industrial effluents and outlines potential directions for future research and practical implementation. The integrated use of these AOPs, when appropriately adapted, holds the potential to achieve sustainable and efficient treatment of industrial wastewater, contributing significantly to environmental preservation and regulatory compliance.

A review of biosensor for environmental monitoring: principle, application, and corresponding achievement of sustainable development goals

Human health/socioeconomic development is closely correlated to environmental pollution, highlighting the need to monitor contaminants in the real environment with reliable devices such as biosensors. Recently, variety of biosensors gained high attention and employed as in-situ application, in real-time, and cost-effective analytical tools for healthy environment. For continuous environmental monitoring, it is necessary for portable, cost-effective, quick, and flexible biosensing devices. These benefits of the biosensor strategy are related to the Sustainable Development Goals (SDGs) established by the United Nations (UN), especially with reference to clean water and sources of energy. However, the relationship between SDGs and biosensor application for environmental monitoring is not well understood. In addition, some limitations and challenges might hinder the biosensor application on environmental monitoring. Herein, we reviewed the different types of biosensors, principle and applications, and their correlation with SDG 6, 12, 13, 14, and 15 as a reference for related authorities and administrators to consider. In this review, biosensors for different pollutants such as heavy metals and organics were documented. The present study highlights the application of biosensor for achieving SDGs. Current advantages and future research aspects are summarized in this paper.Abbreviations: ATP: Adenosine triphosphate; BOD: Biological oxygen demand; COD: Chemical oxygen demand; Cu-TCPP: Cu-porphyrin; DNA: Deoxyribonucleic acid; EDCs: Endocrine disrupting chemicals; EPA: U.S. Environmental Protection Agency; Fc-HPNs: Ferrocene (Fc)-based hollow polymeric nanospheres; Fe₃O₄@3D-GO: Fe₃O₄@three-dimensional graphene oxide; GC: Gas chromatography; GCE: Glassy carbon electrode; GFP: Green fluorescent protein; GHGs: Greenhouse gases; HPLC: High performance liquid chromatography; ICP-MS: Inductively coupled plasma mass spectrometry; ITO: Indium tin oxide; LAS: Linear alkylbenzene sulfonate; LIG: Laser-induced graphene; LOD: Limit of detection; ME: Magnetoelastic; MFC: Microbial fuel cell; MIP: Molecular imprinting polymers; MWCNT: Multi-walled carbon nanotube; MXC: Microbial electrochemical cell-based; NA: Nucleic acid; OBP: Odorant binding protein; OPs: Organophosphorus; PAHs: Polycyclic aromatic hydrocarbons; PBBs: Polybrominated biphenyls; PBDEs: Polybrominated diphenyl ethers; PCBs: Polychlorinated biphenyls; PGE: Polycrystalline gold electrode; photoMFC: photosynthetic MFC; POPs: Persistent organic pollutants; rGO: Reduced graphene oxide; RNA: Ribonucleic acid; SDGs: Sustainable Development Goals; SERS: Surface enhancement Raman spectrum; SPGE: Screen-printed gold electrode; SPR: Surface plasmon resonance; SWCNTs: single-walled carbon nanotubes; TCPP: Tetrakis (4-carboxyphenyl) porphyrin; TIRF: Total internal reflection fluorescence; TIRF: Total internal reflection fluorescence; TOL: Toluene-catabolic; TPHs: Total petroleum hydrocarbons; UN: United Nations; VOCs: Volatile organic compounds.

A comparative study of photocatalytic activity of Na+-Ag+ ion-exchanged glass-ceramics with metallic Ag, semiconductor AgBr, and hybrid Ag-AgBr nanoparticles

Photocatalytic glass-ceramics doped with metallic Ag, semiconductor AgBr, and hybrid metal-semiconductor Ag-AgBr nanostructures were synthesized via low-temperature Na+-Ag+ ion exchange. The spectral features of the nanostructures in the silicate glass matrix as well as their photocatalytic performance were studied in detail. Glass-ceramics containing hybrid metal-semiconductor nanostructures were shown to possess one order of magnitude higher photocatalytic activity compared to their counterparts with metallic and semiconductor nanostructures. Hybrid metal-semiconductor nanostructures allow enhancement of the net density of photogenerated hot electrons.

Water remediation using titanium and zinc oxide nanomaterials through disinfection and photo catalysis process: A review

Various pesticides and organic compounds generated as a result of rapid industrialization and pharmaceutical companies pose a major threat to the environment. Novel photocatalysts based on zinc oxide and titanium oxide exhibit great potential towards absorption of these organic pollutants from wastewater. The photocatalysts possess various extraordinary properties like photocatalytic degradation potential, non-toxic and high stability. However, several limitations are also associated with the applications of these photocatalysts like poor affinity, particle agglomeration, high band gap and recovery issues. Hence, optimization is required to enhance their efficiency and at the same time make them cost effective and sustainable. The review covers the mechanism for water treatment, limitations and development of different modification strategies that improve the removal efficiency of titanium and zinc oxide based photocatalysts. Thus, further research in the field of photocatalysts can be encouraged for carrying out water remediation.

Metal Oxide Nanostructures (MONs) as Photocatalysts for Ciprofloxacin Degradation

In recent years, organic pollutants have become a global problem due to their negative impact on human health and the environment. Photocatalysis is one of the most promising methods for the removal of organic pollutants from wastewater, and oxide semiconductor materials have proven to be among the best in this regard. This paper presents the evolution of the development of metal oxide nanostructures (MONs) as photocatalysts for ciprofloxacin degradation. It begins with an overview of the role of these materials in photocatalysis; then, it discusses methods of obtaining them. Then, a detailed review of the most important oxide semiconductors (ZnO, TiO₂, CuO, etc.) and alternatives for improving their photocatalytic performance is provided. Finally, a study of the degradation of ciprofloxacin in the presence of oxide semiconductor materials and the main factors affecting photocatalytic degradation is carried out. It is well known that antibiotics (in this case, ciprofloxacin) are toxic and non-biodegradable, which can pose a threat to the environment and human health. Antibiotic residues have several negative impacts, including antibiotic resistance and disruption of photosynthetic processes.

A Review on Photocatalysis Used For Wastewater Treatment: Dye Degradation

Water pollution is a global issue as a consequence of rapid industrialization and urbanization. Organic compounds which are generated from various industries produce problematic pollutants in water. Recently, metal oxide (TiO2, SnO2, CeO2, ZrO2, WO3, and ZnO)-based semiconductors have been explored as excellent photocatalysts in order to degrade organic pollutants in wastewater. However, their photocatalytic performance is limited due to their high band gap (UV range) and recombination time of photogenerated electron-hole pairs. Strategies for improving the performance of these metal oxides in the fields of photocatalysis are discussed. To improve their photocatalytic activity, researchers have investigated the concept of doping, formation of nanocomposites and core-shell nanostructures of metal oxides. Rare-earth doped metal oxides have the advantage of interacting with functional groups quickly because of the 4f empty orbitals. More precisely, in this review, in-depth procedures for synthesizing rare earth doped metal oxides and nonocomposites, their efficiency towards organic pollutants degradation and sources have been discussed. The major goal of this review article is to propose high-performing, cost-effective combined tactics with prospective benefits for future industrial applications solutions.

An overview on ZnO-based sonophotocatalytic mitigation of aqueous phase pollutants

Over the past several decades, the increase in industrialization provoked the discharge of harmful pollutants into the environment, affecting human beings and ecosystems. ZnO-based photocatalysts seem to be the most promising photocatalysts for treating harmful pollutants. However, fast charge carrier recombination, photo corrosion, and long reaction time are the significant factors that reduce the photoactivity of ZnO-based photocatalysts. In order to enhance the photoactivity of such photocatalysts, a combined process i.e., sonocatalysis + photocatalysis = sonophotocatalysis was used. Sonophotocatalysis is one of several different AOP methods that have recently drawn considerable interest, as it produces high reactive oxygen species (ROS) which helps in the oxidation of pollutants by acoustic cavitation. This combined technique enhanced the overall efficiency of the individual method by overcoming its limiting factors. The current review aims to present the theoretical and fundamental aspects of sonocatalysis and photocatalysis along with a detailed discussion on the benefits that can be obtained by the combined process i.e., US + UV (sonophotocatalysis). Also, we have provided a comparison of the excellent performance of ZnO to that of the other metal oxides. The purpose of this study is to discuss the literature concerning the potential applications of ZnO-based sonophotocatalysts for the degradation of pollutants i.e., dyes, antibiotics, pesticides, phenols, etc. That are carried out for future developments. The role of the produced ROS under light and ultrasound stimulation and the degradation mechanisms that are based on published literature are also discussed. In the end, future perspectives are suggested, that are helpful in the development of the sonophotocatalysis process for the remediation of wastewater containing various pollutants.

Algal Extracts for Green Synthesis of Zinc Oxide Nanoparticles: Promising Approach for Algae Bioremediation

Zinc oxide nanoparticles (ZnO-NPs) possess unique properties, making them a popular material across various industries. However, traditional methods of synthesizing ZnO-NPs are associated with environmental and health risks due to the use of harmful chemicals. As a result, the development of eco-friendly manufacturing practices, such as green-synthesis methodologies, has gained momentum. Green synthesis of ZnO-NPs using biological substrates offers several advantages over conventional approaches, such as cost-effectiveness, simplicity of scaling up, and reduced environmental impact. While both dried dead and living biomasses can be used for synthesis, the extracellular mode is more commonly employed. Although several biological substrates have been successfully utilized for the green production of ZnO-NPs, large-scale production remains challenging due to the complexity of biological extracts. In addition, ZnO-NPs have significant potential for photocatalysis and adsorption in the remediation of industrial effluents. The ease of use, efficacy, quick oxidation, cost-effectiveness, and reduced synthesis of harmful byproducts make them a promising tool in this field. This review aims to describe the different biological substrate sources and technologies used in the green synthesis of ZnO-NPs and their impact on properties. Traditional synthesis methods using harmful chemicals limit their clinical field of use. However, the emergence of algae as a promising substrate for creating safe, biocompatible, non-toxic, economic, and ecological synthesis techniques is gaining momentum. Future research is required to explore the potential of other algae species for biogenic synthesis. Moreover, this review focuses on how green synthesis of ZnO-NPs using biological substrates offers a viable alternative to traditional methods. Moreover, the use of these nanoparticles for industrial-effluent remediation is a promising field for future research.

Construction of direct FeMoO4/g-C3N4-2D/2D Z-scheme heterojunction with enhanced photocatalytic treatment of textile wastewater to eliminate the toxic effect in marine environment

A novel FeMoO₄/g-C₃N₄-2D/2D Z-scheme heterojunction photocatalyst was prepared via wet chemical method. The observed structural morphology of FeMoO₄/g-C₃N₄ reveals the 2D-iron molybdate (FeMoO₄) nanoplates compiled with the 2D-graphitic carbon nitride (g-C₃N₄) nanosheets like structure. The photocatalytic activity of the g-C₃N₄, FeMoO₄, and FeMoO₄/g-C₃N₄ composites were studied via the degradation of Rhodamine B (RhB) as targeted textile dye under visible light irradiation (VLI). The optimal FeMoO₄/g-C₃N₄ (1:3 ratio of g-C₃N₄ and FeMoO₄) composite show an enhanced degradation performance with rate constant value of 0.02226 min^-1 and good stability even after three cycles. Thus, the h+ and O₂^•－are the key radicals in the degradation of RhB under VLI. It is proposed that the FeMoO₄/g-C₃N₄ Z-scheme heterojunction effectively enhances the transfer and separation ability of e^-/h⁺ pairs, by the way increasing the photocatalytic efficiency towards the RhB degradation. Thus, the newly constructed Z-scheme FeMoO₄/g-C₃N₄ heterojunction photocatalyst is a promising material for the remediation of wastewater relevant to elimination of toxic effect in marine environment.

Preparation of MnO2-Carbon Materials and Their Applications in Photocatalytic Water Treatment

Water pollution is one of the most important problems in the field of environmental protection in the whole world, and organic pollution is a critical one for wastewater pollution problems. How to solve the problem effectively has triggered a common concern in the area of environmental protection nowadays. Around this problem, scientists have carried out a lot of research; due to the advantages of high efficiency, a lack of secondary pollution, and low cost, photocatalytic technology has attracted more and more attention. In the past, MnO₂ was seldom used in the field of water pollution treatment due to its easy agglomeration and low catalytic activity at low temperatures. With the development of carbon materials, it was found that the composite of carbon materials and MnO₂ could overcome the above defects, and the composite had good photocatalytic performance, and the research on the photocatalytic performance of MnO₂-carbon materials has gradually become a research hotspot in recent years. This review covers recent progress on MnO₂-carbon materials for photocatalytic water treatment. We focus on the preparation methods of MnO₂ and different kinds of carbon material composites and the application of composite materials in the removal of phenolic compounds, antibiotics, organic dyes, and heavy metal ions in water. Finally, we present our perspective on the challenges and future research directions of MnO₂-carbon materials in the field of environmental applications.

Bismuth-Based Multi-Component Heterostructured Nanocatalysts for Hydrogen Generation

Developing a unique catalytic system with enhanced activity is the topmost priority in the science of H2 energy to reduce costs in large-scale applications, such as automobiles and domestic sectors. Researchers are striving to design an effective catalytic system capable of significantly accelerating H2 production efficiency through green pathways, such as photochemical, electrochemical, and photoelectrochemical routes. Bi-based nanocatalysts are relatively cost-effective and environmentally benign materials which possess advanced optoelectronic properties. However, these nanocatalysts suffer back recombination reactions during photochemical and photoelectrochemical operations which impede their catalytic efficiency. However, heterojunction formation allows the separation of electron–hole pairs to avoid recombination via interfacial charge transfer. Thus, synergetic effects between the Bi-based heterostructured nanocatalysts largely improves the course of H2 generation. Here, we propose the systematic review of Bi-based heterostructured nanocatalysts, highlighting an in-depth discussion of various exceptional heterostructures, such as TiO2/BiWO6, BiWO6/Bi2S3, Bi2WO6/BiVO4, Bi2O3/Bi2WO6, ZnIn2S4/BiVO4, Bi2O3/Bi2MoO6, etc. The reviewed heterostructures exhibit excellent H2 evolution efficiency, ascribed to their higher stability, more exposed active sites, controlled morphology, and remarkable band-gap tunability. We adopted a slightly different approach for reviewing Bi-based heterostructures, compiling them according to their applicability in H2 energy and discussing challenges, prospects, and guidance to develop better and more efficient nanocatalytic systems.

Transition metal-doped SnO2 and graphene oxide (GO) supported nanocomposites as efficient photocatalysts and antibacterial agents

In the present work, pristine and transition metal (TM) (W, Ag, Zn)-doped SnO₂ nanocrystals using a facile sol-gel approach were synthesized. The grown products were anchored on graphene oxide (GO) sheets via a simple ultrasonication technique to fabricate binary nanocomposites. The structural, optical, and morphological properties of as-synthesized samples were studied by XRD, FTIR, Raman, EDX, UV-Visible, PL, and FE-SEM. The charge transferability of graphene oxide-based samples was investigated by EIS. The XRD exhibited the TM doping in SnO₂ and the development of GO-based nanocomposite. FTIR data evidenced the existence of the metal-oxygen bonds. Raman spectra presented the optical phonon modes of SnO₂ and the existence of oxygen vacancy defects. FE-SEM images demonstrated the anchoring of particles on the GO sheet, and EDX further approved the existence of desired dopants. The integration of SnO₂ with TM doping remarkably reduced optical bandgap (3.65-3.10 eV), which was further decreased (3.10-2.99 eV) by making composite with GO. The photodegradation results exhibited that GO-based nanocomposites have the higher potential to degrade synthetic dyes (methyl red (MR), and methyl orange (MO) and SnZnO₂/GO have shown superb photocatalytic performance after 80-min sunlight illumination (99.9% MR and 95.0% MO dyes) with the higher rate constant and superior stability up to 6th cycle against MR dye. The grown samples were tested for bacterial disinfection, and SnZnO₂/GO sample showed a higher zone of inhibition towards S. aureus and K. pneumoniae bacteria strains. The greater charge transfer rate and lower recombination of charge carriers in GO-based composites were also observed by EIS and PL analysis. Moreover, the present article ascribed that the photocatalytic and antibacterial properties of bare SnO₂ could be improved by TM doping and fabricating their composite with GO.

Assessment of Performance of Photocatalytic Nanostructured Materials with Varied Morphology Based on Reaction Conditions

Synthesis of nanomaterials with specific morphology is an essential aspect for the optimisation of its properties and applications. The application of nanomaterials is being discussed in a wide range of areas, one of which is directly relevant to the environment through photocatalysis. To produce an effective photocatalyst for environmental applications, morphology plays an important role as it affects the surface area, interfaces, crystal facets and active sites, which ultimately affects efficiency. The method of synthesis and synthesis temperature can be the basic considerations for the evaluation of a particular nanomaterial. In this study, we have considered the aspects of morphology with a basic understanding and analyzed them in terms of nanomaterial efficacy in photocatalysis. Different morphologies of specific nanomaterials such as titanium dioxide, zinc oxide, silver phosphate, cadmium sulphide and zinc titanate have been discussed to come to reasonable conclusions. Morphologies such as nanorods, nanoflower, nanospindles, nanosheets, nanospheres and nanoparticles were compared within and outside the domain of given nanomaterials. The different synthesis strategies adopted for a specific morphology have been compared with the photocatalytic performance. It has been observed that nanomaterials with similar band gaps show different performances, which can be linked with the reaction conditions and their nanomorphology as well. Materials with similar morphological structures show different photocatalytic performances. TiO₂ nanorods appear to have the best features of efficient photocatalyst, while the nanoflowers show very low efficiency. For CdS, the nanoflower is the best morphology for photocatalysis. It appears that high surface area is the key apart from the morphology, which controls the efficiency. The overall understanding by analyzing all the available information has enumerated a path to select an effective photocatalyst amongst the several nanomaterials available. Such an analysis and comparison is unique and has provided a handle to select the effective morphology of nanomaterials for photocatalytic applications.

Architecture of visible-light induced Z-scheme MoS2/g-C3N4/ZnO ternary photocatalysts for malachite green dye degradation

The synthesis of bilayer heterojunctions has received considerable attention recently. Fabrication of novel bilayer composites is of significant interest to improve their photocatalytic efficiency. In this study, molybdenum disulfide (MoS₂), a layered dichalcogenide material exhibiting unique properties, in combination with graphitic carbon nitride (g-C₃N₄), a carbon-based layered material, was fabricated with small amounts of zinc oxide (ZnO). Three composites, MoS₂/g-C₃N₄, MoS₂/ZnO, and MoS₂/g-C₃N₄/ZnO were prepared via a simple exfoliation method and characterized by various physicochemical methods. The Z-scheme charge transfer mechanism in the prepared ternary composite improves efficiency by inhibiting the recombination rate of electron-hole pairs. It has shown excellent performance in degrading a major water contaminant, malachite green (MG) dye, under visible light irradiation.

Unraveling the Synergy of Anion Modulation on Co Electrocatalysts by Pulsed Laser for Water Splitting: Intermediate Capturing by In Situ/Operando Raman Studies

Herein, the authors produce Co-based (Co₃ (PO₄ )₂ , Co₃ O₄ , and Co₉ S₈ ) electrocatalysts via pulsed laser ablation in liquid (PLAL) to explore the synergy of anion modulation on phase-selective active sites in the electrocatalytic hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Co₃ (PO₄ )₂ displays an ultralow overpotential of 230 mV at 10 mA cm^-2 with 48.5 mV dec^-1 Tafel slope that outperforms the state-of-the-art Ir/C in OER due to its high intrinsic activity. Meanwhile, Co₉ S₈ exhibits the highest HER performance known to the authors among the synthesized Co-based catalysts, showing the lowest overpotential of 361 mV at 10 mA cm^-2 with 95.8 mV dec^-1 Tafel slope in the alkaline medium and producing H₂ gas with ≈500 mmol g^-1 h^-1 yield rate under -0.45 V versus RHE. The identified surface reactive intermediates over in situ electrochemical-Raman spectroscopy reveal that cobalt(hydr)oxides with higher oxidation states of Co-cation forming under oxidizing potentials on the electrode-electrolyte surface of Co₃ (PO₄ )₂ facilitate the OER, while Co(OH)₂ facilitate the HER. Notably, the fabricated two-electrode electrolyzers using Co₃ (PO₄ )₂ , Co₃ O₄ , and Co₉ S₈ electrocatalysts deliver the cell potentials ≈2.01, 2.11, and 1.89 V, respectively, at 10 mA cm^-2 . This work not only shows PLAL-synthesized electrocatalysts as promising candidates for water splitting, but also provides an underlying principle for advanced energy-conversion catalysts and beyond.

Impact of biosurfactant and iron nanoparticles on biodegradation of polyaromatic hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) are hazardous toxic contaminants and considered as primary pollutants due to their persistent nature and most of them are carcinogenic and mutagenic. The key challenge in PAHs degradation is their hydrophobic nature, which makes them one of the most complex materials and inaccessible by a broad range of microorganisms. This bioavailability can be increased by using a biosurfactant. In the present study mixed PAHs were degraded using the biosurfactant producing bacterial strains. In addition, iron nanoparticles were synthesized and the impact of iron nanoparticles on the growth of the mixed bacterial strains (Pseudomonas stutzeri NA3 and Acinetobacter baumannii MN3) was optimized. The mixed PAHs (anthracene, pyrene, and benzo(a)pyrene) degradation was enhanced by addition of biosurfactant (produced by Bacillus subtilis A1) and iron nanoparticles, resulting in 85% of degradation efficiency. The addition of the biosurfactant increased the bioavailability of the PAHs in the aqueous environment, which might help bacterial cells for the initial settlement and development. The addition of iron nanoparticles increased both bacterial biomass and PAHs adsorption over their surface. These overall interactions assisted in the utilization of PAHs by the mixed bacterial consortia. This study illustrates that this integrated approach can be elaborated for the removal of the complex PAHs pollutants from soil and aqueous environments.

Functional Nanohybrids and Nanocomposites Development for the Removal of Environmental Pollutants and Bioremediation

World population growth, with the consequent consumption of primary resources and production of waste, is progressively and seriously increasing the impact of anthropic activities on the environment and ecosystems. Environmental pollution deriving from anthropogenic activities is nowadays a serious problem that afflicts our planet and that cannot be neglected. In this regard, one of the most challenging tasks of the 21st century is to develop new eco-friendly, sustainable and economically-sound technologies to remediate the environment from pollutants. Nanotechnologies and new performing nanomaterials, thanks to their unique features, such as high surface area (surface/volume ratio), catalytic capacity, reactivity and easy functionalization to chemically modulate their properties, represent potential for the development of sustainable, advanced and innovative products/techniques for environmental (bio)remediation. This review discusses the most recent innovations of environmental recovery strategies of polluted areas based on different nanocomposites and nanohybrids with some examples of their use in combination with bioremediation techniques. In particular, attention is focused on eco-friendly and regenerable nano-solutions and their safe-by-design properties to support the latest research and innovation on sustainable strategies in the field of environmental (bio)remediation.

Energy-levels well-matched direct Z-scheme ZnNiNdO/CdS heterojunction for elimination of diverse pollutants from wastewater and microbial disinfection

Energy-levels well-matched direct Z-scheme ZnNiNdO/CdS heterojunction was successfully fabricated using facile co-precipitation and ultra-sonication techniques and characterized with XRD, FTIR, Raman, PL, UV-vis, and FE-SEM. The XRD diffractograms confirmed the co-doping of Ni-Nd in ZnO and the formation of heterostructured nanocomposite. FTIR and Raman data showed the presence of metal-oxygen vibration and optical phonon modes of ZnO and CdS. FE-SEM images exhibited the network type morphology. The energy bandgap was redshifted by co-doping (3.37-2.9 eV) and was further reduced (2.6 eV) by making a composite with CdS. The ZnNiNdO/CdS catalyst degraded 99.7, 49, 96.6, 98.6, and 98.6% methylene blue (MB), p-nitroaniline (P-Nitro), methyl orange (MO), methyl red (MR), and rhodamine B (RhB) dyes under 50 min sunlight irradiation. Moreover, ZnNiNdO/CdS showed intense inhibition activity towards Staphylococcus aureus, Escherichia coli, Proteus vulgaris, and Pseudomonas aeruginosa bacterial strains with maximum inhibition zone diameters 30, 33, 27, and 31 mm, respectively. The synergistic effects arising from band alignment can lead to efficient vectorial charge separation, transportation, and lower recombination of photoinduced charge carriers, ultimately boosting photocatalytic and antibacterial performance. The ZnNiNdO/CdS photocatalyst has higher stability up to the 7th cycle towards MB dye with ~ 5% deficit in degradation efficiency. The higher generation of superoxide and hydroxyl radical was confirmed by species trapping experiments responsible for photodegradation of dyes molecules. Furthermore, the results showed that the photocatalytic and antibacterial performance of pristine ZnO can be enhanced by co-doping and tuning energy bandgap.

Efficient photocatalytic degradation of industrial contaminants by Piper longum mediated ZnO nanoparticles

Piper longum extract as a reducing agent in green synthesis method is used to synthesize ZnO nanoparticles (ZnO-NPs). The impact of the reductant on the structural, optical and surface morphological properties of ZnO-NPs can be analyzed. Piper longum extract has delicately tuned the band gap of ZnO-NPs. Increase in energy band gap indicates an increase in the number of capping molecules in the prepared ZnO nanoparticles. The carbohydrates and proteins not only play a fundamental role in ZnO capping, which is important for its stability, determination and biocompatibility. Thus obtained nanosized ZnO particles are confirmed by the surface morphological studies. Because of various surface interface properties might have different physical-chemical, desorption-adsorption abilities in the direction towards microbes, create different antibacterial performances. S.aureus has maximum inhibition zone of 23 mm and Escherichia coli has minimum inhibition zone of 7 mm. To assess the photocatalytic activity of the prepared ZnO-NPs under UV light irradiation, methyl orange, malachite green and methylene blue dyes were utilized as model contaminants. The degradation efficiency of MG, MB and MO dyes solution is found that 96%, 69% and 48% of degradation efficiency respectively under ultraviolet light irradiation. The properties of synthetic nanopowders suggest that they have important potential for a variety of biochemical and environmental applications.

Diclofenac removal from the wastewater using activated sludge and analysis of multidrug resistant bacteria from the sludge

Diclofenac is an anti-inflammatory drug and has been frequently detected from the wastewater. In the present study, factors affecting diclofenac adsorption on sewage sludge was evaluated. At 1 mg/L initial diclofenac concentration, more than 80% diclofenac removal was achieved. Adsorption increased at higher concentration (100 mg/L concentration) and more than 99% diclofenac was adsorbed from the wastewater. Significant removal of diclofenac was observed after 5 min contact time. The adsorption efficacy was more than 98% after 50 and 60 min. Pseudo-first and second order kinetics revealed reasonable regression value (0.9) indicated that the model is best fitted. Diclofenac adsorption was extremely high at acidic pHs than alkaline range. The sludge samples showed the presence of multi drug resistant bacteria. Vancomycin-resistant enterococcus stains were 27%, Methicillin-resistant Staphylococcus aureus positive strains were 16.5% and Extended-spectrum betal-lactamase-harbouring Enterobacteriacea were 65.4% in the sludge. The drug resistance Enterobacteriaceae revealed 14 Klebsiella pneumonia strains, 11 strains from E. coli and two from the genus Enterobacter. To conclude, the activated sludge could be effectively utilized for the removal of diclofenac from wastewater.

Plasmonic Ag Nanoparticle-Loaded n-p Bi2O2CO3/α-Bi2O3 Heterojunction Microtubes with Enhanced Visible-Light-Driven Photocatalytic Activity

In this study, n-p Bi2O2CO3/α-Bi2O3 heterojunction microtubes were prepared via a one-step solvothermal route in an H2O-ethylenediamine mixed solvent for the first time. Then, Ag nanoparticles were loaded onto the microtubes using a photo-deposition process. It was found that a Bi2O2CO3/α-Bi2O3 heterostructure was formed as a result of the in situ carbonatization of α-Bi2O3microtubes on the surface. The photocatalytic activities of α-Bi2O3 microtubes, Bi2O2CO3/α-Bi2O3 microtubes, and Ag nanoparticle-loaded Bi2O2CO3/α-Bi2O3 microtubes were evaluated based on their degradation of methyl orange under visible-light irradiation (λ > 420 nm). The results indicated that Bi2O2CO3/α-Bi2O3 with a Bi2O2CO3 mass fraction of 6.1% exhibited higher photocatalytic activity than α-Bi2O3. Loading the microtubes with Ag nanoparticles significantly improved the photocatalytic activity of Bi2O2CO3/α-Bi2O3. This should be ascribed to the internal static electric field built at the heterojunction interface of Bi2O2CO3 and α-Bi2O3 resulting in superior electron conductivity due to the Ag nanoparticles; additionally, the heterojunction at the interfaces between two semiconductors and Ag nanoparticles and the local electromagnetic field induced by the surface plasmon resonance effect of Ag nanoparticles effectively facilitate the photoinduced charge carrier transfer and separation of α-Bi2O3. Furthermore, loading of Ag nanoparticles leads to the formation of new reactive sites, and a new reactive species ·O2− for photocatalysis, compared with Bi2O2CO3/α-Bi2O3.

Laccase producing bacteria influenced the high decolorization of textile azo dyes with advanced study

Recent year, bacterial laccases are increasing interest in the field of industry and environmental applications especially decolorization of azo dyes. In industry, the dyes are present in stable nature including chemicals and lights. Due to these defects, the novel approaches are needed to removal of dyes before discharging into the environment. Among the various technologies, biological treatment methods and their strategies are very important, because of the decolorization and detoxification. Consecutively, biological mediated dyes removal are emerged with high potential especially microbes. Microbial laccases creates up new opportunities for their commercial applications. In this study, laccases were produced from Bacillus cereus (B. Cereus) and Pseudomonas parafulva (P. parafulva) by sub merged fermentation. For immobilization, the produced laccases were subjected to purify using 80% saturated ammonium sulphate and followed by dialysis. Then, crude laccases were immobilized through copper-alginate entrapment method. The maximum immobilized enzyme activity of the immobilized laccases were shown pH 8 at 50 °C and pH 7 at 40 °C for B. Cereus and P. parafulva respectively. In contrast, the normal enzyme activity was pH 10 at 40 °C and pH 8 at 40 °C were indicated for Bacillus cereus and P. parafulva respectively. Next, the free and immobilized laccases were performed the decolorization of three azo dyes T-blue, yellow GR and orange 3R, and exhibited that the 91.69 and 89.21% of Orange 3R were completely decolorized by both the B. Cereus and P. parafulva laccases when compared with free laccases enzymes. The confirmation of decolorization was monitored by UV-vis spectroscopy and FTIR spectroscopy, which clearly confirm the changes of peaks when compared with normal laccases. Finally, we have concluded that the B. Cereus and P. parafulva laccases are very important in azo dye decolorization and these used in future biological treatment of dyeing effluents.

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

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

Effect of Ag doped MnO2 nanostructures suitable for wastewater treatment and other environmental pollutant applications

A modest sol-gel method has been employed to prepare the pure and Ag doped MnO₂ nanoparticles and methodologically studied their physical, morphological, and photosensitive properties through XRD, TEM, EDAX, Raman, UV, PL and N₂ adsorption - desorption study. Tetragonal crystalline arrangement with spherical nanoparticles was found out through XRD and TEM studies. The EDAX studies further supported that formation Ag in the MnO₂ crystal matrix. The bandgap energy of Ag doped MnO₂ was absorbed through UV spectra. Photo -generated recombination process and surface related defects were further recognized by PL spectra. Through visible light irradiation, the photo - degradation of methyl orange (MO) and phenol dye solutions were observed. The optimum condition of (10 wt% of Ag) Ag doped MnO₂ catalyst showed tremendous photocatalytic efficiency towards MO than phenol under same experimental study.

Improved visible light photocatalytic degradation of yttrium doped NiMgAl layered triple hydroxides for the effective removal of methylene blue dye

Fabrication of layered triple hydroxides (LTH) is a typical and remarkable approach to produce new functionalities passionately investigated for photocatalytic removal of organic pollutants from industrial wastewater. The hydrothermal method was used to prepare different weight percentages of yttrium (Y) doped NiMgAl LTH. The structural, functional, optical, and morphological properties of the prepared samples were investigated using X-ray diffraction, Fourier transformed-infrared spectroscopy, ultraviolet-visible diffuse reflectance spectroscopy, and scanning electron microscopy. The photocatalytic degradation of the different percentages of Y-doped LTH samples were assessed through the photocatalytic degradation of methylene blue dye under the visible light irradiation. When compared to other lower concentrations of Y doping, the photocatalytic degradation efficiency of 1 wt.% Y-doped LTH was higher. Thus, the optimized LTH's improved photocatalytic performance was attributed to increased visible light absorption with low transmission and improved electron-hole separation.

Effective removal of heavy metals in industrial wastewater with novel bioactive catalyst enabling hybrid approach

Recent years, heavy metal reduction of contaminated atmosphere using microbes is heightened worldwide. In this context, the current study was focused on heavy metal resistant actinomycete strains were screened from effluent mixed contaminated soil samples. Based on the phenotypic and molecular identification, the high metal resistant actinomycete strain was named as Nocardiopsis dassonvillei (MH900216). The highest bioflocculent and exopolysaccharide productions of Nocardiopsis dassonvillei (MH900216) was confirmed by various invitro experiments result. The heavy metal degrading substances was characterized and effectively confirmed by Fourier transform infrared spectroscopy (FT-IR), X-Ray Diffraction (XRD), Scanning electron microscope (SEM). Further, the heavy metal sorption ability of actinomycete substances bioflocculent was exhibited 85.20%, 89.40%, 75.60%, and 51.40% against Cd, Cr, Pb and Hg respectively. Altogether, the bioflocculent produced actinomycete Nocardiopsis dassonvillei (MH900216) as an excellent biological source for heavy metal reduction in waste water, and it is an alternative method for effective removal of heavy metals towards sustainable environmental management.

Effective degradation of Chlortetracycline using dual bio catalyst

Chlortetracycline (CTC) degradation using potential microbial consortia or individual bacterial strains was useful method for improving bioremediation potential. The co-culture (Klebsiella pneumoniae CH3 and Bacillus amyloliquefaciens CS1) of bacterial strains have the ability to degrade chlortetracycline (91.8 ± 1.7%), followed by sulfamethoxazole (62.1 ± 1.2%) and amoxicillin (73.9 ± 3.3%). It was observed that the degradation potential was maximum after 10 days incubation, 8-10% inoculum, pH 7.5, and antibiotic concentration ranged from 150 to 200 mg/L. The initial concentrations of CTC significantly affected CTC degradation. In strain CH3, maximum biodegradation of CTC (99.4 ± 2.3%) was observed at 200 mg/L initial CTC concentrations. In CS1, maximum biodegradation of CTC was obtained at 150 mg/L concentration (80.5 ± 3.2%) after 10 days of culture. Alkaline pH was found to be suitable for the degradation of antibiotic than acidic range. After initial optimization by one factor at a time approach in free cells, the bacterial strains (CH3 and CS1) were co-immobilized. The co-immobilized bacterial cells showed improved degradation potential than free cells. To determine the biodegradation potential of immobilized cells, the selected strains were immobilized in polymer beads and treated with CTC with 175 mg/L initial concentration. The experimental results revealed that after 3 days of treatment the residual CTC concentration was 150.1 ± 3.2 mg/L and it decreased as 1.28 ± 0.01 mg/L after 10 days of treatment. The present study confirmed the effectiveness and feasibility of biodegradation ability of K. pneumoniae CH3 and B. amyloliquefaciens CS1 immobilized for CTC degradation in wastewater.

Defense pathways of Chlamydomonas reinhardtii under silver nanoparticle stress: Extracellular biosorption, internalization and antioxidant genes

Numerous studies have been investigated the toxic effects of silver nanoparticle (Ag-NPs) on algae; however, little attention has been paid to the defense pathways of algae cells to Ag-NPs. In the study, Chlamydomonas reinhardtii (C. reinhardtii) was selected as a model organism to investigate the defense mechanisms to Ag-NPs exposure. The results showed that exopolysaccharide and protein in bound-extracellular polymeric substances significantly increased under Ag-NPs stress. These metal-binding groups including C-O-C (exopolysaccharide), CH₃/CH₂ (proteins), O-H/N-H (hydroxyl group) and C-H (alkyl groups) played a key role in extracellular biosorption. The internalized or strongly bound Ag (1.90%-17.45% of total contents) was higher than the loosely surface biosorption (0.31%-1.79%). The accumulation of glutathione disulfide (GSSG), together with the decline of reduced glutathione/GSSG (GSH/GSSG) ratio in C. reinhardtii cells, indicated a significant oxidative stress caused by exposure of Ag-NPs. The increasing phytochelatin accompanied with the decreasing GSH level indicated a critical role to intracellular detoxification of Ag. Furthermore, upregulation of antioxidant genes (MSOD, QTOX2, CAT1, GPX2, APX and VTE3) can cope with oxidative stress of Ag-NPs or Ag⁺. The up-regulation of ascorbate peroxidase (APX) and glutathione peroxidase (GPX2) genes and the reduction in GSH contents showed that the toxicity of Ag-NPs could be mediated by an intracellular ascorbate-GSH defense pathway. These findings can provide valuable information on ecotoxicity of Ag-NPs, potential bioremediation and adaptation capabilities of algal cells to Ag-NPs.

Statistical optimization of silver nanoparticle synthesis by green tea extract and its efficacy on colorimetric detection of mercury from industrial waste water

For the optimization of silver nanoparticle production, a central composite design was used with three parameters: AgNO₃ concentration, green tea extract concentration, and temperature at three different levels. The size of the synthesized silver nanoparticle, its UV absorbance, zeta potential, and polydispersity index were set as the response parameters. Silver nanoparticles obtained in the optimization process were characterized and its efficacy on colorimetric detection of mercury was evaluated. The response variables were significant for the factors analyzed, and each variable had a significant model (P < 0.05). The ideal conditions were: 1 mM AgNO₃, 0.5% green tea extract, and 80 °C temperature. To analyze the produced AgNPs under certain ideal conditions, Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and X-ray diffraction (XRD) were used. The UV-visible spectra of AgNPs revealed an absorption maxima at 424 nm. The XRD pattern reveals a significant diffraction peak at 38.25°, 44.26°, 64.43°, and 77.49°, which corresponds to the (111), (200), (220), and (311) planes of polycrystalline face-centered cubic (fcc) silver, respectively. The TEM and SEM analyses confirmed that the particles were spherical, and dynamic light scattering study determined the average diameter of AgNPs to be 77.4 nm. The AgNPs have a zeta potential of -62.6 mV, as determined by the zeta sizer analysis. The AgNPs detects mercury at a micromolar concentration. Furthermore, the environmentally friendly generated AgNPs were used to detect mercury in a colorimetric method that was effectively employed for analytical detection of Hg²⁺ ions in an aqueous environment for the purpose of practical application.

Polyhydroxybutyrate degradation by biocatalyst of municipal sludge water and degradation efficacy in sequencing batch biofilm reactor

The main aim of the study was to degrade poly-β-hydroxybutyrate (P(3HB)) in the sequencing batch biofilm reactor (SBBR) using biocatalyst. Enrichment method was used for the isolation of P(3HB) degrading bacteria. These bacterial strains were isolated from the wastewater sludge sample treated with P(3HB) sheets. A total of 75 bacteria were isolated after 60 days of incubation. The zone of clearance varied between 12 ± 1 mm and 19 ± 2 mm. Two bacterial strains (Nitrobacter vulgaris SW1 and Pseudomonas aeruginosa KS10) showed rapid PHB degradation activity on agar plates. Plate screening experiments confirmed PHB degrading ability of P. aeruginosa KS10 and N. vulgaris SW1. Biodegrading potential improved after 72 h fermentation period. The bacteria produced depolymerase and enzyme activity was maximum after 72 h. The sequencing batch biofilm reactor (SBBR) co-cultured with N. vulgaris SW1 and P. aeruginosa KS10 was operated to remove PHB from the wastewater. Biofilm in the reactor degraded PHB and the production of polyhydroxybutyrate depolymerase influenced on PHB degradation. Polyhydroxybutyrate degradation improved continuously and maximum degradation (95.6%) was achieved after 8 days. The degradation of biopolymers help to reduce environmental pollution associated with the petroleum based polymers.

Effect of Ca2+ ions on naphthalene adsorption/desorption onto calcium oxide nanoparticle: Adsorption isotherm, kinetics and regeneration studies

The adsorptive nature of calcium oxide nanoparticles in aqueous sample of naphthalene in presence of Ca²⁺ ions was estimated. Enhanced efficiency of calcium oxide regeneration (90%) with the aid of calcium chloride in the solution concentration of 0.002-0.1 M was depicted. The less degree of toxic naphthalene desorption merged with SEM, FTIR and XRD characterization data portrays the importance of naphthalene adsorption onto calcium oxide using calcium chloride for regeneration. Batch adsorption studies were performed to evaluate the operating parameters such as pH, naphthalene concentration, contact time and impact of Ca²⁺ on naphthalene study. The adsorption isotherm of naphthalene on calcium oxide nanoparticle was described by Langmuir, Freundlich, Temkin and Dubinin Radushkevich and theoretical maximum monolayer adsorption capacity was found to be 63.81 mg/g at 303 K. The adsorption kinetic best fitted with pseudo second order kinetic model. The positive influence of making the addition of Ca²⁺ ions into naphthalene solution for its rapid adsorption was elucidated which is leaded by a probable increase in sorption capacity for naphthalene molecules at lower concentrations. The stable nature of crystallinity of calcium oxide and a less degree of naphthalene molecules leaching during consecutive cycles of adsorptive process and nanoparticle regeneration was also scrutinized.

Agricultural waste materials for adsorptive removal of phenols, chromium (VI) and cadmium (II) from wastewater: A review

Management of basic natural resources and the spent industrial and domestic streams to provide a sustainable safe environment for healthy living is a magnum challenge to scientists and environmentalists. The present remedial approach to the wastewater focuses on recovering pure water for reuse and converting the contaminants into a solid matrix for permanent land disposal. However, the ground water aquifers, over a long period slowly leach the contaminants consequently polluting the ground water. Synthetic adsorbents, mainly consisting of polymeric resins, chelating agents, etc. are efficient and have high specificity, but ultimate disposal is a challenge as most of these materials are non-biodegradable. In this context, it is felt appropriate to review the utility of adsorbents based on natural green materials such as agricultural waste and restricted to few model contaminants: phenols, and heavy metals chromium(VI), and cadmium(II) in view of the vast amount of literature available. The article discusses the features of the agricultural waste material-based adsorbents including the mechanism. It is inferred that agricultural waste materials are some of the common renewable sources available across the globe and can be used as sustainable adsorbents. A discussion on challenges for industrial scale implementation and integration with advanced technologies like magnetic-based approaches and nanotechnology to improve the removal efficiency is included for future prospects.

A state-of-the-art review on microbial desalination cells

The rapid growth in population has increased the demand for potable water. Available technologies for its generation are the desalination of sea water through reverse osmosis, electrodialysis etc., which are energy and cost intensive. In this context, microbial desalination cell (MDC) presents a low-cost and sustainable option which can simultaneously treat wastewater, desalinate saline water, produce electrical energy and recover nutrients from wastewater. This review paper is focussed on presenting a detailed analysis of MDCs starting from the principle of operation, microbial community analysis, basic architecture, evolution in design, operational challenges, effect of process parameters, scale-up studies, application in multiple arenas and future prospects. After thorough review, it can be inferred that MDCs can be used as a stand-alone option or pre-treatment step for conventional desalination techniques without the application of external energy. MDCs have been used in multiple applications ranging from desalination, remediation of contaminated water, recovery of energy and nutrients from wastewater, softening of hardwater, biohydrogen production to degradation of waste engine oil. Although, MDCs have been used for multiple applications, still a number of operational challenges have been reported viz., interference of co-existing ions during desalination, membrane fouling, pH imbalance and limited potential of exoelectrogens. However, the re-circulation of anolytes with electrodialysis chamber has led to the maintenance of optimal pH for favourable microbial growth leading to improvement in the overall performance of MDCs. In future, genetic engineering may be used for improving the electrogenic activity of microbial community, next generation materials may be used as anode and cathode, varied sources of wastewater may be explored as anolytes, life cycle analysis and exergy analysis may be carried out to study the impact on environment and detailed pilot scale studies have to be carried out for assessing the feasibility of operation at large scale.

Impact of dysprosium doped (Dy) zinc ferrite (ZnFe2o4) nanocrystals in photo- fenton exclusion of recalcitrant organic pollutant

The issue of effluent, especially organic colorants from several manufacturing units overlays an immense delinquent of the current epoch owing to its effect on oncogenic health hazards. Thus, Rare Earth Metal dysprosium (Dy) doped Zinc Ferrite (ZnFe₂O₄) were as-synthesized by a facile co-precipitation technique as an effectual nano photocatalyst intended to the amputation of these noxious dyes. The structural, functional, optical, magnetic, and degradation properties of this RE (Dy³⁺) doped ions were investigated using various characterizations, such as crystallite size (D) and several parameters (cation distribution, oxygen positional parameters, and bond length) were determined using XRD (X-ray diffraction) and it was found that as the dy³⁺ ion concentration increases the speck size decreased and the grain size remained within nano regime, which intern affects the surface area. From BET analysis it was found that on increasing the doping concentration, the surface area increases which pave a substantial role in the photo-Fenton activity. By using FT-IR (Fourier-transform infrared spectroscopy) various functional parameters (elastic, interionic bonds, ion distribution, etc.) were determined. Raman spectra had no extra peak formation which is seen to have pure phase formation of the as-synthesized samples. HR-TEM (High-Resolution Transmission Electron Microscopy analysis were done to determine the nature of the sample, the as-synthesized magnetic samples exhibit a polycrystalline formation with cubical agglomeration. The magnetic property was very significant for x = 0.10 concentration. As-synthesized (Fe_0.9064Zn_0.0936) [Fe_1.0936Dy_0.1Zn_0.8064] O₄) exhibits a momentous photo - Fenton activity against MB (Methylene blue), its removal efficiency was found to be 97.3% after 45 min. Also, this spinel ferrite acts as a magnetic recyclable catalyst even after 5 cycles with an insignificant lessening of elements and photo-Fenton activity.

Mechanochemical synthesis of ternary heterojunctions TiO2(A)/TiO2(R)/ZnO and TiO2(A)/TiO2(R)/SnO2 for effective charge separation in semiconductor photocatalysis: A comparative study

TiO₂, ZnO, and SnO₂ metal oxides were synthesized by the sol-gel method and heterojunctions were fabricated by combining TiO₂ with either ZnO or SnO₂ in a 1:1 ratio using mechanochemical ball milling process. The ball milling process promotes phase transition of TiO₂ from anatase to rutile and yields ternary heterojunction of the type TiO₂(A)/TiO₂(R)/ZnO and TiO₂(A)/TiO₂(R)/SnO₂ (A-anatase and R-rutile). These ternary heterojunctions were characterized by various analytical techniques and its photocatalytic efficiency is evaluated using 4-Chloro Phenol as a model compound under UV and solar light. The enhanced catalytic activity of TiO₂(A)/TiO₂(R)/ZnO heterojunction is attributed to the formation of Ti³⁺-V_o defect states which leads to the efficient charge carrier separation. During the ball milling process severe crystal deformation takes place in TiO₂ and ZnO lattices by creating crystal lattice distortion which leads to the formation of defects due to valency mismatch between Ti⁴⁺ and Zn²⁺. A mechanistic pathway is proposed for the enhanced photocatalytic activity of the ternary heterojunctions.

An efficient CuO/rGO/TiO2 photocatalyst for the synthesis of benzopyranopyrimidine compounds under visible light irradiation

This study reports the synthesis of CuO/rGO/TiO2 in coupling reaction under visible light irradiation. Its photocatalytic performance was explored in a pseudo 4-component and a domino reaction for the synthesis of benzopyranopyrimidine compounds. It can be recovered and recycled for 5 runs.