Effect of sandblasting and acid surface pretreatment on the specific capacitance of CuO nanostructures grown by hot water treatment for supercapacitor electrode applications

Crystalline copper oxide (CuO) nanostructures with micro, nano, and micro-nano surface roughness were grown on Cu sheet substrates by a facile, scalable, low-cost, and low-temperature hot water treatment (HWT) method that simply involved immersing Cu sheet in DI water at 75 °C for 24 h without any chemical additives. Various morphological features and sizes of CuO nanostructures were tuned by using different surface pretreatment techniques including acid treatment, sandblasting, or a combination of those two. The surface morphology of the prepared samples was analyzed by scanning electron microscopy. The crystal structure of the CuO nanostructures was investigated by x-ray diffraction XRD and Raman spectroscopy. To study the pseudocapacitive behavior, their potential supercapacitor performance, and equivalent series resistance, electrochemical analysis was done by cyclic voltammetry and electrochemical impedance spectroscopy for all the CuO/Cu samples in 1 M of Na2SO4electrolyte. Among all, the best supercapacitive performance was achieved for CuO/Cu samples pretreated with Sandblasting followed by Acid treatment resulting in a specific capacitance of about 104 F g-1. The electrode with the sandblasted + acid pretreated sample showed a maximum of ∼69% capacitive retention after 2000 consecutive cycles. Our results indicate that CuO nanostructures on Cu substrates prepared with different surface pretreatment conditions and grown by HWT can be promising electrodes for supercapacitor device applications.

Cationic and anionic cross-assisted synergistic photocatalytic removal of binary organic dye mixture using Ni-doped perovskite oxide

Organic dyes present in industrial wastewater are the major contributor to water pollution, which harm human health and the environment. Photocatalytic dye degradation is an effective strategy for water remediation by converting these organic dyes waste into non-harmful by-products. Therefore, in this study, Ni-doped LaFeO3 (NLFO) perovskite nanoparticles were extensively explored for photocatalytic degradation of cationic and anionic dyes and their mixture. The NLFO nanoparticles were successfully synthesized by surfactant assisted hydrothermal method under controlled Ni doping. The X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) revealed the variation in size (40-70 nm) of orthorhombic crystalline LFO nanoparticles with Ni doping and hence the size of microspheres (0.78. to 1.78 μm). The kinetic studies revealed that the LaFe0·6Ni0·4O3 performed well by providing degradation efficiency of 99.2% in 210 min, 99.1% in 100 min, and 98.4% in 70 min for Crystal Violet (CV), Congo Red (CR), and their mixture with rate constant of 0.019, 0.039, and 0.055 min-1 respectively. The radical scavenger tests indicated the synergetic contributions of O2- and •OH- active radicals in faster degradation of CV and CR dye mixture. The stepwise fragmentation of dye molecule during the photocatalytic degradation identified from the LCMS indicates the degradation of CV dye through de-alkylation and benzene ring breaking, whereas azo bond cleavage and oxidation lead to low molecular weight intermediates for CR dye, which all together helped to degrade their dye mixture (50 mg L-1 and 100 mg L-1) in significantly lesser time (70 min). Overall, the Ni-doped LFO microsphere consisting of nanoparticles acts as a superior catalyst for the more efficient and faster degradation of binary dye mixture.

Heterojunction assembled CoO/Ni(OH)2/Cu(OH)2 for effective photocatalytic degradation and supercapattery applications

Mixed multimetallic-based nanocomposites have been considered a promising functional material giving a new dimension to environmental remediation and energy storage applications. On this concept, a hybrid ternary CoO/Ni(OH)2/Cu(OH)2 (CNC) composite showing sea-urchin-like morphology was synthesized via one-pot hydrothermal approach, and its photocatalytic and electrochemical performances were investigated. The photocatalytic performance was explored using Congo red (CR) as a dye pollutant under visible light illumination. The presence of mixed phases of ternary metal ions could minimize the recombination efficacy of photogenerated charge carriers on the basis of the heterojunction mechanism, resulting in 90% degradation of CR dye (40 mg L-1). The effect of scavengers coupled with electrochemical experiments revealed O2-. radical as the predominating species responsible for the degradation of CR. From the electrochemical analysis of CNC, the well-distinguished redox peaks indicated the redox-type nature with a specific capacity of 405 C g-1. For practical applications, an supercapattery (CNC( +)|KOH|AC( -)) was assembled furnishing an energy density of 42 W h kg-1 at a power density of 5160 W kg-1 at 5 A g-1 along with a high capacity retention and coulombic efficiency of 98.83% over 5000 cycles.

Experimental and computational study of metal oxide nanoparticles for the photocatalytic degradation of organic pollutants: a review

Photocatalysis is a more proficient technique that involves the breakdown or decomposition of different organic contaminants, various dyes, and harmful viruses and fungi using UV or visible light solar spectrum. Metal oxides are considered promising candidate photocatalysts owing to their low cost, efficiency, simple fabricating method, sufficient availability, and environment-friendliness for photocatalytic applications. Among metal oxides, TiO2 is the most studied photocatalyst and is highly applied in wastewater treatment and hydrogen production. However, TiO2 is relatively active only under ultraviolet light due to its wide bandgap, which limits its applicability because the production of ultraviolet is expensive. At present, the discovery of a photocatalyst of suitable bandgap with visible light or modification of the existing photocatalyst is becoming very attractive for photocatalysis technology. However, the major drawbacks of photocatalysts are the high recombination rate of photogenerated electron-hole pairs, the ultraviolet light activity limitations, and low surface coverage. In this review, the most commonly used synthesis method for metal oxide nanoparticles, photocatalytic applications of metal oxides, and applications and toxicity of different dyes are comprehensively highlighted. In addition, the challenges in the photocatalytic applications of metal oxides, strategies to suppress these challenges, and metal oxide studied by density functional theory for photocatalytic applications are described in detail.

Tunable sulphur doping on CuFe2O4 nanostructures for the selective elimination of organic dyes from water

In this work, sulphur doped copper ferrites (S-CuFe₂O₄) photocatalysts were successfully synthesized for the first time using the facile hydrothermal method. The as-synthesized photocatalysts were characterized through XRD, Raman, TGA, FT-IR, UV-Vis-DRS, SEM, EDX and PL techniques. The results revealed that doping with sulphur has been found to be a suitable alternative that causes strain in the lattices as anions replace the oxygen from the CuFe₂O₄ nanostructures. Due to sulphur dopants, photocatalysts are able to efficiently trap and transfer the photoinduced charges, which readily suppress charge recombination. A UV-Vis spectrophotometer was used to monitor the degradation of selective toxic organic dyes (RhB, CR, MO, and CV) in aqueous media. The dye degradation results provide evidence for the surprisingly superior performance of S-CuFe₂O₄ over pristine CuFe₂O₄. On the basis of its efficiencies, this work can be assigned as an excellent candidate for photocatalysis science.

Hierarchical 3D Flower-like Metal Oxides Micro/Nanostructures: Fabrication, Surface Modification, Their Crucial Role in Environmental Decontamination, Mechanistic Insights, and Future Perspectives

Hierarchical micro/nanostructures are constructed by micro-scaled objects with nanoarchitectures belonging to an interesting class of crystalline materials that has significant applications in diverse fields. Featured with a large surface-to-volume ratio, facile mass transportation, high stability against aggregation, structurally enhanced adsorption, and catalytical performances, three dimenisional (3D) hierarchical metal oxides have been considered as versatile functional materials for waste-water treatment. Due to the ineffectiveness of traditional water purification protocols for reclamation of water, lately, the use of hierarchical metal oxides has emerged as an appealing platform for the remediation of water pollution owing to their fascinating and tailorable physiochemical properties. The present review highlights various approaches to the tunable synthesis of hierarchical structures along with their surface modification strategies to enhance their efficiencies for the removal of different noxious substances. Besides, their applications for the eradication of organic and inorganic contaminants have been discussed comprehensively with their plausible mechanistic pathways. Finally, overlooked aspects in this field as well as the major roadblocks to the implementation of these metal oxide architectures for large-scale treatment of wastewater are provided here. Moreover, the potential ways to tackle these issues are also presented which may be useful for the transformation of current water treatment technologies.

Carbon-Based Ternary Nanocomposite: Bullet Type ZnO-SWCNT-CuO for Substantial Solar-Driven Photocatalytic Decomposition of Aqueous Organic Contaminants

A facile two-step synthesis of ternary hetero-composites of ZnO, CuO, and single-walled carbon nanotubes (SWCNTs) was developed through a recrystallization process followed by annealing. A series of nanocomposites were prepared by varying the weight ratio of copper(II) acetate hydrate and zinc(II) acetate dihydrate and keeping the weight ratio of SWCNTs constant. The results revealed the formation of heterojunctions (ZnO-SWCNT-CuO, ZSC) of three crystal structures adjacent to each other, forming a ternary wurtzite-structured nanoparticles along with defects. Enhanced charge separation (electron-hole pairs), reduced band gap, defect-enhanced specific surface area, and promoted oxidation potential were key factors for the enhanced photocatalytic activity of the ternary nanocomposites. OH^• radicals were the main active species during dye degradation, and O₂^-• and h⁺ were also involved to a lesser extent. A type II heterojunction mechanism approach is proposed based on the charge carrier migration pattern. Among the synthesized nanocomposites, the sample prepared using copper(II) acetate hydrate and zinc(II) acetate dihydrate in a 1: 9 ratio (designated a ZSC3) showed the highest photocatalytic activity. ZSC3 achieved 99.2% photodecomposition of methylene blue in 20 min, 94.1% photodecomposition of Congo red in 60 min, and 99.6% photodecomposition of Rhodamine B in 40 min under simulated sunlight. Additionally, ZSC3 showed excellent reusability and stability, maintaining 96.7% of its activity even after five successive uses. Based on overall results, the ZSC sample was proposed as an excellent candidate for water purification applications.

Green calcium-based photocatalyst derived from waste marble powder for environmental sustainability: A review on synthesis and application in photocatalysis

Calcium, with its excellent adsorptive property and higher permissible limits in the environment, emerges as an effective wastewater treatment earth metal. Most of the catalysts, photocatalysts, and adsorbents reported in the literature have heavy metal complex, which creates a leaching problem. Majorly, precursors used for the synthesis of heterogeneous catalysts for wastewater treatment are costly. Therefore, the use of such precursors would be not suitable and feasible approach from an economic point of view. This review work is focused on giving an overview of the utilisation of calcium-based catalysts (adsorbents and photocatalyst) for the removal/degradation of various types of dye water pollutants and summarises the reported effects of calcium as a base on the removal efficiency of dopants. In this article, an extensive literature survey is presented on the various photocatalysts developed and the different syntheses involved in their preparation. As the utilisation of marble powder is a green sustainable approach, the scope of various calcium-based photocatalysts and their application is presented. This article also aims for the elementary and inclusive determination of the effect of introducing calcium as a base for different catalysts and adsorbents.

Direct growth of three-dimensional nanoflower-like structures from flat metal surfaces

Here we report on a facile top-down approach for the direct growth of Co₃O₄ hierarchical nanoflowers from a bulk Co surface via chemical etching and thermal annealing. The effect of the annealing temperature was investigated, showing that amorphous Co₃O₄ was formed at 250 °C, while crystalline Co₃O₄ with notable oxygen vacancies was created at 550 °C. The formed 3D nanostructures exhibited excellent oxygen evolution reaction (OER) activities with a low overpotential of 0.34 V at 10 mA cm^-2 and high durability. The proposed novel approach was further demonstrated by the direct growth of 3D NiO and CuO nanostructures on Ni and Cu substrates.

An effective CuO/Bi2WO6 heterostructured photocatalyst: Analyzing a charge-transfer mechanism for the enhanced visible-light-driven photocatalytic degradation of tetracycline and organic pollutants

Over the past few years, industrial pollution has had a negative impact on aquatic life by releasing significant amounts of hazardous chemicals into the ecosystem. Therefore, it is imperative to develop photocatalytic materials with good photocatalytic activity and easy separation. Photocatalytic degradation has been employed for the removal of such contaminants using binary hybrid nanocomposites as photocatalysts. In the present study, binary CuO/Bi₂WO₆ (CuBW) nanocomposites with different loadings of Bi₂WO₆ (~5, 10, and 15 mg) were successfully constructed using a simple hydrothermal method and used as a potential photocatalyst for the degradation of tetracycline (TC) and methylene blue (MB) under visible-light irradiation. The structure, surface morphology, and optical properties were studied to investigate the formation of the heterostructure. Among the prepared samples, the CuBW nanocomposite containing the optimum content of Bi₂WO₆ (~10 mg) exhibited superior activity toward the photocatalytic degradation of TC (97.72%) in 75 min and MB (99.43%) in 45 min under visible-light illumination. Radical trapping experiments suggested that holes and •OH radicals were the dominant reactive species during the photocatalytic process. The photoelectrochemical results also confirmed the improved separation and transfer of electron-hole pairs at the interface of Bi₂WO₆ and CuO. Our results demonstrate that the binary CuO/Bi₂WO₆ nanocomposite has significant potential applications in the field of photocatalysis due to its enhanced separation of the photoexcited charge carriers and strong synergistic interactions.

Electrospun 1D-NiO hollow nanowires on glass support for the sunlight-driven photodegradation of methylene blue

Sunlight-driven semiconductor photocatalysts have received substantial attention due to environmental degradation, but a simple and reusable photocatalyst design has been a challenging task. Herein, we report the fabrication of a one-dimensional hollow semiconducting nanowire structure by electrospun-mediated nickel oxide nanowires (NiO NWs) as a reusable photocatalyst by direct deposition on glass substrates. The effective control of the sunlight-driven hollow nanowires as the photocatalyst has a high surface area for multiple light-harvesting and interface redox reactions, a nanostructured thin shell for accelerated charge separation, transportation, and a large length-diameter ratio for easy recycling. The electrospun NiO NWs were nest-like hollow nanostructure fibers, crystalline, and with a high density, and the synthesis and parameters were thoroughly investigated to achieve the characteristic shape of the hollow NiO NWs. Further, the photocatalytic activity of the NiO NWs on glass substrates for the selective breakdown of methylene blue (MB) under sunlight irradiation to optimize the efficiency of the NiO NWs, such as degradation techniques, concentration, and pH of the MB solution. The stability and reusability of the NiO NWs were tested successfully in several reusable cycles, with only a 2% degradation difference. The reaction rate was found to be 0.054 min⁻¹ for MB (5 μM) and 0.033 min⁻¹ for MB (10 μM) at pH 11 for 60 min, and the higher activity parameter was calculated to be 3.3 × 10⁻³ min⁻¹ mg⁻¹ L⁻¹ due to their hollow structure and effective area of the NiO NWs. They contain more superficially-entrapped holes that change with chemisorbed oxyhydroxyl OH or H₂O to form OH⁻ radicals. The specific active hollow surface area rises, whereas the rate of optical-electronic hole recombination drops. The photocatalytic degradation performance of the fabricated one-step electrospun hollow NiO NW-based photocatalyst on substrates showed speed, reusability, and promoted the formation of radicals capable of decomposing organic pollutants, which were shown to have application in photocatalysis.

One-step fabrication of hollow NiO NWs photocatalyst on glass substrate by electrospun then tested for their capacity to break down MB in solutions exposed to sunlight.

Fly ash-based nanocomposites: a potential material for effective photocatalytic degradation/elimination of emerging organic pollutants from aqueous stream

Fly ash is readily available and cheaply generated as 47a by-product of the combustion of organic matter. A tremendous amount of fly ash is generated worldwide, and its disposal has imposed 47a severe environmental concern. Its good adsorption capacities attracted several researchers to study the use of fly ash as 47a support for photocatalysts for the degradation of contaminants from wastewater. Undoubtedly the photocatalysts supported on fly ash have represented excellent degradation efficiencies due to the synergistic effect of adsorption and photocatalytic capacity. The utilization of fly ash as 47a precursor has solved the problem of disposal and added value to the waste by-product. Various preparation techniques for fly ash-based nanocomposites such as the sol-gel method, hydrothermal method, solvothermal method, precipitation and co-precipitation, modified metalorganic decomposition, electrospinning, incipient impregnation, and wet chemical synthesis, along with 47a brief study of their characterization using scanning electron microscopy, X-ray diffraction technique and Fourier transform infrared (FTIR) spectroscopy, and the mechanism of photodegradation of dyes have been discussed in this paper. The literature shows that SiO₂, TiO₂, and Al₂O₃ present in fly ash play an essential role in the photodegradation of dyes. Factors affecting the degradation of dyes, their kinetic studies, and methods to enhance photodegradation efficiency have also been discussed.

CuO-ZnO-PANI a lethal p-n-p combination in degradation of 4-chlorophenol under visible light

Recent interest and responsibility to retain the water resources rose among people. Scientists have been engaged to develop the mechanism that involves the freely available sunlight - a sustainable resource - to remove the pollutants from water to make it again suitable for life. Ample research was reported in the removal of dye pollutants present in water. For this they have utilized p type and n type semiconductors or combination of both (p-n type) under the excitation of a wide range of electromagnetic band energy. Most of the interest lies in emerging out of the mechanism with hybrid semiconductors to remove the previously reported flaws. Toward this regard, this manuscript aims to develop unique material using the underlying p-n-p model for harnessing visible light in catalysis. Initially, p-n structure was developed with copper oxide (p-type) and zinc oxide (n-type), then polyaniline (p-type) conjugated at different concentrations (0.5 M, 0.7 M & 1.0 M), to yield p-n-p models, using precipitation followed by sonication techniques. Detailed physicochemical investigations were conducted on the resultant p-n-p material to elucidate its characteristics. Furthermore, the mechanism was advocated for the best photocatalytic activity under visible light excitation for the degradation of 4-chlorophenol and compared with the performance of a standard p-n (CuO/ZnO) combination.

Photoelectrochemical Water-Splitting Using CuO-Based Electrodes for Hydrogen Production: A Review

The cost-effective, robust, and efficient electrocatalysts for photoelectrochemical (PEC) water-splitting has been extensively studied over the past decade to address a solution for the energy crisis. The interesting physicochemical properties of CuO have introduced this promising photocathodic material among the few photocatalysts with a narrow bandgap. This photocatalyst has a high activity for the PEC hydrogen evolution reaction (HER) under simulated sunlight irradiation. Here, the recent advancements of CuO-based photoelectrodes, including undoped CuO, doped CuO, and CuO composites, in the PEC water-splitting field, are comprehensively studied. Moreover, the synthesis methods, characterization, and fundamental factors of each classification are discussed in detail. Apart from the exclusive characteristics of CuO-based photoelectrodes, the PEC properties of CuO/2D materials, as groups of the growing nanocomposites in photocurrent-generating devices, are discussed in separate sections. Regarding the particular attention paid to the CuO heterostructure photocathodes, the PEC water splitting application is reviewed and the properties of each group such as electronic structures, defects, bandgap, and hierarchical structures are critically assessed.

Facile green synthesis of ZnO-CdWO4 nanoparticles and their potential as adsorbents to remove organic dye

In this work, ZnO-CdWO₄ nanoparticles have been synthesized by the ecofriendly green method with lemon leaf extract to favorably anchor functional groups on their surface. The prepared ZnO-CdWO₄ nanoparticles are used as adsorbent to treat Congo red (CR) dye after characterization through FT-IR, UV-Vis, TEM, SEM-EDX, and HRTEM techniques. The equilibrium partition coefficient and adsorption capacity values for CR by ZnO-CdWO₄ are estimated as 21.4 mg g^-1 μM^-1 and 5 mg g^-1, respectively (at an initial dye concentration of 10 mg L^-1). The adsorption process is found as exothermic and spontaneous, as determined by the ΔG°, ΔS°, and ΔH° values. The Boyd plot has been used as a confirmatory tool to fit the adsorption kinetics data along with intraparticle diffusion and pseudo-second-order models. Based on this research, ZnO-CdWO₄ nanoparticles are validated as an effective adsorbent for CR dye in aqueous solutions.

Mixed-valent manganese oxide for catalytic oxidation of Orange II by activation of persulfate: heterojunction dependence and mechanism

The coexistence of aliovalent cations in manganese oxide catalysts with a suitable mole ratio accelerates the activation process of persulfate for the degradation of organic pollutants.

Synthesis and enhanced photocatalytic performance of 0D/2D CuO/tourmaline composite photocatalysts

Photocatalysis is considered to be a green and promising technology for transforming organic contaminants into nontoxic products. In this work, a CuO/tourmaline composite with zero-dimensional/two-dimensional (0D/2D) CuO architecture was successfully obtained via a facile hydrothermal process, and its photocatalytic activity was evaluated by the degradation of methylene blue (MB). Surface element valence state and molecular vibration characterization revealed that CuO chemically interacted with tourmaline via Si-O-Cu bonds. The specific surface area of the CuO/tourmaline composite (23.60 m² g^-1) was larger than that of the pristine CuO sample (3.41 m² g^-1). The CuO/tourmaline composite exhibited excellent photocatalytic activity for the degradation of MB, which was ascribed to the increase in the quantity of the adsorption-photoreactive sites and the efficient utilization of the photoinduced charge carriers. This study provides a facile strategy for the construction of 0D/2D CuO structures and the design of tourmaline-based functional composite photocatalysts for the treatment of organic contaminants in water.

Sunlight-Driven Combustion Synthesis of Defective Metal Oxide Nanostructures with Enhanced Photocatalytic Activity

Synthesis of metal oxide nanostructures through combustion routes is a promising technique owing to its simplicity, rapidity, scalability, and cost-effectiveness. Herein, a sunlight-driven combustion approach is developed to synthesize pristine metal oxides and their heterostructures. Sunlight, a sustainable energy source, is used not only to initiate the combustion reaction but also to create oxygen vacancies on the metal oxide surface. ZnO nanostructures are successfully synthesized using this novel approach, and the products exhibit higher photocatalytic activity in the decomposition of methyl orange (MO) than ZnO nanostructures synthesized by the conventional methods. The higher photocatalytic activity is due to the narrower band gap, higher porosity, smaller and more uniform particle size, surface oxygen vacancies, as well as the enhanced exciton dissociation efficiency induced by the sunlight. Porous Fe₃O₄ nanostructures are also prepared using this environmentally benign method. Surprisingly, few-layer Bi₂O₃ nanosheets are successfully obtained using the sunlight-driven combustion approach. Moreover, the approach developed here is used to synthesize Bi₂O₃/ZnO heterostructure exhibiting a structure of few-layer Bi₂O₃ nanosheets decorated with ZnO nanoparticles. Bi₂O₃ nanosheets and Bi₂O₃/ZnO heterostructures synthesized by sunlight-driven combustion route exhibit higher photocatalytic activity than their counterparts synthesized by the conventional solution combustion method. This work illuminates a potential cost-effective method to synthesize defective metal oxide nanostructures at scale.

Sonochemistry-assisted fabrication of 1D-ZnSb2O6@2D-MoS2 nanostructures: A synergistic energy storage material for supercapacitors

In this work, a novel nanohybrid composing of molybdenum disulphide nanosheets and zinc antimonate nanorods was fabricated using ultrasonication assisted homogenous magnetic stirring approach and investigated their electrochemical performance as an electrode material for supercapacitors. First and foremost, the structural, vibrational, morphological, optical and chemical compositional characteristics of the fabricated nanohybrid electrode material were investigated. Subsequently, the electrochemical properties of the nanohybrid electrode were explored using CV, GCD and EIS studies in 1.0 M KOH solution. The fabricated nanohybrid electrode material exhibited tremendous electrochemical performance by distributing maximum specific capacitance of 469.28 F g^-1 at a current density of 5.0 A g^-1 with high cycling stability of 102.0% even after 2000 cycles at a current density of 10.0 A g^-1. These exceptional electrochemical characteristics of MoS₂/ZnSb₂O₆ nanocomposites are ascribed to the influence of ultrasonication on non-aggregated nanocomposite formation, existence of more number of electrochemical active sites and synergistic interactions between two different nanostructures. The acquired results confirmed that MoS₂/ZnSb₂O₆ nanocomposites could be a prospective and electrochemically active candidate as electrode materials for supercapacitors.

Adsorptive removal and photocatalytic degradation of organic pollutants using metal oxides and their composites: A comprehensive review

Metal oxide nanomaterials and their composites are comprehensively reviewed for water remediation. The controlled morphological and textural features, variable surface chemistry, high surface area, specific crystalline nature, and abundant availability make the nanostructured metal oxides and their composites highly selective materials for efficient removal of organic pollutants based on adsorption and photocatalytic degradation. A wide range of metal oxides like iron oxides, magnesium oxide, titanium oxides, zinc oxides, tungsten oxides, copper oxides, metal oxides composites, and graphene-metal oxides composites having variable structural, crystalline and morphological features are reviewed emphasizing the recent development, challenges, and opportunities for adsorptive removal and photocatalytic degradation of organic pollutants viz. dyes, pesticides, phenolic compounds, and so on. It also covers the deep discussion on the photocatalytic mechanism of metal oxides and their composites along with the properties relevant to photocatalysis. High photodegradation efficiency, economically-viable approaches for the preparation of photocatalytic materials, and controlled band-gap engineering make metal oxides highly efficient photocatalysts for degradation of organic pollutants. The review would be an excellent resource for researchers who are currently focusing on metal oxides-based materials for water remediation as well as for those who are interested in adsorptive and photocatalytic applications of metal oxides and their composites.

Ultrasonication-assisted fabrication of hierarchical architectures of copper oxide/zinc antimonate nanocomposites based supercapacitor electrode materials

In this work, a new nanohybrid consisting of copper oxide and zinc antimonate was designed using ultrasonication assisted homogenous magnetic stirring approach and investigated their performance as an electrode material for supercapacitors. Combination of the duo could enhance the electrical conductivity and charge storage capacity of whole nanostructured electrode, which is very much essential for supercapacitor application. Primarily, the prepared nanohybrid electrode material was investigated through XRD, FT-IR, FE-SEM, HR-TEM, UV-DRS, PL and XPS to determine their structural, morphological, optical and compositional characteristics. Thereafter, the electrochemical properties of the nanohybrid electrode were investigated using CV, GCD and EIS studies in 1.0 M KOH solution. The fabricated nanohybrid electrode material exhibits exceptional electrochemical performance by delivering maximum specific capacitance of 257.14 F g^-1 at a current density of 12.5 A g^-1. The nanocomposite showed high cycling stability of 102.0% even after 2000 cycles at a current density of 10.0 A g^-1. These exceptional electrochemical characteristics of CuO/ZnSb₂O₆ nanocomposites are due to their dual nanorod morphology, influence of ultrasonication on non-aggregated nanocomposite formation, presence of more number of electrochemical active sites, and their synergistic interactions. The obtained results confirmed that CuO/ZnSb₂O₆ nanocomposites could be a potential candidate as electrode materials for supercapacitors.

Adsorption of Congo Red (Acid Red 28) Azodye on Biosynthesized Copper Oxide Nanoparticles

A green synthesis of copper oxide nanoparticles and its removal efficiency of azodye were studied. Biosynthesis of stable copper oxide nanoparticles were preformed using Aloe barbadensis leaf extract as a size and shape-directing agent for preparing of spherical copper oxide nanoparticles by calcination at 400 °C. The leaf extract of Aloe barbadensis was prepared in deionized water. The produced copper particles were calcined at 400 °C to produce copper oxide nanoparticles. The characterization of copper oxide nanoparticles was performed by XRD, SEM, FTIR, UV spectroscopy. The XRD analysis showed that the average particle size was between 5-30 nm. The shape of the copper oxide nanoparticles was spherical and cubic. EDX of the synthesized nanoparticles showed the composition consists of 68 % copper. The UV-visible spectrum analysis confirms an absorption peak at 200-400 nm of the produced CuO nanoparticles. The FTIR analysis of the copper oxide particles indicate the presence of the organometallic Cu-O bond between Cu and O. The obtained copper oxide was used as a removing agent of Congo red dye. The effect of variables like concentration, time, pH, adsorbent dosage were studied. It was observed from the results that the maximum dye removal occurs at pH of 4, the concentration of nanoparticles was 1 mg/L and the maximum time for dye removal was 120 min. The Langmuir isotherm model was calculated to study the adsorption efficiency of the Congo red dye on the produced copper oxide nanoparticles. The kinetics of pseudo second order is followed by adsorption. The calculated sum of square was 0.012 and r2 = 0.98. it was observed that the model fit the best and straight line with r2 value of 0.991 and probability value of 1.6E-5. The nanoparticles remove 70 % of the Congo red dye from its solution. This showed that the copper oxide nanoparticles has efficient capacity of azodye degradation.

Engineering nanomaterials for water and wastewater treatment: review of classifications, properties and applications

Based on their characteristics and applicability, a new category of NMs is proposed for water and wastewater treatment.

Alkyl-capped copper oxide nanospheres and nanoprolates for sustainability: water treatment and improved lubricating performance

Metal oxide nanoparticles of different nature have been used in different fields such as therapeutics, biomarkers, tribology or environmental remediation, among others. Besides, the surface modification of such nanoparticles is of particular interest to bring designed functions. In this paper we describe the synthesis of CuO nanoparticles with two different geometries (spherical and prolate) and decorated with long alkyl chains in order to use as dye removers by adsorption and/or photo-degradation of a persistent model dye (Congo Red) and as lubricant additives to improve the tribological performance of base lubricant oils. Alkyl-functionalized CuO nanoparticles demonstrated a high stability in oily suspensions and an improvement in the friction reducing the CoF ca. 26%; the alkyl-decorated nanoparticles showed also higher adsorption kinetics for Congo Red than the neat ones following a pseudo-second-order trend, although with lower adsorption efficiency. The synthesis, surface modification and physic-chemical characterization of spherical and prolate CuO nanoparticles are described as well as their applications as lubricant additives and Congo Red photocatalytic removal.

Photocatalytic degradation of naphthalene using calcined FeZnO/ PVA nanofibers

Recently, the incorporation of metal oxide nanoparticles into polymers has gained great attention owing to their ample of applications. The green mediated synthesis Fe-doped ZnO nanoparticles have been incorporated into PVA nanofibers through electro spinning for the application of photocatalytic degradation. The PVA polymer concentration was optimized to obtain uniform fibers without beads. The Fe-doped ZnO nanofibers were characterized by various analyzing techniques. The results show that good physicochemical with high surface area, uniformity in fiber with an average diameter ranges from 150 to 300 and 50-200 nm for un-calcined and calcined Fe-doped ZnO nanofiber respectively. The photocatalytic activity of nanofibers was examined by the degradation of naphthalene. The efficiency was observed 96 and 81% for calcined and un-calcined nanofibers, respectively. The reusable efficacy of Fe-doped ZnO calcined nanofiber as a catalyst was studied. These studies corroborated that the calcined Fe-doped ZnO nanofiber as promising material for catalytic applications.

Silver nanoparticle embedded copper oxide as an efficient core–shell for the catalytic reduction of 4-nitrophenol and antibacterial activity improvement

A facile and eco-friendly method was developed to prepare a microporous CuO@Ag⁰ core–shell with high catalytic and antibacterial activities.

Efficient adsorption and antibacterial properties of electrospun CuO-ZnO composite nanofibers for water remediation

On the face of impending global water resources, developing low-cost and efficient water treatment technologies and materials thereof is highly important. Herein, we explore the adsorption capacity and antibacterial properties of CuO-ZnO (CZ) composite nanofibers. The ultrafine nanofibers were fabricated using simple and inexpensive electrospinning technique and were further characterized using Field Emission-Scanning Electron Microscope (FE-SEM), Transmission electron microscope (TEM) and X-Ray Diffraction (XRD), Thermogravimetric analysis (TGA), Fourier transform Infrared Spectroscopy (FTIR). When employed as nanoadsorbents, CZ nanofibers exhibited excellent adsorption capacity for congo red dye. Adsorption Isotherms and kinetics were performed to determine the maximum adsorption capacity and the rate of adsorption, respectively, depicting the better efficiency of composite nanofibers as compared to their single counterparts. The mechanism of adsorption is also proposed with the evaluation of diffusion studies. The second part of this study deals with the examination of antibacterial activity of CZ composite nanofibers against antibiotic resistant GFP-E.coli and S. aureus. The antibacterial efficacy was monitored by visual turbidity assay, SEM analysis and reactive oxygen species (ROS) determination. Hence, such nanofibers have been explored as a single platform for the removal of biological as well organic contaminants so as to make them potential in the field of water remediation.

Novel heterostructured InN/TiO2 submicron fibers designed for high performance visible-light-driven photocatalysis

InN phase was successfully integrated into TiO₂ fiber, which greatly improved its visible-light photocatalytic property.

One-step construction of {001} facet-exposed BiOCl hybridized with Al2O3 for enhanced molecular oxygen activation

The conduction band position of defective Al₂O₃ obtained via a combustion synthesis is proposed and the in situ as-prepared heterojunctions containing Al₂O₃ and {001} facet-exposed BiOCl with surface oxygen vacancies exhibit excellent performance for molecular oxygen activation.