Preparation, characterization and photocatalytic activity of ZnO, Fe2O3 and ZnFe2O4

Degradation of organic Pollutant by Using of BiVO4-NiFe2O4 Heterostructure Photocatalyst under Visible Light Irradiation: Assessment of Detoxicity Study Using Cirrhinus mrigala

The current study mainly concentrates on the photocatalytic activity of composite nanomaterial of BiVO4 (BVO), NiFe2O4 (NFO), and BiVO4-NiFe2O4 (BVO-NFO) under visible light. Among these, BVO-NFO composite degrades crystal violet dye within 60 min with a percentage degradation of 95.65% under visible light illumination. The BVO-NFO composite exhibits better photodegradation performance, which can be attributed to the effective light absorption and reduced recombination of the photoexcited charge carriers. Additionally, by applying a magnetic field, the BVO-NFO composite can be magnetically recovered by using the magnet for subsequent recycling. The synthesized composite was characterized using optical techniques like X-ray diffraction, ultraviolet diffuse reflectance spectroscopy, scanning electron microscopy, Brunauer-Emmett-Teller, and energy dispersive X-ray analysis. The effect of dye, before and after degradation, on vital organs of fish species was examined such as fish gill (pulmonary-toxicity), fish liver (hepato-toxicity), fish kidney (renal toxicity), fish brain (neural toxicity), and fish muscle (myopathy). This work offers a clear and practical method for designing a highly crystalline semiconductor photocatalyst for dye degradation and the remediation of industrial wastewater.

Fabrication of Bi-Bi3O4Cl plasmon photocatalysts for removal of aqueous emerging contaminants under visible light

Photocatalytic oxidation of emerging contaminants (ECs) in water has recently gained extensive attentions. In this study, bismuth oxychloride-based plasmon photocatalysts (Bi-Bi₃O₄Cl) exhibiting high performance were successfully developed by reducing Bi³⁺ on the surface of Bi₃O₄Cl. Consequently, the photocatalysts were used to remove ECs from water. The effects of developmental process and Bi metal plasmon resonance on the photoelectric performances of Bi-Bi₃O₄Cl were investigated through a series of characterizations. The UV-vis diffuse reflection and photoluminescence spectra revealed that the light absorption range of the photocatalyst gradually increased and the electron recombination rate gradually decreased with the introduction of Bi metals. The optimal removal rates of ciprofloxacin and tetrabromobisphenol A by Bi-Bi₃O₄Cl were 93.8% and 96.4%; the respective reaction rate constants were 5.48 and 4.93 times higher than that of Bi₃O₄Cl. The mechanism study indicated that main reactants in the photocatalytic system were •O₂^- radicals and photogenerated holes, and the existence of oxygen vacancies and Bi metals promoted electron transfer in photocatalyst. In conclusion, this research produces a novel, green, highly efficient, and stable visible light photocatalyst for the removal of ECs from water.

Effect of cation configuration and solvation on the band positions of zinc ferrite (100)

Zinc ferrite ZnFe[Formula: see text]O[Formula: see text] belongs to the spinel-type ferrites that have been proposed as photocatalysts for water splitting. The electronic band gap and the band edge positions are of utmost importance for the efficiency of the photocatalytic processes. We, therefore, calculated the absolute band energies of the most stable surface of ZnFe[Formula: see text]O[Formula: see text], the Zn-terminated (100) surface at self-consistent hybrid density functional theory level. The effect of Fe- and Zn-rich environments, cation exchange as antisite defects and implicit solvation on the band positions is investigated. Calculated flat band potentials of the pristine surface model ranges from [Formula: see text] to [Formula: see text] V against SHE in vacuum. For Zn-rich (Fe-rich) models this changes 0.3-0.9 (0.0-0.7) V against SHE. Fe-rich models are closest to the experimental range of reported flat band potentials. Solvent effects lower the calculated flat band potentials by up to 1.8 eV. The calculated band gaps range from 1.5 to 2.9 eV in agreement with previous theoretical work and experiment. Overall, our calculations confirm the experimentally observed low activity of ZnFe[Formula: see text]O[Formula: see text] and its dependence on preparation conditions.

Heterogeneous Gold Nanoparticle-Based Catalysts for the Synthesis of Click-Derived Triazoles via the Azide-Alkyne Cycloaddition Reaction

A supported gold nanoparticle-catalyzed strategy has been utilized to promote a click chemistry reaction for the synthesis of 1,2,3-triazoles via the azide-alkyne cycloaddition (AAC) reaction. While the advent of effective non-copper catalysts (i.e., Ru, Ag, Ir) has demonstrated the catalysis of the AAC reaction, additional robust catalytic systems complementary to the copper catalyzed AAC remain in high demand. Herein, Au nanoparticles supported on Al2O3, Fe2O3, TiO2 and ZnO, along with gold reference catalysts (gold on carbon and gold on titania supplied by the World Gold Council) were used as catalysts for the AAC reaction. The supported Au nanoparticles with metal loadings of 0.7–1.6% (w/w relative to support) were able to selectively obtain 1,4-disubstituted-1,2,3-triazoles in moderate yields up to 79% after 15 min, under microwave irradiation at 150 °C using a 0.5–1.0 mol% catalyst loading through a one-pot three-component (terminal alkyne, organohalide and sodium azide) procedure according to the “click” rules. Among the supported Au catalysts, Au/TiO2 gave the best results.

Formic acid motivated photocatalytic reduction of Cr(VI) to Cr(III) with ZnFe2O4 nanoparticles under UV irradiation

UV-light irradiated photocatalytic reduction of Cr(VI) to Cr(III) in aqueous solution using ZnFe₂O₄ nanoparticles in the presence of formic acid was reported. X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS) and UV-Vis diffuse reflectance spectroscopy (DRS) were employed to characterize ZnFe₂O₄ nanoparticles. The photocatalytic activity of pure ZnFe₂O₄ under UV irradiation was significantly low. However, the Cr(VI) reduction efficiency on nano-sized ZnFe₂O₄ in the presence of 0.40% formic acid reached 95.4% within 4 h. Herein, the effect of pH, photocatalyst amount, initial concentration of Cr(VI) and formic acid concentration on the photocatalytic reduction of Cr(VI) was investigated. The results indicated that the photocatalytic reduction of Cr(VI) decreased with increase in the initial concentration of Cr(VI), photocatalyst dosage and pH. The reduction rate constant declined from 0.017 min^-1 to 0.0023 min^-1 with the increase in initial concentration of Cr(VI) from 5 to 25 mg L^-1. However, the reduction rate constant sharply increased from 0.000075 min^-1 to 0.0127 min^-1 with the increase in formic acid concentration from 0.05% to 0.40%. The formic acid could capture the photogenerated holes, and eventually formate (HCOO^-) ions could be converted into carbon dioxide radicals (•CO₂^-). Because of more negative redox potential for •CO₂^- radicals, Cr(VI) species could easily be reduced to Cr(III) under UV irradiation. The pseudo-first-order kinetic reaction was confirmed for this reduction process. A tenable mechanism for the photocatalytic Cr(VI) reduction has also been demonstrated.

Pulsed Laser in Liquids Made Nanomaterials for Catalysis

Catalysis is essential to modern life and has a huge economic impact. The development of new catalysts critically depends on synthetic methods that enable the preparation of tailored nanomaterials. Pulsed laser in liquids synthesis can produce uniform, multicomponent, nonequilibrium nanomaterials with independently and precisely controlled properties, such as size, composition, morphology, defect density, and atomistic structure within the nanoparticle and at its surface. We cover the fundamentals, unique advantages, challenges, and experimental solutions of this powerful technique and review the state-of-the-art of laser-made electrocatalysts for water oxidation, oxygen reduction, hydrogen evolution, nitrogen reduction, carbon dioxide reduction, and organic oxidations, followed by laser-made nanomaterials for light-driven catalytic processes and heterogeneous catalysis of thermochemical processes. We also highlight laser-synthesized nanomaterials for which proposed catalytic applications exist. This review provides a practical guide to how the catalysis community can capitalize on pulsed laser in liquids synthesis to advance catalyst development, by leveraging the synergies of two fields of intensive research.

Appraisal of water matrix on the removal of fungicide residues by heterogeneous photocatalytic treatment using UV-LED lamp as light source

In this study, the photocatalytic degradation of four fungicides, myclobutanil, penconazole and difenoconazole (triazole compounds) and boscalid (carboxamide), has been examined in different aqueous matrices (tap water, irrigation water and two WWPT effluents). Experiments were conducted at laboratory scale with different reagents-zinc oxide (ZnO), titanium dioxide (TiO₂), sodium persulphate (Na₂S₂O₈) and the combined systems ZnO/Na₂S₂O₈ and TiO₂/Na₂S₂O₈-in water exposed to UV-LED irradiation. Previously, the effect of catalyst and oxidant loading on the disappearance kinetics of the different fungicides was assessed to know maximum degradation efficiency. The influence of water matrices and pesticide loading in removal effectiveness has been evaluated. It was observed a greater efficiency in processes conducted using the tandems ZnO/Na₂S₂O₈ and TiO₂/Na₂S₂O₈ in irrigation and tap waters. Results showed that UV-LED are a suitable alternative for tackling the removal of organic pollutants in water.

Photocatalytic Cellulose-Paper: Deepening in the Sustainable and Synergic Combination of Sorption and Photodegradation

Clean water is one of the sustainable development goals set by the United Nations for 2030. The development of effective but worldwide affordable strategies is essential to guarantee this achievement. Photocatalysis technology fulfills these criteria whenever the photocatalyst is sustainable and nontoxic. In this article, a cellulose-paper modified with a polyamide-titanium dioxide (TiO₂) nanocomposite by dip-coating is evaluated to degrade estrogens efficiently under solar light. The study deepens on the synergic combination of the sorptive capacity of the polyamide and the activity of TiO₂. The photocatalytic performance was studied under artificial and sunlight in a miniaturized experimental setup (batch of six reactors). Also, the effects of the dispersed/immobilized catalyst, irradiation time, and adsorption evaluation were studied under kinetic conditions. The photocatalyst composition, considering the polyamide (nylon-6) and TiO₂ amounts and the dipping cycles, was studied by a response surface methodology, and the reusability of the photocatalytic cellulose-paper was investigated. The LED source provided removal efficiencies of 65, 62, and 52% (for estrone, 17β-estradiol, and estriol, respectively) after 420 min of light exposure. Under sunlight, the efficiency increased up to 99.5% for estrone and 17β-estradiol and 98.5% for estriol after 180 min of irradiation. The sustainable character of the cellulosic substrate, the low toxicity of the nanocomposite ingredients, and its performance under sunlight make the material attractive for in-field application.

Research and application of a non-noble metal catalyst in the removal of trace olefins from aromatics

Cu/ZnO/montmorillonite is a high-performance catalyst in the removal of trace olefins from aromatics.

Hydrodechlorination of 4-Chlorophenol on Pd-Fe Catalysts on Mesoporous ZrO2SiO2 Support

A mesoporous support based on silica and zirconia (ZS) was used to prepare monometallic 1 wt% Pd/ZS, 10 wt% Fe/ZS, and bimetallic FePd/ZS catalysts. The catalysts were characterized by TPR-H₂, XRD, SEM-EDS, TEM, AAS, and DRIFT spectroscopy of adsorbed CO after H₂ reduction in situ and tested in hydrodechlorination of environmental pollutant 4-chlorophelol in aqueous solution at 30 °C. The bimetallic catalyst demonstrated an excellent activity, selectivity to phenol and stability in 10 consecutive runs. FePd/ZS has exceptional reducibility due to the high dispersion of palladium and strong interaction between FeOx and palladium, confirmed by TPR-H₂, DRIFT spectroscopy, XRD, and TEM. Its reduction occurs during short-time treatment with hydrogen in an aqueous solution at RT. The Pd/ZS was more resistant to reduction but can be activated by aqueous phenol solution and H₂. The study by DRIFT spectroscopy of CO adsorbed on Pd/ZS reduced in harsh (H₂, 330 °C), medium (H₂, 200 °C) and mild conditions (H₂ + aqueous solution of phenol) helped to identify the reasons of the reducing action of phenol solution. It was found that phenol provided fast transformation of Pd⁺ to Pd⁰. Pd/ZS also can serve as an active and stable catalyst for 4-PhCl transformation to phenol after proper reduction.

NZF Nanoscale Particles: Synthesis, Characterization and its Effective Adsorption of Bromophenol Blue

The ferrospinels NixZn1_xFe2O4 (x = 0.0 and 0.6) nanoparticles (NPs) were successfully prepared by a sol-gel method and analyzed by TGA/DTA, XRD, SEM-EDS, UV-Vis-DRS, and pHIEP. The adsorption potential of NZF NPs towards the Bromophenol blue (BPB) dye was investigated. The batch adsorption efficiency parameters were studied including contact time, pH, initial dye concentrations and catalyst dosage. Results indicated that NZF crystallized in single-phase and exhibited smaller crystallite size (49 nm vs. 59.24 nm) than that of the pristine (ZF). The SEM analysis showed that the materials are elongated-like shape. NZF catalyst showed a red-shift of absorption bands and a more narrowed band gap (2.30 eV vs. 1.65 eV) as compared to ZF. The adsorption process was found to be highly dependent to the pH of the solution, dye concentration and adsorbent dose. Under optimum conditions of 5 mg.L–1 BPB, 0.5 g.L–1 NZF catalyst, pH = 6, and 25 °C, up to ≈ 86.30%  removal efficiency could be achieved after 60 min. Pseudo-second-order kinetic model gave the best fit with highest correlation coefficients (R2 ≥ 0.99). A high specific surface area, a stabilized dispersion state of NZF NPs and the electrostatic interaction between the BPB-2 anions and the NZF-H3O+active sites on NZF surface were believed to be the main factors that can be responsible for the high adsorption efficiency. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).  

Reduction of Pesticide Toxicity Under Field-Relevant Conditions? The Interaction of Titanium Dioxide Nanoparticles, Ultraviolet, and Natural Organic Matter

In surface waters, the illumination of photoactive engineered nanomaterials (ENMs) with ultraviolet (UV) light triggers the formation of reactive intermediates, consequently altering the ecotoxicological potential of co-occurring organic micropollutants including pesticides due to catalytic degradation. Simultaneously, omnipresent natural organic matter (NOM) adsorbs onto ENM surfaces, altering the ENM surface properties. Also, NOM absorbs light, reducing the photo(cata)lytic transformation of pesticides. Interactions between these environmental factors impact 1) directly the ecotoxicity of photoactive ENMs, and 2) indirectly the degradation of pesticides. We assessed the impact of field-relevant UV radiation (up to 2.6 W UVA/m²), NOM (4 mg TOC/L), and photoactive ENM (nTiO₂, 50 µg/L) on the acute toxicity of 6 pesticides in Daphnia magna. We selected azoxystrobin, dimethoate, malathion, parathion, permethrin, and pirimicarb because of their varying photo- and hydrolytic stabilities. Increasing UVA alone partially reduced pesticide toxicity, seemingly due to enhanced degradation. Even at 50 µg/L, nano-sized titanium dioxide (nTiO₂) reduced but also increased pesticide toxicity (depending on the applied pesticide), which is attributable to 1) more efficient degradation and potentially 2) photocatalytically induced formation of toxic by-products. Natural organic matter 1) partially reduced pesticide toxicity, not evidently accompanied by enhanced pesticide degradation, but also 2) inhibited pesticide degradation, effectively increasing the pesticide toxicity. Predicting the ecotoxicological potential of pesticides based on their interaction with UV light or interaction with NOM was hardly possible, which was even more difficult in the presence of nTiO₂. Environ Toxicol Chem 2020;39:2237-2246. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Historical development and prospects of photocatalysts for pollutant removal in water

Photocatalysis, as a low-cost and environment friendly technology, has demonstrated a significant potential for water pollution purification; it has received extensive attention in recent decades. The key is the photocatalyst; a large number of photocatalysts have been developed. To better understand and further develop the photocatalysis technology for water treatment, this review summarizes its development over time. The development period is divided into four stages (1960s-1993, 1994-2000, 2001-2010, and 2011-present) to provide readers with a better understanding of the development characteristics, and causes and consequences of each historical stage. This review expounds the origin and development of photocatalysis and the obstacles encountered and overcome. It describes the development of mechanisms and methods to solve these problems in each time period. Moreover, it reviews the recent development of new photocatalysts, the concept of designing photocatalysts, and photocatalytic-coupling systems. Finally, it enumerates the problems that continue to exist in the application of photocatalysis technology, and highlights the key issues that must be addressed in future research. The review is aimed at providing the researchers with a deeper understanding of photocatalysis technology and encourage further development of the application of photocatalysis to water treatment.

Synthesis and Characterization of Novel Phyto-Mediated Catalyst, and Its Application for a Selective Oxidation of (VAL) into Vanillin under Visible Light

Here, we report an efficient and highly selective oxidation of lignin model substrate using phyto-mediated ZnFe2O4 nanoparticle using Boswellia carterii extract. The nanocatalyst with an average size of 8 nm showed excellent photocatalytic activity of the synthesized carbonyl containing products under visible light irradiation. The catalytic activity and selectivity towards oxidation of vanillyl alcohol to vanillin with selectivity up to 99% at conversion over 98% and turn-over frequency values up to 1600 h−1 were obtained in the presence of H2O2 and base. The cubic spinel nano-ZnFe2O4 catalyst was characterized by powder-XRD, FESEM, HR-TEM and Mössbauer analysis. The demonstrated catalyst was robust and stable under the reaction conditions. Furthermore, it was easy to be separated from the reaction mixture and be reused for subsequent reactions up to 5 times without significant reactivity or selectivity loss.

High Selectivity to Aromatics by a Mg and Na Co-modified Catalyst in Direct Conversion of Syngas

The demand for aromatics, especially benzene, toluene, and xylene, has been increased in recent years as the crucial feedstocks of coatings and pharmaceutical industry. In this work, a modified Fischer-Tropsch synthesis (FTS) catalyst FeNaMg was fabricated via a sol-precipitation method and integrated with an HZSM-5 aromatization catalyst for the aromatics synthesis from syngas by a one-step process. Syngas was first converted to lower olefins as intermediates on the active component of the FeNaMg catalyst followed by aromatization on zeolite. Different characterization approaches, such as BET, XRD, XPS, hydrogen temperature-programmed reduction, temperature-programmed desorption of CO, TG, and SEM, revealed that Mg efficiently optimized physicochemical properties of the Fe-based catalyst by generating a MgFe2O4 spinel structure. Further investigation demonstrated that the MgFe2O4 spinel structure could increase the syngas adsorption area, facilitating the reduction and carburization of the Fe phase, while Mg decreased CO2 selectivity (31.26 to21%) by restraining the water-gas shift reaction and improved the utilization efficiency of carbon. At the same time, alkali metal Na changed the surface electronic environment of the FTS catalyst to enhance CO adsorption as an electronic promoter, which suppressed methane formation by restraining over hydrogenation. Therefore, the synergism that existed between Mg and Na during the reaction escalated the CO conversion and aromatics selectivity to 96.19 and 51.38%, respectively.

Polymer Nanocomposites Containing Semiconductors as Advanced Materials for EMI Shielding

Miniaturization of electronic devices and systems enhances the complexity of inbuilt circuitry, thereby giving rise to electromagnetic interference (EMI). EMI is a serious cause of concern as it affects the performance of a device, transmission channel, or system. In a quest to find an effective solution to this problem, several materials, apart from the conventional metals, such as carbon derivatives, have been extensively explored recently. In addition to carbon derivatives, hybrid structures such as core-shell, conjugated systems, etc. have also been researched. However, semiconducting fillers have received less attention, especially in this application. Hence, this review article will primarily focus on the systematic understanding of the use of semiconductor-based polymer nanocomposites and how the band gap plays a crucial role in deciding the dielectric properties and subsequently the electromagnetic absorption behavior for shielding applications. Our primary aim is to highlight the mechanism of shielding involved in such nanocomposites in addition to discussing the synthesis and properties that lead to effective shielding. Such nanocomposites containing semiconductors can pave the way for alternate materials for EMI shielding applications that are lightweight, flexible, and easy to integrate.

GW-BSE Calculations of Electronic Band Gap and Optical Spectrum of ZnFe2 O4 : Effect of Cation Distribution and Spin Configuration

The G0W0, evGW0, evGW, and scGW0 approximations to many‐body perturbation theory combined with the Bethe‐Salpeter approach (BSE) are applied to calculate electronic and optical properties of the open‐shell spinel ferrite ZnFe₂O₄. The effect of the various degrees of self‐consistency is assessed by comparison to recent experimental results. Furthermore, the influence of the method for obtaining the ground‐state wavefunction is studied, including the GGA functional PBE with and without an intermediate step using the COHSEX approximation, as well as PBE+U, where we try to minimize the influence of the Hubbard potential U. Best agreement for the optical band gap and the first maxima of the excitation spectrum is obtained with the evGW method based on a PBE+U wavefunction. This method is chosen and converged carefully to yield quantitative results for the optical spectra of four different magnetic structures and cation distributions of ZnFe₂O₄. With the results we provide a possible explanation for inconsistency in experimental results.

Photoelectrochemistry of Ferrites: Theoretical Predictions vs. Experimental Results

This paper gives an overview about recent theoretical and experimental work on electronic and optical properties of spinel ferrites MFe2O4. These compounds have come into focus of research due to their possible application as photocatalyst material for photoelectrochemical water splitting. The theoretical background of state-of-the-art quantum-chemical approaches applied for predicting electronic and optical band gaps, absolute band positions, optical absorption spectra, dielectric functions and Raman spectra, is briefly reviewed. Recent applications of first-principles methods on magnetic and electronic properties of ferrites with M = Mg and the first row of subgroup elements Sc to Zn are presented, where it is shown that the fundamental band gap is strongly dependent on the spin state and the degree of inversion of the spinel structure. The observed variation of electronic properties may serve as an explanation for the large scattering of experimental results. The exchange of M and Fe cations has also a pronounced effect on the Raman spectra of ferrites, which is analyzed at atomic scale from first principles. Calculated optical absorption spectra of ferrites are compared to experimental spectra. The electronic nature of the first excitations and the role of oxygen vacancies are discussed. For the calculation of absolute band positions, which have a significant impact on the photoelectrochemical activity of the ferrites, models of the most stable ferrite surfaces are developed that take into account their polar nature and the interaction with the solvent. Theoretically predicted valence and conduction band edges are compared to results from electrochemical measurements. The role of cation exchange on the surface electronic structure is investigated both theoretically and experimentally.

Construction of ZnFe2O4/rGO composites as selective magnetically recyclable photocatalysts under visible light irradiation

This paper reports on highly active ZnFe₂O₄/reduced graphene oxide (ZnFe₂O₄/rGO) nanocomposites synthesized by a modified sol-gel method. The as-prepared samples have been characterized by XRD, TEM, XPS and other detection methods, which demonstrate that ZnFe₂O₄ nanoparticles (NPs) with a diameter of 15 ∼ 50 nm were densely grown on the rGO substrates. The photocatalytic activities of ZnFe₂O₄/rGO catalysts were evaluated by the degradation of Methylene blue (MB) under visible light. The results showed that the ZnFe₂O₄/rGO catalysts had high photocatalytic activity, and the degradation efficiency of MB was almost 100% within 180 min. Moreover, the ZnFe₂O₄/rGO catalysts also had a great removal effect on Rhodamine B (RhB) and Methyl orange (MO). Mechanistic studies revealed that the rGO acted as a stabilizer to prevent ZnFe₂O₄ from aggregation and improved the separation of photo-generated electrons. The high efficiency for dye degradation was attributed to the generation of hydroxyl radicals (·OH) via the photochemical decomposition of H₂O₂ on ZnFe₂O₄/rGO catalysts, which was responsible for the oxidation of the dyes. Of note, the ZnFe₂O₄/rGO catalyst maintained an efficiency of over 90% after five cycles. The XRD, XPS and VSM characterization revealed that the ZnFe₂O₄/rGO catalysts had a stable crystal structure and can be easily separated.

Controlled Synthesis and Enhanced Catalytic Activity of Well-Defined Close-Contact Pd-ZnO Nanostructures

In this study, PdZn-ordered intermetallic nanoparticles (NPs) were prepared in liquid phase by butyllithium co-reduction of their precursors at 240 °C. Through calcination and subsequent reduction with H₂, the synthesized PdZn NPs were then in situ transformed into Pd-ZnO heteroaggregate nanocatalysts on alumina supports. Various characterization techniques, such as diffuse reflectance Fourier transform infrared with CO probes, transmission electron microscopy, X-ray diffraction, H₂ temperature-programmed reduction, and X-ray photoelectron spectra, reveal that PdZn NPs are ordered intermetallic compounds, and in situ transformation of PdZn alloy NPs results in close-contact Pd-ZnO heteroaggregates, where the interfaces are highly active and the interaction between Pd and ZnO prevents the active particles from agglomeration. The catalytic hydrogenations of nitrophenols over Pd/Al₂O₃ and Pd-ZnO/Al₂O₃ were investigated. The results show that Pd-ZnO/Al₂O₃ illustrates an enhanced catalytic activity relative to Pd/Al₂O₃, and no obvious activity degradation was observed in the recycle catalytic experiments over such nanostructures. It is concluded that the Pd-ZnO interaction not only enhances the catalytic hydrogenation activity but also promotes the thermal and catalytic stability.

Multivariate comparison of photocatalytic properties of thirteen nanostructured metal oxides for water purification

Although the environmental photocatalysis is being developed for many years, the relationships between simple metal oxides have not been explored so far. In this study a multivariate comparison of thirteen nanostructured metal oxides (Bi₂O₃, CeO₂, Co₃O₄, Fe₂O₃, NiO, Pr₆O₁₁, SnO₂, SrTiO₃, TiO₂, WO₃, ZnFe₂O₄, ZnO and ZrO₂) was performed. The solution containing twenty-six psychotropic pharmaceuticals was used as a model mixture. In order to ensure the influence of the dissolved organic matter on the process, all the experiments were conducted in the river water. Simulated solar radiation was applied as the most environmentally relevant. The high-resolution LC-MS profiles, obtained for the photocatalytic samples after 1 h of irradiation, were then submitted to the multivariate chemometric analysis. Graphical representations of principal component analysis and hierarchical cluster analysis enabled visualization of the relationships between the studied oxides. The registered degradation profiles were compared qualitatively and discussed.

Influence of Spin State and Cation Distribution on Stability and Electronic Properties of Ternary Transition-Metal Oxides

This work is a systematic ab initio study of the influence of spin state and cation distribution on the stability, dielectric constant, electronic band gap, and density of states of ternary transition-metal oxides. As an example, the chemical family of spinel ferrites MFe₂O₄, with M = Mg, Sc-Zn is chosen. Dielectric constant and band gap are calculated for various spin states and cation configurations via dielectric-dependent self-consistent hybrid functionals and compared to available experimental data. When choosing the most stable spin state and cation configuration, the calculated electronic properties are in reasonable agreement with measured values. The nature of the excitation is investigated through projected density of states. A pronounced dependence of band gap energy and dielectric constant on the spin state and cation configuration is observed, which is a possible explanation for the large variation of the experimental results, in particular, if several states are energetically close.

Elemental zinc to zinc nanoparticles: is ZnO NPs crucial for life? Synthesis, toxicological, and environmental concerns

The semi-conducting material zinc is one of the essential trace elements for humans, is a co-factor of more than 300 enzymes, and plays an important role in maintaining vital cellular functions. Deficiency of zinc may lead to cancer initiation; however, a high concentration also has toxic effects that might be life threatening. The toxicity can be addressed by the disequilibrium of zinc-mediated proteins and oxidative stress that produce nascent oxygen, hydroxyl radicals, and other reactive oxygen species. Zinc-based nanoparticles (NPs) are among the most important and multifunctional compounds. Zinc oxide (ZnO) NPs exhibit attractive antimicrobial and photocatalytic properties due to the smaller particle size and increased particle surface reactivity. Further, these are more biocompatible compared to other metallic NPs, easily synthesizable, and have high selectivity, enhanced cytotoxicity, and are a promising anticancer agent. However, some of the pertinent concerns regarding nano-zinc still needs to be clarified. Current research also demonstrates their usage in wastewater treatment, textile, medicine, etc. This review covers the importance of zinc for living systems and its NPs, with more emphasis on ZnO NPs. A comprehensive overview of ZnO NPs, their synthesis, characterization techniques, crystal structure, properties, and brief industrial applications are presented.

Photocatalytic degradation of aqueous Methyl Orange using nitrogen-doped TiO2 photocatalyst prepared by novel method of ultraviolet-assisted thermal synthesis

A nitrogen-doped titanium dioxide composite photocatalyst (N-TiO₂) with heterojunction structures is synthesized by three different approaches: a novel UV-assisted thermal synthesis, annealing, and microwave technique. Photocatalytic activities of synthesized photocatalysts are evaluated by the degradation of Methyl Orange under ultraviolet light types A (UV-A), B (UV-B), and C (UV-C), visible light, and direct sunlight irradiation. Results show that by using N-TiO₂ photocatalyst prepared by the UV-assisted thermal synthesis and annealing, the degradation increases by 16.5% and 20.4%, respectively, compared to that by bare TiO₂. The best results are obtained at a nitrogen to TiO₂ mass ratio of 0.15 (N:TiO₂). The enhancement of the photocatalytic activity observed in the visible range is mainly attributed to the increasing separation rate of photogenerated charge carriers. The novel UV-assisted thermal synthesis has produced encouraging results as a preparation method for the nitrogen-doped TiO₂ photocatalyst; thus, further studies are recommended for process optimization, immobilization, and scale-up to evaluate its applicability in wastewater treatment.

Effect of the degree of inversion on optical properties of spinel ZnFe2O4

The effect of the degree of inversion on the electronic transitions and the Raman scattering of ZnFe₂O₄ is revealed.

ZnFe2O4 Nanotapers: Slag Assistant-Growth and Enhanced Photoelectrochemical Efficiency

In this study, ZnFe₂O₄ (ZFO) nanotapers are fabricated on the ZnO nanorods (NRs) by recycling rare-earth oxide (REO) slag as the iron source, which thereby exhibits dramatically enhanced photoelectrochemical (PEC) efficiency. Our studies demonstrate that the electron-hole separation and charge migration can be facilitated by the cascade band alignment of ZFO and ZnO and the branched nanotaper structures. Not only the iron source, the slag particles can also act as the passivation layers, leading to improved electron lifetime and significant PEC enhancement. The current study presents a novel REO-slag-modified PEC anode for high-efficiency PEC devices and offers a possibility of recycling industrial waste for renewable energy generation.

Fabrication of ternary reduced graphene oxide/SnS2/ZnFe2O4 composite for high visible-light photocatalytic activity and stability

Metal sulfides are promising photocatalysts for efficient removal of organic pollutants in wastewater. However, the practical application of these catalysts is limited due to the fast recombination of charge carriers and poor catalyst stability. In this study, ternary reduced graphene oxide/SnS₂/ZnFe₂O₄ (rGO/SnS₂/ZnFe₂O₄) composites were synthesized by a hydrothermal process, and rGO content was optimized. The surface morphology, crystal structure, optical and electrochemical properties of rGO/SnS₂/ZnFe₂O₄ composites were characterized. The adsorption capacity and visible-light photocatalytic activity of rGO/SnS₂/ZnFe₂O₄ were influenced by rGO content with results revealing an optimal rGO content of 7wt.%. The 7% rGO/SnS₂/ZnFe₂O₄ composite demonstrated the highest visible-light photocatalytic activity with almost 100% 2-nitrophenol removal, which could be attributed to the efficient charge separation, and the formation of O₂^-, h⁺ and a few OH radicals. The possible photocatalytic mechanism of rGO/SnS₂/ZnFe₂O₄ composites was also provided based on the role of rGO and the energy bands of SnS₂ and ZnFe₂O₄. Moreover, rGO/SnS₂/ZnFe₂O₄ composites exhibit excellent reusability without an obvious decline in the photocatalytic activity after four degradation-regeneration cycles. The results indicate that ternary rGO/SnS₂/ZnFe₂O₄ composites have good prospect in practical removal of organic pollutants in wastewater due to high efficiency and excellent stability.

Elevated photoelectrochemical activity of FeVO4/ZnFe2O4/ZnO branch-structures via slag assisted-synthesis

By recycling rare-earth slag as the iron source, FeVO₄/ZnFe₂O₄/REO core–shell–shell nanorods are fabricated on ZnO NRs and exhibit enhanced photoelectrochemical efficiency.