Enhanced photocatalytic activity of V₂O₅-ZnO composites for the mineralization of nitrophenols

High photocatalytic efficiency of a ZnO nanoplate/Fe2O3 nanospindle hybrid using visible light for methylene blue degradation

In this work, ZnO nanoplates and Fe2O3 nanospindles were successfully fabricated via a simple hydrothermal method using inorganic salts as precursors. The ZnO/Fe2O3 hybrid was fabricated using a mechanical mixture of two different ZnO : Fe2O3 weight ratios to investigate the effect of weight ratio on catalytic properties. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images showed that ZnO nanoplates (NPls) are about 20 nm thick with lateral dimensions of 100 × 200 nm, and Fe2O3 nanospindles (NSs) are about 500 nm long and 50 nm wide. X-ray diffraction (XRD) patterns revealed the successful formation of the ZnO, Fe2O3, and ZnO/Fe2O3 samples and indicated that their crystallite sizes varied from 20 to 29 nm depending on the ZnO : Fe2O3 weight ratio. Ultraviolet-visible (UV-vis) spectra showed that the bandgap energies of ZnO and Fe2O3 were 3.15 eV and 2.1 eV, respectively. Energy dispersive X-ray spectroscopy (EDS) results revealed the successful combination of ZnO and Fe2O3. Photocatalytic activity of the materials was evaluated through the degradation of methylene blue (MB) in aqueous solution under green light-emitting diode (GLED) irradiation. The results indicated that the ZnO/Fe2O3 composite showed a remarkable enhanced degradation capacity compared to bare ZnO NPls and Fe2O3 NSs. The ZnO : Fe2O3 = 3 : 2 sample demonstrated the best performance among all samples under identical conditions with a degradation efficiency of 99.3% for MB after 85 min. The optimum photocatalytic activity of the sample with ZnO : Fe2O3 = 3 : 2 was nearly 3.6% higher than that of the pure ZnO sample and 1.12 times more than that of the pristine Fe2O3 sample. Moreover, the highest photo-degradation was obtained at a photocatalyst dosage of 0.25 g l-1 in dye solution.

Sphere-shaped ZnO photocatalyst synthesis for enhanced degradation of the Quinolone antibiotic, Ofloxacin, under UV irradiation

The sphere-shaped zinc oxide (ZnO) photocatalyst was synthesized by the homogeneous precipitation method, using Zn(CH3COO)2·2H2O as a zinc precursor and NH4OH as a precipitating agent. The morphology and crystal structure of the prepared ZnO sample were studied by XRD, SEM, FT-IR, XPS, zeta potential measurements, and a low-temperature nitrogen adsorption-desorption technique. The optical characteristics of ZnO were determined by UV - Vis diffuse reflectance spectroscopy. ZnO photocatalyst performance of up to 100% within 210 min was observed in the photodegradation of the ofloxacin antibiotic under ultraviolet (UV) irradiation. The effect of antibiotic concentration, heavy metal ions, and water sources on the photocatalytic activity of ZnO demonstrated both the potential of its application under different conditions, and a good adaptability of this photocatalyst. The photodegradation reaction correlated well with the first-order kinetics model, with a rate constant of 0.0173 min-1. The reusability of the photocatalyst was verified after three cycles of use. Admittedly, photogenerated electrons and holes played a key role in removal of the antibiotic. This work showed the suitability of prepared ZnO for antibiotic removal, and its potential use for environmental protection.

Novel PWO/ ZnO heterostructured nanocomposites: Synthesis, characterization, and photocatalytic performance

Photocatalytic degradation is becoming an increasingly attractive method for addressing environmental remediation challenges. In this work, the novel pure PWO/ZnO and doped PWO: Er/ZnO: Ag heterostructure nanocomposites with premier photocatalytic efficiency were synthesized via a simple co-precipitation method followed by a solvothermal procedure. X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), high-resolution transmission electron microscopy (HRTEM), energy dispersive X-ray (EDX), and ultraviolet-visible (UV-Vis) absorbance measurements techniques were employed to characterize the structural and optical properties. HRTEM images prove the possibility of intimate contact formation at the pure and doped PWO/ZnO heterostructure nanocomposite interfaces. The photocatalytic performance of the PWO/ZnO heterostructure nanocomposites in the degradation of the methylene blue (MB) and methyl orange (MO) dyes under UVA light was evaluated. The photocatalysts' ability in the mineralization of organic pollutants was confirmed by the TOC test. BET and zeta potential analyses were used to study the dye adsorption mechanisms. Additionally, adsorption isotherms and kinetics have been investigated to describe the adsorption of MB and MO into the samples. The degradation rates of MB with PWO/ZnO and PWO: Er/ZnO: Ag heterostructure nanocomposites were 4.7 and 6.6 times higher than those of PWO and PWO: Er nanoparticles. This rate for MO degradation is 5.2 and 3.5 times higher than that of pure PWO and PWO: Er nanoparticles, respectively. This study outlines an easy method to develop innovative, highly effective heterostructure nanocomposites capable of converting UVA light into photocatalytic performance.

Controllable Synthesis of Cobalt-Containing Nanosheet Array-Like Ternary CuCoAl-LDH/rGO Hybrids To Boost the Catalytic Efficiency for 4-Nitrophenol Reduction

A series of Co-doped ternary Cu_xCo_3-xAl-layered double hydroxide (LDH)/rGO nanosheet array hybrids (x = 0.5, 1.0, 1.5, and 2.0) were successfully prepared using the preconditioned pH value aqueous-phase coprecipitation strategy. The Cu_xCo_3-xAl-LDH/rGO hybrids are featured as hexagonal CuCoAl-LDH nanosheets in situ anchoring onto both sides of the rGO surface in an ab-plane vertically interlaced growth pattern. The Cu_xCo_3-xAl-LDH/rGO hybrids show excellent activity for the complete conversion of 4-nitrophenol to 4-aminophenol, especially Cu_1.5Co_1.5Al-LDH/rGO with the highest k_app value of 49.2 × 10^-3 s^-1 and TOF of 232.8 h^-1, clearly higher than most copper-containing samples in the literature and even some precious ones. Thermodynamic analysis was carried out, and the values of Ea, ΔH^#, ΔS^#, and ΔG^# were estimated. The best activity of Cu_1.5Co_1.5Al-LDH/rGO can be mainly ascribed to the in situ-formed ultrafine Cu₂O NPs (∼4.3 nm) along with a small amount of Cu⁰ species, the electron transfer effect induced by atomically dispersed Co²⁺ species leading to the formation of electron-rich Cu species along with the Co²⁺/Co³⁺ redox couple, the strong Cu₂O-CuCoAl-LDH-rGO synergy upon the nanosheet array morphology with a high surface area and pore volume, and enhanced adsorption of reactants upon π-π stacking via an rGO layer. Meanwhile, the Cu_1.5Co_1.5Al-LDH/rGO exhibits an excellent universality and good cycling stability for 10 continuous runs. The Cu_1.5Co_1.5Al-LDH/rGO also shows superior efficiency in the catalytic reduction of 4-NP solution with a high concentration (20 mM) and displays excellent reduction performance in the fixed-bed test, implying the potential applications of the current Co-doped hierarchical ternary Cu-based LDH/rGO hybrids in the continuous treatment of practical wastewater.

Advanced Metal-Organic Frameworks-Based Catalysts in Electrochemical Sensors

Developing efficient catalysts is vital for the application of electrochemical sensors. Metal-organic frameworks (MOFs), with high porosity, large specific surface area, good conductivity, and biocompatibility, have been widely used in catalysis, adsorption, separation, and energy storage applications. In this invited review, the recent advances of a novel MOF-based catalysts in electrochemical sensors are summarized. Based on the structure-activity-performance relationship of MOF-based catalysts, their mechanism as electrochemical sensor, including metal cations, synthetic ligands, and structure, are introduced. Then, the MOF-based composites are successively divided into metal-based, carbon-based, and other MOF-based composites. Furthermore, their application in environmental monitoring, food safety control, and clinical diagnosis is discussed. The perspective and challenges for advanced MOF-based composites are proposed at the end of this contribution.

The role of size-controlled CeO2 nanoparticles in enhancing the stability and photocatalytic performance of ZnO in natural sunlight exposure

In order to enhance the photocatalytic performance and stability, the various proportions of the size controlled cerium oxide (CeO₂) nanoparticles were dispersed at the pre-synthesized ZnO. Although, the expected dual absorption onsets, probably due to the diminutive difference between the bandgaps of CeO₂ (∼2.9 eV) and ZnO (∼3.1 eV), were not observed however, a blue shift in the bandgap energy of ZnO was witnessed with the increasing surface density of CeO₂ particles. The delayed excitons recombination process with the increasing concentration of CeO₂ nanoparticles was verified by the PL spectra. The structural investigation by Raman and XRD analysis revealed the surface attachment of CeO₂ particles without altering the rock-salt lattice of ZnO. The morphological and fine microstructural analysis established the uniform distribution of evenly sized CeO₂ particles at the surface of ZnO with the discrete fringe patterns of both the entities whereas the XPS analysis confirmed the majority of Ce⁴⁺ in dispersed CeO₂. In comparison to pure ZnO, cyclic voltammetric (CV) analysis, under illumination, exposed the supportive role of surface residing CeO₂ particles in eradicating the photo-corrosion of ZnO whereas the chronopotentiometry (CP) predicted the prolonged life-span of the excitons. Compared to pure ZnO, an appreciably high activity was revealed for 10% CeO₂ loading as compared to pure ZnO for the removal of mono and di-nitrophenol derivatives and their mixtures under natural sunlight exposure. The variations in the removal rates in the mixture as compared to individual nitrophenol exposed the structure-based priority of ROS for the respective phenol. The significantly enhanced photocatalytic activity of the composite catalysts revealed the incremental role of surface-mounted CeO₂ entities in boosting the generation of ROS under sunlight irradiation. The experimental observations were correlated and compiled to establish the mechanism of the removal process.

Photocatalytic Degradation of Sulfamethoxazole, Nitenpyram and Tetracycline by Composites of Core Shell g-C3N4@ZnO, and ZnO Defects in Aqueous Phase

The synthesis of photocatalysts with high charge separation and transfer efficiency are of immense significance in the process of using photocatalysis technology for wastewater treatment. In this study core shell g-C₃N₄@ZnO, and ZnO defects photocatalysts presented an improved morphology in its characterization using techniques such as SEM, DRS, PL, MS, EIS, and XRD, and enhanced photodegradation of sulfamethoxazole, Nitenpyram and Tetracycline. Different composites were obtained as confirmed by the various characterization techniques studied, including core shell g-C₃N₄@ZnO, and ZnO defects photocatalyst. The synthesized photocatalysts showed high visible light absorption efficiency within a range of ~655 to 420 nm. Core shell g-C₃N₄@ZnO, and ZnO defects photocatalysts demonstrated high photocatalytic activity ascribed to high load separation and transition as shown in PL, Photocurrent reaction and EIS. It is understandable that core shell g-C₃N₄@ZnO, and ZnO defects photocatalysts have been confirmed to be one of the ultimate promising entrants for photocatalyst scheming.

The role of some metal ions in enhancement of photocatalytic activity of Fe2O3-V2O5 binary oxide

Fe₂O₃-V₂O₅ mixed oxides were synthesized with solid-state dispersion (SSD) and coprecipitation methods. In addition, transition metal oxides such as CuO, NiO, and CO₃O₄ were successfully loaded on the synthesized catalyst (Fe₂O₃-V₂O₅) using the SSD method. The composite catalysts were inspected for their photocatalytic activities in degrading 2,4-dichlorophenol under UV light enforcement. The produced samples were analyzed using X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy, photoluminescence, and the Brunauer–Emmett–Teller method. The addition of transition metal oxides improved the photocatalytic activity of Fe₂O₃-V₂O₅ (SSD). 1CuO wt% Fe₂O₃-V₂O₅ exhibited the highest percentage of 2,4-dichlorophenol degradation (100%) and the highest reaction rate (1.83 mg/L min) in 30 min. This finding is attributed to the distribution of CuO.

The efficacy of Co3O4 loaded WO3 sheets for the enhanced photocatalytic removal of 2,4,6-trichlorophenol in natural sunlight exposure

Owing to the promising photocatalytic performance, the sheet-like WO₃ was modified by depositing nanostructured Co₃O₄ at the surface. The appearance of the varying dual absorption edges in the optical analysis exposed the composite nature of the synthesized materials. The structural analysis revealed the deposition of Co₃O₄ particles at the surface without altering the lattice of WO₃ however, during the processing the cracking of disc was also evidenced. The FESEM and HRTEM analysis corroborated the uniform surface dispersion of Co₃O₄ nanoparticles. The co-existence of 2+ and 3+ oxidation states of Co in the deposited Co₃O₄ was examined by XPS analysis. The efficient trapping of excitons by Co₃O₄ surface entities was witnessed in the emission measurements whereas the same was authenticated by the photo-electrochemical chronopotentiometry. The Co₃O₄ loaded sheets exhibited substantially enhanced activity for the removal of 2,4,6-trichlorophenol as compared to pure WO₃ in the complete spectrum and visible region of natural sunlight exposure. The progress of the degradation process was monitored by HPLC whereas the degradation products were identified by GC-MS. The measurement and identification of the ion released during the photocatalytic process facilitated the estimation of the probable route and role of reactive oxygen species involved in the removal process. Although, the careful analysis of the findings from the analytical tools revealed the major involvement of hydroxyl radicals however, the role of superoxide anions was also exposed. An alternative mechanism of the generation of the superoxide radical involving the 2+ and 3+ oxidation states of Co was also proposed. The effect of the pH and the added concentration of H₂O₂ on the ease of removal process was also investigated.

Facile green synthesis of Ag-Cu decorated ZnO nanocomposite for effective removal of toxic organic compounds and an efficient detection of nitrite ions

A facile and eco-friendly green synthesis of silver-copper@zinc oxide (Ag-Cu@ZnO) nanocomposite using Acacia caesia flower extract and their application on catalytic reduction of toxic compounds and electrochemical sensing of nitrite ions are reported. The phytochemicals present in the extract were utilized for the Ag-Cu metal nanoparticles synthesis and also enhanced the binding capability between ZnO and Ag-Cu NPs. The synthesized nanocomposites were characterized by XRD, UV-Vis spectroscopy, Raman spectra, FTIR, SEM, TEM, EDX, XPS and ICP-AES for the formation of Ag-Cu NPs on ZnO. The Ag-Cu@ZnO nanocomposite showed better catalytic efficiency as compared to monometallic nanoparticles for 4-nitrophenol to 4-aminophenol conversion and Rhodamine B and Congo red dye degradation with 99% efficiency up to four cycles. The Ag-Cu@ZnO modified GC electrode showed enhanced catalytic activity towards nitrite oxidation, and it exhibited better performance compared to the other nanocomposites. An appreciable detection limit (17 μM) was achieved with excellent sensitivity for nitrite detection. The sensor was highly selective even in a many-fold higher concentration of co-existing interfering compounds. The good catalytic and electrochemical sensing is mainly ascribed due to the synergistic effect of Ag-Cu on the ZnO in the Ag-Cu@ZnO nanocomposite materials.

Zinc oxide/vanadium pentoxide heterostructures with enhanced day-night antibacterial activities

Low photocatalytic efficiency of visible light and fast recombination of photo-generated carriers are two challenges facing the applications of photocatalyst sterilant zinc oxide (ZnO). Meanwhile, both light and dark photocatalytic activities are important. It is of great theoretical and practical significance to construct a day-night photocatalytic antibacterial material, which is beneficial to the effective use of energy and to tackle the limitation of using photocatalytic bacteriostat. ZnO nanoflowers decorated vanadium pentoxide (V₂O₅) nanowires heterojunction (ZVH) was firstly fabricated using a facile water-bathing method. The designed ZVH structure efficiently produced abundant reactive oxygen species (ROS) in both light and darkness. It yielded 99.8% and 99.0% of antibacterial rate against S. aureus due to oxidative stress induced by ROS in light and darkness, respectively. The generation of ROS played a major role in the antibacterial activities against S. aureus under both light and dark conditions. The prepared ZVH with improved antibacterial properties provides an alternative for day-night antibacterial agents.

Facile and scalable production of heterostructured ZnS-ZnO/Graphene nano-photocatalysts for environmental remediation

A facile and eco-friendly strategy is described for the synthesis of ZnS-ZnO/graphene heterostructured nano-photocatalysts for the first time. This solvent-free and technologically scalable method involves solid-state mixing of graphite oxide (GO), Zn salt and surfeit yet non-toxic elemental sulfur using ball-milling followed by thermal annealing. The as-formed hybrids are composed of uniformly distributed in-situ formed ZnS-ZnO nanoparticles simultaneously within the thermally reduced GO (graphene) matrix. A series of hybrid compositions with varying content of ZnS/ZnO and graphene were prepared and thoroughly characterized. Further, the effect of heterostructure composition on the photocatalytic properties was investigated under visible-light illumination. The synergistic ZnS-ZnO/graphene hybridization promoted the band-gap narrowing compared to the pristine ZnS nanoparticles. The ZnS:ZnO composition was controlled by graphite oxide under thermal treatment and observed to be a crucial factor in enhancement of photocatalytic activity. As a proof of concept, the phase optimized and surface enhanced ZnS-ZnO/graphene nano-photocatalysts was tested towards visible light driven photocatalytic degradation of environmentally harmful organic dyes and toxic phenol molecules from aqueous media. The presented cost-effective strategy provides high potential in large-scale production of heterostructured nano-photocatalysts for environmental remediation and photocatalytic greener production of hydrogen.

Enhancement Photocatalytic Activity of the Heterojunction of Two-Dimensional Hybrid Semiconductors ZnO/V2O5

In this work, we report the fabrication of the new heterojunction of two 2D hybrid layered semiconductors—ZnO (stearic acid)/V2O5 (hexadecylamine)—and its behavior in the degradation of aqueous methylene blue under visible light irradiation. The optimal photocatalyst efficiency, reached at a ZnO (stearic acid)/V2O5 (hexadecylamine) ratio of 1:0.25, results in being six times higher than that of pristine zinc oxide. Reusability test shows that after three photocatalysis cycles, no significant changes in either the dye degradation efficiency loss, nor the photocatalyst structure, occur. Visible light photocatalytic performance observed indicates there is synergetic effect between both 2D nanocomposites used in the heterojunction. The visible light absorption enhancement promoted by the narrower bandgap V2O5 based components; an increased photo generated charge separation favored by extensive interface area; and abundance of hydrophobic sites for dye adsorption appear as probable causes of the improved photocatalytic efficiency in this hybrid semiconductors heterojunction. Estimated band-edge positions for both conduction and valence band of semiconductors, together with experiments using specific radical scavengers, allow a plausible photodegradation mechanism.

The highly selective oxidation of cyclohexane to cyclohexanone and cyclohexanol over VAlPO4 berlinite by oxygen under atmospheric pressure

Background

The oxidation of cyclohexane under mild conditions occupies an important position in the chemical industry. A few soluble transition metals were widely used as homogeneous catalysts in the industrial oxidation of cyclohexane. Because heterogeneous catalysts are more manageable than homogeneous catalysts as regards separation and recycling, in our study, we hydrothermally synthesized and used pure berlinite (AlPO₄) and vanadium-incorporated berlinite (VAlPO₄) as heterogeneous catalysts in the selective oxidation of cyclohexane with molecular oxygen under atmospheric pressure. The catalysts were characterized by means of by XRD, FT-IR, XPS and SEM. Various influencing factors, such as the kind of solvents, reaction temperature, and reaction time were investigated systematically.

Results

The XRD characterization identified a berlinite structure associated with both the AlPO₄ and VAlPO₄ catalysts. The FT-IR result confirmed the incorporation of vanadium into the berlinite framework for VAlPO₄. The XPS measurement revealed that the oxygen ions in the VAlPO₄ structure possessed a higher binding energy than those in V₂O₅, and as a result, the lattice oxygen was existed on the surface of the VAlPO₄ catalyst. It was found that VAlPO₄ catalyzed the selective oxidation of cyclohexane with molecular oxygen under atmospheric pressure, while no activity was detected on using AlPO₄. Under optimum reaction conditions (i.e. a 100 mL cyclohexane, 0.1 MPa O₂, 353 K, 4 h, 5 mg VAlPO₄ and 20 mL acetic acid solvent), a selectivity of KA oil (both cyclohexanol and cyclohexanone) up to 97.2% (with almost 6.8% conversion of cyclohexane) was obtained. Based on these results, a possible mechanism for the selective oxidation of cyclohexane over VAlPO₄ was also proposed.

Conclusions

As a heterogeneous catalyst VAlPO₄ berlinite is both high active and strong stable for the selective oxidation of cyclohexane with molecular oxygen. We propose that KA oil is formed via a catalytic cycle, which involves activation of the cyclohexane by a key active intermediate species, formed from the nucleophilic addition of the lattice oxygen ion with the carbon in cyclohexane, as well as an oxygen vacancy formed at the VAlPO₄ catalyst surface.

Electronic supplementary material

The online version of this article (10.1186/s13065-018-0405-6) contains supplementary material, which is available to authorized users.

Photocatalytic activity of V doped ZnO nanoparticles thin films for the removal of 2- chlorophenol from the aquatic environment under natural sunlight exposure

Vanadium doped ZnO powders were used as precursors to deposit thin films of V(5+) incorporated ZnO nanoparticles on glass substrates by the pulsed laser deposition technique. The observed variations in Raman signals, visible region shift in the diffuse reflectance spectra along with a small shift in the (101) reflections of the X-ray diffraction (XRD) confirmed the insertion of V(5+) ions in ZnO lattice. No other additional reflection in the XRD results other than ZnO further endorsed the occupation of lattice positions by V entities rather than independent oxide formation. The asymmetric XPS peaks of Zn2p and V2p core levels confirmed the existence of both in the vicinity. The existence of minimal proportion of V(3+) along with V(5+) states varied the alteration of the oxidation states V in the synthetic route. The SEM images at various resolutions displayed the uniform distribution identical nanoparticles without the presence of additional phases in the deposited films. The SEM cross-section measurements revealed the uniform thickness of ∼90 nm of each film, whereas the surface studies of the films were performed by AFM. The as-synthesized films were tested for photocatalytic activity in sunlight illumination for the removal of 2-chlorophenol. The unique feature of the study was the estimation of the photocatalytic activity 20 ppm of 2-chlorophenol by exposing the low exposed area. The degradation of the substrate was measured by liquid phase UV-vis spectroscopy, whereas total organic carbon measurement revealed the mineralization of the substrate. The released Cl(-) ions were also measured by ion chromatography. The estimated flatband potentials and pHzpc values of the V doped materials, by Mott-Schottky analysis and zeta potential measurements respectively, were correlated with the photocatalytic activity. The kinetics of the photocatalytic degradation/mineralization process was estimated and results were correlated with the plausible mechanism.

Visible-light-driven photodegradation of sulfamethoxazole and methylene blue by Cu2O/rGO photocatalysts

The cuprous oxide-reduced graphene oxide (Cu2O/rGO-x) composites were prepared via a simple wet-chemical method by using CuSO4·5H2O and graphene oxide as precursors and ascorbic acid as a reducing agent, respectively. These Cu2O/rGO-x were employed as photocatalysts for degrading emerging contaminants and organic dye pollutants (i.e., sulfamethoxazole (SMX) and methylene blue (MB)) under visible light. A variety of different spectroscopic and analytical techniques, such as X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, Raman scattering spectroscopy and UV-Visible spectroscopy were used to characterize the physical properties of photocatalysts. In the photodegrading experiments, it can be found that the Cu2O/rGO-80 photocatalyst has the superior visible-light response of ca. 50% removal efficiency of SMX within 120 min and 100% removal efficiency of MB within 40 min. These observations may be attributed the well-dispersed and visible-light-responsive Cu2O nanoparticles are supported on the surface of rGO sheets that can enhance absorption of visible light during photocatalysis.

The effect of cerium alteration on the photocatalytic performance of WO3 in sunlight exposure for water decontamination

In an effort to enhance the photocatalytic activity of cubic WO₃ in sunlight exposure, its surface was modified by impregnating the Ce³⁺ ions ranging from 1% to 25% with a step of 5% with respect to the weight of WO₃.

Synthesis, Characterization, and Sunlight Mediated Photocatalytic Activity of CuO Coated ZnO for the Removal of Nitrophenols

CuO@ZnO core-shell catalysts, coated by varying the CuO layer density ranging from 0.5% to 10%, were synthesized with the aim to enhance the photocatalytic activity of ZnO in sunlight and control its photocorrosion. Initially, the Cu(2+) ions were impregnated on presynthesized ZnO by wet impregnation and finally converted to CuO layers by calcination. The optical and structural characterization of the synthesized powders was performed by DRS, PL, Raman spectroscopy, and XRD analysis, respectively. The homogeneity of the coated layers was explored by FESEM. The photocatalytic activity of CuO coated ZnO was investigated for the degradation of mononitrophenols (2-, 3-, and 4-nitrophenol) and dinitrophenols (2,4-, 2,5-, and 2,6-dinitrophenol) in the exposure of the complete spectrum and visible region (420-800 nm) of sunlight. The effect of the increasing density coated layers of CuO on photocatalytic activity was evaluated for the degradation of 4-NP. Compared to pristine ZnO, a substantial increase in the degradation/mineralization ability was observable for the catalysts coated with 0.5% and 1% CuO, whereas a detrimental effect was noticed for higher coating density. Prior to photocatalytic studies, as evaluated by cyclic voltammetry (CV), compared to pure ZnO, a significant suppression of photocorrosion was noticed, under illumination, for catalysts coated with lower CuO coating. The progress of the photocatalytic degradation process was monitored by HPLC while the mineralization ability of the synthesized catalysts was estimated by TOC. The estimation of the released ions and their further interaction with the excited states and the reactive oxygen was monitored by ion chromatography (IC).

Evaluation of sunlight induced structural changes and their effect on the photocatalytic activity of V2O5 for the degradation of phenols

Despite knowing the fact that vanadium pentoxide is slightly soluble in aqueous medium, its photocatalytic activity was evaluated for the degradation of phenol and its derivatives (2-hydroxyphenol, 2-chlorophenol, 2-aminophenol and 2-nitrophenol) in natural sunlight exposure. The prime objective of the study was to differentiate between the homogeneous and heterogeneous photocatalysis incurred by dissolved and undissolved V2O5 in natural sunlight exposure. V2O5 was synthesized by chemical precipitation procedure using Triton X-100 as morphology mediator and characterized by DRS, PLS, Raman, FESEM and XRD. A lower solubility of ∼ 5% per 100ml of water at 23 °C was observed after calcination at 600 °C. The study revealed no contribution of the dissolved V2O5 in the photocatalytic process. In sunlight exposure, V2O5 powder exhibited substantial activity for the degradation, however, a low mineralization of phenolic substrates was observed. The initial low activity of V2O5 followed by a sharp increase both in degradation and mineralization in complete spectrum sunlight exposure, was further investigated that revealed the decrease in the bandgap and the reduction in the particle size with the interaction of UV photons (<420 nm) as this effect was not observable in the exposure of visible region of sunlight. The role of the chemically different substituents attached to an aromatic ring at 2-positions and the secondary interaction of released ions during the degradation process with the reactive oxygen species (ROS) was also explored.

Synthesis, characterization and visible light photocatalytic activity of Cr3+, Ce3+and N co-doped TiO2for the degradation of humic acid

The synthesis, characterization and photocatalytic activity of Cr³⁺and Ce³⁺co-doped TiON (N-doped TiO₂) for the degradation of humic acid with exposure to visible light is reported.