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The monoclinic nanocrystalline Ni1−xMnxWO4 heterostructure has been successfully synthesized by the hydrothermal technique for achieving better sensitive and photocatalytic performances. Different characterization techniques such as X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV–Vis), and photoluminescence (PL) spectroscopy have been employed to investigate their structural, microstructural, and optical properties. Mn-ion incorporation in the NiWO4 lattice reduces the particle size of the sample compared with the pure undoped NiWO4 sample, which has been confirmed from the transmission electron microscope image. The Tauc plot of the Ni1−xMnxWO4 sample exhibits a significant decrease in bandgap energy compared with the pure undoped NiWO4 sample due to the quantum confinement effect. Finally, the material was explored as a photocatalyst for the degradation of methyl orange (MO) dye from wastewater under visible light irradiation. Various reaction parameters such as pH, catalyst dose, reaction time, and kinetics of the photodegradation were studied using the batch method. The results showed that the Ni1−xMnxWO4 is highly efficient (94.51%) compared with undoped NiWO4 (65.45%). The rate of photodegradation by Ni1–xMnxWO4 (0.067) was found to be 1.06 times higher than the undoped NiWO4 (0.062). [ABSTRACT FROM AUTHOR]

Abstract Carbonated hydroxyapatite (CHAp) material was prepared from calcite and phosphate‐containing solution using the wet chemical precipitation method. The CHAp material was used to remove methylene blue (MB) from simulated contaminated water and further degraded the MB with the help of visible light (VL). The structure of the CHAp was characterized using X‐ray diffractometry, infrared spectroscopy, Branuer–Emmett–Teller analysis, and scanning electron microscopy, while the energy bandgap, Eg, reaction rate constant and MB removal/degradation efficiencies were studied using UV‐Vis spectroscopy. The characterization data revealed that the CHAp was a type‐B carbonate‐substituted hydroxyapatite material with a nonmicroporous network with an Eg of 2.26–2.82 eV. The Eg allowed VL entrapment that resulted in reactive free radicals that degraded the MBs in the CHAp. The reaction rate constant, K, and removal efficiencies, R, were modeled using the exponential decay function and descriptive statistics (DS), respectively. In close approximation, the K values of the reaction under VL were doubled when compared to the reaction under dark conditions. Under dark and under VL efficiencies, the DS showed a negative and zero skewness for MB removal by CHAp, respectively. The findings show that VL exposure on the CHAp causes a faster reaction rate constant and a higher MB removal efficiency within the time constraints, which would revolutionize dye removal from water industries in terms of cost‐effectiveness.

Chitosan was used in the sol-gel synthesis of zinc oxide nanoparticles (ZnO NPs) as a capping agent in order to control the size, morphology, optical bandgap, photocatalytic efficiency, and antimicrobial activity. Different chitosan sources were used for the sol-gel synthesis of ZnO NPs, namely chitosan of shrimp shells, crab shells, and Streptomyces griseus bacteria. The photocatalytic efficiency was studied by using the methylene blue (MB) photodegradation test, and the antibacterial activity of the different types of ZnO NPs was investigated by the agar well diffusion technique. The particle size of ZnO NPs varied between 20 and 80 nm, and the band gap energy ranged between 2.7 and 3.2 eV. Due to the different chitosan sources, the ZnO NPs showed different antibacterial activity against Listeria innocua, Bacillus Subtiliis, Staphylococcus Aureus, Salmonella Typhimurium and Pseudomonas Aeruginosa. The ZnO NPs with lower band gap values showed better antibacterial results compared to ZnO NPs with higher band gap values. The MB dye removal of ZnO (shrimp shells), ZnO (crab shells), and ZnO (Streptomyces griseus) reached 60%, 56%, and 44%, respectively, at a contact time of 60 min, a low initial MB dye concentration of 6 × 10−5 M, a solution temperature of 25 °C, and a pH = 7. [ABSTRACT FROM AUTHOR]

Carbonated hydroxyapatite (CHAp) material was prepared from calcite and phosphate‐containing solution using the wet chemical precipitation method. The CHAp material was used to remove methylene blue (MB) from simulated contaminated water and further degraded the MB with the help of visible light (VL). The structure of the CHAp was characterized using X‐ray diffractometry, infrared spectroscopy, Branuer–Emmett–Teller analysis, and scanning electron microscopy, while the energy bandgap, Eg, reaction rate constant and MB removal/degradation efficiencies were studied using UV‐Vis spectroscopy. The characterization data revealed that the CHAp was a type‐B carbonate‐substituted hydroxyapatite material with a nonmicroporous network with an Eg of 2.26–2.82 eV. The Eg allowed VL entrapment that resulted in reactive free radicals that degraded the MBs in the CHAp. The reaction rate constant, K, and removal efficiencies, R, were modeled using the exponential decay function and descriptive statistics (DS), respectively. In close approximation, the K values of the reaction under VL were doubled when compared to the reaction under dark conditions. Under dark and under VL efficiencies, the DS showed a negative and zero skewness for MB removal by CHAp, respectively. The findings show that VL exposure on the CHAp causes a faster reaction rate constant and a higher MB removal efficiency within the time constraints, which would revolutionize dye removal from water industries in terms of cost‐effectiveness. [ABSTRACT FROM AUTHOR]

One of the strategies to decrease the bandgap energy and increase the optical absorption of the catalysts is to dope with transition metal ions. In this paper, the results obtained for the degradation of methylene blue (MB) pollutant in the presence of M2+ (M = Ni, Cu, and Zn) doped KTaTeO6 (M-KTTO) upon visible light irradiation are presented. The parent KTaTeO6 and the M-KTaTeO6 were prepared by solid-state and ion-exchange methods, respectively. All the samples were characterized by XRD, SEM/EDX, FT-IR, UV-vis DRS, XPS, and PL techniques. The metal ion doping in place of K+ has influenced the electronic and optical properties considerably. The doping of M2+ into KTTO lattice has narrowed the bandgap energy, increased the visible light absorbance leading to higher photocatalytic activity. The M-KTTO materials show higher photocatalytic activity compared to parent KTTO, particularly Cu-KTTO. The scavenging experiments indicate that •OH radicals are the main active species involved in the photodegradation of MB. The Cu-KTTO is chemically stable and can be used for at least up to five cycles. The mechanistic pathway of MB degradation was proposed over Cu-KTTO. [ABSTRACT FROM AUTHOR]

The urea-modified ZnWO4 samples were synthesized by hydrothermal method. Urea was used as a nitrogen source. These materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FT-IR), and UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS). Photocatalytic properties of urea-modified ZnWO4 was studied and compared with its parent ZnWO4. Urea-modified ZnWO4 (10 mol%) has shown higher photocatalytic activity in the degradation of methylene blue under the visible light irradiation. Participation of holes, hydroxyl radicals, and super oxide radicals in the photocatalytic dye degradation was investigated. [ABSTRACT FROM AUTHOR]

The photocatalytic activity of isomorphously substituted transition metal (TM) ions into the vanadosilicate AM-6 framework, at TM/V ratios of 0.025-0.10, has been investigated. All 0.025TM-substituted AM-6 products showed enhanced photocatalytic activity under UV light irradiation which was attributed to the bandgap photoexcitation of these products. The photocatalytic activity decreased with increasing TM concentrations (TM > 0.025). Under visible light irradiation, only 0.025Cr-AM-6 showed enhanced photocatalytic activity ( k = 4.6 × 10 −3 min −1 ± 4.0 × 10 −4 min −1 ). This was attributed to the electron excitation for the interfacial charge-transfer in the visible light region. 0.025Fe-AM-6 ( k = 3.1 × 10 −3 min −1 ± 4.0 × 10 −4 min −1 ), 0.025Co-AM-6 ( k = 3.4 × 10 −3 min −1 ± 6.0 × 10 −4 min −1 ), and unmodified AM-6 ( k = 2.9 × 10 −3 min −1 ± 7.0 × 10 −4 min −1 ) were inactive towards the photodegradation of methylene blue under visible light irradiation (direct photolysis k = 2.8 × 10 −3 min −1 ± 4.0 × 10 −4 min −1 ). This was likely attributed to the ineffectiveness of the electron excitation for the interfacial charge-transfer, as suggested by the UV–vis spectroscopic analyses. [ABSTRACT FROM AUTHOR]

Brannerite-type layered vanadomolybdate, KVMoO6, was synthesized by sol-gel method using ethylene glycol as gelating agent. Its silver- and nitrogen-doped analogues were prepared by ion exchange and solid state methods, respectively. All compounds were characterized by powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), Fourier transform IR spectroscopy (FT-IR), and UV-vis diffuse reflectance spectra. The bandgap energy of all compounds was obtained from their diffuse reflectance spectra. Bandgap was reduced considerably upon silver and nitrogen doping in KVMoO6. The photocatalytic activity of parent and doped samples was studied by degradation of methylene blue. The nitrogen-doped KVMoO6 shows higher photocatalytic activity against the degradation of methylene blue. The stability and reusability of the nitrogen-doped KVMoO6 were investigated. N-doped KVMoO6 is a potential catalytic material for cleaning wastewater. [ABSTRACT FROM AUTHOR]

Quaternary oxides containing transition metal and tungsten with the general formula AMWO 6 ( A = K, Rb, Cs; M = Sb, Nb, Ti) have been studied as photocatalysts for decomposition of organic dyes. In this paper, defect pyrochlore of composition KTi 0.5 W 1.5 O 6 was prepared via facile sol–gel method. Its nitrogen and tin doped analogues were prepared by solid state and ion exchange methods respectively. All compounds were characterized by powder X-ray diffraction, Thermogravimetric analysis, FT-IR, Raman, Scanning electron microscopy and UV–Vis diffuse reflectance spectra. X-ray photoelectron spectroscopy and energy dispersive spectroscopy were also used to characterize the incorporation of doped ions into the defect pyrochlore lattice. The photocatalytic activity of all compounds was studied by degradation of methylene blue and Rhodamine B. The tin doped KTi 0.5 W 1.5 O 6 shows higher photocatalytic activity against both the dyes. The experimental results show that the higher photocatalytic activity of tin doped KTi 0.5 W 1.5 O 6 is due to more absorption of light energy in the visible region attributable to the lowering of bandgap energy. Further, the role of reactive intermediate species in the photocatalytic degradation of dyes was studied using their appropriate scavengers and the obtained results show that OH radicals produced in the photocatalytic reaction play dominant role. [ABSTRACT FROM AUTHOR]

Nano sized defect pyrochlores of compositions KCrWO and ACrWO· nHO (A = Sn, Ag, Bi, Sm, Eu, and Gd) have been synthesized by sol-gel and ion exchange methods, respectively. These oxides were characterized by thermogravimetric analysis, powder X-ray diffraction, energy dispersive spectra, transmission electron microscopy, UV-Vis diffuse reflectance spectra, Raman spectra, and Fourier transform infrared spectra. Spontaneous exchange of K with A ion is accompanied by insertion of water also into the lattice. KCrWO and ACrWO· nHO crystallize in cubic lattice and isomorphous with KSbWO. The optical properties of Cr were investigated. Substitution of K by A ion leads to a shift of absorption onset to longer wavelengths marginally. The Raman spectra of all the samples are characteristic of defect pyrochlore system. The photocatalytic degradation of methylene blue aqueous solution was investigated using these oxides. The results obtained were fitted with the Langmuir-Hinshelwood model to study the degradation kinetics. Both Sn and Bi-doped KCrWO exhibit higher photoactivity in the degradation of methylene blue. The structure/composition of the photocatalyst remains the same even after fourth cycle of photodegradation. [ABSTRACT FROM AUTHOR]

In this study, a TiO2 catalyst, modified with tungsten oxide (WO3), was synthesized to reduce its bandgap energy (Eg) and to improve its photocatalytic performance. For the catalyst evaluation, the effect of the calcination temperature on the solar photocatalytic degradation was analyzed. The experimental runs were carried out in a CPC (compound parabolic collector) pilot-scale solar reactor, following a multilevel factorial experimental design, which allowed analysis of the effect of the calcination temperature, the initial concentration of amoxicillin, and the catalyst load on the amoxicillin removal. The most favorable calcination temperature for the catalyst performance, concerning the removal of amoxicillin, was 700 °C; because it was the only sample that showed the rutile phase in its crystalline structure. Regarding the loss of the antibiotic activity, the inhibition tests showed that the treated solution of amoxicillin exhibited lower antibacterial activity. The highest amoxicillin removal achieved in these experiments was 64.4% with 100 ppm of amoxicillin concentration, 700 °C of calcination temperature, and 0.1 g L−1 of catalyst load. Nonetheless, the modified TiO2/WO3 underperformed compared to the commercial TiO2 P25, due to its low specific surface and the particles sintering during the sol-gel synthesis. [ABSTRACT FROM AUTHOR]