White-light emission in Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-dopedα-NiMoO4nanoparticles.

Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-dopedα-NiMoO4nanoparticles were synthesized using a microwave hydrothermal method and studied for white-light emission under 980 nm laser diode excitation. White upconversion (UC) light was successfully obtained with the appropriate control of blue, green, and red emissions by successfully tuning the Er3+and Ho3+concentrations in Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-dopedα-NiMoO4, respectively. In addition, the white color emission was shown by the CIE chromaticity coordinates of samples. The energy transfer mechanisms are explained in detail based on the emission spectra and pump power density-dependent UC luminescence intensity in rare earth (Yb3+/Er3+/Tm3+and Yb3+/Er3+/Tm3+/Ho3+)-dopedα-NiMoO4nanoparticles. The results indicate that Yb3+/Er3+/Tm3+- and Yb3+/Er3+/Tm3+/Ho3+-dopedα-NiMoO4nanoparticles can be good candidates for white-light devices.

A critical review on modulation of NiMoO4-based materials for photocatalytic applications.

Semiconductor photocatalysis has been widely utilized to solve the problems of energy shortage and environmental pollution. Among the explored photocatalysts, nickel molybdate (NiMoO4) has revealed many advantages for photocatalytic applications, which include visible light absorption, low cost, environment-friendly, large surface area, good electrical conductivities, and tailorable band structure. However, the recombination of photogenerated carriers, which diminishes photocatalytic efficiency, has been held as a major hurdle to the widespread application of this material. To overcome this limitation, various surface modulations such as morphology control, doping of heteroatom, deposition of noble metal nanoparticles, and fabrication of composite structures have been explored in many published studies. This article comprehensively reviews the recent progress in the modulations of NiMoO4-based materials to improve the photocatalytic efficiency. The enhanced photocatalytic capabilities of NiMoO4-based materials are reviewed in terms of such applications as pollutant removal, disinfection of bacteria, and water splitting. The current challenges and possible future direction of research in this field are also highlighted. This comprehensive review is expected to advance the design of highly efficient NiMoO4-based materials for photocatalytic applications.

A critical review on strategies for improving efficiency of BaTiO3-based photocatalysts for wastewater treatment.

Barium titanate (BaTiO3) photocatalysts with perovskite structures are promising candidates for the effective removal of hazardous organic pollutants from water/wastewater owing to several advantages, including low cost, non-toxicity, high stability, environmental friendliness, favorable band positions, high oxygen vacancies, multiple crystal phases, rapid migration of charge carriers at the surface, band bending, spontaneous polarization, and easy tailoring of the sizes and morphologies. However, this high dielectric/ferroelectric material is only active in UV light (band gap: 3.2 eV), which reduces the photocatalytic degradation performance. To make barium titanate more suitable for photocatalysis, the surfaces of the powders can be modified to broaden the absorption band. In this paper, various strategies for improving photocatalysis of barium titanate for removing organic pollutants (mostly dyes and drugs) from water/wastewater are critically reviewed. They include modifying the sizes and morphologies of the particles by varying the reaction times and synthesis temperatures, doping with metals/non-metals, loading with noble metal NPs (Ag and Au), and fabrication of heterojunction photocatalysts (conventional type II and Z-scheme). The current challenges and possible future directions of BaTiO3-based materials are also discussed. This comprehensive review is expected to advance the design of highly efficient BaTiO3-based materials for photocatalytic applications in water/wastewater treatment.

Morphologies controlled ZnO for inactivation of multidrug-resistant Pseudomonas aeruginosa in solar light.

The different morphology and size of the zinc oxide (ZnO) were synthesized by a co-precipitation process via variation of calcination temperature from 400 °C to 900 °C. The nanorod, flower, hexagon, pentagon, and microflambeau morphologies were obtained. The flower morphology of ZnO tends to inactivate multidrug-resistant Pseudomonas aeruginosa (P. aeruginosa) completely within 45 min under solar light irradiation better than other morphologies due to efficient separation electron-hole pairs. The prevention of charge recombination was confirmed by transient photocurrent response and electrochemical impedance spectra measurements. Electron spin resonance spectroscopy suggests that [Formula: see text] OH·, and h+ are responsible for P. aeruginosa inactivation in solar light. Furthermore, P. aeruginosa inactivation was confirmed by transmission electron microscope (TEM) images, DNA fragmentation (gel electrophoresis) and protein degradation (Bradford assay). The TEM mapping illustrates the damage of bacteria by active species but not the release of Zn2+ ions in the bacterial cell. So, this work provides a detailed investigation of morphology/size-dependent photocatalytic inactivation of a multidrug-resistant pathogen in solar light.

Upconversion luminescence properties of BaMoO4: Yb3+, Ln3+ (Ln3+ = Er3+/Tm3+, Er3+/Tm3+/Ho3+) micro-octahedrons.

Yb3+, Ln3+ (Ln3+ = Er3+/Tm3+, Er3+/Tm3+/Ho3+) doped BaMoO4 micro-octahedrons were synthesized by a hydrothermal process. The as-prepared phosphors were characterized by x-ray powder diffraction, field emission scanning electron microscopy, elemental mapping, energy-dispersive x-ray spectroscopy, x-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. The upconversion luminescence properties of the samples were investigated under 980 nm near infrared excitation. The different concentrations of Er3+, Tm3+, and Ho3+ were used for tuning the multicolor (blue, green, and red) emissions. The multicolor emissions were investigated by Commission Internationale de l'Elcairage chromaticity and decay lifetime. The photon process as well as the energy transfer mechanism between the Yb3+ to Er3+, Tm3+, and Ho3+ were described.

Decoration of Ag nanoparticles on CoMoO4 rods for efficient electrochemical reduction of CO2.

Hydrothermal and photoreduction/deposition methods were used to fabricate Ag nanoparticles (NPs) decorated CoMoO4 rods. Improvement of charge transfer and transportation of ions by making heterostructure was proved by cyclic voltammetry and electrochemical impedance spectroscopy measurements. Linear sweep voltammetry results revealed a fivefold enhancement of current density by fabricating heterostructure. The lowest Tafel slope (112 mV/dec) for heterostructure compared with CoMoO4 (273 mV/dec) suggested the improvement of electrocatalytic performance. The electrochemical CO2 reduction reaction was performed on an H-type cell. The CoMoO4 electrocatalyst possessed the Faraday efficiencies (FEs) of CO and CH4 up to 56.80% and 19.80%, respectively at - 1.3 V versus RHE. In addition, Ag NPs decorated CoMoO4 electrocatalyst showed FEs for CO, CH4, and C2H6 were 35.30%, 11.40%, and 44.20%, respectively, at the same potential. It is found that CO2 reduction products shifted from CO/CH4 to C2H6 when the Ag NPs deposited on the CoMoO4 electrocatalyst. In addition, it demonstrated excellent electrocatalytic stability after a prolonged 25 h amperometric test at - 1.3 V versus RHE. It can be attributed to a synergistic effect between the Ag NPs and CoMoO4 rods. This study highlights the cooperation between Ag NPs on CoMoO4 components and provides new insight into the design of heterostructure as an efficient, stable catalyst towards electrocatalytic reduction of CO2 to CO, CH4, and C2H6 products.

Magnetic visible-light activated photocatalyst ZnFe2O4/BiVO4/g-C3N4 for decomposition of antibiotic lomefloxacin: Photocatalytic mechanism, degradation pathway, and toxicity assessment.

Magnetic ZnFe2O4/BiVO4/g-C3N4 (ZBC) composites were prepared via a facile hydrothermal and calcination method for the degradation of a representative antibiotics lomefloxacin (LFX) under visible light irradiation. The optimal photocatalyst ZBC-10 with a ZnFe2O4:BiVO4:g-C3N4 mass ratio of 1:8:10 performed 96.1% removal of LFX after 105 min of illumination. The excellent performance is ascribed to the effective construction of heterojunctions and its capacity to form a double Z-scheme charge transmission pathway among the hosts in ZBC-10. The composite enhanced the separation and migration of photoexcited charge carriers and the effective generation of multiple active radicals including ·OH, ·O2-, and 1O2. The LFX degradation process, identified based on an integrated HPLC-Q-TOF-MS analysis and density functional theory computation of the Fukui indices, comprised of three pathways initiated by the opening of the piperazinyl ring, separation of piperazinyl and quinoline moieties, and cleavage of the pyridine ring on the quinoline moieties. Ecotoxicological evaluation confirmed the reduced toxicity of transformation intermediates over photocatalysis. Convenient magnetic recovery, high performance, and high recyclability made ZBC-10 a promising visible-light-activated photocatalyst for practical implementation in eliminating antibiotics from wastewater.

A comprehensive review of mathematical models developed for the estimation of organic disinfection byproducts.

In this review, we present comparative and comprehensive views on the foundations, potentials and limitations of the previously reported mathematical models for the estimation of the concentration of disinfection byproducts (DBPs) generated during the chlor(am)ination of water. To this end, DBPs models were divided into two major categories: static variable (SV) and dynamic variable (DV) or differential models. In SV models, variables remain in their original form throughout a chlor(am)ination modelling period while DV models consider the changes driven by a chlor(am)ination treatment as the variables. This classification and the comparative study of the two types of models led to a better understanding of the assumptions, potentials, and limitations of the existing DBP models. In opposition to several claims in the literature, certain DV models based on UV absorbance/fluorescence failed to selectively track the chromophores responsible for DBP formation. In this critical review, a conceptual model for the photophysics of dissolved organic matter (DOM) based on the theory of electron delocalization was proposed to explain some inconsistent spectroscopic properties of DOM following chlor(am)ination and several unique photophysical properties of DOM. New insights for the development and deployment of mathematical models were also provided to estimate DBPs in various settings.

Visible light driven MoS2/α-NiMoO4 ultra-thin nanoneedle composite for efficient Staphylococcus aureus inactivation.

MoS2/α-NiMoO4 ultra-thin nanoneedle composite was synthesized by microwave hydrothermal process in one step. The nanocomposite revealed the complete destruction of multidrug resistant Staphylococcus aureus (S. aureus) within 150 min under visible light irradiation. According to electron spin resonance measurement and radical trapping experiment, it has been established that O2¯ acts as a major active species for bacterial inactivation in visible light. The bacterial inactivation was further proved by membrane deformities in bacterial cell membrane, DNA fragmentation, and protein destruction. TEM- elemental mapping confirms the inactivation of S. aureus by reactive oxygen species (ROS) but not the toxicity of photocatalyst. Transient photocurrent responses, electrochemical impedance spectroscopy, and cyclic voltammetry measurements reveal the efficient separation of electron-hole pairs in the composite photocatalyst. The composite photocatalyst shows greater ROS production, higher degree of DNA fragmentation and protein degradation, detrimental effects on the morphology of the bacterial cell wall, outstanding transient photocurrent responses, reduction of interfacial charge transfer resistance, superb oxidation/reduction potential, strong visible light absorption, and adequate separation of photogenerated electron-hole pairs as compared to host photocatalyst. The photocatalytic inactivation mechanism was explained. So, this promising composite photocatalyst can be applied for inactivation of multidrug resistant bacteria in biological waste water.

Enhancement of NOx photo-oxidation by Fe- and Cu-doped blue TiO2.

The present work is focused on the removal of NOx with reduced blue TiO2 with Fe (blue Fe-TiO2)- and Cu (blue Cu-TiO2)-doped photocatalyst. TiO2 was reduced via lithium in EDA (blue TiO2). Fe and Cu ions were doped in the reduced TiO2 (blue Fe-TiO2 and blue Cu-TiO2). The material resulted in a core-shell structure of amorphous and anatase phase. XPS suggests the existence of Ti3+ species and oxygen vacancies within the structure of TiO2. Additionally, valence bond (VB)-XPS shows the generation of intermediate levels at the band edge of the doped photocatalyst. Photocurrent, electrochemical impedance spectroscopy and cyclic voltammetry confirmed the enhanced charge-separation process in doped reduced TiO2. The photocatalysts were tested for the photo-oxidation of NOx. Blue Fe-TiO2 reveals the efficiency of 70% for NO elimination and 44.74% for NO2 formation. The improved efficiency of the doped photocatalyst is related to the re-engineered structure with Ti3+ species, oxygen vacancies, and charge traps. Electron spin resonance (ESR) measurement was carried out for blue Fe-TiO2 to confirm the formation of reactive oxygen species (ROS). Furthermore, ion chromatography was used to investigate the mechanism of NOx oxidation. In conclusion, the doped blue TiO2 has a strong tendency to photo-oxidize NOx gasses.

Insight Into Malachite Green Degradation, Mechanism and Pathways by Morphology-Tuned α-NiMoO4 Photocatalyst.

The microwave hydrothermal process was used for the synthesis of various morphologies of α-NiMoO4 by simply adjusting the pH during experimental conditions. The effect of morphology/size on the photocatalytic performances for degradation of malachite green (MG) has been investigated under UV-Vis/visible light irradiation. Nanorod morphology has strong tendency to degrade (88.18%) the MG as compared to spherical quantum-sized (57.65%) and layered square microsheet (37.98%) under UV-Vis irradiation in 180 min. The active species trapping experiment revealed that active species (OH• , O2•- and h+ ) play a crucial role for MG degradation. The high BET surface area, greater amount of oxygen defect and efficient separation of electron-hole pair are responsible for MG degradation. About seventeen types of organic fragments of MG were confirmed by high resolution-quadruple time of flight electrospray ionization mass spectroscopy (HR-QTOF ESI/MS) technique on the basis of retention time and molecular masses. Degradation mechanism and pathways were proposed that follow the demethylation, nitration, decarboxylation, hydrolysis, decarboxylation and oxidation reaction. The reduction of total organic carbon revealed the mineralization of MG during photocatalytic degradation process. Therefore, this article represents the investigation of MG degradation by various morphology of α-NiMoO4 and detailed degradation mechanism and pathways.

Ag-BaMoO4: Er3+/Yb3+ photocatalyst for antibacterial application.

Silver loaded and Er3+/Yb3+ doped BaMoO4 octahedron microcrystals were fabricated by microwave hydrothermal process. The synthesized samples were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Energy dispersive X-ray spectroscopy (EDS), and Ultraviolet-visible diffuse reflection spectroscopy (UV-Vis DRS). The antibacterial application of samples were investigated by visible light irradiation and disk-diffusion method towards representative Gram-negative pathogen (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive pathogen (methicillin resistant Staphylococcus aureus). The complete inactivation of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus were observed by Ag-BaMoO4: Er3+/Yb3+ photocatalyst within 1h, 4h, and 5h, respectively, under visible light irradiation. The high killing percentage and superior zone of inhibition revealed the excellent antibacterial performance. The FESEM images were used to visualize the morphology with the extent of damage in the phospholipid layer present in the cell membrane of bacteria. The synergistic effect of loaded silver particles and doped Er3+/Yb3+ ions in BaMoO4 contributed for efficient antibacterial performance in visible light as well as in the dark. The excellent antibacterial performance of Ag-BaMoO4: Er3+/Yb3+ photocatalyst makes the material suitable for smart weapon for multidrug-resistant microorganisms and disinfectants in biomedical application.