Microwave-assisted synthesis of 3D Bi2MoO6 microspheres with oxygen vacancies for enhanced visible-light photocatalytic activity

Carbon dots decorated cadmium sulfide nanomaterials for boosting photocatalytic activity for ciprofloxacin degradation

This study investigates the utilization of carbon dots (CDs) from neem leaves (Azadirachta indica) decorated onto cadmium sulfide (CdS) for the photocatalytic degradation of ciprofloxacin. A comparative study of ciprofloxacin degradation with pristine CdS and CD decorated CdS demonstrated high degradation of ∼ 75 % with CD/CdS when compared to bare CdS (∼68 %). Process optimization studies were further carried out with CD/CdS catalysts at different solution pH (4-10), feed concentrations (10-50 mg/L), catalyst loadings (25-125 mg/L), temperatures (10 - 30 °C), and lamp power (25, 50, 250 W and sunlight). Higher temperatures, combined with a solution pH of 7 and catalyst loading of 100 mg/L favored the enhanced degradation of 20 mg/L of ciprofloxacin. The ciprofloxacin degradation rate increased linearly with temperature with an apparent activation energy of 27 kJ mol-1. The CD/CdS photocatalyst demonstrated maximum degradation rates with higher lamp powers while it also showed remarkable performance under natural sunlight achieving the same degradation within 3 h.

Tuning of surface oxygen vacancies for enhancing photocatalytic performance under visible light irradiation in Sb2WO6 nanostructures

Tuning of vacancies in photocatalytic materials has emerged as a versatile strategy to enhance visible light absorption and photocatalytic activity. In this study, surface oxygen vacancies (defects) were incorporated on antimony tungstate to boost its photocatalytic activity, which was examined by studying the degradation of model pollutants under visible light irradiation. Specifically, a two-to-three-fold increase in photocatalytic activity was observed for oxygen vacancy-rich antimony tungstate in comparison to its pristine counterpart. This improvement in the photocatalytic performance can be attributed to the presence of oxygen vacancies in the material, which leads to an enhanced absorption of light, decrease in the recombination of charge carriers, and increase in the number of active sites. In addition, owing to the nature of the surface charge present, the photocatalysts were found to be selective for the degradation of cationic pollutants in comparison to anionic and neutral pollutants, and can thus be used for the separation of a mixture of pollutants. Furthermore, scavenger studies illustrate that holes play a major role in the photocatalytic degradation of pollutants. Moreover, the excellent photostability of oxygen vacancy-rich antimony tungstate over three consecutive cycles demonstrates its potential as a good photocatalyst for the degradation of pollutants. Overall, this study demonstrates that the engineering of surface vacancies on perovskite oxide materials can render them as efficient single component photocatalysts for environmental remediation applications.

Constructing a Titanium Silicon Molecular Sieve-Based Z-Scheme Heterojunction with Enhanced Photocatalytic Activity

Titanium silicon molecular sieve (TS-1) is an oxidation catalyst that possesses a long lifetime of charge transfer excited state, high Ti utilization efficiency, large specific surface area, and good adsorption property; therefore, TS-1 acts as a Ti-based photocatalyst candidate. In this work, TS-1 coupled Bi2MoO6 (TS-1/BMO) photocatalysts were fabricated via a facile hydrothermal route. Interestingly, the optimized TS-1/BMO-1.0 catalyst exhibited a decent photodegradation property toward tetracycline hydrochloride (85.49% in 120 min) under the irradiation of full spectrum light, which were 4.38 and 1.76 times compared to TS-1 and BMO, respectively. The enhanced photodegradation property of the TS-1/BMO-1.0 catalyst could be attributed to the reinforced light-harvesting capacity of the photocatalyst, high charge mobility, and suitable band structure for tetracycline hydrochloride degradation. In addition, the mechanism of photocatalytic degradation of tetracycline hydrochloride by the TS-1/BMO-1.0 catalyst was reasonably proposed based on the band structure, trapping, and ESR tests. This research provided feasible ideas for the design and construction of high-efficiency photocatalysts for contaminant degradation.

New visible-light-driven Bi2MoO6/Cs3Sb2Br9 heterostructure for selective photocatalytic oxidation of toluene to benzaldehyde

Herein, new Bi2MoO6/Cs3Sb2Br9 heterostructure (BiMo/CSB) was investigated for the first time as a visible-light-driven photocatalyst for C(sp3)-H bond activation using molecular oxygen as a green oxidant and toluene as a model substrate. The optimized BiMo/CSB photocatalyst exhibited enhanced toluene oxidation activity (2,346 μmol g-1h-1), which was almost two- and five-fold that of pristine CSB (1,165 μmol g-1h-1) and BiMo (482 μmol g-1h-1), respectively. The improved photocatalytic performance was essentially attributed to the formation of staggered band energy lineup in the BiMo/CSB hybrid, which promoted S-scheme charge transfer across the BiMo/CSB heterointerface as supported by ultraviolet photoelectron spectroscopy (UPS), density functional theoretical (DFT), time-resolve photoluminescence (TRPL), and photoelectrochemical studies. Spin-trapping electron paramagnetic resonance (EPR) and radical scavenging studies revealed that photoinduced hole, molecular oxygen, and superoxide radical are key active species in this photocatalytic system. The developed BiMo/CSB catalyst provided good selectivity toward benzaldehyde product (94-98 %), presumably due to the inhibiting effect of benzyl alcohol on benzaldehyde oxidation. No significant change in structure and morphology was observed for the spent catalyst, however small negative shift of Sb 3d and Bi 4f binding energy was found suggesting partial reduction of Sb3+ and Bi3+. This work not only provides a new visible-light-driven photocatalyst for C(sp3)-H bond activation but also opens the doors for exploitation of the conversion and functionalization of this inert bond toward the production of high value-added organic chemicals.

Temperature, Doping, and Chemical Potential Tuning Intrinsic Defects Concentration in Bi2MoO6: GGA + U Method

Using the GGA + U method, the formation energy and concentration of intrinsic defects in Bi₂MoO₆ are explored under different chemical conditions, with/without doping, from 120 to 900 K. We find that the intrinsic defect and carrier concentration can be deduced from the small range of calculated Fermi levels in the diagram of formation energy vs Fermi level under different conditions. Once the doping conditions or/and temperature are determined, the corresponding E_F is only limited to a special region in the diagram of formation energy vs Fermi level, from which the magnitude relationship of defects concentration can be directly derived from their formation energy. The lower the defect formation energy is, the higher the defect concentration is. With E_F moving under different doping conditions, the intrinsic defect concentration changes accordingly. At the same time, the highest electron concentration at the relative O-poor (point H_U) with only intrinsic defects confirms its intrinsic n-type behavior. Moreover, upon A^-/D⁺ doping, E_F moves closer to VBM/CBM for the increasing concentration of holes/electrons. The electron concentration can also be further improved after D⁺ doping, indicating that D⁺ doping under O-poor chemical growth conditions is positive to improve its photogenerated carriers. This provides us with a method to adjust the intrinsic defect concentration and deepens our knowledge about comprehension and application of the diagram of formation energy vs Fermi level.

Influence of oxygen vacancy defects on Aurivillius phase layered perovskite oxides of bismuth towards photocatalytic environmental remediation

The low light absorption and rapid recombination of photogenerated charge carriers are primary contributors to the low activity of various photocatalysts. Fabrication of oxygen vacancy defect-rich materials for improved photocatalytic activities has been attracting tremendous attention from researchers all over the world. In this work, we have compared the photocatalytic activities of oxygen vacancy-rich Bi₂MoO₆(BMO-O_V) and Bi₂WO₆(BWO-O_V) for the degradation of a model pharmaceutical pollutant, ciprofloxacin under visible light irradiation. The photocatalytic activity was increased from 47% to 77% and 40% to-67% for BMO-O_Vand BWO-O_V, respectively in comparison to pristine oxides. This enhancement can be ascribed to suppressed charge carrier recombination and increased surface active sites. In addition, scavenger studies have been done to explain the role of photoinduced charge carriers in the degradation mechanism. Moreover, oxygen vacancy-rich photocatalysts have remained stable even after three consecutive cycles, making them promising materials for practical applications. Overall, this work provides deeper insight into the design and development of oxygen vacancy-rich materials.

A novel mixed matrix polysulfone membrane for enhanced ultrafiltration and photocatalytic self-cleaning performance

Photocatalytic materials can be used as self-cleaning functional materials to alleviate the irreversible fouling of ultrafiltration membranes. In this work, the small size g-C₃N₄/Bi₂MoO₆ (SCB) blended polysulfone (PSF) ultrafiltration membranes was fabricated by hydrothermal and phase inversion methods. As a functional filler of ultrafiltration membranes, the small size g-C₃N₄ nanosheet decorated on the surface of Bi₂MoO₆ can enhance the photocatalytic performance for bovine serum albumin (BSA) degradation, and remove irreversible fouling under visible light irradiation. In addition, the introduction of SCB microspheres into PSF matrix obviously increased the porosity of ultrafiltration membranes. Therefore, the SCB-PSF ultrafiltration membranes displayed excellent antifouling performance (flux recovery ratio is 82.53%) and BSA rejection rates (94.77%). SCB-PSF also had high photocatalytic self-cleaning activity, indicating excellent application prospects in organic wastewater treatment.