2D defect-engineered Ag-doped γ-Fe2O3/BiVO4: The effect of noble metal doping and oxygen vacancies on exciton-triggering photocatalysis production of singlet oxygen.

The selectivity of singlet oxygen (1O2) holds promising applications in complex environmental systems due to its ability to preferentially oxidize target pollutants. Usually, 1O2 in photocatalytic systems is generated via the electron transfer pathway and •O2- plays an important role as an intermediate, while the exciton-based energy transfer pathway for 1O2 generation has been less studied. Here, a 2D Ag-γ-Fe2O3/BiVO4 with oxygen vacancies was designed which was capable of generating 1O2 by an exciton-based energy transfer-dominated approach, as strongly demonstrated by the results of steady-state fluorescence spectroscopy and phosphorescence spectroscopy. In the Z-type heterojunction photocatalyst system, Ag acted as an electron mediator to promote not only the generation of free carriers but also the generation of singlet excitons, while the appropriate concentration of oxygen vacancies further promotes the exciton-triggering photocatalysis production of 1O2. The Ag-γ-Fe2O3/BiVO4 could degrade 99.4% of sulfadiazine within 90 min, and 1O2 played an important role in the degradation of sulfadiazine, as shown by EPR and active species capture experiments. Ecotoxicity predictions indicated that the main byproducts of sulfadiazine degradation by Ag-γ-Fe2O3/BiVO4 were low in toxicity. The prepared photocatalysts provide a new idea for obtaining 1O2 and designing photocatalysts with selectivity.

S-scheme BiVO4/CQDs/ß-FeOOH photocatalyst for efficient degradation of ofloxacin: Reactive oxygen species transformation mechanism insight.

Photocatalysis technology exhibited promising application for advanced treatment of wastewater. Nevertheless, the design of efficient photocatalyst and the mechanism of free radicals in pollutant degradation still remained to be further investigated. Herein, BiVO4/CQDs/ß-FeOOH photocatalyst was fabricated by electrostatic self-assembly method, which exhibited the excellent photocatalytic performance. Under visible-light irradiation, the removal rate of ofloxacin by BiVO4/CQDs/ß-FeOOH (0.25 min-1) was 1.93 times than pristine BiVO4, and the removal efficiency in 15 min reached 99.21%. The perfect reusability of BiVO4/CQDs/ß-FeOOH was ascribed to the persistent catalytic active centers provided by the renewable surface oxygen vacancies on the ß-FeOOH. As electron transfer channels, CQDs facilitated the transfer of BiVO4 photogeneration electrons. The matched band structure allowed the construction of S-scheme heterojunctions, and the higher conduction band position was retained while the carrier separation was promoted. More importantly, this work firstly reported the phenomenon that the main reactive groups in the photocatalysis process would be directionally transformed with the change of pH conditions. Based on the analysis of capture and electron paramagnetic resonance experiments, ·O2- was the main free radicals to photodegrade OFL in neutral and alkaline conditions. However, when the solution pH turned into acidic, the photodegradation of OFL was dominated by 1O2. This innovative phenomenon was due to that acidic condition accelerated the reaction kinetics of spontaneous transformation of ·O2- to 1O2 and inhibited the direct oxidation of pollutants by ·O2-. Accordingly, this research could inspire theoretical study of free radical reaction and the design of S-scheme heterojunction photocatalysts.

CQDs/biochar from reed straw modified Z-scheme MgIn2S4/BiOCl with enhanced visible-light photocatalytic performance for carbamazepine degradation in water.

The application of environmental-friendly and sustainable green materials in constructing photocatalysts to degrade pharmaceuticals and personal care products (PPCPs) attracts more attention. Herein, biochar (BC) or biomass carbon quantum dots (CQDs) were used to modify MgIn2S4/BiOCl (MB) heterojunction photocatalyst with Z-scheme structure, and improved the photocatalytic degradation performance for carbamazepine (CBZ) in the aqueous solution. Both BC and CQDs could form electron transfer interface with MB heterojunction, resulting in the photodegradation rate of MgIn2S4/BiOCl/CQDs (MBC, 96.43%) and MgIn2S4/BiOCl/BC (MBB, 88.09%) to CBZ within 120 min visible-light irradiation, which were significantly higher than that of MB (65.84%). Moreover, photoelectrochemical and photoluminescence tests verified that CQDs could act as a bridge for storing and transferring electrons in the entire Z-scheme system. Thence, compared with MBB, MBC could produce more •OH and •O2- under the visible light, which was indicated by the results of radical quenching experiments and electron paramagnetic resonance. Interestingly, under the natural sunlight, the photocatalytic performance of MBC to CBZ was even better than under laboratory conditions. In addition, the TOC removal efficiencies of MBB and MBC could reach 85.09% and 93.79% respectively, and ECOSAR program was utilized to further evaluate the eco-toxicity of CBZ and the intermediates towards fish, daphnid, and green algae, indicating that the photocatalytic process involving MBB and MBC showed outstanding toxicity reduction performance. Finally, compared with other composites, MBB and MBC showed higher photocatalytic performance and lower energy consumption, which would provide a green strategy for biochar materials in the photocatalytic treatment of PPCPs in water.

Rational design of novel three-dimensional reticulated Ag2O/ZnO Z-scheme heterojunction on Ni foam for promising practical photocatalysis.

Direct Z-scheme heterojunctions composed of Ag2O nanoparticles and ZnO nanorods were immobilized on Ni foam (AZN) via combined hydrothermal and precipitation methods to successfully construct 3D reticulated composites, and their photocatalytic performance were evaluated under simulated sunlight. Just as expected, the AZN samples exhibited excellent photocatalytic effects of 99.26% for the model pollutant (rhodamine B) in water after loading with Ag2O, which was 2.77 times higher than that of regular ZnO NAs/Ni foam composites. Meanwhile, the surface wettability of composite was remarkably enhanced. Besides, a series of photoelectrochemical measurements showed a significant improvement in the charge separation efficiency of AZN, which was attributed to the synergistic effect of direct Z-scheme heterojunction, matched energy band structure as well as 3D porous structure. Moreover, the AZN sample presented satisfactory stability after four cycles, meanwhile it displayed good removal performance against different types of antibiotics (Tetracycline, Sulfadiazine and Ciprofloxacin). The applicability and durability of AZN for rhodamine B degradation were evaluated by sequential batch experiments in a homemade simulated flowing water device. More importantly, the lower value of electrical energy per order indicated the photocatalyst/simulated sunlight system was more energy efficient and effective. Accordingly, this work provided a new strategy for designing 3D reticulated composites with low-dimensional nanomaterials to decompose organic pollutants in impaired waters.