Yawen Wang

Nitrogen-doped carbon quantum dots/Ag3PO4 complex photocatalysts with enhanced visible light driven photocatalytic activity and stability

Novel nitrogen-doped carbon quantum dots/Ag3PO4 (NCQDs/Ag3PO4) complex photocatalysts were synthesized by a facile precipitation method at room temperature. The physical and chemical properties of Ag3PO4 and NCQDs/Ag3PO4 photocatalysts were detected through X-ray powder diffraction, field emission scanning electron microscopy, UV-vis diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy and electron spin resonance techniques. The as-prepared 3-NCQDs/Ag3PO4 composite exhibited much higher activity than the pure Ag3PO4 for eliminating methyl orange and bisphenol A solution under visible light (λ>420nm). Moreover, in the cyclic experiments, the 3-NCQDs/Ag3PO4 exhibited an excellent stability for the decolorization of methyl orange at some level. This suggested that NCQDs played an important role in the process of degradation. The function of NCQDs was discussed and a new mechanism was put forward for the degradation of methyl orange. The high activities and stability were attributed to the transfer of photogenerated charges through the vector of Ag3PO4→NCQDs→Ag in the photocatalytic process, leading to effective charge separation of Ag3PO4.

Controllable synthesis of phosphate-modified BiPO4 nanorods with high photocatalytic activity: surface hydroxyl groups concentrations effects

Surface properties of photocatalysts are crucial to improve their efficiency in the removal of wastewater pollutants. In this study, phosphate-modified BiPO4 photocatalysts with different PO43−/Bi molar ratios were controllably synthesized through a one-pot hydrothermal method. The concentrations of surface hydroxyl groups on BiPO4 samples can be tuned by adjusting the PO43−/Bi3+ molar ratios. XRD results showed that surface modification by phosphate could boost the crystallinity of BiPO4, which was beneficial to photocatalytic performance. XPS and IR spectra revealed that PO43− modified only the surface of BiPO4. The optical absorption of phosphate-modified BiPO4 samples showed an obvious blue shift compared with that of bare BiPO4. Photocatalytic activities of the as-prepared samples were evaluated by the decomposition of methylene orange (MO) under ultraviolet light and simulated solar-light irradiation. Experimental results demonstrated that the photocatalytic performance of the modified samples significantly improved after the BiPO4 surface was modified by different amounts of PO43−. Both an indirect scavenger method and an electron spin resonance method were adopted to determine the production and intensity of free radicals during photocatalytic degradation. Results suggested that MO was removed predominantly through oxidation by OH radicals, as confirmed by theoretical calculations. Moreover, the mechanism of photocatalytic degradation of MO over the as-prepared phosphate-modified BiPO4 was proposed.

Enhanced photocatalytic removal of NO over titania/hydroxyapatite (TiO2/HAp) composites with improved adsorption and charge mobility ability

Effective photocatalysis processes with production of fewer toxic intermediates are highly desirable for air purification. In this study, titania/hydroxyapatite (TiO2/HAp) composites were synthesized by a facile hydrothermal method and employed to decontaminate nitric oxide (NO) in air under simulated solar light irradiation for the first time. It was found that the photocatalytic activity of the as-prepared TiO2/HAp composite (44.61%) was superior to those of the pristine components (TiO2: 38.57%, HAp: 36.73%) and mechanically mixed samples (35.36%). The TiO2/HAp composite with mass ratio of 3u2006:u20061 (75% TiO2/HAp) exhibited the highest NO removal efficiency among them. Moreover, the toxic intermediate NO2 production was significantly inhibited over TiO2/HAp. These synergistically improved properties can be ascribed to the high separation efficiency and faster transfer of the photo-generated charge carriers as evidenced by the experimental results from photocurrent tests and electrochemical impedance spectroscopy (EIS). The results from temperature programmed desorption (TPD) confirmed that the 75% TiO2/HAp sample had stronger chemisorption for NO due to the increased concentration of surface OH groups. Furthermore, the electron spin resonance (ESR) characterization suggested that ˙O2− and ˙OH radicals were the major species involved for NO removal over TiO2/HAp composites. The five recycling tests suggested that the TiO2/HAp has superior photocatalytic stability. This study suggests that the combination of TiO2 with HAp is an effective approach for air purification.

Optimized design of novel Pt decorated 3D BiOBr flower-microsphere synthesis for highly efficient photocatalytic properties

Abstract3D BiOBr flower-microspheres decorated with small amount (0.02–0.5xa0wt%) of Pt nanoparticles were successfully prepared via new electrostatic-adsorption-assisted light-reduction route. The as-prepared samples were characterized by XRD, SEM, HRTEM, EDS, XPS, UV–Vis DRS, PL, and photocurrent measurements. The photocatalytic activities were tested through the photocatalytic degradation of Bisphenol A (BPA) under visible light (420xa0nmu2009<u2009λu2009<u2009680xa0nm) and simulated sunlight (320xa0nmu2009<u2009λu2009<u2009680xa0nm) irradiation. The results indicate that Pt loading do not change the structural morphologies and particle sizes of BiOBr flower-microspheres, but there exists an enhanced photocurrent effect, greatly achieving the highly efficient photocatalytic activity of BiOBr under visible-light and simulated sunlight irradiation. 0.2xa0wt% Pt/BiOBr sample reveals the highest photocatalytic activity for the degradation on BPA with almost 92% under 10xa0min, much better than pure BiOBr and (P25) TiO2. The presence of synergistic effect between Pt4+ and Pt0 has vital impact on the electron capture and transfer from the semiconductor to noble metal, preventing the fast electron/hole recombination and participating in the multi-electron reduction of O2, and, consequently, achieving the formation of effective photocatalytic active species. Our findings should provide the fundamental data for making further research efforts in the hot topic on the monatomic Pt-modified photocatalyst systems.