Shenyuan Bao

Z-scheme CdS–Au–BiVO4 with enhanced photocatalytic activity for organic contaminant decomposition

A Z-scheme heterogeneous photocatalyst CdS–Au–BiVO4 was synthesized for the first time by photo-reduction and deposition–precipitation methods. The microstructures and optical properties of the as-prepared samples were investigated by means of scanning electron microscopy (SEM), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectroscopy (DRS). Due to the oriented accumulation of electrons on the {010} facets of BiVO4 crystals, Au nanoparticles were successfully anchored on the {010} facets of BiVO4 crystals via the photo-reduction process. CdS was further selectively deposited on the surface of Au nanoparticles, benefitting from the strong S–Au interaction. Photocatalytic degradations of tetracycline and Rhodamine B indicated that CdS–Au–BiVO4 exhibits much higher photocatalytic activity than BiVO4, Au–BiVO4, and CdS–BiVO4. Radical trapping experiments confirmed that in the case of CdS–Au–BiVO4, the main reactive species responsible for organic contaminant degradation are h+, ˙OH, and ˙O2−, while only h+ can be produced in the case of CdS–BiVO4. Based on the photoelectrochemical analysis and radical trapping experiments, it can be deduced that the Z-scheme structure of CdS–Au–BiVO4 not only decreases the recombination rate of photo-generated carriers but also makes the holes and electrons keep a higher redox ability.

Synthesis of visible light-driven Eu, N co-doped TiO2 and the mechanism of the degradation of salicylic acid

Europium and nitrogen co-doped TiO2 was successfully synthesized by the precipitation–peptization method. The structure and properties of the catalysts were characterized by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV–vis diffuse reflectance spectra. The photocatalytic efficiency was evaluated by monitoring the photocatalytic degradation of salicylic acid under visible light irradiation. It was verified that TiO2 co-doped with nitrogen and 1% europium showed the highest photocatalytic activity. The adsorption isotherms were obtained by measuring the salicylic acid concentration before and after the dark adsorption at different original solution concentrations. The results illustrated that the doping of Eu was beneficial to the adsorption of salicylic acid. The probable degradation mechanism of salicylic acid was examined by the addition of NaF, Na2S2O3, and K2S2O8 as the probe molecules. It was verified that salicylic acid was first adsorbed on the surface of the catalysts, followed by the degradation by the photogenerated holes (hvb+).

AgBr tetradecahedrons with co-exposed {100} and {111} facets: simple fabrication and enhancing spatial charge separation using facet heterojunctions

The solar energy conversion efficiency of semiconductor materials is closely related to the separation rate of photogenerated charge carriers. Recently, “facet heterojunctions” have attracted much attention because of their outstanding capability for separating the photogenerated charge carriers. In this research, silver bromide (AgBr) crystals with different exposed facets were synthesized using a double-jet precipitation method using the inherent bromide (Br−) ions as the structure directing agent. The morphology and exposed facets of the AgBr crystals were conveniently tailored by adjusting the concentration of Br− ions, i.e., cubes with {100} facets, tetradecahedrons with both {100} and {111} facets, and octahedrons with {111} facets were synthesized when the concentrations of Br− ions were 10−3.0, 10−2.5, and 10−2.0 M, respectively. Br− ions can clearly decrease the surface energies of the (100) and (111) surfaces, by which the growth rate of AgBr nuclei along the [100] and [111] directions can be tuned by adjusting the concentration of Br− ions, leading to the formation of AgBr crystals with different exposed facets. The transient photocurrent, electrochemical impedance, and photoluminescence spectrum measurements indicated that the tetradecahedral AgBr crystals show higher electron–hole separation rate than the cubic and octahedral ones. Mott–Schottky and photo-oxidation deposition experiments revealed that the photogenerated electrons and holes are transferred to AgBr {100} and {111} facets, respectively. The benefit from the effective spatial isolation of photogenerated electrons and holes was that tetradecahedral AgBr crystals with co-exposed {100} and {111} facets showed enhanced photocatalytic activity for the degradation of methyl orange and sulfadiazine.

Photocatalytic degradation pathway of sulfadiazine over Ag–TiO2 under visible light irradiation

In the past decades, TiO2-based photocatalysis has received much research attention as an effective strategy for decomposing the antibiotics in a water system. However, the degradation pathway of antibiotics over TiO2-based photocatalysts has seldom been studied. In this work, Ag–TiO2 was prepared via photo-reduction method and the photocatalytic degradation pathway of sulfadiazine over Ag–P25 under visible light irradiation was explored with the assistance of high performance liquid chromatography-mass spectrometry (HPLC–MS). Based on the HPLC–MS results, the chemical formulas of five degradation intermediates were proposed: one is the product of desulfonating reaction; the second is the product of sulfanilamide bond-breaking reaction; the others are the oxidation and substitution products initiated by ·OH. The contributions of ·O2−, ·OH and h+ during the photocatalytic degrading process of sulfadiazine were investigated by reactive species trapping experiments. On the basis of the above results, it can be deduced that there exist three possible photocatalytic degrading pathways of sulfadiazine, i.e., desulfonation, sulfanilamide bond-breakage and the oxidation of amino groups. Moreover, the photocatalytic mechanism of Ag–P25 was also proposed.