Dramatic Activity of C3N4/BiPO4 Photocatalyst with Core/Shell Structure Formed by Self‐Assembly

Significantly enhancement of photocatalytic performances via core–shell structure of ZnO@mpg-C3N4

Wide-bandgap semiconductors modified with nanoparticles (NPs) of noble metals have been extensively studied for more than forty years owing to possible enhanced photocatalytic activity under UV irradiation since NPs of noble metals work as an electron sink hindering the recombination of charge carriers. The research has intensified over the last decade for photocatalytic activity under visible-light irradiation due to localized surface-plasmon resonance (LSPR) of noble metals, and those materials have been named plasmonic photocatalysts. The mechanism under visible-light irradiation (electron and/or energy transfer) as well as the enhancement of photocatalytic performance (activity and stability) have been intensively examined. Although the photocatalytic activities of plasmonic photocatalysts have been confirmed for various environmental applications such as environmental purification and solar-energy conversion, the photocatalytic activities under visible-light irradiation are much lower (ca. 1-2 orders in magnitude) than that under UV. Therefore, the present study focuses on improvement of photocatalytic activity for possible commercial applications. In our studies, plasmonic photocatalysts composed of commercial or self-synthesized titania and NPs of silver, gold and copper have been examined. In general, the broader the LSPR peak was, the higher was the photocatalytic activity under visible-light irradiation. Various strategies for improvement of the photocatalytic performance have been applied, e.g., (i) enlargement of the interface between titania and noble-metal NPs, (ii) preparation of bimetallic plasmonic photocatalysts, (iii) the use of faceted anatase NPs (octahedral and decahedral), and (iv) preparation of hybrid photocatalysts composed of heterogeneous and homogeneous photocatalysts, i.e., plasmonic photocatalysts and ruthenium complexes. Hybrid photocatalysts were prepared by deposition of gold/silver NPs on commercial titania particles with different structural properties. Ruthenium(II) (Ru(II)) complexes with carboxylic and phosphoric acid-binding groups were synthesized and adsorbed on bare titania and noble metal-modified titania particles. The structural properties of the samples were characterized by diffuse-reflectance spectroscopy (DRS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), scanning transmission electron microscopy (STEM), thin layer chromatography (TLC), proton nuclear magnetic-resonance spectroscopy (1H-NMR) and two-dimensional homonuclear correlation spectroscopy (2D-COSY). Large surface area, small crystallite sizes, low pH value, nature of the deprotected phosphonate binding groups, and pre-deposited noble-metal NPs enhanced the adsorption yield. Modification caused titania activation toward visible light (> 450 nm) for 2-propanol oxidation and for methanol dehydrogenation under UV/vis irradiation. The modified samples exhibited enhanced activity under UV/vis irradiation for acetic-acid oxidation depending on the kind of modifiers and properties of titania, i.e., 2–6, 3–9 and 1–3-fold enhancement was observed after modification with gold NPs and silver NPs with Ru(II) complex, respectively. The time-resolved microwave conductivity (TRMC) method proved that higher photocatalytic activity of modified titania under UV irradiation was caused by scavenging of mobile electrons by noble-metal NPs, and therefore decreasing the recombination of charge carriers. The photocatalytic activity of hybrid photocatalysts under UV/vis irradiation was influenced by the nature of the plasmonic metal and structural properties of the metal and titania particles, e.g., crystallite size and polymorphic form. Different kinds of action were observed for two plasmonic metals in two reaction systems under UV irradiation, e.g., modification with an Ru(II) complex caused 12-times faster dehydrogenation of methanol for silver-modified large anatase titania (ST41) and hardly changed the activity of gold-modified samples, while during acetic acid oxidation, only hybrid photocatalysts composed of gold NPs and Ru(II) complex exhibited a slight increase of photocatalytic activity (1.1-1.3 times). The difference between gold and silver hybrid photocatalysts might have been caused by differences in surface charges of metallic deposits, i.e., the surface of silver NPs was mainly positively charged, while gold was zero-valent. It was proposed that Ru(II) complex bound also to the surface of positively charged silver. Therefore, the sequence of modification (Ru(II) complex adsorption or gold/silver deposition) was investigated to check its influence on the resultant properties and thus photocatalytic performance. Different distributions of gold particle sizes and chemical compositions were obtained for the hybrid photocatalysts prepared with opposite sequence. It was found that photocatalytic activities depended on the range of used irradiation (UV/vis or vis) and the kind of modifiers in different ways. Under visible-light irradiation, fine titania modified with Ru(II) complex exhibited the highest level of photocatalytic activity. The presence of Ru(II) complex highly enhanced photocatalytic activity of titania modified with plasmonic NPs. However, NPs of plasmonic metals hindered the photocatalytic activity of Ru(II)-titania.

Molybdenum disulfide and graphitic carbon nitride (MoS2-g-C3N4) nanocomposites with visible-light induced photocatalytic activity were successfully synthesized by a facile ultrasonic dispersion method. The crystalline structure and morphology of the MoS2-g-C3N4 nanocomposites were characterized by X-ray diffraction (XRD), transmission electron microcopy (TEM), high-resolution TEM (HRTEM) and scanning electron microscopy (SEM). The optical property of the as-prepared nanocomposites was studied by ultraviolet visible diffusion reflection (UV-vis) and photoluminescence(PL) spectrum. It could be observed from the TEM image that the MoS2 nanosheets and g-C3N4 nanoparticles were well combined together. Moreover, the photocatalytic activity of MoS2-g-C3N4 composites was evaluated by the removal of nitric oxide under visible light irradiation (>400nm). The experimental results demonstrated that the nanocomposites with the MoS2 content of 1.5 wt% exhibited optimal photocatalytic activity and the corresponding removal rate of NO achieved 51.67%, higher than that of pure g-C3N4 nanoparticles. A possible photocatalytic mechanism for the MoS2-g-C3N4 nanocomposites with enhanced photocatalytic activity could be ascribed to the hetero-structure of MoS2 and g-C3N4.

A ZnO photocatalyst was hybridized with graphite-like C3N4via a monolayer-dispersed method. After hybridization with C3N4, the photocurrent of ZnO was enhanced by 5 times under UV irradiation and a photocurrent under visible light irradiation was observed. The photocatalytic activity of C3N4/ZnO under UV irradiation was increased by 3.5 times, the visible light photocatalytic activity was generated and the photocorrosion of ZnO was suppressed completely after ZnO was hybridized with C3N4. The enhancement in performance and photocorrosion inhibition under UV irradiation was induced by the high separation efficiency of photoinduced holes from ZnO to the HOMO of C3N4. Under visible light irradiation, the electron excited from the HOMO to the LUMO of C3N4 could directly inject into the CB of ZnO, making C3N4/ZnO present visible light photocatalytic activity. The optimum synergetic effect of C3N4/ZnO was found at a weight ratio of 3%, which corresponded to a monolayer dispersion of C3N4 on the surface of ZnO.

SnO2-core carbon-shell composite nanotubes with enhanced photocurrent and photocatalytic performance

The novel hybrid architectures of BiPO4 nanorods and g-C3N4 nanosheets (defined as BiPO4/g-C3N4) with highly visible-light-driven photocatalytic activity has been synthesized via a facile ultrasonic dispersion method as a composite photocatalyst for environmental treatment of organic pollutant. X-ray diffraction, scanning electron microscope, transmission electron microscopy, X-ray photoelectron spectra, UV–Vis diffuse reflectance spectra and photoluminescence spectra have been employed to characterize the hybrid materials. The as-obtained photocatalysts show remarkable activity for degradation of rhodamine B under visible light irradiation (λ > 420 nm). The enhanced photocatalytic activity for BiPO4/g-C3N4 composite can be ascribed to the facilitated separation and easy transfer of photogenerated electron–hole pairs on the interface of BiPO4 and g-C3N4. Therefore, the photocatalytic activity of catalyst with optimal BiPO4 weight ratio of 7% in the composite is about twice as high as that of pure g-C3N4.

ZnWO4/BiOI heterostructures with different constituents are synthesized via a chemical bath approach under mild conditions by tuning the Zn/Bi molar ratios. The obtained ZnWO4/BiOI heterostructures display high photocatalytic activities in degradation of MO and photocurrent response under visible light irradiation. Combining the experimental findings, first-principles calculations are used to investigate the surface geometry structures and the work functions of the (011) and (010) surfaces of the ZnWO4 phase and the (001) surface of the BiOI phase. The results show that the lattice and energy levels between the ZnWO4 and BiOI phases match well with each other to be capable of forming efficient ZnWO4/BiOI p–n heterojunction structures. This match promotes the separation and transfer of photoinduced electron–hole pairs at the interface, resulting in the excellent photocatalytic performance of the ZnWO4/BiOI heterostructures. Our findings show that the formation of a heterostructure would possess the excellent photocatalytic activities only if the lattice and energy level match between the two semiconductors was satisfied, which is of great importance for designing and developing more efficient heterostructured photocatalysts.

Effects of electronic structure and interfacial interaction between metal-quinoline complexes and TiO2 on visible light photocatalytic activity of TiO2

Facile fabrication of heterostructured bismuth titanate nanocomposites: The effects of composition and band gap structure on the photocatalytic activity performance

Defect-rich ZnO nanosheets of high surface area as an efficient visible-light photocatalyst

g-C3N4/NaTaO3 organic–inorganic hybrid nanocomposite: High-performance and recyclable visible light driven photocatalyst

Ultrasonic chemical synthesis of hybrid mpg-C3N4/BiPO4 heterostructured photocatalysts with improved visible light photocatalytic activity

Preparation, characterization and photocatalytic activity of N-containing ZnO powder

2D a-Fe2O3 doped Ti3C2 MXene composite with enhanced visible light photocatalytic activity for degradation of Rhodamine B

Energy level matching for efficient charge transfer in Ag doped - Ag modified TiO2 for enhanced visible light photocatalytic activity