Wenquan Cui

Novel Cu2O quantum dots coupled flower-like BiOBr for enhanced photocatalytic degradation of organic contaminant

Here we report a highly efficient novel photocatalyst consisting of Cu2O quantum dots (QDs) incorporated into three-dimensional (3D) flower-like hierarchical BiOBr (hereafter designated QDs-Cu2O/BiOBr), which were synthesized via a simple reductive solution chemistry route and applied to decontaminate the hazardous wastewater containing phenol and organic dyes. The deposition of Cu2O QDs onto the surface of the BiOBr was confirmed by structure and composition characterizations. The QDs-Cu2O/BiOBr composites exhibited superior activity for organic contaminant degradation under visible light and 3 wt% QDs-Cu2O/BiOBr composite showed the highest degrade rate for phenol and methylene blue (MB), which was 11.8 times and 1.4 times than that of pure BiOBr, indicated the QDs-Cu2O/BiOBr composite has the great potential application in purifying hazardous organic contaminant. The incorporated Cu2O QDs played an important role in improving the photocatalytic performance, due to the enhancement of visible light absorption efficiency as well as the efficient separation of the photogenerated charge carriers originating from the intimately contacted interface and the well-aligned band-structures, which was confirmed by the results of PL, photocurrent and EIS measurements. The possible photocatalytic mechanism was proposed based on the experiments and theoretical results.

Novel Cu2S quantum dots coupled flower-like BiOBr for efficient photocatalytic hydrogen production under visible light

Cu2S quantum dots (QDs) coupled three-dimensional (3D) flower-like hierarchical BiOBr (QDs-Cu2S/BiOBr) were prepared via a simple precipitation method. The Cu2S QDs, with an average diameters of 10 nm, were uniformly attached on the surface of BiOBr with an intimate contact interface as evidenced by characterization of the structure and composition of the composite. The QDs-Cu2S/BiOBr composite exhibited enhanced water splitting for hydrogen evolution, and 717 μmol g−1 of H2 was produced with 3 wt% QDs-Cu2S/BiOBr containing 1 wt% Pt, which was 3.1 times higher than that of Cu2S nanoparticles. The enhancement of hydrogen evolution was attributed to the synergic effect between BiOBr and Cu2S QDs, where the hybridization could effectively accelerate the separation of the photogenerated charge carriers.

Dramatic activity of a Bi2WO6@g-C3N4 photocatalyst with a core@shell structure

Here we report a Bi2WO6@g-C3N4 core@shell structure which was prepared by a combined ultrasonication–chemisorption method with enhanced photocatalytic degradation. The composites were extensively characterized by X-ray diffraction (XRD), Fourier transform infrared spectra (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV-vis diffuse reflectance spectroscopy (DRS). Compared with bare Bi2WO6 and g-C3N4, the Bi2WO6@g-C3N4 composites exhibited significantly enhanced photocatalytic activity for methylene blue (MB) degradation under visible light irradiation. The 3 wt% Bi2WO6@g-C3N4 showed the highest photocatalytic activity under visible light irradiation, which was about 1.97 times higher than Bi2WO6. In addition, the quenching effects of different scavengers displayed that the reactive h+ and ˙O2− play the major role in the MB decolorization. The core@shell hybrid photocatalyst exhibited dramatically enhanced photo-induced electron–hole separation efficiency, which was confirmed by the results of photocurrent and EIS measurements. On the basis of the experimental results and estimated energy band positions, a mechanism for the enhanced photocatalytic activity was proposed.

Highly ordered TiO2 nanotube arrays wrapped with g-C3N4 nanoparticles for efficient charge separation and increased photoelectrocatalytic degradation of phenol

Novel graphitic carbon nitride nanoparticles (NPs)-wrapped TiO2 nanotube arrays (NTAs) (g-C3N4/TiO2) were fabricated by a two-step method including an electrochemical anodization technique followed by impregnation under vacuum using urea as precursor. The as-prepared photoelectrode exhibited outstanding photoelectric properties and excellent photelectrocatalytic (PEC) performance for the degradation of phenol under stimulated solar light, which was due to the enhanced light absorption property and improved charge separation efficiency. The introduction of g-C3N4 NPs strongly decreased the charge transfer resistance and boosted the charge separation efficiency of TiO2. The optimum ratio of the g-C3N4/TiO2 yielded a pronounced 4.18-fold higher photocurrent density than TiO2. Besides, the combination of g-C3N4 NPs could negatively shift for the flat band potential of TiO2, resulting in an enhanced reduction property for the photoelectrocatalytic degradation of organic pollutants. The PEC process for the degradation of phenol over g-C3N4/TiO2 was much higher than the sum of photocatalytic (PC) and electrocatalytic (EC) processes indicating that a photoelectric synergy was achieved on the as-prepared photoelectrode and resulting in an improved PEC performance for the composite photoelectrode.

Synthesis of a hierarchical BiOBr nanodots/Bi2WO6 p–n heterostructure with enhanced photoinduced electric and photocatalytic degradation performance

Three-dimensional composites of flower-like Bi2WO6 decorated with BiOBr nanodots (designated BiOBr nanodots/Bi2WO6) with varying BiOBr content have been prepared by a simple method. The BiOBr nanodots, with average diameters of 50 nm, adhered tightly to the surface of Bi2WO6 and formed p–n heterojunctions between BiOBr and Bi2WO6, as evidenced by the characterization of its structure and composition. Compared to pure Bi2WO6 and BiOBr, BiOBr/Bi2WO6 showed a lower charge-transfer resistance, higher photocurrent and enhanced photoelectric properties. The photocurrent of the 15% BiOBr/Bi2WO6 composite was 17.2 and 2.39 times higher than that of pure Bi2WO6 and BiOBr, respectively. Meanwhile, this composite showed the highest degradation rate for methylene blue (MB), which was 1.7 and 2.4 times that of pure Bi2WO6 and BiOBr, respectively. The enhanced photoelectric and photocatalytic degradation performances were ascribed to the introduction of BiOBr nanodots and the formation of p–n heterojunctions, which could greatly accelerate the separation of photogenerated charge carriers. In addition, the roles of the radical species were investigated, and ·O2− and h+ are thought to dominate the photocatalytic process. Based on the experimental results, a possible photocatalytic mechanism was proposed.

Synthesis and characterization of a core–shell BiVO4@g-C3N4 photo-catalyst with enhanced photocatalytic activity under visible light irradiation

Novel core–shell structured ellipsoid-like BiVO4@g-C3N4 composites, with different amounts of g-C3N4, have been successfully prepared by a simple hydrothermal-chemisorption method. Their performance as photocatalysts was systematically evaluated during RhB degradation under visible light irradiation. The composite with 7 wt% g-C3N4 was found to be 7 times more efficient as a photocatalyst than pristine BiVO4. Its core–shell structure and activity were also found to be highly stable after it was used for 5 times in RhB degradation. The new composites were examined by various characterization techniques. The core–shell structure enhanced the contact area between the BiVO4 core and g-C3N4 nano-sheet shell, which provided more active sites and strengthened the chemical band interaction. The thin g-C3N4 nano-sheets reduced the charge carrier transfer distance, which further suppressed the recombination of the photo-induced electron–hole pairs and therefore enhanced the photocatalytic activity of the composites. A reaction mechanism of the photocatalytic RhB degradation was proposed and discussed in detail.

Cu2O NPs decorated BiPO4 photo-catalyst for enhanced organic contaminant degradation under visible light irradiation

The surface of BiPO4 was decorated with Cu2O nanoparticles (NPs) (hereafter designed as Cu2O/BiPO4) via an interfacial self-assembly method. The physical and photophysical properties of the Cu2O/BiPO4 hybrid photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), X-ray fluorescence spectrometry (XRF), UV-vis diffuse reflectance spectroscopy (DRS) and photo-electro-chemical (PEC). Compared with bare BiPO4 and Cu2O, the Cu2O/BiPO4 composites exhibited significantly enhanced photocatalytic activity for methylene blue (MB) degradation under visible light irradiation. The 5 wt% Cu2O/BiPO4 showed the highest photocatalytic activity under visible light irradiation, which was about 12.25 times that of BiPO4. Significantly, the superior stability was also observed in the five cyclic runs. The Cu2O/BiPO4 hybrid photocatalysts exhibited dramatically enhanced photo-induced electron–hole separation efficiency, which was confirmed by the results of photocurrent measurements. On the basis of the experimental results and estimated energy band positions, the mechanism of enhanced photocatalytic activity was proposed.

Growth of nano Ag@AgCl on (111) facets of Cu2O microcrystals with an enhanced photocatalytic activity

Single crystalline Cu2O nanoparticles were synthesized under mild conditions. A Ag@AgCl/Cu2O photocatalyst was prepared by directly growing Ag@AgCl nanoparticles (NPs) on (111) facets of octahedral Cu2O via a facile precipitation in situ photoreduction method. The results indicate that Ag@AgCl nanoparticles have a narrow size distribution ranging from 10 to 50 nm and are uniformly distributed on the surface of Cu2O nanoparticles. The surface area of the composite reached up to 19.736 m2 g−1. The photocatalytic performance of the Ag@AgCl/Cu2O composite for the degradation of methylene blue (MB) was evaluated under visible light irradiation. The Ag@AgCl/Cu2O composite with 30 wt% Ag@AgCl showed the highest photocatalytic activity, degrading 93.61% MB after 2 h irradiation. The high photocatalytic activity of the Ag@AgCl/Cu2O composite can be attributed to its high surface area, the crystal effect of Cu2O and the surface plasmon resonance of the Ag NPs. In addition, the Ag@AgCl/Cu2O composite can be used as a photocatalyst for the degradation of phenol. Based on these experimental results, a photocatalytic mechanism for the degradation of hazardous chemical effluents over Ag@AgCl/Cu2O photocatalysts was proposed. The free radicals and holes act as the main reactive species during the degradation.

Surface Decoration of ZnWO4 Nanorods with Cu2O Nanoparticles to Build Heterostructure with Enhanced Photocatalysis

The surface of ZnWO4 nanorods was decorated with Cu2O nanoparticles (Cu2O/ZnWO4) prepared through a precipitation method. The Cu2O nanoparticles were tightly deposited on the ZnWO4 surface and had average diameters of 20 nm. The nanoparticles not only promoted the absorption and utilization of visible light but also facilitated the separation of photogenerated charge carriers. This brought an improvement of the photocatalytic activity. The 5 wt % Cu2O/ZnWO4 photocatalyst displayed the highest degrade efficiency for methylene blue (MB) degradation under visible light, which was 7.8 and 2 times higher than pure ZnWO4 and Cu2O, respectively. Meanwhile, the Cu2O/ZnWO4 composite photocatalyst was able to go through phenol degradation under visible light. The results of photoluminescence (PL), photocurrent, and electrochemical impedance spectra (EIS) measurements were consistent and prove the rapid separation of charge, which originated from the match level structure and the close contact with the interface. The radical and hole trapping experiments were carried out to detect the main active substances in the photodegradation process. The holes and ·O2− radicals were predicted to dominate the photocatalytic process. Based on the characterization analysis and experiment results, a possible photocatalytic mechanism for enhancing photocatalytic activity was proposed.

Oil-in-Water Self-Assembled Synthesis of Ag@AgCl Nano-Particles on Flower-like Bi2O2CO3 with Enhanced Visible-Light-Driven Photocatalytic Activity

In this work, a series of novel flower-like Ag@AgCl/Bi2O2CO3 were prepared by simple and feasible oil-in-water self-assembly processes. The phase structures of as-prepared samples were examined by X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (DRS), X-ray fluorescence spectrometer (XRF), etc. The characterization results indicated that the presence of Ag@AgCl did not affect the crystal structure, but exerted a great influence on the photocatalytic activity of Bi2O2CO3 and enhanced the absorption band of pure Bi2O2CO3. The photocatalytic activities of the Ag@AgCl/Bi2O2CO3 samples were determined by photocatalytic degradation of methylene blue (MB) under visible light irradiation. The Ag@AgCl (10 wt %)/Bi2O2CO3 composite showed the highest photocatalytic activity, degrading 97.9% MB after irradiation for 20 min, which is over 1.64 and 3.66 times faster than that of pure Ag@AgCl (calculated based on the equivalent Ag@AgCl content in Ag@AgCl (10 wt %)/Bi2O2CO3) and pure Bi2O2CO3, respectively. Bisphenol A (BPA) was also degraded to further prove the degradation ability of Ag@AgCl/Bi2O2CO3. Photocurrent studies indicated that the recombination of photo-generated electron–hole pairs was decreased effectively due to the formation of heterojunctions between flower-like Bi2O2CO3 and Ag@AgCl nanoparticles. Trapping experiments indicated that O2−, h+ and Cl° acted as the main reactive species for MB degradation in the present photocatalytic system. Furthermore, the cycling experiments revealed the good stability of Ag@AgCl/Bi2O2CO3 composites. Based on the above, a photocatalytic mechanism for the degradation of organic compounds over Ag@AgCl/Bi2O2CO3 was proposed.