Liqun Ye

Dramatic visible light photocatalytic activity of MnOx–BiOI heterogeneous photocatalysts and the selectivity of the cocatalyst

Charge separation is very important for increasing the activity of semiconductor-based photocatalysts. Here we show that the main active species of BiOI are photo-induced holes, rather than ˙OH and O2˙−, under visible light irradiation. Based on this finding, the cocatalyst MnOx was used to enhance the transfer of the photo-induced holes, resulting in much higher photocatalytic activity, compared with the photocatalyst without MnOx. MnOx–BiOI heterogeneous nanostructure photocatalysts have been prepared by photo-deposition in Mn(NO3)2 solution, and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and photoluminescence (PL) spectroscopy. As-prepared MnOx–BiOI exhibited higher photoactivity than BiOI and Pt–BiOI for the degradation of Rhodamine B (RhB) dye under visible light irradiation. The PL spectrum showed that MnOx enhances the separation efficiency of the photo-induced electrons and holes of BiOI. Finally, BiOI was selectively combined with a deriving-hole-type cocatalyst to enhance the photocatalytic activity, and the reason for the cocatalyst selectivity is also discussed. This finding may be useful in bismuth-based photocatalysts to construct highly efficient solar energy conversion systems.

Facet-Dependent Photocatalytic N2 Fixation of Bismuth-Rich Bi5O7I Nanosheets

Bismuth-rich bismuth oxyhalides (Bi-O-X; X = Cl, Br, I) display high photocatalytic reduction activity due to the promoting conduction band potential. In this work, two Bi5O7I nanosheets with different dominant facets were synthesized using either molecular precursor hydrolysis or calcination. Crystal structure characterizations, included X-ray diffraction patterns (XRD), field emission electron microscopy and fast Fourier transformation (FFT) images, showed that hydrolysis and calcination resulted in the dominant exposure of {100} and {001} facets, respectively. Photocatalytic data revealed that Bi5O7I-001 had a higher activity than Bi5O7I-100 for N2 fixation and dye degradation. Photoelectrochemical data revealed that Bi5O7I-001 had higher photoinduced carrier separation efficiency than Bi5O7I-100. The band structure analysis also used to explain the underlying photocatalytic mechanism based on the different conduction band position. This work presents the first report about the facet-dependent photocatalytic performance of bismuth-rich Bi-O-X photocatalysts.

Oxygen vacancies induced exciton dissociation of flexible BiOCl nanosheets for effective photocatalytic CO2 conversion

Layered bismuth oxychloride (BOC) exhibits highly efficient activity for photocatalytic environmental remediation due to the confinement effect induced excitonic photocatalytic process. However, the strong excitonic process suppresses catalytic reactions with photo-induced electrons, such as hydrogen generation, CO2 conversion and nitrogen fixation. Moreover, the wide band gap of BiOCl limits its application under visible light. In this study, flexible BiOCl nanosheets with oxygen vacancies (BOC-OV) were successfully prepared. Molecular oxygen activation, electronic spin resonance (ESR), transient photocurrent, transient absorption spectroscopy, and transient fluorescence spectroscopy indicated that oxygen vacancies induced exciton dissociation of flexible BiOCl nanosheets. Moreover, oxygen vacancies induced wide spectrum (UV-Vis) absorption. The enhanced exciton dissociation resulted in the superior CO2 conversion of BOC-OV under UV-Vis light irradiation, where the light to carbon monoxide (LTCO) conversion efficiency reached up to 26.5 × 10−6. Theoretical calculations and in situ Fourier transform infrared spectrometry (FT-IR) analysis revealed that the mechanism of oxygen vacancies improves the photocatalytic CO2 conversion with BOC-OV via the CO2 hydrogenation pathway. This study indicates that oxygen vacancies have a great influence on photocatalytic CO2 reduction due to their special surface and electron structure properties.

A dual-cocatalyst-loaded Au/BiOI/MnOx system for enhanced photocatalytic greenhouse gas conversion into solar fuels

Photocatalysis is a green and economical method to convert greenhouse gases such as carbon dioxide (CO2) for environmental remediation and solar fuel generation. In a semiconductor photocatalyst system, cocatalysts play a very important role. They are not only redox-active sites but also can be used to improve the separation efficiency of photo-induced carriers. In this work, a dual-cocatalyst-loaded Au/BiOI/MnOx photocatalyst was prepared to enhance the photocatalytic reduction activity for the conversion of greenhouse gases (CO2) into solar fuels. The as-prepared BiOI, Au/BiOI, MnOx/BiOI and Au/BiOI/MnOx were characterized by using X-ray diffraction patterns (XRD), the Brunauer–Emmett–Teller (BET) method, transmission electron microscopy (TEM), UV-vis diffuse reflectance spectra (DRS) and X-ray photoelectron spectroscopy (XPS). The photocatalytic reduction results showed that Au/BiOI/MnOx had higher activity than pure BiOI, MnOx–BiOI, Au–BiOI and other BiOI-based photocatalysts for solar fuel generation. Photocurrent and electrochemical impedance (EIS) spectroscopy revealed that the efficient photo-induced carrier separation efficiency of Au/BiOI/MnOx induced the high photocatalytic activity.

Photocatalytic Mechanism Regulation of Bismuth Oxyhalogen via Changing Atomic Assembly Method

Exciton and carrier photocatalytic processes have been proved in bismuth oxyhalogen photocatalysts. But, there are no reports about how to regulate the different mechanisms to improve photocatalytic activity for different reaction. Here, we found that the photocatalytic mechanisms could be regulated by changing the assembly method of bismuth, oxygen, and halogen atoms. Reactive oxygen species (ROS) experimentals results concluded that solid solution BiOBr0.5I0.5 showed enhanced exciton photocatalytic process, and coupling 0.5BiOBr/0.5BiOI displayed improved carrier photocatalytic proces. This work promoted the understanding about solid solution and coupling for bismuth oxyhalogen.

Preparation and electrochemical characterization of ultrathin WO3−x /C nanosheets as anode materials in lithium ion batteries

Ultrathin two-dimensional (2D) nanomaterials offer unique advantages compared to their counterparts in other dimensionalities. O-vacancies in such materials allow rapid electron diffusion. Carbon doping often improves the electric conductivity. Considering these merits, the WO3−x/C ultrathin 2D nanomaterial is expected to exhibit excellent electrochemical performance in Li-ion batteries. Here, ultrathin WO3−x/C nanosheets were prepared via an acid-assisted one-pot process. The as-prepared WO3−x/C ultrathin nanosheets showed good electrochemical performance, with an initial discharge capacity of 1,866 mA·h·g−1 at a current density of 200 mA·g−1. After 100 cycles, the discharge and charge capacities were 662 and 661 mA·h·g−1, respectively. The reversible capacity of the WO3−x/C ultrathin nanosheets exceeded those of WO3 and WO3−x nanosheets. The electrochemical testing results demonstrated that WO3−x/C ultrathin nanosheets are promising alternative anode materials for Li-ion batteries.

Black phosphorus quantum dot/g-C 3 N 4 composites for enhanced CO 2 photoreduction to CO

The development of low cost, metal free semiconductor photocatalysts for CO2 reduction to fuels and valuable chemical feedstocks is a practically imperative for reducing anthropogenic CO2 emissions. In this work, black phosphorus quantum dots (BPQDs) were successfully dispersed on a graphitic carbon nitride (g-C3N4) support via a simple electrostatic attraction approach, and the activities of BP@g-C3N4 composites were evaluated for photocatalytic CO2 reduction. The BP@g-C3N4 composites displayed improved carrier separation efficiency and higher activities for photocatalytic CO2 reduction to CO (6.54 μmol g−1 h−1 at the optimum BPQDs loading of 1 wt%) compared with pure g-C3N4 (2.65 μmol g−1 h−1). This work thus identifies a novel approach towards metal free photocatalysts for CO2 photoreduction.摘要开发还原二氧化碳生成燃料和有价值化学品的低成本、非金属半导体光催化剂, 是减少二氧化碳浓度的一种有效方案. 本工作通 过简单的静电吸引方法成功地将黑磷量子点(BPQDs)分散在石墨相氮化碳(g-C3N4)载体上, 成功制备了BP@g-C3N4复合材料, 并对其在紫 外-可见光激发下光催化还原CO2的性能进行了研究. 电化学表征, 瞬态吸收光谱和荧光光谱数据表明BPQDs的负载提高了g-C3N4的载流 子分离效率. 在氙灯的照射下, 与g-C3N4(CO的生成速率为2.1 μmol g−1 h−1)相比, BP@g-C3N4复合材料光催化还原CO2活性显著提高(当 BPQDs的负载量为1 wt%时, CO的生成速率为6.54 μmol g−1 h−1). 本工作发展了一种新型的可还原CO2的非金属基光催化剂.

Selectivity reversal of photocatalytic CO2 reduction by Pt loading

In photocatalysis systems, precious metal co-catalysts play very important roles. Here, a photodeposition method is used to load Pt on different photocatalysts for photocatalytic CO2 conversion testing. The performance results indicate that the selectivity of semiconductor photocatalysts for CO2 reduction was effectively reversed from CO to CH4 due to the introduction of Pt.