Baojiang Jiang

Well‐Dispersed CoS Nanoparticles on a Functionalized Graphene Nanosheet Surface: A Counter Electrode of Dye‐Sensitized Solar Cells

With a facile electrophoretic deposition and chemical bath process, CoS nanoparticles have been uniformly dispersed on the surface of the functionalized graphene nanosheets (FGNS). The composite was employed as a counter electrode of dye-sensitized solar cells (DSSCs), which yielded a power conversion efficiency of 5.54 %. It is found that this efficiency is higher than those of DSSCs based on the non-uniform CoS nanoparticles on FGNS (4.45 %) and built on the naked CoS nanoparticles (4.79 %). The achieved efficiency of our cost-effective DSSC is also comparable to that of noble metal Pt-based DSSC (5.90 %). Our studies have revealed that both the exceptional electrical conductivity of the FGNS and the excellent catalytic activity of the CoS nanoparticles improve the conversion efficiency of the uniformly FGNS-CoS composite counter electrode. The electrochemical impedance spectra, cyclic voltammetry, and Tafel polarization have evidenced the best catalytic activity and the fastest electron transport. Additionally, the dispersion condition of CoS nanoparticles on FGNS plays an important role for catalytic reduction of I3 (-) .

Composites of small Ag clusters confined in the channels of well-ordered mesoporous anatase TiO2 and their excellent solar-light-driven photocatalytic performance

AbstractSmall Ag clusters confined in the channels of ordered mesoporous anatase TiO2 have been fabricated via a vacuum-assisted wet-impregnation method, utilizing well-ordered mesoporous anatase TiO2 with high thermal stability as the host. The composites have been characterized in detail by X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption fine structure (XAFS) spectroscopy, N2 adsorption, UV-visible diffuse reflectance spectroscopy and transmission electron microscopy. The results indicate that small Ag clusters are formed and uniformly confined in the channels of mesoporous TiO2 with an obvious confinement effect. The presence of strong Ag-O interactions involving the Ag clusters in intimate contact with the pore walls of mesoporous TiO2 is confirmed by XAFS analysis, and favors the separation of photogenerated electron-hole pairs, as shown by steady-state surface photovoltage spectroscopy and transient-state surface photovoltage measurements. The ordered mesoporous Ag/TiO2 composites exhibit excellent solar-light-driven photocatalytic performance for the degradation of phenol. This is attributed to the synergistic effects between the small Ag clusters acting as traps to effectively capture the photogenerated electrons, and the surface plasmon resonance of the Ag clusters promoting the absorption of visible light. This study clearly demonstrates the high-efficiency utilization of noble metals in the fabrication of high-performance solar-light-driven photocatalysts.

NaYF4:Er3+/Yb3+–graphene composites: preparation, upconversion luminescence, and application in dye-sensitized solar cells

NaYF4:Er3+/Yb3+–graphene composites were successfully prepared by growing NaYF4:Er3+/Yb3+ nanoparticles in interlayers of expanded graphite, accompanied with the simultaneous exfoliation of expanded graphite under polyvinylpyrrolidone-assisted hydrothermal conditions. The obtained NaYF4:Er3+/Yb3+–graphene composites can emit bright green upconversion emissions under 980 nm excitation. In addition, the NaYF4:Er3+/Yb3+–graphene composites were chosen to design TiO2–NaYF4:Er3+/Yb3+–graphene composite photoanodes, which have the ability to improve the efficiencies of the solar cells. The electron transport and interfacial recombination kinetics were investigated by the electrochemical impedance spectroscopy and intensity-modulated photocurrent/photovoltage spectroscopy in detail.

Nitrogen-doped graphene supported Pd@PdO core-shell clusters for C-C coupling reactions

The introduction of nitrogen significantly decreases the metal particle size and improves the performance of metal-based graphene-supported catalysts. In this work, the density functional theory is used to understand the interaction between nitrogen-doped graphene and Pd@PdO clusters. Experiments show that small size Pd@PdO clusters (1–2 nm) can be grown uniformly on nitrogen-doped graphene sheets by a facile oxidation-reduction method. The nanoscale interaction relationship between nitrogen-doped graphene and Pd@PdO clusters is investigated through X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectra (XAS). The composite catalysts are applied in Suzuki-Miyaura reactions giving high yields and good structural stability. These results have potential impact in design and optimization of future high performance catalyst materials for cross coupling reactions.

Enhanced photoelectric conversion efficiency of dye-sensitized solar cells by the incorporation of dual-mode luminescent NaYF4:Yb3+/Er3+

This work focuses on the design of composite photoanodes with dual-mode luminescent function as well as the effects of luminescent phosphors on the photoelectric properties of dye-sensitized solar cells. Specifically, hexagonal phase NaYF4:Yb(3+)/Er(3+) microcrystals were prepared by a hydrothermal method and added to the TiO2 photoanodes of dye-sensitized solar cells. The results indicated that the TiO2-NaYF4:Yb(3+)/Er(3+) composite photoanodes can emit visible light under 495 or 980 nm excitation, and then the visible light can be absorbed by dye N719 to improve light harvesting and thereby the efficiency of the solar cell. Under simulated solar radiation in the wavelength range of λ≥ 400 nm, the photoelectric conversion efficiency of TiO2-NaYF4:Yb(3+)/Er(3+) cell was increased by 10% compared to pure TiO2 cell. For the electrodes with the same thickness, the amount of dye adsorption of the photoanodes decreased a little after adding NaYF4:Yb(3+)/Er(3+), which was attributed to the decrease of TiO2 in the photoanodes. The electron transport and interfacial recombination kinetics were investigated by the electrochemical impedance spectroscopy and intensity-modulated photocurrent/photovoltage spectroscopy. The TiO2-NaYF4:Yb(3+)/Er(3+) cell has longer electron recombination time as well as electron transport time than pure TiO2 cell. The charge collection efficiency of TiO2-NaYF4:Yb(3+)/Er(3+) cell was little lower than that of pure TiO2 cell. In addition, the interfacial resistance of the TiO2-dye|I3(-)/I(-) electrolyte interface of TiO2-NaYF4:Yb(3+)/Er(3+) cell was much bigger than that of pure TiO2 cell. All these results indicated that the charge transport cannot be improved by adding NaYF4:Yb(3+)/Er(3+). And thus, the enhanced photoelectric conversion efficiencies of TiO2-NaYF4:Yb(3+)/Er(3+) cells were closely related to the dual-mode luminescent function of NaYF4:Yb(3+)/Er(3+).

Black N/H-TiO2 Nanoplates with a Flower-Like Hierarchical Architecture for Photocatalytic Hydrogen Evolution.

A facile two-step strategy was used to prepare black of hydrogenated/nitrogen-doped TiO2 nanoplates (NHTA) with a flower-like hierarchical architecture. In situ nitriding and self-assembly was realized by hydrothermal synthesis using tripolycyanamide as a N source and as a structure-directing agent. After thorough characterization, it was found that the hydrogenation treatment did not damage the flower-like architecture but distorted the anatase crystal structure and significantly changed the band structure of NHTA owing to the increased concentration of oxygen vacancies, hydroxyl groups, and Ti3+ cations. Under AM 1.5 illumination, the photocatalytic H2 evolution rate on the black NHTA was approximately 1500 μmol g-1  h-1 , which was much better than the N-doped TiO2 nanoplates (≈690 μmol g-1  h-1 ). This improvement in the hydrogen evolution rate was attributed to a reduced bandgap, enhanced separation of the photogenerated charge carriers, and an increase in the surface-active sites.

Fabrication of mixed-crystalline-phase spindle-like TiO2 for enhanced photocatalytic hydrogen production

The fabrication of heterojunction between different crystalline phases has been considered to be an effective strategy for promoting charge separation during photocatalytic process. Herein, the mixed-crystalline-phase (MC), spindle-like TiO2 was prepared with a simple hydrothermal method, which was followed by a series of calcination processes. The final products are composed of two crystalline phases including anatase and brookite. The anatase/brookite ratio of the TiO2 is tuned by varying the calcination temperature. The MC TiO2 that consisted of 85.5% anatase and 14.5% brookite has the highest rate of photocatalytic hydrogen evolution (290.2 μmol h−1) compared to the purely anatase TiO2. This is attributed to the mixed-phase heterojunction structure that improves electron-hole separation, and therefore, enhances the photocatalytic hydrogen production.摘要本文采用一种简单的方法制备了混晶相(锐钛矿/板钛矿)纺锤形二氧化钛. 首先, 硫酸氧钛被选择为前驱体, 通过水热合成以及惰性气氛下的热处理过程, 得到一系列混晶相(锐钛矿/板钛矿)二氧化钛, 其中, 组成为85.5%锐钛矿、 14.5%板钛矿的二氧化钛具有最优异的光催化分解水制氢活性, 产氢速率为290.2 μmol h−1. 研究发现锐钛矿/板钛矿晶相间异质结的存在能够有效的分离光生载流子, 同时进一步提高对电子的捕获, 实现光催化分解水制氢效率的显著提高, 这种基于硫酸氧钛水热合成方法得到的高活性光催化剂在制氢领域具有潜在的应用价值.

Fe3W3C/WC/Graphitic Carbon Ternary Nanojunction Hybrids for Dye‐Sensitized Solar Cells

Fe3 W3 C/WC/graphitic carbon (GC) ternary nanojunction hybrids are synthesized through a solid-state pyrolysis process for dye-sensitized solar cells (DSSCs). First-principles calculations have been first employed to investigate the adsorption energy between I3 (-) and Fe3 W3 C and WC nanoclusters. Scanning Kelvin probe images indicate that the work function changes greatly due to the formation of ternary nanojunctions, which favor fast photoelectron transfer. A photoelectrical conversion efficiency of 7.1 % is achieved based on Fe3 W3 C/WC/GC hybrid counter electrodes, which is much higher than those of pure GC (5.02 %) and WC/GC hybrids (6.11 %). It has been further revealed that Fe3 W3 C/WC/GC hybrid counter electrodes exhibit the best catalytic performances according to relevant electrochemical measurements, which can be attributed to fast photoelectron transfer due to the ternary junctions and the addition of Fe3 W3 C with more catalytic metallic atoms.

Inorganic acid-derived hydrogen-bonded organic frameworks to form nitrogen-rich carbon nitrides for photocatalytic hydrogen evolution

Hydrogen-bonded organic framework (HOF) materials, which feature unique structures, are generally used for gas separation. To fabricate HOF-like precursors with diverse morphologies and further extend their application to hydrogen evolution, melamine has been reacted with inorganic acids (H2SO4, HNO3 and HCl) in this work. After calcining, the framework structure can maintain its major features while being converted into porous nitrogen–rich carbon nitrides. Moreover, the influence of different acid radicals on the “N-rich effect” was also investigated. The results show that the reaction procedure enriches the nitrogen content in all the newly synthesized carbon nitride products compared with bulk carbon nitride. This enrichment is attributed to the preferential formation of high-N-ratio triazine over heptazine. The carbon nitrides prepared from the HOF precursors contain more active sites [N-(C)3] and tune the bandgap by stabilizing the energy level of the conduction band. Moreover, heterogeneous sulfur doping using H2SO4 is another key factor in changing the energy-level structure. Thus, our method provides a feasible way to prepare graphite carbon nitride materials with preeminent photocatalytic activity.

A versatile salicylic acid precursor method for preparing titanate microspheres

Mixed-phase MgTiO3/MgTi2O5 microspheres were prepared through a salicylic acid precursor method and further calcined in air. The microspheres were formed through coordination, polymerization, and aggregation processes. Salicylic acid acted as a ligand in coordinating with metal ions, in addition to acting as a structure-directing agent in the polymerization and aggregation of the titanate precursor microspheres via chemical bonds and electrostatic attraction. The mixed-phase MgTiO3/MgTi2O5 microspheres prepared by this method showed excellent photocatalytic hydrogen production efficiencies that were two and four times higher than mixed-phase nanoparticles and pure-phase nanoparticles, respectively, owing to their closed phase junctions and sphere-like morphologies. This versatile and facile salicylic acid precursor method was also used to prepare a number of other bivalent metal-based titanate microspheres, including BaTiO3, ZnTiO3, CoTiO3, NiTiO3, and CdTiO3.摘要本文报道了一种简单通用的水杨酸前驱体路线合成钛酸盐微球的方法, 水杨酸作为配体和结构导向剂诱导前驱体形成球形结构. 利用水杨酸与乙酸镁和钛酸四丁酯的配位作用, 进而通过溶剂热反应得到镁-钛-水杨酸前驱体微球, 在空气下焙烧得到混相MgTiO3/MgTi2O5微球.由于其合适的能带位置和混相结, 混相MgTiO3/MgTi2O5微球表现出了优异的光催化产氢性能, 相比混相MgTiO3/MgTi2O5纳米粒子和纯相纳米粒子产氢性能分别高出2和4倍. 同时, 这种配位前驱体路线可以拓展合成多种二价金属钛酸盐微球, 并用此方法成功制备了BaTiO3, ZnTiO3, CoTiO3, NiTiO3和CdTiO3微球.这种基于配位化学路线的合成方法对于钛酸盐(或钙钛矿、 尖晶石等)等功能微球材料的低温制备具有较高的科学意义和应用价值.