Interfacial charge transfer in carbon nitride heterojunctions monitored by optical methods

Solar energy conversion is inciting tremendous research efforts in many fields due to the vast potential of sunlight as a sustainable energy source. For solar energy to become widely used and become a major component of our energy mix, energy storage on large scales must be addressed and the components used must be abundant. Artificial photosynthesis to produce solar fuels holds promise as a way to convert solar energy into storable energy. Organic photocatalysts have rapidly established themselves as a viable alternative to inorganic systems. Organic photocatalyst can be prepared from inexpensive precursors and offer a synthetic versatility and tunability that can be exploited to improve efficiencies. Carbon nitride (CN_x) has emerged as a leading organic photocatalyst with advantageous chemical and photo stabilities. Recombination of photogenerated electrons and holes limit the efficiency of CN_x materials below levels necessary to become a viable energy production system. To improve the efficiency and key characteristics such as light harvesting, charge carrier lifetime, and interfacial rate of charge transfer, a second material is put in contact with CN_x to form a heterojunction. While there are many examples of heterojunctions improving the photocatalytic activity beyond that of the isolated CN_x, we are still lacking the deep understanding of charge carrier dynamics necessary to rationalize the improvements and design optimal junctions. This review covers the studies of CN_x heterojunctions that have used optical methods to monitor the charge carrier dynamics. Time-resolved photoluminescence (TRPL) is the most common technique used and there are many examples that have used transient absorption spectroscopy (TAS) to probe the charge carrier dynamics. However, attempting to link the lifetime change to the activity differences does not yield a clear trend. It is likely that the reactive charges are not consistently being monitored and is obscuring the expected correlations. Both shorter and longer charge carrier lifetimes can be observed with both TRPL and TAS techniques and can be interpreted as arising from interfacial charge separation. Even when the same materials are used in the junction there is no consistency in observing a shorter or longer lifetime. The holistic view of charge carrier dynamics in CN_x heterojunctions presented here intends to identify overarching themes from a wide range of CN_x-containing systems and help take stock of where our current understanding stands. More specific spectral assignments and linking the observed lifetimes to certain photophysical or photochemical processes are needed to build models to help us understand the links between the charge carrier dynamics and the activity. These are crucial to develop general strategies that will lead to optimal CN_x heterojunctions.     

Unconventional Route to Oxygen-Vacancy-Enabled Highly Efficient Electron Extraction and Transport in Perovskite Solar Cells

The ability to effectively transfer photoexcited electrons and holes is an important endeavor toward achieving high-efficiency solar energy conversion. Now, a simple yet robust acid-treatment strategy is used to judiciously create an amorphous TiO₂ buffer layer intimately situated on the anatase TiO₂ surface as an electron-transport layer (ETL) for efficient electron transport. The facile acid treatment is capable of weakening the bonding of zigzag octahedral chains in anatase TiO₂, thereby shortening staggered octahedron chains to form an amorphous buffer layer on the anatase TiO₂ surface. Such amorphous TiO₂-coated ETL possesses an increased electron density owing to the presence of oxygen vacancies, leading to efficient electron transfer from perovskite to TiO₂. Compared to pristine TiO₂-based devices, the perovskite solar cells (PSCs) with acid-treated TiO₂ ETL exhibit an enhanced short-circuit current and power conversion efficiency.     

Z型光催化材料的研究进展

与植物光合作用相似, Z型光催化材料体系是由电子传输介质、光还原剂和光氧化剂组成的双光子体系, 其应用于光催化反应具有很大的优势: 借助双光子激发过程, 在不同光催化剂上分别完成氧化反应和还原反应, 有效促进了光生电荷的分离和迁移. Z型反应体系中的光催化剂只需分别满足各自的光激发过程和对应的半反应, 为光催化材料的选择和设计提供了很大的空间. 光催化还原位点和氧化位点分别在两个光催化半导体上, 还原和氧化过程相互分离, 可以有效抑制逆反应的发生. 同时, 催化材料光还原剂中的光生空穴被来自光氧化剂中的光生电子复合, 光催化体系的稳定性随之增强. Z型光催化材料体系, 表现出了宽光谱响应, 高稳定性, 高光生载流子的分离效率, 强氧化还原能力, 具有广阔的应用前景.     

Modulation of dendrite growth of cuprous oxide by electrodeposition

Cuprous oxides with different dendrite morphologies were formed on F-doped tin oxide (FTO) covered glass substrates by potentiostatic deposition of cupric acetate. The effects of pH value (varied from 5.00 to 5.80) of electrolytes on the crystal morphologies of cuprous oxide were studied. Different crystal morphologies of cuprous oxides were obtained by the change of velocity of vertical growth and lateral growth through varying the pH value of electrolyte. The processes of Cu₂O dendrite crystal growth were analyzed through SEM images at different deposition times. Photoelectrochemical properties of the Cu₂O thin films prepared in the system are also studied.     

Theoretical Study of Thermodynamics Properties and Bulk Modulus of SiC under High Pressure and Temperature

In extended pressure and temperature ranges, a theoretical study of the isothermal bulk modulus of SiC in B3 structure under high pressure and temperature is carried out by means of first-principles density functional theoretical calculations combined with the quasi-harmonic Debye model. Through the quasi-harmonic Debye model, the isothermal bulk modulus and its first and second pressure derivatives are successfully obtained. The thermodynamics properties of 3C-SiC are investigated in the pressure range of 0-100 GPa and the temperature range of 0-2000 K.     

原位水解沉积制备高效氮化钽微球太阳能分解水光阳极

利用一种新的原位水解沉积方法,以在高湿度空气中老化的甲醇中作为溶剂,通过乙醇钽水解而成前驱体微球颗粒沉积,制备出了高效的Ta₃N₅微球光电极,其1.6 V（vs RHE）电极电位下的光电流值达到了6.6 mA·cm^-2。相反地,在新鲜的甲醇溶液中没有钽前驱体微球颗粒沉积。这表明甲醇中水的含量对Ta₃N₅微球光电极的形成十分重要。另外,本制备方法也能方便地在其他透明导电衬底上制备出Ta₃N₅。     

Dual MOF-Derived MoS2/CdS Photocatalysts with Rich Sulfur Vacancies for Efficient Hydrogen Evolution Reaction

Cocatalyst plays an important role in efficient charge transfer and separation for photocatalysis. Herein, a MoS₂/CdS photocatalyst with MoS₂ as cocatalyst was designed by using Mo-MOF and Cd-MOF as precursors. Due to the existence of rich sulfur vacancies and 1T phase, MoS₂ shows strong charge capture and transport ability. The photo-generated electrons on conduction band (CB) can be bound by the sulfur vacancy of CdS and effectively transported to MoS₂ through the compact interface between the CdS nanoparticles and 2D large-scale MoS₂. The optimal photocatalyst 1 %MoS₂/CdS exhibited dramatically improved photocatalytic hydrogen production activity, which is 28 times that of pristine CdS and even about 2 times that of 1 %Pt/CdS with same loading amount of noble metal Pt. This work highlights the role of Mo-MOF derived MoS₂ with 1T-2H phases as a sustainable and prospective candidate of cocatalyst for improving charge separation and photocatalytic stability of MoS₂/CdS composites.     

Photophysical and photocatalytic properties of ANbO3 (A=Na,K) photocatalysts

Alkali niobates ANbO₃ (A=Na, K) photocatalysts were prepared by a conventional solid state reaction method. The samples were characterized by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, N₂ adsorption–desorption measurement, and scanning electron microscopy. It was found that ANbO₃ (A=Na, K) are indirect band-gap semiconductors with an orthorhombic system. The band structures and density of states (DOS) were theoretically calculated by the density functional theory. The photocatalytic activities were evaluated by photoreduction of CO₂ into CH₄. It was observed that KNbO₃ showed a higher photocatalytic activity than NaNbO₃ due to the narrower band gap and higher mobile charge carriers, which are helpful to enhance the light absorption and promote photoinduced carriers transport in the photocatalysts so as to improve the photocatalytic performance.     

Developing a novel fluorescence chemosensor by self-assembly of Bis-Schiff base within the channel of mesoporous SBA-15 for sensitive detecting of Hg ions

A novel fluorescence chemosensor for Hg²⁺ ion has been developed by the assembly of fluorescence Bis-Schiff base PMBA within the channels of CPTES-modified SBA-15. The ordered porous structure of SBA-15 is still retained on the hybrid chemosensor material PMBA-SBA. A remarkable fluorescence quenching of PMBA-SBA by Hg²⁺ ion was attributed to heavy atom effect of Hg²⁺ ion. The linear detecting range of the hybrid mesoporous chemosensor for Hg²⁺ ion is 2-15 μM and the lowest detection limit is 0.6 μM in ethanol/water (9:1, v/v) solution.