Nitrogen Doping and Carbon Coating Affects Substrate Selectivity of TiO2 Photocatalytic Organic Pollutant Degradation

A series of carbon-coated, nitrogen-doped titanium dioxide photocatalysts was produced and characterized. N-doped TiO₂ powder samples were prepared using a sol-gel method and subsequently used for making doped-TiO₂ thin films on glass substrates. Carbon layers were coated on the films by a thermal decomposition method using catechol. Diffuse reflectance spectra and Mott-Schottky analyses of the samples proved that nitrogen doping and carbon coating can slightly lower the band gap of TiO₂, broaden its absorption to visible light and enhance its n-type character. According to photocatalytic tests against model contaminants, carbon-coated nitrogen-doped TiO₂ films have better performance than simple TiO₂ on the degradation of Rhodamine B dye molecules, but are poorly effective for degrading 4-chlorophenol molecules. Several possible explanations are proposed for this result, supported by scavenging experiments. This reveals the importance of a broad substrate scope when assessing new photocatalytic materials for water treatment, something which is often overlooked in many literature studies.     

HfSe2 monolayer stability tuning by strain and charge doping

Strain and charge doping are the effective ways to modulate the electronic and phonon properties of materials. The effects of biaxial tensile strains and charge dopings on the stabilities of HfSe₂ monolayer have been systematically investigated using first-principles methods. Its two-dimensional Young's modulus is only 65.4 N/m, and it is easy to be stretched. When the tensile strain is applied on HfSe₂ monolayer, two of its phonon modes soften with one frequency decreasing to zero at critical strain. Our results show that electron and hole dopings could suppress the softening of phonon modes, and significantly enhance the ideal strength by 28% and 36%, respectively. The calculations for electronic structures and phonon dispersions provide the theoretical references for future nano-device designing.     

以磷化铁为添加剂沿(111)面生长磷掺杂金刚石大单晶

掺杂是调控金刚石性能的一种重要手段。本文采用温度梯度法,在5.6 GPa、1 312 ℃的条件下,选用Fe₃P作为磷源进行磷掺杂金刚石大单晶的合成。金刚石样品的显微光学照片表明,随着Fe₃P添加比例的增加,金刚石晶体的颜色逐渐变深,包裹体数量逐渐增加,晶形由板状转变为塔状直至骸晶。金刚石晶形的变化表明Fe₃P的添加使生长金刚石的V形区向右偏移,这是Fe₃P改变触媒特性的缘故。红外光谱分析表明,Fe₃P的添加使金刚石晶体中氮含量上升,这说明磷的进入诱使氮原子更容易进入金刚石晶格中。激光拉曼光谱测试表明,随着Fe₃P添加比例的增加,所合成的掺磷金刚石的拉曼峰位变化不大,其半峰全宽(FWHM)值变大,这说明磷的进入使得金刚石晶格畸变增加。XPS测试结果显示,随着Fe₃P添加比例的增加,金刚石晶体中磷相对碳的原子百分含量也会增加,这意味着添加Fe₃P所合成的金刚石晶体中有磷存在。     

Defect Engineering on Boron Nitride for O2 Activation and Subsequent Oxidative Desulfurization

The rational design of highly active hexagonal boron nitride (h-BN) catalysts at the atomic level is urgent for aerobic reactions. Herein, a doping impurity atom strategy is adopted to increase its catalytic activities. A series of doping systems involving O, C impurities and B, N antisites are constructed and their catalytic activities for molecular O₂ have been studied by density functional theory (DFT) calculations. It is demonstrated that O₂ is highly activated on O_N and B_N defects, and moderately activated on C_B and C_N defects, however, it is not stable on N_B and O_B defects. The subsequent application in oxidative desulfurization (ODS) reactions proves the O_N and C-doped (C_B, C_N) systems to be good choice for sulfocompounds oxidization, especially for dibenzothiophene (DBT). While the B_N antisite is not suitable for such aerobic reaction due to the extremely stable B−O^*−B species formed during the oxidation process.     

“Confinement effects for nano-electrocatalysts for oxygen reduction reaction”

Oxygen reduction reaction (ORR) is one of the most technologically relevant reactions. It occurs at the interface of the electrocatalyst and electrolyte, where oxygen reacts with protons and electrons to produce water. Because the electrocatalyst is dispersed on a high surface area support, morphological confinement becomes critical, as it dictates proton and oxygen transport. Furthermore, confinement is induced by ionomer, ionic liquids (ILs), or molecular additives, and their impact on electrocatalyst reactivity and transport properties is currently not well understood. We present an overview of electrostatics and mass transport–induced confinement and zoom in into ILs and molecular additives and try to unravel how local confinement induced by them impacts ORR.     

Spin polarisation in dual catalysts for the oxygen evolution and reduction reactions

Strongly correlated catalysts can be understood from precise quantum approximations. Incorporating properly electronic correlations thus let’s define Spin rules in catalysis, opening a new door towards optimum compositions for the most important reactions for a sustainable future.     

Promoting the Phosphidation Process using an Oxygen Vacancy Precursor for Efficient Hydrogen Evolution Reaction

Based on previous works, most of the transition metal phosphides (TMPs) were directly prepared by decomposing NaH₂PO₂ with the precursors at high temperatures, which resulted in different degrees of phosphidation in the final product. Therefore, it is necessary to design an innovative approach to enhance the degree of phosphidation in the material using crystal defects. Here, oxygen-vacancy iron oxide/iron foam (Ov-Fe₂O₃/IF) was firstly prepared by generating oxygen vacancy in situ in an iron foam through heating in vacuum conditions. Subsequently, FeP/IF was formed by phosphating Ov-Fe₂O₃/IF. Under the effects of oxygen vacancies, oxygen-vacancy iron oxide could be completely phosphatized to produce more active sites on the surface of the material. This, in turn, could result in a catalyst with exceptional hydrogen evolution activity. Thus, the successful fabrication of FeP/IF demonstrated in this work provides an effective and feasible way for the preparation of other high-efficiency catalysts.     

Correlating conductivity and Seebeck coefficient to doping within crystalline and amorphous domains in poly(3-(methoxyethoxyethoxy)thiophene)

Molecular doping of conjugated polymers (CPs) plays a vital role in optimizing organic electronic and energy applications. For the case of organic thermoelectrics, it is commonly believed that doping CPs with a strong dopant could result in higher conductivity (σ) and thus better power factor (PF). Herein, by investigating thermoelectric performance of a polar side-chain bearing CP, poly(3-(methoxyethoxyethoxy)thiophene) (P3MEET), vapor doped with fluorinated-derivative of tetracyanoquinodimethane FnTCNQ (n = 1, 2, 4), we show that using strong dopants can in fact have detrimental effects on the thermoelectric performance of CPs. Despite possessing higher electron affinity, doping P3MEET with F4TCNQ only results in a σ (27.0 S/cm) comparable to samples doped with other two weaker dopants F2TCNQ and F1TCNQ (26.4 and 20.1 S/cm). Interestingly, F4TCNQ-doped samples display a marked reduction in the Seebeck coefficient (α) compared to F1TCNQ- and F2TCNQ-doped samples from 42 to 13 μV/K, leading to an undesirable suppression of the PF. Structural characterizations coupled with Kang-Snyder modeling of the α–σ relation show that the reduction of α in F4TCNQ-doped P3MEET samples originates from the generation of low mobility carrier within P3MEET's amorphous domain. Our results demonstrate that factors such as dopant distribution and doping efficiency within the crystalline and amorphous domains of CPs should play a crucial role in advancing rational design for organic thermoelectrics.     

Ru、Rh、Pd掺杂GaSb的电子结构和光学性质

运用第一性原理计算方法研究了过渡族金属TM(TM=Ru、Rh、Pd)掺杂GaSb的电子结构和光学性质,结果表明:TM掺杂GaSb主要以TM替代Ga(TM @Ga)缺陷存在,并可增强GaSb半导体材料对红外光区光子的响应,使体系光学吸收谱的吸收边红移;TM@Ga所引入的杂质能级分布于零点费米能级附近,这极大地增强了体系的介电性能,促进了电子-空穴对的产生和迁移,因而提升了掺杂体系的光电转换效率;Ru 掺杂对GaSb光学性质的改善最为明显,当掺杂浓度为6.25%(原子数分数)且均匀掺杂时,Ru掺杂GaSb体系对红外光区光子的吸收幅度最大,有效提升了GaSb光电转换效率和光催化活性。     

Enhancement of thermoelectric properties of D-A conjugated polymer through constructing random copolymers with more electronic donors

Developing new D-A conjugated polymer system for thermoelectric (TE) application is highly desirable. Herein, a series of random copolymers by incorporating 3,4-ethylenedioxythiophene (EDOT) electron rich units into a diketopyrrolopyrrole (DPP) D-A conjugated polymer were designed and synthesized. Compared to the alternating conjugated copolymer PDPP-3T, the HOMO level of the random copolymers are increased as part of the electron deficiency acceptor DPP units in the polymer chain were superseded by electron rich EDOT, which could contribute to effective p-doping. Moreover, through incorporating EDOT to construct random copolymers, it can also induce an orientation change from face-on dominated to edge-on dominated orientation as well as enhance the packing of copolymer chains, which is beneficial to the charge transport. Under same doping condition, the electrical conductivities of the doped polymers increase and the Seebeck coefficient decrease as the increasing of EDOT content, resulting in an optimized power factor of 6.4 μW m⁻¹ K⁻² for the random polymer with EDOT content of 40% which is four times higher than that of alternating conjugated copolymer PDPP-3T. These results demonstrated that constructing random copolymers by incorporating more electronic donors into D-A conjugated polymers may be a promising strategy for developing TE conjugated polymers.