Computational study on the half-metallicity in transition metal–oxide-incorporated 2D g-C3N4 nanosheets

In this study, based on the first-principles calculations, we systematically investigated the electronic and magnetic properties of the transition metal–oxide-incorporated 2D g-C₃N₄ nanosheet (labeled C₃N₄– TM–O, TM= Sc–Mn). The results suggest that the TM–O binds to g-C₃N₄ nanosheets strongly for all systems. We found that the 2D C₃N₄–TM–O framework is ferromagnetic for TM= Sc, Ti, V, Cr, while it is antiferromagnetic for TM= Mn. All the ferromagnetic systems exhibit the half-metallic property. Furthermore, Monte Carlo simulations based on the Heisenberg model suggest that the Curie temperatures (T_c) of the C₃N₄–TM–O (TM= Sc, Ti, V, Cr) framework are 169 K, 68 K, 203 K, and 190 K, respectively. Based on Bader charge analysis, we found that the origin of the half-metallicity at Fermi energy can be partially attributed to the transfer of electrons from TM atoms to the g-C₃N₄ nanosheet. In addition, we found that not only electrons but also holes can induce half-metallicity for 2D g-C₃N₄ nanosheets, which may help to understand the origin of half-metallicity for graphitic carbon nitride.     

风力测定仪

风力测定仪用来测量风力的大小，它是根据滑动变阻器改变线路中电流的原理制成的测量类仪器．通过风力的大小改变滑动变阻器的阻值，从而引起线路中电流的变化，由电流表的示数指示风力的大小．本文通过两个例题的形式，从物理的角度来讨论风力测定仪的构造、原理和风力刻度的标定．     

Dissociation of liquid water on defective rutile TiO2 (110) surfaces using ab initio molecular dynamics simulations

In order to obtain a comprehensive understanding of both thermodynamics and kinetics of water dissociation on TiO₂, the reactions between liquid water and perfect and defective rutile TiO₂ (110) surfaces were investigated using ab initio molecular dynamics simulations. The results showed that the free-energy barrier (~4.4 kcal/mol) is too high for a spontaneous dissociation of water on the perfect rutile (110) surface at a low temperature. The most stable oxygen vacancy (V_o1) on the rutile (110) surface cannot promote the dissociation of water, while other unstable oxygen vacancies can significantly enhance the water dissociation rate. This is opposite to the general understanding that V_o1 defects are active sites for water dissociation. Furthermore, we reveal that water dissociation is an exothermic reaction, which demonstrates that the dissociated state of the adsorbed water is thermodynamically favorable for both perfect and defective rutile (110) surfaces. The dissociation adsorption of water can also increase the hydrophilicity of TiO₂.     

复合改性膨胀石墨的制备及对酸性艳蓝染料的吸附

采用相同反离子协同磷酸活化法, 以十六烷基三甲基溴化铵(CTAB)-KBr为复合改性剂, 制备了一种高效吸附剂复合改性膨胀石墨(M-EG), 通过扫描电子显微镜(SEM)、 傅里叶变换红外光谱(FTIR)及X射线电子能谱(XPS)等对膨胀石墨(EG)和改性膨胀石墨(M-EG)的形貌结构、 组成和价态进行了表征, 考察了EG和M-EG对酸性艳蓝染料废水的处理效果. 结果表明, 复合改性后的膨胀石墨孔隙度变大, 表面含氮和溴官能团增多. 吸附剂M-EG对酸性艳蓝染料废水具有较高的吸附性能, 在pH=1.0及30 ℃条件下对染料的去除率达到94.13%; EG符合二级动力学吸附模型, 用Langmuir等温线方程拟合效果较好; M-EG符合二级吸附动力学方程, 同时符合Langmuir和Freundlich等温吸附模型; M-EG的吸附动力学常数大于EG吸附动力学常数.     

Dissociation of liquid water on defective rutile TiO<Subscript>2</Subscript> (110) surfaces using <Emphasis Type="Italic">ab initio</Emphasis> molecular dynamics simulations

In order to obtain a comprehensive understanding of both thermodynamics and kinetics of water dissociation on TiO₂, the reactions between liquid water and perfect and defective rutile TiO₂ (110) surfaces were investigated using ab initio molecular dynamics simulations. The results showed that the free-energy barrier (~4.4 kcal/mol) is too high for a spontaneous dissociation of water on the perfect rutile (110) surface at a low temperature. The most stable oxygen vacancy (Vo₁) on the rutile (110) surface cannot promote the dissociation of water, while other unstable oxygen vacancies can significantly enhance the water dissociation rate. This is opposite to the general understanding that Vo₁ defects are active sites for water dissociation. Furthermore, we reveal that water dissociation is an exothermic reaction, which demonstrates that the dissociated state of the adsorbed water is thermodynamically favorable for both perfect and defective rutile (110) surfaces. The dissociation adsorption of water can also increase the hydrophilicity of TiO₂.     

Computational study on the half-metallicity in transition metal—oxide-incorporated 2D g-C<Subscript>3</Subscript>N<Subscript>4</Subscript> nanosheets

In this study, based on the first-principles calculations, we systematically investigated the electronic and magnetic properties of the transition metal–oxide-incorporated 2D g-C₃N₄ nanosheet (labeled C₃N₄–TM–O, TM = Sc–Mn). The results suggest that the TM–O binds to g-C₃N₄ nanosheets strongly for all systems. We found that the 2D C₃N₄–TM–O framework is ferromagnetic for TM = Sc, Ti, V, Cr, while it is antiferromagnetic for TM = Mn. All the ferromagnetic systems exhibit the half-metallic property. Furthermore, Monte Carlo simulations based on the Heisenberg model suggest that the Curie temperatures (T _c ) of the C₃N₄–TM–O (TM = Sc, Ti, V, Cr) framework are 169 K, 68 K, 203 K, and 190 K, respectively. Based on Bader charge analysis, we found that the origin of the half-metallicity at Fermi energy can be partially attributed to the transfer of electrons from TM atoms to the g-C₃N₄ nanosheet. In addition, we found that not only electrons but also holes can induce half-metallicity for 2D g-C₃N₄ nanosheets, which may help to understand the origin of half-metallicity for graphitic carbon nitride.