Wavelength-sensitive photocatalytic H2 evolution from H2S splitting over g-C3N4 with S,N-codoped carbon dots as the photosensitizer

Photocatalytic splitting of hydrogen sulfide(H2S) for hydrogen evolution is a promising method to solve the energy and environmental issues.In this work,S,N-codoped carbon dots(S,N-CDs)/graphitic carbon nitride(g-C3N4) nanosheet is synthesized by hydrothermal method as an efficient photocatalyst for the decomposition of H2S.In addition to the characterization of the morphology and structure,chemical state,optical and electrochemical performances of S,N-CDs/g-C3N4,hydrogen evolution tests show that the activity of g-C3N4 is improved by introducing S,N-CDs,and the enhancement depends strongly on the wavelength of incident light.The photocatalytic hydrogen production rate of S,N-CDs/g-C3N4 composite reaches 832 μmol g-1h-1, which is 38 times to that of g-C3N4 under irradiation at 460 nm.Density functional theory calculations and electron paramagnetic resonance as well as photoluminescence technologies have altogether authenticated that the unique wavelength-dependent photosensitization of S,N-CDs on g-C3N4;meanwhile,a good match between the energy level of S,N-CDs and g-C3N4 is pivotal for the effective photocatalytic activity.Our work has unveiled the detailed mechanism of the photocatalytic activity enhancement in S,N-CDs/g-C3N4 composite and showed its potential in photocatalytic splitting of H2S for hydrogen evolution.

CsPbBr_(3)纳米晶微观形貌非依赖的线性吸收截面

胶体钙钛矿纳米晶的形貌变化赋予其不同的光学和电子特性,其中,线性吸收截面是决定材料本征光物理特性及其应用潜力的主要参数.本文研究了三种不同形貌的全无机钙钛矿CsPbBr3纳米晶(纳米立方体、纳米片和纳米线),通过飞秒瞬态吸收光谱分析了它们的线性吸收截面值σ.在高于带隙的能量激发下,单个CsPbBr_(3)纳米晶的吸收截面值与形貌无关,且随着粒子的体积(VNC)呈σ400=9.45×10^(4)cm^(−1)×VNC(cm^(2))趋势变化.密度泛函理论证实了形貌对光学选择规则基本没有影响,同时,根据吸收截面值也计算得到了定义本征辐射复合率的爱因斯坦自发辐射系数.然而,当激发能接近带隙(460 nm)时,吸收截面值对纳米晶尺寸的依赖关系变弱,取值满足σ460=2.82×10^(8)cm0.65×(VNC)0.45(cm^(2)),这主要归因于钙钛矿纳米晶的离散能级及靠近带边的较低的态密度.本文的研究结果为洞悉钙钛矿纳米晶的光学特性提供了深入的见解.