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.

InP quantum dots on g-C_(3)N_(4) nanosheets to promote molecular oxygen activation under visible light

Largely limited by the high dissociation energy of the O—O bond,the photocatalytic molecular oxygen activation is highly challenged,which re strains the application of photocatalytic oxidation technology for atmospheric pollutants removal.Herein,we design and fabricate the InP QDs/g-C_(3)N_(4) compounds.The introduction of InP QDs promotes the charge transfer within the interface resulting in the effective separation of photo-generated carriers.Furthermore,InP QDs greatly facilitates the activation of molecular oxygen and promote the formation of O_(2)·under visible-light illuminatio n.These conclusions are identified by experimental and calculation results.Hence,NO can be combined with the O_(2)·to form O—O—N—O intermediate to direct conversion into NO_(3).As a result,the NO removal ratio of g-C_(3)N_(4) has a one fold increase after InP QDs loaded and the generation of NO_(2) is effectively inhibited.This wo rk may provide a strategy to design highly efficient materials for molecular oxygen activation.

通过瞬态可见和瞬态中红外光谱研究InP/ZnS QDs无机配体诱导的表面空穴转移和构型调整过程

光生载流子动力学过程可以显著影响材料光催化活性.通常,光生电子的转移速率远高于光生空穴的,致使空穴的转移和累积成为影响光催化效率的关键因素.因此,深入探究光生空穴转移过程和动力学可以极大地帮助我们认识和理解光催化机理,但该工作鲜有人关注研究.本工作中,时间分辨荧光光谱(TRPL)和飞秒瞬态可见吸收光谱(fsTA)表明空穴会从InP转移至表面S^(2-)配体.此外,瞬态中红外光谱(TRIR)中S^(2-)配体伸缩振动信号表明该空穴转移时间为4.2 ps.转移至S^(2-)配体的空穴具有明显的长寿命特征(>4.5 ns)并且会导致表面活性物的静电解离和构型重组.最后,通过与其他无机配体(Cl^(-)、PO_(4)^(3-))比较,我们发现S^(2-)配体具有最合适平衡的离子半径和净电荷,因此带有该配体的InP/ZnS量子点(InP/ZnS QDs)光催化剂具有最高的光解硫化氢产氢活性(213.6μmol mg^(-1)).本文的研究结果为理解InP QDs光催化过程和机理提供了有价值的见解.