类石墨烯C_3N_4纳米片光催化分解水制氢中的量子限域效应

Quantum Confinement Effect of Graphene-Like C_3N_4 Nanosheets for Efficient Photocatalytic Hydrogen Production from Water Splitting

从层状化合物获得的纳米片是一类新型纳米结构材料,这种二维各向异性的纳米甚至亚纳米级的材料具有独特的物理化学性能,其中最好的一个例证就是从石墨烯C_3N_4到石墨烯C_3N_4纳米片的转变。通过高温氧化热刻蚀方法将体相g-C_3N_4剥离成g-C_3N_4纳米片,应用于染料敏化可见光分解水产氢,表现出了较体相g-C_3N_4高于2.6倍的产氢速率。通过X射线衍射(XRD)、傅里叶变换红外(FTIR)光谱、扫描电子显微镜(SEM)、Brunauer-Emmett-Teller(BET)、荧光光谱和光电化学等表征研究了g-C_3N_4纳米片的结构及曙红(EY)和gC_3N_4纳米片之间的电子迁移过程。热剥离后的g-C_3N_4纳米片具有较高的比表面积,不仅可以更为有效地吸附染料分子,还因其量子限域效应大大增强了光生电荷的分离效率和电子转移效率,改善了电子沿平面方向的传输能力以及光生载流子的寿命,从而显著提高g-C_3N_4纳米片的光催化产氢活性。

Nanosheet materials obtained from laminar compounds are new two-dimensional anisotropic nanomaterials that can even reach the sub-nanometer scale. These materials possess unique physical and chemical properties. An example of such a nanosheet materials is graphitic carbon nitride （g-C3N4） nanosheets transformed from bulk g-C3N4. Here, g-C3N4 nanosheets were prepared from bulk g-C3N4 by high-temperature thermal oxidation. The photocatalytic activity of eosin （EY）-sensitized g-C3N4 nanosheets for hydrogen evolution was about 2.6 times higher than that of bulk g-C3N4. The structure of the g-C3N4 nanosheets and process of electron transfer between EY and the g-C3N4 nanosheets were investigated by X-ray diffraction （XRD）, Fourier transform infrared （FTIR） spectroscopy, scanning electron microscopy （SEM）, Brunauer-Emmett-Teller （BET） analysis, fluorescence spectroscopy, and photoelectrochemical measurements. The g-C3N4 nanosheets possessed high specific surface area. The g-C3N4 nanosheets not only effectively absorbed dye molecules, but also enhanced the separation and electron transport efficiencies of photogenerated charges because of their quantum confinement effect. The quantum confinement effect of g-C3N4 nanosheets widened their bandgap, improved electron transfer ability along the in-plane direction, and lengthened the lifetime of photoexcited charge carriers. As a result, the photocatalytic activity of the g-C3N4 nanosheets was improved compared with that of bulk g-C3N4.