Cr2O3/C@TiO2核壳型复合材料的设计合成及其光催化产氢性能

随着社会经济的快速发展,能源危机和环境污染问题成为世界各国关注的焦点.通过光催化剂将太阳能用于污染物降解、分解水产氢、CO2还原及有机物合成等领域,是解决上述问题的理想途径.过渡金属氧化物TiO2因其稳定性高、催化活性好、制备简单等优点,被认为是最理想的光催化材料.然而,TiO2带隙较宽、光响应范围窄、光量子效率低等缺点限制了其实际应用.将碳或Cr2O3与TiO2结合形成复合结构已被证明可以有效提升其光催化性能.另一方面,金属离子的掺杂可以有效提高氧化钛的可见光响应.本文利用具有高比表面积的金属有机骨架材料MIL-101(Cr)纳米材料作为模板、镉源和碳源,首先在MIL-101(Cr)表面可控生长TiO2纳米颗粒,获得MIL-101(Cr)@TiO2复合结构;然后在氮气保护下碳化形成Cr2O3/C@TiO2核壳型复合材料.碳化后,制备的复合材料具有模板的八面体形貌和高比表面积,MIL-101(Cr)中的Cr元素一部分会形成Cr2O3,一部分会掺杂到TiO2中,使得TiO2的吸收边红移.此外,Cr2O3/C@TiO2中的C有利于光的吸收和载流子的分离.这种独特的纳米结构赋予Cr2O3/C@TiO2复合材料优异的光催化性能.在300 W氙灯照射下,该复合材料光解水产氢的速率为446μmol h?1 g?1,约为纯TiO2的4倍.在可见光照射下,Cr2O3/C@TiO2分解水产氢的速率为25.5μmol h?1 g?1.将获得的粉体催化剂制备成光电极发现,Cr2O3/C@TiO2在全幅光照射下的光电流密度在0.4 V(vs.Ag/AgCl)下达到2.3 mA/cm2,约为纯TiO2的3.5倍.Cr2O3/C@TiO2光催化产氢活性的提高一方面是由于Cr掺杂到TiO2中使得其具有可见光响应,另一方面MIL-101碳化获得的Cr2O3/C有效促进了光生载流子的分离.

Synthesis of core-shell nanostructured Cr2O3/C@TiO2 for photocatalytic hydrogen production

In this study, the Cr2O3/C@TiO2 composite was synthesized via the calcination of yolk–shell MIL-101@TiO2. The composite presented core–shell structure, where Cr-doped TiO2 and Cr2O3/C were the shell and core, respectively. The introduction of Cr3+ and Cr2O3/C, which were derived from the calcination of MIL-101, in the composite enhanced its visible light absorbing ability and lowered the recombination rate of the photogenerated electrons and holes. The large surface area of the Cr2O3/C@TiO2 composite provided numerous active sites for the photoreduction reaction. Con-sequently, the photocatalytic performance of the composite for the production of H2 was better than that of pure TiO2. Under the irradiation of a 300 W Xe arc lamp, the H2 production rate of the Cr2O3/C@TiO2 composite that was calcined at 500 ℃ was 446 μmol h?1 g?1, which was approxi-mately four times higher than that of pristine TiO2 nanoparticles. Moreover, the composite exhibited the high H2 production rate of 25.5 μmol h?1 g?1 under visible light irradiation (λ > 420 nm). The high photocatalytic performance of Cr2O3/C@TiO2 could be attributed to its wide visible light photore-sponse range and efficient separation of photogenerated electrons and holes. This paper offers some insights into the design of a novel efficient photocatalyst for water-splitting applications.