供体-受体型卟啉基金属有机框架实现有效电荷分离高效光催化析氢

Efficient charge separation by a donor‐acceptor system integrating dibenzothiophene into a porphyrin‐based metal‐organic framework for enhanced photocatalytic hydrogen evolution

利用光催化的方法将太阳能转化为氢能,是生产可持续燃料的有效途径之一.金属有机框架(MOFs)作为一类新兴的有机-无机杂化材料引起了研究者的广泛关注.由于MOFs材料的结构可调性,在框架中引入具有良好光吸收性能的基元,可以使MOFs在分子尺度有序排列的同时实现光催化析氢.单组分MOFs由于结构的相对有限性,存在电荷分离效率低的问题,而供体-受体(D-A)型双组分MOFs能够有效地促进电荷转移,同时电荷转移相互作用可以扩大光谱吸收范围,这些优良性能使之成为极具潜力的光催化剂.因此,寻找能够形成D-A结构的MOFs材料,实现高效光催化析氢仍然是一项亟需解决的科学问题.本文采用简单的溶剂热法将供体卟啉与受体二苯并噻吩砜(BTDO)相结合,构筑了一种卟啉基(TCPP)的D-A型MOF(TCPP-Zn-BTDO),其中, TCPP供体分子和BTDO受体分子通过Zn2+离子配位连接.红外吸收光谱中砜基的特征吸收峰以及电感耦合等离子体质谱表明有硫元素存在,说明成功引入了电子受体BTDO.TCPP-Zn-BTDO的光催化析氢效率较好,为1.48 mmolg^(-1)h^(-1),是单组分MOF(TCPP-Zn)的3.14倍.此外, TCPP-Zn-BTDO具有较好的光催化稳定性,连续40 h实验后,光催化活性没有显著降低.紫外可见吸收光谱和光电流测试结果表明, TCPP-Zn-BTDO具有更高的光吸收效率和更强的光电流响应,说明TCPP-Zn-BTDO可以产生更多的光生载流子,从而有利于光催化析氢反应.同时, BTDO的加入增大了分子偶极子,有效增强了内建电场.表面电荷密度以及开路电压等表明, TCPP-Zn-BTDO的内建电场强度是单组分MOF的1.44倍.通过莫特肖特基曲线与禁带宽度计算出TCPP-Zn-BTDO具有更负的导带位置,因而具有较强的热力学驱动力和电子还原能力,从而促进光催化析氢.综上,本文设计了一种简单的方法来构筑高活性的D-A型MOF, D与A之间的电荷转移相互作用能有效促进光生载流子分离,为光催化析氢材料的设计提供参考.

The high selectivity of organic ligands and metal ions that construct metal-organic frameworks(MOFs)enables considerable richness in the MOF structure and confers them with numerous potentials,rendering MOFs extremely interesting to researchers in the field of photocatalytic hydrogen evolution.However,the severe recombination of photoinduced charge carriers significantly restricts the photocatalytic performance of the MOFs.Herein,we report a porphyrin-based donor-acceptor(D-A)MOF consisting of meso-tetra(4-carboxyphenyl)porphyrin(TCPP)donor and a thieno[3,2b:20,30-d]thiophene-S,S-dioxide(BTDO)acceptor via coordination with Zn^(2+)ions,and denoted as TCPP-Zn-BTDO.The charge-transfer interaction from TCPP to BTDO broadened the light absorption range of TCPP-Zn-BTDO,with a high theoretical spectral efficiency of 69.72%.The D-A structure of TCPP-Zn-BTDO effectively enhanced the internal electric field because of its large molecular dipole,which significantly improved the charge-separation efficiency.Based on the aforementioned improvements,TCPP-Zn-BTDO showed a three-fold higher photocatalytic hydrogen evolution rate than the corresponding monocomponent MOF of TCPP-Zn without the BTDO acceptor.The D-A MOF reported in this study provides a new strategy for enhancing the photocatalytic performance of MOF.