Rational design of isostructural 2D porphyrin-based covalent organic frameworks for tunable photocatalytic hydrogen evolution

Rufan Chen,Xiao-Ya Gao,Li-Zhu Wu,Arindam Mal,Yang Wang,Lijie Qiao,Lei Gao,Yuan Ma,Xu-Bing Li,Cheng Wang

doi:10.1038/s41467-021-21527-3

Abstract

Covalent organic frameworks have recently gained increasing attention in photocatalytic hydrogen generation from water. However, their structure-property-activity relationship, which should be beneficial for the structural design, is still far-away explored. Herein, we report the designed synthesis of four isostructural porphyrinic two-dimensional covalent organic frameworks (MPor-DETH-COF, M = H2, Co, Ni, Zn) and their photocatalytic activity in hydrogen generation. Our results clearly show that all four covalent organic frameworks adopt AA stacking structures, with high crystallinity and large surface area. Interestingly, the incorporation of different transition metals into the porphyrin rings can rationally tune the photocatalytic hydrogen evolution rate of corresponding covalent organic frameworks, with the order of CoPor-DETH-COF < H2Por-DETH-COF < NiPor-DETH-COF < ZnPor-DETH-COF. Based on the detailed experiments and calculations, this tunable performance can be mainly explained by their tailored charge-carrier dynamics via molecular engineering. This study not only represents a simple and effective way for efficient tuning of the photocatalytic hydrogen evolution activities of covalent organic frameworks at molecular level, but also provides valuable insight on the structure design of covalent organic frameworks for better photocatalysis.

Highlights

Covalent organic frameworks have recently gained increasing attention in photocatalytic hydrogen generation from water
In order to construct stable porphyrin-based 2D Covalent organic frameworks (COFs) for photocatalytic hydrogen evolution from water, we designed and synthesized porphyrinic aldehydes p-MPor-CHO (M = H2, Co, Ni, and Zn), which could react with 2,5-diethoxyterephthalohydrazide (DETH) to form the designed isostructural MPor-DETH-COF (M = H2, Co, Ni, and Zn) through condensation reaction (Fig. 1)
The condensation reaction was performed in a mixed solvent of 1,2-dichlorobenzene, butanol, and aqueous acetic acid at 120 °C, but the ratio of the solvents, the concentration and the amount of acetic acid and the reaction time were optimized for each COF synthesis

Summary

Introduction

Covalent organic frameworks have recently gained increasing attention in photocatalytic hydrogen generation from water. Our results clearly demonstrate that these four COFs have high crystallinity and surface area, and the incorporation of different transition metal ions into porphyrin rings apparently influences the charge-carrier dynamics properties of corresponding COFs. When irradiated with visible light in the presence of H2PtCl6 and triethanolamine (TEOA), all MPor-DETH-COFs can continually produce hydrogen from water while retaining the framework. When irradiated with visible light in the presence of H2PtCl6 and triethanolamine (TEOA), all MPor-DETH-COFs can continually produce hydrogen from water while retaining the framework These four COFs show rationally tunable activity toward photocatalytic hydrogen evolution with the order of CoPor-DETH-COF (25 μmol g−1 h−1) < H2Por-DETH-COF (80 μmol g−1 h−1) < NiPor-. DETH-COF (211 μmol g−1 h−1) < ZnPor-DETH-COF (413 μmol g−1 h−1), which can be mainly explained by their tailored chargecarrier dynamics via molecular engineering

Methods

Results

Conclusion