A triazole-based covalent organic framework as a photocatalyst toward visible-light-driven CO2 reduction to CH4,Chemical Science

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A triazole-based covalent organic framework as a photocatalyst toward visible-light-driven CO2 reduction to CH4
Chemical Science ( IF 7.6 ) Pub Date : 2024-09-04 , DOI: 10.1039/d4sc03163f
Sandip Biswas ₁ , Faruk Ahamed Rahimi ₁ , R Kamal Saravanan ₁ , Anupam Dey ₁ , Jatin Chauhan ₁ , Devika Surendran ₁ , Sukhendu Nath _{2,

3} , Tapas Kumar Maji ₁

Affiliation

Solar-light driven reduction of CO₂ to CH₄ is a complex process involving multiple electron and proton transfer processes with various intermediates. Therefore, achieving high CH₄ activity and selectivity remains a significant challenge. Covalent organic frameworks (COFs) represent an emerging class of photoactive semiconductors with molecular level structural tunability, modular band gaps, and high charge carrier generation and transport within the network. Here, we developed a new heterocyclic triazole ring containing COF, TFPB-TRZ, through the condensation reaction between 1,3,5-tris(4-formylphenyl)benzene (TFPB) and 3,5-diamino-1,2,4-triazole (TRZ). The TFPB-TRZ COF with multiple heteroatoms shows suitable visible light absorption, high CO₂ uptake capability and an appropriate band diagram for CO₂ photoreduction. Photocatalysis results reveal a maximum CO₂ to CH₄ conversion of 2.34 mmol g⁻¹ with a rate of 128 μmol g⁻¹ h⁻¹ and high selectivity (∼99%) using 1-benzyl-1,4-dihydronicotinamide (BNAH) and triethylamine (TEA) as sacrificial agents. Under similar reaction conditions in the presence of direct sunlight, the TFPB-TRZ COF displays a maximum CH₄ yield of 493 μmol g⁻¹ with a rate of 61.62 μmol g⁻¹ h⁻¹, suggesting the robustness and light-harvesting ability of the COF photocatalyst. A femtosecond transient absorption (TA) spectroscopy study shows fast decay of excited state absorption (ESA) in the COF compared to the TFPB building unit due to efficient electron transfer to the catalytic site in the framework. The mechanism of CO₂ reduction to CH₄ is studied by DFT-based theoretical calculation, which is further supported by an in situ diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) study. The DFT results reveal that the lone pair of electrons on nitrogen heteroatoms present in the triazole ring of the TRZ moiety help in the stabilization of the CO intermediate during CO₂ to CH₄ conversion. Overall, this work demonstrates the use of a metal-free, recyclable COF-based photocatalytic system for solar energy storage by CO₂ reduction.

中文翻译：

基于三唑的共价有机骨架作为光催化剂，用于可见光驱动的 CO2 还原为 CH4

太阳光驱动的CO ₂还原为CH ₄是一个复杂的过程，涉及使用各种中间体的多个电子和质子转移过程。因此，实现高CH ₄活性和选择性仍然是一个重大挑战。共价有机框架 (COF) 代表了一类新兴的光活性半导体，具有分子级结构可调性、模块化带隙以及网络内高电荷载流子生成和传输。在这里，我们通过1,3,5-三(4-甲酰基苯基)苯(TFPB)和3,5-二氨基-1,2,4-之间的缩合反应开发了一种含有COF的新型杂环三唑环TFPB-TRZ 。三唑（TRZ）。具有多个杂原子的TFPB-TRZ COF表现出合适的可见光吸收、高CO ₂吸收能力和合适的CO ₂光还原能带图。光催化结果表明，使用 1-benzyl-1,4-dihydronicotinamide (BNAH) 时，CO ₂向 CH ₄的最大转化率为 2.34 mmol g ⁻¹ ，转化率为 128 μmol g ⁻¹ h ⁻¹且选择性高 (∼99%)和三乙胺（TEA）作为牺牲剂。在存在直射阳光的类似反应条件下， TFPB-TRZ COF 显示出最大 CH ₄产率为 493 μmol g ^{-1 ，}速率为 61。62 μmol g ^-1 h ^-1 ，表明COF光催化剂的稳健性和光捕获能力。飞秒瞬态吸收 (TA) 光谱研究表明，与 TFPB 结构单元相比，COF 中的激发态吸收 (ESA) 快速衰减，这是由于电子有效转移到框架中的催化位点。通过基于DFT的理论计算研究了CO ₂还原为CH ₄的机理，并得到原位漫反射红外傅里叶变换光谱（DRIFTS）研究的进一步支持。 DFT结果表明，TRZ部分的三唑环中氮杂原子上的孤对电子有助于CO中间体在CO ₂转化为CH ₄过程中的稳定。总的来说，这项工作展示了使用无金属、可回收的基于COF的光催化系统通过CO ₂还原来存储太阳能。

更新日期：2024-09-04

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