含錸聯吡啶錯合物之高分子合成與其在二氧化碳光還原反應中的應用

Abstract

本研究成功合成兩類含聯吡啶配位基的高分子材料，並藉由聯吡啶基團與Re金屬中心配位，應用於光還原二氧化碳反應。分別為以降冰片烯為主鏈的P1與P2，以及線性共軛高分子P3與P4，利用核磁共振光譜學、紅外線衰減全反射光譜學、X射線光電子能譜學與掃描式電子顯微鏡搭配X射線能量散布分析儀確認化學結構與Re金屬的成功螯合。熱重分析顯示這些高分子展現優異的熱穩定性，熱裂解溫度皆超過300 °C，並具備良好的光吸收特性，特別是P4因共軛結構延伸而表現出更強的可見光吸收與最低的光學能隙。電化學分析顯示，這些高分子具有適合光驅動CO2還原的最高佔據分子軌域與最低未占分子軌域能階，光響應電流的結果亦與光催化效率正相關。在光催化CO2還原實驗中，P4展現最高初始活性，CO產率2.36 mmol g⁻¹ h⁻¹，催化轉換數達17.64，P1則展現最佳穩定性，其經三次循環照光實驗後仍保有80%活性，顯示空間隔離結構有助於抑制Re雙金屬副產物形成，維持催化性能。控制實驗則交叉驗證CO產生來自CO2光還原反應，且照光結果顯示1,3-二甲基-2-苯基-2,3-二氫-1H-苯並[d]咪唑與三乙醇胺具協同作用，能大幅提升效率。整體而言，本研究展示分子設計對光催化劑性能的影響，提供高分子型光催化劑未來設計的參考方向。

This study has successfully synthesized two types of polymers containing bipyridine ligands, which coordinate to Re metal centers for application in photocatalytic CO2 reduction. The polymers include P1 and P2 with a norbornene-based backbone, and linear conjugated polymers P3 and P4. Their structures and Re coordination have been confirmed by nuclear magnetic resonance spectroscopy, attenuated total reflectance Fourier-Transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy with energy-dispersive X-ray spectroscopy. Thermogravimetric analysis shows that these polymers exhibit excellent thermal stability, with decomposition temperatures exceeding 300 °C, and good light absorption properties, particularly P4, which, due to its extended conjugation, shows stronger visible light absorption and the smallest optical bandgap. Electrochemical analysis indicates that these polymers possess suitable highest occupied molecular orbital and lowest unoccupied molecular orbital levels for driving CO2 reduction, and their photocurrent responses show a positive correlation with photocatalytic efficiency. In photocatalytic CO2 reduction experiments, P4 shows the highest initial activity, with a CO production rate of 2.36 mmol g⁻¹ h⁻¹ and a turnover number of 17.64, while P1 demonstrates the best stability, retaining 80% of its activity after three reaction cycles, indicating that its spatial isolation structure helps suppress the formation of catalytically inactive Re bimetallic byproducts and maintain catalytic performance. Control experiments verify that the generated CO originates from CO2 photoreduction and confirm that 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole and triethanolamine exhibit a synergistic effect that significantly enhances efficiency. Overall, this study demonstrates the influence of molecular design on the performance of photocatalysts and provides guidance for the future development of polymer-based photocatalysts.