Using reduced nicotinamide adenine dinucleotide (NADH) as cofactor, formate dehydrogenase (FDH) can reversely catalyze CO reduction to formic acid. However, the industrialized application of FDH is fairly limited due to its high cost and stoichiometric cofactor consumption. Enzyme immobilization and cofactor regeneration are vital solutions to these problems. Ascribed to the benefits of utilizing a cheap, environmentally friendly, and renewable energy source, photocatalytic NADH regeneration is naturally sustainable and promising. Nonetheless, the rate-matching and compatibility between photocatalysis and enzyme catalysis have not been well revealed. In this study, polyethyleneimine (PEI) modified hollow fiber membrane (HFM) as the enzyme support was integrated with a visible-light-driven NADH regeneration system using thiophene-modified macroporous graphitic carbon nitride (ATCN-CN) as the catalyst. First, NADH regeneration conditions were regulated to accommodate enzyme catalysis. Then, the photo-enzyme coupled system (PECS) for the sustainable synthesis of formic acid with triethanolamine (TEOA) or HO as electron donor was constructed, and the influencing factors were investigated. At last, the PECS was compared with other methods as well as a system that used FDH immobilized on silica nanoparticles. The results show that the reaction pH, electron donor, and catalyst concentration have a significant impact on NADH regeneration. For the PECS with TEOA as electron donor, the optimal pH value and photocatalyst concentration for formic acid synthesis are 7.0 and 1.2 mg mL, respectively. With the initial addition of 1 mmol L NAD, a formic acid yield of 35.3% was obtained after 5 h, standing out among the reported values. HO as a green and low-cost electron donor meets the desire for low-cost photocatalysis. Although the production of formic acid after 5 h was lower in the PECS with HO as electron donor than in the TEOA system, it was still 14.6 times that of the immobilized enzyme system without cofactor regeneration, and the yield of formic acid could reach 14.8% and 98.3% with 1 or 0.1 mmol L NAD, validating that current PECS is feasible to a sustainable and green synthesis of solar fuel from CO.

中文翻译：

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用于二氧化碳转化为太阳能燃料的光酶耦合系统：光催化和酶催化之间的速率匹配和相容性

甲酸脱氢酶（FDH）以还原型烟酰胺腺嘌呤二核苷酸（NADH）为辅因子，可以反向催化CO还原为甲酸。然而，由于FDH成本高、辅因子消耗量大，其工业化应用相当有限。酶固定化和辅因子再生是解决这些问题的重要方案。由于利用廉价、环保和可再生能源的优点，光催化 NADH 再生自然是可持续的和有前途的。尽管如此，光催化和酶催化之间的速率匹配和相容性尚未得到很好的揭示。在本研究中，聚乙烯亚胺（PEI）改性中空纤维膜（HFM）作为酶载体，与使用噻吩改性大孔石墨氮化碳（ATCN-CN）作为催化剂的可见光驱动的NADH再生系统集成。首先，调节 NADH 再生条件以适应酶催化。然后，构建了以三乙醇胺（TEOA）或H2O为电子供体可持续合成甲酸的光酶耦合系统（PECS），并研究了影响因素。最后，将 PECS 与其他方法以及使用固定在二氧化硅纳米颗粒上的 FDH 的系统进行了比较。结果表明，反应pH、电子给体和催化剂浓度对NADH再生有显着影响。对于以TEOA为电子给体的PECS，合成甲酸的最佳pH值和光催化剂浓度分别为7.0和1.2 mg·mL。最初添加 1 mmol·L NAD，5 小时后甲酸产率为 35.3%，在报道的值中脱颖而出。 H2O作为绿色、低成本的电子供体满足了低成本光催化的需求。虽然以H2O为电子供体的PECS系统5 h后甲酸产量低于TEOA系统，但仍是未辅因子再生的固定化酶系统的14.6倍，甲酸收率可达14.8% 1 mmol/L NAD 或 0.1 mmol L NAD 时的转化率为 98.3%，验证了当前的 PECS 对于从 CO 中可持续、绿色合成太阳能燃料是可行的。