RR) under mild conditions is still challenging. Enzyme is well-known for its high efficiency and specificity under mild conditions. Electroenzymatic cascade systems combining the advantages of electrocatalysis andThe electrochemical nitrite reduction reaction provides an alternative approach to offer sustainable ammonia source routes for repairing imbalances in the global nitrogen cycle. In this work, electrocatalysis is combined with enzymatic catalysis to provide an efficient and clean process for recoverable ammonia production. NO 2 − is reduced to NH 3 by electroenzymatic cascade reduction reaction on a bioconjugate, in which 1-butyl-3-methylimidazolium bromide (IL BMB ) modified chloroperoxidase (CPO) is fixed on polyethyleneimine (PEI) modified multi-walled carbon nanotubes (MWCNT) to from bioconjugate (CPO-IL BMB /MWCNT-PEI). 15 N and 14 N isotope labeling reveal that the NH 3 species is derived from NO 2 − reduction. Density functional theory calculations identify that the Fe II species in heme center of CPO serve as the key active site for NO 2 − reduction. The amino groups derived from MWCNT-PEI not only serve as a bridge to covalently immobilize CPO but also enrich the NO 2 − ion at electrode/solution interface through electrostatic interactions. The low energy barrier of NO 2 − reduction and low adsorption free energy of the intermediate result in high Faradaic efficiency (96.4%), NH 3 yield (112.7 mg h −1 mg CPO −1 ), and high selectivity in pH 5.0 solution. The highly efficient electroenzymatic reaction ensurespromising applications in the conversion of NO 2 − to NH 3 .
The integration of enzymatic catalysis and electrocatalysis is promising for developing new green techniques for chemical production; however, how to coordinate the two processes for one-pot cascade reactions is a challenge. In this work, the electrocatalytic reduction of O 2 to H 2 O 2 by a reduced graphene oxide (rGO)/polyethylenimine (PEI) composite to initiate an enzymatic reaction by ionic liquid modified chloroperoxidase (CPO-IL EMB ) is presented. The whole cascade process is very efficient due to the four strategies, including avoiding the inactivation of CPO through the competitive reaction of oxidant (H 2 O 2 ), utilizing nanoproximity effects to construct substrate diffusion channels, fine-tuning the microenvironment of the enzymatic active site by IL EMB to increase the electron transfer efficiency as well as enhance the stability, and improving the selectivity of the 2e-ORR (oxidation reduction reaction) of rGO by PEI. The cascade efficiency is enhanced 5.5 times compared to manually adding H 2 O 2 , and 2.3 times compared to free CPO. Moreover, the rapid generation of intermediate (compounds I and X) and the orientation of substrate lead to ortho-selectivity of phenol chlorination.
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