NiFe-MOF和氮氧自由基协同增强甾醇电催化氧化OA北大核心CSTPCD

Conventional oxidation methods of sterol intermediates using the heavy metal chromium as an oxidant has critical drawbacks,such as high toxicity and environmental pollution.Electrocatalytic oxidation(ECO),on the other hand,is considered a promising alternative to conventional processes owing to its high efficiency,eco-friendliness,and controllability.However,ECO currently faces two major challenges:low current densities and reduced space-time yields.In this study,a single-step solvothermal method was employed to synthesize self-supported nickel-iron metal-organic framework(NiFe-MOF)nanosheet electrocatalysts on graphite felt.Various analytical techniques were employed to comprehensively characterize the synthesized NiFe-MOF,including scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),X-ray diffraction(XRD),Raman spectroscopy,and Brunauer-Emmett-Teller(BET)analysis Furthermore,we implemented a synergistic electrocatalytic strategy by combining the NiFe-MOF catalyst with aminoxyl radicals,i.e.,4-acetamido-2,2,6,6-tetramethyl-1-piperidine-N-oxyl(ACT),to enhance the performance of the ECO reaction.According to the results of structural characterization,the synthesized NiFe-MOF exhibited an amorphous nanosheet structure with a high specific surface area and microporosity.Moreover,we successfully achieved continuous flow with enhanced mass transfer during the electrocatalytic oxidation of 19-hydroxy-4-androstene-3,17-dione(1a)at a current density of 100 mA·cm-2.The optimal reaction conditions for the ECO reaction were as follows:100 mmol·L-1 concentration of 1a,10%(molar fraction)of ACT,a 1 mol·L-1 Na2CO3/acetonitrile electrolyte(6:4),room temperature,pH 12.5,and a flow rate of 225 mL·min-1.Under these conditions,the conversion and selectivity of the reaction reached outstanding levels of 99 and 98%,respectively.Moreover,the space-time yield was calculated to be as high as 15.88 kg·m-3·h-1,with a remarkable 35-fold increase compared to that achieved in a batch reactor.The NiFe-MOF/ACT synergistic system demonstrated a high conversion rate for ECO even after 10 reaction cycles.To assess the system's efficacy in converting other sterols,we conducted an analysis of substrate expansion,which yielded conversion rates exceeding 95%.The SEM,TEM,and XPS results of the catalyst obtained before and after the reaction indicated that the alkaline electrolyte could effectively reconstitute the NiFe-MOF structure,leading to a significant improvement in its performance.By leveraging a ten-fold increased surface area of the NiFe-MOF and constructing a continuous flow electroreactor for ECO with a constant current,we achieved a remarkable space-time yield of 12.99 kg·m-3·h-1.Thus,we developed a synergistic electrocatalytic oxidation strategy based on NiFe-MOF/ACT,and this study not only provides valuable insights for realizing the selective oxidation of sterols but also contributes to the advancement of sustainable and efficient chemical processes.