A Bipolar CdS/Pd Photocatalytic Membrane for Selective Segregation of Reduction and Oxidation Processes

Abstract

A photocatalytically active bipolar membrane consisting of a CdS photocatalyst and Pd electrocatalyst has been constructed to carry out environmentally relevant oxidation and reduction processes. The ion exchange property of a bipolar membrane (BPM) has allowed us to load the CdS photocatalyst on one side and Pd electrocatalyst on the other side. By inserting the photocatalytic BPM-CdS/Pd membrane between the two compartments of an H-cell, we can separate the reduction and oxidation processes. Following visible light excitation of CdS in the BPM-CdS/Pd membrane, we can induce vectorial electron transfer from CdS to Pd and to an electron acceptor (4-nitrophenol). The holes generated at CdS are scavenged by ethanol or 4-chlorophenol. The photocatalytic reduction rate dependence on the Pd loading in the membrane as well as its effect on modulating the rates of electron and hole transfer processes are discussed. The design of a semiconductor and metal loaded membrane paves the way for improving selectivity and efficiency of photocatalytic processes.

Do Sacrificial Donors Donate H2 in Photocatalysis?

“…The preparation of a photocatalytically active bipolar membrane (BPM) with CdS and Pd in the anion-exchange layer (AEL) and cation-exchange layer (CEL), respectively, is described in the Supporting Information. The cell configuration shown in Figure illustrates the design strategy for water electrolysis employed in this study, and it is similar to the earlier investigations. , The photocatalytic BPM separating the CEL and AEL compartments allows isolation of the products formed in the two half-cells. Prior to irradiation, both compartments are purged with N 2 and sealed with a septum.…”

“…Methanol oxidation in the scheme represents an example of sacrificial donor oxidation. Adapted from ref . Copyright 2021 The Authors, published by American Chemical Society.…”

“…Polymer membranes (e.g., Nafion) embedded with a photocatalyst (e.g., CdS) or bipolar membranes embedded with a photocatalyst and a metal electrocatalyst can assist in separating the products formed in a photocatalytic reduction and oxidation. In a recent study, we employed a bipolar membrane containing CdS and Pd to selectively oxidize chlorophenol and reduce nitrophenol under visible light irradiation . This approach of separating oxidation and reduction compartments using a bipolar photocatalytic membrane has now been utilized to assess the contribution of sacrificial donors in photocatalytic H 2 production.…”

“…The sacrificial donor introduced in the CEL compartment scavenged photogenerated holes from CdS. Details on the vectorial electron transfer between CdS and metal nanoparticles within the BPM are presented elsewhere. , …”

“…In a recent study, we employed a bipolar membrane containing CdS and Pd to selectively oxidize chlorophenol and reduce nitrophenol under visible light irradiation. 6 This approach of separating oxidation and reduction compartments using a bipolar photocatalytic membrane has now been utilized to assess the contribution of sacrificial donors in photocatalytic H 2 production.…”