Enhanced Dye Degradation through Multi‐Particle Confinement in a Porous Silicon Substrate: A Highly Efficient, Low Band Gap Photocatalyst

Abstract

Abstract A platform is introduced for fabrication of a reusable and highly efficient low band gap photocatalyst by confining gold nanoparticles (AuNPs) in the pores of a nanopatterned Si monolith (AuNSM). Due to their size, a maximum of two AuNPs can assemble in a single pore, thus preventing agglomerations. Their access to the analyte provides more active sites for redox reaction, leading to enhanced efficiency. While proximity of nanoparticles enhances coupling efficiency, confinement prevents rapid recombination of photogenerated charge carriers, a major factor contributing to low efficiency of photocatalytic materials. Degradation of methyl orange (MO) is used to determine the photocatalytic efficacy of AuNSM compared to 1) bare silicon and 2) AuNPs randomly dispersed on silicon. After 90 min of exposure to UV light (λ = 353 nm) in the AuNSM, the MO absorption is <1%, indicating near complete degradation, while it is still 85% and 70% for systems (1) and (2), respectively. Finite element method simulations of the confined structure suggest that the AuNPs act as a mediator/receptacle for photogenerated charges rather than a source of them at this wavelength and thus enhance the performance of the photocatalyst by creating more effective Schottky junctions—preventing recombination of electrons and holes—rather than by a localized surface plasmonic resonance effect.