Tailored S-scheme directed NiFe-LDH/Ag2S heterojunction for visible light-driven CO2 photoconversion

Abstract

The photocatalytic carbon dioxide reduction reaction (PCRR) faces challenges such as weak light absorption and rapid electron-hole recombination in single-component photocatalysts. To overcome these limitations, a heterojunction was engineered by integrating two-dimensional nickel–iron layered double hydroxides (2D-NiFe-LDH) with zero-dimensional silver sulfide (0D-Ag₂S) nanoparticles. The optimized heterostructure, NFAS15 (containing 15 wt% Ag₂S), exhibits a sharp optical absorption edge, increased surface area, and enhanced porosity. Scanning tunneling microscopy (STM) confirms the migration of Ag and S into the LDH lattice, while X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR) reveals incremented delocalized hydroxyl groups and superior charge transfer properties, underscoring its improved electronic and catalytic performance. Under visible light, NFAS15 achieves outstanding PCRR activity, producing carbon monoxide (CO) and methanol (CH₃OH) at rates of 20.7 µmol g^-1 h⁻¹ and 2.9 µmol g^-1 h⁻¹, respectively. It also demonstrates 88 % selectivity for CO conversion and exceptional photostability, retaining 97 % (CO) and 96 % (CH₃OH) efficiency over five irradiation cycles. Transient photoluminescence studies validate reduced charge recombination, attributed to S-scheme-mediated carrier separation. Density functional theory (DFT) further reveals that NFAS15 possesses lower energy barrier along the reaction pathway compared to pristine NiFe-LDH. This work offers sustainable CO₂ conversion via an efficient S-scheme heterojunction NiFe-LDH/Ag₂S.