Engineering the structural memory of Zn-based LDH to boost the plasmonic responses of AuNP/LDH dual catalysts

A key technological goal in light-energy-driven chemical conversion is the development of high-performance and durable photocatalysts. Zinc-based layered double hydroxides (LDHs) have recently gained attention as a novel class of doped semiconductors due to their unique 2D-layered structure, tuned optical absorption, and high surface area. In this study, we present heterostructures of Zn-based LDH and gold nanoparticles (AuNPs), obtained by engineering the manifestation of the structural memory effect of the LDH in aqueous Au(C₂H₃O₂)₃ solutions. The resulting AuNP/LDH nanoarchitectures evolved the synergistic functionalities of the coupled nanounits, specifically plasmon-induced charge separation (PICS) and co-catalytic effects. The novel plasmonic heterostructures were evaluated for the degradation of p-nitrophenol, a model hazardous pollutant, under solar irradiation.

Zn-based LDH precursors with different M²⁺/M³⁺ molar ratios (M²⁺=Zn²⁺, M³⁺=Al³⁺) were synthesized via co-precipitation at a constant pH. AuNP-ZnLDH catalysts (AuNP/LDH) were obtained through a room-temperature reconstruction process in Au(C₂H₃O₂)₃ solutions. Characterization was performed using XRD, FTIR, SEM/HRTEM/EXAFS, and UV-Vis spectroscopy to assess their structural, morphological, and optical properties. Photocatalytic performance was tested in a solar simulator reactor, and p-NPh degradation was monitored through UV-Vis in the 200–600 nm range.

The XRD and FTIR results confirmed that LDH is the dominant phase after reconstruction. The SEM-HRTEM and UV-VIS results revealed tiny and well-dispersed Au nanoparticles embedded into the LDH matrix, with SAED confirming their crystalline nature. The catalyst defined by Zn/Al (3/1), which evolved after 2 hours of reconstruction, showed PICS behavior and the best activity of ~98% for p-NPh degradation after 4 hours under solar light. Reusability tests showed 79% catalytic activity retention over five cycles. These results demonstrate that the catalytic efficiency of AuNP/LDH catalysts can be finely tuned via the parameters used during the LDH reconstruction procedure to obtain advanced plasmonic photocatalysts for environmental applications.