Experimental, theoretical and mechanistic exploration of Ni role as non-plasmonic dopant in Ag-Ni plasmonic alloy and its co-catalytic boost to semiconductor photocatalysis

Bimetallic nanoparticles (BM NPs) possess unique properties due to metal synergy, offering numerous applications. Semiconductor-bimetallic (SC-BM) nanocomposites enhance photocatalytic activity (PCA) through mechanisms like surface plasmon resonance (SPR) tunability and electronic heterogeneity. Ni, a non-plasmonic metal, has gained attention in SC-BM photocatalysts for enhancing PCA when alloyed with plasmonic metals like Ag. This study investigates how Ni affects the physical characteristics of Ag-Ni alloy, how it magnifies the PCA of Ag-semiconductors taking ZnO as example, and emphasizes Ag-Ni co-catalysis of ZnO photocatalysis. It was implemented with chemical synthesis of Ag-Ni plasmonic-non-plasmonic alloy NPs of varying Ni content (0.3–10.0 mol%) and deposition of ZnO over them to create a SC-BM photocatalyst. The co-catalytic functionality of Ag-Ni in the ZnO@Ag-Ni composite towards the PCA and the influence of Ni were investigated. Detailed XRD analysis confirmed successful Ni doping into the Ag crystal without phase segregation, estimating 7–19 nm sizes for Ag-Ni and 16–19 nm for ZnO@Ag-Ni. Morphologies and coupling of Ag-Ni and ZnO@Ag-Ni were shown by TEM, HRTEM, SEM, and elemental mapping. ICP-AES and EDX confirmed successful variant doping of Ni, with ZnO to Ag+Ni molar ratio around 9–1. XPS confirmed the metallic state of Ag, while details of Ni were limited due to its low content. BET analysis showed concise SSA and porosity around 13 m²/g and 16.5 nm, respectively. Quantum computation predicted SPR red-shifting with Ni doping. DRS measurements showed SPR red-shifts from 416 to 434 nm for 0.3–1.8 mol% Ni, shifting back to 414 nm for 1.8–10.0 mol% Ni, while optical bandgap of ZnO@Ag-Ni remained around 3.3 eV. Photocatalytic degradation of MB with ZnO@Ag-Ni under UV and domestic-visible lights emphasized the co-catalytic function of Ag-Ni and the role of Ni within, where Ni-induced SPR red-shifts improved the PCA by up to 270 % at 1.8 mol% Ni, while PCA declined with blue shifts. SPR red-shifts (by dopant Ni) increased visible-light sensitivity of Ag-Ni and ZnO@Ag-Ni. Theoretical calculations on the experimental results showed that dopant Ni reconfigures electronic structures of both Ag-Ni and ZnO@Ag-Ni, extending charge carriers' lifetime, and Ni inherently boosts the catalytic process even when SPR blue-shifts to its original wavelength.