Influence of Au/Pd alloy on an amine functionalised ZnCr LDH–MCM-41 nanocomposite: A visible light sensitive photocatalyst towards one-pot imine synthesis

Abstract

Achieving photocatalytic organic transformation reactions by using a visible light induced semiconductor-based photocatalyst is promising as a green and sustainable approach. In the present study, Au/Pd bimetallic alloy loaded amine (APTES) functionalised LDH (Layered double hydroxide)–MCM-41 composite was prepared through an in situ co-precipitation followed by a co-reduction method. The structural phases, textural properties, optical behaviour, morphological aspects, chemical states and functional groups of the photocatalysts were thoroughly analysed by powder X-ray diffraction (PXRD), high-resolution transmission electron microscopy (HRTEM), ultraviolet-visible diffuse reflectance (UV-vis DRS), fourier-transform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies. Moreover, the formation of an alloying structure between Au and Pd was confirmed from PXRD, HRTEM and UV-vis absorption spectra. We investigated one-pot synthesis of imines through photoalkylation of benzyl alcohol with nitrobenzene over Au/Pd bimetal alloy loaded on amine functionalised LDH–MCM-41 composite and it demonstrated imine yield of around 3.1 times (68%) more than the parent LDH (22%). The alloy nanoparticless efficiently harvest light and possess higher photocatalytic activity with respect to single Pd and Au nanoparticles. Due to the alloying structure develops charge heterogeneity on the surface of alloyed nanoparticles and enhances the interaction between metal surface with substrate molecule which promotes the coupling between photo generated benzaldehyde with aniline to form imine. Characterisation such as photoluminescence (PL), time-resolved photoluminescence (TRPL), electrical impedance spectroscopy (EIS) and photocurrent density measurements further proved the superior photoactivity towards imine synthesis. These photocatalytic tandem reactions, therefore, have great potential as an effective pathway for the one-pot organic synthesis and transformation of organics in an environmentally friendly way.