Carboxyl functionalized gold nanoparticles in situ grown on reduced graphene oxide for micro-gravimetric ammonia sensing

Abstract

Here, we present an ammonia (NH3) sensor where carboxyl (COOH) functionalized gold nanoparticles (Au-NPs)/reduced graphene oxide (rGO) hybrid film was developed as micro-gravimetric sensing material. With the help of olefin reducing group in oleylamine solvent, gold precursor of HAuCl4 was directly reduced to Au-NPs on the surface of rGO sheets and the Au-NPs was firmly adsorbed by the rGO sheets through Van-der-Walls-force. Therefore, rGO decorated with Au-NPs (i.e., Au-NPs/rGO hybrid) were prepared. After the removal of oleylamine, the rGO sheets served as nano-shelves to support the Au-NPs, and thereby preventing Au-NPs from aggregating. The rGO shelved Au-NPs was dispersed well under ultrasonic in some conventional solvents like water or ethanol. After drying in air, the obtained composite formed into three-dimensional (3D) hierarchical porous-layered nanostructures, providing effective surface areas for NH3 molecules adsorbing and micro-gravimetric sensing. Thereafter, mercaptosuccinic acid (MSA, bearing two -COOH groups) was self-assembled onto the Au-NPs to form NH3-specific micro-gravimetric sensing material based on the base–acid interaction. Moreover, due to the hydrophobic characteristic of rGO with only a few oxygen-containing group residues, which was prepared by using thermal expansion method under inert atmosphere, the resonant microcantilever with -COOH functionalized Au-NPs/rGO hybrid as sensing material facilitates negligible interference from environmental humidity change.