Ag–SnO2 nano-heterojunction–reduced graphene oxide by a stepwise photocatalyzed approach and its application in ractopamine determination

Abstract

Photocatalyzed synthesis by using SnO₂ as a photocatalyst is a green and alternative approach. Here, a nanocomposite of SnO₂–Ag nanoparticles (AgNPs) and reduced graphene oxide (RGO) was prepared by a stepwise photocatalyzed approach. HRTEM shows that SnO₂ and AgNPs were attached along the lattice matching each other and both of them were anchored upon RGO. Under UV irradiation, photo-excited holes from SnO₂ were scavenged by ethanol while electrons were accumulated at the side of SnO₂, leading to the reduction of both graphene oxide (GO) and Ag⁺. Here, SnO₂ and metal Ag formed a heterostructure, and RGO played the dual role of conductor and support. During UV irradiation, the (101) facet of SnO₂ offered a preferential growth direction for the (111) facet of AgNPs with an interfacial angle of 118°, which can be attributed to their similar D-spacings. A unique morphology of a combination of two semi-spheres was established. The energy-band structure of the composite was characterized to understand its mechanism of electrocatalysis. Owing to the difference between their binding energy in the heterostructure, electrons in AgNPs are transferred into SnO₂, inducing AgNPs with positive charge and facilitating the redox of ractopamine (RAC). Under the optimal experimental conditions, a linear relationship between the relative amperometric response to RAC ranges from 5.0 × 10⁻⁸ to 5.5 × 10⁻⁶ M while the lower limit of detection reaches 2 × 10⁻⁸ M (S/N = 3.0).