Fabrication of 3D CeVO₄/graphene aerogels with efficient visible-light photocatalytic activity

Abstract

Hybrid 3-dimensional (3D) structures that were composed of CeVO₄ particles and graphene aerogels were fabricated by the electrostatic-driven self-assembly method. The as-prepared products were characterized by X-ray diffraction, Raman spectra, field-emission scanning electron microscope and UV–vis diffuse reflectance spectroscopy. The results showed that graphene nanosheets loading with CeVO₄ particles self-assembled into a well-defined and interconnected 3D porous network through strong van der Waals and π–π interactions. Benefited from the incorporation of CeVO₄ particles into graphene nanosheets in such a unique structure, hybrid aerogels exhibited higher photodegradation efficiency toward methylene blue (MB) than that over pure CeVO₄ photocatalyst. It is proposed that the efficient physical adsorption of dye molecules and enhanced charge transfer in the composite is account for the improved photocatalytic activity. These findings open a new pathway for the design and fabrication of such functional graphene-based aerogels in water purification and advanced treatment.

Introduction

Nowadays, the growing population and industrial development have caused more and more serious underground and surface water pollution. For instance, dyes are often discharged with wastewater into the local environment without adequate treatment. Photocatalysis has been considered as an effective way to remove different pollutants in wastewater in the field of environmental remediation [1]. The preparation of highly efficient photocatalysts by combining advanced semiconductor materials and photocatalysis technology offers a green and energy saving technology for the degradation of harmful pollutants [2], [3]. Cerium vanadate (CeVO₄), a wide (3.1–4.2 eV) band gap semiconductor, is of much interest due to its useful electronic and catalytic properties for applications in electrochromic materials and gas sensors [4]. However, the fast charge recombination at surfaces of CeVO₄ leads to practical limitations [5].

The effective charge separation can be achieved by the construction of composite photocatalytic systems via loading the co-catalyst or a matrix into the semiconductor [6]. Graphene is an ideal material for forming photocatalytic nanocomposites, due to its fascinating properties such as large surface area, high electrical conductivity, stability and tunable surface properties [7]. Graphene acts as a substrate for the formation of composite materials on its surface, as well as an electrically conductive channel for the fast electron transfer to prevent the recombination [8], [9], [10]. However, graphene nanocomposites are difficult to separate and reclaim in the process of photocatalytic reaction, leading to the impossibility of industrialization [11]. Recent studies have shown that three-dimensional (3D) hybrid structures that are composed of semiconductor photocatalysts and chemically crosslinked graphene may be optimal candidates for removal of water pollutants due to 3D composites can be easily recovered [12]. This 3D structure has (i) effective adsorption afforded by a large surface area and strong interactions between the graphene and dye molecules and (ii) enhanced photocatalytic activity resulting from effective charge transfer from semiconductor photocatalysts to graphene network [12], [13], [14]. Thus, it is highly desirable to design and fabricate novel and well-defined 3D graphene-based composites for applications in water treatment and purification.

In this paper, we demonstrate a simple approach for synthesis of 3D self-assembled CeVO₄/graphene composite aerogels. The formation mechanism for the 3D aerogels is proposed and the photocatalytic properties of CeVO₄/graphene aerogels are investigated.