**1. Introduction**

Semiconducting nanocrystals with tailored shapes have attracted increasing research attention in recent years due to their many intrinsic shape-dependent properties [1,2]. As an important ternary oxide semiconductor, BiVO4 has been extensively investigated due to its peculiar chemical and physical functions in many fields such as dye-treatment, oxygen production, antibiotics degradation and so on [3–5]. However, the specific surface area of BiVO4 is comparatively small mainly due to the large particle size [6]. The poor adsorptive performance and the poor separation e fficiency of photoinduced charge carriers in pure BiVO4 significantly restricts its further photocatalytic application [7].

To improve the photocatalytic performance of BiVO4 photocatalysts, many approaches have been explored, such as combining with metal oxides, doping metal ions and nano-structuring [8–10].

In particular, the photocatalyst hybrids with heterojunction systems represent an effective way to enhance the photoinduced electron and holes separation. The build-in internal electric field caused by the interface of hybrids promotes the electron flow across the heterojunction [11]. Generally speaking, the electron transfer (ET) across the heterojunction interface is a key process in controlling their photocatalytic performance [12]. The challenge of assembling the heterojunction systems lies in finding an appropriate platform favorable to electron transfer between the interfaces.

Among various materials, graphene, two dimensional forms of sp2-hybridized carbon, has exhibited outstanding characteristics such as high mechanical strength, thermal and optical properties and high electrical conductivity [13–15]. It can offer new opportunities to serve as an ideal platform to assemble the heterojunction systems. Research works have reported that the low-dimensional heterojunctions based on graphene is proven effective for ET process. For example, graphene combined with BiVO4 nanoparticles or nanotubes has been synthesized and exhibits high visible-light-driven catalytic effect [7,16]. Recently, 2D dimensional heterojunctions with superior properties have motivated considerable interest in degrading pollutants. Inspired by the process for light-charge conversion in granum of green plants, 2D-2D dimensional heterojunction with BiVO4 nanosheets-graphene stacked structures was fabricated to achieve rapid charge transfer [17,18]. Graphene, as an ideal 2D platform for photocatalysts assembly, benefits the electron transfer across the interface.

Recently, many literatures about BiVO4 and RGO composites have been reported. However, a thoughtful and systematic comparison in BiVO4-graphene nanocomposites with different dimensional heterojunctions is still scarce. Although 2D-2D dimensional heterojunctions with BiVO4/graphene exhibit superior photocatalytic performance, different preparation methods make the materials incomparable. The contribution role of different BiVO4 nanomaterials to enhance the composites photocatalytic activity is still unavailable. The situation may give incomplete or exaggerate information on the contribution of 2D-2D dimensional heterojunction in improving the photocatalytic performance [19]. So far, our knowledge of the specific advantages of 2D interface on developing an effective photocatalytic system is far from satisfactory.

Here a BiVO4 nanosheets/RGO based 2D-2D heterojunction photocatalytic system as well as 0D-2D BiVO4 nanoparticles/RGO and 1D-2D BiVO4 nanotubes/RGO nanocomposites were constructed by a feasible solvothermal method. Systematic comparison with the above nanocomposites was carried out in terms of photocatalytic activity, reactive oxygen species (ROS) generation and electron transfer rate. The results emphasize the key role of interfacial dimensionality on design or fabricate graphene-semiconductor nanocomposites and improvement of the photocatalytic activity.

#### **2. Materials and Methods**
