Research Progress in Silicon Carbide-based Heterojunction Photocatalysts

Currently, the globe is confronted with the dual challenges of energy structure transformation and environmental pollution control. The proposal of China's "dual carbon goals" (carbon peaking and carbon neutrality) imposes higher requirements on the adjustment of energy structure and the innovation of pollution control technologies. As a green and environmentally benign technology, photocatalytic technology can directly utilize solar energy to drive energy conversion (photocatalytic water splitting for hydrogen production) and environmental purification (pollutant degradation) without secondary pollution, thus serving as one of the core approaches to address these issues. Silicon carbide (SiC), as a semiconducting material, exhibits prominent advantages, including tunable band gap (2.3–3.3 eV), excellent chemical stability and high carrier mobility. In particular, 3C-SiC (with a band gap of 2.48 eV) can absorb visible light. Moreover, the positions of its conduction band (CB, −1.32 eV) and valence band (VB, +1.16 eV) are compatible with redox reactions, making it an ideal photocatalyst. However, pristine SiC suffers from intrinsic drawbacks, such as high photogenerated carrier recombination rate, low solar light utilization efficiency and small specific surface area, which seriously restrict its practical application. In contrast, constructing a heterostructure system with SiC as the substrate can significantly enhance the performance of SiC-based photocatalysts through multiple mechanisms, driving the directional separation of carriers via the interfacial built-in electric field, exposing high-active crystal facets through defect engineering and broadening the light absorption range. This strategy holds significant theoretical value and practical significance for promoting the practical application of photocatalytic technology and facilitating the achievement of the dual carbon goals.

In photocatalytic reactions, the valence band (VB)/conduction band (CB) positions of semiconductors, light absorption range, specific surface area, crystallinity and separation efficiency of photogenerated carriers are all key factors affecting photocatalytic performance. However, a single semiconductor often fails to satisfy all these criteria. By compositing different semiconductor materials to construct heterojunction systems, these issues can be addressed simultaneously. In the early research on SiC heterojunction systems, the focus was mainly on the construction of Type-Ⅱ heterojunctions. Nevertheless, the intrinsic defects in their carrier migration pathways cannot realize the maximized utilization of redox potentials. The subsequently proposed Z-scheme heterojunction and S-scheme heterojunction systems not only maintain the advantageous redox potentials of photocatalysts but also exhibit excellent charge separation efficiency, thus demonstrating strong photocatalytic performance. For SiC/metal heterojunctions, the potential difference generated at the contact interface of the two distinct materials enables the directional migration of photogenerated electrons, thereby improving the separation efficiency of photogenerated carriers. For SiC/carbon-based heterojunctions, the excellent electrical conductivity and large specific surface area of carbon-based materials facilitate the rapid migration of electrons, which in turn enhances photocatalytic performance.

Starting from the physical properties of SiC, construction of heterojunction systems and photocatalytic applications, SiC-based heterojunction photocatalysts were focused, as a novel and highly promising material system in the photocatalysis field. Their performance breakthroughs and charge transfer mechanisms are discussed in detail. Heterojunction construction is the core strategy to overcome the performance bottlenecks of pristine SiC. Type-Ⅱ, Z-scheme, S-scheme and metal/carbon-based heterojunctions have been constructed, to solve the problem of high photogenerated carrier recombination rate, while simultaneously broadening the light absorption range and hence improving photocatalytic performance. However, the industrial application of SiC-based heterojunction photocatalysts currently faces three major technical barriers, including the immaturity of large-scale preparation technology, the unclear charge transport kinetic mechanisms and the limitation of material systems. Looking ahead, key breakthroughs should be made in the following three aspects.

(1) Construction of multi-level heterojunction systems. By designing ternary/quaternary structures and leveraging band engineering, efficient separation and directional migration of carriers can be achieved, thereby enhancing the overall catalytic efficiency.

(2) Innovation of in-situ characterization technologies. It is important to develop in-situ dynamic characterization methods with atomic-scale resolution, which is combined with theoretical calculation methods to deeply analyze the microscopic mechanisms of charge transfer in various heterojunction systems, thus providing theoretical guidance for the design of high-performance heterojunctions.

(3) Development of ceramic-based composite systems. The advantageous properties of SiC ceramics (e.g., high hardness, high temperature resistance and excellent chemical stability) can be utilized to construct SiC ceramic-based composite photocatalytic systems. By doing this, it is possible to overcome the drawbacks of traditional powder photocatalysts (such as low mechanical strength and poor cyclic stability) and realize the photocatalytic application of SiC ceramic composite systems.