Gram-scale synthesis of aligned C3N4-polypyrrole heterojunction aerogels with tunable band structures as efficient visible and near infrared light-driven metal-free photocatalysts

The assembly of aligned porous materials from simple building blocks is of widespread interest for engineering materials with enhanced and synergistic properties. To date, however, how to develop 3D heterojunction aerogels with aligned porosity based on 2D semiconductor materials and 1D conducting polymers for solar energy conversion in the visible and near-infrared (NIR) light region remains a significant challenge. Here a new class of gram-scale 3D aligned heterojunction aerogels of polypyrrole (PPy)/C3N4 nanosheets (NSs) were designed and synthesized by directional freezing of polypyrrole (PPy)/polyvinyl alcohol (PVA) and C3N4 NS aqueous suspension. The synthesis of aligned C3N4-PPy heterojunction aerogels can be achieved on a large scale. The formed aerogel expresses stable and uniform dispersion of the two building blocks, long-range channel aligned structures along the whole monolithic sample, and additional special complementary optical properties between PPy and C3N4 NSs. Based on the above unique structure and optical properties, this novel metal-free heterojunction aerogel exhibits excellent photocatalytic activity and long-term stability for direct arylation of heteroaromatics under visible and near infrared (NIR) light irradiation at room temperature, far exceeding those of the single-and two-component systems. Our work therefore not only provides a new approach to obtain aligned heterojunction aerogels based on metal free semiconductors but also paves a way to develop gram-scale aerogels as a new type of highly efficient visible and NIR light induced heterogeneous photocatalyst.