Highly dispersed g-C3N4 on well-designed three-dimensional porous nanostructured ZrO2 for high-performance photocatalytic degradation and H2 production

Abstract

A novel polymer-assisted freeze-drying method was adopted for preparing three-dimensional porous nanostructured ZrO2 (3DPZ) with macro self-supporting properties. Then, g-C3N4 was in-situ grown uniformly on the 3DPZ through a gas-solid reaction, forming 3D nanoporous ZrO2/g-C3N4 heterojunctions (3DP/ZC) with different g-C3N4 loadings that retained self-supporting characteristics. The kapp value of Rhodamine B (RhB) degradation and H2 evolution rate of the 3DP/ZC-2 under visible light reached 0.035 min−1 and 1013.1 μmol h−1 g−1, which were 19.6 and 6.6 times higher than pure g-C3N4, respectively. The ZrO2 nanoparticles (ZNps) prepared via freeze-drying, but without polymer precursor, were used as support to form ZrO2/g-C3N4 nanoparticles (ZCNps-2) for comparison study. The RhB degradation rate and H2 evolution rate of the 3DP/ZC-2 under visible light were about 3.7 and 5.3 times higher than ZCNps-2. Their enhanced photocatalytic activity could be attributed to their unique 3D heterointerface with matched energy bands for rapid charge separation and transfer and a hierarchical porous structure for mass transfer and surface reaction processes. The scavenger trapping and ESR measurements confirmed that the primary reactive radicals for degradation were superoxide radical ions (⋅O2−), hydroxyl radicals (⋅OH), and photogenerated holes (h+). The pH-dependent photocatalytic degradation activity originated from the H+-related ⋅OH conversion reaction. Besides, the macro self-supporting nature could provide excellent separability and recyclability, and self-supporting membranes were also constructed and demonstrated as stable and recyclable photocatalysts. This work provides a new routine for designing 3D-heterojunctions as new kinds of functional materials for applications in environmental remediation and green energy production.