ZnO/black phosphorus/C3N4 composite: An effective photocatalyst for Cr (VI) reduction and degradation of rhodamine B

The utilization of photocatalysts offers a promising approach for the removal of Cr (VI) and rhodamine dyes. Through the generation of reactive species and subsequent degradation reactions, photocatalysis provides an efficient and environmentally friendly method for the remediation of wastewater. In this study, we have synthesized an n-p-n heterojunction of carbon nitride (C3N4), zinc oxide (ZnO), and black phosphorus (BP) through the sonication-stirring method. The photocatalytic ability of this composite was examined for the decomposition rhodamine B (RhB) and detoxification of hexavalent chromium ion (up to 97% during 80 min) under Xenon irradiation. The results of trapper experiments indicated that the active species were hydroxyl radical ((OH)-O-center dot), electron (e(-)), and superoxide anion radical (O-center dot(2)-). Based on the obtained potential of the lowest unoccupied molecular orbitals (LUMO) and the highest occupied molecular orbital (HOMO) for the mentioned semiconductors, through Mutt-Schottky results, the double Z-scheme mechanism was proposed for the studied process. The electrochemical impedance spectroscopy data exhibited good charge transfer for the evaluated composite versus the pure compounds. The impressive separation of holes and electrons along with the low recombination were confirmed by the responses of photocurrent and quenching the photoluminescence (pl) intensity for the composite, respectively. The current density of the composite recorded 66.6%, 87.3%, and 92% higher than those of BP, C3N4, and ZnO, indicating an excellent electron-hole separation for the ternary composite compared to the pure semiconductors. Diffuse reflectance spectra (DRS) data revealed 2.9, 3.17, 1.15, and 2.63 eV as the band gap values for C3N4, ZnO, BP, and composite. The rate constant of the new composite to remove RhB and reduce hexavalent chromium were about 4.79 and 2.64 times higher than that of C3N4, respectively.

Automated summary

The use of photocatalysts is a promising method for the removal of Cr (VI) and rhodamine dyes in wastewater treatment. This study synthesized a composite of carbon nitride (C3N4), zinc oxide (ZnO), and black phosphorus (BP) and investigated its photocatalytic ability for the degradation of rhodamine B (RhB) and detoxification of hexavalent chromium ion. The composite showed high efficiency in removing RhB and reducing hexavalent chromium, and the active species involved in the photocatalysis process were identified. The composite also exhibited impressive charge separation and low recombination, resulting in higher photocurrent density compared to the individual semiconductors. The band gap values and the double Z-scheme mechanism of the composite were determined through various experiments and analysis. The results highlight the potential of this composite as an efficient and environmentally friendly photocatalyst for wastewater treatment.