Charge-separated 3D/2D layered heterojunction of NiNb2O6/E-gC3N4 as an efficient photocatalyst for photo-reduction of Cr6+ and photo-oxidation of dyes under visible and sunlight

Abstract

The major challenge in photocatalysis for environmental remediation is rapid recombination of charge carriers. Recently, the construction of 3D/2D heterojunction is regarded as a viable strategy to overcome this drawback. Towards this objective, 3D NiNb2O6 − 2D E-gC3N4 type-II heterojunction, hitherto not reported, was constructed as a dual catalyst for photo-reduction of Cr6+ to Cr3+ and photo-oxidation of methylene blue (MB), malachite green (MG) and crystal violet (CV) under visible light. After optimizing the parameters, the photocatalytic activity was studied under direct sunlight. Among the prepared catalysts, NG-20 composite (NiNb2O6 −80 % & E-gC3N4 −20 %) exhibits excellent photocatalytic activity in removing 97 % of Cr (VI) under 120 min and degrading 97.4 %, 96.1 % and 98 % of MB, MG and CV respectively in 20 min under direct sunlight. For instance, the rate constant of NG-20 was found to be 4.2 and 5.8 times higher than NiNb2O6 & E-gCN respectively for MB degradation. The superior photocatalytic activity can be attributed to the enhanced charge carrier separation of electron-hole pair due to the construction of 3D/2D heterojunction. Superoxide (0O2−) and hydroxyl (0OH) radicals are the dominant reactive oxygen species (ROS) and a plausible mechanism for photocatalysis is proposed.