Synergistic effect of ZnO–ZnFe2O4 heterostructures for enhanced surface catalytic activity in Cr(vi) reduction, green H2 generation and CO sensing: an experimental study supported by DFT†

Abstract

Increasing energy demand is an indication of progress, but it necessitates careful management of environmental pollution for maintaining a healthy life and ensuring a better planet for future generations. Heterostructure material-based catalysts have emerged as a comprehensive solution to combat the diverse challenges related to energy and environment. Herein, an n–n-type ZnO–ZnFe₂O₄ heterostructure was synthesized via a simple reflux followed by a co-precipitation technique for the same. Detailed photocatalytic and gas sensing studies revealed that a 50% ZnO–50% ZnFe₂O₄-based sample (ZZF-11) showed the highest Cr(VI) degradation with a rate constant of ∼159 × 10⁻⁴ s⁻¹, which was ∼23 times higher than that of pristine ZnO and 6.4 times higher than that of pristine ZnFe₂O₄. Additionally, the ZZF-11 sample produced ∼550 μmol g⁻¹ of H₂ within a 300 minute interval via a photocatalytic water-splitting reaction. The ZZF-11 sensor also showed a significantly high response to 1 ppm CO gas (S = 29.4%) compared to all other pure and composite samples. The formation of the heterostructure and transfer of charges through the interface played an important role here. The most possible mechanism for the enhanced surface catalytic performance of ZZF-11 was critically analysed by corroborating the experimental results with DFT results. This study demonstrates a unified pathway to enhance the various surface catalytic processes by tuning different parameters of the heterostructure material to simultaneously overcome environment- and energy-related issues.