Enhanced phenol degradation in wastewater using non-thermal plasma coupled with NiO/g-C3N4 nanocomposite catalyst

Abstract

In this study, NiO/g-C₃N₄ nanocomposites with varying amounts of NiO were successfully synthesized via the hydrothermal method and demonstrated significant potential for plasma-catalytic phenol degradation. The formation of a p-n heterojunction at the interface between NiO and g-C₃N₄ facilitated enhanced charge separation and transfer under the influence of an internal electric field, effectively suppressing charge recombination. Comprehensive characterizations were conducted to examine the structural, morphological, optical, and textural properties of the catalysts. Density functional theory (DFT) calculations were also employed to elucidate the interface interactions and the mechanism behind the enhanced plasma-catalytic performance. The active species participated in the removal process were identified through quenching experiments and in situ optical emission spectroscopy (OES). The 20 % NiO/g-C₃N₄ composite exhibited the highest phenol degradation performance, achieving 97 % phenol decomposition, compared to 71 % and 62 % for pure g-C₃N₄ and NiO, respectively, under optimized reaction conditions, which included a power of 10 W, an initial phenol concentration of 100 ppm, a catalyst amount of 2 g/L, and an initial solution pH of 7. In addition, the 20 % NiO/g-C₃N₄ composite exhibited excellent recyclability and cyclic stability, with only a minor decrease (7 % decline in degradation efficiency) over five consecutive cycles. Finally, a possible phenol degradation pathway was proposed based on the identified intermediates. This work provides valuable insights into the design of advanced p-n heterojunction catalysts with exceptional UV-Vis and plasma responsiveness, offering a promising approach for improving wastewater treatment and addressing environmental challenges.