Insight Into Malachite Green Degradation, Mechanism and Pathways by Morphology-Tuned α-NiMoO₄ Photocatalyst

The microwave hydrothermal process was used for the synthesis of various morphologies of α-NiMoO₄ by simply adjusting the pH during experimental conditions. The effect of morphology/size on the photocatalytic performances for degradation of malachite green (MG) has been investigated under UV-Vis/visible light irradiation. Nanorod morphology has strong tendency to degrade (88.18%) the MG as compared to spherical quantum-sized (57.65%) and layered square microsheet (37.98%) under UV-Vis irradiation in 180 min. The active species trapping experiment revealed that active species (OH^• , O₂^•- and h⁺ ) play a crucial role for MG degradation. The high BET surface area, greater amount of oxygen defect and efficient separation of electron-hole pair are responsible for MG degradation. About seventeen types of organic fragments of MG were confirmed by high resolution-quadruple time of flight electrospray ionization mass spectroscopy (HR-QTOF ESI/MS) technique on the basis of retention time and molecular masses. Degradation mechanism and pathways were proposed that follow the demethylation, nitration, decarboxylation, hydrolysis, decarboxylation and oxidation reaction. The reduction of total organic carbon revealed the mineralization of MG during photocatalytic degradation process. Therefore, this article represents the investigation of MG degradation by various morphology of α-NiMoO₄ and detailed degradation mechanism and pathways.