Green synthesis of transition metal-based mixed-phase materials from Convolvulus arvensis leaves: structural, cyclic voltammetry and photocatalytic studies.

In this study, Convolvulus arvensis leaf extract was employed as a source of phytochemical constituents that facilitate metal-ion complexation and stabilization during material formation, yielding manganese oxide, Mn2O3 (1), copper hydroxide carbonate, Cu2(OH)2CO3 (2), iron oxide, Fe2O3 (3), and nickel carbonate hydroxide hydrate, Ni2CO3(OH)2·H2O (4). The synthesized materials were systematically characterized to elucidate their structural, morphological and compositional properties using advanced analytical techniques. Cyclic voltammetric (CV) studies showed enhanced charge transfer properties of the synthesized materials (1-4), with appreciable anodic and cathodic peaks in the range ∼0.22 V-∼0.30 V, ∼0.12 V-∼0.14 V, respectively. The photocatalytic performance of the synthesized materials (1-4) was evaluated for the removal of diclofenac potassium (DCF) under visible light irradiation. These materials exhibited excellent photocatalytic efficiency, i.e., 79.4% (1), 70.8% (2), 75.6% (3), and 83.2% (4) in terms of the removal of diclofenac potassium from aqueous solution. Among all, nickel carbonate hydroxide hydrate Ni2CO3(OH)2·H2O (4) demonstrated the highest photocatalytic removal efficiency against DCF, which reached 90.2% under optimized conditions (irradiation time = 80 min, initial DCF concentration = 15 mg L-1, catalyst amount = 5 mg, pH = 5, and temperature = 50 °C). The sustainability of (4) was checked in up to seven consecutive photocatalytic cycles, revealing its good stability. Trapping experiments indicated the potential role of active species (OH˙ > ˙O2 - > h+) during the photocatalytic process to propose a suitable reaction mechanism for DCF removal. Hence, this study highlights the potential of Convolvulus arvensis-mediated green synthesis as an eco-friendly and cost-effective route for synthesizing transition metal-based oxide/carbonate materials with promising electrochemical and photocatalytic applications.