Green synthesis of titanium dioxide nanoparticles using green tea (Camellia sinensis) extract: Characteristics and applications

Titanium dioxide (TiO2) nanoparticles (NPs) are indeed widely recognized and utilized as one of the most prominent photoanode materials in dye-sensitized solar cells (DSSCs). Therefore continuous efforts have been made to improve the performance of TiO2 photoanodes in terms of light absorption, charge carrier mobility, and overall energy conversion efficiency. Green synthesis methods for the production of TiO2 NPs, including the use of plant-based reducing agents, have gained significant attention in recent years. These methods are considered environmental friendly alternatives to traditional physical and chemical synthesis methods, which often involve the use of hazardous chemicals and complex processes. Therefore, in this work, a variety of tea types, including green, white, black, oolong, pu-erh have been used to synthesize TiO2 NPs. The differences in the amount of phenolic compounds and caffeine in various tea varieties can influence the topology, structure, and composition of the as synthesized nanoparticles (NPs). The prepared TiO2 NPs were comprehensively characterized for particle size, morphology, purity, composition, crystalline nature, structural, electrochemical and photovoltaic capabilities. The as synthesized titanium oxide (TiO2) NPs were spherical in shape and particle sizes ranged from 10 to 20 nm with little agglomerations. For DSSC application, thin films of synthesized TiO2 NPs were prepared by making paste of TiO2 NPs with Triton-X and spread onto conducting substrate (FTO) with the help of glass rod and finally sintering for 1 h at 450 degrees C. The prepared TiO2 electrodes were dipped in the standard N719 dye solution (0.1 x 10(-3) M) in acetonitrile medium overnight for complete adsorption. Overall efficiency = 3.0 %, J(SC) = 9.72 mA/cm(2), V-OC = 660 mV and FF = 0.46 was achieved with the DSSC made up with green tea mediated TiO2 NPs based photo anode. Due to high phenolic content and good reductive properties, TiO2 NPs prepared using green tea extract were highly crystalline in nature, have high surface area, high roughness factor, good stability which results in maximum dye loading and hence increase in the overall conversion efficiency.