Green Synthesized Titanium Dioxide-Based Copper Oxide and Zinc Oxide Nanocomposites for Photocatalytic Degradation of Methylene Blue and Solar Cell/Photoelectrochemical Energy Conversion Applications

Abstract

Global energy and clean water consumption is increasing with population growth and technological advancement, which has resulted in serious concerns about scarcity. DSSC energy conversion and photocatalytic water purification have emerged as the most promising methods to address these issues. This work utilized natural dyes from economical and ecologically friendly plant extracts of Impatiens rothii Hook.f. flower (IHF), Impatiens rothii Hook.f. root (IHR), Thymus schimperi Ronniger flower (TRF), and Rumex nepalensis Spreng Flower (RSF). Here, pristine TiO2, TiO2/CuO NCs, and TiO2/ZnO NCs were effectively prepared by a green method using Impatiens rothii Hook f. leaf (IHL) extract as a reducing and capping agent. The average crystallite size and particle size from XRD and TEM analysis were 11, 14, 13 nm and 27, 23, and 21 nm for TiO2 NPs, TiO2/CuO, and TiO2/ZnO NCs, respectively. XPS analysis showed the formation of TiO2, CuO, and ZnO. Based on BET analysis, the specific surface areas were determined to be 65, 94, and 91 m2/g for TiO2 NPs, TiO2/CuO, and TiO2/ZnO NCs, respectively. PL analysis showed that TiO2/CuO NCs have the lowest electron hole recombination rate. The UV-vis-DRS showed the presence of a redshift for TiO2/CuO (2.91 eV) and TiO2/ZnO (2.98 eV) NCs, compared to the TiO2 NPs (3.39 eV). SEM morphological study revealed that all the synthesized nanostructures have spherical shapes. The results of lattice fringes from HRTEM analysis supported the XRD crystal analysis results. MB dye degradation optimized parameters were catalyst dosage (20 mg/L), initial MB dye concentration (15 ppm), pH of the solution (9), and contact time of 80 min. The maximum photodegradation of 99% was obtained at the optimized conditions in the presence of TiO2/CuO NCs. The scavenger test showed that the reactive radicals OH•, O2•−, and h+ for TiO2 NPs, TiO2/CuO (1:1) NCs, and TiO2/ZnO (1:1) NCs, respectively, play important roles in the photodegradation of MB. The reusability test of photocatalysts showed good performance in three cycles with degradation efficiencies of 71%, 95%, and 89% for pristine TiO2, TiO2/CuO (1:1) NCs, and TiO2/ZnO (1:1) NCs, respectively, at the third cycle. The photovoltaic parameters such as Jsc, Voc, FF, and overall conversion efficiencies for the fabricated DSSCs were evaluated. Among the synthesized photoanodes and plant-extracted dyes, the one fabricated with TiO2/CuO (1:1) NCs and IHR (mix) exhibited the highest power conversion efficiency of 1.70%. The IPCE of this device was found to be 56.71 % at its absorption maxima and showed the best stability compared to other synthesized nanomaterials.