Ti-doped ZnO nanocomposites from bio-combustion of cow urine: a sustainable approach to dye degradation

The photocatalytic degradation using semiconductor nanocomposites offers a green approach for treating dye-laden industrial effluents. In this study, TiO2–ZnO nanocomposites were synthesised using a cow urine–assisted combustion method, with Ti content varied from 7% to 12%. Materials were characterised by XPS, SEM, XRD and UV-Vis spectroscopy. XPS revelled characteristic peaks at 458.6 eV (Ti2p3/2), and 464.3 eV (Ti2p1/2) for Ti4+ and at 1021.8 eV, 1044.9 eV indicate Zn2+ states of Zn. Williamson-Hall (W-H) analysis showed crystallite size decreasing from 68 nm (pristine ZnO) to 24 nm with increasing Ti content. XRD confirmed the hexagonal wurtzite phase of pristine ZnO (c/a = 1.73), maintained in composite sintered at 200°C and 600°C. The band gap of pristine ZnO (200°C) was 3.3 eV, increases to 3.39 eV at Ti at.%, then decreased to 3.17 eV (600°C). The pristine ZnO displayed tensile microstraine (3.06 x10−3), which decreased and became compressive with Ti doping. Ti doping enhanced the crystallinity, reduced the grain size, and microstrain and tuned the band gap, improving photocatalytic performance. The 12at.% Ti composite exhibited the highest methylene blue (MB) degradation rate constant (2.135 × 10−2 min−1) under low-power UV light, due to better grain connectivity, suppressed charge recombination and enhanced reactive oxygen species generation. Isopropyl alcohol confirmed hydroxyl radicals as the dominant species. The use of cow urine as a sustainable, low-cost fuel highlights the eco-friendly nature of the synthesis. Overall, the TiO2–ZnO presents a promising solution for efficient and sustainable wastewater treatment.