Effect of pH of the precursor solution on the photocatalytic and biomedical applications of enzyme coupled ZnO and SnO2 nanomaterials: A comparative study

The focus of this study is to investigate the effects of pH of the precursor solution and the addition of vermiwash on the photocatalytic and certain biomedical applications of zinc oxide (ZnO) and tin oxide (SnO2) nanopowders prepared via co-precipitation method. The pH of the starting solution was varied as 8, 9 and 10 through the addition of suitable amount of sodium hydroxide (NaOH) and vermiwash. These vermiwash-derived enzymes activated ZnO and SnO2 nanopowders (prepared at different pH values) were applied for biomedical applications viz. antibacterial, antioxidant and antidiabetic activity for the first time. The prepared samples were also characterized using various analytical techniques viz. XRD, SEM, TEM, EDS, FTIR, XPS, BET, and UV-vis spectra. The results of these analytical studies are correlated with their photocatalytic degradation abilities and also biological applications. The photocatalytic activity of the nanoparticle were analyzed using a visible annular type photo reactor by degrading methylene Blue (MB) -a standard cationic dye -under UV-visible irradiation. A remarkable dye degradation efficiency of 98% and 94% were achieved for the best samples of vermiwash activated ZnO and SnO2 (prepared from starting solution with pH 9), respectively. The lower band gap values (2.97 and 3.1 eV) of these samples as calculated from Tauc's plots and their enhanced surface area as observed from the BET analysis play crucial roles in improving their photocatalytic efficiency. Remarkable antibacterial, antioxidant and antidiabetic activities were also recorded for the samples prepared at pH 9.