Influence of Li-doping on structural characteristics and photocatalytic activity of ZnO nano-powder formed in a novel solution pyro-hydrolysis route

Different types of Li-doped ZnO (LDZ) (Li = 0–10 wt.%) powders were prepared by following a novel pyro-hydrolysis route at 450 °C, and were thoroughly characterized by means of thermo-gravimetry (TG), differential scanning calorimetry (DSC), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR), Fourier-transform Raman (FT-Raman) spectroscopy, diffuse reflectance spectroscopy (DRS), ultra-violet visible (UV–Vis) spectroscopy, Brunauer–Emmett–Teller (BET) surface area (SA), and zeta potential (ζ) measurements. Photocatalytic activity of these powders was evaluated by means of methylene blue (MB) degradation experiments conducted under the irradiation of simulated and natural solar light. Characterization results suggest that both pure ZnO and LDZ powders are quite thermally stable up to a temperature of 700 °C and possess band gap (BG) energies in the range of 3.16–3.2 eV with a direct band to band transition and ζ values of −31.6 mV to −56.4 mV. The properties exhibited by LDZ powders were found to be quite comparable to those exhibited by p-type semi-conducting LDZ powders. In order to study the kinetics of MB degradation reaction under the irradiation of simulated solar light, the Li (0.2–10 wt.%) and Al (0.5 wt.%) co-doped ZnO (0.2LADZ to 10LADZ) powders were also synthesized and employed for this purpose. The photocatalytic degradation of MB over LADZ catalysts followed the Langmuir–Hinshelwood (L–H) first order reaction rate relationship. The 10LDZ catalyst exhibited highest photocatalytic activity among various powders investigated in this study.