Solar/visible lights assisted photocatalyst TiO2/ZnO/CQD: detection and degradation of levofloxacin

Effective remediation of pollutants is challenging; although TiO 2 and ZnO have unique photocatalytic properties, large band gaps/high recombination of electron–hole pairs limit the practical use. ZnO/TiO 2 increases electron mobility, improving the above limitations. The addition of biomass CQDs increases the specific surface area and surface oxygen vacancies due to their up-conversion properties, and is expected to further enhance photocatalytic activity. So, TiO 2 /ZnO-CQDs, which were prepared by dispersing TiO 2 /ZnO NPs in ethanol, to which CQDs were added, were characterized using various analytical techniques. In TEM for TiO 2 /ZnO/CQDs (~ 112 nm), CQDs on the TiO 2 /ZnO surface form a heterojunction between ZnO (d = 3.5 Å) and TiO 2 (d = 2.81 Å). Photoluminescence intensities of TiO 2 /ZnO (361–447 nm) correspond to interfacial defects that create deep oxygen vacancies and reduce radiative recombination. Thus, TiO 2 /ZnO/CQDs exhibit low-intensity emissions, confirming the h + /e − separation and consistent with electrochemical impedance, where a smaller Nyquist semicircle for TiO 2 /ZnO/CQDs results, giving lower interfacial resistance as TiO 2 /ZnO (2689 Ω) than for TiO 2 /ZnO/CQDs (2358 Ω). The greater LEVO adsorption (k = 5.0788 × 10⁻ 5 mol/g) for TiO 2 /ZnO/CQDs, as compared to individual metal oxides; so, TiO 2 /ZnO/CQDs (0.5 g/L) oxidized LEVO efficiently (k = 1.30 × 10 –2 mM/s, 78.32% under sunlight; k = 6.00 × 10 –3 mM/s, 52.06% under visible light). The sample was recyclable over 10 cycles. The intermediates from LEVO oxidation were analyzed using 2D HPLC, agreeing with LC–MS and DFT. TiO 2 /ZnO/CQDs against S. aureus (22.7%) and E. coli (21%) indicate their non-toxicity. This biomass-derived CQDs impacts the electronic properties of TiO 2 /ZnO, offering a sustainable environmental strategy.