Photodegradation of mixed organic dyes and ciprofloxacin antibiotic using spray pyrolyzed Li-Nb co-doped SnO2 thin films

Abstract

Immobilized photocatalysts are emerging in prominence for photocatalytic degradation of various kinds of harmful pollutants. In order to tune SnO₂ thin films as an effective transparent conducting photoelectrode towards photocatalytic degradation, the effects of lithium and niobium co-doping are examined for their structural, morphological, and optoelectronic characteristics. X-ray diffraction patterns reveal successful doping of ‘Nb’ and ‘Li’ into the SnO₂ lattice rendering highly textured growth along (110), (200), (310), and (220) plane directions. X-ray photoelectron spectroscopy confirmed the charge states of Sn⁴⁺, Nb⁵⁺, O^2-, and Li¹⁺ elements to be present in the co-doped SnO₂ films. FESEM micrographs reveal that the tetragonal shaped particles (0 - 1 wt.% Li doped Nb(2 wt.%):SnO₂) undergo a mild agglomeration by forming more slender grains (2 - 4 wt.% Li doped Nb(2 wt.%):SnO₂). The wettability nature by contact angle measurement indicates all the films to be hydrophilic in nature. Nb and Li codoping into the SnO₂ lattice enhances the transmittance from 53 % for pure to 72 % for 4 wt.% Li and 2 wt.% Nb codoped SnO₂ thin film. Photoluminescence emission intensity has been suppressed by the substitution of Nb and Li into the SnO₂ films. Linear four-probe and Hall effect revealed sheet resistance and electrical transport properties with a minimum sheet resistance of 56 Ω/□ and with highest mobility of 34.75 cm² V^-1s^-1 for 4 wt. % Li and 2 wt.% Nb doped SnO₂ thin film, respectively. Based on the determined optoelectronic properties, the photocatalytic activity for solely methyl violet, mixed dyes (methyl orange, malachite green, and methylene blue), and ciprofloxacin antibiotic degradation was carried out using optimal film (1 wt.% Li: 2 wt.% Nb co-doped SnO₂), and a significant degradation efficiency was achieved in both Sunlight and LED light illumination.