Degradation of rhodamine B dye under visible and solar light on zinc oxide and nickel-doped zinc oxide thin films
Manel Sellam, Soulef Azizi, Dikra Bouras, Mamoun Fellah, Aleksei Obrosov, Gamal A. El‐Hiti
Abstract
The kinetic investigation of rhodamine B dye's photocatalytic degradation, chosen as a model pollutant, was conducted at room temperature using Zinc oxide (ZnO) and nickel-doped zinc oxide (Zn 0.97 Ni 0.03 O) photocatalysts synthesized through the spray pyrolysis method. XRD analysis confirmed the formation of hexagonal ZnO and Zn 0.97 Ni 0.03 O films, with crystallite sizes ranging from 19 to 29 nm and varying in mean average grain size from 72 nm to 88 nm. The surface morphology of the Ni-doped ZnO films was influenced by nickel doping, observed through SEM and TEM micrographs, revealing a dense structure of spherical-shaped crystals. Light transmission and optical band gap energy of the films ranged between specified values, ranging from 3.27 to 3.24 eV. The degradation process was assessed under various conditions, including different light sources (UV lamp and solar irradiation), pH levels, and substrate concentrations. Degradation followed a pseudo-first-order kinetic model, with rate constants (k) and half-life times (t 1/2 ) calculated accordingly. The degradation efficiency of undoped ZnO and ZnO doped with nickel decreased with increasing concentration under UV irradiation from (0.1–0.5 M) under UV irradiation decreased from (34.29–45.02) (49.61–56.61), while under visible light are (40–45.07 %) (58.46–60.24 %), removal rates ranged within specific percentages. The porous Zn 0.97 Ni 0.03 O synthesized at 0.5 M exhibited the highest photocatalytic efficiency due to its enhanced crystallinity, resulting in degradation rates of 9.22 and 11.22 × 10 −3 min −1 and half-life times of 75.18 and 61.77 min at 90 min specified for both UV and solar light irradiations, respectively. Acidification of the reaction medium accelerated the photocatalytic degradation kinetics, while alkalization slowed it down. These findings mark a significant advancement in the utilization of oxide semiconductors for water pollutant degradation under natural sunlight. • Zn0.97Ni0.03O photocatalysts were successfully prepared via the spray pyrolysis technique. • Microscopic analyses (SEM and TEM) unveiled compact spherical crystal structures. • Nickel doping induced changes, increasing particle size while decreasing the energy gap. • Photocatalytic removal rates fell within specified ranges. • Enhanced crystallinity led to decomposition rates under UV and solar light exposure.