Development of magnetic recyclable spinel photocatalysts with enhanced sunlight‐driven degradation of industrial dyes

Abstract

AbstractNanocrystalline nickel and copper‐substituted zinc aluminate spinel powders (NixZn1−xAl2O4 and CuxZn1−xAl2O4) with different additional ion concentrations (0 ≤ x ≤ 1) were successfully synthesized by the sol‐gel auto combustion method using diethanolamine (DEA) as a fuel. The structures, chemical bonds, morphologies, composition, surface area, and optical properties including the magnetic behavior of the obtained samples were investigated by X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FT‐IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), the Brunauer‐Emmett‐Teller (BET) method, UV‐visible diffuse reflectance spectroscopy (UV‐DRS), and vibrating sample magnetometer (VSM). All characterization results confirmed that a single‐phase spinel structure was obtained for all calcined aluminate powders with various crystallite sizes and lattice constants. The band gap energy (Eg) of all modified aluminates is in the range of 2.99‐3.15 eV, which was found to be much lower than that of the pure sample (5.60 eV). These results indicate that the Ni2+ and Cu2+‐substituted ZnAl2O4 samples could be effectively photoexcited by both the ultraviolet and visible light. Evaluation of the samples to determine the photocatalytic activity was carried out through investigation of the way the four main pollutant types decompose when irradiated by sunlight. These pollutants were rhodamine B (RhB), methylene blue (MB), methyl orange (MO), and methyl red (MR). For all optimum samples of organic dyes, the efficiency of photocatalytic degradation achieved 96% by the end of 150 min. Furthermore, each of the modified photocatalysts could be reused and showed a high degree of stability. According to magnetic measurements, the S‐shaped curve of ferrimagnetism can arise in those samples with the optimum concentration, although pure ZnAl2O4 exhibits diamagnetic properties. In comparison to pure ZnAl2O4, the modified samples exhibit high enhancement in the remanent magnetization (Mr), which indicates that it is easy to recover those magnetic photocatalyst through the use of an external magnetic field application. These findings therefore serve as a strong indication that ZnAl2O4 powders substituted by both Ni2+ and Cu2+ may offer the capability to serve in environmentally beneficial harvesting of solar energy.