A comparative study on photodegradation of industrial dyes using alkaline earth metal spinel photocatalysts

The sol-gel auto combustion technique was employed to synthesize nanocrystalline alkaline earth metal (M = Mg, Ca) spinel aluminate (MAl2O4) and ferrite (MFe2O4) photocatalysts. Subsequently, XRD, FT-IR, SEM, TEM, BET method, and UV-DRS were performed to examine the resulting photocatalysts to determine their structures, surface texture, morphologies, surface area, pore size distribution, and optical properties. The findings clearly revealed the creation of single-phase spinel structures for each of the calcined samples at varying crystallite sizes (19–45 nm) and differing band gap energies (1.88–4.56 eV). To investigate the activity of MgAl2O4, MgFe2O4, CaAl2O4, and CaFe2O4 samples in terms of photocatalysis, tests were conducted under natural sunlight to decompose four different pollutant types, namely rhodamine B, methylene blue, methyl orange, and methyl red. When compared to MgAl2O4 and CaAl2O4, it was possible to identify MgFe2O4 and CaFe2O4 as potential spinel photocatalysts. For all four of the organic dyes, the efficiency of photocatalytic degradation achieved by the two ferrite photocatalysts reached 95–98% within 150 minutes, whereas in contrast, the aluminate samples reached just 65–89%. Scavenger analysis showed that for pollutants to be converted to safer by-products is it necessary that hydroxyl and superoxide free radicals are present. Moreover, the photocatalysts are cheap and sustainable, and their effectiveness can be maintained for up to four cycles before beginning to decrease.