A new insight into catalytic ozonation of sulfasalazine antibiotic by plasma-treated limonite nanostructures: Experimental, modeling and mechanism

This study investigates the application of novel natural and plasma-treated iron (III) oxide-hydroxide (limonite) catalysts on the degradation/mineralization of sulfasalazine (SSZ) antibiotic by ozone-based advanced oxidation processes (AOPs). The limonite nanostructures were prepared by non-precursor, environmentally friendly, and fast glow discharge plasma technology under oxygen (PTL/O-2) and oxygen/argon (PTL/O-2/Ar) gaseous atmosphere. The characteristic analysis demonstrated enhanced surface area, morphology, active surface sites, and physical stability after the plasma treatment. It was found that SSZ degradation/mineralization was effectively improved (36%) in the heterogeneous catalytic ozonation process (HCOP) using PTL/O-2/Ar compared to sole ozonation. Modeling and optimization of SSZ degradation through the central composite design (CCD) and artificial neural network (ANN, topology of 4:7:1) showed that complete SSZ degradation can be achieved at the optimized condition (initial pH = 7, ozone concentration = 15 mg L-1, catalyst loading = 1.5 g L-1 and treatment time = 50 min). The effect of organic and inorganic salts confirmed that the reactive oxygen species, mainly hydroxyl radicals, were responsible for SSZ degradation by HCOP. The main intermediates during SSZ oxidation were identified. The toxicity of SSZ solution and electrical energy consumption were decreased using PTL/O-2/Ar nanocatalysts in HCOP. Economic studies demonstrated 46% reduction in energy consumption of HCOP using PTL/O-2/Ar compared to NL samples. For the first time, molecular dynamics simulation was applied to provide a deeper insight into the adsorption mechanisms of SSZ and ozone onto limonite surface (111) during HCOP.