Sulfanilamide Oxidative Degradation Over M(II)/Ce(III) Type Layered Double Hydroxide Catalysts

The removal of sulfanilamide (SA) from wastewater remains a critical environmental challenge since it significantly contributes to bacterial resistance, thereby diminishing the efficiency of conventional wastewater treatment. This research aims to investigate the ability of manganese/cerium (Mn/Ce) or cobalt/cerium (Co/Ce) layered double hydroxide (LDH) catalysts to promote the degradation of SA in aqueous solutions using hydrogen peroxide (H₂O₂) as the oxidizing agent.

LDH-derived catalysts: Mn6.4Ce, Mn4Ce, Mn3Ce and Co4Ce (the number represents the molar ratio M(II)/M(III) in the synthesis) were obtained by co-precipitation at pH 10 from metal nitrates precursors using a mixture of NaOH and Na₂CO₃ as precipitation agent. The characterization of the solids was performed using XRD, DRIFT and DR-UV-Vis techniques. The degradation experiments of an aqueous solution of SA (0.1mM) were conducted either under conventional stirring (50rpm) or ultrasonication, at 64 molar ratio H₂O₂/SA. The concentration of the catalysts in the reaction mixture was varied in the range of 0.5-2g/L. After 1h, the ultrasonication allowed reaching a conversion of SA comparable to the one obtained after 2-3h under conventional stirring. Among Mn-containing samples it was noticed that the catalytic activity increased with Mn content. A comparison between the samples Mn4Ce and Co4Ce, showed a slightly higher activity of the Co-containing sample, which was more significant with the increase of reaction time, however the activity of this sample was lower than that of Mn6.4Ce.

The XRD, DRIFT and DR-UV-Vis results for the samples retrieved after reaction evidenced that Mn6.4Ce was less affected than Co4Ce. The synergy between the high oxygen storage capacity of Ce³⁺ and redox properties of Mn²⁺ or Co²⁺ cations would be responsible for the catalytic activity of the solids in the oxidation.