Al/Co-pillaring of clays from concentrated precursors and catalytic performance in the phenol degradation by sulfate radicals

Abstract This study presents the first successful intercalation and pillaring of natural bentonite with mixed Al–Co species using a highly concentrated metal precursor (approx. 5.0 mol l−1). A statistical design of experiments identified optimal preparation parameters for the resulting Al/Co-pillared clay (Al/Co-PILC). The clay materials were extensively characterized by atomic absorption spectroscopy (AAS), powder X-ray diffraction (XRD), N₂ adsorption–desorption, H₂-temperature programmed reduction (H₂-TPR), cationic exchange capacity (CEC), thermal analyses (TGA/DSC), and UV-vis and IR diffuse reflectance spectroscopies (DR-UV-vis and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS)). The catalytic activity was assessed in the phenol degradation by sulfate radicals from sodium persulfate. The determined optimal conditions in terms of atomic metal ratio of cobalt in the interlayering solution (AMRCo ~ 10 mol%) and equivalent hydrolysis ratio (HReq. = 2.0) yielded a well-expanded Al/Co-PILC with basal spacing d001 (18.4 Å) and textural properties (SBET: 194 m² g−1; Sµp: 140 m² g−1) typical of successfully pillared Al-PILCs, alongside a significantly higher amount of cobalt was effectively incorporated as compared with previous reports. This material achieved 72.0 ± 1.24% of phenol degradation and 65.0 ± 2.13% of dissolved organic carbon (DOC) removal within 1 h of reaction under circumneutral pH and ambient conditions of temperature and pressure, with negligible cobalt leaching (approx. 0.01 mg l−1). Al/Co-PILCs so prepared are thus promising active solids for catalytic advanced oxidation of biorefractory organic contaminants in highly polluted wastewater using sulfate radicals (SR-AOP).