Catalytic wet peroxide oxidation of a real textile azo dye Cibacron Red P-4B over Al/Fe pillared bentonite catalysts: kinetic and thermodynamic studies

Abstract

In the present work, Al/Fe pillared clay catalysts (Al/Fe-PILCs) with different active metal ratios (Fe/(Fe + Al) molar ratio in the intercalating solution) were prepared by using bentonite clay from Ordu (Fatsa) area in Turkey. Batch experiments were performed to study the catalytic wet peroxide oxidation of Cibacron Red P-4B azo dye on the obtained heterogeneous catalysts. The raw bentonite and catalyst samples were characterized by means of XRD (X-ray diffraction), XRF (X-ray fluorescence), DTA (differential thermal analysis), TG (thermogravimetric analysis), BET (Brunauer–Emmett–Teller), SEM (scanning electron microscopy), EDS (energy dispersive spectrometry) and FTIR (Fourier transform infrared) techniques. The basal spacing (d001) of Al/Fe-PILCs increased with the increase in active metal ratio up to 17.2 A for the catalyst with 12% active metal ratio (NaBAlFe12). The BET specific surface area and the micropore volume of NaBAlFe12 showed a decrease compared to raw bentonite. The color removal ratio increased with increasing active metal ratio and reached to 99.24% after 4 h reaction for the NaBAlFe12 catalyst. The pseudo-first order kinetic model was well obeyed the experimental data (k = 0.0075 min−1 at 25 °C). The activation energy (Ea) was calculated as 12.26 ± 0.78 kJ mol−1. It was also found that the catalytic oxidation process was endothermic (ΔH = 9.64 ± 0.76 kJ mol−1) and nonspontaneous (ΔG = 95.35 ± 1.46 kJ mol−1). The catalysts were chemically stable and reusable with low release of iron.