Correlation between pore-expanding and dye adsorption of platelet C/SBA-15 prepared by carbonization and oxidation of P123-TMB/SBA-15 composites

Platelet SBA-15 with significantly shortened and larger mesopores were prepared with different dosage of trimethylbenzene (TMB) in the assembly process, and then functionalized with acidic oxygen groups by oxidation of carbon layer that obtained by carbonization of P123-TMB organic species occluded in the silica pores. The preparation procedure involved three steps, namely, (a) synthesis platelet SBA-15 with larger mesopores, (b) carbonization, using P123 in the pore directly as the carbon source, and (c) oxidation with K₂S₂O₈. The resulting oxidation and carbonization of platelet SBA-15 (CST-ox, where C = carbon, S = SBA-15, T = trimethylbenzene, and ox refers to oxidation) composites contained of carbonaceous matter with acid oxygen groups (e.g. –COOH, –C=O and –OH) attached onto the deposited carbon layer. The structural characteristics of the parent silica were retained in the oxidized composite materials, which exhibit high surface area, large pore volume and well-ordered porosity. The oxygen-functionalized CST-ox composites with larger mesopores were found to be excellent adsorbents towards methylene blue. Especially, the adsorption equilibrium time was significantly reduced from 60 to 20 min, and the maximum adsorption capacity was increased from 379 to 420 mg/L, for which may be closely associated with the larger pore size, highly shortened meso-channels and the functionalized carbon layers. The adsorption kinetic data were analysed using pseudo-first-order, pseudo-second-order and Weber’s intraparticle diffusion models. Also equilibrium data were fitted to the Langmuir, Freundlich isotherm models and isotherm constants were determined. Thermodynamic parameters such as changes in the free energy of adsorption (ΔG ⁰), enthalpy (ΔH ⁰) and entropy (ΔS ⁰) were calculated.