Preparation, characterization, and adsorption evaluation of chitosan-functionalized mesoporous composites

• Novel mesoporous composites of natural polymer chitosan and SBA-15 were prepared.
• The mesoporous composites showed good performance towards the uptake of acid red 18.
• The effect of various parameters on the adsorption efficiency was studied.
• The adsorption kinetics, equilibrium, and adsorption thermodynamics were evaluated.

Polymer-modified mesoporous silica materials are of practical interest due to their great potential for adsorption-related applications. In the present work, composites of natural polymer chitosan (CTS) and siliceous mesoporous SBA-15, i.e. SBA-15/CTS(5%), SBA-15/CTS(10%), and SBA-15/CTS(20%), were facilely prepared by prehydrolysis of tetraethyl orthosilicate in the presence of pore-directing agent and subsequent cocondensation with an appropriate amount of CTS-based organosilane. The texture and composition of pure SBA-15 and CTS-functionalized mesoporous products were characterized using various techniques such as TEM, XRD, N2 adsorption/desorption, 29Si MAS NMR, FT-IR, and TGA measurements. To disclose the adsorption properties of the composites, anionic compound acid red 18 (AR18) was selected as model adsorbate. The effects of pH, ionic strength, contact time, adsorption temperature, and initial concentration of AR18 on adsorption efficiency were investigated. It was found that pure SBA-15 had a negligible adsorption capacity while the CTS-functionalized composites showed large adsorption capacities (up to 232.6 mg g−1) with rapid adsorption kinetics (less than 120 min). It was also observed that the adsorption capacity increased with increase in CTS content of the composite. Results of comparative analysis indicated that SBA-15/CTS(20%) had better adsorption capacity than most of common adsorbents. Experimental kinetic and isotherm data were analyzed by theoretical models including pseudo-first-order and pseudo-second-order kinetics, Weber–Morris diffusion, Freundlich and Langmuir models. Moreover, adsorption thermodynamics has also been evaluated. The study suggests that the CTS-functionalized mesoporous composites are prospective adsorbents for adsorption of anionic compounds, and somewhat exemplifies their adsorbent function for adsorbing some other adsorbates.

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