Preparation and characterization of CS/β-CD/Nano-ZnO composite porous membrane optimized by Box-Behnken for the adsorption of Congo red.

In this paper, an effective chitosan/beta-cyclodextrin/nanometer zinc oxide (CS/β-CD/Nano-ZnO) composite porous membrane was synthesized by sol-gel and polymer-assisted inverting method. Preparation conditions of CS/β-CD/Nano-ZnO were investigated by single-factor and Box-Behnken response surface methodology optimizing triethoxyvinylsilane (JH-V151), beta-cyclodextrin (β-CD), and nanometer zinc oxide (Nano-ZnO), and applied to study the adsorption characteristics of Cong red (CR) from aqueous solution using batch experiments. The optimum preparation conditions were determined that the volume fraction of JH-V151 alcohol solution was 11%, the ratio of β-CD to CS was 5.35, and the ratio of Nano-ZnO's mass to solution's volume was 0.36%. Different characterization methods including field-emission scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, UV-visible spectroscopy, and Universal Materials Tester were used to prove the appearance, crystallinity, functional groups, swelling degree, transmittance, and tensile property of CS/β-CD/Nano-ZnO. The optimized batch experimental parameters were 50 mg L, 4 h, 7.0, 0.5 g L, and 55.0 °C as initial concentration, contact time, pH, adsorbent dose, and temperature, respectively. The maximum adsorption capacity on CR reached 96.33 mg g, which is 4.34 times with respect to CS. The batch experimental data were best described by a pseudo-second-order kinetics model and Langmuir isotherm model (R = 0.9965, theoretical saturated adsorption capacity 147.28 mg g). The values ∆G were - 2.09, - 4.73, and - 7.37 kJ mol at 298, 308, and 318 K temperatures, respectively. The ∆H value was 76.68 kJ mol, indicating the endothermic and spontaneous adsorption in nature. The ∆S value was 0.26 kJ mol K, a signal of entropy increase during adsorption. The adsorption capacity decreased only by 5.8% after six recycling runs, which indicated the reusability of CS/β-CD/Nano-ZnO. Therefore, the CS/β-CD/Nano-ZnO composite porous membrane is a promising membrane material for the efficient removal of CR from any water at large and economic scales at moderate concentration.