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-1 , 4 h, 7.0, 0.5 g L-1 , 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-1 , 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 (R2  = 0.9965, theoretical saturated adsorption capacity 147.28 mg g-1 ). The values ∆G were - 2.09, - 4.73, and - 7.37 kJ mol-1 at 298, 308, and 318 K temperatures, respectively. The ∆H value was 76.68 kJ mol-1 , indicating the endothermic and spontaneous adsorption in nature. The ∆S value was 0.26 kJ mol-1  K-1 , 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.