Preparation of SiO2@ZIF-67/CNTs and research on its adsorption performance at low-temperature

It is in urgent demand that preparation of adsorption materials with high performance working at low-temperature, especially for the treatment of organic dyes in sewage. Herein, we prepared SiO2@ZIF-67/CNTs and the obtained composite was characterized by SEM, XRD, FT-IR, BET and contact angle. The results indicated that SiO2@ZIF-67/CNTs had good adsorption performance for methyl orange at low-temperature. At 5 degrees C, the saturated adsorption capacity of the composite for methyl orange reached 112 mg.g(-1), which was 1.49 times larger than that of the activated carbon. The saturated adsorption capacity of the composite can be greatly enhanced because of the increase of specific surface area and enhancement of hydrophobicity after the calcination treatment, reaching 324 mg.g(-1), which was 1.89 times higher than that of the untreated one. Besides, it was found that the electrostatic interaction could significantly accelerate the adsorption rate of the composite, especially after it being treated with the high-voltage discharge. After the treatment, the average adsorption rate of the composite reached 3.03 mg.g(-1).min(-1) (within 60 min), which is 2.59 times larger than that of the untreated one. The adsorption isotherms of the composites fitted well with the Langmuir model and Freundlich model, which indicated that both physical and chemical adsorption existed in the adsorption process. Adsorption kinetics analysis showed that the adsorption process of composites conformed to the first-order kinetic model. Moreover, the composite can be easily regenerated by washing with ethanol, which shows its excellent reusability. Even after 5 cycles of reuse, the regeneration efficiency remains more than 80 % of its original adsorption capacity.