Synthesis of chitosan-modified magnetic metal-organic framework and its adsorption of Congo red and antibacterial activity

Although various nano-adsorbent have been developed for sewage treatment, only a few adsorbents possess antibacterial activities. We aimed to synthesis a double-purpose nano-adsorbent with adsorption and antibacterial activity. Magnetic composite materials (Fe3O4@ZIF-8@SiO2) with a porous crystalline state and large specific surface area were synthesized. Chitosan (CS) with broad-spectrum antimicrobial activity was used to functionalize the magnetic metal-organic framework nanocomposites. Fe3O4@ZIF-8@SiO2@CS were produced of low cost, mild conditions without any calcination step. Fourier transform infrared spectroscopy, scanning electron microscopy, the Brunauer-Emmett-Teller method, transmission electron microscopy, vibrating sample magnetometry, thermogravimetric analysis, X-ray diffractometry and X-ray energy dispersive spectrometry presented evidence that a new porous adsorbent Fe3O4@ZIF-8@SiO2@CS is rich in -NH2 and C--S and have specific surface area of 420.58 m(2)/g. Fe3O4@ZIF-8@SiO2@CS has loose crystals, thermodynamically stable and well-defined structures, which are used for Congo red (CR) adsorption and bacterial cell killing. We determined optimal adsorption conditions by adjusting adsorption time, pH and ionic strength. Fe3O4@ZIF-8@SiO2@CS shows a good adsorption capacity of CR, reaching 310.4 mg/g at 298 K. The adsorption kinetics and adsorption isotherm obeyed the General-order kinetic (GO model) and Liu model, respectively. The Fe3O4@ZIF-8@SiO2@CS can remove dyes from simulated dye effluent, and it can be reproduced easily without centrifugation or filtration, with the adsorption efficiency exceeded 70% even after five cycles. Fe3O4@ZIF-8@SiO2@CS exhibited anti-bacterial activity against Staphylococcus aureus and Bacillus subtilis. Double-purpose Fe3O4@ZIF-8@SiO2@CS can be a potential material for wastewater treatment.