Preparation of C@silica core/shell nanoparticles from ZIF-8 for efficient ciprofloxacin adsorption

Ciprofloxacin (CIP) in water is harmful to fish, human body and potentially harmful to ecological system, thus it needs to be removed. Adsorption is a simple treatment method, but the reported adsorbents rarely showed high adsorption performance. Herein, we present the preparation of a C@silica core/shell nanoparticles material for removal of CIP from aqueous solution. The nanoparticles were prepared by first coating a layer of silica gel on ZIF-8 nanoparticles via hydrolysis of tetraethoxysilane (TEOS), followed by carbonization. XRD, FT-IR, TEM, and N-2 adsorption-desorption analysis were employed to examine the obtained products. TEM images clearly show the core/shell structures with a thickness of the silica layer of 13-28 nm. N-2 adsorption-desorption results exhibit the textural properties of the products with both micro-and meso-pores and a high surface area of 594.4 m(2)/g. More CIP amount can be adsorbed from water with higher surface area. The equilibrium adsorption amount reaches a climax at pH 6. The maximum CIP adsorption amount of the C@silica core/shell nanoparticles is 516.8 mg/g, much higher than the parental carbon. In addition, the maximum CIP adsorption amount is significantly increased to 1575 mg/g with the presence of Cu(II) in the aqueous solution. We investigated the mechanism for the increased adsorption capacity of the C@silica core/shell nanoparticles materials, indicating that the silica coating makes these nanoparticles more negatively charged and thus benefits the adsorption of CIP via stronger electrostatic interaction. The C@silica nanoparticles can be easily prepared and their CIP adsorption capacity is very high. The results show that the C@silica nanoparticles are promising candidates for removal of CIP from water.