Self-assembled magnetic graphene supported ZIF-67 as a recoverable and efficient adsorbent for benzotriazole

• ZIF–MG shows a high adsorption capacity for benzotriazole (BTA) beyond 300 mg g−1.
• Adsorption kinetics, isotherm and thermodynamics are obtained and modeled.
• Factors affecting the BTA adsorption are examined including pH, salts and surfactants.
• ZIF–MG exhibits a higher selectivity toward BTA over benzimidazole in adsorption.
• ZIF–MG is re-used and the regeneration efficiency remains above 98% over 4 cycles.

Benzotriazole (BTA) is extensively-used in industry and households, leading to the increasing detection of BTA in surface water and wastewater. The toxicity of BTA renders it harmful to aquatic organisms and even human; thus BTA has been recognized as an emerging pollutant. Although adsorption is preferable to remove BTA from water, adsorbents proposed for BTA adsorption are quite limited. Considering the positive surface charge and high BTA adsorption capacity of zeolitic imidazole frameworks (ZIFs), a self-assembly of ZIF-67 and negatively-charged magnetic reduced graphene oxide (MG) is prepared via the electrostatic attraction. The resultant ZIF–MG preserves chemical characteristics of ZIF-67 and magnetic property of MG. Thus, ZIF–MG not only shows a high adsorption capacity for BTA but also exhibits magnetic controllability, allowing ZIF–MG to be recovered easily by magnets. The adsorption kinetics, isotherms, and thermodynamics are also determined. With a maximal adsorption capacity of ∼300 mg g−1, ZIF–MG is one of the most effective adsorbents when compared with reported adsorbents. ZIF–MG also exhibited relatively stable adsorption capacities at pH = 4–9 and a higher selectivity over benzimidazole. Effects of salts and ionic surfactants are insignificant on the BTA adsorption to ZIF–MG. ZIF–MG can be also re-used for the BTA adsorption for multiple cycles and the regeneration efficiency remained 98%. The high adsorption capacity and the magnetically recoverable feature make ZIF–MG a promising and potent adsorbent for BTA in water.

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