Adsorptive removal of anionic azo dye by Al 3+ -modified magnetic biochar obtained from low pyrolysis temperatures of chitosan

Magnetic γ-Fe 2 O 3 /Al 3+ @chitosan-derived biochar (m-Fe 2 O 3 /Al 3+ @CB) was prepared by introducing magnetic maghemite (γ-Fe 2 O 3 ) nanoparticles and aluminum sulfate [Al 2 (SO 4 ) 3 ] into chitosan-derived biochar (CB) obtained at low pyrolysis temperatures. m-Fe 2 O 3 /Al 3+ @CB was used to remove typical anionic azo dye (Congo red, CR). Effects of initial CR concentration, contact time, initial pH value, background electrolytes, and temperature on CR adsorption by m-Fe 2 O 3 /Al 3+ @CB were studied. Compared with magnetic chitosan-derived biochar (m-Fe 2 O 3 @CB), m-Fe 2 O 3 /Al 3+ @CB exhibited excellent performance for a wider range of pH values (pH 1–7) and in the presence of background electrolyte. The introduction of Al 3+ is an effective method for improving the properties of magnetic chitosan-derived biochar. High CR adsorption capacity (636.94 mg g −1 ) of m-Fe 2 O 3 /Al 3+ @CB could result from collaborative effect of flocculation/coagulation and electrostatic attraction. These results demonstrated that m-Fe 2 O 3 /Al 3+ @CB is a potential adsorbent for effective removal of organic dyes from aqueous solution due to its high adsorption capacity and convenient magnetic recovery and stronger anti-interference ability against coexisting anions in wastewater.