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

Magnetic γ-FeO/Al@chitosan-derived biochar (m-FeO/Al@CB) was prepared by introducing magnetic maghemite (γ-FeO) nanoparticles and aluminum sulfate [Al(SO)] into chitosan-derived biochar (CB) obtained at low pyrolysis temperatures. m-FeO/Al@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-FeO/Al@CB were studied. Compared with magnetic chitosan-derived biochar (m-FeO@CB), m-FeO/Al@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 is an effective method for improving the properties of magnetic chitosan-derived biochar. High CR adsorption capacity (636.94 mg g) of m-FeO/Al@CB could result from collaborative effect of flocculation/coagulation and electrostatic attraction. These results demonstrated that m-FeO/Al@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.