Method for preparing an iron oxide particle core composite

A method of preparing a composite, comprising:

• treating an activated carbon with an acid to form a carboxylated carbon, wherein the acid is selected from the group consisting of HNO3, H2SO4, H3PO4 and HClO4;
• mixing the carboxylated carbon, a Fe(II) salt, a Fe(III) salt, and a base in the presence of a solvent to form a mixture;
• heating the mixture to form a magnetic carbon;
• mixing the magnetic carbon and a halide reagent to form a magnetic core;
• and
• reacting the magnetic core with a branched polyethylenimine thereby forming the composite,
• wherein the halide reagent is at least one selected from the group consisting of a thionyl halide, an oxalyl halide, phosphorus trihalide, and phosphorous pentahalide,
• wherein the magnetic core comprises Fe3O4 disposed on the activated carbon and the branched polyethylenimine,
• wherein the Fe3O4 is in the form of nanoparticles having an average particle size of 1-100 nm;
• and
• wherein the magnetic core comprises acyl halide groups on a surface of the magnetic core.