Selective removal of anionic and cationic dyes by magnetic Fe3O4-loaded amine-modified hydrochar.

Fe3O4-loaded protonated amine-modified hydrochar (Fe3O4-PAMH) was successfully prepared and characterized by scan electron microscopy equipped with energy-dispersion X-ray spectroscopy, zeta potential analysis, vibration sample magnetometry, Fourier transform infrared and X-ray photoelectron spectroscopies, Brunauer-Emmett-Teller measurement, and X-ray diffraction. Adsorption properties of Fe3O4-PAMH to negatively-charged methyl orange (MO) or positively-charged methylene blue (MB) in one- or two-component systems were evaluated. The Fe3O4-PAMH selectively adsorbed MO and MB at pH 5 and 11, respectively. The maximum MO and MB uptake capacities of Fe3O4-AMHC were 202.02 mg/g (pH 5.0) and 148.84 mg/g (pH 11) respectively. The Fe3O4-PAMH can be reused with simple pH management in adsorption-desorption cycles. The MB and MO adsorption abilities on Fe3O4-PAMH were maintained above 99% and 75% for five consecutive recycles, respectively. Thus, Fe3O4-PAMH shows powerful potential in efficiently and selectively adsorbing anionic or cationic dyes from mixed wastewater.