Mechanism of biosorption of weak acid brilliant blue RAWL by biosorbent derived from Aspergillus niger

The effect of pH on dye biosorption by a biosorbent derived from Aspergillus niger was investigated. The important functional groups in the surface of biomass were analyzed using IR. The contributions of different functional groups to dye biosorption were quantitatively studied with chemical modification method. The results showed that the biomass exhibited efficient dye biosorption at low pH and the capacity of dye biosorption decreased from 39.6 mg/g to 9.3 mg/g with pH increasing from 2.0 to 6.0. The surface of biomass contained amino group, carboxyl group and phosphate group. The repulsion between negative charged dye molecule and negative charged carboxyl & phosphate groups dissociated at high pH caused decrease in capacity of dye biosorption; the electrostatic attraction between negative charged dye molecule and positive charged amino group protonated at low pH caused increase in capacity of dye biosorption. The methylated amidogen still held protonation at low pH. Therefore, the adsorption ability of biomass was almost unchangeable through methylation of amidogen in biomass. The acetylated amidogen lost protonation at low pH, and the capacity of dye adsorption of biomass decreased by 51.6% after acetylation of amidogen in biomass. It was concluded that the electrostatic attraction between negative dye molecule and positive biomass due to amidogen protonation was the important mechanism of dye biosorption by biomass.