Dispersion-Sorption Balance (DSB) of Pickering emulsions of polydopamine-polyethylenimine-modified activated carbon for oil spill treatment

Activated carbon (AC) was modified with a copolymer of polydopamine (PDA) and cationic polyethylenimine (PEI) by dip coating and employed for the treatment of crude oil spill in synthetic seawater. Pristine AC was first prepared by impregnating date palm wastes in ZnCl2 solution in 1:2 and 1:4 w/v ratios. The impregnated biomass was then pyrolyzed and the pristine AC obtained was modified with 10-20 wt.% of polydopaminepolyethylenimine copolymer (PDA-PEI) by dip coating. The relative efficiencies of the modified ACs for crude oil sorption and dispersion were defined using a new term referred to as Dispersion-Sorption Balance (DSB), which takes all crude oil fractions, including the fractions captured by sorption and dispersed and the residual fraction, into account. The pristine AC prepared from 1:4 impregnation ratio showed the highest crude oil sorption efficiency of 53% but no crude oil dispersion, i.e. DSB of zero. Modification of this AC with 10 wt.% PDA-PEI increased the dispersion efficiency of the material to 61% with a surface sorption efficiency of 30%, indicating a total treatment efficiency of 91% and a DSB of 0.82. The increase in the DSB of the pristine AC by 82% when it was modified with 10 wt.% PDA-PEI can be attributed to the abundant nucleophilic N-H chains in the modifier, which altered the AC morphology, ensured amphiphilicity and covalent C-N linkages with the AC. However, a further increase in the % of PDA-PEI modifier from 10% to 20% resulted in a decrease in DSB to 0.22.