Removal of 2,4-dinitrophenol and 2,4-dinitrotoluene from water using surfactant-modified activated carbon

Adsorption of 2,4-dinitrophenol (2,4-DNP) and 2,4-dinitrotoluene (2,4-DNT) onto several surfactant modified activated carbons has been studied. Activated carbon (AC) was produced from pecan shell following a technology developed at New Mexico State University. Five cationic surfactants were used to modify the pecan-shell AC. The surfactants used were dodecyltrimethylammonium bromide (DTAB); dodecylethyldimethylammonium bromide (DEDAB); cetyl pyridium bromide (CPB); hexadecyltrimethylammonium bromide (HTAB); and dimethyl-dioctadecylammonium bromide (DDOAB). An adsorption isotherm model was constructed on the basis of the information obtained from the adsorption experimental data. The results indicate that adsorptive capacity of explosives on AC was increased when DTAB, DEDAB, or HTAB are used as modifiers; while capacity decreased when CPB or DEDAB were used to modify the carbon. Enhancement of surface area was achieved by modification. The maximum surface area obtained for modification with each surfactant was similar, equal to about 13%. However, an increase of surface area did not correspond to an increase in adsorption capacity. DDOAB modifier produced a carbon of large surface area, although adsorption was very poor. Improvement of the adsorption capacity of 2,4-DNP and 2,4-DNT on modified AC is attributable in some part to the available surface area, but more importantly on the affinity between the hydrophobic groups of surfactants and those on the explosives. Compared to adsorption on unmodified AC, DEDAB-modified carbon had an adsorption capacity toward 2,4-DNP and 2,4-DNT, in the amounts of 33% and 39% respectively. DTAB-modified AC resulted in an increased adsorption capacity of 23% for 2,4-DNP and 30% for 2,4-DNT. HTAB-modified AC improved adsorption by 25% and 30%. Experimental adsorption data of both 2,4-DNP and 2,4-DNT was used to build an adsorption model that relates the amount of explosive adsorbed on the modified carbon to the equilibrium explosive concentration in aqueous phase, the initial concentration of modifying surfactant, and the critical micelle concentration of the surfactant.