Surface modification of phosphoric acid activated carbon by using non-thermal plasma for enhancement of Cu(II) adsorption from aqueous solutions

The dielectric barrier discharge (DBD) non-thermal plasma was used to modify the phosphoric acid activated carbon (AC) for enhancing its adsorption performance of Cu(II). The BET, SEM-EDX, FT-IR, elemental analysis and XPS techniques were employed to determine the textural structure and surface chemistry of the raw and plasma modified ACs. The results indicate that the ACs after using plasma modification have much higher Cu(II) adsorption capacity, irrespective of different adsorption conditions, such as solution pH, temperature, dosage and agitation speed. Importantly, the adsorption capacity of Cu(II) on AC has a non-monotonic variation (increasing at first and then decreasing) with the plasma modification time. The optimum modification time was 7.5 min in this study and the Cu(II) adsorption capacity of the modified AC could be improved by about 150% compared to that of the raw AC. Interestingly, the Cu(II) adsorption capacity showed good exponential relationship with the content of carboxylic groups, while it showed significant linear relation with the quantity of phosphates and pyrophosphates groups, indicating that these functional groups play key roles on Cu(II) adsorption. Furthermore, plasma modification improved Cu(II) removal regeneration performance of AC.