The influence of carbon surface area, carbon-oxygen groups associated with the carbon surface and the solution pH on the adsorption of Pb(II) ions from aqueous solutions has been studied using three activated carbons. The adsorption isotherms are Type I of BET classification and the data obeys Langmuir adsorption equation. The BET surface area has little effect on the adsorption while it is strongly influenced by the presence of acidic carbon oxygen surface groups. The amount of these surface groups was enhanced by oxidation of the carbons with different oxidizing agents and reduced by eliminating these groups on degassing at different temperatures. The adsorption of Pb(II) ions increases on each oxidation and decreases on degassing the oxidized carbons. The increase in adsorption on oxidation has been attributed to the formation of acidic carbon-oxygen surface groups and the decrease to the elimination of these acidic surface groups on degassing. The adsorption is also influenced by the pH of the aqueous solution. The adsorption is only small at pH values lower than 3 but is considerably larger at higher pH values. Suitable mechanisms consistent with the adsorption data have been suggested.

The equilibrium and dynamic adsorption of methylene blue from aqueous solutions by activated carbons have been studied. The equilibrium studies have been carried out on two samples of activated carbon fibres and two samples of granulated activated carbons. These activated carbons have different BET surface areas and are associated with varying amounts of carbon oxygen surface groups. The amounts of these surface groups was enhanced by oxidation with HNO3 and O2 gas at 350℃ and decreased by degassing at increasing temperatures of 400˚, 650˚ and 950℃. The adsorption increases on oxidation of the carbon surface and decreases on degassing. The increase in adsorption has been attributed to the formation of acidic carbon-oxygen surface groups and the decrease in adsorption on degassing to their elimination. The dynamic adsorption studies have been carried out on the two granulated activated carbons using two 50 mm diameter glass columns at a feed concentration of 300 mg/L and at different hydraulic loading rates (HLR) and bed heights. The minimum achievable concentrations are comparatively lower while the adsorption capacities are higher for GAC-S under the same operating conditions. The adsorption capacity of a carbon increases with increase in HLR but the rate of increase decreases at higher HLR values.

Adsorption isotherms of p-nitrophenol from its aqueous solutions on two samples of activated carbon fibres and two samples of granulated activated carbons have been determined in the concentration range 40~800 mg/L (ppm). The surface of these carbons was modified by oxidation with nitric acid and oxygen gas, and by degassing the carbon surface under vacuum at temperatures of 400℃, 650℃ and 950℃. The oxidation of carbon enhances the amount of carbon-oxygen surface groups, while degassing decreases the amount of these surface groups. The adsorption of p-nitrophenol does not depend upon the surface area alone but appears to be influenced by the presence of oxygen groups on the carbon surface. The adsorption decreases on oxidation while the degassing of the carbon surface enhances the adsorption. The decrease in adsorption depends upon the strength of the oxidative treatment being much larger in case of the oxidation with nitric acid, while the decrease in adsorption on degassing depends upon the temperature of degassing. The results show that while the presence of acidic surface groups which are evolved as CO2 on degassing suppress the adsorption of p-nitrophenol, the presence of non acidic surface groups which are evolved as CO on degassing tend to enhance the adsorption. Suitable mechanisms compatible with the results have been presented.