Effect of activated carbon surface chemistry on adsorption of phenoxy carboxylic acid herbicides from aqueous solutions
Krzysztof Kuśmierek, Arkadiusz Białek, Andrzej Świątkowski
Abstract
ABSTRACT The adsorption of the phenoxy herbicides including 2-(4-chloro-2-methylphenoxy)acetic acid (MCPA), 2-(4-chloro-2-methylphenoxy)propanoic acid (MCPP), and 4-(4-chloro-2-methylphenoxy) butanoic acid (MCPB) on the activated carbons with different surface chemical properties was investigated. The activated carbon was demineralized (AC–NM) and modified by nitric acid oxidation to produce oxidized adsorbent (AC–OX) which possesses acidic surface. Basic activated carbon (AC–AM) was prepared by heat treatment in ammonia at 900°C. Adsorption of the herbicides was strongly pH dependent; no effect of ionic strength was observed. The adsorption kinetics was analyzed using pseudo-first-order and pseudo-second-order models, while the equilibrium data were examined using Langmuir and Freundlich isotherm equations. The obtained results showed that the pseudo-second-order kinetic and Langmuir isotherm models were that best fitted to the experimental data. The adsorption rate, as well as the adsorption efficiency of the herbicides on all of the adsorbents, increased in the order: MCPA < MCPP < MCPB. All of the adsorbates were preferably adsorbed on the basic activated carbon (AC–AM) although it had the lowest specific surface area, indicating that in the adsorption process the availability of the functional groups on the adsorbent surface was more important than the surface area.