Influence of inorganic acid modification on Cr(VI) adsorption performance and the physicochemical properties of activated carbon

摘要

Macadamiaactivated carbon (MAC) was impregnated with different concentrations of sulphuric or phosphoric or nitric acid ranging from 20 to 60% v/v and heated in a muffle furnace to improve the structural characteristics of the adsorbents for enhanced Cr(VI) removal. The %S content ranging between 2.27 and 3.23% in H2SO4treated MAC corroborated the incorporation of sulphonate groups during modification. Fourier transform infrared spectroscopy displayed presence of CN, NO, sulphur and phosphorus peaks at 1213, 1531, 1204, and 1214?cm?1, respectively, proving efficacious attachment of the functional groups because of acid treatments. The surface area of pristine MAC increased from 545 to 824?m2/g following acid treatment. The optimum performance for the adsorption of Cr(VI) was 98% at pH 1 and 93% at pH 4 after 120?min of contact time. Compared to pristine carbons (22.3?mg/g), there was an improvement in adsorption capacity to 40.99?mg/g when 20% (v/v) HNO3activating agent was used, but the adsorption capacity dropped to 9.66?mg/g when 20% (v/v) H2SO4was used. Materials modified with HNO3and H3PO4exhibited superior performances to H2SO4modified adsorbents indicating the importance of evaluating various concentrations and type of acid as these had positive and negative effects on Cr(VI) removal. The removal mechanism was better explained by both the Langmuir monolayer and Freundlich multilayer isotherms.