DIRECTION OF CHANGES IN POROUS STRUCTURE AND ADSORPTION CAPACITY DURING TOPOCHEMICAL OXIDATION OF COAL ACTIVATED BY ALKALI.

The purpose of the work is to evaluate the influence of topochemical oxidation (H₂O₂, HNO₃) of carbon prepared by alkali activation of coal on porosity and ability to adsorb 4-chlorophenol (CPh), Pb(II) cations and iodine. Carbons were oxidized at the reactant/carbon ratio of 1:1 (mol/mol, 25°C, 24 h). Based on nitrogen adsorption-desorption isotherms, the volumes and specific surfaces of ultramicro- (S_umi), supermicro- (S_smi) and other pores were evaluated. Kinetics and adsorption isotherms (25°C) of CPh and Pb(II) were characterized; adsorption capacities of CPh, Pb(II) and I ₂ were determined. The H₂O₂-assisted modification was found to significantly increase S_umi (from 615 to 829 m²/g), but decrease S_smi(from 515 to 494 m²/g). The HNO₃-assisted modification slightly increases S_umi (from 615 to 651 m²/g), does not change S_smi, but forms mesopores. The CPh adsorption is best approximated by the second-order kinetics, and isotherms are well fitted with the use of the Langmuir model. The H₂O₂ treatment increases the CPh capacity from 314 to 389 mg/g; and the HNO3 modification significantly decreases the CPh capacity (to 189 mg/g). Modifications reduce the iodine capacity by 1.11 times (H₂O₂) and 2.33 times (HNO₃). The Pb(II) absorption was established to describe by the second-order kinetics equation; the adsorption isotherms obey Langmuir (R²≥0.986) and Freundlich (R²≥0.984) models. The Pb(II) capacity slightly increases after H₂O₂-assisted modification (from 87 to 95 mg/g), but increases sharply (from 87 to 298 mg/g) after HNO₃-assisted treatment because of significant increasing OH-acidic groups concentration. [ABSTRACT FROM AUTHOR]