Chemical bond between chloride ions and surface carboxyl groups on activated carbon A Physicochemical and engineering aspects

The formation and nature of hydrogen bonding in the adsorption of chloride ions on activated carbon (AC) were investigated. The cause, nature and existence conditions for hydrogen bonding were analyzed by Fourier transform infrared spectroscopy (FTIR), chemical bond theory and chemical equilibrium measurements and calculations. The experimental results revealed the existence of COOH groups on the surface of the AC. There was a large π bond in the carboxyl groups, and the charge transferred from the O in the OH of the molecule to the C, resulting a in positively charged H. The hydrogen bonding occurred between the strong electropositive H atom and a strong electronegative Cl atom, and the bond energy was 34.87kJmol⁻¹K⁻¹. The stability of the hydrogen bond depended on the solution pH, pH values 10.0 were in the hydrogen bond non-forming region. In the non-forming region, Van der Waals forces played an important role in the adsorption of chloride ions. The pH range from 4.0 to 10.0 was the transition region in which hydrogen bonding and Van der Waals forces were the two primary modes of attractions. Hydrogen bonding explained the change in the adsorption capacity of the chloride ion as the pH changed and the weak effect of SO4²⁻.