Preparation and characterization of surface functionalized activated carbons from date palm leaflets and application for methylene blue removal

The objective of this research is to produce acidic, basic and hydrophobic activated carbon and to test them for methylene blue removal. Activated carbon (AC) was prepared from date palm leaflets using KOH activation followed by nitric acid oxidation to produce oxidized activated carbon (OAC) which possesses acidic surface. Basic activated carbons (BACs) were prepared via surface functionalization of OAC using ethylene diamine (EDA) and propylene diamine (PDA) producing basic activated carbons BAC-EDA and BAC-PDA, respectively. Hydrophobic activated carbons (HACs) were also prepared via OAC surface functionalization using ethylamine (EA) and aniline (AN) producing hydrophobic activated carbons HAC-EA and HAC-AN, respectively. AC surface area is high (823 m²/g) with microporosity domination, however, after oxidation and surface functionalization, both the surface area and surface microporosity decrease tremendously. FTIR spectra show that -COOH group on OAC almost disappeared after surface functionalization. Methylene blue adsorption follows pseudo second order model more than pseudo zero or pseudo first order models with faster adsorption on HACs. Equilibrium adsorption data fit the Langmuir model more than the Freundlich model with HAC-EA showing the largest adsorption capacity of methylene blue. Dominating adsorption forces of methylene blue most probably are hydrophobic for HACs, hydrogen bonding for BACs, electrostatic attraction for OAC and van der Waals forces for AC.