title: Adsorption of 3,4-dihydroxybenzoic acid onto hematite surface in aqueous medium: importance of position of phenolic -OH groups and understanding of the same using catechol as an auxiliary model.
abstract: A comparative adsorption kinetics, isotherms, dissolution and surface complexation of 3,4-dihydroxybenzoic acid (3,4-DHBA) and 1,2-dihydroxybenzene (catechol) at the hematite/electrolyte interface were investigated. The kinetics at pH 10 and 298.15K suggested that the adsorption behaviour of 3,4-DHBA and catechol onto hematite surface is similar and attain same equilibration time of 60 min. The adsorption kinetics data of 3,4-DHBA and catechol fit the pseudo-second-order kinetic equation of nonlinear form best. The adsorption density of 3,4-DHBA at pH≥9 increases and thereby mimics the behaviour of catechol. The solubility of hematite depends on both pH of the suspension and concentration of adsorbate. The inner-sphere complex is formed by 3,4-DHBA and catechol onto hematite surface but the mode orientation is likely to be different in the pH range 5-8 and 9-10. The advance microscopic scanning in conjunction with the vibration spectroscopy would provide better pictorial presentation of the mode of orientation of 3,4-DHBA and catechol onto hematite surface at different pH.
authors.affiliation: Materials Science Division, CSIR-North East Institute of Science and Technology, Jorhat, Assam, India.
authors.forename: Nabanita
authors.initials: N
authors.lastname: Saikia
authors.forename: Jyotirmoy
authors.initials: J
authors.lastname: Sarma
authors.forename: Jayanta M
authors.initials: JM
authors.lastname: Borah
authors.forename: Sekh
authors.initials: S
authors.lastname: Mahiuddin