Amino hydroxyapatite/chitosan hybrids reticulated with glutaraldehyde at different pH values and their use for diclofenac removal.

Diclofenac sodium (DS) is an emergent pollutant, and among the methods investigated for its removal, adsorption is the most widely utilized technique. Hydroxyapatite and chitosan are biomaterials often used for adsorption. However, both biomaterials are limited due to their low chemical stability in an acidic medium; furthermore, pure hydroxyapatite interacts poorly with diclofenac. In this work, hydroxyapatite was organofunctionalized with 3-aminopropyltrimethoxysilane and further used to obtain amino hydroxyapatite /chitosan hybrids by crosslinking with glutaraldehyde at pH 3, 4, 5, and 6. X-ray diffraction patterns indicated the preservation of the hydroxyapatite phase under all pH conditions. Based on the control reaction of the amino hydroxyapatite with glutaraldehyde and its further reduction in sodium borohydride, the formation of CN moieties was highlighted as the main interaction mechanism between the aldehyde and amino groups. Therefore, crosslinking with glutaraldehyde was evaluated by infrared, Raman spectroscopy, and 13C NMR techniques; the results suggested contributions of imine formation and hydrogen bonding. The hybrid obtained at pH 3 exhibited an enhanced adsorption capacity of 125 mg g-1 at 15 min. The synergy between amino hydroxyapatite and chitosan crosslinked by glutaraldehyde was demonstrated.

Monitoring diclofenac adsorption by organophilic alkylpyridinium bentonites.

Organoclays have been applied as efficient adsorbents for pharmaceutical pollutants from aqueous solution. In this work, dodecylpyridinium chloride (C12pyCl) and hexadecylpyridinium chloride (C16pyCl) cationic surfactants were used for the preparation of organobentonites destined for diclofenac sodium (DFNa) adsorption, an anionic drug widely detected in wastewater. The organofunctionalization of the clay samples was performed under microwave irradiation at 50 °C for 5 min with surfactant amounts of 100% and 200% in relation to the cation exchange capacity (CEC) of the pristine bentonite. The amount of incorporated ammonium salts based on CHN elemental analysis was higher for all samples prepared with 200% of the CEC. The basal spacings of the organoclays ranged from 1.54 to 2.13 nm, indicating the entrance of organic cations into the interlayer spacing of the clay samples, and the spacing depended on the size of the alkyl organic chain. The hydrophobic character of the organobentonites was verified by thermogravimetry and infrared spectroscopy (FTIR). The adsorption isotherms showed that the drug capacity adsorption was influenced by the amount of surfactant incorporated into the bentonite, the packing density and the arrangement of the surfactants in the interlayer spacing. Zeta potential measurements of the organobentonites and FTIR analysis after drug adsorption suggested that electrostatic and nonelectrostatic interactions contributed to the mechanism of adsorption.