Document Type
Article
Publication Date
2023
Journal Title
Heliyon
Volume Number
9
Issue Number
3
DOI
https://doi.org/10.1016/j.heliyon.2023.e14341
Version
Publisher PDF: the final published version of the article, with professional formatting and typesetting
Creative Commons License
This work is licensed under a CC BY-NC-ND License.
Disciplines
Chemistry
Abstract
Developing a new adsorbent for fluoride removal from cattle horn waste materials by a facile chemical method has shown great potential for fluoride removal. This paper reports the synthesis of multi-walled carbon nanotubes decorated with hydroxyapatite from cattle horns (MWCNT-CH) using a facile chemical method. Characterization studies using standard techniques showed that the composite is mesoporous with a rough morphology and contained MWCNTs uniformly encapsulated by the hydroxyapatite forming a crystalline MWCNT-CH composite. Optimization of fluoride adsorption by the as-synthesized composite using Response Surface Methodology (RSM) showed that a maximum fluoride removal efficiency of 80.21% can be attained at initial fluoride concentration = 10 mg/L, pH = 5.25, adsorbent dose = 0.5 g and a contact time of 78 min. ANOVA indicates contribution of the process variables in descending order as pH > contact time > adsorbent dose > initial fluoride concentration. Langmuir isotherm (R2 = 0.9991) best described the process, and the maximum adsorption capacity of fluoride onto the as-synthesized MWCNT-CH composite was 41.7 mg/g. Adsorption kinetics data were best fitted in the pseudo-second-order kinetic model (R2 = 0.9969), indicating chemisorption. The thermodynamic parameter (Δ" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 14.4px; font-size-adjust: none; word-spacing: normal; overflow-wrap: normal; text-wrap-mode: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">Δ H = 13.95 J/mol and Δ" role="presentation" style="box-sizing: border-box; margin: 0px; padding: 0px; display: inline-block; line-height: normal; font-size: 14.4px; font-size-adjust: none; word-spacing: normal; overflow-wrap: normal; text-wrap-mode: nowrap; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; position: relative;">Δ S = 65.76 J/mol/K) showed that fluoride adsorption onto the MWCNT-CH composite was a spontaneous, endothermic, and entropy-driving process. Moreover, the adsorption mechanism involves ion exchange, electrostatic interaction, and hydrogen bonding. Fluoride was successfully desorbed (using 0.1 M NaOH) from the composite in four cycles, retaining fluoride removal efficiency in the fourth cycle of 57.3%.
Digital USD Citation
Ojok, Walter; Bolender, James P.; Wasswa, John; Ntambi, Emmanuel; Wanasolo, William; and Moodley, Brenda, "Facile Synthesis and Characterization of Multi-Walled Carbon Nanotubes Decorated With Hydroxyapatite From Cattle Horns for Adsorptive Removal of Fluoride" (2023). Chemistry and Biochemistry: Faculty Scholarship. 46.
https://digital.sandiego.edu/chemistry_facpub/46