Browsing by Author "Bolender, James"

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    Facile synthesis and characterization of multi-walled carbon nanotubes decorated with hydroxyapatite from cattle horns for adsorptive removal of fluoride
    (Heliyon Open access, 2023-03-08) Ojok, Walter; Bolender, James; Wasswa, John; Ntambi, Emmanuel; Wanasolo, William; Moodley, Brenda
    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 H = 13.95 J/mol and 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%.
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    Role of starch in one pot fabrication of mesoporous gamma-alumina with excellent fluoride sorption capacity
    (Sustainable Chemistry for the Environment, 2023-09-23) Ojok, Walter; Moodley, Brenda; Wasswa, John; Ntambi, Emmanuel; Wanasolo, William; Bolender, James
    Green synthesis of mesoporous γ-AƖ2O3, a cutting-edge material for sustainable application in medicine, engineering, energy, and water treatment, is still challenging. Our study used a one-pot strategy for facile synthesis of γ-AƖ2O3 by sol-gel method using starch from cassava waste. AƖ(OH)3 were bound to the O-H groups of the starch molecule to form the AƖ(OH)3-starch complex in a nano-network confined in starch polymer cages. Its calcination at 500 ℃ produced a mesoporous, highly crystalline water stable γ-AƖ2O3 with a pore size of 2.07 nm and an extensive BET surface area (215 cm2/g). Using the response surface methodology (RSM), the as-synthesized γ-AƖ2O3 was optimized for efficient fluoride removal from water. A central composite design (CCD) was used to study the effect of initial fluoride concentration, pH, contact time, and sorbent dose on fluoride removal efficiency and optimization of the process. The relative importance of the sorption process variables to the fluoride removal process was assessed using ANOVA. The quadratic model showed that the predicted response was significantly correlated with the experimental response (R2 = 0.9667), with sorbent dose and pH being the process's most influential factors. Optimum conditions for 93.6% fluoride removal efficiency were sorbent dose of 0.5 g, initial fluoride concentration of 10 mg/L, pH 7, and contact time of 137.5 min. A weakly acidic medium favored fluoride removal from water, while the presence of PO43- and HCO3- retarded the process. The sorption data fitted well in the Langmuir isotherm (0.9783) and pseudo-second-order kinetic model (0.9999), indicative of a chemisorption process. The maximum sorption capacity towards fluoride was 207.5 mg/g. A thermodynamic study indicated that the sorption process was spontaneous and endothermic, with increased randomness at the solid-solution interface. Sorption, desorption, sustainability, and leaching tests showed that the sorbent could be used for sustainable fluoride removal at 8.3 USD/1000 liters of safe drinking water.