Role of starch in one pot fabrication of mesoporous gamma-alumina with excellent fluoride sorption capacity
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Date
2023-08Author
Walter, Ojok
Brenda, Moodley
John, Wasswa
Emmanuel, Ntambi
William, Wanasolo
James, Bolender
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Green synthesis of mesoporous γ-AƖ2O3, a cutting-edge material for sustainable application in medicine, engi-
neering, 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 ef-
ficiency 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 PO4
3- 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.