Control of Al2O3/TiO2 sorbent synthesis parameters to enhance fluoride remediation of impaired water resources

Alumina is widely used for fluoride ion removal due to its high affinity but is limited by low uptake capacity and structural instability. To overcome these issues, innovative alumina-titania sorbents were developed using co-precipitation. These sorbents maintained a surface area of ∼260 m 2 /g and pore volume of ∼0.21 cm 3 /g regardless of feed flow rate. However, low NaOH molarity significantly increased surface area, peaking at 343 m 2 /g with 1 M NaOH. Aging also enhanced surface area, reaching ∼315 m 2 /g. Equilibrium isotherms showed that a feed flow rate of 25 mL/min achieved the highest fluoride uptake (0.19 meq/g). NaOH concentrations ≤4 M produced favourable isotherm profiles, while ≥4 M resulted in unfavourable outcomes. Aging the synthesis mixture for 1–2 h was optimal, as extended aging reduced isotherm performance. The Al 2 O 3 /TiO 2 sorbents also removed calcium, magnesium, barium, strontium, potassium, and silica from groundwater. Optimal synthesis conditions were identified as a 25 mL/min feed flow rate, 2 M NaOH concentration, and a 2-h aging time. The sorption mechanism combined electrostatic attraction and ligand exchange, highlighting the potential of these materials for multifunctional water treatment. • Fluoride uptake increased by controlling synthesis parameters. • Aging promoted sorbent surface areas up to ca. 315 m 2 /g. • NaOH molarity ≤4 M resulted in favourable equilibrium isotherm profiles. • Sorption via a combination of electrostatic attraction and ligand exchange. • Silicates are also removed from solution by the alumina/titania materials.