Temperature effect on the zeta potential and fluoride adsorption at the alpha-Al2O3/aqueous solution interface

Area of Science:

• Materials Science
• Environmental Chemistry
• Surface Chemistry

Background:

• Alumina (alpha-Al2O3) is a potential adsorbent for removing fluoride ions from aqueous solutions.
• Understanding the surface chemistry of alumina, including zeta potential and surface hydroxyl groups, is crucial for optimizing fluoride removal.

Purpose of the Study:

• To investigate the effects of temperature and pH on the zeta potential of alpha-Al2O3.
• To study the adsorption mechanisms of fluoride ions at the alpha-Al2O3/aqueous solution interface.
• To determine the optimal conditions for fluoride removal using alumina.

Main Methods:

• Electrophoretic mobility measurements to determine zeta potential and pH of the point of zero charge (pH(pzc)).
• Adsorption studies to analyze fluoride ion uptake and isotherm behavior.
• Investigated temperature effects ranging from 10 to 40 degrees C.

Main Results:

• Zeta potential and pH(pzc) of alpha-Al2O3 are sensitive to temperature, with increasing temperature causing a shift towards lower pH(pzc) due to proton desorption.
• Fluoride adsorption follows Langmuir-type isotherms and occurs via exchange with surface hydroxyl groups.
• Maximum fluoride adsorption density was observed between pH 5 and 6 at 25 and 40 degrees C, with higher temperatures reducing adsorption.

Conclusions:

• The adsorption of fluoride ions onto alpha-Al2O3 is strongly dependent on surface charge, hydroxyl group density, temperature, and pH.
• Alumina's surface properties, particularly protonation/deprotonation, are temperature-dependent, influencing fluoride adsorption capacity.
• Optimal fluoride removal using alumina occurs under specific pH and temperature conditions, highlighting the importance of surface chemistry in water treatment.