Spray pyrolysis synthesis of mesoporous γ-AlOOH and γ-Al₂O₃ microspheres and their properties for Cr (VI) adsorption

ABSTRACT

In this work, mesoporous spherical γ-AlOOH and γ-Al₂O₃ particles were rapidly prepared by spray pyrolysis (SP) at different temperatures (400°C–700°C) without the use of template materials. A sol-gel-derived colloidal solution of boehmite was ultrasonicated to generate fine droplets, which were continuously and rapidly transferred into a quartz reactor heated at a specific temperature by a constant flow of N₂ gas. Under ultrasonication-assisted spray conditions, a phase change from boehmite to γ-alumina occurred at a temperature of 500°C, leading to a decrease in the surface area and surface hydroxyl group density of the products. At 400°C, the produced γ-AlOOH microspheres exhibited the highest surface area values of ca. ~ 510 m²/g and a surface hydroxyl group density of ca. ~ 2.92 mmol/g, surpassing those of commercial boehmite. The Cr (VI) removal experiments revealed that γ-AlOOH and γ-Al₂O₃ microspheres have good adsorption performance towards Cr⁶⁺. The optimal γ-AlOOH spheres exhibited the highest Cr(VI) adsorption capacity of ca.~ 44.5 mg/g (~74%) at 27 °C and pH = 5.5. After five adsorption-desorption cycles, the synthesised boehmite powder remained a Cr⁶⁺ adsorbing capacity of ~ 78%. Notably, the fabricated SP-γ-AlOOH was capable of simultaneously removing Cr⁶⁺ and textile dye from the solution. This study provides a facile, rapid, and scalable approach for producing boehmite powder with improved properties for Cr (VI) adsorption.

KEYWORDS:

• Spray pyrolysis
• boehmite
• Cr(VI) adsorption
• γ-AlOOH
• simultaneous adsorption

Acknowledgments

This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 104.05-2020.32. This work is also supported by the Industrial University of Ho Chi Minh City, Vietnam. The authors are thankful to Professor Jinsoo Kim (Chemical Engineering Department, Kyung Hee University, Republic of Korea) for analyzing the samples.

Disclosure statement

No potential conflict of interest was reported by the author.

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Funding

This research is funded by Vietnam National Foundation for Science and Technology Development (NAFOSTED) under grant number 104.05-2020.32.