Historical Development of Al30 Highlighting the Unique Characteristics and Application in Water Treatment: A Review

Abstract

With the largest molecule size, most surface charge and highest polymerization degree among Al species with known structure, Al 30 ([(AlO 4 ) 2 Al 28 (OH) 56 (H 2 O) 26 ] 18+ ) has been attached increasing importance to various fields, including water treatment. Based on the relevant literatures in the past decades, this review tries to comprehensively elaborate the historical development of Al 30 , ranging from its discovery and formation, structure and physicochemical property, to potential application. Different from Al 13 , there is semi-pore geometry structure in Al 30 central beltway, and hence the uneven distribution of surface electrostatic potential, which was more positive in beltway than that at cap. Meanwhile, Al 30 exposed different-type oxygen functional groups, and the bound H 2 O located near the beltway was most acidic, making it most easy to deprotonate. The deprotonation and aggregation of Al 30 occurred in similarly successive pattern, but the formed Al 30 aggregate maintained positive charge within a wider pH range than Al 13 aggregate. Moreover, Al 30 is advantageous in high structural stability, which makes it intact under acidic or high-temperature condition. These unique characteristics facilitate the coagulation performance of Al 30 towards organic matter, arsenic and microorganism by enhanced adsorption, charge neutralization and complexation. Meanwhile, with Al 30 , the effective dosage range was broader than that with Al 13 , and the coagulation process was more resistant to pH variation, which was beneficial to overcome the water quality fluctuation in actual water treatment. Another application of Al 30 is the usage as pillaring agent to improve the adsorption and catalysis performance of clay. Moreover, this review highlights the challenge and direction in the future development of Al 30 , including the improvement of characterization and quantitative methods, and pilot-scale investigation in actual water treatment.

Keywords: Al30, formation mechanism, chemical activity, structural stability, application potential