Stability, morphological transformation and flocculability investigation of planar tridecameric Al13(OH)24(H2O)2415+

Abstract Though great efforts have devoted to prepare planar Al 13 [Al 13 (OH) 24 (H 2 O) 24 15+ , M-Al 13 ], the lack of knowledge of its stability and hydrolysis behavior in aqueous solution limits its practical application as coagulant. In this study, the stability, morphological transformation and coagulation property of M-Al 13 were thoroughly investigated. The 27 Al-NMR spectra revealed temperature-dependent morphological transformation from M-Al 13 to K-Al 13 in aqueous solution. This transformation was completely inhabited below 5 °C, but was accelerated with increased temperature from 5 to 70 °C. Moreover, higher temperature and longer aging time led to further transformation of K-Al 13 to the aluminum species with higher degree of polymerization such as Al 30 . Thus, low temperature was favorable for the morphological stability of M-Al 13 . Due to the maintenance of M-Al 13 structure, all as-prepared M-Al 13 crystal, M-Al 13 solution (0 °C) and freeze dried M-Al 13 showed excellent and comparable flocculation property in the terms of floc growth rate, floc size and floc strength. Interestingly, the flocculability dramatically decreased after M-Al 13 solution aged at 25 °C or 40 °C for 120 min with 29% and 62% of M-Al 13 transformed to K-Al 13 , respectively. These results implied that M-Al 13 was an important flocculant with better performance than the well-known and efficient flocculant K-Al 13 . Our study about the stability and hydrolysis behavior of M-Al 13 might prompt its application as a highly efficient flocculent for water purification.