Mechanochemical pre-treatment leading to sustainable synthesis of microporous and layered titanosilicates Isabel C. M. S. Santos-Vieira, Zhi Lin and João Rocha CICECO – Aveiro Institute of Materials, Chemistry Department, University of Aveiro, Portugal E-mail: ivieira@ua.pt; zlin@ua.pt; rocha@ua.pt The pursuit of a sustainable society and civilization is perhaps the main challenge of our time and of future generations [1]. Waste prevention is one of the Twelve Principles of Green Chemistry, according to which it is better to prevent waste formation rather than to clean it up after. Hence, in recent years there has been a growing awareness of the importance of developing environmentally-friendly chemical processes [2]. Chemists are becoming increasingly aware of the potential of mechanical grinding or milling for the synthesis of materials. Indeed, mechanochemistry was identified by IUPAC as one of the 10 world-changing technologies. Mechanochemistry is now considered an excellent Green Chemistry method, offering, e.g., the opportunity of reducing considerably or even avoiding the use of solvents [3]. Synthetic analogues of layered and microporous titanosilicate minerals have attracted much attention in the last two decades or so, because they may have many potential applications in, for instance, catalysis, ion exchange and gas adsorption and separation [4-6]. These materials are normally prepared under mild hydrothermal conditions using several titanium silicon sources, along with a large amount of water. The incorporation of a mechanosynthesis step (ball milling) in the preparation of these microporous titanosilicates, reduces the amount of water used by one to two orders of magnitude., compared to conventional hydrothermal synthesis [7]. Thus, no water was added to the reagents in the synthesis of the synthetic small-pore analogue of the minerals sitinakite (Na2Ti2O3SiO4·2H2O), now a commercial Cs+ ion exchanger, and ivanyukite-K (also known as GTS-1, HK3Ti4O4(SiO4)·4H2O). The preparation of the important microporous titanosilicate ETS-10 ((Na,K)2TiSi5O13·nH2O), microporous AM-2 (K2TiSi3O9·H2O), and the analogue of the layered mineral natisite (Na2TiO(SiO4)) required only the addition of a very small amount of water. The enhanced reactivity of the ball-milled reaction mixture can be attributed to the reduction in the size of the precipitated silica particles and to the increase in the number of silanol groups of silica nanoparticles. Moreover, the ball milling step also considerably shortened the synthesis time, in most cases resulting in significant energy savings (3 to 34 times) over conventional hydrothermal synthesis. References 1. P. T. Anastas and J. B. Zimmerman, Curr. Opin. Green Sustainable Chem., 2018, 13, 150–153. 2. C. C. Piras, S. Fernández-Prieto and W. M. De Borggraeve, Nanoscale Adv., 2019, 1, 937–947. 3. T. Friscic, C. Mottillo, H. M. Titi, Angew.C hem. Int. Ed. 59 (2020) 1018 –1029. 4. L. Bacakova, M. Vandrovcova, I. Kopova and I. Jirka, Biomater. Sci., 2018, 6, 974–989. 5. C. Laurino and B. Palmieri, Nutr. Hosp., 2015, 32, 573–581. 6. B. R. Figueiredo, I. Portugal, J. Rocha and C. M. Silva, Chem. Eng. J., 2016, 301, 276–284. 7. I. A. Perovskiy, E. V. Khramenkova, E. A. Pidko, P. V. Krivoshapkin, A. V. Vinogradov and E. F. Krivoshapkina, Chem. Eng. J., 2018, 354, 727–739.
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