• PDF / 1,094,468 Bytes
• 6 Pages / 612 x 792 pts (letter) Page_size
• 12 Downloads / 257 Views

DOWNLOAD

REPORT

---

NOLOGY OF INORGANIC SUBSTANCES AND MATERIALS

Preparation of Precursor for Hydrothermal Synthesis of Alkaline Titanosilicates L. G. Gerasimovaa, *, A. I. Nikolaeva, E. S. Shchukinaa, and M. V. Maslovaa a

Tananaev Institute of Chemistry and Technology of Rare Elements and Mineral Raw Materials, Kola Science Center, Russian Academy of Sciences, Apatity, 184209 Russia *e-mail: [email protected] Received March 27, 2018; revised April 15, 2018; accepted April 25, 2018

Abstract—The conditions for the preparation of framework titanosilicates with zorite and ivanyukite structures were studied. The preparation of a gel-like precursor for hydrothermal synthesis is preferably performed from solutions. An excess amount of silicon relative to titanium(IV) and an alkaline medium with pH 10.5– 12.5 provide oversaturation of the salt mass in the Na2O–K2O–TiO2–H2SO4–SiO2–H2O system. This makes it possible to regulate phase formation, ensuring the stability of the structure and surface properties of the final products. To inhibit titanium(IV) hydrolysis, the reduction Ti4+ → Ti3+ is performed. This technique leads to the formation of a monophase precipitate. Keywords: mineral, framework titanosilicates, titanosilicate precursor, hydrothermal synthesis, oversaturation of the system, alkaline medium, surface properties, sorbent DOI: 10.1134/S0040579520040077

INTRODUCTION Alkaline titanosilicates of natural and synthetic origin are increasingly attracting the attention of scientists and practical workers. The first information [1] on the synthesis of microporous titanosilicates appeared in 1967. The synthesized materials were called titanium zeolites and had the properties of molecular sieves [2]. In 1986, titanosilicates were synthesized, which became the first representatives of a new class of microporous titanosilicates under the general name ETS. It was shown that the structure of one of the titanosilicates, ETS-4, is similar to that of the natural mineral zorite discovered in 1972 on the Kola Peninsula [3–5]. The structure of zorite is shown in Fig. 1. However, ETS-4 is unstable when heated and has insufficiently high sorption properties. The most famous titanosilicate from the ETS series is ETS-10. It has high thermal stability and wide pores, which leads to its high potential for use in various fields [6, 7]. For the synthesis of ETS-10, an expensive reagent TiCl3 was used as a source of titanium [8]. As reported in [9], ETS-10 was obtained from titanium sulfate Ti(SO4)2. However, the authors noted that the region of formation of a monophase precipitate in the Na2O–K2O– TiO2–H2SO4–SiO2–H2O system is very limited. Also of interest are titanosilicate minerals with the general name ivanyukites. All the four representatives of the ivanyukite group: ivanyukite-Na-T, ivanyukite-

Na-C, ivanyukite-K, and ivanyukite-Cu were discovered in urtites from the Koashva deposit [10, 11]. The common property of all the above titanosilicates (ion-exchange ability) is due to their specific structure. If titanosilicates are compared w