Elsevier

Applied Clay Science

Volume 186, 1 March 2020, 105445
Applied Clay Science

Research Paper
Effect of the acid activation on a layered titanosilicate AM-4: The fine-tuning of structural and physicochemical properties

https://doi.org/10.1016/j.clay.2020.105445Get rights and content

Highlights

  • Layered titanosilicate AM-4 of the synthetic analog of the natural Lintisite group was synthesized.

  • Effect of AM-4 treatment with HNO3 on the structural and textural properties was investigated.

  • Surface acidity rose with increasing HNO3 concentration

  • AM-4 materials were used as catalysts for the cyclocondansation of 1,2-phenylenediamine with acetone.

  • Activity of AM-4 improved with increasing HNO3 concentration.

Abstract

In this work we investigated the microporous layered titanosilicate AM-4 (Aveiro-Manchester material number 4) of a synthetic analogous the mineral Lintisite having edge-shared brookite-type TiO6 chains. The objective of our work was to verify the effects of the acid activation on the AM-4 properties, treated with 0.0625–0.25 M HNO3. The results of the physicochemical characterization by SEM, XRD, IR and DR UV–vis spectroscopy, nitrogen adsorption/desorption at 77 K have provided evidences that texture, chemical composition, structural and physicochemical properties of AM-4 could be adjusted by treatment with 0.0625–0.25 M HNO3. According to the method of mass titration, surface acidity (pHPZC) of AM-4 roses with increasing HNO3 concentration, which was in accord with the increase of the reaction rate and yield of 1,5-benzodiazepine in the reaction of cyclocondansation between 1,2-phenylenediamine and acetone.

Introduction

Acidic modification of aluminosilicates is one of the methods for the synthesis of adsorbents and catalysts to produce materials with desired properties. Thus, acid treatment of zeolites leads to the removal of aluminum from zeolite frameworks. The appearance of lattice deficiencies due to the dealumination of zeolites can cause the formation of mesoporous channels in the zeolite crystal with 5–100 nm in pore diameter (Calsavara et al., 2000). Moreover, the acid treatment of zeolites can tune the acidity of zeolites, i.e. the concentration and strength of acid sites of the Brönsted type that is important for its catalytic application (Chen and Zones, 2010; Beyer, 2002; Fan et al., 2006). Textural and physicochemical properties of layered aluminosilicate materials also can be adjusted by acid treatment. Thus, chemical composition and physicochemical properties of clay materials, such as smectites, vermiculites, kaolinite, among others, can be adjusted by acid treatment (Komadel, 2016). For example, in the acid treatment of smectites, the protons of acid first replace the exchangeable cations (Na+, Ca2+, Mg2+); after that they attack the layers and remove Al in the tetrahedral sheets (Komadel, 2016; Okada et al., 2006). Note that, such treatment of clay materials modifies its textural properties and/or amount of acid sites due to the disaggregation of clay particles, elimination of mineral impurities, changing the type of exchangeable cations.

According to the literature (Lv et al., 2007; Llabrés et al., 2003; Xiong et al., 2017; Lee et al., 2012; Tang et al., 2014) acid modification can be used both the change of properties of titanosilicates and its synthesis. Thus, the removal of the extra-framework TiO2 without significantly affects the framework titanium species was demonstrated for the titatosilicate TS-1 with MFI zeolite structure after acid modification (Xiong et al., 2017). Such treatment leads to increasing amount of the active intermediate species Ti-OOH(η2) in oxidation processes. Moreover, the acid modification was used as one of the steps of the two-step post-synthesis strategy of Ti-Beta zeolite (Tang et al., 2014). In the first step, the dealumination of H-Beta zeolite to Si-Beta and formation of vacant T sites with associated silanol groups proceeded due to the HNO3 treatment. Then, vacant T sites in the Si-Beta zeolite reacted with the organometallic Ti complex Cp2TiCl2 and Ti species were incorporated into the framework of Beta zeolite upon the calcination.

The effect of the acid activation on the titanosilicate having –Ti-O-Ti-chains is the most interesting. For example, a microporous titanosilicate ETS-10 (ETS type, Engelhard titanosilicate) (Kuznicki, 1989) was modified with citric acid, H3PO4, HNO3 (Lv et al., 2007) and HF (Llabrés et al., 2003). It was found that diluted acid solutions and short contact times did not lead to the crystal structure collapsing, also increasing the number of accessible titanium sites. Its amount was up to 2–3 times larger than in the parent material. It was suggested that acids mainly degrade the external surfaces of solid with the appearance of new Ti-OH groups.

Other examples of the titanosilicates having –Ti-O-Ti-chains is the lintisite-kukisvumite-group minerals and their synthetic analogous. Herein, we would like to draw your attention to AM-4 (Aveiro-Manchester material number 4, Na3(Na,H)Ti2O2[Si2O6]2 2H2O) (Ferdov, 2014; Lin et al., 1997; Dadachov et al., 1997; Clearfield et al., 1997; Anderson et al., 1997). AM-4 is analogous to the mineral Lintisite discovered in the hyperalkaline pegmatites of Mount Alluaiv (the north-western part of the Lovozero massif, Kola peninsula) (Merlino et al., 1990). This material has a unique layered structure. According to Dadachov et al. (Dadachov et al., 1997), the structure of AM-4 consists of TiO6 octahedra and SiO4 tetrahedra. These two structural units connect to layers which consist of a sandwich of SiO4:TiO6:SiO4:TiO6:SiO4 (Fig. 1, Supporting Information (SI)). The edge-sharing TiO6 octahedra form the chains along (100), which are connected with each other via corner-sharing with SiO4 tetrahedra. Sodium cations and water molecules are located in the interlamellar space (exchangeable) and in the space within the layer (structural cations). Because of the excellent cation-exchange properties, AM-4 has been reported as adsorbent for Ag+, Zn2+, Cu2+ (Perez-Carvajal et al., 2012; Oleksiienko et al., 2017), cesium and strontium (Yakovenchuk et al., 2012; Oleksiienko et al., 2017) and radionuclides (241Am and 236Pu) (Oleksiienko et al., 2017; Al-Attar et al., 2003). Recently, AM-4 was demonstrated to be used as a solid base catalyst for the aqueous phase isomerisation of glucose, the condensation of benzaldehyde with ethyl acetoacetate (the Knoevenagel reaction) (Lima et al., 2008) and the synthesis of 2-methoxy-propanol-1 from methanol and propylene oxide (Timofeeva et al., 2019). Noteworthy that AM-4 in acid media transforms into layered protonated titanosilicate L3 (Fig. 1, SI) that may serve as a precursor for the synthesis of novel titanosilicate nanomaterials. In spite of the studies mentioned above, a systematic investigation of the acid activation of AM-4 lacks in the literature. The increasing interest in looking for new applications of AM-4 provokes a systematic study of this process. For this reason, our target in this work is to investigate the behavior of AM-4 under acid treatment with HNO3 of several concentrations.

Section snippets

Synthesis of AM-4

The layer titanosilicate AM-4 was synthesized from powder of ammonium sulfate oxytitanium (NH4)2TiO(SO4)2∙H2O (the product of loparite concentrate reprocessing (PJSC PhosAgro, Russia)), Na2SiO3·5H2O (Neva Reactive) and NaOH (Merck). Hydrothermal synthesis of layer titanosilicate was carried out in a Teflon-lined autoclave with an inner volume of 450 cm3. The synthesis was based on the consecutive transformations:Ammonium sulfate oxytitaniumNatisiteSitinakiteAM4.

Stage 1 (Synthesis of

Chemical analysis

The chemical composition of AM-4 modified with 0.0625–0.25 M HNO3 is shown in Table 1. According to the chemical analysis, the amount of Na+ decreases with increasing acid concentration (Fig. 1). After the treatment of AM-4 with 0.0625 M and 0.25 M HNO3, the amount of Na+ decreased by 72.7 and 97.9%, respectively. Based on the changing of Na+ concentration and structure of AM-4 (Lin et al., 1997; Dadachov et al., 1997), we can suggest that Na(2) and Na(3) located into in the interlayer space (

Summary and conclusions

In this work we investigated titanosilicate layered material AM-4 that is related to the synthetic analogue of the natural Lintisite group. AM-4 was synthesized from ammonium sulfate oxytitanium (NH4)2TiO(SO4)2∙H2O (the product of loparite concentrate reprocessing) and Na2SiO3·5H2O as a source of Ti and Si, respectively. The synthesis of AM-4 was based on the consecutive transformations: ammonium sulfate oxytitanium → natisite → sitinakite → AM-4. The effect of the acid activation of AM-4 with

Acknowledgments

This work was conducted within the framework of the budget projects АААА-А17-117041710082-8 for Boreskov Institute of Catalysis and AAAA-A17-117020110075-1 for Nanomaterials Research Centre of the Federal Research Centre “Kola Science Centre of the Russian Academy of Sciences” (NMRC KSC RAS), respectively. AG thanks Santander Bank for funding through the Research Intensification Program.

Declaration of Competing Interest

No conflict of interest exists.

No funding was received for this work.

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