# Topochemical silanization of the Aurivillius phase Bi2SrTa2O9 and post-synthesis complexation

Pacôme Chapel, Thibaud Henry, Frédéric Payet, Cédric Leuvrey, Fabrice Leroux, Nathalie Parizel, Pierre Rabu, Guillaume Rogez

► To cite this version:

Pacôme Chapel, Thibaud Henry, Frédéric Payet, Cédric Leuvrey, Fabrice Leroux, et al.. Topochemical silanization of the Aurivillius phase Bi2SrTa2O9 and post-synthesis complexation. Applied Clay Science, 2025, 278, pp.108017. 10.1016/j.clay.2025.108017. hal-05316789

HAL Id: hal-05316789

https://hal.science/hal-05316789v1

Submitted on 16 Oct 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
<figure><img src="image_2.png" /></figure>

Research Paper

# Topochemical silanization of the Aurivillius phase Bi₂SrTa₂O₉ and post-synthesis complexation

Pacôme Chapel<sup>a</sup>, Thibaud Henry<sup>a</sup>, Frédéric Payet<sup>a</sup>, Cédric Leuvrey<sup>a</sup>, Fabrice Leroux<sup>b</sup>, Nathalie Parizel<sup>c</sup>, Pierre Rabu<sup>a</sup>, Guillaume Rogez<sup>a,∗</sup>

ARTICLE INFO

Keywords:

Layered oxides
Aurivillius phase
silanization
*in situ* complexation
solid state NMR
EPR spectroscopy

ABSTRACT

Functionalization of layered oxides to convey a reactive function prone to coordinate metal cations in-between the inorganic layers is a challenge with respect the potential reactivity of the oxides with these groups. Here, silanization by amine-bearing alkoxysilanes was proposed as a convenient way to bring in free amine groups in the interlayer space. Yet, silanization in itself has seldom been explored for layered oxides.

This study presents a microwave-assisted multistep approach for functionalizing the Aurivillius Bi₂SrTa₂O₉ phase by organosilanes. Three different organosilanes were inserted in the interlayer space, triethoxyoctylsilane, 3-(aminopropyl)triethoxysilane and N-[3(trimethyoxysilyl)propyl]ethylenediamine. The synthetic pathway described here constitutes a fast and efficient approach to silanize the interlayer space of layered perovskites, while preserving the layered structure. The compounds were fully characterized, notably by X-Ray Diffraction (XRD) and solid state Nuclear Magnetic Resonance (NMR), which demonstrated that the organosilanes were effectively grafted onto the oxide layers, forming stable Si-O-Ta bonds, and allowed to precise the grafting scheme, evidencing the very limited formation of siloxane network. Using this approach, free amino groups were introduced in-between the inorganic oxide layers due to the preferential reactivity of the oxide sheets with the alkoxysilane groups compared to amine. These amino groups are available for further coordination by transition metal ions using a post-synthesis complexation reaction. As a proof of concept their complexation ability towards Cu²⁺ ions was demonstrated by UltraViolet-Visible (UV-Vis) and Electron Paramagnetic Resonance (EPR) spectroscopies.

This soft chemistry strategy constitutes a new versatile, fast and efficient method to introduce transition metal cations into layered oxides and paves the way for the design and synthesis of complex architectures, specifically designed for application, in catalysis, sensors, metal cation remediation or luminescence for instance.

# 1. Introduction

Hybrid organic-inorganic materials are of very significant interest because they have the potential to integrate the diverse properties of their individual components into a single structure (Faustini et al., 2018; Gomez-Romero et al., 2024). In this context, layered insertion compounds are particularly appealing, due to the broad range of available inorganic host structures, such as hydroxides, oxides, chalcogenides and clays for instance, as well as the wide variety of applications they enable

(Carrado, 2000; Rogez et al., 2011; Fernandes et al., 2014; Zubair et al., 2017; Uppuluri et al., 2018). Among these layered materials, ion-exchangeable oxides, including layered perovskites, are especially notable for their remarkable physical properties, such as fatigue-free ferroelectricity (de Araujo et al., 1995; Shimakawa et al., 1999), luminescence (Blasse and Brixner, 1989; Ida et al., 2008; Awaya and Ida, 2023) and photocatalytic activity (Wei et al., 2009; Krasheninnikova et al., 2022; Khodabakhsh et al., 2023).

Layered perovskites consist of oxide slabs described by the general

<footnote><sup>a</sup> Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), UMR CNRS-Unistra 7504, 23 rue du Loess, BP 43, 67034 Strasbourg Cedex 2, France</footnote>

<footnote><sup>b</sup> Institut de Chimie de Clermont-Ferrand, Université Clermont Auvergne, UMR CNRS 6296, Clermont Auvergne INP, 24 av Blaise Pascal, BP 80026, 63171 Aubière Cedex, France</footnote>

<footnote><sup>c</sup> Institut de Chimie de Strasbourg, Propriétés Optiques et Magnétiques des Architectures Moléculaires (POMAM), UMR CNRS-Unistra 7177, 1 rue Blaise Pascal, BP296 R8, 67008 Strasbourg Cedex, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: guillaume.rogez@ipcms.unistra.fr (G. Rogez).</footnote>
formula [A<sub>n</sub>·<sub>1</sub>B<sub>n</sub>O<sub>3n+1</sub>], where n accounts for the thickness of the slab, separated by cations or cationic oxides layers. These structures are categorized into three families: Dion-Jacobson X[A<sub>n</sub>·<sub>1</sub>B<sub>n</sub>O<sub>3n+1</sub>] (Dion et al., 1981), Ruddlesden-Popper X<sub>2</sub>[A<sub>n</sub>·<sub>1</sub>B<sub>n</sub>O<sub>3n+1</sub>] (X = K, Li, Na, Rb, Cs) (Ruddlesden and Popper, 1958), which differ by the charge required to compensate the anionic perovskite slab and Aurivillius phases with the general formula Bi<sub>2</sub>O<sub>2</sub>[A<sub>n</sub>·<sub>1</sub>B<sub>n</sub>O<sub>3n+1</sub>], for which the perovskite-like slabs are separated by a fluorine-type bismuth oxide layer (Aurivillius, 1949a, 1949b, 1950, 1952). The possibility to form organic-inorganic hybrids from such layered perovskites by inserting linear alcohols and amines from their protonated forms was widely established (Kikkawa and Koi-zumi, 1980; Rebbah et al., 1980; Clément and Marchand, 1983; Nedjar et al., 1986; Gopalakrishnan et al., 1987; Matsuda et al., 1993b, 1993a; Tahara et al., 2007; Kurnosenko et al., 2022). Recently, our team and others demonstrated the opportunities brought by the use of microwave-assisted routes to ease and speed up the protonation and functionalization of these layered oxides (Akbarian-Tefaghi and Wiley, 2018; Atri and Tomar, 2021), either by alkylamines (Akbarian-Tefaghi et al., 2016; Wang et al., 2016a), alcohols (Boykin and Smith, 2015; Akbarian-Tefaghi et al., 2016; Wang et al., 2016b, 2018, 2019; Poduval et al., 2024) or phosphonic acids (Payet et al., 2022). Alkylamines interact through electrostatic interactions with the charged slabs while alcohols derivatives and phosphonic acid are covalently attached via etherification or esterification reactions respectively. Hybridization with bi-functional or multifunctional molecules is very attractive, as it enables subsequent use of the hybrid materials since their interlayer space then displays available reactive functions which might further interact and/or react with an organic or an inorganic species. For instance, it was possible to functionalize the interlamellar space of the protonated H<sub>2</sub>Bi<sub>0.1</sub>Sr<sub>0.85</sub>Ta<sub>2</sub>O<sub>7</sub> phase by an alkyne function, which was further reacted with molecules bearing an azido group, *via* a "click chemistry" reaction (Wang et al., 2016b). The group of Choy (Han et al., 2001) managed to graft amino-acids into layered KCa<sub>2</sub>Nb<sub>3</sub>O<sub>10</sub> which enabled to control its subsequent exfoliation by means of an *in situ* acid-base reaction. More recently, Wiley and coworkers (Poduval et al., 2024) introduced hydroxyaromatic molecules between the layers of KLaNb<sub>2</sub>O<sub>7</sub>. These molecules were anchored by their hydroxyl group, which leaves the carboxylic acid group available for further reaction.

However, although potentially very interesting, getting available free amines into the interlamellar space of layered oxides with a perovskite structure remains a challenge. It was indeed shown that while diamines form pillars between two adjacent layers (Wang et al., 2016a), amino-alcohols interact preferentially with the inorganic layer through the amine moiety, leaving the alcohol free (Wang et al., 2018). Up to now it has not been possible to favor the reverse situation where the alcohol is grafted leaving the amine free. Here it is proposed to overcome this issue by using an organosilane bearing a terminal amino group.

Functionalization of layered oxides by organosilanes by classical approaches, was far less explored than it has been for alcohols, amines or phosphonic acids, and, to the best of our knowledge was never reported using microwave-assisted reactions, despite the fact that organosilanes are key components in hybrid material development due to their ability to form stable covalent bonds with inorganic surfaces, while introducing versatile functional groups capable for instance of interacting with transition metals or other molecules of interest (Sagiv, 1980; Pujari et al., 2014). Organosilane moieties were successfully grafted onto several other layered materials, including layered double hydroxides (Yang et al., 2015; Guo et al., 2016; Jia et al., 2018; Carrasco et al., 2020), clays (He et al., 2005, 2013; Yuan et al., 2008; Su et al., 2013) or lepidocrocite-type phases (Ide and Ogawa, 2003, 2006; Wang et al., 2013; Kim et al., 2016; Guo et al., 2017), for instance in order to tailor surface properties for capturing different metal cations enabling various applications such as catalysis or exfoliation processes.

Only few examples were presented in the literature concerning functionalization of layered perovskite-type oxides by organosilanes. Osterloh (Osterloh, 2002) described the aggregation of [H<sub>1</sub>.

xCa<sub>2</sub>Nb<sub>3</sub>O<sub>10</sub>]x⁻ nanosheets functionalized by 3-(aminopropyl)triethoxysilane and magnetite nanoparticles, but did not provide information neither on the silanization process nor on its characterization. Sugahara et al. (Tahara et al., 2005; Tahara et al., 2006a) notably demonstrated the functionalization of niobiate layered perovskite phases with PDMS (poly(dimethylsiloxane) and TMOS (tetramethoxysilane), leading to controlled exfoliation.

Here a multi-step approach is described using microwave-assisted route to functionalize the layered perovskite-type Aurivillius phase Bi<sub>2</sub>SrTa<sub>2</sub>O<sub>9</sub> by three distinct organosilanes: triethoxyoctylsilane (OTES), possessing a linear chain of eight carbons, 3-(aminopropyl)triethoxysilane (APTES) and N-[3(trimethyloxysilyl)propyl]ethylenediamine (TPED) which possess amine groups that can be further used to coordinate transition metals cations (Fig. 1) (Klonkowski et al., 1999; Silva et al., 2006; Rassadin et al., 2015).

The silanization mechanism and the structural characterizations are thoroughly discussed and provide a complete description of the covalent functionalization of the layered perovskite by organosilane moieties.

Finally, this approach allows to provide new coordination sites within the interlamellar space of layered oxides. The free amine groups brought by the silanization by APTES and TEPD are available for further coordination by transition metal ions using a post-synthesis complexation reaction. As a proof of concept, the *in situ* complexation of Cu<sup>2+</sup> cations by the free amino groups present in the interlayer space of the hybrids functionalized by APTES and TEPD is demonstrated, whereas the hybrid functionalized by OTES, which does not possess amino group, does not incorporate Cu<sup>2+</sup> in the same reaction conditions. The design of available and efficient coordination sites in the interlayer space paves the way for further developments and applications of these materials.

## 2. Materials and methods

### 2.1. Syntheses

Microwave syntheses were performed with a Monowave 300 (Anton Paar) microwave synthesis reactor (non-acidic conditions) and with a MultiwaveGO (Anton Paar) reactor for strongly acidic conditions (synthesis of HBST). Bi<sub>2</sub>SrTa<sub>2</sub>O<sub>9</sub> (BST) (Ida et al., 2007), H<sub>2</sub>Bi<sub>0.1</sub>Sr<sub>0.85</sub>Ta<sub>2</sub>O<sub>7</sub> (HBST) (Wang et al., 2016a) and (CH<sub>3</sub>(CH<sub>2</sub>)<sub>3</sub>NH<sub>3</sub>)HBi<sub>0.1</sub>Sr<sub>0.85</sub>Ta<sub>2</sub>O<sub>7</sub> (C<sub>4</sub>N-HBST) (Wang et al., 2016a) were synthesized according to published procedures.

All reactants and solvents were used without further purification: Bi<sub>2</sub>O<sub>3</sub> (Thermo-Scientific, 99.9 %), SrCO<sub>3</sub> (Rectapur, 99 %), Ta<sub>2</sub>O<sub>5</sub> (Alfa Aesar, 99 %), HCl (Carlo Erba, 37 % in H<sub>2</sub>O), butylamine (Sigma-Aldrich, 99.5 %), toluene (Honeywell), 3-(aminopropyl)triethoxysilane (APTES) (Sigma-Aldrich, 99 %), N-[3(trimethyloxysilyl)propyl]

<figure><img src="image_3.png" /><figcaption>Fig. 1. Organosilanes used in this study: triethoxyoctylsilane (OTES), 3-(aminopropyl)triethoxysilane (APTES) and N-[3(trimethyloxysilyl)propyl]ethylenediamine (TPED).</figcaption></figure>
ethylenediamine (TPED) (Sigma-Aldrich, 97 %), triethoxy(octyl)silane (OTES) (TCI, >97 %), Cu(NO₃)₂·2.5 H₂O (Alfa Aesar, 98–102 %).

Caution: even though no problem was encountered in the course of this research, special care must be taken while working with sealed glass containers. Containers must be carefully checked for any defect and replaced if necessary to avoid possible explosion. Amines and concentrated hydrochloric acid are corrosive and irritating.

### 2.1.1. [Si(OH)₂-x(OSi⁻)x-Rn]yH₂-βBi₀.₁Sr₀.₈₅Ta₂O₇ (R₁ = -(CH₂)₃NH₂: APTES-HBST; R₂ = -(CH₂)₂NH(CH₂)₂NH₂: TPED-HBST; R₃ = -(CH₂)γCH₃): OTES-HBST)

100 mg of C₄N-HBST (0.14 mmol) were dispersed in a solution of 6 mL of organosilane (25.6, 27.8 and 19.1 mmol for APTES, TPED and OTES respectively) and 10 mL of toluene. The mixture was placed in a 30 mL vial and heated by microwave irradiation at 110 °C during 3 h (maximum incident power: 70 W). In these conditions, the autogenous pressure was about 1 bar. The obtained white powder was collected after three centrifugations (14,000 rpm (18,400 g), 5 min each; the supernatant was replaced after each centrifugation by ethanol) and air-dried.

### 2.1.2. Complexation by Cu: Cu[APTES]-HBST and Cu[TPED]-HBST

50 mg of organosilane-HBST (APTES-HBST or TPED-HBST) and 1 equivalent of Cu(NO₃)₂·2.5 H₂O were dispersed in 10 mL of water. The mixture was stirred at room temperature for 1 h. The obtained blue (Cu [APTES]-HBST) or purple (Cu[TPED]-HBST) powder was collected after three centrifugations (14,000 rpm (18,400 g), 5 min each; the supernatant was replaced once by water, then once by ethanol) and air-dried.

## 2.2. Characterizations

C, N and H elemental analyses were carried out at the Service Commun d'Analyses of the University of Strasbourg. The Ta and Si contents of the obtained products were obtained at the Plateforme d'Analyse of the School of Chemistry Polymers and Materials of Strasbourg (ECPM) by inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), after dissolution in a mixture of hydrochloric, nitric and fluoric acids at 170 °C in a closed autoclave.

Powder X-ray diffraction (PXRD) patterns were collected in a Bragg-Brentano geometry with a Bruker D8DISCOVER diffractometer equipped with a Cu Sealed tube (CuKα₁ = 0.1540598 nm, operating at 40 kV and 40 mA), a quartz front monochromator and an energy resolved Lynxeye linear detector. PXRD patterns were recorded in the 2θ range 1 to 70°, with a step size of 0.02°, over a total acquisition time of 7 h.

Fourier-Transformed Infra-Red (FT-IR) spectra were collected in Attenuated Total Reflectance (ATR) mode on a Spectrum II spectrometer (Perkin-Elmer) (spectral range 4000–400 cm⁻¹, 32 accumulated scans, 2 cm⁻¹ resolution).

For both ¹³C and ²⁹Si nuclei, of nuclear spin quantum number of *I* = 1/2, the solid-state Nuclear Magnetic Resonance (NMR) spectra using a proton-enhanced cross-polarization (CP) method were recorded with a 300 Bruker spectrometer at 75.47 and 59.63 MHz, respectively, using magic angle spinning (MAS) condition at 10 kHz and a 4-mm-diameter zirconia rotor. ¹³C CP-MAS were referenced to the carbonyl of the glycine calibrated at 176.03 ppm with recycling and Hartman–Hahn (HH) contact times of 5 s and 1250 µs respectively. ²⁹Si CP-MAS were calibrated relative to TEOS single peak at -82.04 ppm, a recycling time of 10 s and a HH contact of 6 ms. In both cases, spinal 64 ¹H phase-decoupling was applied during the channel acquisition. Due to the low sensitivity of ²⁹Si (3.67 10⁻⁴ relative to ¹H) and its low spin-lattice relaxation time, direct acquisition of ²⁹Si quantitative signal was performed by repeating a large number of scans and using MAS condition and long recycling time. Experimentally, 3000 up to 5000 scans were accumulated with a recycling time of 60 s to collect a proper signal to noise ratio over the total ²⁹Si chemical shifts dispersion.

Diffuse reflectance spectroscopy (DRS) was performed with a Perkin-

Elmer Lambda 650S spectrometer (spectra recorded in the reflection mode, using a 150 mm integrating sphere, with a resolution of 2 nm and a mean sampling rate of 200 nm·min⁻¹). DRS spectra are then transformed using the Kubelka-Munk function, f(R) = (1-R)²/(2R).

Energy dispersive spectroscopy (EDX Bruker) coupled to scanning electron microscopy (SEM) was performed using a JEOL JSM 6700F microscope equipped with a field emission gun operating at an accelerating voltage of 22 kV. Scanning electron microscopy images were taken using a Zeiss GeminiSEM-500 microscope equipped with a field emission gun (FEG) operating at an accelerating voltage of 3 kV. Morphology information was obtained using the InLens detector (which receives secondary electrons). Relief information was obtained using the detector in the chamber, SE2 or Everhart-Thornley (which receives secondary electrons and backscattered electrons). Finally, composition information was obtained using the detector in the column, ESB (which receives backscattered electrons). Samples were deposited as powders on carbon tape, fixed to the aluminum sample holder, and then covered by carbon by evaporation of carbon fiber threads.

Electron Paramagnetic Resonance (EPR) experiments were performed at room temperature using an EMX X-band spectrometer (EMXplus from Bruker Biospin GmbH, Germany), equipped with a high sensitivity resonator (4119HS-W1, Bruker). The g calibration standard was a strong pitch of known g factor 2.0028. The spectrometer was operated at ca. 9.31 GHz with a Modulation Frequency: 100 kHz. The principal spectrometer settings were: Center Field: 3100 G, Sweep Width: 3000 G, Microwave power: 2.44 mW, Modulation Amplitude: 5 G, Gain: 50 dB, Conversion Time: ca. 80 ms, Time Constant: ca. 20 ms. Here a single scan corresponded to 3000 points swept in 240 s each. Two scans were enough in order to achieve an acceptable S/N ratio. All experimental EPR spectra were analyzed by means of computer simulation using lab made scripts based on Easyspin toolbox under Matlab (MathWorks) environment.

## 3. Result and discussion

### 3.1. Silanization of the Aurivillius phase Bi₂SrTa₂O₉

Following the seminal works of Landis et al. (1991) and of Clearfield et al. (Sylvester et al., 1994) who grafted respectively tetraethyl orthosilicate in a layered trititanate and (3-aminopropyl)trimethoxysilane into a layered tetratitanate, using a pre-intercalation strategy by an alkylamine, the protonated Ruddlesden-Popper phase H₂Bi₀.₁Sr₀.₈₅Ta₂O₇ (HBST) was functionalized after a preintercalation step by butylamine, during which the intermediate compound (CH₃(CH₂)₃NH₃) HBi₀.₁Sr₀.₈₅Ta₂O₇ (C₄N-HBST) was formed. The use of a pre-intercalation step was in line with what we and others have demonstrated for the functionalization of layered oxides with perovskite structure by amines, alcohols and phosphonic acids, especially if the molecules are large (Akbarian-Tefaghi et al., 2016; Wang et al., 2016a, 2018; Payet et al., 2022). In addition, it was reported, for clays, that the grafting of organosilane is likely catalyzed by the alkylamine already present in the layered structure (Isoda et al., 2000).

In the present study, although no water was added to the reaction solvent (toluene), contrary to the case of amine insertion or alcohol grafting (Wang et al., 2018), no peculiar drying of the solvent or of the starting material was performed. Indeed, while some reports of the silanization of other layered materials, layered double hydroxides (LDH) essentially, used anhydrous conditions (Park et al., 2005; Carrasco et al., 2020), others on the contrary pointed to the need for a certain amount of water (Tao et al., 2011). As for alumino-silicate clays and related materials, the conditions used for silanization were usually not specifically dry ones (He et al., 2005; Ide and Ogawa, 2006; Kiba et al., 2010).

Finally, silanization by OTES, APTES and TPED molecules was achieved in 3 h, using microwave-assisted solvothermal reaction, which was much faster than the reported reactions using conventional conditions, typically several days. This acceleration rate was of the same order of
magnitude that the ones observed for the insertion of amine, or the grafting of alcohols (Boykin and Smith, 2015; Wang et al., 2016a; Akbarian-Tefaghi and Wiley, 2018; Atri and Tomar, 2021).

The successful grafting of these organosilanes was first confirmed by X-ray powder diffraction (Fig. 2). Protonated phase (HBST) was characterized by a tetragonal unit cell with a *P*4/mmm symmetry (a = 0.391 nm and c = 0.98 nm) (Tsunoda et al., 2001; Chen et al., 2011). As stated above, the insertion of organosilane required the formation of a preintercalated compound, typically functionalized by an alkyl amine. The grafting of butylamine (*C*4N-HBST) resulted in an expansion of the interlayer space, leading to an increase of the c parameter from 1.0 to 1.9 nm (Wang et al., 2016a). The silanized compounds derived from *C*4N-HBST, namely OTES-HBST, APTES-HBST and TPED-HBST, were characterized by intense reflections at low angles, typical of a layered structure with preferential orientation. The preservation of the perovskite structure was confirmed by the presence of unmodified reflections corresponding to the (100), (110), and (200) planes at 23.2°, 32.3°, and 46.4°, respectively. The low angle reflections provided c = 2.6 nm, 2.0 nm, and 2.3 nm for APTES-HBST, TPED-HBST, and OTES-HBST respectively. The obtained compounds appeared to be single phase, notably the XRD patterns showed no evidence of the starting *C*4N-HBST or HBST phases. The observed interlayer distances (identical to the c cell parameters) were compatible with the size of the inserted molecules. In the case of the insertion of a linear alkyl chain, *via* an amine or an alcohol anchoring group, it was shown that the c lattice parameter could be linearly correlated with the length of the alkyl chain (Wang et al., 2016a, 2018). In the present case, it was not possible to establish a direct relationship between the size of the molecules and the resulting interlayer distance, since many parameters were likely to play an important role, such as the condensation of alkoxysilane moieties (Krasnoslobodtsev and Smirnov, 2002) and the interactions between the alkyl or (poly)aminoalkyl chains.

The FT-IR spectra of APTES-HBST, TPED-HBST, and OTES-HBST compared to the ones of the starting molecules and of C₄N-HBST are presented in Fig. 3. The large band observed at 570 cm⁻¹ corresponds to the Ta—O stretching vibration of the perovskite matrix (Wang et al., 2014). The bands at 1560–1570 cm⁻¹ present in APTES-HBST and TPED-HBST were attributed to NH₂ deformation modes (Socrates, 2004). The spectrum of OTES-HBST presents one band at 1530 cm⁻¹, which could be ascribed to residual co-inserted butylamine, as confirmed by elemental analysis and solid state NMR (see below). The

<figure><img src="image_4.png" /><figcaption>**Fig. 2.** PXRD patterns of HBST (black), C₄N-HBST (red), APTES-HBST (blue), TPED-HBST (green) and OTES-HBST (purple). (Le Bail profile matching and reflections indexation, in line with the primitive cell choice, are presented in Fig. S1). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Infrared spectra of HBST (black), C₄N-HBST (red), APTES-HBST (blue), TPED-HBST (green) and OTES-HBST (purple). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

symmetric and asymmetric stretching vibrations of CH₂ (2865–2960 cm⁻¹) were clearly visible in OTES-HBST, with a shoulder at higher energy, corresponding to stretching of the CH₃ group (Socrates, 2004). This part of the spectrum of OTES-HBST is similar to the one of C₄N-HBST. These stretching vibrations of CH₂ were also present in the spectra of APTES-HBST and TPED-HBST, but far less pronounced. The appearance of a band at 960 cm⁻¹ in all three hybrids was attributed to Ta-O-Si bond vibration (Zhang et al., 2016; Chhetri et al., 2018), and hence evidenced the successful grafting of the organic moieties. The signal observed at 1015, 1025 and 1072 cm⁻¹ for APTES-HBST, TPED-HBST and OTES-HBST respectively could be attributed to the anti-symmetric stretching vibration of Si-O-Si (Culler et al., 1985; Parambadath et al., 2015). The presence of this Si-O-Si motif suggested significant hydrolysis of Si-O-R (R = ethyl, methyl) groups bonds under the synthesis conditions used. Finally, the band at 1148 cm⁻¹ in OTES-HBST could be ascribed to the C—O stretching vibration of an alcohol group when coordinated to the tantalum oxide layer (Wang et al., 2012, 2018). This observation was in line with ¹³C CP-MAS NMR spectroscopy, which indeed indicated the presence of a grafted alkoxy moiety in the case of TPED-HBST and OTES-HBST, the alkoxy group coming from the hydrolysis of the alkoxy-silane. Yet, the C—O stretching vibration was only visible as a shoulder in the IR spectrum of TPED-HBST.

The quantitative composition of the materials, determined by CHN analysis and ICP-AES, confirmed the above findings (Table 1).

As seen from the CHN analysis, OTES-HBST presented noticeable nitrogen content even though OTES did not contain any. Since XRD did not evidence the presence of residual C₄N-HBST phase, the presence of nitrogen in the elemental analysis suggested the incomplete removable of butylamine, and thus the co-insertion of butylamine and OTES in OTES-HBST. The C/Si ratios (3.2; 4.6 and 19.6 for APTES-HBST, TPED-HBST and OTES-HBST respectively) were in accordance with a full hydrolysis of the SiO-R (R = Me or Et) moieties, with a partial grafting of the alkoxy groups for TPED-HBST and OTES-HBST. Finally, the amount of inserted silane groups is 1.62 Si per formula unit (i.e. per 2 Ta) for APTES-HBST, 0.80 for TPED-HBST, and 0.32 for OTES-HBST. The relatively low value of Si content for OTES-HBST was consistent with the incomplete removal of butylamine, which thus left less space available for silane insertion and grafting. As for APTES-HBST and TPED-HBST, the high amount of Si, compared to the ratio of 1 Si per 2 Ta expected by analogy with the insertion of aliphatic amines and alcohols as a maximum value for steric reasons (Tsunoda et al., 2003; Akbarian-Tefaghi et al., 2016; Wang et al., 2016a, 2018), pointed to a significant
<table><caption>**Table 1**

Elemental CHN and ICP-AES analyses and proposed formulae (calc.(exp.)).</caption><thead><tr><th>Sample and proposed formula*</th><th>C</th><th>H</th><th>N</th><th>Ta</th><th>Si</th></tr></thead><tbody><tr><td>APTES-HBST<br/>[Si(OH)<sub>2</sub>-(CH<sub>2</sub>)<sub>3</sub>NH<sub>2</sub>]<sub>1.6</sub>H<sub>0.4</sub>Bi<sub>0.1</sub>Sr<sub>0.85</sub>Ta<sub>2</sub>O<sub>7</sub></td><td>7.6(8.05)</td><td>2.2(2.19)</td><td>2.9(3.00)</td><td>47.5(47.0)</td><td>5.9(5.90)</td></tr><tr><td>TPED-HBST<br/>[Si(OH)<sub>2</sub>-(CH<sub>2</sub>)<sub>3</sub>NH(CH<sub>2</sub>)<sub>2</sub>NH<sub>2</sub>]<sub>0.8</sub>(CH<sub>3</sub>)<sub>0.2</sub>H<sub>1</sub>Bi<sub>0.1</sub>Sr<sub>0.85</sub>Ta<sub>2</sub>O<sub>7</sub></td><td>7.1(6.11)</td><td>1.8(1.73)</td><td>3.2(2.81)</td><td>51.4(50.0)</td><td>3.2(3.10)</td></tr><tr><td>OTES-HBST<br/>[Si(OH)<sub>2</sub>-C<sub>8</sub>H<sub>17</sub>I<sub>0.4</sub>(C<sub>2</sub>H<sub>5</sub>)<sub>0.3</sub>(C<sub>4</sub>H<sub>9</sub>NH<sub>3</sub>)<sub>0.3</sub>H<sub>1</sub>Bi<sub>0.1</sub>Sr<sub>0.85</sub>Ta<sub>2</sub>O<sub>7</sub></td><td>8.9(10.9)</td><td>2.0(2.19)</td><td>0.6(0.53)</td><td>53.8(52.0)</td><td>1.7(1.30)</td></tr></tbody></table>

* these formulae were established considering no condensation between the silanol groups, although FTIR (see above) and NMR (see below) spectroscopies evidenced this condensation phenomenon. Taking into account condensation would have lead to an over-parameterization of the formula. Moreover, considering the large molecular weight due to the amount of heavy atoms, the condensation (i.e. the loss of one water molecule to form a Si-O-Si bridge) does not significantly modify the content ratios.

Si-O-Si condensation.

It is finally worth indicating that SEM images of **APTES-HBST**, **TPED-HBST** and **OTES-HBST** showed the preservation of the platelet-like morphology, and, from the backscattered electron images, did not show the presence of a lighter organic phase, neither separated from the hybrid one, nor concentrated at the surface as it would have been in the case of an external condensation of the organosilane moieties (Fig. S2).

In order to further study the silane grafting and the possible Si-O-Si condensation in the interlamellar space, ¹³C CP/MAS and direct acquisition ²⁹Si MAS NMR spectroscopy were performed.

¹³C NMR spectroscopy was conducted on the starting APTES, TPED and OTES molecules (liquid state) and on the resulting hybrids (CP-MAS solid state) (Fig. 4). The chemical shift assignments, based on the values reported for the starting molecules (Shimizu et al., 1997; Sim et al., 2015), are summarized in Table 2. For the silanized phase **APTES-HBST**, the number of observed signals in ¹³C CP-MAS NMR decreased from five

to three, consistent with the complete hydrolysis of the ethoxy groups. Upon grafting the silane onto the perovskite slab, all signals exhibited an up-field shift, more pronounced for carbon C3, the closest to the Si atom whose environment was strongly modified by the hydrolysis of the ethoxy groups and by the grafting to the Ta atom of the inorganic layer. Similar observations could be made for **TPED-HBST** and **OTES-HBST**, with an up-field of all signals, more pronounced for the C atom next to the Si atom (C2 and C3 respectively). In addition, the signals attributed to C1 (in TPED) and to C1 and C2 (in OTES) disappeared in the spectrum of **TPED-HBST** and **OTES-HBST** which indicated the hydrolysis of the methoxy or ethoxy groups, in accordance with FTIR and elemental analysis observation. Interestingly, a new peak appeared at 70 ppm for **TEDP-HBST** and **OTES-HBST** (labelled g in Fig. 4e), which could be attributed to grafting of some of the hydrolyzed methoxy/ethoxy groups onto the tantalum oxide layer. The observed chemical shift was indeed in perfect accordance with the characteristic values for Ta-O-C moieties

<figure><img src="image_6.png" /><figcaption>**Fig. 4.** ¹³C liquid state NMR spectra of a) APTES, b) TPED and c) OTES.</figcaption></figure>
<table><caption>**Table 2**
$^{13}$C chemical shifts (ppm) for APTES, **APTES-HBST**, TPED and **TPED-HBST**.</caption><thead><tr><th>Sample</th><th>C1</th><th>C2</th><th>C3</th><th>C4</th><th>C5</th><th>C6</th><th>C7</th><th>C8</th><th>C9</th><th>C10</th></tr></thead><tbody><tr><td>APTES</td><td>17.3</td><td>57.7</td><td>7.1</td><td>27.3</td><td>44.7</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>APTES-HBST</td><td></td><td></td><td>17.0</td><td>28.1</td><td>48.7</td><td></td><td></td><td></td><td></td><td></td></tr><tr><td>TPED</td><td>52.9</td><td>6.2</td><td>23.1</td><td>41.8</td><td>50.1</td><td>48.5</td><td></td><td></td><td></td><td></td></tr><tr><td>TPED-HBST</td><td></td><td>16.5</td><td>23.7</td><td>43.8</td><td>55.0</td><td>51.6</td><td></td><td></td><td></td><td></td></tr><tr><td>OTES</td><td>17.9</td><td>56.3</td><td>9.4</td><td>15.7</td><td>25–31</td><td>25–31</td><td>25–31</td><td>25–31</td><td>ca. 20</td><td>11.5</td></tr><tr><td>OTES-HBST</td><td></td><td></td><td>20</td><td>23.9</td><td>30–33</td><td>30–33</td><td>30–33</td><td>30–33</td><td>21</td><td>14.6</td></tr></tbody></table>

(Wang et al., 2018). In addition, the spectrum of **OTES-HBST** presented a signal at 40 ppm (labelled a in Fig. 4f), which could be attributed to the α-carbon of the residual coinserted butylamine identified in the elemental analysis (Tahara et al., 2006b). The three other aliphatic carbon signals of butylamine likely superimposed with the aliphatic carbon signals of the octyl chain of OTES between 25 and 30 ppm. Finally, the peak at 30 ppm in the spectrum of **TPED-HBST**, labelled with an asterisk, might be attributed to aliphatic carbons of a small amount of residual butylamine, which could not be quantified by elemental analysis since TPED contains N atoms. The signal coming from the α-carbon of the coinserted butylamine would superimpose with the signal coming from C4.

and solid state $^{13}$C CP-MAS spectra of d) **APTES-HBST** e) **TPED-HBST** and f) **OTES-HBST**.

Finally, investigation of the $^{13}$C CP/MAS NMR data outside of the chemical shifts range expected for the inserted molecules allowed to evidence signals at 170 ppm for **APTES-HBST** and 130 and 140 ppm for **TPED-HBST**, which could be attributed to chemisorbed CO$_2$ as it was observed in the case of amine-modified silica (Fig. S3) (Mafra et al., 2017; Čendak et al., 2018; Fonseca et al., 2022). On the contrary, the $^{13}$C CP/MAS NMR spectrum of **OTES-HBST** did not present these high chemical shifts signals, in line with the fact that there was no free amine group in this material that favored CO$_2$ adsorption.

To investigate the organo-silane environment and the grafting modes, $^{29}$Si NMR spectroscopy was performed on **APTES-HBST**, **TPED-HBST** and **OTES-HBST**, using direct acquisition so that the ratios of the peaks areas corresponded quantitatively to the ratios of the numbers of Si atoms involved (Fig. 5). The NMR signals were deconvoluted and the obtained peaks were assigned according to reported values (Park et al., 2005; Tao et al., 2010, 2011). The number and position of the peaks observed in direct acquisition were checked to be the same than when using cross-polarization $^{29}$Si CP-MAS NMR, more sensitive but not quantitative (Fig. S4).

The chemical shifts, attribution and relative proportion of the three coordination modes of Si are summarized in Table 3.

For layered oxydes with a perovskite structure, considering the distance between two adjacent Ta—O apical groups (0.39 nm) and the length of a Si—O bond (ca. 0.16 nm) (Kraftory et al., 1998), it was much

<table><caption>**Table 3**
Overview of the solid state direct detection $^{29}$Si NMR spectra fits for **APTES-HBST**, **TPED-HBST** and **OTES-HBST**. The starting molecules presented a single peak at -45.2, -41.5 and -45.9 ppm for APTES, TPED and OTES respectively.</caption><thead><tr><th>Sample</th><th>T<sup>1</sup></th><th>T<sup>2</sup></th><th>T<sup>3</sup></th></tr></thead><tbody><tr><td>APTES-HBST</td><td>-46.6 ppm (5.0 %)</td><td>-56.7 ppm (69.1 %)</td><td>-66.7 ppm (25.9 %)</td></tr><tr><td>TPED-HBST</td><td>-46.6 ppm (31.5 %)</td><td>-55.0 ppm (62.3 %)</td><td>-66.8 ppm (6.3 %)</td></tr><tr><td>OTES-HBST</td><td>-46.4 ppm (39.4 %)</td><td>-55.5 ppm (60.6 %)</td><td></td></tr></tbody></table>

unlikely that a T$^2$ grafting implying a single organosilane could occur (Fig. S5). Furthermore, even though the formation of organosilane pилars between two organic layers could not be excluded, it would be highly mitigated considering the relatively low quantity of organo-silane in the layered hybrids, and very good crystallinity, which are not features usually found in pillared clays or related materials (Sylvester et al., 1994).

Therefore, the present experimental findings suggested that the grafting of the organosilane occurs according to the schemes presented in Fig. 6.

For **APTES-HBST**, considering the experimental ratio T$^2$/T$^3$ = 2.7; the grafting mode C (one T$^3$ for two or three T$^2$) was indeed preponderant (involving 95 % of the organo silane molecules), the grafting mode B was almost non-present, and the grafting mode A was present in a very small proportion (5 %). This general scheme, and notably the preponderant formation of a “thick layer” of condensed alcoxy-silane moieties was in good accordance with the large interlayer distance observed for **APTES-HBTS**, about 2.6 nm, much larger than the one expected in the case of a bilayer arrangement of APTES grafted in T$^1$ mode only (about 2.3 nm, considering that such an arrangement led to an interlayer distance of 1.8 nm in the case of a layered double hydroxide composed of nickel and iron layers (Carrasco et al., 2020) and that the thickness of the LDH inorganic layer is about 0.4 nm, compared to 0.9 nm for the present perovskite sheet).

For **TPED-HBST**, the C mode in the grafting scheme presented above

<figure><img src="image_7.png" /><figcaption>**Fig. 5.** Solid state direct detection $^{29}$Si NMR spectra of a) **APTES-HBST**, b) **TPED-HBST** and c) **OTES-HBST**.</figcaption></figure>
<figure><img src="image_8.png" /><figcaption>Fig. 6. Anchoring schemes for the organosilane molecules in the three hybrid compounds.</figcaption></figure>

could be neglected, with almost only A and B modes present. This feature was in good accordance with the relatively small interlayer distance determined for **TPED-HBST** (2.0 nm). Considering the length of the TPED molecule, this distance was compatible with a bilayer arrangement of the organosilane groups, with an angle of roughly 50° with respect to the normal to the inorganic layer. The same conclusion held for **OTES-HBST**, where no T³ mode could be detected. The interlayer distance of 2.3 nm was also in accordance with this anchoring mode and an arrangement of the alkyl chains almost perpendicular to the inorganic layers.

## 3.2. *In situ* complexation of Cu(II) in APTES-HBST and TPED-HBST

Considering the availability of the amine groups in the interlayer space, the possibility to coordinate these amines by transition metal ions in the confined space was then explored. This approach is indeed very promising, either for catalysis (Silva et al., 2006), or for contaminant metal remediation (Carrasco et al., 2020; Shen et al., 2024) for instance. As a proof of concept in this work, the *in situ* complexation by Cu(II) ions was investigated. Complexation was performed in water, using a copper nitrate salt. Experiments conducted in non-aqueous solvents (acetoni-trile and ethanol) led to the formation of an important quantity of a secondary phase, which might be attributed to Cu₂(OH)₃(NO₃) (Figs. S6

and S7). When the complexation was performed in water, at room temperature, this secondary phase was never obtained, except when using large quantities of Cu(NO₃)₂·2.5 H₂O, typically more than 3 equivalents ([Cu] > 0.02 mol·L⁻¹). The complexation was performed over 1 h, under gentle stirring. Longer reaction times or higher temperatures did not improve the copper intake or the crystallinity, on the contrary, such conditions led to a more pronounced leaching of the silane moiety and favored the formation of copper-rich side phases.

Fig. 7 presents the PXRD patterns and IR spectra of the silanized products after a 1 h reaction with one equivalent of Cu(NO₃)₂·2.5 H₂O, in water at room temperature. For **APTES-HBST** and **TPED-HBST**, a slight decrease in the c lattice parameter was observed, 2.6 nm to 2.2 nm and from 2.0 nm to 1.9 nm respectively, while the higher angle reflections, at 23.2°, 32.3° and 46.4°, corresponding to the (100), (110), and (200) planes assuming a *P4/mmm* space group, remained unchanged, indicating the preservation of the perovskite structure. The FT-IR spectra revealed the bands between 1330 cm⁻¹ and 1390 cm⁻¹, assigned to the stretching vibrations of the nitrate counter ions. For **OTES-HBST**, no significant changes were observed in both PXRD and IR spectra upon reaction with Cu²⁺. Therefore, the decrease of the c lattice parameter for **APTES-HBST** and **TPED-HBST** might be ascribed, at least partly, to Cu²⁺ complexation to the amine groups present in the interlayer space, evidenced in the UV–Vis. and EPR spectroscopies below, all

<figure><img src="image_9.png" /><figcaption>Fig. 7. a) Powder XRD and b) IR spectrum of the silanized compounds reacted with copper.</figcaption></figure>
the more since the c parameter remained unchanged in OTES-HBST where no complexation occurs. Yet, the evolution of the c parameter might also be due to the partial leaching of organosilane groups during the complexation reaction, above all for APTES-HBST (see below).

SEM images underlined the preservation of the stratified morphology of the grains, and the composition analysis using backscattered electrons evidenced the homogeneity of the samples, and in particular did not reveal any copper-rich side-phase (Fig. 8 and Fig. S8 for images over larger areas).

Finally, ICP-AES analysis allowed to determine the Cu uptake as well as the evolution of the Si content (Table 4).

The amount of copper incorporated through complexation confirmed a direct interaction with the amino groups of the organosilane, with 1.26 Cu per Si for Cu [APTES]-HBST and 0.22 Cu per Si for Cu [TPED]-HBST, whereas only 0.03 Cu/Si was observed for Cu [OTES]-HBST, confirmed by the white colour of Cu [OTES]-HBST (Fig. 9 right). The relatively high value of copper content for Cu [APTES]-HBST with a ratio Cu/Si (or N) higher than 1 suggested that part of the copper ions might be adsorbed onto the surface of the slabs or form dimers linked to an APTES group.

Another important features from ICP-AES analysis, was the significant decrease of the Si/2Ta ratio for Cu [APTES]-HBST and Cu [TPED]-HBST with respect to APTES-HBST and TPED-HBST respectively, while the quantity of Si in OTES-HBST was not modified upon reaction with the Cu²⁺ solution. This was in line with the decrease of the interlayer distance in Cu [APTES]-HBST and, less pronounced, in Cu [TPED]-HBST. As stated above, the large interlayer distance observed for APTES-HBST and to a lesser extent for TPED-HBST, could be ascribed to the formation of T² and T³ coordination mode of Si (anchoring scheme C in Fig. 6). It is thus likely that in the reaction conditions used for Cu complexation, the Si-O-Si bridges got hydrolyzed, leading to a leaching of organosilane and to a decrease of the interlayer distance, while the Si-O-Ta bonds remained stable.

The copper environment was different in Cu [APTES]-HBST and Cu [TPED]-HBST as evidenced by the colors of the compounds (Fig. 9 left and middle), and further characterized by UV-Vis. absorption spectroscopy (Fig. 10).

While copper nitrate in aqueous solution presented a maximum absorption at around 800 nm, in the hybrid materials the absorption was shifted to lower wavelengths, with a maximum absorption observed at 785 nm for Cu [APTES]-HBST and 610 nm for Cu [TPED]-HBST. This shift to higher energy indicated a stronger ligand field, in line with the coordination by an amine (Cu [APTES]-HBST) or a diamine (Cu

<table><caption>**Table 4**
Elemental ratios obtained from ICP-AES analysis.</caption><thead><tr><th>Sample</th><th>Si/2Ta</th><th>Cu/Si</th><th>Cu/2Ta</th></tr></thead><tbody><tr><td>APTES-HBST</td><td>1.62</td><td></td><td></td></tr><tr><td>Cu[APTES]-HBST</td><td>0.49</td><td>1.26</td><td>0.62</td></tr><tr><td>TPED-HBST</td><td>0.80</td><td></td><td></td></tr><tr><td>Cu[TPED]-HBST</td><td>0.65</td><td>0.22</td><td>0.14</td></tr><tr><td>OTES-HBST</td><td>0.32</td><td></td><td></td></tr><tr><td>Cu[OTES]-HBST</td><td>0.32</td><td>0.03</td><td>0.01</td></tr></tbody></table>

[TPED]-HBST) (Lever, 1984; Klonkowski et al., 1999).

The environment of the copper ions was then analyzed using EPR spectroscopy (Fig. 11). The fit of the spectrum of Cu [APTES]-HBST led to g⊥ = 2.06, g// = 2.34 and A// = 108 × 10⁻⁴ cm⁻¹, in line with a O₃-N₁ environment of Cu²⁺ in the xy plane (Nowicki, 2019). For Cu [TPED]-HBST, the fit provided g⊥ = 2.09, g// = 2.15 and A// = 122 × 10⁻⁴ cm⁻¹ which indicated a N₄ environment in the xy plane and therefore a coordination by two ethylenediamine moieties from two TPED ligands (Klonkowski et al., 1999; Nowicki, 2019), either grafted on the same inorganic layer or on two face-to-face inorganic layers in a bridging mode. For both hybrid materials g// > g⊥ which indicated that the Cu²⁺ ions were in a tetragonally elongated octahedral surrounding, with the unpaired electron occupying the dₓ₂-y₂ orbital (Garribba and Micera, 2006). The low value of A// might suggest an additional distortion out of the xy plane (Peisach and Blumberg, 1974).

## 4. Conclusion

In conclusion, the interlamellar space of an ion exchangeable layered perovskite derived from the Aurivillius phase Bi₂SrTa₂O₉ was functionalized with three organosilane molecules, triethoxyoctylsilane, 3-(aminopropyl)triethoxysilane and N-[3(trimethyoxysilyl)propyl]ethyl-enediamine, using a multi-step microwave assisted approach. Whereas the silanization of other layered phases (alumino-silicate clays, layered double hydroxides) was thoroughly explored, providing, for instance, a wide variety of pillared clays, the functionalization of layered perovskite by alkoxysilanes was only described for tri- and tetra-titanates by APTES, and for niobiates with polysiloxanes, leading to exfoliation. The synthetic pathway described in this work constitutes a fast and efficient approach to silanize the interlayer space of layered perovskites, while keeping the layered structure of the hybrid material.

The compounds were fully characterized, notably by XRD and solid state NMR which allowed to precise the grafting scheme of the

<figure><img src="image_10.png" /><figcaption>**Fig. 8.** SEM images of a) Cu [APTES]-HBST, b) Cu [TPED]-HBST and c) Cu [OTES]-HBST (Top: In Lens mode, Bottom: ESB mode). The scale bar is 200 nm.</figcaption></figure>
<figure><img src="image_11.png" /><figcaption>Fig. 9. Photographs of Cu [APTES]-HBST, Cu [TPED]-HBST and Cu [OTES]-HBST, from left to right.</figcaption></figure>

<figure><img src="image_12.png" /><figcaption>Fig. 10. Diffuse reflectance spectra of Cu[APTES]-HBST (blue), Cu[TPED]-HBST (green) and Cu[OTES]-HBST (purple). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

organosilanes onto the inorganic layers and evidenced the very limited
formation of siloxane network.

Finally, the present approach was very efficient to introduce a free
amino group in-between the inorganic oxide layers due to the prefer-
ential reactivity of the oxide sheets with the alkoxysilane groups
compared to amines which otherwise cannot be made available. As a
proof of concept the complexation ability of the inserted free amine
groups towards Cu²⁺ ions was demonstrated by UV and EPR
spectroscopies.

This soft chemistry strategy constitutes a new versatile and efficient
method to introduce transition metal cations into layered oxides and
paves the way for the design and synthesis of complex architectures,
specifically designed for application, in catalysis, sensors, metal cation
remediation or luminescence for instance.

CRediT authorship contribution statement

**Pacôme Chapel:** Writing – original draft, Investigation, Formal analysis, Data curation. **Thibaud Henry:** Investigation, Formal analysis, Data curation. **Frédéric Payet:** Investigation, Formal analysis, Data curation. **Cédric Leuvrey:** Investigation, Data curation. **Fabrice Leroux:** Investigation, Formal analysis, Data curation. **Nathalie Parizel:** Investigation, Formal analysis, Data curation. **Pierre Rabu:** Supervision. **Guillaume Rogez:** Writing – review & editing, Supervision, Funding acquisition, Conceptualization.

<figure><img src="image_13.png" /><figcaption>Fig. 11. EPR spectra of Cu [APTES]-HBST (bottom) and Cu [TPED]-HBST (top) (black: exp., red: fit). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)</figcaption></figure>

Declaration of competing interest

The authors declare that they have no known competing financial
interests or personal relationships that could have appeared to influence
the work reported in this paper.

Acknowledgements

The authors thank the CNRS and the Université de Strasbourg for
financial support. This work of the Interdisciplinary Thematic Institute
QMat, as part of the ITI 2021-2028 program of the University of Stras-
bourg, CNRS and Inserm, was supported by Idex Unistra (ANR-10-IDEX-
0002) and EUR (QMat-ANR-18-EUR-0016) under the framework of the
French Investments for the Future Program. The authors thank D. Burger
for his help in recording the TGA-TDA data, C. Kiefer and M.-N. Lalzo for their technical assistance, E. Petit for her help in recording the NMR spectra and Dr. M. Lenertz for his help in acquiring the XRD data. The XRD, and SEM (MEBCro) facility platforms of IPCMS are gratefully acknowledged. The authors thank Dr. S. Baudron and M. Teixeira for the use of the UV spectrometer.

## Appendix A. Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.clay.2025.108017.

## Data availability

Data will be made available on request.

## References

Akbarian-Tefaghi, S., Wiley, J.B., 2018. Microwave-assisted routes for rapid and efficient modification of layered perovskites. Dalton Trans. 47, 2917–2924. https://doi.org/10.1039/C7DT03865H.

Akbarian-Tefaghi, S., Teixeira Veiga, G., Amand, G., Wiley, J.B., 2016. Rapid Topochemical Modification of Layered Perovskites via Microwave Reactions. Inorg. Chem. 55, 1604–1612. https://doi.org/10.1021/acs.inorgchem.5b02514.

de Araujo, C.A.P., Cuchiaro, J.D., McMillan, L.D., Scott, M.C., Scott, J.F., 1995. Fatigue-free ferroelectric capacitors with platinum electrodes. Nature 374, 627–629. https://doi.org/10.1038/374627a0.

Atri, S., Tomar, R., 2021. A Review on the Synthesis and Modification of Functional Inorganic-Organic-Hybrid Materials via Microwave-Assisted Method. ChemistrySelect 6, 9351–9362. https://doi.org/10.1002/slc2.202102030.

Aurivillius, B., 1949a. Ark Kemi 1, p. 463.

Aurivillius, B., 1949b. Ark Kemi 1, p. 499.

Aurivillius, B., 1950. Ark Kemi 2, p. 519.

Aurivillius, B., 1952. Ark Kemi 5, p. 39.

Awaya, K., Ida, S., 2023. Stress-induced photoluminescence change of monolayer nanosheet prepared by delamination of Aurivillius-phase layered perovskite. Chem. Mater. 35, 3713–3721. https://doi.org/10.1021/acs.chemmater.3c00466.

Blasse, G., Brixner, L.H., 1989. Luminescence of perovskite-like niobates and tantalants. Mater. Res. Bull. 24, 363–366. https://doi.org/10.1016/0025-5408(89)90222-5.

Boykin, J.R., Smith, L.J., 2015. Rapid Microwave-Assisted Grafting of Layered Perovskites with n-Alcohols. Inorg. Chem. 54, 4177–4179. https://doi.org/10.1021/ic503001w.

Carrado, K.A., 2000. Synthetic organo- and polymer–clays: preparation, characterization, and materials applications. Appl. Clay Sci. 17, 1–23. https://doi.org/10.1016/S0169-1317(00)00005-3.

Carrasco, J.A., Seijas-Da Silva, A., Oestreicher, V., Romero, J., Márkus, B.G., Simon, F., Vieira, B.J.C., Waerenborgh, J.C., Abellán, G., Coronado, E., 2020. Fundamental Insights into the Covalent Silane Functionalization of NiFe Layered Double Hydroxides. Chem. Eur. J. 26, 6504–6517. https://doi.org/10.1002/chem.201905397.

Cendak, T., Sequeira, L., Sardo, M., Valente, A., Pinto, M.L., Mafra, L., 2018. Detecting Proton Transfer in CO₂ Species Chemisorbed on Amine-Modified Mesoporous Silicas by using ¹³C NMR Chemical Shift Anisotropy and Smart Control of Amine Surface Density. Chem. Eur. J. 24, 10136–10145. https://doi.org/10.1002/chem.201800930.

Chen, Z., Dong, W., Zheng, F., Fang, L., Shen, M., 2011. The effect of annealing on the photoluminescence of layered perovskite H₁.₇₇[Sr₀.₈Bi₀.₂₁Ta₂O₇] powders. Mater. Res. Bull. 46, 52–56. https://doi.org/10.1016/j.materresbull.2010.09.042.

Chhetri, S., Chandra Adak, N., Samanta, P., Chandra Murmu, N., Kuila, T., 2018. Rheological, mechanical, and thermal properties of silane grafted Layered Double Hydroxide/Epoxy composites. Ind. Eng. Chem. Res. 57, 8729–8739. https://doi.org/10.1021/acs.iecr.8b01399.

Clément, P., Marchand, R., 1983. Intercalation d'amines dans la structure en feuillets de H₂TiO₄. C R Acad. Sc Paris 296, 1161–1164.

Culler, S.R., Ishida, H., Koenig, J.L., 1985. Structure of silane coupling agents adsorbed on silicon powder. J. Colloid Interface Sci. 106, 334–346. https://doi.org/10.1016/S0021-9797(85)80007-2.

Dion, M., Ganne, M., Tournoux, M., 1981. Nouvelles familles de phases M¹M²Nb₂O₁₀ à feuillets "perovskites.". Mater. Res. Bull. 16, 1429–1435. https://doi.org/10.1016/0025-5408(81)90063-5.

Faustini, M., Nicole, L., Ruiz-Hitzky, E., Sanchez, C., 2018. History of organic–inorganic hybrid materials: prehistory, art, science, and advanced applications. Adv. Funct. Mater. 28, 1704158. https://doi.org/10.1002/adfm.201704158.

Fernandes, F.M., Baradari, H., Sanchez, C., 2014. Integrative strategies to hybrid lamellar compounds: an integration challenge. Appl. Clay Sci. 100, 2–21. https://doi.org/10.1016/j.clay.2014.05.013.

Fonseca, R., Vieira, R., Sardo, M., Marin-Montesinos, I., Mafra, L., 2022. Exploring molecular dynamics of adsorbed CO₂ species in amine-modified porous silica by solid-state NMR relaxation. J. Phys. Chem. C 126, 12582–12591. https://doi.org/10.1021/acs.jpcc.2c02656.

Garribba, E., Micera, G., 2006. The determination of the geometry of Cu(II) complexes: an EPR spectroscopy experiment. J. Chem. Educ. 83, 1229. https://doi.org/10.1021/ed083p1229.

Gomez-Romero, P., Pokhriyal, A., Rueda-García, D., Bengoa, L.N., González-Gil, R.M., 2024. Hybrid materials: a metareview. Chem. Mater. 36, 8–27. https://doi.org/10.1021/acs.chemmater.3c01878.

Gopalakrishnan, J., Bhat, V., Raveau, B., 1987. A¹LaNb₂O₇: a new series of layered perovskites exhibiting ion exchange and intercalation behaviour. Mater. Res. Bull. 22, 413–417. https://doi.org/10.1016/0025-5408(87)90060-2.

Guo, P.-F., Zhang, D.-D., Guo, Z.-Y., Chen, M.-L., Wang, J.-H., 2017. Copper-decorated titanate nanosheets: novel homogeneous monolayers with a superior capacity for selective isolation of hemoglobin. ACS Appl. Mater. Interfaces 9, 28273–28280. https://doi.org/10.1021/acsami.7b08942.

Guo, W., Zhao, Y., Zhou, F., Yan, X., Fan, B., Li, R., 2016. Silylated layered double hydroxide nanosheets prepared by a large-scale synthesis method as hosts for intercalation of metal complexes. Appl. Catal. A Gen. 522, 101–108. https://doi.org/10.1016/j.apcata.2016.05.001.

Han, Y.-S., Park, I., Choy, J.-H., 2001. Exfoliation of layered perovskite, KC₅Nb₂O₁₀ into colloidal nanosheets by a novel chemical process. J. Mater. Chem. 11, 1277–1282. https://doi.org/10.1039/B060045N.

He, H., Duchet, J., Galy, J., Gerard, J.-F., 2005. Grafting of swelling clay materials with 3-aminopropyltriethoxysilane. J. Colloid Interface Sci. 288, 171–176. https://doi.org/10.1016/j.cjis.2005.02.092.

He, H., Tao, Q., Zhu, J., Yuan, P., Shen, W., Yang, S., 2013. Silylation of clay mineral surfaces. Appl. Clay Sci. 71, 15–20. https://doi.org/10.1016/j.clay.2012.09.028.

Ida, S., Ogata, C., Unal, U., Izawa, K., Inoue, T., Altuntasoglu, O., Matsumoto, Y., 2007. Preparation of a blue luminescent nanosheet derived from layered perovskite Bi₂SrTa₂O₉. J. Am. Chem. Soc. 129, 8956–8957. https://doi.org/10.1021/ja073105b.

Ida, S., Ogata, C., Eguchi, M., Youngblood, W.J., Mallouk, T.E., Matsumoto, Y., 2008. Photoluminescence of perovskite nanosheets prepared by exfoliation of layered oxides, K₂Ln₂Ti₃O₁₀, RbLnNb₂O₇, and RbLnTa₂O₇ (Ln: Lanthanide Ion). J. Am. Chem. Soc. 130, 7052–7059. https://doi.org/10.1021/ja7114772.

Ide, Y., Ogawa, M., 2003. Surface modification of a layered alkali titanate with organosilanes. Chem. Commun. 1262. https://doi.org/10.1039/b301222k.

Ide, Y., Ogawa, M., 2006. Preparation and some properties of organically modified layered alkali titanates with alkylmethoxysilanes. J. Colloid Interface Sci. 296, 141–149. https://doi.org/10.1016/j.cjis.2005.08.058.

Ioda, K., Kuroda, K., Ogawa, M., 2000. Interlamellar grafting of γ-methacryloxypropylsilyl groups on magadiite and copolymerization with methyl methacrylate. Chem. Mater. 12, 1702–1707. https://doi.org/10.1021/cm0000494.

Jia, H., Zhao, Y., Niu, P., Lu, N., Fan, B., Li, R., 2018. Amine-functionalized MgAl LDH nanosheets as efficient solid base catalysts for Knoevenagel condensation. Mol. Catal. 449, 31–37. https://doi.org/10.1016/j.mcat.2018.02.004.

Kafory, M., Kapon, M., Botoshansky, M., 1998. The structural chemistry of organosilicon compounds. In: The Chemistry of Organic Silicon Compounds.

Khodabakhsh, M., Yilmaz, B., Firoozi, S., Fatmehsari Haghighenas, D., Unal, U., 2023. Enhanced photocatalytic properties of restacked unilamellar [SrTa₂O₇]²⁻ nanosheets of aurivillius phase layered perovskites. ACS Omega 8, 10607–10617. https://doi.org/10.1021/acsomega.3c00593.

Kiba, S., Haga, J.-I., Hashimoto, S., Nakato, T., 2010. Adsorptive and photocatalytic removal of phenol by layered niobates organically modified through intercalation and silylation. J. Nanosci. Nanotechnol. 10, 8341–8348. https://doi.org/10.1166/jnn.2010.2665.

Kikkawa, S., Koizumi, M., 1980. Organic intercalation on layered compound KTiNbO₅. Mater. Res. Bull. 15, 533–539. https://doi.org/10.1016/0025-5408(80)90049-6.

Kim, T.W., Kim, I.Y., Park, D.-H., Choy, J.-H., Hwang, S.-J., 2016. Highly stable nanocontainer of APTES-anchored layered titanate nanosheet for reliable protection/recovery of nucleic acid. Sci. Rep. 6, 21993. https://doi.org/10.1038/srep21993.

Klonkowski, A.M., Grobelna, B., Widernik, T., Jankowska-Frydel, A., Mozgawa, W., 1999. The coordination state of copper(II) complexes anchored and grafted onto the surface of organically modified silicates. Langmuir 15, 5814–5819. https://doi.org/10.1021/la981256+.

Krashenninikova, O.V., Syrov, E.V., Smirnov, S.M., Suleimanov, E.V., Fukina, D.G., Knyazev, A.V., Titaev, D.N., 2022. Synthesis, crystal structure and photocatalytic activity of new Dion-Jacobson type titanoniobates. J. Solid State Chem. 315, 123445. https://doi.org/10.1016/j.jssc.2022.123445.

Krasnoslobodtsev, A.V., Smirnov, S.N., 2002. Effect of water on silanization of silica by trimethoxysilanes. Langmuir 18, 3181–3184. https://doi.org/10.1021/la015628h.

Kurnosenko, S.A., Voytovich, V.V., Silyukov, O.I., Minich, I.A., Malygina, E.N., Zvereva, I.A., 2022. Inorganic-organic derivatives of layered perovskite-like titanates HLnTiO₄ (Ln = La, Nd) with n-amines and n-alcohols: synthesis, thermal, vacuum and hydrolytic stability. Ceram. Int. 48, 7240–7252. https://doi.org/10.1016/j.ceramint.2021.11.284.

Landis, M.E., Aufdembrink, B.A., Chu, P., Johnson, I.D., Kirker, G.W., Rubin, M.K., 1991. Preparation of molecular sieves from dense layered metal oxides. J. Am. Chem. Soc. 113, 3189–3190. https://doi.org/10.1021/ja00008a067.

Lever, A.B.P., 1984. Inorganic Electronic Spectroscopy, 2nd edition. Elsevier, Amsterdam.

Mafra, L., Cendak, T., Schneider, S., Wiper, P.V., Pires, J., Gomes, J.R.B., Pinto, M.L., 2017. Structure of chemisorbed CO₂ species in amine-functionalized mesoporous silicas studied by solid-state NMR and computer modeling. J. Am. Chem. Soc. 139, 389–408. https://doi.org/10.1021/jacs.6b11081.
Matsuda, T., Fujita, T., Miyamae, N., 1993a. Intercalation study and catalysis by lanthanum niobium oxides. Catal. Today 16, 455–462. https://doi.org/10.1016/
0920-5861(93)80085-F.

Matsuda, T., Miyamae, N., Takeuchi, M., 1993b. Intercalation of various alcohols in HLaNb207. Bull. Chem. Soc. Jpn. 66, 1551–1553. https://doi.org/10.1246/
bcsj.66.1551.

Nedjar, R., Borel, M.M., Raveau, B., 1986. Intercalation of primary monoamines in the lamellar protonic oxide HNb₃O₈ · H₂O. Z. Für Anorg. Allg. Chem. 540, 198–204.
https://doi.org/10.1002/zaac.19865400921.

Nowicki, W., 2019. Structural studies of complexation of Cu(II) with aminosilane-modified silica surface in heterogeneous system in a wide range of pH. Appl. Surf. Sci. 469, 566–572. https://doi.org/10.1016/j.apsusc.2018.11.066.

Osterloh, F.E., 2002. Solution self-assembly of magnetic light modulators from exfoliated perovskite and magnetite nanoparticles. J. Am. Chem. Soc. 124, 6248–6249. https://doi.org/10.1021/ja025858y.

Parambadath, S., Mathew, A., Jenisha Barnabas, M., Ha, C.-S., 2015. A pH-responsive drug delivery system based on ethylenediamine bridged periodic mesoporous organosilica. Microporous Mesoporous Mater. 215, 67–75. https://doi.org/10.1016/
j.micromeso.2015.05.027.

Park, A.-Y., Kwon, H., Woo, A.J., Kim, S.-J., 2005. Layered double hydroxide surface modified with (3-aminopropyl)triethoxysilane by covalent bonding. Adv. Mater. 17, 106–109. https://doi.org/10.1002/adma.200400135.

Payet, F., Bouillet, C., Leroux, F., Leuvrey, C., Rabu, P., Schosseler, F., Taviot-Guêho, C., Rogez, G., 2022. Fast and efficient shear-force assisted production of covalently functionalized oxide nanosheets. J. Colloid Interface Sci. 607, 621–632. https://doi.org/10.1016/j.jcis.2021.08.213.

Peisach, J., Blumberg, W.E., 1974. Structural implications derived from the analysis of electron paramagnetic resonance spectra of natural and artificial copper proteins. Arch. Biochem. Biophys. 165, 691–708. https://doi.org/10.1016/0003-9861(74)09298-7.

Poduval, A., Jones, K.D., LeBan, L.A., Wiley, J.B., 2024. The grafting of hydroxyaromatic organics within layered perovskites via a microwave-assisted method. Molecules 29, 2888. https://doi.org/10.3390/molecules29122888.

Pujari, S.P., Scheres, L., Marcelis, A.T.M., Zuilhof, H., 2014. Covalent surface modification of oxide surfaces. Angew. Chem. Int. Ed. 53, 6322–6356. https://doi.org/10.1002/anie.201306709.

Rassadin, V.A., Yakimanskiy, A.A., Eliseenkov, E.V., Boyarskiy, V.P., 2015. Synthesis of acyclic diaminocarbene palladium complex featuring triethoxysilane moiety. Inorg. Chem. Commun. 61, 21–23. https://doi.org/10.1016/j.inoche.2015.08.008.

Rebbah, H., Borel, M.M., Raveau, B., 1980. Intercalation of alkylammonium ions and oxide layers [TiNbO₅]⁻. Mater. Res. Bull. 15, 317–321. https://doi.org/10.1016/
0025-5408(80)90175-0.

Rogez, G., Massobrio, C., Rabu, P., Drillon, M., 2011. Layered hydroxide hybrid nanostructures: a route to multifunctionality. Chem. Soc. Rev. 40, 1031–1058.
https://doi.org/10.1039/C0SC00159G.

Ruddlesden, S.N., Popper, P., 1958. The compound Sr₃Ti₂O₇ and its structure. Acta Crystallogr. 11, 54–55. https://doi.org/10.1107/S0365110X58000128.

Sagiv, J., 1980. Organized monolayers by adsorption. 1. Formation and structure of oleophobic mixed monolayers on solid surfaces. J. Am. Chem. Soc. 102, 92–98.
https://doi.org/10.1021/ja00521a016.

Shen, Z., Li, Q., Wei, X., Lu, M., Chang, Z., Chong, R., Li, D., 2024. Highly efficient removal of Pb²⁺ and Cd²⁺ on MgAl-LDH modified with carbon dots, citric acid and amino silane: Kinetic, isothermal and mechanistic studies. J. Environ. Chem. Eng. 12, 113601. https://doi.org/10.1016/j.jece.2024.113601.

Shimakawa, Y., Kubo, Y., Nakagawa, Y., Kamiyama, T., Asano, H., Izumi, F., 1999. Crystal structures and ferroelectric properties of SrBi₂Ta₂O₉ and Sr₀.₈Bi₂·₂Ta₂O₉. Appl. Phys. Lett. 74, 1904–1906. https://doi.org/10.1063/1.123708.

Shimizu, I., Okabayashi, H., Hattori, N., Taga, K., Yoshino, A., O'Connor, C.J., 1997. ¹³C- and ¹H-NMR and FTIR spectroscopic evidence for aggregate formation of organosilanes in toluene. Colloid Polym. Sci. 275, 293–297. https://doi.org/
10.1007/s003960050084.

Silva, A.R., Wilson, K., Whitwood, A.C., Clark, J.H., Freire, C., 2006. Amine-functionalised hexagonal mesoporous silica as support for copper(II) acetylacetonate catalyst. Eur. J. Inorg. Chem. 2006, 1275–1283. https://doi.org/10.1002/ejic.200500979.

Sim, K., Lee, N., Kim, J., Cho, E.-B., Gunathilake, C., Jaroniec, M., 2015. CO₂ Adsorption on Amine-Functionalized Periodic Mesoporous Benzenesilicas. ACS Appl. Mater. Interfaces 7, 6792–6802. https://doi.org/10.1021/acsami.5b00306.

Socrates, G., 2004. Infrared and Raman Characteristic Group Frequencies: Tables and Charts. John Wiley & Sons.

Su, L., Tao, Q., He, H., Zhu, J., Yuan, P., Zhu, R., 2013. Silylation of montmorillonite surfaces: dependence on solvent nature. J. Colloid Interface Sci. 391, 16–20. https://doi.org/10.1016/j.jcis.2012.08.077.

Sylvester, P., Cahill, R., Clearfield, A., 1994. Pillaring of Layered Tetravalent Metal Phosphates and Oxides using (3-Aminopropyl)trimethoxysilane. Chem. Mater. 6, 1890–1898. https://doi.org/10.1021/cm00046a053.

Tahara, S., Takeda, Y., Sugahara, Y., 2005. Preparation of organic–inorganic hybrids possessing nanosheets with perovskite-related structures via exfoliation during a Sol–Gel process. Chem. Mater. 17, 6198–6204. https://doi.org/10.1021/cm0514793.

Tahara, S., Okamoto, T., Sugahara, Y., 2006a. Preparation of a nanocomposite consisting of a siloxane network and perovskite-related nanosheets via a sol–gel process. Sci. Techn. Adv. Mater. 7, 446.

Tahara, S., Yamashita, T., Kajiwara, G., Sugahara, Y., 2006b. Intercalation of α,ω-diaminoalkanes in the interlayer space of the protonated form of the layered perovskite H1.8Bi0.2Sr0.8Ta207. Chem. Lett. 35, 1292–1293. https://doi.org/
10.1246/cl.2006.1292.

Tahara, S., Ichikawa, T., Kajiwara, G., Sugahara, Y., 2007. Reactivity of the Ruddlesden–Popper phase H₂La₂Ti₃O₁₀ with organic compounds: intercalation and grafting reactions. Chem. Mater. 19, 2352–2358. https://doi.org/10.1021/cm0623662.

Tao, Q., Zhu, J., Frost, R.L., Bostrom, T.E., Wellard, R.M., Wei, J., Yuan, P., He, H., 2010. Silylation of layered double hydroxides via a calcination–rehydration route. Langmuir 26, 2769–2773. https://doi.org/10.1021/la902812g.

Tao, Q., Zhu, J., Wellard, R.M., Bostrom, T.E., Frost, R.L., Yuan, P., He, H., 2011. Silylation of layered double hydroxides via an induced hydrolysis method. J. Mater. Chem. 21, 10711–10719. https://doi.org/10.1039/C1JM10328H.

Tsunoda, Y., Shirata, M., Sugimoto, W., Liu, Z., Terasaki, O., Kuroda, K., Sugahara, Y., 2001. Preparation and HREM characterization of a protonated form of a layered perovskite tantalate from an Aurivillius phase Bi₂SrTa₂O₉ via acid treatment. Inorg. Chem. 40, 5768–5771. https://doi.org/10.1021/ic010266m.

Tsunoda, Y., Sugimoto, W., Sugahara, Y., 2003. Intercalation behavior of n-alkylamines into a protonated form of a layered perovskite derived from Aurivillius phase Bi₂SrTa₂O₉. Chem. Mater. 15, 632–635. https://doi.org/10.1021/cm0200893.

Uppuluri, R., Gupta, A.S., Rosas, A.S., Mallouk, T.E., 2018. Soft chemistry of ion-exchangeable layered metal oxides. Chem. Soc. Rev. 47, 2401–2430. https://doi.org/10.1039/C7CS00290D.

Wang, C., Tang, K., Wang, D., Liu, Z., Wang, L., Zhu, Y., Qian, Y., 2012. A new carbon intercalated compound of Dion–Jacobson phase HLaNb₂O₇. J. Mater. Chem. 22, 11086–11092. https://doi.org/10.1039/C2JM14902H.

Wang, L., Liu, W., Wang, T., Ni, J., 2013. Highly efficient adsorption of Cr(VI) from aqueous solutions by amino-functionalized titanate nanotubes. Chem. Eng. J. 225, 153–163. https://doi.org/10.1016/j.cej.2013.03.081.

Wang, Y., Wang, C., Wang, L., Hao, Q., Zhu, X., Chen, X., Tang, K., 2014. Preparation of interlayer surface tailored protonated double-layered perovskite H₂CaTa₂O₇ with n-alcohols, and their photocatalytic activity. RSC Adv. 4, 4047–4054. https://doi.org/
10.1039/C3RA44623A.

Wang, Y., Delahaye, E., Leuvrey, C., Leroux, F., Rabu, P., Rogez, G., 2016a. Efficient microwave-assisted functionalization of the aurivillius-phase Bi₂SrTa₂O₉. Inorg. Chem. 55, 4039–4046. https://doi.org/10.1021/acs.inorgchem.6b00338.

Wang, Y., Delahaye, E., Leuvrey, C., Leroux, F., Rabu, P., Rogez, G., 2016b. Post-synthesis modification of the aurivillius phase Bi₂ SrTa₂ O₉ via *In Situ* microwave-assisted "Click Reaction.". Inorg. Chem. 55, 9790–9797. https://doi.org/10.1021/acs.inorgchem.6b01600.

Wang, Y., Nikolopoulou, M., Delahaye, E., Leuvrey, C., Leroux, F., Rabu, P., Rogez, G., 2018. Microwave-assisted functionalization of the Aurivillius phase Bi₂SrTa₂O₉: dial grafting and amine insertion vs. alcohol grafting. Chem. Sci. 9, 7104–7114. https://doi.org/10.1039/C8SC01754A.

Wang, Y., Leuvrey, C., Delahaye, E., Leroux, F., Rabu, P., Taviot-Guêho, C., Rogez, G., 2019. Tuning the organization of the interlayer organic moiety in a hybrid layered perovskite. J. Solid State Chem. 269, 532–539. https://doi.org/10.1016/j.jssc.2018.10.034.

Wei, Y., Li, J., Huang, Y., Huang, M., Lin, J., Wu, J., 2009. Photocatalytic water splitting with In-doped H₂LaNb₂O₇ composite oxide semiconductors. Sol. Energy Mater. Sol. Cells 93, 1176–1181. https://doi.org/10.1016/j solmat.2009.02.001.

Yang, L., Fan, B., Cui, X., Shi, X., Li, R., 2015. Solvent-free aerobic oxidation of ethylbenzene over Mn-containing silylated MgAl layered double hydroxides. J. Ind. Eng. Chem. 21, 689–695. https://doi.org/10.1016/j.jiec.2014.03.038.

Yuan, P., Southon, P.D., Liu, Z., Green, M.E.R., Hook, J.M., Antill, S.J., Kepert, C.J., 2008. Functionalization of halloysite clay nanotubes by grafting with γ-aminopropyltriethoxysilane. J. Phys. Chem. C 112, 15742–15751. https://doi.org/
10.1021/jp805657t.

Zhang, H., Zhang, J., Yun, R., Jiang, Z., Liu, H., Yan, D., 2016. Nanohybrids of organo-modified layered double hydroxides and polyurethanes with enhanced mechanical, damping and UV absorption properties. RSC Adv. 6, 34288–34296. https://doi.org/
10.1039/C6RA04398D.

Zubair, M., Daud, M., McKay, G., Shehzad, F., Al-Harthi, M.A., 2017. Recent progress in layered double hydroxides (LDH)-containing hybrids as adsorbents for water remediation. Appl. Clay Sci. 143, 279–292. https://doi.org/10.1016/j.clay.2017.04.002.