A facile method to modify bentonite nanoclay with silane
A facile method to modify bentonite nanoclay with silane
Sujani B. Y. Abeywardena 0 1 2 3 4
Srimala Perera 0 1 2 3 4
Nadeeka P. Tissera 0 1 2 3 4
K. M. Nalin de Silva 0 1 2 3 4
0 Division of Polymer, Textile and Chemical Engineering Technology, Institute of Technology, University of Moratuwa , Moratuwa , Sri Lanka
1 Department of Chemical and Process Engineering, Faculty of Engineering, University of Moratuwa , Moratuwa , Sri Lanka
2 & Srimala Perera
3 Department of Chemistry, University of Colombo , Colombo , Sri Lanka
4 Sri Lanka Institute of Nanotechnology (Pvt) Ltd , Nanotechnology and Science Park, Homagama , Sri Lanka
Immobilization of smectite clay onto a desirable surface has received much attention, since its nanospace can be utilized for many applications in material science. Here, we present an efficient method to functionalize surface of bentonite nanoclay (BNC) through the grafting of 3-aminotriethoxysilane (APTES). Infrared spectroscopy and elemental analysis confirmed the presence of organic chains and amine groups in modified nanoclay. XRD analysis confirmed grafting of APTES on the surface of bentonite nanoclay without intercalation. The accomplishment of the surface modification was quantitatively proved by TGA analysis. Modified BNC can covalently couple with different material surfaces, allowing its nanospace to be utilized for intercalation of cations, bio-molecules, and polymeric materials, to be used in advanced military aerospace, pharmaceuticals, and many other commercial applications.
Bentonite nanoclay; Covalent modification; Nanospace; Silane; Surface; Spectroscopy
Introduction
The space in between two layers of smectite clay is in
nanometer scale, which is potentially suitable for the
accommodation of a range of guest molecules. This
nanospace in smectite clay plays an important role in
different fields such as polymer nanocomposites, cation
adsorption, intercalation, and exfoliation [
1–3
]. Smectite
clay has also shown the ability to release intercalated
molecules as and when required [
4
]. It would be
noteworthy if smectite clay can be grafted on different surfaces,
while its nanospace is accommodated for special
requirements such as targeted drug delivery, disintegrated agents
in drug formation, selective removal of heavy metal
contaminants, applications in high-temperature environments,
and conducting polymers in wearable electronics. In
grafting of clay, chemical bonding is more stable and
durable compared to physical bonding.
Silane can be used to graft clay particles onto a range of
material surfaces [
5, 6
]. The hydroxyl groups in clay
provide excellent sites for silane grafting. Hydroxyl groups in
broken edges of clay particles play a vital role in grafting
compared to hydroxyl groups in basal surfaces of clay [5].
Hydrolyzed silane can readily form siloxane bonds with
hydroxyl groups in basal surfaces and ‘‘broken’’ edges of
swelling clay minerals such as montmorillonite and
bentonite. In unrestrained conditions, silane can also be
physically adsorbed or intercalated with clay. Some X-ray
powder diffraction (XRD) data in the literature show an
expansion of nanospace in clay due to intercalation of
silane [
7, 8
]. Silane is very reactive with moisture in the air.
When silane is exposed to moisture, hydrolysis occurs
rapidly, forming self-condensed, water insoluble resinous
oligomer, and polymer structures. This has led to conduct
silylation in anhydrous organic solvents in inert gas
environments. The rates of both silane hydrolysis and
condensation are influenced by variations in pH levels.
However, the optimum pH for hydrolysis is not optimum
for condensation. Finding the best balance between
hydrolysis and condensation is one of the keys to the
successful grafting of silane.
In a carefully controlled environment, silane-grafted
clay compounds contain special functional groups such as
–NH2 and –SH, which can be covalently bonded with
desirable surfaces [
2
]. Here, we report a simple one-pot
reaction of a silane-grafted BNC compound, which
contains –NH2 for further immobilization on various surfaces.
In this study, surface characterization, expansion of
nanospace of BNC, and bond formation between APTES and
BNC were studied.
Materials and methods
A dispersion of BNC was obtained by dissolving 4 g of
nanoclay, hydrophilic bentonite nanoclay (Aldrich), in
100 ml of deionized water. Particles of BNC, 100 nm in
size, were obtained by ball milling (FRITSCH
PULVERISETTE 7 premium line grinder). 2 mmol dm-3 of
APTES solution was prepared by controlled dropwise
addition of APTES (Aldrich 99%) to deionized water. A
precipitation was obtained by 1 ml/min drop rate addition
of BNC to APTES solution without agitation in an ambient
environment. The slurry was immediately centrifuged
(Sigma 3–18) at 9000 rpm for 15 min and washed five
times with deionized water. The collected solid was finally
dried at 110 C for 6 h. Modified and non-modified
samples were cha (...truncated)