Functionalization of SBA-15 mesoporous silica by Cu-phosphonate units: Probing of synthesis route
Graphical abstract
The present study is devoted to mesoporous silica SBA-15 containing propyl-copper phosphonate units. The species were investigated to confirm of synthesis procedure correctness by the micro-Raman technique combined with DFT numerical simulations. Complementary research was carried out to test the structure of mesoporous samples.
Introduction
Functional materials based on porous silica matrix and transition metal-containing active groups are attractive architectures for fundamental understanding of physical phenomena at the interfaces and for potential magneto-optical applications. The bulk physical responses (vibrational, optical) of such materials combine the intrinsic properties of the host matrices and those of the active groups (polarizability, charge transfer, magnetic momentum) as well as the mutual interactions involved at the interfaces between the matrix and its functional groups. Among the possible future applications the following are of particular note: controlled drug delivery [1], [2], bio-sensing [3], separation and recycling [4], catalysis [5], or other molecular engineering [6]. A wide synthesis activity has contributed to control the synthesis routines of mesoporous silica with variable pore sizes (2–20 nm). Additionally, several functional groups grafted either in the pores or in the wall structure were successfully obtained [7], [8], [9]. The main challenge lies in the implementation of samples where the functional groups are homogeneously distributed in the host matrices. This is the main requirement related to the fine-tuning physical properties (electronic, magnetic, optical) of the silica-based architectures following the nature of the active groups.
The present work is devoted to mesoporous silica SBA-15 functionalized by propyl-copper phosphonate units. Schematic representation of this system can be seen in Fig. 1.
The molar concentration of propyl-copper-phosphonate units in silica matrix is 10% (1 propyl-Cu-phosphonate group per 9 SiO2 groups). In the present thesis we consider original approach to probing of synthesis efficiency, in particular activation efficiency and homogeneity of the active units distribution. The Raman scattering measurements combined with numerical models are found relevant to check correctness of the molecular configurations involved in the samples. The proper assignment of bands in experimental Raman spectrum is desired to proper understanding of the spectral changes in the hydrogen-bonded active groups. Additionally, quantitative EDX analysis supported by quantitative elemental analysis is found as a useful tool to confirm reaction between precursor groups and doping agent. Apart from probing the activation efficiency and active groups distribution, the structure order of the SBA-15 silica is examined by X-Ray diffraction, TEM microscopy and N2 adsorption.
Section snippets
Synthesis of SBA-15 mesoporous silica containing copper ions
Synthesis of mesoporous silica SBA-15 functionalized by propyl-phosphonate-copper units was carried out under argon atmosphere using a vacuum line. Solvents were dried out and distilled just before the use. Reagents with the highest available purity were used for reactions. Triblock copolymer (EO20PO70EO20) with EO (poly-ethylene oxide) and PO (poly-propylene oxide), Pluronic P123, copper(II) acetylacetonate (Cu(acac)2) and tetraethylorthosilicate (TEOS) were purchased from Aldrich and used as
Result and discussion
The structure of obtained mesoporous material was studied by the small-angle XRD, TEM observation and N2 sorption. The powder XRD pattern is shown in Fig. 4.
The X-Ray diffraction pattern shows a well ordered structure of hybrid mesoporous material. XRD pattern exhibits an intense diffraction peak corresponding to d100 spacing equals 9.144 nm. Next weak Bragg peaks correspond to 110 and 200 crystallographic planes. All this features are characteristic for 2D hexagonal structure. Further features
Conclusion
On the basis of poly-condensation of PPTES and TEOS in the presence of P123 surfactant a novel copper containing mesoporous silica has been prepared. The species have hexagonal arranged pores with diameter below 5 nm, what was confirmed by X-Ray scattering, TEM imaging and N2 sorption tests. To probe of functionalization efficiency we performed Raman scattering supported by numerical simulations. The structure of silica cluster containing propyl-PO(OH)2 group and propyl-POO2Cu has been optimized
Acknowledgments
Financial support for this investigation has been provided by the National Centre of Science (Grant-no: 2011/03/D/ST5/05996).
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