Assistant template and co-template agents in modeling mesoporous silicas and post-synthesizing organofunctionalizations
Graphical Abstract
The mesoporous SBA-16 can be synthesized from binary (F127/TEOS) or ternary (F127/alcohol/TEOs) systems to give well-ordered mesoporous silicas. The co-templates ethanol or butanol gave the final material with highest wall thickness, mainly with ethanol. After these syntheses the pores were successfully organofunctionalized to give a good incorporation of the silylating agents. The final silicas presented of well-arranged solid characteristics as expressing by three distinct peaks, as indexed by the corresponding planes.
Highlights
► Syntheses of mesoporous silicas by using ternary (F127/agent/TEOS) and binary (F127/TEOS) systems. ► Use of co-templates to synthesize mesoporous silicas with larger wall thicknesses. ► Immobilization of pendant chains inside the porous silicas. ► Ordered mesoposous silicas as new materials for possible applications on sorption and delivering drug systems.
Introduction
A substantial amount of research has been directed towards ordered mesoporous silicas, not only associated with structural features, but also to the enormous potential of applications in many diversified areas. Taking into account the recent development of this research field, a few examples can demonstrate the importance of these well-structured compounds as active agents in catalysis, electric and optical-electronic devices, chemical and biochemical sensors, nanofluidic systems, membranes, sorption and drug delivery systems [1], [2], [3], [4], [5], [6].
This class of mesoporous silicas was previously synthesized in 1992 by Mobil Oil Company researchers, including in this well-known M41S silica [7]. Ordered mesoporous silicas have been synthesized through the use of surfactants as templates, to yield mesoporous materials containing uniform pore sizes, large pore volumes, and high surface areas with large concentrations of silanol groups attached to the surface [8], [9]. In addition, such mesoporous silicas are very useful for a variety of applications due to their hydrothermal stability [10] and the favorable synthetic methodology normally progresses due to the intense use of inexpensive and commercially available reagents [11], [12].
A variety of SBA-type synthesized mesoporous silicas using non-ionic block copolymers as templates [13] was first reported in 1998. In general, these inorganic materials are usually obtained at low-pH solutions, where the expected interaction between template and silica source precursor proceeds through the SiOH+X−I+ mechanism [14], to give ordered silicas that exhibit large pore sizes, thick pore walls and also relevant high stabilities [15].
Among these SBA-type mesoporous silicas, a special class known as SBA-16 has been considered the most interesting mesostructured inorganic material, having a 3D cubic arrangement of the mesopores that corresponds to the Im3m space group. However, few SBA-16 synthetic methods have been reported due to the fact that the cage-like SBA-16 mesostructured silica can only be produced in a narrow window of synthetic parameters [15], [16], [17], [18]. However, SBA-16 is generally obtained through the mixture of copolymers like Pluronic F127 and Pluronic P123 under acidic conditions [19]. Another synthetic procedure is based on the use of Pluronic F127 and cetyltrimethylammonium bromide templates as structural directing agents and tetraethylorthosilicate (TEOS) as silica source [19] or considering the ternary F127–butanol–H2O mixture at low hydrochloric acid concentration [20]. Studies have shown that the physicochemical properties of mesoporous silicas are dependent on several parameters, such as, period of aging of the gel, the silica source, foam control, the appropriate method of synthesis, calcination and pH [21].
Additionally, another way of improve the physicochemical properties of such materials and to increase their potential applicability is through incorporating organic functional groups into the mesoporous silica space [8], [22], [23], [24], [25]. Recently, various research groups have investigated the incorporation of small organic functional groups onto silica surfaces either by covalent and non-covalent bond formation [26], [27, [28]. Covalent functionalization generally occurs through silane chemistry bond formation and, in this case, the silane moiety bonds to silica by both direct, due to the co-condensation process, and indirect, which consists of post-synthetic or grafting methods [29]. This last procedure can be used to incorporate organic functional groups after the silica structure was definitively formed. This technique typically involves reactions between hydroxyl groups on the surfaces of the mesoporous structure with a silane compound [30]. On the other hand, the co-condensation method is based on use of a tetraalkoxysilane such as TEOS that is combined with an another organosilane, for example, 3-aminopropyltriethoxysilane via a sol-gel process by controlling hydrolysis and condensation rates in the presence of a desirable template under basic, neutral or acidic conditions [31].
The present investigation deals with the synthesis of three different SBA-16 mesoporous silicas that were obtained using ternary (F127/alcohol/TEOS) and binary (F127/TEOS) systems. For these syntheses the F127 template was used in the presence of n-butanol and ethanol as co-templates. The next step consisted in organofunctionalizing the mesoporous silicas by using grafting methodology to covalently incorporate 3-iodopropyltrimethoxysilane, followed by reaction with diethyliminodiacetate, which resulted in smaller pores after the functionalization process.
Section snippets
Chemicals
Poly-(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)triblock copolymer (F127, EO106PO70EO106, Sigma), hydrochloric acid (HCl, Synth, 38%), ethanol (EtOH, Synth, 98%), n-butanol (BuOH, Vetec, P.A, ACS) and tetraethylorthosilicate (TEOS, Aldrich, 98%) were used for the syntheses of SBA-16 materials, while 3-iodopropyltrimethoxysilane (IPTMS, Aldrich, 99%) and diethyliminodiacetate (DEIDA, Aldrich, 99%) were used to functionalize SBA-16 silicas.
Synthesis of SBA-16 mesoporous silica
Three SBA-16 samples were synthesized in
Results and discussion
The structured mesoporous silicas were successfully synthesized using the chosen Pluronic F127 template, having TEOS as silica source in binary combination or with ETOH or BuOH participation as co-templates in ternary systems. The synthetic procedure including co-templates was explored due to the fact that this process has ability not only to favor better directing agents to yield mesoporous structures, but also to obtain products with improved mechanical properties, as represented by higher
Conclusions
The present results reveal the success of the syntheses of mesoporous silicas of the type SBA-16, by using binary and tertiary systems, with favorable results for the co-template ethanol due to the highest wall thickness value. From the structural point of view, SAXS presented peaks in the 2θ=0.68–1.4° range, that enabled indexing planes (110), (200) and (211), mainly for SBA-16C, which confirmed the formation of mesoporous materials, as also confirmed by transmission electron microscopy. The
Acknowledgment
The authors are indebted to CNPq for fellowships and financial support, to LNLS for SAXS analyses and to LNNANO for transmission electron microscopy (TEM) images.
References (47)
- et al.
J. Catal.
(2010) - et al.
Biomaterials
(2011) - et al.
J. Mol. Catal. A: Chem.
(2008) - et al.
Solid State Sci.
(2005) - et al.
J. Colloid Interface Sci.
(2009) - et al.
Catal. Commun.
(2008) - et al.
Microporous Mesoporous Mater.
(2008) - et al.
Microporous Mesoporous Mater.
(2005) - et al.
J. Colloid Interface Sci.
(2007) - et al.
J. Mol. Catal. A: Chem.
(2009)
J. Catal.
Colloids Surf. A
Mater. Res. Bull.
J. Colloid Interface Sci.
Microporous Mesoporous Mater.
Microporous Mesoporous Mater.
Colloids Surf. A
J. Hazard. Mater.
Nature
Adv. Mater.
Nature
New J. Chem.
J. Am. Chem. Soc.
Cited by (10)
Evaluation of the applicability of thermogravimetry in the monitoring of the organofunctionalization process of expanded perlite
2019, Thermochimica ActaCitation Excerpt :The process of modification (or functionalization) of materials is carried out with the intention to control the physical-chemical properties of the surface of the material, favoring the use of the same in a specific purpose. As perlite has a high content of silica, generally higher than 70%, it is possible to make modifications through reactions with organic compounds, such as orthophenanthroline, due to the presence of silanols on its surface [3,13,14]. 1,10-phenanthroline, or commonly orthophenanthroline, consists of a poly-condensed heterocyclic compound, which has a planar structure.
Molybdenum(VI) complex with a tridentate Schiff base ligand immobilized on SBA-15 as effective catalysts in epoxidation of alkenes
2015, Microporous and Mesoporous MaterialsCitation Excerpt :For the organic/inorganic hybrid materials Mo-FSAP-Cl-SBA-15 and Mo-FSAP-CH3-Cl-SBA-15, there are additional resonances for the organosiloxane R–Si(HO)2(OSi) (T1), R–Si(HO)(OSi)2 (T2), R–Si(OSi)3 (T3) species. The relative integrated intensities of the organosiloxane T1, T2 and T3 NMR signals can be employed to estimate the degree of grafting Schiff base ligand groups [47]. For two samples Mo-FSAP-Cl-SBA-15 and Mo-FSAP-CH3-Cl-SBA-15, these resonances were found at around −56.9 (T2) and −66.7 ppm (T3), and the resonance of T1 was too low in intensity to be observed.
Hydrophobic contribution to amoxicillin release associated with organofunctionalized mesoporous SBA-16 carriers
2014, Materials Research BulletinThe applicability of ordered mesoporous SBA-15 and its hydrophobic glutaraldehyde-bridge derivative to improve ibuprofen-loading in releasing system
2014, Colloids and Surfaces B: BiointerfacesCitation Excerpt :Thus, in any case the silicon atoms are attached to four oxygen atoms in the inorganic structure. The absence of silanol groups demonstrates the existence of Q4species, which increasing of these groups defines the presence of Q3, Q2 and Q1 species [31], as observed for the peaks between −108 to −120; −98 to −105; −90 to −100 and −80 to −90 ppm, respectively. The type T signals are expected when the silylating agents are directly bonded to silicon in a correspondent covalent bond on the inorganic surface.
Additive induced core and corona specific dehydration and ensuing growth and interaction of Pluronic F127 micelles
2014, Journal of Colloid and Interface ScienceCitation Excerpt :This is reflected in the difference in the time scale of correlation function and relaxation time plots for the two samples. Aqueous Pluronic F127 solutions containing butan-1-ol as co-surfactant have applications as structure directing agents for the formation of mesoporous compounds of different ordered structures [89–93]. Since in these systems butan-1-ol is used to control pore size of the mesoporous structures, formation of room temperature worm like Pluronic F127 micelles in the presence of butan-1-ol and NaCl could have important applications in tuning the morphology of mesoporous structures [94,95].
Free amino and imino-bridged centres attached to organic chains bonded to structurally ordered silica for dye removal from aqueous solution
2014, Journal of Environmental ManagementCitation Excerpt :The obtained results confirm the structure of bridged polysilsesquioxane, as represented in Fig. 2B. The NMR for the silicon nucleus for resulted in a series of typical signals that corresponds to the polymeric compounds, described as Q4 [Si(OSi)4], Q3 [(OSi)3(OH)], T3 [RSi(OSi)3] and T2 [RSi(OSi)2(OH)], originating from the structural unit, indicating the presence of the organic part bonded to the inorganic framework of silica (Oliveira and Airoldi, 2012). The spectrum of SBA-15AP presents T2 and T3 signals at −55.7 and −62.6 ppm, while the Q3 and Q4 species at −96.1 and −104.5 ppm, as shown in Fig. 2C. For SBA-15TE spectrum T2 and T3 signals at −58.8 and −66.5 ppm were followed by Q3 and Q4 at −101.2 and −109.7 ppm, as represented in Fig. 2D. For both mesoporous silicas the absence of the Q2 species was observed, but the presence of Tn sites in the −40 to −60 ppm range, as represented by T2, C–Si(OSi)2OH, and in the −60 to −75 ppm interval of T3 species, C–Si(OSi)3, confirm the presence of the AP and TE groups covalently bonded to the SBA-15 structure.