29Si Solid-state NMR Spectroscopy Research Articles

Solid-State NMR and DFT Combined for the Surface Study of Functionalized Silicon Nanoparticles.

Silicon nanoparticles (NPs) serve a wide range of optical, electronic, and biological applications. Chemical grafting of various molecules to Si NPs can help to passivate their reactive surfaces, "fine-tune" their properties, or even give them further interesting features. In this work, (1) H, (13) C, and (29) Si solid-state NMR spectroscopy has been combined with density functional theory calculations to study the surface chemistry of hydride-terminated and alkyl-functionalized Si NPs. This combination of techniques yields assignments for the observed chemical shifts, including the contributions resulting from different surface planes, and highlights the presence of physisorbed water. Resonances from near-surface (13) C nuclei were shown to be substantially broadened due to surface disorder and it is demonstrated that in an ambient environment hydride-terminated Si NPs undergo fast back-bond oxidation, whereas long-chain alkyl-functionalized Si NPs undergo slow oxidation. Furthermore, the combination of NMR spectroscopy and DFT calculations showed that the employed hydrosilylation reaction involves anti-Markovnikov addition of the 1-alkene to the surface of the Si NPs.

Synthesis and characterization of hydrophobic and mesoporous silicate–silsesquioxane hybrid copolymers

Mesoporous and hydrophobic silicate–silsesquioxane hybrid copolymers were synthesized from tetraethoxysilane and methyltrimethoxysilane by hydrolysis and condensation polymerization using a basic catalyst. The porosity and hydrophobicity of the calcined copolymers were studied by measuring the adsorption isotherms of water and using several other techniques, such as solution and solid-state 29Si-NMR spectroscopy, small-angle X-ray scattering (SAXS), and 1H-MAS NMR spectroscopy. The porous structure of the calcined polymers was influenced by the branched polymer structure and the high condensation ratio of the rigid polymer framework. The hydrophobicity of the polymers depended on the number of residual silanol groups and the degree of polymer branching. The highly branched polymer had an indented surface that caused the polymer to exhibit relatively hydrophobic characteristics owing to segregation of the silanol groups.

Carrageenan–Silica Hybrid Nanoparticles Prepared by a Non‐Emulsion Method

AbstractSpherical and monodispersed sub‐micrometer sized particles of organic–inorganic hybrids were prepared by means of a sol–gel non‐emulsion method using the biopolymer κ‐carrageenan and the alkoxysilane 3‐isocyanatopropyltriethoxysilane (ICPTES). The structural characterization of the carrageenan–silica hybrid particles was performed by using FTIR spectroscopy and solid‐state 29Si and 13C NMR spectroscopy and confirmed that κ‐carrageenan was covalently linked to the siliceous network via urethane bonds. Zeta‐potential measurements indicate the hybrids were functionalized on the surface with sulfonate groups from the polysaccharide. These hybrids display thermal sensitivity, which is of great relevance for biomedical applications such as drug encapsulation and thermally controlled drug‐delivery systems.

Highly fluorescent sub 40-nm aminated mesoporous silica nanoparticles

We report the room temperature synthesis of highly fluorescent, sub-40 nm aminated mesoporous silica nanoparticles in water using triethanolamine (TEA) as catalyst. Co-condensation reactions between silica precursors, i.e., tetraethoxysilane and 3-aminopropyl triethoxysilane, allows the incorporation of amino moieties and conjugated fluorescent dye (tetramethylrhodamine-5(6)-isothiocyanate; TRITC) throughout the silica matrix. Resulting materials are characterized using a combination of transmission electron microscopy, nitrogen sorption measurements, dynamic light scattering, zeta potential measurements, thermogravimetric analysis, fluorescence correlation spectroscopy and solid-state 29Si-NMR spectroscopy. The TEA-catalyzed system leads to the formation of bright and discrete sub-40 nm aminated mesoporous silica nanoparticles with disordered pore structure and high organic content. Resulting nanomaterials may find use as simultaneous fluorescent probes and drug delivery vehicles in future theranostic applications.

ChemInform Abstract: Synthesis and Characterization of 3‐[N,N′‐Bis‐3‐(salicylidenamino)ethyltriamine] Mo(VI)O2@SBA‐15: A Highly Stable and Reusable Catalyst for Epoxidation and Sulfoxidation Reactions.

The efficient and reusable oxidation catalyst 3-[N,N′-bis-3-(salicylidenamino)ethyltriamine] Mo(VI)O2@SBA-15 has been synthesized by the anchoring of the 3-[N,N-bis-3-(salicylidenamino)ethyltriamine] ligand (L or Salpr) on the inner surfaces of organofunctionalized SBA-15 and subsequent complexation with Mo(VI)O2(acac)2. The physico-chemical properties of the functionalized catalysts were analyzed by elemental analysis, ICP-OES, XRD, N2-sorption measurements, TG & DTA, solid state 13C, 29Si NMR spectroscopy, FT-IR, Raman spectroscopy, XPS, DRS UV-Vis spectroscopy, SEM and TEM. XRD and N2 sorption analyses helped to find out the morphological and textural properties of the synthesized catalysts and confirm that an ordered mesoporous channel structure was retained even after the multistep synthetic procedures. The (100), (110) and (200) reflections in SBA-15 provide hints of a good structural stability, the existence of long range ordering and a high pore wall thickness. TG and DTA results reveal that the thermal stability of (L)Mo(VI)O2@SBA-15 was maintained up to 300 °C. The organic moieties anchored over the surface of the SBA-15 support were determined by solid state 13C NMR and FT-IR spectroscopy. Further, solid state 29Si NMR spectroscopy provides the information about the degree of functionalization of the surface silanol groups with the organic moiety. The electronic environment and the oxidation state of the molybdenum site in (L)Mo(VI)O2@SBA-15 were monitored by Raman spectroscopy, XPS and DRS UV-Vis techniques. Moreover, the morphology and topographic information of the synthesized catalysts were confirmed by SEM and TEM imaging. The synthesized catalysts were evaluated in epoxidation and sulfoxidation reactions, and the results show that (L)Mo(VI)O2@SBA-15 exhibits high conversion and selectivity towards epoxidation and sulfoxidation reactions in combination with high stability. The anchored solid catalysts can be recycled effectively and reused several times without major loss in activity. In addition, Sheldon's hot filtration test was also carried out.

Synthesis of a recyclable and efficient Pd(ii) 4-(2-pyridyl)-1,2,3-triazole complex over a solid periodic mesoporous organosilica support by “click reactions” for the Stille coupling reaction

A highly efficient, reusable B-PMO-TZ-Pd(II) catalyst was synthesized by anchoring 4-(2-pyridyl)-4-(2-pyridyl)-1,2,3-triazole ligand over the surface of an organo-functionalized benzene support containing periodic mesoporous organosilica (B-PMO) via “click reaction” and the subsequent complexation with PdCl2. B-PMO materials with uniform hexagonal arrangements were prepared using C16 alkyl trimethyl ammonium bromide [CTAB] surfactant under basic conditions. The physiochemical properties of the functionalised catalyst were analysed by elemental analysis, ICP-OES, XRD, N2 sorption, TGA & DTA, solid state 13C, 29Si NMR spectra, FT-IR, XPS, UV-vis, SEM and TEM. XRD and N2 sorption revealed the morphological and textural properties of the synthesized catalyst, confirming that ordered mesoporous channel structure was retained even after the multistep synthetic procedure. The (100), (110) and (200) reflections in B-PMO are evidence of its good structural stability and the existence of long range order. The TGA-DTA results reveal that the synthesized catalyst B-PMO-TZ-Pd(II) was thermally stable, even at high temperature. The organic moieties anchored over the surface of B-PMO were demonstrated by solid state 13C NMR and FT-IR spectroscopy. Solid state 29Si NMR spectroscopy provides information about the degree of functionalization of the surface silanol group. The electronic environment and oxidation state of Pd in B-PMO-TZ-Pd(II) were monitored by XPS and UV-visible techniques. Moreover, the morphologies and topographic information of the synthesized B-PMO-TZ-Pd(II) catalyst were confirmed by SEM and TEM analyses. The catalytic properties of the catalyst for the Stille coupling reaction were screened, and higher catalytic activities with high TONs were observed. The anchored solid B-PMO-TZ-Pd(II) catalyst can be recycled efficiently and reused several (four) times without a major loss in reactivity.

Surface-Bound Ruthenium Diimine Organometallic Complexes: Excited-State Properties.

Ruthenium complexes of the general formula [Ru(CO)(H)(L2)(L′2)][PF6] (L2 = trans-2PPh3, L′ = η2-4,4′-dicarboxybipyridine (1); L2 =trans-2Ph2PCH2CH2COOH, L′2 = bipyridine (2); L2 = Ph2PCHCHPPh2, L′ = η2-5-amino-1,10-phenanthroline (3); L2 = trans-2PPh3, L′2 = η2-4-carboxaldehyde-4′-methylbipyridine (4)) have been shown to have longer emission lifetimes and higher quantum yields in solution compared with more symmetrical molecules such as [Ru(bpy)3][Cl]2. Compound 4 is obtained as a mixture with the corresponding acetal, 4′. These less symmetrical complexes have been covalently immobilized on the surface of silica polyamine composites, and their photophysical properties have been studied. The surface-bound complexes have been characterized by solid-state CPMAS 13C, 31P, and 29Si NMR, UV–vis, and FT-IR spectroscopies. Excited-state lifetime studies revealed that, in general, the lifetimes of the immobilized complexes are 1.4 to 8 times longer than in solution and are dependent on particle size (300–500 μm versus 10–20 nm average diameter silica gels), polymer structure (linear poly(allylamine) versus branched poly(ethylenimine)), and the type of surface tether. One exception to this trend is the previously reported complex [Ru(bpy)2(5-amino-1,10-phenanthroline)][PF6]2 (5), where only a slight increase in lifetime is observed. Only minor changes in emission wavelength are observed for all the complexes. This opens up the possibility for enhanced heterogeneous electron transfer in photocatalytic reactions.

Synthesis and characterization of 3-[N,N′-bis-3-(salicylidenamino)ethyltriamine] Mo(vi)O2@SBA-15: a highly stable and reusable catalyst for epoxidation and sulfoxidation reactions

The efficient and reusable oxidation catalyst 3-[N,N′-bis-3-(salicylidenamino)ethyltriamine] Mo(VI)O2@SBA-15 has been synthesized by the anchoring of the 3-[N,N-bis-3-(salicylidenamino)ethyltriamine] ligand (L or Salpr) on the inner surfaces of organofunctionalized SBA-15 and subsequent complexation with Mo(VI)O2(acac)2. The physico-chemical properties of the functionalized catalysts were analyzed by elemental analysis, ICP-OES, XRD, N2-sorption measurements, TG & DTA, solid state 13C, 29Si NMR spectroscopy, FT-IR, Raman spectroscopy, XPS, DRS UV-Vis spectroscopy, SEM and TEM. XRD and N2 sorption analyses helped to find out the morphological and textural properties of the synthesized catalysts and confirm that an ordered mesoporous channel structure was retained even after the multistep synthetic procedures. The (100), (110) and (200) reflections in SBA-15 provide hints of a good structural stability, the existence of long range ordering and a high pore wall thickness. TG and DTA results reveal that the thermal stability of (L)Mo(VI)O2@SBA-15 was maintained up to 300 °C. The organic moieties anchored over the surface of the SBA-15 support were determined by solid state 13C NMR and FT-IR spectroscopy. Further, solid state 29Si NMR spectroscopy provides the information about the degree of functionalization of the surface silanol groups with the organic moiety. The electronic environment and the oxidation state of the molybdenum site in (L)Mo(VI)O2@SBA-15 were monitored by Raman spectroscopy, XPS and DRS UV-Vis techniques. Moreover, the morphology and topographic information of the synthesized catalysts were confirmed by SEM and TEM imaging. The synthesized catalysts were evaluated in epoxidation and sulfoxidation reactions, and the results show that (L)Mo(VI)O2@SBA-15 exhibits high conversion and selectivity towards epoxidation and sulfoxidation reactions in combination with high stability. The anchored solid catalysts can be recycled effectively and reused several times without major loss in activity. In addition, Sheldon's hot filtration test was also carried out.

Effect of the nature of silicon oxide structures on the activity of an alumina-chromium catalyst in the reaction of iso-butane dehydrogenation

The formation of silicon oxide structures in the composition of an alumina-chromium catalyst for the dehydrogenation of iso-butane is studied by means of nitrogen adsorption, XRD analysis, solid-state 29Si NMR spectroscopy, temperature-programmed desorption of ammonia, and UV-Vis and Raman spectroscopy. It is established that 0.5–1.2 wt % silicon was distributed on the catalyst surface in the form of Si(OSi)4 structures. As the silicon content was increased to 2.2–3.6 wt %, Si(OSi)3(O-) structural elements were present on the surface in addition to Si(OSi)4. The formation of silicon oxide structures on the catalyst surface was responsible for an increase in the concentration of Cr(III) ions and a decrease in the surface acidity; the activity and selectivity of the catalysts in the reaction of iso-butane dehydrogenation increased.

Synthesis of Poly(Dimethylsiloxane) Networks Functionalized with Imidazole or Benzimidazole for Copper(II) Removal from Water

Functionalized elastomeric networks were obtained via a polycondensation reaction between poly(dimethylsiloxane) (PDMS) containing Si(CH3)2OH as end groups and an imidazole- or benzimidazole-modified alkoxysilane. The structure of the polymeric materials was characterized via attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and solid-state 13C and 29Si NMR spectroscopy, which indicated the presence of silsesquioxane units that acted as nodes on the PDMS chains and linked the functional groups. Thermogravimetric analysis (TGA) of the product indicated high thermal stability with an initial weight-loss temperature around 450 K. The capacity for the removal of copper(II) from aqueous solution was estimated from adsorption isotherms, yielding values of 35.74 and 66.09 mg g-1, respectively, for benzimidazole-and imidazole-functionalized materials. The major adsorption models were evaluated to fit the removal data of copper(II) and the model elaborated by Sips was determined to provide the best fit for both prepared materials.

Synthesis and characterization of novel coatable polyimide-silica nanocomposites

We report synthesis of a novel diamine 1,2-bis(4-(Hydrazonomethyl)phenoxy)ethane (bis- HPE) and a derived novel polyimide. The diamine was reacted with PMDA and ODA to synthesize copolyimide. Unmodified and modified silica particles were dispersed in the polyimide to prepare polyimide-silica hybrids: (a) unmodified (PSH-UM), and (b) modified (PSH-M). The PSH-UM were prepared by generating silica particles in situ in PI. In PSH-M, structural group identical to PI, 2,6- bis(3-(triethoxysilyl)propyl)pyrrolo[3,4-f]isoindole-1,3,5,7(2H,6H)-tetraone was introduced into silica nano-particles. The structural similarity enhanced compatibility between organic–inorganic components by like-like chemical interactions as both contain flexible alkyl groups. PSH-M have shown improved surface smoothness, hydrophobicity and thermal stability. Such properties are mandatory for stable coatings. The structure of silica and PI was affirmed by FTIR, EDX, and solid-state 29Si NMR spectroscopy. Morphological and thermal properties of the prepared PI-SiO2 nano-composites were investigated by field emission scanning electron microscopy, atomic force microscopy, contact angle measurement and thermogravimetric analysis.

Hydration of portland cement in the presence of aluminum-containing setting accelerators

Portland cement hydration in the presence of two different aluminum-containing compounds, highly dispersed amorphous Al(OH)3 and aqueous solution of aluminum hydroxosulfate Al(OH)1.78(SO4)0.61, was studied by solid-state 27Al and 29Si NMR spectroscopy.

Synthesis, Bifunctionalization, and Remarkable Adsorption Performance of Benzene‐Bridged Periodic Mesoporous Organosilicas Functionalized with High Loadings of Carboxylic Acids

Highly ordered benzene-bridged periodic mesoporous organosilicas (PMOs) that were functionalized with exceptionally high loadings of carboxylic acid groups (COOH), up to 80 mol % based on silica, have been synthesized and their use as adsorbents for the adsorption of methylene blue (MB), a basic dye pollutant, and for the loading and release of doxorubicin (DOX), an anticancer drug, is demonstrated. These COOH-functionalized benzene-silicas were synthesized by the co-condensation of 1,4-bis(triethoxysilyl) benzene (BTEB) and carboxyethylsilanetriol sodium salt (CES), an organosilane that contained a carboxylic acid group, in the presence of non-ionic oligomeric surfactant Brij 76 in acidic medium. The materials thus obtained were characterized by a variety of techniques, including powder X-ray diffraction (XRD), nitrogen-adsorption/desorption isotherms, TEM, and (13)C and (29)Si solid-state NMR spectroscopy. Owing to the exceptionally high loadings of COOH groups, their high surface areas, and possible π-π-stacking interactions, these adsorbents have very high adsorption capacities and extremely rapid adsorption rates for MB removal and for the controlled loading/release of DOX, thus manifesting their great potential for environmental and biomedical applications.

The role of the defect groups on the Silicalite-1 zeolite catalytic behavior

Silicalite-1 samples were synthesized from gels of composition: 0.08 Na2O – 0.08 TPABr – 1 SiO2 – 20 H2O (TPABr=tetrapropylammonium bromide) at 170°C under autogeneous pressure during 24h. The gels used without aging yielded large particles of ca. 15μm, while the aged gel led to small particles of ca. 2μm. The acidity of the samples was checked by FTIR of the silanol groups, by the IR spectra of adsorbed pyridine and by temperature programmed desorption of ammonia. The silanol groups were also identified by High Resolution Solid State 29Si NMR spectroscopy. The samples not containing H-bonded silanol groups were not active either in the dehydration of propan-2-ol or the cumene cracking. The samples calcined and NH4+ exchanged by NH4Cl either at pH=5.5 or pH=10.5 showed activity in the propan-2-ol dehydration, but not in cumene cracking. These samples contained acid sites of medium acid strength characterized by the H-bonded silanol groups. A second calcination of the samples was necessary in order to show some activity in cumene cracking. A ZSM-5 sample of Si/Al=25 was synthesized and studied for the sake of comparison. A Silicalite-1 sample composed of small particles first calcined at 550°C, then NH4+ exchanged with NH4Cl at pH=5.5 and finally calcined at 550°C showed the highest activity (10–11%) in cumene cracking. A hypothesis could be advanced on the production of Lewis acid centers, to explain the catalytic activity of this sample.

Hydration of Portland cement in the presence of high activity aluminum hydroxides

The effect of highly dispersed amorphous aluminum hydroxides on the hydration of Portland cement was studied by the solid-state 27Al and 29Si NMR spectroscopy. It was established that in the presence of aluminum hydroxides the decrease in the setting time of a cement paste is due to rapid formation of ettringite phase, with contribution of admixture material the main and contribution of aluminum-containing phases at this stage insignificant.

Effect of alkali cations on silicon ability to bind in cement stone by data of solid-state 29Si NMR spectroscopy

An effect of additive compounds of sodium and lithium (nitrates and chlorides) on the distribution of silicon atoms by a degree of connectivity in the cement paste was studied by the solid-state 29Si NMR spectroscopy at different periods of hydration. Simultaneously, we measured the strength of the hardened cement paste under compression.

Synthesis of poly(aminopropyl/methyl)silsesquioxane particles as effective Cu(II) and Pb(II) adsorbents

Poly(aminopropyl/methyl)silsesquioxane (PAMSQ) particles have been synthesized by a one-step hydrolytic co-condensation process using 3-aminopropyltriethoxysilane (APTES) and methyltrimethoxysilane (MTMS) as precursors in the presence of base catalyst in aqueous medium. The amino functionalities of the particles could be controlled by adjusting the organosilanes feed ratio. The compositions of the amino-functionalized polysilsesquioxanes were confirmed by FT-IR spectroscopy, solid-state 29Si NMR spectroscopy, and elemental analysis. The strong adsorbability of Cu(II) and Pb(II) ions onto PAMSQ particles was systematically examined. The effect of adsorption time, initial metal ions concentration and pH of solutions was studied to optimize the metal ions adsorbability of PAMSQ particles. The kinetic studies indicated that the adsorption process well fits the pseudo-second-order kinetics. Adsorption phenomena appeared to follow Langmuir isotherm. The PAMSQ particles demonstrate the highest Cu(II) and Pb(II) adsorption capacity of 2.29 mmol/g and 1.31 mmol/g at an initial metal ions concentration of 20 mM, respectively. The PAMSQ particles demonstrate a promising application in the removal of Cu(II) and Pb(II) ions from aqueous solutions.

Synthesis and characterization of surface modified SBA-15 silica materials and their application in chromatography

Hexagonally ordered SBA-15 mesoporous silica spheres with large uniform pore diameters are obtained using the triblock copolymer, Pluronic P123, as template with a cosurfactant cetyltrimethylammonium bromide (CTAB) and the cosolvent ethanol in acidic media. A series of surface modified SBA-15 silica materials is prepared in the present work using mono- and trifunctional alkyl chains of various lengths which improves the hydrothermal and mechanical stability. Several techniques, such as element analysis, nitrogen sorption analysis, small angle X-ray diffraction, scanning electron microscopy (SEM), FTIR, solid-state 29Si and 13C NMR spectroscopy are employed to characterize the SBA-15 materials before and after surface modification with the organic components. Nitrogen sorption analysis is performed to calculate specific surface area, pore volume and pore size distribution. By surface modification with organic groups, the mesoporous SBA-15 silica spheres are potential materials for stationary phases in HPLC separation of small aromatic molecules and biomolecules. The HPLC performance of the present SBA-15 samples is therefore tested by means of a suitable test mixture.

Tailored Covalent Grafting of Hexafluoropropylene Oxide Oligomers onto Silica Nanoparticles: Toward Thermally Stable, Hydrophobic, and Oleophobic Nanocomposites

The modification of silica nanoparticles with hexafluoropropylene oxide (HFPO) oligomers has been investigated. HFPO oligomers with two different average degrees of polymerization (DPn = 8 and 15) were first prepared by anionic ring-opening polymerization, deactivated by methanol, and in some cases postfunctionalized by aminopropyl(tri)ethoxysilane or allylamine. The "grafting onto" reactions of these oligomers were then carried out either on bare silica (reaction between a silanol surface and ethoxy-silanized HFPO) or on silica functionalized by amino groups (in an amidation reaction with methyl ester-ended HFPO) or mercapto groups (via the radical addition of allyl-functionalized HFPO). Hybrid nanoparticles thus obtained were characterized by solid-state (29)Si NMR and FTIR spectroscopies as well as elemental and thermogravimetric analyses. The results assessed a significant yield of covalent grafting of HFPO oligomers when performing the hydrolysis-condensation of ethoxylated HFPO on the bare silica surface, compared to the other two methods that merely led to physically adsorbed HFPO chains. Chemically grafted nanohybrids showed a high thermal stability (up to 400 °C) as well as a very low surface tension (typically 5 mN/m) compared to physisorbed complexes.

Spectroscopic Investigation of Ti-Modified Aluminum-Free Zeolite-Beta Crystallization

Crystallization of aluminum-free zeolite-Beta from viscous gel and incorporation of titanium into its framework were investigated by several spectroscopic techniques. Hydrothermal synthesis was stopped at different times and the gels obtained from the autoclaves were analyzed by liquid-state 29Si NMR spectroscopy. The gels were subsequently dried and inspected by solid-state 29Si NMR, Fourier-transform infrared, and X-ray absorption spectroscopy. NMR spectroscopy distinguished signals from oligomers and from two populations of nanoparticles with different typical dimensions. It also provided information about the composition of the oligomers and nanoparticles, in terms of the relative fractions of Qn units within them. Investigation showed that the synthesis of zeolite Ti-Beta started with a quick formation of oligomers. After 20 h of the hydrothermal treatment, oligomers with a high fraction of Q3 units gradually aggregated into primary nanoparticles with a diameter of ∼2 nm. During first 20 h, primary n...