DSpace at VNU: Nanostructured polysilsesquioxanes bearing amine and ammonium groups by micelle templating using anionic surfactants

View Article Online / Journal Homepage / Table of Contents for this issue PAPER www.rsc.org/materials | Journal of Materials Chemistry Nanostructured polysilsesquioxanes bearing amine and ammonium groups by micelle templating using anionic surfactants† Published on 18 March 2010 Downloaded by Universitat Politècnica de València on 22/10/2014 04:06:32 Thy Phuong Nguyen,ab Peter Hesemann,*a Thi My Linh Tranb and Jo€el J E Moreaua Received 3rd December 2009, Accepted 23rd February 2010 First published as an Advance Article on the web 18th March 2010 DOI: 10.1039/b925352a We report the synthesis of new mesoporous nanostructured polysilsesquioxanes by hydrolysis–polycondensation procedures of silylated amine or ammonium precursors The formation of materials with defined architectures and pore arrangements on a mesoscopic length scale was achieved via soft-templating approaches using anionic surfactants as structure directing agents For the first time, nanostructured polysilsesquioxanes were obtained with anionic surfactants following a SÀI+ pathway Structuring was achieved due to electrostatic interactions between the cationic centers of ammonium precursors and the anionic head group of the sulfate surfactant This study highlights that specific precursor–surfactant interactions are essential for the formation of nanostructured materials The obtained new materials are useful for the immobilization of metallic species via the formation of coordination complexes or anion exchange reactions and therefore have high potential as heterogeneous catalysts or adsorbents Introduction The synthesis of ordered silicates via soft-templating approaches has attracted tremendous interest since its discovery in 1992.1,2 This strategy opened the door to a large variety of siliceous materials featuring narrow pore size distribution and regular 2D or 3D arranged pore structures on a mesoscopic length scale Simultaneously, polysilsesquioxanes emerged as a new class of functional organic–inorganic hybrid materials.3,4 These solids, obtained from bridged silylated organic precursors, are characterized by a homogeneous distribution of organic substructures within the materials’ framework on a molecular level and contain covalently linked organic substructures The term ‘polysilsesquioxane’ is related to the elemental silicon/oxygen ratio of RSiO1,5 substructures (sesqui (lat.)—one and a half) and therefore designates hybrid materials synthesized by sol–gel transformation of bridged organic precursors, without addition of a silica source such as TEOS or TMOS.5 In this field, functional materials bearing chiral, metal complexing and p-conjugated substructures for applications in heterogeneous asymmetric catalysis, separation and optics were reported.6–10 On the other side, structured polysilsesquioxanes with defined architectures from the molecular to the microscopic level have also been described.11–13 a Institut Charles Gerhardt de Montpellier, UMR CNRS 5253, Equipe Architectures Mol eculaires et Mat eriaux Nanostructur es, 8, rue de l’Ecole Normale, 34296 Montpellier Cedex 05, France E-mail: peter hesemann@enscm.fr; Fax: +33 67 14 43 53; Tel: +33 67 14 72 17 b Faculty of Chemistry, Hanoi University of Science, 19 Le Thanh Tong, Hanoi, Vietnam † Electronic supplementary information (ESI) available: 1H NMR and FT-IR spectra of precursor 1; FT-IR spectrum of material A; TGA-plots of materials A, B and C; BJH dV/dlog(D) pore volume distribution of materials A–E; 29Si OP MAS NMR spectra and 13C CP MAS NMR spectra of materials B, D and E, 29Si OP MAS NMR spectrum of material C See DOI: 10.1039/b925352a 3910 | J Mater Chem., 2010, 20, 3910–3917 Porous polysilsesquioxanes featuring regular pore architectures were only reported in 1999.14–16 These so-called periodic mesoporous organosilicas (PMOs)17,18 were originally obtained from rather simple precursors such as 1,2-bis(trialkoxysilyl)ethane, bis(trialkoxysilyl)ethylene, 1,4-bis(trialkoxysilyl)benzene or 2,5bis(trialkoxysilyl) thiophene.19 Special attention was paid to the control of the architecture and morphologies of PMO type materials For example, solids with crystal-like wall structures20–22 and materials displaying controlled size and shape such as nanofibers or coiled shaped particles were recently reported.23–25 More recently, PMO type materials bearing more complex organic substructures have been described, i.e chiral fragments,26–30 p-conjugated segments31,32 or chelating entities.33 Bifunctional PMOs bearing more than one type of organic substructure have also been reported The incorporation of multiple bridging groups allows to fine tune the surface properties of PMOs and to achieve the desired functionality and selectivity.34–40 The expression ‘PMO’ refers to the textural properties of this kind of material, in particular to their regular architecture and porosity on a mesoscopic length scale Although several PMO type materials were synthesized by hydrolysis– polycondensation procedures of ‘pure’ bridged silylated precursor molecules, PMOs are in many cases obtained by co-condensation involving bridged organic precursors and silica network formers such as TMOS or TEOS.17 The addition of silica precursors is often necessary in order to generate sufficient mechanical stability which is necessary for the creation of porosity and order within functional siliceous materials especially when flexible and sterically demanding silylated organic substructures were used.41–44 Similar to nanostructured silica phases, PMO type materials are usually synthesized via soft-templating approaches using cationic or nonionic surfactants Structuring of PMOs is generally governed either by electrostatic interactions between cationic This journal is ª The Royal Society of Chemistry 2010 View Article Online Published on 18 March 2010 Downloaded by Universitat Politècnica de València on 22/10/2014 04:06:32 Scheme Structures of the neutral amine precursor and the ionic ammonium precursors and surfactants and anionic silanolates in basic reaction media (S+IÀ-pathway) or by hydrogen bonding between di- or triblock copolymer and silanols under acidic conditions (S0I0-pathway).17 Here we report the first example for the design of ordered pore arrangements within polysilsesquioxanes using anionic structure directing agents following an SÀI+-pathway This approach fundamentally differs from other synthetic strategies for the formation of PMO type materials We show that the formation of structured solid phases can be induced by strong electrostatic interactions between anionic surfactant and the organo-ionic part of a cationic precursor molecule Contrary to conventional PMO synthesis, in this study, the silyl groups have no or little influence on the formation of nanostructured solid phases Since several years, our special concern is the elaboration of nanostructured siliceous materials bearing ionic substructures.45–48 Here, we report that cationic ammonium precursor in the presence of anionic structure directing agents lead to polysilsesquioxanes displaying hexagonally arranged pore structures A related strategy has been used for the synthesis of nanostructured silicas,49,50 but anionic surfactant templated mesoporous polysilsesquioxanes have never been reported yet We studied in particular the syntheses of mesoporous nanostructured functionalized PMO materials from the tris(3-(trimethoxysilyl)propyl)amine precursor and the cationic ammonium precursors and (Scheme 1) As all materials were synthesized by hydrolysis–polycondensation of the sole precursors without addition of silica precursors such as TEOS or TMOS, the obtained solids can be described as mesoporous nanostructured polysilsesquioxanes Experimental General details 3-Aminopropyltrimethoxysilane, 3-(chloropropyl)-trimethoxysilane and the anionic surfactant sodium hexadecyl sulfate (containing 40% sodium stearyl sulfate) were purchased at ABCR The surfactants P123 and CTAB were purchased at Aldrich 1H and 13 C spectra in solution were recorded on Bruker AC 250 or Bruker Avance 400 spectrometers at room temperature Deuterated chloroform was used as solvent for liquid NMR experiments and chemical shifts are reported as d values in parts per million relative to tetramethylsilane IR samples were prepared as KBr pellets FT-IR spectra were measured on a Perkin-Elmer 1000 FT-IR spectrometer MS-ESI were measured on Water Q-Tof mass spectrometer Solid state 13C and 29Si CP MAS NMR experiments were recorded on a Varian VNMRS 400 MHz solid spectrometer using a two channel probe with 7.5 mm ZrO2 rotors The 29Si solid state NMR spectra were recorded using both CP MAS and One Pulse (OP) sequences with samples spinning at kHz CP This journal is ª The Royal Society of Chemistry 2010 MAS was used to get high signal to noise ratio with ms contact time and s recycling delay For OP experiments, p/6 pulse and 60 s recycling delay were used to obtain quantitative information on the silane–silanol condensation degree The 13C CP MAS spectra were obtained using ms contact time, s recycling delay and kHz spinning rate The number of scans was in the range 1000–3000 for 29Si OP MAS spectra and of 2000–4000 for 13C CP MAS spectra Nitrogen sorption isotherms at 77 K were obtained with a Micromeritics ASAP 2020 apparatus Prior to measurement, the samples were degassed for 18 hours at 100  C The surface areas (SBET) were determined from BET treatment in the range 0.04–0.3 p/p0 and assuming a surface coverage of ˚ Pore size distribunitrogen molecules estimated to be 13.5 A tions were calculated from the adsorption branch of the isotherms using the BJH method The pore width was estimated at the maximum of the pore size distribution TEM images were obtained using JEOL 1200 EX II (120 kV) XRD experiments were carried out with an Xpert-Pro (PanAnalytical) diffractometer equipped with a fast X’celerator detector using Cu-Ka radiation TGA experiments were performed with a TA Instruments Q50 apparatus The samples were heated under an air stream from 50 to 800  C with a heating rate of 10  C minÀ1 Precursor syntheses Tris(3-(trimethoxysilyl)propyl)amine A mixture of 10.0 g (55.6 mmol) of 3-aminopropyltrimethoxysilane, 38.8 g (196 mmol) of 3-chloropropyltrimethoxysilane and 28.8 g (224 mmol) of ethyl-diisopropylamine was heated (115  C) with stirring during days After this time, the starting materials have totally been consumed The reaction mixture was cooled to room temperature The formed salts were precipitated by addition of 300 mL of pentane The suspension was filtered and the solvents were evaporated The crude product was finally distilled under reduced pressure to give the title compound as a yellow viscous liquid Yield: 25.2 g (50 mmol, 90%) 1H NMR (400 MHz, CDCl3) d 0.54 (m, 6H), 1.46 (m, 6H), 2.34 (m, 6H), 3.50 (s, 27H); 13 C NMR (CDCl3) d 6.70, 20,14, 50.48, 57.00; FT-IR(KBr) nmax/cmÀ1 2944, 2841, 2804, 1465, 1192, 1089, 820; HRMS [ESI+, m/z] calcd for C18H46NO9 (M + H)+ 504.2480, found 504.2509 Methyl-(tris(3-trimethoxysilyl)propyl) ammonium iodide At room temperature and under argon, 6.8 g (48 mmol) of iodomethane are added carefully to 20.0 g (40 mmol) of tris(3-trimethoxysilyl)propyl) amine The reaction mixture was stirred at room temperature for 15 h After this time, the volatiles were pumped off The title compound was obtained as a brownish oil after repeated washing with pentane and drying under high vacuum at 50  C Yield: 24.8 g (38.4 mmol, 96%) 1H NMR (CDCl3) d 0.64 (t, 2H, J ¼ 8.2 Hz), 1.74 (m, 2H, J ¼ 8.2 Hz), 3.19 (s, 3H), 3.36 (m, 2H, J ¼ 6.0 Hz), 3.52 (s, 27H) 13C NMR (CDCl3) d 5.51, 16.12, 48.90, 50.79, 63.18; MS-ESI (m/z (%)) 518.3 (100) [M+]; HRMS (ESI, m/z) [M]+ calcd for C10H30NO9Si3+ (fully hydrolyzed product) 329.1228, found 392.1218 Tetrakis(3-(trimethoxysilyl)propyl)ammonium iodide At room temperature and under argon, 12.7 g (44 mmol) of J Mater Chem., 2010, 20, 3910–3917 | 3911 Published on 18 March 2010 Downloaded by Universitat Politècnica de València on 22/10/2014 04:06:32 View Article Online 3-iodopropyltrimethoxysilane were added to 20.0 g (40 mmol) of tris(3-trimethoxysilyl)propyl) amine The reaction mixture was heated to 120  C and stirred at this temperature for 24 h After cooling to room temperature, the title compound was obtained as an oil after repeated washing with pentane and drying under high vacuum at 50  C Yield: 30.4 g/38.1 mmol (95%) 1H NMR (CDCl3) d 0.67 (t, 2H, J ¼ 7.8 Hz), 1.75 (m, 2H, J ¼ 7.8 Hz), 3.26 (m, 2H), 3.52 (m, 27H) 13C NMR (CDCl3) d 5.59, 16.04, 50.74, 60.72; MS-ESI (m/z (%)) 666.4 (100) [M+]; HRMS (ESI, m/z) [M]+ calcd for C24H60NO12Si4+, 666.3193, found, 666.3197 Materials’ syntheses Material A 1.00 g (1.98 mmol) of precursor was added to a solution of 531 mg sodium hexadecyl sulfate (containing approx 40% of sodium stearyl sulfate) in 35.8 mL of distilled water and 4.0 mL of M hydrochloric acid at 60  C A white precipitate formed after one minute The formed suspension was vigorously stirred for further 20 min, and filtered The surfactant was eliminated by repeated washing with a solution consisting of 200 mL ethanol/10 mL conc hydrochloric acid The material was finally treated with 200 mL ethanol/30 mL ammonia (10 wt% sol in water) in order to get the amine containing silica hybrid material A after drying Yield: 405 mg The materials D and E were synthesized in a similar way from the precursors and 3, respectively Material B CTAB (362 mg) was dissolved in a solution of 23.7 mL of distilled water and 0.3 mL of NH3 (25 wt% solution in water) This mixture was stirred during 60 to give a homogeneous solution 1.00 g (1.98 mmol) of precursor was added to this solution at room temperature A white precipitate appeared after several minutes The suspension was vigorously stirred for a further h and finally allowed to stand at 70  C for 72 h Material B was isolated in the same way as described for material A Yield: 532 mg Material C Firstly an aqueous solution of P123 was prepared from 48.2 g hydrochloric acid (37%), 215 mL of water and 8.7 g of P123 To 4.61 g of this solution were added 800 mg (1.58 mmol) of precursor A white precipitate is formed after 30 The suspension was stirred for a further 20 h at 40  C and was allowed to stand at 70  C during 72 h Material C was isolated in the same way as described for material A Yield: 387 mg Synthesis of amine and ammonium based polysilsesquioxanes We then used the three precursors 1–3 for the synthesis of polysilsesquioxanes Firstly, sol–gel processing of precursor was performed under different reaction conditions Three hybrid materials were obtained by hydrolysis–polycondensation of the pure precursor using anionic (60% sodium hexadecyl sulfate/40% sodium stearyl sulfate), cationic (CTAB) and neutral (P123) surfactants, yielding the materials A, B and C, respectively The syntheses of materials A and C were performed in acidic reaction media whereas material B was prepared in a basic reaction mixture It has to be mentioned that the trisilylated amine is virtually an ionic precursor as it forms the corresponding ammonium salt in acidic medium Consequently, the materials A and C are formed from the ammonium salt of precursor The amine functions were generated after hydrolysis–polycondensation by basic treatment with an ethanol/ammonia solution In order to confirm the structural integrity of the immobilized trialkylamine entities after the hydrolysis–polycondensation processes, we performed solid state NMR experiments with the materials A–C The 29Si OP MAS and 13C CP MAS spectra obtained with material A are given in Fig and The 29Si spectrum shows two signals at À58.4 ppm and À66.7 ppm related to T2 and T3 sites, respectively The higher intensity was observed for T3 substructures, indicating high condensation degree of the solid The complete absence of Q-resonances in the 29Si spectrum indicates that no Si–C bond cleavage occurred during the hydrolysis–polycondensation and reflects the high chemical stability of the precursor towards acidic hydrolysis–polycondensation conditions The 13C CP MAS spectrum of material A (Fig 2, top) shows three signals at 10.4, 20.6 and 57.5 ppm characteristic for n-propyl chains of the precursor These values are in good agreement with the shifts observed in the liquid NMR spectrum of the precursor (Fig 2, bottom) Furthermore, the absence of other signals than those related to the hydrolyzed precursor strongly suggests complete elimination of the surfactant and confirms the absence of residual or newly formed triethoxysilyl groups Similar spectra were obtained both with materials B and C (see ESI†) 29Si OP MAS spectra of these solids showed higher intensities of T3 signals The highest condensation degree was observed in the case of material B, synthesized in basic Results and discussion Precursor syntheses The synthesis of the trisilylated amine precursor was achieved by alkylation of the commercially available 3-aminopropyltrimethoxysilane with 3-chloropropyl-trimethoxysilane in the presence of ethyl-diisopropyl amine The crude precursor was purified by distillation under reduced pressure The ammonium precursors and were synthesized from the trisilylated amine by alkylation using either methyl iodide or 3-iodopropyltrimethoxysilane The ammonium salts and were obtained after washing with pentane and subsequent drying in high purity and excellent yields 3912 | J Mater Chem., 2010, 20, 3910–3917 Fig 29 Si OP MAS NMR spectrum of material A This journal is ª The Royal Society of Chemistry 2010 Published on 18 March 2010 Downloaded by Universitat Politècnica de València on 22/10/2014 04:06:32 View Article Online Fig 13C liquid NMR spectrum of precursor (bottom) and 13C CP MAS NMR spectrum of material A (top) reaction media Q-Signals were not observed These results confirm the chemical integrity of the immobilized amine substructures and reflect high chemical stability of the precursor under the hydrolysis–polycondensation reactions The thermogravimetric analysis of the materials (see ESI†) shows TGA-plots with very similar shape for all three materials The solids show relatively low thermal stability under an air stream The decomposition starts at 240  C, and the total weight loss in all three cases was found to be around 40%, which is in very good agreement with the expected value (39.3%) This result also reflects the complete elimination of the structure directing agents from the as-made materials by washing In this way, the thermogravimetric analysis of the materials A, B and C also confirms the results obtained by solid state NMR experiments Hydrolysis–polycondensation of this trisilylated precursor using various structure directing agents led to materials featuring different textures Fig shows the X-ray diffractograms of the hybrid materials obtained from the pure precursor using anionic (60% sodium hexadecyl sulfate/40% sodium stearyl sulfate), cationic (CTAB) and neutral (P123) surfactants, yielding the materials A, B and C, respectively While amorphous materials were obtained using CTAB and P123 (Fig 3, B and C), structured solids were obtained with anionic surfactants (Fig 3, A) In this latter case, the formation of the solid takes place according to a SÀI+ pathway The presence of ammonium groups formed by protonation of the amine precursor under acid hydrolysis conditions led to enhanced interactions between the anionic surfactant and the cationic precursor and enabled the formation of a nanostructured material showing a high degree of regularity on a mesoscopic scale The X-ray diffractogram of this solid shows a pattern with a sharp and intense reflection at 2q ¼ 2.41 corresponding to a d-spacing of 3.66 nm and weaker reflections at 2q ¼ 4.18 and 2q ¼ 4.82 (d-spacings 2.11 and 1.83 nm, respectively), characteristic for the (100), (110) and (200) reflections of materials with hexagonal architecture From these values, the distance between two pore centers in material A can be calculated to be 4.2 nm Further information concerning the texture of the materials A, B and C were obtained by nitrogen sorption experiments The adsorption isotherms are shown in Fig 4, the pore size distribution curves are shown in Fig and the surface properties are summarized in Table All three materials are highly porous solids with specific surface areas in the range from 700 to 1200 m2 gÀ1 Materials B and C show nitrogen uptake over a relatively large p/p0 range Both adsorption–desorption isotherms show hysteresis phenomena indicating mesoporosity The materials show specific surface areas of 700 and 875 m2 gÀ1 displaying relatively broad pore size distributions centered at 12 and 4.2 nm, respectively (Fig 5, middle and right) In contrast, the nitrogen sorption isotherm of material A shows a type isotherm with a relatively sharp adsorption step in the range from p/p0 ¼ 0.14–0.2, indicating essentially micro- and supermicroporosity and a relatively narrow pore size distribution The pore volume can be estimated to be 0.57 mL gÀ1 The specific Fig Nitrogen adsorption–desorption isotherms of materials A, B and C Fig X-Ray diffractograms of the solids A, B and C (top to bottom) This journal is ª The Royal Society of Chemistry 2010 Fig Pore size distribution curves of the materials A, B and C J Mater Chem., 2010, 20, 3910–3917 | 3913 View Article Online Published on 18 March 2010 Downloaded by Universitat Politècnica de València on 22/10/2014 04:06:32 Table Surface properties of the materials A–E Material SBET/m2 gÀ1 Used surfactant/reaction mixture ˚ Average pore diameterb/A Pore volume/cm3 gÀ1 Texture A B C D E 1220 690 875 575 910 Anionica/acidic Cationic (CTAB)/basic Nonionic (P123)/acidic Anionica/acidic Anionica/acidic 22 120 42 22 20 0.57 1.17 0.80 0.42 0.54 2D hexagonal Amorphous Amorphous 2D hexagonal ‘Worm-like’ a The used anionic surfactant was a mixture of 60% sodium hexadecyl sulfate/40% sodium stearyl sulfate b Pore diameters were calculated by the BJH method from the adsorption branch of the isotherms The materials A, B and C were obtained from precursor 1, whereas the materials D and E were obtained from the precursors and 3, respectively surface area SBET can be estimated to be 1220 m2 gÀ1 and the BJH ˚ XRD, TEM and nitrogen sorption average pore diameter 22 A experiments give concordant results and indicate that material A is a highly porous solid featuring a regular hexagonal architec˚ (Fig 5, left) and wall ture with an average pore diameter of 22 A ˚ thickness of approx 20 A Thus, the characterization of the materials A–C indicates that the amine precursor can be used for sol–gel processing without chemical decomposition or bond cleavage of the organic substructure Hydrolysis–polycondensation of compound led to the formation of highly porous materials The main result of this study concerns the structuring of the materials The generation of solid phases displaying a highly regular architecture on a mesoscopic length scale and narrow pore size distribution was only observed with anionic structure directing agents under acidic reaction conditions This result can clearly be attributed to specific interactions between the cationic ammonium precursor and the anionic surfactant as illustrated in Scheme On the other side, the formation of materials with pore diameters in the range of nm is rather typical for template assisted hydrolysis–polycondensation using nonionic surfactants as observed in the synthesis of material C.51 However, the lyotropic arrangement of the surfactant in the hydrolysis–polycondensation mixture seems to be disturbed by the presence of the protonated precursor as the obtained solids not show a regular architecture Finally, the utilization of CTAB gives the material with the largest average pore diameter It has to be stressed that the formation of material B took place under alkaline reaction conditions Contrary to the syntheses of the materials A and C, this reaction involves the sol–gel transformation of the neutral amine precursor The formation of materials displaying pore diameters bigger than 10 nm is rather untypical for the utilization of cationic CTAB surfactant and Scheme Sol–gel processing of cationic precursors using anionic structure directing agents according to an SÀI+ pathway 3914 | J Mater Chem., 2010, 20, 3910–3917 suggests the formation of larger aggregates in the hydrolysis– polycondensation mixtures These results prompted us to generalize this new strategy for the synthesis of structured materials using the cationic precursors and in the presence of anionic surfactants Hydrolysis– polycondensation reactions were carried out under similar reaction conditions as applied for the synthesis of material A using a mixture of 60% sodium hexadecyl sulfate/40% sodium stearyl sulfate as structure directing agent in acidic media In this way, the materials D and E were obtained from the precursors and 3, respectively The characterization of the obtained solids by 29Si and 13C solid state NMR spectroscopy indicated the structural integrity of the immobilized ammonium substructures Contrary to the materials A, B and C, synthesized from the amine precursor 1, the 29Si OP MAS spectra of the materials D and E show higher intensities for the T2 signals This result indicates a lower condensation degree in the case of the materials obtained from tetraalkylammonium precursors and This result can be attributed to the basic treatment of the materials A, B and C either during hydrolysis–polycondensation or during washing giving a higher condensation degree in these materials The X-ray diffractograms of these two new materials D and E are shown in Fig together with a diffractogram of material A Whereas the diffractogram of material A clearly displays the reflections characteristic for materials with hexagonal architectures (vide supra), the reflections in the diffractogram of material D are less well defined The (100) reflection in the diffractogram of this material is broader, and the (110) and (200) reflections can hardly be identified The diffractogram of material E only shows Fig X-Ray diffractograms of the solids A, D and E (top to bottom) This journal is ª The Royal Society of Chemistry 2010 Published on 18 March 2010 Downloaded by Universitat Politècnica de València on 22/10/2014 04:06:32 View Article Online a broad (100) reflection The position of the (100) reflections is nearly unchanged in all three cases This result clearly indicates a decreasing structural regularity in these materials in the order A–D–E The material A obtained from the amine precursor shows the highest order whereas material E obtained from the tetrasilylated ammonium precursor is the lowest structured material in this series These results were confirmed by electron microscopy Scanning electron microscopy (SEM) micrograph of material A (Fig 7, upper-left) shows agglomerated particles with a diameter of approx mm TEM image of a Cu(I)-impregnated sample of A shows a regular hexagonal array of 2D aligned channels with high degree of structural regularity (Fig 7, upper-right) The SEM micrograph of material E (Fig 7, lower-left) shows a rough material with agglomerated particles of much smaller size in the range of 100–200 nm The TEM micrograph (Fig 7, lower-right) shows a porous material with a less defined architecture Although well structured domains are visible by transmission electron microscopy, the X-ray diffractogram of material E indicates the formation of a material with low long-range order The results obtained from XRD and TEM concerning the texture of the materials A, D and E were confirmed by nitrogen sorption experiments The isotherms of the materials are as given in Fig The isotherm of material A shows a type isotherm with a relatively sharp adsorption step in the range from p/p0 ¼ 0.14–0.2 A similar isotherm was obtained with material D However, this material shows lower nitrogen uptake indicating lower specific surface area and pore volume Accordingly, the specific surface area SBET of this material was found to be only 574 m2 gÀ1 In contrast, the isotherm obtained with material E displays no inflexion at 0.1 < p/p0 < 0.15 as observed in the isotherms of A and D, but only a lower defined N2 uptake at relative pressures p/p0 < 0.3 This phenomenon indicates broader pore size distribution within material E The specific surface area of this material was found to be slightly lower as in the case of material A (SBET ¼ 908 m2 gÀ1) The surface properties of the materials D and E are summarized in Table together with the data for the materials A–C Fig SEM (left) and TEM (right) images of material A (upper) and E (lower) This journal is ª The Royal Society of Chemistry 2010 Fig Nitrogen adsorption–desorption isotherms of material A, D and E These results clearly indicate that sterical shielding of the cationic center by alkyl chains within the compounds 1, and has a direct impact on the texture in the materials obtained from sol–gel processing of these precursors As illustrated in Scheme 3, the trialkylammonium salt formed from precursor allows the highest surfactant–precursor interaction Furthermore, a hydrogen bonding contribution between precursor and anionic surfactant cannot be excluded In contrast, the cationic tetraalkylammonium groups of precursors and limit the surfactant– precursor interaction and therefore led to the formation of lower structured solids, in particular in the case of the tetraalkylammonium salt Another indication for the decisive influence of ionic precursor–surfactant interaction on the structuring of the PMO type materials was obtained from hydrolysis–polycondensation procedures in alkaline reaction media Precursors and were transformed into the corresponding hybrid materials in the presence of hexadecyl sulfate anions Whereas the material D-OH, obtained from 2, showed similar architecture compared to the related material D (Fig 9), the X-ray diffractogram of material A-OH, obtained from precursor 1, does not show any reflections This result highlights that the presence of a cationic center within the precursor is essential for the generation of structured phases as it enables ionic interactions with the anionic structure directing agents Scheme Ionic precursor–surfactant interactions between the protonated form of precursor (upper) and precursor (lower) with long-chain substituted sulfonates J Mater Chem., 2010, 20, 3910–3917 | 3915 View Article Online Published on 18 March 2010 Downloaded by Universitat Politècnica de València on 22/10/2014 04:06:32 Notes and references Fig X-Ray diffractograms of the solids D, D-OH and A-OH (top to bottom) Conclusions We report the synthesis of new periodic mesoporous organosilica based on amine and ammonium building blocks These materials were obtained by hydrolysis–polycondensation procedures of the pure amine or ammonium precursors without addition of silica network formers The importance of the study is two-fold Firstly, we describe the synthesis of functional mesoporous hybrid materials with high potential in catalysis and separation, in particular for the immobilization of metallic species via the formation of coordination complexes or anion exchange reactions Nanostructured silica containing amine functions are versatile materials for diverse applications in heterogeneous catalysis and separation,52–56 and silica hybrid materials bearing cationic substructures are versatile solid phases for anion exchange reactions and have therefore found widespread utilization as exchange resins.57–61 The immobilization of anionic catalytic species via anion exchange reactions gives rise to the formation of heterogeneous catalysts.62,63 Regarding the formation of the nanostructured and mesoporous materials, we describe here the first synthesis of periodic mesoporous organosilicas using anionic surfactants as structure directing agents following an SÀI+-mechanism This study highlights that specific precursor–surfactant interactions in the sol solution are essential for the formation of structured materials We show that the substitution pattern of the cationic ammonium center has high importance for the interaction with the anionic template, which is determinant for the architecture of the formed materials The materials displaying highest structural regularity were obtained from protonated trialkylammonium precursors The use of a related tetrapropylammonium precursor containing a more shielded cationic nitrogen center led to solids with worm-like architectures under identical hydrolysis–polycondensation conditions In general, this approach opens the door for the elaboration of new porous and nanostructured solids bearing ionic functional groups Acknowledgements The authors thank P Gaveau (Institut Charles Gerhardt de Montpellier) for solid state NMR measurements P Hesemann 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applications in heterogeneous catalysis and separation,52–56 and silica hybrid materials bearing cationic substructures are versatile... hybrid materials were obtained by hydrolysis–polycondensation of the pure precursor using anionic (60% sodium hexadecyl sulfate/40% sodium stearyl sulfate), cationic (CTAB) and neutral (P123) surfactants, ... ethyl-diisopropyl amine The crude precursor was purified by distillation under reduced pressure The ammonium precursors and were synthesized from the trisilylated amine by alkylation using either