Nanostructure Silica Prepared With Organogels As Template And Its Formation Mechanism

Recently, the use of organic compounds as templates for the generation of inorganic structures and materials has been receiving considerable attention. Low molecular weight organic gelators have become the focus of much attention. The gelator molecules self-assemble to form three-dimensional networks superstructures which are used as versatile building blocks in organogels and as templates for sol-gel transcription into nanostructured silica.In this dissertation, a bis-(4-stearoylaminophenyl) methane (BSAPM) organogelator based on 4, 4'-diaminodiphenylmethane was synthesized and possessed a versatile gelation ability. Multi-morphologic nanostructured SiO2 materials with controlled morphologies were prepared successfully by hydrolysis and polycondensation of a tetraethoxysilane (TEOS) precursor through a sol-gel transcription with the self-assembled organic superstructures of BSAPM as template. The addition of cation surfactant, metal-salt, silica precursor and hydrochloric acid will influence the transcription of the organogel as template. The fluorescence of nanostructured silica transcripted from the template method was investigated. On the other hand, the mainly driver of the aggregation of gelator molecules into fibrous network was studied by variable temperature FTIR spectra method.1. Three organogelators were synthesized and characterized by FTIR, 1H NMR and MS. Their gelation abilities of these gelators were evaluated in organic solvents under 1.0 wt %, indicating that the BSAPM possess a versatile and excellent gelation ability. The gelator BSAPM can gelate protic solvents (such as DMSO, DMF, benzene and toluene, etc) and alkyl alcohols. The phase transition temperatures (Tgel) of these organogels were determined by differential scanning calorimetry (DSC). Tgel of BSAPM gel was increased with concentration increasing of BSAPM gelator in n-butanol and boil point increasing of solvents in different organic solvents (such as n-butanol, xylene, DMF and DMSO). Moreover, the different molecular structure of gelator will lead to changes of Tgel.2. SEM, TEM and AFM observations of these nanostructured silica which transcripted from organogel as templates, showed various morphologies (such as stick-like, flake, tublar and granular, etc.). The nanostructured silica with controlled morphology was obtained by the addition of different solvents, cation surfactant, metal-salt and silica precursor in organogel systems. The silica obtained from n-butanol, xylene, DMSO and DMF had fibrous, stick-like, curly and thin flake nanostructured silica, respectively. All kinds of morphologies silica was obtained simply only by changed solvents in the template method. The silica obtained from n-butanol had changes from fibrous aggregation, flake stack, flake incurvate to tube like and granular with concentration increasing of cation surfactant (CTAB), whereas in the presence of A-1891 had a stick-like structure uniformly featuring the smooth surface and multi-layer wall with diameters of 100 nm and lengths of a few micron. The cationic charge generated by protonation of gelator and surfactant play a crucial role in the creation of such tube and stick like. These results indicate that various and novel silica can be prepared by transcription using various superstructures in one organogel as a template.3. The fluorescence property of nanostructured silica was validated by fluorescence spectrophotometer and microscopy. The blue light emission was stable and intense by ultraviolet excitation (330-380 nm) whereas the green and red emission was weak by blue and green (450-480 nm and 510-550 nm, respectively). The fluorescence spectra of nanostructured silica is Exmax=261 nm, Emmax=365 nm. The excitation curve had a symmetrical distribution. The emission curve had an intense main peak with two weak peaks at 279 nm and 304 nm. The different nanostructured silica has indistinct spectra. And that, the nanostructured silica was amorphous through FTIR, XRD and XPS. The nanostructured silica with two pore size distribution of 10-30 nm and 1000-2000 nm had a BET surface area of 148.51 m2/g. The XPS spectra of nanostructured silica displayed mainly O and Si peaks. Their peaks area revealed that the atomic ratio of O to Si is about 2:1. The spectrum of deconvoluted into multiple sub-peaks of Si2p peak (at103.87 eV, Si2p1/2 and 103.08 eV, Si2p3/2) indicated that nanotubes were composed of silica. The peaks area ratio of Si2p1/2 to Si2p3/2 is about 1:1.4, meaning there were Si- appended bonds in the surface of materials. The Si-O and Si- on the inner and outer surface presumably play an important role in the strong blue light emission of the nanotubes4. The gelation mechanism of BSAPM organogel from n-butanol was studied by FTIR, UV and FL spectra with variable temperature. The rudimental experiments results indicated that the organogel was very stable at 5-25℃and the intermolecular hydrogen-bonded play core role in the gelation process. Presumably, the BSAPM gel structure of 1-butanol system was self-assembled three dimension network mainly by intermolecular hydrogen-bonded cooperating with benzene ringπ-πconjugated. The variable temperature UV and FL spectra were important means for study of gel from gelator with aryl.5. The intensity and trend of hydrogen-bonded was investigated primarily with increasing temperature by FTIR in BSAPM organogels. Their weak changes would affect distinctly the aggregation of gelator. The aggregation of BSAPM molecular into fibrous network was driven mainly by hydrogen-bonded interaction in different gelatinized solvents. The intensity of hydrogen-bonded interaction may be decided to couple and twist between aggregation fibrous. On the other hand, different molecular structure of gelator would generate different aggregation morphologies of organogel. The aggregation fibrous of organogel from n-butanol was twisted owing to introducing one unsaturation of aliphatic alkyl chain in BSAPM gelator molecular structure and the nanotube of organogel from n-butanol was obtained due to 4, 4'-diaminodiphenyl sulphone instead of 4, 4'-diaminodiphenylmethane in BSAPM gelator molecular structure.In summary, the various novel nanostructured silicas with blue fluorescence can be prepared by transcription using various superstructures of the small molecular organogels as a template. The formation mechanism of the organogel superstructures was investigated primarily. It is very important that these results could also be expected to get further investigation and show great advantages for future preparation and application of nanostructured silica.