P6mm Structure Research Articles

Tryptophan functionalized framework of nanoporous material as fluorescent sensor for trace detection of Zn2+ ions

A novel fluorescent sensor of tryptophan functionalized mesoporous silica (Trp-Meso-Si) for detecting Zn2+ ion was designed by modifying the framework of nanoporous material with Tryptophan organic silicon source under the template via co-condensation method. Tryptophan organic silicon source was first synthesized by selecting natural amino acid as reagent via multi-steps reactions. The sensing material Trp-Meso-Si was well characterized by various spectroscopic techniques. The results indicate that material 5%-Trp-Meso-Si with low amounts of Tryptophan exhibits well-ordered one-dimensional hexagonal P6mm structure. However, the sample 15%-Trp-Meso-Si with high amounts of Tryptophan shows strongest fluorescent intensity at the same excited wavelength of 285 nm. All the materials Trp-Meso-Si indicate fluorescent signal at excited wavelength because of tryptophan as fluorophore moiety. In the fluorescent recognition experiments, Trp-Meso-Si could selectively and sensitively detect trace concentrations of Zn2+ ions in aqueous solution with satisfactory detection limits of 0.9 × 10−7 M. Tryptophan within the framework of mesoporous silica material showed strong affinity for Zn2+ ions according to a 3:1 ratio of [tryptophan] and [Zn2+] by plenty of groups with lone pair electrons.

Amphiphilic ABC triblock terpolymer templated large-pore mesoporous silicas

The mesoporous silicas with two dimensional p6mm structure and interconnected three dimensional porous structure with large pore size of 16.9–18.0nm were synthesized by the self-assembly of amphiphilic ABC triblock terpolymer, co-structure directing agent and silica source.

Amphiphilic ABC triblock terpolymer templating for mesoporous silica

Self-assembled triblock terpolymers have attracted intense attention in recent years because of their abundant variety of assembly mesostructure. We reported the synthesis of mesoporous silica materials with the amphiphilic ABC triblock terpolymer polyethylene-poly(ethylene oxide)-polycaprolactone(PE-PEO-PCL) as a template and tetraethoxysilane(TEOS) as a silica source. Increasing the hydrophilic head group(PEO) led to the decrease of packing parameter g, which gave rise to the mesophase transformation from a cylindrical two-dimensional hexagonal P6mm structure to a cage-type face centered cubic closed-packing mesostructure. This new templating route provided a new insight into the template factor governed inorganic-organic self-assembly mesophases.

Templated synthesis of highly ordered mesoporous cobalt ferrite and its microwave absorption properties

Based on the nanocasting strategy, highly ordered mesoporous CoFe2O4 is synthesized via the ‘two-solvent’ impregnation method using a mesoporous SBA-15 template. An ordered two-dimensional (P6mm) structure is preserved for the CoFe2O4/SBA-15 composite after the nanocasting. After the SBA-15 template is dissolved by NaOH solution, a mesoporous structure composed of aligned nanoparticles can be obtained, and the P6mm structure of the parent SBA-15 is preserved. With a high specific surface area (above 90 m2/g) and ferromagnetic behavior, the obtained material shows potential in light weight microwave absorption application. The minimum reflection loss (RL) can reach −18 dB at about 16 GHz with a thickness of 2 mm and the corresponding absorption bandwidth is 4.5 GHz.

Fabrication of metallic platinum doped ordered mesoporous titania–silica materials with excellent simulated sunlight and visible light photocatalytic activity

A facile method to prepare metallic platinum doped ordered mesoporous titania–silica materials (Pt–TiO2/SiO2) was demonstrated by using P123 as the soft template. The materials exhibited anatase and rutile biphase with the ratio of 63:37; meanwhile, they possessed 2D hexagonal p6mm structure with large pore size and high surface area. Pt–TiO2/SiO2 materials were used as efficient photocatalysts to degrade two aqueous light insensitive compounds, p-nitrophenol and bisphenol A, under the light irradiation in the region of 320–680nm (simulated sunlight) and 400–680nm (visible light). For comparison, 3D interconnected Pt–TiO2/SiO2, Pt-free TiO2/SiO2, and pure TiO2 were also tested under the identical conditions. The enhanced photocatalytic activity of the ordered mesoporous Pt–TiO2/SiO2 was obtained and then explained in terms of unique porosity, anatase and rutile biphase structure, and strong electron capturing ability as well as surface plasmon resonance (SPR) absorption of metallic Pt.

Synthesis and Characterization of Ordered Mesoporous Carbon/Silica Hybrid Thin Films

Carbon/silica nanocomposite films with a hexagonal P6mm structure were fabricated directly by the oxidation and carbonization of surfactant/silica nanocomposite films, which were obtained by a dip-coating technique through a combination of sol-gel and evaporation-induced self-assembly. The as-synthesized nanocomposite films were characterized by scanning electron microscopy, X-ray diffraction, transmission electron microscopy and N2 adsorption-desorption. These analyses reveal that the carbon/silica nanocomposite films, with a narrow pore size distribution of mesopores, have an ordered symmetric structure. The pore sizes of this hybrid film can be controlled within a certain range by changing the carbonization temperature. In addition, the films are composed of a continuous silica matrix and a continuous carbon coating in about 1 nm adhered well to the silica matrix. The formation of carbon coatings from surfactant acts as a framework support to prevent the pore size of the silica matrix from shrinking.

Expansion of the F127-templated mesostructure in aerosol-generated particles by using polypropylene glycol as a swelling agent

Expansion of the mesostructure in aerosol-generated particles was performed through incorporation of polypropylene glycol (PPG), a non-volatile swelling agent. TEOS was used as silica source and the Pluronic block copolymer, F127, as template. The ratio of TEOS to F127 was kept constant during synthesis, while varying the weight ratio of PPG to F127 systematically. The impact of the PPG on the expansion of the structure was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and nitrogen adsorption. Different methods were used to calculate the pore size distributions, the BJH, the BdB-FHH, the KJS and the NLDFT method. Simple geometrical models of the expansion were derived to interpret the experimental data and establish their accuracy. Experimental data showed a roughly linear expansion of the unit cell and pore size, consistent with that expected by modelling the swelling of a hexagonal ( p6mm) structure assuming constant wall thickness. The expansion is increasing as a function of increasing PPG/F127 ratio by about 25 Å. An expression of the density of the silica wall was calculated from the models resulting in a density of 1.95 ± 0.2 g/cm 3. At a PPG/F127 ratio of approximately 0.31, the p6mm structure (found at lower PPG/F127 ratios) transforms to a microemulsion-templated foam structure. At an even higher PPG/F127 ratio (0.63–1.56), phase separation of the oil from the swollen template occurred, yielding a two-phase system of coexisting foam and large vesicles.

Synthesis of magnetically separable ordered mesoporous carbons using furfuryl alcohol and cobalt nitrate in a silica template

Synthesis of ordered mesoporous carbons containing Co, Ni, and Fe nanoparticles within the mesostructure was performed through carbonization of poly(furfuryl alcohol) in the presence of metal nitrate inside SBA-15 mesoporous silica templates. The use of the transition metal nitrates, instead of Al catalyst, led also to the formation of highly ordered mesoporous carbons having the same structure as CMK-3. The 2-dimensionally hexagonal p6mm structure was constructed from a regular array of uniform nanopores (typically 4–5 nm in diameter) and carbon frameworks (typically 4 nm in thickness). The state of the materials during the carbonization process was characterized by X-ray diffraction, nitrogen physisorption, transmission electron microscopy, and X-ray absorption fine structure spectroscopy of the metal elements. The results showed that metal nanoparticles, 25–40 nm in diameter, were embedded inside the mesoporous carbon networks. The nanoparticles were formed due to spontaneous reduction of the metal elements during carbonization, following the initial action as a catalyst for the polymerization of furfuryl alcohol. The magnetic hysteresis loop for the cobalt-containing carbon showed soft ferromagnetic behaviour at room temperature. In particular, the cobalt nanoparticles could be protected against acidic erosion by repeating impregnation and polymerization of furfuryl alcohol once more before its carbonization treatment. The process is proposed as a method for preparation of magnetically separable mesoporous carbons, for application as an adsorbent or catalyst support.

Organosilica Copolymers for the Adsorption and Separation of Multiple Pollutants

Benzene, diethylbenzene, and ethylenediamine-bridged bistrialkoxy precursors were used in the synthesis of multifunctional PMO copolymers for the adsorption of phenols and metal ions. Polyoxyethylene(10) stearyl ether (Brij 76) was used as the structure director with the surfactant template approach in the synthesis. The resulting PMO copolymers with two or more bridging groups have been characterized by nitrogen gas adsorption, powder X-ray diffraction, and 13C and 29Si solid-state NMR. These organosilicas exhibit large surface areas, narrow pore size distributions, large total pore volumes, and pore ordering consistent with well ordered, hexagonally packed p6mm structures. Minimal competitive effects were observed on the adsorption of p-chlorophenol to the copolymers in the presence of copper ions in solution. Similarly, the presence of p-chlorophenol in solution or adsorbed onto the copolymers did not interfere with copper adsorption. Replacement of a small portion of the benzene bridge in the 90:10 BENZ:EDA copolymer with diethylbenzene produced a copolymer 2.5-fold more efficient for p-chlorophenol adsorption. ICP analysis revealed that greater than 98% of adsorbed copper was removed during extraction with HCl, and this extraction process can be repeated with no difference in copper adsorption after regeneration.

Highly ordered periodic mesoporous ethanesilica synthesized under neutral conditions

Highly ordered mesoporous ethanesilica (MES) with 2D hexagonal structure was synthesized from 1,2-bis(trimethoxysilyl)ethane under neutral conditions for the first time. Divalent salts, such as NiCl2, MgCl2, ZnCl2, ZnSO4 and Zn(NO3)2, were used to help the formation of the ordered mesostructure. The MES samples were characterized by powder X-ray diffraction, nitrogen sorption, transmission electron microscopy, FT-IR, 13C and 29Si solid-state NMR and thermal gravimetric analysis. A phase transition from a disordered wormhole-like structure to an ordered P6mm structure was observed upon the addition of inorganic salts. The pore size of the MES decreases from 4.7 to 3.9 nm with increasing content of the inorganic salts. Fluoride was also found to be important for the formation of ordered MES under neutral conditions.

Synthesis, characterization and catalytic activity of cubic Ia3d and hexagonal p6mm mesoporous aluminosilicates with enhanced acidity

Through a two-step crystallization procedure, an ordered mesoporous aluminosilicate with cubic Ia3d structure denoted as MB48 has been synthesized from the assembly of preformed zeolite beta precursors, utilizing cetyltrimethylammonium bromide (CTAB) as a template. By adjusting the alkalinity during the second crystallization step, an ordered mesoporous aluminosilicate with hexagonal p6mm structure named as MB41 has also been prepared. MB48 and MB41 were characterized with PXRD, FTIR, 27Al-MAS NMR, N2 adsorption–desorption and NH3-TPD techniques, etc. Experiments show that both MB48 and MB41 are pure mesoporous phases, containing the secondary structural units of zeolite beta. Compared with conventional mesoporous aluminosilicates, MB48 and MB41 have enhanced acidity and show higher catalytic activity in the cracking of cumene and the phenol alkylation with tert-butanol.

Crystal structure and hydrogen occupation of LaNi4.9Al0.1Dx (5.0 ≤ x ≤ 6.1) on the desorption isotherm studied by in situ neutron powder diffraction

We performed in situ neutron powder diffraction measurements of LaNi4.9Al0.1Dx along the desorption P–C isotherm using 90° banks of a TOF diffractometer. Structure of the hydride phase for various hydrogen contents was determined by Rietveld refinement. Variation of hydrogen site occupation in the hydride phase was clearly observed. The full hydride LaNi4.9Al0.1D6.1 has a P6mm structure with four hydrogen sites; 3c sites (O[La2Ni4]) with occupancy of 0.95(2) and three T sites, 6e1 (T[La2Ni2]), 6e2 (T[La1Ni3]) and 2b (T[Ni4]), with occupancies of 0.324(6), 0.195(6) and 0.22(1), respectively. In the two-phase region, the hydride phase has the limiting composition LaNi4.9Al0.1D5.0. Decreased hydrogen content from x = 6.1 to 5.0 in the hydride phase involved decrease of occupation in all sites, but behavior of the decrease depended on the sites. The 3c and 6e1 sites are preferably occupied in the limiting composition, whereas extra occupation caused by hydrogen solution in the hydride single-phase region is most preferable in the 6e2 sites.