Yi Meng Wang

Fabrication of photoluminescent ZnO/SBA-15 through directly dispersing zinc nitrate into the as-prepared mesoporous silica occluded with template

Photoluminescent ZnO/SBA-15 mesoporous materials are prepared by directly grind zinc nitrate into the as-prepared samples occluded with template, and this solvent-free method not only saves time and energy, but also enables a large amount of zinc oxide to be highly dispersed in the channels of mesoporous silica. The resulting composites exhibit photoluminescence (PL) properties with the ZnO quantum confinement, and the dispersed ZnO in SBA-15 illustrates a similar UV emission to crystalline ZnO nanostructures. Besides, this photoluminescence is used to try to detect the nitrosamine content in solution by quenching PL spectra for the first time, suggesting potential applications of ZnO/SBA-15 in sensing carcinogens such as N′-nitrosonornicotine (NNN) in the environment.

Solvent-free surface functionalized SBA-15 as a versatile trap of nitrosamines

Dispersion of copper oxide via a solvent-free method enables mesoporous silica SBA-15 to become a versatile trap of nitrosamines, exhibiting a high capability to capture volatile nitrosamines and tobacco special nitrosamines (TSNA). 3%CuO/SBA-15 can remove 85% of N-nitrosopyrrolidine (NPYR) in gaseous flow, one fifth more than that by the analogous via one-pot method, while 5%CuO/SBA-15 traps all N-nitrosonornicotine (NNN) in solution with a concentration of 0.6 mmol l−1, superior to NaY zeolite. The dispersion of the copper guest in SBA-15 is assessed by XRD, H2-TPR, NO2-TPD and UV-Vis methods.

Adsorption and room temperature degradation of N-nitrosodiphenylamine on zeolites

N-Nitrosodiphenylamine (NDPA) is selected as a model compound to reveal the specific adsorption and catalytic function of zeolites in the removal of carcinogenic nitrosamines from the environment. The bulky NDPA molecule is indeed adsorbed in the zeolite KA having a small aperture, by insertion of the –N–NO group into the channel and involving a specific interaction between the nitrosamine and the zeolite. Degradation of NDPA at room temperature on zeolite is reported for the first time, revealing the potential applicability of zeolites to eliminate nitrosamines under mild conditions. The acidity of zeolite is the key factor determining its ability to degrade NDPA and, among the zeolites evaluated, Hβ is the most effective catalyst with an activity much higher than that of other zeolites at ambient temperature.

One-step synthesis of hierarchical pentasil zeolite microspheres using diamine with linear carbon chain as single template

Hierarchical zeolite microspheres were synthesized via a one-step method using a diamine with a linear carbon chain as the single template, where no secondary template and additives were added. The obtained microspheres possessed significant textual porosity (up to 0.24 cm3 g−1), which was tuneable by carefully choosing diamines with different length hydrocarbon chains and the amount of aluminium in the synthetic mixture. The zeolite microspheres not only possessed high activities in catalytic applications but also curtailed to some extent filtration difficulties in their preparation and application. During the hydrothermal synthesis, zeolite nanocrystals (50 nm) were formed and spontaneously assembled into uniform microspheres in size of 5–8 μm following a particle–particle aggregation mechanism.

Synthesis and catalytic properties of multilayered MEL-type titanosilicate nanosheets

Multilayered MEL-type titanosilicate nanosheets (MTS-2) were hydrothermally synthesized through a dual-template method, using cetyltrimethylammonium tosylate (CTATos) and tetrabutylammonium hydroxide (TBAOH) as templates for mesopores and micropores, respectively. The mismatch of nanocrystals and mesophase was minimized by decreasing the size of primary zeolite particles, taking advantage of MEL-type zeolite that tends to form nano-sized crystallites. The titanosilicate nanosheets possess both MEL zeolitic structure and large volume of intersheet mesopores without the formation of a physical mixture of bulky zeolites and mesoporous materials. Moreover, it exhibited improved catalytic activities for bulky molecules compared to those of other ordered mesoporous materials and conventional MFI- and MEL-type titanosilicates, where post-treatment of as-made MTS-2 samples using NH4F could reduce the silanols, and thus enhance their hydrophobicity and epoxidation activity.

Preparation of hierarchically structured Y zeolite with low Si/Al ratio and its applications in acetalization reactions

Hierarchically structured Y zeolites were prepared by a post-synthetic strategy, where the as-made NaY zeolite was sequentially treated by a lactic acid solution and an alkaline solution containing cetyltrimethyl ammonium bromide (CTAB). Many techniques, including X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), N2 adsorption–desorption, Fourier-transform infrared spectroscopy (FT-IR), Thermogravimetric analysis (TG-DTG) and NH3 Temperature Programmed Desorption (NH3-TPD), were applied to characterize the chemical and textural properties of the samples. The results show that lactic acid pre-modification of NaY zeolite may cause on the one hand Na+ cation removal by proton exchange and on the other hand the dealumination of the zeolite framework with the formation of amorphous silicon-rich species offering nutrients for the fabrication of mesoporosity. After alkaline treatment in the presence of surfactant CTAB, mesoporosity can be successfully introduced into the NaHY zeolites with the microporous structures well preserved. Furthermore, the hierarchically structured Y zeolites exhibit much better performances in the acetalization reactions with large sized molecules involved. This could be attributed to the enhanced diffusion ability of large sized guest molecules through the combination of mesoporosity and microstructures compared with pure microporous Y zeolites.

One-step synthesis of mesoporous ZSM-11 composites through a dual-template method

Hierarchical porous ZSM-11 composites were hydrothermally synthesized through a one-step route using binary templates of cetyltrimethylammonium tosylate (CTATos) and tetrabutylammonium hydroxide (TBAOH). Influences of aluminum content and crystallization temperature on the morphology and structure were investigated. Powder X-ray diffraction (XRD) and N2 physisorption results show that the mesoporous ZSM-11 composites possess both a considerable mesoporous structure and zeolitic MEL-structure. Moreover, a large amount of aluminum in the gel composition slows the rate of zeolite crystallization, while a high SiO2/Al2O3 ratio is beneficial for the synthesis of mesoporous ZSM-11 without any phase separation. Mesoporous ZSM-11 aluminosilicates were compared to pure ordered mesoporous materials, zeolites and a mechanical mixture of meso and microphases for their catalytic activity in low-density polyethylene (LDPE) pyrolysis. The results suggest that all mesoporous ZSM-11 composites show higher catalytic performance for LDPE cracking.

Synthesis of hierarchical ferrierite using piperidine and tetramethylammonium hydroxide as cooperative structure-directing agents

Zeolite ferrierite aggregates with hierarchical porosity were synthesized using TMAOH and piperidine as cooperative structure-directing agents (co-SDAs). The effect of the relative amount of TMAOH and piperidine on the crystalline phase and textural properties of the products was investigated. Ferrierite aggregates synthesized herein were ca. 10–15 μm in size, comprised of nanosheets with thickness of less than 50 nm. The ferrierite aggregates possessed similar acidity and crystallinity with respect to the bulk ferrierite prepared using only piperidine as SDA, but exhibited more than 3 times higher mesopore surface area. The ferrierite aggregates with hierarchical porosity were found to be more efficient in catalytic LDPE cracking due to improved accessibility of large polymer molecules to the active sites.

Fabrication of mesoporous Al-SBA-15 as a methylene blue capturer via a spontaneous infiltration route

Different amounts of aluminum (Al) species were infiltrated and incorporated into SBA-15 by grinding the mixture of aluminum nitrate and SBA-15 followed with a subsequent calcination. A novel series of methylene blue adsorbents were thus obtained and characterized by X-ray diffraction, N2 adsorption–desorption, Fourier transform infrared and 27Al Nuclear Magnetic Resonance (NMR) techniques. Results show that the newly synthesized Al-SBA-15 materials have well-preserved mesostructures, high BET surface areas, enlarged pore sizes and predominantly tetrahedrally coordinated Al species. All Al-SBA-15 materials show a greater adsorption capacity to methylene blue than SBA-15, where the sample (Al/Si = 0.05) has the largest capacity to remove MB from water solution. Diffuse reflectance measurements, Langmuir and Freundlich equations and the pseudo-second-order kinetic model were further used to describe the adsorption behavior of MB onto SBA-15 and Al-SBA-15 materials. Finally, recycling tests were performed to evaluate the stability of the Al-SBA-15 material and the textural and NMR properties of the used samples were also detected.

From ill-resolved atomic to ZSM-5 type of ordering in mesoporous lamellar aluminosilica nanoparticles

Mesoporous lamellar aluminosilicate–surfactant nanoparticles as small as 50 nm can be hydrothermally synthesized at 140 °C using a mixture of cationic and anionic surfactants as a templating agent and tetrapropylammonium cations (TPA+), known to be the structure directing agent of the MFI type of zeolite. The nanophases exhibit some ill-resolved atomic ordering after 1 to 3 d of crystallization. A definitive ZSM-5 ordering occurs for longer crystallization times, concomitant with a progressive contraction of the lamellar array. In most cases, calcination at 550 °C leads to a collapse of the lamellar structure, while the zeolitic ordering is preserved. For short crystallization times, the lamellar structure with its atomic ordering is maintained when the aluminium source is the nitrate salt, instead of Al(OH)3 or Boehmite. Then, after 3 d of crystallization, highly porous systems are produced with a surface area of ∼650 m2 g−1 and pore volume of ∼1.1 cm3 g−1. For longer crystallization time, the collapse of the lamellar phase under calcination does not affect the well-defined ZSM-5-like atomic ordering and leads to non-faceted nanoparticles of ca. 200 nm size with rugged shapes. These conclusion are supported by cross investigations using X-ray diffraction patterns, infrared spectra, scanning electron microscopy and high-resolution transmission electron microscopy with selected area electron diffraction. The ordering of the inorganic sheet of the aluminosilicate–surfactant mesophase is likely favoured by the high diffusion rate of TPA+ in the nanosized particles.