Nanoparticles zeolites

Colloidal zeolites have been used as building blocks to fabricate hierarchical porous materials. Infiltrating ethanol sol of zeolite nanoparticles into an ordered array of polystyrene spheres resulted in macroporous zeolites, which involves a self-assembly process. After ethanol evaporation, zeolite nanoparticles were aggregated by capillary forces. High concentration of external silanol groups favored the formation of hydrogen bonds between particles and eventually Si-O-Si bonds after calcination. The method has been further developed to produce transparent and self-standing zeolite membranes with controlled mesoporosity. Concurrently, the preformed zeolite-coated polystyrene spheres have been... 

The strategy of this method is to utilize the inherent porosity of bulky substrates in the construction of hierarchical stractures by incorporating additional pore systems. Diatoms are unicellular algae whose walls are composed of silica with an internal pore diameter at submicron to micron scales. Zeolitization of diatoms, in which zeolite nanoparticles are dispersed on the surface of diatoms followed by a hydrothermal conversation of a portion of the diatom silicas into zeolites, resulted in the formation of a micro/mesoporous composite material. Similarly, wood has also been used as a substrate to prepare meso/macroporous composites and meso/macroporous zeolites. After the synthesis, wood is removed by calcination. ... 

Finally, zeolite nanoparticles have been used as building blocks to construct hierarchical self-standing porous stmctures. For example, multilayers of colloidal zeolite crystals have been coated on polystyrene beads with a size of less than 10 p,m [271,272]. Also, silicalite-1 membranes with a thickness ranging from 20 to several millimeters and controlled mesoporosity [273] have been synthesized by the self-assembly of zeolite nanocrystals followed by high-pressure compression and controlled secondary crystal growth via microwave heating. These structures could be useful for separation and catalysis applications. 

H.T.Wang, Z.B.Wang, L.M. Huang, A. Mitra, and Y.S. Yan, Surface Patterned Porous Films by Convection-assisted Dynamic Self-assembly of Zeolite Nanoparticles. Langmuir, 2001, 17, 2572-2574. 

Fig. 6 Illustration of Nafion-acid functionalized zeolite Beta nanocomposite membranes helping to increase the proton conductivity and decrease the methanol crossover (A) H2O and CH3OH diffusion reduced by zeolite flow resistance (B) sulphonic acid functionalized zeolite nanoparticles increases proton conductivity of composite membranes. (View this art in color at www. dekker. com.)...

Fig. 8 Patterned zeolite films by using (A) soft-lithography (B) convection-assisted assembly of zeolite nanoparticles and (C) selective deposition on Si on a wafer pre-pattemed with gold. (From Refs. - - )...

Specifically for the preparation of zeolite films, zeolite nanoparticles could be used directly to form zeolite films by self-assembly. They could also be combined nicely with the seeded growth and vapor phase transport method to produce high quality polycrystalline zeolite films. There is clear evidence that small zeolite nanoparticles are preferred for producing compact continuous films. 

Another important application for zeolite nanoparticles is the preparation of zeolite matrix composite films. Micrometer-sized crystals have long been used in these types of films, using techniques such as washcoating and sol-gel processing. However, the use of nanoparticles in these films appears to offer many unparalleled advantages in terms of achievable film... 

Wang, H. Wang, Z. Huang, L. Mitra, A. Yan, Y. Surface patterned porous films by convection-assisted dynamic self-assembly of zeolite nanoparticles. Langmuir 2001, 17 (9), 2572-2574. 

A silica sol-gel monohth containing zeolite nanoparticles has been reported [87]. This device had a high stuface area for the immobilized enzyme, allowing for a high load within the microreactor. A 0.5 pL volume containing 0.2 pg/pL of the proteins (cytochrome c and BSA) was digested within 5 s in the microreactor, as indicated by off-line MALDI-TOF (time-of-flight) MS. The microreactor could be used repeatedly and the enzyme remained active for more than a month when it was stored at temperatures below 4 °C. 

Meynen V, Beyers E, Cool P et al (2004) Post-synthesis deposition of V-zeolitic nanoparticles in SBA-15. Chem Commun 898-899... 

It is also possible to add partially formed zeolite nanoparticles as a form of silicate precursor. If these are sufficiently reactive to cluster around the micelles and condense to form mesoporous solids, the resulting phase, once calcined, has both mesoporosity (between the walls) and microporosity (within the walls). This is discussed further in Chapter 10. 

Another approach to introduce mesoporous channels to give better access of reactant molecules to the microporous regions is to assemble zeolite nanoparticles around micellar templates, in a modification of the standard route to mesoporous silicas. Reported examples include structures that possess walls made out of nanocrystals of zeolites such as Beta or ZSM-5. These composite solids possess enhanced hydrothermal stabilities and acidities compared to mesoporous solids with fully amorphous walls. The improved properties are attributed to the presence of the zeolite fragments, because zeolites are known to have higher acidity and hydrothermal stability than amorphous silica/... 

It was also found that the water flux of TFC-RO membranes could be doubled without affecting the salt rejection by incorporating zeolite nanoparticles in the thin layer of the... 

Composite reverse osmosis membranes have been fabricated from sulfonated PAES with amino groups and aminated template free zeolite nanoparticles [91]. These modifications enhance the chlorination resistance and improve the performance of the membranes with respect to water permeability. Also the active layer structure is protected from degradation. 

Kim SG, Hyeon DH, Chun JH, Chun BH, Kim SH. Nanocomposite poly(arylene ether sulfone) reverse osmosis membrane containing functional zeolite nanoparticles for seawater desalination. J Membr Sci 2013 443 10-8. 

In some other successful examples, zeolite nanoparticles have been incorporated into a polymer matrix to form a thin-film nanocomposite RO membrane and to create a preferential flow path for water molecules, leading to enhanced water transport through the membrane [64,65]. Use of zeolite in the development of TFN for RO was first reported by Hoek and co-workers [66]. Similarly, Jeong et al. [64] prepared a thin-film RO nanocomposite membrane by interfacial in situ polymerization on porous polysulfone support, in which NaA zeolite nanoparticles were incorporated into a thin PA film. Introduction of zeolite nanoparticles into a conventional PA RO thin film has enhanced flux to more than double of the conventional membrane with a salt rejection of 99.7%, which is attributed to the smoother and more hydrophilic negatively charged surface. Silica nanoparticles of various sizes have also been incorporated into a PA polymer matrix for RO desalination [67]. Presence of silica nanoparticles was found to remarkably modify the PA network structure, and subsequently the pore structure and transport properties with only 1-2 wt% of silica, a membrane was fabricated with significantly enhanced flux and salt rejection. 

Mixed-matrix interfacial polymerization has been developed to embed nanoparticles throughout the polyamide thin film layer. This concept aims to improve the membrane performances. Super-hydrophilic zeolite nanoparticles are used to enhance the water permeation while maintaining high salts rejection [113]. A similar approach has been developed to fabricate aquaporin-based biomimetic membranes that have superior separation performance [114]. 

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