Surface And Channel Properties Of Nanozeolites Synthesized Under Microwave Irradiation

Zeolite molecular sieves are good candidates for catalysts, adsorbents and ion-exchanger due to their unique properties, such as their large surface areas, defined channel systems, controllable densities of the active sites, and so on. Compared with the traditional zeolites, nanosized zeolites (nanozeolites) exhibit shorter intracrystal nanochannels and much larger external surface area, which results their good performance in the traditional and untraditional area.As a kind of new energy resource, microwave has its unique advantages and properties. The dielectric heating of microwave irradiation not only facilitates a more uniform reaction without thermal gradients, but also leads to elevated reactant temperatures for size focusing due to its special selective heating. The efficiency of "microwave heating" dramatically reduces reaction time from days and hours to minutes and seconds. Microwave heating effects are expected to be thermal and non-thermal effects.Microwave energy has been reported to be very advantageous to the preparation of nanozeolites. Recently studies have documented a significantly reduced time for fabricating zeolites from days to minutes by microwave irradiation. Further, microwave synthesis has often proven to create more uniform products and much more effectively control the size, morphology and purity of products than from conventional hydrothermal synthesis. Till now, the methods and engineer of synthesizing nanozeolites are developed well, which is the base to study the crystal growth process of nanozeoltes and extend their usage in many traditional and untraditional areas. However, the mechanism the enhanced rates of synthesis and crystal processes of nanozeolites under microwave irradiation are unknown and worth to be studied.This study focuses on the surface and defined channels of nanozeolites which are synthesized under the microwave irradiation. The detailed study of the properties of nanozeolites is helpful in developing its application in many areas.A microwave assisted synthesis method is applied to in-situ prepare ZSM-5nanozeolites with different organic groups including NH2, SH, CN and CH2-CH=CH2. It is found that, the in situ synthesized nanozeolites were comprised of aggregates of primary units with size even below20nm. Significantly, it is interesting that all of the crystal plane strings go throughout the whole particles, suggesting the highly orientation and intergrowth of adjacent primary units. The surface functionalization of zeolite nanoparticles can be also proved by the change of their surface charge and wettability. The ζ potentials of nanozeolites ZSM-5change with the surface organic groups. These various surface functional groups lead to diverse capacity and range for protein adsorption on the resulting nanozeolites., extending host-guest interaction between nanozeolites and biomolecules. And the surface-functionalized nanozeolite particles have been employed to prepare the template-free zeolite nanoparticles by the temporary obstructing caused by surface organic groups during calcination. Therefore, the as-prepared surface functionalized nanozeolites are expected to transform to template-free monodispersed nanozeolite particles with opened micropores. Besides the surface properties, the sizes and Si/Al ratio of the surface-functionalized nanozeolites are changeable with the variation of organosilane. It is believed that organosilane can influence the stability of Al species in the nuclear process, and thereby impact the crystalline process of nanozeolites.To indicate the influences of organosilanes on the crystal processes of nanozeolites, we use other kinds of silanes with-CH3and detect products. It is found that along the increase of-CH3, the influences of silanes to the size, crystal time and Si/Al ratio decrease. All these results are consistent with the DFT calculation, which give the theoretical interaction of all the silanes with Al (OH)4-. It is said that, with the addition of-CH3, the interaction of the silane to Al species reduces and causes much less affect on the properties of nanozeolites. For deeper understanding the effects of different silanes on the crystal process of nanozeolites, we developed an in situ Raman method to detect the crystallization of nanozeolites and analyze the building of its framework and Al sites. However, the intrinsical growth mechanism of nanocrystals under the addition of organosilanes and irradiation of microwave are required to research well.The nanozeolites LTL with different exposed crystal planes and sizes were synthesized as an excellent model material to study the effects of crystal plane and size of nanozeolite on the protein adsorption behaviors. A larger protein adsorption amount is observed on the smaller nanocrystals due to their larger surface area and surface charge density. More importantly, it is found that the (001) crystal plane with12-membered ring channel array has a larger contribution for protein adsorption on zeolite LTL nanocrystals than other two dimensions with very small pore-opening (1.5A). It is proposed that the protein adsorption difference of the different crystal planes could be attributed to abundant exposed pore-opennings on the top (bottom) surface and curved surface of the side surface in columned nanozeolites LTL. This fact exhibits that topography at the nanoscale is also an important factor determining protein adsorption on the surface of nanozeolites, and new efforts in the future should be focused on synthesis of nanozeolites LTL with abundant exposed (001) planes. This observation will provide a new view for the bioapplication and design of crystalline nanomaterials.To preserve their monodispersity and large external surface area of p nanozeolites and also avoid the formation of extra-framework aluminum and destruction of the structure, a microwave-assisted Fenton-like oxidation method is developed to rapidly detemplat as-prepared P nanozeolites. Such Fenton-like process can significantly reduce the detemplation time to10-15minutes and avoid the traditional calcination process as well as its destruction for the structure and composition of β nanozeolites. The influence factors are discussed to deeply understand the processes of the detemplation. And the optimum condition is proposed to drastically eliminate SDAs within15minutes under microwave irradiation. Moreover, the well intrinsic framework structure and monodispersity of nanozeolit preserved by Fenton-like oxidation promise its good catalytic behavior in fructose dehydration, which due to the well preserved good monodispersity of β nanozeolites. And thus shorten the diffusion route for guest molecules and avoids the secondary reactions and formation of coke. Besides, the washed P nanozeolite is also detemplated by the same process. It is remarkable to find that the ratio of H2O2/TEAOH must be improved to completely remove SDAs in the micropore of nanzeolite. The content of Fe3+ions also needs a little improvement. Clearly, compared to organic molecules dispersed in the solution, SDAs encaged in the micropores are hard to remove, and a more high concentration of·OH is needed to fully eliminated them. Furthermore, we try to relate the amounts of hydrogen peroxide we used to the stoichiometric demanded for the total oxidation of the SDAs in the system. For the as-prepared β nanozeolite system,80-85%of H2O2is used in the detemplation process.