External Surface-modification Method

In Table 6.15 the reaction data of toluene disproportionation on the CVD-modified mordenite zeolite catalyst at 400°C are presented.1611 As the Si02 deposition amount increases, the toluene conversion decreases gradually. From the product distribution it is seen that the amount of nonaromatics increases slightly whereas the amount of trimethylbenzene is reduced to zero, and the xylene/benzene ratio drops as well, 

The CVD technique can be effective for zeolite pore-size adjustment, and the zeolites after modification through this technique exhibit distinctly enhanced shape-selective adsorption separation and catalytic performances. However, this technique requires vacuum apparatus and the monetary investment for this technique is large. In addition, 

Sample HM SiHM(0.7) SiHM(1.6) SiHM(2.6) SiHM(3.7) SiHM(4.0) HZSM-5 

C stands for conversion NA for nonaromatics B for benzene T for toluene X for xylene TMB for trimethyl benzene. 

After CLD modification, the zeolites exhibit excellent shape selectivity for separation and purification of various isomers. For instance, the pore-size-adjusted NaY zeolite after Si(OCH3)4 modification is very effective for the separation of methylnaphthalene and trimethylbenzene isomers. Because the pore size of NaY itself is large, before modification the zeolite shows no shape selectivity for the two methylnaphthalene isomers, and the adsorption capacities for 1-methylnaphthalene and 2-methylnaphthalene are similar. However, as the pore size decreases, the zeolite exhibits increasing adsorption capacity 

---

Polyimide surface modification by a wet chemical process is described. Poly(pyromellitic dianhydride-oxydianiline) (PMDA-ODA) and poly(bisphenyl dianhydride-para-phenylenediamine) (BPDA-PDA) polyimide film surfaces are initially modified with KOH aqueous solution. These modified surfaces are further treated with aqueous HC1 solution to protonate the ionic molecules. Modified surfaces are identified with X-ray photoelectron spectroscopy (XPS), external reflectance infrared (ER IR) spectroscopy, gravimetric analysis, contact angle and thickness measurement. Initial reaction with KOH transforms the polyimide surface to a potassium polyamate surface. The reaction of the polyamate surface with HC1 yields a polyamic acid surface. Upon curing the modified surface, the starting polyimide surface is produced. The depth of modification, which is measured by a method using an absorbance-thickness relationship established with ellipsometry and ER IR, is controlled by the KOH reaction temperature and the reaction time. Surface topography and film thickness can be maintained while a strong polyimide-polyimide adhesion is achieved. Relationship between surface structure and adhesion is discussed. 

Polyimide surface modification with KOH or NaOH aqueous solution is well defined. The reaction initially gives potassium or sodium polyamate which is then protonated with acid to yield polyamic acid. The outermost layer (5 A) of PMDA-ODA can be completely modified within a minute of reaction in KOH solution. The depth of modification can be measured by a method using an absorbance-thickness relationship established with ellipsometry and external reflectance IR. The modification depth of PMDA-ODA treated with 1 M KOH aqueous solution at 22 °C for 10 min is approximately 230 A. Surface topography and film thickness can be maintained while a strong... 

The first method is a sure way to expose the surface of powder uniformly if one pass is sufficient to achieve the surface modification, but it is not easy to recycle the substrate in the luminous gas phase in vacuum. Therefore, the main issue in this approach is how to repeat the interaction of surface with the luminous gas phase efficiently, which entirely depends on the flow dynamics of powders. Multiple-step operation requires multiple discharge systems or repeated operation. The generation of discharge is more or less the same as the conventional modes used in LCVD reactors. External radio frequency electrodes or coil with glass tube is the most... 

This method is to insert guest molecules or clusters into zeolite channels so as to make the channels narrower and to achieve the goal of pore-size adjustment. This method is also called internal surface modification to stress the variation of the inside of channels, but in fact both the internal and external surfaces are modified during the treatment process. J... 

Another important modification method is the passivation of the external crystallite surface, which may improve performance in shape selective eatalysis (see C2.12.7T Treatment of zeolites with alkoxysilanes, SiCl or silane, and subsequent hydrolysis or poisoning with bulky bases, organophosphorus compounds and arylsilanes have been used for this purpose [39]. In some eases, the improved performance was, however, not related to the masking of unselective active sites on the outer smface but rather to a narrowing of the pore diameters due to silica deposits. 

Physical treatments also clean the impurities of fiber surface, etch and roughen the fiber surface, and improve mechanical interlocking, chemical bonding, and finally better adhesion between the fiber and the matrix. Although physical treatments are ecofriendly, they only affect the external cell walls and do not change the chemical composition of the fibers. So, they are used as a preparation stage for chemical treatments [10], Chemical modification methods and their impact on mechanical properties of the resulting composites are scrutinized later in this chapter. 

In this chapter, a series of recent results in surface modification of various surfaces employing the macromolecular anchoring layer approach was overviewed. It was demonstrated that the approach could be used as a virtually universal method for grafting of functional polymer brushes. The properties of the bmshes can be controlled by polymer nature, structural and morphological factors, and external stimuli. The polymer grafting technique developed can be readily applied to surface modification of fibers and textiles, leading to generation of hydrophobic, hydrophilic and switchable fibrous materials. 

Static deposition is a process where the deposition of polyelectrolytes onto the membrane support is done without any external force to make the polyelectrolyte solution flow through or stay on the membrane support. This also implies that the static deposition method is more inexpensive and easier to be broadly applied in membrane surface modification because less energy is required to complete the modification or fabrication process. Most of the membrane fabrication or modification employing... 

Recently, it is reported that Xi02 particles with metal deposition on the surface is more active than pure Ti02 for photocatalytic reactions in aqueous solution because the deposited metal provides reduction sites which in turn increase the efficiency of the transport of photogenerated electrons (e ) in the conduction band to the external sjistem, and decrease the recombination with positive hole (h ) in the balance band of Xi02, i.e., less defects acting as the recombination center[l,2,3]. Xhe catalytic converter contains precious metals, mainly platinum less than 1 wt%, partially, Pd, Re, Rh, etc. on cordierite supporter. Xhus, in this study, solutions leached out from wasted catalytic converter of automobile were used for precious metallization source of the catalyst. Xhe XiOa were prepared with two different methods i.e., hydrothermal method and a sol-gel method. Xhe prepared titanium oxide and commercial P-25 catalyst (Deagussa) were metallized with leached solution from wasted catalytic converter or pure H2PtCl6 solution for modification of photocatalysts. Xhey were characterized by UV-DRS, BEX surface area analyzer, and XRD[4]. 

---