Two-step templating method

The synthesis of ordered macroporous crystalline materials has been attracting much attention. Walls of macroporous materials are larger than those of mesoporous materials, and this macroporosity can be introduced into a wide variety of transition metal oxides. Potential applications of these materials include photonic materials, catalysts and electrode materials. The ordering scale is close to the wavelength of light, and interest has therefore been shown in photonic materials. In some cases, introduction of macroporosity increases the surface area, and these materials show better catalytic performance than that of nonporous materials. Similar to mesoporous materials, macropores are favoured for diffusion of reactants compared with nonporous materials and many applications, such as in a Li battery electrode, have been reported. 

Metal Precursor solution Template Solidification Template removal Crystal Phase Properties and application Ref. 

Ti Titanium(lV) bis(ammonium lactate) dihydroxide (0.05-0.2 M) in H2O 3DOM carbon treated with polyelectrolytes Hydrothermal treatment at 140-240 °C) Not removed Ti02 (anatase) 140 °C Ti02 (anatase + rutile) 190 °C [182] 

Nd Nb-EDTA (1 mmol) in acetic acid-NH3-H2O (5 ml) 3DOM carbon Air dry Calc. (720 °C) Nd202C03 (600 °C) Nd203 (700 °C) [181] 

We have summarised methods for the synthesis of ordered porous (micro, meso and macro) crystalline transition metal oxides. Crystalline transition metal oxides have unique redox, magnetic and electronic properties due to an incomplete d subshell. Properties such as size selectivity, facile and homogeneous access of reactants to the surface and photonic properties are added by introduction of ordered pores. The design and syntheses of ordered porous crystalline transition metal oxides remain areas of intensive research. 

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Ordered mesoporous crystalline CuO was produced by using a hard carbon template (CMK-3) prepared by using an SBA-15 template. This two-step templating method produced well-ordered hexagonal (similar... 

Table 3.5 Two-step templating method for metal oxides... 

Later, Hosoya et al. 1931 prepared monodisperse polymer-based CSPs from chiral methacrylamides by co-polymerization onto the surface of polymeric particles. These are synthesized by a staged templated suspension polymerization using a two-step swelling method starting from polystyrene seed particles of 1 pm size used as shape templates, onto which methyl methacrylate and later the chiral methacrylamide is co-polymerized. 

Yabuki T, Motoda Y, Hanada K, et al (2007) A robust two-step PCR method of template DNA production for high-throughput cell-free protein synthesis. J Struct Funct Genomics 8 173-191... 

The first option is to improve the calcination process, usually by a two-step calcination. Other different mild template-destructive methods have been proposed. 

The first study of this kind was carried out by Chinese researchers in 2003 [144]. They prepared MIP beads for the SPE of tyrosine by simple suspension in water as well as by two-step swelling and suspension polymerisation. They found no substantial difference in the rebinding capacity of the beads prepared by the two methods. A more thorough analysis of various synthetic approaches to MIP beads was conducted a year later by Perez-Moral and Mayes [145]. They took a standard monomer mixture with propranolol as the template molecule and polymerised it by bulk polymerisation, suspension polymerisation, precipitation polymerisation, two-step-swelling polymerisation and emulsion core-shell polymerisation (see also Sect. 2.2.3). Care was taken to keep the polymerisation... 

The earliest syntheses of rotaxanes were largely based on the statistical or directed methods.2,3 Statistical methods require very precise reaction conditions, and directed methods involve numerous chemicals steps. However, the use of templates allows high control of these synthetic methods resulting in efficient and precise assemblies of rotaxanes that incorporate a wide range of chemical functionalities. Two types of interactions occur in synthetic template methods (1) purely organic and (2) transition-metal-templated. In this latter case, the template can easily be removed at the end of the synthesis, whereas in the former, the interactions between the template and the components of the final rotaxane will often be maintained. Selected examples will now illustrate the statistical, the directed, and templated strategies outlined above. The transition-metal-templated route will be developed separately. 

A novel method of preparing metal membranes with nearly suaight pores has been described by Masuda et al. [1993]. Basically it involves a two-step molding process (Figure 3.15). A porous anodized aluminum structure without the aluminum substrate removed is used as a template and the pores of the anodic alumina is filled with a monomer such as methylmethacrylate (MMA) and an initiator (e.g., benzoyl peroxide)... 

Fig. 17.12. Separation of 3.2 nmol of racemic lV-(3,5-dinitrobenzoyl)-a-methylbenzylamine on poly((5)-(-)-methacryloyl-l-naphtylethylamine-co-EDMA) prepared by a two-step swelling and polymerisation method using racemic A-(3,5-dinitrobenzoyl)-a-methylbenzylamine as template. Isocratic elution at 1 mL/min with hexane-ethyl acetate (1 1). (Adapted from [55], with permission from the American Chemical Society, USA.)...

Organic templates Cp 2 Co+ are usually occluded in the as-synthesized UTD-1. The typical method to remove these organic species from pores is that the samples are heated at 500 °C to decompose Cp 2 Co+ to cobalt oxide, followed by treatment with HC1 to remove cobalt oxide, and then are washed by water and dried in air. The obtained UTD-1 molecular sieve has good thermal stability, and its crystal lattices remain stable upon being heated to 1000 °C. The synthesis of Al-containing high-silicate UTD-1 is very difficult, which needs a two-step synthesis in general. 

Let us take one example to try to visualize more precisely the above discussion. The details of a part of the XRD pattern are shown in fig. 3 for the as synthesized (SYN with tetrapropylammonium template), hydrated (WAT) and four xylene molecules adsorbed per unit-cell (XYL-1) of B-ZSM-5 sample from ref. 35 and 36. The calcined form exhibits a monoclinic structure (P2l/n space group) whereas SYN and WAT forms correspond to orthorhombic phases (Pnma space group). The striking differences in XRD patterns are seen in fig. 3. The p-xylene adsorption is known (27) to take place in two steps. The first one, up to four molecules per u.c. and designated XLY-I, corresponds to the formation of a low coverage complex and the second one (XYL-II) to a maximum of xylene adsorption with 8 molecules per u.c. The location of p-xylene could even be determined in the ZSM-5 channel by careful analysis of powder X-ray diffraction patterns using the trail error method (35) as shown in fig. 4. 

Well-ordered macroporous Fc203 can be prepared by using iron oxa-late. " Iron oxalate is soluble in ethanol-water mixed solvents, which can infiltrate the voids of templates. Iron oxalate can be converted to Fc203 without melting to form well-ordered macroporous material. If the oxalate salts are not soluble in alcoholic solution, oxalate or oxalate derivatives can be produced in the voids by a two-step method or an in situ method. In the two-step method, nitrate or acetate salts of Mn, Co or Ni infiltrate the voids and then react with oxalic acid to form oxalate salts in the voids. These oxalate salts can be converted to oxide by calcina-In the in situ method, nitrate of Mn or Fe is dissolved in EG-methanol solution, and the solution infiltrates the voids of templates. By heating the solution, EG is oxidised by nitrate to form metal oxalate derivatives. The metal oxalate derivatives can be converted to metal oxides. 

In order to improve the structural ordering of zeolite-templated carbons, Ma et al. have investigated systematically the synthesis of microporous carbons using zeolite Y as hard template. They used a two-step method to prepare an ordered, microporous carbon with high surface area, which retained the structural regularity of zeolite Y by filling as much carbon precursor as possible into the zeolite pores so as to prevent any subsequent partial collapse of the resulting carbon framework. In the... 

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