Soft template method oxides

Ordered mesoporous crystalline metal oxides have been synthesised using template methods, which are generally divided into the soft template method and the hard template method , depending on the nature of the templates. 

Miscellaneous Soft-Template Methods Novel Y-junction PANI-NTs, accompanied with nanorods, have been selectively prepared using in situ self-assembly of water-soluble Fe304 nanoparticles coated with PEG(5)-nonylphenylether and cyclodextrin as templates and pH control in an aqueous medium [373]. A chemical oxidative route to synthesize oriented arrays of conducting PANI-NTs in HCl solution by hydrogen-bonding directionality in the presence of a crown ether derivative (CE-SO3K) has also been reported [374]. 

Soft template method by using block copolymers was reported for first time by Liang et al. [72] in 2004. After that, a significant progress on the fabrication of carbon with a well ordered mesopores was achieved [32, 73-77]. Zhao and coworkers performed a widespread study of soft template via the triblock poly (ethylene oxide) (PEO) and poly(propylene oxide) (PPO) based systems, PEO-PPO-PEO [65, 78]. Several ordered pore stmctures corresponding to various surfactant liquid crystal phases were synthesized by liquid crystal template pathway, a schematized synthesis procedure is shown in the Pig. 7.11. 

In general, template method is classified by soft and hard templates. Whereas anodic aluminum oxide (AAO) membrane, track-etched polycarbonate (PC) and zeolite can be used as hard templates, soft templates include surfactant, cyclodextrin, liquid crystal, etc. Compared with soft and hard templates, template-free method represents the fabrication technique of conducting polymer nanomaterials without the template, which is discussed in this section [115]. 

Till date, liquid-crystalline phases [51], colloidal particles [52], and structure-directing molecules [53[ as the soft-template have been employed to synthesize PANI nanostructures. Based on the traditional synthesis method of PANI, in particular, some simple approaches such as interfacial polymerization [54], mixed reactions [55], dilute polymerization [56] and ultrasonic irradiation [57] have also been employed to synthesize PANI. The interfacial polymerization method only allows the oxidative polymerization of aniline to take place at the interface of the organic/water phases and the product directly enters into the water phase, which could facilitate environmentally friendly processing. 

Conductive polymeric nanostructures can be prepared by using hard or soft templates or with template-free methods. The template method has been extensively used because of its simplicity, versatility and controllability. Some further features on this topic are reported in Section 1.3. A typical hard template material can be a thin porous film of aluminum oxide or polycarbonate and polymeric materials ean be deposited into the pores to form nanotubes or nanowires. The electrochemical template method enables a better control of the dimensions compared with the chemical methods. In addition, the nanostructures produced by the electrochemical method are in solid contact with a base electrode that is beneficial for further processing steps when building an electrochemical device. 

Today, even after more than 20 years, almost all developed methods related to the synthesis of mesoporous materials by surfactant soft templates still use knowledge based on mesoporous silica materials. The synthesis of mesoporous oxides of TMs (i.e., Ti, Zr, and Mn), metalloids (i.e., Ge), posttransition metals (i.e., A1 and Ga), and lanthanides (i.e., Ce) has been adapted from the methods developed in mesoporous silica synthesis [44-49]. In other words, one can easily find a silica analog of any procedure for the synthesis of non-silicious mesoporous oxides. Flexible Si—O bonds made via well-known and easily manageable sol-gel chemistry, allow one to use various solvents or solvent mixtures (i.e., aqueous or alcoholic), pH (1-7), temperatures, and pressures to synthesize numerous mesoporous silica materials [50]. However, sol-gel chemistry of other elements especially TMs requires more controlled reaction conditions. The sol-gel chemistry (hydrolysis and condensation) of early (group I-IV) TMs can be controlled in alcoholic solutions with proper pH, temperature, and humidity adjustments [2,4,10,46,47,50]. Typical TM sources are either commercially available alkoxides (i.e., titanium isopropox-ide) or can be formed in situ by the reaction between anhydrous TM chloride salts and alcohols (i.e., WClg + EtOH W(OCH2CH3)6). 

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