Fabrication of Titanium Dioxide (TiO2) Nanostructures Assembled LC Matrix

In this typical synthesis procedure, ordinary metallic titanium powder (Merck) of 0.3 gm was added into 30 ml of 10 M NaOH (sodium hydroxide) and then stirred for a transparent solution. This solution was inserted into a 50 ml capacity stainless steel lined autoclave and the entire system was placed inside an oven 119°C for 19 h. The bluish precipitation that resulted from cooling the system at room temperature was filtered and collected. It was then washed with 0.1 M HC1 (35% concentrated hydrochloric acid, Merck) and distilled water for numerous times. The end product was then dried at 60°C for 4 h. This was annealed at 650°C for 1 h in a heating chamber for oxidation after collecting powder like samples. To maintain the chemical methodology dealing only with bulk anatase Ti0₂ powder [19], 40 ml mixture of 10 M NaOH and 5 M KOH was stirred vigorously in a magnetic stirrer (Remi) for 15 min before the transparent solution emerges. A 0.2 gm of anatase titanium (IV) oxide powder (Sigma Aldrich) was mixed with previous precursor of NaOH and KOH (sodium and potassium hydroxide pellets) in a 100 ml beaker contained deionized distilled water. The solution which resulted was then stirred for 25 min and after properly stirring the solution, it was moved into an autoclave lined in teflon stainless steel with a capacity of 100 ml and the entire system was then inserted into a heating chamber. Following the similar experimental conditions, the white precipitation obtained was filtered and then washed with 0.1 M HC1 solution; 150 ml deionized distilled water and 50 ml ethanol for numerous times till the samples are free from impurities. Sodium-potassium titanate nanowires turned into hydrogen titanate nanowires and finally obtained desired pure Ti0₂ nanowires, due several time of acid washing with deionized distilled water. The desired sample was dried out at 60°C for 4 h in an oven. This final sample was annealed at 650°C for 1 hr in furnace and pure Ti0₂ nanocabbage obtained [21], when it cooled naturally at room temperature and confirmed by FE-SEM micrographs displayed in Figs. 1.3a-d. Ultra- thin hydrogen-titanate nanowires were obtained by anatase Ti0₂ of diameter 1.5 nm and length approximate 750 nm as identified

Figure 1.3 FE-SEM micrograph of anatase Ti0₂ (a) hydrogen-titanate nanowires, (b) nanoparticles, (c) nanocabbages, and (d) coagulated nanoparticles. Reproduced with permission from Pal et al. [21, 22], copyright © 2012, 2013 Elsevier.

in Fig. 1.3a. By applied annealing process in regular laboratory oven that reveals gradually formulated nanoparticles of diameter 40 nm corresponding to Fig. 1.3b. Typical nanocabbages formed during control of chemical methodologies in Fig. 1.3c, and further coagulated nanoparticles formed in Fig. 1.3d.

The controllable growth strategies of Ti0₂ nanostructures summarizes as following Table 1.1.

While, fabricated Ti0₂ nanorods, nanowires [22] and nanocabbage [23] were harvested in high yield fabrication and chemical reduction process from sodium hydrogen titanates with general chemical formula ЫауНг-уТ^Огп+гхНгО. By acid washing of obtained nanomaterials results in ion exchange to produce the layered hydrogen titanates H₂Ti„0_2n+ixH₂0, which exhibits features similar to H₂Ti₃0₇, H₂Ti₄09-H₂0, and other members of the hydrogen-titanate family. After maintaining an oxidation process for several times and previously prepared sample confirms into unique crystalline pure Ti0₂ nanostructure formation. We predicted from

Table l.l Growth dynamics of Ti0₂ nanostructures chemical assisted hydrothermal route [22]

our earliest publication, i.e., there is really a disadvantage of using bulk metal Ti0₂ powder rather than using of Ti0₂ (IV) anatase bulk powder for nanostructure synthesis confirmation through FE- SEM images investigation. The above discussed titanium nanorods synthesis and dehydration reaction mechanism process as follows

• (1) NaOH + Ti0₂ = Na₄Ti0₃ + H₂0
• (2) Na₄Ti0₃ (annealed at 650°C for 1 h) —*■ NaxH₂_xTi₃0₇
• (3) H₂Ti₂0₄(0H)₂ -*■ H₂0+H₂Ti₂05 (Hydrogen titanate nanowires)
• (4) H₂Ti₂05 (annealed at 650°C 1 h) -> H₂0 + 2Ti0₂ (Pure Ti0₂ nanowires from bulk Ti0₂ anatase powder)

Controllable Synthetic Mechanism of Zinc Oxide (ZnO) Nanostructures Assembled LC Matrix

Typical set of experiments introduced a cationic surfactant cetyltrimethylammonium bromide (СТАВ) of 0.8 gm to prepare ZnO nanoparticles. 20 ml СТАВ aqueous solution strongly stirred in a beaker for 15 min. Occasionally, 0.65 gm of Zn(Ac)₂ dissolved into 2 M of 10 ml NaOH, which were previously stirred in separate beaker. Now, aqueous solution of СТАВ dropwise added with zinc acetate solution for several times at continuous stirring. After the dissolution of СТАВ, which resulted in a white aqueous solution

Figure 1.4 FE-SEM images of zinc oxide (ZnO) performed under the controllable chemical acceleration process (a) nanospikes, (b) nanocapsules coagulated with hexagonal nanorods, (c) nanoflakes, (d) nanoparticles, (e) porous surface due to nanoparticle dispersed anti-ferroelectric liquid crystals (W-182), and (f) high magnification images nanoparticles inside porous cavity. Reproduced with permission from Pal et al. [19,23], copyright © 2012, 2013 Elsevier.

obtained, and it transferred into stainless steel coated teflon-lined autoclave. The autoclave was placed for firing at 120°C for 20 h in a regular laboratory oven. The stainless steel coated jacketed vessel of autoclave was allowed to cool to room temperature naturally. The resultant sample was filtered off and washed with deionized distilled water and ethanol for several times until the produced impurity washout and separated from the impurity ingredients. The final products were dried in a hot vacuum chamber at 65' C for 4 h [19, 23]. Furthermore, similar hydrothermal treatment we obtained nanoflakes like structures [19] reported recently [kept all chemical ingredients remain same except 0.75 gm of СТАВ and [Zn(Ac)₂]. FE-SEM investigates the various morphological and structural analysis of ZnO nanospikes, nanocapsules coagulated with nanorods, nanoflakes, nanoparticles as depicted in Figs. 1.4a,b,c and d, respectively. While, surface porosity attributes when ZnO nanoparticles came into contact of anti-ferroelectric liquid crystal [AFLC; W-182) as show in Fig. 1.4e, and as well as captured higher magnification where nanoparticle appeared inside the porous cavity as depicted in Fig. 1.4f.

Different growth dynamics of ZnO nanostructures also summarized in following Table 1.2.

The chemical element Zn existed in [Zn(OH)₄]^2- as a negatively charged tetrahedrons that were formed in presence of СТАВ is a cationic surfactant. When СТАВ is dissolved in water or ethanol, it

Table 1.2 High yield fabrication of ZnO series of nanostructural morphologies under chemical conditions. Reproduced with permission from Pal et al. [23], copyright © 2013 Elsevier

will ionize into CTA⁺ and Br^_ ZnO reaction, as a polar crystal, has a polar axis and possesses a positive face and a negative face on the crystal due to the asymmetrical distribution of Zn atoms and О atoms along its polar axis, and the positive face (0 0 0 1) is occupied by Zn atoms while the negative face (0 0 0 1) is distributed by О atoms.

In typical reaction mechanism, while CTA⁺ was positively charged with a tetrahedral head and a hydrophobic tail. It was found from the assisted hydrothermal process, CTA⁺ and [Zn(OH)₄]^2- ion pairs were formed initially by electrostatic interaction. The СТАВ could accelerate the ionization of [Zn(OH)₄]²^ as it was a strong- acid-weak-base salt. The CTA⁺ and [Zn(OH)₄]^2- ion pairs formed a combination of СТАВ and ZnO. It was inferred that, the СТАВ aggregated in between the ZnO crystallites during hydrothermal crystallization and on washing the material with ethanol, the particle like structures of ZnO were formed. Variation of the growth mechanism of ZnO nanostructures [19, 23] formation obtained through FE-SEM imaging performance.