Hydrochloric Acid Analysis

2. Experimental procedure
2.1. Chemicals and materials
Melamine (99%), titanium dioxide with anatase (99.7%), isoniazid (ISN, >99%), isopropanol anhydrous (IPA, 99.5%), 1, 4-benzoquinone (BQ, ≥98%) and ammonium oxalate (AO, ≥99%) were purchased from Sigma Aldrich. The molecular structure and chemical properties of isoniazid are given in Table 1. Sodium hydroxide (NaOH, 99%) and methanol (MeOH, analysis grade) was purchased from Merck Millipore, Germany. Hydrochloric acid was purchased from PFP Matsunden Chemicals Ltd, South Korea. Ultrapure water was used for the synthesis of TiO2 nanotube and preparation of isoniazid experimental solution. Standard chemical reagents for COD analysis were purchased from Humas Co. Ltd., Daejeon, South Korea.

In a typical procedure, TiO2 nanoparticles (TNP, 3.6 g) with pure anatase was added into a NaOH (10 N, 150 mL) solution in a teflon lined stainless steel autoclave, sonicated (2 min) and heated the autoclave at 403 K for 48 h in an oil bath under autogenesis pressure with stirring (250 rpm). After 48 h, the autoclave was cooled down to room temperature, subsequently the formed nanotube was washed with ultrapure water until the pH of the solution was >7. Afterward the nanotubes were washed with HCl (0.1 M) solution for overnight under stirring at room temperature. Then the nanotubes were filtered (Millipore filtration assembly) under vacuum pump and repeatedly washed with ultrapure water until the filtrate was free from chloride ion, which was checked by the addition of silver nitrate to the filtrate. Finally, the obtained nanotubes were dried in an oven at 343 K for 12 h and calcined in a muffle furnace at 773 K for 4 h. The synthesized nanotube was abbreviated as

The result revealed that the diffraction peak at 11.4°, 28.2°, 29.8° 24.5° and 48.5° corresponds to the presence of layered titanates, brookite and anatase phase in the as-synthesized TNT. In Fig.1b, the diffraction peak values of TNT and x%-CN/TNT (1, 3, 5, 7 and 10%) composite materials at 25.3°, 36.9°, 37.8°, 38.5°, 48.0°, 53.9°, 55.1°, 62.7°, 68.9°, 70.3°, 75.1°, and 76.0° are corresponded to the anatase phase of TNT. In addition all samples shows extra peak at 14.1°, 28.6°, 29.8°, 33.5°, 43.5°, 44.6° and 58.2° are indexed to the crystal planes of metastable TiO2 (B) phase (JCPDS 74-1940). This is because at 500 °C calcination the proton exchanged layered titanates were decomposed into TiO2 (B) phase through dehydration of protonic layered titanates. This transformation has been observed by shifting of diffraction angle of layered titanates from 2θ = 11.4° to higher diffraction angle (2θ =14.1°). Similar results were reported by Suzuki and Yoshikawa [40] and Morgado et al. [41] in the thermal stability study on titanate nanotube. The diffraction peak (at 2θ=27.5°) related to added CN was not observed in the PXRD pattern, because it is merged with the TiO2 (B) phase peak at 28.6°. Further the intensity of peak at 28.6° is increasing with increase in the amount of CN loading. Similar to x%-CN/TNP composite, anatase peak of TNT at 25.3° is shifted to lower diffraction angle (Inset of Fig.1b).