Photocatalytic Activity of Amorphous−Anatase Mixture of Titanium(IV) Oxide Particles Suspended in Aqueous Solutions

TLDR: In this article, an exothermic peak at ca. 723 K in the DSC pattern was assigned to the crystallization of amorphous phase to anatase, and its heat was used to evaluate the weight fraction.

Abstract: Titanium(IV) oxide (TiO2) powders of various amorphous−anatase compositions were prepared by heat treatment (573−1073 K) of amorphous TiO2 in air and characterized by differential scanning calorimetry (DSC), powder X-ray diffraction (XRD), and BET surface area measurements. An exothermic peak at ca. 723 K in the DSC pattern was assigned to the crystallization of amorphous phase to anatase, and its heat was used to evaluate the weight fraction of amorphous phase. The fraction of anatase crystallites (f(anatase)) was calculated as the remainder after the amorphous phase and contaminated water or organic residue. The XRD data showed that the size of anatase crystallites was slightly decreased but almost constant along with the increase in f(anatase), being consistent with the small change in the BET surface area. These results suggest that each amorphous particle transforms into an anatase crystallite of similar size without sintering or crystal growth. The particles of mixture of amorphous and anatase were ...

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Figure 10. Rate of photocatalytic H2 evolution by completely crystallized anatase TiO2 suspended in deaerated aqueous solution of 2-propanol as a function of anatase crystallite size.

Figure 4. Comparison of the fraction of anatase crystallites (f(anatase)), obtained from XRD and DSCmeasurements, in the amorphous-anatase mixtures. Values of(anatase) from XRD without and with correction for smaller particle size (see Figure 6 and text) are plotted with open and closed circles, respectively, against those from DSC.

Figure 5. Plots of crystallite size of anatase and BET surface area of the amorphous-anatase mixtures as a function of fraction of anatase crystallites (f(anatase)).

Figure 3. Calibration curve for anatase fraction as a function of peak intensity ratio of anatase TiO2 and CaCO3 as an internal standard. Merck TiO2 (anatase) was used as standard anatase sample.

Figure 2. Representative XRD pattern of amorphous-anatase mixture of TiO2 powders: (a) as-received amorphous, (b) mixture (f(anatase) ca. 0.3), and (c) completely crystallized anatase. A broad peak at 2θ ) 19° and small peaks at 21° and 23.5° are caused by vaseline used to fix the powders on an XRD sample holder. Sample b contained 20 wt % of CaCO3 as an internal standard.

Figure 6. Ratio of f(anatase) values obtained from XRD and DSC measurements as a function of anatase crystallite size. Open and closed circles show data for predominantly amorphous (f(anatase)< 0.4) and anatase, respectively. Numbers denotef(anatase) obtained from DSC measurements.