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45215-AC10
Synthesis and Polymorphic Control for Visible Light Active TiO2 Nanoparticles

Burtrand I. Lee, Clemson University

Synthesis and Polymorphic Control for Visible Light Active TiO₂ Nanoparticles

1.0              Research Activities

During the first year, research was focused on synthesis of titania nanoparticles and characterization including the photocatalytic activities.

  1.1              Methodology 1.1.1        Titania nanoparticle synthesis

Brookite TiO₂ nanoparticles were prepared by WACS process as shown in Figure 1 as described in our previous papers [1-4].  The SACS technique (U.S. Patent appl. pending^*) developed by our research group [5] has been used as a post-synthesis treatment of WACS process. Reaction specifics can be seen in Table 1.  All calcined TiO₂ powders were heat-treated in air at 200^oC for 2 hours.

Figure 1. Brookite TiO₂ synthesis diagram

Table 1. Experimental Conditions utilized to produce single phase and mixed phase titania

Sample ID	Major TiO2 Phase	Mode of Formation	Temperature (°C)	Solvent	HCl concentration(M)	Time (hr)
WACS	Brookite	WACS	83	2:1 IPA:water	0.3	15
WACS-200	Brookite	Calcination of WACS	200	-	-	2
SACS*	Brookite	SACS	*	*	-	*
SACS-200	Brookite	Calcination of  SACS	200	-	-
P25	Anatase	Obtained from Degussa	N/A	-	-	2

*U.S. Patent applied & info withheld.

1.1.2 Characterizations

All samples were characterized by N₂ Adsorption and X-Ray Diffraction (XRD).  The photocatalytic activities were evaluated by the degradation of the methyl orange (MO) under UV irradiation.  The characterization and photocatalytic activity test conditions were reported in the publications from our group [2-4].

1.2              Results

The X-ray diffraction patterns of the TiO₂ particles are shown in Figure 2.  The TiO₂ phase of uncalcined WACS and SACS samples is predominantly brookite. Calcined titania samples at 200^oC for 2 hours had a small portion of rutile in the structure.  The crystallite sizes calculated from the XRD data as reported in Table 2 are approximately 16 nm which is much smaller than the P25 crystalline size.

The results of BET surface area, pore volume, and average pore diameter of titania samples are given in Table 2.  The BET surface area of our brookite titania samples were three times larger than that of P25 samples.  The photocatalytic activities of brookite titania samples compared to P25 samples, determined by the methyl orange degradation, are shown in Figure 3.  The degradation by the uncalcined samples is significantly slower than those samples calcined at 200°C for 2 hours, due to the removal of surface hydroxyls and/or organic.  The photocatalytic activities, obtained by MO degradation, of the calcined brookite titania samples, WACS-200 and SACS-200, are much better than the commercial P25 sample.  A few papers from our group [2,4] reported that our brookite titania is more photocatalytically active than P25.  The orange color of MO for SACS-200 was degraded ten minutes faster than that of WACS-200 (*further info withheld).  This is supported by data obtained from FTIR and ¹H NMR analysis and the measured pore volume of samples.  The SACS brookite titania paper was submitted to catalysis letters journal in August 2007. 

The antibacterial properties were obtained from collaboration with Biological Sciences Department, Clemson University.  UV light activated brookite titania on Escherichia coli 23848 killed all bacteria within 120 minutes, but P25 did not [6].

Figure 2. The XRD pattern of the brookite titania samples

Table 2. The physical properties of prepared titania samples and the reference P25.

Sample ID	Crystalline size (nm)*			BET surface area (m²/g)	Pore Volume (cm³/g)	Pore size average (Å)
	Brookite	Anatase	Rutile
WACS	14	-	-	163	0.1	25
WACS-200	18	-	-	157	0.1	27
SACS	12	-	-	197	0.1	28
SACS-200	13	-	-	202	0.2	30
P25	-	21	40	56	0.2	169

* calculated from XRD data using the Scherrer equation

Figure3. Methyl orange degradation of brookite titania samples compared to commercial P25.

2.0              Conclusions

Up to now, we can conclude that brookite titania is photocatalytically and antimicrobially superior to P25.  Solvothermal treatment technique enhanced the photocatalytic properties of brookite titania.  We found that our brookite titania has potential to be active under visible light.  The future work will focus more on doped titania to improve visible light photoactivation.

3.0       References

[1]   B.I. Lee, X. Wang, R. Bhave and M. Hu, Mater. Lett. 60 (2006) 1179.

[2]   C.A. Nolph, D.E. Sievers, S. Kaewgun, C.J. Kucera, D.H. McKinney, J.P. Rienties, J.L. White, R. Bhave and B.I. Lee, Catal. lett. 117 (2007) 102.

[3]   R.C. Bhave and B.I. Lee, Mater. Sci. Eng. A 467 (2007) 146.

[4]   R.C. Bhave, C.A. Nolph, S. Kaewgun and B.I. Lee, Catal. Comm. (2007).

[5]   L. Qi, B.I. Lee, P. Badhekaa, L. Wang, P. Gilmourc, W.D. Samuels and G.J. Exarhos, Mater. Lett. 59 (2005) 2794. 

[6]   R.R. Shah, Masters Dissertation, Department of Biological Sciences, Clemson University (2007).

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