1. M. Sidheswaran, Z. Zhang, L. L. Tavlarides, J. Zhang, E. Khalifa
Visible Light Photocatalytic Air Cleaning Surfaces “Photo Catalytic Decomposition of VOCs using Modified TiO2 Catalyst”
M. Sidheswaran, Z. Zhang, L. L. Tavlarides, J. Zhang, E. Khalifa
July 26, 2006

2. Overview and Motivation
A variety of air purification technologies are available to remove harmful VOCs and pathogens from indoor air:
filtration
ozone oxidation
plasma decomposition
TiO2 UV based technologies.
TiO2 – has limited success due to the high energy band gap (Eg = 3.2eV) which requires excitation by high frequency UV radiation (<387.5 nm).
We seek to develop a novel catalyst systems that can purify indoor air using surfaces coated with the photo-catalysts which are actuated by day light and fluorescent radiation.

3. Visible Light Photocatalytic Research so far

4. Deficiencies in Visible Light Photocatalytic Research so far
Literature review shows studies exist on:
Destruction of VOCs in indoor air with doped TiO2 catalysts with UV irradiation
Band gap energy reduction occurs with Ce, V and Fe doped catalysts in visible wavelength light region
Photocatalytic destruction of VOCs in outdoor air with pure titanium dioxide catalysts
Photocatalytic destruction of organics with doped TiO2 catalysts in aqueous systems
No detailed study exists on synthesis and characterization of Ce, Fe and V doped TiO2 catalysts sensitive to visible light activation with application to photocatalytic destruction of VOCs in indoor air

5. Objectives
Synthesize and characterize twenty seven different titanium dioxide based catalyst formulations and 15 replicates.
The catalyst formulation varies according to: Dopant used (3), Dopant concentration (3), Post treatment temperature (3).
These formulations will be characterized using: X-ray diffraction, Vibrational spectroscopy, UV-Vis diffuse reflectance spectroscopy.
Coating and evaluation of visible light catalysts using a bench scale plug flow reactor system.
Develop a kinetic model for photocatalytic destruction of a VOC with a selected catalyst system and, as time permits, reaction pathway analysis.
Model for photocatalytic destruction of selected VOC in office space (time not sufficient for this study).

6. Synthesis Route

7. Why Ceria, Iron and Vanadium?
redox couple Ce+3/Ce+4 with shifts between CeO2 and Ce2O3 under oxidizing and reducing conditions
the easy formation of liable oxygen vacancies providing high mobility of bulk oxygen species.
Iron
Iron reduces electron hole recombination.
Higher selectivity to molecular oxygen.
Increases quantum efficiency of the photocatalytic mineralization process.
Vanadium
Red shift in the doped catalysts is observed.
Changes morphology, structure and electronic property of titania.
Vanadium used as catalyst for chemical synthesis processes.
Vanadium is highly stable in suspensions and enhances catalytic activity.

8. Catalyst Synthesis and Screening: Characterization Technique
Raman Spectroscopy
To study the transformation between anatase-rutile-brukite phases due to temperature treatment: anatase phase desirable
X Ray Diffraction
To study the anatase rutile phase ratio and crystal size
UV Vis Diffuse Reflectance Spectroscopy
To determine band gap energy Eg as a function of dopant concentration and post treatment temperature
BET (ASAP 2020)
Surface area will be determined by BET surface characterization technique

9. Raman Spectra: Vibrational Structure of Titania
Three crystal forms of TiO2 mono-crystal: rutile, anatase, and brookite.
Three different modes of arrangement and links for the three kinds of [TiO6] octahedron because each crystal form belongs to a different structure and has different characteristic Raman bands.
The irreducible representations of optical modes for each structure:
Anatase-type TiO2:
Γopt = A1g(R) + A2u(IR) + 2B1g(R) + B2u(ia) + 3Eg(R) + 2Eu(IR)
Rutile-type TiO2:
Γopt = A1g(R) + A2g(ia) + A2u(IR) + B1g(R) + B2g(R) + B1u(ia) + Eg(R) + 3Eu(IR)
Brookite-type TiO2:
Γopt = 9A1g(R) + 9B1g(R) + 9B2g(R) + 9B3g(R) + 9Au(ia) + 8B1u(IR) + 8B2u(IR) + 8B3u(IR)

10. Raman Spectra and Assignments of TiO2

11. Results: Raman Spectrum – Cerium Doped Titania

12. Results: Raman Spectra – Iron Doped Titania

13. Results: Raman Spectrum – Vanadium Doped Titania

14. The Effect of Calcination on Phase Transformation
At 70 ºC and 400 ºC: one apparent peak ~ 151 cm-1.
At 500 ºC: a strong sharp band at 150 cm-1, three mid-intensity bands at 401, 520, and a weak band at 200 cm-1 The fundamental vibrational modes of anatase TiO2.
At 600 ºC: two new rutile phase peaks, at 451 and 611 appear strong band at 149 cm-1. Indicates presence of anatase (major component) and rutile
At 800 ºC : two strong peaks at 451 and weak peak at a wide mid-intensity peak at ~ 241 cm-1 The fundamental vibrational modes of rutile

15. Results: XRD – Cerium Doped Titania

16. Results: XRD-Iron Doped Titania

17. Results: XRD Crystal Size Estimates:
1.0 wt% of Cerium doped titania treated at 500C nm
2.0 wt% of Cerium doped titania treated at 500C – 5.9 nm
3.0 wt% of Cerium doped titania treated at 500C nm
0.5 wt% Iron doped titania treated at 500C - 4.2nm
1.0 wt% Iron doped titania treated at 500C - 5.1nm
2.0 wt% Iron doped titania treated at 500C- 5.4nm
Samples treated at 500C were dominated by anatase in the bulk phase.
Samples treated at 800C were dominated by rutile in the bulk phase.

18. UV Vis Diffuse Reflectance Spectra- Cerium Doped Titania

19. UV Vis Diffuse Reflectance Spectra- Iron Doped Titania

20. Results: UV Vis Diffuse Reflectance Spectra
Estimation of band gap energy values are
cerium doped catalysts: 2.4 eV
Iron doped catalysts: 2.6 eV
as compared to the value for pure titania, which is about 3.19 eV.

21. BET – Cerium Doped CatalystSl
No.
Weight Percentage of Ceria
BET Surface Area (m2/gm) 1
0.5
81.41 2
0.75
78.56 3
1.0
82.05 4
2.0
80.03
Sl. no
Temperature of Curing(oC)
BET Surface Area (m2/gm) 1.
500
80.03 2.
600
47.82
BET Surface area of 2 wt % Ceria
Doped Titania Treated at Different Temperatures
BET Surface area of Various Concentrations
of Ceria Doped Titania Treated at 500 C

22. BET – Iron Doped Catalysts
Sl. No
Weight Percentage of Ceria
BET Surface Area (m2/gm) 1
0.5
24.0 2
1.0
29.5 3
2.0
28.9
Sl. no
Temperature of Curing(oC)
BET Surface Area (m2/gm) 1.
400
72.3 2.
500
29.5 3.
600
7.8
Table 1. BET Surface area of
Various Concentrations
of Iron Doped Titania Treated at 500 C
Table 2. BET Surface area of
1 wt % Iron Doped Titania Treated at
Different Temperatures

23. Coating and Evaluation of Catalysts in Plug Flow reactor: Reaction Studies
Reactor Tube: 0.5, 1 wt%, and 2 wt% Cerium and 1 wt% Iron Doped Titanium Dioxide sol gel heat treated at 500 0C for 6 hours
Compound Used: Decane, Toluene
Inlet Concentration: ppb

24. Reactor Setup

25. Kinetic Results

26. Kinetic Study

27. Kinetic Results – Different Residence Time – 1wt% Cerium Doped Titania

28. Kinetic Results – Different Inlet Concentrations – Residence Time of 1 sec – 1 wt% Cerium Doped Titania

29. Kinetic Results: Toluene Oxidation using Iron Doped Catalysts

30. Kinetic Results: Comparison of Iron and Cerium Doped Catalysts

31. Results: Kinetic Study
Both Cerium and Iron based catalysts show promise as 50% destruction of toluene was observed (200 ppb to 100 ppb).
No side products were observed for both the oxidation of toluene and decane.
Cerium had more positive characteristics, more rapid desorption of VOC and somewhat better conversion.
Cerium catalysts also show 55% destruction of n-Decane(350ppb to 150ppb).
Acquisition of kinetic data is in progress.

32. Progress To Date
Cerium, Iron and Vanadium doped Titania catalysts have been synthesized at different dopant concentrations and post-treatment temperatures.
Characterization of the Cerium and Iron system have been performed.
Characterization of the vanadium system using X-ray Diffraction (SUNY ESF) is in progress
Photo-catalytic reactor has been constructed and reaction studies have been initiated.
Preliminary kinetic data are promising

33. Future Work
Complete tubular reactor screening studies to select best catalyst from preparations
Execute detailed kinetic analysis and reaction pathway analysis (if time permits) for a selected catalyst to obtain a reaction model for photocatalytic destruction of selected VOC
Prepare and submit final report.

34. Kinetic Results: Effect of Dopant Concentration on Oxidation of Toluene

35. UV Vis Diffuse Reflectance Spectra – Cerium Doped Titania