TOWARD HIGH ACTIVITY WITH PHOTOCATALYST DESIGN Dr. Leny Yuliati January 21-22, 2014 Workshop on Nanomaterials for Photocatalytic Depollution: Science and Engineering

OUTLINES Design of: 1. Highly Dispersed Titanium Dioxide on Silica Support Stud. Surf. Sci. Catal., 172 (2007) Silica-Titania with Tetrahedral Ti(IV) Chem. Eng. J., 222 (2013) Porous Carbon-Coated Titania Chem. Eng. J. 209 (2012)

1. Highly Dispersed TiO 2 Introduction TiO 2 is an active photocatalyst for various oxidation reactions. However, it is usually not suitable for selective oxidation reaction or reaction under reductive condition. 1 H. Yoshida, Curr. Opin. Solid Mater. Sci., 7 (2003) 435. e-e- h+h+ isolated Quantum photocatalyst Example: system of highly dispersed metal oxide on support. 1 This system would not easily be reduced under photoreductive condition.

TEOS EtOH H 2 O HCl Stirred for y min at room temperature. Added dropwise Ti(OBu) 4, EtOH, (CH 3 CO) 2 CH 2 Solution 1 Stirred for x min at room temperature. Step 2: Condensation to form Si-O-Ti bonds TiO 2 -SiO 2 samples TS(x,y) Stirred and dried at 353 K. Dried at 383 K, overnight. Calcination at 773 K, 5 h. Step 3: Condensation to form Si-O-Si bonds Step 1: TEOS hydrolysis to form Si(OH) 4 Solution 2 1. Highly Dispersed TiO 2 Synthesis Ti content = 1 mol%

X-ray Energy/eV Normalized Intensity Ti K-edge XANES spectra TS (30,10) TS (30,60) TS (60,30) TS (30,30) TiO 2 1. Highly Dispersed TiO 2 Properties Hydrolysis of TEOS: Si(OEt) 4 + 4H 2 O → Si(OH) 4 + 4EtOH Condensation reaction to form Si-O-Ti bonds: ≡Ti-OBu + H 2 O → ≡Ti-OH + BuOH ≡Si-OH + ≡Ti-OH → ≡Si-O-Ti≡ + H 2 O All samples mainly consist of tetrahedral titanium species regardless the difference of hydrolysis and condensation time in the sol-gel process. Reaction time (x) : 30 and 60 mins Reaction time (y): 10, 30, and 60 mins Ti (Td)

1. Highly Dispersed TiO 2 Properties Hydrolysis of TEOS: Si(OEt) 4 + 4H 2 O → Si(OH) 4 + 4EtOH Condensation reaction to form Si-O-Ti bonds: ≡Ti-OBu + H 2 O → ≡Ti-OH + BuOH ≡Si-OH + ≡Ti-OH → ≡Si-O-Ti≡ + H 2 O Wavelength/nm Kubelka-Munk function DR UV-Vis Spectra TS (30,10) TS (30,60) TS (60,30) TS (30,30) TS (30,30) sample showed the most narrow band centered around 215 nm corresponding to the charge transfer transition [O 2− →Ti 4+ ] of isolated tetrahedral titanium species. 1 Longer hydrolysis time: ≡Si-OH + ≡Si-OH → ≡Si-O-Si≡ + H 2 O Longer condensation time: ≡Si-O-Ti-OH + ≡Si-O-Ti-OH → ≡Si-O-Ti-O-Ti-O-Si ≡ + H 2 O Optimum time for each process is 30 mins. 1 S. Bordiga, et al., J. Phys. Chem. 98 (1994) 4125.

Most stoichiometric of hydrogen ratio 1. Highly Dispersed TiO 2 Activity Yield of hydrocarbons (%C) and hydrogen (  mol) Photocatalyst Type Reaction time = 12 h 2CH 4 C 2 H 6 + H 2 ∆G K = 68.6 kJ mol -1 h RT, 3 h I = 10 mW/cm 2

OUTLINES Design of: 1. Highly Dispersed Titanium Dioxide on Silica Support Stud. Surf. Sci. Catal., 172 (2007) Silica-Titania with Tetrahedral Ti(IV) Chem. Eng. J., 222 (2013) Porous Carbon-Coated Titania Chem. Eng. J. 209 (2012)

2. Silica-Titania Introduction Hydrolysis of OTS: RSiCl 3 + H 2 O → R-Si-(OH) 3 + 3HCl Condensation reaction to form Si-O-Ti bonds: ≡Ti-OEt + H 2 O → ≡Ti-OH + EtOH R-Si-OH + ≡Ti-OH → R-Si-O-Ti≡ + H 2 O Effect of Water Addition? Silica-titania materials usually have a hydrophilic surface, thus, show low affinity towards the organic substrate. One strategy is employing organic functionalized silane precursor with long chain to enhance the hydrophobicity. In this study, octadecyltrichlorosilane (OTS) and tetraethyl orthotitanate (TEOT) were used as silica and titania source, respectively.

2. Silica-Titania Synthesis OTS TEOT Toluene (y) Ultrasonication Added dropwise Various amounts of H 2 O (x) Solution 1 Ultrasonication SiO 2 -TiO 2 (x,y) samples Stand in open air for 24 h Washing with methanol Drying under vacuum at room temperature Solution 2 x = mol% of added water y = volume of toluene (0 or 10 ml)

2. Silica-Titania Properties Octadecyltrichlorosilane (OTS) + tetraethyl orthotitanate (TEOT) Without Water With Water

2. Silica-Titania Properties SiO 2 -TiO 2 (60,10) Wavelength/nm Kubelka-Munk function Deconvolution of DR UV spectra From four peaks: at 230 nm --- Ti (Td) at 255 nm --- Ti (Td) at 285 nm --- Ti (Oh) at 315 nm --- Ti (Oh) SampleFraction of Ti(Td) TiO 2 SiO 2 -TiO 2 (0,0) SiO 2 -TiO 2 (60,0) SiO 2 -TiO 2 (22,10) SiO 2 -TiO 2 (41,10) SiO 2 -TiO 2 (60,10) SiO 2 -TiO 2 (74,10) SiO 2 -TiO 2 (87,10)

2. Silica-Titania Activity Fraction of Ti(Td)/% Turnover Number Styrene Polystyrene H 2 O 2 80 o C, 8 h

OUTLINES Design of: 1. Highly Dispersed Titanium Dioxide on Silica Support Stud. Surf. Sci. Catal., 172 (2007) Silica-Titania with Tetrahedral Ti(IV) Chem. Eng. J., 222 (2013) Porous Carbon-Coated Titania Chem. Eng. J. 209 (2012)

3. Porous Carbon-Coated Titania Introduction Adsorption is a crucial step in heterogeneous catalysis. Carbon layer has been reported to improve the adsorption of reactants on the surface of catalyst. 1 In the catalysis process on carbon-coated titania: - The reactant molecules have to be adsorbed into carbon layer. - The adsorbed reactant molecules have to be diffused on the surface of titania. Therefore, carbon layer could not be either too thin or too thick. Strategy that can be employed: Preparing the porous carbon layer on the surface of titania catalyst. 1 T. Torimoto, et al., J. Photochem. Photobiol. A: Chem., 103 (1997) 153.

2. Silica-Titania Synthesis

2. Silica-Titania Properties Water Catalyst TiO TiO 2 PS 2 2

2. Silica-Titania Properties TiO

2. Silica-Titania Activity Styrene Products H 2 O 2, ACN 80 o C, 8 h Styrene Products I = 0.78 mW/cm 2 H 2 O 2, ACN h, RT, 8 h d-f : different concentrations of KOH (0.1, 0.5, 1.0, and 2.0 M)

SUMMARY High activity can be achieved through design the suitable catalysts. 1.Highly dispersed titanium dioxide on silica support could be prepared by sol-gel method, in which the hydrolysis and condensation times were important factors to design the highly dispersed titanium dioxide on support. 2.Silica-titania could be prepared by sol-gel method, in which the addition of water affected the formation of titanium tetrahedral species. 3.Porous carbon-coated titania could be prepared by KOH treatment of carbon-coated titania.

ACKNOWLEDGEMENTS

SA = 13 m 2 /gSA = 46 m 2 /g