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

TOWARD HIGH ACTIVITY WITH PHOTOCATALYST DESIGN

Dr. Leny Yuliati

January 21-22, 2014

Workshop onNanomaterials for Photocatalytic Depollution:

Science and Engineering

OUTLINES

Design of:

1. Highly Dispersed Titanium Dioxide on Silica Support Stud. Surf. Sci. Catal., 172 (2007) 457-460

2. Silica-Titania with Tetrahedral Ti(IV) Chem. Eng. J., 222 (2013) 23-31

3. Porous Carbon-Coated Titania Chem. Eng. J. 209 (2012) 486-493

1. Highly Dispersed TiO2 Introduction

TiO2 is an active photocatalyst for various oxidation reactions. However, it is usually not suitable for selective oxidation reaction or reaction under reductive condition.

1H. Yoshida, Curr. Opin. Solid Mater. Sci., 7 (2003) 435.

e-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 H2O HCl

Stirred for y min at room temperature.

Added dropwise Ti(OBu)4, EtOH, (CH3CO)2CH2

Solution 1

Stirred for x min at room temperature.

Step 2:Condensation to form Si-O-Ti bonds

TiO2-SiO2 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 TiO2 Synthesis

Ti content = 1 mol%

4960 5000 5040

X-ray Energy/eV

Ti K-edge XANES spectra

TS (30,10)

TS (30,60)

TS (60,30)

TS (30,30)

TiO2

1. Highly Dispersed TiO2 PropertiesHydrolysis of TEOS:Si(OEt)4 + 4H2O → Si(OH)4 + 4EtOH

Condensation reaction to form Si-O-Ti bonds:≡Ti-OBu + H2O → ≡Ti-OH + BuOH≡Si-OH + ≡Ti-OH → ≡Si-O-Ti≡ + H2O

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 TiO2 Properties

Hydrolysis of TEOS:Si(OEt)4 + 4H2O → Si(OH)4 + 4EtOH

Condensation reaction to form Si-O-Ti bonds:≡Ti-OBu + H2O → ≡Ti-OH + BuOH≡Si-OH + ≡Ti-OH → ≡Si-O-Ti≡ + H2O

200 300 400

Wavelength/nm

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 [O2−→Ti4+] of isolated tetrahedral titanium species.1

Longer hydrolysis time: ≡Si-OH + ≡Si-OH → ≡Si-O-Si≡ + H2O

Longer condensation time: ≡Si-O-Ti-OH + ≡Si-O-Ti-OH →

≡Si-O-Ti-O-Ti-O-Si ≡ + H2O

Optimum time for each process is 30 mins.

1S. Bordiga, et al., J. Phys. Chem. 98 (1994) 4125.

Most stoichiometric of hydrogen

ratio

1. Highly Dispersed TiO2 Activity

Photocatalyst Type

Reaction time = 12 h

2CH4 C2H6 + H2 ∆G0298 K = 68.6 kJ mol-1

h

RT, 3 hI = 10 mW/cm2

OUTLINES

Design of:




2. Silica-Titania Introduction

Hydrolysis of OTS:RSiCl3 + H2O → R-Si-(OH)3 + 3HCl

Condensation reaction to form Si-O-Ti bonds:≡Ti-OEt + H2O → ≡Ti-OH + EtOHR-Si-OH + ≡Ti-OH → R-Si-O-Ti≡ + H2O

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 H2O (x)

Solution 1

Ultrasonication

SiO2-TiO2(x,y)

samples

Stand in open air for 24 hWashing with methanolDrying under vacuum at room temperature

Solution 2

x = mol% of added watery = volume of toluene (0 or 10 ml)

2. Silica-Titania Properties

Octadecyltrichlorosilane (OTS) + tetraethyl

orthotitanate (TEOT)

Without Water

With Water


SiO2-TiO2(60,10)

Wavelength/nm

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)

Sample Fraction of Ti(Td)

TiO2

SiO2-TiO2 (0,0)SiO2-TiO2 (60,0)SiO2-TiO2 (22,10)SiO2-TiO2 (41,10)SiO2-TiO2 (60,10)SiO2-TiO2 (74,10)SiO2-TiO2 (87,10)

2343526165697476

2. Silica-Titania Activity

Fraction of Ti(Td)/%

Styrene PolystyreneH2O2

80 oC, 8 h

OUTLINES

Design of:




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.

1T. Torimoto, et al., J. Photochem. Photobiol. A: Chem., 103 (1997) 153.

2. Silica-Titania Synthesis


Water

Catalyst

TiO2 PS@TiO2 C@TiO2 PC@TiO2

TiO2

PS

PS@TiO2

PC@TiO2

2. Silica-Titania PropertiesTiO2 PS@TiO2

C@TiO2PC@TiO2

2. Silica-Titania Activity

H2O2, ACN

80 oC, 8 h

H2O2, 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 m2/g SA = 46 m2/g

Documents

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