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Photocatalytic activity of SBA-15 silica-supported titania photocatalysts

海峽兩岸工程材料研討會 新竹 - 台灣. Photocatalytic activity of SBA-15 silica-supported titania photocatalysts. 王聖璋 Sheng-Chang Wang 南台科技大學 Southern Taiwan University Institute of Nanotechnology, & Department of Mechanical Engineering, Southern Taiwan University, Tainan 710, Taiwan

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Photocatalytic activity of SBA-15 silica-supported titania photocatalysts

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  1. 海峽兩岸工程材料研討會 新竹-台灣 Photocatalytic activity of SBA-15 silica-supported titania photocatalysts 王聖璋 Sheng-Chang Wang 南台科技大學 Southern Taiwan University Institute of Nanotechnology, & Department of Mechanical Engineering, Southern Taiwan University, Tainan 710, Taiwan 洪玲雅 Ling-Ya Hung 、黃肇瑞 Jow-Lay Huang 國立成功大學材料科學與工程學研究所 2007/11/17

  2. 南台科大 Southern Taiwan University Location Solar-cell car Main Gate Campus Nanotechnology center

  3. Photo catalysis • TiO2 : • Solar energy conversion • Catalyst • Environmental pollution remediation Band gap of semiconductors

  4. TiO2 Nanoparticle • Broader energy band gap • Recombination of electron and hole was decreased. • Higher adsorption surface area

  5. Disadvantages and strategies • Problems: • Ultrafine powders will agglomerate into larger particles • adverse effect on catalyst performance • Separation and recovery of TiO2 powders from wastewater are difficult • limitedlight transmission due to scattering • susceptibility to sintering • Strategies • Supported TiO2 composites • High active surface area • UV-Visible transparent, no absorption. • Stable in chemical and thermal atmospheres

  6. Photocatalyst supporter • activated carbon • clays • alumina • Zeolite, pore size < 1.5 nm • Mesoporous SiO2 • MCM-41, CTABr, < 10 nm • SBA-15, PEO20-PPO79-PEO20

  7. Surfactant-templated synthetic SiO2 mesoporous • P123 • Well mesostructural ordering properties • amphiphilic character • low-cost • commercial availability • Biodegradability • thick silica walls organic structure-directing agents PEO20-PPO70-PE020 poly(ethylene oxide)-poly(propylene Oxide)- Poly(ethylene oxide)

  8. TiO2 synthesis by sol-gel method • Ti(OC3H7)4 + 4 H2O  Ti(OH)4+ 4C3H7OH • The high hydrolysis reactivity of TiO2 precursor, TTIP may cause uncontrolled local precipitation • Acetic acid was added to control the hydrolysis speed

  9. Experimental Procedure

  10. SBA-15 • SBA powder: 2 mm (length), 400 nm (diameter) • well-ordered hexagonal mesoporous silica structures, pore size = 6-7 nm • Wall thickness = 5 nm FFT

  11. SAXS of powder SBA-15 • The calcined SBA-15 powder • Three resolved peaks(100), (110), (200) • Well-ordered hexagonal P6mm Structure

  12. N2 adsorption/ desorption isothermsof SBA-15 Types of physisorption isotherms, IUPAC desorption adsorption • P/P0=0.68 – 0.75, Capillary condensation taking place in mesoporoes • Hysteresis loop, Type IV physisorption isotherms, => mesoporous structure • H1 type, uniform spheres in fairly regular array, narrow distributions of pore size.

  13. Pore size distribution • The synthesized SBA-15 with: • Uniform and narrow pore size distribution • Pore size: 6~7nm 20 nm

  14. Pure TiO2 • Particle size • XRD Rutile Anatase • TEM

  15. XRD patterns of TiO2/SBA-15 Anatase : all TiO2/SBA-15 composites Anatase :20%- 60% TiO2/SBA-15 A+R : 80% TiO2/SBA-15 • TiO2 grain size is decrease by supported on SBA-15 • TiO2 Anatase -> Rutile transition temp. from 700 -> 800C

  16. SAXS spectra of TiO2/SBA-15 • SBA-15 hexagonal structure still maintained after loading different amount of TiO2 • Channels of SBA-15 may contain TiO2 particles

  17. N2 adsorption/desorption isothermsof TiO2/SBA-15

  18. TiO2 contents vs. crystal size, pore size, pore volume Pore size Crystalline size Pore volume Specific area

  19. Pore shape evolution • SBA-15: H1 spherical shape • 20-30 %TiO2/SBA: H1~ H2 type • 60% TiO2/SBA: H2, ink bottle shape, some pores are seal with TiO2 particles • 80% TiO2/SBA: H4, plate-like or slit shaped pores, pores are serious sealed with TiO2 particles H1 H2 H4

  20. TiO2/SBA-15 composites 100 nm 20% TiO2/SBA-15 30% TiO2/SBA-15 60% TiO2/SBA-15

  21. HRTEM • TiO2 nanoparticles are embedded in SBA-15 channel • grain size ~ channel’s diameter Ti TiO2 SiO2 EDS DP 100 nm d spacing=0.357nm =>Anatase TiO2 (101) TEM cross-section image

  22. FTIR spectra • 1090 cm-1: Si-O-Si asymmetric stretching • 470 cm-1: Si-O-Sibending mode • 940 cm-1: Si-O-Ti vibration band • TiO2 , peaks int. Titanium incorporating into the framework of silica

  23. XPS • 532.2 eVSi-O-Ti bonding: chemical bonding occur between TiO2-SiO2 • SBA-15: Si-O tetrahedral • TiO2: Ti-O octahedral • More complicated oxygen coordination states appear in TiO2-SBA-15 • Imply that Si-O-Ti would inhibited the phase transition from of anatase to rutile TiO2

  24. UV-Visible spectra • 300 – 350 nm: TiO2 particle size < 5 nm • 350- 400 nm: TiO2 particle size > 5 nm • Absorption edge: blue shift • calcined temp , absorption edge red shift h [Ti3+-O-L]*  [Ti4+-O2-L]

  25. TiO2/SBA-15 formation mechanism +TTIP hydrolysis calcined SBA-15 Amorphous TiO2 Anatase TiO2 Rutile TiO2 TiO2 temp slit shaped pores Ink-like pore spherical pore TiO2 > 60 % T > 800C TiO2 < 60 %T  700C TiO2 30 %

  26. Standard calibration curve of Methylene Blue (MB) Beer’s Law: A＝b c A:absorption :proportion constant b: light length c: concentration

  27. Degradation of MB • Langmuir-Hinshelwood ln(C/C0)=kt C0: initial concentration of Methylene Blue k: rate constant • kTiO2 : 0.004 min-1 • k30%TiO2 : 0.027 min-1 • k60%TiO2: 0.023 min-1 • 30 % TiO2/SBA15 has the similar degradation rate with 60 %TiO2/SBA15 0 2 4 6 8

  28. Conclusions • High surface area (500 m2/g), high pore volume (0.55 cm3/g) of TiO2 supported on SBA-15 composites have been obtain. (30 %TiO2/SBA-15 calcined at 700C) • Nanosized of 5 nm TiO2 particles embedded in the channel of the mesoporous silica structures. • The SBA-15 supported TiO2 increased the formation temperature of anatase phase to rutile phase from 700C to 800 C and inhibit the TiO2 grain growth by the occurs of Si-O-Ti bonding. • The pore shape from spherical change to plate-like or slit-shaped by increasing the TiO2 content higher than 30 % in the mesoporous silica structure. • Photocatalytic activity of SBA-15 supported TiO2 composite has 3 time increase than the commercial pure TiO2 nanopowder (P25)

  29. Thanks for your attention SnO nanoflower

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