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Fabrication and Surface Properties of Composite Films of SAM/Pt/ ZnO/SiO 2

Fabrication and Surface Properties of Composite Films of SAM/Pt/ ZnO/SiO 2. Ke Xin Yao and Hua Chun Zeng* Department of Chemical and Biomolecular Engineering, Faculty of Engineering, National UniVersity of Singapore, 10 Kent Ridge Crescent, Singapore 119260

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Fabrication and Surface Properties of Composite Films of SAM/Pt/ ZnO/SiO 2

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  1. Fabrication and Surface Properties of Composite Films of SAM/Pt/ZnO/SiO2 Ke Xin Yao and Hua Chun Zeng* Department of Chemical and Biomolecular Engineering, Faculty of Engineering, National UniVersity of Singapore, 10 Kent Ridge Crescent, Singapore 119260 ReceiVed August 5, 2008. ReVised Manuscript ReceiVed September 22, 2008 Advisor：Dr.S.C.Wang Student：Shih-Kai Shu

  2. Outline • Introduction • Experimental Section • Results and Discussion • Conclusion • Future work

  3. Introduction • Through synthetic architecture and functionalization with self-assembled monolayers (SAMs), complex nanocomposite films of SAM/Pt/ZnO/SiO2 have been facilely prepared in this work. • The nanostructured films are highly uniform and porous, showing a wide range of tunable wettabilities from superhydrophilicity to superhydrophobicity (water contact angles: 0° to 170°).

  4. Our approach offers synthetic flexibility in controlling film architecture, surface topography, coating texture, crystallite size, and chemical composition of modifiers (e.g., SAMs derived from alkanethiols). • For example, wettability properties of the nanocomposite films can be finely tuned with both inorganic phase and organic phase.

  5. Due to the presence of catalytic components Pt/ZnO within the nanocomposites, surface reactions of the organic modifiers can further take place at room temperature and elevated temperatures, which provides a means for SAM formation and elimination. • Because the Pt/ZnO forms an excellent pair of metal-semiconductors for photocatalysis, the anchored SAMs can also be modified or depleted by UV irradiation (i.e., the films possess self-cleaning ability).

  6. Potential applications of these nanocomposite films have been addressed. Our durability tests also confirm that the films are thermally stable and structurally robust in modification-regeneration cycles.

  7. Experimental Section (Synthesis of Zinc Carbonate Hydroxide) Zn(OH)2 Na2CO3 水熱法 滴入 Zn4CO3(OH)6 ·H2O Zn(NO3)2 攪拌 Zn4CO3(OH)6 ·H2O 產生白色沉澱 在烘箱中乾燥 60OC12Hr

  8. (Synthesis of Zinc Hydroxide Netlike Film on GlassSlides)(Preparation of Nanostructured ZnO/SiO2 Films)(Coating of Pt Nanoparticles onto the ZnO/SiO2 Films) H2SO4/H2O2混合比例1：3 加熱 90OC4Hr 取定量 0.15-0.25g 的 Zn4CO3(OH)6 ·H2O 置於40ml去離子水中 水熱法 180ml180OC2-24Hr Zn(OH)2/SiO2 composite films 加熱 400OC1Hr Nanostructured ZnO/SiO2 Films 自動塗佈Pt coating current of 10-30mAand a coatingtime of 30-180 s

  9. (Modification withDTand MPA) 上述製程所做的玻璃基板 浸泡在20ml的酒精中 1-dodecanethiol[DT; CH3(CH2)11SH, 98+%, Aldrich] or 3-mercaptopropionicacid [MPA; HS(CH2)2COOH, 99%] 浸泡10-30min 使用酒精清洗多次 DT/Pt/ZnO/SiO2,MPA/Pt/ZnO/SiO2, and MPA-DT/Pt/ZnO/SiO2, respectively, inour discussion In the replacement experiment (by MPA), theas-prepared DT/Pt/ZnO/SiO2 films were immersed in 20 mL ofethanolic solution of MPA (0.46 M) for 5 h.

  10. (Removal of DT and MPA) 上述玻璃基板 在高溫爐中 300OC2Hr the thiolfunctional groups on the nanocomposite films can be removed 由疏水性轉變為親水性 也可以利用紫外光照射薄膜來達到以上效果

  11. Results and Discussion • Growth process of nanostructured Zn(OH)2 flakes on the surface of SiO2 substrate (i.e., formation of Zn(OH)2/SiO2; FESEM images) • (a)4 h • (b) 6 h • (c,d) 10 h (see Experimental Section for details).

  12. (a) Formation of ZnO/SiO2 films through thermal conversion of Zn(OH)2/SiO2. • (b-d) Pt nanoparticles deposited on ZnO/SiO2 films(i.e., formation of Pt/ZnO/SiO2 composite films; the Pt nanoparticles in b and c were deposited with a coating current of 20 mA while those in dwere with a coating current of 30 mA; sputtering time ) 180 s, see Experimental Section).

  13. TEMimages of PtNPs on the detachedZnOflakes • (a) sputteringtime 30 s. • (b) sputtering time 180s(current ) 20 mA, seeExperimental Section).

  14. Contact angle measurements for DT/Pt/ZnO/SiO2 compositefilms prepared with various DT concentrations • (a) 0.3 mM, 100.5° • (b)0.6 mM, 136.7° • (c) 1.3 mM, 168.2° • (d) 2.6 mM, 170.3°

  15. (a)Contact angles of water on different films of SAM/Pt/ZnO/SiO2 prepared with DT and MPA mixed solutions (total thiolconcentration ) 1.3 mM; see Experimental Section, also denoted asMPA-DT/ZnO/SiO2) • (b) contact angles of different water-ethanolmixed solutions on the film of DT/Pt/ZnO/SiO2.

  16. Surface wettability switching between superhydrophobicityand superhydrophilicity with addition of SAM (i.e., DT/Pt/ZnO/SiO2)and thermal removal of SAM (i.e., regenerated Pt/ZnO/SiO2).

  17. Water droplet on a DT/Pt/ZnO/SiO2 composite film withvarious sliding angles in a series of turnover events (photographs of ato e).

  18. Conclusion • In summary, using Zn4CO3(OH)6 ·H2Oas a starting precursor,nanostructured Zn(OH)2 can be deposited on SiO2 substrates(i.e., Zn(OH)2/SiO2) under hydrothermal conditions, which canbe later thermally converted to ZnO phase, producing metaloxidefilms of ZnO/SiO2. The surface topographies of the preparedZn(OH)2/SiO2 and ZnO/SiO2 films are highly uniform and porous.

  19. Our water contact anglemeasurements show that the as-prepared films of ZnO/SiO2 andPt/ZnO/SiO2 are superhydrophilic and hydrophilic, respectively. • On the other hand, they can also be readmitted to the Pt/ZnO/ SiO2 films in order to regenerate desired surface functionalities.Our nanocomposite films have been proved to be thermally stableand structurally robust to withstand all process/treatment cycleswithout any deterioration in performance.

  20. 謝謝聆聽 Thank you for your attention!! 23

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