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 ReceiVed August 5, ReVised Manuscript ReceiVed September 22, 2008 Advisor ： Dr.S.C.Wang Student ： Shih-Kai Shu

Outline  Introduction  Experimental Section  Results and Discussion  Conclusion  Future work

Introduction  Through synthetic architecture and functionalization with self-assembled monolayers (SAMs), complex nanocomposite films of SAM/Pt/ZnO/SiO 2 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°).

 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.

 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).

 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.

Experimental Section (Synthesis of Zinc Carbonate Hydroxide) Zn(OH) 2 Zn 4 CO 3 (OH) 6 ·H 2 O 水熱法 Na 2 CO 3 Zn(NO 3 ) 2 滴入 Zn 4 CO 3 (OH) 6 ·H 2 O 攪拌 在烘箱中乾燥 60 O C 12Hr 產生白色沉澱

(Synthesis of Zinc Hydroxide Netlike Film on Glass Slides) (Preparation of Nanostructured ZnO/SiO2 Films) (Coating of Pt Nanoparticles onto the ZnO/SiO2 Films) H 2 SO 4 /H 2 O 2 混合比例 1 ： 3 取定量 g 的 Zn 4 CO 3 (OH) 6 ·H 2 O 置 於 40ml 去離子水中 加熱 90 O C 4Hr Zn(OH)2/SiO2 composite films 水熱法 180ml 180 O C 2-24Hr Nanostructured ZnO/SiO2 Films 加熱 400 O C 1Hr coating current of mA and a coating time of s 自動塗佈 Pt

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

(Removal of DT and MPA) 上述玻璃基板 the thiol functional groups on the nanocomposite films can be removed 在高溫爐中 300 O C 2Hr 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

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).

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

 TEMimages of PtNPs on the detachedZnOflakes  (a) sputtering time 30 s.  (b) sputtering time 180 s (current ) 20 mA, see Experimental Section).

 Contact angle measurements for DT/Pt/ZnO/SiO 2 composite films 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°

 (a)Contact angles of water on different films of SAM/Pt/ZnO/SiO 2 prepared with DT and MPA mixed solutions (total thiol concentration ) 1.3 mM; see Experimental Section, also denoted as MPA-DT/ZnO/SiO 2 )  (b) contact angles of different water-ethanol mixed solutions on the film of DT/Pt/ZnO/SiO 2.

 Surface wettability switching between superhydrophobicity and superhydrophilicity with addition of SAM (i.e., DT/Pt/ZnO/SiO 2 ) and thermal removal of SAM (i.e., regenerated Pt/ZnO/SiO 2 ).

 Water droplet on a DT/Pt/ZnO/SiO2 composite film with various sliding angles in a series of turnover events (photographs of a to e).

Conclusion  In summary, using Zn 4 CO 3 (OH) 6 ·H 2 O as a starting precursor, nanostructured Zn(OH) 2 can be deposited on SiO 2 substrates (i.e., Zn(OH) 2 /SiO 2 ) under hydrothermal conditions, which can be later thermally converted to ZnO phase, producing metaloxide films of ZnO/SiO 2. The surface topographies of the prepared Zn(OH) 2 /SiO 2 and ZnO/SiO 2 films are highly uniform and porous.

 Our water contact angle measurements show that the as-prepared films of ZnO/SiO 2 and Pt/ZnO/SiO 2 are superhydrophilic and hydrophilic, respectively.  On the other hand, they can also be readmitted to the Pt/ZnO/ SiO 2 films in order to regenerate desired surface functionalities. Our nanocomposite films have been proved to be thermally stable and structurally robust to withstand all process/treatment cycleswithout any deterioration in performance.

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