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 ofSingapore, 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

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/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°).

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

Zn4CO3(OH)6 ·H2O

水熱法

Na2CO3

Zn(NO3)2

滴入

Zn4CO3(OH)6 ·H2O

攪拌

在烘箱中乾燥 60OC 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)

H2SO4/H2O2 混合比例 1 ： 3

取定量 0.15-0.25g 的 Zn4CO3(OH)6 ·H2O 置於 40ml 去離子水中

加熱 90OC 4Hr

Zn(OH)2/SiO2 composite films

水熱法 180ml 180OC 2-24Hr

Nanostructured ZnO/SiO2 Films

加熱 400OC 1Hr

coating current of 10-30 mA and a coating time of 30-180 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 300OC 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/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 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/SiO2 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/SiO2 prepared with DT and MPA mixed solutions (total thiol concentration ) 1.3 mM; see Experimental Section, also denoted as MPA-DT/ZnO/SiO2)

(b) contact angles of different water-ethanol mixed solutions on the film of DT/Pt/ZnO/SiO2.

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

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 Zn4CO3(OH)6 ·H2O as a starting precursor, nanostructured Zn(OH)2 can be deposited on SiO2 substrates (i.e., Zn(OH)2/SiO2) under hydrothermal conditions, which can be later thermally converted to ZnO phase, producing metaloxide films of ZnO/SiO2. The surface topographies of the prepared Zn(OH)2/SiO2 and ZnO/SiO2 films are highly uniform and porous.

Our water contact angle measurements show that the as-prepared films of ZnO/SiO2 and Pt/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 stable and structurally robust to withstand all process/treatment cycleswithout any deterioration in performance.

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