Hybrid metal and metal oxide layers with enhanced activity

Abstract

The invention provides coalesced and un-coalesced organic/inorganic films and methods of use.

Claims

1. A process for producing a permeable organic/inorganic hybrid material comprising a metal oxide material, the process comprising: forming by molecular layer deposition (MLD) an organic/inorganic molecular film on a surface; and annealing said film at a temperature in a range of 200 C. to 900 C. and under an atmosphere of at least one selected from the group consisting of air, nitrogen, hydrogen, an inert gas, or in vacuo, permitting formation of the permeable organic/inorganic hybrid material comprising a photocatalytically active metal oxide material.

2. The process according to claim 1, wherein the organic/inorganic molecular film formed on a surface is prepared by: (1) forming a layer of a metal source on the surface; and (2) treating the layer of the metal source with an organic active material.

3. The process according to claim 2, wherein step (1) involves flowing a metal source one or more times over the surface, thereby permitting a reaction between the metal source and the surface material.

4. The process according to claim 2, wherein step (2) involves flowing the organic active material one or more times over the metal source film to allow reaction between the organic active material and the metal source.

5. The process according to claim 2, wherein following step (2), the film is thermally annealed at a temperature in a range of 200 C. to 900 C. and under an atmosphere of at least one selected from the group consisting of air, nitrogen, hydrogen, an inert gas, or in vacuo.

6. The process according to claim 4, wherein said metal source is of a metal being selected amongst metals, transition metals and metalloids of the Periodic Table of the Elements.

7. The process according to claim 6, wherein said metal is selected from Ti, Zn, Fe, V, Ni, and Cr.

8. The process according to claim 4, wherein said metal source is selected from a metal halide, a metal hydroxide, a metal alkyl and a metal complex with one or more ligand moieties.

9. The process according to claim 4, wherein the organic active material is an organic material comprising two or more alcohol or amine functional groups.

10. The process according to claim 4, wherein the organic active material is an aliphatic material comprising between 2 and 5 carbon atoms and two or more alcohol and/or amine functional groups.

11. The process according to claim 9, wherein the organic active material is selected amongst aliphatic alcohols and aliphatic amines.

12. The process according to claim 11, wherein the aliphatic alcohol is a dialcohol.

13. The process according to claim 12, wherein the dialcohol is ethylene glycol (EG).

14. The process according to claim 5, wherein prior to or after annealing of the film, the film is doped with at least one metal atom, metal cation, a non-metal dopant or an organic or inorganic material.

15. The process according to claim 4, wherein the metal source is Ti-halide and the organic aliphatic alcohol being ethylene glycol (EG), the Ti-EG film being annealed to afford TiO.sub.2.

16. The process according to claim 15, wherein the TiO.sub.2 is anatase TiO.sub.2.

17. The process according to claim 4, wherein said surface is of a material particulate selected amongst (nano)particles and (nano)wires.

18. A process for producing a permeable organic/inorganic hybrid material comprising a metal oxide material, the process comprising: forming by molecular layer deposition (MLD) an organic/inorganic molecular film on a surface, said film comprising at least one metal selected from the group consisting of Zn, Zr, Fe, Ti, V, Cu, Ni, Bi and W; and annealing said film at a temperature in a range of 200 C. to 900 C. and under an atmosphere of at least one selected from the group consisting of air, nitrogen, hydrogen, an inert gas, or in vacuo, permitting formation of the permeable organic/inorganic hybrid material comprising a photocatalytically active metal oxide material, said oxide being of the at least one metal selected from the group consisting of Zn, Zr, Fe, Ti, V, Cu, Ni, Bi and W.

19. A process for producing a permeable organic/inorganic hybrid material comprising a metal oxide material, the process comprising: forming by molecular layer deposition (MLD) an organic/inorganic molecular film on a surface by: (1) forming a layer of a metal source on a surface; and (2) treating the layer of the metal source by flowing an organic active material one or more times over the metal source film to allow reaction between the organic active material and the metal source; and annealing said film at a temperature in a range of 200 C. to 900 C. and under an atmosphere of at least one selected from the group consisting of air, nitrogen, hydrogen, an inert gas, or in vacuo, permitting formation of the permeable organic/inorganic hybrid material comprising a photocatalytically active metal oxide material.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 depicts film thickness vs. number of cycles at 100 C. (.circle-solid.), 110 C. (.box-tangle-solidup.), 120 C. (.square-solid.); for Ti-EG MLD, and (.diamond-solid.) TiO.sub.2 ALD.

(3) FIGS. 2A-C show TEM images of SiNW coated with Ti-EG films annealed at (FIG. 2A) 250 C., (FIG. 2B) 650 C., and (FIG. 2C) 850 C.

(4) FIG. 3 shows refractive index versus wavelength for ALD TiO.sub.2 as compared with Ti-EG films prepared and annealed in accordance with the invention.

(5) FIG. 4 depicts a plot of (h).sup.1/2 versus h for Ti-EG and TiO.sub.2 films.

(6) FIGS. 5A-B show representative XPS spectra of Ti-EG films prepared at 100 C., 40 cycles and doped by Fe (FIG. 5A) and Ni ions (FIG. 5B).

(7) FIGS. 6A-B show the UV-Vis absorption spectra of undoped and doped Ti-EG films that were post-annealed at different temperature: FIG. 6AFe doped; FIG. 6BNi doped film.

(8) FIG. 7 shows plot of (h).sup.1/2 versus h for Ti-EG films post annealed at 750 C. (line a), Ni doped film (line b), Fe doped (dash line c).

(9) FIGS. 8A-B show the adsorption (FIG. 8A) and photodegradation (FIG. 8B) of 4OHTPP on Ti-EG film annealed at 650 C. Photodegradation was induced by illumination of UV light (365 nm).

(10) FIG. 9 shows the enhanced photocatalytic activity of Ti-EG films over TiO.sub.2 films as a function of anneal temperature. High activity related to amorphous-crystalline structure (550-750 C.).

(11) FIG. 10 demonstrates the photocatalytic degradation of methylene blue (MB) in aqueous solution. TiEG and TiO.sub.2 films of same thickness, annealed at 650 C., were immersed in 0.01 mM solution of MB and irradiated with UV; the decrease in absorbance at =664 nm was followed.

(12) FIGS. 11A-C present TEM images of SiNWs coated with Ti-EG (FIG. 11A-B) and TiO.sub.2 (FIG. 11C) exposed to Au.sup.3+ ion solution in the dark (FIG. 11A) and in the light (FIGS. 11B-C).

(13) FIG. 12 demonstrates photocatalytic production of H.sub.2O.sub.2 on SiNWs/Ti-EG/Au in 0.03M HF aqueous solution with (.circle-solid.) and without (.box-tangle-solidup.) O.sub.2, on SiNWs/Ti-EG (.diamond-solid.) and on SiNWs/Ti-EG/Au without HF (.square-solid.). Ti-EG coated SiNWs were annealed at 700 C. prior to Au deposition and a 365 nm UV light source was employed.

(14) FIGS. 13A-B are photograph of TLC chromatogram showing resolution: FIG. 13Aof () 2-methyl-1,4-butanediol: (left to right) spot 1, lower spot ()-isomer and the upper spot for (+)-isomer; mobile phase CH.sub.2Cl.sub.2/C.sub.6H.sub.14 (4:1) and ()-butanediol adsorbed on Ti-EG coated silica gel as a stationary phase. FIG. 13B()-1-phenylethanol: (left to right) spot 1, lower spot ()-isomer and the upper spot (+)-isomer; mobile phase CH.sub.2Cl.sub.2/C.sub.6H.sub.14(1:5) and (+)-phenylethanol-adsorbed on Ti-EG coated silica gel as a stationary phase. Development condition; 10 min; at room temperature; detection by iodine vapor.

(15) FIG. 14 shows water contact angle on glass slides coated with 18 nm Ti-EG layers and treated with perfluoropolyether liquid; without (.square-solid.) and with (.diamond-solid.) temperature treatment of Ti-EG layers.

(16) FIGS. 15A-B show XPS spectra: FIG. 15ACa 2p region for Ti(EG) MLD films and dipped for 30 min in a solution of CaNO.sub.3; FIG. 15BFe 2p region for Ti-EG MLD films and dipped for 30 min in a solution of FeNO.sub.3.

DETAILED DESCRIPTION OF THE INVENTION

(17) 1. General Considerations: Molecular Layer Deposition (MLD)

(18) Ti-EG layers, as exemplary layers according to the invention, were prepared using custom build system by dosing the reactant precursors into viscous flow reactor using Ar carrier gas. The duration of precursor dosing was controlled using computer controlled pneumatic valves. Different process parameters such as precursor chamber temperature, deposition temperature and pressure were optimized for reproducible film formation. The films were grown on various substrates such as SiO.sub.2/Si wafers, quartz/glass slides, TLC slides and Si nanowires.

(19) The MLD process involving TiCl.sub.4 and ethylene glycol (Ti-EG), which is similarly suitable for use with other metal halides and active organic molecules such as diols, was found highly controllable and reproducible. Ellipsometric measurements showed Ti-EG film thickness growing linearly with deposition cycle with 4.5 to 6 thickness increase per TiCl.sub.4/EG cycle at the temperature range studied 100-120 C. (FIG. 1). An exemplary set of experimental conditions for the formation of Ti-EG MLD films and TiO.sub.2 ALD films is summarized in Table 1. TEM imaging showed the morphology change during thermal annealing and extremely conformal films at the nanometric scale (FIG. 2). Based on the annealing temperature, three structures could be indentified: (i) amorphous, (ii) amorphous-crystalline, and (iii) crystalline regions.

(20) TABLE-US-00001 TABLE 1 Process parameters for Ti-EG MLD and TiO.sub.2 ALD films formed at various reaction temperatures. TiCl.sub.4 precursor at 25 C. EG and H.sub.2O precursor temperatures were at 80 and 40 C., respectively. TiCl.sub.4/Ar purge/sec EG/Ar purge/sec T/ C. Oxygen sources 0.3/9 70/30 100 EG 0.3/6 35/35 110 0.3/6 30/30 120 0.3/6 0.4/10 100 H.sub.2O

(21) Additionally, TEM electro diffraction pattern showed only the presence of anatase phase for films annealed at 650 and 850 C. The photocatalytic activity of the resulting structure mainly dependent on the annealing temperature as described below.

(22) Film Optical Properties

(23) FIG. 3 shows the refractive index, n, versus wavelength for Ti-EG film, grown at 100 C. with a thickness of 180 . The as-prepared Ti-EG film yielded refractive value at 590 nm of 1.7. As a result of the annealing, an increase in refractive index was observed. For the Ti-EG films annealed at 650 and 850 C., the refractive index values were 2.1 and 2.4 at 590 nm. The refractive index of TiO.sub.2 ALD films deposited at 100 C. are also displayed for comparison. The TiO.sub.2 film prepared by ALD had a refractive index of 2.4 at 590 nm. It can be concluded, that the refractive index values of as prepared Ti-EG were much lower due to the organic part of the film as compared to TiO.sub.2 ALD film. Ti-EG films annealed at these high temperatures gave similar refractive index values to TiO.sub.2, due to the decomposition of the organic component and retaining the TiO frame.

(24) Band gap for the Ti-EG and TiO.sub.2 ALD films were obtained by using Tauc's equation (Eq. 1).
=[{B.Math.(hE.sub.g).sup.p}/h](Eq. 1)

(25) In Eq. 1, B is a constant and p is an index that characterizes the optical absorption process and is theoretically equal to for direct band gap materials and is 2 for indirect band gap materials. The absorption coefficient () of the films was calculated from the absorbance by using the relation: =2.303 A/t, wherein A is the optical absorbance and t thickness of the film.

(26) Values of the optical band gap for as-prepared Ti-EG and TiO.sub.2 ALD films were extracted by plotting (h).sup.1/2 versus h and extrapolating the linear portion to (h).sup.1/2=0 (FIG. 4).

(27) The band gap of the as-prepared Ti-EG film was measured at 3.5 eV, because of the presence of the organic part in the film the band gap was lower as compare to TiO.sub.2 ALD film (3.3 eV).

(28) After annealing at 250 C. and 650 C., the values of the band gap decreased to 3.45 eV and 3.34 eV, respectively. At a higher temperature the band gap became similar to the anatase phase band gap described in literature 850 C.-3.3 eV.

(29) Doping of TiO.sub.2

(30) Doping is one of the typical approaches to extending the spectral response of TiO.sub.2 to the visible light region. Doping by metal-cations (transition metals) and non-metal dopands (for example C, N, B) has been intensively investigated. Doping TiO.sub.2 with transition metals such as Fe, Ni, V and Cr was used for achieving visible light photocatalytic activity by shifting the adsorption edge to longer wavelengths. Cation doping induced the narrowing of the band gap of TiO.sub.2. It is known that in the metal ion-implanted TiO.sub.2 the overlap of the Ti d-orbital of TiO.sub.2 and the metal d-orbital of the implanted metal ions leads to the narrowing of the band gap of the material. Moreover, the dopant ion induces the formation of new states close to the conduction band. Therefore, doping by metal ions greatly improved the photocatalytic activity in the visible light region. On the other hand, it inhibited the recombination of the photogenerated electron and hole. Metal ions with a suitable concentration could trap the photogenerated electron, which enhanced the utilization efficiency of the photogenerated electron and hole. Decrease of charge carriers recombination resulted in enhanced photoactivity. The absorption edge of metal doped TiO.sub.2 is known to be red-shifted to the visible red light with shift decreased in the following order: V>Cr>Mn>Fe>Ni. The shift increases slightly with the percent content of metal dopands in the modified samples.

(31) Metal Cation Doping

(32) Doping of the films was performed for as-prepared Ti-EG films formed by MLD on quartz slides. Different metal acetylacetonates were used as precursor dopands, Ni(II) acetylacetonate 0.045M and iron(III) acetylacetonate 0.18M in acetonitrile. The coated quartz slides were immersed in the metal acetylacetonate solution for 30 min, rinsed for 10 sec with acetonitrile, and dried under N.sub.2. Then quartz slides were annealed at various temperatures.

(33) Doping of Ti-EG Films by Transition Metals

(34) Ti-EG films showed high affinity towards transition metal cations. FIG. 5 shows representative XPS data obtained for Ti-EG layers exposed to solutions containing Fe.sup.3+ and Ni.sup.2+ ions.

(35) For doping Ti-EG films, quartz slides with Ti-EG films were dipped in acetonitrile solutions of iron acetylacetonate or nickel acetylacetonate for 30 min, dried under N.sub.2 stream and annealed at 250-850 C.

(36) By increasing the anneal temperature, the absorbance red shift increased until 750 C. (FIG. 6). Controlling the dopand concentration allowed producing more uniform films, without formation additional oxide of the dopant phase on the surface of the layer, therefore the optimal concentration of acetylacetonate solutions is 0.18 mM in the case studied here.

(37) The band gap energy values for undoped Ti-EG films annealed at various temperature range from 3.42 to 3.3 eV, for the metal doped films the band gap values in range from 3.3 to 2.7 eV, depend on the activation temperature (Table 2). Maximal red shift was observed for the films annealed at 750 C., with the band gap extracted for Fe-doped and Ni-doped is 2.74 and 2.7 eV, respectively (FIG. 7).

(38) TABLE-US-00002 TABLE 2 Indirect band gap energies for Ti-EG films annealed at different temperatures and treated with different metal cations. T/ C. Ti-EG/eV Fe-/eV Ni-/eV 250 3.42 3.28 3.36 350 3.25 3.19 2.98 450 3.28 2.91 2.94 550 3.29 2.79 2.81 650 3.34 2.91 2.82 750 3.3 2.74 2.7 850 3.3 3.012 3.04
2. Applications
2.1 Photocatalyic Layers
2.1.1 Photo-Decomposition of Compounds; Adsorbed Films of Porphyrin

(39) Porphyrin molecules are versatile molecular probes for studying molecular interfaces using their unique spectroscopic and structural properties. In order to evaluate the photocatalytic and molecular loading properties of films of the invention, 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphine (4OHTPP) was used as a spectroscopic marker to study the adsorption into the films; as well as to study the molecular interactions within the films. The 4OHTPP hydroxyl groups facilitate adsorption of the porphyrin to polar surface groups found in Ti-EG as well as in TiO.sub.2 films from polar aprotic solvents such as acetonitrile.

(40) For measuring the photocatalytic degradation of 4OHTPP on Ti-EG or TiO.sub.2 films, quartz slides coated with Ti-EG or TiO.sub.2 films were annealed at various temperature and immersed in the 0.08 mM solution of porphyrin in acetonitrile for 2 hrs, rinsed three times with acetonitrile, and dried under N.sub.2 stream in the dark. Then, the dry films were subjected to a 365 nm light source for different time intervals and the decrease in Soret band absorbency was followed with UV-Vis spectrophotometry (FIG. 8).

(41) The relative photocatalytic activity of the Ti-EG films were evaluated and compared with TiO.sub.2 films prepared in similar way. The amount of time needed to bleach half of the porphyrin adsorbed was measured. A 5-fold increase in activity was achieved at the annealing conditions (FIG. 9).

(42) 2.1.2 Photo-Decomposition of Compounds; Methylene Blue (MB) in Solution

(43) Methylene blue was used as a model compound in photo-decomposition of organic contaminants. The stability and performance of TiO.sub.2 based catalyst is commonly tested with irradiating an aqueous solution of MB in the presence of the catalyst and compared with known reference. The photocatalytic degradation of methylene blue (MB) in aqueous solution was performed by irradiating 0.01 mM solution of MB in the presence of Ti-EG or TiO.sub.2 films. The results showed that the Ti-EG films of the invention decomposed MB faster than TiO.sub.2 and were stable under the working condition (FIG. 10).

(44) 2.1.3 H.sub.2O.sub.2 Production

(45) The primary process in photocatalytic systems is photo-generation of hole and electron pairs. Proper utilization of the photo generated charge carriers can be used to decompose organic contaminants, generate electric power or store energy as chemical fuels

(46) Silicon nanowires (SiNWs) were grown in a custom built CVD system using vapor-liquid-solid (VLS) mechanism. For nanowires growth on different substrates, poly-L-lysine solution, a polycation for the adsorption of metal catalyst was employed. Au nanoparticles of different diameters ranging 15-80 nm served as the metal catalysts to initiate the nanowire growth. SiH.sub.4 and H.sub.2 were used as reactive gases. The as-prepared nanowires were used as templates for film formation. Electroless deposition of Au in (or on) Ti-EG or TiO.sub.2 coated SiNWs was performed by immersion into solution containing 1 mM AuCl.sub.3 and 0.2 M HF for 5 min, leading to the galvanic deposition of the gold nanostructures in the Ti-EG or TiO.sub.2 coated SiNW.

(47) Silicon nanowires (SiNWs) with diameters of 30 nm were used as scaffold and coated with MLD Ti-EG films and annealed at 700 C. Subsequent treatment of the coated SiNWs with noble metal ions and hydrofluoric acid resulted in noble metal nanostructure deposition, SiNW/Ti-EG/M. Deposition of Au nanoparticles was demonstrated as a typical example; during the process Au nanoparticles deposited by the galvanic displacement reaction and SiNWs were etched with HF leading the formation of hollow Ti-EG tubes coated with Au as confirmed by HRTEM (FIGS. 11A-B). Whereas, SiNWs coated with ALD TiO.sub.2 layers showed no galvanic deposition reaction (FIG. 11C), this was due to the compact nature of the TiO.sub.2 films on SiNW.

(48) Alternatively, silicon or germanium NW, having a diameter of between 5-150 nm, a length of between 0.5 micron to 10 micron have been used. The TiEG layer, formed from 10-80 cycles and annealed at a temp between 450-750 C. was doped with gold particles. Gold solution used for deposition comprised AuCl.sub.3 in water, at a concentration between 0.1 mM and 5 mM with HF at a concentration between 0.1 mM and 500 mM. H.sub.2O.sub.2 was produced by shining UV light on the material when immersed in acidic solution of water (1-100 mM HCl).

(49) The deposition of the metal nanostructure in the SiNW/Ti-EG was possible due to the molecularly permeable nature of Ti-EG. Thermal annealing of SiNW/Ti-EG assembly resulted in the loss of the organic part leaving voids for molecular ion diffusion on the oxide frame work. The gold metal deposition on SiNW/Ti-EG could be performed under light and dark condition. The deposition of gold nanostructure on SiNW/Ti-EG under light proceeded through galvanic displacement and/or initiated by photo excited electrons from Ti-EG film (photoreduction). However, in the dark the deposition mainly took place via galvanic displacement. FIG. 11A shows the formation of gold nanostructure in the dark; Au deposition only occurred inside the Ti-EG nanotube; this indicates the formation gold nanostructure through galvanic displacement assisted by the dissolution of SiNWs by HF.

(50) FIG. 11B shows the deposition of gold nanostructure in and outside of the SiNW/Ti-EG nanotube; this result confirms the photodeposition of the gold nanostructure in addition to the galvanic deposition. Hence, the molecularly permeable Ti-EG nanotube provides best platform for assembling the gold nanostructure-SiNW/Ti-EG composite materials.

(51) Initial experiments on photocatalytic production of H.sub.2O.sub.2 showed that SiNWs/Ti-EG/Au assembly could be used as an efficient catalyst without the use of a sacrificial hole acceptors. FIG. 12 shows typical results obtained for the photocatalytic hydrogen peroxide generation in acidic solution, measured by the iodide oxidation method.

(52) The results demonstrate the catalyst efficiency in the formation of H.sub.2O.sub.2 at different conditions. It can be seen that no activity was observed without the gold deposition. The presence of oxygen showed minor influence on the H.sub.2O.sub.2 production. H.sub.2O.sub.2 formation can be achieved by the oxidation of water or by the reduction of oxygen. HF concentration have a strong effect on the H.sub.2O.sub.2 production it can be explain by the relative stability of H.sub.2O.sub.2 in acidic solution and the activation of the surface. The catalyst was reused for five times and it without showing any decrease in activity.

(53) 2.2 Modification of Ti-EG Surfaces

(54) 2.2.1 Separation of Compounds; Chiral Molecules

(55) The synthesis and separation of chiral organic compounds is the heart of modern research in biochemistry and pharmaceutical industry. Chiral compounds exist as enantiomers and exhibit identical physicochemical properties in conventional isotropic environments. The direct separation of chiral compounds requires the use of chiral environment. Several techniques were developed for the separation of enantiomers, the most popular and general method is liquid chromatography (LC and HPLC) using chiral stationary phases (CSPs). Considerable effort put in developing efficient and affordable chromatographic columns with CSPs. The principle relies on modifying the column packing materials (silica beds, nanoparticles) by a chiral molecule acting as a chiral selector.

(56) Thin Layer Chromatography (TLC) is one of the most widely used separation method in preparatory organic synthesis. This technique provides direct resolution of enantiomers of a variety of compounds and own several advantages that include parallel separation of samples, short analysis time and low cost. Thus, a fast and reliable technique to identify the components of reaction products including chiral molecules is important before running other analytical separation experiments.

(57) Exploiting the unique material properties of the Ti-EG layers (extensive OH functionality, molecular level permeability); they can be used to form a variety of layers with different properties of which chiral layers are of major interest. The Ti-EG layers can prepared on highly porous substrate employing the inherent advantages of MLD (highly uniform and conformal films). The principle using TLC silica gel plates which are commercially available is demonstrated. TLC plates were coated by Ti-EG film using MLD process and then chiral selector was absorbed by immersion of the plates in a solution of chiral compound. FIG. 13A is a photograph of chromatogram separation for (+) and () isomers of 2-methyl-1,4-butanediol in dichloromethane-hexane solution (ration 4:1). The Rf value for the resolved (+) R isomer of butanediol was 0.468.

(58) Another example showing the separation of phenylethanol enantiomers is presented in (FIG. 13B), with Rf of 0.83 and 0.958 for the (+) and () isomers, respectively. This result suggests a facile formation of chiral stationary phase for the separation of enantiomers. The method can be extended to modify other column packing materials.

(59) TLC plates were coated with 18 nm thick Ti-EG layer using MLD process and treated a chiral diol solution in acetonitrile. Two spot of the R- and S-stereoisomers of the target analyte were applied on CSP and were located by exposure to iodine vapors. A mixture dichloromethane and hexane was used as a mobile phase and the chromatogram allowed run for 10 min under a closed vessel at room temperature.

(60) As detailed hereinabove, the chiral separation may alternatively be carried out using a chiral column loaded with a composition comprising the Ti-EG material, employing and chromatographic methodology known in the art.

(61) 2.2.2 Slippery Surfaces; Formation of Hydrophobic Surfaces

(62) Wetting property of surfaces is a very important aspect of surface chemistry, which may have a wide variety of practical applications in biomedical science, textile industry, self cleaning surfaces and agriculture. The preparation and formation of artificial water-repellent surfaces (hydrophobic, super-hydrophobic) is mainly inspired by naturally existing surfaces (Lotus leaf, butter fly wings etc.). The measure of hydrophobicity of surfaces is the contact angle of the water droplet which gives an indication of the wettability of the surface. But for practical application the sliding angle (dynamic angle) in which the droplet start to roll off is important. Methods to prepare hydrophobic surfaces include surface modification with monolayers and polymers, nano-structuring of surfaces and locking lubricating liquids in nanoporous substrate.

(63) The OH functionality of the Ti-EG layers is a key feature for the physical and chemical modification of the surface. The layers can serve as a host material for the immobilization of liquids with different polarity. A proper match between the guest liquid and the Ti-EG layer will result in a stable liquid film owing different wetting properties or buffer surface to reduce friction. High boiling perfluoropolyether liquids have been used to illustrate the principle. Glass plates were coated with few nm thick layer of Ti-EG and immersed in these liquids for 20-30 min followed by careful drying with N.sub.2 stream. This led to the formation of very thin and uniform liquid films on top of the Ti-EG layers. Initial result showed water contact angle of 120-125 stable for days. In contrast, glass plates coated with Ti-EG layers and annealed at 350 C. prior to the treatment of perfluoropolyether liquids exhibits water contact angle of 40. The result shows the Ti-EG layer can potential interact with O atoms of the perfluoropolyether and lock the liquid in place (FIG. 14).

(64) 2.3 Extraction of Heavy Metals

(65) Environmental remediation (removal of heavy metals) is an active field of research with potential industrial application as the strict environmental regulations pushes to more green process. The need for removal of heavy metals from solutions originate; i) some heavy metals (Cd, Hg, Cr and Pb) pose a serious health threat to living organisms and ii) the extracted metals (noble metals) may have commercial values. Most commonly used methods for speciation of heavy metal include precipitation, solvent extraction, activated carbon adsorption, ion exchange resins and biosorption.

(66) Ti-EG layers dipped in different solutions show high affinity towards metal ions. This phenomenon arises due to the functionality of the layer and/or diffusion of the metal ions through the layer. FIG. 15 shows a representative example of the Ti-EG layers exposed to solution containing Fe.sup.3+ and Ca.sup.2+ ions. The incorporation of the ions is monitored by XPS measurements. The simple and straight forward experiment shows Ti-EG layers can potential be used for extraction of heavy metals and integrated with appropriate detection system either spectroscopy or electrochemical methods.

(67) Experimental Section

(68) MLD Process

(69) Ti-EG films were prepared using TiCl.sub.4 (Acros, 99.9%) and ethylene glycol (Aldrich, >99%). Ultra pure water (>18M, ELGA purification system) was used for ALD of TiO.sub.2. Ultrahigh purity Ar gas was used as the carrier gas in viscous flow reactor and for purge between reactant exposures. MLD films were prepared by dosing the reactant precursors into Ar carrier gas. The duration of precursor dosing was controlled using computer controlled pneumatic valves. A steady state pressure of 2.110.sup.1 mBar was maintained during the process. For the MLD process the water and EG precursor chamber temperature was set to 40 and 80 C., respectively. Sample reaction temperature was set to 100, 110, and 120 C. for various processes. The films were prepared on various substrates such as SiO.sub.2/Si wafers, quartz slides, and 40 nm SiO.sub.2 membranes for TEM measurements. Prior to film formation the substrates were cleaned using Oxygen Plasma for 1 min, 60 W RF power. Unless otherwise mentioned the number of cycles performed was set to 40 cycles for Ti-EG and 220 cycles for TiO.sub.2 films with film thickness of 16 nm for both. Films were thermally annealed at the different specified temperature for 30 minutes. For thermal anneal of the films, the oven temperature is equilibrated to the desired temperature prior to sample loading to avoid kinetic effects of temperature ramp rate.

(70) Porphyrin Adsorption and Photocatalytic Degradation Measurements

(71) 5,10,15,20-Tetrakis(4-hydroxyphenyl)-21H,23H-porphine (4OHTPP) was obtained from Aldrich and used as received. 0.08 mM acetonitrile solution of 4OHTPP was prepared and used for adsorption studies as spectroscopic marker. Absorption spectroscopy was performed using a Perkin-Elmer Lambda 1050 spectrophotometer using a custom built slide holder. Ti-EG or TiO.sub.2 films formed on quartz slides were annealed at various temperatures. 4OHTPP adsorption to the films was measured by immersion of the Ti-EG or TiO2 quartz coated slides in the 4OHTPP solution for different time intervals until maximal porphyrin loading was reached as indicated by the Soret absorbency. All porphyrin adsorption studies were carried out in the dark to prevent unintended photodegradation of the surface-adsorbed molecules. For measuring the photocatalytic degradation of 4OHTPP on Ti-EG or TiO.sub.2 films the coated quartz slides were immersed in the porphyrin solution for 2 hrs, rinsed three times with acetonitrile, and dried under N.sub.2 stream in the dark. Then, the dry films were subjected to a 365 nm light source for different time intervals and measurement of the absorption spectra corresponding for each time interval.

(72) SiO.sub.2/Si Nanowire Growth

(73) Si NWs were grown in a custom built CVD system using vapor-liquid-solid mechanism. During the nanowire growth process temperature was set to 440 C., 35 torr pressure, 10 min duration, 50 sccm H.sub.2, and 2 sccm SiH.sub.4 gas flow. 40 nm thick SiO.sub.2 membranes were used as substrates (Ted Pella, Inc.) for nanowire CVD growth and direct TEM imaging without further sample preparation required. For direct SiO.sub.2/Si nanowire growth on the membranes a drop of Poly-L-lysine solution, 0.1% (w/v) in H.sub.2O (Sigma) was placed on the membrane for 5 min followed by rinse with DI water and dried under N.sub.2 stream. Then a drop containing 30 nm Au nanoparticle solution (Ted Pella, Inc.) was placed on the membrane for 2 min, followed by thorough rinse with DI water and dried over N.sub.2 stream.

(74) Characterization Techniques

(75) TEM measurements were performed using FEI Tecnai F20-G.sup.2 system with EFTEM (GATAN GIF 2001).

(76) X-ray photoelectron spectroscopy (XPS) data was collected with a Kratos Axis Ultra X-ray photoelectron spectrometer. Spectra were acquired with monochromatic Al(k) radiation.

(77) Spectroscopic ellipsometry measurements were performed using a VB-200 Spectroscopic Ellipsometer (Woolam Co.).