KR20160036246A - Preparing method of copper oxide - Google Patents

Abstract

A process for producing Cu ₂ O and a process for producing CuO.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a copper-

The present invention relates to a process for producing Cu ₂ O and a process for producing CuO.

Copper (Cu), which is a metallic element with a very high electrical and thermal conductivity and an abundant and toughness, has two oxides: copper (I) (Cu ₂ O) and copper (II) oxide (CuO). Both are p-type semiconductors with narrow band gaps of 1.9-2.2 eV and 1.2-1.7 eV, respectively; The copper (I) oxide and copper (II) oxide are good candidates for solar energy conversion photocatalysts, sensor materials, stable electron sources, and optoelectronic materials. In general, CuO is dark in color because it can absorb both visible and infrared light. Both photoacoustic cathodes have lower chemical stability for the oxidation and reduction of water in aqueous solutions, but CuO is less stable than Cu ₂ O, which is the oxidation-reduction potential of E _{CuO /} Cu ₂ O (+0.60 V vs. NHE) Is more positive than the redox reaction potential of E _{Cu2O / Cu} (+0.47 V vs. NHE); CuO will be Cu ₂ O, which will then become Cu by Cu ₂ O reduction. Therefore, Cu ₂ O is more valuable than CuO in the hydrolysis region, and the researchers are focusing on improving the stability of Cu ₂ O by depositing a protective layer such as ZnO / Al ₂ O ₃ / TiO ₂ .

Much research has been done for the synthesis of copper oxides, irrespective of the difficulties of chemical stability in the electrolyte. Copper oxides / hydroxides [CuO, Cu ₂ O, and Cu (OH) ₂ ] and copper can be converted to one of these by different methods. Copper can be converted to CuO and Cu ₂ O by thermal oxidation at high temperatures in an oxygen atmosphere. Cu ₂ O is stable in a limited range of temperature and oxygen pressure, and during the thermal oxidation of Cu at standard atmospheric pressure, Cu ₂ O can be converted to CuO after a sufficient oxidation time. Musa et al. Reported that only the Cu ₂ O was present in the oxide layer resulting from the oxidation at 1,050 ° C and that the oxide layer grown at 1,040 ° C or less contained a mixed oxide of Cu ₂ O and CuO. They also observed that, in general, lower Cu ₂ O amounts are formed with lower oxidation temperatures [AO Musa, T. Akomolafe and MJ Carter, Sol. Energy Mater. Sol. Cells, 1998, 51, 305.]. It has been reported that Cu ₂ O films can be converted to transparent CuO films by heating in air [KER Brown and K.-S. Choi, Chem. Commun., 2006, 3311.]. For morphology control, CuO wires can also be easily synthesized by heating copper substrates such as Cu TEM grids, foils, and conventional electrical wiring, electrodeposited Cu particle films. It has been reported that the growth of the scroll-type nanotube structure of Cu (OH) ₂ is arranged on copper foil at ambient temperature and pressure by the surface oxidation of Cu foil in an oxidizing agent (NH ₄ ) ₂ S ₂ O ₈ and an alkaline aqueous solution [W. Zhang, X. Wen, S. Yang, Y. Berta and ZL Wang, Adv. Mater., 2003, 15, 822.]. Then, using a small fraction of the yateu Li (Yat Li) group CuO nanowires by the heat treatment wherein the Cu (OH) obtained through the aforementioned method _2, the nanowire at 450 ℃ for one of air time for Cu ₂ O nanowires [F. Qian, G. Wang and Y. Li, Nano Lett., 2010, 10, 4686.]. Pike et al. Reported that bulk CuO was directly reduced to metallic Cu using in situ time-resolved X-ray diffraction (TR-XRD) and nanoscale CuO was completely reduced to Cu ₂ O by isothermal reduction Lt; RTI ID = 0.0 > [J. Pike, SW Chan, F. Zhang, X. Wang and J. Hanson, Appl. Catal., A, 2006, 303, 273.].

As described above, Cu → Cu ₂ O and / or CuO, Cu ₂ O → CuO, Cu (OH) ₂ → Cu ₂ O and CuO, CuO → Cu ₂ O can be performed by thermal oxidation or reduction. However, very high temperatures are required for complete conversion of Cu to Cu ₂ O. In the best knowledge of the present application, there are several reports of Cu to Cu ₂ O conversion under mild experimental conditions. The Cu surface can be electrochemically oxidized with Cu ₂ O, CuO, and Cu (OH) ₂ at different potentials in an alkaline solution. However, the layer of Cu ₂ O film is very thin. Allam and Grimes also reported that various copper oxide nanostructured films were synthesized by anodic oxidation of Cu foils in aqueous and non-aqueous electrolytes containing hydroxide, chloride, and / or fluoride ions at room temperature [NK Allam and CA Grimes, Mater. Lett., 2011, 65, 1949.]. Chu et al. Reported that the hydrothermal reaction of nanoparticles, nanoribbons, nanowires, micro-polyhedra, matte-like, and chrysanthemum-like particles, using different types of surfactants and (NH ₄ ) ₂ S ₂ O ₈ in a high concentration NaOH aqueous solution CuO crystals having different morphologies such as pseudo-nanostructures were synthesized [Y. Liu, Y. Chu, MY Li and LH Dong, J. Mater. Chem., 2006, 16, 192.]. Liu describes the easy fabrication of flower-like and spherical CuO architectures on Cu substrates by immersing the Cu substrate in a low concentration (30.0 mM or 65.0 mM) of NaOH and NH ₃ .H ₂ O solutions at 60 ° C [J. Liu, X. Huang, Y. Li, KM Sulieman, X. He and F. Sun, J. Mater. Chem., 2006, 16, 4427.]. Most recently, Luo has shown that Cu ₂ O polyhedra can be grown directly from Cu foil in 0.3 M NaOH at 60 ° C [ZJ Luo, TT Han, LL Qu and XY Wu, Chin. Chem. Lett., 2012, 23, 953.]. GaO et al. Is CuSO ₄ The introduction of a Cu ₂ O layer on a Cu plate by immersing the Cu foil in solution [T. Gao, Y. Wang, K. Wang, X. Zhang, J. Dui, G. Li, S.Lou and S. Zhou, ACS Appl. Mater. Interfaces, 2013, 5, 7308.]. Surprisingly, there is no detailed report on the mechanism and process of pure Cu ₂ O synthesis and morphology control by simply immersing the different Cu substrates in NaOH solution.

Accordingly, the present invention provides a process for producing Cu ₂ O and a process for producing CuO.

However, the problems to be solved by the present invention are not limited to the above-mentioned problems, and other problems not mentioned can be clearly understood by those skilled in the art from the following description.

A first aspect of the present invention provides a process for producing Cu ₂ O, comprising immersing copper (Cu) in an alkali solution and heating to form a Cu ₂ O film on the substrate.

A second aspect of the present invention provides a process for producing CuO comprising immersing copper (Cu) in an alkali solution and heating to form a CuO film on the substrate.

According to any one of the above-mentioned means for solving the problems, copper (Cu) can be converted directly to Cu ₂ O before forming CuO in a high concentration NaOH aqueous solution by an easy surface oxidation reaction without additional oxidizing agent. By using different Cu substrates, pure Cu ₂ O films with different dominant facets can be obtained.

1A is a graph showing an XRD pattern of two different copper foils (Cu-1 and Cu-2) having different intensity ratios of crystal faces in one embodiment of the present invention.
1B is an image showing a step of forming Cu ₂ O on a Cu foil and an FTO coated glass surface by immersion in an NaOH solution in one embodiment of the present invention.
2A and 2B are XRD patterns and SEM images of Cu ₂ O / Cu-1 obtained according to one embodiment of the present invention.
Figure 3a to 3e shows the Cu ₂ O / _Cu-2 of the SEM image, XRD patterns, and Cu2p and O1s the XPS spectra, photoelectric current and the light response curves under 1 sun lights obtained in accordance with one embodiment of the present application.
FIG. 3F is an SEM image of Cu ₂ O / Cu-2 after checking FIG. 3 e in one embodiment of the present application.
4A is a graph showing XRD patterns of FTO, Cu / FTO and Cu ₂ O / FTO in one embodiment of the present invention.
4B is an SEM image of Cu ₂ O / FTO obtained according to one embodiment of the present application.
Figure 5 is a schematic diagram of the manufacturing process and growth mechanism in one embodiment of the invention.
6 a and b are low magnification SEM images of Cu ₂ O / Cu-1 obtained according to one embodiment of the present application, and FIGS. 6 c and d show the Cu ₂ O / Cu-1 < / RTI > and a SAED pattern.
Figure 7 is a low magnification top-view and cross-sectional SEM image of Cu ₂ O / Cu-2 obtained according to one embodiment of the present application.
Of Figure 8 a and b, and the low magnification and high magnification SEM image of the Cu ₂ O / _Cu-2 obtained in 2 M in accordance with an embodiment of the invention, in Fig. 8 c, and d, according to one embodiment of the present 8 is a low magnification and high magnification SEM image of Cu ₂ O / Cu-2 obtained at 6 M, and FIGS. 8 e and f show a low magnification and low magnification SEM image of Cu ₂ O / Cu-2 obtained at 8 M according to one embodiment of the present invention and High magnification SEM image.
9 a and b are low magnification and high magnification SEM images of the Cu-2 foil surface obtained at 2 M according to one embodiment of the present application, and FIGS. 9 c and d illustrate a low magnification and high magnification SEM image of 4 M 9 is a low magnification and high magnification SEM image of the Cu-2 foil surface obtained at 6 M according to one embodiment of the present application, and Figs. 9 e and f are low and high magnification SEM images of the Cu- 9 g and h are low magnification and high magnification SEM images of the Cu-2 foil surface obtained at 8 M according to one embodiment herein.
10A and 10B are low magnification and high magnification SEM images of the Cu-2 foil surface obtained after 28 hours according to one embodiment of the present application, 10 is a low magnification and high magnification SEM image of the Cu-2 foil surface obtained after 20.5 days according to one embodiment of the present invention.
11a is a 26-plane polyhedron architecture having {111} x 8, {100} x 6 and {110} x 12 planes in one embodiment of the present invention, and Figs. 11b- SEM images at different areas with different magnifications of Cu ₂ O / Cu-2 after photocurrent-potential and photoreaction check in one embodiment.
Figures 12a and b are low and high magnification SEM images of Cu / FTO obtained according to one embodiment of the invention.
13A to 13D are images of contact angle measurement results of Cu-1 foil, Cu ₂ O / Cu-1 film, Cu-2 foil and Cu ₂ O / Cu-2 film in one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention. It should be understood, however, that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. In the drawings, the same reference numbers are used throughout the specification to refer to the same or like parts.

Throughout this specification, when a part is referred to as being "connected" to another part, it is not limited to a case where it is "directly connected" but also includes the case where it is "electrically connected" do.

Throughout this specification, when a member is "on " another member, it includes not only when the member is in contact with the other member, but also when there is another member between the two members.

Throughout this specification, when an element is referred to as "comprising ", it means that it can include other elements as well, without departing from the other elements unless specifically stated otherwise.

The terms "about "," substantially ", etc. used to the extent that they are used throughout the specification are intended to be taken to mean the approximation of the manufacturing and material tolerances inherent in the stated sense, Accurate or absolute numbers are used to help prevent unauthorized exploitation by unauthorized intruders of the referenced disclosure.

The word " step (or step) "or" step "used to the extent that it is used throughout the specification does not mean" step for.

Throughout this specification, the term "combination (s) thereof " included in the expression of the machine form means a mixture or combination of one or more elements selected from the group consisting of the constituents described in the expression of the form of a marker, Quot; means at least one selected from the group consisting of the above-mentioned elements.

Throughout this specification, the description of "A and / or B" means "A or B, or A and B".

Hereinafter, embodiments of the present invention are described in detail, but the present invention is not limited thereto.

A first aspect of the present invention provides a process for producing Cu ₂ O, comprising immersing copper (Cu) in an alkali solution and heating to form a Cu ₂ O film on the substrate.

In one embodiment of the present invention, the film may be formed by holding the formed film at room temperature, followed by washing and drying in a nitrogen (N ₂ ) gas, but the present invention is not limited thereto.

In one embodiment of the invention, the substrate may be, but not limited to, a Cu foil or an FTO.

In one embodiment of the present invention, the heating temperature may be 100 ° C or less, but it is not limited thereto.

In one embodiment of the present invention, the immersion time may be from 30 hours to 100 hours, but the present invention is not limited thereto. For example, the Cu ₂ O crystals may be obtained depending on the immersion time, but the present invention is not limited thereto.

A second aspect of the present invention provides a process for producing CuO comprising immersing copper (Cu) in an alkali solution and heating to form a CuO film on the substrate.

In one embodiment of the present invention, the film may be formed by holding the formed film at room temperature, followed by washing and drying in a nitrogen (N ₂ ) gas, but the present invention is not limited thereto.

In one embodiment of the invention, the substrate may be, but not limited to, a Cu foil or an FTO.

In one embodiment of the present invention, the heating temperature may be 100 ° C or less, but it is not limited thereto.

In one embodiment of the invention, the immersion time may be from 3 days to 21 days, but is not limited thereto. For example, different CuO crystals may be obtained depending on the immersion time, but the present invention is not limited thereto.

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples are given for the purpose of helping understanding of the present invention, but the present invention is not limited to the following Examples.

[ Example ]

<Material>

NaOH (vena Chemicals,> 97.0%), Cu ( NO 3) 2 · 2.5H 2 O ( Aldrich, 99.99 +%), lactic acid (Kanto, 85.0 ~ 92.0% in water solution), ethanol (Aldrich, 95%) of the It was used without further purification. Cu foil (Aldrich, thickness 0.5 mm, 99.98%) cut into small pieces with a size of 2 cm x 2 cm was washed for 5 minutes each in the order of ethanol, deionized water, and ethanol in an ultrasonic bath (inconvenience, Powersonic 410) , And dried rapidly using N ₂ flow. A commercially available fluorine-doped tin oxide (FTO) [Pilkington FTO glass (TEC 8), 6-9 ohm / sq] glass (2 cm x 3 cm) was immersed in deionized water in ethanol, acetone, Washed and quickly dried before use with N ₂ flow. All chemicals were used without further purification.

<Electrodeposition of Cu film (Cu / FTO) on FTO glass>

Cu films were deposited on FTO glass with a similar process as previously reported [JY Zheng, G. Song, CW Kim and YS Kang, Electrochim. Acta, 2012, 69, 340.]. Cu was electrodeposited in a conventional three-electrode battery system using potentiostat PL-9. FTO glass was used as the working electrode. The FTO glass was submerged into the electrolyte solution and the area immersed was 4 cm ² . A platinum wire and an Ag / AgCl electrode in 3 M KCl were used as a counter electrode and a reference electrode, respectively. The Cu film was deposited from an aqueous solution containing 0.1 M Cu (NO ₃ ) ₂ and 3 M lactic acid having a pH of 5 at Ag / AgCl -0.4 V at an atmospheric temperature of 24 ° C without stirring. The pH was adjusted by the addition of 4 M NaOH.

<Synthesis of Cu ₂ O / Cu and Cu ₂ O / FTO film>

Cu ₂ O / Cu -One

The Cu-1 foil was placed in a vial (volume: 100 mL) containing a solution of 20 mL of 4 M NaOH. The bottle was then sealed by a cap and heated to 80 DEG C on a hot plate. After heating for about 1 hour, the bottle was taken out and kept at room temperature for 4 days.

Cu ₂ O / Cu-2

In a typical procedure, a sealed vial (volume: 100 mL) containing 20 mL of the 4 M NaOH was heated to 80 DEG C on a hot plate for about 1 hour, then the bottle was removed from the hot plate and the Cu- 2 was placed vertically in the solution, sealed again and maintained at room temperature for 14 hours.

For comparison, the same experimental procedure was also applied at different concentrations of NaOH (2 M, 6 M, and 8 M). Reaction time-dependent morphology was performed in 2 M NaOH solution using different times of 28, 60, and 20.5 days. Further, a similar immersion process was carried out directly at room temperature (24 占 폚); The Cu-2 foil (2 cm x 2 cm) was held vertically in 20 mL NaOH aqueous solution at different concentrations (2 M, 4 M, 6 M, and 8 M) for 14 hours at room temperature.

Cu ₂ O / FTO

The Cu / FTO film was placed in a vial (volume: 100 mL) containing a solution of 20 mL of 4 M NaOH. The bottle was then sealed by a cap and heated to 80 DEG C on a hot plate. After heating for about 1 hour, the bottle was taken out and kept at room temperature for 5 days.

<Characteristic Analysis>

The patterns of X-ray diffraction (XRD, Rigaku miniFlex-II desktop, Cu-K radiation, λ = 0.154056 nm), high resolution transmission electron microscopy (HRTEM) and limited field electron diffraction (SAED, JEOL JEM-2100 F) And was used to identify the crystal structure. The surface and cross-sectional morphology of the films was obtained using a Hitachi Horiba S-4300 Scanning Electron Microscope (SEM) operated at 20 kV. Surface element binding energy and surface composition were characterized by Thermo VG Scientific (England), Multitab 2000 X-ray photoelectron spectroscopy (XPS). The emission peak position of the XPS spectrum was calibrated using the C1s peak position at 284.5 eV as a reference. A rame-hart Model 200-F1 contact angle measuring instrument was used for the wettability measurement. Water droplets (ca. 60 μL) were injected onto the sample surface by a microliter scale injector. Photoelectrochemical measurements were performed on a V-style using a quartz window cell under a 1-sun (Asahi HAL-320 sun simulator) illumination at room temperature using Pt wire and Ag / Lt; / RTI &gt; was performed using potentiostat PL-9 in a 3-electrode cell. The photocurrent-potentials were measured using a linear principle predistortion (LSV) with a scan speed of 10 mV / s under the light on and off (1 s) 1 sunlight. The photoreaction was measured by using the time-of-field method (chronoamperometry) at constant potentials at Ag / AgCl (light on and off: 20 s) 0 and -0.6 V. 0.5 M Na ₂ SO ₄ was used as an electrolyte solution in the identification of all photoelectrochemical properties.

<Mechanism of Cu growth in Cu ₂ O in NaOH solution>

It is well known that copper can be oxidized in air or under humid conditions; The rate of oxidation is very slow because of the passivation of the surface by the formation of an oxide layer. [J. Liu, X. Huang, Y. Li, KM Sulieman, X. He and F. Sun, J. Mater. Chem., 2006, 16, 4427.] and [Y. Liu, Y. Chu, M. Li, L. Li and L. Dong, J. Mater. Chem., 2006, 16, 192.], in the presence of an alkaline solution, this spontaneous oxidation can be accelerated very much. The Cu ^{2 +} ions are continuously released from the Cu foil into the alkaline solution (for example, NaOH), while the naturally dissolved O ₂ or the oxidizing agent [(NH ₄ ) ₂ S ₂ O ₈ ] is reduced. The released Cu ^{2 +} ions can be immediately captured via coordination with OH ^- to form Cu (OH) ₄ ^2- . Possible reaction processes can be carried out as shown below.

_{2Cu + O 2 + 2H 2 O} → 2Cu 2 + + 4OH -;

Or Cu + S ₂ O ₈ ^{2 -} → Cu ^{2 +} + ² SO ₄ ^{2 -} (when oxidizing agent is present) (1)

Cu ^{2 +} + ² OH ^- ? Cu (OH) ₂ (2)

Cu (OH) ₂ + 2OH ^- ? Cu (OH) ₄ ^2- (3)

Cu (OH) ₂ can be gradually converted to monoclinic CuO at a low temperature of 60 ° C; The Cu (OH) ₄ ^2- complex ion may also be dehydrated with CuO in a hot alkali solution.

Cu (OH) ₂ ? CuO + H ₂ O (4)

Cu (OH) ₄ ^2- ? CuO + H ₂ O + 2OH ^- ????? (5)

If a reducing agent (N ₂ H ₄ or glucose) is present, the final product may be Cu ₂ O as follows:

2Cu (OH) ₄ ^2- + C ₅ H ₁₁ O ₅ -CHO - Cu ₂ O + C ₅ H ₁₁ O ₅ --COOH + 4OH ^- + 2H ₂ O (6)

_{4Cu (OH) 2 + N 2} H 4 → Cu 2 O + 6H 2 O + N 2 (7)

The above-described Cu ₂ O forming process can suitably explain the reaction involving an alkali and a reducing agent. However, this process can not explain the present experiment because there is no additional reducing agent. The above and [A. Survila, P. Kalinauskas and I. Valsiunas, Russ. J. Electrochem., 2002, 38, 1068.], possible reaction processes are given below:

Cu foil or Cu / FTO can continuously release Cu ²⁺ ions into a NaOH solution by naturally-dissolved O ₂ oxidation

2Cu + O ₂ + 2H ₂ O? 2Cu ^{2 +} + 4OH ^- (1)

A certain amount of Cu ^& lt ^{; + &} gt ^; can be prepared by the following process

Cu ^{2 +} + Cu ² Cu ⁺ . (8)

The maximum concentration of [Cu ^&lt; ^{+ &} gt ^; ] is determined by the following relationship

log [Cu ⁺ ] _max = -0.84 - pH. (9)

If the actual Cu ⁺ concentration exceeds the [Cu ⁺ ] _max given in equation (9), the following process will occur.

_{^{2Cu + + 2OH - → Cu 2}} O + H 2 O (10)

In this embodiment, the conversion of Cu to Cu ₂ O will be carried out by a net reaction as follows:

4Cu + O ₂ ? 2Cu ₂ O. (11)

This example shows an easy process for conversion of Cu foil and Cu film into pure Cu ₂ O layer and film without impurities of CuO or Cu (OH) ₂ in a high concentration aqueous sodium hydroxide solution without surfactant and additives do. Among the factors, the most important factors for Cu substrates having different dominant crystal facets, such as alkali concentration, temperature, and reaction time, affecting Cu ₂ O film formation have been discussed.

The relationship of the surface energy (γ) of the bulk face-centered cubic (fcc) metal is known as γ111 <γ100 <γ110. The relationship of surface energy of Fcc Cu also decreases in the order of γCu (111) <γCu (100) <γCu (110). Therefore, the different predominant facets of bulk fcc Cu in solution will have different adsorption-desorption rates and chemical reaction rates. In the present application, three different types of Cu foil and Cu / FTO film substrate were performed for the experiment as XRD patterns shown as fcc-phase copper (JCPDS no. 65-9743) shown in Figs. 1A and 4A. The peak intensity ratios of I (111) / I (200) and I (220) / I (200) were 0.66 and 0.39 for Cu-1, 0.044 and 0.13 for Cu-2 and 2.92 and 0.52 for Cu / FTO, respectively . A typical experimental procedure for one-step conversion of Cu to Cu ₂ O was performed by immersing the Cu substrate in a NaOH solution at 80 ° C for 1 hour and as shown in Figure 5, Lt; 0 &gt; C). After the reaction, the synthesized film was washed with deionized water, ethanol, and then dried under an N ₂ gas flow. As shown in Fig. 1B, a brownish red film was covered on the surface of the Cu foil, and a dark orange colored transparent film was formed on the FTO glass. [Y. Liu, Y. Chu, MY Li and LH Dong, J. Mater. Chem., 2006, 16, 192; J. Liu, X. Huang, Y. Li, KM Sulieman, X. He and F. Sun, J.Mater. Chem., 2006, 16, 4427; (a) WZ Wang, OK Varghese, CM Ruan, M. Paulose and CA Grimes, J. Mater. Res., 2003, 18, 2756; (b) S. Sun, H. Zhang, X. Song, S. Liang, C. Kong and Z. Yang, CrystEngComm, 2011, 13, 6040; (c) A. Survila, P. Kalinauskas and I. Valsiunas, Russ. In accordance with the description J. Electrochem, 2002, 38, 1068. ], has been given as to the possible reaction step: Cu foil or Cu / FTO naturally - Cu ² in the NaOH solution by the oxidation of dissolved O ₂ ⁺ Ions can be released continuously

_{2Cu + O 2 + 2H 2 O} → 2Cu 2 + + 4OH - (1)

Some Cu ^& lt ^{; + &} gt ^; ions can be produced by the following process

Cu ^{2 +} + Cu ² Cu ⁺ (2)

The maximum concentration of [Cu ^&lt; ^{+ &} gt ^; ] is determined by the following equation

log [Cu ⁺ ] _max = - 0.84 - pH (3)

If the actual concentration of Cu ⁺ exceeds a given [Cu ^+] _max in formula (3), it will perform the following process.

_{^{2Cu + + 2OH - → Cu 2}} O + H 2 O (4)

This process is similar to Cu ^{2 +} ions can be reduced to Cu ⁺ ions by a Cu plate and forming a Cu ₂ O layer on the Cu surface through an in situ reduction reaction according to equation (5) below.

_{^{Cu 2 + + Cu + H 2}} O → Cu 2 O + 2H + (5)

In this experiment, the conversion from Cu to Cu ₂ O can be performed by a net reaction as follows.

4Cu + O ₂ ? 2Cu ₂ O (6)

In summary, the present invention has shown the growth mechanism of Cu ₂ O from Cu in a high concentration alkali solution having five steps, as shown in FIG. 5 b. Step 1, O ₂ in air was dissolved in the alkali solution. Step 2, the dissolved O ₂ was adsorbed on the surface of Cu. Step 3, Cu atoms on the surface were oxidized to Cu ^{2 +} by adsorbed O ₂ as in the above reaction scheme 1. Step 4, Cu ^{2 +} ions can be reduced to Cu ⁺ ions by adjoining Cu atoms for a very short period of time, as in the above reaction scheme 2. Step 5, Cu ⁺ ions will react with OH ^- in the solution to form a Cu ₂ O nucleation site, and H ₂ O molecules are released from the Cu surface, as in Scheme 4 above. The obtained Cu ₂ O nucleation site will grow according to the reaction time. As a result, nano / micro-sized Cu ₂ O crystals can be formed. In the entire Cu ₂ O growth process, steps 3 to 5 occur at the in situ Cu surface. Step 2 is the key to initiating the next reaction and depends on the adsorption of O ₂ by the Cu surface. Therefore, the surface properties of the Cu substrate are crucial in the experiment.

The XRD pattern of Cu ₂ O / Cu-1 shows a space group of Pn 3 m (no. 224) of Cu ₂ O (JCPDS no. 65-3288) except for the peak of Cu- And can be displayed completely on the pure cube by using. Physicochemical properties of crystals such as adsorption, catalytic reactivity and selectivity are highly dependent on the degree of surface atomicity and degree of exposure of reaction surface. The predominant crystal face of Cu ₂ O / Cu-1 is (111). As shown in FIG. 2B, the corresponding SEM image shows that a dense and homogeneous Cu ₂ O octahedral particle film is covered on the Cu-1 foil. In FIG. 6, the low magnification SEM image, the TEM image, and the SEAD pattern further illustrate that the Cu ₂ O octahedral film having an average particle size of less than 1.5 μm is a large area scale and the particles are single crystals. As previously described, Cu-1 with high I (111) / I (200) is a regular Cu ₂ O octahedron with a surface energy order of γCu (111) <γCu (100) <γCu A longer reaction time (3 days) is required to form the film. 6A and 6B show that the film is uniform on a large area scale. As shown in Figure 6b, there are slightly larger particles with a size of ~ 3 [mu] m to ~ 5 [mu] m. As shown in Fig. 6c, most of the particles are in the range of ~ 1 [mu] m to ~ 2 [mu] m. The average particle size is <1.5 μm. The SAED pattern can be indexed with cubic phase Cu ₂ O (JCPDS no. 65-3288) as a similar result obtained by Mao [Y. Mao, J. He, X. Suna, W. Li, X. Lua, J. Gan, Z. Liu, L. Gong, J. Chen, P. Liu and Y. Tong, Electrochim. Acta, 2012, 62, 1.].

In contrast, it was assumed that a Cu substrate with a very low I (111) / I (200) would have a shorter reaction time to form a Cu ₂ O film by dipping in an aqueous NaOH solution. To demonstrate this hypothesis, a Cu-2 substrate was used in the experiment. The Cu-2 foil was immersed in a hot 4.0 M NaOH aqueous solution at 80 DEG C and then maintained at room temperature for 14 hours. As shown in FIG. 3A, a dense, incomplete 26-face polyhedron architecture (complete material with exposed 8 {111}, 6 {100}, and 12 {110} planes as shown in the inset of FIG. 3a) &Lt; / RTI &gt; As shown in Fig. 7, the particle size is in the range of a few microns and the film thickness is ca. 3.5 μm. {110} faces were heterogeneously exposed. The dominant aspect is {200}, as shown in the XRD pattern of FIG. 3b. The purity of Cu ₂ O obtained was further confirmed by X-ray photoelectron spectroscopy (XPS). In general, CuO and Cu (OH) ₂ can be characterized by strong Cu (2p) XPS shake-up satellites and wide O (1s) peaks; Cu ₂ O and metal Cu show Cu (2p) satellites and narrower O (1s) peaks that are weaker / lesser.

Unfortunately, since the binding energies of Cu (2p) are similar, it is difficult to distinguish Cu ₂ O and metal Cu by XPS. However, it is necessary to confirm the absence of CuO and Cu (OH) ₂ by XPS. Some very weakly cleaved satellite peaks, rather than strong satellite peaks, showed no impurities of CuO and Cu (OH) _{2 in} the present sample, as shown in Figure 3c. Considering the depth (~ 1 to 10 nm) of the sense of XPS, from the 932.6 eV peak of the Cu (2p _1/2) in Cu (2p _3/2) and 952.4 eV may be a result of the Cu ₂ O. The corresponding O (1s) XPS spectrum shows two peaks at 530.3 and 531.5 eV resulting from Cu ₂ O and surface hydroxides (OH ^- ). Surface hydroxides come from adsorbed and / or residual NaOH on the surface of Cu ₂ O. Pure Cu ₂ O crystals can also be obtained by immersing the Cu-2 foil at different concentrations of NaOH solution at room temperature (24 ° C), as shown in FIGS. 8 and 9. At low concentrations (2.0 M), the particle size was relatively reduced; When the concentration was increased, the film became loose and thin. At room temperature, Cu ₂ O particles are much more irregular and can not be formed at high concentrations (8.0 M).

&Lt; Preparation of CuO / Cu &

Cu ₂ O / Cu can be further oxidized with CuO / Cu when the immersion time is prolonged, as shown in Fig. Generally, the product can be affected by several factors such as temperature, NaOH concentration, and reaction time. When the immersion time is prolonged, the Cu ₂ O film can be converted to CuO. After 60 hours of immersion, the morphology of Cu ₂ O changed from polyhedra to standard grains. After 20.5 days, cabbage-shaped CuO was formed as a similar result reported by Liu [Liu, X. Huang, Y. Li, Z. Li, Q. Chi and G. Li, , &Lt; / RTI &gt; 2008, 10, 1568.]. The results of this example show that the process of changing Cu in the NaOH solution is as follows:

Cu → Cu ₂ O → CuO

Cu foil can be oxidized to Cu ₂ O / Cu, it may be further oxidized to CuO-Cu ₂ O / Cu, or CuO / Cu.

As shown in FIG. 3E, the photoelectrochemical photocurrent switching (PEPS) effect capable of changing the photocurrent polarity by changing the photoelectrode potential was observed using a Cu ₂ O / Cu-2 sample. The cathodic photocurrent decreased gradually because the applied potential was injected in the positive direction at -0.7 V and was switched from -0.48 V to the anodic photocurrent. In the present application, the current-potential performance under modified light illumination indicates that Cu / Cu ₂ O and Cu ₂ O / electrolyte Schottky type junctions are present in the Cu / Cu ₂ O / electrolyte system. Similar results were _first observed in the Ti / Cu ₂ O / electrolyte, ITO / Cu ₂ O / electrolyte, and ITO / Cu ₂ O / Cu _x S systems. When the potential was in the range of -0.7 V to -0.48 V, the Cu / Cu ₂ O junction was dominant and a p-type optical signal (negative photocurrent) was produced; When the potential was in the range of -0.48 V to +0.1 V, the Cu ₂ O / electrolyte junction was dominant and an n-type optical signal (negative photocurrent) was obtained. The positive and negative photocurrents were observed by photoreaction at 0 V and -0.6 V, respectively, as shown in the inset of FIG. 3e. The cathodic photocurrent decreased gradually with increasing time at -0.6 V or less. This indicates that the film is not stable. After photocurrent and photo reaction confirmation, the surface color of the exposed film in the electrolyte was changed to dark, as shown in the inset of FIG. 3f; This indicates that Cu ₂ O has been reduced to Cu from the surface, similar to the results reported by Parquin et al. As shown in the SEM image of FIG. 3F and FIG. 11, the {111} crystal plane is partially dissolved while the other plane is stable. Many nano-sized Cu particles were deposited on the {111} surface. The process is a decomposition-redeposition process. The relative surface energies of the Cu ₂ O crystals are in the order of γ {111} <γ {100} <γ {110} and the photocatalytic activity of Cu ₂ O on one side is {110}>{111}> {100}. Therefore, the {110} surface has the highest surface energy and is the highest one active surface. The {110} should be the highest active surface for reactions such as water decomposition under light illumination. However, the {110} plane is the most unstable plane. For comparison, a Cu / FTO substrate with a high I (111) / I (200) ratio of 2.92 was selected for the experiment. After soaking for 5 days, the Cu film can be completely converted to Cu ₂ O, as shown in the XRD pattern in FIG. 4A. The dominant facet is {111}. However, the film is composed of crystals of irregular polyhedral particles as shown in Fig. 4B. Cu ₂ O / FTO is not perfect because, as shown in FIG. 12, Cu / FTO is composed of Cu particles rather than a continuous, dense film.

To demonstrate a more potential application, the hydrophobic properties of the two Cu ₂ O films of FIG. 2B and FIG. 3A tested the water contact angle, as shown in FIG. The surfaces of Cu-1 (FIG. 13a) and Cu-2 (FIG. 13c) surfaces are hydrophobic with similar water contact angles of 96.8 ± 3 ° and 92.7 ± 3 °, respectively. The surface of the Cu ₂ O / Cu-1 with Cu ₂ O After forming the film, the water contact angle of 125.6 ± 2 ° to the surface of the Cu base material is more hydrophobic than the Cu-base material 1 exposed. In contrast, Cu ₂ O / Cu-2 exhibits hydrophilicity with a water contact angle of 64.6 ± 2 °. Theoretically, a hydrophobic solid surface has a low surface energy and a hydrophilic solid surface has a high surface energy. Cu relative surface energy of the ₂ O crystal is γ (111) <Since the order of γ {100}, the lead (111) the water contact angle of the Cu ₂ O / Cu-1 film having one surface is Cu ₂ having a {100} surface predominantly O / Cu-2 film. Regardless of other factors such as morphology and surface adsorption, this is comparable to experimental results.

In summary, Cu can be converted directly to Cu ₂ O by an easy immersion process without any additional oxidizer prior to the formation of CuO in the aqueous NaOH solution of high concentration. Depending on the different types of Cu substrates, different predominant Cu ₂ O can be obtained. The process of Cu oxidation at a high concentration of aqueous NaOH solution is from Cu to Cu ₂ O, and when the immersion time is continued, Cu ₂ O is CuO. The present invention is a good method for converting Cu particles or Cu films into crystalline Cu ₂ O particles or films and can be an easy method for synthesizing Cu ₂ O films.

It will be understood by those of ordinary skill in the art that the foregoing description of the embodiments is for illustrative purposes and that those skilled in the art can easily modify the invention without departing from the spirit or essential characteristics thereof. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. For example, each component described as a single entity may be distributed and implemented, and components described as being distributed may also be implemented in a combined form.

The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (12)

A method of immersing copper (Cu) in an alkaline solution and heating to form a Cu ₂ O film on the substrate
&Lt; RTI ID = 0.0 &gt; Cu2O. &Lt; / _RTI &gt;
The method according to claim 1,
The method of, Cu ₂ O, which comprises adding to the washing and drying in a nitrogen (N ₂₎ gas was holding the formed film at room temperature.
The method according to claim 1,
The base material is a method for manufacturing a Cu ₂ O comprises a Cu foil or FTO.
The method according to claim 1,
The method of manufacturing a Cu ₂ O wherein the heating temperature is not more than 100 ℃.
The method according to claim 1,
The immersion time is method for producing a, Cu ₂ O being from 30 hours to 100 hours.
6. The method of claim 5,
The method of manufacturing a Cu ₂ O to be obtained is different from Cu ₂ O determined by the immersion time.
Dipping copper (Cu) in an alkali solution and heating to form a CuO film on the substrate
&Lt; / RTI &gt;
8. The method of claim 7,
The method of, CuO comprising adding to the washing and drying in a nitrogen (N ₂₎ gas was holding the formed film at room temperature.
8. The method of claim 7,
Wherein the substrate comprises a Cu foil or FTO.
8. The method of claim 7,
Wherein the heating temperature is not higher than 100 占 폚.
8. The method of claim 7,
Wherein the immersion time is 3 days to 21 days.
12. The method of claim 11,
Wherein different CuO crystals are obtained depending on the immersion time.

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