A honeycomb composite molybdenum oxide coating on a metal surface, a preparation method thereof and application thereof in oil-water separation

Abstract

The application provides a honeycomb composite molybdenum oxide coating of a metal surface and a preparation method and application in oil-water separation thereof, and belongs to the technical field of oil-water separation. The application takes a metal material as a base material, constructs a layer of oxygen-rich titanium metal coating as an intermediate layer on the surface of the metal base material, takes molybdate as a precursor, and successfully constructs a Ti-O-Mo chemical bond on the surface of the oxygen-rich titanium intermediate layer by using a hydrothermal reaction, and therefore successfully constructs a molybdenum oxide and hydrated molybdenum oxide composite coating material on the surface of the oxygen-rich titanium. Since the coating has a unique honeycomb structure composed of nanorods, and contains rich oxygen-containing groups and crystal water, the coating has excellent superhydrophilic-underwater superoleophobic special wettability, and has good oil-water separation performance when used as an oil-water separation membrane.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil-water separation, in particular to a honeycomb-shaped composite molybdenum oxide coating on a metal surface, a preparation method thereof and application thereof in oil-water separation. BACKGROUND

[0002] In order to develop a new energy-saving and high-efficiency oil-water separation technology, researchers in many countries focus on membrane separation technology. The membrane materials currently adopted are mainly divided into three categories according to the material, namely inorganic ceramic membranes, polymer membranes and metal mesh membranes. The common feature of these three types of membrane materials is that they have a pore structure and have special wettability, such as superhydrophobic or superhydrophilic properties, so that the oil or water in the oil-water mixture can selectively pass through the membrane pores, achieving high-efficiency separation. Among them, the superhydrophobic membrane can block the wettability of water and only allow oil to pass through the separation membrane, but the oil has a large viscosity and a small surface tension, which is easy to cause membrane clogging; the superhydrophilic membrane can block the wettability of oil and only allow water to pass through the separation membrane, and the superhydrophilic coating membrane with oil adhesion resistance has greater advantages in oil-water separation.

[0003] At present, the separation membrane surface with oil adhesion resistance is generally prepared with a superhydrophilic-subsea superoleophobic polymer coating, a gel coating or an inorganic micro-nano coating. The polymer coating generally swells in the water phase and is not wear-resistant, the gel coating is easy to lose water in the matrix in the surrounding environment, resulting in a decrease in oil-proof property, and the inorganic micro-nano coating material overcomes the above two shortcomings and has strong practical value.

[0004] Compared with inorganic ceramic membranes and polymer membranes, metal mesh membranes such as stainless steel mesh membranes have the advantages of high mechanical strength, low cost, adjustable membrane pore size and convenient processing, but it is difficult for the stainless steel mesh membrane to react with other inorganic components on the surface to construct a superhydrophilic coating due to its surface chemical inertness. SUMMARY

[0005] Therefore, the present application aims to provide a honeycomb-shaped composite molybdenum oxide coating on a metal surface, a preparation method thereof and application thereof in oil-water separation. The present application can successfully construct an inorganic superhydrophilic coating on a metal substrate such as a stainless steel mesh surface, and the obtained coating has excellent hydrophilicity and subsea superoleophobicity, and has the characteristics of self-cleaning when used as an oil-water separation membrane.

[0006] In order to achieve the above-mentioned application purpose, the present application provides the following technical solutions:

[0007] The present application provides a method for preparing a honeycomb-shaped composite molybdenum oxide coating on a metal surface, comprising the following steps:

[0008] Plating titanium on the surface of the metal substrate to obtain a metal substrate covered with a titanium-rich medium layer; the composition of the titanium-rich medium layer includes, in terms of atomic content, O 20-60%, Ti 15-25%, and the balance C and other unavoidable impurities;

[0009] Providing a molybdate aqueous solution, adjusting the pH value of the molybdate aqueous solution to 1.0 to obtain a molybdate precursor solution;

[0010] Placing the metal substrate covered with the titanium-rich medium layer in the molybdate precursor solution, and sequentially performing ultrasonic treatment and hydrothermal reaction to obtain a honeycomb-shaped composite molybdenum oxide coating on the surface of the metal substrate, the composition of the composite molybdenum oxide coating including molybdenum oxide and hydrated molybdenum oxide.

[0011] Preferably, the metal substrate is a metal mesh, and the material of the metal substrate is one or more of stainless steel, copper, titanium, nickel, aluminum alloy, copper alloy, zinc alloy, titanium-cobalt alloy, and cobalt-nickel alloy.

[0012] Preferably, the titanium plating method includes one or more of magnetron sputtering, water plating black titanium, thermal evaporation, and ion plating.

[0013] The thickness of the titanium-rich medium layer is 500-600 nm.

[0014] Preferably, the titanium plating method is magnetron sputtering, the target material of the magnetron sputtering is a titanium target, and the vacuum degree is (5-5.5)×10 -4 Pa.

[0015] The gas of the magnetron sputtering is Ar gas, and the gas flow is 30-35 sccm.

[0016] The discharge gas pressure during the magnetron sputtering is 2-2.5 Pa, the direct current power is 100-120 W, the negative bias voltage is 150-160 V, and the plating time is 15-20 min.

[0017] Preferably, after plating titanium on the surface of the metal substrate, heating oxidation is further performed to obtain a metal substrate covered with a titanium-rich medium layer, and the composition of the titanium medium layer includes titanium oxide.

[0018] The heating oxidation temperature is 400-500℃, and the holding time is 2-4 h.

[0019] Preferably, the molybdate includes one or more of ammonium dimolybdate, ammonium molybdate, sodium molybdate, magnesium molybdate, zinc molybdate, molybdenum isopoly acid salt, and molybdenum heteropoly acid salt.

[0020] The concentration of the molybdate aqueous solution is 10-40 mmol / L.

[0021] Preferably, the ultrasonic treatment is performed at a power of 200-600 W for 30-40 min.

[0022] Preferably, the hydrothermal reaction is performed at a temperature of 175-180 ℃ for 6-24 h.

[0023] The application provides a honeycomb-shaped composite molybdenum oxide coating on a metal surface prepared by the method, which comprises a metal substrate, an oxygen-rich titanium medium layer covering the metal substrate, and molybdenum oxide nanorods and hydrated molybdenum oxide nanorods grown on the surface of the oxygen-rich titanium medium layer.

[0024] The application provides an application of the honeycomb-shaped composite molybdenum oxide coating on the metal surface in oil-water separation.

[0025] The application provides a method for preparing a honeycomb-shaped composite molybdenum oxide coating on a metal surface, which comprises the following steps: titanium plating on the surface of a metal substrate to obtain a metal substrate covered with an oxygen-rich titanium medium layer; providing a molybdate aqueous solution, adjusting the pH value of the molybdate aqueous solution to 1.0 to obtain a molybdate precursor solution; placing the metal substrate covered with the oxygen-rich titanium medium layer in the molybdate precursor solution, and sequentially performing ultrasonic treatment and hydrothermal reaction to obtain a honeycomb-shaped composite molybdenum oxide coating on the surface of the metal substrate, wherein the composition of the composite molybdenum oxide coating comprises molybdenum oxide and hydrated molybdenum oxide.

[0026] The application constructs an oxygen-rich titanium metal coating layer as a medium layer on the surface of a metal substrate, and then successfully constructs a Ti-O-Mo chemical bond on the surface of the oxygen-rich titanium medium layer by using a molybdate as a precursor and a hydrothermal reaction, and thus successfully constructs a molybdenum oxide (MoO3) and hydrated molybdenum oxide (HMo 5.35 O 15.75 (OH) 1.6 ·1.7H2O) composite coating material on the surface of the oxygen-rich titanium. Due to the unique honeycomb structure composed of nanorods and the rich oxygen-containing groups and crystal water contained in the coating, the coating has excellent superhydrophilic and underwater superoleophobic special wettability, and has the characteristics of self-cleaning when used as an oil-water separation membrane, and the applications include but are not limited to anti-adhesion of oil substances, crude oil-water separation, oil-water separation of catering sewage, other industrial applications involving oil and water separation, and photocatalytic or thermal catalytic removal of oil stains on the surface of the coating to realize self-cleaning.

[0027] Metal substrates have the advantages of high mechanical strength, low cost, adjustable pore size, and easy processing compared to inorganic ceramic membranes and polymer membranes, but it is difficult to react other chemicals on the surface of the metal substrate to build a coating layer due to its chemical inertness. There are many schemes for preparing various molybdenum oxide powders in the prior art, but there are few reports on in-situ building uniform molybdenum oxide and hydrated molybdenum oxide coating on the surface of the substrate. The methods for preparing molybdenum oxide coating on the surface of the substrate mainly include solution precursor plasma spraying (SPPS) and physical vapor deposition (PVD). Compared with the present application, the coating prepared by SPPS does not contain molybdenum oxide coating with crystallization water, which is unknown for the hydrophilicity and underwater oleophobicity of the coating. The high-density thermal energy of plasma and high-temperature annealing process consume a lot of energy compared with the hydrothermal method of the present application. The coating prepared by PVD is generally smooth, and the surface has no specific three-dimensional structure, so it cannot realize the magnification of the wettability of the coating depending on the surface structure. The present application adopts the method of building oxygen-rich titanium intermediate layer + hydrothermal reaction, which can successfully build a honeycomb coating composed of uniform molybdenum oxide and hydrated molybdenum oxide nanorods on the surface of the metal substrate, and endow the metal mesh film with good oil-water separation performance and not easy to be adhered and blocked by crude oil. At the same time, the preparation method provided by the present application is simple in operation, low in cost and easy to realize industrialized mass production. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 X-ray diffraction (XRD) patterns of the coating obtained in Examples 1 and 2;

[0029] Figure 2 Appearance photos of the 500-mesh stainless steel mesh as received, the stainless steel mesh after magnetron sputtering titanium plating, and the hydrothermally modified titanium-plated stainless steel mesh used in Example 1;

[0030] Figure 3 Low-magnification and high-magnification SEM photos of the 500-mesh stainless steel mesh after titanium plating on the surface of the mesh by magnetron sputtering method in Example 1;

[0031] Figure 4 Low-magnification, medium-magnification, and high-magnification SEM photos of the coating sample prepared in Example 1;

[0032] Figure 5 X-ray photoelectron spectroscopy (XPS) patterns of the titanium-plated stainless steel mesh prepared in Example 1 and the titanium-plated stainless steel mesh after hydrothermal modification with ammonium paramolybdate solution;

[0033] Figure 6 Photo of the contact angle of crude oil on the surface of the molybdenum oxide and hydrated molybdenum oxide composite coating modified titanium-plated stainless steel mesh in Example 1 in water phase;

[0034] Figure 7 Photo of the crude oil-water separation process and test results of 20 cycles of crude oil-water separation.

[0035] Figure 8 Low, medium and high magnification SEM photos of the coating prepared by the hydrothermal reaction for 6h and 24h in Example 3. DETAILED DESCRIPTION

[0036] The application provides a method for preparing a honeycomb-shaped composite molybdenum oxide coating on a metal surface, comprising the following steps:

[0037] Titanium is plated on the surface of the metal substrate to obtain a metal substrate covered with a titanium-rich medium layer; the composition of the titanium-rich medium layer comprises, in terms of atomic content, O 20-60%, Ti 15-25%, and the balance of C and other inevitable impurity elements;

[0038] A molybdate aqueous solution is provided, and the pH value of the molybdate aqueous solution is adjusted to 1.0 to obtain a molybdate precursor solution;

[0039] The metal substrate covered with the titanium-rich medium layer is placed in the molybdate precursor solution, and ultrasonic treatment and hydrothermal reaction are sequentially performed to obtain a honeycomb-shaped composite molybdenum oxide coating on the surface of the metal substrate, wherein the composite molybdenum oxide coating comprises molybdenum oxide and hydrated molybdenum oxide.

[0040] The application plates titanium on the surface of the metal substrate to obtain a metal substrate covered with a titanium-rich medium layer. In the application, the metal substrate is preferably a metal mesh, and the pore size of the metal mesh is preferably 5-25 μm, more preferably 10-20 μm. The application does not make special limitations on the specific type of the metal substrate as long as the surface can be plated with titanium. In the application, the material of the metal substrate is preferably one or more of stainless steel, copper, titanium, nickel, aluminum alloy, copper alloy, zinc alloy, titanium-cobalt alloy and cobalt-nickel alloy.

[0041] Before the titanium plating, the application preferably performs pretreatment on the metal substrate, and the pretreatment preferably comprises the following steps:

[0042] The metal substrate is subjected to ultrasonic cleaning and drying.

[0043] In the application, the cleaning solution used in the ultrasonic cleaning is preferably a mixed solution of anhydrous ethanol and isopropyl alcohol, and the volume ratio of anhydrous ethanol to isopropyl alcohol in the mixed solution is preferably 1:0.5-1, more preferably 1:1. In the application, the power of the ultrasonic cleaning is preferably 200-600 W, more preferably 300-500 W, and the time is preferably 20-30 min, more preferably 25 min.

[0044] The application does not make special requirements on the drying method, and any drying method known to those skilled in the art can be used.

[0045] In the present application, the titanium plating method includes one or more of magnetron sputtering, water plating black titanium, thermal evaporation and ion plating.

[0046] In the present application, the titanium plating method includes one or more of magnetron sputtering, water plating black titanium, thermal evaporation and ion plating.

[0047] In the present application, when the titanium plating method is magnetron sputtering, the magnetron sputtering is preferably carried out in a magnetron sputtering plating machine. In the present application, the target material of the magnetron sputtering is a titanium target material, and the purity of the titanium target material is preferably 99.995%.

[0048] In the present application, the vacuum degree of the magnetron sputtering is preferably (5-5.5) x 10 -4 Pa; the gas of the magnetron sputtering is preferably Ar gas, and the gas flow is preferably 30-35 sccm, more preferably 32-34 sccm. In the present application, the discharge gas pressure during the magnetron sputtering is preferably 2-2.5 Pa, more preferably 2.2-2.4 Pa; the direct current power is preferably 100-120 W, more preferably 110 W; the negative bias voltage is preferably 150-160 V, more preferably 155 V; and the plating time is preferably 15-20 min, more preferably 16-18

[0049] min.

[0050] The present application does not have special requirements for the specific operation method of the water plating black titanium method, thermal evaporation method and ion plating method, and the above-mentioned plating method known to those skilled in the art can be used.

[0051] In the present application, after plating, the present application preferably performs ultrasonic cleaning and drying on the obtained oxygen-rich titanium medium layer. In the present application, the power of the ultrasonic cleaning is preferably 200-600 W, more preferably 300-500 W; and the time is preferably 20-30 min, more preferably 25 min. In the present application, the drying temperature is preferably 60°C.

[0052] In the present application, after plating titanium on the surface of the metal substrate, heating oxidation is also preferably included to obtain a metal substrate covered with an oxygen-rich titanium medium layer. In the present application, the heating oxidation is preferably carried out in a muffle furnace, and the atmosphere of the heating oxidation is preferably an air atmosphere. In the present application, the heating oxidation temperature is preferably 400-500°C, more preferably 450°C; and the holding time is preferably 2-4 h, more preferably 2-3 h.

[0053] The present application can increase the oxygen content of the oxygen-rich titanium medium layer by the heating oxidation. In the present application, the composition of the titanium medium layer after the heating oxidation includes titanium oxide.

[0054] In the present application, when the heating oxidation is needed to obtain the oxygen-rich titanium layer, the vacuum degree of the magnetron sputtering is preferably 5×10 -5 Pa, and the remaining magnetron sputtering parameters are the same as above, which will not be repeated here.

[0055] The present application provides a molybdate aqueous solution, adjusts the pH value of the molybdate aqueous solution to 1.0 to obtain a molybdate precursor solution. In the present application, the molybdate preferably includes one or more of ammonium dimolybdate, ammonium molybdate, sodium molybdate, magnesium molybdate, zinc molybdate, molybdenum isopoly acid salt and molybdenum heteropoly acid salt; in the present application, the molybdenum isopoly anion in the molybdenum isopoly acid salt preferably includes one or more of [MoO4] 2- , [Mo7O 24 ] 6- , [Mo8O 26 ] 4- , [H8Mo7O 28 ] 6- The molybdenum heteropoly acid salt preferably includes one or more of nickel-zirconium-molybdenum heteropoly acid salt, vanadium-molybdenum heteropoly acid salt and arsenic-molybdenum heteropoly acid salt.

[0056] In the present application, the concentration of the molybdate aqueous solution is preferably 10-40 mmol / L, and more preferably 20-30 mmol / L. In the present application, the pH value of the molybdate aqueous solution is preferably 5.0-5.2.

[0057] In the present application, the preferred way to adjust the pH value of the molybdate aqueous solution is to mix the molybdate aqueous solution with acid liquid by magnetic stirring. In the present application, the acid liquid for adjusting the pH value of the molybdate aqueous solution is preferably sulfuric acid, and the concentration of the sulfuric acid is preferably 2-5 mol / L, and more preferably 3-4 mol / L.

[0058] The present application places the metal substrate coated with the oxygen-rich titanium medium layer in the molybdate precursor solution, and sequentially performs ultrasonic treatment and hydrothermal reaction to obtain a honeycomb-shaped composite molybdenum oxide coating on the surface of the metal substrate. In the present application, the power of the ultrasonic treatment is preferably 200-600 W, and more preferably 300-500 W; the time is preferably 30-40 min, and more preferably 35 min.

[0059] In the present application, the hydrothermal reaction is preferably carried out in a reaction kettle lined with Teflon; the temperature of the hydrothermal reaction is preferably 175-180℃, and the time is preferably 6-24 h, and more preferably 12-18 h.

[0060] After the hydrothermal reaction, the application preferably performs natural cooling, removes the metal substrate with the honeycomb-shaped composite molybdenum oxide coating prepared, and sequentially performs washing and drying.

[0061] In the application, the washing is preferably deionized water flushing, and the drying is preferably drying in a 50℃ oven.

[0062] The application provides a honeycomb-shaped composite molybdenum oxide coating on a metal surface prepared by the above method, which comprises a metal substrate, an oxygen-rich titanium medium layer covering the metal substrate, and molybdenum oxide nanorods and hydrated molybdenum oxide nanorods grown on the surface of the oxygen-rich titanium medium layer.

[0063] In the application, the component of the oxygen-rich titanium medium layer is preferably titanium metal and / or titanium oxide, and the thickness of the oxygen-rich titanium medium layer is preferably 500-600 nm.

[0064] In the application, the length of the molybdenum oxide nanorods and the hydrated molybdenum oxide nanorods is preferably 1-2 μm, and the diameter is preferably 50-100 nm.

[0065] The application provides an application of the honeycomb-shaped composite molybdenum oxide coating on a metal surface in oil-water separation. The coating provided by the application has a unique honeycomb structure composed of nanorods, and contains abundant oxygen-containing groups and crystal water, so that it has excellent superhydrophilic and underwater superoleophobic special wettability, and has the characteristics of self-cleaning when used as an oil-water separation membrane. Its applications include but are not limited to anti-adhesion of oil substances, crude oil-water separation, oil-water separation of catering sewage, application scenarios involving oil substances and water separation in other industrial applications, and photocatalytic or thermal catalytic removal of oil stains on the coating surface to achieve self-cleaning.

[0066] The honeycomb-shaped composite molybdenum oxide coating on a metal surface provided by the application, the preparation method thereof and the application thereof in oil-water separation will be described in detail below in combination with examples, but they should not be understood as limitations on the protection scope of the application.

[0067] Example 1

[0068] The method for preparing the honeycomb-shaped composite molybdenum oxide coating on the surface of the stainless steel is as follows:

[0069] Step (1): titanium coating on the surface of the stainless steel mesh and cleaning: 500-mesh stainless steel mesh is ultrasonically treated in a mixture of anhydrous ethanol / isopropanol with a volume ratio of 1:1 for 20 min, and after drying, it is placed in a vacuum chamber of a magnetron sputtering coating machine, and the vacuum degree of the sputtering system cavity is extracted to 5×10 -4After the coating, the sputtering target material is titanium target material with a purity of 99.995%, and the gas used is Ar gas with a flow rate of 30 sccm. During the sputtering process, the discharge gas pressure is 2 Pa, the direct current power is 100 W, the negative bias voltage is 150 V, and the coating time is 15 min. After the titanium coating of the stainless steel mesh is completed, the mesh is again ultrasonically cleaned with an ethanol / isopropanol mixture (volume ratio 1:1), and then dried at 60°C for standby use.

[0070] Step (2): Preparation of the precursor solution of the reaction system: 7.416 g (6 mmol) of ammonium paramolybdate tetrahydrate solid was weighed and dissolved in 150 mL of deionized water, continuously stirred for 1 h to form a uniform solution, at this time the concentration of ammonium paramolybdate in the solution was about 40 mmol / L, then the pH value of the solution was adjusted to 1.0 with a 2.0 mol / L sulfuric acid solution, and a precursor solution for preparing the coating was obtained.

[0071] Step (3): Hydrothermal reaction of the titanium-coated stainless steel mesh to prepare the coating: The precursor solution obtained in step (2) was transferred to a 300 mL Teflon-lined reaction kettle, and the titanium-coated stainless steel mesh obtained in step (1) was placed in the solution so that the mesh was completely submerged in the solution and ultrasonically treated for 30 min. Then the hydrothermal reaction was carried out at 180°C, and the reaction interval was 12 h. After the reaction was completed, the coated mesh was naturally cooled, washed repeatedly with deionized water, and dried in a 50°C oven to obtain a composite mesh coated with a molybdenum oxide and hydrated molybdenum oxide coating.

[0072] Example 2

[0073] The preparation method of the composite molybdenum oxide coating is the same as that of Example 1, except that in step (2), the amount of ammonium paramolybdate tetrahydrate is halved, i.e., 3.708 g (3 mmol), so the concentration of the precursor ammonium paramolybdate solution is also reduced to 20 mmol / L, and a 2.0 mol / L sulfuric acid solution is still used to adjust the solution pH to 1.0, and the other reaction conditions remain unchanged.

[0074] The XRD pattern of the coating sample obtained in Example 2 is shown in Figure 1 From Figure 1 it can be seen that when the amount of the precursor ammonium paramolybdate tetrahydrate is halved, a molybdenum oxide and hydrated molybdenum oxide composite coating can still be obtained.

[0075] Structural characterization

[0076] (1) The powder X-ray diffraction (XRD) pattern of the coating obtained in Examples 1 and 2 is shown in Figure 1 . Figure 1The table includes the XRD patterns of the coating samples prepared in Example 1 (40 mmol / L ammonium paramolybdate) and Example 2 (20 mmol / L ammonium paramolybdate) of the present invention and two standard cards (PDF#21-0569, PDF#47-0872) retrieved from the XRD database. Figure 1 It can be seen that, first, by comparing the two standard cards (PDF#21-0569 and PDF#47-0872) retrieved from the XRD database, it is easy to find that the peak position of PDF#47-0872 is generally shifted to a smaller angle than the peak position of PDF#21-0569 (the two peak positions do not overlap, but are very close, so a broad peak will appear in theory). At the same time, the coatings prepared in Examples 1 and 2 of the present invention are Figure 1 There are obvious broad peaks at multiple positions (marked by black dotted boxes), and the peak positions are completely consistent with the positions of the above two cards, which shows that the coatings prepared in Examples 1 and 2 of the present invention are molybdenum oxide (MoO3) and hydrated molybdenum oxide (HMo 5.35 O 15.75 (OH) 1.6 In addition, through careful comparison, it can be found that when the concentration of the solution precursor ammonium paramolybdate is 40mmol / L, the content of hydrated molybdenum oxide in the prepared coating is higher. The reason is that Figure 1 The peaks at positions 1 and 2 are broader than those of the coating obtained at 20 mmol / L. In other words, within a certain concentration range, the higher the concentration of the precursor ammonium paramolybdate, the higher the content of hydrated molybdenum oxide in the coating.

[0077] (2) The appearance photos of the 500-mesh stainless steel mesh used in Example 1 are as follows: Figure 2 As shown. Figure 2 It can be seen that compared with the original stainless steel mesh, its surface becomes colorful after being plated with titanium by magnetron sputtering. The color difference mainly comes from the slight difference in the thickness of the coating film, which is similar to the titanium plating on the surface of industrial metals. When the titanium-plated stainless steel mesh is subjected to a hydrothermal reaction with acidic ammonium paramolybdate, the color of the modified sample fades and turns gray-blue.

[0078] (3) The low-magnification (a) and high-magnification (b) SEM photos of the 500-mesh stainless steel mesh after titanium coating by magnetron sputtering in Example 1 are shown in FIG. Figure 3 By comparing the scanning electron microscope (SEM) photos, it can be clearly observed that the pore structure of the titanium-coated stainless steel mesh is clear and there are no other impurities attached to the surface.

[0079] (4) Low-magnification (a), medium-magnification (b) and high-magnification (c, d) SEM photos of the coating sample prepared in Example 1 of the present invention are as follows: Figure 4 As shown.Figure 4 It can be seen that after hydrothermal modification, the pore structure is still clear, and a layer of coating is evenly attached to the surface of the metal wire. The overall coating has a honeycomb structure, which is composed of a large number of nanorods.

[0080] (5) X-ray photoelectron spectroscopy (XPS) of the titanium-coated stainless steel mesh prepared in Example 1 (black line) and the titanium-coated stainless steel mesh after hydrothermal modification with ammonium paramolybdate solution (red line) is shown in FIG. Figure 5 shown. Figure 5 The illustration in the lower right corner is the high-resolution XPS spectrum of titanium element of titanium-coated stainless steel mesh. Figure 5 It can be seen that the main components of the surface of the titanium-coated stainless steel mesh are carbon (C), oxygen (O), titanium (Ti) and other elements, among which the atomic concentration of Ti is about 18.88%, and the atomic concentration of O is about 47.25%. The high-resolution XPS spectrum of Ti shows that its valence state is tetravalent, that is, Ti (VI), which shows that the surface titanium mainly exists in the form of oxygen-rich titanium dioxide; after hydrothermal modification, the main components of the surface are C, O, molybdenum (Mo) and other elements, and the Ti element almost disappears, which shows that the surface of the titanium-coated stainless steel mesh is successfully covered by Mo-containing compounds. Furthermore, combined with Figure 1 It can be seen that the XRD test shows that the coating material is composed of molybdenum oxide (MoO3) and hydrated molybdenum oxide (HMo 5.35 O 15.75 (OH) 1.6 ·1.7H2O) two composite materials.

[0081] Performance Testing

[0082] (1) The contact angle of crude oil on the surface of the titanium-plated stainless steel mesh modified by the composite coating of molybdenum oxide and hydrated molybdenum oxide prepared in Example 1 is shown in the following figure: Figure 6 As shown. The composite coating provided by the present invention contains abundant oxygen-containing groups and crystalline water, as well as a unique honeycomb structure composed of unique nanorods, which gives it excellent underwater superoleophobic properties. Contact angle tests show that in the aqueous phase, the contact angle of crude oil on its surface is approximately 158±2°.

[0083] (2) The stainless steel mesh material coated with molybdenum oxide and hydrated molybdenum oxide prepared in Example 1 was used as an oil-water separation membrane, and a crude oil-water separation test was performed 20 times. During the 20 cycles of crude oil-water separation, 500 mL of oil-water mixture was separated each time (the volumes of crude oil and water were 150 mL and 350 mL, respectively). After each separation, the oil / water mixture was mixed and the separation was continued.

[0084] Photos of the crude oil-water separation process (a) and the test results of 20 cycles of crude oil-water separation (b) are shown in the figure. Figure 7 As shown. Figure 7The crude oil-water separation data of the membrane can be seen that in 20 cycles of separation, the water flux of the membrane is stable at 18-20 tons / m2 / h, and the oil content in the water is also stable at 10-15 mg / L (ppm), which shows that the composite coating modified titanium-plated stainless steel mesh membrane has the characteristics of self-cleaning in water and is not easy to be blocked by crude oil.

[0085] Example 3

[0086] The preparation method of the composite molybdenum oxide coating is the same as that of Example 1, with two differences: in step (2), the amount of ammonium paramolybdate tetrahydrate is reduced to 1 / 4, i.e. 1.854 g (1.5 mmol), and therefore the concentration of the precursor ammonium paramolybdate solution is also reduced to 10 mmol / L, and a 2.0 mol / L sulfuric acid solution is still used to adjust the solution pH to 1.0; in step (3), the hydrothermal reaction time is shortened to 6 h or extended to 24 h, and the reaction temperature remains unchanged at 180°C.

[0087] The low, medium and high magnification SEM photos of the coatings prepared in Example 3 for 6 h and 24 h of hydrothermal reaction are shown in Figure 8 It can be seen that when the precursor ammonium paramolybdate concentration is reduced to 10 mmol / L and the hydrothermal reaction time is 6 h, the SEM photos of the obtained sample are shown in Figure 8 a-c, and almost no gaps of the steel mesh can be seen, and the surface is covered with a large amount of hexagonal prism-shaped molybdenum oxide material; when the hydrothermal reaction time is extended to 24 h, the SEM photos of the obtained sample are shown in Figure 8 d-f, the steel mesh gaps can be observed, and the surface is still covered with a large amount of hexagonal prism-shaped molybdenum oxide material, only the size of the hexagonal prism is significantly smaller with the extension of time. Importantly, by comparing with Example 1, it is found that the difference in precursor concentration has a great influence on the morphology of the obtained coating sample.

[0088] The stainless steel mesh material coated with molybdenum oxide and hydrated molybdenum oxide coating prepared in Example 3 is used as an oil-water separation membrane, and 20 cycles of crude oil-water separation test are carried out, which also has good crude oil-water separation effect. Therefore, it can be seen that the composite molybdenum oxide coating composed of hexagonal prism-shaped nanorods also has good crude oil-water separation effect.

[0089] Comparative Example 1

[0090] Effect of whether the surface of the stainless steel mesh is titanium-plated on the preparation of the coating:

[0091] Comparing with Example 1, the process of titanium plating on stainless steel was omitted, and the stainless steel mesh was directly put into the precursor solution prepared in step (2) of Example 1, and then the hydrothermal reaction of step (3) was carried out. The result showed that there was no obvious change on the surface of the stainless steel mesh, and no coating was observed to adhere to the surface of the stainless steel mesh, indicating that the titanium plating on the surface of the stainless steel mesh played a key role in the preparation of the molybdenum oxide and hydrated molybdenum oxide coating by the method.

[0092] Comparative Example 2

[0093] Effect of high vacuum titanium plating (low oxygen content in titanium layer) on the surface of the stainless steel mesh on the preparation of the coating:

[0094] The vacuum degree of the magnetron sputtering system in step (1) of Example 1 was increased to 5x10 -5 Pa, and the oxygen content on the surface of the titanium-plated stainless steel mesh was low. At this time, the steps (2-3) were continued, and the coating could not be constructed on the surface, indicating that the titanium plating on the surface of the stainless steel mesh needed to contain rich oxygen elements to prepare the molybdenum oxide and hydrated molybdenum oxide composite coating.

[0095] Comparative Example 3

[0096] Effect of different pH values of the precursor solution on the preparation of the coating:

[0097] ①The preparation method was the same as that of Example 1, except that in step (2), the sulfuric acid solution was not used to adjust the pH value, i.e. the pH value of the system was between 5.0-5.2, and the other conditions were kept unchanged. The coating could not be grown on the surface of the titanium-plated stainless steel mesh.

[0098] ②The preparation method was the same as that of Example 1, except that in step (2), the ammonia solution (alkali solution) was used to replace the sulfuric acid to adjust the pH value of the reaction system to 10, and the other conditions were kept unchanged. Similarly, the coating could not be prepared on the substrate material.

[0099] Comparing the two sets of control tests with Example 1, it was indicated that only when the pH value of the reaction system was strongly acidic, the composite coating could be prepared on the surface of the titanium-plated stainless steel mesh.

[0100] Example 4

[0101] The preparation method of the composite coating was the same as that of Example 1, except that the vacuum degree of the magnetron sputtering system was increased to 5x10 -5 Pa, and after the titanium plating was completed, it was placed in a muffle furnace and heated at 400-500°C for 2 hours, and then steps (2), (3) in Example 1 were carried out. The composite mesh material coated with the molybdenum oxide and hydrated molybdenum oxide coating could also be obtained, and the performance was similar to that of Example 1.

[0102] Example 5

[0103] The preparation method of the composite material is the same as that in Example 1, except that in step (2) "weigh 7.416 g (6 mmol) of solid ammonium molybdate dihydrate" is changed to "weigh 8.233 g (42 mmol) of ammonium molybdate solid", and then step (3) in Example 1 is performed, to obtain the composite mesh material coated with a molybdenum oxide and hydrated molybdenum oxide coating, which has similar performance to that in Example 1.

[0104] The above only describes the preferred embodiments of the present application, and it should be noted that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

Claims

1. A method for preparing a honeycomb-like composite molybdenum oxide coating on a metal surface, comprising the following steps: plating titanium on a surface of a metal substrate to obtain a metal substrate covered with an oxygen-rich titanium intermediate layer; the oxygen-rich titanium intermediate layer comprises, in terms of atomic content, O 20-60%, Ti 15-25%, and the balance being C and other inevitable impurity elements; providing an aqueous molybdate solution, adjusting the pH value of the aqueous molybdate solution to 1.0 to obtain a molybdate precursor solution; placing the metal substrate covered with the oxygen-rich titanium intermediate layer in the molybdate precursor solution, and sequentially performing ultrasonic treatment and hydrothermal reaction to obtain a honeycomb-like composite molybdenum oxide coating on the surface of the metal substrate, the composite molybdenum oxide coating comprising molybdenum oxide and hydrated molybdenum oxide.

2. The method of claim 1, wherein, The metal substrate is a metal mesh, and the metal substrate is made of one or more of stainless steel, copper, titanium, nickel, aluminum alloy, copper alloy, zinc alloy, titanium-cobalt alloy, and cobalt-nickel alloy.

3. The method of claim 1, wherein, The plating method comprises one or more of magnetron sputtering, water plating black titanium, thermal evaporation, and ion plating. The thickness of the oxygen-rich titanium intermediate layer is 500-600 nm.

4. The method according to claim 1 or 3, characterized in that, The method for plating titanium is magnetron sputtering, the target material of the magnetron sputtering is a titanium target material, the vacuum degree is (5-5.5)×10 -4 Pa; The gas for magnetron sputtering is Ar gas, and the gas flow rate is 30-35 sccm. During the magnetron sputtering, the discharge gas pressure is 2-2.5 Pa, the direct current power is 100-120 W, the negative bias voltage is 150-160 V, and the plating time is 15-20 min.

5. The method according to claim 1 or 3, characterized in that, After plating titanium on the surface of the metal substrate, the method further comprises heating and oxidizing to obtain the metal substrate covered with the oxygen-rich titanium intermediate layer, and the titanium intermediate layer comprises titanium oxide. The heating and oxidizing temperature is 400-500℃, and the holding time is 2-4 h.

6. The method of claim 1, wherein, The molybdate comprises one or more of ammonium dimolybdate, ammonium molybdate, sodium molybdate, magnesium molybdate, zinc molybdate, molybdenum isopoly acid salt, and molybdenum heteropoly acid salt. The concentration of the aqueous molybdate solution is 10-40 mmol / L.

7. The method of claim 1, wherein, The ultrasonic treatment power is 200-600 W, and the time is 30-40 min.

8. The method of claim 1, wherein, The hydrothermal reaction temperature is 175-180℃, and the time is 6-24 h. 9.The honeycomb-like composite molybdenum oxide coating on the metal surface prepared by the method of any one of claims 1-8, comprising a metal substrate, an oxygen-rich titanium intermediate layer covering the metal substrate, and molybdenum oxide nanorods and hydrated molybdenum oxide nanorods grown on the surface of the oxygen-rich titanium intermediate layer. 10.Use of the honeycomb-like composite molybdenum oxide coating on the metal surface of claim 9 in oil-water separation.

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