A method of surface modification of titanium by producing titanium dioxide nanotubes and graphene transfer or vacuum deposition of carbon

Abstract

The object of the invention is a method of surface modification of titanium by producing a layer of titanium dioxide nanotubes (TNT) on a titanium substrate using anodisation in a two-electrode system, where the working electrode is a titanium foil and the reference electrode is a platinum foil, comprising the steps, followed by chemical modification by transfer of graphene to the surface of the nanotubes using a PMMA matrix, or vacuum deposition of carbon of different thicknesses of the deposited layer using carbon fibres.

Description

[0001] The object of the present invention is a method for the surface modification of titanium by producing titanium dioxide nanotubes (TNT) and either graphene transfer or vacuum deposition (also known as vacuum spraying) of carbon. The method makes it possible to adjust the wettability and stationary potential of titanium.

[0002] Canadian patent application CA2633531A1 describes a method of producing a nanotube titanium substrate that includes the steps of anodising the titanium substrate with producing of self-organising titanium oxide nanotubes, dispersing gold nanoparticles on the titanium oxide surface, annealing the titanium oxide surface with gold nanoparticles in a non-oxidising atmosphere and depositing carbon on the annealed titanium oxide surface.

[0003] Chinese patent application CN113096968A discloses a method for the preparation of anodised titanium oxide nanotubes doped with metal ions. The matrix layer of titanium dioxide nanotubes and a low melting point metal are annealed together. The deposited metals can be metals with a low melting point lower than 430°C, including tin (Sn, melting point 231.89°C), zinc (Zn, melting point 419.53°C) and cadmium (Cd, melting point 320.90°C).

[0004] Korean patent application KR20220037109A describes a method of producing a nitrogen-doped titanium dioxide / nitride nanotube composite for photocatalysts.

[0005] Chinese patent application CN110394169A relates to a method of producing activated carbon nanotubes and doping titanium nanodioxide with them.

[0006] Chinese patent application CN102151561A discloses a method of manufacturing a photocatalyst consisting of carbon nanotubes loaded with titanium dioxide on external surfaces.

[0007] US patent application US2011135827A1 describes a method of producing CNT carbon nanotubes coated with TiO 2 .

[0008] The aim of the invention was to develop a means of regulating the wettability, surface free energy and stationary potential of titanium. No document from the state of the art solves the technical problem indicated above by modifying previously produced titanium dioxide nanotubes (TNT) with carbon compounds.

[0009] This was achieved through a two-step chemical modification of titanium, i.e. the production of titanium dioxide nanotubes (TNT) and further modification with carbon compounds (vacuum-deposited carbon or graphene).

[0010] Thus, an object of the invention is a method of surface modification of titanium by forming a layer of TNT titanium dioxide nanotubes on a titanium substrate using anodisation in a two-electrode system, where the working electrode is a titanium film and the reference electrode is a platinum film, comprising the steps of: the titanium foil is cleaned in acetone and distilled water in an ultrasonic cleaner and then dried in a stream of nitrogen; titanium nanotubes with a diameter of 50 ± 5 nm and a height of 1,000 ± 100 nm are produced by modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol and 0.65 wt% NH 4 F, applying a potential of 17 V for 3750 s; titanium foil with a layer of titanium nanotubes is further chemically modified by: graphene transfer onto the surface of nanotubes using a PMMA matrix, in which the total surface of the wetted graphene / PMMA film is placed on a titanium film with a layer of titanium nanotubes, the titanium film is then heated to approximately 70°C and treated with acetone vapour to ensure adhesion of the graphene to the surface of the titanium nanotubes, after which the PMMA film is removed by dissolving in acetone or vacuum deposition of carbon of different deposited layer thicknesses under high vacuum in a deposition chamber using carbon fibres.

[0011] Advantageously, the PMMA film is removed by dissolving in acetone for 24 hours.

[0012] Advantageously, titanium foil with a purity of 99.70% is used.

[0013] Advantageously, platinum foil of 99.95% purity is used.

[0014] Advantageously, the titanium foil is cleaned in acetone and distilled water for 10 minutes each, respectively, in a 300 W ultrasonic cleaner.

[0015] Also an object of the invention is a method of imparting highly hydrophilic properties to the titanium surface with a contact angle (WCA) of 5 to 35° as defined above, wherein titanium nanotubes with a diameter of 50 ± 5 nm and a height of 1000 ± 100 nm are produced, modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol + 0.65 wt% NH 4 F, applying a potential of 17 V for 3750 s and subjecting the TNT layer to further chemical modification by said graphene transfer.

[0016] Also an object of the invention is a method of imparting weakly hydrophilic properties to the titanium surface with a contact angle (WCA) of 75 to 90° as defined above, wherein titanium nanotubes with a diameter of 50 ± 5 nm and a height of 1000 ± 100 nm are produced by modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol and 0.65 wt% NH 4 F at a potential of 17 V for 3750 s and subjecting it to further chemical modification by vacuum deposition of carbon with a thickness < 60 ± 5 nm.

[0017] A further object of the invention is a method of imparting hydrophobic properties to the titanium surface with a contact angle (WCA) above 90° as defined above, wherein titanium nanotubes of 50 ± 5 nm in diameter and 1000 ± 100 nm in height are produced by modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol and 0.65 wt% NH 4 F at a potential of 17 V for 3750 s and subjecting it to further chemical modification by vacuum deposition of carbon with a thickness of > 60 ± 5 nm.

[0018] Also an object of the invention is a method of imparting a negative surface charge to a titanium surface with an open circuit potential (OCP) of -300 to -10 mV relative to an Ag / AgCI chlorosilver electrode as defined above, wherein: titanium nanotubes with a diameter of 50 ± 5 nm and a height of 1000 ± 100 nm are produced by modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol + 0.65 wt% NH4F at a potential of 17 V for 3750 s and subjecting it to further chemical modification by vacuum deposition of carbon with a thickness < 60 ± 5 nm.

[0019] A further object of the invention is a method of imparting a positive surface charge to a titanium surface with an open circuit potential (OCP) of more than 10 mV relative to an Ag / AgCI chlorosilver electrode as defined above, wherein: titanium nanotubes with a diameter of 50 ± 5 nm and a height of 1,000 ± 100 nm are produced by modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol + 0.65 wt% NH 4 F, applying a potential of 17 V for 3750 s and undergoing further chemical modification by said graphene transfer.

[0020] The object of the invention is shown in the figures, where: Fig. 1 shows SEM images of the surface of pure titanium - Ti (a), TiO 2 nanotube-coated - TNT (b), TNT with vacuum-deposited carbon (c), TNT with transferred graphene (d); Fig. 2 shows an example of an open circuit permeation (OCP) measurement plot for a TNT sample modified with vacuum-deposited carbon with a layer thickness of 60 ± 5 nm measured in artificial plasma solution.

[0021] The invention relates to a method of surface modification of titanium by producing titanium dioxide nanotubes (TNT) with a well-defined morphology and applying chemical modification by either vacuum deposition of carbon or graphene transfer. The developed method of surface modification of titanium allows control over a wide range of physico-chemical properties of titanium, such as surface wettability, surface free energy and stationary potential measured in artificial plasma solution. The fabricated layer is composed of homogeneous, vertically aligned titanium dioxide nanotubes (TNT) on a substrate with a height of 1000 ± 100 nm and a circular base with an outer diameter of 50 ± 5 nm.

[0022] This layer is formed by anodising in an ethylene glycol solution with ammonium fluoride. In the following, the description of the invention shows the relationship between the process parameters of the modification of the titanium substrate coated with either TNT graphene or vacuum-deposited carbon and the wettability, surface free energy and stationary potential of the layer formed on the titanium substrate.

[0023] The TiO 2 nanotube layer is the subject of research by many scientists to determine the physico-chemical properties and potential application mainly in medicine. The uniqueness of the developed method of fabrication and thermal modification lies in its adjustability: wettability - from hydrophobic to superhydrophilic surfaces, and stationary potential in artificial plasma solution - from strongly negative values to positive values over a very wide range.

[0024] These properties allow TNT to be used in a variety of industries, particularly in biomedical engineering as an osteosynthesis-regulating layer, as an antibacterial layer or coating for urological catheters.

[0025] In order to produce a layer of titanium dioxide nanotubes (TNT) on a titanium substrate, anodisation was performed in a two-electrode system, where the working electrode was a titanium foil with a purity of 99.70% and a thickness of 0.25 mm, and the reference electrode was a platinum foil with a size of 25 x 25 x 0.05 mm and a purity of 99.95%.

[0026] The titanium foil was cut into 20 x 5 x 0.25 mm samples and then subjected to cleaning in acetone and distilled water for 10 minutes each, respectively, in a 300 W ultrasonic cleaner.

[0027] After cleaning, the titanium substrates were dried in a stream of nitrogen.

[0028] The anodising process was carried out by applying a potential of 17 V for 3750 s. The electrolyte consisted of an aqueous solution containing 85 wt% ethylene glycol with 0.65 wt% ammonium fluoride. The samples were then chemically modified by graphene transfer or vacuum deposition of carbon.

[0029] The transfer of HSMG graphene onto the TNT surface (diameter: 50 ± 5 nm, height: 1000 ± 100 nm) was carried out using a poly(methyl methacrylate) - PMMA matrix, in order to maintain high graphene quality and continuous coverage of up to 99% of the surface. Due to the type of graphene transferred onto the TNT surface, the process did not need to be optimised. The complete surface of the wetted graphene / PMMA film was placed on the TNT target substrate. The sample was placed on a hot plate and heated to approximately 70°C. After stretching the film on the TNT-film-graphene system substrate, the adhesion of graphene to the TNT surface was ensured by the action of acetone vapour, which was carried out for about 10 minutes. The sample was then cooled and the PMMA film was dissolved by immersing it in acetone for 24 hours (changing the solvent four times).

[0030] The modification of TNT with carbon compounds consisted of deposition carbon on the TNT surface with different deposited layer thicknesses, i.e. 35, 50, 60 ± 5 nm. The deposition process was carried out under high vacuum conditions in the chamber of a QUORUM Q150T ES deposition machine using carbon fibres.

[0031] A field emission scanning microscope (FESEM, JEOL JSM-7600F) was used to study the morphology of the TNTs produced, with diameter and height values determined.

[0032] Wettability tests were conducted using a Klimatest PG-3 goniometer.

[0033] Open-circuit potential (open-circuit potential, OCP) measurements were carried out in 0.01 M buffered saline in a three-electrode system, over a period of four hours, with the chlorosilver electrode as the reference electrode.

[0034] The surface free energy of the substrate was calculated using the formula: E se = E v 1 × cosθ where: E v1 - surface energy between distilled water and air determined at 20 ± 2°C (72.8 mJ / m 2< ), θ - static wetting angle. 1) Wettability (WCA) of Ti was regulated using the following conditions: (a) Strong surface hydrophilicity (WCA 5-35°) was obtained by: ▪ producing a TNT with a diameter of 50 ± 5 nm and a height of 1000 ± 100 nm, modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol + 0.65 wt% NH 4 F, applying a potential of 17 V for 3750 s and subjecting the TNT layer to further chemical modification by transferring graphene as described above onto the TNT surface using a PMMA matrix, provided that high quality graphene is maintained and up to 99% of the surface is continuously covered. (b) Weak hydrophilicity (WCA 75-90°) was obtained by: ▪ producing a TNT with a diameter of 50 ± 5 nm and a height of 1000 ± 100 nm, modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol + 0.65 wt% NH 4 F at a potential of 17 V for 3750 s and undergoing further chemical modification by vacuum deposition of carbon with a thickness < 60 ± 5 nm. (c) Hydrophobicity (WCA >90°) was obtained by: ▪ to produce TNT with a diameter of 50 ± 5 nm and a height of 1,000 ± 100 nm by modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol + 0.65 wt% NH. NH 4 F at a potential of 17 V for 3750 s and undergoing further chemical modification by vacuum deposition of carbon with a thickness > 60 ± 5 nm. 2) The surface charge of titanium (-465 ± 5 mV) was adjusted using the following conditions: (a) Negative surface charge (OCP -300 to -10 mV vs. Ag / AgCI) was obtained by: ▪ producing a TNT with a diameter of 50 ± 5 nm and a height of 1000 ± 100 nm, modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol + 0.65 wt% NH 4 F at a potential of 17 V for 3750 s and undergoing further chemical modification by vacuum deposition of carbon with a thickness of < 60 ± 5 nm. (b) A positive surface charge (OCP>10 mV) was obtained by: ▪ producing a TNT with a diameter of 50 ± 5 nm and a height of 1000 ± 100 nm, modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol + 0.65 wt% NH 4 F, applying a potential of 17 V for 3750 s and subjecting the TNT layer to further chemical modification by transferring graphene as described above onto the TNT surface using a PMMA matrix, provided that high quality graphene is maintained and up to 99% of the surface is continuously covered. Table 1. Examples of conditions for chemical modification of titanium by anodising and carbon compound deposition to adjust surface wettability Forming conditions WCA [°] Surface free energy E se [mJ / m 2< ] Pure titanium56±139.6÷41.8 strong hydrophilicity (WCA 5-35°)TNT manufactured in 85% ethylene glycol + 0.65 wt% NH 4 F, voltage: 17 V, time: 3750 s20±267.5÷69.2 medium hydrophilicity (WCA 35-75°)TNT manufactured in 85% ethylene glycol + 0.65 wt% NH 4 F, voltage: 17 V, time: 3750 s58±434.2÷42.8Chemical modification: graphene transfer poor hydrophilicity (WCA 75-90°)TNT manufactured in 85% ethylene glycol + 0.65 wt% NH 4 F, voltage: 17 V, time: 3750 s81±28.9÷13.9Chemical modification: vacuum-deposited carbon with a layer thickness of 35 nm.TNT manufactured in 85% ethylene glycol + 0.65 wt% NH 4 F, voltage: 17 V, time: 3750 s86±22.5÷7.6Chemical modification: vacuum-deposited carbon with a layer thickness of 50 nm. hydrophobicity (WCA >90°)TNT manufactured in 85% ethylene glycol + 0.65 wt% NH 4 F, voltage: 17 V, time: 3750 s>90=> 0Chemical modification: vacuum-deposited carbon with a layer thickness of 60 nm. Table 2. Examples of conditions for chemical modification of titanium by anodising and carbon compound deposition allowing the regulation of the stationary potential in artificial plasma solution Forming conditions OCP [mV vs. Ag / AgCl] Pure titanium-465±5 negative surface charge (OCP -300 to 0 mV vs. Ag / AgCl)TNT manufactured in 85% ethylene glycol + 0.65 wt% NH 4 F, voltage: 17 V, time: 3750 s-282±30TNT manufactured in 85% ethylene glycol + 0.65 wt% NH 4 F, voltage: 17 V, time: 3750 s-185±10Chemical modification: vacuum-deposited carbon with a layer thickness of 35 nm.TNT manufactured in 85% ethylene glycol + 0.65 wt% NH 4 F, voltage: 17 V, time: 3750 s-160±10Chemical modification: vacuum-deposited carbon with a layer thickness of 50 nm.TNT manufactured in 85% ethylene glycol + 0.65 wt% NH 4 F, voltage: 17 V, time: 3750 s-140±10Chemical modification: vacuum-deposited carbon with a layer thickness of 60 nm. positive surface charge (OCP>0 mV)TNT manufactured in 85% ethylene glycol + 0.65 wt% NH 4 F, voltage: 17 V, time: 3750 s5±2Chemical modification: graphene transfer

Claims

1. A method of surface modification of titanium by forming a layer of TNT titanium dioxide nanotubes on a titanium substrate using anodization in a two-electrode system, wherein the working electrode is a titanium foil and the reference electrode is a platinum foil, comprising the steps of: - the titanium foil is cleaned in acetone and distilled water in an ultrasonic cleaner and then dried in a stream of nitrogen; - the titanium nanotubes with a diameter of 50 ± 5 nm and a height of 1000 ± 100 nm are produced by modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol and 0.65 wt% NH4F, applying a potential of 17 V for 3750 s; - the titanium foil with a layer of titanium nanotubes is further chemically modified by: - graphene transfer onto the surface of nanotubes using a PMMA matrix, in which the total surface of the wetted graphene / PMMA film is placed on a titanium film with a layer of titanium nanotubes, the titanium film is then heated to approximately 70°C and treated with acetone vapour to ensure adhesion of the graphene to the surface of the titanium nanotubes, after which the PMMA film is removed by dissolving in acetone or - vacuum deposition of carbon of different deposited layer thicknesses under high vacuum in a deposition chamber using carbon fibres.

2. The method according to claim 1, wherein the PMMA film is removed by dissolving in acetone for 24 hours.

3. The method according to claim 1 or 2, wherein a titanium foil having a purity of 99.70% is used.

4. The method according to claim 1 or 2 or 3, wherein a platinum film having a purity of 99.95% is used.

5. The method according to any of the claims 1-4, wherein the titanium foil is cleaned in acetone and distilled water for 10 minutes each, respectively, in an ultrasonic cleaner of 300 W6. A method of imparting highly hydrophilic properties to a titanium surface with a wetting angle (WCA) of 5 to 35° as defined in any of the claims 1-5, wherein titanium nanotubes with a diameter of 50 ± 5 nm and a height of 1000 ± 100 nm are produced by modifying the titanium by anodizing in an aqueous solution containing 85 wt% ethylene glycol + 0.65 wt% NH4F, applying a potential of 17 V at 3750 s and subjecting the TNT layer to further chemical modification by said graphene transfer.

7. A method of imparting weakly hydrophilic properties to the surface of titanium with a wetting angle (WCA) of 75 to 90° as defined in any of the claims 1-5, wherein titanium nanotubes with a diameter of 50 nm and a height of 1000 nm are produced by modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol and 0.65 wt% NH4F at a potential of 17 V for 3750 s and undergoing further chemical modification by vacuum deposition of carbon with a thickness of < 60 ± 5 nm.

8. A method of imparting hydrophobic properties to a titanium surface with a wetting angle (WCA) greater than 90° as defined in any of the claims 1-5, wherein titanium nanotubes with a diameter of 50 ± 5 nm and a height of 1000 ± 100 nm are produced by modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol and 0.65 wt% NH4F at a potential of 17 V for 3750 s and subjecting it to further chemical modification by vacuum deposition of carbon with a thickness of > 60 ± 5 nm.

9. A method of imparting a negative surface charge to a titanium surface with an open circuit potential (OCP) of -300 to -10 mV relative to an Ag / AgCI chlorosilver electrode as defined in any of the claims 1-5, wherein: - titanium nanotubes with a diameter of 50 ± 5 nm and a height of 1000 ± 100 nm are produced by modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol + 0.65 wt% NH4F at a potential of 17 V for 3750 s and subjecting it to further chemical modification by vacuum deposition of carbon with a thickness < 60 ± 5 nm.

10. A method of imparting a positive surface charge to a titanium surface with an open circuit potential (OCP) of greater than 10 mV relative to an Ag / AgCI chlorosilver electrode as defined in any of the claims 1-5, wherein: - titanium nanotubes with a diameter of 50 ± 5 nm and a height of 1,000 ± 100 nm are produced by modifying the titanium by anodising in an aqueous solution containing 85 wt% ethylene glycol + 0.65 wt% NH4F, applying a potential of 17 V for 3750 s and undergoing further chemical modification by said graphene transfer.