A METHOD FOR MANUFACTURING THIN LAYERS OF VERTICALLY ORIENTED Ti3C2Tx AND ITS PRODUCTS

Abstract

This invention relates to a method for manufacturing thin layers of vertically oriented Ti3C2Tx used for NO2 gas sensors and the characteristics of the products it creates. The manufacturing method in this invention consists of 3 main stages. The first stage consists of making a Ti3C2Tx solution using the selective AI etching method. Next, a thin layer of Ti3C2Tx is made using the electrophoretic deposition method. The next stage consists of freezing and drying to obtain vertically-oriented Ti3C2Tx that attaches to a stainless steel substrate. The thin layers of vertically-oriented Ti3C2Tx used for NO2 gas sensors are characterized by a thickness of 150-250 µm and a sensitivity value of 28-30 at an NO2 gas concentration of 50 ppm. This invention's thin layers of Ti3C2Tx are 2.8 times more sensitive to nitrogen oxide / NO gas2 than Ti3C2Tx powder. Therefore, the product in this invention can be applied to air pollution control.

Description

[0001] Description

[0002] A METHOD FOR MANUFACTURING THIN LAYERS OF VERTICALLY ORIENTED

[0003] Ti3C2TxAND ITS PRODUCTS

[0004] Technical Field of the Invention

[0005] This invention relates to a method for manufacturing thin layers of vertically oriented TisC2Txthat can be used for NO2 gas sensors and the characteristics of the products it creates. This invention's thin layers of TisC2Txare 2.8 times more sensitive to nitrogen oxide / NO gas2 than TisC2Txpowder. Therefore, the product in this invention can be applied to air pollution control.

[0006] Background of the Invention

[0007] Rapid industrialization has caused environmental quality to degrade on a massive scale despite bringing economic benefits and prosperity to humans. Air pollution, one of the serious environmental problems induced by various anthropogenic activities, has been identified as a problem of great concern by the global community due to its destructive impact on human health and the surrounding ecosystem (de Gennaro et al., 2013; Esplugues et al., 2010; Hermawan et al., 2019) . For example, volatile organic gases (VOCs) , which come from reagents widely used in industries and laboratories, are harmful to humans and must be detected immediately. As VOCs evaporate quickly at relatively low temperatures, the amount of VOCs in the atmosphere can gradually increase, putting our environment and other living things at risk. In addition, nitrogen oxides, NOX, are deadly atmospheric contaminants resulting from the combustion of hydrocarbons in vehicle engines and power plants, which usually occur at high temperatures. Moreover, electricity generation from non-recycled fuels and the widespread use of vehicles, especially in metropolitan cities, has made NOx pollution a serious problem. Therefore, there is an urgent need to develop materials that are highly responsive to VOC and NOXdetection for environmental pollution control (Gu et al., 2020; Hermawan et al., 2020) . 2D transition metal carbides, carbonitrides, and nitrides, also known as MXenes, have attracted significant attention because of their remarkable electronic, physical, chemical, and mechanical properties derived from their diverse chemical composition, large surface dimensional ratios, adjustable surface functionality, high electrical conductivity, and exceptional strength and stability (Gogotsi & Anasori, 2019) . MXene ' s remarkable performance makes it a suitable candidate for energy and environmental applications, such as supercapacitors, sensors, solid batteries, thermoelectric devices, fuel production, photodegradation, and more. In addition, due to their layered free-standing crystal structure and their unique stack of delaminated layers, 2D MXene materials can become easily assembled building blocks for nanoparticle insertion, forming a nanoarchitecture. Ti3C2Tx(T = -F, - OH, 0) is the first synthesized 2D MXene and one of the most explored among the MXene family (Shuck et al., 2020) . It has also been used for many applications because it has a large specific surface area, narrow band gap, and fast electron transfer capability. Additionally, previous studies have proven that 2D MXene Ti3C2Txcan effectively detect various volatile organic compounds (VOC) with a sub-ppm detection limit (A. Hermawan et al. ACS ANM 2020, 3 (5) , 4755- 4766; A. Hermawan et al. JMST 2021, 73,128-138; A. Hermawan et al. FML 2022, 15, 2251007) . However, 2D MXene typically has a dense horizontal stack structure against the sensor electrodes (Shang et al., 2019) due to the highly anisotropic nature of nanosheets. This stacked structure limits mass transfer and the full utilization of their active surfaces for the adsorption of gases and molecules.

[0008] To inhibit the aggregation of Ti3C2Txsheets and facilitate the transport of film ions, Ti3C2Txcan be arranged vertically on the electrode. Forming vertically-oriented Ti3C2Txnanosheets enables ion transport channels to be engineered in such a way that increases the rate of ion and electron transport, which has been well-developed in supercapacitors (Luo et al., 2019b; Pang et al., 2019) . For example, a template-based strategy for creating a 3- dimensional macroporous Ti3C2Txelectrode has been developed. This structure ef fectively inhibits Ti3C2Txwhile improving electrochemical active sites and ion accessibility . Another study created vertical MXene nanosheets on a substrate by mechanically retracting Ti3C2Txin its liquid crystal phase ( Zhang et al . , 2020 ) . These electrodes exhibit fast charging capabilities compared to hori zontally stacked Ti3C2Txfilms . The channel between vertically- oriented TisC2Txwalls also of fers signi ficant advantages for chemical molecule adsorption and charge transport , which benefits gas sensor performance . In addition, by vertically orienting the MXene on the sensor electrode , the TisC2Txside will be signi ficantly open and fully usable . In this case , the vertically- oriented TisC2Txcan provide a superior trans fer path and increase the active surface accessible from the side .

[0009] The fabrication of MXene-based thin- film electrodes has been described in patent number RU0002709599 titled "Gas Sensor, a Chemoresistive Type Multi-Sensor Ruler Based on Oxidi zed Two- Dimensional Titanium Carbide (Mxene ) and A Method for Production Thereof , " where the chemoresistive sensor electrodes were fabricated using the drip method or Langmuir-Blodgett . The synthesi zed Ti3C2Txwas mixed into alcohol or acetone , then deposited on the desired substrate ( silicon, ceramic, glass , sapphire , quartz , or polymer ) , and then heated . However, the resulting film is thin with a relatively low homogeneity, which af fects its conductivity .

[0010] The W02016049109 patent titled "Physical Forms of Mxene Materials Exhibiting Novel Electrical and Optical Characteristics" describes MXene-based electrodes success fully fabricated using the ( roll ) or drop-casting method . In this invention, the synthesi zed Mxene can be molded like clay, then dried and rolled into a thin film or mixed with water to form a solution, which would then be dripped onto the desired substrate . However, the resulting film is thin with a relatively low homogeneity, which af fects its conductivity .

[0011] Other MXene-based electrode fabrication methods , such as spin coating, have also been disclosed in patent number US20220085224 , titled" MXene Optoelectronic Systems and Devices . " This method is also used in patent number US20230165033 , titled "MXene Transparent Conducting Layers for Digital Displays and Method Thereof . " In this invention, the MXene-based electrodes fabricated on a PET substrate could produce high conductivity and transmittance ( 11 . 668 S / cm and 85% ) . However, the resulting film has a relatively low homogeneity and only covers a small area of the substrate used .

[0012] Other methods , such as the dip-coating method, have also been success fully applied to fabricate conductive textiles (woven and non-woven) for superconductors and pressure sensors . This invention is described in two patents numbered W02020097514A1 and US20210396607A1 , titled "MXene-based Sensor Devices . "However , there is a disadvantage to the method in the mentioned patents regarding the MXene solution preparations . A large amount of MXene solution is needed during fabrication, making the proces s inef ficient .

[0013] The dry li ft-of f technique can also be used to fabricate MXene-based electrodes as described in patent number US20200405165 , titled " Implantable Devices Using 2D Metal Carbides and Nitrides (Mxenes ) " . The electrodes success fully fabricated in this invention were then applied in the manufacturing process of multi-electrode sensor prototypes for recording nerve signals . The thickness of the thin film produced from the method is 5-30 nm . MXene-based electrodes in the form of disks or thin f ilms have also been success fully fabricated by the cold press method using hydraulic pellet presses and vacuum filtration, as stated in patents US20160336088 ( Compositions Comprising Free-Standing Two- Dimensional Nanocrystals ) and US20210096096 ( Sensor Electrode , sensors , and Method of Production) . However, the patent uses relatively sophisticated tools that increase production costs .

[0014] Based on the patents mentioned earlier, the most common methods for fabricating MXene-based thin films are the Langmuir- Blodgett , the cold press , dry li ft-of f , vacuum filtration, roll - , drip - , drop- , and spin-coating methods . Additionally, the inventions mentioned above still produce hori zontally-stacked

[0015] MXene structures . Therefore , this present invention aims to present a more ef fective MXene-based thin film fabrication method through an electrophoretic deposition technique . The advantage of this present method is the production of vertically oriented MXene , which provides many advantages for sensor applications .

[0016] Summary of the Invention

[0017] This invention aims to overcome the shortcomings of previous inventions and describe a method for manufacturing thin layers of vertically-oriented Ti3C2Txfor NO2 gas sensors along with the characteristics of the products it creates .

[0018] The manufacturing method of this invention comprises three main stages . The first stage involves making a Ti3C2Txsolution using the selective Al etching method . Next , a thin layer of Ti3C2Txis made using the electrophoretic deposition method . The next stage consists of freezing and drying to obtain vertically-oriented Ti3C2Txthat attaches to a stainless steel substrate .

[0019] The thin layers of vertically-oriented Ti3C2Txused for NO2 gas sensors are characteri zed by a thickness of 150-250 pm and a sensitivity value of 28-30 at an NO2 gas concentration of 50 ppm . The thin layers of Ti3C2Txdescribed in this invention are 2 . 8 times more sensitive to NO2 gas than Ti3C2Txpowder .

[0020] Brief Description of the Figures

[0021] Figure 1 exhibits the stages involved in manufacturing thin layers of vertically oriented TisC2Txobtained from this invention .

[0022] Figure 2 is a schematic diagram of the stages of the electrophoretic deposition method used to produce thin layers of vertically-oriented Ti3C2Txobtained from this invention .

[0023] Figure 3 is a thin-layer X-ray di f fraction (XRD) di f f ractogram of the vertically-oriented Ti3C2Txobtained from this invention .

[0024] Figure 4 is a thin layer scanning electron microscopy ( SEM) image of the vertically-oriented Ti3C2Txobtained from this invention . Figure 5 is the thin-layer Raman spectrum of the vertically- oriented Ti3C2Txobtained from this invention .

[0025] Figure 6 is the sensitivity curve of vertically-oriented Ti3C2Txagainst an increase in NO2 gas concentration, as obtained from this invention .

[0026] Description of the Invention

[0027] This section will explain the invention further and describe Figure 1 . The manufacturing method of thin layers of vertically- oriented TisC2Txand the products it creates have the following process stages :

[0028] 1 . The preparation of the Ti3C2Txsolution by the selective Al etching method

[0029] 2 . The preparation of the thin layer TisC2Txby the electrophoretic deposition method

[0030] 3 . The freezing in liquid nitrogen and drying processes

[0031] The stages are described in detail as follows :

[0032] The first stage is the process of making the Ti3C2Txsolution . Ti3C2Txis first created from Ti3AlC2 by the selective Al etching method . The etching solution is made by mixing hydrochloric acid (HC1 ) with lithium fluoride ( LiF) . The etching product is mixed with a Trimethylammonium hydroxides ( TMAOH) solution and sonicated .

[0033] The second stage is fabricating thin layers of T±3C2 TXby the electrophoretic deposition (EPD) method . The fabricated TisC2Txsolution is then deposited on a stainless steel ( SS ) substrate . The electrophoretic deposition process lasted for 30 minutes at a voltage of 8V, as shown in Figure 2 .

[0034] The third stage comprises freezing the thin-layer stainless steel ( SS ) substrate modi fied by vertically-oriented Ti3C2Txin liquid nitrogen and drying it under vacuum conditions .

[0035] Next , material characteri zation was performed to determine the structure and properties of the thin layers of vertically- oriented Ti3C2Txand the products it creates .

[0036] The XRD analysis is shown in Figure 3 . XRD testing was conducted to see the structural changes of the thin layers of Ti3C2Txcompared with the Ti3C2Txsolution. The peak position of the

[0037] XRD test result was then processed to obtain the d-spacing (distance between layers) value using Bragg's law formula. The XRD testing was performed from 20 3° to 60°, with a scanning rate of 3 ° / minute. The manufacturing process of thin layers of Ti3C2Txwith the electrophoretic deposition method will form vertically- oriented, thin layers on the positive pole / cathode because TisC2Txhas a negative charge on its surface. In Figure 3, the XRD result shows that TisC2Txpowder has a diffraction peak at an angle of 20 = 6.4°, representing diffraction in the plane (002) . This plane is the basal surface of the TisC2Txfrom the delamination, with the distance between the laminates / d-spacing being 13.8 A. The absence of H3AIC2 peak diffractions shows that the Al selectivity etching process was successful and produced TisC2Txproducts with high purity. After the electrophoretic deposition process, the diffraction peak position of the thin layers of TisC2Txwill be vertically shifted to 20 = 6.0°. The smaller angle of the thin layers of vertically-oriented Ti3C2Txto the peak position indicates the increase in distance between the Ti3C2Txlayers to 14.7 A after the electrophoretic deposition process.

[0038] The SEM analysis is shown in Figure 4. Figure 4 (a) illustrates the typical exfoliated morphology of delaminated Ti 3C2TJ, powder. The figure exhibits the successful removal of the Al layer from the T13A1C2- The overall powder size and space between the TisC2Txlayers is estimated to be around 10-20 pm and 10-50 nm. Meanwhile, Figure 4 (b) exhibits an SEM image of thin TisC2Txlayers, vertically oriented by the electrophoretic deposition method. Its thickness is about 180 pm. The thickness of these layers will depend on several parameters: (i) the duration of the electrophoretic deposition, (ii) the magnitude of the electrophoretic deposition voltage, and (ill) the concentration of Ti3C2Tx. Liquid nitrogen helps the freezing process, which maintains the vertical orientation of the thin TisC2Txlayers. The SEM image shows that the distance between the Ti3C2Txlayers increased when compared with Ti3C2Txpowder, with a 15-20 pm distance between the layers. Such an increase in the distance between the layers will support the charge transfer process on the surface of the thin layers of vertically-oriented Ti3C2Tx.

[0039] The Raman analysis of the TisC2Txpowder and the thin layers of vertically-oriented Ti3C2Txis are shown in Figure 5. Raman spectroscopy can be used to identify the structure of a material by observing the vibrations of the atoms contained in the material. In general, Ti3C2Txhas four active Raman modes: e.g., in-plane vibrations of the Ti and C atoms, as well as Aig, out-of-plane vibrations of the Ti and C atoms. The other two modes correspond to in-plane and out-of-plane vibrations from atom C. The Raman spectroscopic measurements were conducted in the 0-2500 cur1range. Additionally, the 230-470 cur1range represents the in-plane vibrations (Eg) of surface groups bonded to titanium atoms. This range is only affected by surface atoms. Therefore, it can be potentially used to investigate the surface chemical properties of TisC2Txand its changes because of chemical or electrochemical reactions. The range between 580 and 730 cur1is mainly related to carbon vibrations (both Eg and Alg) . Figure 4 shows two distinct sharp peaks: Aig(Ti, 0, C) at about 200cm-1and Aig(C) at about 630cm-1. For Ti3C2Txpowder, its Aig(Ti, 0, C) is 200 cm-1, and Aig(C) is 637 cm-1. The 10 cm-1shift between these two peaks indicates increased distance between the layers. The vertical stacking of the Ti3C2Txlayers amplifies the out-of-plane vibrations and prevents the plates from sliding past each other. It is important to note that the vertical arrangement of the TisC2Txlayer's structure has a significant impact. The vertical stacking of the TisC2Txlayers amplifies out-of-plane vibrations (Aig) and prevents the plates from sliding past each other. This arrangement results in unique mechanical and electronic properties, which can be used in various advanced technology applications.

[0040] The sensitivity analysis of the thin layers of vertically- oriented TisC2Txto nitrogen dioxide gas (NO2) is illustrated in Figure 6. This gas sensitivity analysis aims to test the material's detection ability of certain gases. Sensitivity is defined as the ratio between the resistance when gas is detected (Rg) and basic resistance in ambient air conditions (Ra) . The sensitivity value of the thin layers of vertically-oriented Ti3C2Txincreases with the rise in NO2 gas concentration . In this case , a thin layer of vertically-oriented Ti3C2Txshowed a sensitivity value of 28 at an NO2 gas concentration of 50 ppm . This sensitivity value is 2 . 8 times higher than that of Ti3C2Txpowder . This increase in sensitivity occurs due to the more ef ficient movement of NO2 gas molecules and smoother load trans fer on the thin layers of vertically-oriented Ti3C2Tx. These benefits are caused by the greater distance between the thin layers of TisC2Txcompared to TisC2Txpowder .

Claims

Claims1. A manufacturing method for thin layers of vertically-oriented Ti3C2Txthat can be used for NO2 gas sensors, which consists of: i. the preparation of a Ti3C2Txsolution by using the selective Al etching method consists of the following stages: a. to make an etching solution by mixing 9M HC1 with LiF with a ratio of 20:2.1% v / w until homogeneous; b. adding 0.5:20% w / v of T13A1C2 powder ; c. heating in an oil bath for 60-72 hours at 40-60 C until the mixture turns black; d. cooling the mixture to room temperature; e. washing the mixture with pure distilled water and centrifuging it at 3000-4000 rpm for 5-15 minutes until the mixture reaches a pH of 5-6 and results in a fine Ti3C2Txpowder; f. mixing the Ti3C2Txpowder with a solution of 0.1-0.2 %b TMAOH at a ratio of 0.1:100; g. ultrasonic processing of the mixture for 30-60 minutes to produce a Ti3C2Txsolution; h. exfoliating the Ti3C2Txsolution with a planetary shaker for seven days; i. obtaining a Ti3C2Txsolution; ii. the fabrication of thin layers of Ti3C2Txby the electrophoretic deposition method consists of the following stages : a. preparing two pieces of stainless-steel substrate plates and cleaning them with 0.5 M HNO3; b. soaking the plates in 5 - 15 mL of Ti3C2Txsolution (i) ; c. connecting the submerged plates (b) with a DC source; d. conducting the electrophoretic deposition process at a voltage of 7-9 V for 15-45 minutes; e. obtaining a thin layer of Ti3C2Txon one of the stainless steel plates;ill. the freezing and drying process consists of the following stages : a. taking the plate with the thin layer of Ti3C2Txfrom stage ( ii ) ; b. soaking the plate in liquid nitrogen for 30-60 minutes to freeze a thin layer of Ti3C2Tx; c. vacuuming at a pressure of -1-0 atm; d. drying for 6-12 hours; e. obtaining a vertically-oriented Ti3C2Txthat attaches to a stainless steel substrate.

2. A thin layer of vertically-oriented Ti3C2Txthat can be used for NO2 gas sensors has the following characteristics: a. a thickness of 150-250 pm; b. a sensitivity value of 28-30 at a NO2 gas concentration of 50 ppm.

3. The thin layers of vertically-oriented Ti3C2Txthat can be used for gas sensors of claim 2 are 2.8 times more sensitive to NO2 gas than Ti3C2Txpowder.

Images