RO134263A2 - Chemiresistive humidity sensor based on nanocarbon composites - Google Patents

Abstract

The invention relates to a process for preparing a humidity sensor based on nanocarbon composites. According to the invention, the process consists of the stages of preparation of a solution of polyvinylpyrrolidone or polyvinyl alcohol in water, while magnetically stirring, for 1 h at the temperature of 50°C, addition of oxidized carbon nanohorns, while stirring for 2 h at the temperature of 70°C, electrospinning of the solution, to result in composite nanofibers which are deposited on a dielectric substrate with linear or interdigitated electrodes.

Description

Chemistry-resistant humidity sensor based on nanocarbon composites

Description

Relative humidity monitoring is an essential process in various fields of domestic and industrial activity, such as indoor air quality control, textile and paper industry, medical field (transfusion centers, sterilization premises, sterilizers), pharmaceutical industry (synthesis and control quality of medicines, drug storage facilities, pharmacies), agriculture (silos, soil moisture control), chemical industry (dryers, ovens), electronics industry (clean rooms), food industry (food production and storage spaces), transport ( food, medicine), etc. [1 - 3] Thus, due to the multitude of applications, the humidity sensor market is estimated to reach a global level of around USD 1.88 billion by 2023 [4],

An optimal humidity sensor should have a pronounced sensitivity, fast response time, low cost, low hysteresis, reliability and be able to operate in a wide range of temperature and humidity values. In recent decades, a multitude of techniques for measuring relative humidity have been developed, the most used sensors being those of capacitive type [5, 6] and resistive [7 - 9], Other types of humidity sensors work based on other detection principles such as: gravimetric [10 - 12], optical [13], piezoresistive [14], magnetoelastic [15],

Along with semiconductor metal oxides, ceramics, polymers, etc., nanocarbon materials are used extensively as sensing elements in the design of humidity sensors [3],

Single-walled carbon nanotubes functionalized with carboxyl-type groups were used by Han et al [16] as a sensitive layer in a humidity sensor, cellulose providing the supporting role. The change in the conduction of the carbon nanotube network is proportional to the analyzed moisture level. The sensor response is linear up to a relative humidity of 75%, with good repeatability and low hysteresis.

The exceptional properties of graphene oxide - such as its two-dimensional nature, as well as its superpermeability to water - make this material an excel sensitive layer.

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11/29/2018 humidity sensor. Using graphene oxide to monitor the humidity level, Borini et al [17] obtained a response time of 30 ms.

Patent application US20050081625A1 with title! 'Humidity sensor element, device and method for manufacturing thereof' (Hui Chen, Ren Wu, Yi Sun, Pi Su) refers to a humidity sensor that has a sensitive layer based on nanocoraposite matrix carbon-polymer nanotubes perfluorinated with groups functional acid in weight ratio of 0.01 - 20. The sensitive layer used can detect even an infinitesimal amount of moisture, with a minimum detection limit of 15.76 pprav.

U.S. Pat. No. 9,178,129B2, entitled "Graphene-based films in sensor applications" (Woo Young Lee, Linh Tung Le, De Kong), refers to a humidity sensor having a graphene film as a sensitive layer. The electrical resistance of the graphene film increases proportionally, in response to increasing ambient humidity.

Carbon nanotubes (Fig. 1) are materials with a tubular structure, related to carbon nanotubes [18], despite structural similarities with carbon nanotubes, there is, however, a significant difference between nanotubes and carbon nanocorns due to the fact that the latter have long cone-shaped tips with cone angles of about 20 ° and large tube diameters of 2 - 5 nm [19],

The synthesis of carbon nanowires is achieved by laser ablation of graphite and does not require a metal catalyst. This procedure can produce significant amounts of Single Wall Carbon Nanohorns (SWCNHs), or about 1 kg / day. Carbon nanocorns can be oxidized in air [20], by treatment with acids [21] or hydrogen peroxide [22], obtaining carbon nanocorns with carboxylic groups (Fig. 2).

These materials have a hydrophilic character and are easily dispersible in water and organic solvents such as ethanol, isopropyl alcohol, etc.

Carbon nanohorns have proven useful in gas detection. Sano et al [23] have developed chemoresistive gas sensors for the detection of ammonia and ozone at room temperature, using single-walled carbon nanohorns (S WCNHs) as a sensitive layer. It has been proven

a2018 01005 29/11/2018 that the electrical resistance of the SWCNH film decreases with the adsorption of O3, while the adsorption of NH3 increases the resistance of the sensitive layer.

The technical problem solved by the present invention consists in obtaining new layers sensitive to the variation of the relative humidity value.

The sensitive layers described in this invention, used to obtain chemoresistive sensors of relative humidity are nanocomposites consisting of oxidized carbon nanowires / hydrophilic polymer.

The hydrophilic polymers selected are PVP (polyvinylpyrrolidone, Fig. 3) and PVA (polyvinyl alcohol, Fig. 4) ·

The synthesis of oxidized nanowires is performed by two different methods, using nitric acid treatment and oxidation with hydrogen peroxide at 100 ° C, respectively.

The synchronous use of oxidized carbon nanohorns together with hydrophilic polymers of PVP or PVA type, deposited by spin coating, drop casting or electrospinning methods on a dielectric substrate, gives the sensor some significant advantages:

• improving the mechanical properties and processability of the sensitive layer;

o the presence of oxidized carbon nanohorns gives a high specific area / volume ratio;

• rapid response of the sensor to variations in relative humidity values;

• detection at room temperature.

The dielectric substrate is made of glass, PET or Kapton and can be between 50 microns and 5 millimeters thick. Electrodes can be deposited on the surface of the dielectric substrate by direct printing, sputtering or evaporation. Electrodes can be made of the same material (aluminum, chrome, copper, gold) or different materials. They can be linear (Fig. 5) or have an interdigitated configuration (Fig. 6).

The following are the steps required to obtain the relative humidity sensitive layers, as well as to obtain the relative humidity chemoresistive sensors.

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Example 1

A. The raw materials necessary for the synthesis of the sensitive layer are, in the first case, polyvinylpyrrolidone (M = 1,300,000 Da) and oxidized carbon nanohorns.

The solution of polyvinylpyrrolidone in water is prepared by dissolving 2 g of polymer in 100 ml of deionized water, under magnetic stirring (for one hour, at a temperature of 50 ° C). Subsequently, 0.02 g of oxidized carbon nanowires are added to the previously prepared solution and the magnetic stirring is continued for 2 hours at 70 ° C.

B. The obtained solution is subjected to electroplating, using as collectors the PET substrate with linear electrodes or the one with interdigitated electrodes (after previously masking the contact area).

C. The sensitive layer obtained from PVP nanofibers and oxidized carbon nanowires, deposited on the substrate, is dried in an oven at 70 ° C for 40 minutes.

Example 2

A. The raw materials necessary for the synthesis of the sensitive layer are polyvinyl alcohol (M = 10,000 Da) and oxidized carbon nanohorns.

The solution of polyvinyl alcohol in water is prepared by dissolving 1 g of polymer in 100 ml of deionized water, under magnetic stirring (1 h, at a temperature of 70 ° C). Subsequently, 0.01 g of oxidized carbon nanohorns are added to the previously prepared solution and the magnetic stirring is continued for 2 hours at 70 ° C.

B. The solution obtained is deposited, using the drop casting method, on a Kapton substrate with linear electrodes or on the one with interdigitated electrodes (after previously masking the contact area).

C. The sensitive layer obtained from polyvinyl alcohol and oxidized carbon nanowires, deposited on the substrate, is dried in an oven at 70 ° C for 60 minutes.

Claims (16)

1. Process for the preparation of a new binary composition PVP / oxidized carbon nanohorns characterized in that the oxidized carbon nanowires are synthesized by treating simple carbon nanowires with nitric acid at 100 ° C and that their mass percentage in the sensitive layer varies between 0.1 and 1%. 2. Process for the preparation of a new binary composition PVA / oxidized carbon nanowires characterized in that the oxidized carbon nanowires are synthesized by treating simple carbon nanowires with nitric acid at 100 ° C and that their mass percentage in the sensitive layer varies between 0,1 and 1%. 3. The dielectric substrate is characterized in that it can be constructed of Kapton®, glass, PET and can have a thickness between 50 microns and 5 millimeters. 4. Electrodes are characterized in that they are deposited on the surface of the dielectric substrate by direct printing, cathodic spraying, or evaporation. 5. Electrodes are characterized in that they can be made of the same material (aluminum, chromium, copper, gold) or different materials. 6. The electrodes used are characterized in that they can be linear or have an interdigitated configuration. The deposition of the composition obtained under the conditions of claim 1 is made of aqueous solution and is characterized in that it is performed by the “spin coating” method on the substrate of Kapton®, glass, or PET - with linear electrodes. The deposition of the composition obtained under the conditions of claim 1 is made of aqueous solution and is characterized in that it is done by the “spin coating” method on the substrate of Kapton®, glass, or PET - with interdigitated electrodes. and 2018 01005 11/29/2018 ϋ. The deposition of the composition obtained under the conditions of claim 1 is made of aqueous solution and is characterized in that it is made by the drop-casting method, on the substrate of Kapton®, glass, or PET - with linear electrodes. (0. The deposition of the composition obtained under the conditions of claim 1 is performed from aqueous solution and is characterized in that it is performed by the drop-casting method on the substrate of Kapton®, glass, or PET - with interdigitated electrodes. The deposition of the composition obtained under the conditions of claim 1 is made of aqueous solution and is characterized in that it is made by the method of electrophilation on the substrate of Kapton®, glass, or PET - with linear electrodes. The composition of the composition obtained under the conditions of claim 1 is made of aqueous solution and is characterized in that it is made by the method of electrofilting on the substrate of Kapton®, glass, PET with interdigitated electrodes. The composition of the composition obtained under the conditions of claim 2 is made of aqueous solution and is characterized in that it is made by the “spin coating” method on the substrate of Kapton®, glass, or PET - with linear electrodes. The deposition of the composition obtained under the conditions of claim 2 is made of aqueous solution and is characterized in that it is done by the method "spin coating" on the substrate of Kapton®, glass, or PET - with interdigitated electrodes. The composition of the composition obtained under the conditions of claim 2 is made of aqueous solution and is characterized in that it is made by the drop-casting method on the substrate of Kapton®, glass, or PET - with linear electrodes. The composition of the composition obtained under the conditions of claim 2 is made of aqueous solution and is characterized by the fact that it is made by the drop-casting method on the substrate of Kapton®, glass, or PET - with interdigitated electrodes. The deposition of the composition obtained under the conditions of claim 1 is carried out from aqueous solution and is characterized in that it is carried out by the method of electrofilament on the substrate of Kapton®, glass, or PET - with linear electrodes. and 2018 01005 11/29/2018 The deposition of the composition obtained under the conditions of claim 1 is carried out in aqueous solution and is characterized in that it is carried out by the method of electrofilament on the substrate of Kapton®, glass, or PET - with interdigitated electrodes. The use of the chemoresistive sensors obtained under the conditions of claims 7 to 18 in monitoring humidity is characterized in that a voltage is applied between two electrodes and the electric current passing through the sensitive layer is measured at various humidity values.