IT201900007229A1 - Chemoresistive gas sensor - Google Patents
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- IT201900007229A1 IT201900007229A1 IT102019000007229A IT201900007229A IT201900007229A1 IT 201900007229 A1 IT201900007229 A1 IT 201900007229A1 IT 102019000007229 A IT102019000007229 A IT 102019000007229A IT 201900007229 A IT201900007229 A IT 201900007229A IT 201900007229 A1 IT201900007229 A1 IT 201900007229A1
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- metal oxide
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- 239000007789 gas Substances 0.000 claims description 29
- 239000002105 nanoparticle Substances 0.000 claims description 18
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- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 3
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- 239000002082 metal nanoparticle Substances 0.000 claims description 3
- 150000002739 metals Chemical class 0.000 claims description 3
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- BERDEBHAJNAUOM-UHFFFAOYSA-N copper(I) oxide Inorganic materials [Cu]O[Cu] BERDEBHAJNAUOM-UHFFFAOYSA-N 0.000 claims description 2
- KRFJLUBVMFXRPN-UHFFFAOYSA-N cuprous oxide Chemical compound [O-2].[Cu+].[Cu+] KRFJLUBVMFXRPN-UHFFFAOYSA-N 0.000 claims description 2
- 238000010438 heat treatment Methods 0.000 claims description 2
- PJXISJQVUVHSOJ-UHFFFAOYSA-N indium(III) oxide Inorganic materials [O-2].[O-2].[O-2].[In+3].[In+3] PJXISJQVUVHSOJ-UHFFFAOYSA-N 0.000 claims description 2
- GNRSAWUEBMWBQH-UHFFFAOYSA-N nickel(II) oxide Inorganic materials [Ni]=O GNRSAWUEBMWBQH-UHFFFAOYSA-N 0.000 claims description 2
- ZNOKGRXACCSDPY-UHFFFAOYSA-N tungsten(VI) oxide Inorganic materials O=[W](=O)=O ZNOKGRXACCSDPY-UHFFFAOYSA-N 0.000 claims description 2
- 229910052799 carbon Inorganic materials 0.000 claims 1
- 230000002452 interceptive effect Effects 0.000 claims 1
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- 239000004065 semiconductor Substances 0.000 description 8
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 7
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- 230000035945 sensitivity Effects 0.000 description 5
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- 241000894007 species Species 0.000 description 3
- IKHGUXGNUITLKF-UHFFFAOYSA-N Acetaldehyde Chemical compound CC=O IKHGUXGNUITLKF-UHFFFAOYSA-N 0.000 description 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 2
- RRHGJUQNOFWUDK-UHFFFAOYSA-N Isoprene Chemical compound CC(=C)C=C RRHGJUQNOFWUDK-UHFFFAOYSA-N 0.000 description 2
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- QGLKJKCYBOYXKC-UHFFFAOYSA-N nonaoxidotritungsten Chemical compound O=[W]1(=O)O[W](=O)(=O)O[W](=O)(=O)O1 QGLKJKCYBOYXKC-UHFFFAOYSA-N 0.000 description 1
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- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 description 1
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
- G01N27/125—Composition of the body, e.g. the composition of its sensitive layer
- G01N27/127—Composition of the body, e.g. the composition of its sensitive layer comprising nanoparticles
Description
Descrizione della domanda di brevetto per invenzione industriale avente per titolo: Description of the patent application for industrial invention entitled:
"Sensore di gas chemoresistivo” "Chemoresistive gas sensor"
Campo tecnico dell’invenzione Technical field of the invention
La presente invenzione riguarda un sensore di tipo chemoresistivo per la rilevazione della quantità di un gas target in una miscela di gas. The present invention relates to a chemoresistive sensor for detecting the quantity of a target gas in a gas mixture.
Tecnica nota Known technique
Sono noti sensori di gas di tipo chemoresistivo, in cui viene applicata un potenziale costante tra due semi-elementi conduttivi di un elettrodo interdigitato, tra i quali è deposto uno strato sottile comprendente un semiconduttore nanostrutturato (ossia provvisto di nanoparticelle di semiconduttori). Fornendo un’idonea energia di attivazione ai semiconduttori, normalmente mantenendoli ad una temperatura elevata, che può essere compresa tra i 200 e i 400 °C a seconda della tipologia, si provoca la riduzione o l’ossidazione sulla loro superficie del gas target, ossia del gas da rilevare. Tali reazioni di riduzione o ossidazione provocano un cambiamento nella concentrazione delle cariche superficiali sullo strato semiconduttore nanostrutturato, in particolare rispettivamente una diminuzione o un aumento di elettroni nella banda di conduzione. Pertanto, cambia altresì la conduttività elettrica dello strato semiconduttore e varia la corrente che scorre tra i due elettrodi. Tale variazione è legata alla quantità di gas target, che può quindi essere misurata dal sensore. Chemoresistive gas sensors are known, in which a constant potential is applied between two conductive semi-elements of an interdigitated electrode, between which a thin layer comprising a nanostructured semiconductor (ie provided with semiconductor nanoparticles) is deposited. By supplying a suitable activation energy to the semiconductors, normally keeping them at a high temperature, which can be between 200 and 400 ° C depending on the type, it causes the reduction or oxidation on their surface of the target gas, i.e. gas to be detected. Such reduction or oxidation reactions cause a change in the concentration of surface charges on the nanostructured semiconductor layer, in particular, respectively, a decrease or an increase of electrons in the conduction band. Therefore, the electrical conductivity of the semiconductor layer also changes and the current flowing between the two electrodes varies. This variation is related to the amount of target gas, which can then be measured by the sensor.
Sensori siffatti trovano svariate applicazioni, quali ad esempio: monitoraggio ambientale, controllo dei processi chimici, controllo qualità nella produzione industriale, nella protezione ambientale e nella sicurezza sul lavoro, monitoraggio della qualità dell’aria nelle aree urbane, applicazioni mediche. Such sensors find various applications, such as: environmental monitoring, control of chemical processes, quality control in industrial production, environmental protection and workplace safety, air quality monitoring in urban areas, medical applications.
Con particolare riferimento alle applicazioni mediche, in tempi recenti ha avuto un notevole sviluppo la diagnostica medica non invasiva basata sull’analisi del respiro. Il respiro umano include principalmente N2, O2, CO2, H2O e altri gas inerti. Esiste poi una piccola frazione del respiro che comprende ulteriori composti organici volatili (VOC) con concentrazioni molto basse (dell’ordine di grandezza compreso tra parti per milione e parti per trilione), quali: ammoniaca, acetone, isoprene, metanolo, etanolo, propanolo, acetaldeide. With particular reference to medical applications, in recent times non-invasive medical diagnostics based on breath analysis has had a notable development. Human breath mainly includes N2, O2, CO2, H2O and other inert gases. There is also a small fraction of the breath that includes additional volatile organic compounds (VOCs) with very low concentrations (of the order of magnitude between parts per million and parts per trillion), such as: ammonia, acetone, isoprene, methanol, ethanol, propanol , acetaldehyde.
E’ noto in letteratura medica che la presenza in certe quantità dei VOC presenti nel respiro umano è correlata a certe malattie. Ad esempio, alti livelli di etano e pentano possono indicare malattie respiratorie; alti livelli di acetone possono essere collegati a problemi nel metabolismo del destrosio e al diabete; alta concentrazione di composti contenenti zolfo può indicare insufficienza epatica o rigetto di allotrapianto; elevate concentrazioni di NO e/o NO2 possono indicare asma atopica o infiammazione polmonare. It is known in medical literature that the presence in certain quantities of VOCs present in human breath is related to certain diseases. For example, high levels of ethane and pentane can indicate respiratory diseases; high levels of acetone may be linked to problems in dextrose metabolism and diabetes; high concentration of sulfur-containing compounds may indicate liver failure or allograft rejection; high concentrations of NO and / or NO2 may indicate atopic asthma or lung inflammation.
Pertanto è nata l’esigenza di avere a disposizione sensori in grado di rilevare in maniera semplice la concentrazione di VOC nel respiro a scopo diagnostico. Therefore, the need arose to have sensors that can easily detect the concentration of VOC in the breath for diagnostic purposes.
Tali sensori devono avere un’alta sensibilità (data la bassissima concentrazione dei VOC nel respiro) e un’elevata selettività, ossia la capacità di distinguere in maniera sufficientemente affidabile i diversi gas. Inoltre, tali sensori dovrebbero garantire risposte rapide, elevata sensibilità anche in presenza di umidità e preferibilmente bassi costi di produzione e manutenzione. These sensors must have a high sensitivity (given the very low concentration of VOCs in the breath) and a high selectivity, i.e. the ability to distinguish the different gases in a sufficiently reliable manner. Furthermore, such sensors should guarantee rapid responses, high sensitivity even in the presence of humidity and preferably low production and maintenance costs.
I sensori a base di semiconduttori nanostrutturati di tipo chemoresistivo rappresentano una tipologia di sensore di gas aventi le potenzialità per raggiungere tali scopi. Tali sensori tuttavia presentano ancora dei problemi che li rendono di difficile applicazione, specialmente nel settore medico. In particolare, come detto, essi lavorano a temperature tra i 200 e i 400 °C, cosa che li rende di difficile utilizzo in dispositivi portatili, per la scarsa maneggiabilità legata all’utilizzo di un circuito di riscaldamento/raffreddamento. Inoltre, l’ottenimento di un’adeguata selettività, necessaria per distinguere tra loro ad esempio i molteplici VOC presenti nel respiro umano, risulta tutt’oggi ancora problematico. Chemoresistive nanostructured semiconductor sensors represent a type of gas sensor having the potential to achieve these purposes. However, these sensors still have problems which make them difficult to apply, especially in the medical sector. In particular, as mentioned, they work at temperatures between 200 and 400 ° C, which makes them difficult to use in portable devices, due to the poor handling associated with the use of a heating / cooling circuit. Furthermore, obtaining adequate selectivity, necessary to distinguish between them, for example, the multiple VOCs present in the human breath, is still problematic today.
Breve sommario dell’invenzione Brief summary of the invention
Scopo della presente invenzione è pertanto quello di rendere disponibile un sensore di gas avente adeguate sensibilità e selettività e che sia in grado di lavorare a basse temperature, in modo tale che il sensore possa essere utilizzato a scopo diagnostico, ma anche, più in generale, per ridurre i consumi energetici associati al sensore. The purpose of the present invention is therefore to make available a gas sensor having adequate sensitivity and selectivity and which is able to work at low temperatures, so that the sensor can be used for diagnostic purposes, but also, more generally, to reduce the energy consumption associated with the sensor.
Questo ed altri scopi vengono raggiunti da un sensore di gas secondo la rivendicazione 1. This and other purposes are achieved by a gas sensor according to claim 1.
Le rivendicazioni dipendenti definiscono possibili vantaggiose forme di realizzazione dell’invenzione. The dependent claims define possible advantageous embodiments of the invention.
Breve descrizione dei disegni Brief description of the drawings
Per meglio comprendere l’invenzione ed apprezzarne i vantaggi verranno di seguito descritte alcune sue forme di realizzazione esemplificative non limitative, facendo riferimento alle annesse figure, in cui: To better understand the invention and appreciate its advantages, some of its non-limiting exemplary embodiments will be described below, referring to the attached figures, in which:
la figura 1 è un’illustrazione schematica in prospettiva di un sensore di gas secondo una forma di realizzazione dell’invenzione. Figure 1 is a schematic illustration in perspective of a gas sensor according to an embodiment of the invention.
Descrizione dettagliata dell’invenzione Detailed description of the invention
Con riferimento alle annesse figure, un sensore di gas chemoresistivo è complessivamente indicato con il riferimento 1. With reference to the attached figures, a chemoresistive gas sensor is generally indicated with reference 1.
Il sensore di gas 1 comprende un elettrodo 10, preferibilmente interdigitato, avente un primo 2 ed un secondo 3 semi-elemento conduttore, ai quali può essere applicata una tensione (ad esempio per mezzo di contatti metallici 5 e 6), preferibilmente costante da parte di una sorgente di tensione (non mostrata nelle figure). Il sensore 1 comprende inoltre uno strato attivo 7 tale da consentire il collegamento elettrico tra il primo 2 ed il secondo 3 semielemento conduttivo. In accordo con una forma di realizzazione, il sensore 1 comprende un substrato 4 su cui i semi-elementi conduttivi 2 e 3 nonché lo strato attivo 7 sono depositati. The gas sensor 1 comprises an electrode 10, preferably interdigitated, having a first 2 and a second 3 conducting semi-element, to which a voltage can be applied (for example by means of metal contacts 5 and 6), preferably constant on the part of a voltage source (not shown in the figures). The sensor 1 further comprises an active layer 7 such as to allow the electrical connection between the first 2 and the second 3 conductive semi-element. According to an embodiment, the sensor 1 comprises a substrate 4 on which the conductive half-elements 2 and 3 as well as the active layer 7 are deposited.
Lo strato attivo 7 è realizzato in un materiale composito comprendente una matrice carboniosa e nanoparticelle semiconduttive a base metallo ossido intimamente legate alla matrice carboniosa. The active layer 7 is made of a composite material comprising a carbonaceous matrix and metal-oxide-based semiconductive nanoparticles intimately bonded to the carbonaceous matrix.
In accordo con una forma di realizzazione, la matrice carboniosa è realizzata in grafene o in derivati del grafene. Il grafene è un materiale non semiconduttore che si caratterizza per alta resistenza meccanica, buona stabilità termica, conduttività elettrica, elevata mobilità dei portatori di carica a temperatura ambiente, basso rumore elettrico grazie alla sua conformazione a reticolo a nido d'ape. Inoltre, il grafene e i suoi derivati sono economici e facili da produrre su larga scala. Secondo una forma di realizzazione, la matrice carboniosa è realizzata in ossido di grafene. According to one embodiment, the carbonaceous matrix is made of graphene or graphene derivatives. Graphene is a non-semiconductor material that is characterized by high mechanical strength, good thermal stability, electrical conductivity, high mobility of charge carriers at room temperature, low electrical noise thanks to its honeycomb lattice conformation. Furthermore, graphene and its derivatives are cheap and easy to produce on a large scale. According to one embodiment, the carbonaceous matrix is made of graphene oxide.
Le nanoparticelle di ossido di metallo possono essere di differente natura a seconda del o dei gas che si intendono rilevare e possono includere ad esempio uno o più tra: ZnO, SnO2, TiO2, WO3, In2O3, Cu2O, NiO, da sole o in combinazione tra loro per incrementare la selettività del sensore. Ad esempio, le combinazioni SnO2-TiO2 e NiO-SnO2 migliorano il sensing nei confronti di acetone; alta selettività all’etanolo può essere, invece, raggiunta grazie alla combinazione fra ZnO e SnO2 nanometrici. The metal oxide nanoparticles can be of different nature depending on the gas or gases to be detected and can include, for example, one or more of: ZnO, SnO2, TiO2, WO3, In2O3, Cu2O, NiO, alone or in combination between them to increase the selectivity of the sensor. For example, the combinations SnO2-TiO2 and NiO-SnO2 improve the sensing towards acetone; high selectivity to ethanol can, on the other hand, be achieved thanks to the combination of nanometric ZnO and SnO2.
Secondo una possibile forma di realizzazione, il sensore 1 comprende un riscaldatore 8 tale da riscaldare lo strato attivo 7 e termoattivare le nanoparticelle di metallo ossido semiconduttive. According to a possible embodiment, the sensor 1 comprises a heater 8 such as to heat the active layer 7 and thermoactivate the semiconductive metal oxide nanoparticles.
In alternativa o in aggiunta al riscaldatore, il sensore 1 comprende una sorgente di luce ultravioletta (UV) 9, ad esempio una sorgente UV o visibile, tale da illuminare lo strato attivo 4 e fotoattivare le nanoparticelle di ossido di metallo semiconduttive. Alternatively or in addition to the heater, the sensor 1 comprises an ultraviolet (UV) light source 9, for example a UV or visible source, such as to illuminate the active layer 4 and photoactivate the semiconductive metal oxide nanoparticles.
E’ stato osservato che gli effetti sinergici tra la matrice carboniosa e tali nanoparticelle di ossido di metallo (che di per sé richiederebbero temperature generalmente superiori ai 300 °C per essere attivate) consentono di ridurre la temperatura (fino a temperatura ambiente) a cui va mantenuto lo strato attivo 7. It has been observed that the synergistic effects between the carbonaceous matrix and these metal oxide nanoparticles (which in themselves would require temperatures generally higher than 300 ° C to be activated) allow to reduce the temperature (down to room temperature) at which it goes. maintained active layer 7.
Infatti, il grafene o l’ossido di grafene consentono di ottenere una elevata conduttività dello strato attivo. In fact, graphene or graphene oxide allow to obtain a high conductivity of the active layer.
Inoltre, l’impiego in particolare dell’ossido di grafene consente di aumentare la quantità di elettroni nella banda di conduzione nell'ossido di metallo sulla sua superficie. Grazie alla presenza di un numero elevato di elettroni eccitati, molte più specie di ossigeno (O<- >and O<2->) altamente reattive sono debolmente adsorbite sulla superficie dello strato attivo 7. Queste specie possono reagire con i gas target, provocando quindi l'effettiva variazione di corrente/resistenza. Quindi, maggiore è la disponibilità di specie ossigeno adsorbite, più intensa è la risposta finale. In questo modo, la sensibilità del sensore 1 nei confronti dei differenti gas sarà molto elevata. In addition, the use of graphene oxide in particular allows to increase the amount of electrons in the conduction band in the metal oxide on its surface. Due to the presence of a large number of excited electrons, many more highly reactive oxygen species (O <-> and O <2->) are weakly adsorbed on the surface of the active layer 7. These species can react with target gases, causing hence the actual change in current / resistance. Hence, the greater the availability of adsorbed oxygen species, the more intense the final response. In this way, the sensitivity of the sensor 1 towards the different gases will be very high.
In accordo con una forma di realizzazione, le nanoparticelle semiconduttive di ossido di metallo sono drogate con specie aventi funzioni catalitiche nei confronti di una specifica molecola. Ad esempio, il drogaggio può avvenire mediante metalli o mediante non metalli. Il drogaggio produce un miglioramento significativo della risposta del sensore. According to one embodiment, the semiconductive metal oxide nanoparticles are doped with species having catalytic functions towards a specific molecule. For example, the doping can take place by metals or by non-metals. Doping produces a significant improvement in sensor response.
In accordo con una forma di realizzazione, le nanoparticelle di ossido di metallo semiconduttore sono decorate esternamente con nanoparticelle metalliche o non metalliche. According to one embodiment, the semiconductor metal oxide nanoparticles are externally decorated with metallic or non-metallic nanoparticles.
I metalli impiegati per il drogaggio e/o per la decorazione, possono includere metalli nobili (rutenio, rodio, palladio, argento, osmio, iridio, platino e oro), mentre i non-metalli possono includere silicio, fosforo, azoto o zolfo. In definitiva, le nanoparticelle di metalli nobili/non metalli catalitici possono facilitare la dissociazione delle molecole di gas, incrementando così la sensibilità del gas e aumentando la conduttività elettronica. Ad esempio, nanoparticelle di ossido di stagno decorate con nanoparticelle di argento hanno elevata selettività nei confronti di molecole di etanolo. Parallelamente, nanomateriali a base ossido di tungsteno drogato silicio mostrano buona attività sensoristica nei confronti dell’acetone presente in una miscela complessa di gas, quale ad esempio il respiro umano. The metals used for doping and / or decoration can include noble metals (ruthenium, rhodium, palladium, silver, osmium, iridium, platinum and gold), while non-metals can include silicon, phosphorus, nitrogen or sulfur. Ultimately, noble metal / catalytic non-metal nanoparticles can facilitate dissociation of gas molecules, thereby increasing gas sensitivity and increasing electronic conductivity. For example, tin oxide nanoparticles decorated with silver nanoparticles have high selectivity towards ethanol molecules. At the same time, silicon-doped tungsten oxide-based nanomaterials show good sensory activity against the acetone present in a complex gas mixture, such as human breath.
In accordo con una forma di realizzazione, il sensore 1 comprende uno o più filtri atti a ridurre la quantità di specie ulteriori rispetto al gas target che possono interferire con lo strato attivo 7. Ad esempio, tali filtri possono includere un filtro fisico per ridurre la quantità di vapore acqueo, che è il principale interferente nel caso in cui il sensore analizzi il respiro umano. According to an embodiment, the sensor 1 comprises one or more filters adapted to reduce the amount of additional species with respect to the target gas that can interfere with the active layer 7. For example, such filters can include a physical filter to reduce the amount of water vapor, which is the main interferer in case the sensor analyzes the human breath.
Secondo un ulteriore aspetto dell’invenzione, un sensore complesso comprende un array di sensori ciascuno realizzato in accordo con l’invenzione, in cui lo strato attivo 7 di ciascun sensore dell’array è realizzato in maniera tale che tale sensore sia selettivo verso uno specifico gas target. In questo modo, il sensore complesso è in grado di rilevare selettivamente più gas contemporaneamente mediante ciascuno dei sensori dell’array. According to a further aspect of the invention, a complex sensor comprises an array of sensors each made in accordance with the invention, in which the active layer 7 of each sensor of the array is made in such a way that said sensor is selective towards a specific target gas. In this way, the complex sensor is able to selectively detect multiple gases simultaneously using each of the sensors in the array.
Alla descrizione sopra fornita la persona esperta, allo scopo di soddisfare esigenze contingenti specifiche, potrà apportare numerose aggiunte, modifiche, o sostituzioni di elementi con altri funzionalmente equivalenti, senza tuttavia uscire dall’ambito delle annesse rivendicazioni. To the description provided above, the skilled person, in order to meet specific contingent needs, may make numerous additions, modifications, or replacements of elements with other functionally equivalent ones, without however departing from the scope of the attached claims.
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