Abstract:Graphene is a new type of carbon material with a flexible, two-dimensional structure. Due to the excellent stability of its lattice structure and its mechanical flexibility, graphene-based materials can be applied in flexible humidity sensors. At present, the application of graphene-based flexible humidity sensors in the fields of medical care and environmental monitoring is attracting widespread attention. In this review, the basic properties of graphene oxide (GO) and reduced graphene oxide (rGO) as moisture… Show more
“…The existence of defects and subsequent formation of various oxygen functional groups are responsible for the remarkable adsorption of water molecules on the GO surface. The details are discussed in the sensing mechanism section 43 , 44 . Figure 4 Graphene oxide characterizations, ( a ) Raman spectra, and ( b ) FT-IR analysis.…”
Section: Resultsmentioning
confidence: 99%
“…Among them, reduced graphene oxide (rGO) and graphene oxide (GO) hold great potential for sensing due to the existence of different functional groups on their surface. Particularly, GO is considered as one of the best-known materials for water vapors detection due to the existence of a large number of oxygen functional groups on its surface and edges 44 , 47 . For our study, the electrically insulated GO droplets were deposited onto a highly conductive Si resonator surface and dried at 45 °C for 30–45 min followed by direct sensing characterizations without further annealing.…”
This work reports highly selective multiple analyte detection by exploiting two different mechanisms; absorption and thermal conductivity using a single MEMS device. To illustrate the concept, we utilize a resonator composed of a clamped-guided arch beam connected to a flexural beam and a T-shaped moveable mass. A finite element model is used to study the mode shapes and mechanical behavior of the device with good agreement reported with the experimental data. The resonator displays two distinct out-of-plane modes of vibration. For humidity detection, we utilize physisorption by functionalizing the surface with graphene oxide (GO), which has strong affinity toward water vapors. The GO solution is prepared and drop-casted over the mass surface using an inkjet printer. On the other hand, cooling the heated flexural beams is used for helium (He) detection (thermal-conductivity-based sensor). The sensor characteristics are extensively studied when the modes are individually and simultaneously actuated. Results affirm the successful utilization of each mode for selective detection of relative humidity and He. This novel mode-dependent selective detection of multiple analytes can be a promising building block for the development of miniature, low-powered, and selective smart sensors for modern portable electronic devices.
“…The existence of defects and subsequent formation of various oxygen functional groups are responsible for the remarkable adsorption of water molecules on the GO surface. The details are discussed in the sensing mechanism section 43 , 44 . Figure 4 Graphene oxide characterizations, ( a ) Raman spectra, and ( b ) FT-IR analysis.…”
Section: Resultsmentioning
confidence: 99%
“…Among them, reduced graphene oxide (rGO) and graphene oxide (GO) hold great potential for sensing due to the existence of different functional groups on their surface. Particularly, GO is considered as one of the best-known materials for water vapors detection due to the existence of a large number of oxygen functional groups on its surface and edges 44 , 47 . For our study, the electrically insulated GO droplets were deposited onto a highly conductive Si resonator surface and dried at 45 °C for 30–45 min followed by direct sensing characterizations without further annealing.…”
This work reports highly selective multiple analyte detection by exploiting two different mechanisms; absorption and thermal conductivity using a single MEMS device. To illustrate the concept, we utilize a resonator composed of a clamped-guided arch beam connected to a flexural beam and a T-shaped moveable mass. A finite element model is used to study the mode shapes and mechanical behavior of the device with good agreement reported with the experimental data. The resonator displays two distinct out-of-plane modes of vibration. For humidity detection, we utilize physisorption by functionalizing the surface with graphene oxide (GO), which has strong affinity toward water vapors. The GO solution is prepared and drop-casted over the mass surface using an inkjet printer. On the other hand, cooling the heated flexural beams is used for helium (He) detection (thermal-conductivity-based sensor). The sensor characteristics are extensively studied when the modes are individually and simultaneously actuated. Results affirm the successful utilization of each mode for selective detection of relative humidity and He. This novel mode-dependent selective detection of multiple analytes can be a promising building block for the development of miniature, low-powered, and selective smart sensors for modern portable electronic devices.
“…(ii) Water is a small molecule and, especially at higher humidity levels, can intercalate between individual graphene layers in a single flake or between whole flakes. This causes an increase in the distance between the individual layers in a graphene flake or an increase in the distance between flakes, thus increasing the resistance of the entire layer [25]. These two phenomena can have a synergistic effect at high humidity values.…”
This article addresses reliability under the sweat of interconnection techniques for the mounting surface mounted device (SMD) components and fully printed humidity sensors onto conductive stretchable textile ribbons. Samples underwent testing for the effect of ageing by artificial sweat on their electrical resistance using both alkaline and acidic artificial sweat. The best results in terms of electrical resistance change were obtained for samples soldered to the conductive fibers interwoven in the ribbon. However, this method can damage the ribbon due to the high temperature during soldering and significantly reduce the mechanical properties and flexibility of the ribbon, which can lead to a limited service life of samples. On the other hand, adhesive bonding is a very interesting alternative, where the above-mentioned properties are preserved, but there is a significant effect of sweat ageing on electrical resistance. The results of fully printed graphene-based humidity sensors show that, for the intended use of these sensors (i.e., detection of changes in moisture on the human body), usage of the samples is possible, and the samples are sufficiently reliable in the case of sweat degradation. In addition, the response of the sensor to humidity is quite high: 98% at a relative humidity of 98%.
“…A GQDs-based humidity sensor was also designed by citric acid carbonation and found that GQDs have an exceptional ability to detect the ratio between the quantity of water vapor pressure in the air at a selected temperature and the same amount needed to be saturated at the same temperature at lower relative humidity levels for different humidity levels of RH [144].…”
Section: Humidity Sensormentioning
confidence: 99%
“…water vapor pressure in the air at a selected temperature and the same amount needed to be saturated at the same temperature at lower relative humidity levels for different humidity levels of RH [144].…”
Graphene quantum dots (GQD) is an efficient nanomaterial composed of one or more layers of graphene with unique properties that combine both graphene and carbon dots (CDs). It can be synthesized using carbon-rich materials as precursors, such as graphite, macromolecules polysaccharides, and fullerene. This contribution emphasizes the utilization of GQD-based materials in the fields of sensing, bioimaging, energy storage, and corrosion inhibitors. Inspired by these numerous applications, various synthetic approaches have been developed to design and fabricate GQD, particularly bottom-up and top-down processes. In this context, the prime goal of this review is to emphasize possible eco-friendly and sustainable methodologies that have been successfully employed in the fabrication of GQDs. Furthermore, the fundamental and experimental aspects associated with GQDs such as possible mechanisms, the impact of size, surface alteration, and doping with other elements, together with their technological and industrial applications have been envisaged. Till now, understanding simple photo luminance (PL) operations in GQDs is very critical as well as there are various methods derived from the optical properties of manufactured GQDs can differ. Lack of determining exact size and morphology is highly required without loss of their optical features. Finally, GQDs are promising candidates in the after-mentioned application fields.
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