Literature Review Of Influence Of Structural Parameters Of Nano-Material On Sensing Properties Of Humidity Sensor
In the paper by Tsung-TsongWu, a highly sensitive humidity sensor are reported. The humidity sensor is configured by a 128◦YX-LiNbO3 based surface acoustic wave (SAW) resonator whose operating frequency is at 145 MHz. A dual delay line configuration is realized to eliminate external temperature fluctuations. Moreover, for nanostructured materials possessing high surface-to-volume ratio, large penetration depth and fast charge diffusion rate, camphor sulfonic acid doped polyaniline (PANI) nanofibres are synthesized by the interfacial polymerization method and further deposited on the SAW resonator as selective coating to enhance sensitivity. The humidity sensor is used to measure various relative humidities in the range 5–90% at room temperature. Results show that the PANI nanofibre based SAW humidity sensor exhibits excellent sensitivity and short-term repeatability.
The Review by Chengzhou Zhu, et al focuses on recent advances in electrochemical sensors and biosensors based on nano materials and nanostructures during 2013 to 2014. The aim of that work is to provide the reader with a clear and concise view of new advances in areas ranging from electrode engineering, strategies for electrochemical signal amplification, and novel electro analytical techniques used in the miniaturization and integration of the sensors. Moreover, the authors have attempted to highlight areas of the latest and significant development of enhancedelectrochemical nano sensors and nano biosensors that inspire broader interests across various disciplines. Electrochemical sensors for small molecules, enzyme-based biosensors, geno sensors, immunosensors, and cytosensors are reviewed. Such novel advances are important for the development of electrochemical sensors that open up new avenues and methods for future research. We recommend readers interested in the general principles of electrochemicalsensors and electrochemical methods to refer to other excellent literature for a broad scope in this area. However, due to the explosion of publications in this active field, we do not claimthat this Review includes all of the published works in the past two years and we apologize to the authors of excellent work, which is unintentionally left out.
Ning Du, et al firstly used layer-by-layer assembly to form a polyelectrolyte such as sodium poly(styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDDA) on the surfaces of the pristine CNTs, as previously reported. Secondly, a mixed aqueous solution of InCl3 and citric acid was added into the solution of the polyelectrolyte-modified CNTs. The complex of InCl3 and citric acid was adsorbed on the surface of the CNTs because of the electrostatic attraction between the charged species. Thirdly, a NaBH4 solution was dropped into the above-mentioned solution; in that way, In3+ was reduced into indium and then deposited onto the surface of the CNTs. Fourthly, the indium on the surface of the CNTs was quickly oxidized into In2O3–x because of the oxygen dissolved in the solution from the surrounding ambient air. Finally, porous In2O3 nanotubes were obtained by calcinations.
Firat Gider, et al worked on methods of monitoring breathing require cumbersome, inconvenient, and often expensive devices; this requirement sets practical limitations on the frequency and duration of measurements. that article describes a paper-based moisture sensor that uses the hygroscopic character of paper (i. e. the ability of paper to adsorb water reversibly from the surrounding environment) to measure patterns and rate of respiration by converting the changes in humidity caused by cycles of inhalation and exhalation to electrical signals. The changing level of humidity that occurs in a cycle causes a corresponding change in the ionic conductivity of the sensor, which can be measured electrically. By combining the paper sensor with conventional electronics, data concerning respiration can be transmitted to a nearby smart phone or tablet computer for post-processing, and subsequently to a cloud server. This means of sensing provides a new, practical method of recording and analyzing patterns of breathing.
Isolation and characterization of mechanically exfoliated black phosphorus flakes with a thickness down to two single-layers is presented. A modification of the mechanical exfoliation method, which provides higher yield of atomically thin flakes than conventional mechanical exfoliation, has been developed. We present general guidelines to determine the number of layers using optical microscopy, Raman spectroscopy and transmission electron microscopy in a fast and reliable way. Moreover, we demonstrate that the exfoliated flakes are highly crystalline and that they are stable even in free-standing form through Raman spectroscopy and transmission electron microscopy measurements. A strong thickness dependence of the band structure is found by density functional theory calculations. The exciton binding energy, within an effective mass approximation, is also calculated for different number of layers. Our computational results for the optical gap are consistent with preliminary photoluminescence results on thin flakes. Finally, we study the environmental stability of black phosphorus flakes finding that the flakes are very hydrophilic and that long term exposure to air moisture etches black phosphorus away. Nonetheless, we demonstrate that the aging of the flakes is slow enough to allow fabrication of field-effect transistors with strong ambipolar behavior. Density functional theory calculations also give us insight into the water-induced changes of the structural and electronic properties of black phosphorus.
Manisha B. Erande, et al investigations on two dimensional black phosphorous material mainly highlight work on few atomic layers and multi layers. It is unknown that if the black phosphorous atomically thin sheet as an ideal structure for the enhanced gas-solid interactions due to the large surface area. To further investigate this concern, they have synthesized few atomic layer thick nano sheets of black phosphorous using electrochemical exfoliation method. The surface morphology and thickness of the nano sheet were identified by using AFM, TEM, and Raman spectroscopy. The black phosphorous nano sheet thick film device was used for the gas sensing application with exposure to different humidites. Further, few layer black phosphorous nanosheet based transistor shows good mobility and on/off ratio. The UV light irradiation on black phosphorous nano sheet shows good response time. The overall results show that the few layer thick film of black phosphorous nano sheets sample exhibits creditable sensitivity and better recovery time to be used in humidity sensor and photo detector applications.
Georgios Niarchos, et al in his paper investigated the effect of humidity on paper substrates and propose a simple and low-cost method for their passivation using ZnO nano particles. To this end, they built paper-based micro devices based on an interdigitated electrode (IDE) configuration by means of a mask-less laser patterning method on simple commercial printing papers. Initial resistive measurements indicate that a paper substrate with a porous surface can be used as a cost-effective, sensitive and disposable humidity sensor in the 20% to 70% relative humidity (RH) range. Successive spin-coated layers of ZnO nano particles then, control the effect of humidity. Using this approach, the sensors become passive to relative humidity changes, paving the way to the development of ZnO-based gas sensors on paper substrates insensitive to humidity.
0D/2D heterojunctions, especially quantum dots (QDs)/nanosheets (NSs) have attracted significant attention for use of photoexcited electrons/holes due to their high charge mobility. Unprecedented heterojunctions of vanadate (AgVO3, BiVO4, InVO4 and CuV2O6) QDs/graphitic carbon nitride (g-C3N4) NSs exhibiting multiple unique advances beyond traditional 0D/2D composites have been developed. The photoactive contribution, up-conversion absorption, and nitrogen coordinating sites of g-C3N4 NSs, highly dispersed vanadate nanocrystals, as well as the strong coupling and band alignment between them lead to superior visible-light-driven photoelectrochemical (PEC) and photocatalytic performance, competing with the best reported photocatalysts. That work is expected to provide a new concept to construct multifunctional 0D/2D nanocomposites for a large variety of opto-electronic applications, not limited in photocatalysis.
Meng Sun, et al in his paper, Graphitic carbon nitride (g-C3N4) nanocrystals (NCs) decorated Ag3PO4 hybrids were synthesized by a facile method. The obtained samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscope (TEM), and UV–vis diffuse reflectance spectra (DRS). The SEM and TEM images showed that the as-prepared Ag3PO4 were composed of particles with diameters of 200-500 nm, while the obtained nanocrystalline g-C3N4 were composed of smaller particles with average diameter of 10 nm. For nanocrystalline g-C3N4/Ag3PO4 hybrids, the particle surfaces of Ag3PO4 were decorated with numerous g-C3N4 NCs, result in a larger contact area between g-C3N4 and Ag3PO4. The photocatalytic performances were evaluated by decomposing MO, phenol, bisphenol A, and RhB under visible light. Compared with Ag3PO4 and g-C3N4, the g-C3N4/Ag3PO4 hybrid (mass ratio = 1:4) exhibited the best activity, which was much higher than that of bulk-g-C3N4/Ag3PO4 composite under the same conditions. The enhanced activities should be mainly ascribed to the enhanced separation efficiency of photo generated carriers, which was proved by the photoluminescence (PL) spectra measurement. Controlled experiments proved that O2− and h+ played the chief role in the degradation process. A possible Zscheme degradation mechanism of organic contaminant over g-C3N4/Ag3PO4 hybrid was proposed.
In the paper By Yuxiao Gong, semiconducting metal oxide (SMO) gas sensors have attracted the attention of researchers for high conductivity, labile features by environment, low cost, easy preparation, etc. However, traditional SMOs have some defects such as higher operating temperature and lower response value, which greatly limit their application in the field of gas sensor. In this work, the carbon nitride decorated ball-flower like Co3O4 composite was successfully synthesized via a facile hydrothermal method, the composition and morphology of the as-synthesized samples were studied by the techniques of X-ray powder diffraction (XRD), Field-emission scanning electron microscopy (FESEM), Transmission electron microscopy (TEM), Fourier transform infrared spectrometer (FT-IR) and N2-sorption. As a consequence, the pure Co3O4 and the carbon nitride decorated Co3O4 both possess ball-flower like structure, and the as-synthesized carbon nitride decorated Co3O4 composite exhibits significant sensing properties to ethanol which is 1. 6 times higher than that of pure Co3O4, furthermore, the composite possesses high selectivity and stability towards ethanol detection.
Kyo Sang Choi, et al in his paper describes the design, fabrication, and characterization of a capacitive humidity sensor with water vapor inlet holes of different depths. The humidity sensors were composed of a SiO2 insulation layer, a bottom electrode, a polyimide (PI) sensing layer, and a top electrode containing water vapor inlet holes. The sensors were 3. 5 mm × 3. 5 mm with a 0. 7-μm thick PI-based sensing layer. A humidity sensor with a partially etched PI layer in the water vapor inlet holes had the following characteristics: sensitivity 1500 fF∕%RH, hysteresis 0. 37%, and a response time of 70 s.
Peng Zhang, et al says, the higher-order structures of semiconductor-based photocatalysts play crucial roles in their physicochemical properties for efficient light-to-energy conversion. A novel perovskite SrTiO3 mesocrystal superstructure with well-defined orientation of assembled cubic nanocrystals was synthesized by topotactic epitaxy from TiO2 mesocrystals through a facile hydrothermal treatment. The SrTiO3 mesocrystal exhibits three times the efficiency for the hydrogen evolution of conventional disordered systems in alkaline aqueous solution. It also exhibits a high quantum yield of 6. 7% at 360 nm in overall water splitting and even good durability up to 1 day. Temporal and spatial spectroscopic observations revealed that the synergy of the efficient electron flow along the internal nanocube network and efficient collection at the larger external cubes produces remarkably long-lived charges for enhanced photocatalysis.
Shama Perween, et al report a facile and novel approach to produce zinc titanate (ZnTiO3) powders of nanoporous nanoparticulate matter which show an improved photocatalytic activity under visible light illumination. That method consists of calcining the electrospun fibrous mats obtained by electrospinning a sol with a solution of guiding polymer that yields a white crystalline nanopowder. The powder's crystallinity was characterized by XRD which confirmed ZnTiO3 with a hexagonal structure. They have examined the photocatalytic activity of these powders by studying the photocatalytic degradation reaction of phenol in the presence of visible light from an incandescent light bulb. A comparison of the photocatalytic activity of our material with that of the powders prepared by other standard routes such as the bulk sol-gel method and the sol-gel method in presence of surfactant (CTAB) shows that the nanopowders obtained by calcining the electrospun-sols afford a much better photocatalytic activity in presence of the visible light. Surface area analysis of these nanopowders suggest an enhanced surface area per unit volume and that the nanoparticles are nanoporous. The enhanced visible-light photocatalytic activity is believed to be originating chiefly from the enhanced surface area as confirmed by the BET analysis, and larger carrier lifetimes as confirmed by the photoluminescence spectra. The reaction kinetics studied by monitoring the UV–Visible absorption spectra of phenol shows a first order decay kinetics in each case with the powder samples of calcined electrospun-sols giving the highest rate constant.
