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High-performance and Multifunctional Colorimetric Humidity Sensors Based on Mesoporous Photonic Crystals and Nanogels
摘要： Colorimetric sensors, as a key branch of the application of photonic crystals (PCs), sets off enthusiasm of scientists to make research. Here, simple mesoporous and structurally colored one-dimensional photonic crystals (1DPCs) constructed by alternating assembly of poly(acrylamide-N,N'-methylene bisacrylamide) (P(AM-MBA)) nanogels and TiO2 nanoparticles are reported as high-performance colorimetric humidity sensors. The sensors with bright colors display rapid response to relative humidity (RH) change and reach sensing balance in 0.5 s. By varying RH from 47.0% to 89.3%, stopband of a sensor changes from 426 nm to 668 nm, almost spanning the whole visible range. Meanwhile, visual sensing of RH possesses good reversibility and repeatability. Moreover, the sensors with delicate patterns are facilely fabricated by partial UV photodegradation of the polymer layers with nano TiO2 as catalyst. The delicate patterns and backgrounds show different colors, and change color simultaneously and quickly by varying the ambient humidity. Accurate QR code pattern is also realized on the PC sensor, it is found successful reading of the data is only achieved by increasing RH to realize high color contrast between the code and background. Given their excellent properties, the porous hybrid PCs are promising as high-performance humidity sensors with potential display, decoration, information-storage and encryption functions.
关键词： colorimetric humidity sensors,photonic crystals,nanogels,patterning,mesoporous structure
更新于2025-09-23 15:21:21
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Bare Silica Opals for Real-Time Humidity Sensing
摘要： The photonic properties of 3D colloidal crystals made of St?ber silica spheres are shown to significantly depend on the relative humidity of the environment. The photonic bandgap of bare artificial opals formed by hydrophilic silica markedly varies in humid air along the entire range of water vapor concentration without the need for infiltration of functionalization. The optical changes are highly sensitive to humidity variation (especially in low-humidity range) and very fast response times of 60 ms, mainly ascribed to the absence of intermediate processes, the favorable bandgap characteristics (high intensity and sharp edges) and the high air accessibility to the open opal voids. Contrary to common approaches for photonic crystal sensors—seeking visual detection via large spectral shifts but having important shortcomings,—it is demonstrated that the well-defined photonic bandgap of bare silica opals allows, even for moderate shifts, outstanding sensing performance by proper monitoring with inexpensive equipment (no spectroscopic detection is needed). As a result, the rapid and reproducible photonic response enables accurate, real-time retrieval of the ambient humidity. The economical, one-step fabrication, and the efficient performance make silica artificial opals suitable for a new type of precise, low-cost, and real-time humidity sensors.
关键词： water vapor adsorption/desorption,real-time sensing,humidity sensors,artificial silica opals,photonic colloidal crystals
更新于2025-09-23 15:21:01
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Silicon as a ubiquitous contaminant in graphene derivatives with significant impact on device performance
摘要： Silicon-based impurities are ubiquitous in natural graphite. However, their role as a contaminant in exfoliated graphene and their influence on devices have been overlooked. Herein atomic resolution microscopy is used to highlight the existence of silicon-based contamination on various solution-processed graphene. We found these impurities are extremely persistent and thus utilising high purity graphite as a precursor is the only route to produce silicon-free graphene. These impurities are found to hamper the effective utilisation of graphene in whereby surface area is of paramount importance. When non-contaminated graphene is used to fabricate supercapacitor microelectrodes, a capacitance value closest to the predicted theoretical capacitance for graphene is obtained. We also demonstrate a versatile humidity sensor made from pure graphene oxide which achieves the highest sensitivity and the lowest limit of detection ever reported. Our findings constitute a vital milestone to achieve commercially viable and high performance graphene-based devices.
关键词： device performance,supercapacitors,graphene,humidity sensors,silicon contamination
更新于2025-09-23 15:21:01
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Ultrafast Response Polyelectrolyte Humidity Sensor for Respiration Monitoring
摘要： Respiration monitoring is important for evaluating human health. Humidity sensing is a promising way to establish a relationship between human respiration and electrical signal. This work describes polymer humidity sensors with ultrafast response for respiration monitoring. The humidity-sensitive polyelectrolyte is in situ crosslinked on the substrate printed with interdigitated electrodes by a thiol-ene click reaction. The polyelectrolyte humidity sensor owns rapid water adsorption/desorption ability, excellent stability and repeatability. The sensor with ultrafast response and recovery (0.29 s/0.47 s) when changing humidity between 33% and 95% shows good application prospects in breath monitoring and touchless sensing. Different respiration patterns can be distinguished and the breath rate/depth of detection subjects can also be determined by the sensor. In addition, the obtained sensor can sense the skin evaporation by a non-contact way.
关键词： breath monitoring,in situ preparation,ultrafast response,click reaction,polyelectrolyte humidity sensors
更新于2025-09-19 17:15:36
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Photocatalytic Activity and Humidity Sensor Studies of Magnetically Reusable FeWO <sub/>4</sub> –WO <sub/>3</sub> Composite Nanoparticles
摘要： Different mole ratios of (8:2, 6:4, 4:6 and 2:8) iron tungstate–tungsten trioxide (FeWO4–WO3) composite nanoparticles were synthesized by solid state method. The synthesized composite nanoparticles were characterized by powder X-ray diffraction analysis (XRD), field-emission scanning electron microscopy (FE-SEM) with energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM) studies. The crystalline nature and particle size of the samples were characterized by powder X-ray diffraction analysis (XRD). The morphology was confirmed by field-emission scanning electron microscopy (FE-SEM) analysis and transmission electron microscope (TEM). The energy dispersive X-ray spectroscopy (EDX) proved the purity of nanocomposites. Vibrating sample magnetometer reveals that the sample shows paramagnetic property based on the metal present in the prepared nanocomposites at room temperature. The magnetic property is due to the structural defects rather than the impurity phase. Magnetization saturation value (Ms = 398.7 emu/g) of FWWO-46 composite nanoparticles is high enough to be magnetically removed by applying a magnetic field. The composites were subjected to DC conductance measurement as a function of relative humidity in the range of 5–98%, achieved by different water vapour buffers thermostated at room temperature. The sensitivity factor, Sf = R5%/R98%, where R5% and R98% the values of the resistances measured at different RH respectively, are evaluated in Table I. If the composite has the greater value of Sf, then those materials possess the greater sensitivity towards moisture. The sensitivity factor (Sf) of the prepared composite nanoparticles was FWWO-10 (473), FWWO-82 (209), FWWO-64 (323), FWWO-46 (3956), FWWO-28 (361) and FWWO-01 (373). From this experimental value FWWO-46 exhibit the maximum Sf value of 3956 among the composites. This was due to the presence of more pores and cavities in the morphology of FWWO-46 then the other composite nanoparticles. Meanwhile the composite FWWO-46 can interact with water molecules easily then the others. The absorption and desorption of water molecules vary from the other composites. In the presence of water molecules on the morphology of FWWO-46 shows higher conductivity and higher sensitivity factor (Sf). At low relative humidity, water adsorption on the surface of the sample was likely the dominant factor for electronic conduction. The adsorbed water increases the surface electrical conductivity of the ceramic due to the increased charge carrier, protons in the ceramic/water system. The conductivity was further increased by the presence of pores on the sample surface. In the initial stage of water adsorption, a few water vapour molecules chemisorbed on the grain surface by a dissociative mechanism to form two surface hydroxyls per water molecule. In this chemisorbed layer charge transport occurs by the hopping mechanism. Conduction probably occurs by the Grotthus transport mechanism.
关键词： Composite,Photocatalytic Activity,Iron Tungstate,VSM,Humidity Sensors,Tungsten Trioxide
更新于2025-09-09 09:28:46
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Humidity sensors based on AlN microcantilevers excited at high-order resonant modes and sensing layers of uniform graphene oxide
摘要： Resonant humidity sensors base on interdigital transducers (IDTs) excited microcantilevers are proposed for high sensitivity. The microcantilevers are coated with uniform graphene oxide (GO) thin films as sensing layers. For the first time, IDTs are used to excite piezoelectric microcantilevers to operate at very high-order resonant modes with intense signal. A small temperature coefficient of frequency (-23.6 ppm/?C) of the microcantilvers is obtained by using AlN/Si (surface highly doped) layered structure. Uniform and thickness-controllable GO films covering the surface of microcantilevers are formed by vacuum filtration. Compared with the normal electrodes excited sensor with the same structure size, the sensitivity of the IDTs excited sensor is increased from 9.67 to 84.41 Hz/%RH. The thicker GO film, the higher sensitivity of the humidity sensor. Very little humidity hysteresis (< 3%RH) of the sensors is observed in a wide test range from 10%RH to 90%RH. Moreover, the sensors have excellent short term repeatability, fast response and short recovery time (about 10 s).
关键词： Humidity sensors,interdigital transducers,uniform graphene oxide films,microcantilevers,high-order resonant mode
更新于2025-09-09 09:28:46
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The enhancement of humidity sensing performance based on Eu-doped ZnO
摘要： In this work, a high performance impedance-type humidity sensor based on Europium-doped ZnO with abundant surface oxygen vacancy defects was synthesized by sol-gel method. Response of the Eu-doped ZnO with di?erent molar ratio were investigated by exposing them to humidity environments in wide range of 11–95% RH at room temperature. The Eu-doped ZnO (2 mol%) exhibits a three orders impedance change, along with short response/recovery time (5 s/19 s), low hysteresis and best linearity. Complex impedance spectra indicates that dopant Eu can enhance humidity sensing performance of ZnO, which is resulted from the introduction of Eu3+ ions into ZnO structure to produce more defects of surface oxygen vacancy and more active sites on the surface of ZnO. The results show that this is a feasible method to achieve high humidity sensing performance by Eu doped ZnO, which make it a promising candidate for humidity sensing materials and broaden the use of ZnO materials.
关键词： Eu dopant,Humidity sensors,Sol-gel,Zinc oxide
更新于2025-09-04 15:30:14