A novel quartz-crystal microbalance humidity sensor based on solution-processible indium oxide quantum dots

Green synthesis of carbon quantum dots toward highly sensitive detection of formaldehyde vapors using QCM sensor

In the present study, an eco-friendly method for the preparation of carbon quantum dots (CQDs) is demonstrated using hydrothermal treatment of laurel leaves. The optical and structural characteristics of the prepared CQDs are investigated using transmission electron microscopy (TEM), X-ray photoelectron (XPS), fluorescent and UV-visible spectroscopies, Fourier transform infrared (FTIR), and X-ray diffraction (XRD). The quartz crystal microbalance (QCM) sensor designed and modified with CQDs is capable of detecting formaldehyde vapors in the presence of other interfering chemical-vapor analytes. The changes in the frequency of the QCM sensor are linearly correlated with the injected formaldehyde concentrations. The sensing properties of formaldehyde, including sensitivity and reversibility, are investigated. Detection of formaldehyde in the presence of humidity is carefully discussed for home or workplace room environment use. The adsorption kinetics of various VOCs vapors are also calculated and discussed.

Graphene oxide quantum dots attached on wood-derived nanocellulose to fabricate a highly sensitive humidity sensor

Herein, cellulose nanofibril (CNF) with various carboxyl amounts were prepared via regulating its oxidation degree using TEMPO oxidation. The CNF dispersion was dropped onto the interdigital electrode to be capacitive humidity sensor by the subsequent vacuum freeze-drying. Pure CNF-7 (NaClO content of 7 mmol/g) humidity sensor involves in orderly porous structure, which displays better performance than other CNFs for its moderate carboxyl content and dimension. As uniformly adding appropriate content of graphene oxide quantum dots (GOQD) with larger surface area and active sites, it can be attached on the CNF to construct a three-dimensional interconnected porous structure for their excellent aqueous dispersity as well as differences in morphology and size. Consequently, the CNF/GOQD sensor exhibits the sensitivity as high as 51,840.91 pF/% RH, short response time (30 s)/recovery time (11 s) and excellent reproducibility. The proposed method can provide effective guidance for the design of humidity sensors based on nanomaterials.

Highly Selective Metal-Organic Framework Textile Humidity Sensor

The increase in demand and popularity of smart textiles brings new and innovative ideas to develop a diverse range of textile-based devices for our daily life applications. Smart textile-based sensors (TEX sensors) become attractive due to the potential to replace current solid-state sensor devices with flexible and wearable devices. We have developed a smart textile sensor for humidity detection using a metal-organic framework (MOF) as an active thin-film layer. We show for the first time the use of the Langmuir-Blodgett (LB) technique for the deposition of a MIL-96(Al) MOF thin film directly onto the fabrics containing interdigitated textile electrodes for the fabrication of a highly selective humidity sensor. The humidity sensors were made from two different types of textiles, namely, linen and cotton, with the linen-based sensor giving the best response due to better coverage of MOF. The TEX sensor showed a reproducible response after multiple cycles of measurements. After 3 weeks of storage, the sensor showed a moderate decrease in response. Moreover, TEX sensors showed a high level of selectivity for the detection of water vapors in the presence of several volatile organic compounds (VOCs). Interestingly, the selectivity is superior to some of the previously reported MOF-coated solid-state interdigitated electrode devices and textile sensors. The method herein described is generic and can be extended to other textiles and coating materials for the detection of toxic gases and vapors.