Integrated Capacitive- and Resistive-Type Bimodal Relative Humidity Sensor Based on 5,10,15,20-Tetraphenylporphyrinatonickel(II) (TPPNi) and Zinc Oxide (ZnO) Nanocomposite.

The development of high-performance humidity sensors to cater for a plethora of applications, ranging from agriculture to intelligent medical monitoring systems, calls for the selection of a reliable and ultrasensitive sensing material. A simplistic device architecture, robust quantification of ambient relative humidity (% RH), and compatibility with the contemporary integrated circuit technology make a bimodal (capacitive and resistive) surface-type sensor to be a prominent choice for device fabrication. Herein, we have proposed and demonstrated a facile realization of a 5,10,15,20-tetraphenylporphyrinatonickel (II)-zinc oxide (TPPNi-ZnO) nanocomposite-based bimodal surface-type % RH sensor. The TPPNi macromolecule and ZnO nanoparticles have been synthesized by an eco-benign microwave-assisted technique and a thermal-budget chemical precipitation method, respectively. It is speculated from the morpohological study that specific surface area improvement, via the provision of ZnO nanoparticles on micro-pyramidal structures of TPPNi, may reinforce the sensing properties of the fabricated humidity sensor. The relative humidity sensing capacitive and resistive characteristics of the sensor have been monitored in 40-85% relative humidity (% RH) bandwidth. The fabricated sensor under the biasing conditions of 1 V of applied bias (V rms) and 500 Hz AC test frequency exhibits a significantly higher sensitivity of 387.03 pF/% RH and 95.79 kΩ/% RH in bimodal operation. The average values of both the response and recovery times of the capacitive sensor have been estimated to be ∼30 s. It has also been debated why this high degree of sensitivity and considerable reduction in response/recovery time has been obtained. In addition, the intense and wide bandwidth spectral response of the TPPNi-ZnO nanocomposite indicates that it may also be utilized as a potential light-harvesting heterostructured nanohybrid in future studies.

Synthesis and characterization of pristine and strontium-doped zinc oxide nanoparticles for methyl green photo-degradation application.

Herein we describe an effective route for the degradation of methyl green (MG) dye under visible light illumination by pristine and strontium (Sr)-doped zinc oxide (ZnO) photocatalysts (synthesized by the simple chemical precipitation method). The x-ray diffraction structural analysis has confirmed that both photocatalysts exhibit the hexagonal wurtzite structure; without any additional phase formation in Sr-doped ZnO, in particular. The optical properties of the synthesized photocatalysts have been investigated using UV-vis absorption spectroscopy in the wavelength range of 250-800 nm. Through Tauc's plot, the slight decrease from 3.3 to 3.2 eV in band gap energy has been elucidated (in the case of Sr-doped ZnO), which has been further confirmed by the quenching in the intensity of Photoluminescence (PL) emission spectrum. This may be due to sub-band level formation between valence and conduction band, caused by the impregnation of Sr2+ions into ZnO host. The morphological study has also been performed using Field Emission Scanning Electron Microscope, which indicates nanoparticles (NPs) based surface texture for both photocatalysts. During the photocatalytic activity study, after 30 min irradiation of visible light, ∼65.7% and ∼84.8% photocatalytic degradation of MG dye has been achieved for pristine and Sr-doped (2 wt%) ZnO photocatalysts, respectively. The rate of photocatalytic reaction (K) has been observed to be âˆ¼0.06399 min-1for Sr-doped (2 wt%), whereas nearly half magnitude âˆ¼0.03403 min-1has been observed for pristine ZnO, respectively. The significantly improved photodegradation activity may be ascribed to the relatively broader optical absorption capability, surface defects and the enhanced charge separation efficiency of the Sr-doped ZnO photocatalyst.

Capacitive and Conductometric Type Dual-Mode Relative Humidity Sensor Based on 5,10,15,20-tetra Phenyl Porphyrinato Nickel (II) (TPPNi).

(1) Background: A quest for a highly sensitive and reliable humidity monitoring system for a diverse variety of applications is quite vital. Specifically, the ever-increasing demand of humidity sensors in applications ranging from agriculture to healthcare equipment (to cater the current demand of COVID-19 ventilation systems), calls for a selection of suitable humidity sensing material. (2) Methods: In the present study, the TPPNi macromolecule has been synthesized by using a microwave-assisted synthesis process. The layer structure of the fabricated humidity sensor (Al/TPPNi/Al) consists of pair of planar 120 nm thin aluminum (Al) electrodes (deposited by thermal evaporation) and ~160 nm facile spin-coated solution-processable organic TPPNi as an active layer between the ~40 µm electrode gap. (3) Results: Electrical properties (capacitance and impedance) of sensors were found to be substantially sensitive not only on relative humidity but also on the frequency of the input bias signal. The proposed sensor exhibits multimode (capacitive and conductometric) operation with significantly higher sensitivity ~146.17 pF/%RH at 500 Hz and 48.23 kΩ/%RH at 1 kHz. (4) Conclusions: The developed Al/TPPNi/Al surface type humidity sensor's much-improved detecting properties along with reasonable dynamic range and response time suggest that it could be effective for continuous humidity monitoring in multi environmental applications.