A Novel Trace-Level Ammonia Gas Sensing Based on Flexible PAni-CoFe2O4 Nanocomposite Film at Room Temperature

In this study, we developed a new chemi-resistive, flexible and selective ammonia (NH3) gas sensor. The sensor was prepared by depositing thin film of polyaniline-cobalt ferrite (PAni-CoFe2O4) nanocomposite on flexible polyethylene terephthalate (PET) through an in situ chemical oxidative polymerization method. The prepared PAni-CoFe2O4 nanocomposite and flexible PET-PAni-CoFe2O4 sensor were evaluated for their thermal stability, surface morphology and materials composition. The response to NH3 gas of the developed sensor was examined thoroughly in the range of 1–50 ppm at room temperature. The sensor with 50 wt% CoFe2O4 NPs content showed an optimum selectivity to NH3 molecules, with a 118.3% response towards 50 ppm in 24.3 s response time. Furthermore, the sensor showed good reproducibility, ultra-low detection limit (25 ppb) and excellent flexibility. In addition, the relative humidity effect on the sensor performance was investigated. Consequently, the flexible PET-PAni-CoFe2O4 sensor is a promising candidate for trace-level on-site sensing of NH3 in wearable electronic or portable devices.

Relative humidity effect on encapsulation properties of coproducts obtained from wet milling of amaranth grain

The co-products of the amaranth starch extraction have recently aroused the interest of the industry, mainly due to their functional characteristics. In this paper, the encapsulating efficiencies of starch-enriched fraction (SEF) and native starch (NS) obtained, respectively, by dry or wet milling were studied. The storage humidity effect (11 to 84%, 21 days) on β-carotene retention were evaluated. Significant effects of amaranth protein present in SEF matrix on emulsification and subsequent retention of β-carotene were found. The best encapsulation performance was showed by ball milled starch enriched fraction (SEF-BM) fraction, with up to three times of total β-carotene content in comparison with the NS containing matrices. The glass transition temperature (Tg) of the samples decreased with the increase in relative humidity due to the plasticizing effect of the water. The starch-enriched amaranth fraction showed a high technological potential as an encapsulating agent and its own protein content served as a good emulsifier-stabilizer.

Temperature and relative humidity effect on equilibrium moisture content of cassava pulp

The purpose of this research was to study the effect of temperature and relative humidity on the equilibrium moisture content of cassava pulp. In experiments, cassava pulp was tested with a static method that controlled the temperature at 30, 50 and 70°C and controlled relative humidity in a range 10–90% with standard saturated salt solutions as LiCl, MgCl2, NaBr, NaCl and KNO3. Five equations of equilibrium moisture isotherm were analysed to predict the equilibrium moisture content, which was a guideline to develop a new isotherm equation. The experimental results showed that the equilibrium moisture content was increased with increased relative humidity whereas it decreased with increased drying temperature. Therefore, the drying process and storage method of cassava pulp must control temperature and relative humidity of no more than 50°C and 60%, respectively. The analysis of isotherm equations revealed that the new isotherm equation has high accuracy to predict the equilibrium moisture content of cassava pulp and higher R2 correlation with the experimental data than five isotherm equations.

Relative humidity effect on the formation of highly oxidized molecules and new particles during monoterpene oxidation

It has been widely observed around the world that the frequency and intensity of new particle formation (NPF) events are reduced during periods of high relative humidity (RH). The current study focuses on how RH affects the formation of highly oxidized molecules (HOMs), which are key components of NPF and initial growth caused by oxidized organics. The ozonolysis of α-pinene, limonene, and Δ3-carene, with and without OH scavengers, were carried out under low NOx conditions under a range of RH (from ∼3 % to ∼92 %) in a temperature-controlled flow tube to generate secondary organic aerosol (SOA). A Scanning Mobility Particle Sizer (SMPS) was used to measure the size distribution of generated particles, and a novel transverse ionization chemical ionization inlet with a high-resolution time-of-fight mass spectrometer detected HOMs. A major finding from this work is that neither the detected HOMs nor their abundance changed significantly with RH, which indicates that the detected HOMs must be formed from water-independent pathways. In fact, the distinguished OH- and O3-derived peroxy radicals (RO2), HOM monomers, and HOM dimers could mostly be explained by the autoxidation of RO2 followed by bimolecular reactions with other RO2 or hydroperoxy radicals (HO2), rather than from a water-influenced pathway like through the formation of a stabilized Criegee intermediate (sCI). However, as RH increased from ∼3 % to ∼92 %, the total SOA number concentrations decreased by a factor of 2–3 while SOA mass concentrations remained relatively constant. These observations show that, while high RH appears to inhibit NPF as evident by the decreasing number concentration, this reduction is not caused by a decrease in RO2-derived HOM formation. Possible explanations for these phenomena were discussed.

Relative Humidity Effect on the Formation of Highly Oxidized Molecules and New Particles during Monoterpene Oxidation

It has been widely observed around the world that the frequency and intensity of new particle formation (NPF) events are reduced during periods of high relative humidity (RH). The current study focuses on how RH affects the formation of highly oxidized molecules (HOMs), which are key components of NPF and initial growth caused by oxidized organics. The ozonolysis of α-pinene, limonene, and △3-carene, with and without OH-scavenger, were carried out under low NOx conditions under a range of RH (from ~3 % to ~90 %) in a temperature-controlled flow tube. A Scanning Mobility Particle Sizer (SMPS) was used to measure the size distribution of generated particles and a novel transverse-ionization chemical ionization inlet with a high-resolution time-of-fight mass spectrometer detected HOMs. A major finding from this work is that neither the detected HOMs nor their abundance changed significantly with RH, which indicates that the detected HOMs must be formed from water-independent pathways. In fact, the distinguished OH- and O3-derived peroxy radicals (RO2), HOM monomers, and HOM dimers could mostly be explained by the autoxidation of RO2 followed by bimolecular reactions with other RO2 or hydroperoxy radicals (HO2), rather than from a water-influenced pathway like through the formation of a stabilized Criegee intermediate (sCI). However, as RH changed from 3 to 90 % the particle number concentrations decreased by a factor of 2~3 while particle mass concentrations increased or decreased slightly within a factor of 2. These observations show that, while high RH appears to inhibit NPF as evident by the decreasing number concentration, this reduction is not caused by a decrease in RO2-derived HOMs formation. One possible explanation is the existence of other extremely low volatility compounds (ELVOCs), like gas phase formed sCI-included accretion products, which are responsible for the very first steps of NPF but are not detected by nitrate-based chemical ionization mass spectrometry. These ELVOCs may be preferentially reduced at high RH compared to more volatile compounds, the latter of which mainly determine the final mass concentration of particles. Another possibility is that a fraction of HOMs cluster with water (but detected as the declustered molecules) at high RH in such a way that they may no longer be able to participate in cluster formation, thereby suppressing NPF.