Showing papers on "Vapours published in 2021"

Antibacterial Activity of Thymus vulgaris L. Essential Oil Vapours and Their GC/MS Analysis Using Solid-Phase Microextraction and Syringe Headspace Sampling Techniques

Abstract: While the inhalation of Thymus vulgaris L. essential oil (EO) is commonly approved for the treatment of mild respiratory infections, there is still a lack of data regarding the antimicrobial activity and chemical composition of its vapours. The antibacterial activity of the three T. vulgaris EOs against respiratory pathogens, including Haemophilus influenzae, Staphylococcus aureus, and Streptococcus pyogenes, was assessed in both liquid and vapour phases using the broth microdilution volatilisation (BMV) method. With the aim of optimising a protocol for the characterisation of EO vapours, their chemical profiles were determined using two headspace sampling techniques coupled with GC/MS: solid-phase microextraction (HS-SPME) and syringe headspace sampling technique (HS-GTS). All EO sample vapours exhibited antibacterial activity with minimum inhibitory concentrations (MIC) ranging from 512 to 1024 μg/mL. According to the sampling technique used, results showed a different distribution of volatile compounds. Notably, thymol was found in lower amounts in the headspace—peak percentage areas below 5.27% (HS-SPME) and 0.60% (HS-GTS)—than in EOs (max. 48.65%), suggesting that its antimicrobial effect is higher in vapour. Furthermore, both headspace sampling techniques were proved to be complementary for the analysis of EO vapours, whereas HS-SPME yielded more accurate qualitative results and HS-GTS proved a better technique for quantitative analysis.

Enhancing alcohol sensing properties of hydroxyapatite via synthesis of its composite with TiO2 nano-tube

Abstract: Nano-composites are emerging class of materials with venerable physical and chemical properties useful for gas sensor applications. In the present work, we have successfully demonstrated utilization of TiO2 nano-tube and hydroxyapatite nano-composite thick films for sensing of alcohol vapours at lower temperature and lower concentrations. Various composites have been prepared by adding wt.% TiO2 nano-tube in hydroxyapatite host material. Various characterizations like XRD, TGA, FTIR and SEM were performed to know structural identification, thermal stability, functional groups and surface morphology, respectively. Among all composites, the 2 wt.% TiO2 nano-tube-hydroxyapatite nano-composite film exhibits pronounced sensing behaviour for the detection of alcohol vapour even at 10 ppm. The operating temperature was observed to be 30/45/105 °C for methanol/ethanol/propanol, whereas, for the same nano-composite material there was fast response and recovery time (100 and 30)/(110 and 40)/(180 and 90) seconds, respectively. These results concluded that nano-composite of TiO2 nano-tube and hydroxyapatite is capable of sensing alcohol vapours with their existence in ambient conditions as low as 10 ppm concentration compared to their native counterparts.

Detection of formic acid and acetic acid gases by a QCM sensor coated with an acidified multi-walled carbon nanotube membrane.

Abstract: In this paper, the acidified multi-walled carbon nanotubes (MWCNTs) film was coated on the quartz crystal microbalance (QCM) to prepare a high-performance sensor for the real-time detection of organic acid gases. The material characteristics of the thin films were analysed by field emission scanning electro microscopy (FESEM), Raman spectra and X-ray photoelectron spectroscopy (XPS). The organic acid vapours' sensing results indicated that acidized-MWCNTs thin film exhibited good frequency response, repeatability, reversibility and stability. There is a clear linear relationship between the frequency offset and the organic acid vapours with concentration below 5.0 ppm, and the detection limit of 0.77 and 0.73 ppm for formic and acetic acid vapours, respectively. The sensor shows the highest response to formic acid vapour than acetic acid vapour which may be ascribed to molecular polarity. Furthermore, a sensing mechanism model was introduced to understand the adsorption reaction between organic acid molecules and acidized-MWCNTs. This paper proves that acidized-MWCNTs is a potential and suitable material for organic acid vapour detection when combined with a QCM sensor.

Chemosensitive Thin Films Active to Ammonia Vapours.

Abstract: The paper presents various dispersive systems developed for sensing toxic substance-ammonia. Polycarbonate dissolved in methylene chloride was used as a polymer matrix, which was enriched with: multi-walled carbon nanotubes (MWCNs), reduced graphene oxide (rGO) and conductive polymer (polyaniline-PANi). Dispersive systems were applied to the prefabricated substrates with comb electrodes by two methods: spraying and drop-casting, forming an active chemosensitive to ammonia vapours films. The spraying method involved applying the dispersion to the substrate by an aerograph for a specific time, whereas drop-casting involves depositing of the produced dispersive systems using a precision automatic pipette. The electrical responses of the obtained films were examined for nominal concentrations of ammonia vapours. Different types of dispersions with various composition were tested, the relationships between individual compounds and ammonia were analysed and the most promising dispersions were selected. Sensor containing rGO deposited by drop-casting revealed the highest change in the resistance (14.21%).

Estimation of mercury and zinc concentration in the vapour phase by measuring oxygen partial pressure

Abstract: Indirect on-line estimation of metal vapours of Hg and Zn using YSZ based electrochemical oxygen sensor is attempted. Change in oxygen partial pressure, in presence and absence of these metals vapours, enables the estimation by using oxygen sensor. Using this method, the Zn metal vapours has been detected down to 13.3 ± 0.7 vppm and for Hg vapour, the lowest detection limit is 68.1 ± 0.7 vppm. The measured vapour pressure is in agreement with the predicted values.

Antimicrobial activities of plant essential oil vapours against Acidovorax citrulli and Xanthomonas campestris on Cucurbitaceae, Brassicaceae and Solanaceae seeds.

Abstract: AIM This study was done to develop a seed decontamination treatment for organic seeds against plant pathogens (Acidovorax citrulli and Xanthomonas campestris) using essential oil (EO) vapours without affecting the seeds' germination rate. METHODS AND RESULTS By using a diffusion assay and determining minimum inhibitory and lethal concentrations, we screened two EO vapours which were most inhibitory to A. citrulli (cinnamon bark and garlic EO vapours) and X. campestris (onion and garlic EO vapours). After 48 h of exposure to EO vapours at 25°C and 43% or 85% relative humidity (RH), no significant decrease (p > 0.05) in germination rates was observed compared with those of control seeds. It was observed that EO vapour treatment at 25°C and 43% or 85% RH for 48 h caused significant population reductions (p ≤ 0.05) (ca. 0.3-2.6 log colony forming unit/g) compared to those of untreated seeds. CONCLUSION Applications of EO vapours showed significant (p ≤ 0.05) antimicrobial effects against A. citrulli and X. campestris on both laboratory mediums and plant seeds without decreasing the germination rate of seeds. SIGNIFICANCE AND IMPACT OF THE STUDY This study provides useful information for the development of natural seed sterilization treatments using EO vapours.

Spectroscopy peculiarities of electric arc discharge plasma with iron vapours

Abstract: This work is devoted to spectroscopy peculiarities of electric arc discharge plasma with iron vapours. The solution of the main issue of optical emission spectroscopy, namely, selection of iron spectral lines, to study the parameters of non-uniform and non-steady-state plasma source, was considered within this paper. Specifically, the Boltzmann plots technique was used for detailed analysing of application possibility of Fe I spectral lines as well as for determination of plasma temperature. The spatial profiles of selected spectral line emission intensities were used to measure the radial distributions of plasma temperature of free-burning arc discharge between consumable electrodes at 3.5 A.