Ammonia gas sensors based on undoped and Ca-doped ZnO nanoparticles.

Due to its large use in different industrial sectors, high toxicity, and corrosion, the demand for sensing techniques towards ammonia gas has become urgent. In this study we report on the sensing performances of a conductometric sensor for NH3 gas based on Ca-doped ZnO nanoparticles with different calcium concentrations (0, 1, and 3 at%) synthesized using the sol-gel process under supercritical dry conditions of ethanol. All samples were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier-transform infrared (FTIR) spectroscopy. Pure and Ca-doped ZnO are polycrystalline and well crystallized in the hexagonal wurtzite structure. TEM images revealed that pure ZnO is composed of spherical particles with dimensions in the nanometer range. Larger particles were observed after the incorporation of Ca ions. The average crystallite size, estimated by the Williamson-Hall method, was 43, 80, and 96 nm for pure, Ca-1 at% and Ca-3 at%, respectively. Furthermore, FTIR spectroscopy was used to prove the formation of ZnO and the incorporation of calcium ions in the Ca-doped ZnO samples. The gas sensing performances towards ammonia gas clearly ameliorated after the addition of Ca ions in the ZnO structure. The gas response to NH3, R0/Rg, of the 1% Ca-doped ZnO sensor reached a value of 33 for 4000 ppm of ammonia at T = 300 °C with good selectivity compared to other gases such as CO, CO2, and NO2. The response and recovery times were 5 s and 221 s, respectively. The reported good sensing performances indicate the potential application of Ca-doped ZnO as a sensor material for ammonia detection.

Study of the effect of the substitution of Fe by Ti on the microstructure and the physical properties of the perovskite system La0.67Ca0.2Ba0.13Fe1-xTixO3 with x = 0 and 0.03 at low temperatures.

La0.67Ca0.2Ba0.13Fe1-xTixO3 samples (x = 0 and 0.03) were synthesized by the auto-combustion method. Analysis of XRD diffractograms revealed that these compounds crystallize in the cubic system with the space group Pm3̄m. The dielectric properties have been studied in the 102-106 frequency range and the 120-280 K temperature range. Analysis of AC conductivity shows that the conduction mechanisms are of polaronic origin and that they are co-dominated by the NSPT and OLPT models. The monotonic increase in conductivity with increasing temperature results from the reduction of defect centers and the increase in charge carrier mobility. Such variation is consistent with impedance variation at different frequencies and temperatures indicating semiconductor behavior. Nyquist diagrams are characterized by the appearance of semi-circular arcs. These spectra are modeled in terms of equivalent electrical circuits confirming the contribution of grains (Rg//CPEg) and grain boundaries (Rgb//CPEgb). The dielectric analysis showed an evolution of the dielectric constant in accordance with Koop's theory and the phenomenological model of Maxwell-Wagner. The low conductivity and the high values of the real permittivity at low frequency make our compounds potential candidates for energy storage and applications for electronic devices and microwaves.

Electronic, electrical and thermoelectric properties of Ba0.95Ca0.05Ti0.95Y0.05O2.975 compound: Experimental study and DFT-mBJ calculation.

This article explores the impact of co-doping BaTiO3 ceramics with Ca2+ and Y3+ using solid-state reactions to improve its dielectric constant and decrease losses. The oxide BCTYO (Ba0.95Ca0.05Ti0.95Y0.05O2.975) exhibits a tetragonal crystal structure, characterized by a space group of P4mm. By examining the behavior of the doped BaTiO3 sample and performing simulations, researchers can better understand the underlying mechanisms and optimize material properties for specific applications. DFT study shows a semiconductor behavior with an indirect gap (Eg = 2.5 eV). The partial DOS proves that the hybridization between the orbitals Ti 3d, Y 3d, and O 2p is responsible for the band gap and the hopping processes. The analysis of conductivity curves provides evidence for the semiconductor characteristics of the material under investigation. By determining the activation energy (Ea) through analyzing Ln(fmax) and conductivity as a function of 1000/T, the interconnection between conduction and relaxation phenomena is demonstrated. The study of the real part of the dielectric permittivity (ε') shows a transition at Tc = 380 K. The obtained results are promising and indicate that the studied material has the potential for various electronic applications (energy storage and diode fabrication …). Moreover, the thermal, electrical, and thermoelectric characteristics were examined utilizing the semi-classical Boltzmann theory. The findings revealed an intriguing result, suggesting that Ba0.95Ca0.05Ti0.95Y0.05O2.975 holds promise as a potential candidate for application in thermoelectric devices.

Study of the structural, electrical, dielectric properties and transport mechanisms of Cu0.5Fe2.5O4 ferrite nanoparticles for energy storage, photocatalytic and microelectronic applications.

Cu0.5Fe2.5O4 nanoparticles were synthesized by the self-combustion method whose XRD and FTIR analyzes confirm the formation of the desired spinel phase. The thermal evolution of conduction shows a semiconductor behaviour explained by a polaronic transport mechanism governed by the Non-overlapping Small Polaron Tunnelling (NSPT) model. DC conductivity and hopping frequency are positively correlated. The scaling of the conductivity leads to a single universal curve where the scaling parameter α has positive values, which testifies to the presence of Coulomb interactions between the mobile particles. Conduction and relaxation processes are positively correlated by similar activation energies. Nyquist diagrams are characterized by semicircular arcs perfectly modeled by an equivalent electrical circuit (R//C//CPE) indicating the contribution of the grains. The dielectric behaviour shows a strong predominance of conduction by the phenomenological theory of Maxwell-Wagner. The low values of electrical conductivity and dielectric loss and the high value of permittivity, make our compound a promising candidate for energy storage, photocatalytic and microelectronic applications.

High occurrence of enterotoxigenic isolates and low antibiotic resistance rates of Staphylococcus aureus isolated from raw milk from cows and ewes.

This study aimed to analyse the frequency of genes encoding virulence factors and to characterize resistance profiles of Staphylococcus aureus isolated from raw milk. In total, 47 and 9 S. aureus isolates were recovered from 150 and 100 raw bovine and ovine milk samples, respectively, in Tunisia. The majority of isolates was resistant to penicillin, and no methicillin-resistant S. aureus was detected. Eighteen and two isolates harboured etd and eta genes respectively. Sixteen enterotoxin-encoding genes were detected (n, %): sed (25, 44·6%), sec (16, 28·6%), sei (16, 28·6%), seh (13, 23·2%), seln (13, 23·2%), sell (10, 17·8%), seg (9, 16%), selu (8, 14·3%), selq (7, 12·5%), selo (7, 12·5%), selm (7, 12·5%), seb (7, 12·5%), sea (6, 10·7%), selk (3, 5·4%), ser (1, 1·8%) and selp (1, 1·8%). Ten isolates carried the tsst1 gene. All isolates carried the haemolysin toxin (hla, hld and hlg). The immune evasion cluster system-type B was predominant (20 isolates) followed by C (3 isolates), A and E (1 isolate each). The occurrence of enterotoxigenic S. aureus in raw milk constitutes a potential risk for human health. SIGNIFICANCE AND IMPACT OF THE STUDY: This paper describes the characteristics of Staphylococcus aureus isolated from raw milk samples from healthy cows and ewes collected from small family farms in Tunisia. Fifty-six strains were analysed by determining their antibiotic susceptibility and genes encoding antibiotic resistance and virulence factors. Methicillin-resistant strains were not detected, and overall low level of antimicrobial resistance was reported. However, our strains harboured several genes encoding virulence factors and 87·5% of them carried at least one gene encoding for enterotoxins showing a high risk of spread of food-borne diseases.

[SAPHO syndrome]. / Le syndrome SAPHO.

SAPHO (synovitis, acne, pustulosis, hyperostosis, osteitis) syndrome is a rare entity characterized by the association of heterogeneous osteoarticular and cutaneous manifestations that have for common denominator an aseptic inflammatory process. The etiopathogeny of this disease is still a matter of debate. Although it has been related to the spondylarthritis family, an infectious origin is suggested. Diagnosis is based on the presence of at least one of the three diagnostic criteria proposed by Kahn. The treatment includes NSAIDs, antibiotics, corticosteroids, methotrexate and more recently the bisphosphonates and the TNFα inhibitors.

Seroepidemiology of hepatitis B, C and delta viruses in Tunisia.

Serum samples from 33,363 healthy people in Tunisia have been tested for serological markers of hepatitis B, C and delta viruses (HBV, HCV and HDV). Hepatitis B surface antigen (HBsAg) was detected in 6.5% of sera. The overall seroprevalence of HBV was 37.5%. Vertical and perinatal transmission of HBV in the first 3 months of life occurred in only 0.4% of 177 mother and child pairs. HBV seroprevalence was 10.7% in infants under 5 years old and increased with age rapidly till 25 years of age and then more slowly in adulthood, reaching 54% for people aged over 40 years. HBsAg seropositivity varied throughout the country, ranging from 3% to 13% with higher prevalences in the south and central-west regions. Overall seroprevalences for HDV and HCV were 17.7% and 0.4%, respectively. HDV superinfection occurred later than HBV and increased with age in parallel with HBV. Overall, HCV and HBV infections had different geographical distributions throughout the country. The study confirmed the high prevalence of HBV infection in Tunisia; it occurs mainly in children and teenagers, and vertical and perinatal transmission of HBV does not appear to be significant. HDV superinfection is quite common in Tunisia and occurs in almost 44% of individuals infected with HBV. In contrast, seroprevalence of HCV in the Tunisian general population was low (0.4%). These results indicate differences in the distribution of the viruses and/or different routes of transmission.