Highly permeable, anti-bacterial, gas selective membranes for the measurement of intra-ruminant gas production

In the recent past, researchers have turned to advancements in membrane technology for gas separation to help solve the enormous challenges faced by society in regards to limited resources and environmental sustainability. Compared with conventional gas separation methods, membrane technology is environmentally benign and energy-efficient. Furthermore, membranes require less space and can be operated in a continuous mode at low cost. Ideal membrane attributes include high permeate flux, high gas selectivity and operational longevity. The aim of this PhD project is to synthesise, optimise, characterise and evaluate the gas permeation properties of polymdimethylsiloxane (PDMS) nanocomposites and finally to prolong their lifetime through the addition of antimicrobial properties. The author of this thesis thoroughly reviewed the fundamental properties and synthesis methods for gas permeable nanocomposite membranes. Based on the literature, the author recognised the lack in a standardised synthesis condition for the chosen base polymer PDMS. Additionally the author identified the significant enhancements that two dimensional (2D) nanomaterials had over other standard fillers when engineering the composites properties, due to an increased surface to volume ratio. Finally, in order to prolong the lifetime of membranes operating in aqueous or humid environments, bacterial growth needs to be controlled. The author explores novel experimental techniques to evaluate the antimicrobial effects of the developed material. Overall, the author strongly believes that the objectives achieved in this PhD research work, have contributed significantly to the advancement of gas separating membranes, antimicrobial materials and in vivo experimental techniques regarding the investigation of microbial growth onto materials, thus creating new systems and adding significantly to the knowledge of the field

CNT/PDMS composite membranes for H2 and CH4 gas separation

Polydimethylsiloxane (PDMS) composites with different weight amounts of multi-walled carbon nanotubes (MWCNT) were synthesised as membranes to evaluate their gas separation properties. The selectivity of the membranes was investigated for the separation of H2 from CH4 gas species. Membranes with MWCNT concentrations of 1% increased the selectivity to H2 gas by 94.8%. Furthermore, CH4 permeation was almost totally blocked through membranes with MWCNT concentrations greater than 5%. Vibrational spectroscopy and X-ray photoelectron spectroscopy techniques revealed that upon the incorporation of MWCNT a decrease in the number of available Si–CH3 and Si–O bonds as well as an increase in the formation of Si–C bonds occurred that initiated the reduction in CH4 permeation. As a result, the developed membranes can be an efficient and low cost solution for separating H2 from larger gas molecules such as CH4

Economical implications and the impact of gonadotropin-releasing hormone administration at the time of artificial insemination in cows raised in the extensive system in North Romania

Artificial insemination (AI) is the first and the most used biotechnologies in reproduction all over the world. Many studies reported the beneficial role of gonadotropin-releasing hormone (GnRH) administrated some hours before the AI or at the artificial insemination time. This study aimed to assess the effect of GnRH analogs given at the time of insemination on the first, second, and third AIs and to assess the economical implications of GnRH administration. We hypothesized that administration of GnRH at the time of insemination would increase ovulation and pregnancy rate. The study was conducted on small farms in northwestern Romania and included animals of the Romanian Brown and Romanian Spotted breeds. Animals in estrous at the first, second, and third inseminations were randomly divided into groups that received GnRH at insemination and groups that did not. A comparison between the groups was performed and the cost of GnRH administration to obtain one gestation was calculated. The GnRh administration increased the pregnancy rate at the first and the second inseminations by 12 and 18%, respectively. For one pregnancy, the cost of GnRH administration was approximately 49 euros for the first insemination group and around 33 euros for the second insemination group. No improvement of the pregnancy rate was observed after the GnRH administration for the cows at the third insemination, so, for this group, no economic statistics were performed

The Diagnosis of Fetal Sexing in Cattle Using Ultrasound

The purpose of this research was to conduct an ultrasound exam in the interval between 49-120 days of gestation for the determination of fetus sex and to establish the interval when the fetal sexing is possible. The research was carried out in three farms from Transylvania. In farm A were examined 25 animals, in farm B 13 animals and in farm C 11 animals. The diagnosis of the fetal sexing was possible for 35 cases, 14 animals were diagnosed as female and 21 were male. In the interval between 56-65 days of gestation the diagnosis of fetal sexing was established by viewing the genital tubercle and in the interval between 65-90 days of gestation the diagnosis was established by viewing the secondary genital organs. In 14 cases the diagnosis was not set; in 4 cases the conception product has not been sufficiently developed, the genital tubercle was not visible, and in 10 cases the fetus was too big and was impossible to localize the genital organs

Exfoliation solvent dependent plasmon resonances in two-dimensional sub-stoichiometric molybdenum oxide nanoflakes

Few-layer two-dimensional (2D) molybdenum oxide nanoflakes are exfoliated using a grinding assisted liquid phase sonication exfoliation method. The sonication process is carried out in five different mixtures of water with both aprotic and protic solvents. We found that surface energy and solubility of mixtures play important roles in changing the thickness, lateral dimension, and synthetic yield of the nanoflakes. We demonstrate an increase in proton intercalation in 2D nanoflakes upon simulated solar light exposure. This results in substoichiometric flakes and a subsequent enhancement in free electron concentrations, producing plasmon resonances. Two plasmon resonance peaks associated with the thickness and the lateral dimension axes are observable in the samples, in which the plasmonic peak positions could be tuned by the choice of the solvent in exfoliating 2D molybdenum oxide. The extinction coefficients of the plasmonic absorption bands of 2D molybdenum oxide nanoflakes in all samples are found to be high (Îμ > 109 L mol-1 cm-1). It is expected that the tunable plasmon resonances of 2D molybdenum oxide nanoflakes presented in this work can be used in future electronic, optical, and sensing devices

Nanocomposite carbon-PDMS membranes for gas separation

Polydimethylsiloxane (PDMS) composites containing variable weight amounts of carbon black (CB) have been synthesized as membranes to evaluate the effect of CB concentration on gas selectivity and separation. The membranes were used in conjunction with a commercial semiconducting methane (CH4) gas sensor that had a strong cross-talk with hydrogen (H2) gas. The selectivity of the CB-PDMS composite membranes for gas separation was tested using CH4 and H2. It was found that at 6 wt% of CB in PDMS, the permeability of CH4 was significantly and selectively attenuated through the composite membrane. This work demonstrates that CB is an effective additive for tuning H2/CH4 gas selectivity of the composite membranes. The selectivity is attributed to a chemical transition occurring with increasing CB doping, which was observed by vibrational spectroscopy measurements

Exfoliation of quasi-stratified Bi2S3 crystals into micron-scale ultrathin corrugated nanosheets

There is ongoing interest in exploring new two-dimensional materials and exploiting their functionalities. Here, a top-down approach is used for developing a new morphology of ultrathin nanosheets from highly ordered bismuth sulfide crystals. The efficient chemical delamination method exfoliates the bulk powder into a suspension of corrugated ultrathin sheets, despite the fact that the Bi2S3 fundamental layers are made of atomically thin ribbons that are held together by van der Waals forces in two dimensions. Morphological analyses show that the produced corrugated sheets are as thin as 2.5 nm and can be as large as 20 mu m across. Determined atomic ratios indicate that the exfoliation process introduces sulfur vacancies into the sheets, with a resulting stoichiometry of Bi2S2.6. It is hypothesized that the nanoribbons were cross-linked during the reduction process leading to corrugated sheet formation. The material is used for preparing field effect devices and was found to be highly p-doped, which is attributed to the substoichiometry. These devices show a near-linear response to the elevation of temperature. The devices demonstrate selective and relatively fast response to NO2 gas when tested as gas sensors. This is the first report showing the possibility of exfoliating planar morphologies of metal chalcogenide compounds such as orthorhombic Bi2S3, even if their stratified crystal structures constitute van der Waals forces within the fundamental planes