Thiol adsorption on metal oxide nanoparticles Grimm, Owen C; Somaratne, R. M. Dulanga S; Wang, Yiwen ...
Physical chemistry chemical physics : PCCP,
04/2021, Letnik:
23, Številka:
14
Journal Article
Recenzirano
The adsorption of 2-naphthalenethiol (2-NPT) and methanethiol (MT) on 13 different metal oxide nanoparticles, of approximately 30 nm average primary particle size, has been investigated. In the case ...of 2-NPT, which is fluorescent, a screening method to assess adsorption was developed that consists of mixing the nanoparticles with a dilute ethanolic solution of 2-NPT and performing several cycles of centrifuging and rinsing with ethanol. Fluorescence measurements on the re-dispersed particle suspensions were then used to diagnose whether or not adsorption had occurred. Complementary experiments were performed by mounting powder samples of each of the metal oxide nanoparticles onto sample stubs and performing X-ray photoelectron spectroscopy (XPS) before and after
in situ
dosing with MT. In both cases, adsorption was observed only on ZnO, TiO
2
, and In
2
O
3
. Adsorption did not occur on Al
2
O
3
, CeO
2
, Fe
2
O
3
, Gd
2
O
3
, Ho
2
O
3
, NiO, SiO
x
, WO
3
, Y
2
O
3
, and ZrO
2
. Density functional theory (DFT) calculations were performed using small metal oxide clusters, assuming that dissociative adsorption occurs by replacement of a hydroxyl group attached to a metal site and the formation of water. The theoretical and experimental results generally agree, suggesting that this is indeed the adsorption mechanism for most of the nanoparticles. The agreement also suggests that the size and geometry of the nanoclusters play a minor role and that the relative strengths of the metal-sulfur and metal-hydroxyl bonds dictate thiol adsorption. This work has important implications related to the functionalization of metal oxide nanoparticles and surfaces.
Does thiol adsorption occur on (naturally hydroxylated) metal oxide nanoparticles?
Photoluminescence (PL) changes of ZnO nanospheres at room temperature have been measured during exposure to gases and vapors using a traditional fluorometer and a portable, ultraviolet (UV) ...light-emitting diode-based instrument. Thermal gravimetric analysis indicates that the nanospheres are essentially fully hydroxylated, with OH groups and H atoms attached to surface Zn and O sites, respectively. The PL spectrum has both a UV excitonic emission peak and a visible, defect-related one. Exposure to the gases and vapors studied, whether they physisorb or chemisorb, causes a decrease in the intensity of the visible emission peak relative to pure nitrogen, although to different degrees. Electron-donating molecules, such as hydrogen and methanol, cause a reversible increase in the UV emission peak intensity due to formation of an electron-rich accumulation layer around the nanoparticles. Electron-withdrawing molecules, such as oxygen and water, cause a corresponding decrease due to a depletion layer. For reactive adsorption, such as by sulfur dioxide and methanethiol (MT), surface hydroxyl groups play an important role in reactivity and PL changes. X-ray photoelectron spectroscopy, coupled with density functional theory calculations, confirms that MT adsorption occurs by replacement of hydroxyl groups adsorbed on Zn sites, while SO2 adsorption leads to sulfite formation and removal of H atoms attached to O sites. The latter process causes a more dramatic decrease in visible emission, and it is postulated that hydroxyl groups formed by adsorbed H on O sites act as efficient charge traps that enhance visible PL. Their removal decreases visible PL, partially shutting down this energy pathway and causing an increase in UV emission. While SO2 and MT adsorption occur mainly by replacement of surface hydroxyls, benzene adsorbs at defect sites, such as oxygen vacancies. HCl and Cl2 decrease the visible and UV emission peaks by transforming the surface of the ZnO to ZnCl2, while H2S causes the emergence of a PL peak at 422 nm, which is postulated to arise from the formation of Zn interstitial defects.
Large artery atherosclerotic disease is an important cause of stroke, accounting for 15-46% of ischaemic strokes in population-based studies. Therefore, current guidelines from west recommend urgent ...carotid imaging in all ischaemic strokes or transient ischaemic attacks and referral for carotid endarterectomy. However, the clinical features and epidemiology of stroke in Asians are different from those in Caucasians and therefore the applicability of these recommendations to Asians is controversial. Data on the prevalence of carotid artery stenosis (CAS) among South Asian stroke patients is limited. Therefore, we sought to determine the prevalence and associated factors of significant CAS in a cohort of Sri Lankan patients with ischaemic stroke.
We prospectively studied all ischaemic stroke patients who underwent carotid doppler ultrasonography admitted to the stroke unit of a Sri Lankan tertiary care hospital over 5 years. We defined carotid stenosis as low (< 50%), moderate (50-69%) or severe (70-99%) or total-occlusion (100%) by North American Symptomatic Trial Collaborators (NASCET) criteria. We identified the factors associated with CAS ≥ 50% and ≥ 70% by stepwise multiple logistic regression analysis.
A total of 550 ischaemic stroke patients (326 (59.3%) male, mean age was 58.9 ± 10.2 years) had carotid doppler ultrasonography. Of them, 528 (96.0%) had low-grade, 12 (2.2%) moderate and 7 (1.3%) severe stenosis and 3 (0.5%) had total occlusion. On multivariate logistic regression, age was associated with CAS ≥ 50% (OR 1.12, p = 0.001) and CAS ≥ 70% (OR 1.14, p = 0.016), but none of the other vascular risk factors studied (sex, hypertension, diabetes mellitus, smoking, past history of TIA, stroke or ischemic heart disease) showed significant associations.
Carotid stenosis is a minor cause of ischemic stroke in Sri Lankans compared to western populations with only 4.0% having CAS ≥ 50 and 3.5% eligible for carotid endarterectomy. Our findings have implications for the management of acute strokes in Sri Lanka.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Measuring the levels of sources of ICT self-efficacy of undergraduates in Humanities and Social Sciences (HSS) of universities especially in Sri Lanka has not been adequately explored. In this study, ...therefore it is aimed to make an effort to address this important issue. The main objective of this research study was to identify the levels of the factors that are affecting the ICT self-efficacy among the HSS undergraduates in Sri Lanka and the differences between the factors based on the university. The survey research design was employed and final year HSS undergraduates from four universities were selected randomly, out of ten universities where HSS streams are taught. The sample included 604 undergraduates. Data gathered through structured questionnaire was piloted and validated. The data were subjected to descriptive statistics. The results identified four factors affected with the efficacy level of the undergraduates. It indicated that the ICT Self-efficacy levels and ICT Anxiety were varying between less (22%) and highest (50%) across universities. Factors such as ICT Training (27%) and Library Support provided (32%) by the universities were also in the lowest level. The ICT Self-efficacy was low (29%) among students who used the library ‘rarely’ (< 2 per week) and average level of anxiety 47%. ICT Anxiety and ICT Self-efficacy were the most strongly correlated factors in the study (-0.144, p = 0.01). However, the gender was largely diluted and not correlated with self-efficacy. The introduction of effective Library Support and ICT Training would help reduce the higher levels of ICT Anxiety and improve the ICT Self-efficacy level among undergraduates. The study recommends conducting a cross-sectional, longitudinal research study to better understand the levels of ICT Anxiety, ICT Training and the Library Support.
Nanotechnological improvements such as nano-fertilizers are important in agriculture due to higher capability of penetration into plants, nutrient use efficiency and reduced off-target wastage of ...fertilizers. Rice being the second most important cereal crop in the world, is the national staple food in Sri Lanka. Insufficiency of soil Zn in paddy fields led to a reduction in plant growth and yield. Present study was conducted to assess the effect of nano-ZnO-fertilizer and bulk ZnO on growth and yield performances of commonly cultivated traditional (Pachchaperumal, Suwandel) and inbred (Bg94-1) rice varieties in Sri Lanka. Nano-ZnO particles were synthesized by thermal decomposition route and characterized using powder X-ray diffraction and FE-SEM. Sizes of the nano-ZnO particles varied from 50 nm to 500 nm. Pots were arranged in randomized complete block design with twenty replicates per treatment and treated with distilled water, bulk ZnO 60 mg L-1, nano-ZnO 60 mg L-1 (Conc.1), and nano-ZnO 120 mg L-1 (Conc. 2), Growth related characters were measured at 30, 60, and 90 days after sowing (DAS). Yield characters were measured at the harvesting stage. Analysis of variance showed a significant effect of nano-ZnO-fertilizer on yield parameters than growth parameters of three rice varieties. Varietal responses to the applied nano-ZnO-fertilizer vary and higher responses were observed in Bg94-1. Effect of nano-ZnO-fertilizers on Pachchaperumal and Suwandel were almost similar; however, weight of 100-seed of Suwandel treated with nano-ZnO 120 mg L-1 was prominent. Findings of the study revealed, a better yield performance for three rice varieties with foliar application of nano-ZnO-fertilizers.
Mathematical modeling has widely been used to predict soil organic carbon (SOC). However, there are characteristics of the models such as over simplification, ignorance of complex nonlinear ...interactions etc., which limit their use in accurately assessing the distribution of the C across the landscapes. Artificial neural network (ANN) modeling approach that provides a tool to solve complex problems related to larger data sets was therefore used here to predict SOC contents across different land use patterns in a study conducted in Sri Lanka. Selection of variables was made using a priori knowledge of the relationships between the variables. Thus, soils of the sites were sampled and analyzed for organic C by internal heat of dilution (Ci) and external heat of dilution (Ce), and the results were presented as grams per kilogram (g kg(-1)). In addition, some landscape attributes and environmental parameters of the sites were also collected. The predictive performance of ANN was compared with multi-linear regression (MLR) models. The best ANN model predicted the measured Ci content with R2 of 0.92. However, comparison of the two types of models indicated less bias and high accuracy of the ANN compared with MLR in predicting Ci, but the reverse for Ce. In order to better predict Ce, it is recommended to use other architectures of neural networks and training algorithms for improving predictive accuracy. The predictive capability of the ANN developed with easily available climatic and terrain data are of importance in predicting SOC with minimum cost, labor, and time.
The purpose of the study was to identify the ICT self-efficacy (ICTSE) of users, factors affecting ICTSE, and the EIR usage of undergraduates based on the four sources in relation to the ...self-efficacy theory. The Survey research design was used in carrying out this research. A structured questionnaire was validated through experts and piloted among the final year undergraduates studying Humanities and Social Sciences of four state universities in Sri Lanka. The structural equation modelling was performed using partial least square. The model revealed that ICTSE has a direct, negative, and significant relationship with ICT anxiety and that ICT training also has a direct, negative, and significant relationship with EIR. The model explained that there is a 27% of variance in the EIR use variable. The management of the library may deem it a worthy investment to instil adequate self-efficacy in users and encourage them to engage in more self-reliant search practices and decrease their dependence on staff. The finalized scales provide a potential tool applicable to different domains and disciplines to yield more common managerial implications in relation to training, teaching, and learning along with can be used as a tool when policy-level decision are made about the behavioral changes among university users on EIR usage in the current ICT domains within the university library systems.
Gold and lithium have been deposited on clean, stoichiometric TiO2(110) to study the evolution of the electronic structure of the surface. For thermally deposited gold, X-ray and ultraviolet ...photoelectron spectroscopies (XPS and UPS) indicate that the first monolayer (ML) grows two dimensionally, while additional gold forms islands, and that the surface becomes metallic by 1 ML. Downward band bending for low coverage is confirmed by a comparison of the XPS valence and UPS spectra, which have different detection depths. Inverse photoelectron spectroscopy (IPES) shows that the deposited gold attenuates the Ti 3d states, which dominate the conduction band. In the case of lithium, XPS analysis indicates that deposited atoms penetrate into the bulk, with a gradual buildup in the near-surface region. UPS shows the formation of a Ti3+ 3d gap state 1.4 eV below the Fermi level. Band bending is not observed for low Li coverage due to pinning of the Fermi level to the gap state. Deposition of more than 10 ML is required for the work function to reach that of bulk Li. Unoccupied 3d states disappear from the IPES spectrum as they are filled by electrons injected from Li.
Response of Codariocalyx motorius to Western pop music and Pirith chanting was examined by conducting an experiment with three months old C. motorius saplings, kept in a sound proof confined chamber. ...Completely Randomized Design (CRD) was used with five replicates. One week after planting, plants were exposed to three treatments; Western pop music, Pirith and silence. Music and Pirith were played separately for an hour, 30 cm distance away from plants with a sound level of 58 – 63 dB for two months continuously, maintaining equal environmental conditions. Measurements on growth performance were taken once in a fortnight. Percentage difference of parameters was calculated and data were analysed using ANOVA. Significant differences (p < 0.05) between the treatment of Pirith and Western pop music were observed for plant height, leaf width, leaf area, and chlorophyll content and leaflet length. However,thin layer chromatographic profiles observed under UV light and Anisaldehyde spray reagent exhibited no difference in chemical components. Magnitudes of the percentage difference between measured parameters of C. motorius under Pirith chanting and Western pop music indicated that there was discernible effect of Pirith chanting on the measured plant parameters in the study implying that rhythmic chanting of Pirith is the most appropriate type of music which improved the growth performance of C. motorius.
Use of biologically safe, essential oil-incorporated fruit coatings to reduce postharvest losses has become an attractive alternative to synthetic fungicides in recent years. Increase in shelf life ...due to reduced water loss and reduced evaporation of essential oils (EO) within the coating are key advantages of incorporating EOs to fruit coatings. The effect of beeswax as a fruit coating with and without essential oil on the postharvest quality and natural disease development of mango (cv. Willard) was evaluated by conducting a laboratory experiment. Pure Beeswax, dissolved either in vegetable oil (1:3 w/v) or petroleum ether (1:4 w/v), served as the coating material. Basil oil at 400 or 600 μL L-1 was incorporated to the different coating material. Fruits with no coating and no essential oil served as controls. Eight replicate fruits were used per treatment and three trials were performed. Treated fruits were arranged in a Completely Randomized Design and kept under ambient conditions. Daily observations were made on natural disease development and weight loss. The Total Soluble Solid content and titrable acidity were measured at eating ripe stage and sensory evaluation by a taste panel was also obtained. Data were analyzed using ANOVA with SPSS software version 20.0 package. Results indicated that basil oil in beeswax significantly reduced physiological weight loss, delayed fruit ripening and also delayed and reduced postharvest disease development.
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