RESUMEN

Whitish-blue light emitting fluorescent ZIF-8 structures were synthesized by means of bis-carboxylate functional calix[4]pyrrole (BCCP) modification. The calix[4]pyrrole concentration was also manipulated to tune the sizes of the ZIF-8 structures. Moreover, the BCCP-modified ZIF-8 samples exhibited enhanced organic micropollutant removal capacity from aqueous solutions.

RESUMEN

An AB2 -type monomer comprised of a calix[4]pyrrole skeleton and alternating bis-carboxylate units is reported and used for the construction of a novel supramolecular hyperbranched polymer based on anion recognition ability of calix[4]pyrrole. 1 H-, DOSY-NMR spectroscopy, viscosity measurements, and dynamic light scattering techniques are used for the characterization of the supramolecular hyperbranched polymer exhibiting thermo-, pH-, and chemical responsiveness, as well as concentration dependent morphology tune as inferred from electron microscopy analyses. The present study enriches the field of supramolecular polymers with a new construction motif, building block, and provides a simple approach for the fabrication of smart polymer material with multi-responsiveness and -morphologies.

Asunto(s)

RESUMEN

Carbon dots (CDs) are carbon-based fluorescent nanomaterials that are of interest in different research areas due to their low cost production and low toxicity. Considering their unique photophysical properties, hydrophobic/amphiphilic CDs are powerful alternatives to metal-based quantum dots in LED and photovoltaic cell designs. On the other hand, CDs possess a considerably high amount of surface defects that give rise to two significant drawbacks: (1) causing decrease in quantum yield (QY), a crucial drawback that limits their utilization in LEDs, and (2) affecting the efficiency of charge transfer, a significant factor that limits the use of CDs in photovoltaic cells. In this study, we synthesized highly luminescent, water-insoluble, slightly amphiphilic CDs by using a macrocyclic compound, calix[4]pyrrole, for the first time in the literature. Calix[4]pyrrole-derived CDs (CP-DOTs) were highly luminescent with a QY of over 60% and size of around 4-10 nm with graphitic structure. The high quantum yield of CP-DOTs indicated that they had less amount of surface defects. Furthermore, CP-DOTs were used as an additive in the active layer of organic solar cells (OSC). The photovoltaic parameters of OSCs improved upon addition of CDs. Our results indicated that calix[4]pyrrole is an excellent carbon precursor to synthesize highly luminescent and water-insoluble carbon dots, and CDs derived from calix[4]pyrrole are excellent candidates to improve optoelectronic devices.

RESUMEN

Since export has a key role in economic growth in terms of national production quantity, export quality can be considered another important factor regarding the revenue from the export product. Hence, both export and export quality can contribute to the economic growth process positively when the countries' terms of trade have moved in a favorable direction from this point of view, it is essential to examine the relationship between the energy-growth nexus and export quality. Although available seminal studies are monitoring the energy-growth nexus, there exists a limited number of works employing the export quality. Besides, one might claim that there exists no research on how the terms of trade (export quality) alter the economic growth and energy use through regime shifts. Markov regime-shifting models estimate (a) the impact of export and terms of trade on growth, and (b) the effect of growth on the use of fossil energy and renewable energy for the USA at regime 1 and regime 2 for the period 1980:Q4-2019:Q2. After conducting the non-linear analyses, this paper (i) reveals the estimated parameters varying from one regime to another regime through transition probabilities, (ii) finds evidence that (a) export and export quality growths affect positively GDP growth, (b) GDP growth increases fossil fuel consumption growth, (c) renewable energy growth increases at decreasing rate due to GDP growth, and (iii) yields relevant energy-environmental policy proposals by underlying the prominence of terms of trade within growth-energy nexus.

Asunto(s)

RESUMEN

There exist many seminal studies in the literature searching the influences of total renewable usage (or usage of its some components) on CO2 emissions. However, to the best of our knowledge, there does not exist a research work in the literature considering the co-movements between waste energy consumption and CO2 emissions. This paper aims at observing the possible negative or positive impacts of waste energy consumption on environmental quality (in terms of CO2) by monitoring the whole sample period and all subsample periods in the USA for the monthly period 1980:1-2018:12. This paper searches also the positive or negative lead-lag relations between waste and CO2 emissions, if exist, by considering high frequency (1-3-year cycle) and low frequency (3-8-year cycle) of the same sample period and subsample periods. The findings obtained by this research in general might underline (a) the outcome indicating that waste energy usage has been effective in diminishing the carbon emissions after the second half of the 2010s in the USA and (b) the energy policy act(s) in the USA implemented which eventually resulted in lower CO2 emissions in the USA especially after the second half of the 2000s. The paper suggests as well some policy proposals which might result in positive contribution of waste energy on environmental quality.

Asunto(s)

RESUMEN

This article aims at answering the following questions: (1) What is the influence of age structure on the spread of coronavirus disease 2019 (COVID-19)? (2) What can be the impact of stringency policy (policy responses to the coronavirus pandemic) on the spread of COVID-19? (3) What might be the quantitative effect of development levelincome and number of hospital beds on the number of deaths due to the COVID-19 epidemic? By employing the methodologies of generalized linear model, generalized moments method, and quantile regression models, this article reveals that the shares of median age, age 65, and age 70 and older population have significant positive impacts on the spread of COVID-19 and that the share of age 70 and older people in the population has a relatively greater influence on the spread of the pandemic. The second output of this research is the significant impact of stringency policy on diminishing COVID-19 total cases. The third finding of this paper reveals that the number of hospital beds appears to be vital in reducing the total number of COVID-19 deaths, while GDP per capita does not affect much the level of deaths of the COVID-19 pandemic. Finally, this article suggests some governmental health policies to control and decrease the spread of COVID-19.

RESUMEN

Advanced analytical approaches consisting of both LC-LTQ-Orbitrap Fourier transformed (FT)-MS and LC-time-of-flight-(TOF)-MS coupled to solid-phase extraction (SPE) NMR were used to obtain more insight into the complex phenolic composition of tea. On the basis of the combined structural information from (i) accurate mass fragmentation spectra, derived by using LC-Orbitrap FTMS(n), and (ii) proton NMR spectra, derived after LC-TOFMS triggered SPE trapping of selected compounds, 177 phenolic compounds were annotated. Most of these phenolics were glycosylated and acetylated derivatives of flavan-3-ols and flavonols. Principal component analysis based on the relative abundance of the annotated phenolic compounds in 17 commercially available black, green, and white tea products separated the black teas from the green and white teas, with epicatechin-3,5-di-O-gallate and prodelphinidin-O-gallate being among the main discriminators. The results indicate that the combined use of LC-LTQ-Orbitrap FTMS and LC-TOFMS-SPE-NMR leads to a more comprehensive metabolite description and comparison of tea and other plant samples.

Asunto(s)