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Jun 5, 2025

Solvent effects on the synthesis of piezoelectric membranes, based on nanofibers of the polyvinylidene polyfluoride polymer

The qualitative and quantitative characteristics of piezoelectric membranes manufactured with the polymer polyvinylidene fluoride, through the electrospinning (TEH) technique were compared. We fabricated microfiber membranes of polyvinylidene fluoride (PVDF) using the electrospinning technique in Methyl Ethyl Ketone (MEK) solution at a ratio of 2:1 and compared them with those manufactured by other authors, who used Dimethylformamide (DMF) as a solvent. During the process, a potential difference of 15.0 kV was applied and the viscoelastic solution of PVDF was maintained at a temperature of 60$^{\circ} \mathrm{C}$. The working hypothesis was based on analyzing the influence of the polymer solute on two specific properties: (1) the diameter of the microfibers of the PVDF polymeric material, synthesized through TEH and; (2) the formation of the rotational crystalline structure of the polymer, specifically in the beta ( $\beta$ ) piezoelectric phase. The following techniques were used to characterize the synthesized samples: (1) Scanning electron microscopy (SEM), with which we were able to record the diameter of the microfibers between 85 and 113 nm . (2) X-ray diffraction (XRD), where the samples generated dispersions at 2 $\theta$=18.3$^{\circ}$, 19.9$^{\circ}$ and 20.6$^{\circ}$ , which indicated that the crystalline structure obtained is typical of the alpha ( $\alpha$ ) and beta ( $\beta$ ) piezoelectric phases. (3) Raman spectroscopy, with which a spectrum with wave number (k) between 800 $\mathrm{~cm}^{-1}$ and 840 $\mathrm{~cm}^{-1}$ was determined, which supported the changes we caused in the internal structure of the polymer, using the DMF/MEC mixture as the polymer solvent. The characterization of the samples obtained allowed us to discover that the properties of PVDF microfiber membranes are affected by the solvent used in the synthesis process. When comparing membranes that used only DMF as a solvent with our membranes manufactured with the DMF/MEC solvent, a higher concentration of the piezoelectric beta ($\beta$) structural phase was generated in the latter, which have greater application in power-generating devices.

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16

Dec 23, 2021

Preparation of PbTiO3-CdS nanocomposite material and its microstructure and photocatalytic properties

In order to explore the influence of the ferroelectric surface on the structure and properties of semiconductor oxides, the growth of CdS nanocrystals was regulated and controlled by taking single-crystal perovskite PbTiO₃ nanosheets as the substrate through a simple hydrothermal method. Through composition design, a series of PbTiO₃-CdS nanocomposite materials with different loading concentrations were prepared, and their microstructure and photocatalytic properties were systematically analyzed. Studies show that in the prepared product, CdS nanoparticles selectively grow on the surfaces of PbTiO₃ nanosheets, and their morphology is affected by the exposed surfaces of PbTiO₃ nanosheets. There is a clear interface between the PbTiO₃ substrate and CdS nanoparticles. The concentration of the initial reactant and the time of hydrothermal reaction also significantly affect the crystal morphology of CdS. Photocatalysis studies have shown that the prepared PbTiO₃-CdS nanocomposite material has a significant degradation effect on 10 mg/L of Rhodamine B aqueous solution. The degradation efficiency rises with the increase of CdS loading concentration. When degrading 10 mg/L Rhodamine B aqueous solution, the PbTiO₃-CdS sample with a mass fraction of 3% can reach a degradation rate of 72% within 120 min.

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15

Jun 26, 2025

Design, synthesis and application of pyrazole-based Schiff base chitosan hybrids for Cu(II) removal and antibacterial inhibition

Modified chitosan hybrids were obtained via chemical reaction of chitosan with two pyrazole aldehyde derivatives to produce two chitosan Schiff bases, Cs-SB1, and Cs-SB2, respectively. FTIR spectroscopy and scanning electron microscopy confirmed both chemical structures and morphology of these Schiff bases. Thermal gravimetric analysis showed an improvement of thermal properties of these Schiff bases. Both chitosan Schiff bases were evaluated in a batch adsorption approach for their ability to remove Cu(II) ions from aqueous solutions. Energy dispersive X-ray for the Schiff bases adsorbed metal ions in various aqueous solutions was performed to confirm the existence of adsorbed metal ions on the surface substrate and their adsorptive efficiency for Cu(II) ions. Results of the batch adsorption method showed that prepared Schiff bases have good ability to remove Cu(II) ions from aqueous solutions. The Langmuir isotherm equation showed a better fit for both adsorbents with regression coefficients (R² = 0.97 and 0.99, respectively) with maximum adsorption capacity for Cu(II) of 10.33 and 39.84 mg/g for Cs-SB1 and Cs-SB2, respectively. All prepared compounds, pyrazoles and two chitosan Schiff bases, showed good antimicrobial activity against three Gram +ve bacteria, three Gram –ve bacteria and Candida albicans, with varying degrees when compared to the standard antimicrobial agents.

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15

Jun 15, 2023

Socially responsible activities and the economic performance of family businesses

Promoting the idea of socially responsible business is an undeniably important topic that resonates in both theory and practice. Its influence on business performance has been theoretically substantiated and has been confirmed in many empirical studies, though this has been based on research conducted in large companies. It is only recently that studies connecting the principles of CSR and the business activities of SMEs or family businesses that make up a decisive proportion of SMEs have appeared. This article is devoted to research into the implementation of the principles of CSR in family businesses and their economic performance. The research was conducted on the basis of data obtained both from a questionnaire survey among owners of family businesses and from accounting data. The attitudes of owners of family businesses towards activities typical of CSR were proven to be reflected in the economic results of the companies in a sample of Czech family MSMEs. Our research proved that family businesses that support work-life balance and good relations with employees achieve better performance, namely higher profitability and lower indebtedness. These results confirm the positive impact of CSR principles on longterm sustainability of family businesses and their importance to the country’s overall economy.

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14

Jun 8, 2023

Thermal effects of electromagnetic origin from heating processes to biological disturbances due to field exposure—A review

This contribution aims to appraise, analyze and evaluate the literature relating to the interaction of electromagnetic fields (EMF) with matter and the resulting thermal effects. This relates to the wanted thermal effects via the application of fields as well as those uninvited resulting from exposure to the field. In the paper, the most popular EMF heating technologies are analyzed. This involves on the one hand high frequency induction heating (HFIH) and on the other hand microwave heating (MWH), including microwave ovens and hyperthermia medical treatment. Then, the problem of EMF exposure is examined and the resulting biological thermal effects are illuminated. Thus, the two most common cases of wireless EMF devices, namely digital communication tools and inductive power transfer appliances are analyzed and evaluated. The last part of the paper concerns the determination of the different thermal effects, which are studied and discussed, by considering the governing EMF and heat transfer (or bio heat) equations and their solution methodologies.

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14

Apr 1, 2024

Green recovery of NaF-Na2CO3-NaCl ternary fluxing agent from aluminum dross

The present study deliberates the recovery of sodium fluoride (NaF)-natrite (Na₂CO₃)-sodium chloride (NaCl) ternary fluxing agent from hazardous aluminum dross waste using three types of heating methods, including direct heating on a hotplate, heating by a drying oven, and microwave heating. Deionized water was used as a green solvent for the recovery experiments. Investigating the effects of time and temperature on recovery percentage showed that a recovery percentage of around 96.5% can be achieved under time and temperature of 90 min and 95 ℃, respectively. The recovered fluxing agent salt was characterized by XRD, FTIR spectroscopy, FESEM, and energy dispersive X-ray spectroscopy (EDS) elemental analysis. Rietveld fitting analysis of phases detected in the XRD patterns showed that the recovered fluxing agent contained 74–81 wt.% NaF, 8–11 wt.% NaCl, and 11–14.7 wt.% Na₂CO₃. The FESEM micrographs revealed that the retrieved salts were in nano scale. The recovered fluxing agent showed different morphologies including needle-like, round shape, and a mixture of both, corresponding to microwave, drying oven, and hotplate heating methods, respectively. The nano-needles exhibited diameter of the tip and base in the range of 39–60 nm and 50–103 nm, respectively.

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