Gheorghe Nechifor

Anisotropic etching of silicon in a complexant redox alkaline system

Abstract This paper presents the results from the investigation of the chemical anisotropic etching of single-crystal silicon 〈100〉 in the following solutions: KOH, K3[Fe(CN)6] 0.1 M, K4[Fe(CN)6] · 3H2O 0.1 M, KNO3 0.1 M and or complexant added. The complexants added in KOH solution were: calix[4]arenes, phenols and ether dibenzo-18-crown-6. The reaction mechanism, the etch rate, the roughness and the hillocks are analysed. The results allow us to use the redox system and/or the organic complexants to monitor the etching process, to obtain a smooth silicon surface with increased etch rate and to utilize the usual mask material resistant at the new etchants.

Poly(methyl methacrylate) with TiO2 nanoparticles inclusion for stereolitographic complete denture manufacturing − the fututre in dental care for elderly edentulous patients?

OBJECTIVES The aim of this study was to obtain a Poly(methylmethacrylate) (PMMA)-TiO2 nanocomposite material with improved antibacterial characteristics, suitable for manufacturing 3D printed dental prosthesis. METHODS 0.2, 0.4, 0.6, 1, 2.5 by weight% of TiO2 nanoparticles have been added to the commercially available stereolithographic PMMA material and the obtained nanocomposites have been analyzed using FTIR, SEM and also tested for antimicrobial efficacy against bacterial cultures from Candida species (C. scotti). RESULTS SEM images and EDX results highlighted the presence of TiO2 in PMMA nanocomposites. The elemental composition (EDX) also showed the presence of other fillers included in stereolithographic PMMA solution. FTIR analysis clearly revealed changes in polymeric matrix structure when adding TiO2 nanoparticles. Sample containing 0.4, 1 and 2.5wt% TiO2 nanoparticles inhibited the growth of Candida scotti strain in standard conditions according to the toxicity control method (DHA). Increasing quantity of nano-titania has resulted in particles fooling, forming new aggregates instead of the homogenous dispersion of nanoparticles with modified viscosity characteristics and expected lower mechanical parameters. CONCLUSIONS Significant improvements in polymer characteristics and nice dispersion of the TiO2 nanoparticles have been noticed for 0.4wt%, therefore it was used for stereolitographic complete denture prototyping. CLINICAL SIGNIFICANCE Incorporation of TiO2 nanoparticles in PMMA polymer matrix was proved to have antibacterial effects, specifically on Candida species. The newly obtained 0.4% nanocomposite was successfully used with stereolitographic technique for complete denture manufacturing. However, mechanical and biocompatibility tests need to be performed in order to extend the clinical usage.

Polysulfone-functionalized multiwalled carbon nanotubes composite membranes for potential sensing applications

In order to combine the advantages of functionalized multiwalled carbon nanotubes as a highly electronic conductive chemical species to that of polysulfone as a membrane material this paper reports the results concerning the synthesis of new polymeric-carbon nanotubes composite membranes based on polysulfone with functionalized double wall (DWNT) amino carbon nanotubes with sulfated cyclodextrine, are shown, with potential applications in gas sensing. The above synthesized membranes were structurally characterized using Scanning Electron Microscopy, Atomic Force Microscopy, FT-IR spectroscopy, thermal analysis.

Polysulfone- doped polyaniline composite membranes. synthesis and electrochemical characteristics

In order to combine the advantages of polysulfone (PSf) as a membrane material to that of polyaniline as a conductive polymer, one has attempted to obtain novel polysulfone-polyaniline composite membranes by a newly improved technique comparing to the existing ones. The strong point of this technique consists in a phase inversion by immersion precipitation accompanying by chemical reaction followed by the activation of polyaniline with sulfonated beta-cyclodextrine. The above synthesized membranes were structurally characterized using Scanning Electron Microscopy, FT-IR spectroscopy, thermal analysis. The ionic conductivity and electrochemical characteristics were also determined by Electrochemical Impedance Spectroscopy.

The mechanism of anisotropic etching of silicon in a complexant alkaline system

This paper presents the results of the study and experiments of the chemical anisotropic etching of silicon in a complexant alkaline system (KOH 4.5 M and complexants added). The great results obtained using calix[4]arene like complexant make necessary the study of the mechanism of the silicon etch rate increasing and of the roughness minimizing. A new macrocyclic complexant (azocalix[4]arene) and indicator of pH for silicon etching solution, the etch rate and the roughness are analysed. The complexant alkaline system for anisotropic etching of silicon is an absolutely original idea of the authors.

Production and characterization of cellulose acetate – titanium dioxide nanotubes membrane fraxiparinized through polydopamine for clinical applications

The present paper introduces a study on the preparation and characterization of cellulose acetate - TiO2 nanotubes membrane. In order to be used as a hemodialysis membrane, fraxiparinized nanotubes have been incorporated into the cellulose matrix. Fraxiparine embedding was performed via strong binding ability of dopamine. Composite membrane was characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, and water contact angle measurement. Electrochemical impedance spectroscopy was used to correlate the morphology of composite membrane with its electrochemical properties. Mott-Schottky test proved titanium dioxide semiconductor incorporation in composite membrane. Permeation test was made to determine pure water flux. The obtained results showed that addition of nanotubes had a positive impact on membrane permeation compared with a control polymeric membrane.

Case studies on the physical-chemical parameters' variation during three different purification approaches destined to treat wastewaters from food industry.

The paper presents a set of three interconnected case studies on the depuration of food processing wastewaters by using aeration & ozonation and two types of hollow-fiber membrane bioreactor (MBR) approaches. A secondary and more extensive objective derived from the first one is to draw a clearer, broader frame on the variation of physical-chemical parameters during the purification of wastewaters from food industry through different operating modes with the aim of improving the management of water purification process. Chemical oxygen demand (COD), pH, mixed liquor suspended solids (MLSS), total nitrogen, specific nitrogen (NH4+, NO2-, NO3-) total phosphorous, and total surfactants were the measured parameters, and their influence was discussed in order to establish the best operating mode to achieve the purification performances. The integrated air-ozone aeration process applied in the second operating mode lead to a COD decrease by up to 90%, compared to only 75% obtained in a conventional biological activated sludge process. The combined purification process of MBR and ozonation produced an additional COD decrease of 10-15%, and made the Total Surfactants values to comply to the specific legislation.

Aqueous Phase Biosorption of Pb(II), Cu(II), and Cd(II) onto Cabbage Leaves Powder

Abstract In this study, the biosorption of lead (Pb(II)), copper (Cu(II)), and cadmium (Cd(II)) ions from aqueous solution using waste of cabbage leaves powder (CLP) was investigated as a function of pH, shaking time, initial metal concentration, and biosorbent dose. The maximum removal efficiency at optimum condition in single biosorption system was 95.67, 92.42, and 88.92 % for Pb(II), Cu(II), and Cd(II) ions, respectively. These values reduced in ternary systems in the same sequence. Langmuir and extended Langmuir isotherm models were found to be the best fit of the isotherm data for single and ternary biosorption systems, respectively. The kinetic data of the three metals were better fit by the pseudo-second-order model with higher coefficient of determination and more closely predicted uptake. In addition, the results showed that the intraparticle diffusion was the dominating mechanism. Thermodynamic study showed that the biosorption of Pb(II), Cu(II), and Cd(II) onto CLP was a chemical reaction which was exothermic in nature. Finally, SEM image shows that CLP has a number of heterogeneous small pores while the Fourier transform infrared (FTIR) spectroscopic analysis showed that the carboxyl, amine, and hydroxyl groups are the major groups that are responsible for the biosorption process.

Transport and separation through bulk liquid membrane of some biologic active compounds

Abstract Transport through liquid membranes of various chemical species is a viable method for different applications in analytical or technological domain. This paper presents the transport and separation results of two compounds of pharmaceutical importance: salicylic acid and aspirin, using bulk liquid membrane technique. We studied the effect of the feed source and receiving phase pH on the transport efficiency of the two compounds throught chloroform membrane. These results were correlated with speciation diagrams of salicylic acid and aspirin. The speciation diagrams shows that in these pH conditions, for aqueous phase of the membrane system, the two compounds are mostly undissociated form and therefore active for transport. In this system it can be achieve separation of the two compounds, salicylic acid and aspirin, using a suitable complexing agent in the feed source such as Fe3+. In this way salicylic acid forms an inactive complex structure for transport while aspirin crosses the membrane and it is recovered in a percentage of 80% in the receiving phase membrane system.

Development of Stabilized Magnetite Nanoparticles for Medical Applications

We report a facile method to synthesize magnetite nanoparticles with mesoporous structure by coprecipitation method using different stabilizing agents like salicylic acid, glutamic acid, and trichloroacetic acid. The stabilizing agents were used to prevent the aggregation of the magnetite nanocrystals and to obtain stable nanostructures even in the biological environment. The structure and morphology of magnetic nanocrystals were determined using X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET) analysis, infrared (IR) spectra, scanning and transmission electron microscopy (SEM and TEM), high-resolution transmission electron microscopy (HRTEM), and selected area electron diffraction (SAED). The results reveal important differences between these magnetic nanoparticles (MNPs), which are mainly attributed to the stabilizing agents. The smallest nanoparticles were obtained in the presence of trichloroacetate ions. The mechanism of formation of these suprastructures is strongly correlated with the end functional groups of the stabilizing agent. Thus, the obtained nanoparticles are potential candidates for contrast agents as well as targeted carrier for specific diseases, especially cancer.