Chimica

This study investigates the removal of malachite green (MG) dye by adsorption process using as adsorbent a waste byproduct from lightweight composite brick production, composed of clay and 5 wt.% argan nut shell and designed as waste bricks (WB). Characterization of the adsorbent (WB) was conducted using several techniques such as XRD, XRF, FTIR, etc. Optimal conditions for the adsorption process of MG dye with WB were carried out, considering adsorbent dose (0.02–0.4 g/mL), pH (2–12), contact time (0–360 min), and MG dye concentration (20–210 mg/L). The obtained outcomes indicated that the optimal parameters for a dye concentration of 20 mg/L are an adsorbent dose of 0.15 g/mL, a pH of 10, and an adsorption time of 180 minutes. Furthermore, kinetic, isotherm, and thermodynamic adsorption have been evaluated. The results highlighted that the pseudo second-order and Langmuir model described accurately the adsorption process with an adsorption capacity of about 2.66 mg/g and 23.48 mg/g respectively. While the thermodynamic study conducted at four temperatures (298 K, 308 K, 318 K, 328 K) revealed that the adsorption process is spontaneous and endothermic in nature. Finally, a phytotoxicity test of malachite green dye solutions was carried out using wheat and lentil seeds confirming the treatment effectiveness of the adsorbent.

The purpose of this study is to use the hydrogen – diesel mixture in Audi/VW 1.9 TDI turbocharged CI engine equipped with dynamometer and examine the performance and emission indicators by comparing it with sole diesel mode. The recent diesel emission scandals because of manufacturers cheating the laboratory tests, have initiated the discussions about the sustainable and environmentally friendly diesel engines. The CI engine without major engine modifications was set to operate at two speeds of 1900 rpm and 2500 rpm. At each of speed, the experiment was conducted at three BMEP: 0.4 MPa, 0.6 MPa, and 0.8 MPa. The test engine was operated using diesel fuel with amounts of 10 l/min, 20 l/min, and 30 l/min of hydrogen gas, supplied with air into intake manifold before the turbocharger. Relatively low hydrogen fraction (max. 15.74%) has effect on diesel combustion process and performance indicators at the all range of BMEP. The in-cylinder peak pressure at both speeds of 1900 rpm and 2500 rpm was lower than that with pure diesel fuel, as the small amount of hydrogen shortens the CI engine ignition delay period and decreases the rate of pressure rise. The decrease of BTE noticed, and increase of BSFC was registered with low hydrogen fraction (hydrogen amounts of 10 l/min, 20 l/min). However, with increase of hydrogen amount to 30 l/min, the BTE increased and BSFC decreased to the level, which was lower than that at the pure diesel test. The supply of hydrogen positively effects on engine emissions: the smokiness, NOx, CO2, CO decreased, the only hydrocarbon increased. The effect of hydrogen fraction on the combustion and emission characteristics of the diesel - hydrogen mixture was validated by AVL (Anstalt für Verbrennungskraftmaschinen List) BOOST and analysed with presentations of the main limitations and perspectives.

Total internal reflection ellipsometry (TIRE) was utilized in its dynamic data acquisition mode to reveal the percentage of mercury present in an amalgam surface layer. In determining the optical constants of the amalgam film, the non-homogeneities of the formed surface layer were taken into account. The composition of the amalgam layer by percentage was determined using the EMA Bruggemann model for the analysis of the TIRE data. Regression results showed that amalgam layer consisted of mercury 16.00±0.43% and gold 84.00±0.43%. This real time TIRE analysis has shown that for these studies method can detect 0.6±0.4% of mercury on a gold surface, proving that this is a suitable optical technique for obtaining real time readouts. The structural analysis of SEM and AFM have shown that the amalgam layer had a dendritic structure, which formation was determined by the weak adhesion of the gold atoms onto its surface.

Sm3+-Doped and Eu3+/Sm3+-co-doped yttrium aluminium garnets (YAG) have been synthesized by an environmentally friendly sol–gel method. The results of X-ray diffraction (XRD) analysis of the powders sintered at 1000 1C showed the high purity of the end products with formation of monophasic compounds. The phase composition of the samples was also investigated by FTIR spectroscopy. The microstructural features of the polycrystalline samples were studied by scanning electron microscopy (SEM). The local environments of Eu3+ and Sm3+ activator ions in the garnet crystal structure compounds were investigated by nuclear magnetic resonance (NMR) and Raman spectroscopy. The luminescence properties were discussed using the results from photoluminescence (PL) study. The effective concentration of Sm in YAG was estimated and optimum ratio between two activators (Eu3+ and Sm3+) was analysed. The correlation between structural features and luminescence was determined. With a constant amount of samarium in Y2.9Sm0.1Al5O12:Eu garnet the strongest luminescence was determined in the sample with 1% of europium when characteristic excitation for europium was used.

Thermite welding of Cu–Nb microcomposite wires was investigated. Suitable compositions of thermite material and slag were determined from the equation of the exothermic combustion synthesis reaction. The phase compositions of the thermite mixture and slag determined by X-ray diffraction analysis correspond to those assessed from the equation. According to non-destructive radiographic testing, the joint structure does not have welding defects. Microstructural examination of the joint cross-section with scanning electron microscopy showed that the Cu–Nb wire retained its shape and microstructure and only a thin surface layer of wire was melted during welding. The difference in electrical resistances of the conductor and welded joint was below 20 %. The thermite joint can withstand a maximum load equal to 62.5 % of the load-bearing capacity of microcomposite conductor.

Glucose oxidase (GOx) is an enzyme, which is used for the development of enzymatic biofuel cells. Therefore in this research redox competition mode of scanning electrochemical microscopy (RC-SECM) was applied for the investigation of glucose oxidase (GOx) catalyzed reaction kinetics. The GOx was immobilized by glutaraldehyde on substrates of different electrical conductivity: (i) gold covered glass was used as conducting substrate and (ii) plastic poly(methyl methacrylate) was used as non-conducting substrate. Current vs distance dependencies were registered by SECM at different concentrations of glucose in the absence of redox mediator. The potential of 750 mV vs Ag/AgCl(3 M KCl) was applied to the microelectrode (ME), which was used as a probe in SECM, in order to register oxygen reduction current. Consumption of oxygen by the GOx based layer was evaluated according to principles determined by Michaelis-Menten kinetics. Apparent Michaelis constants KM(app.) were calculated from the dependencies of current vs glucose concentration. In both these cases the KM(app.) value increased when the distance between ME and enzyme modified surface was increasing from 10 to 30 mm, while the KM(app.) value decreased by increasing the distance from 30 to 60 mm.

The number of polymers successfully electrospun is increasing, and methods are needed predict the electrospinnability of polymers. With such methods, researchers should consider the polymer solution parameters and perform measurements in conditions that mimic the electrospinning process. A novel test method based on the electromechanical simulation of the fiber formation was developed. We formed fibers by mechanically dragging a conductive ball from the solution at an applied voltage and measuring the electrical current. The changes in the time of the electrical current (the ball current) reflect the fiber-formation process, which depended on certain polymer solution properties (e.g., viscosity, surface tension, liquid flow) and on the influence of charges on the fiber surface. The data obtained with the proposed method was compared with experimental data from electrospinning trials with the spinneret and bubble electrospinning. The results demonstrate that the ball-current method made it possible to predict the polymer solution behavior in the electrospinning process.