Preconcentration and determination of chromium in water with flame atomic absorption spectrometry by thiourea-formaldehyde as chelating resin

Thiourea-formaldehyde chelating resin is synthesized simply and rapidly from thiourea and formaldehyde by condensation polymerization and characterized by IR spectra and studied for the preconcentration and determination of trace Cr(III) ion from solution samples. The optimum pH value for sorption of the metal ion was 6.5. The sorption capacity of resin for Cr(III) was determined. The chelating resin can be reused for 20 cycles of sorption-desorption without any significant change in sorption capacity. A recovery of 96% was obtained for the metal ion with 0.5M HNO₃ as eluting agent. The equilibrium adsorption data of Cr(III) on modified resin were analyzed by Langmuir, Freundlich and Temkin models. Based on equilibrium adsorption data the Langmuir, Freundlich and Temkin constants were determined as 0.016, 0.040 and 0.074 at pH 6.5 and 20°C. The method was applied for chromium ion determination from river water sample.     

Silver-zinc oxide nanocomposite: From synthesis to antimicrobial and anticancer properties

A green method by Verbascum speciosum was used to synthesize zinc oxide nanoparticles (ZnO NPs). ZnO NPs were coated with silver to synthesize Ag–ZnO nanocomposite (NCs). The physicochemical properties of Ag–ZnO NCs were analyzed by Fourier-transform infrared spectroscopy (FTIR), powder X-ray diffraction (PXRD), field emission scanning electron microscope (FESEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential. The FTIR indicated the peak of Zn–O vibration and some hydroxyl and carboxyl groups. PXRD analyses confirmed the synthesis of ZnO NPs and Ag–ZnO NCs. Due to the size of the crystallite obtained from PXRD, solid-phase sizes (from FESEM and TEM images), and dynamic sizes from DLS, agglomeration was observed. The Ag–ZnO NCs showed a negative charge surface (?49.3 mV). Ag–ZnO NCs had a high antibacterial activity towards two most important infectious bacteria (i.e., Escherichia coli and Staphylococcus aureus) and anticancer activity against human liver-carcinoma cells (HepG2). Later, it depended on time and concentration of Ag–ZnO NCs. The cytotoxicity properties of Ag–ZnO NCs were also studied against NIH-3T3 as a normal cell, where the results verified the lower cell toxicities of nanocomposite than the HepG2.     

Fast-settling CMOS Op-Amp with improved DC-gain

In this paper a new operational amplifier is presented based on the conventional folded cascode Op-Amp structure. A new method of positive feedback is used to increase DC-gain. Contrary to conventional designs this method does not decrease the speed of the folded cascode Op-Amp in the closed loop configuration. Simplicity is the other advantage of the proposed Op-Amp in comparison with the conventional structures. In this method, DC-gain improves by adding only two devices to the folded cascode structure. The additional devices neither decrease the bandwidth nor increase the power consumption, to a great extent. Proposed structure has been simulated by HSPICE software using level 49 parameters (BSIM3v3) in a typical 0.35 μm CMOS technology. HSPICE simulation confirms the theoretical estimated improvements.     

Molecular simulation,experiments and modelling of single adsorption capacity of 4A molecular sieve for CO2–CH4 separation

Monte Carlo simulation of CO₂ and CH₄ adsorption on zeolite 4A is carried out in grand canonical Monte Carlo (GCMC) simulation. LTA framework was used to reproduce the structure of zeolite 4A. A comparison between the structure and properties of this zeolite and 13X, ZSM-5, 4A and 3A is performed and the results are included in the article. Universal force field was used for calculation of intermolecular forces. Our own experiments were also carried out to reinvestigate the simulation results. Ewald summation method was used for calculating electrostatic forces and atom based method was applied for van der Waals forces. The simulation results show good agreement with experimental results. Highest CO₂ adsorption capacity of zeolite 4A was in good agreement with experiments at the same pressure ranges, and was found to be 3.17 mol/kg from GCMC. Isosteric heat of adsorption was calculated to find the heat released during adsorption of each gas. Finally simulation results were fitted to four isotherms to find the best fit.     

Experimental study of combustion characteristics of nanoscale metal and metal oxide additives in biofuel (ethanol)

An experimental investigation of the combustion behavior of nano-aluminum (n-Al) and nano-aluminum oxide (n-Al₂O₃) particles stably suspended in biofuel (ethanol) as a secondary energy carrier was conducted. The heat of combustion (HoC) was studied using a modified static bomb calorimeter system. Combustion element composition and surface morphology were evaluated using a SEM/EDS system. N-Al and n-Al₂O₃ particles of 50- and 36-nm diameters, respectively, were utilized in this investigation. Combustion experiments were performed with volume fractions of 1, 3, 5, 7, and 10% for n-Al, and 0.5, 1, 3, and 5% for n-Al₂O₃. The results indicate that the amount of heat released from ethanol combustion increases almost linearly with n-Al concentration. N-Al volume fractions of 1 and 3% did not show enhancement in the average volumetric HoC, but higher volume fractions of 5, 7, and 10% increased the volumetric HoC by 5.82, 8.65, and 15.31%, respectively. N-Al₂O₃ and heavily passivated n-Al additives did not participate in combustion reactively, and there was no contribution from Al₂O₃ to the HoC in the tests. A combustion model that utilized Chemical Equilibrium with Applications was conducted as well and was shown to be in good agreement with the experimental results.     

A new high-speed, high-resolution open-loop CMOS sample and hold

A new open loop, high resolution CMOS sample and hold (S/H) circuit is introduced in this article. This circuit is constructed based on a new method which leads to a great reduction in dependency of the storing charge of the holding capacitors to the charge injection of transistors. It is a combination of dummy switches and auxiliary capacitors in order to decrease the voltage spikes that are produced during the sampling mode. Due to the high linearity feature of our proposed design in comparison with previous works, it is reached to a great improvement in signal to noise and distortion ratio up to about 15 dB and it’s ENOB is equivalent with about 16 bits. Another advantages of our proposed design are it’s lower power dissipation and it’s high input voltage range. Also the optimum functionality of our proposed circuit does not damaged by the threshold voltage’s variations in different corners. As our proposed S/H circuit has been designed in open loop structure, it is suitable for high speed applications.