STUDIA CHEMIA - Issue no.1 / 2021 - Table of contents

Prof. Dr. Luminita Silaghi-Dumitrescu at her 70th anniversary
Editor in chief Studia UBB Chemia
The 9th of March 2021

On the occasion of Prof. Dr. Luminita Silaghi-Dumitrescu’s 70th birthday anniversary, the editorial board of Studia Universitatis Babes-Bolyai journal, at which she is serving as Editor in Chief for Chemia series since the year 2000, wish to honor her as an outstanding member of Babes-Bolyai University’s academic community (dean of the Faculty of Chemistry and Chemical Engineering in 2000-2007, vice-rector of Babes-Bolyai University in 2008-2011) with a lifetime of academic and scientific experience characterized by great devotion, integrity and morality. It has been our privilege to be the colleagues of Prof. Dr. Luminita Silaghi-Dumitrescu and we express the best wishes to her for a good health and every success in her future endeavors.
On behalf of the Editorial Board of Studia UBB Chemia
Castelia Cristea
Executive Editor

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In this work, the electrochemical studies were carried out to improve the purity of rough thallium. The results were obtained by the rough thallium refining through the anodic deposition of thallium oxide (Tl2O3), followed by its reduction to Tl+ by hydroxylamine and repeated electrolysis. At the same time, platinum anode material was replaced with glassy carbon material to reduce economic costs in production. It was found that the addition of ammonium thiocyanate after the dissolution of thallium oxide(III) in nitric acid promotes the inhibition of re-formation of thallium oxide at the anode, as well as more complete oxidation of trivalent thallium to a monovalent state. The thallium obtained in this way is characterized by a purity of 99.96%. Based on the obtained experimental data the principal schemes for obtaining pure thallium are proposed.

Keywords: thallium, glassy carbon, discharge ionization, refining, thallium oxide, reduction, polarity reversal, electrolysis

The aim of this study was preparation of one low cost and environmentally friendly material for wastewater treatment toward both inorganic and organic pollutants, based on natural zeolite from one of the largest zeolite deposits in Serbia (Zlatokop, Vranjska Banja). The idea was to integrate zero-valent bimetallic FeNi particles onto zeolite, based on liquid-phase reduction method. Obtained material zvFeNi@zVB showed good sorption properties with high removal efficiency under the investigated conditions toward inorganic (M(II) heavy metal ions Cu, Cd, Pb, Zn) and organic (dyes Reactive Blue 19 and Methylene Blue) pollutants. Compared with pure FeNi material, modified zeolite (zvFeNi@zVB) showed better sorption properties and “faster clean” water from evaluated pollutants.

Keywords: low cost-, environmentally friendly- material, bimetallic zerovalent FeNi particles, zeolite, wastewater treatment.

Silicon-based mesoporous materials have become increasingly used in various fields as industry, medicine, environment, etc. We developed five samples in mild conditions, at room temperature, of mesoporous silica by substituting tetra-ethyl-orthosilicate (TEOS) with different amount of sodium silicate (Na2Si3O7) precursor by maintaining the total ratio for SiO2 at 1.8g. Acetic acid (CH3COOH)/hydrochloric acid (HCl) aqueous solution was used as catalyst keeping the pH at 5. The samples were examined by FT-IR, Raman Spectroscopy, Scanning Laser Confocal Microscopy and Nitrogen Adsorption-Desorption Isotherms. The results indicate enhancements when Na2Si3O7 was added. Sample with TEOS and lowest amount of Na2Si3O7 displayed the best surface area value (750 m2/g) and total pore volume (0.63 cm3/g). Highest amount of Na2Si3O7 in the sample (P5) has considerably influenced the roughness of the material.

Keywords: Na2Si3O7, TEOS, mesoporous materials, roughness, porosity

The behavior of high-silicon cast irons in AC polarization was studied in terms of elementary composition and morphological structure to find suitable materials for inert anodes used in various electrochemical processes with polarization in AC or DC with superimposed AC signal. Experimentally, through optical emission spectrometry, XRD, and SEM-EDAX techniques, the investigated samples' morphology and composition were determined. The behavior in AC polarization at Jac current density between 1 and 300 A/m2 was assessed through electrochemical and gravimetric methods. The results showed that the mass losses in AC polarization at Jac less than 10 A/m2 are insignificant (below 8.5x10-5 g/Ah), and at Jac 100 A/m2, samples with a Si content higher than 8% were below 3.75x10–4 g/Ah (approx. 150x less than in the case of similar anodically polarized materials in DC). It was also noted that the main processes that occur in the AC polarization of silicone cast iron in aqueous media consist of the anodic oxidation of iron with the formation of iron oxide films and the anodic dissolution with the formation of soluble compounds of some metals from the composition of silicone cast irons (Mn, Cr, Cu, etc.). Furthermore, these anodic processes are coupled with the cathodic processes, which in natural environments consist most probably in reducing the dissolved oxygen.

Keywords: cast iron, corrosion, AC polarization, mass loss, inert anodes

From past years, the demand of clean water has been increased due to shortage of portable fresh water. Parallel, the use of composite materials for the catalytic degradation of pollutants particularly dyes in industrial effluents has attracted good attention. In this work, bismuth doped ZnO/MoO2 composites were synthesized by co-precipitation method using bismuth chloride, zinc sulphate and sodium molybdate as starting precursors. The structural/morphological studies of these composites were accomplished by UV–Visible spectroscopy, Fourier Transform Infrared Spectroscopy and Scanning Electron Microscopy. The catalytic activity of the bismuth doped ZnO/MoO2 composites was investigated by degradation of methylene blue (MB) dye. The degradation of MB was observed to be 75% at only 45 sec and enhanced catalytic activity was observed by increasing Bi content in synthesized composites.

Keywords: ZnO/MoO2 composites; Bismuth doping; Methylene blue; Catalytic degradation

Bentonite is a clay mineral whose chemical structure can be easily modified by pillaring process for introduction of various cations such as aluminum, chromium, nickel, zinc etc. fact that conducts to attractive and versatile products suitable for diverse applications going from gas separation to pollutants removal or excipients for food industry for example. This paper deals with the synthesis of aluminum pillared bentonite based on a process involving bentonite suspension and pillaring agent preparation, bentonite intercalation and calcination. The raw material and the obtained products were analyzed by X-ray diffraction, nitrogen adsorption-desorption technique, ammonia-temperature programmed desorption and scanning electronic microscopy. Three ratios of aluminum cations – amount of bentonite (5 mmol/g, 12.5 mmol/g, 20 mmol/g) and three calcination temperatures (300 °C, 400 °C, 500 °C) were used according to a Response Surface Methodology program aiming to attain the highest interlamellar distance, specific surface area and surface acidity. Collected data were fitted to second order polynomial equations. An aluminum cation – bentonite amount ratio of 12.5 mmol/g and a calcination temperature of 400 °C were found as appropriate conditions for bentonite pillaring process. Tests conducted on these settings showed that mathematical models were in good agreement with the experimental values presenting a high degree of accuracy.

Keywords: bentonite, mathematical modelling, pillared clay, Response Surface Methodology

In this paper is presented a simple possible model which can explain the thermal explosion problem, the existence of an induction period and a sudden rapid temperature rise. As state variables used for modeling are: the pressure, the temperature and the concentration. The time evolutions of these state parameters are analogically modeled using ordinary differential equations. The numerical simulations of the obtained model are made in Matlab/SimulinkTM. The validation of the model is realized by comparison between experimental data and simulation results, presenting a good accuracy.

Keywords: thermal explosion, analogical modeling, numerical simulation, state Parameters

The aim of this paper was the synthesis of some citric esters with potential biodegradable properties and their use as plasticizers or PVC lubricants. Citric esters were obtained in a bubbling column-type esterification reactor, using citric acid as the acid component, and monoethylene glycol, n-butanol, t-butanol as the hydroxyl components. The esters were characterized by FT-IR spectrometry to reveal the existence of the esteric bonds. Esters present a good thermal stability. The TCS criterion shows a level of compatibility specific to secondary plasticizers. There is a similarity between the values of the tested compounds and the standard DOF regarding hardness. The breaking strength are better and the values of elongation at break are close to the considered standards. The esters prove a very good migration towards rubber and are comparable to tribological fluids. The four balls test showed that without additives and at a test level of 40 daN for 60 min time period, the diameters of the wear spot are generally very good, being in the range of 0.43-0.62 mm. By adding oils, their behavior improves. The welding load values are also good (200-220 daN). The synthesized citrus esters have clear characteristics of plasticizers and/or lubricants for PVC.

Keywords: citrus esters, bubble column reactor, plasticizer, lubricant

This study includes the most important physico-chemical parameters monitoring of the shallow wells from Sândominic commune, Harghita County, Romania, in order to establish if the water sources can be used as drinking water. The pH, dHT, acidity, alkalinity, CCO-Mn, NO2-, NO3- , NH4+, Cl- and Fetotal parameters were determined using appropriate standard methods and compared with allowable values for drinking water, according to Romanian legislation. Based on the determined parameter values, most of the samples were characterized by a moderate or high mineralization (288-980 mg/L), and for some of them there was a contamination with organic substance and nitrate ions.

Keywords: groundwater, monitoring, shallow wells, pollution

The present study was aimed to assess the surface water pollution sources in a semiarid region of Algeria by characterizing the physicochemical quality of the water of the main Wadis of the El Hodna watershed and determining the water quality index according to the uses of drinking water, irrigation, and aquatic life. This index is calculated in purpose to communicate information on the water quality for concerned citizens and policymakers. The calculated WQI values of the studied Wadis were higher than 100, which indicates that the waters of the El Hodna watershed are unfit for human consumption, irrigation, and aquatic life. The obtained results have shown that different types of pollution (industrial, domestic and agricultural) affect the waters of the El Hodna watershed, which lead to degrade the water quality of this aquatic ecosystem and consequently its biodiversity and public health.

Keywords: Water quality index, surface water quality, El Hodna watershed, Pollution, semiarid region, Algeria.

Microbial degradation is to be considered a perspective solution in the elimination of microporous organic compounds in the environment. Various studies attest to the Pseudomonas putida species as being capable of aerial biodegradation of numerous organic compounds including chlorinated aromatic compounds. The aim of this study was to demonstrate the ability of Pseudomonas putida to grow on various organic substrates, being a possible candidate for dehalogenation of various chlorinated organic compounds Water samples were prepared by contamination with a solution containing 1,1,1-trichloroethane, 1,1,1,2-tetrachloroethane, trichloromethane and tetrachloromethane. The concentrations of halogenated organic compounds, before and after inoculation, were determined by gas chromatographic method. The results obtained showed the reduction, in the presence of Pseudomonas putida, of various halogenated organic compounds such as 1,1,1- trichloroethane, 1,1,1,2-tetrachloroethane, trichloromethane and tetrachloromethane with values ranging from 23% to 45% over a time interval of 120 days. The present study demonstrates the ability of Pseudomonas putida to grow on various organic substrates, being a possible candidate for dehalogenation of various types of chlorinated organic compounds.

Keywords: biodegradation, dehalogenation, groundwater, halogenated organic compounds, Pseudomonas putida

The article reports the AMS (accelerator mass spectrometry) radiocarbon dating results of the Big baobab of Outapi, which is the largest African baobab of Outapi, Namibia. The investigation of this monumental baobab revealed that it consists of 8 fused stems, out of which 4 are false stems. The Big baobab exhibits a closed ring-shaped structure. Three stems build the ring, which is now incomplete due to previous damage to the false cavity. Three wood samples were collected from the false cavity and from the longest false stem. Seven segments were extracted from the samples and dated by radiocarbon. The oldest investigated sample segment had a radiocarbon date of 820 ± 17 BP, corresponding to a calibrated age of 780 ± 10 calendar years. According to dating results, the Big baobab of Outapi is 850 ± 50 years old.

Keywords: AMS radiocarbon dating, Adansonia digitata, dendrochronology, age determination, false cavity, multiple stems

A new and efficient immobilization method of phenylalanine ammonia-lyase was obtained using hydroxyapatite (HAP) and hydroxyapatite - carbon nanotube, gelatin and chitosan - composites (HAP-CNT, HAP-GEL and HAP-CS) as support material. HAP and HAP composites were characterized by transmission electron microscopy (TEM), laser diffraction particle size analyzer and XRD measurements. The obtained nanobioconjugates were tested in the ammonia elimination reactions from L-phenylalanine (L-1). The reusability and the time-course profile of the immobilized enzyme preparation was also tested. While the biocatalyst obtained by using HAP-CS-15 as support material provided the highest conversion rate in the ammonia elimination reaction from L-1 (98,1% compared to 98,5% obtained using the non-immobilized enzyme), the most stable biocatalyst proved to be HAP-PAL, which maintained more than 80% of its initial activity even after 5 cycles of reuse.

Keywords: hydroxyapatite, composites, carbon nanotubes, gelatin, chitosan, phenylalanine ammonia-lyase, immobilization, ammonia elimination

A new high-throughput, inexpensive and selective LC-MS method for determining fenbendazole, albendazole and albendazole sulfoxide from human and ovine plasma was developed and validated in accordance with current guidelines in bioanalysis. Analytes (fenbendazole, albendazole, albendazole sulfoxide) and internal standard (fluconazole) were separated on a Gemini NX-C18 analytical column in reversed phase chromatography in gradient elution using mobile phase composed of acetonitrile and aquenous 0.2% formic acid with a flow rate of 0.6 mL/min. After positive electrospray ionization analytes were detected in the mass spectrometer in selected reaction monitoring mode, monitoring fragment ion m/z 268.05 from m/z 300.08 for fenbendazole, ion m/z 234.07 from m/z 266.09 for albendazole, ion m/z 240.04 from m/z 282.09 for albendazole sulfoxide and ion m/z 220.06 from m/z 307.60 for fluconazole. Sample preparation was performed using protein precipitation. Validation of the analytical method was performed with respect to selectivity, stability, linearity (r>0.9901), precision (RSD<12.9%) and accuracy (bias<12.7%) over the concentration ranges of 5-250 ng/mL for each analyte (lower limit of quantification was 5 ng/mL for all analytes). The analytical method is simple, versatile and suitable for bioanalysis of these azole anthelmintic drugs from human and ovine samples, and applicable in pharmacokinetic studies involving fenbendazole and albendazole.

Keywords: fenbendazole, albendazole, pharmacokinetics, bioavailability, LC-MS