Высоковольтная деградация электродов, обусловленная электрохимической инжекцией в жидких диэлектриках

The results of experimental studies of the electrode degradation caused by electrochemical reactions under the action of high-voltage fields are presented. Under study were technical hydrocarbon and polymethylsiloxane (PMS) liquids, their solutions with iodine (I2) at chemically active (Cu) and indifferent (Ti) electrodes. It is shown that in hydrocarbons the Cu electrodes interact intensively with I2, and the cathodic degradation is more intense than the anodic one. The Ti electrodes do not degrade, but physical adsorption of I2 occurs on them in hydrocarbons, and a polymer film forms on them in PMS. The kinetics of degradation in time was studied.

Evaluation of Kinetic Pseudo-Order in the Photocatalytic Degradation of Oflaxicin

Ofloxacin is an extensively used efficient antibiotic. However, since it is a refractory pollutant, it is found in water sources, requiring methods to remove it from the environment. Advanced Oxidation Processes (AOPs) offer efficient alternatives since it yields complete degradation not achieved in adsorption or membrane processes. Kinetics of degradation process require monitoring the "pseu-do-order" of it to deliver evaluation of the proposed AOPs. Most studies assume ofloxacin degra-dation follows pseudo-first or -second order processes, whereas for full removal of refractory pol-lutants – lower pseudo-orders are required. This study presents a simple procedure to evaluate pseudo-orders of AOPs. Photolysis of 20 M ofloxacin follows pseudo-zero order, with half-life time (t1/2) of ~ 60 min. Very low TiO2 concentration in heterogeneous catalysis (0.2 mg L-1) has no in-fluence but increasing catalyst to 2.0 mg L-1 reduces t1/2 to 20 min, increasing pseudo-order to 0.8. Similar results are obtained with 2.0 mg L-1 H2O2 homogenous catalysis. Combining H2O2 with TiO2 reduces t1/2, but pseudo-order increases further (1.2). The conclusions are (1) ofloxacin can be ef-fectively degraded by both heterogenous and homogenous photocatalysis, (2) combined photoca-talysis yields higher pseudo-order, being less prone to achieve full removal, (3) analysis of specific pseudo-order in AOPs of refractory pollutants helps to further elucidate the efficiency of the process presented.

Effect of pH and concentration on the chemical stability and reaction kinetics of thiamine mononitrate and thiamine chloride hydrochloride in solution

Thiamine (vitamin B1) is an essential micronutrient in the human diet, found both naturally and as a fortification ingredient in many foods and supplements. However, it is susceptible to degradation due to heat, light, alkaline pH, and sulfites, among effects from other food matrix components, and its degradation has both nutritional and sensory implications as in foods. Thiamine storage stability in solution was monitored over time to determine the effect of solution pH and thiamine concentration on reaction kinetics of degradation without the use of buffers, which are known to affect thiamine stability independent of pH. The study directly compared thiamine stability in solutions prepared with different pHs (3 or 6), concentrations (1 or 20 mg/mL), and counterion in solution (NO3−, Cl−, or both), including both commercially available salt forms of thiamine (thiamine mononitrate and thiamine chloride hydrochloride). Solutions were stored at 25, 40, 60, and 80 °C for up to one year, and degradation was quantified by high-performance liquid chromatography (HPLC) over time, which was then used to calculate degradation kinetics. Thiamine was significantly more stable in pH 3 than in pH 6 solutions. In pH 6 solutions, stability was dependent on initial thiamine concentration, with the 20 mg/mL thiamine salt solutions having an increased reaction rate constant (kobs) compared to the 1 mg/mL solutions. In pH 3 solutions, kobs was not dependent on initial concentration, attributed to differences in degradation pathway dependent on pH. Activation energies of degradation (Ea) were higher in pH 3 solutions (21–27 kcal/mol) than in pH 6 solutions (18–21 kcal/mol), indicating a difference in stability and degradation pathway due to pH. The fundamental reaction kinetics of thiamine reported in this study provide a basis for understanding thiamine stability and therefore improving thiamine delivery in many foods containing both natural and fortified thiamine.

LC-UV and UPLC-MS/MS Methods for Analytical Study on Degradation of Three Antihistaminic Drugs, Ketotifen, Epinastine and Emedastine: Percentage Degradation, Degradation Kinetics and Degradation Pathways at Different pH

Evaluation of pH-dependent reactivity of drugs is an essential component in the pharmaceutical industry. Thus, the stability of three antihistaminic drugs, i.e., ketotifen, epinastine and emedastine, was tested, in solutions of five pH values, i.e., 1.0, 3.0, 7.0, 10.0 and 13.0, at high temperature (70 °C). LC-UV isocratic methods were developed to estimate percentage degradation as well as the kinetics of degradation. Generally, epinastine was shown to be the most stable compound with degradation below 14%. Emedastine was labile in all pH conditions, with degradation in the range 29.26–51.88%. Ketotifen was moderately stable at pH 1–7 (degradation ≤ 14.04%). However, at pH ≥ 10, its degradation exceeded 30%. The kinetics of degradation of ketotifen, epinastine and emedastine was shown as a pseudo-first-order reaction with the rate constants in the range 10−4–10−3 min−1 Finally, the UPLC-MS/MS method was applied to identify the main degradants and suggest degradation pathways. Degradation of ketotifen proceeded with oxidation and demethylation in the piperidine ring of the molecule. As far as epinastine was concerned, opening of the imidazole ring with formation of the amide group was observed. Unfortunately, no degradation products for emedastine were detected. The present results complete the literary data and may be important for both manufacturing of these drugs and their administration to patients.

Desorption and re-adsorption of PAHS on aircraft soot surface

Polycyclic Aromatic Hydrocarbons (PAHs) in aircraft soot are capable to distribute in the gas phase and particulate phase in chemical transformations in the atmosphere. The desorption of PAHs from the soot surface is a preliminary step in the study of the reactivity of particulate PAHs. The desorption kinetics of PAHs are measured from soot samples to determine desorption rate constants for different PAHs as a function of temperature and the binding energies between PAHs and soot. The kinetics of degradation of particulate PAHs were studied in the flow reactor. The soot samples previously deposited on a Pyrex tube are introduced into the reactor along its axis and the concentrations of PAHs adsorbed on soot are determined by the High-Performance Liquid Chromatography (HPLC) as a function of the desorption time. The results show a correlation between the size of PAHs and the thermodynamics of desorption: with the PAHs have the same number of carbon atoms, their energies of desorption are very similar and increase with this number. The activation energies EA and the number of carbon atoms in PAHs have a linear correlation. It is consistent with the additivity of the laws Van der Waals. The similarity between the activation energies of desorption of PAHs and the corresponding sublimation enthalpies is consistent with the similarity between the graphitic structure of soot and the structure of PAHs.

The effect of nonwoven structure on thermomechanical properties of feather waste reinforced polyester composite

Natural fibers offer good prospective as reinforcements in polymer composites due to their superior properties, they are preferred over synthetic fibers in various applications such as construction, automotive and aerospace. This experimental study emphasizes the effect of nonwoven structure on the mechanical, thermal and biodegradability properties of feathers nonwoven reinforced polyester composite. Vacuum molding method was adopted for manufacturing of the biocomposites with two contents of polyester resin (30% and 50%) and different composition of nonwovens. As a result, the morphological analysis revealed excellent compatibility and regular distribution of fiber in the polyester matrix. The thermal conductivity of manufactured composites varies considerably from 0.0378 W/(m•K) to 0.0778 W/(m•K) at 10°C. The origin of the variation of this property is due to differences in composition of nonwovens, densities and the percentage of the resin. After soaking for 240 h, the biodegradability test show that the kinetics of degradation of the composites decreased with the addition of nonwovens. The biodegradability rate was found between 62 to 92% depending on the sample nature. The mechanical results showed that the nonwoven structure clearly affected the performance of the composites. The results obtained from this study can be useful to develop new low cost, sustainable, light product and environmentally friendly materials.