Kinetics Of Oxidative Degradation Research Articles

Accelerated in vitro oxidative degradation testing of polypropylene surgical mesh.

Polypropylene (PP) surgical mesh had reasonable success in repair of hernia and treatment of stress urinary incontinence (SUI); however, their use for the repair of pelvic organ prolapse (POP) resulted in highly variable results with lifelong complications in some patients. One of several factors that could be associated with mesh-related POP complications is changes in the properties of the implanted surgical mesh due to oxidative degradation of PP in vivo. Currently, there are no standardized in vitro bench testing methods available for assessing the susceptibility to oxidative degradation and estimating long-term in vivo stability of surgical mesh. In this work, we adapted a previously reported automated reactive accelerated aging (aRAA) system, which uses elevated temperatures and high concentrations of hydrogen peroxide (H2 O2 ), for accelerated bench-top oxidative degradation testing of PP surgical mesh. Since H2 O2 is highly unstable at elevated temperatures and for prolonged periods, the aRAA system involves a feedback loop based on electrochemical detection methods to maintain consistent H2 O2 concentration in test solutions. Four PP mesh samples with varying mesh knit designs, filament diameter, weight, and % porosity, were selected for testing using aRAA up to 4 weeks and characterized using thermal analysis, Fourier-transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR) and scanning electron microscopy (SEM). Additionally, the oxidation index (OI) values were calculated based on the FTIR-ATR spectra to estimate the oxidative degradation and oxidation reaction kinetics of PP surgical mesh. The OI values and surface damage in the form of surface flaking, peeling, and formation of transverse cracks increased with aRAA aging time. The aRAA test method introduced here could be used to standardize the assessment of long-term stability of surgical mesh and may also be adopted for accelerated oxidative degradation testing of other polymer-based medical devices.

Green micellar stability-indicating high-performance liquid chromatography method for determination of rupatadine fumarate in the presence of its main impurity desloratadine: Oxidative degradation kinetics study.

A green micellar stability-indicating high-performance liquid chromatography method was developed for rupatadine fumarate determination in existence with its main impurity desloratadine. Separation was attained using Hypersil ODS column (150×4.6mm, 5μm), the micellar mobile phase consisted of 0.13M sodium dodecyl sulfate, 0.1M disodium hydrogen phosphate adjusted by phosphoric acid to pH 2.8 and 10% n-butanol. The column was maintained at 45◦ C and detection was carried out at 267nm. A linear response was achieved over the range of 2-160μg/ml for rupatadine and 0.4-8μg/ml for desloratadine. The method was applied for rupatadine determination in alergoliber tablets and alergoliber syrup without the interference of methyl paraben and propyl paraben present as main excipients. Rupatadine fumarate revealed pronounced susceptibility to oxidation; further study of oxidative degradation kinetics was carried out. Rupatadine was found to follow pseudo-first-order kinetics when exposed to 10% H2 O2 at 60 and 80°C and the activation energy was found to be 15.69Kcal/mol. At a lower temperature (40°C), degradation kinetics regression was best fitted as a polynomial quadratic relationship, thus rupatadine oxidation at a lower temperature tends to adopt a second-order kinetics rate. Oxidative degradation product structure was revealed using infrared and found to be rupatadine N-oxide at all temperature values.

Heterogeneous and Photosensitized Oxidative Degradation Kinetics of the Plastic Additive Bisphenol-A in Sea Spray Aerosol Mimics.

Plastics have become ubiquitous in the world's oceans, and recent work indicates that they can transfer from the ocean to the atmosphere in sea spray aerosol (SSA). Hazardous chemical residues in plastics, including bisphenol-A (BPA), represent a sizable fraction of consumer plastics and have been measured consistently in air over both terrestrial and marine environments. However, the chemical lifetimes of BPA and mechanisms by which plastic residues degrade with respect to photochemical and heterogeneous oxidation processes in aerosols are unknown. Here, we present the photosensitized and OH-initiated heterogeneous oxidation kinetics of BPA in the aerosol phase consisting of pure-component BPA and internal mixtures of BPA, NaCl, and dissolved photosensitizing organic matter. We found that photosensitizers enhanced BPA degradation in binary-component BPA + photosensitizer aerosol mixtures when irradiated in the absence of OH. OH-initiated degradation of BPA was enhanced in the presence of NaCl with and without photosensitizing species. We attribute this enhanced degradation to greater mobility and thus reaction probability between BPA, OH, and reactive chlorine species (RCS) formed through reaction between OH and dissolved Cl- in the more liquid-like aerosol matrix in the presence of NaCl. Addition of the photosensitizers in the ternary-component BPA + NaCl + photosensitizer aerosol led to no enhancement in the degradation of BPA following light exposure compared to the binary-component BPA + NaCl aerosol. This was attributed to quenching of triplet state formation by dissolved Cl- in the less viscous aqueous aerosol mixtures containing NaCl. Based upon measured second-order heterogeneous reaction rates, the estimated lifetime of BPA with respect to heterogeneous oxidation by OH is one week in the presence of NaCl compared to 20 days in the absence of NaCl. This work highlights the important heterogeneous and photosensitized reactions and the role of phase state, which affect the lifetimes of hazardous plastic pollutants in SSA with implications for understanding pollutant transport and exposure risks in coastal marine environments.

Ecofriendly stability-indicating UHPLC-PDA method for determination of the new influenza antiviral prodrug Baloxavir Marboxil; application to degradation kinetic studies and structure elucidation of the major degradation products using LC-MS

Implementation of green chemistry principles in analytical procedures is of great importance. Green analytical chemistry minimizes the dangerous impact on human beings and the environment that is the primary objective nowadays. In the proposed work, a well-developed, fully validated and ecofriendly stability indicating UHPLC coupled with photodiode array detector (PDA) method was established for the determination of Baloxavir Marboxil (BXM), a novel antiviral drug for the treatment of influenza A and B, in raw materials and pharmaceutical formulations. The method employed Inertsil ODS-3 C18 column to separate BXM from its forced degradation products using a mobile phase composed of 0.1% citric acid (pH 2.5 ± 0.05)-methanol (50:50, v/v), at a flow rate of 0.8 mL/min in an isocratic separation mode. BXM was monitored using diode array detector at 260.0 nm. BXM stability was inspected using various stress conditions as per ICH recommendations. The impact of acid, base hydrolysis, and oxidative stress conditions was greater on BXM in comparison to photo and thermal hydrolysis. The formed degradation products were injected into the mass spectrometer (MS) to elucidate their structures. The suggested pathways for degradation mechanisms were presented. Moreover, the proposed method was effectively utilized to study the degradation kinetics of acid, base and oxidative degradation of BXM. Additionally, four assessment tools were employed to evaluate the greenness of the developed method, namely; the National Environmental Method Index, the Analytical Eco-scale, Green Analytical Procedure tool, and the Analytical Greenness metric. Moreover, a comparative study of the method's greenness was conducted with the reported HPLC method and the results confirming that the suggested method is superior regarding the guidelines and principles of green chemistry. In addition to, having higher qualitative and quantitative scores in comparison to the reported method, and providing reliable and precise results of the method greenness.

The first validated stability-indicating HPLC/DAD method for quantitation of Vericiguat in its pharmaceutical formulation; Application to degradation kinetic studies

The stability of innovative drug formulations and the development of appropriate stability-indicating methods remain major focuses of recent pharmaceutical analysis. In the present study, an efficient stability-indicating HPLC-DAD technique has been described and validated for the determination of Vericiguat (VER); a novel oral soluble guanylate cyclase (sGC) stimulator used in heart failure. VER's stability under various stress conditions was examined. It was shown that VER was sensitive to alkaline, oxidative and thermal degradation. Mass spectrometry (MS) in electrospray ionization mode was performed to figure out the structure of the alkaline and oxidative degradation products. Efficient separation of VER and its induced degradation products was accomplished using isocratic elution mode on the Inertsil ODS-C18 column. The mobile phase composed of water: acetonitrile (70:30 v/v) with 0.1% O-phosphoric acid; pH was adjusted to 2.22 and a flow rate of 0.80 mL/min. VER was detected at 332 nm over a concentration range of 2.00–20.00 μg/mL. The retention time was 4.500 ± 0.005 min and the correlation coefficient was 0.9996. Following the International Conference of Harmonization's guidelines, the analysis was validated to be specific, fast, simple, precise and accurate for utilization in routine analysis and quality control of VER in its pharmaceutical formulation. Additionally, the suggested technique was expanded to investigate the kinetics of alkaline, oxidative and dry heat degradation.

Oxidative degradation of sulfafurazole drug by chromium trioxide in different acidic media: a kinetic and mechanistic study

Although antibiotics are fundamentally vital for treating human diseases, they became harmful to the ecosystem if they reach to the environment. Due to antibiotics are intensely vulnerable to oxidation, oxidation of antibiotics can be considered as a recognized tool for removal or degradation of antibiotics to save the humans and ecosystem. The existing research illuminates the kinetics of oxidative degradation of sulfafurazole antibiotic (SFZ) using chromium trioxide (CrO3) in both H2SO4 and HClO4 media. The reactions in both acidic media showed a 1: 1.33 ± 0.07 stoichiometry (SFZ: CrO3). The reliance of the rates of oxidation reactions on the reactants’ concentrations illuminated that the reactions were first order in [CrO3], whereas in [SFZ] and [H+], their orders were fractional-first and fractional-second, respectively. The rate of oxidation of SFZ in H2SO4 was discovered to be higher than that observed in HClO4. The oxidation rates were not influenced by the change in ionic strength (I) or dielectric constant (D). Addition of Cr(III) had not remarked effect on the rates. Free radical intervention tests were positive. The activation quantities were calculated then discussed. A conceivable mechanism of oxidation was anticipated. Furthermore, the rate-law expressions were also derived.

The fate of extracellular proteins and polysaccharides of waste activated sludge oxidative in aqueous and granular sludge phase upon degradation using Fe(II)-persulfate conditioning

Dissolved organic matter, particularly proteins (PN) and polysaccharides (PS) in extracellular polymeric substances (EPS), are regarded as the key factors influencing the dewaterability of waste activated sludge (WAS). An investigation was conducted on the treatment of WAS by Fe(II) activated sodium persulfate (SPS) to evaluate the kinetics of oxidative degradation of EPS in the aqueous and granular sludge phase, and to quantify the oxidation of SPS in aqueous and granular sludge phase in Fe(II)-SPS system. The WAS was divided into granular sludge (GS) and raw sludge filtrate (RSF) by filtration and elutriation. The PN and PS components underwent rapid degradation on treatment with Fe(II)-SPS, which followed pseudo-first-order kinetics for both GS and RSF. EPS protein was preferentially oxidatively degraded over EPS polysaccharide in the same phase system. However, the degradation rates of PN and PS in GS were 1/6 and 16 times higher than those in RSF, respectively. 23% of the sodium persulfate was consumed by all the substances in the bulk solution where the GS was located, reducing the amount of “effective free radicals” that degrade EPS in the system. The mass balance of PN and PS indicated that the use of Fe(II)-SPS conditioning has an obvious degradative effect on EPS, and PN and PS in WAS were oxidized by 76.2% and 58.3%, respectively. These findings provide mechanistic insight into the oxidation and competitive reactions of PN and PS between sludge aqueous and granular sludge phases, which is beneficial to the selection and optimization of sludge conditioning.

Generation of predictive models for oxidative degradation kinetics of dapagliflozin with the applications of DOE and stability indicating HPLC method

AbstractApplying kinetics principles to drug degradation studies helps in determine the expiration dates of drugs and formulations. An accurate, precise and sensitive stability‐indicating high‐performance liquid chromatographic method was developed and validated to study the degradation kinetics of Dapagliflozin (DGZ). DGZ was degraded under different stress conditions and degraded samples were chromatographed on C18 (150 mm × 4.6 mm, 5 µm) column, separated using solvent system acetonitrile and 0.01% triethylamine solution (pH 5 adjusted with orthophosphoric acid) in a ratio of 70:30 v/v and detected at 270 nm. The design of experiments (DOEs) was applied to study the degradation kinetics of DGZ in the oxidative medium. The effect of temperature and concentration of H2O2 on the order of reaction and % degradation was studied at three levels using a full factorial design. The linearity range for DGZ was 1–60 µg/mL (correlation coefficient = 0.9996) with an average recovery of 99.98%. The limit of detection (LOD) and limit of quantitation (LOQ) for DGZ were 0.07 and 0.22 µg/mL, respectively. Degradation of DGZ in the oxidative medium was found to follow first‐order kinetics. Contour plots have been generated to predict the degradation rate constant and % degradation of DGZ in different combinations of temperature and concentration of H2O2 using Design Expert software (Trial version).

Effect of torrefaction on thermal oxidative degradation kinetics of lignite using multi-distributed activation energy model

Torrefaction treatment is a promising method for lignite upgrading. However, its effect on the combustion characteristics has not been fully evaluated. In this study, the combustion characteristics of lignite and its upgrading samples by torrefaction were studied via non-isothermal thermogravimetric analysis. Results show that increasing the torrefication temperature decreases the volatile content while increasing the fixed-carbon in the fuels. The mole ratios of both H/C and O/C in the samples decreases as the torrefaction temperature increases. Torrefaction treatment significantly improves the combustion performance of lignite with a higher reactivity index S, and the optimum torrefaction temperature was determined to be 200 °C. The upgrading lignite by torrefaction at 200 °C has the lowest temperatures of Tf and Tp as well as the maximum corresponding DTG value. Furthermore, the results of three-parallel-DAEM model analysis results show that the activation energies corresponding to the three peaks are 176.1 kJ/mol, 186.5 kJ/mol and 221.7 kJ/mol, respectively, and that increasing torrefaction temperature had no significant effects on activation energies. With the torrefaction temperature increasing, the first standard deviation decreased while the third standard deviation increased.

1,2-Bis(4-Pyridyl) Ethane Catalysed Oxidative Conversion of D-Lactose to Lactobionic Acid by Cr(VI) in Aqueous Acetic Acid Medium: A Kinetic and Mechanistic Study

The kinetics of oxidation reactions and the investigations of the reaction mechanisms from the kinetic data have been always the more interesting in the chemical research and industrial applications. The kinetics of oxidation of sugars has been a subject of extensive research in recent years. The biological as well as the economic importance of carbohydrates is responsible for the great interest in the study of their bio- and physio -chemical properties. The kinetics of oxidative degradation of different sugars by metal ions including Cr (VI) has been studied under different conditions. Chomium (VI) compounds are powerful oxidants at low or neutral pH as well as Cr (VI) is a well-known oxidant in acetic media. Aim of our present investigation deals with oxidation of D-Lactose using Cr (VI) Oxidizing agent, Trimethylammonium fluorochromate [TriMAFC] which was carried out in protic solvent as a medium at 308 K in the presence of 1,2-bis(4-pyridyl)ethane as a catalyst . The oxidation of D-Lactose yields the corresponding aldonic acid and Cr3+ as final products. Lactobionic Acid (LBA) has been used for food and pharmaceutical applications. Thus the kinetics and mechanism of carbohydrates using Cr (VI) as oxidant, 1,2-bis(4-pyridyl)ethane as a catalyst is very important from biochemical and kinetic viewpoints. Our experimental studies showed that reaction progressed with first order kinetics with respect to [TriMAFC], [1,2-bis(4-pyridyl)ethane] and [H+] with the fractional Order dependence on [DLactose]. It was found that introduction of sodium perchlorate results in decrement of the reaction rate substantially. The rate constant increased with increase in the concentration of perchloric acid. Also, the rate of reaction decreases with increasing the concentration of acetic acid. For acrylonitrile, no polymerization occurs. The reaction was carried out at four different temperatures to determine the activation parameters. An appropriate mechanism was suggested based on the observed kinetic effects.

Degradation and Mineralization Study of Promecarb by Electro Fenton Process

Organic substances as pesticides, especially aromatic compounds are a major environmental concern. In the present work, solutions of Promecarb or 3-isopropyl-5-methylphenyl-N-methylcarbamate of pH = 3 have been degraded by electro Fenton process, using a volumic electrochemical reactor filled with carbon graphite. Effects of nature of material of cathode, initial concentration of insecticide and applied current on the kinetics of oxidative degradation and mineralization efficiency have been investigated. Kinetic analysis showed that the oxidation of Promecarb by hydroxyl radicals follows a reaction kinetic of pseudo first order. The absolute rate constant for Promecarb oxidation by hydroxyl radicals was determined as 10.88 × 10⁹ L mol^-1 s^-1 by competitive kinetics method and benzoic acid was used as reference compound. Mineralization of this pesticide by hydroxyl radicals consists in its transformation to mineral products. The evolution of the mineralization during Promecarb treatment by electro Fenton process was followed by analysis of Total Organic Carbon TOC. Thus, after 3 hours of electrolysis and at I = 800 mA, more than 50% of the organic carbon present in the solution is mineralized. Several degradation products were formed during its electro Fenton treatment. These intermediates were identified using High Performance Liquid Chromatography HPLC, Ionic Chromatography IC and Liquid Chromatography - Mass Spectrometry LC-MS. Based on identification of aromatic intermediates and carboxylic acids, a plausible Promecarb mineralization pathway is proposed. Also, we realized the measurement of the Biochemical Oxygen Demand BOD₅ of insecticide solution after treatment by electro Fenton process, to evaluate its biodegradability.

Rapid removal of fungicide thiram in aqueous medium by electro-Fenton process with Pt and BDD anodes

• Advanced oxidation processes (AOP) are effective for the wastewater treatment. • These processes are based to the production of power oxidizing hydroxyl radicals ( • OH). • Electro-Fenton (EF) process is one of the AOP widely used to treat water polluted by pesticides. • Constant rate for oxidation of thiram by • OH was found to be 5.54 × 10 9 M −1 s −1 . • Almost complete mineralization of thiram was reached by electro-Fenton with BDD anode. The electro-Fenton (EF) process was used to assess the electrochemical degradation of the fungicide thiram and its complete removal from water using an undivided electrolytic cell equipped with Pt or BDD anode and carbon felt cathode. Hydroxyl radicals, produced homogeneously in bulk solution from electrochemically generated Fenton's reagent ( • OH) and heterogeneously on the anode surface (M( • OH)) from oxidation of water, reacted with thiram leading to its fast oxidation. Oxidative degradation and mineralization kinetics were monitored by chromatographic analysis (HPLC) and total organic carbon (TOC) measurements. The electrochemical degradation of thiram by hydroxyl radicals followed a pseudo-first-order reaction kinetics with an absolute rate constant k abs(Thir) of 5.54 (±0.03) × 10 9 M −1 s −1 , determined by competition kinetics method. The TOC removal rate values were found significantly higher with BDD anode than Pt anode. Thus, almost complete mineralization (92%) of thiram solution was obtained when using BDD anode. These results highlight the major role of heterogeneous BDD( • OH) formed in the mineralization of thiram. The contribution of homogeneous • OH in mineralization of thiram was found relatively low due to its specific aliphatic structure. The efficiency of the EF process was evaluated by determining mineralization current efficiency and energy consumption per gram of TOC removed. Degradation by-products and inorganic ions, such as nitrate (NO 3 − ), nitrite (NO 2 − ), ammonium (NH 4 + ) and sulfate (SO 4 2 − ) formed during mineralization process, were identified by GC–MS and ionic chromatography analyses and a plausible mineralization pathway was proposed.

Auspicious water treatment approach. Oxidative degradation of fluconazole and voriconazole antibiotics by CrO3 in different acidic environments: Kinetics, mechanistic and thermodynamic modelling

The kinetics of oxidative degradation of two significant triazole antibiotics (A), viz. fluconazole (Flz) and voriconazole (Vcz), was examined using chromium (VI) oxide (CrVI) in sulfuric and perchloric acid environments. The oxidation reactions were followed spectrophotometrically at fixed ionic strength and at different temperatures. In both acidic environments, the oxidative degradations of the two examined antibiotics were acid-catalyzed. The kinetics of the oxidative degradations in both acids were first order concerning to [CrVI] and fractional-first orders with regard to [A] and [H+] during their alteration. The rates of oxidative reactions exhibited insignificant influences upon disparity of ionic strengths and dielectric constants of the reactions’ media. No intervention of free radicals was detected during the degradation reactions. Some activation methods like heat and addition of certain metal cations (Mg2+ & Ca2+) were also investigated. Under analogous experimental circumstances, the degradation rates in perchloric acid environment were slightly higher than those occurred in sulfuric acid one and the degradation rates of Flz were higher than those of Vcz. The believable oxidative degradation mechanism consistent with the kinetic outcomes was proposed. The derived rate-law expression was set to be in a good harmony with the acquired results. The activation and thermodynamic parameters were computed and discussed. This study announce a simple, safe and inexpensive promising procedure involving a double benefit for the environment and human health: degradation of Flz and Vcz drugs and transformation of the extremely toxic and carcinogenic CrVI oxide to a safe CrIII compound.

Kinetics of Aqueous Persulfate-Induced Oxidative Degradation of Heptafluorobutanoate, Pentafluoropropionate, and Trifluoroacetate

The kinetics of reaction of three fluorinated carboxylates (heptafluorobutanoate, pentafluoropropionate, and trifluoroacetate) with ammonium persulfate were studied by in situ 19F nuclear magnetic resonance and Raman spectroscopies in acidic aqueous solutions at temperatures between 323 and 363 K. Oxidative decarboxylation of the carboxylates yields a terminal perfluoroalkyl radical intermediate; the dominant reaction of this intermediate is recombination with hydroxyl radical followed by rearrangement to the acid fluoride and then hydrolysis, but other minor recombination products are observed. Arrhenius parameters for the initial decomposition of ammonium persulfate and the reaction of sulfate radical with the fluorinated carboxylates were derived. Heptafluorobutanoate and pentafluoropropionate were found to have similar reaction rates with sulfate radical, while the reaction with trifluoroacetate was 30–50% slower. Reaction rates did not show a strong dependence on pH in the range of 2 – 7.

Comparative Performance of Ten Electrodes in Electro‐Fenton Process for Removal of Organic Pollutants from Water

AbstractElectrochemical advanced oxidation processes (EAOPs), based on the in situ generation of the powerful oxidant, hydroxyl radical (.OH), have been developed for effective destruction of recalcitrant organic pollutants. Electrode materials used both as anode and cathode constitute one of the key parameters affecting the process efficiency. The electro‐Fenton (EF) process is one of the most powerful EAOPs in water/wastewater treatment. Inversely to other EAOPs, in the EF process, .OH can be generated both in the bulk solution (from reagents formed at the cathode) and on anode surface. Therefore, the role of anode/cathode couple is of great importance for this process. This study focuses on the comparative performance of ten electrodes (5 anodes, 5 cathodes) through more than fifty combinations during removal of the antibiotic p‐aminosalicylic acid (p‐ASA), taken as target pollutant. The following parameters were chosen for performance assessment: oxidative degradation kinetics, the time needed for complete destruction of p‐ASA, mineralization rate, mineralization current efficiency and energy consumption. The results obtained highlight the following sequence for the performance of anodes: BDD > PbO2 > Ti4O7 > Pt≈DSA, and that of cathodes: carbon sponge ≥ carbon felt > graphite > stainless steel≈titanium.

Kinetics of thermal oxidative degradation of poly (vinyl chloride) containing Ca and Sn at low temperature

Calcium metal soap and polyol (dipentaerythritol) additives are replacing or partially replacing organotin in poly(vinyl chloride) (PVC) heat stabilizers due to their low cost, nontoxicity and safety. Therefore, investigating the low-temperature thermal oxidative degradation of stabilized plasticized PVC from the source is essential for recycling. This work uses isothermal thermogravimetry to investigate the thermal degradation process and isothermal discoloration of PVC/calcium metal soap/dipentaerythritol/organotin soft products with excellent heat resistance at 453–503 K and under air atmosphere. The chemical kinetics method is used to fit a single equation model of mass loss and time during the thermal oxidation degradation of PVC, and the kinetic equation obtained is: −ln(1 − α) = 3.83 × 103exp (−6834.4/T)t. When the temperature is 453–503 K, the calculation results are basically consistent with the experimental data and are independent of the heating rate and temperature changes. In addition, the isothermal discoloration of different PVC materials was tested under air atmosphere at 468 K. The results show that when the test material is PVC/calcium metal soap/dipentaerythritol/organotin, the heat aging time to become completely blackened is longer than that of the blank sample, which indicates a strong interaction occurs between Sn, Ca and dipentaerythritol complexes and PVC molecules, inhibiting the release of hydrogen chloride. At the same time, in order to recover PVC and prevent it from carbonization, if the temperature is set to 486 K, the thermal oxidation degradation time of PVC should be less than 130 min.

Removal of p-aminobenzenesulfanilamide from water solutions by catalytic photo-oxidation over Fe-pillared clay

The catalytic photo-oxidation of p-aminobenzenesulfanilnamide (ABS) with hydrogen peroxide in the presence of Fe-pillared clay as heterogeneous catalyst has been investigated under UV-irradiation (λmax = 254 nm). Fe-pillared clay was synthesized by intercalating the iron polyhydroxycomplexes into the interlayer space of a natural layered aluminosilicate - montmorillonite and a subsequent heat treatment at 500 °C. The catalyst was characterized by chemical analysis, low temperature nitrogen adsorption and XRD. The kinetics of photocatalytic oxidative degradation of ABS in aqueous solutions under various experimental conditions was studied. The dependence of the photo-oxidation rate on such experimental factors as pH, hydrogen peroxide concentration and catalyst content was established. The conversion of ABS was 100% and the mineralization efficiency was 52.3% at optimal conditions. The intermediate products of ABS photo-oxidation identified by HPLC were a sulfanilic acid, benzenesulfonamide, benzenesulfonic acid, hydroquinone, pyrocatechol, benzoquinone and aliphatic acids. Fe-pillared clay remained highly active in three consecutive catalytic cycles without regeneration. The results of the study suggested that the heterogeneous photo-system «Fe-pillared clay/H2O2/UV» was effective in the oxidative degradation of aminobenzenesulfanilnamide. This system may be of interest for use in organic wastewater treatment processes.

Degradation Behavior of Polypropylene during Reprocessing and Its Biocomposites: Thermal and Oxidative Degradation Kinetics.

Non-isothermal thermogravimetric analysis (TGA) was employed to investigate the degradation of polypropylene (PP) during simulated product manufacturing in a secondary process and wood–plastic composites. Multiple batch mixing cycles were carried out to mimic the actual recycling. Kissinger–Akahira–Sunose (KAS), Ozawa–Flynn–Wall (OFW), Friedman, Kissinger and Augis models were employed to calculate the apparent activation energy (Ea). Experimental investigation using TGA indicated that the thermograms of PP recyclates shifted to lower temperatures, revealing the presence of an accelerated degradation process induced by the formation of radicals during chain scission. Reprocessing for five cycles led to roughly a 35% reduction in ultimate mixing torque, and a more than 400% increase in the melt flow rate of PP. Ea increased with the extent of degradation (α), and the dependency intensified with the reprocessing cycles. In biocomposites, despite the detectable degradation steps of wood and PP in thermal degradation, a partial coincidence of degradation was observed under air. Deconvolution was employed to separate the overlapped cellulose and PP peaks. Under nitrogen, OFW estimations for the deconvoluted PP exposed an upward shift of Ea at the whole range of α due to the high thermal absorbance of the wood chars. Under air, the Ea of deconvoluted PP showed an irregular rise in the initial steps, which could be related to the high volume of evolved volatiles from the wood reducing the oxygen diffusion.

Stability-Indicating HPLC method for estimation of omarigliptin in tablets – Oxidative and photolytic kinetics and degradation products formed under oxidative conditions

After the development and validation of a stability indicating analytical method for omarigliptin (OMG) using the HPLC method, a study of oxidative and photolytic degradation kinetics and identification of the main degradation products obtained after stress testing under oxidative conditions of this substance and the degradation pathway, was proposed. The separations were performed using an Agilent ZORBAX C8 250 × 4.6 mm column and the mobile phase consisted of 10 µM phosphate buffer and methanol 45:55 (v/v) with 230 nm wavelength detection. The HPLC method was validated according to official guides. It showed to be sensitive, accurate, precise, linear, robust and specific and was successfully used to determine the drug in its pharmaceutical formulation, to investigate the degradation kinetics of omarigliptin in the oxidative and photolytic medium and to get to know the reaction rate. Mass spectrometry was useful to identify the main oxidative degradation products and chemical analysis was used as a proposal to estimate the degradation routes of OMG.

Kinetic Evolution of Chalcopyrite Thermal Degradation under Oxidative Environment

The oxidative degradation kinetics of chalcopyrite have been studied by thermogravimetric analysis (TGA). The obtained data are necessary for the kinetic description of the flash fusion process, which can contribute to the optimization of the smelting process in copper extractive metallurgy. Activation energy (Ea) evolutions of the involved processes have been determined by several isoconversional methods; in this sense, the chalcopyrite oxidation processes could be adequately described, among studied models (E1641–16, Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose and Friedman), by the Kissinger–Akahira–Sunose kinetic model. Using this method, Ea and A values are found to be very dependent on the conversion. Under lower conversion levels, higher Ea and A values have been calculated with respect to that found for medium and higher conversion levels.