Degradation Studies Research Articles

Study of adsorption-oxidative degradation of PAHs over organic–inorganic hybrid layered double hydroxides

Polycyclic aromatic hydrocarbons (PAHs) are well-known hazardous pollutants.

An experimental apparatus for the study of high-temperature degradation and solid-deposit formation of lubricants.

When exposed to high surface temperatures, engine lubricating oils degrade and may form solid deposits, which cause operational issues and increase shutdown time and maintenance costs. Despite its being a common issue in engine operation, the information available on the mechanics of this phenomenon is still lacking, and the experimental data and conditions must be updated to match the improvements in both lubricant stability and engine efficiency. To this end, an experimental apparatus has been developed to study the mechanisms that lead to the degradation and deposit formation of lubricants at high temperatures. The apparatus is designed to operate at pressures up to 69 bar, surface temperatures up to 650 °C, oil bulk temperatures up to 550 °C, and flow rates of <14 mL/min. In this apparatus, the oil is cycled through a heated test section, and deposits accumulate on the heated surface. The time required for deposits to start accumulating under the test conditions is determined based on the recorded temperature traces, and collected oil and deposit samples may be analyzed to determine changes in composition over time due to high-temperature exposure. The removable test section can be modified to accommodate different geometries, surface materials, and flow paths to adapt the instrument to a range of potential research directions. This paper presents the technical details of the new apparatus and the steps taken to characterize the experimental conditions. In addition, sample data are provided to show the unique capabilities of the new instrument, and an Arrhenius plot for Castrol Perfecto X 32 in the surface temperature range of 445-475 °C is presented as a demonstration of its use for quantifying the coking delay time. The new instrument detailed herein is the first such device to demonstrate a reliable, lab-scale technique for studying lube oil coke formation and deposition at temperatures and pressures of interest to power generation gas turbines.

Green Synthesis, Characterization, Biological Activities of CuO Nanoparticles and Their Photocatalytic Degradative Mechanistic Study of Methylene Blue Dye Using Mass Spectroscopy

Green Synthesis, Characterization, Biological Activities of CuO Nanoparticles and Their Photocatalytic Degradative Mechanistic Study of Methylene Blue Dye Using Mass Spectroscopy

Electrospun nylon 6/hyaluronic acid/chitosan bioactive nanofibrous composite as a potential antibacterial wound dressing.

Hyaluronic acid (HA) and chitosan (CS), as natural biomaterials, display excellent biocompatibility and stimulate the growth and proliferation of fibroblasts. Furthermore, nylon 6 (N6) is a low-cost polymer with good compatibility with human tissues and high mechanical stability. In this study, HA and CS were applied to modify N6 nanofibrous mat (N6/HA/CS) for potential wound dressing. N6/HA/CS nanofibrous composite mats were developed using a simple one-step electrospinning technique at different CS concentrations of 1, 2, and 3 wt%. The results demonstrated that incorporating HA and CS into N6 resulted in increased hydrophilicity, as well as favorable physical and mechanical properties. In addition, the minimum inhibitory concentration and (MIC) optical density techniques were used to determine the antibacterial properties of N6/HA/CS nanofibrous composite mats, and the results demonstrated that the composites could markedly inhibit the growth of Gram-positive bacteria Staphylococcus aureus and Gram-negative bacteria Escherichia coli. Because of its superior mechanical properties, substantial antimicrobial effects, and hydrophilic surface, N6/HA/CS at 2 wt% of CS (N6/HA/CS2) was chosen as the most suitable nanofibrous mat. The swelling, porosity, gel content, and in vitro degradation studies imply that N6/HA/CS2 nanofibrous composite mat has proper moisture retention and biodegradability. Furthermore, the N6/HA/CS2 nanofibrous composite mat was discovered to be nontoxic to L929 fibroblast cells and to even improve cell proliferation. Based on the findings, this research offers a simple and rapid method for creating material that could be utilized as prospective wound dressings in clinical environments.

Alkaline stability of pendant C2-protected poly(imidazolium)s

Synthesis of polycations with C2-sterically protected imidazolium pendant groups incorporated via an olefinic backbone accompanied by accelerated hydroxide-promoted degradation studies.

Stability Indicating RP-HPLC Method for the Estimation of Impurities in Esomeprazole Gastro-Resistant Tablets by AQbD Approach

Abstract Background: Esomeprazole (ESO) gastro-resistant tablets (40 mg) are sold under the brand name, Zosa, which effectively manages conditions associated with the overproduction of gastric acid, including peptic ulcer disease and Zollinger-Ellison syndrome. The present study quantifies impurities in esomeprazole using advanced analytical techniques known as analytical quality by design with high-performance liquid chromatography. Methods: Buffer selection (pH 7.6) and mobile phase composition (75:25 v/v) were optimized utilizing a YMC C18 column (150 mm × 4.6 mm; particle size, 3 μm) with a flow rate of 1.0 mL/min. The analyte was monitored with a UV/PDA detector at a wavelength of 280 nm. The stability-indicating nature of the method was confirmed based on forced degradation studies. The method validation was performed per ICH guidelines. Linearity, specificity, limit of detection, limit of quantification, precision, accuracy, solution stability, and robustness parameters were validated. Results: All validation parameters were within an acceptable range. Excellent linearity with correlation coefficient values &gt; 0.99 was achieved across the quantification limit. The solution stability study demonstrated no significant increase in percent impurity over a 24-h period. Analytical quality by design was instrumental in defining the design range for buffer pH and mobile phase composition, ensuring robust method performance. It was confirmed that 75% buffer solution, 25% acetonitrile, and pH 7.6 were the ideal conditions for determination of ESO impurities. Conclusion: The validated method provides a reliable tool for accurately quantifying impurities in ESO tablet formulations.

A comparative photocatalytic degradation study of Thymol blue dye over pristine ZnO and Er-doped ZnO

A comparative photocatalytic degradation study of Thymol blue dye over pristine ZnO and Er-doped ZnO

Analytical quality by design approach to develop an eco-friendly RP-HPLC method for estimation of irbesartan in chitosan polymeric nanoparticles: forced degradation studies and assessment of in vitro release mathematical modelling.

Irbesartan is an angiotensin converting enzyme blocker, primarily utilized for the management of hypertension and the mitigation of diabetic nephropathy progression. The present study introduces rapid, robust and environmentally sustainable reverse phase high performance liquid chromatography (RP-HPLC) validated under the analytical quality by design (AQbD) framework according to ICH guidelines. Utilizing a central composite design, the method's systemic optimization was achieved, ensuring reproducibility and accuracy. Chromatographic separation was accomplished utilizing an ethanol and sodium acetate buffer (60 : 40 v/v) isocratic mobile phase system on a zorbax sb C18 column, with a flow rate of at 0.6 mL min-1. Studies on forced degradation outlined stability of irbesartan and its degradation processes, enhancing our understanding of its chemical robustness under varied conditions. Complementing the green chemistry paradigm, the method's environmental impact was critically assessed, affirming its alignment with sustainability objectives. The validated method proved pivotal in determining the percent entrapment and loading efficiency of the formulated nanoparticles and holds potential for application in biological matrices. Furthermore, the encapsulation of IRB within chitosan nanoparticles was explored to assess release kinetics and enhance bioavailability. This study not only advances the analytical sciences by merging eco-friendly practices with method development but also broadens the applicative landscape of HPLC methodologies in drug delivery research.

"Zelena" RP-HPLC metoda za određivanje profila nečistoća amlodipina u tabletama

Increased awareness of nature preservation has encouraged the introduction of the green analytical chemistry (GAC) practice concepts concerning several important aspects, including sustainable development, environmental impact, and minimum waste. The aim of this research was to contribute to the implementation of this approach for the pharmaceutical industry while retaining the crucial aspects and strict requirements of quality control of medicines. Therefore, an ethanolbased, green and robust high-performance liquid chromatography (HPLC) method for the determination of related substances of amlodipine (AML) in film-coated tablets was developed and optimized using the Design of Experiments (DoE). The chromatographic separation was performed on an RP-select B column (250 x 4.0 mm, 5 mm), using a mixture of 0.04 M sodium dihydrogen phosphate monohydrate (pH 4.0) and ethanol (60:40 % v/v) as a mobile phase. The optimized conditions provided the separation of two specified impurities (impurity D and impurity F). The selectivity of the method was confirmed using forced degradation studies. The Analytical Eco-scale approach and AGREE metrics confirmed that the method conforms to the GAC principles. The validated method was successfully applied for the determination of related substances in three samples from the market, demonstrating the applicability of the method in routine analysis.

Not all silicon quantum dots are equal: photostability of silicon quantum dots with and without a thick amorphous shell.

Luminescent colloidal silicon quantum dots (SiQDs) are sustainable alternatives to metal-based QDs for various optical applications. While the materials are reliant on their photoluminescence efficiency, the relationship between the structure and photostability of SiQDs is yet to be well studied. An amorphous silicon (a-Si) shell was recently discovered in SiQDs prepared by thermally-processed silicon oxides. As a-Si is known as a source of defects upon UV irradiation, the disordered shell could potentially have an adverse effect on the optical properties of nanoparticles. Herein, the photostability of ∼5 nm diameter SiQDs with an amorphous shell was compared with that of over-etched SiQDs of equivalent dimensions that bore an a-Si shell of negligible thickness. An UV-induced degradation study was conducted by subjecting toluene solutions of SiQDs to 365 nm light-emitting diodes (LEDs) under an inert atmosphere for predetermined times up to 72 hours. The structure, composition, and optical responses of the exposed SiQDs were evaluated.

Synthesis and performance evaluation of zinc oxide tubes/alginate microfibre composites for photodegradation of methylene blue: a novel reporting approach.

This research investigates the efficacy of zinc oxide (ZnO) tubes in decontaminating polluted water using a substrate-free hydrothermal synthesis process for ZnO tubes. The synthesized tubes are impregnated into calcium alginate microfibres, strategically chosen for their high surface area to enhance photocatalytic degradation performance and for practical handling during decontamination and subsequent collection, thereby preventing secondary contamination. Structural and morphological analyses, conducted using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), thoroughly characterize the properties of the ZnO tubes and the composite material. The efficacy of this composite is demonstrated through the photocatalytic degradation of methylene blue (MB), as a representative organic pollutant, resulting in an 88% degradation of MB after 5 hours of irradiation by a sun simulator. Cyclic tests exhibit consistent degradation levels in the first four cycles (81-89%), followed by a subsequent decrease to 72% in the fifth cycle, coinciding with the breakdown of the microfibres into shorter fragments. Innovatively, this study introduces an approach to reporting photocatalytic degradation results, utilizing normalized pollutant concentration plotted against irradiated energy instead of time, as energy encompasses irradiated power, time, and surface area. This reveals that the 88% degradation of MB is achieved by irradiating the sample with an approximately 18 kJ. Additionally, a new metric, Specific Energy Efficiency (SEE), is introduced. It expresses the ratio of degraded pollutant mass to the mass of photocatalytic active material per unit of irradiated energy, with the maximum and cumulative SEE in this study being 1.044 μg g-1 J-1 and 326 ng g-1 J-1, respectively. This research not only contributes to the understanding of ZnO tubes' efficiency in polluted water decontamination but also introduces valuable insights for standardized reporting in photocatalytic degradation studies.

Liquid Chromatographic Peak Purity Assessments in Forced Degradation Studies: An Industry Perspective

This review article discusses scientific rationales and current best practices in the pharmaceutical industry for performing chromatographic peak purity assessments (PPA). These activities are associated with the development and validation of liquid chromatographic (LC) stability-indicating analytical methods applicable to regulatory submissions of small-molecule drug candidates. The discussion includes a comprehensive overview of the PPA-related regulatory and scientific landscape and common industry approaches to obtain PPA results, as well as the strengths and weaknesses of PDA-facilitated ultraviolet (UV) PPA and other PPA techniques.

Removal of metronidazole from simulated wastewater using Fe/C catalyst with a combination of heterogenous Fenton and ozonation

This study examined roles of iron oxide/porous carbon material (Fe/C) for removing metronidazole in simulated wastewater by adsorption and then followed by a degradation using advanced oxidation process (H2O2, O3 and combination of H2O2/O3). Fe/C was produced by an impregnation of iron oxide precursors during resorcinol-formaldehyde synthesis followed by pyrolysis at 800 °C. For comparison, blank carbon (without iron loading) was also synthesized. The properties of porous carbon were investigated by SEM-EDX and N2-sorption analyzer. Blank carbon and Fe/C featured the specific surface area of 755 m2g-1 and 394 m2g-1, respectively. The loading of iron oxide altered the pore structures of material. The adsorption isotherm data were followed by the Langmuir isotherm model with metronidazole uptake up to 46.07 mg g-1 and 39.97 mg g-1 at 30oC by Fe/C and blank carbon. The degradation study was then carried out with catalyst dosage of 0.1 g/100 mL solution and 120 min reaction time at 30 oC. It is noticeably that, the degradation of metronidazole was better when a combination of H2O2/O3 was employed, compared with an individual of H2O2 or O3. Regarding the stability, Fe/C maintained its high activity upon four consecutive runs.

Green Mediated Synthesis of Zinc Oxide Nanoparticles using Tamarind Bark Extract and their Applications in Textile Dye Degradation and Antimicrobial Studies

ZnO nanoparticles were synthesized using tamarind bark extract as a green reducing agent in alkaline medium. The tamarind bark solution acts both as a stabilizing and a reducing agent which regulates the size and the shape of the green synthesized zinc oxide nanoparticles. The progressive growth of ZnO nanoparticles was monitored by using UV-visible spectral studies. A sharp peak at 349 nm indicates the formation of spherical shaped zinc oxide nanoparticles. The size and shape of the ZnO nanoparticles were observed using scanning electron microscopy (SEM). The catalytic behaviour of a ZnO nanoparticle was studied for the degradation of textile dyes like methylene blue and Congo red and observed that the degradation reaction follows pseudo first-order kinetics with a rate constant k =0.0331 min-1, 0.0283 min-1 and 0.1175 min-1, 0.1167 min-1, respectively for ZnO nanoparticles at 50 µg and 100 µg. The antimicrobial activity of ZnO nanoparticles was also tested for various Gram-positive, Gram-negative bacteria and fungi in which higher zone of inhibition was observed for Gram-negative microorganism.

Cyclic-induced deformation and the degradation of Al-doped LLZO electrolytes in all-solid-state Li-metal batteries

This paper presents the results of a study of the mechanical degradation of Li-oxide garnet solid electrolyte, Li7La3Zr2O12 (LLZO) in all-solid-state lithium metal batteries. A coupled thermo-electro-chemo-mechanical model was used to analyze stress-strain distribution and cracking phenomena within the electrolyte. A combination of in-situ/ex-situ microscopic observations, strain mapping and finite element modeling were deployed to study the progressive deformation and cracking phenomena that occur as a result of electrochemical charging and discharging, thermal runaway, and joule heating phenomenon. The results show that strains induced during discharge cycles are more significant than those induced during charging phase. The accumulation of strains during charging and discharging is also shown to result ultimately in cracking that impedes Li ion transport, while accelerated electro-chemical degradation. The implications of these processes are discussed for the development of robust and durable all-solid-state batteries.

Development and validation of an HPLC method for the simultaneous estimation of salbutamol, theophylline and ambroxol in tablet dosage form

A simple, accurate and precise reverse phase high performance liquid chromatographic (RP-HPLC) method has been developed and validated for the simultaneous estimation of Salbutamol, Theophylline and Ambroxol in pharmaceutical formulations. The chromatographic separation was achieved on a Inertsil ODS-3V (250 × 4.6 mm, 5μ) column using a mobile phase consisting of phosphate buffer (pH 3.0): acetonitrile in the ratio of 55:45 v/v at a flow rate of 1 mL/min. Detection was carried out at 225 nm. The retention times for Salbutamol, Theophylline and Ambroxol were found to be 2.317, 3.808 and 5.863 min respectively. The proposed method was validated as per the ICH guidelines and was found to be linear in the concentration range of 0.5-3.0 μg/mL, 25-150 μg/mL and 7.5-45 μg/mL for Salbutamol, Theophylline and Ambroxol respectively with correlation coefficients greater than 0.999. The developed method was found to be precise, accurate, robust and specific. Forced degradation studies proved the stability-indicating capability of the developed HPLC method. The developed method can be successfully applied for the routine analysis of Salbutamol, Theophylline and Ambroxol in pharmaceutical dosage forms.

Assessment of desertification in the brazilian semiarid region using time series of climatic and biophysical variables

The municipality of Irauçuba, located in the Semiarid region of Ceará, Brazil, has faced the effects of desertification resulting from the scarcity of rainfall. This study aimed to assess the progression of desertification in the area from 2003 to 2020, using climatic and biophysical data collected during this period. We used supplementary data from automatic meteorological stations operated by the National Agency of Water and Basic Sanitation to determine the rainfall anomaly index of the historical series. Additionally, we performed annual scale validation of the CHIRPS data using statistical indicators such as Pearson Correlation Coefficient, Mean Error, Percentage BIAS, and Root Mean Square Error. Subsequently, we analyzed land cover and land use changes over the 17 years (2003-2020) in the municipality by processing CHIRPS, MODIS product (MOD16A2 and MOD11A2), and MapBiomas data in the Google Earth Engine digital platform and QGIS software. We analyzed land cover and land use changes using MapBiomas data. Finally, we analyzed the aridity index for the same 17-year period. The research findings revealed a significant correlation between rainfall and biophysical parameters, with the lowest aridity index of 0.255 observed between 2012 and 2014 and the highest of 0.464 between 2018 and 2020. The area's susceptibility to the desertification process was classified as high, which is consistent with the Semiarid climate of the region. The methodology employed during the research proved to be a sustainable technology of low economic cost and telling and easy access, which enabled the creation of a scientific contribution for future works in the region, besides being able to add knowledge for studies of environmental degradation.

THERMOGRAVIMETRIC STUDY OF THE FORMS OF MOISTURE BONDS IN KNEADING FLOUR SEMI-FINISHED PRODUCTS WITH THE ADDITION OF CRICKET FLOUR

Thermal analysis methods, primarily thermogravimetric analysis (TGA), play an important role in the study of phase transitions and degradation of active food components and auxiliary substances during heating or cooling. The most important areas of application of TGA in the food industry include the analysis of patterns of changes in the mass of the studied system during its heating or cooling due to the presence of phase transitions of the first kind and chemical reactions. In this work, a study of the change in mass of biscuit products during heating was carried out. The effect of replacing wheat flour with cricket flour in the amount of 5.0% on the structure of the resulting biscuit product compared to the control was determined. This study showed a change in the distribution of forms of connection of system water with dry substances of the system and, as a result, an expansion of the range of temperatures at which water evaporation from this sample took place. However, with a further increase in the amount of cricket flour in the recipe, which has an increased protein content, an increase in the part of the system water associated with the proteins of this raw material was observed. As a result, the range of temperatures at which water evaporation occurred from biscuit products with cricket flour in the amount of 10.0% and 15.0% decreased. It was noted in the work that the most acceptable functional and technological property of biscuit products is a wider range of forms of connection of system water with dry substances of such food products, since the presence of different forms of connection of water significantly determines the organoleptic indicators of finished products, terms and conditions its storage. The results obtained by the method of thermogravimetric analysis showed that, from the point of view of expanding the spectrum of forms of connection of system water with dry substances of the studied samples, the sample with the replacement of wheat flour with flour from crickets in the3 amount of 5.0% should be considered more acceptable.

Development and Validation of a New HPLC Method for the Estimation of Sulfamoxole in Bulk and Tablet Formulations

To quantify the sulfamoxole content in bulk as well as tablet formulation, a new isocratic RP-HPLC method was developed and then validated. Kromasil C18 column with a dimension of 250 X 4.6mm was used which was filled with a particle size of 5μ. A mixture containing CH3OH, CH3CN and H2O in the volume ratio of 55, 30 and 15 was used as a mobile phase at room temperature with an optimized flow rate of 1ml/min. UV detector was set at 241nm for sulfamoxole determination. The run time of the current method is ten minutes. Accomplished the forced degradation studies to understand the stability indicating nature of the current method. As per the current ICH guides (Q2R1), validation of the method was conducted.

Lyophilized platelet rich fibrin and gelatin incorporated bioadhesive bone cement composite for repair of mandibular continuity defects

Mandibular continuity defects stem from conditions such as malignancies, trauma, cysts, osteomyelitis and osteoradionecrosis, presenting significant challenges. If mandibular reconstruction fails, it can result in facial collapse, causing significant aesthetic and functional concerns for the patient. In the present study we developed a bio-adhesive Bone Cement (BC) enriched with lyophilised PRF and gelatin to enhance bone repair and induce regeneration. The developed BC consisted of a mixture of Tetracalcium Phosphate (TTCP) and O-Phospho-l-serine (OPLS) in addition to lyophilised Platelet Rich Fibrin (PRF) for sustained growth factor release and gelatin (GE) for improved cement resorption. It is primarily designed for in-situ application, conforming to the shape and size of the defect for effective bone repair and regeneration. The study evaluated four groups: (i) BC (control), (ii) BC-GE (control), (iii) BC-PRF, and (iv) BC-GE-PRF. All the four groups were characterised using FTIR, SEM and XRD. The mechanical studies of the prepared beads exhibited a significant increase in the compressive strength of the PRF loaded bone cement composites. In vitro degradation study of the beads over a 60-day period revealed a significantly higher percentage of bone cement resorption in the gelatin-incorporated groups, BC-GE (44 ± 0.5 %), and BC-GE-PRF (45 ± 2 %). The assessment of growth factor release (TGF-β and VEGF) using ELISA revealed a prolonged and sustained release of both growth factors over a 28-day period. In vitro studies were performed on human Dental Follicle Stem Cells (DFSCs) to assess cell attachment, proliferation, mineralisation and osteogenic differentiation. These studies clearly depicted that BC-PRF and BC-GE-PRF showed significantly greater proliferation of DFSCs. Furthermore, BC-PRF and BC-GE-PRF samples exhibited notably elevated expression of Runx2 and OPN (osteogenic markers), as well as a higher intensity of alizarin red stain (mineralisation). Therefore, it was concluded that PRF incorporated bioadhesive bone cement composites greatly enhance the cell attachment, proliferation, mineralisation and osteogenic differentiation of the DFSCs. Thus, the PRF and gelatin incorporated bone cement composites is expected to facilitate effective and faster bone regeneration and healing in a wide range of dental and maxillofacial defects.