Browsing by Author "Waclawek, Stanislaw"
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- ItemA new method for assessment of the sludge disintegration degree with the use of differential centrifugal sedimentation(TAYLOR & FRANCIS LTD, 2-4 PARK SQUARE, MILTON PARK, ABINGDON OR14 4RN, OXON, ENGLAND, 2019) Silvestri, Daniele; Waclawek, Stanislaw; Goncukova, Zuzanna; Thekkae Padil, Vinod Vellora; Grubel, Klaudiusz; Černík, MiroslavA novel method for assessing the disintegration degree (DD) of waste activated sludge (WAS) with the use of differential centrifugal sedimentation method (DCS) was shown herein. The method was validated for a WAS sample at four levels of disintegration in the range of 14.4-82.6% corresponding to the median particle size range of 8.5-1.6 mu m. From the several sludge disintegration methods used (i.e. microwave, alkalization, ultrasounds and peroxydisulfate activated by ultrasounds), the activated peroxydisulfate disintegration resulted in the greatest DD 83% and the smallest median particle size of WAS. Particle size distribution of pretreated sludge, measured by DCS, was in a negative correlation with the DD, determined from soluble chemical oxygen demand (SCOD; determination coefficient of 0.995). Based on the obtained results, it may be concluded that the DCS analysis can approximate the WAS disintegration degree.
- ItemBenchtop 19F NMR spectroscopy as a practical tool for testing of remedial technologies for the degradation of perfluorooctanoic acid, a persistent organic pollutant(John Wiley and Sons Ltd, 2020) Heerah,Kavi; Waclawek, Stanislaw; Konzuk, Julie; Longstaffe, James G.The development of effective remedial technologies for the destruction of environmental pollutants requires the ability to clearly monitor degradation processes. Nuclear magnetic resonance (NMR) spectroscopy is a powerful tool for understanding reaction progress; however, practical considerations often restrict the application of NMR spectroscopy as a tool to better understand the degradation of environmental pollutants. Chief among these restrictions is the limited access smaller environmental research labs and remediation companies have to suitable NMR facilities. Benchtop NMR spectroscopy is a low-cost and user-friendly approach to acquire much of the same information as conventional nuclear magnetic resonance (NMR) spectroscopy, albeit with reduced sensitivity and resolution. This paper explores the practical application of benchtop NMR spectroscopy to understand the degradation of perfluorooctanoic acid using sodium persulfate, a common reagent for the destruction of groundwater contaminants. It is found that Benchtop 19F NMR spectroscopy is able to monitor the complete degradation of perfluorooctanoic acid into fluoride; however, the observation of intermediate degradation products formed, which can be observed using a conventional NMR spectrometer, cannot be readily distinguished from the parent compound when measurements are performed using the benchtop instrument. Under certain reaction conditions, the formation of fluorinated structures that are resistant to further degradation is readily observed. Overall, it is shown that benchtop 19F NMR spectroscopy has potential as a quick and reliable tool to assist in the development of remedial technologies for the degradation of fluorinated contaminants.
- ItemBioplastic Fibers from Gum Arabic for Greener Food Wrapping Applications(AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2019-03-18) Padil, Vinod V. T.; Senan, Chandra; Waclawek, Stanislaw; Černík, Miroslav; Agarwal, Seema; Varma, Rajender S.The fabrication of bioplastic fibers from gum arabic (GA), a natural tree gum exudate, is described via the electrospinning method. The enrichment in surface properties of this bioplastic fiber was evaluated by methane plasma and gamma-ray irradiation treatments. The fibers with their modified forms, both treated and untreated, were investigated by various characterization techniques such as scanning electron microscopy, atomic force microscopy, X-ay diffraction and attenuated total reflectance Fourier transform infrared spectroscopy, thermogravimetric analysis, BET surface area, water contact angle, and tensile strength measurements. A switchable hydrophobic/hydrophilic functionality on GA bioplastic fibers was established through CH4 plasma and gamma-ray irradiation treatments; higher water contact angle (130 degrees) was observed in GA bioplastic fibers that had undergone methane plasma treatment. However, the untreated and gamma-ray-irradiated GA bioplastics exhibited hydrophilic behavior. The comparative properties such as water resistance, antioxidant potency, gas barrier attributes, antibacterial effectiveness, biodegradability and food contact migration through the GA bioplastic fibers (untreated, plasma treated, and gamma-ray-irradiated) were assessed. The present work, in contrast to other existing bioplastic fibers, has the potential of becoming a viable option in greener food packaging as well as in environmental and medically related products based on tree gums.
- ItemChemical oxidation and reduction of hexachlorocyclohexanes: A review(2019) Waclawek, Stanislaw; Silvestri, Daniele; Hrabák, Pavel; Padil, Vinod V. T.; Torres-Mendieta, Rafael; Waclawek, Maria; Černík, Miroslav; Dionysiou, Dionysios D.Lindane (gamma-hexachlorocyclohexane) and its isomers (HCH) are some of the most common and most easily detected organochlorine pesticides in the environment. The widespread distribution of lindane is due to its use as an insecticide, accompanied by its persistence and bioaccumulation, whereas HCH were disposed of as waste in unmanaged landfills. Unfortunately, certain HCH (especially the most reactive ones: gamma- and alpha-HCH) are harmful to the central nervous system and to reproductive and endocrine systems, therefore development of suitable remediation methods is needed to remove them from contaminated soil and water. This paper provides a short history of the use of lindane and a description of the properties of HCH, as well as their determination methods. The main focus of the paper, however, is a review of oxidative and reductive treatment methods. Although these methods of HCH remediation are popular, there are no review papers summarising their principles, history, advantages and disadvantages. Furthermore, recent advances in the chemical treatment of HCH are discussed and risks concerning these processes are given.
- ItemEffect of CoSi2 interfacial layer on the magnetic properties of Si vertical bar CoSi2 vertical bar Sm-Co thin films(ELSEVIER, RADARWEG 29, 1043 NX AMSTERDAM, NETHERLANDS, 2020-01-01) Saravanan, P.; Boominathasellarajan, S.; Sobel, Bartlomiej; Waclawek, Stanislaw; Vinod, Vellora Thekkae Padil; Černík, MiroslavMagnetic thin films with a layer sequence of Si vertical bar CoSi2 vertical bar Sm-Co were grown by direct sputter deposition at elevated temperatures, through interfacial diffusion between Si (1 0 0) substrate and the overlying Sm-Co layer. HR-TEM analysis revealed the occurrence of CoSi2 -interfacial layer close to the Si-substrate surface, with controllable thicknesses of similar to 20 and 35 nm at deposition temperatures: 450 and 500 degrees C, respectively. XRD studies confirmed the crystallization of Sm2Co17 and SmCo5 magnetic phases accompanied by the other phases such as CoSi2 and SmCoSi2 due to the intermixing of Co and Si-atoms at higher deposition temperatures. The measured coercivity values are found to be increased from 8.7 to 11.6 kOe at higher CoSi2-layer thickness. The angular-dependent hysteresis measurements demonstrated a distinct isotropic and uniaxial magnetic anisotropy characteristics for the Sm-Co films consisting of 35 and 20-nm thick CoSi2 interfacial layers, respectively and the associated magnetization reversal mechanisms are discussed using the Stoner-Wohlfarth model. The temperature coefficients of remanence (alpha) and coercivity (beta) were determined from the temperature-dependent hysteresis curves. The Sm-Co films consisting of 35-nm thick CoSi2-layer exhibited a better thermal stability with 'alpha' and 'beta' values of 0.35 +/- 0.05%/degrees C and -0.13 +/- 0.02%/degrees C, respectively. The results of present study provide splendid opportunities for exploiting the potential of CoSi2 as an under layer, for growing the Sm-Co films towards high-temperature applications.
- ItemImprovement of the thermophilic anaerobic digestion and hygienisation of waste activated sludge by synergistic pretreatment(2019-06-07) Grubel, Klaudiusz; Waclawek, Stanislaw; Kuglarz, Mariusz; Waclawek, Maria; Cernik, MiroslavHybrid disintegration of waste activated sludge (WAS) before the thermophilic anaerobic stabilization of WAS contributes to the intensification of organic compounds decomposition and increases the effectiveness of the anaerobic stabilization process compared to the fermentation of raw WAS. This article investigates the influence of a chemical-thermal pretreatment procedure with the use of NaOH and freezing by the dry ice on WAS. We found that the hybrid pretreatment of WAS causes higher concentration of released organics in the liquid phase (represented here as a change in soluble chemical oxygen demand - SCOD value) in comparison to these disintegration techniques used separately. The use of disintegrated WAS (WASD) as an additional material in the digester chambers impacts (varying on its proportion added), the generation of biogas and its yield. The recorded amount of the produced biogas and biogas yield after 21days of fermentation increased by 26.6% and 2.7%, respectively (in comparison to blank sample). In addition, it was observed that the hybrid process before anaerobic stabilization contributes to a higher hygienisation of the digested sludge.
- ItemInterfacial layer formation during high-temperature deposition of Sm-Co magnetic thin films on Si (100) substrates(ELSEVIER SCI LTD, THE BOULEVARD, LANGFORD LANE, KIDLINGTON, OXFORD OX5 1GB, OXON, ENGLAND, 2019-03) Saravanan, P.; Boominathasellarajan, S.; Sobel, Bartlomiej; Waclawek, Stanislaw; Vinod, Vellora Thekkae Padil; Talapatra, A.; Mohanty, J.; Černík, MiroslavThe interfacial layer that has formed during the deposition of similar to 240-nm thick Sm-Co films on the bare Si (100) substrate was investigated at different deposition temperatures, T-d,T-Sm-Co: 400, 450 and 500 degrees C with respect to structural and magnetic properties of Sm-Co films. X-ray diffraction analysis showed the crystallization of both Sm2Co17(R) and SmCo5(H) magnetic phases. Rutherford back scattering studies demonstrated that the surface-diffusion reactions between the Sm-Co layer and Si-surface not only accompanied by the quasi-layered growth of CoSi2-phase; but also led to the formation of SmCoSi2-phase. Cross-sectional transmission electron microscopy analysis revealed uneven boundary with deeply grown CoSi2-layer and Moire fringes at limited regions of Co/Si interface. Magnetic measurements showed a square hysteresis loop with maximum values of coercivity (11.6 kOe) and remanence ratio (0.99) for the films grown at 500 degrees C. Magnetic force microscopy images depicted patch-like domains with increasing phase contrast against T-d,T-Sm-Co. In addition, the changes that has occurred in the magnetization reversal processes accompanied by coercivity enhancement due to higher T-d,T-Sm-Co is discussed in the context of domain morphology and first-order reversal curves.
- ItemMicroscopic Techniques for the Analysis of Micro and Nanostructures of Biopolymers and Their Derivatives(MDPI, 2020-03) Venkateshaiah, Abhilash; Padil, Vinod V. T.; Nagalakshmaiah, Malladi; Waclawek, Stanislaw; Černík, Miroslav; Varma, Rajender S.Natural biopolymers, a class of materials extracted from renewable sources, is garnering interest due to growing concerns over environmental safety; biopolymers have the advantage of biocompatibility and biodegradability, an imperative requirement. The synthesis of nanoparticles and nanofibers from biopolymers provides a green platform relative to the conventional methods that use hazardous chemicals. However, it is challenging to characterize these nanoparticles and fibers due to the variation in size, shape, and morphology. In order to evaluate these properties, microscopic techniques such as optical microscopy, atomic force microscopy (AFM), and transmission electron microscopy (TEM) are essential. With the advent of new biopolymer systems, it is necessary to obtain insights into the fundamental structures of these systems to determine their structural, physical, and morphological properties, which play a vital role in defining their performance and applications. Microscopic techniques perform a decisive role in revealing intricate details, which assists in the appraisal of microstructure, surface morphology, chemical composition, and interfacial properties. This review highlights the significance of various microscopic techniques incorporating the literature details that help characterize biopolymers and their derivatives.
- ItemProduction of electrospun nanofibers based on graphene oxide/gum Arabic(ELSEVIER SCIENCE BV, PO BOX 211, 1000 AE AMSTERDAM, NETHERLANDS, 2019-03-01) Silvestri, Daniele; Mikšíček, Jiří; Waclawek, Stanislaw; Torres-Mendieta, Rafael; Padil, Vinod V. T.; Černík, MiroslavOver the last few years, the electrospinning technique has attracted significant attention for the production of novel nanofibrous materials. At the same time, the use of graphene oxide and the natural products extracted from plants and/or trees have become very popular in various fields of science. In this work, a new method for the production of nanofibers based on a combination of Gum Arabic (GA), as a natural tree gum exudate, PVA, as an environmentally-friendly stabilizer, and graphene oxide (GO) has been developed and characterized. SEM analysis showed fundamental differences on the surface of bare nanofibers with and without GO, and also significantly smaller fiber diameters in the case of the presence of GO (fibers <100 nm present). Raman spectroscopy confirmed and TGA analysis approximated the content of GO in the nanofibers. Adsorption of methylene blue on the produced nanofibrous membrane was about 50% higher in the presence of GO, which opens the possibility to use GO/GA/PVA fibers in several applications, for example for the removal of dyes.
- ItemRecycling non-food-grade tree gum wastes into nanoporous carbon for sustainable energy harvesting(ROYAL SOC CHEMISTRY, THOMAS GRAHAM HOUSE, SCIENCE PARK, MILTON RD, CAMBRIDGE CB4 0WF, CAMBS, ENGLAND, 2020-02-21) Venkateshaiah, Abhilash; Cheong, Jun Young; Shin, Sung-Ho; Akshaykumar, K. P.; Yun, Tae Gwang; Bae, Jaehyeong; Waclawek, Stanislaw; Černík, Miroslav; Agarwal, Seema; Greiner, Andreas; Padil, Vinod V. T.; Kim, Il-Doo; Varma, Rajender S.The disposal of natural wastes has become a global problem and the use of lower-grade gums is very limited owing to their impurities as well as sticky nature. Rather than disposing these wastes, nanoporous carbon (nC) has instead been synthesized by carbonization and exfoliation. The synthesized nC exhibits a substantially high surface area along with abundant micro/mesopores. This desirable and useful nature of nC is well-suited for water-driven effective electrical energy conversion, which enables the fast evaporation of water via a capillary action through nanopores. Under asymmetric wetting in a water container and ambient conditions, the nC-based energy harvesters showed high capability of electricity production and reliable output generation, easily turning on a blue light-emitting diode (2.5 V and 20 mA) using a stored power source. In summary, many energy harvesters can be manufactured for the scale-up of electricity, and the suitability of regenerated carbon nanomaterials for green energy harvesting can contribute toward alleviating chronic environmental issues.
- ItemTree Gum-Graphene Oxide Nanocomposite Films as Gas Barriers(AMER CHEMICAL SOC, 1155 16TH ST, NW, WASHINGTON, DC 20036 USA, 2020-01) Venkateshaiah, Abhilash; Cheong, Jun Young; Habel, Christoph; Waclawek, Stanislaw; Lederer, Tomáš; Černík, Miroslav; Kim, Il-Doo; Padil, Vinod V. T.; Agarwal, SeemaTo reduce the dependency on petro-based conventional plastics, research focusing on bioplastics derived from biological origin has gained precedence. Herein, we report an ecofriendly and a facile synthetic route to develop a freestanding nanocomposite film prepared from the combination of nonedible biodegradable tree gum waste and graphene oxide (GO). Three variants of bionanocomposite films such as GO-gum arabic (GA-GO), GO-gum karaya (GK-GO), and GO- kondagogu gum (KG-GO) were fabricated via solution casting of respective gums with GO (0.5% and 1.0%) in an aqueous environment. GO was thoroughly blended within different types of gum matrices via the hydrogen bond interaction and electrostatic attraction, thus forming interconnected homogeneous GO-gum layered structure. Morphological analysis revealed a natural nacre-like structure comprised of gum-intercalated graphene sheets, which was further confirmed by X-ray diffraction studies. The addition of GO further transformed the brittle gum film into a freestanding film with substantial mechanical strength. Furthermore, the layered nanocomposite films demonstrated enhanced oxygen gas barrier property as well as reduced water vapor transmittance. The barrier properties are comparable to the plastics traditionally used in packaging, emphasizing the potential of tree gums nanocomposite films in packaging applications. Such frugally viable gums can be a cost-effective alternative in the development of nanocomposite films that could be readily used for applications in food packaging, pharmaceutical, and various biomedical industries.