8639 research outputs found
Sort by
Sample preparation for cavitation erosion testing of 3D-printed metal
No full textCavitation erosion is a common occurrence in machine parts and elements operating under cavitation conditions (presence of high-speed working liquid in contact with parts’ working surfaces). This paper describes the comprehensive preparation of samples for testing resistance to cavitation erosion. The samples are 3D-printed metal parts, which is significant considering the increasing use of additive manufacturing technologies in the production of machine parts. The test samples were obtained by recycling samples previously used in rotational bending tests. These samples were made from MS1 maraging steel powder, 3D printed using Direct Metal Laser Sintering (DMLS). The study follows ASTM standard G32-16 for cavitation erosion testing, using
a vibrating apparatus with a water bath for immersing the test samples. Samples will
be subjected to cavitation for 1, 2, and 4 hours, with periodic mass loss measurements.
The obtained data will be used to determine the cavitation rate of the tested material.
Additionally, optical and SEM structural and morphological analyses will be conducted
before and after testing to characterize the erosion damage process
Crystal structure of a trinuclear Zn(II)-acetato complex with an azopyridine-based ligand
No full textРеакцијом 2-(4-додецилоксифенилазо)пиридина (L) са Zn(OAc)2∙2H2O (OAc = ацетат-јон) добијен је дискретни, центросиметрични, тринуклеарни комплекс, чија је формула [Zn3(OAc)6(L)2]. Рендгенска структурна анализа показала је да комплекс кристалише у триклиничној просторној групи Р1̅ са Z = 1. Комплекс се састоји из три атома Zn који су повезани преко шест мостовних ацетато-јона и са два хелатна L-лиганда (Слика 1). Атоми Zn, од којих атом Zn2 заузима специјални положај 1̅, јесу у деформисаном октаедарском окружењу. Структурни фрагменти повезани су C−H···O и π-π интеракцијама у траке паралелне равни (6 6 16), док је супрамолекулско умрежавање постигнуто C−H···N и C–H···π интеракцијама, као и хидрофобним интеракцијама између дугачких репова L-лиганда. Интермолекулске интеракције испитане су Хиршфелдовом анализом и анализом одговарајућих 2D отисака. C–H···O, C–H···N и C–H···π интеракције и, нарочито, хидрофобне интеракције доминантно учествују у формирању и стабилизацији кристалне структуре.Reaction of 2-(4-dodecyloxyphenylazo)pyridine (L) with Zn(OAc)2∙2H2O (OAc = acetate ion) yielded a discrete, centrosymmetric, trinuclear complex which formulae is [Zn3(OAc)6(L)2]. X-ray analysis revealed that the complex crystallizes in triclinic P1 space group with Z = 1. The complex consists of three Zn atoms coordinated with six bridging acetato ions and two chelate L ligands (Figure 1). The Zn atoms, of which Zn2 occupies special position 1, are in a deformed octahedral environment. The structural fragments are connected via C−H···O and π-π interactions into ribbons parallel to the plane (6 6 16), while supramolecular networking of the ribbons is achieved through C−H···N and C–H···π interactions as well as hydrophobic interactions between long tails of the L ligand. Intermolecular interactions were investigated using the Hirshfeld surface analysis and 2D fingerprint analysis. C–H···O, C–H···N and C–H···π interactions and, especially, hydrophobic interactions were confirmed as the source of an attraction within this crystal structure
Zinc(II) complex with an azopyrimidine-based ligand: a crystallographic and quantum-chemical study
No full textСветлонаранџасти дискретни, мононуклеарни комплекс [Zn(NO3)2(L)2] (где је
L = 2-(4-додецилoксифенилазо)пиримидин) добијен је из ацетонитрила при
загревању уз рефлукс, а његова структура одређена је рендгенском структурном
анализом. Kомплекс чине атом Zn(II) са два хелатно координованa лиганда L и два
јона нитрата (Слика 1). Структурни фрагменти повезани су у траке дуж правца
[101] преко C–H···O интеракција, док је супрамолекулско тродимензионално
кристално паковање формирано C–H···O, C–H···N и π-интеракцијама и
стабилизовано многобројним хидрофобним интеракцијама између дугачких алкилланаца лиганада L. Анализом Хиршфелдових површина одређен је квалитативни и
кватитативни допринос ових интеракција у изградњи кристалног паковања
комплекса.Light orange discrete mononuclear complex [Zn(NO3)2(L)2] (where L = 2-(4- dodecyloxyphenylazo)pyrimidine) was synthesized in acetonitrile under reflux conditions and its crystal structure was determined by single crystal X-ray diffraction. The complex is formed of six-coordinated Zn(II) atom bonded with two chelate L ligand and two nitrate ions (Figure 1). The structural fragments are connected into ribbons along [101] direction by C–H···O interactions, while supramolecular three dimensional crystal packing is achieved through C–H···O, C–H···N and π-interactions and stabilized by numerous hydrophobic interactions between the long alkyl chains of L ligands. An analysis of the Hirshfeld surface elaborated the qualitative and quantitative contributions of these interactions to the crystal packing
Development of alginate/activated-charcoal platform for topical treatment of resistant pathogens in chronic wounds
No full textThe aim of this work was to produce novel composites based on either Ca- or Zn-alginate hydrogels and activated charcoal (AC) particles that
would, upon contact with physiological fluids,
continuously release at least one bioactive agent
directly into the wound area. In addition, AC particles served as carriers of other active substances
such as povidone iodine (PVP-I), a powerful antiseptic which was used as a model substance.
The developed Ca- and Zn alginate composites
with incorporated AC particles impregnated with
PVP-I were comprehensively investigated in vitro
regarding its antimicrobial activity against wide
range of wild multi-resistant pathogens (MRSA,
E. coli, P. aeruginosa, A. baumannii, P. mirabilis, E.
faecalis, C. albicans), all isolated from patients’
wounds. Also, the composites were characterized
regarding its textural parameters, morphology,
iodine presence, AC and Zn2+ ions release profiles
as well as iodine adsorption/desorption from AC
particles. The obtained composites have exhibited excellent antimicrobial activity. Precisely,
synergistic activity of AC particles and adsorbed
iodine was shown to be crucial for antibacterial activity while synergy of AC particles and Zn2+
ions showed equally strong antifungal effect.
However, Zn2+ ions alone proved to be selectors
of resistant strains of bacteria which could be of
relevance in everyday life, since Zn compounds
are widely used in ointments and skin preparations from a very early age. Also, it was shown
that PVP-I is firmly adsorbed on AC particles and
that its release in the surrounding medium is
negligible which is very important in regards of
preventing often reported systemic iodine absorption after its prolonged medical usage. This
novel platform enables further development of
efficient multifunctional wound dressings with
sustained release of one or more potent bioactive agents in situ for prevention and topical treatment of resistant infections and thus address one
of the most significant clinical problems today
Modified Fly Ash as an Adsorbent for the Removal of Pharmaceutical Residues from Water
No full textIn this work, different methods for fly ash modification were applied to obtain an adsorbent
for the efficient removal of selected pharmaceuticals from a multiclass aqueous solution.
Morphological and surface properties of the modified fly ash samples were analyzed by scanning
electron microscopy, X-ray fluorescence, X-ray diffraction, Fourier transform infrared spectroscopy,
and point of zero charge, and the influence of the applied modifications was determined by comparison with the results obtained for unmodified fly ash. Experimental parameters of the adsorption of the pharmaceutical onto the modified fly ash were optimized, and special attention was paid to the influence of different parameters on the adsorption capacities. Multivariate methods of analysis, such as artificial neural networks, applied to the obtained results showed that the contact time, the initial concentration of the pharmaceutical solution, and the pH value had the strongest influence on the adsorption process. Fly ash modified with chitosan and magnetic iron oxide showed the best adsorption properties (removal efficiency above 80% for the majority of the selected pharmaceuticals), and artificial neural networks confirmed its susceptibility to the modeling process
Cobalt and Tungsten Extraction from Diamond Core Drilling Crowns by Aqua Regia Leaching
No full textIn this work, a hydrometallurgical process for the recycling of diamond core drilling crowns by means of aqua regia leaching and subsequent alkali leaching was investigated. This investigation continues a previous study in which nitric acid was used for the acid leaching phase. In the current study, higher tungsten recovery was achieved, reaching 98.2%, which is an improvement of about 1.5%. Another advancement of this study was the high Co recovery (97.21%) and the high purity of the tungsten trioxide obtained, comparable to the previously proposed technological process. Furthermore, a novel laboratory method for testing recycled diamond drilling crowns based on infrared thermography was introduced. Although this innovative approach is not the most accurate, it is fast and cost-effective and provides valuable results before the actual field test is conducted as a final evaluation. In addition, the infrared thermography method offers the advantage of non-destructive testing, ensuring that the diamond drilling crowns can be assessed without compromising their structural integrity. Other instrumental methods used to characterize the products and intermediates were X-ray diffraction (XRD), scanning electron microscope with energy dispersive X-ray spectroscopy (SEM-EDS), and laser desorption ionization mass spectrometry (LDI-MS). The analytical method for the concentrations in all working solutions was ICP-AES
Novel hybrid biomimetic macroporous composites with tuned biodegradability, improved osteointegration and anticancer properties for bone tissue regeneration (HyBioComBone)
No full textThe treatment of large bone defects (LBDs) represents a major challenge in clinical orthopedics. Patients with LBDs caused by trauma, infections, or tissue resections due to cancer, often undergo multiple surgeries with long recovery times leading to deteriorated life quality and increased healthcare costs. The project HyBioComBone aims to develop novel biomimetic macroporous composites with multifunctional properties for bone repair, regeneration, and cancer treatment. ...ExcellMater Conference 2024: Innovative Biomaterials for Novel Medical Devices, Belgrade, Serbia, April 10-12, 202
Stability of Halogen Bonded Perovskite Solar Cells
No full textHybrid metal halide perovskites have emerged as promising materials for photovoltaics in the past decade. Despite achieving high solar-to-electric power conversion efficiencies and possessing excellent optoelectronic properties, these materials face significant stability challenges under operational conditions. A major contributor to these instabilities is ion migration occurring at the interfaces with charge transport layers. To mitigate this issue, researchers have focused on interfacial engineering, employing supramolecular modulators that utilize halogen bonding (XB). Metal oxides, commonly used as charge transport layers in hybrid perovskite solar cells, are particularly amenable to XB, which can enhance operational stability. XB influences hydrophobicity, ion migration, and charge transfer, thereby affecting the photovoltaic performance. In our study, we introduced 1,4-diiodotetrafluorobenzene (TFDIB) as an XB agent at the TiO2 interface in perovskite solar cells. We employed various techniques, including scanning electron microscopy, X-ray diffraction, UV-visible absorption, photoluminescence spectroscopy, and X-ray and ultraviolet photoelectron spectroscopy, to investigate the structural and optoelectronic properties and identify interfacial changes resulting from XB modulation. Our findings demonstrate enhanced operational stability in perovskite solar cells, showcasing a versatile supramolecular approach for improving hybrid photovoltaics
A Comprehensive Analysis, Source Apportionment and Health Risk Assessment of Polycyclic Aromatic Hydrocarbons in Urban Shallow Lake Sediment
No full textPolycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental
pollutants. Based on their toxicity and potential for human exposure, the US EPA
and the EU have designated 16 priority PAHs. PAHs in the environment originate
primarily from two sources, petrogenic and pyrogenic. Lake sediments are the
most valuable natural archive documenting PAH contamination. PAHs can persist
in lake sediment systems, posing a long-term threat to the environment. PAHs that
were historically deposited can be remobilized upward in sediments and
resuspended into the aquatic environment1. PAHs in sediment from urban shallow
lake in Central Serbia were investigated in terms of their concentration,
distribution, and potential effects on the environment and human health by
calculating the toxic equivalent quantities (TEQs) and incremental lifetime cancer
risk (ILCR). This study revealed the pollution characteristics of PAHs and their
possible sources in lake sediments, clarified its correlation to regional
anthropogenic activities, and provided corresponding risk management strategies
for human and aquatic organisms
Exploring the Impact of Oxygen Functional Groups on Copper Nanoparticles Deposition on Graphitic Carbon Nitride for Enhanced Photocatalytic Reduction of Cr(VI)
No full textOwing to its special properties such as high stability in acidic conditions, facile synthesis from inexpensive precursors, and visible light activity due to its moderate band gap (~ 2.7 eV), graphitic carbon nitride (CN) has been used in many photocatalysis applications, including photocatalytic reduction of Cr(VI). Despite all the advantages, the poor photocatalytic performance of pure CN is mainly the result of high recombination rate of charge carriers. To improve the photoactivity of CNs, many strategies have been presented, including defect engineering or combination with different ions, metals, semiconductors or other materials by doping or deposition [1]. Furthermore, it has been reported that functionalization of the CN surface with oxygen-containing groups could improve the separation of photogenerated carriers by considering them as electron-withdrawing groups and also provide better contact in heterojunction [2]. In this work, CN was synthesized from urea by a direct thermal polymerization method and modified with oxalic acid for the synthesis of oxygen-doped CN (O-CN), while the Dielectric Barrier Discharge (DBD) plasma process was used to create defects in the form of oxygen-containing functional groups (CN-pl, O-CN-pl) [3,4]. Finally, the obtained samples were modified by deposition of Cu nanoparticles by chemical reduction of Cu2+ with NaBH4 to form heterojunctions (Cu-CN, Cu-CN-pl, Cu-O-CN, Cu-O-CN-pl) [5].
FESEM showed that all CN based samples are composed of irregular, curved layered particles, that are randomly agglomerated to form a porous structure (Fig. 1). Even though it wasn’t possible to observe copper nanoparticles, the change in colour of the samples indicated their presence. EDS analysis confirmed that Cu was present and also in the higher amounts in the previously treated samples compared to pure CN (Table 1), meaning that they had a higher adsorption capacity for Cu2+. This also implies that Cu nanoparticles were better attached to the surface of O-doped and plasma treated samples, which was the aim. Diffuse reflectance spectroscopy (DRS) showed that the deposition of Cu nanoparticles slightly red-shifted the absorption edge of the samples, probably due to heterojunction formation (Fig. 2).
The obtained photocatalysts were used for photocatalytic reduction of Cr(VI) under simulated visible irradiation, at pH = 3 and with citric acid as a hole scavenger. Prior to Cu nanoparticle deposition, the photocatalytic activity under visible irradiation of all CN samples, except O-CN, was similar, although treated samples had a slightly narrower band gap. In addition, all samples had a similar adsorption capacity for Cr(VI), as indicated by the almost identical decrease in Cr(VI) concentration after 30 min of equilibration in the dark. When the samples were tested after the Cu deposition, the Cr(VI) concentration decreased significantly during dark equilibration, while their photoactivity under simulated visible light was surprisingly reduced. This requires further research to discover the nature of the deposited nanoparticles and the influence of citric acid as a hole scavenger in order to explain the photocatalysis results