22 research outputs found
Correlation between MWCNT aspect ratio and the mechanical properties of composites of PMMA and MWCNTs
The correlation between MWCNT aspect ratio and the quasi-static and dynamic mechanical properties of composites of MWCNTs and PMMA was studied for relatively long MWCNT lengths, in the range 0.3mm to 5mm (aspect ratios up to 5 x 105) and at low loading (0.15wt%). The height of the MWCNTs prepared were modulated by controlling the amount of water vapour introduced in the reactor limiting Ostwald ripening of the catalyst, the formation of amorphous carbon and any increase in CNT diameter. The Tg of PMMA increased by up to 4 ÂșC on addition of the longest tubes as they have the ability to form physical junctions with the polymer chains which lead to enhanced PMMA-MWCNTs interactions and increased mechanical properties, Young's modulus by 20% on addition of 5mm long MWCNTs. Predictions of the Young's modulus of the composites of PMMA and MWCNT with the Mori-Tanaka theory show that future micromechanical models should account for MWCNT agglomeration and polymer-nanotube interactions as a function of CNT length
Graphene oxide and reduced graphene oxide nanoflakes coated with glycol chitosan, propylene glycol alginate, and polydopamine: Characterization and cytotoxicity in human chondrocytes
Recently, graphene and its derivatives have been extensively investigated for their interest-ing properties in many biomedical fields, including tissue engineering and regenerative medicine. Nonetheless, graphene oxide (GO) and reduced GO (rGO) are still under investigation for improving their dispersibility in aqueous solutions and their safety in different cell types. This work explores the interaction of GO and rGO with different polymeric dispersants, such as glycol chitosan (GC), propylene glycol alginate (PGA), and polydopamine (PDA), and their effects on human chondro-cytes. GO was synthesized using Hummerâs method, followed by a sonication-assisted liquid-phase exfoliation (LPE) process, drying, and thermal reduction to obtain rGO. The flakes of GO and rGO exhibited an average lateral size of 8.8 ± 4.6 and 18.3 ± 8.5 ”m, respectively. Their dispersibility and colloidal stability were investigated in the presence of the polymeric surfactants, resulting in an improvement in the suspension stability in terms of average size and polydispersity index over 1 h, in particular for PDA. Furthermore, cytotoxic effects induced by coated and uncoated GO and rGO on human chondrocytes at different concentrations (12.5, 25, 50 and 100 ”g/mL) were assessed through LDH assay. Results showed a concentration-dependent response, and the presence of PGA contributed to statistically decreasing the difference in the LDH activity with respect to the control. These results open the way to a potentially safer use of these nanomaterials in the fields of cartilage tissue engineering and regenerative medicine
Graphene OxideâDoped Gellan GumâPEGDA Bilayered Hydrogel Mimicking the Mechanical and Lubrication Properties of Articular Cartilage
Articular cartilage (AC) is a specialized connective tissue able to provide a low-friction gliding surface supporting shock-absorption, reducing stresses, and guaranteeing wear-resistance thanks to its structure and mechanical and lubrication properties. Being an avascular tissue, AC has a limited ability to heal defects. Nowadays, conventional strategies show several limitations, which results in ineffective restoration of chondral defects. Several tissue engineering approaches have been proposed to restore the AC's native properties without reproducing its mechanical and lubrication properties yet. This work reports the fabrication of a bilayered structure made of gellan gum (GG) and poly (ethylene glycol) diacrylate (PEGDA), able to mimic the mechanical and lubrication features of both AC superficial and deep zones. Through appropriate combinations of GG and PEGDA, cartilage Young's modulus is effectively mimicked for both zones. Graphene oxide is used as a dopant agent for the superficial hydrogel layer, demonstrating a lower friction than the nondoped counterpart. The bilayered hydrogel's antiwear properties are confirmed by using a knee simulator, following ISO 14243. Finally, in vitro tests with human chondrocytes confirm the absence of cytotoxicity effects. The results shown in this paper open the way to a multilayered synthetic injectable or surgically implantable filler for restoring AC defects
Optical Properties and Ultrafast NearâInfrared Localized Surface Plasmon Dynamics in Naturally pâType Digenite Films
Copper chalcogenides are materials characterized by intrinsic doping properties, allowing them to display high carrier concentrations due to their defect-heavy structures, independent of the preparation method. Such high doping enables these materials to display plasmonic resonances, tunable by varying their stoichiometry, as shown previously for Cu2-xS, Cu2-xSe, and Cu2-xTe, with 0 1 ns) signal associated with phonon-phonon scattering relaxation. These results confirm the possibility of fabricating Cu9S5 films retaining the plasmonic properties of individual NCs, anticipating integrating these films into heterojunctions with suitable hole acceptor materials to build hot-hole-transfer-based optoelectronic devices
Chemical-Vapor-Deposition-Synthesized Two-Dimensional Non-Stoichiometric Copper Selenide (ÎČ-Cu<sub>2âx</sub>Se) for Ultra-Fast Tetracycline Hydrochloride Degradation under Solar Light
The high concentration of antibiotics in aquatic environments is a serious environmental issue. In response, researchers have explored photocatalytic degradation as a potential solution. Through chemical vapor deposition (CVD), we synthesized copper selenide (ÎČ-Cu2âxSe) and found it an effective catalyst for degrading tetracycline hydrochloride (TC-HCl). The catalyst demonstrated an impressive degradation efficiency of approximately 98% and a reaction rate constant of 3.14 Ă 10â2 minâ1. Its layered structure, which exposes reactive sites, contributes to excellent stability, interfacial charge transfer efficiency, and visible light absorption capacity. Our investigations confirmed that the principal active species produced by the catalyst comprises O2â radicals, which we verified through trapping experiments and electron paramagnetic resonance (EPR). We also verified the TC-HCl degradation mechanism using high-performance liquid chromatographyâmass spectrometry (LC-MS). Our results provide valuable insights into developing the ÎČ-Cu2âxSe catalyst using CVD and its potential applications in environmental remediation
Role of Catalyst Oxidation State in the Growth of Vertically Aligned Carbon Nanotubes
The impact of gas-phase pretreatment of supported iron-oxide
catalyst
utilized in aligned carbon nanotube (CNT) growth is studied to understand
the correlation between the catalyst oxidation state and the growth
characteristics of the aligned CNT forests. By varying the pretreatment
conditions from a reducing to an oxidizing environment, notable changes
are observed in both the collective CNT array growth behavior and
the individual CNT characteristics. Although the greatest catalytic
activity was observed following a full reduction to the zerovalent
(metallic) Fe catalyst, growth is also observed from a catalyst composed
of both Fe<sub>2</sub>O<sub>3</sub> and Fe<sub>3</sub>O<sub>4</sub> particles. XPS core-level analysis, following pretreatment of the
catalyst, emphasizes the critical nature of the combined catalystâunderlayer
interaction to achieve optimal catalyst activity during growth and
hence the most efficient catalyst reduction process. Additionally,
CNT diameters during growth were strongly affected by the pretreatment
process. Overall, this work gives a collective picture of how the
catalyst oxidation state affects the CNT growth based on the catalyst
pretreatment environment and the nature of the catalystâunderlayer
interactions. Such concepts are critical for the rational design of
alternative catalystâunderlayer systems for efficient CNT synthetic
processes
Phase-Dependent Photocatalytic Activity of Bulk and Exfoliated Defect-Controlled Flakes of Layered Copper Sulfides under Simulated Solar Light
Sunlight-driven photocatalysis is an environmentally friendly approach to solve ecological issues. The development of simple yet sufficiently stable photocatalytic materials capable of responding to the full-spectrum light remains challenging. Here, we demonstrate the phase transformations of bulk copper sulfides from digenite (Cu9S5) to djurleite (Cu1.97S) and low chalcocite (Cu2S) by the reactive thermal annealing during ambient pressure chemical vapor deposition, followed by their top-down exfoliation. Using multiple techniques, we confirm that monoclinic Cu2S is primarily formed at higher temperatures or greater reaction times and using a reducing atmosphere. We measured the average thickness to be approximately 4 nm for the exfoliated flakes with relatively large lateral sizes of up to 10 ÎŒm. We tested the three phases of bulk copper sulfides and their exfoliated forms as photocatalysts for dye degradation under simulated solar light irradiation. Exfoliated Cu2S flakes exhibited superior photocatalytic activity (0.007 minâ1), roughly twice higher than that of bulk chalcocite, which could be predominantly attributed to their 2D structure and also 2D planar defects, which could serve as active centers for dye photodegradation. Our study paves the way for developing nextgeneration full-spectrum-responsive 2D copper sulfide photocatalysts for environmental decontamination