Lazaros Tzounis

Controlled growth of Ag nanoparticles decorated onto the surface of SiO2 spheres: a nanohybrid system with combined SERS and catalytic properties

A versatile water-based method for depositing silver nanoparticles (Ag NPs) with controllable and uniform metal size onto the surface of silica (SiO2) spheres is reported. The hybrid particles exhibited a raspberry-like morphology, and their potential for SERS and catalytic applications has been demonstrated. SiO2 spheres (∼120 nm) were synthesized first and modified with polyethyleneimine (PEI) to introduce amine surface functionalities. The amine groups were coordinated with silver ions (Ag+) and reduced to Ag seeds (∼4 nm), uniformly distributed onto the SiO2 surface (SiO2@Ag-seed). In order to improve the optical responses and catalytic activity of SiO2@Ag-seed system, two subsequent silver growth steps were performed. The diameter of Ag seeds was increased to 12 and 19 nm, respectively, hereafter denoted as SiO2@Ag-1 and SiO2@Ag-2. The immobilization and controlled growth of Ag NPs was confirmed by UV-vis spectroscopy, and scanning and transmission electron microscopy (SEM and TEM, respectively). All specimens displayed satisfactory SERS activity increasing with the Ag NP size, showing clear Raman peaks of Rhodamine 6G (R6G) at very low concentration. The SiO2@Ag particles were also tested and compared for their catalytic efficiency towards the reduction of 4-nitrophenol (4-Nip) by NaBH4. The principal advantages of this study lie in the ability to tune the Ag NP size, the long-term colloidal stability of all fabricated SiO2@Ag systems in aqueous media, and the limited use of hazardous chemicals and pollutant organic solvents during the synthetic process.

Oxygen-plasma-modified biomimetic nanofibrous scaffolds for enhanced compatibility of cardiovascular implants

Summary Electrospun nanofibrous scaffolds have been extensively used in several biomedical applications for tissue engineering due to their morphological resemblance to the extracellular matrix (ECM). Especially, there is a need for the cardiovascular implants to exhibit a nanostructured surface that mimics the native endothelium in order to promote endothelialization and to reduce the complications of thrombosis and implant failure. Thus, we herein fabricated poly-ε-caprolactone (PCL) electrospun nanofibrous scaffolds, to serve as coatings for cardiovascular implants and guide tissue regeneration. Oxygen plasma treatment was applied in order to modify the surface chemistry of the scaffold and its effect on cell attachment and growth was evaluated. The conditions of the surface modification were properly adjusted in order to define those conditions of the treatment that result in surfaces favorable for cell growth, while maintaining morphological integrity and mechanical behavior. Goniometry (contact angle measurements), scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) measurements were used to evaluate the morphological and chemical changes induced by the plasma treatment. Moreover, depth-sensing nanoindentation was performed to study the resistance of the plasma-treated scaffolds to plastic deformation. Lastly, the cell studies indicated that all scaffolds were cytocompatible, with the plasma-treated ones expressing a more pronounced cell viability and adhesion. All the above findings demonstrate the great potential of these biomimetic tissue-engineering constructs as efficient coatings for enhanced compatibility of cardiovascular implants.

CNT-grafted glass fibers as a smart tool for epoxy cure monitoring, UV-sensing and thermal energy harvesting in model composites

A ‘hierarchical’ reinforcement of glass fibers (GFs) chemically grafted with multiwall carbon nanotubes (MWCNTs) has been utilized for epoxy cure monitoring, UV-sensing, and thermal energy harvesting in model composites. MWCNTs were covalently attached to the surface of glass fiber yarns (GF-yarns) in a dip-coating deposition process. Hereafter, the hybrid yarns are denoted as GF-CNT. Scanning electron microscopy (SEM) demonstrated a highly uniform CNT-layer covering the fiber surfaces. In turn, GF-CNT reached a maximum conductivity of 2060 S m−1, being of the same order of magnitude as the CNT-only bucky paper film. A GF-CNT in a uni-directional arrangement within a dog-bone shaped mould was employed for epoxy cure monitoring, recording the resistance changes during the curing process. In addition, three yarns connected in parallel highlighted the potential for detecting the resin position upon filling a mould. GF-CNT embedded in epoxy has been proposed also as an integrated non-invasive composite UV-sensor, allowing polymer matrix health monitoring. Besides, the semi-conductive nature of MWCNTs offered the opportunity of thermoelectric energy harvesting by the GF-CNT and its model composite when exposed to a temperature gradient. This work reports some new insights into and potential of fiber/CNT multi-scale reinforcements giving rise to multi-functional structural composites.

Production of hierarchical all graphitic structures: A systematic study.

We report the production of hierarchical all graphitic structures through a systematic study involving the use of wet chemical treatments for dip coating of carbon fibers (CFs) for surface grafting with multiwalled carbon nanotubes (CNTs). Realization of a thin homogeneous veil of CNTs onto the CF surface was achieved through an extensive parametric survey. Optimization of aqueous dispersions of CNTs eliminated the need for oxidation of the CF surface. The effects of chemical processes onto the surface and structural characteristics of the involved graphitic species were evaluated via thermogravimetric analysis, and X-ray photoelectron, infrared and Raman spectroscopies. The dielectric properties of the produced CNT aqueous dispersions were monitored via electrochemical impedance spectroscopy. A final assessment of the produced hierarchical CFs was performed through scanning electron microscopy.

Halloysite Nanotubes Noncovalently Functionalised with SDS Anionic Surfactant and PS-b-P4VP Block Copolymer for Their Effective Dispersion in Polystyrene as UV-Blocking Nanocomposite Films

A simple and versatile method is reported for the noncovalent functionalisation of natural and “green” halloysite nanotubes (HNTs) allowing their effective dispersion in a polystyrene (PS) thermoplastic matrix via solvent mixing. Initially, HNTs (pristine HNTs) were modified with physically adsorbed surfactant molecules of sodium dodecyl sulphate (SDS) and PS-b-P4VP [P4VP: poly(4-vinylpyridine)] block copolymer (BCP). Hereafter, SDS and BCP modified HNTs will be indicated as SDS-m-HNT and BCP-m-HNT. Nanocomposite films with 1, 2, and 5 wt.% HNT loadings were prepared, abbreviated as PS-SDS-m-HNT1, PS-SDS-m-HNT2, and PS-SDS-m-HNT5 and PS-BCP-m-HNT1, PS-BCP-m-HNT2, and PS-BCP-m-HNT5 (where 1, 2, and 5 correspond to the wt.% of HNTs). All nanocomposites depicted improved thermal degradation compared to the neat PS as revealed by thermogravimetric analysis (TGA). Transmission electron microscopy (TEM) confirmed the good dispersion state of HNTs and the importance of modification by SDS and BCP. X-ray diffraction (XRD) studies showed the characteristic interlayer spacing between the two silicate layers of pristine and modified HNTs. The PS/HNT nanocomposite films exhibited excellent ultraviolent-visible (UV-vis) absorbance properties and their potential application as UV-filters could be envisaged.

The Effect of WO3 Modification of ZrO2 Support on the Ni-Catalyzed Dry Reforming of Biogas Reaction for Syngas Production

The time-on-stream catalytic performance and stability of 8wt% Ni catalyst supported on two commercially available catalytic supports, ZrO2 and 15wt% WO3-ZrO2, was investigated under the biogas dry reforming reaction for syngas production, at 750oC and a biogas quality equal to CH4/CO2=1.5, that represents a common concentration of real biogas. A number of analytical techniques such as N2 adsorption/desorption (BET method), X-Ray diffraction (XRD), temperature programmed reduction (H2-TPR), temperature programmed desorption (NH3- and CO2-TPD), scanning electron microscopy (SEM), inductively coupled plasma emission spectroscopy (ICP), thermal analysis (TGA/DTG) and Raman spectroscopy were used in order to determine textural, structural and other physicochemical properties of the catalytic materials, and the type of carbon deposited on the catalytic surface of spent samples. These techniques were used in an attempt to understand better the effects of WO3-induced modifications on the catalyst morphology, physicochemical properties and catalytic performance. Although Ni dispersion and reducibility characteristics were found superior on the modified Ni/WZr sample than that on Ni/Zr, its dry reforming of methane (DRM) performance was inferior; a result attributed to the enhanced acidity and complete loss of the basicity recorded on this catalyst, an effect that competes and finally overshadows the benefits of the other superior properties.