Silver/poly(vinyl alcohol)/chitosan/graphene hydrogels – Synthesis, biological and physicochemical properties and silver release kinetics

Neš,ovi&#x107,, Katarina,Jankovi&#x107,, Ana,Koji&#x107,, Vesna,Vuka&#x161,inovi&#x107,-Sekuli&#x107,, Maja,Peri&#x107,-Gruji&#x107,, Aleksandra,Rhee, Kyong Yop,Mi&#x161,kovi&#x107,-Stankovi&#x10 Elsevier 2018 Composites. Part B, Engineering Vol.154 No.-

<P><B>Abstract</B></P> <P>This study presents the synthesis of novel silver/poly(vinyl alcohol)/chitosan/graphene (Ag/PVA/CHI/Gr) nanocomposite hydrogels by <I>in situ</I> electrochemical reduction of silver ions in the hydrogel matrix and their thorough characterization by UV–visible and Raman spectroscopies, field-emission scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), and silver release measurements. The influence of chitosan content on the incorporation and stabilization of silver nanoparticles (AgNPs) was investigated, and we found that hydrogels with higher chitosan content contain higher amounts of AgNPs. In addition, the cytotoxicity and antibacterial activity of Ag/PVA/CHI/Gr nanocomposite hydrogels were evaluated. Based on <I>in vitro</I> investigations, the obtained materials exhibit diffusion-controlled release profiles over 28 days, strong antibacterial activity against <I>Staphylococcus aureus</I> and <I>Escherichia coli</I> bacterial strains, and no cytotoxicity toward human and mice fibroblast cell lines.</P> <P><B>Highlights</B></P> <P> <UL> <LI> <I>In situ</I> electrochemical synthesis of silver nanoparticles in PVA/CHI/Gr hydrogels. </LI> <LI> Effect of chitosan concentration on the amount of embedded silver nanoparticles. </LI> <LI> Effect of chitosan concentration on the silver release kinetics. </LI> <LI> Strong antibacterial activity against <I>S. aureus</I> and <I>E. coli</I>. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

A combinatorial constraint satisfaction problem dichotomy classification conjecture

Neš,et&#x159,il, Jaroslav,Siggers, Mark H.,Zá,dori, Lá,szló Elsevier 2010 European journal of combinatorics : Journal europ& Vol.31 No.1

<P><B>Abstract</B></P><P>We further generalise a construction–the <I>fibre construction</I>–that was developed in an earlier paper of the first two authors. The extension in this paper gives a polynomial-time reduction of CSP(H) for any relational system H to CSP(P) for any relational system P that meets a certain technical partition condition, that of being <SUB>K3</SUB>-<I>partitionable</I>.</P><P>Moreover, we define an equivalent condition on P, that of being <I>block projective</I>, and using this show that our construction proves NP-completeness for exactly those CSPs that are conjectured to be NP-complete by the CSP dichotomy classification conjecture made by Bulatov, Jeavons and Krohkin, and by Larose and Zádori. We thus provide two new combinatorial versions of the CSP dichotomy classification conjecture.</P><P>As with our previous version of the fibre construction, we are able to address restricted versions of the dichotomy conjecture. In particular, we reduce the Feder–Hell–Huang conjecture to the CSP dichotomy classification conjecture, and we prove the Kostochka–Nešetřil–Smolíková conjecture. Although these results were proved independently by Jonsson et al. and Kun respectively, we give different, shorter, proofs.</P>

Investigation of corrosion behaviour of carbon nanotubes coated basalt fabric as a reinforcement material

Mittal, Garima,Neš,ovi&#x107,, Katarina,Rhee, Kyong Yop,Mi&#x161,kovi&#x107,-Stankovi&#x107,, Vesna Elsevier 2019 Composites Part B, Engineering Vol.178 No.-

<P><B>Abstract</B></P> <P>In this study, the corrosion behaviour of carbon nanotubes (CNTs) coated basalt fibre (BF) (BFCNTs) obtained by chemical vapour deposition (CVD), was studied. During CVD, the CNTs were grown on BF, (a) at different growth temperatures and (b) for different growth times. The physicochemical measurements were performed using X-ray diffraction, Raman spectroscopy, and field-emission scanning electron microscopy. The corrosion performances were investigated using electrochemical impedance spectroscopy (EIS), potentiodynamic sweep (PDS), linear polarization resistance (LPR) and weight loss measurements. The BFCNT prepared at 650 °C for 120 min exhibited the best corrosion stability during the prolonged exposure to 0.1 M NaCl electrolyte. The outcomes of this study would be useful in designing the carbon nanotubes coated basalt fibre with the best corrosion resistance.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CNTs coated basalt fibres were obtained using chemical vapour deposition. </LI> <LI> CNTs were grown at different growth temperatures and for different growth times. </LI> <LI> BFCNTs prepared for longer growth time showed better CNT formation on BF. </LI> <LI> Better CNT formation on BF improved the corrosion stability of the BFCNTs composite. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

<i>In situ</i> electrochemical synthesis of silver-doped poly(vinyl alcohol)/graphene composite hydrogels and their physico-chemical and thermal properties

Abudabbus, Mohamed M.,Jevremovi&#x107,, Ivana,Neš,ovi&#x107,, Katarina,Peri&#x107,-Gruji&#x107,, Aleksandra,Rhee, Kyong Yop,Mi&#x161,kovi&#x107,-Stankovi&#x107,, Vesna Elsevier 2018 Composites Part B, Engineering Vol.140 No.-

<P><B>Abstract</B></P> <P>This paper presents silver/poly(vinyl alcohol) (Ag/PVA) and silver/poly(vinyl alcohol)/graphene (Ag/PVA/Gr) composites prepared by the immobilization of silver nanoparticles (AgNPs) in PVA and PVA/Gr hydrogel discs previously cross linked by the freezing/thawing method. The AgNPs inside the hydrogel matrices were synthesized following an innovative <I>in situ</I> method of electrochemical reduction of Ag<SUP>+</SUP> ions within PVA and PVA/Gr hydrogel discs. In addition, the novel materials introduced here were characterized by UV–visible spectroscopy, cyclic voltammetry, Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, silver release measurements, and thermogravimetric analysis. The effective immobilization of the AgNPs inside the PVA and PVA/Gr hydrogel networks was achieved by their bonding with the exposed hydroxyl groups in PVA. Also, the incorporation of graphene into the PVA matrix and the bonding between PVA molecules and incorporated graphene sheets improves thermal stability of Ag/PVA/Gr and prevents aggregation and growth of AgNPs as observed by Fourier transform infrared spectroscopy and field emission scanning electron microscopy.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel biomedical silver/(polyvinyl alcohol) and silver/(polyvinyl alcohol)/graphene hydrogels. </LI> <LI> <I>In situ</I> electrochemical synthesis of silver nanoparticles in hidrogel polymer matrix. </LI> <LI> Cyclic voltammetric investigation of silver nanoparticles (AgNPs) oxidation/reduction mechanism. </LI> <LI> Silver release kinetics show prolonged stability and good immobilization of AgNPs. </LI> <LI> Potential for application as wound dressings. </LI> </UL> </P>

Comprehensive electrochemical study on corrosion performance of graphene coatings deposited by chemical vapour deposition at atmospheric pressure on platinum-coated molybdenum foil

Naghdi, Samira,Neš,ovi&#x107,, Katarina,Mi&#x161,kovi&#x107,-Stankovi&#x107,, Vesna,Rhee, Kyong Yop Pergamon Press 2018 Corrosion science Vol.130 No.-

<P><B>Abstract</B></P> <P>In this work, we present the results of electrochemical, Raman, FE-SEM/EDS, and XPS studies of graphene coatings deposited by chemical vapour deposition at atmospheric pressure on Mo foil and Pt-coated Mo foil as catalysts. The results showed that the graphene coating synthesized on Pt-coated molybdenum foil was bi-layer and had fewer defects, while the graphene coating on Mo foil was few-layer with more defects. The corrosion studies indicated that both graphene coatings on bare Mo and Pt-coated Mo exhibited good protective properties and can act as a barrier against corrosion in 0.1M NaCl.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Graphene chemical vapour deposition (CVD) at atmospheric pressure on molybdenum. </LI> <LI> Platinum thin film on molybdenum provided catalytic effect for CVD of graphene. </LI> <LI> Graphene coating on Pt-coated Mo samples had larger grain size and fewer defects. </LI> <LI> Both graphene coatings on Mo and Pt-coated Mo exhibited corrosion protection. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>