Electrochemical synthesis and characterization of poly(vinyl alcohol) nanocomposites with silver nanoparticles

Abstract

In this doctoral dissertation, a composite hydrogel consisting of poly(vinyl alcohol), graphene and silver nanoparticles, (Ag/PVA/Gr), was prepared by the immobilization of silver nanoparticles (AgNPs) in poly(vinyl alcohol)/graphene (PVA/Gr) hydrogel matrix in two steps. The first step was cross linking of the PVA/Gr colloid solution by the freezing/thawing method, while in the second step, in situ electrochemical method was used to incorporate AgNPs inside the PVA/Gr hydrogel matrix. The main aim of this study was to produce the nanocomposite graphene-based biomaterial with incorporated silver nanoparticles using in situ electrochemical method, aimed for soft tissue implants, wound dressings and drug delivery. The electrochemical route of nanoparticles synthesis is especially attractive for biomedical applications due to high purity and precise size control of metal particles and the absence of chemical cross linking agents and undesired products. Repeated cyclic freezing/thawing method was used to prepare poly(vinyl alcohol) PVA and poly(vinyl alcohol)/graphene (PVA/Gr) hydrogel discs, followed by electrochemical reduction method of different concentrations of Ag+ ions (0.25, 0.5,1.0 and 3.9 mM AgNO3 swelling solution) inside the hydrogel polymer matrices at a constant voltage that enables the silver particle size control, in a specially designed electrochemical cell. Silver/poly(vinyl alcohol) (Ag/PVA) and silver/poly(vinyl alcohol)/graphene (Ag/PVA/Gr) nanocomposites were characterized by UV–visible spectroscopy. The absorption spectra at about 405-420 nm proved existence of AgNPs in both Ag/PVA and Ag/PVA/Gr nanocomposites. Cyclic voltammetry revealed some oxidation and reduction peaks suggesting the presence of AgNPs between polymer chains. Raman spectroscopy analysis confirmed the graphene structure in its pure form, X-ray diffraction was used to reveal the additional interactions established between the PVA molecules and graphene sheets and the AgNPs situated between the polymer chains in viii the Ag/PVA/Gr nanocomposite. The calculated interspacing (d-spacing) value for (002) lattice plane of the PVA and Ag/PVA hydrogels was 0.457 nm, while the obtained value changed slightly with the introduction of graphene sheets (0.449 nm for Ag/PVA/Gr nanocomposite). Fourier transform infrared spectroscopy (FTIR) results for both Ag/PVA and Ag/PVA/Gr nanocomposites suggested the interaction between AgNPs and hydroxyl groups of the PVA molecules through decoupling between the corresponding vibrations. Thermogravimetric analysis and corresponding differential thermal analysis were done to investigate the role of graphene sheets in the thermal stability of thus prepared nanocomposite samples, and the results showed higher stability of Ag/PVA/Gr than Ag/PVA nanocomposites. Morphology of the prepared PVA, PVA/Gr, Ag/PVA and Ag/PVA/Gr samples were examined by field-emission scanning electron microscopy (FE-SEM) technique and the microphotographs showed sphere-shaped AgNPs at nanoscale levels which were around 36 nm in the Ag/PVA and around 17 nm in the Ag/PVA/Gr nanocomposites...

Ova doktorska disertacija se bavi sintezom hidrogelova polivinil-alkohola, grafena i nanočestica srebra (Ag/PVA/Gr), imobilizacijom nanočestica srebra u matrici hidrogela polivinil-alkohol/grafen (PVA/Gr) u dva koraka. Prvi korak je umrežavanje koloidnog rastvora PVA/Gr metodom zamrzavanja i odmrzavanja, dok je u drugom koraku primenjena in situ elektrohemijska metoda za inkorporaciju nanočestica srebra u matrici PVA/Gr hidrogela. Glavni cilj ovog istraživanja je bila priprema nanokompozitnih biomaterijala na bazi grafena sa inkorporisanim nanočesticama srebra, sa mogućom primenom u vidu implantata mekog tkiva, obloga za rane i nosača za lekove. Elektrohemijski postupak sinteze nanočestica je posebno atraktivan za primene u biomedicini, zbog velike čistoće i mogućnosti precizne kontrole dobijenih nanočestica, kao i zbog odsustva hemijskih agenasa i neželjenih produkata. Metoda umrežavanja cikličnim zamrzavanjem i odmrzavanjem je korišćena u cilju dobijanja polivinil-alkohol (PVA) i polivinil-alkohol/grafen (PVA/Gr) hidrogelova u obliku diskova, a zatim je izvršena elektrohemijska redukcija Ag+ jona različitih koncentracija (0,25, 0,5,1,0 i 3,9 mM AgNO3 swelling solution) u polimernoj matrici hidrogela, na konstantnom naponu, što omogućava kontrolu dimenzija čestica srebra, u posebno dizajniranoj elektrohemijskoj ćeliji. Srebro/polivinil-alkohol (Ag/PVA) i srebro/polivinil-alkohol/grafen (Ag/PVA/Gr) nanokompoziti su karakterisani UV-vidljivom spektroskopijom. Apsorpcioni spektri sa maksimumom na oko 405-420 nm su dokazali prisustvo nanočestica srebra u Ag/PVA i Ag/PVA/Gr nanokompozitima. Cikličnom voltametrijom su pokazani pikovi oksidacije i redukcije koji ukazuju na prisustvo nanočestica srebra u polimernoj matrici. Ramanova spektroskopija je potvrdila čistu grafensku strukturu, dok je rendgenska difrakcija korišćena za ispitivanje interakcija između PVA molekula sa grafenom i nanočesticama srebra, smeštenim između polimernih lanaca Ag/PVA/Gr nanokompozita. Izračunato rastojanje između krisalnih xi ravni za (002) ravan u PVA i Ag/PVA hidrogelovima je iznosilo 0.457 nm, dok se ova vrednost promenila nakon inkorporacije grafena (0.449 nm za Ag/PVA/Gr nanokompozit). Rezultati analize infracrvenom spektroskopijom sa Furijeovom transformacijom (FTIR) za Ag/PVA i Ag/PVA/Gr nanokompozite su ukazali na interakcije između nanočestica srebra i hidroksilnih grupa na PVA molekulima, na osnovu razdvajanja odgovarajućih vibracionih traka. Termogravimetrijska analiza i diferencijalna termogravimetrijska analiza su korišćene radi ispitivanja termičke stabilnosti dobijenih uzoraka hidrogelova, a rezultati su pokazali povećanu stabilnost Ag/PVA/Gr u odnosu na Ag/PVA nanokompozite. Morfologija dobijenih uzoraka PVA, PVA/Gr, Ag/PVA i Ag/PVA/Gr je ispitana tehnikom skenirajuće elektronske mikroskopije (FE-SEM), a na mikrografijama su uočene čestice srebra sfernog oblika i nanometarskih dimenzija oko 36 nm u Ag/PVA i oko 17 nm u Ag/PVA/Gr nanokompozitu...