Electrochemical properties of composites of graphene-oxide and cobalt-ferrite doped with zink and gallium

U ovom radu prikazana su elektrohemijska svojstva kompozita grafen-oksida i nanočestica kobalt-ferita, kao i kobalt-ferita dopiranog sa cinkom i galijumom. Grafen-oksid (GO) sintetisan je modifikovanom Hamerovom metodom. Magnetne nanočestice sintetisane su solvotermalnom metodom, nakon čega je izvršena izmena oleinske kiseline dihidrokofeinskom kiselinom sa ciljem dobijanja hidrofilnog materijala. Kompoziti grafen-oksida i magnetnih nanočestica sintetisani su hidrotermalnom metodom, prilikom čega je udeo magnetnih čestica bio 5 i 15 težinskih % u odnosu na grafen-oksid. Rezultati rendgeno-strukturne i FTIR analize potvrdili su potpunu oksidaciju grafenskih slojeva. SEM i TEM analize pokazale su depoziciju magnetnih nanočestica na sloju grafen-oksida, bez promene veličine ili oblika nanočestica. FTIR analiza hidrotemalno tretiranog grafen-oksida i kompozita pokazala je da dolazi do delimične redukcije epoksi grupa, kao i da se uspostavlja vodonična veza između komponenti kompozita. Ciklovoltamogrami pokazuju da su kompoziti stabilni pri brzinama polarizacije od 5 do 400 mV s-1, kao i da je njihov kapacitet pretežno pseudokapacitivne prirode. Pseudokapacitivnost potiče od oksidoredukcionih reakcija H+ jona iz elektrolita i površinskih funkcionalnih grupa grafen oksida. Na osnovu ciklovoltamograma izračunati su specifični kapaciteti svih kompozita, pri čemu je najveću vrednost pokazao kompozit CFO_GO_15% koja iznosi 36,86 F g-1 pri brzini polarizacije od 5 mV s-1.This paper presents the electrochemical properties of graphene-oxide composites and nanoparticles of cobalt-ferrite, as well as cobalt-ferrite doped with zinc and gallium. Graphene-oxide (GO) was synthesized by a modified Hummer's method. The magnetic nanoparticles were synthesized by the solvothermal method, after which the oleic acid was exchanged with dihydrocaffeic acid to obtain the hydrophilic material. Composites of graphene-oxide and magnetic nanoparticles were synthesized by the hydrothermal method, where the share of magnetic particles was 5 and 15 wt.% on graphene-oxide. The results of X-ray structural and FTIR analysis confirmed the complete oxidation of graphene layers. SEM and TEM analyzes showed deposition of magnetic nanoparticles on the graphene-oxide layer, without changing the size or shape of the nanoparticles. FTIR analysis of hydrothermally treated graphene oxide and composites showed that there is a partial reduction of epoxy groups, also a hydrogen bond is established between the components of the composite. Cyclic voltammograms show that the composites are stable at polarization rates of 5-400 mV s-1, and that their capacity is predominantly pseudocapacitive in nature. Pseudocapacitance originates from the oxidoreduction reactions of H+ ions from electrolytes and surface functional groups of graphene-oxide. Based on the cyclic voltammograms, the specific capacities of all composites were calculated and the highest value being shown by the CFO_GO_15% composite, which is 36.86 F g-1 at a polarization rate of 5 mV s-1

Sezonska dinamika glivne kolonizacije korenin visokega trpotca v presihajočem mokrišču

Fungal colonisation in an amphibious plant species from an intermittent lake may differ significantly among plant specimens growing under contrasting water regimes. We examined the effect of the presence of surface water on the level of fungal colonisation in tall plantain(Plantago altissima L.). We investigated the presence and abundance of arbuscular-mycorrhizal (AM) structures, dark-septate-endophyte (DSE) fungal structures, and plant growth parameters. The observed overall frequency of fungal structures during the vegetative season was relatively high, ranging from 50% to 90%. Mycorrhizal frequency was little affected by water level fluctuations. However, it dropped significantly at the end of the season in the senescence phase. The densities of arbuscules, vesicles, and hyphal coils reached the highest levels in peak season in June and July. The density of DSE structures, namely microsclerotia, showed similar dynamics over the season as forAM structures. Mycorrhizal frequency was positively related to leaf water content.Glivna kolonizacija amfibijskih rastlinskih vrst na presihajočem jezeru se lahko znatno razlikuje med rastlinami, ki rastejo v razmerah različnega vodostaja. Preučili smo učinek prisotnosti površinske vode na raven glivne kolonizacije pri visokem trpotcu (Plantago altissima L.). Raziskali smo prisotnost in številčnost struktur arbuskularne mikorize (AM), struktur temnih septiranih endofitov (DSE) in parametrerasti rastlin. Pogostnost glivnih struktur med je bila med rastno sezono rarmeroma visoka, saj je segala od 50 % do 90 %. Pogostno stmikorize je ostala na isti ravni ne glede na spremembe vodostaja, vendar se je ob koncu sezone v fazi senesence znatno znižala. Gostota arbuskulov, veziklov in svitkov je dosegla najvišjo raven v juniju in juliju. DSE strukture, mikrosklerociji, so imele podobno dinamiko ko tAM strukture. Pogostnost mikorize je bila pozitivno povezana z vsebnostjo vode v listih