33 research outputs found
Synthesis and characterization of calcium based mixed oxide catalysts and their application in heterogenously catalyzed biodiesel synthesis
U ovom radu prouÄavana je primena mehanohemije u sintezi prekursora aktivnih
katalizatora reakcije transesterifikacije suncokretovog ulja. Ispitivan je uticaj razliÄitih
metoda sinteze ā mehanohemijske, sa i bez dodatka vode i, radi poreÄenja, taložne ā na
osobine dobijenog prekursora CaZn2(OH)6Ā·2H2O. SmeÅ”a prahova Ca(OH)2 i ZnO u
molskom odnosu od 1:2 je podvrgnuta mlevenju u planetarnom mlinu tokom
vremenskog perioda od 7 h, uz dodatak stehiometrijski potrebne koliÄine vode, kao i
bez dodatka vode. IzvrŔena je i sinteza prekursora katalizatora koprecipitacijom
Ca(OH)2 i ZnO u vodenom rastvoru KOH radi poreÄenja. Prekursorski prahovi dobijeni
u sve tri sinteze su viÅ”efazni, a njihova aktivacija izvrÅ”ena je na temperaturi od 700 Ā°C,
Äime su prevedeni u meÅ”oviti oksid CaOĀ·ZnO. Nakon kalcinacije, katalizatori su
primenjeni u sintezi metil estara masnih kiselina (MEMK) suncokretovog ulja. IzvrŔena
je i detaljna fiziÄko-hemijska karakterizaciju pripremljenih prahova, pre i posle
kalcinacije: strukturna karakterizacija dobijenih prahova uraÄena je metodom
rendgenske strukturne analize (XRD), dok je morfoloŔka karakterizacija prahova nakon
žarenja uraÄena skenirajuÄom elektronskom mikroskopijom (SEM/EDS). TakoÄe,
primenjivana je i termijska analiza (TGA/DSC), i infracrvena (IC) spektroskopija radi
dobijanja dodatnih informacija o strukturi i sastavu katalizatora. Kako pomenuti
katalizatori daju razliÄite prinose u reakciji transesterifikacije triglicerida sa metanolom,
utvrÄena je bitna povezanost izmeÄu baznosti katalizatora pripremljenih razliÄitim
metodama i katalitiÄke efikasnosti. Mehanohemijska sinteza se, u odnosu na
konvencionalnu koprecipitaciju, pokazala kao jednostavnija metoda koja ne ukljuÄuje
rastvaraÄ i dodatak alkalija koje mogu ometati uvid u stvarnu katalitiÄku aktivnost, a
ujedno i kao efikasnija metoda za dobijanje aktivnih prekursora meŔovitih oksida.
Pored Ca(OH)2, kao polazni prah koriÅ”Äen je i CaO, dobijen nakon žarenja
Ca(OH)2 na 700 Ā°C, kao i negaÅ”eni kreÄ, a sve sa ciljem smanjenja koliÄine prisutnih
karbonata u sintetisanim prekursorima. Uticaj dodatka promotora (K2CO3) tokom
mehanohemijske sinteze na strukturu i katalitiÄku aktivnost je ispitivan variranjem odnosa K:Ca...The use of mechanochemical synthesis to obtain active catalyst precursors and
testing their activity in transesterification of sunflower oil with methanol was
investigated. The effect of different methods for preparation of catalytic precursor
(CaZn2(OH)6Ā·2H2O) ā mechanochemical, with or without the addition of water and
coprecipitation were investigated. A powder mixture of Ca(OH)2 and ZnO, with the
molar ratio of 1:2, with, as well as without stoichiometrically required addition of water
were milled in a planetary ball mill for a period of 7 hours. The classical coprecipitation
procedure of Ca(OH)2 and ZnO powders in KOH solution was also performed for
comparison.
Precursor powders obtained after above mentioned procedures were multiphase,
and their activation was carried out at temperature of 700 Ā°C, in order to convert them to
CaOĀ·ZnO mixed oxide. After calcination, the catalytic activity was tested in the
synthesis of fatty acid methyl esters (FAME) from sunflower oil. Structural
characterization of obtained powders was done by X-ray diffraction (XRD) analysis,
while morphology was observed by scanning electron microscopy (SEM/EDS).
Thermal analysis (TG / DSC) was also applied, as well as infrared spectroscopy (IR) in
order to obtain additional information on the structure and composition of the catalysts.
The difference in the activity of mechanochemically synthesized catalysts and catalyst
prepared by coprecipitation procedure could be related to the difference in their basicity.
Mechanochemical synthesis has an advantage over the coprecipitation due to its relative
simplicity ā solid phase reactions without usage of solvents or precipitants which can
interfere with catalytic activity.
Using CaO, obtained after calcination of Ca(OH)2 at 700 Ā°C, and lime as a
starting powders was investigated in order to reduce the amount of carbonates present in
the synthesized precursors. Influence of promoter (K2CO3) added to starting mixture of
lime and ZnO for mechanochemical synthesis on precursor structure and catalytic
activity was examined by varying the ratio of K:Ca..
Antimikrobno dejstvo eteriÄnih ulja na oralne patogene
Periodontal disease and Dental caries associated with dental plaque are the most common bacterial diseases, but also, significant oral health problem is Candidiasis. Candida albicans, is an opportunistic pathogen that can, under certain conditions proliferate and cause infections. The need for prevention and alternative forms of treatment and products for oral diseases comes from the rise in disease incidence, increased resistance by pathogenic bacteria to currently used chemotherapeutics. The products derived from medicinal plants have proven to be a source of biologically active substances, and thanks to their active principles, products based on medical herbs are more prevalent in modern phytotherapy. Essential oils are complex natural mixtures of volatile secondary metabolites - aliphatic and aromatic, terpinen and phenyl- propane compounds isolated from plants. The main constituents of essential oils are terpenes and sesquiterpenes including carbohydrates, alcohols, ethers, aldehydes and ketones, which are responsible for the fragrant and biological properties of plants. Different oils produce various pharmacological effects such as anti-inflammatory, antioxidant and anticancerogenic properties, but also oils are biocides. There are numerous in vitro studies that dealt with the research activities of natural herbal substances against oral bacteria that are known to be etiological factors in the development of oral and dental diseases. The phenolic major compounds of essential oils have been suggested to have a potential antifungal activity. There is ample of evidence that plant extracts and essential oils have the potential to be developed into agents that can be used as preventative or treatment therapies of oral diseases.Parodontopatija i dentalni karijes, Äiji je nastanak povezan sa dentalnim plakom, predstavljaju najÄeÅ”Äa bakterijska oboljenja. TakoÄe, znaÄajni oralni zdravstveni problem predstavlja i kandidijaza. Candida albicans je oportunistiÄki patogen koji pod pojedinim okolnostima može da proliferiÅ”e i uzrokuje infekciju. Potreba za prevencijom i alternativnim oblicima leÄenja i produktima za oralna oboljenja proizilazi zbog poveÄanja uÄestalosti oboljenja i poveÄane rezistencije patogenih bakterija na primenu hemoterapeutika koji se trenutno upotrebljavaju. Dokazano je da su produkti dobijeni od lekovitog bilja izvor bioloÅ”ko aktivnih supstanci, a zahvaljujuÄi svojim aktivnim principima, produkti na bazi lekovitog bilja zastupljeniji su u modernoj fitoterapiji. EteriÄna ulja su kompleksne prirodne meÅ”avine isparljivih sekundarnih metabolita - alifatiÄnih i aromatiÄnih, terpenskih i fenil-propanskih jedinjenja izolovanih iz biljaka. Glavni sastojci etarskih ulja su terpeni i seskviterpeni, ukljuÄujuÄi i ugljene hidrate, alkohol, etar, aldehide i ketone, koji su odgovorni za mirisna i bioloÅ”ka svojstva biljaka. RazliÄita ulja imaju brojne farmakoloÅ”ke efekte, kao Å”to su antiinflamatorno, antioksidativno i antikancerogeno dejstvo, ali su takoÄe i biocidi. Postoje brojne in vitro studije koje su se bavile istraživanjem aktivnosti prirodnih biljnih supstanci usmerenih na oralne bakterije za koje je poznato da su etioloÅ”ki faktori u nastanku oralnih i dentalnih oboljenja. Navedeno je da glavne fenolne komponente eteriÄnih ulja imaju potencijalnu antigljiviÄnu aktivnost. Postoje brojni dokazi da biljni ekstrakti i eteriÄna ulja imaju potencijal da se razviju u agense koji se mogu koristiti u preventivi ili u leÄenju oralnih oboljenja