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Migration of metals into aqueous media from recycled plastics
No full textUporaba plastike na globalnoj razini raste, a recikliranje se smatra ključnim za očuvanje resursa i zatvaranja ciklusa materijala. Prilikom recikliranja može doći do narušavanja strukture polimera. Plastika može biti sastavljena od raznih polimera i sadržavati različite tvari koje se dodaju kako bi se poboljšala svojstva plastike (aditivi). Pojedine tvari mogu migrirati iz reciklirane plastike u vodeni medij poput metala koji su sastavni dio aditiva. Cilj rada je ispitati razlike u svojstvima plastike PP (polipropilen) tijekom procesa recikliranja. Recikliranje je provedeno u ekstruderu, mehaničkim recikliranjem PP-a uz dodatnu namjernu kontaminaciju uzorka u različitim ciklusima recikliranja. Praćena je promjena u strukturi polimera povećanjem broja ciklusa recikliranja raspodjelom veličina čestica i DSC analizom (diferencijalna pretražna kalorimetrija). Također, pomoću ICP-MS analize (induktivno spregnute plazme s masenom spektrometrijom) utvrđena je koncentracija metala koji izlaze iz strukture tako reciklirane plastike i dospijevaju u vodeni medij tzv. testovima ispitivanja migracija metala. Analizom su utvrđene koncentracije sljedećih metala: Sb, Ca, Mg, Na, K, V, Ga, Rb, Sr, Ag, Sn, Pb, Cd, Cr, As, Ni, Mn, Zn, Al, Ba, Co, Cu, Fe i Li. Kako bi se dobila šira slika o potencijalno negativnom učinku recikliranja, uzorci nakon ispitivanja migracije metala podvrgnuti su testovima ekotoksičnosti i biorazgradivosti. Ekotoksičnost je ispitana na dvije vrste organizama; slatkovodnim vodenbuhama Daphnia Magna i morskim bakterijama Vibrio Fischeri. Biorazgradivost je određena pomoću testova KPK (kemijska potrošnja kisika) i BPK5 (biokemijska potrošnja kisika u 5 dana). Nakon provedenih analiza utvrđeno je narušavanje strukture PP povećanjem ciklusa recikliranja. Temeljem rezultata o raspodjeli veličina čestica utvrđeno je povećanje krtosti materijala dok je DSC analizom pokazano povećanje stupnja kristalnosti. Testovi ispitivanja migracije metala iz uzorka utvrđuju manju koncentraciju migriranih metala kod povećanog broja ciklusa recikliranja zbog ugradnje metala u strukturu polimera. Ekotoksičnost vodenih uzoraka nakon procesa ispitivanja migracija metala iz recikliranih uzoraka povećava se brojem ciklusa recikliranja, dok se biorazgradivost s povećanjem ciklusa recikliranja smanjuje.The use of plastics is increasing globally, and recycling is considered key to conserving resources and closing the material cycle. During recycling, the structure of the polymer may be damaged. Plastic can be composed of various polymers and contain various substances that are added to improve the properties of the plastic (additives). Certain substances can migrate from recycled plastic into the aqueous medium, such as metals that are an integral part of additives. The aim of the work is to examine the differences in the properties of PP (polypropylene) plastic during the recycling process. Recycling was carried out in an extruder, by mechanical recycling of PP with additional intentional contamination of the sample in different recycling cycles. The change in the polymer structure by increasing the number of recycling cycles was monitored by particle size distribution and DSC analysis (differential scanning calorimetry). Concentration of metals that comes out of the structure of recycled plastics and ends up in the water medium was determined by ICP-MS analysis (inductively coupled plasma with mass spectroscopy) and socalled metal migration tests. The analysis determined the concentrations of the following metals Sb, Ca, Mg, Na, K, V, Ga, Rb, Sr, Ag, Sn, Pb, Cd, Cr, As, Ni, Mn, Zn, Al, Ba, Co, Cu, Fe and Li. In order to get a broader picture of the potentially negative effect of recycling, the samples after the metal migration test were subjected to ecotoxicity and biodegradability tests. Ecotoxicity was tested on two types of organisms: the freshwater daphnia Daphnia Magna and the marine bacterium Vibrio Fischeri. Biodegradability was determined using COD (chemical oxygen demand) and BOD5 (biochemical oxygen demand in 5 days) tests. After the analysis, it was determined that the PP structure was damaged by increasing the recycling cycle. Based on the results on the distribution of particle sizes, an increase in the brittleness of the material was determined, while the DSC analysis showed an increase in the proportion of the crystalline phase. Tests of metal migration from the sample determined a lower concentration of migrated metals with an increased number of recycling cycles due to the incorporation of metals into the polymer structure. The ecotoxicity of water samples after the process of testing the migration of metals from recycled samples increases with the number of recycling cycles, while the biodegradability decreases with increasing recycling cycles
Biocatalytic synthesis of (R)-4-chloro-3-hydroxybutyronitrile catalysed by halohydrin dehalogenase
No full textEnzimi su biokatalizatori koji kataliziraju reakcije u živim organizmima. Njihova primjena omogućuje niz prednosti, poput odvijanja reakcija u blažim uvjetima te smanjenje nastanka štetnih nusprodukata. Prirodna uloga halogenhidrin-dehalogenaza je kataliza halohidrina u odgovarajuće epokside (reakcija dehalogenacije), odnosno kataliza reakcije zatvaranja epoksidnog prstena pri čemu dolazi do otpuštanja halogenih iona. U ovom radu je ispitana reakcija biokatalitičke sinteze (R)-4-klor-3-hidroksibutironitrila uz B-tip halogenhidrin-dehalogenaze. Sinteza optički čistih tvari izuzetno je važan dio farmaceutske industrije s obzirom na to da dva enantiomera mogu imati potpuno različita svojstva, a vrlo često jedan od njih može pokazivati štetno i toksično biološko djelovanje. Epoksidi su visoko vrijedni spojevi u organskoj sintezi zbog toga što se epoksidni prsten može kemijski transformirati u brojne sintetski korisne intermedijere. Reakcije u kojima su uključeni enzimi potrebno je pomno istražiti i okarakterizirati kako bi se mogle provoditi u industrijskom mjerilu. Reakcija biokatalitičke sinteze (R)-4-klor-3-hidroksibutironitrila provedena je u kotlastom reaktoru uz natrijev cijanid kao nukleofil, a uzorci su analizirani uporabom plinske kromatografije. Ispitan je utjecaj koncentracija reakcijskih komponenti na brzinu enzimske reakcije te je pokazan nizak afinitet enzima prema supstratu i nukleofilu kod oba enzima, a također je uočen značajan inhibicijski učinak produkta. Aktivnost enzima praćena je spektrofotometrijski, a rezultati su pokazali da aktivnost kod oba enzima pada s vremenom, odnosno dolazi do njihove deaktivacije.Enzymes are biocatalysts that catalyze reactions in living cells. Their usage provides a number of advantages, such as conducting a reaction in milder conditions and a reduction in the occurrence of harmful by-products. The natural role of halohydrin-dehalogenases is the catalysis of halohydrins to the corresponding epoxides (dehalogenation). Halohydrin-dehalogenase catalyzes the epoxy ring closure in which halogen ions are released. In this work, the reaction of biocatalytic synthesis of (R)-4-chloro-3-hydroxybutyronitrile with type B halohydrin-dehalogenase was investigated. The synthesis of optically pure substances is an extremely important part of the pharmaceutical industry since two enantiomers can have completely different properties and very often one of them can show harmful and toxic biological effects. Epoxides are highly valuable compounds in organic synthesis because the epoxy ring can be chemically transformed into a number of synthetic beneficial intermediates. Reactions involving enzymes need to be carefully investigated and characterized in order to be carried out on an industrial scale. The biocatalytic synthesis of (R)-4-chloro-3-hydroxybutyronitrile was carried out in a batch reactor with sodium cyanide as a nucleophile. The samples were analyzed using gas chromatography. The influence of the concentration of the reaction components on the rate of the enzymatic reaction was tested. Low enzyme affinity for the substrate and nucleophile was observed in reactions with both enzymes. A significant inhibitory effect of the product was also shown. The activity of the enzyme was monitored by spectrophotometer and it was observed that in both enzymes there is a decrease in activity over time
Modifying the properties of hydrogels by adding material from a biogenic source
No full textU inženjerstvu mekog tkiva stavlja se veliki naglasak na proizvodnju strukturnih nosača od biomaterijala. Oni se često proizvode od hidrogelova decelularizirane izvanstanične matrice (dECM) jer se postupkom decelularizacije uklanjaju stanice svojstvene izvornoj matrici uz očuvanje biološko-kemijskih karakteristika iste. Nosači moraju imati odgovarajuću mehaničku čvrstoću i stabilnost kako bi podupirali prianjanje, rast i razvoj stanica u čemu sam dECM često ne zadovoljava. Stoga se fizikalno-kemijska i mehanička svojstva modificiraju dodatkom prirodnih polisaharida poput natrijeva alginata. Osim toga, geliranje samog natrijeva alginata može se potaknuti dodatkom kalcijeva klorida, čime se neposredno utječe i na njegovu čvrstoću. Takvom pripremom nastaju hibridni hidrogelovi natrijeva alginata uz kalcijev klorid i dECM-a. Hidrogelovima pripremljenim od natrijeva alginata (3 % i 5 % mas.) uz dodatak kalcijeva klorida (1 – 5 i 8 % mas.) ispitivalo se reološko ponašanje i određivala viskoznost kako bi se istražio utjecaj CaCl2 na mehanička svojstva gelova. Hidrogelove pripremljene kombiniranjem različitih koncentracija natrijeva alginata uz 5% CaCl2 s dECM-om karakteriziralo se pomoću razlikovne pretražne kalorimetrije (engl. differential scanning calorimetry, DSC) te infracrvenom spektroskopijom s Fourierovom transformacijom (engl. Fourier-transform infrared spectroscopy, FTIR). Na taj način su se ispitale stabilnost i potencijalne novonastale veze u hibridnim hidrogelovima. Rezultati reoloških ispitivanja pokazali su da su hidrogelovi natrijeva alginata uz dodatak 5% kalcijeva klorida najprimjenjiviji za daljnja ispitivanja. Rezultati ispitivanja pomoću DSC-e pokazali su da je uzorak 25 dECM/75 5% ALG najstabilniji, a rezultati FTIR analize upućuju da su najčvršće veze u uzorku 50 dECM/50 3% ALG. Dakle, rezultati nisu jednoznačno uputili na uzorak koji se može smatrati najpogodnijim za buduću analizu što se često događa u ispitivanju svojstava hidrogelova. Zahtjevi za in vivo primjenu i 3D ispis često su kontradiktorni i potrebno je pomno ugađanje parametara poput viskoznosti, stupnja umrežavanja i termičkih svojstava za pripremu odgovarajućeg hidrogelnog nosača.In soft tissue engineering, there is a great emphasis on the production of scaffolds from biomaterials. They are often produced from decellularized extracellular matrix (dECM) hydrogels because during the decellularization process native cells are removed with the preservation of biological and chemical characteristics. Scaffolds must meet certain requirements such as mechanical stiffness and stability to support cell adhesion, growth, and development, in which dECM alone frequently does not suffice. Therefore, the physico-chemical and mechanical properties are modified with the addition of natural polysaccharides such as sodium alginate. In addition, the gelation of sodium alginate itself can be stimulated by the addition of calcium chloride, which directly affects its mechanical strength. Such preparation creates hybrid hydrogels of sodium alginate with calcium chloride and dECM. To characterize the hydrogels prepared from sodium alginate (3% and 5% wt%) and calcium chloride (1-5 and 8% wt%), their rheological behaviour was examined, determining the viscosity to investigate the influence of CaCl2 on the mechanical properties of gels. Hydrogels prepared by combining different concentrations of sodium alginate with dECM were characterized using differential scanning calorimetry (DSC) and Fourier-transform infrared spectroscopy (FTIR). In this way, the stability and potential newly formed bonds in the combined hydrogels were tested. The results of rheological testing showed that sodium alginate hydrogels with 5% calcium chloride were most applicable for further testing, The results of DSC tests showed that the 25 dECM/75 3% ALG sample is the most stable, and the FTIR analysis results indicate that the strongest bonds are in the 50 dECM/50 3% ALG sample. Thus, the results did not unequivocally point to the sample that can be considered the most suitable for future analysis, which commonly happens in testing the properties of hydrogels. Requirements for in vivo application and 3D printing are often contradictory and it’s necessary to carefully adjust parameters such as viscosity, degree of crosslinking and thermal properties for preparation of the appropriate hydrogel scaffold
The measurement of polarization potential of cathodic protection on steel coupons
No full textRazličiti metali se primjenjuju svakodnevno u izgradnji cjevovoda i drugih konstrukcija te stoga ne čudi pridavanje velikog zanimanja njihovoj zaštiti od vanjskih utjecaja, tj. utjecaja okoline koji dovode do njihove korozije. U današnje vrijeme postoje razni načini za zaštitu materijala od korozije, ali ako se razmatraju cjevovodi, onda je najčešći način njihove zaštite, uz korištenje organskih premaza, katodna zaštita. Ovaj diplomski rad bavi se kontrolom katodne zaštite na štićenoj konstrukciji, odnosno određivanjem potencijala štićene konstrukcije, kao glavnim kriterijem djelotvornosti katodne zaštite. U tu svrhu ispitivani su kuponi bez IR pada napona (engl. IR-free) koji se upotrebljavaju za mjerenje uključno-isključnog (ON-OFF) potencijala na način da svojom konstrukcijom uklanjaju dodatnu komponentu pada potencijala u elektrolitu (IR komponentu). Za provođenje ispitivanja izrađen je IR-free kupon na temelju postojećih komercijalnih kupona. Tijekom mjerenja se, osim načina ostvarivanja katodne zaštite na konstrukciji, mijenjala i ispuna Lugginove kapilare (vodovodna voda, zemlja i smjesa bentonita i kvarca u vodovodnoj vodi), koja je bila dio konstrukcije IR-free kupona te elektrolit u kojem se eksperiment provodio. Nadalje, parametri čiji se utjecaj na veličinu dodatnog pada potencijala u elektrolitu pratio su bili duljina Lugginove kapilare i promjer njezina dna. Konačna ideja samoga rada je, dakle, bila ispitati uklanjaju li stvarno IR-free kuponi u potpunosti dodatni pad potencijala u elektrolitu i ako ne u kojoj ga mjeri smanjuju. Pritom je kupon bio izrađen od konstrukcijskog čelika, a referentna elektroda je bila Cu/CuSO4 referentna elektroda. Na kraju istraživanja provedena je karakterizacija komercijalnih kupona.Different metals are used every day in the construction of pipelines and other structures, and therefore it is not surprising that there is a great interest in their protection from external influences, i.e. environmental influences that lead to their corrosion. Nowadays, there are various ways to protect materials from corrosion, but if pipelines are considered, then the most common way to protect them, along with the use of organic coatings, is cathodic protection. This diploma work deals with controlling the cathodic protection on the protected structure, that is, determining the potential of the protected structure, as the main criterion for the effectiveness of the cathodic protection. For this purpose, IR-free coupons were tested, which are used to measure the structure ON-OFF potential, in such a way that their design removes the potential drop component in the electrolyte (IR component). An IR-free coupon based on existing commercial coupons was created. During the measurement, in addition to the method of cathodic protection, the filling of the Luggin capillary (tap water, soil and a mixture of bentonite and quartz in the tap water), which was part of the construction of the IR-free coupon, and the electrolyte in which the experiment was conducted, was examined. Furthermore, the influence of length of the Luggin capillary and the diameter of its bottom on the size of the additional potential drop in the electrolyte was studied. The final idea of the work was to examine whether IR-free coupons completely remove the additional potential drop in the electrolyte and, if not, to what extent they reduce it. The coupon was made of structural steel, and the reference electrode was a Cu/CuSO4 electrode. At the end of the research, the characterization of commercial coupons was carried out
The preparation of strontium doped manganites for multiple applications
No full textModerno se društvo vrlo brzo razvija, procesi urbanizacije i industrijalizacije sve su izraženiji, a kvaliteta života raste na račun velike potrošnje energije. Prema statističkim podacima, više od 80 % utrošene energije dobiva se sagorijevanjem fosilnih goriva što rezultira povećanim emisijama štetnih tvari i izraženim klimatskim promjenama. Stoga je za održivi razvoj društva potrebno razvijati nove tehnologije za proizvodnju i skladištenje energije, a nove tehnologije zahtijevaju i nove radne materijale. Skupina novih funkcionalnih materijala su perovskitni oksidi, materijali opće formule ABO3 u kojima se na mjestu A nalazi kation zemnoalkalijskog metala ili metala rijetkih zemalja, a mjesto B okupirano je kationom nekog polivalentnog prijelaznog metala. Zbog prisutnosti miješanih valencija kationa B unutar kristalne rešetke, perovskiti imaju brojna atraktivna svojstva kao što su električna vodljivost, magnetska svojstva, fotokatalitička i katalitička aktivnost. U ovom doktoratu proučavani su perovksitni oksidi na bazi mangana koji se skraćeno nazivaju manganitima. Tema istraživanja bili su
Sr-dopirani kalcijevi (Ca1–xSrxMnO3, CSMO), barijevi (Ba1–xSrxMnO3, BSMO) i lantanovi (La1–xSrxMnO3, LSMO) manganiti. Svi navedeni materijali pripremljeni su dvama različitim postupcima sinteze iz otopine – limunskim i koprecipitacijskim postupkom. Nastanak ciljanih manganitnih faza potvrđen je rendgenskom difrakcijskom analizom, a parametri kristalnih rešetki te okupancije (zaposjednutosti) pojedinih atoma određene su Rietveldovom metodom utočnjavanja. Budući da je za manganite karakterističan nestehiometrijski sadržaj kisika, on je određen permanganatnom titracijom uz Mohrovu sol. Nakon što je utvrđeno da su u svim pripremljenim materijalima nastale ciljane manganitne faze, pristupilo se istraživanju primjenskih svojstava materijala. Impedancijskom spektroskopijom određena je električna vodljivost materijala u široku rasponu frekvencija i temperatura. Za LSMOi CSMO-materijale ta je vodljivost bila frekvencijski neovisna u cijelom području što ukazuje na brzi transport elektrona bez blokirajućih efekata. Također je rasla s porastom temperature što ukazuje na poluvodički karakter tih materijala, a pokazalo se i da ju povećavaju kisikove vakancije. Stoga su LSMO- i CSMO-materijali prepoznati kao potencijalni katodni materijali u gorivnim ćelijama s čvrstim oksidom kao elektrolitom (engl. solid oxide fuel cells, SOFC). S druge strane, električna vodljivost BSMO-materijala bila je frekvencijski ovisna, a materijali su također pokazali poluvodički karakter. Iako neprikladni za SOFC, prepoznati su kao atraktivni za primjenu u uređajima za pohranu podataka. Istraživanja magnetskih svojstava pokazala su da se LSMO-i ponašaju kao meki feromagneti s Curiejevom temperaturom koja raste s porastom udjela Sr-dopiranja te za udjele od 0,2 i 0,3 prelazi sobnu temperaturu, što ih čini prikladnima za širok spektar primjena. Osim toga, LSMO-i pokazuju i magnetokalorični učinak što ih čini potencijalnom zamjenom gadoliniju u magnetskim hladnjacima. Za razliku od njih, CSMO-i i BSMO-i po svojem su magnetskom uređenju antiferomagneti kod kojih zbog distorzija kristalne rešetke uslijed dopiranja dolazi do naginjanja, tj. kantiranja spinova. Njihove temperature faznog prijelaza (antiferomagnet – paramagnet) daleko su ispod sobne, no bez obzira na to prikladni su za primjenu u suvremenim uređajima za pohranu podataka i u novom polju fizike – spintronici jer se na njihovu električnu vodljivost može utjecati promjenom orijentacije spina. Svi pripremljeni manganiti pokazali su izvrsnu katalitičku aktivnost pri simultanoj razgradnji četiriju hlapljivih organskih komponenti: benzena, toluena, etilbenzena i o-ksilena. Pritom su sve komponente osim benzena potpuno ili gotovo potpuno uklonjene na konačnoj temperaturi od 450 °C, dok je benzen bilo teže ukloniti zbog njegove visoke stabilnosti i činjenice da je razgradni produkt svih ostalih komponenata u smjesti. Katalitička aktivnost s obzirom na uspješnost uklanjanja benzena rasla je u nizu LSMO < CSMO < BSMO, a najbolji rezultati dobiveni su za BSMO-uzorke pripremljene limunskim postupkom. Na temelju svega navedenog zaključeno je da se manganiti mogu uspješno pripremiti jednostavnim i ekološki prihvatljivim postupcima iz otopine. Uz to, dokazano je da su po svojim višestrukim svojstvima potencijalni materijali za primjenu u novim tehnologijama važnim za održivi rast i razvoj društva kao što su gorivne ćelije, magnetski hladnjaci i suvremeni uređaji za pohranu podataka. Osim toga, potencijalna su ekonomična zamjena za katalizatore na bazi plemenitih metala u procesima katalitičke oksidacije štetnih organskih tvari.Modern society is developing rapidly, with increasing urbanization and industrialization processes, and the quality of life is improving by relying on high energy consumption. According to statistical data, over 80% of the consumed energy is derived from the combustion of fossil fuels, resulting in increased emissions of harmful substances and pronounced climate changes. Therefore, sustainable development of society requires the development of new technologies for energy production and storage, and these new technologies demand new functional materials. One group of such materials are perovskite oxides, which have a general formula ABO3, where the A site is occupied by an alkaline earth metal or a rare earth metal cation, and the B site is occupied by a multivalent transition metal cation. Due to the presence of mixed valences of the B cation within the crystal lattice, perovskites exhibit numerous attractive properties such as electrical conductivity, magnetic properties, photocatalytic and catalytic activity. This dissertation is focused on the study of perovskite oxides based on manganese, commonly referred to as manganites. The subject of this research are strontium-doped calcium manganites (Ca1–xSrxMnO3, CSMO), barium manganites (Ba1–xSrxMnO3, BSMO), and lanthanum manganites (La1–xSrxMnO3, LSMO). All mentioned materials were prepared using two different solution-based synthesis methods – the citrate method and the coprecipitation method. The formation of the desired manganite phases was confirmed by the X-ray diffraction analysis, and the parameters of crystal lattices and occupancies of individual atoms were determined using the Rietveld refinement method. Since manganese oxides exhibit oxygen non-stoichiometry, the oxygen content was determined by permanganate titration with Mohr's salt. After confirming the formation of the desired manganite phases in all prepared materials, the research shifted towards investigating the application properties of the materials. The electrical conductivity of the materials was determined over a wide range of frequencies and temperatures using impedance spectroscopy. For LSMO and CSMO materials, the frequency-independent conductivity was observed throughout the entire range, indicating fast electron transport without blocking effects. Conductivity also increased with temperature, suggesting their semiconductor character, and it was demonstrated that oxygen vacancies enhance conductivity. Therefore, LSMO and CSMO materials were recognized as potential cathode materials in solid oxide fuel cells (SOFC). On the other hand, the electrical conductivity of BSMO materials was frequency-dependent, and they also exhibited semiconductor characteristics. Although unsuitable for SOFC, they were identified as attractive for application in data storage devices. Research on magnetic properties revealed that LSMO behaves as a soft ferromagnet with its Curie temperature increasing with the Sr-doping content, surpassing room temperature for the doping level of 0.2 and 0.3. This makes them suitable for a wide range of applications. Additionally, LSMO showed magnetocaloric effects, making them a potential substitute for gadolinium in magnetic refrigerators. In contrast, CSMO and BSMO exhibited antiferromagnetic ordering due to distortions in the crystal lattice resulting from doping, causing spin canting. Their phase transition temperatures (antiferromagnet – paramagnet) were well below room temperature. However, they are suitable for application in modern data storage devices and in the emerging field of physics, spintronics, as their electrical conductivity can be influenced by changing spin orientation. All prepared manganites showed excellent catalytic activity in the simultaneous degradation of four volatile organic components: benzene, toluene, ethylbenzene, and o-xylene. All components except benzene were completely or nearly completely removed at the final temperature of 450 °C. Benzene removal was more challenging due to its high stability and the fact that it is the degradation product of all other components in the mixture. Catalytic activity, regarding the success of benzene removal, increased in the sequence LSMO < CSMO < BSMO, with the best results obtained for BSMO samples prepared using the citrate method. In conclusion, it was determined that manganites can be successfully prepared using simple and environmentally friendly solution-based methods. Furthermore, these materials were proven to be potential candidates for various applications in new technologies crucial for sustainable growth and development, such as fuel cells, magnetic refrigerators, and modern data storage devices. Additionally, they have the potential to be cost-effective substitutes for noble metal catalysts in catalytic oxidation processes of harmful organic substances
The formation of inhibiting layers on the calcium electrode in Ca(BF4)2/acetonitrile electrolyte
No full textU ovom radu ispitana je ćelija s metalnom kalcijevom anodom i katodom od aktivnog ugljika uz 0,5 M otopinu elektrolita Ca(BF4)2 u acetonitrilu, s ciljem razvijanja reverzibilne kalcijeve negativne elektrode. Za određivanje elektrokemijskih svojstava mjerenja su provedena u troelektrodnom sustavu metodama cikličke voltametrije i elektrokemijske impedancijske spektroskopije, a nastali sloj na elektrodi karakteriziran je infracrvenom spektroskopijom s Fourierovim transformacijama. Predloženi su modeli ekvivalentnih električnih krugova. Mjerenje napona otvorenog kruga pokazuje pad napona uslijed aktivacije elektrode, te postupni porast popraćen inhibiranjem površine zbog nastajanja SEI sloja. Iz rezultata cikličke voltametrije vidljivo je intenzivno otapanje kalcija, praćeno pojavom jamičaste korozije. Rezultati ukazuju na stvaranje SEI sloja koji prekriva površinu elektrode i onemogućuje difuziju Ca2+ iona, čineći elektrodu ireverzibilnom.In this study, a cell with a metallic calcium anode and an activated carbon cathode was examined using a 0,5 M solution of Ca(BF4)2 electrolyte in acetonitrile, with the aim of developing a reversible calcium negative electrode. To determine the electrochemical properties, measurements were conducted in a three-electrode system using cyclic voltammetry and electrochemical impedance spectroscopy, and the resulting layer on the electrode was characterized by Fourier transform infrared spectroscopy. Equivalent electrical circuit models are proposed. The open circuit voltage measurement showed a drop in voltage due to electrode activation, followed by a gradual increase accompanied by surface inhibition due to the formation of a solid electrolyte interphase (SEI) layer. Cyclic voltammetry measurements reveal intense calcium stripping, accompanied by pitting corrosion.
The results indicate the formation of an SEI layer that covers the electrode surface and prevents the diffusion of Ca2+ ions, rendering the electrode irreversible
Application of natural deep eutectic solvents for improvement of active pharmaceutical ingredient's solubility
No full textNiskotemperaturna eutektička otapala nova su klasa otapala dobivena jednostavnim miješanjem najmanje dviju komponenti, donora i akceptora vodikove veze. Karakterizira ih značajno snižena temperatura tališta u odnosu na tališta čistih komponenata, nizak tlak para i veća gustoća od gustoće vode. Zbog povoljnih fizikalno-kemijskih svojstava u farmaceutskoj se industriji koriste za poboljšanje topljivosti, permeabilnosti, stabilnosti i apsorpcije djelatne tvari, što vodi do povećanja bioraspoloživosti. U ovome su radu pripremljena i karakterizirana niskotemperaturna eutektička otapala nastala miješanjem različitih netoksičnih komponenata u određenim omjerima. U tako pripremljena otapala dodana je određena masa djelatne tvari, ceritiniba. Cilj je dobiti stabilno niskotemperaturno otapalo boljih svojstava koje će povećati topljivost djelatne tvari. Pripremljenim otapalima određena su gustoća, viskoznost i pH vrijednost. Kako bi se potvrdio nastanak vodikovih veza među komponentama, provedena je analiza na infracrvenom spektrofotometru s Fourierovom transformacijom. Primjenom UV/VIS spektrofotometrijske analize i određivanjem indeksa loma na refraktometru praćena je koncentracija pri ispitivanju topljivosti ceritiniba.Deep eutectic solvents are a new class of solvents obtained by simply mixing at least two components, a hydrogen bond donor and an acceptor. They have a significantly lower melting point than pure components, a lower vapor pressure and a higher density than water. As a result of their physicochemical characteristics, they are utilized in the pharmaceutical industry to enhance drug solubility, permeability, stability and absorption, which leads to increased bioavailability. This paper prepared and characterized deep eutectic solvents by mixing different non-toxic components in a specific molar ratio. A certain amount of an active pharmaceutical ingredient, ceritinib, was added to the prepared solvents. The purpose of the work is to prepare a stable, deep eutectic solvent with better properties that will increase the solubility of an active pharmaceutical ingredient. The densities, viscosities, and pH values of the prepared solvents were determined. In order to confirm the formation of hydrogen bonds between the mixed components, an analysis was performed on an infrared spectrofotometer with Fourier transformation. The solubility of ceritinib was tested by measuring its concentration using refractive index and UV/VIS spectrofotometric analysis
The comparison of the combination of Ni-Mn-Co oxides with lithium iron phosphate as cathodic materials for lithium-ion batteries
No full textSvrha ovog rada je bila pripraviti elektrode od nikal-mangan-kobalt oksida i litijevog ferofosfata te ih testirati kao pozitivne elektrode u litij ionskim galvanskim člancima. Elektrode su dobivene prevlačenjem paste na strujni kolektor od aluminijske folije. Pasta se sastoji od aktivnog materijala, veziva i aditiva. Litij ionski galvanski članci su priređeni u komercijalnoj El-Cell ćeliji. Elektrokemijska mjerenja su provedena u dvo-elektrodnom i tro-elektrodnom sustavu metodom punjenja/pražnjenja članka te cikličkom voltametrijom i elektrokemijskom impedancijskom spektroskopijom u dvo-elektrodnom sustavu. Za određivanje veličine čestica je korišteno dinamičko raspršenje svjetlosti dok se FTIR koristio za detekciju mogućih onečišćenja. Ciklička voltametrija upućuje na dvofaznu reakciju interkalacije kod LFP materijala te stupnjevitu elektrokemijsku reakciju kod NMC materijala. NMC materijal potencijalno postiže veću snagu zbog reakcija pri višim potencijalima. Ciklički voltamogram LFP-a pokazuje jedan elektroaktivan redoks (Fe2+/Fe3+) dok NMC ukazuje na dva para sa različitim stupnjem oksidacije (Ni2+/Ni4+ i Co3+/Co4+). Naponski profil LFP pozitivne elektrode je plato karakterističan za dvofaznu reakciju (de)interkalacije dok je naponski profil NMC elektrode u konstantnom padu. NMC postiže više specifične kapacitete punjenja i pražnjenja, no posjeduje slabiju retenciju kapaciteta na većim strujama punjenja/pražnjenja od LFP pozitivne elektrode. Na oba materijala je vidljiv gubitak kapaciteta u prvom ciklusu punjenja zbog SEI sloja, no izraženiji je kod NMC. Elektrokemijska impedancijska spektroskopija ukazuje na bolju elektronsku i ionsku vodljivost NMC materijala. Dinamičko raspršenje svjetlosti pokazuje bolju uniformnost i optimalniju veličinu čestica kod NMC materijala. Na FTIR spektrima se vidi slabi signal mogućeg sadržaja molekula vode na NMC prahu.The purpose of this work was to prepare electrodes from nickel-manganese-cobalt oxide and lithium ferrophosphate and test them as positive electrodes in lithium-ion galvanic cells.
The electrodes were obtained by applying the paste to the aluminum foil current collector. The paste consists of active material, binders and additives. Lithium-ion galvanic cells were prepared in a commercial El-Cell cell. Electrochemical measurements were carried out in a two-electrode and three-electrode system using the cell charging/discharging method and cyclic voltammetry and electrochemical impedance spectroscopy in a two-electrode system. Dynamic light scattering was used to determine particle size, while FTIR was used to detect possible contaminants. Cyclic voltammetry points to a two-phase intercalation reaction in LFP materials and a stepwise electrochemical reaction in NMC materials. NMC material potentially achieves higher power due to reactions at higher potentials. The cyclic voltammogram of LFP shows one electroactive redox (Fe2+/Fe3+), while NMC indicates two couples with different degrees of oxidation (Ni2+/Ni4+ and Co3+/Co4+). The voltage profile of the LFP positive electrode is a plateau characteristic of a twophase (de)intercalation reaction, while the voltage profile of the NMC electrode is in constant decline. NMC achieves higher specific charge and discharge capacities but has weaker capacity retention at higher charge/discharge currents than the LFP positive electrode. Both materials show a loss of capacity in the first charging cycle due to the SEI layer formation, but it is more pronounced in NMC. Electrochemical impedance spectroscopy indicates better electronic and ionic conductivity of NMC material. Dynamic light scattering shows better uniformity and optimal particle size for NMC materials. The FTIR spectra show a weak signal of the possible content of water molecules on the NMC powder
Natural gas in petrochemical industry in Republic of Croatia
No full textOvaj rad istražuje potrošnju prirodnog plina u petrokemijskoj industriji u Republici Hrvatskoj,
s posebnim naglaskom na analizu trendova, izazova i potencijala za budući razvoj. Prirodni plin igra ključnu ulogu kao energetski izvor i sirovina u petrokemijskim procesima, stoga je važno razumjeti njegovu potrošnju u ovom sektoru. Rad započinje pregledom petrokemijske industrije u Republici Hrvatskoj, uključujući povijesni razvoj, glavne tvrtke i proizvode. Poseban naglasak stavljen je na tvrtku Petrokemija d.d. kao nositeljicu petrokemijske industrije u Republici Hrvatskoj. Objašnjeni su najvažniji petrokemijski procesi za proizvodnju osnovnih petrokemijskih proizvoda. Analizirani su podaci o potrošnji prirodnog plina, uključujući promjene u potražnji i ponudi, cijene te faktore koji utječu na potrošnju.This paper researches the consumption of natural gas in the petrochemical industry in the Republic of Croatia, with a special focus on the analysis of trends, challenges, and potential for future development. Natural gas plays a key role as an energy source and raw material in petrochemical processes, so it is important to understand its consumption in this sector.
The paper begins with an overview of the petrochemical industry in the Republic of Croatia, including historical development, major companies, and products. Special emphasis is placed on Petrokemija d.d. as the leading company in Croatia's petrochemical industry. The most important petrochemical processes for the production of basic petrochemical products are explained. Data on natural gas consumption are analyzed, including changes in demand and supply, prices, and factors affecting consumption
The influence of molecular plugging on the permeability and separation of reverse osmosis membranes - an overview
No full textReverzna osmoza je tlačni membranski separacijski proces koji se koristi u obradi voda. Najvaţniju ulogu ima u desalinaciji morske vode, u pročišćavanju vode za piće te obradi industrijskih voda. Jedan od fenomena, a ujedno i problema do kojeg dolazi u reverzno osmotskom procesu je pojava blokiranja membrana kojim se smanjuje propusnost membrane, čime se mora povećati tlak potreban za pokretanje procesa, a skraćuje se i ţivotni vijek membrana. Modifikacijom membrana moguće je poboljšati njihove performanse. U ovom radu prikazan je literaturni pregled najnovijih istraţivanja vezanih za modifikaciju komercijalnih reverzno osmotskih membrana kojima je cilj poboljšanje izvedbe membrana pri uklanjanju organskih spojeva iz vode. Linearni alifatski amini kao modifikatori membrane poboljšavaju izvedbu membrane pri uklanjanju bora, soli i N-nitrozamina iz vode, a polivinil alkohol smanjuje propusnost soli i rodamin boje.Reverse osmosis is a pressure membrane separation process used in water treatments. It plays the most important role in seawater desalination, drinking water purification and industrial water treatment. One of the phenomenon, and at the same time the problem that occurs in the reverse osmosis process, is the occurrence of membrane fouling which reduces the permeability of the membrane, which means that the pressure nedded to start the process must be increased and the lifetime of the membranes is shortened. By modifying the membranes, it is possible to improve their performance. This paper presents a literature rewiew of the latest research related to the modification of the commercial reverse osmosis membranes; the goal of which is to improve the performance of the membranes when removing organic compounds from the water. Linear aliphatic amines as membrane modifiers improve the performance of the membrane while removing boron, salt and N-nitrosamines from the water while polyvinyl alcohol reduces the permeability of the salt and
Rhodamine-WT