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Synthesis and application of nanostructured titania thin films and their composites with barium titanate
No full textU ovom doktorskom radu istražen je utjecaj uvjeta pripreme na strukturna i optoelektrična svojstva tankih filmova usmjerenih nanocjevčica titanijeva dioksida i kompozita s barijevim titanatom, te optimizacija njihovih svojstva za primjenu u fotokatalizi i kao slojevi za prijenos elektrona u perovskitnim solarnim ćelijama. Kombinacijom fizikalnih i kemijskih sintetskih metoda, te optimizacijom uvjeta sinteze pripremili su se homogeni, transparentni tankoslojni uzorci nanocjevčica s optimalnom širinom i duljinom pora. U prvom koraku metodom magnetronskog rasprašenja najprije su naneseni tanki filmovi titanija na podlogu stakla prekrivenog prozirnim vodljivim oksidom. U drugom koraku elektrokemijskom anodizacijom slojeva titanija i naknadnom termalnom obradom pripremljeni su tanki filmovi vertikalno usmjerenih nanocjevčica titanijeva dioksida. U trećem koraku ispitala se priprema kompozitnih materijala nanocjevčica s barijevim titanatom hidrotermalnom sintezom, rotacijskim oblaganjem otopina barijevog hidroksida, sol-gel sintezom i magnetronskim rasprašivanjem. Uvjeti pripreme kao npr. trajanje depozicije titanijeva sloja magnetronskim rasprašenjem, sastav elektrolita i napon kod elektrokemijske anodizacije, koncentracija otopina prekursora mijenjani su u širokom rasponu i detaljno je analiziran njihov utjecaj na svojstva tankih filmova nanocjevčica titanijeva dioksida. Sol-gel sinteza i magnetronsko rasprašivanje barijevog titanata pokazale su se neprikladnima za sintezu slojeva barijevog titanata na titanijevom dioksidu budući da je za kristalizaciju tih slojeva potrebna previsoka temperaturna obrada koja bi narušila strukturna, optička i električna svojstva titanijeva dioksida i podloge. U doktorskom radu pokazano je da čiste, odnosno nemodificirane nanocjevčice imaju veliki potencijal za primjenu u fotokatalizi, pogotovo u slučaju razgradnje diklofenaka. Efikasnost fotokatalize ispitivala se praćenjem promjene koncentracije onečišćujuće tvari diklofenaka u vremenu. Modificiranjem rotacijskim oblaganjem površine nanocjevčica s barijevim hidroksidom uzrokovalo je povećanje efikasnosti fotokatalize za 28 % što je rezultiralo fotokatalitičkom razgradnjom ≈ 90 % diklofenaka unutar 60 min. Međutim pripremom kompozitnog materijala hidrotermalnom reakcijom rezultiralo je smanjenjem efikasnosti fotokatalize uslijed narušavanja optičkih i električnih svojstava nanocjevčica i smanjivanja specifične površine nanocjevčica titanijeva dioksida nastankom sloja barijevog titanata. Tanki filmovi nanocjevčica titanijeva dioksida su također uspješno primijenjeni kao sloj za prijenos elektrona u perovskitnim solarnim ćelijama sa standardnom konfiguracijom. Pri tome je najveća postignuta efikasnost konverzije perovskitnih solarnih ćelija s ugrađenim slojem nanocjevčica titanijeva dioksida iznosila 13,5 %. Za daljnje poboljšanje efikasnosti solarnih ćelija potrebno je provesti optimizaciju i ostalih slojeva perovskitne solarne ćelije, što prelazi okvire ovog doktorskog rada i predmet je budućih istraživanja. Kompozitni slojevi pripremljeni u sklopu ovog doktorskog rada su se također ispitali za primjenu u perovskitnim solarnim ćelijama kao slojevi za prijenos elektrona. Korištenje kompozitnog materijala pripremljenog hidrotermalnom reakcijom rezultiralo je smanjenjem efikasnosti i padom parametara solarnih ćelija uslijed smanjenja specifične površine pokrivanjem pora nanocjevčica, rasta električnog otpora i smanjenja transmisije rastom sloja barijevog titanata. Zaključno, tanki filmovi titanatnih nanocjevčica pripremljeni u sklopu ovog doktorskog rada imaju veliki potencijal za daljnji razvoj i primjenu, pogotovo u području primjene sunčeve energije kao npr. za fotokatalizu i solarne ćelije. Međutim, kompozitni materijali barijevog titanata i tankih filmova vertikalno usmjerenih nanocjevčica zahtijevaju daljnja detaljna istraživanja te optimizaciju svojstava i postupaka pripreme kako bi bili uspješno iskorišteni u raznim primjenama.This doctoral dissertation investigates the influences of different preparation conditions on structural and optoelectrical properties of vertically oriented titania nanotube thin films and their composites with barium titanate, and also the optimisation of the materials’ properties for uses in photocatalysis and as electron transport layers in perovskite solar cells. Transparent thin film titania nanotubes with optimal pore length and thickness were prepared by implementing optimised physical and chemical methods of synthesis. Using magnetron sputtering, titanium thin films were deposited onto conductive oxide glass substrates. The titanium thin films were converted into vertically oriented titania nanotube thin films through electrochemical anodization followed by thermal annealing. In the last step, the composite materials were prepared by hydrothermal reactions, by spin coating barium hydroxide solutions or sol-gel mixtures, and by magnetron sputtering of barium titanate targets. The preparation conditions (e.g. sputtering duration of titanium thin films, electrolyte composition, anodization voltage, barium titanate precursor concentration) have been varied in a wide range and their influence on the properties of the titania nanotube thin films has been thoroughly analysed. Sol-gel and magnetron sputtering methods used for depositing barium titanate films have been proven to be incompatible because of the necessary high temperature processing needed to prepare crystalline barium titanate which would be detrimental to the structural, optical and electrical properties of titanium dioxide and the substrate. In this doctoral dissertation it has been shown that pure, unmodified titania nanotube thin films have great potential in photocatalysis, especially in the case of diclofenac degradation. Photocatalytic degradation has been investigated by tracking the change in diclofenac concentration during photocatalysis experiments. Composite materials prepared by spin coating solutions of barium hydroxide resulted in an increase in photocatalysis rates by 28 % and with the degradation of ≈ 90 % diclofenac under 60 min. However, the composite materials prepared by hydrothermal reactions with barium hydroxide showed a decrease in photocatalytic capabilities due to negative effects on optical and electrical properties of the nanotubes and due to the decrease in the specific surface of the nanotubes with the growth of the barium titanate layer. Titania nanotube thin films were also successfully implemented as an electron transport layer in perovskite solar cells with a standard layer configuration. The highest obtained solar conversion efficiency was 13,5 % for the solar cells containing titania nanotube thin films. To further increase the efficiency of the perovskite solar cells it would require the optimization of other layers which is above the scope of this dissertation, and will be investigated in future research. However, implementing composite electron transport layers in the perovskite solar cells showed a decrease in solar energy conversion efficiencies and solar cell parameters due to the coverage of nanotube pores with barium titanate, increases in electrical resistance, and decreases in transmittances correlated with the growth of the barium titanate layer. Overall, this transparent thin film nanotube technology is a promising new material with great potential for future uses and technological improvements, especially in the field of solar energy conversion such as photocatalysis and solar cells. On the other hand, the barium titanate and vertically oriented titania nanotube composite material requires further detailed research and optimization to fine-tune its properties to be successfully implemented in different use cases
Chemometric approaches in the analysis of toxic behavior of substances
No full textGlobalni razvoj industrije povezuje se s onečišćenjem okoliša. Štetni utjecaj raznih tvari antropogenog porijekla na organizme u okolišu postao je ozbiljni problem te su razvijene razne metode kako bi se mogao procijeniti rizik prisutnosti toksičnih tvari u okolišu kao i metode koje određuju toksični učinak tvari na organizme. Procjena rizika temelji se na poznatim vrijednostima toksičnosti pojedinih tvari koje se mogu odrediti za različite testne organizma. S obzirom da se štetne tvari u okolišu u pravilu ne nalaze samostalno već kao smjesa tvari, ovakav pristup najčešće nije koristan. Tvari u smjesama mogu djelovati zajedno na način da je štetni utjecaj intenzivniji nego da sumiramo utjecaj dviju zasebnih tvari. Zbog beskonačnog broja različitih smjesa koji mogu egzistirati u okolišu, nije moguće za svaku smjesu odrediti toksičnost već se razvijaju matematički modeli kojima se predviđa toksičnost takvih smjesa. Najčešće korišten model je aditivni model, potom model neovisnog djelovanja te zatim modeli nastali njihovom integracijom. Na krilima intenzivnog razvoja računala sve više na važnosti dobivaju i napredni računalni pristupi, pri čemu treba istaknuti modeliranje kvantitativnog odnosa strukture i aktivnosti (tzv. QSAR modeli) te primjenu umjetne inteligencije. Statističke metode koje se primjenjuju kod određivanja toksičnog učinka tvari dijele se na parametarske i neparametarske. Kada god je moguće koriste se parametarski testovi, najčešće Studentov t-test, Tukeyjev test, Dunnettov test i Williamsov test. Svaki parametarski test ima ekvivalentan neparametarski test.Global development of industry has been related with environmental pollution. An adverse effect on various anthropogenic substances on organisms in the environment has become a serious problem. Therefore, various methods have been developed in order to determine the toxic effect of hazardous substances on organisms and assess the risk of their presence in the environment. The risk assessment is based on the known toxicity values of individual substances that can be tested on various test organisms. Such approach has a deficiency if applied for environmental risk assessment considering that hazardous substances are not found alone in the environment but as a mixture of various substances. Substances in mixtures can act together, possibly resulting in more intense harmful effect than a cumulative effect of two pure substances. Due to the infinite number of different mixtures that can occur in the environment, mathematical models that predict their toxicity have been developed and used in risk assessment. The most commonly used model is the concentration addition model, followed by the independent action model and models resulting from their combination. The intensive development of computers with high performances supported application of advanced mathematical approaches such as quantitative structure-activity relationship (QSAR) modeling and artificial intelligence. Statistical methods used to determine the toxic effect of substances on organisms are generally divided into parametric and nonparametric methods. Whenever possible, parametric tests are used, and the most commonly ones are Student's t-test, Tukey's test, Dunnett's test and Williams' test. Every parametric test has an equivalent nonparametric test
Removal of organic matter from wastewater by biodegradation
No full textSve značajnija prisutnost organskih onečišćujućih tvari u okolišu predstavlja jedan od najvećih ekoloških izazova modernog doba. Uporaba organskih tvari u proizvodima poput farmaceutika, kozmetike, pesticida te plastičnih masa uzrok je onečišćenju voda koje predstavlja ozbiljnu opasnost za ekosustave. Sve veći značaj ovog ekološkog problema doveo je do razvoja tehnologija obrade otpadnih voda, što uključuje i proces biološke obrade, odnosno biorazgradnje organskih tvari iz otpadnih voda uz pomoć mikrobnog katabolizma. Temeljni cilj ovakvog postupka obrade otpadnih voda je potpuno ukloniti neku organsku onečišćujuću tvar ili ju uz pomoć metabolizma mikroorganizama pretvoriti u tvari koje nisu toksične. Biorazgradnja organskih tvari se zbog svoje ekonomičnosti i izrazite sigurnosti za okoliš nametnula kao jedan od dominantnih postupaka obrade otpadnih voda i s vremenom njena uporaba biva sve češća. Biorazgradnja se često koristi u obradi voda onečišćenih farmaceutskim proizvodima i njihovim derivatima koji nastaju pod utjecajem okolišnih čimbenika, a mogu biti toksične za ljude i ostale organizme s kojima nerijetko dolaze u izravan kontakt. Neki od najčešće prisutnih organskih ksenobiotika farmaceutskog podrijetla u okolišu su lijekovi protiv bolova poput diklofenaka i paracetamola te lijekovi koji se koriste za liječenje dijabetesa tipa 2 poput metformina. U ovom radu opisana su svojstva navedenih farmaceutika, ekotoksikološki rizici njihove prisutnosti u okolišu te načini na koje se nad istima može provesti postupak biorazgradnje.The increasing presence of organic pollutants in the environment is one of the greatest environmental challenges of today. The use of organic substances in products such as pharmaceuticals, cosmetics, pesticides, and plastics is the cause of water pollution, which poses a serious threat to ecosystems. The increasing importance of this ecological problem has led to the development of wastewater treatment technologies, which include the process of biological treatment, i.e. the biodegradation of organic substances from wastewater by microbial catabolism. The main objective of this wastewater treatment process is to completely remove an organic pollutant or convert it into non-toxic substances with the help of the metabolism of microorganisms. Due to its cost-effectiveness and exceptional environmental safety, biodegradation of organic matter has become one of the most important wastewater treatment processes and is being used more and more frequently over time. Biodegradation is often used in the treatment of water contaminated with pharmaceutical products and their derivatives, which are formed by environmental factors and can be toxic to humans and other organisms with which they frequently come into direct contact. The most common organic xenobiotics of pharmaceutical origin found in the environment include painkillers such as diclofenac and paracetamol, and drugs used to treat type 2 diabetes such as metformin. This paper therefore describes their properties, the ecotoxicological risks of their presence in the environment and the possibilities of biodegradation
State-of-the art in assessing passivation condition of stainless steels
No full textNehrđajući čelici svoju korozijsku otpornost duguju stvaranju zaštitnog pasivnog sloja oksida na površini. U radu je dan pregled niza metoda kojima se ispituje pasivno stanje nehrđajućih čelika. ASTM standardi A967 i A380 nude metode poput testa uranjanja u vodu i feroksil testa koji samo kao prolaz/pad testovi utvrđuju nalazi li se nehrđajući čelik u pasivnom stanju. Na tržištu se pronalaze i uređaji dizajnirani za ispitivanje postojanja pasivnog stanja. Tehnike analize površine XPS i AES daju uvid u kemijski sastav pasivnog sloja i omjere koncentracija pojedinačnih prisutnih oksida. Elektrokemijska mjerenja CPDP i EIS daju informacije o mjeri otpornosti nehrđajućeg čelika na pojavu korozije. U radu su prikazana i neka novije provedena istraživanja te metode novijeg vremena koje su često sinkrotron bazirane tehnike i mikroskopije skenirajućom sondom poput sinkrotron bazirane XRR i SKP. Daljnja napredovanja u području ispitivanja pasivnog stanja nehrđajućeg čelika potrebna su i korisna posebno u svrhu dobivanja saznanja koja će se upotrijebiti za prevenciju korozije.Stainless steels are corrosion resistant due to formation of a protective passive oxide layer on their surface. This study provides an overview of a number of methods used to assess the passive state of stainless steels. ASTM standards A967 and A380 offer methods such as the water immersion test and the ferroxyl test that are pass/fall tests which determine whether stainless steel is in a passive state. On the market, there are stainless steel passivation testers designed to verify the existence of a passive state. Surface analysis techniques,
XPS and AES provide insight into the chemical composition of the passive layer and the concentration ratios of the present oxides Electrochemical CPDP and EIS measurements provide information on a stainless steel's resistance to corrosion. This study also presents some more recently conducted research and recent methods, which are often
synchrotron-based techniques and scanning probe microscopies, such as
synchrotron-based XRR and SKP. Further advances in the field of testing passive state of stainless steels are necessary and useful especially for the purpose of obtaining knowledge to be used for corrosion prevention
Membrane biodegradation of xenobiotics
No full textKsenobiotici postaju sve veći problem u sustavima pročišćavanja otpadnih voda jer su relativno nove tvari i teško ih je ukloniti, a u okolišu se pojavljuju u količinama koje su neprirodne zbog ljudskog djelovanja. Posljedica njihovog neučinkovitog uklanjanja iz otpadnih voda je njihova bioakumulacija u prehrambenim lancima što čini izravnu prijetnju na ekosustave i ljudsko zdravlje. Konvencionalna biološka metoda obrade aktivnim muljem, koja se u najvećem broju koristi u postrojenjima za obradu otpadnih voda, nije se pokazala učinkovita za uklanjanje ksenobiotika. Niska učinkovitost njihovog uklanjanja posljedica je djelomičnog zadržavanja ksenobiotika u mulju ili njihovog metabolizma u hidrofilnije i postojanije oblike koji prolaze kroz postrojenja za obradu otpadnih voda. Stoga je potrebno usmjeriti razvoj novih tehnologija koje će pospješiti njihovo uklanjanje u sustavima za pročišćavanje otpadnih voda. Alternativu konvencionalnoj obradi otpadnih voda predstavljaju membranski bioreaktori koji kombiniraju biološku obradu aktivnim muljem s membranskim procesima separacije. Cilj ovog rada je dati pregled primjene tehnologije obrade otpadnih voda membranskim bioreaktorima te ispitati učinkovitost uklanjanja antihelmintika febantela te pesticida acetamiprida i tiakloprida membranskom biorazgradnjom. Proces biorazgradnje ksenobiotika provodio se tijekom 48 h, a analitičko praćenje ksenobiotika provedeno je tekućinskom kromatografijom visoke djelotvornosti. Utjecaj ksenobiotika na aktivnost aktivnog mulja ispitan je praćenjem broja razvijenih kolonija. Membranskom biorazgradnjom ksenobitoika tijekom 48 h postignuta je najveća učinkovitost uklanjanja febantela od 98,5 %, acetamiprida 57 % te tiakloprida 42 %. Tijekom biorazgradnje detektirani su novi razgradni i/ili transformacijski produkti. Niska učinkovitost uklanjanja acetamiprida i tiakloprida posljedica je njihove toksičnosti na organizme prisutne u aktivnom mulju što ih čini neprikladnim za procese membranske biorazgradnje.Xenobiotics are becoming an increasing problem in wastewater treatment systems because they are relatively new substances and difficult to remove, and they appear in the environment in amounts that are unnatural due to human activity. The consequence of their ineffective removal from wastewater is their bioaccumulation in food chains, which poses a direct threat to ecosystems and human health. The conventional biological method of activated sludge treatment, which is mostly used in wastewater treatment plants, is ineffective for removing xenobiotics. The low efficiency of their removal is the result of the partial retention of xenobiotics in the sludge or their metabolism into more hydrophilic and stable forms that pass through wastewater treatment plants. Therefore, it is necessary to direct the development of new technologies that will facilitate their removal in wastewater treatment systems. An alternative to conventional wastewater treatment is represented by membrane bioreactors combining biological treatment with activated sludge and membrane separation processes. This paper aims to provide an overview of the application of wastewater treatment technology with membrane bioreactors and to examine the effectiveness of removing the anthelmintic febantel and the pesticides acetamiprid and thiacloprid by membrane biodegradation. The process of biodegradation of xenobiotics is carried out for 48 h, and analytical monitoring of xenobiotics was carried out by high-performance liquid chromatography. The influence of xenobiotics on the activity of activated sludge was examined by monitoring the Colony Forming Units. Membrane biodegradation of xenobiotics during 48 h achieved the highest removal efficiency of febantel at 98.5 %, acetamiprid at 57 %, and thiacloprid at 42 %. During biodegradation, new degradation and/or transformation products were detected. The low removal efficiency of acetamiprid and thiacloprid is a consequence of their toxicity to organisms present in activated sludge, which makes them unsuitable for membrane biodegradation processes
Supercapacitors prepared from the coconut shell active carbon
No full textU današnjem svijetu gdje održivost korištenja energije postaje jedno od važnijih pitanja, sve više se skreće pozornost na korištenje obnovljivih izvora energije. Kako bi se što više iskoristio potencijal takvih izvora, ključno je usavršiti koncept skladištenja energije u spremnicima kao što su baterije, gorive ćelije i superkondenzatori. U ovom radu istražena je mogućnost korištenja različitih vrsta aktivnog ugljika kao materijala za izradu elektroda superkondendzatora. Ispitani su aktivni ugljik dobiven iz kokosove ljuske CS i Norit DLC SUPER 30 (OVIA INOVACIJE). Za oba materijala je dobivena raspodjela veličina čestica metodom dinamičkog raspršenja svjetlosti DLS, krivulje termičke stabilnosti termogravimetrijskom analizom te FTIR spektri. Od oba materijala su zatim izrađene elektrode te su sastavljena dva superkondenzatora i ispitani elektrokemijskim analitičkim metodama. Provedena je elektrokemijska impedancijska spektroskopija EIS u rasponu frekvencija od 10 mHz do 100 kHz i kao rezultat su dobiveni Nyquistovi prikazi. Zatim je provedena ciklička voltametrija u rasponu potencijala od 0 do 2 V brzinom promjene potencijala od 20 mV/s. Također je provedeno galvanostatsko punjenje/pražnjenje GCD u 30 ciklusa u dvo- i troelektrodnom sustavu pri struji od 20 mA, nakon čega su se ponovila mjerenja EIS i cikličke voltametrije da se zabilježe promjene u kapacitetima i otporima u sustavu. Iz Nyquistovih prikaza moglo se zaključiti da ponašanje kondenzatora nije idealno, a vidljiv je veći unutarnji otpor CS elektroda u odnosu na Norit, te je u oba slučaja došlo do porasta unutarnjeg otpora nakon provedenih 30 ciklusa punjenja i pražnjenja. Iz oblika cikličkog voltamograma dalo se zaključiti da CS pokazuje bolje kapacitivne karakteristike na osnovu gotovo konstantnih vrijednosti struje prije i poslije 30 ciklusa. Iz krivulja punjenja i pražnjenja izračunati su specifični kapaciteti te se također vidi veći pad kapaciteta i niže vrijednosti kod Norita u odnosu na CS. Također su izračunati unutarnji otpori na osnovi pada napona te su pokazali puno veće vrijednosti kod CS što se može objasniti lošijim kontaktom između aktivnog materijala i strujnog kolektora.In today's world, where the sustainable use of energy use is becoming one of the most important issues, more and more attention is being drawn to the use of renewable energy sources. In order to make the most of their potential, it’s crucial to perfect the concept of energy storage in devices such as batteries, fuel cells and supercapacitors. In this paper, the possibility of using different types of activated carbons as materials for supercapacitor electrodes was investigated. Activated carbon obtained from coconut shell CS and Norit DLC SUPER 30 were the two materials tested. For both materials, the particle size distribution was obtained using the DLS dynamic light scattering method, the thermal stability curve was obtained using thermogravimetric analysis, as well as the FTIR spectra. Electrodes were made from different materials, then two supercapacitors were assembled and tested using electrochemical analytical methods. Electrochemical impedance spectroscopy, EIS was performed in the frequency range from 10 mHz to 100 kHz and as a result Nyquist plots were obtained. Cyclic voltammetry was performed in the potential range from 0 to 2 V with a potential change rate of 20 mV/s. A 30-cycle galvanostatic charge/discharge, GCD, was also performed in a two- and three-electrode system at a constant current of 20 mA, after which EIS and cyclic voltammetry measurements were repeated to record changes in system capacitances and resistances. From Nyquist plots it was concluded that the behavior of the capacitor is not ideal, the internal resistance of CS electrodes seemed higher compared to Norit, and in both cases the internal resistance increased after 30 charging and discharging cycles. From the shape of the cyclic voltammogram, it was concluded that CS shows better capacitive characteristics based on almost constant current values before and after 30 cycles. Specific capacities were calculated from the charge/discharge curves, with a bigger drop in capacity and lower values found for Norit compared to CS. Internal resistances were also calculated based on the voltage drop and showed much higher values for CS, which can be explained by poorer contact between the active material and the current collector
Application of BiVO4 for the photoelectrocatalytic degradation of aromatic compounds
No full textCilj ovog rada bio je ispitati fotoelektrokemijska svojstva BiVO4 i BiVO4/rGO elektroda elektrokemijskim metodama karakterizacije, te odrediti djelotvornost fotoelektrokemijskog (PEC) elektrokemijskog (EC) i fotokatalitičkog (PC) procesa. Ispitivanja su provedena u otopinama 5-aminosalicilne kiseline i fenola masenih koncentracija 28 mg/L, salicilne kiseline masenih koncentracija 28 mg/L i 14 mg/L, te 0,1 M otopini NaCl. Cilj je bio utvrditi koja aromatska tvar pokazuje najveći stupanj razgradnje te odrediti kako pH, napona i koncentraciju utječu na brzinu razgradnje. Primjenom kronoamperometrije i linearne voltametrije pokazano je da se uz BiVO4/rGO elektrodu postiže veća djelotvornost razgradnje u odnosu na BiVO4 elektrodu. Utvrđeno je da najvjerojatnije dolazi i do ireverzibilnih promjena u rGO strukturi tijekom izvedbe PEC procesa. Metodom tekućinske kromatografije visoke djelotvornosti (HPLC) praćena je koncentracija tijekom razgradnje iz čega su određeni optimalni pH uvjeti za razgradnju pojedine aromatske molekule korištene u ovom radu. Osim toga utvrđeno je kako napon i koncentracija utječu na proces razgradnje.The main goal of this study was to investigate photoelectrochemical properties of BiVO4 and BiVO4/rGO electrodes by electrochemical methods of characterization, as well as, to determine efficiency of photoelectrochemical (PEC), electrochemical (EC) and photocatalytic process (PC). Electrodes were tested in 0,1 M aqueous solution of NaCl before and after PEC process. Degradation of salicylic acid, 5-aminosalicylic acid and phenol was carried out. The selected compounds were tested in order to find out which aromatic compound is most susceptible to degradation under certain conditions of pH, voltage and concetration. Chronoamperometry and linear sweep voltametry have shown that higher degradation efficacy is achieved by using BiVO4/rGO electrode compared to BiVO4 electrode. Results also indicate that irreversible changes of rGO structure take place during PEC procces. The decrease in concetration value during degradation process was monitored by high preformance liquid chromatography (HPLC). The obtain results indicate the optimal pH value for degradation of each aromatic compound used in this study. In addition, the influence of voltage and concentration on degradation proces was found
Modelling of pharmaceutical synthesis catalysed by immobilized enzyme
No full textStatini su farmaceutici koji se koriste pri snižavanju kolesterola te sprečavanju pojave kardiovaskularnih bolesti. Sve je veća potražnja za novim alternativnim načinima dobivanja kemikalija s kiralnim centrima čija je sinteza kompleksna zbog potrebe za visokom kemijskom i stereokemijskom čistoćom, a upravo jedan od njih je uporaba enzima 2-deoksiriboze-5-fosfat aldolaze (DERA). DERA katalizira reakciju sinteze (3R, 5R)-6-kloro-3,5-dihidroksiheksanala (laktola), prekursora u proizvodnji statina, dvostrukom aldolnom adicijom acetaldehida i kloroacetaldehida. U radu, imobiliziran je enzim DERA na magnetske nanočestice obložene silikom u svrhu povećanja stabilnosti enzima u prisustvu aldehida. Ispitani su utjecaji različitih pH vrijednosti 0,1 M fosfatnog pufera na aktivnost i stabilnost enzima DERA gdje se kao optimalna pH vrijednost pokazao pH 6 u kojem je enzim pokazao najveću aktivnost i stabilnost. U reakciji acetaldehida i kloroacetaldehida te u reakciji acetaldehida i 4-kloro-3-hidroksibutanala kinetika je opisana dvosupstratnom Michaelis-Menteničinom jednadžbom te je postavljen matematički model procesa u kotlastom reaktoru. Ispitana je stabilnost enzima u prisutnosti različitih koncentracija acetaldehida i kloroacetaldehida.Statins are pharmaceuticals used to lower cholesterol and prevent cardiovascular disease. There is a growing demand for new alternative ways to obtain chemicals with chiral centers, whose synthesis is complex due to the need for high chemical and stereochemical purity. One of the possibility is the use of the enzyme 2-deoxyribose-5-phosphate aldolase (DERA). DERA catalyzes the synthesis reaction of (3R, 5R)-6-chloro-3,5-dihydroxyhexanal (lactol), a precursor in statin production, by double aldol addition of acetaldehyde and chloroacetaldehyde. The DERA enzyme was immobilized on magnetic nanoparticles coated with silica to enhance the stability of the enzyme in the presence of aldehydes. The effects of different pH values of 0.1 M phosphate buffer on the activity and stability of DERA were investigated, and pH 6 was found to be the optimal pH with respect to the enzyme activity and stability. In the reaction of acetaldehyde and chloroacetaldehyde and in the reaction of acetaldehyde and 4-chloro-3-hydroxybutanal, the kinetics was described by the two-substrate Michaelis-Menten equation and a mathematical model of the process in the batch reactor was set. Enzyme stability was examined in the presence of different concentrations of acetaldehyde and chloroacetaldehyde
Development and validation of a chromatographic method for the determination of nitroso compounds
No full textU ovom radu razvijena je SPE-HPLC-DAD metoda za određivanje pet N-nitrozamina u vodi: N-nitrozodietilamina (NDEA), N-nitrozodipropilamina (NDPA), N-nitrozodibutilamina (NDBA), N-nitrozopirolidina (NPYR) i N-nitrozomorfolina (NMOR). Za pripremu uzorka vode primijenjena je ekstrakcija čvrstom fazom (SPE) uz korištenje sorbensa od kokosovog ugljena. Uspješna kromatografska separacija svih pet analita postignuta je na Kinetex 5 μm C18 koloni 100 Å, 150 x 4,6 mm, uz pokretnu fazu sastavljenu od MilliQ vode i acetonitrila te gradijentno eluiranje pri protoku 0,5 mL min^-1. Razvijena SPE-HPLC-DAD metoda je validirana pri čemu su ispitane sljedeće izvedbene karakteristike: selektivnost, linearnost, granice detekcije i kvantifikacije te točnost kroz istinitost i preciznost. Postignuta je dobra linearnost uz koeficijente korelacije veće od 0,99, dobra preciznost uz RSD < 10 % te dobro iskorištenje unutar raspona 70 – 120 % za sve ispitivane analite. Metoda je uspješno primijenjena u analizi uzoraka tijekom reverzno osmotske membranske separacije: ulazne otopine, permeata i retentata.In this work, a SPE-HPLC-DAD method was developed for the determination of five N-nitrosamines in water: N-nitrosodiethylamine (NDEA), N-nitrosodipropylamine (NDPA), N-nitrosodibutylamine (NDBA), N-nitrosopyrrolidine (NPYR) and N-nitrosomorpholine (NMOR). For the preparation of the water sample, solid phase extraction (SPE) was applied with the use of coconut charcoal sorbent. Successful chromatographic separation of all five analytes was achieved on a Kinetex 5 μm C18 column 100 Å, 150 x 4.6 mm, with a mobile phase composed of MilliQ water and acetonitrile and gradient elution at a flow rate of 0.5 mL min^-1. The developed SPE-HPLC-DAD method was validated by testing the following performance characteristics: selectivity, linearity, limits of detection and quantification, and accuracy through trueness and precision. Good linearity with correlation coefficients higher then 0.99, good precision with RSD < 10% and good extraction recovery within the range of 70-120% for all analyzed analytes was achieved. The method was successfully applied in the analysis of samples during reverse osmosis membrane separation: feed solution and permeate and retentate
Biocatalytic properties of group B halohydrin dehalogenases in nucleophilic ring-opening reactions of epoxides
No full textHalogenhidrin-dehalogenaze (HHDH) su enzimi koji imaju sposobnost uvođenja novih funkcionalnih skupina u molekulu, kataliziranjem reakcije otvaranja epoksida s različitim nukleofilima. Aktivno mjesto enzima može primiti više različitih neprirodnih nukleofila poput azida, cijanida i nitrita, zbog čega su enzimi privukli pažnju sintetske organske kemije. Njihova enantioselektivnost ovisi o strukturi supstrata, te često nije dovoljno visoka za sintetsku primjenu. Enzim HheB2 iz grupe B u prethodnim istraživanjima testiran je na relativno malom broju supstrata gdje je pokazao nisku enantioselektivnost, te je dugi niz godina ostao zanemaren u biokatalitičkim istraživanjima. U okviru ovog rada provedeno je opsežno ispitivanje dva divlja tipa HHDH iz skupine B: HheB iz Croynebacterium sp. soj N-1074 i HheB2 iz Mycobacterium sp. soj GP1 na nizu supstrata i nukleofila. Otkriveno je nekoliko visoko enantioselektivnih reakcija (E > 200), gdje je HheB pokazao bolju enantioselektivnost i aktivnost prema većem broju strukturno različitih supstrata u usporedbi s HheB2. Ova dva enzima dijele visoku homologiju sekvence i razlikuju se u samo četiri aminokiseline (F36I, T120A, C124Y, H125Q). Ispitivanjem mutanata HheB2 s modificiranim pojedinačnim aminokiselinama utvrđene su aminokiseline ključne za veću enantioselektivnost HheB u odnosu na HheB2. Eksperimentalni rezultati potvrđeni su i dodatno pojašnjeni računalnim analizama. Zbog izuzetne selektivnosti i aktivnosti B grupa HHDH nameće se kao odličan katalizator za sintezu velikih tercijarnih alkohola. Ispitivanjem različitih nukleofila prikazana je mogućnost sinteze enantiomerno čistih azido-alkohola i oksazolidinona, a kinetičkim mjerenjima određen je stupanj inhibicije enzima prihvaćenim nukleofilma.Halohydrin dehalogenases (HHDH) have the ability to introduce new functionalities into the molecule through the ring-opening reactions of epoxides with different nucleophiles. These enzymes draw the attention of synthetic chemistry due to their ability to accept unnatural nucleophiles such as azide, cyanide and nitrite ions. The enantioselectivity of HHDHs is substrate-dependent and not always sufficient for synthetic applications. HheB2 from B group of HHDHs has been neglected in the biocatalytic research due to the low enantioselectivity observed on a relatively small number of tested substrates. In this work, extensive screening of substrates and nucleophiles was carried out on two B wild-type HHDHs: HheB2 from Mycobacterium sp. GP1 and HheB from Corynebacterium sp. N-1074. Several highly enantioselective reactions were discovered (E > 200), with HheB showing higher enantioselectivity and activity towards larger panel of substrates compared to HheB2. These two enzymes share high sequence homology and differ by only four amino acids (F36I, T120A, C124Y, H125Q). HheB2 mutants with individual amino acids replacement are examined to determine key residues. Experimental results were confirmed and further clarified by computer analysis. Due to remarkable activity and enantioselectivity, B-group HHDHs emerged as a catalyst of choice for the synthesis of bulky tertiary alcohols. Nucleophile screening showed possibility for the synthesis of enantiomerically pure azido alcohols and oxazolidinones. Kinetic measurements were used to determine enzyme inhibition by accepted nucleophiles