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Od 19. do 21. svibnja 2023.na Zagrebačkom Velesajmu, u Paviljonu 10A, održano je drugo izdanje MUZZA Tjedna Znanosti. U sklopu MUZZA LAB- a održano je je šest radionica "Vodik na dlanu" koje su bile dobro posjećene. Radionice su održane u sklopu promicanja znanosti i Fakulteta kemijskog inženjerstva i tehnologije u STEM području pod nazivom "Mi vidimo nevidljivo". U radionici je pokazano kako je vodik moguće proizvesti elektrolizom vode i koristiti ga za pokretanje električnog automobila. Sudionici radionice su upoznati s važnosti korištenja obnovljivih izvora energije s ciljem ostvarivanja ekonomske i ekološke održivosti.

Titanium is a widely employed material in the aerospace industry, biomedicine and dentistry due to the combination of favorable mechanical properties, great corrosion resistance and good tissue compatibility. Some of the titanium properties are attributed to the passive oxide layer, which spontaneously forms on the titanium surface in an oxygen-containing environment. The protective oxide layer, few nanometers thick, mainly consists of amorphous TiO2. Many properties of titanium can be improved by introducing polyelectrolyte films on its surface. For example, polyelectrolyte coatings offer a new way for antibacterial protection of titanium dental implants. Properties of such films are controlled by the interplay of various interactions between surface and adsorbed polymer molecules. A comprehensive understanding of these interactions may enable very fine-tuning of titanium surface properties. In this study, the surface properties of Ti/TiO2 substrate before and after the adsorption of polyelectrolytes were investigated. As a model polyelectrolytes, strongly charged polycation poly(diallyldimethylammonium chloride) (PDADMA) and strongly charged polyanion poly(sodium 4- styrenesulfonate) (PSS) were used. First, the bare titanium substrate was characterized by means of ellipsometry, atomic force microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. It was shown that the substrate surface is very flat with an average roughness of only 2.3 nm and oxide layer thickness of 3.8 nm. Furthermore, electrochemical measurements revealed a good corrosion resistance of Ti/TiO2 substrate. After the adsorption of polyelectrolytes, coated titanium surface was again examined using the above-mentioned methods. Enhanced anticorrosion characteristics were observed for surfaces fabricated by both polyelectrolyte films, while the surface roughness didn't significantly change. These results lead us to the conclusion that polyelectrolyte molecules form a stable nanofilm on Ti/TiO2 surface that partially or fully covers the surface. Our previous work made on the adsorption of PSS to rutile surface strongly corroborates these findings.

In this study, TiO2 oxide layer on titanium was formed spontaneously (S) and potentiostatically in phosphate buffer solution (EC). It was shown by means of ellipsometry and atomic force microscopy, that the Ti/TiO2 surface is very flat with an average roughness of only 2.3 nm (S) and 3.4 nm (EC) and oxide layer thickness of 4.1 nm (S) and 16.1 nm (EC). The electrochemical properties and corrosion protective effectiveness were examined by means of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and single crystal electrode (SCrE). The CV indicates the behavior of the valve metals with the anodic formation of the barrier oxide film. The semiconducting properties were studied by Mott- Schottky analysis. A preponderance of anion vacancies, which act as electron donors, over cation vacancies within the passive film formed electrochemically, was established providing n- type semiconducting behavior of the film. The obtained EIS data were modelled utilizing electrical equivalent circuit. The corrosion protection effectiveness value of 94.7 % indicates that the corrosion properties were greatly enhanced upon modification by TiO2 oxide layer. The EIS results also indicate that the oxide film on the Ti surface consists of two layers, an inner barrier layer associated with higher impedance values and responsible for corrosion protection, and an outer porous layer characterized by lower impedance values and lower compactness.

The main goal of this study was to examine the effect of calcium phosphate coating (CaP coating) on the corrosion resistance of titanium alloy, Ti– 6Al–7Nb, commercially used as an implant material in orthopedic devices. In addition to enabling osseointegration, the CaP coating forms a kinetic barrier to the electrochemical corrosion reaction, thus protecting the material from corrosion- induced degradation. This further increases the biocompatibility of the implant material. The CaP coating was deposited to the Ti–6Al–7Nb alloy by the electrochemical cathodic deposition method. Electrodeposition of the calcium phosphate film was performed from an aqueous solution of Ca(NO3)2 and NH4H2PO4 salts and film formation parameters were investigated using cyclic voltammetry (CV). Electrochemical characterization of the Ti–6Al–7Nb alloy in simulated body fluid, Hank’s solution was performed before and after the surface modification. The following electrochemical experimental techniques were used: electrochemical impedance spectroscopy (EIS) and linear polarization (LP) in the narrow (±20 mV vs. open circuit potential) and in the wide (±200 mV vs. open circuit potential) potential range at a scan rate of 0.1667 mV/s. The morphology and microstructure of CaP deposit obtained was characterized by scanning electron microscopy (SEM) and chemical composition was assessed by attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR).

Uslijed mehaničke traume, ozljede ili zbog nepravovremeno liječenog karijesa i paradontoze može doći do djelomičnog ili potpunog gubitka zuba/zubiju. Kako bi se održala kakvoća života pojedinca problem se rješava ugradnjom dentalnih implantata – metalni vijak, kao baza za keramičku krunicu, most ili zubnu protezu, ugrađuje se u kost čeljusti. Za izradu dentalnih implantata najčešće se koriste materijali na osnovi titanija. Za uspješnu implantaciju i kako bi se izbjegle bolne korekcijske operacije, po ugradnji implantata mora doći do brze oseointegracije s okolnom kosti i tkivima. Kako formiranje postojanih interakcija implantni materijal/kost i implatni materijal/okolno tkivo ovisi o mikrostrukturi, morfologiji i sastavu te hidrofilnosti površine, funkcionalizacija površine implatnog materijala je od ključne važnosti. U ovom istraživanju, provedena je funkcionalizacija površine titanijeva dentalnog implantata kemisorpcijom bioaktivnih molekula, mogućih pojačivača oseointegracije. Morfologija modificiranih površina Ti|TiO2|bioaktivna prevlaka ispitana je koristeći SEM, a svojstva močenja pomoću mjerenja kontaktnog kuta. In vitro karakterizacija nemodificiranih i modificiranih površina provedena je u otopini umjetne sline upotrebom elektrokemijske impedancijske spektroskopije. Eksperimentalna otkrića potvrđena su DFT izračunima i predložen je mehanizam formiranja bioaktivnih prevlaka.

Since implantation success strongly depends on the osseointegration process, current trends in dental implant research are based on surface properties modifications by biomimetic and bioactive coatings that mimic biochemical surroundings and architecture of the human bone. Calcium phosphate ceramics, like hydroxyapatite, with mineral composition similar to natural bone, as a single compound coating or as a composite with collagen, bioglass, or silica are used to promote osseointegration or overall implant system’s characteristics. Drug-based coatings with bisphosphonates like Zolendronate or Alendronate, drugs for bone diseases, promote mechanical fixation of implant and bone mineralization. However, it must not be forgotten that a fundamental prerequisite for the success of osseointegration is a long-term corrosion stability of implant materials. Human body fluids, especially oral cavity fluids, in which pH is constantly changing, represent very aggressive media with high concentrations of chloride ions that are among the most aggressive and corrosive to metals. Although titanium is a gold standard in dental implantology due to its exceptional biocompatibility and corrosion resistivity, there is an increasing data reported regarding complications caused by titanium dental implant fixation. It was shown that titanium ions, that originated as product from corrosion reaction in body fluids, caused negative immune reactions or skin allergies immediately or shortly after implant fixation. Therefore, it is crucial to design a coating which will make titanium surface more bioactive/osseoinductive and at the same time more corrosion resistant during a long-term exposure to oral cavity fluids. In this study the titanium surface was modified by vitamin D3, molecules that are crucial for maintaining bone mineral density and normal functioning of the immune system. The main goals were (i) to improve titanium corrosion resistivity during exposure to an artificial saliva solution and simultaneously (ii) to induce in vitro processes of “new bone” formation. According to results of all techniques, the D3 vitamin layer imparted very good corrosion protection to the oxide-covered titanium and induced a formation of biocompatible bone-like calcium phosphates what confirmed enhanced titanium's bioactivity level.

Although dental implants have been used since ancient times, there is a continuing need to improve characteristics to ensure their long- term integration into the jaw.^1 Current trends in dental implant research are focused on surface properties modification by biomimetic and bioactive coatings that mimic architecture of the human bone and biosurrounding.^2-4 Therefore, the titanium dental implant was functionalized by two different molecules, Cholecalciferol (vitamin D3) and Alendronate sodium (Fosamax®T). D3 vitamin and Alendronate were chosen due to their known positive influences on human organism, especially on the bone-system. The aim of functionalization was (i) to improve anti-corrosion properties of the implant and simultaneously (ii) make implant´s surface potentially more bioactive (to promote and accelerate osseointegration). An integrated experimental-theoretical approach was applied to study coating´s formation mechanism, wetting properties and corrosion behaviour in an artificial saliva solution (during 7 days). In general, the results indicate improved surface properties of the implant after functionalization and are in a direct corelation with chemical nature and structure of coating molecules.

Life inevitably leaves its traces on the teeth. A mechanical trauma, an accident or untimely treated caries and periodontitis frequently lead to permanent tooth loss. Dentists and dental specialists have a contemporary solution: the small titanium body fixed into the jawbone acts as the base for single crowns, larger bridges or dentures. Titanium dental implants, in the form of screw (endosseous implants), are various-age appropriate secure solution and are the most used implants. Since a dental implant, generally metal-made, represents a foreign body for the patient, many difficulties can occur. Therefore, for successful implant application, the dental industry has to consider all relevant factors that are related to dental reconstruction and restoration like biocompatibility, osseointegration, corrosion resistance, implant geometry design, mechanical stability, and implant/bone and implant/surrounding tissue interactions. Once the implant is placed within the jaw, it should rapidly osseointegrate with surrounding bones and tissues and create a stable implant/surrounding bone interface. It is clear, implant-bone and implant-surrounding tissue interactions are affected by the implant surface microstructure, composition, morphology, roughness and hydrophilicity. Hence, surface engineering plays a significant role in the improvement of the implantation process, especially osseointegration. Many studies report about surface modification of dental implants (e.g., sandblasting, acid etching, anodization, self-assembling etc.) in order to optimize and improve their surface characteristics and enhance implantation. In this study, the titanium implant surface was functionalized by chemisorption of osseoinductive molecule using a facile and effective approach. The morphology of the modified implant surface, Ti/TiO2/bioactive coating, was examined by SEM and wetting properties by contact angle measurements. Electrochemical properties of the Ti/TiO2/bioactive coating were studied in vitro in artificial saliva solution using electrochemical impedance spectroscopy. The experimental findings were corroborated by means of DFT calculations. The formation mechanism of bioactive implant coating was proposed considering experimental results and a computational study of Gibbs free energies of bioactive molecule/TiO2 molecular interactions.

Significant efforts have been made to develop new semiconductor catalysts for energy conversion and photocatalytic degradation of organic pollutants, pigments and dyes. It is challenging to identify, and design new semiconductor materials that are efficient, stable and abundant. Therefore, the knowledge of fundamental semiconductor (photo)electrochemistry principles is of the great importance. The crucial step in photoelectrochemical processes connected with solar energy conversion, including (photo)catalytic organic pollutant degradation is electron transfer, which occurs between the same energy levels of semiconductor and redox electrolyte species at the semiconductor|electrolyte interface. The flat band potential, EFB (Fermi level) as experimentally determined parameter, correlates the electron transfer between the semiconductor and the electrolyte solution and is linked to the semiconductor’s band edge position. For EFB determination, the Mott-Schottky (MS) analysis or photocurrent measurements can be used. In this work special attention was given to the accuracy of EFB determination. The aim of this work was also to broaden the photocatalytic system forward from single component catalyst’s to multi-component configuration. Composite semiconductor- semiconductor junction structure of the n-type Bi2S3 (narrow-band gap semiconductor), and the n- type Bi2O3 (wide-band gap semiconductor) was proposed. Both semiconductors have recently attracted much attention due to the natural abundance, non-toxicity, high catalytic activity and excellent electrical conductivity. Bi-films, formed potentiostatically on bismuth in an aqueous sodium hydroxide solution with and without the addition of sulfide ions, were investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and diffuse reflectance spectroscopy (DRS). The energy-band diagram for the proposed composite structure, n-Bi2S3| n-Bi2O3, was constructed taking into account the semiconducting parameters of the both semiconductors (deduced from the Mott-Schottky analysis and Tauc plots) and the thermodynamic data for the redox reactions occurring at the semiconductor|electrolyte interface. Special attention was given to the reactions that include the formation of free radical species prerequisite for the solar-driven photocatalytic degradation processes of organic pollutants. Absolute energy values of the conduction band edge, ECB and the valence band edge, EVB positions of n-Bi2O3 and n-Bi2S3 were deduced from the EFB (Fermi level) and correlated with the semiconductor’s stability against decomposition. The n-Bi2S3|n-Bi2O3 catalyst satisfies simultaneously the light adsorption and charge separation criteria, acting as possible suitable visible light-driven catalyst in advanced oxidation processes for wastewater treatment application.

Anorganski poluvodički spojevi prijelaznih metala u fokusu su interesa kao potencijalni fotokatalizatori u održivim tehnologijama konverzije energije i zaštite okoliša. Unatoč velikom broju istraživanja u području fotokatalize, još uvijek postoji problem dizajniranja fotokatalitičkih sustava visoke djelotvornosti za pročišćavanje voda. Za rješavanje problema potrebno je razviti koncept temeljem kojeg bi bilo moguće predložiti osmišljenu konstrukciju poluvodičkog fotokatalizatora s povećanom fotokatalitičkom učinkovitosti i stabilnosti samog fotokatalizatora u kontaktu s vodenim medijem. U ovom radu definirani su potrebni uvjeti koji osiguravaju uzajamnu povezanost između termodinamičkih karakteristika komponenata fotokatalitičkog sustava i energetske kompatibilnosti procesa u kojima se dobivaju slobodne radikalske vrste nužne za odvijanje fotokatalitičkih procesa degradacije organskih polutanata. S namjerom razvoja toga koncepta konstruirani su energija-vrpce dijagrami, za poluvodički fotokatalizator n-Bi2S3 i ko- katalizator n-Bi2O3, koristeći rezultate poluvodičkih parametara dobivenih Mott-Schottky i Kubelka-Munk analizom. Zašto ko-katalizator? Pri osvjetljavanju fotokatalizatora Bi2S3, koji uz širinu zabranjene zone od 1.4 eV apsorbira u vidljivom dijelu Sunčevog spektra, paralelno s fotokatalitičkom pretvorbom organskih polutanata do željenih produkata, odvijaju se i deaktivacijski procesi. Kako bi se spriječili ti neželjeni procesi, kao što je rekombinacija svjetlom generiranih elektrona i šupljina, fotokatalitički sustav mora biti kompleksniji. Stoga je kao ko-katalizatorski materijal korišten Bi2O3, poluvodič široke zabranjene zone od 2.8 eV koji može sudjelovati u tamnom periodu fotokatalitičkog procesa. Deaktivacija katalizatora izbjegnuta je prijelazom elektrona između vodljivih vrpci poluvodičkog katalizatora i ko-katalizatora.

Kositrov (IV) oksid (SnO2) je poluvodič n-tipa široke zabranjene zone (3.6 eV) koji pokazuje visoku kemijsku stabilnost, električnu vodljivost i optičku transparentnost, anti-fotokorozijsku i korozijsku otpornost. Netoksičnost, niska cijena i poželjna elektronska, optička, magnetska i katalitička svojstva čine ga atraktivnim multifunkcionalnim materijalom koji se koristi u mnogim područjima od tehnološkog interesa: transparentna vodljiva stakla, fotokatalizatori, senzori plina, pohrana i konverzija energije (protuelektroda u bojilom senzitiviziranim solarnim ćelija, anodni materijal u litij-ionskim baterijama). Prisutnost površinskog pasivnog oksidnog filma na kositru utječe na fotokatalitičke, katalitičke i korozijske procese koji se odvijaju na međufaznoj granici film|elektrolit. Kako bi se predvidjela dugotrajna korozijska otpornost kositra, koji je umjereno korozijski otporan materijal, potrebno je razviti duboko razumijevanje elektronske strukture (poluvodičkih svojstava) njegovog pasivnog filma.

The narrow band gap of SnS enables the utilization of solar energy and makes it a potential candidate for the low-cost solar energy conversion material and the efficient visible- light-driven photocatalyst. The sustainable manufacturing of solar devices is feasible if tin sulfide materials are used as cheap, nonstrategic and ubiquitous in nature, leading to the development of environmentally safe devices. A wide application of tin sulfides includes: solar collectors, photodetectors in photovoltaic solar energy devices, photocatalysts in advanced oxidation processes, as well as promising alternative for anode materials to replace commercial carbonaceous electrodes (graphite) in lithium-ion and sodium-ion batteries due to their high capacities. In this work, environment friendly and facile approach has been introduced for synthesis of the passive sulfide films on tin, employing non–toxic and low–cost materials. The tin sulfide film, formed by potentiostatic anodic polarization on tin in aqueous electrolyte solution, containing sulfide ions, was investigated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and diffuse reflectance spectroscopy (DRS). The electronic structure of the tin sulfide film was discussed on the basis of the band structure model of the surface film, the potential distribution across the film and at the metal|film|electrolyte interfaces as well as the availability of free charge carriers on the electrode|solution interface. The electronic structure of the tin sulfide film influences its susceptibility to the oxidative as well as to the reductive solid–state decomposition. The results presented in this work enable a better insight into the electronic structure semiconducting properties of the tin sulfide film that are essential to predict its suitability for optoelectronic and photovoltaic device applications.

Nikal je izvrstan katalizator za reakciju razvijanja vodika (RRV) budući da posjeduje mehaničku stabilnost, katalitičku selektivnost, dostupan je, moguće ga je nanositi u obliku prevlaka na različite geometrijske oblike i korozijski je otporan u elektrolitnim otopinama niskih i visokih pH vrijednosti. Korozijska otpornost nikla usko je povezana sa zaštitinim svojstvima pasivnog filma niklovog oksida/hidroksida, koji se spontano formira na njegovoj površini u vodenim otopinama. Međutim, taj film smanjuje elektrokatalitičku djelotvornost nikla za RRV u alkalnim generatorima vodika/elektrolizerima. Temeljeno na elektrokemijskim i spektroskopskim istraživanjima pasiviteta nikla, današnje stajalište je da pasivni film na Ni posjeduje duplex-tip strukture ; unutrašnji NiO film i vanjski Ni(OH)2 film. Vanjski Ni(OH)2 film se sastoji od reducibilne α– Ni(OH)2 forme i ireducibilne β–Ni(OH)2 forme koja usporava RRV.Budući da elektronska struktura α– Ni(OH)2 izravno utječe na djelotvornost RRV na Ni katalizatoru, u ovom radu su proučavana elektronska svojstva α–Ni(OH)2 filma koji se ponaša kao visoko-dopirani poluvodič n-tipa (s anionskim vakancijama kao dominantnim točkastim defektima). Informacije o raspodjeli potencijala i naboja na međufaznoj granici film|elektrolit dobivene su koristeći eksperimentalne metode: cikličku voltametriju, mjerenja kapaciteta i Mott- Schottky analizu.

The oxide film (TiO2) was formed on Nitinol potentiostatically in an acetic acid solution. Deep understanding of electronic properties of this film is needed to predict long-term corrosion properties of Nitinol implant material in simulated body fluid conditions. The capacitance measurements were performed under depletion conditions to study electronic (semiconducting) properties. The space charge, formed at the solid|liquid interface, creates the barrier for the corrosion processes in aggressive (bio)environment. According to the results of electrochemical impedance spectroscopy (EIS) and Mott-Schottky analysis (MS), the passive film on Nitinol behaves as amorphous highly-doped n-type semiconductor. The values of electronic structure parameters (the flat-band potential, Efb and the carrier (donor) density, ND) were corrected for frequency dispersion.

Za izradu metalnih implantnih materijala najčešće se koriste: (i) nehrđajući čelici, (ii) kobalt- kromove slitine, (iii) titanij i titanijeve legure. Osnovni uvjet za njihovu ugradnju u agresivni biookoliš ljudskog tijela je visoki stupanj korozijske otpornosti, koja je ključni čimbenik biokompatibilnosti. Stoga se reaktivne površine metalnih implantata modificiraju različitim prevlakama, kao što su npr. anorganski (oksidni filmovi), organski (samoorganizirajući filmovi molekula fosfonske kiseline) i biokeramički filmovi (prevlake kalcijevih fosfata ) i dr. U istraživanju korozijske otpornosti metalnih implantnih materijala primjenjuju se elektrokemijske metode budući da su procesi degradacije implantata u agresivnom biookolišu tkivnih tekućina elektrokemijske prirode. U ovom radu elektrokemijske metode su korištene i za: (i) formiranje prevlaka hidroksiapatita (HA) na Nitinolu, kao i za (ii) karakterizaciju korozijske otpornosti modificirane površine Nitinola u in vitro uvjetima realne primjene.

Nitinol is an attractive material for various types of medical implants due to its superior mechanical and unique properties (shape memory effect, superelasticity, high damping capacity etc). The Nitinol surface was modified with biocompatible coatings of calcium phosphate prepared by the sol-gel dip-coating method. The surface morphology, structure, and chemical composition of coatings were investigated by field emission scanning electron microscopy (FE – SEM)/energy dispersive X-ray spectroscopy (EDS), and Fourier transform infrared spectroscopy (FTIR). The barrier properties were investigated in vitro in simulated physiological solution using electrochemical impedance spectroscopy (EIS). It has been shown that the cycling dip-coating- calcining procedure produces homogeneous films with excellent barrier properties.

Various surface modifications have been applied to titanium and titanium alloys implants to improve their corrosion resistance and biocompatibility1. In this work Nitinol surface was modified with bioactive, bone-like hydroxyapatite coatings(HA), obtained by two deposition steps: electrochemical and chemical. Each of them has individual formation mechanism and deposited films posses different protection and biocompatible (bioactive) properties. The kinetics of the first step, nucleation of HA precursor film, was studied in situ using chronoamperometry (CA) and cyclic voltammetry (CV). The morphology, microstructure and barrier properties of HA coatings were characterized by field emission scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS). The chemical composition was examined using energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR).

Uz produljenje čovjekove životne dobi, brz način života i porast ukupne populacije, raste i potreba za ugradnjom implantata u ljudsko tijelo kako bi se održala kvaliteta života pojedinca. Uslijed povećane potrebe za ugradnjom implantata, raste i nužnost za detaljnim razumijevanjem interakcija površine implantata s okolnim fiziološkim okruženjem. Nitinol, približno ekviatomska legura nikla i titana (NiTi), je materijal od posebnog interesa u biomedicinskom inženjerstvu zbog svojih specifičnih mikrostrukturnih svojstava (svojstvo “pamćenja” oblika i superelastičnost). Kao implantni materijal, Nitinol se koristi za izradu krvožilnih i plućnih usadaka/stentova i ortodontskih implantata. Tjelesne tkivne tekućine predstavljaju vrlo agresivan okoliš za metalne implantate, stoga je kemijska stabilnost materijala osnovni preduvjet biokompatibilnosti. Relativno dobra korozijska stabilnost površine Nitinola temelji se na spontanom formiranju površinskog oksidnog TiO2 filma. S vremenom, u agresivnim tkivnim tekućinama, koje sadrže visoku koncentraciju kloridnih iona, može doći do lokalnog razaranja oksidnog filma i neželjenog otpuštanja alergenih i toksičnih iona nikla u okolna tkiva. Stoga, da bi se stvorila djelotvorna barijera između agresivnog okruženja i implantata čime bi se produljio njegov vijek trajanja i izbjegle bolne korekcijske operacije, reaktivna površina Nitinola modificira se biokompatibilnim prevlakama. Površina Nitinola modificirana je anorganskim prevlakama (oksidni filmovi dobiveni anodizacijom) i organskim prevlakama (samoorganizirajući filmovi fosfonskih kiselina) kako bi se poboljšala njegova korozijska otpornost i smanjila otpuštena količina iona nikla u okolna tkiva. Elektrokemijska karakterizacija nemodificiranih i modificiranih površina Nitinola provedena je in vitro u simuliranoj tjelesnoj otopini (Hankova otopina) koristeći ac i dc elektrokemijske metode (voltametrija, pulsne metode, impedancijska spektroskopija). Visoko-sofisticirane površinsko-analitičke metode (infracrvena refleksijsko apsorpcijska spektroskopija, rendgenska fotoelektronska spektroskopija i goniometrija) korištene su za površinsku karakterizaciju anorganskih i organskih prevlaka. Kinetika formiranja i rasta oksidnih filmova na Nitinolu je istraživana pod potenciostatskim i galvanostatskim uvjetima. In situ rast amorfnih oksidnih filmova (galvanostatski uvjeti) odvija se pod utjecajem visokog polja kooperativnim mehanizmom ionske vodljivosti (uključuje migraciju iona metala i kisika). Za kristalinične oksidne filmove (potenciostatski uvjeti) utvrđena je dominacija anionskih nad kationskim vakancijama. Elektronska, poluvodička svojstva pasivnih kristaliničnih filmova istražena su u uvjetima u kojima prevladava elektronska vodljivost. Oksidni filmovi na Nitinolu ponašaju se kao n-tip poluvodiča s kisikovim vakancijama kao elektron donorima. Tanki nanometraski oksidni filmovi na Nitinolu, građeni većinom od TiO2 sa samo 2% Ni, pružaju visoku korozijsku otpornost. Modifikacija površine Nitinola samoorganiziranjem fosfonskih kiselina rezultira formiranjem bidentantno kovalentno vezanih fosfonatnih filmova na oksidom prekrivenoj površini Nitinola što je potvrđeno fotoelektronskom spektroskopijom. Rezultati infracrvene spektroskopije pokazali su kako su formirani filmovi visoko uređeni i gusto pakirane strukture. Prema impedancijskim mjerenjima vidljivo je da se fosfonatni filmovi u simuliranoj tjelesnoj tekućini ponašaju kao neidealni dielektrici sa visokim vrijednostima otpora. Međufazna granica Nitinol|fosfonatni film|elektrolit predstavlja blokirajući kontakt koji djelotvorno sprječava odvijanje reakcija prijenosa naboja. Površine Nitinola modificirane anorganskim i organskim filmovima pokazuju povećanu korozijsku otpornost u odnosu na nemodificiranu površinu, čime je ostvaren osnovni preduvjet za povećanje biokompatibilnosti. Formirani sustav Nitinol|film predstavlja novi bioinženjerski materijal za izradu biokompatibilnih implantata.

Nitinol, nickel-titanium alloy derives its attractiveness from unique properties like shape memory effect and superelasticity. Owing to these desirable mechanical properties and good chemical stability, Nitinol is a popular material with a widespread use in biochemical engineering with application in medicine for manufacturing cardiovascular and orthodontic implants. In this work, to prevent the unwanted release of toxic/allergenic nickel ions, Nitinol surface was modified by biocompatible phosphonic acid self-assembled monolayers (SAMs) that form an effective interface between the human body and the implant surface. In order to determine the influence of the terminal functional group of SAM on the corrosion behavior, dodecyl-phosphonic acid SAMs with different terminal functional groups (-OH and –CH3) were prepared on Nitinol. The corrosion resistivity and biocompatibility of Nitinol modified by phosphonic acid SAMs in simulated body fluid (Hank’s solution) were studied using electrochemical ac and dc methods. Surface characterizations of unmodified and modified surfaces of Nitinol were done by goniometry and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT). The obtained results have revealed that both phosphonic acid molecules show bidentate bonding on Nitinol surface, but SAM with hydrophilic terminal group provides better corrosion resistance in comparison to SAM with hydrophobic terminal group.

Having in mind a need to extend the quality of life there is an ever-expanding requirement for implantation of metal implants in human body because of their superior properties. Nitinol, nickel-titanium alloy with near-equiatomic composition, derives its attractiveness and widespread use in biochemical engineering from unique mechanical properties known as shape memory effect and superelasticity. In spite of its good corrosion resistance due to the spontaneous passivation, it is of huge importance to prevent the unwanted release of toxic nickel ions. Hence, Nitinol surface was modified by biocompatible organic self-assembled monolayers and inorganic films (anodically formed passive films) in order to prevent release of nickel. In vitro characterization of modified and unmodified surfaces of Nitinol was performed in simulated body fluid (Hank’s solution) using electrochemical ac and dc methods. Surface films will be characterized by electronic microscopy and spectroscopic methods.

Produljenjem čovjekove životne dobi, kako bi se održala kvaliteta života pojedinca, raste i potreba za ugradnjom nadomjestaka/implantata u ljudsko tijelo. Porast ukupne populacije u svijetu i povećana potreba za implantatima potiču razvoj biomedicinskih inženjerskih sustava i tehnologija. Za izradu implantata koristi se i materijal Nitinol, približno ekviatomska legura nikla i titana (NiTi). Nitinol posjeduje specifična mikrostrukturna svojstva (svojstvo “pamćenja” oblika i superelastičnosti) i stoga je izuzetno važan u biokemijskom inženjerstvu s primjenom u medicini za izradu krvožilnih i plućnih usadaka (stentova) i ortodontskih implantata. Osnovni uvjet za ugradnju materijala u agresivan biookoliš ljudskog tijela, uz izvrsna mehanička i kemijska svojstva, je i visok stupanj biokompatibilnosti. Relativno dobra biokompatibilnost nemodificirane površine Nitinola temelji se na spontanom formiranju površinskog oksidnog filma koji predstavlja barijeru prijelazu toksičnih iona nikla i korozijskih produkata u biookoliš implantata. Za daljnje povećanje korozijske otpornosti koriste se različite metode modifikacije površine Nitinola kako bi se spriječila degradacija implantata, produljio njegov vijek trajanja i izbjegle bolne korekcijske operacije. Površina Nitinola modificirana je samoorganizirajućim monoslojevima fosfonskih kiselina. Samoorganizirajući monoslojevi predstavljaju jednostavan i jeftin način modifikacije površine uz dodatnu mogućnost naknadne modifikacije završnih skupina formiranih monoslojeva s ciljem dobivanja sustava s novim fizikalno-kemijskim svojstvima. In vitro karakterizacija nemodificiranih i modificiranih površina Nitinola provedena je u simuliranoj tjelesnoj otopini (Hankova otopina) koristeći elektrokemijske metode (ciklička voltametrija i elektrokemijska impedancijska spektroskopija) i goniometriju. Ispitivan je utjecaj pripreme površine prije modifikacije samoorganizirajućim monoslojevima i utjecaj duljine lanca fosfonskih kiselina na barijerne karakteristike modificirane površine Nitinola.

The enhanced catalytic activity of Au nanoparticles has recently attracted particular attention of scientists in various disciplines such as surface chemistry and heterogeneous catalysis. It was suggested that the Au-oxide (Au(III)) is at the interface of metallic Au nanoparticles and oxide supports and the Au(III) species contribute to stabilize Au nanoparticles on the surface. The formation of thin oxide films on gold coated quartz crystal electrode in 0.1 mol dm^-3 NaClO4 solution at pH 5.45 has been investigated by means of nanogravimetry using an electrochemical quartz crystal nanobalance which provides a new dimension for such studies. Anodic oxide film nucleation, growth and reduction processes were also investigated using cyclic voltammetry and potentiostatic chronoamperometric techniques. The oxide film nucleation kinetics was explained through a 3D nucleation mechanism with diffusion controlled growth and nucleation parameters were determined. Characterization of the oxide layer and the structural composition of the gold surface were examined by X-ray photoelectron spectroscopy and observed XPS spectrum were characteristic for Au(III) species. In addition to XPS, photoelectrochemical method was also used to characterize the surface. Anodically formed oxide film on gold acted as n-type semiconductor.

Occlusive coronary artery disease (CAD) is reported to be the single largest cause of death in developed countries, such as Canada and United States. The disease is characterized mostly by the formation of a plaque, resulting in considerable narrowing and hardening of the vessels. Stenting following percutaneous transluminal balloon angioplasty has proved to be the less invasive treatment for CAD. Nitinol, a roughly equiatomic alloy of nickeltitanium, has been used extensively in biomedical devices, particularly in cardiovascular stents, due to its outstanding mechanical characteristics, such as the ability to remember its original shape. However, all current bare-metal stents, including Nitinol, offer low biocompatibility. This results in occurrence of in-stent restenosis in up to ca. 30% patients, and the need for further medical treatment. Therefore, various stent-surface modification approaches have been employed in order to minimize in-stent restenosis, but none of them have proven to give long-term satisfactory benefits. Furthermore, one the major concerns of using Nitinol in cardiovascular stents is the release of nickel ions to the body, which has proved to be carcinogenic and allergic. Thus, the aim of this work was to develop a new method for the Nitionol (stent) surface functionalization, with the ultimate goal decreasing the in-stent restenosis rate. We functionalized a Nitinol surface with a phosphonic acid self-assembled monolayer (SAM) which not only acts as a surface corrosion inhibitor that minimizes the nickel ions release to the human body, but also potentially enable us to further functionalize the surface with a (bio)molecule of choice, such as proteins and drugs.

Hematit (α-Fe2O3) se zbog svojih karakteristika poput male vrijednosti energijskog procijepa (oko 2.1 eV), izuzetne stabilnosti, netoksičnosti i niske cijene, intenzivno istražuje kao fotokatalizator i materijal za izradu fotoanoda. Međutim, njegov veliki nedostatak je loša električna vodljivost koju treba povećati. Jedan od načina je dopiranje, odnosno ugradnja primjesa koje će zamijeniti osnovni atom (Fe3+) na njegovu mjestu u kristalnoj rešetki. U ovom radu metodom elektroispredanja provedena je sinteza 1D hematita u obliku vlakana bez i sa dodatkom 2 at. % i 5 at. % Ru3+ kao ekstrinsične primjese. Kako bi se utvrdio utjecaj Ru3+ dopanda na morfološka, strukturna, optička i poluvodička svojstva hematita, vlakana su karakterizirana sljedećim metodama: UV/Vis, ATR-FTIR, SEM, EDS i XRD. Prema rezultatima svih metoda, vlakna se dominantno sastoje od hematitne faze. Usporedbom ATR-FTIR spektara i difraktograma dopiranih i nedopiranih vlakana vidljiv je pomak vrpci (ATR-FTIR) i pomak maksimuma (XRD), što potvrđuje uspješnu ugradnju Ru3+ iona u strukturu hematita. Utjecaj dopiranja na optička i poluvodička svojstva hematita jasno je vidljiv i u smanjenoj vrijednosti energijskog procijepa dopiranih uzoraka [Ebg (5 at. % Ru3+) = 2,05 eV, direktni prijelaz] u odnosu na nedopirani uzorak (Ebg = 2,10 eV, direktni prijelaz) što ukazuje na povećanje električne vodljivosti dopiranih uzoraka. Materijal ovakvih karakteristika potencijalni je kandidat za primjenu u procesima pročišćavanja otpadnih voda kao fotokatalizator. Hematite (α-Fe2O3) is being intensively investigated for use as a photocatalyst and photoanode material due to its properties such as low energy gap value (about 2.1 eV), exceptional stability, nontoxicity, and low cost. However, its major drawback is poor electrical conductivity, which needs to be enhanced. One of the ways is doping, which is the incorporation of impurities to replace the base atom (Fe3+) in its place in the crystal lattice. In this work, the synthesis of 1D hematite in the form of fibers was carried out by electrospinning method, without and with the addition of 2 at. % and 5 at. % Ru3+ as extrinsic impurities. To determine the effect of Ru3+ doping on the morphological, structural, optical, and semiconducting properties of hematite, the fibers were characterized by the following methods: UV/Vis, ATR-FTIR, SEM, EDS, and XRD. According to the results of all methods, the fibers are predominantly composed of the hematite phase. Comparison of ATR-FTIR spectra and diffractograms of doped and undoped fibers shows a band shift (ATR-FTIR) and a maximum shift (XRD), confirming the successful incorporation of Ru3+ ions into the hematite structure. The influence of doping on the optical and semiconducting properties of hematite is reflected in the reduced value of the energy gap of the doped samples [Ebg (5% at. Ru3+) = 2.05 eV, direct transition] to the undoped sample (Ebg = 2.10 eV, direct transition), indicating an increase in the electrical conductivity of the doped samples. Material with such properties is a potential candidate for application in wastewater treatment processes as a photocatalyst.