Synthesis, characterization and application of undoped and doped nanostructured photocatalysts based on titanium(IV) oxide

Titan(IV)-oksid (TiO2) je zbog svoje fotokatalitičke aktivnosti, hemijske i biološke inertnosti, otpornosti na fotoindukovanu i hemijsku koroziju, netoksičnosti i relativno niske cene, jedan od najčešće proučavanih poluprovodničkih materijala za primenu u dekontaminaciji životne sredine, samo-čišćenju, uklanjanju mirisa, sterilizaciji i obnovljivim izvorima energije. Zbog široke zabranjene zone i velike brzine rekombinacije fotogenerisanih parova elektron-šupljina, efikasnost fotokatalizatora na bazi TiO2 je i dalje mala za potencijalnu praktičnu primenu. U poslednje četiri decenije veliki napor je uložen u istraživanja vezana za poboljšanje fotokatalitičke efikasnosti TiO2 i njegovu moguću praktičnu primenu. Generalno, fotokatalitička efikasnost TiO2 se može povećati: (1) smanjenjem energije zabranjene zone dopiranjem i/ili proširenjem apsorpcije (u vidljivu oblast) upotrebom fotosenzitizera, (2) poboljšanjem razdvajanja (smanjenjem brzine rekombinacije) fotogenerisanih nosilaca naelektrisanja (elektron/šupljina) i (3) povećanjem specifične površine i kvaliteta aktivnih mesta (za adsorpciju polutanata koje je potrebno fotokatalitički razgraditi). Cilj ove doktorske disertacije je proučavanje procesa formiranja nedopiranih i dopiranih nanostrukturnih prahova i tankih filmova titan(IV)-oksida znatno poboljšane fotokatalitičke efikasnosti. Da bi se postigla visoka fotokatalitička aktivnost u vidljivoj oblasti, neophodno je generisati aktivne apsorpcione centre za vidljivu svetlost. Pokazalo se da dopiranje anjonima nemetala predstavlja veliki potencijal u indukovanju takve apsorpcije i dosta napora se ulaže u razvijanje metoda za sintezu anjon-dopiranih TiO2 fotokatalizatora sa visokom aktivnošću u vidljivom delu spektra. Prema tome, u ovoj doktorskoj disertaciji prvo je predstavljeno dobijanje TiO2 filmova pulsnom laserskom depozicijom na staklenim supstratima u atmosferi kiseonika, metana, azota i mešavini kiseonika i azota. Inkorporacija azota u rešetku TiO2 je uspešno ostvarena, što je i pokazano merenjem optičke apsorpcije i fotoelektronske spektroskopije X-zracima (XPS). Apsorpciona ivica N-dopiranih TiO2 filmova pokazuje crveni pomeraj do ~480 nm u odnosu na 360 nm u slučaju nedopiranih filmova. Fotokatalitička aktivnost TiO2 filmova ispitivana je u reakciji fotoredukcije toksičnih Cr(VI) u Cr(III) jone u vodenoj sredini uz ozračivanje vidljivom i UV svetlošću. Najveću fotokatalitičku aktivnost u prisustvu vidljive svetlosti pokazuju TiO2 filmovi deponovani u atmosferi azota, dok su u prisustvu UV svetlosti najbolji rezultati dobijeni za TiO2 filmove deponovane u atmosferi čistog metana i kiseonika...Titania (TiO2) due to its photocatalytic activity, chemical and biological inertness, resistance to chemical- and photo-corrosion, non-toxicity, and relatively low cost, is one of the most studied semiconductors for environmental protection, selfcleaning, deodorizing, sterilizing and renewable energy sources. Owing to its wide band gap and high speed of electron/hole recombination, the efficiency of photocatalysts based on TiO2 is however small for potential practical applications. In the last four decades, much effort has been invested in research related to improving the photocatalytic efficiency of TiO2 and its possible practical applications. Generally, the photocatalytic efficiency of TiO2 can be increased by: (1) reducing the band gap energy by doping and/or enlargement of its absorption in the visible region using photosensitizes, (2) improving the separation (reducing the recombination rate) of photogenerated charge carriers (electron/hole) and (3) increasing the specific surface area and the quality of the active sites (for adsorption of pollutants to be photocatalytically degraded). The aim of this doctoral dissertation was the study of the process of the formation of undoped and doped nanostructured powders and thin films of titanium(IV) oxide with significantly enhanced photocatalytic efficiency. To this end, in order to obtain high photocatalytic activity in the visible light region, it was therefore mandatory to generate active visible light absorption centers. Anion doping proved itself to process great potential in inducing such absorption, and intensive efforts have been directed towards the development of methods for synthesizing anion-doped titania-based photocatalysts with a large visible light response. Therefore, in this doctoral thesis, first pulsed laser deposition of TiO2 films on glass substrates under oxygen, methane, nitrogen and mixture of oxygen and nitrogen atmospheres is presented. Nitrogen incorporation into the TiO2 lattice was successfully achieved, as demonstrated by optical absorption and XPS measurements. The absorption edge of the N-doped TiO2 films was red-shifted by ≈480 nm from the undoped value of 360 nm. The photocatalytic activity of TiO2 films was investigated during toxic Cr(VI) ions photoreduction to the Cr(III) state in aqueous media under irradiation with visible and UV light. Under visible light irradiation, the TiO2 films deposited under a nitrogen atmosphere showed the highest photocatalytic activity, whereas on UV light exposure, the best results were obtained for the TiO2 structures deposited under a pure methane or oxygen atmosphere..

The influence of synthesis conditions on the redox behaviour of LiFePO4 in aqueous solution

To contribute to the knowledge on the influence of synthesis procedure on the intercalation kinetics of lithium ions into phospho-olivines, LiFePO4/C composite samples (LFPC) were synthesized in two ways, the first one in a sol-gel procedure (SG), and the other in a solid-state reaction (SS). The X-ray diffractograms (XRD) of both samples overlapped with that of pure LiFePO4, taken from the crystallographic database. Scanning electron microscopy pictures indicated the high degree of interparticle sintering, which caused a considerable agglomerate growth. The results of potentiodynamic measurements in aqueous LiNO3 solution revealed that for SS sample, three times higher initial capacity from that of SG one, (amounting to 74 mAh g−1 at 5 mV s−1). However, capacity fade on rising scan rate is much more expressed for SS sample than for SG one. We suggest that a different degree of material utilization due to the incomplete coverage of olivine particles by carbon explains this difference. The technique of separation of diffusion and capacitance currents was applied in a kinetic analysis, but it was shown to be inappropriate. We suggest the inapplicability of classic CV theory to the intercalation system accompanied by phase transition. Instead, a model of ohmic resistance determination of process kinetics was considered. LFPC-SS sample delivers three times larger capacity in LiNO3, amounting to 74 mAh g−1 at 1 mV s−1.This is the peer-reviewed version of the article: Georgijević, R., Vujković, M., Gutić, S., Aliefendić, M., Jugović, D., Mitrić, M., Đokić, V., Mentus, S., 2019. The influence of synthesis conditions on the redox behaviour of LiFePO4 in aqueous solution. Journal of Alloys and Compounds 776, 475–485. [https://doi.org/10.1016/j.jallcom.2018.10.246]Supporting information: [https://hdl.handle.net/21.15107/rcub_dais_5975]Published version: [https://hdl.handle.net/21.15107/rcub_dais_4568

Periodate oxidized horseradish peroxidase@ZIF-8 nanocomposite

Metal-organic frameworks (MOFs) are a class of materials well-known for their high degree of crystallinity andultrahigh porosity. Modular synthesis from organic linkers and metal nodes allows for precise control of structure,pore size and chemical functionality of MOFs. Recently, MOFs have been explored for their potential to form novelbiocomposites with proteins by a process termed biomimetic mineralization. These novel MOF biocomposites showgreat promise for application to industrial biocatalysis where strategies for enhancing enzyme stability are ofsignificant interest. The protective capacity and applications of biomimetically mineralized biomacromolecule zeoliticimidazolate framework (ZIF-8) composites are likely dependent on the charge of the biomolecule and the topologyof the mineralized ZIF-8 coating. Herein, we identify conditions to reliably yield the porous periodate oxidizedhorseradish peroxidase@ZIF-8 sodalite topology biocomposite in preference to other more dense phases.Book of Abstract

Periodate oxidized horseradish peroxidase@ZIF-8 nanocomposite

Metal-organic frameworks (MOFs) are a class of materials well-known for their high degree of crystallinity and ultrahigh porosity. Modular synthesis from organic linkers and metal nodes allows for precise control of structure, pore size and chemical functionality of MOFs. Recently, MOFs have been explored for their potential to form novel biocomposites with proteins by a process termed biomimetic mineralization. These novel MOF biocomposites show great promise for application to industrial biocatalysis where strategies for enhancing enzyme stability are of significant interest. The protective capacity and applications of biomimetically mineralized biomacromolecule zeolitic imidazolate framework (ZIF-8) composites are likely dependent on the charge of the biomolecule and the topology of the mineralized ZIF-8 coating. Herein, we identify conditions to reliably yield the porous periodate oxidized horseradish peroxidase@ZIF-8 sodalite topology biocomposite in preference to other more dense phases.Book of Abstract

Periodate oxidized glucose oxidase@ZIF-8 nanocomposite

The durability of enzymes in harsh conditions can be enhanced by immobilization within metal-organic frameworks(MOFs) via a process called biomimetic mineralisation. Zeolitic imidazolate framework-8 (ZIF-8) is widely used as aprotective coating to encapsulate proteins. The formation of nucleation centres and further biocomposite particlegrowth is entirely governed by the pure electrostatic interactions between the protein’s surface and positively chargedZn(II) metal ions. It was previously shown that enhancing these electrostatic interactions by a chemical modificationof surface amino acid residues can lead to a rapid biocomposite formation. However, a chemical modification ofcarbohydrate components by periodate oxidation for glycoproteins can serve as an alternative strategy. In the presentstudy, an industrially important enzyme glucose oxidase (GOx) was selected as a model system. Periodate oxidationof GOx by 2.5 mM sodium periodate increased negative charge on the enzyme molecule. Biomineralizationexperiments with oxidized GOx resulted in higher specific activity, effectiveness factor, and higher thermostability ofthe ZIF-8 biocomposites

Periodate oxidized glucose oxidase@ZIF-8 nanocomposite

The durability of enzymes in harsh conditions can be enhanced by immobilization within metal-organic frameworks (MOFs) via a process called biomimetic mineralisation. Zeolitic imidazolate framework-8 (ZIF-8) is widely used as a protective coating to encapsulate proteins. The formation of nucleation centres and further biocomposite particle growth is entirely governed by the pure electrostatic interactions between the protein’s surface and positively charged Zn(II) metal ions. It was previously shown that enhancing these electrostatic interactions by a chemical modification of surface amino acid residues can lead to a rapid biocomposite formation. However, a chemical modification of carbohydrate components by periodate oxidation for glycoproteins can serve as an alternative strategy. In the present study, an industrially important enzyme glucose oxidase (GOx) was selected as a model system. Periodate oxidation of GOx by 2.5 mM sodium periodate increased negative charge on the enzyme molecule. Biomineralization experiments with oxidized GOx resulted in higher specific activity, effectiveness factor, and higher thermostability of the ZIF-8 biocomposites.Book of Abstract

Evaluation of nonlinear and linear constants of materials

Razvoj kvantnih generatora i pojačavača, (u području od kontinualne do atto oblasti) doneo je nove zahteve postojećim i razvoj novih teorija. Eksperiment i teorija su stalno zamenjivali mesta. Rezultati određenog procesa, se ne mogu pratiti on line i uključuju se i rezonantni efekti, da bi se indirektno izmerila pojedina veličina optičke, termodinamičke, akustičke ili druge prirode. Interakcija sa materijalom, traži poznavanje i novih konstanti nelinearne prirode, koje uključuju zavisnost od intenziteta zračenja. Šeme merenja nelinearnih delova indeksa prelamanja, koeficijenta refleksije i drugih optičkih konstanti zahtevaju složene aparature. Zato se planiranje novih eksperimenata i podešavanje angularnih položaja snopova, koji stupaju u interakciju, moraju simulirati i unapred predviđati mogući položaji. Iako su cene optike, koja služi kao eksperimentalna baza sada prihvatljivije, traženje materijala pogodnih za određene namene mora da uključi specifične tehnološke procese. U ovom radu se koriste teorije, koje polazeći od linearnih konstanti materijala, ocenjuju nelinearne i disperzivne doprinose i koriste vezu optičkih veličina sa veličinama drugih oblasti.The development of quantum generators and amplifiers (from continuous to atto range) has brought new demands for the existing theories as well as the development of new ones. Experiment and theory have been switching places continuously. The results of certain process can not be monitored on line and resonant effects are included in order to indirectly measure optical, thermodynamic, acoustic or any other value (quantity). Interaction with material is demanding the knowledge of new nonlinear constants which include dependence on beam intensity. Schemes for measurement of nonlinear parts of refraction index, reflection coefficient and other optical constants demand complicated devices. Therefore, the planning of new experiments and adjustment of beams which interact must be simulated and possible positions must be predicted in advance. Although the prices of optics which serves as experimental base are now more acceptable, searching for materials that are suitable for certain purposes must include specific technological processes. The theories starting from linear material constants, which estimate nonlinear and dispersive contributions as well as relationship between optical quantities and quantities from other fields are analyzed in this paper

Evaluation of nonlinear and linear constants of materials

Razvoj kvantnih generatora i pojačavača, (u području od kontinualne do atto oblasti) doneo je nove zahteve postojećim i razvoj novih teorija. Eksperiment i teorija su stalno zamenjivali mesta. Rezultati određenog procesa, se ne mogu pratiti on line i uključuju se i rezonantni efekti, da bi se indirektno izmerila pojedina veličina optičke, termodinamičke, akustičke ili druge prirode. Interakcija sa materijalom, traži poznavanje i novih konstanti nelinearne prirode, koje uključuju zavisnost od intenziteta zračenja. Šeme merenja nelinearnih delova indeksa prelamanja, koeficijenta refleksije i drugih optičkih konstanti zahtevaju složene aparature. Zato se planiranje novih eksperimenata i podešavanje angularnih položaja snopova, koji stupaju u interakciju, moraju simulirati i unapred predviđati mogući položaji. Iako su cene optike, koja služi kao eksperimentalna baza sada prihvatljivije, traženje materijala pogodnih za određene namene mora da uključi specifične tehnološke procese. U ovom radu se koriste teorije, koje polazeći od linearnih konstanti materijala, ocenjuju nelinearne i disperzivne doprinose i koriste vezu optičkih veličina sa veličinama drugih oblasti.The development of quantum generators and amplifiers (from continuous to atto range) has brought new demands for the existing theories as well as the development of new ones. Experiment and theory have been switching places continuously. The results of certain process can not be monitored on line and resonant effects are included in order to indirectly measure optical, thermodynamic, acoustic or any other value (quantity). Interaction with material is demanding the knowledge of new nonlinear constants which include dependence on beam intensity. Schemes for measurement of nonlinear parts of refraction index, reflection coefficient and other optical constants demand complicated devices. Therefore, the planning of new experiments and adjustment of beams which interact must be simulated and possible positions must be predicted in advance. Although the prices of optics which serves as experimental base are now more acceptable, searching for materials that are suitable for certain purposes must include specific technological processes. The theories starting from linear material constants, which estimate nonlinear and dispersive contributions as well as relationship between optical quantities and quantities from other fields are analyzed in this paper

Simulations in explosive processes area

Saglasnost teorije i eksperimenata eksplozivnih procesa pripada kategorijama kod kojih se traži visoka pouzdanost. Eksperimenti sa daljinskom kontrolom ili izazivanjem detonacionih procesa predstavljaju jednu od oblasti u kojoj se primenom optičkih metoda može da smanji rizik povezan sa ljudskim faktorom. Simulacije dinamike kad će pojedini zaštitini materijal da dostigne kritične parametre donose razne aproksimacije. U zavisnosti od primene bira se strožiji kriterijum. U radu je data analiza nekih primena lasera u svrhe eksplozivih procesa. Daće se aspekti preplitanja odnosa laser-eksplozivni proces sa nekoliko strana. Analiziraće se neki softverski paketi, kojima se modeluju procesi u kojima laser dovodi do promene temperature lokalnog suda sa eksplozivnim materijalom. Izborom osnovnih jednačina jednog prilaza daju se rezultati temperaturnih polja. Proračun može da posluži kao metod za modelovanje i nalaženje potrebnih uslova rada lasera za obezbeđenje eksplozivnog procesa.The agreement between theory and experiments of explosive processes belongs to a category at which the high reliability is needed. Experiments with remote control and initiation of detonation processes represent such field in which the risk for human factor could be decreased if optical methods are applied. Simulations in dynamics of reaching the critical parameters for different protective materials bring a various approximations. Depending from the application, the stronger criteria could be chosen. The application of some lasers for an explosive process is analyzed in this paper. The interrelations between laser-explosive process will be analyzed from a few sides. Some software packages, for modeling the processes in which the laser brings temperature changes into the container with an explosive material, will be critically analyzed. By choosing the principal equations in one approach, the results of temperature field distribution are given. This calculation may serve as method for modeling and finding the needed conditions of laser action for successful providing an explosive process

PRIMENA NANOČESTICA SEPIOLITA ZA DOBIJANJE PAPIRA POBOLJŠANIH MEHANIČKIH SVOJSTAVA

Tehničko rešenje koje se odnosi na primenu nanočestičnog sepiolita za poboljšanje mehaničkih svojstava papira proizvedenog u Fabrici Hartije Beograd je uspešno realizovano kroz laboratorijska ispitivanja i industrijsku probu. U laboratorijskim uslovima praćenjem promene viskoznosti disperzija skroba sa različitim udelom sepiolita utvrđeno je da dodatak sepiolita menja prirodu disperzije od dilatantnog, preko njutnovskog do pseudoplastičnog fluida. Skenirajuća elektronska mikroskopija je pokazala da su sepiolitska nanovlakna homogeno dispergovana na površini papira. Prisustvo sepiolita je uticalo na povećanje gramature papira. Ispitivanjem mehaničkih svojstava uzoraka papira utvrđeno je da se sa povećanjem sadržaja sepiolita u disperziji skroba povećava vrednosti otpornosti na pucanje i otpornosti na pritisak. U industrijskim uslovima takođe dolazi do poboljšanja mehaničkih svojstava papira što otvara mogućnost primene nanočestičnog sepiolita u proizvodnji ambalažnog papira u Fabrici Hartije Beograd.Tehničko rešenj