Nanomaterials based on zirconium(iv) oxide: synthesis, characterization and application in photocatalysis under simulated solar light

Predmet istraživanja ove doktorske disertacije je razvoj metoda sinteze nanomaterijala na bazi cirkonijum(IV)-oksida (ZrO2), karakterizacija dobijenih materijala primenom različitih fizičkohemijskih metoda kao i ispitivanje mogućnosti njihove primene u fotokatalitičkoj razgradnji model jedinjenja pod uticajem simuliranog sunčevog zračenja. Prvi deo teze se odnosi na ispitivanje strukturnih, morfoloških, površinskih, optičkih i fotokatalitičkih svojstava nanomaterijala na bazi ZrO2 velike specifične površine sintetisanih primenom hidrotermalne metode. U cilju dobijanja uzoraka što veće specifične površine, tokom sinteze u strukturu ZrO2 ugrađeni su joni silicijuma (Si4+). Čist ZrO2 odlikuje prisustvo monoklinične kristalne faze i veličina čestica od oko 20 nm. Ugrađivanje jona Si4+ u kristalnu strukturu ZrO2 uzrokuje stabilizaciju metastabilne tetragonalne faze i smanjenje veličine čestica ZrO2. Ugrađivanje jona Si4+ takođe rezultuje povećanjem (oko 7 puta) specifične površine i smanjenjem efektivnog energetskog procepa sintetisanih ZrO2 nanomaterijala, od 5 eV za čist ZrO2 do 3,8 eV za dopirane uzorke. FTIC merenja su dokazala prisustvo Zr-O-Si veza u uzorcima. Svi ZrO2 uzorci su pokazali značajnu fotokatalitičku aktivnost u degradaciji 2,4,6-trihlorfenola pod uticajem simuliranog sunčevog zračenja koja je povećana ugradnjom Si4+ jona u strukturu ZrO2...The subject of this PhD thesis is the synthesis of nanomaterials based on zirconium(IV) oxide (ZrO2), their characterization by various physicochemical methods, as well as an investigation of their potential application in the photocatalytic degradation of selected model compounds under simulated solar light. The first section of the thesis refers to the investigation of structural, morphological, surface, optical and photocatalityc properties of ZrO2 nanomaterials with high specific surface area synthesized using hydrothermal method. In order to gain as high specific surface area as possible, Si4+ ions were introduced in ZrO2 matrix during synthesis. Pure ZrO2 crystallizes in a monoclinic crystalline phase with particles of approximately 20 nm in size. The incorporation of Si4+ ions resulted in the stabilization of the tetragonal crystalline phase and the reduction of particle sizes. Furthermore, doping ZrO2 matrix with Si4+ ions resulted in an increase in specific surface area (about seven times) and a decrease in effective band gap of ZrO2 powders from 5 eV for pure ZrO2 to 3.8 eV for doped samples. FTIR measurements proved existence of Zr-O-Si bond in the synthesized samples. All ZrO2 powders showed significant photocatalytic activity regarding degradation of 2,4,6-triclorophenol under simulated solar light, which increases with the incorporation of Si ions in the host matrix..

enzimska lipofilizacija vitamina C linolnom kiselinom - određivanje antioksidativnih i difuzionih svojstava L-askorbil-linolata

Lipophilic derivatives of vitamin C are additives with antioxidant properties, attractive for application in food, cosmetics and pharmaceutics. They could be synthesized in lipase-catalyzed processes by using various acyl donors. Hereby, we present application of linoleic acid, which is polyunsaturated fatty acid essential in human nutrition, for esterification of vitamin C catalyzed by immobilized enzyme preparation Novozym® 435 in acetone. Highest specific ester yield, 9.7 mmol/g of immobilized lipase, was accomplished with 0.15 M of vitamin C, 0.6 M of linoleic acid, 3 g/l of enzyme and 0.07% (v/v) of water, at 60°C. NMR analyses of purified product proved that synthesized molecule was identical to 6-O-ascorbyl linoleate. Capacity of ester for scavenging 2,2-diphenyl-1-picrylhydrazyl radicals was two times higher comparing to parent molecule, vitamin C. Its diffusion coefficient, determined using Franz cell and cellulose acetate membrane, was 40% higher than palmitate and 62% higher than oleate. Obtained results showed that L-ascorbyl linoleate could be successfully synthesized in biocatalyzed processes. Furthermore, it was demonstrated that it possess high potential for application in different lipophilic products due to its liposolubility, high antioxidant efficiency and good diffusion properties.Lipofilni derivati vitamina C su aditivi sa antioksidativnim dejstvom pogodni za primenu u prehrambenim, kozmetičkim i farmaceutskim proizvodima. Mogu biti sintetisani u procesima katalizovanim lipazama korišćenjem različitih acil-donora. U ovom radu, opisana je primena linolne kiseline, polinezasićene masne kiseline esencijalne u ljudskoj ishrani, u esterifikaciji vitamina C katalizovanoj imobilisanim enzimskim preparatom Novozym® 435 u acetonu. Najviši specifični prinos estra od 9,7 mmol/g imobilisane lipaze, ostvaren je sa 0,15 M vitamina C, 0,6 M linolne kiseline, 3 g/l enzima i 0,07 zapr. % vode, na 60°C. NMR analize prečišćenog proizvoda dokazale su da je sintetisani molekul identičan 6-O-askorbil-linolatu. Kapacitet estra za vezivanje 2,2- difenil-1-pikrilhidrazil radikala bio je dva puta viši u odnosu na sam vitamin C. Njegov koeficijent difuzije, određen korišćenjem Franz-ove ćelije i celuloza-acetatne membrane, bio je za 40% viši u odnosu na palmitat i za 62% u odnosu na oleat. Ostvareni rezultati pokazali su da L-askorbil-linolat može uspešno biti sintetisan u biokatalizovanom procesu. Pored toga, dokazano je da ovaj estar poseduje značajan potencijal za primenu u različitim lipofilnim proizvodima zbog svoje liposolubilnosti, snažnog antioksidativnog dejstva i pogodnih difuzionih karakteristika

Synthesis of CdIn2S4 mesocrystals

Ternary nanosized sulfide CdIn2S4was synthesized using hot-injectionmethod in oleic acid/oleylamine mixture as reaction media at 270ºC. TEM images have shown that obtained material grows through multistep process, forming marigold structures built out from mesocrystals. Influence of oleic acid and oleic acid/oleylaminemixture as reaction media on mesocrystal formation is tracked and discussed.Physical chemistry 2016 : 13th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-30 September 201

Characterization of hydrothermaly synthesized zirconia nanopowders

In this paper,a hydrothermal method for synthesis of zirconia nanopowders: pure and with incorporated Si4+ions is presented. Zirconyl chloride and tetraethyl orthosilicate were used as precursors. As prepared powders were annealed at 600 °C and their structural (XRD), morphological (TEM) and textural (BET method) properties were obtained.It has been shown that by using hydrothermal synthesis method pure monoclinic ZrO2highly crystalline powder can be obtainedwithcrystallites of about 25nm. Incorporation of Si4+ions induced stabilization of tetragonal crystalline phase at room temperature, decreasing particle sizes to about 3-6 nm and increasing specific surface area of nanopowders.Physical chemistry 2016 : 13th international conference on fundamental and applied aspects of physical chemistry; Belgrade (Serbia); 26-30 September 201

Surface modification of zirconia nanoparticles with selected enediol ligands

The colloidal ZrO2 nanoparticles were hydrolytically synthesized and characterized using x-ray diffraction and UV/Vis spectroscopy. The surface modification of nanocrystalline particles with selected enediol ligands: catechol (CAT), 2,3-dihydroxynaphthalene (2,3-DHN), anthrarobin (ANT) and quercetin, was found to alter the optical properties of nanoparticles. The formation of the inner-sphere charge-transfer (CT) complexes results in a red shift of the semiconductor absorption onset compared to unmodified nanocrystallites, and a decrease of effective band gap upon increase of the electron delocalization after the inclusion of additional ring

The influence of reaction media on CdIn2S4 and ZnIn2S4 nanocrystallite formation and growth of mesocrystal structures

A hot-injection method for the synthesis of CdIn2S4 in three different compositions of organic media/solvents was studied. Nanosized CdIn2S4 is successfully synthesized in an oleic acid/oleylamine mixture of complexing/capping agents. The obtained mesocrystals of 20-30 nm in diameter are self-organized in marigold-like structures. The estimated band-gap of synthesized semiconductor is in the visible spectral region and has a value of about 2.1 eV. The potential of the band edges is calculated using an empirical equation. The as-prepared material was successfully transferred from organic to aqueous media by using 2-mercaptoethanol in a surface ligand exchange process. Using a similar synthetic procedure, ZnIn2S4 synthesis was performed. The obtained materials were characterized using UV/vis spectroscopy, XRD and TEM. Formation and growth mechanisms of the synthesized materials are proposed

Supplementary data for article: Milivojević, A.; Ćorović, M.; Carevic, M.; Banjanac, K.; Vujisić, L. V.; Velickovic, D.; Bezbradica, D. Highly Efficient Enzymatic Acetylation of Flavonoids: Development of Solvent-Free Process and Kinetic Evaluation. Biochemical Engineering Journal 2017, 128, 106–115. https://doi.org/10.1016/j.bej.2017.09.018.

Supplementary material for: [https://doi.org/10.1016/j.bej.2017.09.018]Related to published version: [http://cherry.chem.bg.ac.rs/handle/123456789/2558

Dextransucrase entrapment as an efficient alternative for increased recycling efficiency of free enzyme within agar-agar film matrix

Dextransucrase (DS), the extracellular enzyme is of immense industrial importance, due to ability to produce dextran and oligosaccharides (OS). Worldwide interest in OS has been increasing, since they have been accorded the prebiotic status. However, the industrial application of DS for OS synthesis is limited, due to low yield of enzyme production and its low catalytic activity. Hence, there is a great interest for development of new technologies that can provide improved performance of biocatalyst. Enzyme immobilization technology is considered to be a crucial step for cheaper and more efficient usage of DS. Entrapment is one of the widely investigated immobilization methods, where enzymes are enclosed or confined within the polymer matrix without altering their native structure, developing bioreactors for commercial applications. Different matrices such as polyacryl-amide gel, alginate beads and agar–agar have been used for the entrapment of different enzymes and among them agar–agar is a biocompatible, non-toxic and strong solidifying agent for immobilization of various enzymes. In this work, the entrapment of DS was initiated by different quantity (1:9, 1:4 and 1:1) of dialyzed enzyme into agar- agar solution. Agar solution was prepared in distilled water by vigorous shaking at 100°C, autoclaved and was allowed to cool to 40–45°C. Afterwards, enzyme was incorporated and mixed thoroughly. This mixture was immediately poured into a clean Petri plate and left to solidify at room temperature. Polymer films with and without immobilized DS were analyzed in terms of enzyme activity and reusability and mechanical properties (tensile strength, elongation at break and elastic modulus). In order to remove un-entrapped enzyme the films were washed with double deionized water and sodium acetate buffer (pH 5.4) three times prior to enzymatic assay. For quantitative analysis of samples for OS production a Dionex Ultimate 3000 HPLC system was used. Results showed that maximum immobilization yield (74.11%) was achieved by use of 2 % agar and (1:9) enzyme: agar ratio. HPLC analysis confirmed the similar trend of OS formation in immobilized samples compared to free enzyme. The lowest tested fraction of enzyme immobilized into polymer matrix (1:9) improved tensile strength of films in comparison with control film, whereas higher concentration of enzyme led to decrease in mechanical resistance of films. Scanning electron microscopy of agar films before and after DS entrapment revealed significant morphological change on the matrix surface. Considering the economic feasibility, the entrapped DS indicated imperative recycling efficiency up to six reaction cycles. The results of this study revealed that an easily available and inexpensive matrix could be successfully employed for DS immobilization and OS production

Nanomaterials based on zirconium(iv) oxide: synthesis, characterization and application in photocatalysis under simulated solar light

Predmet istraživanja ove doktorske disertacije je razvoj metoda sinteze nanomaterijala na bazi cirkonijum(IV)-oksida (ZrO2), karakterizacija dobijenih materijala primenom različitih fizičkohemijskih metoda kao i ispitivanje mogućnosti njihove primene u fotokatalitičkoj razgradnji model jedinjenja pod uticajem simuliranog sunčevog zračenja. Prvi deo teze se odnosi na ispitivanje strukturnih, morfoloških, površinskih, optičkih i fotokatalitičkih svojstava nanomaterijala na bazi ZrO2 velike specifične površine sintetisanih primenom hidrotermalne metode. U cilju dobijanja uzoraka što veće specifične površine, tokom sinteze u strukturu ZrO2 ugrađeni su joni silicijuma (Si4+). Čist ZrO2 odlikuje prisustvo monoklinične kristalne faze i veličina čestica od oko 20 nm. Ugrađivanje jona Si4+ u kristalnu strukturu ZrO2 uzrokuje stabilizaciju metastabilne tetragonalne faze i smanjenje veličine čestica ZrO2. Ugrađivanje jona Si4+ takođe rezultuje povećanjem (oko 7 puta) specifične površine i smanjenjem efektivnog energetskog procepa sintetisanih ZrO2 nanomaterijala, od 5 eV za čist ZrO2 do 3,8 eV za dopirane uzorke. FTIC merenja su dokazala prisustvo Zr-O-Si veza u uzorcima. Svi ZrO2 uzorci su pokazali značajnu fotokatalitičku aktivnost u degradaciji 2,4,6-trihlorfenola pod uticajem simuliranog sunčevog zračenja koja je povećana ugradnjom Si4+ jona u strukturu ZrO2...The subject of this PhD thesis is the synthesis of nanomaterials based on zirconium(IV) oxide (ZrO2), their characterization by various physicochemical methods, as well as an investigation of their potential application in the photocatalytic degradation of selected model compounds under simulated solar light. The first section of the thesis refers to the investigation of structural, morphological, surface, optical and photocatalityc properties of ZrO2 nanomaterials with high specific surface area synthesized using hydrothermal method. In order to gain as high specific surface area as possible, Si4+ ions were introduced in ZrO2 matrix during synthesis. Pure ZrO2 crystallizes in a monoclinic crystalline phase with particles of approximately 20 nm in size. The incorporation of Si4+ ions resulted in the stabilization of the tetragonal crystalline phase and the reduction of particle sizes. Furthermore, doping ZrO2 matrix with Si4+ ions resulted in an increase in specific surface area (about seven times) and a decrease in effective band gap of ZrO2 powders from 5 eV for pure ZrO2 to 3.8 eV for doped samples. FTIR measurements proved existence of Zr-O-Si bond in the synthesized samples. All ZrO2 powders showed significant photocatalytic activity regarding degradation of 2,4,6-triclorophenol under simulated solar light, which increases with the incorporation of Si ions in the host matrix..

Zirconium dioxide nanopowders with incorporated Si4+ ions as efficient photocatalyst for degradation of trichlorophenol using simulated solar light.

We present a hydrothermal method for synthesis of zirconia nanopowders: pure and with incorporated Si4+ ions. Zirconyl chloride and tetraethyl orthosilicate were used as precursors. As prepared powders were annealed at 600 degrees C and characterized using structural (XRD), morphological (SEM and TEM) and optical techniques (UV/vis DR, FTIR and photoluminescence spectroscopy). Their textural properties (BET method) and photocatalytic activity toward degradation of model compounds (tricholophenol and Rhodamine B) using simmulated solar light were obtained. We showed that by using hydrothermal synthesis method pure monoclinic ZrO2 highly crystalline powder can be obtained. Incorporation of Si4+ ions induced stabilization of tetragonal crystalline phase at room temperature and decreasing of particle sizes. Incorporation of Si4+ ions in zirconia matrix also resulted in increase of specific area of nanopowders. FTIR measurements were used as proof for existence of Zr-O-Si bond. Effective band gap of zirconia powders was reduced from 5 (pure ZrO2) to 3.8 eV for samples with Si4+ ions. All zirconia powders showed significant photocatalytic activity regarding degradation of triclorophenol and no activity regarding RB (Rhodamine B dye). Photocatalytic activity of zirconia was increased by incorporation of Si ions in the host matrix. The source of this observation is discussed correlating all obtained properties of pure and Si-incorporated nanopowders. Optimization of synthesis parameters and composition of zirconia samples obviously can lead to their photocatalytic activity comparable to Degussa TiO2 powder, famous and commercial photocatalyst. (C) 2016 Elsevier B.V. All rights reserved