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11.
Synthesis and characterization of metal/semiconductor nanocomposites for photocatalysis
Tina Mavrič, doktorska disertacija

Opis: The doctoral dissertation focused on improving photocatalytic activity of nanopowdered ZnO by constructing I) Metal-Semiconductor and II) Semiconductor-Semiconductor heterostructures. Both heterostructure types have been reported to have a beneficial effect on photocatalytic efficiency. For the first part (I) Ag/ZnO nanocomposite was synthesized. Here we investigated an influence of polyvinylpyrrolidone (PVP) addition during the synthesis on the particle properties and their photoactivity. The second part (II) describes procedure development of ZnO based semiconductor-semiconductor composite that resulted in synthesis of highly efficient ZnO/CuWO4 composite. Ag/ZnO nanocomposite was synthesized from precursors in ethylene glycol (EG) in a hydrothermal reactor at 180 °C for 3h. No further thermal treatment was required after the synthesis since all samples showed good crystallinity. Silver precursor loading was 2.7 wt%, because this amount has shown the best photoactivity in preliminary sample testings. Two separate batches of Ag/ZnO nanopowders were prepared, one with addition of PVP, one without (labelled Ag/ZnO and Ag/ZnO*, respectively). All powders were in nanometer range, TEM images showed a major difference between the samples with and without PVP. While Ag nanoparticles were deposited uniformly over ZnO, Ag/ZnO* exhibited a substantial agglomeration of Ag. The photocatalytic efficiency was assessed under UV-Vis light. Ag/ZnO reached complete decolourization of 10–5 M methyl orange (MO) already in 80 min after the beginning of irradiation. The calculated degradation rate constant (k) for the Ag/ZnO was almost 2-times larger than for TiO2 P25 and 4-times larger than for ZnO. Ag/ZnO* also showed higher activity than pure ZnO*, but was inferior to Ag/ZnO (1.6-times of Ag/ZnO*). A reusability test performed on Ag/ZnO showed an excellent photoactivity of reused powders; second and third cycle exhibited higher photoactivity than the first cycle. The supreme photocatalytic activity of Ag/ZnO was also confirmed by degradation of terephthalic acid. To develop an efficient semiconductor-semiconductor heterostructure we have synthesized a combination of several materials with ZnO. We performed preliminary photocatalytic tests in order to assess the functionality of these heterostructures. The tested systems were the following: ZnO/MWCNT, ZnO/GO, ZnO/SiC, ZnO/Co3O4, ZnO/AgVO3. The synthesis of heterostructures was done via hydrothermal synthesis. The commercial or synthesized powers were dispersed together with the ZnO precursor in EG medium (180 °C/3h). The aim was to obtain higher photoactivity than that of pure ZnO. None of these systems was able to outperform pure ZnO. ZnO/CuWO4 system has, however, significantly improved ZnO photoactivity. Several synthesis routes were investigated, including the influence of different structure directing agents (PVP, CTAB, starch). The best performing system was obtained by separate hydrothermal synthesis of ZnO and CuWO4 in water with PVP. XRD analysis confirmed that to obtain the crystalline CuWO4 thermal treatment (500 °C) is needed. The heterostructure was also synthesized in ethanolic solution. ZnO particles were in a nanometer range, CuWO4 were larger and ranged from 200 to 400 nm. CuWO4 has successfully decreased the charge recombination in ZnO, which was confirmed by transient absorption spectroscopy studies. The photocatalytic activity was assessed for both MO and TPA (10–4 M) degradation. The ZnO/CuWO4 composite has completely decolourized the dye in 60 min of UV-Vis irradiation. k for ZnO/CuWO4 was ~2.5-times larger than that of ZnO. A 3-cycle reusability test with MO showed a small decrease in efficiency in the last cycle. TPA degradation has revealed lower efficiency for ZnO/CuWO4 in air but high efficiency in O2 and N2 atmosphere, where it reached 90% and 55% degradation rate, respectively.
Najdeno v: osebi
Ključne besede: photocatalysis, zinc oxide, heterostructures, powders, Ag/ZnO composites, ZnO/CuWO4 composites
Objavljeno: 31.05.2017; Ogledov: 3743; Prenosov: 231
.pdf Polno besedilo (4,11 MB)

12.
Involving CeVO4 in improving the photocatalytic activity of a Bi2WO6/allophane composite for the degradation of gaseous acetaldehyde under visible light 
Masashi Hasegawa, Saim Emin, Nobuhiro Matsushita, Gangqiang Zhu, Yuki Makinose, Zuhra Kadirova, Mirabbos Hojamberdiev, Kiyoshi Okada, 2017, izvirni znanstveni članek

Opis: Indoor air quality is affected by hazardous chemical substances emitted from buildings, construction and decoration materials, indoor equipments or even due to human activities. In this study, the hydrothermal synthesis and mechanical mixing were applied to synthesize Bi2WO6/CeVO4/allophane composites (BW/CV/A), and their photocatalytic performance for the degradation of acetaldehyde, as a common indoor air pollutant, was evaluated under visible-light irradiation. The as-prepared composites were characterized by X-ray diffraction (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), and UV–visible (UV–vis) spectroscopy. The results demonstrated that the prepared composites had microstructures consisting of nanosheets of hierarchical flower-like Bi2WO6 microspheres on which the CeVO4 nanocrystals were fully embedded in the presence of allophane nanoparticles. The specific surface areas of the as-synthesized and mechanically mixed BW1/CV1/A composites were in the range of 110–182 m2 g−1. The effect of the amount of CeVO4 on photocatalytic activity of the Bi2WO6/allophane composite was explored, and the highest photocatalytic activity was observed for the BW1/CV1/A composite (Bi2WO6:CeVO4 = 1:1 mass ratio). Compared with the Bi2WO6/allophane and CeVO4/allophane composites, the hydrothermally synthesized BW1/CV1/A composite showed a significantly higher photocatalytic activity for the degradation of acetaldehyde under visible-light irradiation. The enhancement in the photocatalytic activity of the Bi2WO6/allophane composite achieved by involving the CeVO4 nanocrystals is due presumably to an extended light absorption range, appropriate band structures of Bi2WO6 and CeVO4, the formed p–n heterojunction, and the co-existence of Ce3+ and Ce4+ in CeVO4, resulting in effective separation of photogenerated electron-hole pairs.
Najdeno v: osebi
Objavljeno: 16.08.2017; Ogledov: 2356; Prenosov: 0
.pdf Polno besedilo (2,75 MB)

13.
Metal oxide and metal carbides thin films for photo/electrochemical water splitting studies
Saim Emin, 2017, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: We used wet-chemistry techniques to prepare colloidal tungsten (W) nanoparticles (NPs). The synthesis of W NPs was conducted using the so called hot-matrix method in 1-octadecene [1]. The sizes of obtained W NPs are in the order of 2 - 5 nm. These W NPs are coated with hydrophobic molecules which allow their dispersion in organic solvents like choloroform (CHCl3). It was found that the colloidal stability of the dispersions is exceptionally high exceeding several years. The stability of W NPs which prevents coagulation allows the preparation of thin films with uniform thicknesses by spin-coating, inkjet-printing and spray coating. We have prepared both tungsten trioxide (WO3) and tungsten carbide (W2C, WC) thin films. The preparation of WO3 thin films was achieved by spin-coating of W NPs on fluorine doped tin oxide (FTO) glass substrates and following thermal treatment in air at 500°C. The preparation of W2C and WC were done after spin-coating of W NPs on graphite substrate and following heat treatment under Ar atmosphere at 1000 and 1450°C. The obtained WO3 and W2C (e.g WC) films were used both in photo/electrochemical water splitting studies. In conclusion, we have developed a procedure for the synthesis of W NPs which can be used for the preparation of different class of materials for water splitting studies.
Najdeno v: osebi
Ključne besede: metal oxides, metal carbides, tungsten nanoparticles
Objavljeno: 09.10.2017; Ogledov: 2617; Prenosov: 0
.pdf Polno besedilo (364,61 KB)

14.
Tungsten carbide thin films for electrochemical water splitting studies
Hasan Okuyucu, Matjaz Valant, Ali Semerci, Cesur Altinkaya, Saim Emin, Abdullah Yildiz, 2017, objavljeni povzetek znanstvenega prispevka na konferenci

Opis: We used wet-chemistry techniques to prepare colloidal tungsten (W) nanoparticles (NPs). The synthesis of W NPs was conducted using the so called hot-matrix method in 1-octadecene [1]. The sizes of obtained W NPs are in the order of 2 - 5 nm. These W NPs are coated with hydrophobic molecules which allow their dispersion in organic solvents like choloroform (CHCl3). It was found that the colloidal stability of the dispersions is exceptionally high exceeding several years. The stability of W NPs which prevents coagulation allows the preparation of thin films with uniform thicknesses by spin-coating, inkjet-printing and spray coating. We have prepared tungsten carbide (W2C, WC) thin films. The preparation of W2C and WC was achieved by spin-coating of pre-synthesized W NPs on graphite substrate and following heat treatment under Ar atmosphere at 1000 and 1450°C. The obtained W2C and WC films were used both in electrochemical water splitting studies. We also made a composite W2C-Pt films where we used only 5 at.% of Pt. The W2C-Pt composite has shown similar performance as pure Pt-C for hydrogen (H2) evolution. In conclusion, we have developed a procedure for the synthesis of W NPs which can be applied for the preparation of tungsten carbides films and their use for electrochemical water splitting.
Najdeno v: osebi
Ključne besede: water splitting, nanoparticles, hot-matrix
Objavljeno: 09.10.2017; Ogledov: 3496; Prenosov: 0
.pdf Polno besedilo (376,30 KB)

15.
Photoelectrochemical Water Splitting Studies with nanostructured n and p-type semiconductor electrodes
Matjaz Valant, Saim Emin, 2017, objavljeni povzetek znanstvenega prispevka na konferenci (vabljeno predavanje)

Opis: Photoelectrochemical water splitting has been demonstrated as a promising way to efficiently split water. Currently, solar-to-hydrogen conversion efficiency using state-of-the-art material combinations in PEC system is in the order of 7%. Fabrication of nanostructured materials with unique morphologies and compositions is an important factor to fully utilize the possibilities in this field. We will present different strategies for the preparation of nanostructured metal oxide thin films by using electrodeposition and wet-chemistry techniques. Focus will be given on the preparation of ZnO and CuO thin films where intermediate phases like Zn(OH)8Cl2.H2O and CuX (X=Br, Cl) were electrodeposited. Wet-chemistry synthesis techniques will be also explored for the preparation of nanostructured WO3 and a-Fe2O3 thin films. Especially, the hot-pyrolysis technique for the preparation of colloidal W and Fe/Fe-oxide nanoparticles will be shown. Spin-coating of W and Fe/Fe-oxide NPs onto optically conductive substrates and subsequent heat treatment of the obtained films was found to be a convenient way for the preparation of nanostructured WO3 and a-Fe2O3 thin films.
Najdeno v: osebi
Ključne besede: photoelectrochemical water splitting, colloidal nanoparticles, semiconductor
Objavljeno: 24.10.2017; Ogledov: 2395; Prenosov: 0
.pdf Polno besedilo (1,47 MB)

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18.
International Conference on Functional Nanomaterials and Nanodevices
Polina Mladenova, Dominik Eder, Saim Emin, 2018, druge monografije in druga zaključena dela

Najdeno v: osebi
Ključne besede: energy conversion, catalysis, nanomaterials, nanobiotechnologies
Objavljeno: 17.09.2018; Ogledov: 1765; Prenosov: 0
.pdf Polno besedilo (3,62 MB)

19.
FOTOELEKTROKEMIČNI RAZKROJ BARVILA RODAMIN B V ODPADNIH VODAH Z UPORABO NANOSOV S FLUOROM DOPIRANEGA KOSITROVEGA OKSIDA
Matjaž Reya, 2019, diplomsko delo

Opis: V diplomskem delu smo z metodo fotoelektrokatalitičnega procesa opazovali razgradnjo barvila rodamin B v vodi. Izmerili smo čas, ki je bil potreben, da se je barvilo razgradilo in se je voda razbarvala. Vzorce smo analizirali s pomočjo UV-Vis spektroskopije. Raziskavo smo izvajali v foto-elektrokemijski celici, pri čemer smo uporabili anodo, katodo in referenčno elektrodo. Za anodo smo uporabili steklo z nanosom s fluorom dopiranim kositrovim oksidom (ang. fluorine doped tin oxide - FTO). Enako steklo smo izbrali za katodo, premazali smo jo s platino (Pt), za referenčno elektrodo pa smo uporabili srebro-srebrovo kloridno elektrodo (Ag|AgCl). Eksperiment je bil sestavljen iz treh obravnav z namenom primerjanja podatkov v različnih pogojih. Uporabili smo svetila treh valovnih dolžin 365 nm, 405 nm, in Vis svetlobo (> 400 nm). Potek reakcije smo preverili z uporabo 0,01 M žveplove kisline (H2SO4) in 0,001 M natrijevega hidroksida (NaOH). Ugotovili smo, da se je barvilo rodamin B koncentracije 1 × 10-5 mol/L, razgradilo samo v kislem mediju, z uporabo svetila valovne dolžine  = 405 nm. Razgradnja je v tem primeru potekala od 30 do 80 min. Na čas, ki je bil potreben za razgradnjo barvila, je bistveno vplivala aktivacija filma FTO. Eksperiment smo izvedli tudi brez svetila, v popolni temi, ta je, glede na poskuse z svetilom, potekel bistveno počasneje ali sploh ni potekel.
Najdeno v: osebi
Ključne besede: Fotoelektrokataliza, rodamin B, FTO, razgradnja barvila, čiščenje vode
Objavljeno: 21.10.2019; Ogledov: 1737; Prenosov: 66
.pdf Polno besedilo (1,73 MB)

20.
Volframov trioksid
Aleš Vaupotič, Narvika Bovcon, 2014, umetniško delo

Opis: Narvika Bovcon, Aleš Vaupotič, v sodelovanju z: Saim Emin (priprava vzorcev), Mattia Fanetti (operater vrstičnega elektronskega mikroskopa). Digitalna grafika, steklo, okvir, dimenzije: 136 × 136 cm, črno-belo. 2014. Produkcija: Univerza v Novi Gorici, projekt SUNGREEN.
Najdeno v: osebi
Povzetek najdenega: ...Narvika Bovcon, Aleš Vaupotič, v sodelovanju z: Saim Emin (priprava vzorcev), Mattia Fanetti (operater vrstičnega...
Ključne besede: tehniška slika, novomedijska umetnost, materiali, mikroskopija, vrstični elektronski mikroskop, SEM
Objavljeno: 12.05.2016; Ogledov: 3062; Prenosov: 18

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