Successful immobilization of lanthanides doped TiO2 on inert foam for repeatable hydrogen generation from aqueous ammonia

We describe the successful possibility of the immobilization of a photocatalyst on foam, which is beneficial from a practical point of view. An immobilized photocatalyst is possible for use in a continuous experiment and can be easily separated from the reactor after the reaction concludes. Parent TiO2, La/TiO2, and Nd/TiO2 photocatalysts (containing 0.1 wt.% of lanthanide) were prepared by the sol-gel method and immobilized on Al2O3/SiO2 foam (VUKOPOR A) by the dip-coating method. The photocatalysts were investigated for the photocatalytic hydrogen generation from an aqueous ammonia solution under UVA light (365 nm). The evolution of hydrogen was compared with photolysis, which was limited to zero. The higher hydrogen generation was observed in the presence of 0.1 wt.% La/TiO2 than in 0.1 wt.% Nd/TiO2. This is, besides other things, related to the higher level of the conduction band, which was observed for 0.1 wt.% La/TiO2. The higher conduction band's position is more effective for hydrogen production from ammonia decomposition.Web of Science135art. no. 125

The role of fluorine in F-La/TiO2 photocatalysts on photocatalytic decomposition of methanol-water solution

F-La/TiO2 photocatalysts were studied in photocatalytic decomposition water-methanol solution. The structural, textural, optical, and electronic properties of F-La/TiO2 photocatalysts were studied by combination of X-ray powder diffraction (XRD), nitrogen physisorption, Ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS), Electrochemical impedance spectroscopy (EIS), and X-ray fluorescence (XPS). The production of hydrogen in the presence of 2.8F-La/TiO2 was nearly up to 3 times higher than in the presence of pure TiO2. The photocatalytic performance of F-La/TiO2 increased with increasing photocurrent response and conductivity originating from the higher amount of fluorine presented in the lattice of TiO2.Web of Science1218art. no. 286

Synthesis of vacant graphitic carbon nitride in argon atmosphere and its utilization for photocatalytic hydrogen generation

Graphitic carbon nitride (C3N4) was synthesised from melamine at 550 degrees C for 4 h in the argon atmosphere and then was reheated for 1-3 h at 500 degrees C in argon. Two band gaps of 2.04 eV and 2.47 eV were observed in all the synthetized materials. Based on the results of elemental and photoluminescence analyses, the lower band gap was found to be caused by the formation of vacancies. Specific surface areas of the synthetized materials were 15-18 m(2)g(-1) indicating that no thermal exfoliation occurred. The photocatalytic activity of these materials was tested for hydrogen generation. The best photocatalyst showed 3 times higher performance (1547 mu mol/g) than bulk C3N4 synthetized in the air (547 mu mol/g). This higher activity was explained by the presence of carbon (V-C) and nitrogen (V-N) vacancies grouped in their big complexes 2V(C) + 2V(N) (observed by positron annihilation spectroscopy). The effect of an inert gas on the synthesis of C3N4 was demonstrated using Graham ' s law of ammonia diffusion. This study showed that the synthesis of C3N4 from nitrogen-rich precursors in the argon atmosphere led to the formation of vacancy complexes beneficial for hydrogen generation, which was not referred so far.Web of Science121art. no. 1362

Photocatalytic H-2 evolution, CO2 reduction, and NOx oxidation by highly exfoliated g-C3N4

g-C3N4, with specific surface area up to 513 m(2)/g, was prepared via three successive thermal treatments at 550 degrees C in air with gradual precursor mass decrease. The obtained bulk and exfoliated (1ex, 2ex and 3ex) g-C3N4 were characterized and tested as photocatalysts for H-2 production, CO2 reduction and NOx oxidation. The exfoliated samples demonstrated graphene-like morphology with detached (2ex) and sponge-like framework (3ex) of layers. The surface area increased drastically from 20 m(2)/g (bulk) to 513 m(2)/g (3ex). The band gap (E-g) increased gradually from 2.70 to 3.04 eV. Superoxide radicals (O-center dot(2)-) were mainly formed under UV and visible light. In comparison to the bulk, the exfoliated g-C3N4 demonstrated significant increase in H-2 evolution (similar to 6 times), CO2 reduction (similar to 3 times) and NOx oxidation (similar to 4 times) under UV light. Despite the E-g widening, the photocatalytic performance of the exfoliated g-C3N4 under visible light was improved too. The results were related to the large surface area and low e(-)-h(+) recombination. The highly exfoliated g-C3N4 demonstrated selectivity towards H-2 evolution reactions.Web of Science1010art. no. 114

Photocatalytic reduction of CO2 over Ti3+ self-doped TiO2-based nanomaterials

In this study, we explored the photocatalytic efficacy of Ti3+-doped TiO2-based photocatalysts for CO2 reduction. The Ti3+ self-doped photocatalysts were synthesized using a straightforward chemical reduction with sodium borohydride (NaBH4). Our investigation aimed to elucidate the intricate interplay between the synthesis process and the quantity of NaBH4 reductant on the physical-chemical and photocatalytic attributes of the defective TiO2-based photocatalysts. We explored three different commercially available TiO2 materials labeled P25, (S)TiO2, and KRONOClean7050, which were reduced (2 g of TiO2) with 0.75 and 1.5 g of NaBH4. The reduction with 0.75 g of NaBH4 led to a significant decrease of photocatalytic activity in all three cases. It was caused by clogging of the photocatalysts surface by sodium ions which resulted in the surface recombination of charge carriers. Oppositely, the reduction with 1.5 g of NaBH4, led to an increase of the photocatalytic activity with superior performance of KRONOClean7050. The comprehensive characterization of all the samples explained this superior performance of KC7050_RED_1.5 sample. Importantly, it did not contain any amorphous phase and the crystal size was two times higher compared to other 2 samples reduced by 1.5 g of NaBH4. In the addition to higher crystallinity, the formation of a disordered TiO2−x layer, enriched with Ti3+ defects and oxygen vacancies, was confirmed. These structural features enhance the light absorption and mitigate undesired recombination of photogenerated charge carriers. These results would trigger farther investigation of defect engineering towards enhancement of the efficiency of metal oxide photocatalysts.European Union's Horizon 2020 project SAN4Fuel, (101079384, HORIZON-WIDERA-2021-ACCESS-03–01); European Commission, EC, (101120397, CZ.10.03.01/00/22_003/0000048, HORIZON-WIDERA-2022-TALENTS, RRC/12/2022); Grantová Agentura České Republiky, GA ČR, (GA CR 21-24268K); Narodowe Centrum Badań i Rozwoju, NCBR, (NOR/POLNORCCS/PhotoRed/0007/2019-00)Large Research Infrastructure ENREGAT [LM2023056]; Norway Grants 2014-2021 via the National Centre for Research and Development [NOR/POLNORCCS/PhotoRed/0007/2019-00]; Czech Science Foundation [GA CR 21-24268K]; European Union [HORIZON-WIDERA-2021-ACCESS-03-01: 101079384, CZ.10.03.01/00/22_003/0000048]; Support for Science and Research in the Moravia- Silesia Region 2022 [RRC/12/2022]; APPROACH [101120397

Effect of ZnO preparation method on the photocatalytic decomposition of ammonia in aqueous suspensions

Import 22/07/2015Diplomová práce se zabývá vlivem metody přípravy oxidu zinečnatého na fotokatalytický rozklad amoniaku, přičemž jako modelová reakční směs byl použit hydroxid amonný. Fotokatalytickým rozkladem vznikal vodík a dusík. Fotokatalytický rozklad amoniaku byl realizován ve vsádkovém anulárním míchaném reaktoru se suspendovaným fotokatalyzátorem. Ve středu symetrie reaktoru byla umístěna UV lampa poskytující záření s vlnovou délkou 254 nm. Fotokatalyzátor oxid zinečnatý byl připraven třemi různými způsoby a to: tepelným žíháním octanu zinečnatého (ZnO(1)), srážecí reakcí octanu zinečnatého a hydroxidu sodného s následným tepelným žíháním (ZnO(2)) a srážecí reakcí octanu zinečnatého hydroxidem sodným při UV záření a s následným tepelným žíháním (ZnO(3)). Připravené nanočástice byly charakterizovány termogravimetrií, rentgenovou difrakční analýzou, UV-Vis spektroskopií, fotoluminiscenční spektroskopií, fyzisorpcí dusíku a transmisní elektronovou mikroskopií. Při fotokatalytickém i fotochemickém rozkladu modelové reakční směsi docházelo k produkci vodíku. Produkce vodíku v přítomnosti ZnO fotokatalyzátorů byla srovnávána s produkcí H2 v přítomnosti komerčně vyráběného fotokatalyzátoru TiO2 Evonik P25. Aktivita testovaných katalyzátorů klesala v pořadí: ZnO(1) < ZnO(3) = Evonik P25 < ZnO(2). Experimentální data fotokatalytického rozkladu amoniaku byla vyhodnocena integrální metodou, byly určeny kinetické konstanty a byl potvrzen předpoklad, že reakci lze popsat rovnicí 1. řádu. Korelací fotokatalytické aktivity a fyzikálně-chemických charakteristik připravených fotokatalyzátorů bylo zjištěno, že klíčovými parametry ovlivňující fotokatalytický rozklad amoniaku jsou odlišné defekty v krystalové mřížce ZnO (kyslíkové vakance (VO) nebo kyslík intersticiální (Oi) a kyslík v místě Zn (OZn)), které vznikají v důsledku různé přípravy fotokatalyzátorů. Nejaktivnější fotokatalyzátor ZnO(1), který byl připraven tepelným žíháním, měl nejmenší specifický povrch, ale současně nejmenší množství kyslíkových vakancí. Nejmenší aktivitu fotokatalyzátoru ZnO(2) připraveného srážecí reakcí lze přisoudit nejvyššímu množství kyslíkových vakancí. Tyto vakance zachytávají excitované elektrony, které pak nejsou k dispozici pro fotokatalytickou reakci.This thesis examines the influence of the preparation method of zinc oxide on the photocatalytic decomposition of ammonia, where as ammonium hydroxide was used as a model reaction mixture. Hydrogen and nitrogen were generated by photocatalytic decomposition of ammonia. The photocatalytic decomposition of ammonia was carried out in a batch annular stirred reactor with suspended photocatalyst. In the axis of symmetry of the reactor the UV lamp providing a radiation having a wavelength of 254 nm was placed. Zinc oxide photocatalyst was prepared by three different ways, namely: thermal annealing of zinc acetate (ZnO(1)), precipitation reaction of zinc acetate and sodium hydroxide followed by thermal annealing (ZnO(2)) and a precipitation reaction of zinc acetate with sodium hydroxide under the UV radiation and followed by thermal annealing (ZnO(3)). Prepared nanoparticles were characterized by thermogravimetry, X-ray diffraction analysis, UV-Vis spectroscopy, photoluminescence spectroscopy, nitrogen physisorption and transmission electron microscopy. The hydrogen production was observed in both, photocatalytic and photochemical decomposition of model reaction mixture. The hydrogen production in the presence of a ZnO photocatalysts was compared to the production of H2 in the presence of a commercially manufactured photocatalyst TiO2 Evonik P25. The activity of tested photocatalysts was decreasing in this order: ZnO(1) < ZnO(3) = Evonik P25 < ZnO(2). Experimental data of the photocatalytic decomposition of ammonia were evaluated by integral method, kinetic constants were calculated and the assumption the reaction can be described by the equation of 1st order was confirmed. Based on the correlation between the photocatalytic activity and physico-chemical characteristics of prepared photocatalysts. It was found out the key parameters influencing photocatalytic decomposition of ammonia are different defects in the crystal lattice of the ZnO oxygen vacancies (VO) or interstitial oxygen (Oi) and the oxygen in the place of Zn (OZn) which originate from different preparation way of photocatalysts. The most active photocatalyst ZnO(1), which was prepared by thermal annealing, had the lowest specific surface area, but also the lowest amount of oxygen vacancies. The lowest activity of ZnO(2) photocatalyst, prepared by precipitation reaction, can be attributed to the highest amount of oxygen vacancies. These vacancies capture excited electrons, which arenot available for the photocatalytic reaction itself.619 - Katedra fyzikální chemie a teorie technologických pochodůvýborn

Factors affecting photocatalytic properties of TiO2 based materials in environmentally important reactions

Disertační práce se zabývá vlivem modifikování oxidu titaničitého na fotokatalytické vlastnosti při dvou environmentálně významných reakcích, fotoakatalytické redukci oxidu uhličitého a fotokatalytickém rozkladu metanolu. Celkem bylo zkoumáno deset sad fotokatalyzátorů, šest při fotokatalytické redukci oxidu uhličitého a čtyři při fotokatalytickém rozkladu metanolu. Fotokatalytická redukce CO2 probíhala ve třech geometricky odlišných vsádkových reaktorech za použití UVC záření. Pro tuto reakci byl různými metodami připraven oxid titaničitý a byl modifikován zirkonem, dusíkem, mědí (Cu anebo CuO), platinou a platinou s uhlíkem současně. Produkty fotokatalytické redukce CO2 byly metan a oxid uhelnatý a vodík, který vznikal z vody. Fotokatalytický rozklad metanolu probíhal ve vsádkovém reaktoru za použití UVA záření a při stejných reakčních podmínkách. Pro tuto reakci byl různými metodami připraven oxid titaničitý, který byl modifikován lanthanem, neodymem a lanthanem a fluorem současně. Hlavním faktorem ovlivňujícím produkci vodíku z fotokatalytického rozkladu metanolu byly vakance kyslíku a povrchový kyslík ve fotokatalyzátorech. S rostoucím množstvím vakancí kyslíku a snižujícím se povrchovým kyslíkem (mřížkový kyslík a hydroxylový) se výtěžky vodíku zvyšovaly.The dissertation thesis deals with the effect of modification of titanium dioxide on photocatalytic properties in two environmentally important reactions, photoacatalytic reduction of carbon dioxide and photocatalytic decomposition of methanol. In total, ten sets of photocatalysts were examined, six in photocatalytic reduction of carbon dioxide and four in photocatalytic decomposition of methanol.Photocatalytic reduction of CO2 was carried out in three geometrically different batch reactors using UVC radiation. For this reaction, titanium dioxide was prepared by various methods and was modified with zirconium, nitrogen, copper (Cu or CuO), platinum and platinum with carbon simultaneously. Photocatalytic decomposition of methanol was carried out in a batch reactor using UVA radiation and under the same reaction conditions. For this reaction, titanium dioxide was prepared by various methods, which was modified with lanthanum, neodymium and lanthanum and fluorine simultaneously. The main factors influencing hydrogen production from photocatalytic decomposition of methanol were oxygen vacancies and surface oxygen in photocatalysts. With increasing oxygen vacancies and decreasing surface oxygen (lattice oxygen and hydroxyl), hydrogen yields increased.9350 - Institut environmentálních technologiívyhově

Fabrication of highly stable CdS/g-C3N4 composite for enhanced photocatalytic degradation of RhB and reduction of CO2

CdS/g-C3N4 (CdS/CN) type II heterojunction photocatalyst was prepared by an improved successive ionic layer adsorption and reaction process. TEM results show that the CdS nanoparticles (CdS NPs) were successfully loaded on the surface of CN. The results of PL and PEC display that the construction of CdS/CN heterojunction benefits the transmission of the photogenerated carriers and effectively inhibits the photogenerated carrier recombination in photocatalytic process. The photodegradation experiments exhibit that the 3-CdS/CN photocatalyst possesses the highest photodegradation performance over the other samples. The yields of H-2 and CH4, in the presence of the best CdS/CN photocatalyst (1-CdS/CN) are 50 and 13 times stronger, respectively, than in the case of the pure CN in the photoreduction process of CO2. The CN coupling effectively improves the photocatalytic performance of CdS-based photocatalyst and inhibits the hole-induced photocorrosion of CdS NPs. A possible type II heterojunction photocatalytic mechanism has been provided.Web of Scienc

Photocatalytic decomposition of N2O over ceramics cordierite/CeO2 nanoparticles

The study is focused on the testing of the photocatalytic ability to decompose nitrous oxide (N2O) over cordierite/CeO2 nanoparticles ceramic photocatalysts. The activity of ceramic materials was compared with the activity of industrially produced TiO2 (Evonik photocatalyst). Photocatalytic decomposition of N2O over the ceramic samples and the TiO2 Evonik was performed in annular batch reactor illuminated with 8 W Hg lamp (lambda = 254 nm wavelength). Reaction kinetics was well described by pseudo 1st rate law. Photocatalytic activity of cordierite/CeO2 was better in comparison with TiO2 Evonik P25. The highest N2O conversion (56%) after 20 h of irradiation in inert gas was achieved over the sample with higher amount of CeO2. This photocatalyst sample was examined for photocatalytic activity in the decomposition of N2O in the three various gaseous feed mixtures. The gaseous feed mixtures were: N2O enriched with O-2 (6.5 mol.%); N2O enriched with H2O(25 mol.%) and N2O enriched with mixture of O-2 and H2O(6.5 mol.% and 25 mol.%, respectively). It is assumed that the reduced conversion of N2O (47%) observed in the flow of the mixture of N2O and H(2)Ocould be affected by the sorption of water vapor on/onto the photocatalyst "active sites" causing less penetration of light and thus reducing the efficiency of photocatalytic decomposition of N2O. The presence of oxygen in the N2O mixture had only little effect to photocatalytic decomposition of N2O.Web of Science19117344733

Influence of high temperature synthesis on the structure of graphitic carbon nitride and its hydrogen generation ability

Graphitic carbon nitride (g-C3N4) was obtained by thermal polymerization of dicyandiamide, thiourea or melamine at high temperatures (550 and 600 degrees C), using different heating rates (2 or 10 degrees C min(-1)) and synthesis times (0 or 4 h). The effects of the synthesis conditions and type of the precursor on the efficiency of g-C(3)N(4)were studied. The most efficient was the synthesis from dicyandiamide, 53%, while the efficiency in the process of synthesis from melamine and thiourea were much smaller, 26% and 11%, respectively. On the basis of the results provided by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-vis), thermogravimetric analysis (TGA), elemental analysis (EA), the best precursor and the optimum conditions of synthesis of g-C(3)N(4)were identified to get the product of the most stable structure, the highest degree of ordering and condensation of structure and finally the highest photocatalytic activity. It was found that as the proton concentration decreased and the degree of condensation increased, the hydrogen yields during the photocatalytic decomposition of water-methanol solution were significantly enhanced. The generation of hydrogen was 1200 mu mol g(-1)and the selectivity towards hydrogen of more than 98%.Web of Science1312art. no. 275