Martin Reli

Investigation of low Ce amount doped-TiO2 prepared by using pressurized fluids in photocatalytic N2O decomposition and CO2 reduction

Ce doped TiO2 anatase/brookite composites with 0.6–5.5 wt% of Ce, as well as parent TiO2 anatase/brookite were synthesized to be investigated in two environmentally-beneficial reactions, the photocatalytic decomposition of N2O and the photocatalytic reduction of CO2. Composites were prepared unconventionally, by using sol–gel method combined with the processing by pressurized hot fluids (in the sequence water/methanol/water). The physicochemical and electronic properties of all synthesized composites were characterized by organic elementary analysis, nitrogen physisorption, powder X-ray diffraction, X-ray fluorescence spectroscopy, diffuse reflectance UV-vis spectroscopy and work function measurements. It was revealed that all composites show comparable textural properties, crystallite size, as well as optical properties, except for the 5.5 wt% Ce/TiO2 composite which showed significantly lowered band gap energy due to the significantly higher population of Ce. Concerning the composite structural properties, the addition of different amounts of Ce in the range of 0.6–5.5 wt% affected markedly the phase composition of composites, namely the anatase-to-brokite weight ratio. Concerning the photocatalytic tests the 5.5 wt% Ce/TiO2 composite showed the highest photocatalytic performance. The highest photocatalytic performance of the 5.5 wt% Ce/TiO2 composite can be attributed to the lowest composite work function which is affected by both the amount of Ce, as well as the phase composition.Graphical Abstract

EFFECT OF CALCINATION TEMPERATURE AND CALCINATION TIME ON THE KAOLINITE/TIO2 COMPOSITE FOR PHOTOCATALYTIC REDUCTION OF CO2 VLIV KALCINAČNÍ TEPLOTY A DOBY KALCINACE NA KOMPOZIT KAOLINIT/TIO2 PRO FOTOKATALYTICKOU REDUKCI CO2

Abstract The kaolinite/TiO2 composite (60 wt% of TiO2) was prepared by thermal hydrolysis of a raw kaolin suspension in titanyl sulphate and calcined at different temperatures (600, 650 and 700°C) and for different times (1, 2 and 3 h). The obtained samples were characterized by XRPD, N2 physical adsorption and SEM, and tested for photocatalytic reduction of CO2. The different calcination conditions did not influence TiO2 phase composition, only slightly changed the specific surface area, and significantly affected crystallite size of kaolinite/TiO2 composite. A higher temperature and longer duration of calcination lead to higher crystallinity of the powder. The photocatalytic results showed that the crystallite size determined the efficiency of kaolinite/TiO2 photocatalysts Abstrakt Kompozit kaolinit/TiO2 (60 hm% TiO2) byl připraven termální hydrolýzou suspenze surového kaolinu v síranu titanylu a kalcinován při různých teplotách (600, 650 a 700°C) a po různou dobu (1, 2 a 3 h). Získaný vzorek byl charakterizován pomocí XRPD, N2 fyzikální adsorpcí a SEM, a testován na fotokatalytickou redukci CO2. Rozdíl kalcinačních podmínek neovlivnil složení fáze TiO2, pouze se mírně pozměnila specifická povrchová plocha a výrazně byla ovlivněna velikost krystalitu kompozitu kaolinit/TiO2. Vyšší teplota a delší doba kalcinace vedly k vyšší krystalitě prášku. Fotokatalytické výsledky ukázaly, že velikost krystality určuje účinnost fotokatalyzítoru kaolinit/TiO2

Influence of Reaction Medium on CO2 Photocatalytic Reduction Yields Over Zns-MMT / Vliv Reakčního Prostření Na Výtěžky Fotokatalytické Redukce CO2 V Přítomnosti Zns-MMT

Abstract The reduction of CO2 by photocatalysts is one of the most promising methods since CO2 can be reduced to useful compounds by irradiating it with UV light at room temperature and ambient pressure. The aim of this work was to assess the effect of a reaction media on CO2 photocatalytic reduction yields over ZnS nanoparticles deposited on montmorillonite (ZnS-MMT). Four different reaction media, such as NaOH, NaOH+Na2SO3 (1:1), NH4OH, NH4OH+Na2SO3 (1:1), were tested. The pure sodium hydroxide was better than ammonium hydroxide for the yields of the both gas phase (CH4 and CO) and liquid phase (CH3OH). The addition of Na2SO3 improved methanol yields due to the oxidation prevention of incipient methanol to carbon dioxide. The gas phase yields were decreased by the Na2SO3 addition. The best tested reaction medium for the photocatalytic reduction of CO2 was the solution of sodium hydroxide. Abstrakt Redukce CO2 pomocí fotokatalyzátorů je jedna z nejslibnějších metod, jelikož CO2 může být redukován na užitečné sloučeniny ozařováním UV zářením při pokojové teplotě a tlaku. Tato práce byla zaměřena na posouzení vlivu reakčních prostředí na výtěžky fotokatalytické redukce CO2 v přítomnosti nanočástic ZnS nanesených na montmorillonit (ZnS-MMT). Byla testována čtyři různá reakční prostředí, NaOH, NaOH+Na2SO3 (1:1), NH4OH, NH4OH+Na2SO3 (1:1). Výtěžky v obou fázích, plynné (CH4 a CO) i kapalné (CH3OH), byly vyšší v čistém hydroxidu sodném než v hydroxidu amonném. Přídavek Na2SO3 zvýšil výtěžky methanolu a to díky zamezení oxidace vznikajícího methanolu zpět na oxid uhličitý. Výtěžky plynné fáze se však po přídavku Na2SO3 snížily. Nejlepším z testovaných reakčních prostředí pro fotokatalytickou redukci CO2 byl roztok hydroxidu sodného.

Photocatalytic CO2 reduction by mesoporous polymeric carbon nitride photocatalysts

In this paper, a sol-gel derived mesoporous polymeric carbon nitride has been investigated as a photocatalyst for CO2 photocatalytic reduction. Noble-metal Pt nanoparticles were deposited on carbon nitride (sg-CN) in order to investigate the performance of both Pt-sg-CN and sg-CN for photocatalytic CO2 reduction. Physicochemical properties of prepared nanocomposites were comprehensively characterized by using powder XRD, N2 physisorption, UV-Vis DRS, ICP-AES, FTIR, solid-state NMR, SEM, TEM and photoelectrochemical measurements. Compared with pure sg-CN, the resulting Pt-loaded sg-CN (Pt-sg-CN) exhibited significant improvement on the CO2 photocatalytic reduction to CH4 in the presence of water vapor at ambient condition under UV irradiation. 1.5 wt.% Pt-loaded sg-CN (Pt-sg-CN) photocatalyst formed the highest methane yield of 13.9 μmol/gcat. after 18 h of light irradiation, which was almost 2 times and 32 times improvement in comparison to pure sg-CN and commercial TiO2 Evonik P25, respectively. The substantial photocatalytic activity of Pt-sg-CN photocatalyst for the yield product of the CO2 photocatalytic reduction was attributed to the efficient interfacial transfer of photogenerated electrons from sg-CN to Pt due to the lower Fermi level of Pt in the Pt-sg-CN hybrid heterojunctions as also evidenced by photo-electrochemical measurements. This resulted in the reduction of electron-hole pairs recombination for effective spatial charge separation, consequently increasing the photocatalytic efficiency.

Nd/TiO2 anatase-brookite photocatalysts for photocatalytic decomposition of methanol

Neodymium enriched TiO2 anatase-brookite powders were prepared by unconventional method via using pressurized hot fluids for TiO2 crystallization and purification. The photocatalysts were tested in the CH3OH photocatalytic decomposition and they were characterized with respect to the textural (nitrogen adsorption), structural (XRD, XPS, and Raman spectroscopies), chemical (XRF), and optical (DR UV-Vis spectroscopy) and photoelectrochemical measurement. All prepared materials were nanocrystalline, had biphasic (anatase- brookite) structure and relatively large specific surface area (125 m2.g−1). The research work indicates that the doping of neodymium on TiO2 photocatalysts significantly enhances the efficiency of photocatalytic reaction. The photocatalytic activity increased with increasing portion of hydroxyl oxygen to the total amount of oxygen species. It was ascertained that the optimal amount of 1 wt% Nd in TiO2 accomplished the increasing of hydrogen production by 70% in comparison with pure TiO2. The neodymium doped on the titanium dioxide act as sites with accumulation of electrons. The higher efficiency of photocatalytic process was achieved due to improved electron-hole separation on the modified TiO2 photocatalysts. This result was confirmed by electrochemical measurements, the most active photocatalysts proved the highest photocurrent responses.