20338-08-3Relevant academic research and scientific papers
Charge carrier dynamics and photocatalytic behavior of TiO2 nanopowders submitted to hydrothermal or conventional heat treatment
Patrocinio,Schneider,Fran?a,Santos,Caixeta,Machado,Bahnemann
, p. 70536 - 70545 (2015)
The sol-gel technique followed by conventional (TiO2-1) and hydrothermal (TiO2-2) thermal treatment was employed to prepare TiO2-based photocatalysts with distinct particle sizes and crystalline structures. The as prepared metal oxides were evaluated as photocatalysts for gaseous HCHO degradation, methanol, and dye oxidation reactions. Additionally, metallic platinum was deposited on the TiO2 surfaces and H2 evolution measurements were performed. The photocatalytic activities were rationalized in terms of morphologic parameters along with the electron/hole dynamics obtained from transient absorption spectroscopy (TAS). TiO2-2 exhibits smaller particle size, poorer crystallinity, and higher surface area than TiO2-1. Moreover the hydrothermal treatment leads to formation of the metastable brookite phase, while TiO2-1 exhibits only the anatase phase. TAS measurements show that the electron/hole recombination of TiO2-2 is faster than that of the latter. Despite that, TiO2-2 exhibits higher photonic efficiencies for photocatalytic oxidation reactions, which is attributed to its larger surface area that compensates for the decrease of the surface charge carrier concentration. For H2 evolution, it was found that the surface area has only a minor effect and the photocatalyst performance is controlled by the efficiency of the electron transfer to the platinum islands. This process is facilitated by the higher crystallinity of TiO2-1, which exhibits higher photonic efficiency for H2 evolution than that observed for TiO2-2. The results found here provide new insights into the correlations between thermal treatment conditions and photocatalytic activity and will be useful for the design of high performance photocatalysts.
Morphology-Engineered Highly Active and Stable Ru/TiO2 Catalysts for Selective CO Methanation
Chen, Shilong,Abdel-Mageed, Ali M.,Li, Dan,Bansmann, Joachim,Cisneros, Sebastian,Biskupek, Johannes,Huang, Weixin,Behm, R. Jürgen
, p. 10732 - 10736 (2019)
Ru/TiO2 catalysts exhibit an exceptionally high activity in the selective methanation of CO in CO2- and H2-rich reformates, but suffer from continuous deactivation during reaction. This limitation can be overcome through the fabrication of highly active and non-deactivating Ru/TiO2 catalysts by engineering the morphology of the TiO2 support. Using anatase TiO2 nanocrystals with mainly {001}, {100}, or {101} facets exposed, we show that after an initial activation period Ru/TiO2-{100} and Ru/TiO2-{101} are very stable, while Ru/TiO2-{001} deactivates continuously. Employing different operando/in situ spectroscopies and ex situ characterizations, we show that differences in the catalytic stability are related to differences in the metal–support interactions (MSIs). The stronger MSIs on the defect-rich TiO2-{100} and TiO2-{101} supports stabilize flat Ru nanoparticles, while on TiO2-{001} hemispherical particles develop. The former MSIs also lead to electronic modifications of Ru surface atoms, reflected by the stronger bonding of adsorbed CO on those catalysts than on Ru/TiO2-{001}.
Polyol mediated synthesis of tungsten trioxide and Ti doped tungsten trioxide. Part 1: Synthesis and characterisation of the precursor material
Porkodi,Yegnaraman,Jeyakumar
, p. 1476 - 1486 (2006)
Polyol mediated synthesis for the preparation of tungsten trioxide and titanium doped tungsten trioxide has been reported. The reaction was carried out using chlorides of tungsten and titanium in diethylene glycol medium and water as the reagent for hydrolysis at 190 °C. Formation of a blue coloured dimensionally stable suspension of the precursor materials was observed during the course of the reaction. The particle sizes of the precursor materials were observed to be around 100 nm. The precursor materials were annealed to give tungsten trioxide and titanium doped tungsten trioxide. The precursor materials were characterised using TGA/DTA, FT-IR, optical spectra, SEM, TEM and powder XRD methods. It was observed that the doping of titanium could be effected at least up to 10% of Ti in WO3. The TGA/DTA studies indicated that WO3-x·H2O is the dominant material that formed during the polyol mediated synthesis. The XRD data of the annealed samples revealed that the crystalline phase could be manipulated by varying the extent of titanium doping in the tungsten trioxide matrix.
Interplay of Pt and Crystal Facets of TiO2: CO Oxidation Activity and Operando XAS/DRIFTS Studies
Zhou, Ying,Doronkin, Dmitry E.,Chen, Menglu,Wei, Shiqian,Grunwaldt, Jan-Dierk
, p. 7799 - 7809 (2016)
In this work, the influence of the terminating or exposed crystal planes of anatase TiO2 support on the catalytic activity of Pt/TiO2 catalysts is reported. Strong effects were observed when using CO oxidation as a probe reaction. The CO oxidation activity over these catalysts ranks in the following order: Pt/TiO2-{101} > Pt/TiO2-{100} > Pt/TiO2-{001}. The combination of in situ X-ray absorption spectroscopy, X-ray emission spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and density functional theory calculations unravelled a strong interaction between platinum particles and different dominating facets of anatase. The catalytic activity of the Pt/TiO2 catalysts can be correlated with the spectroscopic/structural results. Compared to {001} facets, the {100} and {101} facets of TiO2 can stabilize active highly dispersed Pt species and avoid sintering Pt particles. This finding provides some important insights into understanding the metal-support interfacial interactions of Pt/TiO2 catalysts for tuning their catalytic performance. (Graph Presented).
Removal of ciprofloxacin from aqueous solution using long TiO2 nanotubes with a high specific surface area
Zheng, Kai,Zheng, Xingye,Yu, Fei,Ma, Jie
, p. 3625 - 3631 (2016)
Long TiO2 nanotubes (TNs) were successfully prepared by the reaction of TiO2 and NaOH. The raw materials were treated by stirring, ion exchange, centrifugation, and freeze-drying, and then the target TNs was synthesized. Anatase TNs were obtained by calcinating the TNs at 823 K for 4.5 h. The TNs were characterized by Brunauer-Emmett-Teller surface area analysis, X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectrometry. The results indicated that the TNs had a larger specific surface area (ca. 160 m2 g-1) and pore volume (ca. 0.6 cm3 g-1) than the commercial product P25. The adsorption of ciprofloxacin onto the TNs was compared with their adsorption onto P25. The adsorption isotherm, kinetics, and regeneration performance were investigated. The experimental results indicated that the maximum adsorption capacity of the TNs and P25 was 26.38 and 5.32 mg g-1, respectively, and their adsorption behavior was better fitted by the Langmuir model than by the Freundlich model. The kinetic regression results showed that the adsorption kinetics were more accurately represented by a pseudo-second-order model than by a pseudo-first-order model; the rate of the pseudo-second-order reactions on P25 and the anatase TNs were 0.0442 and 0.27463 min-1, respectively. After adsorption, the TNs had better regeneration properties than P25 under UV irradiation at 500 W for 3 h in 5 mL of aqueous solution. These results show that long TNs have a better adsorption capacity and regeneration properties than P25. This study provides a green method for the removal of organic pollutants by combining enrichment by adsorption with photocatalytic degradation.
Effect of electron transfer on the photocatalytic hydrogen evolution efficiency of faceted TiO2/CdSe QDs under visible light
Chen, Weiwei,Yu, Shan,Zhong, Yunqian,Fan, Xiang-Bing,Wu, Li-Zhu,Zhou, Ying
, p. 4811 - 4817 (2018)
Quantum dot (QD)/TiO2 composites are widely used materials in the field of photocatalysis. However, the influence of different exposed facets of TiO2 in composites on photocatalytic hydrogen evolution is rarely reported. In this work, CdSe QD-TiO2 composites with dominant {001} or {101} faceted anatase were synthesized and specifically characterized using X-ray powder diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. Photocatalytic hydrogen evolution tests reveal that {001}-TiO2/CdSe QDs exhibit a 213.1- and 9.0-fold increase in photocatalytic activity compared to {001}-TiO2 and CdSe QDs, respectively. Notably, the photocatalytic activity of {001}-TiO2/CdSe QDs is 2.2 times higher than that of {101}-TiO2/CdSe QDs. Based on the results from UV-Vis diffuse reflectance spectroscopy, Brunauer-Emmett-Teller surface area testing, Mott-Schottky testing and steady-state and time-resolved emission spectroscopy, the main reason for enhanced photocatalytic activity is the faster electron transfer from CdSe QDs to {001}-TiO2 compared with to {101}-TiO2. This research on tailored facets in QD/TiO2 composites provides primary insights for the design of effective photocatalysts.
Low-temperature synthesis of anatase TiO2 nanoparticles with tunable surface charges for enhancing photocatalytic activity
Li, Ye,Qin, Zhenping,Guo, Hongxia,Yang, Hanxiao,Zhang, Guojun,Ji, Shulan,Zeng, Tingying
, (2014)
In this work, the positively or negatively charged anatase TiO2 nanoparticles were synthesized via a low temperature precipitation-peptization process (LTPPP) in the presence of poly(ethyleneimine) (PEI) and poly(sodium4- styrenesulfonate) (PSS). X-ray diffraction (XRD) pattern and high-resolution transmission electron microscope (HRTEM) confirmed the anatase crystalline phase. The charges of the prepared TiO2, PEI-TiO2 and PSS-TiO2 nanoparticles were investigated by zeta potentials. The results showed that the zeta potentials of PEI-TiO2 nanoparticles can be tuned from +39.47 mV to +95.46 mV, and that of PSS-TiO2 nanoparticles can be adjusted from -56.63 mV to -119.32 mV. In comparison with TiO2, PSS-TiO2 exhibited dramatic adsorption and degradation of dye molecules, while the PEI modified TiO2 nanoparticles showed lower photocatalytic activity. The photocatalytic performances of these charged nanoparticles were elucidated by the results of UV-vis diffuse reflectance spectra (DRS) and the photoluminescence (PL) spectra, which indicated that the PSS-TiO2 nanoparticles showed a lower recombination rate of electron-hole pairs than TiO2 and PEI-TiO2.
Enhanced photocatalytic degradation of Amaranth dye on mesoporous anatase TiO2: Evidence of C-N, NN bond cleavage and identification of new intermediates
Naik, Amarja P.,Salkar, Akshay V.,Majik, Mahesh S.,Morajkar, Pranay P.
, p. 1126 - 1138 (2017)
The photocatalytic degradation mechanism of Amaranth, a recalcitrant carcinogenic azo dye, was investigated using mesoporous anatase TiO2 under sunlight. Mesoporous anatase TiO2 of a high photocatalytic activity has been synthesized using a sol-gel method and its photocatalytic activity for the degradation of Amaranth dye has been evaluated with respect to Degussa P25. The effect of bi-dentate complexing agents like oxalic acid, ethylene glycol and urea on the surface properties of TiO2 catalyst has been investigated using TG-DTA, FTIR, HR-TEM, SAED, PXRD, EDS, UV-DRS, PL, BET N2 adsorption-desorption isotherm studies and BJH analysis. The influence of catalyst properties such as the mesoporous network, pore volume and surface area on the kinetics of degradation of Amaranth as a function of irradiation time under natural sunlight has been monitored using UV-Vis spectroscopy. The highest rate constant value of 0.069 min-1 was obtained for the photocatalytic degradation of Amaranth using TiO2 synthesized via a urea assisted sol-gel synthesis method. The effect of the reaction conditions such as pH, TiO2 concentration and Amaranth concentration on the photodegradation rate has been investigated. The enhanced photocatalytic activity of synthesized TiO2 in comparison with P25 is attributed to the mesoporous nature of the catalyst leading to increased pore diameter, pore volume, surface area and enhanced charge carrier separation efficiency. New intermediates of photocatalytic degradation of Amaranth, namely, sodium-3-hydroxynaphthalene-2,7-disulphonate, 3-hydroxynaphthalene, sodium-4-aminonaphthalenesulphonate and sodium-4-aminobenzenesulphonate have been identified using LC-ESI-MS for the very first time, providing direct evidence for simultaneous bond cleavage pathways (-C-N-) and (-NN-). A new plausible mechanism of TiO2 catalysed photodegradation of Amaranth along with the comparison of its toxicity to that of its degradation intermediates and products is proposed.
Fabrication and characterization of nano TiO2 thin films at low temperature
Ge, Lei,Xu, Mingxia,Sun, Ming,Fang, Haibo
, p. 1596 - 1603 (2006)
Anatase TiO2 thin films were successfully prepared on glass slide substrates via a sol-gel method from refluxed sol (RS) containing anatase TiO2 crystals at low temperature of 100 °C. The influences of various refluxing time on crystallinity, morphology and size of the RS sol and dried TiO2 films particles were discussed. These samples were characterized by infrared absorption spectroscopy (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission-scanning electron microscopy (FE-SEM) and UV-vis absorption spectroscopy (UV-vis). The photocatalytic activities of the TiO2 thin films were assessed by the degradation of methyl orange in aqueous solution. The results indicated that titania films thus obtained were transparent and their maximal light transmittance exceeded 80% under visible light region. The TiO2 thin films prepared from RS-6 sol showed the highest photocatalytic activity, when the calcination temperature is higher than 300 °C. The degradation of methyl orange of RS-6 thin films reached 99% after irradiated for 120 min, the results suggested that the TiO2 thin films prepared from RS sol exhibited high photoactivities.
Redox processes in fine-particle TiO2-Cr2O 3 oxides
Belaya,Viktorov
, p. 1323 - 1325 (2007)
We have studied the stability of the Cr6+ ion in fine-particle TiO2-Cr2O3 oxides during storage after calcination in air. The results indicate that, during storage under normal conditions for 720 days, Cr6+
