Photocatalytic production of hydrogen over tailored Cu-embedded TiO2 (original) (raw)
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Photocatalytic Production of Hydrogen Over Tailored Cu-Embedded TiO2
Nanoscience and Nanotechnology Letters, 2009
Copper nanoparticles embedded into TiO 2 showed promising photocatalytic hydrogen production using water/methanol solution. Preformed metal nanoparticles, surrounded by a porous TiO 2 matrix, were prepared by microemulsion method. XRD and HRTEM analysis indicated the presence of the anatase polymorph with minor traces of rutile and brookite. The performances of this nanostructured system were compared with those of a similar material prepared by conventional impregnation method. Using TiO 2 with identical structural and textural properties, a significantly lower CO chemisorption was measured for the impregnated sample with respect to the embedded one. Even though it is not possible to discriminate between the different ratio of the Cu containing species in the two samples, this is an indication that the embedded system presents highly accessible copper species and in a slightly larger quantity with respect to the corresponding impregnated sample. Consistently XRD and preliminary HRTEM investigations indicates presence of smaller Cu/CuO x particles in the embedded catalyst. A CO adsorption capacity similar to that of the embedded system was obtained by impregnating with copper nitrate a TiO 2 , obtained by sol-gel method. This last system present however a more significant contribution of the rutile phase. Notably, Cu embedded material showed significantly superior performances with respect to all the other samples. In this regard an optimal combination of low particle size, accessible active phase, ratio of Cu/CuO x , presence of the more active anatase phase and excellent interfacial contact between Cu and surrounding TiO 2 particles was found critical. This latter aspect can lead to a better synergic electron/hole transfer which allow improved activity.
Journal of Physics and Chemistry of Solids, 2018
In this work, 1wt% Cu doped TiO 2 was prepared by incipient wetness impregnation by using pure TiO 2 which was synthesized by sol-gel method. From XRD results, the enlargement of TiO 2 unit cells was observed which indicated the incorporation of Cu into TiO 2 lattice. The optical property showed more visible region absorption of Cu-doped TiO 2 sample which was due to a reduction of band gap energy. Ti K-edge XANES spectra of pure and doped TiO 2 confirmed the anatase (Ti 4+) form while Cu K-edge XANES of Cu-doped catalyst presented the oxidation state of Cu as Cu 2+ in octahedral symmetry. The EXAFS spectra of Ti K-edge and Cu K-edge of 1wt% Cu/TiO 2 evidenced the substitution of Cu into Ti site by observing the variation in bond distance between probe atom and the neighboring environment. According to the photodegradation performance study, the photodegradation rate of Cu-doped TiO 2 under UV irradiation exhibited almost 2 times higher than that of pure TiO 2. The enhancement of photocatalytic activity can be proofed by Ti L 2,3-edge XANES spectra. These results indicated that Cu acts as an electron trapping site which resulted from the creation of impurity energy levels below the conduction band of TiO 2. Moreover, an oxygen vacancy production upon the addition of Cu can also trap an excited electron from the valence band of TiO 2. Therefore, the electron scavenger behavior together with oxygen vacancy can suppress the electron-hole recombination, yielding more electrons and holes to further undergo the reaction.
TiO2-supported copper nanoparticles prepared via ion exchange for photocatalytic hydrogen production
Journal of Materials Chemistry A, 2014
Ion exchange (IE) has been used to prepare Cu/TiO 2 for photocatalytic hydrogen generation. The IE Cu/ TiO 2 particles comprised a mixture of large and fine copper/copper oxide deposits which were well dispersed across the TiO 2 surface. Hydrogen generation photoactivity by the IE Cu/TiO 2 was $44% greater than the activity displayed by Cu/TiO 2 prepared via wet impregnation (WI) at a similar copper loading. Temperature programmed reduction studies indicated the IE Cu/TiO 2 possessed a greater portion of highly dispersed fine copper deposits than the WI Cu/TiO 2 which may account for the higher photoactivity. The hydrogen generation activity of IE Cu/TiO 2 was maintained over three 5 h reaction cycles. the research and experimental design.
Applied Surface Science, 2016
Copper dopants are varyingly reported to enhance photocatalytic activity at titanium dioxide surfaces through uncertain mechanisms. In order to interpret how copper doping might alter the performance of titanium dioxide photocatalysts in aqueous media we applied density functional theory methods to simulate surface units of doped anatase (101) planes. By including van der Waals interactions, we consider the energetics of adsorbed water at anatase surfaces in pristine and copper doped systems. Simulation results indicate that copper dopant at anatase (101) surfaces is most stable in a 2+ oxidation state and a disperse configuration, suggesting the formation of secondary CuO phases is energetically unfavourable. In agreement with previous reports, water at the studied surface is predicted to exhibit molecular adsorp-tion with this tendency slightly enhanced by copper. Results imply that the enhancement of photoactivity at anatase surfaces through Cu doping is more likely to arise from electronic interactions mediated by charge transfer and inter-bandgap states increasing photoexcitation and extending surface-hole lifetimes rather than through the increased density of adsorbed hydroxyl groups.
Applied Catalysis B: Environmental, 2015
The influence of different TiO 2 supports on the Cu active species has been studied. It was found that the photocatalytic H 2 evolution is highly affected by the structural and electronic features of surface Cu species. Thus, metal dispersion and oxidation state appears strongly conditioned by the structural and surface properties of the TiO 2 support. We have examined three TiO 2 supports prepared by different synthetic methods; sol-gel, hydrothermal and microemulsion. In addition, we have induced structural and surface modifications by sulfate pretreatment over freshly prepared TiO 2 precursors and subsequent calcination. Notably different copper dispersion and oxidation state is obtained by using these different TiO 2 supports. From the wide structural and surface analysis of the catalysts we are able to propose that the occurrence of highly disperse Cu 2+ species, the sample surface area as well as the crystallinity of the TiO 2 support are directly related to the photocatalytic activity for H 2 production reaction.
Applied Catalysis B: Environmental
This paper shows that incorporation of Cu inhibits the anatase to rutile phase transition at temperatures above 500°C. The control sample, with 0% Cu contained 34.3% anatase at 600°C and transitioned to 100% rutile by 650°C. All copper doped samples maintained 100% anatase up to 600°C. With 2% Cu doping, anatase fully transformed to rutile at 650°C, at higher Cu contents of 4% & 8% mixed phased samples, with 27.3% anatase and 74.3% anatase respectively, are present at 650°C. All samples had fully transformed to rutile by 700°C. 0%, 4% and 8% Cu were evaluated for photocatalytic degradation of 1, 4 dioxane. Without any catalyst, 15.8% of the 1,4 dioxane degraded upon irradiation with light for 4 h. Cu doped TiO 2 shows poor photocatalytic degradation ability compared to the control samples. Density functional theory (DFT) studies of Cu-doped rutile and anatase show formation of charge compensating oxygen vacancies and a Cu 2+ oxidation state. Reduction of Cu 2+ to Cu + and Ti 4+ to Ti 3+ was detected by XPS after being calcined to 650-700°C. This reduction was also shown in DFT studies. Cu 3d states are present in the valence to conduction band energy gap upon doping. We suggest that the poor photocatalytic activity of Cu-doped TiO 2 , despite the high anatase content, arises from the charge recombination at defect sites that result from incorporation of copper into TiO 2 .
International Journal of Hydrogen Energy, 2018
To utilize the full spectrum of solar light, we prepared a series of self-organized CueTiO 2 photocatalysts via the sonothermal-hydrothermal route with high reactivity under both UV and visible region. The obtained catalysts were characterized by XRD, UVeVis, BET surface area, SEM, TEM, XPS, and TPR. The Cu species were doped in the lattice of TiO 2 and also present on the surface of TiO 2 as revealed by TEM, XPS, and TPR. Catalytic potential of prepared catalysts was checked for photocatalytic reduction of CO 2. The effects of the different base including K 2 CO 3 , Na 2 CO 3 , NaOH, KOH, the concentration of base, catalyst amount, copper doping amount, light source, reaction medium and reaction time were monitored to get optimum reaction conditions. The Cu 2 eTiO 2 catalyst performed the best; 6.6 mmol g À1 of methane, 472.5 mmol g À1 methanol, and 743.8 mmol g À1 of acetone were obtained in KOH/H 2 O medium in 24 h under UVA. While in acetonitrile (ACN)/Triethanolamine (TEOA)/H 2 O mixture, the Cu 2 eTiO 2 catalyst was able to selectively catalyze methanol formation (99.99%) 8469.6 mmol g À1 in 24 h under visible light. The formation of H is also an intermediate step in the photocatalytic reduction of CO 2. Therefore, the Cu 2 eTiO 2 catalyst was also tested for H 2 production with or without CO 2 at different reaction media such as H 2 O, KOH/H 2 O, ACN/H 2 O, ACN/TEOA/H 2 O under UVA light. The highest H 2 production, i.e., 152.0 mmol g À1 was observed with ACN/TEOA/H 2 O in the presence of CO 2 in 8 h. The prepared series of CueTiO 2 catalysts are highly active for CO 2 reduction and H 2 production.