Effect of non-ionic surfactant in the solvothermal synthesis of anatase TiO2 nanoplates with a high percentage of exposed {001} facets and its role in the photocatalytic degradation of methylene blue dye.

The synthesis of anatase TiO2 nanoparticles with controlled morphology and increased {001} facets exposed without the presence of fluorine-derived substances is a challenge. Herein, we report a highly effective approach to fabricate anatase TiO2 nanoplates with exposed {001} facets and their exploitation as robust photocatalytic materials for dye remediation. These materials were synthesized under controlled hydrolysis and condensation reactions, using titanium (IV) n-butoxide in an ethanolic solution, with acetic and sulfuric acids, by a solvothermal method at 190 °C with or without the presence of the non-ionic surfactant Triton® X-100 and then characterized. During TiO2 crystal synthesis, the effect of a non-ionic surfactant on the TiO2 particle growth was investigated. Our results demonstrate that the proposed method can synthesize pure and crystalline anatase TiO2 square nanoplates that form nanostructured spheres with high surface area, uniformly sized mesopores, and exposed {001} facets. The presence of non-ionic surfactant increased the exposed {001} facets percentage of the formed nanoplates from 69 to 80%, decreased the crystallite thickness, but unaffected its crystalline phase and band gap energy. The kinetic constants (Ka e Kb) for the synthesized TiO2 anatase nanoplates are considerably higher than the commercial TiO2 anatase constant (Kc). The synthesized photocatalysts show higher efficiency in the photocatalytic removal of methylene blue (MB) than commercial TiO2 (for t = 120 min).

In situ characterization of Pt catalysts supported on ceria modified TiO2 for the WGS reaction: influence of ceria loading.

This work analyzes the influence of cerium content (6-15 wt%) on a TiO(2) support over the structure and water gas shift (WGS) activity of Pt catalysts. The structural properties of these Pt/Ce-TiO(2) catalysts were characterized by XRD, TEM and XANES. Physicochemical characterization of the catalysts showed differences in the structure and dispersion of Ce entities on the support with Ce loading. For the samples with low ceria content (6 wt%), cerium is deposited on the support in the form of CeO(x) clusters in a highly dispersed state in close interaction with the Ti atoms. The formation of CeO(x) clusters at low Ce-loading on the support facilitates the dispersion of small particles of Pt and improves the reducibility of ceria component at low temperatures. The changes in platinum dispersion and support reducibility with Ce-loading on the TiO(2) support lead to significant differences in the WGS activity. Pt supported on the sample with lower Ce content (6 wt%) shows better activity than those corresponding to catalysts with higher Ce content (15 wt%). Activity measurements coupled with catalysts characterization suggest that the improvement in the reducibility of the support with lower Ce content was associated with the presence of CeO(x) clusters of high reducibility that improve the chemical activity of the oxide-metal interfaces at which the WGS reaction takes place.

Biomass gasification chars for mercury capture from a simulated flue gas of coal combustion.

The combustion of coal can result in trace elements, such as mercury, being released from power stations with potentially harmful effects for both human health and the environment. Research is ongoing to develop cost-effective and efficient control technologies for mercury removal from coal-fired power plants, the largest source of anthropogenic mercury emissions. A number of activated carbon sorbents have been demonstrated to be effective for mercury retention in coal combustion power plants. However, more economic alternatives need to be developed. Raw biomass gasification chars could serve as low-cost sorbents for capturing mercury since they are sub-products generated during a thermal conversion process. The aim of this study was to evaluate different biomass gasification chars as mercury sorbents in a simulated coal combustion flue gas. The results were compared with those obtained using a commercial activated carbon. Chars from a mixture of paper and plastic waste showed the highest retention capacity. It was found that not only a high carbon content and a well developed microporosity but also a high chlorine content and a high aluminium content improved the mercury retention capacity of biomass gasification chars. No relationship could be inferred between the surface oxygen functional groups and mercury retention in the char samples evaluated.

Structural and surface analysis of unsupported and alumina-supported La(Mn,Fe,Mo)O3 perovskite oxides.

A series of bulk and Al(2)O(3)-supported perovskite oxides of the type LaMn(1-x-y)Fe(x)Mo(y)O(3) (x = 0.00-0.90 and y = 0.00-0.09) were synthesized by the citric acid complexation-gelation method followed by annealing in air at 800 degrees C. For all samples, the local environment and the chemical state and concentration of surface species were determined. Mössbauer spectra revealed the only presence of octahedral Fe(3+) ions dispersed in the perovskite structure, however well-crystallized together with a poorly crystalline LaFeO(3) phases were detected for larger substitutions (x = 0.90). A similar picture was obtained for Mo-loaded (y = 0.02 and 0.05) samples but a new phase most likely related to Fe(3+) ions dispersed aside from the perovskite structure was found for larger substitutions (y = 0.09). Together with these structures, supported samples showed the presence of LaFeO(3) nanoparticles. Finally, photoelectron spectroscopy indicated that the chemical state and composition of the samples in the surface region (2-3 nm) approaches that of the bulk. For the unsupported substituted samples, iron (and molybdenum) enters into the perovskite structure while manganese tends to be slightly segregated. Moreover, in supported perovskites, a fraction of Mo and La atoms interact with the alumina surface. All these oxides were active in methane combustion and best performance was recorded for the Fe-rich composition (x = 0.9) in which both Mn(3+) and Mo(3+) ions were in the same proportion (y = 0.05).

Methanol Synthesis from CO2: A Review of the Latest Developments in Heterogeneous Catalysis.

Technological approaches which enable the effective utilization of CO2 for manufacturing value-added chemicals and fuels can help to solve environmental problems derived from large CO2 emissions associated with the use of fossil fuels. One of the most interesting products that can be synthesized from CO2 is methanol, since it is an industrial commodity used in several chemical products and also an efficient transportation fuel. In this review, we highlight the recent advances in the development of heterogeneous catalysts and processes for the direct hydrogenation of CO2 to methanol. The main efforts focused on the improvement of conventional Cu/ZnO based catalysts and the development of new catalytic systems targeting the specific needs for CO2 to methanol reactions (unfavourable thermodynamics, production of high amount of water and high methanol selectivity under high or full CO2 conversion). Major studies on the development of active and selective catalysts based on thermodynamics, mechanisms, nano-synthesis and catalyst design (active phase, promoters, supports, etc.) are highlighted in this review. Finally, a summary concerning future perspectives on the research and development of efficient heterogeneous catalysts for methanol synthesis from CO2 will be presented.

Data on TGA of precursors and SEM of reduced Cu/ZnO catalysts co-modified with aluminium and gallium for methanol synthesis.

The modification of Cu-Zn catalysts with low amount of Al and Ga (Al+Ga = 3%) was investigated and data corresponding to its influence on the decomposition of the calcined precursors and on the nanomorphology and surface concentration of reduced catalysts were presented in this contribution. The data presented here are supplementary material of the catalysts presented in the research article "Structure and activity of Cu/ZnO catalysts co-modified with aluminium and gallium for methanol synthesis" published in Catalysis Today [1].

Highly active Cu/ZnO-Al catalyst for methanol synthesis: effect of aging on its structure and activity.

The influence of aging of precipitates on the physical and catalytic properties of a copper/zinc oxide-aluminium (Cu/ZnO-Al) catalyst with an optimized composition (low Al concentration, Cu/Zn/Al = 68/29/3) prepared using co-precipitation has been investigated in detail. The change in the structure of precipitates with aging (from amorphous zincian georgeite to crystalline zincian malachite) strongly influences the micro- and nano-structure (Cu and ZnO crystallite size, exposed copper surface area, Cu-ZnO interactions and stability of ZnO) of the final Cu/ZnO-Al catalysts obtained after calcination and reduction of the precipitates. The results of catalytic activity in methanol synthesis from syngas show the higher intrinsic activity of the catalysts derived from aged zincian malachite precipitates as consequence of the increase in the exposed copper surface area and the Cu-ZnO contacts. The stability of catalysts under the reaction conditions was also improved in the catalysts derived from precipitates aged after crystallization of malachite. The catalyst derived from the precipitate removed close to the point of crystallization of malachite shows very poor activity in the methanol synthesis as consequence of its segregated large Cu crystallites in low contact with ZnO derived from the absence of carbonate retention after calcination of the precipitate and the presence of sodium species after conventional washing which favour the strong sintering and crystallization of Cu during reduction.

Relevance in the Fischer-Tropsch synthesis of the formation of Fe-O-Ce interactions on iron-cerium mixed oxide systems.

A series of Fe-Ce mixed oxides (95 atom % Fe-5 atom % Ce) has been prepared by different methods: coprecipitation, impregnation, and physical mixture of Ce and Fe oxides. These solids have been tested in the Fischer-Tropsch synthesis. The characterization of the catalytic precursors was carried out by X-ray diffraction (XRD), Raman, Mössbauer, and X-ray photoelectron (XPS) spectroscopic techniques. When the preparation method ensures a microscopic contact between Fe and Ce cations in the solid, several types of Fe-Ce interactions are present in the calcined solids. The interactions take the shape of Fe-O-Ce bridges that can exist either in the hematite-like solid solution or in the interphase between the Fe oxide covered by microcrystals of Ce oxide. In the case of the hematite-like solid solution, Ce(IV) cations are dissolved in the alpha-Fe2O3 network. The promotion by Ce of the catalytic properties observed in the final catalysts can be directly related with the detection of these Fe-O-Ce bridges in the calcined solids. The Ce promotion results in a larger yield to hydrocarbons, a higher production of olefins, and a higher selectivity to medium and large chain hydrocarbons (larger than six carbon atoms). It is proposed that the Ce promotion is due to the presence of Fe0-Ce(III) ensembles in the final catalysts arising from the initial Fe-O-Ce bridges developed in the parent calcined samples.

Production and stability of mechanochemically exfoliated graphene in water and culture media.

The preparation of graphene suspensions in water, without detergents or any other additives is achieved using freeze-dried graphene powders, produced by mechanochemical exfoliation of graphite. These powders of graphene can be safely stored or shipped, and promptly dissolved in aqueous media. The suspensions are relatively stable in terms of time, with a maximum loss of ∼25% of the initial concentration at 2 h. This work provides an easy and general access to aqueous graphene suspensions of chemically non-modified graphene samples, an otherwise (almost) impossible task to achieve by other means. A detailed study of the stability of the relative dispersions is also reported.

Structure and Activity of Pt-Ni Catalysts Supported on Modified Al2O3 for Ethanol Steam Reforming.

Modification of alumina with La-, Ce-, Zr- and Mg-oxides was studied with the aim to use them as supports of bimetallic Pt-Ni catalysts for the steam reforming of ethanol. Activity results showed that modifications of Al2O3 support with the incorporation of La, Ce, Zr or Mg oxides play an essential role in the catalytic behaviour of PtNi catalysts. Bimetallic PtNi catalyst supported on bare Al2O3 showed evolution of the reaction products with time on stream consisting in the increase of C2H4 production with concomitant decrease of CH4 and CO2 production. The addition of Mg or Zr to γ-A1203 did not inhibit the appearance of ethylene but delayed its production. In the case of Ce- or La-supported catalysts, the product selectivities were stable with time-on-stream, with no changes being observed in the product distribution for 24 h. Characterization results showed that La- and Ce-containing supports improves the Pt and Ni metal exposure values. The better stability achieved for Ce and La containing catalysts was inferred to be related with a participation/assistance of lanthanum and cerium entities in the gasification of coke deposits together with a modification of Pt and Ni dispersion which lower the probability of the nucleation of coke precursors on their surfaces.

Sulfonic acid-functionalized silica through quantitative oxidation of thiol groups.

A simple procedure for the preparation of amorphous silica containing thiol groups which quantitatively affords sulfonic acid groups has been developed, resulting in site densities and activity for the esterification of acetic acid with methanol greater than a commercial Nafion silica composite.

Breakthrough in the direct conversion of methane into c1-oxygenates.

The partial oxidation of methane to CH3OH and HCHO (C1-oxygenates) was evaluated over a low surface area V2O5/SiO2 catalyst. The introduction of low amounts of NO (0-2.92% vol) to the reaction feed strongly enhanced both the conversion of methane and selectivity to C1-oxygenates. In the presence of NO, both the reaction temperature and the CH4/O2 ratio affected selectivity to CH3OH and HCHO. Selectivity values of C1-oxygenates as high as 40% at a methane conversion close to 40% were obtained.

Microwave single walled carbon nanotubes purification.

A new single walled carbon nanotubes (SWCNTs) purification procedure has been developed; it consists in a combination of air treatment and acid microwave digestion leading to a high purity SWCNTs material; the procedure reaches high metal removal percentages and the operation time is drastically reduced compared to conventional acid reflux treatments.

Silylation and surface properties of chemically grafted hydrophobic silica.

A commercial mesoporous silica (Grace Davison) was chemically grafted with trimethylsilyl chloride (TMSCl) and hexamethyldisilanaze (HMDS). The silylation process brought about some reduction in the specific BET area, the pore volume, and the pore sizes of the samples. Thermogravimetric studies of the silylated samples revealed that the grafting process is kinetically controlled at short reaction times. In the kinetic regime, increasing concentrations of the silylant agent up to 2 wt% in the solvent led to an increase of the extent of the silylated surface, although this limitation disappeared at higher concentrations. Silylation was confirmed by diffuse reflectance infrared Fourier transform (DRIFTS), (29)Si CP-MAS NMR, and photoelectron (XPS) spectroscopic techniques. Solid-state (29)Si MAS-NMR spectra of the silylated samples revealed the presence of -SiCH(3) groups (9.5 ppm) together with two resonances, Q3 (approximately equal to -104 ppm) and Q4 (approximately equal to -114 ppm), coming from siloxane [Qn approximately Si(OSi)n(OH)(4-n), n approximately 2-4] groups, the Q3 signal decreasing upon silylation. The DRIFT spectra of the silylated samples exhibited two well defined bands at 2970 and 2907 cm(-1), due to stretching vibration modes of the C-H bonds in surface -CH(3) groups formed during the silylation process, and also the disappearance of the band at 3740 cm(-1). This observation indicates the complete removal of terminal and geminal hydroxyl groups by grafting with the silylating agent. Similarly, high-resolution photoelectron spectra of the Si2p core levels showed a high binding-energy component (103.5 eV) in all the samples, coming from the Si coordinated with oxide anions in SiO(2), together with a second component at 102.1 eV, which is the fingerprint of Si coordinated by oxide anions and an organic group. Finally, the samples were ranked according to their hydrophobicity, as determined from the temperature-programmed desorption profiles of adsorbed water and 2-methylbutane.

Manganese micro-nodules on ancient brick walls.

Romans, Jews, Arabs and Christians built the ancient city of Toledo (Spain) with bricks as the main construction material. Manganese micro-nodules (circa 2 microm in diameter) have grown under the external bio-film surface of the bricks. Recent anthropogenic activities such as industrial emissions, foundries, or traffic and housing pollution have further altered these old bricks. The energy-dispersive X-ray microanalyses (XPS) of micro-nodules show Al, Si, Ca, K, Fe and Mn, with some carbon species. Manganese atoms are present only as Mn(4+) and iron as Fe(3+) (FeOOH-Fe(2)O(3) mixtures). The large concentration of alga biomass of the River Tagus and the Torcón and Guajaraz reservoirs suggest manganese micro-nodules are formed either from water solutions rich in anthropogenic MnO(4)K in a reduction environment (from Mn(7+) to Mn(4+)) or by oxidation mechanisms from dissolved Mn(2+) (from Mn(2+) to Mn(4+)) linked to algae biofilm onto the ancient brick surfaces. Ancient wall surfaces were also studied by scanning electron microscopy (SEM-EDS) and X-ray diffraction (XRD). Chemical and biological analyses of the waters around Toledo are also analysed for possible sources of manganese. Manganese micro-nodules on ancient brick walls are good indicators of manganese pollution.

The fabrication and characterization of Cu-nanoparticle immobilization on a hybrid chitosan derivative-carbon support as a novel electrochemical sensor: application for the sensitive enzymeless oxidation of glucose and reduction of hydrogen peroxide.

New hybrid chitosan derivatives (chitosan (Chit)), amine group grafted chitosan (N-Chit), and thiol group grafted chitosan (S-Chit) modified-carbon (carbon nanotubes or graphite) were prepared and used as supports for Cu-nanoparticles. The synthesized materials were characterized with different methods such as transmission electron microscopy, Brunauer-Emmett-Teller and cyclic voltammetry. The electrocatalytic effect of the nanohybrid was investigated in the reduction of hydrogen peroxide and the oxidation of glucose. It was found that the Cu nanoparticles decorate on the modified chitosan-CNT (Cu@M-Chit-CNT) exhibit a remarkable catalytic performance for H2O2 reduction and glucose oxidation. Hydrodynamic amperometry was used for the electrochemical determination of H2O2 and glucose. The linear range for H2O2 was from 0.1 to 1000 µmol L-1 with a detection limit of 0.025 µmol L-1, whereas the linear range for glucose was from 0.5 to 1000 µmol L-1 with a detection limit of 0.05 µmol L-1. In addition, Cu@N-Chit-CNT/GCE and Cu@Chit-CNT/GCE showed a good selectivity for H2O2 and glucose detection in the presence of dopamine, ascorbic acid and uric acid. The kinetic parameters such as the electron transfer coefficient and the catalytic reaction rate constant were also determined for glucose and H2O2. Finally, the modified electrode is the most sensitive probe ever reported and can be used to achieve the real-time quantitative detection of H2O2 and glucose for biological applications.

A photoresponsive graphene oxide-C60 conjugate.

An all-carbon donor-acceptor hybrid combining graphene oxide (GO) and C60 has been prepared. Laser flash photolysis measurements revealed the occurrence of photoinduced electron transfer from the GO electron donor to the C60 electron acceptor in the conjugate.

3D free-standing porous scaffolds made of graphene oxide as substrates for neural cell growth.

The absence of efficient therapies for the treatment of lesions affecting the central nervous system encourages scientists to explore new materials in an attempt to enhance neural tissue regeneration while preventing inhibitory fibroglial scars. In recent years, the superlative properties of graphene-based materials have provided a strong incentive for their application in biomedicine. Nonetheless, a few attempts to date have envisioned the use of graphene for the fabrication of three-dimensional (3D) substrates for neural repair, but none of these involve graphene oxide (GOx) despite some attractive features such as higher hydrophilicity and versatility of functionalization. In this paper, we report novel, free-standing, porous and flexible 3D GOx-based scaffolds, produced by the biocompatible freeze-casting procedure named ISISA, with potential utility in neural tissue regeneration. The resulting materials were thoroughly characterized by Fourier-transform infrared, Raman, and X-ray photoelectron spectroscopies and scanning electron microscopy, as well as flexibility testing. Embryonic neural progenitor cells were then used to investigate adhesion, morphology, viability, and neuronal/glial differentiation. Highly viable and interconnected neural networks were formed on these 3D scaffolds, containing both neurons and glial cells and rich in dendrites, axons and synaptic connections, and the results are in agreement with those obtained in initial studies performed with two-dimensional GOx films. These results encourage further investigation in vivo on the use of these scaffolds as guide substrates to promote the repair of neural injuries.

A soluble hybrid material combining carbon nanohorns and C60.

A soluble hybrid nanomaterial that combines fullerenes and carbon nanohorns (CNHs) has been prepared and fully characterized. Electrochemical investigations revealed that the CNHs modify the electron accepting ability of C(60) in the hybrid material.