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A-site and B-site substitutions are effective methods towards improving well-studied oxygen carrier materials that are vital for emerging gasification technologies. Such materials include SrFeO3 , which greatly benefits from the inclusion of calcium and/or cobalt, and Sr0.8 Ca0.2 Fe0.4 Co0.6 O3 has been regarded as the best-performing composition. In this study, systems with higher calcium and lower cobalt contents are investigated with a view to lessening the societal and economic burdens of these dual-doped carriers. Density functional theory calculations are performed to illustrate the Fe-O bonding and relaxation contributions to the oxygen vacancy formation energy in Sr1-x Cax Fe1-y Coy O3 systems (x=0.1875, 0.25, 0.3125; y=0.125, 0.25, 0.375, 0.5) and determine that increased calcium A-site substitution requires the use of less cobalt B-site doping to reach the same oxygen vacancy formation. These findings are experimentally validated in situ and ex situ characterization of bulk Sr0.7 Ca0.3 Fe1-y Coy O3 materials. Sr0.7 Ca0.3 Fe0.7 Co0.3 O3 is found to have similar O2 adsorption/desorption rates and storage capacity to Sr0.8 Ca0.2 Fe0.4 Co0.6 O3 in air/N2 cycling experiments. Additionally, both materials are outperformed by Sr0.7 Ca0.3 Fe1-y Coy O3 systems with y=0-0.10 at 400-500 °C, which cycle 1.5 wt% O2 in under ten minutes.

Reversible oxygen absorption/desorption in earth-abundant materials is fundamental towards many advanced technologies that require a pure oxygen stream including oxy-combustion via chemical looping and oxygen-blown coal gasification. The Sr1−xCaxFeO3 system is one of many perovskite oxides that have drawn attention given the large quantities of oxygen it can produce during mild cycling conditions. In this work, we employ hybrid functional based DFT calculations to establish the oxygen vacancy formation energy, ΔEf,vac, as an effective parameter for describing the Sr1−xCaxFeO3 system. We validate these calculations experimentally using XPS, O2-TPD, TGA, and synchrotron pXRD. In all cases, we find that increasing calcium content lowers both the oxygen desorption temperature and preferred operating temperature for the system. Importantly, we are able to experimentally show the structural and functional cyclability of these materials, achieving rapidly accessible maximum oxygen storage capacities of 1.51–2.41 wt% for temperatures of 400–700 °C.

Coinage metals (Au, Cu and Ag) are state-of-the-art electrocatalysts for the CO2 reduction reaction (CO2RR). Size-dependent CO2RR activity of Au and Cu has been studied, and increased H2 evolution reaction (HER) activity is expected for small catalyst particles with high population of undercoordinated corner sites. A similar consensus is still lacking for Ag catalysts because the ligands and stabilizers typically used to control particle synthesis can block specific active sites and mask inherent structure-property trends. This knowledge gap is problematic because increased performance and catalyst utilization are still needed to improve economic viability. We combined density functional theory, microkinetic modeling, and experiment to demonstrate a strong size-dependence for pristine Ag particles in the sub-10 nm range. Small diameter particles with a high population of Ag edge sites were predicted to favor HER, whereas CO2RR selectivity increased towards that of bulk Ag for larger diameter particles as the population of Ag(100) surface sites grew. Experimental results validated these predictions and we identified an optimal particle diameter of 8-10 nm that balanced selectivity and activity. Particles below this diameter suffered from poor selectivity, while larger particles demonstrated bulk-like activity and reduced catalyst utilization. These results demonstrate the size-dependent CO2RR activity of pristine Ag catalysts and will help guide future development efforts.

Transition metal oxides have gained attention as promising oxygen evolution reaction (OER) electrocatalysts in alkaline electrolytes, but heterogeneities in typical catalyst samples often obscure k...

In this work, we have investigated a hierarchical CuO-derived inverse opal (CuO-IO) catalyst with high CO selectivity up to 80–90% and minimal H2 evolution at moderate potentials for CO2 electroreduction. The three-dimensionally (3D) structured, porous catalyst was composed of small CuO nanoparticles and exhibited a peak CO faradaic efficiency (FE) of 72.5% (±1.8), complete suppression of H2 formation, and good stability over 24 hours operation at −0.6 V versus the reversible hydrogen electrode (RHE). In situ Raman, X-ray absorption spectroscopy and X-ray diffraction measurements indicated reduction of the catalyst into metallic Cu0 oxidation state with dominant Cu(111) orientation under electrocatalytic conditions. We suggest that rapid depletion of CO2 and protons at the highly roughened catalyst surface likely increased the local pH during the electrolysis. The combination of C1 favoring Cu(111) surfaces and reduced local proton/CO2 availability facilitated selective conversion of CO2 into CO and reduced H2 and C2 products. Our work provides additional understanding of the structure–property relationships of 3D porous electrocatalysts for CO2 reduction applications by evaluating the crystallographic orientation, oxidation state, and crystallite size of a CO-selective CuO-IO catalyst under realistic working conditions.

Coinage metals (Au, Ag and Cu) have shown propensity to reduce CO2 under electrochemical condition. For Au and Cu, nanoparticle size has been used as a lever to tune their activity and selectivity and it was found that the competing hydrogen evolution reaction (HER) becomes an issue for small catalyst particles. For the Ag case, which has been shown to produce CO, the effect of the particle size remains a subject of ongoing discussion because of the lack of thorough benchmark studies. In this presentation, we highlight our detailed investigation of electrochemical CO2 reduction on Ag to ascertain whether size variation can be used to tune the reactivity of the catalyst material. Our combined density functional theory, microkinetic modeling, and experiment demonstrate a strong size-dependence for pristine Ag particles in the sub-10 nm range. The modeling reveals that the enhanced activity can be correlated to the population of a moderately high index facet. Experimental results validated these predictions and we identified an optimal particle diameter that balanced selectivity and activity. The availability of synthetic method to make Ag nanoparticle with different sizes and predictive computational methods that factor in the kinetic aspects could potentially enhance future outlook for material design.

A-site and B-site substitutions are effective methods towards improving well-studied oxygen carrier materials that are vital for emerging gasification technologies. Such materials include SrFeO

Hydrogenated TiO2 has recently attracted considerable attention as potential electrode materials for supercapacitors due to its abundance, low cost, high conductivity, remarkable rate capability, and outstanding long-term cycling stability. Herein, we demonstrate the synthesis of hydrogenated TiO2 nanoparticles anchored on reduced graphene oxide nanosheets (HTG) in the form of sandwich-like nanosheet composites. Further, we explored their implementation as electrode materials for high voltage, symmetric supercapacitors, operating in the voltage window of 0–1.8 V. The HTGs were prepared by a sol-gel method, followed by hydrogenation in the temperature range 300–500 °C. Of the prepared composites, HTG prepared at 400 °C exhibited the largest specific capacitance of 51 F g−1 at the current density of 1.0 A g−1 and excellent rate capability with 82.5% capacitance retention as the current density increased 40-fold, from 0.5 to 20.0 A g−1. HTG's excellent rate capability was attributed to its sandwich-like nanostructure, in which ultrasmall hydrogenated TiO2 nanoparticles densely anchored onto both surfaces of the two-dimensional reduced graphene oxide sheets. Moreover, HTG-based supercapacitors also exhibited long-term cycling stability with the retention over 80% of its initial capacitance after 10,000 cycles. These properties suggest that HTG is a promising electrode material for the scalable manufacture of high-performance supercapacitors.

The splitting of water into molecular hydrogen and oxygen with the use of renewable solar energy is considered one of the most promising routes to yield sustainable fuel. Herein, we report the H2 evolution performance of gallium doped TiO2 photocatalysts with varying degrees of Ga dopant. The gallium(III) ions induced significant changes in the structural, textural and electronic properties of TiO2 nanoparticles, resulting in remarkably enhanced photocatalytic activity and good stability for H2 production. Ga3+ ions can act as hole traps that enable a large number of excited electrons to migrate towards the TiO2 surface, thereby facilitating electron transfer and charge separation. Additionally, the cationic dopant and its induced defects might introduce a mid-gap state, promoting electron migration and prolonging the lifetime of charge carrier pairs. We have discovered that the optimal Ga dopant concentration was 3.125 at% and that the incorporation of platinum (0.5 wt%) as a co-catalyst further improved the H2 evolution rate up to 5722 μmol g−1 h−1. Pt not only acts as an electron sink, drastically increasing the electron/hole pair lifetime, but it also creates an intimate contact at the heterojunction between Pt and Ga-TiO2, thus improving the interfacial electron transfer process. These catalyst design strategies provide new ways of designing transition metal photocatalysts that improve green fuel production from renewable solar energy and water.

M-OMS-2 materials (M = K+, Cu2+, Co2+) were prepared by an uncomplicated reflux method, and the cryptomelane crystalline structure was confirmed by X-ray diffraction patterns. Element analysis recorded ~56 - ~59 wt.% of Mn in the three synthesized samples and ~2.8 wt.% loadings of dopants over Co-OMS-2 and Cu-OMS-2 materials. A titration method valued the average oxidation states of manganese at 3.60, 3.71 and 3.77 for K-OMS-2, Co-OMS-2 and Cu-OMS-2, respectively. In comparison with K-OMS-2, Co and Cu dopants depicted a significant enhancement catalytic activity in removal of formaldehyde at low (5%) and high (65 %) relative humidity (RH). Cu-OMS-2 showed the highest catalyst performance with ~90 % of formaldehyde conversion at 150 °C, 65% RH, whereas only ~40 % (for Co-OMS-2) and ~26 % (for K-OMS-2) of that were observed. The finding results promised a potential Cu-OMS-2 material for designed low-costly catalyst in formaldehyde removal at a wide range of RH.

The dry reforming of methane (DRM) is a promising process for generating syngas (CO + H2) while consuming CO2, but industrial applications have been limited due to the high temperatures required to prevent coke formation. Microwave-assisted DRM (MW-DRM) is a promising approach to enable high temperature reactions because it can utilize excess renewable electrons to rapidly and selectively heat the catalyst bed without wasting time and energy heating the entire reactor. Here we demonstrate the MW-DRM reaction by modifying lanthanum strontium cobaltite (LSC) to serve as both microwave absorber and catalyst. Catalyst doping studies revealed the addition of oxophilic transition metals prevented over-reduction and stabilized the perovskitic phases under reaction conditions. In situ, synchrotron-based x-ray diffraction revealed the catalyst becomes active once metallic cobalt forms on a retained perovskitic support. The best performing Mn doped LSC catalyst showed 80–90 % single-pass conversions, stable operation for over 10 h, and easy microwave regeneration.

CO2 and H2 production from the water–gas shift (WGS) reaction was studied over Pt/CeOx–TiO2 catalysts with incremental loadings of CeOx, which adopts variations in the local morphology. The lowest loading of CeOx (1 wt % to 0.5 at. %) that is configured in its smallest dimensions exhibited the best WGS activity over larger dimensional structures. We attribute this to several factors including the ultrafine dispersed one-dimensional nanocluster geometry, a large concentration of Ce3+ and enhanced reducibility of the low loadings. We utilized several in situ experiments to monitor the active state of the catalyst during the WGS reaction. X-ray diffraction (XRD) results showed lattice expansion that indicated reduced ceria was prevalent during the WGS reaction. On the surface, Ce3+ related hydroxyl groups were identified by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The enhanced reducibility of the catalyst with the introduction of ceria was further revealed by H2-temperature progr...

We have studied the catalytic carbon monoxide (CO) oxidation (CO + 0.5O 2 → CO 2 ) reaction using a powder catalyst composed of both copper (5 wt.% loading) and titania (CuO x –TiO 2 ). Our study was focused on revealing the role of Cu, and the interaction between Cu and TiO 2 , by systematic comparison between two nanocatalysts, CuO x –TiO 2 and pure CuO x . We interrogated these catalysts under in situ conditions using X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) to probe the structure and electronic properties of the catalyst at all stages of the reaction and simultaneously probe the surface states or intermediates of this reaction. With the aid of several ex situ characterization techniques including transmission electron microscopy (TEM), the local catalyst morphology and structure were also studied. Our results show that a CuO x –TiO 2 system is more active than bulk CuO x for the CO oxidation reaction due to its lower onset temperature and better stability at higher temperatures. Our results also suggest that surface Cu + species observed in the CuO x –TiO 2 interface are likely to be a key player in the CO oxidation mechanism, while implicating that the stabilization of this species is probably associated with the oxide–oxide interface. Both in situ DRIFTS and XAFS measurements reveal that there is likely to be a Cu(Ti)–O mixed oxide at this interface. We discuss the nature of this Cu(Ti)–O interface and interpret its role on the CO oxidation reaction.

The use of metal nanoparticles (NPs), including Au and Pt, supported over oxides has been pivotal, and is ever increasing in enabling catalytic reactions which target the production of hydrogen. We review here the most recent works pertaining to the fundamental understanding of the structure, morphology, growth, characterization, and intrinsic phenomenological properties of Au- and Pt-based catalysts that influence the reactivity and selectivity to target hydrogen production. We draw on surface science and theoretical methods of model and powder catalysts using high resolution imaging, spectroscopy, scattering experiments, and theoretical studies. Based on these insights we identify key aspects of studies of supported metal nanoparticle (NP) catalysts for several reactions. The main focus of this review is on the intersection of catalytic chemistry related to the water-gas shift (WGS), oxygenate steam reforming (OSR), and solar-assisted reactions (SAR).

The functionalization of graphene oxide (GO) and graphene by TiO2 and other metal oxides has attracted considerable attention due to numerous promising applications in catalysis, energy conversion, and storage. Hydrogenation of this class of materials has been proposed as a promising way to tune catalytic properties by altering the structural and chemical transformations that occur upon H incorporation. Herein, we investigate the structural changes that occur during the hydrogenation process using in situ powder X-ray diffraction and pair distribution function analysis of GO–TiO2 and TiO2 under H2 reduction. Sequential Rietveld refinement was employed to gain insight into the evolution of crystal growth of TiO2 nanoparticles in the presence of two-dimensional (2D) GO nanosheets. GO sheets not only significantly retarded the nucleation and growth of rutile impurities, stabilizing the anatase structure, but was also partially reduced to hydrogenated graphene by the introduction of atomic hydrogen into the h...

Photocatalytic thin films on quartz substrates were simply prepared by spraying a sol of copper metal (Cu)-doped titanium dioxide (TiO 2 ) combined with reduced graphene oxide (RGO). Cu-doped TiO 2 /RGO powders containing different amounts of Cu were synthesized to investigate the effect of Cu content upon the photodegradation of methylene blue in water, and were used in the preparation of sols of Cu-doped TiO 2 /RGO. The Cu-doped TiO 2 /RGO film photocatalysts showed better performance in the photodegradation of methylene blue than an undoped TiO 2 /RGO film. After 180 min of UV irradiation, 7.5-CTG-5 (7.5 wt% of Cu and 5 wt% of RGO) photocatalyst removed 63% of methylene blue from aqueous solution with an initial concentration of 10 ppm, whereas 0-CTG-5 (0 wt% of Cu and 5 wt% of RGO) decomposed only 28% of the methylene blue, indicating that the presence of Cu enhanced the photocatalytic activity. Doped Cu could narrow the bandgap of TiO 2 , thereby influencing the reduction of graphene oxide and enhancing the hydrophilicity of the materials, and thus producing the observed increase in photocatalytic activity. The relationships between hydrophilicity and photocatalytic activity are discussed herein.

The splitting of water into molecular hydrogen and oxygen with the use of renewable solar energy is considered one of the most promising routes to yield sustainable fuel. Herein, we report the H

Graphane, graphone, and hydrogenated graphene (HG) have been extensively studied in recent years due to their interesting properties and potential use in commercial and industrial applications. The present study reports investigation of hydrogenated graphene/TiO2–x (HGT) nanocomposites as photocatalysts for H2 and O2 production from water without the assistance of a noble metal cocatalyst. By combination of several techniques, the morphologies, bulk/atomic structure, and electronic properties of all the powders were exhaustively interrogated. Hydrogenation treatment efficiently reduces TiO2 nanoparticles, while the graphene oxide sheets undergo the topotactic transformation from a graphene-like structure to a mixture of graphitic and turbostratic carbon (amorphous/disordered) upon altering the calcination atmosphere from a mildly reducing to a H2-abundant environment. Remarkably, the hydrogenated graphene–TiO2–x composite that results upon H2-rich reduction exhibits the highest photocatalytic H2 evolution...

A rapid, facile, one-pot microwave-assisted polyol synthesis of novel hierarchical nickel titanate (NTN) is first reported in the present study. This method successfully fabricated rhombohedral NiTiO3 in the shape of a cylindrical storage tank with two elliptical end caps that were constructed from ellipsoid-like nanoparticles. By contrast, irregular NTN aggregates composed of loose granular particles were formed through solvothermal treatment. Varying the dielectric of the solvent with water, n-butanol, acrylic acid, N,N-dimethylformamide, and an ethylene glycol : butanol mixture significantly affected the crystallographic structure and morphology of the final products due to differences in the loss tangent of each medium under microwave irradiation. Using a nickel source with acetate and halide counterions, which are more readily substituted and have better coordination ability with metal cations than nitrate, resulted in the formation of 3D hexagonal prismatic NiTiO3 and undesirable 1D rod-like TiO2 aggregates, respectively. Notably, this study provides a valuable means of developing a rapid, effective method to synthesize NiTiO3 with uniform morphology, high purity and potential photocatalysis application.

In this study, the morphological evolution of hierarchical nickel titanates was first-ever investigated by simply raising the solvothermal temperature. At room temperature, irregular aggregates of anatase TiO2 nanoparticles were reluctantly formed. Increasing the temperature to 100 °C resulted in the assembly of 3D drum-shaped nickel titanate clusters where the three-dimensional geometry was constructed via coalescent nanoparticles with a mean size of 126.8 nm. An intermediate stage containing circular cylinders and irregular prisms was obtained at intermediate temperatures. Further elevation of the solvothermal temperature to 160 °C and 180 °C gave 1D uniform hexagonal nanoprisms of nickel titanates. Increasing the solvothermal temperature accelerates the nucleation rate, which drastically promotes crystallization and self-assembly, thereby evolving to the hierarchical structure of NiTiO3.

Composite materials of Sn-doped TiO 2 nanoparticles (4–6 nm) uniformly anchored onto reduced graphene oxide (RGO) sheets were fabricated by a hydrothermal process. When compared with an undoped TiO 2 /RGO composite material, the partial substitution of Sn 4+ for Ti 4+ in TiO 2 /RGO in different doping concentrations not only increased the specific surface area, but also narrowed the band gap energy of the material. It also resulted in a shift in the photoresponse of the material into the visible light region, an increase in the relative intensity of its Raman (D/G) band, and changes in its X-ray photoelectron spectra; these results implied strong interactions between the Sn species and nanosized TiO 2 as well as between the TiO 2 and RGO layers. The presence of RGO led to enhanced adsorptivity of methyl orange onto the material compared with that of either pure TiO 2 or Sn-doped TiO 2 . Increasing the Sn dopant content to optimal value facilitated photoactivity under both UV and visible light irradiation. The incorporation of both RGO and Sn dopants significantly modified the electronic structure of TiO 2 , altering the electron transfer direction and efficiently prohibiting the recombination of photo-induced charge carriers.

The production of value-added chemicals and fuels from CO2 and water by highly efficient, selective, robust electrocatalytic materials is of vital interest to address the energy challenges. In this work, we report a hierarchical CuO-derived inverse opal (CuO-HIO) electrocatalyst which demonstrated impressive CO selectivity and negligible H2 evolution at high current densities (achieved ~35 mA cm-2 at -1.2 V vs. RHE). Such a three-dimensional interconnected porous network with voids about 200 nm surprisingly exhibited a Faradaic efficiency (FE) of 72.5% for CO production at -0.6 V vs. RHE and was very stable during 24-hour CO2 electrolysis. The in situ Cu K-edge XANES and Fourier transformed EXAFS spectra dynamically revealed the direct transformation of Cu2+ to Cu0 species within few minutes at -0.6 V vs. RHE and CuO was entirely reduced to metallic copper after 60 min. Such an observation was well consistent with the in situ time-resolved XRD patterns which illustrated the gradual emergence of (111), (200), (220), (311), and (222) diffractions of cubic copper under the working condition. CO2-to-CO outperformance of CuO-HIO catalyst over typical oxidized copper catalysts could be ascribed to (i) the mass transport limitation and local pH effect induced by unique hierarchical morphology, (ii) highly roughened surface, and (iii) in situ reduction of Cu2+ to stabilized metallic Cu active sites during the CO2 electrolysis. Our findings may open an opportunity for rational design of promising, high-performance, less expensive electrocatalysts for renewable fuel production from fossil fuel-generated CO2 emission.

Three-dimensional (3D) monodispersed sea urchin-like Ru-doped rutile TiO2 hierarchical architectures composed of radially aligned, densely-packed TiO2 nanorods have been successfully synthesized via an acid-hydrothermal method at low temperature without the assistance of any structure-directing agent and post annealing treatment. The addition of a minuscule concentration of ruthenium dopants remarkably catalyzes the formation of the 3D urchin structure and drives the enhanced photocatalytic H2 production under visible light irradiation, not possible on undoped and bulk rutile TiO2. Increasing ruthenium doping dosage not only increases the surface area up to 166 m(2) g(-1) but also induces enhanced photoresponse in the regime of visible and near infrared light. The doping introduces defect impurity levels, i.e. oxygen vacancy and under-coordinated Ti(3+), significantly below the conduction band of TiO2, and ruthenium species act as electron donors/acceptors that accelerate the photogenerated hole and electron transfer and efficiently suppress the rapid charge recombination, therefore improving the visible-light-driven activity.

Ni-CeO2is a highly efficient, stable and non-expensive catalyst for methane dry reforming at relative low temperatures (700 K). The active phase of the catalyst consists of small nanoparticles of nickel dispersed on partially reduced ceria. Experiments of ambient pressure XPS indicate that methane dissociates on Ni/CeO2at temperatures as low as 300 K, generating CHxand COxspecies on the surface of the catalyst. Strong metal–support interactions activate Ni for the dissociation of methane. The results of density-functional calculations show a drop in the effective barrier for methane activation from 0.9 eV on Ni(111) to only 0.15 eV on Ni/CeO2−x(111). At 700 K, under methane dry reforming conditions, no signals for adsorbed CHxor C species are detected in the C 1s XPS region. The reforming of methane proceeds in a clean and efficient way. Fil: Liu, Zongyuan. University of New York; Estados Unidos Fil: Grinter, David C.. Brookhaven National Laboratory; Estados Unidos Fil: Lustemberg, Pablo German. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Nguyen Phan, Thuy Duong. Brookhaven National Laboratory; Estados Unidos Fil: Zhou, Yinghui. University of Wyoming; Estados Unidos Fil: Luo, Si. University of New York; Estados Unidos Fil: Waluyo, Iradwikanari. Brookhaven National Laboratory; Estados Unidos Fil: Crumlin, Ethan J.. Lawrence Berkeley National Laboratory; Estados Unidos Fil: Stacchiola, Dario Jose. Brookhaven National Laboratory; Estados Unidos Fil: Zhou, Jing. University of Wyoming; Estados Unidos Fil: Carrasco, Javier. CIC Energig; España Fil: Busnengo, Heriberto Fabio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario. Instituto de Física de Rosario. Universidad Nacional de Rosario. Instituto de Física de Rosario; Argentina Fil: Ganduglia Pirovano, Maria Veronica. Consejo Superior de Investigaciones Científicas; España Fil: Senanayake, Sanjaya D.. Brookhaven National Laboratory; Estados Unidos Fil: Rodriguez, José A.. University of New York; Estados Unidos. Brookhaven National Laboratory; Estados Unidos

The immobilization of miniscule quantities of RuO2 (∼0.1%) onto one-dimensional (1D) TiO2 nanorods (NRs) allows H2 evolution from water under visible light irradiation. Rod-like rutile TiO2 structures, exposing preferentially (110) surfaces, are shown to be critical for the deposition of RuO2 to enable photocatalytic activity in the visible region. The superior performance is rationalized on the basis of fundamental experimental studies and theoretical calculations, demonstrating that RuO2(110) grown as 1D nanowires on rutile TiO2(110), which occurs only at extremely low loads of RuO2, leads to the formation of a heterointerface that efficiently adsorbs visible light. The surface defects, band gap narrowing, visible photoresponse, and favorable upward band bending at the heterointerface drastically facilitate the transfer and separation of photogenerated charge carriers. U.S. Department of Energy DE-SC0012704

In the present study, TiO 2 and graphene oxide (GO)/TiO 2 composite films were simply fabricated by hot-plate spray coating technique. The influences of TiO 2 dimension and GO content on the self-cleaning activity of methylene blue (MB)-stained films were investigated. The matrix of anatase TiO 2 quasi-cubic and octahedral particles in diameter of 6–9 nm (ST film) degraded 80% stained dye, much higher than those either in bigger size (30–50 nm) or in flower morphology due to the nano effect. Moreover, the photocatalytic performance of such nanostructured film was strongly enhanced by the combination with GO sheets. Increasing GO content led to significant enhancement in film transmittance and MB adsorptivity. In the aspect of the self-cleaning activity for MB, the addition of GO up to 1 wt.% showed higher efficiency but excess content led to similar performance in comparison with pure TiO 2 film.

The reduced graphene oxide–titanate (RGO–Ti) hybrids were fabricated by incorporating spherical TiO2 nanoparticles with graphene oxide (GO) layers in aqueous NaOH solution following by the solvothermal treatment. The morphologic evolution of RGO–Ti hybrid by varying alkali-solvothermal temperatures has been first investigated. The titanate nanosheets peeled off, folded and scrolled into tubular structure; and eventually, cracked and destroyed to be ribbon-like shape. The chemical interaction and attachment of low-dimensional titanate onto RGO layers and the reverse order were elucidated by X-ray photoelectron spectra. The hybrids in sheet and tubular titanate structures possessed larger surface areas (>350 m2/g) and higher pore volumes (>1 cm3/g) than the other. The presence of RGO sheets as a two-dimensional (2D) platform for the deposition of titanate significantly promoted much better adsorptivity of dye contaminants compared to pure materials.

Reduced graphene oxide–TiO2 hybrids were successfully prepared by the hydrothermal approach using triethanolamine and acetylacetone as the chelating agents. Without any additive, large aggregated TiO2 clusters were randomly distributed dominantly at the edge and less on the basil plane of coagulated reduced graphene oxide (RGO) layers. The presence of chelating ligands remarkably facilitated the selective growth and regular spread of TiO2 nanocrystals onto individually exfoliated RGO sheet. Such sandwich-like structure with stronger coupling and chemical interaction resulted in the surface area increase, the rearrangement of energy level, the enhanced concentration of oxygen vacancies, leading to much higher adsorbability and photocatalytic degradation of Rhodamine B under both UV and visible irradiations. These RGO–TiO2 hybrid systems are potentially beneficial for widely practical applications in air/water purification, electronic devices, batteries, solar cells or supercapacitors.

Thermally-reduced graphene oxide/TiO2 composites (TRGO/Ti) were prepared by the thermal reduction of graphene oxide/TiO2 composite that was obtained from a simple, environmentally friendly, one-step colloidal blending method. The changes in structural and textural properties as well as their corresponding photocatalytic activities were investigated as a function of calcination temperature. The presence of stacked TRGO sheets significantly retarded both the aggregation and the crystalline phase transformation of TiO2 as increasing the temperature from 200 to 600 °C. TRGO/Ti composites exhibited higher photocatalytic activity for the degradation of methylene blue in comparison with pure TiO2 due to the increase in specific surface area and the formation of π-π conjugations between dye compounds and aromatic regions of TRGO. However, increasing the calcination temperature resulted in the lower photoactivity and slower kinetics, which can be ascribed to the decrease in surface area, the reduction of oxygen vacancies, and the loss of functional groups at the edges or on the basal planes of the TRGO sheets.

Titanium dioxide/graphene oxide composites were prepared using a simple colloidal blending method. Superior adsorption and photocatalysis performance under both UV and visible radiation were achieved in the presence of the composites rather than in pure TiO2. Gradually increasing the content of graphene oxide up to 10 wt% promoted the removal efficiency and correspondingly, facilitated the photodegradation rate of methylene blue. The good photocatalytic performance on the TiO2–graphene oxide composite systems irrespective of light sources could be attributed to a synergy effects including the increase in specific surface area with graphene oxide amount as well as the formation of both π–π conjugations between dye molecules and aromatic rings and the ionic interactions between methylene blue and oxygen-containing functional groups at the edges or on the surfaces of carbon-based nanosheets. Graphene oxide worked as the adsorbent, electron acceptor and photosensitizer to efficiently enhance the dye photodecomposition.

In our previous study, we reported a simple hydrothermal preparation of TiO2 materials using concentrated hydrochloric acid and controlled the morphology of TiO2 by changing the hydrochloric acid amounts. In this study, we employed the TiO2 materials with different morphologies in the photocatalytic degradation of methylene blue. In the photocatalytic results, the TiO2 particles with the prisms and flower-like morphology (DTC-5.0) exhibited the highest photocatalytic activity with kapp = 12.33 × 10−3 min−1 due to the synergetic effect of morphology and mixed-phase crystal of TiO2.

One-dimensional titania nanomaterials were synthesized by soft chemical processes in an alkali medium. The effect of alkali-treatment temperature on the morphology, porosity, and crystalline phase of TiO2 nanomaterials was investigated. Nanotubes having an opening end were observed when aging the sample at 130 °C, while conducting the process at 180 °C resulted in nanoribbons with a high aspect ratio. Post-treatment at 300 °C led to the partial transformation from tubular structures into nanoparticles or ribbons into nanobelts. While the monoclinic sodium hexatitanate and anatase crystal had a tubular structure, nanoribbons and nanobelt TiO2 also showed the presence of hydrogen titanate and sodium trititanate. High surface areas were achieved in as-prepared nanotubes and nanoribbons, 456.5 and 72.1 m2/g, respectively, and a drastic reduction was obtained upon post-treatment at 300 °C to 72.1 and 19.2 m2/g, respectively.

In this study, mesoporous TiO2 crystals were synthesized with a sol–gel process in the presence of hexadecylamine which was used as a structure-directing agent. The neutral template was removed by either supercritical CO2 extraction (SCE) or conventional calcinations to produce mesopores, and the pore characteristics of mesoporous TiO2 were investigated with TGA, XRD, FT-IR, SEM and N2 sorption analysis. The results showed that hexadecylamine was completely combusted by a thermal treatment above 400 °C, whereas SCE successfully removed more than 62% of the surfactant with methanol used as a modifier. However, in contrast to SCE, calcination at 400 °C accompanied a reduction in surface area and pore volume, as well as the partial collapse of the mesostructure. The combination of SCE and subsequent heat treatment at 400 °C not only improved the porosity but also retarded the structure destruction due to much less exothermal behavior. The SCE approach provided mesoporous TiO2 nanocrystals with remarkably high mesoporosity. The SCE technique can result in numerous advantages such as high mesoporosity, short processing time, low energy consumption, and environmental benefit.

TiO 2 films were successfully deposited onto hot quartz substrates by airbrush spraying using an aqueous dispersion. The films consisting of cubic or cauliflower-shaped structures expressed higher photodegradation efficiencies of methylene blue than those with prism-, flower- or fan-blade-shaped morphology due to the difference in the optical band gap energy. The photodegradation obeyed the pseudo-first-order Langmuir–Hinshelwood kinetic model with apparent rate constants ranging from 3.95 × 10 − 3 to 19.38 × 10 − 3 min − 1 based on the film surface morphology.

A TiO 2 nanostructure was synthesized via a simple method using only concentrated hydrochloric acid as the morphological/crystallographic controlling agent. Microscopy images showed that the texture of the TiO 2 powder could be easily engineered and tuned by tailoring the HCl volume, creating cuboid, flower, cauliflower, and ball-shaped particles. Three-dimensional TiO 2 microparticles resulted from the self-assembly of nanostructured sub-units including nanocubes, nanoprisms, and nanorods. The crystalline anatase and rutile phases were also identified depending on the acidic medium. HCl played a key role in orchestrating the structures and morphologies of the TiO 2 nanoscale materials. The phase transformation and morphological changes were strongly related to the crystal growth mechanism of the TiO 2 nanostructure.

The adsorptive removal of benzene from cerium- and lanthanum-doped mesoporous TiO2 adsorbents was performed in a continuous-flow, fixed-bed reactor. The influences of lanthanide content and adsorption temperature were investigated. The adsorption efficiency of benzene was remarkably promoted in the presence of lanthanide. The adsorption capacity for benzene increased with lanthanide dosage, which was attributed to the enhancement in a specific surface area. It was determined that 5 mol% rare earth metal was the optimal amount for the highest benzene-adsorption, irrespective of adsorption temperature. Furthermore, the drastic reduction of adsorption capacities at higher temperature implied that benzene molecules were weakly adsorbed to the adsorbents. Additionally, X-ray photoelectron spectroscopy showed a correlation between the adsorption behavior and the chemical properties of mesostructure materials, typically the interaction of surface hydroxyl groups and the pi-electron of benzene, and the formation of sigma-bonding and d-pi* back-donation between the adsorbent and gaseous adsorbate.

Cerium and lanthanum-incorporated mesoporous TiO 2 with up to 10 mol% metal were synthesized by a sol–gel method using a neutral structure-directing agent. The textural properties and surface structure of samples were investigated by means of N 2 sorption measurements, SEM images and XRD patterns. The doping of lanthanide elements resulted in not only an increase in the surface area, pore volume and average pore size of mesoporous TiO 2 , but also in inhibition of mesostructure collapse and the growth of TiO 2 nanocrystallites. In both cerium and lanthanum-incorporated mesoporous TiO 2 , the fact that only the anatase TiO 2 phase was present indicated substantial incorporation of metal species into the framework or significant dispersion inside the channel. However, Ce and La-incorporated mesoporous TiO 2 differed with regard to the surface chemical states of the metal elements. According to XPS of x Ce-TiO 2 powders, Ti mainly existed in a coordinatively unsaturated titanium (IV) state for low doping amounts, whereas the Ti 3+ state was observed when the Ce/Ti ratio exceeded one. In contrast, no apparent difference in peak intensity and position was seen for lanthanum samples. While only the La 3+ state was found in x La–TiO 2 , Ce 3d spectra showed a mixture of Ce 3+/4+ oxidation states on the surface which led to changes in the chemical environment of oxygen.

Mesoporous molecular sieve SBA-15 modified by titanium has been utilized for removing organic pollutants, such as benzene, from air. Titanium was impregnated inside SBA-15 by wetness impregnation after synthesis of SBA-15 (impregnation method) or was doped into the SBA-15 framework by the direct addition of Ti precursor into the sol during synthesis (doping method). In the breakthrough curves for gas-phase benzene adsorption, Ti addition into SBA-15 resulted in the enhancement of benzene adsorption capacity, depending on Ti loading amounts. An increase in adsorption temperature remarkably reduced the benzene adsorption capacity, indicating that the interaction between benzene and the materials was weak.

In this study, the interaction between surfactant-containing mesoporous silicates and Pb2+ ions in water was investigated through adsorption tests and characterizations. The mesoporous silicates containing dodecylamine as the surfactant showed a Pb2+ adsorption capacity of 198.6 mg g−1, a value obtained from the fit of the adsorption isotherm to the Langmuir model. X-ray diffraction patterns revealed that the intensity of the main peak for the mesoporous silicates decreased after the adsorption test, implying that Pb2+ ions attached to dodecylamine. Scanning electron microscopy images of the adsorbent before and after Pb2+ adsorption indicated that there was no morphological change in the mesoporous silicate. When comparing FT-IR patterns for the adsorbent before and after Pb2+ adsorption, a new IR band was observed at 1394 cm−1 after Pb2+ adsorption, which proved that coordination bonding occurs between Pb2+ ions and amino groups in the surfactant.

Mixed oxide interfaces are critical for delivering active components of demanding catalytic processes such as the photocatalytic splitting of water. We have studied CeOx–TiO2 catalysts with low ceria loadings of 1, 3, and 6 wt % that were prepared with wet impregnation methods to favor a strong interaction between CeOx and TiO2. In these materials the interfaces between CeOx–TiO2 have been sequentially loaded (1%, 3%, and 6%), with and without Pt (0.5 wt %). The structure and properties of the catalysts were characterized using several X-ray and electron based techniques including XRD, XPS, UPS, NEXAFS, UV–vis, and HR-STEM/STEM-EELS to unravel the local morphology, bulk structure, surface states, and electronic structure. The combination of all these techniques allows us to analyze in a systematic way the complete structural and electronic properties that prevail at the CeOx–TiO2 interface. Fluorite structured nanocrystallites of ceria on anatase-structured titania were identified by both XRD and NEXAFS. A sequential increase of the CeOx loading led to the formation of clusters, then plates, and finally nanoparticles in a hierarchical manner on the TiO2 support. The electronic structures of these catalysts indicate that the interaction between TiO2 and CeO2 is closely related to the local morphology of nanostructured CeO2. Ce3+ cations were detected at the surface of CeO2 and at the interface of the two oxides. In addition, the titania is perturbed by the interaction with ceria and also with Pt. The photocatalytic activity for the splitting of H2O using UV light was measured for these materials and correlated with our understanding of the electronic and structural properties. Optimal catalytic performance and photoresponse results were found for the 1 wt % CeOx–TiO2 catalyst where low dimensional geometry of the ceria provided ideal electronic and geometrical properties. The structural and electronic properties of the interface were critical for the photocatalytic performance of this mixed-oxide nanocatalyst system., The research carried out in this manuscript was performed at Brookhaven National Laboratory, supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, and Catalysis Science Program under Contract DE-SC0012704. L.B. also acknowledges financial support from the JAE-CSIC grant program