In this paper, we use density functional theory corrected for on-site Coulomb interactions (DFT + U) and hybrid DFT (HSE06 functional) to study the defects formed when the ceria (110) surface is ...doped with a series of trivalent dopants, namely, Al3+, Sc3+, Y3+, and In3+. Using the hybrid DFT HSE06 exchange-correlation functional as a benchmark, we show that doping the (110) surface with a single trivalent ion leads to formation of a localized MCe / + OO • (M = the 3+ dopant), O− hole state, confirming the description found with DFT + U. We use DFT + U to investigate the energetics of dopant compensation through formation of the 2MCe ′ +VO ·· defect, that is, compensation of two dopants with an oxygen vacancy. In conjunction with earlier work on La-doped CeO2, we find that the stability of the compensating anion vacancy depends on the dopant ionic radius. For Al3+, which has the smallest ionic radius, and Sc3+ and In3+, with intermediate ionic radii, formation of a compensating oxygen vacancy is stable. On the other hand, the Y3+ dopant, with an ionic radius close to that of Ce4+, shows a positive anion vacancy formation energy, as does La3+, which is larger than Ce4+ ( J. Phys.: Condens. Matter 2010, 20, 135004 ). When considering the resulting electronic structure, in Al3+ doping, oxygen hole compensation is found. However, Sc3+, In3+, and Y3+ show the formation of a reduced Ce3+ cation and an uncompensated oxygen hole, similar to La3+. These results suggest that the ionic radius of trivalent dopants strongly influences the final defect formed when doping ceria with 3+ cations. In light of these findings, experimental investigations of these systems will be welcome.
Doping of metal oxides can be used to modify their reactivity with respect to oxygen vacancy formation and molecular adsorption, key reactions in the applications of oxides in catalysis. In this ...article, we study the effects of Ti, Zr, and Hf doping on CO adsorption on the (110) surface of cerium dioxide and NO adsorption at the same surface with oxygen vacancy defects, using density functional theory, corrected for on-site Coulomb interactions (DFT+U). The dopants substitute a Ce atom in the surface layer, resulting in strong structural distortions to the surface and smaller oxygen vacancy formation energies compared to the undoped surface. On the doped surfaces, CO adsorbs much more strongly compared to the undoped surface, forming a structure similar to a carbonate unit (CO3)2−, in which a CO2 unit points away from the surface. The presence of a carbonate is confirmed by analysis of the electronic structure and vibrational frequencies. On the defective surface with one oxygen vacancy, NO adsorption is weak, so that NO sits above a defective surface. Consistent with the literature, adsorption of two NO molecules at neighboring vacancy sites results in strong adsorption and formation of a NN-like bond, as well as lengthening of the NO bonds. However, the energetics of this process at the doped surfaces are not as favorable as at the undoped surface. Computed energetics for CO oxidation and NO reduction show that improving the oxidative power of the oxide makes molecular reduction less favorable.
In recent experiments Tada et al. have shown that TiO(2) surfaces modified with iron oxide display visible light photocatalytic activity. This paper presents first principles simulations of iron ...oxide clusters adsorbed at the rutile TiO(2) (110) surface to elucidate the origin of the visible light photocatalytic activity of iron oxide modified TiO(2). Small iron oxide clusters adsorb at rutile (110) surface and their presence shifts the valence band so that the band gap of the composite is narrowed towards the visible, thus confirming the origin of the visible light activity of this composite material. The presence of iron oxide at the TiO(2) surface leads to charge separation, which is the origin of enhanced photocatalytic efficiency, consistent with experimental photoluminesence and photocurrent data. Surface modification of a metal oxide is thus an interesting route in the development of visible light photocatalytic materials.
The capture and conversion of CO2 are of significant importance in enabling the production of sustainable fuels, contributing to alleviating greenhouse gas emissions. While there are a number of key ...steps required to convert CO2, the initial step of adsorption and activation by the catalyst is critical. Well-known metal oxides such as oxidized TiO2 or CeO2 are unable to promote this step. In addressing this difficult problem, a recent experimental work shows the potential for bismuth-containing materials to adsorb and convert CO2, the origin of which is attributed to the role of the bismuth lone pair. In this paper, we present density functional theory (DFT) simulations of enhanced CO2 adsorption on heterostructures composed of extended TiO2 rutile (110) and anatase (101) surfaces modified with Bi2O3 nanoclusters, highlighting in particular the role of heterostructure reduction in activating CO2. These heterostructures show low coordinated Bi sites in the nanoclusters and a valence band edge that is dominated by Bi–O states, typical of the Bi3+ lone pair. The reduction of Bi2O3–TiO2 heterostructures can be facile and produces reduced Bi2+ and Ti3+ species. The interaction of CO2 with this electron-rich, reduced system can produce CO directly, reoxidizing the heterostructure, or form an activated carboxyl species (CO2 –) through electron transfer from the reduced heterostructure to CO2. The oxidized Bi2O3–TiO2 heterostructures can adsorb CO2 in carbonate-like adsorption modes, with moderately strong adsorption energies. The hydrogenation of the nanocluster and migration to adsorbed CO2 is feasible with H-migration barriers less than 0.7 eV, but this forms a stable COOH intermediate rather than breaking C–O bonds or producing formate. These results highlight that a reducible metal oxide heterostructure composed of a semiconducting metal oxide modified with suitable metal oxide nanoclusters can activate CO2, potentially overcoming the difficulties associated with the difficult first step in CO2 conversion.
In contrast to studies on class I histone deacetylase (HDAC) inhibitors, the elucidation of the molecular mechanisms and therapeutic potential of class IIa HDACs (HDAC4, HDAC5, HDAC7 and HDAC9) is ...impaired by the lack of potent and selective chemical probes. Here we report the discovery of inhibitors that fill this void with an unprecedented metal-binding group, trifluoromethyloxadiazole (TFMO), which circumvents the selectivity and pharmacologic liabilities of hydroxamates. We confirm direct metal binding of the TFMO through crystallographic approaches and use chemoproteomics to demonstrate the superior selectivity of the TFMO series relative to a hydroxamate-substituted analog. We further apply these tool compounds to reveal gene regulation dependent on the catalytic active site of class IIa HDACs. The discovery of these inhibitors challenges the design process for targeting metalloenzymes through a chelating metal-binding group and suggests therapeutic potential for class IIa HDAC enzyme blockers distinct in mechanism and application compared to current HDAC inhibitors.
We studied the reduction of CuO(111) surface using density functional theory (DFT) with the generalized gradient approximation corrected for on-site Coulomb interactions (GGA + U) and screened hybrid ...DFT (HSE06 functional). The surface reduction process by oxygen vacancy formation and H2 adsorption on the CuO(111) surface is investigated as two different reduction mechanisms. It is found that both GGA + U and HSE06 predict the same trend in the relative stability of oxygen vacancies. We found that loss of the subsurface oxygen is initially thermodynamically favourable. As the oxygen vacancy concentration increases, mixture of subsurface and surface vacancies is energetically preferred over full reduction of the surface or subsurface monolayer. The reduction of Cu(2+) to Cu(+) is found to be more favourable than that of Cu(+) to Cu(0) in the most stable vacancy structures at all concentrations. Consistent with the oxygen vacancy calculations, H2 adsorption occurs initially on under-coordinated surface oxygen. Water molecules are formed upon the adsorption of H2 and this gives a mechanism for H2 reduction of CuO to Cu. Ab initio atomistic thermodynamics shows that reducing CuO to metallic Cu at the surface is more energetically difficult than in the bulk so that the surface oxide protects the bulk from reduction. Using H2 as the reducing agent, it is found that the CuO surface is reduced to Cu2O at approximately 360 K and that complete reduction from Cu2O to metallic Cu occurs at 780 K.
Although the main focus of immuno-oncology has been manipulating the adaptive immune system, harnessing both the innate and adaptive arms of the immune system might produce superior tumour reduction ...and elimination. Tumour-associated macrophages often have net pro-tumour effects, but their embedded location and their untapped potential provide impetus to discover strategies to turn them against tumours. Strategies that deplete (anti-CSF-1 antibodies and CSF-1R inhibition) or stimulate (agonistic anti-CD40 or inhibitory anti-CD47 antibodies) tumour-associated macrophages have had some success. We hypothesized that pharmacologic modulation of macrophage phenotype could produce an anti-tumour effect. We previously reported that a first-in-class selective class IIa histone deacetylase (HDAC) inhibitor, TMP195, influenced human monocyte responses to the colony-stimulating factors CSF-1 and CSF-2 in vitro. Here, we utilize a macrophage-dependent autochthonous mouse model of breast cancer to demonstrate that in vivo TMP195 treatment alters the tumour microenvironment and reduces tumour burden and pulmonary metastases by modulating macrophage phenotypes. TMP195 induces the recruitment and differentiation of highly phagocytic and stimulatory macrophages within tumours. Furthermore, combining TMP195 with chemotherapy regimens or T-cell checkpoint blockade in this model significantly enhances the durability of tumour reduction. These data introduce class IIa HDAC inhibition as a means to harness the anti-tumour potential of macrophages to enhance cancer therapy.
Surface modification of TiO2 with metal oxide nanoclusters is a strategy for the development of new photocatalyst materials. We have studied modification of TiO2 rutile (110) with ceria nanoclusters ...using density functional theory corrected for on-site Coulomb interactions (DFT+U). We focus on the impact of surface modification on key properties governing the performance of photocatalysts, including light absorption, photoexcited charge carrier separation, reducibility and surface reactivity. Our results show that adsorption of the CeO2 nanoclusters, with compositions Ce5O10 and Ce6O12, is favourable at the rutile (110) surface and that the nanocluster–surface composites favour non-stoichiometry in the adsorbed ceria so that reduced Ce ions will be present in the ground state. The presence of reduced Ce ions and low coordinated O sites in the nanocluster lead to the emergence of energy states in the energy gap of the TiO2 host, which potentially enhance the visible light response. We show, through an examination of oxygen vacancy formation, that the composite systems are reducible with moderate energy costs. Photoexcited electrons and holes localize on Ce and O sites of the supported nanoclusters. The interaction of CO2 and H2O is favourable at multiple sites of the reduced CeOx–TiO2 composite surfaces. CO2 adsorbs and activates, while H2O spontaneously dissociates at oxygen vacancy sites.
The development of environmental catalysts is an urgent subject to be tackled by scientists and engineers all over the world due to the borderless nature of environmental pollution. We named the ...catalyst enabling the decomposition of the pollutants by effectively utilizing the solar energy from ultraviolet to infrared as “solar environmental catalysts”. This Feature Article reviews the recent studies on a novel class of solar environmental catalysts consisting of TiO2 and molecular scale oxides of 3d metals and for comparison d10 (Sn) on the surface (MOs/TiO2). The TiO2 surface modification with MO clusters by the chemisorption–calcination cycle (CCC) technique presents novel band engineering for finely tuning the top of the valence band, while the unique physicochemical and electronic properties of MOs/TiO2 give rise to the outstanding photo- and thermocatalytic activities for the decomposition of organic pollutants. In the first part following the Introduction, the CCC technique for forming extremely small MO clusters on TiO2, the structures, physicochemical properties, and electronic structures of MOs/TiO2 are described. The second part deals with their thermo- and photocatalytic activities for the degradation of model organic pollutants and the essential action mechanisms of the MO clusters. The combination of experiments and first-principles density functional theory simulations shows that Co2O3/TiO2 can be a prototype of the solar environmental catalyst with high levels of photo(UV and visible)- and thermocatalytic activities.
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