Photocatalytic reduction of CO<Subscript>2</Subscript> with H<Subscript>2</Subscript>O over modified TiO<Subscript>2</Subscript> nanofibers: Understanding the reduction pathway

Nanosized metal (Pt or Pd)-decorated TiO₂ nanofibers (NFs) were synthesized by a wet impregnation method. CdSe quantum dots (QDs) were then anchored onto the metal-decorated TiO₂ NFs. The photocatalytic performance of these catalysts was tested for activation and reduction of CO₂ under UV-B light. Gas chromatographic analysis indicated the formation of methanol, formic acid, and methyl formate as the primary products. In the absence of CdSe QDs, Pd-decorated TiO₂ NFs were found to exhibit enhanced performance compared to Pt-decorated TiO₂ NFs for methanol production. However, in the presence of CdSe, Pt-decorated TiO₂ NFs exhibited higher selectivity for methanol, typically producing ～90 ppmg^?1·h^?1 methanol. The CO₂ photoreduction mechanism is proposed to take place via a hydrogenation pathway from first principles calculations, which complement the experimental observations.

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Systematic investigation of the effect of oxygen mobility on CO oxidation over AgPt nanoshells supported on CeO<Subscript>2</Subscript>, TiO<Subscript>2</Subscript> and Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Here, we have systematically investigated how the nature of the support influenced the oxygen mobility and activities in catalysts comprised of AgPt nanoshells deposited over inorganic oxides. We first synthesized AgPt nanoshells by galvanic replacement reaction between Ag nanospheres and PtCl₆ ^2? _(aq) combined with Pt reduction using hydroquinone as an auxiliary reducing agent. The nanoshells were then supported over TiO₂, Al₂O₃ and CeO₂. Through this methodology, we prepared materials with similar metallic nanoparticle AgPt compositions (~0.99 wt% Pt), sizes (43 ± 2 nm diameter), spherical shapes, surface morphologies, number of active sites \( (\sim4.5\;\upmu{\text{mol}}\;{\text{g}}_{{{\text{cat}} .}}^{ - 1} ) \) and uniform distribution over the supports, differing only in terms of the nature of the support. The oxide reduction temperature, its capability of re-oxidation and the presence of oxygen mobility were strongly dependent on the metal–support interaction between AgPt nanoshells and oxide supports. These properties have significantly influenced their catalytic performances toward the CO oxidation. At 230 °C, the CO oxidation TOF was 40.4 ± 0.4, 6.9 ± 1, 1.4 ± 0.8 min^?1 for AgPt/CeO₂, AgPt/TiO₂, AgPt/Al₂O₃, respectively. These differences were attributed to the concentration of oxygen vacancies in each catalyst, which presented exactly the same trend as that of the catalytic activities. Our results may have important contributions to the design of highly active metal oxide-based catalysts toward gas-phase oxidation transformations.     

Ultrasonic-assisted synthesis of amorphous Bi<Subscript>2</Subscript>S<Subscript>3</Subscript> coupled (BiO)<Subscript>2</Subscript>CO<Subscript>3</Subscript> catalyst with improved visible light-responsive photocatalytic activity

A series of Bi₂S₃/(BiO)₂CO₃ composite photocatalysts with different loadings of amorphous Bi₂S₃ were successfully synthesized through an ultrasonic-assisted ion-exchange reaction between thioacetamide (CH₃CSNH₂) and (BiO)₂CO₃, and characterized by XRD, XPS, BET, EELS, EDX, SEM, TEM/HRTEM, UV–Vis, and photoluminescence (PL) techniques. The results of TEM/HRTEM, EELS, and EDX indicate that the composite catalyst Bi₂S₃/(BiO)₂CO₃ has been successfully synthesized with the deposited Bi₂S₃ present in amorphous state on the surface of (BiO)₂CO₃. The activities of the catalysts for RhB degradation under visible light show that the catalyst prepared under ultrasonic is more active than the one synthesized without ultrasonic. The optimized sample Bi₂S₃/(BiO)₂CO₃ (U5.0) exhibits a much higher activity, about 4.8 times to that of pure (BiO)₂CO₃. Based upon the band structures of Bi₂S₃/(BiO)₂CO₃, it is deduced that the migration of the visible light-induced electrons from the conduction band of Bi₂S₃ to that of (BiO)₂CO₃ should have facilitated the separation of photogenerated carriers, as confirmed by the suppressed photoluminescence spectra. Using different scavengers, the ·O₂ ^? and holes are clearly identified as the main oxidative species for RhB photodegradation. In light of these observations, a potential photocatalytic mechanism of RhB degradation over Bi₂S₃/(BiO)₂CO₃ is proposed.     

Conductivity of Sm<Subscript>2</Subscript>TiO<Subscript>5</Subscript> and Sm<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

The oxygen-ion conductivity of porous materials, the coarse-grained pyrochlore-like Sm₂Ti₂O₇ and fine-grained Sm₂TiO₅ compounds, produced by mechanical activation of initial oxides is studied at 400–1000 °C. The Sm₂TiO₅ samples contain ～15 wt % of the nanosized pyrochlore-like Sm₂TiO₅ phase in addition to the rhombic phase. As determined by impedance spectroscopy, the ionic conductivities of Sm₂TiO₅ and Sm₂Ti₂O₇ at 1000°C are 1.3 × 10^?3 and 1.8 × 10^?4 S cm^?1, and the activation energies of the bulk and grainboundary conductivities of the materials are 1.04 and 1.24 eV for Sm₂TiO₅ and 1.69 and 1.80 eV for Sm₂Ti₂O₇.     

Ni-doped ZnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> atomic layers to boost the selectivity in solar-driven reduction of CO<Subscript>2</Subscript>

Regulating the selectivity of CO₂ photoreduction is particularly challenging. Herein, we propose ideal models of atomic layers with/without element doping to investigate the effect of doping engineering to tune the selectivity of CO₂ photoreduction. Prototypical ZnCo₂O₄ atomic layers with/without Ni-doping were first synthesized. Density functional theory calculations reveal that introducing Ni atoms creates several new energy levels and increases the density-of-states at the conduction band minimum. Synchrotron radiation photoemission spectroscopy demonstrates that the band structures are suitable for CO₂ photoreduction, while the surface photovoltage spectra demonstrate that Ni doping increases the carrier separation efficiency. In situ diffuse reflectance Fourier transform infrared spectra disclose that the CO₂^·? radical is the main intermediate, while temperature-programed desorption curves reveal that the ZnCo₂O₄ atomic layers with/without Ni doping favor the respective CO and CH₄ desorption. The Ni-doped ZnCo₂O₄ atomic layers exhibit a 3.5-time higher CO selectivity than the ZnCo₂O₄ atomic layers. This work establishes a clear correlation between elemental doping and selectivity regulation for CO₂ photoreduction, opening new possibilities for tailoring solar-driven photocatalytic behaviors.

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Scalable fabrication of SnO<Subscript>2</Subscript>/eo-GO nanocomposites for the photoreduction of CO<Subscript>2</Subscript> to CH<Subscript>4</Subscript>

Artificial photosynthesis uses a catalyst to convert CO₂ into valuable hydrocarbon products by cleaving the C=O bond. However, this technology is strongly limited by two issues, namely insufficient catalytic efficiency and complicated catalyst-fabrication processes. Herein, we report the development of a novel spray-drying photocatalyst-engineering process that addresses these two issues. Through one-step spray drying, with a residence time of 1.5 s, nanocomposites composed of tin oxide (SnO₂) nanoparticles and edge-oxidized graphene oxide (eo-GO) sheets were fabricated without post-treatment. These nanocomposites exhibited 28-fold and five-fold enhancements in photocatalytic efficiency during CO₂ reduction compared to SnO₂ and commercialized TiO₂ (P25), respectively, after irradiation with simulated sunlight for 4 h. This scalable approach, based on short residence times and facile equipment setup, promotes the practical application of artificial photosynthesis through the potential mass production of efficient photocatalysts.

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Redox processes in fine-particle TiO<Subscript>2</Subscript>-Cr<Subscript>2</Subscript>O<Subscript>3</Subscript> oxides

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⁺ is reduced to Cr³⁺. The redox process is due to partial surface hydration of the Cr₂O₃ and TiO₂ crystallites.     

Synthesis of In(OH)<Subscript>3</Subscript> and In<Subscript>2</Subscript>O<Subscript>3</Subscript> nanomaterials incorporating Au

In(OH)₃ and In₂O₃ nanocrystals of rectangular shape and incorporating Au were synthesized with a hydrothermal process and thermal decomposition. Powder X-ray diffraction, electron microscopy (SEM, TEM), and energy-dispersive spectroscopy studies reveal that elemental Au nanoparticles are dispersed on the surface of In(OH)₃ rectangular nanocrystals and incorporated into In₂O₃ nanoporous particles. UV–vis spectral measurements reveal a surface-enchanced plasma band near λ ~532 nm for both Au-incorporating nanomaterials. The BET surface areas of Au-incorporating In(OH)₃ and In₂O₃ are 26.2 and 35.5 m²/g, respectively. The incorporation of elemental Au in In(OH)₃ and In₂O₃ nanomaterials is attractive for sensor, catalyst and solar-cell applications.     

Co-production of power and urea from coal with CO<Subscript>2</Subscript> capture: performance assessment

Coal-based power plants are largest emitter of CO₂ as a single sector. To use fossil fuels (including coal), CO₂ capture and storage is a visible option. But large energy requirement for this process and risk associated with storage of CO₂ demand alternative solutions including recycling of captured CO₂. In this paper, a co-production of power and urea is proposed using coal with captured CO₂. Detailed ASPEN Plus^® model is developed for this plant. As shift reaction for producing H₂ has significant effect on output parameters, analysis is done for two different values of shift reaction, i.e., 90 and 95 % conversion. Plant consumes substantial auxiliary power (~19 % for the base case). Auxiliary power becomes a minimum for about 25 % captured CO₂ utilization for 95 % shift conversion. An economy factor is also defined to estimate the economic advantage of utilizing captured CO₂. Results show that economic advantage is obtained for CO₂ utilization beyond ~5 % for 95 % water gas shift reaction and it is beyond ~10 % for a 90 % shift reaction.     

Effect of Mn<Superscript>2+</Superscript> doping on the temperature coefficient of capacitance of TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>-doped BaTiO<Subscript>3</Subscript> ceramics

The effect of Mn²⁺ on the temperature coefficient of capacitance (TCC) of TiO₂/SiO₂-doped BaTiO₃ ceramics has been investigated. The experiment has shown that the high temperature peak of TCC exhibited a continuous enhancement when Mn²⁺ concentration increased and X8R specification was gradually met. The secondary phase Ba₂TiSi₂O₈ was found in all samples. SEM and XRD analyses have proved that Mn²⁺ could depress the crystallization of TiO₂/SiO₂ in BaTiO₃ ceramics. The microstrain study through MAUD analysis depicted that the high temperature peak of TCC was dependent on the microstrain of samples to a certain extent. The Mn²⁺ could be a useful dopant for ameliorating the TCC of TiO₂/SiO₂-doped BaTiO₃ ceramics. The text was submitted by the authors in English.     

Synthesis and crystal structure of [UO<Subscript>2</Subscript>(OH)(CO(NH<Subscript>2</Subscript>)<Subscript>2</Subscript>)<Subscript>3</Subscript>]<Subscript>2</Subscript>(ClO<Subscript>4</Subscript>)<Subscript>2</Subscript>

The complex [UO₂(OH)(CO(NH₂)₂)₃]₂(ClO₄)₂ (I) was synthesized. A single crystal X-ray diffraction study showed that compound I crystallizes in the triclinic system with the unit cell parameters a = 7.1410(2), b = 10.1097(2), c = 11.0240(4) Å, α = 104.648(1)°, β = 103.088(1)°, γ = 108.549(1)°, space group \(P\bar 1\), Z = 1, R = 0.0193. The uranium-containing structural units of the crystals are binuclear groups [UO₂(OH)· (CO(NH₂)₂)₃] ₂ ²⁺ belonging to crystal-chemical group AM²M ₃ ¹ [A = UO ₂ ²⁺ , M² = OH^?, M¹ = CO(NH₂)₂] of uranyl complexes. The crystal-chemical analysis of nonvalent interactions using the method of molecular Voronoi-Dirichlet polyhedra was performed, and the IR spectra of crystals of I were analyzed.     

Photocatalytic CO<Subscript>2</Subscript> reduction highly enhanced by oxygen vacancies on Pt-nanoparticle-dispersed gallium oxide

Photocatalytic CO₂ reduction on metal-oxide-based catalysts is promising for solving the energy and environmental crises faced by mankind. The oxygen vacancy (V _o) on metal oxides is expected to be a key factor affecting the efficiency of photocatalytic CO₂ reduction on metal-oxide-based catalysts. Yet, to date, the question of how an V _o influences photocatalytic CO₂ reduction is still unanswered. Herein, we report that, on V _o-rich gallium oxide coated with Pt nanoparticles (V _o-rich Pt/Ga₂O₃), CO₂ is photocatalytically reduced to CO, with a highly enhanced CO evolution rate (21.0 μmol·h^?1) compared to those on V _o-poor Pt/Ga₂O₃ (3.9 μmol·h^?1) and Pt/TiO₂(P25) (6.7 μmol·h^?1). We demonstrate that the V _o leads to improved CO₂ adsorption and separation of the photoinduced charges on Pt/Ga₂O₃, thus enhancing the photocatalytic activity of Pt/Ga₂O₃. Rational fabrication of an V _o is thereby an attractive strategy for developing efficient catalysts for photocatalytic CO₂ reduction.

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Preparation of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript>/TiO<Subscript>2</Subscript> bio-ceramic on titanium substrate by micro-arc oxidation

K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings are prepared successfully by micro-arc oxidation on titanium substrate in pure KOH electrolyte solution. The coating is prepared at various applied current density (150–500 mA/cm²) and in KOH electrolyte with different concentrations (0.5–1.2 mol/L). The composition and surface morphologies of coatings are strongly dependent on the applied current density and the electrolyte concentration. On the condition of lower current density and electrolyte concentration, K₂Ti₆O₁₃ phase almost cannot be formed. The phase is mainly composed of rutile and K₂Ti₆O₁₃ with increasing current density and electrolyte concentration. The surface morphologies are composed of whiskers and porous structures. The ability of K₂Ti₆O₁₃/TiO₂ bio-ceramic films inducing apatite deposition is evaluated by soaking it in biological model fluids. The results show the K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings possess excellent capability of inducing bone-like apatite to deposit.     

Fabrication and properties of SiO<Subscript>2</Subscript>/TiO<Subscript>2</Subscript> composites

Composites in the form of precipitated powders, hybrid xerogels, and SiO₂ core/TiO₂ shell particles have been produced via hydrolysis of precursors (alkoxides and inorganic derivatives of titanium and silicon) and have been characterized by differential thermal analysis, X-ray diffraction, adsorption measurements, and macroelectrophoresis. The results demonstrate that heat treatment of the composites leads to crystallization of the titanium-containing component and, accordingly, reduces their specific surface area. Hydrothermal treatment enables the fabrication of materials in which TiO₂ nanocrystals are evenly distributed over an amorphous SiO₂ matrix.     

<Emphasis Type="Italic">In situ</Emphasis> loading of Cu<Subscript>2</Subscript>O nanoparticles on a hydroxyl group rich TiO<Subscript>2</Subscript> precursor as an excellent catalyst for the Ullmann reaction

An in situ method has been used to load Cu₂O nanoparticles on the surface of a hydroxyl group rich TiO₂ precursor. Cu₂O nanoparticles are formed by in situ reduction of Cu(OH)₂ with Sn²⁺ ions linked to the surface of the TiO₂ precursor. The initial Cu₂O nanoparticles serve as seeds for subsequent particle growth. The resulting Cu₂O nanoparticles are evenly dispersed on the surface of the TiO₂ precursor, and are heat and air stable. The as-prepared composite is an excellent catalyst for Ullmann type cross coupling reactions of aryl halides with phenol. The composite catalyst also showed good stability, remaining highly active after five consecutive runs.     

Transparent TiO<Subscript>2</Subscript> sol nanocrystallites mediated homogeneous-like photocatalytic reaction and hydrosol recycling process

Lanthanide metal europium ion modified titanium dioxide (Eu³⁺-TiO₂) sol nanocrystallites was fabricated by the wet-chemical coprecipitation-peptization method under low temperature (80°C). Eu³⁺-TiO₂ sol particles show the anatase-rutile mixed crystal structure and the narrow particles distribution with the mean size of 6 nm. Comparing with pure TiO₂ sol, Eu³⁺-TiO₂ sol possesses smaller primary particle size and better particulate dispersion. Transparent sol catalyst could conduct the homogeneous-like photocatalysis rather than heterogeneous one for organic pollutants degradation reaction. This crystallized Eu³⁺-TiO₂ sol particles exhibits better interfacial adsorption effect and electron-transfer efficiency between dye molecules and catalyst particles, which contributed to stronger photocurrent response in the photoelectrochemical process. For photocatalytic degradation of azo dye, fresh Eu³⁺-TiO₂ sol catalyst showed higher photocatalytic activity and photomineralization capability than P25 TiO₂ powder and pure TiO₂ sol under either ultraviolet light (UV) or visible light (Vis) irradiation. The recycling application of the crystallized sol catalysts was well attempted by taking advantage of its sensitivity to the medium pH value. Although Eu³⁺-TiO₂ recycle sol had better dispersion effect and smaller secondary particles size, the absolute recovery efficiency of Eu³⁺-TiO₂ sol particles was obvious inferior to TiO₂ sol due to its poor flocculation-separation effect. For continuous recycle use of hydrosol photocatalysis, pure TiO₂ sol demonstrates the better total discolouration efficiency than Eu³⁺-TiO₂ sol although instinctive photochemical reactivity of fresh TiO₂ was inferior to fresh Eu³⁺-TiO₂.     

TiO<Subscript>2</Subscript> type influences fibronectin adsorption

Human fibronectin (FN) plays a key role in the biointegration of implants as the success depends on adsorption of proteins like FN [1]. Indeed FN can be an intermediary between the biomaterial surface and cells. The adsorption of human fibronectin (FN) on commercially pure titanium with a titanium oxide layer formed in a H₂O₂ solution (TiO₂ cp) and TiO₂ sputtered on Si (TiO₂ sp) was studied. Adsorption isotherms and the work of adhesion were assessed by wettability studies, X-ray photoelectron spectroscopy (XPS), and by radiolabelling of FN with ¹²⁵I, ¹²⁵I-FN. Exchangeability of bound FN by free FN, was also evaluated by the radiolabelling technique. Contact angle determinations have shown that FN displays higher affinity for the TiO₂ cp surface than for the TiO₂ sp. As expected from the surface free energy values, the work of adhesion of FN is higher for the TiO₂ cp substrate, the more hydrophilic one, and lower for the TiO₂ sp substrate, the more hydrophobic one. The adsorption isotherms were evaluated by two different techniques: radiolabelling of FN (¹²⁵I-FN) and XPS. TiO₂ cp adsorbs more FN than the TiO₂ sp surfaces as shown by the radiolabelling data. FN molecules are also more strongly attached to the former surface as indicated by the work of adhesion and by the exchangeability studies. Results using ¹²⁵I-FN also suggests that FN adsorbs as a multilayer for FN concentrations in solution higher than 100 μg/mL.     

TiO<Subscript>2</Subscript> crystalline structure and electrochemical performance in two-ply yarn CNT/TiO<Subscript>2</Subscript> asymmetric supercapacitors

Solid-state flexible energy storage devices play a crucial role in the development of wearable electronic textiles. In this study, we fabricated flexible asymmetric two-ply yarn supercapacitors from carbon nanotube yarns and surface-oxidized titanium filament. The crystalline structure of the TiO₂ surface layer can be adjusted to amorphous, anatase and rutile states by altering the annealing temperature. The titanium filament with a rutile TiO₂ surface layer produced at high annealing temperature showed far superior electrochemical performance over the filaments with amorphous and anatase TiO₂ surface layers. The as-prepared asymmetric two-ply yarn supercapacitors in aqueous gel electrolyte can achieve a durable operating voltage up to 1.4 V, with a maximum energy density of 11.7 Wh kg^?1 and a maximum power density of 2060 W kg^?1. The asymmetric two-ply yarn supercapacitors exhibited excellent flexibility and cycling stability over 1200 cycles at straight, twisted and bent states.     

Ultraviolet upconversion luminescence in Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Yb<Superscript>3+</Superscript>,Tm<Superscript>3+</Superscript> nanocrystals and its application in photocatalysis

Infrared-to-ultraviolet upconversion luminescence agent Y₂O₃:Yb³⁺,Tm³⁺ was prepared by a combustion method using citrate as a fuel/reductant. The prepared sample was characterized by X-ray diffraction, SEM, and fluorescence spectrophotometer. Two unusual ¹I₆ → ³H₆ (~297 nm) and ¹D₂ → ³H₆ (~363 nm) emissions from Tm³⁺ ions were observed at room temperature under 980-nm laser excitation. The change of upconversion emission intensity depending on the Yb³⁺ concentrations was discussed. The results showed that modest Yb³⁺ doping could make the upconversion emission of Tm³⁺ intense, and high Yb³⁺ concentrations might lead to fluorescence quenching. Moreover, the influence of ultraviolet upconversion luminescence on the photodegradation of methyl orange aqueous solution under solar light irradiation in the presence of TiO₂ catalyst doped with Y₂O₃:Yb³⁺,Tm³⁺ was also investigated. It was concluded from the experiment of this study that TiO₂/Y₂O₃:Yb³⁺,Tm³⁺ composite had higher photocatalytic activity than pure TiO₂ under solar light. This study would make TiO₂ utilize sunlight more efficiently and accelerate the practical application of photocatalytic technology in water treatment region.     

Effect of Au ions on structural,optical, magnetic,dielectric, and antibacterial properties of TiO2 dip-coated thin films

Physical properties of the TiO₂ and Au-doped TiO₂ films fabricated by sol–gel dip-coating route are investigated. The diffraction peaks of XRD spectra confirmed the formation of anatase phase. Crystallite size was found to be decreased by increasing dopant concentration from 12.02 to 10.10 nm. All the thin films annealed in air exhibit significant room-temperature ferromagnetism displaying anatase phase that can be employed in spintronic devices. The saturation magnetization increases from 6.8 to 10.35 emu/cm³ with the increase in Au concentration. The coercivity values vary between 360.82 and 478.515 Oe and remnant magnetization ranges between 0.46 and 0.71 emu/cm³. Dielectric parameters obeyed Maxwell-Wagner model and Koop’s theory and were explained by hopping mechanism. Small values of dielectric constant made them favorable for high-frequency devices. The band gaps of the undoped and Au-doped TiO₂ thin films is in the range 3.5 to 3.38 eV, which are lesser than those of reported pure TiO₂ (3.7 eV) that is favorable for enhancing solar cells efficiency. Au-doped TiO₂ leads to an optimum antimicrobial agent. The photocatalysts having 5 wt% Au exhibit the highest photoactivities. The degradation of methylene blue under sunlight made them promising materials for water treatment.