Domain-Confined Multiple Collision Enhanced Catalytic Soot Combustion over a Fe₂O₃/TiO₂–Nanotube Array Catalyst Prepared by Light-Assisted Cyclic Magnetic Adsorption

The ordered TiO₂ nanotube array (NA)-supported ferric oxide nanoparticles with adjustable content and controllable particulate size were prepared through a facile light-assisted cyclic magnetic adsorption (LCMA) method. Multiple techniques such as SEM, TEM, EDX, XRD, EXAFS, XPS, UV–vis absorption, and TG were employed to study the structure and properties of the catalysts. The influencing factors upon soot combustion including the annealing temperature and loading of the active component in Fe₂O₃/TiO₂–NA were also investigated. An obvious confinement effect on the catalytic combustion of soot was observed for the ferric oxide nanoparticles anchored inside TiO₂ nanotubes. On the basis of the catalytic performance and characterization results, a novel domain-confined multiple collision enhanced soot combustion mechanism was proposed to account for the observed confinement effect. The design strategy for such nanotube array catalysts with domain-confined macroporous structure is meaningful and could be well-referenced for the development of other advanced soot combustion catalysts

States and Function of Potassium Carbonate Species in the Polytitanate Nanobelt Supported Catalysts Used for Efficient NOx Storage and Reduction

A series of polytitanate nanobelt supported lean-burn NOx trap catalysts Pt-<i>x</i>K₂CO₃/K₂Ti₈O₁₇ with different weight loading of K₂CO₃ (<i>x</i> = 0%, 5%, 15%, 20%, 25%, or 30%) were synthesized by successive impregnation. The nanobelt support K₂Ti₈O₁₇ displays a specific surface area as high as 302 m²/g, and the corresponding catalysts Pt-<i>x</i>K₂CO₃/K₂Ti₈O₁₇ show excellent NOx storage performance. As K₂CO₃ loading increases from 5% to 30%, the NOx storage capacity (NSC) exhibits a volcano-type altering tendency with the maximum appearing at 25% (2.68 mmol/g); the highest NOx reduction efficiency of 99.2% was also achieved over this catalyst in cyclic alternative lean/rich atmospheres. Further increase of K₂CO₃ loading induces the formation of more bulk or bulk-like K₂CO₃ species, decreasing the performance of the catalysts for NOx storage and reduction. HR-TEM and FT-IR results indicate that the K species exist as highly dispersed phases including K₂O, K₂CO₃, and −OK groups, which are undetectable by X-ray diffraction (XRD) even at the K₂CO₃ loading of 30%. Several carbonate species with different thermal stability and reactivity are identified by FT-IR and CO₂-TPD. In situ diffuse reflectance FT-IR (DRIFTS) reveals that at low K₂CO₃ loading (<20%) NOx is mainly stored as monodentate nitrates and monodentate nitrites, while at higher K₂CO₃ loading NOx is mainly stored as bidentate nitrite species, which results from the decrease of oxidation ability of the catalysts due to the potential covering of K₂CO₃ on Pt sites

Facet Cutting and Hydrogenation of In₂O₃ Nanowires for Enhanced Photoelectrochemical Water Splitting

Semiconductor nanowires (NWs) are useful building blocks in optoelectronic, sensing, and energy devices and one-dimensional NWs have been used in photoelectrochemical (PEC) water splitting because of the enhanced light absorption and charge transport. It has been theoretically predicted that the {001} facets of body center cubic (bcc) In₂O₃ nanocrystals can effectively accumulate photogenerated holes under illumination, but it is unclear whether facet cutting of NWs can enhance the efficiency of PEC water splitting. In this work, the photocurrent of square In₂O₃ NWs with four {001} facets is observed to be an order of magnitude larger than that of cylindrical In₂O₃ NWs under the same conditions and subsequent hydrogen treatment further promotes the PEC water splitting performance of the NWs. The optimized hydrogenated In₂O₃ NWs yield a photocurrent density of 1.2 mA/cm² at 0.22 V versus Ag/AgCl with a Faradaic efficiency of about 84.4%. The enhanced PEC properties can be attributed to the reduced band gap due to merging of the disordered layer-induced band tail states with the valence band as well as improved separation of the photogenerated electrons/holes between the In₂O₃ crystal core and disordered layer interface. The results provide experimental evidence of the important role of facet cutting, which is promising in the design and fabrication of NW-based photoelectric devices

Enhanced Photodegradation of Methyl Orange Synergistically by Microcrystal Facet Cutting and Flexible Electrically-Conducting Channels

By performing precise facet cutting during hydrothermal synthesis, single-morphological and uniform-sized octahedral and cubic Cu₂O microcrystals respectively with {111} and {100} facets are synthesized and subsequently encapsulated with reduced graphene oxide (rGO). Electrochemical impedance spectroscopy shows that the rGO/Cu₂O polyhedral composite has excellent conductivity, indicating that rGO can serve as a flexible electrically conducting channel. On account of the accumulation of a large amount of photoexcited electrons on the {111} facets of the octahedrons and efficient electron transfer to the rGO sheet, photodegradation of methyl orange by the rGO/Cu₂O octahedral composite is enhanced by a factor of 4 compared to both bare Cu₂O octahedrons and rGO-encapsulated cubes with hole accumulation on the {100} facets, and the stability of the rGO/Cu₂O octahedrons is obviously improved due to no direct touch with water molecules in comparison with Cu₂O microcrystals without rGO wrap reported previously. This work shows that the combination of crystal facet cutting and conducting channels is an effective strategy to design new composites with enhanced photocatalytic properties

Photothermal Contribution to Enhanced Photocatalytic Performance of Graphene-Based Nanocomposites

Photocatalysts possessing high efficiency in degrading aquatic organic pollutants are highly desirable. Although graphene-based nanocomposites exhibit excellent photocatalytic properties, the role of graphene has been largely underestimated. Herein, the photothermal effect of graphene-based nanocomposites is demonstrated to play an important role in the enhanced photocatalytic performance, which has not been considered previously. In our study on degradation of organic pollutants (methylene blue), the contribution of the photothermal effect caused by a nanocomposite consisting of P25 and reduced graphene oxide can be as high as ∼38% in addition to trapping and shuttling photogenerated electrons and increasing both light absorption and pollutant adsorptivity. The result reveals that the photothermal characteristic of graphene-based nanocomposite is vital to photocatalysis. It implies that designing graphene-based nanocomposites with the improved photothermal performance is a promising strategy to acquire highly efficient photocatalytic activity

Strong Facet-Induced and Light-Controlled Room-Temperature Ferromagnetism in Semiconducting β‑FeSi₂ Nanocubes

Crystalline β-FeSi₂ nanocubes with two {100} facets and four {011} lateral facets synthesized by spontaneous one-step chemical vapor deposition exhibit strong room-temperature ferromagnetism with saturation magnetization of 15 emu/g. The room-temperature ferromagnetism is observed from the β-FeSi₂ nanocubes larger than 150 nm with both the {100} and {011} facets. The ferromagnetism is tentatively explained with a simplified model including both the itinerant electrons in surface states and the local moments on Fe atoms near the surfaces. The work demonstrates the transformation from a nonmagnetic semiconductor to a magnetic one by exposing specific facets and the room-temperature ferromagnetism can be manipulated under light irradiation. The semiconducting β-FeSi₂ nanocubes may have large potential in silicon-based spintronic applications

Synergistic Effect of Titanate-Anatase Heterostructure and Hydrogenation-Induced Surface Disorder on Photocatalytic Water Splitting

Black TiO₂ obtained by hydrogenation has attracted enormous attention due to its unusual photocatalytic activity. In this contribution, a novel photocatalyst containing both a titanate–anatase heterostructure and a surface disordered shell was in situ synthesized by using a one-step hydrogenation treatment of titanate nanowires at ambient pressure, which exhibited remarkably improved photocatalytic activity for water splitting under simulated solar light. The as-hydrogenated catalyst with a heterostructure and a surface disordered shell displayed a high hydrogen production rate of 216.5 μmol·h^–1, which is ∼20 times higher than the Pt-loaded titanate nanowires lacking of such unique structure. The in situ-generated heterostructure and hydrogenation-induced surface disorder can efficiently promote the separation and transfer of photoexcited electron–hole pairs, inhibiting the fast recombination of the generated charge carriers. A general synergistic effect of the heterostructure and the surface disordered shell on photocatalytic water splitting is revealed for the first time in this work, and the as-proposed photocatalyst design and preparation strategy could be widely extended to other composite photocatalytic systems used for solar energy conversion

Cubic In₂O₃ Microparticles for Efficient Photoelectrochemical Oxygen Evolution

Cubic In₂O₃ microparticles with exposed {001} facets as well as single morphology and size are produced on a large scale on silicon with a high yield. The morphological evolution during chemical vapor deposition is investigated and the new knowledge enables precise facet cutting. The synthesized Cubic In₂O₃ microparticles possess superior photoelectrocatalytic activity and excellent chemical and structural stability in oxygen evolution reaction on account of the unique surface structure and electronic band structure of the {001} facets. Our results reveal that it is feasible to promote the photolectrochemical water splitting efficiency of photoanode materials by controlling the growth on specific crystal facets. The technique and concept can be extended to other facet-specific materials in applications such as sensors, solar cells, and lithium batteries