Comparative study on CeO2 catalysts with different morphologies and exposed facets for catalytic ozonation: performance, key factor and mechanism insight

Morphology and facet effects of metal oxides in heterogeneous catalytic ozonation (HCO) are attracting increasing interests. In this paper, the different HCO performances for degradation and mineralization of phenol of seven ceria (CeO2) catalysts, including four with different morphologies (nanorod, nanocube, nanooctahedron and nanopolyhedron) and three with the same nanorod morphology but different exposed facets, are comparatively studied. CeO2 nanorods with (110) and (100) facets exposed show the best performance, much better than that of single ozonation, while CeO2 nanocubes and nanooctahedra show performances close to single ozonation. The underlying reason for their different HCO performances is revealed using various experimental and density functional theory (DFT) calculation results and the possible catalytic reaction mechanism is proposed. The oxygen vacancy (OV) is found to be pivotal for the HCO performance of the different CeO2 catalysts regardless of their morphology or exposed facet. A linear correlation is discerned between the rate of catalytic decomposition of dissolved ozone (O3) and the density of Frenkel-type OV. DFT calculations and in-situ spectroscopic studies ascertain that the existence of OV can boost O3 activation on both the hydroxyl (OH) and Ce sites of CeO2. Conversely, various facets without OV exhibit similar O3 adsorption energies. The OH group plays an important role in activating O3 to produce hydroxyl radical (∙OH) for improved mineralization. This work may offer valuable insights for designing Facet- and OV-regulated catalysts in HCO for the abatement of refractory organic pollutants.

Recent Advances of CeO2-Based Composite Materials for Photocatalytic Applications

Photocatalysis has the advantages of practical, sustainable and environmental protection, so it plays a significant role in energy transformation and environmental utilization. CeO2 has attracted widespread attention for its unique 4 f electrons, rich defect structures, high oxygen storage capacity and great chemical stability. In this paper, we review the structure of CeO2 and the common methods for the preparation of CeO2-based composites in the first part. In particular, we highlight the co-precipitation method, template method, and sol-gel method methods. Then, in the second part, we introduce the application of CeO2-based composites in photocatalysis, including photocatalytic CO2 reduction, hydrogen production, degradation, selective organic reaction, and photocatalytic nitrogen fixation. In addition, we discuss several modification techniques to improve the photocatalytic performance of CeO2-based composites, such as elemental doping, defect engineering, constructing heterojunction and morphology regulation. Finally, the challenges faced by CeO2-based composites are analyzed and their development prospects are prospected. This review provides a systematic summary of the recent advance of CeO2-based composites in the field of photocatalysis, which can provide useful references for the rational design of efficient CeO2-based composite photocatalysts for sustainable development.

Recent Developments in Nickel-Based Layered Double Hydroxides for Photo(-/)electrocatalytic Water Oxidation

Layered double hydroxides (LDHs), especially those containing nickel (Ni), are increasingly recognized for their potential in photo(-/)electrocatalytic water oxidation due to the abundant availability of Ni, their corrosion resistance, and their minimal toxicity. This review provides a comprehensive examination of Ni-based LDHs in electrocatalytic (EC), photocatalytic (PC), and photoelectrocatalytic (PEC) water oxidation processes. The review delves into the operational principles, highlighting similarities and distinctions as well as the benefits and limitations associated with each method of water oxidation. It includes a detailed discussion on the synthesis of monolayer, ultrathin, and bulk Ni-based LDHs, focusing on the merits and drawbacks inherent to each synthesis approach. Regarding the EC oxygen evolution reaction (OER), strategies to improve catalytic performance and insights into the structural evolution of Ni-based LDHs during the electrocatalytic process are summarized. Furthermore, the review extensively covers the advancements in Ni-based LDHs for PEC OER, including an analysis of semiconductors paired with Ni-based LDHs to form photoanodes, with a focus on their enhanced activity, stability, and underlying mechanisms facilitated by LDHs. The review concludes by addressing the challenges and prospects in the development of innovative Ni-based LDH catalysts for practical applications. The comprehensive insights provided in this paper will not only stimulate further research but also engage the scientific community, thus driving the field of photo(-/)electrocatalytic water oxidation forward.

Role of Facets and Morphologies of Different Bismuth-Based Materials for CO2 Reduction to Fuels

Carbon dioxide (CO2) emission has been a global concern over the past few decades due to the increase in the demand of energy, a major source of which is fossil fuels. To mitigate the emission issues, as well as to find a solution for the energy needs, an ample load of research has been carried out over the past few years in CO2 reduction by catalysis. Bismuth, being an active catalyst both photocatalytically and electrocatalytically, is an interesting material that can be formed into oxides, sulphides, oxyhalides, etc. Numerous works have been published based on bismuth-based materials as active catalysts for the reduction of CO2. However, a proper understanding of the behavior of the active facets and the dependence of morphology of the different bismuth-based catalysts is an interesting notion. In this review, various bismuth-based materials will be discussed regarding their activity and charge transfer properties, based on the active facets present in them. With regard to the available literature, a summarization, including photocatalysis, electrocatalysis as well as photoelectrocatalysis, will be detailed, considering various materials with different facets and morphologies. Product selectivity, varying on morphological difference, will also be realized photoelectrochemically.

Recent advances in nanoflowers: compositional and structural diversification for potential applications

In recent years, nanoscience and nanotechnology have emerged as promising fields in materials science. Spectroscopic techniques like scanning tunneling microscopy and atomic force microscopy have revolutionized the characterization, manipulation, and size control of nanomaterials, enabling the creation of diverse materials such as fullerenes, graphene, nanotubes, nanofibers, nanorods, nanowires, nanoparticles, nanocones, and nanosheets. Among these nanomaterials, there has been considerable interest in flower-shaped hierarchical 3D nanostructures, known as nanoflowers. These structures offer advantages like a higher surface-to-volume ratio compared to spherical nanoparticles, cost-effectiveness, and environmentally friendly preparation methods. Researchers have explored various applications of 3D nanostructures with unique morphologies derived from different nanoflowers. The nanoflowers are classified as organic, inorganic and hybrid, and the hybrids are a combination thereof, and most research studies of the nanoflowers have been focused on biomedical applications. Intriguingly, among them, inorganic nanoflowers have been studied extensively in various areas, such as electro, photo, and chemical catalysis, sensors, supercapacitors, and batteries, owing to their high catalytic efficiency and optical characteristics, which arise from their composition, crystal structure, and local surface plasmon resonance (LSPR). Despite the significant interest in inorganic nanoflowers, comprehensive reviews on this topic have been scarce until now. This is the first review focusing on inorganic nanoflowers for applications in electro, photo, and chemical catalysts, sensors, supercapacitors, and batteries. Since the early 2000s, more than 350 papers have been published on this topic with many ongoing research projects. This review categorizes the reported inorganic nanoflowers into four groups based on their composition and structure: metal, metal oxide, alloy, and other nanoflowers, including silica, metal-metal oxide, core-shell, doped, coated, nitride, sulfide, phosphide, selenide, and telluride nanoflowers. The review thoroughly discusses the preparation methods, conditions for morphology and size control, mechanisms, characteristics, and potential applications of these nanoflowers, aiming to facilitate future research and promote highly effective and synergistic applications in various fields.

Directional Assembly of Large-Area Silica Nanorod Film Using the Electric-Field-Assisted Capillary Channel Method

The self-assembly of colloidal particles, especially colloidal particles with anisotropic geometry, is important for applications in the construction of many functional materials. Compared with the self-assembly of colloidal particles with isotropic geometries, not only does the geometric orientation among neighboring anisotropic particles need to be considered for the reduction of Gibbs free energy, the orientations of the particles are best to be externally influenced. Because of this, the preparation of assembled nanorod arrays with uniform alignment across a large area is still a significant challenge. In this work, an electric-field-assisted capillary channel method is reported, using an external electric field to influence the orientation of silica nanorods or FeOOH ellipsoids during assembly. By application of an external electric field, the alignment of the nanorods is effectively controlled. The capillary channel method provides continuous replenishment of a colloidal solution containing nanorods or spheres for assembly of large-area films. The area of the formed films was influenced by the assembly temperature, channel width, colloidal solution concentration, and solvent surface tension. The competition between the thermal Brownian motion and torque generated by the external electric field impacted the nanorod array quality in the film. While increasing the intensity of the electric field improved nanorod alignment, applying a potential greater than 6 V also produced a heating effect, negatively affecting the quality of the nanorod arrays. The nematic order parameter S which characterizes the degree of alignment of FeOOH ellipsoids with smaller length is significantly lower than the one for silica nanorods due to the higher critical field strength and the increased susceptibility to the effects of thermal motion. The assembly of silica nanorods at 35 °C under an effective potential of 4-6 V provides a compromise between achieving uniform nanorod orientation and maximizing the coverage area of the colloidal film.

Strain and Surface Engineering of Multicomponent Metallic Nanomaterials with Unconventional Phases

Multicomponent metallic nanomaterials with unconventional phases show great prospects in electrochemical energy storage and conversion, owing to unique crystal structures and abundant structural effects. In this review, we emphasize the progress in the strain and surface engineering of these novel nanomaterials. We start with a brief introduction of the structural configurations of these materials, based on the interaction types between the components. Next, the fundamentals of strain, strain effect in relevant metallic nanomaterials with unconventional phases, and their formation mechanisms are discussed. Then the progress in surface engineering of these multicomponent metallic nanomaterials is demonstrated from the aspects of morphology control, crystallinity control, surface modification, and surface reconstruction. Moreover, the applications of the strain- and surface-engineered unconventional nanomaterials mainly in electrocatalysis are also introduced, where in addition to the catalytic performance, the structure-performance correlations are highlighted. Finally, the challenges and opportunities in this promising field are prospected.

Advances in CO2 utilization employing anisotropic nanomaterials as catalysts: a review

Anisotropic nanomaterials are materials with structures and properties that vary depending on the direction in which they are measured. Unlike isotropic materials, which exhibit uniform physical properties in all directions, anisotropic materials have different mechanical, electrical, thermal, and optical properties in different directions. Examples of anisotropic nanomaterials include nanocubes, nanowires, nanorods, nanoprisms, nanostars, and so on. These materials have unique properties that make them useful in a variety of applications, such as electronics, energy storage, catalysis, and biomedical engineering. One of the key advantages of anisotropic nanomaterials is their high aspect ratio, which refers to the ratio of their length to their width, which can enhance their mechanical and electrical properties, making them suitable for use in nanocomposites and other nanoscale applications. However, the anisotropic nature of these materials also presents challenges in their synthesis and processing. For example, it can be difficult to align the nanostructures in a specific direction to impart modulation of a specific property. Despite these challenges, research into anisotropic nanomaterials continues to grow, and scientists are working to develop new synthesis methods and processing techniques to unlock their full potential. Utilization of carbon dioxide (CO₂) as a renewable and sustainable source of carbon has been a topic of increasing interest due to its impact on reducing the level of greenhouse gas emissions. Anisotropic nanomaterials have been used to improve the efficiency of CO₂ conversion into useful chemicals and fuels using a variety of processes such as photocatalysis, electrocatalysis, and thermocatalysis. More study is required to improve the usage of anisotropic nanomaterials for CO₂ consumption and to scale up these technologies for industrial use. The unique properties of anisotropic nanomaterials, such as their high surface area, tunable morphology, and high activity, make them promising catalysts for CO₂ utilization. This review article discusses briefly about various approaches towards the synthesis of anisotropic nanomaterials and their applications in CO₂ utilization. The article also highlights the challenges and opportunities in this field and the future direction of research.

Nanoshaped Cerium Oxide with Nickel as a Non-Noble Metal Catalyst for CO2 Thermochemical Reactions

Four different nanoshapes of cerium dioxide have been prepared (polycrystals, rods, cubes, and octahedra) and have been decorated with different metals (Ru, Pd, Au, Pt, Cu, and Ni) by incipient wetness impregnation (IWI) and ball milling (BM) methods. After an initial analysis based on oxygen consumption from CO₂ pulse chemisorption, Ni-like metal, and two forms of CeO₂ cubes and rods were selected for further research. Catalysts were characterized using the Brunauer-Emmett-Teller formula (BET), X-ray spectroscopy (XRD), Raman spectroscopy, scanning electron microscopy (SEM), UV-visible spectrophotometry (UV-Vis), X-ray photoelectron spectroscopy (XPS), temperature programmed reduction (H₂-TPR) and CO₂ pulse chemisorption, and used to reduce of CO₂ into CO (CO₂ splitting). Adding metals to cerium dioxide enhanced the ability of CeO₂ to release oxygen and concomitant reactivity toward the reduction of CO₂. The effect of the metal precursor and concentration were evaluated. The highest CO₂ splitting value was achieved for 2% Ni/CeO₂-rods prepared by ball milling using Ni nitrate (412 µmol/g_cat) and the H₂ consumption (453.2 µmol/g_cat) confirms the good redox ability of this catalyst.

Selective Control of Novel TiO2 Nanorods: Excellent Building Blocks for the Electron Transport Layer of Mesoscopic Perovskite Solar Cells

Novel TiO2 nanorods (NRs) with various lengths of 70-200 nm and uniform widths of 46-48 nm are selectively synthesized by a solvothermal reaction under a basic environment. The length of TiO2 NRs is reproducibly tuned by varying the concentration of tetramethylammonium hydroxide (TMAH), while the NRs in the pure anatase phase are grown in the [001] direction, caused by the preferential binding affinity of TMAH to the TiO2 (101) facet. TiO2 NRs of various lengths are then applied to form the electron transporting layer (ETL) of mesoscopic perovskite solar cells (PSCs). We found that PSC devices with NRs exhibit superior photovoltaic (PV) performance to those with conventional 46 nm-sized TiO2 nanoparticles (NP46). Particularly, the PSC with TiO2 NRs of 110 nm length (NR110) exhibits the optimum PV conversion efficiency (PCE): the average PCE is 22.64% with a VOC of 1.137 V, a JSC of 24.60 mA·cm-2, and a FF of 80.96%, while the champion PCE is 23.18%. In addition, the PSC with NR110 (PSC-NR110) reveals significantly improved long-term stability in air with a relative humidity of 40-50%. In 1000 h, its PCE is reduced by only 9% whereas that of PSC with NP46 decreases by 25%. The PSC properties analyzed by impedance spectroscopy and J-V curve measurements under dark conditions and at various light intensities provide evidence that PSC-NR110 has fewer defects and shows significantly reduced charge recombination. We discuss the advantages of NR structures in preparing the ETL of PSC devices and also explain why the charge recombination is suppressed.

Switchable ROS Scavenger/Generator for MRI-Guided Anti-Inflammation and Anti-Tumor Therapy with Enhanced Therapeutic Efficacy and Reduced Side Effects

Photosensitizer in photodynamic therapy (PDT)  accumulates in both tumor and adjacent normal tissue due to low selective biodistribution, results in undesirable side effect with limited clinic application. Herein, an intelligent nanoplatform is reported that selectively acts as reactive oxygen species (ROS) scavenger in normal tissue but as ROS generator in tumor microenvironment (TME) to differentially control ROS level in tumor and surrounding normal tissue during PDT. By down-regulating the produced ROS with dampened cytokine wave in normal tissue after PDT, the nanoplatform reduces the inflammatory response of normal tissue in PDT, minimizing the side effect and tumor metastasis in PDT. Alternatively, the nanoplatform switches from ROS scavenger to generator through the glutathione (GSH) responsive degradation in TME, which effectively improves the PDT efficacy with reduced GSH level and amplified oxidative stress in tumor. Simultaneously, the released Mn ions provide real-time and in situ signal change of magnetic resonance imaging (MRI) to monitor the reversal process of catalysis activity and achieve accurate tumor diagnosis. This TME-responsive ROS scavenger/generator with activable MRI contrast may provide a new dimension for design of next-generation PDT agents with precise diagnosis, high therapeutic efficacy, and low side effect.

Recent advances and perspectives of CeO2-based catalysts: Electronic properties and applications for energy storage and conversion

Cerium dioxide (CeO₂, ceria) has long been regarded as one of the key materials in modern catalysis, both as a support and as a catalyst itself. Apart from its well-established use (three-way catalysts and diesel engines), CeO₂ has been widely used as a cocatalyst/catalyst in energy conversion and storage applications. The importance stems from the oxygen storage capacity of ceria, which allows it to release oxygen under reducing conditions and to store oxygen by filling oxygen vacancies under oxidizing conditions. However, the nature of the Ce active site remains not well understood because the degree of participation of f electrons in catalytic reactions is not clear in the case of the heavy dependence of catalysis theory on localized d orbitals at the Fermi energy E _F . This review focuses on the catalytic applications in energy conversion and storage of CeO₂-based nanostructures and discusses the mechanisms for several typical catalytic reactions from the perspectives of electronic properties of CeO₂-based nanostructures. Defect engineering is also summarized to better understand the relationship between catalytic performance and electronic properties. Finally, the challenges and prospects of designing high efficiency CeO₂-based catalysts in energy storage and conversion have been emphasized.

Insight into the Crystal Facet Effect of {101} and {100} Facets of CeVO4 in the Photochemical Property and Photocatalysis

To investigate the photochemical property of specific crystal facets, two well-defined CeVO₄ dodecahedrons with exposed {101} and {100} facets are prepared, which have distinguishing appearances and unequal {101}/{100} area ratios (A_{101}/A_{100}), i.e., compressed dodecahedra (CeVO₄ CD, A_{101}/A_{100} ≈ 1) and elongated dodecahedra (CeVO₄ ED, A_{101}/A_{100} ≈ 0.3). During the visible-light-irradiated process, the {101} and {100} facets are certified to selectively deposit photogenerated holes (h⁺) and electrons (e^-), thus exhibiting the photooxidability and photoreducibility, respectively. Meanwhile, a surface heterojunction could form at the adjacent facet interface and facilitate the spatial separation of carriers. Benefiting from the large exposure extent of the {101} facet and the rational A_{101}/A_{100} (∼1), the CeVO₄ CD shows a superior photocatalytic performance for the degradation of tetracycline to the CeVO₄ ED. Finally, simulation calculations reveal that the energy deviations of the valence band (VB) and conduction band (CB) between CeVO₄{101} and CeVO₄{100} impel the photogenerated h⁺ and e^- to transfer in opposite directions, resulting in the facet-dependent photoactivity of the CeVO₄ dodecahedron.

Oxidation States Regulation of Cobalt Active Sites through Crystal Surface Engineering for Enhanced Polysulfide Conversion in Lithium-Sulfur Batteries

In this work, unique Co₃ O₄ /N-doped reduced graphene oxide (Co₃ O₄ /N-rGO) composites as favorable sulfur immobilizers and promoters for lithium-sulfur (Li-S) batteries are developed. The prepared Co₃ O₄  nanopolyhedrons (Co₃ O₄ -NP) and Co₃ O₄  nanocubes mainly expose (112) and (001) surfaces, respectively, with different atomic configurations of Co²⁺ /Co³⁺ sites. Experiments and theoretical calculations confirm that the octahedral coordination Co³⁺ (Co³⁺ _Oh ) sites with different oxidation states from tetrahedral coordination Co²⁺ sites optimize the adsorption and catalytic conversion of lithium polysulfides. Specially, the Co₃ O₄ -NP crystals loaded on N-rGO expose (112) planes with ample Co³⁺ _Oh active sites, exhibiting stronger adsorbability and superior catalytic activity for polysulfides, thus inhibiting the shuttle effect. Therefore, the S@Co₃ O₄ -NP/N-rGO cathodes deliver excellent electrochemical properties, for example, stable cyclability at 1 C with a low capacity decay rate of 0.058% over 500 cycles, superb rate capability up to 3 C, and high areal capacity of 4.1 mAh cm^-2 . This catalyst's design incorporating crystal surface engineering and oxidation state regulation strategies also provides new approaches for addressing the complicated issues of Li-S batteries.

Elucidating the origin mechanism of a morphology-dependent layered double hydroxide catalyst toward organic contaminant oxidation via persulfate activation

Understanding how the morphology of a layered double hydroxide (LDH)-based catalyst alters its catalytic activity provides an available strategy for the rational design and fabrication of high-efficiency catalysts at a micro-scale. Herein, three nickel-iron layered double hydroxide (NiFe-LDH) catalysts including 2D-plate-like hexagon (P-NiFe-LDH), 2D/3D-flower-like solid sphere (FS-NiFe-LDH), and 2D/3D-flower-like hollow sphere (FH-NiFe-LDH) with regulable oxygen vacancies (OVs) were fabricated via a morphological regulation method of Ostwald ripening. The experimental results demonstrated that the three types of NiFe-LDH exhibited different abilities to activate persulfate (PS) for the abatement of acid orange 7 (AO7) with a sequence of FH-NiFe-LDH > FS-NiFe-LDH > P-NiFe-LDH. Particularly, the FH-NiFe-LDH with a hollow structure exhibited the most considerable activity with the first-order rate constant up to k = 0.02639 min^-1, benefiting from the highly accessible surface areas, higher intrinsic activity of the exposed crystal planes, and abundant OVs. Characterizations further confirmed that these properties could profoundly allow for more exposure of active sites and enhance the reactivity of OV-connected Ni or Fe to facilitate electron transfer and generate more reactive radicals, therefore elucidating the morphologic origin of catalytic performance. Based on the quenching experiments, sulfate radicals (SO₄^·-), hydroxyl radicals (^·OH), and oxygen radicals (O₂^·-) were identified to be involved in the decomposition process. Furthermore, the continuous redox cycle of Ni(II)/Ni(III)/Ni(II) and Fe(II)/Fe(III)/Fe(II) was responsible for the generation of active radicals via activating PS.

Chemically Synthesized Iron-Oxide-Based Pure Negative Electrode for Solid-State Asymmetric Supercapacitor Devices

Among energy storage devices, supercapacitors have received considerable attention in recent years owing to their high-power density and extended cycle life. Researchers are currently making efforts to improve energy density using different asymmetric cell configurations, which may provide a wider potential window. Many studies have been conducted on positive electrodes for asymmetric supercapacitor devices; however, studies on negative electrodes have been limited. In this study, iron oxides with different morphologies were synthesized at various deposition temperatures using a simple chemical bath deposition method. A nanosphere-like morphology was obtained for α-Fe₂O₃. The obtained specific capacitance (C_s) of α-Fe₂O₃ was 2021 F/g at a current density of 4 A/g. The negative electrode showed an excellent capacitance retention of 96% over 5000 CV cycles. The fabricated asymmetric solid-state supercapacitor device based on α-Fe₂O₃-NF//Co₃O₄-NF exhibited a C_s of 155 F/g and an energy density of 21 Wh/kg at 4 A/g.

Solid-State Construction of CuOx/Cu1.5Mn1.5O4 Nanocomposite with Abundant Surface CuOx Species and Oxygen Vacancies to Promote CO Oxidation Activity

Carbon monoxide (CO) oxidation performance heavily depends on the surface-active species and the oxygen vacancies of nanocomposites. Herein, the CuO_x/Cu_1.5Mn_1.5O₄ were fabricated via solid-state strategy. It is manifested that the construction of CuO_x/Cu_1.5Mn_1.5O₄ nanocomposite can produce abundant surface CuO_x species and a number of oxygen vacancies, resulting in substantially enhanced CO oxidation activity. The CO is completely converted to carbon dioxide (CO₂) at 75 °C when CuO_x/Cu_1.5Mn_1.5O₄ nanocomposites were involved, which is higher than individual CuO_x, MnO_x, and Cu_1.5Mn_1.5O₄. Density function theory (DFT) calculations suggest that CO and O₂ are adsorbed on CuO_x/Cu_1.5Mn_1.5O₄ surface with relatively optimal adsorption energy, which is more beneficial for CO oxidation activity. This work presents an effective way to prepare heterogeneous metal oxides with promising application in catalysis.

Mesoporous LaCoO3 perovskite oxide with high catalytic performance for NOx storage and reduction

A mesoporous LaCoO₃ perovskite oxide (LaCoO₃-Meso) with three-dimensionally ordered helical interwoven structure was synthesized by a nano-casting method using KIT-6 as the hard template. The obtained LaCoO₃-Meso with high surface area was tested for its catalytic performance in the NO_x storage and reduction (NSR) reaction and compared with a sample synthesized by the conventional sol-gel method. The LaCoO₃-Meso showed a significant advantage for NO_x storage, with a NO_x storage capacity 2 times higher than the regular sample. LaCoO₃-Meso also exhibited improved NSR catalytic performance in the 150-450 °C temperature range, especially within 350-400 °C, where the NO_x conversion was raised for 40%. The results of X-ray photoelectron spectroscopy and X-ray absorption fine structure measurements suggested the presence of a high concentration of oxygen defects on the LaCoO₃-Meso surface. Further results provided by temperature programmed reduction and temperature programmed desorption indicated that the oxygen defects not only increase the amount of trapped NO_x, but also improve the low-temperature redox performance of the catalyst. The lower stability of NO_x species adsorbed on oxygen defects promotes the NO_x release step in the NSR reaction and benefits the regeneration of storage sites.

Analyzing the Local Electronic Structure of Co3O4 Using 2p3d Resonant Inelastic X-ray Scattering

We present the cobalt 2p3d resonant inelastic X-ray scattering (RIXS) spectra of Co₃O₄. Guided by multiplet simulation, the excited states at 0.5 and 1.3 eV can be identified as the ⁴ T ₂ excited state of the tetrahedral Co²⁺ and the ³ T _2g excited state of the octahedral Co³⁺, respectively. The ground states of Co²⁺ and Co³⁺ sites are determined to be high-spin ⁴ A ₂(T _d ) and low-spin ¹ A _1g (O_h ), respectively. It indicates that the high-spin Co²⁺ is the magnetically active site in Co₃O₄. Additionally, the ligand-to-metal charge transfer analysis shows strong orbital hybridization between the cobalt and oxygen ions at the Co³⁺ site, while the hybridization is weak at the Co²⁺ site.

Direct visualisation of the surface atomic active sites of carbon-supported Co3O4 nanocrystals via high-resolution phase restoration

The atomic arrangement of the terminating facets on spinel Co₃O₄ nanocrystals is strongly linked to their catalytic performance. However, the spinel crystal structure offers multiple possible surface terminations depending on the synthesis. Thus, understanding the terminating surface atomic structure is essential in developing high‐performance Co₃O₄ nanocrystals. In this work, we present direct atomic‐scale observation of the surface terminations of Co₃O₄ nanoparticles supported on hollow carbon spheres (HCSs) using exit wavefunction reconstruction from aberration‐corrected transmission electron microscopy focal‐series. The restored high‐resolution phases show distinct resolved oxygen and cobalt atomic columns. The data show that the structure of {100}, {110}, and {111} facets of spinel Co₃O₄ exhibit characteristic active sites for carbon monoxide (CO) adsorption, in agreement with density functional theory calculations. Of these facets, the {100} and {110} surface terminations are better suited for CO adsorption than the {111}. However, the presence of oxygen on the {111} surface termination indicates this facet also plays an essential role in CO adsorption. Our results demonstrate direct evidence of the surface termination atomic structure beyond the assumed stoichiometry of the surface.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

Tailor the crystal planes of MIL-101(Fe) derivatives to enhance the activity of SCR reaction at medium and low temperature

Mainly exposed crystal facets and controllable morphology play a key role in the final performance of the preparation of specific nanomaterials. In the present study, a metal-organic framework pyrolysis method without adding solvent modifiers was developed. By adding CO in the calcination atmosphere to change atmosphere ratio, Fe₃O₄ nanostructures are exposed with different crystal planes and evaluated their performance in NH₃-SCR reaction. This study proves that SCR catalytic activity of Fe₃O₄ nanocrystals is dependent on morphology and crystal facet. Compared with materials exposed (100), catalysts with more (111) show stronger deNO_x performance. The preferential exposure of Fe₃O₄ (111) crystal facets increases the concentration of adsorbed oxygen on the catalyst, showing higher surface acidity, and enhances the interaction among NO, O₂ and catalyst, which is conducive to SCR reaction. This is supported by DFT calculations. The results present a great application prospect in preparing nanomaterials with specific crystal structures to effectively treat pollutants.

Catalytic nanoparticles and magnetic nanocatalysts in organic reactions: A mini review

Nanocatalysts, as a part of nanotechnology, have been seen very useful for various fileds of applications capturing a large contribution of the world market. Indeed, several unsolved issues of catalysts have been reconsidered by employing the new nanocatalysts including single core metal atoms and ions with surrounding holes. Moreover, it was expected that the future of catalytic reactions, especially those organic ones, will deal with the nanocatalyst applications. To this aim, the features of catalytic nanoparticles and magnetic nanocatalysts regarding evaluation of their advantages and applications in organic reactions were investigated in this work. Developments of catalytic nanoparticles and magnetic nanocatalysts were discussed in this work regarding the novel applications of such materials at the nanoscale for approaching advantageous features. Increased availability, activity, and stability are very important for applications of the catalysts in various organic reactions. Therefore, it is a must to discuss features of such nanocatalytic systems to provide more information about their advantages and even disadvantages of their applications.

Surface differences of oxide nanocrystals determined by geometry and exogenously coordinated water molecules

Both atomic geometry and the influence of surroundings (e.g., exogenously coordinated water) are key issues for determining the chemical environment of oxide surfaces, whereas the latter is usually ignored and should be considered in future studies.

Water-induced stacked α-Fe2O3 hexagonal nanoplates along [001] direction and its facet-dependent catalytic performances

Controlling the growth of nanocrystal to expose a specific facet is of great significance for the rational design of effective crystal catalysts. Herein, a water-induced stacking process was developed to...

Printed copper-nanoplate conductor for electro-magnetic interference

As one of the conductive ink materials with high electric conductivity, elemental copper (Cu) based nanocrystals promise for printable electronics. Here, single crystalline Cu nanoplates were synthesized using a facile hydrothermal method. Size engineering of Cu nanoplates can be rationalized by using the LaMer model and the versatile Cu conductive ink materials are suitable for different printing technologies. The printed Cu traces show high electric conductivity of 6 MS m^-1, exhibiting electro-magnetic interference shielding efficiency value of 75 dB at an average thicknesses of 11μm. Together with flexible alumina ceramic aerogel substrates, it kept 87% conductivity at the environmental temperature of 400 °C, demonstrating the potential of Cu conductive ink for high-temperature printable electronics applications.

Morphology effect of ceria supports on gold nanocluster catalyzed CO oxidation

The interfacial perimeter is generally viewed as the catalytically active site for a number of chemical reactions over oxide-supported nanogold catalysts. Here, well-defined CeO₂ nanocubes, nanorods and nanopolyhedra are chosen to accommodate atomically precise clusters (e.g. Au₂₅(PET)₁₈) to give different Au cluster-CeO₂ interfaces. TEM images show that Au particles of ∼1.3 nm are uniformly anchored on the ceria surface after annealing in air at 120 °C, which can rule out the size hierarchy of nanogold in CO oxidation studies. The gold nanoclusters are only immobilized on the CeO₂(200) facet in Au₂₅/CeO₂-C, while they are selectively loaded on CeO₂(002) and (111) in the Au₂₅/CeO₂-R and Au₂₅/CeO₂-P catalysts. X-ray photoelectron spectroscopy (XPS) and in situ infrared CO adsorption experiments clearly demonstrate that the gold species in the Au₂₅/CeO₂ samples are similar and partially charged (Au ^δ+, where 0 < δ < 1). It is observed that the catalytic activity decreases in the order of Au/CeO₂-R ≈ Au/CeO₂-P > Au/CeO₄-C in the CO oxidation. And the apparent activation energy over Au₂₅/CeO₂-C (60.5 kJ mol^-1) is calculated to be about two-fold of that over the Au₂₅/CeO₂-R (28.6 kJ mol^-1) and Au₂₅/CeO₂-P (31.3 kJ mol^-1) catalysts. It is mainly tailored by the adsorbed [O] species on the ceria surface, namely, Au₂₅/CeO₂(002) and Au₂₅/CeO₂(111) which were more active than the Au₂₅/CeO₂(200) system in the CO oxidation. These insights at the molecular level may provide guidelines for the design of new oxide-supported nanogold catalysts for aerobic oxidations.

Advances in the Application of Nanocatalysts in Photocatalytic Processes for the Treatment of Food Dyes: A Review

The use of food additives (such as dyes, which improve the appearance of the products) has become more prominent, due to the rapid population growth and the increase in demand for beverages and processed foods. The dyes are usually found in effluents that are discharged into the environment without previous treatment; this promotes mass contamination and alters the aquatic environment. In recent years, advanced oxidation processes (AOPs) have proven to be effective technologies used for wastewater treatment through the destruction of the total organic content of toxic contaminants, including food dyes. Studies have shown that the introduction of catalysts in AOPs improve treatment efficiency (i.e., complete decomposition without secondary contamination). The present review offers a quick reference for researchers, regarding the treatment of wastewater containing food dyes and the different types of AOPs, with different catalyst and nanocatalyst materials obtained from traditional and green chemical syntheses.