Accelerated radical generation from visible light driven peroxymonosulfate activation by Bi2MoO6/doped gCN S-scheme heterojunction towards Amoxicillin mineralization: Elucidation of the degradation mechanism

A novel S-scheme photocatalyst Bi₂MoO₆ @doped gCN (BMO@CN) was prepared through a facile microwave (MW) assisted hydrothermal process and further employed to degrade Amoxicillin (AMOX), by peroxymonosulfate (PMS) activation with visible light (Vis) irradiation. The reduction in electronic work functions of the primary components and strong PMS dissociation generate abundant electron/hole (e^-/h⁺) pairs and SO₄^*-,*OH,O₂^*-reactive species, inducing remarkable degeneration capacity. Optimized doping of Bi₂MoO₆ on doped gCN (upto 10 wt%) generates excellent heterojunction interface with facile charge delocalization and e^-/h⁺ separation, as a combined effect of induced polarization, layered hierarchical structure oriented visible light harvesting and formation of S-scheme configuration. The synergistic action of 0.25 g/L BMO(10)@CN and 1.75 g/L PMS dosage can degrade 99.9% of AMOX in less than 30 min of Vis irradiation, with a rate constant (k_obs) of 0.176 min^-1. The mechanism of charge transfer, heterojunction formation and the AMOX degradation pathway was thoroughly demonstrated. The catalyst/PMS pair showed a remarkable capacity to remediate AMOX-contaminated real-water matrix. The catalyst removed 90.1% of AMOX after five regeneration cycles. Overall, the focus of this study is on the synthesis, illustration and applicability of n-n type S-scheme heterojunction photocatalyst to the photodegradation and mineralization of typical emerging pollutants in the water matrix.

Biomimetic Catalysts Based on Au@TiO2-MoS2-CeO2 Composites for the Production of Hydrogen by Water Splitting

The photocatalytic hydrogen evolution reaction (HER) by water splitting has been studied, using catalysts based on crystalline TiO₂ nanowires (TiO₂NWs), which were synthesized by a hydrothermal procedure. This nanomaterial was subsequently modified by incorporating different loadings (1%, 3% and 5%) of gold nanoparticles (AuNPs) on the surface, previously exfoliated MoS₂ nanosheets, and CeO₂ nanoparticles (CeO₂NPs). These nanomaterials, as well as the different synthesized catalysts, were characterized by electron microscopy (HR-SEM and HR-TEM), XPS, XRD, Raman, Reflectance and BET surface area. HER studies were performed in aqueous solution, under irradiation at different wavelengths (UV-visible), which were selected through the appropriate use of optical filters. The results obtained show that there is a synergistic effect between the different nanomaterials of the catalysts. The specific area of the catalyst, and especially the increased loading of MoS₂ and CeO₂NPs in the catalyst substantially improved the H₂ production, with values of ca. 1114 μm/hg for the catalyst that had the best efficiency. Recyclability studies showed only a decrease in activity of approx. 7% after 15 cycles of use, possibly due to partial leaching of gold nanoparticles during catalyst use cycles. The results obtained in this research are certainly relevant and open many possibilities regarding the potential use and scaling of these heterostructures in the photocatalytic production of H₂ from water.

Probing the role of surface activated oxygen species of CeO2 nanocatalyst during the redox cycle in CO oxidation

The oxygen species of CeO₂ nanocatalysts plays a key role in the CO oxidation. In this work, nanocrystalline CeO₂ with infrared spectroscopy detectable surface superoxide (O₂⁻) species at room temperature is fabricated and CO oxidation is used as a probe reaction for the exploration of the characteristics of surface O₂⁻ species on the CeO₂ surface. We discover that the surface O₂⁻ species have ignorable influences on the overall reaction rate of CO oxidation on pure ceria by comparing P-CeO₂ (CeO₂ prepared by precipitation method) with HT-CeO₂ (CeO₂ prepared by hydrothermal method). It is concluded that the reaction between CO molecules and surface O₂⁻ species is the first and the fast step in the whole redox cycle, while the release of surface lattice oxygen is the second and the rate determining step of the catalysts. This work gives an intuitionistic exploration on the redox properties of pure nanocrystalline CeO₂ with surface O₂⁻ species and reveals the influences of these species in the whole redox circle of CO oxidation.

Pure CeO₂ nanocatalysts fabricated by different methods are obtained and the impact of surface oxygen species on their CO oxidation is compared and evaluated.

Selective oxidation of glycerol on morphology controlled ceria nanomaterials

It is reported, for the first time, that morphology controlled ceria without any addition of other metal exhibits catalytic activity for selective oxidation of glycerol. Moreover, development of {111} nanofacets plays an important role in both activity and selectivity.

Thermally stable core-shell Ni/nanorod-CeO2@SiO2 catalyst for partial oxidation of methane at high temperatures

During partial oxidation of methane (POM), the greatest challenge is to maintain the thermal stability of the catalyst at high temperatures. One of the most effective ways to improve thermal stability is to construct core-shell structure. Herein, using a microemulsion method, we synthesized a core-shell Ni/nanorod-CeO2@SiO2 catalyst, in which the Ni nanoparticles were supported on the CeO2 nanorods and encapsulated by SiO2 shells. Based on a series of characterizations, we found that the Ni particles are of nanosize (2.2 nm) and the thickness of the SiO2 shell is about 8 nm in the core-shell catalyst. Moreover, the Ni/nanorod-CeO2@SiO2 catalyst can perfectly maintain rod-like structures of the CeO2 support and enhance interaction between the metal Ni and CeO2, significantly reducing the sintering of metal Ni particles at high temperatures. Therefore, the as-prepared Ni/nanorod-CeO2@SiO2 catalyst shows high catalytic activity and good thermal stability during the POM reaction.

Remarkable improved electro-Fenton efficiency by electric-field-induced catalysis of CeO2

In this study, we designed a novel combined electro-Fenton system for the treatment of wastewater containing biological recalcitrant using electric-field-induced ceria (CeO₂) as the synergistic catalysts. It was found that by applying this CeO₂ electro-Fenton system, the current efficiency improved from 74.49% to 109.82% within 2.5 min; the removal efficiency for dimethyl phthalate (DMP) increased from 85.5% to 94.9% within 20 min; and the mineralization rate increased from 76.01% to 93.58% after 120 min. The effects of parameters such as the applied potential, electrolyte, and concentration of Fe²⁺ on the current efficiency were systematically studied. Investigations by LSV, zeta titration, X-ray photoelectron spectroscopy (XPS), X-Ray Diffraction (XRD)and electron spin resonance (ESR)revealed the reasons for achieving a current efficiency of over 100% in the CeO₂ electro-Fenton system. A mechanism that involved Brønsted acid sites and the redox cycle of sulfate CeO₂ was proposed.

Anisotropic growth of gas–liquid precipitated ceria mesocrystals to wires several micrometers in length

Ceria (CeO₂) wires with lengths of 6 μm and diameters of tens of nanometers are fabricated through the anisotropic growth of mesocrystals. In the gas–liquid precipitation process, an aqueous Ce(NO₃)₃ solution is used as a starting material and NH₃ gas is used to induce CeO₂ precipitation at the gas–liquid interface. CeO₂ mesocrystals, formed by this process at 60 °C, grow in the direction of 〈011〉 into micrometer length wires exposing {001} and {011} on their side walls. It is shown that the initial pH of the starting material solution is a key parameter to attain anisotropic growth of the CeO₂ mesocrystals. We thus propose the formation mechanism of micrometer length-CeO₂ wires from mesocrystals.

CeO₂ wires several micrometers in length were formed through anisotropic growth of mesocrystals by oriented attachment on {111} surfaces.

Sub-15 nm CeO2 nanowires as an efficient non-noble metal catalyst in the room-temperature oxidation of aniline

We described the facile synthesis of sub-15 nm CeO₂ nanowires for catalyzing the selective synthesis of nitrosobenzene from aniline at room temperature.

Quasi-zero-dimensional cobalt-doped CeO2 dots on Pd catalysts for alcohol electro-oxidation with enhanced poisoning-tolerance

Deactivation of an anode catalyst resulting from the poisoning of CO_ad-like intermediates is one of the major problems for methanol and ethanol electro-oxidation reactions (MOR & EOR), and remains a grand challenge towards achieving high performance for direct alcohol fuel cells (DAFCs). Herein, we report a new approach for the preparation of ultrafine cobalt-doped CeO₂ dots (Co-CeO₂, d = 3.6 nm), which can be an effective anti-poisoning promoter for Pd catalysts towards MOR and EOR in alkaline media. Compared to Pd/CeO₂ and pure Pd, the hybrid Pd/Co-CeO₂ nanocomposite catalyst exhibited a much enhanced activity and remarkable anti-poisoning ability for both MOR and EOR. The nanocomposite catalyst showed much higher mass activity (4×) than a state-of-the-art PtRu catalyst. The promotional mechanism was elucidated using extensive characterization and density-functional theory (DFT). A bifunctional effect of the Co-CeO₂ dots was discovered to be due to (i) an enhanced electronic interaction between Co-CeO₂ and Pd dots and (ii) the increased oxygen storage capacity of Co-CeO₂ dots to facilitate the oxidation of CO_ad. Therefore, the Pd/Co-CeO₂ nanocomposite appears to be a promising catalyst for advanced DAFCs with low cost and high performance.

Catalytic oxidation of aromatic amines to azoxy compounds over a Cu–CeO2 catalyst using H2O2 as an oxidant

Highly dispersed Cu-nanoparticles supported on nanocrystalline CeO₂ were prepared which showed good catalytic activity toward selective oxidation of aromatic amines.

Ceria Nanotube Formed by Sacrificed Precursors Template through Oswald Ripening

Controllable preparation of ceria nanotube was realized by hydrothermal treatment of Ce(OH)CO₃ precursors. The gradually changing morphologies and microstructures of cerium oxide were characterized by X-ray powder diffraction, scanning electron microscopy and transmission electron microscopy. A top-down path is illuminated to have an insight to the morphological transformation from nanorod to nanotube by adjusting the reaction time. The growth process is investigated by preparing a series of intermediate morphologies during the shape evolution of CeO₂nanostructure based on the scanning electron microscopy image observation. On the basis of the time-dependent experimental observation, the possible formation mechanism related to oriented attachment and Oswald ripening was proposed, which might afford some guidance for the synthesis of other inorganic nanotubes.

Facile synthesis of highly ordered mesoporous cobalt–alumina catalysts and their application in liquid phase selective oxidation of styrene

We illustrate the preparation of highly ordered mesoporous cobalt–alumina catalysts with highly homogeneously dispersed Co(ii) species via an evaporation-induced triconstituent cooperative co-assembly method.

Morphology-mediated tailoring of the performance of porous nanostructured Mn2O3 as an anode material

The experiments determined the effects of different morphologies of synthesized porous Mn₂O₃ on its performance as an anode material in Li-ion batteries.

Facile electrochemical synthesis of CeO2 hierarchical nanorods and nanowires with excellent photocatalytic activities

A simple, cost-effective and controllable electrochemical method has been developed to synthesize free-standing CeO₂ hierarchical nanorods and nanowires.