Fe-Ce/Layered Double Hydroxide Heterostructures and Their Derived Oxides: Electrochemical Characterization and Light-Driven Catalysis for the Degradation of Phenol from Water

Fe-Ce/layered double hydroxides (LDHs) were synthesized via a facile route by exploiting the "structural memory" of the LDH when the calcined MgAlLDH and ZnAlLDH were reconstructed in the aqueous solutions of FeSO₄/Ce(SO₄)₂. XRD analysis shows the formation of heterostructured catalysts that entangle the structural characteristics of the LDHs with those of Fe₂O₃ and CeO₂. Furthermore, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, TG/DTG, SEM/EDX and TEM results reveal a complex morphology defined by the large nano/microplates of the reconstructed LDHs that are tightly covered with nanoparticles of Fe₂O₃ and CeO₂. Calcination at 850 °C promoted the formation of highly crystallized mixed oxides of Fe₂O₃/CeO₂/ZnO and spinels. The photo-electrochemical behavior of Fe-Ce/LDHs and their derived oxides was studied in a three-electrode photo-electrochemical cell, using linear sweep voltammetry (LSV), Mott-Schottky (M-S) analysis and photo-electrochemical impedance spectroscopy (PEIS) measurements, in dark or under illumination. When tested as novel catalysts for the degradation of phenol from aqueous solutions, the light-driven catalytic heterojunctions of Fe-Ce/LDH and their derived oxides reveal their capabilities to efficiently remove phenol from water, under both UV and solar irradiation.

Surface basicity mediated rapid and selective adsorptive removal of Congo red over nanocrystalline mesoporous CeO2

Herein we first report surface basicity mediated rapid and selective adsorptive removal of organic pollutants over nanocrystalline mesoporous CeO₂. The role of surface features in controlling the selectivity and efficiency of adsorption is well known. Nevertheless, the possibility of tuning the adsorption capacity and selectivity of adsorbents through their surface characteristics remains less explored. In this work, the surface basicity of mesoporous CeO₂ nanoparticles was improved by Er³⁺ doping under two different reaction conditions: via sol-gel and sol-hydrothermal methods. The nature and amount of surface basic sites were determined with the help of CO₂ temperature programmed desorption (TPD). The adsorption capacity and selectivity of four different CeO₂ samples were investigated using Congo red, methyl orange, and methylene blue as the model pollutants. From the adsorption studies, Er³⁺ doped CeO₂ synthesized by the sol-gel method, having the highest amount of surface basic sites, proved to be the most efficient and highly selective adsorbent among the four developed variants of CeO₂ towards Congo red. According to the proposed mechanism, surface basicity can be employed as a controlling parameter capable of tuning the adsorption capacity as well as the selectivity of CeO₂ towards organic pollutants.

Highly Efficient Photoelectrocatalytic Reduction of CO2 to Methanol by a p-n Heterojunction CeO2/CuO/Cu Catalyst

Photoelectrocatalytic reduction of CO2 to fuels has great potential for reducing anthropogenic CO2 emissions and also lessening our dependence on fossil fuel energy. Herein, we report the successful development of a novel photoelectrocatalytic catalyst for the selective reduction of CO2 to methanol, comprising a copper catalyst modified with flower-like cerium oxide nanoparticles (CeO2 NPs) (a n-type semiconductor) and copper oxide nanoparticles (CuO NPs) (a p-type semiconductor). At an applied potential of - 1.0 V (vs SCE) under visible light irradiation, the CeO2 NPs/CuO NPs/Cu catalyst yielded methanol at a rate of 3.44 μmol cm-2 h-1, which was approximately five times higher than that of a CuO NPs/Cu catalyst (0.67 μmol cm-2 h-1). The carrier concentration increased by ~ 108 times when the flower-like CeO2 NPs were deposited on the CuO NPs/Cu catalyst, due to synergistic transfer of photoexcited electrons from the conduction band of CuO to that of CeO2, which enhanced both photocatalytic and photoelectrocatalytic CO2 reduction on the CeO2 NPs. The facile migration of photoexcited electrons and holes across the p-n heterojunction that formed between the CeO2 and CuO components was thus critical to excellent light-induced CO2 reduction properties of the CeO2 NPs/CuO NPs/Cu catalyst. Results encourage the wider application of composite semiconductor electrodes in carbon dioxide reduction.

Hectogram-scale green synthesis of hierarchical 4A zeolite@CuOx(OH)(2−2x) (0 ≤ x < 1) nanosheet assemblies core–shell nanoarchitectures with Superb Congo red adsorption performance

Delicate design of hierarchical nanoarchitectures has become a highly effective strategy to develop novel adsorbents with improved adsorption capacity. Herein, hectogram-scale green fabrication of hierarchical 4A zeolite@CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies core–shell nanoarchitectures (4A-Cu-T, T was the calcination temperature) with terrific Congo red (CR) dye adsorption performance was achieved through a simple, template-free and surfactant-free hydrothermal approach. A series of characterization techniques, including scanning electron microscopy, transmission electron microscopy, X-ray diffraction and photoelectron spectroscopy demonstrated that all resultant adsorbents featured a core–shell structure with 4A zeolite as core ingredients and CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies as shell components. The adsorption experimental results pointed out that 4A-Cu-300 with a maximum adsorption capacity of 512.987 mg g⁻¹ showed the best adsorption performance amongst all as-prepared adsorbents, and the adsorption capacity of shell component-CuO_xCu(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies was calculated up to 3685.500 mg g⁻¹. The shell thickness and phase ratio of CuO and Cu(OH)₂ in CuO_x(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies played key roles in improving the adsorption capacity. The successive tests suggested that the “carbon deposition” resulted in the decreased adsorption capacity of first-regenerated adsorbents, but little variance in adsorption performance among regenerated samples demonstrated the good stability of such adsorbents. This work unlocks a method for the rational design of high-performance adsorbents via delicate decoration of poor-performance materials with nanosheet assemblies, which will endow the non-active materials with enhanced adsorption properties.

The growth of CuO_xCu(OH)_(2−2x) (0 ≤ x < 1) nanosheet assemblies on the surface of 4A zeolite transforms poor-performance 4A zeolite adsorbents into high-performance 4A-Cu-300 adsorbents for Congo red study.

The Effect of CeO2 Preparation Method on the Carbon Pathways in the Dry Reforming of Methane on Ni/CeO2 Studied by Transient Techniques

The present work discusses the effect of CeO2 synthesis method (thermal decomposition (TD), precipitation (PT), hydrothermal (HT), and sol-gel (SG)) on the carbon pathways of dry reforming of methane with carbon dioxide (DRM) applied at 750 °C over 5 wt% Ni/CeO2. In particular, specific transient and isotopic experiments (use of 13CO, 13CO2, and 18O2) were designed and conducted in an attempt at providing insights about the effect of support’s preparation method on the concentration (mg gcat−1), reactivity towards oxygen, and transient evolution rates (μmol gcat−1 s−1) of the inactive carbon formed under (i) CH4/He (methane decomposition), (ii) CO/He (reverse Boudouard reaction), and (iii) the copresence of the two (CH4/CO/He, use of 13CO). Moreover, important information regarding the relative contribution of CH4 and CO2 activation routes towards carbon formation under DRM reaction conditions was derived by using isotopically labelled 13CO2 in the feed gas stream. Of interest was also the amount, and the transient rate, of carbon removal via the participation of support’s labile active oxygen species.

The selective catalytic reduction of NO over Ce0.3TiOx-supported metal oxide catalysts

A Ce_0.3TiO_x oxide carrier was synthesized via a sol-gel process, and Ce_0.3TiO_x supported metal (M=Cd, Mn, Fe, W, Mo) oxide catalysts were prepared by the method of incipient-wetness impregnation. The catalysts were characterized by means of X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), and Temperature-programmed reduction with H₂ (H₂-TPR). The catalytic activities for de-NO_x were evaluated by the NH₃-SCR reaction. Among all the catalysts tested, the 2wt.% Cd/Ce_0.3TiO_x catalyst exhibited the best NH₃-SCR performance, with a wide temperature window of 250-450°C for NO conversion above 90%. Moreover, the catalyst showed N₂ selectivity greater than 99% from 200 to 450°C.

Endurance and Cycle-to-cycle Uniformity Improvement in Tri-Layered CeO2/Ti/CeO2 Resistive Switching Devices by Changing Top Electrode Material

Resistance switching characteristics of CeO2/Ti/CeO2 tri-layered films sandwiched between Pt bottom electrode and two different top electrodes (Ti and TaN) with different work functions have been investigated. RRAM memory cells composed of TaN/CeO2/Ti/CeO2/Pt reveal better resistive switching performance instead of Ti/CeO2/Ti/CeO2/Pt memory stacks. As compared to the Ti/CeO2 interface, much better ability of TaN/CeO2 interface to store and exchange plays a key role in the RS performance improvement, including lower forming/SET voltages, large memory window (~102) and no significant data degradation during endurance test of >104 switching cycles. The formation of TaON thinner interfacial layer between TaN TE and CeO2 film is found to be accountable for improved resistance switching behavior. Partial charge density of states is analyzed using density functional theory. It is found that the conductive filaments formed in CeO2 based devices is assisted by interstitial Ti dopant. Better stability and reproducibility in cycle-to-cycle (C2C) resistance distribution and Vset/Vreset uniformity were achieved due to the modulation of current conduction mechanism from Ohmic in low field region to Schottky emission in high field region.

Impact of the synthesis parameters on the solid state properties and the CO oxidation performance of ceria nanoparticles

A direct quantitative correlation of surface-to-bulk (O_s/O_b) reducible oxygen of ceria nanoparticles (NPs) with catalytic activity was revealed.

One pot synthesis of CeO2 nanoparticles on a carbon surface for the practical determination of paracetamol content in real samples

Sucrose derived carbon decorated with CeO₂ nanoparticles (CeO₂–C) was prepared using a one pot synthesis and used for the electrochemical sensing of paracetamol.

Surface engineering on CeO₂ nanorods by chemical redox etching and their enhanced catalytic activity for CO oxidation

Controllable surface properties of nanocerias are desired for various catalytic processes. There is a lack of efficient approaches to adjust the surface properties of ceria to date. Herein, a redox chemical etching method was developed to controllably engineer the surface properties of ceria nanorods. Ascorbic acid and hydrogen peroxide were used to perform the redox chemical etching process, resulting in a rough surface and/or pores on the surface of ceria nanorods. Increasing the etching cycles induced a steady increase of the specific surface area, oxygen vacancies and surface Ce(3+) fractions. As a result, the etched nanorods delivered enhanced catalytic activity for CO oxidation, compared to the non-etched ceria nanorods. Our method provides a novel and facile approach to continuously adjust the surface properties of ceria for practical applications.

A 1D anionic coordination polymer showing superior Congo Red sorption and its dye composite exhibiting remarkably enhanced photocurrent response

A 1D coordination polymer, [Zn(1,2,3-BTA)(H₂O)]·(H₂L)_0.5·2H₂O, shows superior Congo red sorption and its dye composite demonstrates significantly amplified photocurrent responses.

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.

Boron nitride ultrathin fibrous nanonets: one-step synthesis and applications for ultrafast adsorption for water treatment and selective filtration of nanoparticles

Novel boron nitride (BN) ultrathin fibrous networks are firstly synthesized via an one-step solvothermal process. The average diameter of BN nanofibers is only ~8 nm. This nanonets exhibit excellent performance for water treatment. The maximum adsorption capacity for methyl blue is 327.8 mg g(-1). Especially, they present the property of ultrafast adsorption for dye removal. Only ~1 min is enough to almost achieve the adsorption equilibrium. In addition, the BN fibrous nanonets could be applied for the size-selective separation of nanoparticles via a filtration process.

Porous boron nitride with a high surface area: hydrogen storage and water treatment

We report on the synthesis of high-quality microporous/mesoporous BN material via a facile two-step approach. An extremely high surface area of 1687 m(2) g(-1) and a large pore volume of 0.99 cm(3) g(-1) have been observed in the synthesized BN porous whiskers. The formation of the porous structure was attributed to the group elimination of organic species in a BN precursor, melamine diborate molecular crystal. This elimination method maintained the ordered pore structure and numerous structural defects. The features including high surface area, pore volume and structural defects make the BN whiskers highly suitable for hydrogen storage and wastewater treatment applications. We demonstrate excellent hydrogen uptake capacity of the BN whiskers with high weight adsorption up to 5.6% at room temperature and at the relatively low pressure of 3 MPa. Furthermore, the BN whiskers also exhibit excellent adsorption capacity of methyl orange and copper ions, with the maximum removal capacity of 298.3 and 373 mg g(-1) at 298 K, respectively.

Porous Pr(OH)3 nanostructures as high-efficiency adsorbents for dye removal

Herein we report the electrochemical synthesis of porous Pr(OH)(3) nanobelt arrays (NBAs), nanowire arrays (NWAs), nanowire bundles (NWBs), and nanowires (NWs) and their applications as dye absorbents in water treatment. These Pr(OH)(3) nanostructures exhibit high efficient and selective adsorption of the dyes with amine (-NH(2)) functional groups such as Congo red, reactive yellow, and reactive blue. The high efficiency and selectivity is attributed to the large effective surface area of the porous structure, plentiful hydroxyl groups, and basic sites on the Pr(OH)(3) surface. Furthermore, the toxicity studies of these porous Pr(OH)(3) nanostructure show a negligible effect on seed germination, indicating that they hold great potential as environmentally friendly absorbents in water treatment.