Synthesis of Hierarchical Layered Quasi-Triangular Ce(OH)CO3 and Its Thermal Conversion to Ceria with High Polishing Performance

Layered quasi-triangular Ce(OH)CO₃ assembled from primary nanoparticles was synthesized via a solvothermal method and converted into CeO₂ abrasive particles by calcination at 800-1000 °C. With the increase of calcination temperature, the primary particle size increased and the microstructure, mechanical hardness, and chemical activity of the CeO₂ particles changed, thus affecting the polishing performance. The calcined products obtained at 800, 850, and 900 °C maintained the layered edge structure of the Ce(OH)CO₃ precursor and had a relatively high specific surface area and surface Ce³⁺ concentration. The samples calcined at 950 and 1000 °C lost the layered structure due to the large-scale melting of the primary particles, and their surface chemical activity decreased. The polishing experiments on K9 glass showed that, with the calcination temperature rising from 800 to 1000 °C, the material removal rate (MRR) first increased and then decreased sharply. The initial increase of MRR was attributed to the increase of mechanical hardness of the layered quasi-triangular CeO₂, and the subsequent decrease of MRR was related to the decrease in surface chemical activity and disappearance of the layered edge structure. The product calcined at 900 °C had the highest MRR and best surface quality after polishing due to the layered edge structure and optimal match of chemical activity and mechanical hardness.

The modification of biomass waste by cerium-based MOFs for efficient phosphate removal: excellent performance and reaction mechanism

Due to the possibility of causing eutrophication, excessive phosphate discharged into water bodies always threatens the stabilization of aquatic ecosystem. A promising strategy is to remove phosphate from water by the utilization of biomass waste as adsorbents. In this paper, the corn straw (CS) and pine sawdust (PS) are chosen for adsorption; however, the phosphate removal capacities of them are very limited. Considering the high phosphate uptake of trivalent cerium, Ce (III)-based nanoparticles (CD and CT) are selected to be loaded on the biomass by hydrothermal synthesis to obtain four modified materials. CD is metal organic frameworks (MOFs) with Ce5(BDC)7.5(DMF)4 as its molecular structure, while CT is MOFs derivatives with [Ce (HCOO)]n as its crystal structure. The adsorption capacities of CS-CD, PS-CD, CS-CT and PS-CT reach 181.38, 183.27, 225.55 and 186.23 mg/g. But on account of the different molecular structures, CS-CD and PS-CD achieve great phosphate uptake under wide applicable scope of pH from 2 to 11, whereas CS-CT and PS-CT only under acidic conditions. The analysis of the adsorption mechanism indicates that due to the unsaturated coordination bond of CD, it could remove phosphate through coprecipitation and ion exchange even under alkaline conditions.

α-calcium sulfate hemihydrate with a 3D hierarchical straw-sheaf morphology for use as a remove Pb2+ adsorbent

Novel three-dimensional hierarchical α-calcium sulfate hemihydrate with a straw-sheaf morphology (3D α-HH straw-sheaves) are synthesized successfully in glycerin aqueous solution by a simple one-pot method, using as an efficient adsorbent for Pb²⁺ removal from water. The 3D straw-sheaf morphology, that closely depends on the glycerin/water volume ratio (V_Gly/V_H2O), can be accurately fabricated only when V_Gly/V_H2O is not lower than 3/1. 3D α-HH straw-sheaves are generated via multistep-splitting growth coupled with self-assembly. The obtained 3D α-HH straw-sheaves are further used as an adsorbent to remove Pb²⁺ from water, exhibiting excellent Pb²⁺ removal performance with an equilibrium adsorption capacity of 79.19 mg_Pbg_α-HH^-1 and removal efficiency of 98.98%, that both higher than those of plate- and columnar-like α-HH. Moreover, the experimental adsorption data for the 3D α-HH straw-sheaves is well fitted with pseudo-second-order kinetic model, and the adsorption isotherm is in good agreement with Langmuir model. The Pb²⁺ adsorption mechanism is thought to be a chemical adsorption process enforced by chemical bonding and ion exchange. This work demonstrates that 3D α-HH straw-sheaves are highly promising in removing Pb²⁺ from wastewater, thereby broadening the research field for the practical application of gypsum-based materials.

Hierarchical Au/CeO2 systems – influence of Ln3+ dopants on the catalytic activity in the propane oxidation process

The catalytic activity of the hierarchical tube-like Au/Ce1−xLnxO2−x/2 in the propane oxidation process depends not only on the presence of Au nanoparticles on the support surface but also on the type of deformation in the CeO2 network.

Hierarchical macroparticles of ceria with tube-like shape – synthesis and properties

The hierarchical organization of CeO2 nanoparticles into tube-like macroparticles has a great influence on the properties of the material.

Ce(OH)2Cl and lanthanide-substituted variants as precursors to redox-active CeO2 materials

The cerium(iii) hydroxide chloride Ce(OH)2Cl crystallises directly as a polycrystalline powder from a solution of CeCl3·7H2O in poly(ethylene) glycol (Mn = 400) heated at 240 °C and is found to be isostructural with La(OH)2Cl, as determined from high-resolution synchrotron powder X-ray diffraction (P21/m, a = 6.2868(2) Å, b = 3.94950(3) Å, c = 6.8740(3) Å, β = 113.5120(5)°). Replacement of a proportion of the cerium chloride in synthesis by a second lanthanide chloride yields a set of materials Ce1-xLnx(OH)2Cl for Ln = La, Pr, Gd, Tb. For La the maximum value of x is 0.2, with an isotropic expansion of the unit cell, but for the other lanthanides a wider composition range is possible, and the lattice parameters show an isotropic contraction with increasing x. Thermal decomposition of the hydroxide chlorides at 700 °C yields mixed-oxides Ce1-xLnxO2-δ that all have cubic fluorite structures with either expanded (Ln = La, Gd) or contracted (Ln = Pr, Tb) unit cells compared to CeO2. Scanning electron microscopy shows a shape memory effect in crystal morphology upon decomposition, with clusters of anisotropic sub-micron crystallites being seen in the precursor and oxide products. The Pr- and Tb-substituted oxides contain the substituent in a mixture of +3 and +4 oxidation states, as seen by X-ray absorption near edge structure spectroscopy at the lanthanide LIII edges. The mixed oxide materials are examined using temperature programmed reduction in 10%H2 in N2, which reveals redox properties suitable for heterogeneous catalysis, with the Pr-substituted materials showing the greatest reducibility at lower temperature.

Function of various levels of hierarchical organization of porous Ce0.9REE0.1O1.95 mixed oxides in catalytic activity

Each level of hierarchical structure of the star-like Ce_0.9REE_0.1O_1.95 mixed oxides has its own functionality and is susceptible to modification.

Single-phase cerium oxide nanospheres: An efficient photocatalyst for the abatement of rhodamine B dye

Single-phase mesoporous CeO₂ nanospheres were synthesized by template-free hydrothermal approach by the synthesis of CeCO₃OH precursor combined with the calcination at 350 °C for 3.0 h. Precursor and calcined products were characterized by XRD, TGA, FESEM, EDX, TEM, N₂ adsorption-desorption and pore size distribution analysis, UV-vis diffuse reflectance (UV-vis DRS), and photoluminescence (PL) analysis. The morphologies of CeO₂ nanospheres were controlled via the optimization of urea concentration during the synthesis. Calcined CeO₂ exhibited excellent photocatalytic activity of rhodamine B (RhB) dye degradation under UV-visible irradiation and mild acidic condition. Scavenger test analysis was used to confirm that the hydroxyl radicals, superoxide radicals, and photogenerated holes are the active photoinduced species of RhB degradation. A comparative study of PL intensity, dye adsorption, and zeta potential measurement revealed the efficient dye adsorption over different CeO₂ photocatalysts. The RhB degradation rate constant has been found to raise linearly with increase of the surface properties. Repeatability test analysis proved the higher catalytic stability of CeO₂ nanospheres without any noticeable loss of activity. Mass spectroscopy and ion chromatography analyses were used to detect the intermediate by-product formation. Finally, based on the results of intermediate detection, possible degradation pathways were also proposed including radical reactions, ring opening, and de-nitrification.

CeO2-covered nanofiber for highly efficient removal of phosphorus from aqueous solution

The lowering phosphorus concentration of lakes or rivers using adsorbents has been considered to be the most effective way to prevent water eutrophication. However, the development of an adsorbent is still challenging because conventional adsorbents have not shown a sufficient phosphorus adsorption capacity (0.3-2.0mmol/g) to treat industrial, agricultural or domestic wastewater at a large scale. Herein, a novel and effective strategy to remove phosphorus efficiently with a CeO2-covered nanofiber is shown. The CeO2-covered nanofiber was synthesized through (1) amine group immobilization onto an electrospun polyacrylonitrile nanofiber and (2) adsorption of Ce(3+) on it. The CeO2-covered nanofiber played a role in catching phosphate ions in an aqueous solution by the oxidation, reduction, and ion-exchange of adsorbed Ce(3+) on the nanofiber from CeO2 to CePO4, and enabled remarkable phosphate adsorption capacity of the nanofiber (ca. 17.0mmol/g) at the range of ca. pH 2-6. Our strategy might be the most feasible method to efficiently lower the phosphorus concentration in lakes or rivers owing to the easy and inexpensive preparation of CeO2-covered nanofiber at an industrial scale, with a high phosphate adsorption capacity.

Controlled synthesis of barium chromate multi-layered microdiscs and their photocatalytic activity

BaCrO₄ microdiscs composed of multi-layered microplates were successfully synthesized by a facile oxalate-assisted precipitation method. Based on time-dependent experiments, a dissolution–recrystallization–self-assembly process has been proposed.

CeO2 hollow nanospheres synthesized by a one pot template-free hydrothermal method and their application as catalyst support

Uniform ceria hollow nanospheres composed of ceria nanocrystals have been synthesized via a simple one-step hydrothermal method without using any template.

Synthetic versatility of nanoparticles: A new, rapid, one-pot, single-step synthetic approach to spherical mesoporous (metal) oxide nanoparticles using supercritical alcohols

A simple, rapid (10 min), one-pot, single-step method for the preparation of solid and hollow spherical porous TiO2 nanoparticles with large surface areas (100–211 m2/g) was developed in supercritical alcohols using carboxylic acids as organic additives. The shell thickness of the hollow TiO2 nanoparticles (20–280 nm) was controlled by adjusting the heating rate (2.0–10.0 °C/min). The preparation of different spherical porous metal oxide nanoparticles, including CeO2, SiO2, TiO2, ZrO2, and ZnO, demonstrated the versatility of the synthetic approach. In addition, several rare earth-doped spherical mesoporous metal oxide nanoparticles, including CeO2:Er, CeO2:Er,Yb, ZrO2:Er, and TiO2:Er, which exhibit energy upconversion emission, were successfully prepared using this one-pot, single-step, supercritical methanol method. The obtained spherical mesoporous CeO2:Er and CeO2:Er,Yb nanoparticles emit green light upon excitation, even when irradiated with a low-power IR laser (980 nm, 10 mW) without calcination. Several other (metal) elements were also easily doped into spherical, mesoporous TiO2 nanoparticles, such as Eu, Ce, Yb, Fe, and N, using a similar procedure. Furthermore, the spherical mesoporous TiO2 nanoparticles were successfully applied as a new material for the transport of DNA via biolistic bombardment.

Mesoporous CeO2 nanoparticles assembled by hollow nanostructures: formation mechanism and enhanced catalytic properties

In this paper, novel hierarchically mesoporous CeO₂ nanoparticles assembled by hollow nanocones were prepared through a facile solvothermal strategy using Ce(HCOO)₃ as the precursor.

Template-free and non-hydrothermal synthesis of CeO2nanosheets via a facile aqueous-phase precipitation route with catalytic oxidation properties

Petal and belt-like CeO₂nanosheets are synthesized using an aqueous phase precipitation method under template-free and non-hydrothermal conditions and exhibit excellent catalytic oxidation performance.

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.

Shape-controlled synthesis and catalytic application of ceria nanomaterials

Because of their excellent properties and extensive applications, ceria nanomaterials have attracted much attention in recent years. This perspective provides a comprehensive review of current research activities that focus on the shape-controlled synthesis methods of ceria nanostructures. We elaborate on the synthesis strategies in the following four sections: (i) oriented growth directed by the crystallographic structure of cerium-based materials; (ii) oriented growth directed by the use of an appropriate capping reagent; (iii) growth confined or dictated by various templates; (iv) other potential methods for generating CeO(2) nanomaterials. In this perspective, we also discuss the catalytic applications of ceria nanostructures. They are often used as active components or supports in many catalytic reactions and their catalytic activities show morphology dependence. We review the morphology dependence of their catalytic performances in carbon monoxide oxidation, water-gas shift, nitric oxide reduction, and reforming reactions. At the end of this review, we give a personal perspective on the probable challenges and developments of the controllable synthesis of CeO(2) nanomaterials and their catalytic applications.