Green-synthesized CeO2 nanoparticles for photocatalytic, antimicrobial, antioxidant and cytotoxicity activities.

Cerium oxide nanoparticles (CeO2 NPs) are a sought-after material in numerous fields due to their potential applications such as in catalysis, cancer therapy, photocatalytic degradation of pollutants, sensors, polishing agents. Green synthesis usually involves the production of CeO2 assisted by organic extracts obtained from plants, leaves, flowers, bacteria, algae, food, fruits, etc. The phytochemicals present in the organic extracts adhere to the NPs and act as reducing and/or oxidizing agents and capping agents to stabilize the NPs, modify the particle size, morphology and band gap energy of the as-synthesized materials, which would be advantageous for numerous applications. This review focuses on the green extract-mediated synthesis of CeO2 NPs and discusses the effects on CeO2 NPs of various synthesis methods that have been reported. Several photocatalytic, antimicrobial, antioxidant and cytotoxicity applications have been evaluated, compared and discussed. Future prospects are also suggested.

Bio-based synthesis of Nano-Ceria and evaluation of its bio-distribution and biological properties.

Bio-based synthesis of Nano-Ceria (NC) was performed in Linum usitatissimum L. (Lu) seeds extract as capping agent. Obtained gel was calcined at 400, 500, and 600 °C to investigate the effect of temperature on the size and morphology of the particles. All samples had spherical morphology which their crystallite size was decreased in higher temperature. Products were characterized by TGA/DTA, UV-vis, FESEM, FTIR and XRD. The band gap of the prepared samples was calculated through Tauc plot in the range of 3.2-3.4 eV. The results of MTT assay confirmed that NC has been shown no significant toxicity on A549 cell line. 2',7'-dichlorofluorescin diacetate (DCFDA) was used to determine antioxidant properties of NC on A549 cell and the results showed that all concentrations of NC could reduce reactive oxygen species (ROS). NC was labeled with technetium (99mTc) for in vivo bio-distribution study in Wistar rat. Radiolabeled NC was stable in different environments of PBS buffer and human serum with radiochemical purity of more than 95% according to the instant thin layer chromatography (ITLC) method. DLS analysis showed radiolabeled particles had small size and pleasant colloidal stability. Bio-distribution of radiolabeled NC illustrated the highest accumulation in kidneys (1 h: 5.94 ±â€¯0.77%ID/g, 4 h: 10.95 ±â€¯5.99%ID/g, 24 h 7.94 ±â€¯0.36%ID/g). Moreover, low uptake of 99mTc-NC in stomach confirmed the in vivo stability of 99mTc-NC. Accordingly, NC could be a worthy candidate for biological purposes and in vivo studies.

Recovery of Rare Earth Elements from Wastewater Towards a Circular Economy.

The use of rare earth elements is a growing trend in diverse industrial activities, leading to the need for eco-friendly approaches to their efficient recovery and reuse. The aim of this work is the development of an environmentally friendly and competitive technology for the recovery of those elements from wastewater. Kinetic and equilibria batch assays were performed with zeolite, with and without bacterial biofilm, to entrap rare earth ions from aqueous solution. Continuous assays were also performed in column setups. Over 90% removal of lanthanum and cerium was achieved using zeolite as sorbent, with and without biofilm, decreasing to 70% and 80%, respectively, when suspended Bacillus cereus was used. Desorption from the zeolite reached over 60%, regardless of the tested conditions. When in continuous flow in columns, the removal yield was similar for all of the rare earth elements tested. Lanthanum and cerium were the elements most easily removed by all tested sorbents when tested in single- or multi-solute solutions, in batch and column assays. Rare earth removal from wastewater in open setups is possible, as well as their recovery by desorption processes, allowing a continuous mode of operation.

Partitioning of Ag and CeO2 nanoparticles versus Ag and Ce ions in soil suspensions and effect of natural organic matter on CeO2 nanoparticles stability.

This study examined the solid-liquid distribution of 14.8-nm Ag and 6.2-nm CeO2 nanoparticles in soil suspensions and compared it to that of Ag+ and Ce3+ ions, to better understand their environmental behaviour and fate. After 24 h incubation, more than 51% or 29% of the spiked amounts of Ag or CeO2 nanoparticles, respectively, can be retrieved in the liquid phase of (re)suspended soils. The Ag or Ce concentration remaining in solution depends on the incubation time and was influenced by soil properties. Significant correlations are obtained between, on the one hand, the relative amounts of Ag or CeO2 nanoparticles in suspension and the soil-pH, CEC, texture, suspended matter, nitrogen, phosphorus, TOC and main and trace elements content on the other hand. The presence of dissolved natural organic matter stabilizes CeO2 nanoparticles in the aqueous phase. In soil suspensions, Ag+ and Ce3+ ions seemingly interact more strongly with soil constituents compared to their nanoparticle counterparts, rendering the Ag and CeO2 nanoparticles to be more stable and potentially bioavailable.

Solid phase extraction, separation and preconcentration of rare elements thorium(IV), uranium(VI), zirconium(IV), cerium(IV) and chromium(III) amid several other foreign ions with eriochrome black T anchored to 3-D networking silica gel.

The present work reports the systematic studies on extraction, separation and preconcentration of Th(IV), U(VI), Zr(IV), Ce(IV) and Cr(III) amid several other foreign ions using EBT anchored {SiO2}n3-D microarray. The effect of various sorption parameters, such as pH, concentration, temperature, sample volume, flow-rate and co-existing foreign ions were investigated. Quantitative sorption was ensured at solution pH: 6.0-6.5 for Th(IV), Ce(IV), Cr(III) and pH: 2.75-3.0 for Zr(IV), U(VI) couple. Analysis on extracted species and extraction sites reveals that [Th4(µ(2)-OH)8(H2O)4](8+), [Ce6(µ(2)-OH)12(H2O)5](12+), [Cr3(µ(2)-OH)4(H2O)](5+), [(UO2)3(µ(2)-OH)5(H2O)3](+) and [Zr4(µ(2)-OH)8(H2O)0.5](8+) for the respective metal ions gets extracted at HOMO of the extractor. HOMO-{metal ion species} was found to be 1:1 complexation. Sorption was endothermic, entropy-gaining, instantaneous and spontaneous in nature. A density functional theory (DFT) calculation has been performed to analyze the 3-D structure and electronic distribution of the synthesized extractor.

Synthesis of activated carbon-based amino phosphonic acid chelating resin and its adsorption properties for Ce(III) removal.

This work aims to investigate the adsorption of Ce(III) onto chelating resin based on activated carbon (CRAC). The CRAC adsorbent was prepared from activated carbon (AC) followed by oxidation, silane coupling, ammoniation and phosphorylation, and characterized by Fourier transform-infrared spectrometry, nitrogen adsorption measurements and scanning electron microscopy. The effects of solution pH, adsorbent dosage and contact time were studied by batch technique. Langmuir and Freundlich isotherms were used to describe the adsorption behaviour of Ce(III) by CRAC, and the results showed that the adsorption behaviour well fitted the Langmuir model. The maximum uptake capacity (qmax) calculated by using the Langmuir equation for cerium ions was found to be 94.34 mg/g. A comparison of the kinetic models and the overall experimental data was best fitted with the type 1 pseudo second-order kinetic model. The calculated thermodynamic parameters (ΔG°, ΔH° and ΔS°) showed that the adsorption for Ce(III) was feasible, spontaneous and exothermic at 25-45 °C. The CRAC showed an excellent adsorptive selectivity towards Ce(III). Moreover, more than 82% of Ce(III) adsorbed onto CRAC could be desorbed with HCl and could be used several times.

Linking the chemical speciation of cerium to its bioavailability in water for a freshwater alga.

Over the past decade, researchers have begun to use metals of the lanthanide family for numerous applications, including liquid crystal display (LCD) screens, optical fibers, and laser technology. Unfortunately, little is presently known about their bioavailability or the mechanisms by which they might cause toxicity. The present study focuses on cerium (Ce), one of the most widely used lanthanides, and on validating the biotic ligand model as a means to predict Ce bioaccumulation. Short-term exposures to Ce were performed using the unicellular alga Chlamydomonas reinhardtii, to better relate Ce bioavailability to its chemical speciation in solution. Maximum uptake fluxes (Jmax ) and affinity constants for the binding of Ce to the biological uptake sites (KS ) were established at pH 5.0 and pH 7.0. An apparent affinity constant of 1.8 × 10(7) M(-1) was observed at pH 5.0, with a larger value obtained at pH 7.0 (6 × 10(7) M(-1) ), albeit under conditions where equilibrium could not be confirmed. By evaluating Ce speciation using centrifugal ultrafiltration and single-particle inductively coupled plasma spectrometry, it could be concluded that very little (∼30%) Ce was truly dissolved at pH 7.0, with the majority of the metal being present in colloidal species. Speciation was also monitored by fluorescence to evaluate Ce complexation by natural organic matter (NOM). The presence of NOM decreased Ce bioaccumulation in line with free Ce concentrations. Finally, competition with calcium for the metal uptake sites was shown to result in a decrease in Ce uptake by C. reinhardtii.

Biogenic unmodified gold nanoparticles for selective and quantitative detection of cerium using UV-vis spectroscopy and photon correlation spectroscopy (DLS).

The ability of self-functionalized biogenic GNPs towards highly selective colorimetric detection of rare earth element cerium is being reported for the first time. GNPs underwent rapid aggregation on addition of cerium indicated by red shift of SPR peak followed by complete precipitation. Hereby, this concept of co-ordination of cerium ions onto the GNP surface has been utilized for detection of cerium. The remarkable capacity of GNPs to sensitively detect Ce without proves beneficial compared to previous reports of colorimetric sensing. MDL was 15 and 35 ppm by DLS and UV-vis spectroscopy respectively, suggesting DLS to be highly sensitive and a practical alternative in ultrasensitive detection studies. The sensing system showed a good linear fit favouring feasible detection of cerium in range of 2-50 ppm. Similar studies further showed the superior selectivity of biogenic GNPs compared to chemically synthesized counterparts. The sensing system favours on-site analysis as it overcomes need of complex instrumentation, lengthy protocols and surface modification of GNP.

Persistence of engineered nanoparticles in a municipal solid-waste incineration plant.

More than 100 million tonnes of municipal solid waste are incinerated worldwide every year. However, little is known about the fate of nanomaterials during incineration, even though the presence of engineered nanoparticles in waste is expected to grow. Here, we show that cerium oxide nanoparticles introduced into a full-scale waste incineration plant bind loosely to solid residues from the combustion process and can be efficiently removed from flue gas using current filter technology. The nanoparticles were introduced either directly onto the waste before incineration or into the gas stream exiting the furnace of an incinerator that processes 200,000 tonnes of waste per year. Nanoparticles that attached to the surface of the solid residues did not become a fixed part of the residues and did not demonstrate any physical or chemical changes. Our observations show that although it is possible to incinerate waste without releasing nanoparticles into the atmosphere, the residues to which they bind eventually end up in landfills or recovered raw materials, confirming that there is a clear environmental need to develop degradable nanoparticles.

The effect of alkali and Ce(III) ions on the response properties of benzoxazine supramolecules prepared via molecular assembly.

A series of benzoxazine monomer supramolecules with different substituted groups on their benzene ring was prepared with a Mannich reaction and characterized by FTIR, 1H-NMR and MS. The obtained products were 3,4-dihydro-3-(2'-hydroxyethylene)-6-methyl-2H-benzoxazine (BM1), 3,4-dihydro-3-(2'-hydroxyethylene)-6-ethyl-2H-benz-oxazine (BM2), and 3,4-dihydro-3-(2'-hydroxyethylene)-6-methoxy-2H-benzoxazine (BM3). The efficiency of alkali metal ion extraction from the products was determined with Pedersen's technique, while the complexation of the Ce(III) ion was confirmed by the Job's and the mole ratio methods. The evidence of complex formation between benzoxazine monomers and Ce(III) ions was obtained with FTIR and a computational simulation. Single phase ceria (CeO2) as observed with XRD was successfully prepared by calcinating the Ce(III)-benzoxazine monomer complexes at 600 °C for 2 h. In addition, the geometry of the ceria nanoparticles confirmed by TEM is spherical, with an average diameter of 10-20 nm.

Removal of cerium ions from aqueous solution by hydrous ferric oxide--a radiotracer study.

Radiotracer technique has been used to study the removal behavior of Ce (III) ions from aqueous solutions by synthesized and well characterized hydrous ferric oxide (HFO). Adsorptive concentration (10(-4)-10(-8) mol dm(-3)), pH (ca 4.0-10.0) and temperature (303-333 K) were examined for assessing optimal conditions for removal of these ions. The uptake of Ce (III) ions, which fitted well for Freundlich and D-R isotherms, increased with increase in the temperature and no significant desorption took place in the studied temperature range. The presence of some anions/cations affected the uptake of metal ion markedly. Irradiation of hydrous ferric oxide and tungsten oxide by using a 11.1×10(9) Bq (Ra-Be) neutron source having a neutron flux of 3.9×10(6) cm(-2) s(-1) with associated γ-dose rate of 1.72 Gy/h did not influence the extent of adsorption of Ce (III) significantly.

Uptake and inflammatory effects of nanoparticles in a human vascular endothelial cell line.

The mechanisms governing the correlation between exposure to nanoparticles and the increased incidence of cardiovascular disease remain unknown. Nanoparticles appear to cross the pulmonary epithelial barrier into the bloodstream, raising the possibility of direct contact with the vascular endothelium. Because endothelial inflammation is critical for the development of cardiovascular pathology, we hypothesized that direct exposure of human aortic endothelial cells (HAECs*) to nanoparticles induces an inflammatory response and that this response depends on the composition of the particles. To test this hypothesis, we incubated HAECs for 1 to 8 hours with different concentrations (0.001-50 microg/mL) of iron oxide (Fe2O3), yttrium oxide (Y2O3), cerium oxide (CeO2), and zinc oxide (ZnO) nanoparticles. Using real-time reverse transcriptase-polymerase chain reaction (RT-PCR), we subsequently measured messenger RNA (mRNA) levels of three markers of inflammation: intercellular cell adhesion molecule-1 (ICAM-1), interleukin-8 (IL-8), and monocyte chemotactic protein-1 (MCP-1). The particles were well characterized in terms of size, surface area, composition, and crystal structure. To determine the interactions of nanoparticles with HAECs, we used inductively coupled plasma-mass spectrometry (ICP-MS) to measure the concentration of internalized particles. Our data indicate that the delivery of nanoparticles to the HAEC surface and their uptake within the cells correlate directly with the concentration of particles in the cell culture medium. Transmission electron microscopy (TEM) revealed that the Fe2O3, Y2O3, and ZnO nanoparticles are internalized by HAECs and are often found within intracellular vesicles (the CeO2 particles were not imaged). Fe2O3 nanoparticles did not provoke an inflammatory response in HAECs at any of the concentrations tested, CeO2 particles elicited no response at low concentrations and a weak response above 10 microg/mL, and Y2O3 and ZnO nanoparticles elicited a pronounced inflammatory response above a threshold concentration of 10 microg/mL. We used fluorescent markers to identify the production of reactive oxygen species (ROS) in cells; the results showed that Y2O3 and ZnO particles at the highest concentrations may lead to the production of ROS. At the highest concentration, ZnO nanoparticles caused significant loss of cell adherence. These results demonstrate that inflammation in HAECs after acute exposure to metal oxide nanoparticles depends on the concentration and composition of the particles.

Recovery of rare metal compounds from nickel-metal hydride battery waste and their application to CH4 dry reforming catalyst.

The recovery of valuable components such as nickel from nickel-metal hydride (Ni-MH) battery waste by chemical processes and their applications to CH(4) dry reforming catalysts were investigated. Three types of compound, identified by XRD analysis as NiO, CeO(2) and LaCoO(3) phases, were successfully separated from the waste by a series of chemical processes at room temperature using aqueous solutions of HCl, NaOH and NH(3), and Ni component of approximately 70% in Ni-MH battery waste was recovered. The separated NiO, CeO(2) and LaCoO(3) showed catalytic activities for CH(4) dry reforming. In particular, the separated NiO easily reduced to Ni(0) at an initial stage, and exhibited excellent catalytic activity in terms of CH(4) conversion and stability. Furthermore, it was found that the resulting Ni from separated NiO exhibited an anomalous catalysis from the comparison with that from regent NiO.

Removal of oxide nanoparticles in a model wastewater treatment plant: influence of agglomeration and surfactants on clearing efficiency.

The rapidly increasing production of engineered nanoparticles has created a demand for particle removal from industrial and communal wastewater streams. Efficient removal is particularly important in view of increasing long-term persistence and evidence for considerable ecotoxicity of specific nanoparticles. The present work investigates the use of a model wastewater treatment plant for removal of oxide nanoparticles. While a majority of the nanoparticles could be captured through adhesion to clearing sludge, a significant fraction of the engineered nanoparticles escaped the wastewater plant's clearing system, and up to 6 wt % of the model compound cerium oxide was found in the exit stream of the model plant. Our study demonstrates a significant influence of surface charge and the addition of dispersion stabilizing surfactants as routinely used in the preparation of nanoparticle derived products. A detailed investigation on the agglomeration of oxide nanoparticles in wastewater streams revealed a high stabilization of the particles against clearance (adsorption on the bacteria from the sludge). This unexpected finding suggests a need to investigate nanoparticle clearance in more detail and demonstrates the complex interactions between dissolved species and the nanoparticles within the continuously changing environment of the clearing sludge.

[The research on preparing CeO2 nanocrystalline by homogeneous precipitation method].

CeO2 nanocrystallines were prepared by homogeneous complexed-precipitation method, using cerous nitrate and ammonium tartrate as raw materials. The effects of cerous tartrate complex compound and the way of producing precipitation on the particle size of samples were investigated. The samples were characterized by XRD, TEM and SEM. The SEM micrograph shows that the foam exhibits a perforated porousness stereostructure in shape, and the HRTEM picture of the particles reveals the clear crystal lattice. All the results indicate that the samples were CeO2 nanocrystalline.

Preparation and structure of CeSc2N@C80: an icosahedral carbon cage enclosing an acentric CeSc2N unit with buried f electron spin.

Herein, we report the preparation, purification, and characterization of a mixed trimetallic nitride endohedral metallofullerene, CeSc(2)N@C(80). Single-crystal X-ray diffraction shows that CeSc(2)N@C(80) consists of a four-atom asymmetric top (CeSc(2)N) inside a C(80) (I(h)()) carbon cage. Unlike the situation in most endohedrals of the M(3)N@C(2)(n)() type, the nitride ion is not located at the center of the carbon cage but is offset by 0.36 A in order to accommodate the large Ce(III) ion. The cage carbon atoms near the endohedral Ce and Sc atoms exhibit significantly larger pyramidal angles than the other carbon atoms on the C(80) cage. Surprisingly, at ambient temperature, the (13)C NMR spectrum exhibits isotropic motional averaging yielding only two signals (3 to 1 intensity ratio) for the icosahedral C(80) cage carbons. At the same temperature, the (45)Sc NMR exhibits a relatively narrow, symmetric signal (2700 Hz) with a small temperature-dependent Curie shift. A rotation energy barrier (E(a) = 79 meV) was derived from the (45)Sc NMR line-width analysis. Finally, the XPS spectrum for CeSc(2)N@C(80) confirms a +3 oxidation state for cerium, Ce(3+)(4f(1)5d(0)). This oxidation state and the Curie shift are consistent with a weakly paramagnetic system with a single buried f electron spin.

Biosorption of rare earth metal ion on aerobic granules.

Aerobic granules are microbial aggregates possessing excellent settling ability and high-porosity structure. In this study, aerobic granules as a novel type of biosorbent were used for cerium's removal from aqueous solution simulating the polluted industrial wastewater. Batch trials were conducted at different initial cerium ion and granule concentration. Biosorption kinetics was also studied. The biosorption conformed to a first-order kinetics model. The results showed that the biosorption ability of aerobic granules was related to both initial cerium ion and granule concentration. The maximum biosorption capacity of cerium by aerobic granules was 357 mg g(-1) granules. The aerobic granules were settled down by gravity from the aqueous solution in one minute after the biosorption experiments. Thus, the post-separation of the conventional suspended biosorbents from the treated effluent could be ignored in the aerobic granule-based biosorption process. All the results confirmed the technical feasibility of the biosorption process by aerobic granules.