Efficient biomimetic aerobic oxidation of phenylethane catalyzed by P(4VP-co-St)/SiO2-supported metalloporphyrins

In this work, three kinds of metalloporphyrins (CoPs, FePs, and MnPs) were immobilized on the grafting particles P(4VP-co-St)/SiO₂ through the axial coordination reaction, respectively, and the supported biomimetic catalysts MP-P(4VP-co-St)/SiO₂ (M = Co, Fe and Mn) were prepared. The catalytic performances of various supported biomimetic catalysts for the oxidation of phenylethane in the absence of any reductant and solvent were investigated and compared detailedly. The experimental results show that the supported catalysts MP-P(4VP-co-St)/SiO₂ can effectively activate dioxygen, and obviously catalyze the oxidation of phenylethane to hypnone. When MPs are immobilized on the supports P(4VP-co-St)/SiO₂, the catalytic activity of MP-P(4VP-co-St)/SiO₂ is improved greatly. Also the catalytic activities of MP-P(4VP-co-St)/SiO₂ differ among the different metals, according to the following series: Co(II) > Fe(III) > Mn(III). Under the reaction conditions of 393 K and the ordinary pressure of oxygen, the catalyst CoP-P(4VP-co-St)/SiO₂ gave wonderful results with 24 mol% yield and 95% selectivity to the main product hypnone, and the another product, α-phenylethanol was few. All these results indicate that the grafting particles P(4VP-co-St)/SiO₂ can not only protect metalloporphyrin from oxidation, but also promote it to activate O₂. Additionally, some rules were specially found in the studies: (1) CoPs as a biomimetic catalyst had an optimum used amount, and excess addition would make the catalyst activity worse; (2) the immobilization density of CoPs on P(4VP-co-St)/SiO₂ surface still had the high-point; (3) the catalyst activity trended to steady during nine cycle.     

A novel method for immobilization of Co tetraphenylporphyrins on P(4VP-co-St)/SiO2: Efficient catalysts for aerobic oxidation of ethylbenzenes

In this paper, poly(4vinylpyridine-co-styrene) (P(4VP-co-St)) was grafted on silica gel particles in the manner of “grafting from”, and the grafting particle P(4VP-co-St)/SiO₂ was gained. The grafting particle P(4VP-co-St)/SiO₂ is a novel kind of supports for immobilizing metalloporphyrin catalysts. Then, the immobilization of cobalt tetraphenylporphyrin (CoTPP) on the supports P(4VP-co-St)/SiO₂ was carried out via the axial coordination reaction between CoTPP and the pyridine groups of the grafted P(4VP-co-St), resulting in the heterogenised catalysts CoTPP-P(4VP-co-St)/SiO₂. The synthesized catalysts were characterized by FTIR and the axial coordination process between CoTPP and the grafted P(4VP-co-St) was confirmed by UV-vis. The effects of various factors on the immobilization reaction of CoTPP were studied in detail. Finally, the catalytic performance of CoTPP-P(4VP-co-St)/SiO₂ in the catalytic oxidation process of ethyl benzene was investigated. The experimental results show that the axial coordination reaction is a very easy and novel method for favorably immobilizing CoTPP onto the P(4VP-co-St)/SiO₂ surfaces. During the immobilization process of CoTPP on P(4VP-co-St)/SiO₂, the most bonding amount of CoTPP (0.19 g/g) is obtained under the lower temperature (5 °C) and the higher concentration of CoTPP(6.0 mg/ml) lasting 4 h. Moreover, the supported catalyst CoTPP-P(4VP-co-St)/SiO₂ can effectively activate the dioxygen, and obviously catalyze the transform of ethylbenzene into acetophenone. So it exhibits the fine catalytic activity.     

Immobilization of quaternary ammonium salts on grafting particle polystyrene/SiO2 and preliminary study of application performance

Polystyrene (PSt) was grafted on the surface of silica gel particles in the manner of “grafting from” in a solution polymerization system, and grafting particles PSt/SiO₂ was obtained. The chloromethylation reaction of the grafted polystyrene was performed using a novel chloromethylation reagent, 1,4-bis(chloromethyoxy)butane which is un-carcinogenic, and grafting particles CMPS/SiO₂ was gained. Subsequently, grafted CMPS was quaternized (denoted as QPS) using tertiary amine, and finally functional composite-type particles QPS/SiO₂, on which quaternary ammonium groups were immobilized, were prepared. The catalysis activity of the particle QPS/SiO₂ as a triphase catalyst in phase-transfer catalysis systems and its antibacterial activity as a water-insoluble antibacterial material were studied preliminarily. The experimental results show that the particle QPS/SiO₂ exhibits higher catalysis activity as a triphase catalyst for the reaction between benzyl chloride in organic phase and sodium acetate in aqueous phase to form benzyl acetate, and under a mild condition of 60 °C for 7 h of reaction time a conversion of 66% for benzyl chloride can be obtained. The particle QPS/SiO₂ has high antibacterial activity as a water-insoluble antibacterial material against Escherichia coli (E. coli).     

Adsorption performance and mechanism of 2,4,6-trinitrotoluene on a novel adsorption material polyvinylbenzyl acid/SiO2

Polyvinylbenzene (PVB, namely polystyrene, PSt) was grafted on the surface of silica gel particles by “grafting from” in solution polymerization system, and grafting particles PVB/SiO₂ were obtained. The chloromethylation reaction of the grafted polyvinylbenzene was performed using a novel chloromethylation reagent, 1,4-bis (chloromethyoxy) butane that is un-carcinogenic, and grafting particles CMPVB/SiO₂ were obtained. Subsequently, chloromethyl groups on grafting particles CMPVB/SiO₂ were hydrolyzed and oxidized, and finally adsorption material polyvinylbenzyl acid/SiO₂ (PVBA/SiO₂) was prepared. The adsorption performances and mechanism of 2,4,6-trinitrotoluene (TNT) on PVBA/SiO₂ were investigated through static methods. The experimental results showed that PVBA/SiO₂ possessed strong adsorption ability for TNT with adsorption amount of 26.84 mg g⁻¹. The empirical Freundlich isotherm was also found to agree well with the equilibrium adsorption data. In addition, pH was found to have great influence on the adsorption amount. Finally, PVBA/SiO₂ was observed to possess excellent reusability as well.     

焙烧温度对SiO2负载的Co3O4纳米粒子表面氧缺陷浓度和CO氧化催化性能的影响

以传统的浸渍法,在不同焙烧温度下制备了用于CO氧化反应的Co₃O₄/SiO₂催化剂．通过激光拉曼光谱(Raman)、X射线光电子能谱(XPS)、X射线衍射(XRD)、程序升温还原(TPR)和X射线吸收精细结构谱(XAFS)表征了该系列催化剂的结构．在所有的催化剂中,XRD和Raman光谱都只检测到了Co₃O₄晶相的存在．与Co₃O₄体相相比,XPS结果表明在200 oC焙烧的(Co₃O₄(200)/SiO₂)催化剂中Co₃O₄表面上存在着过量的Co²⁺．与XPS的结果一致,TPR结果表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄表面上存在氧缺陷, 并且XAFS结果也表明Co₃O₄(200)/SiO₂催化剂中Co₃O₄具有更多的Co²⁺．提高焙烧温度使得过量的Co²⁺进一步氧化为Co³⁺,同时降低了表面氧缺陷浓度,从而得到计量比的Co₃O₄4/SiO₂催化剂．在所有的负载催化剂中Co₃O₄(200)/SiO₂催化剂表现出了最好的CO氧化催化性能,表明过量Co²⁺和表面氧缺陷的存在能够促进Co₃O₄催化CO氧化反应的活性.     

Preparation of functional composite grafted particles PDMAEMA/SiO2 and preliminarily study on functionality

Micron-sized silica gel particles were first surface-modified with coupling agent, γ-methacryloylpropyl trimethoxysilane (MPS), and the polymerizable double bonds were introduced onto the surfaces of silica gel particles, forming the modified particles MPS-SiO₂. Subsequently, N,N-dimethylaminoethyl methacrylate (DMAEMA) was graft-polymerized on the surfaces of particles MPS-SiO₂ in the manner of “grafting through”, resulting in the grafted particles PDMAEMA/SiO₂. The grafted particles PDMAEMA/SiO₂ were fully characterized with several means. The graft polymerization process of DMAEMA on particles MPS-SiO₂ was studied in detail, and the optimal reaction conditions were determined. Thereafter, the adsorption properties of the grafted particles PDMAEMA/SiO₂ for chromate anion and Cu²⁺ ion were preliminarily examined respectively. The experimental results indicate that the PDMAEMA grafting degree on PDMAEMA/SiO₂ particles is limited because an enwinding polymer layer as a kinetic barrier on the surfaces of silica gel particles will be formed during the graft polymerization, and blocks the graft polymerization. In order to enhance PDMAEMA grafting degree, reaction time and temperature, and the used amount of initiator as well as the monomer concentration should be effectively controlled. The preliminary adsorption tests show that the grafted particles PDMAEMA/SiO₂ are multi-functional. They possess very strong adsorption ability for CrO₄²⁻ anion by right of strong electrostatic interaction, and have also adsorption action towards heavy metal ion by dint of complexing action.     

Preparation and characterization of novel Pd/SiO2 and Ca-Pd/SiO2 egg-shell catalysts with porous hollow silica

Novel egg-shell structured monometallic Pd/SiO₂ and bimetallic Ca-Pd/SiO₂ catalysts were prepared by an impregnation method using porous hollow silica (PHS) as the support and PdCl₂ and Ca(NO₃)₂·4H₂O as the precursors. It was found from transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) that Pd was loaded on PHS with a particle size of 5-12 nm in Pd/SiO₂ samples and the Pd particle size in Ca-Pd/SiO₂ was smaller than that in Pd/SiO₂ since Ca could prevent Pd particles from aggregating. X-ray photoelectron spectroscopy (XPS) analyses exhibited that Pd 3d_5/2 binding energies of Pd/SiO₂ and Ca-Pd/SiO₂ were 0.2 and 0.9 eV lower than that of bulk Pd, respectively, as a result of the shift of the electron cloud from Pd to oxygen in Pd/SiO₂ and to both oxygen and Ca in Ca-Pd/SiO₂. The activity of Ca-Pd/SiO₂ egg-shell catalyst for CO hydrogenation and the selectivity to methanol, with a value of 36.50 mmol_CO mol⁻¹_Pd s⁻¹ and 100%, respectively, were much higher than those of the catalysts prepared with traditional silica gel as the support, owing to the porous core-shell structure of the PHS support.     

Synthesis and characterization of Mn-doped Zn2SiO4/SiO2 phosphor particles in core-shell structure

Manganese-doped zinc silicate (Zn₂SiO₄:Mn) is a kind of phosphor material that has a photo-luminescent (PL) and cathode-luminescent (CL) properties with intensive green light emission at 520 nm. The particles consisting of SiO₂@Zn₂SiO₄:Mn (SiO₂ core-Zn₂SiO₄:Mn shell) were synthesized via colloidal process and forced precipitation. After drying, the Zn/Mn precipitates were coated on the surface of SiO₂ particles. The Zn/Mn precipitates reacted with SiO₂ and transformed to Zn₂SiO₄:Mn by suitable calcination. The microstructure, crystalline phase, and luminescent characteristics of the products were studied. Besides, a CL device consisting of the core-shell powder was characterized.     

Size-Dependent HCl Generation of PVC/SiO2 Micro- and Nanocomposites

In this study HCl generation of polyvinyl (chloride) (PVC)/SiO₂ composites during its combustion was investigated. SiO₂ with different particle sizes were used as HCl absorbers and their HCl uptake ability results were compared to that of CaCO₃. It was found that the amount of released HCl gas during PVC combustion decreased in the presence of SiO₂. The HCl uptake ability of SiO₂ improved with decreasing of its particle size. Although thermogravimetric analysis (TGA) results showed that SiO₂ particles decreased the first thermal degradation temperature (T _onset) of PVC by initiating dehydrochlorination of PVC at lower temperatures, SiO₂ particles had more effective HCl uptaking ability than that of CaCO₃. Scanning electron microscopy (SEM) micrographs showed that some aggregates whose size was less than 100 nm were formed when Si-25 nm was used as filler. When SiO₂ with micron size was added to PVC as filler, more uniform and better distribution of the SiO₂ on the surface was observed.     

Effect of combination of noble metals and metal oxide supports on catalytic reduction of NO by H2

We investigated the effects of combination of noble metals M (Rh, Pd, Ir, Pt) and metal oxide supports S (Al₂O₃, SiO₂, ZrO₂, CeO₂) on the NO + H₂ reaction using planar catalysts with M/S two layered thin films on Si substrate. In this study, NO reduction ability per metal atom were evaluated with a specially designed apparatus employing pulse valves for the injection of reactant molecules onto catalysts and a time-of-flight mass spectrometer to measure multiple transient products: NH₃, N₂ and N₂O simultaneously as well as with an atomic force microscopy to observe the surface area of metal particles. The catalytic performances of Rh and Ir catalysts were hardly affected by a choice of a metal oxide support, while Pd and Pt catalysts showed different catalytic activity and selectivity depending on the metal oxide supports. This assortment is consistent with ability to dissociate NO depending on metals without the effect of any support materials. There, the metals to the left of Rh and Ir on the periodic table favor dissociation of NO and those to the right of Pd and Pt tend to show molecular adsorption of NO. Therefore, the catalytic property of noble metals could be assorted into two groups, i.e. Rh and Ir group whose own property would mainly dominate the catalytic performance, and Pd and Pt group whose interaction with metal oxides supports would clearly contribute to the reaction of NO with H₂. NO reduction activity of Pd and Pt was found to be promoted above that of Rh and Ir, provided that Pd and Pt were supported by CeO₂ and ZrO₂.     

Formation of Y-junction carbon nanotubes by catalytic CVD of methane

Y-junction carbon nanotubes were grown by catalytic CVD of methane at 700 ^°C on NiO-CuO-MoO(7:2:1) (w/w/w)/SiO₂ catalyst. For comparison, NiO-CuO(8:2) (w/w)/SiO₂ and NiO-MoO(8:2) (w/w)/SiO₂ catalysts were tested for carbon nanotube formation. TEM analysis indicates that no Y-junction structures were formed with the latter two catalysts. This finding elucidates why the addition of a small amount of MoO to NiO-CuO/SiO₂ catalyst is crucial for enhancing the formation of Y-junction carbon nanotubes.     

Flowability and Mechanical and Thermal Properties of Nylon 6/Ethylene bis-Stearamide/Carboxylic Silica Composites

Nylon 6 (PA 6)/ethylene bis-stearamide (EBS)/SiO₂- carboxylic acid-functionalized silica nanoparticles (COOH) composites were prepared by in-situ polymerization of caprolactam. SiO₂-COOH was used to enhance the compatibility between SiO₂ and PA 6 matrix. For comparison, pure PA 6 and PA 6/EBS composites were also prepared via the same method. The PA 6/EBS/SiO₂-COOH composites with low content of EBS and SiO₂-COOH had greater melt-flow index (MFI) (the value of MFI increased by 50%–80%) than the pure PA 6. The results of mechanical properties showed almost no decrease in the tensile strength of PA 6/EBS/SiO₂-COOH composites, with the bending strength decreasing by 17%–21%. However, the Izod impact strength of the PA 6/EBS/SiO₂-COOH composites was greatly improved compared with pure PA 6, which indicated that the toughness of PA 6/EBS/SiO₂-COOH had been greatly improved. The morphology of Izod impacted fractured surfaces of PA 6/EBS/SiO₂-COOH was observed by scanning electron microscopy. The results revealed that the PA 6/EBS/SiO₂-COOH composites presented a typical ductile fracture behavior with large amounts of long and large strip-like cracks. When the content of SiO₂-COOH was 0.2 wt%, the SiO₂-COOH particles were uniformly dispersed over the entire body of the PA 6 matrix. The results from differential scanning calorimetry indicated that the melting point (T_m), degree of crystallinity (X_c), and crystallization temperatures (T_c) of PA 6/EBS/SiO₂-COOH composites were lower than the pure PA 6.     

A Study on the Morphology and Mechanical Properties of PVC/nano‐SiO2 Composites

Three methods were used to modify nano‐SiO₂ particles with various interfaces and interfacial interactions between the particles and Poly(vinyl chloride) (PVC) matrix. The experimental results show that direct surface treatment of nano‐SiO₂ particles with a silane coupling agent (KH‐550) is not effective for improving the mechanical properties of PVC/SiO₂ composites. Both ultrasonic oscillations and high energy vibromilling improve the interfacial interactions between SiO₂ particles and PVC matrix. With these methods, the aggregation of SiO₂ particles was inhibited and a good dispersion of SiO₂ particles in PVC matrix was obtained, which improved the mechanical properties of the PVC/SiO₂ composite. The mechanical properties of the PVC/SiO₂ composite with high energy vibromilling modified SiO₂ particles were remarkably improved. Scanning electronic microscopy (SEM), transmission electronic microscopy (TEM), dynamic mechanical analysis (DMA), and theoretical calculations demonstrate these improvements.     

A versatile sonication-assisted deposition–reduction method for preparing supported metal catalysts for catalytic applications

This work aims to develop a rapid and efficient strategy for preparing supported metal catalysts for catalytic applications. The sonication-assisted reduction–precipitation method was employed to prepare the heterogeneous mono- and bi-metallic catalysts for photocatalytic degradation of methyl orange (MO) and preferential oxidation (PROX) of CO in H₂-rich gas. In general, there are three advantages for the sonication-assisted method as compared with the conventional methods, including high dispersion of metal nanoparticles on the catalyst support, the much higher deposition efficiency (DE) than those of the deposition–precipitation (DP) and co-precipitation (CP) methods, and the very fast preparation, which only lasts 10–20 s for the deposition. In the AuPd/TiO₂ catalysts series, the AuPd(3:1)/TiO₂ catalyst is the most active for MO photocatalytic degradation; while for PROX reaction, Ru/TiO₂, Au–Cu/SBA-15 and Pt/γ-Al₂O₃ catalysts are very active, and the last one showed high stability in the lifetime test. The structural characterization revealed that in the AuPd(3:1)/TiO₂ catalyst, Au–Pd alloy particles were formed and a high percentage of Au atoms was located at the surface. Therefore, this sonication-assisted method is efficient and rapid in the preparation of supported metal catalysts with obvious structural characteristics for various catalytic applications.     

Synthesis of Au-CeO2/SiO2 catalyst via adsorbed-layer reactor technique combined with alcohol-thermal treatment

Au-CeO₂/SiO₂ was prepared via adsorbed-layer reactor technique combined with alcohol-thermal treatment. The catalytic performance in complete oxidation of benzene was investigated. TEM, Raman characterization showed that Au particles grew up obviously during alcohol-thermal process, while CeO₂ particles maintained 4 nm in diameter. The content of oxygen vacancies and adsorbed oxygen species on catalysts surface increased apparently. Alcohol-thermally treated Au-CeO₂/SiO₂ and CeO₂/SiO₂ showed similar change in catalytic performance, and were much superior to calcined CeO₂/SiO₂. Of alcohol-thermally treated and calcined CeO₂/SiO₂, initial temperatures of the reaction were 80 °C and 150 °C, respectively. The benzene conversions reached 85% and 40% at 300 °C.     

Mechanochemically conjugated PMHS/nano-SiO2 hybrid and subsequent optimum grafting density study

In this paper, we reported the preparation of poly(methylhydrosiloxane) (PMHS)/SiO₂ hybrid particles by mechanochemical method based on high energy ball milling (HEBM). The obtained hybrid particles were characterized by Fourier transform infrared (FT-IR) spectroscopy, ²⁹Si CP (cross-polarization) MAS NMR, viscosity measurement, particle size distribution, thermal analysis (TGA, DSC and DTG), static contact angle (CA), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). FT-IR and ²⁹Si CP MAS NMR spectra indicate that PMHS is chemically anchored onto the surface of nano-SiO₂. Viscosity measurement, particle size distribution, FE-SEM and TEM demonstrate that an appropriate grafting density optimizes the dispersion of nanoparticles in poly(dimethylsiloxane) (PDMS) matrix, so lower viscosity can be achieved. Too high or too low grafting density may only achieve suboptimal and poor dispersions. The optimum grafting density of PMHS on nano-SiO₂ was determined by thermal analysis, with approximately 0.0531 PMHS/nm². Static contact angle measurement indicates that the water contact angle of hybrid particles is modulated by changing the grafting density of PMHS on nano-SiO₂. The CA value of PMHS/SiO₂ hybrid with optimum grafting density is 139.4°, and the highest CA value of PMHS/SiO₂ hybrid is approximately 158.2°.     

A facile synthesis of monodisperse CoFe2O4/SiO2 nanoparticles

Aminated-CoFe₂O₄/SiO₂ magnetic nanoparticles (NPs) were prepared from primary silica particles using modified StÖber method. By optimizing the preparation conditions, monodisperse CoFe₂O₄/SiO₂ NPs with high amino groups’ density were obtained, which is necessary for enzyme immobilization. TEM confirm that the sample is a core/shell structure. These aminated-CoFe₂O₄/SiO₂ NPs have narrow size distributions with a mean size of about 60 nm. Moreover, the aminated-CoFe₂O₄/SiO₂ NPs can be easily dispersed in aqueous medium. The experimental results also show that the NPs have superparamagnetism, indicating that the aminated-CoFe₂O₄/SiO₂ NPs can be used as an effective carrier for the enzyme immobilization.     

Spherical Zn2SiO4:Eu@SiO2 phosphor particles in core-shell structure: Synthesis and characterization

Spherical SiO₂ particles have been coated with Zn₂SiO₄:Eu³⁺ phosphor layers by a Pechini sol-gel process. The microstructure and luminescent properties of the obtained Zn₂SiO₄:Eu³⁺@SiO₂ particles were well characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), photoluminescence (PL) spectra, and lifetime. The results demonstrate that the Zn₂SiO₄:Eu³⁺@SiO₂ particles, which have regular and uniform spherical morphology, emitted an intensive red light emission at 613 nm under excitation at 395 nm. Besides, the effects of the Eu³⁺ concentration, annealing temperature and charge compensators of Li⁺ ions on the PL emission intensities were investigated in detail.     

Synthesis and characterization of monodisperse spherical core-shell structured SiO2@Y3Al5O12:Ce3+/Tb3+ phosphors for field emission displays

Nanocrystalline Y₃Al₅O₁₂: Ce³⁺/Tb³⁺ (average crystalline size 30 nm) phosphor layers were coated on non-aggregated, monodisperse and spherical SiO₂ particles by the sol-gel method, resulting in the formation of core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles. X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy, photoluminescence, cathodoluminescence spectra, as well as lifetimes were utilized to characterize the core-shell structured SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ phosphor particles. The obtained core-shell structured phosphors consist of well-dispersed submicron spherical particles with a narrow size distribution. The thickness of the Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ shells on the SiO₂ cores (average size about 500 nm, crystalline size about 30 nm) could be easily tailored by varying the number of deposition cycles (100 nm for four deposition cycles). Under the excitation of ultraviolet and low-voltage electron beams (1–3 kV), the core-shell SiO₂@Y₃Al₅O₁₂:Ce³⁺/Tb³⁺ particles show strong yellow-green and green emission corresponding to the 5d–4f emission of Ce³⁺ and ⁵D₄–⁷F _J (J = 6, 5, 4, 3) emission of Tb³⁺, respectively. These phosphors may have potential application in field emission displays.     

Synthesis and Optical Properties of SiO2-Coated CeO2 Nanoparticles

Silica (SiO₂)-coated ceria (CeO₂) nanoparticles were prepared using water-in-oil microemulsion. Polyoxyethylene (15) cetylether and cyclohexane were used as a surfactant and organic solvent. SiO₂-coated CeO₂ nanoparticles were obtained by hydrolysis of metal alkoxide (tetraethylorthosilicate, TEOS) in the solution containing CeO₂ precursor nanoparticles. The effects of CeO₂ sources (Ce metal salt) and CeO₂ particle-forming agents on the morphology of SiO₂–CeO₂ particles were investigated. Observation via transmission electron microscopy revealed that the type of particle-forming agent affected the nanoparticles' morphology and that CeO₂ nanoparticles were spherically coated with SiO₂ when using oxalic acid ((COOH)₂) as a particle-forming agent of CeO₂. Furthermore, the transmittance of the particles was high in the visible region (above 400 nm) and decreased in the ultraviolet region.