Nanosized GdVO4 powders synthesized by sol-gel method using different carboxylic acids
来源期刊:Rare Metals2018年第7期
论文作者:Sulawan Kaowphong Nawapong Chumha Piyarat Nimmanpipug Sila Kittiwachana
文章页码:561 - 567
摘 要:Nanosized GdVO4 powders were synthesized via a sol-gel method using different carboxylic acids as chelating agent, followed by calcination at 600 ℃ for 3 h.The effect of different carboxylic acids such as citric acid,malic acid, and tartaric acid on the characteristics of the nanosized GdVO4 powders was investigated. The GdVO4 powder was also synthesized without carboxylic acid for comparison. The thermal decomposition process of the carboxylate precursors was investigated by thermogravimetric differential thermal analysis(TG-DTA). X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR),field emission scanning electron microscope(FESEM),transmission electron microscope(TEM), and surface area measurement data were used to confirm the formation of nanocrystalline GdV04 powders. It is found that the synthesis using the carboxylic acid with higher heat of combustion results in the powder with larger crystallite size. The difference in the steric effect of the acids used,which was evaluated by a computational method, also affects the degree of agglomeration of the synthesized powders.
稀有金属(英文版) 2018,37(07),561-567
Sulawan Kaowphong Nawapong Chumha Piyarat Nimmanpipug Sila Kittiwachana
Department of Chemistry, Faculty of Science, Chiang Mai University
作者简介:*Sila Kittiwachana e-mail:silacmu@gmail.com;
收稿日期:30 May 2015
基金:financially supported by the Chiang Mai University (CMU) Junior Research Fellowship Program;the National Research University (NRU) Project from Thailand's Office of the Higher Education Commission;
Sulawan Kaowphong Nawapong Chumha Piyarat Nimmanpipug Sila Kittiwachana
Department of Chemistry, Faculty of Science, Chiang Mai University
Abstract:
Nanosized GdVO4 powders were synthesized via a sol-gel method using different carboxylic acids as chelating agent, followed by calcination at 600 ℃ for 3 h.The effect of different carboxylic acids such as citric acid,malic acid, and tartaric acid on the characteristics of the nanosized GdVO4 powders was investigated. The GdVO4 powder was also synthesized without carboxylic acid for comparison. The thermal decomposition process of the carboxylate precursors was investigated by thermogravimetric differential thermal analysis(TG-DTA). X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR),field emission scanning electron microscope(FESEM),transmission electron microscope(TEM), and surface area measurement data were used to confirm the formation of nanocrystalline GdV04 powders. It is found that the synthesis using the carboxylic acid with higher heat of combustion results in the powder with larger crystallite size. The difference in the steric effect of the acids used,which was evaluated by a computational method, also affects the degree of agglomeration of the synthesized powders.
Keyword:
GdVO4; Electron microscopy; Sol-gel processes; X-ray method;
Received: 30 May 2015
1 Introduction
Gadolinium vanadate (GdVO4) has been extensively used as laser material
A sol-gel method is a promising method for synthesizing nanosized powders.For the sol-gel synthesis,a chelating agent is one of the factors crucial to the success of the process.Generally,citric acid is used as the chelating agent since theα-hydroxycarboxylic functional groups of this acid could easily form stable complexes with the metal ions,thereby facilitating homogeneous mixing of the cations in the solution which assists good stoichiometry control
However,the effect of changing the chelating agent on the synthesis of the nanosized GdVO4 particles is interesting.This is because different chelating agents differ in both the number of carboxylic groups and the combustion heat provided,which can have an effect on the characteristics of the synthesized products.In this research,the nanosized GdVO4 particles were synthesized by a sol-gel method using different carboxylic acids such as citric acid,malic acid,and tartaric acid as chelating agents.The characteristics such as purity,crystallite size,morphology,specific surface area,and nature of agglomeration of the synthesized GdVO4 powders were examined in relation to the chelating agent used.
2 Experimental
Gd(OAc)3 and NH4VO3 with 1:1 in mole ratio were separately dissolved in deionized water and mixed into a homogeneous solution.The carboxylic acid (citric acid,malic acid,and tartaric acid) was then added into the solution,where the mole ratio of the total metal ions to the acid was 1:2.Then,the solution was heated under continuous stirring at 80℃.After a viscous gel was formed,the gel was subsequently dried at 80℃overnight to obtain a carboxylate precursor.The precursor was calcined at 600℃for 3 h,which resulted in a yellow powder.The GdVO4 powder was also synthesized without the carboxylic acid serving as chelating agent for comparison.
Thermogravimetric (TG) analysis and differential thermal analysis (DTA) of the carboxylate precursors were measured using PerkinElmer TGA7 and DTA7 devices,respectively,with a heating rate of 10℃·min-1 from 50 to800℃under a flowing nitrogen atmosphere.Structure,purity,and crystallinity of the products were analyzed by X-ray diffraction (XRD,Rigaku MiniFlex II) using Cu Ka radiation (λ=0.154 nm).Fourier transform infrared spectroscopy (FTIR,Bruker TENSOR27) was used to investigate the vibration modes and the residual organic molecules.Particle size and morphology of the products were investigated by field emission scanning electron microscope (FESEM,JEOL JSM-6335F) operating at accelerating voltage of 15 kV and transmission electron microscope (TEM,JEOL JEM-2010) operating at 200 kV.Specific surface areas of the nanopowders were obtained by the Brunauer-Emmett-Teller (BET) method using QuantaChrome AutoSorb-1-MP analyzer.
3 Results and discussion
The thermal decomposition behaviors of the carboxylate precursors between 50 and 800℃were investigated by TG-DTA,as shown in Fig.1.All precursors show similar behavior,with three main steps of thermal decomposition described as follows.The first step is weight loss in the temperature range of 50-200℃,with weight loss of about10%-11%,and accompanied by the endothermic peak at about 100℃in the DTA curve of the precursors.This is attributed to the vaporization of the physically absorbed water.The second step is in the temperature range of200-470℃,with weight loss of about 43%-49%,and accompanied by an exothermic peak in the DTA curve.This implies the decomposition and the combustion reactions of acetate ions,carboxylate ions,and residual organic constituents
FTIR spectra of the carboxylate precursors (Fig.2a)show that O-H stretching band of residual water and the acid is detected at 2700-3700 cm-1
Fig.1 TG-DTA curves of a citrate,b malate,and c tartrate precursors
Fig.2 FTIR spectra of powders a before and b after calcination
The XRD spectra of the powders before calcination are shown in Fig.3a.Corresponding to the FTIR results in Fig.2a,although the GdVO4 signals could be observed only in the XRD pattern of the powder synthesized without chelating agent,they are not sharp and intense.The XRDspectra of all powders after the calcination at 600℃are shown in Fig.3b.It can be seen that all diffraction peaks are found to match well with JCPDS No.17-0260,whichcorresponds to the GdVO4 tetragonal structure.No diffraction peaks from any other impurities are detected,confirming high purity of the products.The intensities of the diffraction peaks of the GdVO4 powders synthesized using the carboxylic acids as chelating agents are relatively higher than that synthesized without the acid,suggesting the improvement of the crystallization of the GdVO4 particles.It could be that the energy evolved from the combustion reaction which can rapidly heat the system to a high temperature and raise the local temperature during calcination
Fig.3 XRD patterns of powders a before and b after calcination
Table 1 Crystallite size (DXRD) based on Debye-Scherrer equation,specific surface area (SSABET),average particle size (DBET),and degree of agglomeration (DBET/DXRD) of synthesized GdVO4powders
where DXRD is the crystallite size in nanometers,λis the wavelength of Cu Kα,βis the full width at half-maximum(FWHM),andθis the half-diffraction angle.The most intense peaks corresponding to (200) plane were used to calculate the crystallite sizes.The calculated crystallite sizes are shown in Table 1.The GdVO4 powder synthesized using citric acid presents a larger crystallite size,whereas those synthesized using malic acid and tartaric acid is smaller.Since the acids during the calcinations act as energy suppliers or fuels
Fig.4 FESEM images of GdVO4 particles synthesized with a citric acid,b malic acid,c tartaric acid,and d without acid
The FESEM images of the GdVO4 powders synthesized using different carboxylic acids,as presented in Fig.4a-c,demonstrate a homogeneous distribution of spherical particles with average particle sizes of about 50-100 nm.To present statistically reliable average size data,the histograms of the particle size distribution of the GdVO4nanoparticles obtained by measuring 800 particles are presented in Fig.5.The particle size distributions are very close to normal curves.The average particle sizes are(62.43±11.62),(73.85±16.79),(55.25±10.78),and(86.13±18.47) nm for the powders prepared using citric acid,malic acid,tartaric acid,and without acid,respectively.The specific surface areas (SSABET) were obtained using BET adsorption of nitrogen gas at the temperature of liquid nitrogen,and the average particle sizes (DBET) were calculated using the following equation;
Fig.5 Particle size distribution curves of GdVO4 particles synthesized with a citric acid,b malic acid,c tartaric acid,and d without acid (dave average particle size,SD standard deviation,dmax maximum particle size,dmin minimum particle size,N total particle numbers)
whereρis the theoretical density of GdVO4 (5.47 g·cm-3)
The TEM images of the GdVO4 powders prepared with and without the acids are shown in Fig.6.The powders are composed of nanoparticles with diameter in the range of50-70,70-110,40-65,and 85-120 nm for the powders prepared using citric acid,malic acid,tartaric acid,and without acid,respectively.The selected area electron diffraction (SAED) patterns illustrated as the insets in Fig.6 show bright concentric rings of the poly crystalline particles.Lattice spacing (d) of the nanoparticles is determined using the following equation
Fig.6 TEM images of GdVO4 particles synthesized with a citric acid,b malic acid,c tartaric acid,and d without acid.Insets in TEM images being SAED patterns (left) and HRTEM images (right)
Lλ=Rd (3)where Lλis the camera constant (2.49630 mm-nm)and R is the radius distance between the rings.The calculated lattice spacing corresponds to (101),(200),(112),(301),and (312) diffraction planes,in agreement with the XRD results,confirming the tetragonal structure of the GdVO4 nanocrystals.High-resolution TEM (HRTEM)images indicate that the GdVO4 nanoparticles have good crystallinity and the crystal lattice fringes of the 0.36,0.25,and 0.28 nm planar spaces correspond well with the (200),(220),and (211) planes of tetragonal GdVO4,respectively.
4 Conclusion
The carboxylic acid-as sis ted sol-gel method is a promising way to synthesize the nanosized GdVO4 powders.The energy released from the combustion process and the steric structures of the carboxylic acids are found to have an effect on the crystallite sizes and the degree of agglomeration of the synthesized nanoparticles.The GdVO4 powder synthesized using citric acid exhibits larger crystallite size than those derived from malic acid and tartaric acid due to the intense heat released during the combustion process which causes the crystallites to grow in size.Considering the synthesis route using the acids,the powder synthesized using malic acid demonstrates the highest degree of agglomeration due to the least steric structure of the chelating agent used.
Acknowledgments This work was financially supported by the Chiang Mai University (CMU) Junior Research Fellowship Program and the National Research University (NRU) Project from Thailand's Office of the Higher Education Commission.
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