Synthesis Of Metal Oxide Nanopowders Using Granulated Sodium Alginate Or Alginic Acid Via Ion-exchange Process

Metal oxide nanoparticles have attracted extensive attention in recent years due to the wide range of applications in electronics,optics,catalysis and energy storage.Various preparation routes for metal oxide nanoparticles have consequently seen a rapid development.Among them,the sol-gel method as a low temperature synthesis approach has become a focus of study.However,the sol-gel process often uses the precursor(ester compound or metal alkoxide)or organic solvents with certain toxicity.Taking this into consideration,from the perspective of environmental protection and commercial,it is necessary to select environment-friendly and inexpensive precursors and solvents to prepare metal oxide nanoparticles in batch.Sodium alginate is a natural polysaccharide and non-toxic raw material.It has a wide range of sources and has a strong chelating and adsorption effect on metal ions.However,as a result of high viscosity of sodium alginate and the long and complicated experimental process,large-scale production of metal oxide nanoparticles has to overcome some limitations.On the basis of the above argument,how to improve synthetic efficiency,shorten reaction time and successfully achieve large-scale production of metal oxide materials is one of research emphasis in this field.In this work,we have developed a new route using the sol-gel method for synthesis of metal oxide nanoparticles,using the granulated sodium alginate particles or alginic acid particles as the gel medium to prepare various metal oxide nanoparticles.The main research contents,results,and conclusions are as follows:(1)The granulation process of sodium alginate had been studied by high shear wet granulator(HSWG),and granule size distribution(GSD)of sodium alginate under different granulation conditions was optimized.The particle size changes under different granulation time were compared at three different agglomeration rate models,and the mass distribution data of sodium alginate particles obtained from the sieve experiment were compared and analyzed.The result showed that the population balance models-equi-kinetic energy kernel(PBM-EKE)can accurately simulate the mass distribution of sodium alginate particles.Then,it was observed that the particle size of sodium alginate granulation increased with the increase of binder water content by imaging analysis.The near infrared spectral data of different water volumes were collected,and the binder content prediction model was established.(2)With regard to the synthesis of Ni_xFe_yO₄ nanoparticles,a new process route was presented that used granulated sodium alginate(Na-ALG)as gelation media.X-ray diffraction(XRD)result showed that single-phase nickel ferrite nanoparticles were obtain at 400°C for 2h.The grain sizes of Ni_0.4Fe_2.6O₄,Ni_0.6Fe_2.4O₄,Ni Fe₂O₄,Ni_1.25Fe_1.85O₄,and Ni_1.43Fe_1.7O₄nanoparticles(500°C-2h)obtained by XRD Rietveld refinement analysis were about 8 nm,6nm,11 nm,10 nm,and 8 nm,respectively.XRD and transmission electron microscopy(TEM)results indicated that particle sizes increased with calcination temperatures increased.The structural differences of Ni_xFe_yO₄ were investigated with nominal compositions and confirmed by inductively coupled plasma-atomic emission spectrometry(ICP-AES).The magnetic investigations were carried out using a vibrating sample magnetometer(VSM)and a maximum saturation magnetization(Ms=37.26 emu g^-1)was recorded at 20000 Oe with the Ni_0.4Fe_2.6O₄nanoparticles.All samples showed supermagnetic properties when the Ms values decreased as the Ni²⁺concentrations increased.Finally,the synthesized Ni_1.25Fe_1.85O₄samples exhibited a maximum discharge-storage capacity(1023.6 m Ah g^-1)even after 200 cycles at 1 A g^-1.This new process not only ensured that the operation was easier to scale up but also much greener since it consumed less than 4%of the water compared with other processes in the literature.(3)Co Fe₂O₄(CFO)nanoparticles were synthesized using granulated sodium alginate as gelation media.The single-phase cubic structure of CFO nanoparticles was confirmed by XRD.The mean crystallite sizes had calculated using XRD Rietveld refinement analysis matched the particle sizes observed by TEM.The magnetic properties of the obtained CFO nanoparticles under different heat treatment conditions had been measured using VSM at room temperature.As the calcination temperature increased,larger particles with higher crystallinities were obtained,which resulted in the overall magnetic properties increasing logarithmically as a function of crystalline size.The maximum saturation magnetization(76.61 emu g^-1)had been obtained using the sample calcined at 900?for 2 h.(4)A new process was presented that used granulated alginic acid(H-ALG)instead of granulated sodium alginate as gelation media for Co₃O₄and Co O nanoparticles synthesis,and the influence of Na⁺ions in the remaining solution after ion-exchange reaction was removed.The granulation process of alginic acid was studied by high shear wet granulator,and granule size distribution of alginic acid under different granulation conditions was optimized.High temperature decomposition mechanisms of alginic acid(H-ALG)were investigated studied using the simultaneous thermo-gravimetric analysis(TGA)coupled with differential scanning calorimetry(DSC),infrared spectroscopy(IR)and mass spectroscopy(MS)analysis,respectively.It was found that the main emissions were water,carbon dioxide and carbon monoxide at temperature between 200 and 500°C using the H-ALG sample.In addition,the energy released of Co-ALG was higher than H-ALG during thermal decomposition.HT-XRD result showed that the oxidation states gradually converted from Co₃O₄ to Co O at high temperature.TEM result indicated that the grain sizes of Co₃O₄(900°C)and Co O(1000°C)were about 277 nm and 731 nm,respectively.(5)Using granulated alginic acid as gelation media,Y₂O₃ nanoparticles were synthesized at different temperatures.During the process of ion-exchange reaction,the effect of different conditions on the reaction rate of H⁺with Y³⁺had been investigated by online p H technology.Under the optimal experimental conditions,whether the on-line p H technique or off-line ICP-AES technique,the result indicated that initial reaction rate of the ion-exchange reaction was very fast and reached equilibrium gradually in about 15 min.Meanwhile,the simulation result of the rate constant of 2^nd order kinetic reaction showed that the actual concentration ratio of H⁺and Y³⁺in the ion-exchange reaction process was about C_H⁺:C_Y³⁺=1:1.733.The result of XRD analysis showed that with the increase of calcination temperature,the grain size and crystallinity of the synthesized Y₂O₃ nanoparticles also increased.The grain sizes of Y₂O₃nanoparticles obtained by XRD Rietveld refinement analysis were about 4 nm(500?-2h)and 15 nm(800?-2h),respectively.