| The inorganic hollow microspheres have special hollow structure and high specific surface,which have important applications in adsorption,catalysis,drug release,environmental protection,papermaking,electronic materials and so on.The inorganic hollow microspheres mainly synthesized by template method.For the template method,the material to be synthesized is fixed on the surface of the template,and form a spherical shell,and then remove the template by dissolving,calcination or chemical reaction to obtain the hollow microsphere.The template method has the advantages with simple requirements,mild reaction conditions,suitable for a variety of materials,and easy to control the particle size and wall thickness of the microspheres.It is the most commonly used and most important method to prepare hollow microspheres.On the other hand,aluminum phosphate has strong surface acidity and excellent adsorption performance.It is often used as catalyst for organic synthesis reactions and as adsorbent for heavy metal pollutants.It is also often used as a support carrier for vaccines.In this paper,AlPO4 hollow microspheres with uniform size were prepared by in-situ adsorption-homogenous precipitation method using polystyrene(PS)latex as template.The effects of pH value of reaction system,different aluminum sources(Al(NO3)3,AlCl3 and Al2(SO4)3),different phosphorus source(Na2HP04,(HN4)2HPO4 and K2HPO4),and the amount of urea and PS latex on the morphology and yield of AlPO4 hollow microspheres were studied.The samples were characterized by FESEM,TEM,XRD,TG/DSC,BET.The adsorption properties of heavy metal ions(Pb2+,Cr2+,Cu2+,Zn2+)and the luminescence properties of loaded rare earth ions(La3+,Ce3+,Pr3+,Nd3+)were also investigated.The main contents and results are as follows:(1)Effect of reaction conditions on the morphology of AlPO4 hollow microspheres.When the initial pH value of the reaction system was controlled as 2.20,the final pH value was controlled as 3.0,and the amount of urea and PS latex were 1.8g and 6mL in 200mL solution,the synthesized AlPO4 hollow microspheres has the best morphology with uniform particle size.The average diameter and thickness of the shell of the microspheres were about 250nm and 100nm,respectively.(2)Effects of aluminum salts and phosphate on the morphology of AlPO4 hollow microspheres.AlPO4 hollow microspheres with regular morphology can be obtained by using Al(NO3)3 or AlCl3 as raw material.The Na+,K+ ions in phosphate has no effect on the structure and morphology of hollow microspheres,while SO42-has a great influence on the structure and morphology of hollow microspheres.(3)The effect of de-templating ways on the morphology and specific surface of AlPO4 hollow microspheres.While the PS template was removed by solvent resolving and calcination respectively,both the BET surface area of AlPO4 hollow microspheres are almost the same as 128 m ·g-1,but the pore diameter shows obvious different,the pore diameter of AlPO4 hollow microspheres obtained by solvent resolving is about 6 nm,while the pore diameter is 18 nm when obtained by calcination method.(4)The chemical formula of the prepared AlPO4 hollow microspheres is AlPO4·2H20,and the crystal form is amorphous.But after calcined at 500 ℃,the sample starts to crystallization.the crystal phase is transformed into monoclinic system with the space group of Pc7 after calcined at 900 ℃,the unit cell parameters are as follows:a = 37.399 A,B = 5.047 A,c = 26.224 A,V =4376.33 A3,meantime,the structure of hollow microspheres is distroyed completely.(5)The adsorption capacity of AlPO4 hollow microspheres to four heavy metal ions is in the order of Pb2+>>Cr2+>Cu2+≈Zn2+,in which the adsorption capacity of Pb2+ is 3 times of Cr2+ and 7 times of Cu2+ or Zn2+,which showing a special adsorption for Pb2+ ions.The optimum adsorption pH value is 6.0.The adsorption mechanism is suggested to the synergy of ion exchange and co-precipitation.The adsorption type is complied with Langmiur monolayer adsorption which belongs to chemical adsorption.(6)Rare earth ions can be successfully loaded onto the surface of AlPO4 hollow microspheres by synergy of ion exchange and co-precipitation.The luminescence wavelengths of the prepared AlPO4:RE(La,Ce,Pr,Nd)are mainly in the near ultraviolet region.However,the blue light area will be strengthened to some extent when the carrier is different. |
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