非定域密度函数计算铁掺杂羟基磷灰石的介孔分布
柳旭升;马军;杨晶;史风梅
【摘 要】采用离子交换法制备了铁掺杂羟基磷灰石(Fe-HAp)介孔材料,并以非定域密度函数理论(NLDFT)计算了不同浓度铁离子掺杂羟基磷灰石的孔径分布曲线.NLDFT模型结果表明,羟基磷灰石以集合体间孔隙为主,当铁离子浓度大于0.01 mol·L-1时,Fe-HAp的集合体内孔隙逐渐增加.在铁离子浓度为0.05 mol· L-1时制备的Fe-HAp具有最大量的集合体内孔隙.当铁离子浓度大于0.05 mol·L-1时,Fe-HAp粒子尺寸急剧减小,导致集合体内孔隙相应地减少.透射电子显微镜很好地证实了所选择NLDFT模型的结果,相比传统BJH模型,NLDFT模型更为准确.
【期刊名称】《黑龙江大学自然科学学报》
【年(卷),期】2014(031)005
【总页数】7页(P639-645)
【关键词】羟基磷灰石;离子交换;非定域密度函数理论;孔径分布
【作 者】柳旭升;马军;杨晶;史风梅
【作者单位】哈尔滨工业大学市政环境工程学院,哈尔滨150090;哈尔滨工业大学水资源与环境国家重点实验室,哈尔滨150090;哈尔滨工业大学市政环境工程学院,哈尔滨150090;哈尔滨工业大学水资源与环境国家重点实验室,哈尔滨150090;哈尔滨工业大学建筑设计研究院,哈尔滨150090;黑龙江省农业科学院农村能源研究所,哈尔滨150086
【正文语种】中 文
【中图分类】O647
0 Introduction
Hydroxyapatite(HAp)is a promising material becau of its good biocompatibility and low cost［1－3］．Therefore，HAp has been successfully ud in biomedical，biotechnological and environmental fields［4］．Recently，the design and development of metal-doped HAp mesoporous materials as drug carriers have drawn a great attention becau mesoporous structure can be ud for drug storage and relea［5－6］．Amo
ng metal dopants，iron has a prominent advantage in cost in comparison with other metals such as strontium or europium．Furthermore，Fe(III)-doped HAp(Fe-HAp)is a blood compatible biomaterial［7］．However，most of Fe-HAp was prepared by a co-precipitation technique，which confines the iron content by the differences of ionic radii and charges between Ca2+and Fe3+ions［8］．On the contrary，the iron content of Fe-HAp is no longer limited by an ion-exchange method until an amorphous FePO4pha is formed［9－10］．To the best of our knowledge，previous investigation on Fe-HAp prepared by an ion-exchange method was focud on local geometry and distribution of Fe3+ions in the HAp lattice．The relationship between the mesopore size distribution and the concentration of substituted Fe3+ions solution was not investigated［11］．Meanwhile，becau the pore sizes provided by a traditional Barrett-Joyner-Halenda(BJH)method are smaller than the actual sizes，it is interesting to investigate the pore size distribution(PSD)of Fe-HAp by a modern non-local density functional theory(NLDFT)method which supplies accurate consistency between calculations and experiments basing on the molecular level models［12－13］．Therefore，study on me
sopore size distribution of Fe-HAp bad on the NLDFT method would supply guides for application of Fe-HAp mesoporous material．
In this work，Fe-HAp was prepared by an ion-exchange method with different concentrations of Fe(NO3)3solution．The mesopore size distribution of Fe-HAp was analyzed by the N2absorption technique and the NLDFT method．The relationship between the mesopore size distribution of Fe-HAp and the concentration of substituted Fe3+ions solution was investigated by a lected NLDFT model．The transmission electron microscopy(TEM)was ud to compare the results between the lected NLDFT model and the traditional BJH model．
1 Experimental ction
1.1 Materials
Powder HAp was obtained from Ningbo Kingo Advanced Materials R＆D Co．，Ltd．，China．Iron(III)nitrate nonahydrate was supplied by Xilong Chemical Factory，Guangdon
g，China．All chemicals were ud as Received without purification and deionized water was ud to prepare all solutions．
1.2 Experimental procedure
Fe-HAp was prepared as follows:1.00 g of HAp was disperd in 100 mL of Fe(NO3)3solution with concentration in a range of 0.01～0.1 mol·L－1．The mixture was vigorously stirred for 15 min at 25 ℃．Then the suspension particles were washed three times with 1 L deionized water and filtered with filter paper．The filtered particles were dried at 105 ℃ in air for 8 h to obtain yellow powder，Fe-HAp．
1.3 Characterization
The surface area and porosity were analyzed by an ASAP 2020 surface area and pore size analyzer(Micromeritics)，using N2adsorption-desorption isotherms at－196℃．The samples before analysis were degasd at 150℃for 6 h．The specific surface area was calculated by the Brunauer-Emmett-Teller(BET)method．The Quantachrome Quadra Win
software was ud to perform calculation．The TEM measurements were performed with a Tec-nai G2 F30 microscope(FEI Corporation)．The fresh prepared Fe-HAp suspension was dropped on a carbon-coated copper grid，and then the carbon-coated copper grid with the Fe-HAp particles loaded was dried at 105℃ for 30 min in an oven in air．
2 Results and discussion
2.1 Appearance of Fe-HAp in preparation
Yellow gel-like flocs appeared when the concentration of Fe(NO3)3solution was higher than 0.01 mol·L－1 and the maximum amount of the flocs was obtained for 0.05 mol·L －1Fe(NO3)3solution．However，such flocs were not obrved when the concentration of Fe(NO3)3solution was higher than 0.05 mol·L －1．Therefore，three concentrations(0.01，0.05 and 0.1 mol·L－1，respectively)of Fe(NO3)3solution were prepared．The samples were noted as Fe-HAp0.01，Fe-HAp0.05and Fe-HAp0.1，respectively with the footnotes reprenting the concentration of Fe(NO3)3solution．
2.2 Pore structure analysis of N2adsorption-desorption isotherms
Pore structures of the HAp and Fe-HAp samples were investigated by a low temperature N2adsorption-desorption technique．As shown in Fig．1，the isotherms of the HAp and three Fe-HAp samples were identified as a type IV isotherm corresponding to mesoporou materials．Meanwhile，typical H3 hysteresis loops in a relative pressure(P/P0)range of 0.8～1 were characterized by isotherms of the HAp and three Fe-HAp samples．The H3 hysteresis loops did not have any limiting adsorption at high P/P0，indicating the prence of slit-shaped pores caud by aggregation of particles［14］．However，a typical H2 hysteresis loop was obrved for the Fe-HAp0.05particles in addition to the H3 hysteresis loop at high P/P0(e Fig．1(c))．Although the H2 hysteresis loop nominally corresponds to pores with narrow necks and wider bodies(ink bottle pores)，the network effect of inorganic oxide gels should be considered for the gel-like appearance of Fe-HAp0.05in the preparation［15］．It is interesting to note that such H2 hysteresis loop was not obrved for the Fe-HAp0.1particles which were prepared at a much high Fe(NO3)3concentration(e Fig．1(d))．Since intra-aggregate pores were characterized by hysteresis in a P/P0 range of 0.5～0.7，the H2 hysteresis loop indicates the possible
existence of predominant intra-aggregate pores in the Fe-HAp0.05particles［16］．On the contrary，such intra-aggregate pores decread in the Fe-HAp0.1particles with
Fig．1 Adsorption-desorption isotherms of HAp(a)，Fe-HAp0.01(b)，Fe-HAp0.05(c)and Fe-HAp0.1(d)
smaller particle sizes．This deduction is in according with the fact we obrved in the preparation of Fe-HAp．When concentration of the Fe(NO3)3solution was higher than 0.05 mol·L－1，some yellow powder-like particles appeared in contrast to the yellow flocs obtained at 0.05 mol·L－1Fe(NO3)3solution．Meanwhile，the hysteresis in a P/P0range of 0.5～0.7 was very weak for the Fe-HAp0.01particles whereas such range hysteresis did not appear for the HAp particles．Therefore，we deduced that there were no intra-aggregate pores in HAp particles and the amount of intra-aggregate pores in Fe-HAp0.01particles was less than either that of Fe-HAp0.05particles or that of Fe-HAp0.1particles．
2.3 Specific surface area analysis
