聚乙二醇对羟基磷灰石除氟性能的影响

Effect of polyethylene glycol on fluoride removal performance of hydroxyapatite

为改善羟基磷灰石(HAP)合成过程易团聚导致其除氟效率不高的不足,本文应用清洁简便、绿色环保的电化学合成法,将亲水性强、分散性优异的非离子型表面活性剂聚乙二醇(PEG)加入到制备HAP的混合支持电解液中,在铜片作工作电极的表面制备出新型HAP复合材料(PEG/HAP),并与纯HAP的晶体结构、孔径、比表面积、表面形貌、元素占比和官能团对比,以揭示PEG/HAP除氟效率高于HAP的内在机制。结果发现,PEG/HAP与HAP有相同的晶面结构特征蜂、元素和化学键,但PEG/HAP的各元素含量占比、羟基和磷酸根离子官能团的吸收峰位和吸收强度与HAP有一定差异;PEG使HAP从短棒状的表面形貌变成有利于交换和吸附氟离子的多孔和孔隙结构,其平均孔径由16.58 nm减小到11.93 nm,比表面积从24.29 m^(2)/g增加到29.83 m^(2)/g;虽然PEG/HAP与HAP的吸附类型均为Ⅳ型的H3滞后环,二者介孔分布范围一致,但PEG/HAP的微孔和介孔数量明显高于HAP。尽管两种材料对氟离子的吸附反应均显示熵增、吸热和自发过程特征,吸附等温模型均符合Langmuir-Freundlich,但PEG/HAP的颗粒内扩散速率常数略大于HAP,PEG/HAP的吸附氟离子容量(9.56 mg/g)高于HAP(8.36 mg/g);且去除氟离子的循环再生次数从HAP的4次增加到PEG/HAP的6次。此外,PEG的存在并没有影响制备条件参数如支持电解液pH值对HAP吸附氟离子容量的影响趋势,但却使HAP吸附氟离子容量增加。共存阴离子如Cl^(-)、NO_(3)^(-)、SO_(4)^(2-)、CO_(3)^(2-)均不干扰PEG/HAP和HAP对氟离子的吸附。

The removal efficiency of hydroxyapatite(HAP)to fluoride was low due to its easy agglomeration during the synthesis process.Based on this,a clean,simple,green and environmentally fiendly electrochemcial synthesis method was applied to improve the fluoride removal efficiency.Polyethylene glycol(PEG),a non ionic surfactant with strong hydrophilicity and excellent dispersion,was added to the mixed support electrolyte for preparing HAP.A new type of HAP composite(PEG/HAP)was prepared on the surface of copper sheet as the working electrode.By contrast to HAP,the crystal structure,pore size,specific surface area,surface morphology,elemental proportion,and functional groups of PEG/HAP were analyzed to reveal the instrinsic mechnism of the higher fluoride removal efficiency of PEG/HAP than HAP.The results show that PEG/HAP and HAP have the same crystal plane structure characteristics,elements and chemical bonds,while the proportion of various elements as well as the absorption peaks and intensity of hydroxyl and phosphate ion functional groups in PEG/HAP have certain differences compared to HAP.PEG transformed HAP from a short rod-shaped surface morphology to a porous and porous structure that facilitated the exchange and adsorption of fluoride ions.Average pore size of PEG/HAP decreased from 16.58 nm of HAP to 11.93 nm,and its specific surface area increased from 24.29 m^(2)/g OF HAP to 29.83 m^(2)/g.Although the adsorption types of PEG/HAP and HAP were both Ⅳ type H3 hysteresis loop,and their mesoporous distribution ranges were consistent,the number of micropores and mesopores in PEG/HAP were significantly higher than those in HAP.Although the adsorption reactions of both materials for fluoride ions exhibited entropy increase,endothermic,and spontaneous process characteristics with the adsorption isotherm model conforming to Langmuir-Freundlich,the intra particle diffusion rate constant of PEG/HAP was slightly higher than HAP.Therefore,the maximum adsorption capacity of PEG/HAP for fluoride ions can reach 9.56 mg/g,which was higher than that of HAP of 8.36 mg/g.Compared with 4 times of recycle regeneration for removing fluoride ions of HAP,PEG/HAP can arrived at 6.In addition,the presence of PEG did not affect the change trend of preparation parameters such as electrolyte pH on the adsorption capacity of HAP for fluoride ions.However,PEG increased the adsorption capacity of HAP for fluoride ions.All coexisiting ions such as Cl^(-),NO_(3)^(-),SO_(4)^(2-),CO_(3)^(2-)did not interfere with the adsorption of fluoride ions for PEG/HAP and HAP.