CAJ | 학술논문

应用延展X射线吸收精细结构(EXAFS)方法,研究了不同pH对Zn(Ⅱ)在锐钛矿型TiO_2表面吸附产物的微观构型的影响.宏观的吸附-解吸实验表明,随着pH值由5.8增大至6.8,吸附等温线明显升高,Freundlich吸附常数由1.345 L/g增加到15.385 L/g;而体系的不可逆性逐渐降低,不可逆吸附系数(TⅡ)由0.43降低到0.23.不同pH条件下吸附样品的EXAFS结果表明,Zn(Ⅱ)主要通过共用水合离子及TiO_2表面的O原子结合到TiO_2表面上,第一配位层(Zn-O层)原子间距和配位数随着pH值增大逐渐降低,Zn(Ⅱ)在TiO_2表面吸附形态从六配位向四配位转化;第二配位层(Zn-Ti层)分析结果表明,存在2个典型的Zn-Ti原子间距,即R_1=0.319～0.334 nm(双齿方式结合的强吸附)和R_2=0.366～0.378 nm(单齿方式结合的弱吸附),随着pH值的升高,强吸附位(CN1)逐渐减少而弱吸附位(CN2)逐渐增加,其比值由2.12降低至0.89,从而导致其在高pH值的条件下吸附量和可逆性明显增大.EXAFS结果从分子水平说明了该体系在不同pH值条件下表现出的可逆性差异是由于微观吸附状态不同所致.
응용연전X사선흡수정세결구(EXAFS)방법,연구료불동pH대Zn(Ⅱ)재예태광형TiO_2표면흡부산물적미관구형적영향.굉관적흡부-해흡실험표명,수착pH치유5.8증대지6.8,흡부등온선명현승고,Freundlich흡부상수유1.345 L/g증가도15.385 L/g;이체계적불가역성축점강저,불가역흡부계수(TⅡ)유0.43강저도0.23.불동pH조건하흡부양품적EXAFS결과표명,Zn(Ⅱ)주요통과공용수합리자급TiO_2표면적O원자결합도TiO_2표면상,제일배위층(Zn-O층)원자간거화배위수수착pH치증대축점강저,Zn(Ⅱ)재TiO_2표면흡부형태종륙배위향사배위전화;제이배위층(Zn-Ti층)분석결과표명,존재2개전형적Zn-Ti원자간거,즉R_1=0.319～0.334 nm(쌍치방식결합적강흡부)화R_2=0.366～0.378 nm(단치방식결합적약흡부),수착pH치적승고,강흡부위(CN1)축점감소이약흡부위(CN2)축점증가,기비치유2.12강저지0.89,종이도치기재고pH치적조건하흡부량화가역성명현증대.EXAFS결과종분자수평설명료해체계재불동pH치조건하표현출적가역성차이시유우미관흡부상태불동소치.
Microscopic structures and thermodynamic characteristics of Zn( Ⅱ ) adsorbed onto anatase TiO_2 at different pH were studied using extended X-ray absorption fine structure(EXAFS) spectroscopy. Macroscopic adsorption-desorption experiments indicated that as pH increased from 5.8 to 6. 8, the adsorption capacity coefficient(K_F) increased from 1,345 L/g to 15. 385 L/g, while the adsorption irreversibility coefficient (TⅡ) decreased from 0. 43 to 0. 23. EXAFS spectra results showed that Zn(Ⅱ) was adsorbed onto the solid surface in a mixed form of octahedral and tetrahedral hydrous Zn(Ⅱ) ions, which were linked to TiO_2 surface by sharing O atoms. Both the bond length and the coordination number of the first Zn-O coordination sphere decreased as pH increased. Analysis of the second Zn-Ti coordination sphere indicated two Zn-Ti atomic distances: R_1 =0.319-0.334 nm and R_2 =0.366-0.378 nm, referring to bidentate( stronger adsorption site) and monodentate( weaker adsorption site) complexation respectively. The number of stronger adsorption sites( CN1 ) decreased while the number of weaker adsorption sites(CN2) increased remarkably with increasing pH, resulting in a drop of CN1/CN2 from 2.12 to 0.89. EXAFS results revealed that the macroscopic adsorption phenomena were directly related to the changes in microscopic adsorption structures of Zn (Ⅱ) on thesurface of TiO_2 under different pH conditions.