摘要
绘制了不同温度下溴化十四烷基吡啶(MPB)在膨润土上的等温吸附曲线,探讨了MPB的吸附热力学及作用机理;并用XRD,FTIR和UV固体漫反射表征了MPB在固相上的有序化作用.研究结果表明,MPB的吸附热力学、作用机制及有序化过程取决于其在膨润土上的负载量.不同负载量下标准吉布斯自由能ΔG—m0<0,表明为自发吸附过程,但存在3个不同阶段.在低负载量(<0.8CEC)时为吸热吸附[焓变ΔH—m0=7.92kJ/mol,熵变ΔSm—0≈110J/(K.mol)],以阳离子交换作用吸附为主;在高负载量阶段为放热吸附[ΔH—m0=-34.41kJ/mol,ΔS—m0≈-50J/(K.mol)],以脂肪链间的疏水性相互作用为主;最大吸附量随温度的升高(278K→328K),从2.8CEC降低为1.5CEC,相应的ΔH—0m=-9.74kJ/mol.在负载量由低到高的吸附过程中,吸附态MPB的状态从无序"液态"逐渐演变为有序"固相",吸附过程从熵驱动(ΔSm—0>0)过渡为焓驱动(ΔH—m0<0).
Sorption of myristylpyridinium bromide (MPB) on a model mineral, bentonite, was investigated under different temperatures (278, 283, 298, 308, 318 and 328 K). The sorption thermodynamics and interaction mechanisms are discussed. The resultant complexes of MPB-mineral were characterized with XRD, FTIR and UV-Vis diffuse reflectance spectra to probe the organized assemblies of adsorbed-MPB. The thermodynamics, mechanism and organized process are dominated by the MPB-loadings. For the whole isotherms, the molar standard Gibbs free energy of adsorption( △A m ) is negative, suggesting that adsorption is a spontaneous process, but the assembled process divided into three stages: sorption was driven by cationic exchanged firstly, then controlled by hydrophobic interaction after cationic exchanged reach maximum level. At low MPB- loadings( 〈0. 8 emc), the principal contribution to the △G m of negative value( -25-- 30 kJ/mol) is the maximum positive value of molar standard adsorption entropy( △S m is about 110 J· K^-1·mol^-1) , whereas the molar standard adsorption enthalpy(△H m) is negative( -7.92 kJ/mol). At high loadings, the main contribution to the △A m of negative value ( - 30--20 kJ/mol ) is the maximun negative value of △H m ( -34.41 kJ/mol), whereas the △S m is negative(about -50 J·K^-1·mol^-1 ). The saturated amount of MPB decreased from about 2.8CEC at 278 K to about 1.5CEC at 328 K, and the corresponding △H m = -9.74 kJ/mol. With the increase of loading, the adsorbed-MPB transited from a disordered liquid-like state to an ordered solid-like state, and the spontaneous adsorption evolved from an entropy-driven process( △S m 〉 0) to an enthalpy-driven process (△H m 〈 0). These observations provide a theoretical base to further understanding the adsorption behavior of cationic surfactant to mineral and an engineered reference to synthesize surfactant-mineral complexes for environmental applications.
出处
《高等学校化学学报》
SCIE
EI
CAS
CSCD
北大核心
2009年第9期1830-1834,共5页
Chemical Journal of Chinese Universities
基金
国家自然科学基金(批准号:20207007)
浙江省科技厅计划项目(批准号:2006C33050)资助
关键词
溴化十四烷基吡啶
膨润土
吸附热力学
作用机理
有序结构
Myristylpyridinium bromide
Bentonite
Sorption thermodynamics
Interaction mechanism
Organized structure