不同价态Ce-MOF衍生材料的吸附除磷性能及机理比较

The influence of valence states for Ce-MOF derived nanocomposites on the capability of phosphate adsorption and the mechanisms

通过在N2气氛中的热处理,从Ce-MOF中衍生出一系列多级的微/纳米铈基复合材料.Ce-MOF在空气中完全分解形成二氧化铈,价态由三价转变为四价.而在N2中较低温度(400℃或500℃)下煅烧会形成稳定的部分热解的Ce-MOF(N),具有较高的Ce(Ⅲ)含量.与完全分解的产物相比,虽然完全分解的产物具有较高的比表面积,但是部分分解的样品对磷酸盐的吸附效果是完全分解产物的2—4倍.这种差异证明铈基材料的不同价态对除磷性能有显著影响,相比于四价铈离子,三价铈在与磷酸盐结合中起主要作用.与Ce-MOF(A)相比,Ce-MOF(N)是一种高Ce(Ⅲ)含量的铈基纳米材料,其饱和吸附容量为187.2 mg·g-1,吸附速度快,pH适用范围极广,为pH 2—12,并且在竞争阴离子存在下也对磷酸盐具有很高的选择性.与此同时,相比于常用的金属盐吸附剂,Ce-MOF(N)在碱性条件下具有明显增强的磷酸盐吸附能力.这是因为表面Ce(Ⅲ)的部分水解带来了更多的羟基,增加了磷酸根离子交换的活性位点.此外,通过分析FTIR、XPS、XRD和Zeta电位,Ce(Ⅲ)样品对磷酸根的吸附机理主要为静电吸引,离子交换和表面沉积,而对于完全分解的铈基材料Ce-MOF(A)静电吸引是主要机理.

Through heat treatment in N2 atmosphere,a series of multi-stage micro/nano cerium matrix composites were derived from Ce-MOF.Ce-MOF completely decomposes in air to form cerium dioxide,and the valence state changed from trivalent to tetravalent.However,calcination at a lower temperature(400℃or 500℃)in N2 would result in a stable partial pyrolysis of Ce-MOF(N)with a higher Ce(Ⅲ)content.Compared with the completely decomposed product,although the completely decomposed product had a higher specific surface area,the phosphate adsorption effect of the partially decomposed sample was 2—4 times of that of the completely decomposed product.This difference showed that the different valence states of Cerium based materials had a significant impact on the phosphorus removal performance.Compared with cerium ions(Ⅳ),cerium ions(Ⅲ)played a major role in the combination with phosphate.Compared with Ce-MOF(A),Ce-MOF(N)was a kind of Ce based nano material with high Ce(Ⅲ)content.Its saturated adsorption capacity was 187.2 mg·g-1,and the adsorption speed was fast.The pH range was very wide,from 2 to 12,and it also had high selectivity for phosphate in the presence of competitive anions.At the same time,Ce-MOF(N)had significantly enhanced phosphate adsorption capacity under alkaline conditions compared with the commonly used metal salt adsorbents.This was because the partial hydrolysis of Ce(Ⅲ)on the surface brings more hydroxyl groups and increases the active sites of phosphate ion exchange.In addition,through the analysis of FTIR,XPS,XRD and zeta potential,the adsorption mechanism of Ce(Ⅲ)on phosphate was mainly electrostatic attraction,ion exchange and surface deposition,while the electrostatic attraction of Ce-MOF(A)was the main mechanism.