杂质元素在天然金属氧化物纳米颗粒晶格中的嵌入及其环境效应

Nature is abundant with metal oxide nanoparticles (MNPs) produced from biotic and abiotic pathways. These naturally formed MNPs have significant influence in controlling geochemical processes including carbon storage, immobilization of heavy metal ions including radionuclides, controlling the redox environment (Eh/ pH) of soil and sediments, nutrient supply as well as carrier of contaminants through environmental media. However, unlike their anthropogenic counterparts, naturally formed MNPs were investigated sparsely; because heterogeneity of the natural environment has elevated their structural complexity. Specifically, impurities may be associated during the biotic and abiotic processes of natural MNP formation. General modes of impurity incorporation in natural MNPs include lattice incorporation, formation of an alloy like solid solution, surface precipitation and subsequent restructuring of gel-phase. Incorporation of these impurities can significantly alter natural MNP crystallinity and stability, and consequently their fate and environmental functions. This study is designed to establish a comprehensive understanding on the difference between pristine and impurity-laden MNPs. Impurity incorporation and the consequent environmental implications will be highlighted. We primarily focus on two objectives. (1) The crystallinity of MNPs in the presence of impurities. (2) The stability and speciation of the impurities (especially when considered contaminants) in the lattice of natural MNPs. Since impurity elements with different ionic radius can occupy the edge and face sharing sites during hydrolysis of Mn affecting the growth of MNPs significantly +. The co-ordination environment of MNPs without or with impurities within the lattice will be evaluated and compared using X-ray absorption spectroscopy measurements (EXAFS and XANES). We hypothesize that the impurity elements with considerable variation in ionic radii to Mn+ will prevent polymorph formation and thus result in weaker crystallinity. Interatomic pair distribution function (PDF) will be fitted and compared with pure MNPs and standard mineral data. A combination of X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopic hyperfine splitting data would enable us to identify whether impurity elements entered into the lattice or adhered to the surface of MNPs. Considering the heterogeneity of natural environment, role of solution conditions including pH, ionic strength as well as natural organic matter on crystallization of MNPs need to be evaluated in the presence and absence of impurities. The co-ordination environment of the MNPs will be deduced and compared from EXAFS spectra and wavelet analysis. Moreover, fractionation behavior of various NOMs during MNPs formation and their implications on electro-kinetic phenomena will be examined. This study will provide fundamental information regarding natural MNPs formation and their role in several critical environmental processes.

自然环境中广泛存的金属氧化物纳米颗粒（MNPs），在碳循环、元素固定、氧化还原条件、污染物携带等地化过程中起到非常重要的作用。然而，相比工程MNPs而言，天然MNPs的特征和效应很少得到关注。本研究抓住天然MNPs与工程MNPs的主要区别，杂质元素的掺杂在天然MNPs中普遍发生的现象展开研究，一方面关注杂质引入以后的MNPs晶格结构特征，另一方面关注MNPs晶格中杂质的存在形态和稳定性。拟引入离子半径不同的杂质进行MNPs掺杂，用EXAFS 和XANES技术对MNPs晶格中配位环境进行分析，用原子对分布函数对掺杂和无掺杂的MNPs进行拟合比对，结合XPS和穆斯保尔谱的超精细裂分，细致分辨杂质是进入了晶格内部还是附着在表面。考虑环境因素的复杂性和异质性，本研究也探讨水环境条件，如离子强度、pH值和天然有机质引入影响下的杂质掺杂及效应。本研究将为理解天然MNPs的性质和功能提供重要的理论基础。

我们研究了极小尺寸的赤铁矿与结构不同的NOM和阳离子的作用，作为基于纳米尺度力测量的二氧化硅和粘土之间的粘合剂。由于NOM的表面钝化和其他元素的成核以及晶体中配位环境的不规则性导致的颗粒尺寸的减小导致了包括点缺陷在内的缺陷的显著增加。我们研究了杂质元素(如重金属离子)对胶体晶体或生物纳米缀合物生长几何形状的作用，或由纳米粒子的NOM辅助淀粉样蛋白控制组装产生的共沉淀，模拟生物矿化或多晶型形成。然而，生物分子支架内重金属离子的成核和由局部弹性应变产生的不规则性以及随后对基于随机游走的原子扩散(在我们的情况下是粒子)的扰动导致胶体晶体/团簇的塑性变形。在pH 4时，由于Pb2+与富含半胱氨酸的β-片和二硫桥成核时形成PbS间隙，具有均匀螺旋带曲率半径的规则位错滑移运动经历了位错滑移带的严重钉扎。胶体团簇的严重塑性变形导致滑移运动，包括交叉滑移、形成位错偶极子、堆垛层错四面体和孪晶界。然而，在pH 7时，胶体团簇的多面体几何形状和位错滑移带的螺旋成分之间的位错反应导致位错堆积，并最终形成与边缘缺陷相关的洛美-科特雷尔锁。我们还研究了淀粉样蛋白手性转移在天然共沉淀物生长中的作用。此外，Cd2+与富含羧酸根的聚丙烯酸(PAA)和腐殖酸(HA)修饰的磁铁矿纳米粒子的相互作用表现出纳米线和胶体晶体的弹性应变驱动生长。产生的纳米团簇伴随着位错偶极子的发展而发生塑性变形，并表现出多重孪晶。胶体探针力显微镜研究揭示了Cd2+浓度的增加增加了胶体晶体的杨氏模量。从杨氏模量来看，蛋白质中普遍存在的氨基酸对羧酸盐的表面覆盖显示出弹性应变降低的迹象。我们还进行了锈纳米粒子的原位溶解和由磁赤铁矿纳米团簇支撑的金属-有机骨架的聚合和生长。由XRD和XPS数据检测，所产生的缀合物与银离子的相互作用显示了银纳米粒子的原位生长。这些复合材料显示出对染料降解的显著效率。