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Vibrational Behavior of Water Adsorbed on Forsterite (Mg2SiO4) Surfaces
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2020-06-09 , DOI: 10.1021/acsearthspacechem.0c00084
Tingting Liu 1 , Siddharth S. Gautam 1 , Luke L. Daemen 2 , Alexander I. Kolesnikov 2 , Lawrence M. Anovitz 3 , Monika Hartl 4 , David R. Cole 1
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2020-06-09 , DOI: 10.1021/acsearthspacechem.0c00084
Tingting Liu 1 , Siddharth S. Gautam 1 , Luke L. Daemen 2 , Alexander I. Kolesnikov 2 , Lawrence M. Anovitz 3 , Monika Hartl 4 , David R. Cole 1
Affiliation
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The dynamics of water on or in a mineral substrate plays an important role in interfacial processes. This is because the structure and dynamics of interfacial water deviate from those of bulk water due to the change of interactions between surface water molecules and the interactions between the surface water and the substrate. This work presents a study of the vibrational behavior of water on a forsterite (Mg- end member of olivine) surface using inelastic neutron scattering (INS) and molecular dynamics (MD) simulations as complementary tools. The synthetic nano-forsterite used (dominated by the (010) crystal face), i.e., “dry” sample, inherently has a partial hydration/hydroxylation layer on the surface, as shown by previous studies and TGA. In the INS experiments, three water loadings (0.5, 1, and 2 monolayers) were added to the nano-forsterite surfaces. For samples with lower water loadings, i.e., dry and 0.5 monolayers, the INS spectra exhibited a red shift (lower frequency) of the water libration band and strengthening (blue shift, higher frequency) of the O–H stretching modes, implying weakening of the hydrogen bonding acting on the water molecules. In the simulations, we modeled the forsterite (010) surface and titrated it with two water loadings representing the lower and higher experimental water loadings. The lower loading in the simulation is equivalent to the dry and 0.5 monolayer samples in the experiment, thus suggesting weak hydrogen bonding between water molecules. The higher-loading simulation emulates the multilayer adsorption experiment. This produced a more significant shift of the vibrational bands, implying increased hydrogen-bonding strength and disorder between water molecules. The MD simulations complement the INS study by providing a detailed interfacial structure, and the combination of the two approaches provides a fundamental understanding of how the presence of the olivine surface impacts the vibrational behavior of water under different degrees of hydration—a phenomenon widely associated with terrestrial and extraterrestrial surfaces and near-surface processes.
中文翻译:
镁橄榄石(Mg 2 SiO 4)表面吸附水的振动行为
矿物基质之上或之中的水动力学在界面过程中起着重要作用。这是因为由于地表水分子之间的相互作用以及地表水与底物之间的相互作用的变化,界面水的结构和动力学与散装水的结构和动力学不同。这项工作使用非弹性中子散射(INS)和分子动力学(MD)模拟作为补充工具,对镁橄榄石(橄榄石的Mg端成员)表面上水的振动行为进行了研究。如先前的研究和TGA所示,所使用的合成纳米镁橄榄石(以(010)晶面为主),即“干”样品,其表面固有地具有部分水合/羟基化层。在INS实验中,三个水负荷(0.5、1,和2个单层)添加到纳米镁橄榄石表面。对于水分含量较低的样品,即干层和0.5个单层样品,INS光谱显示出水释放带的红移(低频)和O–H拉伸模式的增强(蓝移,高频),这意味着水的减弱。氢键作用在水分子上。在模拟中,我们对镁橄榄石(010)的表面进行了建模,并用两个水负荷(分别表示实验水负荷的较高和较低)进行了滴定。模拟中的较低负载相当于实验中的干燥样品和0.5个单层样品,因此表明水分子之间的氢键弱。高负荷模拟模拟了多层吸附实验。这使振动带发生了更显着的变化,暗示增加的氢键强度和水分子之间的无序。MD模拟通过提供详细的界面结构来补充INS研究,并且两种方法的结合提供了对橄榄石表面的存在如何在不同水化程度下影响水的振动行为的基本理解,这种现象广泛存在。地面和地外表面以及近地表过程。
更新日期:2020-07-16
中文翻译:
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镁橄榄石(Mg 2 SiO 4)表面吸附水的振动行为
矿物基质之上或之中的水动力学在界面过程中起着重要作用。这是因为由于地表水分子之间的相互作用以及地表水与底物之间的相互作用的变化,界面水的结构和动力学与散装水的结构和动力学不同。这项工作使用非弹性中子散射(INS)和分子动力学(MD)模拟作为补充工具,对镁橄榄石(橄榄石的Mg端成员)表面上水的振动行为进行了研究。如先前的研究和TGA所示,所使用的合成纳米镁橄榄石(以(010)晶面为主),即“干”样品,其表面固有地具有部分水合/羟基化层。在INS实验中,三个水负荷(0.5、1,和2个单层)添加到纳米镁橄榄石表面。对于水分含量较低的样品,即干层和0.5个单层样品,INS光谱显示出水释放带的红移(低频)和O–H拉伸模式的增强(蓝移,高频),这意味着水的减弱。氢键作用在水分子上。在模拟中,我们对镁橄榄石(010)的表面进行了建模,并用两个水负荷(分别表示实验水负荷的较高和较低)进行了滴定。模拟中的较低负载相当于实验中的干燥样品和0.5个单层样品,因此表明水分子之间的氢键弱。高负荷模拟模拟了多层吸附实验。这使振动带发生了更显着的变化,暗示增加的氢键强度和水分子之间的无序。MD模拟通过提供详细的界面结构来补充INS研究,并且两种方法的结合提供了对橄榄石表面的存在如何在不同水化程度下影响水的振动行为的基本理解,这种现象广泛存在。地面和地外表面以及近地表过程。