Corno Marta, Delle Piane Massimo, Monti Susanna, Moreno-Couranjou Maryline, Choquet Patrick, Ugliengo Piero
†Dipartimento di Chimica and NIS - Nanostructured Interfaces and Surfaces - Centre, Università degli Studi di Torino, via P. Giuria 7, 10125 Torino, Italy.
‡CNR Institute of Chemistry of Organometallic Compounds, Area della Ricerca, via G. Moruzzi l, I-56124 Pisa, Italy.
Langmuir. 2015 Jun 16;31(23):6321-31. doi: 10.1021/acs.langmuir.5b01828. Epub 2015 Jun 5.
In silico modeling of acidic (CH2COOH) or basic (CH2NH2) functionalized silica surfaces has been carried out by means of a density functional approach based on a gradient-corrected functional to provide insight into the characterization of experimentally functionalized surfaces via a plasma method. Hydroxylated surfaces of crystalline cristobalite (sporting 4.8 OH/nm(2)) mimic an amorphous silica interface as unsubstituted material. To functionalize the silica surface we transformed the surface Si-OH groups into Si-CH2COOH and Si-CH2NH2 moieties to represent acidic/basic chemical character for the substitution. Structures, energetics, electronic, and vibrational properties were computed and compared as a function of the increasing loading of the functional groups (from 1 to 4 per surface unit cell). Classical molecular dynamics simulations of selected cases have been performed through a Reax-FF reactive force field to assess the mobility of the surface added chains. Both DFT and force field calculations identify the CH2NH2 moderate surface loading (1 group per unit cell) as the most stable functionalization, at variance with the case of the CH2COOH group, where higher loadings are preferred (2 groups per unit cell). The vibrational fingerprints of the surface functionalities, which are the ν(C═O) stretching and δ(NH2) bending modes for acidic/basic cases, have been characterized as a function of substitution percentage in order to guide the assignment of the experimental data. The final results highlighted the different behavior of the two types of functionalization. On the one hand, the frequency associated with the ν(C═O) mode shifts to lower wavenumbers as a function of the H-bond strength between the surface functionalities (both COOH and SiOH groups), and on the other hand, the δ(NH2) frequency shift seems to be caused by a subtle balance between the H-bond donor and acceptor abilities of the NH2 moiety. Both sets of data are in general agreement with experimental measurements on the corresponding silica-functionalized materials and provide finer details for a deeper interpretation of experimental spectra.
通过基于梯度校正泛函的密度泛函方法，对酸性（CH2COOH）或碱性（CH2NH2）官能化二氧化硅表面进行了计算机模拟，以深入了解通过等离子体方法对实验官能化表面的表征。晶体方石英的羟基化表面（每平方纳米有4.8个OH）模拟了未取代材料的无定形二氧化硅界面。为了官能化二氧化硅表面，我们将表面的Si-OH基团转化为Si-CH2COOH和Si-CH2NH2部分，以代表取代的酸性/碱性化学性质。计算并比较了结构、能量、电子和振动性质与官能团负载量增加（从每个表面晶胞1个到4个）的函数关系。通过Reax-FF反应力场对选定案例进行了经典分子动力学模拟，以评估表面添加链的迁移率。密度泛函理论（DFT）和力场计算均表明，CH2NH2的适度表面负载量（每个晶胞1个基团）是最稳定的官能化方式，这与CH2COOH基团的情况不同，后者更倾向于较高的负载量（每个晶胞2个基团）。已将表面官能团的振动指纹（酸性/碱性情况下为ν（C═O）伸缩和δ（NH2）弯曲模式）表征为取代百分比的函数，以指导实验数据的归属。最终结果突出了两种官能化类型的不同行为。一方面，与ν（C═O）模式相关的频率随着表面官能团（COOH和SiOH基团）之间氢键强度的增加而向更低波数移动，另一方面，δ（NH2）频率移动似乎是由NH2部分的氢键供体和受体能力之间的微妙平衡引起的。这两组数据总体上与相应二氧化硅官能化材料的实验测量结果一致，并为更深入解释实验光谱提供了更详细的信息。
