Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by 1H solid-state NMR
Hydrogen bonding of water confined in mesoporous silica MCM-41 and SBA-15 studied by 1H solid-state NMR
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DOI：
10.1002/chem.200400351
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发表时间：
2004-11-19
影响因子：
4.3
通讯作者：
Buntkowsky, G
中科院分区：
文献类型：
--
作者：
Grünberg, B;Emmler, T;Buntkowsky, G
采用H-1 MAS（MAS =魔角旋转）和静态固体NMR研究了水在两种具有均匀直径圆柱孔的介孔氧化硅材料MCM-41和SBA-15中的吸附。所有观察到的氢原子都是表面-SiOH基团或氢键合的水分子。与MCM-41不同的是，SBA-15的内表面存在一些强结合的水分子，这些水分子被分配给表面缺陷。在更高的填充水平下，观察到MCM-41和SBA-15之间的进一步差异。水分子在MCM-41中的化学位移呈双峰分布，其中一个峰位于水分子内部，另一个峰位于水分子与表面-SiOH基团快速交换的位置。在SBA-15中，观察到随着孔填充增加而连续移位的单条线。这一结果归因于两种二氧化硅材料的不同孔隙填充机制。在MCM-41中，由于其小的孔径（3.3 nm），通过孔冷凝（轴向孔填充模式）的孔填充在低相对压力下发生，大致对应于单个吸附单层。对于SBA-15，由于其较大的孔径（8 nm），逐渐增加的吸附层的厚度（径向孔隙填充模式）占主导地位，直到孔冷凝发生在较高水平的孔隙填充。
The adsorption of water in two mesoporous silica materials with cylindrical pores of uniform diameter, MCM-41 and SBA-15, was studied by H-1 MAS (MAS = magic angle spinning) and static solid-state NMR spectroscopy. All observed hydrogen atoms are either surface -SiOH groups or hydrogen-bonded water molecules. Unlike MCM-41, some strongly bound water molecules exist at the inner surfaces of SBA-15 that are assigned to surface defects. At higher filling levels, a further difference between MCM-41 and SBA-15 is observed. Water molecules in MCM-41 exhibit a bimodal line distribution of chemical shifts, with one peak at the position of inner-bulk water, and the second peak at the position of water molecules in fast exchange with surface -SiOH groups. In SBA-15, a single line is observed that shifts continuously as the pore filling is increased. This result is attributed to a different pore-filling mechanism for the two silica materials. In MCM-41, due to its small pore diameter (3.3 nm), pore filling by pore condensation (axial-pore-filling mode) occurs at a low relative pressure, corresponding roughly to a single adsorbed monolayer. For SBA-15, owing to its larger pore diameter (8 nm), a gradual increase in the thickness of the adsorbed layer (radial-pore-filling mode) prevails until pore condensation takes place at a higher level of pore filling.