Abstract
Tuning the water concentration in the synthesis of three UiO MOFs allows crystal phase selection via ordering of defects.
Highlights
In this paper we demonstrate that the amount of water in the reaction mixture in the synthesis of UiO family metal-organic frameworks (MOFs) is an important factor, as it controls the phase which forms for both UiO-67(Hf) and UiO-66(Hf) (F4BDC)
Inspired by our previous work showing that formic acid plays a crucial role in the formation of the hcp UiO-67(Hf) phase, 9 we investigated the effect of different concentrations of formic acid in the synthesis of UiO-67(Hf) [Fig. 2(a)]
We have demonstrated that water plays a key role in the synthesis of defect phases of UiO family MOFs
Summary
9 In this UiO-67(Hf) phase, the missing-linker defects order within a (111) plane of the parent fcu structure, resulting in the condensation of pairs of 12-coordinate M6(μ3-O)4(μ3-OH)[4] clusters into 18-coordinate [M6(μ3-O)4(μ3-OH)4]2(μ2-OH)[6] double clusters, giving a hexagonal hcp topology [Fig. 1]. Rather than nano-domains, hcp UiO-67(Hf) is obtained as an ordered single phase bulk material These new defective frameworks have different properties from the parent non-defective UiO frameworks. Nano reo UiO66(Hf) displays significantly enhanced high-pressure gravimetric gas sorption compared to fcu UiO-66(Hf). 11 In hcp UiO-67(Hf), the directionality of the structure means that selective topotactic delamination under gentle conditions produces the crystalline layered hxl structure, and under more forcing conditions (such as sonication or grinding) gives two-dimensional nanosheets, hereafter named hns UiO-67(Hf) [Fig. 1]. 9,11,35
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