Regulating the Orientation of Hydrogen-Bonded Organic Framework Membranes Based on Substrate Modification

Because of the advantages of ordered porosity, self-healing ability, and solution processability, hydrogen-bonded organic frameworks (HOFs) are promising candidates to construct membranes for molecule separation. Due to crystal anisotropy, the orientation regulation of membranes can efficiently adjust their separation performance. However, the field in oriented growth of hydrogen-bonded organic framework (HOF) membranes is still vacant because it is hard to regulate the growth process, and the development of facial fabrication methods to realize oriented and continuous nanocrystal membranes remains challenging. Herein, the HOF membranes with preferred orientation in the b-axis based on the graphene oxide (GO)-modified substrate are prepared for the first time. Through a systematic study, we find that the quality of oriented membranes is closely related to precursor concentration, surface roughness, and charging, which directly affect the anchoring direction and positions of nutrients. Furthermore, with the introduction of protonated hydrogen-bonded organic framework (pHOF) monomers as seeds, the orientation turns to be more regular, which is attributed to the electrostatic interaction between GO and pHOF. The preferred b-oriented HOF membranes transfer the gas molecules based on mainly the spacing between two-dimensional (2D) layers, thus possessing much lower gas permeance compared with that of nonoriented HOF membranes, further proving the successful preparation of highly oriented HOF membranes. We believe that this study would give hints to the oriented growth of HOF materials and the regulation of HOF membrane performance.