Pore‐Surface Engineering by Decorating Metal‐Oxo Nodes with Phenylsilane to Give Versatile Super‐Hydrophobic Metal–Organic Frameworks (MOFs)

Abstract

Hydrophobization of metal-organic frameworks (MOFs) is important to push forwardt heir practical use and thus has attracted increasing interest. In contrast to the previous reports,w hich mainly focused on the modification of organic ligands in MOFs,h erein, we reported an ovel strategy to decorate the metal-oxo nodes of MOFs with phenylsilane to affords uper-hydrophobic NH 2 -UiO-66(Zr), which shows highly improved base resistance and holds great promise in versatile applications,s uch as organic/water separation, selfcleaning,a nd liquid-marble fabrication. This work demonstrates the first attempt at metal-oxon ode modification for super-hydrophobic MOFs,a dvancing an ew concept in the design of MOFs with controlled wettability for practical applications.Smart solid materials with special surface wettability are being sought owing to their diverse potential applications. [1,2] Super-hydrophobic porous materials are of interest since they can provide both aw ater-repellent surface and inherent porosity,w hich enable them to be used for some special applications,s uch as contaminatedwater treatments and fuel purification. [3,4] Metal-organic frameworks (MOFs) constructed from metal-oxo nodes interconnected by polydentate organic ligands are ac rystalline porous materials which have shown great promise in various applications. [5][6][7][8][9][10][11][12][13] Recent research has involved preparing hydrophobic MOFs,n ot only to combat their failure in applications under humid conditions,b ut also endow them with improved or even novel functional properties. [14][15][16][17][18][19][20][21][22][23][24][25] Enabled by the designable and flexible features of MOFs,decorating MOFs with hydrophobic moieties has been widely used for imparting hydrophobicity to MOFs.E ncouraging progress has been made in improving the water-repelling capacity of MOFs by functionalizing the organic ligands with hydrophobic groups. [25][26][27][28] Surprisingly,t here is no attempt to design the metal-oxo nodes for functional hydrophobic MOFs,i ns pite of their easily modified nature. [26][27][28][29][30][31] In addition, the intrinsic presence of metal-OH groups at metal-oxo nodes of MOFs enables af acile and direct decoration process, [30,32] offering advantages over the ligand modification process that requires extra functional groups as "tags" for post modification steps.Herein we initiated an attempt to prepare super-hydrophobic MOFs by modification of the metal-oxo nodes.N H 2functionalized MOFs have attracted interest owing to their unique properties distinguished from the bare MOFs.N H 2 -UiO-66(Zr) represents one of the most appealing MOFs showing great potential in different applications and was thus selected. [28,31,[33][34][35][36] Phenylsilane (PhSiH 3 )was grafted onto the Zr-O metal-oxo nodes of NH 2 -UiO-66(Zr) by allowing it to react with the Zr-OH groups,e xposing the hydrophobic phenyl groups to form the super-hydrophobic NH 2 -UiO-66(Zr) (NH 2 -UiO-66(Zr)-shp) with ah igh water contact angle of 1618 8 (Scheme 1). Thet hus ...

Hydrophobic Metal–Organic Frameworks: Assessment, Construction, and Diverse Applications

“…The results also proved that the NMOF‐1 coating was stable to acidic (pH: 1–6), weakly basic (pH: ≤ 9), and high‐ionic‐strength aqueous solutions, as suggested by the slight change in contact angles among the surfaces. A similar self‐cleaning property was also demonstrated for a superhydrophobic MOF (water contact angle: 161°), UiO‐66‐NH 2 ‐shp, which was obtained by reacting phenylsilane with the hydroxyl groups in the Zr 6 O 4 (OH) 4 clusters of UiO‐66‐NH 2 …”

“…Instead of using the coordination bonding between open metal sites and hydrophobic terminal ligands, covalent bonding between inorganic SBUs and reactive species has also been applied to the hydrophobization of MOFs. Recently, Sun et al reported the hydrophobization of UiO‐66‐NH 2 (formulated as [Zr 6 O 4 (OH) 4 (1,4‐bdc‐NH 2 ) 6 ]) by the reaction of phenylsilane (PhSiH 3 ) with the hydroxyl groups on its Zr 6 O 4 (OH) 4 clusters ( Figure ) . While the pristine UiO‐66‐NH 2 showed a water contact angle of 0°, in contrast, a silylated sample of UiO‐66‐NH 2 (UiO‐66‐NH 2 ‐shp) showed a very high water contact angle of 161°, although, its BET surface area decreased from 974.4 m 2 g −1 to 656.5 m 2 g −1 .…”

“… Schematic representation of the preparation of UiO‐66‐NH 2 ‐shp and its potential applications. Adapted with permission . Copyright 2019, John Wiley and Sons.…”

Triplet–Triplet Annihilation Upconversion in a MOF with Acceptor‐Filled Channels

“…The design concept is also applicable to other TTA‐UC pairs and enables tuning of the UCL color, for example, by replacing DPA with other dyes as exemplarily shown for 2,5,8,11‐tetra‐ tert ‐butyl‐perylene, that yields UCL at 450 nm (Supporting Information, Figure S20). Current work aims to reduce the oxygen sensitivity and to increase the retention of the trapped annihilators in organic environments, for example, by tuning the chain length of the carboxylic acid and by coating the MOF surface . In addition, the TTA‐UC efficiency will be further enhanced by reducing the reabsorption of the UC emission caused by Pd(TCPP) and by optimizing the sensitizer/annihilator interface …”

“…Current work aims to reduce the oxygen sensitivity and to increase the retention of the trapped annihilators in organic environments, for example, by tuning the chain length of the carboxylic acid and by coating the MOF surface. [43] In addition, the TTA-UC efficiencyw ill be furthere nhanced by reducing the reabsorption of the UC emission caused by Pd(TCPP) and by optimizing the sensitizer/annihilator interface. [12,22,39,44,45]…”