Dichromate is known for severe health impairments to organisms. New and valid strategies have been developed to rapidly detect and efficiently remove this pollutant. Constructing stable luminescent metal-organic frameworks (MOFs) for dichromate recognition and removal from aqueous solution could provide a feasible resolution to this problem. Herein, a new luminescent Zr(IV)-MOF, ZrO(OH)(HO)(BTBA) (BUT-39, BUT = Beijing University of Technology) was constructed through the reaction of a newly designed functionalized T-shaped ligand 4,4',4″-(1 H-benzo[ d]imidazole-2,4,7-triyl)tribenzoic acid (HBTBA) with zirconium salt. BUT-39 has a unique porous framework structure, in which Zr cluster acts as a rare low-symmetric 9-connected node and BTBA as a T-shaped 3-connected linker. As far as we know, this represents the first case of a (3,9)-connected Zr(IV)-MOF. BUT-39 could retain its framework integrity in boiling water, 2 M HCl aqueous solution, and pH 12 NaOH aqueous solution. Due to its good water stability and strong fluorescent emission, BUT-39 is then employed in fluorescence sensing for various ions in aqueous solution and shows good performance toward CrO selectively, at a low concentration and a short response time (<1 min). Simultaneously, it also exhibits excellent capacity to rapidly capture CrO (within 1 min) with a high uptake up to 1 mmol g. Taking advantage of its excellent stability, sensitive and selective sensing, as well as rapid and high adsorption, BUT-39 is expected to be useful in CrO detection in and removal from water.

Three new water-stable In(III)-based metal-organic frameworks, namely, [In(TTTA)(OH)(HO)]·(DMA) (BUT-70, DMA = N,N-dimethylacetamide), [In(TTTA)(CHO)] (BUT-70A), and [In(TTTA)(OH)] (BUT-70B), with rod-shaped secondary building units (SBUs) and an new acrylate-based ligand, (2E,2'E,2″E)-3,3',3″-(2,4,6-trimethylbenzene-1,3,5-triyl)-triacrylate (TTTA) were obtained and structurally characterized. BUT-70A and -70B were generated in a single-crystal to single-crystal transformation fashion from BUT-70 through guest exchange followed by their removal. The solvents used for guest exchange were methanol and dichloromethane, respectively. Single-crystal structure analyses show that the guest exchange and removal process is accompanied by the substitution of coordinated water molecules of In(III) centers with uncoordinated carboxylate O atoms of TTTA ligands. Moreover, hydroxyl groups bridging two In(III) centers are also replaced by methoxyl groups in the transformation from BUT-70 to -70A. Overall, three metal-organic frameworks (MOFs) are constructed by infinite chains consisting of corner-sharing InO(OR) (R = H or Me) octahedral entities, which are interconnected by TTTA ligands to form three-dimensional frameworks. Unlike most reported MOFs with infinite chains as SBUs, such as well-known MIL-53 and M-MOF-74, which have one-dimensional channels along the chain direction, the BUT-70 series contain two-dimensional intersecting channels. The Brunauer-Emmett-Teller surface area and pore volume of BUT-70A were estimated to be 460 m g and 0.18 cm g, respectively, which are obviously lower than those of BUT-70B (695 m g and 0.29 cm g). Gas adsorption experiments demonstrated that BUT-70A and -70B are able to selectively adsorb CH over CO and CH. At 1 atm and 298 K, BUT-70A uptakes 3.1 mmol g CH, which is 3.6 times that of the CO uptake and 7.2 times that of the CH uptake. Compared with BUT-70A, BUT-70B presents an even higher CH uptake of 3.9 mmol g at the same conditions, but slightly lower Ideal Adsorbed Solution Theory CH/CO and CH/CH selectivities.

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