Qihan Gong

A Multifunctional Organic–Inorganic Hybrid Structure Based on MnIII–Porphyrin and Polyoxometalate as a Highly Effective Dye Scavenger and Heterogenous Catalyst

A two-step synthesis strategy has led to a unique layered polyoxometalate-Mn(III)-metalloporphyrin-based hybrid material. The hybrid solid demonstrates remarkable capability for scavenging of dyes and for heterogeneous selective oxidation of alkylbenzenes with excellent product yields and 100% selectivity.

Enhancing gas adsorption and separation capacity through ligand functionalization of microporous metal-organic framework structures

Hydroxyl- and amino- functionalized [Zn(BDC)(TED)(0.5)]·2DMF·0.2H(2)O leads to two new structures, [Zn(BDC-OH)(TED)(0.5)]·1.5DMF·0.3H(2)O and [Zn(BDC-NH(2))(TED)(0.5)]·xDMF·yH(2)O (BDC=terephthalic acid, TED=triethylenediamine, BDC-OH=2-hydroxylterephthalic acid, BDC-NH(2)=2-aminoterephthalic acid). Single-crystal X-ray diffraction and powder X-ray diffraction studies confirmed that the structures of both functionalized compounds are very similar to that of their parent structure. Compound [Zn(BDC)(TED)(0.5)]·2DMF·0.2H(2)O can be considered a 3D porous structure with three interlacing 1D channels, whereas both [Zn(BDC-OH)(TED)(0.5)]·1.5DMF·0.3H(2)O and [Zn(BDC-NH(2))(TED)(0.5)]·xDMF·yH(2)O contain only 1D open channels as a result of functionalization of the BDC ligand by the OH and NH(2) groups. A notable decrease in surface area and pore size is thus observed in both compounds. Consequently, [Zn(BDC)(TED)(0.5)]·2DMF·0.2H(2)O takes up the highest amount of H(2) at low temperatures. Interestingly, however, both [Zn(BDC-OH)(TED)(0.5)]·1.5DMF·0.3H(2)O and [Zn(BDC-NH(2))(TED)(0.5)]·xDMF·yH(2)O show significant enhancement in CO(2) uptake at room temperature, suggesting that the strong interactions between CO(2) and the functionalized ligands, indicating that surface chemistry, rather than porosity, plays a more important role in CO(2) adsorption. A comparison of single-component CO(2), CH(4), CO, N(2), and O(2) adsorption isotherms demonstrates that the adsorption selectivity of CO(2) over other small gases is considerably enhanced through functionalization of the frameworks. Infrared absorption spectroscopic measurements and theoretical calculations are also carried out to assess the effect of functional groups on CO(2) and H(2) adsorption potentials.

Effective Detection of Mycotoxins by a Highly Luminescent Metal-Organic Framework.

We designed and synthesized a new luminescent metal-organic framework (LMOF). LMOF-241 is highly porous and emits strong blue light with high efficiency. We demonstrate for the first time that very fast and extremely sensitive optical detection can be achieved, making use of the fluorescence quenching of an LMOF material. The compound is responsive to Aflatoxin B1 at parts per billion level, which makes it the best performing luminescence-based chemical sensor to date. We studied the electronic properties of LMOF-241 and selected mycotoxins, as well as the extent of mycotoxin-LMOF interactions, employing theoretical methods. Possible electron and energy transfer mechanisms are discussed.

Solution Processable MOF Yellow Phosphor with Exceptionally High Quantum Efficiency

An important aspect in the research and development of white light-emitting diodes (WLEDs) is the discovery of highly efficient phosphors free of rare-earth (RE) elements. Herein we report the design and synthesis of a new type of RE-free, blue-excitable yellow phosphor, obtained by combining a strongly emissive molecular fluorophore with a bandgap modulating co-ligand, in a three-dimensional metal organic framework. [Zn6(btc)4(tppe)2(DMA)2] (btc = benzene-1,3,5-tricarboxylate, tppe = 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethene, DMA = dimethylacetamide) crystallizes in a new structure type and emits bright yellow light when excited by a blue light source. It possesses the highest internal quantum yield among all RE-free, blue-excitable yellow phosphors reported to date, with a value as high as 90.7% (λex = 400 nm). In addition to its high internal quantum yield, the new yellow phosphor also demonstrates high external quantum yield, luminescent and moisture stability, solution processability, and color tunability, making it a promising material for use in phosphor conversion WLEDs.

The first example of commensurate adsorption of atomic gas in a MOF and effective separation of xenon from other noble gases

In industry, cryogenic rectification for separating xenon from other noble gases such as krypton and argon is an energy and capital intensive process. Here we show that a microporous metal–organic framework, namely Co3(HCOO)6 is capable of effective capture and separation of xenon from other noble gases. Henrys constant, isosteric heat of adsorption (Qst), and IAST selectivity are calculated based on single component sorption isotherms. Having the highest Qst reported to date, Co3(HCOO)6 demonstrates high adsorption capacity for xenon and its IAST selectivity for Xe–Kr is the largest among all MOFs investigated to date. To mimic real world conditions, breakthrough experiments are conducted on Xe–Kr binary mixtures at room temperature and 1 atmosphere. The results are consistent with the calculated data. These findings show that Co3(HCOO)6 is a promising candidate for xenon capture and purification. Our gas adsorption measurements and molecular simulation study also reveal that the adsorption of xenon represents the first example of commensurate adsorption of atomic gases near ambient conditions.

From 1D Chain to 3D Network: A New Family of Inorganic–Organic Hybrid Semiconductors MO3(L)x (M = Mo, W; L = Organic Linker) Built on Perovskite-like Structure Modules

MO3 (M = Mo, W) or VI-VI binary compounds are important semiconducting oxides that show great promise for a variety of applications. In an effort to tune and enhance their properties in a systematic manner we have applied a designing strategy to deliberately introduce organic linker molecules in these perovskite-like crystal lattices. This approach has led to a wealth of new hybrid structures built on one-dimensional (1D) and two-dimensional (2D) VI-VI modules. The hybrid semiconductors exhibit a number of greatly improved properties and new functionality, including broad band gap tunability, negative thermal expansion, largely reduced thermal conductivity, and significantly enhanced dielectric constant compared to their MO3 parent phases.

Chromophore-Based Luminescent Metal-Organic Frameworks as Lighting Phosphors

Energy-efficient solid-state-lighting (SSL) technologies are rapidly developing, but the lack of stable, high-performance rare-earth free phosphors may impede the growth of the SSL market. One possible alternative is organic phosphor materials, but these can suffer from lower quantum yields and thermal instability compared to rare-earth phosphors. However, if luminescent organic chromophores can be built into a rigid metal-organic framework, their quantum yields and thermal stability can be greatly improved. This Forum Article discusses the design of a group of such chromophore-based luminescent metal-organic frameworks with exceptionally high performance and rational control of the important parameters that influence their emission properties, including electronic structures of chromophore, coligands, metal ions, and guest molecules.

CO catalytic oxidation by a metal organic framework containing high density of reactive copper sites

A new metal organic framework containing high density of active Cu sites demonstrates 100% oxidative conversion of CO to CO(2).

Influence of gas packing and orientation on FTIR activity for CO chemisorption to the Cu paddlewheel

In situ Fourier-transform infrared (FTIR) spectroscopy is able to probe structural defects via site-specific adsorption of CO to the Cu-BTC (BTC = 1,3,5-benzenetricarboxylate) metal-organic framework (MOF). The temperature-programmed desorption (TPD) of CO chemisorbed to Cu-TDPAT (TDPAT = 2,4,6-tris(3,5-dicarboxylphenylamino)-1,3,5-triazine) is virtually identical to Cu-BTC, suggesting CO chemisorbs to the open metal site at the axial position of the copper paddlewheel that is the building unit of both MOFs. Yet, despite an increased gravimetric CO : Cu ratio, CO chemisorbed to Cu-TDPAT is FTIR inactive. We rule out the presence of residual solvent, thermal degradation, adsorption temperature, and ligand-induced electronic effects at the adsorption site. TPD at increased pressure suggests the multiple CO per Cu site rearrange in Cu-TDPAT as a dynamic function of temperature and pressure. Thus, the FTIR inactivity of CO chemisorbed to Cu-TDPAT is attributed to orientation and/or packing of the CO relative to the Cu binding site. The results suggest dynamic chemisorption complicate extension of a site-specific in situ FTIR probe of gas adsorption. For both Cu-BTC and Cu-TDPAT, the in situ FTIR probe is a less sensitive probe of defects than X-ray photoelectron spectroscopy and nitrogen adsorption.

Design and synthesis of new 1D and 2D R-isophthalic acid-based coordination polymers (R = hydrogen or bromine).

Three new R-isophthalic acid-based (R = H or Br) coordination polymers have been designed and synthesized. By changing the N-containing ligand in the system, we are able to tune the dimensionality of coordination polymers from one-dimension (1D) to two-dimensions (2D) with the same basic building unit. Also, different metal ions can be incorporated into the same structures. Compound 1 [Cu(bipa)(py)2]·0.5(H2O) (H2bipa = 5-bromoisophthalic acid; py = pyridine) and compound 2 [Co(bipa)(py)2] are 1D chain structures. Compound 3 [Cu8(ipa)8(bpe)8]·2(bpe)·4(H2O) (bpe=1,2-bis(4-pyridyl)ethane) is a 2D layered structure.