Xiuling Ma

High Anhydrous Proton Conductivity of Imidazole-Loaded Mesoporous Polyimides over a Wide Range from Subzero to Moderate Temperature

On-board fuel cell technology requires proton conducting materials with high conductivity not only at intermediate temperatures for work but also at room temperature and even at subzero temperature for startup when exposed to the colder climate. To develop such materials is still challenging because many promising candidates for the proton transport on the basis of extended microstructures of water molecules suffer from significant damage by heat at temperatures above 80 °C or by freeze below -5 °C. Here we show imidazole loaded tetrahedral polyimides with mesopores and good stability (Im@Td-PNDI 1 and Im@Td-PPI 2) exhibiting a high anhydrous proton conductivity over a wide temperature range from -40 to 90 °C. Among all anhydrous proton conductors, the conductivity of 2 is the highest at temperatures below 40 °C and comparable with the best materials, His@[Al(OH)(1,4-ndc)]n and [Zn3(H2PO4)6(H2O)3](Hbim), above 40 °C.

Metal–organic frameworks with a large breathing effect to host hydroxyl compounds for high anhydrous proton conductivity over a wide temperature range from subzero to 125 °C

It is important but still challenging to develop high-performance proton conducting materials for proton exchange membrane fuel cells (PEMFCs), as such materials should meet the following requirements: stable proton-transport pathway over a wide temperature range, high conductivity at work temperature, and small activation energy Ea to maintain high conductivity at start temperature. Here, we firstly demonstrated that flexible metal–organic frameworks (FMOFs) are good hosts to seek out better proton carriers for such high-performance proton conducting materials. A FMOF [Zn3(tz)2(bdc)2]n (FJU-31, Htz = 1H-1,2,3-triazole, H2bdc = terephthalic acid) with high thermal stability up to 400 °C, which can be readily synthesized from the Zn5(tz)6(NO3)4 precursor and H2bdc, has been employed to host various organic hydroxyls as new proton carriers. Three resulting FMOFs Zn3(tz)2(bdc)2@G (FJU-31@G, G = hydroquinone (Hq), cyclohexanol (Ch) or butanol (Bu)) show large breathing effect amplitudes up to 65% and guest-related single-crystal to single-crystal structural transformations by temperature stimulus. Most importantly, FJU-31@Hq hosting hydroquinone with a high melting point and small pKa exhibits a high anhydrous proton conductivity of 2.65 × 10−4 S cm−1, low activation energy Ea of 0.18 eV, and the widest temperature range from −40 to 125 °C for stable proton conduction among the crystalline porous materials.

Cobalt–citrate framework armored with graphene oxide exhibiting improved thermal stability and selectivity for biogas decarburization

A series of metal–organic framework (UTSA-16)–graphene oxide composites was synthesized. These composites are the first reported examples of core–shell type metal–organic framework composites armored with graphene oxide film. The parent materials (UTSA-16 and graphene oxide) and the nanocomposites were characterized using XRD, SEM, TEM, TGA and gas adsorption. The composites showed a greatly improved thermal stability compared with their parent materials. The UTSA-16–GO19 composite has a CO2/CH4 selectivity of 114.4, which is three times greater than that of UTSA-16 alone; of the previously reported metal–organic frameworks, only the polyamine-incorporated amine-MIL-101(Cr) has a higher CO2/CH4 selectivity. These graphene oxide composites provide a new direction for practical high-performance metal–organic framework materials.

40-Fold Enhanced Intrinsic Proton Conductivity in Coordination Polymers with the Same Proton-Conducting Pathway by Tuning Metal Cation Nodes.

Three isostructural imidazole-cation-templated metal phosphates (FJU-25) are the first examples to demonstrate that the tuning of metal cation nodes can be an efficient strategy to significantly improve the proton conductivity without changing the structure of the proton-conducting pathway.

Ultrasensitive sensing of tris(2,3-dibromopropyl) isocyanurate based on the synergistic effect of amino and hydroxyl groups of a molecularly imprinted poly(o-aminophenol) film

A facile approach for sensing an emerging persistent organic pollutant, tris(2,3-dibromopropyl) isocyanurate (TBC) is developed based on coupling molecularly imprinting with electro-polymerization of o-aminophenol (OAP), which is an electro-active monomer containing multifunctional groups. The poly-OAP film was deposited in an OAP solution by the potentiodynamic cycling of the potential with and without the template (TBC) on a glassy carbon electrode. Using K3[Fe(CN)6] as an electro-active marker, the properties of the TBC imprinted electrode were investigated by electrochemical measurements. The results showed that the sensor with a low detection limit of 6.64 × 10−11 mol L−1 (S/N = 3) for TBC determination was significantly different from the non-imprinted electrode. By selecting aniline, without a hydroxyl group, as a reference for controlled trials, the limit of detection for the poly-OAP film-coated electrode is ca. 10 times smaller than that of the polyaniline-coated one, and the sensitivity of the poly-OAP film is ca. 2 times higher than that of the polyaniline one. It demonstrates that more binding sites might improve the detection ability of the imprinted sensor.

The cooperative utilization of imprinting, electro-spinning and a pore-forming agent to synthesise β-cyclodextrin polymers with enhanced recognition of naringin

The aim of this study was to identify if the addition of an inorganic pore-forming agent (PFA) could provide an efficient route to significantly improve the binding capacity of molecularly imprinted nanofibers (MINs), along with increasing their imprinting effect and selectivity. A non-covalently imprinted composite nanofiber (MIN–PFA) with in situ generated silica as a pore-forming agent was prepared using an electro-spinning technique with naringin (NG) as a template, β-cyclodextrin as a functional monomer, hexamethylene diisocyanate as a cross-linker, and polyvinyl butyral as an electro-spinning matrix. For comparison purposes, two imprinted polymers (MIN and MIP) were prepared in the absence of PFA, with or without electro-spinning employed. The binding properties and selectivity of the nanofibers were evaluated using equilibrium binding experiments. MIN–PFA exhibited a high specific binding capacity (∼13.0 μmol g−1) towards naringin, binding 30% and 57% more than MIN and MIP, respectively. The N2 gas adsorption isotherm at 77 K also demonstrated that the addition of PFA could enhance the surface area of the imprinted nanofibers.

Molecularly Imprinted Nanofiber Film for Sensitive Sensing 2,4,6-Tribromophenol

The determination of brominated flame retardants is of great importance, but remains a challenge. Particularly, universal and facile approaches are limited. Here we report a new general approach, combining molecular imprinting and electrospinning, for the efficient and facile imprinting sensor of 2,4,6-tribromophenol (TBP), which was used as a “novel” brominated flame retardant. With TBP as the template molecular, β-cyclodextrin (β-CD) as the functional monomer, and poly-vinylbutyral (PVB) as the electro-spinning matrix, the nanofiber film was deposited on the glassy carbon electrode (GCE) via electrospinning technique directly. The β-CD-PVB/GCE sensor system exhibited excellent TBP sensing performances, such as a low detection limit (6.29 × 10−10 mol·L−1) at room temperature, selective recognition to TBP/phenol/4-methyl-phenol, and good regeneration performance. The approach of fabricating a molecular imprinting nanofiber sensor may shed new light in the detection of other phenolic pollutants.

Facile synthesis of oxidized activated carbons for high-selectivity and low-enthalpy CO2 capture from flue gas

The prospect of a worsening climatic situation prompts us to develop energy-saving and cost-effective CO2 capture technologies. In this work, three oxidized activated carbons (ACO-n, n is 1–3) were prepared through a facile synthesis approach via oxidation in the presence of KMnO4 and concentrated H2SO4 for 0.5, 1.0 or 2.0 hours. Interestingly, these carbon materials ACO-n can exhibit high CO2 capacity with low adsorption enthalpy and the selectivity toward flue gas can be adjusted by altering the period of oxidation. Among the pristine activated carbon and ACO-n materials, ACO-2 can exhibit the highest CO2 capacity of 3.01 mmol g−1 under ambient conditions with an adsorption enthalpy of only 23.1 kJ mol−1, slightly larger than the CO2 vaporization enthalpy. Its selectivity of 48.5 is double the value of the pristine activated carbon. A column breakthrough experiment was conducted to evaluate the CO2 separation capability on ACO-2 toward a CO2/N2 (15 : 85 v/v) mixture under kinetic flow conditions, which suggests that the oxidized activated carbon made from sustainable sources is promising for CO2 capture.

MOF-derived binary mixed carbon/metal oxide porous materials for constructing simultaneous determination of hydroquinone and catechol sensor

AbstractIt is a top priority to simultaneously and accurately detect hydroquinone (HQ) and catechol (CC). Here, a new strategy for constructing simultaneous determination of HQ and CC sensor was proposed by one-step pyrolysis of MIL series metal-organic frameworks materials (MIL-125 (Ti), MIL-101 (Cr), and MIL-101 (Fe)) to obtain uniform-mixed carbon/metal oxide porous materials (TiO2/C900, Cr2O3/C900, and Fe2O3/C900, respectively). And, cyclic voltammetry (CV) was utilized to investigate the electrochemical behavior of the composite materials. It was found that the simultaneous detection of catechol (CC) and hydroquinone (HQ) could be achieved by the sensor consisted of TiO2/C900 with the superior BET-specific surface area and micro-mesoporous characteristics. And, the linear range and detection limit of HQ and CC for the TiO2/C900 sensor were further studied. In addition, it was also found that the pyrolysis temperature and metal centers would affect the internal structures and component of the materials, thus affecting the properties of materials. The experiment provides a new idea for optimizing the simultaneous detection of the dihydroxybenzene isomers. Graphical abstractA new feasible strategy was proposed by introducing the binary uniform-mixed carbon/metal oxide porous materials, by which the calcination temperature and the metal centers of MOFs would be considered to construct the sensor for simultaneous determination of catechol (CC) and hydroquinone (HQ).