Zr-based Metal Research Articles

Rapid adsorptive removal of cationic and anionic dyes from aqueous solution by a Ce(III)-doped Zr-based metal–organic framework

Abstract Porous metal–organic frameworks (MOFs) exhibit excellent characteristics for the adsorptive removal of environmental pollutants. Herein, the surface charge, adsorption sites, and adsorption spaces in the pore channels of UiO-67 nanocrystals were modulated by Ce(III) doping to reveal the effects of these parameters on the removal of organic dyes such as methylene blue (MB), methyl orange, and Congo red from aqueous solution. The MB adsorption capacity of Ce(III)-doped UiO-67 (398.9 mg g−1) exceeded that reported for pristine UiO-67 by 85%, which was rationalized by zeta potential measurements and adsorption isotherm analyses. As a result, it was revealed that whereas electrostatic repulsion occurred between MB and pristine UiO-67, electrostatic attraction occurred between MB and Ce(III)-doped UiO-67. Furthermore, Ce(III) doping promoted π–π interactions between the adsorbent and the adsorbate. Thus, Ce(III) doping increased MB adsorption capacity despite decreasing the number of adsorption sites and spaces in channels. The obtained results shed light on the mechanism of organic dye adsorption on MOFs and revealed that the synergetic interplay of electrostatic and π–π interactions, adsorption sites, and adsorption spaces increases the adsorption capacity for cationic dyes while decreasing that for anionic dyes.

Protons Make Possible Heterolytic Activation of Hydrogen Peroxide over Zr-Based Metal–Organic Frameworks

The catalytic performance of zirconium-based metal–organic frameworks (UiO-66, UiO-67, and MOF-801) in cyclohexene oxidation with aqueous hydrogen peroxide can be greatly improved by adding a sourc...

Adsorptive removal of Cr(VI) onto UiO-66-NH2 and its determination by radioanalytical techniques

UiO-66-NH2 (UNH), a Zr-based metal organic framework was synthesised by solvothermal technique. The formation of UNH was confirmed by XRD and SEM–EDX results. The adsorptive behaviour of UNH towards Cr(VI) was investigated with respect to pH, temperature, contact time and adsorbent dose. Radioanalytical techniques such as PIXE and INAA were employed for determination of adsorbed Cr(VI), which was well validated from Diphenylcarbazide method. Adsorption process was endothermic and followed pseudo second order kinetics. The maximum adsorption capacity was found to be 25.9 mg g−1 at pH 2.0 and adsorbent dose of 1 g L−1 in 3 h.

Tuning the Connectivity, Rigidity, and Functionality of Two-Dimensional Zr-Based Metal–Organic Frameworks

Presented herein is a group of highly stable Zr-based metal-organic frameworks with bowl-shaped dihydroanthracene-based tetratopic linkers as building blocks. Structural analysis reveals that these frameworks are all two-dimensional but comprise three distinct connectivities of Zr6 nodes. By using the steric hindrance of the nonplanar linker, the connectivity of Zr6 node can be tuned from 8-c to unusual 4-c. Further, through either one-pot synthesis or postsynthetic linker installation strategies, the connectivity of Zr6 node can be tuned from 8-c to 10-c by the insertion of a secondary linear dicarboxylate linker, from which not only the temperature-dependent flexibility of the structure can be effectively controlled with enhanced rigidity and thermal stability but also a scaffold for postsynthetic metalation of Pd(II) catalyst for Heck coupling reaction is offered.

Interplay of Lewis and Brønsted Acid Sites in Zr-Based Metal-Organic Frameworks for Efficient Esterification of Biomass-Derived Levulinic Acid.

We report the performance of UiO-66 and its Brønsted acid functionalized derivative, UiO-66-(COOH)2, as heterogeneous catalysts for levulinic acid esterification with ethanol. Importantly, compared with UiO-66, UiO-66-(COOH)2 displayed superior catalytic performance (up to 97.0 ± 1.1% yield of ethyl levulinate) attributed to the synergistic effect between Lewis acidic Zr clusters and Brønsted acidic -COOH groups. Furthermore, UiO-66-(COOH)2 was stable and reusable without an appreciable loss in catalytic activity for at least five consecutive cycles. This study demonstrates that the interplay of Brønsted and Lewis acid sites in zirconium metal-organic frameworks leads to more efficient catalytic conversion of a biomass feedstock to biofuel, and with further hypothesis driven research, additional materials that show promise as candidates for catalytic conversion of biomass feedstocks to biofuels and valuable chemicals can be developed.

The impact of crystal size and temperature on the adsorption-induced flexibility of the Zr-based metal-organic framework DUT-98.

In this contribution we analyze the influence of adsorption cycling, crystal size, and temperature on the switching behavior of the flexible Zr-based metal–organic framework DUT-98. We observe a shift in the gate-opening pressure upon cycling of adsorption experiments for micrometer-sized crystals and assign this to a fragmentation of the crystals. In a series of samples, the average crystal size of DUT-98 crystals was varied from 120 µm to 50 nm and the obtained solids were characterized by X-ray diffraction, infrared spectroscopy, as well as scanning and transmission electron microscopy. We analyzed the adsorption behavior by nitrogen and water adsorption at 77 K and 298 K, respectively, and show that adsorption-induced flexibility is only observed for micrometer-sized crystals. Nanometer-sized crystals were found to exhibit reversible type I adsorption behavior upon adsorption of nitrogen and exhibit a crystal-size-dependent steep water uptake of up to 20 mmol g−1 at 0.5 p/p0 with potential for water harvesting and heat pump applications. We furthermore investigate the temperature-induced structural transition by in situ powder X-ray diffraction. At temperatures beyond 110 °C, the open-pore state of the nanometer-sized DUT-98 crystals is found to irreversibly transform to a closed-pore state. The connection of crystal fragmentation upon adsorption cycling and the crystal size dependence of the adsorption-induced flexibility is an important finding for evaluation of these materials in future adsorption-based applications. This work thus extends the limited amount of studies on crystal size effects in flexible MOFs and hopefully motivates further investigations in this field.

Efficient removal of metal contaminants by EDTA modified MOF from aqueous solutions

Herein a versatile adsorbent has been synthesized by immobilization of ethylenediaminetetraacetic acid (EDTA) into the pores of the Zr-based metal organic framework (UiO-66) through a facile method. The as-prepared EDTA modified UiO-66 (UiO-66-EDTA) was characterized completely to investigate its physical and chemical properties. It shows great chemical stability with octahedral structure and carboxylic groups and amine groups. Through batch experiments, UiO-66-EDTA shows no specificity for the removal of diverse heavy metal ions (three categories: soft acids, hard acids, and borderline acids) because of its both hard and relatively softer chemical characters of functional groups. The maximum removal capacities of UiO-66-EDTA for Eu3+ (hard acids), Hg2+ (soft acids) and Pb2+ (borderline acids) are 195.2, 371.6 and 357.9 mg g−1, respectively. Notably, 11 metal ions removal efficiency reaches over 99% in co-existing system. The results from X-ray photoelectron spectroscopy (XPS) analysis reveal the coordination of Eu3+, Hg2+ and Pb2+ with carboxyl groups (COOH) and tertiary amine groups (CN(C)C) is responsible for their removal by UiO-66-EDTA. Given the fact that UiO-66-EDTA possesses high chemical stability, facile synthesis method, efficient removal performance and superior reusability, it can be applied in treatment of seriously polluted water with multi-pollutants.

Improving the photocatalytic hydrogen evolution of UiO-67 by incorporating Ce4+-coordinated bipyridinedicarboxylate ligands

UiO-67 is a Zr-based metal–organic framework (MOF) containing an organic linker namely, the dianion of biphenyl-4,4′-dicarboxylic acid (bpdc). Ce4+ metal ions (0.02 Ce to Zr atom ratio) were incorporated into UiO-67 via partially replacing bpdc with the dianion of 2,2′-bipyridine-5,5′-dicarboxylic acid (bpydc); thus, the latter forms a bpydc-Ce complex. The resulting product (i.e., UiO-67-Ce) demonstrated a photocatalytic hydrogen evolution rate that was over 10 times higher than that of UiO-67. Through this modification, a new energy transfer channel is opened up. The energy transfer between the bpdc and bpydc-Ce ligands (i.e., from excited bpdc to bpydc-Ce) weakened the recombination of the charge carriers, which was confirmed by photoluminescence, emission lifetime, and transient absorption measurements. This study presents a new way to construct highly efficient MOF photocatalysts.

A Zr-based metal organic frameworks towards improving fire safety and thermal stability of polycarbonate

Zr-based metal organic frameworks (Zr-BDC) with high porosity were synthesized by a solvothermal method and then compounded with polycarbonate (PC, one of the most important engineering plastic) to reduce the fire hazard and improve the thermal stability of PC. It was found that Zr-BDC could prolong the time to ignition (TTI) and time to peak of heat release rate (t-PHRR) of PC up to 90 and 75 s, respectively. Compared with the neat PC, 2 wt% Zr-BDC could increase the temperature at the maximum degradation rate (Tmax) of PC in N2 atmosphere by 33 °C; 4 wt% Zr-BDC reduced the values of peak heat release rate (PHRR) and total smoke release (TSR) by 48% and 34%, respectively. Moreover, only 4 wt% Zr-BDC made the composites reach UL-94 V-0 rating in vertical burning test. Unsaturated Zr metal site made Zr-BDC have activity in catalytic oxidation, isomerization reactions etc., which imparted it the ability to catalyze char formation (cross-linking) in the degradation process of PC matrix, therefore more compact, and highly graphitized char layers were obtained.

Studies of Zr-based C15 type metal hydride battery anode alloys prepared by rapid solidification

The objective of the present work was to study an interrelation between the conditions of the rapid solidification casting and electrochemical properties of a C15 Laves-type Zr-based metal hydride battery anode alloy. A 7-component overstoichiometric with B/A>2 alloy (Ni + Mn + V + Fe/Zr + Ti + La = 2.078) was Zr- and Ni-rich. Melt spinning was performed using as cast mother ingot at different rotation speeds of 5, 16.5, and 33 Hz with a 20-cm diameter Cu cooling wheel. The phase composition and morphology of the ribbons were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM) along with X-ray energy dispersive spectroscopy (EDS). Partial Mn vaporization took place during the melt spinning and became more pronounced with the increase in the quenching rate at higher wheel rotation speeds. The SEM study showed a successful refinement and a more homogeneous distribution of La in the melt-spun alloys. However, the alloys demonstrated a more difficult activation performance as compared to the as-cast sample which was associated with introduction of Zr into the composition of the secondary La-and Ni-rich phase when quenching the melt. Presence of Zr in the secondary phase results in inferior rate of its hydrogenation. The formed during the rapid solidification (La,Zr) (Ni,Mn) secondary phase also contained a significant amount of oxygen additionally worsening the activation performance. The grain size gradually decreased from 3.5 μm in the as-cast alloy to approximately 250 nm for the melt spun sample obtained at the highest cooling rate. The two-phase alloys contained a mixture of two Laves type intermetallics, C15 and C14 ones. The abundance of the secondary C14 phase decreased with increase of the cooling rate as compared to the as-cast sample. The electrochemical performance was significantly affected by the compositional and microstructural changes associated with the variation in the cooling rate. The highest electrochemical discharge capacity of 414 mAh/g was obtained for the 16.5 Hz melt spun rate because of an optimized composition of the Laves phase. Furthermore, the diffusion coefficient of hydrogen in this alloy was the highest in a full state of charge, which indicates that faster hydrogen diffusion and shorter hydrogen diffusion paths were achieved via an application of the rapid solidification process. An optimization of the rapid solidification conditions is required to improve an activation behavior of the studied Laves types metal hydride anode alloys.

Recovery of polyphenols from water using Zr-based metal-organic frameworks and their nanocomposites with graphene nanoplatelets

In this study, Zr-based metal organic frameworks (UiO-66) and graphene nanoplatelets UiO-66 nanocomposites (GNP/UiO-66) were prepared using acid promoted method, and used for adsorption of two different polyphenols; oleuropein and hydroxytyrosol. Different characterization techniques used for exploring the morphological and structure properties of the UiO-66 and GNP/UiO-66 nanocomposites. The adsorption of oleuropein and hydroxytyrosol was studied by UiO-66 and different GNP/UiO-66 nanocomposites and results showed that most of the oleuropein and hydroxytyrosol were removed from the solution in 60min and 180min, respectively. The kinetic modelling of adsorption was studied. The adsorption isotherms were constructed at different pH values.

Microstructure and corrosion behaviour of ferritic steel–Zr-based metal waste form alloys in simulated ground water

ABSTRACTThe microstructure and corrosion behaviour of the metal waste form (MWF) alloys based on ferritic steel with Zr content in the range of 3–15 wt-% were investigated. The MWF alloys are composed of α-Fe and Fe-Zr phases and with the increase of Zr content, α-Fe phase gradually decreases and the relative content of Fe–Zr intermetallic phase also increases. TEM and XRD confirmed the presence of Fe2Zr and Fe23Zr6 intermetallics. Potentiodynamic polarisation curves showed The MWF alloys exhibited passivation behaviour in the simulated Kalpakkam (KGW) and Rajasthan ground water (RGW) media. Electrochemical impedance spectra revealed improved passive film stability in RGW than in KGW which is related to the formation of more stable adherent insoluble passive film in RGW. Higher Zr containing MWF alloy exhibited higher corrosion resistance than lower Zr containing MWF alloys. The relative content of Fe–Zr intermetallics is attributed for the corrosion resistance of The MWF alloys.

Development of highly permeable polyelectrolytes (PEs)/UiO-66 nanofiltration membranes for dye removal

With suitable pore size, narrow pore size distribution and charged surface, nanofiltration (NF) membranes show great potential in removing or recovering dyes from effluents of printing and dyeing industries. However, low permeance of commercial nanofiltration membranes hampers their widespread application. Herein, we design a kind of high permeance mixed matrix membranes through layer-by-layer (LbL) self-assembly of polyelectrolytes (PEs). The additional solvent pathways constructed by incorporation of UiO-66, a type of Zr-based metal organic frameworks (MOFs), accelerate the water passing through the membranes; the pure water permeance of UiO-66 incorporated PEs membrane (PEM/UiO-66) achieves at as high as 14.8 L m−2 h−1 bar−1 which is 160% higher than the pristine PEs membrane. Meanwhile, the membrane exhibits 96.3% rejection towards MgSO4 with molecular weight cut off (MWCO) of 464.2 g mol−1. The comprehensive separation performance of the mixed matrix membrane outperforms most of state-of-the-art NF membranes fabricated by LbL self-assembly to the best of our knowledge. Most interestingly, the mixed matrix membrane demonstrates solution flux as high as 102 L m−2 h−1 with 99.9% rejection of Congo Red under optimized operation conditions in 240 h continuous operation. Taken together, the UiO-66 incorporated NF membranes show strong promise in removing and recovery of dyes in industrial scale.

Zr-Based Metal-Organic Frameworks with Intrinsic Peroxidase-Like Activity for Ultradeep Oxidative Desulfurization: Mechanism of H2O2 Decomposition.

The restriction of sulfur content in fuels has become increasingly stringent as a result of the growing environmental concerns. Although several MOF-derived materials like POM@MOF composites have shown the ability to catalyze oxidative desulfurization (ODS), their catalytic activities inevitably obstructed by the encapsulated catalytic sites like POM due to the blockage of cavities. Therefore, MOFs with intrinsic and accessible catalytic sites are highly desirable for their applications in ultradeep ODS. Herein, four representative Zr-based MOFs (Zr-MOFs), namely, UiO-66, UiO-67, NU-1000, and MOF-808, were assessed for catalytic ODS. These MOFs were confirmed that they have peroxidase-like activity and can catalyze ODS with H2O2 as oxidant. Among them, MOF-808 showed the highest catalytic activity and it can fully desulfurize dibenzothiophene (DBT) in a model gasoline with a S concentration of 1000 ppm under 40 °C within 5 min. An extremely low apparent Arrhenius activation energy (22.0 KJ·mol-1) and an extraordinarily high TOF value (42.7 h-1) were obtained, ranking MOF-808 among the best catalysts for the catalytic DBT oxidation. Further studies confirmed that the excellent catalytic activity is mainly responsible for the high concentration of the accessible Zr-OH(H2O) catalytic sites decorated in MOF-808. The superoxide radicals (•O2-) and hydroxyl radicals (•OH) were identified and were proved to involve in the DBT oxidation. Besides, the effects of Brönsted and lewis acidity to the catalytic efficiency were also discussed. Based on the experimental results, a plausible mechanism concerning on Zr-OH(H2O) groups promoting the H2O2 decomposion in to both •O2- and •OH was first proposed. Moreover, MOF-808 can be facilely reused for at least eight runs without significant loss of its catalytic activity. By the integration of facile synthesis, high catalytic efficiency, and good stability, MOF-808 thus represents a new benchmark catalyst for catalytic oxidative desulfurization.

Enhancing the Water Capacity in Zr-Based Metal–Organic Framework for Heat Pump and Atmospheric Water Generator Applications

According to the European Commission, in 2016 the residential sector represented 25.4% of the final energy consumption. Heating and cooling in EU households account for 69.1% of the total energy consumption. The fraction of 84% for heating and cooling is still generated from fossil fuels, and only 16% is generated from renewable energy. To decrease carbon dioxide emissions of fossil fuel consumption, it is crucial to find alternatives to supply the heating and cooling demand. Alternatives such as adsorption-based heat pumps and desiccant cooling systems are receiving much attention because of their moderate energy consumption. These systems are based on the energetic exchange during the adsorption/desorption of working fluids. In this work, we combined experiments and simulations to evaluate the viability of several zeolites and MOFs with water for cooling systems applications. We combined the study of adsorption mechanisms and the dynamics of water inside the pores of the structures, thereby obtaining an overall understanding of the working pair. We found that the Al content in FAU-topology zeolites is a key factor for an efficient process. We also identify ZJNU-30 metal-organic framework as a suitable candidate for cooling applications because of its outstanding water capacity, cooling capacity, and coefficient of performance.

Effects of lithium addition in AB2 metal hydride alloy by solid-state diffusion

In this study, microstructures and electrochemical properties of a Zr-based AB2-type metal hydride alloy (Ti12.1Zr21.3V10.5Cr7.5Mn8.1Co8.0Ni31.7Al0.8) doped with 6 wt% LiH by solid-state diffusion at different temperatures were investigated and compared with those of the base alloy sintered at the same conditions. Structural study by x-ray diffraction analysis exhibited a lattice expansion in the main C14 phase of the Li-doped alloys with a relatively low sintering temperature, indicating that Li incorporated into the C14 Laves phase but was evaporated at higher sintering temperatures. Addition of Li deteriorated both the electrochemical capacity and activation easiness; however, it improved the high-rate dischargeability (HRD). The benefit of Li addition on HRD can be associated with the increase in amount of metallic nickel clusters embedded in the surface oxide (estimated by the saturated magnetic susceptibility) and was a strong function of sintering temperature. As the sintering temperature increased, HRD increased due to the increase in amount of surface catalytic metallic nickel.

Photoelectrochemical immunosensor for N6-methyladenine detection based on Ru@UiO-66, Bi2O3 and Black TiO2

A novel photoelectrochemical (PEC) immunosensor was successfully constructed for N6-methyladenine (m6A) detection based on the photoactive materials of black titanium dioxide (B-TiO2) and bismuth trioxide (Bi2O3) and the signal amplification unit of [Ru(bpy)3]2+-doped metal organic framework (MOF). The Bi2O3/B-TiO2/ITO electrode was first fabricated, then decorated with gold nanoparticles (AuNPs) which provided sites for anchoring m6A antibodies. After the capture of m6A via immunoreaction with the antibody, the Zr-based metal organic framework (UiO-66)-[Ru(bpy)3]2+ compound was further attached specifically to the phosphate group of m6A. With visible light irradiation, a large and stable photocurrent response was produced in the presence of ascorbic acid (AA). Under optimized experimental conditions, the linear range of the PEC biosensor was 0.05–30 nM, with a low detection limit of 0.0167 nM (S/N = 3). This method showed high specificity, selectivity, stabilization and repeatability. Moreover, it was successfully used for the detection of m6A in rice seedling leaves that had been subjected to heavy metal treatment during their development.

Selective hydrogenation of phenol by the porous Carbon/ZrO2 supported Ni[sbnd]Co nanoparticles in subcritical water medium

Phenol is a typical aromatic organic byproduct in the coking industry, which can be also as a raw material for producing some useful chemicals by catalytic hydrogenation. In this paper, by constructing carbon/ZrO2 porous support with abundant vacancies for loading nickel and cobalt nanoparticles (i.e., NixCoy@C/ZrO2) with using Zr-based metal organic frameworks as the precursor, the significant phenol converting enhancement in both hydrothermalcatalytic activity and stability has been fulfilled. Specially, the physiochemical characteristics of the NixCoy@C/ZrO2 particles have been analyzed, which verified the presence of NiCo alloy and its high homogeneity and dispersity. The catalytic results showed that the Ni3Co1@C/ZrO2 catalyst has the best catalytic performance at the desired temperature of 200 °C for 240 min, and the conversion of phenol is 96.33% while the selectivity of cyclohexanol is 91.14%. Kinetic study showed that the activation energy was only 44.31 kJ/mol, which reflected that the hydrogenation could be easily carried out with Ni3Co1@C/ZrO2 catalyst. These findings can provide a good guidance for designing and developing the non-noble-metal catalysts for achieving the industrial utilization of phenol in coking wastewater in the future.

Preparation and Characterization of UiO-66-Supported Cu–Ce Bimetal Catalysts for Low-Temperature CO Oxidation

A series of Zr-based metal–organic frameworks (UiO-66) supported CuO–CeO2 catalysts with various total metal loadings and various Cu/Ce ratios were prepared by using a co-impregnation method. The catalytic activities of the catalysts for low temperature oxidation of carbon monoxide were compared with that supported on the ZrO2 and mesostructured cellular foam silica. The results show that the catalysts supported by UiO-66 are expected to give the best catalytic activity, which should be attributed to the special construction of UiO-66. The samples were further characterized by XRD, TEM, N2 adsorption–desorption, H2-TPR, XPS, and in situ DRIFT. And the catalyst with a bimetallic loading of 50 wt% and Cu/Ce ratio of 3:7 (wt/wt) has the highest catalytic activity, which can be attributed to the larger amount of finely dispersed Cu species strongly interacting with CeO2, the highest amounts of oxygen vacancies and Cu+ species on the catalyst surface.

Polyoxomolybdic Cobalt Encapsulated within Zr-Based Metal–Organic Frameworks as Efficient Heterogeneous Catalysts for Olefins Epoxidation

The encapsulation of polyoxomolybdic cobalt (CoPMA) and polyoxomolybdic acid (PMA) within the Zr-based metal–organic frameworks (Zr-MOFs) of UiO-bpy (connected by 2,2′-bipyridine-5,5′-dicarboxylic ...