Construction of Porous Solids from Hydrogen-Bonded Metal Complexes of 1,3,5-Benzenetricarboxylic Acid

Terephthalate and trimesate metal-organic frameworks of Mn, Co, and Ni: exploring photostability by spectroscopy

We report a rapid synthesis for the fabrication of terephthalate and trimesate metal-organic frameworks (MOFs) of Mn, Co, and Ni by ultrasonication of organic linkers with freshly prepared metal hydroxides. The MOFs were characterized by various microscopic and spectroscopic techniques to understand their structural, functional, and optical properties. MOFs with low bandgap energy (1.88-2.73 eV) showed strong absorbance in the UV-visible range. MOFs were exposed to UV irradiation for 40 h to understand their photostability. The MOFs showed decreased surface area and porosity with CoBTC as an exception. PXRD was less convincing for exploring functional changes in the UV-irradiated MOFs. XPS predicted changes in the oxidation states of metal nodes, the degradation of the organic linkers, and decarboxylation process in many of the transition MOFs. The study predicted terephthalate-based MOFs as more photostable than corresponding trimesate-based MOFs. This study is one of the first attempts in exploring photostability of MOFs with Mn, Co, and Ni as nodes.

Zinc Based Metal-Organic Frameworks as Ofloxacin Adsorbents in Polluted Waters: ZIF-8 vs. Zn3(BTC)2

Two different zinc-based metal-organic frameworks (MOFs) were investigated to remove one of the most used fluoroquinolone antibiotic, Ofloxacin (OFL), from polluted water. The most common zeolitic imidazolate framework-8 (ZIF-8) and the green Zn(II) and benzene-1,3,5-tri-carboxylate (Zn3(BTC)2) were prepared through a facile synthetic route and characterized by means of Fourier-Transform Infrared (FT-IR) Spectroscopy, X-ray Powder Diffraction (XRPD), and Scanning Electron Microscopy (SEM) analyses. The two MOFs were compared in terms of both adsorption and kinetic aspects under real conditions (tap water, natural pH). Results showed that OFL was adsorbed in remarkable amounts, 95 ± 10 and 25.3 ± 0.8 mg g-1 on ZIF-8 and Zn3(BTC)2, respectively, following different mechanisms. Specifically, a Langmuir model well described the ZIF-8 profile, while for Zn3(BTC)2, cooperative adsorption occurred. Moreover the kinetic results were quite different, pseudo-second-order and sigmoidal, respectively. The suitability of ZIF-8 and Zn3(BTC)2 as adsorbent phases for water depollution was tested on tap water samples spiked with OFL 10 µg L-1. The obtained removal efficiencies, of 88% for ZIF-8 and 72% for Zn3(BTC)2, make these materials promising candidates for removing fluoroquinolone antibiotics (FQs) from polluted waters, notwithstanding their limited reusability in tap water, as demonstrated by in-depth characterization of the two MOFs after usage.

A nickel ion-incorporating zinc-mesoporous metal organic framework thin film nanocomposite modified glassy carbon electrode for electrocatalytic oxidation of methanol in alkaline media

In this work, we have successfully synthesized a nickel ion-incorporating zinc-mesoporous metal–organic framework thin films (Zn-mMOFTFs) modified glassy carbon electrode (GCE), Ni/Zn-mMOFTFs/GCE, for electrooxidation of methanol in alkaline solution.

Deep eutectic solvents for the preparation and post-synthetic modification of metal- and covalent organic frameworks

The use of deep eutectic solvents (DES) as media for the preparation of metal- and covalent organic frameworks (MOFs and COFs) and their post-synthetic modification towards composites is reviewed.

A critical review on recent developments in MOF adsorbents for the elimination of toxic heavy metals from aqueous solutions

Effective and substantial remediation of contaminants especially heavy metals from water is still a big challenge in terms of both environmental and biological perspectives because of their adverse effects on the human health. Many techniques including adsorption, ion exchange, co-precipitation, chemical reduction, ultrafiltration, etc. are reported for eliminating heavy metal ions from the water. However, adsorption has preferred because of its simple and easy handlings. Several types of adsorbents are observed and documented well for the purpose. Recently, highly porous metal-organic frameworks (MOFs) were developed by incorporating metals and organic ligands together and claimed as potent adsorbents for the remediation of highly toxic heavy metals from the aqueous solutions due to their unique features like greater surface area, high chemical stability, green and reuse material, etc. In this review, the authors discussed systematically some recent developments about secure MOFs to eliminate the toxic metals such as arsenic (both arsenite and arsenate), chromium(VI), cadmium (Cd), mercury (Hg) and lead (Pb). MOFs are observed as the most efficient adsorbents with greater selectivity as well as high adsorption capacity for metallic contamination. Graphical abstract.

Superparamagnetic MOF@GO Ni and Co based hybrid nanocomposites as efficient water pollutant adsorbents

A series of highly efficient adsorbents were developed using Ni₃(BTC)₂ and Co₃(BTC)₂ metal-organic frameworks (MOFs) and Fe₃O₄ magnetic nanoparticles (MNPs) to functionalize graphene oxide (GO). XRD results show high crystallinity of the prepared nanomaterials and the successful decoration of Ni₃(BTC)₂ and Co₃(BTC)₂ MOFs over the GO substrate (BTC = benzene-1,3,5-tricarboxylic acid). SEM and TEM imaging show the successful formation of nanoscale MOFs and Fe₃O₄ MNPs over GO. IR spectroscopy supports the characterization and successful preparation of the Fe₃O₄/MOF@GO hybrid composite nanoadsorbents. The prepared composite nanoadsorbents were used to sorb Methylene Blue (MB) as a model for common organic pollutants in water and common ions (Na⁺, Ca²⁺, Mg²⁺, SO₄^2-, SiO₃^2-) from a brackish water model. The adsorbed concentration at equilibrium of MB of the prepared composite nanoadsorbents increases by an average of 30.52 and 13.75 mg/g for the Co and Ni composite, respectively, when compared to the MOFs parent materials. The adsorbed amount of sulfate ions increases by 92.1 mg/g for the Co composite and 112.1 mg/g for the Ni composite, when compared to graphene oxide. This adsorption enhancement is attributed to suppressed aggregation through increased dispersive forces in the MOFs due to the presence of GO, formation of nanoscale MOFs over the GO platform, and the hindering of stacking of the graphene layers by the MOFs. Leaching tests show that the release of Co and Ni ions to water is reduced from 105.2 and 220 mg/L, respectively, in the parent MOF materials to 0.5 and 16.4 mg/L, respectively, in the composite nanoadsorbents. These findings show that the newly developed composite nanoadsorbents can sorb organic pollutants, and target sulfate and silicate anions, which makes them suitable candidates for water and wastewater treatments.

A Metal-Organic Framework as a Multifunctional Ionic Sieve Membrane for Long-Life Aqueous Zinc-Iodide Batteries

The introduction of the redox couple of triiodide/iodide (I₃ ^- /I^- ) into aqueous rechargeable zinc batteries is a promising energy-storage resource owing to its safety and cost-effectiveness. Nevertheless, the limited lifespan of zinc-iodine (Zn-I₂ ) batteries is currently far from satisfactory owing to the uncontrolled shuttling of triiodide and unfavorable side-reactions on the Zn anode. Herein, space-resolution Raman and micro-IR spectroscopies reveal that the Zn anode suffers from corrosion induced by both water and iodine species. Then, a metal-organic framework (MOF) is exploited as an ionic sieve membrane to simultaneously resolve these problems for Zn-I₂ batteries. The multifunctional MOF membrane, first, suppresses the shuttling of I₃ ^- and restrains related parasitic side-reaction on the Zn anode. Furthermore, by regulating the electrolyte solvation structure, the MOF channels construct a unique electrolyte structure (more aggregative ion associations than in saturated electrolyte). With the concurrent improvement on both the iodine cathode and the Zn anode, Zn-I₂ batteries achieve an ultralong lifespan (>6000 cycles), high capacity retention (84.6%), and high reversibility (Coulombic efficiency: 99.65%). This work not only systematically reveals the parasitic influence of free water and iodine species to the Zn anode, but also provides an efficient strategy to develop long-life aqueous Zn-I₂ batteries.

Pd/APN-Mn(BTC) as novel, highly efficient, and recyclable catalyst for Suzuki–Miyaura cross coupling reaction

A novel, heterogeneous, and bifunctional metal organic framework containing palladium and manganese, Pd/APN-Mn(BTC), has been prepared and completely characterized using FTIR, XRD, SEM-EDS, N2 adsorption–desorption, TG-DTG, NH3-TPD, and ICP analytical techniques. The APN-Mn(BTC) framework has been shown to be a useful platform for the stabilization and support of palladium nanoparticles (Pd NPs). Very effective catalytic activity has been exhibited by the highly dispersed Pd particles, Pd-NPs/APN-Mn(BTC), in the Suzuki–Miyaura cross-coupling reaction with reasonable to excellent reaction yields under mild conditions in H2O–ethanol solvent.

A solvent-assisted ligand exchange approach enables metal-organic frameworks with diverse and complex architectures

Unlike inorganic crystals, metal-organic frameworks do not have a well-developed nanostructure library, and establishing their appropriately diverse and complex architectures remains a major challenge. Here, we demonstrate a general route to control metal-organic framework structure by a solvent-assisted ligand exchange approach. Thirteen different types of metal-organic framework structures have been prepared successfully. To demonstrate a proof of concept application, we used the obtained metal-organic framework materials as precursors for synthesizing nanoporous carbons and investigated their electrochemical Na+ storage properties. Due to the unique architecture, the one-dimensional nanoporous carbon derived from double-shelled ZnCo bimetallic zeolitic imidazolate framework nanotubes exhibits high specific capacity as well as superior rate capability and cycling stability. Our study offers an avenue for the controllable preparation of well-designed meta-organic framework structures and their derivatives, which would further broaden the application opportunities of metal-organic framework materials.

Metal organic frameworks decorated with free carboxylic acid groups: topology, metal capture and dye adsorption properties

In this report, metal organic frameworks (MOFs) are designed and tuned for structural variations in order to induce metal capture which in turn directs dye adsorption properties. The three MOFs, Cu-MOF-2COOH, Ni-MOF-COOH and Cd-MOF, are synthesized by employing 1,3,5-benzenetricarboxylic acid (H3-BTC) as the main ligand and 4,4'-dipyridyl (bipy) as the spacer. The MOFs have been characterized using various spectral techniques and single crystal X-Ray studies. A topological analysis using TOPOS Pro reveals that the MOFs possess varying topologies i.e.hcb, hxl, sql and 2C1. Cu-MOF-2COOH and Ni-MOF-COOH contain two and three uncoordinated carboxylic acid groups, respectively, and in Cd-MOF, all three -COOH groups are utilized in bonding. The dye adsorption properties of the MOFs with free carboxylate group(s) were checked and we found that both MOFs are unable to adsorb any of the dyes significantly. The free carboxylate group(s) in the MOFs inspire us to elaborate their metal capturing properties. In different solvents we checked the metal capturing properties of Cu-MOF-2COOH and Ni-MOF-COOH with different metal salts. Surprisingly, both MOFs show better metal capturing properties towards the hard and highly polarizing Fe3+ ion in aqueous medium. Theoretical studies show that the free carboxylate(s) are involved in binding with metals. The post synthetically modified materials (Fe@Cu-MOF-2COOH and Fe@Ni-MOF-COOH) were further checked for their dye adsorption properties and both the doped MOFs show better adsorption properties towards the MB and MO. Furthermore, three kinetic models were employed to understand the reaction mechanism of adsorption and the pseudo second order kinetic model fits the best in both cases. The uncoordinated carboxylate groups in the channels act as post synthetic modification sites for metal capture and the post synthetically modified material thus formed attracts organic dyes following the HSAB concept. The strong interaction existing between the hard Fe3+ ion and hard donors of the dyes is responsible for the enhanced adsorption.

Cobalt Metal-Organic Framework Based on Two Dinuclear Secondary Building Units for Electrocatalytic Oxygen Evolution

The synthesis of a new microporous metal-organic framework (MOF) based on two secondary building units, with dinuclear cobalt centers, has been developed. The employment of a well-defined cobalt cluster results in an unusual topology of the Co₂-MOF, where one of the cobalt centers has three open coordination positions, which has no precedent in MOF materials based on cobalt. Adsorption isotherms have revealed that Co₂-MOF is in the range of best CO₂ adsorbents among the carbon materials, with very high CO₂/CH₄ selectivity. On the other hand, dispersion of Co₂-MOF in an alcoholic solution of Nafion gives rise to a composite (Co₂-MOF@Nafion) with great resistance to hydrolysis in aqueous media and good adherence to graphite electrodes. In fact, it exhibits high electrocatalytic activity and robustness for the oxygen evolution reaction (OER), with a turnover frequency number value superior to those reported for similar electrocatalysts. Overall, this work has provided the basis for the rational design of new cobalt OER catalysts and related materials employing well-defined metal clusters as directing agents of the MOF structure.

Development of Nickel-BTC-MOF-Derived Nanocomposites with rGO Towards Electrocatalytic Oxidation of Methanol and Its Product Analysis

In this study, electrochemical oxidation of methanol to formic acid using the economical and highly active catalytic Nickel Benzene tricarboxylic acid metal organic framework (Ni-BTC-MOF) and reduced graphene oxide (rGO) nanocomposites modified glassy carbon electrode GCE in alkaline media, which was examined via cyclic voltammetry technique. Nickel based MOF and rGO nanocomposites were prepared by solvothermal approach, followed by morphological and structural characterization of prepared samples through X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and energy dispersive X-ray (EDX) analysis. The electrochemical testing of synthesized materials represents the effect of the sequential increase in rGO concentration on electrocatalytic activity. The Ni-BTC/4 wt % rGO composite with a pronounced current density of 200.22 mA/cm2 at 0.69 V versus Hg/HgO electrode at 50 mV/s was found to be a potential candidate for methanol oxidation in Direct Methanol Fuel Cell (DMFC) applications. Product analysis was carried out through Gas Chromatography (GC) and Nuclear Magnetic Resonance (NMR) spectroscopy, which confirmed the formation of formic acid during the oxidation process, with approximately 62% yield.

Convergent and Divergent Paired Electrodeposition of Metal-Organic Framework Thin Films

Employing the environmentally friendly methods for synthesis of the metal-organic frameworks (MOFs) is an urgent need and sustainable development in the synthesis of these compounds is essential. In this way, ignoring the counter electrode reaction is a potentially negative point from green chemistry standpoint which increases some issues like energy consumption and reaction time. We wish to introduce the "paired electrodeposition" (PED) technique as a new method for the simultaneous synthesis and deposition of the MOF thin films (MOFTFs). This protocol implements the uniform pattern of two MOFTF modified substrates by "convergent (CPED: Zn_a/Zn_c-MOFTFs) and divergent (DPED: Cu_a/Zn_c-MOFTFs) paired electrodeposition" via a one-step synthesis. With the rule of thumb, enhanced energy efficiency and atom economy, increasing electrochemical yield, time-saving along with a variety of products are advantages of this technique. Besides, the "Electrode Modification Efficiency" has introduced for the evaluation of functionality and modification efficiency of electrochemical heterogeneous systems, especially MOFTFs. To investigate this concept, we synthesized Zn₃(BTC)₂ and Cu₃(BTC)₂ as MOF models under constant current electrolysis in water and at room temperature. This work can make a breakthrough in the green synthesis of metal-organic frameworks.

A new luminescent anionic metal-organic framework based on heterometallic zinc(II)-barium(II) for selective detection of Fe3+ and Cu2+ ions in aqueous solution

Over the past two decades, the development of novel inorganic-organic hybrid porous crystalline materials or metal-organic frameworks (MOFs) using crystal engineering has provoked significant interest due to their potential applications as functional materials. In this context, luminescent MOFs as fluorescence sensors have recently received significant attention for the sensing of ionic species and small molecules. In this work, a new luminescent heterometallic zinc(II)-barium(II)-based anionic metal-organic framework, namely poly[imidazolium [triaqua(μ₆-benzene-1,3,5-tricarboxylato)bariumtrizinc] tetrahydrate], {(C₃H₄N₂)[BaZn₃(C₉H₃O₆)₃(H₂O)₃]·4H₂O}_n (1), was synthesized under hydrothermal conditions and characterized. Compound 1 presents a three-dimensional framework with an unprecedented (3,5)-connected topology of the point symbol (3.9²).(3³.4².5.9³.10), and exhibits `turn-off' luminescence responses for the Cu²⁺ and Fe³⁺ ions in aqueous solution based on significantly different quenching mechanisms.

Nitrogen-Doped Carbon Nanotube Confined Co-Nx Sites for Selective Hydrogenation of Biomass-Derived Compounds

Biomass is the most abundant renewable resource on earth and developing high-performance nonprecious selective hydrogenation (SH) catalysts will enable the use of biomass to replace rapidly diminishing fossil resources. This work utilizes ZIF-67-derived nitrogen-doped carbon nanotubes to confine Co nanoparticles (NPs) with Co-N_x active sites as a high-performance SH catalyst. The confined Co NPs with Co-N_x exhibit excellent catalytic activity, selectivity, and stability toward a wide range of biomass-derived compounds. Such active sites can selectively hydrogenate aldehyde, ketone, carboxyl, and nitro groups of biomass-derived compounds into value-added fine chemicals with 100% selectivity. The reported approach could be adopted to create other forms of catalytically active sites from other nonprecious metals.

A Novel Two-Dimensional Non-Interpenetrating Coordination Polymer [Ag2.5L(NO3)2.5]∞ with three different coordination modes of AgI (L = diquinoxalino[2,3-a:2′,3′-c]phenazine)

A novel 2-D AgI neutral infinite framework of a large delocalised system diquinoxalino[2,3-a:2′,3′-c]phenazine (L), [Ag2.5L(NO3)2.5]∞ (1), has been synthesised and structurally determined, in which three kinds of different coordination modes are found for the AgI centers.

An Extended Network via Hydrogen Bond Linkage of the Linear Coordination Polymer [Cd(μ-dptz)(NO3)2]∞

The crystal structure of [Cd(μ-dptz)(NO3)2]∞ reveals a neutral one-dimensional coordination polymer exhibiting a two-dimensional architecture through inter-chain hydrogen-bonding.

Synthesis, Structures and Electrochemical Properties of Lithium 1,3,5-Benzenetricarboxylate Complexes

Four lithium coordination polymers, [Li₃(BTC)(H₂O)₆] (1), [Li₃(BTC)(H₂O)₅] (2), [Li₃(BTC)(μ₂-H₂O)] (3), and [Li(H₂BTC)(H₂O)] (4) (H₃BTC = 1,3,5-benzenetricarboxylatic acid), have been synthesized and characterized. All the structures have been determined using single crystal X-ray diffraction studies. Complexes 1 and 2 have two-dimensional (2-D) sheets, whereas complex 3 has three-dimensional (3-D) frameworks and complex 4 has one-dimensional (1-D) tubular chains. The crystal-to-crystal transformation was observed in 1⁻3 upon removal of water molecules, which accompanied the changes in structures and ligand bridging modes. Furthermore, the electrochemical properties of complexes 3 and 4 have been studied to evaluate these compounds as electrode materials in lithium ion batteries with the discharge capacities of 120 and 257 mAhg-1 in the first thirty cycles, respectively.

Fabrication of a magnetic metal–organic framework molecularly imprinted polymer for extraction of anti-malaria agent hydroxychloroquine

A new magnetic metal–organic framework molecularly imprinted polymer was synthesized by the sol–gel method for the determination of hydroxychloroquine sulfate.

Ultrafast Synthesis of Ni-MOF in One Minute by Ball Milling

A mechanical ball milling method for ultrafast synthesis of a nickel-based metal organic framework (Ni-MOF) has been proposed. The Ni-MOF was successfully synthesized in merely one minute without any solvent, additives, or preliminary preparation. The effect of milling time, mechano-frequency, type of assistant liquid, and amount of assistant water were systematically explored. It was found that the product can be obtained even only at a mechano-frequency of 10 Hz within one minute without any external solvent-assist, which indicated that the crystal water present in the nickel precursor was sufficient to promote MOF formation. Increasing the milling time, raising the mechano-frequency, and the addition of assistant solvent could promote the reaction and increase the yield. The method is rapid, highly efficient, eco-friendly, and has great scalability. The product generated within merely one minute even exhibited high capacitance.

Fabrication of Tris(bipyridine)ruthenium(II)-Functionalized Metal-Organic Framework Thin Films by Electrochemically Assisted Self-Assembly Technique for Electrochemiluminescent Immunoassay

A simple strategy for one-step fabrication of tris(bipyridine)ruthenium(II) (Ru(bpy)₃²⁺)-functionalized metal-organic framework (Ru-MOF) thin films using a self-assembly approach assisted by an electrochemical way was introduced. In this protocol, the electrochemically driven cooperative reaction of Ru(bpy)₃²⁺ as an electrochemiluminescent (ECL) probe and a structure-directing agent, trimesic acid (H₃btc) as a ligand, and Zn(NO₃)₂ as the Zn²⁺ source leads to an one-step and simultaneous synthesis and deposition of the MOF onto the electrode surface. Characterization of the Ru-MOF thin films was performed with scanning electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy. Scanning ion conductance microscopy was specially applied in situ to image the topography and thickness of the Ru-MOF thin films. The Ru-MOF thin films as a sensing platform show excellent ECL behavior because of plenty of Ru(bpy)₃²⁺ molecules encapsulated in the frameworks. On the basis of the Ru-MOF modified electrodes, an ultrasensitive label-free ECL immunosensing method for the human heart-type fatty-acid-binding protein has been developed with a wide linear response range (150 fg mL^-1-150 ng mL^-1) and a very low limit of detection (2.6 fg mL^-1). The prepared immunosensor also displayed excellent stability and good specificity in the test of practical samples.

Sponge-Like Water De-/Ad-Sorption versus Solid-State Structural Transformation and Colour-Changing Behavior of an Entangled 3D Composite Supramolecuar Architecture, [Ni₄(dpe)₄(btc)₂(Hbtc)(H₂O)₉]·3H₂O

An entangled composite compound, [Ni₄(dpe)₄(btc)₂(Hbtc)(H₂O)₉]·3H₂O (1), where H₃btc = 1,3,5-benzenetricarboxylic acid and dpe = 1,2-bis(4-pyridyl)ethane, has been synthesized and structurally characterized. Single-crystal structural determination reveals that compound 1 consists of four coordination polymers (CPs), with two two-dimensional (2D) (4,4) layered metal-organic frameworks (MOFs) of [Ni(dpe)(Hbtc)(H₂O)] and [Ni(dpe)(btc)(H₂O)]^- anion, and two one-dimensional (1D) polymeric chains of [Ni(dpe)(btc)(H₂O)₃]^- anion and [Ni(dpe)(H₂O)₄]²⁺ cation, respectively. The three-dimensional (3D) supramolecular architecture of 1 is constructed via the inter-penetration of inter-digited, double-layered, 2D rectangle-grid MOFs by two 1D coordination polymeric chains, and tightly entangled together via the combination of inter-CPs π⁻π stacking and hydrogen bonding interactions. The ad-/de-sorption isotherms of 1 for water displays a hysteresis profile with a maximum adsorption of 17.66 water molecules of per molecule unit at relative P/P₀ < 0.89. The reversible de-/re-hydration processes in 1 monitored by cyclic water de-/ad-sorption TG analysis and PXRD measurements evidence a sponge-like water de-/ad-sorption property associated with a thermal-induced solid-state structural transformation. The magnetic property of 1 suggests that the ferromagnetic coupling might refer to a stronger inter-Ni(II) interaction, which could be along the btc^3- or Hbtc^2- ligands; the antiferromagnetic coupling corresponding to the weaker inter-Ni(II) interactions, which could be the dpe ligands for the 2D framework.

Bioactive nano-metal-organic frameworks as antimicrobials against Gram-positive and Gram-negative bacteria

More effective antibiotics are needed to overcome the problem of multidrug resistance. The antibacterial efficacies of three Zn-based nano metal-organic frameworks (nMOFs) - IRMOF-3, MOF-5, and Zn-BTC - were explored, both alone and as mixtures with ampicillin and kanamycin. When tested against Escherichia coli, Staphylococcus aureus, Staphylococcus lentus, and Listeria monocytogenes, the nMOF/drug mixtures demonstrated synergistic (IRMOF-3/kanamycin) or additive (other nMOF/drug combinations) effects compared with the nMOFs or antibiotics alone. Zn-Based nMOFs can reduce the burden of the new discovery of antimicrobial pharmaceuticals by increasing the potency of existing antibiotics.

Curve-fitting techniques improve the mid-infrared analysis of soil organic carbon: a case study for Brookston clay loam particle-size fractions

Few studies have evaluated structural features of soil organic carbon (SOC) in different soil particle fractions, especially SOC changes induced by tillage, using Fourier transformed mid-infrared (MIR) spectroscopy. To make a contribution in this context, soil samples of a Brookston clay loam (mesic Typic Argiaquoll) with averaged pH and organic matter concentration at 7.28 and 43.9 g kg^-1, respectively, were collected from short-term no-tillage (NT97) and mouldboard plow (CT97) treatments initiated in 1997 and long-term no-tillage (NT83) and mouldboard plow (CT83) treatments initiated in 1983 under a corn-soybean rotation, and were separated into sand, silt, and clay fractions using sonication. Structural features of SOC in these soil fractions were investigated using curve-fitting analysis of mid-infrared (MIR) spectra. Aromatic C content was found to be greater in clay- than in sand-sized fractions, while aliphatic C content was higher in sand- than in silt- and clay-sized particles. With decrease in tillage intensity, the aliphatic C gradually increased in sand- and clay-sized fractions but not in the silt-sized fraction. The aliphatic C content in sand fraction was significantly greater in NT83 than CT83 (P < 0.05). The aromatic C in silt- and clay-sized fractions was greater in NT83 than in both CT soils, whereas aromatic C contents were higher in both CT soils than in NT83 soil. Significantly higher aromatic/aliphatic C ratio in CT83 than NT83 was found in sand-sized fractions, while the opposite trend was found in the silt-sized fraction. These findings were not apparent until the curve-fitting technique was employed, which has the capacity to quantify many overlapped bands in the spectra. This study demonstrates that the curve-fitting of MIR spectra advances the analysis of organic matter in soil samples.

Morphology-dependent electrochemical sensing performance of metal (Ni, Co, Zn)-organic frameworks

To clarify the morphology effect of metal-organic frameworks (MOFs) on their electrochemistry as well as to explore their electrochemical applications, three MOFs with metal centers of nickel, cobalt, and zinc are synthesized. The used organic ligand is only 1,3,5-benzenetricarboxylic acid. Characterizations using Fourier Transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, and electrochemical techniques reveal that these MOFs possess similar bonding properties, crystalline structures and phase purity, but various morphology and electrochemical activities, including their own redox behavior, electrochemical response toward redox probes and analytes in solutions. As a case study of analytes, voltammetry of Ponceau 4R is investigated on three MOFs. Its sensitive and selective monitoring is further achieved on nickel MOFs with a linear range from 0.5 to 150 nM and a detection limit of 80 pM. Therefore, the morphology of MOFs determines electrochemistry of MOFs and their electrochemical sensing applications.

Oriented growth of cross-linked metal-organic framework film on graphene surface for non-enzymatic electrochemical sensor of hydrogen peroxide in disinfectant

High-density and cross-linked copper-based metal-organic framework (Cu-MOF) sheets were successfully prepared via a simple oriented growth method on a carboxylated graphene-modified electrode surface. Hydrogen peroxide (H₂O₂) was selected as a model molecule to examine the performance of the thin film of Cu-MOF/graphene. The proposed sensor showed an extended linear detection range from 2.00 × 10^-7 to 1.85 × 10^-4 mol L^-1 (R = 0.998), a high sensitivity of 0.792 A (mol L^-1)^-1, and a low detection limit of 6.7 × 10^-8 mol L^-1, due to the synergistic catalysis from the porous structure and favorable electron transfer mediating function of the electroactive Cu-MOFs and the high conductive property of the graphene. The reduction peak current of H₂O₂ changed less than 3.7% in the presence of 57-fold high concentrations (2.0 × 10^-4 mol L^-1) of the potential interfering species. The good selectivity of the prepared modified electrode was acquired by the size exclusion (molecular sieving) for H₂O₂ because of the proper pore shape and pore size of Cu-MOFs. The feasibility of the assay was verified by test of H₂O₂ in disinfectant samples. The proposed strategy presents valuable information related to the construction of non-enzymatic electrochemical sensors.