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We have selected a semi-rigid hexacarboxylic acid ligand H6L enriched with oxygen-active sites with Cd2+ salt, successfully synthesising a 3-D anionic material MOF-1 ([(CH3)2NH2]2[Cd2L]·3DMA·2H2O, H6L = 5,5',5"-(benzene-1,3,5-triyltris(oxy))triisophthalic acid). The structure of this carboxylic acid ligand is triangular in shape, which contributes to the formation of the 3-D framework structure, and its semi-rigidity facilitates entry of dye molecules by slightly adjusting the pore size. The larger pore size of MOF-1 is 1.45 nm x 0.86 nm. The oxygen spacer groups are uniformly distributed throughout the framework, promoting the adsorption of MOF-1 for dyes. Based on these factors, there is a significant advantage in that the anionic material MOF-1 containing [(CH3)2NH2]+ selectively adsorbs cationic organic dyes from aqueous contaminants for recycling. It was discovered that the adsorption process' equilibrium and kinetics followed the Langmuir isothermal model and pseudo-secondary kinetics, respectively. And we measured the adsorption rate of MOF-1' on MB+ to be 1.77 x 10-3 g mg-1 min-1. Its relatively high capacity is ca. 1220 mg g-1. After five cycles of adsorption and desorption, the dye adsorption performance was reduced to ca. 80% and the framework stability remained well. [ABSTRACT FROM AUTHOR]

The problems of easy oil contamination, easy oxidation, and low dye removal ability of 2D MXene hinder its practical application in high-efficiency oil/water separation and dye removal. In this study, Ti3C2Tx was first modified using NH3·H2O to obtain intercalated Ti3C2Tx (TN), and then, N-[3-(trimethoxysilyl) propyl] ethylenediamine (AEAPTMS) was used to conduct the surface aminated-modification of TN to achieve functional Ti3C2Tx (TN–AEAPTMS), which was then loaded onto polyurethane (PU) sponge to get TN–AEAPTMS@PU sponge. The low oil adhesion and super hydrophilicity/underwater super oleophobicity of TN–AEAPTMS@PU sponge enable excellent separation performance for oil/water mixtures of different densities. After being soaked in water for 45 days, TN–AEAPTMS can still maintain its original accordion-like morphology and hold good oil/water separation performance, overcoming the performance degradation caused by easy oxidation of Ti3C2Tx under water. More importantly, TN–AEAPTMS@MCE, which is acquired through vacuum suction filtration with TN–AEAPTMS loaded onto mixed cellulose ester microporous membrane, can remove various anionic and cationic organic dyes with high flux and removal rate, innovatively overcoming the poor adsorption performance of Ti3C2Tx for anionic dyes. Therefore, the TN–AEAPTMS composite exhibits excellent potential for practical applications in oil/water separation and dye removal. [ABSTRACT FROM AUTHOR]

Hydrothermal synthesis was used to create four different POM-based compounds, namely {[Co(Hptpm)2(β-Mo8O26)0.5(ξ-Mo8O26)0.5]}·H2O (1), [Co(Hptpm)2(δ-Mo8O26)]·H2O (2), [Co(Hptpm)2(β-Mo8O26)] (3) and [Zn(Hptpm)2(β-Mo8O26)] (4) (ptpm = 4-[3-(3-pyridine-2-yl-[1,2,4]triazol-4-yl)-propyl]- morpholine). 1-4 containing different octamolybdate isomers were characterized. Compounds 1-4 showed good electrochemical performance and can be utilized as bifunctional sensors for NO2 -, H2O2, Cr(VI) and Fe(III). Taking compound 1 as an example, the detection limits are 0.081 μM for NO2 -, 0.072 μM for H2O2, 0.054 μM for Cr(VI) and 0.063 μM for Fe(III), respectively. Compounds 1-4 have good capacitance. Moreover, compounds 1-4 also show good adsorption properties for organic cationic dyes. The cationic dyes include methylene blue (MB), crystal violet (CV) and neutral red (NR). In addition, 1-4 have excellent characteristics that can reduce Cr(VI) to Cr(III) by photocatalytic technology. Within 30 min, the reduction rates were 95.85% for 1, 93.99% for 2, 90.29% for 3 and 88.18% for 4. [ABSTRACT FROM AUTHOR]

Environmental problems can potentially be solved by covalent organic frameworks (COFs) that contain predesigned porous architectures. Herein, we developed an amorphous tetrazine–triazine-functionalized covalent organic framework (TzTPT-COF) by performing one-pot polycondensations of 2,4,6-tris-(4-formylphenoxy)-1,3,5-triazine (TPT-CHO) and s-tetrazine-diamine (Tz). The TzTPT-COF possesses ordered-disordered accessible nano-channels with an experimental pore width of 8.5 nm and simulated pore width of 6.4 nm. We detail the characterization of two-dimensional TzTPT-COF with readily accessible 8.5 nm-sized pores, which was subsequently employed as a porous adsorbent for the static and dynamic adsorption of small dye molecules, especially methylene blue from dye-adulterated water. Additionally, the COF quickly attained up to 99% of its maximum adsorption capacity within 15 min. The thermal stability of the COF was maintained, with the onset of gradual weight loss observed at 280 °C. Furthermore, the COF exhibited no crystallinity and possesses a mesoporous structure. The experimental findings and in silico simulation revealed that to create COF-based adsorbents with effective dye adsorption capabilities, it is necessary to concurrently consider the inherent pore size of the COF material as well as the size of the organic dye molecules. The TzTPT-COF has a great deal of potential as an adsorbent material for eliminating cationic dyes and other organic pollutants from wastewater due to the high adsorption efficiencies, ultrafast kinetics, and outstanding reusability. Hence, the present findings suggest that COFs can also be proven to be highly versatile porous materials for various environmental remediation applications. [ABSTRACT FROM AUTHOR]

In this work, two defective zirconium-based metal–organic frameworks (Zr-MOFs), MOF-808-OH and MOF-808-NH2, were synthesized by partially replacing the 1,3,5-benzenetricarboxylate building block with 5-hydroxyisophthalate and 5-aminoisophthalate, respectively. The structural features of the defective materials were analyzed by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), nitrogen physisorption at 77 K, and thermogravimetric analysis (TGA). Importantly, the number of defect sites determined via proton nuclear magnetic resonance (1H-NMR) analysis of the digested materials was approximately 7 mol% for MOF-808-OH and 3 mol% for MOF-808-NH2. The presence of the defect sites increased the number of acidic centers on Zr-clusters originating from missing-linker nodes which accounted for a remarkable adsorption capacity towards various anionic organic dyes and chromium (VI) species. Compared to standard MOF-808, the defect-engineered ones showed significant increments by 30–60% in trapping capacity for anionic contaminants including sunset yellow, quinoline yellow, methyl orange, and potassium dichromate, while they exhibited modest improvements by 5–15% in the removal of cationic dyes, namely malachite green and methylene blue. [ABSTRACT FROM AUTHOR]

One-pot co-precipitation of target molecules e.g. organic dyes and the synthesis of a crystal containing microporous–mesoporous regimes of zeolitic imidazolate frameworks-8 (ZIF-8) are reported. The synthesis method can be used for cationic (rhodamine B (RhB), methylene blue (MB)), and anionic (methyl blue (MeB)) dyes. The crystal growth of the ZIF-8 crystals takes place via an intermediate phase of zinc hydroxyl nitrate (Zn5(OH)8(NO3)2) nanosheets that enabled the adsorption of the target molecules i.e., RhB, MB, and MeB into their layers. The dye molecules play a role during crystal formation. The successful encapsulation of the dye molecules was proved via diffuse reflectance spectroscopy (DRS) and electrochemical measurements e.g., cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The materials were investigated for carbon dioxide (CO2) adsorption and adenosine triphosphate (ATP) biosensing. ZIF-8, RhB@ZIF-8, MB@ZIF-8, and MeB@ZIF-8 offered CO2 adsorption capacities of 0.80, 0.84, 0.85, and 0.53 mmol g−1, respectively. The encapsulated cationic molecules improved the adsorption performance compared to anionic molecules inside the crystal. The materials were also tested as a fluorescent probe for ATP biosensing. The simple synthesis procedure offered new materials with tunable surface properties and the potential for multi-functional applications. [ABSTRACT FROM AUTHOR]

A multifunctional anionic Zn-MOF, formulated as {[NH2(CH3)2][Zn7(μ3-OH)3(L)6(H2O)]·24H2O·6DMA}n (1) (where H2L = 6-methoxy-2,2′-sulfone-4,4′-dicarboxylic acid and DMA = dimethylacetamide) has been solvothermally synthesized, which is based on rare heptanuclear [Zn7(μ3-OH)3(COO)12] clusters possessing large 3D intersecting channels. Through a cation-exchange process, 1 can selectively adsorb cationic organic dyes, and the adsorption capacities for methylene blue (MB), rhodamine B (RhB) and crystal violet (CV) are 219.9, 114.6 and 197.6 mg g−1, respectively. Moreover, the obtained RhB@1 composite features dual-emissive characteristics and can serve as a dual-channel sensor for selective sensing of traces of NF antibiotics (NFT and NFZ), with detection limits of 0.89 μM and 0.95 μM, respectively. The mechanism study shows that the quenching process is mainly ascribed to the synthetic effect of IFE and FRET. [ABSTRACT FROM AUTHOR]

Multinuclear cluster-based metal–organic frameworks (MOFs) have shown excellent activity in toxic chemical removal from wastewater due to their high porosity, functionality and water stability. In this regard, a highly porous, water-stable Fe-MOF was fabricated and the efficiency of its acyl amide-functionalized pores for organic dye removal was investigated. Different anionic and cationic dyes including methyl orange (MO), methyl red (MR), congo red (CR), rose-bengal B (Ros B), rhodamine B (Rhod B) and methylene blue (MB) were applied to determine the Fe-MOF efficiency. The presence of acyl amide improves the host-guest interaction of the framework towards anionic dyes, specifically MO with an adsorption capacity of 232.5 mg g−1. Interestingly, the Fe-MOF shows one of the fastest adsorptions of MO with a kinetic constant of 0.013 g mg−1 min−1 which is faster than those of some of the well-known MOFs such as UiO-66, MOF-235, MIL-53, MIL-101, UiO-66-NO2 and ZIF-67. The adsorption mechanism, uptake kinetics and selectivity of the framework for different dyes were also studied. Overall, water stable Fe-MOF with a high permanent porosity as well as rational decoration of pores with specific functions, improved the size and charge selective dye removal by the preferred H-bonding and π–π interactions. [ABSTRACT FROM AUTHOR]

This work discusses the synthesis of fluorescent undoped and boron-doped carbon nanodots (BDCNDs) by a simple hydrothermal approach using Tribulus terrestris as the carbon precursor and boric acid as the boron source. The morphology of BDCNDs was analyzed by HRTEM, which confirmed the spherical-shape and its size was found to be 3.6 nm. The XRD results reveal the amorphous nature and Raman spectroscopy was used to investigate the graphitic structure of BDCNDs. The obtained BDCNDs were exposed to blue fluorescence with a quantum yield (QY) of 19.2%. The synthesized green nano catalysts (BDCNDs) were used to reduce organic dyes, with NaBH4 and the findings showed that they had a high catalytic activity against two cationic dyes (Congo red (CR) and Eosin Yellow (EY)), and two anionic dyes (Malachite Green (MG) and Methylene Blue (MB)). The Langmuir--Hinshelwood mechanism was used to assess the catalytic effect of BDCNDs on dyes. Further, we designed an anti-counterfeiting system for up-gradation of the security level by the stencil printing method. The fluorescent security label known as ''confidential info'' was encoded on a quick response (QR) system and a mobile is used to read the decoded information under 365 nm UV light irradiation. [ABSTRACT FROM AUTHOR]

Anionic metal–organic frameworks (MOFs) are beginning to have a great impact in the field of absorption and separation of ionic organic molecules due to the enhanced electrostatic interactions between their anionic frameworks and counter-ionic guests. Herein, the rational design and synthesis of two mesoporous anionic MOFs, [Zn3(ITTC)3](Me2 NH2)3·3DMF·H2O (1) and [Cd2(ITTC)3](Me2NH2)5·2DMF (2), where H3ITTC = 4,4′,4′′-(1H-imidazole-2,4,5-triyl) tribenzoic acid, is reported. Structural analysis revealed that both materials are anionic MOFs with a 2-fold interpenetrating three dimensional (3D) framework. The cross sectional area of the open one-dimensional rectangular channels is 31.7 Å × 15.6 Å for 1, of which the architecture is indicative of an unprecedented (3,3,4,5)-connection topology. For 2, the diameter of the open one-dimensional regular hexagonal channel is about 34.1 Å, decorated with uncoordinated carboxyl O atoms, and the framework exhibits a (3,4)-connected fcu network. Due to their anionic frameworks and bulky pore window sizes, both MOFs can be employed for absorbing and separating the cationic organic dye methylene blue (MB). The results reveal that both MOFs have better dye adsorption selectivity for MB, than for MO and SDI, because of charge and size-matching effects, enabling them to be potential candidates for use in environmental cleaning. By comparison, 2 presents superior selectivity and adsorptivity for cationic MB which depends on the presence of a basic functionalized pore surface. [ABSTRACT FROM AUTHOR]

Net-stacked hierarchical CdOHF architectures were controllably synthesized via a simple hydrothermal method. The SEM and TEM results show that the hierarchical CdOHF structure is made up of many CdOHF nanobelts. Different pH values and reaction times make the CdOHF feature adjustable structural variations with 1D nanobelts, nanobelt-woven 2D nets and net-stacked 3D hierarchical structures. With a first-order reaction rate constant that was 5 times higher than those of other CdOHF morphologies, the obtained net-stacked hierarchical CdOHF architectures exhibited high efficiency and selectivity for degrading the cationic dye malachite green (MG) under visible light irradiation, for example, the decolorization rate for MG (40 mg L−1) solution reached approximately 100% within 30 min. Moreover, the hierarchical CdOHF also displayed good photochemical stability for the degradation of MG after five recycles. The improved photocatalytic efficiency of the 3D net-stacked hierarchical CdOHF is ascribed to the synergistic effects of the porous hierarchical architectures, narrower band gap energy and large BET surface areas. This work provides a simple and feasible strategy for controllable synthesis of 3D hierarchical micro/nanomaterials with high performance, and such inexpensive high-performance hierarchical CdOHF architectures can find potential applications for the degradation of organic dyes. [ABSTRACT FROM AUTHOR]

Herein, two Ni(II)-based one-dimensional (1D) coordination polymers (CPs), namely, [Ni(Hpdc)(H2O)(μ-H2O)]n (CP-1) and [Ni(pyc)2(H2O)]n (CP-2), where H3pdc = 3,5-pyrazoledicarboxylic acid and Hpyc = pyrazine-2-carboxylic acid, were successfully synthesized under solvothermal reaction conditions. Both the polymers were thoroughly characterized through single-crystal X-ray diffraction, UV-visible, FTIR and TGA techniques. Variable-temperature magnetic-susceptibility data indicated the presence of antiferromagnetic (AF) interactions in both the CPs. The crystal structures showed hexa-coordinated environments around the Ni(II) ions. The 2,2,4C1 and 2C1 topologies of the resulting 4-c net and 2-c net uninodals were acquired for CP-1 and CP-2, respectively. The CPs were then exploited for their adsorption properties towards organic pollutants such as organic dyes. Both the CPs were demonstrated to have the structural features necessary to adsorb the cationic dyes from waste water. The CPs adsorbed the cationic dyes (MB and Rh-B) even in the presence of an anionic dye, giving rise to the separation of the two types of dyes. Moreover, with evidence from the kinetics of the reaction, it could be concluded that both CPs bestowed the reaction with pseudo-second-order kinetics. The plausible mechanism associated with the adsorption of cationic dyes was also elaborated, which suggested that mainly electrostatic, H-bonding and π–π interactions were responsible for the adsorption process. Thus, the design and characterization of polymer-based adsorbents for the treatment of wastewater has potential as an emerging field and deserves to be addressed in future endeavours. [ABSTRACT FROM AUTHOR]