Bimetallic Co/Zn zeolitic imidazolate framework ZIF-67 supported Cu nanoparticles: An excellent catalyst for reduction of synthetic dyes and nitroarenes

Magnetic CoFe hydrotalcite composite Co metal-organic framework material efficiently activating peroxymonosulfate to degrade sulfamethoxazole: Oxygen vacancy-mediated radical and non-radical pathways

Herein, a novel rich oxygen vacancy (Ov) cobalt-iron hydrotalcite composite cobalt metal-organic framework material (ZIF-67/CoFe-LDH) was prepared by simple urea water and heat reduction approach and utilized for the peroxymonosulfate (PMS) system to remove sulfamethoxazole (SMX). 95 ± 1.32 % SMX (20 mg/L) was able to degraded in 20 min with TOC removal of 53 ± 1.56 % in ZIF-67/CoFe-LDH/PMS system. The system maintained a fantastic catalytic capability with wide pH range (3-9) and common interfering substances (Cl-, NO3-, CO32-, PO42- and humic acid (HA)), and the degradation efficiency could even remain 80.2 ± 1.48 % at the fifth cycle. Meanwhile, the applicability and feasibility of the catalysts for practical water treatment was verified by the degradation effects of SMX in different water environments and several other typical pollutants. Co and Fe bimetallic active centers synergistically activate PMS, and density functional theory (DFT) predicted adsorption energy about Ov in ZIF-67/CoFe-LDH for PMS was 1.335 eV, and OO bond length of PMS was stretched to 1.826 Å. As a result, PMS was more easily activated and broken, which accelerated the singlet oxygen (1O2), sulfate radical (SO4•-), high-valent metals and other reactive oxygen species (ROS). Radical and non-radical jointly degrading the pollutants improved the catalytic effect. Finally, SMX degradation intermediates were analyzed to explain the degradation pathway and their biotoxicity was also evaluated. This paper provides a new research perspective of oxygen vacancy activating PMS to degrade pollutants.

A MOF-Templated Double-Shelled Co3O4/NiCo2O4 Nanocomposite for Electrochemical Detection of Alfuzosin

We developed a novel electrochemical sensor for the detection of alfuzosin (AFZ), a drug used to treat benign prostatic hyperplasia, using a double-shelled Co3O4/NiCo2O4 nanocomposite-modified electrode. The nanocomposites were synthesized using a template-assisted approach, with zeolitic imidazole framework-67 (ZIF-67) as the sacrificial template, involving the formation of uniform ZIF-67/Ni-Co layered double hydroxide (LDH) hollow structures followed by calcination to achieve the final nanocomposite. The nanocomposite was characterized by various techniques and showed high porosity, large surface area, and good conductivity. The nanocomposite-modified electrode exhibited excellent electrocatalytic activity towards AFZ oxidation, with a wide linear range of 5-180 µM and a low limit of detection of 1.37 µM. The sensor also demonstrated good repeatability, reproducibility, and stability selectivity in the presence of common interfering substances. The sensor was successfully applied to determine the AFZ in pharmaceutical tablets and human serum samples, with satisfactory recoveries. Our results suggest that the double-shelled Co3O4/NiCo2O4 nanocomposite is a promising material for the fabrication of electrochemical sensors for AFZ detection.

Third-Order Nonlinear Optical Modulation Behavior of Photoresponsive Bimetallic MOFs

Bimetallic metal-organic frameworks (MOFs) capable of sensing external stimuli will provide more possibilities for further regulating third-order nonlinear optical (NLO) properties. In this work, we synthesized bimetallic MOFs (ZnCu-MOF and ZnCd-MOF) through central metal exchange using a photoresponsive Zn-MOF as a precursor. Compared with Zn-MOF, both ZnCu-MOF and ZnCd-MOF exhibit significantly enhanced third-order NLO absorption properties. This is mainly attributed to the introduction of metal ions with different electron configurations that can adjust the bandgap of MOFs and enhance electron delocalization, thus promoting electron transfer. Interestingly, the bimetallic MOFs show a transition from reverse saturation absorption (RSA) to saturation absorption (SA) after exposure to ultraviolet irradiation, as they retain the properties of directional photogenerated electron transfer. Photoresponsive bimetallic MOFs not only have the effect of bimetallic modulation of electronic structures but also have the characteristics of photoinduced electron transfer, exhibiting diversified optical properties. These findings provide a novel method for the development of multifunctional NLO materials.

Novel magnetic bimetallic AuCu catalyst for reduction of nitroarenes and degradation of organic dyes

Herein, core-shell magnetic nanoparticles are modified with imidazolium-tagged phosphine and propylene glycol moieties and used for the stabilization of bimetallic AuCu nanoparticles. The structure and morphology of the prepared material are identified with SEM, TEM, XRD, XPS, atomic absorption spectroscopy, Fourier translation infrared spectroscopy, and a vibrating sample magnetometer. This hydrophilic magnetic bimetallic catalyst is applied in the reduction of toxic nitroarenes and reductive degradation of hazardous organic dyes such as methyl orange (MO), methyl red (MR), and rhodamine B (RhB), as well as in the degradation of tetracycline (TC). This magnetic AuCu catalyst indicated superior activity in all three mentioned reactions in comparison with its single metal Au and Cu analogs. This catalyst is recycled for 17 consecutive runs in the reduction of 4-nitrophenol to 4-aminophenol without a significant decrease in catalytic activity and recycled catalyst is characterized.

ZIF-8-derived Zn, N-codoped porous carbon as a high-performance piezocatalyst for organic pollutant degradation and hydrogen production

The development of highly efficient piezocatalysts has attracted widespread attention for energy conversion and pollution abatement. This paper reports for the first time exceptional piezocatalytic properties of a Zn- and N-codoped porous carbon piezocatalyst (Zn-N_x-C) derived from the zeolitic imidazolium framework-8 (ZIF-8) for both hydrogen production and degradation of organic dyes. The Zn-N_x-C catalyst has a high specific surface area of 810.6 m²/g and retains the dodecahedron structure of ZIF-8. Under ultrasonic vibration, the hydrogen production rate of Zn-N_x-C has achieved 6.29 mmol/g/h, surpassing most recently reported piezocatalysts. Additionally, the Zn-N_x-C catalyst demonstrates a 94% degradation efficiency for organic rhodamine B (RhB) dye during 180 min of ultrasonic vibration. This work sheds new light on the potential of ZIF-based materials in the field of piezocatalysis and provides a promising avenue for future developments in the area.

Bismuth-Rich Co/Ni Bimetallic Metal-Organic Frameworks as Photocatalysts toward Efficient Removal of Organic Contaminants under Environmental Conditions

Active photocatalysts with an efficiency of 99% were prepared for the degradation of the industrial dye, methylene blue (MB), under visible light irradiation. These photocatalysts comprised Co/Ni-metal-organic frameworks (MOFs), to which bismuth oxyiodide (BiOI) was added as a filler to prepare Co/Ni-MOF@BiOI composites. The composites exhibited remarkable photocatalytic degradation of MB in aqueous solutions. The effects of various parameters, including the pH, reaction time, catalyst dose, and MB concentration, on the photocatalytic activity of the prepared catalysts were also evaluated. We believe that these composites are promising photocatalysts for the removal of MB from aqueous solutions under visible light.

Multifunctional ZnO:Gd@ZIF-8 hybrid nanocomposites with tunable luminescent-magnetic performance for potential bioapplication

Novel multifunctional ZnO:Gd@ZIF-8 hybrid inorganic-organic nanocomposites with tunable luminescent-magnetic performance were successfully fabricated using wet chemistry synthesis routes. Physico-chemical characterization including crystal structure, phase compositions, morphology, surface properties, as well as photoluminescent and magnetic characteristics was performed using powder X-ray diffraction (XRD), FT-IR analysis, transmission and scanning electron microscopies (TEM/SEM), N₂ adsorption/desorption, SQUID magnetometer, and photoluminescence spectroscopy. The biological studies of obtained materials, such as cytotoxicity profile and in vitro MRI imaging also investigated for potential use as contrast agents. Results showed that the doping with Gd³⁺ in a broad concentration range and the presence of ZIF-8 layer on ZnO affect the physico-chemical properties of the obtained composites. The obtained porous ZnO:Gd@ZIF-8 composites were highly crystalline with a large surface area. The XRD study indicated the formation of hexagonal wurtzite structure for ZnO and ZnO:Gd³⁺ (1-5 at.%). Luminescent studies showed, that ZnO is an ideal matrix for the incorporation of Gd³⁺ ions in a broad concentration range with efficient green luminescence. The PL intensity reached the maximum up to 5 at.% of Gd³⁺. The zeta potential values indicated the good stability of obtained nanoparticles. Proposed new materials with paramagnetic behavior and outstanding MR imaging capability could be used as potential contrast agents for magnetic resonance imaging.

Nickel foam supported porous copper oxide catalysts with noble metal-like activity for aqueous phase reactions

Contiguous metal foams offer a multitude of advantages over conventional powders as supports for nanostructured heterogeneous catalysts; most critically a preformed 3-D porous framework ensuring full directional coverage of supported catalyst, and intrinsic ease of handling and recyclability. Nonetheless, metal foams remain comparatively underused in thermal catalysis compared to more conventional supports such as amorphous carbon, metal oxides, zeolites and more recently MOFs. Herein, we demonstrate a facile preparation of highly-reactive, robust, and easy to handle Ni foam-supported Cu-based metal catalysts. The highly sustainable synthesis requires no specialized equipment, no surfactants or additive redox reagents, uses water as solvent, and CuCl2(H2O)2 as precursor. The resulting material seeds as well-separated micro-crystalline Cu2(OH)3Cl evenly covering the Ni foam. Calcination above 400 °C transforms the Cu2(OH)3Cl to highly porous CuO. All materials display promising activity towards the reduction of 4-nitrophenol and methyl orange. Notably, our leading CuO-based material displays 4-nitrophenol reduction activity comparable with very reactive precious-metal based systems. Recyclability studies highlight the intrinsic ease of handling for the Ni foam support, and our results point to a very robust, highly recyclable catalyst system.

Mechanistic insight into the removal of aqueous Cd using an immobilized ZIF-8 and microflora cooperative composite

Biotechnology and metal-organic-frameworks (MOFs) materials have been investigated intensively for the removal of heavy metal from wastewater. However, the cooperative effect of bacteria and MOFs on heavy metal adsorption was less reported. Considering this, this study has screened out microflora with cadmium (Cd) adsorption ability. Furthermore, it was combined with zeolitic imidazolate framework-8 (ZIF-8) to form a ZIF-8 and microflora complex (ZMC). Moreover, ZMC was further immobilized to improve its Cd adsorption effect and reusability. Results revealed that the immobilized ZMC exhibited 99.91% and 78.83% Cd adsorption rate for 20 mg L^-1 and 300 mg L^-1 Cd, respectively. Meanwhile, the immobilized ZMC maintained a relatively stable adsorption effect under varied external pH. The reaction mechanism was summarized as covalent binding accompanied with a small amount of electrostatic attraction. Microflora could enhance the surface electronegativity of ZIF-8. ZIF-8 could strengthen the response of antioxidant activity of microflora and augmented the affinity of microflora secretions for Cd. This proposed method may provide a new insight for the removal of heavy metal contaminants in water.

Designing bimetallic zeolitic imidazolate frameworks (ZIFs) for aqueous catalysis: Co/Zn-ZIF-8 as a cyclic-durable catalyst for hydrogen peroxide oxidative decomposition of organic dyes in water

ZIF-8 is well known hybrid material that is self-assembled from inorganic and organic moieties. It has several potential applications due to its unique structure. One of these potential applications is in advanced oxidation processes (AOP) via a heterogeneous catalysis system. The use of modified ZIF-8/H2O2 for the destruction of the azo dye methyl orange (MO) is presented in this work to explore its efficacy. This work presents the bimetallic Co/Zn-ZIF-8 as an efficient catalyst to promote H2O2 oxidation of the MO dye. Co/Zn-ZIF-8 was synthesized through a hydrothermal process, and the pristine structure was confirmed using XRD, FTIR, and XPS. The Co/Zn-ZIF-8/H2O2 system successfully decolorized MO at the selected pH 6.5. It was found that more than 90% of MO (10 ppm) was degraded within only about 50 minutes. Proposed radical and redox mechanisms are presented for H2O2 decomposition where the redox mechanism is suggested to predominate via a Co(ii)/Co(iii) redox consecutive cyclic process.

Ultrafine and well-dispersed Pd-Ni bimetallic catalyst stabilized by dendrimer-grafted magnetic graphene oxide for selective reduction of toxic nitroarenes under mild conditions

A facile and efficient strategy is introduced for growing a dendrimer structure on the surface of magnetic graphene oxide by using thiol-ene click reaction. The as-synthesized dendrimer-grafted magnetic graphene oxide was used as a suitable support for bimetallic Pd-Ni nanoparticles. The prepared nanocomposite was utilized for the reduction of toxic nitroarenes to aminoarenes by using sodium borohydride in aqueous medium at room temperature. Various nitroarenes with functional groups like nitrile, halogen, carbonyl, hydroxyl, acid, and heterocycles were converted to their corresponding anilines with good to excellent yields. The enhanced performance of the catalyst could be attributed to the synergistic effect between Ni and Pd which causes the reaction to proceed more efficiently. Moreover, the catalyst could be readily isolated from the reaction mixture by utilizing an external magnet and reused till 5th cycles with marginal loss of activity.

Tuning the electronic property of Pd nanoparticles by encapsulation within ZIF-67 shells towards enhanced performance in 1,3-butadiene hydrogenation

The low olefin selectivity of Pd-based catalysts is a long-term challenge for the selective hydrogenation of 1,3-butadiene.

Synergistic Catalysis of the Synthesis of Ammonia with Co-Based Catalysts and Plasma: From Nanoparticles to a Single Atom

In this study, a series of Co nanoparticles (NPs) with different sizes and Co single-atom catalysts (SACs) with different cobalt-nitrogen coordination numbers (Co-N2, Co-N3, and Co-N4) were synthesized and applied to the synthesis of ammonia catalyzed by plasma at low temperatures and atmospheric pressures. Under the same reaction conditions, the yield of nitrogen obtained from the reduction to ammonia over a series of Co NP catalysts varies with the Co particle size. The smaller the size of the Co NPs, the greater the number of exposed active centers, and the catalytic activity is higher. Among the Co SACs, the best catalyst was Co-N2 with two coordinated nitrogen atoms, and the ammonia yield was 181 mg·h-1·gcat-1. The experimental and theoretical calculations were consistent in that a low Co-N coordination number was beneficial to the adsorption and dissociation of N2, thereby enhancing the reduction activity of N2 and promoting the increase of ammonia production.

Insight into the Morphology-Dependent Catalytic Performance of CuO/CeO2 Produced by Tannic Acid for Efficient Hydrogenation of 4-Nitrophenol

The construction of a heterogeneous nanocatalyst with outstanding catalytic performance via an environmentally benign and cost-effective synthetic category has long been one of the challenges in nanotechnology. Herein, we synthesized highly efficient and low-cost mesoporous morphology-dependent CuO/CeO₂ -Rods and CuO/CeO₂ -Cubes catalysts by employing a green and multifunctional polyphenolic compound (tannic acid) as the stabilizer and chelating agent for 4-nitrophenol (4-NP) reduction reaction. The CuO/CeO₂ -Rods exhibited excellent performance, of which the activity was 3.2 times higher than that of CuO/CeO₂ -Cubes. This can be connected with the higher density of oxygen vacancy on CeO₂ -Rods (110) than CeO₂ -Cubes (100), the oxygen vacancy favors anchoring CuO species on the CeO₂ support, which promotes the strong interaction between finely dispersed CuO and CeO₂ -Rods at the interfacial positions and facilitates the electron transfer from BH₄ ^- to 4-NP. The synergistic catalytic mechanism illustrated that 4-NP molecules preferentially adsorbed on the CeO₂ , while H₂ from BH₄ ^- dissociated over CuO to form highly active H* species, contributing to achieving efficient hydrogenation of 4-NP. This study is expected to shed light on designing and synthesizing cost-effective and high-performance nanocatalysts through a greener synthetic method for the areas of catalysis, nanomaterial science and engineering, and chemical synthesis.

Synergistic adsorption and photocatalytic degradation of persist synthetic dyes by capsule-like porphyrin-based MOFs

The synergistic effects involving surface adsorption and photocatalytic degradation commonly play significant roles in the removal of persistent synthetic organics from wastewater in the case of porous semiconductors. Inspired by the visible-light harvesting advantages of porphyrin-based MOFs, a capsule-like bimetallic porphyrin-based MOF (PCN-222(Ni/Hf)) has been successfully constructed through a facile hydrothermal method. In which, the Hf (IV) ions were exactly bonded to the carboxyl groups substituted on the porphyrin rings, meanwhile the Ni (II) ions were finely bonded to the -N inside the porphyrin rings. The adsorption/photocatalytic performances were assessed by using four persistent dyes including rhodamine B (RhB), basic violet 14 (BV14), crystal violet, and acid black 210 (AB210) as the target substances, and enhanced total removal efficiency was obtained by the bimetallic PCN-222(Ni/Hf) in comparison with that of single PCN-222(Hf). The electrochemical analyses and the sacrificial agent capture experiments were carried out to elucidate the photocatalytic mechanism, and the adsorption/photocatalytic stability of PCN-222(Ni/Hf) is also investigated. The work has broadened the applications of porphyrin-based MOFs in the removal of organics by combining their excellent surface adsorption capacity and photocatalytic activities.

Smart hydrogel-microsphere embedded silver nanoparticle catalyst with high activity and selectivity for the reduction of 4-nitrophenol and azo dyes

A simple method is reported for the preparation of silver nanoparticle (AgNP) embedded pH-responsive hydrogel microparticle catalyst via Michael addition gelation and in-situ silver nitrate (AgNO₃) reduction. The AgNP-hydrogel microsphere exhibited an efficient reduction of pollutants like 4-Nitrophenol (4-NP) and Congo red (CR) under acidic medium with turn over frequency (TOF) of ~170 h^-1 and ~124 h^-1 respectively. Interestingly, the activity of the catalysts was turned-OFF under a basic medium (≥ pH 12) due to the deswelling pH-responsive matrix surrounding the AgNPs. On the contrary, turning-OFF the hydrogenation of a cationic pollutant like methylene blue (MB) using high pH (≥ 12) was not possible, due to ionic interaction of MB molecules with the negatively charged catalyst at this pH. This feature was used to demonstrate selective hydrogenation of only MB from a mixture of 4-NP and MB. Finally, five recycling steps confirmed the reusability and practical application potential of the catalyst.