Chemisorption of hydrogen sulfide over copper-based metal–organic frameworks: methanol and UV-assisted regeneration

Carbon Nanosheet Preparation By Low-Temperature Two-Step Carbonization: A Study of Their Properties and Mechanism of Adsorption of Oxidized H2S

Straw, as a kind of biomass waste, has the advantages of low cost and abundant storage, which makes it a promising renewable resource. Using rice straw as a carbon source, carbon nanosheets were prepared by a two-step carbonization method combining low-temperature pyrolysis and low-temperature hydrothermal, and they were used as H2S removal agents. The results showed that during the two-step carbonization process, the adsorption performance of carbon nanosheets for H2S showed a tendency of enhancing and then weakening with the increase of pyrolysis temperature in the first step, and the sulfur capacity could reach 3.1 mg/g at the maximum of the pyrolysis temperature of 200 °C, which was superior to or close to that of the modified or activated carbon. The XPS, EPR, and CO2-TPD tests showed that the surface of carbon nanosheets was alkaline, containing a large number of hydroxyl groups and the presence of phenoxy persistent free radicals or semiquinone persistent free radicals. It was analyzed that the direct or indirect oxidation of H2S by the persistent radicals under an alkaline environment could convert the -2-valent sulfur into -1-, 0- and +6-valent sulfur to realize the adsorption and removal of H2S. This work, while offering the possibility of utilizing carbon nanosheets made from straw as a material for H2S adsorption and removal, also expands the application of straw waste in exhaust gas treatment.

Defective copper-based metal-organic frameworks for the efficient extraction of organosulfur compounds from garlic-processing wastewater

Organosulfur compounds (OSCs) in garlic-processing wastewater are decomposed and generated to toxic and harmful substances with unpleasant odors under anaerobic conditions. Herein, were report the successful development of novel copper-based metal organic framework (Cu-MOF) adsorbents with high adsorption capacities for OSCs in aqueous media. Defect-rich Cu-MOF-X samples, with particle sizes between 360 and 750 nm, synthesized hydrothermal in the presence of acetic acid (where X denotes the molar ratio of acetic acid relative to the pentadentate MOF linker H4PPYD). OSC adsorption experiments using allicin, ajoene and 2-ethenyl-4H-1,3-dithiine (2-VDT) showed that Cu-MOF-200 delivered fast adsorption kinetics and high OSC adsorption capacities (149.02-171.33 mg g-1) owing to the pore accessibility and range of adsorption sites in the MOF. FT-IR, Raman, and XPS analyses, together with density functional theory (DFT) calculations, verified the strong yet reversible adsorption of OSCs in Cu-MOF-200. Results guide the development of improved adsorbents for OSC capture from garlic-processing wastewater.

Adsorptive removal of heavy metals from wastewater using Cobalt-diphenylamine (Co-DPA) complex

Heavy metals like Cadmium, Lead, and Chromium are the pollutants emitted into the environment through industrial development. In this work, a new diphenylamine coordinated cobalt complex (Co-DPA) has been synthesized and tested for its efficiency in removing heavy metals from wastewater, and its adsorption capacity was investigated. The effectiveness of heavy metals removal by Co-DPA was evaluated by adjusting the adsorption parameters, such as adsorbent dose, pH, initial metals concentration, and adsorption period. Heavy metal concentrations in real sample were 0.267, 0.075, and 0.125 mg/L for Cd2+, Pb2+, and Cr3+ before using as-synthesized Co-DPA to treat wastewater. After being treated with synthesized Co-DPA the concentration of heavy metals was reduced to 0.0129, 0.00028, 0.00054 mg/L for Cd2+, Pb2+, and Cr3+, respectively, in 80 min. The removal efficiency was 95.6%, 99.5%, and 99.5% for the respective metals. The adsorption process fitted satisfactorily with Freundlich isotherm with R2(0.999, 0.997, 0.995) for Cd2+, Pb2+, and Cr3+, respectively. The kinetic data obeyed the pseudo-second order for Cd2+ and Cr2+ and the pseudo-first order for Pb2+. Based on the results obtained within the framework of this study, it is concluded that the as-synthesized Co-DPA is a good adsorbent to eliminate heavy metal ions like Cd2+, Pb2+, and Cr3+from wastewater solution. In general, Co-DPA is a promising new material for the removal of heavy metal ions from water.

Pd@HKUST-1@Cu(II)/CMC composite bead as an efficient synergistic bimetallic catalyst for Sonogashira cross-coupling reactions

We fabricated an efficient Pd@HKUST-1@Cu(II)/CMC composite bead catalyst through an innovative strategy based on the unique properties of metal-organic frameworks (MOFs) and carboxymethylcellulose (CMC). In this strategy, HKUST-1 MOFs were grown in-situ on the surface of micrometer-sized Cu-based CMC beads (Cu(II)/CMC), then Pd(II) ions were incorporated into the pores of the MOF and further be partially reduced to Pd(0) NPs, which is an active species for oxidative addition with aryl halides in Sonogashira reactions. The micron-sized Cu(II)/CMC beads were formed through inter/intramolecularly crosslinking facilitated by Cu(II) ions, which was achieved by the metathesis of Cu(II) with numerous carboxylic groups of CMC. Such Cu(II)/CMC bead offers many Cu(II) ions as interaction sites for in-situ nucleation and growth of HKUST-1 MOFs. The architecture and composition of the prepared Pd@HKUST-1@Cu(II)/CMC composite were fully verified by various techniques such as FTIR, XRD, TGA, BET, XPS, SEM, TEM, EDX, and elemental mapping analysis. This novel composite bead was applied as an efficient and reusable heterogeneous Pd/Cu bimetallic catalyst for Sonogashira reactions, decarbonylative Sonogashira reaction, and Sonogashira cyclization tandem reactions. The catalyst is readily isolated by simple filtration, and can be reused for five consecutive runs with retaining its activity and structural integrity.

β-Ketoallylic methylsulfones synthesis via inert C(sp3)-H bond activation by magnetic Ag-Cu MOF

Herein, the one-pot tandem synthesis of β-ketoallylic methylsulfones has been achieved from readily available dimethyl sulfoxide and acetophenones as coupling partners in one step. In this procedure, dimethyl sulfoxide serves as a triple role including solvent, dual synthon and as an oxidant agent. The use of magnetic Ag-Cu MOF as a bimetallic catalyst is the key to the progress of the reaction due to its accessible active sites. It provides facile access to various β-ketoallylic methylsulfone derivatives from direct C(sp3)-H bond activation and functionalization of aromatic methyl ketones especially acetophenones with electron-rich and electron-poor groups. Moreover, the present work offers a synthetically powerful strategy to form products in good to excellent yields (74-96%) with the atom, step, and pot economics. It has also delivered a new chromane-4-one derivative from 2-hydroxy acetophenone with intramolecular Michael-addition of related β-ketoallyl methylsulfone product. In the final step, the electronic properties of some products have been predicted with the theoretical studies.

Construction of Well-Defined Two-Dimensional Architectures of Trimetallic Metal-Organic Frameworks for High-Performance Symmetric Supercapacitors

The high surface-to-volume ratio and extraordinarily large-surface area of two-dimensional (2D) metal-organic framework (MOF) architectures have drawn particular interest for use in supercapacitors. To achieve an excellent electrode material for supercapacitors, well-defined 2D nanostructures of novel trimetallic MOFs were developed for supercapacitor applications. Multivariate MOFs (terephthalate and trimesate MOF) with distinctive nanobrick and nanoplate-like structures were successfully synthesized using a straightforward one-step reflux condensation method by combining Ni, Co, and Zn metal species in equimolar ratios with two different ligands. Furthermore, the effects of the tricarboxylic and dicarboxylic ligands on cyclic voltammetry, charge-discharge cycling, and electrochemical impedance spectroscopy were studied. The derived terephthalate and trimesate MOFs are supported with stainless-steel mesh and provide a suitable electrolyte environment for rapid faradaic reactions with an elevated specific capacity, excellent rate capability, and exceptional cycling stability. It shows a specific capacitance of 582.8 F g-1, a good energy density of 40.47 W h kg-1, and a power density of 687.5 W kg-1 at 5 mA cm-2 with an excellent cyclic stability of 92.44% for 3000 charge-discharge cycles. A symmetric BDC-MOF//BDC-MOF supercapacitor device shows a specific capacitance of 95.22 F g-1 with low capacitance decay, high energy, and power densities which is used for electronic applications. These brand-new trimetallic MOFs display outstanding electrochemical performance and provide a novel strategy for systematically developing high-efficiency energy storage systems.

Anchoring Cu-N active sites on functionalized polyacrylonitrile fibers for highly selective H2S/CO2 separation

As an essential part of clean energy, natural gas is often mixed with varying degrees of H₂S and CO₂, which poses a serious environmental hazard and reduces the fuel's calorific value. However, technology for selective H₂S removal from CO₂-containing gas streams is still not fully established. Herein, we synthesized functional polyacrylonitrile fibers with Cu-N coordination structure (PANF_EDA-Cu) by an amination-ligand reaction. The results showed that PANF_EDA-Cu exhibited a remarkable adsorption capacity (143 mg/g) for H₂S at ambient temperature, even in the presence of water vapor, and showed a good separation of H₂S/CO₂. X-ray absorption spectroscopy results confirmed the Cu-N active sites in as-prepared PANF_EDA-Cu and the formed S-Cu-N coordination structures after H₂S adsorption. The active Cu-N sites on the fiber surface and the strong interaction between highly reactive Cu atoms and S are the main reasons for the selective removal of H₂S. Additionally, a possible mechanism for the selective adsorption/removal of H₂S is proposed based on experimental and characterization results. This work will pave the way for the design of highly efficient and low-cost materials for gas separation.

Ternary metal oxide nanocomposite for room temperature H2S and SO2 gas removal in wet conditions

A ternary Mn–Zn–Fe oxide nanocomposite was fabricated by a one-step coprecipitation method for the remotion of H₂S and SO₂ gases at room temperature. The nanocomposite has ZnO, MnO₂, and ferrites with a surface area of 21.03 m² g⁻¹. The adsorbent was effective in mineralizing acidic sulfurous gases better in wet conditions. The material exhibited a maximum H₂S and SO₂ removal capacity of 1.31 and 0.49 mmol g⁻¹, respectively, in the optimized experimental conditions. The spectroscopic analyses confirmed the formation of sulfide, sulfur, and sulfite as the mineralized products of H₂S. Additionally, the nanocomposite could convert SO₂ to sulfate as the sole oxidation by-product. The oxidation of these toxic gases was driven by the dissolution and dissociation of gas molecules in surface adsorbed water, followed by the redox behaviour of transition metal ions in the presence of molecular oxygen and water. Thus, the study presented a potential nanocomposite adsorbent for deep desulfurization applications.

Probing the origin and stability of bivalency in copper based porous coordination network and its application for H2S gas capture

A bivalent Cu(I,II) metal–organic framework (MOF) based on the 4,4′,4″-s-Triazine-2,4,6-triyl-tribenzoate linker was synthesized via a solvothermal method. The MOF possessed 43.8% of the Cu sites as Cu⁺ with a surface area of 1257 m² g⁻¹. The detailed spectroscopic analysis confirmed dimethylformamide (DMF) solvent as the reductant responsible for Cu⁺ sites in the synthesized MOF. The Cu⁺ sites were easily accessible and prone to oxidation in hot water or acidic gas environment. The MOF showed water-induced structural change, which could be partially recovered after soaking in DMF solvent. The synthesized MOF showed a high hydrogen sulfide (H₂S) uptake capacity of 4.3 mmol g^–1 at 298 K and an extremely low H₂S pressure of 0.0005 bar. The adsorption capacity was the highest among Cu-based MOFs with PCN-6-M being regenerable, which made it useful for deep desulfurization applications. The adsorbed H₂S was mineralized to sulfide, sulfur, and sulfates, mediated by the Cu⁺/Cu²⁺ redox cycle in the presence of adsorbed water and molecular oxygen. Thus, the study confirmed that DMF as a reductant is responsible for the origin of bivalency in PCN-6-M and possibly in other Cu-based MOFs reported in the literature. Also, the developed MOF could be a potential candidate for flue gas desulfurization and gas purification applications.

Single-Step Synthesized Functionalized Copper Carboxylate Framework Meshes as Hierarchical Catalysts for Enhanced Reduction of Nitrogen-Containing Phenolic Contaminants

Nitrogen-containing phenolic contaminants (NCPCs) represent typical pollutants of industrial wastewaters. As catalytic reduction of NCPCs is a useful technique and Cu is an efficient metal catalyst, Cu-carboxylate frameworks (CuCF) are favorable materials. However, they are in powder form, making them difficult to use; thus, in this study, CuCF was grown on macroscale supports. Herein, we present a facile approach to develop such a CuCF composite by directly using a Cu mesh to grow CuCF on the mesh through a single-step electrochemical synthesis method, forming CuCF mesh (CFM). CFM could be further modified to afford CuCF mesh with amines (NH2) (CFNM), and CuCF mesh with carboxylates (COOH) (CFCM). These CuCF meshes are compared to investigate how their physical and chemical characteristics influenced their catalytic behaviors for reduction/hydrogenation of NPCPs, including nitrophenols (NPs) and dyes. Their nanostructures and surface properties influence their behaviors in catalytic reactions. In particular, CFCM appears to be the most efficient mesh for catalyzing 4-NP, with a much higher rate constant. CFCM also shows a significantly lower Ea (28.1 kJ/mol). CFCM is employed for many consecutive cycles, as well as convenient filtration-type 4-NP reduction. These CuCF meshes can also be employed for decolorization of methylene blue and methyl orange dyes via catalytic hydrogenation.

Role of Bimetallic Solutions in the Growth and Functionality of Cu-BTC Metal-Organic Framework

Bimetallic solutions play a vital role in the growth and functionality of copper trimesate (Cu-BTC) metal–organic frameworks (MOFs). The effect of Ag⁺, Ca²⁺, Mn²⁺, Co²⁺, and Zn²⁺ on the growth of Cu-BTC was studied by fabricating M-Cu-BTC MOFs at room temperature using bimetallic M-Cu solutions. While Ag⁺ in the MOF had a rod-like morphology and surface properties, divalent cations deteriorated it. Moreover, unconventional Cu⁺ presence in the MOF formed a new building unit, which was confirmed in all the MOFs. Apart from Ag and Mn, no other MOF showed any presence of secondary cations in the structure. While Ag-Cu-BTC showed an improved H₂S uptake capacity, other M-Cu-BTC MOFs had superior organic pollutant adsorption behavior. Thus, we have demonstrated that the physicochemical properties of Cu-BTC could be modified by growing it in bimetallic solutions.

Metal-organic framework-derived NaMxOy adsorbents for low-temperature SO2 removal

This work reported the fabrication of NaM_xO_y-type adsorbents from air calcination of (Na, M)-trimesate metal-organic frameworks. NaMn_xO_y (NMO) crystallized as disc-shaped microsheets, whereas NaCo_xO_y (NCO) crystallized as smooth microsheets with surface deposition of polyhedral nanoparticles. The oxides have a surface area of 1.90-2.56 m² g^-1. The synthesized adsorbents were studied for low-temperature SO₂ removal in breakthrough studies. The maximum adsorption capacity of 46.8 mg g^-1 was recorded for NMO at 70 °C. The adsorption capacity increased with the increasing temperature due to the chemisorptive nature of the adsorption process. The capacity increased with the increasing bed loading and decreasing flow rate due to the improved SO₂ retention time. The elemental mapping confirmed the uniform distribution of sulfur species over the oxide surface. X-ray diffraction showed the absence of metal sulfate nanoparticles in the SO₂-exposed samples. The X-ray photoelectron analysis confirmed the formation of surface sulfate and bisulfate. The formation of oxidized sulfur species was mediated by hydroxyl groups over NMO and lattice oxygen over NCO. Thus, the work demonstrated here is the first such report on the use of NaM_xO_y-type materials for SO₂ mineralization.

Application of hybrid MOF composite in extraction of f-block elements: Experimental and computational investigation

An attempt was made to understand the sorption behaviour of UO₂²⁺, Th⁴⁺ and Eu³⁺ on novel hybrid metal-organic framework composites, FeBDC@CoBDC. The XRD pattern revealed the composite nature of the hybrid MOF materials, while FTIR and Raman spectroscopic analyses evidenced the presence of different functional moieties. The thermal stability of the hybrid MOF composites was investigated through thermogravimetric analysis. The sorption predominantly followed Langmuir isotherm with sorption capacity of 189 mg g^-1, 224 mg g^-1 and 205 mg g^-1 for UO₂²⁺, Th⁴⁺ and Eu³⁺ respectively. The sorption proceeded through chemisorption following pseudo 2^nd order rate kinetics. The processes were found to be thermodynamically favourable and endothermic in nature. However, they were entropically driven. Multiple contacts of complexing agents were necessary for quantitative elution of f-elements from loaded MOF. The MOF showed moderate stability towards radiation exposure. DFT calculation was used for the optimization of structures, estimation of bond length and estimation of binding energy. In hybrid MOF composites, the Fe atom was having six coordination with 4 O atoms of BDC moieties and 2 O atoms of -OH groups. The O atoms of BDC and -OH groups were coordinated to Eu, Th and U atoms during their sorption.

One-Pot Synthesis of Porous Crystal Structured Nanosponge-Like Pristine Copper Metal-Organic Framework for Hybrid Supercapacitor Application

Hybrid supercapacitors are promising energy storage devices where high-power delivery is needed in continuous supply (like e-vehicles, cranes, industrialized machines, etc.). Metal-Organic Frameworks (MOFs) are the leading porous materials, and...

From MOF-199 Microrods to CuO Nanoparticles for Room-Temperature Desulfurization: Regeneration and Repurposing Spent Adsorbents as Sustainable Approaches

MOF-199 is one of the well-studied metal-organic frameworks (MOFs) for the capture of small gas molecules. In this study, we have investigated the thermal transformation of MOF-199 microrods to CuO nanoparticles by various microscopic and spectroscopic techniques. The growth of oxide was initiated by the formation of ∼2.5 nm particles at 200 °C, which ended up as CuO nanoparticles of ∼100-250 nm size at 550 °C. An intermediate presence of Cu2O along with CuO was recorded at 280 °C. The MOF and calcined products were tested for the room-temperature desulfurization process. MOF-199 showed the maximum adsorption capacity for H2S gas (77.1 mg g-1) among all adsorbents studied. Also, MOF-199 showed a better regeneration efficiency than the derived oxide. For a sustainable process, the exhausted adsorbents were used for the photocatalytic degradation of methylene blue. The exhausted materials showed better degradation efficiencies than the fresh materials. This study reports new sustainable approaches for MOF-199 application in air and water decontamination.

A novel one-step synthesis of Ce/Mn/Fe mixed metal oxide nanocomposites for oxidative removal of hydrogen sulfide at room temperature

In this study, CeO₂/Fe₂O₃, CeO₂/Mn₂O₃, and CeO₂/Mn₂O₃/Fe₂O₃ nanocomposites were synthesized by the calcination of molten salt solutions. The microscopic images confirmed polyhedral nanocrystals of 10–20 nm size, clustered to form nanospheres. The elemental mapping confirmed the uniform distribution of transition metal oxides in the CeO₂ matrix. The X-ray diffraction analysis confirmed the phase purity of metal oxides in nanocomposites. The surface area of nanocomposites was in the range of 16–21 m² g⁻¹. X-ray photoelectron spectroscopy confirmed 25–28% of Ce³⁺ ions in the CeO₂ of nanocomposites. These nanocomposites were tested for the removal of hydrogen sulfide gas at room temperature. The maximum adsorption capacity of 28.3 mg g⁻¹ was recorded for CeO₂/Mn₂O₃/Fe₂O₃ with 500 ppm of H₂S gas and 0.2 L min⁻¹ of flow rate. The adsorption mechanism probed by X-ray photoelectron spectroscopy showed the presence of sulfate as the only species formed from the oxidation of H₂S, which was further confirmed by ion chromatography. Thus, the study reports room-temperature oxidation of H₂S over mixed metal composites, which were synthesized by a novel one-step approach.

In this study, CeO₂/Fe₂O₃, CeO₂/Mn₂O₃, and CeO₂/Mn₂O₃/Fe₂O₃ nanocomposites were synthesized by the calcination of molten salt solutions.

Metal organic framework derived NaCoxOy for room temperature hydrogen sulfide removal

Novel NaCoxOy adsorbents were fabricated by air calcination of (Na,Co)-organic frameworks at 700 °C. The NaCoxOy crystallized as hexagonal microsheets of 100-200 nm thickness with the presence of some polyhedral nanocrystals. The surface area was in the range of 1.15-1.90 m2 g-1. X-ray photoelectron spectroscopy (XPS) analysis confirmed Co2+ and Co3+ sites in MOFs, which were preserved in NaCoxOy. The synthesized adsorbents were studied for room-temperature H2S removal in both dry and moist conditions. NaCoxOy adsorbents were found ~ 80 times better than the MOF precursors. The maximum adsorption capacity of 168.2 mg g-1 was recorded for a 500 ppm H2S concentration flowing at a rate of 0.1 L min-1. The adsorption capacity decreased in the moist condition due to the competitive nature of water molecules for the H2S-binding sites. The PXRD analysis predicted Co3S4, CoSO4, Co3O4, and Co(OH)2 in the H2S-exposed sample. The XPS analysis confirmed the formation of sulfide, sulfur, and sulfate as the products of H2S oxidation at room temperature. The work reported here is the first study on the use of NaCoxOy type materials for H2S remediation.

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.

Bimetallic Ag–Cu-trimesate metal–organic framework for hydrogen sulfide removal

Bimetallic Ag-Cu-trimesate metal-organic framework was fabricated for H2S mineralization. The MOF was partially regenerated using H2O2 solution for five cycles.