One-pot synthesis of enhanced fluorescent copper nanoclusters encapsulated in metal–organic frameworks

The encapsulation of Cu nanoclusters (Cu NCs) in metal–organic frameworks (MOFs) would improve the properties of Cu NCs. So far, these composites were reported by a two-step synthesis process. In this work, a facile one-pot synthesis of hybridization of glutathione (GSH) protected Cu NCs (Cu NCs@GSH) and MOF-5 (Cu NCs@GSH/MOFs) composites was reported for the first time. The results of UV-vis, TEM, XPS and SEM proved Cu NCs@GSH were distributed homogeneously over the entire MOF structure. The fluorescence intensity of Cu NCs encapsulated in MOF-5 was enhanced about 35-fold owing to the confining scaffold of the MOF and the stability was extended from 3 days to 3 months. Cu NCs@GSH/MOFs composites exhibited strong orange fluorescence and the emissions could change between blue, orange and red as they were partially reversible in different pH environments. This one-pot synthetic strategy could be extended for the encapsulation of fluorescent Ag NCs in MOFs as well. As-prepared Cu NCs@GSH/MOF-5 composites had high stability, and were easily recycled by centrifugation in aqueous solution, therefore, it would be utilized to develop a reusable sensor for detection of metal ions in the future.

The encapsulation of Cu nanoclusters (Cu NCs) in metal–organic frameworks (MOFs) would improve the properties of Cu NCs.     

Synthesis of heterometallic metal–organic frameworks and their performance as electrocatalyst for CO2 reduction

Herein we report the solventless synthesis and doping of the benchmark HKUST-1(Cu) as a facile route to afford heterometallic metal–organic frameworks (MOFs) having proficient behavior as electrocatalytic materials in the reduction of carbon dioxide. Zn(ii), Ru(iii) and Pd(ii) were selected as doping metals (M_D) with the aim of partially replacing the Cu(ii) atoms of the pristine structure to afford HKUST-1(Cu,M_D) type materials. Apart from the high yield and good crystallinity of the obtained materials, the extremely high reagent concentration that the reaction conditions imply makes it feasible to control dopant loading in all cases. Prepared samples were processed as electrodes and assembled in a continuous flow filter-press electrochemical cell. Faraday efficiency to methanol and ethanol at Ru(iii)-based electrodes resulted in activity as high as 47.2%, although the activity of the material decayed with time. The interplay of the dopant metal and copper(ii), and the long-term performance are also discussed.

The solventless synthesis of heterometallic metal–organic frameworks and their proficient behavior as electrocatalysts in the CO₂ reduction to alcohols is presented.     

Strongly visible light-absorbing metal–organic frameworks functionalized by cyclometalated ruthenium(ii) complexes

Four different ruthenium(ii) complexes were incorporated into the metal–organic framework (MOF) UiO-67 using three different synthetic strategies: premade linker synthesis, postsynthetic functionalization, and postsynthetic linker exchange. One of these complexes was of the type (N–N)₃Ru²⁺, and three of the complexes were of the type (N–N)₂(N–C)Ru⁺, where N–N is a bipyridine-type ligand and N–C is a cyclometalated phenylpyridine-type ligand. The resulting materials were characterized by PXRD, SC-XRD (the postsynthetic functionalization MOFs), N₂ sorption, TGA-DSC, SEM, EDS, and UV-Vis spectroscopy, and were digested in base for subsequent ¹H NMR analysis. The absorption profiles of the MOFs that were functionalized with cyclometalated Ru(ii) complexes extend significantly further into the visible region of the spectrum compared to the absorption profiles of the MOFs that were functionalized with the non-cyclometalated reference, (N–N)₃Ru²⁺.

The metal–organic framework (MOF) UiO-67 was functionalized by incorporating different cyclometalated ruthenium(ii) complexes using three different methods: premade linker synthesis, postsynthetic functionalization, and postsynthetic linker exchange.     

Metal–organic frameworks incorporating azobenzene-based ligands as a heterogeneous Lewis-acid catalyst for cyanosilylation of imines

In this work, two novel metal–organic frameworks (MOFs) were synthesized by the reaction of azobenzene-based ligands and Zn(NO₃)₂/CdCO₃ under solvothermal conditions with the formula of {[Zn₂(abtc)(azpy)(H₂O)₂]·4H₂O}_n (1) and {[Cd(abtc)_0.5(azpy)_0.5(H₂O)]·3H₂O}_n (2) (H₄abtc = 3,3′,5,5′-azobenzene tetracarboxylic acid, azpy = 4,4′-azobipyridine). According to the single-crystal X-ray diffraction (SC-XRD) analysis, complexes 1 and 2 possessed quite similar structures except for the coordination modes of the central metal nodes attributed to the difference between the cationic radius of Zn(ii) and Cd(ii). The Zn(ii) cations in 1 adopted a distorted seesaw coordination geometry and the coordination between Zn(ii) and organic linkers gave two-dimensional (2D) coordination networks, while the Cd(ii) cations in 2 could also bind with the carboxylate groups from neighboring coordination networks to form a three-dimensional (3D) coordination framework. Furthermore, complexes 1 and 2 showed high catalytic activity as heterogeneous Lewis-acid catalysts towards the cyanosilylation of imines with satisfactory reusability under mild conditions and the similar catalytic performance of 1 and 2 could be attributed to the similarity in their structures. A prudent mechanism has been proposed as well to elucidate the role of complexes 1 and 2 in the catalytic process.

Two novel MOFs were synthesized by the reaction of azobenzene-based ligands with Zn(NO₃)₂/CdCO₃ and could both function as heterogeneous Lewis-acid catalysts towards cyanosilylation of imines.     

Zinc(ii) and cadmium(ii) amorphous metal–organic frameworks (aMOFs): study of activation process and high-pressure adsorption of greenhouse gases

Two novel amorphous metal–organic frameworks (aMOFs) with chemical composition {[Zn₂(MTA)]·4H₂O·3DMF}_n (UPJS-13) and {[Cd₂(MTA)]·5H₂O·4DMF}_n (UPJS-14) built from Zn(ii) and Cd(ii) ions and extended tetrahedral tetraazo-tetracarboxylic acid (H₄MTA) as a linker were prepared and characterised. Nitrogen adsorption measurements were performed on as-synthesized (AS), ethanol exchanged (EX) and freeze-dried (FD) materials at different activation temperatures of 60, 80, 100, 120, 150 and 200 °C to obtain the best textural properties. The largest surface areas of 830 m² g⁻¹ for UPJS-13 (FD) and 1057 m² g⁻¹ for UPJS-14 (FD) were calculated from the nitrogen adsorption isotherms for freeze-dried materials activated at mild activation temperature (80 °C). Subsequently, the prepared compounds were tested as adsorbents of greenhouse gases, carbon dioxide and methane, measured at high pressures. The maximal adsorption capacities were 30.01 wt% CO₂ and 4.84 wt% CH₄ for UPJS-13 (FD) and 24.56 wt% CO₂ and 6.38 wt% CH₄ for UPJS-14 (FD) at 20 bar and 30 °C.

Two novel amorphous metal–organic frameworks UPJS-13 and UPJS-14, constructed of Zn(ii)/Cd(ii) ions and extended tetrahedral linker were prepared, characterised and applied as adsorbents for carbon dioxide and methane.     

Temperature tuned syntheses of two new d10-based Cd(ii) cluster metal–organic frameworks: luminescence sensing and photocatalytic properties

The solvothermal reactions of 5,5′-(1,4-phenylenebis(methyleneoxy))diisophthalic acid (H₄L) and the N-donor ancillary ligand 3,3′,5,5′-tetramethyl-4,4′-bipyrazole (bpz) with cadmium(ii) salts at two different reaction temperatures yielded two new metal–organic frameworks (MOFs), viz., [Cd(H₂L)(bpz)]_n (1) and [Cd₂(H₄L)(L)(bpz)₂]_n (2), which have been characterized by FTIR and single crystal X-ray diffraction. The single crystal X-ray diffraction studies revealed that 1 displays a 3-periodic network with monometallic SBU, while 2 exhibits a 3-periodic network with a 2-fold interpenetration feature. The effects of variation in reaction temperature on the architecture of MOFs 1 and 2 have been discussed. The luminescence investigation indicates that both 1 and 2 displayed good turn-off luminescence sensing against nitroaromatic compounds (NACs), especially m-nitrophenol (MNP), via a decrease in their luminescence intensities with a K_sv value of 6.43 × 10³ for 1 and 2.03 × 10⁴ for 2 and LOD values of 1.09 and 0.81 ppm for 1 and 2, respectively. The plausible mechanism for the decline in luminescence intensity of the MOFs with NACs has been addressed using theoretical calculations. The photocatalytic properties for both the MOFs demonstrated that they display efficient photocatalytic performances to degrade methyl violet (MV) under UV irradiation. The plausible mechanism through which these MOFs exhibited photocatalytic properties has been suggested using band gap calculations.

Two new d¹⁰-based Cd(ii) MOFs were synthesized and their photoluminescence sensing to selectively detect m-nitrophenol (MNP) and ability to decompose the organic dye methyl violet (MV) were explored.     

Graphene inclusion controlling conductivity and gas sorption of metal–organic framework

A general approach to prepare composite films of metal–organic frameworks and graphene has been developed. Films of copper(ii)-based HKUST-1 and HKUST-1/graphene composites were grown solvothermally on glassy carbon electrodes. The films were chemically tethered to the substrate by diazonium electrografting resulting in a large electrode coverage and good stability in solution for electrochemical studies. HKUST-1 has poor electrical conductivity, but we demonstrate that the addition of graphene to HKUST-1 partially restores the electrochemical activity of the electrodes. The enhanced activity, however, does not result in copper(ii) to copper(i) reduction in HKUST-1 at negative potentials. The materials were characterised in-depth: microscopy and grazing incidence X-ray diffraction demonstrate uniform films of crystalline HKUST-1, and Raman spectroscopy reveals that graphene is homogeneously distributed in the films. Gas sorption studies show that both HKUST-1 and HKUST-1/graphene have a large CO₂/N₂ selectivity, but the composite has a lower surface area and CO₂ adsorption capacity in comparison with HKUST-1, while CO₂ binds stronger to the composite at low pressures. Electron paramagnetic resonance spectroscopy reveals that both monomeric and dimeric copper units are present in the materials, and that the two materials behave differently upon hydration, i.e. HKUST-1/graphene reacts slower by interaction with water. The changed gas/vapour sorption properties and the improved electrochemical activity are two independent consequences of combining graphene with HKUST-1.

Changed electrochemical activity and CO₂/H₂O adsorption by graphene inclusion in Cu₃(1,3,5-benzenetricarboxylate)₂ and covalent tethering to glassy carbon electrodes.     

Amino group dependent sensing properties of metal–organic frameworks: selective turn-on fluorescence detection of lysine and arginine

Recently, metal–organic frameworks (MOFs) have been extensively investigated as fluorescence chemsensors due to their tunable porosity, framework structure and photoluminescence properties. In this paper, a well-known Zr(iv)-based MOF, UiO-66-NH₂ was demonstrated to have capability for detection of l-lysine (Lys) and l-arginine (Arg) selectively from common essential amino acids in aqueous media via a fluorescence turn-on mechanism. Further investigation reveals its high sensitivity and strong anti-interference properties. Moreover, the possible mechanism for sensing Lys and Arg was explored by FT-IR and ¹H-NMR, and the results indicate that the enhancement of the fluorescence could be ascribed to the adsorption of Lys/Arg and the hydrogen bonding interactions between Lys/Arg and the amino group of UiO-66-NH₂. The difference of the sensing capacity and sensitivity between UiO-66 and UiO-66-NH₂ revealed that the amino group plays an essential role in the sensing performance. This work presents a unique example of the functional group dependent sensing properties of MOFs.

The amino group of UiO-66-NH₂ was demonstrated to play an important role in selective fluorescence turn-on sensing of lysine and arginine.     

Ligand functionalization of defect-engineered Ni-MOF-74

Incorporating functionality into the framework of metal–organic frameworks (MOFs) has attracted substantial interest because the physical and chemical properties of MOFs can be tuned by functionalizing pores. The ligand functionalization of MOF-74 is challenging because of its pristine organic ligand and framework structure. Herein, we report a series of ligand-functionalized Ni-MOF-74 derivatives synthesized by defect engineering using a mixed-ligand approach. Defect generation and ligand functionalization of Ni-MOF-74 were simultaneously achieved by incorporation of fragmented organic ligands such as 5-formylsalicylic acid, 3-hydroxysalicylic acid, 2-hydroxynicotinic acid and 5-hydroxy-1H-benzimidazole-4-carboxylic acid. The resulting defect-engineered Ni-MOF-74 derivatives maintained relatively good crystallinity up to fragment incorporation levels of ∼20% and exhibited modified permanent porosity and CO₂ adsorption properties depending on the functional groups and defect concentrations in the framework.

Ni-MOF-74 incorporated with functionalized ligand fragments exhibits modified porosity and CO₂ adsorption depending on the amount of fragment and the type, position, and size of the functional groups.     

Cyclometalation of lanthanum(iii) based MOF for catalytic hydrogenation of carbon dioxide to formate

The hydrogenation of carbon dioxide (CO₂) to formic acid is of great importance due to its useful properties in the chemical industry. In this work, we have prepared a novel metal–organic framework (MOF), JMS-1, using bipyridyl dicarboxylate linkers, with molecular formula [La₂(bpdc)₃(DMF)₃]_n. Network analysis of JMS-1 revealed a new 7-connected topology (zaz). The MOF backbone of the activated phase (JMS-1a) was functionalized by cyclometalation using [RuCl₂(p-cymene)]₂ to produce Ru(ii)@JMS-1a. Both JMS-1a and Ru(ii)@JMS-1a were able to convert CO₂ in the presence of hydrogen to formate. Ru(ii)@JMS-1a displayed outstanding conversion evidenced by a yield of 98% of formate under optimized conditions of total pressure 50 bar (CO₂/H₂ = 1 : 4, temperature 110 °C, time 24 h, 5 mmol KOH, 8 mL ethanol). This work is significant in providing new strategies of incorporating active catalytic centres in MOFs for efficient and selective conversion of CO₂ to formate.

A novel metal–organic framework JMS-1 with rare topology zaz shows catalytic activity towards conversion of carbon dioxide to formate.     

Modelling drug adsorption in metal–organic frameworks: the role of solvent

Solvent plays a key role in biological functions, catalysis, and drug delivery. Metal–organic frameworks (MOFs) due to their tunable functionalities, porosities and surface areas have been recently used as drug delivery vehicles. To investigate the effect of solvent on drug adsorption in MOFs, we have performed integrated computational and experimental studies in selected biocompatible MOFs, specifically, UiO-AZB, HKUST-1 (or CuBTC) and NH₂-MIL-53(Al). The adsorption of three drugs, namely, 5-fluorouracil (5-FU), ibuprofen (IBU), and hydroxyurea (HU) were performed in the presence and absence of the ethanol. Our computational predictions, at 1 atmospheric pressure, showed a reasonable agreement with experimental studies performed in the presence of ethanol. We find that in the presence of ethanol the drug molecules were adsorbed at the interface of solvent and MOFs. Moreover, the computationally calculated adsorption isotherms suggested that the drug adsorption was driven by electrostatic interactions at lower pressures (<10⁻⁴ Pa). Our computational predictions in the absence of ethanol were higher compared to those in the presence of ethanol. The MOF–adsorbate interaction (U_HA) energy decreased with decrease in the size of a drug molecule in all three MOFs at all simulated pressures. At high pressure the interaction energy increases with increase in the MOFs pore size as the number of molecules adsorbed increases. Thus, our research shows the important role played by solvent in drug adsorption and suggests that it is critical to consider solvent while performing computational studies.

Solvent plays a key role in drug loading in metal–organic frameworks.     

Cd(ii) removal by Fe(ii) surface chemically modified layered double hydroxide–graphene oxide: performance and mechanism

Cd(ii) adsorption onto Fe(ii) modified Layered double hydroxide–graphene oxide (LDH–GO@Fe(ii)) was investigated using batch experiments. With the modification of Fe(ii), LDH–GO maintained its structure, while Fe(ii) species formed non-crystalline iron oxide clusters on the surface of the LDH/GO. A kinetics study indicated that adsorption obeyed a pseudo-second-order rate law. The equilibrium data were fitted well with the Langmuir isotherm model. The maximum adsorption capacity of LDH–GO@Fe(ii)₁₀ was 28.98 mg g⁻¹, higher those that of pure LDH–GO and LDH–GO@Fe(ii)₅₀. The increased sorption capacities could be explained by the increased specific surface area. Modification with Fe(ii) would lead to the generation of amorphous Fe oxides and Fe could occupy the binding sites for Cd(ii), thus excess Fe in the structure will restrain the adsorption of Cd(ii). The XRD and XPS patterns revealed the formation of Cd(OH)₂ after adsorption. Batch experiments indicated that precipitation and surface complexation were the main pathways for Cd(ii) removal.

Fe(ii)-decorated LDH–GO composites had a high capacity for Cd(ii) removal. The mechanisms were controlled by surface-induced precipitation and complex formation.     

Palladium supported on mixed-metal–organic framework (Co–Mn-MOF-74) for efficient catalytic oxidation of CO

Successful monometallic and bimetallic metal–organic frameworks with different Co/Mn ratios have been synthesized under solvothermal conditions. The as-synthesized MOFs followed by deposition of Pd nanoparticles with 0.5 to 7 wt%. The XRD, BET, SEM, TEM, EDAX and FT-IR characterization results reveal that bimetallic MOFs and Pd nanoparticles were finely dispersed on the prepared MOFs surfaces. XRD results confirm the formation of the desire MOFs and show the high degree of dispersion of Pd nanoparticles. TEM images show that Pd nanoparticles are nano-sized with almost uniform shape. EDAX shows that Pd nanoparticles successfully loaded on Co_0.5–Mn_0.5-MOF-74 catalyst. CO oxidation as a model reaction was then used to assess the catalytic performance of the prepared catalysts. The catalytic activity results show enhancement in the catalytic activities of monometallic MOFs after introducing another metal in the same framework and show an excellent improvement in CO conversion after loading with Pd nanoparticles. Furthermore, the samples that contain Pd nanoparticles exhibits higher catalytic activities which raised with increasing the content of Pd nanoparticles.

Pd nanoparticles were loaded on Co_x–Mn_(1−x)-MOF-74. 5 wt% Pd@Co_0.5–Mn_0.5-MOF-74 was the most effective catalyst for CO oxidation. The prepared catalysts displayed excellent stability during CO oxidation without significant decrease in catalytic performance.     

Tailoring of the electronic property of Zn-BTC metal–organic framework via ligand functionalization: an ab initio investigation

Metal–organic frameworks (MOFs) are porous materials of recent interest due to their promising properties for technological applications. In this paper, the structure–property relationships of pristine and functionalized Zn-BTC (Zn₃(BTC)₂) MOFs are investigated. The results based on density functional theory (DFT) find that MOFs with coordinatively saturated secondary building units (SBU) are metallic, and MOFs with coordinatively unsaturated SBU are semi-conducting. The ligand functionalization with electron acceptor (cyano-) and electron donor (amino-) groups appears to tailor the electronic properties of Zn-BTC MOFs; amino-functionalization led to a significant upward shift of the band-edges whereas cyano-functionalization yields shifting of band-edges in the opposite direction, which led to a narrowing of the band gap. Modifying the electronic properties through such ligand functionalization design principles can be useful in engineering MOFs for gas sensing and device applications.

The structure–property relationships of pristine and functionalized Zn-BTC (Zn₃(BTC)₂) metal–organic frameworks are investigated.     

Biguanide–transition metals complexes as potential drug for hyperglycemia treatment

Coordination compounds of Cu(ii), Ni(ii), Co(ii), and Zn(ii) with a type of biguanide (known commercially as metformin) have been synthesized and characterized using spectroscopic techniques (FT-IR, UV/VIS), X-ray diffraction techniques and thermal analysis. For all compounds, single crystals were obtained for single-crystal X-ray diffraction. For the first time, an octahedral cobalt compound with the formula [Co(C₄H₁₁N₅)₃]Cl₂·2H₂O that crystallizes in the monoclinic space group C2/c with one molecule in the asymmetric unit has been obtained. Also, a novel nickel compound with the formula [Ni(C₄H₁₁N₅) (C₄H₁₀N₅)]Cl·H₂O that crystallizes in the monoclinic space group P2₁/c with two molecules in the asymmetric unit was obtained. Finally, we obtained copper and zinc compounds that crystallize in the monoclinic space groups P2₁/n and P2₁/c with the general formula [Cu(C₄H₁₁N₅)₂]Cl₂·H₂O and [Zn(C₄H₁₂N₅)Cl₃], respectively. A structural and supramolecular analysis was developed for all compounds using Hirshfeld surface analysis and electrostatic potential maps. The cell viability of the obtained compounds was evaluated in C2C12 (ATCCCRL-1772™) mouse muscle cells and HepG2 (ATCC HB-8065™) human liver carcinoma cells by the MTT assay to determine the potential of the compounds as new safe drugs. The results demonstrate that the compounds exhibit low cytotoxicity at doses less than 250 μg mL⁻¹ with a cell viability greater than 80%.

Coordination compounds of Cu(ii), Ni(ii), Co(ii), and Zn(ii) with a type of biguanide were obtained and structurally characterized. The new metal-drugs present biological applications as potential drugs for diabetes and metabolic syndrome.     

Simultaneous removal of Sb(iii) and Cd(ii) in water by adsorption onto a MnFe2O4–biochar nanocomposite

In this study, a jacobsite–biochar nanocomposite (MnFe₂O₄–BC) was fabricated and used to simultaneously remove Sb(iii) and Cd(ii) from water via adsorption. The MnFe₂O₄–BC nanocomposite was prepared via a co-precipitation method and analyzed using various techniques. The results confirm the successful decoration of the biochar surface with MnFe₂O₄ nanoparticles. The maximum Sb(iii) removal efficiency was found to be higher from bi-solute solutions containing Cd(ii) than from single-solute systems, suggesting that the presence of Cd(ii) enhances the removal of Sb(iii). The Langmuir isotherm model describes well Sb(iii) and Cd(ii) removal via adsorption onto the MnFe₂O₄–BC nanocomposite. The maximum adsorption capacities are 237.53 and 181.49 mg g⁻¹ for Sb(iii) and Cd(ii), respectively, in a bi-solute system. Thus, the prepared MnFe₂O₄–BC nanocomposite is demonstrated to be a potential adsorbent for simultaneously removing Sb(iii) and Cd(ii) ions from aqueous solutions.

In this study, a jacobsite–biochar nanocomposite (MnFe₂O₄–BC) was fabricated and used to simultaneously remove Sb(iii) and Cd(ii) from water via adsorption.     

Efficient removal of heavy metals from polluted water with high selectivity for Hg(ii) and Pb(ii) by a 2-imino-4-thiobiuret chemically modified MIL-125 metal–organic framework

A highly porous adsorbent based on a metal–organic framework was successfully designed and applied as an innovative adsorbent in the solid phase for the heavy metal removal. MIL-125 was densely decorated by 2-imino-4-thiobiuret functional groups, which generated a green, rapid, and efficacious adsorbent for the uptake of Hg(ii) and Pb(ii) from aqueous solutions. ITB-MIL-125 showed a high adsorption affinity toward mercury(ii) ions of 946.0 mg g⁻¹ due to covalent bond formation with accessible sulfur-based functionality. Different factors were studied, such as the initial concentration, pH, contact time, and competitive ions, under same circumstances at the room temperature. Moreover, the experimental adsorption data were in excellent agreement with the Langmuir adsorption isotherm and pseudo-second order kinetics. At a high concentration of 100 ppm mixture of six metals, ITB-MIL-125 exhibited a high adsorption capacity, reaching more than 82% of Hg(ii) compared to 62%, 30%, 2%, 1.9%, and 1.6% for Pb(ii), Cu(ii), Cd(ii), Ni(ii), and Zn(ii), respectively.

A highly porous adsorbent based on a metal–organic framework was successfully designed and applied as an innovative adsorbent in the solid phase for the heavy metal removal.     

Cu(ii)-alginate-based superporous hydrogel catalyst for click chemistry azide–alkyne cycloaddition type reactions in water

A novel sustainable hydrogel catalyst based on the reaction of sodium alginate naturally extracted from brown algae Laminaria digitata residue with copper(ii) was prepared as spherical beads, namely Cu(ii)-alginate hydrogel (Cu(ii)-AHG). The morphology and structural characteristics of these beads were elucidated by different techniques such as SEM, EDX, BET, FTIR and TGA analysis. Cu(ii)-AHG and its dried form, namely Cu(ii)-alginate (Cu(ii)-AD), are relatively uniform with an average pore ranging from 200 nm to more than 20 μm. These superporous structure beads were employed for the copper catalyzed [3 + 2] cycloaddition reaction of aryl azides and terminal aryl alkynes (CuAAC) via click chemistry at low catalyst loading, using water as a solvent at room temperature and pressure. The catalytic active copper(i) species was generated by the reduction of copper(ii) by terminal alkyne via the oxidative alkyne homocoupling reaction. The prepared catalysts were found to be efficient (85–92%) and regioselective by affording only 1,4-disubstituted-1,2,3-triazoles. They were also recoverable and reused in their dried form for at least four consecutive times without a clear loss of efficiency. A mechanistic study was performed through density functional theory (DFT) calculations in order to explain the regioselectivity outcome of Cu(ii)-alginate in CuAAC reactions. The analysis of the local electrophilicity (ω_k) at the electrophilic reagent and the local nucleophilicity (N_k) at the nucleophilic confirms the polar character of CuAAC. This catalyst has the main advantage of being sustainably ligand-free and recyclable.

The Cu(ii)-alginate-based superporous hydrogel was prepared and used as a heterogenous catalyst in the regioselective click of 1,4-disubstituted-1,2,3-triazoles by CuAAC reactions.     

Three-dimensional mesoporous calcium carbonate–silica frameworks thermally activated from porous fossil bryophyte: adsorption studies for heavy metal uptake

In this paper, three-dimensional mesoporous calcium carbonate–silica frameworks have been created from the straw tufa (ST) originating from porous fossil bryophyte by a thermal activation technique. A batch of adsorption kinetic and thermodynamic experiments were used to investigate the adsorption capacity of Cd(ii) onto the samples. The ST after thermal activation has shown a significant ability for the uptake of heavy metals. It exhibited maximum adsorption capacities of 12.76 mg g⁻¹, 14.09 mg g⁻¹, 17.00 mg g⁻¹, and 33.81 mg g⁻¹ for Cd(ii) at the activation temperature of 300, 450, 600 and 750 °C, respectively. Through competitive adsorption for Cd(ii)and Pb(ii), the ST thermally activated at 750 °C exhibited maximum equilibrium adsorption capacities of 24.65 mg g⁻¹, 25.91 mg g⁻¹, and 30.94 mg g⁻¹ for Cd(ii) uptake at 298.1 K, 308.1 K and 318.1 K, respectively, whereas it exhibited values of 91.59 mg g⁻¹, 101.32 mg g⁻¹, and 112.19 mg g⁻¹ for Pb(ii) removal. The adsorption capacities of Cd(ii) and Pb(ii) both decrease with the addition of the other heavy metal cations, indicating that the adsorption is hindered by the competitive adsorption and the adsorption active sites on the mineral surface are readily exchangeable. The adsorption of Cd(ii) and Pb(ii) followed the pseudo-second order kinetics model well. In addition, the Langmuir model could accurately describe the adsorption isotherms. Based on the results of characterization with TEM, XRD and XPS, the adsorption mechanisms could be primarily explained as formation of Cd(OH)₂ and CdCO₃ as well as Cd(HCO₃)₂ precipitation on the surface of ST. These characteristics of ion-exchange and the adsorptive property for ST modified allow it to be widely used in artificial wetland landfill and environmental protection.

Three-dimensional mesoporous calcium carbonate–silica frameworks have been created and have shown excellent adsorption capacities for Cd(ii) and Pb(ii).     

Synthesis of FeO@SiO2–DNA core–shell engineered nanostructures for rapid adsorption of heavy metals in aqueous solutions

Creating novel and innovative nanostructures is a challenge, aiming to discover nanomaterials with promising properties for environmental remediation. In this study, the physicochemical and adsorption properties of a heterogeneous nanostructure are evaluated for the rapid removal of heavy metal ions from aqueous solutions. Core–shell nanostructures are prepared using iron oxide cores and silica dioxide shells. The core is synthesized via the co-precipitation method and modified in situ with citric acid to grow a carboxyl layer. The shell was hydrolyzed/condensed and then functionalized with amine groups for ds-DNA condensation via electrostatic interaction. The characterization techniques revealed functional FeO@SiO₂–DNA nanostructures with good crystallinity and superparamagnetic response (31.5 emu g⁻¹). The predominant superparamagnetic nature is attributed to the citric acid coating. This improves the dispersion and stability of the magnetic cores through the reduction of the dipolar–dipolar interaction and the enhancement of the spin coordination. The rapid adsorption mechanism of FeO@SiO₂–DNA was evaluated through the removal of Pb(ii), As(iii), and Hg(ii). A rapid adsorption rate is observed in the first 15 min, attributed to a heterogeneous chemisorption mechanism based on electrostatic interactions. FeO@SiO₂–DNA shows higher adsorption efficiency of 69% for Pb(ii) removal compared to As(iii) (51%) and Hg(ii) (41%). The selectivity towards Pb(ii) is attributed to the similar acid nature to ds-DNA, where the ionic strength interaction provides good affinity and stability. The facile synthesis and rapid adsorption suggest a promising nanostructure for the remediation of water sources contaminated with heavy metal ions and can be extended to other complex molecules.

Facile synthesis of well-dispersed and magnetic FeO@SiO₂–DNA nanostructures with electrostatic active sites for interaction and rapid adsorption of heavy metals.