Search Results (173)

Tetracycline antibiotics are increasingly detected in aquatic environments because of their ecological risks and persistence, while conventional wastewater treatment processes are often insufficient for their effective removal from water. Here, we introduce a novel 3D graphene oxide-based nanocomposite that stacks Cu-NPs and amino-functionalized MIL-101(Fe) (denoted by Cu/NH₂-MIL-101(Fe)@GO) to effectively remove tetracycline (TC) and oxytetracycline (OTC) from environmental water samples. XPS, XRD, TEM, SEM, and FTIR analyses were conducted to characterize the structure and surface morphology of the Cu/NH₂-MIL-101(Fe)@GO nanocomposite. Overall, it was confirmed that GO, NH₂-MIL-101(Fe), and Cu-NPs were successfully incorporated, resulting in a porous material with high access to Cu-related sites as well as oxygen- and nitrogen-based functionalities (such as amino-, hydroxy-, and carboxy-groups). This hybrid system facilitates the adsorption by complementary mechanisms like surface complexation/chelation at Cu and Fe centers with the pH-dependent tetracycline species in electrostatic interactions, hydrogen bonding, π–π stacking, and molecule confinement in the metal–organic framework (MOF) pores, and by the synergistic effects at the GO–MOF(Fe)–Cu junction interfaces. The batch adsorption studies showed that the quick and efficient uptake of the two antibiotics at pH 6.5, with removal rates of 99.65–99.83%, was achieved by 15.0 mg of Cu/NH₂-MIL-101(Fe)@GO at an initial concentration of 20 ppm in 40 min at 25 °C. Equilibrium data were found to be well-fitted by the Langmuir isotherm (R² = 0.908–0.909), suggesting monolayer-dominated adsorption with the maximum capacity of 769.8–775.2 mg g⁻¹. The adsorption kinetics was well-described by the pseudo-second order model (R² = 0.9641–0.9749), which agreed with the strong binding between the tetracyclines and active sites of the nanocomposite. The main novelty of this work consists of the design of a single recoverable platform integrating GO-based preconcentration, pore accessibility of NH₂-MIL-101(Fe), and Cu-driven complexation, which led to the strong removal of tetracyclines under a relevant range of water conditions. These findings demonstrate that Cu/NH₂-MIL-101(Fe)@GO could serve as a promising high-efficiency and potentially reusable adsorbent for removing tetracycline from aqueous solution, which provides a more sustainable approach for pharmaceutical wastewater treatment. Full article

The synthesis of nitrogen-containing heterocycles remains a subject of significant interest due to their applications in medicinal chemistry and materials science. This paper describes the preparation of imidazo[1,2-a]pyridine using a catalytic system consisting of the deep eutectic solvent (DES) choline chloride (ChCl)–tartaric acid (1:2) and I₂ by reaction between 2-aminopyridines and chalcones (1,3-diphenylprop-2-en-1-ones). The proposed mechanism suggests the activation of the chalcone carbonyl by the DES, enhancing the polarization of the conjugated system which suffers electrophilic addition by I₂ to the C=C bond. The resulting intermediate undergoes a nucleophilic attack by 2-aminopyridine followed by cyclization and iodine-promoted oxidation and aromatization to yield the corresponding imidazo[1,2-a]pyridine products. The role of the DES is crucial, as it facilitates carbonyl activation through hydrogen bond interactions, stabilizes reactive intermediates, and promotes protonation–deprotonation steps, thereby eliminating the need for metal catalysts or toxic organic solvents. Theoretical calculations at the PM6 level of theory suggest that the DES acts as a catalyst in this reaction, due to the nature of its components enabling the development of more sustainable synthetic strategies. Full article

The aza-Michael reaction is a fundamental transformation for carbon–nitrogen bond formation, providing efficient access to β-amino carbonyl compounds, nitriles, and related nitrogen-containing building blocks of broad importance in medicinal chemistry and organic synthesis. Over the past two decades, ionic liquids (ILs) have attracted considerable attention as alternative reaction media, promoters, and catalysts for aza-Michael reactions, owing to their distinctive physicochemical properties and tunable structures. This review presents a comprehensive and critical overview of ionic-liquid-mediated aza-Michael reactions, emphasizing the evolution of IL design from early imidazolium-based systems to modern task-specific, supported, and bio-derived ionic liquids. Conventional room-temperature ionic liquids are discussed as non-innocent solvents capable of stabilizing charged intermediates and enhancing electrophilicity, thereby enabling catalyst-free or metal-assisted aza-Michael additions. Subsequent sections focus on task-specific ionic liquids incorporating Brønsted acidic, basic, hydrogen-bond-donating, or bifunctional motifs, highlighting how rational structural design translates into improved activity, selectivity, and substrate scope. Particular attention is devoted to guanidine-, DABCO-, and DBU-based ionic liquids, where mechanistic studies reveal cooperative activation modes rather than simple acid–base catalysis. Recent advances in supported and polymeric ionic liquids are also reviewed, demonstrating effective strategies to combine IL-like reactivity with enhanced recyclability and operational simplicity. Overall, this review clarifies the diverse roles of ionic liquids in aza-Michael chemistry and outlines current challenges and future perspectives toward more sustainable and efficient C–N bond-forming methodologies. Full article

The efficient conversion of CO₂ into valuable chemicals using highly efficient, environmentally friendly, and renewable heterogeneous catalysts is paramount for the progression of a carbon circular economy. In pursuit of this goal, this study introduces a metal-free, scalable melamine-based organic polymer catalyst designed to integrate CO₂ adsorption with customizable functional properties. Employing both solid-state thermal synthesis (SST) and hydrothermal methods, we synthesized three amine-based hydrogen bond donor catalysts, thereby balancing environmentally conscious practices with scalable synthesis: MCA, a high-nitrogen-content polymer derived from trichlorocyanuric acid; MCA-SST; and MTAB, a triazine-trichlorocyanuric acid polymer. Under mild conditions (100 °C, 0.1 MPa, 24 h), MCA demonstrated superior catalytic performance in the CO₂ cycloaddition of epichlorohydrin, achieving a 99% conversion rate, significantly surpassing MCA-SST (60%) and MTAB (78%). MCA’s high specific surface area and structural integrity facilitate efficient catalysis under mild conditions, and it retains 79% of its initial activity after five cycles, indicating exceptional stability. These results suggest that while the incorporation of secondary amines and increased nitrogen content generally promote the reaction, densely packed adjacent secondary amine linkages can induce repulsion between nitrogen atoms, thereby weakening active sites and reducing catalytic activity. Consequently, this study not only presents MCA as a novel metal-free catalyst exhibiting remarkable performance in catalyzing CO₂ cycloaddition under ambient pressure and mild conditions, but also elucidates the structure–activity relationship between secondary amine density and catalytic activity. This work provides a deeper mechanistic understanding and offers a theoretical foundation for future rational catalyst design. Full article

For those who did not follow the invention and development of enantioselective catalysis, this review introduces pertinent historical aspects of the field and presents the scientific concepts of asymmetric bio- and organocatalysis. They are powerful technologies applied in organic laboratories and industry. They realize chiral amplification by converting inexpensive achiral substrates and reagents into enantiomerically enriched products using readily recoverable solvents, if any are used. Racemic substrates can also be deracemized catalytically. More sustainable fabrications are now available that require neither toxic metallic species nor costly reaction conditions in terms of energy, atmosphere control, product purification, and safety. Nature has been the source of the first asymmetric catalysts (microorganisms, enzymes, alkaloids, amino acids, peptides, terpenoids, sugars, and their derivatives). They act as temporary chiral auxiliaries and lower the activation free energy of the reaction by altering the reaction mechanism. Reductions, oxidations, carbon-carbon and carbon-heteroatom bond-forming reactions are part of the process panoply. Asymmetric catalyzed multicomponent and domino reactions are becoming common. Typical modes of activation are proton transfers, hydrogen bonded complex formation, charged or uncharged acid/base pairing (e.g., σ-hole catalysts), formation of equilibria between achiral aldehydes and ketones with their chiral iminium salt or/and enamine intermediates, umpolung of aldehydes and ketones by reaction with N-heterocyclic carbenes (NHCs), phase transfer catalysis (PTC), etc. Often, the best enantioselectivities are observed with polyfunctional catalysts derived from natural compounds, but not always. They may combine to form chiral structures containing nitrogen, phosphorus, sulfur, selenium, and iodine functional moieties. Today, man-made enantiomerically enriched catalysts, if not enantiomerically pure, are available in both enantiomeric forms. Being robust, they are recovered and reused readily. Full article

Chromium complexes with triamidoamine derivatives bearing bulky substituents at the terminal positions of the ligands, tris(2-(3-pentylamino)ethyl)amine (H₃L^Pen) and tris(2-dicyclohexylmethylaminoethyl)amine (H₃L^Cy), are prepared: [{Cr(L^Pen)}₂(μ-N₂)] (1), [{CrK(L^Pen)(μ-N₂)(Et₂O)}₂] (2), [CrCl(L^Pen)] (3), [Cr(L^Cy)] (4), [CrK(L^Cy)(μ-N₂)(18-crown-6)(THF)] (5(THF)), and [CrCl(L^Cy)] (6). The preparation of these complexes is confirmed by X-ray diffraction analysis. Complexes 1, 2, and 5(THF) have coordinated dinitrogen molecules, with N–N bond lengths of 1.185(3), 1.174(9), and 1.162(3) Å, respectively. These lengths are significantly elongated compared to that of a free dinitrogen molecule (1.10 Å), indicating that the N₂ ligands are activated. The ν(¹⁴N–¹⁴N) values of 1, 2, and 5(THF) are 1715 cm⁻¹ for 1 (Raman, in solution), 1787, 1743 cm⁻¹ for 2 (IR, in solid), and 1824 cm⁻¹ for 5(THF) (IR, in solid), respectively. These values are markedly smaller than free nitrogen (2331 cm⁻¹), confirming that the dinitrogen is interacting with the metal ions and is activated. The structures of 2 and 5(THF) in solution are also studied by ¹H NMR and solution IR spectroscopies. ¹H NMR spectra of these complexes reveal that the peaks of 2 and 5(THF) are observed in the diamagnetic region, whereas those for the other complexes (1, 3, 4, and 6) exhibit paramagnetic shifts. The reactions of these complexes with K[C₁₀H₈] and HOTf under N₂ in THF yield hydrazine and a small amount of ammonia; however, they are not catalytic. The ¹H NMR and IR spectra of the products obtained by reacting 1 or 3 with reductant K in THF under N₂ atmosphere indicate that 2 is formed based on spectral agreement. Similarly, upon examining for 4 or 6, it is confirmed that a species similar to 5(THF) is generated. Full article

Ligands L1 and L2 are composed, respectively, by a diethylenetriamine or a dipropylenetriamine moiety linked at their extremities to anthracene units through methylene bridges and form stable 1:1 complexes with Zn(II), in which the metal is coordinated by all three nitrogens of the ligands. Zn(II) binding by L1 leads to a marked enhancement of the fluorescence emission, thanks to the inhibition of the photoinduced electron transfer (PET) process from the benzylic amine groups of the triamine sub-unit to the excited fluorophore, which normally quenches the emission of fluorescent polyamine receptors. Conversely, the emission of L2 is somewhat quenched by Zn(II) binding likely due—as also indicated by ab initio calculations and molecular dynamics simulations—to the formation of cation π quenching contacts between the metal and the anthracene moieties that overcome the effects of PET inhibition. The Zn(II) complexes of both ligands are able to bind ketoprofen (KP) in its anionic form, thanks to the formation of COO⁻—Zn(II) coordinative bonds, to form [KPZnL]⁺ and [(KP)₂ZnL] (L = L1 or L2) ternary adducts. While KP binding to [ZnL2]²⁺ enhances the fluorophore emission, coordination of KP to [ZnL1]²⁺ slightly reduces the anthracene emission, due, once again, to the formation in the L1 ternary complexes of marked cation π contacts. Full article

Coplanar tridentate nitrogen-donor ligands have been extensively employed to stabilize transition metal complexes by chelation. Some complexes exhibit interesting structures and photoluminescent properties. In this work, 2,6-bis(5-isopropyl-1H-pyrazole-3-yl)pyridine (denoted as L), its iron(II) and manganese(II) dichlorido complexes, and its bis-chelate iron(II) complexes, viz. [FeCl₂(L)]·2(MeOH) and [MnCl₂(L)]·2(MeOH), and [Fe(L)₂](PF₆) ·5(thf), respectively, were synthesized and characterized by single-crystal X-ray structural analysis. These solid-state structures contained N–H donors that formed hydrogen bonds with the coordinated halogenide ions and lattice solvent molecules, methanol or tetrahydrofuran. The iron(II) and manganese(II) dichlorido complexes [FeCl₂(L)]·2(MeOH) and [MnCl₂(L)]·2(MeOH) displayed distorted trigonal pyramidal structures in the solid state. However, [FeCl₂(L)]·2(MeOH) was not stable in methanol and formed the bis-chelate iron(II) complex [Fe(L)₂](FeCl₄). Therefore, the bis-chelate iron(II) complex [Fe(L)₂](PF₆)·5(thf) was also synthesized and structurally and spectroscopically authenticated. Full article

Residual-free eutectic Au80Sn20 soldering is still the dominant assembly technology for optoelectronic devices such as high-power lasers, LEDs, and photodiodes. Due to the high cost of gold, alternatives are desirable. This paper investigates the thermal performance of copper-based sintering for optoelectronic submodules on first and second level to obtain thermally efficient thin bondlines. Sintered interconnects obtained by a new particle-free copper ink, based on complexed copper salt, are compared with copper flake and silver nanoparticle sintered interconnects and benchmarked against AuSn solder interconnects. The copper ink is dispensed and predried at 130 °C to facilitate in situ generation of Cu nanoparticles by thermal decomposition of the metal salt before sintering. Submounts are then sintered at 275 °C for 15 min under nitrogen with 30 MPa pressure, forming uniform 2–5 µm copper layers achieving shear strengths above 31 MPa. Unpackaged LEDs are bonded on first level using the copper ink but applying only 10 MPa to avoid damaging the semiconductor dies. Thermal performance is evaluated via transient thermal analysis. Results show that copper ink interfaces approach the performance of thin AuSn joints and match silver interconnects at second level. However, at first level, AuSn and sintered interconnects of commercial silver and copper pastes remained superior due to the relative inhomogeneous thickness of the thin Cu copper layer after predrying, requiring higher bonding pressure to equalize surface inhomogeneities. Full article

Nitrogen (N) and phosphorus (P) play vital roles in crop growth. However, conventional fertilizers exhibit low utilization efficiency, making them prone to causing resource wastage and water eutrophication. Although metal–organic frameworks (MOFs) have shown great potential for application in controlled-release fertilizers (CRFs), currently reported MOF-based CRFs suffer from low nutrient content, which limits their further application. To address this issue, this study synthesized a series of hierarchically porous MOFs, denoted as MIL-156(X), using sodium acetate as a modulator under hydrothermal conditions. These materials were subsequently loaded with urea and phosphate from aqueous solution to form MOFs-based CRFs (N-P-MIL-156(X)). Results indicate that MIL-156(X) retain microporous integrity while incorporating abundant mesopores. Increasing modulator content reduced particle size and average pore diameter but increased specific surface area and adsorption capacity for urea and phosphate. MIL-156-H (with a high modulator content addition) exhibited the highest adsorption capacity, conforming to Langmuir isotherm and pseudo-second-order kinetics. The adsorption mechanisms of urea and phosphate involved hydrogen bonding and the formation of Ca intra-spherical complexes, respectively. N-P-MIL-156-H contained 10.8% N and 16.3% P₂O₅, with sustained release durations exceeding 42 days (N) and 56 days (P₂O₅) in an aqueous solution. Pot trials demonstrated significantly higher nutrient use efficiency (N-44.8%, P₂O₅-16.56%) and a 12.22% yield increase compared to conventional fertilization (N-35.6%, P₂O₅-13.32%). Thus, N-P-MIL-156-H-based fertilization significantly promotes rice growth and N/P utilization efficiency, offering a promising strategy for developing controlled-release fertilizers and improving nutrient management. Full article

2,2-Bis(3,5-dimethylpyrazol-1-yl)-1,1-diphenylethanol (HL) is a heteroscorpionate ligand capable of coordinating metal ions through two nitrogen atoms and one oxygen atom. We report a base free synthetic route to metal complexes of L and explore the resulting structural diversity. Notably, complex composition varies substantially depending on the metal ion, including dinuclear molybdenum species and distinct coordination behavior with silicon and copper. The isolated compounds include the dinuclear, oxygen-bridged complexes (LMoO₂)₂O and (LMoO)(μ-O)₂, as well as the mononuclear complexes LTi(NMe₂)₃, LZrCl₃, LGeCl₃, LWO₂Cl, LCu(acetate)₂H, and LSiMe₂Cl. Single crystal X-ray diffraction reveals that the bulky complex structures generate cavities in the crystal lattice, frequently occupied by solvent molecules. The titanium, zirconium, molybdenum, tungsten, and germanium complexes exhibit octahedral coordination, while structural peculiarities are observed for copper and silicon. The copper(II) complex shows a distorted octahedral geometry with one elongated ligand bond; the silicon complex is pentacoordinated in the solid state. Additional characterization includes melting points, NMR, and IR spectroscopy. The developed synthetic strategy provides a straightforward and versatile route to heteroscorpionate metal complexes. Full article

In recent years, apatite-based materials have garnered significant interest, particularly for applications in tissue engineering. Apatite is most commonly employed as a coating for metallic implants, as a component in composite materials, and as scaffolds for bone and dental tissue regeneration. Among its various forms, hydroxyapatite (HAP) is the most widely used, owing to its natural occurrence in human and animal hard tissues. An emerging area of research involves the use of fluoride-substituted apatite, particularly fluorapatite (FAP), which can serve as a direct fluoride source at the implant site, potentially offering several biological and therapeutic advantages. However, substituting HAP with FAP may lead to unforeseen changes in material behavior due to the differing physicochemical properties of these two calcium phosphate phases. This study investigates the effects of replacing hydroxyapatite with fluorapatite in ceramic–polymer composite materials incorporating β-1,3-glucan as a bioactive polymeric binder. The β-1,3-glucan polysaccharide was selected for its proven biocompatibility, biodegradability, and ability to form stable hydrogels that promote cellular interactions. Nitrogen adsorption analysis revealed that FAP/glucan composites had a significantly lower specific surface area (0.5 m²/g) and total pore volume (0.002 cm³/g) compared to HAP/glucan composites (14.15 m²/g and 0.03 cm³/g, respectively), indicating enhanced ceramic–polymer interactions in fluoride-containing systems. Optical profilometry measurements showed statistically significant differences in profile parameters (e.g., Rp: 134 μm for HAP/glucan vs. 352 μm for FAP/glucan), although average roughness (Ra) remained similar (34.1 vs. 27.6 μm, respectively). Microscopic evaluation showed that FAP/glucan composites had smaller particle sizes (1 μm) than their HAP counterparts (2 μm), despite larger primary crystal sizes in FAP, as confirmed by TEM. XRD analysis indicated structural differences between the apatites, with FAP exhibiting a reduced unit cell volume (524.6 ų) compared to HAP (528.2 ų), due to substitution of hydroxyl groups with fluoride ions. Spectroscopic analyses (FTIR, Raman, ³¹P NMR) confirmed chemical shifts associated with fluorine incorporation and revealed distinct ceramic–polymer interfacial behaviors, including an upfield shift of PO₄³⁻ bands (964 cm⁻¹ in FAP vs. 961 cm⁻¹ in HAP) and OH vibration shifts (3537 cm⁻¹ in FAP vs. 3573 cm⁻¹ in HAP). The glucan polymer showed different hydrogen bonding patterns when combined with FAP versus HAP, as evidenced by shifts in polymer-specific bands at 888 cm⁻¹ and 1157 cm⁻¹, demonstrating that fluoride substitution significantly influences ceramic–polymer interactions in these bioactive composite systems. Full article

Metal–organic frameworks (MOFs) are materials with extremely valuable properties. The latter depend largely on the ligand used; therefore, the design of new organic linkers is a priority task today. A series of s-triazines possessing variable heteroatom-bridged identical substituents, useful ligands for the synthesis of MOFs, is obtained in good to excellent yields. The problem of obtaining free carboxyl groups without forming salts with nitrogen atoms is solved. The products are characterized by NMR spectra and single crystal XRD of selected samples. Unexpected O-triazine bond cleavage under basic hydrolysis conditions is observed. Full article

Four different MIL-68(Al) catalysts were synthesized and characterized by XPS, SEM, TEM, XRD, DLS, Nitrogen adsorption removal, and other methods. An aluminum-based MOF (Metal Organic Framework) (MIL-68(Al))/graphite oxide (GO) composite with TiO₂ showed the largest BET specific area with best adsorption performance. Representation demonstrated that MIL-68(Al) and TiO₂ nanoparticles are uniformly dispersed on the surface of the GO lamellar, and a tight heterojunction structure is formed between them. The MIL-68(Al)/GO/TiO₂ exhibits good pore characteristics, structural morphology, and catalytic performance. Adsorption experiments of methyl orange can reach 99.7% with the effect of MIL-68(Al)/GO/TiO₂ in water for 20 min. Moreover, the pH range can be applied to 1–13 and a high concentration of 200 mg/L methyl orange solution also worked well. In addition, this kind of catalyst can also be used for rhodamine B, methylene blue, congo red, and tetracycline in 20 min with good adsorption. Meanwhile, simple filtration can quickly recover MIL-68(Al)/GO/TiO₂ and effectively reuse it. Free radical capture experiments showed a large number of •OH radicals during the adsorption of MO (Methyl Orange) solution by MIL-68(Al)/GO/TiO₂. Meanwhile, the electrostatic interaction, π-π packing and hydrogen bonding make MIL-68(Al)/GO/TiO₂ have a higher adsorption capacity for MO. Therefore, co-doping optimized the structure of MIL-68(Al), enhancing its stability in strong acids and bases while improving adsorption performance across a broader pH range than previously reported. This work addresses the instability of MIL-68(Al) under extreme conditions, demonstrating its significant potential for wastewater treatment applications. Full article

The development of heterogeneous nanocatalysts with high performance is essential for improving hydrogen production through formic acid dehydrogenation, but challenging. Herein, highly dispersed Pd nanoparticles (NPs) were successfully immobilized on porous nitrogen-doped carbon cages (PNCCs) derived from zeolitic imidazole frameworks. By virtue of the synergistic effect, the optimized Pd/PNCC nanocatalytic systems exhibit an excellent catalytic kinetics toward catalyzing FA dehydrogenation with a turnover frequency (TOF) value as high as 3174 h⁻¹ at 323 K, which is 59 times relative to that of Pd nanoparticles. The exceptional activity may be ascribed to the PNCC solid support may induce a strong electronic metal–support interaction to optimize the electron configuration of Pd active sites and accelerate the kinetics of O-H bond cleavage, resulting in an enhanced catalytic performance toward FA dehydrogenation. This work will supply a novel strategy for the development of supported nanocatalysts with high performance for tremendous catalytic applications in the future. Full article