Fabrication, functionalization and advanced applications of magnetic hollow materials in confined catalysis and environmental remediation

Sulfonate-Bonded Conjugated Microporous Polymer Hollowed-Out Spheres to Capture Fluoroquinolone Antibiotics and Cationic Dyes from Wastewater

Developing adsorbent materials for the efficient removal of multiple organic pollutants in water is of importance technological significance. In the present work, a kind of conjugated microporous polymer (CMP) with a hollow sphere structure was constructed by applying SiO2 nanoparticles as a template and 1,3,5-triethynylbenzene (TEB) and 2,7-dibromocarbazole (27-DBCZ) as building blocks via the Sonogashira-Hagihara cross-coupling reaction. In order to further improve the dispersibility of the as-resulting CMPs in water, hydrophilic CMPs (H-S-CMPs) were obtained by a sulfonation modification. The adsorption performance of H-S-CMPs on dyes and antibiotics was investigated, which was based on different experimental parameters such as the initial concentration, contact time, temperature, pH, and adsorbent dose. The adsorption isotherm, kinetics, and thermodynamics were also studied, and the possible adsorption mechanism of H-S-CMPs was discussed. The experimental results illustrated that the adsorption process of H-S-CMPs on dyes and antibiotics is more consistent with the Langmuir isotherm model and the pseudo-second-order kinetic model. The maximum adsorption capacities of H-S-CMPs for rhodamine B (RhB), methylene blue (MB), ciprofloxacin, and norfloxacin were 206.2, 324.7, 222.2, and 216.9 mg/g, respectively, which were determined according to the Langmuir isothern model. In addition, the adsorption mechanism of H-S-CMPs may be attributed to the synergistic effects of hydrogen bonding, electrostatic attraction, π-π stacking, and pore filling. After 5 cycles, H-S-CMPs still maintained good stability, and their removal rate of dyes could reach more than 70%. Notably, this polymeric hollow microsphere has been less extensively investigated as an adsorbent for the removal of dyes and antibiotics. As a result, based on the designable flexibility of CMPs and the unique structure of hollow microspheres, the material holds great promise for wastewater treatment in the presence of multiple pollutants.

Enhanced Visible-Light Photocatalytic Activity of Bismuth Ferrite Hollow Spheres Synthesized via Evaporation-Induced Self-Assembly

Semiconductor hollow spheres have garnered significant attention in recent years due to their unique structural properties and enhanced surface area, which are advantageous for various applications in catalysis, energy storage, and sensing. The present study explores the surfactant-assisted synthesis of bismuth ferrite (BiFeO3) hollow spheres, emphasizing their enhanced visible-light photocatalytic activity. Utilizing a novel, facile, two-step evaporation-induced self-assembly (EISA) approach, monodisperse BiFeO3 hollow spheres were synthesized with a narrow particle size distribution. The synthesis involved Bi/Fe citrate complexes as precursors and the triblock copolymer Pluronic P123 as a soft template. The BiFeO3 hollow spheres demonstrated outstanding photocatalytic performance in degrading the emerging pollutants Rhodamine B and metronidazole under visible-light irradiation (100% degradation of Rhodamine B in <140 min and of metronidazole in 240 min). The active species in the photocatalytic process were identified through trapping experiments, providing crucial insights into the mechanisms and efficiency of semiconductor hollow spheres. The findings suggest that the unique structural features of BiFeO3 hollow spheres, combined with their excellent optical properties, make them promising candidates for photocatalytic applications.

Applications of hollow nanostructures in water treatment considering organic, inorganic, and bacterial pollutants

One of the major issues of modern society is water contamination with different organic, inorganic, and contaminants bacteria. Finding cost-effective and efficient materials and methods for water treatment and environment remediation is among the scientists' most important considerations. Hollow-structured nanomaterials, including hollow fiber membranes, hollow spheres, hollow nanoboxes, etc., have shown an exciting capability for wastewater refinement approaches, including membrane technology, adsorption, and photocatalytic procedure due to their extremely high specific surface area, high porosity, unique morphology, and low density. Diverse hollow nanostructures could potentially eliminate organic contaminants, including dyes, antibiotics, oil/water emulsions, pesticides, and other phenolic compounds, inorganic pollutants, such as heavy metal ions, salts, phosphate, bromate, and other ions, and bacteria contaminations. Here, a comprehensive overview of hollow nanostructures' fabrication and modification, water contaminant classification, and recent studies in the water treatment field using hollow-structured nanomaterials with a comparative attitude have been provided, indicating the privilege abd detriments of this class of nanomaterials. Eventually, the future outlook of employing hollow nanomaterials in water refinery systems and the upcoming challenges arising in scaling up are also propounded.

Overlooked role of void-nanoconfined effect in emerging pollutant degradation: Modulating the electronic structure of active sites to accelerate catalytic oxidation

The efficient removal of emerging pollutant from water is the ultimate frontiers of advanced oxidation processes (AOPs), yet it is challenging to obtain higher catalytic activity and oxidation rate. Herein, a sustainable solution was proposed by optimizing the curvature of confined structure to modulate the electronic state of the active sites in nanochannels for improving the catalytic activity. In addition, the confined effect can enhance the oxidation rate by shorting the mass transfer of active species and pollutants. A void-nanoconfined nanoreactor was prepared by loading Fe2O3 into the nanochannels (<5 nm) of the hollow carbon sphere. An enhancement of 3 orders of magnitude was obtained in the degradation rate constant of void-nanoconfined catalytic system toward sulfamethoxazole (SMX) (6.25 min-1) compared with the non-confined system. The kinetics enhancement was attributed to the larger electron potential difference between the outer and inner nanochannel caused by the curvature increase of carbon sphere, accelerating the electron transfer, so that the energy barrier of SMX degradation reaction was reduced by 31 kcal/mol with the assistance of confinement energy. Importantly, the NC-IN/PDS system exhibited outstanding removal efficiency for the actual river water using a continuous flow reactor. This work provides a new insight into designing an efficient and stable catalytic nanoreactor, enriching the domain of advanced wastewater treatment strategies.

Iron-Cobalt magnetic porous carbon beads activated peroxymonosulfate for enhanced degradation and Microbial inactivation

Magnetic carbon-based catalysts are promising materials for advanced oxidation processes, offering both high catalytic activity and environmental friendliness, and hold great potential in environmental remediation. In this work, Fe and Co zeolite imidazole frameworks (ZIFs) derived micron-sized magnetic porous carbon beads (MPCBs) were prepared by phase inversion and following the carbonization procedure, and the morphological and structural characteristics of the MPCBs were confirmed. The presence of pores and channels in the MPCBs provides a specific microenvironment for the for the catalysis of the core. Bisphenol A (BPA) was selected for the targeted pollutant, and the catalytic experiments confirmed that the effective catalytic activity of MPCBs in the presence of peroxymonosulfate (PMS), which could almost completely degrade BPA in 20 min with a reaction rate of 0.368 min-1. Furthermore, the MPCBs were used to effectively bacterial inactivation. Intermediate products of the BPA degradation process were validated and the toxicological studies showed a gradual decrease in toxicity, indicating effective reduction of potential hazards. The macroscopic preparation methods we developed for MPCBs that is promising for industrial applications and has the potential to cope with complex environmental remediation.

Hydrothermal Synthesis of Bismuth Ferrite Hollow Spheres with Enhanced Visible-Light Photocatalytic Activity

In recent years, semiconductor hollow spheres have gained much attention due to their unique combination of morphological, chemical, and physico-chemical properties. In this work, we report for the first time the synthesis of BiFeO3 hollow spheres by a facile hydrothermal treatment method. The mechanism of formation of pure phase BiFeO3 hollow spheres is investigated systematically by variation of synthetic parameters such as temperature and time, ratio and amount of precursors, pressure, and calcination procedures. The samples were characterized by X-ray powder diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and UV-vis diffuse reflectance spectroscopy. We observe that the purity and morphology of the synthesized materials are very sensitive to synthesis parameters. In general, the chemically and morphologically very robust hollow spheres have diameters in the range of 200 nm to 2 μm and a wall thickness of 50-200 nm. The synthesized BiFeO3 hollow spheres were applied as catalysts in the photodegradation of the model pollutant Rhodamine B under visible-light irradiation. Notably, the photocatalyst demonstrated exceptionally high removal efficiencies leading to complete degradation of the dye in less than 150 min at neutral pH. The superior efficiencies of the synthesized material are attributed to the unique features of hollow spheres. The active species in the photocatalytic process have been identified by trapping experiments.

Pd@l-asparagine-EDTA-chitosan: a highly effective and reusable bio-based and biodegradable catalyst for the Heck cross-coupling reaction under mild conditions

In this research, a novel supramolecular Pd(ii) catalyst supported on chitosan grafted by l-asparagine and an EDTA linker, named Pd@ASP-EDTA-CS, was prepared for the first time. The structure of the obtained multifunctional Pd@ASP-EDTA-CS nanocomposite was appropriately characterized by various spectroscopic, microscopic, and analytical techniques, including FTIR, EDX, XRD, FESEM, TGA, DRS, and BET. The Pd@ASP-EDTA-CS nanomaterial was successfully employed, as a heterogeneous catalytic system, in the Heck cross-coupling reaction (HCR) to afford various valuable biologically-active cinnamic acid derivatives in good to excellent yields. Different aryl halides containing I, Br and even Cl were used in HCR with various acrylates for the synthesis of corresponding cinnamic acid ester derivatives. The catalyst shows a variety of advantages including high catalytic activity, excellent thermal stability, easy recovery by simple filtration, more than five cycles of reusability with no significant decrease in its efficacy, biodegradability, and excellent results in the HCR using low-loaded Pd on the support. In addition, no leaching of Pd into the reaction medium and the final products was observed.

Recent advances in spinel ferrite-based magnetic photocatalysts for efficient degradation of organic pollutants

Although spinel ferrite (MFe₂O₄, M = Zn, Ni, Mn, etc.) has been reported as a promising catalyst, its low photocatalytic activity under visible light greatly restricts its practical application. Spinel ferrite-based photocatalytic composites have exhibited improved efficiency for pollutant degradation, due to interface charge carrier mobility and structural modification. Meanwhile, due to its magnetism and stability, spinel ferrite composite can be easily recycled for long-term utilization, showing its high application potential. In this review, the recent advances in the construction and photocatalytic degradation of spinel ferrite composites are discussed, with an emphasis on the relationship between structural property and photocatalytic activity. In addition, to improve their photocatalytic application, the challenges, gaps and future research prospects are proposed.

Fabrication and characterization of the Fe3O4@SiO2-rGO nanocomposite: a catalyst for multi-component reactions

A novel nanocomposite is synthesized by covalently modifying reduced graphene oxide (rGO) with Fe₃O₄@SiO₂ nanoparticles. Fe₃O₄ was synthesized using a co-precipitation method, and SiO₂ was then coated onto the Fe₃O₄via a sol-gel method. Graphene oxide was synthesized using the Hummers' method. Furthermore, a hydrothermal method was applied to create the Fe₃O₄@SiO₂-GO composite, and a simple reduction was used to obtain three-dimensional (3D) Fe₃O₄@SiO₂-rGO core-shell spheres. XRD, FTIR, FE-SEM, VSM, BET, TGA, and Raman analyses were used to characterize the prepared nanocomposites. X-Ray diffraction (XRD) and Raman spectra reveal that the nanostructures consist of highly crystallized cubic Fe₃O₄, amorphous SiO₂, and rGO sheets stacked in a disordered fashion. Field emission scanning electron microscopy (FE-SEM) characterization indicates that the form of the Fe₃O₄@SiO₂ core-shell structures is spherical, with an average size of about 25 nm. Magnetic hysteresis loops reveal the super-paramagnetic behavior of the samples at room temperature. All of the results obtained confirm the synthesis of high-quality nanocomposites, which can be a good candidate for use as a catalyst in multi-component reactions.

Synthesis of phenol esters by direct C–H activation of aldehydes using a highly efficient and reusable copper-immobilized polyimide covalent organic framework (Cu@PI-COF)

In the present study, we report the design and fabrication of a thermally and chemically stable copper-based polyimide covalent organic framework (Cu@PI-COF) via a facile and straightforward synthetic approach for the oxidative esterification of aldehydes.