Spindle-shaped nanoscale yolk/shell magnetic stirring bars for heterogeneous catalysis in macro- and microscopic systems

Recent progress of functional metal-organic framework materials for water treatment using sulfate radicals

Human health is being threatened by the ever-increasing water pollution. Sulfate radical (SO₄^•-)-based advanced oxidation processes (SR-AOPs) are rapidly being developed and gaining considerable attention due to their high oxidation potential and selectivity as a way to purify water by degrading organic contaminants in it. Among the catalytic materials that can activate the precursor to generate SO₄^•-, metal-organic frameworks (MOFs) are the most promising heterogeneous catalytic material in SR-AOPs because of their various structure possibilities, large surface area, ordered porous structure, and regular activation sites. Herein, an in-depth overview of MOFs and their derivatives for water purification with SR-AOPs is provided. The latest studies on pristine MOFs, MOF composites, and MOF derivatives (metal oxides, metal-carbon hybrids, and carbon materials) are summarized. The mechanisms of decomposition of pollutants in water via radical and non-radical pathways are also discussed. This review suggests future research directions for water purification through MOF-based SR-AOP.

Fabrication of multifunctional integrated catalysts by decorating confined Ag nanoparticles on magnetic nanostirring bars

Catalysis benefits from biomimetic materials with sophisticated structures because a variety of functions can be integrated into one structure, satisfying the demands of a diverse range of applications. Magnetic catalysts have been widely used in various applications, but the magnetic components are most commonly used for recycling. In this study, we report the fabrication of magnetic nanocatalysts composed of a support of magnetic nanobars and Ag nanoparticles confined between two silica layers. Notably, the catalysts are constructed as nanoscale stirring bars that are able to generate disturbances at this scale. More importantly, the catalysts can be applied in both macro- and micro-systems, effectively addressing the conventional mixing method. The catalysts can then be conveniently separated from the system after use. The performances of magnetic nanoscale catalysts are well maintained through recycling.

Enhancing reaction rate in a Pickering emulsion system with natural magnetotactic bacteria as nanoscale magnetic stirring bars

Pickering emulsion is emerging as an advanced platform for catalysis because of the large oil/water interface area for reaction and its superior efficiency. How to enhance the mass transportation within the micro-droplets is the biggest obstacle in further improving the efficiency of the Pickering emulsion system. In this study, we propose and solve this problem for the first time using natural magnetotactic bacteria as nanoscale magnetic stirring bars, which can be encapsulated into each micro-droplet and used to stir the solution to accelerate the mass transportation under an external magnet, and thus significantly enhance the reaction rate of Pickering emulsion. Taking the epoxidation of cyclooctene in the Pickering emulsion system as a demonstration, the reaction rate was enhanced three times with nanoscale magnetic stirring bars compared to that of traditional Pickering emulsion, and was even thirty times higher than that of conventional stirrer-driven biphasic systems. We envision that this strategy will bring biphasic reactions with fundamental innovations toward more green, efficient and sustainable chemistry.

A general route to coat poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) on various substrates and the derived N, P, S-doped hollow carbon shells for catalysis

The construction of core-shell structures through surface coating, and then making use of the synergistic effects between the core and shell to design and synthesize heterogeneous catalysts is a hot topic in the heterogeneous catalysis field. Developing a general coating route with functional shell materials is further highly desirable. Here we found that a poly(cyclotriphosphazene-co-4,4'-sulfonyldiphenol) (PZS) layer can be generally coated on various substrates with different components and morphologies, including metal oxides, noble metal nanoparticles, carbon materials and metal-organic frameworks (MOFs). In addition, the coating thickness could be well controlled through simply adjusting the amount of monomers. Taking advantage of the heteroatoms in the PZS layer and the synergistic effect between the core and shell, new methods for fabrication of co-doped hollow carbon shell catalysts and transition metal phosphide nanoparticles were developed. As a proof-of-concept application, the N, P, S-doped hollow carbon shells prepared by calcination of a ZnCo-ZIFs@PZS core-shell structure could act as a good carbo-catalyst for selective oxidation of C-H bonds in water.

Fabrication of Ellipsoidal Silica Yolk-Shell Magnetic Structures with Extremely Stable Au Nanoparticles as Highly Reactive and Recoverable Catalysts

A novel strategy was reported for the fabrication of yolk-shell magnetic MFSVmS-Au nanocomposites (NCs) consisting of double-layered ellipsoidal mesoporous silica shells, numerous sub-4 nm Au nanoparticles (NPs), and magnetic Fe central cores. The hierarchical FSVmS NCs with ellipsoidal α-Fe₂O₃@mSiO₂/mSiO₂ as yolks/shells were first prepared through the facile sol-gel template-assisted method, and plenty of extremely stable ultrafine Au NPs were postencapsulated within interlayer cavities through the unique deposition-precipitation method mediated with Au(en)₂Cl₃ compounds. Notably, ethylenediamine ligands were used to synthesize the stable cationic complexes, [Au(en)₂]³⁺, that readily underwent the deprotonation reaction to chemically modify negatively charged mesoporous silica under alkaline conditions. The subsequent two-stage programmed hydrogen annealing initiated the in situ formation of Au NPs and the reduction of α-Fe₂O₃ to magnetic Fe, where the synthesized Au NPs were highly resistant to harsh thermal sintering even at 700 °C. Given its structural superiority and magnetic nature, the MFSVmS-Au was demonstrated to be a highly efficient and recoverable nanocatalyst with superior activity and reusability toward the reduction of 4-nitrophenol to 4-aminophenol, and the pristine morphology was retained after six recycling tests.

Synthesis of double-shell hollow magnetic Au-loaded ellipsoids as highly active and recoverable nanoreactors

A schematic for the synthesis of double-shell magnetic Au-loaded ellipsoids (Fe@MO₂–Au@H–SiO₂) and the reaction mechanism for the catalytic reduction of 4-NP.

Noncontact Synergistic Effect between Au Nanoparticles and the Fe2O3 Spindle Inside a Mesoporous Silica Shell as Studied by the Fenton-like Reaction

An Au-Fe₂O₃@mesoporous SiO₂ nanoreactor with a multiyolks/shell structure was synthesized through a multistep method. In this nanoreactor, the spindle Fe₂O₃ and Au nanoparticles were inside the same mesoporous SiO₂ shell as the yolks but in a noncontact manner. The noncontact synergistic effect between Au nanoparticles and the Fe₂O₃ spindle was studied with a Fenton-like reaction. The catalytic activity of the Au-Fe₂O₃@mesoporous SiO₂ nanoreactor to the Fenton-like reaction for the degradation of organic dyes was dramatically enhanced by the noncontact synergistic effect.

Yolk–shell structured CoFe2O4 microspheres as novel catalysts for peroxymonosulfate activation for efficient degradation of butyl paraben

Three-dimensional yolk–shell structured CoFe₂O₄ microspheres were successfully fabricated to activate peroxymonosulfate (PMS) for efficiently catalytic degradation of butyl paraben (BPB) in wastewater.

A Pd–Cu2O nanocomposite as an effective synergistic catalyst for selective semi-hydrogenation of the terminal alkynes only

A new type lead-free Pd–Cu₂O nanocomposite catalyst shows “double” selectivities for hydrogenation of alkynes: only terminal alkynes hydrogenated and only alkenes produced, i.e. no internal alkyne is hydrogenated.