Magnetically Separable Nanocatalysts: Bridges between Homogeneous and Heterogeneous Catalysis

Anisotropically structured magnetic aerogel monoliths

Texturing of magnetic ceramics and composites by aligning and fixing of colloidal particles in a magnetic field is a powerful strategy to induce anisotropic chemical, physical and especially mechanical properties into bulk materials. If porosity could be introduced, anisotropically structured magnetic materials would be the perfect supports for magnetic separations in biotechnology or for magnetic field-assisted chemical reactions. Aerogels, combining high porosity with nanoscale structural features, offer an exceptionally large surface area, but they are difficult to magnetically texture. Here we present the preparation of anatase-magnetite aerogel monoliths via the assembly of preformed nanocrystallites. Different approaches are proposed to produce macroscopic bodies with gradient-like magnetic segmentation or with strongly anisotropic magnetic texture.

Magnetic composite BiOCl-SrFe12O19: a novel p-n type heterojunction with enhanced photocatalytic activity

The magnetic composite BiOCl-SrFe12O19, a novel p-n type heterojunction was synthesized by hydrolysis with a medium temperature sintering method. The microstructure and magnetic properties of the prepared material were characterized by FTIR, XRD, SEM, TEM, HRTEM, SAED, and VSM. The results showed the [001] facet of BiOCl with high photocatalytic activity was exposed in the BiOCl-SrFe12O19. The heterostructured BiOCl-SrFe12O19 had better magnetic properties, contributing to its reuse and improvement in photocatalysis. Moreover, the composite was blessed with excellent photocatalytic activity and stability. In the BiOCl-SrFe12O19 system, SrFe12O19 not only inhibited the growth of BiOCl along the [001] direction to enhance the exposure of the [001] wafer, but also acted as a sensitizer absorbing light irradiation. The magnetic field generated from SrFe12O19 made BiOCl, under light irradiation, produce more photo-induced electrons and holes and simultaneously hampered their recombination. For the first time we propose the possible mechanism of how to enhance photocatalytic activity by a magnetic field effect originating from the magnetic photocatalyst itself.

Recycling nanoparticle catalysts without separation based on a pickering emulsion/organic biphasic system

A conceptually novel methodology is explored for in situ recycling of nanoparticle catalysts based on transforming a conventional organic/aqueous biphasic system into a Pickering emulsion/organic biphasic system (PEOBS). The suggested PEOBS exists as two phases, with the nanoparticle catalyst "anchored" in the Pickering emulsion phase, but is "continuous" between the organic phase and the continuous phase of the Pickering emulsion. Aqueous hydrogenations are used to evaluate the reaction performances of PEOBS, and the underlying principles of PEOBS are preliminarily elaborated. The unique properties of PEOBS lead to many intriguing findings, which are unlikely to be achieved in the reported biphasic systems. PEOBS exhibits more than a fourfold enhancement in catalysis efficiency in comparison with a conventional biphasic system. Impressively, PEOBS enables the organic product to be facilely isolated through simple decantation and the nanoparticle catalyst can be recycled in situ without the need for "separation". Its recycling effectiveness is justified by ten reaction cycles without significant catalyst loss. The simple protocol, in conjunction with the stability to simultaneously achieve high catalysis efficiency and excellent catalyst recyclability, makes PEOBS a promising methodology to develop more sustainable nanocatalysis.

Multifunctional ScF3:Ln3+ (Ln = Tb, Eu, Yb, Er, Tm and Ho) nano/microcrystals: hydrothermal/solvothermal synthesis, electronic structure, magnetism and tunable luminescence properties

A facile, hydrothermal/solvothermal route has been developed to synthesize a series of multifunctional lanthanide ion (Tb(3+), Eu(3+), Yb(3+), Tm(3+), Er(3+) and Ho(3+))-activated ScF3 nanocrystals. The morphology and size of ScF3 can be tuned in a controlled manner by altering the additives and volume ratios of H2O : EtOH in the initial solution. Under ultraviolet (UV), vacuum ultraviolet (VUV) or low-voltage electron-beam excitation, the as-obtained Tb(3+), Eu(3+) codoped ScF3 product exhibits multicolor photoluminescence (PL) and cathodoluminescence (CL), and possible luminescence mechanisms are discussed. Moreover, under 980 nm excitation, upconversion (UC) emissions have been achieved in Yb(3+)-Er(3+), Yb(3+)-Tm(3+), and Yb(3+)-Ho(3+) codoped ScF3. Ferromagnetic property of ScF3 is detected due to the nanocrystal defects. The results obtained indicate that the lanthanide ion-doped ScF3 nanocrystals exhibit multicolor UV/VUV PL, CL, and UC luminescence as well as ferromagnetic properties. Thus, they may have potential applications in PL areas, field emission display devices, bioseparation and magnetic resonance imaging.

Direct synthesis of MOF-derived nanoporous carbon with magnetic Co nanoparticles toward efficient water treatment

Nanoporous carbon particles with magnetic Co nanoparticles (Co/NPC particles) are synthesized by one-step carbonization of zeolitic imidazolate framework-67 (ZIF-67) crystals. After the carbonization, the original ZIF-67 shapes are preserved well. Fine magnetic Co nanoparticles are well dispersed in the nanoporous carbon matrix, with the result that the Co/NPC particles show a strong magnetic response. The obtained nanoporous carbons show a high surface area and well-developed graphitized wall, thereby realizing fast molecular diffusion of methylene blue (MB) molecules with excellent adsorption performance. The Co/NPC possesses an impressive saturation capacity for MB dye compared with the commercial activated carbon. Also, the dispersed magnetic Co nanoparticles facilitate easy magnetic separation.