Nanoparticle-free magnetic mesoporous silica with magneto-responsive surfactants

Abstract

Magneto-responsivity can be imprinted in hard mesoporous silica materials using soft colloidal templates formed by magnetic surfactants. The materials exhibit a low to high spin transition due to geometrical constraints of the isolated iron ions grafted on the silica walls.While metallosurfactants have been known for many years 1 and are already used in the eld of catalysis, sensing, 2 or for biomedical applications, 3 only recently the magnetic properties of surfactants bearing magneto-responsive centers (Fe, Gd, Ho, and Ce) have been demonstrated. 4 The magnetic responsiveness of these surfactants is fundamentally different from molecular magnets or ferrouids, arising from electronic and molecular spin, associated with the ordering in the selfassembled architectures. Magneto-surfactants (MAGS) have been used to date as novel molecular tools in designing magnetic colloids such as microemulsions 5 or emulsions 6 and were proposed for potential applications in elds that require interfacing magnetic materials, i.e. information storage, electronic or spintronic devices. Moreover, due to the absence of metallic nanoparticles that are subjected to strict regulation as hazardous products, MAGS are suitable for biomedical (i.e. MRI contrast agents or hyperthermia probes) or for environmental applications (i.e. recovery of heavy metals).For the rst time, we show the application of magnetic surfactants for the preparation of nanoparticle-free magnetic mesoporous silica (MMS) materials. In this case MAGS are used as both template and magnetic source for the design of magnetic hard matter. Indeed, imprinting mesoporous silica materials with magnetic properties is of great fundamental interest since it combines high surface area and pore volume with magnetic responsiveness. MMS may have applications in catalysis, 7 sensing, 8 separation 8c,9 or biomedical elds for simultaneous MR imaging and targeted drug delivery. 10 While the structuring of inorganic matter with surfactants was extensively investigated, the magnetisation of the inorganic matter with surfactants is a new concept. Moreover, to date magnetic mesoporous silica are only formed from magnetic nanoparticles embedded into mesoporous silica 11 through multi-step syntheses and their main drawbacks are the inhomogeneities of the nal material. Here, we propose a straightforward method based on the sol-gel procedure, by using a magneto-surfactant as a structure directing agent and a source of magnetic responsiveness.Moreover, since the magnetic centres are homogeneously distributed in the micellar shells, which directly interact with the silica precursors, it is reasonable to assume they are also found evenly distributed in the pore channels of the resulting MMS materials. 1a,b,d The surfactant used in this study is cetyltrimethylammoniumtrichloromonobromoferrate, CTAF, and it was prepared simply from the common surfactant cetyltrimethylammonium bromide, CTAB and a stoichiometric amount of paramagnetic FeCl 3 (see ESI †). CTAF is an ionic liquid with a melting...

Metallo-Solid Lipid Nanoparticles as Colloidal Tools for Meso–Macroporous Supported Catalysts

“…26 Briefly, 1.77 g of FeCl3 (11.0 mol) was added to 4.0 g of CTAB (11.0 mmol) that was already dissolved in 50 mL of methanol. Then, the solution was heated to reflux overnight.…”

“…analysis was performed using an Online TOC-VCSH Total Organic Carbon Analyzer (Shimadzu, Japan). 26 Solid lipid nanoparticles were prepared from cetylpalmitate, pluronic P123 and CTAF by the ultra-sonication of hot emulsions followed by solidification. By adding TMOS, the dispersions were mineralized through a dual templating mechanism combining micellar cooperativity and templating with the SLNs.…”

Magnetic surfactants

“…Stébé et al imprinted hard mesoporous silica with magneto-responsivity by using soft colloidal templates formed by magnetic surfactants (Figure 7) [65]. While structuring inorganic material with surfactants is well established [65], this concomitant magnetization is a new concept.…”

“…While structuring inorganic material with surfactants is well established [65], this concomitant magnetization is a new concept. Such materials are of fundamental interest as they combine high surface area and pore volume with magnetic responsivity with potential applications in catalysis and separations, as well as for simultaneous MR imaging and drug delivery [66].…”

Magnetic and Phase Behavior of Magnetic Water‐in‐Oil Microemulsions

“…Over the past 5 years magnetic surfactants have found demonstrated application ranging from protein separations [4] and DNA manipulation [5], to water remediation [6] and soft colloidal templates [7].…”