title: Hierarchical Formation Mechanism of CoFe2O4 Mesoporous Assemblies.
abstract: The development of synthetic hybrid organic-inorganic approaches and the understanding of the chemico-physical mechanisms leading to hierarchical assembly of nanocrystals into superstructures pave the way to the design and fabrication of multifunction microdevices able to simultaneously control processes at the nanoscale. This work deals with the design of spherical mesoporous magnetic assemblies through a surfactant assisted water-based strategy and the study of the formation mechanism by a combined use of transmission electron microscopy, X-ray diffraction, and time-resolved small angle X-ray scattering techniques. We visualize the hierarchical mechanism formation of the magnetic assemblies in the selected sodium dodecylsulfate (SDS)-assisted water-based strategy. At the first stage, an intermediate lamellar phase (L) represented by β-Co(OH)2 and FeOOH hexagonal plates is formed. Then, the nucleation of primary CoFe2O4 (N1) nanocrystals of about 6-7 nm occurs by the dissolution of FeOOH and the reaction of Fe(III) ions coordinated to the SDS micelles, at the reactive sites provided by vertices and edges of the β-Co(OH)2 plates. The intermediate phase consumes as the primary crystalline nanoparticles form, confined by the surfactant molecules around them, and assembly in spherical mesoporous assemblies. The key role of the surfactant in the formation of porous assemblies has been evidenced by an experiment carried out in the absence of SDS and confirmed by the pore size diameter of the assemblies (about 2-3 nm), that can be correlated with the length of the surfactant dodecylsulfate molecule.
authors.forename: Carla
authors.initials: C
authors.lastname: Cannas
authors.forename: Andrea
authors.initials: A
authors.lastname: Ardu
authors.forename: Anna
authors.initials: A
authors.lastname: Musinu
authors.affiliation: §CNR-Istituto di Struttura della Materia, Via Salaria, Km 29.300, Monterotondo Stazione, RM I-00015, Italy.
authors.forename: Lorenza
authors.initials: L
authors.lastname: Suber
authors.affiliation: ∥Istituto di Fisica, Università Cattolica del Sacro Cuore, Largo F. Vito 1, 00168, Roma, Italy.
authors.forename: Gabriele
authors.initials: G
authors.lastname: Ciasca
authors.affiliation: ⊥Sincrotrone ELETTRA, S.S.14, km 163,5 in AREA Science Park, 34012 Basovizza, Trieste, Italy.
authors.forename: Heinz
authors.initials: H
authors.lastname: Amenitsch
authors.affiliation: #CNR-Istituto di Cristallografia, Via Salaria, Km 29.300, Monterotondo Stazione, RM I-00015, Italy.
authors.forename: Gaetano
authors.initials: G
authors.lastname: Campi
keywords: in situ time-resolved SAXS; mechanism; mesoporous assemblies; nanoparticle synthesis; spinels; surfactants