Induced Synthesis And Application Of Brucite-based Micro-nano Materials

Magnesium-containing micro-nano materials have been one of the focuses since human beings stride into nanometer era due to their size effect and specific morphology. Controllable fabrication and high performance application have been extensively reported. However, magnesium in magniferous micro-nano materials almost derive from soluble magnesium salts, such as magnesium chloride, magnesium nitrate and magnesium sulfate, which results in complicated and high-cost synthesis. In contrast, natural brucite, highest magnesium-containing in the nature, has been neglected all the time. To date, utilization of brucite remains rough application, such as MgO product by calcination and agents for neutralization. Direct synthesis of fine micro-nano materials from brucite without further dissolution and purification has been rarely reported. In this doctoral thesis, combining the recent nanotechnology and structural nature of brucite, we hope to develop a series of brucite-based micro-nano materials through induced method, to discuss their formation mechanism and roles of induced agents, and to improve the properties of Mg(OH)2 flame retardants (FRs) prepared by in-situ hybrid method in polyolefin matrix.Stable brucite undergoes disaggregation (or coordination) into thin nanosheets (primary crystal nucleus) and subsequent solid-solid transformation in the presence of particular organic molecules, circumvents the threshold of size effect from bulk brucite to Mg(OH)2 nanoplates with uniform morphology. FTIR, XRD, TG/TGA and NMR have been employed to characterize the product and organic molecules in solution, which indicates the organic molecules would not be incorporated into Mg(OH)2 nanoplates. Meantime, experimental results verified the mother solution with organic molecules could be recycled to synthesize Mg(OH)2 nanoplates. Based on the analysis mentioned above and TEM images, the formation mechanism of Mg(OH)2 nanoplates from bulk brucite without dissolution has been proposed. It is demonstrated that the molecules with ringed groups play a controllable role in the formation of hexagonal Mg(OH)2 nanoplates, which could be attributed to theπ-πinteraction between ringed groups.A series of basic magnesium salts can be obtained through anion directly inducing brucite. Flower-like and urchin-like MgBO2(OH) could be directly synthesized by brucite particles and boric acid under appropriate hydrothermal condition. Similar shaped Mg3B2O6 would be obtained by calcination at 650℃for 3 h. In addition, it is found that variable architectures of Mg3B2O6:Eu3+ from flower-like to urchin-like displayed tunable emission 592 nm (5D0→7F1) to 611 nm (5D0→7F2) through the altering of symmetry of the crystal field around Eu3+ ions. Carnation-like basic magnesium carbonate was fabricated via brucite powder and carbonic acid. With the reaction going along, cubic magnesium carbonate without crystal water would be obtained. The whiskers of magnesium phosphate hydroxide and magnesium sulfate hydroxide (Mg1.33SO4(OH)o.66·0.33H20) can be fabricated through brucite and monobasic sodium phosphate and magnesium sulfate under hydrothermal condition, respectively.In the synthesis process of magnesium-containing micro-nano materials by anion inducing brucite, partial hydroxide groups may be substituted by anionic groups through acid-base neutralization. The lattice of the brucite substituted by anionic groups would be further restructured under hydrothermal condition, which resulting in the growth direction of crystal could be tuned to another one. In comparison with the morphology of brucite-based products and corresponding anionic configuration, the effect of anionic groups on the morphology of micro-nano materials has been proposed:planar configuration of borate and carbonate anions is according with the planar shape of MgBO2(OH) and Mg5(CO3)4(OH)2·4H2O. When the phosphate and sulfate anions with tridimensional configuration are introduced into brucite-based micro-nanoparticles, crystal morphology would display tridimensional feature.An unconventional method for controlling nanostructures evolution from lamellar to rose-like, then to torispherical has been successfully developed through introducing diverse valent cations (Zn2+, Al3+, Sn4+). It is believed that the contribution of different cations on lattice distortion is hierarchical due to the distinction of their chemical bonding configuration and radius. Distinct lattice distortion induced by that invasive cations substitute some Mg2+ which easily leads to the polytypism or heterostructure emerged in nanostructure, would be responsible for the morphology transformation of metal hydroxide. Unconspicuous distortion resulted from isomorphic substitution could play a role of conservation rather than modification in nanostructure control.Organic acid@Mg(OH)2 and N-P-Mg all-in-one FR have been prepared by in-situ hybrid modification, respectively. Compared with Silane coupling agent@Mg(OH)2, organic acid@ Mg(OH)2 products, N-P-Mg all-in-one FR exhibited the best performance in POE on both compatibility and fire resistance when all filling amount is 50%. The tensile strength, elongation at break and LOI were improved to 16.6 MPa,858% and 33, respectively.