Synthesis And Growth Mechanism Of Carbonates Under Synergetic Control Of Polyelectrolyte And Interface Effect

In this dissertation, the basic mechanisms in biomineralization process and the state of the art of carbonates biomimetic mineralization have been firstly reviewed, focusing on mediation over the nucleation and growth of carbonates exerted by several parameters. Based on previous achievements, combining the synergetic control of interface, solvent mixture and polyelectrolyte, we have further developed and enriched the controlled synthesis of CaCO₃ and FeOOH minerals. A series of inorganic and inorganic-organic composite materials with novel morphologies, stable polymorphs and complicated architectures have been successfully synthesized by altering reaction conditions. Then, we have further deeply studied and discussed the polymorphs selection, growth mechanisms and properties of these as-prepared materials. The detailed research fruits are summarized as follows:1. Using polyelectrolyte polyacrylic acid (PAA) and electrospun cellulose acetate (CA) fiber scaffold as crystal growth modifier and template respectively, uniform CaCO₃ film coatings composed of different building blocks have been successfully synthesized on each CA fibers by altering the concentration of PAA and mineralization time. This coating process improved the hardness of the scaffold to some extent while maintaining their previous frameworks. After the CaCO₃@CA composite treated with acetone, macroscopic CaCO₃ bulk materials with complex network structures consisting of a great deal of microtubes has been successfully prepared. Especially, it is worth to note that the synergetic control between the inhibiting effects of PAA and the templating effects of CA fibers played crucial role in inducing the formation of uniform CaCO₃ film coatings. Besides, with extended incubation time, the first deposited CaCO₃ film coatings would act as secondary substrates leading to the growth of thinner fibrous calcite mesocrystals. This work also provided a novel prove that a relatively high mismatch between organic and inorganic counterparts is tolerated when inorganic crystals growth occurs at organic interface.2. By introducing natural plant membrane into mineralization system, we further studied its synergy with solvent mixture and polyelectrolyte on the crystallization behavior of CaCO₃. The mineralization process of CaCO₃ was carried out by a double diffusion technology in water-ethanol solvent mixture with Allium fistulosum L. bulb inner membrane and PAA acting as ion-exchange membrane and crystal growth modifier respectively. By adjusting different surface of bulb membrane, concentration of PAA, volume ratio of water-ethanol and initial pH value, several CaCO₃ crystals with novel structures can be obtained, such as ultralong ribbon, macroscopic blossom, thin film, spiny sphere and shuttle. The bulb inner membrane, acting as both ion-exchange membrane and depositing interface, can provide CaCO₃ crystals with a large amount of nucleation sites. What is more, this novel synthesis route involving biological systems can be extended to the controlled growth of other inorganic and inorganic-organic composite materials.3. The synergy of solvent mixture and polyelectrolyte over the balance between thermodynamic control and kinetic control in CaCO₃ crystallization process has been investigated. In the presence of PSS, the switch from thermodynamic control to kinetic control in CaCO₃ crystallization process has been realized by increasing the content of ethanol in water-ethanol mixed solvent, which can be displayed by significant variations of the final morphologies and polymorphs of target mineral. Calcite mesocrystals and vaterite complex aggregates with different growth forms and developmental phases can be obtained. The phase transition of CaCO₃ from pure calcite to calcite dominated mixture and finally to vaterite dominated mixture has also been nicely captured. Thus, the addition of simple alcohols can balance the competition of thermodynamic control versus kinetic control in inorganics crystallization process, resulting in effective control over their morphologies, polymorphs and organized structures.4. Biomimetic mineralization routes have been applied to other inorganic materials except for CaCO₃. Using PAA as crystal growth modifier, large scale synthesis of FeOOH nanostructure array films have been achieved at air-water interface at ambient conditions. With the increase of PAA content, the building blocks making up FeOOH array films mainly underwent a morphological transformation of"flake—rice spike—branched fiber—fine fibers". Distinct microstructures can endow FeOOH film with different hydrophobicities. The film composed of nanoflakes exhibited superhydrophobicity with a contact angle of 163°. The uptake capacity of FeOOH for Cd²⁺ from water can also be influenced by microshapes. The fibrous sample displayed largest Cd²⁺ removal capacity, up to 95 % when the pH value is 9.64. Thus, by selecting suitable precursor ions, a variety of functional inorganic materials with novel structures and outstanding properties can be prepared through biomimetic mineralization routes.