Efficient occlusion of oil droplets within calcite crystals

Interfacial Supra-Assembly of Copolymer Nanoparticles Enables the Formation of Nanocomposite Crystals with a Tunable Internal Structure

It is highly desirable but technically challenging to precisely control the spatial composition and internal structure of crystalline nanocomposite materials, especially in a one-pot synthetic route. Herein, we demonstrate a versatile pathway to tune the spatial distribution of guest species within a host inorganic crystal via an incorporation strategy. Specifically, well-defined block copolymer nanoparticles, poly(methacrylic acid)x-block-poly(styrene-alt-N-phenylmaleimide)y [PMAAx-P(St-alt-NMI)y], are synthesized by polymerization-induced self-assembly. Such anionic nanoparticles can supra-assemble onto the surface of larger cationic nanoparticles via an electrostatic interaction, forming colloidal nanocomposite particles (CNPs). Remarkably, such CNPs can be incorporated into calcite single crystals in a spatially controlled manner: the depth of CNPs incorporation into calcite is tunable. Systematic investigation indicates that this interesting phenomenon is governed by the colloidal stability of CNPs, which in turn is dictated by the PMAAx-P(St-alt-NMI)y adsorption density and calcium ion concentration. This study opens up a general and efficient route for the preparation of a wide range of crystalline nanocomposite materials with a controlled internal composition and structure.

Multi-Functionalization of Single crystals Mediated by Gel-Incorporation: A Bioinspired Strategy

Biominerals are inherently organic-inorganic crystal composites. Drawing inspiration from this biomineral structure, functionalized single crystals can be synthesized using the gel-grown method, resulting in the incorporation of gel-networks into the host crystals. By incorporating gel-networks, diverse guest materials, such as nanoparticles and dye molecules, can be uniformly and isotropically distributed within the crystals, thereby imparting non-intrinsic optical or magnetic properties to the host crystals. Additionally, gel-incorporation enhances the toughness and stability of the crystals as the incorporated gel-fibers and accompanying guest materials act as bridges to prevent crack propagation. Furthermore, gel-incorporation enables protein crystals to exhibit self-healing properties, which can be attributed to the dynamic bonding interaction between gel-networks and crystals. Notably, recent research has demonstrated that the incorporation of zwitterionic gel-networks enhances the charge effects on crystal morphology evolution as the charged groups become bound to the developing crystal surfaces, and their detachment is impeded by the interconnected gel-networks. Therefore, preparing single crystals with gel-incorporation is a remarkable strategy for synthesizing functionalized crystal materials.

Synergistic Effect of Hydroxyl and Carboxyl Groups on Promoting Nanoparticle Occlusion within Calcite

Direct occlusion of guest nanoparticles into host crystals enables the straightforward preparation for various of nanocomposite materials with emerging properties. Therefore, it is highly desirable to elucidate the 'design rules' that govern efficient nanoparticle occlusion. Herein, a series of sterically-stabilized nanoparticles are rationally prepared, where the surface stabilizer chains of such nanoparticles are composed of either poly(methacrylic acid), or poly(glycerol monomethacrylate), or poly((2-hydroxy-3-(methacryloyloxy)propyl)serine). Systematic investigation reveals that hydroxyl groups and carboxyl groups play a synergistic role in driving nanoparticle incorporation into calcite crystals, where the hydroxyl groups enhance colloidal stability of the nanoparticles and the carboxyl groups provide binding sites for efficient occlusion. The generality of these findings is further validated by extending it to polymer-stabilized gold nanoparticles. This study demonstrates that precision synthesis of polymer stabilizers comprising of synergistic functional groups can significantly promote nanoparticle occlusion, thus enabling the efficient construction of organic-inorganic hybrid materials via nanoparticle occlusion strategy.

Metal-Organic Frameworks@Calcite Composite Crystals

The direct incorporation of guest crystals into another type of host crystals during the formation of the latter is technically challenging due to the large difference in surface energy for different crystalline components. Nevertheless, we herein demonstrate that metal-organic frameworks (MOFs, UiO-66-NH₂ as a model guest crystal) after postsynthetic modification with poly(methacrylic acid) can be efficiently incorporated into calcite single crystals, forming a unique composite structure where the MOF crystals are uniformly distributed throughout the whole calcite host crystals. Remarkably, such MOF@calcite composite crystals exhibit superior performance in fluoride removal compared with the MOF or calcite alone. Moreover, this incorporation strategy is general as it can be extended to other guest particles. In principle, this study opens up a versatile avenue for the rational design and preparation of a wide range of hybrid functional materials with controllable compositions and enhanced physicochemical properties.

Micron-sized biogenic and synthetic hollow mineral spheres occlude additives within single crystals

Incorporating additives within host single crystals is an effective strategy for producing composite materials with tunable mechanical, magnetic and optical properties. The type of guest materials that can be occluded can be limited, however, as incorporation is a complex process depending on many factors including binding of the additive to the crystal surface, the rate of crystal growth and the stability of the additives in the crystallisation solution. In particular, the size of occluded guests has been restricted to a few angstroms – as for single molecules – to a few hundred nanometers – as for polymer vesicles and particles. Here, we present a synthetic approach for occluding micrometer-scale objects, including high-complexity unicellular organisms and synthetic hollow calcite spheres within calcite single crystals. Both of these objects can transport functional additives, including organic molecules and nanoparticles that would not otherwise occlude within calcite. Therefore, this method constitutes a generic approach using calcite as a delivery system for active compounds, while providing them with effective protection against environmental factors that could cause degradation.

Occlusion of micron-sized algae cells and calcitic hollow spheres within calcite single crystals, mediated by the positively charged polymer poly(allylamine hydrochloride). Both objects are used to transport functional additives to the host lattice.

Polymer-Inorganic Crystalline Nanocomposite Materials via Nanoparticle Occlusion

Efficient occlusion of guest nanoparticles into host single crystals opens up a straightforward and versatile way to construct functional crystalline nanocomposites. This new technique has attracted increasing research interest because it enables the composition, structure and property of the resulting nanocomposites to be well-controlled. In this review article, we aim to provide a comprehensive summary of nanoparticle occlusion within inorganic crystals. First, we summarize recently-developed strategies for the occlusion of various colloidal particles (e.g., diblock copolymer nanoparticles, polymer-modified inorganic nanoparticles, oil droplets, etc.) within host crystals (e.g., CaCO₃ , ZnO or ZIF-8). Second, new results pertaining to spatially-controlled occlusion and the physical mechanism of nanoparticle occlusion are briefly discussed. Finally, we highlight the physicochemical properties and potential applications of various functional nanocomposite crystals constructed via nanoparticle occlusion and we also offer our perspective on the likely future for this research topic. This article is protected by copyright. All rights reserved.

Generality of liquid precursor phases in gas diffusion-based calcium carbonate synthesis

We confirm the presence of liquid calcium carbonate precursor species in absence of additives in gas diffusion systems.

Particle-attachment crystallization facilitates the occlusion of micrometer-sized Escherichia coli in calcium carbonate crystals with stable fluorescence

Inspired from the occlusion of macromolecules in mineral crystals during the biomineralization process, the occlusion mechanism of functional guest species into a host matrix is gradually revealed in artificial systems. However, the guest species within calcite crystals are limited to the nanometer scale. Herein, using amorphous calcium carbonate (ACC) as a precursor and taking advantage of the crystallization of vaterite by the attachment of ACC nanoparticles, micrometer-sized modified Escherichia coli (E. coli) was incorporated into vaterite crystals. The occlusion content of bacteria within the vaterite crystal could reach up to 16 wt%. On the contrary, the occlusion of E. coli into calcite crystals, which proceeded via ion-by-ion addition growth, was only confined to the surface layer. Through modifying the surface structure or chemical composition of bacteria, the strong interaction between the surface of the bacteria and calcium carbonate has proved to be the key factor for successful occlusion. Interestingly, the genetically modified green fluorescent protein (GFP)-E. coli/vaterite composites exhibited stable fluorescence for more than six months with little attenuation and the lifetime could be more than 1.2 μs. It was demonstrated that a combination of the amorphous precursor crystallization pathway and a suitable surface structure of the foreign species can significantly enhance the occlusion efficiency of micrometer-sized species in crystals.

Exerting Spatial Control During Nanoparticle Occlusion within Calcite Crystals

In principle, nanoparticle occlusion within crystals provides a straightforward and efficient route to make new nanocomposite materials. However, developing a deeper understanding of the design rules underpinning this strategy is highly desirable. In particular, controlling the spatial distribution of the guest nanoparticles within the host crystalline matrix remains a formidable challenge. Herein, we show that the surface chemistry of the guest nanoparticles and the [Ca²⁺ ] concentration play critical roles in determining the precise spatial location of the nanoparticles within calcite crystals. Moreover, in situ studies provide important mechanistic insights regarding surface-confined nanoparticle occlusion. Overall, this study not only provides useful guidelines for efficient nanoparticle occlusion, but also enables the rational design of patterned calcite crystals using model anionic block copolymer vesicles.

Efficient Occlusion of Nanoparticles within Inorganic Single Crystals

In principle, the incorporation of guest nanoparticles within host crystals should provide a straightforward and versatile route to a wide range of nanocomposite materials. However, crystallization normally involves expelling impurities, so nanoparticle occlusion is both counter-intuitive and technically challenging. Clearly, the nanoparticles should have a strong interaction with the growing crystalline lattice, but quantifying such an affinity has been challenging; the basic principles that govern efficient nanoparticle occlusion within inorganic single crystals are rather poorly understood. In the past few years, we have focused on the elucidation of robust design rules for such systems; our progress is summarized in this article.Polymerization-induced self-assembly (PISA) is widely recognized as a powerful platform technology for the preparation of a broad range of model organic nanoparticles. Herein, PISA was exploited to prepare sterically stabilized diblock copolymer nano-objects (e.g., spheres, worms, or vesicles) of varying size using steric stabilizers of well-defined chain length, variable anionic charge density, tunable surface density, and adjustable chemical functionality (e.g., carboxylic acid, phosphate, sulfate or sulfonate groups). Thus, we were able to systematically investigate how such structural parameters influence nanoparticle occlusion. Given its commercial importance for many industrial sectors, calcium carbonate was selected as the model host crystal for nanoparticle occlusion studies. Perhaps surprisingly, the extent of nanoparticle occlusion is not particularly sensitive to nanoparticle size or morphology. However, the steric stabilizer chain length can play a key role: relatively short chains lead to surface-confined occlusion, while sufficiently long chains enable uniform nanoparticle occlusion to be achieved throughout the crystal lattice (albeit sometimes inducing a significant change in crystal morphology). Optimizing the anionic charge density and surface density of the stabilizer chains is required to maximize the extent of nanoparticle occlusion, while steric stabilizer chains comprising anionic carboxylate groups led to greater occlusion compared to those composed of phosphate, sulfate, or sulfonate groups when examining a model vesicle system.Subsequently, our occlusion studies were extended to include functional hybrid nanocomposite crystals. For example, the spatially controlled occlusion of poly(glycerol monomethacrylate)-stabilized gold nanoparticles was achieved within semiconductive ZnO crystals by either controlling the nanoparticle concentration or by delaying their addition to the reaction mixture. Moreover, oil droplets of up to 500 nm have been incorporated into calcite crystals at up to 11% by mass, despite the large mismatch in surface energy between the hydrophobic oil droplets and the ionic crystal lattice. We have also explored a "Trojan horse" strategy, whereby cargos comprising nanoparticles or soluble dye molecules are first encapsulated within anionic block copolymer vesicles prior to their incorporation within calcite crystals. This approach offers a generic and efficient strategy for the occlusion of many types of guest species into single crystals. In summary, we have established important guidelines for efficient nanoparticle occlusion within crystals, which opens up new avenues for the synthesis of next-generation hybrid materials.

Polymerization-induced self-assembly for the fabrication of polymeric nano-objects with enhanced structural stability by cross-linking

This review discusses the strategies of core-cross-linking in most of the PISA literatures (including post-polymerization cross-linking, photo-cross-linking and in situ cross-linking) and the applications of the cross-linked nano-objects.