Bio-inspired formation of functional calcite/metal oxide nanoparticle composites

Abstract

Biominerals are invariably composite materials, where occlusion of organic macromolecules within single crystals can significantly modify their properties. In this article, we take inspiration from this biogenic strategy to generate composite crystals in which magnetite (Fe 3 O 4 ) and zincite (ZnO) nanoparticles are embedded within a calcite single crystal host, thereby endowing it with new magnetic or optical properties. While growth of crystals in the presence of small molecules, macromolecules and particles can lead to their occlusion within the crystal host, this approach requires particles with specific surface chemistries. Overcoming this limitation, we here precipitate crystals within a nanoparticle-functionalised xyloglucan gel, where gels can also be incorporated within single crystals, according to their rigidity. This method is independent of the nanoparticle surface chemistry and as the gel maintains its overall structure when occluded within the crystal, the nanoparticles are maintained throughout the crystal, preventing, for example, their movement and accumulation at the crystal surface during crystal growth. This methodology is expected to be quite general, and could be used to endow a wide range of crystals with new functionalities. IntroductionAdvances in technology demand an ever-increasing degree of control over material structure, properties and function. As the range of properties that can be obtained from monolithic materials is necessarily limited, one potential strategy for the development of new materials is the creation of composites in which two or more dissimilar materials are combined. 5-8In the work described here, we use biominerals, and specifically their occlusion of organic species, as an inspiration to generate composites in which inorganic nanoparticles (magnetite and ZnO) are incorporated within single crystals of calcite (CaCO 3 ). In doing so, we can endow the host crystal with novel properties -here magnetic or optical -while maintaining the intrinsic single crystal character of the parent crystal. It is well recognized that growth of crystals in the presence of organic molecules can lead to the occlusion of both small molecules 9 and macromolecules, 10 and this strategy has been adapted to achieve encapsulation of polymer latexes and copolymer micelles within single crystals of calcite 11,12 and ZnO crystals. 13 However, while this method is experimentally facile, it requires particles with specific surface chemistries, and aggregation of the nanoparticles is a problem in many crystal growth solutions.Notably, some biominerals also occlude fibres, reflecting their growth in a gel-like medium. 8,14,15 Again, an analogous result has also been achieved synthetically, where sponge-like agarose gels were preserved within calcite crystals. 16,17 Indeed, incorporation of the gel is subject to far fewer constraints than isolated particles/ molecules, and effective occlusion can be achieved according to the gel rigidity and the rate of crystal growth. 17 Our methodology there...

Functionalizing Single Crystals: Incorporation of Nanoparticles Inside Gel‐Grown Calcite Crystals

“…The optical and magnetic functionalizations are achieved through nanoparticle incorporation inside the single crystals. [48] This work creates a novel and facile pathway to design functionalized single-crystalline materials to expand their potential applications. In contrast to other mechanisms of particle incorporation that are associated with fast crystallization and/or crystal-particle mutual wetting, [47] the gel-mediating strategy described here allows a wide range of particles to be incorporated.…”

Gel-incorporated PbS and PbI2 single-crystals

“…Afterwards, Garcia-Ruiz et al found that gelgrown protein (lysozyme, ferritin and thaumatin) crystals also incorporate gel (silica and/or agarose) matrix [5,8,9]. More recently, calcite, again, were shown to incorporate gelatine [10], poly-acrylamide [11], agarose [12][13][14][15] and xyloglucan gels [16]. Although the total amount is still very limited as compared with the large amount of gel-grown crystals, the examples of gelincorporated single-crystals are increasing [17][18][19][20].…”

Physical Confinement Promoting Formation of Cu2O–Au Heterostructures with Au Nanoparticles Entrapped within Crystalline Cu2O Nanorods

“…34,35,57 The encapsulation of inorganic and metallic guest particles has only been achieved by functionalizing the nanoparticles with diblock copolymers, 58,59 or immobilizing them within hydrogel matrices. 39,40 In all of these cases, the encapsulated nanoparticles are surrounded by an insulating organic layer at the interface between the guest nanoparticle and the host crystalline material. In electronic materials, such an insulating layer would be a barrier to the transport of carriers between the two crystalline materials.…”

“…34 This approach has been widely demonstrated for single crystal carbonates, where the encapsulation of organic colloids, 35 micelles, 36,37 and fibers 38 has been achieved by the vapor diffusion of ammonium carbonate into an aqueous matrix (e.g., dispersion of particles or hydrogel) containing dissolved alkali metal salts. 39,40 As an extension of this approach, we hypothesized that a solution-vapor phase crystallization of an oxide (e.g., Cu 2 O) could be accomplished by the diffusion of a low vapor pressure basic species or reducing agent 41 into a transition metal oxide salt solution with the application of heat to drive the system to the oxide phase. 42 Experimental Design.…”