Recovering and Exploiting Aragonite and Calcite Single Crystals with Biologically Controlled Shapes from Mussel Shells

Control over the shape and morphology of single crystals is a theme of great interest in fundamental science and for technological application. Many synthetic strategies to achieve this goal are inspired by biomineralization processes. Indeed, organisms are able to produce crystals with high fidelity in shape and morphology utilizing macromolecules that act as modifiers. An alternative strategy can be the recovery of crystals from biomineralization products, in this case, seashells. In particular, waste mussel shells from aquaculture are considered. They are mainly built up of single crystals of calcite fibers and aragonite tablets forming an outer and an inner layer, respectively. A simple mechanochemical treatment has been developed to separate and recover these two typologies of single crystals. The characterization of these single crystals showed peculiar properties with respect to the calcium carbonate from quarry or synthesis. We exploited these biomaterials in the water remediation field using them as substrate adsorbing dyes. We found that these substrates show a high capability of adsorption for anionic dye, such as Eosin Y, but a low capability of adsorption for cationic dyes, such as Blue Methylene. The adsorption was reversible at pH 5.6. This application represents just an example of the potential use of these biogenic single crystals. We also envision potential applications as reinforcing fillers and optical devices

Revealing the Formation Mechanism and Optimizing the Synthesis Conditions of Layered Double Hydroxides for the Oxygen Evolution Reaction

Layered double hydroxides (LDHs), whose formation is strongly related to OH− concentration, have attracted significant interest in various fields. However, the effect of the real-time change of OH− concentration on LDHs’ formation has not been fully explored due to the unsuitability of the existing synthesis methods for in situ characterization. Here, the deliberately designed combination of NH3 gas diffusion and in situ pH measurement provides a solution to the above problem. The obtained results revealed the formation mechanism and also guided us to synthesize a library of LDHs with the desired attributes in water at room temperature without using any additives. After evaluating their oxygen evolution reaction performance, we found that FeNi-LDH with a Fe/Ni ratio of 25/75 exhibits one of the best performances so far reported

Self-assembly of amorphous calcium carbonate microlens arrays

Biological materials are often based on simple constituents and grown by the principle of self-assembly under ambient conditions. In particular, biomineralization approaches exploit efficient pathways of inorganic material synthesis. There is still a large gap between the complexity of natural systems and the practical utilization of bioinspired formation mechanisms. Here we describe a simple self-assembly route leading to a CaCO3 microlens array, somewhat reminiscent of the brittlestars' microlenses, with uniform size and focal length, by using a minimum number of components and equipment at ambient conditions. The formation mechanism of the amorphous CaCO3 microlens arrays was elucidated by confocal Raman spectroscopic imaging to be a two-step growth process mediated by the organic surfactant. CaCO3 microlens arrays are easy to fabricate, biocompatible and functional in amorphous or more stable crystalline forms. This shows that advanced optical materials can be generated by a simple mineral precipitation

Crystallization by particle attachment in synthetic, biogenic, and geologic environments.

Field and laboratory observations show that crystals commonly form by the addition and attachment of particles that range from multi-ion complexes to fully formed nanoparticles. The particles involved in these nonclassical pathways to crystallization are diverse, in contrast to classical models that consider only the addition of monomeric chemical species. We review progress toward understanding crystal growth by particle-attachment processes and show that multiple pathways result from the interplay of free-energy landscapes and reaction dynamics. Much remains unknown about the fundamental aspects, particularly the relationships between solution structure, interfacial forces, and particle motion. Developing a predictive description that connects molecular details to ensemble behavior will require revisiting long-standing interpretations of crystal formation in synthetic systems, biominerals, and patterns of mineralization in natural environments

Uniform hexagonal plates of vaterite CaCO3 mesocrystals formed by biomimetic mineralization

Vaterite mesocrystals with hexagonal morphology and uniform size have been successfully synthesized in the presence of a N-trimethylammonium derivative of hydroxyethyl cellulose via aggregation mediated crystallization using a simple gas-diffusion method. The uniform hexagonal plates display sharp facets and edges even though they are formed by the aggregation of nanocrystals. The results demonstrate that each vaterite plate can be explained as consisting of aggregates of nanoparticles that share the same three dimensional orientation. A mechanism for the formation of hexagonal vaterite mesocrystals made of primary nanoparticles and hexagonal units si also presented. An understanding of the mesoscale transformation process will be helpful in controlling the aggregation driven formation of complex higher order structured materials and will provide new insights into biomineralization mechanisms. For example the spines of sea urchins can be discussed within the framework of the mesocrystal concept. This study could provide an additional tool for designing advanced materials and could be used for the synthesis of more complex crystalline three-dimensional structures

Local Light-Controlled Generation of Calcium Carbonate and Barium Carbonate Biomorphs via Photochemical Stimulation

The authors thank the European Research Council under the European Union's Seventh Framework Program (FP7/20072013)/ERC grant agreement no 340863 and ERC PoC LACRYS (837874) as well as Junta de Andalucia for financing the project P18-FR-5008. HC thanks the Deutsche Forschungsgemeinschaft DFG for financial support of the work on Biomorphs (CO 194/28-1). M.M., A.M., and A.M.-P. thank MIUR, (PRIN 2017) 2017E44A9P. Open access funding enabled and organized by Projekt DEAL.Photochemical activation is proposed as a general method for controlling the crystallization of sparingly soluble carbonates in space and time. The photogeneration of carbonate in an alkaline environment is achieved upon photo-decarboxylation of an organic precursor by using a conventional 365 nm UV LED. Local irradiation was conducted focusing the LED light on a 300 μm radius spot on a closed glass crystallization cell. The precursor solution was optimized to avoid the precipitation of the photoreaction organic byproducts and prevent photo-induced pH changes to achieve the formation of calcium carbonate only in the corresponding irradiated area. The crystallization was monitored in real-time by time-lapse imaging. The method is also shown to work in gels. Similarly, it was also shown to photo-activate locally the formation of barium carbonate biomorphs. In the last case, the morphology of these biomimetic structures was tuned by changing the irradiation intensity.European Research Council under the European Union's Seventh Framework Program (FP7/20072013)/ERC grant 340863ERC PoC LACRYS 837874Junta de Andalucia P18-FR-5008German Research Foundation (DFG) CO 194/28-1Ministry of Education, Universities and Research (MIUR)Research Projects of National Relevance (PRIN) 2017E44A9PProjekt DEA