•Renewable calcite material prepared under environmentally benign conditions•Calcite crystals recombine in the presence of the natural biopolymer present•Sponge-like material can absorb dyes and crude oil from polluted water With the global population increasing, so does demand for protein. Aquaculture is sustainable in comparison with land-based meat agriculture and is on the rise to fulfill protein demands. With increased production comes increased waste, and in aquaculture this means shells. Blue mussel shells are a viable source of renewable calcium carbonate, probably the most widely studied and exploited mineral. Here, we present a renewable and absorbent form of calcium carbonate with a nest-like morphology, soft calcite. To prepare this material, we heat waste mussel shells and treat them with acid at room temperature. This causes the crystals in the shell to break apart and then recombine in agglomerates with gentle stirring. With a differing and distinct morphology, this soft calcite material opens many doors in materials science to create new materials with differing properties to those that use calcite mined from the Earth's crust. Mussel shells are a source of renewable CaCO3 and can be obtained from aquaculture waste streams. Valorization of waste shells relieves strain on landfills and aligns with the goals of a circular economy. Here, we present the preparation of an absorbent CaCO3 material, soft calcite (SC), prepared from waste blue mussel shells under mild conditions. Calcite is the only polymorph present in SC, despite the presence of aragonite in the shell. SC has a nest-like morphology, unlike the highly ordered calcite in the shell. SC is formed by the reassembly of calcite prisms and may be held together by the organic matrix “glue” from the original shell as evidenced by NMR spectroscopy. This inorganic sponge adsorbs dyes from aqueous solution and absorbs crude oil from seawater with good recyclability. Our results demonstrate how a natural structure can be modified in a sustainable fashion to yield a higher-value material. Mussel shells are a source of renewable CaCO3 and can be obtained from aquaculture waste streams. Valorization of waste shells relieves strain on landfills and aligns with the goals of a circular economy. Here, we present the preparation of an absorbent CaCO3 material, soft calcite (SC), prepared from waste blue mussel shells under mild conditions. Calcite is the only polymorph present in SC, despite the presence of aragonite in the shell. SC has a nest-like morphology, unlike the highly ordered calcite in the shell. SC is formed by the reassembly of calcite prisms and may be held together by the organic matrix “glue” from the original shell as evidenced by NMR spectroscopy. This inorganic sponge adsorbs dyes from aqueous solution and absorbs crude oil from seawater with good recyclability. Our results demonstrate how a natural structure can be modified in a sustainable fashion to yield a higher-value material. Nature's ability to create sophisticated structures with impressive mechanical properties drives a broad field of biomimetic materials research.1Wegst U.G.K. Bai H. Saiz E. Tomsia A.P. Ritchie R.O. Bioinspired structural materials.Nat. Mater. 2015; 14: 23-36Crossref PubMed Scopus (2429) Google Scholar The most abundant biomineral found in nature is CaCO3, where it serves a number of structural, protection, and mechanical functions in freshwater and marine organisms.2Nudelman F. Sommerdijk N.A.J.M. Biomineralization as an inspiration for materials chemistry.Angew. Chem. Int. Ed. 2012; 51: 6582-6596Crossref PubMed Scopus (347) Google Scholar,3Lowenstam H.A. Weiner S. On Biomineralization. Oxford University Press, 1989Crossref Google Scholar Biomineralized crystals differ structurally from geological and synthetic crystals and are difficult to simulate.4Heuer A.H. Fink D.J. Laraia V.J. Arias J.L. Calvert P.D. Kendall K. Messing G.L. Blackwell J. Rieke P.C. Thompson D.H. et al.Innovative materials processing strategies: a biomimetic approach.Science. 1992; 255: 1098-1105Crossref PubMed Scopus (515) Google Scholar The morphology and growth of CaCO3 materials can be controlled biomimetically5Gao H.-L. Chen S.-M. Mao L.-B. Song Z.-Q. Yao H.-B. Cölfen H. Luo X.-S. Zhang F. Pan Z. Meng Y.-F. et al.Mass production of bulk artificial nacre with excellent mechanical properties.Nat. Commun. 2017; 8: 287Crossref PubMed Scopus (192) Google Scholar, 6Mao L.-B. Gao H.-L. Yao H.-B. Liu L. Cölfen H. Liu G. Chen S.-M. Li S.-K. Yan Y.-X. Liu Y.-Y. et al.Synthetic nacre by predesigned matrix-directed mineralization.Science. 2016; 354: 107-110Crossref PubMed Scopus (496) Google Scholar, 7Kim Y.-Y. Carloni J.D. Demarchi B. Sparks D. Reid D.G. Kunitake Miki E. Tang C.C. Duer M.J. Freeman C.L. Pokroy B. et al.Tuning hardness in calcite by incorporation of amino acids.Nat. Mater. 2016; 15: 903-910Crossref PubMed Scopus (133) Google Scholar, 8Natalio F. Corrales T.P. Panthofer M. Schollmeyer D. Lieberwirth I. Muller W.E.G. Kappl M. Butt H.J. Tremel W. Flexible minerals: self-assembled calcite spicules with extreme bending strength.Science. 2013; 339: 1298-1302Crossref PubMed Scopus (100) Google Scholar and by other anthropogenic means.9Loste E. Park R.J. Warren J. Meldrum F.C. Precipitation of calcium carbonate in confinement.Adv. Funct. Mater. 2004; 14: 1211-1220Crossref Scopus (128) Google Scholar, 10Han Y.-J. Wysocki L.M. Thanawala M.S. Siegrist T. Aizenberg J. Template-dependent morphogenesis of oriented calcite crystals in the presence of magnesium ions.Angew. Chem. Int. Ed. 2005; 44: 2386-2390Crossref PubMed Scopus (48) Google Scholar, 11Han T.Y.-J. Aizenberg J. Calcium carbonate storage in amorphous form and its template-induced crystallization.Chem. Mater. 2008; 20: 1064-1068Crossref Scopus (85) Google Scholar Many have drawn inspiration from mollusk shells (>95% CaCO3) for materials synthesis and attempted to mimic natural CaCO3 prisms or nacre. Nacre is by far the most studied structural motif. Over the last three decades, nacre-inspired materials research has come a long way,12Yao H.-B. Ge J. Mao L.-B. Yan Y.-X. Yu S.-H. 25th anniversary article: artificial carbonate nanocrystals and layered structural nanocomposites inspired by nacre: synthesis, fabrication and applications.Adv. Mater. 2014; 26: 163-188Crossref PubMed Scopus (184) Google Scholar and there are now many methods to synthesize nacre-layer materials for use as a biomaterial in orthopedic and tissue engineering applications,13Gerhard E.M. Wang W. Li C. Guo J. Ozbolat I.T. Rahn K.M. Armstrong A.D. Xia J. Qian G. Yang J. Design strategies and applications of nacre-based biomaterials.Acta Biomater. 2017; 54: 21-34Crossref PubMed Scopus (51) Google Scholar as well as armor14Li L. Ortiz C. Pervasive nanoscale deformation twinning as a catalyst for efficient energy dissipation in a bioceramic armour.Nat. Mater. 2014; 13: 501-507Crossref PubMed Scopus (107) Google Scholar and electronics.15Loste E. Meldrum F.C. Control of calcium carbonate morphology by transformation of an amorphous precursor in a constrained volume.ChemComm. 2001; : 901-902https://doi.org/10.1039/B101563JCrossref Google Scholar The study of prismatic calcite in mollusks is becoming more popular, and understanding its formation is also valuable.16Nudelman F. Chen H.H. Goldberg H.A. Weiner S. Addadi L. Spiers memorial lecture: lessons from biomineralization. Comparing the growth strategies of mollusc shell prismatic and nacreous layers in Atrina rigida.Faraday Discuss. 2007; 136: 9-25Crossref PubMed Scopus (196) Google Scholar For example, prismatic-type CaCO3 thin films17Xiao C. Li M. Wang B. Liu M.-F. Shao C. Pan H. Lu Y. Xu B.-B. Li S. Zhan D. et al.Total morphosynthesis of biomimetic prismatic-type CaCO3 thin films.Nat. Commun. 2017; 8: 1398Crossref PubMed Scopus (44) Google Scholar similar to materials found in mollusks and flexible calcite needles that resemble spicules from Sycon sp. (a calcareous sponge) have recently been reported.8Natalio F. Corrales T.P. Panthofer M. Schollmeyer D. Lieberwirth I. Muller W.E.G. Kappl M. Butt H.J. Tremel W. Flexible minerals: self-assembled calcite spicules with extreme bending strength.Science. 2013; 339: 1298-1302Crossref PubMed Scopus (100) Google Scholar Natural materials are appealing for applications in the environment, such as oil spill remediation, and are potentially more economic than high-performance absorbent materials made from polymers and various carbons.18Bi H. Yin Z. Cao X. Xie X. Tan C. Huang X. Chen B. Chen F. Yang Q. Bu X. et al.Carbon fiber aerogel made from raw cotton: a novel, efficient and recyclable sorbent for oils and organic solvents.Adv. Mater. 2013; 25: 5916-5921Crossref PubMed Scopus (522) Google Scholar While mollusk shells are a great source of inspiration to scientists, we propose taking advantage of the ocean-based biorefinery19Kerton F.M. Liu Y. Omari K.W. Hawboldt K. Green chemistry and the ocean-based biorefinery.Green. Chem. 2013; 15: 860-871Crossref Scopus (172) Google Scholar,20Yan N. Chen X. Don't waste seafood waste.Nature. 2015; 524: 155-157Crossref PubMed Scopus (525) Google Scholar to create new CaCO3 materials. This approach is a commonsense way to manage waste, as aquaculture production increases globally to produce sustainable animal protein.21Gentry R.R. Gaines S.D. Halpern B.S. Froehlich H.E. Halpern B.S. Grimm D. Kareiva P. Parke M. Rust M. Halpern B.S. Mapping the global potential for marine aquaculture.Nat. Ecol. Evol. 2017; 1: 1317-1324Crossref PubMed Scopus (218) Google Scholar To date, waste mollusk shells have been utilized in many areas where CaCO3 is traditionally used, including in building materials, catalysis, and wastewater treatment.22Murphy J.N. Kerton F.M. Fuels, chemicals and materials form the oceans and aquatic sources.in: Kerton F.M. Yan N. Fuels, Chemicals and Materials Form the Oceans and Aquatic Sources. Wiley, 2017: 189-225Crossref Scopus (6) Google Scholar,23Morris J.P. Backeljau T. Chapelle G. Shells from aquaculture: a valuable biomaterial, not a nuisance waste product.Rev. Aquacult. 2018; 11: 42-57Crossref Scopus (65) Google Scholar It is important for researchers to consider the use of renewable feedstocks and green synthetic routes in their preparation of new materials. Here, we report a new morphology of biogenic calcite prepared from waste Mytilus edulis shells. This CaCO3 material is produced alongside calcium acetate, which can be used as a dietary supplement to increase calcium levels as well as a treatment for hyperphosphatemia (too much phosphate in the blood).24Mai M.L. Emmett M. Sheikh M.S. Santa Ana C.A. Schiller L. Fordtran J.S. Calcium acetate, an effective phosphorus binder in patients with renal failure.Kidney Int. 1989; 36: 690-695Abstract Full Text PDF PubMed Scopus (154) Google Scholar It can be made quite simply at room temperature in aqueous medium using food-grade white vinegar. The calcite material isolated contains the same components of the strong, highly ordered prismatic calcite layer found in shells, but is soft and absorbent and forms an interesting architecture composed of calcite crystals in a nest-like formation. We term this material soft calcite (SC). While absorbent sponges made from renewable materials have been reported, they are typically carbon materials prepared via pyrolysis (a high-temperature process).18Bi H. Yin Z. Cao X. Xie X. Tan C. Huang X. Chen B. Chen F. Yang Q. Bu X. et al.Carbon fiber aerogel made from raw cotton: a novel, efficient and recyclable sorbent for oils and organic solvents.Adv. Mater. 2013; 25: 5916-5921Crossref PubMed Scopus (522) Google Scholar,25Bi H. Huang X. Wu X. Cao X. Tan C. Yin Z. Lu X. Sun L. Zhang H. Carbon microbelt aerogel prepared by waste paper: an efficient and recyclable sorbent for oils and organic solvents.Small. 2014; 10: 3544-3550Crossref PubMed Scopus (177) Google Scholar Our inorganic sponge is a first and uses a material sourced from aquaculture waste and transformed at room temperature. We also report the application of SC toward absorption of crude oil and dyes from water. Mollusk shells are mainly composed of CaCO3 (95%–99.9%), with small amounts of other minerals and an organic matrix composed of silk-fibroin-like proteins, β-chitin, and glycoproteins that have a number of functions, which include holding crystals of CaCO3 in place as well as controlling nucleation and polymorph formation.26Jackson A.P. Vincent J.F.V. Turner R.M. The mechanical design of nacre.Proc. R. Soc. Lond. B Biol. Sci. 1988; 234: 415-440Crossref Google Scholar,27Nudelman F. Nacre biomineralisation: a review on the mechanisms of crystal nucleation.Semin. Cell Dev. Biol. 2015; 46: 2-10Crossref PubMed Scopus (54) Google Scholar Mollusk shells are composed of two main polymorphs of CaCO3, calcite and/or aragonite. If both polymorphs are present in the shell, they are always separated into two layers. Scheme 1 presents a selection of scanning electron microscopy (SEM) images of the starting shell material, with polymorphs labeled, and how it is transformed to SC. In Scheme 1A, a cross-section of a blue mussel (BM) shell shows that they are composed of an outer prismatic calcite layer and an inner nacreous aragonite layer. The myostracum3Lowenstam H.A. Weiner S. On Biomineralization. Oxford University Press, 1989Crossref Google Scholar (Scheme 1A), a small layer that connects the inner nacreous aragonite and outer prismatic calcite layer of BM shells, is composed of aragonite and allows the prismatic calcite to be held in its natural organized state. Recently, we reported that heat treatment decreases the amount of organic matrix in the BM shells and allows easy separation of the inner nacreous aragonite layer from the outer prismatic calcite layer, as depicted in Scheme 1B.28Murphy J.N. Schneider C.M. Mailänder L.K. Lepillet Q. Hawboldt K. Kerton F.M. Wealth from waste: blue mussels (Mylitus edulis) offer up a sustainable source of natural and synthetic nacre.Green. Chem. 2019; 21: 3920-3929Crossref Google Scholar In this study, BM shells were heated to 220°C for 48 h and mechanical separation of the two main layers was possible. However, upon separation part of the myostracum remains on the prismatic calcite layer.28Murphy J.N. Schneider C.M. Mailänder L.K. Lepillet Q. Hawboldt K. Kerton F.M. Wealth from waste: blue mussels (Mylitus edulis) offer up a sustainable source of natural and synthetic nacre.Green. Chem. 2019; 21: 3920-3929Crossref Google Scholar We believe this to be crucial to the formation of SC, which results from two acid treatments of heated blue mussel (HBM) shells. We think that the myostracum protects the calcite in the outer prismatic calcite layer from reacting during the first acid treatment and then, once it is completely deteriorated during the second acid treatment, the calcite prisms are liberated and recombine to form SC (Scheme 1C). An overview of the preparation of SC from BM shells is shown in Figure 1. The cleaned shells29Murphy J.N. Hawboldt K. Kerton F.M. Enzymatic processing of mussel shells to produce biorenewable calcium carbonate in seawater.Green. Chem. 2018; 20: 2913-2920Crossref Google Scholar are heated to 220°C for 48 h (Figure 1A); here these shells are termed HBM shells. HBM shells are reacted with 5% CH3COOH for 24 h at room temperature on an orbital shaker to make what we term “prepped shells” (Figure 1B) and calcium acetate. This step is important in the preparation of SC. In fact, SC cannot be made directly in a single step from HBM shells upon CH3COOH treatment. The prepped shells undergo a second reaction with 5% CH3COOH for 24 h at room temperature on an orbital shaker to produce a mixture of calcium acetate, SC, and unreacted shell material (Figure 1C). The difference in buoyancy between SC and the remaining shells makes their separation simple. The calcium acetate and SC are decanted from the remaining shells. The calcium acetate solution is then decanted from the SC, as shown in Figure 1D. Finally, SC is washed with water to remove residual calcium acetate and then washed using absolute ethanol (Figure 1E). Moist SC has a sponge-like texture and a large amount of water within the agglomerates (Video S1). Therefore, solvent exchange with ethanol was used to assist in the drying process whereby ethanol was exchanged five times over a period of 5 h. Once the SC is dried (Figure 1F), it is ready for use and has a candy-floss (cotton candy) texture (Video S2). Typically, SC agglomerates are spherical in shape (Figure 1G). Visual inspection by tearing apart SC by hand and aggressive stirring in acetone to break apart SC revealed no residual pieces of shell within them. It is also important to note that SC is produced alongside calcium acetate monohydrate (Figure 1H), which crystallizes upon evaporation of water and is itself a useful compound for nutritional calcium supplementation. Absorptions in the infrared (IR) spectrum of the calcium acetate confirmed the formation of the monohydrate species (Figure S1).30Tennent N.H. Baird T. The deterioration of mollusca collections: identification of shell efflorescence.Stud. Conserv. 1985; 30: 73-85Google Scholar,31Musumeci A.W. Frost R.L. Waclawik E.R. A spectroscopic study of the mineral paceite (calcium acetate).Spectrochim. Acta A. 2007; 67: 649-661Crossref Scopus (64) Google Scholar Oven-dried SC can absorb 10 times its mass in liquid water. No absorption of moisture from air was observed when the SC was stored in a humidity chamber over a period of a week at 20°C, as no mass increase was observed. https://www.cell.com/cms/asset/97c89176-ad09-46e0-a9d7-13bd2891d8c6/mmc2.mp4Loading ... Download .mp4 (8.45 MB) Help with .mp4 files Video S1. Video of As-Prepared SC and Visual Demonstration of Water Content https://www.cell.com/cms/asset/0ff3d517-f5df-4f04-a449-820489a80a33/mmc3.mp4Loading ... Download .mp4 (14.29 MB) Help with .mp4 files Video S2. Video of Dried SC to Demonstrate the Texture of the Dried Material To support our observations regarding SC formation from HBM shells, we performed control experiments to try to prepare SC with (1) alternative sources of CaCO3 with acetic acid and (2) different organic acids with HBM shells. Three additional CaCO3 sources were evaluated using our experimental procedure: reagent-grade CaCO3, biogenic aragonite isolated from HBM shells, and biogenic calcite isolated from HBM shells. A small amount of SC formed when using the calcite only from HBM shells, and no SC formed using reagent-grade CaCO3 or the biogenic aragonite. This suggests that SC yields are increased when whole HBM shells are used, that is, a mixture of calcite and aragonite. As mentioned above, part of the myostracum remains on the prismatic calcite layer,28Murphy J.N. Schneider C.M. Mailänder L.K. Lepillet Q. Hawboldt K. Kerton F.M. Wealth from waste: blue mussels (Mylitus edulis) offer up a sustainable source of natural and synthetic nacre.Green. Chem. 2019; 21: 3920-3929Crossref Google Scholar and we propose that the myostracum reacts with CH3COOH in order for prisms of calcite to be liberated. We hypothesize that because biogenic aragonite (nacre and myostracum) has a higher dissolution rate and slightly higher Ksp than calcite,32Koehler S.J. Cubillas P. Rodriguez-Blanco J.D. Bauer C. Prieto M. Removal of cadmium from wastewaters by aragonite shells and the influence of other divalent cations.Environ. Sci. Technol. 2007; 41: 112-118Crossref PubMed Scopus (96) Google Scholar the aragonite layers preferentially react with CH3COOH to form calcium acetate. It should be noted that in this process the base (CaCO3) is present in excess relative to the acid (CH3COOH), and therefore not all of the CaCO3 present will react. The preferential reaction of aragonite could also be because calcite prisms in mollusks are known to be coated in a thick layer of organic matrix,33Bayerlein B. Zaslansky P. Dauphin Y. Rack A. Fratzl P. Zlotnikov I. Self-similar mesostructure evolution of the growing mollusc shell reminiscent of thermodynamically driven grain growth.Nat. Mater. 2014; 13: 1102Crossref PubMed Scopus (62) Google Scholar and this is likely protecting the calcite from dissolution to some degree. Several weak organic acids were explored as an alternative to acetic acid, and we found that none resulted in the formation of SC. For SC to be separated easily, the calcium carboxylate by-product formed must be soluble. Oxalic, propanoic, citric, and oleic acids (5%) were tested. Calcium oxalate and citrate have low solubility in water, so the products could be seen precipitating very quickly and no SC was produced. Oleic acid (5% in ethanol) did not result in the formation of SC, even when some water was added to try to drive the reaction via hydrophobic interactions. Based on our initial hypothesis, we thought that propanoic acid should be suitable for making SC because calcium propanoate is very soluble in water; however, no SC was formed. We also note that gentle agitation (a shaker or rotating platform rather than a magnetic stirrer) is imperative for the formation of SC from HBM shells, as SC did not form in control experiments performed using more vigorous magnetic stirring. Further experiments are needed to fully understand both the chemical and mechanical requirements to obtain good yields of SC. IR spectroscopy can be used to distinguish between different polymorphs of calcium carbonate. The IR spectrum of SC (Figure S2) contains bands at 1,388 cm−1, 870 cm−1, and 712 cm−1, and these correspond to the ν3, ν2, and ν4 bands of calcite.34Weir C.E. Lippincott E.R. Infrared studies of aragonite, calcite, and vaterite type structures in the borates, carbonates, and nitrates.J. Res. Natl. Bur. Stand. A Phys. Chem. 1961; 65A: 173-183Crossref PubMed Google Scholar These match with the outer prismatic calcite layer of the HBM shell28Murphy J.N. Schneider C.M. Mailänder L.K. Lepillet Q. Hawboldt K. Kerton F.M. Wealth from waste: blue mussels (Mylitus edulis) offer up a sustainable source of natural and synthetic nacre.Green. Chem. 2019; 21: 3920-3929Crossref Google Scholar (Scheme 1B) and there are no peaks corresponding to aragonite, the other polymorph present in the HBM shell that makes up the inner nacreous layer.28Murphy J.N. Schneider C.M. Mailänder L.K. Lepillet Q. Hawboldt K. Kerton F.M. Wealth from waste: blue mussels (Mylitus edulis) offer up a sustainable source of natural and synthetic nacre.Green. Chem. 2019; 21: 3920-3929Crossref Google Scholar The powder X-ray diffractogram of SC (Figure S3) confirmed the absence of aragonite and that the only crystalline phase present was calcite. Therefore, these results are satisfactory in proving that aragonite within the shells preferentially reacts with the acetic acid to form calcium acetate during the preparation of SC. The morphology of SC was investigated via SEM analyses and compared with the prismatic layer of HBM shells (Figure 2). In the micrographs of SC at differing scales, shown in Figures 2B and 2C, it can be seen that some of the prismatic calcite crystals are hundreds of micrometers in length, which is in common with the prismatic calcite layer of mollusk shells.16Nudelman F. Chen H.H. Goldberg H.A. Weiner S. Addadi L. Spiers memorial lecture: lessons from biomineralization. Comparing the growth strategies of mollusc shell prismatic and nacreous layers in Atrina rigida.Faraday Discuss. 2007; 136: 9-25Crossref PubMed Scopus (196) Google Scholar However, there is a key difference between SC and the prismatic calcite from mollusks, namely the nest-like structure of the SC. Individual calcite crystals in a mollusk shell are surrounded by a layer of organic matrix, making the prisms highly organized along the direction of crystal growth and in close contact with one another,3Lowenstam H.A. Weiner S. On Biomineralization. Oxford University Press, 1989Crossref Google Scholar whereas this close contact and organization is not present in SC. In addition, it is clear that during the SC formation process some of the calcite has reacted with CH3COOH because the prisms of SC are slightly degraded compared with natural shells, as shown in Figure 2. We are not the first to isolate calcite from mollusk shells via chemical treatment. Individual prisms of calcite from mollusks Atrina rigida and Pinna nobilis have been liberated previously in dilute sodium hypochlorite solutions.16Nudelman F. Chen H.H. Goldberg H.A. Weiner S. Addadi L. Spiers memorial lecture: lessons from biomineralization. Comparing the growth strategies of mollusc shell prismatic and nacreous layers in Atrina rigida.Faraday Discuss. 2007; 136: 9-25Crossref PubMed Scopus (196) Google Scholar,35Marin F. Luquet G. Molluscan shell proteins.Comptes Rendus Palevol. 2004; 3: 469-492Crossref Scopus (261) Google Scholar,36Pokroy B. Fitch A.N. Zolotoyabko E. The microstructure of biogenic calcite: a view by high-resolution synchrotron powder diffraction.Adv. Mater. 2006; 18: 2363-2368Crossref Scopus (105) Google Scholar However, these approaches did not lead to reagglomeration or formation of a nest-like microstructure. In terms of morphology, the only somewhat similar carbonate material is synthetic barium carbonate nanowires,37García-Ruiz J.M. Nakouzi E. Kotopoulou E. Tamborrino L. Steinbock O. Biomimetic mineral self-organization from silica-rich spring waters.Sci. Adv. 2017; 3: e1602285Crossref PubMed Scopus (50) Google Scholar but these are non-biogenic. From fitting the Brunauer-Emmett-Teller (BET) isotherm (Figure S4), the surface area of SC (dried using supercritical carbon dioxide) is 37 m2 g−1. This surface area is ∼9 times greater than the surface area of ground HBM shells28Murphy J.N. Schneider C.M. Mailänder L.K. Lepillet Q. Hawboldt K. Kerton F.M. Wealth from waste: blue mussels (Mylitus edulis) offer up a sustainable source of natural and synthetic nacre.Green. Chem. 2019; 21: 3920-3929Crossref Google Scholar (6.4 m2 g−1) and is visually represented in Figures 3A and 3B where 0.5 g of SC is much more voluminous than 0.5 g of ground HBM shells. This surface area is higher than any reported for mollusk shells that contain CaCO3.38Jones M.I. Wang L.Y. Abeynaike A. Patterson D.A. Utilisation of waste material for environmental applications: calcination of mussel shells for waste water treatment.Adv. Appl. Ceram. 2011; 110: 280-286Crossref Scopus (19) Google Scholar, 39Rombaldi C. de Oliveira Arias J.L. Hertzog G.I. Caldas S.S. Vieira J.P. Primel E.G. New environmentally friendly MSPD solid support based on golden mussel shell: characterization and application for extraction of organic contaminants from mussel tissue.Anal. Bioanal. Chem. 2015; 407: 4805-4814Crossref PubMed Scopus (17) Google Scholar, 40Tekin K. Hydrothermal conversion of Russian olive seeds into crude bio-oil using a cao catalyst derived from waste mussel shells.Energy Fuels. 2015; 29: 4382-4392Crossref Scopus (30) Google Scholar, 41Abeynaike A. Wang L. Jones M.I. Patterson D.A. Pyrolysed powdered mussel shells for eutrophication control: effect of particle size and powder concentration on the mechanism and extent of phosphate removal.Asia Pac. J. Chem. Eng. 2011; 6: 231-243Crossref Scopus (39) Google Scholar Thermogravimetric analysis (TGA) and elemental analysis were used to assess the purity of SC. In our previous work,28Murphy J.N. Schneider C.M. Mailänder L.K. Lepillet Q. Hawboldt K. Kerton F.M. Wealth from waste: blue mussels (Mylitus edulis) offer up a sustainable source of natural and synthetic nacre.Green. Chem. 2019; 21: 3920-3929Crossref Google Scholar we showed that the mass loss for the organic matrix primarily occurs between 585°C and 615°C. While we believe some mass loss below 585°C is due to organic matrix, in our previous work we could not measure in this region because the aragonite in the BM and HBM shell affords a significant mass loss when aragonite changes to calcite at 400°C–500°C, releasing moisture (and organic matrix).42Shariffuddin J.H. Yean W.C. Ghazali S.S. Investigating the catalytic properties of calcium compounds derived from marine based shell waste for wastewater treatment.Mater. Today Proc. 2018; 5: 21718-21727Crossref Scopus (4) Google Scholar For SC, there is no significant mass loss in this region via TGA (Figure S5). Regardless, this area was analyzed for mass loss and a loss of 0.06 wt % was determined, which is much less than the mass loss afforded during TGA of the outer prismatic calcite layer of HBM shell (0.40 wt %) previously reported.28Murphy J.N. Schneider C.M. Mailänder L.K. Lepillet Q. Hawboldt K. Kerton F.M. Wealth from waste: blue mussels (Mylitus edulis) offer up a sustainable source of natural and synthetic nacre.Green. Chem. 2019; 21: 3920-3929Crossref Google Scholar Careful inspection of the derivative of these data showed a small mass loss at 400°C for SC and, as we had previously seen this in TGA data of the outer layer of the HBM shell, it is very likely organic matrix.28Murphy J.N. Schneider C.M. Mailänder L.K. Lepillet Q. Hawboldt K. Kerton F.M. Wealth from waste: blue mussels (Mylitus edulis) offer up a sustainable source of natural and synthetic nacre.Green. Chem. 2019; 21: 3920-3929Crossref Google Scholar For full comparison purposes, we analyzed the mass loss between 200°C and 650°C of the outer prismatic calcite layer of HBM shell and compared it with SC. We found that the mass loss in this region for the outer layer of HBM shell and SC was 0.96 wt % and 1.14 wt %, respectively. These similar results are expected because SC is made up of HBM shell. Mass losses correspo