| China has abundant resource of gypsum(calcium sulfate)with a reserve of 60 billion tons.In addition,a mass of industrial gypsum by-products are produced,for example,phosphogypsum,fluorgypsum,gypsum citrate and flue gas desulfurization gypsum and the annual yield of them is about 185 million tons.The development of new and high-value-added products of calcium sulfate is an optimal route for the transformation and upgrading of the gypsum industry.Among several phases of calcium sulfate,a-calcium sulfate hemihydrate(a-HH)with the highest economic value has expansive applications as ceramic models,high-grade building materials and functional fillers.Thanks to its biocompatibility,biodegradability and excellent cementitious property,a-HH has a great potential to be utilized in the field of biomedicine.a-HH has been regarded as a class of materials with rich source,low cost and wide market prospect.However,the property of a-HH down-stream products depends on its crystallization process,crystalline morphology,structural size and phase transformation.To develop a-HH products with high-added value,we need to have a deep understanding of the crystallization of a-HH.As thus,this research focuses on the phase transformation,crystallization pathway and morphology characteristics of calcium sulfate,especially on the formation mechanism of mesocrystal structure,from the aspect of non-classical crystallization theory,to achieve new technology and calcium sulfate products with high performance through regulation of its structure,morphology and size.Some preliminary study is conducted for the exploration of the controlled release platform of calcium ions,expecting to widen their applications in the field of nano-biomedicine.In conclusion,this work aims at providing theoretical basis and technical guidance for the development of calcium sulfate products and realization of high-valued utilization of gypsum resources.This work chose ethylene glycol-water solution as the crystallization medium,since it held lower dielectric constant and stronger solvability in comparison with salt solution.We precisely controlled the structure,morphology and crystal size of a-HH through regulation of volume ratio of ethylene glycol to water(G/W)by taking Na2EDTA as the additive.When G/W was increased from 0.4 to 50,the morphology of a-HH crystals experienced an evolution from prismatic,discoid to spherical and finally to ellipsoidal shape.At G/W under 5,the crystallization of a-HH went through the classical nucleation-growth pathway,which leaded to single crystalline particles in shape of prism with micro-size.In comparison,the crystallization of a-HH went through the non-classical nucleation-aggregation pathway,resulting in polycrystalline particles with nano-size at G/W above 5.This strategy effectively overcomes the challenge for structure control of a-HH crystals and achieves various morphologies for a-HH,laying a solid foundation for development of down-stream calcium sulfate products.To achieve mesoporous calcium sulfate microspheres,we synthesized the monodisperse a-HH microspheres in size of 2 μm for controlled calcination to create the mesopores.The phase composition of the microspheres could be maintained at 30-35 wt%of hemihydrate and 65-70 wt%of anhydrate,in which they gained higher surface area.Specifically,the mesoporous calcium sulfate microspheres obtained surface area of 30.62 m2/g after calcination at 500 ℃ for 120 s,which is ten times higher than that of a-HH microspheres before calcination.In addition,the ibuprofen loading capacity of these calcined microspheres was 22.44 mg/g,which was improved of nine times in comparison with the control group.The obtained surface area in this work is the highest reported value in the world,which is about one hundred times than that of the traditional single-crystalline calcium sulfate particles.Moreover,we successfully load drugs to the surface of calcium sulfate,shedding light on the utilization of calcium sulfate as drug carriers.Apart from single crystals and polycrystals,we achieved a-HH mesocrystals in the ethylene glycol-water solution.The obtained a-HH mesocrystals in length of 300-500 nm and width of 200-300 nm had shape of ellipsoid and possessed uniform size distribution and good monodispersity.The ellipsoid of a-HH mesocrystal was constructed by rod-like nanocrystals in size of 50 nm,and could be disorganized by hot-water washing to obtain the uniform nano-sized subunits once the interspaced EDTA was removed.This work proposes a new strategy for nanoparticles preparation through disorganization of the mesocrystal structure.To investigate the formation mechanism of a-HH mesocrystals,we carefully observed and analyzed the variation of crystal structure,morphology and orientation of subunits during the formation of the mesocrystal structure.The results indicated that the crystalline growth and orientation of the subunits started from the outer sphere and moved inwardly step by step.This work reveals a subunit growth controlled orientation process,which provides significant evidence for particle-mediated non-classical crystallization theory.Afterwards,we developed a controlled release platform of calcium ions,aiming at killing the cancer cells and the idea was inspired by utilizing calcium sulfate as drug carriers.The delivery platform was designed by taking gold nanocages as the carrier and phase change material as the switch for release of calcium ions.Upon the irradiation of near-infared laser,the phase change material transformed from solid state to liquid state through the photothermal property of gold nanocages and swiftly released the encapsulated calcium ions.The dramatically increased intracellular calcium concentration gave rise to the loss of mitochondria membrane potential to cause irreversible damage to cancer cells and thus resulted in cell death.This calcium-based controlled release system had higher biocompatibility and lower side effects in comparison with traditional chemotherapy,holding the potential to serve as a new technology for cancer therapy. |
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