Alkaline Earth Metal Silicates Nanostructures:Oriented Growth,Assembly And Properties

Silicates have aroused widespread concern for their versatile compositions and complicated structure.Up to now,the transition metal silicates have been widely used as adsorbents,electrode materials and catalyst supports,etc.However,for the alkaline earth metal group,only magnesium silicate has been used in the fields of wastewater treatment and catalyst.It is of great significance to develop the novel alkaline earth silicates nanostructures in both academia and industry.Calcium silicate has become widely available for drug delivery,photoluminescence host and bioactive materials owing to their distinct advantages such as non-toxicity,good biocompatibility,and degradability.In particular,the unique one-dimensional?1D?morphology can render the 1D nanostructures of calcium silicate as reinforcement additives in the ceramics and polymers such as rubber,etc.The conventional methods for 1D calcium silicate generally exhibited apparent high-energy consumption and requisite organic species such as organic solvent and surfactant,which were inevitably harmful to health and environment.In contrast,barium silicate is a kind of excellent photoluminescence host material,which has typically been synthesized via the high temperature based solid state technique.Herein,a facile controllable green hydrothermal route was developed for the synthesis of the 1D calcium silicate and three-dimensional?3D?barium silicate microspheres as great potential photoluminescence host and adsorbent.High aspect ratio Ca₆Si₆O₁₇?OH?₂ nanowires with uniform morphology were obtained via a facile controllable green hydrothermal route.Meanwhile,the effects of the process parameters on the hydrothermal products were investigated in detail,and based on which an intrinsic highly anisotropic crystal structure induced hydrothermal formation mechanism of the high aspect ratio Ca₆Si₆O₁₇?OH?₂ nanowires was proposed.The polystyrene?PS?/Ca₆Si₆O₁₇?OH?₂ composite materials was achieved via modulating the mixing condition of PS microspheres and Ca₆Si₆O₁₇?OH?₂nanowires.And also,the 3D Ca₆Si₆O₁₇?OH?₂ nest-like interconnected structure was obtained via the removal of PS microspheres.Moreover,a series of Ca₆Si₆O₁₇?OH?₂:x%RE³⁺?RE=Tb,Eu?nanophosphors were successfully synthesized via RE³⁺?RE=Tb,Eu?doping.The Ca₆Si₆O₁₇?OH?₂:1.2%RE³⁺?RE=Tb,Eu?nanophosphors demonstrated the most excellent luminescence property,with the CIE coordinates of?0.3191,0.5984?and?0.6673,0.3324?,respectively.A facile thermal conversion was used for the fabrication of CaSiO₃ nanowires,and the corresponding structure and function integrated CaSiO₃:x%RE³⁺?RE=Tb,Eu?nanophosphors were also fabricated.The CaSiO₃:1.2%RE³⁺?RE=Tb,Eu?nanophosphors with well-preserved 1D morphology exhibited the strongest emission intensity,with the CIE coordinates of?0.3144,0.5912?and?0.6654,0.3344?,respectively,indicating the as-obtained nanowires of a promising photoluminescent candidate materials.Uniform Ba5Si8O21 microspheres self-assembled by nanorods/nanosheets were first synthesized via a facile green process.Besides,the effects of the process parameters on the hydrothermal products were investigated to better understand the formation mechanism of the Ba₅Si₈O₂₁ microspheres.The high crystallinity Ba₅Si₈O₂₁microspheres with secondary units as nanosheets were employed for Tb³⁺doping,and the Ba₅Si₈O₂₁:10.0%Tb³⁺phosphors delivered the strongest emission intensity,with the CIE coordinate of?0.3129,0.5931?.Furthermore,the hierarchical Ba₅Si₈O₂₁microspheres with secondary units as nanorods were used as adsorbents for the removal of Congo red?CR?.The Ba₅Si₈O₂₁ microspheres demonstrated a high adsorption rate and excellent capacity(maximum adsorption capacity:1238.65 mg g^-1).The adsorption of CR on Ba₅Si₈O₂₁ microspheres was well fitted with Langmuir isothermal and pseudo-second kinetic models.Novel green hydrothermal synthetic strategies for the alkaline earth metal silicates nanostructures have been extended in the present work,and the great potential applications of the as-obtained 1D or 3D alkaline earth metal silicates as the promising photoluminescent candidates are investigated,and thus indicating the bright future of the structures in related fields.