Construction Of Chiral Inorganic Multilevel Structures By CTAB Template

Chirality is a fundamental property of nature,which exists widely from molecules to macrocosmic universe.Chiral inorganic multilevel structure is a special form of the chiral family,commonly found in various spiral structure of Biominerals,such as the spiral shell（CaCO₃）,the spiral tooth（HA）of Narwhal,pathologic otolith（globulinite）,etc.Due to the unique properties of chiral inorganic multilevel structures in the fields of mechanics,optics,chiral catalysis,electron transmission,etc.,relevant researches have received extensive attention in recent years.However,due to the complexity of the multilevel structure of chiral inorganic,the formation mechanism of natural biological minerals is still unclear,and the types of biomimetic synthesis are very limited.In view of the shortcomings of the current research in this field,this paper uses the non-chiral cetyltrimethyl ammonium bromide（CTAB）as the template.Firstly,the gas diffusion method was used to prepare the pure aragonite multi-stage chiral structure CaCO₃ which is highly similar to the Turritella terebra shell,and the formation mechanism is discussed deeply.Secondly,the chiral spiral structure B₂O₃,which has been widely used in neutron absorption,was prepared by liquid phase template method.The relevant research results of this paper have two important meanings:On the one hand,the formation mechanism of natural chiral inorganic multilevel structure is analyzed from the new perspective of"chiral adsorption",on the other hand,the family treeof biomimetic synthetic chiral inorganic multilevel structures is extended,which lays a material foundation for the application of chiral inorganic multilevel structures in the field of neutron absorption.The main conclusions of this paper are as follows:（1）Pure aragonite phase chiral multilevel structure CaCO₃:with NH₄HCO₃ as carbon source and p H regulator,the pure aragonite phase CaCO₃ with chiral multilevel structure was synthesized by gas diffusion method under the cooperative induction of CTAB and Mg²⁺.The effects of Mg²⁺concentration and CTAB concentration on chiral mineralization process were systematically studied.The physicochemical analysis shows that the multilevel mechanism is highly similar to Turritella terebra shell in terms of composition and micromorphology.Materials Studios were used to simulate the formation mechanism of chiral multilevel structure CaCO₃,showing that Mg²⁺is the crystal growth control agent and CTAB is the inducer to control the chiral growth of crystal.The asymmetric chiral adsorption of end groups of CTAB on aragonite（012）,（021）,（022）and other crystal planes is the key to the formation of chiral structures.（2）Chiral helix B₂O₃:with tributyl borate（B（OC₄H₉）₃）as boron source,under the action of CTAB template,through p H control,the chiral helix structure of boron oxide was synthesized.Among them,fine control of CTAB and p H value is the key to the formation of chiral structure.The results of comparative test show that:without addition,the product is random lamellar boric acid;when p H was 8.3,the initial product was hexagonal lamellar NH₄B₅O₈.4H₂O;when the concentration of CTAB is 0.12 mol·L^-1,the p H value of the solution is 8.3,the molar ratio of B（OC₄H₉）₃:H₂O:ethanol is 1:2.5:11.5 and the temperature is 80°C,the precursor of chiral helical structure can be formed.After calcination,the chiral helical structure B₂O₃ can be obtained.Mechanism analysis shows that the assembly of the chiral multilevel structure of B₂O₃ is mainly through the strong electrostatic interaction between CTA⁺and B₅O₈^-.