Study On Synthesis,performance And Formation Mechanism Of Micro-nano A Molecular Sieve With Kaolin As Raw Material

As a microporous material,A molecular sieve has a rich pore structure and regular pore distribution.Therefore,it has a wide range of applications in the fields of catalytic materials,adsorption materials,separation materials,optoelectronic materials,and functional materials,creating huge value for social development.At present,the synthesis of molecular sieves using kaolin and other mineral materials as raw materials is its development trend.Kaolin is a natural aluminosilicate mineral,and its reserves are very rich in China.In this thesis,kaolin is used as raw material to synthesize A molecular sieve by hydrothermal synthesis.The effects of aging temperature,aging time,crystallization temperature,crystallization time and alkali concentration on the crystallinity of 4A molecular sieve were studied,and the optimal process parameters for the synthesis of A molecular sieve were obtained.Meanwhile,a preliminary study on the formation mechanism of kaolin synthetic A molecular sieve.The effect of the amount of KCl added on the crystallinity and static saturated water absorption of 3A molecular sieve was studied.Two-dimensional A molecular sieve material was synthesized by hydrothermal-template method and its microstructure was studied.This research has certain theoretical and application value in the aspects of environmental protection,deep processing of kaolin,reduction of preparation cost of molecular sieve,and broadening the application field of molecular sieve.The innovations of this paper are as follows:?1?The 3A molecular sieve material is synthesized by one-step hydrothermal synthesis method using kaolin as raw material,which solves the problems of complicated synthesis process and long synthesis cycle of the 3A molecular sieve.?2?Using the hydrothermal-template method,kaolin is used as the raw material to synthesize the two-dimensional A molecular sieve material with lamellar structure.The results and main conclusions of this paper are as follows:?1?The ratio of silicon to aluminum of kaolin is about 2.5,which is suitable for the synthesis of A molecular sieve material.Thermogravimetric-differential thermal analysis results show that the activation temperature range is 600?800?.?2?Kaoline synthesis 4A molecular sieve,in the hydrothermal synthesis process,the single-factor experimental method was used to determine the best process conditions:alkali concentration 2.5 mol·L^-1;aging temperature 60?;aging time 4h;crystallization Temperature 90?;crystallization time 3h.The results show that the crystallinity of the synthesized 4A molecular sieve is 90.7%and the specific surface area is 13.3723 m²·g^-1.TEM research results show that the crystal structure of 4A molecular sieve belongs to body-centered cubic structure and 4A molecular sieve is polycrystalline.The EDX spectrum analysis results show that the Si/Al ratio of 4A molecular sieve is 1.0.Through the thermal stability study of 4A molecular sieve,the phase transition temperature of 4A molecular sieve is about 600?;At the phase transition temperature,the total mass loss of 4A molecular sieve is 14.7%.In addition,the formation mechanism of Kaolin synthetic A molecular sieve can be divided into three main stages:?a?Silicon-oxygen tetrahedron and aluminum-oxygen tetrahedron combine with each other to form four-membered ring and six-membered ring of secondary structural unit;?b?Connect secondary structural units to each other through polymerization to form large hexagonal column cages and?cage structural units.?c?A molecular sieve crystal growth.By analyzing the experimental results of hydrothermal synthesis of A molecular sieve,it can be concluded that the synthesis of A molecular sieve from kaolin is a liquid phase transition mechanism.?3?3A molecular sieve synthesized by kaolin.When the amount of KCl added is20%,the crystallinity of 3A molecular sieve is 73.4%,the specific surface area is17.6526 m²·g^-1,and the static saturated water absorption is 190.992 mg·g^-1.?4?Two-dimensional A molecular sieve synthesized by kaolin.When the amount of graphene added is 10.0%,the crystallinity of molecular sieve is 69.0%and the specific surface area is 39.7994 m²·g^-1.