Basic Research On Controllable Assembly And Application Of C-A-S-H

C-A-S-H is the product of Al substitution of C-S-H,which will play an important role in many aspects of the chemical behavior of cement slurry.Moreover,the abundant Si-OH in the chain of C-A-S-H can be linked with many catalysts and adsorbents through chemical bonds.C-A-S-H has good adsorption performance,good stability,low production cost,and good biocompatibility,which is an excellent functional material.If C-A-S-H can be synthesized in a controllable way to modify the surface of the material,the specific surface area and the number of active sites of the carrier material will be greatly enhanced,which has great potential for functional application.However,the relationship between C-A-S-H reaction conditions,microstructure and morphology has not yet been established and the study on its reasonable structure and model is still controversial.Up to now,the morphology of C-A-S-H gel is mainly in the accumulation state.It is very difficult to control its structure and morphology to make it grow into a specific structure,and there are few reports on relevant studies.Inspired by the honeycomb C-A-S-H naturally generated on the surface of light aggregate in steam cured concrete,the honeycomb network C-A-S-H was successfully synthesized by chemically method and the synthesis mechanism and precise morphology regulation were studied.The controllable synthesis of the microstructure and morphology of C-A-S-H was realized.The empirical equation for the relationship between reaction conditions and microstructure parameters and morphology regulation criterion are proposed.The light aggregate surface modified by C-A-S-H with different morphologies was designed for different application scenarios to prepare photocatalytic materials and heavy metal ion adsorption materials,and their catalytic and adsorption properties were studied.The research of the controllable assembly and application of C-A-S-H,not only of great significance for the further development of a series of functional carrier materials,is also the further exploration of the possibility of the structure and the morphology regulation for C-A-S-H,which can provide a new thought for concrete materials in the field of functional research.The main work and innovative achievements are as follows:（1）The chemical environment for the formation of honeycomb C-A-S-H in steam-cured concrete was analyzed and the reaction conditions for honeycomb C-A-S-H were found.A new method for the chemical synthesis of honeycomb C-A-S-H was proposed and the chemically synthesized honeycomb C-A-S-H was characterized.According to the internal chemical environment design experiment of steam cured concrete,the synthetic conditions of honeycomb gel were found,and the material selection criteria of honeycomb gel were determined.Among them,the presence of Ca²⁺and the control of p H value are the main factors affecting the reaction process.In addition,the reaction process is accelerated,the preparation time of the material is reduced and the practical application potential of the material is increased.The chemically synthesized honeycomb gel was characterized and verified to be C-A-S-H with special morphology.The morphology of C-A-S-H observed by SEM indicated that the gel had a cellular network structure with high internal connectivity,which was composed of a 50-300 nm nano-grid.（2）The necessary conditions for the controllable assembly of C-A-S-H are presented.The relationship among the reaction conditions,microstructure parameters and microstructure of C-A-S-H was established and the empirical equation expressing the relationship between the reaction conditions and microstructure parameters of C-A-S-H was proposed.The criterion for controlling the microstructure was established,and the precise control method of C-A-S-H microstructure was put forward.The growth process of honeycomb C-A-S-H was analyzed.Compared with the traditional hydrothermal synthesis method,the source of[Si O₄]^4-in this paper was dissolved from the surface of the material.This controllable dissolution process is an important basis for realizing the controllable assembly of C-A-S-H.In addition,C-A-S-H takes[Si O₄]^4-on the surface of the material as the nucleation site,which is used as a template to extend and connect with each other.This is the key to the controllable morphology of C-A-S-H gel.The effects of reaction conditions,such as temperature,time,Al/Si ratio and p H value,on the average chain length,crystallinity and layer spacing of C-A-S-H were investigated and an empirical equation expressing the relationship between reaction conditions and microstructure parameters of C-A-S-H is proposed for the first time.By substituting the experimental conditions for the formation of honeycomb C-A-S-H into the empirical equation,the boundary value of the structure factor A for the formation of honeycomb C-A-S-H is obtained:when the range is about 2.08≤A≤5.71,the C-A-S-H can generate the honeycomb morphology.The criterion of reaction conditions controlling the microstructure was established,and the precise control method of C-A-S-H microstructure was proposed:The reaction time can control the growth degree of honeycomb network C-A-S-H;the pore wall thickness of honeycomb C-A-S-H is mainly affected by p H value;the Al/Si ratio mainly affects the structure of honeycomb network C-A-S-H;the reaction temperature will affect the reaction speed of C-A-S-H.（3）Based on the microscopic morphology regulation criteria of honeycomb C-A-S-H,different types of C-A-S-H were designed according to the characteristics of different types of load media.It was applied in the field of photocatalytic air purification and heavy metal ion adsorption,and excellent performance was obtained.In the application of photocatalysis,C-A-S-H with thick pore wall was designed.The photocatalytic aggregates supported with Ag/Ag Br nanocatalyst could completely degrade 2μL formaldehyde within 1 hour.The catalytic activity of the aggregates remained close to 100%after 5 months,while it decreased to 60%for the control group without surface modification.The long-term performance of the functional aggregates was greatly improved.In the application of heavy metal ion adsorption,C-A-S-H with high connectivity is used for liquid organic TCPS to adsorb heavy metal ions Cd²⁺.As a large-particle filter material,functional filter showed the adsorption capacity of Cd（II）close to nano-adsorbent,up to 18.27 mg g^-1,while TCPS loaded on blank ceramsite sand almost had no adsorption capacity.The adsorption capacity of Cd（II）ions per surface area of functional filter is as high as 4.07 mg m^-2,which is much higher than that of many nanometer adsorbents.Over a wide range of p H values（p H=3-11）,high adsorption rates（>85%）were shown.Moreover,the functional filter also has excellent desorption performance,and can recover nearly 100%heavy metal ions through economical and simple steps.