Study On Adsorption Mechanism Of Inorganic Silicate Porous Materials Towards Pollutants In Water

Inorganic porous materials with high specific surface area exhibit excellent adsorption ability,which can remove organic pollutants and heavy metal ions in water quickly and effectively.The study on the adsorption mechanism of inorganic porous materials towards pollutants not only helps to improve the adsorption ability of adsorbents,but also has important significance for the development of new adsorbent materials.The aim of this dissertation is to research the structural properties,surface morphology and adsorption ability of several inorganic porous silicate materials,and investigate the corresponding adsorption mechanisms.The main research works are as follows:（1）Disc-like diatomite（DL-D）and rod-like calcium silicate（RL-CS）have been chosen as the typical silicate adsorbents to study the adsorption mechanisms of silicate adsorbents with different morphologies and pore structures.Taking formaldehyde as the target pollutant,adsorption ability of both silicate adsorbents was investigated,and the comparative analysis of corresponding adsorption mechanisms was conducted through batch experiments.Results show that the adsorption capacity of RL-CS with higher specific surface area and pore volume was prior to that of DL-D.Firstly,the pseudo-first-order and pseudo-second-order models were employed to fit the dynamic behaviors of adsorption process,and it shows that the pseudo-second-order model was more suitable one.On this basis,the adsorption data was also modeled by the internal particle diffusion model.Results indicate that the adsorption mechanism of DL-D towards formaldehyde includes surface adsorption and internal particle diffusion,while surface adsorption is the main mechanism for RL-CS.Furthermore,four adsorption isotherm models were used to describe the isotherm adsorption process.It is found that Freundlich isotherm model shows the best fitting result,which indicates that both adsorbents are multilayer adsorption.It can be classified as physical adsorption.（2）Based on the above research,a tremella-like porous calcium silicate（PCS）with large specific surface area(122.83 m² g^-1)was prepared via a hydrothermal method.The surface morphology,specific surface area,pore size,and crystal structure of PCS were characterized.Results show that PCS presents a tremella-like morphogical structure with abundant surface folds and the porous interior.It has a high Ca/Si ratio（1.95）,and the crystal strucuture belongs to wollastonite.Taking formaldehyde as the target pollutant,the adsorption ability of the as-prepared PCS under different experimental conditions was studied and the adsorption mechanism towards formaldehyde was explored in terms of adsorption kinetics and thermodynamics.The results of batch adsorption experiments show that PCS can remove formaldehyde form water rapidly and effectively with the maximum removal efficiency of 98.94%,which shows excellent adsorption ability.The adsorption process agrees well with the pseudo-second-order model and Freundlich isotherm model.The micro morphology and crystal structure of PCS samples before and after formaldehyde adsorption were analyzed and compared by scanning eletron microscopy and X-ray diffractometer;and the changes of binding energy of PCS before and after formaldehyde adsorption were also examined by X-ray photoelectron spectroscopy.It is found that the surface structure and the crystal form of PCS changed when formaldehyde has been absorbed;in combination with the fact that the chelation between the silicon group in the PCS and formaldehyde results in the change of chemical bond energy,the adsorption should be chemisorption.To further explore the adsorption mechanism,the adsorption process of PCS towards formaldehyde was studied by molecular dynamic simulation.The simulation results further confirmed that the silicon groups in the PCS acted as adsorption sites to produce chemisorption interactions with the negatively charged oxygen atoms of formaldehyde.Regeneration performance of PCS can be achieved by simply immersing PCS in absolute ethanol.Results show that the removal efficiency of formaldehyde in water by PCS can still reach about 99.50%after five adsorption-desorption cycles.This demonstrates that PCS has an important reused value in the practical application.