Study On Adsorption Property Of Hydrophobic Silica Aerogels For Organic Pollutants In Groundwater

In recent years,groundwater has become increasingly polluted as an important water resource,and as many as 44 organic pollutants have been detected.Among them,non-aqueous liquid organic compounds?NAPLs?exist in the form of free phase,dissolved phase and residual phase in high concentration pollution areas.Free-phase organic pollutants will continue to migrate and spread,becoming a long-term source of groundwater pollution.Hydrophobically modified SiO₂ aerogel has excellent adsorption performance due to its low density,high porosity,high surface area,etc.,especially as an oil-absorbing sponge,which is often used for oil spill cleanup,so it is excellent for NAPL phase organic matter.The adsorption effect can be used as an adsorption material to adsorb and block the free-phase organic matter in the high-concentration pollution source region of organic pollution.In this paper,two hydrophobic SiO₂ aerogels were prepared by sol-gel method using tetraethyl orthosilicate as raw material.One is modified by trimethylchlorosilane,a common hydrophobic modifier,and the other is aromatic.The compound is targeted to an N-phenyl-3-aminopropyltrimethoxysilane modified aerogel.The adsorption process,adsorption kinetics and adsorption mechanism of NAPL phase organic benzene and nitrobenzene were adsorbed by two hydrophobic SiO₂ aerogels.Then the adsorption effect of organic pollutants benzene,nitrobenzene and naphthalene under dissolved phase conditions was studied.Finally,the hydrophobic SiO₂ aerogel was used as a packed sorbent material for the suspended permeable reaction barrier to simulate the tank experiment,which proved the feasibility of adsorbing the free phase NAPL.The experimental results lead to the following conclusions:?1?Two hydrophobic SiO₂ aerogels were prepared.The specific surface area of methyl SiO₂ aerogel was 502.15 m²/g,the pore size is mainly distributed between 10-30 nm,the average pore diameter is 19.21 nm,the left contact angle is 157.39°,and the right contact angle is 156.94°.The surface area of the anilino SiO₂ aerogel was 469.21m²/g.The pore size is mainly distributed between 4-8 nm,the average pore diameter is6.31 nm,the left contact angle is 122.64°,and the right contact angle is 121.94°.Both aerogels were successfully hydrophobically modified and were both hydrophobic surfaces.?2?In the experiment of adsorbing pure phase organic matter,the aerogel adsorbed by the capillary force generated by the internal pores and the osmotic driving force of the organic matter.The adsorption of benzene by methyl SiO₂ aerogel can reach 10.50 g/g,and the adsorption of nitrobenzene can reach 14.39 g/g.The anilino-based SiO₂ aerogel adsorbed benzene 8.53 g/g and adsorbed nitrobenzene 11.66 g/g.It is indicated that the hydrophobic SiO₂ aerogel not only has good adsorption effect on dissolved organic matter,but also has better adsorption effect on pure phase organic matter.The hydrophobic modified SiO₂ aerogel has a fast and efficient adsorption process for pure phase organics.The higher the concentration of the silane coupling agent,the stronger the hydrophobicity of the surface of the material,and the stronger the ability to adsorb pure phase organic matter.The experimental data better fit the quasi-secondary kinetic model.The absorption process consists of two steps,a rapid absorption step,due to the pore structure of the sample,the capillary system may generate a large amount of absorption immediately after the sample contacts the organic matter,and the subsequent slow equilibrium process,that is,the gradual migration process of the pure phase organic matter inside the pore.?3?Hydrophobic SiO₂ aerogel can adsorb dissolve pollutants such as benzene,nitrobenzene and naphthalene.The adsorption capacity of the three kinds of methyl SiO₂ aerogels reached 182.33 mg/g,223.17 mg/g and 5.12 mg/g under the experimental conditions.The adsorption capacity of aniline SiO₂ aerogel for benzene,nitrobenzene and naphthalene was 206.33 mg/g,286.51 mg/g and 5.69 mg/g,respectively.Adsorption rate naphthalene>nitrobenzene>benzene,although the adsorption capacity of naphthalene is less than benzene and nitrobenzene due to low solubility,the adsorption rate of naphthalene SiO₂ aerogel to naphthalene can reach more than 99%.Therefore,the hydrophobic SiO₂ aerogel has better adsorption capacity for macromolecular polycyclic aromatic hydrocarbon pollutants.The adsorption capacity of aniline-based SiO₂ aerogel for organic matter has been improved to some extent,indicating that N-phenyl-3-aminopropyltrimethoxysilane modified aerogel has better adsorption capacity for aromatic pollutants.The adsorption process is more in line with the Freundlich adsorption model and the pseudo second-order kinetic model,and the adsorption process proceeds spontaneously.?4?In the simulation experiment,after the hydrophobic SiO₂ aerogel suspension type PRB was set,the diesel oil migrated by capillary force and hydrodynamic force and was quickly adsorbed into the SiO₂ aerogel.The filled SiO₂ aerogel 5.66 g absorbed about 46 mL of diesel oil,and the simulated injection of 60 mL of diesel oil.After48 h,the aerogel adsorbed about 76.67%of the total leakage,indicating its good adsorption capacity.In the experimental process,SiO₂ aerogel actively adsorbs diesel oil into PRB,and it has strong adsorption capacity and rapid adsorption rate to achieve the purpose of adsorption blocking.The feasibility of using hydrophobic SiO₂ aerogel as an adsorption blocking material was demonstrated in the high-concentration pollution source region of the free phase.