Preparation Of Functionalized Silica Aerogel And Its Adsorption Performance On Heavy Metal Ions(Pb²⁺,Cu²⁺) In Wastewater

Water is the source of life,providing a continuous driving force for human survival and development.Accelerated industrialization has led to serious problems of heavy metal water pollution.Among the various treatment methods,adsorption is recognized as an effective and attractive method due to its low cost,high efficiency and environmental friendliness.As a new functional material,silica aerogel has low density,high porosity and high specific surface area,however,the surface of silica aerogel lacks the appropriate active functional groups and the preparation conditions are harsh.In order to better introduce them into the heavy metal wastewater treatment market,this study synthesized functionalized silica aerogel materials with excellent performance by tailoring functional groups with specific adsorption to heavy metal ions under atmospheric pressure drying conditions,in order to seek practical and effective water pollution treatment methods.The main research contents and results are as follows:（1）Mercapto-functionalized silica aerogels（MA-X）were prepared using a simple sol-gel method and an atmospheric pressure drying technique.The experimental results showed that the maximum adsorption capacities of MA2 could reach 163.99 and 172.41 mg/g for Pb（II）and Cu（II）in the single heavy metal ion system,and 90.42 and 161.29 mg/g for Pb（II）and Cu（II）in the binary heavy metal ion system,respectively.The adsorption kinetics were well fitted by the pseudo second kinetic model and the adsorption isotherms were consistent with the Langmuir model,indicating that MA2 adsorbed Pb（II）and Cu（II）via a single molecular layer.The selective adsorption experiments showed that MA2 had a greater tendency to adsorb Cu（II）,suggesting that Cu（II）was more readily adsorbed on MA2.The XPS analysis and DFT calculations indicated that the main adsorption mechanism of MA2 was through the-SH coordination with Pb（II）and Cu（II）.The environmental impact of producing 1 kg of adsorbent were studied using Life Cycle Analysis（LCA）,which identified the main factors that had an impact on the environment and suggested corresponding solutions.（2）Mesoporous amino-functionalized silica aerogels（MASA-X）with high adsorption capacity were prepared by the introduction of 3-aminopropyltriethoxysilane（APTES）.The maximum adsorption capacities of MASA-1,MASA-2,MASA-3 and MASA-4 were 444.4,628.93,549.45 and 286.53 mg/g for Pb（II）and 426.53,427.71,426.59 and 404.78 mg/g for Cu（II）,respectively.The adsorption kinetics showed that the adsorption was in accordance with the pseudo second kinetic model,the adsorption isotherms showed that the adsorption was in accordance with the Langmuir model,and the adsorption thermodynamics showed that the adsorption was an endothermic and spontaneous process.After 8 repeated cycles of adsorption-desorption,the removal efficiency of Pb（II）and Cu（II）by MASA-2 was still above 90%,indicating its good recycling performance.Combined with FTIR,XPS analysis and DFT calculations,it was shown that the N atom of-NH₂ in MASA-2 provided the lone pair of electrons to bind to Pb（II）and Cu（II）,relying on the coordination adsorption to achieve the removal of Pb（II）and Cu（II）from the wastewater.The environmental impact of producing 1 kg of MASA-2 material was evaluated through an environmental impact analysis and a more environmentally friendly production solution was proposed.（3）A new Schiff base silica aerogel（SCA-X）with excellent adsorption performance for Pb（II）and Cu（II）was successfully developed using a simple condensation reaction.The maximum adsorption capacities of SCA1,SCA2,SCA3 and SCA4 were 270.2,357.1,322.5and 256.4 mg/g for Pb（II）and 212.7,243.9,204.0 and 181.8 mg/g for Cu（II）,respectively.The adsorption of Pb（II）and Cu（II）by SCA-X was in accordance with the pseudo second kinetic model and the Langmuir isotherm model,and the adsorption was a spontaneous endothermic process.In terms of the adsorption mechanism,the interaction between SCA2and Pb（II）occurred through the coordination of the N atom donor in the Schiff base and the O atom donor on the benzene ring with Pb（II）,while the interaction between SCA2 and Cu（II）occurred mainly through the coordination of the N atom in the Schiff base with Cu（II）.The environmental impact of the SCA2 preparation process were revealed in conjunction with LCA analysis,providing a more environmentally friendly preparation process.（4）Amidoxime functionalized silica aerogels（AOSA-X）were prepared by a two-step method.The effect of the introduction of different levels of cyanosilane coupling agents（CTES）on the morphology and adsorption performance of the AOSA-X was investigated.It was found that AOSA3 had a large specific surface area and a homogeneous microscopic morphology,and its adsorption performance for the heavy metal ions Cu（II）and Pb（II）was optimal.The infrared spectra showed that the cyanide had successfully reacted to form the kaiamine oxime group.The maximum adsorption capacities of AOSA1,AOSA2,AOSA3 and AOSA4 for Pb（II）were 453.53,505.14,598.05 and 511.75 mg/g,respectively,and the maximum adsorption capacities for Cu（II）were 417.08,480.40,534.10 and 417.51 mg/g,respectively.The adsorption process was in accordance with the pseudo second kinetic model and the Langmuir isotherm model,and it was a spontaneous endothermic process.XPS analysis and DFT calculations revealed that the adsorption of Pb（II）and Cu（II）by AOSA3occurred mainly through the formation of ligand bonds by the lone pair of electrons provided by the N and O atom donors of the ketamine oxime group,which has a strong coordination capacity for Pb（II）and Cu（II）.In addition,the environmental impact of the preparation process was determined and effective solutions were proposed by assessing the environmental impact of the various materials used in the production of 1 kg AOSA3,providing a solid basis for sustainable and environmentally friendly AOSA3 production.