Preparation Of Indole-based Porous Material And Their Adsorption Properties For Heavy Metal Ions

At present,the health of human being is endangered by heavy metal ions,and adsorption is one of the better methods to deal with heavy metal ions pollution.How to develop efficient,economical,green and environment-friendly adsorbents for heavy metal ions has become a great challenge.Aerogels and conjugated microporous polymers are two kinds of new nano-porous materials,which have high porosity and large specific surface area.Therefore,two novel indole-based aerogels and one conjugated microporous polymer were successfully prepared.Moreover,their adsorption properties and mechanisms for heavy metal ions were studied in detail.The obtained results are as follows:1.A novel indole-based aerogel?4-HIFA?has been obtained by the condensation of4-hydroxyindole and formaldehyde via sol-gel technology,which proceeds easily by acid catalysis in one pot.The successful formation of the indole-based aerogel was confirmed by Fourier Transform Infrared?FT-IR?spectrometry and solid-state cross-polarization magic-angle-spinning?CP/MAS?NMR spectrometry.Scanning electron microscopy?SEM?and N₂ adsorption-desorption isotherms showed that 4-HIFA had good porous structure and specific surface area was 130 m² g^-1.Due to the synergistic effects of the complexation and cation-?interactions of the hydroxyl and indole groups of 4-HIFA skeleton,4-HIFA exhibited excellent adsorption ability for four kinds of heavy metal ions(Ni²⁺,Cu²⁺,Cr³⁺and Zn²⁺),its adsorption quantity increased with time and achieved dynamic equilibrium within5 min,the saturated adsorption capacity of 4-HIFA aerogel on Ni²⁺,Cu²⁺,Cr³⁺and Zn²⁺obtained by fitting the Langmuir equation was 240.4,264.6,92.2 and 126.6 mg/g,respectively.2.Carboxyl-functionalized indole-aerogel?CHIFA?was prepared by the condensation of5-hydroxyindole-3-acetic acid and formaldehyde via sol-gel technology,which proceeds easily by sodium carbonate catalysis in one pot.The successful formation of the Carboxyl-functionalized indole-aerogel was confirmed by FT-IR spectrometry and CP/MAS NMR spectrometry.SEM and N₂ adsorption-desorption isotherms showed that CHIFA had good porous structure and specific surface area was 143 m² g^-1.Owing to the synergistic effects of the complexation and cation-?interactions of the hydroxyl,carboxyl and indole groups of CHIFA skeleton,CHIFA displayed much more outstanding adsorption ability for four kinds of heavy metal ions(Ni²⁺,Cu²⁺,Cr³⁺and Zn²⁺),its adsorption quantity increased with time and achieved dynamic equilibrium within 2 min,the saturated adsorption capacity of CHIFA aerogel on Ni²⁺,Cu²⁺,Cr³⁺and Zn²⁺obtained by fitting the Langmuir equation was 298.5,383.1,196.9 and 217.4mg/g,respectively.3.A novel indole-conjugated microporous polymer?PTIA?was prepared by oxidative coupling polymerization by using triazatruxene.The successful formation of the indole-conjugated microporous polymer was confirmed by FT-IR spectrometry and CP/MAS NMR spectrometry.SEM and N₂ adsorption-desorption isotherms showed that PTIA had good porous structure and specific surface area was 139 m² g^-1.Because of the cation-?interaction between large conjugate indole skeleton of PTIA with heavy metal ions,PTIA demonstrated excellent adsorption ability for four kinds of heavy metal ions(Ni²⁺,Cu²⁺,Cr³⁺and Zn²⁺),its adsorption quantity increased with time and achieved dynamic equilibrium within 1 min,the saturated adsorption amount of PTIA on Ni²⁺,Cu²⁺,Cr³⁺and Zn²⁺obtained by fitting the Langmuir equation was 289.9,323.6,179.9 and 205.3 mg/g,respectively.