| Polyaniline (PANI) and polypyrrole (PPy) are two kinds of polymers containing abundant nitrogen functional groups, are widely used in adsorptive removal of environmental pollutants. Heavy metal ions, especially Hg(Il) and Cr(VI), could be removed by PANI and PPy. However, low adsorption capacity and difficulty in solid-liquid separation of powder adsorbent after adsorption limited their applications in pollution control and remediation.In this paper, PANI or PPy were selected as research object, and their adsorption capacities for heavy metal ions were enhanced by compositing with reduced graphene oxide (RGO), doping with complexing agent and introducing of electrochemical assistance, respectively. To facilitate the adsorbent recovery and regeneration, composite membrane adsorbent, composite electrode and magnetic adsorbent were synthesized to improve recovery efficiency of nitrogen-containing conductive polymers through immobilization of polymers and magnetic separation, respectively.Forcusing on the above research contents, the following results were obtained through conducted research:(1) PANI/RGO composite was synthesized by in-situ polymerization of aniline in the presence of graphene oxide (GO) and followed reduction with hydrazine hydrate. For Hg(II) adsorption, the optimal GO content was 15 wt.% of aniline, and the presence of RGO resulted 7.24 times enhancement in the specific surface area. For both PANI and PANI/RGO, the adsorption process could be well explained by pseudo-second-order kinetic model. The isotherm data of PANI/RGO fitted Freundlich isotherms model. The equilibrium adsorption capacity of PANI/RGO for Hg(II) was 1.59 times that of pure PANI. PANI/RGO maintained its adsorption capacity in the presence of NO3- or sodium humate.(2) PANI/RGO/Fe3O4 composite was prepared by solvothermal synthesis of RGO/Fe3O4 and followed in-situ polymerization of aniline. Composite adsorbent with 30 wt.% GO/aniline had the maximum adsorption capacity for Hg(II), and the presence of RGO/Fe3O4 resulted 3.56 times enhancement in the specific surface area. The prepared PANI/RGO/Fe3O4 could be easily recovered under magnetic field as the specific saturation magnetization reached 21.4 emu·g-1. For both adsorbents, adsorption kinetics fitted well with pseudo-second-order kinetic model. The adsorption behavior of PANI/RGO/Fe3O4 was in good accordance with Freundlich isotherms model. The equilibrium adsorption capacity of PANI/RGO/Fe3O4 for Hg(II) was 1.57 times that of pure PANI. HC1 solution (pH=2.0) was optimal for desorption and regeneration of Hg(Ⅱ) loaded PANI/RGO/Fe3O4, and PANI in PANI/RGO/Fe3O4 could inhibit leaching of Fe3O4 in acidic solution.(3) With cellulose acetate (CA) as matrix, phytic acid doped polyaniline/cellulose acetate (PANI-PA/CA) composite membrane was prepared through in-situ polymerization of aniline and phase-inversion process. For Hg(Ⅱ) adsorption, the optimum content of CA, aniline and PA were 8.0 wt.%,3.0 wt.% and 6.0 wt.%, respectively. Optimum pH for the adsorption of Hg(II) and Cr(VI) on the prepared PANI-PA/CA composoite membrane were 5.0 and 2.0, respectively. For both Hg(II) and Cr(VI), adsorption kinetics fitted pseudo-second-order kinetic model. Hg(II) adsorption was better fitted using Langmuir isotherm model, and both Langmuir and Freundlich isotherm models correlated well with adsorption isotherm data of Cr(VI). The maximum adsorption capacities reached 280.14 and 94.34 mgg-1 for Hg(Ⅱ) and Cr(VI), respectively. Both acidic and basic solutions were effective desorption medium for Hg(II) loaded PANI-PA/CA. Meanwhile, doping of phytic acid could increase removal ratio of other divalent heavy metal cations by polyaniline composite membrane.(4) With carbon fiber cloth as base substrate, PPy modified electrode (PPy electrode) was prepared through electrochemical polymerization and adsorption of Pb(Ⅱ) ions on PPy electrode under electrochemical assistance was investigated. In batch adsorption tests, modification with PPy improved electro-adsorption efficiency of electrode for Pb(Ⅱ). The electro-adsorption capacity of Pb(Ⅱ) increased with the increase of solution pH. The electro-adsorption process fitted pseudo-first-order kinetic model, and value of equilibrium adsorption capacity at-0.1 V was found to be 19.11 times of that for open circuit adsorption. The isotherm data fitted Langmuir isotherms model, and the maximum adsorption capacity reached 339.24 mg·g-1 at -0.2 V. In addition, the desorption of Pb(II) loaded PPy electrode could be accelerated when a positive potential (+0.1 V) was applied.In this work, adsorption capacity of nitrogen-containing conductive polymers for heavy metal ions was improved through increasing effective functional group density, enriching types of functional groups and introducing of electrochemical assistance. Immobilization on membrane or compositing with magnetic material provided two options for convenient recovery of adsorbents. The high efficiency and adsorption capacity brought by functional materials make nitrogen-containing conductive polymer composite adsorbents particularly attractive and applicable in treatment of practical heavy metal pollution. |
PDF Full Text Request