Preparation of Polyhydroxybutyrate/Carbon Nanotubes Composite Nanofiber Membrane and Their Adsorption Performance for Heavy Metal Ions

Polyhydroxybutyrate/carbon nanotubes composite nanofiber membrane was successfully prepared via electrospinning technique using polyhydroxybutyrate and carbon nanotubes as raw materials and chloroform/dimethylformamide blend as co-solvent. The effect of carbon nanotube content on the membrane's morphology and mechanical properties was investigated, and its adsorption performance to heavy metal ions was evaluated. Increasing the content of carbon nanotubes from 0 to 1 wt%, it was found that the average diameter of composite nanofibers decreased from (728 +/- 146) nm to (468 +/- 89) nm while their specific surface area increased from 27.24 m(2)/g to 43.45 m(2)/g; meanwhile, the nanofiber membrane was significantly strengthened with the optimum mechanical performance obtained at the content equal to 1 wt%. A tensile stress of 5.85 MPa was achieved then, which was about 115% improvement compared with the pure polyhydroxybutyrate nanofiber membrane. Good adsorption performance was exhibited by the composite nanofiber membrane for Cu(II), Cd(II) and Pb(II) ions from aqueous solution. Under the optimum pH of 5, the maximum adsorption capacity was measured as about 91.04, 171.05 and 197.03 mg/g for Cu(II), Cd(II) and Pb(II) ions, respectively; the corresponding equilibrium time and adsorption rate were about 50, 60 and 60 min and 1.79, 2.83 and 3.28 mg/g/min, respectively. Langmuir, Freundlich and Temkin models were used to analyze the thermodynamics parameters during adsorption while Pseudo-first-order, Pseudo-second-order and Intraparticle diffusion models were applied for analysis of the kinetics parameters. It was indicated that the adsorption isotherm data fitted well with Freundlich model and the kinetic process matched Pseudo-second order model. Cycle experiments demonstrated that above 87% of initial adsorption capacity could be maintained after 5 times of usage, which suggested the nanofiber membrane's potential of applications in wastewater treatment for the removal of heavy metal ions as a nano-adsorbent.