Kinetics and thermodynamics of adsorption for arsenate ions on the hierarchical porous adsorbent of α-Fe_2O_3/Fe_3O_4/C with bamboo bio-template

摘要

A novel hierarchical porous adsorbent of alpha-Fe2O3/Fe3O4/C (HPA-Fe/C-B) was prepared with bamboo bio-template and investigated for its adsorption capacity of arsenic(V). The result indicated that the HPA-Fe/C-B adsorbent had a specific surface area of 198.1 m(2)/g and retained the hierarchical porous microstructure of bamboo with three kinds of pores (widths 50 similar to 75 mu m, 1 similar to 30 mu m and 0.0017 similar to 0.2891 mu m) originating from vessels, fibres or parenchyma cells and pits on the walls of the vessels and parenchyma cells, respectively. With increasing initial arsenic(V) concentrations from 5 mg/L to 100 mg/L, the amounts of arsenic(V) adsorbed on the pulverized HPA-Fe/C-B adsorbent (<0.149 mm) increased from 0.50 mg/g to 4.55 mg/g at 25 degrees C, from 0.50 mg/g to 5.33 mg/g at 35 degrees C and from 0.50 mg/g to 4.89 mg/g at 45 degrees C. The corresponding removal rates decreased from 99.97% to 45.58% at 25 degrees C, from 99.98% to 53.30% at 35 degrees C and from 100.00% to 48.94% at 45 degrees C. At the initial arsenic(V) concentrations of 5, 10 and 50 mg/L, the adsorption capacities for the un-pulverized HPA-Fe/C-B adsorbent (>3 mm) were 0.45, 0.86 and 3.02 mg/g, respectively, which were nearly equal to the mean value for iron oxides particles or nanoparticles. The pseudo-second-order kinetic model fitted the experimental data very well. The adsorption followed both Langmuir and Freundlich isotherms.