Synthesis, characterization of amino-modified walnut shell and adsorption for Pb(II) ions from aqueous solution

In this paper, a biodegradable, green, easy renewable heavy metal capture agent, amino-modified walnut shell (AMWNS), was synthesized, and the adsorption behavior for Pb(II) ions from aqueous solution was also investigated. The AMWNS was prepared, where triethylene tetramine (TETA) was used as modified monomer, and the structure of AMWNS was characterized by Fourier transform infrared spectroscopy, scanning electron microscope, X-ray diffraction and thermogravimetric analysis. Then, adsorption capacity of AMWNS for Pb(II) was investigated in different pH (2–9) and different adsorbent dosage (0.5–2.0 g/L), and the result showed when solution pH value was 7, the adsorption capacity of the AMWNS on Pb(II) ions was optimal. The maximum Pb(II) ions adsorption capacity ( Q m ) obtained by Langmuir fitting model was 56.81 mg/g at 298 K. The adsorption kinetics was well confirmed by pseudo-second-order equation. The results of thermodynamic studies showed the adsorption of AMWNS for Pb(II) ions was an endothermic reaction and spontaneous process. Furthermore, the result showed AMWNS had excellent regeneration capability.