Bio-inspired one-step structure adjustment and chemical modification of melamine foam toward highly efficient removal of hexavalent chromium ions

Providing highly efficient and economical adsorbents is the prerequisite for the heavy metal ions removal from wastewater through the adsorption method. Herein, the polydopamine (PDA)-coated melamine foam (MF) skeleton (MF-PDA) was achieved through the bio-inspired functionalization method. The results showed that the smooth surface of MF skeleton was successfully coated by PDA nanoparticles, leading to the changes of surface roughness and chemical features of MF skeleton. Studies on the adsorption behaviors toward highly toxic Cr(Ⅵ) by the MF-PDA samples showed that the MF-PDA samples had the good removal ability and the maximum adsorption capacity was about 240 mg/g at pH value of 2. In addition, the MF-PDA sample also showed high adsorption selectivity, high desorption ability and good reusability. Further analysis found that the coated PDA had a strong reduction effect on Cr(Ⅵ), and about 53.7% toxic Cr(Ⅵ) was reduced to low-toxic Cr(III) during the adsorption. Although PDA decoration method has already been used to assist the secondary modification or to enhance the modification efficiency of the other functionalization method, this work clearly declares that PDA exhibits great role in removing Cr(Ⅵ) and the MF-PDA sample is a promising adsorbent for removing highly toxic Cr(Ⅵ) from sewage.