Introduction of copper nanoparticles in chitosan matrix as strategy to enhance chromate adsorption

In this study, copper nanoparticles (CuNPs) were incorporated to chitosan (CHI) matrix as strategy to enhance the chromate adsorption by CHI membrane. The CuNPs were synthesized using NaBH4 as the reducing agent. Dispersive X-ray Absorption Spectroscopy (DXAS) was used to monitor the in situ reduction of Cu(II). The influence of the presence of CuNPs on the hygroscopic behavior was also evaluated. DXAS technique showed that the adsorbed Cu(II) was reduced to Cu(I) (63%) and Cu(0) (37%) species, at the end of the reduction reaction (using NaBH4, after ∼30 min). The hygroscopic behavior of the proposed sorbent was more influenced by CuNPs when the water vapor adsorption was conducted under synthetic air atmosphere. A decrease in the energy of interaction among the water molecules adsorbed on the monolayer was observed. The chromate adsorption study has shown a higher equilibrium concentration of adsorbed chromium species when the CHI membrane containing CuNPs was used as sorbent. The CuNPs offered a second active adsorption site, which was characterized by a higher coefficient of affinity (12 L mmol−1, against 0.18 L mmol−1 reported for CHI). The enhanced adsorption of chromium in the presence of CuNPs was associated to the redox reaction between the CuNPs and chromate anions.