Synthesis of Copper Nanoparticles from Cu(2+)-Spiked Wastewater via Adsorptive Separation and Subsequent Chemical Reduction

Copper in ionic form (Cu(2+)) should be removed from wastewater because of its harmful effects on human health. Meanwhile, Cu-metal nanoparticles (Cu(0) NPs) are widely used in various applications such as catalysts, optical materials, sensors, and antibacterial agents. Here, we demonstrated the recovery of Cu(2+) from wastewater and its subsequent transformation into Cu(0) NPs, a value-added product, via continuous adsorption followed by chemical reduction by hydrazine. To separate and enrich Cu(2+) from wastewater, a biosorbent that exhibits excellent selectivity and adsorption capacity toward Cu(2+), i.e., polyethyleneimine-grafted cellulose nanofibril aerogel (PEI@CNF), was packed into a column and used to treat 20 mg/L Cu(2+) wastewater at a flow rate of 5 mL/min. The Cu(2+) adsorption reached equilibrium at 72 h, and the Cu(2+)-saturated column was eluted using 0.1 M of HCl. After five consecutive elutions of Cu(2+) from the adsorbent column, a Cu(2+)-enriched solution with a concentration of 3212 mg/L was obtained. The recovered Cu(2+) concentrate was chemically reduced to obtain Cu(0) NPs by reaction with hydrazine as a reductant in the presence of sodium dodecyl sulfate (SDS) as a stabilizer. The solution pH and hydrazine/Cu(2+) ratio strongly affected the reduction efficiency of Cu(2+) ions. When 0.1 M of SDS was used, spherical 50–100 nm Cu(0) NPs were obtained. The results demonstrate that Cu(2+)-spiked wastewater can be converted into Cu(0) NPs as a value-added product via adsorption followed by chemical reduction.