Synthesis of Copper Nanoparticles from Cu²⁺-Spiked Wastewater via Adsorptive Separation and Subsequent Chemical Reduction

Copper in ionic form (Cu²⁺) should be removed from wastewater because of its harmful effects on human health. Meanwhile, Cu-metal nanoparticles (Cu⁰ NPs) are widely used in various applications such as catalysts, optical materials, sensors, and antibacterial agents. Here, we demonstrated the recovery of Cu²⁺ from wastewater and its subsequent transformation into Cu⁰ NPs, a value-added product, via continuous adsorption followed by chemical reduction by hydrazine. To separate and enrich Cu²⁺ from wastewater, a biosorbent that exhibits excellent selectivity and adsorption capacity toward Cu²⁺, i.e., polyethyleneimine-grafted cellulose nanofibril aerogel (PEI@CNF), was packed into a column and used to treat 20 mg/L Cu²⁺ wastewater at a flow rate of 5 mL/min. The Cu²⁺ adsorption reached equilibrium at 72 h, and the Cu²⁺-saturated column was eluted using 0.1 M of HCl. After five consecutive elutions of Cu²⁺ from the adsorbent column, a Cu²⁺-enriched solution with a concentration of 3212 mg/L was obtained. The recovered Cu²⁺ concentrate was chemically reduced to obtain Cu⁰ NPs by reaction with hydrazine as a reductant in the presence of sodium dodecyl sulfate (SDS) as a stabilizer. The solution pH and hydrazine/Cu²⁺ ratio strongly affected the reduction efficiency of Cu²⁺ ions. When 0.1 M of SDS was used, spherical 50-100 nm Cu⁰ NPs were obtained. The results demonstrate that Cu²⁺-spiked wastewater can be converted into Cu⁰ NPs as a value-added product via adsorption followed by chemical reduction.