Selective Adsorption and Recovery of Silver from Acidic Solution Using Biomass-Derived Sulfur-Doped Porous Carbon

It is vital to recycle precious metals effectively suchas silverfrom waste sources because of limited natural reserves. Herein, passionfruit (Passiflora edulis Sims) shell-derived S-doped porous carbons (SPCs) were newly synthesizedby hydrothermal carbonization and following with activation by KOH/(NH4)(2)SO4, and the adsorption of Ag+ on SPC under acidic solutions was investigated. It was foundthat the activator of (NH4)(2)SO4 cannot only introduce the doping of S elements but also increase theproportion of mesopores in the as-prepared SPC. As the active site,the increasing S doping can improve the adsorption of Ag+ on SPC. The kinetic data of Ag+ adsorption by SPC wasconsistent with the pseudo-second-order kinetic model. The Langmuirisothermal model was used to well fit the Ag+ adsorptionisotherms of SPC, and the maximum adsorption capacity of the optimizedSPC-3 for Ag+ is up to 115 mg/g in 0.5 mol/L HNO3 solution. SPC-3 showed good selectivity toward Ag+ overdiverse competing cations, which is mainly attributed to the strongbonding between Ag+ ions and the sulfur-containing functionalgroups on the surface of SPC-3 resulting in the formation of Ag2S nanoparticles. The adsorbed Ag could be recovered as anelemental form by a simple calcination. This study provides a newinsight into the design of an environmentally friendly and efficientadsorbent for the selective recovery of silver from acidic aqueousmedia.