Green and facile modification of mesoporous activated carbon for selective indium and gallium recovery from waste photovoltaic modules

With the increasing deployment and subsequent retirement of photovoltaic (PV) modules, it is urgent to selectively recover critical metals involved, such as indium (In) and gallium (Ga). Activated carbon, a widely used eco-friendly adsorbent for metal ions, often requires large amounts of toxic chemicals and complicated modifications to achieve selective adsorption. Herein, a novel adsorbent with outstanding ability for In and Ga recovery, phosphoryl-functionalized waste biomass-derived mesoporous activated carbon (P-PDA@MAC), was synthesized via a green and facile one-pot method. This approach eliminates the use of toxic organic reagents and enables functionalization at ambient temperature and pressure, aligning with the principles of green chemistry. Using ethyl phenylphosphinate (EPP) as a precursor, the obtained EPP-PDA@MAC exhibited superior adsorption capacity for In3+ (125.1 mg g-1) and Ga3+ (140.7 mg g-1) and high selectivity (SFXIn = 382.4, SFXGa = 239.0) over competing ions Al3+, Zn2+, Cd2+, Cu2+, and Mg2+. Surprisingly, this adsorbent demonstrated excellent reusability, maintaining adsorption efficiencies above 85% over 9 cycles in a static system and 98% over 50 cycles in a capacitive deionization system. The superior adsorption ability of EPP-PDA@MAC was ascribed to the abundant and stable phosphoryl groups, facilitated by the adhesive polydopamine coating and covalent phosphoryl-functionalization on the high surface area of MAC. Furthermore, a comparison of the adsorption ability, green metrics, and production costs with those of commercial adsorbents underscores the significant industrial application potential of EPP-PDA@MAC. The successful extraction of 99.9% In (purity = 97.79%) and Ga (purity = 90.40%) from waste copper indium gallium selenide PV modules by EPP-PDA@MAC highlights its potential and industrial viability for the circular economy.