Importance of a nano-sized molybdenum composite synthesized using a microwave oven in the sorption enhancement of Au(iii) from the aqueous phase

Abstract

To significantly enhance the unsatisfactory Au(III) sorption performance (2280 mg g⁻¹) by a material designed in our previous work, we ingeniously fabricated a nano-sized and uniform molybdenum composite (MoCOM) using a household microwave oven; it was embedded in a nanofiber mat by electrospinning technique to synthesize a novel material (CS-MoCOM-Th) for effective Au(III) sorption. After embedding MoCOM, an ultrahigh maximum sorption capacity (4090 mg g⁻¹) of Au(III) at high concentrations and a sorption efficiency at low concentrations by CS-MoCOM-Th (99.59%) were achieved at pH 4.0. Mechanistically, the excellent Au(III) sorption performance was mainly driven by electrostatic attraction by protonated C–N⁺ groups and coordination interaction with N- or S-containing moieties: C–N, CN, C–N⁺, CS, S(−II), and S_n(−II). During sorption, 69.42% of Au(III) was directly reduced to elemental gold on CS-MoCOM-Th, and gold foils precipitated on the nanofiber mat. Notably, excellent sorption selectivity of Au(III) on CS-MoCOM-Th was achieved when heavy metals, including Cu(II), Ni(II), Pb(II), and Zn(II), and noble metal Pt(IV) were co-present at 2 × 10⁻³ mg mL⁻¹. CS-MoCOM-Th could still sorb 82.15% of Au(III) at 0.01 mg mL⁻¹ after four cycles. Overall, this study highlights that CS-MoCOM-Th is one of the most competitive candidates for Au(III) recovery from the aqueous phase.