Transition-Metal Antimonides as Highly Efficient and Reusable Adsorbents for Hexavalent Chromium Removal from Water

Herein, two mesoporous intermetallic compounds, CoSb and NiSb, synthesized using a green and cost-effective coprecipitation method, are investigated as efficient adsorbents for Cr(VI) removal. The synthesized samples were subjected to comprehensive characterization through X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET) isotherm, X-ray photoelectron spectroscopy (XPS), and ζ-potential analyses. Batch adsorption experiments were conducted to evaluate the efficacies of CoSb and NiSb nanoparticles in removing Cr(VI) ions, considering key parameters such as the initial Cr(VI) concentration (2–50 mg L–1), contact time (24 h), pH (1.7, 4.5, 8.5), adsorbent dosage (0.3–0.9 g L–1), and recyclability (5 cycles). The results revealed that Cr(VI) adsorption on CoSb followed a pseudo-second-order kinetic model, while NiSb displayed a pseudo-first-order kinetic model. The Langmuir isotherm model best described the equilibrium data, indicating maximum adsorption capacities of 33.3 mg g–1 for CoSb and 30 mg g–1 for NiSb. A plausible mechanism regarding the adsorptive removal of Cr(VI) onto CoSb and NiSb particle surfaces is proposed in the discussion. Overall, this study underscores the effectiveness of CoSb and NiSb as promising candidates for the efficient removal of toxic Cr(VI), opening avenues for the use of other intermetallic compounds in heavy metal removal and various water treatment applications.