Tandem incorporation and encapsulation of Ag2S nanoparticles onto a nickel metal-organic framework decorated with Ag NPs heterojunction for efficient photoreduction of Cr (VI)

Abstract

Cr(VI) pollution has become a growing concern, posing significant challenges to the chemical industry and environmental protection efforts. Addressing this issue is critical for ensuring ecological and industrial sustainability. In this work, a novel ternary heterojunction nanocomposite Ag/Ag₂S@Ni-MOF was successfully engineered and synthesized using a hydrothermal method. The Ag₂S content was optimized, with the best performance achieved at 30% Ag₂S, resulting in a material named Ag/30%Ag₂S@Ni-MOF. This material demonstrated enhanced photocatalytic activity for chromium reduction under UV light irradiation. The Ag/30%Ag₂S@Ni-MOF hybrid photocatalyst effectively reduces 20 mg/L of Cr (VI) in an aqueous solution to nearly 100% within 70 min under UV-light illumination. The photocatalyst exhibits maximum photoreduction efficiency, as indicated by a first-order rate constant of 0.103 × 10⁻¹ min⁻¹. The most favorable Cr (VI) photoreduction performance was recorded at an optimal pH of 2. The remarkable photocatalytic efficiency of Ag/30%Ag₂S@Ni-MOF can be assigned to the synergistic interaction among Ag nanoparticles, Ag₂S, and Ni-MOF, which facilitates the formation of photocatalyst heterojunctions, and thus enhances the migration of photoexcited electrons from Ag₂S to Ni-MOF, successfully minimizes electron-hole recombination and improves the overall photocatalytic performance. Additionally, the surface plasmon resonance effect of Ag/30%Ag₂S@Ni-MOF plays a crucial role in boosting the photoreduction performance of Cr (VI).