Visible light-driven photocatalytic reduction of monovalent silver using a composite of Ni3Bi2S2 and O-doped gC3N4

In this study, nickel bismuth sulphide (Ni2Bi2S3) was synthesized through solvothermal method and was used to functionalize oxygen-doped graphitic carbon nitride to form a nanocomposite (Ni2Bi2S3/O-gC(3)N(4)). Characterizations of the nanocomposite were carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and UV-vis spectrophotometer. The nanocomposite was used to photocatalytically reduce monovalent silver to useful metallic silver. The effects of process parameters including Ag+ concentration, pH of the solution, the dosage of the photocatalyst, light intensities, addition of persulfate and mixed organic pollutants were studied, and the data obtained were fitted into pseudo-first order kinetics. About 93.08% (pseudo first order rate constant of 0.0460 min(-1)) of Ag+ was photocatalytically removed within 1 h using 25 mg of the photocatalyst. Mixed organic pollutants and persulfate were found to have inhibitory effects on the rate of photocatalytic reduction. Finally, the Ni2Bi2S3/O-gC(3)N(4) photocatalyst was found to retain over 80% of its efficiency even after three cycles, and the scavenging experiment revealed that electrons, holes and superoxide played prominent roles in the photocatalytic process.