Unfolding Photocatalytic Efficiency of a Newly One-Pot Synthesized n-n-AgBi3S5-Bi2S3 Photocatalyst for Removal of Rhodamine-B from Aqueous Systems under Natural Light Illumination

Abstract

Nanoparticles of n-AgBi₃S₅, n-Bi₂S₃, and n-n-AgBi₃S₅-Bi₂S₃ nanocomposite were synthesized by a facile one-pot hot chemical (90 °C) method using ethylene glycol as a medium without further calcination. The nanocomposite on exposure to natural sunlight exhibits significant and synergistic photocatalytic activity towards degradation of pollutant dye Rhodamine-B (Rh-B) in aqueous solution. The as-synthesized monoclinic AgBi₃S₅, orthorhombic Bi₂S₃, and their nanocomposite were identified and characterized by various spectroscopic, diffraction (XRD), and microscopic techniques. The UV-visible spectroscopic study reveals significant absorption of visible light and narrow band gaps/eV: 2.8 and 1.9 for synthesized Bi₂S₃ and AgBi₃S₅ respectively. The spectroscopically evaluated maximum % of degradation of Rh-B (99.9) and related high-rate constant (0.059 min^–1) were achieved within 25 min with 0.7 g/L AgBi₃S₅-Bi₂S₃ nanocomposite at pH 3. The radical trapping experiments reveal that both ^•O₂^– and ^•OH are almost equally involved in the degradation, while hole, h⁺ is the main initiator of the degradation as usual. Studies of the products of degradation reveal both de-ethylation and ring breaking of Rh-B, indicating simultaneous absorption of sunlight by it and the catalyst. The very high efficiency and synergistic effect of the nanocomposite might be due to either/both Z scheme/S scheme charge separation. The 95% retention of the photocatalytic activity by the 5th time used catalyst AgBi₃S₅-Bi₂S₃ signifies its superiority by auto surface improvement during a reaction.