Insights into the Photocatalytic Memory Effect of Magneto-Plasmonic Ag–Fe₃O₄@TiO₂ Ternary Nanocomposites for Dye Degradation and H₂ Production under Light and Dark Conditions

Abstract

This study explores the preparation of Ag plasmons-sensitized magnetic-Fe 3 O 4 integrated TiO 2 (Ag−Fe 3 O 4 @TiO 2 ) ternary nanocomposites and their defectinduced electron storage properties to exploit their photocatalytic memory effect toward dye degradation and H 2 generation under light and dark conditions. The crystalline phase formation and elemental states of the individual materials and elements in the nanocomposite are analyzed using X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The existence of Ti and Fe ions with dual oxidation states of Ti 4+/3+ and Fe 3+/2+ , respectively, is observed by XPS, which revealed the presence of defects in the system. The observed red shift along with a distinct plasmonic band (corresponding to metallic Ag nanoparticles) in the UV−visible absorption spectrum and the observed modified radiative recombination emission in the PL spectrum confirmed the plasmon-driven visible light activity along with the improved carrier separation and transfer characteristics in the synthesized ternary composite. Accordingly, the Ag− Fe 3 O 4 @TiO 2 photocatalyst degraded almost 100% of MB (methylene blue) and RhB (rhodamine B) dyes under simulated solar light in 90 min, while it is found to be around 42% and 36% in 60 min under dark conditions, respectively (which is preirradiated for 60 min). Further, it produced H 2 at the rate of 911 μmol g −1 h −1 under light conditions and is decreased to ∼96 μmol g −1 h −1 under dark conditions which is preirradiated for 1 h. However, when the composite is preirradiated for 3 h, it showed a maximum H 2 evolution of 144 μmol g −1 h −1 under dark. Further, the photocurrent and electrochemical impedance under light and dark conditions suggested the mechanism of photocatalytic charge storage and transfer process in the composite. Although the photocatalytic memory effect of the composite is meager toward H 2 production due to the insufficient potential of the stored−released electrons to reduce the protons (2H + ) to H 2 under dark conditions, their degradation efficiency is considerably good.

Effect of Different Amounts of Pt on Fe3O4−TiO2 for Photocatalytic H2 Production Under Solar Light

“…In the literature, the H 2 production via Ag plasmons‐sensitized magnetic‐Fe 3 O 4 integrated TiO 2 (Ag−Fe 3 O 4 @TiO 2 ) ternary nanocomposites was 911 μ mol/g.h under light conditions as seen in Table 2. However, this article used higher amounts of Ag particles (noble metal like Pt in our study) in their study which is the most probable reason for the high H 2 production rate [28] . Another study that uses Fe 3 O 4 and Co 3 O 4 doped TiO 2 indicated that Fe and Co ions together improved solar light absorption of TiO 2 , inhibited the recombination of photogenerated charges, and enhanced the photocatalytic activity of hydrogen production.…”

“…In another study, Ag plasmons‐sensitized magnetic‐Fe 3 O 4 integrated TiO 2 (Ag−Fe 3 O 4 @TiO 2 ) ternary nanocomposites were used for both dye degradation and H 2 generation under light and dark conditions. They observed red shift along with a distinct plasmonic band in the UV‐visible absorption spectrum due to metallic Ag nanoparticles, which was confirmed by the PL spectrum with an effective electron and hole separation [28] . Furthermore, mono‐ and co‐doped TiO 2 (Co n+ and Fe n+ ) were prepared by sol‐gel technique under solar light.…”

“…However, this article used higher amounts of Ag particles (noble metal like Pt in our study) in their study which is the most probable reason for the high H 2 production rate. [28] Another study that uses Fe 3 O 4 and Co 3 O 4 doped TiO 2 indicated that Fe and Co ions together improved solar light absorption of TiO 2 , inhibited the recombination of photogenerated charges, and enhanced the photocatalytic activity of hydrogen production. They didn't observe H 2 in the case of pure TiO 2 while the 5 % Fe 3 O 4 /TiO 2 gave a small amount of H 2 (~125 μmol/g) compared with 5 % Fe 3 O 4 / Co 3 O 4 À TiO 2 after 5 h as seen in Table 2.…”

2022 Pioneers in Energy Research: Jinhua Ye

“…Chen and Shi presented a new approach to enhance photocatalytic oxidation of tetracycline by introducing boron nitride quantum dots to BiOBr with a permanent magnet to improve the charge carrier transfer . Venkatakrishnan and his co-workers reported a ternary composite consisting of TiO 2 , Fe 3 O 4 , and Ag that shows a photocatalytic memory effect toward dye degradation and H 2 production under light and dark conditions …”

“…30 Venkatakrishnan and his co-workers reported a ternary composite consisting of TiO 2 , Fe 3 O 4 , and Ag that shows a photocatalytic memory effect toward dye degradation and H 2 production under light and dark conditions. 31 ■ PHOTOREDUCTION There are eight papers on the topic of photoreduction. Yang et al reviewed the recent research progress and perspectives on porphyrin-based porous photocatalysts in CO 2 photoreduction.…”