We report a facile immobilization of riboflavin (RF) over in situ synthesized CeO 2 −reduced graphene oxide (RGO) nanohybrid surface synthesized through a simple wetchemical approach for photocatalytic degradation of organic pollutants under visible light (λ ≥ 420 nm). The hybrid containing 3% w/w RGO shows an excellent photocatalytic activity under visible light. The UV−visible diffuse reflectance spectra, photoluminescence (PL) analysis, and transient photocurrent measurements corroborate that the hybrid RF@CeO 2 − RGO significantly absorbs visible light and exhibits lower recombination of charge carriers in comparison to RF@CeO 2 . The catalyst, RF@CeO 2 −RGO, offers enhancement in photocatalytic rate, i.e., 2.8-fold increase for methyl orange (MO) and 3.5-fold for p-nitrotoluene (PNT) in comparison to RF@CeO 2 under visible light (2 h). This enhancement could be attributed to the synergistic effect among CeO 2 , RF (broadens visible light absorption region), and RGO (an electron-shuttling agent), which lead to an efficient separation of charge carriers. Consequently, the hybrid photocatalyst shows higher rate constant values, 2.31 × 10 −2 and 2.00 × 10 −2 min −1 for PNT and MO dye, respectively. The catalytic studies were monitored using UV− vis spectroscopy, high-performance liquid chromatography−photodiode array (HPLC−PDA), and gas chromatography−mass spectrometry (GC−MS) techniques. From the radical trapping experiments, the involvement of both superoxide and hydroxyl radicals was inferred. The present study provides more insights into the photochemical activity of metal-free sensitizer, RF, on metal oxide/hybrids (CeO 2 and CeO 2 −RGO hybrids) and its viability for the remediation of water pollutants.
Recently, utilization of solar light for chemical reactions has become a popular approach. Inspired by nature, we fabricated a ternary system, BiOI-CD-CdS, which is more durable and shows multiple photocatalytic applications. The incorporated carbon dots (CD) serve as a solid-state electron mediator and Zscheme facilitator. The material was employed for photooxidative degradation of 4-nitrophenol (a pollutant) and selective oxidation of benzyl alcohol into the corresponding aldehyde in an acetonitrile medium. In this study, 10 wt % BiOI-CD-CdS (denoted as 10 wt % BCC) shows the highest photocatalytic performance compared to the individual semiconductors BiOI and CdS, and gave a degradation rate constant (k) of 12.67 × 10 À 3 min À 1 (4-nitrophenol), which is 17.5 times and 6.5 times higher than its individual components. Moreover, the catalyst offers a 90 % conversion of benzyl alcohol to benzaldehyde with high selectivity (98 %). Directed by mechanistic insight, the charge transfer process was observed between BiOI and CdS, where CD serves as an electron mediator/charge separator. The radicals formed by the photocatalysis are superoxide (O 2 * À ), hydroxyl radicals ( * OH), and holes (h + ). The intermediates and mechanistic pathways were traced using HPLC, GC-MS, and EPR studies. Moreover, the work demonstrated a smart strategy for designing a ternary Z-scheme photocatalytic system, which could be useful for environmental decontamination and selective organic transformation under visible light.
In this study, we demonstrated a Step‐scheme (S‐scheme) based S‐C3N4/Ce2Zr2O7 (SCN/CZ) organic‐inorganic heterostructure, which was synthesized by a facile wet chemical route. The photocatalyst was highly efficient for the remediation of organic pollutants (POPs), namely 2,4‐dichlorophenol (2,4‐DCP, 20 ppm), 4‐chlorophenol (4‐CP, 20 ppm), and phenol (20 ppm) via dehalogenation under visible light (λ≥420 nm). Our finding reveals that a 20 wt.% S‐C3N4 on the surface of the SCN/CZ hybrid is an optimum requirement for potential catalytic activity. We achieve excellent photocatalytic performances i. e., 94 % for 2,4‐DCP, 92 % for 4‐CP, and 90 % for phenol removal, respectively. It was identified that superoxide and hydroxyl radicals (O2⋅− and ⋅OH) are diligently participating in the reaction medium. However, the content of O2⋅− species is more, which we have quantified as ∼66 μM when 20 % SCN/CZ is used. Furthermore, we have established the reaction pathways via an S‐scheme mechanism, which has great importance for photocatalysis. The prepared catalyst is highly stable and reusable for more than five cycles. The work presented here can contribute to the new perspective for pollutant removal via the dehalogenation route over the S‐C3N4/Ce2Zr2O7 surface.
Photocatalytic water splitting is an intriguing technology for sustainable hydrogen production. Bismuth-based oxyhalides are excellent photocatalysts that perform water splitting more efficiently. They also provide a wide scope for materials selection and design. The heterostructures afford abundant interfaces that offer plentiful active sites, rapid charge and mass transfer that synergistically boost the photocatalytic water oxidation and reduction reaction. This chapter describes the fundamentals of bismuth-based oxyhalides for photocatalytic water splitting and CO2 photoreduction. It also presents the strategies and efforts developed to increase efficiency, which includes improving light absorption and charge transfer.
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