The strategic use of sulfite in bismuth oxyhalide (BiOX, X = Cl, Br, I) photocatalytic systems unlocks a powerful mechanism for in-operando structural and electronic engineering, leading to substantial improvements in solar energy conversion and pollutant degradation efficiency. This study presents compelling evidence that sulfite acts as a multifunctional agent, not only scavenging photogenerated holes but also driving the spontaneous formation of plasmonic bismuth (Bi⁰) metal and oxygen vacancies (OVs) under visible light irradiation. These dynamic transformations fundamentally alter the physicochemical properties of BiOX materials, resulting in enhanced light absorption, prolonged charge carrier lifetimes, and tailored redox capabilities.
Comprehensive characterization confirms the formation of active species. Raman spectra exhibit new peaks at 68.1 and 95.2 cm⁻¹ on BiOI-x samples after sulfite exposure, assigned to the first-order scattering modes of metallic Bi. XRD patterns reveal a transient decrease in crystallinity followed by partial recovery, indicating reversible reduction of Bi³⁺ to Bi⁰ and reformation of defective BiOI. HRTEM imaging clearly resolves lattice fringes of ~0.332 nm and ~0.238 nm, corresponding to the (012) and (104) planes of Bi nanoparticles (~20 nm), with close interfacial contact to BiOX—direct visual proof of a Bi/BiOX heterojunction. XPS analysis confirms the presence of zero-valent Bi through a distinct peak at 157.6 eV and a negative shift in Bi³⁺ binding energy, reflecting electron transfer from Bi⁰ to the oxide matrix.
EPR signals intensify initially due to OV generation, then decline over time, confirming their transient nature. UV-Vis DRS shows enhanced absorption across the visible spectrum, particularly in the 550–800 nm range, attributed to surface plasmon resonance (SPR) from Bi⁰ and defect-related states. Transient absorption spectroscopy (TAS) and photoluminescence (PL) analyses demonstrate improved charge separation: the average lifetime of photogenerated holes increases from ~0.41 s to ~0.56 s, indicating effective suppression of recombination. However, excessive defect accumulation eventually leads to performance decline, highlighting the need for optimal sulfite concentration.
The functional impact is evident in pollutant degradation kinetics. On BiOBr and BiOCl, sulfite enhances photooxidation—4-nitrophenol removal rates increase 11.5- and 9.1-fold, respectively—driven by efficient •OH generation. In contrast, on BiOI, the system undergoes a dramatic shift toward photoreduction: 4-NP is selectively reduced to 4-aminophenol at a rate accelerated by ~31.7 times. This divergence stems from the more negative conduction band (CB) potential of BiOI, which favors electron accumulation and inhibits O₂ activation.N-Fmoc-8-aminooctanoic acid In stock
Radical quenching experiments clarify the dominant pathways.Nitrendipine Protocol In BiOI/sulfite systems, TBA and methanol inhibit 4-NP removal primarily due to solution acidification from sulfite decomposition, which promotes BiOI dissolution. In BiOBr systems, TBA inhibition confirms the critical role of •OH in oxidation.PMID:35050073 Under anaerobic conditions, 4-NP removal shifts entirely to photoreduction, confirming that O₂ availability governs the reaction pathway.
A mechanistic model explains the process: sulfite consumes holes via oxidation to SO₃²⁻, releasing electrons that reduce Bi³⁺ to Bi⁰ and generate OVs. The resulting Bi/BiOX heterojunction enhances charge separation, while SPR improves light harvesting. Once sulfite is depleted, BiOI regenerates through reconstruction involving ion exchange and OV refilling, though with reduced activity.
This work establishes sulfite as a transformative agent capable of dynamically tuning the structure and function of BiOX photocatalysts. It provides a robust framework for designing high-efficiency, environmentally responsive systems that maximize solar utilization for sustainable water purification.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com