Key Takeaways & Executive Findings
- •• • Presence of C60 significantly increased sulfate formation during H2O2 gas-phase oxidation of SO2, with higher C60 amounts leading to greater sulfate yields, indicating a direct catalytic role. • • Elevated H2O2 concentrations and UV irradiation enhanced the promoting effect of C60 on sulfate formation, suggesting that oxidant availability and photochemical conditions are critical for maximizing sulfate production. • • XPS analysis revealed electron transfer on the C60 surface, converting adsorbed S(IV) to S(VI), confirming that C60 directly participates in the oxidation process. • • Free radical trapping experiments and model calculations confirmed that C60 promotes the generation of hydroxyl radicals (·OH) and superoxide radicals (·O2−), which are key oxidants driving SO2 oxidation to sulfate.
Abstract
Fullerene (C60) is an emerging atmospheric pollutant that may influence sulfate formation during haze events. This study investigated the effect of C60 on sulfate production in the gas-phase oxidation of SO2 by H2O2 using a flow tube reactor. Results demonstrated that the presence of C60 significantly increased sulfate yields. Control experiments varying C60 loading, H2O2 concentration, and ultraviolet (UV) irradiation revealed that higher C60 amounts, elevated H2O2 levels, and UV exposure enhanced the promoting effect. Mechanistic investigations via free radical trapping and X-ray photoelectron spectroscopy (XPS) indicated a pre-adsorption-oxidation pathway. XPS analysis showed electron transfer on the C60 surface, converting adsorbed S(IV) to S(VI), confirming direct participation of C60 in sulfate formation. Radical trapping experiments and model calculations confirmed that C60 promotes the generation of hydroxyl radicals (·OH) and superoxide radicals (·O2−), which are key oxidants driving SO2 conversion to sulfate. The study reveals that C60 particles markedly enhance atmospheric sulfate formation, offering a novel pathway for understanding sulfate generation mechanisms. These findings have implications for air quality modeling and haze mitigation strategies, as C60 may act as a catalytic surface for sulfate production in polluted atmospheres.
1. Introduction
Atmospheric sulfate formation is a critical driver of haze pollution, primarily originating from the homogeneous oxidation of SO2 by hydroxyl radicals (·OH) and stabilized Criegee intermediates, as well as heterogeneous pathways involving transition metal ions, ozone, nitrogen dioxide, and hydrogen peroxide (H2O2). Among these, H2O2 is a significant oxidant in both aerosol and liquid phases, decomposing to produce ·OH, which efficiently oxidizes S(IV) species to sulfate. However, the efficiency of this process in the presence of particulate matter, particularly emerging carbonaceous nanoparticles, remains poorly constrained.
Fullerene (C60), a novel atmospheric pollutant, is ubiquitously present in ambient air, primarily from combustion sources, and can accumulate on PM2.5 surfaces. Despite its prevalence, the role of C60 in sulfate formation has not been previously explored. This study addresses this gap by systematically investigating the effect of C60 on H2O2-driven SO2 oxidation in a flow tube reactor. The findings reveal that C60 significantly enhances sulfate production through a pre-adsorption-oxidation mechanism, promoting radical generation and direct electron transfer. This work provides new insights into heterogeneous sulfate formation pathways and highlights the potential impact of engineered nanoparticles on atmospheric chemistry.
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LIU Yiting, QIAN Qingxiang, CHEN Huan, GUO Shixiang, GUO Zhaobing (2026). Effect of Fullerene C60 on Sulfate Formation during Gas-Phase Oxidation of SO2 by H2O2. Environmental Chemistry. https://doi.org/10.7524/j.issn.0254-6108.2024122501
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Frequently Asked Questions
What is the quantitative enhancement of sulfate formation when C60 is present compared to without C60?
The study reports that sulfate formation increased significantly in the presence of C60, but exact quantitative values are not provided in the abstract. However, control experiments showed that higher C60 amounts led to greater sulfate yields, indicating a dose-dependent enhancement.
How does UV irradiation influence the C60-mediated sulfate formation?
UV irradiation was found to enhance the promoting effect of C60 on sulfate formation. This suggests that photochemical activation of C60 or H2O2 increases the production of reactive oxygen species, thereby accelerating SO2 oxidation.
What is the proposed mechanism for C60's role in sulfate formation?
The mechanism involves pre-adsorption of SO2 and H2O2 onto the C60 surface, followed by electron transfer that converts S(IV) to S(VI). C60 also promotes the generation of ·OH and ·O2− radicals, which are key oxidants for SO2 conversion.
Are there any potential implications for atmospheric sulfate levels in regions with high C60 emissions?
Yes, the findings suggest that C60 particles could significantly enhance sulfate formation in the atmosphere, potentially contributing to haze pollution. This is particularly relevant in urban areas with combustion sources that emit C60.
What are the limitations of this study in terms of extrapolating to real atmospheric conditions?
The experiments were conducted in a flow tube under controlled conditions, which may not fully replicate the complex atmospheric matrix. Additionally, the concentrations of C60 used may be higher than ambient levels, and the interactions with other pollutants were not considered.
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