4/2/2023 0 Comments Ammonium sulfide mmassThe dopant of nitrogen in carbon materials, aimed at tuning their electronic features and hence the adsorption and catalytic properties, has been extensively studied in pollutant degradation. Occasionally, we observed that nitrogen-doped PCM could further reduce the stagnate phase of the azo dye decolorization by sulfide compared to that without nitrogen doping, while the reasons behind this phenomenon are unexplored. This new finding further improves our understanding of PCM influence on the organic pollutants transformation under anaerobic aqueous conditions and particularly reveals the important role of polysulfides in transforming pollutants in natural environments. Interestingly, our recent study discovered a new mechanism: PCM could reduce the stagnate phase of azo dye decolorization by sulfide, due to the formation of reactive intermediate polysulfides that react quickly with the azo dye. Other works demonstrate that the excellent electrical conductivity of carbon materials may play important roles in organic pollutants reduction by sulfide, enhancing electron transfer from sulfide to the pollutants and facilitating the formation of some critical intermediate. Some studies attributed the facilitation of carbon materials for pollutant reduction to oxygen functional groups, especially quinones on the surface of PCM that may help activate pollutant molecules and enhance electron transfer. The enhanced mechanisms of PCM for the reductive removal of various organic pollutants by sulfide are diverse. For example, black carbon facilitates trifluralin and pendimethalin abiotic reduction by sulfide, and graphene accelerates nitrobenzene degradation by sulfide. Recent studies indicate that PCM could catalyze the reduction of various organic pollutants by sulfide coming from the microbial reduction of sulfate. Traditionally, PCM has been merely viewed as a passive adsorbent for concentrating, capturing, and sequestering contaminants in an aquatic environment. Pyrogenic carbonaceous matter (PCM), including environmental black carbon (biomass char and fossil fuel soot), engineered carbons (activated carbon), and carbon nanomaterials (graphene and carbon nanotubes), constitute between 10% and 30% of organic carbon in sediments. This study not only provides a better understanding of PCM impact on transformations and fates of organic pollutants in natural environments, but also offer a new regulation strategy for more efficient wastewater treatment processes in PCM-catalyzed engineering systems. This is attributed to the improved electron conductivity through graphitic nitrogen doping, and the enhanced interactions between sulfide and carbon atoms bonded to graphitic nitrogen. Gas chromatography-mass spectrometry and in-situ surface Raman analysis demonstrated that doping nitrogen, especially graphite one facilitated reactive intermediate polysulfides formation. Particularly, graphitic nitrogen played a critical role in NGs-catalyzed MO decolorization by sulfide. In this study, we found that stagnate time of azo dye methyl orange (MO) decolorization was reduced to 0.54-18.28 min in the presence of various nitrogen-doped graphenes (NGs), remarkably lower compared to graphene itself. Pyrogenic carbonaceous matter (PCM) catalyzes azo dye decolorization by sulfide, but the nitrogen doping catalytic mechanisms are poorly understood.
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