Although it has long been known that carbonaceous materials (CMs) can facilitate the reduction of organic contaminants by sulfide, the underlying mechanisms and controlling factors, particularly the surface property dependence, are not well understood. Here, sulfide-induced nitrobenzene reduction was explored as a model reaction to compare the mediation efficiency of a variety of CMs, including rice straw-derived black carbon (R-BC) and pine wood-derived black carbon (P-BC), a commercial activated carbon (AC), multi-walled carbon nanotube (MCNT), and graphite. Given the same load (250 mg L-1 ), the observed pseudo-first-order rate constant (kobs ) of nitrobenzene reduction was ordered as AC > R-BC > MCNT > P-BC > graphite. The surface area-normalized rate constant (kSN ) was ordered as R-BC > graphite > MCNT > AC > P-BC. Neither the kobs nor the kSN followed the order of mediator's electron conductivity (graphite > MCNT > AC > P-BC > R-BC). For the low-graphitized R-BC and P-BC, increasing surface oxygen content by HNO3 oxidation enhanced nitrobenzene reduction, whereas decreasing the content by NaBH4 reduction impeded the reaction. Opposite trends were observed with the high-graphitized AC, MCNT, and graphite. The quinone moieties of low-graphitized CMs were found to facilitate nitrobenzene reduction by serving as one-electron acceptors to generate reactive reducing sulfur species (polysulfides and polysulfide free radicals) from sulfide. In contrast, the surface oxygen groups of high-graphitized CMs suppressed the reaction by lowering the electron conductivity. These results demonstrate that the types of CMs and their surface chemistry properties are key determinants in mediating redox transformation of organic contaminants.

中文翻译：

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由各种不同碳质材料介导的硫化物诱导硝基苯还原的机制：石墨化碳促进电子转移与醌促进活性硫物种形成

尽管人们早就知道含碳材料 (CMs) 可以促进硫化物对有机污染物的还原，但其潜在机制和控制因素，特别是表面性质的依赖性，尚不清楚。在这里，硫化物诱导的硝基苯还原作为模型反应进行了探索，以比较各种 CM 的介导效率，包括稻草衍生的黑碳 (R-BC) 和松木衍生的黑碳 (P-BC)，商用活性炭 (AC)、多壁碳纳米管 (MCNT) 和石墨。给定相同的负载（250 mg L-1 ），观察到的硝基苯还原的伪一级速率常数（kobs）被排序为 AC > R-BC > MCNT > P-BC > 石墨。表面积归一化速率常数 (kSN) 的顺序为 R-BC > 石墨 > MCNT > AC > P-BC。kobs 和 kSN 都不遵循介体的电子传导性顺序（石墨 > MCNT > AC > P-BC > R-BC）。对于低石墨化的 R-BC 和 P-BC，通过 HNO3 氧化增加表面氧含量会增强硝基苯还原，而通过 NaBH4 还原降低含量会阻碍反应。使用高石墨化 AC、MCNT 和石墨观察到相反的趋势。发现低石墨化 CM 的醌部分通过作为单电子受体从硫化物生成活性还原硫物质（多硫化物和多硫化物自由基）来促进硝基苯的还原。相比之下，高石墨化 CM 的表面氧基团通过降低电子电导率来抑制反应。