Nitrogen-Doped Carbon Materials as Metal-Free Catalyst for the Dechlorination of Trichloroethylene by Sulfide

Abstract

A new method for trichloroethylene (TCE) dechlorination is proposed using sulfide (HS − and S 2− ) as reductant under the mediation of nitrogen-doped carbon materials (NCMs). About 99% of the TCE was converted to acetylene after 200 h using this method. Dechlorination of TCE in the NCMs−sulfide system (NCSS) followed pseudo-first-order kinetics. Pyridinic N (N6) on surface of the NCMs appeared to play a critical role in NCSS as shown by the good linear relationship between the surface content of N6 and k obs . Nucleophilic substitution was suggested as the first step in TCE dechlorination, and the nucleophilic reagent was identified as a sulfur intermediate with C−S−S−H as the functional group. The generation of C−S−S−H could be ascribed to the interaction between positively charged carbon atoms in N6 and negative charged sulfide. This work is the first to demonstrate that sulfide combined with NCMs can produce active substances that are effective in TCE dechlorination and the findings will assist in the development of strategies that use natural sulfide as reductant for detoxicating organic chloroethene contaminants.

Biochar Derived from Agricultural Wastes as a Means of Facilitating the Degradation of Azo Dyes by Sulfides

“…With the difference in pyrolysis temperature, heating time, preparation of raw materials, and other factors, the properties of biochar will differ, its functions will be more abundant, and its development potential is virtually unlimited [26][27][28][29]. In the pollutant treatment process, these carbon materials, including commercial carbon materials, biochar, and its modified materials, exhibit a wide range of effective applications for the treatment of halogenated hydrocarbons [30,31], benzene series [32,33], heavy metals [34,35], and other pollutants. As a matter of course, these series of carbon materials can be applied to the treatment of dyes, most of which feature adsorption and advanced oxidation [36,37], but few have been used as catalysts for the sulfide-based reduction of dyes.…”

Abiotic reductive removal of organic contaminants catalyzed by carbon materials: A short review

“…However, it is not able to conclude a consistent finding of contaminant dependence from currently available studies, for the reason that contrary results were reported even for the same contaminant, for example, nitroaromatic compounds mentioned before. Third, many other properties other than quinone moieties and graphitic regions were affecting the activity of carbon materials, including N elements (Ding et al, 2018;Liu et al, 2017), and affinities to different substrates. The extent of their influences may be small, but they can function with other properties synergistically to result in the diversity of catalytic performance.…”

“…Obviously, any reduction of a contaminant in the cathodic cell can confirm that the reaction of contaminants can-at least partially-arise from direct electron transfer through the carbon material, if not, the intermediates formed by the interaction of the carbon material with the reductant should be responsible for the reduction. This approach has been applied to investigate the degradation pathway for RDX, nitroglycerin (Xu et al, 2010), 3-bromonitrobenzene (Xu et al, 2015), DDT (Ding & Xu, 2016), TCE (Ding et al, 2018), and (di)chloroacetamides (Xu et al, 2020), with sulfide as a reductant. Among them, only nitroglycerin has been observed to decay in the cathodic cell, indicating the reduction of most contaminants in carbon-sulfide systems relies on the intermediates.…”

“…For carbon-sulfide systems, the majority of related studies concluded surface intermediates, either surfacebound sulfur nucleophiles or adsorbed sulfides, were the intermediates responsible for the reduction because (i) graphite pretreated with sulfides could mediate RDX reduction without aqueous sulfides (Xu et al, 2013) and (ii) sulfur was detected on the pretreated or reacted carbon materials with characterization methods; for example, Ding et al (2018) found active intermediate C S S H on the nitrogen-doped carbon material after its reaction with sulfide. The surface-bound sulfur nucleophiles or adsorbed sulfides intermediates were reported to be responsible for different contaminants.…”

“…Nevertheless, intentionally doping N and O atoms to a carbon material can possibly improve its performance. N-doped biochar catalyzed the reductive transform of TCE to acetylene that undoped biochar cannot do (Ding et al, 2018). Fujita et al thermally pretreated a commercial GAC in NH 3 atmosphere to produce an N-and O-codoped GAC.…”