Abstract
The incomplete combustion of biomass and fossil fuels results in the formation of not only black carbon (BC) but also black nitrogen (BN), the dissolved fractions of which (i.e., DBC and DBN) are important components of dissolved organic matter pool. Relative to DBC, the activity and reactivity of DBN are much less understood. Here, we investigated the catalytic effect of DBN derived from N-enriched biomass in the abiotic transformation of chlorophenols by sulfides. The medium-temperature DBN (450 °C) exhibited 13–144% higher catalytic efficiency than other DBN samples and 9.3 times higher than its DBC counterpart. Both electron paramagnetic resonance spectra and fluorescent probe technique indicated that the attached sulfides contributed to the formation of reactive oxygen species (ROS) as the “primary” radicals by favoring electron transfer from DBN to chemisorbed oxygen, and then the generated ROS reacted with N-oxides in DBN to form reactive nitrogen species (RNS) as the “secondary” radicals. The contribution of RNS to the decay of 2-chlorophenol by DBN450 was up to 72%, much higher than that of ROS and non-radical mechanism. These findings suggest that the catalytic effect of DBN is distinct but no less significant than that of DBC to the abiotic transformation of micropollutants in water/soil systems.
Graphical Abstract
![](http://media.springernature.com/lw685/springer-static/image/art%3A10.1007%2Fs42773-024-00342-1/MediaObjects/42773_2024_342_Figa_HTML.png)
Highlights
-
Dissolved black nitrogen is an overlooked active nano-catalyst in the natural environment.
-
The medium-temperature dissolved black nitrogen exhibited the highest catalytic efficiency.
-
Not only ROS but also RNS were generated in the dissolved black nitrogen-sulfide system.
-
The contribution of RNS to the decay of 2-CP was higher than that of ROS and non-radical mechanism.
Similar content being viewed by others
Avoid common mistakes on your manuscript.
1 Introduction
Pyrogenic carbon is a series of carbonaceous residue derived from incomplete combustion of biomass and fossil fuel, which represents one of the largest organic carbon pools on the earth and plays a critical role in the global carbon cycle and transformation of contaminants (Chen et al. 2022). Pyrogenic carbon can be viewed as a heterogeneous mixture of thermally altered biomacromolecules, the configuration of which is highly dependent on the chemistry of original precursor (Knicker et al. 2008). Nitrogen (N) is an essential element for plant growth and present mainly in the form of peptides in biomass. During biomass burning, a majority of the organic N is rearranged and incorporated into the polyaromatic carbon matrix in the form of heterocyclic aromatic N, i.e., black N (BN) (Knicker 2010). Not only composition and structure but also (photo)electrochemistry of pyrogenic carbon could be modified by the incorporated heteroaromatic N (Liu et al. 2019; Wu et al. 2021). Nevertheless, the heterocyclic-N induced modification to the role of pyrogenic carbon in critical biogeochemical processes is much less explored.
Characterized by a heteroatomic nature and lower graphitic carbon content, BN is to an extent more active in chemical oxidation than black carbon (de la Rosa and Knicker 2011). In a recent study we found that dissolved BN (DBN), the water-soluble fraction of BN (size < 0.45 μm), was more easily photo-transformed than dissolved black carbon (DBC) and the half-life of DBN produced at 500 °C was two times shorter than that of the DBC counterpart, mainly ascribed to the generation of not only reactive oxygen species (ROS) but also reactive nitrogen species (RNS) in DBN under simulated solar irradiation (Lian et al. 2021). However, the intensity of sunlight decreases rapidly with depth of water for many aquatic ecosystems (Zepp and Cline 1977; Häder et al. 2015). The catalytic transformation of microcontaminants by DBN in the dark also needs scrutiny and has more profound implications in the deep water and sediment. Hence, an interesting question confronting us is how and to what extent DBN induces the catalytic degradation of organic contaminants in subsurface waters, where quite a few natural reductants and electron shuttles prevail.
Sulfides such as H2S, HS−, and S2− are mainly derived from the biological sulfate reduction and viewed as one of the most widely distributed nucleophiles and reductants in subsurface waters (Barton et al. 2014; Ding et al. 2022). Pyrogenic carbon has been reported to effectively mediate the transformation of certain sorbed organic pollutants (e.g., nitrobenzene and azo dyes) by sulfides (Weber and Quicker 2018; Ren et al. 2019). The proposed mechanisms responsible for this pyrogenic carbon-mediated transformation mainly include: (i) the oxygen-containing groups (especially quinone moieties) in pyrogenic carbon accelerate the electron transfer from sulfides to target contaminants (Kemper et al. 2008; Yu et al. 2011); (ii) the conductive graphitic regions in pyrogenic carbon promote electron transfer from sulfides to sorbed organic compounds (Ding and Xu 2016; Oh et al. 2005); and (iii) sulfides are oxidized on carbon surfaces to reactive sulfur species that serve as potent nucleophiles promoting the transformation of contaminants (Xu et al. 2013; Ding et al. 2018). Yet, little is known regarding the possible synergies between heterocyclic aromatic N and sorbed sulfides on the transformation of microcontaminants. A recent study found that high pyrolytic temperature resulted in large specific surface area, more pores, and thus high catalytic capacity of N-doped biochar for the dichlorination of carbon tetrachloride in sulfide-containing aqueous solutions (Ding et al. 2022). Relative to N-doped biochar, however, DBN has typical colloidal properties including less porous, high dispersible, and more surface O/N-containing groups (Lian et al. 2021). Meanwhile, the formation and temperature-dependent decomposition of N species endow the graphene sheets in DBN with a defect-rich feature (Yang et al. 2016; Wan et al. 2023), favorable to the generation of delocalized/unpaired electrons and persistent free radicals (PFR) (Wan et al. 2021). The synergistic effect of colloidal properties and heterocyclic N might provide DBN with a distinct reaction pathway in catalyzing dichlorination by sulfides, which has received little attention in previous studies. Given the ubiquitous presence of DBN in dissolved organic matter (DOM) (Jaffe et al. 2012; Maie et al. 2006), unraveling the reactivity of DBN is crucial to expanding our understanding in the transformation and fate of microcontaminants in aquatic ecosystems.
Herein, we extracted DBNs from N-rich pyrogenic carbon prepared at different charring temperatures. Chlorophenols including 2-chlorophenol (2-CP), 3-chlorophenol (3-CP), and 4-chlorophenol (4-CP) were selected as the targeted organic compounds because they are typical microcontaminants and widely detected in the environmental medium (Yang et al. 2021). The objectives of the present work were to (i) explore the differences between DBN and DBC in the catalyzing transformation of chlorophenols by sulfides and (ii) reveal the unique dichlorination mechanisms in the DBN-sulfide catalytic system on the basis of degradation products, electrochemical analysis, and electron paramagnetic resonance (EPR)/free radical quenching results. This study also compared the efficiency between DBC and DBN in the degradation of chlorophenols. Our findings provide mechanistic insights into the crucial role of heteroaromatic N for dissolved pyrogenic carbon in regulating the transformation of organic contaminants in water and soil systems.
2 Materials and methods
2.1 Preparation of BN
BN samples were prepared through slow pyrolysis of N-rich green algae biomass (oven-dried at 60 °C before use) at different charring temperatures (350, 450, 550, 650, or 750 °C) for 3 h in a lab-scale tubular furnace under oxygen-limited conditions (Lian et al. 2021). The obtained solids were ground to pass through a 0.125 mm mesh and labeled as BBN350–BBN750, respectively, where the numbers indicated the temperature. For comparison, BC was produced from wood shavings as a control with the same pyrolytic procedure but only at 450 °C, labelled as BC450. These pyrogenic carbons were exposed to air for 2 months to complete chemisorption of oxygen.
2.2 Extraction of DBN
An aliquot (50 g) of BN was added into 500 mL deionized water and stirred magnetically for 72 h in the dark at 25 °C, followed by 1.0 h sonication at 100 W (Fu et al. 2016). The stirred suspension was passed through a glass fiber membrane (0.7 μm). The retained BN on the membrane was stirred, sonicated, and filtrated three times to ensure that most of the desired fractions could pass through the membrane. The filtrate was collected and freeze-dried to obtain DBN samples. DBN obtained at different temperatures was labeled as DBN350–DBN750, respectively. DBC450 was also extracted with the same procedure. The stock suspensions (100mg L–1) of DBN and DBC450 were prepared in deionized water and stored at 4 °C in the dark before use. The total organic carbon (TOC) of DBN samples was measured by a TOC analyzer (Elementar, Germany), which was in the range of 24.2 to 40.1 mg TOC/L with various charring temperatures.
2.3 Characterization of BN, DBN, and DBC
The bulk elemental composition of BN and DBN was measured with an Elemental Analyzer (Unicube, Elementar, Germany), and their trace elements were determined with an inductively coupled plasma mass spectrometer (ICP-MS) (iCAP-TQ, Thermo-Fisher, USA) after microwave-assisted nitric acid digestion. The surface chemical composition of DBN was determined by X-ray photoelectron spectrometer (XPS) (ESCALAB250Xi, Thermo-Fisher, USA). The N1s spectra were fitted with pyridine-N, pyrrolic-N, and/or pyridone-N, graphitic-N, and oxidized-N peaks, where the positions were around 398.1–398.4 eV, 399.1–400.5 eV, 400.8–401.3 eV, 402.8 eV, respectively (Lian et al. 2016). The functional groups of DBN were characterized by Fourier transform infrared (FTIR) spectrometer (Nexus 870, Nicolet, USA) with 4 cm−1 resolution in the range of 400 and 4000 cm−1. The graphitization tendency was determined by Raman spectrometer (RM 2000, Wotton-under-Edge, UK). Solid-state 13C cross-polarization magic angle spinning nuclear magnetic resonance (CPMAS NMR) spectra were recorded on an Agilent NMR vnmrs600 spectrometer under the following conditions: spinning rate, 10.0 kHz; contact time, 3.5 μs; and pulse delay time, 2.0 s. The hydrodynamic diameter of DBN samples after sonication was measured by a dynamic light scattering analyzer (ZEN3600, Malvren, UK). The electron accepting capacity (EAC) and electron donor capacity (EDC) of DBN and DBC were measured by the mediated electrochemical reduction and mediated electrochemical oxidation methods used in the literature (Klüpfel et al. 2014; Aeschbacher et al. 2010). The electron exchange capacity (EEC) of DBN and DBC was calculated from the sum of EAC and EDC. The specific procedures are provided in the Text S1.
2.4 Degradation experiment of chlorophenols
A certain amount of DBN was well mixed with 19 mL of 20 mM pH 7 phosphate buffer in 20 mL brown glass vials capped with Teflon-lined septa. The vials received a certain volume (< 0.1%) of chlorophenol (purity, 99%) stock solutions in methanol by syringe injection through the vial cap septum. The mixture was magnetically stirred at 30 rpm for 24 h in the dark to achieve an apparent sorption equilibrium. Then, the mixtures were purged with nitrogen gas for 30 min and 1 mL of sodium sulfide nonahydrate (Na2S·9H2O) stock solution (0.1 M) was injected into the vials by syringe through the cap septum to eliminate the headspace. Note that the Na2S·9H2O stock solution was made freshly before use by dissolving Na2S·9H2O in N2-purged phosphate buffer. The final concentrations of DBN, chlorophenol, and sulfides were 100 mg L–1, 5.0 mM, and 50 mM, respectively. The same degradation experiment was also carried out using DBC450 as a mediator for comparison with DBN. The final pH of the solution was 6.9 ± 0.2. During the rotation, triplicates of the vials were sacrificed for analysis at predetermined intervals (0, 24, 48, 72, 96, 120 h). One mL aliquant of the aqueous solution was sampled from the sacrificed vials and immediately mixed with 0.5 mL ethanol to terminate the free radical reactions (if any). Then, the solutions were centrifuged at 4000×g for 30 min using a membrane with a pore size of 3 kDa (Millipore Amicon, Ultra, USA) to separate from solids and used for the determination of aqueous concentrations of chlorophenols and sulfides by high-performance liquid chromatography (HPLC, Agilent 1200, USA) and inductively coupled plasma mass spectrometry (ICP-MS) (iCAP-TQ, Thermo-Fisher, USA), respectively. The concentration of chloride ions (Cl−) produced during the degradation was determined by the mercury thiocyanate method (EPA method 8113) (Lokesh et al. 2020). The detailed analysis methods are presented in the Text S2.
The effect of sulfide concentration on the degradation was also examined, wherein the concentration of sulfides was set from 10 to 100 mM in the reaction systems as mentioned above. All the degradation experiments were performed in triplicate. The main degradation products of chlorophenols were identified by liquid chromatography-mass spectrometer (LC–MS/MS) (Agilent, USA) equipped with an electrospray ionization source. Molecular formulas and structures of degradation products were determined based on accurate m/z analysis using Agilent software. All mathematically possible formulas for each ion were calculated with a mass tolerance of ± 5 ppm. The detailed parameters can be found in the Text S3.
2.5 Sorption experiment of sulfides by DBN
The sorption capacity of DBN for sulfides might greatly affect the degradation of chlorophenols in the DBN-sulfide system. Thus, a single-point sorption experiment was conducted by mixing a certain amount of DBN with 19 mL of phosphate buffer in 20 mL vials as mentioned above. Then, the mixtures were purged with nitrogen gas for 30 min, and 1 mL of Na2S·9H2O stock solution was injected into vials. The final concentrations of DBN and sulfides were 100 mg L–1 and 50 mM, respectively. These vials were stirred in the dark for 48 h to achieve apparent sorption equilibrium and then the mixtures were centrifuged and filtered using the 3 kDa pore size membrane. The concentration of sulfides in the filtered solution was determined by ICP-MS. The vials containing sulfides but without DBN addition were used as control. The mass of sorbed sulfides was calculated by mass balance. All experiments were performed in triplicate. Quality control and quality assurance during the analysis process were conducted using a standard reference material (Shrub Leaves, GBW07602, provided by Nanjing Elida Biotechnology Co., Ltd).
To further explore the reactions between sulfides and DBN, the bound S species on the surfaces of DBN was examined by XPS. Both the sorption experiment and XPS analysis were also carried out using DBC450 as a sorbent for comparison.
2.6 Electron paramagnetic resonance and quenching experiments
To explore whether PFRs were generated from the DBN samples in aqueous suspensions, 0.15 g of the sample was loaded into a quartz tube and then detected using an EPR spectrometer (Bruker A300, Germany) at room temperature. The production of ROS and RNS from DBN suspensions containing various sulfide concentrations (10–100 mM) was probed by EPR coupling with a spin-trapping technique. Specifically, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO, > 97%) was used to trap ⋅OH and O2⋅−; while 2,2,6,6-tetramethyl-4-piperidone (TEMP) was used to detect the production of 1O2 as spin-trapping agents, respectively. Also, the production of nitrogen oxide radical (NO⋅) was determined using an iron complex of ferrous irons and sodium diethyldithiocarbamate trihydrate (DETC, 99%), (DETC)2–Fe(II), as a chelating agent, and the generated NO–(DETC)2–Fe(II) complex in the reaction of (DETC)2–Fe(II) and NO⋅ was determined by EPR spectrometer (Zhu et al. 2022). More detailed measurements and parameters can be found in the Text S4.
A quenching experiment was carried out to explore the possible effect of various free radicals in the degradation of 2-CP. Isopropanol (IPV), 1,4-benzoquinone, NaN3, and flavanone as quenching agents for ⋅OH, O2⋅−, 1O2, and NO⋅ were added to the reaction systems, respectively. To further explore the forming mechanism of NO⋅, an important intermediate peroxynitrite (ONOO−) was determined by an established fluorescent probe technique with a commonly used fluorescent dye 2,7-dichlorodihydrofluorescein diacetate (DCFH2) as an indicator (300 μm), which could react with ONOO− to produce a highly fluorescent oxidized species (i.e., DCF) (McQuade and Lippard 2010). Briefly, DCFH2 was dissolved in anhydrous dimethyl sulfoxide to prepare a 5 mM of stock solution. Before the observation, the stock solution was diluted by PBS buffer to a working concentration of 1–10 μM and observed under a fluorescence microscope (Eclipse Ni-U, Nikon, Japan), with the excitation/emission wavelength of 504/529 nm.
3 Results and discussion
3.1 Structural properties of BN and DBN derived from N-enriched biomass
The elemental analysis suggests that BN derived from algae biomass contained relatively high content of N, which exhibited a decreasing trend from 12.53% (BN350) to 8.69% (BN750) with increasing charring temperature. The BN samples also contained a range of metal and mineral elements such as Fe, Ca, K, and Na, but their respective contents were remarkably lower (< 2.5%) (Table S1). Comparatively, the N contents of BN are higher than many other N-doped carbon materials prepared by N-doping techniques such as the pyrolysis of crop straw in an ammonia atmosphere (the N content in the obtained samples was in the range of 0.36–7.72%) (Wu et al. 2021) and ammonium nitrate soaking followed by pyrolysis, where the N content in obtained carbons was reported less than 10% (Zhu et al. 2018). Besides green algae in this study, direct pyrolysis of N-rich biomass such as plants and leaf litter can also produce BC with nonnegligible N content (Wagner et al. 2015), indicating that BN is ubiquitous in water/soil environments and the N-containing groups might alter electrochemical characteristics including EDC, EAC, and electron transfer capacity of carbon matrices. The surface N content in DBN extracted from BN ranged from 2.31 to 7.56% based on the XPS results (Table S2). The deconvolution of high-resolution spectra for N1s suggests that the N species in DBN mainly included pyridinic-N (398.25 eV), pyrrolic-N (399.8 eV), graphitic-N (401.1 eV), and oxidized-N (402.8 eV) (Lian et al. 2016). As shown in Figure S1, pyridinic- and pyrrolic-N accounted for over 43 atom% for all the DBN samples except DBN650 (31.79%). Comparatively, DBN750 possessed the highest content of graphitic N (41.68%) due to the increased condensation of carbon matrix; while the samples prepared at moderate temperatures (450–650 °C) exhibited significantly higher yield of oxidized-N, which played a critical role in enhancing the yield of N-containing free radicals (Zhu et al. 2020) (see more discussion below).
FTIR spectra reflect the variation of functionalities in DBN samples, where the N-associated structures are labelled in the Fig. 1a. The peak at 3412 cm−1 was generated by N–H stretching, while the N–H strain appeared at 1631 cm−1. The peak at 1404 cm−1 was denoted as C(sp2)=N stretching, and the peak at 1127 cm−1 can be identified as C(sp2)–N stretching vibration (Bai et al. 2014). The peak intensity of N-containing groups enhanced initially and then decreased when the charring temperature increased from 350 to 750 °C. The solid-state 13C NMR spectra (Fig. 1b) were employed to illustrate the molecular structure of DBN and each peak was relatively quantified to determine the respective content of functional moieties (Table S3). Three evident characteristic peaks of O/N-alkyls (40–90 ppm), aromatic C–C (90–150 ppm), and carboxyl/ester/quinone (165–200 ppm) were observed and their percentages increased with pyrolytic temperature and roughly peaked at 550 °C, consistent with the trend of FTIR data. Additionally, the Raman spectra of DBN (Fig. 1c) showed that all the samples had peaks at 1336–1351 cm−1 and 1565–1595 cm−1, which could be identified as D peak and G peak, respectively (Geng et al. 2011). The relative intensity ratio of D to G bands (ID/IG), a measure of disorder degree, decreased from 1.065 (DBN350) to 0.889 (DBN550), indicating the formation of graphitic domains; however, with further increasing pyrolytic temperature, the ratio increased to 0.984 (DBN750), probably due to enhanced vacancy defects caused by the breakdown of graphitic domains at higher temperature (Wan et al. 2023).
Heterocyclic N structures are reported to improve the electron shuttling capacity of carbon matrixes and thus favor the redox-involved environmental processes such as microbial Fe(III) reduction (Wu et al. 2021) and transformation of Cr(VI). The EAC, EDC, and EEC values of DBN samples were in the range of 2.6 to 3.0 mmol e−/g, 1.5 to 1.9 mmol e−/g, and 4.1 to 4.8 mmol e−/g, respectively (Table S4), which roughly decreased with charring temperature. Owing to the higher electronegativity of the doped-N, all the DBNs possessed higher EAC than EDC values. For comparison, the EDC, EAC, and EEC of DBC450 were also determined (Table S4), which exhibited similar EDC values (1.9 mmol e−/g) but significantly (p < 0.05) lower EAC (2.2 mmol e−/g) and EEC (4.1 mmol e−/g) than those of DBN450 (2.8 mmol e−/g for EAC and 4.7 mmol e−/g for EEC). These results suggest that N enrichment enhanced the electron accepting capacity of DBN, which might benefit the acquisition of electrons from sulfides.
3.2 DBN-mediated catalytic dichlorination in sulfide-containing aqueous solutions
The catalytic activities of DBN350–750 and DBC450 were evaluated by monitoring the dichlorination of CPs in the presence of sulfides (Fig. 2). About 39.1% of 2-CP was removed within 120 h by DBN450 in the presence of sulfides and followed by DBN550 (34.7%), DBN650 (21.8%), DBN750 (18.7%), and DBN350 (16.0%). Note that sulfides or DBN450 alone exhibited negligible removal of 2-CP (< 4.2%), indicative of the important synergistic role of DBN and sulfides in the degradation of 2-CP. In contrast, only 12.9% of 2-CP was removed by the combination of DBC450 and sulfides, which further reflected the important catalytic role of heterocyclic N in pyrogenic carbon. However, the degradations of 3-CP and 4-CP were no more than 11.92% and 9.92% in the period of 120 h by all the DBN samples (Fig. 2b and c), much lower those that of 2-CP, indicating the nonnegligible effect of molecular structure of CPs in their degradation (see more discussion below). The degradation kinetics of 2-CP can be well-fitted by the pseudo-first-order model (Table S5) and the highest kinetic constants (Ka) of degradation was 4.1 × 10–3 h−1 (DBN450), which was comparable to that of N-doped graphene (7.61 × 10–3 h−1) and N-doped carbon nanotubes (5.5 × 10–3 h−1) in the chlorine elimination of hexachloroethane in sulfide-containing solutions (Liu et al. 2021), reflecting the remarkable catalytic degradation potential of DBN in the presence of reduced sulfur species (e.g., S2−). It is generally believed that the degradation efficiency of graphitized carbons could be greatly improved by the doped N (especially pyridine-N and pyrrolic-N) due to the facilitated electron transfer (Wu et al. 2021). However, no significantly positive correlation between Ka values and the content of pyridine-N/pyrrolic-N or the total N content in DBN samples was observed (Figures S2–S4). Similarly, the Ka values were also not positively correlated with the EAC or EDC of DBN (Figures S5 and S6). These observations suggest that besides the facilitated electron shuttling by N-doping, other mechanisms might play more important roles in the removal of CPs in the present work.
The degradation kinetics of 5.0 mM chlorophenols (CPs) by different DBN or DBC with 50 mM sulfides for 5 days: (a) 2-CP; (b) 3-CP; (c) 4-CP. Controls also contained 50 mM sulfides in the absence of DBN, or DBN in the absence of sulfides indicating no degradation. Error bars represent the standard deviation of triplicates
Multiple lines of existing evidence indicate that the sorption of sulfides to conductive carbon surfaces could enhance the degradation of organic contaminants by increasing the electron transfer efficiency (Ding et al. 2018; Xu et al. 2020). Thus, the sorption of DBN samples for sulfides was conducted and the results implied that DBN450 had a significantly (p < 0.05) higher sorption capacity than other samples (Fig. 3a), which was probably due to its higher content of active sites for sulfides. The molecular structure of char materials is highly regulated by carbonization temperature, which generally develops from transition phases to turbostratic ones in the temperature range from 300 to 1000 °C (Keiluweit et al. 2010; Yoo et al. 2018). The medium-temperature chars (e.g., 450–550 °C) possess not only abundant oxyl groups but also newly formed graphitic phases. Noncovalent interactions such as hydrogen bonding and electrostatic interaction may occur between the oxyl groups and negatively charged sulfides at pH 7.0 considering the pKa values of carboxyl and phenolic hydroxyl groups are around 4.3 and 9.8, respectively (Zhao et al. 2015). For graphitic domains, the positively charged C atoms triggered by N-doping may sorb and/or interact with sulfides to form intermediate structures (e.g., C–S–S group), which was identified by K-edge X-ray absorption spectroscopy (Liu et al. 2021). As a result, the medium-temperature DBN exhibited the highest sorption affinity for sulfides. Furthermore, DBN450 possessed the highest colloidal stability in aqueous solutions among the samples with the hydroynamic diameter closely centered at 500 nm during 120 min, evidenced by the aggregation kinetics (Figure S7). The high dispersion capacity endowed the DBN450 more active sites for the binding of sulfides, which was favorable to the sorption of sulfides. More importantly, XPS results suggested that the S2p spectra of DBN450 and DBN650 after sulfide attachment displayed not only a pair of peaks located at 163.6 eV that was probably attributed to S(II) or S0 but also a new pair of peaks at 168.4 eV that was from high valance sulfur such as S(IV)/(VI) (Sun et al. 2022). In contrast, only low valance sulfur peaks at 163.6 eV can be clearly identified in the S2p spectra of DBC550 after sulfide sorption (Figure S8). These variations indicate that the attached sulfides could be oxidized by DBN.
The removal efficiency of 2-CP was closely related to the sorption of DBN samples for sulfides (R2 = 0.991, p < 0.05) (Fig. 3b), which demonstrated that the binding of sulfides might be one of the most important rate-limiting steps for the decay of CPs by DBN under the reducing conditions. To further explore the contribution of sulfides, the degradation of 2-CP by DBN450 in the presence of various sulfide concentrations (10–100 mM) was compared (Fig. 3c). It is clear that the decay of 2-CP increased initially to reach peak at 50 mM of sulfides and then dropped with higher sulfide concentrations. This indicates that excess sulfides might inhibit the degradation of 2-CP by occupying more active sites for 2-CP and/or consuming oxidizing substances. Besides the binding of sulfides, the sorption affinity of DBN for 2-CP could also influence the removal efficiency (Machado et al. 2020; Channei et al. 2020). Hence, the sorption of 2-CP by DBN samples without the addition of sulfides was conducted and the results showed that the sorption capacity at the end of the experiment was comparable among the DBN samples (Figure S9), which further highlights the critical role of sulfide attachment in facilitating the catalytic degradation of 2-CP.
3.3 Importance of ROS and RNS in the transformation of 2-CP
Besides activating the neighboring C atoms (Kong et al. 2014), the embedded N is favorable to the formation of carbon-centered radicals and their electron donating capacity (Zhu et al. 2020). In the present study, the binding of reduced sulfur species (e.g., S2−) might further increase the electron density of DBN by providing an extra electron donor. Thus, we proposed that the presence of sulfides could contribute to the production of ROS by favoring electron transfer from carbon matrix or PFRs to the chemisorbed oxygen on DBN surfaces. Specifically, the quinone moiety of DBN accepted electrons from sulfides to be reduced to hydroquinone. The formed hydroquinone subsequently donated electrons to oxygen molecules and was converted into quinone (Yang et al. 2017). This reversible redox reactions between quinone and hydroquinone allow electrons to continuously transfer from sulfides to oxygen via DBN (like an electron shuttle), which promotes the production of ROS. The EPR spectra of DBN350-750 indicated that DBN450 possessed the highest EPR signal intensity, followed by DBN350, DBN550, DBN650, and DBN750 (Fig. 4a). The corresponding g-values of the EPR signals were ~ 2.002, which can be designated as carbon-centered radical species (Lachocki et al. 1989). The significantly reduced intensity of EPR signals at higher pyrolytic temperatures was probably due to the elimination of oxygen functionalities and increased graphitization (Zhu et al. 2018), which is consistent with previous studies. A positive correlation between the PFR yield of DBN samples (except DBN350) and the Ka values of 2-CP (R2 = 0.868, Figure S10) is indicative of the great potential of PFRs in promoting the degradation of 2-CP. For DBN350, however, the much lower sorption affinity for sulfides resulted in its decreased catalytic degradation for 2-CP although it had relatively high content of PFR.
(a) EPR spectra of DBN350–DBN750; (b–d) the effect of sulfide concentrations (10, 50, 100 mM of Na2S·9H2O) on the formation of O2⋅−,·OH, 1O2 trapped by DMPO and TEMP in the DBN450/sulfide system; (e) the generation of NO⋅ using (DETC)2–Fe(II) as a spin-trapping agent; (f) the effect of different quenching agents on the degradation of 2-CP by DBN450/sulfide system, where the concentration of quenching agents was 10 mM
DBN450 was selected as a representative of DBN samples and used for the determination of ROS in the aqueous suspension containing different concentrations of sulfides (Fig. 4b–d). Spin-trapping agents were employed to detect the production of ROS. Three characteristic peaks with intensities of 1:1:1 of TEMP-1O2 adducts, signals of DMPO-O2⋅− adducts with six typical peaks, and typical four-line (1:2:2:1) signals of DMPO-OH adducts were detected, demonstrating the generation of 1O2, O2⋅−, and ⋅OH. Notably, the yields of these ROS were significantly (p < 0.05) higher in the suspensions added with 50 or 100 mmolL–1 Na2S than that with 10 mmol L–1 Na2S, indicating that the production of ROS was closely related to the participation of sulfides. Multiple lines of evidences highlight the pivotal role of ROS in the transformation of organic contaminants both in water/wastewater treatments and exploring their environmental fate (Nidheesh et al. 2021; Fang et al. 2017; Ruan et al. 2019). Hence, we believed that the produced free radicals played a critical role in the dichlorination of CPs in the sulfide-containing aqueous system. To quantitatively determine the contributions of ROS to the decay of CPs, IPV, NaN3, and p-benzoquinone (Wang and Wang 2020) were used as quenching agents for ⋅OH, 1O2, and O2⋅−, respectively, in the representative reaction system of DBN450 and 2-CP (Fig. 4f). The reduction for the degradation of 2-CP followed an order of NaN3 (42.6%), IPV (25%), and p-benzoquinone (13.09%) after the quenching treatment. As a result, it seems that the non-radical mechanism accounted for at least 50% of the 2-CP removal. It is reported that the non-radical mechanism was more prevalent in the degradation of compounds by high-temperature BCs (e.g., 800 °C) due to their higher size of polyaromatic sheets and/or vacancies (Wan et al. 2021; Pignatello et al. 2017). Thus, for the DBN450, we inferred that other mechanism(s) might contribute more to the removal of CPs. Besides ROS, evident isotropic EPR signals of (DETC)2–Fe(II)–NO spin adduct was also identified (Fig. 4e), reflecting the generation of NO⋅, a typical RNS, from DBN450 using (DETC)2–Fe(II) as a spin-trapping agent. It was reported that RNS was effective in degrading various organic contaminants including bisphenol A, ibuprofen, estradiol, and ethinylestradiol (Wu et al. 2019; Wang et al. 2019). To explore the possible contribution of NO⋅ to the decay of 2-CP, the quenching experiment was carried out simultaneously using flavanone as the quenching agent (Wang et al. 2019). We noted that the decrease of 2-CP degradation was up to 72.2% after the quenching of NO⋅, significantly higher than that caused by ROS (Fig. 4f). Consistently, the degradation efficiency was positively related to the content of NO⋅ in DBN samples (Figure S11, R2 = 0.74), implying the dominating contribution of RNS in the decay of 2-CP. Based on the EPR results and ROS/RNS quenching experiments, it was concluded that the contributions to the removal of 2-CP by DBN450 followed an order of RNS > ROS > non-radical mechanism.
An interesting question confronting us is how the RNS was produced in the reactive systems. It is frequently reported that RNS such as NO⋅ and NO2⋅ can be formed through the UV photolysis of nitrate/nitrite or as secondary radicals from the reaction of ⋅OH with nitrite (⋅OH + NO2− → OH− + NO2⋅) (Wu et al. 2019). A recent work developed a photocleaved O2-released nanoplatform to switch ROS into RNS by combining with nitric oxides for repressing hypoxic breast tumor (Luo et al. 2021). We noticed that the DBN samples except DBN750 possessed considerable content of N-oxides as shown by the XPS results (Figure S1), which was likely to react with the generated ROS to form RNS. To justify the hypothesis, the generation of peroxynitrite (ONOO−/ONOOH), an important intermediate to produce multiple RNS (e.g., ONOOH → ⋅OH + NO2⋅) (Bartesaghi and Radi 2018), was monitored in the mixture of DBN450 and sulfides using DCFH2 as a fluorescent probe (Fig. 5). It was shown that extraordinarily stronger green fluorescence signals launched from DBN450 surfaces could be detected than those from the control (without sulfides), which visually evidenced the presence of ONOO−/ONOOH. However, it should be noted that the oxidization of DCFH2 to DCF was not specifically initiated by ONOO−, the conversion of which was also reported using other oxidants such as O2⋅−, CO3⋅−, and NO2⋅ (Wardman 2007). Nevertheless, DCFH2 has very low reactivity with O2⋅− and hydrogen peroxide relative to ONOO− (Wrona et al. 2005). Furthermore, only ROS and RNS as two major oxidants presented in the DBN450/sulfides system, and thus we believed that RNS (i.e., ONOO−) were mainly responsible for the oxidative fluorescence of DCFH2. The overall results indicate that ROS (e.g., ⋅OH, 1O2, and O2⋅−) generated by the electron transfer from DBN to the chemisorbed oxygen on DBN might be the “primary” radicals and RNS (e.g., ONOO−/ONOOH, NO⋅ and/or NO2⋅) resulted from the reactions between ROS and N-oxides in DBN might be the “secondary” radicals, both of which lead to the decay of CPs. By contrast, the non-radical mechanisms (e.g., degradation by reactive sulfur intermediates) only play a minor role in this process. The related mechanisms are illustrated in Fig. 6.
The fluorescence image of DCF in the DBN450/sulfide system (Ex/Em = 504/529 nm). The green fluoresce of DCF was generated by RNS oxidization of DCFH2, where (a) is the bright field, (b) is the dark field, and (c) is the merge channel. The control added with only DBN450 but without sulfides is presented in (d), (e), and (f). (d) bright field; (e) dark field; (f) merge channel
The contributions of different mechanisms to the decay of chlorophenols. (I) the attached sulfides were oxidized by DBN to form reactive sulfur intermediate structures; (II) the attached sulfides transferred electrons to chemisorbed oxygen via DBN forming ROS (e.g., O2⋅− and ·OH) as the “primary” radicals; and (III) the formed ROS reacted with N-oxides in DBN to generate RNS (e.g., ONOO−/ONOOH, NO⋅) serving as the “secondary” radicals
3.4 By-product analysis and possible reaction pathway
Based on the analysis of degradation intermediates by LC–MS/MS, the main fragmentations (m/z) and chemical structures are summarized in Figure S12. The proposed degradation pathways of 2-CP by the DBN450/sulfides system were mainly involved substitution, benzene ring cleavage, and hydroxylation reactions. The possible intermediate products were mainly composed of aromatic halides (e.g., 2,4,6-trichlorophenol and chlorohydroquinone), alcohols (phenol, hydroquinone, pyrocatechol, phloroglucinol, crotonyl alcohol, hydrobenzoquinone), and ketones (1,4-benzoquinone). The concentration of Cl− generated in the reaction between DBN450 and 2-CP in the sulfide-containing solutions was monitored during the degradation process. The generation of Cl− was fast at the beginning and more than 66.67% of Cl− was produced in the initial 24 h (Figure S13), which indicated that dichlorination was probably the first step in the degradation of 2-CP and then followed by the cleavage of benzene ring. The removal of TOC was also determined and ~ 22% removal was completed at the end of the experiment. Recalling that the decay of 2-CP by DBN450 was around 40% (Fig. 2), we concluded that the tested CPs were not necessarily decomposed completely and a portion of the intermediate products might retain the benzene ring structure (mainly quinone chemicals) with a nonnegligible toxicity potential (Gu et al. 2022). Thus, the impact of DBN-induced transformations of CPs on their ecotoxicity, i.e., secondary toxicity, also needs investigation in exploring the role of DBN in the biogeochemical processes. The possible reaction pathway for 2-CP degradation is presented in Fig. 7.
It is notable that the degradation efficiency of 2-CP was significantly (p < 0.05) higher than that of 3-CP and 4-CP (Fig. 2). This could probably be explained by the sorption pattern of CPs by DBN samples and reactivity of CPs due to the substituent of Cl. We noticed that the binding affinity of 2-CP to DBN prepared at different temperatures (350–750 °C) was similar (Figure S8), which indicated that surface functionality of DBN might play a more important role than its polyaromatic structure in the sorption. Otherwise, if the π-electron interactions dominated the sorption of CPs (Zhu et al. 2004), the binding affinity would have enhanced with the increasing pyrolytic temperature due to larger polyaromatic structures in the high-temperature DBN. Thus, the hydroxyl group in CP molecular structure might be the preferred site for the binding with DBN and consequently the adjacent C–Cl bonds at ortho positions were more easily to be attacked by ROS and RNS. Additionally, Cl substituent on the aromatic ring could also influence the reactivity of CPs. The electron-donating effect of hydroxyl group is more significant to the Cl at ortho positions than that at meta and para positions and thus the C–Cl bonds at ortho positions could contribute more electrons to ROS/RNS during the reactions.
4 Environmental implications
We are among the first to investigate the catalytic transformation of organic contaminants mediated by DBN in the sulfide-containing aqueous solutions. The present study demonstrates that DBN is a ubiquitous but overlooked mediator in the water and soil environments, widely involved in the abiotic transformation of organic contaminants especially in the presence of reduced sulfur species. Different from previously reported mechanisms, we noticed that in the DBN-sulfide system the sulfides were favorable to the production of ROS on DBN and the generated ROS reacted with N-oxides in DBN to produce RNS, which played a dominating role in the decay of CPs. The generation of RNS is widely observed in the atmosphere, air–water interface, and surface water (Simoes et al. 2021; Rana and Guzman 2022). This work provides new information that RNS might also be formed in deep water and DBN probably possesses higher catalytic activity than we expected through reacting with reduced sulfur species to produce RNS in anaerobic environments, which would have profound implications for many critical biogeochemical processes including the transformations of contaminants and minerals, microbial community dynamics, and the elemental cycling in terrestrial/aquatic systems as well as for scalable applications in the wastewater treatment. Additionally, we also found that the benzene ring structures in the tested chlorophenols could not be completely decomposed in the DBN-sulfide systems in a relatively short time (120 h), and thus the secondary toxicity caused by contaminant transformation in the reaction with DBN also needs more investigations.
Availability of data and materials
The datasets generated and analyzed during the current study are available from the corresponding author on reasonable request.
Abbreviations
- BC:
-
Black carbon
- DBC:
-
Dissolved black carbon
- BN:
-
Black nitrogen
- DBN:
-
Dissolved black nitrogen
- ROS:
-
Reactive oxygen species
- RNS:
-
Reactive nitrogen species
- PFR:
-
Persistent free radicals
- DOM:
-
Dissolved organic matter
- EPR:
-
Electron paramagnetic resonance
- TOC:
-
Total organic carbon
- ICP MS:
-
Inductively coupled plasma mass spectrometer
- XPS:
-
X-ray photoelectron spectrometer
- FTIR:
-
Fourier transform infrared
- CPMAS NMR:
-
Cross-polarization magic angle spinning nuclear magnetic resonance
- EAC:
-
Electron accepting capacity
- EDC:
-
Electron donor capacity
- EEC:
-
Electron exchange capacity
- 2-CP, 3-CP, 4-CP:
-
2-Chlorophenol, 3-chlorophenol, and 4-chlorophenol
- HPLC:
-
High-performance liquid chromatography
- LC–MS/MS:
-
Liquid chromatography-mass spectrometer
- DMPO:
-
5,5-Dimethyl-1-pyrroline-N-oxide
- TEMP:
-
2,2,6,6-Tetramethyl-4-piperidone
- DETC:
-
Diethyldithiocarbamate trihydrate
- IPV:
-
Isopropanol
- ONOO-:
-
Peroxynitrite
- DCFH2 :
-
Dye 2,7-dichlorodihydrofluorescein diacetate
References
Aeschbacher M, Sander M, Schwarzenbach RP (2010) Novel electrochemical approach to assess the redox properties of humic substances. Environ Sci Technol 44:87–93. https://doi.org/10.1021/es902627p
Bai X, Wang L, Wang Y, Yao W, Zhu Y (2014) Enhanced oxidation ability of g-C3N4 photocatalyst via C60 modification. Appl Catal B 152–153:262–270. https://doi.org/10.1016/j.apcatb.2014.01.046
Bartesaghi S, Radi R (2018) Fundamentals on the biochemistry of peroxynitrite and protein tyrosine nitration. Redox Biol 14:618–625. https://doi.org/10.1016/j.redox.2017.09.009
Barton LL, Fardeau M-L, Fauque GD (2014) Hydrogen sulfide: a toxic gas produced by dissimilatory sulfate and sulfur reduction and consumed by microbial oxidation. Met Ions Life Sci 14:237–277. https://doi.org/10.1007/978-94-017-9269-1_10
Channei D, Nakaruk A, Khanitchaidecha W, Jannoey P, Phanichphant S (2020) Equilibrium, kinetics, and thermodynamic studies concerning the removal of 2–chlorophenol using chemically carbonized rice husk waste. Naresuan Univ J Sci Technol (NUJST) 28:94–104
Chen Y, Sun K, Wang Z, Zhang E, Yang Y, Xing B (2022) Analytical methods, molecular structures and biogeochemical behaviors of dissolved black carbon. Carbon Res 1:23. https://doi.org/10.1007/s44246-022-00022-4
de la Rosa JM, Knicker H (2011) Bioavailability of N released from N-rich pyrogenic organic matter: an incubation study. Soil Biol Biochem 43:2368–2373. https://doi.org/10.1016/j.soilbio.2011.08.008
Ding K, Xu W (2016) Black carbon facilitated dechlorination of DDT and its metabolites by sulfide. Environ Sci Technol 50:12976–12983. https://doi.org/10.1021/acs.est.6b03154
Ding L, Zhang P, Luo H, Hu Y, Norouzi Banis M, Yuan X, Liu N (2018) Nitrogen-doped carbon materials as metal-free catalyst for the dechlorination of trichloroethylene by sulfide. Environ Sci Technol 52:14286–14293. https://doi.org/10.1021/acs.est.8b03565
Ding L, Wang Y, Tong L, Liu N, Wang C, Hu Q (2022) N-doped biochar-catalyzed dechlorination of carbon tetrachloride in sulfide-containing aqueous solutions: Performances, mechanisms and pathways. Water Res 223:119006. https://doi.org/10.1016/j.watres.2022.119006
Fang G, Liu C, Wang Y, Dionysiou DD, Zhou D (2017) Photogeneration of reactive oxygen species from biochar suspension for diethyl phthalate degradation. Appl Catal B 214:34–45. https://doi.org/10.1016/j.apcatb.2017.05.036
Fu H, Liu H, Mao J, Chu W, Li Q, Alvarez PJ, Qu X, Zhu D (2016) Photochemistry of dissolved black carbon released from biochar: Reactive oxygen species generation and phototransformation. Environ Sci Technol 50:1218–1226. https://doi.org/10.1021/acs.est.5b04314
Geng DS, Yang SL, Zhang Y, Yang JL, Liu J, Li RY, Sham TK, Sun XL, Ye SY, Knights S (2011) Nitrogen doping effects on the structure of graphene. Appl Surf Sci 257:9193–9198. https://doi.org/10.1016/j.apsusc.2011.05.131
Gu A, Wang P, Chen K, Djam Miensah E, Gong C, Jiao Y, Mao P, Chen K, Jiang J, Liu Y, Yang Y (2022) Core-shell bimetallic Fe-Co MOFs to activated peroxymonosulfate for efficient degradation of 2-chlorophenol. Sep Purif Technol 298:121461. https://doi.org/10.1016/j.seppur.2022.121461
Häder D-P, Williamson CE, Wängberg S-Å, Rautio M, Rose KC, Gao K, Helbling EW, Sinha RP, Worrest R (2015) Effects of UV radiation on aquatic ecosystems and interactions with other environmental factors. Photochem Photobiol Sci 14:108–126. https://doi.org/10.1039/c4pp90035a
Jaffe R, Yamashita Y, Maie N, Cooper WT, Dittmar T, Dodds WK, Jones JB, Myoshi T, Ortiz-Zayas JR, Podgorski DC, Watanabe A (2012) Dissolved organic matter in headwater streams: compositional variability across climatic regions of North America. Geochim Cosmochim Acta 94:95–108. https://doi.org/10.1016/j.gca.2012.06.031
Keiluweit M, Nico PS, Johnson MG, Kleber M (2010) Dynamic molecular structure of plant biomass-derived black carbon (biochar). Environ Sci Technol 44:1247–1253. https://doi.org/10.1021/es9031419
Kemper JM, Ammar E, Mitch WA (2008) Abiotic degradation of hexahydro-1, 3, 5-trinitro-1, 3, 5-triazine in the presence of hydrogen sulfide and black carbon. Environ Sci Technol 42:2118–2123. https://doi.org/10.1021/es702402a
Klüpfel L, Keiluweit M, Kleber M, Sander M (2014) Redox properties of plant biomass-derived black carbon (biochar). Environ Sci Technol 48:5601–5611. https://doi.org/10.1021/es500906d
Knicker H (2010) “Black nitrogen”—an important fraction in determining the recalcitrance of charcoal. Org Geochem 41:947–950. https://doi.org/10.1016/j.orggeochem.2010.04.007
Knicker H, Hilscher A, Gonzalez-Vila FJ, Almendros G (2008) A new conceptual model for the structural properties of char produced during vegetation fires. Org Geochem 39:935–939. https://doi.org/10.1016/j.orggeochem.2008.03.021
Kong XK, Chen CL, Chen QW (2014) Doped graphene for metal-free catalysis. Chem Soc Rev 43:2841–2857. https://doi.org/10.1039/c3cs60401b
Lachocki TM, Church DF, Pryor WA (1989) Pesistent free radicals in woodsmoke: An ESR spin trapping study. Free Radical Biol Med 7:17–21. https://doi.org/10.1016/0891-5849(89)90095-6
Lian F, Cui G, Liu Z, Duo L, Zhang G, Xing B (2016) One-step synthesis of a novel N-doped microporous biochar derived from crop straws with high dye adsorption capacity. J Environ Manage 176:61–68. https://doi.org/10.1016/j.jenvman.2016.03.043
Lian F, Zhang Y, Gu S, Han Y, Cao X, Wang Z, Xing B (2021) Photochemical transformation and catalytic activity of dissolved black nitrogen released from environmental black carbon. Environ Sci Technol 55:6476–6484. https://doi.org/10.1021/acs.est.1c00392
Liu C, Chen L, Ding D, Cai T (2019) From rice straw to magnetically recoverable nitrogen doped biochar: efficient activation of peroxymonosulfate for the degradation of metolachlor. Appl Catal B 254:312–320. https://doi.org/10.1016/j.apcatb.2019.05.014
Liu N, Hu Q, Wang C, Tong L, Weng C-H, Ding L (2021) Hexachloroethane dechlorination in sulfide-containing aqueous solutions catalyzed by nitrogen-doped carbon materials. Environ Pollut 281:116915. https://doi.org/10.1016/j.envpol.2021.116915
Lokesh S, Kim J, Zhou Y, Wu D, Pan B, Wang X, Behrens S, Huang CH, Yang Y (2020) Anaerobic dehalogenation by reduced aqueous biochars. Environ Sci Technol 54:15142–15150. https://doi.org/10.1021/acs.est.0c05940
Luo T, Wang D, Liu L, Zhang Y, Han C, Xie Y, Liu Y, Liang J, Qiu G, Li H, Su D, Liu J, Zhang K (2021) Switching reactive oxygen species into reactive nitrogen species by photocleaved O2-released nanoplatforms favors hypoxic tumor repression. Adv Sci 8:e2101065. https://doi.org/10.1002/advs.202101065
Machado LMM, Lütke SF, Perondi D, Godinho M, Oliveira MLS, Collazzo GC, Dotto GL (2020) Treatment of effluents containing 2-chlorophenol by adsorption onto chemically and physically activated biochars. J Environ Chem Eng 8:104473. https://doi.org/10.1016/j.jece.2020.104473
Maie N, Parish KJ, Watanabe A, Knicker H, Benner R, Abe T, Kaiser K, Jaffe R (2006) Chemical characteristics of dissolved organic nitrogen in an oligotrophic subtropical coastal ecosystem. Geochim Cosmochim Acta 70:4491–4506. https://doi.org/10.1016/j.gca.2006.06.1554
McQuade LE, Lippard SJ (2010) Fluorescent probes to investigate nitric oxide and other reactive nitrogen species in biology (truncated form: fluorescent probes of reactive nitrogen species). Curr Opin Chem Biol 14:43–49. https://doi.org/10.1016/j.cbpa.2009.10.004
Nidheesh PV, Gopinath A, Ranjith N, Praveen Akre A, Sreedharan V, Suresh Kumar M (2021) Potential role of biochar in advanced oxidation processes: a sustainable approach. Chem Eng J 405:126582. https://doi.org/10.1016/j.cej.2020.126582
Oh SY, Cha DK, Kim BJ, Chiu PC (2005) Reductive transformation of hexahydro-1,3,5-trinitro-1,3,5-triazine, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, and methylenedinitramine with elemental iron. Environ Toxicol Chem 24:2812–2819. https://doi.org/10.1897/04-662r.1
Pignatello JJ, Mitch WA, Xu W (2017) Activity and reactivity of pyrogenic carbonaceous matter toward organic compounds. Environ Sci Technol 51:8893–8908. https://doi.org/10.1021/acs.est.7b01088
Rana MS, Guzman MI (2022) Oxidation of catechols at the air–water interface by nitrate radicals. Environ Sci Technol 56:15437–15448. https://doi.org/10.1021/acs.est.2c05640
Ren W, Xiong L, Yuan X, Yu Z, Zhang H, Duan X, Wang S (2019) Activation of peroxydisulfate on carbon nanotubes: electron-transfer mechanism. Environ Sci Technol 53:14595–14603. https://doi.org/10.1021/acs.est.9b05475
Ruan X, Sun Y, Du W, Tang Y, Liu Q, Zhang Z, Doherty W, Frost RL, Qian G, Tsang DCW (2019) Formation, characteristics, and applications of environmentally persistent free radicals in biochars: a review. Bioresour Technol 281:457–468. https://doi.org/10.1016/j.biortech.2019.02.105
Simoes EFC, Almeida AS, Duarte AC, Duarte R (2021) Assessing reactive oxygen and nitrogen species in atmospheric and aquatic environments: analytical challenges and opportunities. TrAC, Trends Anal Chem 135:116149. https://doi.org/10.1016/j.trac.2020.116149
Sun S, Zhao C-Z, Yuan H, Fu ZH, Chen X, Lu Y, Li YF, Hu JK, Dong J, Huang JQ, Ouyang MG, Zhang Q (2022) Eliminating interfacial O-involving degradation in Li-rich Mn-based cathodes for all-solid-state lithium batteries. Sci Adv 8:5189. https://doi.org/10.1126/sciadv.add5189
Wagner S, Dittmar T, Jaffé R (2015) Molecular characterization of dissolved black nitrogen via electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Org Geochem 79:21–30. https://doi.org/10.1016/j.orggeochem.2014.12.002
Wan Z, Xu Z, Sun Y, He M, Hou D, Cao X, Tsang DCW (2021) Critical impact of nitrogen vacancies in nonradical carbocatalysis on nitrogen-doped graphitic biochar. Environ Sci Technol 55:7004–7014. https://doi.org/10.1021/acs.est.0c08531
Wan Z, Cao Y, Xu Z, Duan X, Xu S, Hou D, Wang S, Tsang DCW (2023) Revealing intrinsic relations between Cu scales and radical/nonradical oxidations to regulate nucleophilic/electrophilic catalysis. Adv Funct Mater 33:2212227. https://doi.org/10.1002/adfm.202212227
Wang J, Wang S (2020) Reactive species in advanced oxidation processes: formation, identification and reaction mechanism. Chem Eng J 401:126158. https://doi.org/10.1016/j.cej.2020.126158
Wang Z, Sun P, Li Y, Meng T, Li Z, Zhang X, Zhang R, Jia H, Yao H (2019) Reactive nitrogen species mediated degradation of estrogenic disrupting chemicals by biochar/monochloramine in buffered water and synthetic hydrolyzed urine. Environ Sci Technol 53:12688–12696. https://doi.org/10.1021/acs.est.9b04704
Wardman P (2007) Fluorescent and luminescent probes for measurement of oxidative and nitrosative species in cells and tissues: progress, pitfalls, and prospects. Free Radical Biol Med 43:995–1022. https://doi.org/10.1016/j.freeradbiomed.2007.06.026
Weber K, Quicker P (2018) Properties of biochar. Fuel 217:240–261. https://doi.org/10.1016/j.fuel.2017.12.054
Wrona M, Patel K, Wardman P (2005) Reactivity of 2’,7’-dichlorodihydrofluorescein and dihydrorhodamine 123 and their oxidized forms toward carbonate, nitrogen dioxide, and hydroxyl radicals. Free Radical Biol Med 38:262–270. https://doi.org/10.1016/j.freeradbiomed.2004.10.022
Wu Z, Chen C, Zhu BZ, Huang CH, An TC, Meng F, Fang J (2019) Reactive nitrogen species are also involved in the transformation of micropollutants by the UV/monochloramine process. Environ Sci Technol 53:11142–11152. https://doi.org/10.1021/acs.est.9b01212
Wu S, Wang D, Liu C, Fang G, Sun T-R, Cui P, Yan H, Wang Y, Zhou D (2021) Pyridinic- and pyrrolic nitrogen in pyrogenic carbon improves electron shuttling during microbial Fe(III) reduction. ACS Earth Space Chem 5:900–909. https://doi.org/10.1021/acsearthspacechem.1c00012
Xu W, Pignatello JJ, Mitch WA (2013) Role of black carbon electrical conductivity in mediating hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) transformation on carbon surfaces by sulfides. Environ Sci Technol 47:7129–7136. https://doi.org/10.1021/es4012367
Xu X, Sivey JD, Xu W (2020) Black carbon-enhanced transformation of dichloroacetamide safeners: role of reduced sulfur species. Sci Total Environ 738:139908. https://doi.org/10.1016/j.scitotenv.2020.139908
Yang HB, Miao J, Hung S-F, Chen J, Tao HB, Wang X, Zhang L, Chen R, Gao J, Chen HM, Dai L, Liu B (2016) Identification of catalytic sites for oxygen reduction and oxygen evolution in N-doped graphene materials: development of highly efficient metal-free bifunctional electrocatalyst. Sci Adv 2:e1501122. https://doi.org/10.1126/sciadv.1501122
Yang J, Pignatello JJ, Pan B, Xing B (2017) Degradation of p-nitrophenol by lignin and cellulose chars: H2O2-mediated reaction and direct reaction with the char. Environ Sci Technol 51:8972–8980. https://doi.org/10.1021/acs.est.7b01087
Yang KC, Zhao YX, Ji M, Li ZL, Zhai SY, Zhou X, Wang Q, Wang C, Liang B (2021) Challenges and opportunities for the biodegradation of chlorophenols: Aerobic, anaerobic and bioelectrochemical processes. Water Res 193:116862. https://doi.org/10.1016/j.watres.2021.116862
Yoo S, Kelley SS, Tilotta DC, Park S (2018) Structural characterization of loblolly pine derived biochar by X-ray diffraction and electron energy loss spectroscopy. ACS Sustain Chem Eng 6:2621–2629. https://doi.org/10.1021/acssuschemeng.7b04119
Yu X, Gong W, Liu X, Shi L, Han X, Bao H (2011) The use of carbon black to catalyze the reduction of nitrobenzenes by sulfides. J Hazard Mater 198:340–346. https://doi.org/10.1016/j.jhazmat.2011.10.052
Zepp RG, Cline DM (1977) Rates of direct photolysis in aquatic environment. Environ Sci Technol 11:359–366. https://doi.org/10.1021/es60127a013
Zhao J, Liu F, Wang Z, Cao X, Xing B (2015) Heteroaggregation of graphene oxide with minerals in aqueous phase. Environ Sci Technol 49:2849–2857. https://doi.org/10.1021/es505605w
Zhu D, Hyun S, Pignatello JJ, Lee LS (2004) Evidence for π−π electron donor−acceptor interactions between π-donor aromatic compounds and π-acceptor sites in soil organic matter through pH effects on sorption. Environ Sci Technol 38:4361–4368. https://doi.org/10.1021/es035379e
Zhu S, Huang X, Ma F, Wang L, Duan X, Wang S (2018) Catalytic removal of aqueous contaminants on N-doped graphitic biochars: Inherent roles of adsorption and nonradical mechanisms. Environ Sci Technol 52:8649–8658. https://doi.org/10.1021/acs.est.8b01817
Zhu S, Huang X, Yang X, Peng P, Li Z, Jin C (2020) Enhanced transformation of Cr (VI) by heterocyclic-N within nitrogen-doped biochar: impact of surface modulatory persistent free radicals (PFRs). Environ Sci Technol 54:8123–8132. https://doi.org/10.1021/acs.est.0c02713
Zhu K, Jia H, Jiang W, Sun Y, Zhang C, Liu Z, Wang T, Guo X, Zhu L (2022) The first observation of the formation of persistent aminoxyl radicals and reactive nitrogen species on photoirradiated nitrogen-containing microplastics. Environ Sci Technol 56:779–789. https://doi.org/10.1021/acs.est.1c05650
Acknowledgements
Not applicable.
Funding
This work was supported by the National Natural Science Foundation of China (41977278), the Natural Science Foundation of Hebei province (D2022202004), the Natural Science Foundation of Tianjin (23JCYBJC00940), and the Central Government-guided Local Science and Technology Development Foundation of Hebei province (236Z7301G).
Author information
Authors and Affiliations
Contributions
ZYK: Sampling, Lab analysis, Writing-original draft, Writing-review & editing. WMY: Conceptualization, Writing-review & editing, Funding acquisition. WYW: Supervision, Visualization. WF: Data curation. GY: Supervision. YKY: Writing-review & editing. LF: Conceptualization, Methodology, Supervision, Funding acquisition. XBS: Conceptualization, Methodology, Supervision. The author(s) read and approved the final manuscript.
Corresponding author
Ethics declarations
Ethics approval and consent to participate
Not applicable.
Consent for publication
The corresponding author consents on behalf of all the authors that this is original work and has permission to be published.
Competing interests
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Additional information
Handling editor: Kitae Baek
Supplementary Information
Rights and permissions
Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.
About this article
Cite this article
Zhang, Y., Wang, M., Wang, Y. et al. Dissolved black nitrogen: an overlooked active nano-catalyst in the abiotic transformation of chlorophenols by sulfides in the subsurface water. Biochar 6, 48 (2024). https://doi.org/10.1007/s42773-024-00342-1
Received:
Revised:
Accepted:
Published:
DOI: https://doi.org/10.1007/s42773-024-00342-1