Co-catalysis of N, S-codoped biochar toward photo-Fenton reaction for degradation of organic micropollutants in water

Junhuan Zhang; Ying Lv; Jinxuan Li; Jinhong Lü; Jianfa Li

doi:10.25259/AJC_350_2025

View/Download PDF

Buy Reprints

PDF

Translate this page into:

Original Article

ARTICLE IN PRESS

doi:

10.25259/AJC_350_2025

Co-catalysis of N, S-codoped biochar toward photo-Fenton reaction for degradation of organic micropollutants in water

Junhuan Zhang, Ying Lv^,*, Jinxuan Li, Jinhong Lü, Jianfa Li^,*

Department of Chemistry, College of Chemistry and Chemical Engineering, Shaoxing University, Shaoxing, Zhejiang, China

*Corresponding authors: E-mail addresses: lvying@usx.edu.cn (Y. Lv); ljf@usx.edu.cn (J. Li)

Received: 2025-04-07, Accepted: 2025-11-24, Epub ahead of print: 2026-03-10,

Licence

This is an open-access article distributed under the terms of the Creative Commons Attribution-Non Commercial-Share Alike 4.0 License, which allows others to remix, transform, and build upon the work non-commercially, as long as the author is credited and the new creations are licensed under the identical terms.

Abstract

Photo-Fenton reaction can degrade organic pollutants with less consumption of H₂O₂ and iron sources than conventional Fenton processes, but suffers from the problem of slow regeneration of Fe²⁺. Herein, an N, S-codoped biochar (NSB) co-catalyst was developed to accelerate iron redox cycling and enhance the oxidation of organic micropollutants in a visible-light-driven photo-Fenton system. Under optimized conditions (1.0 g L^–1 of NSB, 1.0 mg L^–1 of Fe³⁺, and initial pH = 3.5), the co-catalytic system (NSB+Fe³⁺+H₂O₂) achieved 95% sulfadiazine (an antibiotic) degradation within 30 min, with an observed rate constant (k_obs = 0.108 min^–1) 10 times higher than that of the photo-Fenton process (Fe³⁺+H₂O₂). This co-catalytic photo-Fenton process exhibits broad applicability to degrade diverse micropollutants and in real water matrices (e.g., river water and tap water). Mechanistic investigations reveal that defects, pyridinic N, and thiophenic S sites on NSB facilitated the regeneration of Fe²⁺ via electron transfer, thereby promoting the production of ^•OH and subsequent degradation of micropollutants. Thus, this research contributes to the advancement of the catalytic photo-Fenton reaction.

Keywords

Advanced oxidation

Carbon

Co-catalysis

Heteroatom doping

Show Related Articles from PubMed

1. Introduction

Most of the organic micropollutants, including pharmaceuticals and chlorinated aromatic compounds, are refractory to biodegradation and persistent in water, posing long-term risk to human health and ecological safety. For example, antibiotic pollutants are often detected in urban wastewater and can rarely be removed completely by conventional wastewater treatment [1]. Superior to biological and other physical/chemical processes, advanced oxidation processes (AOPs) have the potential to break down these recalcitrant antibiotic molecules, and convert them into less toxic compounds or even completely mineralized products like CO₂, H₂O, and inorganic ions [2-4]. The strong oxidation capacity of AOPs toward organic micropollutants stems from the reactive oxygen species (ROS) such as hydroxyl radicals (^•OH, E^Ɵ(^•OH/H₂O) = 2.73 V), sulfate radicals (SO₄^•–) produced by activation of H₂O₂, persulfates, and O₃ [5-7]. Especially, the AOPs based on the Fenton reaction have the advantages of cheap and readily available reagents, mild reaction conditions, and easy operation. However, a large amount of Fe²⁺ (18–410 mmol L^–1) is required in conventional Fenton processes because the consumption of Fe²⁺ in Reaction 1 (k₁ = 63–76 L mol^–1 s^–1) is much faster than its regeneration by Reaction 2 (k₂ = 0.01–0.02 L mol^–1 s^–1) [8,9]. Consequently, iron sludge composed of ferric hydroxides and other potentially hazardous substances is inevitably produced in the following-up step of the Fenton process, which leads to extra disposal costs and environmental risk.

(1)

{Fe}^{2+} {+ H}_{2} O_{2} \to {Fe}^{3 +} {+ OH}^{-} +^{•} OH

(2)

{Fe}^{3+} {+ H}_{2} O_{2} \to {Fe}^{2 +} {+ H}^{+} {+ HO}_{2}^{•}

The photo-Fenton process, defined as the combination of photo-catalysis with Fenton reaction, can be operated with a lower requirement of Fe²⁺/Fe³⁺ supply, because Fe²⁺ can also be regenerated by photo-reduction of Fe³⁺ (Reaction 3). In addition to the ^•OH produced by Reactions 1 and 3, ^•OH can be produced by direct photo-decomposition of H₂O₂ (Reaction 4). Thus, the higher ^•OH yield in the photo-Fenton process makes it more powerful for oxidation of organic pollutants than conventional Fenton/Fenton-like processes [10-12]. Despite these advantages of photo-Fenton reaction, its oxidative performance toward organic micropollutants remains limited by Fe²⁺/Fe³⁺ redox cycling, because Reactions 3 and 4 are several orders of magnitude slower than Reaction 1 [13]. In other words, Reaction 1 should dominate the generation of ^•OH if Fe²⁺ regeneration were sufficiently rapid. To address this challenge, carboxylic acids [14], graphene-based materials [15], heterojunction architectures [16], and carbon materials [17,18] have been used to accelerate the iron redox cycling and to boost the photo-Fenton reaction.

(3)

{Fe}^{3+} {+ H}_{2} O + h ν \to {Fe}^{2 +} {+ H}^{+} +^{•} OH

(4)

H_{2} O_{2} + h ν \to 2^{•} OH

Biochar, a carbon-rich solid product derived from the pyrolysis of renewable biomass, is a multi-functional material in environmental applications [19]. The active moieties, such as persistent free radicals (PFRs) and defects in biochar, enable it to participate in redox reactions [20,21]. Specifically, biochar can act as an electron donor to ferric species and accelerate the iron redox cycling in Fenton/Fenton-like reactions [22,23]. Doping with heteroatoms (e.g., N and/or S) further enhances the electron donation capacity of biochar, because N- and/or S-doping introduces new functional groups and more defects in biochar, disrupting the chemical inertness of the carbon matrix [24,25]. Thus, N-doped or N, S-codoped biochars are more reactive toward activation of persulfates or H₂O₂ than undoped biochar [26-28], while N, S-codoped biochar (NSB) outperforms N-doped biochar on co-activation of H₂O₂ with trace Fe³⁺ [29]. The high reactivity of NSB gives it the potential to boost the photo-Fenton reaction, although little is known about its practical performance till now. For the purpose of filling this knowledge gap, in this work, NSB was tested as a co-catalyst of photo-Fenton reaction, in which Fe³⁺ of a typical 1 mg L^–1 concentration was used to minimize the formation of iron sludge. An antibiotic sulfadiazine (SD) was used as a representative micropollutant, along with other common organic micropollutants (sulfamethazine, ciprofloxacin, and 2,4-dichlorophenol), to assess the performance of this novel co-catalytic photo-Fenton process on pollutant removal. The influence of reaction conditions on the degradation of SD was evaluated, and the dominant ROS and co-catalytic roles of NSB in the photo-Fenton reaction were investigated.

2. Materials and Methods

The reagents have been listed in the (Text S1).

Text S1 and S2

Download

2.1. N, S-codoped biochar preparation and characterizations

NSB was prepared by co-pyrolysis of thiourea (CS(NH₂)₂) and softwood sawdust (mass ratio = 1:10) at 700°C for 3 h in a tube furnace filled with nitrogen gas, based on the optimized preparation conditions in a previous study [29]. The flowchart for the preparation method has been presented in Figure S1. The undoped wood biochar (WB) was prepared under the same conditions, except that no thiourea was added. The characterization methods, including elemental (C, H, O, N, S) analysis, specific surface area (SSA), X-ray photoelectron spectroscopy (XPS), and fourier transform infrared spectroscopy (FTIR), were also described in this study [29]. Transmission electron microscopy (TEM) was observed on a JEOL JEM-1011 instrument (Japan).

Figure S1

Download

2.2. Photo-Fenton degradation of organic pollutants

The photo-Fenton reaction was performed under irradiation from a 300 W Xenon lamp with a 420 nm UV filter (Figure 1). Typically, 1 g L^-1 of NSB and 50 mL of SD (C₀ = 20 mg L^-1) were added to a 250 mL jacketed beaker with the reaction temperature controlled at 25 ± 1°C by cooling water. 1 mol L^–1 H₂SO₄ or 0.5 mol L^–1 NaOH was used to adjust the initial pH (pH₀). A 30 min pre-adsorption in the dark was conducted before the reaction. The lamp was then turned on, and the reaction was initiated by adding 1 mg L^–1 of Fe³⁺ solution and 2 mmol L^–1 of H₂O₂ solution. A 300 μL solution sample was taken at intervals, and immediately quenched by adding an equal volume of methanol. Then the solution was filtered through a 0.22 μm microporous membrane, and the residual SD concentration was tested by high-performance liquid chromatography (HPLC). The degradation experiments of other pollutants (C₀ = 20 mg L^-1) were performed in the same procedure as that for SD. All experiments were repeated twice independently, and the average values and standard deviations were recorded. Furthermore, SD degradation in real water matrices was evaluated using solutions prepared with river water and tap water. The reusability of NSB in degradation experiments was evaluated using the recycled NSB separated by centrifugation from the reaction system.

The set-up schematic for conducting the photo-Fenton reaction.

2.3. Analytical methods

The HPLC methods for measuring the pollutant concentration (C, mg L^-1) were included in Text S2. ^•OH, as the major ROS of the photo-Fenton process, was detected on an electron paramagnetic resonance (EPR) spectrometer (JEOL JES-FA200, Japan) using 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) as the spin-trapping agent. The cumulative production of ^•OH was calculated from the amount of p-hydroxybenzoic acid produced by rapid reaction between ^•OH and benzoic acid (k = 5.9×10⁹ L mol^–1 s^–1) according to a method reported previously [22]. The Fe²⁺ concentration was detected spectrometrically using 1,10-phenanthroline as chromogenic reagent. The residual H₂O₂ was measured by the titanate method [30].

3. Results and Discussion

3.1. Characteristics of N, S-codoped biochar (NSB)

Elemental analysis of NSB confirms successful N, S-doping of biochar, as both N (2.55 wt.%) and S (0.66 wt.%) were detected. NSB exhibits a lower C content (83.6 wt.%) than the undoped WB (89.7 wt.%), indicating partial substitution of C atoms by N and S heteroatoms. The molar (O+N)/C ratio of NSB is 0.105, higher than that of WB (0.0527), suggesting a greater abundance of polar groups in the doped biochar. However, the SSA value calculated by the Brunauer–Emmett–Teller (BET) model of NSB (53.8 m² g^–1) is only ∼1/4 of WB (239 m² g^–1), due to the pore blockage by heat treatment byproducts of thiourea [26,31,32]. There are some nanosized darker spots in the TEM image of NSB, which makes it different from WB, having a homogeneous structure (Figure 2). These darker spots indicate the introduction of dense heterostructure in biochar through N, S-doping, and imply the pore blockage by such dense heterostructure.

TEM images of (a) N, S-codoped biochar and (b) wood biochar.

Figure 3(a) shows the Raman spectra of WB and NSB, in which the D peak (∼1330 cm^–1) and G peak (∼1580 cm^–1) reveal the defective structure and graphitization degree of the carbon matrix, respectively. The calculated intensity ratios of these two peaks (I_D/I_G) are 0.886 for WB and 0.971 for NSB. The higher I_D/I_G value of NSB indicates that N and S incorporation disrupted the biochar surface structure and affected the graphitization of the carbon matrix, thus increasing the defective degree of biochar. FTIR spectra (Figure 3b) were used to identify surface functional groups of NSB and WB. It can be seen that the absorption peak at 3436 cm^–1 corresponds to –OH/>NH stretching vibrations, the peaks at 1600–1650 cm^–1 are assigned to C=C/C=O absorption, and the peaks at 980–1150 cm^–1 represent C–O stretching vibration. Combined with the larger molar (O+N)/C ratio of NSB, these results indicate that NSB contains more oxygen- or nitrogen-containing functional groups (C=O, –OH, or >NH) than WB. These functional groups, along with the defective structure in the doped biochar, can provide additional active sites for activation of H₂O₂ and persulfate [24,33]. XPS spectra (Figures 3c-f) further verify the introduction of N and S species into the biochar. The high-resolution C 1s and O 1s spectra confirm the presence of polar functional groups (C=O, C–O, –COOH) in NSB. The N 1s spectrum indicates three N species in NSB: pyridinic N (398.38 eV), pyrrolic N (399.58 eV), and graphitic N (400.98 eV) [34,35]. Deconvolution of the S 2p spectrum yields S 2p_1/2 and S 2p_3/2 peaks, which are ascribed to thiophenic C–S–C moieties (164.18 and 165.08 eV) incorporated into the carbon matrix, as well as oxidized S species [C–SO_x–C (x = 2∼4)] (168.68 and 170.08 eV) [26,32,36].

(a) Raman spectra and (b) FT-IR of wood biochar and N, S-codoped biochar (NSB). High resolution XPS spectra of NSB: (c) C 1s, (d) O 1s, (e) N 1s, and (f) S 2p.

3.2. Co-catalytic effect of NSB toward photo-Fenton reaction

Figure 4 shows the degradation of SD in various reaction systems, illustrating the advantage of using NSB in the photo-Fenton reaction. First of all, NSB exhibited negligible adsorption for SD (Figure 4a), as no significant change in SD concentration was observed during the 30 min of pre-adsorption in the dark and after another 90 min of light irradiation. The poor adsorption of NSB to SD should be attributed to the small surface area of biochar [37]. Despite its weak adsorption, NSB significantly enhanced SD degradation in the co-catalytic system (NSB+Fe³⁺+H₂O₂), achieving a 95% removal efficiency within 30 min under visible light compared to only 30% in the Fe³⁺+H₂O₂ system (Figure 4a). The observed rate constant (k_obs) calculated by the first-order reaction kinetics model ( $ln (C / C_{0} = - k_{obs} t$ ) for SD removal is 0.108 min^–1 (R² = 0.945) in the NSB+Fe³⁺+H₂O₂ system, which is 10 times higher than that in the Fe³⁺+H₂O₂ system (Table S1). These results indicate that NSB dramatically accelerates the photo-Fenton oxidation of SD, even though NSB itself is not an effective H₂O₂ activator, as only 6.0% of SD was removed by NSB+H₂O₂ after 90 min of irradiation. Therefore, NSB played a co-catalytic role in the photo-Fenton degradation of organic micropollutants.

Table S1

Download

Removal of SD (20 mg L–1) in various reaction systems: (a) NSB, NSB+H2O2, Fe3++H2O2, and NSB+Fe3++H2O2 under light irradiation; (b) NSB+Fe3+, WB+Fe3++H2O2, and NSB+Fe3++H2O2 under light irradiation, and NSB+Fe3++H2O2 in the dark. Reaction conditions: NSB or WB = 1.0 g L–1, Fe3+ = 1.0 mg L–1, H2O2 = 2.0 mmol L–1, and pH0 = 3.5

Time-dependent ultraviolet (UV) spectra of SD solution in the NSB+Fe³⁺+H₂O₂ system under light irradiation (Figure S2) confirmed the oxidation of SD, as evidenced by the gradual attenuation and eventual disappearance of the aromatic ring-characteristic absorption peak at 265 nm. The degradation of SD by NSB+Fe³⁺+H₂O₂ in the dark (Figure 4b) proved that the Fenton-like reaction (Fe³⁺+H₂O₂) proceeded sustainably with NSB assistance. Under light irradiation, SD degradation was significantly accelerated, with a k_obs value 2.67 times higher than that in the dark (Table S1), highlighting the advantage of NSB-catalyzed photo-Fenton reaction. Furthermore, NSB outperformed WB in co-catalyzing the photo-Fenton reaction, consistent with observations from the Fenton-like reactions in the dark [29,31]. N, S-doping disrupts the chemical inertness of the carbon matrix, inducing high spin and localized charge distribution at adjacent C atoms. Additionally, N, S-doping introduces more defective structure into the biochar and enhances its electron-donating capability and electron transfer efficiency [21,24,38]. Thus, NSB is more efficient than the undoped biochar in activating H₂O₂ and persulfates, as well as in accelerating Fe²⁺/Fe³⁺ cycling in Fenton-like reaction [26,27,31,39]. Furthermore, Fe²⁺ regeneration via photo-reduction of Fe³⁺ (Reaction 3) and ^•OH generation by direct photodecomposition of H₂O₂ (Reaction 4) collectively contributed to the enhanced pollutant degradation under light irradiation.

Figure S2

Download

3.3. Influence of reaction conditions

Figure 5(a) shows that SD was removed more or less by NSB+Fe³⁺+H₂O₂ under light irradiation in the pH₀ range of 2.0–4.5. Specifically, nearly complete SD degradation was achieved at pH₀ of 3.0–4.0, with the fastest degradation observed at pH₀ = 3.5. In contrast, little SD removal occurred at pH₀ = 5.65 (the original pH of the SD solution), which is attributed to the termination of the photo-Fenton reaction by precipitation of Fe³⁺ as hydroxides [40]. Figure 5(b) demonstrates that increasing the NSB dosage (in the range of 0.3–1.0 g L^–1) accelerated the photo-Fenton reaction, as indicated by the corresponding increase in k_obs values. This improvement is attributed to the greater number of active sites provided by more NSB, which facilitates heterogeneous reactions, including the regeneration of Fe²⁺ and activation of H₂O₂. However, further increasing the NSB dosage to 1.2 g L^–1 decelerated SD degradation. This may be attributed to the excessive presence of biochar particles, which could adversely affect light transmission through the suspension.

Removal of Sulfadiazine by N,S-codoped biochar+Fe3++H2O2 under light irradiation at: (a) different pH0, (b) different N,S-codoped biochar dosage, (c) different Fe3+ concentration, and (d) different H2O2 concentration.

Figure 5(c) shows that even at a low Fe³⁺ concentration of 0.3 mg L^–1, nearly complete SD degradation was still achieved after 90 min of reaction. This Fe³⁺ level is equal to the iron concentration limit for drinking water established by the World Health Organization (WHO) [41]. The iron concentration of ∼0.3 mg L^–1 has also been reported in some natural waters [42], thus, this co-catalytic photo-Fenton process would be applicable for in-situ remediation of natural water contaminated by micropollutants. Furthermore, Figure 5(d) indicates that the change of H₂O₂ concentration in the range of 1.0–3.0 mmol L^–1 did not bring about a significant change in the SD degradation rate by NSB+Fe³⁺+H₂O₂. Therefore, these results demonstrate that the NSB co-catalytic photo-Fenton reaction can operate efficiently at minimal concentrations of Fe³⁺ and H₂O₂, offering advantages in terms of both operational cost and environmental friendliness [43].

Figure 6(a) indicates that NSB+Fe³⁺+H₂O₂ is applicable for the removal of other organic pollutants, including antibiotics sulfamethazine (SMZ) and ciprofloxacin (CIP), and a chlorinated pollutant 2,4-dichlorophenol (2,4-DCP), but the degradation rate was influenced by the pollutant’s properties. For instance, 2,4-DCP (Figure 6(b)), a compound with a small molecular weight, was degraded rapidly and almost completely within 60 min. In contrast, CIP, which has a larger molecular weight and a stable structure, achieved a lower removal efficiency of 80% after 90 min. As shown in Figure 6(c), the co-catalytic photo-Fenton process maintained high efficiency for SD removal in various real water matrices such as tap water and river water, indicating its strong resistance to the changes of water quality and pollutant species. Furthermore, NSB exhibited excellent reusability and stable co-catalytic activity over five consecutive cycles, with SD being almost completely removed in each run using the recycled NSB (Figure 6(d)).

(a) Removal of sulfamethazine, ciprofloxacin and 2,4-dichlorophenol by N,S-codoped biochar+Fe3++H2O2. (b) Molecular structures of organic pollutants. (c) Removal of sulfadiazine by N,S-codoped biochar+Fe3++H2O2 in river water, tap water, and pure water. (d) Removal of sulfadiazine by N,S-codoped biochar+Fe3++H2O2 using the recycled NSB. Reaction conditions: C0= 20 mg L–1, NSB = 1.0 g L–1, Fe3+ = 1.0 mg L–1, H2O2 = 2.0 mmol L–1, and pH0 = 3.5.

3.4 Investigation on the co-catalytic mechanism

The dominant ROS responsible for pollutant degradation in the co-catalytic photo-Fenton process was identified through radical scavenging experiments and EPR analysis. Figure 7(a) shows that the addition of tert-butyl alcohol (TBA) (20 mmol L^-1), a well-known scavenger of ^•OH, drastically suppressed SD degradation, resulting in only 8.8% removal after 90 min (k_obs = 0.0024 min^–1). This k_obs value represents only 2.2% of that observed in the absence of TBA (Figure S3). Inhibition of superoxide anion radical (O₂^•−) by p-benzoquinone (BQ) (20 mmol L^-1) decelerated the degradation (k_obs = 0.0236 min^–1), resulting in 66.9% removal after 90 min, which demonstrates a secondary role of O₂^•− in SD oxidation. EPR analysis with DMPO trapping (Figure 7b) confirms the formation of DMPO–^•OH, as evidenced by the characteristic quartet (1:2:2:1) peaks. In contrast, the signal of DMPO–O₂^•− is negligible. Therefore, ^•OH should be the dominant ROS for degradation of pollutants by NSB+Fe³⁺+H₂O₂ under light irradiation, while O₂^•− acts as an intermediate in the photo-Fenton reaction. Furthermore, using AgNO₃ (20 mmol L^-1) as the scavenger of photo-generated electrons made the degradation slower (k_obs= 0.0301 min^–1), although the removal efficiency remained relatively high (89.8% after 90 min). This result confirms that the photo-generated electrons contribute to the regeneration of Fe²⁺ in the NSB+Fe³⁺+H₂O₂ system [44].

Figure S3

Download

(a) Removal of SD by NSB+Fe3++H2O2 with various scavengers, (b) EPR spectra of •OH and O2•− trapped by 5,5-dimethyl-1- pyrroline-N-oxide . (c) Cumulative amount of •OH produced and (d) Fe2+ concentration in different reaction systems under light irradiation.

The cumulative amount of ^•OH produced in different reaction systems under light irradiation follows the order: NSB+Fe³⁺+H₂O₂ > Fe³⁺+H₂O₂ >> NSB+H₂O₂ (Figure 7c), which is consistent with their rankings in pollutant removal efficiency. Specifically, the amount of ^•OH produced in the NSB+Fe³⁺+H₂O₂ system accumulated to 0.27 mmol L^–1 after 90 min, which is 1.5 times greater than that in the Fe³⁺+H₂O₂ system. Correspondingly, H₂O₂ consumption in the NSB+Fe³⁺+H₂O₂ system is apparently higher than that in the NSB+H₂O₂ system, and is comparable to that in the Fe³⁺+H₂O₂ system (Figure S4). These results demonstrate that NSB as the co-catalyst can enhance the activation efficiency of H₂O₂ to produce more ROS. The enhanced production of ^•OH should be related to the more Fe²⁺ presented in the NSB+Fe³⁺+H₂O₂ system than that in the Fe³⁺+H₂O₂ system (Figure 7d). In the Fe³⁺+H₂O₂ system, the Fe²⁺ concentration varied between 0.2–0.9 mg L^–1 during the reaction, likely due to the photo-reduction of Fe³⁺. In particular, the Fe²⁺ concentration surged to 0.9 mg L^–1 at 30 min, which is synchronous with the speedup of SD degradation by Fe³⁺+H₂O₂ (Figure 4a). The reason should be related to the accumulation of carboxylic acids as the degradation intermediates of SD as the reaction proceeded. The carboxylic acids formed complexes with Fe³⁺ and accelerated its photo-reduction and accompanied production of ^•OH (Reaction 3). In contrast, a significantly higher Fe²⁺ concentration (0.4–0.95 mg L^–1) was measured in the NSB+Fe³⁺+H₂O₂ system, indicating the extra reduction of Fe³⁺ by NSB. This was further supported by the detection of ∼ 0.4 mg L^–1 Fe²⁺ in a mixture of NSB and Fe³⁺ (initially 1.0 mg L^–1) in the absence of H₂O₂. These results indicate that NSB, as an electron donor, improved the regeneration of Fe²⁺ and consequently enhanced the production of ^•OH as the dominant ROS under light irradiation.

Figure S4

Download

XPS analyses of the NSB recycled after reaction in the NSB+Fe³⁺+H₂O₂ system provide insights into the electron donation from NSB (Figure 8). An increased abundance of oxygen-containing functional groups (e.g., C=O) was observed in the C 1s spectrum of the recycled NSB, indicating the oxidation of the carbon matrix. Previous studies have shown that defective structure (e.g., edge sites) of carbon acts as electron donors for activation of H₂O₂ and reduction of Fe³⁺ [21,29,38], and our XPS data suggest that the oxidized surface sites on NSB contribute similarly. Specifically, the N 1s spectrum of the recycled NSB reveals a decreased proportion of pyridinic N species (25.5% vs. 31.7% in pristine NSB) after the photo-Fenton reaction, while the S 2p spectrum shows a decreased proportion of C–S–C (25.5% vs. 46.1% in pristine NSB) (Table S2). These results indicated that pyridinic N and C–S–C in NSB serve as additional electron donors that made NSB more reactive toward the reduction of Fe³⁺, thus explaining its superior co-catalytic performance compared to WB. In addition, –COOH in NSB could form complexes with Fe³⁺ and facilitate its reduction (Reactions 5 and 6) [45-47].

Table S2

Download

(5)

NSB - {COOH + Fe}^{3+} \to NSB - {COO}^{-} {Fe}^{3+} {+ H}^{+}

(6)

\begin{matrix} NSB - {COO}^{-} {Fe}^{3+} {+ H}_{2} O + h ν \\ \to NSB - {COO}^{-} {+ Fe}^{2+} {+ H}^{+} +^{\cdot} OH \end{matrix}

High resolution XPS spectra of the NSB recycled after reaction in NSB+Fe3++H2O2: (a) C 1s, (b) O 1s, (c) N 1s, and (d) S 2p.

Based on the above results and discussion, a mechanism for NSB as a multifunctional co-catalyst in the photo-Fenton reaction is proposed (Figure 9). Two key pathways operate synergistically: (1) Defective carbon structures (e.g., edge sites), pyridinic N, and thiophenic S sites directly donate electrons to reduce Fe³⁺ into Fe²⁺ (Reaction 7) [29,48]. (2) NSB activates both O₂ and H₂O₂ (Reactions 8 and 9), generating O₂^•− and ^•OH, respectively. The produced O₂^•− subsequently reduces Fe³⁺ (Reaction 10) or reacts with HO₂^• to amplify ROS (Reactions 11 and 12).

(7)

NSB \to e^{-} {+ NSB}^{+} e^{-} {+ Fe}^{3+} \to {Fe}^{2 +}

(8)

NSB \to e^{-} {+ NSB}^{+} e^{-} {+ O}_{2} \to O_{2} {^{•}}^{-}

(9)

{NSB + H}_{2} O_{2} \to {NSB}^{+} {+ OH}^{-} +^{•} OH

(10)

{Fe}^{3+} {+ O}_{2} {^{•}}^{-} \to {Fe}^{2 +} {+ O}_{2}

(11)

{NSB}^{+} {+ H}_{2} O_{2} \to {NSB + HO}_{2}^{•} {+ H}^{+}

(12)

{HO}_{2}^{•} {+ H}^{+} + O_{2} {^{•}}^{-} \to H_{2} O_{2} {+ O}_{2}

The schematic diagram for the co-catalytic mechanism of NSB and the generation of ROS in NSB+Fe3++H2O2 under light irradiation.

4. Conclusions

A novel photo-Fenton process co-catalyzed by NSB was evaluated for its efficacy in removing organic micropollutants from water. The active moieties, including defective structure, pyridinic N, and thiophenic S in NSB, endowed it with the capability of accelerating the iron redox cycling in photo-Fenton reaction, resulting in more Fe²⁺ and ^•OH produced in the NSB+Fe³⁺+H₂O₂ system. Consequently, the much faster degradation of SD was observed in the NSB+Fe³⁺+H₂O₂ system under light irradiation, with a k_obs enhanced by 10 times compared to that in the photo-Fenton process without NSB. NSB also showed good reusability in repetitive experiments. The low dosage requirement for Fe³⁺ and H₂O₂ made this co-catalytic process more cost-efficient and environmentally friendly. Therefore, this study proposes a novel strategy for enhancing the efficiency of photo-Fenton reaction for the removal of organic micropollutants, and highlights the significant potential of biochar in catalytic AOPs.

CRediT authorship contribution statement

Junhuan Zhang: Data curation, Investigation, Methodology, Writing-original draft. Ying Lv: Methodology, Visualization, Writing-review & editing. Jinxuan Li: Investigation. Jinhong Lü: Validation. Jianfa Li: Conceptualization, Investigation, Funding acquisition, Writing-review & editing

Declaration of competing interest

There are no conflicts of interest.

Declaration of generative AI and AI-assisted technologies in the writing process

The authors confirm that there was no use of artificial intelligence (AI)-assisted technology for assisting in the writing or editing of the manuscript and no images were manipulated using AI.

Acknowledgment

This work was supported by the National Natural Science Foundation of China (No. 21777103).

Supplementary data

Supplementary material to this article can be found online at https://dx.doi.org/10.25259/AJC_350_2025

References

Wu Q., Lu D., Kondamareddy K.K., Ho W., Cao D., Zeng Y., Zhang B., Zhang Y., Xie L., Zhao B, Wang Z., Hao H., Fan H., Wang H.. Highly efficient photocatalytic degradation for antibiotics and mechanism insight for Bi₂S₃/g-C₃N₄ with fast interfacial charges transfer and excellent stability. Arabian Journal of Chemistry. 2022;15:103689. https://doi.org/10.1016/j.arabjc.2022.103689
[Google Scholar]
Pignatello J.J., Oliveros E., MacKaym A.. Advanced oxidation processes for organic contaminant destruction based on the Fenton reaction and related chemistry. Critical Reviews in Environmental Science and Technology. 2006;36:1-84. https://doi.org/10.1080/10643380500326564
[Google Scholar]
Roy K., Moholkar V.S.. Sulfadiazine degradation using hybrid AOP of heterogeneous Fenton/persulfate system coupled with hydrodynamic cavitation. Chemical Engineering Journal. 2020;386:121294. https://doi.org/10.1016/j.cej.2019.03.170
[Google Scholar]
Li H., Luo D., Guo P., Gao S., Lin M., Sun H., Wang J., Yu D., Cheng S., Li J.. Pd octahedra nanocubes mediated photo-Fenton catalytic performance for sustainable degradation of methylene blue. Arabian Journal of Chemistry. 2024;17:105936. https://doi.org/10.1016/j.arabjc.2024.105936
[Google Scholar]
Miklos D.B., Remy C., Jekel M., Linden K.G., Drewes J.E., Hübner U.. Evaluation of advanced oxidation processes for water and wastewater treatment – A critical review. Water Research. 2018;139:118-131. https://doi.org/10.1016/j.watres.2018.03.042
[Google Scholar]
Li X., Luo W., Zhu K., Chen Y., Huang Y., Jin C, Qiu R., Luo S., Guan G., Yan K.. Electronic modulation of S and N co-implanted carbon as fenton-like photocatalysts for water remediation. Chemical Engineering Journal. 2023;474:146016. https://doi.org/10.1016/j.cej.2023.146016
[Google Scholar]
Lyu H., Wang X., Li P., Yan P., Tang J.. Mn/Co bimetallic catalyst immobilized on N-doped biochar for enhanced photocatalytic degradation of sulfanilamide in water. Applied Catalysis B: Environment and Energy. 2024;354:124123. https://doi.org/10.1016/j.apcatb.2024.124123
[Google Scholar]
Xing M., Xu W., Dong C., Bai Y., Zeng J., Zhou Y., Zhang J., Yin Y.. Metal sulfides as excellent co-catalysts for H₂O₂ decomposition in advanced oxidation processes. Chem. 2018;4:1359-1372. https://doi.org/10.1016/j.chempr.2018.03.002
[Google Scholar]
Zhou C., Zhou P., Sun M., Liu Y., Zhang H., Xiong Z., Liang J., Duan X., Lai B.. Nitrogen-doped carbon nanotubes enhanced Fenton chemistry: Role of near-free iron(III) for sustainable iron(III)/iron(II) cycles. Water Research. 2022;210:117984. https://doi.org/10.1016/j.watres.2021.117984
[Google Scholar]
Behrouzeh M., Parivazh M.M., Danesh E., Dianat M.J., Abbasi M., Osfouri S., Rostami A., Sillanpää M., Dibaj M., Akrami M.. Application of photo-fenton, electro-fenton, and photo-electro-fenton processes for the treatment of DMSO and DMAC wastewaters. Arabian Journal of Chemistry. 2022;15:104229. https://doi.org/10.1016/j.arabjc.2022.104229
[Google Scholar]
Wang R., Liu Z., Li L., Zhang Y., Dong Q., Huang Z., Cheng Q.. Impact of pretreatment with photocatalysis sequential coupling Fenton oxidation on physicochemical properties, pyrolysis behaviors, and product distribution of walnut shell. Chemical Engineering Journal. 2024;481:148425. https://doi.org/10.1016/j.cej.2023.148425
[Google Scholar]
Wang J., Cai J., Zhou X., Wang S., Luo F., Yang L., Yu J., Chi R., Chen Z.. Accelerating of Fe²⁺ regeneration in Fenton reaction by biochar: Pivotal roles of carbon defects as electron donor and shuttle. Separation and Purification Technology. 2025;354:128945. https://doi.org/10.1016/j.seppur.2024.128945
[Google Scholar]
Tokumura M., Morito R., Hatayama R., Kawase Y.. Iron redox cycling in hydroxyl radical generation during the photo-Fenton oxidative degradation: Dynamic change of hydroxyl radical concentration. Applied Catalysis B: Environmental. 2011;106:565-576. https://doi.org/10.1016/j.apcatb.2011.06.017
[Google Scholar]
Baba Y., Yatagai T., Harada T., Kawase Y.. Hydroxyl radical generation in the photo-Fenton process: Effects of carboxylic acids on iron redox cycling. Chemical Engineering Journal. 2015;277:229-241. https://doi.org/10.1016/j.cej.2015.04.103
[Google Scholar]
Cheng F., Zhou P., Liu Y., Huo X., Zhang J., Yuan Y., Zhang H., Lai B., Zhang Y.. Graphene oxide mediated Fe(III) reduction for enhancing Fe(III)/H₂O₂ Fenton and photo-Fenton oxidation toward chloramphenicol degradation. Science of the Total Environment. 2021;797:149097. https://doi.org/10.1016/j.scitotenv.2021.149097
[Google Scholar]
Wang X., Zhang X., Zhang Y., Wang Y., Sun S.-P., Wu W.D., Wu Z.. Nanostructured semiconductor supported iron catalysts for heterogeneous photo-Fenton oxidation: a review. Journal of Materials Chemistry A. 2020;8:15513-15546. https://doi.org/10.1039/D0TA04541A
[Google Scholar]
Wang L., Yang H., Yang Y., He Z.. A novel scheme to improve the photo-Fenton performance of iron oxychloride by carbon: Three existent states and roles of carbon in the degradation of tetracycline in water. Journal of Colloid and Interface Science. 2023;641:916-928. https://doi.org/10.1016/j.jcis.2023.03.113
[Google Scholar]
Wu C., Guo T., Chen Y., Tian Q., Zhang Y., Huang Z, Hu H., Gan T.. Facile synthesis of excellent Fe₃O₄@starch-derived carbon Photo-Fenton catalyst for tetracycline degradation: Rapid Fe³⁺/Fe²⁺ circulation under visible light condition. Separation and Purification Technology. 2024;329:125174. https://doi.org/10.1016/j.seppur.2023.125174
[Google Scholar]
Javanmard A., Bin Wan Daud W.M.A., Patah M.F.A., Zuki F.M., Verdugo A.S.. Harnessing the potential of biochar-based catalysts for sustainable adsorptive and photocatalytic applications: A comprehensive review. Process Safety and Environmental Protection. 2024;189:387-413. https://doi.org/10.1016/j.psep.2024.05.118
[Google Scholar]
Fang G., Gao J., Liu C., Dionysiou D.D., Wang Y., Zhou D.. Key role of persistent free radicals in hydrogen peroxide activation by biochar: Implications to organic contaminant degradation. Environmental Science & Technology. 2014;48:1902-1910. https://doi.org/10.1021/es4048126
[Google Scholar]
Miao X., Chen X., Wu W., Lin D., Yang K.. Intrinsic defects enhanced biochar/peroxydisulfate oxidation capacity through electron-transfer regime. Chemical Engineering Journal. 2022;438:135606. https://doi.org/10.1016/j.cej.2022.135606
[Google Scholar]
Zhu X., Li J., Xie B., Feng D., Li Y.. Accelerating effects of biochar for pyrite-catalyzed Fenton-like oxidation of herbicide 2,4-D. Chemical Engineering Journal. 2020;391:123605. https://doi.org/10.1016/j.cej.2019.123605
[Google Scholar]
Feng D., Lü J., Guo S., Li J.. Biochar enhanced the degradation of organic pollutants through a Fenton process using trace aqueous iron. Journal of Environmental Chemical Engineering. 2021;9:104677. https://doi.org/10.1016/j.jece.2020.104677
[Google Scholar]
Qu S., Yuan Y., Yang X., Xu H., Mohamed A.K., Zhang J., Zhao C., Liu L., Wang B., Wang X., Rinklebe J., Li Y.C., Wang S.. Carbon defects in biochar facilitated nitrogen doping: The significant role of pyridinic nitrogen in peroxymonosulfate activation and ciprofloxacin degradation. Chemical Engineering Journal. 2022;441:135864. https://doi.org/10.1016/j.cej.2022.135864
[Google Scholar]
Choong Z.-Y., Gasim M.F., Lin K.-Y.A., Hamidon T.S, Hussin H., Oh W.-D.. Unravelling the formation mechanism and performance of nitrogen, sulfur codoped biochar as peroxymonosulfate activator for gatifloxacin removal. Chemical Engineering Journal. 2023;451:138958. https://doi.org/10.1016/j.cej.2022.138958
[Google Scholar]
Oh W.-D., Zaeni J.R.J., Lisak G., Lin K.-Y.A., Leong K.-H., Choong Z.-Y.. Accelerated organics degradation by peroxymonosulfate activated with biochar co-doped with nitrogen and sulfur. Chemosphere. 2021;277:130313. https://doi.org/10.1016/j.chemosphere.2021.130313
[Google Scholar]
Xu Y., Liu S., Wang M., Zhang J., Ding H., Song Y., Zhu Y., Pan Q., Zhao C., Deng H.. Thiourea-assisted one-step fabrication of a novel nitrogen and sulfur co-doped biochar from nanocellulose as metal-free catalyst for efficient activation of peroxymonosulfate. Journal of Hazardous Materials. 2021;416:125796. https://doi.org/10.1016/j.jhazmat.2021.125796
[Google Scholar]
Huang J., Wang M., Luo S., Li Z., Ge Y.. In situ preparation of highly graphitized N-doped biochar geopolymer composites for efficient catalytic degradation of tetracycline in water by H₂O₂. Environmental Research. 2023;219:115166. https://doi.org/10.1016/j.envres.2022.115166
[Google Scholar]
Lai M., Li J., Li H., Gui Y., Lü J.. N,S-codoped biochar outperformed N-doped biochar on co-activation of H₂O₂ with trace dissolved Fe(Ⅲ) for enhanced oxidation of organic pollutants. Environmental Pollution. 2023;334:122208. https://doi.org/10.1016/j.envpol.2023.122208
[Google Scholar]
Feng D., Shou J., Guo S., Ya M., Li J., Dong H., Li Y.. Co-catalysis of trace dissolved Fe(III) with biochar in hydrogen peroxide activation for enhanced oxidation of pollutants. RSC Advances. 2022;12:17237-17248. https://doi.org/10.1039/d2ra01647h
[Google Scholar]
Zhong S., Pan J., Tian K., Qin J., Qing T., Zhang J.. Efficient degradation of p-chlorophenol by N,S-codoped biochar activated perxymonosulfate. Process Safety and Environmental Protection. 2023;169:437-446. https://doi.org/10.1016/j.psep.2022.10.081
[Google Scholar]
Zhang Y., Xu M., He R., Zhao J., Kang W., Lv J.. Effect of pyrolysis temperature on the activated permonosulfate degradation of antibiotics in nitrogen and sulfur-doping biochar: Key role of environmentally persistent free radicals. Chemosphere. 2022;294:133737. https://doi.org/10.1016/j.chemosphere.2022.133737
[Google Scholar]
Atchudan R., Perumal S., Edison T.N.J.I., Albasher G., Sundramoorthy A.K., Vinodh R, Lee Y.R.. Lotus-biowaste derived sulfur/nitrogen-codoped porous carbon as an eco-friendly electrocatalyst for clean energy harvesting. Environmental Research. 2022;214:113910. https://doi.org/10.1016/j.envres.2022.113910
[Google Scholar]
Hung C.-M., Chen C.-W., Huang C.-P., Dong C.-D.. N-doped metal-free biochar activation of peroxymonosulfate for enhancing the degradation of antibiotics sulfadiazine from aquaculture water and its associated bacterial community composition. Journal of Environmental Chemical Engineering. 2022;10:107172. https://doi.org/10.1016/j.jece.2022.107172
[Google Scholar]
Cheng Y., Wang B., Yan P., Shen J., Kang J., Zhao S., Zhu X., Shen L., Wang S., Shen Y., Chen Z.. In-situ formation of surface reactive oxygen species on defective sites over N-doped biochar in catalytic ozonation. Chemical Engineering Journal. 2023;454:140232. https://doi.org/10.1016/j.cej.2022.140232
[Google Scholar]
Wang X., Wu H., Jing J., Song G., Zhang X., Zhou M., Dewel R.. Synergistically S/N self-doped biochar as a green bifunctional cathode catalyst in electrochemical degradation of organic pollutant. Green Energy & Environment. 2025;10:214-230. https://doi.org/10.1016/j.gee.2024.03.001
[Google Scholar]
Li H., Gui Y., Li J., Zhang J., Lü J.. Development of lignin-derived hierarchically porous carbon by one-step pyrolysis in an air/N₂ flow for efficient adsorption of organic pollutants. Joural of Analytical and Applied Pyrolysis. 2024;177:106344. https://doi.org/10.1016/j.jaap.2023.106344
[Google Scholar]
Wang J., Cai J., Zhou X., Wang S., Luo F., Yang L., Yu J., Chi R., Chen Z.. Accelerating of Fe²⁺ regeneration in Fenton reaction by biochar: Pivotal roles of carbon defects as electron donor and shuttle. Separation and Purification Technology. 2025;354:128945. https://doi.org/10.1016/j.seppur.2024.128945
[Google Scholar]
Gasim M.F., Veksha A., Lisak G., Low S.-C., Hamidon T.S., Hussin M.H., Oh W.-D.. Importance of carbon structure for nitrogen and sulfur co-doping to promote superior ciprofloxacin removal via peroxymonosulfate activation. Journal of Colloid and Interface Science. 2023;634:586-600. https://doi.org/10.1016/j.jcis.2022.12.072
[Google Scholar]
Gao J., Liu Y., Xia X., Wang L., Shao L., Cai T., Dong W.. Mechanisms for photo assisted Fenton of synthesized pyrrhotite at neutral pH. Applied Surface Science. 2019;463:863-871. https://doi.org/10.1016/j.apsusc.2018.09.007
[Google Scholar]
World Health Organization. Guidelines for Drinking-water Quality (fourth ed.). 2011. https://portals.iucn.org/library/node/28887
Serra-Clusellas A., De Angelis L., Lin C.-H., Vo P., Bayati M., Sumner L., Lei Z., Amaral N.B., Bertini L.M., Mazza J., Pizzio L.R., Stripeikis J.D., Rengifo-Herrera J.A., de Cortalezzi M.M.F.. Abatement of 2,4-D by H₂O₂ solar photolysis and solar photo-Fenton-like process with minute Fe(III) concentrations. Water Research. 2018;144:572-580. https://doi.org/10.1016/j.watres.2018.07.072
[Google Scholar]
Xu H., Ye Q., Wang Q., Zhou P., Huo X., Wang Y., Huang X., Zhou G., Zhang J.. Enhancement of organic contaminants degradation at low dosages of Fe(III) and H₂O₂ in g-C₃N₄ promoted Fe(III)/H₂O₂ system under visible light irradiation. Separation and Purification Technology. 2020;251:117333. https://doi.org/10.1016/j.seppur.2020.117333
[Google Scholar]
Cui Y., He Y., Jin Y., Yang Z., Shan C., Zhang Q., Zhang W., Pan B.. Autocatalytic oxidation of thiophene derivatives and co-degradation of refractory contaminants in Fenton reaction. Chemical Engineering Journal. 2024;496:153954. https://doi.org/10.1016/j.cej.2024.153954
[Google Scholar]
Nichela D.A., Donadelli J.A., Caram B.F., Haddou M., Nieto F.J.R., Oliveros E., Einschlag F.S.G.. Iron cycling during the autocatalytic decomposition of benzoic acid derivatives by Fenton-like and photo-Fenton techniques. Applied Catalysis B: Environmental. 2015;170-171:312-321. https://doi.org/10.1016/j.apcatb.2015.01.028
[Google Scholar]
Cui K.-P., Yang T.-T., Chen Y.-H., Weerasooriya R., Li G.-H., Zhou K., Chen X.. Magnetic recyclable heterogeneous catalyst Fe₃O₄/g-C₃N₄ for tetracycline hydrochloride degradation via photo-Fenton process under visible light. Environmental Technology. 2021;43:3341-3354. https://doi.org/10.1080/09593330.2021.1921052
[Google Scholar]
Yang S., Tian D., Wang X., Zhou P., Xiong Z., Zhang H., Liu Y., Yao G., Lai B.. The enhanced mechanism of Fe(III)/H₂O₂ system by N, S-doped mesoporous nanocarbon for the degradation of sulfamethoxazole. Separation and Purification Technology. 2023;308:122900. https://doi.org/10.1016/j.seppur.2022.122900
[Google Scholar]
Fang G., Liu C., Wang Y., Dionysiou D.D., Zhou D.. Photogeneration of reactive oxygen species from biochar suspension for diethyl phthalate degradation. Applied Catalysis B: Environmental. 2017;214:34-45. https://doi.org/10.1016/j.apcatb.2017.05.036
[Google Scholar]

1. Introduction

2. Materials and Methods

2.1. N, S-codoped biochar preparation and characterizations
2.2. Photo-Fenton degradation of organic pollutants
2.3. Analytical methods

3. Results and Discussion

3.1. Characteristics of N, S-codoped biochar (NSB)
3.2. Co-catalytic effect of NSB toward photo-Fenton reaction
3.3. Influence of reaction conditions
3.4 Investigation on the co-catalytic mechanism

4. Conclusions

Fulltext Views
421

PDF downloads
552

View/Download PDF
Download Citations

BibTeX
RIS

Show Sections

[1] Wu Q., Lu D., Kondamareddy K.K., Ho W., Cao D., Zeng Y., Zhang B., Zhang Y., Xie L., Zhao B, Wang Z., Hao H., Fan H., Wang H.. Highly efficient photocatalytic degradation for antibiotics and mechanism insight for Bi₂S₃/g-C₃N₄ with fast interfacial charges transfer and excellent stability. Arabian Journal of Chemistry. 2022;15:103689. https://doi.org/10.1016/j.arabjc.2022.103689
[Google Scholar]

[2] Pignatello J.J., Oliveros E., MacKaym A.. Advanced oxidation processes for organic contaminant destruction based on the Fenton reaction and related chemistry. Critical Reviews in Environmental Science and Technology. 2006;36:1-84. https://doi.org/10.1080/10643380500326564
[Google Scholar]

[3] Roy K., Moholkar V.S.. Sulfadiazine degradation using hybrid AOP of heterogeneous Fenton/persulfate system coupled with hydrodynamic cavitation. Chemical Engineering Journal. 2020;386:121294. https://doi.org/10.1016/j.cej.2019.03.170
[Google Scholar]

[4] Li H., Luo D., Guo P., Gao S., Lin M., Sun H., Wang J., Yu D., Cheng S., Li J.. Pd octahedra nanocubes mediated photo-Fenton catalytic performance for sustainable degradation of methylene blue. Arabian Journal of Chemistry. 2024;17:105936. https://doi.org/10.1016/j.arabjc.2024.105936
[Google Scholar]

[5] Miklos D.B., Remy C., Jekel M., Linden K.G., Drewes J.E., Hübner U.. Evaluation of advanced oxidation processes for water and wastewater treatment – A critical review. Water Research. 2018;139:118-131. https://doi.org/10.1016/j.watres.2018.03.042
[Google Scholar]

[6] Li X., Luo W., Zhu K., Chen Y., Huang Y., Jin C, Qiu R., Luo S., Guan G., Yan K.. Electronic modulation of S and N co-implanted carbon as fenton-like photocatalysts for water remediation. Chemical Engineering Journal. 2023;474:146016. https://doi.org/10.1016/j.cej.2023.146016
[Google Scholar]

[7] Lyu H., Wang X., Li P., Yan P., Tang J.. Mn/Co bimetallic catalyst immobilized on N-doped biochar for enhanced photocatalytic degradation of sulfanilamide in water. Applied Catalysis B: Environment and Energy. 2024;354:124123. https://doi.org/10.1016/j.apcatb.2024.124123
[Google Scholar]

[8] Xing M., Xu W., Dong C., Bai Y., Zeng J., Zhou Y., Zhang J., Yin Y.. Metal sulfides as excellent co-catalysts for H₂O₂ decomposition in advanced oxidation processes. Chem. 2018;4:1359-1372. https://doi.org/10.1016/j.chempr.2018.03.002
[Google Scholar]

[9] Zhou C., Zhou P., Sun M., Liu Y., Zhang H., Xiong Z., Liang J., Duan X., Lai B.. Nitrogen-doped carbon nanotubes enhanced Fenton chemistry: Role of near-free iron(III) for sustainable iron(III)/iron(II) cycles. Water Research. 2022;210:117984. https://doi.org/10.1016/j.watres.2021.117984
[Google Scholar]

[10] Behrouzeh M., Parivazh M.M., Danesh E., Dianat M.J., Abbasi M., Osfouri S., Rostami A., Sillanpää M., Dibaj M., Akrami M.. Application of photo-fenton, electro-fenton, and photo-electro-fenton processes for the treatment of DMSO and DMAC wastewaters. Arabian Journal of Chemistry. 2022;15:104229. https://doi.org/10.1016/j.arabjc.2022.104229
[Google Scholar]

[11] Wang R., Liu Z., Li L., Zhang Y., Dong Q., Huang Z., Cheng Q.. Impact of pretreatment with photocatalysis sequential coupling Fenton oxidation on physicochemical properties, pyrolysis behaviors, and product distribution of walnut shell. Chemical Engineering Journal. 2024;481:148425. https://doi.org/10.1016/j.cej.2023.148425
[Google Scholar]

[12] Wang J., Cai J., Zhou X., Wang S., Luo F., Yang L., Yu J., Chi R., Chen Z.. Accelerating of Fe²⁺ regeneration in Fenton reaction by biochar: Pivotal roles of carbon defects as electron donor and shuttle. Separation and Purification Technology. 2025;354:128945. https://doi.org/10.1016/j.seppur.2024.128945
[Google Scholar]

[13] Tokumura M., Morito R., Hatayama R., Kawase Y.. Iron redox cycling in hydroxyl radical generation during the photo-Fenton oxidative degradation: Dynamic change of hydroxyl radical concentration. Applied Catalysis B: Environmental. 2011;106:565-576. https://doi.org/10.1016/j.apcatb.2011.06.017
[Google Scholar]

[14] Baba Y., Yatagai T., Harada T., Kawase Y.. Hydroxyl radical generation in the photo-Fenton process: Effects of carboxylic acids on iron redox cycling. Chemical Engineering Journal. 2015;277:229-241. https://doi.org/10.1016/j.cej.2015.04.103
[Google Scholar]

[15] Cheng F., Zhou P., Liu Y., Huo X., Zhang J., Yuan Y., Zhang H., Lai B., Zhang Y.. Graphene oxide mediated Fe(III) reduction for enhancing Fe(III)/H₂O₂ Fenton and photo-Fenton oxidation toward chloramphenicol degradation. Science of the Total Environment. 2021;797:149097. https://doi.org/10.1016/j.scitotenv.2021.149097
[Google Scholar]

[16] Wang X., Zhang X., Zhang Y., Wang Y., Sun S.-P., Wu W.D., Wu Z.. Nanostructured semiconductor supported iron catalysts for heterogeneous photo-Fenton oxidation: a review. Journal of Materials Chemistry A. 2020;8:15513-15546. https://doi.org/10.1039/D0TA04541A
[Google Scholar]

[17] Wang L., Yang H., Yang Y., He Z.. A novel scheme to improve the photo-Fenton performance of iron oxychloride by carbon: Three existent states and roles of carbon in the degradation of tetracycline in water. Journal of Colloid and Interface Science. 2023;641:916-928. https://doi.org/10.1016/j.jcis.2023.03.113
[Google Scholar]

[18] Wu C., Guo T., Chen Y., Tian Q., Zhang Y., Huang Z, Hu H., Gan T.. Facile synthesis of excellent Fe₃O₄@starch-derived carbon Photo-Fenton catalyst for tetracycline degradation: Rapid Fe³⁺/Fe²⁺ circulation under visible light condition. Separation and Purification Technology. 2024;329:125174. https://doi.org/10.1016/j.seppur.2023.125174
[Google Scholar]

[19] Javanmard A., Bin Wan Daud W.M.A., Patah M.F.A., Zuki F.M., Verdugo A.S.. Harnessing the potential of biochar-based catalysts for sustainable adsorptive and photocatalytic applications: A comprehensive review. Process Safety and Environmental Protection. 2024;189:387-413. https://doi.org/10.1016/j.psep.2024.05.118
[Google Scholar]

[20] Fang G., Gao J., Liu C., Dionysiou D.D., Wang Y., Zhou D.. Key role of persistent free radicals in hydrogen peroxide activation by biochar: Implications to organic contaminant degradation. Environmental Science & Technology. 2014;48:1902-1910. https://doi.org/10.1021/es4048126
[Google Scholar]

[21] Miao X., Chen X., Wu W., Lin D., Yang K.. Intrinsic defects enhanced biochar/peroxydisulfate oxidation capacity through electron-transfer regime. Chemical Engineering Journal. 2022;438:135606. https://doi.org/10.1016/j.cej.2022.135606
[Google Scholar]

[22] Zhu X., Li J., Xie B., Feng D., Li Y.. Accelerating effects of biochar for pyrite-catalyzed Fenton-like oxidation of herbicide 2,4-D. Chemical Engineering Journal. 2020;391:123605. https://doi.org/10.1016/j.cej.2019.123605
[Google Scholar]

[23] Feng D., Lü J., Guo S., Li J.. Biochar enhanced the degradation of organic pollutants through a Fenton process using trace aqueous iron. Journal of Environmental Chemical Engineering. 2021;9:104677. https://doi.org/10.1016/j.jece.2020.104677
[Google Scholar]

[24] Qu S., Yuan Y., Yang X., Xu H., Mohamed A.K., Zhang J., Zhao C., Liu L., Wang B., Wang X., Rinklebe J., Li Y.C., Wang S.. Carbon defects in biochar facilitated nitrogen doping: The significant role of pyridinic nitrogen in peroxymonosulfate activation and ciprofloxacin degradation. Chemical Engineering Journal. 2022;441:135864. https://doi.org/10.1016/j.cej.2022.135864
[Google Scholar]

[25] Choong Z.-Y., Gasim M.F., Lin K.-Y.A., Hamidon T.S, Hussin H., Oh W.-D.. Unravelling the formation mechanism and performance of nitrogen, sulfur codoped biochar as peroxymonosulfate activator for gatifloxacin removal. Chemical Engineering Journal. 2023;451:138958. https://doi.org/10.1016/j.cej.2022.138958
[Google Scholar]

[26] Oh W.-D., Zaeni J.R.J., Lisak G., Lin K.-Y.A., Leong K.-H., Choong Z.-Y.. Accelerated organics degradation by peroxymonosulfate activated with biochar co-doped with nitrogen and sulfur. Chemosphere. 2021;277:130313. https://doi.org/10.1016/j.chemosphere.2021.130313
[Google Scholar]

[27] Xu Y., Liu S., Wang M., Zhang J., Ding H., Song Y., Zhu Y., Pan Q., Zhao C., Deng H.. Thiourea-assisted one-step fabrication of a novel nitrogen and sulfur co-doped biochar from nanocellulose as metal-free catalyst for efficient activation of peroxymonosulfate. Journal of Hazardous Materials. 2021;416:125796. https://doi.org/10.1016/j.jhazmat.2021.125796
[Google Scholar]

[28] Huang J., Wang M., Luo S., Li Z., Ge Y.. In situ preparation of highly graphitized N-doped biochar geopolymer composites for efficient catalytic degradation of tetracycline in water by H₂O₂. Environmental Research. 2023;219:115166. https://doi.org/10.1016/j.envres.2022.115166
[Google Scholar]

[29] Lai M., Li J., Li H., Gui Y., Lü J.. N,S-codoped biochar outperformed N-doped biochar on co-activation of H₂O₂ with trace dissolved Fe(Ⅲ) for enhanced oxidation of organic pollutants. Environmental Pollution. 2023;334:122208. https://doi.org/10.1016/j.envpol.2023.122208
[Google Scholar]

[30] Feng D., Shou J., Guo S., Ya M., Li J., Dong H., Li Y.. Co-catalysis of trace dissolved Fe(III) with biochar in hydrogen peroxide activation for enhanced oxidation of pollutants. RSC Advances. 2022;12:17237-17248. https://doi.org/10.1039/d2ra01647h
[Google Scholar]

[31] Zhong S., Pan J., Tian K., Qin J., Qing T., Zhang J.. Efficient degradation of p-chlorophenol by N,S-codoped biochar activated perxymonosulfate. Process Safety and Environmental Protection. 2023;169:437-446. https://doi.org/10.1016/j.psep.2022.10.081
[Google Scholar]

[32] Zhang Y., Xu M., He R., Zhao J., Kang W., Lv J.. Effect of pyrolysis temperature on the activated permonosulfate degradation of antibiotics in nitrogen and sulfur-doping biochar: Key role of environmentally persistent free radicals. Chemosphere. 2022;294:133737. https://doi.org/10.1016/j.chemosphere.2022.133737
[Google Scholar]

[33] Atchudan R., Perumal S., Edison T.N.J.I., Albasher G., Sundramoorthy A.K., Vinodh R, Lee Y.R.. Lotus-biowaste derived sulfur/nitrogen-codoped porous carbon as an eco-friendly electrocatalyst for clean energy harvesting. Environmental Research. 2022;214:113910. https://doi.org/10.1016/j.envres.2022.113910
[Google Scholar]

[34] Hung C.-M., Chen C.-W., Huang C.-P., Dong C.-D.. N-doped metal-free biochar activation of peroxymonosulfate for enhancing the degradation of antibiotics sulfadiazine from aquaculture water and its associated bacterial community composition. Journal of Environmental Chemical Engineering. 2022;10:107172. https://doi.org/10.1016/j.jece.2022.107172
[Google Scholar]

[35] Cheng Y., Wang B., Yan P., Shen J., Kang J., Zhao S., Zhu X., Shen L., Wang S., Shen Y., Chen Z.. In-situ formation of surface reactive oxygen species on defective sites over N-doped biochar in catalytic ozonation. Chemical Engineering Journal. 2023;454:140232. https://doi.org/10.1016/j.cej.2022.140232
[Google Scholar]

[36] Wang X., Wu H., Jing J., Song G., Zhang X., Zhou M., Dewel R.. Synergistically S/N self-doped biochar as a green bifunctional cathode catalyst in electrochemical degradation of organic pollutant. Green Energy & Environment. 2025;10:214-230. https://doi.org/10.1016/j.gee.2024.03.001
[Google Scholar]

[37] Li H., Gui Y., Li J., Zhang J., Lü J.. Development of lignin-derived hierarchically porous carbon by one-step pyrolysis in an air/N₂ flow for efficient adsorption of organic pollutants. Joural of Analytical and Applied Pyrolysis. 2024;177:106344. https://doi.org/10.1016/j.jaap.2023.106344
[Google Scholar]

[38] Wang J., Cai J., Zhou X., Wang S., Luo F., Yang L., Yu J., Chi R., Chen Z.. Accelerating of Fe²⁺ regeneration in Fenton reaction by biochar: Pivotal roles of carbon defects as electron donor and shuttle. Separation and Purification Technology. 2025;354:128945. https://doi.org/10.1016/j.seppur.2024.128945
[Google Scholar]

[39] Gasim M.F., Veksha A., Lisak G., Low S.-C., Hamidon T.S., Hussin M.H., Oh W.-D.. Importance of carbon structure for nitrogen and sulfur co-doping to promote superior ciprofloxacin removal via peroxymonosulfate activation. Journal of Colloid and Interface Science. 2023;634:586-600. https://doi.org/10.1016/j.jcis.2022.12.072
[Google Scholar]

[40] Gao J., Liu Y., Xia X., Wang L., Shao L., Cai T., Dong W.. Mechanisms for photo assisted Fenton of synthesized pyrrhotite at neutral pH. Applied Surface Science. 2019;463:863-871. https://doi.org/10.1016/j.apsusc.2018.09.007
[Google Scholar]

[41] World Health Organization. Guidelines for Drinking-water Quality (fourth ed.). 2011. https://portals.iucn.org/library/node/28887

[42] Serra-Clusellas A., De Angelis L., Lin C.-H., Vo P., Bayati M., Sumner L., Lei Z., Amaral N.B., Bertini L.M., Mazza J., Pizzio L.R., Stripeikis J.D., Rengifo-Herrera J.A., de Cortalezzi M.M.F.. Abatement of 2,4-D by H₂O₂ solar photolysis and solar photo-Fenton-like process with minute Fe(III) concentrations. Water Research. 2018;144:572-580. https://doi.org/10.1016/j.watres.2018.07.072
[Google Scholar]

[43] Xu H., Ye Q., Wang Q., Zhou P., Huo X., Wang Y., Huang X., Zhou G., Zhang J.. Enhancement of organic contaminants degradation at low dosages of Fe(III) and H₂O₂ in g-C₃N₄ promoted Fe(III)/H₂O₂ system under visible light irradiation. Separation and Purification Technology. 2020;251:117333. https://doi.org/10.1016/j.seppur.2020.117333
[Google Scholar]

[44] Cui Y., He Y., Jin Y., Yang Z., Shan C., Zhang Q., Zhang W., Pan B.. Autocatalytic oxidation of thiophene derivatives and co-degradation of refractory contaminants in Fenton reaction. Chemical Engineering Journal. 2024;496:153954. https://doi.org/10.1016/j.cej.2024.153954
[Google Scholar]

[45] Nichela D.A., Donadelli J.A., Caram B.F., Haddou M., Nieto F.J.R., Oliveros E., Einschlag F.S.G.. Iron cycling during the autocatalytic decomposition of benzoic acid derivatives by Fenton-like and photo-Fenton techniques. Applied Catalysis B: Environmental. 2015;170-171:312-321. https://doi.org/10.1016/j.apcatb.2015.01.028
[Google Scholar]

[46] Cui K.-P., Yang T.-T., Chen Y.-H., Weerasooriya R., Li G.-H., Zhou K., Chen X.. Magnetic recyclable heterogeneous catalyst Fe₃O₄/g-C₃N₄ for tetracycline hydrochloride degradation via photo-Fenton process under visible light. Environmental Technology. 2021;43:3341-3354. https://doi.org/10.1080/09593330.2021.1921052
[Google Scholar]

[47] Yang S., Tian D., Wang X., Zhou P., Xiong Z., Zhang H., Liu Y., Yao G., Lai B.. The enhanced mechanism of Fe(III)/H₂O₂ system by N, S-doped mesoporous nanocarbon for the degradation of sulfamethoxazole. Separation and Purification Technology. 2023;308:122900. https://doi.org/10.1016/j.seppur.2022.122900
[Google Scholar]

[48] Fang G., Liu C., Wang Y., Dionysiou D.D., Zhou D.. Photogeneration of reactive oxygen species from biochar suspension for diethyl phthalate degradation. Applied Catalysis B: Environmental. 2017;214:34-45. https://doi.org/10.1016/j.apcatb.2017.05.036
[Google Scholar]

Co-catalysis of N, S-codoped biochar toward photo-Fenton reaction for degradation of organic micropollutants in water

Abstract

Keywords

Advanced oxidation

Carbon

Co-catalysis

Heteroatom doping

1. Introduction

2. Materials and Methods

2.1. N, S-codoped biochar preparation and characterizations

2.2. Photo-Fenton degradation of organic pollutants

2.3. Analytical methods

3. Results and Discussion

3.1. Characteristics of N, S-codoped biochar (NSB)

3.2. Co-catalytic effect of NSB toward photo-Fenton reaction

3.3. Influence of reaction conditions

3.4 Investigation on the co-catalytic mechanism

4. Conclusions

CRediT authorship contribution statement

Declaration of competing interest

Declaration of generative AI and AI-assisted technologies in the writing process

Acknowledgment

Supplementary data

References

Suggested read for related articles: