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Article

Regenerable Biochar Catalyst from Biogas Residue for Peroxymonosulfate Activation in Bisphenol A-Containing Wastewater Treatment

by
Yating Pan
1,
Xue Yang
2,
Haijuan Wei
3,
Xiang Liu
1,*,
Pan Wang
2,
Nina Duan
2 and
Miao Lin
4,*
1
Department of Environmental Science and Engineering, Fudan University, Shanghai 200438, China
2
Shanghai Municipal Engineering Design Institute (Group) Co., Ltd., Shanghai 200092, China
3
Shanghai Chengtou Wastewater Treatment Co., Ltd., Shanghai 201203, China
4
Shanghai Academy of Agricultural Sciences, Shanghai 201403, China
*
Authors to whom correspondence should be addressed.
Water 2025, 17(5), 744; https://doi.org/10.3390/w17050744
Submission received: 9 February 2025 / Revised: 25 February 2025 / Accepted: 28 February 2025 / Published: 4 March 2025
(This article belongs to the Topic Advanced Oxidation Processes for Wastewater Purification)
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Abstract

:
The biogas residue (BR) from the anaerobic digestion of sludge poses a threat to the environment due to the presence of toxic and hazardous substances. Furthermore, emerging contaminants, such as bisphenol A (BPA), are widespread in domestic and industrial wastewater, requiring efficient and sustainable treatment technologies. In this study, the BR-based biochar was pyrolyzed from urea-modified BR and employed as a catalyst to activate peroxymonosulfate (PMS) for BPA degradation. With BR-based biochar pyrolyzed at 750 °C as a catalyst, 20 mg/L of BPA was completely removed. Free radical detection confirmed that hydroxyl radical (•OH) and sulfate radical (•SO4−) generation decreased with the increase in catalyst reuse times. The X-ray photoelectron spectra showed that the catalyst deactivation mainly resulted from -COOH and C-OH group loss, which acted as active sites for generating •OH and •SO4−, and HCl or NaOH regeneration for catalysts could recover oxygen-containing functional groups, boosting BPA removal from 54.7% to 91.5% and 100%, respectively. Thermal regeneration could only enlarge the catalyst’s specific surface area (SSA) to recover adsorption capacity, but might not restore the free radical generation capability. This research offered a theoretical basis for the sustainable utilization of BR and provided a reference for reusing catalysts in wastewater treatment.

1. Introduction

The rapid pace of urbanization has led to a continuous rise in the quantity of sludge generated by municipal wastewater treatment plants (WWTPs) [1]. Anaerobic digestion (AD) has become one of the most widely used methods for stabilizing sludge [2]. This process involves the decomposition of organic matter in the sludge by microorganisms in an anoxic environment, resulting in the production of biogas, with biogas residue (BR) remaining. The BR contains an array of toxic and harmful substances, such as heavy metals, pathogens, and persistent organic pollutants [3]. The improper disposal of BR could result in the leaching of hazardous substances into aquatic systems, posing significant risks to water quality and ecosystem health [4]. Among the disposal methods for BR, pyrolysis could produce cost-effective and functional biochar and avoid the problem of secondary pollution caused by incineration and landfill disposal [5]. Additionally, the solid product, biochar, characterized by its high specific surface area (SSA) and abundant catalytic groups, is extensively utilized for the adsorption and catalytic removal of pollutants in wastewater [6].
In recent years, increasing concerns have been raised regarding the accumulation of endocrine-disrupting chemicals (EDCs) in the water environment and their associated adverse effects [7]. Among these, bisphenol A (BPA), a representative EDC, is widely used in industrial applications and can be released into aquatic environments through product leaching and wastewater discharge [8]. Its presence poses significant risks to ecosystems and biodiversity, while also threatening human reproductive health and developmental processes [9]. Sulfate-radical-based advanced oxidation processes (SR-AOPs) have emerged as an effective strategy for eliminating these emerging contaminants in water environments [10]. In recent years, a variety of materials, including carbon-based [11], aluminum-based [12], and perovskites materials [13], have been extensively investigated as catalysts for peroxymonosulfate (PMS) activation, demonstrating excellent catalytic performance. Due to the simple preparation methods and low cost, BR-based biochar has been utilized as a catalyst in PMS activation to degrade contaminants [14].
However, current research primarily focuses on exploring the mechanisms of activating PMS with new catalysts [15], with comparatively limited attention given to the deactivation and regeneration of catalysts and the underlying mechanisms involved. In practical wastewater treatment, the decrease in pollutant removal efficiency caused by catalyst deactivation was inevitable, thereby limiting the long-term sustainability of heterogeneous advanced oxidation processes (HAOPs) [16,17]. Although some studies have identified some reasons for catalyst deactivation, such as the adsorption of intermediates of contaminants, leading to the coverage of catalytic active sites and inactivation [18], the systematic and comprehensive investigation of the factors and mechanisms contributing to catalyst deactivation still needs to be explored.
Therefore, ensuring the stability and efficiency of HAOPs in wastewater treatment requires effective catalyst regeneration strategies. It is worth noting that physical and chemical modification methods, including acid, alkali, and thermal treatments, have been explored to restore catalytic activity [19,20]. Current research on catalyst deactivation and regeneration has primarily focused on Al2O3-based catalysts [21]. For carbon-based catalysts, studies have shown that porous carbon could effectively regain its catalytic performance through alkali and thermal treatment [22]. However, research on regenerating sludge-derived biochar catalysts remains limited, despite their potential for viable wastewater treatment [23]. Most importantly, the regeneration outcomes vary with the type of catalyst and regeneration conditions [19]. A comprehensive comparison of different regeneration strategies is essential to optimize catalyst reusability and enhance its practical applicability in water treatment.
This study first synthesized BR-based biochar with urea modification through pyrolysis. Subsequently, the prepared BR-based biochar was utilized to catalytically degrade BPA by activating PMS, and the stability of the catalysts with the increase in catalyst reuse times was evaluated. Then, three methods (HCl, NaOH, and thermal) were used to regenerate the used BR-based biochar catalysts, and the structural and morphological features, surface functional groups, elemental composition, and electron transfer capability of the catalysts before and after use and regeneration were comprehensively investigated and assessed. Combined with the catalytic performance of BPA removal, BR-based biochar’s deactivation and regeneration mechanisms for PMS activation were revealed. This study aimed to provide a viable strategy for the environmental disposal of BR and a reference for the efficient use of catalyst recycling in activating PMS.

2. Materials and Methods

2.1. Materials

In this study, the BR was obtained from a water treatment plant in Shanghai, China. Other chemicals were analytical-grade (Text S1) and purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All aqueous solutions were prepared with deionized water (Milli-Q/18.2 MΩ cm).

2.2. BR-Based Biochar Preparation

Firstly, BR was subjected to dehydration and freeze-drying, ground into a uniform powder, and stored at ambient temperature. The BR was mixed with urea at a mass ratio of 1:1 and meticulously ground in an agate mortar for 15 min to ensure thorough blending [24,25]. Then, three ceramic crucibles, each containing 15 g of the prepared samples, were positioned at the center of a quartz tube (length: 1000 mm, inner diameter: 50 mm) inside the tubular furnace to ensure uniform heating. The furnace stopper was secured at the end of the tube, and the system’s seal was checked for integrity. Prior to the pyrolysis experiment, N2 was introduced into the pyrolysis system at a flow rate of 100 mL/min for 10 min to purge the air from the system [26]. Then, the samples were heated gradually in N2 at a rate of 10 °C/min to 550 °C, 650 °C, and 750 °C, respectively, and each maintained at the target temperature for 1 h [27]. The prepared N-doped biochar samples were named NBC550, NBC650, and NBC750. Contrastingly, the samples without N-doping were prepared under identical thermal conditions and labeled BC550, BC650, and BC750. All the prepared biochar was used as the catalysts for the activation of PMS.

2.3. BPA Degradation by Peroxymonosulfate Activation Test and Catalyst Stability Evaluation

In this study, the performance of the synthesized catalysts was assessed by activating PMS and degrading BPA. Experiments were conducted at room temperature (25.0 ± 1.0 °C) in 100 mL conical flasks using a magnetic stirrer (SN-MS-H280D, Sunne, Shanghai, China) at a rate of 450 rpm. Initially, the catalyst (0.3 g/L) was dispersed in a 100 mL solution containing 20 mg/L BPA and stirred for 30 min to establish adsorption–desorption equilibrium. Subsequently, PMS (0.1 g/L) was added to initiate the reaction. A 1 mL sample was periodically extracted using a pipette, followed by immediate filtration through a 0.45 μm filter membrane for analysis to assess the degradation of the pollutant.
To assess the stability of the catalyst, the NBC750 was subjected to five repeated use tests, and the catalyst after repeated uses was named NBC750-5th. The catalysts were vacuum-filtered, rinsed with ultrapure water, and dried at 60 °C. Furthermore, three methods (HCl, NaOH, and thermal regeneration) were used to regenerate the catalysts sequentially, named as NBC750-HCl, NBC750-NaOH, and NBC750-500 °C, respectively. Specifically, 1 g of deactivated catalyst was added to 100 mL of either 1 M NaOH or 1 M HCl solution and stirred at room temperature for 3 h. After filtration, catalysts were rinsed with deionized water to a neutral pH and dried at 60 °C, yielding regenerated HCl or NaOH regeneration catalysts. Moreover, 1 g of deactivated catalyst was thermally treated at 500 °C under a N2 atmosphere for 30 min to obtain thermally regenerated catalysts. The reusability of the regenerated catalysts was assessed by reapplying them in PMS activation for BPA degradation, with repeated cycles of regeneration and application. The specific experimental procedures were identical to those used in the stability tests of fresh catalysts.
Reactive oxygen species (ROSs) generated during catalysis on BPA degradation were analyzed using quenching assays and electron paramagnetic resonance (EPR) technology [28]. For quenching experiments, some quenchers were selected based on the literature [29,30], and their concentrations were determined by experimental validation. In this study, 2000 mM of tert-butyl alcohol (TBA) was used to quench free hydroxyl radicals (•OHfree), while the same dose of ethyl alcohol (EtOH) was applied to quench both •OHfree and free sulfate radicals (•SO4−free), and 30 mM of dimethyl sulfoxide (DMSO) was employed to quench the surface-bound •OH and •SO4− (•OHads and •SO4−ads). Moreover, 10 mM of trichloromethane (CHCl3) was applied as a quencher for superoxide anions (•O2−). Each experimental condition was conducted in triplicate.

2.4. Structural Characterizations

The structural and morphological features of the biochar were investigated by a scanning electron microscope (SEM, Sigma 300, Zeiss, Oberkochen, Germany) equipped with an energy dispersive X-ray detector (EDS). The X-ray photoelectron spectroscopy (XPS, Nexsa, Thermo Fisher, Waltham, MA, USA) was employed to identify the elemental composition and content of the catalysts. The N2 adsorption–desorption isotherms were determined using a fully automated surface and porosity analyzer (Autosorb-iQ, Quantachrome, Boynton Beach, FL, USA). The SSA and pore size distribution of catalysts were determined by the Brunauer–Emmett–Teller (BET) method and the Density Functional Theory (DFT) model. X-ray diffraction (XRD, Panalytical Empyrean, Malvern Panalytical, Almelo, NL, USA) was used to examine the crystal structure of the catalysts. Raman spectra of the materials were obtained at an excitation wavelength of 532 nm by a Raman spectrometer (XploRA, Horiba, Longjumeau, France). Fourier-transform infrared spectroscopy (FT-IR, Nicolet 6700, Thermo Fisher, Waltham, MA, USA) was accepted to detect the surface functional groups of the catalysts. The elemental composition of BR (C, H, N, S) was analyzed by an elemental analyzer (EA3000, Euro Vector, Pavia, Italy), and the O content was calculated by subtracting the ash mass (from drying BR at 600 °C for 1 h in a muffle furnace) and the masses of C, H, N, and S from the total sample weight. Additionally, the electron transfer capability of the catalysts was assessed using an electrochemical workstation (CHI 600C, CH Instruments, Shanghai, China), where a Ag/AgCl electrode served as the reference electrode, a Pt wire electrode acted as the counter electrode, and a glassy carbon electrode (GCE) acted as the working electrode. To prepare the working electrodes, 5 mg of biochar powder was mixed with 5 μL of Nafion solution (5.0 wt%), 200 μL of ethanol, and 400 μL of deionized water. The mixture was then subjected to ultrasonic dispersion for 1 h to form a uniform suspension. Afterward, 6 μL of the suspension was dropped onto the surface of the glassy carbon electrode, and the catalyst-loaded electrode was dried at 60 °C for 20 min.

2.5. Analytical Methods

A high-performance liquid chromatograph (HPLC, Agilent 1260 infinity, Agilent, Santa Clara, CA, USA) was used for the determination of BPA concentration. The mobile phase comprised acetonitrile and water (60/40, v/v) with a 1.0 mL/min flow rate. PMS concentration was measured at 352 nm using a UV spectrophotometer (DR3900, Hach, Loveland, CO, USA). Total organic carbon (TOC) was tested by a total organic carbon analyzer (TOC-L, Shimadu, Kyoto, Japan). EPR spectroscopy (EMX nano, Bruker, Rheinstetten, Germany) with 5,5-dimethyl-1-pyrroline N-oxide (DMPO) as a spin-trapping agent was employed to detect the generated ROSs. The pH of the solution was measured using a pH meter (WTW PH/Oxi340i, Shanghai Jinbi Trading Co., Ltd., Shanghai, China), and the electrode was calibrated before each test. Each experimental condition was conducted in triplicate.

3. Results and Discussion

3.1. Catalytic Performance of BR-Based Biochar Catalysts

The catalytic activity of BR-based biochar catalysts was systematically evaluated by activating PMS and the degradation of BPA in aqueous solutions. Initially, catalysts were stirred in BPA solutions for 30 min to achieve adsorption–desorption equilibrium, and the adsorption ability of the prepared catalysts for BPA was similar at about 27–35%. After the adsorption, it was observable in Figure 1A that the removal rate of BPA within 60 min was only 4.5% without catalysts. In the systems with the addition of the catalysts, removal rates of 94.0% and 88.0% were obtained in NBC650 and NBC550 systems, revealing that a higher preparation temperature for biochar was also beneficial for catalytic activity. In BR-based biochar catalyst systems, N-doping enhanced the catalytic performance of catalysts, with NBC750 achieving 100% BPA removal in 60 min and the highest PMS consumption (Figure 1A,B). As modeled by first-order kinetic fits in various systems, the rate constants (k) for BPA degradation were calculated (Figure 1A), supporting the above conclusion. Moreover, the 69.3% TOC removal within 60 min in the NBC750 system indicated nearly 70% BPA mineralization (Figure S1).
To investigate the impact factors of BPA degradation, the pollutant degradation tests were carried out under different initial conditions with NBC750 catalyst (Figure S2) [10,31]. The results showed that BPA degradation efficiency nearly peaked at an NBC750 dosage of 0.3 g/L, with no significant improvement at 0.4 g/L. For PMS, increasing the dosage from 0.1 g/L to 0.2 g/L only minimally enhanced BPA degradation. Additionally, NBC750 effectively activated PMS for BPA degradation in the pH range of 3–9, with the highest efficiency at pH 7. Therefore, for subsequent experiments, NBC750 and PMS dosages of 0.3 g/L and 0.1 g/L were selected, with a pH of 7, under the 20 mg/L BPA condition.

3.2. Stability Tests and Reactivation of BR-Based Biochar Catalysts

The stability and reusability of BR-based biochar catalysts are critical for their practical engineering application [32]. As illustrated in Figure 2A, compared with the first run (100% removal in 60 min) of the NBC750 system, the BPA removal decreased to 76.6%, 66.0%, 55.8%, and 54.7% in its continuous use of the 2nd–5th, respectively, which denoted that NBC750 gradually lost its catalytic activity with the increase in catalyst reuse times.
After five consecutive applications, the BR-based biochar catalysts were regenerated through HCl, NaOH, and thermal regeneration, respectively, and then re-employed to activate PMS for BPA degradation. From Figure 2B, the NBC750-500 °C system achieved 50.7% BPA removal, with 23.8% due to adsorption, but showed no sustained catalytic activity after 10 min. However, NBC750-HCl or NBC750-NaOH achieved a 91.5% or 100% BPA removal, demonstrating that acid or alkali methods were more effective than thermal treatment in catalyst regeneration. Consequently, no further experiments were conducted on the thermally regenerated catalysts. In the subsequent four runs, the BPA removal rates with NBC750-HCl were 63.4%, 59.2%, 55.2%, and 53.5%, while those with NBC750-NaOH were 65.5%, 62.3%, 57.3%, and 56.3%, revealing that the HCl and NaOH groups exhibited similar BPA removal rates.
Then, the BR-based biochar catalysts were regenerated a second time and used again, with the results shown in Figure 2C. The BPA removal rates with NBC750-HCl and NBC750-NaOH increased from 53.5% and 56.3% to 72.3% and 82.4%, respectively, indicating that the BR-based biochar catalysts could be regenerated again.

3.3. Role of Radical and Non-Radical Process in BR-Based Biochar Catalysts in PMS System

The ROSs in BR-based biochar catalysts for activating PMS were systematically investigated. From Figure 3A, in the NBC750 system, TBA, EtOH, and DMSO inhibited BPA removal by 33.8%, 44.4%, and 36.8%, respectively, indicating that free and surface-bound •OH and •SO4− were the dominant ROSs, while CHCl3 caused only 5.3% inhibition, suggesting a minor role for •O2−. In the NBC750-5th system, TBA, EtOH, DMSO, and CHCl3 inhibited BPA removal by 17.1%, 22.0%, and 6.5%, 8.4%, respectively, reflecting reduced the production of •OH and •SO4−. Therefore, •OH and •SO4− were identified as the primary ROSs in BPA degradation by PMS catalyzed with BR-based biochar, and their decreased production with repeated catalyst use led to lower BPA removal efficiency.
In NBC750-HCl and NBC750-NaOH systems (Figure 3B), TBA and EtOH inhibited BPA degradation by 46.3% and 56.6% for NBC750-HCl, and 46.5% and 56.7% for NBC750-NaOH, while DMSO reduced BPA degradation by 25.5% and 25.8%, indicating an increased production of •OH and •SO4− after HCl or NaOH regeneration. Moreover, CHCl3 inhibited degradation by 9.2% in the NBC750-HCl system and 15.4% in the NBC750-NaOH system, showing that NaOH regeneration favored •O2− production. Overall, HCl and NaOH regeneration enhanced •OH and •SO4− production, which were crucial factors in improving BPA degradation efficiency.
The EPR technology confirmed the presence of •OH and •SO4− by using DMPO as a spin-trapping agent [33]. From Figure 3C, the weaker signals of NBC750-5th confirmed that the production of •OH and •SO4− decreased with repeated use of the catalyst. In contrast, the enhanced signals of NBC750-HCl and NBC750-NaOH further demonstrated restored catalytic activity through HCl or NaOH regeneration.
Additionally, it has been reported that the BPA degradation did not depend exclusively on free radical reactions [34]. Consequently, electrochemical methods were utilized to examine the non-radical mechanism [29]. As presented in Figure 3D, there was no reduction in open circuit potential when BPA was introduced to the bare GCE electrode, which inferred that direct electron transfer from BPA to PMS was not feasible without a catalyst to mediate the process. The open circuit potential of the NBC750-coated glassy carbon electrode (NBC750-GCE) rose immediately after PMS addition, followed by a significant drop with BPA addition, revealing electron transfer with BPA as an electron donor [35]. However, the quenching experiments demonstrated a potent inhibition of BPA degradation by EtOH and DMSO. Therefore, non-radical pathways might also play a subsidiary role in BPA degradation.

3.4. Characteristic Changes in BR-Based Biochar Catalysts in PMS System

3.4.1. Surface Morphology and Porosity Analysis

The elemental composition of BR (Figure S3) indicated that BR was rich in organic and inorganic materials, which helped form biochar with abundant functional groups [36]. The morphology of the BR-based biochar catalysts was observed using SEM (Figure 4A–F) [37], revealing the surface adorned with irregular nanoparticles. Additionally, in Figure 4G and Figure S4, the EDS images and corresponding EDS spectrum showed a uniform distribution of N and O in NBC750. At the same time, minimal surface texture differences across samples confirmed the stability of the BR-based biochar catalysts during use and regeneration.
The SSA and porous structure of BR-based biochar catalysts were characterized using N2 adsorption–desorption isotherms [38]. As shown in Figure 5A, all samples exhibited type-IV isotherms with significant hysteresis loops, indicating a wide distribution of micropores and mesopores [39]. Moreover, the pore size of the catalysts was mainly within 0–10 nm (Figure 5B), supporting the above conclusions. From Table S1, the SSA of NBC750-5th decreased to 28.70 m2/g, and the pore size also increased to 18.81 nm compared to NBC750 (64.56 m2/g, 8.13 nm), denoting that the changes in SSA and pore structure might contribute to the deactivation of catalysts. For regenerated catalysts, NBC750-NaOH achieved the highest SSA (149.76 m2/g) and smallest pore size (7.50 nm), followed by NBC750-HCl (127.45 m2/g, 7.86 nm) and NBC750-500 °C (94.21 m2/g, 7.92 nm), denoting that HCl, NaOH, and thermal regeneration all significantly adjusted the SSA and pore size of catalysts.

3.4.2. Molecular Structure Analysis

XRD was used to check the crystallinity of the BR-based biochar catalysts [29]. As depicted in Figure 6A, the XRD patterns of all samples were similar, indicating that the reuses and regeneration of catalysts had minimal influence on the crystallinity.
The FT-IR was employed to analyze the surface functional groups of the BR-based biochar catalysts [40]. From Figure 6B, all samples showed consistent functional groups, including -OH/-COOH, C=O/C=C, C-O, and C-H bonds [41,42]. Thermal regeneration removed a new peak at 1506 cm−1 in NBC750-5th, caused by adsorbed organics. Considering the regeneration experimental results, thermal treatment eliminated these adsorbed organics, but probably only released the adsorption sites with little effect on the catalytic performance of catalysts.
Raman spectroscopy was used to analyze the structural characteristics of the BR-based biochar catalysts. The D band (1350 cm−1) indicated defects, and the G band (1580 cm−1) reflected graphitization [43]. Based on previous studies, the ID/IG ratio was calculated by fitting the D and G peaks and determining the ratio of the integrated areas of these two peaks [44]. In Figure 6C, the ID/IG value of NBC750-5th decreased to 1.12 with increased catalyst reuse times, symbolizing that the defect sites were destroyed. Moreover, none of the regeneration methods could restore these sites.

3.4.3. Chemical Components on the BR-Based Biochar Catalyst Surface

The XPS spectra of catalysts were further analyzed to determine the key species involved in the deactivation and regeneration mechanisms of the BR-based biochar catalysts (Figure 7A and Table S2). The C 1 s XPS spectrum (Figure S5) displayed four peaks centered around 284.8, 285.8, 286.6, and 293.6 eV, corresponding to C-C, C-O, O-C=O, and C=C [45]. As shown in Figure 7B, binding energies of 398.6, 399.8, 400.8, and 402.5 eV in N 1 s XPS spectrum indicated pyridinic N, pyrrolic N, graphitic N, and NOx [23]. The total N content of NBC750-5th decreased from 4.04 at% to 2.84 at% with the increase in catalyst reuse times (Table S2), suggesting that the N loss impacted the catalytic activity of BR-based biochar. However, the N content of NBC750-HCl, NBC750-NaOH, and NBC750-500 °C was measured at 2.76 at%, 2.52 at%, and 2.66 at%, respectively, indicating that none of the three regeneration methods were able to restore N content.
Equally, the O 1 s XPS spectrum (Figure 7C) peaked at 531.3, 532.3, and 533.4 eV, matching -COOH, C=O, and C-OH, respectively [22]. Due to multiple reuses of catalysts, the O content of NBC750-5th decreased from 31.98 at% to 25.59 at%, with -COOH, C=O, and C-OH dropping from 8.92 at% to 5.06 at%, 15.69 at% to 14.49 at%, and 7.37 at% to 6.04 at%, respectively, reflecting the consumption of oxygen-containing functional groups. It has been demonstrated that -COOH and C-OH could promote the generation of •OH and •SO4− [46], while the C=O could serve as the active sites for •O2− generation [22]. Therefore, the loss of active sites was the primary cause of catalyst deactivation. After regeneration, O content decreased to 23.14 at% in NBC750-HCl and increased to 28.74 at% in NBC750-NaOH. Specifically, the content of -COOH increased to 6.18 at% in NBC750-HCl, and the percentage of C-OH increased to 7.08 at% after NaOH regeneration. However, thermal regeneration could not restore the oxygen-containing functional groups (-COOH or C-OH), which limited the recovery of the catalytic performance of BR-based biochar. Generally, the (O + N)/C and O/C ratios of BR-based catalysts indicated the hydrophilicity of biochar [47]. The (O + N)/C and O/C ratios of NBC750-5th decreased from 0.79 and 0.64 to 0.44 and 0.39, respectively, but improved to 0.50 and 0.46 after NaOH regeneration, unlike HCl or thermal regeneration (Table S2). This suggested that enhanced hydrophilicity may contribute to the higher catalytic effect of NBC750-NaOH.
The linear sweep voltammetry (LSV) result (Figure 7D) showed reduced electron transfer capacity in NBC750-5th, fully restored by NaOH, partially by HCl, and unaffected by thermal regeneration. Since functional groups such as -COOH, C-OH, and C=O on BR-based biochar could facilitate the electron transfer process [48], this result further confirmed that these oxygen-containing functional groups of biochar could be recovered by HCl or NaOH regeneration.

3.4.4. Mechanism of Catalytic and Regeneration of the BR-Based Biochar Catalysts

In this study, the BPA removal rate gradually decreased with increased reuse times in stability tests for BR-based biochar catalysts. Subsequently, HCl, NaOH, and thermal regeneration were used to recover the catalytic activity of catalysts. Compared with HCl and NaOH regeneration, thermal regeneration was unsatisfactory in restoring the catalytic activity of the catalysts.
Based on the experimental results, BPA degradation mainly relied on •OH and •SO4−, and the decrease in BPA removal was closely related to the decline in ROS production, which could effectively be restored by the HCl or NaOH regeneration. XPS analysis revealed that the depletion of -COOH and C-OH, key active sites for •OH and •SO4− production [38], was the main cause of inactivation, with HCl regenerating -COOH and NaOH restoring C-OH, while thermal regeneration had no effect on any oxygen-containing functional groups. In conclusion, the gradual depletion of -COOH and C-OH reduced ROS production during the repeated uses of biochar catalysts, leading to the deactivation of the BR-based catalysts. Through HCl generation, -COOH functional groups could be restored, and the NaOH method effectively regenerated C-OH. However, thermal regeneration did not have any beneficial effects on the above either, thus failing to recover the catalytic performance of BR-based biochar.
Moreover, BPA strongly interacted with the defect sites on the BR-based biochar catalysts during PMS activation, enabling PMS to extract electrons and directly oxidize BPA [21]. Unfortunately, none of the three regeneration methods restored these sites. Although thermal regeneration partially restored adsorption by increasing SSA, it did not recover catalytic active sites.
Cost-effectiveness is crucial for ensuring the sustainability and practical application of SR-AOPs. The low cost and easy availability of BR make BR-based biochar catalysts cost-effective, reducing raw material expenses. Additionally, the BR-based biochar catalysts are regenerable, which helps lower operational costs. Both HCl and NaOH regeneration methods are economically viable, as the regenerated liquids could be recycled. Thermal regeneration was excluded due to its poor regeneration performance. Future studies could focus on optimizing the biochar production process to reduce its environmental footprint, as well as assessing its long-term sustainability and potential for large-scale applications in engineering.

4. Conclusions

In this study, BR-based biochar was prepared to activate PMS for BPA degradation. It was found that the activation of PMS was associated with oxygen-containing functional groups, N content, and defect sites of the BR-based biochar catalysts, and with the increase in catalyst reuse times, all the above were greatly affected or inhibited. Through the recovery of oxygen-containing functional groups and SSA, HCl or NaOH regeneration can effectively or even completely restore the catalytic activity, thus greatly improving the removal rate of BPA. However, thermal regeneration had little impact on the recovery of the catalytic activity. This research provided an efficient approach to improving the stability and recyclability of BR-based biochar catalysts, and provided new insights into the advancement of high-performance water treatment technologies for the removal of emerging contaminants.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/w17050744/s1, Text S1: Chemicals and materials; Text S2: Measurement of PMS concentration; Text S3: Determination of ROSs; Text S4: Reaction rate constant measurement equation; Text S5: Measurement of LSV and open-circuit potential; Figure S1: TOC removal rate of NBC750; Figure S2: Effect of catalyst dosage, PMS dosage, and initial pH on removal of BPA; Figure S3: The elemental composition of BR; Figure S4: The EDS spectrum of NBC750; Figure S5: C 1 s XPS spectrum; Table S1: Surface physical structure parameters of catalysts; Table S2: Atom contents (at%) of BR-derived biochar.

Author Contributions

Conceptualization, X.L. and M.L.; methodology, X.Y. and M.L.; investigation, Y.P.; resources, H.W., P.W. and N.D.; data curation, Y.P.; writing—original draft preparation, Y.P.; writing—review and editing, X.L.; supervision, X.L.; funding acquisition, X.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work is financially supported by Shanghai Rising-Star Program (No. 23QB1404700).

Data Availability Statement

The data used in this study are available on request.

Conflicts of Interest

Xue Yang, Wang and Nina Duan were employed by Shanghai Municipal Engineering Design Institute (Group) Co., Ltd. Haijuan Wei was employed by Shanghai Chengtou Wastewater Treatment Co., Ltd. The research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. All of the authors have declared that there are no conflicts of interests.

References

  1. Zhao, L.; Sun, Z.F.; Pan, X.W.; Tan, J.Y.; Yang, S.S.; Wu, J.T.; Chen, C.; Yuan, Y.; Ren, N.Q. Sewage sludge derived biochar for environmental improvement: Advances, challenges, and solutions. Water Res. X 2023, 18, 12. [Google Scholar] [CrossRef]
  2. Chen, L.Y.; Qin, Y.J.; Chen, B.Q.; Wu, C.L.; Zheng, S.H.; Chen, R.L.; Yang, S.H.; Yang, L.; Liu, Z.J. Enhancing degradation and biogas production during anaerobic digestion of food waste using alkali pretreatment. Environ. Res. 2020, 188, 9. [Google Scholar] [CrossRef]
  3. Ho, S.H.; Chen, Y.D.; Yang, Z.K.; Nagarajan, D.; Chang, J.S.; Ren, N.Q. High-efficiency removal of lead from wastewater by biochar derived from anaerobic digestion sludge. Bioresour. Technol. 2017, 246, 142–149. [Google Scholar] [CrossRef] [PubMed]
  4. Kummu, M.; Guillaume, J.H.A.; De Moel, H.; Eisner, S.; Flörke, M.; Porkka, M.; Siebert, S.; Veldkamp, T.I.E.; Ward, P.J. The world’s road to water scarcity: Shortage and stress in the 20th century and pathways towards sustainability. Sci. Rep. 2016, 6, 38495. [Google Scholar] [CrossRef]
  5. Xiao, H.P.; Li, K.; Zhang, D.Q.; Tang, Z.H.; Niu, X.J.; Yi, L.Z.; Lin, Z.; Fu, M.L. Environmental, energy, and economic impact assessment of sludge management alternatives based on incineration. J. Environ. Manag. 2022, 321, 115848. [Google Scholar] [CrossRef]
  6. Zeng, L.; Chen, Q.; Liang, N.; Ji, P.X.; Lu, M.; Wu, M.; Oleszczuk, P.; Pan, B.; Xing, B.S. The promoted degradation of biochar-adsorbed 2,4-dichlorophenol in the presence of Fe(III). J. Hazard. Mater. 2023, 458, 131774. [Google Scholar] [CrossRef] [PubMed]
  7. Han, H.K.; Chen, M.F.; Sun, C.T.; Han, Y.Y.; Xu, L.L.; Zhao, Y.M. Synergistic enhancement in hydrodynamic cavitation combined with peroxymonosulfate fenton-like process for bpa degradation: New insights into the role of cavitation bubbles in regulation reaction pathway. Water Res. 2025, 268, 13. [Google Scholar] [CrossRef] [PubMed]
  8. Deblonde, T.; Cossu-Leguille, C.; Hartemann, P. Emerging pollutants in wastewater: A review of the literature. Int. J. Hyg. Environ. Health 2011, 214, 442–448. [Google Scholar] [CrossRef]
  9. Guo, Y.J.; Ma, C.Y.; Gao, Z.Y.; Wu, M.Z.; Shen, C.C.; Xu, Z.H. Insights into mechanism of peroxymonosufate activation by Mo single-atom catalysts: Singlet oxygen evolution and role of Mo-N coordination. J. Environ. Manag. 2024, 358, 120846. [Google Scholar] [CrossRef]
  10. Jiang, S.F.; Ling, L.L.; Chen, W.J.; Liu, W.J.; Li, D.C.; Jiang, H. High efficient removal of bisphenol A in a peroxymonosulfate/iron functionalized biochar system: Mechanistic elucidation and quantification of the contributors. Chem. Eng. J. 2019, 359, 572–583. [Google Scholar] [CrossRef]
  11. Hou, S.Y.; Hu, H.L.; Fu, Q.; Xiao, T.Y.; Xie, J.Q.; Chan, S.H.; He, M.J.; Miao, B.; Zhang, L. Undaria pinnatifida (wakame)-derived Fe, N co-doped graphene-like hierarchical porous carbon as highly efficient catalyst for activation of peroxymonosulfate (PMS) toward degradation of tetracycline (TC). Sep. Purif. Technol. 2024, 333, 13. [Google Scholar] [CrossRef]
  12. Zhang, H.; Zhao, J.; Liu, F.; Yin, J.L.; Li, W.; Dai, X.Q.; Zhou, P.; Liu, Y.; Lai, B. Immobilizing cobalt-iron bimetal on Al2O3 by electroless plating-calcination for peroxymonosulfate activation: Performance, mechanistic and practicality. Chem. Eng. J. 2024, 488, 11. [Google Scholar] [CrossRef]
  13. Yang, L.; Jiao, Y.; Xu, X.M.; Pan, Y.L.; Su, C.; Duan, X.G.; Sun, H.Q.; Liu, S.M.; Wang, S.B.; Shao, Z.P. Superstructures with Atomic-Level Arranged Perovskite and Oxide Layers for Advanced Oxidation with an Enhanced Non-Free Radical Pathway. ACS Sustain. Chem. Eng. 2022, 10, 1899–1909. [Google Scholar] [CrossRef]
  14. Huang, S.M.; Wang, T.; Chen, K.; Mei, M.; Liu, J.X.; Li, J.P. Engineered biochar derived from food waste digestate for activation of peroxymonosulfate to remove organic pollutants. Waste Manag. 2020, 107, 211–218. [Google Scholar] [CrossRef]
  15. Kohantorabi, M.; Moussavi, G.; Giannakis, S. A review of the innovations in metal- and carbon-based catalysts explored for heterogeneous peroxymonosulfate (PMS) activation, with focus on radical vs. non-radical degradation pathways of organic contaminants. Chem. Eng. J. 2021, 411, 26. [Google Scholar] [CrossRef]
  16. He, C.; Wang, J.B.; Wang, C.R.; Zhang, C.H.; Hou, P.; Xu, X.Y. Catalytic ozonation of bio-treated coking wastewater in continuous pilot- and full-scale system: Efficiency, catalyst deactivation and in-situ regeneration. Water Res. 2020, 183, 116090. [Google Scholar] [CrossRef]
  17. Kong, X.T.; Garg, S.; Chen, G.F.; Waite, D. Investigation of the deactivation and regeneration of an Fe2O3/Al2O3·SiO2 catalyst used in catalytic ozonation of coal chemical industry wastewater. J. Hazard. Mater. 2023, 451, 131194. [Google Scholar] [CrossRef]
  18. Yang, S.J.; Qiu, X.J.; Jin, P.K.; Dzakpasu, M.; Wang, X.C.C.; Zhang, Q.H.; Zhang, L.; Yang, L.; Ding, D.H.; Wang, W.D.; et al. MOF-templated synthesis of CoFe2O4 nanocrystals and its coupling with peroxymonosulfate for degradation of bisphenol A. Chem. Eng. J. 2018, 353, 329–339. [Google Scholar] [CrossRef]
  19. Hou, J.F.; Xu, L.X.; Han, Y.X.; Tang, Y.Q.; Wan, H.Q.; Xu, Z.Y.; Zheng, S.R. Deactivation and regeneration of carbon nanotubes and nitrogen-doped carbon nanotubes in catalytic peroxymonosulfate activation for phenol degradation: Variation of surface functionalities. RSC Adv. 2019, 9, 974–983. [Google Scholar] [CrossRef] [PubMed]
  20. Hu, W.R.; Tong, W.H.; Li, Y.L.; Xie, Y.; Chen, Y.D.; Wen, Z.Q.; Feng, S.F.; Wang, X.Q.; Li, P.Y.; Wang, Y.B.; et al. Hydrothermal route-enabled synthesis of sludge-derived carbon with oxygen functional groups for bisphenol A degradation through activation of peroxymonosulfate. J. Hazard. Mater. 2020, 388, 121801. [Google Scholar] [CrossRef]
  21. Cheng, C.; Li, J.P.; Wen, Y.Z.; Wang, J.L.; Jin, C.Y.; Sun, C.L.; Wang, H.L.; Wei, H.Z.; Yang, X.J. Deactivation mechanism of Fe/Al2O3 catalyst during the ozonation of reverse osmosis concentrates (ROCs): Effect of silicate. Chem. Eng. J. Adv. 2020, 1, 8. [Google Scholar] [CrossRef]
  22. Wang, G.L.; Chen, S.; Quan, X.; Yu, H.T.; Zhang, Y.B. Enhanced activation of peroxymonosulfate by nitrogen doped porous carbon for effective removal of organic pollutants. Carbon 2017, 115, 730–739. [Google Scholar] [CrossRef]
  23. Mian, M.M.; Liu, G.J. Activation of peroxymonosulfate by chemically modified sludge biochar for the removal of organic pollutants: Understanding the role of active sites and mechanism. Chem. Eng. J. 2020, 392, 123681. [Google Scholar] [CrossRef]
  24. Chen, M.; Yang, C.X.; Yu, M.H.; Han, M.Y.; Meng, Z.H.; Zhao, T.; Niu, J.R.; Mu, S.T.; Zhang, J.; Ma, J.J.; et al. N-doped carbon achieved by pyrolyzing urea and active carbon for the capacitive deionization coupled PMS oxidation system. Desalination 2024, 587, 12. [Google Scholar] [CrossRef]
  25. Edwin, N.N.; Garcia, T.; Solsona, B.; Taylor, S.H. The influence of cerium to urea preparation ratio of nanocrystalline ceria catalysts for the total oxidation of naphthalene. Catal. Today 2008, 137, 373–378. [Google Scholar] [CrossRef]
  26. Chen, Z.G.; Lei, C.; Yao, L.L.; Mo, Y.; Li, J.X.; Qu, H.W.; Zhou, Z.; Luo, W. Synergistic pyrolysis of rice and chili straw under N2/CO2 atmosphere: Nutritional elements (N/P/K) migration and transformation from straw to pyrolysis products. Energy 2025, 316, 13. [Google Scholar] [CrossRef]
  27. Xiao, T.; Zhou, P.K.; Liu, Y.; Zhang, K.K.; Liu, F.Y.; Guo, G.; Ni, F.Q.; Deng, Y. Impact of pyrolysis temperature on heavy metals environmental risk in biochar derived from co-pyrolysis of Alternanthera philoxeroides and sludge. J. Environ. Chem. Eng. 2024, 12, 9. [Google Scholar] [CrossRef]
  28. Zhao, C.H.; Shao, B.B.; Yan, M.; Liu, Z.F.; Liang, Q.H.; He, Q.Y.; Wu, T.; Liu, Y.; Pan, Y.; Huang, J.; et al. Activation of peroxymonosulfate by biochar-based catalysts and applications in the degradation of organic contaminants: A review. Chem. Eng. J. 2021, 416, 128829. [Google Scholar] [CrossRef]
  29. Wang, J.; Duan, X.G.; Gao, J.; Shen, Y.; Feng, X.H.; Yu, Z.J.; Tan, X.Y.; Liu, S.M.; Wang, S.B. Roles of structure defect, oxygen groups and heteroatom doping on carbon in nonradical oxidation of water contaminants. Water Res. 2020, 185, 116244. [Google Scholar] [CrossRef] [PubMed]
  30. Wang, L.L.; Lan, X.; Peng, W.Y.; Wang, Z.H. Uncertainty and misinterpretation over identification, quantification and transformation of reactive species generated in catalytic oxidation processes: A review. J. Hazard. Mater. 2021, 408, 124436. [Google Scholar] [CrossRef]
  31. Tang, W.Q.; Liu, Y.Y.; You, Q.L.; Yang, X.F.; Liao, G.Y.; Wang, D.S.; Yan, Y.; Shang, Q.G. Constructing a 3D ordered macroporous cobalt monoatomic catalyst for efficient SMX degradation via PMS activation. J. Environ. Chem. Eng. 2024, 12, 12. [Google Scholar] [CrossRef]
  32. Oh, W.D.; Lim, T.T. Design and application of heterogeneous catalysts as peroxydisulfate activator for organics removal: An overview. Chem. Eng. J. 2019, 358, 110–133. [Google Scholar] [CrossRef]
  33. Zhu, K.M.; Wang, X.S.; Geng, M.Z.; Chen, D.; Lin, H.; Zhang, H. Catalytic oxidation of clofibric acid by peroxydisulfate activated with wood-based biochar: Effect of biochar pyrolysis temperature, performance and mechanism. Chem. Eng. J. 2019, 374, 1253–1263. [Google Scholar] [CrossRef]
  34. Ren, W.; Xiong, L.L.; Yuan, X.H.; Yu, Z.W.; Zhang, H.; Duan, X.G.; Wang, S.B. Activation of Peroxydisulfate on Carbon Nanotubes: Electron-Transfer Mechanism. Environ. Sci. Technol. 2019, 53, 14595–14603. [Google Scholar] [CrossRef] [PubMed]
  35. Chen, H.; Li, X.; Li, W.Z.; Feng, J.; Zhao, Y.; Zhang, H.X.; Ren, Y.M. Nitrogen-doped biochar/MnO2 as an efficient PMS activator for synergistic BPA degradation via non-free radical pathways in the water. J. Environ. Chem. Eng. 2024, 12, 112446. [Google Scholar] [CrossRef]
  36. Ahmed, M.J.; Hameed, B.H. Insight into the co-pyrolysis of different blended feedstocks to biochar for the adsorption of organic and inorganic pollutants: A review. J. Clean. Prod. 2020, 265, 17. [Google Scholar] [CrossRef]
  37. Cai, S.; Zhang, Q.; Wang, Z.Q.; Hua, S.; Ding, D.H.; Cai, T.M.; Zhang, R.H. Pyrrolic N-rich biochar without exogenous nitrogen doping as a functional material for bisphenol A removal: Performance and mechanism. Appl. Catal. B Environ. 2021, 291, 120093. [Google Scholar] [CrossRef]
  38. Fan, H.L.; Wang, J.X.; Wu, P.P.; Zheng, L.; Xiang, J.F.; Liu, H.L.; Han, B.X.; Jiang, L. Hydrophobic ionic liquid tuning hydrophobic carbon to superamphiphilicity for reducing diffusion resistance in liquid-liquid catalysis systems. Chem 2021, 7, 1852–1869. [Google Scholar] [CrossRef]
  39. Sing, K.S.W.; Everett, D.H.; Haul, R.A.W.; Moscou, L.; Pierotti, R.A.; Rouquerol, J.; Siemieniewska, T. Reporting Physisorption Data for Gas Solid Systems with Special Reference To the Determination of Surface-Area and Porosity (Recommendations 1984). Pure Appl. Chem. 1985, 57, 603–619. [Google Scholar] [CrossRef]
  40. Song, W.; Yu, Z.H.; Li, H.; Ji, Y.Q.; Cao, L.L.; Ren, L.Y.; Li, X.G.; Li, Y.F.; Xu, X.; Yan, L.G. Insights into the factors influencing the oxidation of antibiotic pollutants in nitrogen-doped biochar/PMS system: The roles of physicochemical properties and reaction pathways. Chem. Eng. J. 2024, 498, 155601. [Google Scholar] [CrossRef]
  41. Silva, T.L.; Ronix, A.; Pezoti, O.; Souza, L.S.; Leandro, P.K.T.; Bedin, K.C.; Beltrame, K.K.; Cazetta, A.L.; Almeida, V.C. Mesoporous activated carbon from industrial laundry sewage sludge: Adsorption studies of reactive dye Remazol Brilliant Blue R. Chem. Eng. J. 2016, 303, 467–476. [Google Scholar] [CrossRef]
  42. Liu, W.J.; Nie, C.Y.; Li, W.L.; Ao, Z.M.; Wang, S.B.; An, T.C. Oily sludge derived carbons as peroxymonosulfate activators for removing aqueous organic pollutants: Performances and the key role of carbonyl groups in electron-transfer mechanism. J. Hazard. Mater. 2021, 414, 125552. [Google Scholar] [CrossRef]
  43. Wang, J.; Chen, Z.M.; Chen, B.L. Adsorption of Polycyclic Aromatic Hydrocarbons by Graphene and Graphene Oxide Nanosheets. Environ. Sci. Technol. 2014, 48, 4817–4825. [Google Scholar] [CrossRef]
  44. Shi, M.M.; Bao, D.; Li, S.J.; Wulan, B.R.; Yan, J.M.; Jiang, Q. Anchoring PdCu Amorphous Nanocluster on Graphene for Electrochemical Reduction of N2 to NH3 under Ambient Conditions in Aqueous Solution. Adv. Energy Mater. 2018, 8, 6. [Google Scholar] [CrossRef]
  45. Wu, C.X.; Li, L.F.; Zhou, H.; Ai, J.; Zhang, H.T.; Tao, J.L.; Wang, D.S.; Zhang, W.J. Effects of chemical modification on physicochemical properties and adsorption behavior of sludge-based activated carbon. J. Environ. Sci. 2021, 100, 340–352. [Google Scholar] [CrossRef]
  46. Chen, X.; Oh, W.D.; Hu, Z.T.; Sun, Y.M.; Webster, R.D.; Li, S.Z.; Lim, T.T. Enhancing sulfacetamide degradation by peroxymonosulfate activation with N-doped graphene produced through delicately-controlled nitrogen functionalization via tweaking thermal annealing processes. Appl. Catal. B Environ. 2018, 225, 243–257. [Google Scholar] [CrossRef]
  47. Shaheen, S.M.; Niazi, N.K.; Hassan, N.E.E.; Bibi, I.; Wang, H.L.; Tsang, D.C.W.; Ok, Y.S.; Bolan, N.; Rinklebe, J. Wood-based biochar for the removal of potentially toxic elements in water and wastewater: A critical review. Int. Mater. Rev. 2019, 64, 216–247. [Google Scholar] [CrossRef]
  48. Li, M.; Li, D.Y.; Guan, Z.Y.; Xu, Q.Q.; Shi, Y.T.; Xia, D.S. Carboxy-functionalized sludge-derived biochar for efficiently activating peroxymonosulfate to degrade bisphenol A. Sep. Purif. Technol. 2022, 297, 121525. [Google Scholar] [CrossRef]
Water 17 00744 g001
Figure 1. (A) Removal performance of BPA catalyzed by different BR-based biochar and corresponding k (−ln (Ct/C0) vs. time) values. (B) Consumption of PMS in catalyst/PMS/BPA solution.
Figure 1. (A) Removal performance of BPA catalyzed by different BR-based biochar and corresponding k (−ln (Ct/C0) vs. time) values. (B) Consumption of PMS in catalyst/PMS/BPA solution.
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Figure 2. (A) Reusability tests of NBC750. (B) First and (C) second cycle tests of NBC750 catalysts regenerated by different reactivation methods (HCl, NaOH, and thermal regeneration).
Figure 2. (A) Reusability tests of NBC750. (B) First and (C) second cycle tests of NBC750 catalysts regenerated by different reactivation methods (HCl, NaOH, and thermal regeneration).
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Figure 3. (A) Effects of different radical scavengers on removal of BPA in NBC750/PMS/BPA and NBC750-5th/PMS/BPA systems. (B) Effects of different radical scavengers on removal of BPA in NBC750-HCl/PMS/BPA and NBC750-NaOH/PMS/BPA systems. (C) EPR spectra of DMPO adducts (DMPO-•OH, DMPO-•SO4−). (D) Open-circuit potential curves of the GCE and NBC750-GCE in different systems.
Figure 3. (A) Effects of different radical scavengers on removal of BPA in NBC750/PMS/BPA and NBC750-5th/PMS/BPA systems. (B) Effects of different radical scavengers on removal of BPA in NBC750-HCl/PMS/BPA and NBC750-NaOH/PMS/BPA systems. (C) EPR spectra of DMPO adducts (DMPO-•OH, DMPO-•SO4−). (D) Open-circuit potential curves of the GCE and NBC750-GCE in different systems.
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Figure 4. (A–F) SEM images of (A) BC750; (B) NBC750; (C) NBC750-5th; (D) NBC750-HCl; (E) NBC750-NaOH; (F) NBC750-500 °C; (G) EDS image of NBC750 and corresponding N, O, and C elemental mapping images.
Figure 4. (A–F) SEM images of (A) BC750; (B) NBC750; (C) NBC750-5th; (D) NBC750-HCl; (E) NBC750-NaOH; (F) NBC750-500 °C; (G) EDS image of NBC750 and corresponding N, O, and C elemental mapping images.
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Figure 5. (A) N2 adsorption–desorption isotherms and (B) pore size distribution of different BR-based biochar catalysts and regenerated catalysts.
Figure 5. (A) N2 adsorption–desorption isotherms and (B) pore size distribution of different BR-based biochar catalysts and regenerated catalysts.
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Figure 6. (A) XRD patterns, (B) FT-IR spectra, and (C) Raman spectra of different BR-based biochar catalysts and regenerated catalysts.
Figure 6. (A) XRD patterns, (B) FT-IR spectra, and (C) Raman spectra of different BR-based biochar catalysts and regenerated catalysts.
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Figure 7. (A) Wide XPS spectrum of different BR-based biochar catalysts and regenerated catalysts. High-resolution XPS spectra for catalysts (B) N 1 s and (C) O 1 s. (D) Linear sweep voltammograms under different conditions.
Figure 7. (A) Wide XPS spectrum of different BR-based biochar catalysts and regenerated catalysts. High-resolution XPS spectra for catalysts (B) N 1 s and (C) O 1 s. (D) Linear sweep voltammograms under different conditions.
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MDPI and ACS Style

Pan, Y.; Yang, X.; Wei, H.; Liu, X.; Wang, P.; Duan, N.; Lin, M. Regenerable Biochar Catalyst from Biogas Residue for Peroxymonosulfate Activation in Bisphenol A-Containing Wastewater Treatment. Water 2025, 17, 744. https://doi.org/10.3390/w17050744

AMA Style

Pan Y, Yang X, Wei H, Liu X, Wang P, Duan N, Lin M. Regenerable Biochar Catalyst from Biogas Residue for Peroxymonosulfate Activation in Bisphenol A-Containing Wastewater Treatment. Water. 2025; 17(5):744. https://doi.org/10.3390/w17050744

Chicago/Turabian Style

Pan, Yating, Xue Yang, Haijuan Wei, Xiang Liu, Pan Wang, Nina Duan, and Miao Lin. 2025. "Regenerable Biochar Catalyst from Biogas Residue for Peroxymonosulfate Activation in Bisphenol A-Containing Wastewater Treatment" Water 17, no. 5: 744. https://doi.org/10.3390/w17050744

APA Style

Pan, Y., Yang, X., Wei, H., Liu, X., Wang, P., Duan, N., & Lin, M. (2025). Regenerable Biochar Catalyst from Biogas Residue for Peroxymonosulfate Activation in Bisphenol A-Containing Wastewater Treatment. Water, 17(5), 744. https://doi.org/10.3390/w17050744

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