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Article

Visible Light Modulating Abatement of Pharmaceuticals in Water by Zinc Single-Atom Catalyst on Biochar Support

by
Zhiyuan Zhang
1,
Cong Li
1,
Jieming Yuan
1,*,
Zhengming He
1,
Chengzhang Wu
1 and
Wanning Yang
2
1
School of Environment and Architecture, University of Shanghai for Science and Technology, Shanghai 200093, China
2
School of Economics and Management, Beijing Forestry University, Beijing 100083, China
*
Author to whom correspondence should be addressed.
Water 2026, 18(3), 313; https://doi.org/10.3390/w18030313
Submission received: 21 December 2025 / Revised: 22 January 2026 / Accepted: 23 January 2026 / Published: 26 January 2026
(This article belongs to the Special Issue Advances in Water and Stormwater Networks: Modelling and Pollutant Degradation, 2nd Edition)
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Abstract

The widespread occurrence of pharmaceutical contaminants in aquatic environments poses significant risks to ecosystems and public health, necessitating the development of efficient and sustainable treatment technologies. Herein, a visible-light (VL)–active zinc single-atom catalyst supported on biochar (SAZn@BC) was synthesized via pyrolysis and applied for the degradation of ibuprofen (IBP), sulfamethoxazole (SMX), trimethoprim (TMP), and carbamazepine (CBZ) in water. Structural characterization confirmed the presence of g-C3N4 domains, abundant oxygen-containing functional groups, and atomically dispersed Zn sites with a Zn–N4 coordination environment. Under VL irradiation, SAZn@BC achieved degradation efficiencies of 43.9%, 64.4%, and 61.9% for IBP, SMX, and TMP, respectively, within 30 min, while CBZ exhibited limited removal. Mechanistic investigations combining quenching experiments, electrochemical analyses, and X-ray photoelectron spectroscopy revealed that superoxide and hydroperoxyl radicals were the dominant reactive oxygen species, with hydroxyl radicals and singlet oxygen contributing to a lesser extent. In addition, a nonradical pathway involving direct interfacial electron transfer between oxygen functional groups on the biochar support and pharmaceutical molecules played a critical role, mediated by single-atom Zn sites and enhanced under VL irradiation. These findings demonstrate that SAZn@BC enables synergistic radical and nonradical pathways for pharmaceutical degradation and represents a promising strategy for water treatment applications.

1. Introduction

Among the Sustainable Development Goals (SDGs) of the United Nations, providing safe and clean water is one of the most important constituents [1,2]. However, achieving the goal for human consumption is challenging considering the rapid population growth, intensifying global climate change, worsening water quality, and continued industrialization, especially in developing countries [3]. Globally, water scarcity is making water reuse an acceptable, or even necessary alternative to achieve SDGs for sufficient clean water for human consumption [4]. Conventional treatment methods have served well for several decades, but newer strategies to treat water, especially those contaminated with pharmaceuticals, are urgently needed to address the imminent water shortages [5,6,7,8]. Advanced treatments are being investigated for degrading pharmaceuticals in water, including applying new materials to increase the efficiency of the processes [9,10,11]. The current paper applies the use of innovative materials like single-atom catalysts (SACs) for the abatement of pharmaceuticals in water.
Single-atom catalysts (SACs) have gained tremendous attention due to their nearly complete metal utilization, higher reusability, excellent stability, and outstanding catalytic performance, rendering them favorable materials in environmental applications [5,12,13]. Carbon-based materials are one of the most desirable supporting materials for metal SACs because of their large specific surface area, variable functionalities, and cost-effectiveness [10,14]. Even though more exotic carbon materials such as carbon nanotubes were commonly used in earlier investigations, biochar has emerged as a potentially more practical and economic support material for SAC synthesis [15,16,17]. We have therefore applied biochar as a novel support of SACs because of its cost-effectiveness and unique nature as a net negative carbon material with desirable properties [14].
Recent work from our laboratory demonstrated that a zinc single-atom catalyst supported on biochar (SAZn@BC) could effectively degrade pharmaceuticals in water under dark conditions without the addition of external oxidants [15]. Notably, light irradiation has been reported to further enhance the catalytic activity of SAC-based systems by modifying their electronic structures [18]. Given the abundance of visible light (VL) in the solar spectrum, this study investigates the synergistic effects of VL irradiation and SAZn@BC on pharmaceutical degradation.
Accordingly, this work aims to elucidate the performance and mechanisms of SAZn@BC for the removal of pharmaceuticals with diverse physicochemical properties, including ibuprofen (IBP), sulfamethoxazole (SMX), trimethoprim (TMP), and carbamazepine (CBZ), which are frequently detected in aquatic environments [19,20,21,22].

2. Materials and Methods

2.1. Materials

Detailed information on the sources and purity of chemicals used in this study is provided in the Supplementary Information. All chemicals were used as received.

2.2. Synthesis of Zn Single-Atom Catalyst on Biochar Support

Oak wood powder was selected as the carbon precursor for preparing the zinc single-atom-anchored biochar (ZnSA@BC). In a typical synthesis, 10.0 g of oak wood powder was dispersed in 150 mL of ultrapure water containing 5.0 g of dicyandiamide and 0.29 g of zinc nitrate. The suspension was heated to 90 °C and stirred at 450 rpm for 1 h to ensure homogeneous impregnation, followed by drying at 85 °C for 24 h. The dried precursor was subsequently subjected to thermal treatment in a box furnace under a continuous nitrogen atmosphere. The temperature was increased at a rate of 5 °C min−1 to 800 °C and maintained for 3 h. After cooling, the obtained material was acid-leached using 200 mL of 2.0 M HCl at 90 °C with stirring at 450 rpm for 2 h to remove unstable species. The resulting solid was recovered by vacuum filtration using a 0.45 µm membrane, thoroughly rinsed with 2.0 L of ultrapure water, and air-dried for 10 h before storage. Using this procedure, SAZn@BC samples with Zn loadings of 0 (BC) and 1.0 wt% were prepared.

2.3. Characterization

The chemical composition and electronic states of the catalyst were characterized by X-ray photoelectron spectroscopy (XPS) using a Phi 560 ESCA/SAM instrument (PerkinElmer, Waltham, MA, USA). Wide-scan spectra were collected over a binding energy range of 0–1200 eV with a step size of 0.2 eV, while high-resolution spectra of the C, N, O, and Zn regions were recorded at 0.1 eV intervals. The catalyst morphology and dispersion of isolated Zn sites were examined by transmission electron microscopy using a Titan Themis 300 S/TEM (Thermo Fisher Scientific, Hillsboro, OR, USA) equipped with a high-angle annular dark-field (HAADF) detector. Elemental distribution maps of C, N, O, and Zn in SAZn@BC were obtained with an integrated Super-X energy-dispersive X-ray spectroscopy (EDS) system. X-ray absorption spectroscopy (XAS) measurements were carried out in continuous scanning mode using a water-cooled, detuned Si(111) double-crystal monochromator. The XAS data were collected at the Advanced Photon Source, Argonne National Laboratory.

2.4. Contaminant Degradation

All experiments were performed in ultrapure water. The initial contaminant concentration was 10.0 μM, and the catalyst loading (SAZn@BC) was 0.2 g/L. Photocatalytic reactions were conducted in 50.0 mL quartz reactors exposed to simulated solar irradiation generated by a 1000 W metal halide lamp (model GLBULBM1000, iPower Inc., Irwindale, CA, USA) positioned approximately 15 cm from the reaction vessels. The emitted light covered the visible range (400–700 nm) with an intensity of 39.8 mW/cm2, corresponding to a photon flux of 1830 μmol·s−1·m−2. Control experiments in the absence of light were carried out in 40.0 mL polypropylene tubes shielded with aluminum foil. All reaction vessels were maintained on an orbital shaker operating at 300 rpm and a constant temperature of 25 ± 0.5 °C. At predetermined time intervals (0, 2, 5, 10, 20, and 30 min), aliquots of 1.0 mL were withdrawn and immediately passed through 0.45 μm syringe filters. The concentrations of target contaminants were quantified using a Dionex UltiMate 3000 high-performance liquid chromatography system (Thermo Fisher Scientific, Sunnyvale, CA, USA). Solution pH values were recorded both before and after the reactions using an Accumet AE150 pH meter (Thermo Fisher Scientific, Waltham, MA, USA).

2.5. Electrochemical Measurement

Electrochemical measurements were carried out using a standard three-electrode configuration connected to a CH Instruments potentiostat to probe direct electron exchange between the contaminants and SAZn@BC. In this setup, a glassy carbon electrode was employed as the working electrode, accompanied by a graphite counter electrode and an Ag/AgCl reference electrode filled with 3.0 M KCl. Open-circuit potential (OCP) responses were tracked after introducing 3.0 mL of contaminant solution (50.0 μM) into suspensions containing SAZn@BC under both illuminated and dark conditions. The catalyst suspensions were prepared by dispersing 15.0 mg of SAZn@BC in 30.0 mL of RO water prior to analysis.

2.6. Quenching

The roles of different reactive species in the degradation of IBP and TMP by the SAZn@BC system were examined under both illuminated and dark conditions using selective scavengers. Methanol (0.5 M), L-histidine (10.0 mM), and superoxide dismutase (50 U·mL−1) were introduced to suppress hydroxyl radicals (•OH), singlet oxygen (1O2), and superoxide radicals (O2•−), respectively.

2.7. Superoxide Radical Detection

The formation of superoxide radicals (O2•−) was confirmed using nitroblue tetrazolium chloride (NBT), a widely used probe that exhibits a characteristic UV–Vis absorption band near 260 nm upon reaction with O2•−. For this assay, 10.0 mg of SAZn@BC was dispersed in 10.0 mL of a 0.5 mM NBT solution and agitated at 300 rpm for 10 h. Experiments were conducted separately under illuminated and dark conditions. After the reaction period, 2.0 mL aliquots were collected, passed through 0.45 μm syringe filters, and subsequently analyzed using a UV–Vis–NIR spectrophotometer (Hitachi High-Tech Corp., Tokyo, Japan).

2.8. Degradation Products of TMP

Trimethoprim (TMP) was employed as a representative compound to elucidate contaminant transformation pathways in the SAZn@BC system. Reaction aliquots collected at 0, 10, and 30 min were analyzed to characterize intermediate and final transformation products. Prior to analysis, TMP byproducts were isolated using solid-phase extraction (SPE). Oasis HLB cartridges (6 cc/200 mg, Waters Corporation, Milford, MA, USA) were sequentially conditioned with 5.0 mL of methanol followed by 5.0 mL of ultrapure water, after which 1.0 mL of each sample was loaded. The cartridges were then subjected to vacuum drying for 5 min, and retained compounds were recovered with 1.0 mL of methanol and collected in 2.0 mL microcentrifuge tubes. Non-target screening of the extracted samples was conducted using liquid chromatography coupled with high-resolution accurate-mass spectrometry (LC-HRAM) on a Q Exactive Plus Orbitrap mass spectrometer (Thermo Fisher Scientific, Waltham, MA, USA) interfaced with an UltiMate 3000 binary HPLC system (Thermo Fisher Scientific, Sunnyvale, CA, USA).

3. Results and Discussion

3.1. Catalyst Characterizations

The formation of single-atom Zn sites is confirmed by the HAADF-TEM images (Figure 1). The bright dots in Figure 1a,b indicate the Zn single-atom sites with a diameter of approximately 2 Å. The Zn single atoms are highlighted by red circles in Figure 1b, and no aggregation is observed. The EDS mapping results (Figure 1 c–f) confirm the uniform distribution of C, N, O, and Zn atoms in the biochar, which implies the formation of C-N-Zn bonds in the biochar matrix.
The Zn single-atom sites were further confirmed by the XAS results. The normalized Zn K-edge X-ray absorption near edge structure (XANES) spectra of SAZn@BC and Zn foil are measured in Figure 1g, which indicates an oxidation state of +2 for Zn in SAZn@BC. The Fourier transformed EXAFS result in Figure 1h indicated that SAZn@BC had a dominant peak at approximately 1.6 Å, which corresponded to the Zn-N bond [23,24,25]. In addition, the coordinate structure of the Zn atom was calculated by Artemis (version 0.9.26) software, and the fitting result (Figure 1i) suggested a Zn-N4 structure with a mean bond length of 2.08 Å. Further attempts to add a Zn-Zn path to the fit failed, confirming that all Zn atoms are in the single-atom form.

3.2. Degradation of TMP by SAZn@BC Catalyst and Quenching Test

The degradation of TMP by BC and SAZn@BC under light irradiation and in the dark confirmed the enhancive role of Zn atoms (Figure 2). The TMP removal, mainly dominated by adsorption in the dark, was improved from 14.8% to 27.9% with the incorporation of 1.0 wt% Zn single atoms. The BET surface area was increased from 313.2 m2/g to 430.4 m2/g after the incorporation of SAZn into the biochar with a similar pore size of 18.88 and 19.02 Å for BC and SAZn@BC, respectively. Thus, the enhanced TMP removal in the dark could be attributed to the increased adsorption resulting from the larger surface area. The removal of TMP was further enhanced from 27.9% to 61.9% for the SAZn@BC with light irradiation. In contrast, the removal of TMP by the VL or BC was less affected by light irradiation. These results clearly demonstrated that the SAZn@BC is photoactive under VL irradiation, and the photoactivity was due to the incorporation of Zn single atoms.
Radical quenching experiments were conducted to elucidate the reactive species responsible for TMP degradation in the SAZn@BC/(VL) system (Figure 2). Upon the addition of methanol (MeOH), a scavenger for hydroxyl radicals (•OH), the TMP removal efficiency decreased from 61.9% to 41.1% within 30 min. This result clearly indicates that •OH participates in the photocatalytic degradation process, consistent with its strong oxidative capability and frequent involvement in photocatalytic reactions [26]. Additionally, the introduction of L-histidine (L-his), a selective quencher for 1O2, led to a reduction in TMP degradation efficiency from 61.9% to 46.3%, confirming the contribution of 1O2, a common reactive species generated in photocatalysis systems [27,28], to TMP degradation in the SAZn@BC/VL system. Furthermore, the addition of superoxide dismutase (SOD), a specific scavenger for O2•−, resulted in the most significant inhibition, with TMP removal declining sharply from 61.9% to 28.8% (Figure 2b). This pronounced suppression demonstrates that O2•− plays a dominant role in the photocatalytic degradation process, and the generation of O2•− was also corroborated by the NBT test under both dark and VL conditions (Figure S1). Although O2•− possesses a relatively lower redox potential compared with other reactive oxygen species [29], it can be protonated under acidic conditions to form hydroperoxyl radicals (•OOH), which subsequently generate H2O2. These secondary reactive species can further participate in oxidative degradation pathways, thereby enhancing TMP removal [30]. Furthermore, the stability of the catalyst was also tested for TMP degradation (Figure S2). The SAZn@BC/VL system was tested for three rounds, and the decline of the catalyst performance was not observed in the system. Thus, the SAZn@BC/VL system was considered to be a sustainable and renewable solution for pharmaceutical removal in water.

3.3. Degradation of Pharmaceuticals by SAZn@BC and Direct Electron Transfer

The removal of the four pharmaceuticals by SAZn@BC under both light and dark conditions is shown in Figure 3a,b. Under dark conditions, the removal efficiencies of TMP, SMX, IBP, and CBZ were 27.9%, 29.0%, 17.5%, and 8.2%, respectively, and were mainly governed by adsorption on the SAZn@BC. CBZ exhibited substantially lower adsorption than the other pharmaceuticals, which can be attributed to its relatively low hydrophobicity, limiting hydrophobic association with the carbonaceous matrix of the catalyst [31]. In addition, its high pKa (13.9) results in predominantly neutral speciation at the experimental pH (5.5), leading to negligible electrostatic interaction with the catalyst surface and further suppressing adsorption [31]. IBP (pKa = 4.3) is mainly deprotonated at pH 5.5 [32], and electrostatic repulsion between negatively charged IBP species and the negatively charged biochar surface weakens its adsorption relative to TMP and SMX. Interestingly, the SAZn@BC/VL system displayed different removal efficiencies for the four pharmaceuticals. The VL irradiation demonstrated little effect on CBZ removal, which is likely due to the high structural stability of CBZ arising from its tricyclic aromatic framework and the absence of highly reactive functional groups [33]. With the VL irradiation, the removal of TMP, SMX, and IBP was enhanced from 27.9% to 61.9%, 29% to 64.4%, and 26.9% to 43.9%, respectively. And the corresponding pseudo-first-order rate constants for CBZ, IBP, SMX, and TMP were 0.27 × 10−2 min−1, 1.70 × 10−2 min−1,3.17 × 10−2 min−1, and 3.04 × 10−2 min−1, respectively. To further evaluate the degradation performance, Table S1 compares the kobs value for SMX and TMP degradation by different photocatalysts under visible light [34,35,36,37,38,39,40,41,42,43]. Results indicated that SAZn@BC exhibited kobs comparable to most reported data, making it a promising VL active catalyst. The mechanisms for removing SMX, TMP, and IBP may behave differently. Adsorption, direct oxidation/reduction via electron transfer between contaminants and oxygen functional groups in biochar, and radical-induced oxidation are possible processes for contaminant removal by the single-atom catalyst [44,45]. It is postulated that the dominant mechanisms for the removal of different contaminants vary for the contaminants, leading to their varied removal efficiency and response to light irradiation. To support the hypothesis, a three-electrode system was used to determine the electron transfer between contaminants and SAZn@BC.
Direct electron transfer between contaminants and single-atom catalysts plays an important role in removing contaminants [46,47,48]. The change in OCPs of the SAZn@BC system after the addition of different pharmaceuticals (IBP, TMP, SMX, and CBZ) in both light and dark conditions reflect the electron transfer in the reaction system [49], As shown in Figure 3c–f, the emergence of the peaks after the addition of pharmaceuticals (highlighted by red arrows) indicated an electron transfer between the SAZn@BC and the added compounds upon the formation of the compound–catalyst complex via adsorption. The Zn-free BC was also tested by the same method, and the results (Figure S3) showed a minor change in the potential with the addition of pharmaceuticals, indicating the critical role of SAZn for this direct electron transfer to take place in such a system. Remarkably, the addition of SMX and TMP led to a signal drop, indicating a direct electron transfer from these contaminants to SAZn@BC, or the direct oxidization of SMX and TMP by the catalyst, while the addition of IBP resulted in a positive signal peak, suggesting a reversed electron transfer or the direct reduction of IBP. This could be related to the different redox potential of the contaminants compared with the SAZn@BC. IBP has a high redox potential (E0 = +1.4 V) and is more oxidizing than the SAZn@BC [50], while SMX (E0 = +1.0 V) [51] and TMP (E0 = +1.1 V) [52] have lesser redox potentials and are more likely to donate electrons to the biochar. The minimal peak observed in the CBZ OCP (Figure 3f) indicated low electron transfer between SAZn@BC and CBZ. This behavior is mainly attributed to the weak adsorption of CBZ on the catalyst surface, which limits the formation of CBZ–catalyst complexes required for direct electron-transfer pathways. The light irradiation resulted in increased peak intensity for all of the other three compounds involved in direct electron transfer with SAZn@BC, suggesting that light irradiation could enhance the direct electron transfer.

3.4. The Role of Oxygen Functional Groups

XPS spectra of the catalyst before and after reaction with TMP in both dark and light conditions were obtained (Figure 4). Hydroquinone, as an electron donor, was one of the most common oxygen functional groups in biochar, which could form quinones by losing electrons to generate radicals and reduce contaminants [14]. Figure 4a shows the O 1s spectra of the catalyst, and the peaks at 531.2 eV and 533.2 eV correspond to the C=O and C-O bonds, respectively [53]. After the reaction with TMP, the peak intensity of C=O increased, while the peak intensity of C-O decreased in both dark and light conditions, indicating the transformation of hydroquinone moieties to the quinone moieties, and the donated electrons could be transported to the dissolved oxygen to form O2•− mediated by the conductive single-atom sites [15]. A similar conclusion could be drawn from Figure 4b that the C 1s spectra showed an increase in the C=O peak intensity at 288.2 eV and a decrease in the C-O peak intensity at 286.0 eV under both dark and light conditions.
In the IBP/SAZn@BC system, a similar electron transfer can happen from hydroquinone to the Zn-N4 site and then to the IBP, reducing IBP via direct electron transfer. The reaction could also happen in the opposite direction via the direct electron transfer from SMX and TMP to the catalyst, supported by the three-electron system. The quinone moieties could serve as electron acceptors and Zn-N4 sites as conductive bridges. These reactions happened in both dark and light systems, and with light irradiation, the g-C3N4 moieties in the biochar can further generate electrons and positive holes [54]. The photo-generated electrons could be transferred via the Zn-N4 sites to contaminants adsorbed on the SAZn@BC, while the positive holes could lead to the generation of radicals [55].

3.5. TMP Degradation Products

Untargeted analysis was carried out to study the possible degradation pathways of the TMP degradation in SAZn@BC/VL systems. As shown in Figure 5, the hydroxylation of TMP resulted in the production of 2,6-diamino-5-(hydroxy(3,4,5-trimethoxyphenyl)methyl)pyrimidin-4(3H)-one (m/z = 323) and 2,4-diamino-5-(3,4,5-trimethoxybenzyl)-4,5-dihydropyrimidin-5-ol (m/z = 309), which could be attributed to the attraction of •OH to the TMP [56]. The oxidization of TMP by 1O2 and O2•− leads to the generation of (2,4-diaminopyrimidin-5-yl)(3,4,5-trimethoxyphenyl)methanone (m/z = 305) and the following bond cleavage, or the direct bond cleavage of TMP by the racials can generate 2,4-diaminopyrimidine-5-carbaldehyde (m/z = 139) and 2,6-dimethoxybenzene-1,4-diol (m/z = 171) [57]. All detected transformation products, and the proposed degradation pathways were consistent with those reported in previous studies [58,59,60], and no intermediates commonly associated with high acute toxicity were identified in the untargeted analysis, suggesting that the overall toxicity of TMP could be reduced after degradation. The MS1 and MS2 spectra of TMP degradation metabolites were included in Figure S4.

4. Conclusions

Photoactive SAZn@BC was successfully synthesized via the pyrolysis of wood powder, dicyandiamide, and zinc nitride. Structural characterization confirmed the formation of atomically dispersed Zn sites, with a Zn–N4 coordination environment identified by HAADF-STEM and XAS. Under VL irradiation, SAZn@BC exhibited high degradation efficiencies of 43.9%, 64.4%, and 61.9% for IBP, SMX, and TMP, respectively, whereas CBZ showed relatively low removal. Reactive species trapping experiments revealed that •OH, 1O2, and O2•− were the primary reactive species responsible for pharmaceutical degradation under VL irradiation. SAZn@BC demonstrated strong catalytic activity toward a range of pharmaceuticals; however, the dominant removal mechanisms were highly compound-dependent, reflecting differences in molecular structure and redox properties. In addition to radical-mediated oxidation, the atomically dispersed Zn sites facilitated a non-radical degradation pathway by mediating direct electron transfer between oxygen-containing functional groups on the biochar surface and the target contaminants. This mechanism was supported by X-ray photoelectron spectroscopy (XPS) analysis and three-electrode electrochemical measurements. Visible-light irradiation could further enhance the catalytic performance by promoting interfacial electron transfer and inducing the generation of reactive oxygen species. Overall, these results demonstrate that SAZn@BC is a promising and sustainable single-atom photocatalyst for the efficient removal of organic contaminants from aquatic environments.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/w18030313/s1, Figure S1: Detection of superoxide radical in SAZn@BC system under dark and light conditions; Figure S2: The SAZn@BC recycle test for TMP degradation; Figure S3: OCP measurements of Zn-free BC system in light condition with the addition of IBP, TMP, SMX, and CBZ; Figure S4: MS1 and MS2 spectra of possible TMP degradation metabolites; Table S1: SXM and TMP removal by different photocatalysts under visible light.

Author Contributions

Conceptualization, Z.Z. and C.L.; methodology, J.Y.; investigation, J.Y., Z.H., and W.Y.; resources, C.L.; data curation, Z.Z. and C.L.; writing—original draft preparation, Z.Z.; J.Y., Z.H., C.W., and W.Y.; writing—review and editing, C.W., J.Y., and W.Y.; supervision, J.Y. and C.L.; project administration, J.Y.; funding acquisition, J.Y. All authors have read and agreed to the published version of the manuscript.

Funding

This work was sponsored by the National Natural Science Foundation of China (Project No. 52442006), Science and Technology Commission of Shanghai Municipality (Project No. 24DZ2306400), and the Guangxi Key Research and Development Program (2025FN9610713).

Data Availability Statement

The original contributions presented in this study are included in the article/Supplementary Material. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

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Water 18 00313 g001
Figure 1. (a,b) HAADF-TEM images of SAZn@BC at resolutions of 5 nm and 2 nm. (c–f) EDS mapping images of SAZn@BC for C, N, O, and Zn, respectively. (g) Normalized Zn K-edge XANES spectrum of Zn foil and SAZn@BC. (h) Fourier transformed EXAFS of SAZn@BC and Zn foil. (i) EXAFS fitting with a Zn-N4 structure.
Figure 1. (a,b) HAADF-TEM images of SAZn@BC at resolutions of 5 nm and 2 nm. (c–f) EDS mapping images of SAZn@BC for C, N, O, and Zn, respectively. (g) Normalized Zn K-edge XANES spectrum of Zn foil and SAZn@BC. (h) Fourier transformed EXAFS of SAZn@BC and Zn foil. (i) EXAFS fitting with a Zn-N4 structure.
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Figure 2. (a) The degradation efficiency of TMP by BC and Zn SAZn@BC. (b) The degradation of TMP by SAZn@BC with different quenchers. Reaction conditions: [TMP0] = 10.0 μM, [Catalyst] = 0.2 g/L, pH = 5.5, T = 25.0 °C.
Figure 2. (a) The degradation efficiency of TMP by BC and Zn SAZn@BC. (b) The degradation of TMP by SAZn@BC with different quenchers. Reaction conditions: [TMP0] = 10.0 μM, [Catalyst] = 0.2 g/L, pH = 5.5, T = 25.0 °C.
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Figure 3. Degradation of pharmaceuticals by SAZn@BC under dark (a) and visible light (b) conditions. OCP measurements of the SAZn@BC system in both dark and light conditions with the addition of (c) IBP, (d) SMX, (e) TMP, and (f) CBZ.
Figure 3. Degradation of pharmaceuticals by SAZn@BC under dark (a) and visible light (b) conditions. OCP measurements of the SAZn@BC system in both dark and light conditions with the addition of (c) IBP, (d) SMX, (e) TMP, and (f) CBZ.
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Figure 4. Deconvoluted XPS spectra showing the (a) O1s spectra and (b) C1s spectra of SAZn@BC before and after reaction with TMP in the dark and light, respectively.
Figure 4. Deconvoluted XPS spectra showing the (a) O1s spectra and (b) C1s spectra of SAZn@BC before and after reaction with TMP in the dark and light, respectively.
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Figure 5. Plausible degradation metabolites and proposed degradation pathways of TMP by the SAZn@BC system.
Figure 5. Plausible degradation metabolites and proposed degradation pathways of TMP by the SAZn@BC system.
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MDPI and ACS Style

Zhang, Z.; Li, C.; Yuan, J.; He, Z.; Wu, C.; Yang, W. Visible Light Modulating Abatement of Pharmaceuticals in Water by Zinc Single-Atom Catalyst on Biochar Support. Water 2026, 18, 313. https://doi.org/10.3390/w18030313

AMA Style

Zhang Z, Li C, Yuan J, He Z, Wu C, Yang W. Visible Light Modulating Abatement of Pharmaceuticals in Water by Zinc Single-Atom Catalyst on Biochar Support. Water. 2026; 18(3):313. https://doi.org/10.3390/w18030313

Chicago/Turabian Style

Zhang, Zhiyuan, Cong Li, Jieming Yuan, Zhengming He, Chengzhang Wu, and Wanning Yang. 2026. "Visible Light Modulating Abatement of Pharmaceuticals in Water by Zinc Single-Atom Catalyst on Biochar Support" Water 18, no. 3: 313. https://doi.org/10.3390/w18030313

APA Style

Zhang, Z., Li, C., Yuan, J., He, Z., Wu, C., & Yang, W. (2026). Visible Light Modulating Abatement of Pharmaceuticals in Water by Zinc Single-Atom Catalyst on Biochar Support. Water, 18(3), 313. https://doi.org/10.3390/w18030313

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