Biocarbon based organic photocatalytic composite material achieves efficient removal of tetracycline hydrochloride under visible light

Biocarbon based organic photocatalytic composite material achieves efficient removal of tetracycline hydrochloride under visible light | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 12 March 2025 V1 Latest version Share on Biocarbon based organic photocatalytic composite material achieves efficient removal of tetracycline hydrochloride under visible light Authors : Fengping Yang , Dengsheng Zheng , Libin Zhang , Jiamin Yuan , Liliang Wang , Min Long , Yanzhen Yin , Ke Sun , Cong Liu , Hongxiang Zhu , and Tao Liu 0000-0001-6017-0827 [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.174180272.23906813/v1 194 views 172 downloads Contents Abstract Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract The emergence of antibiotic-resistant superbugs has heightened concerns about environmental pollutants such as tetracycline hydrochloride, necessitating effective removal strategies. Among various treatment approaches, photocatalysis has demonstrated particular promise. In this study, we present a groundbreaking advancement in photocatalytic technology through the development of a novel material that combines superior adsorption capabilities with enhanced photocatalytic properties. The innovation lies in our pioneering implementation of a third-component doping strategy, which enabled the construction of an organic semiconductor intrinsic heterojunction photocatalytic layer with an A-D-A structure, integrated onto a natural biomass carbon substrate. This strategic integration creates a synergistic system wherein the natural biomass carbon component rapidly concentrates pollutants, while the organic semiconductor bulk heterojunction photocatalytic layer generates electrons and free radicals for degradation. The material’s exceptional performance is evidenced by its ability to completely degrade 20 mg/L of tetracycline hydrochloride within 30 minutes, establishing a new benchmark in treatment efficiency. Through density-functional theory (DFT) analysis, we have elucidated the underlying degradation mechanism, providing theoretical insights that may facilitate the development of advanced treatment solutions for a broader spectrum of organic pollutants through adsorption photocatalysis. Biocarbon based organic photocatalytic composite material achieves efficient removal of tetracycline hydrochloride under visible light Fengping Yang, [a] [d] [e] Dengsheng Zheng, [a] [e] Libin Zhang,* [a] [e] Jiamin Yuan, [a] Liliang Wang, [a] Min Long, [a] Yanzhen Yin*, [b] Ke Sun, [c] Cong Liu,* [a] Hongxiang Zhu, [a] Tao Liu,* [a] [c] [a] F. Yang, D. Zheng, L. Zhang, J. Yuan, L. Wang, M. Long, Prof. C. Liu, Prof. H. Zhu, Prof. T. Liu School of Resources, Environments and Materials, Department Guangxi Key Laboratory of Clean Pulp & Papermaking and Pollution Control；School of Light Industry and Food Engineering; School of Chemistry and Chemical Engineering, Guangxi University, Nanning 530004, China. E-mail: [email protected] [b] Prof. Y. Yin Guangxi Key Laboratory of Green Chemical Materials and Safety Technology，Beibu Gulf University, Beibu Gulf 530201, China. E-mail: [email protected] [c] c. Prof. K. Sun, Prof. T. Liu Department of Biochemistry and Cell Biology, Youjiang Medical University for Nationalities, Baise City 533000, China. E-mail: [email protected] [d] F. Yang School of Environment and Energy, South China University of Technology, Guangzhou 510006, China. [e] These authors contributed equally. Abstract The emergence of antibiotic-resistant superbugs has heightened concerns about environmental pollutants such as tetracycline hydrochloride, necessitating effective removal strategies. Among various treatment approaches, photocatalysis has demonstrated particular promise. In this study, we present a groundbreaking advancement in photocatalytic technology through the development of a novel material that combines superior adsorption capabilities with enhanced photocatalytic properties. The innovation lies in our pioneering implementation of a third-component doping strategy, which enabled the construction of an organic semiconductor intrinsic heterojunction photocatalytic layer with an A-D-A structure, integrated onto a natural biomass carbon substrate. This strategic integration creates a synergistic system wherein the natural biomass carbon component rapidly concentrates pollutants, while the organic semiconductor bulk heterojunction photocatalytic layer generates electrons and free radicals for degradation. The material’s exceptional performance is evidenced by its ability to completely degrade 20 mg/L of tetracycline hydrochloride within 30 minutes, establishing a new benchmark in treatment efficiency. Through density-functional theory (DFT) analysis, we have elucidated the underlying degradation mechanism, providing theoretical insights that may facilitate the development of advanced treatment solutions for a broader spectrum of organic pollutants through adsorption photocatalysis. Key words: organic photocatalysis, photodegradation, wastewater treatment, tetracycline hydrochloride Introduction Tetracycline hydrochloride (TC), a broad-spectrum antibiotic, is extensively employed in both human and veterinary medicine for therapeutic and prophylactic purposes. [1,2] Despite its widespread application, studies indicate that only a minor portion of TC undergoes absorption and metabolic processes, with the majority being eliminated through excretory pathways in feces and urine. [3] The combination of TC’s high water solubility and chemical stability enables its persistence in aquatic ecosystems, subsequently presenting significant risks to human health and facilitating the development of antibiotic-resistant bacterial strains. [4] While conventional treatment approaches, including precipitation, [5] biodegradation, [6] and advanced oxidation processes, [7] have been implemented to address TC contamination, these methods are frequently hampered by their substantial energy requirements, inefficient removal kinetics, and potential generation of secondary pollutants. In response to these limitations, photocatalysis has emerged as a particularly promising remediation strategy, offering distinct advantages such as direct solar energy utilization, environmental compatibility, cost-effectiveness, high degradation efficiency, and long-term sustainability. [8] Inorganic semiconductor heterojunctions, including those based on co-doped TiO 2 , [9] Bi-based, [10-12] ZnO-based, [13,14] and g-C 3 N 4 -based, [15,16] have demonstrated effectiveness in removing organic pollutants. Nevertheless, these conventional inorganic photocatalysts exhibit several limitations when treating industrial wastewaters containing complex organic compounds such as TC. These limitations include restricted absorption ranges, low photogenerated electron-hole separation efficiency, poor regulatory flexibility, inadequate recyclability, and confinement to ultraviolet irradiation. In contrast, organic semiconductor materials offer distinct advantages, as their photoexcitation generates more active polarizers and solitons, resulting in enhanced production of electrons (e - ) and holes (h + ) compared to inorganic alternatives. Additionally, these materials demonstrate superior electrical conductivity, leading to more efficient photocatalytic reaction activity. [17] Nevertheless, single photocatalyst systems face challenges due to the rapid recombination or trapping of electron-hole pairs, making it difficult to achieve both strong redox capacity and broad spectral absorption simultaneously. [18] While the development of semiconductor heterojunction photocatalysts has emerged as a promising strategy to enhance photocatalytic activity, conventional materials still struggle with slow photocatalytic degradation rates due to the localized concentration of photogenerated free radicals and electrons on the photocatalyst surface. [19, 20] Consequently, the development of efficient organic semiconductor photocatalysts with rapid enrichment capabilities remains crucial for effective TC-contaminated wastewater purification. In this study, we have engineered an innovative material that synergistically integrates superior adsorption capabilities with enhanced photocatalytic properties. The material’s architecture consists of an organic semiconductor intrinsic heterojunction photocatalytic layer, structured as an Acceptor-Donor-Acceptor (A-D-A) configuration, which was successfully synthesized on a natural biomass carbon substrate through a strategic third-component doping approach. This design effectively addresses several inherent limitations commonly associated with inorganic photocatalysts, including their rigid regulation mechanisms, limited reusability, and restricted absorption ranges, while simultaneously mitigating the stability issues and susceptibility to water and oxygen degradation typically observed in solar cells. The natural biomass carbon substrate serves as an efficient pollutant concentrator, facilitating rapid accumulation of target compounds at reaction sites. This concentrated positioning enables optimal interaction between the pollutants and the photogenerated electrons and free radicals produced by the organic semiconductor heterojunction photocatalytic layer, thereby accelerating the redox degradation processes. The material’s exceptional performance is evidenced by its ability to achieve complete degradation of tetracycline hydrochloride (20 mg/L) within 30 minutes, representing unprecedented efficiency in the field. Notably, the catalyst demonstrated remarkable stability, with degradation efficiency varying by merely 7% across twenty consecutive experimental cycles. To elucidate the underlying mechanisms, Density Functional Theory (DFT) simulations were employed to model the tetracycline hydrochloride degradation pathway, establishing a theoretical framework that can be extended to predict and optimize the adsorption photocatalytic degradation of other organic pollutants. Materials and methods Materials Biochar was purchased from Guangye Sugar Group Co. Tetracycline hydrochloride (TC), trichloromethane (CHCl 3 ), sodium carbonate, benzoquinone (BQ), isopropanol (IPA), dimethyl-1-pyrroline-N-oxide (DMPO), methanol and 2,2,6,6-tetramethylpiperidin-1-yloxy (TEMPO) used in this study were purchased from Aladdin. Organic semiconductor materials PM6 and PPCBM were purchased ONE material. MeIc were purchased Ossila. Since every material utilized in this experiment was of analytical grade, no additional purification was necessary. Preparation of materials We utilized the heterojunction active layer of organic solar cells with natural biomass biochar after mixing, bonding construction, and drying and drying to obtain organic semiconductor photocatalytic materials with A-D-A structure labeled as C-PM6:PPCBM, C-PM6:MeIc and C-PM6:PPCBM:MeIc, respectively (Figure S1). Photocatalytic degradation experiment In this paper, Visible light in the wavelength range of 420-780 nm was simulated using a 300 W xenon lamp (CEL-LB70, Beijing China Education Au-lIght Co., Ltd, China), the degradation of tetracycline hydrochloride (TC) was used to measure the photocatalytic activity. At room temperature, 50 mg of C-PM6:PPCBM, C-PM6:MeIc, and C-PM6:MeIc:PPCBM photocatalysts were placed into each 50 ml of TC solution (20 mg/L), and the samples (5 mL) were collected periodically and filtered through a filter membrane (0.22 µm, PES), and measure its concentration using UV. The recirculation experiment consists of filtering and drying the used catalyst and then repeating the above experimental steps. Trapping experiments: In order to trap the reactive species •O 2 - , h + , and •OH, benzoquinone (BQ), sodium carbonate, and isopropanol (IPA) were employed as trapping agents. The experimental procedures were identical to those used in the aforementioned photocatalytic degradation experiments, with the exception of the trapping agents. Analysis and calculation The TC concentration was measured at 357 nm using a UV-visible spectrophotometer (UV-2600i, Shimadzu, China). Equation (1) was used to compute the tetracycline hydrochloride elimination efficiency (η), where C 0 represents the starting concentration and C represents the concentration at the time of sampling. \(\eta=(1-C/C_{0})\times 100\%\) (1) The intermediates in the degradation process of TC were analysed by liquid mass spectrometer (HPLC-MS) (Agilent Technologies Inc, USA). Ecotoxicity assessment of TC and its degradation intermediates was carried out using the toxicity assessment software version 2.2 (ECOSAR 2.2 software version). Characterizations Sample morphology was observed by transmission electron microscopy (TEM, JEOL, JEM-2100F) and scanning electron microscopy (SEM, Thermo Fisher Scientific, Helios G4 CX). The thickness of the photocatalysts was measured on an atomic force microscope (AFM, Bruker Dimension Edge). The Brunauer-Emmett-Teller (BET) specific surface area was studied on a Micromeritics ASAP 2460 analyser. Ultraviolet-visible (UV-2700, Shimadzu) absorption spectra were recorded by a UV-Vis spectrometer (Lambda 950) equipped with an integrating sphere accessory in diffuse reflection mode (R). BaSO 4 served as the standard material. Photoluminescence spectra (PL) and time-resolved photoluminescence spectra (TRPL) were recorded on a confocal Raman imaging system (WITec alpha 300R). Electron spin resonance (ESR) spectra of holes and radicals were analysed on a Bruker EMX PLUS. The chemical composition was determined using X-ray photoelectron spectroscopy (XPS, ThermoFisher). The PL-SPV/IPCE1000 steady-state surface photovoltage spectrometer (Beijing Perfectlight Technology Co.,Ltd, China) was utilized for the measurement of surface photovoltage (SPV) in organic semiconductor materials. A CHI600E series electrochemical workstation (Shanghai Chenhua Instrument Co., Ltd., China) equipped with a three-electrode setup was used to measure the photoelectrochemical characteristics. Ag/AgCl and Pt were utilized as the reference and counter electrodes, respectively, while ITO glass coated with photocatalyst was created and used as the working electrode. In a 0.5 mol/L Na 2 SO 4 solution, electrochemical impedance spectra (EIS) were acquired. On a CHI660E series electrochemical workstation, a visible light source (Xe lamp, λ>420 nm, 300 W) was used to evaluate the transient photocurrent response (i-t) in Na 2 SO 4 solution. Results and Discussion Physical-chemical properties of the material The chemical structural formulae of PM6, PPCBM and MeIc are shown in Figure 1 a. While PPCBM is a polymeric fullerene derivative acceptor with octyloxybenzene embedding, PM6 is a polymer donor based on fluorothiophene-substituted benzodithiophene. MeIc is a novel non-fullerene acceptor with a methyl-embedded thiophene end group. In the visible spectrum, C-PM6:PPCBM, C-PM6:MeIc, and C-PM6:PPCBM:MeIc all showed significant absorption between 450 and 750 nm, as seen in Figure 1b. The maximum absorption wavelengths in the visible range for C-PM6:PPCBM, C-PM6:MeIc and C-PM6:PPCBM:MeIc were 519 nm, 526 nm and 584 nm. The greater absorption of visible light by C-PM6:PPCBM:MeIc in comparison to C-PM6:PPCBM and C-PM6:MeIc indicates that the photocatalytic activity of the ternary system can be enhanced by absorbing a greater quantity of visible light. Figure 1c shows the C-PM6:PPCBM:MeIc energy level diagram. the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels of PM6 are -5.50 and -3.61 eV, respectively. the HOMO/LUMO energy levels of MeIc and PPCBM are -5.57/-3.92 and -5.53/-3.74 eV, respectively. Moreover, the highest occupied molecular orbital (HOMO) energy level of PPCBM (-5.53 eV) is also between that of PM6 (-5.50 eV) and MeIc (-5.57 eV), and the staggered LUMO and HOMO positions of the three organic semiconductors are in accordance with the matched band structure of type II heterojunction photocatalysts. [20] The formation of this structure facilitates the transport of electrons and holes. Figure 1. (a) Chemical structures of PM6 and PPCBM and MeIc, (b) The UV–vis DRS of organic semiconductor photocatalyst, (c) Energy diagrams of PM6 and PPCBM and MeIc. XPS was used to analyze the material’s surface elements’ valence states and chemical makeup. Figure 2 a-c and Figure S2 shows the whole spectrum of the C-PM6:PPCBM:MeIc composite as well as the high-resolution spectra of each element. As can be seen in Figure 2a, the full spectrum of biochar has C, N, and O diffraction peaks, while the full spectrum of C-PM6:PPCBM:MeIc has C, N, O, S, and F diffraction peaks. These bonds are identified as C-F, C=O, C-O, C=C, C-S and C-C by the peaks in the C 1s and O 1s spectra (Figure S2(a, b)); C-S and C-F are identified as peaks in the S 2p and F 1s spectra, respectively, at 162.22 eV and 688.80 eV (Figure 2(b, c)). C-N is identified as peaks in the N 1s spectra at 399.14 eV (Figure S2c). These findings unequivocally show that C-PM6:PPCBM:MeIc was successfully loaded onto biochar. As can be seen from the SEM image (Figure 2d), the rough and porous surface of the biochar is favourable for the loading of the material. The SEM of the materials loaded on biochar (Figure 2e-h and Figure S3 ) showed that the surface of biochar was covered by a thin film, indicating that the photocatalytic materials were uniformly loaded on biochar without affecting its adsorption performance. As shown in Figure 2g, TiO 2 aggregation occurred on the surface after loading on the biochar, and the surface area of the photocatalytic functional layer decreased dramatically, which seriously affected the adsorption performance. The specific surface area and porous structure of the biochar-loaded C-PM6:PPCBM:MeIc catalysts were analysed using the N 2 adsorption-desorption isotherm method. As shown in Figure 2f-j, the N 2 adsorption-desorption isotherms before and after loading of materials on the biochar base showed a typical type IV isotherm, which is a typical H3-type hysteresis loop adsorption isotherm, demonstrating that the sample contains mesopores. [21] Before and after loading the material, the pore area of the biochar changed very little, indicating that loading the material on the biochar hardly affects its pore area, so the biochar base still has a strong adsorption capacity. The BET analysis results indicate that following the loading of materials onto the biochar, there was an increase in the specific surface area and no change in the adsorption capacity. This resulted in an improvement in the degradation of organic pollutants by the catalyst. Figure S4 a-d illustrates the surface morphology of the binary and ternary blended films, as observed by atomic force microscopy (AFM). In the AFM height images, the root-mean-square (RMS) surface roughness of C-PM6:MeIc and C-PM6:PPCBM:MeIc were 1.06 nm and 1.64 nm, respectively. The high crystallinity of PPCBM is the cause of the surface roughness of C-PM6:PPCBM:MeIc. [22] The TEMs of the three photocatalytic materials are shown in Figure S4e-g. By comparison, C-PM6:PPCBM:MeIc formed a heterojunction, which led to a better power transfer mechanism; moreover, the doping of the third component made the surface morphology of C-PM6:PPCBM:MeIc more ordered. In conclusion, mixing PM6 with PPCBM and MeIc increases the specific surface area of the material, the ternary surface is more ordered than the binary surface, and the dissociation of excited electrons at the donor-acceptor interface is enhanced, resulting in superior photocatalytic performance of the hybrid material. Figure 2. (a) xps spectra of C-PM6:PPCBM:MeIc and biochar, high resolution spectrum of (b) S 2p and (c) F 1s, sem of (d) Biochar, (e) C-PM6:PPCBM, (f) Nitrogen adsorption-desorption isotherms of the as-prepared samples, sem of (g) TiO 2 , (h) C-PM6:PPCBM:MeIc, (j) the corresponding pore diameter. Performance of photocatalytic degradation of tetracycline hydrochloride Figure 3 a-c show the effects of pollutant concentration, photocatalyst dosage, and pH on the TC removal rate. As shown in Figure 3a, the removal rate could reach more than 98% when the initial mass concentration of TC solution was 10 mg/L and 20 mg/L, respectively. However, when the concentration exceeded 20 mg/L, the catalyst’s capacity for degradation exhibited a progressive decline. This decline could be attributed to the high number of adsorbed pollutant molecules on the surface of the catalyst and the •OH dispersed in the water, which degraded the catalyst and inhibited the interactions with the free radicals generated from the internal active sites. [23] The overall removal of TC increased when the amount of C-PM6:PPCBM:MeIc was increased from 10 mg to 200 mg (Figure 3b), which may be due to the increase in irradiated area and catalyst contact area. [24] As shown in Figure 3c, the reaction system was significantly inhibited under strong acidic and alkaline conditions, which could be attributed to the fact that the materials were easily decomposed under strong acidic conditions, whereas the excessively high pH generated a weak electrostatic interaction between the pollutants and the photocatalysts, which affected the pollutants’ adsorption on the photocatalysts’ surface and significantly reduced their ability to oxidize capacity. [25,26] Figure 3d shows the curves of tetracycline hydrochloride concentration with time for different photocatalytic materials. Based on the consideration of cost and photocatalytic effect, the photocatalytic materials of 20 mg/L TC and 50 mg were used in this paper. As can be seen from the figure, under visible light irradiation, all photocatalytic materials produce holes and reactive oxide species that react with tetracycline hydrochloride, leading to photocatalytic oxidation and degradation of tetracycline hydrochloride. Among them, the degradation efficiencies of C-PM6:PPCBM, C-PM6:MeIc and C-PM6:PPCBM:MeIc for tetracycline hydrochloride were 98.3%, 96% and 98.5%, respectively.The highest degradation rate of tetracycline hydrochloride was achieved by C-PM6:PPCBM:MeIc in 30 min of light exposure. Three possible reasons for the improved removal of tetracycline hydrochloride using C-PM6:PPCBM:MeIc material are (i) the introduction of the third component improves the light absorption energy; (ii) the incorporation of the third component allows the material to maintain good crystallinity, grain size, and surface orientation, which is conducive to the maintenance of good charge transport properties; [21] and (iii) C-PM6:PPCBM:MeIc combining the morphological advantages of these three materials to form form an interpenetrating network structure. Reusability is an important factor in the practical application of catalysts. Therefore, twenty rounds of replicated experiments were conducted using C-PM6:PPCBM:MeIc catalysts under the same operating conditions to investigate the reusability efficiency of the catalysts. After each round of experiments, the spent catalyst was recovered by filtration, washing and drying, and then used in the next round of experiments. As shown in Figure 3e, the degradation of TC was maintained in the range of 91% to 96% after 20 cycles of operation, indicating that the synthesised C-PM6:PPCBM:MeIc catalyst was very stable and could be reused for the photocatalytic removal of TC. As shown in Figure 3f and Table S1 , in comparison with other literature, the present work showed high removal rate and short time. Therefore, the C-PM6:PPCBM:MeIc catalyst has a potential applications. Figure 3 .(a) Photocatalytic performance of TC degradation at different initial concentrations of TC, catalyst dosage (b), pH (c), (d) TC removal by different materials at [TC] = 20 mg/L; [catalyst] = 50 mg; pH = 7], (e) Twenty cycling of C-PM6:PPCBM:MeIc photodegradation of TC, (f) Degradation rates compared to other literature. One crucial parameter that can be assessed using PL spectroscopy, time-resolved photoluminescence spectroscopy (TRPL), transient photocurrent response, EIS spectroscopy, and surface photovoltaic (SPV) is the division and relocation efficiency of photogenerated charges in photocatalytic compounds. [27-29] As shown in Figure 4 a, C-PM6:PPCBM has strong emission at 788 nm, while C-PM6:MeIc and C-PM6:PPCBM:MeIc exhibit strong emission at 771 nm and 735 nm, respectively. The C-PM6:PPCBM:MeIc material exhibits a lower PL emission intensity compared to both C-PM6:MeIc and C-PM6:PPCBM. Based on this, it appears that C-PM6:PPCBM:MeIc can efficiently block light-induced electron-hole pair complexation and promote photogenerated charge transfer. [15] Figure 4b illustrates that the lifetimes of C-PM6:PPCBM, C-PM6:MeIc, and C-PM6:PPCBM:MeIc are 0.28, 0.32, and 0.34 ns, respectively. The lifetime of C-PM6:PPCBM:MeIc is greater than that of C-PM6:PPCBM and C-PM6:MeIc, demonstrating that the C-PM6:PPCBM:MeIc material favors electron hole pair separation. [30] EIS spectra (Figure 4c) were used to develop explore the photogenerated separation of carriers and transfer behaviour.C-PM6:PPCBM:MeIc showed the smallest charge transfer resistance, suggesting a higher charge carrier separation and transfer capability. [31,32] As shown in Figure S5 , C-PM6:PPCBM:MeIc has the highest surface photovoltage and C-PM6:PPCBM has the lowest, indicating that C-PM6:PPCBM:MeIc has the highest photogenerated carrier separation efficiency and reacts more readily with TC. [29] The transient photographic current responses of C-PM6:PPCBM, C-PM6:MeIc, and C-PM6:PPCBM:MeIc material recorded are shown in Figure 4d. Noticeably, the current density of C-PM6:PPCBM:MeIc is stronger compared to that of C-PM6:PPCBM and C-PM6:MeIc, which suggests that C-PM6:PPCBM:MeIc has a higher carrier separation efficiency. [33] The results of this investigation are in agreement with the results of the UV-Vis diffuse reflectance spectroscopy. Figure 4. (a) Photoluminescence (PL) spectra, (b)TRPL spectra of C-PM6:MeIc, C-PM6:PPCBM and C-PM6:PPCBM:MeIc, (c) EIS Nyquist plots C-PM6:MeIc, C-PM6:PPCBM and C-PM6:PPCBM:MeIc, and (d) transient photocurrent responses spectra. Possible degradation mechanisms We investigated the main active ingredients for C-PM6:PPCBM:MeIc pollution remediation by free radical trapping research and ESR testing. Sodium carbonate, BQ, and IPA were introduced as trapping agents for holes (h + ), superoxide radicals (•O 2 - ), and hydroxyl radicals (•OH) in the free radical trapping tests. Following the addition of IPA, the degradation rate of TC reduced from 98.5% to 55.2%, as seen in Figure 5 a. The rate at which TC degraded dropped from 98.5% to 75.3% when sodium carbonate was present. When BQ was added, the rate of TC degradation dropped from 98.5% to 86.4%. According to the aforementioned data, h + , •OH, and •O 2 - all participated in the photocatalytic reaction, but •OH was crucial to the process. Figure 5. (a) Effects on TC over C-PM6:PPCBM:MeIc with different scavengers, The ESR spectra of (b) •O 2 - and (c) •OH and (d) h + . The active substances in the photocatalytic reaction were further determined by electron spin resonance (ESR) method. Dimethyl-1-pyrroline-N-oxide (DMPO) was used as a trapping agent to determine •O 2 - in methanol solution and •OH in aqueous solution. 2,2,6,6-tetramethylpiperidine-1-yloxy (TEMPO) was used to trap h + in aqueous solution. As shown in Figure 5b, C-PM6:PPCBM:MeIc has a strong •O 2 - signal, which suggests that the photogenerated electrons in C-PM6:PPCBM:MeIc have adequate reducing power to reduce O 2 to •O 2 - . [34] This adsorption process is described in Text S1 . As shown in Figure 5c-d, four typical signals of DMPO-OH and three typical signals of TEMPO-h + were observed, respectively, which further confirmed the results of the free radical trapping experiments. This suggests that both hole and superoxide radicals are involved in the oxidation of organic pollutants during the photocatalytic degradation of TC at high concentrations. Based on the above, Figure 6 illustrates the reaction mechanism of C-PM6:PPCBM:MeIc photocatalytic degradation of TC. The C-PM6:PPCBM:MeIc hetero junction conforms to the structure of type II, as shown by Figure 1c. When light energy from a light source is absorbed by the C-PM6:PPCBM:MeIc photocatalyst, PM6, PPCBM, and MeIc produce electrons along with holes. Following the formation of the type II heterojunction, the Fermi energy level equilibrium causes the three semiconductors’ energy band positions to reorganize. Specifically, photogenerated electrons in PM6 are moved to the E LUMO of PPCBM, photogenerated electrons in PPCBM are moved to the E LUMO of MeIc, and photogenerated electrons in the E HOMO of MeIc turn into holes that are administered into the E HOMO of PPCBM, and the E HOMO of PPCBM of photogenerated electrons into holes were injected into the E HOMO of PM6. [35,36] Furthermore, as demonstrated by the photocatalysts’ ESR assay (Figure 5b-d), the materials generated h + , •O 2 - , and • OH when exposed to xenon light. The findings demonstrated that e and O 2 contributed to the production of •O 2 - , and h + and H 2 O to the production of •OH, all of which were involved in the degradation of TC. In summary, the donor polymer PM6 was combined with the fullerene derivative receptor PPCBM and the non-fullerene receptor MeIc to create the novel type II heterojunction photocatalyst C-PM6:PPCBM:MeIc. This combination not only greatly improved the light-harvesting ability of the material, but also greatly accelerated the carriers’ separation efficiency, which in turn effectively enhanced the material’s ability to degrade TC. Figure 6. Plausible mechanism for C-PM6:PPCBM:MeIc photocatalytic degradation of TC. Degradation pathway and toxicity analysis The electrons that were detected on HOMO were primarily focused on the bond C-N and dimethylamino group on the fourth ring, suggesting that this group, as well to be the main electron donor, is susceptible to attack through electrically conductive reagents (•OH, •O 2 - , etc.), which can lead to electrophilic reactions. [37,38] On the other hand, on LUMO, the ring of aromatic compounds as well as the hydroxyl group that is present on the aromatic ring have a dense electron distribution and are susceptible to nucleophilic reactions. [39,40] Figure 7. Possible photocatalytic degradation pathways. The degradation intermediates of tetracycline hydrochloride were characterised by HPLC-MS. The mass spectra of the intermediates are shown in Figure S7 . The mass spectra of the intermediates were shown in Figure S8 . Meanwhile, the detailed calculation of the DFT was shown in Text S2 and the Fukui index (f 0 ) was calculated as Table S2 . The six major degradation processes are depicted in Figure 7. Tetracycline hydrochloride’s molecular weight is shown by the product m/z=445. Pathway 1: As shown in Figure 7, The 28N atom with high f 0 (0.830) is attacked by h + ,which leads to the formation of P1 (m/z=415). Thereafter the product P1 was also oxidised by h + and •O 2 - to form the product P2 due to 25C with high f 0 (0.102). Afterwards, P2 was further oxidised by ROS to form two possible structural ring-opening products P3 and P4. Pathway 2:Because of its strong spatial site resistance on TC and low bond energy, N-C can be targeted by h + . [33] In addition, h + may attack 28N atoms with high f 0 values (0.830) on TC, leading to the loss of N-methyl and -NH 2 and the formation of P5 (m/z = 410). [41] The following reactions then take place: The 5O, 11O, 14C, 17O, 27O, and 13O atoms with high f 0 values (0.102, 0.107, 0.567, 0.051, 0.113, and 0.543, respectively) are attacked by •O 2 - and h + . With the benzene ring as the first ring, the separation of methyl, aldehyde, and H 2 O molecules on the fourth ring allowed for the conversion to P6 (m/z=318). P7 (m/z = 301) is then produced by breaking the fourth ring. At this point, the 20C and 21C atoms—whose f 0 values are greater at 0.107 and 0.123, respectively—are attacked by the active species. Either hydroxylating straight to P9 (m/z = 274) or removing -NH 2 and hydroxylating to P8 (m/z = 274) will yield P7 (m/z = 301). The active species will now proceed to target the 20C and 21C atoms with higher f 0 values of 0.107 and 0.123, respectively. P7 (m/z = 301) can be produced directly by hydroxylating to P9 (m/z = 274) or by eliminating -NH 2 and hydroxylating to P8 (m/z = 274). After that, the active species attacks the second and third rings to create P10 (m/z = 230). The ring is then cleaved and decarbonylated to give P11 (m/z = 109). Pathway 3: Furthermore, P12 (m/z = 319) was generated similarly to pathway 2. High f 0 values (0.567, 0.043, 0.107, 0.116, 0.543, and 0.051, respectively) led to reactive oxygen species (ROS) attacking 14C, 16C, 20C, 23C, 13O, and 17O atoms. Concurrently, the strong spatial site resistance of the C-N bond causes the fourth ring to fracture, resulting in the elimination of the •OH, -N-CH 3 , and -NH 2 groups, [38] which forms P12 (m/z = 319). Subsequently, when the 20C atom with the higher f 0 value (0.107) was exposed to •O 2 - , the molecular chain was further broken to produce P13 (m/z = 274). Additionally, P14 (m/z = 230) was created via a ring opening reaction including the attack of the 16C, 15C, 21C, and 23C atoms with higher f 0 values (0.043, 0.029, 0.123, and 0.116, respectively). Following the nearly total destruction of the ring structure, hydroxylation and amination processes give rise to P15 (m/z = 148). P16 (m/z = 135) is formed when the stabilised ring structure fully opens. Pathway 4: Through the breaking of double bonds and the creation of hydroxyl and ketone groups, TC synthesizes P17 (m/z=481). Subsequently, •OH attacks a methyl group on the tertiary amine, resulting in P18 (m/z=347). [42] P18 can then be transferred to P19 (m/z=344) by removing the keto group and altering the hydroxyl group. P20 (m/z=217) and P21 (m/z=164) are finally found. Pathway 5: After TC (m/z = 445) was hydroxylated and broken up into P22 (m/z = 459). [43,44] Then, P22 was converted to P23 (m/z = 443) by dehydroxylation. [45] Next, P23 underwent a deamination process to become P24 (m/z = 371). [43] The C=C of the P24 benzene ring is attacked by •OH/•O 2 - , which then forms P 25 (m/z=301) and P26 (m/z = 149). Pathway 6: The generation process of P27-29 is analogous to that of Pathway 1. Eventually, all intermediates were converted to CO 2 and H 2 O. Figure 8. Toxicity of TC degradation products. Six photocatalytic degradation pathways were identified from the study of TC photocatalytic degradation mechanisms and pathways by HPLC-MS analysis. The ECOSAR program was employed to analyse and predict the acute and chronic toxic effects of tetracycline hydrochloride and the intermediate products of its breakdown in fish, daphnia, daphnia and green algae, as well as to assess their effects on the aquatic environment. As illustrated in Figure 8 , the majority of the intermediates generated during the reaction were non-toxic or exhibited low toxicity. Furthermore, the toxicity of the remaining intermediates had a minimal impact on the aquatic environment. Conclusions In conclusion, we have made a breakthrough by introducing the third component strategy for the first time to prepare highly efficient and stable novel biochar-based organic photocatalytic adsorbents for the treatment of TC, utilizing MeIc and PPCBM for the acceptors and PM6 for the donor. As we know, 98.5% photodegradation efficiency of tetracycline hydrochloride was obtained under a single sunlight irradiation for 30 min, while the photocatalytic material showed high stability for the degradation of TC in twenty cycle experiments. This is the best result reported so far for the degradation of tetracycline hydrochloride via organic photocatalysts. The enhancement to photocatalysis is primarily attributed to the introduction of the third composition which improves the light absorption energy and allows the material to maintain good crystallinity, grain size and surface orientation, which promotes carrier generation and transport. Furthermore, HPLC-MS-based identification of the intermediates and DFT calculations revealed the TC degradation pathway. The major reaction processes include N-dealkylation, hydroxylation, dehydration and ring-opening reactions.This study offers new perspectives for the reasonable design of organic semiconductor photocatalytic adsorbents with practical environmental applications. Supporting Information Supporting Information is available online from the Online Library or from the author. Conflict of Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Author Contributions F. Yang, D. Zheng, L. Zhang contributed equally to this work. T. Liu and L. Zhang proposed this project’s idea. H. Zhu Funding acquisition. F. Yang Writing - original draft. D. Zheng Writing - review & editing. J. Yuan and L. Wang Data curation. M. Long and Y. Yin Software. K. Sun Formal Analysis. Cong Liu Resources and Validation. T. Liu and L. Zhang gave instructions regarding the project. Acknowledge T. 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Keywords organic photocatalysis photodegradation tetracycline hydrochloride wastewater treatment Authors Affiliations Fengping Yang Guangxi University View all articles by this author Dengsheng Zheng Guangxi University View all articles by this author Libin Zhang Guangxi University View all articles by this author Jiamin Yuan Guangxi University View all articles by this author Liliang Wang Guangxi University View all articles by this author Min Long Guangxi University View all articles by this author Yanzhen Yin Guangxi University View all articles by this author Ke Sun Guangxi University View all articles by this author Cong Liu Guangxi University View all articles by this author Hongxiang Zhu Guangxi University View all articles by this author Tao Liu 0000-0001-6017-0827 [email protected] Guangxi University View all articles by this author Metrics & Citations Metrics Article Usage 194 views 172 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Fengping Yang, Dengsheng Zheng, Libin Zhang, et al. Biocarbon based organic photocatalytic composite material achieves efficient removal of tetracycline hydrochloride under visible light. Authorea . 12 March 2025. DOI: https://doi.org/10.22541/au.174180272.23906813/v1 If you have the appropriate software installed, you can download article citation data to the citation manager of your choice. Simply select your manager software from the list below and click Download. For more information or tips please see 'Downloading to a citation manager' in the Help menu . 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