English

• Among the numerous of endocrine disrupting compounds we are exposed to, bisphenol A (BPA) stands out due to its widespread application, high environmental risk and refractory characterization [1]. Bisphenol A enters the environmental water body through different ways, such as effluent from sewage treatment plants or factory, landfill leachate and degradation by-product of plastic litter [2]. BPA can infiltrate into food and beverage through their containers and threaten human health. The widespread occurrence of BPA in our daily clothes and their relatively high exposure risk cannot be ignored [3]. BPA can be observed in human body, such as serum, urine, placental tissue and breast milk, and accumulation of BPA in human can lead to tumorigenic and birth defects [4]. In some epidemiological studies, BPA exposure is potentially associated with changes in hormone levels, impairment of ovarian and uterine functions as well as sperm quality decline [5]. Therefore, the development of efficient water treatment technology for BPA causes great concerns, such as adsorption [6], biodegradation [7] and advanced oxidation processes (AOPs) [8, 9].

  AOPs relied on the reactive oxygen species (ROS), such as hydroxyl radical (·OH) and superoxide radical (·O₂^-), effectively oxide the organic pollutants, including BPA. [10] Among the many advanced oxidation techniques, photocatalysis technology is an efficiency and eco-friendly mean for emerging organic contaminant removal [11]. In order to improve the photodegradation efficiency of target containment, many photocatalysts have been designed, which have the advantages of enhanced light absorption, high separation efficiency of photogenerated electron-hole pairs and prolonged life of ROS. For example, Fe-doped TiO₂/PSF composite could achieve 90.78% of BPA removal rate within 3 h visible-light irradiation [12]. Moreover, Yu et al. proposed a cobaltto-oxygen doped graphitic carbon nitride (0.78% Co-OCN_VN), which could degrade 100% BPA within 3 h visible light illumination and total organic carbon (TOC) removal rate up to 66% [13]. Although those new materials can highly improve the removal rate of BPA, BPA cannot be totally mineralized into inorganic small molecule during the photocatalysis oxidized process. Organic aromatic ring compounds, such as 4-hydroxybenzaldehyde, 4'-(methylmethylene) bisphenol, 4-(2-hydroxypropan-2-yl) phenol, benzoquinone can be detected in the photooxidation system [14, 15]. Compared with BPA, those oxidization by-products may exhibit higher environmental risk due to its relative high toxicity, mutagenicity and bioaccumulation factors. However, no comprehensive study on these photooxidation byproducts especially their environmental risks has been reported so far [16]. Therefore, the toxicity intervention of photocatalytic oxidation process on BPA need to be furtherly investigated. According to the previous work [17], modification with cyclodextrin can facilitate the advanced degradation of BPA oxidation intermediates.

  In this work, the photocatalytic degradation of BPA was employed to evaluate the performance of different cyclodextrin modified photocatalytic oxidation system. The photodegradation intermediates and products of different photocatalytic oxidation systems were detected. Moreover, the acute toxicity, bioaccumulation factor, developmental toxicity and mutagenicity of these oxidation products were analyzed in detail. And the comprehensive toxicity of different kinds of photoxodiation intermediates were proposed. Furthermore, the effects of different photooxidation system on the toxicity of BPA and its oxidation intermediates were also investigated. The considerate assessment system of water treatment technology was proposed.

  Photocatalytic oxidation of BPA was employed to evaluate the photoactivity of different oxidation system (Fig. 1 and Table S1 in Supportinginformation).Thephoto-decomposition efficiency of BPA (20 mg/L) was 11% under ultraviolet light irradiation for 1 h. Under the same conditions, 74% and 92% of BPA were photodegraded by commercial titanium dioxide (P25) and carboxymethyl-β-cyclodextrin modified titanium dioxide, respectively. Only the 8.6% of BPA was photodegraded under the visible light irradiation for 2 h, which was lower than that of ultraviolet oxidation system. The enhanced photodegradation efficiency of BPA was obtained by the carbon nitride nanosheet (39%) and the hollow CdS nanoreactor (86%), owing to their high visible light absorption and high concentration of photogenerated electrons and holes. Moreover, the 33% and 100% of BPA were photocatalytic oxidized by CM-β-CD-C₃N₄ and SH-β-CDAM/CdS, respectively, owing to the unique hydrophobic cavity of β-CD [18].BPAandβ-CD caneasilyform1:1inclusion complexwitha high association constant (56, 000 L/mol) [19], owing to the molecular sizes of BPA (1.24 nm × 0.54 nm × 0.44 nm) and β-CD cavity (0.60–0.65 nm × 0.79 nm, diameter × height) match each other best [20]. It facilitates the entrapment of target organic containment and promotes the transmission of electrons between the pollutant molecule and the photocatalyst [21].

  Figure 1

  

  Figure 1.  The removal of bisphenol A by different photocatalytic oxidation systems. Reaction condition: [BPA]₀ = 20 mg/L. [photocatalyst] = 1 mg/mL, pH_ini = 6.8, T = 298 ± 1 K.

  DownLoad: Full-Size Img PowerPoint

  Fig. 2 presents the pseudo-first-rate constants of BPA photodegradation over the different cyclodextrin photooxidation systems. The pseudo-first-order kinetic model could well interpret the experimental data (R² > 0.9). The apparent pseudo-first-order rate constant (k₁) of BPA photooxidation under the UV light and the visible light irradiation without any photocatalyst were 0.20 × 10^-2 min^-1 and 0.17 × 10^-2 min^-1, respectively.

  Figure 2

  

  Figure 2.  The apparent rate constant (Ka) of different cyclodextrin modified photooxidation systems for photocatalytic degradation of bisphenol A. Reaction condition: [BPA]₀ = 20 mg/L. [photocatalyst] = 1 mg/mL, pH_ini = 6.8, T = 298 ± 1 K.

  DownLoad: Full-Size Img PowerPoint

  Compared with the pure TiO₂ (1.98 × 10^-2 min^-1) and C₃N₄ nanosheet (0.22 × 10^-2 min^-1), the CM-β-CD-TiO₂ and CM-β-CDC₃N₄ exhibited a high photooxidation rate of BPA with 3.92 × 10^-2 min^-1 and 0.32 × 10^-2 min^-1, respectively, owing to its accelerated transmission of photogenerated electrons by the covalent bond between semiconductor and CM-β-CD [22]. Moreover, the BPA photodecomposition rate of SH-β-CD-AM/CdS nanoreactor (9.04 × 10^-2 min^-1) was more than 5 times higher than that of the hollow CdS nanoreactor (1.6 × 10^-2 min^-1) [17]. The directional transfer of photogenerated charges induced by spatial separated co-catalysts and the enhanced adsorption of BPA over the SH-β-cyclodextrin should have significantly contributed to the high photooxidation rate [23].

  The TOC analysis was used to investigate the mineralization of BPA over the different photooxidation system (Fig. 3). 5.63% and 1.27% of BPA were mineralized within 1 h UV light irradiation and 2 h visible light irradiation, respectively. Compared with the pure titanium dioxide and carbon nitride, carboxymethyl-β-cyclodextrin modified photocatalysts showed a higher TOC removal of BPA, indicating that β-cyclodextrin promote the mineralization of BPA. TOC removal of BPA in CM-β-CD-TiO₂ (25.4%) and CM-β-CD-C₃N₄ (15.7%) photooxidation system were 1.4 times higher than that of bare titanium dioxide (18.6%) and C₃N₄ (10.9%), respectively. Moreover, 19.2% of BPA can be removed by hollow CdS nanoreactors. Furthermore, the relatively high TOC removal of BPA observed in the oxidation system of SH-β-CD-AM/CdS nanoreactor (73.4%) could be attributed to the synergistic effect of spatial separated co-catalysts and the SH-β-cyclodextrin. According to the results of TOC analysis over the different photooxidation system, modification with cyclodextrin can facilitate the mineralization of BPA in photocatalytic oxidation process. Although some oxidation intermediates may bind with the β-cyclodextrin, this kind of inclusion complexes will not cause catalyst poisoning, but is conducive to accelerated degradation.

  Figure 3

  

  Figure 3.  TOC removal of different cyclodextrin modified photooxidation systems for photocatalytic degradation of bisphenol A. Reaction condition: [BPA]₀ = 20 mg/L. [photocatalyst] = 1 mg/mL, pH_ini = 6.8, T = 298 ± 1 K.

  DownLoad: Full-Size Img PowerPoint

  The photocatalytic oxidation intermediates of BPA in different oxidation system are identified by the UPLC-MS analysis, as shown in Table S2 (Supporting information). The detail UPLC-MS data are shown in Fig. S1 (Supporting information). During the photocatalytic oxidation process, the quaternary carbon atom of BPA is attacked by hydroxyl radical, phenoxyl (PhO) and isopropenylphenol (IPP) radicals are produced by the β-scission [24, 25]. Subsequently, numerous of aromatic by-products were formed through addition, substitution, dehydration and oxidative skeletal rearrangement reaction [26]. After ring-opening reaction, different kinds of carboxylic acids were detected, such as P17-19, which were ultimately mineralized into carbon dioxide and water. Different oxidation intermediates were obtained from different oxidation systems. The P11 and the polymers intermediate, such as P12 and P13, have not been detected in the photooxidation system without any catalyst. However, it can be obtained in the oxidation system of TiO₂, CM-β-CD-TiO₂ and CdS. Compared with UV oxidation system (Control-UV), visible light oxidation system (Control-visible) has lower TOC removal rate, but the fewer intermediates were detected in this system. Typically, P2, P5, P9, P10, P14 and P15 have not been detected in the Control-visible oxidation system. Moreover, according to the comparison of oxidation intermediates of pure catalysts and the cyclodextrin modified catalysts, the modification of cyclodextrin can effectively promote advanced degradation of oxidation intermediates [17]. For example, compared with hollow CdS nanoreactor, SH-β-CDAM/CdS can not only has higher TOC removal rate, but also avoid the generation of many polycyclic aromatic hydrocarbon (PAH) oxidation intermediates, such as P12-P15. These PAHs have huge potential environmental risk due to its high toxicity [27]. Interestingly, although the degradation rate and TOC removal of BPA in CM-β-CD-C₃N₄ oxidation system were lower than those of other catalysts, the number of intermediates detected in this system was the least. Therefore, the evaluation index of water treatment technology should not only consider the mineralization rate of target pollutant, but also the environmental risk of oxidation intermediates should be considered.

  Toxicity estimation software tool (T.E.S.T.) based on quantitative structure-activity relationship (QSAR) prediction [28] was used to evaluate the corresponding toxicity of BPA and its photooxidation intermediates (Fig. S2 in Supporting information). QSAR model provides the corresponding toxicity data according to the quantitative relationship between the chemical structure and its toxicological activity [29]. The concentration of chemicals that cause 50% of blackhead fish to die after 96 h (LC_{50–96 h}) is less than 1 mg/L, 1-10 mg/L and higher than 10 mg/L, which is defined as "very toxic", "toxic" and"harmful", respectively (Fig. S2a). Among the 21 detected oxidation intermediates, P10, P12, P13 and P16 are defined as "very toxic" oxidation products owing to its extremely high acute toxicity. These photooxidation intermediates pose a huge threat to aquatic organism and need attention because of their high environmental risks. Moreover, P7, P9, P11, P14 and P15 are defined as "toxic" compounds, which are more toxic than parent compound (BPA). In addition, the acute toxicity (LC_{50–96 h}) of other oxidation intermediates are higher than 10 mg/L and lower than 100 mg/L, thus they are defined as "harmful" pollutants. So, the rest of other oxidation intermediates are defined as "harmful" compounds except P18 and P19. Because P18 and P19 are defined as "low-toxic" compound, owing to its acute toxicity (LC_{50–96 h}) are higher than 100 mg/L. Furthermore, Fig. 4 shows the number of oxidation intermediates with different acute toxicity produced in different photocatalytic oxidation systems. According to the statistical results, the number of the oxidation intermediates with high acute toxicity is in the following order, CM-β-CD-P25 > P25 > CdS > Control-UV > Control-visible > SH-β-CD-AM/CdS > C₃N₄ > CM-β-CD-C₃N₄. There is no significant positive correlation between the target pollutant removal and the acute-toxicity of the oxidation intermediates. Therefore, the removal rate of target pollutants cannot be the only factor to evaluate the oxidation system.

  Figure 4

  

  Figure 4.  The number of intermediates with different acute toxicity in different photocatalytic oxidation system.

  DownLoad: Full-Size Img PowerPoint

  Moreover, the bioaccumulation factor (BAF) of P7, P9, P10, P12, P13 and P16 are larger than that of BPA (Fig. S2b). Among all of them, P7, P9 and P10 can be classified as potential bioaccumulative compounds due to those BAF higher than 500 [30]. Its worth noting that these oxidation intermediates are easy to threaten the ecological security through the food chain. The rest of oxidation intermediates have lower BAF than BPA owing to their low lipophilicity, indicating that they are difficult to accumulate in organisms than BPA [31]. After photodecomposition process, oxidation products without developmental toxicity can be detected in oxidation system, including P4, P5, P8-10, P14-16, P19 and P22 (Fig. S2c). It demonstrates that photooxidation can reduce the developmental toxicity of pollutants. However, the photooxidation process still produces oxidation products with higher developmental toxicity, such as P11 and P19. These intermediates interfere with the translation and expression of nucleic acids and thus affect the growth and development of individuals [32]. Furthermore, BPA and its oxidation products except P20 have negative mutagenicity [33], indicating that photooxidation hardly effect on the mutagenicity of BPA (Fig. S2d). Acute toxicity, bioaccumulation factor, developmental toxicity and mutagenicity were considered as the determinants of comprehensive toxicity. Some oxidation products, such as P10, P12, P13, P7 and P9, have high environmental risk due to their higher comprehensive toxicity.

  According to the results of identification of photooxidation intermediates in different oxidation system, modification of β-cyclodextrin effectively inhibit the production of high-risk intermediates. Interestingly, although the degradation rate and TOC removal of BPA in the CM-β-CD-C₃N₄ oxidation system is lower than that of CM-β-CD-TiO₂, no high-risk oxidation intermediates have been detected in this system. Therefore, decomposition of parent BPA cannot be regarded as the only factor to evaluate photooxidation treatment technology, but neglected the high-risk intermediates produced in the photooxidation process.

  In summary, β-cyclodextrin in several cyclodextrin oxidation systems can facilitate the entrapment of target organic containment and accelerate the transmission of electrons between the semiconductors and target organic pollutants. Thus, the CM-β-CDTiO₂, CM-β-CD-C₃N₄ and SH-β-CD-AM/CdS exhibit higher photodecomposition efficiency and photo-degradation rate of BPA than that of bare catalysts. TOC removal of BPA in CM-β-CD-TiO₂ (25.4%) and CM-β-CD-C₃N₄ (15.7%) photooxidation system were 1.4 times higher than that of bare titanium dioxide (18.6%) and C₃N₄ (10.9%), respectively. Among all oxidation systems, the highest TOC removal of BPA observed in the oxidation system of SH-β-CDAM/CdS nanoreactor (73.4%), owing to the synergistic effect of spatial separated co-catalysts and the SH-β-cyclodextrin. Different kinds of oxidation intermediates were detected in these oxidation systems. And T.E.S.T. based on QSAR prediction revealed that some photooxidation intermediates, such as P10, P12, P13, P7 and P9, have high environmental risk due to their higher comprehensive toxicity. It worth noting that even in the oxidation system with high mineralization rate of BPA, many oxidation intermediates with high comprehensive toxicity can be detected. On the contrary, almost no high-risk oxidation intermediates were detected in the CM-β-CD-C₃N₄ oxidation system with low TOC removal rate. In conclusion, decomposition of target contaminant cannot be regarded as the only factor to evaluate oxidation treatment technology, the high-risk intermediates produced in the oxidation process shall also be considered.

  Declaration of competing interest

  The authors declare that there are no conflicts of interest.

  Acknowledgments

  This work was supported by the National Natural Science Foundation of China (Nos. 51778230, 21906056), Shanghai Rising-Star Program (No. 17QA1401000), China Postdoctoral Science Foundation (No. 2018M641943), Shanghai Sailing Program (No. 19YF1411900) and the Fundamental Research Funds for the Central Universities (No. 222201718003).

  Appendix A. Supplementary data

  Supplementary material related tothisarticle canbefound, in the online version, at doi:https://doi.org/10.1016/j.cclet.2020.02.008.

  
  
• 1. [1]

     D. Chen, K. Kannan, H. Tan, et al., Environ. Sci. Technol. 50 (2016) 5438-5453. doi: 10.1021/acs.est.5b05387

  2. [2]

     J. Moreman, A. Takesono, M. Trznadel, et al., Environ. Sci. Technol. 52 (2018) 6656-6665. doi: 10.1021/acs.est.8b01095

  3. [3]

     L. Wang, Y. Zhang, Y. Liu, et al., Environ. Sci. Technol. 53 (2019) 7095-7102. doi: 10.1021/acs.est.9b02090

  4. [4]

     Y. Wang, S. Zhao, W. Fan, Y. Tian, X. Zhao, Environ. Sci. Nano 5 (2018) 1933-1942. doi: 10.1039/C8EN00366A

  5. [5]

     Y. Zhou, G. Cheng, K. Chen, et al., Ecotoxicol. Environ. Saf. 170 (2019) 278-285. doi: 10.1016/j.ecoenv.2018.11.117

  6. [6]

     Y. Zhou, R. Zhang, K. Chen, et al., J. Taiwan Inst. Chem. Eng. 78 (2017) 510-516. doi: 10.1016/j.jtice.2017.06.025

  7. [7]

     G. Moussavi, F.A. Haddad, Chemosphere 222 (2019) 549-555. doi: 10.1016/j.chemosphere.2019.01.190

  8. [8]

     Q. Liu, Y. Zhou, J. Lu, Y. Zhou, Chemosphere 241 (2020) 125043. doi: 10.1016/j.chemosphere.2019.125043

  9. [9]

     Y. Zhou, X. Fang, T. Wang, Y. Hu, J. Lu, Chem. Eng. J. 313 (2017) 638-645. doi: 10.1016/j.cej.2016.09.111

  10. [10]

      J. Li, Y. Li, Z. Xiong, G. Yao, B. Lai, Chin. Chem. Lett. 30 (2019) 2139-2146. doi: 10.1016/j.cclet.2019.04.057

  11. [11]

      C. Buck, N. Skillen, J. Robertson, P.K.J. Robertson, Chin. Chem. Lett. 29 (2018) 773-777. doi: 10.1016/j.cclet.2018.04.022

  12. [12]

      Q. Wang, C. Yang, G. Zhang, L. Hu, P. Wang, Chem. Eng. J. 319 (2017) 39-47. doi: 10.1016/j.cej.2017.02.145

  13. [13]

      Y. Yu, S. Wu, J. Gu, et al., J. Hazard. Mater. 384 (2020) 121247. doi: 10.1016/j.jhazmat.2019.121247

  14. [14]

      S. Luo, J. Xu, Z. Li, et al., Nanoscale 9 (2017) 15484-15493. doi: 10.1039/C7NR05320G

  15. [15]

      L. Yang, X. Bai, J. Shi, et al., Appl. Catal. B 256 (2019) 117759. doi: 10.1016/j.apcatb.2019.117759

  16. [16]

      X. Xu, S. Liu, K. Smith, Y. Wang, H. Hu, Chem. Eng. J. 373 (2019) 508-518. doi: 10.1016/j.cej.2019.05.063

  17. [17]

      Y. Zhou, J. Lu, Q. Liu, et al., J. Hazard. Mater. 384 (2020) 121267. doi: 10.1016/j.jhazmat.2019.121267

  18. [18]

      Y. Zou, X. Wang, Y. Ai, et al., J. Mater. Chem. A 4 (2016) 14170-14179. doi: 10.1039/C6TA05958A

  19. [19]

      A. Alsbaiee, B.J. Smith, L. Xiao, et al., Nature 529 (2015) 190-194.

  20. [20]

      W. Huang, Y. Hu, Y. Li, et al., J. Taiwan Inst. Chem. Eng. 82 (2018) 189-197. doi: 10.1016/j.jtice.2017.11.021

  21. [21]

      B. Wang, H. Wang, X. Zhong, et al., Chem. Commun. 52 (2016) 5049-5052. doi: 10.1039/C5CC10491B

  22. [22]

      M.T. Sikder, M.M. Rahman, M. Jakariya, et al., Chem. Eng. J. 355 (2019) 920-941. doi: 10.1016/j.cej.2018.08.218

  23. [23]

      H. Zhu, N. Goswami, Q. Yao, et al., J. Mater. Chem. A 6 (2018) 1102-1108. doi: 10.1039/C7TA09443D

  24. [24]

      C. Qi, X. Liu, Y. Li, et al., J. Hazard. Mater. 328 (2017) 98-107. doi: 10.1016/j.jhazmat.2017.01.010

  25. [25]

      Y. Zhou, X. Gu, R. Zhang, J. Lu, Ind. Eng. Chem. Res. 54 (2015) 426-433. doi: 10.1021/ie503414k

  26. [26]

      W.H.M. Abdelraheem, M.K. Patil, M.N. Nadagouda, D.D. Dionysiou, Appl. Catal. B 241 (2019) 598-611. doi: 10.1016/j.apcatb.2018.09.039

  27. [27]

      L.M. Salvo, D. Severino, H.C. Silva de Assis, J.R.M.C. da Silva, Chemosphere 144 (2016) 540-547. doi: 10.1016/j.chemosphere.2015.09.013

  28. [28]

      N. Klüver, C. Vogs, R. Altenburger, B.I. Escher, S. Scholz, Chemosphere 164 (2016) 164-173. doi: 10.1016/j.chemosphere.2016.08.079

  29. [29]

      B. Peric, J. Sierra, E. Martí, R. Cruañas, M.A. Garau, Ecotoxicol. Environ. Saf. 115 (2015) 257-262. doi: 10.1016/j.ecoenv.2015.02.027

  30. [30]

      K. Grabicova, R. Grabic, G. Fedorova, et al., Water Res. 124 (2017) 654-662. doi: 10.1016/j.watres.2017.08.018

  31. [31]

      R. Guo, Y. Du, F. Zheng, et al., Environ. Pollut. 227 (2017) 460-467. doi: 10.1016/j.envpol.2017.05.010

  32. [32]

      N. Yin, X. Liang, S. Liang, et al., Ecotoxicol. Environ. Saf. 176 (2019) 330-338. doi: 10.1016/j.ecoenv.2019.03.115

  33. [33]

      M. Iqbal, I.A. Bhatti, J. Hazard. Mater. 299 (2015) 351-360. doi: 10.1016/j.jhazmat.2015.06.045

• 

  Figure 1  The removal of bisphenol A by different photocatalytic oxidation systems. Reaction condition: [BPA]₀ = 20 mg/L. [photocatalyst] = 1 mg/mL, pH_ini = 6.8, T = 298 ± 1 K.

  下载: 全尺寸图片 幻灯片
  

  Figure 2  The apparent rate constant (Ka) of different cyclodextrin modified photooxidation systems for photocatalytic degradation of bisphenol A. Reaction condition: [BPA]₀ = 20 mg/L. [photocatalyst] = 1 mg/mL, pH_ini = 6.8, T = 298 ± 1 K.

  下载: 全尺寸图片 幻灯片
  

  Figure 3  TOC removal of different cyclodextrin modified photooxidation systems for photocatalytic degradation of bisphenol A. Reaction condition: [BPA]₀ = 20 mg/L. [photocatalyst] = 1 mg/mL, pH_ini = 6.8, T = 298 ± 1 K.

  下载: 全尺寸图片 幻灯片
  

  Figure 4  The number of intermediates with different acute toxicity in different photocatalytic oxidation system.

  下载: 全尺寸图片 幻灯片
•