Nucleophiles promotes the decomposition of electrophilic functional groups of tetracycline in ZVI/H2O2 system: Efficiency and mechanism
Xin Li , Wanting Fu , Ruiqing Guan , Yue Yuan , Qinmei Zhong , Gang Yao , Sheng-Tao Yang , Liandong Jing , Song Bai
Antibiotics are emerging pollutants because they are not biodegradable and can persist in the environment as parent compounds and their metabolites [1]. Antibiotics and their metabolites have been reported in surface water, groundwater, and drinking water in recent years [2–4]. Tetracycline (TC) is a broad-spectrum antibiotic that targets most Gram-positive and Gram-negative bacteria. Due to their outstanding therapeutic value and cheap cost of use, TCs are widely used in human medicine, animal husbandry and aquaculture to control diseases and promote biological growth. High usage results in large amounts of TC entering the environment through wastewater discharge and animal waste, causing potential negative effects on environment and organisms [5]. The antimicrobial and refractory to degradation of TC pose challenges for conventional biological methods. Various treatment measures have been actively explored to efficiently eliminate TC from the aquatic environment, such as electrochemistry [6], photocatalysis [7], ultrasonic [8,9], biodegradation [10], adsorption [11,12]. These methods have great limitations in application due to cumbersome operation, high cost and some of their own shortcomings.
Zero-valent iron (ZVI) has received a lot of attention in applications to remove contaminants from the environment due to its high reducing ability and environmental friendliness [13]. As a strong reducing agent, the electrons provided by ZVI could be used in aqueous solution in three ways: Oxidants (e.g., H2O2, peroxysulphate, peroxyacetic acid) gain electrons to produce reactive oxygen species (path 1), protons get electrons to produce hydrogen (path 2), and pollutants get electrons to be reduced (path 3) [14,15]. Reactive oxygen species produced by path 1 can oxidize pollutants in aqueous, while path 3, with higher electron utilization efficiency in ZVI system, can directly reduce pollutants in aqueous systems. Most reducing agents, such as sodium borohydride, are either non-environmentally friendly or generate hazardous byproducts, while ZVI as a green reducing agent has been widely concerned by researchers [16].
Due to the high reactivity, it is easy to form oxides or hydroxides on the surface of ZVI during preparation and applications [17]. The corrosion reaction of ZVI can only be initiated under acidic conditions, which requires a low pH environment. In other words, the reaction of ZVI exhibits a significant pH dependence. Generally, the efficacy of ZVI in eliminating targeted contaminant is enhanced under acidic conditions [18]. Moreover, the deposition of iron (hydrogen) oxide on the surface during its application hinders the capacity of ZVI to release and transfer electrons [19].
Many strategies have been developed to overcome the deficiency of ZVI: (Ⅰ) The intrinsic oxides present on the surface of ZVI are eliminated through pretreatment, such as pickling or ultrasound, which can improve the contact area between ZVI and the environment. Lin and Lo employed pickling pretreatment to enhance the reaction rate of ZVI for trichloroethylene to two times [20]. (Ⅱ) The electron-releasing capacity of ZVI can be improved by plating it with metals of higher redox potential [21]. Fe-Cu bimetals was prepared by plating zero-valent copper on the surface of microscale ZVI, which improved the release rate of electrons and the effective utilization rate of electrons in the process of hexavalent chromium reduction. (Ⅲ) Coupling ZVI with other technologies such as ultrasound, ultraviolet, magnetic fields. The removal efficiency of p-nitrophenol achieved a 144.5-fold by utilizing a magnetic field to enhance ZVI, compared to ZVI alone [22]. (Ⅳ) Enhanced with an oxidant, the efficiency of ZVI in degrading pollutants is improved. Zhang employed Fe-Cu bimetallic particles coupled with persulfate to enhance nitrophenol contaminants [23].
In recent years, there has been a growing focus on Fe(Ⅲ)/Fe(Ⅱ) cycling in the application of (like) Fenton system [24,25]. Song et al. incorporated chelating agents into ZVI/O2 system to mitigate the reduction potential for Fe(Ⅲ)/Fe(Ⅱ) cycling and thereby enhance the production of oxygen-active species [26]. Apart from facilitating the elimination of contaminants, the chelating agents in ZVI system also compete with pollutants for electrons [27].
In this study, nucleophiles were introduced into ZVI/H2O2 system to enhance the removal efficiency of electrophilic functional groups in organics. TC was designated as the target organic pollutant, and the impacts of complexing agent type and dosage on TC removal by ZVI were investigated, as well as exploring the effect of nucleophilic complexing agents on the degradation of TC by ZVI. The initial pH, and the dosage of ZVI, H2O2, nucleophilic reagents on TC removal efficiency of ZVI/H2O2 system were discussed. Moreover, the underlying mechanism of electrophilic reagent was revealed.
The presence of co-existing organics exerts a significant influence on the removal of pollutants in ZVI system. Fig. 1a illustrates the TC removal efficiencies of the ZVI/H2O2 system with different co-existing organics at pH 6. The TC removal rate is 56.69% in the absence of organic, while with the addition of EDTA-2Na and OA, the TC degradation rate is reduced to 10.64% and 30.48%, respectively. However, with the addition of EDA and Gly, TC degradation rates are 94.91% and 91.33%, respectively. Fig. 1b shows the pseudo-first-order rate constant (Kobs) of the reaction without/with different complexing agents. Compared to 0.001267 s−1 for the blank group (in the absence of organic), the Kobs of EDTA-2Na and OA, which has an inhibitory effect, decreases to 0.0002 s−1 and 0.0006 s−1. The Kobs of EDA and Gly, which have a facilitating effect on the reaction, increases to 0.06623 s−1 and 0.0043 s−1. The results indicate that TC removal rate is greatly influenced by the organic species present in the ZVI/H2O2 system. Among the four added organic compounds, EDTA-2Na and OA exhibit electrophilic properties, while EDA and Gly-display nucleophilic characteristics. In other words, in neutral conditions of ZVI/H2O2 system, the nucleophiles can promote TC removal while electrophiles inhibit it. However, this differs from the previous electrophilic functional group (such as carboxyl group) complexing with iron ions to decrease redox potential of Fe3+/Fe2+ and thus improve the removal efficiency of pollutants [28].
To further demonstrate the promotion of TC degradation in Fe/H2O2 system by nucleophiles, several nucleophiles, such as MA, DA, TEA, DEA and EDA, were selected as co-existing organics. The impact of various nucleophiles on the degradation of TC is illustrated in Fig. 2. As shown in Fig. 2a, the addition of nucleophiles all facilitates TC degradation. The addition of EDA, in particular, demonstrates the most significant promotion effect with a 94.39% removal efficiency of TC achieved within 45 s. Fig. 2b illustrates the Kobs values for various nucleophilic additions, with DEA, MA, DA, TEA and the control group, exhibiting Kobs of 0.01226 s−1, 0.009 s−1, 0.00405 s−1, 0.00445 s−1 and 0.00127 s−1, respectively. As complexing agents, nucleophiles can capable of forming complexes with iron ions that alter the redox potential of Fe3+/Fe2+ [26]. Meanwhile, nucleophiles exhibit a relatively weak electron-accepting ability compared to electrophiles in the complexing agent, which significantly diminishes the competitiveness for electrons [27].
The varying effects of distinct nucleophilic reagents on the reaction may be attributed to their differing functional groups. The ethyl group exhibits a stronger electron-donating ability than the methyl group, thereby facilitating complexation of the amine with iron ions and promoting ZVI corrosion and electron transfer. This accelerates TC degradation. DA has an additional methyl group compared to MA, and the increased number of methyl groups on the amine results in fewer complexation sites with iron ions, thereby impeding electron transfer and TC degradation reaction.
To investigate the influence of the key parameters, pH of the mixture, additions of nucleophilic reagents, ZVI and H2O2 on efficiency of TC degradation in ZVI/EDA/H2O2 system were examined. Fig. 3a depicts the degradation efficiency and the Kobs of TC at different additions of EDA within 10 min. As shown in Fig. 3a, an increase in the addition of EDA within the range of 0–3 mmol/L results in a significant enhancement of degradation efficiency and the Kobs of TC degradation, and the removal rate of TC and the reaction rate Kobs increases to 94.85% and 0.0662 s−1. However, as the EDA addition increases, both degradation efficiency and the Kobs of TC degradation exhibit a decreasing trend. Probably because the low concentration of EDA competes more with TC for electrons than promotes the release of electrons from ZVI. When the concentration increases to 15 mmol/L, the removal rate of TC and the reaction rate Kobs decrease to 71.49% and 0.0216 s−1. Perhaps due to the high concentration of EDA results in electron competition with TC. Therefore, 3 mmol/L has been selected as the optimal concentration of EDA.
The pH level exerts a significant influence on both electron release and the dissolution of iron ions in ZVI system, with effective pollutant removal only achievable under acidic conditions; conversely, neutral and alkaline conditions inhibit ZVI activity [22,29]. Hence, the efficiency of ZVI/EDA/H2O2 system in TC removing was confirmed under acidic (pH 3), neutral (pH 6) and alkaline (pH 8) conditions. Fig. 3b shows effect of pH on removal rate of TC and the reaction rate Kobs in ZVI/EDA/H2O2 system. Evidently, the acidic and neutral conditions are in favor of TC removal, as both the removal rate of TC and the reaction rate Kobs remain consistent. However, the removal rate of TC and the reaction rate Kobs in ZVI/EDA/H2O2 system under alkaline condition are obviously inhibited. The high pH promotes the formation of iron hydroxide precipitation, which can eventually lead to the development of a passivation film on ZVI particles, thereby inhibiting the further dissolution of ZVI and limiting the electron transfer [18]. Higher pH reduces the corrosion rate of ZVI, and the accumulation of iron hydroxide precipitates on the surface of ZVI forms a passivation layer impeding the release of iron ions from ZVI and the electron transfer, ultimately affecting reduction rates.
H2O2 could facilitate the release of electrons from ZVI, thus, effect of H2O2 dosage on removal rate of TC and the reaction rate Kobs was investigated [14]. Fig. 3c illustrates the removal rate of TC and the reaction rate Kobs at varying H2O2 dosage. It is evident that the removal rate of TC and the reaction rate Kobs exhibit an increase with the increasing of H2O2 dosage from 20 µmol/L to 50 µmol/L. However, with the increasing dosage of H2O2, the reaction efficiency diminishes. This is attributed to the self-quenching effect of excessive H2O2, which diminishes treatment efficiency and reactivity of ZVI/EDA/H2O2 system [29].
The effect of ZVI dosage on the removal rate of TC and the reaction rate Kobs in the ZVI/EDA/H2O2 system is illustrated in Fig. 3d. Fig. 3d shows a significant enhancement in the removal rate of TC and the reaction rate Kobs as the ZVI dosage increases from 20 mg/L to 50 mg/L. However, as the dosage of ZVI increases to 80 mg/L, the reaction efficiency decreases and the reaction rate Kobs remains constant. This is attributed to that the increase of ZVI dose could enhance the mass transportation rate of TC, intermediates and ZVI, while the excessive ZVI inhibits the effect [22,30].
The coexistence of ions in solution exerts a different influence on the reactivity of ZVI because they tend to form precipitates on ZVI surface, inhibit electron transfer, and shorten the lifetime of ZVI [31]. Fig. 4 depicts the effect of ions present in solution on the degradation of TC in ZVI/EDA/H2O2 systems. According to Fig. 4, the presence of Cl−, NO3−, Ca2+, and Mg2+ ions could inhibit the reaction, and the inhibitory effect is positively correlated with the dosage of ions. Among these, Ca2+ ions exert the most significant impact on TC degradation, with a reduction rate of 89.09% and the reaction rate Kobs of 0.0395 s−1 at 1 mmol/L Ca2+ ions.
According to literature studies, the presence of complexing agents can facilitate hydroxylation of ZVI, inhibit the formation of iron oxide on the surface of ZVI particles, and increase the concentration of soluble iron in the system [32]. It is worth noting that the separation of oxidizing substances is a rate-limiting step in the process of dissolving iron ions in ZVI system. Fe(Ⅱ) and Fe(Ⅲ) oxides typically results in the formation of a several nanometers thick passivation layer, which significantly alters the electrochemical response of ZVI at the solid-liquid interface and impedes the electron transport. As a pollutant, TC also exhibits a propensity for complexation with iron ions, which can promote Fe(Ⅱ)/Fe(Ⅲ) cycle [33].
Fig. 5 depicts the dissolution of iron ions in the solution containing various complexing agents. The addition of nucleophlic reagent EDA results in a total iron content increase to 48.98 µmol/L, predominantly presenting as dissolved ferrous iron with a concentration of 34.94 µmol/L in the solution. What is more, the introduction of electrophilic agent EDTA-2Na also facilitates the augmentation of iron content in the solution with 15.98 µmol/L total iron, predominantly as ferric ions with negligible ferrous ion presence. However, simultaneous addition of the nucleophilic reagent EDA and electrophilic reagent EDTA-2Na results in a total iron content of 11.94 µmol/L, with a higher ferrous iron content of 1.55 µmol/L compared to the addition of EDTA-2Na alone (0.52 µmol/L).
The dissolved ferrous irons in the solution have ability to accept/give electrons and are more easily complexed with the nucleophilic reagent EDA, which is beneficial to promote the electron transfer. The complexation constant of EDTA-2Na with Fe(Ⅱ) is 14.32, which is lower than that of 25.1 with Fe(Ⅲ), so iron ions are more likely to exist in the form of ferric ions in ZVI/EDTA-2Na system. In addition, the elevated Fe(Ⅲ) caused oxides precipitation on the surface of ZVI, which resulted in the isolation of ZVI from contact with the solution and prevented the release of electrons from ZVI. Furthermore, the complexation constant of EDA with iron ions is lower than that of EDTA-2Na with iron ions, which is also consistent with the absence of a significant increase in iron ion concentration with the simultaneous addition of these two complexing agents described in Fig. 5. The results demonstrate that nucleophilic reagent EDA facilitates the release of electrons and iron ions from ZVI, while maintaining the presence of iron ions in ferrous form.
In order to investigate the iron ions valence states of ZVI particles before and after the reaction, the particles were characterized by XPS. Fig. 6 shows XPS spectra of Fe 2p of the fresh ZVI particles (Fig. 6a), the used ZVI particles in ZVI/H2O2 system (Fig. 6b), the used ZVI particles in ZVI/EDA/H2O2 system (Fig. 6c) and the used ZVI particles in ZVI/EDTA-2Na/H2O2 system (Fig. 6d). Compared with the fresh ZVI particles, the Fe(Ⅱ) contents on the surface of the reacted ZVI increases. The Fe(Ⅱ) content on the ZVI surface increases to 57.59% after the reaction in ZVI/EDA/H2O2 system, which is much higher than 27.8% Fe(Ⅱ) content on the unreacted ZVI particles and 48.37% Fe(Ⅱ) content on the used ZVI particles in ZVI/EDTA-2Na/H2O2 system. The result is consistent with the observation that EDA has a higher affinity for Fe(Ⅱ) to facilitate electron transfer, thereby facilitating the production and release of Fe(Ⅱ) on the surface of ZVI.
The presence of the electrophilic reagent EDTA-2Na enhances the liberation of iron ions from ZVI. As depict in Fig. 6d, the Fe(Ⅱ) content on the reacted ZVI surface increases to 48.37% with EDTA-2Na, surpassing that without complexing agent (28.58%). It is consistent with the addition of EDTA-2Na to enhance the iron content in solution as depicted in Fig. 5. The XPS characterization results indicate that the addition of complexing agents promote the release of iron ions from ZVI and change the valence distribution of Fe on the surface of ZVI. However, the addition of nucleophilic reagents accelerates the corrosion of ZVI and promotes complexation with iron ions, leading to enhanced electron release and accelerated reductive degradation of TC. Electrophilic reagents also facilitate iron ion release from ZVI for electron transfer. On the one hand, since TC is removed as an electrophilic reagent in the system, EDTA-2Na competes with TC for electrons, resulting in a decrease in received electrons. On the other hand, the presence of EDTA-2Na results in the formation of an iron oxide layer on the surface of ZVI, which impedes electron transfer as previously described.
The effect of nucleophilic reagent, electrophilic reagent, H2O2 and TC on the electron transfer in solution was investigated by measuring the open-circuit voltage of the solution using an electrochemical workstation. Fig. 7a depicts the variation of open-circuit voltage in the solution. The addition of nucleophilic reagent EDA makes the open-circuit voltage higher than that of the blank group without the addition of complexing agent. The results indicate that the addition of EDA does promote electron transfer in the solution, resulting in a decrease in the relative potential between positive and negative electrodes [34]. The addition of electrophilic reagent EDTA-2Na decreases the open-circuit voltage compared to the blank group, so the addition of EDTA-2Na impedes the electron transfer and leads to an increase in the potential between the positive and negative electrodes. Fig. 7a shows that, the open circuit voltage increases with the addition of H2O2 and TC, indicating that the addition promotes the transfer of electrons to reduce the potential. In addition, H2O2 and TC have stronger effect on the increase of the open circuit voltage in the presence of the nucleophilic reagent EDA. That is to say, the ability to promote the transfer of electrons is stronger in the presence of the nucleophilic reagent.
Fig. 7b depicts the curves of different systems measured by CV, with the blank group showing a pair of oxidation and reduction peaks at −0.144 V and −1.105 V with an average potential E1/2 = −0.63 V. The EDA group shows a pair of oxidation and reduction peaks at −0.481 V and −1.016 V with an average potential E1/2 = −0.75 V. The difference in peak potential (Epa-Epc) between the blank and EDA groups was 0.961 and 0.577, respectively. The result indicates that the system with EDA has a lower reaction potential and faster reaction kinetics than the blank group. The excellent symmetry of the curve exhibits heightened responsiveness to current, indicating favorable reversibility of electron gain and loss, with EDA facilitating efficient electron transfer within the system. Fig. 7c illustrates that a decrease in the applied voltage leads to a simultaneous reduction of the current, and it is noteworthy that the EDA-added system consistently exhibits the highest current among all three systems, which substantiates that incorporating EDA enhances electron transfer within the system and promotes reaction kinetics.
The Fukui function is a very important tool of molecular orbital theory, which can be used to describe the changes of electron structure and reaction pathways during intramolecular reactions. Theoretically, Fukui function can calculate the local reactivity of TC molecules and probe the TC reaction sites [34]. The Fukui index provides information on the relative reactivity of atoms, and has three main indicators: (1) The electrophilic attack index f− = qN − qN+1 (qN is the initial charge and qN+1 is the charge after gaining an electron), with higher values of f− indicating greater susceptibility to electrophilic attack; (2) The nucleophilic attack index f+= qN-1 − qN (qN-1 is the charge after losing an electron), with higher values of f+ indicating greater susceptibility to nucleophilic attack; (3) The radical attack index f0 = (qN-1 − qN+1)/2 [35]. The 3D structure of TC molecule is illustrated in Fig. 8a. The calculated Fukui functions of TC molecules are presented in Fig. 8b, which provides insight into the relative reactivity. According to Fig. 8b, O4 site has the highest f+ value, indicating that this position is susceptible to electron attack. LUMO exhibits a strong electron affinity and functions as an electron acceptor. The LUMO diagram of TC molecule and the Fukui function were calculated by molecular orbital theory to probe TC reaction sites [36–38]. Fig. 8c depicts the LUMO diagram of TC molecule, according to the diagram, the LUMO orbitals are all mainly on the O3 side, this side of the C=O double bond to the strong electron accepting ability easy to accept electrons.
Fig. 9a shows FTIR spectrum of TC before and after reaction, and the main vibration bands observed from FTIR spectra are at 1035, 1320, 1360, 1515, 1600, 1682, 3024 and 3477 cm−1, which can be attributed to C-O, CH3, CH2, C=C, C=O, C-H and O-H, respectively [1,39,40]. The unreacted TC FTIR spectrum exhibits characteristic peaks of C=O at 1682 cm−1 and O-H characteristic peaks at 3385 cm−1. After the treatment by ZVI/EDA/H2O2 system, moreover, the characteristic peak at 1682 cm−1 corresponding to the C=O bond was observed to be absent, while the characteristic peaks of O-H and C-O bonds were found to be intensified. According to the theoretical calculation, it is evident that the C=O bond in TC molecule is susceptible to electronic attack, and the observed changes in the characteristic peak of its FTIR spectrum are in line with this inference.
Figs. 9b and c depict the toxicity of TC to white rot fungus pre- and post-treatment with ZVI/EDA/H2O2 system, while Figs. 9b and c illustrate the enzymatic activities of MnP and Lac, respectively. Compared with the control group, the addition of TC significantly reduced the activity of both enzymes in the experimental group, indicating that TC toxicity has an inhibitory effect on enzyme activity of white rot fungus [41]. The addition of TC post-degradation results in an increase in manganese activity, possibly due to the toxicity decreases significantly after degradation. Moreover, there is no significant difference in laccase activity compared to the blank group.
As depicted in Fig. 9d, the toxicity of both untreated and treated TC to E. coli was evaluated. The number of E. coli colonies in the blank group is 2.7 × 107, and after adding TC the CFU number is 1.1 × 107, which proves that TC has an inhibitory effect on the growth of E. coli. Surprisingly, the colony count of E. coli in the experimental group exposed to degraded TC was 4.2 × 107, indicating a decrease in toxicity towards E. coli. The discovery is in line with the result of toxicity testing on white rot fungus. Overall, the elimination of the electrophilic functional group C=O bond in TC significantly mitigates its biological toxicity.
In the neutral condition, the presence of co-existing organic matter exerts diverse effects on TC degradation in ZVI/H2O2 system. Specifically, nucleophiles facilitate the TC degradation and increase its rate, while electrophiles impede it. The EDA in the nucleophiles shows the most effective promotion, and the optimal parameters for TC degradation by the ZVI/EDA/H2O2 system are achieved at pH 6, with ZVI concentration of 50 mg/L, H2O2 concentration of 50 µmol/L, and EDA concentration of 3 mmol/L. The degradation of TC by the ZVI/EDA/H2O2 system is inhibited in the presence of Cl−, NO3−, Ca2+, and Mg2+ ions, with a stronger inhibition effect observed at higher ion concentrations. The addition of EDA in neutral aqueous solution increases the release rate of ferrous iron ions from ZVI, as evidenced by their concentration levels. Moreover, based on XPS spectra analysis of ZVI particles, EDA acts as an electron shuttle and facilitates the conversion of Fe(Ⅲ) to Fe(Ⅱ) on the surface of ZVI. Compared to nucleophile, electrophile facilitates the release of iron ions but decreases the open-circuit voltage and impedes the electron transfer. The Fukui index indicates that the O3 on the TC molecule with the highest f− value is the most subject to electron attack, and the LUMO plot here also indicates that the strong affinity for electrons here has the nature of an electron acceptor. The FTIR characterization diagram also shows that the C=O bond of TC disappears after degradation, while exhibiting a noticeable increase in intensity for the characteristic peaks of C-H and O-H of the degraded TC. Degraded TC displays a significant reduction in its harmful effects on microorganisms. In a word, under neutral conditions, the addition of nucleophiles in ZVI system can promote the elimination of electrophilic functional groups in pollutant molecules, which may broaden the application field of ZVI.
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.
The authors would like to acknowledge the financial support from Sichuan Science and Technology Program (No. 2023NSFSC0345), the Fundamental Research Funds for the Central Universities (Southwest Minzu University, No. ZYN2022002), the Innovation Scientific Research Program for Graduates of Southwest Minzu University (Southwest Minzu University, No. 3300222156) and the China Scholarship Council (No. 202008510077).
Supplementary material associated with this article can be found, in the online version, at doi:
G. Gopal, C. Natarajan, A. Mukherjee, Environ. Technol. Innov. 25 (2022) 102187. doi: 10.1016/j.eti.2021.102187
Y. Dai, M. Liu, J. Li, et al., Sep. Sci. Technol. 55 (2020) 1005–1021. doi: 10.1080/01496395.2019.1577445
F. Saadati, N. Keramati, M.M. Ghazi, Crit. Rev. Environ. Sci. Technol. 46 (2016) 757–782. doi: 10.1080/10643389.2016.1159093
Y. Cheng, Y. Zhang, W. Xiong, et al., J. Water Process. Eng. 42 (2021) 102158. doi: 10.1016/j.jwpe.2021.102158
F. Ahmad, D. Zhu, J. Sun, Environ. Sci. Eur. 33 (2021) 64. doi: 10.1186/s12302-021-00505-y
H. Zhang, F. Liu, X. Wu, et al., Asia-Pac. J. Chem. Eng. 4 (2009) 568–573. doi: 10.1002/apj.286
X. Feng, Z. Wang, Y. Chen, et al., J. Environ. Eng. 138 (2012) 873–879. doi: 10.1061/(ASCE)EE.1943-7870.0000530
M. Malakootian, S.N. Asadzadeh, Desalin. Water Treat. 193 (2020) 392–401. doi: 10.5004/dwt.2020.25810
M. Malakootian, S.N. Asadzadeh, Desalin. Water Treat. 197 (2020) 191–199. doi: 10.5004/dwt.2020.25975
Z. Cetecioglu, B. Ince, S. Azman, et al., Appl. Biochem. Biotechnol. 172 (2014) 631–640. doi: 10.1007/s12010-013-0559-6
Z. Mengting, T.A. Kurniawan, R. Avtar, et al., J. Hazard. Mater. 405 (2021) 123999. doi: 10.1016/j.jhazmat.2020.123999
J. Ma, Y. Lei, M.A. Khan, et al., Int. J. Biol. Macromol. 124 (2019) 557–567. doi: 10.1016/j.ijbiomac.2018.11.235
Y. Sun, J. Li, T. Huang, et al., Water Res. 100 (2016) 277–295. doi: 10.1016/j.watres.2016.05.031
Y. Yuan, Z. Zhou, X. Zhang, et al., Chin. Chem. Lett. 34 (2023) 107932. doi: 10.1016/j.cclet.2022.107932
H. Ji, Y. Zhu, J. Duan, et al., Chin. Chem. Lett. 30 (2019) 2163–2168. doi: 10.1016/j.cclet.2019.06.004
Z.H. Farooqi, R. Begum, K. Naseem, et al., Catal. Rev. Sci. Eng. 64 (2022) 286–355. doi: 10.1080/01614940.2020.1807797
X. Guan, Y. Sun, H. Qin, et al., Water Res. 75 (2015) 224–248. doi: 10.1016/j.watres.2015.02.034
Y. Yuan, B. Lai, P. Yang, et al., J. Taiwan Inst. Chem. Eng. 65 (2016) 286–294. doi: 10.1016/j.jtice.2016.05.021
Z. Xiong, D. Yuan, P. Yang, et al., J. Taiwan Inst. Chem. Eng. 80 (2017) 669–677. doi: 10.1016/j.jtice.2017.08.048
C.J. Lin, S. Lo, Water Res. 39 (2005) 1037–1046. doi: 10.1016/j.watres.2004.06.035
B. Lai, Y. Zhang, Z. Chen, et al., Appl. Catal. B 144 (2014) 816–830. doi: 10.1016/j.apcatb.2013.08.020
Z. Xiong, B. Lai, P. Yang, Chemosphere 194 (2018) 189–199. doi: 10.1016/j.chemosphere.2017.11.167
H. Zhang, Q. Ji, L. Lai, et al., Chin. Chem. Lett. 30 (2019) 1129–1132. doi: 10.1016/j.cclet.2019.01.025
P. Zhou, W. Ren, G. Nie, et al., Angew. Chem. lnt. Ed. 59 (2020) 16517–16526. doi: 10.1002/anie.202007046
Y. Wang, P. Zhou, Q. Wang, et al., Chem. Eng. J. 402 (2020) 126176. doi: 10.1016/j.cej.2020.126176
X. Song, C. Zhang, B. Wu, et al., J. Environ. Sci. 86 (2019) 131–140. doi: 10.1016/j.jes.2019.05.023
Y. Zhang, M. Zhou, J. Hazard. Mater. 362 (2019) 436–450. doi: 10.1016/j.jhazmat.2018.09.035
Y. Qian, W. Pan, J. Li, et al., Chem. Eng. J. 426 (2021) 130894. doi: 10.1016/j.cej.2021.130894
J. Li, Q. Ji, B. Lai, et al., J. Taiwan Inst. Chem. Eng. 80 (2017) 686–694. doi: 10.1016/j.jtice.2017.09.002
H. Zhang, Z. Xiong, F. Ji, et al., Chemosphere 176 (2017) 192–201. doi: 10.1016/j.chemosphere.2017.02.122
M. He, W. Li, Z. Xie, et al., Water Res. 222 (2022) 118887. doi: 10.1016/j.watres.2022.118887
Z. Haiyan, S. Qian, W. Xun, et al., Sep. Purif. Technol. 132 (2014) 346–353. doi: 10.1016/j.seppur.2014.05.037
P. Zhang, X. Zhang, X. Zhao, et al., J. Hazard. Mater. 424 (2022) 127653. doi: 10.1016/j.jhazmat.2021.127653
A. Wang, P. Zhou, D. Tian, et al., Appl. Catal. B 316 (2022) 121631. doi: 10.1016/j.apcatb.2022.121631
J. Peng, H. Zhou, W. Liu, et al., Chem. Eng. J. 397 (2020) 125387. doi: 10.1016/j.cej.2020.125387
M. Liu, H. Chen, P. Xiao, et al., J. Hazard. Mater. 461 (2024) 132658. doi: 10.1016/j.jhazmat.2023.132658
Y. Liu, L. Chen, X. Liu, et al., Chin. Chem. Lett. 33 (2022) 1385–1389. doi: 10.1016/j.cclet.2021.08.061
C. Dang, F. Sun, H. Jiang, et al., J. Hazard. Mater. 400 (2020) 123225. doi: 10.1016/j.jhazmat.2020.123225
P. Ouyang, C. Liang, F. Liu, et al., Chemosphere 294 (2022) 133702. doi: 10.1016/j.chemosphere.2022.133702
Q. Li, R. Hu, Z. Chen, et al., Ecotoxicol. Environ. Saf. 242 (2022) 113885. doi: 10.1016/j.ecoenv.2022.113885
H. Yuan, J. Li, L. Pan, et al., Ecotoxicol. Environ. Saf. 247 (2022) 114275. doi: 10.1016/j.ecoenv.2022.114275
Figure 1 Removal rate (a) and pseudo-first-order rate constant (b) of TC 10 min in different co-existing organic compounds by ZVI/H2O2 system. Reaction conditions T = 30 ℃, pH 6, ZVI dosage = 50 mg/L, [H2O2] = 50 µmol/L, the amount of co-existing organic matter = 3 mmol/L.
Figure 2 Removal efficiency (a) and pseudo-first-order rate constant (b) of TC by ZVI/H2O2 system with different electrophiles. Reaction conditions: T = 30 ℃, pH 6, ZVI dosage = 50 mg/L, [H2O2] = 50 µmol/L, electrophiles dosage = 3 mmol/L.
Figure 3 Parameters optimization of TC degradation by ZVI/EDA/H2O2 system: (a) EDA dosage, (b) initial pH of ZVI/EDA/H2O2 system, (c) H2O2 concentration and (d) ZVI dosage.
Figure 4 Effect of ions present in aqueous solution on the removal efficiency and pseudo-first-order rate constant of ZVI/EDA/H2O2 system to degrade TC. Reaction conditions: T = 30 ℃, pH 6, ZVI = 50 mg/L, [H2O2] = 50 µmol/L, EDA = 3 mmol/L.
Figure 5 Effects of different complexing agents on iron ion dissolution in ZVI/H2O2 system. Reaction conditions: T = 30 ℃, pH 6, ZVI = 50 mg/L, [H2O2] = 50 µmol/L, EDA = 3 mmol/L.
Figure 6 XPS spectra of Fe 2p of the fresh ZVI particles (a), the used ZVI particles in ZVI/H2O2 system (b), the used ZVI particles in ZVI/EDA/H2O2 system (c) and the used ZVI particles in ZVI/EDTA-2Na/H2O2 system (d).
Figure 7 (a) Effect of adding H2O2 and TC on the circuit voltage of the solution in the presence of different reagents. (b) CV curves of different reagent solutions, (c) Effect of different reagents on the current measured by linear scanning voltammetry.
Figure 8 Chemical structure (a), LUMO diagram (b) (Yellow corresponds to positive and blue to negative regions of wave functions) and Fukui index (c) of TC.
扫一扫看文章
扫一扫关注我们
DownLoad:
下载:
下载: