Improvement,of,synergistic,effect,photocatalytic/peroxymonosulfate,activation,for,degradation,of,amoxicillin,using,carbon,dots,anchored,on,rod-like,CoFe2O4

Weilong Shi, Yanan Liu, Wei Sun, Yuanzhi Hong, Xiangyu Li, Xue Lin,*, Feng Guo,Junyou Shi,*

1 School of Material Science and Engineering, Beihua University, Jilin 132013, China

2 School of Material Science and Engineering, Jiangsu University of Science and Technology, Zhenjiang 212003, China

3 School of Energy and Power, Jiangsu University of Science and Technology, Zhenjiang 212003, China

4 College of Chemistry, Zhengzhou University, Zhengzhou 450001, China

Keywords:Carbon dots (CDs)CoFe2O4(CFO)Peroxymonosulfate (PMS)Photocatalytic Amoxicillin (AMX)

ABSTRACT β-lactam antibiotics in aquatic environment have severely damaged ecological stability and caused a series of environmental pollution problems to be solved urgently.Herein, a novel composite photocatalyst prepared by loading carbon dots(CDs)onto rod-like CoFe2O4(CFO),which can effectively degrade amoxicillin (AMX) by photocatalytic/peroxymonosulfate (PMS) activation under visible light irradiation.The degradation results exhibits that the optimal degradation efficiency with 97.5%within 80 min is achievd by the CDs-CFO-5 composite.Such enhanced activity is ascribed to the introduction of CDs that effectively improves the separation efficiency of photogenerated electron pairs and creates new active sites as electron bridges that improve the photocatalytic performance.More importantly, a strong synergistic between CDs and photo-induced electrons generated from CFO can further activiate PMS to provide more ∙ and ·OH radicals for boosting the degradation ability towards AMX.The present study aims to elucidate positive role of CDs in photocatalytic/peroxymonosulfate activation during the degradation reaction.

Amoxicillin (AMX) is widely used in disease prevention as a broad spectrum β-lactam antibiotic.However, due to the poor metabolism of the organisms, most of the AMX is continuously excreted into the ecological environment through the original forms of excretion, posing a greater threat to the ecosystem [1–4].Unfortunately, conventional wastewater treatment techniques,such as oxidation,filtration and adsorption,etc., cannot effectively remove antibiotics from the water body, thereby leaving them immersed in soil or aquatic ecosystems, which may lead to increased resistance to antibiotics in microbes or other organisms[5–7].In view of the frequent application of AMX in medicine and other fields, there is an urgent need to find new removal methods to effectively address the problem of antibiotic contamination.

Recently, an advanced oxidation technology based on the generation of sulfate radicals (SR-AOP) has attracted much attention that can generate sulfate radicals (∙) and hydroxyl radicals(·OH) by activating peroxymonosulfate (PMS) to improve the catalytic degradation efficiency [8–11].It is well known that metal ions, heat, and metal oxides can easily activate PMS to provide more ideas for the development of SR-AOP [12–14].Furthermore,photocatalysis is recognized as a promising strategy to eliminate environmental pollutants and overcome the energy crisis because of its clean,environmental protection and low energy consumption[15–17].Nevertheless,the synthesis of an efficient photocatalyst to achieve efficient removal of contaminants remains a huge challenge [18–23].Therefore, combining SR-AOP with photocatalytic technology is expected to produce a huge synergy to effectively solve the problem of antibiotic pollution [24,25].

CoFe2O4, as a spinel ferrite oxide, has received widespread attention due to its low cost, good photochemical stability, strong magnetism,wide visible light response and so on[26,27].Furthermore,previous studies found that Co,Fe transition metal elements can promote PMS activation, increase the rate of radical generation, and improve photocatalytic properties [28,29].However, the photocatalytic performance of pure CoFe2O4under visible light irradiation is also limited due to the rapid recombination of photo-induced charges [30–32], and further enhancement of its photocatalytic activity is required.Carbon materials have been well applied in the field of photocatalysis in recent years.Among them, carbon nanostructures include carbon nanotubes, C60, nanodiamonds, carbon dots,etc., which have attracted wide attention because of their good performance in the fields of optics,electronics, catalysis, and so on [33–35].Among them, compared with other carbon materials, carbon dots (CDs) are a novel type of zero-dimensional(0D)quantum dots with unique optical and electronic properties, chemical stability, low cost, and unique characteristics of light-induced electron transfer and storage [7,36–40].Thus, combining the magnetic spinel ferrite CoFe2O4and the unique physical and chemical properties of CDs,forming a composite material to activate PMS, may exhibit better photocatalytic activity, effectively alleviating environmental pollution for the degradation of AMX.

In this work,carbon dots(CDs)modified rod-like CoFe2O4(CFO)to form CDs-CFO composite for photocatalytic degradation of AMX based on the SR-AOP under visible light irradiation.In addition,various reaction parameters including PMS concentration,catalyst dosage, and the influence of AMX concentration on catalytic performance were investigated.Free radical trapping experiments and electron spin resonance (ESR) experiments were also carried out to further propose the photocatalytic reaction mechanism.

CDs were synthesizedviaan electrochemical method of etching graphite rods based on previously reported literature[41].The synthesis of CDs-CFO is through a simple two-step process consisting of a solvothermal method and a calcination process, as shown in Fig.1.First, the Fe(acac)3and Co(NO3)2∙6H2O with a molar ratio of 2:1 were added into DMF and ethanol mixed solvent.Next,the above solvent was added terephthalic acid, and then stirred vigorously for 30 min until mixed evenly.After that, different amounts of CDs (2.5, 5 and 10 mg) were replenished in the mixed solution and stirred for 30 min.Then, the mixed solution was transferred to a 100 ml autoclave and kept for 120 ℃for 12 h.After cooling to room temperature, the obtained product was washed with ethanol and dried at 60°C.Finally,the dried product was further calcined in a muffle furnace at a heating rate of 1°C∙min-1and kept at 400 °C for 1 h.In addition, the different ratios of CDs-CFO composite materials with adding 2.5, 5 and 10 mg were prepared and expressed as CDs-CFO-X(X=2.5, 5 and 10).The steps for preparing pure phase CFO are similar to the above method expect for adding CDs.The detailed characterizations and photocatalytic experimental process in this wok were given in the Supplementary Material.

Fig.1. The synthetic process diagram of CDs-CoFe2O4 composite.

As exhibited in Fig.2(a), the crystal structures of CFO and CDs-CFO composites was characterized by X-ray diffraction (XRD).It can be clearly observed that the characteristic peaks at 18.1°,30.2°, 35.6°, 43.3°, 53.6°, 57.2° and 62.7° are corresponded to the(1 1 1), (2 2 0), (3 1 1), (4 0 0), (4 2 2), (5 1 1) and (4 4 0) lattice planes of CFO(JCPDS card No.22-1086)[42].In the CDs-CFO composites, no obvious characteristic peaks of CDs can be observed,which may be attributed to the low content of CDs [43].The samples were further characterized by Fourier transform infrared (FTIR) to detect the functional groups of the surface.As displayed in Fig.2(b), the vibration bands located at 3422 cm-1and 1629 cm-1in CDs were ascribed to O—H bonds and C=O/C=C[44].For pristine CFO, the absorption bands at 570 cm-1and 420 cm-1are due to the stretching vibration of the Fe—O and Co—O bonds [45–47].The characteristic peaks of CDs and CFO can be found in CDs-CFO composites,which can prove the successful formation of composite materials.

Fig.2. (a) XRD patterns and (b) FT-IR spectra of CFO and CDs-CFO composites.

The morphology and nanostructure of the as-prepared samples were analyzed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).Fig.S1(a) (Supplementary Material) shows the SEM image of CFO, and the CFO is a rod-like structure with rough surfaces.For CDs-CFO-5 composite (Fig.S1(b)), it can be observed that after coating CDs, the rod-like structure of CFO is well preserved.TEM image of CDs-CFO-5 in Fig.3(a) exhibits the rod-like structure of CFO microrods is composed of large numbers of nanoparticles.And the high-resolution TEM(HRTEM)image of CDs-CFO-5 in Fig.3(b)shows the lattice spacing of 0.25 nm and 0.21 nm are corresponded to (3 1 1) and (1 0 0)crystal planes of CFO and CDs, respectively [42,46], confirming the successful synthesis of CDs-CFO-5 composite.The high-angle annular darkfield scanning transmission electron microscopy(HAADF-STEM) and corresponding elemental mapping images in Fig.3(c) shows the C, Co, Fe and O elements were equally distributed in the composite.

Fig.3. (a) TEM, (b) HRTEM and (c) HAADF-STEM and corresponding elemental mapping images of CDs-CFO-5 composite.

The surface chemical element composition of as-prepared samples was determined by X-ray photoelectron spectroscopy (XPS)and presented in Fig.4.Fig.4(a) shows the full spectra of CFO and CDs-CFO-5, and it can be clearly observed that the four elements of C,Co,Fe and O are presented in the sample,which proves the successful preparation of the sample without any impurities.Unexpectedly, the presence of C element can be observed in CFO,which may be attributed to the ashesive tape of XPS instrument.The C 1s spectrum of CDs-CFO-5 is displayed in Fig.4(b), and the two satellite peaks at 284.85 and 288.45 eV are belonged to C—C and C=O bonds [48].Fig.4(c) displays the Co 2p spectra of CFO and CDs-CFO-5, and two characteristic peaks at 780.3 and 795.8 eV can be observed and attributed to Co 2p3/2and Co 2p1/2and are accompanied by two satellite peaks[49].At the same time,the peak of Co 2p3/2and its satellite peaks prove the existence of Co2+oxide species, while the characteristic peak of Co2p1/2and its satellite peaks prove the existence of Co3+oxide species [50].Fig.4(d) exhibits the Fe 2p spectra of CFO and CDs-CFO-5, and there are two distinct characteristic peaks at 711.25 and 724.74 eV,which are attributed to Fe 2p2/3and Fe 2p1/2,and there is a satellite peak of Fe at 719.4 eV [51].Similarly, the peak at Fe 2p2/3and its satellite peaks prove the existence of Fe2+oxide species, while the characteristic peak at Fe 2p1/2proves the existence of Fe3+oxide species[52].Fig.4(e)are the O 1s spectra of CFO and CDs-CFO-5, and the characteristic peaks at 529.9, 531.6 and 533.3 eV are attributed to the lattice oxygen, surface hydroxyl and lattice oxygen in the chemically adsorbed H2O in the CFO,respectively [53].

Fig.4. XPS spectra of CFO and CDs-CFO-5: (a) survey and high-resolution XPS spectra of (b) C 1s, (c) Co 2p, (d) Fe 2p and (e) O 1s.

As depicted in Fig.5, in order to detect the optical absorption capacity, all samples were analyzed by UV–vis diffuse reflectance spectroscopy.It can be clearly observed that all samples exhibit a relatively wide absorption capacity in the range of 200–800 nm.Among them,after the introduction of CDs,the absorption capacity of the composite material is significantly improved compared to the pristine CFO, which is beneficial to utilize more visible light for enhancing the photocatalytic activity.

As displayed in Fig.6(a) and (b), photocatalytic degradation of amoxicillin (AMX) based on the activation of peroxymonosulfate(PMS) under visible light irradiation were explored to evaluate the synergistic catalytic effect of as-prepared materials.Blank experiments demonstrates that AMX is difficult to undergo selfdegradation under visible light irradiation.The degradation activity of CFO is negligible without visible light, while the CDs-CFO-5 degradation efficiency is slightly improved, but still negligible.When PMS is added, the degradation rate of AMX by CFO can be reached 50%in the absence of light in 80 min,which may be attributed to the great promotion of PMS activation by Co and Fe ions.Similarly, the photocatalytic degradation efficiency of CDs-CFO-5 activated PMS to AMX reaches 60% in dark, which may be due to the synergistic effect of CDs and CFO.It is worth noting that when visible light and PMS coexist, the degradation efficiency of CDs-CFO-5 reaches 97.5% within 80 min, indicating that CDs can combine photoinduced electrons produced by CFO to further activate PMS, realizing the efficient photocatalytic degradation efficiency.Meanwhile,it can also show the light and PMS play the important roles in the degradation of AMX in the CDs-CFO composite system.In addition,the corresponding ln(C0/C)presents good linearity(Fig.S2), indicating that the degradation of AMX is suitable for firstorder kinetics [54,55].The corresponding degradation rate constant shows that the CDs-CFO-5-PMS system displays the highest degradation rate constant.Therefore, the combination of CDs-CFO-5 composite material with visible light irradiation and PMS indeed exhibits a strong synergistic effect on the degradation of AMX.

The effects of the loading contents of CDs,the dose of photocatalyst, the concentration of AMX and PMS on the degradation efficiency of CDs-CFO-5-PMS systems under visible light irradiation were further studied.As displayed in Fig.7(a), it can be seen that with the increasing the CDs in the composite, the photocatalytic activity of CDs-CFO first increases and then decreases.When the content of CDs in the composite material increases from 2.5 to 5 mg,the introduction of CDs can accelerate the charge separation and improve the photocatalytic activity.Unfortunately, when the content of CDs further increases to 10 mg, excessive CDs around the composite will lead to competition for visible light absorption,internal shielding effect could reduce the visible-light photocatalytic activity [56,57].Thus, CDs-CFO-5 showed the highest visible-light photocatalytic degradation efficiency of AMX in the presence of PMS activiation.The degradation results reveal that the introduction of CDs not only can effectively promote the charge separation of CFO,but also can enhance the adsorption capacity of the pollutants.In addition, the effect of the dose of photocatalyst on the degradation performance of AMX base on PMS activiation is exhibited in Fig.7(b).When the amount of the catalyst is increased from 5 to 15 mg, the degradation efficiency improves significantly,because more catalysts can provide more active sites.However,under the same conditions,when the amount of the catalyst increases to 25 mg, the degradation efficiency of the AMX decreases slightly, which may be due to the excessive CDs-CFO-5 photocatalyst hindering the penetration of light in the reactor,resulting in a reduced surface area of the photocatalyst [58,59],thus reducing the photocatalytic degradation efficiency.Moreover,Fig.7(c) shows the effect of AMX concentration on catalytic activity.Obviously, the degradation efficiency decreases with the increase of AMX concentration.This is mainly because when the concentration of AMX is low, CDs-CFO-5 and PMS are excessive,which can effectively decompose each AMX molecule.On the contrary,the higher the concentration of AMX, the more molecules in the medium, while CDs-CFO-5 and PMS are limited and cannot effectively destroy AMX molecules,resulting in the decline of photocatalytic efficiency.Fig.7(d) displays the effect of PMS concentration on degradation efficiency.With the concentration of PMS increases, the degradation efficiency increases, which may be attributed to the existence of more PMS to provide a large amounts of free radicals for CDs-CFO-5.However, if the PMS concentration continues to increase,the degradation efficiency decreases slightly,which may be due to the fact that the limited number of photogenerated carriers cannot continue to satisfy the activation of PMS.In order to further evaluate the synergistic mechanism between CDs and CFO, we simply physically mixed CDs and CFO to prepare a control sample PM-CDs-CFO-5 composite material, and degraded AMX under the same conditions for comparison.As shown in Fig.S3,obviously,the degradation efficiency of PM-CDs-CFO-5 only reaches 75% within 80 min, which is significantly lower than the degradation efficiency of CDs-CFO-5, indicating that there is a significant synergy between CDs and CFO, which can effectively improve the sepreation efficiency of photo-induced chargs, thus enhancing the photocatalytic performance.At the same time, the photocatalytic performance of CDs-CFO-5 was compared with other systems, as shown in Table.S1.As can be seen, it has better photocatalytic performance than some similar literatures that have been reported in recent year,demonstrating that our system works well.The most important thing is that the degradation activity of CDs-CFO-5 still maintains a high degradation efficiency after running for 4 cycles,indicating that the CDs-CFO-5 composite material has excellent stability (Fig.7(e)).The concentrations of Co and Fe ions in the AMX solution after photocatalysis were tested by inductively-coupled plasma (ICP) technique (Fig.S4).After the reaction, the leaching concentrations of Co and Fe ions in the AMX solution were measured to be 0.36 and 0.32 mg.L-1, respectively, indicating that the CDs-CFO-5 composite sample exhibits excellent chemical stability.In addition, the XRD patterns before and after the photocatalytic reaction showed that the crystal structure of the CDs-CFO-5 composite material remained unchanged after running for 4 cycles,indicating that the CDs-CFO-5 composite material had higher stability and recyclability (Fig.7(f)).In addition, the inset of Fig.7(f) is a magnetic recovery picture of CDs-CFO-5, and it can be clearly observed that the samples show good magnetic recovery ability.

Fig.5. UV–vis diffuse reflectance spectra of CFO and CDs-CFO composites.

As exhibited in Fig.8(a), in order to determine the main active free radicals involved in the photocatalytic degradation of AMX by CD-CFO-5-PMS system, the free radicals quenching experiments were carried out.The scavengers tert-butyl alcohol (TBA) and methanol (EtOH) are used to capture·OH and∙, respectively.It can be clearly observed that the degradation efficiency is significantly reduced after adding the scavengers, indicating that·OH and∙are the main active substances in the degradation process.The electron spin resonance(ESR)spin trap experiments were used to further confirm the main active free radicals.As shown in Fig.8(b) and (c), no signal peak was observed in the dark, indicating that no active species could be produced in the dark.It can be observed from Fig.8(b)that in the absence of PMS,only the signal peak of·OH can be detected after 5 min visible light irradiation.Fig.8(c)shows that after adding PMS,obvious characteristic peaks of·OH and∙appear after 5 min visible light irradiation, which proves that the introduction of PMS in the process of photocatalytic reaction can increase the production of free radicals and further improve the photocatalytic performance.

Changes in the total organic carbon (TOC) removal rate can reflect the degree of mineralization of the reaction system.As exhibited in the Fig.9(a), it can be seen that the TOC removal rate of amoxicillin is 8.4% without adding any catalyst, while the removal rate can reach 71.4%over CDs-CFO-5 composite,revealing that the CDs-CFO-5 composite photocatalyst poeessesses high TC mineralization efficiency.In addition, to reveal the case of separation of the recombination of the photogenerated carriers,photoluminescence(PL)spectra of CFO and CDs-CFO-5 were given in Fig.9(b).Under the excitation wavelengths of 325 nm,pure CFO exhibits a strong PL emission peak at around 495 nm, and the PL peak intensity of pure CFO is significantly higher than CDs-CFO-5 composite,which demonstrates that the introduction of CDs effectively improves the efficiency of photogenerated electron transfer, thus improving the photocatalytic performance [60–64].In order to explore the reasons for the improved photocatalytic performance of CDs-CFO-5, the N2adsorption–desorption curves were carried out and given in Fig.S5(a) and (b).It can be found that both CFO and CDs-CFO-5 exhibit typical IV isotherms and H3hysteresis loops, indicating that the samples have a mesoporous structure.The Brunauer Emmett and Teller (BET) specific surface areas of CFO and CDs-CFO-5 were 77.122 and 90.405 m2∙g-1, respectively.The introduction of CDs significantly increased the surface area of CFO, indicating that the larger the specific surface area of the composite photocatalyst, the better photocatalytic activity duiring the reaction.In addition, the Barrett-Joyner-Halenda (BJH) measurement further analyzed the pore size distributions of the photocatalysts (Fig.S5(c) and (d)).The pore diameters of CFO and CDs-CFO-5 are concentrated at 8.4 nm and 6.87 nm, respectively, indicating that both CFO and CDs-CFO-5 have a mesoporous structure.

Fig.6. (a), (b) Degradation curves of AMX in different systems (catalyst dosage=15 mg, AMX concentration=10 mg.L-1, PMS concentration=0.2 mol.L-1, initial pH ～7).

Fig.7. The effect of (a) CDs contents (catalyst dosage=15 mg, AMX concentration=10 mg.L-1, PMS concentration=0.2 mol.L-1, initial pH ～7), (b) catalyst dosage (AMX concentration=10 mg.L-1,PMS concentration=0.2 mol.L-1,initial pH ～7),(c)AMX concentration(catalyst dosage=15 mg,PMS concentration=0.2 mol.L-1,initial pH ～7)and(d)PMS concentration(catalyst dosage=15 mg,AMX concentration=10 mg.L-1,initial pH ～7)on the photocatalytic activity of CDs-CFO-5-PMS systems under visible light irradiation.(e)Degradation rates of AMX in different cycles(catalyst dosage=15 mg,AMX concentration=10 mg.L-1,PMS concentration=0.2 mol.L-1,initial pH ～7).(f)The XRD patterns of CDs-CFO-5 sample befor and after photocatalytic reaction.

In order to study the separation and recombination of photogenerated charges, transient photocurrent responses and electrochemical impedance spectroscopy(EIS)were carried out.Fig.10(a)presents the transient photocurrent curves of CFO and CDs-CFO-5,and it can be found that compared with CFO, the CDs-CFO-5 composite exhibits a higher current density, indicating that the addition of CDs can effectively improve the separation of photogenerated electron-hole pairs [65–69].Furthermore, from the Fig.10(b)the CDs-CFO-5 composite exhibits a smaller semicircular radius compared to the CFO, which demonstrates that the composite has a higher interface electron transfer speed [70–74].Meanwhile, the equivalent circuit diagram is used to further analyze the impedance spectrum (inset in Fig.10(b)).Among them,CPE,RsandRctrepresent the constant phase element of the electrode and electrolyte interface, the resistance of the electrolyte solution and the interface charge transfer resistance between the electrode and electrolyte, respectively.In short, the addition of CDs in CDs-CFO composite improves the separation efficiency of the photogeneration carriers and improves the photocatalytic activity.

Fig.8. (a)Effect of radical scavenging experiment on the degradation of AMX by CD-CFO-5-PMS system.(b),(c)ESR spectra of CD-CFO-5-PMS system for detecting DMPO-·OH and DMPO-∙.

Fig.9. (a) TOC removal rates and (b) PL spectra of prisitne CFO and CDs-CFO-5 composite.

Fig.10. (a) Transient photocurrent responses and (b) electrochemical impedance spectroscopy of prisitne CFO and CDs-CFO-5 composite.

According to the above results, a possible reaction mechanism for the degradation of AMX by the CD-CFO-PMS system is proposed,as illustrated in Fig.11.At first,the optical band gap energy(Eg)of CFO was calculated using the Kubelka-Munk function,based on the relationship: (αhv)2=f(hv), in which α is the absorption coefficient, andhv is the light energy [59].As exhibited in Fig.S6(a), theEgof CFO is calculatied to be about 1.37 eV, which is consistent with literature report [75].In addition, through the VBXPS spectrum, it can be btained that theEVBof the CFO is 1.96 eV(Fig.S6(b)).Therefore,the conduction band(ECB)potential of CFO is calculated as -0.59 eV by the formula (ECB=EVB-Eg)[76,77].Based on the measured energy band position,the possible mechanism of CD-CFO-PMS system photocatalytic degradation of AMX is further described.Under visible light irradiation, CFO can be excited to generate electron-hole pairs due to its narrow band gap(Eq.(1)).In addition,due to the excellent electronic conductivity of CDs,the electrons(e-) transferred from CB to CDs and accumulated, which effectively promotes the separation of photogenerated electron-hole pairs of CFO.Meanwhile, the accumulated e-is captured by Fe3+to generate Fe2+(Eq.(2)).In addition, Fe3+can form·OH with OH-(Eq.(3)) [78].However, the VB potential of CFO does not span the reaction potential of·OH(～2.4 eVvs.NHE)[79],thus CFO cannot directly generate·OH.Fortunately,the addition of PMS can be activated to produce more·OH and∙.Generation steps for specific active species are as follows: on the one hand, Co2+can activate PMS to produce∙and Co3+, and then part of∙and H2O to produce·OH (Eqs.(4)and (5)).At the same time, Co3+can oxidize PMS to produce SO-5∙and Co2+, so as to realize the recovery of Co2+(Eq.(6)).Similarly,Fe3+activates PMS to produce Fe2+and SO-5∙and then Fe2+further activates PMS to produce Fe3+(Eqs.(7)and(8)).On the other hand,PMS can capture photo-induced e-from CDs-CFO and be activated directly to generate∙(Eq.(9)), or combine with h+to generate SO-5∙(Eq.(10))and further generate∙(Eq.(11))[6,80].Further-more,∙interacts with H2O and OH-to generate·OH (Eqs.(5)and (12)) [13,81].In this way, due to the synergy between CDs and CFO, more electrons are transferred to participate in the reaction, which promotes the effective separation of photogenerated carriers and accelerates the degradation process of AMX(Eq.(13)).

Fig.11. Possible mechanism of CDs-CFO-PMS system for photocatalytic degradation of AMX based on PMS activation.

In conclusion,CDs-CFO composites were synthesized by a facile two-step process consisting of a solvothermal method and a calcination route,and cooperated with PMS to photocatalytic degradation of AMX (the optimal degradation efficiency can reach 97.5%within 80 min).In CDs-CFO-PMS system, the introduction of CDs not only significantly improves the separation efficiency of photogenerated electron pairs, but also combines the photo-induced electrons for further activiating PMS to provide more free radicals for the photocatalytic reaction.The as-prepared CDs-CFO composite have fairly good magnetic recovery ability and still maintain high degradation efficiency after 4 cycles, which unambiguously disclosed the promising potential for photocatalytic application.This work is endeavoured to shed light on the role of CDs in composite for photocatalytic/peroxymonosulfate activation for degradation reaction.

Declaration of Competing 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.

Acknowledgements

The authors would like to acknowledge the founding support from the National Natural Science Foundation of China (Nos.21906072,22006057 and 31971616),the Natural Science Foundation of Jiangsu Province (BK20190982), ‘‘Doctor of Mass Entrepreneurship and Innovation” Project in Jiangsu Province,Henan Postdoctoral Foundation (202003013), Doctoral Scientific Research Foundation of Jiangsu University of Science and Technology(China)(1062931806 and 1142931803),the Science and Technology Research Project of the Department of Education of Jilin Province (JJKH20200039KJ), the Science and Technology Research Project of Jilin City (20190104120, 201830811) and the Project of Jilin Provincial Science and Technology Development Plan(20190201277JC, 20200301046RQ, YDZJ202101ZYTS070).

Supplementary Material

Supplementary data to this article can be found online at https://doi.org/10.1016/j.cjche.2021.10.030.