C Magnetic Hierarchical Porous Carbon with

Article Cite This: Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Fe3C/Fe/C Magnetic Hierarchical Porous Carbon with Micromesopores for Highly Efficient Chloramphenicol Adsorption: Magnetization, Graphitization, and Adsorption Properties Investigation Jiangdong Dai,*,†,§ Sujun Tian,† Yinhua Jiang,† Zhongshuai Chang,† Atian Xie,† Ruilong Zhang,‡ Chunxiang Li,*,†,§ and Yongsheng Yan† †

Institute of Green Chemistry and Chemical Technology, School of Chemistry and Chemical Engineering, Jiangsu University, Zhenjiang 212013, China ‡ School of Material Science and Engineering, Jiangsu University, Zhenjiang 212013, China S Supporting Information *

ABSTRACT: Here, the magnetic hierarchical porous carbon (MHPC) with micromesopores was first prepared using ethylenediaminetetraacetic acid tripotassium (EDTA-3K) and iron nitrate by simultaneous magnetization/ activation method. The optimal product was MHPC-20 with a high graphitization, which possessed a large SBET (1688 m2 g−1) and saturation magnetization (3.679 emu g−1). As expected, MHPC-20 had a very high maximum adsorption capacity (534.2 mg g−1) toward chloramphenicol (CAP) from water solution at 298 K with a positive correlation between SBET and adsorption amount. Additionally, MHPC20 had a fast adsorption kinetic, only 250 min, and isothermal and kinetics data were well fitted by Langmuir and pseudo-second-order kinetic models, respectively. Moreover, the effect of ion strength, solution pH, and humic acid on CAP adsorption onto MHPC-20 were investigated, indicating a better stability. Besides, MHPC-20 showed good reusability and excellent magnetic separation performance, which implied MHPC-20 as a candidate could be applied in various complex wastewater environments.

1. INTRODUCTION

In recent years, magnetic carbon composites (MCCs) derived from carbon-based materials (i.e., graphene, biochar), have been extensively developed for application in environmental remediation owing to their good separation ability.8−11 Traditionally, the approaches for preparation of MCCs mainly include pyrolysis activation,12 hydrothermal coprecipitation reaction,13 and microwave irradiation.14 Chen et al. reported the mesoporous carbon nanospheres modified by Fe3O4 for removing hexavalent chromium.15 Liang et al. utilized magnetic mesoporous N-doped carbon (Fe3O4@N-mC) for simultaneous removal of methyl orange (MO) and methyl blue (MB).16 Nevertheless, complex preparation process, low specific surface area, and poor efficiency for pollutants removal can limit the large-scale application for MCCs. Thus, it is imperative to explore a MCCs with excellent porosity and high efficiency for contaminants treatment. Generally, the specific surface area, pore volume, and pore size are closely associated with the removal of pollutants such as dyes and antibiotics. To improve removal efficiency, the carbon

Antibiotics have been recognized as a class of new pollutants, owing to their high biological activity, durability, and bioaccumulation, causing serious harm to ecosystems and human health.1−3 On the basis of these potential risks, it is urgently expected to develop highly effective techniques and advanced materials for antibiotics removal. Porous carbon materials (PCMs) have received extensive attention due to their large specific surface area, developed porosity, high chemical stability (acid and alkali resistance), strong mechanical property, and adjusted pore structure or size1,3−6 and were widely used for antibiotic adsorption in a wastewater environment. Li et al. reported the nanoporous carbon derived from metal−organic frameworks (MOFs) for ciprofloxacin removal with an adsorption amount of 416.7 mg g−1.7 Ahmed et al. prepared a microporous carbon from sins seedpods via a microwave-assisted method to adsorb metronidazole with the maximum adsorption capacity of 180.7 mg g−1.8 However, some potential problems still need to be solved such as adsorbents’ collection and low adsorption rate. Therefore, it is essential to explore a versatile porous carbon with both highly efficiency adsorption and easy separation from aqueous solution. © XXXX American Chemical Society

Received: Revised: Accepted: Published: A

December 23, 2017 February 7, 2018 February 26, 2018 February 26, 2018 DOI: 10.1021/acs.iecr.7b05300 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research Scheme 1. Schematic Illustration for Preparation of Magnetic Hierarchical Porous Carbon

adjusted by a digital acidity meter (PHS-3C, Shanghai, China). A specific surface area analyzer (ASAP 2460, Micromeritics, USA) was employed to test pore structure property. 2.3. Preparation of Magnetic Hierarchical Porous Carbon. Magnetic hierarchical porous carbons were prepared using EDTA-3K and Fe(NO3)2·9H2O as raw materials. Typical experimental procedure was presented as follows: 10 g of EDTA-3K and Fe(NO3)2·9H2O were uniformly ground by a certain mass ratio in a mortar (Fe(NO3)2·9H2O:EDTA-3K = 1:5, 1:10, 1:20) and then put into a nickel crucible. The mixture was pyrolyzed at 750 °C for 1.0 h in an open vacuum tube furnace (SK-G06123K, Tianjin Zhonghuan Experimental Equipment Co., Ltd., China) under N2 atmosphere with a heating speed of 3.0 °C min−1. Then the sample was cooled to ambient temperature, washed several times with mixture of ethanol and distilled water to remove impurities, and dried at 60 °C to obtain magnetic hierarchical porous carbon (MHPC). According to the mass ratio of raw materials, the sample was denoted as MHPC-x, in which x represents mass ratio of Fe(NO3)2·9H2O:EDTA-3K, for example, MHPC-5 means that the mass ratio between Fe(NO3)2·9H2O and EDTA-3K is 1:5. 2.4. Batch Adsorption Experiments. To discuss the influence of mass ratio on adsorption performance of carbon, 2.0 mg of MHPC-x was put into 10 mL of a centrifuge tube containing 300 mg L−1 of initial CAP solution and kept for 24 h at 298 K to thoroughly reach equilibrium. The mixture was filtered with 0.22 μm of mixed cellulose membrane to the obtain supernatant, and the residual CAP concentration was determined with UV−vis spectra at 278 nm. The results showed that MHPC-20 exhibited the optimal adsorption capacity, thus MHPC-20 was used for further study of CAP adsorption performance. For adsorption kinetics, 2.0 mg of MHPC-20 was added into 10 mL of centrifuge tubes with 300 mg L−1 of initial CAP concentration. The experiment was conducted at 298 K, and then the supernatant was taken out at a certain intervals (5.0, 10, 15, 30, 45, 60, 90, 120, 180, 240, 300, and 420 min). The CAP adsorption capacity at t time Qt (mg g−1) was calculated by following equation:

materials with high porosity must be prepared. As far as we know, chemical activation can produce abundant pore structure in carbon skeleton to improve porosity.17−20 However, the frequent usage of chemical reagents might cause potential environmental risks and sustainability concerns; some problems cannot be ignored, such as high cost and low graphitization, which hinder the large-scale production. Therefore, it is still a challenge to prepare low cost, superior porosity, and high graphitization MCCs for pollutants treatment. In this work, the magnetic hierarchical porous carbon (MHPC) with high specific surface area and graphitization was prepared by using ethylenediaminetetraacetic acid tripotassium (EDTA-3K) as a carbon source and iron nitrate nonahydrate (Fe(NO3)3 9H2O) as a magnetic precursor to remove typical chloramphenicol (CAP) antibiotic, and the preparation process for magnetic hierarchical porous carbon are illustrated in Scheme 1. Surprisingly, the as-synthesized MHPC not only possessed a large amount of micropores but also a small amount of mesopores. In addition, as-prepared carbon materials exhibited excellent adsorption ability, fast adsorption rate, and magnetization separation performance. Simultaneously, the effect factors of such as ion strength, solution pH, and humic acid on CAP adsorption onto MHPC prepared under different condition were also studied in detail.

2. EXPERIMENTAL SECTION 2.1. Materials and Reagents. CAP (C11H12C12N2O5, 98%), EDTA-3K (C10H13K3N2O8·2H2O, 99%), and humic acid (FA, ≥90%) were of analytical grade without any further purification and provided by Aladdin Chemicals Co., Ltd. (Shanghai, China). Potassium hydroxide (KOH, ≥85%) and iron nitrate nonahydrate (Fe(NO3)2·9H2O, ≥98.5%) were purchased from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). 2.2. Instruments. Field emission scanning electron microscopy (FE-SEM, S-4800, Hitachi Japan) and transmission electron microscopy (TEM, JEOL IEM-200C, Japan) were used to characterize the microscopic morphology. And ultraviolet visible spectrophotometer (UV−vis, UV-2450, Shimadzu, Japan) was used to determine antibiotic concentration. X-ray photoelectron spectroscopy (XPS, Thermo Science ESCALAB 250Xi, UK) was utilized to analyze the bonding mode and ratio of elements. A Raman spectrometer (Raman, DXR, USA) and an X-ray diffractometer (XRD, SmartLab, Rigaku, Japan) were used to test the graphitization degree and crystal structures, respectively. Magnetic properties were measured by a vibrating sample magnetometer (VSM, MPMS, SQUID) at room temperature. Solution pH was

Qt =

(C 0 − C t )V M

(1)

where C0 (mg L−1) represents initial concentration of CAP. Ct (mg L−1) is CAP concentration at t time. V (L) and M (g) are solution volume and mass of adsorbent, respectively. To investigate adsorption equilibrium and isothermal property, 2.0 mg of MHPC-20 were placed into a CAP solution with different initial concentrations (30, 40, 50, 70, 90, B

DOI: 10.1021/acs.iecr.7b05300 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research

Figure 1. SEM images of MHPC-5 (a,b), MHPC-10 (c), and MHPC-20 (d−f).

Figure 2. TEM images of MHPC-5.

100, 110, 150, 200, 250, 300 mg L−1), which was maintained at 288, 298, 308 K for 24 h, respectively. The mathematical formula of equilibrium adsorption amount Qe (mg g−1) was listed as follows: Qe =

(C0 − Ce)V M

where Ce (mg L−1) means equilibrium CAP concentration. Simultaneously, the effects of ionic strength, solution pH and humic acid on CAP adsorption were also studied. 2.0 mg of MHPC-20 was added into 300 mg L−1 of initial CAP solution with different metal ion (Na+, Ca2+ and Fe3+) at different concentrations (0.01, 0.05, and 0.1 mol L−1), respectively. The solution pH was adjusted using NaOH and HCl solution. To

(2) C


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Figure 3. TEM and HRTEM images of MHPC-20.

number of discrete nanoparticles closely aggregated for MHPC5 (Figure 1a,b). With Fe mass content decreasing, MHPC-10 presented irregular particles with a small amount of bulk, as seen in Figure 1c. MHPC-20 showed a big bulk (Figure 1d,e) with a rough surface (Figure 1f), which indicated the addition amount of iron salt could affect the morphology of carbon materials. It was guessed that iron on the surface of carbon bulk might sinter together during calcination process resulting in the aggregation of carbon bulk. Figures 2 and 3 showed the TEM images of MHPC-5 and MHPC-20, respectively. A small amount of black particles and pore structure could be clearly observed from Figure 2a,b. What is more, black particles sintered together and linked between carbon sheets, which was consistent with the guess in Figure 1. From Figure 3, black particles distributed on the surface of carbon materials and obvious and uniform pore structure could be seen, which was beneficial to provide more adsorption sites

replace the metal cations with humic acid (solution concentration of 10, 30, 50, 70 mg L−1) and keep other conditions constant, the adsorption experiments were carried out at 298 K for 24 h. The regeneration performance of MHPC was investigated by cyclic adsorption experiments. In this experiment, the desorption treatment of saturated MHPC-20 was conducted to release adsorbed CAP molecule by using 0.2 mol L−1 of KOH(aq) at 298 K, which was then washed with distilled water to neutral. The adsorption−desorption cyclic experiments were carried out three times to evaluate reusability capability.

3. RESULTS AND DISCUSSION 3.1. Characterization Analysis. To study the effect of mass ratio on the morphology and adsorption ability of carbon, the SEM images of MHPC-5, MHPC-10, and MHPC-20 were investigated, as shown in Figure 1. Clearly, there was a large D


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Industrial & Engineering Chemistry Research for target pollutants. These results demonstrated that the iron compound was successfully introduced in carbon material by the one-pot simultaneous magnetization/activation method. Figure 3e,f showed the HRTEM images of MHPC-20. From Figure 3e, it can be seen that the spacing of crystalline lattices was 0.204 and 0.36 nm, corresponding to the Fe phase and graphitic carbon phase, respectively, which was consistent with the reported literature.21 Figure 3f disclosed that the lattice distance of the nanoparticles was 0.21 nm, ascribed to crystallographic phase planes of Fe3C phase. Obviously, the Fe and Fe3C were wrapped by graphitic carbon. These results illustrated the existence of graphitic carbon, Fe, and Fe3C. The XRD patterns of MHPC-5, MHPC-10, and MHPC-20 was shown in Figure 4, respectively. As revealed in Figure 4, a

Figure 5. Raman spectra of MHPC-5, MHPC-10, and MHPC-20.

enhanced by hybridizing graphene nanoribbons (GNRs) with M3C.27 Nitrogen adsorption−desorption isotherms and pore size distribution of MHPC-5, MHPC-10, and MHPC-20 were presented in Figure 6a,b. According to the IUPAC classification, three samples showed a main type I and a part type IV isotherm, which were reflective of a large amount of micropores and some mesopores, respectively.28 Figure 6b showed the pore size distribution was below 2.0 nm, and only a small amount above 2.0 nm, implying the presence of mesopores. Meanwhile, as mass ratio changed, the BET specific surface area of MHPC-5, MHPC-10, and MHPC-20 changed from 1448 and 1597 to 1688 m2 g−1. Abundant micropores implied that there could exist micropore-filling effect for CAP adsorption onto carbon materials, and the corresponding porosity characteristics of MHPC-x and previously reported magnetic carbon in the literature29−31 are listed in Supporting Information (SI), Table S1. Obviously, the specific surface area for MHPC-x was far more than reported literature, implying a high adsorption capacity for antibiotics due to the positive correlation between adsorption amount and specific surface area.32 The elemental composition and bonding relationship of MHPC-5 and MHPC-20 were analyzed by XPS, as shown in Figure 7. Three typical peaks corresponding to the binding energies of C 1s (284.5 eV), O 1s (532.0 eV), and Fe 2p (725.0 eV) could be seen in the survey spectra (Figure 7a), and the Fe 2p peak of MHPC-20 was not very conspicuous due to a low Fe content. In Figure 7b,d, the spectra of C 1s was resolved into four peaks at 284.6, 285.1, 286.1, and 288.2 eV, ascribed to C C, C−C, C−O, and CO, respectively.33−37 The O 1s spectrum could be deconvoluted into three individual peaks at 531.1, 532.9, and 533.1 eV, as seen in Figure 7c,e, corresponding to OC, C−O, and C−O−C, respectively,38,39 and the peaks at 725.3, 712.8, and 707.1 eV confirmed existence of Fe3C and Fe. For quantitative analysis, detailed content of functional groups and atomic content are summarized in SI Table S2 (calculated by peak area). It is noteworthy that the percentage of sp2 carbon for MHPC-20 (53.07%) increased compared with MHPC-5 (41.82%) while the content of sp3 carbon reduced, revealing that Fe content also had a great impact on bonding relationship of carbon materials. Also, the atomic content further verified Fe was

Figure 4. XRD patterns of MHPC-5, MHPC-10, and MHPC-20.

relatively broad typical peak at 2θ = 26.1° (PDF no. 00-0350772) illustrated the formation of graphitic carbon which could be assigned to (002) facets.22 In addition, among these three samples, there were many sharp peaks, suggesting a welldefined crystal structure. These diffraction peaks at 2θ = 37.8°, 43.9°, 45.0°, 46.0°, 49.2°, and 54.5° could be indexed to the Fe3C (JCPDS 35-0772),23 and a diffraction peak of Fe was observed at 2θ = 65° corresponding to (200) facets (JCPDS no. 06-0696).24 Furthermore, the peak was more obvious for MHPC-5, indicating a higher Fe3C content than MHPC-10 and MHPC-20, which was in good agreement with SEM results. The XRD results demonstrated that Fe and Fe3C nanoparticles were successfully introduced to carbons, further verifying SEM and HRTEM results. Similar finds were also reported in previous work.21 Raman spectrum is a powerful technique to test the crystallinity of samples. Figure 5 showed Raman spectrum of MHPC-5, MHPC-10, and MHPC-20. From the figure, two typical characteristic peaks for the D band at approximately 1360 cm−1 and the G band at 1580 cm−1 were identified, which provided important information on the disorder and crystallinity of sp2 carbon materials, respectively.25,26 Additionally, the graphitization degree of three samples could be easily evaluated by calculating intensity ratio of ID/IG. The value of ID/IG slightly decreased with Fe content increasing, which was 1.064 for MHPC-5, 1.031 for MHPC-10, as well as 1.003 for MHPC20 (see the inset in Figure 5), suggesting an enhanced graphitization degree which might be ascribed to the intercalation of potassium and iron into carbon layer. Similarly, as reported by Fan et al., the graphitization was greatly E


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Figure 6. Nitrogen adsorption−desorption isotherms (a) and pore size distribution (b) of MHPC-5, MHPC-10, and MHPC-20.

Figure 7. XPS spectra: (a) Survey scans, (b,c) MHPC-5, (d,e) MHPC-20, (f) Fe 2p spectrum of MHPC-20.

evaporation of residual water, and then the weight decreased by 13.05% from 200 to 350 °C due to the evaporation of impurities. When the temperature reached 350−850 °C, weight losses of 19.69% was caused by the pyrolysis of carbon−oxygen functional groups. The final residue of MHPC-20 was presumably the carbon and iron compound. Additionally, the

introduced into carbon materials, which was consistent with TEM results. The thermogravimetric analysis/differential scanning calorimetry (TGA/DSC) curves of MHPC-20 is shown in SI Figure S1. Obviously, there were three key steps of weight loss. The weight loss (14.27%) below 200 °C might be attributed to F


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Figure 8. Adsorption equilibrium curves of CAP onto MHPC-5, MHPC-10, and MHPC-20 at 298 K (a) and adsorption amount of CAP onto MHPC-20 at 288, 298, and 308 K (b).

Figure 9. Experimental plots and nonlinear fitting curves of Langmuir, Freundlich, and Temkin isotherms models (a) and RL curves (b) for CAP toward MHPC-20.

results are shown in Figure 8. Compared with MHPC-5 and MHPC-10, MHPC-20 exhibited a more obvious growth tendency (Figure 8a) during CAP adsorption process, indicating MHPC-20 possessed the optimal adsorption ability. Figure 8b displayed that with increasing temperature and initial concentration, CAP adsorption amount onto MHPC-20 gradually increased. Those results illustrate that mass ratio, reaction temperature, and initial CAP concentration had a great impact on CAP adsorption toward MHPC. Simultaneously, it can be found from SI Table S3 that with specific surface area increasing, the maximum CAP adsorption amount by MHPC also increased, illustrating a great effect of specific surface area on CAP adsorption. In addition, the specific surface area and CAP adsorption amount of MHPC is far higher than that of activation carbon, suggesting the superiority of MHPC. 3.2.2. Adsorption Isotherms. The adsorption capacity of CAP on MHPC-20 at different temperatures was evaluated by adsorption isotherms. In this study, the Langmuir, Freundlich, and Temkin models were used to analyze the experimental adsorption data. The Langmuir model described a monolayer adsorption, indicating there exists no interaction between adsorbed species, and the essential characteristics can be depicted by a dimensionless adsorption equilibrium coefficient RL. The Freundlich model described a multilayer adsorption based on the exponential distribution for adsorption sites and energies.42 Meanwhile, the strong electrostatic interaction between positive and negative charges was described through

DSC curves displayed energy change of the sample during weight change, which was well consistent with TGA curve. The magnetic behavior of as-prepared MHPC-x were evaluated by magnetic measurements conducted at 300 K between 10 and −10 kOe. SI Figure S2a displays the hysteresis loops of MHPC-5, MHPC-10, and MHPC-20. It can be seen that the magnetization curves were symmetrical about the origin with a very little hysteresis, suggesting a good superparamagnetic property for MHPC.40 The saturation magnetization value of MHPC-5, MHPC-10, and MHPC-20 were 27.49, 19.14, and 3.679 emu g−1, respectively, indicating a potential application for magnetic separation in water solution,41 which could be further verified by the photograph of magnetic separation of MHPC-20 in SI Figure S2b. Significantly, adsorbents were well separated from water by an external magnet. Furthermore, MHPC-20 had the lowest saturation magnetization owing to a small amount of iron compound, which was consistent with XRD results. Importantly, there was a good linear relationship between saturation magnetization and mass ratio of raw materials (see SI Figure S2c), which suggested the regulation of magnetization for carbon material could be achieved by controlling mass ratio of raw materials. 3.2. Adsorption Performance. 3.2.1. Influencing Factors of CAP Adsorption. Batch experiments were carried out to investigate the effects of different mass ratio, initial concentration, and contact temperature on CAP adsorption, and the G


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Figure 10. Adsorption kinetics (a), linear fitting curves of pseudo-first-order (b), pseudo-second-order kinetics (c), and intraparticle diffusion model (d) for CAP adsorption onto MHPC-5, MHPC-10, and MHPC-20.

samples at different temperature are summarized in SI Table S4. The determination coefficient R2 of the Langmuir model was higher than 0.99, while R2 value of the Freundlich and Temkin models were lower than 0.99, indicating the isothermal data was better fitted to the Langmuir model. These results illustratea a monomolecular adsorption of CAP onto MHPC20. Figure 9b shows that RL values gradually reduced with initial concentration increasing, which suggested increasing concentration was beneficial to CAP adsorption by MHPC-20, further confirming the results in Figure 9a. Moreover, with the rise in temperature, the RL values decreased and were all below 1, which demonstrated increased temperature was conducive to adsorption process, and similar finds have been also reported in previous literature.51 It is worth mentioning that the value of 1/ n from the Freundlich equation was higher than 0.42, suggesting 42% of active sites at least that had equivalent energy where adsorption occurred and the relative distribution of energy sites relied on the nature and strength in adsorption process.52 3.2.3. Adsorption Kinetics. The adsorption kinetics results are shown in Figure 10a. The adsorption amount of CAP onto MHPC-5, MHPC-10, and MHPC-20 increased rapidly in the first 30 min, followed by growing slowly and reaching adsorption equilibrium at around 250 min, illustrating a fast adsorption kinetic. This was because there were enough unoccupied binding sites at original stage for three adsorbents, making the target molecule easier to be bound, and then most of the binding sites were occupied by CAP molecule, leading to a decreased adsorption rate and finally reaching equilibrium. Additionally, the adsorption amount of CAP onto MHPC-5, MHPC-10, and MHPC-20 sequentially increased, which

the Temkin model. The general expression of three models can be defined as follows:43−45 Ce 1 1 = + Ce Qe Q mKL Qm

Langmuir Freundlich

Temkin

ln Q e = ln KF +

1 ln Ce n

Q e = b ln KT + b ln Ce

(3) (4) (5)

−1

where Qm (mg g ) is the maximum adsorption amount for CAP per unit mass of carbon, KL (L mg−1) is connected to adsorption free energy and affinity of adsorbents for adsorbates, and KF ((mg g−1) (L mg−1)1/n) is the Freundlich constant, respectively. b is related to the adsorption heat is Temkin constant, and KT is the equilibrium binding constant. Whatis s more, the separation factor RL can be expressed as follows:46 1 RL = 1 + KLCo (6) The isothermal plots and nonlinear fitting curves of CAP adsorption on MHPC-20 at different temperature are presented in Figure 9a. With increasing concentration and temperature, the adsorption amount gradually increased with a maximum adsorption capacity of 493.8, 503.5, and 534.2 mg g−1 at 288, 298, and 308 K, respectively, which were far higher than the reported adsorbents,47−49 as seen in SI Figure S3. This was due to increased molecule motion rate and decreased viscosity of solution,50 which might provide more probability for capturing CAP molecule. Simultaneously, increasing concentration could provide adequate driving force thereby increasing adsorption amount. The detailed adsorption equilibrium constants of three H


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where K0 is the distribution coefficient, T (K) is the temperature, and R (8.3145 J mol−1 K−1) is ideal gas constant, respectively. Cas and Cae are the activity of equilibrium concentration of CAP and in solution, respectively. K0 is the intercept of fitting curve ln(Qe/Ce) vs Qe on the vertical axis. The ΔHθ and ΔSθ were calculated from the slope and intercept of ΔGθ vs T plot. The calculated adsorption thermodynamic parameters of CAP on MHPC-20 are listed in SI Table S7. The ΔHθ value was 2.776 kJ mol−1, indicating an endothermic reaction, Moreover, some forces could be involved in CAP adsorption such as hydrogen bond forces (2−40 kJ mol−1) and dipole bond forces (2−29 kJ mol−1) judged by ΔHθ values reported in a previous work,58 and the value of ΔSθ was 0.028 kJ mol−1, which illustrated an increased randomness of solid−liquid interface during adsorption process.59 Meanwhile, the values of ΔGθ decreased from −5.377 to −5.943 kJ mol−1 with the increasing temperature, demonstrating a spontaneity and feasibility of physisorption (−20 to 0 kJ mol−1) and high temperature was more conducive to the adsorption process.57 3.2.5. Effect of Humic Acid. As displayed in Figure 11, humic acid had a great effect on CAP adsorption onto MHPC-

indicates that MHPC-20 has more adsorption sites for rapid adsorption. To more intuitively describe the adsorption dynamics and mechanism, pseudo-first-order53 and pseudo-second-order models54 were used to analyze the relevant kinetic data, the empirical equation of which arepresented as follows, respectively: ln(Q t − Q e) = ln(Q e) − K1t

(7)

t 1 1 = + t Qt Qe K 2Q e 2 −1

(8) −1

−1

where K1 (min ) and K2 (g mg min ) are adsorption constants of pseudo-first-order and pseudo-second-order kinetic equation, respectively. Parts b and c of Figure 10 show the linear fitting curves of pseudo-first-order and pseudo-second-order models for CAP adsorption, respectively. It can be observed that pseudosecond-order exhibited better linear correlation. The calculated values of kinetic parameters are summarized in SI Table S5. The determination coefficients (R2) of pseudo-second-order equation for all samples were more than 0.99, far higher that of pseudo-first-order equation (

C Magnetic Hierarchical Porous Carbon with

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