Efficient removal of oxytetracycline from aqueous solution using magnetic montmorillonite-biochar composite prepared by one step pyrolysis

Science of the Total Environment 695 (2019) 133800

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Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv

Efficient removal of oxytetracycline from aqueous solution using magnetic montmorillonite-biochar composite prepared by one step pyrolysis Guiwei Liang, Zhaowei Wang ⁎, Xing Yang, Tingting Qin, Xiaoyun Xie, Jing Zhao, Shan Li Key Laboratory of Western China's Environmental Systems (Ministry of Education) and Key Laboratory for Environmental Pollution Prediction and Control, Gansu Province, College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• Magnetic montmorillonite biochar material is first prepared by one step pyrolysis. • The composite performs excellent adsorption capacity for oxytetracycline. • Adsorption is mainly controlled by hydrogen bond, π-π and ion exchange reactions. • Fe3O4 nanoparticles on composite provide extra adsorption sites. • The spent composite is successfully regenerated and collected by magnet.

a r t i c l e

i n f o

Article history: Received 20 May 2019 Received in revised form 19 July 2019 Accepted 5 August 2019 Available online 05 August 2019 Editor: Daniel CW Tsang Keywords: Oxytetracycline Removal mechanisms Adsorption Magnetic montmorillonite-biochar Reusable composites

a b s t r a c t Three adsorbents, namely, original biochar (CLB), montmorillonite (MMT)-biochar composite (MBC), and magnetic MMT-biochar composite (MMBC) were successfully fabricated by one step pyrolysis of original cauliflower (Brassica oleracea L.) leaves, mixture of cauliflower leaves and MMT, and FeCl3-laden mixture of cauliflower leaves and MMT under limited oxygen atmosphere, respectively. The characterizations of samples indicated that substantial MMT mineral particles and Fe3O4 nanoparticle were dispersed on the surface of MMBC. Due to the introduction of Fe3O4, MMBC performed excellent magnetization property. The adsorption experiments of oxytetracycline (OTC) indicated that the maximum adsorption ability of MMBC was 58.85 mg·g−1, which was 2.63 times as large as CLB, also, larger than that of MBC. Meanwhile, pH, ionic strength, and humic acid (HA) performed slight effects for adsorption of OTC on MMBC. In addition, MMBC still removed 92% OTC after five regeneration cycles. Finally, primary mechanisms of OTC adsorption onto MMBC were attributed to hydrogen bonding and π-π reaction, and ion exchange reaction was considered to exist. Meanwhile, functional groups including Si-O-Al, Si-O-Si, Si-O, and Fe3O4 nanoparticles would provide extra binding sites for OTC adsorption. Therefore, MMBC had an obvious potential to apply into water purification as a reliable, low-cost, and environmentally friendly adsorbent. © 2019 Elsevier B.V. All rights reserved.

1. Introduction ⁎ Corresponding author at: College of Earth and Environmental Sciences, Lanzhou University, Tianshui South Road 222, Lanzhou 730000, Gansu, China. E-mail address: [email protected] (Z. Wang).

https://doi.org/10.1016/j.scitotenv.2019.133800 0048-9697/© 2019 Elsevier B.V. All rights reserved.

As one kind of the tetracycline, oxytetracycline (OTC) is generally used to prevent diseases and protect human health, besides applying

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in aquaculture because of its broad spectrum antimicrobial activity and low cost (Boonsaner and Hawker, 2015; Harja and Ciobanu, 2018; Moussavi et al., 2013; Shi et al., 2017). However, about 70–90% of OTC and metabolites are discharged into the receiving aquatic environments due to low adsorption rate and incomplete metabolism in intestine. As a result, so much OTC is released to water areas, which can result in spreading of antibiotic-resistance genes and disturbing the function of the ecosystem (Huang et al., 2011; Michael et al., 2013; Shao et al., 2018). Additionally, OTC is difficult to be degraded by conventional water treatment plants such as biodegradation owing to the stable ring and toxicity to the microorganism (Zhao et al., 2010). Hence, how to efficiently remove OTC from water environment has emerged as a hot research topic. Among various techniques, advanced oxidation processes are considered as effective methods to degrade organic pollutants, while the intermediates, high operation cost, and complex process hinder its application (Yaghmaeian et al., 2014). On the other hand, adsorption has been proved to be one of the simplest and most effective methods of removing various contaminants from contaminated water bodies (Chayid and Ahmed, 2015). Biochar is a pyrogenic carbon material produced from various biomass such as agricultural, forestry, and other organic discarding residues by thermal pyrolysis under oxygen-limited condition (Yao et al., 2015). The conversion of biomass into biochar has been deemed to a possible method for long-term carbon sequestration (Singh et al., 2012). When biochar is applied into soils, it can enhance soil fertility and soil nutrients, improve water holding ability, and promote yield of agricultural products (Ahmed et al., 2015; Boonsaner and Hawker, 2015; Harvey et al., 2012; Lehmann, 2006; Moussavi et al., 2013; Shi et al., 2017). Meanwhile, the biochar has been studied as cheap adsorbent to remove various organic contaminants, as well as heavy metals (Lonappan et al., 2018; Ni et al., 2011; Rajec et al., 2016; Uchimiya et al., 2010; Xiang et al., 2019; Xu et al., 2017;). Our previous research indicated that the cauliflower leaves as agriculture waste were suitable raw material to fabricate biochar due to its huge yield (Qin et al., 2017), while, similar to other researches, original biochar generally shows the poor adsorption capacity to organic contaminants (Wang et al., 2018). Therefore, engineered biochar has attracted tremendous research interests recently, since it can improve adsorption ability for various pollutants compared with pure biochar (Li et al., 2018a; Peng et al., 2017; Premarathna et al., 2019a; Rajapaksha et al., 2016; Wang et al., 2018; Yang et al., 2018; Zhou et al., 2017). Clay minerals are considered as great adsorbents to remove various pollutants (e.g., heavy metal, dyes, some organic compounds, etc.) resulting from their lamellar structure, relatively high surface area, high ion exchange capacity, and low-cost (Bilgic, 2005; Gurses et al., 2006). But, for neat clay minerals, the drawbacks including the difficulty of recovering mineral particles from solutions and relatively unsatisfied adsorption capacity for micropollutants limit their actual application (Benhouria et al., 2015). The biochar performs great porous property supporting and holding the distribution of the particles in its structure. Therefore, mineral particles can disperse onto biochar surface or interior for clay mineral-biochar composites (Premarathna et al., 2019b; Yao et al., 2014), which dramatically improves the adsorption ability of composite materials because of combining the advantages of biochar and clay minerals (Zhao and Zhou, 2019). Premarathna et al. (2019b) had prepared the clay-biochar composites to remove tetracycline antibiotic in solution, it indicated that the adsorption ability of tetracycline on MMT-municipal solid waste biochar composite was very high compared to red earth-municipal solid waste biochar composite, which might be resulted from the non-layered structure of red earth clay. Meanwhile, for layered silicate minerals (MMT, kaolinite, etc.), Yao et al. (2014) found that the MMT modified bagasse biochar could remove 84.3% methylene blue, while kaolinite modified bagasse biochar could only remove 30.0% methylene blue. Therefore, MMT is the most popular among the studied clays, and it performes negatively charged layers, remarkable specific surface area and cation exchange capacity

(CEC) (Chen et al., 2017a; Yao et al., 2014). Besides, MMT consists of two tetrahedral and one octahedral unit forming a platelet approximately 10 Å thick (Chen et al., 2017b; Segad et al., 2010; Yao et al., 2014). However, how to recover adsorbents from contaminated environmental media must be considered, especially for these fine particle materials. The introduction of magnetic media (e.g., γ-Fe2O3, Fe3O4) on biochar for fast separating the adsorbent by external magnet has attracted widespread attention (Yang et al., 2016). The chemical coprecipitation method is frequently employed, while it often has a negative effect on the porosity of materials (Yang et al., 2016). Meanwhile, another prepared way of magnetic biochar is created by calcination of ferric chloride laden biomass, and the microstructure and surface functional groups of composites can be improved in process of pyrolysis (Zhu et al., 2014). Whereas, few efforts has concentrated on magnetic MMT-biochar composite. In the present study, the three adsorbents were fabricated by using one step pyrolysis of original biomass, the mixture of biomass and MMT, and FeCl3-laden mixture of biomass and MMT, respectively. Meanwhile, the removal ability of the adsorbents for OTC was tested. The major objectives of this study were illustrated below: (1) characterized the prepared three materials by using Brunauer-Emmett-Teller (BET) analysis, scanning electron microscope (SEM), high-resolution TEM (HRTEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and vibrating sample magnetometer (VSM), (2) assessed and compared the adsorption ability of different adsorbents, (3) evaluated effect of experimental parameters (e.g., adsorption dynamics and isotherms, pH, ion strength, HA, etc.), (4) obtained the adsorption mechanisms of OTC onto MMBC. 2. Materials and methods 2.1. Chemicals and materials The used chemicals and materials in the present study were displayed in Supporting information. 2.2. Preparation of adsorbents The adsorbents were produced by one step pyrolysis of original biomass, the mixture of biomass and MMT, and FeCl3-laden mixture of biomass and MMT at 500 °C for 6 h under O2-limited condition in the muffle furnace, respectively. The detailed processes were shown in Supporting information and the products were denoted as CLB (original biochar), MBC, and MMBC, respectively. Meanwhile, the iron oxide (Fe), iron oxide and MMT composite (Fe-MMT), and iron oxide and biochar composite (Fe-BC) were prepared in the same conditions. The experimental conditions were determined by relative works (Baig et al., 2014; Li et al., 2017b; Liu et al., 2014; Qin et al., 2017; Yao et al., 2014). 2.3. Characterization of adsorbents The characteristics of adsorbents including surface morphology and area, structure of pore, functional groups, crystallographic structure, surface elemental composition, magnetism, and point of zero surface charge were described in detail in Supporting information. 2.4. Adsorption experiments All adsorption experiments of OTC on adsorbents were carried out in 50 mL polyethylene tubes with 25 mL OTC solution contained 0.01 M CaCl2 as the background electrolyte. The 0.05 g of adsorbent was added in polyethylene tube, the agitation was set to 250 rpm and kept constant throughout adsorption procedure. Meanwhile, every polyethylene tube was sealed and stored in dark places. The adsorption kinetic

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for further OTC adsorption test by adding 0.05 g aforementioned adsorbent into 20 mg·L−1 OTC solution. The adsorption regeneration procedure was repeated five times as the above mentioned method. 2.6. Analytical methods The UV–vis spectrophotometer (UNICAM UV300) was employed to measure the concentration of OTC solution at the maximum absorption peak (268 nm). For the experiment of the effect of pH, the concentration of OTC was determined by UHPLC (Ultimate 3000, Dionex, USA) with RS diode array detector and Accucore XL C18 column (250 mm × 4.6 mm, 5 μm). The flow rate was 0.7 mL min−1, and the 0.01 M ammonium dihydrogen phosphate /acetonitrile (80/20, volume ratio) was used as the mobile phase. Meanwhile, the dissolved iron contents of MBC and MMBC after adsorption were determined by flame atomic absorption spectrometer (Thermo ICE3000, Thermo Fisher, USA). The adsorption experiments of OTC on materials were all carried out for three replicates, and the final results were reported by average values, meanwhile, the error bars were displayed in figures. The removal rate and adsorption ability of OTC on adsorbents were calculated by the equations described in Supporting information.

Fig. 1. The spectra of XRD for CLB, MBC and MMBC.

data on adsorbents was measured with 20 mg·L−1 OTC solution at 298 K. At time intervals of 5 min, 10 min, 20 min, 30 min, 1 h, 2 h, 4 h, 6 h, 8 h, 12 h, 18 h, 24 h, the solution was centrifuged (4500 rpm, 5 min), filtered, and determined. Adsorption isotherms were investigated by carrying out adsorption study at 288, 298, and 308 K respectively with varying initial concentrations of OTC (10, 20, 30, 40, 50, 60, 80, 100, 120, and 150 mg·L−1) and the pH value of the solution was adjusted to 6.5. The effects of pH on the adsorption experiment of OTC were measured at different pH values (2, 4, 6, 8, 10) and the pH values were adjusted by prepared 0.1 M or 0.01 M NaOH and HCl. After 24 h, 2.0 mL solution was taken out and filtered by using 0.22 μm membrane filters. The effects of ionic strength on the adsorption experiment of OTC were evaluated by adding different concentrations of CaCl2 (0, 0.001, 0.01, and 0.1 M) to OTC solution with varying concentrations (20, 30, 40, 50, 60, 80 mg·L−1) at 298 K, respectively. The effects of humic acid on the experiment of OTC were recorded by adding varying concentrations of HA (0, 10, 20 mg·L−1) to 20 mg·L−1 OTC solution with 0.01 M CaCl2 at 298 K. 2.5. The effect of actual sewage and regeneration experiments The effect of actual sewage of OTC on MMBC was carried out adding 0.05 g adsorbents into 20 mL 20 mg·L−1 OTC solution prepared with deionized water and actual sewage to test its performance in the complex water environment. The initial pH values of solutions were set to 6.5 and then shaken at 250 rpm for 24 h in constant temperature oscillator. After centrifugation and filtration, the supernatant was measured. The regeneration experiment of OTC on MMBC was conducted to evaluate its reusability in actual application. The used material adsorbed OTC was collected from adsorption isotherm experiment after discarding the supernatant OTC solution. In addition, the collected adsorbent was rinsed three times with methanol, afterward washed one time with deionized water. The adsorbent was recovered by centrifugation after every cleaning, however, it was recovered by a magnet after the last cleaning. Subsequently, regenerated MMBC was dried at 80 °C

3. Results and discussion 3.1. Characteristics of samples Fig. 1 displayed the XRD pattern of CLB, MBC, and MMBC. The sharply characteristic peaks at 30.2°, 35.6°, 43.3°, 53.82°, 57.4°, 63.0°, and 74.5° were identified as Fe3O4. Similar patterns were reported in other reports (Brigante et al., 2016; Fu et al., 2019; Zhao et al., 2013), and there were relative faint peaks attributed to iron oxides in the range of 5°-80° of 2θ values. Herein, biomass was a significant component for the formation of Fe3O4, because some reducing components (H2, CO, etc.) derived from biomass were produced during pyrolysis, which reduced the FeO(OH) produced from the hydrolysis of FeCl3 to form Fe3O4 at 500 °C (Yang et al., 2016). In addition, the peaks located at 19.9° (d = 4.449 Å) and 35.1° (d = 2.555 Å) were contributed to expansible phyllosilicates (MMT), the peaks at 21.8° and 27.9° were mainly deemed to Quartz (SiO2) (Yao et al., 2014). Meanwhile, the carbon peaks were not observed on MMBC, which indicated that MMBC remained amorphous carbons. As displayed in Table 1, the major physicochemical properties and elemental compositions of CLB, MBC, as well as MMBC were represented. The yields of MBC and MMBC were very high compared to CLB. The specific surface area of MBC was decreased from 53.31 to 37.44 m2·g−1, however, slightly increased from 53.31 to 67.77 m2·g−1 for MMBC compared to original biochar. The decrease of the specific surface area of MBC might attributed to coating or blockage of pores on biochar due to the presence of MMT minerals (Yao et al., 2014). Whereas the increase of the specific surface area of MMBC was likely to result from the existence of MMT mineral particles and formation of Fe3O4 nanoparticle onto the surface of biochar (Li et al., 2019; Mohan et al., 2015; Yang et al., 2016). The total pore volume and the average pore diameter were increased from 0.0434 to 0.0969, 0.1478 cm3·g−1 and 3.16 to 10.35, 8.72 nm in comparison with CLB for MBC and MMBC respectively, these results were similar with the previous study (Yang et al., 2016).

Table 1 Physicochemical properties of CLB, MBC and MMBC. Samples

Yield (%)

Specific surface area (m2/g)

Total pore volume (cm3/g)

Micropores volume (m3/g)

Mesopores volume (cm3/g)

Average pore width (nm)

Elemental compositions (weight %) C

O

Na

Ca

Mg

Al

Si

Fe

CLB MBC MMBC

67.88 91.48 91.87

53.31 37.44 67.77

0.0434 0.0969 0.1478

0.0105 0.0032 0.0099

0.0329 0.0937 0.1379

3.26 10.35 8.72

83.12 24.93 26.89

14.03 38.16 39.72

– 0.20 0.25

1.76 3.43 0.73

0.84 1.05 0.74

0.09 4.54 2.36

0.09 22.36 9.47

0.07 2.32 19.09

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Fig. 2. SEM images of CLB (a, b), MBC (c) and MMBC (d).

The SEM micrographs (Fig. 2a and b) showed that CLB had stem structure with considerable pore networks. Fig. 2c and d illustrated much attached fine particles on the MBC and MMBC surface and completely coated the pure biochar, which changed the surface morphologies of composites (Viglašová et al., 2018). Thus, the surfaces of MBC and MMBC performed smoother than that of CLB. Meanwhile, MMBC had more uniform surface than MBC owing to the formation and adhering of iron oxide (Zhao et al., 2013). The EDX spectra of MBC and MMBC (Fig. 3b and c) displayed extremely high peaks attributing to iron, aluminum, silicon, and magnesium. The elemental compositions of composites (Table 1) also represented the existence of sodium. All results were the typical elemental composition of MMT, verified that MMT was successfully combined with CLB. Moreover, the element of Fe (19.09 wt%) on MMBC was noticed a larger scale of increment comparing to MBC (2.32 wt%) and CLB (0.07 wt%). Therefore, the above

results further proved that MMT and formed iron oxide particles had been covered on MMBC, which could provide extra adsorption sites. Meanwhile, the high yield would be in favor of the actual application of MMBC, since the substantial adsorbents could be obtained in the preparation process. As displayed in Fig. 4, the TEM and HRTEM images of CLB, MBC and MMBC showed their morphology and microstructure. According to the results, the MMT and Fe3O4 particles were dispersed on the surface of biochar for MBC and MMBC, which corresponded to the SEM. Therefore, biochar could act as supporting materials to disperse MMT and Fe3O4 nanoparticles during pyrolysis. The image in Fig. 4i proved that Fe3O4 particles were nanoscale with the diameter of 6–8 nm. Meanwhile, the clear lattice fringes of magnetite Fe3O4 deemed to the (220) (d = 0.30 nm) plane was found on MMBC (Fu et al., 2019). In addition, the clear lattice spacing of 0.255 nm on MBC and MMBC (Fig. 4e and

Fig. 3. EDX spectra of CLB (a), MBC (b) and MMBC (c).

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Fig. 4. TEM images CLB (a, b), MBC (d) and MMBC (h). HRTEM images of CLB (c), MBC (e) and MMBC (i). SAED images of MBC (f) and MMBC (j).

i) was attributed to expansible phyllosilicates (MMT) (Yao et al., 2014). Moreover, the images of the SAED were represented in Fig. 4f and j. In particular, the MMBC showed a polycrystalline aggregate instead of a single crystalline phase, which was determined by the presence of diffraction dots and diffraction rings (Yang et al., 2019). The FTIR spectra of CLB, MBC, and MMBC were illustrated in Fig. 5a. Besides, the FTIR spectra of Fe, MMT and OTC were displayed in Fig. S2. The spectrum of CLB showed stretching vibrations of OH groups at 3428 cm−1 (Pezoti et al., 2016; Dano et al., 2017), followed by 1566 cm−1 was deemed to stretching vibration of C_C or C_O of the aromatic ring. Meanwhile, 1430 cm−1 was related to the presence of C_O of carboxyl groups (Kyzas and Deliyanni, 2015; Luo et al., 2018), 1039 cm−1 was identified by stretching vibrations of C-OH from phenols and hydroxyl groups (Ding et al., 2016). Moreover, stretching vibrations of Si-O-Si was apparent at 871 cm−1, the characteristic peak of aromatic ring or polysaccharide heterocyclic compounds was appeared at 575 cm−1 (Brigante et al., 2016; Özdemir et al., 2011). The similar peaks were shown in the spectra of MBC and MMBC, while some weak peaks at 673, 871, 1249, 1566, 2169, 2922 cm−1 were disappeared or weakened. Besides, the new peaks appeared in modified materials. In the spectra of the MBC and MMBC, the peaks at 468, 519, 793, 3624 cm−1 and 467, 520, 793, 3614 cm−1 were related to the vibration of Si-O-Si, Si-O-Al, Si\\O, O\\H bonded with Al3+ cations, respectively (Chen et al., 2017a). Moreover, the maximum peaks at 1036 and 1041 cm−1 could be deemed to Si\\O or C-OH stretching vibrations for MBC and MMBC (Chen et al., 2017a). These results all suggested that MMT clay mineral particles were deposited on the surface of biochar successfully. From above information, the MBC and MMBC could

provide more potential adsorption sites due to more function groups in comparison with CLB. Magnetism played a significant role in collecting adsorbent from solution by a green and simple way. The magnetic hysteresis curve of MMBC was used to describe its magnetic property. Fig. 5d illustrated the magnetic saturation of MMBC was around of 35.10 emu.g−1, which suggested adsorbent could be rapidly recovered by magnetism. Meanwhile, the fabricated magnetic sample was a superparamagnetic material, evidenced by a negligible value of the remanence magnetization (Saber-Samandari et al., 2017). Furthermore, the inserted picture in Fig. 5d showed that the solid particles were attracted by the external magnet within a short period, which directly proved the excellent magnetic property of MMBC. The chemical composition and crystalline states of CLB, MBC, and MMBC were evaluated by the results of XPS. The full XPS spectra of three adsorbents were displayed in Fig. 6a, and S3a, S4a. For MMBC, the three obvious peaks at 284.6, 531.9, and 711.2 ev were attributed to C, O, and Fe elements on the surface, respectively, while there is no peak corresponded to Fe element in images of CLB and MBC. In Fig. S3b and S4b, we could divide spectra of fresh (unused) CLB and MBC (O 1 s) into three components: 530.3 ev (lattice oxygen in metal oxides, O2−), 531.8 ev (chemisorbed oxygen, O⁎), and 533.1 ev (C\\O) (Yang et al., 2016). The peaks at 530.3 ev of fresh CLB and MBC were extremely tiny, however, the fresh MMBC performed an enhanced peak at this position, which could be attributed to the presence of Fe3O4 (lattice oxygen in metal oxides, O2−) (Yang et al., 2016). Besides, the XPS spectra of C 1 s for the fresh and spent (used) adsorbents (CLB, MBC, and MMBC) were also divided into three peaks: 284.7 ev corresponded to

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Fig. 5. FTIR spectra of CLB, MBC and MMBC before adsorption (a) and FTIR spectra of MBC (b) and MMBC (c) before and after adsorption. Magnetization curve of MMBC (the insert picture showed the MMBC could be easily separated with a permanent magnet) (d).

C_C, 286.3 ev corresponded to C\\O, and 289.0 ev corresponded to C_O (Yang et al., 2016). Fig. 6d illustrated the spectra of Fe 2 p, the peaks at 710.2 and 711.2 ev attributed to Fe2+ and Fe3+ in octahedral coordination (Fe3+(o)) of Fe3O4, and 713.0 ev attributed to Fe3+ in tetrahedral coordination (Fe3+(t)) of Fe3O4, which was observed on the fresh and spent MMBC (Yang et al., 2016). 3.2. OTC removal ability and adsorption kinetics The adsorption abilities of OTC on different adsorbents were represented in Fig. S5. Compared to MMBC, the other materials performed the relatively low removal efficiency (26.0% for Fe, 44.5% for CLB, 71% for MMT, 83.1% for Fe-MMT, 84.3 for Fe-BC, and 91.8% for MMT). The removal abilities of binary composites (Fe-MMT, Fe-BC, MBC) were improved when we combined single materials with each other. Besides, it was noteworthy that MMBC showed the best removal ability (98.9%) in the prepared materials. Meanwhile, CLB, MBC, and MMBC were selected for further investigations. Fig. S6 depicted adsorption capacities of OTC on CLB, MBC, and MMBC at different time. Adsorption capacities of all samples rapidly increased within 30 min, next gradually increased to equilibrium. The equilibrium times were around 8 h for three adsorbents, and the removal efficiency of OTC was 44.5%, 91.8%, and 98.9% for CLB, MBC, and MMBC, respectively. Besides, adsorption kinetics on three adsorbents were described with the pseudo-first-order kinetic, pseudo-secondorder kinetic, and intra-particle diffusion models and the equations were given in Supporting information.

As seen in Table S1, the pseudo-second-order kinetic model described experimental data well owing to the high R2 over 0.999, and the equilibrium adsorption capacities (Qe) obtained from the pseudosecond-order kinetic model were extremely near to the experimental values (Qe,exp). Therefore, this suggested chemisorption might be the major rate-limiting step of adsorption of OTC on adsorbents (Li et al., 2018b; Li et al., 2017a; Tsai and Chen, 2013). The intra-particle diffusion model was generally applied to evaluate the rate-controlling step in the adsorption procedure (Hu et al., 2018; Li et al., 2018b). According to experimental data, the three stages fitting were used. At the first step, the rapid increase of adsorption capacity was due to the easily accessible sites on the external surface and more OTC molecules in the solution. Followed by, the slope of curve gradually flattened, which might be caused by decrease of adsorption sites and intra-particle diffusion of OTC molecules. Finally, the adsorption reached to adsorptiondesorption equilibrium (Yu et al., 2012). Furthermore, the lines of the intra-particle diffusion plots could not go through the origin, suggesting that intra-particle diffusion was not the only rate-controlling step (Yu et al., 2012). Therefore, the adsorption of OTC might be controlled by multi reasons, including both surface adsorption and intra-particle diffusion (Li et al., 2018b; Vadivelan and Kumar, 2005). The results in Table S1 showed that R2 was over 0.900 except for the third linear portion, which represented that adsorption data exhibited multilinear so that the adsorption process had been decided by two or more steps (Hu et al., 2018). Meanwhile, some other mechanisms such as complexation, π-π reaction, electrostatic reaction, and other specific interactions might involve in adsorption process of OTC (Yu et al., 2012).

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Fig. 6. XPS full survey of MMBC (a). The XPS spectra of MMBC: O 1 s (b), C 1 s (c), Fe 2p (d).

3.3. Adsorption isotherms Adsorption isotherms were very important to analyze how to target pollutants interact with active sites on the adsorbent surface (Wang et al., 2016). The experimental results indicated maximum OTC adsorption capacities were 22.39, 55.77, and 58.85 mg·g−1 on CLB, MBC, and MMBC at 308 K, respectively (Fig. S7). Modified materials showed outstanding OTC adsorption potential compared to original biochar. Besides, MMBC exhibited slightly higher adsorption capacity than MBC, which was corresponded to results obtained from adsorption kinetics. Langmuir and Freundlich models were employed to fit the adsorption isotherm data, RL was the dimensionless constant separation factor. The equations were given in Supporting information, and the calculated adsorption constants were recorded in Table S2. According to the results in Table S2, the Freundlich model gave the better fitting performance for CLB and MBC than the Langmuir model because of higher R2, indicating OTC adsorption behaviors onto CLB and MBC were multilayer adsorption and occurred on the energetically heterogeneous adsorbent surface (Li et al., 2016b; Zhao and Lang, 2018). However, the adsorption isotherm of OTC on MMBC could be fitted by two adopted models well, while, the maximum adsorption capacities based on Langmuir isotherm (Qm) was extremely close to experimental data (Qe,exp). Thus, Langmuir isotherm was suitable for analyzing the results, which suggested the formation of monolayer coverage of OTC on the surface of MMBC, and OTC adsorption behaviors onto MMBC took place at specific homogeneous binding sites (Li et al.,

2017a). The adsorption performances of OTC onto multiple adsorbents were further analyzed by RL, whether it was favorable (0 b RL b 1), linear (RL = 1), irreversible (RL = 0), and unfavorable (RL N 1) (Pathak and Mandavgane, 2015). The RL values of three materials were all between 0 and 1, suggesting that the adsorption of OTC was favorable. n was index indicating adsorption intensity, herein, n N 1 also illustrated adsorption of OTC on all adsorbents was favorable (Pathak and Mandavgane, 2015). In addition, MMBC displayed a higher affinity for OTC in comparison with CLB and MBC owing to the bigger values of b corresponding for the affinity of the adsorption binding sites. The higher adsorption potential of MMBC could be attributed towards more functional groups and Fe3O4 particles than other adsorbents, which was further confirmed by the abovementioned results of characteristics and previous reporting (Li et al., 2018b). 3.4. Thermodynamic studies The feasibility and spontaneity of the adsorption of OTC on adsorbents were analyzed by thermodynamic studies. Thermodynamic parameters including gibbs free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS) were evaluated using the relative equations (Supporting information), and the related parameters were displayed in Table S3. As displayed in Table S3, ΔG was negative for OTC adsorption on three materials, suggesting that the adsorption process was spontaneous. With increasing of temperature, the absolute value of ΔG also

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accordant with our previous results (Qin et al., 2017). Thus, the adsorption capacity was basically unchanged except for MBC. From Fig. 7a, it could be found that electrostatic attraction and repulsion between adsorbents and adsorbates was not significant for three materials.

increased, indicating that OTC adsorption on adsorbents was more favorable at the higher temperature (Pathak and Mandavgane, 2015), which was identical with the results of isotherms. The positive values of ΔH indicated that the adsorption process was endothermic (Pathak and Mandavgane, 2015). Moreover, ΔH value is an index that could differentiate between physical and chemical adsorption, when the ΔH value is in the range of 80 to 200 kJ·mol−1 and 2.1 to 20.9 kJ·mol−1, the adsorption behavior is attributed to chemical and physical adsorption, respectively (Liu et al., 2010; Sag and Kutsal, 2000). Therefore, the calculated enthalpy change values were 8.4 and 6.7 kJ·mol−1 for CLB and MBC, respectively, suggesting that physical adsorption might exist in adsorption of OTC. Meanwhile, the calculated enthalpy change value was 28.4 kJ·mol−1 for MMBC, which indicated that chemisorptions and physical adsorption might exist in adsorption of OTC (Liu et al., 2010). The positive value of ΔS explained randomness and disorder of adsorption of OTC on the three materials increased with increasing of time (Lonappan et al., 2018). By comparing with three prepared materials, MMBC performed prominent adsorption potential than CLB and MBC.

Studying of adsorption influence of existing cation on adsorbents was important owing to complex nature in actual bodies. Fig. 8a and b revealed that different concentration of Ca2+ could influence OTC adsorption on MBC and MMBC. With increasing of Ca2+ concentration, adsorption capacities slightly reduced for all adsorbents in same OTC concentration, which could be resulted from competitive effect for adsorption sites between the Ca2+ and OTC cation (Li et al., 2016a). As showed in Fig. 8c, the removal efficiency of OTC on MBC and MMBC had a slight decrease with increasing of HA concentration. The inhibition effect of HA could be ascribed to its direct competition for adsorption sites or blocking of pores and interstices of MBC and MMBC (Xie et al., 2014).

3.5. The effect of solution pH

3.7. The effect of actual sewage and the regeneration study

The pH is one of the most significant factors in adsorption process because adsorption is considered as a surface controlled process, especially for ionizable micropollutants. OTC has three pKa (3.27, 7.32, and 9.11) (Fig. S1). Thus, it would coexist in following several states under different conditions of pH: cationic form OTC+ (pH b 3.27), zwitterionic and neutral form OTC±/OTC0 (3.27 b pH b 7.32), and anionic form OTC− (pH N 7.32) (Li et al., 2018b; Liu et al., 2012). As seen in Fig. 7b, the point of zero surface charge (pHpzc) was 6.32, 6.85, and 8.76 for MMBC, MBC, and CLB, respectively. Changing pH of the solution would affect the surface charge of biochar. When pH value was lower than pHpzc, the surface charge of adsorbent was negative, while surface charge would turn to positive with pH becoming higher than pHpzc (Liu et al., 2012). Fig. 7a illustrated the effects of pH on OTC adsorption onto three absorbents. For CLB, Fig. 7a illustrated that its adsorption capacity slightly changed with pH increasing from 2 to 10. Meanwhile, for MBC and MMBC, the adsorption capacity of OTC gradually decreased with increasing of pH, which could be interpreted by ionic exchange interaction. The equilibrium pH values of CLB, MBC, and MMBC were also presented in Fig. 7a. According to equilibrium pH, it could be found that equilibrium pH increased with the increase of initial pH of solution for MBC and MMBC, which resulted in ionic exchange between cation released from clay mineral and cation of OTC becoming weak because of decrease of OTC+, while the effect of pH for MBC was greater than MMBC. For three adsorbents, When pH values increased from 4 to 10, the equilibrium pH of the solution changed insignificantly, attributing to excellent buffer performance of the materials (Fig. 7a), which was

It could be seen that two composites had a little loss of adsorption capacity in OTC solution prepared with sewage compared to OTC solution prepared with ultrapure water (Fig. 8d), meanwhile, the properties of sewage were presented in Supporting information. Therefore, MBC and MMBC still kept excellent removal abilities for OTC, suggesting that prepared materials had good availability in the practical process. Regeneration of MMBC was extremely important to the application of the adsorbent. From Fig. 9, the removal percentage of OTC was 92.5% in the first cycle. Meanwhile, MMBC could still remove about 92% pollutants after five cycles. Moreover, the recovery rate of the magnetic material was around 95% using extra magnet after every cycle. Besides, as displayed in Table S4, the iron ions dissolution rates of MBC and MMBC after adsorption were 0.024% and 0.167%, respectively, suggesting the adsorbents could keep extremely stable during the process of reaction. Meanwhile, MMBC performed higher adsorption capacity for OTC in comparison with some other materials (Table S5). Therefore, MMBC could effectively remove OTC in water due to its outstanding adsorption ability, stability, and magnetic recovery capacity.

3.6. The effect of ionic strength and HA

3.8. The mechanism study of OTC removal on MMBC For original biochar, the low surface area (53.31 m2·g−1) seemed in accordance with its low removal efficiency for OTC. According to this presumption, the low removal efficiency should be expected for OTC on MBC (with the lower surface area, 37.44 m2·g−1) and MMBC (with slightly enhanced surface area, 67.77 m2·g−1). However, the result

Fig. 7. Effect of pH on OTC adsorption by CLB, MBC and MMBC, and equilibrium pH of CLB, MBC and MMBC (a). The pHpzc of CLB, MBC and MMBC (b).

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Fig. 8. Effect of ionic strength on OTC adsorption by MBC (a) and MMBC (b). The effects of HA (c) and actual sewage (d) on OTC adsorption by MBC and MMBC.

was in conflict with the assumption. Thus, other mechanisms were likely to exist, which accounted for the excellent performances of MBC and MMBC (Fang et al., 2014). According to previous studies, the presence of MMT with high cation exchange capacity could substantially improve the adsorption capacity of OTC via cation exchange reaction (Chen et al., 2017a; Yao et al.,

Fig. 9. The regeneration experiment of MMBC.

2014). In addition, from Fig. 7a, the adsorption capacity of MBC and MMBC gradually reduced with the increasing of pH from 2 to 10 (especially for MBC), which might result from OTC+ decrease when equilibrium pH increased. This confirmed cation exchange participated in the adsorption process of OTC, while it could not be the major mechanism due to high removal ability for OTC at high pH value. Besides, the result of pHpzc showed that surface charge on the MBC and MMBC was negative in wide pH range (e.g., 7–10), and the negative charge increased with increasing of pH value. Meanwhile, at this pH range, the OTC anion was the main form of OTC. While, removal ability for OTC on MMBC was less sensitive to the initial pH variation, which suggested that electrostatic attraction and repulsion were not important to remove the OTC by MMBC (Yu et al., 2012). The FTIR spectra of MMBC before and after adsorption were illustrated in Fig. 5c. The peaks had a slight change for MMBC adsorbed OTC. It could be speculated that the groups participated in the OTC adsorption reaction. In Fig. 5c, the shift and increase of peak related to C=O/C=C bands, and the shift of medium peak attributed to C\\H bands both suggested the critical role of π–π interactions between OTC and MMBC in the adsorption processes (Kyzas and Deliyanni, 2015; Li et al., 2018b; Luo et al., 2018). The amino functional groups and O and/or N-hetero-aromatic rings of OTC might serve as πelectron-acceptor. The –OH, C_C, and C_O bends on the surface of adsorbents could act as π-electron-donor. Thus, adsorption of OTC on MMBC could be controlled by π-π interaction (Ahmed et al., 2017; Luo et al., 2018). Moreover, for MMBC, the peaks attributed to –OH had slight red-shift and weakened or strengthened, which verified hydrogen-bonding interaction played a significant role (Pezoti et al.,

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Fig. 10. The adsorption mechanisms of OTC on MMBC.

2016). Furthermore, the FTIR spectrum of MMBC after adsorption OTC showed that the peaks attributed to Si-O-Al, Si-O-Si, and Si-O bends all shifted and changed their strength, which confirmed that these functional groups provided more adsorption sites adsorbing OTC in the adsorption process. For MMBC, it had a specific adsorption mechanism due to the existence of Fe3O4. The study showed that the cation-π bonds could be formed between cations and π-electrons because Fe3O4 film surfaces were terminated by a hexagonal oxygen layer covered by quarter monolayer of iron cations (Zhao et al., 2013). So Fe3O4 nanoparticles could provide extra adsorption sites for aromatic compounds, which was consistent with previous reports (Peng et al., 2014; Zhao et al., 2013; Zhong et al., 2018). In addition, adsorption experiments showed that MMBC performed slightly higher removal efficiency compared to MBC, which supported that Fe3O4 could act as extra adsorption sites. Therefore Fe3O4 nanoparticles not only acted as binding sites for OTC adsorption but also provided effective magnetic separation performance. In order to confirm the aforementioned mechanisms, the XPS spectra of MMBC adsorbed OTC were carried out and displayed in Fig. 6. According to the C 1 s spectra of fresh and spent MMBC, the C_C group (at 284.61 ev; 73.1%) performed a slight shift to 284.56 ev, and the proportion it occupied increased to 76.63% after adsorption, which further demonstrated that π-π interaction involved in the adsorption of OTC (Liu et al., 2019). Moreover, the peaks at 286.3 ev (C-O; 20.2%) and at 289 ev (C=O; 6.7%) also had tiny move, and their occupied proportion decreased (19.06% for C\\O, 4.3% for C_O), implying the involvement of oxygen-containing functional groups. The oxygen-containing functional groups could bind with OTC by hydrogen bonds (Liu et al., 2019). Meanwhile, obvious variation was seen about the Fe3 + (t) coordination over the spent MMBC comparing to fresh MMBC, suggested that the Fe3+(t) coordination in Fe3O4 could provide the extra adsorption sites to remove OTC (Yang et al., 2016). From the aforementioned information, the mechanisms of OTC adsorption onto MMBC were described in Fig. 10. 4. Conclusions The MMBC was synthesized successfully and applied in OTC removal in the present study. The MMBC exhibited the best removal efficiency

(98.9%) compared to MBC (91.8%) and CLB (44.5%). While, the maximum adsorption capacity of MMBC (58.85 mg·g−1) was 2.63 times and 1.09 times in comparison with CLB and MBC at 308 K, respectively. Thermodynamic results confirmed the adsorption was spontaneous and endothermic process. The pH performed tiny influence for OTC adsorption on MMBC, and the ionic strength and HA slightly inhibited removal ability of OTC. In addition, MMBC still showed high removal efficiency after five regeneration cycles and 95% adsorbent could be recovered using the external magnet. The removal mechanisms of OTC onto MMBC were mainly attributed to hydrogen bonding and π-π reaction, and the ion exchange reaction was deemed to participate in the adsorption process. Meanwhile, functional groups (Si-O, Si-O-Al, Si-O-Si, etc.) and Fe3O4 nanoparticles could act as extra binding sites for OTC adsorption. In conclusion, MMBC had obvious potential to apply into the environment to remove OTC as a outstanding, reliable and recyclable adsorbent. Acknowledgments This work was supported by Gansu Natural Science Fund, China (17JR5RA218) and National Key Research and Development Program of China (2018YFC1903703). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi. org/10.1016/j.scitotenv.2019.133800. References Ahmed, M.B., Zhou, J.L., Ngo, H.H., Guo, W.S., 2015. Adsorptive removal of antibiotics from water and wastewater: progress and challenges. Sci. Total Environ. 532, 112–126. Ahmed, M.B., Zhou, J.L., Ngo, H.H., Guo, W.S., Johir, M.A.H., Belhaj, D., 2017. Competitive sorption affinity of sulfonamides and chloramphenicol antibiotics toward functionalized biochar for water and wastewater treatment. Bioresour. Technol. 238, 306–312. Baig, S.A., Zhu, J., Muhammad, N., Sheng, T.T., Xu, X.H., 2014. Effect of synthesis methods on magnetic Kans grass biochar for enhanced As(III, V) adsorption from aqueous solutions. Biomass Bioenergy 71, 299–310. Benhouria, A., Islam, M.A., Zaghouane-Boudiaf, H., Boutahala, M., Hameed, B.H., 2015. Calcium alginate–bentonite–activated carbon composite beads as highly effective adsorbent for methylene blue. Chem. Eng. J. 270, 621–630.

G. Liang et al. / Science of the Total Environment 695 (2019) 133800 Bilgic, C., 2005. Investigation of the factors affecting organic cation adsorption on some silicate minerals. J. Colloid Interface Sci. 281, 33–38. Boonsaner, M., Hawker, D.W., 2015. Transfer of oxytetracycline from swine manure to three different aquatic plants: implications for human exposure. Chemosphere 122, 176–182. Brigante, M., Pecini, E., Avena, M., 2016. Magnetic mesoporous silica for water remediation: synthesis, characterization and application as adsorbent of molecules and ions of environmental concern. Microporous Mesoporous Mater. 230, 1–10. Chayid, M.A., Ahmed, M.J., 2015. Amoxicillin adsorption on microwave prepared activated carbon from Arundo donax Linn: isotherms, kinetics, and thermodynamics studies. J. Environ. Chem. Eng. 3, 1592–1601. Chen, L., Chen, X.L., Zhou, C.H., Yang, H.M., Ji, S.F., Tong, D.S., Zhong, Z.K., Yu, W.H., Chu, M.Q., 2017a. Environmental-friendly montmorillonite-biochar composites: facile production and tunable adsorption-release of ammonium and phosphate. J. Clean. Prod. 156, 648–659. Chen, T.X., Zhao, Y.L., Song, S.X., 2017b. Correlation of electrophoretic mobility with exfoliation of montmorillonite platelets in aqueous solutions. Colloids Surf. A Physicochem. Eng. Asp. 525, 1–6. Dano, M., Viglasova, E., Galambos, M., Rajec, P., Novak, I., 2017. Sorption behaviour of pertechnetate on oxidized and reduced surface of activated carbon. J. Radioanal. Nucl. Chem. 314, 2219–2227. Ding, Z.H., Wan, Y.S., Hu, X., Wang, S.S., Zimmerman, A.R., Gao, B., 2016. Sorption of lead and methylene blue onto hickory biochars from different pyrolysis temperatures: importance of physicochemical properties. J. Ind. Eng. Chem. 37, 261–267. Fang, Q.L., Chen, B.L., Lin, Y.J., Guan, Y.T., 2014. Aromatic and hydrophobic surfaces of wood-derived biochar enhance perchlorate adsorption via hydrogen bonding to oxygen-containing organic groups. Environ. Sci. Technol. 48, 279–288. Fu, H.C., Zhao, P., Xu, S.J., Cheng, G., Li, Z.Q., Li, Y., Li, K., Ma, S.L., 2019. Fabrication of Fe3O4 and graphitized porous biochar composites for activating peroxymonosulfate to degrade p-hydroxybenzoic acid: insights on the mechanism. Chem. Eng. J. 375, 121980. Gurses, A., Dogar, C., Yalcin, M., Acikyildiz, M., Bayrak, R., Karaca, S., 2006. The adsorption kinetics of the cationic dye, methylene blue, onto clay. J. Hazard. Mater. 131, 217–228. Harja, M., Ciobanu, G., 2018. Studies on adsorption of oxytetracycline from aqueous solutions onto hydroxyapatite. Sci. Total Environ. 628-629, 36–43. Harvey, O.R., Kuo, L.J., Zimmerman, A.R., Louchouarn, P., Amonette, J.E., Herbert, B.E., 2012. An index-based approach to assessing recalcitrance and soil carbon sequestration potential of engineered black carbons (biochars). Environ. Sci. Technol. 46, 1415–1421. Hu, H., Sun, L.L., Jiang, B.Q., Wu, H.X., Huang, Q.M., Chen, X.H., 2018. Low concentration Re (VII) recovery from acidic solution by Cu-biochar composite prepared from bamboo (Acidosasa longiligula) shoot shell. Miner. Eng. 124, 123–136. Huang, L.H., Sun, Y.Y., Wang, W.L., Yue, Q.Y., Yang, T., 2011. Comparative study on characterization of activated carbons prepared by microwave and conventional heating methods and application in removal of oxytetracycline (OTC). Chem. Eng. J. 171, 1446–1453. Kyzas, G.Z., Deliyanni, E.A., 2015. Modified activated carbons from potato peels as green environmental-friendly adsorbents for the treatment of pharmaceutical effluents. Chem. Eng. Res. Des. 97, 135–144. Lehmann, J., 2006. Drop of the black stuff: terra preta contrasts strongly with normal soil in colour (left) and produces much more vigorous crops (below). Nature 442, 624–626. Li, X.L., Lu, H.J., Zhang, Y., He, F., Jing, L.Y., He, X.H., 2016a. Fabrication of magnetic alginate beads with uniform dispersion of CoFe 2 O 4 by the polydopamine surface functionalization for organic pollutants removal. Appl. Surf. Sci. 389, 567–577. Li, X.L., Zhang, Y., Jing, L.Y., He, X.H., 2016b. Novel N-doped CNTs stabilized Cu2O nanoparticles as adsorbent for enhancing removal of Malachite Green and tetrabromobisphenol A. Chem. Eng. J. 292, 326–339. Li, X.L., Lu, H.J., Zhang, Y., He, F., 2017a. Efficient removal of organic pollutants from aqueous media using newly synthesized polypyrrole/CNTs-CoFe2O4 magnetic nanocomposites. Chem. Eng. J. 316, 893–902. Li, Y., Wang, Z.W., Xie, X.Y., Zhu, J.M., Li, R.N., Qin, T.T., 2017b. Removal of Norfloxacin from aqueous solution by clay-biochar composite prepared from potato stem and natural attapulgite. Colloids Surf. Physicochem. Eng. Aspects 514, 126–136. Li, R.H., Wang, J.J., Gaston, L.A., Zhou, B.Y., Li, M.L., Xiao, R., Wang, Q., Zhang, Z.Q., Huang, H., Liang, W., Huang, H., Zhang, X.F., 2018a. An overview of carbothermal synthesis of metal–biochar composites for the removal of oxyanion contaminants from aqueous solution. Carbon 129, 674–687. Li, R.N., Wang, Z.W., Zhao, X.T., Li, X., Xie, X.Y., 2018b. Magnetic biochar-based manganese oxide composite for enhanced fluoroquinolone antibiotic removal from water. Environ. Sci. Pollut. Res. Int. 25, 31136–31148. Li, M.X., Liu, H.B., Chen, T.H., Chen, D., Sun, Y.B., 2019. Synthesis of magnetic biochar composites for enhanced uranium(VI) adsorption. Sci. Total Environ. 651, 1020–1028. Liu, Q.S., Zheng, T., Wang, P., Jiang, J.P., Li, N., 2010. Adsorption isotherm, kinetic and mechanism studies of some substituted phenols on activated carbon fibers. Chem. Eng. J. 157, 348–356. Liu, P., Liu, W.J., Jiang, H., Chen, J.J., Li, W.W., Yu, H.Q., 2012. Modification of bio-char derived from fast pyrolysis of biomass and its application in removal of tetracycline from aqueous solution. Bioresour. Technol. 121, 235–240. Liu, W.J., Tian, K., Jiang, H., Yu, H.Q., 2014. Harvest of Cu NP anchored magnetic carbon materials from Fe/Cu preloaded biomass: their pyrolysis, characterization, and catalytic activity on aqueous reduction of 4-nitrophenol. Green Chem. 16, 4198–4205. Liu, S.B., Li, M.F., Liu, Y.G., Liu, N., Tan, X.F., Jiang, L.H., Wen, J., Hu, X.J., Yin, Z.H., 2019. Removal of 17β-estradiol from aqueous solution by graphene oxide supported activated magnetic biochar: adsorption behavior and mechanism. J. Taiwan Inst. Chem. Eng. https://doi.org/10.1016/j.jtice.2019.05.002.

11

Lonappan, L., Rouissi, T., Brar, K.S., Verma, M., Surampalli, R.Y., 2018. An insight into the adsorption of diclofenac on different biochars: mechanisms, surface chemistry, and thermodynamics. Bioresour. Technol. 249, 386–394. Luo, J.W., Li, X., Ge, C.J., Muller, K., Yu, H.M., Huang, P., Li, J.T., Tsang, D.C.W., Bolan, N.S., Rinklebe, J., Wang, H.L., 2018. Sorption of norfloxacin, sulfamerazine and oxytetracycline by KOH-modified biochar under single and ternary systems. Bioresour. Technol. 263, 385–392. Michael, I., Rizzo, L., McArdell, C.S., Manaia, C.M., Merlin, C., Schwartz, T., Dagot, C., FattaKassinos, D., 2013. Urban wastewater treatment plants as hotspots for the release of antibiotics in the environment: a review. Water Res. 47, 957–995. Mohan, D., Singh, P., Sarswat, A., Steele, P.H., Pittman Jr, C.U., 2015. Lead sorptive removal using magnetic and nonmagnetic fast pyrolysis energy cane biochars. J. Colloid Interface Sci. 448, 238–250. Moussavi, G., Alahabadi, A., Yaghmaeian, K., Eskandari, M., 2013. Preparation, characterization and adsorption potential of the NH4Cl-induced activated carbon for the removal of amoxicillin antibiotic from water. Chem. Eng. J. 217, 119–128. Ni, J.Z., Pignatello, J.J., Xing, B.S., 2011. Adsorption of aromatic carboxylate ions to black carbon (biochar) is accompanied by proton exchange with water. Environ. Sci. Technol. 45, 9240–9248. Özdemir, M., Bolgaz, T., Saka, C., Şahin, Ö., 2011. Preparation and characterization of activated carbon from cotton stalks in a two-stage process. J. Anal. Appl. Pyrol. 92, 171–175. Pathak, P.D., Mandavgane, S.A., 2015. Preparation and characterization of raw and carbon from banana peel by microwave activation: application in citric acid adsorption. J. Environ. Chem. Eng. 3, 2435–2447. Peng, L., Ren, Y.Q., Gu, J.D., Qin, P.F., Zeng, Q.R., Shao, J.H., Lei, M., Chai, L.Y., 2014. Iron improving bio-char derived from microalgae on removal of tetracycline from aqueous system. Environ. Sci. Pollut. Res. 21, 7631–7640. Peng, H.B., Gao, P., Chu, G., Pan, J.H., Xing, B.S., 2017. Enhanced adsorption of Cu(II) and Cd(II) by phosphoric acid-modified biochars. Environ. Pollut. 229, 846–853. Pezoti, O., Cazetta, A.L., Bedin, K.C., Souza, L.S., Martins, A.C., Silva, T.L., Santos Júnior, O.O., Visentainer, J.V., Almeida, V.C., 2016. NaOH-activated carbon of high surface area produced from guava seeds as a high-efficiency adsorbent for amoxicillin removal: kinetic, isotherm and thermodynamic studies. Chem. Eng. J. 288, 778–788. Premarathna, K.S.D., Rajapaksha, A.U., Sarkar, B., Kwon, E.E., Bhatnagar, A., Ok, Y.S., Vithanage, M., 2019a. Biochar-based engineered composites for sorptive decontamination of water: a review. Chem. Eng. J. 372, 536–550. Premarathna, K.S.D., Rajapaksha, A.U., Adassoriya, N., Sarkar, B., Sirimuthu, N.M.S., Cooray, A., Ok, Y.S., Vithanage, M., 2019b. Clay-biochar composites for sorptive removal of tetracycline antibiotic in aqueous media. J. Environ. Manag. 238, 315–322. Qin, T.T., Wang, Z., Xie, X., Xie, C., Zhu, J., Li, Y., 2017. A novel biochar derived from cauliflower (Brassica oleracea L.) roots could remove norfloxacin and chlortetracycline efficiently. Water Sci. Technol. 76, 3307–3318. Rajapaksha, A.U., Chen, S.S., Tsang, D.C., Zhang, M., Vithanage, M., Mandal, S., Gao, B., Bolan, N.S., Ok, Y.S., 2016. Engineered/designer biochar for contaminant removal/immobilization from soil and water: potential and implication of biochar modification. Chemosphere 148, 276–291. Rajec, P., Rosskopfova, O., Galambos, M., Fristak, V., Soja, G., Dafnomili, A., Noli, F., Ðukic, A., Matovic, L., 2016. Sorption and desorption of pertechnetate on biochar under static batch and dynamic conditions. J. Radioanal. Nucl. Chem. 310, 253–261. Saber-Samandari, S., Saber-Samandari, S., Joneidi-Yekta, H., Mohseni, M., 2017. Adsorption of anionic and cationic dyes from aqueous solution using gelatin-based magnetic nanocomposite beads comprising carboxylic acid functionalized carbon nanotube. Chem. Eng. J. 308, 1133–1144. Sag, Y., Kutsal, T., 2000. Determination of the biosorption activation energies of heavy metal ions on Zoogloea remigera and Rhizopus arrhizus. Process Biochem. 35, 801–807. Segad, M., Jonsson, B., Akesson, T., Cabane, B., 2010. Ca/Na montmorillonite: structure, forces and swelling properties. Langmuir 26, 5782–5790. Shao, S.C., Hu, Y.Y., Cheng, J.H., Chen, Y.C., 2018. Degradation of oxytetracycline (OTC) and nitrogen conversion characteristics using a novel strain. Chem. Eng. J. 354, 758–766. Shi, Z.J., Hu, H.Y., Shen, Y.Y., Xu, J.J., Shi, M.L., Jin, R.C., 2017. Long-term effects of oxytetracycline (OTC) on the granule-based anammox: process performance and occurrence of antibiotic resistance genes. Biochem. Eng. J. 127, 110–118. Singh, B.P., Cowie, A.L., Smernik, R.J., 2012. Biochar carbon stability in a clayey soil as a function of feedstock and pyrolysis temperature. Environ. Sci. Technol. 46, 11770–11778. Tsai, W.T., Chen, H.R., 2013. Adsorption kinetics of herbicide paraquat in aqueous solution onto a low-cost adsorbent, swine-manure-derived biochar. Int. J. Environ. Sci. Technol. 10 (6), 1349–1356. Uchimiya, M., Lima, I.M., Thomas Klasson, K., Chang, S., Wartelle, L.H., Rodgers, J.E., 2010. Immobilization of heavy metal ions (CuII, CdII, NiII, and PbII) by broiler litter-derived biochars in water and soil. J. Agric. Food Chem. 58, 5538–5544. Vadivelan, V., Kumar, K.V., 2005. Equilibrium, kinetics, mechanism, and process design for the sorption of methylene blue onto rice husk. J. Colloid Interface Sci. 286, 90–100. Viglašová, E., Galamboš, M., Danková, Z., Krivosudsky, L., Lengauer, C.L., Hood-Nowotny, R., Soja, G., Rompel, A., Matík, M., Briancin, J., 2018. Production, characterization and adsorption studies of bamboo-based biochar/montmorillonite composite for nitrate removal. Waste Manag. 79, 385–394. Wang, Y.H., Li, L.L., Luo, C.N., Wang, X.J., Duan, H.M., 2016. Removal of Pb2+ from water environment using a novel magnetic chitosan/graphene oxide imprinted Pb2+. Int. J. Biol. Macromol. 86, 505–511. Wang, B., Gao, B., Fang, J., 2018. Recent advances in engineered biochar productions and applications. Critical Reviews in Environ. Sci. and Technol. 47, 2158–2207.

12

G. Liang et al. / Science of the Total Environment 695 (2019) 133800

Xiang, Y.J., Xu, Z.Y., Wei, Y.Y., Zhou, Y.Y., Yang, X., Yang, Y., Yang, J., Zhang, J.C., Luo, L., Zhou, Z., 2019. Carbon-based materials as adsorbent for antibiotics removal: mechanisms and influencing factors. J. Environ. Manag. 237, 128–138. Xie, M.X., Chen, W., Xu, Z.Y., Zheng, S.R., Zhu, D.Q., 2014. Adsorption of sulfonamides to demineralized pine wood biochars prepared under different thermochemical conditions. Environ. Pollut. 186, 187–194. Xu, X.B., Hu, X., Ding, Z.H., Chen, Y.J., Gao, B., 2017. Waste-art-paper biochar as an effective sorbent for recovery of aqueous Pb(II) into value-added PbO nanoparticles. Chem. Eng. J. 308, 863–871. Yaghmaeian, K., Moussavi, G., Alahabadi, A., 2014. Removal of amoxicillin from contaminated water using NH4Cl-activated carbon: continuous flow fixed-bed adsorption and catalytic ozonation regeneration. Chem. Eng. J. 236, 538–544. Yang, J.P., Zhao, Y.C., Ma, S.M., Zhu, B.B., Zhang, J.Y., Zheng, C.G., 2016. Mercury removal by magnetic biochar derived from simultaneous activation and magnetization of sawdust. Environ. Sci. Technol. 50, 12040–12047. Yang, F., Zhang, S.S., Sun, Y.Q., Cheng, K., Li, J.S., Tsang, D.C.W., 2018. Fabrication and characterization of hydrophilic corn stalk biochar-supported nanoscale zero-valent iron composites for efficient metal removal. Bioresour. Technol. 265, 490–497. Yang, F., Zhang, S.S., Sun, Y.Q., Du, Q., Song, J.P., Tsang, D.C.W., 2019. A novel electrochemical modification combined with one-step pyrolysis for preparation of sustainable thorn-like iron-based biochar composites. Bioresour. Technol. 274, 379–385. Yao, Y., Gao, B., Fang, J., Zhang, M., Chen, H., Zhou, Y.M., Creamer, A.E., Sun, Y.N., Yang, L.Y., 2014. Characterization and environmental applications of clay–biochar composites. Chem. Eng. J. 242, 136–143. Yao, Y., Gao, B., Wu, F., Zhang, C.Z., Yang, L.Y., 2015. Engineered biochar from biofuel residue: characterization and its silver removal potential. ACS Appl. Mater. Interfaces 7, 10634–10640. Yu, F., Chen, J.H., Chen, L., Huai, J., Gong, W.Y., Yuan, Z.W., Wang, J.H., Ma, J., 2012. Magnetic carbon nanotubes synthesis by Fenton's reagent method and their potential

application for removal of azo dye from aqueous solution. J. Colloid Interface Sci. 378, 175–183. Zhao, H.X., Lang, Y.H., 2018. Adsorption behaviors and mechanisms of florfenicol by magnetic functionalized biochar and reed biochar. J. Taiwan Inst. Chem. Eng. 88, 152–160. Zhao, Z.D., Zhou, W.J., 2019. Insight into interaction between biochar and soil minerals in changing biochar properties and adsorption capacities for sulfamethoxazole. Environ. Pollut. 245, 208–217. Zhao, C., Deng, H.P., Li, Y., Liu, Z.Z., 2010. Photodegradation of oxytetracycline in aqueous by 5A and 13X loaded with TiO 2 under UV irradiation. J. Hazard. Mater. 176, 884–892. Zhao, R.S., Liu, Y.L., Chen, X.F., Yuan, J.P., Bai, A.Y., Zhou, J.B., 2013. Preconcentration and determination of polybrominated diphenyl ethers in environmental water samples by solid-phase microextraction with Fe3O4-coated bamboo charcoal fibers prior to gas chromatography-mass spectrometry. Anal. Chim. Acta 769, 65–71. Zhong, D.L., Zhang, Y.R., Wang, L.L., Chen, J., Jiang, Y., Tsang, D.C.W., Zhao, Z.Z., Ren, S.P., Liu, Z.H., Crittenden, J.C., 2018. Mechanistic insights into adsorption and reduction of hexavalent chromium from water using magnetic biochar composite: key roles of Fe3O4 and persistent free radicals. Environ. Pollut. 243, 1302–1309. Zhou, Y.Y., Liu, X.C., Xiang, Y.J., Wang, P., Zhang, J.C., Zhang, F.F., 2017. Modification of biochar derived from sawdust and its application in removal of tetracycline and copper from aqueous solution: adsorption mechanism and modelling. Bioresour. Technol. 245, 266–273. Zhu, X.D., Liu, Y.C., Qian, F., Zhou, C., Zhang, S.C., Chen, J.M., 2014. Preparation of magnetic porous carbon from waste hydrochar by simultaneous activation and magnetization for tetracycline removal. Bioresour. Technol. 154, 209–214.