Application of goethite modified biochar for tylosin removal from aqueous solution

Colloids and Surfaces A: Physicochem. Eng. Aspects 502 (2016) 81–88

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Colloids and Surfaces A: Physicochemical and Engineering Aspects journal homepage: www.elsevier.com/locate/colsurfa

Application of goethite modified biochar for tylosin removal from aqueous solution Xuetao Guo a , Hao Dong a , Chen Yang b,∗ , Qian Zhang c , Changjun Liao d , Fugeng Zha a , Liangmin Gao a a

School of Earth and Environment, Anhui University of Science and Technology, Huainan 232001, China College of Environment and Energy, South China University of Technology, Guangzhou, 510006, China c School of Life and Environmental Science, Guilin University of Electronic Technology, Guilin, Guangxi, 541000,China d Department of Environmental Engineering, Guangdong Polytechnic of Environmental Protection Engineering, Foshan 528216, PR China b

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

• Goethite biochar composite (BCF) was simplified created with higher sorption for tylosin (TYL) in aqueous. • Goethite loaded on biochar played a key role in TYL remove. • The removal efficiency of BCF was greater than pure BC film.

a r t i c l e

i n f o

Article history: Received 21 February 2016 Received in revised form 22 April 2016 Accepted 3 May 2016 Available online 4 May 2016 Keywords: Goethite Biochar Tylosin Sorption

∗ Corresponding author. E-mail address: [email protected] (C. Yang). http://dx.doi.org/10.1016/j.colsurfa.2016.05.015 0927-7757/© 2016 Elsevier B.V. All rights reserved.

a b s t r a c t Recent investigations have shown frequent detection of pharmaceuticals in soils and waters posing potential risks to human and ecological health. Here, we report the enhanced removal of tylosin (TYL) from water by a novel goethite biochar (BCF) composite. Characterization by scanning electron microscopy (SEM) images showed good dispersion of goethite nanoparticles on the biochar surface. The coating was constructed by well-crystallized cubic phase goethite nanoparticles as examined by Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analysis. To evaluate the feasibility of BCF composite as a potential adsorbent for antibiotic removal, batch sorption experiments were conducted using TYL as the model antibiotic molecule. The results showed that this adsorbent showed rapid and high sorption of TYL. According to the Henry and Freundlich model, the maximum capacities of TYL on BCF were 8132.89 L/kg and 5386.76 (␮g/g)/(mg/L)n respectively. Besides, the sorption capacity of TYL on BCF was obviously affected by pH and ionic strength. The sorption mechanisms of TYL on BCF were contributed to hydrophobic, electrostatic, H-bonding, cation exchange and ␲-␲ EDA interaction. The present work suggests that BCF composite, owing to their simple preparation procedures, high sorption capacity, low cost, and environmentally benign nature, have great potential as the next-generation adsorbent in the removal of antibiotics and other emerging contaminants. © 2016 Elsevier B.V. All rights reserved.

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X. Guo et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 502 (2016) 81–88

Fig. 1. FTIR spectrum of biochar (BC) and biochar-goethite complexes (BCF).

the most thermodynamically stable iron oxide which has been extensively researched especially the structure (including surface structure), the sorption capacity to anions, organic/organic acid (especially for the soil organic carbon) and cations in the natural environment and its potential application in environmental protection [4,18]. However, separation of goethite from an aqueous medium often requires centrifugation which is rather tedious and expensive. Recently, biochar (BC) which can be rapidly separated by filtration field have been developed for the sorption of antibiotics and exhibited high sorption capacities [19,20]. The objective of this work was to develop and evaluate a new method to prepare goethite-biochar composites for the removal of TYL from aqueous solution. The goethite-biochar adsorbents were prepared through co-precipitation of the iron metal ions onto biochar. The adsorbents were tested for TYL sorption capacity in batch experiments. The specific objectives of this work were to: (1) characterize the goethite-biochar composites, and (2) determine the sorption ability and mechanisms of the goethite-biochar composites for TYL in aqueous solution. 2. Materials and methods

1. Introduction 2.1. Reagents Tylosin (TYL), a macrolides antibiotic, is widely applied for the treatment of bacterial, protozoal and fungal infections in human therapy, livestock production and aquaculture [1]. Residues of TYL and metabolites discharged from municipal wastewater treatment plants and agricultural runoff have a high potential to enter surfacewater and groundwater [2,3]. Concerns arising from exposure to TYL in aquatic environments include acute and chronic toxic effects and microorganism antibiotic resistance [4]. However, the removal of TYL by existing water treatment technologies is incomplete [5]. To date, many technologies, such as photocatalytic degradation, membrane filtration, ion-exchange and sorption, have been explored for the removal of antibiotics from aqueous solution [6–8]. Compared to other techniques, sorption is considered simpler and more economical, and remains one of the most attractive methods for antibiotic removal [9]. Among the current available adsorbents, biochar has been greatly studied due to its outstanding properties like high sorption capacity, low cost, geological abundance, and environmentally benign nature [3]. Biochar is analogous to black carbon and derived from burning plant residues [10]. It is an ubiquitous geosorbent that is long lasting in the natural environment and thus influences the environmental behavior of antibiotics [11]. Rajapaksha et al. [12] investigated the removal of sulfamethazine by tea waste biochars and found that the ␲-␲ interaction and cation exchange were the primary sorption mechanisms. Teixidó et al. [13] found that sorption of sulfamethazine by black carbon was via ␲-␲ electron donor-acceptor interaction. Li et al. [14] indicated that sorption of sulphamethoxazole (SMX) by the biochar derived from rice straw was mainly via ␲-␲ electron donor-acceptor, while the electrostatic interaction might control the sorption of SMX by the biochar derived from alligator flag. TYL adsorptions have been studied on clays, humic substances and soils [1,15–17]. Their ionization (cationic and neutral) depends on the pH of the media as is shown in Fig. 1 [16]. Hence, the sorption of TYL is complex. The adsorption of TYL is known to be governed by surface complexation or cation exchange mechanisms [15,16]. Among many different parameters, pH, ionic speciation, ionic strength, soil texture, cation exchange capacity (CEC), and soil organic carbon (SOC) were considered as the most important factors influencing the sorption of TYL to clays, goethite, humic acid and soils [1,2,15–17]. Goethite (a-FeOOH) is a wide spread soil mineral and a major component of many ores, sediments and soils and it is one of

Tylosin tartrate (purity > 95%) was purchased from SigmaAldrich Corporation (St. Louis, MO). Acetonitrile and formic acid (HPLC grade, Merck Chemicals Co. AQ5) were used as received. Pure water was prepared by Milli-Q® water machine (Millipore Co., Guangzhou, China). All the other chemicals were analytical reagent grade and used without further purification. Primary stock solutions of TYL at 1000 mg/L were prepared with pure water and stored at 4 ◦ C for a maximum of 1 month. The work solutions were prepared by diluting stock solution using 0.01 M KNO3 solution. 2.2. Preparation of goethite-biochar composites(BCF) Pristine biochar (palm, obtained from fast pyrolysis at 600 ◦ C) was supplied by Guangdong institute of eco-environment and soil sciences. The sample was milled through a 200-mesh sieve, stirred by 2 mol/L hydrochloric acid (HCl) for 12 h to remove the salt, and centrifuged to remove floater on the surface. After that, the residue was washed with deionized water until the aqueous phase was neutral, and dried at 105 ◦ C for 24 h. A typical procedure for the preparation of BCF was as follows (Scheme 1) [21]: Briefy, 4 g of biochar was added to 800 mL distilled water, agitated with a magnetic stirrer, and continuously purged with N2 gas for 30 min. The composite dispersion was sonicated until it became clear with no visible particulate matter. Then 50 g Fe(NO3 )3 ·9H2 O was dispersed into the solution. 5 M KOH was added into the suspension until red colloid was generated. The yielding ferrihydrite-biochar complex was aged at 60 ◦ C in a capped Teflon container for 60 h and then was dialyzed with double distilled deionized water until the pH of the supernatant reached 8.5 close to the point of zero charge. After that, the solid was freezedried and employed as sorbent. 2.3. Characterization Fourier transform infrared (FTIR) spectra were recorded with a KBr pellet in the mid-infrared region using a Nicolet 6700 Infrared Detector (Thermo Fisher Scientific, USA). The Brunauer-EmmettTeller (BET) surface area of the samples was determined by nitrogen adsorption at 77 K (GEMINT VII 2390, USA). The constituents of the samples were identified using an X-ray powder diffractometer (XRD) (XD-2X/M4600, Beijing Purkinje General Instrument Co.,

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Scheme 1. Illustration of strategy for preparation of goethite-biochar composite.

Ltd, China). During the analysis, the samples were scanned from 20 to 70◦ at a speed of 4◦ min−1 using CuK␣ radiation at 40 kV. The microscopic features of the materials were recorded with an environmental scanning electron microscope (SEM) (XL-30-ESEM, Philips, Netherlands). The point of zero charge (PZC) was measured by potentiometric titrations at three KCl concentrations. 2.4. Sorption procedure The sorption experiments were conducted using a batch equilibrium technique at 25 ◦ C and pH 7.0. The initial TYL concentrations were set from 0.5 to 50 mg/L. The background solution contained 0.003 M NaN3 to minimize bioactivity and 0.01 M KNO3 to adjust ionic strength. A predetermined amount of sorbent was filled with the initial aqueous solution in completely mixed batch reactor (CMBR) systems with teflon gaskets and mixed for sorption equilibrium on a shaker at 150 rpm. After the sorption experiments, the screw cap vials were centrifuged at 4000 rpm for 30 min, and 1 mL of supernatant was transferred into a pre-weighted 1.5 mL amber glass vial for chemical analyses. Each concentration level, including blanks, was run in triplicate. KOH or HNO3 solutions were used for pH adjustment. Kinetic studies of TYL sorption were carried out from aqueous solutions with a certain concentration 5 ppm. A mixed volume of the aliquot was withdrawn at designated time points while the reactors were run continuously. 2.5. Chemical analysis The concentrations of TYL in aqueous solution were measured by a reverse-phase high-performance liquid chromatography (Hitachi D-2000 Elite-HPLC) with C18 column (5 ␮m, 4.6 × 250 mm; Agilent) and diode array UV detector (wavelength at 290 nm for TYL). The mobile phase (at a flow rate of 0.5 mL/min) for TYL was a mixture of acetonitrile (35%) and an aqueous solution (65%) containing 0.01 mol/L KH2 PO4 (pH = 2.0). The injection volume was 20 ␮L. External standards of TYL (0.1–100 mg/L) were employed to establish a linear calibration curve and the sample concentrations were calculated from its integrated peak areas. The solid phase concentrations were calculated based on the mass balance of the solute between the two phases. 2.6. Sorption models 2.6.1. Sorption isotherms models The equilibrium sorption data was fitted using Henry (Eq. (1)) and Freundlich (Eq. (2)) models [22]: qe = kd Ce

(1)

qe = kf Ce n

(2)

where Ce (mg/L) and qe (mg/kg) are the equilibrium concentration of TYL in the liquid phase and solid phase, respectively. kd (L/kg) is the distribution coefficient of solute between soil and water. kf (␮g/g)/(mg/L) is the capacity affinity parameter and n (dimensionless) is the exponential parameter. Parameters were estimated by nonlinear regression weighted by the dependent variable. 2.6.2. Sorption kinetic models To investigate the potential rate-controlling steps involved in the sorption of TYL on sorbent, kinetics data were fitted by pseudo-first-order, pseudo-second order, Elovich models and the intraparticle diffusion model. Governing equations of the models can be written as follows [1]: log(qe − qt ) = logqe −

k1 t 2.303

(3)

t 1 t = + qt qe k2 q2e

(4)

qt = ˇ−1 ln(ˇ˛t + 1)

(5)

qt = ki t 0.5 + Constant

(6)

where qt and qe are the amounts of sorption TYL at time t and at equilibrium respectively. k1 and k2 are the first-order and secondorder apparent adsorption rate constants, respectively. Also, ␣ is the initial adsorption rate (mg/kg) and ␤ is the desorption constant (kg/mg). The first-order and second-order models describe the kinetics of the solid-solution system based on mononuclear and binuclear adsorption, respectively, with respect to the sorbent capacity [23], while the Elovich model is an empirical equation considering the contribution of desorption. 3. Results and discussion 3.1. Characterization of adsorbents Fig. 1 shows the FTIR spectra of BC and BCF particles. For the BC spectrum, the index peak at 3402 cm−1 are assigned to the –OH vibration which are related to non-stoichiometric hydroxyl units (excess water) in the BC structure. The band at 1632 cm−1 was assigned to aromatic C C or COO– groups. Nevertheless, in the FTIR spectrum of BCF (Fig. 1), six obvious bands are centered around 3125, 1465, 1325, 803, 782 and 621 cm−1 relative to goethite after the dipping of BC. The strong and intense band at 3125 cm−1 possibly corresponded to the bulk –OH stretching [16]. The absorbance band at 1465 and 1325 cm−1 is the C O stretching vibration in BCF

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X. Guo et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 502 (2016) 81–88 Table 1 Kinetics models parameters for the adsorption of TYL onto BC and BCF. Conditions

BC BCF

pseudo-first-order pseudo-second-order Elovich model k1 (L/kg)

R2

k2 (g/␮g/h)

R2

␣

ˇ

R2

0.91 0.82

0.97 0.94

0.46 30.90

0.98 0.99

8.38 13.4

0.29 0.46

0.98 0.98

Table 2 Isotherm parameters for TYL sorption onto BC/BCF. Conditions

BC BCF

Fig. 2. XRD patterns of biochar (BC) and biochar-goethite complexes (BCF).

[24]. Three bands less than 1000 cm−1 in the FTIR spectra of the BCF are corresponding to signal of Fe-O of iron oxides [2]. The high-angle XRD diffractograms (Fig. 2) are used to identify the crystalline phases formed upon modification of BCF, and further indicate the presence of goethite. The peaks at 2 = 20.1, 27.2, and 28.3 were ascribed to BC phase of C substrate, while the peaks at 2 = 21.2, 33.4, 36.6, 47.6, and 63.51 could be agreed well with the standard orthorhombic phase of goethite (PDF No. 29-0713), corresponding to (110), (130), (111), (041) and (061) planes, respectively [25]. The raw products (Fig. 3b) have distinct morphology in comparison to the starting reagents (Fig. 3a). Stacked goethite particles with a needle shaped were observed on the surface of BC, which was consistent with the XRD results. As shown in Fig. 3b goethite particles were closely embedded in the surface of BC, and the particle were density on BCF, which could be attributed to the dissolution of goethite from the BC skeleton. The N2 adsorption-desorption isotherms and pore size distribution curves for the BC and BCF were shown in Fig. 4 which belong to type IV adsorption isotherms with a sharp upward extension branch. The type H1 hysteresis loops at higher P/P0 according to IUPAC, indicating that the two materials had uniform mesoporous structures. The pore size distributions of BC and BCF calculated from the adsorption branch clearly determines the pore size to be mainly in the range of 20–60 nm, and the average pore size of BC and BCF are both 38 nm. In addition, with the introduction of goethite particles into BC, the surface area (from 230.5 to 120.5 m2 /g) and pore volume area (from 4.85 to 2.43 cm3 /g) were decreased. The reason of the decrease might be that the introduction of goethite would occupy or block pore canals. Fig. 5 showed the relationship between zeta potential and pH, and the iso-electric points (IEPs) of BC and BCF. The results indicated that the IEPs of BC and BCF approximately occurred in the pH of 3.1 and 7.0 respectively. The IEPs of BCF was higher than that of BC, suggesting that the amino modification made biochar with more negative charge due to the large introduction of goethite. 3.2. Sorption kinetics of TYL on BC and BCF The sorption of TYL to both BC and BCF samples showed two phases: a rapid initial sorption during the first three hours followed by a much slower phase till reaching sorption equilibria after roughly 12 h (Fig. 6). The first phase could be ascribed to rapid occupation of easily accessible external surface sorption sites such as outer sphere complexation [3]. The slow phase could be related to the formation of inner layer complexes. Alternatively,

Henry model

Freundlich model 2

kd (L/kg)

R

n

kf (␮g/g)/(mg/L)n

R2

2017.51 8132.89

0.99 0.94

0.64 0.48

3962.38 5386.76

0.93 0.99

the slower phase may be related to kinetic inhibition of TYL movement through narrow pore channels. In comparison with the BC, the BCF showed faster and higher sorption of TYL, suggesting that the goethite particles may serve as adsorption sites for TYL in aqueous solution. The sorption kinetics data were fitted with pseudo-first-order, pseudo-second order, and Elovich kinetic models. The second order and Elovich models are better fitted models with R2 above 0.98 (Table 1). Based on the fitted Elovich model, the BCF has higher initial adsorption rate (a) of TYL than BC while BC has higher desorption potential (b) than BCF. BCF has the highest b value, suggesting that modified biochars have greater affinity for TYL in aqueous solution. Good fit of second and Elovich models implies that TYL was retained with several possible mechanisms [26]. In addition, the intraparticle diffusion model is employed to further analyze the adsorption kinetics and to assess the importance of diffusion during the adsorption process. As seen from Fig. 7, the fact that the model curves did not pass through the origin with positive intercepts (C = / 0) indicated that both surface sorption and intraparticle diffusion contributed to the actual sorption process of TYL on BC and BCF [27]. The initial phase is attributed to the diffusion of TYL through the solution to the exterior surface of the composite BCF, which can be regarded as external diffusion. The secondary stage shows the gradual sorption where intraparticle diffusion is rate-limiting. In the third stage, the intra-particle diffusion rate was obviously lower than the former stage of surface diffusion due to the diameter of micropore which was relatively small compared to the larger molecule-sized of TYL. 3.3. Sorption isotherms of TYL on BC and BCF The sorption isotherm of TYL on BC and BCF at 25 ◦ C and pH 7.0 was performed in Fig. 8. To illustrate the sorption characterization, the sorption data were analyzed on the basis of the Henry and Freundlich equation. The Henry and Freundlich parameters, together with regression coefficients, are also listed in Table 2. As shown in this table, the sorption of TYL over BC and BCF were well fitted with Henry and Freundlich model. Compared with the TYL sorption capacities of other adsorbents reported in literature, the BCF exhibited an excellent sorption performance. Zhang et al. [15,17] reported the kd for TYL on agricultural soils and clay minerals were from 12 and 1078 L/kg respectively. In our previously studies the estimated kd for TYL on goethite and humic acid were 11.54 and 386.1 L/kg respectively [1,2,16]. The linear partitioning process might be driven by hydrophobic interactions delineated above [2]. The BCF isotherm (R2 = 0.99) fitted slightly better than BC with the Freundlich model (R2 = 0.93), suggesting its sorption on BCF may be controlled by the heterogeneous chemisorption. The isotherms

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Fig. 3. SEM images of biochar (a) and biochar-goethite complexes (b).

Fig. 4. N2 adsorption–desorption isotherms and corresponding pore size distribution curves (inset) of biochar (BC) and biochar-goethite complexes (BCF).

Fig. 5. Zeta potentials of biochar (BC) and biochar-goethite complexes (BCF).

become more nonlinear as goethite modified BC, reflected by the evidently decreasing n values (e.g., n decreases from 0.86 to 0.48). The gradually nonlinear sorption could be accounted by the fact that the hydroxy phase in complexes is existed and converted into condensed more heterogeneous sorption sites for TYL [3]. Because TYL have the charged functional group and electro deficient ␲ structure, it may interact with both the goethite and the aromatic structure inside BC basal planes. Under the experimental condi-

Fig. 6. Sorption kinetics of TYL on biochar (BC) and biochar-goethite complexes (BCF).

tions, the electrostatic attraction between BC/BCF and TYL could be the first step controlled the sorption [28]. The macrolide ring of TYL is an effective ␲-electron acceptor because electron-withdrawing amidogen groups can attract electron. In addition, the ␲-electron density of its macrolide heterocyclic group may also be decreased by the contained oxygen atom because of high electron negativity [29]. As a result, the substituted macrolide ring and the aromatic

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Fig. 7. Intraparticle diffusion model of on biochar (BC) and biochar-goethite complexes (BCF).

Fig. 8. TYL sorption isotherms on biochar (BC) and biochar-goethite complexes (BCF).

heterocyclic group of TYL may invoke extra ␲-␲ EDA interaction with the BCF/BC surfaces of carbonaceous adsorbents [29]. 3.4. Effects of pH on the sorption of TYL on BC and BCF The sorption of TYL on BC and BCF surface is most likely controlled by two factors, namely speciation of the TYL and the charge of the sorbent surface, it is important to investigate the pH effect on the sorption. Batch sorption experiment was conducted at solution pH of 3.0–11.0 (Fig. 9). The results showed that TYL sorption on BCF significantly increased with the pH increased from 3.0 to 9.0 then decreased with the pH increased to 11.0, while for BC the sorption slowly increased with the pH increased from 3.0 to 6.0 and then decreased with the pH increased. The sorption capacity of TYL on BCF composite is much higher than on the BC under the same experimental condition. In the composite BCF can effectively adsorb TYL through formation of stable metal-ligand complex, while BC provides the support for goethite deposition [2,25]. In a comparison with free goethite tend to aggregate and cannot be fully recovered from an aqueous medium, the composite BCF can be easily separated, and the recovery is high [30]. TYL sorption on metal oxide was reported to be highly influenced by solution pH [2,16]. The change of pH can affect the speciation of TYL and the surface properties of BCF, for example, the amount of hydroxyl on its surfaces. By evaluating the change in surface charges, the observed pH dependence could be rationalized [31]. Several major sorption mechanisms should be considered in the interactions between TYL and BC/BCF according to their physicochemical properties [1,2,16,32–34]: (1) hydrophobic partitioning; (2) cation bridging and exchange; (3) electrostatic attraction; (4) H-bonding; and (5) ␲-␲ EDA interactions. TYL molecules are most positively charged in the pH below 7.0, leading to remarkable increase of hydrophilicity relative to the neutral species. When the pH of the solution is below 7.0, the dominant TYL species and BCF particles are positively charged. The charge repulsion is the factor which controlled the sorption and the sorption could be contributed to the H-bonding and cation exchange. Thus, hydrophobic partitioning into the BC/BCF may be predominant in the sorption progress in the studied pH ranges [13]. Alternatively, anion exchange and cation bridging interactions may be involved in the strong sorption of TYL+ to BCF. The pHPZC value of BC was 3.0, so the electrostatic attraction will be the main factor controlled the sorption in this pH ranges [13,35]. We propose that, in the higher pH values, TYL sorption is facilitated by ␲-␲ electron donoracceptor (EDA) interactions, which are those that arise from attraction

Fig. 9. Sorption of TYL on biochar (BC) and biochar-goethite complexes (BCF) at different pH values (Contact time for TYL were 24 h; temperature = 25 ◦ C; ionic strength was 0.01 mol/L KNO3 ).

between oppositely polarized quadrapoles of arene systems orienting in a parallel planar fashion [13]. 3.5. Effects of ionic strength on the sorption of TYL on BC and BCF In this study, different amounts of KNO3 were added to the mixture of TYL and BC/BCF suspensions to investigate the effect of ionic strength on the sorption capacities. The results are shown in Fig. 10. It can be seen that the sorption capacities decrease with the addition of KNO3 . It should be noted that the removal percentages would be different for BC and BCF, as they are tempered by several factors such as competitive ions [19]. Various mechanisms such as hydrophobic, electrostatic, hydrogen bond and ␲-␲ interactions may simultaneously participate in TYL sorption [36]. TYL molecules may interact with BCF via ␲-␲ electron donor-acceptor (EDA) interactions between the protonated amino ring of the TYL molecule and the ␲-␲ electron rich grapheme surface of BCF [25,36]. This strong ␲-␲ EDA interaction has previously been verified between SMT molecules and carbon black [36]. Electrostatic cation exchange could be another possible mechanism. Since TYL molecules contain several moieties capable of hydrogen bonding as hydrogen acceptors or donors, TYL may bind through hydrogen bonding depending on the pH of the media [27]. For instance, in the pH values of 5.0 where TYL+ is dominant, the sorption process is governed mainly by

X. Guo et al. / Colloids and Surfaces A: Physicochem. Eng. Aspects 502 (2016) 81–88

Fig. 10. Sorption of TYL on biochar (BC) and biochar-goethite complexes (BCF) at different ionic strength levels. Contact time for TYL were 24 h; equilibrium pH for TYL was 5.0; temperature = 25 ◦ C.

a near stoichiometric proton exchange process known as positive charge-assisted hydrogen bonding [10]. 4. Conclusions We report the synthesis of composite BCF with goethite coating on BC via a two-step method. The goethite coating significantly improved the activity of the BCF. BCF showed rapid and high sorption of TYL in aqueous solution. According to the Henry and Freundlich model, the maximum capacities of TYL on BCF were 8132.89 L/kg and 5386.76 (␮g/g)/(mg/L)n respectively. Besides, the sorption capacity of TYL on BCF was obviously affected by pH and ionic strength. The excellent sorption performance was mainly attributed to the good dispersion of goethite nanoparticles on the biochar network, as well as the unique surface of the biochar. The sorption mechanisms of TYL on BCF were contributed to hydrophobic, electrostatic, H-bonding, cation exchange and ␲-␲ EDA interaction. The present work suggests that BCF composite, owing to their simple preparation procedures, high sorption capacity, low cost, and environmentally benign nature, have great potential as the next-generation adsorbent in the removal of antibiotics and other emerging contaminants. Acknowledgements The study was supported by the National Natural Science Foundation of China (Nos. 41503095, 41501342, 41173104), the Natural Science Foundation of Universities of Anhui Province (KJ2015A016), the PhD Fund of Anhui University of Science and Technology (ZY540) and the Key Science Foundation for Young Teachers of Anhui University of Science and Technology (QN201507). References [1] X. Guo, J. Ge, C. Yang, R. Wu, Z. Dang, S. Liu, Sorption behavior of tylosin and sulfamethazine on humic acid: kinetic and thermodynamic studies, RSC Adv. 5 (2015) 58865–58872. [2] X. Guo, C. Yang, Y. Wu, Z. Dang, The influences of pH and ionic strength on the sorption of tylosin on goethite, Environ. Sci. Pollut. Res. 21 (2014) 2572–2580. [3] F. Lian, B. Sun, X. Chen, L. Zhu, Z. Liu, B. Xing, Effect of humic acid (HA) on sulfonamide sorption by biochars, Environ. Pollut. 204 (2015) 306–312 (Barking, Essex : 1987).

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