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purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature
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Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature Nan Sun a, Ying Zhang b,∗, Lixin Ma c, Shuili Yu d,∗, Jinxuan Li a a
School of Water Conservancy and Civil Engineering, Northeast Agricultural University, Harbin 150030, China School of Resources and Environment, Northeast Agricultural University, Harbin 150030, China Environmental Protection of Heilongjiang Province, Harbin 150090, China d State Key Laboratory of Pollution Control and Resources Reuse, Tongji University, Shanghai 200092, China b c
a r t i c l e
i n f o
Article history: Received 15 August 2016 Revised 13 February 2017 Accepted 17 March 2017 Available online xxx Keywords: Adsorption Humic acid Purified attapulgite Chitosan
a b s t r a c t In the adsorption treatment of water polluted with humic acid (HA), it is equally important to recover clean water with inexpensive raw materials, mild treatment environments and excellent adsorption capacity. Herein, a composite structured CPA (chitosan-modified purified attapulgite) composed of uniform PA (purified attapulgite) nanorods modified by chitosan was successfully fabricated under acetic acid conditions. Benefiting from the mesoporous structure of the PA nanorods and the carboxyl groups of chitosan, the prepared hybrid CPA exhibited a quick response and excellent adsorption capacity towards HA. The effects of pH, adsorbent dose, adsorption time, initial HA concentration and temperature were systematically studied using PA-90 (PA with purity of 90%) and CPA, respectively. The results show that CPA has a high capture affinity towards HA with a short response time (2 min for 80%) and the maximum adsorption capacity could reach 112.07 mg/g, which is superior to most results that have been reported. We believe CPA could be considered as an efficient and green heterogeneous adsorbent for the adsorption of humic acid, as well as provide a versatile platform for further development of functional hybrid composites for the adsorption of other pollutants. © 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Humic acid (HA), which generally generates an undesirable color, odor and taste, has seriously polluted drinking water resources and poses an enormous threat to our health [1]. On the one hand, the excessive intake of HA may lead to some diseases, such as blackfoot and Kashin-Beck [2,3]. On the other hand, HA can produce by-products, specifically trihalomethanes and haloacetic acids, during the chlorination process that could possibly be carcinogenic to human beings [1]. In addition, HA also has a strong binding capacity for many contaminants, such as heavy metals, pesticides and herbicides, and thus could increase the contaminant concentration in water [4]. Polluted drinking water directly or indirectly entering human beings through the food chain could also cause great threat to our health. Therefore, sorbents with high adsorption capacity and quick response are desired for HA removal.
∗
Corresponding authors. E-mail addresses: [email protected] (Y. Zhang), [email protected] (S. Yu).
HA in drinking water has strict standards, which makes it urgent to develop appropriate technologies for HA removal. Adsorption is considered a promising method because of its advantages of simple fabrication, operability, efficiency and relatively low cost. A number of adsorption materials, such as zeolites [1], activated carbon [5], resins [6], chitosan [7], metal oxides [8], attapulgite [9], and organic or inorganic nanostructured fibers [10–13] have been successfully applied to dispose of sewage to improve water quality. Most of these adsorbents can only be effectively operated at high temperature, which is energy consuming [1,4,6,7,9]. Simultaneously, higher temperature is not always operable in practice, particularly in some severely cold areas. Therefore, the development of functional absorbents that could be operated at low temperature for effective HA removal is urgent. Attapulgite has the potential to meet the above requirements owing to its unique layered chain structure with high specific surface area, moderate cation exchange capacity, good liquidity, and selective adsorption and is equipped with strong sterilization, deodorization, detoxification and insecticidal properties [9]. In our previous study, we found that natural attapulgite exhibited relatively higher adsorption capacity towards HA at low temperature
http://dx.doi.org/10.1016/j.jtice.2017.03.017 1876-1070/© 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
Please cite this article as: N. Sun et al., Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.03.017
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Fig. 1. Schematic diagram of interaction between PA-90 and chitosan.
compared with other adsorbents due to the adsorption process being exothermic in nature [14], but the limited adsorption capacity could not satisfy the increasing concentration of HA in practice. Therefore, it is critical to prepare purified attapulgite to improve the adsorption properties. Chitosan, generally extracted from the alkaline deacetylation of chitin, was chosen as a functional modifier polymer for the preparation of hybrid functional materials owing to its biocompatibility, biodegradability and high adsorption capabilities [15]. However, the raw material has a tendency to agglomerate in aqueous solution and can be easily dissolved in acidic media. The low specific gravity of chitosan makes itself difficult to separate from other aqueous solutions, which has limited its usage in either batch or column modes [16]. Until now, considerable effort has been devoted to modifying chitosan beads or chitosan immobilized on inorganic nanomaterials to enhance HA adsorption in aqueous solution [17–22]. To the best of our knowledge, no effort has been made to develop a promising strategy to fabricate chitosan-modified attapulgite hybrid functional materials for effective HA removal in water at low temperature. In this contribution, we aimed to investigate the high adsorption capability of hybrid adsorbents for effective removal of HA from high-color water at low temperature. The as-prepared attapulgite was further functionalized by chitosan, and the fabrication process is illustrated in Fig. 1. More importantly, chitosan-modified porous attapulgite was used as a composite adsorbent for HA removal for the first time, and the initial motivation of this study was to develop an environmental composite adsorbent with high and ultrafast response to HA for potential applications in drinking water. 2. Materials and methods 2.1. Materials Attapulgite (particle size: 200 mesh, compacted bulk density: 0.8–0.9 g/ml) was collected from the Xuyi City, Jiangsu Province, China. Chitosan (deacetylation degree of 90% and average molecular weight of 4 × 105 ) was purchased from Shanghai Boao Biotechnology Co. Ltd., China. HA powder was purchased from Jufeng Chemical Technology Company, Shanghai, China. Acetic acid, sodium hydroxide and hydrochloric acid were purchased from Sinopharm Chemical Reagent Co. Ltd., China.
(purity, 90%). Simultaneously, the sample with a ratio of attapulgite (PA-70) and distilled water in the initial mixing step at 1:99 is denoted PA-99 (purity, 99%). Then, 2.50 g of chitosan was dispersed in 150 ml of 2 wt% acetic acid solution with continuous stirring at 60 °C for 4 h. Then, 50 g PA was slowly added to the above chitosan solution, and the mixture was stirred at room temperature for 3 h. Subsequently, the pH of the PA/chitosan mixture was neutralized using 0.1 mol/l NaOH solution. The chitosan-modified attapulgite powder was centrifuged, washed by deionized water at least three times, and then dried at 65 °C for 24 h. The obtained chitosan-modified PA-90 is denoted CPA. 2.3. Adsorption experiments Detailed information on the preparation of the HA solutions and the pH value determination of zero point charge (pHzpc ) is given in the ESI. For the adsorption experiments, the designated adsorbents (PA and CPA) were added into the HA solution (5 mg/l, 100 ml) at the desired pH. Then, the mixtures in conical flasks were oscillated at 200 rpm in a bath shaker for a predetermined time. The obtained solution after oscillation was centrifuged and filtered through a 0.45 μm glass filter membrane. Subsequently, the residual concentration of HA was analyzed by UV–vis spectroscopy at λmax = 400 nm. The experimental processes and corresponding conditions are listed in Table S1. The results were evaluated based on the adsorption efficiency (%) and the HA equilibrium adsorption capacity (qe , mg/g), which can be calculated based on the following equation:
qe =
(C0 − Ce )V M
(1)
where V is the solution volume (l); C0 and Ce are the initial concentration and the equilibrium adsorption concentration (mg/l), respectively; and M is the adsorbent dose (g). To verify the stability of CPA, the adsorbents were tested using adsorption–desorption cycling, where 0.1 mol/l NaOH (25 ml) was employed in the HA desorption treatment. The adsorption capacity of CPA for HA adsorption was measured 6 times. 2.4. Characterization The morphology of the relevant samples was examined by a scanning electron microscope (FE-SEM Hitachi S-4800). The crystal structure of the relevant samples was measured by an X-ray diffractometer (XRD, Rigku, Ultima IV). The specific surface area and pore diameter distribution of the relevant samples were derived from N2 ad/desorption measurements using an automatic microspore physisorption analyzer (ASAP 2020). Fourier-transform infrared spectroscopy (FT-IR, PerkinElmer) was applied to detect the presence of clay mineral. The weight loss of RA, chitosan and CPA were obtained by thermogravimetric analysis (TGA) (Perkin-Elmer, USA). 3. Results and discussion
2.2. Preparation of PA and chitosan-modified PA
3.1. Morphology and structural characterization
First, 5.0 g of raw attapulgite (RA) powder was dispersed in 95 g of distilled water with vigorous stirring at 10,0 0 0 r/min for 10 min, and then the sediment was filtered by gravity after 72 h and dried in an oven at 60 °C for 24 h; this sample is denoted PA-70 (purity, 70%). Subsequently, the dispersive clay mineral slurry (PA-70) was then precipitated in a high-speed centrifuge for further separation. The clay mineral slurry from the middle layer of the precipitated material was dried at 60 °C for 24 h and is denoted PA-90
Representative FE-SEM images of RA and PA of various purity fabricated from different treatment processes are shown in Fig. 2. A large amount of impurities, such as block SiO2 , could be observed, and nanorods with an average diameter of 50 nm and length of 20 0–30 0 nm were entangled and aggregated with each other. To the best of our knowledge, the aggregation of RA nanorods with impurities seriously limited the response rate and adsorption capacity towards HA [23]. Thus, it is very important to purify RA
Please cite this article as: N. Sun et al., Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.03.017
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Fig. 2. SEM images of RA and PA of different purity: (a) RA, (b) PA-70, (c) PA-90 and (d) PA-99. RA: raw attapulgite; PA: purified attapulgite.
to improve its adsorption performance. FE-SEM images of different purity RA, shown in Fig. 2(b)–(d), revealed that impurities (SiO2 ) in the PA sample decreased significantly, and the nanorods become slender with an unconsolidated structure without obvious entangled aggregation. Moreover, the large number of holes formed in Fig. 2(c) indicated that the combined method of full hydration and strong shearing could effectively remove impurities and disperse the aggregated crystalline bundles of nanorods. However, the crystalline bundles of PA-99, shown in Fig. 2(d), seem slim and short and exhibited non-three-dimensional (3D) random structures with uniform mesoporous porous structures. 3.2. XRD diffraction patterns of PA of different purity XRD diffraction patterns were used to confirm the component and structure of RA and PA (Fig. 3). The typical peaks rose at 2θ of 8.38°, 13.82°, 16.46°, 19.78°, 20.86° and 27.48°, which can be attributed to the (110), (200), (130), (040), (121) and (311) planes of ATP phase (JCPDS No. 21-0957). Additionally, a high-intensity diffraction peak at 2θ of 26.66° was accordance to SiO2 phase (JCPDS No. 33-1161). Phase identification (Search–Match) was calculated by the d spacing and relative intensities of relevant samples with standard reference data in the JCPDS file, which was used to analyze the phase content. The result showed that RA contains a high percentage of the impurities (SiO2 , 41%) (Fig. 3(a)). Similarly, we could calculate that the purity of PA-70, PA-90 and PA-99 could reach to approximately 70, 90 and 99%, respectively (Fig. 3(b)–(d)). The peak intensity of PA-99 at 26.66° clearly decreased and disappeared. This results demonstrated that we have successfully fabricated high purity PA. 3.3. BET analysis and porous structure of RA, purified PA and CPA The RA, purified PA-70, PA-90, and PA-99 and CPA samples were studied using N2 ad/desorption (Fig. 4(a)). According to the IUPAC classification, all of the isotherms were type IV isotherms with a variety of typical adsorption behaviors, including monolayer adsorption, multilayer adsorption and capillary condensation, which indicates the presence of mesopores [24]. Furthermore, the hysteresis loop shifts towards a relative pressure of (P/P0 ) = 1, which
Table 1 Surface area and pore characteristics of different adsorbents.
2
BET surface area (m /g) Average pore diameter (nm) Total pore volume (cm3 /g)
RA
PA-70
PA-90
PA-99
CPA
136 10.0 0.23
154 8.4 0.24
170 8.2 0.33
110 8.9 0.20
92 7.2 0.18
indicates the presence of macropores in the samples [18]. The results of these analyses are in good agreement with the pore diameter distributions of the relevant samples (Fig. 4(b)). As is well known, a large surface area is a prerequisite for adsorbent materials because the adsorption properties depend on the effective surface area having more active sites. The surface areas, average pore diameters and total pore volumes are summarized in Table 1. The surface area of initial purified PA was increased from 136 to 170 m2 /g because of strong shearing and full hydration, forming dispersed PA-90 into rods or fibers. However, with excessive of purification of PA, the surface area was dramatically decreased to 110 m2 /g due to damage of the rod crystals, suggesting that over purification decreases the surface area for effective HA adsorption. The experimental data is shown in Fig. S1 and illustrated that PA90 was the optimal structure for HA removal. Finally, PA-90 was chosen for the next step of modification. However, after chitosan modification, the surface area decreased to 92 m2 /g, which could be attributed to the smoothing effect. In addition, the Barrett– Joyner–Halenda (BJH) method was employed to quantitatively describe the pore size distribution of PA. The pore size distribution, shown in Fig. 4(b), indicated that all purities of PA exhibited a mesoporous structure, and the smaller pore size of CPA (7.2 nm) could be attributed to the filling of chitosan. 3.4. FT-IR spectra and TGA of PA-90 before and after chitosan modification The PA-90 sample before and after chitosan modification was also examined by FT-IR spectroscopy and TGA analysis (Fig. 5). For CPA, the adsorption bands at 3427 cm−1 , 2852 cm−1 and 1421 cm−1 were assigned to O–H and N–H, the aliphatic C–H of –CH2 and the aliphatic C–H bending vibration, respectively, suggesting that chitosan was successfully immobilized on the surface of PA-90 [25].
Please cite this article as: N. Sun et al., Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.03.017
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Fig. 3. XRD diffraction patterns of RA and PA purified by different steps (•—ATP; — SiO2 ). RA: raw attapulgite; PA: purified attapulgite; Meas is the measure mode.
Fig. 4. (a) N2 ad/desorption isotherms and (b) pore distribution analysis of RA, purified PA-70, PA-90, and PA-99 and CPA, respectively.
The weight loss of PA-90 and CPA were ca. 3.43 and 14.04 wt%, respectively, indicating that approximately 10.61 wt% chitosan was loaded. In addition, the broadening of the adsorption bands in the 360 0–320 0 cm−1 region is indicative of hydrogen bonding interactions between the silanol groups of PA-90 and the hydroxyl and amino groups of chitosan [5]. Furthermore, in the acidic solution during CPA preparation, amino (–NH2 ) groups in the chitosan molecules are protonated by H+ , forming –NH3 + , which can interact with the negatively charged sites of PA-90 through electrostatic attraction [6,26]. 3.5. Effect of adsorption conditions The adsorbent dose is an important factor for the removal of HA from pollutant water because it determines the adsorption rate
and removal efficiency of HA for a given initial concentration. The effect of HA adsorption was performed by adjusting the CPA dose. The adsorbent dose of CPA and PA-90 were increased from 0.1 to 1 g/l, as shown in Fig. 6(a) and (b). When the CPA and PA dose were more than 1 g/l, the HA removal ratio tended to be stable, and the adsorption rate was faster than that of PA, which can be attributed to the enhanced surface area and abundant active adsorption sites of CPA [18]. The HA adsorption capacity decreased with increasing amount of adsorbents because the adsorption sites remained unsaturated during the adsorption process [7]. For the other experiments, the optimal dose of PA-90 and CPA were 2 g/l and 1 g/l, respectively. According to a previous study, the highly effective adsorption of HA by adsorbents could also be influenced by pH due to the
Please cite this article as: N. Sun et al., Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.03.017
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Fig. 5. (a) FT-IR spectra and (b) TGA curves of PA-90 before and after chitosan modification.
Fig. 6. Effect of adsorbent dose on HA adsorption: (a) PA-90 and (b) CPA. (c) Effect of pH on HA adsorption. (d) Effect of pH on pHf (temperature: 5 °C; HA concentration: 5 mg/l; contact time: 180 min; CPA dose: 1 g/l; PA-90 dose: 2 g/l).
surface charge of the adsorbents as well as the degree of ionization of HA. It is necessary to study the influence of pH on HA adsorption. For PA-90 and CPA, the adsorption capacity of HA was markedly increased and then decreased with increasing pH. In this experiment, both qe, PA and qe, CPA reached their maximum adsorption capacity (1.03 mg/g for PA-90 and 4.86 mg/g for CPA) when the pH was 6 (Fig. 6(c)). The cause of this behavior could be explained as follows. First, in the tested pH range (pH = 4–10), HA molecules in aqueous solution carry negative charges due to deprotonation of the carboxylic (–COOH) and phenolic (–OH) groups [27]. When the solution pH is less than the pHZPC of the adsorbent (pHZPC values of PA-90 and CPA were 7.81 and 7.17) (Fig. 6d), the adsorbent surface becomes considerably more positive, and thus electrostatic attraction is more likely to occur between the negative charge on the HA surface and the positive charge on the adsorbent surface [28]. With increasing pH, the electrostatic repulsion between the adsorbent and HA resulted in a decreased adsorption capacity [29]. Second, under extreme conditions, such as pH < 4 and pH > 10, the screening effect from the counter ions (i.e., Cl− and Na+ ) shields the charge of –NH3 + on chitosan or ionizes the carboxyl groups on
HA, making the HA molecules more difficult to transfer [30]. Thus, the efficient treatment of HA in neutral water conditions has great promise for practical application. 3.6. FE-SEM images and FT-IR spectra before and after HA adsorption The FE-SEM images of PA-90 and CPA, shown in Fig. 7, exhibited a smooth cleavage surface and sharp edges. After adsorption of HA, the surface of PA-90 becomes smooth and less porous due to the coverage of HA. However, the surface of CPA was observed to have more pores and exhibited an irregular structure after adsorption (Fig. 7(d)), which indirectly indicates that a chemical reaction occurred between CPA and HA. FT-IR spectroscopy was also used to study the adsorption of HA. As shown in Fig. S2, no obvious changes were observed for PA-90 before and after adsorption. However, after CPA adsorption, two obvious peaks at 1571 cm−1 and 1421 cm−1 disappeared, which likely indicates that the adsorption of HA onto CPA could be controlled by complexation reactions, such as the formation of –NH3 + • • •− OOC–R or –NH3 + • • •− O–C6 H4 –R complexes between the –NH3 + groups of
Please cite this article as: N. Sun et al., Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.03.017
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Fig. 7. FE-SEM images of PA-90 and CPA before and after adsorption: (a) PA-90, (b) PA-90-HA, (c) CPA, and (d) CPA-HA.
chitosan and the –RCOO− and –RO− groups of HA [21]. Moreover, the adsorption capacity of CPA for HA capture was stable for 6 cycles, in which the adsorption capacity was decreased from 4.31 to 3.44 mg/g, as shown in Fig. S3, which exhibited the regeneration of the prepared adsorbent. 3.7. Adsorption kinetics To gain a better understanding of the adsorption properties of HA onto PA-90 and CPA, the adsorption performance of HA on PA90 and CPA were fitted by the pseudo-first-order kinetics, pseudosecond-order kinetics and intra-particle diffusion equations, and the adsorption kinetics behavior is shown in Eqs. (S1), (S2) and (S3), respectively [31]. The adsorption processes were fitted at 278 K, and the concentrations of HA were 5 mg/l, 10 mg/l, 60 mg/l and 100 mg/l. These fitting curves are illustrated in Fig. 8(a) and (c), and the detailed parameters and correlation coefficients obtained from these plots are listed in Table S2. The HA adsorption process on PA-90 and CPA, including rapid adsorption in the initial phase and gradual adsorption, is shown in Fig. 8(a) and (c). The adsorption capacity after 2 min reached approximately 80% for CPA in contrast with PA-90, which took 10 min to reach the same capacity. Equilibrium could be achieved within 30, 60 and 180 min with pristine HA in concentrations of 5, 10, 60 and 100 mg/l. The qe, PA values reached 2.07, 4.42, 14.77 and 18.16 mg/g within 30, 60 and 180 min, which were lower than the qe, CPA values of 4.48, 9.31, 32.08 and 40.83 mg/g, respectively. This indicates that chitosanmodified PA-90 could successfully achieve increased HA adsorption because of its surface functional groups. The pseudo-second-order model has a higher regression factor (R2 ≥ 0.963 for CPA and 0.943 for PA-90) than the pseudo-first-order model (R2 ≥ 0.928, CPA, and 0.863, PA-90), suggesting that it is more suitable to describe HA adsorption on PA-90 and CPA. The theoretical qe values calculated using the pseudo-second-order equation are similar to the experimental qe,exp values. Similar results have been demonstrated in previous works [32–34]. The effects of pore size on the diffusion of HA were also simulated by the intra-particle diffusion equation. The intra-particle diffusion fitting curves, as shown in Fig. 8(b) and (d), demonstrated the nonlinear relationship between qt and t1/2 and revealed the HA diffusion–adsorption process. This process was controlled by two steps, including film diffusion (boundary layer diffusion in the initial 2 min) on the external surface and interior surface diffusion. The diffusion resistance increases with increasing HA adsorption
capacity, making the intra-particle diffusion rate (Kint ) decrease and then gradually achieve adsorption equilibrium [18]. The intercept C on the y-axis, shown in Fig. 8(b) and (d), indicates that the interface thickness increased with increasing contact time, illustrating that diffusion of the adsorbents plays an important role, along with the abundant active sites, in PA-90 and CPA for HA adsorption [35]. The intra-particle diffusion rates Kint,1 and Kint,2 of CPA were higher than those of PA-90 (Table S2), indicating the fast HA adsorption of CPA compared with that of PA-90 [28]. The Kint,1 and Kint,2 values increased with increasing initial concentration, which can be attributed to the intra-particle diffusion model based on Fick’s law [36]. The temperature, a key adsorption factor, could also significantly influence the adsorption capacity. The adsorption equilibrium isotherms of PA-90 and CPA at different temperatures are presented in Fig. S4, and detailed information on the relevant estimated parameters is given in Table S2. Correlation coefficients (R2 ) of both the pseudo-second-order kinetics equation and the intra-particle diffusion equation were relatively higher, indicating that the two equations could suitably describe the HA adsorption process at different temperatures. Furthermore, it is observed that the temperature has a different effect on the adsorbents for the adsorption process. For CPA, there was a negative correlation between temperature and adsorption capacity (Fig. S4) because the adsorption of CPA towards HA was exothermic. This can be explained by the fact that at high temperature, the kinetic energy of HA is low, and therefore, contact between HA and the active sites of CPA is insufficient, leading to a decrease in adsorption efficiency. Furthermore, at lower temperature, the kinetic energy of HA is higher than the attractive potential between HA and the active sites of CPA. This condition causes a decrease in adsorption efficiency, showing that adsorption is more of a physical property than a chemical property. In contrast, there was a positive correlation between temperature and the adsorption capacity of PA90, indicating that PA-90 was favorable for HA adsorption at high temperature. The presented results are in agreement with previous work, illustrating that changes in temperature could accelerate the adsorption rate or create new active sites on the surface of PA-90 [28,29]. Therefore, the active sites of PA-90 could be enhanced at high temperatures, but there were no obvious changes after 80 min of adsorption at different temperatures (Fig. S4(a) and (c)), demonstrating that the adsorption process reached equilibrium after 80 min.
Please cite this article as: N. Sun et al., Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.03.017
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Fig. 8. The kinetics of HA adsorption on (a) and (b) CPA and (c) and (d) PA-90 at different HA concentrations (pH: 6; contact time: 180 min; CPA dose: 1 g/l; PA dose: 2 g/l).
Fig. 9. HA adsorption isotherms of (a) CPA and (b) PA-90 (initial HA concentration: 5 mg/l; pH: 6; temperature: 5 °C; contact time: 180 min; CPA dose: 1 g/l; PA dose: 2 g/l).
3.8. Adsorption isotherms To explore the effect of initial HA concentration on the performance of PA-90 and CPA, adsorption equilibrium uptakes under various initial HA concentrations (from 0 to 10 0 0 mg/l) were tested (pH = 6 and at 5 °C). The results, shown in Fig. 9, revealed a typical L-shaped plot with increasing HA concentration, indicating that PA-90 and CPA have a high affinity for HA. The values of qe,PA and qe,CPA first increased sharply when the concentration of Ce ranged from 1 to 200 mg/l and then reached a plateau at equilibrium. Furthermore, to quantitatively analyze the adsorption process of HA on PA-90 and CPA, five classical isotherm models were employed to fit the experimental data; the Langmuir, Freundlich, Temkin, Langmuir–Freundlich and Redlich–Peterson models are described by Eqs. (S4)–(S8), respectively [5,37].
Based on the five adsorption isotherm models, curve fitting of the experimental data is shown in Fig. 9. The calculated isotherm parameters are listed in Table S3. For PA-90 and CPA, it was evident that the Langmuir–Freundlich equation (R2 = 0.992) and the Freundlich equation (R2 = 0.995) matched better than the other sorption processes. This indicates that HA sorption on PA-90 was affected by the Langmuir and Freundlich processes, whereas the interaction between HA and CPA was solely affected by Freundlich processes. The varied sorption processes indicated that sorption of HA on PA-90 and CPA is governed by different mechanism [37]. Moreover, the adsorption of CPA was also well fit by the Langmuir–Freundlich model. The theoretical maximum capacities calculated based on the Langmuir–Freundlich model were 35.85 and 112.07 mg/g when the concentration of C0 ranged from 0 to 10 0 0 mg/l. Our experimental results were much better than those
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of most previous reports in the literature, which are listed in Table S4 [1,4–6,8,9,19,38] Therefore, chitosan-modified purified attapulgite could be considered to be a promising adsorbent for removing HA at low temperature in high-color source water. 4. Conclusions In summary, we have successfully demonstrated a facile strategy to achieve high HA adsorption performance based on the combination of an attapulgite purification process and surface modification. The pseudo-second-order model (R2 ≥ 0.963 for CPA and R2 ≥ 0.943 for PA-90), Langmuir-Freundlich equation (R2 = 0.991 for PA-90) and Freundlich equation (R2 = 0.995 for CPA) described the adsorption process well. Based on the Langmuir–Freundlich isotherm, PA-90 and CPA exhibited excellent adsorption capacity (35.85 and 112.07 mg/g, respectively) at 278 K. Electrostatic attraction, the physical characteristics (porous structure and large surface area) and the protonated amino groups of CPA interacting with the carboxyl and phenolic groups of HA resulted in the sharp response and ideal adsorption capacity. The experimental results also demonstrated the HA adsorption performance on CPA was favorable at lower temperatures. Acknowledgments This study was supported by Postdoctoral Science Foundation of Heilingjiang Province, China (LBH-Z13025) and the Science and Technology Research Project of Heilongjiang Provincial Education Department (No. 11541024). Supplementary materials Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.jtice.2017.03.017. References [1] Moussavi G, Talebi S, Farrokhi M, Sabouti RM. The investigation of mechanism, kinetic and isotherm of ammonia and humic acid co-adsorption onto natural zeolite. Chem Eng J 2011;171:1159–69. [2] Hseu Y-C, Kumar KS, Chen C-S, Cho H-J, Lin S-W, Shen P-C, et al. Humic acid in drinking well water induces inflammation through reactive oxygen species generation and activation of nuclear factor-κ B/activator protein-1 signaling pathways: a possible role in atherosclerosis. Toxicol Appl Pharmacol 2014;274:249–62. [3] Badis A, Ferradji F, Boucherit A, Fodil D, Boutoumi H. Removal of natural humic acids by decolorizing actinomycetes isolated from different soils (Algeria) for application in water purification. Desalination 2010;259:216–22. [4] Wang S, Zhu Z. Humic acid adsorption on fly ash and its derived unburned carbon. J Colloid Interface Sci 2007;315:41–6. [5] Maghsoodloo S, Noroozi B, Haghi AK, Sorial GA. Consequence of chitosan treating on the adsorption of humic acid by granular activated carbon. J Hazard Mater 2011;191:380–7. [6] Wang J, Zhou Y, Li A, Xu L. Adsorption of humic acid by bi-functional resin JN-10 and the effect of alkali-earth metal ions on the adsorption. J Hazard Mater 2010;176:1018–26. [7] Mohseni-Bandpi A, Kakavandi B, Kalantary RR, Azari A, Keramati A. Development of a novel magnetite–chitosan composite for the removal of fluoride from drinking water: adsorption modeling and optimization. RSC Adv 2015;5:73279–89. [8] Peng X, Luan Z, Zhang H. Montmorillonite–Cu (II)/Fe (III) oxides magnetic material as adsorbent for removal of humic acid and its thermal regeneration. Chemosphere 20 06;63:30 0–6. [9] Wang J, Han X, Ma H, Ji Y, Bi L. Adsorptive removal of humic acid from aqueous solution on polyaniline/attapulgite composite. Chem Eng J 2011;173:171–7. [10] Li G, Zhu Z, Qi B, Liu G, Wu P, Zeng G, et al. Rapid capture of Ponceau S via a hierarchical organic–inorganic hybrid nanofibrous membrane. J Mater Chem A 2016;4:5423–7.
[11] Zhu Z, Wu P, Liu G, He X, Qi B, Zeng G, et al. Ultrahigh adsorption capacity of anionic dyes with sharp selectivity through the cationic charged hybrid nanofibrous membranes. Chem Eng J 2017;313:957–66. [12] Zhu Z, Li G, Zeng G, Chen X, Hu D, Zhang Y, et al. Fast capture of methyl-dyes over hierarchical amino-Co0.3Ni0.7Fe2 O4 @SiO2 nanofibrous membranes. J Mater Chem A 2015;3:220 0 0–4. [13] Zhu Z, Xu Y, Qi B, Zeng G, Wu P, Liu G, et al. Adsorption-intensified degradation of organic pollutants over bifunctional α -Fe@ carbon nanofibres. Environ Sci Nano 2017;4:302–6. [14] Sun N, Yu SL, editors. Adsorption mechanism of humic acid on attapulgite based on Stumm–Schindle surface complexation model. Adv Mater Res 2012;630:99–105. [15] Deng Y, Wang L, Hu X, Liu B, Wei Z, Yang S, et al. Highly efficient removal of tannic acid from aqueous solution by chitosan-coated attapulgite. Chem Eng J 2012;181:300–6. [16] Chang M-Y, Juang R-S. Adsorption of tannic acid, humic acid, and dyes from water using the composite of chitosan and activated clay. J Colloid Interface Sci 2004;278:18–25. [17] Dong C, Chen W, Liu C. Preparation of novel magnetic chitosan nanoparticle and its application for removal of humic acid from aqueous solution. Appl Surf Sci 2014;292:1067–76. [18] Lin J, Zhan Y. Adsorption of humic acid from aqueous solution onto unmodified and surfactant-modified chitosan/zeolite composites. Chem Eng J 2012;200:202–13. [19] Ngah WW, Fatinathan S, Yosop N. Isotherm and kinetic studies on the adsorption of humic acid onto chitosan-H2 SO4 beads. Desalination 2011;272:293–300. [20] Dong C, Chen W, Liu C, Liu Y, Liu H. Synthesis of magnetic chitosan nanoparticle and its adsorption property for humic acid from aqueous solution. Colloids Surf Physicochem Eng Asp 2014;446:179–89. [21] Zhang X, Bai R. Mechanisms and kinetics of humic acid adsorption onto chitosan-coated granules. J Colloid Interface Sci 2003;264:30–8. [22] Xie J, Li C, Chi L, Wu D. Chitosan modified zeolite as a versatile adsorbent for the removal of different pollutants from water. Fuel 2013;103:480–5. [23] Cai D, Zhang H, Tang Y, Chu PK, Yu Z, Wu Z. Nano-networks have better adsorption capability than nano-rods. Nano Commun Netw 2010;1:257–63. [24] Tang Y, Liang S, Yu S, Gao N, Zhang J, Guo H, et al. Enhanced adsorption of humic acid on amine functionalized magnetic mesoporous composite microspheres. Colloids Surf Physicochem Eng Asp 2012;406:61–7. [25] Liu J, Cao J, Chen H, Zhou D. Adsorptive removal of humic acid from aqueous solution by micro-and mesoporous covalent triazine-based framework. Colloids Surf Physicochem Eng Asp 2015;481:276–82. [26] Su D, Wang C, Cai S, Mu C, Li D, Lin W. Influence of palygorskite on the structure and thermal stability of collagen. Appl Clay Sci 2012;62:41–6. [27] Tao Q, Xu Z, Wang J, Liu F, Wan H, Zheng S. Adsorption of humic acid to aminopropyl functionalized SBA-15. Microporous Mesoporous Mater 2010;131:177–85. [28] Shuang C, Wang J, Li H, Li A, Zhou Q. Effect of the chemical structure of anion exchange resin on the adsorption of humic acid: behavior and mechanism. J Colloid Interface Sci 2015;437:163–9. [29] Wang M, Liao L, Zhang X, Li Z. Adsorption of low concentration humic acid from water by palygorskite. Appl Clay Sci 2012;67:164–8. [30] Wang Y, Zeng L, Ren X, Song H, Wang A. Removal of Methyl Violet from aqueous solutions using poly (acrylic acid-co-acrylamide)/attapulgite composite. J Environ Sci 2010;22:7–14. [31] Colombo C, Palumbo G, Angelico R, Cho HG, Francioso O, Ertani A, et al. Spontaneous aggregation of humic acid observed with AFM at different pH. Chemosphere 2015;138:821–8. [32] Bouras HD, Benturki O, Bouras N, Attou M, Donnot A, Merlin A, et al. The use of an agricultural waste material from Ziziphus jujuba as a novel adsorbent for humic acid removal from aqueous solutions. J Mol Liq 2015;211:1039–46. [33] Wang L, Zhang J, Wang A. Fast removal of methylene blue from aqueous solution by adsorption onto chitosan-g-poly (acrylic acid)/attapulgite composite. Desalination 2011;266:33–9. [34] Zhang J, Gong J-L, Zenga G-M, Ou X-M, Jiang Y, Chang Y-N, et al. Simultaneous removal of humic acid/fulvic acid and lead from landfill leachate using magnetic graphene oxide. Appl Surf Sci 2016;370:335–50. [35] Moussavi G, Khosravi R. Removal of cyanide from wastewater by adsorption onto pistachio hull wastes: parametric experiments, kinetics and equilibrium analysis. J Hazard Mater 2010;183:724–30. [36] Ujihara T, Fujiwara K, Sazaki G, Usami N, Nakajima K. New method for measurement of interdiffusion coefficient in high temperature solutions based on Fick’s first law. J Cryst Growth 2002;241:387–94. [37] Jiang W, Pelaez M, Dionysiou DD, Entezari MH, Tsoutsou D, O’Shea K. Chromium (VI) removal by maghemite nanoparticles. Chem Eng J 2013;222:527–33. [38] Lin J, Zhan Y. Adsorption of humic acid from aqueous solution onto unmodified and surfactant-modified chitosan/zeolite composites. Chem Eng J 2012;200-202:202–13.
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Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature Nan Sun a, Ying Zhang b,∗, Lixin Ma c, Shuili Yu d,∗, Jinxuan Li a a
School of Water Conservancy and Civil Engineering, Northeast Agricultural University, Harbin 150030, China School of Resources and Environment, Northeast Agricultural University, Harbin 150030, China Environmental Protection of Heilongjiang Province, Harbin 150090, China d State Key Laboratory of Pollution Control and Resources Reuse, Tongji University, Shanghai 200092, China b c
a r t i c l e
i n f o
Article history: Received 15 August 2016 Revised 13 February 2017 Accepted 17 March 2017 Available online xxx Keywords: Adsorption Humic acid Purified attapulgite Chitosan
a b s t r a c t In the adsorption treatment of water polluted with humic acid (HA), it is equally important to recover clean water with inexpensive raw materials, mild treatment environments and excellent adsorption capacity. Herein, a composite structured CPA (chitosan-modified purified attapulgite) composed of uniform PA (purified attapulgite) nanorods modified by chitosan was successfully fabricated under acetic acid conditions. Benefiting from the mesoporous structure of the PA nanorods and the carboxyl groups of chitosan, the prepared hybrid CPA exhibited a quick response and excellent adsorption capacity towards HA. The effects of pH, adsorbent dose, adsorption time, initial HA concentration and temperature were systematically studied using PA-90 (PA with purity of 90%) and CPA, respectively. The results show that CPA has a high capture affinity towards HA with a short response time (2 min for 80%) and the maximum adsorption capacity could reach 112.07 mg/g, which is superior to most results that have been reported. We believe CPA could be considered as an efficient and green heterogeneous adsorbent for the adsorption of humic acid, as well as provide a versatile platform for further development of functional hybrid composites for the adsorption of other pollutants. © 2017 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.
1. Introduction Humic acid (HA), which generally generates an undesirable color, odor and taste, has seriously polluted drinking water resources and poses an enormous threat to our health [1]. On the one hand, the excessive intake of HA may lead to some diseases, such as blackfoot and Kashin-Beck [2,3]. On the other hand, HA can produce by-products, specifically trihalomethanes and haloacetic acids, during the chlorination process that could possibly be carcinogenic to human beings [1]. In addition, HA also has a strong binding capacity for many contaminants, such as heavy metals, pesticides and herbicides, and thus could increase the contaminant concentration in water [4]. Polluted drinking water directly or indirectly entering human beings through the food chain could also cause great threat to our health. Therefore, sorbents with high adsorption capacity and quick response are desired for HA removal.
∗
Corresponding authors. E-mail addresses: [email protected] (Y. Zhang), [email protected] (S. Yu).
HA in drinking water has strict standards, which makes it urgent to develop appropriate technologies for HA removal. Adsorption is considered a promising method because of its advantages of simple fabrication, operability, efficiency and relatively low cost. A number of adsorption materials, such as zeolites [1], activated carbon [5], resins [6], chitosan [7], metal oxides [8], attapulgite [9], and organic or inorganic nanostructured fibers [10–13] have been successfully applied to dispose of sewage to improve water quality. Most of these adsorbents can only be effectively operated at high temperature, which is energy consuming [1,4,6,7,9]. Simultaneously, higher temperature is not always operable in practice, particularly in some severely cold areas. Therefore, the development of functional absorbents that could be operated at low temperature for effective HA removal is urgent. Attapulgite has the potential to meet the above requirements owing to its unique layered chain structure with high specific surface area, moderate cation exchange capacity, good liquidity, and selective adsorption and is equipped with strong sterilization, deodorization, detoxification and insecticidal properties [9]. In our previous study, we found that natural attapulgite exhibited relatively higher adsorption capacity towards HA at low temperature
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Please cite this article as: N. Sun et al., Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.03.017
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Fig. 1. Schematic diagram of interaction between PA-90 and chitosan.
compared with other adsorbents due to the adsorption process being exothermic in nature [14], but the limited adsorption capacity could not satisfy the increasing concentration of HA in practice. Therefore, it is critical to prepare purified attapulgite to improve the adsorption properties. Chitosan, generally extracted from the alkaline deacetylation of chitin, was chosen as a functional modifier polymer for the preparation of hybrid functional materials owing to its biocompatibility, biodegradability and high adsorption capabilities [15]. However, the raw material has a tendency to agglomerate in aqueous solution and can be easily dissolved in acidic media. The low specific gravity of chitosan makes itself difficult to separate from other aqueous solutions, which has limited its usage in either batch or column modes [16]. Until now, considerable effort has been devoted to modifying chitosan beads or chitosan immobilized on inorganic nanomaterials to enhance HA adsorption in aqueous solution [17–22]. To the best of our knowledge, no effort has been made to develop a promising strategy to fabricate chitosan-modified attapulgite hybrid functional materials for effective HA removal in water at low temperature. In this contribution, we aimed to investigate the high adsorption capability of hybrid adsorbents for effective removal of HA from high-color water at low temperature. The as-prepared attapulgite was further functionalized by chitosan, and the fabrication process is illustrated in Fig. 1. More importantly, chitosan-modified porous attapulgite was used as a composite adsorbent for HA removal for the first time, and the initial motivation of this study was to develop an environmental composite adsorbent with high and ultrafast response to HA for potential applications in drinking water. 2. Materials and methods 2.1. Materials Attapulgite (particle size: 200 mesh, compacted bulk density: 0.8–0.9 g/ml) was collected from the Xuyi City, Jiangsu Province, China. Chitosan (deacetylation degree of 90% and average molecular weight of 4 × 105 ) was purchased from Shanghai Boao Biotechnology Co. Ltd., China. HA powder was purchased from Jufeng Chemical Technology Company, Shanghai, China. Acetic acid, sodium hydroxide and hydrochloric acid were purchased from Sinopharm Chemical Reagent Co. Ltd., China.
(purity, 90%). Simultaneously, the sample with a ratio of attapulgite (PA-70) and distilled water in the initial mixing step at 1:99 is denoted PA-99 (purity, 99%). Then, 2.50 g of chitosan was dispersed in 150 ml of 2 wt% acetic acid solution with continuous stirring at 60 °C for 4 h. Then, 50 g PA was slowly added to the above chitosan solution, and the mixture was stirred at room temperature for 3 h. Subsequently, the pH of the PA/chitosan mixture was neutralized using 0.1 mol/l NaOH solution. The chitosan-modified attapulgite powder was centrifuged, washed by deionized water at least three times, and then dried at 65 °C for 24 h. The obtained chitosan-modified PA-90 is denoted CPA. 2.3. Adsorption experiments Detailed information on the preparation of the HA solutions and the pH value determination of zero point charge (pHzpc ) is given in the ESI. For the adsorption experiments, the designated adsorbents (PA and CPA) were added into the HA solution (5 mg/l, 100 ml) at the desired pH. Then, the mixtures in conical flasks were oscillated at 200 rpm in a bath shaker for a predetermined time. The obtained solution after oscillation was centrifuged and filtered through a 0.45 μm glass filter membrane. Subsequently, the residual concentration of HA was analyzed by UV–vis spectroscopy at λmax = 400 nm. The experimental processes and corresponding conditions are listed in Table S1. The results were evaluated based on the adsorption efficiency (%) and the HA equilibrium adsorption capacity (qe , mg/g), which can be calculated based on the following equation:
qe =
(C0 − Ce )V M
(1)
where V is the solution volume (l); C0 and Ce are the initial concentration and the equilibrium adsorption concentration (mg/l), respectively; and M is the adsorbent dose (g). To verify the stability of CPA, the adsorbents were tested using adsorption–desorption cycling, where 0.1 mol/l NaOH (25 ml) was employed in the HA desorption treatment. The adsorption capacity of CPA for HA adsorption was measured 6 times. 2.4. Characterization The morphology of the relevant samples was examined by a scanning electron microscope (FE-SEM Hitachi S-4800). The crystal structure of the relevant samples was measured by an X-ray diffractometer (XRD, Rigku, Ultima IV). The specific surface area and pore diameter distribution of the relevant samples were derived from N2 ad/desorption measurements using an automatic microspore physisorption analyzer (ASAP 2020). Fourier-transform infrared spectroscopy (FT-IR, PerkinElmer) was applied to detect the presence of clay mineral. The weight loss of RA, chitosan and CPA were obtained by thermogravimetric analysis (TGA) (Perkin-Elmer, USA). 3. Results and discussion
2.2. Preparation of PA and chitosan-modified PA
3.1. Morphology and structural characterization
First, 5.0 g of raw attapulgite (RA) powder was dispersed in 95 g of distilled water with vigorous stirring at 10,0 0 0 r/min for 10 min, and then the sediment was filtered by gravity after 72 h and dried in an oven at 60 °C for 24 h; this sample is denoted PA-70 (purity, 70%). Subsequently, the dispersive clay mineral slurry (PA-70) was then precipitated in a high-speed centrifuge for further separation. The clay mineral slurry from the middle layer of the precipitated material was dried at 60 °C for 24 h and is denoted PA-90
Representative FE-SEM images of RA and PA of various purity fabricated from different treatment processes are shown in Fig. 2. A large amount of impurities, such as block SiO2 , could be observed, and nanorods with an average diameter of 50 nm and length of 20 0–30 0 nm were entangled and aggregated with each other. To the best of our knowledge, the aggregation of RA nanorods with impurities seriously limited the response rate and adsorption capacity towards HA [23]. Thus, it is very important to purify RA
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Fig. 2. SEM images of RA and PA of different purity: (a) RA, (b) PA-70, (c) PA-90 and (d) PA-99. RA: raw attapulgite; PA: purified attapulgite.
to improve its adsorption performance. FE-SEM images of different purity RA, shown in Fig. 2(b)–(d), revealed that impurities (SiO2 ) in the PA sample decreased significantly, and the nanorods become slender with an unconsolidated structure without obvious entangled aggregation. Moreover, the large number of holes formed in Fig. 2(c) indicated that the combined method of full hydration and strong shearing could effectively remove impurities and disperse the aggregated crystalline bundles of nanorods. However, the crystalline bundles of PA-99, shown in Fig. 2(d), seem slim and short and exhibited non-three-dimensional (3D) random structures with uniform mesoporous porous structures. 3.2. XRD diffraction patterns of PA of different purity XRD diffraction patterns were used to confirm the component and structure of RA and PA (Fig. 3). The typical peaks rose at 2θ of 8.38°, 13.82°, 16.46°, 19.78°, 20.86° and 27.48°, which can be attributed to the (110), (200), (130), (040), (121) and (311) planes of ATP phase (JCPDS No. 21-0957). Additionally, a high-intensity diffraction peak at 2θ of 26.66° was accordance to SiO2 phase (JCPDS No. 33-1161). Phase identification (Search–Match) was calculated by the d spacing and relative intensities of relevant samples with standard reference data in the JCPDS file, which was used to analyze the phase content. The result showed that RA contains a high percentage of the impurities (SiO2 , 41%) (Fig. 3(a)). Similarly, we could calculate that the purity of PA-70, PA-90 and PA-99 could reach to approximately 70, 90 and 99%, respectively (Fig. 3(b)–(d)). The peak intensity of PA-99 at 26.66° clearly decreased and disappeared. This results demonstrated that we have successfully fabricated high purity PA. 3.3. BET analysis and porous structure of RA, purified PA and CPA The RA, purified PA-70, PA-90, and PA-99 and CPA samples were studied using N2 ad/desorption (Fig. 4(a)). According to the IUPAC classification, all of the isotherms were type IV isotherms with a variety of typical adsorption behaviors, including monolayer adsorption, multilayer adsorption and capillary condensation, which indicates the presence of mesopores [24]. Furthermore, the hysteresis loop shifts towards a relative pressure of (P/P0 ) = 1, which
Table 1 Surface area and pore characteristics of different adsorbents.
2
BET surface area (m /g) Average pore diameter (nm) Total pore volume (cm3 /g)
RA
PA-70
PA-90
PA-99
CPA
136 10.0 0.23
154 8.4 0.24
170 8.2 0.33
110 8.9 0.20
92 7.2 0.18
indicates the presence of macropores in the samples [18]. The results of these analyses are in good agreement with the pore diameter distributions of the relevant samples (Fig. 4(b)). As is well known, a large surface area is a prerequisite for adsorbent materials because the adsorption properties depend on the effective surface area having more active sites. The surface areas, average pore diameters and total pore volumes are summarized in Table 1. The surface area of initial purified PA was increased from 136 to 170 m2 /g because of strong shearing and full hydration, forming dispersed PA-90 into rods or fibers. However, with excessive of purification of PA, the surface area was dramatically decreased to 110 m2 /g due to damage of the rod crystals, suggesting that over purification decreases the surface area for effective HA adsorption. The experimental data is shown in Fig. S1 and illustrated that PA90 was the optimal structure for HA removal. Finally, PA-90 was chosen for the next step of modification. However, after chitosan modification, the surface area decreased to 92 m2 /g, which could be attributed to the smoothing effect. In addition, the Barrett– Joyner–Halenda (BJH) method was employed to quantitatively describe the pore size distribution of PA. The pore size distribution, shown in Fig. 4(b), indicated that all purities of PA exhibited a mesoporous structure, and the smaller pore size of CPA (7.2 nm) could be attributed to the filling of chitosan. 3.4. FT-IR spectra and TGA of PA-90 before and after chitosan modification The PA-90 sample before and after chitosan modification was also examined by FT-IR spectroscopy and TGA analysis (Fig. 5). For CPA, the adsorption bands at 3427 cm−1 , 2852 cm−1 and 1421 cm−1 were assigned to O–H and N–H, the aliphatic C–H of –CH2 and the aliphatic C–H bending vibration, respectively, suggesting that chitosan was successfully immobilized on the surface of PA-90 [25].
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Fig. 3. XRD diffraction patterns of RA and PA purified by different steps (•—ATP; — SiO2 ). RA: raw attapulgite; PA: purified attapulgite; Meas is the measure mode.
Fig. 4. (a) N2 ad/desorption isotherms and (b) pore distribution analysis of RA, purified PA-70, PA-90, and PA-99 and CPA, respectively.
The weight loss of PA-90 and CPA were ca. 3.43 and 14.04 wt%, respectively, indicating that approximately 10.61 wt% chitosan was loaded. In addition, the broadening of the adsorption bands in the 360 0–320 0 cm−1 region is indicative of hydrogen bonding interactions between the silanol groups of PA-90 and the hydroxyl and amino groups of chitosan [5]. Furthermore, in the acidic solution during CPA preparation, amino (–NH2 ) groups in the chitosan molecules are protonated by H+ , forming –NH3 + , which can interact with the negatively charged sites of PA-90 through electrostatic attraction [6,26]. 3.5. Effect of adsorption conditions The adsorbent dose is an important factor for the removal of HA from pollutant water because it determines the adsorption rate
and removal efficiency of HA for a given initial concentration. The effect of HA adsorption was performed by adjusting the CPA dose. The adsorbent dose of CPA and PA-90 were increased from 0.1 to 1 g/l, as shown in Fig. 6(a) and (b). When the CPA and PA dose were more than 1 g/l, the HA removal ratio tended to be stable, and the adsorption rate was faster than that of PA, which can be attributed to the enhanced surface area and abundant active adsorption sites of CPA [18]. The HA adsorption capacity decreased with increasing amount of adsorbents because the adsorption sites remained unsaturated during the adsorption process [7]. For the other experiments, the optimal dose of PA-90 and CPA were 2 g/l and 1 g/l, respectively. According to a previous study, the highly effective adsorption of HA by adsorbents could also be influenced by pH due to the
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Fig. 5. (a) FT-IR spectra and (b) TGA curves of PA-90 before and after chitosan modification.
Fig. 6. Effect of adsorbent dose on HA adsorption: (a) PA-90 and (b) CPA. (c) Effect of pH on HA adsorption. (d) Effect of pH on pHf (temperature: 5 °C; HA concentration: 5 mg/l; contact time: 180 min; CPA dose: 1 g/l; PA-90 dose: 2 g/l).
surface charge of the adsorbents as well as the degree of ionization of HA. It is necessary to study the influence of pH on HA adsorption. For PA-90 and CPA, the adsorption capacity of HA was markedly increased and then decreased with increasing pH. In this experiment, both qe, PA and qe, CPA reached their maximum adsorption capacity (1.03 mg/g for PA-90 and 4.86 mg/g for CPA) when the pH was 6 (Fig. 6(c)). The cause of this behavior could be explained as follows. First, in the tested pH range (pH = 4–10), HA molecules in aqueous solution carry negative charges due to deprotonation of the carboxylic (–COOH) and phenolic (–OH) groups [27]. When the solution pH is less than the pHZPC of the adsorbent (pHZPC values of PA-90 and CPA were 7.81 and 7.17) (Fig. 6d), the adsorbent surface becomes considerably more positive, and thus electrostatic attraction is more likely to occur between the negative charge on the HA surface and the positive charge on the adsorbent surface [28]. With increasing pH, the electrostatic repulsion between the adsorbent and HA resulted in a decreased adsorption capacity [29]. Second, under extreme conditions, such as pH < 4 and pH > 10, the screening effect from the counter ions (i.e., Cl− and Na+ ) shields the charge of –NH3 + on chitosan or ionizes the carboxyl groups on
HA, making the HA molecules more difficult to transfer [30]. Thus, the efficient treatment of HA in neutral water conditions has great promise for practical application. 3.6. FE-SEM images and FT-IR spectra before and after HA adsorption The FE-SEM images of PA-90 and CPA, shown in Fig. 7, exhibited a smooth cleavage surface and sharp edges. After adsorption of HA, the surface of PA-90 becomes smooth and less porous due to the coverage of HA. However, the surface of CPA was observed to have more pores and exhibited an irregular structure after adsorption (Fig. 7(d)), which indirectly indicates that a chemical reaction occurred between CPA and HA. FT-IR spectroscopy was also used to study the adsorption of HA. As shown in Fig. S2, no obvious changes were observed for PA-90 before and after adsorption. However, after CPA adsorption, two obvious peaks at 1571 cm−1 and 1421 cm−1 disappeared, which likely indicates that the adsorption of HA onto CPA could be controlled by complexation reactions, such as the formation of –NH3 + • • •− OOC–R or –NH3 + • • •− O–C6 H4 –R complexes between the –NH3 + groups of
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Fig. 7. FE-SEM images of PA-90 and CPA before and after adsorption: (a) PA-90, (b) PA-90-HA, (c) CPA, and (d) CPA-HA.
chitosan and the –RCOO− and –RO− groups of HA [21]. Moreover, the adsorption capacity of CPA for HA capture was stable for 6 cycles, in which the adsorption capacity was decreased from 4.31 to 3.44 mg/g, as shown in Fig. S3, which exhibited the regeneration of the prepared adsorbent. 3.7. Adsorption kinetics To gain a better understanding of the adsorption properties of HA onto PA-90 and CPA, the adsorption performance of HA on PA90 and CPA were fitted by the pseudo-first-order kinetics, pseudosecond-order kinetics and intra-particle diffusion equations, and the adsorption kinetics behavior is shown in Eqs. (S1), (S2) and (S3), respectively [31]. The adsorption processes were fitted at 278 K, and the concentrations of HA were 5 mg/l, 10 mg/l, 60 mg/l and 100 mg/l. These fitting curves are illustrated in Fig. 8(a) and (c), and the detailed parameters and correlation coefficients obtained from these plots are listed in Table S2. The HA adsorption process on PA-90 and CPA, including rapid adsorption in the initial phase and gradual adsorption, is shown in Fig. 8(a) and (c). The adsorption capacity after 2 min reached approximately 80% for CPA in contrast with PA-90, which took 10 min to reach the same capacity. Equilibrium could be achieved within 30, 60 and 180 min with pristine HA in concentrations of 5, 10, 60 and 100 mg/l. The qe, PA values reached 2.07, 4.42, 14.77 and 18.16 mg/g within 30, 60 and 180 min, which were lower than the qe, CPA values of 4.48, 9.31, 32.08 and 40.83 mg/g, respectively. This indicates that chitosanmodified PA-90 could successfully achieve increased HA adsorption because of its surface functional groups. The pseudo-second-order model has a higher regression factor (R2 ≥ 0.963 for CPA and 0.943 for PA-90) than the pseudo-first-order model (R2 ≥ 0.928, CPA, and 0.863, PA-90), suggesting that it is more suitable to describe HA adsorption on PA-90 and CPA. The theoretical qe values calculated using the pseudo-second-order equation are similar to the experimental qe,exp values. Similar results have been demonstrated in previous works [32–34]. The effects of pore size on the diffusion of HA were also simulated by the intra-particle diffusion equation. The intra-particle diffusion fitting curves, as shown in Fig. 8(b) and (d), demonstrated the nonlinear relationship between qt and t1/2 and revealed the HA diffusion–adsorption process. This process was controlled by two steps, including film diffusion (boundary layer diffusion in the initial 2 min) on the external surface and interior surface diffusion. The diffusion resistance increases with increasing HA adsorption
capacity, making the intra-particle diffusion rate (Kint ) decrease and then gradually achieve adsorption equilibrium [18]. The intercept C on the y-axis, shown in Fig. 8(b) and (d), indicates that the interface thickness increased with increasing contact time, illustrating that diffusion of the adsorbents plays an important role, along with the abundant active sites, in PA-90 and CPA for HA adsorption [35]. The intra-particle diffusion rates Kint,1 and Kint,2 of CPA were higher than those of PA-90 (Table S2), indicating the fast HA adsorption of CPA compared with that of PA-90 [28]. The Kint,1 and Kint,2 values increased with increasing initial concentration, which can be attributed to the intra-particle diffusion model based on Fick’s law [36]. The temperature, a key adsorption factor, could also significantly influence the adsorption capacity. The adsorption equilibrium isotherms of PA-90 and CPA at different temperatures are presented in Fig. S4, and detailed information on the relevant estimated parameters is given in Table S2. Correlation coefficients (R2 ) of both the pseudo-second-order kinetics equation and the intra-particle diffusion equation were relatively higher, indicating that the two equations could suitably describe the HA adsorption process at different temperatures. Furthermore, it is observed that the temperature has a different effect on the adsorbents for the adsorption process. For CPA, there was a negative correlation between temperature and adsorption capacity (Fig. S4) because the adsorption of CPA towards HA was exothermic. This can be explained by the fact that at high temperature, the kinetic energy of HA is low, and therefore, contact between HA and the active sites of CPA is insufficient, leading to a decrease in adsorption efficiency. Furthermore, at lower temperature, the kinetic energy of HA is higher than the attractive potential between HA and the active sites of CPA. This condition causes a decrease in adsorption efficiency, showing that adsorption is more of a physical property than a chemical property. In contrast, there was a positive correlation between temperature and the adsorption capacity of PA90, indicating that PA-90 was favorable for HA adsorption at high temperature. The presented results are in agreement with previous work, illustrating that changes in temperature could accelerate the adsorption rate or create new active sites on the surface of PA-90 [28,29]. Therefore, the active sites of PA-90 could be enhanced at high temperatures, but there were no obvious changes after 80 min of adsorption at different temperatures (Fig. S4(a) and (c)), demonstrating that the adsorption process reached equilibrium after 80 min.
Please cite this article as: N. Sun et al., Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.03.017
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Fig. 8. The kinetics of HA adsorption on (a) and (b) CPA and (c) and (d) PA-90 at different HA concentrations (pH: 6; contact time: 180 min; CPA dose: 1 g/l; PA dose: 2 g/l).
Fig. 9. HA adsorption isotherms of (a) CPA and (b) PA-90 (initial HA concentration: 5 mg/l; pH: 6; temperature: 5 °C; contact time: 180 min; CPA dose: 1 g/l; PA dose: 2 g/l).
3.8. Adsorption isotherms To explore the effect of initial HA concentration on the performance of PA-90 and CPA, adsorption equilibrium uptakes under various initial HA concentrations (from 0 to 10 0 0 mg/l) were tested (pH = 6 and at 5 °C). The results, shown in Fig. 9, revealed a typical L-shaped plot with increasing HA concentration, indicating that PA-90 and CPA have a high affinity for HA. The values of qe,PA and qe,CPA first increased sharply when the concentration of Ce ranged from 1 to 200 mg/l and then reached a plateau at equilibrium. Furthermore, to quantitatively analyze the adsorption process of HA on PA-90 and CPA, five classical isotherm models were employed to fit the experimental data; the Langmuir, Freundlich, Temkin, Langmuir–Freundlich and Redlich–Peterson models are described by Eqs. (S4)–(S8), respectively [5,37].
Based on the five adsorption isotherm models, curve fitting of the experimental data is shown in Fig. 9. The calculated isotherm parameters are listed in Table S3. For PA-90 and CPA, it was evident that the Langmuir–Freundlich equation (R2 = 0.992) and the Freundlich equation (R2 = 0.995) matched better than the other sorption processes. This indicates that HA sorption on PA-90 was affected by the Langmuir and Freundlich processes, whereas the interaction between HA and CPA was solely affected by Freundlich processes. The varied sorption processes indicated that sorption of HA on PA-90 and CPA is governed by different mechanism [37]. Moreover, the adsorption of CPA was also well fit by the Langmuir–Freundlich model. The theoretical maximum capacities calculated based on the Langmuir–Freundlich model were 35.85 and 112.07 mg/g when the concentration of C0 ranged from 0 to 10 0 0 mg/l. Our experimental results were much better than those
Please cite this article as: N. Sun et al., Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.03.017
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of most previous reports in the literature, which are listed in Table S4 [1,4–6,8,9,19,38] Therefore, chitosan-modified purified attapulgite could be considered to be a promising adsorbent for removing HA at low temperature in high-color source water. 4. Conclusions In summary, we have successfully demonstrated a facile strategy to achieve high HA adsorption performance based on the combination of an attapulgite purification process and surface modification. The pseudo-second-order model (R2 ≥ 0.963 for CPA and R2 ≥ 0.943 for PA-90), Langmuir-Freundlich equation (R2 = 0.991 for PA-90) and Freundlich equation (R2 = 0.995 for CPA) described the adsorption process well. Based on the Langmuir–Freundlich isotherm, PA-90 and CPA exhibited excellent adsorption capacity (35.85 and 112.07 mg/g, respectively) at 278 K. Electrostatic attraction, the physical characteristics (porous structure and large surface area) and the protonated amino groups of CPA interacting with the carboxyl and phenolic groups of HA resulted in the sharp response and ideal adsorption capacity. The experimental results also demonstrated the HA adsorption performance on CPA was favorable at lower temperatures. Acknowledgments This study was supported by Postdoctoral Science Foundation of Heilingjiang Province, China (LBH-Z13025) and the Science and Technology Research Project of Heilongjiang Provincial Education Department (No. 11541024). Supplementary materials Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.jtice.2017.03.017. References [1] Moussavi G, Talebi S, Farrokhi M, Sabouti RM. The investigation of mechanism, kinetic and isotherm of ammonia and humic acid co-adsorption onto natural zeolite. Chem Eng J 2011;171:1159–69. [2] Hseu Y-C, Kumar KS, Chen C-S, Cho H-J, Lin S-W, Shen P-C, et al. Humic acid in drinking well water induces inflammation through reactive oxygen species generation and activation of nuclear factor-κ B/activator protein-1 signaling pathways: a possible role in atherosclerosis. Toxicol Appl Pharmacol 2014;274:249–62. [3] Badis A, Ferradji F, Boucherit A, Fodil D, Boutoumi H. Removal of natural humic acids by decolorizing actinomycetes isolated from different soils (Algeria) for application in water purification. Desalination 2010;259:216–22. [4] Wang S, Zhu Z. Humic acid adsorption on fly ash and its derived unburned carbon. J Colloid Interface Sci 2007;315:41–6. [5] Maghsoodloo S, Noroozi B, Haghi AK, Sorial GA. Consequence of chitosan treating on the adsorption of humic acid by granular activated carbon. J Hazard Mater 2011;191:380–7. [6] Wang J, Zhou Y, Li A, Xu L. Adsorption of humic acid by bi-functional resin JN-10 and the effect of alkali-earth metal ions on the adsorption. J Hazard Mater 2010;176:1018–26. [7] Mohseni-Bandpi A, Kakavandi B, Kalantary RR, Azari A, Keramati A. Development of a novel magnetite–chitosan composite for the removal of fluoride from drinking water: adsorption modeling and optimization. RSC Adv 2015;5:73279–89. [8] Peng X, Luan Z, Zhang H. Montmorillonite–Cu (II)/Fe (III) oxides magnetic material as adsorbent for removal of humic acid and its thermal regeneration. Chemosphere 20 06;63:30 0–6. [9] Wang J, Han X, Ma H, Ji Y, Bi L. Adsorptive removal of humic acid from aqueous solution on polyaniline/attapulgite composite. Chem Eng J 2011;173:171–7. [10] Li G, Zhu Z, Qi B, Liu G, Wu P, Zeng G, et al. Rapid capture of Ponceau S via a hierarchical organic–inorganic hybrid nanofibrous membrane. J Mater Chem A 2016;4:5423–7.
[11] Zhu Z, Wu P, Liu G, He X, Qi B, Zeng G, et al. Ultrahigh adsorption capacity of anionic dyes with sharp selectivity through the cationic charged hybrid nanofibrous membranes. Chem Eng J 2017;313:957–66. [12] Zhu Z, Li G, Zeng G, Chen X, Hu D, Zhang Y, et al. Fast capture of methyl-dyes over hierarchical amino-Co0.3Ni0.7Fe2 O4 @SiO2 nanofibrous membranes. J Mater Chem A 2015;3:220 0 0–4. [13] Zhu Z, Xu Y, Qi B, Zeng G, Wu P, Liu G, et al. Adsorption-intensified degradation of organic pollutants over bifunctional α -Fe@ carbon nanofibres. Environ Sci Nano 2017;4:302–6. [14] Sun N, Yu SL, editors. Adsorption mechanism of humic acid on attapulgite based on Stumm–Schindle surface complexation model. Adv Mater Res 2012;630:99–105. [15] Deng Y, Wang L, Hu X, Liu B, Wei Z, Yang S, et al. Highly efficient removal of tannic acid from aqueous solution by chitosan-coated attapulgite. Chem Eng J 2012;181:300–6. [16] Chang M-Y, Juang R-S. Adsorption of tannic acid, humic acid, and dyes from water using the composite of chitosan and activated clay. J Colloid Interface Sci 2004;278:18–25. [17] Dong C, Chen W, Liu C. Preparation of novel magnetic chitosan nanoparticle and its application for removal of humic acid from aqueous solution. Appl Surf Sci 2014;292:1067–76. [18] Lin J, Zhan Y. Adsorption of humic acid from aqueous solution onto unmodified and surfactant-modified chitosan/zeolite composites. Chem Eng J 2012;200:202–13. [19] Ngah WW, Fatinathan S, Yosop N. Isotherm and kinetic studies on the adsorption of humic acid onto chitosan-H2 SO4 beads. Desalination 2011;272:293–300. [20] Dong C, Chen W, Liu C, Liu Y, Liu H. Synthesis of magnetic chitosan nanoparticle and its adsorption property for humic acid from aqueous solution. Colloids Surf Physicochem Eng Asp 2014;446:179–89. [21] Zhang X, Bai R. Mechanisms and kinetics of humic acid adsorption onto chitosan-coated granules. J Colloid Interface Sci 2003;264:30–8. [22] Xie J, Li C, Chi L, Wu D. Chitosan modified zeolite as a versatile adsorbent for the removal of different pollutants from water. Fuel 2013;103:480–5. [23] Cai D, Zhang H, Tang Y, Chu PK, Yu Z, Wu Z. Nano-networks have better adsorption capability than nano-rods. Nano Commun Netw 2010;1:257–63. [24] Tang Y, Liang S, Yu S, Gao N, Zhang J, Guo H, et al. Enhanced adsorption of humic acid on amine functionalized magnetic mesoporous composite microspheres. Colloids Surf Physicochem Eng Asp 2012;406:61–7. [25] Liu J, Cao J, Chen H, Zhou D. Adsorptive removal of humic acid from aqueous solution by micro-and mesoporous covalent triazine-based framework. Colloids Surf Physicochem Eng Asp 2015;481:276–82. [26] Su D, Wang C, Cai S, Mu C, Li D, Lin W. Influence of palygorskite on the structure and thermal stability of collagen. Appl Clay Sci 2012;62:41–6. [27] Tao Q, Xu Z, Wang J, Liu F, Wan H, Zheng S. Adsorption of humic acid to aminopropyl functionalized SBA-15. Microporous Mesoporous Mater 2010;131:177–85. [28] Shuang C, Wang J, Li H, Li A, Zhou Q. Effect of the chemical structure of anion exchange resin on the adsorption of humic acid: behavior and mechanism. J Colloid Interface Sci 2015;437:163–9. [29] Wang M, Liao L, Zhang X, Li Z. Adsorption of low concentration humic acid from water by palygorskite. Appl Clay Sci 2012;67:164–8. [30] Wang Y, Zeng L, Ren X, Song H, Wang A. Removal of Methyl Violet from aqueous solutions using poly (acrylic acid-co-acrylamide)/attapulgite composite. J Environ Sci 2010;22:7–14. [31] Colombo C, Palumbo G, Angelico R, Cho HG, Francioso O, Ertani A, et al. Spontaneous aggregation of humic acid observed with AFM at different pH. Chemosphere 2015;138:821–8. [32] Bouras HD, Benturki O, Bouras N, Attou M, Donnot A, Merlin A, et al. The use of an agricultural waste material from Ziziphus jujuba as a novel adsorbent for humic acid removal from aqueous solutions. J Mol Liq 2015;211:1039–46. [33] Wang L, Zhang J, Wang A. Fast removal of methylene blue from aqueous solution by adsorption onto chitosan-g-poly (acrylic acid)/attapulgite composite. Desalination 2011;266:33–9. [34] Zhang J, Gong J-L, Zenga G-M, Ou X-M, Jiang Y, Chang Y-N, et al. Simultaneous removal of humic acid/fulvic acid and lead from landfill leachate using magnetic graphene oxide. Appl Surf Sci 2016;370:335–50. [35] Moussavi G, Khosravi R. Removal of cyanide from wastewater by adsorption onto pistachio hull wastes: parametric experiments, kinetics and equilibrium analysis. J Hazard Mater 2010;183:724–30. [36] Ujihara T, Fujiwara K, Sazaki G, Usami N, Nakajima K. New method for measurement of interdiffusion coefficient in high temperature solutions based on Fick’s first law. J Cryst Growth 2002;241:387–94. [37] Jiang W, Pelaez M, Dionysiou DD, Entezari MH, Tsoutsou D, O’Shea K. Chromium (VI) removal by maghemite nanoparticles. Chem Eng J 2013;222:527–33. [38] Lin J, Zhan Y. Adsorption of humic acid from aqueous solution onto unmodified and surfactant-modified chitosan/zeolite composites. Chem Eng J 2012;200-202:202–13.
Please cite this article as: N. Sun et al., Preparation and characterization of chitosan/purified attapulgite composite for sharp adsorption of humic acid from aqueous solution at low temperature, Journal of the Taiwan Institute of Chemical Engineers (2017), http://dx.doi.org/10.1016/j.jtice.2017.03.017