Characterization and ciprofloxacin adsorption properties of activated carbons prepared from biomass wastes by H3PO4 activation

Accepted Manuscript Characterization and ciprofloxacin adsorption properties of activated carbons prepared from biomass wastes by H3PO4 activation Yuanyuan Sun, Hong Li, Guangci Li, Baoyu Gao, Qinyan Yue, Xuebing Li PII: DOI: Reference:

S0960-8524(16)30341-8 http://dx.doi.org/10.1016/j.biortech.2016.03.047 BITE 16237

To appear in:

Bioresource Technology

Received Date: Revised Date: Accepted Date:

30 December 2015 7 March 2016 8 March 2016

Please cite this article as: Sun, Y., Li, H., Li, G., Gao, B., Yue, Q., Li, X., Characterization and ciprofloxacin adsorption properties of activated carbons prepared from biomass wastes by H3PO4 activation, Bioresource Technology (2016), doi: http://dx.doi.org/10.1016/j.biortech.2016.03.047

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Characterization and ciprofloxacin adsorption properties of activated carbons prepared from biomass wastes by H3PO4 activation Yuanyuan Suna,1, Hong Lia,1, Guangci Li a, Baoyu Gaoa,b, Qinyan Yueb, Xuebing Lia, * a

Key Laboratory of Biofuels, Qingdao Institute of Bioenergy and Bioprocess

Technology, Chinese Academy of Sciences, Qingdao 266101, China b

School of Environmental Science and Engineering, Shandong University, Jinan

250100, China * Corresponding author. Tel: +86 532 80662759, Fax: +86 532 80662778, [email protected] (X. Li) 1

These two authors contributed equally to this work

Abstract: As biomass wastes, Arundo donax Linn and pomelo peel were used as precursors for activated carbons (ALAC and PPAC) preparation by phosphoric acid activation. The pore structure and surface acidic functional groups of both carbons were characterized by nitrogen adsorption/desorption experiment, NH3-temperature-programmed desorption (NH3-TPD) and Fourier transform infrared spectroscopy (FTIR). A batch of experiments was carried out to investigate the adsorption performances of ciprofloxacin under different conditions. Results showed that PPAC exhibited larger surface area (1252 m2/g) and larger portion of mesoporous, while ALAC was typical of microporous materials. Results from NH3-TPD suggested that ALAC was characteristic of more acidic functional group than PPAC. The maximum monolayer adsorption capability was

1

244 mg/g for ALAC and 400 mg/L for PPAC. Kinetics studies showed intra-particle diffusion was not the unique rate-controlling step. Boundary layer resistance existed between adsorbent and adsorbate. Key words: Biomass waste; Activated carbons; Ciprofloxacin removal; H3PO4 activation 1. Introduction Activated carbon is a preferred adsorbent for the removal of pollutants from wastewater. However, its widespread use is restricted due to high costs. To decrease treatment costs, attempts have been made to find inexpensive alternative precursors for carbon preparation, such as renewable waste materials. As one kind of wetland plants, Arundo donax Linn are generated abundantly every year. Previous studies have reported many methods to make full use of this lignocellulosic biomass waste (Sun et al., 2013; You et al., 2016). Fruit peels have also been used for carbon preparation, such as orange peel (Fernandez et al., 2015; Nemr et al., 2009), jackfruit peel (Foo & Hameed, 2012) and pomegranate peel (Nemr et al., 2009). Pomelo peel is available from the fruit juice processing plants as an industrial waste. Carbons produced from pomelo peel by KOH and NaOH activation have been used for the removal of anionic and cationic dyes (Foo & Hameed, 2011; Li et al., 2016). Ciprofloxacin (CIP) is one of the extensively used fluoroquinolone antibiotics in the world. The presence of antibiotics in environments can cause serious damages to the ecosystem and human health through inducing growth of antibiotic-resistant bacteria

2

even at low concentration (Lapworth et al., 2012). Recently, the wide occurrence of CIP in groundwater has attracted broad attentions (Yu et al., 2012). Adsorption may be an effective way to remove antibiotics like CIP due to high efficiency and good feasibility (Yu et al., 2016). Compared with zinc chloride and hydroxides, H3PO4 shows advantages for producing activated carbon used for wastewater treatment (Diao et al., 2002; Li et al., 2010). (i) Precursors can be activated by H3PO4 at lower temperature (about 450 oC) in the atmosphere, while hydroxides at higher temperature (above 700 oC) with the protection of inner atmosphere. (ii) H3PO4 has low corrosivity to the equipment and no metal residues, thus environmental friendly. (iii) Carbons prepared by H3PO4 activation have large particles and good sedimentation performance, which is very suitable for water treatment. (iv) H3PO4 activation is beneficial for the development of mesoporous, which is beneficial for lager molecules adsorption. Thus, carbons from H3PO4 activation are cost-effective and environmental friendly. The properties of precursors have a great effect on the physicochemical of obtained carbons. However, carbons produced from pomelo peel and Arundo donax Linn by H3PO4 activation for CIP adsorption have not been studied. The main object of this work was to present the comparative study on physicochemical and adsorption properties of activated carbons from Arundo donax Linn and pomelo peel using H3PO4 as activating agent. CIP was chosen as adsorbate to evaluate the sorption behavior as a function of condition variables (effect of time, pH

3

and initial concentration). The properties of activated carbons were correlated with their adsorption ability and the interaction mechanisms were also investigated. 2. Materials and methods 2.1. Chemicals Ciprofloxacin hydrochloride (C17H18FN3O3·HCl, molecular size 13.5 × 3 × 7.4 Å) from Aladdin was used as adsorbate. With pKa1 = 6.1 and pKa2 = 8.7 for the carboxylic acid and the basic-N-moiety group, the speciation of cation (CIP+), zwitterion (CIP±) and anion (CIP–) were existed under different pH (Gu & Karthikeyan, 2005). 2.2. Synthesis of activated carbons Activated carbons were prepared using the following simple method. Arundo donax Linn and pomelo peel were precursors for activated carbons. The dried and clean precursor was ground and sieved. Particles with sizes lower than 0.35 mm (45 mesh) diameter were used. After immersing in 85 wt. % H3PO4 solution at a ratio of 1:2.5 (g precursor/g H3PO4), which was the optimum impregnation ratio used for lignocellulosic biomass activation (Huang et al., 2014), the wet sample was soaked for 10 h. Then, the samples were transferred into a muffle furnace with widely used preparation conditions by H3PO4 activation (temperature of 450 oC and activation time of 60 min). After cooling to room temperature, the obtained carbons were washed with tap water and afterwards deionized water repeatedly until the pH of the filtrate became steady. Then, the adsorbents were filtered, dried and crushed. Particles with sizes between 0.074 and 0.15 mm (100-200 mesh) were stored in a desiccator for further experiments.

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2.3. Characterization methods SDT Q600 equipment was used to obtain thermo gravimetric analysis (TGA) information. The two samples (the compounds of Arundo donax Linn and H3PO4, pomelo peel and H3PO4) were heated at a rhyme of 5 °C/min in N2 atmosphere. The pore structure of carbons was performed on a surface area analyzer at 77K (Micrometrics, ASAP 2020). Prior to N2 adsorption/desorption, the samples were degassed at 200 °C under vacuum for 5 h. The surface area (S BET) was determined by the Brunauer–Emmett–Teller (BET) model from relative pressures (P/P0) in the range of 0.01-0.1 with correlation coefficient high than 0.9999. The total pore volume (Vt) was obtained by single point adsorption of N2 at a high relative pressure (∼0.99). Micropore area (S mic) and micropore volume (Vmic) were determined by t-plot method. Mesoporous area (S meso) and mesoporous volume (Vmeso) were calculated using BJH model. The equation 4V/SBET was used to calculate the average pore width. The pore size distribution was auto-generated by applying the density functional theory (DFT) method to the N2 adsorption isotherms using the software supplied by ASAP 2020. The NH3-temperature-programmed desorption (NH3-TPD) was tested on a Micromeritics Autochem 2920 instrument in a quartz reactor with a TCD as detector. The sample (0.10 g) was pretreated with Ar gas at 200 °C for 1 h to remove free and weakly adsorbed gas. After cooling down to 100 °C, 10% NH3/Ar mixture gas of 20 mL/min was introduced and the catalyst was purged for 3 h. After adsorption, pure Ar was introduced. The sample was then heated up to 500 °C at a heating rate of 5 °C/min.

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Surface oxygenated groups on carbon decomposed upon heating, releasing CO and/or CO2. To deduct the produced gas, TPD without NH3 adsorption process was carried out. The NH3-TPD results of activated carbon were recorded by deducting TPD results. The types of surface functional groups of both activated carbons were also recorded with Nicolet 6700 FTIR Spectrometer (Thermo Fisher). The spectra were recorded from 4000 to 400 cm−1 and the resolution was 4 cm-1. 2.4. Adsorption experiments Batch adsorption experiments were performed by contacting 0.1 g of the adsorbents with 100 mL of CIP solution. To obtain adsorption isotherms, initial CIP concentrations in the range of 100-800 mg/l at natural solution pH were tested. The flasks were sealed and placed in an oscillator at a speed of 125 rpm with a temperature control of 298 K until equilibrium was reached. To study the effect of adsorption time, samples with an initial concentration of 350 mg/g were withdrawn at predefined time and analyzed to determine the residual liquid-phase CIP concentration. The effect of pH on CIP adsorption was evaluated by adjusting the pH values of the solutions (initial concentration of 350 mg/L) using concentrated HCl or NaOH to the designated values. The solution was filtered using a syringe with 0.45 µm filter membrane and then determined by UV-Vis spectrophotometer (UV-752, Shanghai) at 275 nm. 2.5. Data analysis To determine the adsorption kinetics of CIP onto both carbons, the experimental data at various contact time corresponding to the adsorption capacity of CIP was fitted

6

with three kinetic models, including pseudo-first-order, pseudo-second-order, and intra-particle diffusion model. The linear expression of pseudo-first-order (Eq. (1)), pseudo-second-order (Eq. (2)), and intra-particle diffusion models (Eq. (3)) are expressed as follows:

ln( qe − qt ) = ln qe − k1t

(1)

t 1 1 = + t 2 qt k 2 qe q e

(2)

qt = k p i t 1 / 2 + C

(3)

where k1 (min-1) is the rate constant of the pseudo-first-order model, k2 (g/(mg.min)) is the rate constant of second-order model, kpi (mg/g min1/2) is the diffusion rate constant of intra-particle model, C gives an idea about the thickness of boundary layer, qe and qt (mg/g) are the amount of CIP adsorbed at equilibrium and at time t (min). Adsorption isotherm was used to evaluate the characteristic of the adsorption process between liquid and solid phases when the adsorption reached equilibrium. Four commonly used isotherm models, Langmuir (Eq. (4)), Freundlich (Eq. (5)), Temkin (Eq. (6)) and Dubinin–Radushkevich (D–R) (Eq. (7)) were selected to analyze the equilibrium experimental data for the adsorption of CIP onto ALAC and PPAC. The Langmuir isotherm assumes the surface of adsorbent is homogeneous and the binding sites on the surface have identical sorption energies. There is no interaction between the adsorbed molecules. The Freundlich isotherm supposes that the surface is heterogeneous. The Temkin isotherm supposes that the adsorption is characterized by a uniform distribution of the binding energies, and the adsorption heat would decrease

7

linearly with coverage due to adsorbent–adsorbate interactions. The D-R isotherm model can be applied to examine the characteristics, free energy and the porosity of adsorbents. The equations of four models are given as follows: Ce 1 1 = + Ce qe Q0 K l Q0

(4)

1 ln q e = ln k F + ln Ce n

(5)

qe = A ln K T + A ln Ce

(6)

ln qe = ln qm - βε2

(7)

where Ce (mg/L) is the equilibrium concentration after adsorption, qe (mg/g) is the adsorption capacity of CIP adsorbed under equilibrium, Kl (L/mg) is the Langmuir adsorption constant, and Q0 (mg/g) is the maximum adsorption amount calculated by Langmuir model, KF and n are Freundlich constants, n gives an indication of how favorable the adsorption process and KF (mg/g (L/mg)1/n) is the adsorption capacity of the adsorbent. A= RT/bt, where R (8.314 J /mol.K) is the gas constant and T (K) is the absolute temperature. β is related to the mean free energy of adsorption (mol2/ KJ2), qm is the theoretical saturation capacity (mg/g). ε is the Polanyi potential, which is equal to RT ln(1 + (1/Ce)), 3. Results and discussion 3.1. TGA analysis of raw materials

For lignocellulosic biomass, the weight losses from room temperature to 400 oC

8

could reach up to 60% (Fu et al., 2013; Tiryaki et al., 2014), which was attributed to the removal of molecular bound water and decomposition of some volatile organic compounds. About 25% of weight was lost when the temperature reached 400 oC (Fig. 1). Thus, the addition of H3PO4 prevented the volatilization of organic matter in raw material. The weight loss was attributed to the rupture of weaker linkages in the plant structure, resulting in the early development of a rigidly cross-linked product. Compared with Arundo donax Linn, pomelo peel had more weight loss in the studied range, suggesting that the mixture of pomelo peel/H3PO4had higher reactivity than that of Arundo donax Linn under the same temperature. The extent of the reaction was closely related to the degree of activation reached, as well as the subsequent properties of activated carbons (Linares-Solano et al., 2012). Pomelo peel might produce activated carbon with larger specific surface area. 3.2. Porous structure observed by N2 adsorption/desorption at 77K

The N2 adsorption/desorption isotherms and pore size distributions are shown in Fig. 2. According to the results, the isotherm of ALAC is typical of microporous materials (type I) where the micropore filling takes place at very low P/P0 (Fig. 2a). For PPAC, the isotherm is a mixture of type I and type IV with hysteresis loops, indicating the co-existence of micropores and mesopores. The porous structural parameters are shown in Table 1. The BET surface area of PPAC (1252 m2/g) is higher than that of PLAC (675 m2/g). PPAC has total pore volume of 1.33 cm3/g and mesoporous volume of 0.931 cm3/g, while ALAC has total pore volume of 0.312 cm3/g and mesoporous

9

volume of 0.0506 cm3/g. The mean pore size of PPAC and ALAC is 4.26 and 1.85 nm, respectively. It is reported that the precursor has a great effect on the pore size distribution of activated carbon. Fig. 2b shows that PPAC has a larger portion of mesoporous located in 20 nm, which is large mesoporous and not common for carbons activated by H3PO4. These pores are advantage for large size molecular adsorption. 3.3. Surface chemistry of the samples

The information obtained from FTIR spectra (Fig. S1) revealed that different surface functional groups were produced during H3PO4 activation process. In the case of ALAC, the main characteristic absorption peaks were presented at: (i) 3353 cm−1 attributed to the stretching vibrations of –OH groups which originated from chemisorbed water and phenolic groups, (ii) 1702 cm−1 due to the stretching vibration of C=O in -COOH group, (iii) 1560 cm−1 related to stretching vibration of C=C band of the aromatic ring or highly conjugated C=C bond; (iv) 950-1300 cm−1 assigned to the stretching vibration of C-O, C-X or C-C. The peak at 1169 cm−1 was identified as C-O in phenol. The peak at 1039 cm−1 corresponded to C-O in benzyl hydroxyl, suggesting there were still some residual hydroxymethyl groups though they were consumed to form methylene bridges during curing process (Huang et al., 2015). Compared with ALAC, PPAC showed no peak at 1702 cm−1, indicating that the surface of PPAC did not have C=O band. Both carbons showed no peak at about 2900 cm−1, indicating the absence of C-H bond of –CH3 group. When heated, the surface oxygenated groups on carbon decomposed to CO and/or

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CO2 at different temperatures. TPD spectra (Fig. 3a) shows that ALAC has a high amount of carboxylic acid groups which evolve into CO2 below 400 oC (Faria et al., 2008), which is consistent with FTIR results. NH3-TPD (Fig. 3b) results also confirmed that ALAC had more surface functional group than PPAC. The amount of NH3 released from ALAC and PPAC was 0.80 and 0.67 mmol/g, respectively. 3.4. Effect of pH

The pH of solution is a significant controlling parameter because pH affects not only the speciation of adsorbate but also the surface charge of adsorbent (Babel & Kurniawan, 2004). The speciation of CIP under different pH is shown in Fig. 4. As pH increased, the uptake amount of CIP onto carbons gradually increased for both samples (Fig. S2). The electrostatic interaction between cationic CIP molecules and negatively charged carbon was strengthened with pH increasing. Lower adsorption capacity, especially for ALAC, at lower pH was mainly due to the protonation of CIP in acidic medium and the presence of excess H+ ions that could compete with the cationic molecules for adsorption sites (Foo and Hameed, 2011). Moreover, at lower pH, the carbon surface was positively charged. The electrostatic repulsion between cation and positive surface charge surface resulted in the decreased adsorption capacity. 3.5. The effect of contact time and adsorption kinetics of CIP onto adsorbents

The effect of contact time on CIP adsorption is shown in Fig. 5a. For both adsorbents, the adsorption capacity increased sharply at initial 2 h, and slowed down gradually, then reached equilibrium at about 24 h. ALAC had adsorption capacity of 127

11

mg/g, while PPAC had 266.8 mg/g. To evaluate the adsorption kinetics of CIP, different models were used to fit the experimental data. The linear plots are shown in Fig. 5b–d and the kinetic parameters, correlation coefficient are listed in Table 2. For both adsorbents, the correlation coefficients of pseudo-second-order kinetics were higher than 0.99. The calculated qe values agreed very well with the experimental data. Thus, compared with pseudo-first-order kinetic, pseudo-second-order kinetic model was more appropriate to fit the experimental data. Most of previous studies have reported the same results (Yari et al., 2015). It was found that in the adsorption process, the pH of solution decreased with the adsorption time, confirming that H+ was ionized from surface acidic functional group. Moreover, ion exchange between CIP and H+ on surface acidic functional group was involved in the adsorption process because carbons activated by H3PO4 had the ability of ion exchange. Intra-particle diffusion was used to fit the experimental data to appraise the nature of adsorption. The overall adsorption process includes the following three stages: (1) outer diffusion: the diffusion of adsorbate through the bulk solution to the external adsorbent surface, which is also called boundary layer diffusion or film diffusion; (2) inner diffusion: transportation of adsorbate from the exterior surface of adsorbent to the pores of the adsorbent, which is also called intra-particle diffusion; (3) adsorption of adsorbate onto the active sites on outer surface and/or inner of the adsorbent through strong adsorbate-adsorbent interactions equivalent to covalent bond formation or weak adsorption very similar to van der Waals forces (Singh et al., 2012). The third step is

12

very fast and thus cannot be considered as rate-limiting step. Thus, the adsorption rate was controlled by outer diffusion or inner diffusion or both. The linear portion of did not pass though the origin, indicating that intra-particle diffusion (inner diffusion) was not the unique rate-controlling step. Boundary layer resistance existed between adsorbent and adsorbate, and the deviation from the origin was proportional to the boundary layer thickness. 3.6. Adsorption isotherms for the adsorption of CIP onto adsorbents

The residual equilibrium concentration of CIP increases with the increase of initial solution concentration, whereas the amount of CIP adsorbed (qe) does not change significantly, indicating that the adsorption of CIP onto two carbons was monolayer adsorption, which is in agreement with the Langmuir model. Meanwhile, isotherm parameters and the correlation coefficient obtained from linear fits (Fig. S3) of Langmuir, Freundlich, Temkin and D-R isotherms are shown in Table 3. The adsorption process of CIP onto the activated carbons followed the Langmuir isotherm model with the maximum monolayer adsorption capability of 244 mg/g for ALAC and 400 mg/L for PPAC. This result confirmed that CIP molecules formed monolayer coverage on PPAC and ALAC, which were homogenous in nature. In addition, the values of RL for Langmuir isotherm were in the range of 0-1, and the Freundlich constant 1/n were smaller than 1, suggesting favorable process for both adsorbents. It was obvious that the PPAC adsorbent was more effective in removing CIP from aqueous solutions due to the higher availability of adsorption sites on PPAC with larger surface area.

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The mean free energy of adsorption (Ea) was calculated from the Dubinin–Radushkevich isotherm parameters using the equation: Ea=1/(2β)1/2. Ea values gave information about adsorption mechanism, physical or chemical. Generally, physical adsorption existed in the adsorption process if the value of Ea was below 8 kJ/mol, while ion exchange was dominant if the value was between 8 and 16 kJ/mol, and its value in the range of 20-40 kJ/mol was indicative of chemisorption (Li et al., 2010). However, the values of Ea for ALAC and PPAC were 0.5 and 3.67 kJ/mol, which were less than 8 kJ/mol. Therefore, the adsorption process on two carbons should be physical adsorption. This result also indicated possibility of better regeneration of the adsorbents. 4. Conclusions

Activated carbons from biomass wastes (Arundo donax Linn and pomelo peel) by H3PO4 activation were prepared. PPAC had larger specific surface area, but lower surface acidic functional group. PPAC acted as a better adsorbent for the removal of CIP from aqueous solutions with maximum monolayer adsorption capacities of 400 mg/g, which was mainly attributed to its higher surface area and more available adsorption sites. Both intra-particle diffusion and outer diffusion dominated the adsorption process. Physical adsorption, electrostatic attraction and ion exchange were involved in the adsorption mechanisms. Acknowledgements

This work was financially supported by Postdoctoral Science Foundation of China

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(No. 2015M572093), National Natural Science Foundation of China (NSFC Grant No. 21306214), National Natural Science Foundation of China (NSFC Grant No. 21276263) and Qingdao Indigenous Innovation Program (No. 15-9-1-76-jch). References

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112, 143-150. [7] Fu, K., Yue, Q., Gao, B., Sun, Y., Zhu, L. 2013. Preparation, characterization and application of lignin-based activated carbon from black liquor lignin by steam activation. Chem. Eng. J., 228, 1074-1082. [8] Gu, C., Karthikeyan, K.G. 2005. Sorption of the Antimicrobial Ciprofloxacin To Aluminum and Iron Hydrous Oxides. Environ. Sci. Technol., 39(23), 9166-9173. [9] Huang, Y., Li, S., Chen, J., Zhang, X., Chen, Y. 2014. Adsorption of Pb(II) on mesoporous activated carbons fabricated from water hyacinth using H3PO4 activation: Adsorption capacity, kinetic and isotherm studies. Appl. Surf. Sci., 293, 160-168. [10] Huang, Y., Ma, E., Zhao, G. 2015. Thermal and structure analysis on reaction mechanisms during the preparation of activated carbon fibers by KOH activation from liquefied wood-based fibers. Ind. Crops Prod., 69, 447-455. [11] Lapworth, D.J., Baran, N., Stuart, M.E., Ward, R.S. 2012. Emerging organic contaminants in groundwater: A review of sources, fate and occurrence. Environ. Pollut., 163, 287-303. [12] Li, H., Sun, Z., Zhang, L., Tian, Y., Cui, G., Yan, S. 2016. A cost-effective porous carbon derived from pomelo peel for the removal of methyl orange from aqueous solution. Colloid Surf. A-Physicochem. Eng. Asp., 489, 191-199. [13] Li, K., Zheng, Z., Li, Y. 2010. Characterization and lead adsorption properties of activated carbons prepared from cotton stalk by one-step H3PO4 activation. J.

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Figure captions

Fig. 1. Thermal analysis (TGA) of the compounds of Arundo donax Linn and H3PO4, pomelo peel and H3PO4 Fig. 2. (a) Nitrogen adsorption/desorption isotherms at 77 K, (b) pore size distribution, of ALAC and PPAC Fig. 3. (a) TPD profiles for samples; (b) NH3-TPD Fig. 4. Speciation of CIP under different pH Fig. 5. (a) Effect of time on CIP adsorption onto ALAC and PPAC, (b) fit using pseudo-first-order model, (c) pseudo-second-order model, (d) intra-particle diffusion model ([CIP] initial 350 mg/L; natural pH 5.05; temperature 25 oC)

19

AL-H3PO4 PP-H3PO4

100 14.2%

Weight (%)

80

26.2%

29.1%

60 40

36.9%

37.6%

20 0 0

200

400 T (oC)

Fig. 1

20

600

800

a

Relative pressure (P/P0)

b

Pore diameter (nm)

Fig. 2

21

a

Temperature (°C)

b

Temperature (°C)

Fig. 3

22

CIP+

CIP±

pH Fig. 4

23

CIP-

(b) Pseudo-first order kinetic model 4

200

3

ln(qe-qt)

qt(mg CPFX/g AC)

5

ALAC (a) Effect of time on CPFX adsorption PPAC

300

100

2 1 0

0 0

400

800

Time (min)

0

1200

800

1200

Time (min)

12

(d) Intraparticle diffusion kinetic model

(c) Pseudo-second order kinetic model 10

240

8

qt (mg CPFX/g AC)

t/qt (t g AC/mg CPFX)

400

160

6 4

80

2

0

0 0

400

800

Time (min)

0

1200

Fig. 5

24

10

20

t0.5 (min0.5)

30

40

Table 1. Porous structure parameters of adsorbents Type

SBET

Smic

Smes

Vtot

Vmic

Vmes

Dp

(m2/g)

(m2/g)

(m2/g)

(cm3/g)

(cm3/g)

(cm3/g)

nm

ALAC

675

613

62

0.312

0.255

0.0506

1.85

PPAC

1252

662

539

1.33

0.300

0.931

4.26

25

Table 2. Estimated kinetic model constants for CIP adsorption Kinetic models

Parameters

Adsorbent ALAC

PPAC

Pseudo-first-order

qe,exp (mg/g)

127.0

266.8

parameters

qe,cal (mg/g)

100.8

132.9

K1(min-1)

0.0031

0.004

R2

0.990

0.963

Pseudo-second-order qe,exp (mg/g)

127.0

266.8

parameters

qe,cal (mg/g)

135.1

270.3

K2(g/(mg.min))

0.618×10-4

1.04×10-4

R2

0.990

0.999

Intra-particle

Kp1(mg/g min0.5)

5.288

21.98

diffusion parameters

C1

1.321

11.74

(R1)2

0.999

0.980

Kp2(mg/g min0.5)

2.127

3.784

C2

52.76

165.8

(R2)2

0.996

0.974

26

Table 3. R2 and constant values for the different isotherm models Adsorbent

Langmuir constants qm

Kl

(mg

(L/mg)

R2

Freundlich constants KF

Temkin constants R2

n

(mg/g(L/mg)1/n)

KT (L/mg)

bt

R2

Dubinin–Radushkevich qm

β

R2

(mg/g) (mol2/ k J2)

/g) ALAC

244

0.0226 0.977 72.12

5.74 0.947 6.40

94.73 0.878 184

2.0

0.653

PPAC

400

0.200

6.30 0.887 172.9

67.83 0.966 364

0.07

0.977

0.997 166.5

27




Biomass wastes-derived activated carbon were prepared by one-step method




The properties of precursors were characterized by thermogravimetric analysis




The surface acidic functional groups were determined by NH3-TPD




The characterization and adsorption properties of both carbons were compared

28