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Fast and selective adsorption of As(V) on prepared modified cellulose containing Cu(II) moieties
⁎Corresponding author. Tel.: +20 10 4548447; fax: +20 48 2222753. amm_yousif_000@hotmail.com (Ahmed M. Yousif)
-
Received: ,
Accepted: ,
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.
Peer review under responsibility of King Saud University.
Abstract
Arsenic is one of the major pollutants and a worldwide concern because of its toxicity and chronic effects on human health. The synthesis of copper containing modified cellulose (Cell-N-Cu) adsorbent was achieved. The adsorbent was used to purify different waters from As(V) at different experimental conditions using batch method. Kinetic and thermodynamic properties as well as the mechanism of interaction between As(V) and adsorbent active sites were discussed. The adsorption behavior of the obtained samples showed high adsorption capacity as well as fast kinetics towards As(V) in their solutions. The maximum adsorption capacities of As(V) on Cell-N-Cu adsorbent were found to be 1.32 mmol/g. Regeneration and durability of the loaded adsorbent towards the successive reuse were also investigated. Fast and selective separation of As(V) from a real wastewater sample indicated that the investigated resin is potentially attractive for arsenic removal from different waste streams.
Keywords
Cellulose
Adsorption
Arsenic
Water treatment
1 Introduction
Arsenic is toxic and its presence in drinking water causes toxic and carcinogenic effects on human beings. It is reported that long-term drinking of arsenic contaminated water causes gastrointestinal, skin, liver, and nerve tissue injuries (Saha et al., 1999; ATSDR, 2002).
United States Environmental Protection Agency (USEPA) in 2001 reduced the limit of arsenic in drinking water to 10 mg/L from an earlier value of 50 mg/L (Zaspalis et al., 2007; Kundu and Gupta, 2007; Pagana et al., 2008). During the last 20 years, naturally occurring arsenic was found to be widespread in natural water in the USA, Argentina, Taiwan, China, Hungary, Vietnam, Chile, Bangladesh and India. It was estimated that some 35–77 million people were at extreme risk of groundwater arsenic poisoning in Bangladesh (Chakravarty et al., 2002; Souter et al., 2003; Singh et al., 2004; Kundu and Gupta, 2005).
Arsenic exists in natural waters in both inorganic as well as organic forms. The inorganic form of arsenic is more toxic than its organic form. Inorganic arsenic exists in natural waters in two oxidation states, As(III) and As(V). As(III) is dominant in more reduced conditions whereas As(V) is dominant in an oxidizing environment (Xu et al., 1991; Anawar et al., 2003; Ng et al., 2003). Several technologies have been employed to remove arsenic from water, including reverse osmosis, electrodialysis, coagulation, ion exchange, adsorption, and chemical precipitation. Adsorption is an economical and a reliable technique which is considered as an efficient alternative for removal of arsenic (Aredes et al., 2012). Different adsorbents such as activated carbons (Lorenzen et al., 1995), biological materials (Oehmen et al., 2006; Halttunen et al., 2007; Devi et al., 2008; Mondal et al., 2008), mineral oxides (Cumbal et al., 2003; Sun et al., 2006) were applied. Metal-loaded resins were also successfully used for arsenic adsorption. Metal-loaded chelating resins have advantages of large binding energy, good stability, high preconcentration factor, mechanical stability and good reproducibility. Iron(III)-containing resins and Zr(IV)-loaded chelating resin were studied for the removal of As(V) and As(III) from aqueous solutions (Matsunga et al., 1996; Haron et al., 1999; Balaji et al., 2005). In our group of research, we earlier reported on synthetic resins containing Cu(II) moieties loaded on GMA/MBA-TEPA resin and discussed its adsorption behavior towards As(V) (Donia et al., 2013).
In this study, renewable, inexpensive and eco-friendly copper containing biosorbent (Cell-N-Cu) has been successfully utilized for adsorption of As(V) from aqueous medium, with high adsorption capacity as well as fast uptake. The uptake characteristics have been studied using batch method at different experimental conditions. Kinetic and thermodynamic parameters of the uptake process were also calculated and discussed. The regeneration of the loaded resin for the repeated use was investigated.
2 Experimental
2.1 Chemicals
Cellulose (Cell), phosphorous oxychloride (POCl3), dimethylformamide (DMF), and tetraethylenepentamine (TEPA) were Aldrich products. All other chemicals were Prolabo products and used as received. Copper acetate [Cu(CH3COO)2] and sodium arsenate [Na2HAsO4·7H2O] were used as a source of Cu(II) and As(V), respectively.
2.2 Preparation of cellulose adsorbent
2.2.1 Preparation of chlorodeoxy cellulose (Cell-Cl)
A sample of 10 g of Cell was suspended in 200 mL DMF for one hour then reacted with 6 mL of POCl3 under mechanical stirring for more than 15 min. The cellulose chloride (Cell-Cl) obtained was filtered off then washed with DMF, distilled water and 5% NaOH followed by distilled water again and then dried in air for 24 h. (Gennaro et al., 1983).
2.2.2 Preparation of amine chelating resin (Cell-N)
A sample of 1.0 g Cell-Cl was directly reacted with 6 mL of TEPA without using any solvent. The reaction mixture was stirred under heating for 3 h at 130 °C. The product obtained was filtered off, washed with distilled water followed by methanol and then dried in air (Da Silva Filho et al., 2006). Synthetic route followed to obtain Cell-Cl and Cell-N from cellulose was represented in Scheme 1.
Synthetic route followed to obtain Cell-Cl and Cell-N from cellulose.
2.2.3 Estimation of amino group content
The concentration of amino group of Cell-N was estimated using a volumetric method as follows (Atia et al., 2008). A 40 mL of 0.05 M HCl solution was added to 0.1 g of Cell-N and conditioned for 15 h on a Vibromatic-384 Shaker. The residual concentration of HCl was estimated through the titration against 0.05 M NaOH solution and phenolphthalein as indicator. The number of moles of HCl interacted with amine groups and consequently the amine group concentration (mmol/g) was calculated from the following equation
2.2.4 Loading of Cell-N adsorbent by Cu(II)
A 0.1 g of Cell-N adsorbent was stirring with 100 mL of 1 × 10−2 M copper acetate solution on a Vibromatic shaker at 300 rpm at room temperature and natural pH for 2 h. The adsorbed amount was calculated from the residual concentration of Cu(II) in the equilibrated solutions via titration against 5 × 10−3 M EDTA using murexide as indicator (Atia et al., 2003). The product obtained was filtered off, washed with distilled water and then dried in air and named Cell-N-Cu.
2.2.5 Characterization of the adsorbent
2.2.5.1 SEM–EDX analysis
The morphology of sorbent particles and the EDX analysis were determined using an FESEM–EDX system (Quanta FEG 200, equipped with an OXFORD Inca 350 Energy Dispersive X-ray microanalysis (EDX) system) at an accelerating voltage of 30 keV and a working distance of 10 μm.
2.3 Adsorption measurements using batch method
2.3.1 Preparation of solutions and concentration measurements
Stock solution (1 × 10−2 M) of As(V) was prepared from sodium arsenate in distilled water. The desired concentrations were then obtained by dilution. The concentration of As(V) was measured using the molybdene blue spectrophotometric method (Lenoble et al., 2003). Calibration curve of As(V) in distilled water was constructed from the absorbance against concentration of As(V) at wave length of 870 nm. The measurements were carried out using double beam UV/visible spectrophotometer, CECIL CE 7400, Aquarius. The path cell length was 1.0 cm. Each measurements reading was an average of three replicates.
2.3.2 Effect of initial pH
A 0.1 g portions of the adsorbent was placed in a series of flasks each contained 100 mL of 1 × 10−3 M As(V) solutions. The desired pH solutions were adjusted using 0.1 N HCl or 0.1 N NaOH. The flasks were conditioned on a Vibromatic shaker at 300 rpm for 1 h at 25 °C. The uptake of As(V) was calculated by determining the residual concentration of As(V) following the above method and according to equation
2.3.3 Effect of contact time
A 0.1 g portions of the adsorbent was placed in flasks containing 100 mL of 1 × 10−3 M As(V) at natural pH 8.4 (natural). The contents of the flasks were equilibrated on the shaker at 300 rpm and 25 °C. Two mL of the solution (free from adsorbent particles) was taken from the flasks at different time intervals and the residual concentrations of As(V) were determined.
2.3.4 Adsorption isotherms
The effect of initial concentration of As(V) on the adsorption was carried out by placing 0.1 g portions of the adsorbent in a series of flasks each contains 100 mL of As(V) with different concentrations at pH 8.4 (natural). The contents of the flasks were equilibrated on the shaker at 300 rpm and at 25, 35, 45 and 55 °C for 15 min. After equilibration, the residual concentration of As(V) in each flask was determined to calculate the amount adsorbed of As(V).
2.4 Regeneration of the loaded adsorbent
Regeneration experiments were performed by placing 0.1 g of the adsorbent with 100 mL of 1 × 10−3 M As(V) solutions at suitable pH. The solution was decanted and the adsorbent was washed by distilled water. The total uptake was estimated. The loaded adsorbent was then subjected for elution using ammonium hydroxide solution (1.6 M). The adsorbent was then carefully washed with distilled water to become ready for reuse in the second uptake run. The regeneration efficiency was calculated according to equation
2.5 Selective adsorption of As(V) from a real wastewater sample
To minimize arsenic hazards and get cleaner wastewater, a 100 mL wastewater real sample obtained from a water treatment plant was conditioned with 0.1 g of Cell-N-Cu adsorbent till equilibrium time at natural pH and 28 °C. The concentrations of As(V) were analyzed before and after treatment using inductively coupled plasma (ICP) following the above method.
3 Results and discussion
3.1 Adsorbent characterization
The synthesis of modified cellulose containing copper (II) moieties was carried out by loading Cell-N that contains amine groups (estimated value of amine groups was 4.8 mmol/g) by Cu(II). The presence of amine modified cellulose (Cell-N) was confirmed by FT-IR spectra and TGA measurements (Donia et al., 2013).
The morphology of Cell-N-Cu before and after loading with arsenic was examined using scanning electron microscopy (SEM) (Fig. 1a and b). The SEM micrograph of Cell-N-Cu showed a coarse surface with several small pores inside and suggests interconnected pores within the resin (Fig. 1a). However, an apparent difference in the surface morphology of the sorbent after As(V) adsorption was observed (Fig. 1b). The surface roughness was decreased. Some of formerly existing pores disappeared and small particles were found to adhere to the surface of the sorbent. These results partially demonstrated that the chemical interactions took place between As(V) ions and Cell-N-Cu.
Scanning electron micrographs of Cell-N-Cu before (a) and after (b) loading with As(V).
The success of treatment and presence of copper in Cell-N-Cu was confirmed using titration against 5 × 10−3 M EDTA (from which the loaded Cu(II) was found to be 1.58 mmol/g). Quantitative value of loaded Cu(II) was slightly equal to one third of the concentration of the amine groups (4.8 mmol/g). Therefore, Cu(II) may be coordinated with three amine groups as illustrated in Scheme 2.
The coordination mode of Cu(II) moieties with amino groups in Cell-N-Cu adsorbent.
To map elemental copper and arsenic qualitatively, EDX measurements were performed and Cell-N-Cu showed distinct signals at 0.9 and 8.0 keV corresponding to copper while As(V) loaded Cell-N-Cu showed distinct signals at 1.3 and 10.5 keV corresponding to Arsenic (Fig. 2).
EDX spectra of Cu(II) and As(V) on loaded Cell-N-Cu adsorbent.
3.2 Adsorption studies
3.2.1 Effect of initial pH
The adsorption of As(V) on Cell-N-Cu adsorbent as a function of pH was shown in Fig. 3 using batch process. The highest uptake value was observed at pH 8.4 (natural) and reached 0.82 mmol/g. This may be related to the presence of As(V) as HAsO42− species which has a good capability to interact with positively charged Cu(II) on the adsorbent (strong Lewis base species) (Gupta and Chen, 1978; Fryxell et al., 1999). The lower adsorbed amount of As(V) compared to the estimated quantitative amount of Cu(II) present in Cell-N-Cu may be related to the bulky size of HAsO42− group which leads to insufficient saturation of active sites.
Effect of pH on the adsorption of As(V) by Cell-N-Cu adsorbent using initial concentrations of 1 × 10−3 M, 1 h equilibrium time and 25 °C.
The decrease in the uptake value was observed with lower pH may be attributed to the presence of As(V) as H2AsO4− species (with relative lower ability for interaction with Cu(II)) (Ghosh and Yuan, 1987; Ramana and Sengupta, 1992). On the other hand, when the pH of solution is above 9, the competitive adsorption of hydroxyl ions with arsenic ions HAsO42− in solution causes a decrease in uptake of arsenic on Cell-N-Cu adsorbent (An et al., 2005).
3.2.2 Kinetic studies
The adsorption of As(V) by Cell-N-Cu adsorbent as a function of time was shown in Fig. 4. The indicated figure showed that the adsorption was initially rapid, and was followed by a slower removal that gradually approaches equilibrium: about 60% of arsenic was removed within the first minute of contact. The rapid adsorption in the beginning stage can be attributed to the greater concentration gradient and more available sites for adsorption. The maximum uptake capacity was achieved within five minutes. This too fast rate of adsorption makes this adsorbent promising for practical applications if compared with other reported sorbents (Table 1) (Gupta and Babu, 2009; Martinson and Reddy, 2009; Zhang et al., 2013). This may be attributed to the hydrophilic as well as the swelling characters of cellulose.
Effect of time on the adsorption of As(V) by Cell-N-Cu adsorbent using initial concentrations of 1 × 10−3 M and 25 °C.
Adsorbent
Initial pH
Time
Conc. range (mg/L)
Adsorption capacity (mg/g)
References
Fe(III)–Ti(IV) oxide
7.0
6 h
5.0–250
14.3
Gupta and Ghosh (2009)
CuO nanoparticles
8.0
3 h
0–100
22.6
Martinson and Reddy (2009)
Fe–Cu binaryoxide
7.0
24 h
0–60
82.7
Zhang et al. (2013)
Cell-N-Cu
8.4
5 min
100–700
98.9
This work
The adsorption/time data obtained in Fig. 4 were applied to two simplified kinetic models, including pseudo-first-order model and pseudo-second-order model. The linear pseudo-first-order model may be expressed as (Shin et al., 2011).
The linear pseudo-second order kinetic model was expressed as (Hoda et al., 2006)
Pseudo-first order plots for the adsorption of As(V) on Cell-N-Cu adsorbent.
Pseudo-second order plots for the adsorption of As(V) on Cell-N-Cu adsorbent.
qe (exp) (mmol/g)
Pseudo-first order
Pseudo-second order
k1 (min−1)
qe (calc) (mmol/g)
R2
k2 (g/mmol min)
qe (calc) (mmol/g)
R2
0.83
0.44
0.57
0.9711
1.4
0.88
0.9974
Most of the adsorption reactions take place through a multi-step mechanism comprising; (i) external film diffusion, (ii) intraparticle diffusion and (iii) interaction between adsorbate and active sites.
To examine the rate determining step of the adsorption reaction, the uptake/time data obtained were treated according to the Fickian diffusion low (Guibal et al., 1998).
The intraparticle diffusion plots for the adsorption of As(V) on Cell-N-Cu adsorbent.
3.2.3 Adsorption isotherms
The adsorption isotherms of As(V) at different temperatures were shown in Fig. 8. Obviously, At 25 °C, increasing arsenic concentrations involves an increase in the uptake As(V) till reaching the maximum uptake value of 1.32 mmol/g. Moreover, the adsorption capacity showed a decrease with increasing temperature, this may be related to the decrease of the electrostatic attraction between As(V) and Cu(II) active sites at higher temperatures.
Adsorption isotherms of As(V) on Cell-N-Cu adsorbent at different temperatures.
The adsorption data were treated according to linear Langmuir equation (Gupta and Babu, 2009).
Temp. (°C)
qe(exp.) (mmol/g)
Qmax (mmol/g)
KL (L/mmol)
25
1.32
1.41
1.98
35
1.26
1.37
1.46
45
1.21
1.34
1.19
55
1.12
1.25
1.16
Degree of suitability of Cell-N-Cu adsorbent towards As(V) was estimated from the values of the separation factor (RL) which is defined by the following equation (Deniz and Saygideger, 2010).
Thermodynamic parameters of the adsorption reaction were calculated using van’t Hoff equation (Al-Degs et al., 2008).
Van’t Hoff plots for the adsorption of As(V) by Cell-N-Cu adsorbent.
Temp.(K)
ΔH° (kJ/mol)
ΔS° (kJ/mol K)
ΔG° (kJ/mol)
TΔS° (kJ/mol)
298
−14.8
−0.045
−1.5
−13.28
308
−1.1
−13.73
318
−0.7
−14.17
328
−0.2
−14.62
The negative values of ΔG° indicate that the adsorption is spontaneous. For Cell-N-Cu adsorbent, ΔG° values decrease as temperature increase which indicates that the process of adsorption of As(V) become less favorable at higher temperatures. This may be attributed to the exothermic nature of the adsorption process. The data given in Table 4 for Cell-N-Cu adsorbent show that |TΔS°| < |ΔH°| at all temperatures. This indicates that the adsorption reaction is dominated by enthalpic rather than entropic changes. These thermodynamic features of the adsorbent towards the adsorption of As(V) confirm our suggestion on the effective role of the structural characteristics of the adsorbent on the strength of interaction.
3.3 Regeneration experiments
Sorption/desorption cycles were performed repeatedly using ammonium hydroxide as an eluent. The efficiency of regeneration was found to be 98%. This value was reported after three cycles with standard deviation of ±1%. This finding reveals the stability of the adsorbent for the repeated use.
3.4 Selective adsorption of As(V) from a real wastewater sample
A real sample was obtained from a wastewater treatment plant containing sulfate, chloride, carbonate, nitrate and phosphate ions, Their concentrations were measured before and after treatment with the adsorbent and the data were recorded in Table 5 which are considered as competing ions in the arsenic adsorption process. It was expected that sulfate and carbonate ions would noticeably decrease the adsorbent efficiency due to their divalent state, but the obtained results indicate no significant influence on the capacity of studied adsorbent for arsenic adsorption. These results make Cell-N-Cu promising in arsenic selective separation in wastewater treatment.
Ion
Ci (mg/L)
Cf (mg/L)
Removal ratio (%)
SO42−
110.6
90.6
18.08
CO32−
100.2
86.3
13.87
PO43−
3.00
2.10
30.0
NO3−
1.26
1.18
6.35
Cl−
90.4
80.2
11.28
As(V)
102.2
28.4
72.21
4 Conclusion
Copper loaded (Cell-N-Cu) adsorbent was prepared and investigated. The adsorbent obtained is characterized by a fast and high adsorption capacities towards As(V) from aqueous media at natural pH (8.4). The equilibrium adsorption was reached within 5 min and reached 1.32 mmol/g. The adsorption process was found to follow pseudo-second order kinetics. The regeneration efficiency of the loaded adsorbent was found to be 98% ± 1% for As(V) using ammonium hydroxide. High arsenic uptake capability obtained from real sample results and cost-effectiveness of modified cellulose sorbent made it potentially attractive for arsenic removal from different waste streams.
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