Facile fabrication of polyacrylic acid-polyvinyl chloride composite adsorbents for the treatment of cadmium-contaminated wastewater

Accepted Manuscript Title: Facile fabrication of polyacrylic acid-polyvinyl chloride composite adsorbents for the treatment of cadmium-contaminated wastewater Authors: Sang Won Park, John Kwame Bediako, Mung-Hee Song, Jong-Won Choi, Hyun-Cheol Lee, Yeoung-Sang Yun PII: DOI: Reference:

S2213-3437(18)30159-3 https://doi.org/10.1016/j.jece.2018.03.038 JECE 2279

To appear in: Received date: Revised date: Accepted date:

5-1-2018 16-3-2018 18-3-2018

Please cite this article as: Sang Won Park, John Kwame Bediako, Mung-Hee Song, Jong-Won Choi, Hyun-Cheol Lee, Yeoung-Sang Yun, Facile fabrication of polyacrylic acid-polyvinyl chloride composite adsorbents for the treatment of cadmium-contaminated wastewater, Journal of Environmental Chemical Engineering https://doi.org/10.1016/j.jece.2018.03.038 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Facile fabrication of polyacrylic acid-polyvinyl chloride composite adsorbents for the treatment of cadmium-contaminated wastewater Sang Won Park†,1, John Kwame Bediako†,1, Mung-Hee Song1, Jong-Won Choi1, Hyun-Cheol

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Lee2, Yeoung-Sang Yun*,1 Division of Semiconductor and Chemical Engineering, Chonbuk National University, Jeonju,

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Jeonbuk-do, 561-756, Republic of Korea

Department of Clinical Pathology, Hanlyo University, 94-13, Hallyeodae-gil, Gwangyang-eup,

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Gwangyang, Jeonnam 57764, Republic of Korea

*Corresponding author. Tel.: +82 63 270 2308, fax: +82 63 270 2306, E-mail address:

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[email protected] (Y.-S. Yun) †

The authors contributed equally to this work and should be regarded as first co-authors.

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Graphical Abstract

Highlights

A facile method for preparing PAA-PVC composite adsorbents is presented.

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High capacity of Cd(II) sorption was obtained using the prepared adsorbents.

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The recorded Cd(II) uptake was extremely higher than most recently reported values.

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The Cd(II)-loaded adsorbents were fully regenerated using 0.1 M EDTA solution.

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Abstract

Facile fabrication of polyacrylic acid-polyvinyl chloride (PAA-PVC) composite adsorbents and

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their evaluation for Cd(II) adsorption is reported in this study. The sorbents were prepared via a simple phase inversion process by spinning PAA-PVC polymer blends into mixed solution of

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water and methanol. The prepared fibers were characterized by scanning electron microscopy, energy disperse X-ray microscopy and Fourier transform infra-red microscopy, and their sorption

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performances were evaluated by batch sorption experiments. Through sorption isotherm experiments, the maximum sorption capacity was estimated as 331.59 mg/g using the Langmuir isotherm model. Intra-particle diffusion played a major role in reaching the adsorption equilibrium. Ion-exchange between the charged carboxyl groups of PAA and the Cd(II) solution 2

was observed to be the main mechanism of Cd(II) sorption. This study is believed to pave way for preparing cost-effective polymeric composite sorbents for the removal of heavy metals from

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polluted waters.

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Keywords: Polyacrylic acid; Polyvinyl chloride; Composite sorbent; Cadmium; Sorption

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1. Introduction Cadmium is present in the wastewaters of metallurgical, ceramics, electroplated, photographic, pigments, and textile industries [1, 2]. It is produced as a by-product from the

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processing of zinc and copper minerals [3]. Like many other toxic metals, cadmium is very persistent and non-biodegradable. When ingested into the systems of living organisms, it

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accumulates and consequently destabilizes the organisms’ metabolisms [1-3]. Several methods including solvent extraction, chemical precipitation, chemical oxidation, membrane separation,

and cementation have been evaluated for the treatment of cadmium-polluted wastewaters [4-6].

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However, common constraints with such methods include inefficient metal removal in dilute

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solutions, high capital and operational costs, high reagent requirements and energy usage, and

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generation of toxic secondary sludge that require further disposals [4, 7]. In recent years,

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adsorption, including biosorption, has been extensively studied and has proven to be more efficient [4, 7-9]. Adsorption is usually noted for its simplicity, low-cost, and eco-friendliness,

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and hence has gained much recognition in the area of metal remediation [4, 7, 8]. Adsorption is shown to be effective in treating huge variety of organic and inorganic pollutants ranging from

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metal ions, dyes, petrochemical and pharmaceutical waste pollutants [5, 10, 11]. Although adsorption is simple and effective, the type of adsorbent and manufacturing

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requirements can greatly influence the pricing and thus the overall operational cost of the adsorption process. At the commercial level in particular, ion exchange/chelation resins and

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activated carbons are mainly used; however, these commercial adsorbents are mostly very expensive [11]. Specifically regarding the complexity of preparing activated carbons [12], it may not only be expensive to manufacture, but also, there could be huge concerns on clean

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production and green environment. It is thus necessary to develop novel low-cost adsorbents by simple techniques, with high performances and potentials for regeneration and reuse [12, 13]. As a precursor to finding better alternatives, various studies had evaluated a variety of biomaterials

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such as microbial biomass, agricultural residues, and industrial wastes [4, 14]. These adsorbents were usually applied as powdered or lump adsorbents; however, powdered adsorbents can clog

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pipelines and filters, while lump adsorbents exhibit slow sorption rates. These limitations are

significant technical hitches, especially when the adsorbents must be applied to large-scale and continuous processes [4, 15]. Attempts to address the above challenges gave rise to biomass

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immobilization using natural and synthetic materials [4, 15-17] and surface coating/modification

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of adsorbent materials [18-20]. Nevertheless, immobilization leads to decrease in sorbent

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performance, while modifications such as surface coating and grafting involve long and

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complicated steps [4]. For effective application in large-scale flow-through systems, fiber type adsorbents are very good candidates owing to their relatively thin sizes which facilitate easy

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access and interaction with adsorbates [21]. The type of parent materials (backbone materials in the cases of composite adsorbents) used for the fabrication, however, determines the successful

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application of the eventual fibrous adsorbents. Advances in recent adsorption research have shown that certain polymeric materials contain

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large numbers of functional groups that could sequester contaminants in water. Examples of such polymeric materials include poly(acrylic acid), poly(styrene-alt-maleic acid), poly(methacrylic

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acid), and poly(styrene sulfonic acid), which have shown promising prospects for sorption applications owing to the specific functional groups they possess [22-24]. The key issues with these materials, however, are their mechanical weaknesses, instability in water, and ultra-fine textures. That is, even though these materials have shown high binding affinities, they could not 5

be directly applied to metal sorption without being given mechanical supports and modifications such as crosslinking or grafting. Non-functional synthetic polymers such as polyvinyl chloride, polysulfone, polyvinyl alcohol, and polyurethane have good mechanical stabilities over long pH

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ranges and could provide the needed spinal anchorages for these materials through composite formations [4, 25].

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In this study, we outlined a facile process of synthesizing polyacrylic acid-polyvinyl chloride

(PAA-PVC) composite fiber adsorbents and their application to treating wastewater polluted with Cd(II) ions. PVC was used as a backbone material to stabilize the carboxyl-rich functional

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polymer, PAA which was expected to provide the needed binding sites for sorption. The PAA-

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PVC composite fibers were fabricated by phase inversion process after extruding heated blends

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of the PAA and PVC into mixed solutions of water and methanol. The sorbents were

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characterized by scanning electron microscopy (SEM), energy disperse X-ray spectroscopy (EDX), and Fourier transforms infrared spectroscopy (FTIR), and finally evaluated through

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adsorption studies using Cd(II) as model heavy metal solution. 2. Materials and methods

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2.1. Materials

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Polyvinyl chloride, PVC (Mw: 40kDa) was obtained from Sigma-Aldrich Korea Ltd. (Yongin, Korea), polyacrylic acid, PAA (Mw: 4,000,000) was purchased from Polysciences Inc., and N,N-

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dimethylformamide (DMF, 99.8%) was supplied by Daejung Chemical Company, Korea. Methanol and cadmium nitrate (Cd(NO3)2.4H2O) were purchased from Samchun Pure Chemical

Co., Ltd. and Junsei Chemical Company, respectively. Double distilled water was used for all experiments requiring water either for dissolution, dilution, or washing. 6

2.2 Methods 2.2.1. Fabrication of PAA-PVC composite sorbents The process for the fabrication of PAA-PVC composite fibers is described as follows: 2 g

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each of PVC and PAA were separately dissolved in 15 mL and 30 mL volumes of DMF, respectively. The separate solutions were then mixed together in a beaker placed in an oil bath

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(100 °C) under constant magnetic stirring for 2 h. At this stage, most of the DMF was evaporated and flowable composite gel-like slurry was obtained. This slurry was extruded through a spinneret into a mixed solution of water and methanol (1:1 v/v) to solidify into thin fibers

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(approx. 400 ~ 500 µm) by phase inversion mechanism. The fibers were washed with distilled

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water to remove the remaining DMF and re-suspended in 10% w/v NaCl solution for 1 h. The

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now sodium-form fibers hereafter referred to as PAA-PVC fibers, were washed, oven-dried at

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40 °C for 24 h and stored in a desiccator for characterization and sorption evaluation. For

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comparison purpose, a control group consisting PVC fibers without PAA were also fabricated and evaluated alongside the PAA-PVC fibers. The fabrication process is summarized in scheme 1.

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2.2.2. Sorbent characterization

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The surface morphologies and elemental compositions of the pure PVC and PAA-PVC fibers (before and after sorption) were studied using a scanning electron microscope embedded with an

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energy-disperse X-ray spectroscope (JEOL, JSM-6000 series WDS/EDS system, Japan). Likewise, the functional groups of PVC and PAA-PVC fibers (before and after sorption) were characterized using Fourier transform infrared spectroscope (Perkin Elmer spectrophotometer,

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FTIR/NIR Spectrometer). The samples were prepared as KBr pellets and analyzed in the wavelength range of 4000 – 400 Cm-1. 2.2.3. Sorption experiments

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To evaluate the sorption performance of the PAA-PVC fibers, sorption isotherm, kinetics and

sorption-desorption experiments were conducted in batch modes. The isotherm experiments were

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conducted in a series of 50 mL falcon tubes filled with different concentrations (10‒1000 mg/L)

of model Cd(II) solution in aliquots of 30 mL each and in contact with weighed amounts of the fibers (~0.03 g dry weight) under constant shaking in a multi-shaking incubator at 25 ± 2 oC.

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Using 1 M NaOH or 1 M HNO3, the pH of each solution was controlled to the desired value of

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pH 6, which is the optimum pH for Cd(II) sorption [6, 26]. After shaking for 24 h, portions of the

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sorbed samples were taken and centrifuged for analyses. For the kinetic experiment, the sorbent

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dose was 0.1 g in 100 mL of 500 mg/L Cd(II) solution. During sorption, approximately 1000 µL

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of the solution was taken at predetermined times from 0 ~ 360 min and centrifuged. Regeneration experiment was conducted by first evaluating different eluents and then eventually selecting the best eluent to perform detailed sorption-desorption cycles. In this experiment,

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sorption was first performed as described above, and the metal-loaded fibers were re-suspended in the eluent solutions containing either HNO3 or EDTA in different concentrations. After the

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sorption and desorption experiments, the solutions were centrifuged, diluted when necessary, and analyzed for residual metal concentrations using an inductively coupled plasma spectrometer

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(Shimadzu, ICP-7510, Japan). The Cd(II) uptakes, q, after the ICP analyses were calculated from Eq. (1);

=

(

−

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(1) 8

where Co and Ce are initial and equilibrium metal concentrations in mg/L, V is volume in L, and M is dry mass of sorbent in g. The data obtained from the sorption isotherm studies were modeled with the Langmuir and

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Freundlich isotherm models, which equations are given below in Eq. (2) and (3), respectively.

=

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Langmuir isotherm model [27]:

(2)

1+

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where qm is the maximum adsorbate uptake at equilibrium (mg/g), b is the coefficient related to

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the affinity between the adsorbent and adsorbate (L/mg), qe is the amount of adsorbate adsorbed

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at equilibrium (mg/g), and Ce is the adsorbate concentration at equilibrium (mg/L).

(3)

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=

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Freundlich model [28]:

where KF ((mg/g)L/g ) and n are the Freundlich constants denoting relative adsorption capacity

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and intensity of adsorption, respectively. 3. Results and discussion

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3.1. Sorbent formulation and effects of PAA composition The ratio of 2 g PAA to 2 g PVC was the best composition for the fabrication of the PAA-

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PVC fibers, based on the results shown in Fig. 1. That is, to find the best composition for easy

extrusion and maximum Cd(II) sorption, the amount of PAA was varied from 0.5, 1 and 2g. On the other hand, the amount of PVC was kept constant at 2 g because it did not improve the

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sorption capacity but provided the required rigidity for the fibers. When the amount of PAA was increased beyond 2 g, the polymer mixture became too viscous to extrude and hence the fibers could not form. Consequently, the Cd(II) sorption capacity of the respective fibers including the

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control group were evaluated through single-point sorption tests. From the sorption results in Fig. 1, it could be observed that the control group containing only PVC barely recorded any Cd(II)

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sorption, whilst the composite fibers bearing PAA showed good Cd(II) sorption. The sorption

uptakes were in the order of increasing amount of PAA, indicating the possibility that PAA provided the main binding sites through its carboxyl groups (section 3.2) [6, 21, 29, 30]. More

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fibers were fabricated using the optimum formulation, characterized, and evaluated through

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detailed sorption studies.

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3.2. Characterization

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3.2.1. Surface morphology and elemental composition

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The SEM and EDX images in Fig. 2 were taken at low and high magnifications for easy clarity and comparison. The morphological outlook of the pristine PVC as depicted by its images was very fine, smooth, and dense. As expected, the EDX graph displayed C and Cl peaks, which

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are typical of PVC materials [25]. The introduction of PAA into the PVC matrix resulted in a

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rough PAA-PVC fibers with loose surfaces. The surface roughness was not altered much even after interaction with the metal solution; however, minimal cracks were observed, which could

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be attributed to the agitation during the sorption process. Besides, the appearance of the O and Na peaks in the EDX graph could be respectively traced to the presence of PAA after the composite formation and NaCl treatment. The Na peak was totally displaced after sorption and a Cd peak emerged. Generally, PAA has a carboxyl group on every two carbon atoms of the main 10

chain; above pH 4 (i.e., pKa 4.2), dissociation of the carboxyl groups begin and a high negative charge density is developed [31, 32]. This high negative charge density makes it very reactive with cationic species according to their valence or charge. The reactive affinity is stronger in

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divalent species than in monovalent species. Therefore the disappearance of the Na peak and appearance of the Cd peak after sorption supports a possible ion exchange mechanism between

monovalent Na(I). 3.2.2. FTIR analysis and identification of functional groups

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the negatively charged carboxyl groups of PAA and the Cd(II) ions after displacement of the

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Fig. 3 presents the FTIR graphs of the pristine PVC and PAA-PVC fibers before and after

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Cd(II) sorption. Characteristic peaks of C‒H (2922, 1443 cm-1; stretching in CH2), C‒C (1253

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cm-1; stretching in CH2‒CHCl), and C‒Cl (850, 629 cm-1, stretching in ‒CHCl) were present in

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the spectrum of the pristine PVC fibers [25, 33]. The remaining peaks were attributed to

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presence of moisture residues from the surrounding atmosphere. Noteworthily, the strong C‒Cl band was lessoned after formation of the PAA-PVC fibers, and this was evidence that most of the C‒Cl bonds were broken to enable reaction between the PVC and PAA. This was possible

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through heating of the polymer slurry to 100 oC where chlorine easily detaches [34]. In the spectra of the PAA-PVC fibers, two distinct peaks corresponding to the stretching vibrations of

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non-ionic carboxyl (COOH) and ionic carboxyl (COO‒) groups could be confirmed at 1698 and 1575 cm-1, respectively [6, 13, 29]. A low intensity bending vibration of COO‒ was also

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observed at 1423 cm-1. These peaks represent the presence of PAA in the composite fibers, and

they experienced shifts after sorption, which indicate their involvement in the sorption process [6,

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21, 29]. Particularly, the COO‒ peak at 1575 cm-1 shifted from its original location to 1560 cm-1, and that at 1423 cm-1 shifted to 1438 cm-1. 3.3. Sorption performance evaluation

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3.3.1. Sorption isotherm study

Sorption isotherms are used to describe how adsorbates interact with adsorbents in solution

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of varying concentrations at constant temperature, and the constants of the isotherm models are

very useful in determining the amounts of adsorbents needed to adsorb required amounts of

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adsorbates [13, 35, 36]. The result of the sorption isotherm is shown in Fig. 4. From the results, it

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could be observed that affinity between the sorbents and sorbate increased with increase in the

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initial metal concentrations. Through the sorption isotherm studies, the maximum equilibrium

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uptake and overall affinity were determined by the Langmuir isotherm model with a good coefficient of correlation (R2) value. The Langmuir model assumes monolayer adsorption onto

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homogenous surfaces and suggests that the intermolecular forces pulling the sorbate towards the sorbent decrease rapidly with the distance from the adsorptive surface [2]. The sorption affinity of the prepared sorbents towards the Cd(II) ions was good as can be seen from the initial slope of

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the sorption isotherm curve (Fig. 4). The maximum equilibrium uptake extrapolated by the

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Langmuir model suggested that the adsorptive sites were fully saturated with the metal ions at lower concentrations, but inter-repulsive forces existed at higher concentrations, leaving some

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sites unoccupied by the highly competitive ions. The intensity of adsorption was predicted by the Freundlich model, which depicted the favorability of Cd(II) sorption onto the sorbents. The Freundlich model is based on multilayer adsorption with the adsorption energy decreasing with the surface coverage. Generally, values of the Freundlich constant, n ranging between 1 ~ 10 12

portray favorable sorption [35]. Hence from the results in Table 1, the sorption of Cd(II) onto the PAA-PVC fibers was favorable. The favorability of a sorption process could further be ascertained by a dimensionless parameter called the separation factor, RL, which is extracted

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from the Langmuir model, and is defined as RL = [1/ (1+bC0)]. The values of RL calculated over the range of initial concentrations investigated in this study were between 0.1 ~ 0.9 inclusive,

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which fell within 0 < RL < 1, and confirmed that the sorption process was indeed favorable. 3.3.2. Sorption kinetics and effects of contact time

It is undeniable that equilibrium kinetic study is necessary for the design of adsorption

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systems for large-scale applications. The equilibrium kinetic study depicts the sorbate uptake rate,

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which in turn controls the residence time of the sorbate uptake at the solid‒liquid interface [36].

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With the kinetic study, the time required to attain sorption equilibrium can be estimated by

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studying the effect of contact time over a chosen time period [13]. In this study, the rate of Cd(II)

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removal from the aqueous phase onto the solid PAA-PVC fiber surfaces was examined over 360 min, within which samples were taken and analyzed. It was observed from the kinetics results that more than 90% of the total sorption capacity was reached in just about 15 min of contact,

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and the uptake further increased slightly until 20 min after which it remained steady and equilibrated (Fig. 5a). Thus full sorption saturation was attained after just 20 min of contact

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between the solid sorbent and the liquid sorbate.

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The adsorption kinetics data were analyzed using the pseudo-first- and pseudo-second-order

models, which are respectively expressed by Eq. 4 and Eq. 5 [37, 38]. =

(1 −

( − )) (4)

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=

(5)

1 +

where qe1 and qe2 are the amounts of Cd (II) adsorbed at equilibrium (mg/g), qt is the amount adsorbed at time, t (mg/g), k1 is first-order equilibrium rate constant (1/min), and k2 is second-

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order equilibrium rate constant (g mg-1 min-1). The parameters estimated from the models, along with the experimental sorption capacities, are presented in Table 2. From the tabulated results, it

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was observed that the correlation coefficient from the pseudo-second-order model was far higher

than that from the pseudo-first-order model. Moreover, the theoretical sorption capacity

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estimated by the pseudo-second-order model was very close to the experimental sorption capacity, which indicates that the pseudo-second-order model accurately describes the kinetics of

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adsorption of the present study, which also suggests some form of chemical adsorption process

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between the metal ions and the fibrous sorbents [38, 39].

given by Eq. 6. =

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+

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Furthermore, the kinetic data were assessed with the intra-particle diffusion model which is

(6)

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where ki represents the intraparticle diffusion rate constant and Ci is the thickness of the boundary layer [25]. If the plot of qt versus t0.5 is linear and passes through the origin, intra-

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particle diffusion is the rate-limiting step of the adsorption process. In this study however, the adsorption proceeded in three stages; i.e., a short swift initial adsorption phase involving the

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external surface functional groups, a long transition phase involving diffusion of the ions deep into the inner parts of the composite fibers, and a prolonged final equilibrium stage which was characterized by a plateau-like top (Fig. 5b, Table 2b). Therefore, the adsorption process may

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consist of complex mechanisms of surface adsorption and intra-particle diffusion [25]. Because the fibers are composites, the functional groups are expectedly present both on the surface and in the inside. This thus explains the long transition phase which was controlled by the intra-particle

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diffusion mechanism. Moreover, the decreasing concentration gradient at the interface between the bulk solution and the adsorbent surfaces also contributed to the slower diffusion rate, thus

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slightly delaying the final equilibrium time.

For any adsorption system, the initial adsorption rate, h (mg g-1 min-1) could be calculated from the pseudo-second-order model, according to the following equation [36, 40].

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(7)

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ℎ =

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The initial adsorption rate is a measure of the adsorption rate estimated at the initial stages where

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the adsorption process is very swift. From the values of k2 and qe2 extracted from the pseudosecond-order model, the value of h was calculated as 83.66 g mg-1 min-1. This high h value

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shows a very fast initial sorption rate, which is particularly important for the design of an upscale adsorption system using the fabricated sorbents.

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3.4. Metal desorption and sorbent regeneration

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It is not only important to produce sorbents with high sorption capacities but also with potentials for regeneration [26, 41]. This is important for economic and environmental viability

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as far as the sorption process is concerned. To assess whether the PAA-PVC fibers meet the above criteria, different concentrations of HNO3 and EDTA were evaluated for their efficiency in

effectively eluting the Cd(II) from the loaded fibers [9]. As presented in Fig. 6a, 0.1 M EDTA achieved 100% desorption efficiency, as against 1 and 3 M HNO3 which eluted up to 92 and 15

98%, respectively. Based on this, 0.1 M EDTA was chosen and used to run three cycles of sorption-desorption (Fig. 6b). The PAA-PVC fibers showed very good regeneration efficiency in the first two cycles but decreased significantly to about 84% sorption efficiency in the third

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cycle. The desorption efficiency was however, maintained throughout the three cycles. 3.5. Comparison of the PAA-PVC fibers with other sorbents

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The performance of the PAA-PVC fibers was compared with the most recent sorbents reported on Cd(II) sorption. The comparison was based on the sorbents’ physical structures and

their performances in terms of uptakes, kinetics, pH, and temperatures. It is obvious from Table

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3 that the PAA-PVC fibers are competitive to the existing sorbents, particularly considering their

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high Cd(II) uptake and fast sorption rate.

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4. Conclusions

This study described the fabrication of PAA-PVC fibers for effective treatment of water

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polluted with heavy metal ions such as Cd(II). The ratio of 2 g each of PAA and PVC was found best for fabricating stable and high-performance fibers. The sorption isotherm was better

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described by the monolayer Langmuir model, which estimated the maximum equilibrium uptake to be 331.59 mg/g, and the kinetic data was better fitted to the pseudo-second-order model,

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which predicted the initial sorption rate at 83.66 g mg-1 min-1, and suggested that majority of the Cd(II) ions were bound to the composite fibers by chemical sorption. A very swift initial sorption

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phase followed by a sluggish diffusion phase characterized the overall kinetic regime. Ionexchange between the deprotonated carboxyl groups of PAA and the metal solution was the main binding mechanism between the fibers and Cd(II) ions. Considering the simplicity of preparation

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and high-performance, the PAA-PVC fibers could be applied as suitable sorbents for removing heavy metal ions from wastewaters. Acknowledgements

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This work was supported by the Korean Government through the National Research

Foundation, NRF (2014R1A2A1A09007378 and 2017R1A2A1A05001207) grants. The authors

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also wish to extend their profound gratitude to the Center for University-wide Research Facility (CURF) for most of the spectroscopy analyses.

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recovery, J. Hazard. Meter. 157 (2008) 620-627.

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23

Table Captions Table 1 Langmuir and Freundlich model parameters for Cd(II) sorption onto PAA-PVC composite fibers.

A

CC

EP

TE D

M

A

N

U

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Table 3 Comparison of PAA-PVC composite sorbent with other sorbents.

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Table 2 Kinetic model parameters for Cd(II) sorption onto PAA-PVC composite fibers.

24

Table 1 Langmuir and Freundlich model parameters for Cd(II) sorption onto PAA-PVC composite fiber Langmuir

Freundlich

qm,exp (mg/g)

qm (mg/g)

b (L/mg)

R2

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

n

R2

259.05

331.59

0.01

0.94

19.14

2.35

0.85

A

CC

EP

TE D

M

A

N

U

SC R

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Experimental

25

Table 2a Kinetic model parameters for Cd(II) sorption onto PAA-PVC composite fiber Pseud-1st-order

Pseud-2nd-order

qe,exp (mg/g)

qe1 (mg/g)

k1 (1/min)

R2

qe2 (mg/g)

k2 (g/mg.min)

R2

244.67

232.14

0.21

0.96

244.45

0.0014

0.99

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Experimental

ki (mg/g min0.5)

Ci

1st

58.21

10.90

2nd

10.71

160.75

3rd

0.25

242.90

A

CC

EP

TE D

M

A

N

U

Phase

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Table 2b Intra-particle diffusion model parameters

26

R2

0.98

0.97

0.95

Table 3 Comparison of PAA-PVC composite sorbent with other sorbents

Physical structure

Sorption rate

pH

Granules Powder Aerogel

6h ~5 min > 20 min

Gel

83.2

90 min

Powder

145

4h

Powder

69.4

1.5 h

Fiber Aerogel

137.8 134.9

>2h 60 min

Gel

14.3

Powder

Temp. C

Ref.

8 7 6

25 25 65

[42] [43] [44]

4

25

[45]

5

25

[46]

5

25

[47]

6 -

25 -

[26] [48]

60 min

6

30

[49]

141.7

120 min

6.5

25

[50]

Gel Bead

83.8 133.3

2h

7 3

25 25

[51] [52]

Bead

60

24 h

-

20

[53]

Fiber

150.6

2 min

6

25

[6]

Fiber

331.59

20 min

6

25

This work

27

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o

U

N A

M

A

CC

EP

Bamboo charcoal Eggshell adsorbent Sulfonated reduced graphene oxide EGTA-modified chitosan EDTA-modified chitosan Activated carbonchitosan CMC-Lyocell Methacrylic acid grafted cellulose Polyaniline grafted chitosan Modified Okra cellulose fiber Crosslinked chitosan Iminodisuccinic acid-modified chitosan Alginate-Moringa Oleifera Epichlorohydrin crosslinked CMC PAA-PVC composite

Sorption capacity (qm, mg/g) 12.08 328.9 234.8

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Adsorbent

Scheme & Figure Captions Scheme 1 Fabrication process of PAA-PVC composite fibers. Fig. 1 Cd(II) uptakes from single-point sorption by PAA-PVC composite sorbents with different

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PAA compositions. Experimental conditions: concentration = 500 mg/L, sorbent dose = 0.03 g/

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30 mL, pH = 6, temperature = 25  2 oC, reaction time = 24 h. Fig. 2 (a) SEM images and EDX elemental peaks of the samples. Fig. 3 FTIR functional groups analyses.

U

Fig. 4 Sorption isotherm of Cd(II) sorption onto PAA-PVC composite fibers. Experimental

N

conditions: concentration = 10-1000 mg/L, sorbent dose = 0.03 g/ 30 mL, pH = 6, temperature =

M

A

25  2 oC, reaction time = 24 h.

Fig. 5 Sorption kinetics of Cd(II) sorption onto PAA-PVC composite fibers. Experimental

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conditions: concentration = ~500 mg/L, sorbent dose = 0.03 g/ 30 mL, pH = 6, temperature = 25  2 oC, reaction time = 0-360 min.

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Fig. 6 Desorption and sorbent regeneration study (a) desorption using different eluents and (b)

A

CC

sorbent regeneration through sorption-desorption cycles.

28

A

CC

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TE D

M

A

N

U

SC R

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Scheme 1 Fabrication process of PAA-PVC composite fibers

29

Fig. 1 Cd(II) uptakes from single-point sorption by PAA-PVC composite sorbents with different PAA compositions. Experimental conditions: concentration = 500 mg/L, sorbent dose = 0.03 g/

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30 mL, pH = 6, temperature = 25  2 oC, reaction time = 24 h.

300

SC R

200

150

100

U

Cd(II) uptake, mg/g

250

N

50

0 0.5 g

PAA

1gP

AA

2gP

AA

A

C)

Amount of PAA, g

A

CC

EP

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M

V nly P AA (o 0gP

30

Fig. 2 (a) SEM images and EDX elemental peaks (b) XRD graph of samples

PVC

PVC

PAA-PVC

PAA-PVC

PAA-PVC after sorption

PAA-PVC after sorption

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PVC

A

CC

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M

A

N

U

PAA-PVC

31

PAA-PVC after sorption

Fig. 3 FTIR functional groups analyses

850

PVC

2922

SC R

1345

1108 972

IP T

3395

629 1443

1253

U

N

836

A

1365

1164

608

M

1698

2924

1423

Transmittance (%)

1255

PAA-PVC

3390

TE D

1575

PAA-PVC after sorption

A

1438

CC

3403

4000

1560

3000

2000

1000

Wavenumber (Cm-1)

32

813 622

2923

1110 980

1346 1270

EP

1728

Wavenumber (Cm-1)

Fig. 4 Sorption isotherm of Cd(II) sorption onto PAA-PVC composite fibers. Experimental conditions: concentration = 10-1000 mg/L, sorbent dose = 0.03 g/ 30 mL, pH = 6, temperature =

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25  2 oC, reaction time = 24 h.

350

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250

200

150

Langmuir Freundlich

50

0 200

400

600

800

A

0

U

100

N

Cd(II) uptake (mg/g)

300

A

CC

EP

TE D

M

Equilibrium concentration of Cd(II)(mg/L)

33

Fig. 5 Sorption kinetics of Cd(II) sorption onto PAA-PVC composite fibers. Experimental conditions: concentration = ~500 mg/L, sorbent dose = 0.03 g/ 30 mL, pH ~6, temperature = 25

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 2 oC, reaction time = 0-360 min.

300

(a)

SC R

200

150

50

Pseudo-first-order Pseudo-second-order

0 100

200

400

M

(b)

250

TE D

200

150

100

50

0

5

10

t0.5 (min 0.5 )

1st phase 2nd phase 3rd phase 15

20

A

CC

0

EP

Cd(II) uptake (mg/g)

300

Time (min)

A

0 300

U

100

N

Cd(II) uptake (mg/g)

250

34

Fig. 6 Desorption and sorbent regeneration study (a) desorption using different eluents and (b) sorbent regeneration through sorption-desorption cycles.

120

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(a)

80

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Desorption efficiency, %

100

60

40

U

20

0 3 M HNO3

0.1 M EDTA

N

1 M HNO3

Eluent 300

A

(b)

Sorption Desorption

M

200

150

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Cd(II) uptake, mg/g

250

100

0

EP

50

2nd

3rd

Cycle

A

CC

1st

35