Elsevier

Desalination

Volume 281, 17 October 2011, Pages 429-437
Desalination

Ultrasound assisted preparation of nanoclay Bentonite-FeCo nanocomposite hybrid hydrogel: A potential responsive sorbent for removal of organic pollutant from water

https://doi.org/10.1016/j.desal.2011.08.031Get rights and content

Abstract

Synthesis of poly(acrylic acid)-bentonite-FeCo (PAA-B-FeCo) hydrogel nanocomposite via ultrasound assisted in situ emulsion polymerization was carried out. Addition of exfoliated bentonite clay platelets and Fe–Co increased the strength and stability of hydrogel and assisted the adsorption of an organic pollutant. The response of the nanocomposite hydrogel was evaluated using a cationic dye, crystal violet (CV) under different temperature, pH, and cavitation environment. The optimum temperature was found to be 35 °C and basic pH (optimum at 11) was responsible for the higher adsorption of dye due to dissociation of COO ions at higher pH. Bimetallic components form the metal ions in hydrogel which shows repulsion at low pH resulting to lower response. Thermodynamic parameters for adsorption indicated that the dye adsorption onto PAA-B-FeCo hydrogel was spontaneous and endothermic in nature.

Highlights

► Synthesis Poly acrylic bentonite-FeCo hydrogel nanocomposite using cavitation. ► Assess the feasibility of nanocomposite hydrogel for the removal of dye. ► Optimize experimental conditions to apply for industrial applications.

Introduction

Hydrogels are three dimensionally dense cross linked polymer network structures composed of functional hydrophilic groups which have the ability to absorb significant amount of water and solute molecules [1], [2], [3], [4], [5]. Hydrogels are also known as smart materials which show response and swelling when there is small change in external environment [4], [6], [7]. The response of hydrogel is dependent on the presence of hydrophilic functional groups such as single bondOH, single bondCOOH [8], [9]. These groups make the hydrogel hydrophilic and due to capillary action and difference in the osmotic pressure, water diffuses into the hydrogel. Polymerization methods, the presence of functional groups and the nature of cross linking agents are important parameters that control the swelling ability of the hydrogen [10]. The external environmental conditions such as, pH, temperature, electric field, ionic strength, and light act as stimuli for the responsiveness of the hydrogels [9], [10], [11], [12]. Hydrogels are useful in a variety of applications such as tissue engineering [13], drug delivery [10], separation of bimolecules [14], separation of the metal ions, and inorganic compounds [15] etc. The pH-sensitive hydrogels contain ionizable groups in polymer, e.g. COO ions in polyacrylic acid, which shows response to pH change [11], [16].

Nanosized magnetic iron oxide particles are extensively studied as new adsorbents with large surface area and small diffusion resistance for the separation and removal of chemical species such as metals, dyes and gasses [17]. Different types of magnetic nano-adsorbents with tailored surface reactivity by using natural or synthetic polymers such as chitosan, alginate, poly(acrylic acid) are used for heavy metal removal from waste water [18]. Zhu et al. [19] successfully used magnetically separable γ-Fe2O3/crosslinked chitosan adsorbent for the removal of hazardous azo dye.

A number of adsorbents are used in dye adsorption, e.g. activated charcoal, clay materials such as bentonite, flyash, kaolin and montmorillonite [20], [21], [22]. These adsorbents generate secondary waste and some of the materials are not efficient adsorbents because of their limitations in the cation exchange capacity, lower adsorption rate, etc.[23]. Hence, the enhancement of adsorption process has been achieved using cavitation, changing cation exchange capacity or hybrid nanocomposites [24]. The limitations of existing water treatment methods (ion exchange, adsorption, and wet air oxidation, etc.) could be overcome by developing efficient hydrogels to intensify the process of removal of organic components from waste water [25]. A number of attempts are made to use the hydrogels for adsorption of the dye components from water [26], [27], [28].

Ultrasonic irradiation is used to initiate the emulsion polymerization to form hydrogel through the generation of free radicals. The high shear gradients generated by the acoustic cavitation process helps to control the molecular weights of hydrogels formed in aqueous solutions. Ultrasound was found to be an effective method for polymerization of monomers and for the production of hydrogel in the absence of a chemical initiator [29]. Several acrylic hydrogels have been prepared via ultrasonic polymerization of water soluble monomers and macro monomers [30].

Nanocomposite hydrogels are loaded with the different types of clays like bentonite, Laponite, Sepiolite. These clays enhance the mechanical properties and adsorption capacity of hydrogels. Compared to other adsorbents, clays are the natural, abundant and inexpensive materials having good mechanical strength and porous structure [31], [32], [33], [34], [35], [36], [37]. Li et al. [31] prepared nanocomposite hydrogels by incorporating Laponite clay into a poly(acryl amide) hydrogel by the in situ polymerization for the adsorption of CV. The cationic dye adsorption ability of the hydrogel increased with increasing clay content in the hydrogel.

In this manuscript attempt was made to synthesize polymer nanocomposite hydrogels using metal hybrid polymer along with clay. No reports are available in the literature on the synthesis of nanocomposite using metal and clay composite hydrogel. It is also important to note that magnetic nanoparticles were used in hydrogels so that the material can be used in a number of applications [38]. In this study, clay platelets were used as support for the metal particles and to increase the mechanical strength of the hydrogel composite. Metallic iron nanoparticles are, undoubtedly, promising materials for magnetic, drug delivery systems and other medical applications. Combination of cobalt with Fe nanoparticles may increase the magnetic characteristics [39], [40]. Hence an attempt was made in this study to synthesize clay supported metal nanocomposite hydrogel using ultrasound assisted emulsion method. Clay and Fe–Co combination is used to enhance the mechanical properties and to improve the efficiency of water treatment.

The objectives of the present investigation are: (i) To synthesize poly(acrylic acid)-bentonite-FeCo (PAA-B-FeCo) hydrogel via in situ ultrasonic emulsion polymerization and (ii) To assess the feasibility of PAA-B-FeCo hydrogel for the removal of crystal violet dye. The adsorption equilibrium studies are carried out under different pH, temperature, and dye initial concentration conditions. The data obtained is processed using the adsorption isotherm models and the thermodynamic behavior of the cationic dye adsorption is also evaluated.

Section snippets

Materials

Acrylic acid (AA), ammonium persulphate (APS), sodium dodecyl sulfate (SDS) and crystal violet dye (CV) were of analytical grade and procured from M/s CDH, India. Natural Bentonite clay was obtained from MD Chemicals, Pune, India. Millipore deionized water was used for all experiments. N-acetyl-N,N,N-trimethyl ammonium bromide (CTAB), ferric chloride, cobalt chloride and sodium borohydride (NaBH4) were procured from Sigma Aldrich.

Synthesis of pure poly(acrylic acid) and PAA-B-FeCo hydrogel

Initially, pristine bentonite clay was washed 3–4 times with

Results and discussion

Nanoclay supported Fe and Co particles were initially incorporated into the gallery spacing of bentonite clay by reducing Fe and Co ions inside the clay. To facilitate the incorporation of these metal particles, initially natural bentonite clay was intercalated using quaternary ammonium salts. The long chain of CTAB molecules (C16–C18) of the quaternary ammonium salt increases the cation exchange capacity of bentonite clay from 96 to 120 meq/g of clay. The acoustic cavitation generated physical

Conclusion

PAA-B-FeCo hydrogel was synthesized by ultrasonic polymerization of AA and cross-linked by B-FeCo. The network formation of crosslinked polymer hydrogels shows a good swelling behavior due to the presence of B-FeCo. Adsorption process for dye removal was shown to be highly efficient for higher pH and temperature. The lower concentration and higher quantity of hydrogel is more favorable for maximum removal efficiency. The combined effect of hydrogel and ultrasound show a higher percent removal

Acknowledgment

Dr Shirish H. Sonawane acknowledges to the Ministry of Environment and Forest (MoEF, Govt of India) for providing the financial support.

References (49)

  • K. Mishra et al.

    Intensification of degradation of Rhodamine B using hydrodynamic cavitation in the presence of additives

    Sep. Purif. Technol.

    (2010)
  • J. Yun et al.

    Photocatalytic treatment of acidic waste water by electrospun composite nanofibers of pH-sensitive hydrogel and TiO2

    Mater. Lett.

    (2010)
  • S. Mak et al.

    Fast adsorption of methylene blue on polyacrylic acid-bound iron oxide magnetic nanoparticles

    Dyes Pigm.

    (2004)
  • A. Paulino et al.

    Removal of methylene blue dye from an aqueous media using superabsorbent hydrogel supported on modified polysaccharide

    J. Colloid Interface Sci.

    (2006)
  • P. Cass et al.

    Preparation of hydrogels via ultrasonic polymerization

    Ultrason. Sonochem.

    (2010)
  • Y. Xiang et al.

    A new polymer/clay nano-composite hydrogel with improved response rate and tensile mechanical properties

    Eur. Polym. J.

    (2006)
  • N. Churochkina et al.

    Swelling and collapse of the gel composites based on neutral and slightly charged poly(acrylamide) gels containing Namontmorillonite

    Polym. Gels Netw

    (1998)
  • S. Sonawane et al.

    Combined effect of ultrasound and nanoclay on adsorption of phenol

    Ultrason. Sonochem.

    (2008)
  • S. Sonawane et al.

    Ultrasound assisted synthesis of polyacrylic acid–nanoclay nanocomposite and its application in sonosorption studies of malachite green dye

    Ultrason. Sonochem.

    (2009)
  • T. Caykara et al.

    Thermosensitive poly(N-isopropylacrylamide-co-acrylamide) hydrogels: synthesis, swelling and interaction with ionic surfactants

    Eur. Polym. J.

    (2006)
  • M. Purkait et al.

    Determination of thermodynamic parameters for the cloud point extraction of different dyes using TX-100 and TX-114

    Desalination

    (2009)
  • B. Peppas et al.

    Equilibrium swelling behavior of pH-sensitive hydrogels

    Chem. Eng. Sci.

    (1991)
  • H. Kazutoshi

    Nanocomposite hydrogels

    Rev. Art. Curr. Opin. Solid State Mater. Sci.

    (2007)
  • S.K. Samba et al.

    Preparation and characterization of pH-responsive hydrogel magnetite nanocomposite

    Colloids Surf., A

    (2009)
  • Cited by (86)

    • P(HMA-co-ATU) hydrogel synthesis via gamma radiation and its use for in situ metal nanoparticle preparation and as catalyst in 4-nitrophenol reduction

      2022, Radiation Physics and Chemistry
      Citation Excerpt :

      The ability of hydrogels to respond to environmental factors by swelling or shrinking accordingly is due to the interaction of hydrophilic groups with each other in the polymer chains and with the surrounding factors that can result in absorption of large amounts of water. Because of the hydrophilic nature, hydrogels have a wide variety of applications in medical applications (Jiang et al., 2021), environment (Shirsath et al., 2011; Wu et al., 2022), sensors (Hu et al., 2021), and various techniques including separation and purification (Guichardon et al., 2005). The reactive functional groups on the hydrogel networks are the responsible moieties and afford multiple tasks including metal ion reduction/oxidation, catalysis, sensor, metal ion recovery and so on (Badsha et al., 2021).

    • Synthesis and characterization of biodegradable cellulose-based polymer hydrogel

      2022, Nanotechnology in Paper and Wood Engineering: Fundamentals, Challenges and Applications
    View all citing articles on Scopus
    1

    Current Address: Sinhagad College of Engineering, Pune, India.

    2

    Current Address: Chemical Technology Dept, North Maharashtra University Jalgaon, India.

    View full text