Synthesis, characterization of PMDA/TMSPEDA hybrid nano-composite and its applications as an adsorbent for the removal of bivalent heavy metals ions
Graphical abstract
Introduction
Effluents discharged from mining, electroplating, metal finishing, welding, and alloy manufacturing industries provide a major route for heavy metals to ecosystem. Toxicity, persistency, and bioaccumulation tendency make heavy metals a serious threat to both humans and environmental health. Heavy metals can easily enter the food chain through numerous pathways. Many of them above permissible levels are highly toxic or carcinogenic. Therefore, stringent regulations have been imposed world over for removing or minimizing heavy metals to permissible limits. Heavy metals such as cadmium [Cd(II)], and lead [Pb(II)] have no essential biological functions but these metals could be extremely toxic to living organisms. Furthermore, zinc [Zn(II)] is an essential element for human health, but it could be toxic when present in excessive concentrations.
Treatment techniques such as ion-exchange [1], chemical precipitation, chemical oxidation or reduction, electrochemical treatment, evaporation, flocculation [2], membrane filtration [3], and reverse osmosis [4] have been used to remove or to minimize heavy metal ions concentration in industrial wastewater and municipal water supplies. High capita, incomplete heavy metal ions removal, low selectivity, high energy requirements, and generation of toxic slurry are the major flaws of these processes [5]. Adsorption, another treatment technique, considered effective and economical for treating both industrial effluents and potable water. Effectiveness even to remove trace amount of heavy metal ions present in aqueous phase is the major merit of adsorption process [5]. In addition, it is an important process to understand the accumulation of heavy metal ions at solid-solution interfaces [6]. Clay minerals [7], plant wastes [8], [9], carbon nano-tubes [10], activated carbon [11], nano-graphite encapsulated alginate beads [12], and lignite [13] have been widely investigated adsorbents for the removal of heavy metal ions from aqueous solution and wastewater.
The use of polymeric (inorganic–organic) hybrid materials as an adsorbent is regarded as one of the most effective methods for the abatement of heavy metal ions from aqueous phase, as these materials have a tendency to bound heavy metal ions via co-ordinate and electrostatic interactions [14]. On other hand, structural flexibility, mechanical stability, and potential applications in harsh environmental conditions are some of the major merits of these polymeric materials. Research is going on to synthesize and test the applicability of the hybrid polymeric adsorbents for removing heavy metals from aqueous solutions [15], [16], [17], [18], [19]. Several novel routes to synthesize these adsorbents have already been proposed by various research groups. Pan et al. [15] developed a polymer-based hybrid adsorbent (HFO-001) for an efficient removal of heavy metals from contaminated waters. Ge et al. [16] synthesized and modified an iron oxide derived magnetic nanoparticles for the removal of divalent heavy metal ions from aqueous solution. Iesan et al. [17] synthesized hybrid adsorbents by in situ encapsulation of hydrated ferric oxide in the porous structure of a strong base anion exchange resins based on the styrene divinyl benzene copolymer and investigated their adsorptive performance for arsenic removal from drinking water [17]. Liu et al. [18] synthesized a series of zwitterionic hybrid adsorbents by ring-opening polymerization of pyromellitic acid dianhydride and N-[3-(trimethoxysilyl)propyl] ethylene diamine or phenylaminomethyltrimethoxysilane for heavy metal ions removal from aqueous phase. The zwitterionic inorganic–organic hybrids adsorbents were synthesized by Dong et al. [19], and their suitability was tested in Cu(II) removal.
Considering the merits of aforementioned polymeric adsorbents for heavy metal ions removal from aqueous phase, here in, we have synthesized thermally stable novel hybrid polymeric nano-composite (HPNC) by ring opening polymerization and sol–gel reaction. Moreover, the applicability of the adsorbent for the removal of divalent heavy metal ions [Cd(II), Pb(II), and Zn(II)] from aqueous phase was studied. Kinetics, thermodynamics, and isotherms studies were carried out to evaluate the adsorptive potential of synthesized HPNC. The economic feasibility of HPNC was estimated by desorption and regeneration studies.
Section snippets
Chemicals and reagents
Pyromellitic acid dianhydride, PMDA, purity: ⩾97%; N-(3-(trimethoxysilyl) propyl ethylene diamine, TMSPEDA, ⩾97%; N,N-dimethylformamide anhydrous, DMF, purity: ⩾99.8%; and tetraethyl orthosilicate, TEOS, purity: ⩾99.99% were purchased from Aldrich (Sigma–Aldrich Inc., St. Louis, MO, USA). Heavy metal stock solutions (1000 mg/L) were prepared by using their nitrate and chloride salts (BDH Chemical, England). The other chemical and reagents used were of analytical reagent grade.
Preparation of HPNC
The HPNC was
Adsorbate selectivity
The synthesized adsorbent was tested for the removal of Cd(II), Pb(II), and Zn(II) from aqueous solution. Preliminary adsorption studies as presented in Table 1, showed maximum adsorption of Pb(II) ions followed by Cd(II) > Zn(II). Here, it is noteworthy that hydrated ionic radii and electronegativity of heavy metal ions are playing a significant role in controlling adsorption process. The higher hydrated ionic radius induces a quick saturation of adsorption sites, because of a steric hindrance
Conclusions
In summary, a novel route to synthesize a HPNC by TMSPEDA and PMDA monomers ring opening polymerization and in situ thermal sol–gel reaction at pH 2 and 80 °C was proposed, and it adsorptive potential for bivalent heavy metals was testified. Characterization study revealed formation of thermally stable polymeric adsorbent. The IR analysis revealed –NH groups of silica precursor and –COOH groups on HPNC acting as main active sites for the heavy metals adsorption from aqueous phase. The binding of
Acknowledgement
This project was supported by King Saud University, Deanship of Scientific Research, College of Science Research Center.
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