New glucosamine Schiff base grafted poly(acrylic acid) as efficient Cu2+ ions adsorbent and antimicrobial agent
Graphical abstract
Introduction
Adsorbents derived from polymeric materials have attracted the attention of researchers’ worldwide and these also reflect contemporary advances in the adsorption chemistry [1]. Such adsorbents synthesized through the simple polymer analogous reactions possess active functional groups as selective ligands [[2], [3], [4]]. Therefore, tailor-made structural and functional design impart characteristic adsorption properties to the polymers [5,6]. In view of the preceding arguments, the synthesis of a new polymer as efficient Cu2+ ions adsorbent is reported in the present work. Cu2+ ions present in the drinking water can be a huge health threat and have been reported to cause many life-threatening diseases in human beings such as the impairment of thyroid gland, Wilson disease, bronchitis, hypertension, kidney damage, cirrhosis and stomach and intestinal cancers [[7], [8], [9]]. These ions are also associated with the malfunctioning of many critical enzymes through binding with nitrogen or sulfur atoms present in the proteins and nucleic acids [10,11]. The extent of toxicity of Cu2+ ions in drinking water can be evidenced from the very low permissible limit, less than 2 mg/L, set by WHO [12]. Industries like steel, mining, copper electrorefining, etc., release enormous amount of copper into fresh water streams everyday [13]. Copper may also add to the drinking water by the corrosion of interior pipes or fittings used in water distribution systems and copper concentration in such incidences has been reported to be lethal to the newborns [14]. Moreover, copper is also used as a corrosion resistant coating material in nuclear reactors and the traces of these ions have been reported in water present in the vicinity of the nuclear reactors [15,16]. Hence, it is imperative to develop effective materials and techniques for the efficient removal of Cu2+ ions from wastewater before consumption.
A number of adsorbents such as activated carbon [17,18], zeolites [19], those based on biowaste [20,21] and polymer-based materials [4,22] have been reported for the removal of toxic heavy metal ions from the wastewater. Besides this, the polymeric materials consisting of active functional groups like amine [23], amide [5], azomethine [24,25], thiourea [26,27], amidoxime [[28], [29], [30]], pyridyl [31], etc., also exhibit excellent metal ions binding affinities and have been extensively used for adsorption applications. Therefore, controlling of the functional attributes of polymers significantly affect their attractive interactions with the targeted heavy metal ions and can be handy in designing new selective polymeric adsorbents. Water contamination by the harmful microorganisms poses another serious problem that requires serious attention and immediate redressal. Hence, synthesizing materials with multifunctional properties reflect contemporary inventions in the field of water treatment.
In view of the above arguments a new Schiff base-based polymer was synthesized from N,N-dimethylaminobenzaldehyde, glucosamine (a monomer of chitosan) and poly(acrylic acid) [p-AAc] in the present work. The synthesized polymer exhibited bi-functional characteristics as apart from being efficient Cu2+ ions adsorbent it also possessed significant antimicrobial properties. Ease of the synthesis of Schiff base structures makes them an important precursor to develop target oriented materials. Schiff bases are generally considered less stable and usually perform low on reusability [32]. Hence, the as-synthesized Schiff base was grafted to a preformed polymer, poly(acrylic acid) [p-AAc], which significantly enhanced its structural stability and the resulting polymer, SB-g-p-AAc, exhibited excellent reusability and water holding capacity. Pendent tertiary amine functionalities in the form of N,N-dimethylbenzaldehyde attract cationic Cu2+ ions with ease and favors initial interactions of the polymer with these ions. High local concentration of azomethine groups of Schiff base structure on the polymer imprisons Cu2+ ions firmly and the attractive interactions are reinforced by the adjacent lying −OH functional groups of glucosamine moieties, Scheme 1.
Therefore, tailor-made structural and functional design of the polymer, SB-g-p-AAc, favors active adsorption of targeted Cu2+ ions. The use of chitosan derived Schiff bases for active Cu2+ ions adsorption has also been reported elsewhere [33,34]. In their work Monier et al. have shown that the Schiff base derivatives of chitosan exhibited preferential adsorption of Cu2+ ions in the presence of Co2+, Ni2+, and Zn2+ ions [35,36]. Therefore, it can be stated that the Schiff base-based polymeric materials can affect preferential adsorption of Cu2+ ions in the presence of some other bivalent ions present in the solution. However, more structure-activity based functional modifications are indicative of inducing more selectivity and specificity in polymer functions. The Schiff bases have also been reported in literature to possess excellent antimicrobial properties [[37], [38], [39]]. Hence, the antimicrobial activity of SB-g-p-AAc was also evaluated. In view of the above stated, the synthesis of a new Schiff base-based bi-functional polymer as efficient Cu2+ ions adsorbent and antimicrobial agent is reported in the present work.
Section snippets
Materials
Glucosamine hydrochloride, N,N-dimethylaminobenzaldehyde (SD Fine Chemicals, Ltd., Mumbai, India), acrylic acid (AAc), hydrochloric acid and lipase [Hi Media Lab Pvt. Ltd., Mumbai, India) were of reagent grade and used as received. Sodium hydroxide (Rankem, RFCLLtd., Faridabad, India), sodium borohydride (Merck India Ltd., Mumbai, India) and ammonium per-sulfate (APS) [Sigma-Aldrich Inc., St. Lucia US], were used as received. Potato dextrose broth, inoculating loop (Hi Media Lab Pvt. Ltd.,
Characterization studies
A new Schiff base-based polymeric adsorbent, SB-g-p-AAc, was synthesized from glucosamine hydrochloride, N,N-dimethylaminobenzaldehyde and AAc. The polymer was characterized by FTIR, NMR, XRD and FESEM techniques to get evidence of the structure and formation. The FTIR spectra of glucosamine Schiff base (Glu-SB), and its polymeric derivative SB-g-p-AAc are presented in Fig. 1.
Glu-SB spectrum shows characteristic band due to >CN stretching of Schiff base structure at 1640 cm−1 [43]. The broad
Conclusions
A new Schiff base was synthesized from glucosamine hydrochloride and N,N-dimethylaminobenzaldehyde followed by its grafting to p-AAc which generated a new Schiff base-based bi-functional polymer, SB-g-p-AAc. Latter was used as an adsorbent for the adsorption of Cu2+ ions in the aqueous solution. The polymer was found to be efficient Cu2+ ions adsorbent and exhibited excellent qmax value of 208.33 mg g−1. It was also found to be selective Cu2+ ions adsorbent in the presence of competing Mg2+ and
Conflicts of interest
The authors declared that there are no competing interests.
Acknowledgements
The authors thank Professor Duni Chand, Department of Biotechnology, Himachal Pradesh University, Shimla, India, for providing microorganisms and laboratory facilities for the antimicrobial studies. YS, expresses his gratitude to the University Grants Commission for BSR fellowship and the facilities provided under the UGC(SAP)-DST FIST programme.
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