Fabrication of zwitterionic histidine/layered double hydroxide hybrid nanosheets for highly efficient and fast removal of anionic dyes
Graphical abstract
Introduction
A growing number of contaminants are entering water supplies through human activities, resulting in inadequate access to clean water for the growing global population. Organic dyes are widely used as coloring agents in many industries, such as textile, dyeing, paper and pulp, tannery and paint, and hence the effluents of these industries tend to contain dyes in excessive quantities [1]. The discharged organic dyes, almost all soluble in water, are difficult to remove due to their poor biodegradability [2], and some are even toxic or carcinogenic to humans and will jeopardize the environment [3], [4]. Increasingly, and due to the demand for advanced clean-water technologies, it is becoming more and more urgent to purify water with a lower cost, less energy, improved safety, minimum use of chemicals and a minimum impact on the environment [5], [6]. Therefore, their removal from industrial effluents as most urgent task make possible to either a safe and clean environment. To remove dyes and other colored contaminants from wastewaters, several physical, chemical, and biological methods such as membrane separation, flocculation-coagulation, adsorption, ozonatioin, ion exchange, oxidation, and aerobic or anaerobic treatment have been developed [7]. However, these techniques suffer certain limitations including cost-effectiveness, production of toxic byproducts hazardous to the environment, production of a large amount of sludge, and low adsorption capacity or inadequate affinity in removing dye from wastewater. However, the removal processes based on adsorption are much more popular because of their high efficiency, simple operation and lower price. Adsorption is a complex phenomenon and involves the passive separation of the adsorbate from an aqueous phase onto the solid phase. It occurs between two phases in transporting pollutants from one phase into another [7].
It has been reported that many different types of adsorbents are effective in removing color from aqueous effluents. The most commonly used adsorbent in industrial wastewater treatment systems is activated carbon because it has a large specific surface area, but it is expensive to run such systems [8]. The cost of this process has motivated numerous studies on alternative removal methods that uses less expensive natural materials and waste by-products such as chitosan, bagasse pith, peanut hull, sludge, perlite, rice husk, wood sawdust, montmorillonite, sepiolite, zeolite, diatomite, sawdust, bentonite, organophilic bentonites and layered double hydroxides [9], [10], [11], [12], [13], [14]. Among these, layered double hydroxides (LDHs) have attracted more attention not only because of their low-cost but also because of their excellent adsorption performance as well as other potential applications, such as catalysts, ion exchange hosts, decolorizing agents and so on [15], [16].
Layered double hydroxides (LDHs), also known as anionic or hydrotalcite-like clays, are a class of lamellar compounds that consist of positively charged brucite-like host layers and hydrated exchangeable anions located in the interlayer gallery for charge balance [17]. The charge of the brucite-like layers arises from the isomorphous substitution of a part of the divalent metal ions with the trivalent ones. The chemical composition of LDHs are expressed by the general formula [MII1−xMIIIx(OH)2][An−x/n, mH2O], where MII and MIII represent di- and trivalent metal ions within the brucite-like layers and An− is an interlayer anion [16], [17], [18]. The incorporation of organic guests into LDHs has already received some attention because of the potential uses of the inorganic-organic hybrids produced in catalysis, sorption, photochemistry, and electrochemistry [19]. Recently, the intercalation of biomolecules such as sugar [20], nucleotide [21], DNA [22], amino acids [23], [24] and polypeptide [25] for LDH has been investigated in order to prepare novel biomolecule/LDH nanohybrids as bio-nanocomposite materials class.
Biomolecules are widely used as low-cost functional materials for diverse applications in materials chemistry. Amino acids, zwitterion functionalized materials containing both anionic and cationic groups, have received great attention in the past decade due to the presence of oppositely charged ionic groups on their surface and unique structures. Moreover, amino acids, where positive and negative charges are located in close proximity, exhibit alternative ion selectivity to standard anion and cation ion-exchangers [26]. These features make amino acids very promising materials for membrane, ion chromatography, removal of carbon dioxide, removal of heavy metal ions, and removal of organic dyes [26], [27], [28].
In this study, we report a new strategy for highly fast and extremely efficient removal of acidic dyes from aqueous solutions using zwitterionic histidine intercalated layered double hydroxide (His-LDH). This inorganic-organic bio-nanohybrids were preparation as low cost, and green material for removal. Hence, to investigate the effect of zwitterionic histidine on the adsorption capacity and adsorption mechanism of LDHs, two MgAl-LDHs intercalated with different interlayer anions, including NO3− and histidine, were synthesized. For the removal of organic acidic dyes, the adsorption kinetics and isotherms were investigated.
Section snippets
Chemicals and materials
All chemicals were of analytical reagent grade. l-histidine, Mg(NO3)2·6H2O and Al(NO3)3·9H2O salts were purchased from Sigma-Aldrich (Milwaukee, WI, USA). Analytical grade Congo red (CR), indigo carmine (IC) and sunset yellow FCF (SY) were procured from Sigma-Aldrich (Milwaukee, WI, USA) and were used without any further purification. The water consumed was purified on a Youngling ultrapure water purification system model Aqua MaxTM-ultra (Seoul, South Korea). Other chemicals applied were of
Structural characterization of His-LDH
FT-IR spectra for the NO3-LDH and His-LDH are shown in Fig. 1a. The FT-IR spectrum of NO3-LDH was roughly attributed as follows: 3440 cm−1 to the OH stretching vibration (νOH) of the metal hydroxide layer and interlayer water molecules; 1627 cm−1 to the OH stretching band of H2O; 1372 cm−1 to the stretching vibration of NO3−; 500–1010 cm−1 to the MO, MOM, and OMO (M = Al or Mg) lattice vibrations. These observations confirmed the formation of NO3-LDH. In the His-LDH spectrum, the band at:
Conclusions
From the present study, it can be concluded that the His-LDH shows excellent acidic dyes removal efficacy from aqueous solutions. The His-LDH showed a higher adsorption capacity toward dyes than NO3-LDH. The remarkably high adsorption capacity of dyes on the His-LDH compared whit NO3-LDH is rationalized on the basis of electrostatic interactions as well as π-π and H-bonding interactions between the His-LDH adsorbent and acidic dye molecules. The prepared His-LDHs have been demonstrated to be
Acknowledgement
Financial support from Tarbiat Modares University is gratefully acknowledged.
The authors have declared no conflict of interest.
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