Cu-Ca-Al-layered double hydroxide modified by itaconic acid as an adsorbent for anionic dye removal: Kinetic and isotherm study

https://doi.org/10.1016/j.inoche.2021.108914Get rights and content

Highlights

  • The Cu-Ca-Al-LDH and itaconic acid-modified LDH adsorbents were synthesized.

  • The synthesis procedure was simple and green applying water as the solvent.

  • Adsorption of Congo red from aqueous media was studied using the adsorbents.

  • The prepared adsorbents exhibited fast and effective adsorption toward Congo red.

Abstract

Here, for the first time, Cu-Ca-Al-based layered double hydroxide (LDH) was prepared using a facile co-precipitation method. Itaconic acid (ITA) was used as a biodegradable and green organic molecule to modify the LDH and then physicochemical properties of the ITA-modified LDH (LDH-ITA) were studied using FTIR, FE-SEM, TEM, XRD, and TGA techniques. Then the synthesized LDH and LDH-ITA were applied as novel adsorbents for the removal of Congo red as a model of an anionic dye from aqueous media. Several parameters such as the solution pH, contact time, adsorbent amount, and initial concentration of the dye on the adsorption process were monitored and kinetic and isotherm studies were conducted to gain a more in-depth insight into the adsorption mechanism in the process. The results demonstrated that the adsorption of Congo red onto both the LDH and LDH-ITA adsorbents followed the pseudo-second-order kinetic model. Also, isotherm investigations revealed that the Freundlich model provided the best fit with the equilibrium data of both adsorbents. Maximum adsorption capacities of 81 and 84 mg g−1 for Cong red were obtained using Cu-Ca-Al-LDH and LDH-ITA adsorbents, respectively, surpassing those values obtained for most adsorbents reported in the previous studies.

Introduction

As a subgroup of inorganic layered nanomaterials, layered double hydroxides (LDHs) are ionic lamellar mixed hydroxides that consisted of positively charged main layers and an interlayer region with charge-compensating anions undergoing anion-exchange chemistry [1]. They are generally demonstrated with a stoichiometry of M1-x2+Mx3+OH2x+An-x/n.mH2O [2]. In this formula, M2+ and M3+ represent divalent and trivalent metals of the layers, respectively, and An- is charge balancing anion in the interlayer region which can be readily replaced. Owing to their fantastic properties, nowadays LDHs with different compositions have received remarkable attention from academia and industry [3]. They are exhibited important properties such as ion exchange capability, acid-base properties, and adsorption capacity. They are also low-cost materials and their properties can be easily tailored. The use of these materials in drug delivery, catalysis, energy conversion and storage, environmental remediation, and sample preparation have been reported [4].

Despite the unique characteristics of LDHs, various functionalization strategies have been reported for the modification of LDHs to increase their performance and applications. Functionalization of LDHs can drastically improve their performance and properties. Until now, various functionalization strategies have been used for the modification of LDHs. Some common functionalization strategies included intercalation, hybrid assembly, surface modification, size and morphology regulation, layer composition tuning, and defect introduction which are discussed in detail in a reported review by Laipan et al [5]. Surface modification of nanoparticles with organic molecules bearing functional groups is a smart and common strategy to increase the adsorption capacity of adsorbents [6]. Due to its biodegradability and active functional groups (two carboxylic groups), itaconic acid (ITA) can play the role of a surface modifier [7]. More interestingly, it is reported that due to the ability of dicarboxylic acids to form a dianion (in the case of ITA, it can be converted to itaconate anion), these molecules can replace anions between layers of LDHs, which in turn increases the distance between the LDH layers [8].

As an important environmental concern in both developing and industrial countries, the lack of clean water due to the disposal of various toxic compounds into the environment caused drastic concerns about the creature’s health. Among the well-known pollutants, synthetic organic dyes are one of the important groups of water pollutants [9], [10]. The release of these contaminants is an increasing and serious global challenge from an environmental point of view. These relatively complex organic molecules are widely used in different industries such as leather tanning, food processing, paper making, cosmetics, textile, and plastics. As a water-soluble member of synthetic dyes, Congo red is used in a huge quantity in textile and biochemistry-based industries [11], [12]. It is a benzidine-based anionic dye that was discovered by Paul Bottinger in 1883. Generally, benzidine-based dyes are toxic and highly carcinogenic. Congo red is known to metabolize to benzidine, which is a carcinogen and mutagen compound for humans.

Until now, various decontamination techniques have been adopted to remove toxic compounds especially synthetic organic dyes from environmental media in both industrial and municipal wastewaters. Among the treatment techniques, the adsorption strategy provided a simple, low cost, and relatively fast methodology with high efficiency [13]. This conventional strategy is used in advanced wastewater treatment due to its ease of operation, and flexibility in adsorbent design. Recently, various synthetic and natural adsorbents including LDHs, mesoporous silica materials [14], metal-organic frameworks and their composites [15], [16], [17], [18], covalent organic polymers and their composites [19], [20], [21], and polysaccharide-based polymers [22] have been utilized as adsorbent materials for environmental applications like removal of pollutants from water. Notably, developing adsorbents with improved characteristics to be used for the adsorption process is an ongoing trend.

Herein, for the first time, we present the synthesis and characterization of a novel adsorbent of itaconic acid-modified Cu-Ca-Al LDH for adsorption purposes. To the best of our knowledge, this is the first report to study the potential application of itaconic acid-modified Cu-Ca-Al layered double hydroxide for adsorption purposes. To study the applicability of the prepared materials for adsorption purposes, Congo red as an anionic dye was selected to be removed from the aqueous solution. Kinetic studies were also conducted for the prepared materials.

Section snippets

Materials and methods

All materials were purchased from Sigma-Aldrich and Merck (Darmstadt, Germany). The stock standard solution of Congo red (2000 mg L−1) was prepared in water. Working standard solutions were prepared daily by diluting the stock solution. Deionized water was prepared by a lab-made water purification system.

Synthesis of Cu-Ca-Al-LDH

The Cu-Ca-Al-LDH was prepared according to the following procedure. At first, 976 mg of Cu(NO3)2·3H2O (4 mmol), 954 mg of Ca(NO3)2·4H2O (4 mmol), and 1.532 g of Al(NO3)3·9H2O (4 mmol) were

Synthesis of the materials

In this study, Cu-Ca-Al-LDH was prepared in a simple strategy. For the modification of the prepared LDH, ITA was applied. Due to their ability to establish a hydrogen bond between surface hydroxyl groups on the surface of the LDH and functional groups of organic dyes, as well as their ion exchangeability, LDH-ITA can be used as adsorbents to remove organic dyes from aqueous media. This molecule also has the advantage of biodegradability, which is a very important factor in the design of a green

Conclusions

In conclusion, the novel LDH-ITA nanoparticles were synthesized through an environmentally friendly synthetic approach by using ITA as a biodegradable surface modifier. Owing to its hydroxyl and carboxyl groups, the prepared LDH-ITA was applied as a novel adsorbent for the adsorption of Congo red from water. Carbon binds to the Cu-CA-Al-LDH surface through hydrogen bonding and also penetrates Cu-CA-Al-LDH layers as itaconate anions, replacing the anions between the pure Cu-CA-Al-LDH layers to

CRediT authorship contribution statement

Shirin Shabani: Software, Visualization, Writing – original draft, Conceptualization, Validation, Formal analysis, Investigation. Mohammad Dinari: Supervision, Project administration, Conceptualization, Validation, Investigation, Resources, Writing – review & editing.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

The authors wish to thank the research council of the Isfahan University of Technology.

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