Hemicelluloses-based magnetic aerogel as an efficient adsorbent for Congo red
Introduction
Dyes have been widely used in cosmetics, food, medicine, spinning and printing industries [1]. Due to their toxic, carcinogenic and mutagenic effects on aquatic species and human beings, the presence of dyes in water is a serious environmental problem [2]. Therefore, the removal of various dyes is particularly important to environmental protection and safety. The contamination of the environment by textile chemicals, dyestuffs, and other industrial chemicals is a cause for significant concern and demands immediate effective ways to limit the release [3]. A number of techniques have been investigated for dye and heavy metal ion removal, including membrane separation, biological treatment, chemical oxidation, ozonation, coagulation, flocculation, and adsorption via various adsorbents [4,5]. Among these methods, adsorption has been recognized as one of the most promising methods owing to its superior efficiency, lower cost and easier-to-operation [6,7]. Aerogel, a three-dimensional (3D) porous solid material has been considered a promising adsorbent candidate in heavy metal and dyes for wastewater treatment, with ultralow density, high specific surface, recyclable and excellent mechanical property [[8], [9], [10]]. It can be formed in various shapes and sizes from a variety of raw materials. Accordingly, bio-based materials are increasingly utilized in preparation of the aerogel.
Furthermore, potential bio-based products include biofuels, biochemicals, and biomaterials, especially bioenergy and biofuels have received greater attention [11], due to the depletion of petroleum resources. Wheat straw, which is an abundant agricultural residue in many countries, has the potential for use as a low-cost raw material for the industrial production of higher-added value products. Among various functional materials, hemicelluloses have attracted plenty of attentions because of their biodegradability, biocompatibility, abundant resources, and non-toxic properties [12]. Hemicelluloses, representing about 20–35% of lignocellulosic biomass, have emerged as an immense renewable resource of biopolymers. And they were always discarded resulting in a waste of biomass resources. In order to high value-added the hemicelluloses, more application aereas should be detected. These properties open new alternatives for hemicelluloses composites, such as hydrogels, aerogels, macro-particle, and films intended for adsorbent, coating, drug delivery, and sensor. The chemical modification of hemicelluloses presents a better manner for preparing materials with unique properties (hydrophobicity, conductivity, thermos-plasticity, and stimuli-responsiveness) that can increase application value and efficiency of hemicelluloses [[13], [14], [15]]. Oxidation is a facile and practicable way to introduce multiple aldehyde groups, enabling hemicellulose as a reductant to form nano-silver composite, polymer intermediate for super-molecule through by chain propagation, or crosslinker for polymers abundant in amino groups to prepare function materials [16].
Chitosan (CS), a deacetylated derivative of chitin, is the second most abundant polysaccharide found in the nature and mainly derived from shellfish processing waste [17]. Chitosan has been also well recognized with some advantageous characteristics, including biocompatibility, hydrophilicity, biodegradability, non-toxicity, and bio-adherence as well as non-antigenicity and cell affinity [18,19]. Therefore, Chitosan and its derivatives have emerged essentially as an important constituent in the production of hydrogels, aerogels, macro-particle, and edible and non-edible types of functional films intended for food packing, adsorbent, coating, drug delivery, and sensor.
Recently, the polymers separation form forestry and agricultural residues have been widely used in absorption applications. Not only is the environmental pollution urgent to be solved, but the natural polymers also exhibiting excellent performances on the absorption of dyes and heavy metal ion. Choi et al. fabricated a series of membranes based on cellulose nanofiber, exhibited an adsorption capacity (qmax) of 49.0, 45.9, and 22.0 mg·g−1 for Cu (II), Cd (II), and Pb (II) in water, respectively [20]. Lei et al. synthesized a sequence of aerogels adsorbent based on MOFs and cellulose for removal of heavy metal ions in water. The aerogels could remove Pb (II) efficiently and its saturated adsorption capacity was up to 89.40 mg/g [21]. Zha et al. prepared a kind of spheres based on polystyrene and chitosan, the porous spheres could remove chromium ions (III) efficiently and its saturated adsorption capacity was up to 270 mg/g. In addition, the porous spheres can completely reduce the methylene blue in short time [22]. However, these types of adsorbing materials are single-use and cannot be recycled easily or have a complex preparation process. Therefore, how to synthesize and prepare a high-efficiency and recyclable adsorbent is urgently needed.
In this study, the magnetic aerogel based on hemicellulose and chitosan was developed in the present investigation. The formation mechanism of the aerogel was discussed, and the optimum adsorption condition of the aerogel was investigated. The characterizations of dialdehyde hemicelluloses/chitosan aerogel were conducted with by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM), thermogravimetric analysis (TGA), mechanical property and absorption property of Conge red.
Section snippets
Materials
The hemicelluloses utilized were isolated from wheat straw following previously reported [23]. The result of size-exclusion chromatography (SEC) showed that the native hemicelluloses had a weight-average molecular weight (Mw) of 14,320 g/mol with a polydispersity of 1.33. Chitosan (degree of acetylation of 80–95%, Mw = 200,000 g/mol, PDI = 1.5), was purchased from Macklin Chemical Reagent Co. Ltd. Sodium periodate and ferroferric oxide (grain size 20 nm) were both provided by Aladdin Reagent
The structure of DAH
The structural and chemical changes of the hemicelluloses before and after modification were investigated by FT-IR, which are shown in Fig. 1A. From the spectra of DAH and hemicellulose, the curve of DAH was almost the same as that of the raw hemicellulose. The new signal at 1726 cm−1 was presented in the DAH spectrum, which was related to the CO vibration in the aldehyde groups [26]. This result was indicated that the hydroxyl groups of xylose unit were oxidized and transformed into aldehyde
Conclusion
In this study, the dialdehyde hemicelluloses were prepared successfully by oxidation using sodium periodate, which can be demonstrate according to FT-IR and NMR results. Then, a 3D crosslinking network of the aerogel can be achieved by crosslinking dialdehyde hemicelluloses with chitosan by Schiff-Base. With DAH/chitosan aerogel, magnetic aerogel stronger adsorption ability of Congo red, when 0.5 g Fe3O4 content of the best adsorption performance were 137.74 mg/g, the addition of Fe3O4 render a
Author statement
Ying Guan: Writing and Editing
Jun Rao: Data curation, Writing - Original draft preparation
Yule Wu: Experimental data analysis
Hui Gao: Article revision, Supervision
Shengquan Liu: Supervision
Gegu Chen: Conceptualization, Methodology
Feng Peng: Article revision
Declaration of competing interest
The authors declare that there are no conflicts of interest associated with this manuscript.
Acknowledgments
This work was supported by Anhui Science Foundation Grant (1908085QC112), Beijing Municipal Natural Science Foundation (641802006), Anhui Postdoctoral Science Foundation Grant (2017B157), Anhui High-School Natural Science Foundation Grant (KJ2018A0152), and Open Research Fund of Biomass Molecular Engineering Center at Anhui Agricultural University.
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