Carbon nanotube-grafted chitosan and its adsorption capacity for phenol in aqueous solution
Graphical abstract
A novel chitosan/multi-walled carbon nanotube (CS/MWCNT) material was successfully prepared through covalently grafting chitosan (CS) onto the surface of multi-walled carbon nanotubes (MWCNT). The adsorptive ability of the CS/MWCNT was assessed for phenol. Theoretical models were used to describe the adsorption isotherms of phenol and the adsorption parameters were evaluated.
Introduction
Nowadays, functional polymers are present in nearly all aspects of daily life. As the function of polymer is determined by its structure and the moieties attached to the carbon backbone, there is an intensive research focus on the synthesis of new polymers with novel structures and enhanced capabilities (Choi et al., 2010; Zare et al., 2018a, Zare et al., 2018b; Deng et al., 2019). Polymers from natural sources such as biomass, are a prospective research area that has future applications (Marin et al., 2002; You et al., 2018).
Many composite materials have been assessed for their capacity to remove contaminants from water (Wei et al., 2019; Yang et al., 2019). Superparamagnetic nanocomposites prepared using sodium alginate and chitosan as raw materials displayed good adsorptive capacities for heavy metal ions (Lakouraj et al., 2014a, Lakouraj et al., 2014b). Polyaniline/paste synthesized by in-situ polymerization was able to remove heavy metal ions such as Cu (II), Cd (II) and Pb (II) from water (Zare et al., 2015). Nanocomposites derived from cyclodextrin grafted to poly-m-phenylenediamine were able to effectively adsorb heavy metal cations as well as methylene blue (Zare et al., 2015; Nazarzadeh et al., 2018). Magnetic nanocomposites incorporating maleic anhydride were also effective at heavy metal ion removal (Nazarzadeh et al., 2014, Nazarzadeh et al., 2016; Hasanzadeh et al., 2016; Zare et al., 2018a, Zare et al., 2018b). In the current study, chitosan was used as a raw material to synthesize the adsorbent. Chitosan is a natural polysaccharide that is abundant, cheap, biodegradable and non-toxic (X. Liu et al., 2018; B. Liu et al., 2018). Its usage has increased in prominence. The development of new CS-based materials with novel structures and applications is important.
Phenol is prevalent in industrial effluents from coking, printing and dyeing, plastic production, chemical and petroleum processes (Guo et al., 2017; Zangrando et al., 2019). Phenolic wastewaters are highly toxic and detrimentally affect macrobiotic aquatic life, microbial growth and ecology (Fajardo et al., 2017; Yan et al., 2019). Adsorption is commonly used to remove phenol and other organic pollutants from aqueous media (Yu et al., 2014; Huang et al., 2018). It is necessary to find an efficient adsorbent, as large-scale application of adsorbents (such as activated carbon, biochar, clay or fly ash is hampered by less effective adsorption or recycling difficulties) (Mousset et al., 2016; Luo et al., 2018; Zhang et al., 2019).
Chitosan is the only alkaline polysaccharide. It is an excellent adsorbent (Cui et al., 2013) and considered environmentally-friendly because of its biodegradability (X. Liu et al., 2018; B. Liu et al., 2018). However, its use is restricted by a low adsorption capacity for organic matter due to its solubility in dilute acids (Li et al., 2017). The functional surface groups on adsorbents can be modified to improve its adsorption capacity (Wu et al., 2016, Wu et al., 2017; Li et al., 2019). In recent years, surface chemical modification of carbon nanotubes has become a popular topic in nanotechnology research (Phan et al., 2018). Biological materials such as chitosan, cyclodextrin, cellulose can be used to modify the surface carbon nanotubes to prepare functional materials with enhanced dispersibility and substrate binding ability (Phan et al., 2018; Xia et al., 2019). Adsorption materials using carbon nanotubes and chitosan as raw materials are of great interest (Wu et al., 2007; Dai et al., 2012; Ding et al., 2017) and various composite materials are able to efficiently remove heavy metal ions from aqueous solutions (Ke et al., 2007; Zhuang et al., 2016; Lu et al., 2018).
In this research, a functional CS/MWCNT graft polymer was prepared by chemical grafting. The static and dynamic adsorption properties of the graft polymer towards phenol were investigated.
Section snippets
Materials and reagents
The following compounds were used: CS (deacetylation degree ≥90%, Sinopharm Chemical Reagent Limited Company); carbon nanotubes (MWCNT, 95%, Shenzhen Bill Technology Company); thionyl chloride (SOCl2, AR, Shanghai Jinshan Tingxin Chemical Reagent Factory); N, N-dimethylformamide (DMF, 99%, Energy Chemical); H2SO4 (AR, Zhejiang Quzhou Juhua Reagent Limited Company). All other chemicals used in this study were of an analytical grade.
Preparation of CS/MWCNT
Carboxyl carbon nanotubes (MWCNT-COOH) were prepared according
Synthesis of CS/MWCNT
The surface of the MWCNT was enriched in carboxyl groups (via acidification) and then chloridated to MWCNT-COCl (by SOCl2). The MWCNT-COCl reacted with chitosan in DMF solution to generate the new covalently-bonded chitosan grafted to carbon nanotubes (CS/MWCNT). The grafting ratio (GP) of the CS/MWNTs copolymer was calculated using the formula (Eq. (1)):where, W1 and W0 are the mass (g) of CS/MWNTs copolymer and MWNTs-COCl, respectively. According to the mass balance, the grafting
Conclusions
Chitosan (CS) was successfully grafted to the surface of carbon nanotubes (MWCNT). The CS/MWCNT graft polymer displayed an improved maximum adsorptive capacity for phenol (86.96 mg/g) compared to chitosan (61.69 mg/g). A pseudo-second order equation provided better correlation to the sorption data than first order kinetics. Therefore, this study can provide a reference for preparing functional materials from biological substrates to remove toxic pollutants from an aqueous environment.
Acknowledgments
This work was supported by the Natural Science Foundation of Zhejiang Province (LY18B070003), the National Natural Science Foundation of China (21577131, 21876027) and the Natural Science Foundation of Guangdong Province, China (2017A030311019).
References (58)
- et al.
The removal of phenol from aqueous solutions by adsorption using surfactant-modified bentonite and kaolinite
J. Hazard. Mater.
(2009) - et al.
Adsorption of 2-nitrophenol by multi-wall carbon nanotubes from aqueous solutions
Appl. Surf. Sci.
(2010) - et al.
Adsorption of fluoride onto crystalline titanium dioxide: effect of pH, ionic strength, and co-existing ions
J. Colloid Interface Sci.
(2013) - et al.
Synthesis characterization and self-assemble behavior of chitosan-O-poly (ε-caprolactone)
Eur. Polym. J.
(2009) - et al.
Preparation and application of Aliquat 336 functionalized chitosan adsorbent for the removal of Pb(II)
Chem. Eng. J.
(2013) - et al.
Schiff base-chitosan grafted multiwalled carbon nanotubes as a novel solid-phase extraction adsorbent for determination of heavy metal by ICP-MS
J. Hazard. Mater.
(2012) - et al.
Carbamazepine removal from water by carbon dot-modified magnetic carbon nanotubes
Environ. Res.
(2019) - et al.
Preparation of cellulose-graft-poly(ε-caprolactone) nanomicelles by homogeneous ROP in ionic liquid
Carbohydr. Polym.
(2013) - et al.
Hydrated salts as both solvent and plasticizer for chitosan
Carbohydr. Polym.
(2010) - et al.
Effects of metal ions and pH on ofloxacin sorption to cassava residue-derived biochar
Sci. Total Environ.
(2018)