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Porous chitosan doped with graphene oxide as highly effective adsorbent for methyl orange and amido black 10B
Accepted Manuscript Title: Porous chitosan doped with graphene oxide as highly effective adsorbent for methyl orange and amido black 10B Author: Ying Wang Guangmei Xia Cong Wu Jing Sun Rui Song Wei Huang PII: DOI: Reference:
S0144-8617(14)00939-4 http://dx.doi.org/doi:10.1016/j.carbpol.2014.09.041 CARP 9299
To appear in: Received date: Revised date: Accepted date:
16-6-2014 14-8-2014 6-9-2014
Please cite this article as: Wang, Y., Xia, G., Wu, C., Sun, J., Song, R., and Huang, W.,Porous chitosan doped with graphene oxide as highly effective adsorbent for methyl orange and amido black 10B, Carbohydrate Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.09.041 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Porous chitosan aerogels doped with graphene oxide as
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highly effective adsorbent for methyl orange and amido
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black 10B
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Ying Wang, a Guangmei Xia,b Cong Wu, a Jing Sun,c Rui Song, a* Wei Huang d
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a
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Academy of Sciences, Beijing, 100049, People’s Republic of China
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b
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Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences,
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Beijing, 100190, China
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College of Chemistry and Chemical Engineering, University of Chinese
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Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of
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c
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Academy of Sciences, Shanghai 200050, China
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Ac ce p
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Shanghai Institute of Microsystem and Information Technology, Chinese
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amount of graphene oxide (CSGO aerogels) with high porosity (97.96 % −
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98.78 %), extraordinarily high water absorption (5848 % − 8917 %) and low
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density (0.021-0.035 g cm-3) were prepared and used as adsorbents for two
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azo dyes methyl orange (MO) and amido black 10B (AB10B). The adsorption
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d
Laboratory of Advanced Polymer Materials, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100080, China
ABSTRACT: In the current study, porous chitosan aerogels doped with small
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behavior of these CSGO aerogels and some influence factors such as pH
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value, graphene oxide (GO) loading, concentration of pollutants, as well as
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adsorption kinetics were studied. Specifically, the adsorption capacity for MO
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is 686.89 mg g-1, the highest comparing with other publication results, and it is
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573.47 mg g-1 for AB10B. Since they are biodegradable, non-toxic, efficient,
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low-cost and easy to prepare, we believe that these porous CSGO aerogels
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will be a promising candidate for dye removal.
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KEYWORDS: Chitosan, Graphene oxide, Methyl orange, Amido black 10B,
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Adsorption.
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1. Introduction
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Nowadays the treatment of dyeing effluents has long been a major
31
concern. Most dye molecules in the effluent are known to be toxic, mutagenic
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and carcinogenic (Chatterjee, Chatterjee, Lim & Woo, 2011b). Azo dyes
34 35 36
te
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d
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constitute the largest class of colorants and are common aquatic pollutants, which own the –N=N– chromophore group and the aromatic structure. They are normally difficult to remove because they are largely non-biodegradable and are resistant to light and oxidizing agents (Anirudhan, Radhakrishnan &
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Vijayan, 2013; Cheah, Hosseini, Khan, Chuah & Choong, 2013), and
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adsorption process is proven as a reliable and effective act for this dye
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treatment (Cheah, Hosseini, Khan, Chuah & Choong, 2013; Vimonses, Lei, Jin,
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Chow & Saint, 2009). Aerogel is a porous material and has been used in the
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area of organic pollutants adsorption. Rao (Venkateswara Rao, Hegde &
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Hirashima, 2007) et al. investigated the adsorption of organic liquids on silica
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aerogel and found that the aerogel could adsorb the organic liquids and oils by
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nearly 15 times of its own mass. El-Rassy (Abramian & El-Rassy, 2009) et al.
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prepared titania aerogels by supercritical drying of wet alcogels which are
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synthesized through a one-pot sol–gel process and its adsorption capacity for
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Orange II is 420 mg g-1 at the optimal conditions.
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Chitosan (CS), the cationic (1-4)-2-amino-2-deoxy-β-D-glucan, is manily
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produced from marine chitin by deacetylation (Muzzarelli, Boudrant, Meyer,
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Manno, DeMarchis & Paoletti, 2012). As one of the most representative
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biopolymers, it is a multifunctional polysaccharide comprising of copious
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chelating groups including primary and secondary hydroxyl groups, as well as
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highly reactive amino groups (Rinaudo, 2006). Meanwhile, it is low-cost,
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non-toxic and biodegradable, so it has been considered as a green adsorbent
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an
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for the removal of dyes (Crini & Badot, 2008; Chatterjee, Chatterjee, Lim & Woo, 2011a). However, the application of chitosan is limited because of its solubility in acid solution. Hence, it is necessary to crosslink chitosan in order to make it stable in acid solution (Liu et al., 2012).
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Graphene oxide (GO) is an oxygen-rich carbonaceous layered material. It
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has gained considerable attention as a significant adsorbent as plenty of
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oxygen atoms on the basal plane and the edge of the sheets in the forms of
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epoxy, hydroxyl, and carboxyl groups, protruding from its layers (Chen, Chen,
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Bai & Li, 2013; Travlou, Kyzas, Lazaridis & Deliyanni, 2013). Meanwhile, as a
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significant carbonaceous layered material, the GO incorporation can enhance
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the strength of polymer composites (Zhang, Qiu, Si, Wang & Gao, 2011).
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Therefore, it will be interesting to prepare porous CS materials with
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incorporation of GO.
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In this work, we prepared porous chitosan aerogels doped with graphene
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oxide (CSGO aerogels) by crosslinking and freeze drying and used them as
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highly effective adsorbents for two azo dyes, methyl orange (MO) and amido
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black 10B (AB10B), which are widely used in chemical, textile, paper industries,
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biological stain, paints, inks, plastics, and leather industries (Jalil et al., 2010;
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Mittal, Thakur & Gajbe, 2013). Its adsorption capacity for MO is 686.89 mg g-1,
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which is the highest compared to those existing literatures, and the adsorption
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capacity for AB10B also reaches 573.47 mg g-1. Meanwhile, the effects of pH
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values, concentration of pollutants, loading of graphene oxide on the
78 79 80
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adsorption for MO and AB10B as well as adsorption kinetics were studied.
2. Experiment 2.1 Materials
CS (Mn = 700 K, degree of deacetylation (DD) = 95 %) was purchased
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from Zhejiang Yuhuan Marine Bio-chemical Co. Ltd. GO was prepared by
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Hummer’s method, and the detail about its synthesis could be found elsewhere
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(Cao, Yin & Song, 2013). Acetic acid, nitric acid, sodium hydroxide were
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analytical-grade while MO and AB10B were biological stain and they were all
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from commercial suppliers (Sinopharm, Beijing) and used without further
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purification. Methyl aldehyde (37% w/w aqueous solution) was from Alfa
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Aesar.
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2.2 Preparation of porous CSGO aerogels
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Firstly, various amounts of GO aqueous solution (8mg mL-1) were added to
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2 % (V/V) acetic acid aqueous solution to form GO acetic acid aqueous
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solution (solution A). Then 0.6 g CS was dissolved into 15 ml solution A and
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formed homogeneous CSGO mixture after being stirred for 1 h. Subsequently,
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20μL 37 % methyl aldehyde aqueous solution was added to the CSGO mixture
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dropwise with stirring in water bath at 50℃ and then CSGO hydrogels were
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formed in one minute, following one hour standstill at 50℃. After that we cut
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these hydrogels into small pieces and put them into water to swell for 40 min.
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Subsequently, the swollen hydrogels were frozen below -18℃ and then
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transferred to a lyophilizer (FD-1CE, Boyikang Co. Ltd., Beijing) with a
100 101 102 103
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cr
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condenser temperature of -55℃ and inside pressure 20-30 Pa. After 2-day lyophilization process CSGO aerogels were obtained. In this case, CSGO aerogels with different GO contents, which is 1 wt%
(CSGO1), 3 wt% (CSGO3), were prepared, respectively. Similarly, CS aerogel was prepared in the absence of GO. 2.3 Calculation of the water absorption of CSGO aerogels
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These CSGO aerogels were put into deionized water for one hour, and
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their water adsorption was calculated according to the following equation:
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Water absorption (%) =
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( Mt − M0) × 100% M0
where, M0 (g) and Mt (g) are the weight of the CSGO aerogels before and after
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immersing into deionized water respectively. 2.4 Porosity and Density of porous CSGO aerogels
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The porosity and apparent density of the porous CSGO aerogels was
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Porosity (%) =
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Density =
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calculated according to the following equation:
(Vt − Va) (Vt − Ma / ρ ) × 100%= × 100% Vt Vt
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M
Vt Ma
where, Vt (cm3) is the total volume of CSGO aerogels, Va (cm3) is the actual
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volume of the material, Ma (g) is the mass of the aerogels, and ρ (g cm-3) is the
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actual density of the material. Each sample was measured in triplicate and the
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average value was adopted.
120 121 122 123
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2.5 Batch adsorption experiments The stored MO and AB10B solution were prepared by directly dissolving
these compounds with known weight in deionized water. Batch adsorption experiments were carried out in 25 mL flasks, where M = 0.013-0.015 g of the adsorbents were put into V = 13-15 mL of MO or AB10B aqueous solutions
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（the V/M was kept at 1 L/g） and allowed to adsorb at room temperature
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(20±1℃) without stirring or shaking. At given time intervals, the concentrations
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of pollutant solutions were measured and adsorbents were collected. The dye
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concentration was determined by the absorbance at 464 nm for MO and 610
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nm for AB10B in the ultraviolet-visible (UV-Vis) spectrum. The adsorption capacity (Q) and adsorption efficiency (Ade) was calculated
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( C0 − Ct ) V M
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Qt=
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Ade (%) =
( C0 − Ct ) × 100% C0
cr
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according to the following equation:
us
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where C0 (mg L-1) and Ct (mg L-1) are the concentrations of pollutants in
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solution after 0 and t h, V (L) is the volume of solution and M (g) is the mass of
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the adsorbent. Qt (mg g-1) is the apparent adsorption capacity of the porous
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monoliths after t h , which if given a long enough adsorption period (the time
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required to achieve the equilibrium adsorption state), is equal to the equilibrium
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adsorption capacity Qe (mg g-1).
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The time required to achieve the equilibrium adsorption state (te) was
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determined by the adsorption kinetic curve. The adsorption time in the adsorption experiments measuring Qe was set longer than te. 2.6 Characterization
X-ray powder diffraction data were collected on MSAL-XD3 with Cu Kα
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radiation (λ = 0.1542 nm) at 40 kV and 40 mA. Scanning electron microscopy
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was performed on a field emission SEM (Hitachi S-4800) at an accelerating
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voltage of 10 kV. Thermo gravimetric analyzer curves were determined by
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SDT-Q600 analyzer (TA Corp., US) at a heating rate of 10 ℃ min-1 in N2
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atmosphere. UV-visible spectra were recorded on a UV-2550 (Shimadzu
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Corporation, Japan) at room temperature. Fourier transform infrared spectroscopy was carried out on a Nicolet
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VERTEX 70 (Bruker) spectrometer using the attenuated total reflectance (ATR)
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method at a resolution of 4 cm-1. The spectrum was generated and collected
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16 times and corrected for the background noise.
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X-ray photoelectron spectrometer (XPS) measurements were taken via an
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ESCALAB250Xi (Thermo Scientific, USA) using a unmonochromatic Al Kα line
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at 1486.6 eV in an ultra-high-vacuum system with a base pressure 3 × 10−9
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mbar and an analyzer pass energy of 150 eV, giving a full width at
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half-maximum of 1.7 eV for the Au 4f7/2 peak. The binding-energy scale was
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calibrated by assigning the main C1s peak at 284.8 eV. The XPS core-level
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spectra were analyzed by decomposing each spectrum into individual mixed
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Gaussian−Lorentzian peaks.
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Dynamic mechanical properties were measured using a dynamic
mechanical analyzer (DMA Q800, TA, US). Tests were carried out in the DMA multi-frequency – strain module with frequency of 0.1-15 Hz at a 35℃. Compressive strength of the porous CSGO aerogels were measured by
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material testing machine (HY-0580，Hengyi Corp., Shanghai) with 50 %
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compressed at a compressing rate of 2 mm min-1. The samples for
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compressive strength were prepared without swelling in water for 40 min
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before freeze drying. Each sample was measured in triplicate and the average
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value was adopted.
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3. Results and discussion
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3.1 Characterization of the CSGO monoliths
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Fig. 1A-C shows the optical and SEM images of the CSGO aerogels,
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indicating the porous network structure of the prepared aerogels. Fig. 1D-F
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reveals water absorption, porosity and density of the prepared CSGO aerogels.
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All the obtained aerogels have high porosity (97.96 − 98.78 %), extraordinarily
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high water absorption ability (5848 − 8917 %) and low density (0.021 − 0.035 g
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cm-3). The high porosity and water absorption ability should contribute to the
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diffusion of dyes to the surface and interior regions of the porous CSGO
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aerogels, leading to high adsorption abilities and rates for dyes .
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Fig.1. Optical image (A) of CSGO1 aerogel; SEM image of CSGO1 (B) and CSGO3
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(C) aerogels. Porosity (D), water absorption (E) and density (F) of the prepared
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CSGO aerogels with different GO contents.
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Fig. 2 shows the XRD spectra of GO, CS and CSGO aerogels. Both the CS
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and CSGO aerogels show a characteristic peak at about 2θ = 12.34゜and
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20.25゜ attributed to chitosan, and no distinct changes are observed with the
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increase of GO content, indicating that the GO has no obvious influence on the
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crystalline properties of CS (Zhang, Qiu, Si, Wang & Gao, 2011). Meanwhile,
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the characteristic diffraction peak of GO at 2θ = 11.76 ゜ is not clearly
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demonstrated in the CSGO aerogels because of its low content.
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Fig. 2. XRD spectra of CS and CSGO aerogels (A) and GO (B).
Fig. 3A shows the FTIR spectra of CS, CSGO aerogels and GO. Spectrum
of GO shows characteristic absorption bands of vibration of C–O at 1042 cm-1, C=C stretching mode of the sp2 carbon skeletal network at 1620 cm-1 and the
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stretching vibration of carboxyl groups on the edges of the layer planes or
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conjugated carbonyl groups at about 1714 cm-1, respectively (Szabó et al.,
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2006; Titelman, Gelman, Bron, Khalfin, Cohen & Bianco-Peled, 2005;
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Seredych, Petit, Tamashausky & Bandosz, 2009; Travlou, Kyzas, Lazaridis &
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Deliyanni, 2013). In comparison, all the GO-related peaks are not detected in
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the CSGO spectra because of GO’s low content. The band at 1551 cm−1
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corresponds to N-H bending of -NH2 (Fan, Luo, Li, Lu, Qiu & Sun, 2012; Ma,
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Liu, Li & Wang, 2012). In the case of GO doped by 1% to 3% , the band of
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–NH2 has shifted to a lower value from 1551 cm-1 to 1540 cm-1, which proves
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that -NH2 groups on the CS chains have been reacted with the
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oxygen-containing functional groups of GO (Fan, Luo, Li, Lu, Qiu & Sun,
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2012).
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To further confirm the above issue, X-ray photoelectron spectra of CS,
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CSGO1 and CSGO3 aerogels were analyzed (Fig.3B and Fig.3C ). The O1s
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spectra were curve-fitted by two peaks: the first peak at 532.1 eV is due to O-H
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groups, and the second at about 532.7 eV is relevant to O-C moieties (epoxy,
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carboxyl groups) (Travlou, Kyzas, Lazaridis & Deliyanni, 2013). The peak
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attributed to O-H groups increased in these CSGO aerogels, indicating the
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M
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O-H formation by the reaction of the chitosan amino groups with the oxygen-containing functional group of GO, which is consistent with the FTIR result. The reaction mechanism can be shown as follow: R1-NH2 + :O-R2
Where R1 is the remaining structure besides –NH2 of chitosan, R2 is the
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R1-NH2…O-R2
remaining structure besides –O: of GO.
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Fig. 3. FTIR spectra of CS, GO, CSGO1 and CSGO3 aerogels (A); O1s XPS spectra
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of neat CS (B) and CSGO1, CSGO3 aerogels (C).
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The mechanical properties of the CSGO aerogels were investigated by the
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value over the entire angular frequency (0.1-15 rad s-1), which reveals that the
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elastic response is predominant, implying that these aerogels have a
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permanent network (Wu, Wen, Guo, Yang, Wang & Xu, 2013). The storage
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modulus increases from 2.2-3.1 MPa to 3.3-4 MPa with the addition of 1 wt%
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compression tests and the dynamic mechanical analysis (DMA), as shown in Fig. 4A-C. The compressive strength of the obtained samples was increased with the increase of GO content (Fig. 4A). The viscoelastic property and inter-structure can be further assessed by DMA test. For both CS and CSGO1 aerogels, the storage modulus value is much higher than the loss modulus
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GO, while the loss modulus decrease from 0.31-0.66 MPa to 0.1-0.4 MPa,
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indicating that GO can improve the elastic response of the prepared aerogel.. Thermogravimetric (TG) analysis was carried out to investigate thermal
239
decomposition behavior of the CSGO aerogels, as shown in Fig. 4E and Fig.
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4F. The differential thermogravimetric (DTG) curve of CSGO presents two
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peaks with maxima at 180 °C and 280 °C respectively, corresponding to the
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two weight loss stage of the thermogravimetry curves. The first peak is related
243
to the decomposition of surface functional groups of GO and the second peak
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related to the degradation of chitosan based on the previous reports (Travlou,
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Kyzas, Lazaridis & Deliyanni, 2013) and current results of pure GO and CS.
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The CSGO aerogels show almost identical thermogravimetric curves
247
regardless of the different GO contents, indicating that low content of GO has
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no detectable effect on the thermal stability of the CSGO material.
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Fig.4. Histograms of the compressive strength of CS, CSGO1 and CSGO3
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aerogels(A). Dynamic mechanical analysis of CS aerogel (B) and CSGO1 aerogel (C).
257
Thermogravimetry (E) and differential thermogravimetry (F) curves of GO, CS,
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CSGO1 and CSGO3.
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3.2.1 Effect of pH
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te
3.2 Adsorption of MO and AB10B by CSGO aerogel
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adsorption is electrostatic attraction between the MO/AB10B and the
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protonated amino groups. At lower pH, the amino groups of the CS
268
macromolecules become protonated, and electrostatic attraction between the
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MO/AB10B and the protonated amino groups may contribute to the adsorption
261 262 263 264
Fig. 5A and Fig. 5B shows the equilibrium adsorption capacity for MO and
AB10B of the CSGO1 aerogel in 800 mg L-1 initial dye solution with different pH values, which were adjust at first and allowed to be free during adsorption. For both MO and AB10B, the adsorption ability of the CSGO1 aerogel decreases with the increasing of pH values. It is because the main force of the
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of the MO/AB10B onto the CSGO aerogel (Travlou, Kyzas, Lazaridis &
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Deliyanni, 2013).
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3.2.1 Effect of GO content Fig. 5C and Fig. 5D shows the equilibrium adsorption capacity for MO and
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AB10B of the prepared aerogels in 800 mg L-1 initial dye solution at pH 8.45
275
and 7.79, respectively. The result show that the addition of 1 wt% or 3 wt% GO
276
has almost no effect on the adsorption capacity. The reason can be attributed
277
two aspects. On one hand, recent reports shows that GO exhibits low affinity
278
for anionic dyes, due to the strong electrostatic repulsion between them (Chen,
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Chen, Bai & Li, 2013; Travlou, Kyzas, Lazaridis & Deliyanni, 2013). On the
280
other hand, although GO may enhance adsorption ability for dyes when
281
introduced into the porous material, the existence of carboxyl groups might
283 284 285 286
cr
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reduce the binding capacity of the amine groups for dyes due to electrostatic forces between the carboxyl and amine groups, which may decrease the adsorption capacity of the CSGO aerogel (Zhang, Qiu, Si, Wang & Gao, 2011). These two aspects cause the limited growth of the adsorption capacity as a whole.
3.2.3 Effect of contact time (adsorption kinetics)
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Fig. 5E and Fig. 5F shows the effect of contact time on dye adsorption of
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CSGO1 aerogel in 800 mg L-1 MO and AB10B solution. For the MO adsorption,
290
very fast dye removal occurs at the initial stage (0-10 h). Then, the dye
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adsorption is milder and more gradual during the second time period (10-60 h).
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And at the last stage (60-84 h) the dye adsorption is characterized by the
293
equilibrium state. The fast adsorption in the initial stage might be due to the
294
fact that a large number of surface sites are available for adsorption. After a
295
period of adsorption, the remaining surface sites are more resistive for the dye
296
molecules to occupy because of the repulsion between the solute molecules of
297
the solid and bulk phases, which makes it milder and take a long time to reach
298
equilibrium (Travlou, Kyzas, Lazaridis & Deliyanni, 2013). And AB10B displays
299
the similar adsorption behavior.
M
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.
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te
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Fig. 5. Adsorption of the CSGO1 aerogel for MO (A, C, E) and AB10B (B, D, F) in solutions (800 mg L-1) with different pH values, GO contents and time, respectively. Inset : optical images of diluted dye solution after adsorption.
To investigate the controlling mechanism of the adsorption processes,
308
pseudo-first-order and pseudo-second-order kinetic models were used to
309
study the experimental data obtained. The pseudo-first-order kinetic model is given as (Chiou & Li, 2002; Jiang,
310 311
Fu, Zhu, Yao & Xiao, 2012)
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log(Qe-Qt) = logQe-
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The pseudo-second-order kinetic model can be expressed as (Chiou & Li,
313
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2002; Jiang, Fu, Zhu, Yao & Xiao, 2012) t 1 t = + 2 Qt Qe k 2Qe
315
cr
314
K1 t 2. 303
where Qe and Qt are the amounts of MO/AB10B adsorbed (mg g-1) per unit of
317
adsorbent at equilibrium and at time t, respectively. k1 is the pseudo-first-order
318
rate constant (h-1). The rate constant (k1) and correlation coefficients (R2) are
319
determined from the linear plots of log(Qe - Qt) versus t. k2 is the
320
pseudo-second-order rate constant of adsorption (g mg-1 h-1). The rate
321
constant (k2) and correlation coefficients (R2) are determined from the linear
322
plots of
324 325 326 327
an
M
d te
t versus t. Qt
According to the correlation coefficients (R2), the pseudo-second-order
Ac ce p
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equation provided an excellent fit for the experimental data of both MO (R2 = 0.9995) and AB10B (R2 = 0.9988) adsorption, compared with the (R2) data from pseudo-first-order equation, 0.9814 of MO and 0.9405 of AB10B, respectively.
3.2.3 Adsorption mechanism
328 329
We discuss the adsorption mechanism by FTIR (Fig.6) and take the
330
adsorption for AB10B as a representative. As shown, the amino peak at 1546
331
cm−1 of CSGO1 aerogel after dye adsorption presents a decrease and shifted
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to a lower wavenumber, which confirms the mechanism explaining the
333
interactions between the dye molecules and adsorbents (Travlou, Kyzas,
334
Lazaridis & Deliyanni, 2013; Liu, Zheng & Wang, 2010).
M
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Fig. 6. FTIR spectra of CSGO1 aerogel (a), AB10B loaded CSGO1 aerogels (b) and
337
AB10B dye (c).
te
The resultant CSGO1 aerogel presents a prominent adsorption capacity for
340 341 342 343
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d
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MO and AB10B comparing with other reported adsorbents, and detail could be found in Table 1 and Table 2. As indicated, the adsorption capacity (Q) of the prepared porous CSGO1 aerogel is much higher than most reported adsorbents. In particular, the CSGO1 aerogel owns the highest Q value of MO among the related publications available. So the prepared porous CSGO
344
aerogels can be a kind of promising adsorbent for the removal of MO and
345
AB10B from aqueous solutions owing to its very high adsorption capacity,
346
low-cost, eco-friendly and easy preparation.
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Table 1 Comparison of the adsorption capacity of CSGO1 aerogel for MO removal
349
with other adsorbents
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γ- Fe2O3/MWCNTs/chitosan (Zhu, Jiang, Xiao & Zeng, 2010)
an
us
Hypercrosslinked chloromethylated PS adsorbent functionalized with formaldehyde carbonyl groups (HJ-1) (Huang, Huang, Liu, Wang & Yan, 2008)
60.5–66.1
70.9–76.9
380
Acid modified carbon coated monolith (Cheah, Hosseini, Khan, Chuah & Choong, 2013)
132.7
Calcined layered double hydroxides (Ni, Xia, Wang, Xing & Pan, 2007)
200
Alkali-Activated Multiwalled Carbon Nanotubes (Ma et al., 2012)
149
Pinecone derived activated carbon (Samarghandi, Hadi, Moayedi & Askari, 2009)
404.4
Ac ce p
te
d
M
mesoporous magnetic Co-NPs/carbon nanocomposites (Zhang, An, Guo & Wang, 2013)
Carbon nanotubes (Yao, Bing, Feifei & Xiaofeng, 2011)
351
29.41
cr
γ- Fe2O3/chitosan composite films (Jiang, Fu, Zhu, Yao & Xiao, 2012)
ip t
Q (mg g-1)
Adsorbents
35.4–64.7
Chitin/alginate magnetic nano-gel beads (MCAs) (Li, Du, Tao, Deng, Luo & Yang, 2010)
107.5
Porous CSGO1 aerogel (this work)
686.89
352 353 354 355
20
Page 20 of 28
Table 2 Comparison of the adsorption capacity of CSGO1 aerogel for AB10B
356
removal with other adsorbents
357
Q (mg g-1)
protonated crosslinked chitosan (Huang, Yang, Liu & Gong, 2013) Cross-linked chitosan (Yang, Huang & Liu, 2012)
9.43
ip t
Adsorbents
11.47
990.10
cr
cross-linked amino-starches (Cheng, Jiang, Ou, Li & Xiang, 2009)
14.51
Conducting Polyaniline/Iron Oxide Composite (Ahmad & Kumar, 2010)
about 60
us
Activated carbon prepared from scrap tires (Hoseinzadeh, Rahmanie, Asgari, McKay & Dehghanian, 2012)
an
Porous CSGO1 aerogel (this work) 358
4. Conclusions
M
359
573.47
We have prepared porous chitosan aerogels doped with graphene oxide
361
(CSGO aerogels) as highly effective adsorbent for two azo dyes MO and
362
AB10B. These aerogels have the property of high porosity (97.96 − 98.78 %),
363
extraordinarily high water absorption (5848 − 8917 %) and low density (0.021
365 366 367
te
Ac ce p
364
d
360
− 0.035 g cm-3). Its adsorption capacity for methyl orange (MO) can reach 686.89 mg g-1, which is the highest compared to those existing literature, and the adsorption capacity for AB10B is 573.47 mg g-1. Characterization of CSGO aerogels show that -NH2 groups on the CS chains have been reacted with the
368
oxygen-containing functional groups of GO, and the addition of GO can
369
improve the compressive strength and elastic response of these aerogels;
370
while low loading of GO present no obvious influence on the crystalline
371
properties of CS and the thermal stability of the CSGO material.
21
Page 21 of 28
Study of adsorption behavior shows that the adsorption ability of the CSGO
373
aerogel decreases with the increasing of pH values, and the adsorption
374
processes fit well with pseudo-second-order process. Since the prepared
375
porous aerogels are biodegradable, non-toxic, efficient, low-cost and easy to
376
prepare, these porous CSGO aerogels would be a potential alternative for dye
377
removal, and the current investigations may pave a way to the facile
378
fabrication of efficient CS-based porous materials for water purification and
379
environment remediation.
an
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ip t
372
380
Acknowledgment
382
This work was supported by the National Science Foundation of China
383
(21072221, 21172252). Supports from Mrs. Jin Huang, Institute of Organic
384
Chemistry, CAS (Shanghai, China) for DMA test are also appreciated.
385
Corresponding Author
386
* E-mail: [email protected]
388 389
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Tel: +86 -10-8825 6843; Fax: +86-10-8825 6092;
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Zhang, N., Qiu, H., Si, Y., Wang, W., & Gao, J. (2011). Fabrication of highly
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Page 26 of 28
516
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Co-NPs/carbon
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518
Sci, 389(1), 10-15. Zhu, H. Y., Jiang, R., Xiao, L., & Zeng, G. M. (2010). Preparation,
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characterization, adsorption kinetics and thermodynamics of novel
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multi-walled carbon nanotubes with enhanced adsorption properties for
523
methyl orange. Bioresour Technol, 101(14), 5063-5069.
enwrapping
nanosized
gamma-Fe2O3
and
cr
chitosan
ip t
519
us
524
Ac ce p
te
d
M
an
525
27
Page 27 of 28
Highlights
526
1. Porous chitosan aerogels doped with graphene oxide were simply prepared.
527
2. These aerogels own high porosity, high water adsorption and low density.
528
3. Its adsorption capacity for methyl orange can reach 686.89 mg g-1.
529 530
4. Its adsorption capacity for amido black 10B can reach 573.47 mg g-1.
ip t
525
Ac ce p
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d
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Page 28 of 28
S0144-8617(14)00939-4 http://dx.doi.org/doi:10.1016/j.carbpol.2014.09.041 CARP 9299
To appear in: Received date: Revised date: Accepted date:
16-6-2014 14-8-2014 6-9-2014
Please cite this article as: Wang, Y., Xia, G., Wu, C., Sun, J., Song, R., and Huang, W.,Porous chitosan doped with graphene oxide as highly effective adsorbent for methyl orange and amido black 10B, Carbohydrate Polymers (2014), http://dx.doi.org/10.1016/j.carbpol.2014.09.041 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Porous chitosan aerogels doped with graphene oxide as
2
highly effective adsorbent for methyl orange and amido
3
black 10B
4
Ying Wang, a Guangmei Xia,b Cong Wu, a Jing Sun,c Rui Song, a* Wei Huang d
us
cr
ip t
1
5
a
6
Academy of Sciences, Beijing, 100049, People’s Republic of China
7
b
8
Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences,
9
Beijing, 100190, China
an
College of Chemistry and Chemical Engineering, University of Chinese
d
M
Beijing National Laboratory for Molecular Sciences, CAS Key Laboratory of
10
c
11
Academy of Sciences, Shanghai 200050, China
15
Ac ce p
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Shanghai Institute of Microsystem and Information Technology, Chinese
16
amount of graphene oxide (CSGO aerogels) with high porosity (97.96 % −
17
98.78 %), extraordinarily high water absorption (5848 % − 8917 %) and low
18
density (0.021-0.035 g cm-3) were prepared and used as adsorbents for two
19
azo dyes methyl orange (MO) and amido black 10B (AB10B). The adsorption
12 13 14
d
Laboratory of Advanced Polymer Materials, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100080, China
ABSTRACT: In the current study, porous chitosan aerogels doped with small
1
Page 1 of 28
behavior of these CSGO aerogels and some influence factors such as pH
21
value, graphene oxide (GO) loading, concentration of pollutants, as well as
22
adsorption kinetics were studied. Specifically, the adsorption capacity for MO
23
is 686.89 mg g-1, the highest comparing with other publication results, and it is
24
573.47 mg g-1 for AB10B. Since they are biodegradable, non-toxic, efficient,
25
low-cost and easy to prepare, we believe that these porous CSGO aerogels
26
will be a promising candidate for dye removal.
27
KEYWORDS: Chitosan, Graphene oxide, Methyl orange, Amido black 10B,
28
Adsorption.
an
M
1. Introduction
29
us
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20
Nowadays the treatment of dyeing effluents has long been a major
31
concern. Most dye molecules in the effluent are known to be toxic, mutagenic
32
and carcinogenic (Chatterjee, Chatterjee, Lim & Woo, 2011b). Azo dyes
34 35 36
te
Ac ce p
33
d
30
constitute the largest class of colorants and are common aquatic pollutants, which own the –N=N– chromophore group and the aromatic structure. They are normally difficult to remove because they are largely non-biodegradable and are resistant to light and oxidizing agents (Anirudhan, Radhakrishnan &
37
Vijayan, 2013; Cheah, Hosseini, Khan, Chuah & Choong, 2013), and
38
adsorption process is proven as a reliable and effective act for this dye
39
treatment (Cheah, Hosseini, Khan, Chuah & Choong, 2013; Vimonses, Lei, Jin,
40
Chow & Saint, 2009). Aerogel is a porous material and has been used in the
2
Page 2 of 28
area of organic pollutants adsorption. Rao (Venkateswara Rao, Hegde &
42
Hirashima, 2007) et al. investigated the adsorption of organic liquids on silica
43
aerogel and found that the aerogel could adsorb the organic liquids and oils by
44
nearly 15 times of its own mass. El-Rassy (Abramian & El-Rassy, 2009) et al.
45
prepared titania aerogels by supercritical drying of wet alcogels which are
46
synthesized through a one-pot sol–gel process and its adsorption capacity for
47
Orange II is 420 mg g-1 at the optimal conditions.
us
cr
ip t
41
Chitosan (CS), the cationic (1-4)-2-amino-2-deoxy-β-D-glucan, is manily
49
produced from marine chitin by deacetylation (Muzzarelli, Boudrant, Meyer,
50
Manno, DeMarchis & Paoletti, 2012). As one of the most representative
51
biopolymers, it is a multifunctional polysaccharide comprising of copious
52
chelating groups including primary and secondary hydroxyl groups, as well as
53
highly reactive amino groups (Rinaudo, 2006). Meanwhile, it is low-cost,
54
non-toxic and biodegradable, so it has been considered as a green adsorbent
56 57 58
M
d
te
Ac ce p
55
an
48
for the removal of dyes (Crini & Badot, 2008; Chatterjee, Chatterjee, Lim & Woo, 2011a). However, the application of chitosan is limited because of its solubility in acid solution. Hence, it is necessary to crosslink chitosan in order to make it stable in acid solution (Liu et al., 2012).
59
Graphene oxide (GO) is an oxygen-rich carbonaceous layered material. It
60
has gained considerable attention as a significant adsorbent as plenty of
61
oxygen atoms on the basal plane and the edge of the sheets in the forms of
62
epoxy, hydroxyl, and carboxyl groups, protruding from its layers (Chen, Chen,
3
Page 3 of 28
Bai & Li, 2013; Travlou, Kyzas, Lazaridis & Deliyanni, 2013). Meanwhile, as a
64
significant carbonaceous layered material, the GO incorporation can enhance
65
the strength of polymer composites (Zhang, Qiu, Si, Wang & Gao, 2011).
66
Therefore, it will be interesting to prepare porous CS materials with
67
incorporation of GO.
cr
ip t
63
In this work, we prepared porous chitosan aerogels doped with graphene
69
oxide (CSGO aerogels) by crosslinking and freeze drying and used them as
70
highly effective adsorbents for two azo dyes, methyl orange (MO) and amido
71
black 10B (AB10B), which are widely used in chemical, textile, paper industries,
72
biological stain, paints, inks, plastics, and leather industries (Jalil et al., 2010;
73
Mittal, Thakur & Gajbe, 2013). Its adsorption capacity for MO is 686.89 mg g-1,
74
which is the highest compared to those existing literatures, and the adsorption
75
capacity for AB10B also reaches 573.47 mg g-1. Meanwhile, the effects of pH
76
values, concentration of pollutants, loading of graphene oxide on the
78 79 80
an
M
d
te
Ac ce p
77
us
68
adsorption for MO and AB10B as well as adsorption kinetics were studied.
2. Experiment 2.1 Materials
CS (Mn = 700 K, degree of deacetylation (DD) = 95 %) was purchased
81
from Zhejiang Yuhuan Marine Bio-chemical Co. Ltd. GO was prepared by
82
Hummer’s method, and the detail about its synthesis could be found elsewhere
83
(Cao, Yin & Song, 2013). Acetic acid, nitric acid, sodium hydroxide were
84
analytical-grade while MO and AB10B were biological stain and they were all
4
Page 4 of 28
85
from commercial suppliers (Sinopharm, Beijing) and used without further
86
purification. Methyl aldehyde (37% w/w aqueous solution) was from Alfa
87
Aesar.
ip t
2.2 Preparation of porous CSGO aerogels
88
Firstly, various amounts of GO aqueous solution (8mg mL-1) were added to
90
2 % (V/V) acetic acid aqueous solution to form GO acetic acid aqueous
91
solution (solution A). Then 0.6 g CS was dissolved into 15 ml solution A and
92
formed homogeneous CSGO mixture after being stirred for 1 h. Subsequently,
93
20μL 37 % methyl aldehyde aqueous solution was added to the CSGO mixture
94
dropwise with stirring in water bath at 50℃ and then CSGO hydrogels were
95
formed in one minute, following one hour standstill at 50℃. After that we cut
96
these hydrogels into small pieces and put them into water to swell for 40 min.
97
Subsequently, the swollen hydrogels were frozen below -18℃ and then
98
transferred to a lyophilizer (FD-1CE, Boyikang Co. Ltd., Beijing) with a
100 101 102 103
us
an
M
d
te
Ac ce p
99
cr
89
condenser temperature of -55℃ and inside pressure 20-30 Pa. After 2-day lyophilization process CSGO aerogels were obtained. In this case, CSGO aerogels with different GO contents, which is 1 wt%
(CSGO1), 3 wt% (CSGO3), were prepared, respectively. Similarly, CS aerogel was prepared in the absence of GO. 2.3 Calculation of the water absorption of CSGO aerogels
104
These CSGO aerogels were put into deionized water for one hour, and
105 106
their water adsorption was calculated according to the following equation:
5
Page 5 of 28
Water absorption (%) =
107
( Mt − M0) × 100% M0
where, M0 (g) and Mt (g) are the weight of the CSGO aerogels before and after
109
immersing into deionized water respectively. 2.4 Porosity and Density of porous CSGO aerogels
110
cr
The porosity and apparent density of the porous CSGO aerogels was
111
113
Porosity (%) =
114
Density =
us
calculated according to the following equation:
(Vt − Va) (Vt − Ma / ρ ) × 100%= × 100% Vt Vt
an
112
ip t
108
M
Vt Ma
where, Vt (cm3) is the total volume of CSGO aerogels, Va (cm3) is the actual
116
volume of the material, Ma (g) is the mass of the aerogels, and ρ (g cm-3) is the
117
actual density of the material. Each sample was measured in triplicate and the
118
average value was adopted.
120 121 122 123
te
Ac ce p
119
d
115
2.5 Batch adsorption experiments The stored MO and AB10B solution were prepared by directly dissolving
these compounds with known weight in deionized water. Batch adsorption experiments were carried out in 25 mL flasks, where M = 0.013-0.015 g of the adsorbents were put into V = 13-15 mL of MO or AB10B aqueous solutions
124
（the V/M was kept at 1 L/g） and allowed to adsorb at room temperature
125
(20±1℃) without stirring or shaking. At given time intervals, the concentrations
126
of pollutant solutions were measured and adsorbents were collected. The dye
6
Page 6 of 28
127
concentration was determined by the absorbance at 464 nm for MO and 610
128
nm for AB10B in the ultraviolet-visible (UV-Vis) spectrum. The adsorption capacity (Q) and adsorption efficiency (Ade) was calculated
129
( C0 − Ct ) V M
131
Qt=
132
Ade (%) =
( C0 − Ct ) × 100% C0
cr
ip t
according to the following equation:
us
130
where C0 (mg L-1) and Ct (mg L-1) are the concentrations of pollutants in
134
solution after 0 and t h, V (L) is the volume of solution and M (g) is the mass of
135
the adsorbent. Qt (mg g-1) is the apparent adsorption capacity of the porous
136
monoliths after t h , which if given a long enough adsorption period (the time
137
required to achieve the equilibrium adsorption state), is equal to the equilibrium
138
adsorption capacity Qe (mg g-1).
140 141 142 143
M
d
te
The time required to achieve the equilibrium adsorption state (te) was
Ac ce p
139
an
133
determined by the adsorption kinetic curve. The adsorption time in the adsorption experiments measuring Qe was set longer than te. 2.6 Characterization
X-ray powder diffraction data were collected on MSAL-XD3 with Cu Kα
144
radiation (λ = 0.1542 nm) at 40 kV and 40 mA. Scanning electron microscopy
145
was performed on a field emission SEM (Hitachi S-4800) at an accelerating
146
voltage of 10 kV. Thermo gravimetric analyzer curves were determined by
147
SDT-Q600 analyzer (TA Corp., US) at a heating rate of 10 ℃ min-1 in N2
7
Page 7 of 28
148
atmosphere. UV-visible spectra were recorded on a UV-2550 (Shimadzu
149
Corporation, Japan) at room temperature. Fourier transform infrared spectroscopy was carried out on a Nicolet
150
VERTEX 70 (Bruker) spectrometer using the attenuated total reflectance (ATR)
152
method at a resolution of 4 cm-1. The spectrum was generated and collected
153
16 times and corrected for the background noise.
us
cr
ip t
151
X-ray photoelectron spectrometer (XPS) measurements were taken via an
155
ESCALAB250Xi (Thermo Scientific, USA) using a unmonochromatic Al Kα line
156
at 1486.6 eV in an ultra-high-vacuum system with a base pressure 3 × 10−9
157
mbar and an analyzer pass energy of 150 eV, giving a full width at
158
half-maximum of 1.7 eV for the Au 4f7/2 peak. The binding-energy scale was
159
calibrated by assigning the main C1s peak at 284.8 eV. The XPS core-level
160
spectra were analyzed by decomposing each spectrum into individual mixed
161
Gaussian−Lorentzian peaks.
163 164 165
M
d
te
Ac ce p
162
an
154
Dynamic mechanical properties were measured using a dynamic
mechanical analyzer (DMA Q800, TA, US). Tests were carried out in the DMA multi-frequency – strain module with frequency of 0.1-15 Hz at a 35℃. Compressive strength of the porous CSGO aerogels were measured by
166
material testing machine (HY-0580，Hengyi Corp., Shanghai) with 50 %
167
compressed at a compressing rate of 2 mm min-1. The samples for
168
compressive strength were prepared without swelling in water for 40 min
8
Page 8 of 28
before freeze drying. Each sample was measured in triplicate and the average
170
value was adopted.
171
3. Results and discussion
172
3.1 Characterization of the CSGO monoliths
ip t
169
Fig. 1A-C shows the optical and SEM images of the CSGO aerogels,
174
indicating the porous network structure of the prepared aerogels. Fig. 1D-F
175
reveals water absorption, porosity and density of the prepared CSGO aerogels.
176
All the obtained aerogels have high porosity (97.96 − 98.78 %), extraordinarily
177
high water absorption ability (5848 − 8917 %) and low density (0.021 − 0.035 g
178
cm-3). The high porosity and water absorption ability should contribute to the
179
diffusion of dyes to the surface and interior regions of the porous CSGO
180
aerogels, leading to high adsorption abilities and rates for dyes .
Ac ce p
te
d
M
an
us
cr
173
181 182
Fig.1. Optical image (A) of CSGO1 aerogel; SEM image of CSGO1 (B) and CSGO3
183
(C) aerogels. Porosity (D), water absorption (E) and density (F) of the prepared
184
CSGO aerogels with different GO contents.
9
Page 9 of 28
185
Fig. 2 shows the XRD spectra of GO, CS and CSGO aerogels. Both the CS
187
and CSGO aerogels show a characteristic peak at about 2θ = 12.34゜and
188
20.25゜ attributed to chitosan, and no distinct changes are observed with the
189
increase of GO content, indicating that the GO has no obvious influence on the
190
crystalline properties of CS (Zhang, Qiu, Si, Wang & Gao, 2011). Meanwhile,
191
the characteristic diffraction peak of GO at 2θ = 11.76 ゜ is not clearly
192
demonstrated in the CSGO aerogels because of its low content.
te
d
M
an
us
cr
ip t
186
194
195 196 197
Ac ce p
193
Fig. 2. XRD spectra of CS and CSGO aerogels (A) and GO (B).
Fig. 3A shows the FTIR spectra of CS, CSGO aerogels and GO. Spectrum
of GO shows characteristic absorption bands of vibration of C–O at 1042 cm-1, C=C stretching mode of the sp2 carbon skeletal network at 1620 cm-1 and the
198
stretching vibration of carboxyl groups on the edges of the layer planes or
199
conjugated carbonyl groups at about 1714 cm-1, respectively (Szabó et al.,
200
2006; Titelman, Gelman, Bron, Khalfin, Cohen & Bianco-Peled, 2005;
201
Seredych, Petit, Tamashausky & Bandosz, 2009; Travlou, Kyzas, Lazaridis &
10
Page 10 of 28
Deliyanni, 2013). In comparison, all the GO-related peaks are not detected in
203
the CSGO spectra because of GO’s low content. The band at 1551 cm−1
204
corresponds to N-H bending of -NH2 (Fan, Luo, Li, Lu, Qiu & Sun, 2012; Ma,
205
Liu, Li & Wang, 2012). In the case of GO doped by 1% to 3% , the band of
206
–NH2 has shifted to a lower value from 1551 cm-1 to 1540 cm-1, which proves
207
that -NH2 groups on the CS chains have been reacted with the
208
oxygen-containing functional groups of GO (Fan, Luo, Li, Lu, Qiu & Sun,
209
2012).
an
us
cr
ip t
202
To further confirm the above issue, X-ray photoelectron spectra of CS,
211
CSGO1 and CSGO3 aerogels were analyzed (Fig.3B and Fig.3C ). The O1s
212
spectra were curve-fitted by two peaks: the first peak at 532.1 eV is due to O-H
213
groups, and the second at about 532.7 eV is relevant to O-C moieties (epoxy,
214
carboxyl groups) (Travlou, Kyzas, Lazaridis & Deliyanni, 2013). The peak
215
attributed to O-H groups increased in these CSGO aerogels, indicating the
217 218 219
d
te
Ac ce p
216
M
210
O-H formation by the reaction of the chitosan amino groups with the oxygen-containing functional group of GO, which is consistent with the FTIR result. The reaction mechanism can be shown as follow: R1-NH2 + :O-R2
Where R1 is the remaining structure besides –NH2 of chitosan, R2 is the
220 221
R1-NH2…O-R2
remaining structure besides –O: of GO.
222
11
Page 11 of 28
ip t cr us an M
223
Fig. 3. FTIR spectra of CS, GO, CSGO1 and CSGO3 aerogels (A); O1s XPS spectra
225
of neat CS (B) and CSGO1, CSGO3 aerogels (C).
te
d
224
The mechanical properties of the CSGO aerogels were investigated by the
231
Ac ce p
226
232
value over the entire angular frequency (0.1-15 rad s-1), which reveals that the
233
elastic response is predominant, implying that these aerogels have a
234
permanent network (Wu, Wen, Guo, Yang, Wang & Xu, 2013). The storage
235
modulus increases from 2.2-3.1 MPa to 3.3-4 MPa with the addition of 1 wt%
227 228 229 230
compression tests and the dynamic mechanical analysis (DMA), as shown in Fig. 4A-C. The compressive strength of the obtained samples was increased with the increase of GO content (Fig. 4A). The viscoelastic property and inter-structure can be further assessed by DMA test. For both CS and CSGO1 aerogels, the storage modulus value is much higher than the loss modulus
12
Page 12 of 28
236
GO, while the loss modulus decrease from 0.31-0.66 MPa to 0.1-0.4 MPa,
237
indicating that GO can improve the elastic response of the prepared aerogel.. Thermogravimetric (TG) analysis was carried out to investigate thermal
239
decomposition behavior of the CSGO aerogels, as shown in Fig. 4E and Fig.
240
4F. The differential thermogravimetric (DTG) curve of CSGO presents two
241
peaks with maxima at 180 °C and 280 °C respectively, corresponding to the
242
two weight loss stage of the thermogravimetry curves. The first peak is related
243
to the decomposition of surface functional groups of GO and the second peak
244
related to the degradation of chitosan based on the previous reports (Travlou,
245
Kyzas, Lazaridis & Deliyanni, 2013) and current results of pure GO and CS.
246
The CSGO aerogels show almost identical thermogravimetric curves
247
regardless of the different GO contents, indicating that low content of GO has
248
no detectable effect on the thermal stability of the CSGO material.
cr
us
an
M
d
te
Ac ce p
249 250 251 252 253
ip t
238
13
Page 13 of 28
ip t cr us
254
Fig.4. Histograms of the compressive strength of CS, CSGO1 and CSGO3
256
aerogels(A). Dynamic mechanical analysis of CS aerogel (B) and CSGO1 aerogel (C).
257
Thermogravimetry (E) and differential thermogravimetry (F) curves of GO, CS,
258
CSGO1 and CSGO3.
d
M
an
255
3.2.1 Effect of pH
265
Ac ce p
260
te
3.2 Adsorption of MO and AB10B by CSGO aerogel
259
266
adsorption is electrostatic attraction between the MO/AB10B and the
267
protonated amino groups. At lower pH, the amino groups of the CS
268
macromolecules become protonated, and electrostatic attraction between the
269
MO/AB10B and the protonated amino groups may contribute to the adsorption
261 262 263 264
Fig. 5A and Fig. 5B shows the equilibrium adsorption capacity for MO and
AB10B of the CSGO1 aerogel in 800 mg L-1 initial dye solution with different pH values, which were adjust at first and allowed to be free during adsorption. For both MO and AB10B, the adsorption ability of the CSGO1 aerogel decreases with the increasing of pH values. It is because the main force of the
14
Page 14 of 28
270
of the MO/AB10B onto the CSGO aerogel (Travlou, Kyzas, Lazaridis &
271
Deliyanni, 2013).
272
3.2.1 Effect of GO content Fig. 5C and Fig. 5D shows the equilibrium adsorption capacity for MO and
274
AB10B of the prepared aerogels in 800 mg L-1 initial dye solution at pH 8.45
275
and 7.79, respectively. The result show that the addition of 1 wt% or 3 wt% GO
276
has almost no effect on the adsorption capacity. The reason can be attributed
277
two aspects. On one hand, recent reports shows that GO exhibits low affinity
278
for anionic dyes, due to the strong electrostatic repulsion between them (Chen,
279
Chen, Bai & Li, 2013; Travlou, Kyzas, Lazaridis & Deliyanni, 2013). On the
280
other hand, although GO may enhance adsorption ability for dyes when
281
introduced into the porous material, the existence of carboxyl groups might
283 284 285 286
cr
us
an
M
d
te
Ac ce p
282
ip t
273
reduce the binding capacity of the amine groups for dyes due to electrostatic forces between the carboxyl and amine groups, which may decrease the adsorption capacity of the CSGO aerogel (Zhang, Qiu, Si, Wang & Gao, 2011). These two aspects cause the limited growth of the adsorption capacity as a whole.
3.2.3 Effect of contact time (adsorption kinetics)
287
Fig. 5E and Fig. 5F shows the effect of contact time on dye adsorption of
288 289
CSGO1 aerogel in 800 mg L-1 MO and AB10B solution. For the MO adsorption,
290
very fast dye removal occurs at the initial stage (0-10 h). Then, the dye
15
Page 15 of 28
adsorption is milder and more gradual during the second time period (10-60 h).
292
And at the last stage (60-84 h) the dye adsorption is characterized by the
293
equilibrium state. The fast adsorption in the initial stage might be due to the
294
fact that a large number of surface sites are available for adsorption. After a
295
period of adsorption, the remaining surface sites are more resistive for the dye
296
molecules to occupy because of the repulsion between the solute molecules of
297
the solid and bulk phases, which makes it milder and take a long time to reach
298
equilibrium (Travlou, Kyzas, Lazaridis & Deliyanni, 2013). And AB10B displays
299
the similar adsorption behavior.
M
300
an
us
cr
ip t
291
.
Ac ce p
te
302
d
301
16
Page 16 of 28
ip t cr us an M te
d 304 305 306
307
Ac ce p
303
Fig. 5. Adsorption of the CSGO1 aerogel for MO (A, C, E) and AB10B (B, D, F) in solutions (800 mg L-1) with different pH values, GO contents and time, respectively. Inset : optical images of diluted dye solution after adsorption.
To investigate the controlling mechanism of the adsorption processes,
308
pseudo-first-order and pseudo-second-order kinetic models were used to
309
study the experimental data obtained. The pseudo-first-order kinetic model is given as (Chiou & Li, 2002; Jiang,
310 311
Fu, Zhu, Yao & Xiao, 2012)
17
Page 17 of 28
log(Qe-Qt) = logQe-
312
The pseudo-second-order kinetic model can be expressed as (Chiou & Li,
313
ip t
2002; Jiang, Fu, Zhu, Yao & Xiao, 2012) t 1 t = + 2 Qt Qe k 2Qe
315
cr
314
K1 t 2. 303
where Qe and Qt are the amounts of MO/AB10B adsorbed (mg g-1) per unit of
317
adsorbent at equilibrium and at time t, respectively. k1 is the pseudo-first-order
318
rate constant (h-1). The rate constant (k1) and correlation coefficients (R2) are
319
determined from the linear plots of log(Qe - Qt) versus t. k2 is the
320
pseudo-second-order rate constant of adsorption (g mg-1 h-1). The rate
321
constant (k2) and correlation coefficients (R2) are determined from the linear
322
plots of
324 325 326 327
an
M
d te
t versus t. Qt
According to the correlation coefficients (R2), the pseudo-second-order
Ac ce p
323
us
316
equation provided an excellent fit for the experimental data of both MO (R2 = 0.9995) and AB10B (R2 = 0.9988) adsorption, compared with the (R2) data from pseudo-first-order equation, 0.9814 of MO and 0.9405 of AB10B, respectively.
3.2.3 Adsorption mechanism
328 329
We discuss the adsorption mechanism by FTIR (Fig.6) and take the
330
adsorption for AB10B as a representative. As shown, the amino peak at 1546
331
cm−1 of CSGO1 aerogel after dye adsorption presents a decrease and shifted
18
Page 18 of 28
to a lower wavenumber, which confirms the mechanism explaining the
333
interactions between the dye molecules and adsorbents (Travlou, Kyzas,
334
Lazaridis & Deliyanni, 2013; Liu, Zheng & Wang, 2010).
M
an
us
cr
ip t
332
335
Fig. 6. FTIR spectra of CSGO1 aerogel (a), AB10B loaded CSGO1 aerogels (b) and
337
AB10B dye (c).
te
The resultant CSGO1 aerogel presents a prominent adsorption capacity for
340 341 342 343
Ac ce p
338 339
d
336
MO and AB10B comparing with other reported adsorbents, and detail could be found in Table 1 and Table 2. As indicated, the adsorption capacity (Q) of the prepared porous CSGO1 aerogel is much higher than most reported adsorbents. In particular, the CSGO1 aerogel owns the highest Q value of MO among the related publications available. So the prepared porous CSGO
344
aerogels can be a kind of promising adsorbent for the removal of MO and
345
AB10B from aqueous solutions owing to its very high adsorption capacity,
346
low-cost, eco-friendly and easy preparation.
347
19
Page 19 of 28
348
Table 1 Comparison of the adsorption capacity of CSGO1 aerogel for MO removal
349
with other adsorbents
350
γ- Fe2O3/MWCNTs/chitosan (Zhu, Jiang, Xiao & Zeng, 2010)
an
us
Hypercrosslinked chloromethylated PS adsorbent functionalized with formaldehyde carbonyl groups (HJ-1) (Huang, Huang, Liu, Wang & Yan, 2008)
60.5–66.1
70.9–76.9
380
Acid modified carbon coated monolith (Cheah, Hosseini, Khan, Chuah & Choong, 2013)
132.7
Calcined layered double hydroxides (Ni, Xia, Wang, Xing & Pan, 2007)
200
Alkali-Activated Multiwalled Carbon Nanotubes (Ma et al., 2012)
149
Pinecone derived activated carbon (Samarghandi, Hadi, Moayedi & Askari, 2009)
404.4
Ac ce p
te
d
M
mesoporous magnetic Co-NPs/carbon nanocomposites (Zhang, An, Guo & Wang, 2013)
Carbon nanotubes (Yao, Bing, Feifei & Xiaofeng, 2011)
351
29.41
cr
γ- Fe2O3/chitosan composite films (Jiang, Fu, Zhu, Yao & Xiao, 2012)
ip t
Q (mg g-1)
Adsorbents
35.4–64.7
Chitin/alginate magnetic nano-gel beads (MCAs) (Li, Du, Tao, Deng, Luo & Yang, 2010)
107.5
Porous CSGO1 aerogel (this work)
686.89
352 353 354 355
20
Page 20 of 28
Table 2 Comparison of the adsorption capacity of CSGO1 aerogel for AB10B
356
removal with other adsorbents
357
Q (mg g-1)
protonated crosslinked chitosan (Huang, Yang, Liu & Gong, 2013) Cross-linked chitosan (Yang, Huang & Liu, 2012)
9.43
ip t
Adsorbents
11.47
990.10
cr
cross-linked amino-starches (Cheng, Jiang, Ou, Li & Xiang, 2009)
14.51
Conducting Polyaniline/Iron Oxide Composite (Ahmad & Kumar, 2010)
about 60
us
Activated carbon prepared from scrap tires (Hoseinzadeh, Rahmanie, Asgari, McKay & Dehghanian, 2012)
an
Porous CSGO1 aerogel (this work) 358
4. Conclusions
M
359
573.47
We have prepared porous chitosan aerogels doped with graphene oxide
361
(CSGO aerogels) as highly effective adsorbent for two azo dyes MO and
362
AB10B. These aerogels have the property of high porosity (97.96 − 98.78 %),
363
extraordinarily high water absorption (5848 − 8917 %) and low density (0.021
365 366 367
te
Ac ce p
364
d
360
− 0.035 g cm-3). Its adsorption capacity for methyl orange (MO) can reach 686.89 mg g-1, which is the highest compared to those existing literature, and the adsorption capacity for AB10B is 573.47 mg g-1. Characterization of CSGO aerogels show that -NH2 groups on the CS chains have been reacted with the
368
oxygen-containing functional groups of GO, and the addition of GO can
369
improve the compressive strength and elastic response of these aerogels;
370
while low loading of GO present no obvious influence on the crystalline
371
properties of CS and the thermal stability of the CSGO material.
21
Page 21 of 28
Study of adsorption behavior shows that the adsorption ability of the CSGO
373
aerogel decreases with the increasing of pH values, and the adsorption
374
processes fit well with pseudo-second-order process. Since the prepared
375
porous aerogels are biodegradable, non-toxic, efficient, low-cost and easy to
376
prepare, these porous CSGO aerogels would be a potential alternative for dye
377
removal, and the current investigations may pave a way to the facile
378
fabrication of efficient CS-based porous materials for water purification and
379
environment remediation.
an
us
cr
ip t
372
380
Acknowledgment
382
This work was supported by the National Science Foundation of China
383
(21072221, 21172252). Supports from Mrs. Jin Huang, Institute of Organic
384
Chemistry, CAS (Shanghai, China) for DMA test are also appreciated.
385
Corresponding Author
386
* E-mail: [email protected]
388 389
d
te
Ac ce p
387
M
381
Tel: +86 -10-8825 6843; Fax: +86-10-8825 6092;
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enwrapping
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chitosan
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Highlights
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1. Porous chitosan aerogels doped with graphene oxide were simply prepared.
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2. These aerogels own high porosity, high water adsorption and low density.
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3. Its adsorption capacity for methyl orange can reach 686.89 mg g-1.
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4. Its adsorption capacity for amido black 10B can reach 573.47 mg g-1.
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