Polyethylenimine-Functionalized Corn Bract, an Agricultural Waste

Article pubs.acs.org/JAFC

Polyethylenimine-Functionalized Corn Bract, an Agricultural Waste Material, for Efficient Removal and Recovery of Cr(VI) from Aqueous Solution Tiantian Luo,† Xike Tian,*,† Chao Yang,† Wenjun Luo,† Yulun Nie,† and Yanxin Wang‡ †

Faculty of Materials Science and Chemistry and ‡School of Environmental Studies, China University of Geosciences, Wuhan, Hubei 430074, People’s Republic of China ABSTRACT: In this study, polyethylenimine-functionalized corn bract (PEI−CB) was first used to remove aqueous Cr(VI) via the “waste control by waste” concept. The results indicated that PEI−CB had an excellent performance for Cr(VI) removal and the maximum removal capacity was 438 mg/g. The adsorption of Cr(VI) was fitted to the Langmuir model, and kinetics of uptake could be described by a pseudo-second-order rate model well. Amine was proven to be the active center for Cr(VI) adsorption and partial reduction to Cr(III), while removal efficiency was enhanced at a lower pH value and higher temperature. Besides, nanosized Cr2O3 with a high purity was obtained by simple calcination of a Cr(VI)-laden adsorbent. Hence, this study provided a novel strategy for Cr(VI) wastewater remediation and pure Cr2O3 recovery. Prepared PEI−CB was then a promising alternative of low cost for replacement of the current expensive absorbent of removing Cr(VI) from wastewater from the view of sustainability. KEYWORDS: corn bract, modification, polyethylenimine, Cr(VI) removal, recovery

1. INTRODUCTION Hexavalent chromium, Cr(VI), is hazardous at high levels as a result of its high biotoxicity and carcinogenicity.1 The maximum contaminant limits of total chromium in drinking water were set at 100 and 50 μg/L by the United States Environmental Protection Agency (U.S. EPA) and the World Health Organization (WHO), respectively.2,3 Because improper treatment will damage the environment and the health of people seriously, low-cost and highly effective strategies for treating Cr(VI)-containing wastes are in great demand all over the world.4,5 At present, conventional methods for the Cr(VI) removal include adsorption, chemical reduction precipitation, membrane separation, ion exchange, etc.6−11 However, the reduction precipitation can consume chemical reagents and produce toxic sludge, resulting in secondary pollution. The membrane separation and ion-exchange processes are costly and complex.12 Therefore, there is a strong need to develop a cheap and environmentally friendly solid adsorbent with high efficiency for Cr(VI) removal. For corn bract (CB), as a typical agricultural waste,13 open burning is a usual disposal method and occurs more frequently in grain-producing regions, with increasing crop yields in China.14 However, the burning has been considered as an important source of carbonaceous species. It has been estimated that elemental carbon (EC) emission from agricultural field burning was 26 times higher in 2009 than in 1980 in China.15,16 The emissions have become more serious in recent years and cause regional environmental pollution. Hence, it is also necessary to find a new way for CB disposal to be environmentally friendly. CB has a two-dimensional (2D) framework and is composed of lignocellulosic materials (54− 58%) that contain many functional groups,17 which are suitable for use as adsorbents. The use of CB as an adsorbent can not only save money as a result of the reduced need for traditional © 2017 American Chemical Society

agricultural waste disposal but also promote recycling and reuse. However, the original CB has little or no capacity for the removal of heavy metal cations because there is little or no adsorption sites on the surfaces. Therefore, it is necessary to develop effective methods to modify the surface of CB.18,19 Amine-functionalized clay is effective in removing anionic metal species because the amine groups are easily protonated and, thus, could remove anionic metal species via electrostatic interaction or hydrogen binding. Polyethylenimine (PEI)modified halloysite showed good adsorption ability for Cr(VI) as a result of the presence of a large number of primary and secondary amine groups per molecule.4,20 The high surface area, natural shape, abundant surface active site, and tunable surface chemistry of CB enabled it to be modified by an organic polymer and used as a promising adsorbent. However, few studies have been conducted to use the modified CB for Cr(VI) adsorption. Moreover, Cr is an expensive element, in which Cr2O3 was widely used in lithium storage and corrosion protection.12 To recover Cr2O3 from the Cr-laden adsorbent has great economic incentives and good potential for technology development. Chemical, electrochemical, and biological methods have been used to convert Cr(VI) to less toxic Cr(III) and even recover the Cr element, which are generally energy- and chemically intensive.3,21−23 Hence, a novel strategy on Cr(VI) removal and Cr2O3 recovery was proposed in this study. PEI grafting was used to increase the adsorption capacity of CB, and calcination of a Cr-laden-modified CB adsorbent was used to recover Cr2O3 via the carbonization process. The results indicated that Received: Revised: Accepted: Published: 7153

June 11, 2017 July 25, 2017 July 28, 2017 July 28, 2017 DOI: 10.1021/acs.jafc.7b02699 J. Agric. Food Chem. 2017, 65, 7153−7158

Article

Journal of Agricultural and Food Chemistry

experiments. The isothermal adsorption experiments were conducted by varying the concentration of Cr(VI) from 20 to 200 mg/L (pH 2). The flasks were kept in an isothermal shaker for 24 h to reach equilibrium of the solution with the solid mixture. Langmuir and Freundlich isotherm models were used to fit the equilibrium data of adsorption of Cr(VI) on the PEI−CB. The influence of solution pH (2, 3, 4, 5, 6, and 7) and temperature (293, 303, 313, and 323 K) on Cr(VI) adsorption was also investigated. Finally, the Cr-laden absorbent was calcined at 500 °C for 2 h in a muffle furnace; the residue was collected; and pure Cr2O3 was then recovered.

Cr(VI) was efficiently removed with a maximum capacity of 438 mg/g at 323 K and nanosized Cr2O3 with high purity was also obtained. The proposed strategy was in accordance with the “waste control by waste” concept. The modified CB as an inexpensive and efficient solid adsorbent provides a promising alternative for Cr(VI) wastewater remediation from the view of sustainability.

2. MATERIALS AND METHODS 2.1. Chemicals and Materials. Original CB was collected from Henan province, central China, and naturally air-dried before use. Epichlorohydrin (ECH) and sodium hydroxide (NaOH) were obtained from Sinopharm Chemical. Aluminum chloride (AlCl3) was purchased from KaiTong Chemical Reagent, Ltd. (Tianjin, China). Arginine (Arg) and urea was purchased from Aladdin Chemical Company. PEI (molecular weight of 70 000) was purchased from Shanghai Macklin Biochemical Co., Ltd. Other chemicals were of analytical grade and used without further purification. 2.2. PEI Functionalization of CB. As shown in Figure 1, CB was first treated by a 7 wt % NaOH and 12 wt % urea solution for 30 min

3. RESULTS AND DISCUSSION 3.1. Characterization of PEI−CB. Figure 2 depicted the FTIR spectra of CB before and after PEI modification. For CB

Figure 2. FTIR spectra of (a) original CB and (b) PEI−CB.

in Figure 2a, the broad band at 3424 cm−1 can be assigned to the O−H stretching vibration and the band at 2900 cm−1 was attributed to the C−H stretching of the methyl group.25,26 The peaks at 1732 and 1520 cm−1 corresponded to CO and the benzene stretching vibration of lignin as a result of the decrystallization process by NaOH and urea, respectively.27 Besides, the bands at 1637 and 1042 cm−1 are the characteristic peaks of the CC bond and skeletal vibrations involving C−O stretching, respectively.28 After modification of CB by PEI (Figure 2b), the spectrum of PEI−CB exhibits obvious changes. The new peaks at 2924 and 2873 cm−1 are ascribed to the C−H stretching from the −CH2 group of PEI,26,29 while the decreased peak intensity at 3424, 1732, 1637, and 1042 cm−1 further indicated the disappearance of the −OH group and successful grafting of PEI on the surface of CB. As shown in Figure 3, the surface morphology of CB also changed a lot after

Figure 1. Synthetic route of PEI−CB. at −12 °C to expose hydroxyl groups by reducing the crystallinity of cellulose macromolecules.24 Then, 5.0 g of CB was put into 200 mL of 5 wt % arginine solution and reacted for 12 h at 313 K in the presence of 0.25 g of AlCl3. After washing with deionized water several times and drying for 6 h at 50 °C, the obtained material was transferred into a mixture of 10 mL of ECH and 20 mL of 2.5 mol/L NaOH under stirring at 40 °C for 12 h. After washing with methyl alcohol several times and being kept in a hot air oven at 50 °C for 6 h, the obtained CB was put into 10 mL of PEI (30%, w/v) solution for 24 h at 100 °C, followed by drying in air at 50 °C for 6 h. PEI−CB was then obtained and used for further experiments. 2.3. Characterization. A scanning electron microscopy (SEM) image was used to examine the morphology by Hitachi SU8010 field emission scanning electron microscopy (FESEM, 15 kV, Hitachi, Japan) and transmission electron microscopy (TEM, CM 12, Philips, Netherlands). Fourier transform infrared (FTIR) spectra were obtained on an instrument (Thermo Nicolet AVATAR360, , Waltham, MA, U.S.A.) using the standard KBr disk method. X-ray photoelectron spectroscopy (XPS, MULTILAB2000, Thermo Electron Corporation, Waltham, MA, U.S.A.) was used in the surface analysis of samples. Powder X-ray diffraction (XRD) patterns of materials were obtained with a diffractometer (Rigaku D/max-βB) using a Cu Kα radiation source (λ = 0.154 32 nm, Bruker AXS D8-Focus X, Germany). The Cr(VI) concentration was detected with the 1,5-diphenylcarbazide method, using an ultraviolet−visible (UV−vis, TU-1800PC, China) spectrophotometer at λ = 540 nm. 2.4. Batch Experiments. Adsorption experiments were carried out in a 150 mL conical flask containing about 20 mg of PEI−CB and 100 mL of Cr(VI) solution prepared with K2Cr2O7, which was shaken at 200 rpm in a thermostatic shaker. For the adsorption kinetic tests, about 20 mg of adsorbent was added to 100 mL of 100 mg/L Cr(VI) under stirring at pH of 2.0 and stirring continued for a specified time (0−24 h). The pseudo-first-order and pseudo-second-order kinetic models were applied to fit experimental data obtained from batch

Figure 3. SEM images of (a) original CB and (b) PEI−CB.

PEI modification. In comparison to original CB in Figure 3a, the surface of PEI−CB (Figure 3b) became smoother and denser with a plastic-like coat, which indicated that PEI was successfully anchored on the surface of CB. Furthermore, in comparison to CB in Figure 4a, the existence of the N element (8.86 atomic % in Figure 4b) on the surface of PEI−CB by 7154

DOI: 10.1021/acs.jafc.7b02699 J. Agric. Food Chem. 2017, 65, 7153−7158

Article


model.30 Moreover, Langmuir and Freundlich models were applied to fit to experimental data. It can be clearly seen from Figure 5B and Table 2 that higher correlation coefficients are obtained with the Langmuir model. The model assumes a monolayer adsorption onto a homogeneous surface, where binding sites have equal affinity and energy.31 The results revealed that the adsorption capacity was 438 mg/g at an ambient temperature of 323 K, which showed much higher capacity toward Cr(VI) than that of TiO2 (33.9 mg/g),32 ethylenediamine (EDA)-modified magnetic chitosan resin (51.8 mg/g),33 amino-functionalized MSC composite (171.5 mg/g),34 and PEI-immobilized acrylate-based beads (140.6 mg/g),35 and its capacity was also comparable to aerobic granules functionalized with PEI (401.5 mg/g).36 Figure 6 showed the effect of initial solution pH (2−7) on the adsorption capacity of PEI−CB for Cr(VI). Obviously, the Cr(VI) adsorption was significantly pH-dependent. The adsorption capacity decreased with the rising solution pH, and lower pH favored the Cr(VI) adsorption. The amino group of PEI will be protonated to form the positively charged sites (such as −NH3+) and result in the electrostatic attraction with negatively charged Cr(VI).37,38 Hence, pH 2.0 was selected as the optimum pH value for the following adsorption experiments. The effect of the temperature on Cr(VI) adsorption was also investigated, and the results were present in Figure 7. The Cr(VI) adsorption uptake was found to increase with an increasing solution temperature from 293 to 323 K, which indicates the endothermic nature of the adsorption process. The Gibbs free energy is the fundamental indicator for criterion of spontaneity, and the adsorption can occur spontaneously at a given temperature if ΔG is negative.39 Hence, as depicted in Table 3, a higher temperature results in a much lower ΔG and an great increase of entropy change, which were then beneficial to the increased rate of diffusion of Cr(VI) as the adsorbate across the external boundary layer and its removal efficiency over PEI−CB.40,41 3.3. Adsorption Mechanism. As depicted in panels c and d of Figure 4, the Cr element appeared on PEI−CB after adsorption with a content of 19.94 atomic %. The EDX mapping analysis further showed that the Cr element was highly dispersed on the surface of PEI−CB. Because the adsorption process followed the Langmuir model (monolayer adsorption), Cr(VI) was anchored on the surface of PEI−CB via electrostatic attraction and hydrogen binding (Figure 8a) As reported, a surface complex was formed between the ligand in the absorbent and the metal ions; hence, the immobilization of PEI can provide more adsorption sites for Cr(VI) adsorption.42 Although it was difficult to clarify their separate contribution to Cr(VI) removal, the hydrogen-bonding interactions were between hydrogen atoms in amino groups and oxygen atoms in HCrO4−.43 The adsorption process was usually determined by the functional groups on the surface of the adsorbent. Hence, the XPS technique was used to study the surface chemical composition of PEI−CB before and after Cr(VI) adsorption. As shown in Figure 9B, two strong peaks at 397.9 and 398.6 eV were attributed to N− and −NH2 groups of

Figure 4. EDX analysis of (a) CB, (b) PEI−CB, and (c) Cr-loaded PEI−CB and (d) mapping of the Cr element.

energy-dispersive X-ray (EDX) analysis also proved the successful PEI immobilization on CB. 3.2. Excellent Performance of PEI−CB for Cr(VI) Removal. Figure 5A showed the effect of the contact time

Figure 5. (A) Effects of the contact time on Cr(VI) adsorption of PEI−CB and (B) adsorption isotherm study model: Langmuir and Freundlich.

on Cr(VI) adsorption over PEI−CB using the initial concentration of 100 mg/L at pH 2.0. The adsorption capacity of PEI−CB to Cr(VI) increased rapidly within 6.6 h. Thereafter, it continued to increase at a slower rate and finally approached adsorption equilibrium after 24 h. The pseudo-firstorder and pseudo-second-order kinetic models were fitted to the adsorption kinetic data. The parameters of kinetic models were illustrated in Table 1. In comparison to that of the pseudo-first-order kinetic model, the calculated value qcal of the pseudo-second-order kinetic model was closer to the experimental value qexp, and the plots show quite good linearity, with R2 values of 0.986. Therefore, the adsorption kinetics followed the pseudo-second-order model well, suggesting a chemisorption process. It also means that the adsorption rate is proportional to the square of the number of free sites, which corresponds to the term (qe − qt)2 in the pseudo-second-order

Table 1. Kinetic Parameters for Adsorption of Cr(VI) onto PEI−CB pseudo-first-order kinetic model

pseudo-second-order kinetic model 2

adsorbate

qexp (mg/g)

qcal (mg/g)

k1

R

Cr(VI)

438.1406

399.01

0.01941

0.903 7155

qcal (mg/g)

k2

R2

432.41

0.00061

0.986


Article

Journal of Agricultural and Food Chemistry Table 2. Adsorption Isotherm Constants for Cr(VI) Adsorption onto PEI−CB Langmuir isotherm constants

Freundlich isotherm constants

T (K)

qm (mg/g)

KL (L/g)

R2

KF (mg1 − 1/n L1/n g−1)

1/n

R2

323

517.01674

0.0646

0.985

101.89

0.31304

0.934

Figure 8. (a) Possible linkages of Cr(VI) on PEI−CB and (b) possible reduction process of Cr(VI) to Cr(III) on PEI−CB. Figure 6. Effect of the initial pH on Cr(VI) adsorption by PEI−CB.

Figure 7. (a) Effect of the temperature on Cr(VI) adsorption by PEI− CB and (b) linear plot of ln(qe/Ce) versus 100/T for the adsorption of Cr(VI) on PEI−CB.

PEI in PEI−CB. After adsorption of Cr(VI), the peak intensity of N− decreased greatly and a new peak of the protonated amine group (−NH3+) centered at 400.1 eV appeared. It indicated that Cr(VI) was bonded onto the protonated amine groups of PEI. The high-resolution XPS spectra of the Cr 2p region can be curve-fitted with four components (Figure 9A), in which the peaks at 578.4 and 587.4 eV can be assigned to Cr(VI), while the binding energies at 575.6 and 585.6 eV are the characteristic peaks of Cr(III).44 The existence of Cr(III) suggested that adsorbed Cr(VI) was partially reduced to less toxic Cr(III) as a result of the electron transfer from the amine group of PEI.20 As shown in Figure 8b, the process of adsorption and reduction can be explained as follows: First, the amine groups on the PEI−CB are protonated to adsorb Cr(VI). Then, the reduction reactions may proceed. The electrons required for reduction of Cr(VI) came from electron-donor groups of the biomass.45 Finally, with the help of electrons, Cr(VI) can be reduce to Cr(III). Similar results have also been reported. The thermodynamic behavior of Cr(VI) adsorption onto PEI−CB was also evaluated. As shown in Figure 7B,

Figure 9. XPS of (A) Cr 2p after adsorption, (B) N 1s before and after Cr(VI) adsorption, and (C) Cr 2p after calcination at 500 °C.

plotting ln(qe/Ce) against 100/T gave a straight line. The slope and intercept are equal to −ΔH/R and ΔS/R, respectively. As shown in Table 3, the four negative ΔG values showed that the adsorption process was spontaneous and a higher temperature favored the adsorption. At a higher temperature, the interaction between the solvent and solid surface led to a greater number of adsorption sites, enhancing the possibility of Cr(VI) adsorption onto PEI−CB.40 3.4. Successful Cr2O3 Recovery. A Cr-laden absorbent was calcined at 500 °C for 2 h in a muffle furnace, and the residue was collected and characterized by XPS. The peaks at binding energies of 576.4 and 586.4 eV were assigned to Cr(III). No signal for the characteristic peaks of Cr(VI) was found, indicating the total reduction of Cr(VI) to Cr(III). As shown in Figure 10a, the obtained product exhibited a

Table 3. Thermodynamic Parameters at Four Different Temperaturesa

a

absorbent

ΔS (J mol−1 K−1)

ΔH (kJ mol−1)

T (K)

ΔG (kJ mol−1)

PEI−CB

55.45

12.35

293 303 313 323

−3.897 −4.451 −5.006 −5.560

Reaction conditions: Cr(VI) ion concentration, 100 mg/L; pH, 2.0; and contact time, 24 h. 7156


Article


Efficient Removal of Cr(VI). ACS Sustainable Chem. Eng. 2016, 4 (8), 4361−4369. (6) Lu, A.; Zhong, S.; Chen, J.; Shi, J.; Tang, J.; Lu, X. Removal of Cr(VI) and Cr(III) from Aqueous Solutions and Industrial Wastewaters by Natural Clino-pyrrhotite. Environ. Sci. Technol. 2006, 40 (9), 3064−3069. (7) Kocurek, P.; Kolomazní, K.; Bařinová, M. Chromium removal from wastewater by reverse osmosis. WSEAS Trans. Environ. Dev. 2014, 10 (1), 358−365. (8) D’Angelo, A.; Galia, A.; Scialdone, O. Cathodic abatement of Cr(VI) in water by microbial reverse-electrodialysis cells. J. Electroanal. Chem. 2015, 748, 40−46. (9) Dharnaik, A. S.; Ghosh, P. K. Hexavalent chromium [Cr(VI)] removal by the electrochemical ion-exchange process. Environ. Technol. 2014, 35 (18), 2272−2279. (10) Sun, M.; Zhang, G.; Qin, Y.; Cao, M.; Liu, Y.; Li, J.; Qu, J.; Liu, H. Redox Conversion of Chromium(VI) and Arsenic(III) with the Intermediates of Chromium(V) and Arsenic(IV) via AuPd/CNTs Electrocatalysis in Acid Aqueous Solution. Environ. Sci. Technol. 2015, 49 (15), 9289−9297. (11) Goyal, R. K.; Jayakumar, N. S.; Hashim, M. A. A comparative study of experimental optimization and response surface optimization of Cr removal by emulsion ionic liquid membrane. J. Hazard. Mater. 2011, 195 (1), 383−390. (12) Sun, B.; Reddy, E. P.; Smirniotis, P. G. Visible light Cr(VI) reduction and organic chemical oxidation by TiO2 photocatalysis. Environ. Sci. Technol. 2005, 39 (16), 6251−6259. (13) Xu, C.; Ma, F.; Zhang, X.; Chen, S. Biological pretreatment of corn stover by Irpex lacteus for enzymatic hydrolysis. J. Agric. Food Chem. 2010, 58 (20), 10893−10898. (14) Hahnen, S.; Joeris, T.; Kreuzaler, F.; Peterhänsel, C. Quantification of photosynthetic gene expression in maize C3 and C4 tissues by real-time PCR. Photosynth. Res. 2003, 75 (2), 183−192. (15) Wang, X.; Chen, Y.; Tian, C.; Huang, G.; Fang, Y.; Zhang, F.; Zong, Z.; Li, J.; Zhang, G. Impact of agricultural waste burning in the Shandong Peninsula on carbonaceous aerosols in the Bohai Rim, China. Sci. Total Environ. 2014, 481 (1), 311−316. (16) Cheng, M. T.; Horng, C. L.; Su, Y. R.; Lin, L. K.; Lin, Y. C.; Chou, C. K. Particulate matter characteristics during agricultural waste burning in Taichung City, Taiwan. J. Hazard. Mater. 2009, 165 (1−3), 187. (17) Yang, M. X.; Zhou, R. Research on Degumming Experiment of Corn Bracts. Adv. Mater. Res. 2012, 550−553, 1242−1247. (18) Zhou, Y.; Jin, Q.; Zhu, T.; Ma, T.; Hu, X. Removal of Chromium (VI) from Aqueous Solution by Cellulose Modified with DGlucose. Sep. Sci. Technol. 2012, 47 (1), 157−165. (19) Gurgel, L. V.; Perin de Melo, J. C.; de Lena, J. C.; Gil, L. F. Adsorption of chromium (VI) ion from aqueous solution by succinylated mercerized cellulose functionalized with quaternary ammonium groups. Bioresour. Technol. 2009, 100 (13), 3214−3220. (20) Tian, X.; Wang, W.; Tian, N.; Zhou, C.; Yang, C.; Komarneni, S. Cr(VI) reduction and immobilization by novel carbonaceous modified magnetic Fe3O4/halloysite nanohybrid. J. Hazard. Mater. 2016, 309, 151−156. (21) Zhang, H. K.; Lu, H.; Wang, J.; Zhou, J. T.; Sui, M. Cr(VI) Reduction and Cr(III) Immobilisation by Acinetobacter sp. HK-1 with the Assistance of a Novel Quinone/Graphene Oxide Composite. Environ. Sci. Technol. 2014, 48 (21), 12876−12885. (22) Yang, Y.; Wang, G.; Deng, Q.; Ng, D. H.; Zhao, H. Microwaveassisted fabrication of nanoparticulate TiO2 microspheres for synergistic photocatalytic removal of Cr(VI) and methyl orange. ACS Appl. Mater. Interfaces 2014, 6 (4), 3008. (23) Cheng, Y.; Yan, F.; Huang, F.; Chu, W.; Pan, D.; Chen, Z.; Zheng, J.; Yu, M.; Lin, Z.; Wu, Z. Bioremediation of Cr(VI) and Immobilization as Cr(III) by Ochrobactrum anthropi. Environ. Sci. Technol. 2010, 44 (16), 6357−6363. (24) Das, R.; Ghorai, S.; Pal, S. Flocculation characteristics of polyacrylamide grafted hydroxypropyl methyl cellulose: An efficient biodegradable flocculant. Chem. Eng. J. 2013, 229 (4), 144−152.

Figure 10. (a) XRD patterns, (b) TEM image, and (c) photograph of the calcined product at 500 °C.

characteristic XRD pattern of pure Cr2O3. It was reported that a reduction process occurred in carbonization of the metalcontained carbon precursor. For example, formaldehyde can serve as a reducing agent for AgNO3. Hence, adsorbed Cr(VI) was converted to Cr(III), and Cr2O3 was then recovered during the carbonization of the Cr-laden PEI−CB. The TEM image further suggested that nanosized Cr2O3 was obtained with a diameter below 100 nm.

■

AUTHOR INFORMATION

Corresponding Author

*Telephone/Fax: +86-27-67884574. E-mail: [email protected]. cn. ORCID

Xike Tian: 0000-0001-9406-5291 Funding

The authors are grateful to the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (41521001) for the financial support. The project was also supported by the National Natural Science Foundation of China (51371162) and the “Fundamental Research Funds for the Central Universities”. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The authors are deeply indebted to a number of people without whose encouragement and assistance this thesis would not have been completed.

■

REFERENCES

(1) Namieśnik, J.; Rabajczyk, A. Speciation Analysis of Chromium in Environmental Samples. Crit. Rev. Environ. Sci. Technol. 2012, 42 (4), 327−377. (2) Jiang, W.; Cai, Q.; Xu, W.; Yang, M.; Cai, Y.; Dionysiou, D. D.; O’Shea, K. E. Cr(VI) adsorption and reduction by humic acid coated on magnetite. Environ. Sci. Technol. 2014, 48 (14), 8078−8085. (3) Bick, A. N. California’s Office of Environmental Health Hazard Assessment (OEHHA) Proposes New, More Stringent, Drinking Water Standard for Hexavalent Chromium; Office of Environmental Health Hazard Assessment (OEHHA): Oakland, CA, 2009. (4) Chen, J. H.; Xing, H. T.; Guo, H. X.; Weng, W.; Hu, S. R.; Li, S. X.; Huang, Y. H.; Sun, X.; Su, Z. B. Investigation on the adsorption properties of Cr(VI) ions on a novel graphene oxide (GO) based composite adsorbent. J. Mater. Chem. A 2014, 2 (31), 12561−12570. (5) Zhu, K.; Gao, Y.; Tan, X.; Chen, C. Polyaniline-Modified Mg/Al Layered Double Hydroxide Composites and Their Application in 7157


Article


photocatalytic reduction of Cr(VI) in aqueous solution. Mater. Sci. Semicond. Process. 2015, 39, 362−370. (44) Ai, Z.; Cheng, Y.; Zhang, L.; Qiu, J. Efficient removal of Cr(VI) from aqueous solution with Fe@Fe2O3 core−shell nanowires. Environ. Sci. Technol. 2008, 42 (18), 6955−6960. (45) Park, D.; Yun, Y. S.; Park, J. M. Studies on hexavalent chromium biosorption by chemically-treated biomass of Ecklonia sp. Chemosphere 2005, 60 (10), 1356−1364.

(25) Tang, F.; Huang, X.; Zhang, Y.; Guo, J. Effect of dispersants on surface chemical properties of nano-zirconia suspensions. Ceram. Int. 2000, 26 (1), 93−97. (26) Anirudhan, T.; Rauf, T. A. Adsorption performance of amine functionalized cellulose grafted epichlorohydrin for the removal of nitrate from aqueous solutions. J. Ind. Eng. Chem. 2013, 19 (5), 1659− 1667. (27) Ralph, J.; Akiyama, T.; Coleman, H. D.; Mansfield, S. D. Effects on Lignin Structure of Coumarate 3-Hydroxylase Downregulation in Poplar. J. Biol. Chem. 2012, 5 (13), 8843−8853. (28) Jermakowicz-Bartkowiak, D. Preparation, characterisation and sorptive properties towards noble metals of the resins from poly(vinylbenzyl chloride) copolymers. React. Funct. Polym. 2005, 62 (1), 115−128. (29) Patil, S. K. R.; Heltzel, J.; Lund, C. R. F. Comparison of Structural Features of Humins Formed Catalytically from Glucose, Fructose, and 5-Hydroxymethylfurfuraldehyde. Energy Fuels 2012, 26 (8), 5281−5293. (30) Yu, F.; Wu, Y.; Li, X.; Ma, J. Kinetic and thermodynamic studies of toluene, ethylbenzene, and m-xylene adsorption from aqueous solutions onto KOH-activated multiwalled carbon nanotubes. J. Agric. Food Chem. 2012, 60 (50), 12245−12253. (31) Redlich, O.; Peterson, D. L. A Useful Adsorption Isotherm. J. Phys. Chem. 1959, 63 (6), 1024. (32) Asuha, S.; Zhou, X. G.; Zhao, S. Adsorption of methyl orange and Cr(VI) on mesoporous TiO2 prepared by hydrothermal method. J. Hazard. Mater. 2010, 181 (1−3), 204−210. (33) Hu, X. J.; Wang, J. S.; Liu, Y. G.; Li, X.; Zeng, G. M.; Bao, Z. L.; Zeng, X. X.; Chen, A. W.; Long, F. Adsorption of chromium (VI) by ethylenediamine-modified cross-linked magnetic chitosan resin: Isotherms, kinetics and thermodynamics. J. Hazard. Mater. 2011, 185 (1), 306−314. (34) Sun, X.; Yang, L.; Li, Q.; Zhao, J.; Li, X.; Wang, X.; Liu, H. Amino-functionalized magnetic cellulose nanocomposite as adsorbent for removal of Cr(VI): Synthesis and adsorption studies. Chem. Eng. J. 2014, 241 (4), 175−183. (35) Bayramoğlu, G.; Yakuparica, M. Adsorption of Cr(VI) onto PEI immobilized acrylate-based magnetic beads: Isotherms, kinetics and thermodynamics study. Chem. Eng. J. 2008, 139 (1), 20−28. (36) Sun, X. F.; Ma, Y.; Liu, X. W.; Wang, S. G.; Gao, B. Y.; Li, X. M. Sorption and detoxification of chromium(VI) by aerobic granules functionalized with polyethylenimine. Water Res. 2010, 44 (8), 2517− 2524. (37) Li, Y.; Gao, B.; Wu, T.; Sun, D.; Li, X.; Wang, B.; Lu, F. Hexavalent chromium removal from aqueous solution by adsorption on aluminum magnesium mixed hydroxide. Water Res. 2009, 43 (12), 3067−3075. (38) Zhao, G.; Li, J.; Ren, X.; Chen, C.; Wang, X. Few-layered graphene oxide nanosheets as superior sorbents for heavy metal ion pollution management. Environ. Sci. Technol. 2011, 45 (24), 10454− 10462. (39) Wang, S.; Zhai, Y.-Y.; Gao, Q.; Luo, W.-J.; Xia, H.; Zhou, C.-G. Highly Efficient Removal of Acid Red 18 from Aqueous Solution by Magnetically Retrievable Chitosan/Carbon Nanotube: Batch Study, Isotherms, Kinetics, and Thermodynamics. J. Chem. Eng. Data 2014, 59 (1), 39−51. (40) Gao, Q.; Zhu, H.; Luo, W. J.; Wang, S.; Zhou, C. G. Preparation, characterization, and adsorption evaluation of chitosan-functionalized mesoporous composites. Microporous Mesoporous Mater. 2014, 193 (3), 15−26. (41) Lequin, S.; Chassagne, D.; Karbowiak, T.; Gougeon, R.; Brachais, L.; Bellat, J. P. Adsorption equilibria of water vapor on cork. J. Agric. Food Chem. 2010, 58 (6), 3438−3445. (42) Shukla, A.; Zhang, Y. H.; Dubey, P.; Margrave, J. L.; Shukla, S. S. The role of sawdust in the removal of unwanted materials from water. J. Hazard. Mater. 2002, 95 (1−2), 137. (43) Fu, X.; Yang, H.; Lu, G.; Tu, Y.; Wu, J. Improved performance of surface functionalized TiO2/activated carbon for adsorption− 7158


Polyethylenimine-Functionalized Corn Bract, an Agricultural Waste

Recommend Documents