Bioinspired Polydopamine Sheathed Nanofibers Containing

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Bioinspired Polydopamine Sheathed Nanofibers Containing Carboxylate Graphene Oxide Nanosheet for High-Efficient Dyes Scavenger Ruirui Xing, Wei Wang, Tifeng Jiao, Kai Ma, Qingrui Zhang, Wei Hong, Hui Qiu, jingxin zhou, Lexin Zhang, and Qiuming Peng ACS Sustainable Chem. Eng., Just Accepted Manuscript • Publication Date (Web): 24 Apr 2017 Downloaded from http://pubs.acs.org on April 27, 2017

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ACS Sustainable Chemistry & Engineering

Bioinspired Polydopamine Sheathed Nanofibers Containing Carboxylate Graphene Oxide Nanosheet for High-Efficient Dyes Scavenger Ruirui Xing,† Wei Wang,† Tifeng Jiao,*†,‡ Kai Ma,† Qingrui Zhang,*† Wei Hong,§ Hui Qiu⊥ ， Jingxin Zhou,† Lexin Zhang† and Qiuming Peng‡

†

Hebei Key Laboratory of Applied Chemistry, School of Environmental and Chemical Engineering,

Yanshan University, Qinhuangdao 066004, P. R. China. ‡

State Key Laboratory of Metastable Materials Science and Technology, Yanshan University,

Qinhuangdao 066004, P. R. China. §

Qinghuangdao Entry-Exit Inspection & Quarantine Bureau Coal Inspection Technique Center,

Qinhuangdao 066003, P. R. China. ⊥Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology (CICAEET), School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing, 210044, P. R. China Correspondence and requests for materials should be addressed to School of Environmental and Chemical Engineering, Yanshan University, 438West Hebei Street, Qinhuangdao 066004, P. R. China.

E-mail: T. Jiao ([email protected]), and Q. Zhang ([email protected]).

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ABSTRACT New

hierarchical

bioinspired

nanocomposite

materials

of

poly(vinyl

alcohol)/poly(acrylic

acid)/carboxylate graphene oxide nanosheet@polydopamine (PVA/PAA/GO-COOH@PDA) were successfully prepared by electrospinning technique, thermal treatment, and polydopamine modification. The obtained composite membranes are composed of polymeric nanofibers with carboxylate graphene oxide nanosheets, which are anchored on the fibers by heat-induced crosslinking reaction. The preparation

process

demonstrate

eco-friendly

and

controllable

manner.

These

as-formed

nanocomposites were characterized by various morphological methods and spectral techniques. Due to the unique polydopamine and graphene oxide containing structures in composites, the as-obtained composite demonstrate well efficient adsorption capacity towards dye removal, which is primarily due to the specific surface area of electrospun membranes and the active polydopamine/graphene oxide components. In addition, the composite membranes reported here are easy to regenerate. In comparison with other composite adsorbents, the preparation process of present new composite materials is highly eco-friendly and facile to operate and regulate, which demonstrates potential large-scale applications in wastewater treatment and dye removal.

KEYWORDS: Electrospun nanocomposite, Polydopamine, Dyes removal, Wastewater treatment

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INTRODUCTION In last several decades, various chemical pollutants (e.g., dyes) have drawn wide interests owing to the dangerous effects on public health and living environment1,2. Thus, efficient and convenient removal of these chemical pollutants from wastewater is becoming an urgent and challenging problem for researchers3-6. For instance, it is greatly important to design and develop efficient adsorption and catalyst materials for dye removal with high capacity, good compatibility, and long recyclability. It is well known that electrospinning is a facile method to produce continuous fibers with micro/nanoscale diameters7. The prepared fibrous materials demonstrate many novel properties, such as large specific surface area, large porosity, and great flexibility. The controllable thickness and diverse architecture of electrospun fibers make them ideal candidates as drug carriers, nanocatalysts, biosensors, protective clothing, and ultrafiltration and separation devices8-10. In recent reports, functionalized electrospun membranes have been utilized for removing chemical contaminants11,12. For example, Zhang et al. have reported the preparation of a bilayer biomimetic membrane based on electrospun polyacrylonitrile linked with chitosan and Cibacron Blue F3GA as modifier and surface ligand. The prepared electrospun membranes show good performance to capture bromelain13. Miao et al. have designed and prepared hierarchical SiO2@γ-AlOOH (Boehmite) core/shell fiber materials by the combination of electrospinning and hydrothermal treatment for water remediation14. On the other hand, dopamine demonstrate the properties of self-polymerization under basic systems to form a polydopamine (PDA) film onto various solid substrates15,16. The obtained PDA films can show a highly stable/active chemically-modified surface on the targeted nanostructures and demonstrate novel adhesive capability, suggesting the potential reaction process with designed molecules and possibility

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for wide applications17. More importantly, it can readily attach the organic-inorganic compatibility by one-step mixing. The unique nanostructured film along with intrinsic π-π component can further remove organic dyes in wastewaters efficiently. Thus, electrospun fiber-based material provides an excellent platform to host the deposition of PDA films, which can be used as highly effective and long lasting adsorption composites18-22. And recently, the PDA decorated electrospun nanostructures have also been synthesized and applied for enhanced mechanical properties for nanomaterials, drug delivery vehicles, and secondary lithium-ion batteries23-29. Moreover, due to good specific surface area, easy chemical modification, and excellent mechanical strength of graphene sheet, the graphene oxide could be an ideal component for anchoring various functional nanoparticles for environmental remediation30-34. Thus, some recent reports demonstrated that GO showed application as novel nanofiller in polymer based composite materials35-37. However, some practical problems appeared, such as lacking stability and hybridizing difficulty for inorganic GO component with organic fibers. In this work, in order to solve the above mentioned challenge, we designed and successfully prepared electrospun poly(vinyl alcohol)/poly(acrylic acid)/carboxylate graphene oxide nanosheets (PVA/PAA/GO-COOH) composite membrane materials, which were next functionalized with PDA coating

for organic dyes removal. Water soluble PVA/PAA and GO system were selected as matrix

materials for electrospinning due to the preferred well chemical and mechanical properties as well as large specific surface area38. At the same time, in comparison with common used organic solvents, pure water is used as the solvent in present preparing electrospun solution, demonstrating the eco-friendly features and low cost. As compared to the other kinds of composites, some significant advantages for the obtained multi-component electrospun composites are speculated. Firstly, the PDA coating layer can achieve the well compatibility between the flexible surface of fiber and efficient GO nanosheets. Then, the strong π-π component within PDA and GO materials can attach the powerful adsorption for

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various dyes in waters. In addition, the fixed carbonyl group within GO nanosheet can construct a strong electrostatic field by its highly negative-charges property, which can promote the target dyes diffusion and enrichment. Moreover, the obtained composited fiber can also be easily separated from the used dye solutions and regenerated for many cycles, demonstrating broad applications in dye removal and wastewater treatment.

EXPERIMENTAL SECTION Materials The experimental used materials, polyvinyl alcohol (PVA, 98-99% hydrolyzed, average M.W. 57,000-66,000), poly(acrylic acid) (PAA, M.W. ~2,000), hydroxyphenethylamine hydrochloride (dopamine,

98%),

tris(hydroxymethyl)

aminomethane

(TRIS,

99%),

tris(hydroxylmethyl)

aminomethane hydrochloride (Tris–HCl, 99%), and chloroacetic acid were purchased from TCI Shanghai Chemicals, Aladdin Chemicals and Alfa Aesar Chemicals. Graphene oxide was synthesized from graphite powder (8000 mesh, 99.95%, Aladdin Chemicals) according to a modified Hummers method39. Congo red (CR), Rhodamine B (RhB), and methylene blue (MB) were obtained from Tianjin KaiTong Chemical Reagent and Sinopharm Chemical Reagent Co., Ltd. without further purification. Sulfuric acid (H2SO4, 98%), potassium nitrate (KNO3), hydrogen peroxide (H2O2, 30%, w/w), potassium permanganate (KMnO4), and hydrochloric acid (HCl, 37%) were of analytical reagent grade from Sinopharm Chemical Reagent Co., Ltd. and used as received. Deionized (DI) water was used to prepare aqueous solutions in all experiments.

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Fabrication of the Nanocomposites Firstly, carboxyl-functionalized graphene oxide (abbreviated as GO-COOH) was prepared according to a reported method40, and freeze-dried in low temperature (-50 °C). The 10 wt% aqueous solution of PVA was obtained by dissolving PVA in deionized water at 80 °C for 12 h under magnetic stirring. PAA solution (30 wt%) was prepared in deionized water under magnetic stirring at room temperature for 1 h. GO-COOH solid was then supplied to the above PAA solution and stirred at room temperature for another 1 h to prepare solutions with different concentrations (0.3, 0.5, and 0.8 mg/g). The above as-obtained PVA and PAA/GO-COOH solutions were then mixed with a 1:1 volume ratio and next stirred at room temperature for 1 h to achieve a homogeneous solution for subsequent electrospinning41. For the electrospinning process, a syringe connected to a stainless steel needle with an inner diameter of 0.6 mm was used to load 10 mL of the above PVA/PAA/GO-COOH precursor solution. During electrospinning, a voltage of 20 kV and a flow rate of 0.5 mL h-1 were used for the spinneret. The produced electrospun nanofiber composite were deposited on a flat aluminum collector placed 15 cm away from the needle, and then dried in a vacuum oven at room temperature for 24 h, as demonstrated in Figure 1. After that, the obtained membrane samples were heated at 120 °C for 3 h for heat-induced crosslinking reaction between carboxyl acid groups in PAA/GO-COOH components and hydroxyl groups in PVA molecules. The designed PVA/PAA/GO-COOH@PDA nanocomposites were prepared according to similar process42. After annealing treatment at 120 °C and crosslinking reaction, PVA/PAA/GO-COOH membrane materials became insoluble in water due to the chemical esterification reaction between carboxylic acid groups and hydroxyl groups41. Next, the water insoluble monolithic composite materials were easily separated from aluminum substrate and

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were immersed into aqueous dopamine solution (2.0 mg mL-1 in 10 mM Tris buffer, pH 8.5) with mild stirring at 50 °C for PDA modification. Thus, the PVA/PAA/GO-COOH@PDA nanocomposite membranes were prepared by changing the immersed times (5 h, 15 h, and 35 h), respectively. The composite membranes were then removed from aqueous PDA suspension, thoroughly washed with deionized water and ethanol for several times to completely remove the free/non-adhered PDA components, and finally dried in vacuum at 80 °C for 24 h.

Batch Adsorption Tests for Dyes Removal For adsorption experiment, the adsorption properties of present nanocomposite materials were investigated via an absorption spectroscopy. To test the adsorption activity of the PVA/PAA/GO-COOH@PDA nanocomposites at room temperature, 30 mg freshly prepared PVA/PAA/GO-COOH@PDA nanocomposite adsorbents were added to a 100 mL dye solutions that contains CR (25mg/L), RhB (4 mg/L), and MB solution (10 mg/L), respectively. After dispersion of composite materials under magnetic stirring, the mixed solution was stirred under dark condition and the concentrations of the used model dyes in solution were measured and calculated at different time intervals. For the control test of PVA/PAA/GO-COOH nanocomposite, similar experimental procedures were adopted. Upon removal of the solid absorbents samples by centrifugation, the supernatant solutions were measured by 752 UV-vis spectrometer (Sunny Hengping scientific instrument Co., Ltd, Shanghai) at the wavelength of 497 nm (CR), 632 nm (MB), and 554 nm (RhB) with the pre-established calibration curves, respectively. For the recycling experiments, the as-prepared PVA/PAA/GO-COOH@PDA nanocomposite materials (30 mg) were added into 100 mL MB solution (10 mg L−1) under mild

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stirring. After 4 h of adsorption process, the composite membranes were washed thoroughly with deionized water and ethanol for several times. The whole adsorption processes were repeated for ten consecutive cycles using the same composite membrane materials and initial fresh MB solution.

Characterization The morphologies of all the obtained composite materials were investigated by a field-emission scanning electron microscopy (FE-SEM, SUPRA 55 SAPPHIRE, CARL ZEISS (Shanghai), Co., Ltd) with the accelerating voltage of 5-15 kV. Raman spectroscopy study was measured using a Horiba Jobin Yvon Xplora PLUS confocal Raman microscope equipped with a motorized sample stage. The wavelength of the excitation laser was 532 nm and the laser power was kept below 1 mW without noticeable sample heating. X-ray photoelectron spectroscopy (XPS) was measured on the Thermo Scientific ESCALab 250Xi using 200 W monochromated Al Kα radiation. Both survey scan and individual high-resolution scan were recorded. Thermogravimetry-differential scanning calorimetry (TG-DSC) analyses of the samples were obtained in air condition by NETZSCH STA 409 PC Luxxsi multaneous thermal analyzer (Netzsch Instruments Manufacturing Co., Ltd., Germany). FTIR spectra were measured by a Fourier infrared spectroscopy (Thermo Nicolet Corporation) using the conventional KBr disk tablet method. The specific surface areas and pore diameter distribution were determined by the BET measurement (NOVA 4200-P, US).

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RESULTS AND DISCUSSION Preparation and Characterization of Nanocomposites. Firstly, Figure 1 depicts the experimental procedure through several steps, including the preparation of precursor solutions, electrospinning process of all precursor materials, next thermal treatment and PDA modification for obtained electrospun membranes, and final dye adsorption and recovery capacities of the obtained PDA-modified composites membranes for three model dyes. Firstly, SEM characterization was utilized to investigate the morphologies and nanostructures of all prepared composite materials. The pristine PVA/PAA electrospun membranes from different mixed molar ratios were prepared and characterized (Figure S1). The obtained images clearly demonstrate that the membrane from PVA/PAA with volume ratio of 5:2 show uniform nanostructures with main fiber diameter distribution of 300–500 nm. When different amounts of GO-COOH were added to the mixed electrospinning solution, the formed PVA/PAA/GO-COOH nanocomposite electrospun membranes were also characterized (Figure S2). With increment of the concentrations of GO-COOH in the mixed solutions, the prepared electrospun membranes showed more GO sheets connected with nanofibers in plane and finally form sandwich-like GO layer in the membranes. In consideration of the uniformity and stability of the designed composite materials, the preparation condition of PVA/PAA/GO-COOH composite membrane (PVA/PAA with volume ratio of 5:2, GO-COOH 0.3 mg/g) was preferred to continue next experimental steps. In addition, from the photographs in Figure S3, it can be easily observed the obtained electrospun PVA/PAA/GO-COOH nanocomposite membranes show white monolithic material on aluminum substrate. And the color change to dark brown after modification with PDA layers. Then, SEM images from Figure 2a and 2a’ show that the prepared PVA/PAA/GO-COOH nanocomposite membrane by electrospinning and thermal treatment demonstrate porous fibers composed nanostructures with some GO sheet cross-linked with nanofibers in plane. In addition, with the time increment of PDA

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component modification, as shown in Figure 2b-d, it clearly shows that the surfaces of PVA/PAA/GO-COOH membranes were modified with more PDA nanoparticles stacked onto the fibers surface. This obvious change confirmed the successful preparation of PDA-modified composite materials. It should be noted that the main driving forces for the PDA nanoparticles modification process onto membrane structures could be mainly assigned to the hydrophilic forces, hydrogen bonding, and electronic interactions, as well as the adsorption of GO surface43-45. It can be estimated that the increased amount of PDA component and their possible aggregation in composite materials could induce the change of adsorption capacities and stability properties of the obtained composite membrane materials. In addition, Raman spectroscopy has been applied to characterize present composite membrane materials46. The measured Raman data for present composite materials are demonstrated in Figure 3. Two characteristic bands of graphene sheets in Raman spectra appeared. One band at 1601 cm-1 can be attributed to the G band, which comes from the first-order scattering of the E2g phonons of the sp2-hybridized carbon atoms. In addition, another band at 1351 cm-1 can be assigned to the D band, which originates from a breathing mode of κ-point phonons of A1g symmetry of the defects involved in the sp3-hybridized carbon bonds such as hydroxyl and/or epoxide bonds47,48. In addition, it is well known that the D/G peak intensity ratio can serve as a measurement of the sp2 domain size of graphene sheets containing sp3 and sp2 bonds due to the origination of G and D bands49-51. For research system reported here, the obtained results indicated that the D/G ratio shifted from 0.91-0.92 for GO and GO-COOH to the values of 1.66 for the PVA/PAA/GO-COOH (PVA/PAA with volume ratio of 5:2, GO-COOH 0.3 mg/g) and 0.86 for PVA/PAA/GO-COOH@PDA (modified time of 35 h), as shown in Figure 3b. This result confirmed the successful modification of PDA component in the electrospun membrane as well as and the presence of the polymeric alkyl chains linked to GO sheets.

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Since the obtained PVA/PAA/GO-COOH@PDA nanocomposite membranes were designed and prepared for the adsorption purposes, it is important to perform interfacial analysis and composition analysis using XPS technique. First of all, the survey data of XPS spectra from PVA/PAA/GO-COOH (PVA/PAA with volume ratio of 5:2, GO-COOH 0.3 mg/g) and PVA/PAA/GO-COOH@PDA nanocomposites (modified time of 35 h) in Figure 4A demonstrated the characteristic peaks, such as C(1s), O(1s), and N(1s). And the relative elemental composition and the O/C atomic ratios in both materials

have

been

obtained

and

calculated

(PVA/PAA/GO-COOH,

46.4%;

PVA/PAA/GO-COOH@PDA, 27.5%), indicating the decrement of oxygen element after PDA nanoparticles modification. In addition, the deconvolution of C(1s), O(1s), and N(1s) peaks for the PDA modified electrospun nanocomposite materials were analyzed and demonstrated. For the peak deconvolution of C(1s) core levels (Figure 4B), the peak centered at 284.2 eV could be assigned to the C-C, C=C and C-H bonds. In addition, the other deconvoluted peaks at positions of 285.1, 287.9 and 289.0 eV were attributed to C-OH and C-N, C=O, and O=C-O oxygen-containing bonds, respectively52-54. Moreover, the O(1s) peak shown in Figure 4C could be deconvoluted into three main Gaussian component peaks after subtraction treatment of Shirley background. The first component peak centered at 532.4 eV could be assigned to the oxygen in water molecules existed in the nanostructure or adsorbed on the membrane material surface. The second peak centered at 531.6 eV could be assigned to the oxygen of C-O bond in the nanocomposite, which was helpful to adsorption processes55,56. The third deconvoluted O(1s) peak centered at 530.5 eV was attributed to the oxygen of C=O bond in composites57. This means that the surface of PVA/PAA/GO-COOH@PDA nanocomposite was still functional and porous, which show an advantage for next adsorption application. Furthermore, in order to characterize the chemical state of nitrogen element, the analysis and deconvolution of N(1s) peak was also finished. As shown in Figure 4D, strong high-resolution N(1s) spectrum revealed the

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presence of amine (399.3 eV), C–N bond (400.5 eV), and N+ species (401.2 eV), indicating the presence of PDA polymer layers in the composite materials, either in their original amine forms or in grafted forms through the covalent bonding and weak interaction forces with the electrospun membrane and/or GO sheets. In addition, Figure 5 demonstrated the thermograms of PVA/PAA/GO-COOH and PVA/PAA/GO-COOH@PDA composites with modification time of 35 h. According to TG results, PVA/PAA/GO-COOH@PDA composites showed higher thermal stability in comparison with PVA/PAA/GO-COOH due to the addition of PDA nanoparticles. And it indicated that two mass loss bands between 230 and 550 °C appeared, which could originated from the pyrolysis of various oxygen containing chemical groups, alkyl chains, and GO sheets, respectively58,59. With increment of temperature up to 550 °C, the qualities retention was not changed with the ratios of 0 and 9.5%, respectively, indicating that abundant PDA components and/or nanoparticles were deposited onto PVA/PAA/GO-COOH membrane with the deposition time. FT-IR spectra of pristine PAA and PVA, the as-obtained PVA/PAA/GO-COOH nanocomposite, and PVA/PAA/GO-COOH@PDA composites with different modification times were demonstrated in Figure 6. For the spectrum curve of PVA/PAA/GO-COOH nanocomposite, the peak corresponding to the -OH vibration stretching appeared at 3430 cm-1, while other peaks at 2922, 2850, 1723, and 1461 cm-1 could be attributed to the stretching of CH2 and carboxyl C=O, as well as the scissoring vibration of CH2 alkyl chains60-64. In addition, with the PDA modification, the peak at 3430 cm-1 shifted to new position of 3421 cm-1, and some new characteristic peaks appeared at 1710, 1635, and 1559 cm-1, which could be attributed to the stretching of hydroxyl group, aromatic benzene ring, and amide band in the modified PDA component. The IR data of as-formed PVA/PAA/GO-COOH@PDA composite

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showed all characteristic peaks, indicating the successful hybrid of PDA component in the electrospun membranes and preparation of objective composite materials. In addition, the microstructural characteristics of as-prepared composites were further investigated with the N2 adsorption–desorption isotherms. The pore size distribution data were calculated by BJH methods, and the properties of the obtained composite materials were summarized in Table S1. The pore size for PVA/PAA/GO-COOH nanocomposite and PVA/PAA/GO-COOH@PDA nanocomposite modified at time of 35 h were in the range of 14–26 nm. The 3D hierarchical porous structure of PVA/PAA/GO-COOH@PDA nanocomposite could adsorb more nitrogen and demonstrated relatively high BET specific surface area of 54.5571 m2g-1, which was much larger than that of PVA/PAA/GO-COOH (32.7095 m2g-1). Furthermore, the pore volume and average pore diameter of PDA-modified membrane material were also larger than that of PVA/PAA/GO-COOH. It can be speculated that higher specific surface areas could increase adsorbent activity points and the contact chance between dye molecules and active points. In addition, larger pore diameters and pore volumes give vast channels for dye solutions and reduce the mass transfer resistance, suggesting better absorption performance.

Adsorption Performances toward Dye Removal. The adsorption properties of the as-prepared PVA/PAA/GO-COOH@PDA nanocomposite membranes were investigated for the three model dyes solutions (MB, RhB, and CR). The dye removal procedures were characterized by placing the as-prepared PVA/PAA/GO-COOH@PDA nanocomposites in different aqueous dye solutions. In addition, the present adsorption experiments were measured and repeated for three times, respectively. The adsorption kinetic experiments of the as-obtained PVA/PAA/GO-COOH@PDA nanocomposites were performed, and the results were shown in Figure 7.

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In control experiment of PVA/PAA/GO-COOH nanocomposite without PDA modification (Figure S4 and Table S2), the removal performances of the model dyes were significantly reduced. In addition, classical kinetic models were used to demonstrate the mentioned adsorption mechanism as the following formulas: The pseudo-first-order model can be demonstrated by equation (1): log(qe -qt ) = logqe -

k t 2.303

(1)

The pseudo-second-order model can be demonstrated by equation (2):

t 1 t = + 2 q t k qe qe

(2)

where qe and qt demonstrate the amount of dye adsorbed (mg/g) at equilibrium and time t, respectively, and the k1 and k2 values represent the kinetic rate constants65,66. The kinetic results (Table 1) can be good characterized by either pseudo-first-order model with a correlation coefficient (R2>0.983) or pseudo-second-order model with a correlation coefficient (R2>0.985). The present obtained adsorption kinetics curves of synthesized PVA/PAA/GO-COOH@PDA nanocomposites on used three dye solutions indicated present designed functional composite materials can act as excellent adsorbents with pseudo-first-order model or pseudo-second-order model with good correlation coefficient. In addition,

it

should

be

noted

that

the

adsorption

capacities

of

the

as-obtained

PVA/PAA/GO-COOH@PDA nanocomposites on MB show better performance than two other used dyes. The main reason for the difference can be speculated to the matched strong π-π stacking and electrostatic interactions between nanocomposites and MB molecules. At the same time, the abundant amino and hydroxyl groups in PDA surface give more adsorbent activity points for dye molecules, which demonstrate the tailored strategy to improve the absorption performance.

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On the other hand, good recovery and stability are expected and preferable for the large-scale applications of composite nanomaterials. For examples, in our recent study, the facile preparation and the phosphate sequestration capacity of nano-La(III) (hydr)oxides or sandwich-like MXene/magnetic iron oxide nanocomposites have been characterized and investigated in details, in which the obtained composite materials can be easily reused and recycled several times, suggesting the long term stability and application prospect in water purification67,68. Here, the as-prepared PVA/PAA/GO-COOH@PDA nanocomposite materials were used to investigate the potential application for MB removal. Unlike other reported adsorbents containing nanoparticle, the as-obtained composite materials can be easily separated from the used wastewater solutions. And it should be noted that, after saturated adsorption process, the used composite materials were treated by thoroughly cleaning procedures to remove possible byproducts and to regenerate the materials. The adsorption experiments were repeated for ten consecutive cycles by the same composite material and fresh MB solution, as presented in Figure 8. The results indicated that the adsorbed amount towards MB maintains at about 21.54 mg/g (about 81.4%, compared to 26.45 mg/g in the first adsorption process) for PVA/PAA/GO-COOH@PDA nanocomposite membranes after 10 consecutive cycles, demonstrating an excellent stability and reutilization of the composite materials in this study. In addition, further recycling steps indicated slight decrement of adsorption efficiency, which could be attributed to the byproduct deposition on composite surfaces or slight loss of PDA components from the fibers surface by many washing steps. The above reused data suggested that the prepared composite membrane materials can be potentially applied for wastewater treatment.

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CONCLUSIONS We have demonstrated the facile preparation and dye adsorption capacities of new composite absorbent materials, i.e., electrospun PVA/PAA/GO-COOH nanofibers modified with PDA component via an eco-friendly and self-assembled process. Because of the characteristic high surface area of electrospun membranes and the high active of PDA nanoparticles, the obtained PVA/PAA/GO-COOH@PDA composite materials showed efficient adsorption capacity towards the three model dyes used in this study. In addition, the composite membranes can be easily separated and regenerated from wastewater dye solution and demonstrated excellent reusability. The present work is expected to open a new avenue for the design and preparation of eco-friendly electrospun composites loaded with functional GO and nanoparticles, which could enhance practical application in wastewater treatment by using functionalized composite nanofibers materials.

ASSOCIATED CONTENT Supporting Information SEM images of electrospun fibers with different mixed volume ratios and concentrations, control adsorption kinetics curves, and the photograph of the electrospun composite materials. The Supporting Information is available free of charge on the ACS Publications website at DOI:XXXX.

AUTHOR INFORMATION Corresponding Authors

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E-mail address: [email protected] (T.J.); and [email protected] (Q.Z.) Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (Nos. 21473153 and 51578476，21607080), the Support Program for the Top Young Talents of Hebei Province, the China Postdoctoral Science Foundation (No. 2015M580214), the Science & Technology Pillar Program of Hebei Province (Nos. 16211250 and 15273626), and the Scientific and Technological Research and Development Program of Qinhuangdao City (No. 201502A006).

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Table 1. Kinetic parameters of PVA/PAA/GO-COOH@PDA nanocomposites for MB, RhB, and CR adsorption at 298 K (experimental data from Figure 7).

PDA

Pseudo-first-order model

Dyes

K1 (x 102)

qe

(min-1)

(mg/g)

0.983

2.37

31.29

0.996

1.13

26.92

0.998

1.86

34.05

0.992

0.44

35h

25.61

0.992

1.96

28.81

0.996

0.69

RhB

5h

6.75

0.983

1.64

8.40

0.985

2.32

CR

5h

9.62

0.994

1.50

12.94

0.995

0.996

Anchored

qe

time

(mg/g)

MB

5h

25.91

MB

15h

MB

R2

Pseudo-second-order model R2

K2(x 103) (g/min·mg)

Figure captions

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Figure 1. Schematic illustration of the fabrication and dye adsorption of PVA/PAA/GO-COOH@PDA nanocomposites by electrospinning and thermal treatment. Figure 2. SEM images of the prepared PVA/PAA/GO-COOH nanocomposite (a and a’) by electrospinning and thermal treatment, and next modified with PDA at different time intervals (b and b’, 5h; c and c’, 15 h; d and d’, 35 h). Figure 3. Raman spectroscopy (a) and D/G ratios (b) of different prepared composites. Figure 4. Survey XPS spectra of both samples (A): a, PVA/PAA/GO-COOH nanocomposite; b, PVA/PAA/GO-COOH@PDA nanocomposite modified at time of 35 h. Deconvolution of XPS peaks in spectra b: B, C(1s); C, O(1s); D, N(1s). Figure 5. TG curves of electrospun PVA/PAA/GO-COOH nanocomposite and next modified PDA at time of 35 h. Figure 6. IR spectra of the obtained PVA, PAA, the electrospun PVA/PAA/GO-COOH nanocomposite, and next modified PDA at time intervals of 5, 15, and 35 h. Figure 7. Adsorption kinetics curves of as-prepared PVA/PAA/GO-COOH@PDA nanocomposites on MB (a, b), RhB (c, d), and CR (e, f) at 298 K. Figure

8.

Relative

adsorption

capacity

and

regeneration

studies

of

as-prepared

PVA/PAA/GO-COOH@PDA nanocomposite with modified time of 35 h towards MB at room temperature for different consecutive cycles.

25



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Figure 1. Schematic illustration of the fabrication and dye adsorption of PVA/PAA/GO-COOH@PDA nanocomposites by electrospinning and thermal treatment.

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Figure 2. SEM images of the prepared PVA/PAA/GO-COOH nanocomposite (a and a’) by electrospinning and thermal treatment, and next modified with PDA at different time intervals (b and b’, 5h; c and c’, 15 h; d and d’, 35 h).

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Figure 3. Raman spectroscopy (a) and D/G ratios (b) of different prepared composites.

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Figure 4. Survey XPS spectra of both samples (A): a, PVA/PAA/GO-COOH nanocomposite; b, PVA/PAA/GO-COOH@PDA nanocomposite modified at time of 35 h. Deconvolution of XPS peaks in spectra b: B, C(1s); C, O(1s); D, N(1s).

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Figure 5. TG curves of electrospun PVA/PAA/GO-COOH nanocomposite and next modified PDA at time of 35 h.

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Figure 6. IR spectra of the obtained PVA, PAA, the electrospun PVA/PAA/GO-COOH nanocomposite, and next modified PDA at time intervals of 5, 15, and 35 h.

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Figure 7. Adsorption kinetics curves of as-prepared PVA/PAA/GO-COOH@PDA nanocomposites on MB (a, b), RhB (c, d), and CR (e, f) at 298 K.

32


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Figure


8.

Relative

adsorption

capacity

and

regeneration

studies

of

as-prepared

PVA/PAA/GO-COOH@PDA nanocomposite with modified time of 35 h towards MB at room temperature for different consecutive cycles.

.

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For Table of Contents Use Only.

Bioinspired Polydopamine Sheathed Nanofibers Containing Carboxylate Graphene Oxide Nanosheet for High-Efficient Dyes Scavenger

Ruirui Xing, Wei Wang, Tifeng Jiao, Kai Ma, Qingrui Zhang, Wei Hong, Jingxin Zhou, Lexin Zhang and Qiuming Peng

Synopsis Hierarchical bioinspired polydopamine sheathed nanocomposites containing carboxylate graphene oxide nanosheet are prepared via electrospinning technique and polydopamine modification, demonstrating high-efficient dyes scavenger for wastewater treatments.

34


Bioinspired Polydopamine Sheathed Nanofibers Containing

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