Mussel-inspired cellulose-based nanocomposite fibers for adsorption

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Mussel-inspired cellulose-based nanocomposite fibers for adsorption and photocatalytic degradation Rui Liu, Lin Dai, and Chuanling Si ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.8b04320 • Publication Date (Web): 24 Sep 2018 Downloaded from http://pubs.acs.org on September 25, 2018

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ACS Sustainable Chemistry & Engineering

Mussel-inspired cellulose-based nanocomposite fibers for adsorption and photocatalytic degradation Rui Liu,† Lin Dai,†,‡* Chuan-Ling Si†*

†

Tianjin Key Laboratory of Pulp and Paper, Tianjin University of Science and Technology,

Tianjin 300457, P.R. China ‡

Tianjin Key Laboratory of Marine Resources and Chemistry, Tianjin University of Science and

Technology, Tianjin, 300457, P.R. China

*Corresponding authors. Lin Dai and Chuan-Ling Si Present address: Tianjin University of Science and Technology, No.29 at 13th Avenue, TEDA, Tianjin 300457, P.R. China E-mail: [email protected], [email protected] (Lin Dai); [email protected] (Chuan-Ling Si). Tel: (+86) 022-60601313

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ACS Paragon Plus Environment

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Abstract We present a green and low-cost approach to fabricate titanium dioxide nanoparticles (TiO2 NPs)/polydopamine (PDA)/cellulose fibers (CF) composite (TiO2/PDA/CF) by using PDA as functional layer and a protective agent. Mussel-inspired PDA layer robustly adhered to CF, and TiO2 NPs were immobilized on the surface of PDA layer through facile hydrolysis of TiOSO4. The TiO2/PDA/CF composite exhibited an improved stability of CF and a good reutilization property, which benefitted from the PDA layer between CF substrate and TiO2 NPs. Moreover, the TiO2/PDA functional layer remarkably enhanced the adsorption capacities of Pb2+ (~20 mg/g) and methylene blue (MB, ~15 mg/g). And the better photocatalytic performance of this composite further improved the efficiency of MB removing. This cellulose-based nanocomposite has great potentials in photocatalysis and wastewater treatment with low energy consumption, economic and environmental sustainability.

Keywords: Cellulose, Nanocomposite, Adsorption, Photocatalytic degradation, Sustainability

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Introduction Water pollutants including heavy metals, synthetic dyes, and aromatic compounds have been greatly do harm to the environment and human health.1 Many technologies are developed for pollutants removal including biological treatments, chemical coagulation, electrolysis, photocatalytic degradation, and adsorption.2 Among them, adsorption is an easy and effective way. In recent years, a lot of composite adsorbents were reported to compensate the drawbacks of single-compound adsorbents such as difficult to achieve adsorption and catalysis simultaneously. However, most of advanced adsorbents were prepared from petrochemicals. Hence, it is necessary to develop advanced composite adsorbents with abundant natural resources. Cellulose is the most abundant biopolymer on earth, and it has been extensively investigated for functional materials for decades.3-6 Cellulose has much hydroxyl groups that can clear the heavy metal ions or organic compounds via metal chelates and strong hydrogen bonding. Therefore, cellulose and its derivants have been gained increasing attention as functional materials for wastewater treatment.1 However, pure cellulose unable to achieve satisfactory performance of adsorption. Previous studies showed that the immobilizing TiO2 NPs on the surface of cellulose can significantly improve their capacity in pollutants clearing.7-8 But there are still some drawbacks of TiO2 NPs/cellulose composite for adsorption and photocatalytic degradation, such as low enrichment ability of carriers and the photo-degraded of cellulose substrate by the loaded TiO2 NPs at high temperature or UV-light environment. This is hostile to the high-quality and long term recycling use of TiO2 NPs/cellulose composite.9-10 Therefore, it is necessary to develop novel TiO2/cellulose composite materials with advanced components for 3



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protecting cellulose substrate and enhancing its adsorption and photocatalytic performance simultaneously. Polydopamine (PDA) is a polymer derived from dopamine which is the major origin of the extraordinarily robust adhesion of mussels. Inspired by its unique wet adhesion capability, many studies found that PDA can form a hydrophilic coating layer and robustly adhered to virtually all types of surface.11 Moreover, various functional groups in PDA molecules such as amino, imine and phenol groups can also aid the adsorption of metal ions and organic pollutants via electrostatic interaction, chelation, hydrogen bonding, and π-π stacking interactions.12-15 Hence, PDA has attracted strong interest in modified adsorbents. In this study, we presented a facile approach to prepare a sandwiched TiO2/PDA/CF composite, where PDA acted as a protect layer of CE and adhesion of TiO2 NPs. The formation of PDA and TiO2 NPs were investigated in detail by using scanning electron microscopy, X-ray diffractometer, X-ray photoelectron spectroscopy. The protective effects of PDA to CF, the adsorption, photocatalytic, and cyclic performance were also studied systematically. The PDA layer and TiO2 NPs anchored CF showed attractive advantages including low energy consumption, economic and environmental sustainability.

Experimental Materials Hardwood (Populus tomentosa) bleached Kraft pulp was provided free from Tianjin Woodelfbio Cellulose Co. Ltd. Titanium oxysulfate solution (TiOSO4‧H2SO4‧H2O, ~15 wt%) in dilute sulfuric acid was purchased from Sigma-Aldrich. Dopamine hydrochloride (DA‧HCl) was 4


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brought from Ark Pharm, Inc. (USA). Tris (hydroxymethyl) amiomethane (Tris), lead nitrate, methylene blue (MB) and other agents were obtained from Signopharm Chemical Reagent Co. All other chemical reagents were analytical grade and used as received.

Preparation of PDA/CF The bleached Kraft pulp was treated with acetone to remove impurities on the surface of cellulose fibers (CF). CF (1.0 wt%) was dispersed by using a pulp disintegrator at 5000 rpm for 5 min, and then diluted to 0.5 wt% for avoiding aggregation. 4.94 g DA‧HCl was added to CF solution (800 mL, 0.5 wt%). Subsequently, the pH value of the system was adjusted to 8.5 by using NaOH (0.1 M) rapidly. After a certain time, PDA/CF production were centrifugal separated, washed by deionized water and dried in a freezing dyer. The productions with 12 h, 24 h and 72 h reaction time were marked as PDA12/CF, PDA24/CF, and PDA72/CF, respectively, for the following study.

Preparation of TiO2/PDA/CF The TiO2/PDAx/CF (x = 12, 24, or 72) samples were prepared as the following process. 2.0 g PDAx/CF was suspended in 600 mL deionized water under vigorous stirring overnight. Then, 2.0 mL sulfuric acid (98%) and TiOSO4·H2SO4·H2O (1.4 mL) were added dropwise to a vortexing solution, successively. The mixture was kept in 70 °C oil-bath for 4.5 h. The resultant TiO2/PDAx/CF composite fibers were centrifugal separated, washed by deionized water and dried in a freezing dyer. Pure CF without TiOSO4 addition and TiO2/CF were preparation for comparative studies. 5



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Characterization X-ray diffraction (XRD) patterns were recorded within the 2θ range from 5° to 80° at 4 °/min on XRD-6100 X-ray diffractometer (Shimadzu, Japan), operating at 40 KV, 30 mA with Ni-filtered Cu Kα radiation at room temperature. X-ray photoelectron spectroscopy (XPS) were carried out on a Kratos-Axis spectrometer with monochromatic Al Kα (1486.71 ev) X-ray radiation (15 kV and 10 mA) and hemispherical electron energy analyzer. All XPS spectra were corrected according to the C 1s line at 284.6 eV. Curve fitting and background subtraction were accomplished using Casa XPS software. The morphology of the samples was captured by using scanning electron microscope (SEM, JSM-IT300LV, JEOL, Japan) and high-resolution transmission electron microscope (HRTEM, JEOL-F2100, JEOL, Japan). The specific surface areas and pore size distributions of the sample were measured by Brunauer−Emmett−Teller (BET) method at a relative pressure ratio of 0.05 to 0.3 based on nitrogen adsorption at the liquid-nitrogen temperature using an Autosorb-IQ (Quantachrome, USA). And specific surface areas were calculated from a multipoint analysis of the volume of nitrogen adsorbed as a function of relative pressure. Thermal gravimetry (TG) and differential thermal analysis (DTA) were carried out on a TA T-650 apparatus using a temperature range from 25 to 700 °C at a heating rate of 20 °C/min.

Adsorption for Pb2+ Adsorption experiments were carried out at room temperature to investigate the adsorption behaviors of Pb2+. Typically, 40 mg TiO2/PDAx/CF samples were placed into 100 mL Pb2+ solutions with different concentrations and incubated in a constant temperature incubator for 6


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period of time to achieve adsorption equilibrium, respectively. Then TiO2/PDAx/CF samples were removed by centrifugation. The concentrations of Pb2+ were determined by atomic absorption spectrophotometer (900T, PE, Singapore). The adsorption capacity at equilibrium (qe) of TiO2/ CF and TiO2/PDAx/CF were calculated by the following equation. qe=(C0-Ce)V/m

(1)

where C0 and Ce are the initial and equilibrium concentrations (mg/L), respectively, where V is the volume of the solutions (L), and m is the amount of the sample (g). For regenerate of the TiO2/PDAx/CF, 0.1 M HCl was used to remove adsorbed metal ion in constant temperature incubator for 12 h.

Adsorption and photocatalytic degradation of MB The adsorption capacity and rate of MB were investigated before photocatalytic degradation. Photocatalytic activity of the TiO2/PDA72/CF was evaluated by monitoring the degradation of MB under UV-irradiation. Typically, an accurately weighed amount of TiO2/PDA72/CF was place into MB aqueous solution in a quartz vial and stirred for 150 min in dark to reach the adsorption-desorption equilibrium. And then, the equilibrium suspension was irradiated with UV light (Hg lamp, Philips HOK lamps, 400 W, >320 nm). The concentrations of MB were monitored by UV/Vis spectrometry (UV2500, Shimadzu, Japan) at 664 nm.

Result and discussion Preparation of TiO2/PDAx/CF

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Figure 1. Illustration of fabrication and application of TiO2/PDAx/CF. (a) Preparation process, (b) mechanism, and (c) the application for water treatment.

Previous studies showed that PDA can be well coated on the surface of various substrates and performed a powerful biomimetic adherent.11, 16-17 It also can be used as reducing agent and the stabilization agent of composite materials.11 As shown in Figure 1, the sandwiched PDA layer was coated on the surface of CF via oxidation and self-polymerization of DA in mild condition. Then TiO2 NPs was immobilized on the surface of PDA layer. During the reaction, the colour of CF suspension and PDAx/CF products became dark brown (Figure S1 and S2), which was a common phenomenon of PDA layer formation on the surface of materials. XPS measurements is routinely used to analyse the formation of composite materials. In Figure 2a, the signals of C1s 8


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and O1s were captured in CF and PDA/CF72, while a new signal attributed to N1s presented in PDA72/CF, indicating the PDA layer anchored to the surface of CF. Compared to CF (-CHx, 284.61 eV and C-O, hydroxyl, 286.48 eV), PDA72/CF and TiO2/PDA72/CF almost presented the same C1s picks and the extra picks of C=O (287.57 eV), which originate from the indolic compounds during the auto-oxidative and self-polymerization process of DA (Figure 2b).18 The O=C (532.95 eV) and O-C (532.28 eV) picks in Figure 2c were consistent with the results of O1s. The representative signal of PDA containing R-NH2 (401.26 eV), substituted amines RNH-R/indole groups (399.35 eV), and imino groups =N-R (398.86 eV) were showed in Figure 2d, indicating successfully preparation of PDA72/CF composite.18 Noteworthy, the noncovalently self-assembled DA could inhibit the transformation of primary amine. A small amount of secondary amine might be due to the formulation of indolic compounds during the autooxidation and self-polymerization processes.

Figure 2. XPS spectra of CF, PDA72/CF TiO2/PDA72/CF (a), and high-resolution XPS spectra of C1s (b), O1s (c), N1s (d), and Ti2p (e). 9



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PDA is hydrophilic with plentiful active hydroxyl, amino, and quinone groups, which can offer a lot of efficient bonding sites to promote nucleation and nanoparticles formation.19-20 In this work, TiOSO4H2SO4H2O was used to prepare TiO2 NPs via thermal hydrolysis process. The hydrolysis of TiOSO4 leaded to TiO2 NPs formation according to the following equations.21: TiOSO4•H2SO4•H2O→TiO2•H2Osolution+H2SO4

(2)

TiO2•H2Osolution→TiO2•H2Oseed

(3)

TiO2•H2Oseed→TiO2 +H2O

(4)

Figure 3. XRD patterns (a), krypton adsorption isotherm curves (b), and UV-vis spectra (c) of CF, PDA72/CF, TiO2/CF and TiO2/PDA72/CF.

Heterogeneous nucleation and homogeneous condensation were achieved in the formation of TiO2 NPs. In the first stage, there was a heterogeneous nucleation that actualized by chelating the hydroxyl groups on PDA surface and TiO2 NPs in the solution. And the homogeneous condensation was induced by the chelated TiO2 NPs on the PDA layer, which could be acted as seed layer to facilitate the growth of TiO2 NPs (Figure 1b). XPS results appeared strong peaks at 528.91 eV (O1s) and 459.21 eV (Ti2p) which attributed to O and Ti elements of TiO2 NPs, respectively (Figure 2c and e). Moreover, in the XRD pattern (Figure 3a), the diffraction peaks 10


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recorded at 2θ=25.62° (101), 38.43° (112), 48.35° (200), 54.32° (105), 55.65° (211), and 62.8° (204) relating to the plane of the anatase phase, which also indicated the formation of TiO2.22 The surface topography of TiO2/CF and TiO2/PDAx/CF were observed by using SEM. Figure 4a~d was clearly showed that TiO2 NPs presented in smaller size on the surface of TiO2/PDAx/CF than that TiO2/CF without PDA layer. The BET values of TiO2/PDA12/CF (35.47m2/g), TiO2/PDA24/CF (37.76m2/g) and TiO2/PDA72/CF (38.95m2/g) were also significantly increased than TiO2/CF (28.656m2/g) (Figure 3b), which can also indicate changing trends of TiO2 NPs size. In order to measure the size of the TiO2 NPs, TiO2 NPs were peeled off from the TiO2/CF and TiO2/PDA72/CF via vigorous sonication and imaged by HRTEM, the selected area electron diffraction (SEAD) pattern obtained as well. Different from TiO2 NPs (30~50 nm) on TiO2/CF, TiO2 NPs on TiO2/PDA72/CF showed smaller size (< 20 nm) (Figure 4e and f). This indicated that the PDA layer may promote the homogeneously finegrained TiO2 deposition, thereby helping to provide nucleation site (amino and quinone groups of PDA) to TiO2 via electrostatic and van der Waals interaction.11, 20, 23

Figure 4. SEM images of TiO2/CF(a), TiO2/PDA12/CF (b), TiO2/PDA24/CF (c), and TiO2/PDA72/CF (d). TEM and SEAP images of TiO2 NPs on the surface of (e) TiO2/CF and (f) TiO2/PDA72/CF. 11



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Thermal properties of TiO2/PDAx/CF Thermogravimetric analysis is an acceptable approach be to study the effect of metal substances on the thermal decomposition of cellulose.24-26 Figure 5a, b, and Table 1 showed TG results of CF, TiO2/CF, TiO2/PDA12/CF, TiO2/PDA24/CF and TiO2/PDA72/CF. The pure CF had a highest decomposition temperature (Tonset, 340.23°C). But the Tonset of TiO2/CF decreased to 305.69 °C after immobilization of TiO2 NPs, which might be the catalytic effect of TiO2 NPs.10 Interestingly, with the PDA layer, TiO2/PDAx/CF samples presented dramatically better thermal stabilities than TiO2/CF. The Tonset increased (TiO2/PDA72/CF > TiO2/PDA24/CF > TiO2/PDA12/CF) with the increasing content of PDA layer. This phenomenon could benefit from the organic PDA layer between CF substrate and TiO2 NPs which enhanced the corrosion protection via a buffer layer insulating the electric pathway.23 During thermal degradation, nitrogen gas (N2 and NH3) and catechol from PDA would have effects of physical barrier and radicals scavenging, respectively.27 Moreover, PDA layer was also showed good anti-UV effect (Figure 3c).11 From the above, the PDA layer could effective protect CF from catalytic degradation of TiO2 NPs.

Table 1. Thermal stability data of the samples. sample CF TiO2/CF TiO2/PDA12/CF TiO2/PDA24/CF TiO2/PDA72/CF

Tonset (°C) 340.23 309.36 317.84 328.23 327.07

Tendset (°C) 378.14 365.54 362.85 367.79 367.07

Tmax (°C) 363.06 340.83 343.24 355.00 349.90

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Figure 5. TG (a) and DTG (b) curves of the samples.

Adsorption behavior of Pb2 pH conditions greatly affect the physico-chemical properties of the adsorbents and adsorption behaviors of metal ion. Here, considering the possible formation of Pb2+ precipitation, the effect of pH values was investigated in the range from 3.0~6.0.28 All the samples showed poor adsorption capacities of Pb2+ with lower pH solutions, and the adsorption capacities were increased with increasing pH values (Figure 6a). The TiO2/PDAx/CF showed higher adsorption capacity at equilibrium (qe) (TiO2/PDA12/CF 19.8 mg/g, TiO2/PDA24/CF 20.53mg/g, and TiO2/PDA72/CF 22.12mg/g) than TiO2/CF (15.2mg/g) at pH 6.0. It is well recognized that both cellulose and PDA are negatively charged over a wide range of pH,29 and the TiO2 NPs also 13



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presents isoelectric point at pH 6.2.30 Therefore, the poor adsorption capacities of Pb2+ in acidic condition were due to the surface protonation of adsorbents in acidic solution and strong electrostatic repulsion generated between absorbents and metal ions.31 Since the TiO2/PDA72/CF showed highest adsorption capacity at pH 6, it was selected for the following study of adsorption isotherms and kinetics.

Figure 6. (a) Initial pH effects on Pb2+ adsorption by different samples. (b) The curves of Pb2+ adsorption by TiO2/CF and TiO2/PDA72/CF at different times. (c) Adsorption capacities of TiO2/CF and TiO2/PDA72/CF as a function of repeated adsorption−desorption cycles. Fitting of (d) pseudo-first-, (e) pseudo-second-order, (f) Langmuir and Freundlich isotherms models (L and F model).

Figure 6b showed the adsorption kinetics of Pb2+ at room temperature pH 6.0. The amount of Pb2+ adsorbed onto TiO2/PDA72/CF increased rapidly within the initial 60 min, then increased slowly and finally reached adsorption saturation in 240 min (Figure 6b). The pseudo-first order

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and pseudo-second-order kinetic models were adapted to fit the experimental data according to the following equations: log(qe-qt) = log(qe)-K1t

(5)

t/qt =1/K2qe+t/qe

(6)

where qe and qt are the amounts of Pb2+ adsorbed at equilibrium and at contact time t (min), respectively; K1 (min-1) is the rate constant of pseudo-first-order, K2 (min g/mg) is the kinetic rate constant of pseudo-second-order. The relative parameters were obtained from the fitting results (Figure 6d and e). According to the value of correlation coefficient (R2), pseudo-second-order model showed better fit (R2 = 0.9976), indicating the chemisorption is the rate-determining step. This can be attributed to large amounts of hydroxyl and amino groups on the surface of absorbent which provide many chemical binding sites for Pb2+.31-33

Table 2. Isotherm parameters for Pb2+ adsorption at 25 °C. sample TiO2/CF TiO2/PDA72/CF

Langmuir model qmax KL 32.39 0.11 57.69 0.16

2

R 0.9048 0.9915

Freundlich model KF n 13.56 3.11 10.95 3.98

R2 0.9276 0.9981

Adsorption isotherms can reflect the adsorption capacity at a constant temperature. In this work, Langmuir and Freundlich models were selected to determine the isotherm parameters. qe= qmaxKLCe/(1+KLCe)

(7)

qe=KFCe1/n

(8)

where qe and qmax are the equilibrium and maximum adsorption capacity (mg/g), respectively, Ce is the equilibrium concentration (mg/L), KL and KF are the adsorption constants of Langmuir and 15



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Freundlich models, respectively, n is a constant depicting the adsorption intensity. The relative parameters fitted from Freundlich and Langmuir model were listed in Table 2. As the fitting results in Figure 6f and Table 2, the Freundlich model showed better fit than the Langmuir model for both TiO2/CF and TiO2/PDA72/CF adsorption, reflecting a multilayer and heterogeneous distribution of active sites on the surface of TiO2/PDA72/CF composite.

Figure 7. The high-resolution XPS spectra of Pb4f (a), O1s (b), Ti2p (c), and N1s (d) of TiO2/PDA72/CF before and after Pb2+ adsorption.

XPS was employed to further reveal the interaction mechanism between TiO2/PDA72/CF and Pb2+. In Figure 7, the peaks assigned to Pb4f7/2 (~138.91 eV) and Pb4f5/2 (143.60 eV) were recorded. Moreover, it was found that the binding energy of Ti2p, O1s shifted to lower value and N1s on TiO2/PDA72/CF shifted to higher value after adsorption for Pb2+. These results demonstrated the deposition of Pb2+ on the surface of TiO2/PDA72/CF through combined effect of TiO2 NPs, alcoholic, phenolic and amine groups of PDA and CF. TiO2 NPs offered abundant 16


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surface sites and formed to chelate complex with Pb2+ through the inner sphere surface complex formation,8,

34

thus the binding energy of Ti2p and O1s shifted to lower value after

Pb2+adsorption. Besides, the phenolic and amine groups or their deprotonated form also contributed for Pb2+ removing.31 In practical applications, regenerated and reutilization are very important properties for adsorbents. 0.12 M HCl solution was used as desorption agent for desorption of Pd2+ and regeneration of TiO2/PDAx/CF. The results of regeneration adsorption cycles were shown in Figure 6c. Although acid solution could affect the stability of PDA, the TiO2/PDA72/CF almost maintained its capacity after five repeated adsorption and desorption cycles. which suggested that TiO2/PDA72/CF has good stability for reutilization.

Adsorption and photocatalytic degradation of MB TiO2 is a well-known n-type semiconductor which has been widely used as an efficient photocatalyst to degrade organic compound in wastewater. In recent years, some composite materials based on TiO2 NPs and cellulose have been reported for organic pollutants treatment.10, 35

However, the performance of photocatalytic degradation is not only depended on the catalyst

capacity itself, but also the enrichment ability of carriers to reactants.36 PDA is believed to have a promising application in various catalytic systems serving as a catalyst carrier. Because it has excellent ability to improve the photocatalytic activity of the catalysts through the presence of the π−π* electron transition and delay of reconstruction of charge and holes.11,

37

Herein,

experiments were carried out to study the adsorption and the photocatalytic activity for MB of the samples. 17



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Figure 8a presented the adsorption capacity of different samples at same condition: 100 mg samples, 100 mL MB aqueous (10 mg/L, pH 6.5). It can be easily observed that both CF and TiO2/CF had a lower adsorption rate and longer time (about 180 min) to reach equilibrium state. By contrast, TiO2/PDA72/CF showed a higher adsorption rate at the initial stage, shorter time (~150 min) to get adsorption saturation, and increasing adsorption capacity (~3.1 and 2.2 times higher than CF and TiO2/CF respectively). These results could be due the introduction of PDA layer, intermolecular forces between PDA and MB were increased which including hydrogen bonding, π-π interactions and especially the strongly electrostatic interaction.

Figure 8. (a) Adsorption capacity of MB of different samples. (b) The performance of photocatalytic degradation of TiO2/CF and TiO2/PDA72/CF under UV irradiation. (c) Recycling performance and illustration of TiO2/PDA72/CF for MB adsorption and photocatalytic degradation.

After reaching the adsorption equilibrium, photocatalytic degradation effects of MB by TiO2/CF and TiO2/PDA72/CF were also evaluated under UV radiation. In Figure 8b, the 18


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concentration difference at t=0 was derived from the different adsorption capacity of this two sample that had discussed above. During the process of photocatalytic degradation, 80.6% of MB was degraded by TiO2/PDA72/CF, which was higher than that of TiO2/CF (56.8%) which gave a compelling fact that the sandwiched PDA layer is helpful to the adsorption and photocatalytic performance of TiO2 NPs simultaneously.38-40 The TiO2/PDA72/CF maintained a stable and efficient adsorption and photocatalytic performance after the five-cycle test (Figure 8c). The photocatalytic process involves a complex interaction among substrate, carrier and catalyst.41 Based on all the results, we believed that two main effects were anticipated to the improved performance of MB removing (Figure 8d): First, TiO2 NPs smaller size on TiO2/PDA72/CF undoubtedly promoted the catalytic efficiency. Second, PDA layer may offer great help for the rapid enrichment of MB molecules onto the surface of TiO2 NPs and CF by strong electrostatic interaction and enhance the catalytic performance remarkably.

4. Conclusions A sandwiched TiO2/PDA72/CF composite was successfully fabricated for highly efficient removing of heavy metal ions (Pb2+) and organic dyestuff (MB). By introducing of the PDA layer, the TiO2/PDA72/CF composite showed a higher stability and a good reutilization property. More importantly, the adsorption capacities of Pb2+ and MB were improved obviously. The better photocatalytic performance further improved the efficiency of MB removing. The TiO2/PDA72/CF composite with a facile, green and low-cost approach are promising for photocatalysis and wastewater treatment.

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Acknowledgments We gratefully acknowledge the financial support from the National Natural Science Foundation of China (21706193), Natural Science Foundation of Tianjin (17JCQNJC05200), Young Elite Scientists Sponsorship Program by Tianjin (TJSQNTJ-2017-19), and the Foundation of Tianjin Key Laboratory of Marine Resources and Chemistry (201603).

Notes The authors declare no competing financial interest.

Supporting Information The photo of the products, UV-vis spectra of MB, element mapping and EDX spectra of TiO2/PDA72/CF.

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For Table of Contents Use Only

Mussel-inspired cellulose-based nanocomposite fibers showed great potentials in wastewater treatment with low energy consumption, economic and environmental sustainability.

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Mussel-inspired cellulose-based nanocomposite fibers for adsorption

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