Facile in-situ synthesis of PEI-Pt modified bacterial cellulose bio-adsorbent and its distinctly selective adsorption of anionic dyes

Journal Pre-proof Facile in-situ synthesis of PEI-Pt modified bacterial cellulose bio-adsorbent and its distinctly selective adsorption of anionic dyes Xin Huang, Bohao Lia, Shaobo Wang, Xianyang Yue, Zhengguo Yu, Xinjie Deng, Jimei Maa

PII:

S0927-7757(19)31156-2

DOI:

https://doi.org/10.1016/j.colsurfa.2019.124163

Reference:

COLSUA 124163

To appear in:

Colloids and Surfaces A: Physicochemical and Engineering Aspects

Received Date:

5 August 2019

Revised Date:

6 October 2019

Accepted Date:

27 October 2019

Please cite this article as: Huang X, Lia B, Wang S, Yue X, Zhengguo Y, Deng X, Maa J, Facile in-situ synthesis of PEI-Pt modified bacterial cellulose bio-adsorbent and its distinctly selective adsorption of anionic dyes, Colloids and Surfaces A: Physicochemical and Engineering Aspects (2019), doi: https://doi.org/10.1016/j.colsurfa.2019.124163

This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2019 Published by Elsevier.

Facile in-situ synthesis of PEI-Pt modified bacterial cellulose bio-adsorbent and its distinctly selective adsorption of anionic dyes

Xin Huanga, b,*, Bohao Lia, Shaobo Wang a, b,*, Xianyang Yue a, b, Zhengguo Yua, Xinjie Denga, and Jimei Maa, b

a

School of Textiles, Zhongyuan University of Technology, No. 41 Zhongyuan Road

b

ro of

(M), Zhengzhou, Henan Province 450007, China

Collaborative Innovation Centre of Textile and Garment Industry, Zhengzhou, Henan

Correspondence information:

re

-p

Province 450007, China

lP

* Xin Huang and Shaobo Wang, School of Textiles, Zhongyuan University of Technology, No. 41 Zhongyuan Road (M), Zhengzhou, Henan Province 450007, China,

na

E-mail: [email protected] (X. Huang) and [email protected] (S. Wang),

Jo

ur

Tel.: +86-(0)371-6997-5723.

Graphical abstract

1

lP

re

-p

ro of

Polyethylenimine (PEI) caged platinum nanomaterials modified bacterial cellulose (PEI-Pt@BC) bioadsorbent was synthesized via a facile in-situ reduction method and this versatile membrane has a preferential absorbability of anionic dye than cationic analogue mainly attributed to the interaction between positive-charged PEI and dye molecules.

Abstract

na

With the continuous civilization and industrialization, the problem of dye wastewater treatment has been drawn widespread attention. This study focuses on in-situ reduction

ur

of cationic polyethylenimine (PEI) caged platinum nanomaterials (PEI-Pt) onto the bacterial cellulose (BC) substrate to fabricate a versatile bio-adsorbent (PEI-Pt@BC

Jo

membrane). Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA) were employed to confirm that PEI-Pt composite could anchor onto BC without any damage of its original three-dimensional porous structure. Thereafter, the distinguishing

2

adsorption behaviors of PEI-Pt@BC membrane were studied choosing acid black ATT as a target and methylene blue (MB) as a control group. The maximum amount of acid black ATT adsorption reaches to 1157.9 mg/g, which conforms to the quasi-secondorder kinetic model and Freundlich isothermal model. Whereas, the adsorption capacity of MB is only 13.5 mg/g. Obviously, the PEI-Pt@BC membrane has a preferential adsorbability of anionic dye than cationic analogue mainly attributed to the interaction

ro of

between positive-charged PEI and dye molecules. Thus, this PEI-Pt@BC adsorbent exhibits eco-friendly and highly-efficient merits, showing a promising potential in treatment of anionic dyes especially from the textile printing and dyeing effluent.

Jo

ur

na

lP

re

adsorption behaviors; High adsorption capacity

-p

Keywords: Bacterial cellulose; Bio-adsorbent; Environmental-friendly; Distinct

1. Introduction

3

Accompanying with the continuous civilization construction and rapid industrialization, dye wastewater originated from various industrial fields, especially the textile printing and dyeing industry, became a noticeable and concerned problem around the world [1]. Dye wastewater, as one of the main sources of pollutant, possesses enormous special traits like complex pollutant component, large chemical oxygen demand (COD) and biochemical oxygen demand (BOD), high alkalinity, which makes

ro of

it difficult and time-consuming to tackle. Once the effluent containing residual dyes is discharged into natural and domestic water environment, it will definitely and

powerfully endanger the aquatic environment, and living plant or animal species, even

resulting in the irreversible diseases like carcinogenic sensitization, asthma, and anemia

-p

for human-being [2, 3].

re

The common processing methodology of dye wastewater can be divided into chemical proposal, physical method and biological treatment. Among them, adsorption

lP

technique is one of the most effective candidates in the wastewater treatment, based on its relatively low cost and high efficiency [4]. Activated carbon, graphene, and clay as

na

the favored and widely-used adsorbent materials have been already studied in depth [5, 6]. With a view to readily available and eco-friendly raw materials, realizable

ur

degradation, and considerable biocompatibility [7], bio-based polymers (e.g. cellulose, biochar, etc.) obtained from microbial biomasses or agricultural and industrial wastes,

Jo

had drawn enormous attention and intensively investigated as the bio-sorbents to remove heavy metal ions and organic dyes from wastewater [8]. Wang et al. reported the biochar adsorbent (defined as SBs) produced by the pyrolysis of switchgrass under 600 and 900 °C, has the adsorption capacity for methylene blue (MB) dyes at 196.1, and 37.6 mg/g, respectively [9]. According to the high surface area, the adsorption of MB

4

under the high temperature is larger than that of under 600 °C. More interesting is that SBs exhibited the better adsorption capacity of cationic dyes than that of anionic dyes on account of strong π-π interaction, electrostatic property, and small molecular weight. Achaby’s group proposed the hydrated cellulose microfibrils (CMFs) prepared from coffee pulp waste presented the excellent water-uptake capacity with the swelling ratio at 265% [10]. This kind of CMFs has the maximum adsorption capacity at 182.5 mg/g

ro of

and fit to the pseudo-second-order kinetic mode. Moreover, Zhou et al. prepared one novel nano-paper by quaternized cellulose nanofibrils and this nano-paper demonstrated excellent adsorption ability of anionic acid green dye with the uptake ability at 650 mg/g [11].

-p

Bacterial cellulose (BC), as one kind of bio-polymers, has a good porous fibril

re

structure and durable mechanical properties, presenting a great potential application in the fields of wastewater treatment, paper industry, and tissue engineering [12-14].

lP

However, there are three main issues of BC for practical utilization need to be considered: (1) the unsatisfied adsorption performance in spite of acceptable cost

na

efficiency; (2) the lack of selective adsorption of target pollutants; (3) the multifunctionality to meet diverse demands. Therefore, a plenty of attempts were made

ur

recently by the mean of appropriate modification of BC’s functional group or deliberate recombination of versatile materials onto the BC matrix, which could endow or enhance

Jo

its novel properties and expand its application [15-19]. For instance, Qi et al. put forward the interconnected anatase nanowires with a mesoporous structure deposited on the BC membranes, exhibited the strengthening photocatalytic activity of Rhodamine B on account of large accessible surface areas [20]. Similarly, Wei’s group [21] and Ji’s group [22] assembled nitrogen-doped carbon dots (CDots) and CdTe quantum dots

5

(QDots) onto the BC substrate to fabricate blue and green fluorescent nanofibers. The synthesized QDots-BC and CDots-BC composites own the new optical properties on the premise of retaining BC’s porous structure, and reveal the excellent detection ability for iron ion and glucose, respectively. In consideration of fluorescence, noble metal nanomaterials such as gold, silver as well as platinum nanoclusters, are the ideal candidates owing to their lower toxicity, ultra-small size and better biocompatibility,

ro of

compared to the QDots and organic dyes [23]. Therefore, the introduction of metal nanoclusters to modify the BC is a preferable way to give their fluorescence properties, showing the potential in the fabrication of fluorescent probe for the detection of heavy metals or organic dyes. As a usual cationic polymer, polyethylenimine (PEI) with

-p

primary, secondary, and tertiary amino groups can be easily self-assembled onto diverse

re

matrix materials to form a monolayer, achieving the change of physicochemical properties of substrate surface [24]. For example, the co-deposition of catechol and

lP

polyethyleneimine is effective to endow the polypropylene microfiltration membranes with superior adsorbability of anionic dye, and the treating capacity of acid black

na

reaches 170 mg/g [25]. Thus, decoration BC with PEI could achieve the surface functionalization, promotion of adsorptive capacity and possible selective dispose of

ur

anionic contaminant.

Herein, cationic polymer PEI caged platinum nanomaterials (PEI-Pt) was in-situ

Jo

synthesized onto the BC substrate to form a versatile bio-adsorbent (PEI-Pt@BC membrane) with fluorescent features. Scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), Xray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) were used to determine the morphology and

6

structure of resultant PEI-Pt@BC bio-adsorbent and proved that PEI-Pt composite could anchor to BC nanofibers without any obvious damage of BC’s original structure. Thereafter, the distinguishing adsorption behaviors of PEI-Pt@BC bio-adsorbent were studied choosing acid black ATT as a target and MB as a control group. This kind of PEI-Pt@BC had a considerable and preferential adsorbance ability of anionic organic dye than cationic analogue based on the interaction between positive-charged PEI and

ro of

dye molecules. These results illuminate that bio-based PEI-Pt@BC membrane exhibits eco-friendly, highly efficient and facilely acquired merits, showing a great potential in

the distinct absorbability of anionic dyes from industrial wastewater, especially for the textile printing and dyeing effluent.

-p

2. Materials and methods

re

2.1. Materials

All chemicals used were analytical grade and without any further purification.

lP

Hydrogen hexachloroplatinate (IV) hexahydrate (H2PtCl6·6H2O, 99.9%), L-ascorbic acid (99.0%), sodium hydroxide (NaOH, 99.0%), hydrochloric acid (HCl, 36.0-38.0%),

na

ethanol absolute (99.7%), spectrum pure potassium bromide (KBr, 99.9%) were purchased from National Medicines Corporation Ltd. of China. Acid black ATT and

ur

MB were bought from Tianjin Shengda Ruitai Technology Development Co., Ltd. of China and Tianjin Kemiou Chemical Reagent Co., Ltd. of China, respectively. Hyper-

Jo

branched PEI (Mw = 10,000, 99.0%) were obtained from Alfa Aesar, A Johnson Matthey Company. BC hydrogel membrane (water content = 98%, diameter = 30-100 nm and length = 10-20 μm) was brought from Guilin Qihong Technology Co., Ltd. of China. The ultra-pure water utilized in all experiments was handled by a Milli-Q Direct

7

- Q5 ultrapure water system (Millipore, Billerica, MA, USA) and removed the air by N2 over 30 min prior to use. 2.2. Synthesis of PEI-Pt@BC bio-adsorbent BC hydrogel (Size: 30 mm × 30 mm × 3 mm) prepared by the common “Nata de coco” method [26], was immersed in NaOH solution (0.1 mol/L) under 90 °C for over 30 min in order to remove excess strain and culture medium. After the pH value

ro of

changed to neutral, the BC hydrogel was washed by ethanol and deionized water completely, and then put into sufficient ethanol for the solvent exchange. The 6 mL mixture of H2PtCl6 solution (0.67 mM) and PEI (2 mM) solution was stirring

adequately for over 2 h. Thereafter, the dried BC was added into this mixture for 24 h

-p

under 4 °C in order to complete immersion. L-AA (0.16 mL, 0.80 mM) was drop-wisely

re

dropped under 85 °C and the reducing processes lasted for 8 h. The pre-product was washed by ethanol and deionized water three times to get rid of unreacted small

lP

molecules. After freezing-dry for over 24 h, the resultant PEI-Pt@BC bio-adsorbent were stored under the temperature at 4 °C and dry condition prior to use.

na

2.3. Adsorption experiments

Anionic acid black ATT was selected as the target dyes while cationic MB was

ur

employed as the control group. Batch equilibrium adsorption experiments were carried out to examine the adsorption ability of different organic dyes for PEI-Pt@BC bio-

Jo

adsorbent. The synthesized PEI-Pt@BC membrane (13 mg) was put into an Erlenmeyer flask containing 100 mL of acid black ATT dye aqueous solution at various concentration (50-210 mg/L). The desired pH of whole solution was changed from 1-12 by adjusting the amount of NaOH (0.1 M) and HCl (0.1 M) solution. The experiments were carried out under the temperature at 298 K and the rotation speed for stirring set at

8

600 r/min. The obtained supernatant was centrifuged for 15 min (10000 × g). Afterwards, ultraviolet-visible (UV-vis) spectrophotometry was employed to measure the concentration of ATT at its characteristic adsorption peak. The value of adsorbed acid black ATT per unit mass of PEI-Pt@BC bio-adsorbent was calculated utilized the following Equation 1: qt

C0 Ct V m

（1

ro of

）

Where qt (mg/g) is the adsorption capacity at different time. C0 (mg/L) is the initial

concentration of dyes and Ct (mg/L) is the concentration of dyes at variational time. m (g)

-p

represents the mass of the adsorbent and V (L) stands for the volume of initial dye

re

solution.

The kinetic studies of adsorption were carried out in an Erlenmeyer flask containing

lP

250 mL of acid black ATT dye aqueous solution with the initial concentration at 180 mg/L and the mass of adsorbent at 40 mg wherein the extent of adsorption was

na

investigated as a function of time. The supernatant was obtained successively from 0-260 min at a certain time interval. The amount of adsorption at time t, that is qt (mg/g), was

ur

also calculated by the Equation 1. Besides, the effect of temperature on adsorption ability was carried out as the same as the adsorption kinetic experiment procedure under the

Jo

different temperature at 298 K, 308 K, 318 K, respectively. The adsorption process of MB dyes is similar to that of acid black ATT. The difference

is as follows: the synthesized PEI-Pt@BC membrane (6 mg) was put into an Erlenmeyer flask containing 100 mL of MB dye aqueous solution at various concentration (5-80 mg/L). The kinetic studies of adsorption were executed in an Erlenmeyer flask containing

9

250 mL of MB dye aqueous solution with the initial concentration at 10 mg/L and the mass of adsorbent at 15 mg wherein the extent of adsorption was investigated as a function of time from 0-360 min, controlling the temperature at 298 K and rotation speed at 600 r/min. 2.4. Characterization SEM (Zeiss MERLIN Compact, German) was used to determine the porous

ro of

morphology of PEI-Pt@BC bio-adsorbent at 5.00 kV and the test samples were treated by spray-gold before the measurement. Elemental compositions of bio-adsorbent were analyzed by energy dispersive spectrometer (EDS) equipping XFlash® 6 | 30 detector (Bruker Co. Ltd., German). The details of combination between BC and PEI-Pt were

-p

measured by TEM (Tecnai G2 F20 S-TWIN TMP, Thermo Fisher Scientific Inc., USA)

re

using ultra-thin carbon grids at 200 kV. pH was recorded by Precision PH meter (PHS3C, Hangzhou aurilong instrument Co. Ltd., China). XRD data were collected on the

lP

X'Pert PRO MPD (Panalytical, Holland) with the Cu Ka radiation (scanning rate is 2 s−1). The oxidation state of Pt was examined by Thermo ESCALAB 250XI (Thermo Fisher

na

Scientific Inc., USA) with reference to the C 1s peak at 284.6 eV. The TGA data were collected under the temperature range from 40 to 700 °C and N2 atmosphere at a heating

ur

rate of 10 °C/min by NETZSCH TG 209 F1 Libra Thermogravimetric Analyzer (NETZSCH Inc., Germany). UV-vis and FTIR data were tested by Agilent Cary 5000

Jo

Spectrometer (Agilent Technologies, Inc., USA) and Thermo Nicolet Nexus-870 FTIR Spectrometer (Thermo Fisher Scientific Inc., USA) using KBr pellet method, respectively.

3. Results and discussion 3.1. Synthesis and characterization of PEI-Pt@BC bio-adsorbent.

10

The synthetic proposal of PEI-Pt@BC bio-adsorbent were selected a simple in-situ reduction method. The BC film was completely immersed in the complex solution between Pt ions precursor and PEI. Then the Pt ions were reduced to Pt nanoclusters among the BC nanofibers, which could realize the sufficient anchor of the PEI-Pt composite onto BC substrate and finally formation of desired PEI-Pt@BC bio-adsorbent (Fig. 1a). In this materials, PEI-Pt composite plays dual-functionality that is endowing

ro of

the fluorescence to adsorbent, and supplying a mass of cationic properties to achieve the selective adsorbance of targeted pollutant. Fig. 1b-c indicates this synthesized bio-

adsorbent is in yellow color under the daylight while weak cyan fluorescence under the irradiation of UV light (λ = 365 nm). It's worth noticing that the fluorescence of PEI-

-p

Pt@BC will quench after achieving the adsorption of organic dyes (Fig. S1a, b).

re

Furthermore, PEI-Pt@BC membrane could present the flexible and durable mechanical properties even under the water environment (Fig. S1c), which makes them feasible to

lP

recycle and avoids the complicated post-processing in comparison with powder or fragile bulk adsorbent. Hence, the modification of BC with PEI-Pt composite could

na

accomplish the functionality of BC with fluorescence and enlarge the application range of this kind of bio-sorbent.

ur

The morphology of PEI-Pt@BC bio-adsorbent was determined by SEM and TEM. Fig. 2a indicates that pure BC film has three-dimensional (3D) interconnected

Jo

nanofibrous networks with average diameter at 40 ± 20 nm (Fig. 2b). Similarly, the prepared PEI-Pt@BC bio-adsorbent still maintain BC’s initial structure, proving that the porous structure does not affect by doping PEI-Pt composite (Fig. 2c). EDS technique was also employed to check the element of pre-synthesized bio-adsorbent. It is obvious to notice that Pt element is existing in the membrane and the amount of weight is near 3

11

% (Fig.2d). Besides, it is obvious that the PEI-Pt composite was anchored onto the BC nanofibers identified by TEM graph (Fig. 2e). The Pt stabilized by PEI was reduced to sphere structure and the statistical diameter is near 1.4 ± 0.5 nm (Fig. 2f). The size distribution of Pt is not quite narrow because of the less protection by PEI ligands of which some of primary amines were connected to BC surface via hydrogen-bond interaction.

ro of

Moreover, the thermal behaviors of BC, PEI and BC-PEI@Pt were investigated by TGA analysis. The TG and corresponding DTG (derivative of mass on temperature used as mass changing rate) curves are shown in Fig. 3. Based on the results, it is found that the onset degradation temperatures (Tonset) of all three samples are very similar and

-p

ranging from 282.6 °C to 283.4 °C. However, more information can be revealed by

re

DTG curves, because DTG is more sensitive to the charge of degradation rate [27]. The small peaks showed under 200 °C are assigned to the loss of adsorbed water, and no

lP

need to specified in degradation analysis. The two main weight loss stages of PEI are clearly demonstrated by two peaks at 321.4 °C and 380.1 °C, which corresponds to the

na

degradation of side chain and backbone structure, respectively. On the other hand, there is one main peak showed in DTG curves of pure BC at 339.1 °C. As for PEI-Pt@BC

ur

bio-adsorbent, there is only one main peak occurred at 326.6 °C, within the range of 321.4 °C and 339.1 °C, which also implies that PEI-Pt composite is well composited

Jo

with the BC matrix.

Fig. 4a shows the XRD diffraction patterns of BC and PEI-Pt@BC. The broad peaks

at 14.5°, 16.7° and 22.6° emerged in both patterns, are assigned to the typical peaks ——

corresponding to the crystallographic plane of (1 1 0), (110), and (200) reflection of BC, respectively [28]. Compared with pure BC sample, the main diffraction peaks of PEI-

12

Pt@BC remain unchanged. The result of XRD patterns suggests that the crystalline morphology of BC substrate could still be maintained after the in-situ synthesis process to form the desired PEI-Pt@BC. Additionally, FTIR spectra of PEI, BC and PEIPt@BC are shown in Fig. 4b. The characteristic peaks of BC at 3337 cm-1 and 2893 cm−1 are ascribed to stretching vibration of O-H and C-H, respectively. The peaks at 1163, 1109, and 1033 cm-1 are assigned to the glycosidic link of C1-O-C4, C3-O3, C6O6, respectively [21]. Meanwhile, characteristic peaks of PEI are observed at 1604 cm-1

ro of

(N-H, bending), 1465 cm−1 (C-H, bending), 1120 and 1043 cm−1 (C-N, stretching),

which are all coincident with previous works [29]. As for the synthesized PEI-Pt@BC

bio-adsorbent, the characteristic peak for PEI (1604 cm−1, N-H, bending) and BC (1163

-p

cm-1, glycosidic link of C1-O-C4) are all appeared, suggesting a successful self-

re

assembly between PEI-Pt composite and BC matrix.

The oxidation state of Pt component was examined by XPS technique. The XPS

lP

spectrum of Pt 4f region show that 4f7/2 and 4f5/2 binding energy (B.E.) are at 72.4 and 75.9 eV, respectively (Fig. 4c). Since these values approximate to the range of the Pt(0)

na

state (71.3-72.4 eV), we conclude that the Pt component were reduced to zero state using in-situ reduction method. In addition, the 1s B.E.s of O for BC and PEI-Pt@BC

ur

are 530.9 and 531.0, respectively (Fig. S2a, b). This results further proved the doping of PEI-Pt composite will not affect the structure of BC substrate. Meanwhile, the 1s B.E.

Jo

of N for PEI-Pt@BC is 398.7 eV (Fig. S1c), which is a bit higher than that of typical N (398.4 eV), suggesting reduced Pt are caged by amino groups in PEI ligands. In sum, the results of morphological and structural analysis displayed above

demonstrated that PEI-Pt@BC bio-adsorbent in nano scale possess 3D porous structures and exhibit fluorescent properties. Moreover, the PEI-Pt composite has successfully

13

doped onto the BC substrate without any side effect of BC’s original structure, exhibiting the great potential in the adsorption of organic dyes. 3.2. Adsorption behaviors of anionic dyes PEI-Pt@BC bio-adsorbent was employed to adsorb two kinds of different organic dyes, e.g. acid black ATT and MB. The effect of pH, temperature, initial concentrations of dyes, as well as the adsorption isothermal and kinetics analysis were put forward to

ro of

evaluate the adsorption behaviors on the chosen dyes. 3.2.1. Effect of pH and temperature on anionic dye adsorption

pH plays a crucial role on the adsorption behavior of acidic black ATT due to the

-p

different ionic states of the PEI under the alkaline and acid environment. That is to say,

the pH of initial acidic black ATT solution could influence the adsorption ability for the

re

adsorbent. From Fig. 5a, it can be seen that the adsorbability of PEI-Pt@BC bio-

lP

adsorbent under different pH ranged from 2-12 was measured. The maximum of adsorptive amount is at 5.2. As the pH increases larger than 5.2, the data of adsorbance will go down dramatically to a third, smaller than 250 mg/g. However, the amount of qe

na

(mg/g) will not decrease obviously when the pH is under acid situation (< 5.2) and the value is all larger than 700 mg/g. On the whole, the PEI-Pt@BC bio-adsorbent exhibits

ur

the optimal adsorbability at acid conditions. The mechanism is because the amine

Jo

groups in PEI could be protonated to appear the positive property when the pH is at the acid condition, which easily electrostatic attract with the sulfonic acid group in acid black ATT. while with the increasing of pH, the amine groups are disable to protonation, resulting in the relatively lower adsorption ability of acid black ATT. The alteration of temperature is always related to the change of dyes’ diffusion rate and solution viscosity, which may influence the adsorption capacity at equilibrium

14

condition. Fig. 5b illustrates the effect of temperature on the acid dye adsorption, fixing the value of temperature at 298 K, 308 K, and 318 K. When the time of adsorption is below 60 min, the adsorbing capacity is all most the same under these three temperatures. As the time increased, the evident difference appears. The equilibrium of adsorption reaches a maximum at 298 K and it decreases gradually as the temperatures go up to 308 K and 318 k. Obviously, the rising temperature decline the equilibrium

ro of

uptake capacity of materials towards acid black ATT. This result indicates that the adsorptive forces between the dyes and the active sites on the surface of PEI-Pt@BC

membrane are weakened as the temperature increased, namely, an exothermic process

occurred [30]. In a conclusion, the temperature of near 298 K is the favorable condition

-p

for the adsorption of acid black ATT.

re

3.2.2. Effect of initial dye concentration on anionic dye adsorption

In general, the initial dye concentration strongly affects the amount of dye adsorption.

lP

From Fig. S3, it can be seen that the equilibrium adsorption capacity rises up with an increase of the initial concentration of acid black ATT because of the high driving force

na

for mass transfer at a high initial dye concentration [31]. As the concentration of dyes increases continually (> 180 mg/L), the active sites of PEI were almost occupied by dye

ur

molecules. Consequently, the diffusion resistance goes up, leading to a slight reducing of adsorption rate. However, the trend of qe remains growing based on the concentration

Jo

gradient compel more dye molecules adsorb on the surface of membrane. 3.2.3. Adsorption isotherms analysis The Langmuir, Freundlich and Temkin models were selected to evaluate the

adsorption isotherms of acid black ATT using the PEI-Pt@BC bio-adsorbent (Supplementary materials SM-4) [32, 33]. The summarize of the linear fitting results for

15

three models, Langmuir, Freundlich, and Temkin, was shown in Table 1 and Fig. S4. Apparently, the adsorbance of acid black ATT using the PEI-Pt@PEI bio-adsorbent is more qualified to Freundlich model with higher correlation coefficient (R2 = 0.9936). This result explicates that the adsorption procedure of acid black ATT onto PEI-Pt@PEI bio-adsorbent is a multi-layer adsorption with both homogeneous and inhomogeneous adsorption on the surface of adsorbent. Besides, n > 1 means the adsorbent is favorable to

ro of

adsorption [34]. Since the R2 values of Langmuir and Freundlich models are 0.9746 and 0.9936, the maximum adsorption capacities of PEI-Pt@PEI bio-adsorbent for acid black ATT could be simulated by the Langmuir isotherm [35], which is calculated as 1157.9

-p

mg/g. 3.2.4. Effect of contact time on anionic dye adsorption

re

The effect of contact time on acid dye adsorption was put forward in order to

lP

investigate the efficiency and dynamics of the adsorption, namely adsorption kinetics. Fig. 6a illustrates the tendency of time-dependence uptake for acid black ATT. The adsorption increased rapidly within 50 min, indicating that the composite membrane

na

material adsorbs the acid black ATT by a large number of active sites (amino groups in PEI) attract the sulfonic groups in the dyes via strong electrostatic effects, as well as the

ur

van der Waals force from the pore structure. Moreover, the presence of amino and

Jo

hydroxyl groups on the membrane recedes the resistance to the migration of ATT molecules, resulting in a fast adsorption rate at the beginning of adsorption. After 120 min, the upward trend flattens out and finally becomes a platform, expressing no change as the time further increased. The value of adsorbability is over 900 mg/g. 3.2.5. Adsorption kinetics analysis

16

The pseudo-first-order, pseudo-second-order and intraparticle diffusion models were chosen to examine the adsorption kinetics of acid black ATT using the PEI-Pt@BC bioadsorbent (Supplementary materials SM-5) [9, 36-38]. The fitting curves were show in Fig. 6b-c using three models described above. The kinetic parameters were summarized in Table 2. It can be seen that the adsorption of acid black ATT by the PEI-Pt@BC conforms to quasi-second-order kinetic equation, and the corresponding R2 is 0.9919.

ro of

This result indicates that the adsorption process of PEI-Pt@BC bio-adsorbent to acid black ATT has a chemical reaction between amine groups from PEI and sulfonic groups from acid black ATT, which the whole process is mainly affected by chemical

adsorption. Moreover, this kind of membrane also has an ability to physically adsorb

-p

acid black ATT by the van der Waals force depend on its pore structure. The calculated

re

adsorption equilibrium is 1076.8 mg/g.

lP

3.3. Adsorption behaviors of cationic dyes

In order to examine the selective adsorption behaviors of PEI-Pt@PEI membrane, cationic MB was chosen as the comparative group. The same procedure as the acid

na

black ATT was carried out. The effect of pH was proved that MB have a better adsorption under the alkaline environment (Fig. 7a). In the view of the pH condition at

ur

2-3, amine groups in PEI are protonated. There is an electrostatic repulsion between

Jo

amine groups and cationic MB molecules. While the protonation will recede and even disappear as the pH increases to over 10.5, resulting in the promotion of adsorption. It is worth noticing that the adsorbing capacity of MB is much lower than ATT using PEIPt@BC bio-adsorbent. The influence of initial concentration of dye was also check. Fig. 7b shows that the amount of MB decreased as the initial concentration of dye rises, which can be

17

explained by the larger number of cations leads to the greater repulsion. The linear fitting results for Langmuir, Freundlich, and Temkin isothermal models, were shown in Fig. S5 and Table S1. The adsorbance of MB using PEI-Pt@PEI bio-adsorbent relatively conforms to Langmuir models with R2 at 0.6385, in comparison with other two models with R2 both smaller than 0.1. The effect of contact time on MB dye adsorption was tested as well. At the first 10

ro of

mins, the adsorption capacity increases because of van der Waals force between the porous materials and MB dyes as well as the existence of concentration gradient (Fig. 8a). Thereafter, it declines abruptly due to the repulsive force between MB molecules and amine groups from PEI. As the time raised, the trend of adsorptive performance

-p

presented a slight twist, which is originated from the synergistic competitive effect

re

between the electrostatic repulsion and Van der Waals attraction. Most important is that the amount of adsorption for MB is below 25 mg/L, which is much lower than that of

lP

acid black ATT using the PEI-Pt@BC bio-adsorbent. Furthermore, the pseudo-firstorder, pseudo-second-order and intraparticle diffusion models were chosen to examine

na

the adsorption kinetics of MB (Fig. 8c-d). The results declare that all the models were not fit for this situation, proved by R2 is all smaller than 0.18 (Table S2). In sum, the

ur

PEI-Pt@BC bio-adsorbent could achieve preferable adsorbance of anionic dyes (acid black ATT) than cationic dyes (MB).

Jo

3.4. The machenism of distinct adsorption behaviours According to the data of adsorption isothermal and kinetic analysis shown above, we

deduced the mechanism of distinct adsorbance performance on selected two organic dyes using BC-PEI@Pt membrane as the adsorbent. Firstly, when the membrane was immersed in dye solution, BC as a matrix with superior hydrophilicity and multiple-

18

macropores structure is in favor of gathering the dye molecules around the surface of membrane (Fig. 9). Then, the dyes could diffuse inside of materials. At this stage, the positively charged primary and secondary amine in PEI@Pt composite will play the leading role in the dye adsorption dependent on the electrostatic attraction principle. And the selectivity of anionic dyes adsorption of BC-PEI@Pt is also well explained. As for anionic acid black ATT group, amine groups from PEI manifest positive charge

ro of

while sulfonic groups from acid black ATT show negative charge. Opposite charges exhibit mutual attraction and the whole adsorption procedure is mainly affected by

chemical force. Besides, the nitroso groups connected with benzene in ATT also appear the negative charge, which have a slight interaction with amine groups from PEI as

-p

well. In view of MB group, dimethyle(methylidene)ammonium groups at the terminal

re

of MB molecule are positive and it will emerge the mutual exclusion towards amine groups in PEI part, giving a rise to the much weaker adsorbance capacity than the acid

lP

black ATT group. This reasonable explanation could provide a helpful guidance in the adsorbent selecting for different dyes.

na

4. Conclusion

In conclusion, polyelectrolyte PEI caged Pt nanomaterials (PEI-Pt) were successfully

ur

assembled onto the BC substrate to fabricate a novel and fluorescent bio-based adsorbent (PEI-Pt@BC membrane) via a facile in-situ reduction method. The

Jo

morphology of PEI-Pt@BC bio-adsorbent was 3D porous with an average size of nanofibers and reduced Pt nanomaterials at 40 ± 20 nm and 1.4 ± 0.5 nm, identified by SEM and TEM technique. Furthermore, XPS, XRD, FTIR, and TGA proved that PEI-Pt composite could anchor onto BC nanofibers without any damage of BC’s original structure. Thereafter, the distinguishing adsorption behaviors of PEI-Pt@BC membrane

19

were studied choosing acid black ATT as a target and MB as a control group. The adsorption capacity of acid black ATT reaches to 1157.9 mg/g, which conforms to the quasi-second-order kinetic model and Freundlich isothermal model. As for MB dyes, the adsorption capacity is only 13.5 mg/g. Obviously, the PEI-Pt@BC bio-adsorbent had a considerable and preferential adsorbance ability of anionic organic dye than cationic analogue. The possibly mechanism of distinct adsorbance performance can be

ro of

inferred as the electrostatic attraction between positive charged amine group from PEI and negative anionic groups from acid black ATT, whereas the repulsive interaction between the positive charged amine group from PEI and the same charged MB

molecules. Therefore, this kind of bio-polymer based PEI-Pt@BC membrane exhibits

-p

eco-friendly, highly efficient and easily acquired merits, showing a great potential in the

re

treatment of anionic dyes from industrial wastewater, especially for the textile printing

lP

and dyeing effluent.

Appendix A. Supplementary data

na

Supplementary material related to this article can be found, in the online version, at

ur

doi:.

Declaration of interests

Jo

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

20

Funding This work was supported by the National Natural Science Foundation of China [21807121]; 2019 Youth Talents Promotion Project of Henan Province [2019HYTP039]; and the Project for Fundamental Research Funds of Zhongyuan

ro of

University of Technology [K2018YY020].

Acknowledgements

Dr. X. H. and Dr. S. W. thanks the supporting form “The 2018 Backbone Teachers of

-p

Zhongyuan University of Technology”, and “Program for Interdisciplinary Direction

Jo

ur

na

lP

re

Team in Zhongyuan University of Technology, China”.

21

References [1]

A. Sharma, Z. Syed, U. Brighu, A.B. Gupta, C. Ram, Adsorption of textile wastewater on alkali-activated sand, J. Clean. Prod., 220 (2019) 23-32. https://doi.org/10.1016/j.jclepro.2019.01.236.

[2]

F. Rafii, J.D. Hall, C.E. Cerniglia, Mutagenicity of azo dyes used in foods, drugs

ro of

and cosmetics before and after reduction by Clostridium species from the human intestinal tract, Food and Chem. Toxicol., 35 (1997) 897-901. https://doi.org/10.1016/S0278-6915(97)00060-4. [3]

P.V. Nidheesh, M. Zhou, M.A. Oturan, An overview on the removal of synthetic

-p

dyes from water by electrochemical advanced oxidation processes, Chemosphere,

[4]

re

197 (2018) 210-227. https://doi.org/10.1016/j.chemosphere.2017.12.195. I. Ali, New generation adsorbents for water treatment, Chem. Rev., 112 (2012)

[5]

lP

5073-5091. https://doi.org/10.1021/cr300133d.

N.K. Amin, Removal of direct blue-106 dye from aqueous solution using new

na

activated carbons developed from pomegranate peel: adsorption equilibrium and kinetics, J. Hazard. Mater., 165 (2009) 52-62.

[6]

ur

https://doi.org/10.1016/j.jhazmat.2008.09.067. K. Thakur, B. Kandasubramanian, Graphene and graphene oxide-based

Jo

composites for removal of organic pollutants: a review, J. Chem. Eng. Data, 64 (2019) 833-867. https://doi.org/10.1021/acs.jced.8b01057.

[7]

L. Xia, Z. Huang, L. Zhong, F. Xie, C.Y. Tang, C.P. Tsui, Bagasse cellulose grafted with an amino-terminated hyperbranched polymer for the removal of

22

Cr(VI) from aqueous solution, Polymers, 10 (2018) 931. https://doi.org/10.3390/polym10080931. [8]

M.E. Russo, F. Di Natale, V. Prigione, V. Tigini, A. Marzocchella, G.C. Varese, Adsorption of acid dyes on fungal biomass: equilibrium and kinetics characterization, Chem. Eng. J., 162 (2010) 537-545. https://doi.org/10.1016/j.cej.2010.05.058. J.H. Park, J.J. Wang, Y.L. Meng, Z. Wei, R.D. DeLaune, D.C. Seo,

ro of

[9]

Adsorption/desorption behavior of cationic and anionic dyes by biochars prepared at normal and high pyrolysis temperatures, Colloids Surf. A: Physicochem. Eng. Aspects, 572 (2019) 274-282. https://doi.org/10.1016/j.colsurfa.2019.04.029.

-p

[10] M. El Achaby, M. Ruesgas-Ramon, N.E. Fayoud, M.C. Figueroa-Espinoza, V.

re

Trabadelo, K. Draoui, H. Ben Youcef, Bio-sourced porous cellulose microfibrils from coffee pulp for wastewater treatment, Cellulose, 26 (2019) 3873-3889.

lP

https://doi.org/10.1007/s10570-019-02344-w.

[11] A. Pei, N. Butchosa, L.A. Berglund, Q. Zhou, Surface quaternized cellulose

na

nanofibrils with high water adsorbency and adsorption capacity for anionic dyes, Soft Matter, 9 (2013) 2047-2055. http://dx.doi.org/10.1039/C2SM27344F.

ur

[12] R. Jonas, L.F. Farah, Production and application of microbial cellulose, Polym. Degrad. and Stabil., 59 (1998) 101-106. https://doi.org/10.1016/S0141-

Jo

3910(97)00197-3.

[13] R.J. Moon, A. Martini, J. Nairn, J. Simonsen, J. Youngblood, Cellulose nanomaterials review: structure, properties and nanocomposites, Chem. Soc. Rev., 40 (2011) 3941-3994. http://dx.doi.org/10.1039/C0CS00108B.

23

[14] H. Tian, J. He, Cellulose as a scaffold for self-assembly: from basic research to real applications, Langmuir, 32 (2016) 12269-12282. https://doi.org/10.1021/acs.langmuir.6b02033. [15] M. Zeng, A. Laromaine, W. Feng, P.A. Levkin, A. Roig, Origami magnetic cellulose: controlled magnetic fraction and patterning of flexible bacterial cellulose, J. Mater. Chem. C, 2 (2014) 6312-6318.

ro of

http://dx.doi.org/10.1039/C4TC00787E. [16] L.S. Sobhanadhas, L. Kesavan, P. Fardim, Topochemical engineering of cellulose-based functional materials, Langmuir, 34 (2018) 9857-9878. https://doi.org/10.1021/acs.langmuir.7b04379.

-p

[17] N. Yin, S. Chen, Z. Li, Y. Ouyang, W. Hu, L. Tang, W. Zhang, B. Zhou, J. Yang,

re

Q. Xu, Porous bacterial cellulose prepared by a facile surfactant-assisted foaming method in azodicarbonamide-NaOH aqueous solution, Mater. Lett., 81 (2012)

lP

131-134. https://doi.org/10.1016/j.matlet.2012.04.133. [18] B. Wicklein, J. Arranz, A. Mayoral, P. Aranda, Y. Huttel, E. Ruiz-Hitzky,

na

Nanostructured carbon–metal hybrid aerogels from bacterial cellulose, RSC Adv., 7 (2017) 42203-42210. http://dx.doi.org/10.1039/C7RA07534K.

ur

[19] Y. Hu, F. Liu, Y. Sun, X. Xu, X. Chen, B. Pan, D. Sun, J. Qian, Bacterial cellulose derived paper-like purifier with multifunctionality for water

Jo

decontamination, Chemical Engineering Journal, 371 (2019) 730-737. https://doi.org/10.1016/j.cej.2019.04.091.

[20] D. Zhang, L. Qi, Synthesis of mesoporous titania networks consisting of anatase nanowires by templating of bacterial cellulose membranes, Chem. Commun., (2005) 2735-2737. http://dx.doi.org/10.1039/B501933H.

24

[21] P. Lv, Y. Yao, D. Li, H. Zhou, M.A. Naeem, Q. Feng, J. Huang, Y. Cai, Q. Wei, Self-assembly of nitrogen-doped carbon dots anchored on bacterial cellulose and their application in iron ion detection, Carbohyd. Polym., 172 (2017) 93-101. https://doi.org/10.1016/j.carbpol.2017.04.086. [22] J. Yao, P. Ji, B. Wang, H. Wang, S. Chen, Color-tunable luminescent macrofibers based on CdTe QDs-loaded bacterial cellulose nanofibers for pH and glucose

ro of

sensing, Sensors and Actuat. B: Chem., 254 (2018) 110-119. https://doi.org/10.1016/j.snb.2017.07.071.

[23] X. Le Guevel, Recent advances on the synthesis of metal quantum nanoclusters and their application for bioimaging, IEEE J. Sel. Top. Quantum Electron., 20

-p

(2014) 45-56. http://dx.doi.org/10.1109/JSTQE.2013.2282275.

re

[24] J. Wang, X. Lu, P.F. Ng, K.I. Lee, B. Fei, J.H. Xin, J.-y. Wu, Polyethylenimine coated bacterial cellulose nanofiber membrane and application as adsorbent and

lP

catalyst, J. Colloid Interf. Sci., 440 (2015) 32-38. https://doi.org/10.1016/j.jcis.2014.10.035.

na

[25] W.-Z. Qiu, H.-C. Yang, L.-S. Wan, Z.-K. Xu, Co-deposition of catechol/polyethyleneimine on porous membranes for efficient decolorization of

ur

dye water, J. Mater. Chem. A, 3 (2015) 14438-14444. http://dx.doi.org/10.1039/C5TA02590G.

Jo

[26] M. Tabuchi, Nanobiotech versus synthetic nanotech?, Nat. Biotechnol., 25 (2007) 389. https://doi.org/10.1038/nbt0407-389.

[27] S. Kim, J.K. Park, Characterization of thermal reaction by peak temperature and height of DTG curves, Thermochim. Acta, 264 (1995) 137-156. https://doi.org/10.1016/0040-6031(95)02316-T.

25

[28] C. Tokoh, K. Takabe, M. Fujita, H. Saiki, Cellulose synthesized by acetobacter xylinum in the presence of acetyl glucomannan, Cellulose, 5 (1998) 249-261. https://doi.org/10.1023/A:1009211927183. [29] O. Yemul, T. Imae, Synthesis and characterization of poly(ethyleneimine) dendrimers, Colloid Polym. Sci, 286 (2008) 747-752. http://dx.doi.org/10.1007/s00396-007-1830-6.

ro of

[30] M.A.M. Salleh, D.K. Mahmoud, W.A.W.A. Karim, A. Idris, Cationic and anionic dye adsorption by agricultural solid wastes: a comprehensive review,

Desalination, 280 (2011) 1-13. https://doi.org/10.1016/j.desal.2011.07.019.

[31] Y. Bulut, H. Aydın, A kinetics and thermodynamics study of methylene blue

re

https://doi.org/10.1016/j.desal.2005.10.032.

-p

adsorption on wheat shells, Desalination, 194 (2006) 259-267.

[32] J. Li, H.Y. Zhao, C.G. Ma, Q.X. Han, M.X. Li, H.L. Liu, Preparation of

lP

Fe3O4@polyoxometalates nanocomposites and their efficient adsorption of cationic dyes from aqueous solution, Nanomaterials, 9 (2019).

na

https://doi.org/10.3390/nano9040649.

[33] Y. Wu, M. Su, J. Chen, Z. Xu, J. Tang, X. Chang, D. Chen, Superior adsorption of

ur

methyl orange by h-MoS2 microspheres: Isotherm, kinetics, and thermodynamic studies, Dyes Pigments, 170 (2019) 107591.

Jo

https://doi.org/10.1016/j.dyepig.2019.107591.

[34] A. Leshaf, H.Z. Cherif, K. Benmansour, Adsorption of acidol red 2BE-NW dye from aqueous solutions on carboxymethyl cellulose/organo-bentonite composite: Characterization, kinetic and thermodynamic studies, J. Polym. Environ., 27 (2019) 1054-1064. https://doi.org/10.1007/s10924-019-01395-1.

26

[35] M. Makrygianni, Z.G. Lada, A. Manousou, C.A. Aggelopoulos, V. Deimede, Removal of anionic dyes from aqueous solution by novel pyrrolidinium-based polymeric ionic liquid (PIL) as adsorbent: Investigation of the adsorption kinetics, equilibrium isotherms and the adsorption mechanisms involved, Journal of Environmental Chemical Engineering, 7 (2019) 103163. https://doi.org/10.1016/j.jece.2019.103163.

ro of

[36] J. Fu, J. Zhu, Z. Wang, Y. Wang, S. Wang, R. Yan, Q. Xu, Highly-efficient and selective adsorption of anionic dyes onto hollow polymer microcapsules having a high surface-density of amino groups: Isotherms, kinetics, thermodynamics and

https://doi.org/10.1016/j.jcis.2019.01.131.

-p

mechanism, J. Colloid Interf. Sci., 542 (2019) 123-135.

re

[37] A. Rodríguez, J. García, G. Ovejero, M. Mestanza, Adsorption of anionic and cationic dyes on activated carbon from aqueous solutions: Equilibrium and

lP

kinetics, J. Hazard. Mater., 172 (2009) 1311-1320. https://doi.org/10.1016/j.jhazmat.2009.07.138.

na

[38] A. Aichour, H. Zaghouane-Boudiaf, Highly brilliant green removal from wastewater by mesoporous adsorbents: Kinetics, thermodynamics and equilibrium

ur

isotherm studies, Microchem. J., 146 (2019) 1255-1262.

Jo

https://doi.org/10.1016/j.microc.2019.02.040.

27

Tables:

Table 1 Isotherm constants and values of acid black ATT adsorption using the PEI-Pt@BC bioadsorbent.

Langmuir

Parameters1

Value

qm (mg/g)

1157.9

ro of

Isotherms

KL (L/mg)

0.0649

R2

0.9746

KF (mg/g) Freundlich

207.8

2.7930

-p

n R2

re

AT (L/mg)

1.5188

bT (J/mol)

11.0106

R2

0.9566

lP

Temkin

The temperature of experiments is 298 K.

Jo

ur

na

1

0.9936

28

Table 2 Kinetic constants and values of acid black ATT adsorption using the PEI-Pt@BC bioadsorbent. Model

Parameters1

Value

qe, cal (mg/g)

1057.6

k1 (min-1)

0.0213

R2

0.9777

Pseudo-first-

Pseudo-

qe, cal (mg/g)

second-

k2 (g/mg·min)

order

R2

ro of

order

1076.8

0.00003261 0.9919

-p

ki (mg/g/min1/2) Intraparticle C (mg/g)

re

diffusion R2

The temperature of experiments is 298 K.

Jo

ur

na

lP

1

29

66.1662 40.6724 0.9657

Figure captions: Fig. 1. (a) The schematic process for in-situ synthesis of PEI-Pt@BC bio-adsorbent.

na

lP

re

-p

ro of

The photographs of PEI-Pt@BC under (b) daylight and (c) UV light (λ = 365 nm).

ur

Fig. 2. SEM graph of (a) pure BC and (b) corresponding histogram of size distribution.

Jo

(c) SEM graph and (d) EDS spectrum of PEI-Pt@BC bio-adsorbent. Insert is the weight ratio and atomic ratio of each element. (e) TEM graph of PEI-Pt@BC and (f) corresponding histogram of Pt’s size distribution.

30

ro of -p re lP na ur Jo

Fig. 3. The curves of weight loss versus temperature (upper) and corresponding derivative of weight loss versus temperature (lower) for BC, PEI and PEI-Pt@BC.

31

ro of -p re lP

Fig. 4. (a) XRD spectrum of BC and PEI-Pt@BC. (b) FTIR spectra of BC, PEI and PEI-

Jo

ur

na

Pt@BC. (c) XPS spectra of PEI-Pt@BC for Pt 4f regions.

32

ro of -p re lP

Fig. 5. Effect of (a) pH and (b) temperature on the acid black ATT adsorption using the

na

PEI-Pt@BC bio-adsorbent (Positive triangle plots, rounded plots, and inverted

Jo

ur

triangular plots stand for 298 K, 308 K, 318 K, respectively).

33

Fig. 6. (a) Effect of contact time on the acid black ATT adsorption using the PEIPt@BC bio-adsorbent. (b) Pseudo-first-order, (c) pseudo-second-order, and (d)

Jo

ur

na

lP

re

-p

ro of

intraparticle diffusion models of acid black ATT using the PEI-Pt@BC bio-adsorbent.

Fig. 7. Effect of (a) pH and (b) initial concentration of dye on the MB adsorption using the PEI-Pt@BC bio-adsorbent.

34

ro of

Fig. 8. (a) Effect of contact time on the MB adsorption using the PEI-Pt@BC bio-

-p

adsorbent. (b) Pseudo-first-order, (c) pseudo-second-order, and (d) intraparticle

Jo

ur

na

lP

re

diffusion models of MB using the PEI-Pt@BC bio-adsorbent.

35

ro of -p re lP

na

Fig. 9. The schematic mechanism of distinct adsorption behaviors for anionic acid black

Jo

ur

ATT and cationic MB using the PEI-Pt@BC bio-adsorbent.

36

37

ro of

-p

re

lP

na

ur

Jo