ChitosanâSilica Hybrid Composites for Removal of Sulfonated Azo

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Chitosan-silica hybrid composites for removal of sulfonated azo dyes from aqueous solutions Magdalena Blachnio, Tetyana M Budnyak, Anna DeryloMarczewska, Adam W. Marczewski, and Valentin A. Tertykh Langmuir, Just Accepted Manuscript • DOI: 10.1021/acs.langmuir.7b04076 • Publication Date (Web): 18 Jan 2018 Downloaded from http://pubs.acs.org on January 18, 2018

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Chitosan-silica hybrid composites for removal of sulfonated azo dyes from aqueous solutions Magdalena Blachnio1*, Tetyana M. Budnyak2,3*, Anna Derylo-Marczewska1, Adam W. Marczewski1, Valentin A. Tertykh2 1

*

Faculty of Chemistry, Maria Curie-Sklodowska University, M. Curie-Sklodowska Sq. 3, 20-031 Lublin, Poland 2 Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine, General Naumov Street 17, 03164 Kyiv, Ukraine 3 KTH Royal Institute of Technology, Teknikringen 56-58, SE-100 44 Stockholm, Sweden

corresponding authors:

[email protected], +48 81 537 56 37; [email protected], +38 044 422 9604

Abstract In this study, the influence of chitosan immobilization method on properties of final hybrids materials was performed. Chitosan immobilized on the surface of mesoporous (ChS2) and fumed silica (ChS3) by physical adsorption and through sol-gel method (ChS1). It was found that physical immobilization of chitosan allow to obtain hybrid composites (ChS) with homogeneous distribution of polymer on the surface, relatively wide pores and specific surface area about 170 m2/g, pHPZC=5.7 for ChS3 and 356 m2/g, pHPZC=6.0 for ChS2. The microporous chitosan-silica material with specific surface area 600 m2/g and more negatively charged surface (pHPZC=4.2) was obtained by sol gel reaction. The mechanisms of azo dyes adsorption were studied and correlation with composite structure was distinguished. The Generalized Langmuir equation, and its special cases, i.e. Langmuir-Freundlich and Langmuir equations, were applied for analysis of adsorption isotherm data. The adsorption study showed that physically adsorbed chitosan (ChS1 and ChS2) on silica surface have higher sorption capacity, eg. 0.48 mmol/g for AR88 dye (ChS2) and 0.23 mmol/g for AO8 dye (ChS1), comparing to the composite obtained by sol gel method (ChS1, 0.05 mmol/g for AO8 dye). For deeper understanding of the behavior of immobilized chitosan in adsorption processes, various kinetic equations were applied: first-order, second-order, mixed 1,2-order (MOE), multi-exponential, fractal-like MOE as well as intraparticle and pore diffusion models equations. In the case of AO8 dye the adsorption rates were differentiated for three composites: for ChS3 50% of dye was removed from the solution after merely 5 min and almost 90% after 80 min. The slowest adsorption process controlled by a diffusion rate of dye molecules into the internal space of pore structure was found for ChS1 (225 min halftime). In the case of ChS2 the rates for various dyes change in the following order: AO7 > OG > AR1 > AR88 > AO8 (half-times: 10.5 < 15.7 < 23.7 < 34.9 < 42.9 min). Keywords: pollution removing, azo dyes adsorption, chitosan, fumed silica, gel silica, chitosan-silica composites, adsorption kinetics, thermal analysis Acknowledgements The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union’s Seventh Framework Programme FP7/2007-2013/under REA grant agreement no. PIRSES-GA-2013-612484. 1. Introduction The discovery of synthetic dyes with low production costs, bright colors and high resistance towards environmental factors redefine the role of natural dyes. This has led to higher consumption of synthetic dyes over natural ones for most types of industrial applications.1 Thousands of synthetic dyes are used in printing and dyeing industries generating hazardous wastes. However, synthetic dyes are very often highly toxic, carcinogenic and mutagenic. Even at low concentrations, they affect the aquatic ecosystem.2 Additionally, they can also cause severe damages to human beings such as dysfunction of the kidney, reproductive system, liver, brain and central nervous system. Among these, azo dyes are dangerous because of the presence of toxic amines in the effluent.3 Hence, ways and means are required to remove the dyes from wastewaters.1-3 Nevertheless, it remains a difficult challenge to remove these dyes from wastewaters, even at low concentrations.

1 ACS Paragon Plus Environment

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During last decades, numerous technics, as physical, chemical and biological, have been reported to remove dyes from wastewaters. Recently authors reported about using of adsorption, coagulation, membrane separation, chemical oxidation, photocatalytic degradation, electrochemical, and aerobic and anaerobic microbial degradation, etc for such purposes.4-5 Among the numerous techniques for dyes removal, adsorption has been proved as the best method for removing different types of coloring substances. High adsorption activity of activated carbon towards different pollutants brought this material to the top-using sorbents for the majority of commercial systems.2, 6 However, activated carbon could not be used mainly because of its high cost. In order to decrease the cost of adsorption treatment, attempts have been made to find inexpensive alternative adsorbents.7 Recently, numerous approaches have been studied for the development of cheap and effective adsorbents containing natural polymers. From that point of view, chitin, the second most abundant polysaccharide (after cellulose), and its derivative, chitosan, deserve particular attention. These biopolymers represent an interesting and attractive alternative as adsorbents because of their particular structure, physicochemical characteristics, chemical stability, high reactivity and excellent selectivity towards aromatic compounds and metals, due to the presence of chemical reactive groups (hydroxyl, acetamido or amino groups) in polymer chains. Those functional groups have a capacity to interact by physical and chemical forces with a wide variety of molecules. Hence, adsorption on polysaccharide derivatives can be a low-cost procedure of choice in water decontamination, for extraction and separation of compounds, and a useful tool for protecting the environment.8-10 Various methods of preparation of hybrid materials based on inorganic materials, and chitin and chitosan for different applications have been studied.11-12 It was found, that such hybrid composites have high selectivity and capacity as well as show fast kinetics.13-15 Chaudhuri et al.16 synthesized mesoporous chitin- and chitosan-based composites and applied obtained composites as sorbents for dyes removal from natural waters and wastewaters. Cho with co-workers17 described adsorption of methylene blue and methyl orange by magnetic composite material composed of nanomagnetite, heulandite, and cross-linked chitosan. Besides, the increasing the number of publication in that specific topic, there is an interest in the development of new polysaccharide-contained sorbents and systematic investigation of their ability to remove dyes from wastewaters. In our work we compare the physicochemical and adsorption properties of three types of chitosan-silica composites: two materials obtained by adsorption of chitosan on silica gel and fumed silica, and nanomaterial synthesized by sol-gel method. The physicochemical properties of obtained materials were compared by using various techniques: elemental analysis, FTIR, SEM/EDX, adsorption/desorption of nitrogen, potentiometric titration. Their adsorption properties towards anionic azo dyes were investigated on the basis of equilibrium and kinetic experiments in order to verify their applicability for removing these compounds from aqueous solutions. The model of adsorption on energetically heterogeneous solids was used for isotherm analysis, however, for interpretation of kinetic measurements simple equations were applied including pseudo first- and pseudo second-order, and multiexponential ones. The mechanisms of dye adsorption were studied and correlated with composite properties. Additionally, thermal behavior of dye-composite systems were investigated. 2. Experimental and calculation procedures 2.1. Preparation of chitosan-silica composites 2.1.1. Materials Chitosan (Sigma Aldrich, No 417963), molecular weight from 190 000 to 370 000 Da, degree of deacetylation – not less than 75% and solubility 10 mg/ml; silica gel with a specific surface area of 430 m2/g, particle size of 0.2-0.5 mm and an average pore size of 7 nm (Merck); fumed silica, specific surface area 175 m2/g, obtained from State Enterprise “Kalush Test Experimental Plant of Institute of Surface Chemistry of National Academy of Sciences of Ukraine”; 99.9 % tetraethoxysilane (TEOS), Sigma Aldrich, were used for the synthesis. All chemicals purchased from Sigma Aldrich were reagent grade. 2.1.2. Methods of synthesis Chitosan-silica composite (ChS1) was obtained by the sol-gel method. For that the hydrolysis of TEOS was performed in pre-formed chitosan solution in acetic acid with concentration 5 g/l. ChS1 was synthesized by the following technique: At first stage 15.5 ml of TEOS was mixed with 10 ml of C2H5OH, 0.3 ml of distilled water in acidic conditions (adjusted by adding of 0.1 ml of concentrated


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HCl). The obtained mixture was stirred with pre-formed chitosan solution during 24 hours. The gel formed after 2 weeks. Obtained composite was dried at 60°С during 1 day. Chitosan-silica gel composite (ChS2) and chitosan-fumed silica composite (ChS3) were obtained by impregnation of 10 g of silica gel or fumed silica, respectively, from chitosan solution. Silica gel and fumed silica were impregnated from chitosan solution (1 g of chitosan dissolved in 100 ml of 2 % acetic acid) and stirred for a day. Then, the obtained substances were dried at 60°С. 2.2. Adsorbates For the present studies the commercial, anionic dyes: acid orange 7 (AO7) (also known as orange II), acid orange 8 (AO8), orange G (OG), acid red 88 (AR88) and acid red 1 (AR1) were used. They were purchased from the Sigma–Aldrich with a stated purity of 60-100%. These substances are sulfonated azo dyes, possessing one or two sulfonate groups and the presence of azo group (-N=N-), bound to aromatic rings. The complex molecular structures make them resistant to biological or even chemical degradation.18 In Fig. 1 and Table 1 the chemical structures and the physicochemical properties of the studied adsorbates are shown. 2.3. Methods of investigations 2.3.1. Elemental analysis Carbon, hydrogen, and nitrogen analysis of the chitosan–silica composites was carried out by using Series II CHNS/O Analyzer 2400 (Perkin Elmer, USA). The temperature of the reduction and the combustion processes were 650 and 950°С, respectively. 2.3.2. FTIR analysis FTIR spectra of the pure chitosan and chitosan-silica composite samples were recorded over the 4000-400 cm−1 range using Nicolet 8700A FTIR spectrometer (Thermo Scientific, USA) in a diffuse reflectance mode. The KBr pellet technique during preparation of the samples was used. 2.3.3. SEM/EDX Surface morphology of the chitosan-silica composites was studied by field emission Scanning Electron Microscopy employing a QuantaTM 3D FEG (FEI Company, USA) apparatus operating at 30 kV. Elemental analysis of materials was performed by using energy-dispersive X-ray spectroscopy (EDX). 2.3.4. Nitrogen adsorption/desorption measurements The porosity of the composites was analyzed by using nitrogen adsorption/desorption isotherms measured at 77 K (ASAP 2020 analyzer, Micromeritics). The following parameters characterizing the porosity were calculated: the BET specific surface area (SBET) (assessed from the linear BET plot of adsorption data), the external surface area (Sext), the total pore volume (Vt) (from the adsorption value at the relative pressure p/po~0.98), the micropore volume (Vmic) (from the t-plot method) and primary micropore and mesopore volume (Vp) (from the αs plot method applying the silica gel LiChrospher Si1000 as a reference.19-20 The calculations of pore size distributions (PSD) followed the BJH procedure. The micropore size distribution for ChS1 was calculated by using the DFT approach (Micromeritics). The pore diameters were estimated from PSD maxima (mode, Dmo). The mean hydraulic pore diameters were calculated from the BET surface areas and pore volumes Dh=4V/S. 2.3.5. Potentiometric titration measurements The surface charge density and point of zero charge were determined from the potentiometric titration measurements of the acidified suspension of composite samples with NaOH solution. In measurements the sorbent suspension in NaCl electrolyte with ionic strength of I=0.1 mol/dm3 were used.21 The experimental relations pH=f(VNaOH) allowed to determine the surface charge density of the solids. 2.3.6. Adsorption equilibrium


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The adsorption isotherms for aqueous solutions of dyes were measured by using a static method. First, 1.8 mmol/dm3 stock solutions were prepared by dissolving dyes in redistilled water. The pH values of stock solutions were estimated by pH-meter (pH CPC-501) and were equal to 6.2, 8.0, 6.7, 5.9, 8.5 for AO8, AR88, AO7, OG and AR1, respectively. The initial 0.03–1.8 mmol/dm3 dye solutions were prepared from the stock solutions. In calculations the dye purity (percentage content) was taken into account. The chitosan-silica composite samples were heated at 55°С and kept in a desiccator. Then, 50 mg samples of adsorbents were added to flasks with 100 cm3 of the dye solutions placed in an incubator shaker (Innova 40R, New Brunswick Scientific), and kept for 2 days at 25°С and 110 rpm speed. Equilibrium concentrations were estimated by using UV-Vis spectra (Cary 4000, Varian) at λ=490, 505, 484, 475 and 532 nm for AO8, AR88, AO7, OG and AR1, respectively. The adsorbed amounts of substances aeq were calculated from the mass balance equation. In order to analyze the experimental data of dyes adsorption from aqueous solutions the Generalized Langmuir (GL) equation was chosen:22

 (Kc eq )n  (1) θ = n  1 + ( Kc eq )  where: θ= aeq /am is global (overall) adsorption isotherm (overall coverage), aeq is equilibrium amount adsorbed on adsorbent (mmol/g), am is adsorption capacity, ceq is equilibrium dye concentrations (mmol/dm3), m and n are heterogeneity parameters characterizing a shape (width and asymmetry) of quasi-gaussian adsorption energy distribution function, where 0 AO8. Analyzing physicochemical properties of particular dyes one can see the correlation between their adsorption rates and chemical structures. AO7 having the lowest Mw and size is adsorbed at the fastest rate. However, OG and AR1 have two sulfonate groups (weakly interacting with composite surface) and the largest Mw. AR88 possessing two strongly adsorbing naphthalene moieties is removed from solution at slower rate, though it is the first to approach maximum uptake (due to the highest adsorption capacity, the conditions for its adsorption remain more favorable than for systems with lower capacity). The adsorption process for AO8 proceeds the slowest, although chemical structure of this compound is the nearest of AO7. Observed differentiation in adsorption rate for these two dyes may result from the presence of competing impurities in AO8. In the stationary stage (near the equilibrium) we may observe both rate and equilibrium uptake differentiation. The largest dye residue (ceq/co) occurs for OG and AR1 dyes (~3.3% and 2.5%, respectively) with the lowest adsorption capacities, whereas for AR88 it is only 0.8% (the highest adsorption capacity) and for AO8 and AO7 is ~1.3% (intermediate capacities). However, in practical application the removal efficiency would depend not only on the rate (and assumed time to equilibrium and stirring) and adsorption capacity, but also on adsorbate/adsorbent ratio (i.e. coV / wam ) and adsorbate concentration.31 In Figs. 9 and S9 and Table S6 (Supplementary Material) the parameter spectra (fi vs. logt05,i and fi vs. logki) of multi-exponential equation are shown (points). Adsorption half-times t0.5, i.e. time required to adsorb half of equilibrium amount (aeq) were determined for the various terms of multi-exponential equation from the relationship: t 05,i = (ln 2) / ki , whereas overall half-times t05 were determined numerically and average rate coefficients were calculated as k avg ( t ) = (ln 2) / t 05 (vertical bars). Weighted mean rate coefficients logkavg and logk dispersions (∆logk) were also calculated (Tables S1 and S6). The broad distribution of rate parameters means that the adsorption process proceeds in stages: from a very fast initial one, over intermediate to the slowest stage. Faster kinetics on mesoporous ChS2 and ChS3 corresponds to higher contribution fi of shorter half-times t05,i (higher rate coefficients ki) in comparison to microporous ChS1 (high fi for low ki). Similarly, differentiation in distribution of rate parameters are observed for dyes adsorbed on ChS2. The shapes of spectra are similar, though with different widths and positions on half-time axis. 3.4. Thermal analysis In Fig.10 the TG, DTG and DSC curves measured for the pure chitosan, composite ChS2, dyes and ChS2 loaded with 0.07 mmol/g of dyes are presented. TG, DTG and DSC curves of chitosan are characterized by single endothermic event with the maximum degradation rate at 76°C and the mass loss of 2.1 % corresponding to water bound to the hydroxyl and amine groups (physically adsorbed and/or weakly hydrogen-bonded) (Zawadzki and Kaczmarek 2010).63 A second event is observed in 230-390°C range with an exothermic peak at 295°C corresponding to a mass loss (52 %) which may be attributed to the thermal degradation of polymeric chain with vaporization of volatile compounds. The pyrolysis of polysaccharide structure begins from a disruption of the glycosidic bonds, followed by producing a series


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of low fatty acids like: forming acetic, butyric with predomination of C2, C3 and C6.64-65 A third thermal event (exothermic) can be observed between 390–600°C with maximum peak at 492°C corresponding to the degradation of remaining cross-linked chitosan (37.4% mass loss). 8.5 % residual mass shows that nearly all of the chitosan was decomposed up to 600°C. The curves for ChS2 composite show endothermic peak (corresponding to the loss of chitosanadsorbed water and Si–OH condensation water) broader than for pure chitosan66 evaporation occurs between 40 and 160°C with maximum at 132°C (1.6% mass loss). Following thermal degradation in 160590°C range corresponds to predominant exothermic peak with maximum rate at 288°C and a shoulder at 450°C (depolymerization and decomposition of the composite polymeric component) (total mass loss 8.7%). A sample residual mass is high at 88.7%. Impregnation of silica by organic polymer (physisorbed without cross-linking) corresponds a lower thermal decomposition temperature of composite in comparison to the pristine material. The residual mass at 950°C for pure chitosan and ChS2 (after correction for the initial water evaporation) allows to estimate ChS2 organic/inorganic ratio as 1:10, which agrees with elemental CHN analysis estimate. Thermal degradation of pure dyes show many stages as a result of their complex structures including aromatic rings and multiple bonds.27 The range 25-200°C corresponds to water removal (endothermic), though it is not eminent for all analyzed dyes. OG and AR1, having two hydrophilic sulfonate groups (other dyes have only one) exhibit highest mass losses in the temperature interval attributed to water elimination. With increasing temperature the thermooxidation (exothermic) starts with DTG curves showing many peaks. At lower temperatures ( AR1 > AR88 > AO8 (half-times: 10.5 < 15.7 < 23.7 < 34.9 < 42.9 min). It may be correlated with chemical structures of dyes: AO7 with the lowest molecular weight and molecular dimension is adsorbed at the fastest rate, AR88 possessing two strongly interacting naphthalene rings is adsorbed at slower rate, adsorption of AO8 is the slowest (differences in adsorption rates for AO7 and AO8 may be also explained by the presence of impurities).


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Tables Table 1. Physicochemical properties of the studied azo dyes. Dye Molecular Chemical Adsorbate content, weight formula [%] [g/mol]

nAc

Ionization constant, pKa

Water solubility [%]

Dmax [nm]

AO8

C17H13N2NaO4S

65

364.35

1

-1; 13.569

-

1.3

AR88

C20H13N2NaO4S

75

400.38

1

11.0670

0.471

1.4

AO7

C16H11N2NaO4S

100

350.32

1

8.26; 11.472

473

1.3

OG

C16H10N2Na2O7S2

80

452.37

2

12.872

7.174

1.3

AR1

C18H13N3Na2O8S2

60

509.42

2

10.575

1075

1.4

nAc - number of acidic groups in a molecule, Dmax - distance between the most remote atoms in a molecule measured along longitudinal axes by means of a computer program (Marvin 14.8.25.0)76 tools. Table 2. Percentage of carbon, hydrogen, nitrogen for chitosan and chitosan-silica composites. Sorbent

%C

%H

%N

Chitosan

40.72

7.25

7.33

ChS1

1.89

2.57

1.04

ChS2

3.66

0.97

0.66

ChS3

4.73

1.02

0.86

Table 3. Elemental analysis for five sites of composites performed with the energy-dispersive X-ray spectroscopy (EDX). ChS2x data are collected at the point marked with a green cross in the Fig. 2 (bottom left). Element

ChS2x

ChS2

ChS3

site

1

2

3

4

5

X

1

2

3

4

5

C

15.6

7.8

16.9

14.8

4.8

41.1

41.7

7.4

6.3

6.3

6.4

N

1.1

0.7

1.0

1

0.6

2.2

0.7

0.7

0.8

0.7

0.7

O

45.4

66.3

58.1

59.4

66.4

47.1

52.9

57.0

60.7

63.4

57.5

Si

37.5

25

23.7

24.7

28

6.1

4.7

34.8

32.2

29.4

35.4

S

0.4

0.1

0.2

0.1

0.1

3.6

0.1

0.2

0.1

0.1

0

Table 4. The values of parameters characterizing porous structure of adsorbents calculated from nitrogen adsorption/desorption isotherms. SBET Dh Dmo Vt Vp Sext Vmic Dmo Sorbent [m2/g] [cm3/g] [cm3/g] [m2/g] (t-plot) (ads. BJH) (des. BJH) [nm]


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[cm3/g]

[nm]

[nm]

ChS1

600

0.32

0.31

7

0.21

2.16

1.73

1.72

ChS2

356

0.62

0.61

3

0

7.12

6.06

6.10

ChS3

170

1.14

1.08

17

0.01

26.8

39.8

29.9

Table 5. Parameters of Generalized Langmuir equation (GL) (optimized to Langmuir-Freundlich or Langmuir isotherms) characterizing adsorption of dyes from dilute aqueous solutions on the chitosansilica composites. Isotherm

am

m=n

log K

R2

SD(a)

AO8 (ChS1)

LF

0.07

0.35

2.12

0.971

0.003

AO8 (ChS2)

LF

0.20

0.84

2.35

0.994

0.007

AO8 (ChS3)

LF

0.24

0.70

1.97

0.985

0.012

AO7 (ChS2)

LF

0.25

0.82

1.86

0.995

0.008

AR88 (ChS2)

LF

0.48

0.40

1.24

0.957

0.031

OG (ChS2)

LF

0.12

0.55

2.04

0.992

0.004

AR1 (ChS2)

L

0.09

1.00

2.48

0.985

0.004

System

Table 6. Comparison of optimization quality (relative deviation, SD(c)/co) for various kinetic equations. IDM IDM System FOE SOE MOE f-FOE m-exp IDM (c) PDM (a) (b) 0.134% AO8 3.84% 2.53% 2.28% 1.07% 7.56% 0.560% 1.68% 2.10% 5-exp (ChS1) AO8 (ChS2)

2.32%

2.85%

1.26%

1.14%

0.116% 5-exp

9.10%

0.560%

0.560%

2.25%

AO8 (ChS3)

3.12%

2.47%

2.45%

1.72%

0.593% 4-exp

2.80%

1.68%

2.66%

1.81%

AR88 (ChS2)

2.50%

3.47%

1.67%

1.84%

0.252% 3-exp

8.96%

1.12%

1.12%

3.12%

AO7 (ChS2)

2.41%

1.67%

1.18%

0.951%

0.182% 5-exp

6.85%

1.26%

1.26%

1.37%

OG (ChS2)

2.67%

1.17%

0.85%

0.570%

0.124% 5-exp

6.29%

1.12%

1.12%

0.968%

AR1 (ChS2)

2.61%

1.62%

1.00%

0.503%

0.143% 5-exp

7.70%

0.700%

0.700%

1.31%

average

2.78%

2.25%

1.53%

1.11%

0.221%

7.04%

1.00%

1.30%

1.85%


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IDM (a) – full model (S13) with variable concentration, (b) IDM (S13) with independently optimized ueq and ceq, (c) classic IDM equation (S12) (derived for constant concentration).


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Figures

acid orange 7 (AO7)

acid orange 8 (AO8)

OH N N O S

O

O

O S

Na O

O

Na

orange G (OG)

acid red 88 (AR88)


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O

Na O S

N

N

O OH H

O

N CH3

O S O

O

Na

acid red 1 (AR1)

Fig. 1. Chemical structures of the studied azo dyes.

Fig. 2. The SEM images of chitosan-silica composites ChS1 (a-c), ChS2 (d-f) and ChS3 (g-i) at 100, 2000 and 3500 magnifications.


Langmuir

3429 1080

1660

2880

1380 1580 1420 1310

2345

1080

1120 1097

803

Chitosan 1

3140 2886 3660

Absorbance (a.u.)

0.8

1650 1420 1528 1857 2000

0.6

472

3440

ChS1

0.4

2925 2853

3726 0.2 ChS2 I

807

1636 1417 1384 1736 1555 I I

I

649 669 I

ChS3

0 4000

3000

2000

1000

Wavenumber (cm-1)

Fig. 3. FTIR spectra of chitosan and chitosan-silica composites.

ChS1 (ads) ChS1 (des) ChS2 (ads) ChS2 (des) ChS3 (ads) ChS3 (des)

600

dV/dD [cm3g-1nm-1]

0.1

800

dV/dD [cm3g-1nm-1]

a [cm3/g STP]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 18 of 28

0.08

0.3

0.2

0.1

0.06

0

400

0

1

2

3

D [nm]

4

0.04 ChS1 (ads)

200

0.02

ChS2 (ads) ChS3 (ads)

0

0 0

0.2

0.4

0.6

0.8

p/po

1

0

20

40

60

80 D [nm]

a b Fig. 4. (a) The nitrogen adsorption/desorption isotherms for the chitosan-silica composites. (b) Pore size distributions for the chitosan-silica composites calculated using BJH method.


Page 19 of 28

0.3 a [mmol/g]

Qs [µC/cm2]

20

0

0.2

-20

-40 0.1

-60

-80 2

ChS1

AO8 (ChS3)

LF fit

ChS2

AO8 (ChS2)

LF fit

ChS3

AO8 (ChS1)

LF fit

0

4

6

8

0

10

0.5

1

1.5

pH

2

ceq [mmol/l]

a b Fig. 5. (a) Dependence of surface charge density on pH for the chitosan-silica composites determined by potentiometric titration. (b) Comparison of dye (acid orange 8) adsorption isotherms from aqueous solutions on the chitosan-silica composites.

log a [mmol/g]

0.4 a [mmol/g]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

0.3

-0.5

-1 0.2

-1.5 0.1 AR88 (ChS2) AO7 (ChS2) AO8 (ChS2) OG (ChS2) AR1 (ChS2)

0 0

0.5

1

AR88 (ChS2) AO7 (ChS2) OG (ChS2) AR1 (ChS2)

LF fit LF fit LF fit LF fit LF fit

1.5

LF fit LF fit LF fit LF fit

-2 2

-6

ceq [mmol/l]

-5

-4

-3

-2

-1

log ceq/cs

a b Fig. 6 Comparison of isotherms of the dyes on the chitosan-silica composite (ChS2) in (a) classic and (b) log-log coordinates with reduced concentration scale.


Langmuir 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

AO8 (ChS1) AO8 (ChS1) (5-exp fit) AO8 (ChS2) AO8 (ChS2) (5-exp fit) AO8 (ChS3) AO8 (ChS3) (4-exp fit)

c/co 0.8

Page 20 of 28

1 c/co 0.8 0.6 0.4

0.6

0.2 0

0.4

0

20

40t1/2 [min]60

80

0.2

0 0

5000 6000 t [min] Fig. 7. Comparison of adsorption kinetics for AO8 on various chitosan-silica composites. Lines correspond to the fitted multi-exponential equation. 1

1000

2000

OG (ChS2) OG (ChS2) (5-exp fit) AO7 (ChS2) AO7 (ChS2) (5-exp fit) AR88 (ChS2) AR88 (ChS2) (3-exp fit) AO8 (ChS2) AO8 (ChS2) (5-exp fit) AR1 (ChS2) AR1 (ChS2) (5-exp fit)

c/co 0.8

0.6

3000

c/co

4000

1

0.8 0.6 0.4 0.2 0

0.4

0

10

20

30 t1/2 [min]40

0.2

0 0

500

1000

1500

2000

t [min] Fig. 8. Comparison of adsorption kinetics for the dyes on (ChS2) composite. Lines correspond to the fitted multi-exponential equation.


Page 21 of 28

1

1 fi 0.8 0.6

AR88 (ChS2) avg AR88 (ChS2) AR1 (ChS2) avg AR1 (ChS2) OG (ChS2) avg OG (ChS2) AO8 (ChS2) avg AO8 (ChS2) AO7 (ChS2) avg AO7 (ChS2)

fi

AO8 (ChS1) avg AO8 (ChS1) AO8 (ChS2) avg AO8 (ChS2) AO8 (ChS3) avg AO8 (ChS3)

0.8 0.6

0.4

0.4

0.2

0.2 0

0 -2

0

2

-2

4

0

2 log t05.i

log t05.i

Fig. 9. Parameter spectra for multi-exponential equation fitted to dyes adsorption kinetics on the chitosansilica composites. Vertical bars correspond to overall half-times. 100

100 0

76 oC-2.1%

-1.6%

exo

exo

0

98 80

TG (%) 40

-2 96

132 oC

94

-8.7%

-4

DTG (%/min)

DTG (%/min)

DSC/(mW/mg)

-52% 60

TG (%)

-3

DSC/(mW/mg)

-0.1

492 oC

92

20

90

0

200

295 oC

Rm: 8.5% 400

600

b) ChS2

88 0

800

288 oC 200

Rm: 88.7% 400

600

0 312 oC -14%

699 oC

0 100

-0.4%

exo exo 95 oC

-2

533 oC

-0.1

96

DTG (%/min)

94

TG (%)

DSC/(mW/mg)

DTG (%/min)

-53%

-4 92

-8

Rm: 29% -12 400

600

800

-0.3

88

344 oC 200

-0.4

512 oC

-6 -3%

-0.2

-6.3% 90

40

c) AO8

0

-4.9%

-4

575 oC

0

-1.2

800

98

20

-0.4

Temperature (oC)

100

60

-0.6

-1

Temperature (oC)

80

-0.4

-6

DSC/(mW/mg)

a) Chitosan

-9

-0.2

-0.8

-37.4%

TG (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

d) AO8(ChS2) 272 oC

-8 86 0

200

Temperature (oC)

Rm: 88.2% 400

600

-0.6

800

Temperature (oC)


Langmuir

100

-2.2% 130 oC

0.2

100

541 oC 606 oC 552 oC

815 oC

exo

-0.9%

0 exo

0.1

98

-31.3% 80

94 -4

DTG (%/min)

88 oC

521 oC

92 40 -11.9%

0

DSC/(mW/mg)

-25.1%

-0.1

-4.8%

-2 96

TG (%)

DSC/(mW/mg)

60

DTG (%/min)

TG (%)

-10

-0.1

-0.2

-4.5% -0.3

-6

90

-0.3

-30 360 oC

e) AR88

20 0

200

Rm: 27.6%

400

600

o f) AR88 (ChS2) 265 C

-8 88

0

800

200

Rm: 88.9% 400

600

-0.4

800

Temperature (oC)

Temperature (oC) 100

100

exo

-13.9%

-0.7%

exo

0 98

0

-3

-4.5% -0.1

89 oC

-4 94

-4.2%

-6

DSC/(mW/mg)

527oC 506oC

96

TG (%)

-59.2%

DSC/(mW/mg)

60

DTG (%/min)

TG (%)

-2

DTG (%/min)

80

-0.1

-0.2

525 oC

92

40 -0.3 90

200

400

-8

Rm: 23% 600

h) AO7(ChS2) 266 oC

88

800

0

200

Temperature (oC)

600

-0.4

800

Temperature (oC)

100

100

0

-0.5%

0 -12.3%

exo

exo

98

-8%

0

728oC

-4.2%

468oC -9.8%

-5

98 oC

DTG (%/min)

87oC -15.8% 579oC

DSC/(mW/mg)

96

284oC

-10

TG (%)

80

60

Rm: 90% 400

94

-4.7%

-19.3% -15 -2.6%

-4

-0.1

-0.2

508 oC

92

40

-0.1

DSC/(mW/mg)

0

-0.3

DTG (%/min)

20

-12

340oC

g) AO7

TG (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Page 22 of 28

-0.3 90 -0.3

i) OG

20 0

519oC 200

400

600

Rm: 30.9% 800

j) OG(ChS2) 266 oC

-20 88

0

200

Rm: 90% 400

600

-0.4

800

Temperature (oC)

Temperature (oC)


Page 23 of 28

163 oC -4.3% 329 oC 96 oC -9.3%

100

0.1

-0.5% exo

0 exo

98 506 oC

0

-4.7%

-4

80

99 oC

96

-0.1

-20

-9.9%

DTG (%/min)

60

94

TG (%)

DTG (%/min)

-35.6%

DSC/(mW/mg)

-10

92

-6.1%

DSC/(mW/mg)

100

TG (%)

-0.1

-0.2

518 oC

90

40

-0.3 -30 88

-16

k) AR1

20 0

Rm: 33.9%

405 oC 200

400

600

l) AR1(ChS2) 262 oC

86 0

800

200

400

600

Rm: 88.4% -0.4 800

-0.4

Temperature (oC)

Temperature (oC)

Fig. 10. Comparison of TG, DTG and DSC curves measured for (a) the chitosan, (b) chitosan-silica composite ChS2, (c) acid orange 8 (AO8), (d) ChS2 loaded with AO8, (e) acid red 88 (AR88), (f) ChS2 loaded with AR88 (g) acid orange 7 (AO7) (h) ChS2 loaded with AO7 (i) orange G (OG) (j) ChS2 loaded with OG (k) acid red 1 (AR1) (l) ChS2 loaded with AR1. 0.02

ChS2 (441oC)

ChS2 (289oC)

0.2

0

Absorbance (a.u.)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Langmuir

Chitosan (448oC) 2357 2310

3883 0 4000

1770 1797

3566 3736

1509 1183

o

Chitosan (295 C) 3500

3000

2500

2000

1500

670

1000

Wavenumber (cm-1)

Fig. 11. FTIR spectra of gas products of pyrolysis of chitosan and chitosan-silica composite ChS2 at the temperatures corresponding to the process rate maxima. References

1. Ngah, W. W.; Teong, L.; Hanafiah, M. Adsorption of Dyes and Heavy Metal Ions by Chitosan Composites: A Review. Carbohyd. Polym. 2011, 83 (4), 1446-1456.


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2. Aguiar, J.; De Oliveira, J.; Silvino, P.; Neto, J.; Silva, I.; Lucena, S. Correlation between PSD and Adsorption of Anionic Dyes with Different Molecular Weigths on Activated Carbon. Colloid Surf. A: Physicochem. Eng. Aspects 2016, 496, 125-131. 3. Yagub, M. T.; Sen, T. K.; Afroze, S.; Ang, H. M. Dye and Its Removal from Aqueous Solution by Adsorption: A Review. Adv. Colloid Interfac. 2014, 209, 172-184. 4. Kadam, A. A.; Lade, H. S.; Lee, D. S.; Govindwar, S. P. Zinc Chloride as a Coagulant for Textile Dyes and Treatment of Generated Dye Sludge under the Solid State Fermentation: Hybrid Treatment Strategy. Bioresource Technol. 2015, 176, 38-46. 5. Mu, B.; Wang, A. Adsorption of Dyes onto Palygorskite and Its Composites: A Review. J. Environ. Chem. Eng. 2016, 4 (1), 1274-1294. 6. Sayğılı, H.; Güzel, F. High Surface Area Mesoporous Activated Carbon from Tomato Processing Solid Waste by Zinc Chloride Activation: Process Optimization, Characterization and Dyes Adsorption. J. Clean. Prod. 2016, 113, 995-1004. 7. Kyzas, G. Z.; Lazaridis, N. K.; Mitropoulos, A. C. Removal of Dyes from Aqueous Solutions with Untreated Coffee Residues as Potential Low-Cost Adsorbents: Equilibrium, Reuse and Thermodynamic Approach. Chem. Eng. J. 2012, 189, 148-159. 8. Crini, G. Recent Developments in Polysaccharide-Based Materials Used as Adsorbents in Wastewater Treatment. Prog. Polym. Sci. 2005, 30 (1), 38-70. 9. Salehi, E.; Daraei, P.; Shamsabadi, A. A. A Review on Chitosan-Based Adsorptive Membranes. Carbohyd. Polym. 2016, 152, 419-432. 10. Zhang, L.; Zeng, Y.; Cheng, Z. Removal of Heavy Metal Ions Using Chitosan and Modified Chitosan: A Review. J. Mol. Liq. 2016, 214, 175-191. 11. Park, S. Y.; Lee, B. I.; Jung, S. T.; Park, H. J. Biopolymer Composite Films Based on κCarrageenan and Chitosan. Mater. Res. Bull. 2001, 36 (3), 511-519. 12. Yeh, J.-T.; Chen, C.-L.; Huang, K.-S. Synthesis and Properties of Chitosan/SiO2 Hybrid Materials. Mater. Lett. 2007, 61 (6), 1292-1295. 13. Budnyak, T.; Tertykh, V.; Yanovska, E. Chitosan Immobilized on Silica Surface for Wastewater Treatment. Mater. Sci.-Medziagotyra 2014, 20 (2), 177-182. 14. Budnyak, T.; Tertykh, V.; Yanovska, E.; Kołodyńska, D.; Bartyzel, A. Adsorption of V (V), Mo(VI) and Cr(VI) Oxoanions by Chitosan–Silica Composite Synthesized by Mannich Reaction. Ads. Sci. Tech. 2015, 33 (6-8), 645-657. 15. Budnyak, T. M.; Pylypchuk, I. V.; Tertykh, V. A.; Yanovska, E. S.; Kolodynska, D. Synthesis and Adsorption Properties of Chitosan-Silica Nanocomposite Prepared by Sol-Gel Method. Nanoscale Res. Lett. 2015, 10 (1), 87. 16. Chaudhuri, H.; Dash, S.; Ghorai, S.; Pal, S.; Sarkar, A. SBA-16: Application for the Removal of Neutral, Cationic, and Anionic Dyes from Aqueous Medium. J. Environ. Chem. Eng. 2016, 4 (1), 157-166. 17. Cho, D.-W.; Jeon, B.-H.; Chon, C.-M.; Schwartz, F. W.; Jeong, Y.; Song, H. Magnetic Chitosan Composite for Adsorption of Cationic and Anionic Dyes in Aqueous Solution. J. Ind. Eng. Chem. 2015, 28, 60-66. 18. Singh, R. L.; Singh, P. K.; Singh, R. P. Enzymatic Decolorization and Degradation of Azo Dyes–a Review. Int. Biodeter. Biodegr. 2015, 104, 21-31. 19. Jaroniec, M.; Marczewski, A. W., Physical Adsorption of Gases on Energetically Heterogeneous Solids I. Generalized Langmuir Equation and Its Energy Distribution. In Monatshefte Für Chemie/Chemical Monthly, 1984; Vol. 115, pp 997-1012. 20. Jaroniec, M.; Kruk, M.; Olivier, J. P. Standard Nitrogen Adsorption Data for Characterization of Nanoporous Silicas. Langmuir 1999, 15 (16), 5410-5413. 21. Deryło-Marczewska, A.; Marczewski, A. Nonhomogeneity Effects in Adsorption from Gas and Liquid Phases on Activated Carbons. Langmuir 1999, 15 (11), 3981-3986. 22. Marczewski, A. W.; Jaroniec, M., A New Isotherm Equation for Single-Solute Adsorption from Dilute Solutions on Energetically Heterogeneous Solids. In Monatshefte Für Chemie/Chemical Monthly, 1983; Vol. 114, pp 711-715. 24 ACS Paragon Plus Environment

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46. Boyd, G.; Adamson, A.; Myers Jr, L. The Exchange Adsorption of Ions from Aqueous Solutions by Organic Zeolites. II. Kinetics1. J. Am. Chem. Soc. 1947, 69 (11), 2836-2848. 47. Crank, J., Diffusion in a Plane Sheet. In The Mathematics of Diffusion, 1975; Vol. 2, pp 4468. 48. Reichenberg, D. Properties of Ion-Exchange Resins in Relation to Their Structure. III. Kinetics of Exchange. J. Am. Chem. Soc. 1953, 75 (3), 589-597. 49. Azizian, S. Kinetic Models of Sorption: A Theoretical Analysis. J. Colloid Interf. Sci. 2004, 276 (1), 47-52. 50. Derylo-Marczewska, A.; Blachnio, M.; Marczewski, A. W.; Swiatkowski, A.; Buczek, B. Adsorption of Chlorophenoxy Pesticides on Activated Carbon with Gradually Removed External Particle Layers. Chem. Eng. J. 2017, 308, 408-418. 51. Marczewski, A. W. Extension of Langmuir Kinetics in Dilute Solutions to Include Lateral Interactions According to Regular Solution Theory and the Kiselev Association Model. J. Colloid Interf. Sci. 2011, 361 (2), 603-611. 52. Rudzinski, W.; Plazinski, W. Kinetics of Solute Adsorption at Solid/Solution Interfaces: A Theoretical Development of the Empirical Pseudo-First and Pseudo-Second Order Kinetic Rate Equations, Based on Applying the Statistical Rate Theory of Interfacial Transport. J. Phys. Chem. B 2006, 110 (33), 16514-16525. 53. Rudzinski, W.; Plazinski, W. Theoretical Description of the Kinetics of Solute Adsorption at Heterogeneous Solid/Solution Interfaces: On the Possibility of Distinguishing between the Diffusional and the Surface Reaction Kinetics Models. Appl. Surf. Sci. 2007, 253 (13), 58275840. 54. Chassary, P.; Vincent, T.; Guibal, E. Metal Anion Sorption on Chitosan and Derivative Materials: A Strategy for Polymer Modification and Optimum Use. React. Funct. Polym. 2004, 60, 137-149. 55. Puchol, V.; El Haskouri, J.; Latorre, J.; Guillem, C.; Beltrán, A.; Beltrán, D.; Amorós, P. Biomimetic Chitosan-Mediated Synthesis in Heterogeneous Phase of Bulk and Mesoporous Silica Nanoparticles. Chem. Commun. 2009, (19), 2694-2696. 56. Zou, H.; Wu, S.; Shen, J. Polymer/Silica Nanocomposites: Preparation, Characterization, Properties, and Applications. Chem. Rev. 2008, 108 (9), 3893-3957. 57. Spirk, S.; Findenig, G.; Doliska, A.; Reichel, V. E.; Swanson, N. L.; Kargl, R.; Ribitsch, V.; Stana-Kleinschek, K. Chitosan–Silane Sol–Gel Hybrid Thin Films with Controllable Layer Thickness and Morphology. Carbohyd. Polym. 2013, 93 (1), 285-290. 58. Liu, H.; Gong, C.; Wang, J.; Liu, X.; Liu, H.; Cheng, F.; Wang, G.; Zheng, G.; Qin, C.; Wen, S. Chitosan/Silica Coated Carbon Nanotubes Composite Proton Exchange Membranes for Fuel Cell Applications. Carbohyd. Polym. 2016, 136, 1379-1385. 59. Saha, J.; Bhowmik, K.; Das, I.; De, G. Pd–Ni Alloy Nanoparticle Doped Mesoporous Sio 2 Film: The Sacrificial Role of Ni to Resist Pd-Oxidation in the C–C Coupling Reaction. Dalton Trans. 2014, 43 (35), 13325-13332. 60. Persello, J. Surface and Interface Structure of Silicas. Surf. Sci. Series 2000, 297-342. 61. Singh, A. N.; Singh, S.; Suthar, N.; Dubey, V. K. Glutaraldehyde-Activated Chitosan Matrix for Immobilization of a Novel Cysteine Protease, Procerain B. J. Agr. Food Chem. 2011, 59 (11), 6256-6262. 62. Aharoni, C.; Sideman, S.; Hoffer, E. Adsorption of Phosphate Ions by Collodion-Coated Alumina. J. Chem. Technol. Biot. 1979, 29 (7), 404-412. 63. Zawadzki, J.; Kaczmarek, H. Thermal Treatment of Chitosan in Various Conditions. Carbohyd. Polym. 2010, 80 (2), 394-400. 64. López, F.; Mercê, A.; Alguacil, F.; López-Delgado, A. A Kinetic Study on the Thermal Behaviour of Chitosan. J. Therm. Anal. Calorim. 2008, 91 (2), 633-639. 65. Wanjun, T.; Cunxin, W.; Donghua, C. Kinetic Studies on the Pyrolysis of Chitin and Chitosan. Polym. Degrad. Stabil. 2005, 87 (3), 389-394. 26 ACS Paragon Plus Environment

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Langmuir

66. Al-Sagheer, F.; Muslim, S. Thermal and Mechanical Properties of Chitosan/SiO2 Hybrid Composites. J. Nanomater. 2010, 2010, 3. 67. Lapides, I.; Yariv, S.; Golodnitsky, D. Simultaneous DTA-TG Study of Montmorillonite Mechanochemically Treated with Crystal-Violet. J. Therm. Anal. Calorim. 2002, 67 (1), 99-112. 68. Budnyak, T.; Yanovska, E.; Kołodyńska, D.; Sternik, D.; Pylypchuk, I. V.; Ischenko, M.; Tertykh, V. Preparation and Properties of Organomineral Adsorbent Obtained by Sol–Gel Technology. J. Therm. Anal. Calorim. 2016, 125 (3), 1335-1351. 69. Elizalde-González, M.; García-Díaz, L. Application of a Taguchi L 16 Orthogonal Array for Optimizing the Removal of Acid Orange 8 Using Carbon with a Low Specific Surface Area. Chem. Eng. J. 2010, 163 (1), 55-61. 70. Perez-Urquiza, M.; Ferrer, R.; Beltran, J. Determination of Sulfonated Azo Dyes in River Water Samples by Capillary Zone Electrophoresis. J. Chromatogr. A 2000, 883 (1), 277-283. 71. Peters, A. T.; Freeman, H. S., Physico-Chemical Principles of Color Chemistry. Springer: 1996. 72. Sabnis, R. W., Handbook of Biological Dyes and Stains: Synthesis and Industrial Applications. John Wiley & Sons: 2010. 73. Armarego, W. L.; Chai, C. L. L., Purification of Laboratory Chemicals. Pdf. 2016. 74. Ochei, J. O.; Kolhatkar, A. A., Medical Laboratory Science: Theory and Practice. McGraw Hill Education: 2000. 75. Thomas, S.; Sreekanth, R.; Sijumon, V.; Aravind, U. K.; Aravindakumar, C. Oxidative Degradation of Acid Red 1 in Aqueous Medium. Chem. Eng. J. 2014, 244, 473-482. 76. Marvin 14.8.25.0 Suite Program (Copyright © 1998-2014 Chemaxon Ltd.).

Supporting Information. Kinetics equations and applied models.


Langmuir

adsorption

Graphical abstract Adsorption kinetics Cyclic collection Orange G (ChS2) 144 spectra 39 hours

AR88 (ChS2) AO7 (ChS2) AO8 (ChS2) OG (ChS2) AR1 (ChS2)

c/co

Absorbance [a.u.]

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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equilibrium concentration 350

Wavelength [cm-1]

550

0

20

√t

40


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