^{1}

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The adsorption of reactive red 239 (RR239) dye onto chitosan 8B was studied in aqueous solution at various pHs, initial dye concentrations, ionic strengths and temperatures, respectively. The adsorption of dye onto chitosan 8B was confirmed by diffuse reflectance electronic absorption spectra. The adsorption of RR239 onto chitosan 8B was greatly influenced by solution pHs, initial dye concentrations, ionic strengths and temperatures. The kinetics and me
chanism of dye adsorption process were analyzed by pseudo first-,
second-order, Elovich and intraparticle diffusion kinetic models. The adsorption kinetics of RR239 dye follow
ed
a pseudo second-order model very well. The surface sorption and intraparticle diffusion mechanisms
were
involved in the actual sorption process. The equilibrium isotherm data were fitted well with the Langmuir model rather than the Freundlich, Temkin and Dubinin-Radushkevich models. The maximum dye adsorption onto chitosan 8B was estimated to be 163.93 μmol/g at 45°C. The activation energy (E_{a}) was obtained to be 23.30 kJ/mol. The computed thermodynamic parameters such as ΔG, ΔH, ΔS, ΔG, ΔH and ΔS confirmed that the adsorption of RR239 dye onto chitosan 8B
was
a spontaneous endothermic physisorption process. Desorption test was carried out in NaOH solution (pH 12.5) and the chitosan flakes c
ould
be reused.

Rapid industrialization has led to increased various types of pollutants into aquatic systems that have been identified as among the main causes of environmental pollution and degradation. Dyes, which are widely used in different industries, can impede light penetration into water, retard photosynthetic activity, inhibit the growth of biota and have a tendency to chelate metal ions [^{1} - N = N - R^{2}), represent approximately 70 wt% [

The adsorption process is an efficient method for the removal of dyes from effluent due to its low initial cost, simplicity of design, ease of operation and insensitivity to toxic substances. Activated carbon is the most widely used as an adsorbent due to its large surface area, microporous structure and high adsorption capacity [

The aim of this study was to examine the ability of chitosan 8B (80% deacetylated chitin) as a low cost adsorbent to separate reactive red 239 (RR239) from aqueous solution. The influences of significant aspects, such as solution pHs, initial dye concentration, ionic strengths and temperatures on RR239 adsorption onto chitosan 8B were studied in batch mode. The potential rate controlling step and adsorption mechanisms were analyzed by several kinetic equations (i.e., pseudo first-, pseudo second-order equations, Elovich and intraparticle diffusion models). Freundlich, Temkin, Dubinin-Radushkevich and Langmuir adsorption isotherms were applied to compute the adsorption equilibrium. Activation and apparent thermodynamic parameters were also evaluated.

Katokichi Bio Co., Ltd., Japan provided chitosan 8B (80% deacetylated chitin) which was used without further purification. A laser scattering particle size analyzer (LDSA-2400A, Tonichi Computer Applications, Japan) equipped with a dry dispersing apparatus (PD-10S, Tonichi Computer Applications, Japan) was used to determine the particle size of chitosan 8B. The mass median diameters of the chitosan 8B flakes were found to be 247 ± 9 µm.

Reactive red 239 (RR239;

For spectroscopic measurements, the samples were prepared by mixing solid RR239, chitosan 8B, and chitosan 8B flake-RR239 complex with solid KBr. The diffuse reflectance electronic absorption spectra of solid samples were recorded by a Varian, Cary 5000 UV-visible-NIR spectrometer (Varian Inc., USA) in the wavelength region of 200 - 800 nm.

Batch adsorption experiments were conducted with slight modifications of previously described method for the adsorption of reactive yellow 145 (RY145) onto chitosan in aqueous solution [_{max} value of 541 nm. The λ_{max} (541 nm) of RR239 solution was found to be constant at the pH ranges between 4 and 10. The apparent molar absorptivity of RR239 was estimated to be 15 × 10^{3} L/mol/cm at 541 nm and pH 4 - 10.

The amount of RR239 adsorbed onto chitosan 8B at time t, q_{t} (µmol/g) was determined by

q t = V ( C 0 − C t ) m (1)

where C_{0} (µmol/L) and C_{t} (µmol/L) are the liquid-phase concentrations of RR239 at initial and any time t, respectively; V(L) is the volume of RR239 solution and m (g) is the amount of dry chitosan 8B used.

The adsorption kinetics was also performed varying initial concentration of dye solutions (30 - 200 µmol/L), ionic strengths (0.01 - 0.04 mol/L) and temperatures (30˚C, 35˚C, 40˚C and 45˚C), respectively. The ionic strength of dye solutions was adjusted with 1 mol/L Na_{2}SO_{4} solution. The equilibrium adsorption was carried out at four different temperatures (30˚C, 35˚C, 40˚C and 45˚C), and at pH 4 in absence of Na_{2}SO_{4}.

The amount of RR239 adsorbed onto chitosan 8B at equilibrium time, q_{e} (µmol/g) was determined by

q e = V ( C 0 − C e ) m (2)

where C_{e} (µmol/L) is the liquid-phase concentrations of RR239 at equilibrium time; C_{0}, V and m remain same as described above.

In the desorption study, 25 mL of 0.1 mol/L NaOH solution was used to desorb RR239 from the chitosan 8B flakes. The adsorbent was contacted with 25 mL of 100 µmol/L RR239 solution for 120 min, filtered and the adsorbent was dried at room temperature (30˚C) overnight. The dye loaded-adsorbent was transferred into 25 mL desorbing solution and the mixture was stirred for 90 min. The amount of adsorption was determined in the same way as described above. All data presented in this paper are the mean of double measurements.

The chitosan 8B-RR239 complex was formulated by combining chitosan 8B flakes with a solution of RR239 at pH 4. The dye adsorption onto chitosan 8B flakes was confirmed by diffuse reflectance electronic absorption spectra. In

The surface charge of adsorbents and the configuration of dye molecules are significantly affected by solution pH [_{e}) was observed to be 49.70 µmol/g at pH 4 and 19.20 µmol/g at pH 10 (_{zpc} of chitosan is 6.3. It assumes that the 99% of chitosan is protonated at pH 4.3 [

Parameters | Pseudo first-order model | Pseudo second-order model | Elovich model | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|

q_{e}_{(exp)} (µmol/g) | k_{1 } (1/min) | q_{e}_{(cal)} (µmol/g) | R^{2} | k_{2} (g/µmol min)_{ } | q_{e}_{(cal)} (µmol/g) | h (µmol/g min) | R^{2} | α (µmol/g min) | β (g/µmol) | R^{2} | |

pH | |||||||||||

4 | 49.70 | 0.0578 | 15.99 | 0.946 | 0.0114 | 50.51 | 29.07 | 0.999 | 946.87 | 0.1890 | 0.953 |

5 | 43.33 | 0.0366 | 23.78 | 0.971 | 0.0043 | 44.64 | 8.67 | 0.999 | 49.86 | 0.1531 | 0.981 |

6 | 41.13 | 0.0389 | 26.41 | 0.995 | 0.0036 | 42.92 | 6.68 | 0.999 | 33.62 | 0.1538 | 0.967 |

7 | 34.13 | 0.0493 | 27.09 | 0.939 | 0.0041 | 35.71 | 5.19 | 0.999 | 29.01 | 0.1890 | 0.986 |

8 | 33.27 | 0.0379 | 23.21 | 0.989 | 0.0035 | 35.21 | 4.34 | 0.999 | 16.25 | 0.1719 | 0.953 |

9 | 30.10 | 0.0417 | 20.41 | 0.991 | 0.0045 | 31.75 | 4.49 | 0.999 | 23.07 | 0.2089 | 0.945 |

10 | 19.20 | 0.0387 | 15.59 | 0.995 | 0.0046 | 20.70 | 1.96 | 0.999 | 5.99 | 0.2721 | 0.983 |

[RR239] (µmol/L) | |||||||||||

30 | 14.57 | 0.0603 | 1.23 | 0.676 | 0.1941 | 14.62 | 41.49 | 1.000 | 3.40 × 10^{6} | 1.3187 | 0.732 |

50 | 25.03 | 0.0739 | 2.30 | 0.730 | 0.1148 | 25.13 | 72.46 | 1.000 | 2.29 × 10^{6} | 0.7278 | 0.762 |

100 | 49.33 | 0.0645 | 18.53 | 0.954 | 0.0108 | 50.25 | 27.39 | 1.000 | 1.35 × 10^{3} | 0.1998 | 0.963 |

150 | 59.77 | 0.0479 | 24.61 | 0.993 | 0.0062 | 60.98 | 23.09 | 0.999 | 1.17 × 10^{3} | 0.1633 | 0.979 |

200 | 71.67 | 0.0419 | 33.16 | 0.995 | 0.0039 | 72.99 | 20.79 | 0.999 | 6.17 × 10^{2} | 0.1259 | 0974 |

Ionic strength (mol/L) | |||||||||||

0.01 | 49.07 | 0.0606 | 10.74 | 0.929 | 0.0195 | 49.50 | 47.85 | 1.000 | 2.38 × 10^{4} | 0.2628 | 0.934 |

0.02 | 48.93 | 0.0672 | 13.67 | 0.976 | 0.0171 | 49.50 | 42.02 | 1.000 | 1.08 × 10^{4} | 0.2463 | 0.943 |

0.03 | 48.80 | 0.0539 | 12.48 | 0.946 | 0.0154 | 49.26 | 37.31 | 1.000 | 9.08 × 10^{3} | 0.2445 | 0.953 |

0.04 | 48.67 | 0.0534 | 12.71 | 0.953 | 0.0150 | 49.26 | 36.49 | 1.000 | 8.29 × 10^{3} | 0.2433 | 0.954 |

Temperatures (˚C) | |||||||||||

30 | 48.97 | 0.0458 | 20.31 | 0.939 | 0.0075 | 49.75 | 18.45 | 1.000 | 3.52 × 10^{2} | 0.1743 | 0.972 |

35 | 49.47 | 0.0610 | 20.51 | 0.972 | 0.0095 | 50.51 | 24.21 | 1.000 | 5.04 × 10^{2} | 0.1764 | 0.957 |

40 | 49.50 | 0.0534 | 18.20 | 0.974 | 0.0097 | 50.25 | 24.57 | 1.000 | 2.44 × 10^{3} | 0.2159 | 0.979 |

45 | 49.53 | 0.0619 | 17.03 | 0.941 | 0.0120 | 50.25 | 30.30 | 1.000 | 1.68 × 10^{3} | 0.2032 | 0.956 |

The initial concentration supplies a significant pouring strength to overcome all mass transfer resistance of the dye between the aqueous and solid phases [_{e} (μmol/g), increases (

The solution ionic strength is an essential issue that influences both electrostatic and non-electrostatic interactions between dyes and adsorbent surfaces. The effect of ionic strength on the adsorption kinetics of RR239 onto chitosan 8B in aqueous solution (pH 4) was successively inspected by the adding various amounts of Na_{2}SO_{4} salt to the 100 µmol/L dye solution at 30˚C. Results presented in _{e} (µmol/g), with increasing solution ionic strengths (_{2}SO_{4}) are competing for the active sorption sites, which is good agreement with previous reports [

The kinetics of RR239 dye adsorption onto chitosan 8B was investigated in aqueous solution (pH 4) at four different temperatures, 30˚C, 35˚C, 40˚C and 45˚C and the results are depicted in _{e} (µmol/g), increased with increasing the solution temperature (˚C). Therefore,

the RR239 dye molecules interact more efficiently with functional groups of chitosan 8B at higher temperatures because the mobility of the dye molecules increased with rising solution temperature. This is expected that rising of the solution temperature may generate a swelling effect within the internal structure of chitosan 8B [

The adsorption kinetics illustrates the dye uptake rate onto the adsorbent in adsorption reaction. This is an essential feature in expressing the efficacy of adsorption. Various kinetic models have been utilized to investigate the dye adsorption mechanisms in aqueous solutions. Here, pseudo first- [

log ( q e − q t ) = log q e − k 1 2.0303 t (3)

where k_{1} (1/min) is the pseudo first-order sorption rate constant estimated from the slope of a plot log ( q e − q t ) versus t.

The pseudo second-order kinetic model is expressed as:

q t = k 2 q e 2 t 1 + k 2 q e t (4)

where k_{2} (g/μmol min) is the pseudo second-order adsorption rate constant calculated from a linearized form of this equation, represented by Equation (5):

t q t = 1 k 2 q e 2 + 1 q e t (5)

The plot of t/q_{t} versus t would exhibit a straight line if pseudo second-order kinetics is applicable. The values of k_{2} and q_{e} were obtained from intercept and slope of the straight line. The initial rate of adsorption, h (µmol/g min), is able to know by Equation (6):

h = k 2 q e 2 (6)

The Elovich model is generally expressed as:

q t = 1 β ln ( α β ) + 1 β ln t (7)

where α (µmol/g min) is an initial rate of dye adsorption and β (g/μmol) is associated to the degree of surface coverage and the activation energy for chemisorption. The Elovich coefficients can be estimated from the plot of q_{t} versus lnt.

The values of correlation coefficients (R^{2}) and kinetic parameters obtained from various applied kinetic models are presented in ^{2} obtained from pseudo first-order (≤0.995) and Elovich (≤0.986) kinetic models are insignificant compare to the values of R^{2} (≥0.999) found in the cases of pseudo second-order kinetic model. Moreover, the calculated q_{e}_{(cal)} values from pseudo second-order kinetic model and the experimental q_{e}_{(exp)} values are comparable (

The intraparticle diffusion model equation can be written as:

Intraparticle diffusion model: q t = k i d t 0.5 + I (8)

where k_{id} (μmol/g min^{0.5}) is the intraparticle diffusion rate constant and I (μmol/g) is the intercept. The typical intraparticle diffusion plots for the effect of initial dye concentration on the adsorption of RR239 onto chitosan 8B were shown in _{id}_{1} (μmol/g min^{0.5}) and k_{id}_{2} (μmol/g min^{0.5}), are calculated from the slope of the corresponding linear regions of _{id}_{1} (μmol/g min^{0.5}) and k_{id}_{2} (μmol/g min^{0.5}) express diffusion rates of the different stages in the adsorption (

The changes of k_{id}_{1} (μmol/g min^{0.5}) and k_{id}_{2} (μmol/g min^{0.5}) represent to the adsorption levels of the exterior and interior surfaces of adsorbent [

Parameters | k_{id}_{1} (µmol/g min^{0.5}) | I_{1 } (µmol/g) | R^{2} | k_{id}_{2} (µmol/g min^{0.5}) | I_{1 } (µmol/g) | R^{2} | |
---|---|---|---|---|---|---|---|

pH | |||||||

4 | 5.544 | 22.100 | 0.967 | 0.306 | 46.599 | 0.728 | |

5 | 5.333 | 9.932 | 0.996 | 1.137 | 31.363 | 0.924 | |

6 | 4.667 | 8.656 | 0.992 | 1.251 | 28.031 | 0.958 | |

7 | 3.656 | 7.972 | 0.928 | 1.468 | 19.223 | 0.888 | |

8 | 4.009 | 4.440 | 0.97 | 1.058 | 22.120 | 0.957 | |

9 | 2.776 | 7.396 | 0.989 | 0.927 | 20.559 | 0.878 | |

10 | 2.592 | 0.867 | 0.973 | 0.869 | 10.193 | 0.928 | |

[RR239] (µmol/L) | |||||||

30 | 3.535 | 27.157 | 0.869 | 0.124 | 37.630 | 0.857 | |

50 | 8.005 | 27.232 | 0.828 | 0.169 | 50.767 | 0.790 | |

100 | 8.405 | 36.348 | 0.794 | 0.324 | 61.113 | 0.788 | |

150 | 12.422 | 29.015 | 0.965 | 0.498 | 71.02 | 0.699 | |

200 | 13.042 | 33.453 | 0.994 | 2.399 | 77.333 | 0.807 | |

Ionic strength (mol/L) | |||||||

0.01 | 4.169 | 29.033 | 0.945 | 0.143 | 47.591 | 0.865 | |

0.02 | 4.339 | 27.757 | 0.931 | 0.175 | 47.138 | 0.935 | |

0.03 | 4.130 | 27.730 | 0.925 | 0.203 | 46.638 | 0.976 | |

0.04 | 4.162 | 27.457 | 0.922 | 0.225 | 46.282 | 0.979 | |

Temperatures (˚C) | |||||||

30 | 5.449 | 19.013 | 0.989 | 0.628 | 42.233 | 0.987 | |

35 | 6.066 | 19.591 | 0.939 | 0.534 | 44.113 | 0.836 | |

40 | 3.991 | 26.162 | 0.983 | 0.519 | 44.106 | 0.787 | |

45 | 4.999 | 24.046 | 0.969 | 0.267 | 46.763 | 0.947 | |

The values of k_{2} at various temperatures recorded in _{2}), temperature (T) and activation energy (E_{a}) can be expressed by Equation (9):

ln k 2 = − E a R T + constant (9)

where R (8.314 J/mol K) is the gas constant. The value of E_{a} was determined be 23.30 kJ/mol from the slope of straight line obtained from lnk_{2} versus 1/T plot (R^{2} = 0.928) in temperature range 30˚C - 45˚C. Literature survey showed that the values of E_{a} were obtained to be 33.35 kJ/mol for the reactive dye adsorption on carbon nanotubes [_{a} (23.30 kJ/mol) suggests that the present adsorption is a physisorption process.

The other thermodynamic activation parameters such as changes in entropy of activation (ΔS^{‡}), changes in enthalpy of activation (ΔH^{‡}), and changes in Gibbs free energy of activation (ΔG^{‡}), are expressed by the following relations [

ln ( k 2 T ) = − Δ H ‡ R T + ln k B h P + Δ S ‡ R (10)

Δ G ‡ = Δ H ‡ − T Δ S ‡ (11)

where k_{2} (g/mol min), R and T are same as described before, k_{B} is the Boltzman constant (k_{B} = 1.381 × 10^{-23} J/K) and h_{P} is the Plank constant (h_{P} = 6.626 × 10^{-34} Js). The values of ΔH^{‡} and ΔS^{‡} were determined from the slope and y-intercept of the straight line obtained from the plot ln(k_{2}/T) versus 1/T (R^{2} = 0.911). The ΔH^{‡} value was estimated to be 20.72 kJ/mol. The low value of ΔH^{‡} shows that the interactions between RR239 and chitosan 8B are weak. The value of ΔS^{‡} was determined to be -102.33 J/mol K, which indicates that the RR239 anions at activated state and at the interface are always more organized than those in the bulk solution phase [_{av}ΔS^{‡} was calculated to be -31.77 kJ/mol where T_{av} represents the average value of four temperatures used for adsorption studies. The value of ΔH^{‡} was found to be smaller than that of T_{av}ΔS^{‡} (ΔH^{‡} < T_{av}ΔS^{‡}) which indicates that the impact of entropy is more significant than enthalpied in activation [^{‡} were found to be 51.72, 52.23, 52.75 and 53.26 kJ/mol at 30˚C, 35˚C, 40˚C and 45˚C, respectively. The positive values of ΔG^{‡} suggest the existence of an energy barrier in the adsorption process [

The typical phenomena of RR239 dye adsorption-desorption-adsorption onto chitosan 8B flakes in aqueous are shown in

The analysis of the adsorption isotherm data is important to know the nature of the interaction between adsorbate and the adsorbent used for the eliminating of organic pollutants. A plot of q_{e} versus C_{e} at various temperatures is presented in _{e} increased with increasing solution temperature from 30˚C to 45˚C indicating that the present adsorption is an endothermic process.

The adsorption isotherm data were examined by using four isotherm models such as Ferundlich [

Freundlich model:

Nonlinear form q e = K F C e 1 n (12)

Linear form ln q e = 1 n ln C e + ln K F (13)

Temkin model:

Nonlinear form q e = R T b ln ( K T C e ) (14)

Linear form q e = R T b ln K T + R T b ln C e (15)

Dubinin-Radushkevich model:

Nonlinear form q e = q D R exp ( − K D R ε 2 ) (16)

Linear form ln q e = ln q D R − K D R ε 2 (17)

where ε = R T ln ( 1 + 1 C e )

Langmuir model:

Nonlinear form q e = K L C e 1 + a L C e (18)

Linear form C e q e = 1 K L + a L K L C e (19)

where C_{e} (µmol/L) is the equilibrium RR239 dye concentration in solution, K_{F} ((µmol/g) (µmol/L)^{−1/n}) and n are Freundlich isotherm constants indicating the capacity and intensity of the adsorption, respectively. K_{T} (µmol/L) is the Temkin isotherm constant, b (J/mol) is a constant related to heat of adsorption, R (8.314 J/mol K) is an ideal gas constant and T is the absolute temperature (K). The q_{e} (µmol/g) is the amount of equilibrium RR239 dye adsorbed per unit weight of adsorbent, q_{DR} is the maximum adsorption capacity, K (mol^{2}/kJ^{2}) is the activity coefficient useful in obtaining the mean sorption energy E (kJ/mol) and ε is the Polanyi potential. K_{L} (L/g) and a_{L} (L/µmol) are the characteristic constants of the Langmuir equation, and the ratio of K_{L}/a_{L} gives the maximum dye adsorption capacity q_{m} (µmol/g) of chitosan 8B. The values of isotherm parameters are given in ^{2}), which is considerably a better fit compared with Freundlich, Temkin and Dubinin-Radushkevich adsorption isotherms.

Parameters | Freundlich isotherm | |||
---|---|---|---|---|

T (˚C) | 30 | 35 | 40 | 45 |

K_{F} ((µmol/g) (µmol/L)^{−1/n}) | 36.885 | 38.425 | 38.502 | 49.824 |

n | 5.266 | 4.933 | 4.955 | 5.485 |

R^{2} | 0.900 | 0.940 | 0.919 | 0.967 |

Parameters | Temkin isotherm | |||

T (˚C) | 30 | 35 | 40 | 45 |

K_{T} (µmol/L) | 24.487 | 14.702 | 14.919 | 64.777 |

b (J/mol) | 201.741 | 171.848 | 175.616 | 182.991 |

R^{2} | 0.963 | 0.957 | 0.957 | 0.965 |

Parameters | Dubinin-Radushkevich isotherm | |||

T (˚C) | 30 | 35 | 40 | 45 |

q_{DR} (µmol/g) | 107.32 | 116.75 | 120.00 | 129.67 |

K (J^{2}/mol^{2}) | 2.00 × 10^{?7} | 2.00 × 10^{?7} | 2.00 × 10^{?7} | 3.00 × 10^{?7} |

E (kJ/mol) | 1.58 | 1.58 | 1.58 | 4.08 |

R^{2} | 0.899 | 0.825 | 0.895 | 0.816 |

Parameters | Langmuir isotherm | |||

T (˚C) | 30 | 35 | 40 | 45 |

K_{L} (L/g) | 7.148 | 8.496 | 8.496 | 10.225 |

a_{L} (L/µmol) | 0.0579 | 0.0595 | 0.0603 | 0.0624 |

q_{m} (µmol/g) | 123.46 | 142.86 | 140.85 | 163.93 |

R_{L} | 0.0113 | 0.0111 | 0.0109 | 0.0106 |

R^{2} | 0.999 | 0.999 | 0.999 | 0.999 |

Thermodynamic parameters | ||||

T (˚C) | 30 | 35 | 40 | 45 |

∆G (kJ/mol) | ?27.63 | ?28.15 | ?28.64 | ?29.19 |

∆H (kJ/mol) | 3.80 | |||

∆S (J/K mol) | 103.72 | |||

R^{2} | 0.977 |

It is stated that the characteristics of the Langmuir isotherm can be expressed in terms of separation factor (R_{L}) [

R L = 1 1 + a L C 0 (20)

where a_{L} (L/µmol) is the Langmuir equilibrium constant and C_{0} (μmol/L) is the highest initial dye concentration. The shape of the isotherm can be interpreted as shown in _{L}. The values of R_{L} were found to be from 0 to 1 at 30˚C, 35˚C, 40˚C and 45˚C, respectively, which indicates that the adsorption is favorable at all temperatures [

The applicability of the Langmuir model suggests homogeneous surfaces of the chitosan 8B and monolayer coverage of RR239 dye onto the adsorbent. According to Langmuir, the maximum dye adsorption capacity of chitosan 8B was found to be 123.46 µmol/g at 30˚C and 163.93 µmol/g at 45˚C, respectively. This value is much higher than that of previously reported adsorbents as shown in

Thermodynamic parameters related to the adsorption process, i.e., Gibb’s free energy change (∆G, kJ/mol), enthalpy change (∆H, kJ/mol), and entropy change (∆S, J/mol K) are determined by using the values of Langmuir binding constant (a_{L}, L/mol) and the following equations:

Δ G = − R T ln a L (21)

ln a L = Δ S R − Δ H R T (22)

Value of R_{L} | Type of adsorption |
---|---|

R_{L} > 1.0 | Unfavorable |

R_{L} = 1.0 | Linear |

0 < R_{L} < 1.0 | Favorable |

R_{L} = 0 | Irreversible |

Adsorbents | q_{m} (µmol/g) | Reference |
---|---|---|

2,2’-(butane-1,4-diylbis(oxy))dibenzaldehyde cross-linked magnetic chitosan nanoparticles | 176.01 | [ |

Chitosan 8B | 163.93 | This study |

Hexamethylenediamine (HMDA)-modified zeolite | 25.14 | [ |

Formaldehyde treated carra sawdust | 13.29 | [ |

Hexadecyltrimethylammonium bromide (HTAB)-modified zeolite | 9.78 | [ |

Hexadecyltrimethylammonium bromide (HTAB)-modified sepiolite | 9.58 | [ |

Cetyltrimethylammonium bromide (CTAB)-modified zeolite | 8.01 | [ |

where R (8.314 J/mol K) is the universal gas constant and T is the absolute temperature (K). ∆H and ∆S values can be calculated from the slope and y-intercept of the linear polt of lna_{L} versus 1/T (R^{2} = 0.978). The thermodynamic results are presented in

In the present study, RR239 dye adsorption onto chitosan 8B was investigated in an aqueous solution. The effect of working parameters such as solution pHs, initial dye concentrations, ionic strengths and temperatures on the adsorption of RR239 was investigated. The obtained results suggested that all the parameters had a strong effect on the adsorption kinetics and equilibrium adsorption of RR239 onto the adsorbent. The batch adsorption kinetics was well explained by pseudo second-order model while intraparticle diffusion performed significant role in the rate limiting step. The batch adsorption kinetic profiles were absolutely reproduced by numerical analysis based on the pseudo second-order kinetic model in Equation (4) using the values of k_{2} and q_{e}_{(cal)} given in

The authors have declared no conflict of interest. We are indebted to the authority of the Ministry of Science and Technology, Government of the People’s Republic of Bangladesh for giving a research grant to carry out this work (FY 2013-2014). We gratefully acknowledge the support by the Alexander von Humboldt Foundation (George Forster Research Fellowship to T.K.S at Göettingen University, Germany where he has taken the diffuse reflectance electronic absorption spectra of solid samples). Authors are thankful to Prof. Yoshinobu Fukumori and Prof. Hideki Ichikawa (Kobe Gakuin University, Kobe, Japan) for providing the sample of chitosan 8B and measuring its particle size.

The authors declare no conflicts of interest regarding the publication of this paper.

Karmaker, S., Sintaha, F. and Saha, T.K. (2019) Kinetics, Isotherm and Thermodynamic Studies of the Adsorption of Reactive Red 239 Dye from Aqueous Solution by Chitosan 8B. Advances in Biological Chemistry, 9, 1-22. https://doi.org/10.4236/abc.2019.91001