Studies of the adsorptive decoloration of aqueous solutions by MDFSD

Khaled Hartani; Khaled Alsousy; Hisham Aila

doi:10.1016/j.arabjc.2011.02.016

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Original article

9 (

1_suppl

); S73-S78

doi:

10.1016/j.arabjc.2011.02.016

Studies of the adsorptive decoloration of aqueous solutions by MDFSD

Khaled Hartani^⁎, Khaled Alsousy, Hisham Aila

Department of Chemistry, Alaqsa University, GAZA Strip, Palestine

⁎Corresponding author. khartani@yahoo.com (Khaled Hartani)

Received: 2010-12-21, Accepted: 2011-2-14, Published: 2011-09-01

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

The present study deals with the decoloration of water. Adsorptivity of moderate density fiberboard saw dust (MDFSD) for different dyes has been tested. Continuous as well as batch systems were used to evaluate the adsorptivity of three different dyes (crystal violet, methyl blue and brilliant green). Breakthrough times of the three dyes were compared. Crystal violet was chosen for more detailed studies. The adsorption kinetics and the saturation equilibrium were studied using batch system as a function of the related parameters. Adsorption isotherms were established and compared.

Breakthrough plots were obtained beside the three isotherms. The breakthrough times were found as CV > MB > BG. These results were compatible to the adsorptivity estimated from the isotherms. It was found through this study that adsorption of CV followed pseudo-first order kinetics, the adsorption rate constant increases with increasing temperature, adsorbent concentration, MDFSD dose and pH. The adsorption equilibrium was shifted toward higher adsorption capacity by increasing the substrate concentration, temperature and pH. The adsorption data fit Freundlich, Langmuir, but attained a better correlation with the Langmuir model. Langmuir and freundlich constants, activation enthalpy of adsorption and the adsorption thermodynamic parameters were obtained.

Keywords

Adsorptive decoloration

MDFSD

Water treatment

Crystal violet

Thermodynamic parameters

Breakthrough time

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1 Introduction

Color removal from textile effluents has been the subject of great attention in the last few years, not only because of its toxicity but also mainly due to its visibility (Meyer et al., 1992). Many industries especially textile industries, pulp and paper industries, often use dyes and pigments to color their products.

Fifteen percent of the total world production of dyes is lost during the dyeing process and is released in textile effluents (Zollinger, 1987). Effluents discharged from dyeing industries are highly colored and they can be toxic to aquatic life in receiving water (Dani et al., 1998). The release of these colored waste waters in the ecosystem is a dramatic source of esthetic pollution. Colored wastes in the receiving streams interfere with the transmission of sunlight into the streams and, therefore, reduce photosynthetic activity. Majority of these dyes are synthetic in nature and are usually composed of aromatic rings in their structure, inert and non-biodegradable when discharged into waste streams. Crystal violet (CV) is also known under the name of gentians violet. It is a protein dye, which stains the fatty portions of sebaceous sweat a deep purple color, it also can be used as an enhancer for a bloody finger print. However, in humans, CV causes skin irritation, it stains the area of contacted skin, may cause upper respiratory tract and mucous membrane irritation. Industries use biological treatment, coagulation, flotation, oxidation and adsorption for removing color from the aqueous medium. Biological treatment is disadvantageous as it requires a large land area and its constrained by sensitivity toward diurnal variation as well as toxicity of some chemicals.

The adsorption process provides an attractive treatment, especially if the adsorbent is inexpensive and readily available. A number of adsorbent, such as chitin (McKay et al., 1982), silica gel (McKay et al., 1980), wood (Poots et al., 1976), natural clay (McKay et al., 1980) bagasse pith fibers, and polymeric adsorbents (Hwang and Chen, 1993) have been used recently. Activated carbon is the most widely used adsorbent for this purpose because of its high capacity for adsorption of organic matter, but its use is limited due to its high initial and regeneration cost.

Consequently, many investigators have studied the visibility of using low-cost substances for the removal of various dyes and pollutants from waste water (Mall et al., 2005a,b).

MDFSD is a wood substitute which is made from fine wood fiber in a resin which is bonded under heat and pressure. MDFSD may be used instead of plywood or chipboard. It is dense, flat, stiff, has no knots and easily machined. It is made up of fine particles and therefore does not have an easily recognizable surface grain.

The physical and mechanical properties of MDFSD are mainly dependent upon the properties of the raw materials (wood, Binders, and other additives) and manufactured parameters (Akbulut et al., 2004; Ayrilmis, 2007, 2008; Bowyer and Smith, 1998 ).

The aim of this work was to investigate the possibility of utilizing MDFSD for the absorptive removal of water soluble dyes from aqueous solution.

2 Experimental

2.1

2.1 Materials and methods

All reagents used in the experimental work, are analytical grade and were from E. MERCK. MDFSD was used as the waste saw dust and was obtained locally. MDFSD was taken, washed with distilled water, and then immersed in boiling water for 15 min to extract any possibly water soluble components, filtered to discard the water soluble substances. The filtrate was dried at 95 °C for 48 h, sieved between 0.01 and 0.1 mm diameter. The produced powder was kept dry and was used with no further treatment. The adsorbate crystal violet (C₂₅H₃₀N₃Cl, FW = 407.98,) was obtained from sigma, methyl blue and brilliant green dyes, which were products of Aldrich.

2.2

2.2 Instrumentation

The pH values of the solutions were adjusted using a micro-processor combined pH-meter and thermometer, model pH 211 by Hanna instruments.

Continuous system locally built with a thermostated column was used for the breakthrough study, a thermo-stated inlet (298 K) with a flow rate of 0.066 L min⁻¹, pumped to 8.0 atm pressure, PVC cylindrical column with 10.0 g of MDFSD, adsorption bed dimensions were 1.25 × 32.0 cm.

A thermo-stated automatic shaker associated with circulation model YCW, USA was used for the batch experiments. The centrifugation was done with Wirowka Type WE-1 centrifuge machine at 4500 rpm. Absorbance of the three dyes was measured (λ_max of crystal violet, methyl blue and brilliant green are 590, 668, 623 nm, respectively) using Shimadzu-1601 UV–VIS spectrophotometer.

2.3

2.3 Adsorption studies

Breakthrough behaviors were tested using the continuous system, the inlet solution was prepared and thermostated. The system was run when ready and the outlet absorbance of each dye with respect to time then recorded.

The adsorption kinetics of CV on MDFSD was studied by batch technique (Sumra et al., 2009; Sumra and Uzma, 2009). A known weight (i.e., 0.5 g of MDFSD) was equilibrated with 100 mL of different concentration of aqueous CV solution (10–100 ppm) in a well-sealed 200 mL bottle, at a fixed temperature in a thermo-stated shaker water bath for a known period of time. A relatively large amount of MDFSD was used (0.5 g) to establish a pseudo-first order adsorption condition to simplify the calculations. The uptake was calculated from the initial and first one hour concentrations. The initial adsorption rate was taken as an observed rate constant (s⁻¹).

After equilibrium the suspension was filtered through Whatman 41 filter paper.

All absorbance measurements were taken at pH 7.0. For kinetic study, 2 mL samples of the previous solution were taken in different time intervals (5 min to 1 h) and were isolated for analysis.

The effect of pH was investigated in the range of (2.5–10.0) and it was adjusted by using NaOH and H₂SO₄.

Ionic strength effect was studied by using different concentrations of K₂SO₄ (0.01–0.1 M).

Adsorption capacity of crystal violet has been evaluated from the Freundlich and Langmuir adsorption isotherms which were studied at (298 K). The CV concentration studied was in the range of 10–100 ppm. All the experiments were carried out in triplicates with respect to each condition and mean values were used for further calculations. Identical blanks were used for every condition to account for any unexpected deviation.

Adsorption capacity of crystal violet has been evaluated from the Freundlich and Langmuir adsorption isotherms which were studied at (298 K). The CV concentration studied was in the range of 10–100 ppm. All experiments were carried out in triplicates with respect to each condition and mean values were used for further calculations, standard deviation was with accuracy of ±2%. Identical blanks were used for every condition to account for any unexpected inner deviation like bottle surface adsorption or heat auto decomposition of the dye.

3 Results and discussion

Breakthrough of adsorption behaviors were followed and compared with each other. Adsorption kinetics, saturation equilibrium, and isotherms were tested by changing the following; parameters: contact time, the amount of each adsorbent and adsorbate, ionic strength, pH and temperature.

3.1

3.1 Breakthrough behavior

Breakthrough data are listed in Table 1, it can be estimated that the adsorptivity of the three dyes are in the order of BG > CV > MB using dyes concentration of 10.0 mg/L.

Table 1 Breakthrough data by MDFSD for decoloration of aqueous solutions, 10.0 g of MDFSD, T = 298 K, flow rate = 0.071 L/ min, adsorption bed 1.25 × 32.0 cm. Inlet concentration = 10.0 mg/L.

Adsorbent dye	Breakthrough time (h)	Breakthrough volume (L)	Q_ads (mg/g)
Crystal violet	42	178	170
Methyl blue	11.5	46	46
Brilliant green	58	234	234

Outlet adsorbate concentration was below limit of quotation along the mentioned breakthrough times of the three dyes.

The difference in adsorption capacity can be referred to the nature and size of the adsorbed molecules under the experimental conditions.

3.2

3.2 Adsorption kinetics

The elimination rate of CV by adsorption on MDFSD was followed with respect to contact time under the experimental conditions. As shown in Fig. 1, the adsorption follows a pseudo-first order model; where the natural logarithm of (C₀/C) has straight line relation with time. It can be estimated also that a 24 h period is adequate time to achieve practical equilibrium.

The relation between in C0/C vs. time to verify pseudo-first order kinetics of crystal violate adsorption on 0.5 g MDFSD.

The study of the initial adsorbate concentration influence; shows that the rate of adsorption (mg dm⁻³s⁻¹) is directly proportional to adsorbate concentration in the studied range (10–100 ppm) as shown in Fig. 2.

Variation of the initial rate of adsorption vs. either CV concentration [10–110 ppm], mass of MDFSD [0.1–1.0 g], pH [1–12 ] at 22 °C .

The influence of MDFSD dosage on the adsorption rate was shown in Fig. 2. It shows that the rate increases with increase in the amount of MDFSD up to 0.5 g and reach to a plateau in the studied range, this indicates that the proper weight of adsorbent is 0.5 g for the present conditions. The effect of pH was investigated at the range 1–12 as illustrated in Fig. 2 increase in the pH increases adsorption rate. Maximum adsorption rate was found at pH 7 when MDFSD was 0.5 g and [CV] was 100 ppm. Adsorption rate due to pH change alone may be due to the structural changes being effected to the dye molecules (Mall et al., 2005a,b, 2006 ).

Increasing temperature enhances adsorption rate (284–333 K). The relation was found to fit an Arrhenius equation (Eq. (1))

(1)

ln k_{obs} = ln A - \frac{E_{a}^{*}}{RT}

by showing a straight line when (ln k_obs) is plotted against (1/T) at (pH 7, MDFSD = 0.05 g T = 284–333 K). The activation energy

E_{a}^{*}

of the process was calculated from Arrhenius plot shown in Fig. 3. Where A is Arrhenius factor, R is the universal gas constant = 8.303 J mol⁻¹ K⁻¹ and T is absolute temperature in K.

Relationship between ln kobs vs. 1/T to verify Arrhenius equation for 100 ppm CV adsorption on 1.0 g MDFSD.

According to Aliola and Oforka (2002) and Damaskin (1971) a value of activation energy less than 80 kJ/mol represents physisorption. Hence, in the present observation, a considerably lower value of activation energy (25.5 kJ mol⁻¹) indicates that the transfer of adsorbate from the aqueous phase to the solid surface passes through a physical adsorption with low activation energy. From the study it was found that ionic strength (0.0–0.4) has no influence on the adsorption rate constant, which confirms that the adsorption process does not involve any ionic reaction (House, 2007).

3.3

3.3 Adsorption equilibrium

Adsorption equilibrium was studied under conditions of relatively low amount of MDFSD (0.5 g), higher CV concentration 100.0 ppm and suitable time (24 h) to reach saturation equilibrium according to kinetic testing results. The standard equilibrium constant (K°) was obtained from Eq. (2),

(2)

K^{°} = \frac{C_{solid}}{C_{liquid}}

where, C_solid is the solid phase concentration at equilibrium (mg/g); C_liquid is the liquid phase concentration at equilibrium (mg/L).

The influence of the initial concentration of CV on the adsorption rate in the bulk shows that the equilibrium is shifted toward higher adsorption capacity by increasing initial concentrations as shown by the slightly lower equilibrium constant (K°) in Fig. 6.

Adsorption isotherms of different adsorbated dyes on MDFSD. [Dyes] = 10–100 ppm; [MDFSD] = 0.5 g.

On the other hand, equilibrium constant (K°) increases with increasing dose of MDFSD in the studied range (0.1–1.0 g) as shown in Fig. 4.

Variation of equilibrium constant (K°) vs. variation either of, initial concentration of CV [10–110 ppm]; MDFSD [0.1–1.0 g]; pH [1–12] and temperature [11–60 °C].

The effect of pH on K° is shown in Fig. 4, which shows a trend of increase in K° with increase in pH. So, the pH of the aqueous media has a strong influence on the adsorption equilibrium constant.

Ionic strength has no significant influence on the adsorption equilibrium as all other parameters are kept constant. The absence of any effect of ionic strength shows that the adsorption process of the dye on MDFSD does not involve any ionic reaction.

The influence of temperature on the adsorption equilibrium revealed that, the equilibrium is shifted sharply toward higher adsorption capacity by increasing the temperature. The relation between equilibrium constant K and temperature is plotted in Fig. 4. This relation within the studied range of temperature (284–333 K) shows that the adsorption supports an endothermic process. Thermodynamic equilibrium parameters such as change in free energy (ΔG°, kJ/mol), enthalpy (ΔH°, kJ/mol) and entropy (ΔS°, J/mol K) were determined using the Van‘t Hoff Eqs. (3) and (4):

(3)

Δ G^{°} = - RT \ln K^{°}

(4)

\ln K^{°} = \frac{Δ S^{°}}{R} - \frac{Δ H^{°}}{RT}

The ΔH° and ΔS° values were obtained from the slope and intercept respectively of Van’t Hoff plots of ln K° vs. 1/T as shown in Fig. 5. The positive and lower value of ΔH° (7.8 kJ mol⁻¹) shows the endothermic nature of adsorption and the possibility of physical adsorption (Gong and Sun, 2005; Vadivelan and Vasanthkumar, 2005). The negative values of ΔG° (−8.3 kJ mol⁻¹) shows the adsorption is favorable and spontaneous. The positive values of ΔS° (54.2 J mol⁻¹ K⁻¹) shows that the increased disorder at the solid solution interface components. The higher adsorption capacity of MDFSD at higher temperatures was attributed to the enlargement of pore size and activation of the adsorbent surface.

Van’t Hoff plot of ln K° vs. 1/T, [CV] = 100 ppm and 0.5 g of MDFSD.

3.4

3.4 Adsorption isotherm

The adsorption isotherms were plotted at optimum conditions for, methyl blue, brilliant green and crystal violet. It is found that the adsorption of Crystal violet on MDFSD showed higher adsorption capacity, using relatively wide range of adsorbate concentrations [10–100 ppm CV], the results are shown in Fig. 6.

The adsorption isotherms of different adsorbents, MDFSD and Activated carbon, were constructed for comparison purpose under the same experimental conditions.

Fig. 7 shows the isotherms of each of them; it is obvious that the overall (ignoring the differences in porosity, surface specific area and particle average size) adsorption capacity of adsorbents is arranged as (activated carbon < MDFSD).

Adsorption isotherms of CV on different adsorbent. [CV] = 100 ppm; [Adsorbent] = 0.1–1.0 g.

Several adsorption models have been published in the literature to verify the experimental data in which the most common models are the Langmuir and Freundlich isotherms.

In order to facilitate the estimation of the adsorption capacities at various concentrations, Langmuir and Freundlich adsorption isotherms, typical models for monolayer adsorption, were applied. The linearized Langmuir model can be written as: (Arivoli and Kalpana, 2007; Casey, 1997; Damaskin, 1971a,b; Arab and Al-Turkustani, 2006 .)

(5)

\frac{1}{Q_{e}} = \frac{1}{K_{L}} + \frac{1}{{bK}_{L}} \times \frac{1}{C_{e}}

where C_e is the concentration of adsorbate equilibrium (mg/L), Q_e is the amount of CV adsorbed at equilibrium (mg/g), K_L (g/mg) and b (dm³/mg) are the Langmuir constants, representing the maximum adsorption capacity for the solid phase loading and the energy constant related to the heat of adsorption. The constants b and K_L can be evaluated from the intercept and slope of the linear plot of the experimental data of 1/Q_e vs. 1/C_e, respectively. The linearized Langmuir isotherm was developed and is shown in Fig. 8. The Langmuir constants were calculated from the figure (K_L = 62.9 g/mg, b = 0.047 dm³/mg).

Linearized Langmuir isotherm plot (1/Qe vs. 1/Ce) of CV adsorption on MDFSD at 22 °C.

The Freundlich isotherm has been widely used to characterize the adsorption capacity of organic pollutants using different adsorbents by fitting the adsorption data.

The Freundlich isotherm in its linearized form can be written as: (Arivoli and Kalpana, 2007; Casey, 1997; Damaskin, 1971a,b; Arab and Al-Turkustani, 2006 ). $\ln Q_{e} = \ln K_{F} + \frac{1}{n} \ln C_{e}$ where, K_F is Freundlich constant related to the adsorption capacity (mg/g), and 1/n is the intensity of adsorption. The values of K_F and 1/n can be determined from the intercept and slope, respectively, of linear plot of ln Q_e vs. ln C_e. The linearized Freundlich adsorption isotherm was developed and is shown in Fig. 9. The Freundlich constants were calculated from the figure (K_F = 5.35 mg/g, n = 19.3).

Freundlich isotherm plot (1/Qe vs. 1/Ce) of CV adsorption on MDFSD at 22 °C.

The equilibrium data was better fitted Langmuir model more than Freundlich model.

4 Conclusion

It was concluded in this study that the MDFSD can be successfully used as a discoloration adsorbent, the adsorption process can be applied in continuous reactor system. The application can be economic since the SDMDF is a waste material which is priceless.

References

Akbulut T., Ayrilmis N., Koc E., . Drev Vysk. 2004;49(3):17.
Aliola O.K., Oforka N.C., . Corros. Sci. Eng.. 2002;3:21.
Arab S.T., Al-Turkustani A.M., . Port. Electrochim. Acta. 2006;24:53.
Arivoli S., Kalpana K., . E-J. Chem.. 2007;4:238.
Ayrilmis N., . J. Mater. Sci.. 2007;42:8551.
Ayrilmis N., . Silva Fennica. 2008;42(2):285.
Bowyer J., Smith R.L., . The nature of wood and wood products. Madison, WI, USA: University of Minnesota and The Forest Products Management Development Institute. Self-Study Educational CD-ROM. Forest Products Society; 1998.
Casey T.J., . Unit Treatment Processes in Water and Wastewater Engineering. London, England: John Wiley and Sons Ltd.; 1997. p .133
Damaskin B.B., . Adsorption of Organic Compound on Electrodes. New York: Plenum Press; 1971. p. 22115
Damaskin B.B., . Adsorption of Organic Compounds on Electrodes. New York: Plenum Press; 1971. p.221.
Dani, U., Gurses, A., Canpolat, N. 1998. 1st International Workshop on Environmental quality and Environmental Engineering in the Middle East Region, Konya, Turkey.
Gong R.Y., Sun A., . Dyes Pigm.. 2005;67:175.
House J.E., . Principles of Chemical Kinetics (2nd ed.). Elsevier Science and Technology; 2007.
Hwang M.C., Chen K.M., . J. Appl. Polym. Sci.. 1993;49(6):975.
Mall I.D., Srivastava V.C., Agarwal N.K., Mishra I.M., . Chemosphere. 2005;61:492.
Mall I.D., Srivastava V.C., Agarwal N.K., Mishra I.M., . Colloids Surf. A. 2005;264:17.
Mall I.D., Srivastava V.C., Agarwal N.K., . Dyes Pigm.. 2006;69:210.
McKay G., Blair H.S., Gardner J.R.J., . Appl. Polym. Sci.. 1982;27(8):3043.
McKay G., Otterburn M.S., Sweeney A.G., . Water Res.. 1980;14:15.
Meyer V., Carlsson F.H.H., Oellermann R.A., . Water Sci. Technol.. 1992;26(5):1205.
Poots V.J.P., McKay G., Healy J.J., . Water Res.. 1976;10(12):1067.
Sumra N., Uzma Z., . Pak. J. Anal. Environ. Chem.. 2009;10:83.
Sumra N., Uzma Z., Arifa A., Asma I., . J. Chem. Soc. Pak.. 2009;31:379.
Vadivelan V., Vasanthkumar K., . J. Colloid Interf. Sci.. 2005;286:125.
Zollinger H., . Color Chemistry System, Properties and Applications of Organic Dyes and Pigments. New York: VCH Publishers; 1987. p. 92

Introduction

Experimental

Materials and methods
Instrumentation
Adsorption studies

Results and discussion

Breakthrough behavior
Adsorption kinetics
Adsorption equilibrium
Adsorption isotherm

Conclusion

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[1] Akbulut T., Ayrilmis N., Koc E., . Drev Vysk. 2004;49(3):17.

[2] Aliola O.K., Oforka N.C., . Corros. Sci. Eng.. 2002;3:21.

[3] Arab S.T., Al-Turkustani A.M., . Port. Electrochim. Acta. 2006;24:53.

[4] Arivoli S., Kalpana K., . E-J. Chem.. 2007;4:238.

[5] Ayrilmis N., . J. Mater. Sci.. 2007;42:8551.

[6] Ayrilmis N., . Silva Fennica. 2008;42(2):285.

[7] Bowyer J., Smith R.L., . The nature of wood and wood products. Madison, WI, USA: University of Minnesota and The Forest Products Management Development Institute. Self-Study Educational CD-ROM. Forest Products Society; 1998.

[8] Casey T.J., . Unit Treatment Processes in Water and Wastewater Engineering. London, England: John Wiley and Sons Ltd.; 1997. p .133

[9] Damaskin B.B., . Adsorption of Organic Compound on Electrodes. New York: Plenum Press; 1971. p. 22115

[10] Damaskin B.B., . Adsorption of Organic Compounds on Electrodes. New York: Plenum Press; 1971. p.221.

[11] Dani, U., Gurses, A., Canpolat, N. 1998. 1st International Workshop on Environmental quality and Environmental Engineering in the Middle East Region, Konya, Turkey.

[12] Gong R.Y., Sun A., . Dyes Pigm.. 2005;67:175.

[13] House J.E., . Principles of Chemical Kinetics (2nd ed.). Elsevier Science and Technology; 2007.

[14] Hwang M.C., Chen K.M., . J. Appl. Polym. Sci.. 1993;49(6):975.

[15] Mall I.D., Srivastava V.C., Agarwal N.K., Mishra I.M., . Chemosphere. 2005;61:492.

[16] Mall I.D., Srivastava V.C., Agarwal N.K., Mishra I.M., . Colloids Surf. A. 2005;264:17.

[17] Mall I.D., Srivastava V.C., Agarwal N.K., . Dyes Pigm.. 2006;69:210.

[18] McKay G., Blair H.S., Gardner J.R.J., . Appl. Polym. Sci.. 1982;27(8):3043.

[19] McKay G., Otterburn M.S., Sweeney A.G., . Water Res.. 1980;14:15.

[20] Meyer V., Carlsson F.H.H., Oellermann R.A., . Water Sci. Technol.. 1992;26(5):1205.

[21] Poots V.J.P., McKay G., Healy J.J., . Water Res.. 1976;10(12):1067.

[22] Sumra N., Uzma Z., . Pak. J. Anal. Environ. Chem.. 2009;10:83.

[23] Sumra N., Uzma Z., Arifa A., Asma I., . J. Chem. Soc. Pak.. 2009;31:379.

[24] Vadivelan V., Vasanthkumar K., . J. Colloid Interf. Sci.. 2005;286:125.

[25] Zollinger H., . Color Chemistry System, Properties and Applications of Organic Dyes and Pigments. New York: VCH Publishers; 1987. p. 92

Studies of the adsorptive decoloration of aqueous solutions by MDFSD

Abstract

Keywords

Adsorptive decoloration

MDFSD

Water treatment

Crystal violet

Thermodynamic parameters

Breakthrough time

1 Introduction

2 Experimental

2.1 Materials and methods

2.2 Instrumentation

2.3 Adsorption studies

3 Results and discussion

3.1 Breakthrough behavior

3.2 Adsorption kinetics

3.3 Adsorption equilibrium

3.4 Adsorption isotherm

4 Conclusion

References

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