6. EFFICIENCY OF REACTIVE DYES ADSORPTION ONTO CHITIN, CHITOSAN AND CHITOSAN BEADS Urszula Filipkowska Department of Ecological Engineering University of Warmia and Mazury in Olsztyn ul. Janowicza 15/29, 10-692 Olsztyn e-mail: urszula.filipkowska@uwm.edu.pl 1. Introduction Imperfection of the dying process leads to considerable amounts of colour compounds, i.e. from 2 to 50%, being transferred to wastewaters and, consequently, reaching the natural environment. The use of cheap waste materials in the treatment process of wastewaters containing dyes has raised considerable interest recently. Much attention is paid to the elaboration of technologies with the use of natural and effective sorbents, including chitin. Of biosorbents, chitin is characterized by a high adsorption capacity [1, 2]. Chitin is a natural polymer of acetylated or non-acetylated glucosamine with ever increasing application in medicine, pharmacology, biotechnology as well as plant and environmental protection [3, 4]. The most important parameters characterizing chitin are its molecular weight and acetylation degree (percentage of N acetylglucosamine in a chitin or chitosan chain). The study evaluated the effect of a preparation method of chitin on the adsorption efficiency of reactive dyes Black B and Black DN. Both dyes tested belonged to a group of helactine dyes but differed in their chemical structures. Black B contained a vinylsulphone active group, whereas Black DN a chlorotriazine active group. The study was aimed at determining the most beneficial method of chitin preparation, in respect of its adsorption capacity, that would provide a high removal efficiency of dyes. Conditions of the process, determined based on the results obtained, may be applied for designing technological systems for dye removal from wastewaters using the method of adsorption. Polish Chitin Society, Monograph XI, 2006 53
U. Filipkowska 2. Methods 2.1. Characteristics and preparation of chitin In the experiment, krill chitin originating from the Sea Fisheries Institute in Gdynia was used. Contents of dry matter and ash in the experimental chitin reached 95.64% and 0.32%, respectively. The chemical structure of chitin was presented in Figure 1. Figure 1. Chemical structure of a chitin molecule Studies into dye adsorption were carried out on modified chitin. The chitin was prepared according to the following procedures: sorbent 1 weighed amount of commercial chitin (10 g) was waterlogged with distilled water at a 1:10 weight ratio and left for 24 hours at room temperature for expanding. The expanded chitin was transferred into Büchner s funnel and filtered off under vacuum. The weighed amount of chitin after expanding was washed with 6 N HCl, rinsed with distilled water to reach a filtrate of neutral ph, and filtered off under vacuum. Next, 18% KOH solution was added to chitin which was then boiled for 3 h in water bath. After cooling down, the chitin was rinsed with distilled water to reach neutral ph and filtered off under vacuum; sorbent 2 the weighed amount of chitin after expanding was washed with 6 N HCl. Next, 70% KOH solution was added to chitin which was then boiled for 3h in water bath. After cooling down, the chitin was rinsed with distilled water to reach neutral ph and filtered off under vacuum; sorbent 3 100 g of sorbent 2 were dissolved in 5% acetic acid of chitin. Solution was dropped into 1M NaOH with a micropipette. The size of the instilled beads was controlled by the size of the micropipette. The average size of a chitin flake used in the experiment reached 314x184 µm. The characteristics of sorbents used in the study was presented in Table 1: Table 1. Characteristics of sorbents. Type of sorbent Deacetylation degree, % Sorbent 1 chitin flakes 5 Sorbent 2 chitosan flakes 75 Sorbent 3 chitosan beads 75 2.2. Characteristics and preparation of dye Reactive helactine dyes produced by Boruta S.A. Dye Plant in Zgierz were used in the study: Black DN (Black 8) of the chlorotriazine group and Black B (Black 5)of 54 Polish Chitin Society, Monograph XI, 2006
Efficiency of reactive dyes adsorption onto chitin, chitosan and chitosan beads the vinylsulfone group of dyes. Their structures and characteristics were presented in Table 2. Table 2. Characteristics of dyes. Reactive group Structural formula Dye tested chlorotriazine Black DN vinylosulfone dye O 2 CH 2 CH 2 OSO 3 Na Black B Stock solution of dye was prepared by weighing 1.00 g of pure powdered dye. The dye was quantitatively transferred into a 1dm 3 measuring flask which was then filled up with distilled water. Dye concentration in the solution reached 1000 mg/dm 3. The stock solution was used to prepare working solutions. The 100 cm 3 measuring flasks were filled with 2.5; 5.0; 10; 20; 30; 40; 50; 60; 70; 80; 90 and 100 cm 3 of dye stock solution and then filled with distilled water up to 100 cm 3. Dye concentration in the working solution reached: 25; 50; 100; 200; 300; 400; 500; 600; 700; 800; 900 and 1000 mg/ dm 3, respectively. The solutions ph was adjusted with 0.1 N HCl to ph 3.0 during adsorption onto chitin and to ph 5.0 during adsorption onto chitosan and chitosan beads. These values were experimental determined. Dye concentration was estimated spectrophotometrically by monitoring the absorbance at 587 nm for Black B and 597 for Black DN using a U-vis spectrophotomether HITACHI 1200. 2.3. Experimental procedures To determine the adsorption capacity of sorbent 1, 2, and 3 prepared according to different procedures, 200 cm 3 Erlenmayer flasks were filled with 1 g/dm 3 of the sorbent and 100 cm 3 a working solution of dye at an appropriate concentration. The flasks were transferred into a shaker and shaken for 2h at a constant speed agitation of 200 r.p.m. After shaking, the samples were sedimented for 1 min. The dye solution was decanted and centrifuged in an MPW 210 centrifuge for 10 min, at 10 000 r.p.m. After centrifugation, samples were collected and concentration of dye released from the sorbent was determined. Polish Chitin Society, Monograph XI, 2006 55
U. Filipkowska A model of an experiment into the determination of dye adsorption onto chitin from aqueous solutions was presented in Figure 2. Figure 2. Model of an experiment into determination of the effect of chitin preparation procedure on the adsorption capacity 3. Results and discussion The efficiency of Black B and Black DN adsorption from aqueous solutions onto chitin and chitosan was analyzed. Correlations between the amount of dye adsorbed Q (mg/g d.m.) and its equilibrium concentration C (mg/dm 3 ) in liquid were evaluated. The results obtained were analyzed with the Langmuir model assuming that the adsorbent s surface is energetically heterogenous and possesses adsorption centres with different energies of binding adsorbate molecules. Each type of the centres is described by the Langmuir isotherm equation [5], and the active sites are characterized by constants K 1, b 1 and K 2, b 2, respectively (1). Double Langmuir equation have been successfully applied to interpret results of metal adsorption by activated sludge [6, 7] and to evaluate adsorption of metals in soils [8]. where: Q equilibrium weight of dye adsorbed on chitin (mg/g d.m.) b 1 maximum adsorption capacity of chitin for type I active sites (mg/g d.m.) b 2 maximum adsorption capacity of chitin for type II active sites (mg/g d.m.) K 1 constant in Langmuir equation (dm 3 /mg) K 2 constant in Langmuir equation (dm 3 /mg) C equilibrium dye concentration in the solution (mg/dm 3 ). (1) The total adsorption capacity of chitin (b) equals the sum of the maximum adsorption capacities determined for active sites of type I and type II (b = b 1 + b 2 ). The K 1 and K 2 constants are characterized by adsorption affinity of the dye to the active sites of type I and type II, respectively, and correspond to the converse 56 Polish Chitin Society, Monograph XI, 2006
Efficiency of reactive dyes adsorption onto chitin, chitosan and chitosan beads of the equilibrium concentration of the dye at which the adsorption capacity of chitin equals half the maximum capacity of b 1 or b 2. The higher values of the K constant indicate an increased adsorption affinity of the dye to the active sites of chitin. The K 1 and K 2 constants as well as the maximum adsorption capacity (b 1 and b 2 ) were determined with the method of non-linear regression. The coefficient of fit (R 2 ) was accepted as a measure of curve fit to experimental data (at determined parameters) [9]. Low ϕ 2 values indicate good matching of the selected model to the experimental data obtained. The experimental results illustrating the relationship between the amount of dye adsorbed on chitin, prepared according to different procedures, and the equilibrium concentration as well as curves plotted from the double Langmuir equation were presented in Figure 3. The course of adsorption curves and the adsorption capacity values determined point out to the various efficiency of Black B and Black DN removal depending on the chitin preparation procedure. The results obtained show that the total adsorption capacities of chitin (sorbent 1) at the sorption of Black B and Black DN were alike and accounted for 260 and 258 mg/g d.m., respectively. A 15-fold increase in the deacetylation degree from 5 to 75 % (sorbent 2) evoked augmentation of the adsorption capacity both in the case of Black B and Black DN, yet it was not proportional to the increase in the deacetylation degree and reached 650 mg/g d.m. (a 3.5-fold increase) and 387 mg/g d.m (a 1.5-fold increase), respectively. In order to increase adsorbent s stability and to facilitate its separation from a solution, chitosan was used in the form of beads (sorbent 3). The experiment demonstrated that the formation of beads from chitosan did not diminish the total adsorption capacity in the case of both the dyes tested. In the case of Black B, the adsorption capacities of chitosan in the form of beads and flakes were alike (690 and 650 mg/g d.m.), whereas in the case of Black DN the adsorption on chitosan beads was higher by 25% than that on chitosan flakes (487 and 387 mg/g d.m.) An analysis of the adsorption capacity demonstrated that the adsorption mechanisms of both dyes under scrutiny was different (fig. 4). In the case of Black B a dye with the vinylsulfone active group, the adsorption was observed at the active sites of both type I and type II, irrespective of the preparation method of chitin, which indicates that the adsorption of Black B proceeded on the pathway of ionic exchange as well as physical binding (Figure 4a). On the contrary, during the adsorption of Black DN a dye with the chlorotriazine active group, also irrespective of chitin preparation procedure, the adsorption proceeded Polish Chitin Society, Monograph XI, 2006 57
U. Filipkowska Figure 3. Experimental results of Black B and Black DN adsorption on sorbents prepared with different methods and approximation of adsorption with Langmuir isotherms plotted from Langmuir equation; a, b and c Black B, d, e and f Black DN. mainly at the active sites of type I, which indicates that this dye was removed from the solution as a result of ionic exchange (Figure 4b). Tables 3 and 4 present constants determined from the Langmuir equation that describe the adsorption capacity and affinity at type I and type II active sites for three types of sorbents differing in both preparation procedure and properties. Table 3. Constants in Langmuir equation Black B. Type of sorbent Constants in Lamgmuir equation K 1 b 1 K 2 b 2 ϕ 2 chitin 15 130 0.005 130 0.004 chitosane 0.09 480 0.009 170 0.012 chitosan beads 0.02 400 0.02 290 0.009 58 Polish Chitin Society, Monograph XI, 2006
Efficiency of reactive dyes adsorption onto chitin, chitosan and chitosan beads Figure 4. Adsorption capacity and values of K 1 and K 2 constants in Langmuir equation for 3 types of sorbents. a- Black B, b Black DN. Table 4. Constants in Langmuir equation Black DN. Type of sorbent Constants in Lamgmuir equation K 1 b 1 K 2 b 2 ϕ2 chitin 50 248 0.001 10 0.004 chitosan 0.05 375 0.05 12 0.010 chitosan beads 0.05 475 0.05 12 0.035 The highest values of the K 1 constant, i.e. 15 and 50 dm 3 /mg d.m., were obtained for chitin with the deacetylation degree of 5% (sorbent 1). The high values of the K constant point to a strong affinity of the adsorbate to the adsorbent. Taking this as well as adsorption capacity into account, it may be concluded that in the case of sorbent 1 and the dye with the chlorotriazine active group Black DN, highly efficient and strong binding of the dye - chemical in character - proceeded at the active sites of type I. In the case of sorbents 2 and 3 with a higher deacetylation degree, the K 1 constant of the Langmuir equation was observed to decrease substantially to a value of 0.09 0.02 dm 3 /mg d.m. For all the examined types of chitin, the obtained values of K 2 Langmuir constant were considerably lower than those of K 1. The values of the K 2 constant determined for sorbent 1 were at a similar level, i.e. from 0.001 to 0.005 dm 3 /mg d.m. In the case of the other sorbents, the values of the K 2 constants were comparable with those of the K 1 ones. 4 Conclusions The experiment led to the following conclusions: 1. Investigations demonstrated a correlation between the adsorption capacity and affinity and the method of sorbent preparation. 2. Chitosan in the form of beads did not show a lower adsorption capacity and was characterized by slightly lower adsorption affinity, still it demonstrated considerably better mechanical and sedimentation properties. 3. In the case of chitin with a low deacetylation degree, both dyes tested were demonstrated to display a high affinity to the adsorbent. With an increasing degree of Polish Chitin Society, Monograph XI, 2006 59
U. Filipkowska deacetylation, the affinity of dye to chitin was observed to decrease at active sites of type I and to increase at those of type II. 5. References 1. Šafarik I.; Removal of organic polycyclic compounds from water solutions with a magnetic chitosan basad sorbent bearing copper phthalocyanine dye. Wat. Res. 1995, 29, 101. 2. Filipkowska U., Klimiuk E., Siedlecka E., Grabowski S.; Adsorption of reactive dyes by modified chitin from aqueous solutions. Polish J. Environ. Stusies 2002, 11, 315. 3. Juang R. S., Shao H. J.; A simplified equilibrium model for sorption of heavy metal ions from aqueous solutions on chitosan. Wat. Res. 2002, 36, 2999. 4. Divakaran R., Pillai V. N. S.; Flocculation of kaolinite suspensions in water by chitosan. Wat. Res. 2001, 35, 3904. 5. Chemia fizyczna. Praca zbiorowa. PWN 1980 6. Sterritt R. M., Lester J. N.; Heavy metal immobilisation by bacterial extracellular polymers. W: Immobilisation of ions by bio-sorption. Ed.: Chichester: Ellis Horwood. London, 1986, 121. 7. Hughes M. N., Poole R. K.; Metals and micro-organisms. Ed.: Chapman, Hall. London. 1989. 8. Amacher M. C., Kotuby-Amacher J., Selim H. M., Iskandar I. K.; Retention and release of metals by soils evaluation of several models. Geoderma, 1986, 38, 131-154. 9. Krysicki W., Bartos J., Dyczka W., Królikowska K., Wasilewski M.; Rachunek prawdopodobieństwa i statystyka matematyczna w zadaniach: Cz II. PWN, Warszawa, 1986. 60 Polish Chitin Society, Monograph XI, 2006