P-07 ADSORPTION AND DESORPTION EFFICIENCY OF BLACK 8 AND BLACK 5 ONTO CHITIN AND CHITOSAN Urszula Filipkowska Department of Environmental Protection Engineering University of Warmia and Mazury in Olsztyn ul. Prawocheńskiego 1,10-957 Olsztyn e-mail: urszula.filipkowska@uwm.edu.pl 1. Introduction Synthetic dyes are widely applied in such industries as: textile, leather, papermaking, plastics and others for lending color to end products. Reactive dyes are one of the most often applied forms of structural dyes due to their color values, color fastness and simplicity of application. The most important groups of reactive dyes include triazine, pyrimidine and vinylsulfone ones. In their triazine ring, the chlorotriazine dyes contain chlorine atoms capable of reactions with cellulose, whereas the vinylsulfone dyes contain a vinylsulfonyl group SO 2 CH=CH 2 or more often a sulfatoethylsulfonyl group SO 2 CH 2 CH 2 OSO 3 Na transforming into the vinylsulfonyl group in the dyeing process. Toxicity of reactive dyes has not been explicitly confirmed so far. The reactive dyes that contain nitrogen bonds are likely to negatively affect aquatic organisms. Nowadays, however, there dominates a view that their negative impact of aquatic ecosystems is caused, to a greater extent, by a limited degree of light permeability in water than by toxicity [1]. Reactive dyes evoke a distinct coloration and reduced transparency of water already at the concentration of ca. 1 mg/dm3 [2]. Removal of dyes is difficult and poorly efficient upon the use of conventional physicochemical and biological methods. Usually, dye-containing sewage are treated by means of adsorption, ozonization, membrane processes, coagulation with flocculation and biological processes. The process of adsorption is one of more efficient methods for dye removal from sewage, especially when the adsorbent is cheap and easily available. Recently, chitin and chitosan Polish Chitin Society, Monograph XII, 2007 57
U. Filipkowska have been considered as attractive adsorbents that demonstrate a high efficiency of dye removal due to a high number of functional groups: amine and hydroxyl ones. In addition, chitin is attractive for its abundance in nature, non-toxicity, hydrophilicity or biocompatibility. It is easily biodegradable, it demonstrates antibacterial properties and is characterized by a high adsorption capacity [3, 4]. The potential of an adsorbent to be used in practice is determined not only by binding the greatest possible amount of adsorbate but also by the possibility of its regeneration. Investigations into the efficiency of the desorption process may, however, serve not only for obtaining an economically-attractive adsorbent but for elucidation and evaluation of the mechanism of the adsorption process as well. 2. Methods 2.1. Characteristics and preparation method of chitin The experiment was carried out on krill chitin obtained from the Sea Fisheries Institute in Gdynia. Chitin was characterized by dry matter content of 95.64% and ash content of 0.32%. An average size of a chitin flake used in the study was 314x184 µm. Analyses of dyes adsorption were carried out on modified chitin. In the experiment three sorbents were used chitin (sorbent 1), chitosan (sorbent 2) and chitosan beads (sorbent 3) Preparation procedure and the characteristics of sorbents are presented in the work of Filipkowska [5]. 2.2. Characteristics and preparation method of dyes. In the experiments use was made of the following reactive dyes: of the chlorotriazine group Black 8 (RB8) and of the vinylsulfone group Black 5 (RB5), produced by ZPB Boruta SA in Zgierz. Their characteristics and structures were presented in the work of Filipkowska [5] A stock solution of a dye was prepared by weighing 1 g of pure dye in the powdered form. Next, the dye was quantitatively transferred to a 1dm3 measuring flask and filled up with distilled water with ph 6.0. Dye s concentration in the solution reached 1000 mg/dm3. The stock solution was then used to prepare working solutions as follows: 2.5; 5.0; 10; 20; 30; 40; 50; 60; 70; 80; 90 and 100 cm 3 of the stock solutions were added to 100cm 3 measuring flasks and filled up to 100cm 3 with distilled water (ph 6.0). Dye s concentration in the working solutions accounted for: 25; 50; 100; 200; 300; 400; 500; 600; 700; 800; 900 and 1000 mg/dm3, respectively. 2.3. Experimental procedures In order to determine the adsorption capacity of sorbent 1, 2, or 3, 0.1 g d.m. of the sorbent was weighed into 200 cm3 Erlenmayer flasks and supplemented with 100 cm3 of the working solution of the dye at an appropriate concentration, i.e. from 25 to 1000 mg/dm3. Samples were fixed on a shaker and shaken for 2 hours at a constant rate of 200 rpm. After shaking, the samples were sedimented for 1 minute. Dye solution was decanted and centrifuged for 10 minutes in an MPW 210 centrifuge at 10 000 rpm. After centrifugation, samples were collected for determination of dye concentration. To assay dye concentration, the solution was adjusted to ph 6. The concentration of dyes was determined with the spectro- 58 Polish Chitin Society, Monograph XII, 2007
Adsorption and desorption efficiency of black 8 and black 5 onto chitin and chitosan photometric method using a UV-VIS Spectrophotometer SP 3000. A wave length at which absorbance was measured was determined for each of the two dyes examined (Table 1). Table 1. Wave length at extinction measurement of the dyes examined. Dyes Wave length λ ( nm) RB5 597 RB8 587 Analyses of desorption efficiency of the reactive dyes from the three sorbents examined were carried out after the prior adsorption process. The process of desorption was run at ph = 11. The solution s reaction was adjusted to ph 11 with an NaOH solution. After two hours samples were collected and concentration of the residual dye was determined. To assay dye concentration, the solution was adjusted to ph 6. 3. Results and discussion The efficiency of adsorption and desorption of a dye from solution was analyzed based on changes in its concentration in the solution. The quantity of the adsorbed dye was calculated from the following dependence: Q s = (C 0 - C s )/m (1) where: Q s the quantity of dye adsorbed, mg/g d.m. C 0 initial concentration of dye, mg/dm 3 C s concentration of dye after adsorption, mg/dm 3 m chitin mass, g d.m./dm3 The quantity of the desorbed dye was calculated from the following dependence: Q d = (C 0 - C s )/m (2) where: Q d the quantity of dye desorbed, mg/g d.m. C d concentration of dye after desorption, mg/dm 3 C s concentration of dye before desorption (after adsorption), mg/dm 3 m chitin mass, g d.m./dm3 The results obtained were analyzed with the use of the Langmuir s model taking into account the fact that adsorbent s surface is energetically non-uniform and possesses adsorption centers with different energy of binding adsorbate s molecules. Each of their types is described by an isotherm of Langmuir s equation [6], and the active sites are characterized by constants reaching: K 1, b 1 and K 2, b 2 respectively (1). A double Langmuir s equation has been successively applied for the interpretation of results of metals adsorption by activated sludge [7, 8] as well as for the assessment of metals adsorption in soils [9]. Adsorption efficiency of RB8 and RB5 from aqueous solutions onto chitin was analyzed based Polish Chitin Society, Monograph XII, 2007 59
U. Filipkowska on a dependency between the amount of adsorbed dye Q (mg/g d.m.) and its equilibrium concentration C (mg/dm3). (3) Q mass of dye adsorbed onto chitin (mg/g d.m.) b 1, b 2 maximum adsorption capacity of chitin at type I and II active sites (mg/g d.m.) K 1, K 2 constants in Langmuir equation (dm3/mg) C dye concentration in the solution (mg/dm 3 ) The total adsorption capacity of chitin (b) is equal to the sum of the maximum adsorption capacity determined for type I and type II active sites (b = b 1 + b 2 ). The K 1 and K 2 constants characterize the adsorption affinity of a dye to the active sites of type I and type II, respectively, and correspond to a converse of the equilibrium concentration of the dye at which the adsorption capacity of chitin is equal to over half the maximum capacity of b 1 or b 2. Higher values of the constant K indicate an increase in the 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. Experimental results indicating a correlation between the quantity of adsorbed and desorbed dye and the equilibrium concentration as well as isotherms determined from the Langmuir s equation were presented in Figure 1. The efficiency of adsorption and desorption process depended on both the type of the adsorbent applied and the type of the dye. The amount of dye adsorbed onto chitin for both dyes examined was alike and reached 260 mg/g d.m. The efficiency of chitin desorption was determined by the type of dye and reached 79% in the case of Black 8 and 50% in the case of Black 5 (Figure 1.a, 1.d). During the adsorption of the dyes tested onto chitosan, both in the form of flakes and beads, a significant increase was observed in the adsorption capacity as compared to chitin. A higher increase was recorded in the case the dye with a vinylsulfone active group 2.1-fold (chitosan flakes) and 2.7-fold (chitosan beads) (Figure 3.b, 3.c). In the case of the dye with a chlorotriazine active group, the amount of dye adsorbed was observed to increase 1.5-times (chitosan flakes) and 1.9-times (chitosan beads) (Figure 1.e, 1.f). With an increased adsorption capacity of Black 5 on chitosan no analogous increase was observed in the amount of desorbed dye. The results obtained point to a substantially lower efficiency of desorption as compared with the adsorption process. In the case of the second dye tested Black 8 the increase in the amount of dye adsorbed affected the amount of the desorbed dye. 60 Polish Chitin Society, Monograph XII, 2007
Adsorption and desorption efficiency of black 8 and black 5 onto chitin and chitosan Figure 1. Experimental results of Black 5 and Black 8 adsorption on sorbents prepared with different methods and approximation of adsorption with Langmuir isotherms plotted from Langmuir equation; a, b and c Black 5, d, e and f Black 8. According to Chiou et al. [10], a different adsorption capacity of chitin and chitosan depends on their structure. This results from a difference in the structure between chitin and chitosan. The latter contains amine groups NH 2 that are easily protonated to NH 3 + groups in acidic solutions. High adsorption capacities result from electrostatic activity between the NH 3 + groups of chitosan and anionic dyes. Chitin, in turn, contains amide groups CO NH that are not easily protonated in acidic solutions. An electron is more strongly attracted by a carbonyl group, as a result of which nitrogen in the amide group is less electronegative than in the amine group, hence interactions of the amide groups with anionic dyes are considerably poorer than those of the amine groups. The lowest adsorption capacity of chitin results from a lack of electrostatic interaction between chitin and the anionic dye. Polish Chitin Society, Monograph XII, 2007 61
U. Filipkowska Table 2 presents constants, determined from the Langmuir s equation, which describe the adsorption capacity and affinity for the three sorbents differing in the method of preparation and properties. Table 2. Constants in Langmuir adsorption. Type of sorbent Constants in Lamgmuir equation K 1 b 1 K 2 b 2 b 1 + b 2 ϕ 2 Reactive Black 5 chitin 70.00 130 0.005 130 260 0.004 chitosan flakes 0.09 480 0.009 170 650 0.012 chitosan beads 0.02 400 0.020 290 690 0.009 Reactive Black 8 chitin 50.00 248 0.001 10 258 0.004 chitosan flakes 0.05 375 0.050 12 387 0.010 chitosan beads 0.05 475 0.050 12 487 0.035 Values of K 1 constants in the Langmuir s equation, that describe adsorption affinity of RB5 and RB8 during adsorption onto chitin, were extremely high from 50 to 70 dm3/mg and, simultaneously, remarkably higher as compared to K 1 constants determined for sorbet 2 and 3. In the description of experimental data of the desorption process use was also made of the double Langmuir s model, yet values of K 2 and b 2 constants were very low for all dyes and adsorbents examined. This suggested that the second term of the double equation could be omitted as insignificantly small. Experimental results of the desorption of the dyes analyzed have been successfully described with the single Langmuir s mode. The obtained values of K and b constants were presented in Table 3. Table 3. Constants in Langmuir desorption. Type of sorbent Constants in Lamgmuir equation K 1 b 1 ϕ 2 Reactive Black 5 chitin 25.00 130 0.005 chitosan 0.08 180 0.020 chitosan beads 0.02 280 0.006 Reactive Black 8 chitin 50.00 205 0.003 chitosan 0.03 310 0.016 chitosan beads 0.06 340 0.009 An analysis of the values obtained enables concluding that, contrary to the adsorption process, no significant difference was observed in the quantity of the dye RB5 desorbed along with an increase in the degree of deacetylation sorbent 1 as well as sorbent 2. In addition, 62 Polish Chitin Society, Monograph XII, 2007
Adsorption and desorption efficiency of black 8 and black 5 onto chitin and chitosan the investigations demonstrated that the efficiency of dye RB8 desorption from chitosan in the form of both flakes (sorbent 2) and beads (sorbent 3) was comparable. In turn, when comparing the quantity of the desorbed dye to that of the adsorbed dye it can be concluded that in the case of chitin (sorbent 1) the efficiency of desorption was the highest. The effect of the chemical structure of the dye on the quantity of desorbed dye can be observed. RB8 a dye with the chlorotriazine active group demonstrated the highest desorption efficiency, i.e. 80%. In the case of RB 5 a dye with the chlorovinyl active group the quantity of desorbed dye was lower and accounted for 50% of the quantity of the adsorbed dye. The other analyzed adsorbents 2 and 3 were characterized by a considerably lower efficiency of desorption of RB5. In the case of RB 8 dye a high capacity for releasing a dye bound on adsorbents 2 and 3, as compared with adsorbent 1, was observed. A low adsorption of a dye may suggest that the dye was bound with the adsorbent in the process of chemisorption. The shape of an adsorption isotherm as well as high values of K 1 constants in the Langmuir s equation determined for sorbent 1 chitin were indicative of the chemical adsorption. This was not, however, confirmed by the results of desorption. In the case of chitin, irrespective of the type of dye, the efficiency of the desorption process was the highest. 4. Conclusions 1. Investigations demonstrated a correlation between the quantity of the absorber and desorbed dye and the type of dye. 2. An increase in the adsorption capacity of Black 5 onto chitosan was not accompanied by analogous increase in the quantity of desorbed dye. The results obtained point to a definitely lower efficiency of desorption as compared to the adsorption process.. 3. In the case of Black 8, an increase in the quantity of dye absorbed onto the sorbent affected the quantity of the desorbed dye. 5. References 1. Churchley J. H., Greaves A. J., Hutchings M. G., James A. E., Phillips D. A. S.; The development of a laboratory method for quantifying the bioelimination of anionic, water soluble dyes by a biomass. Wat. Res. 2000,.34, 1673. 2. Al.-Degs Y., Khraisheh A. M., Allen S. J., Ahmad M. N.; Effect of carbon surface chemistry on the removal of reactive dyes from textile effluent. Wat. Res. 2000, 34(3), 927. 3. Šafarik I.; Removal of organic polycyclic compounds from water solutions with a magnetic chitosan based sorbent bearing copper phthalocyanine dye. Water Res 1995; 29; 101. 4. Filipkowska U., Klimiuk E., Siedlecka E., Grabowski S.; Adsorption of reactive dyes by modified chitin from aqueous solutions. Polish J. Environ. Studies 2002, 11, 315. 5. Filipkowska U.; Efficiency of reactive dyes adsorption onto chitin and chitosan beads. Progress on Chemistry and application of chitin and its derivatives. 2006,.XI: 53-60. 6. Chemia fizyczna. Praca zbiorowa. PWN 1980. 7. 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. 8. Hughes M. N., Poole R. K.; Metals and micro-organisms. Ed.: Chapman, Hall. London. 1989. 9. 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. 10. Chiou M. S., Ho P-Y., Li H-Y.; Adsorption of anionic dyes in acid solutions using chemically cross- linked chitosan beads. Dyes Pigments 2004, 60, 69. Polish Chitin Society, Monograph XII, 2007 63