Preparation and Dye Adsorption of Low-cost Polyaniline-tea Saponin Nanocomposites

ZOU Zhijin, LI Yunlong, MA Zhengwei, JIN Yanqiao, LÜ Qiufeng

(Key Laboratory of Advanced Materials Technology (Fuzhou University), Fujian Province University, College of Materials Science an d Engineering, Fuzhou University, Fuzhou 350116, China)

Abstract: Four polyaniline-tea saponin (PTS) nanocomposites were prepared by an in-situ polymerization with tea saponin (TS) as a biosurfactant, and they were used to remove organic dyes from aqueous solution. The PTS nanocomposites were characterized by using field emission scanning electron microscopy, the Fourier transform infrared spectroscopy, the Ultraviolet-visible spectroscopy, and the thermogravimetric analysis. The adsorption performances of the PTS nanocomposites for organic dyes were studied by a static adsorption method. The experimental results reveal that adsorption capacities of the PTS nanocomposites are higher than that of pure polyaniline. Especially, the PTS nanocomposites exhibit excellent adsorption performances for anionic dyes because of the electrostatic interaction between the positively charged nitrogen atoms on the PTS chains and the negatively charged sulfonate ions in the anionic dyes. According to the adsorption kinetics and thermodynamics results, the adsorption processes of PTS20 for CR and AB74 follow well with the pseudo second-order and Langmuir isotherm models. It is indicated that TS should be very useful in the preparation of PTS nanocomposite and in removal of toxic dyes from waste water.

Key words: polyaniline; tea saponin; nanocomposite; adsorption

1 Introduction

In recent years, dye wastewater pollution is worsening, and the dye treatment issues have become the focus of attention. Around 100,000 companies around the world emit 70,000 tons of dye waste every year, which poses a huge threat to human water safety.In general, dye wastewater contains complex materials with different chemical properties, which are available in a variety of colors[1,2]. Therefore, how to deal with dye waste is one of the intractable problems of human society.

At present, many processing methods have been developed and applied in wastewater pollution.Chemical method is the use of chemical reactions to separate or decompose pollutants in wastewater,including precipitation, coagulation, flocculation,electrolysis, chemical oxidation, radiation, and so on[3-5]. Biological treatment is the use of microbial flocculation, accumulation, enrichment, metabolism or other functions to converted organic pollutants and inorganic microbial nutrients of wastewater into stable and harmless substances[6,7]. Physical-chemical method is the general term for various methods of using physicochemical to treat wastewater, including extraction, membrane separation, reverse osmosis,ultrafiltration and adsorption[8-10].

Especially, adsorption is an important physicalchemical method for treatment wastewater, and it has a significant advantage for treating low concentration wastewater[10]. However, to prepare and seek inexpensive and high-performance adsorbents is the key to development of new adsorption method. Polyaniline has unique anion doping and dedoping function, and its molecular chains contain a large amount of amino and imino groups that make it exist a strong force to anionic dyes[11]. This shows that polyaniline can interact with organic matter. Since polyaniline has more advantages of easy raw materials, good environmental stability, good chemical stability, compound simply,unique doping phenomenon, and potential workability,it becomes one of the fastest growing polymer in present research progress, and it is widely used in adsorb industrial dyes[12,13]. In order to obtain efficient and cheap adsorbents, polyaniline-based adsorbents are increasingly valued.

Tea saponin (TS) is a good reproducible natural surfactant with a large number of adsorption active sites and excellent performance, and it has wide range applications[14]. TS can be used to produce detergents,emulsifiers, pesticide chemicals, oil flotation agent,textile auxiliaries, mining lubricants, aerated concrete foam stabilizer, and highway antifreeze[14-17]. Therefore,in this study, TS was selected as a support material and a dispersing agent and biosurfactant of polyaniline, and an in-situ polymerization method was used to prepare polyaniline-tea saponin (PTS) nanocomposites. A static adsorption method was used to investigate the adsorption performances of the PTS nanocomposites for organic dyes by varying the TS feed content in the PTS composites, initial pH value, PTS concentration,adsorption time, initial dyes concentration, and adsorption temperature. Finally, the adsorption kinetics and adsorption thermodynamics were studied based on experimental data.

2 Experimental

2.1 Materials

Aniline monomers (ANI) (Sinopharm Chemical Reagent Co., Ltd) were distilled twice before use.Ammonium Persulfate (APS) is purchased from Tianjin Fuchen Chemical Reagents Factory, tea saponin (TS)was obtained from Anhui Yingshanhong Biotechnology Co., Ltd. Hydrochloric acid (HCl), Congo red(CR), and acid blue 74 (AB74) were obtained from Sinopharm Chemical Reagent Co., Ltd.

2.2 Preparation of PTS nanocomposites

Polyaniline-tea saponin nanocomposites were prepared via an in-situ polymerization. The PTS5,PTS10, PTS15, PTS20, and PTS30 nanocomposites were obtained, while the feed content of TS was 5wt%,10wt%, 15wt%, 20wt%, and 30wt%, respectively.The preparetion process of PTS is described in Fig.S1.A representative polymerization for PTS20 is shown as follows: 0.466 g TS powder was first added in 70 mL HCl (1 mol·L-1) solution and dissolved thoroughly by stirring. Then, 1.83 mL aniline was added into the above solution and stirred until it become a homogeneous yellow-brown solution in 25 ℃ water bath. In addition, 4.564 g APS was dissolved totally in 30 mL HCl (1 mol·L-1) solution, and then added it into the above aniline-TS yellow-brown solution. Thirdly,the well-mixed solution was placed in a constant temperature at 25 ℃ water bath for 24 h. After the reaction, the above dark-green solution was suction filtered and washed repeatedly with deionized water until the filtrate became colorless and transparent.Finally, the composite was detached from filter paper and placed in drying oven at 60 ℃ for 48 h. Pure polyaniline (PANI) was obtained with the absence of TS under the similar preparation condition.

2.3 Adsorption of dyes on nanocomposite

For static adsorption tests, the adsorbent and dye solution were put in a conical flask, and shocked by ultrasound for 5 min, and then the adsorption solution in a water bath maintained a certain time. After the adsorption, the solution was filtered and the equilibrium dye concentration was obtained by using a Varian Cary50 UV-Vis spectrophotometer. Then the adsorption capacity and adsorption rate of the composite adsorbed dye were calculated according to the Ref.[10]. The structures of CR and AB74 used in the experiment are shown in Fig.S2 and the UV-Vis spectroscopy wavelengths of CR and AB74 are 497 and 610 nm[10],respectively.

Fig. S1 Preparation process of the PTS nanocomposite

Fig.S2 Molecular structures of (a) CR and (b) AB74

2.4 Characterization

Morphology of PANI and PTS were observed on a field emission scanning electron (SEM) microscope(Carl Zeiss SUPRA 55). Fourier transform infrared spectrometer (FT-IR 5700) was used for infrared testing. A Varian Cary50 UV-Vis spectrophotometer was used for UV-Vis spectra testing, and its scan range was 200-800 nm. TGA curves of TS, PANI, and the PTS nanocomposites were tested using a thermal analyzer (SDT-Q 600) at nitrogen atmosphere.

3 Results and discussion

3.1 Morphology and structure

The SEM images of PTS nanocomposites are shown in Fig.1. It can be seen that both PANI (Fig.S3)and PTS are formed amorphous nanorods, and the length of these nanorods are between 200 and 300 nm. These nanorods are intertwined to form many specific pore structures, and these pore structures not only increases specific surface area of PANI and PTS nanocomposites, but also are beneficial to expose more adsorption sites[12]. Fig.S3 shows that the surface of PANI nanorods is relatively smooth. Compared to PANI, the surface of PTS5 nanorods becomes relatively rough. When the feed content of TS is 10wt%, the surface of PTS10 nanorods becomes rougher. As the feed content of TS is 20wt%, the surface of PTS20 is rougher than PTS10. However, when the TS feed content is up to 30wt%, the surface roughness of PTS30 is smoother than PTS20. Therefore, the addition of TS biosurfactant can significantly affect the morphology of the PTS composites, indicating that TS is successfully supported on PANI.

Fig.S3 FE-SEM image

As seen from Fig.2(a), the FT-IR spectra of PTS nanocomposites have similar structures to that of PANI, but the positions of the peaks are diverse. The two strong peaks at 1 570 cm-1and 1 490 cm-1are characteristic peaks of quinoid structure and benzene structure, respectively[12]. The peak of 1 570 cm-1is the C=C stretching vibration of quinoid structure of PANI chains, and the peak of 1 490 cm-1is the C=C stretching vibration of benzene ring of polyaniline chains. The peak at around 1 300 cm-1is the C-N stretching vibration. For the PTS composites, duing to the influence of carboxyl and hydroxyl groups in TS,the intensity of the 1 570 cm-1peak becomes strong,and have a slight blue shift, indicating an increase of the quinoid structure. The intensity of the characteristic peak of TS at 3 480 cm-1is low[18], whereas for the PTS composites, the intensity of this peak enhanced. The peak of 1 130 cm-1is the characteristic peak of the C-H in-plane bending vibration of benzene. The peak at 820 cm-1corresponds to 1,4-substituted benzene ring C-H in-plane bending vibration characteristics. The peak of 1 060 cm-1is the vibration of C-O, which belongs to the methoxy of TS[18].

Fig.2 (a) FTIR spectra of TS, PANI, and PTS; (b) UV-Vis spectra of TS, PANI, and PTS; (c) TGA curves of TS, PANI, and PTS20

The UV-Visible spectra of PANI and PTS nanocomposites are similar (Fig.2(b)), and there are two peaks at 340 and 625 nm. It shows that the introduction of TS into PANI does not destroy the original structure of PANI, and TS only plays the role of biosurfactant. For PANI, the peak at 305 - 325 nm is produced through π-π*transition[13]on the benzene ring, whereas the peaks of PTS are moved to 340 nm duing to the introduction of TS. In this study, Eigen PANI has a peak at 625 nm, and this peak is determined byn-π*transitions[13]between high occupied benzenering molecular orbital and low occupied quinoid ring molecular orbital. Compared with PANI, the peaks of PTS have a blue shift from eigenstate 625 to 620 nm.The blue shift in the peaks of PTS might be due to the electronic interaction exists between the carboxyl groups on TS and the protonated PANI chains. In addition, the hydrogen bonds between TS and PANI can also cause blue shift. The above results indicate that PANI chains and PTS chains all exist quinone structures.

Fig.2(c) shows the TGA curves of PANI, PTS20,and TS. It shows that the TGA curve of PTS20 is substantially above the TGA curves of PANI and TS. Therefore, compared with PANI and TS, the thermal stability of PTS20 enhances. It may be due to the hydrogen bonds between the molecular chains of PANI and TS molecules. Ahead of 100℃, the thermogravimetric loss is mainly caused by the evaporation of water in the samples[19]. For PTS20, it starts to lose weight at 180 ℃ and begins to decompose, and it has a maximum weight loss rate at 400 ℃. When the decomposition temperature reached at 1 000 ℃, the residual carbon of PTS20 (38%) is higher than that of PANI (32%) because of the strong interactions between PANI and TS.

3.2 Adsorption performance of PTS for organic dyes

3.2.1 Optimization of different composites

In order to explore the effect of the TS feed content in PTS on the adsorption for organic dyes,PANI, PTS5, PTS10, PTS15, PTS20, and PTS30 were used to select an optimal adsorbent with CR solution as a research target. The results in Table S1 indicate that the TS feed content in PTS can siginificantly affect the adsorption performance of PTS for the CR dye.Especially, the adsorption capacity and adsorption rate of PTS20 are the most prominent compared to those of other PTS samples. The adsorption capacity of PTS20 is 24.6 mg·g-1, and adsorption rate of PTS20 is 98.5%.Therefore, the introduction of carboxyl and hydroxyl groups on TS biosurfactant into the PANI chains can effectively enhance the adsorption performance of the PTS20 composite for CR molecules. It may be attributed to the optimal combination of imino, and carboxyl and hydroxyl groups on the PTS20 composite chains, which is beneficial to their efficient interaction of CR molecules.

Table S1 Adsorption performances of PANI and the PTS composites for CR

3.2.2 Selective adsorption for different dyes

Six dyes, that is, methylene blue, malachite green,CR, AB74, amaranth, and orange, were selected to explore the selective adsorption of PTS20. Wherein methylene blue and malachite green are cationic dyes,and the other four dyes are anionic dyes. Table S2 reveals that PTS20 has good adsorption for anionic dyes, and adsorption rate are all more than 95%. PTS20 has the best effect of adsorption for AB74 and CR, and the adsorption rates are 100% and 98.5%, respectively.But the adsorption rate of PTS20 for the cationic dye methylene blue is less than 85%, and malachite green is only 29.2%. These results indicate that the adsorption performance of PTS20 is selective for the anionic dyes.This is mainly because there are electrical attractions between the positive charges on PTS20 chians and negative charges on the AB74, CR, orange, and methyl orange anionic dye molecules[20]. In particular, the addition of TS in PTS makes the adsorbent contain a large number of hydroxyl groups, which can form hydrogen bonds with the amine groups of CR and amine sub-groups of AB74. Therefore, in order to achieve efficient adsorption, AB74 solution and CR solution were used as adsorbates in the following researches.

Table S2 Adsorption performance of PTS20 for different dyes

3.2.3 Effect of initial pH values

Fig.3 shows the effect of initial pH value of the dyes solution on the PTS20 adsorption for AB74 and CR. When the initial pH values are less than 6.2, the adsorption capacity and adsorption rate show a rising trend with the increase of pH value. When the initial pH values are higher than 6.2, the adsorption capacity and adsorption rate decrease. This is because PTS20 is an acidic adsorbent, the adsorption is difficult when the initial pH value of AB74 solution is less than 6.2, and therefore, with the increase of pH value, the adsorption capacity and adsorption rate of PTS20 adsorption AB74 increase. Furthermore, AB74 contains sulfonic acid groups, and these functional groups can neutralize a small amount of protons, so when the pH value is 6.2, adsorption capacity of PTS20 on AB74 reaches the greatest. When the pH value increases continuously,adsorption capacity and adsorption rate begin to decline[21].

Fig.3 Effects of initial pH values on (a) AB74 and (b) CR adsorption; Effects of different initial concentrations of PTS20 on (c) CR and (d)AB74 adsorption

From Fig.3(b), it can be observed that when the initial pH value is less than 6.2, with the increase of pH value, the adsorption capacity and adsorption rate show downward trend. When the initial pH value is greater than 6.2, adsorption capacity and adsorption rate decline rapidly with the increase of pH value.The similar phenomenon is also found in the Ref.[22],so the initial pH value in the following adsorption experiments is fixed at 6.2.

Comparing Figs.3(a) and 3(b), it is found that the adsorption capacity of PTS20 on CR changed dramatically when the initial pH value exceeds 6.2.So, the initial pH value has an important influence on PTS20 for adsorbing CR. However, the adsorption capacity of PTS20 for AB74 changes very gently, it proves that the initial pH value has a small impact on the adsorption of AB74. This might be due to the different structure and functional groups of the CR molecule compared to the AB74 molecule, which makes it different in sensitivity to pH values.

3.2.4 Effect of initial concentration of PTS20

Figs.3(c) and 3(d) illustrate the CR and AB74 adsorption uptake of at the different initial concentration from 0.4 to 2.0 g·L-1at dyes concentration of 50 mg·L-1, adsorption temperature of 30 ℃ for 24 h. With increasing the initial concentration of PTS20, the adsorption capacity decreases, while the adsorption rate increases. Owing to the availability of numerous uncovered adsorption sites on the PTS20 surface, the adsorption rate increasing will not stop untill the process of adsorption is finished. Fig.3(c)shows that when the initial concentration of PTS20 is 2.0 g·L-1, the adsorption rate for CR is close to 100%.In Fig.3(d), when the initial concentration of PTS20 is 1.2 g·L-1, the adsorption rate of AB74 reaches 100%,indicating that PTS20 displays higher adsorption for AB74 dye than CR.

3.2.5 Effect of adsorption time and adsorption kinetics

In order to explore the influences of adsorption time on dyes adsorption of PTS20, adsorption time arranged from 0.5 to 24 h (Fig.4). With increasing the adsorption time, the adsorption capacity and adsorption rate of CR show a rapidly increasing trend (Fig.4(a)).After 6 h, this upward trend has slowed down. When the adsorption time is less than 6 h, the surface active sites of PTS20 are not fully occupied, so the adsorption process is fast. When the adsorption time is more than 6 h, the adsorption capacity and adsorption rate increase slowly, which shows that the adsorption sites have nearly been occupied. Finally, the adsorption of PTS20 for CR reached equilibrium in 24 h. For the AB74 adsorption, the adsorption capacity and adsorption rate of CR show a steady increasing trend (Fig.4(b)), and reach their equilibrium values at 24 h.

Fig.4 Effects of adsorption time on (a) CR and (b) AB74 adsorption

Pseudo-first-order kinetics assumes that the adsorption process is controlled by the diffusion step,and it is expressed as equation (1)[10]:

where,Qe(mg·g-1) is the adsorption capacity per unit mass of adsorbent at adsorption equilibrium;Qt(mg·g-1) is the adsorption capacity at adsorption timet;k1(h-1) is the adsorption rate constant.

Linear analysis of ln (Qe-Qt) -tis shown in Fig.S4.According to the equation (1), calculatedQeis from the intercept of the line,k1is derived from the slope.Pseudo-first order equation parametersQe,k1and correlation coefficientR2are shown in Table S3.

Table S3 Kinetic model parameters of CR and AB74 adsorption on PTS20

Fig.S4 Pseudo-first-order adsorption kinetics models of PTS20 for (a) CR and (b) AB74 adsorption

Pseudo-second-order adsorption kinetics assumes that the adsorption process may be the chemical adsorption, which is expressed as equation (2)[10]:

where,k2(g·(mg·h)-1) is the pseudo-second-order kinetic rate constant.

To analyze the relationship oft/Qt-tby fitting,a linear is shown in Fig.S5. According to the equation(2),Qewas calculated from the slope;k2was calculated by the intercept; the results and the value of the correlation coefficientR2are shown in Table S3. As can be seen that the correlation coefficients obtained from pseudo-second-order kinetic model of PTS20 adsorbents toward CR and AB74 are lower than those of obtained from pseudo-first-order kinetic model.Moreover, theQevalues of CR and AB74 adsorption calculated by the pseudo-second order model are closed to the experimental values. These results prove that the pseudo-second-order kinetics model is suitable for CR and AB74 adsorption of PTS20, suggesting that the main adsorption processes are chemisorption.There must be some other factors, which influence the adsorption process significantly. The main reason may be that the adsorption occurs mainly on the surface of the adsorbent and a small amount of the dye molecules diffuses into the interior of adsorbent.

Fig.S5 Pseudo-second-order adsorption kinetics models of PTS20 for (a) CR and (b) AB74 adsorption

3.2.6 Effect of initial dyes concentration and adsorption isotherm

Fig.5 shows the results achieved at the initial CR and dyes concentration ranged from 5 to 600 mg·L-1.When the initial CR concentration is below 50 mg·L-1and the initial AB74 concentration is less than 100 mg·L-1, the adsorption rate decreases but the adsorption capacity increases dramatically with the increase of the initial concentration of CR and AB74. When the initial CR and AB74 concentrations exceed 50 mg·L-1and 100 mg·L-1, respectively, the adsorption capacities increase slowly, and the declining trend of adsorption rates are obvious.

Fig.5 Effects of the initial concentrations of (c) CR and (d) AB74 on PTS20 adsorption

With the initial concentration increasing, the surface adsorption sites of PTS20 reach maximum,which results in adsorption rate decreasing obviously[23]. When the initial CR and AB74 concentrations reach 600 mg·L-1, the maximum adsorption capacity is 80.0 mg·L-1and 219.1 mg·L-1,whereas the adsorption rate is 26.7% and 57.9%,respectively. Therefore, an initial CR and AB74 concentrations were fixed at 50 mg·L-1to achieve a higher adsorption rate in other experiments.

In order to analyze the adsorption type of CR and AB74 on PTS20, two isotherm models are used to process the data. Langmuir isotherm model assumes a uniform surface of the adsorbent, and there is no interaction between the adsorbent and adsorbed materials. There will be the maximum adsorption capacity theoretically by using Langmuir isotherm model. Langmuir equation expression is shown as follows[10]:

where,Qmis the maximum adsorption capacity of per unit adsorbent (mg·L-1);Ceis the equilibrium concentration in solution (mg·L-1);Qeis the equilibrium adsorption capacity (mg·g-1);kLis the Langmuir constant (L·mg-1), represents the size of the binding force between adsorbent and dyes.

The Langmuir linear regression curve is shown in Fig.S6, and the values of the calculation results and the correlation coefficientR2are shown in Table S4.

Fig.S6 Langmuir models of (a) CR and (b) AB74 adsorption on PTS20

Freundlich equation is an empirical formula that used to describe an uneven surface adsorption, and Freundlich equation expression is shown as follows[10]:

where,kF(g·mg-1(L·mg-1)n-1) and 1/nis the Freundlich constant;Ceis the equilibrium concentration of dye adsorption (mg·L-1),Qeis the equilibrium adsorption capacity (mg·g-1).

The Freundlich linear curves are shown in Fig.S7,and the parameters are shown in Table S4. The 1/nrelated to the unevenness of the surface of the adsorbent, when 0＜1/n＜1, adsorption reaction gets easy; when 1/n=1, the adsorption is uniform and there is no interaction between the adsorbed substances;when 1/n＞1, adsorption is more difficult to carry out.kFis the coefficient associated with the adsorption capacity.

Fig.S7 Freundlich models of (a) CR and (b) AB74 adsorption on PTS20

Table S4 Isotherm model parameters of CR and AB74 adsorption on PTS20

As confirmed in Table S4, the Langmuir isotherms is favorable for the CR and AB74 adsorption on PTS20,and the correlation coefficients are higher than 0.96.The maximum adsorption capacities calculated from the model are close to the experimental values. Clearly,these results suggest that the adsorption processes of CR and AB74 on PTS20 could be well fitted by the Langmuir isotherm model. It proves that the interaction between PTS20 adsorbent and dyes is monolayer adsorption[24], and there is no interaction between the adsorbent and adsorbed materials. In addition, as Table S5 shows, PTS20 has better adsorption performance on CR than other reported adsorbents. As for AB74,PTS20 shows better adsorption performance than that of the polypyrrole-chitosan-lignosulfonate[10].

Table S5 Maximum adsorption capacity (Qm) values for the removal of CR on various adsorbents

3.2.7 Effect of adsorption temperature

The adsorption performance of PTS20 for CR and AB74 is explored at adsorption temperature from 25 to 50 ℃ (Fig.6). With increasing the adsorption temperature from 25 to 40 ℃, the equilibrium adsorption capacities and adsorption rates of PTS20 adsorption for CR and AB74 dyes increase, and they reach the maximum values at 40 ℃. This indicates that the adsorption processes of PTS20 for CR and AB74 are endothermic. Besides, the effect of temperature on PTS20 adsorption for CR is significant, whereas it has a small impact on PTS 20 adsorption for AB74. This may be due to the structural difference between AB74 and CR molecules, which makes their interaction with PTS20 different.

Fig.6 Effects of adsorption temperatures on (a) CR and (b) AB74 adsorption

3.2.8 Adsorption mechanism

The adsorption mechanism of PTS20 for CR and AB74 adsorption is related to the chemical structure of PTS20, the characteristics of dye molecules and the solution environment. As shown in Fig.7, the PTS20 nanocomposite has a large amount of active functional imino groups from polyaniline chains[25]and carboxyl and the hydroxyl groups from TS[26]. That is to say,there are more active sites on the PTS20 nanocomposite surfaces, which could increase the contact areas with the dye molecules. Moreover, the imino groups PTS20 will be protonated and become positively charged groups in the acidic adsorption solution[10]. Meanwhile,the CR and AB74 dye molecules not only carry negatively charged sulfonic acid groups, but also carry positively charged amino or imino groups, respectively,in the acidic adsorption solution. During the adsorption process, the functional groups between PTS20 and dye molecules can form hydrogen bonds[27]and electrostatic interaction[28], which could effectively increase the adsorption rate and the adsorption capacity. This is why PTS20 exhibits selective adsorption for the anionic CR and AB74 dyes.

Fig.7 Adsorption mechanism of (a) CR and (b) AB74 adsorption on PTS20

In addition, the adsorption performance of PTS for AB74 is better than that of CR. Main reasons are as follows: on the one hand, the molecular size of AB74 is smaller than CR (Fig.S2), which makes the AB74 molecules more easily to shuttle in the pore structure of PTS20, and more easily adsorbed on the surface of PTS20. On the other hand, AB74 has a unique molecular structure, the imino and sulfonic acid groups are evenly distributed on the AB74 surface,which makes the AB74 molecules easier to interact closely with PTS20. Therefore, PTS20 exhibit a higher adsorption performance for AB74.

4 Conclusions

A serial of PTS nanocomposites were successfully prepared from aniline monomers in the presence of TS. The results reveal that the introduction of TS biosurfactant into the PANI chains plays a great role on the structure, morphology and selective dyes adsorption performance of the PTS nanocomposites. The addition of TS can effectively enhance the adsorption performance of the PTS composite for dye molecules.In particular, the PTS nanocomposites have a selective adsorption on anionic CR and AB74 dyes. PTS20 has the highest adsorption performance for the CR and AB74 dyes. The results of the kinetic and isothermal adsorption model of PTS20 show that the adsorption processes of PTS20 for CR and AB74 are in accordance with the pseudo-second order kinetic and Langmuir isotherm models. This indicates that the adsorption processes of CR and AB74 dyes on the PTS20 nanocomposite are mainly controlled by the chemical interaction between dye molecules and the binding sites of PTS20. Therefore, the PTS nanocomposites can be used as efficient and practical adsorbents for the removal of CR and AB74 dyes from wastewater.