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Removal of transition metal ions from aqueous solution using dialdehyde phenylhydrazine starch as adsorbent Rou Wang, Jun-Tao Liu, Chun-Yang Li and Rong Li
ABSTRACT Dialdehyde phenylhydrazine starch (DASPH) was synthesized by reacting dialdehyde starch (DAS) with phenylhydrazine (PH) and it was characterized by Brunauer–Emmett–Teller (BET), scanning electron microscope, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques. FT-IR of DASPH revealed the incorporation of the Schiff Base group (C ¼ N) group and the disappearance of the C ¼ O (carbonyl) group. The adsorption behaviors of transition metal ions (Cd2þ, Zn2þ, Pb2þ and Cu2þ) were investigated as a function of pH and adsorption time. The results indicated that pH 5.0 and 120 min were the optimal conditions. Experimental results revealed that
Rou Wang Jun-Tao Liu Chun-Yang Li Rong Li (corresponding author) The Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China E-mail: [email protected]
the maximum adsorption capacity of DASPH for the four transition metal ions was as follows: Cd2þ (4.9 mmol/g) > Zn2þ (3.3 mmol/g) >Pb2þ (1.7 mmol/g) >Cu2þ (0.83 mmol/g). In addition, the regeneration method of DASPH was also studied. Key words
| adsorption, dialdehyde phenylhydrazine starch, dialdehyde starch, transition metal ions
INTRODUCTION In recent years, with the rapid development of modern industry, large numbers of transition metal ions were discharged into water from plating plants, metal finishing, dyeing factories and several other sources. Their acute toxicity, non-biodegradable nature and build-up of high concentrations in water bodies all over the world raise increasing concern (Rivaro et al. ). Moreover, transition metal ions are absorbed by animals and plants, and enter the human body through the food chain and cause health problems. Thus, effective measures for the removal of transition metal ions from water is urgently required. Several techniques have been proposed for the removal of transition metal ions from industrial effluents such as chemical precipitation (Shih et al. ), ion-exchange methods (Budak ), electro-deposition and adsorption (Safa et al. ; Graillot et al. ; Rajkumar et al. ). Among these techniques, adsorption is generally preferred for the removal of transition metal ions due to its high efficiency, easy handling and the availability of different adsorbents (Gupta et al. ). It is well known that adsorption on activated carbon is a commonly used technology for removing transition ions, but the higher cost of carbon limits its large-scale usage. Therefore, it is desirable to develop lower cost, more efficient and reusable adsorbent material. doi: 10.2166/wst.2013.571
Numerous adsorbent materials such as zeolites (Zhang et al. ), activated carbons (El Zayat & Smith ) and silica beads (Dang Viet et al. ) have been successfully utilized for wastewater remediation. Recently, many approaches have been studied for developing cheaper and more effective adsorbents containing natural polymers (Nurchi et al. ; Hu & Zhu ). As adsorbents, biopolymers attract more and more attention from chemists because of their economical and effective characteristics (Gupta et al. ). Among biopolymers, polysaccharides (Gupta et al. ; Gupta & Rastogi ) deserve particular attention. As a natural polysaccharide, starch is biodegradable, abundant and environmentally friendly. Different approaches are currently used. At present, a commonly used method is oxidation of starch to dialdehyde starch in the presence of sodium periodate. Earlier works report that dialdehyde starch with o-phenylenediamine (Zhao et al. ), m-phenylenediamine (Liu et al. ) and 5-aminophenanthroline (Liu et al. ) could form stable complexes with ions. However, their adsorption capacities for ions were relatively poor. Up to now, few studies have focused on the difference in adsorption ability between ions. The main objective of this work was to evaluate the adsorption of transition metal ions on dialdehyde phenylhydrazine starch (DASPH), which was obtained from the
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reaction of dialdehyde starch and inexpensive phenylhydrazine. Experimental data concerning the characterization of material as well as adsorption were presented. Moreover, the adsorbents can be reused.
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respectively. C1 and C2 (mol/L) represent the concentrations of H2SO4 and NaOH, and 161 is the average molecular weight of the repeated unit in dialdehyde starch. The Da of the adsorbent was 76%. Preparation of DASPH
EXPERIMENT Materials and apparatus W
Potato starch (food-grade) was dried at 105 C before using. Sodium periodate (NaIO4), sulphuric acid (H2SO4) and 98% phenylhydrazine were purchased from Sichuan Chemical Factory (Sichuan AR China). All other commercial chemicals were of analytic reagent grade and used without further purification. Cadmium nitrate tetrahydrate (Cd(NO3)2·4H2O), zinc nitrate hexahydrate (Zn(NO3)2·6H2O), lead nitrate (Pb(NO3)2) and cupric nitrate trihydrate (Cu(NO3)2·3H2O) were used as sources for Cd2þ, Zn2þ, Pb2þ and Cu2þ, respectively. Elemental analysis was performed using a PerkinElmer 2400 CHN analyzer. The surface area of DASPH was measured by the N2 adsorption–desorption technique using a Micromeritics Chemisorb 2750 surface area analyzer. The size and morphology of the materials were observed by a JEOC JSM6701F scanning electron microscope (SEM) at accelerating voltages of 5.0 KV. Infrared spectra were obtained by the KBr pellet technique and were recorded on NEXUS670. X-ray diffraction (XRD) was confirmed by X-ray Diffractometer (D/ Max-2400). The pH value of solutions was determined using a PHS-3C pH meter. Atomic absorption spectrometry was carried out using an Analyst 240 instrument (Varian American).
Preparation of dialdehyde starch 4.0 g sodium periodate used as oxidant was added into 4.0 g potato starch suspension to prepare DAS. The mixture was stirred slowly at 30 C in the dark for 4 h. At the end of the reaction time, the product was washed several times with deionized water and one time with ethanol. The aldehyde group content was determined by the rapid quantitative alkali consumption method (Hofreiter et al. ). The percentage of dialdehyde units is given as the equation: W
Da% ¼
(V1 C1 2V2 C2 ) × 100% W=161
(1)
V1, V2 and W represent the total volumes (L) of H2SO4, NaOH and the dry weight (g) of the oxidized starch,
4.0 g DAS was suspended in 50 mL deionized water in a 100 mL two-necked flask, which was equipped with an electromagnetic stirrer and thermostat oil bath. Afterwards, 3.57 mL phenylhydrazine was slowly put into the flask. The pH of the reaction system was adjusted to 5.0 with acetic acid. The reaction was stirred for 4 hours at 60 C under nitrogen protection. The slurry was separated from the solution by filtration, then extensively rinsed with deionized water and rinsed once with ethanol, and then dried at 50 C to a constant weight. The preparation of DASPH was shown schematically in Figure 1(a). W
W
Adsorption properties of DASPH for transition metal ions The actual application of DASPH was demonstrated through adsorption of Cd2þ, Zn2þ, Pb2þ and Cu2þ. The stock solutions of metal salts (100 mmol/L) were prepared by dissolving Cd(NO3)2·4H2O, Zn(NO3)2·6H2O, Pb(NO3)2 and Cu(NO3)2·3H2O in deionized water. The synthetic wastewater solutions (20 mmol/L) were then obtained by dilution of the stock solutions of each transition metal ion by using deionized water. The coexistent metal ion solution was prepared as follows: accurately measured 12.5 mL metal ion solutions from the above-mentioned solution (Cd2þ, Zn2þ, Pb2þ and Cu2þ, respectively), were poured into 100 mL Erlenmeyer flasks. The real wastewater was derived from the Lan Zhou Section of the Yellow River. Batch experiments were carried out in 100 mL Erlenmeyer flasks using 50 mL of metal ion solutions at 20 C to determine the effects of pH on the adsorption of metal ions. The pH value of the solution was adjusted to a predetermined value using 0.1 mol/L HNO3 or NaOH and 100 mg of DASPH was added to the solution. The resulting suspension was stirred for a specified time with a magnetic stirrer at 150 rpm while keeping the pH value constant through measuring with a pH meter. At the end of each experiment, the solutions were separated by filtration. The filtrate was then analyzed for residual metal ions by atomic absorption spectrometry. The standard deviation obtained is 0.00415 W
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Figure 1
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(A) Reagents and conditions: (a) NaIO4 and (b) phenylhydrazine; (B) SEM images; (C) FT-IR spectra; and (D) XRD pattern of potato starch, DAS and DASPH.
and within the error limits of ±1.54%. Each set of resulting data was replicated three times in all experiments. In the adsorption-regeneration cycles, no replicates were done and each bar reflects a single experiment. The adsorption capacity of DASPH for different transition metal ions was measured by adsorption capacity Q (mmol/g). Q is the adsorbed transition metal ions quantity per gram of adsorbent at equilibrium time.
RESULTS AND DISCUSSION Characterization of DAS and DASPH BET The Brunauer–Emmett–Teller (BET) technique was applied to analyze the adsorbent. The surface area, pore volume and
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pore size of DASPH were 31.2 m2/g, 0.00196 cm3/g, and 17.5 nm, respectively. Ding et al. reported 29.0 m2/g of surface area in studying the adsorption capacity of dialdehyde starch with 8-aminoquinoline for Zn2þ (Ding et al. ). Liu et al. achieved 30.5 m2/g in studying the adsorption behavior of Zn2þ on dialdehyde m-phenylenediamine starch (Liu et al. ). On comparing these data, it may be concluded that the DASPH has a large surface area and excellent adsorbtion performance.
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potato starch, the crystallinity of DAS decreased. It is supposed that the aggregation phase of the original starch was changed from its semicrystalline state to an amorphous aggregation state during the periodate oxidative and the chain breakage reactions (Ding et al. ). However, after DAS was grafted to phenylhydrazine, the peak became weaker than DAS, which indicated that its crystallinity was further reduced. Adsorption of adsorbent for coexistent ions
Structures of DASPH The SEM images of potato starch, DAS and DASPH were shown in Figure 1(b). The original potato starch particles appeared dispersed and smooth, but after oxidization by periodate, the particles appeared obviously diverse. Clearly, the cleavage of glucoside rings leads to an altered uneven surface, creating pores on the particles. After a reaction with phenylhydrazine, the particles of DASPH revealed many pores and irregular structures, which might be due to the reduction or disappearance of cross-linking. These pores and structures indicate that the composite of DASPH has a large surface area (31.2 m2/g) and excellent adsorbtion performance (Yang et al. ). The Fourier transform infrared spectroscopy (FT-IR) spectra of the products were stated in the 4,000–500 cm1 domain on KBr pellet using NEXUS670. Figure 1(c) exhibits the IR spectra of DAS and DASPH. Absorption at 2,932.7 cm1 represented the C-H stretching vibration of methyl and methylene groups in DAS (Zhao et al. ). It is notable that after reacting with NaIO4, one peak at 1733.4 cm1 appeared on the spectrum of DAS, which corresponds to the stretching vibration of the C¼O groups (Ding et al. ). The conjugation of DAS with phenylhydrazine resulted in two peaks at 1601.1 and 3,435.9 cm1. The sharp peak at 1601.1 cm1 could be assigned to the stretching vibration of C¼N groups (Mane et al. ), which was the identity of the connection between DAS and phenylhydrazine. The peak appearing on the DASPH base at 3435.9 cm1 was due to the stretching vibrations of N-H bonds (Yang et al. ), demonstrating that phenylhydrazine was added to DAS to form DASPH. The effect of periodate oxidative and graft copolymerization on the crystallinity of starch, DAS and DASPH were studied by XRD. The results were given in Figure 1(d). The potato starch showed scattering at 2θ ¼ 17.3 , 24.2 , which are characteristic peaks of starch. Compared with W
The adsorption properties of DASPH toward metal ions were determined and the results indicated that the coexistent metal ions display too much interference for the adsorbent. The maximum adsorption capacity for Cd2þ was only 0.76 mmol/g, followed by Zn2þ 0.47 mmol/g, Cu2þ 0.13 mmol/g, Pb2þ 0.08 mmol/g, a result attributed to the competitive adsorption among different transition metal ions. The experiment of adsorbing transition metal ions in real wastewater was also carried out and the results revealed that the adsorbent with the C¼N structure held a very poor adsorbability to different transition metal ions (almost no adsorption). This might be due to the low concentration of transition metal ions in real wastewater. In conclusion, the present work focused on the adsorption capacity of DASPH for different transition metal ions under the initial concentration of 20 mmol/L. Effect of pH An important factor affecting the adsorption capacity of DASPH was the pH of the solution. Calculated from solubility products (Ksp), formation of metal hydroxides occurs at pH 5.8 for Cd2þ, pH 5.2 for Zn2þ, pH 5.5 for Pb2þ and pH 4.2 for Cu2þ with an initial transition metal ion concentration of 20 mmol/L. When pH value goes beyond the pH threshold of metal precipitation, the removal process could be considered as a combination of adsorption and precipitation of metal hydroxides. To eliminate the effect of metal precipitation and in order to compare the results of other experimental studies, all adsorption of Cd2þ, Zn2þ, Pb2þ and Cu2þ were done between pH 1.0–6.0, and the results are shown in Figure 2(a). It may be due to the partial protonation of the Schiff bases (C¼N), which hold back the DASPH adsorbent/M2þ interaction as shown below:
W
Ph-NH-N¼CH- þ Hþ ! Ph-NH-NHþ¼CH-
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(a) Effect of pH and (b) contact times on the adsorption of different transition metal ions by DASPH (the work was done in triplicate): [M(NO3)2] ¼ 20 mmol/L; T ¼ 25 C; the dose of W
each DASPH is 100 mg; (▪) Cd2þ, (•) Zn2þ, (▴) Pb2þ, (▾) Cu2þ.
The Ph-NH-NHþ¼CH- sites on the adsorbent exclude the ions to be adsorbed due to the electrostatic repulsion (Xie et al. ). With the pH increased from 3.0 to 5.0, the active sites became increasingly ionized and the M2þ ions were more adsorbed. At pH 5.0, the adsorbent had a maximum adsorption capacity, which involved competitive reactions of protonation and complex binding (Juang & Chen ). Above pH 5.0, the adsorption capacity decreased sharply because both ion adsorption and M(OH)2 precipitation contribute to transition metal ion removal from the solution. The same trends were indicated in different transition metal ions. Previous studies also reported that the maximal adsorption efficiency for transition metal ions on adsorbents was observed at pH 5.0 (Saygideger et al. ; Min et al. ). It is notable that the adsorbent DASPH showed the satisfactory adsorption capacity for Cd2þ and Zn2þ, a result that might be attributed to the two ions in IIB group and holding the same number of the outermost electron, which enhanced the stability of adsorbent and metal ions (Ding et al. ). The adsorption amount of DASPH was greatly affected by the pH of the transition metal ion solution. The pH of the solution was measured before and after the adsorption and no change was noticed. Effect of adsorption time As shown in Figure 2(b), the removal of transition metal ions by DASPH as a function of contact time was investigated. Clearly, the adsorption capacity increased with the increase of treatment time during the first 120 min and reached the
maximum at that time. Similar results have been reported by other researchers (Saraswat & Rai ; Xie et al. ). However, the adsorption capacity hardly increased as the adsorption time reached 90 min. The reduced metaladsorption was possibly caused by the increased amount of dissolved starch. The initial rapid increase (within 30 min) may be attributed to a large number of vacant binding sites initially being available for adsorption. In the subsequenting slow increase, the occupation of the remaining vacant sites would be difficult due to the repulsive forces between the transition metal ions. According to the results from the experiments, the Q values were 4.9 mmol/g for Cd2þ, 3.3 mmol/g for Zn2þ, 1.7 mmol/g for Pb2þ, 0.83 mmol/g for Cu2þ, respectively. The adsorption of Cd2þ was preferential compared to the other metal ions, and might be attributed to the fact that the special structure (-NH-N¼C-) on DASPH has a higher affinity for Cd2þ than the other transition metal ions (Ravat et al. ). Therefore, DASPH has affinity with transition metal ions in the following order: Cd2þ > Zn2þ > Pb2þ > Cu2þ. A wide variety of adsorbents containing similar structures used to adsorb Cd2þ have been reported. Xie et al. achieved 1.2 mmol/g Cd2þ with amino modified starch (Xie et al. ). Liu et al. reported 2.7 mmol of Cd2þ/g as the adsorption capacity for 5-aminophenanthroline modified dialdehyde starch (Liu et al. ). Zhou et al. reported 279.33 mg of Cd2þ/g cellulose modified with thiosemicarbazide (Zhou et al. ). Compared with these data, it may concluded that DASPH is a promising biodegradable adsorbent for the removal of Cd2þ.
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Adsorbent reuse The reusability of an effective adsorbent is especially important. In the present study, DASPH loaded with Cd2þ was transferred into 50 mL of 1.0 mol/L HCl solution while stirring for 120 min at 20 C. The concentration of transition metal ions in the solution was also determined by atomic absorption spectrometry. After desorption, the DASPH was repeatedly washed with deionized water and then dried for reuse. Six adsorption-desorption cycles for Cd2þ were conducted and in each cycle the initial concentration of Cd2þ was 20 mmol/L. As shown in Figure 3, the adsorption/desorption cycles were performed six times with no significant loss of adsorption capacity. During the sixth adsorption, the adsorption capacity was 91% of the capacity in the first adsorption. In addition, after six adsorption/desorption cycles, no breakdown of the adsorbent was noticed. Therefore, the adsorbent can be reused. W
CONCLUSIONS A novel starch chelating agent, DASPH, was prepared by reacting dialdehyde starch with phenylhydrazine. The BET, SEM, FT-IR and XRD characterization techniques confirmed the formation of DASPH. The adsorption between transition metal ions and dialdehyde phenylhydrazine starch was found to be dependent on the pH of the solution as well as on the treatment time. Maximum removal of transition metal ions on DASPH was at pH 5.0
Figure 3
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Adsorption capacity of DASPH for Cd2þ in different cycles (No replicates were done and each bar reflect a single experiment).
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and 120 min. The results revealed that the adsorption capacities of DASPH for Cd2þ and Zn2þ were 4.9 mmol/g, 3.3 mmol/g, followed by Pb2þ 1.7 mmol/g, Cu2þ 0.83 mmol/g. Having a powerful adsorbability of Cd2þ and other transition metal ions, a high regeneration rate, synthesis in aqueous and moderate reaction conditions, the DASPH demonstrates a prospectively wide application in the recovery of ions from wastewater. The adsorbent can be used widely by putting it inside a reactor at a wastewater treatment plant for the removal of transition metal ions from their aqueous solutions or wastewater.
ACKNOWLEDGEMENT This work was supported by the Fundamental Research Funds for the Central Universities (lzujbky-2012-68).
REFERENCES Budak, T. B. Removal of heavy metals from wastewater using synthetic ion exchange resin. Asian Journal of Chemistry 25 (8), 4207–4210. Dang Viet, Q., Lee, J. E., Kim, J. K., Kim, Y. N., Shao, G. N. & Kim, H. T. A gentle method to graft thiol-functional groups onto silica gel for adsorption of silver ions and immobilization of silver nanoparticles. Powder Technology 235, 221–227. Ding, W., Zhao, P. & Li, R. Removal of Zn (II) ions by dialdehyde 8-aminoquinoline starch from aqueous solution. Carbohydrate Polymers 83 (2), 802–807. Ding, W., Zhai, S-y., Liu, J-t., Wang, R. & Li, R. Preparation and adsorption properties of dialdehyde 8-aminoquinoline starch. Water Science and Technology 67 (2), 306–310. El Zayat, M. & Smith, E. Modeling of heavy metals removal from aqueous solution using activated carbon produced from cotton stalk. Water Science and Technology 67 (7), 1612– 1619. Graillot, A., Bouyer, D., Monge, S., Robin, J. J. & Faur, C. Removal of nickel ions from aqueous solution by low energyconsuming sorption process involving thermosensitive copolymers with phosphonic acid groups. Journal of Hazardous Materials 244, 507–515. Gupta, V. K., Jain, C. K., Ali, I., Sharma, M. & Saini, V. K. Removal of cadmium and nickel from wastewater using bagasse fly ash – a sugar industry waste. Water Research 37 (16), 4038–4044. Gupta, V. K., Saini, V. K. & Jain, N. Adsorption of As(III) from aqueous solutions by iron oxide-coated sand. Journal of Colloid and Interface Science 288 (1), 55–60. Gupta, V. K. & Rastogi, A. Biosorption of lead(II) from aqueous solutions by non-living algal biomass Oedogonium
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sp and Nostoc sp – A comparative study. Colloids and Surfaces B-Biointerfaces 64 (2), 170–178. Gupta, V. K., Rastogi, A. & Nayak, A. Adsorption studies on the removal of hexavalent chromium from aqueous solution using a low cost fertilizer industry waste material. Journal of Colloid and Interface Science 342 (1), 135–141. Hu, H. & Zhu, H. Adsorption of heavy metal ions by chitosan and its derivatives. Progress in Chemistry 24 (11), 2212–2223. Hofreiter, B. T., Alexander, B. H. & Wolff, I. A. Rapid estimation of dialdehyde content of periodate oxystarch through quantitative alkali consumption. Analytical Chemistry 27 (10), 1930–1931. Juang, R. S. & Chen, M. N. Measurement of binding constants of poly(ethylenimine) with metal ions and metal chelates in aqueous media by ultrafiltration. Industrial & Engineering Chemistry Research 35 (6), 1935–1943. Liu, J-t., Dong, Z-P., Ding, W., Zhao, P., Sun, J., Jin, X-D. & Li, R. Adsorption of Zn(II) on dialdehyde m-phenylenediamine starch. Water Science and Technology 66 (2), 321–327. Liu, J-T., Zhang, K-Y., Wang, P., Ding, W., Zhao, P., Dong, Z-P. & Li, R. Adsorption behavior of Cd (II) from aqueous solution using dialdehyde 5-aminophenanthroline starch. Separation Science and Technology 48 (5), 766–774. Mane, G. P., Dhawale, D. S., Anand, C., Ariga, K., Ji, Q. M., Wahab, M. A., Mori, T. & Vinu, A. Selective sensing performance of mesoporous carbon nitride with a highly ordered porous structure prepared from 3-amino-1,2,4triazine. Journal of Materials Chemistry A 1 (8), 2913–2920. Min, M., Shen, L., Hong, G., Zhu, M., Zhang, Y., Wang, X., Chen, Y. & Hsiao, B. S. Micro-nano structure poly(ether sulfones)/ poly(ethyleneimine) nanofibrous affinity membranes for adsorption of anionic dyes and heavy metal ions in aqueous solution. Chemical Engineering Journal 197, 88–100. Nurchi, V. M., Crisponi, G. & Villaescusa, I. Chemical equilibria in wastewaters during toxic metal ion removal by agricultural biomass. Coordination Chemistry Reviews 254 (17–18), 2181–2192. Rajkumar, P., Kumar, P. S., Kirupha, S. D., Vidhyadevi, T., Nandagopal, J. & Sivanesan, S. Adsorption of Pb(II) ions onto surface modified Guazuma ulmifolia seeds and batch adsorber design. Environmental Progress & Sustainable Energy 32 (2), 307–316. Ravat, C., Monteil-Rivera, F. & Dumonceau, J. Metal ions binding to natural organic matter extracted from wheat bran: application of the surface complexation model. Journal of Colloid and Interface Science 225 (2), 329–339.
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Rivaro, P., Cullaj, A., Frache, R., Lagomarsino, C., Massolo, S., De Mattia, M. C. & Ungaro, N. Heavy metals distribution in suspended particulate matter and sediment collected from Vlora Bay (Albania): a methodological approach for metal pollution evaluation. Journal of Coastal Research special issue 58, 54–66. Safa, M., Larouci, M., Meddah, B. & Valemens, P. The sorption of lead, cadmium, copper and zinc ions from aqueous solutions on a raw diatomite from Algeria. Water Science and Technology 65 (10), 1729–1737. Saraswat, S. & Rai, J. P. N. Heavy metal adsorption from aqueous solution using Eichhornia crassipes dead biomass. International Journal of Mineral Processing 94 (3–4), 203–206. Saygideger, S., Gulnaz, O., Istifli, E. S. & Yucel, N. Adsorption of Cd(II), Cu(II) and Ni(II) ions by Lemna minor, L.: effect of physicochemical environment. Journal of Hazardous Materials 126 (1–3), 96–104. Shih, Y-J., Lin, C-P. & Huang, Y-H. Application of FeredFenton and chemical precipitation process for the treatment of electroless nickel plating wastewater. Separation and Purification Technology 104, 100–105. Xie, G., Shang, X., Liu, R., Hu, J. & Liao, S. Synthesis and characterization of a novel amino modified starch and its adsorption properties for Cd(II) ions from aqueous solution. Carbohydrate Polymers 84 (1), 430–438. Yang, L., Li, Y., Hu, H., Jin, X., Ye, Z., Ma, Y. & Zhang, S. Preparation of novel spherical PVA/ATP composites with macroreticular structure and their adsorption behavior for methylene blue and lead in aqueous solution. Chemical Engineering Journal 173 (2), 446–455. Yang, Z-Z., He, L-N., Gao, J., Liu, A-H. & Yu, B. Carbon dioxide utilization with C-N bond formation: carbon dioxide capture and subsequent conversion. Energy & Environmental Science 5 (5), 6602–6639. Zhang, H., Zhao, D., Chen, L. & Yu, X. J. Investigation of Cu (II) adsorption from aqueous solutions by NKF-6 zeolite. Water Science and Technology 63 (3), 395–402. Zhao, P., Jiang, J., Zhang, F-W., Zhao, W-F., Liu, J-T. & Li, R. Adsorption separation of Ni(II) ions by dialdehyde ophenylenediamine starch from aqueous solution. Carbohydrate Polymers 81 (4), 751–757. Zhou, Y., Hu, X., Zhang, M., Zhuo, X. & Niu, J. Preparation and characterization of modified cellulose for adsorption of Cd(II), Hg(II), and acid Fuchsin from aqueous solutions. Industrial & Engineering Chemistry Research 52 (2), 876–884.
First received 26 June 2013; accepted in revised form 26 September 2013. Available online 25 October 2013
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Removal of transition metal ions from aqueous solution using dialdehyde phenylhydrazine starch as adsorbent Rou Wang, Jun-Tao Liu, Chun-Yang Li and Rong Li
ABSTRACT Dialdehyde phenylhydrazine starch (DASPH) was synthesized by reacting dialdehyde starch (DAS) with phenylhydrazine (PH) and it was characterized by Brunauer–Emmett–Teller (BET), scanning electron microscope, Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) techniques. FT-IR of DASPH revealed the incorporation of the Schiff Base group (C ¼ N) group and the disappearance of the C ¼ O (carbonyl) group. The adsorption behaviors of transition metal ions (Cd2þ, Zn2þ, Pb2þ and Cu2þ) were investigated as a function of pH and adsorption time. The results indicated that pH 5.0 and 120 min were the optimal conditions. Experimental results revealed that
Rou Wang Jun-Tao Liu Chun-Yang Li Rong Li (corresponding author) The Key Laboratory of Nonferrous Metal Chemistry and Resources Utilization of Gansu Province, College of Chemistry and Chemical Engineering, Lanzhou University, Lanzhou 730000, China E-mail: [email protected]
the maximum adsorption capacity of DASPH for the four transition metal ions was as follows: Cd2þ (4.9 mmol/g) > Zn2þ (3.3 mmol/g) >Pb2þ (1.7 mmol/g) >Cu2þ (0.83 mmol/g). In addition, the regeneration method of DASPH was also studied. Key words
| adsorption, dialdehyde phenylhydrazine starch, dialdehyde starch, transition metal ions
INTRODUCTION In recent years, with the rapid development of modern industry, large numbers of transition metal ions were discharged into water from plating plants, metal finishing, dyeing factories and several other sources. Their acute toxicity, non-biodegradable nature and build-up of high concentrations in water bodies all over the world raise increasing concern (Rivaro et al. ). Moreover, transition metal ions are absorbed by animals and plants, and enter the human body through the food chain and cause health problems. Thus, effective measures for the removal of transition metal ions from water is urgently required. Several techniques have been proposed for the removal of transition metal ions from industrial effluents such as chemical precipitation (Shih et al. ), ion-exchange methods (Budak ), electro-deposition and adsorption (Safa et al. ; Graillot et al. ; Rajkumar et al. ). Among these techniques, adsorption is generally preferred for the removal of transition metal ions due to its high efficiency, easy handling and the availability of different adsorbents (Gupta et al. ). It is well known that adsorption on activated carbon is a commonly used technology for removing transition ions, but the higher cost of carbon limits its large-scale usage. Therefore, it is desirable to develop lower cost, more efficient and reusable adsorbent material. doi: 10.2166/wst.2013.571
Numerous adsorbent materials such as zeolites (Zhang et al. ), activated carbons (El Zayat & Smith ) and silica beads (Dang Viet et al. ) have been successfully utilized for wastewater remediation. Recently, many approaches have been studied for developing cheaper and more effective adsorbents containing natural polymers (Nurchi et al. ; Hu & Zhu ). As adsorbents, biopolymers attract more and more attention from chemists because of their economical and effective characteristics (Gupta et al. ). Among biopolymers, polysaccharides (Gupta et al. ; Gupta & Rastogi ) deserve particular attention. As a natural polysaccharide, starch is biodegradable, abundant and environmentally friendly. Different approaches are currently used. At present, a commonly used method is oxidation of starch to dialdehyde starch in the presence of sodium periodate. Earlier works report that dialdehyde starch with o-phenylenediamine (Zhao et al. ), m-phenylenediamine (Liu et al. ) and 5-aminophenanthroline (Liu et al. ) could form stable complexes with ions. However, their adsorption capacities for ions were relatively poor. Up to now, few studies have focused on the difference in adsorption ability between ions. The main objective of this work was to evaluate the adsorption of transition metal ions on dialdehyde phenylhydrazine starch (DASPH), which was obtained from the
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reaction of dialdehyde starch and inexpensive phenylhydrazine. Experimental data concerning the characterization of material as well as adsorption were presented. Moreover, the adsorbents can be reused.
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respectively. C1 and C2 (mol/L) represent the concentrations of H2SO4 and NaOH, and 161 is the average molecular weight of the repeated unit in dialdehyde starch. The Da of the adsorbent was 76%. Preparation of DASPH
EXPERIMENT Materials and apparatus W
Potato starch (food-grade) was dried at 105 C before using. Sodium periodate (NaIO4), sulphuric acid (H2SO4) and 98% phenylhydrazine were purchased from Sichuan Chemical Factory (Sichuan AR China). All other commercial chemicals were of analytic reagent grade and used without further purification. Cadmium nitrate tetrahydrate (Cd(NO3)2·4H2O), zinc nitrate hexahydrate (Zn(NO3)2·6H2O), lead nitrate (Pb(NO3)2) and cupric nitrate trihydrate (Cu(NO3)2·3H2O) were used as sources for Cd2þ, Zn2þ, Pb2þ and Cu2þ, respectively. Elemental analysis was performed using a PerkinElmer 2400 CHN analyzer. The surface area of DASPH was measured by the N2 adsorption–desorption technique using a Micromeritics Chemisorb 2750 surface area analyzer. The size and morphology of the materials were observed by a JEOC JSM6701F scanning electron microscope (SEM) at accelerating voltages of 5.0 KV. Infrared spectra were obtained by the KBr pellet technique and were recorded on NEXUS670. X-ray diffraction (XRD) was confirmed by X-ray Diffractometer (D/ Max-2400). The pH value of solutions was determined using a PHS-3C pH meter. Atomic absorption spectrometry was carried out using an Analyst 240 instrument (Varian American).
Preparation of dialdehyde starch 4.0 g sodium periodate used as oxidant was added into 4.0 g potato starch suspension to prepare DAS. The mixture was stirred slowly at 30 C in the dark for 4 h. At the end of the reaction time, the product was washed several times with deionized water and one time with ethanol. The aldehyde group content was determined by the rapid quantitative alkali consumption method (Hofreiter et al. ). The percentage of dialdehyde units is given as the equation: W
Da% ¼
(V1 C1 2V2 C2 ) × 100% W=161
(1)
V1, V2 and W represent the total volumes (L) of H2SO4, NaOH and the dry weight (g) of the oxidized starch,
4.0 g DAS was suspended in 50 mL deionized water in a 100 mL two-necked flask, which was equipped with an electromagnetic stirrer and thermostat oil bath. Afterwards, 3.57 mL phenylhydrazine was slowly put into the flask. The pH of the reaction system was adjusted to 5.0 with acetic acid. The reaction was stirred for 4 hours at 60 C under nitrogen protection. The slurry was separated from the solution by filtration, then extensively rinsed with deionized water and rinsed once with ethanol, and then dried at 50 C to a constant weight. The preparation of DASPH was shown schematically in Figure 1(a). W
W
Adsorption properties of DASPH for transition metal ions The actual application of DASPH was demonstrated through adsorption of Cd2þ, Zn2þ, Pb2þ and Cu2þ. The stock solutions of metal salts (100 mmol/L) were prepared by dissolving Cd(NO3)2·4H2O, Zn(NO3)2·6H2O, Pb(NO3)2 and Cu(NO3)2·3H2O in deionized water. The synthetic wastewater solutions (20 mmol/L) were then obtained by dilution of the stock solutions of each transition metal ion by using deionized water. The coexistent metal ion solution was prepared as follows: accurately measured 12.5 mL metal ion solutions from the above-mentioned solution (Cd2þ, Zn2þ, Pb2þ and Cu2þ, respectively), were poured into 100 mL Erlenmeyer flasks. The real wastewater was derived from the Lan Zhou Section of the Yellow River. Batch experiments were carried out in 100 mL Erlenmeyer flasks using 50 mL of metal ion solutions at 20 C to determine the effects of pH on the adsorption of metal ions. The pH value of the solution was adjusted to a predetermined value using 0.1 mol/L HNO3 or NaOH and 100 mg of DASPH was added to the solution. The resulting suspension was stirred for a specified time with a magnetic stirrer at 150 rpm while keeping the pH value constant through measuring with a pH meter. At the end of each experiment, the solutions were separated by filtration. The filtrate was then analyzed for residual metal ions by atomic absorption spectrometry. The standard deviation obtained is 0.00415 W
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Figure 1
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(A) Reagents and conditions: (a) NaIO4 and (b) phenylhydrazine; (B) SEM images; (C) FT-IR spectra; and (D) XRD pattern of potato starch, DAS and DASPH.
and within the error limits of ±1.54%. Each set of resulting data was replicated three times in all experiments. In the adsorption-regeneration cycles, no replicates were done and each bar reflects a single experiment. The adsorption capacity of DASPH for different transition metal ions was measured by adsorption capacity Q (mmol/g). Q is the adsorbed transition metal ions quantity per gram of adsorbent at equilibrium time.
RESULTS AND DISCUSSION Characterization of DAS and DASPH BET The Brunauer–Emmett–Teller (BET) technique was applied to analyze the adsorbent. The surface area, pore volume and
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pore size of DASPH were 31.2 m2/g, 0.00196 cm3/g, and 17.5 nm, respectively. Ding et al. reported 29.0 m2/g of surface area in studying the adsorption capacity of dialdehyde starch with 8-aminoquinoline for Zn2þ (Ding et al. ). Liu et al. achieved 30.5 m2/g in studying the adsorption behavior of Zn2þ on dialdehyde m-phenylenediamine starch (Liu et al. ). On comparing these data, it may be concluded that the DASPH has a large surface area and excellent adsorbtion performance.
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potato starch, the crystallinity of DAS decreased. It is supposed that the aggregation phase of the original starch was changed from its semicrystalline state to an amorphous aggregation state during the periodate oxidative and the chain breakage reactions (Ding et al. ). However, after DAS was grafted to phenylhydrazine, the peak became weaker than DAS, which indicated that its crystallinity was further reduced. Adsorption of adsorbent for coexistent ions
Structures of DASPH The SEM images of potato starch, DAS and DASPH were shown in Figure 1(b). The original potato starch particles appeared dispersed and smooth, but after oxidization by periodate, the particles appeared obviously diverse. Clearly, the cleavage of glucoside rings leads to an altered uneven surface, creating pores on the particles. After a reaction with phenylhydrazine, the particles of DASPH revealed many pores and irregular structures, which might be due to the reduction or disappearance of cross-linking. These pores and structures indicate that the composite of DASPH has a large surface area (31.2 m2/g) and excellent adsorbtion performance (Yang et al. ). The Fourier transform infrared spectroscopy (FT-IR) spectra of the products were stated in the 4,000–500 cm1 domain on KBr pellet using NEXUS670. Figure 1(c) exhibits the IR spectra of DAS and DASPH. Absorption at 2,932.7 cm1 represented the C-H stretching vibration of methyl and methylene groups in DAS (Zhao et al. ). It is notable that after reacting with NaIO4, one peak at 1733.4 cm1 appeared on the spectrum of DAS, which corresponds to the stretching vibration of the C¼O groups (Ding et al. ). The conjugation of DAS with phenylhydrazine resulted in two peaks at 1601.1 and 3,435.9 cm1. The sharp peak at 1601.1 cm1 could be assigned to the stretching vibration of C¼N groups (Mane et al. ), which was the identity of the connection between DAS and phenylhydrazine. The peak appearing on the DASPH base at 3435.9 cm1 was due to the stretching vibrations of N-H bonds (Yang et al. ), demonstrating that phenylhydrazine was added to DAS to form DASPH. The effect of periodate oxidative and graft copolymerization on the crystallinity of starch, DAS and DASPH were studied by XRD. The results were given in Figure 1(d). The potato starch showed scattering at 2θ ¼ 17.3 , 24.2 , which are characteristic peaks of starch. Compared with W
The adsorption properties of DASPH toward metal ions were determined and the results indicated that the coexistent metal ions display too much interference for the adsorbent. The maximum adsorption capacity for Cd2þ was only 0.76 mmol/g, followed by Zn2þ 0.47 mmol/g, Cu2þ 0.13 mmol/g, Pb2þ 0.08 mmol/g, a result attributed to the competitive adsorption among different transition metal ions. The experiment of adsorbing transition metal ions in real wastewater was also carried out and the results revealed that the adsorbent with the C¼N structure held a very poor adsorbability to different transition metal ions (almost no adsorption). This might be due to the low concentration of transition metal ions in real wastewater. In conclusion, the present work focused on the adsorption capacity of DASPH for different transition metal ions under the initial concentration of 20 mmol/L. Effect of pH An important factor affecting the adsorption capacity of DASPH was the pH of the solution. Calculated from solubility products (Ksp), formation of metal hydroxides occurs at pH 5.8 for Cd2þ, pH 5.2 for Zn2þ, pH 5.5 for Pb2þ and pH 4.2 for Cu2þ with an initial transition metal ion concentration of 20 mmol/L. When pH value goes beyond the pH threshold of metal precipitation, the removal process could be considered as a combination of adsorption and precipitation of metal hydroxides. To eliminate the effect of metal precipitation and in order to compare the results of other experimental studies, all adsorption of Cd2þ, Zn2þ, Pb2þ and Cu2þ were done between pH 1.0–6.0, and the results are shown in Figure 2(a). It may be due to the partial protonation of the Schiff bases (C¼N), which hold back the DASPH adsorbent/M2þ interaction as shown below:
W
Ph-NH-N¼CH- þ Hþ ! Ph-NH-NHþ¼CH-
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Figure 2
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(a) Effect of pH and (b) contact times on the adsorption of different transition metal ions by DASPH (the work was done in triplicate): [M(NO3)2] ¼ 20 mmol/L; T ¼ 25 C; the dose of W
each DASPH is 100 mg; (▪) Cd2þ, (•) Zn2þ, (▴) Pb2þ, (▾) Cu2þ.
The Ph-NH-NHþ¼CH- sites on the adsorbent exclude the ions to be adsorbed due to the electrostatic repulsion (Xie et al. ). With the pH increased from 3.0 to 5.0, the active sites became increasingly ionized and the M2þ ions were more adsorbed. At pH 5.0, the adsorbent had a maximum adsorption capacity, which involved competitive reactions of protonation and complex binding (Juang & Chen ). Above pH 5.0, the adsorption capacity decreased sharply because both ion adsorption and M(OH)2 precipitation contribute to transition metal ion removal from the solution. The same trends were indicated in different transition metal ions. Previous studies also reported that the maximal adsorption efficiency for transition metal ions on adsorbents was observed at pH 5.0 (Saygideger et al. ; Min et al. ). It is notable that the adsorbent DASPH showed the satisfactory adsorption capacity for Cd2þ and Zn2þ, a result that might be attributed to the two ions in IIB group and holding the same number of the outermost electron, which enhanced the stability of adsorbent and metal ions (Ding et al. ). The adsorption amount of DASPH was greatly affected by the pH of the transition metal ion solution. The pH of the solution was measured before and after the adsorption and no change was noticed. Effect of adsorption time As shown in Figure 2(b), the removal of transition metal ions by DASPH as a function of contact time was investigated. Clearly, the adsorption capacity increased with the increase of treatment time during the first 120 min and reached the
maximum at that time. Similar results have been reported by other researchers (Saraswat & Rai ; Xie et al. ). However, the adsorption capacity hardly increased as the adsorption time reached 90 min. The reduced metaladsorption was possibly caused by the increased amount of dissolved starch. The initial rapid increase (within 30 min) may be attributed to a large number of vacant binding sites initially being available for adsorption. In the subsequenting slow increase, the occupation of the remaining vacant sites would be difficult due to the repulsive forces between the transition metal ions. According to the results from the experiments, the Q values were 4.9 mmol/g for Cd2þ, 3.3 mmol/g for Zn2þ, 1.7 mmol/g for Pb2þ, 0.83 mmol/g for Cu2þ, respectively. The adsorption of Cd2þ was preferential compared to the other metal ions, and might be attributed to the fact that the special structure (-NH-N¼C-) on DASPH has a higher affinity for Cd2þ than the other transition metal ions (Ravat et al. ). Therefore, DASPH has affinity with transition metal ions in the following order: Cd2þ > Zn2þ > Pb2þ > Cu2þ. A wide variety of adsorbents containing similar structures used to adsorb Cd2þ have been reported. Xie et al. achieved 1.2 mmol/g Cd2þ with amino modified starch (Xie et al. ). Liu et al. reported 2.7 mmol of Cd2þ/g as the adsorption capacity for 5-aminophenanthroline modified dialdehyde starch (Liu et al. ). Zhou et al. reported 279.33 mg of Cd2þ/g cellulose modified with thiosemicarbazide (Zhou et al. ). Compared with these data, it may concluded that DASPH is a promising biodegradable adsorbent for the removal of Cd2þ.
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Adsorbent reuse The reusability of an effective adsorbent is especially important. In the present study, DASPH loaded with Cd2þ was transferred into 50 mL of 1.0 mol/L HCl solution while stirring for 120 min at 20 C. The concentration of transition metal ions in the solution was also determined by atomic absorption spectrometry. After desorption, the DASPH was repeatedly washed with deionized water and then dried for reuse. Six adsorption-desorption cycles for Cd2þ were conducted and in each cycle the initial concentration of Cd2þ was 20 mmol/L. As shown in Figure 3, the adsorption/desorption cycles were performed six times with no significant loss of adsorption capacity. During the sixth adsorption, the adsorption capacity was 91% of the capacity in the first adsorption. In addition, after six adsorption/desorption cycles, no breakdown of the adsorbent was noticed. Therefore, the adsorbent can be reused. W
CONCLUSIONS A novel starch chelating agent, DASPH, was prepared by reacting dialdehyde starch with phenylhydrazine. The BET, SEM, FT-IR and XRD characterization techniques confirmed the formation of DASPH. The adsorption between transition metal ions and dialdehyde phenylhydrazine starch was found to be dependent on the pH of the solution as well as on the treatment time. Maximum removal of transition metal ions on DASPH was at pH 5.0
Figure 3
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Adsorption capacity of DASPH for Cd2þ in different cycles (No replicates were done and each bar reflect a single experiment).
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and 120 min. The results revealed that the adsorption capacities of DASPH for Cd2þ and Zn2þ were 4.9 mmol/g, 3.3 mmol/g, followed by Pb2þ 1.7 mmol/g, Cu2þ 0.83 mmol/g. Having a powerful adsorbability of Cd2þ and other transition metal ions, a high regeneration rate, synthesis in aqueous and moderate reaction conditions, the DASPH demonstrates a prospectively wide application in the recovery of ions from wastewater. The adsorbent can be used widely by putting it inside a reactor at a wastewater treatment plant for the removal of transition metal ions from their aqueous solutions or wastewater.
ACKNOWLEDGEMENT This work was supported by the Fundamental Research Funds for the Central Universities (lzujbky-2012-68).
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First received 26 June 2013; accepted in revised form 26 September 2013. Available online 25 October 2013
