Application of modified starches in wastewater … of modified starches in wastewater treatment ......

Application of modified starches in wastewater treatment

Rumei Cheng*, 1 and Shengju Ou2 1 Institute of Advanced Materials for Nano-Bio Applications, School of Ophthalmology & Optometry, Wenzhou Medical

University, 270 Xueyuan Road, Wenzhou, Zhejiang 325027, China 2 Nanjing Landa Festosecond Inspection Technology Co. Ltd., 10 Xinghuo Road, Nanjing, Jiangsu 210032, China * Corresponding author: email: [email protected]

Recently natural polysaccharides have been developed as environmentally friendly materials for removing toxic pollutants from aqueous solutions. Amongst numerous polysaccharides starch is an abundant, inexpensive, renewable and fully biodegradable natural raw material. The main criterion in the design of modified starch with substantial stability is fast complexation of toxic pollutants. A new class of modified starches has been synthesized and applied as adsorbents for dyes and heavy metals. In this chapter, the preparation and application of the modified starches were introduced. The adsorption kinetics, equilibrium isotherm and interaction mode were discussed. Moreover, the advancement of surface structures and adsorption mechanism were reviewed. Some suggestions in design of starch-based materials for wastewater treatment were put forward in consideration of the stability of modified starches.

Keywords: Modified starch; Wastewater treatment; Adsorption; Design; Mechanism

1. Introduction

Starch is an abundant, inexpensive, renewable and fully biodegradable natural raw material. It is the second most abundant biomass material in nature, and found in plant roots, stalks, crop seeds, and staple crops such as rice, corn, wheat, tapioca, and potato [1, 2]. Starch is a branched homopolymer of glucose, with α-(1→4) linear links and α-(1→6) branched links. As shown in Fig. 1, starch comprises two types of polymers, each of which has a broad distribution of molecular sizes and molecular weights: amylose, which is of moderate molecular weight (~106) and with a few long chain branches, and amylopectin, whose molecular weight is about two orders of magnitude higher and whose branches are much shorter. The structure and chemical composition of amylose and amylopectin were shown in Fig.1, respectively.

Fig. 1 Schematic of structure and chemical composition of amylose and amylopectin.

Starch extracted from the plant is called “native starch”. Starch undergoes one or more chemical modifications to reach specific properties and is called “modified starch”. So far, starch has been extensive used in food and drug processing [3, 4], biocatalysts [5], food, beverages, papermaking, packaging, and textiles [6, 7]. However, its application in engineering is limited due to the poor physical properties such as mechanical properties, dimensional stability and so on. To improve it, crosslinking reaction is applied to acquire stable modified starches [8]. Furthermore functional group (such as amine, carbamate and so on) is grafted onto the cross-linked starch, which enhances affinity with various molecules. Applications of modified starch for wastewater treatment (organic dyes or metal ions polluted water) have received much attention in recent years because of its environmental friendliness, easy handling, and availability. Water pollution produced by various kinds of synthetic dyes or metal ions discharged from textile and industrial mining wastewaters was a serious environmental problem. Thus, removal of dyes and heavy metals from wastewater before discharging to environment is essential for the protection of health and environment. The main criterion in the design of modified starches with substantial stability is fast fixation of the pollutants. This chapter mainly focuses on the different methods of preparation of modified starches including their modifications and applications as adsorbents for the wastewater (organic dyes or metal ions) treatments.

Polymer science: research advances, practical applications and educational aspects (A. Méndez-Vilas; A. Solano, Eds.) _______________________________________________________________________________________________

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2. Modified starch for organic wastewater treatment

The ethylenediamine modified starch (CAS) was a novel material [9]. It exhibited great potential for the removal of acid dyes (acid orange 10, acid green 25 and amido black 10B) from aqueous solutions. The capacity of CAS for each dye was pH dependent, and the adsorption was governed by electrostatic attraction and hydrogen bonding (Fig. 2). The removal process of acid green 25 and amido black 10B involved a smoothly increase stage followed by a slower stage, whereas the acid orange 10 removal smoothly increased with time until equilibrium achieved. The adsorption kinetics followed the pseudo-second-order equation. The equilibrium data fitted well with Langmuir isotherm and the capacities followed the order amido black 10B > acid green 25 > acid orange 10. Dye release in sodium sulfate solutions related to salt concentration. Also the nature of dyes affected the desorption efficiency. The utmost desorption of acid orange 10, acid green 25 and amido black 10B was 92%, 28% and 10%, respectively. Their adsorption and desorption behaviours varied mostly due to difference in the amount of hydrophilic functional groups on dyes molecules.

O O

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Fig. 2 Main interactions between acid green 25 and CAS. Reproduced from reference [9], copyright Elsevier 2009. When ethylenediamine was replaced by diethylenetriamine, the diethylenetriamine-modified starches were synthesized [10]. The native starch and enzymatic hydrolysis starch reacted with diethylenetriamine producing cross-linked amined starch (CTAS) and cross-linked amined enzyme-hydrolyzed starch (CAES). The CAES has exhibited higher sorption ability than that of CTAS due to high surface area, and the increment for these dyes took the sequence of acid orange 7 (0.944mmol g−1) > acid orange 10 (0.592mmol g−1) > acid red 18 (0.411mmol g−1) > acid green 25 (0.047mmol g−1). Sorption kinetics and isotherms analysis showed that these sorption processes were well fitted to pseudo-second-order equation and Langmuir equation. Adsorption mechanism was studied by investigating the effects of pH, ionic strength and the contribution of hydrogen bonding.

Fig. 3 Synthesis of dithiocarbamate-modified starch (DTCS). Reproduced from reference [11], copyright Elsevier 2011.


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Furthermore, the CAS reacted with the CS2 in alkaline solution produced the dithiocarbamate-modified starch (DTCS) (Fig. 3). It can be employed to remove dyes from aqueous solutions [11]. The capacity of dithiocarbamate-modified starch for dyes is pH dependent. The pH 4 of solution is appropriate. The kinetic studies indicate that the sorption of the dyes tends to follow pseudo-first-order equation. The sorption equilibrium is best described by the Langmuir-Freundlich isotherm model at 298 K. The maximum adsorption capacities sequence is acid orange 7 > acid orange 10 > acid red 18 > acid black 1 > acid green 25, which is inverse order of molecular size. The negative values of enthalpy indicate that adsorption process is exothermic. The adsorption mechanism based on the electrostatic attraction between starch-NH2

+CSSH···-O3S-dye. Moreover, the dithiocarbamate-modified starch can be recycled in weak basic solution containing sodium sulfate. The metal complex of DTCS can strongly fix the anionic dyes. The equilibrium and molecular mechanism of anionic dyes adsorbing onto Cu(II) complex of dithiocarbamate-modified starch (DTCSCu) were reported [12]. The DTCSCu complex was prepared by reacting DTCS with CuCl2 in water and was used to remove anionic dyes from aqueous solutions as an adsorbent. The sorption studies showed that the interaction mechanism based on chelating adsorption between dinuclear copper of DTCSCu and sulfonate groups of dyes. The equilibrium data fitted well with Langmuir-Freundlich isotherm, and the capacities followed the order acid orange 7> acid green 25> acid red 18> acid orange 10. The adsorption capacity depended on structure of dyes. The molar n(dye): n(Cu) ratios for acid orange 10, acid red 18, and acid green 25 were approximately 1: 2 (Fig. 4), whereas the molar n(dye): n(Cu) ratio for the smallest dye acid orange 7 approached 1: 1, which revealed the difference in capacity. Furthermore, the ternary dye-metal-polymer complexes were more stable than DTCSCu.

OO

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Fig. 4 Formation of a surface complex of acid green 25 with DTCSCu. Reproduced from reference [12], copyright American Chemical Society 2009.

Ionic starch is another kind of modified starch used in wastewater treatment. Three kinds of hydrogels were prepared by using acrylic acid (AA), sodium acrylate(SA) and AA/hydroxy ethyl methacrylate (HEMA) in the presence of starch in water via a free radical polymerization [13]. The concentration of the initiator, monomer, and crosslinker affected product yields. The ammonium persulfate and sodium metabisulfide as initiators and N, N’-methylene bisacrylamide (MBA) as crosslinker were used in the experiment, respectively. The gels showed high adsorption and removal% of safranineT (ST) and brilliant cresyl blue (BCB) dyes from water. The removal of dyes was pH dependent in the pH 3~7. The adsorption data showed better fitting to first-order kinetics for both ST and BCB dyes. Amongst the three kinds of hydrogels, the starch incorporated sodium polyacrylate gel exhibited the highest adsorption of 9.7–85.3 mg L−1 (97–61% removal) of BCB dye and 9.1–83 mg/L (91–60% removal) of ST dye for a feed dye concentration of 10–140 mg/L. Xiang’ group reported the preparation and adsorption behaviour of cationic starch intercalated clay composite matrix for the removal of brilliant blue X-BR [14]. Firstly, cationic starch was synthesized by grafting 2,3-epoxypropyltrimethyl-ammonium chloride onto the surface of corn starch. Then the cationic starch and clay was mixed by vigorous stirring producing cationic starch intercalated clay composite. It found that adsorption capacity increased


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with increasing the weight ratio of clay to cationic starch from 0.1 to 0.2, and then decreased when the weight ratio of clay to cationic starch up to 0.3. The maximum adsorption capacity was 122.0 mg L−1. The adsorption data well fitted to the Langmuir isotherm, and the adsorption kinetics data was described by pseudo-second-order kinetic model. The positive value of △H and negative value of △G indicated that the adsorption process is endothermic.

The novel crosslinked starch microspheres were synthesized by microwave-assisted inversed emulsion system with soluble starch as a raw material, methylene-bis-acrylamide as a crosslinker, and K2S2O8–NaHSO3 as an initiator [15]. Compared to native soluble starch, crosslinked starch microsphere has higher surface area. Adsorption performance was investigated in methyl violet solution. The maximum adsorption capacity was 99.3 mg g−1 at 298 k for methyl violet solution. The adsorption kinetics data fitted pseudo-second-order kinetic model well with correlation coefficients greater than 0.99. The adsorption behaviour obeyed the Langmuir model. The pH of solution did not significantly affect the adsorption capacity of dye. Diao’ group designed new adsorbents-SGCn (SGC4, SGC6, SGC8) by grafting p-Tert-butyl-calix(4,6,8) arene onto starch through epichlorohydrin [16]. Static adsorption behaviour is studied by using SGC8 as adsorbent to remove butyl Rhodamine B solution from dye wastewater. The adsorption of Rhodamine B onto SGC8 fits the second order kinetic model and the apparent adsorption rate constant is 0.002 g mg−1 min−1 at 25 ◦C. The adsorption behaviour of Rhodamine B onto SGC8 better fitted to Langmuir model. The adsorbent can be recycled by desorption of dye from SGC8 in ethanol. The desorption efficiency of Rhodamine B is dependent on the concentration of ethanol and the temperature.

The inorganic-starch composites have been studied for dyes fixation. The magnetic soluble starch-functionalized carbon nanotube (MWCNT-starch) was synthesized and its application for adsorption of the dyes was investigated [17]. The soluble starch-functionalized multiwall carbon nanotube (MWCNT) composites were prepared by covalently graft starch onto the surface of MWCNT, and MWCNT-starch was further combined iron oxide nanoparticles at the surface of MWCNT-starch producing MWCNT-starch-iron oxide composites. MWCNT-starch-iron oxide exhibits superparamagnetic properties with a saturation magnetization (23.15 emu g−1). The MWCNT-starch-iron oxide possesses the properties of magnetic separation. MWCNT-starch-iron oxide exhibited a better second-order rate constant and adsorption for methyl orange and methylene blue at equilibrium than MWCNT-iron oxide. Kumar et al. reported the synthesis and characterization of starch-AlOOH-FeS2 nanocomposite for the adsorption of congo red dye from aqueous solution [18]. The specific BET surface area and pore structure of nanocomposite affected the adsorption capacity. The adsorption capacity is pH dependent from 5-9 and maximum adsorption is found to be at pH 5. The adsorption behaviour of congo red onto starch-AlOOH-FeS2 is spontaneous and endothermic in nature. The interaction mechanism based on electrostatic interaction complexation and coordination effect between metal atoms and –NH2 and –SO3

- groups. The adsorption kinetics data fitted well to the pseudo-first-order equation whereas the Freundlich equation exhibits better correlation to the experimental data.

3. Modified starch for metal ions wastewater treatment

The performance of dithiocarbamate-modified starch derivatives for the heavy metal ions removal is superior [19]. Three modified starch derivatives, DTC starch (DTCS), DTC enzymolysis starch (DTCES) and DTC mesoporous starch (DTCMS) were synthesized by reacting dithiocarbamate (DTC) with native starch, enzymolysis-starch (ES) and mesoporous starch (MS), respectively. The SEM images of DTCS, DTCES and DTCMS (Fig. 5) showed that they were microspheres and had different specific surface areas. The specific surface area of native starch, enzymolysis starch and mesoporous starch was 0.5302, 0.8161 and 35.8006 m2 g−1, respectively. Meanwhile, the specific surface area of DTCS, DTCES and DTCMS was 0.08302, 1.5780, 15.2163 m2 g−1, respectively. The adsorption capacity of heavy metal ions onto the modified starches followed the orders: Cu(II)> Ni(II)> Cr(VI)> Zn(II)> Pb(II). Furthermore, the Cu(II) adsorption rate for different DTC modified starch derivatives followed the sequence: DTCMS > DTCES > DTCS. The adsorption mechanism based on chelation interaction between dithiocarbamate groups and heavy metal ions through the pH effect measurement. The adsorption kinetics data well fitted to pseudo-second-order model. The adsorption capacities of heavy metal ions onto three dithiocarbamate-modified starch derivatives were unaffected even in the presence of EDTA.


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Fig. 5 SEM images of (a) as-received starch, (b) DTCS, (c) ES, (d) DTCES, (e) MS, and (g) DTCMS; enlarged SEM images of (f) MS, and (h) DTCMS. Reproduced from reference [19], copyright Elsevier 2016. Cheng et al. designed dithiocarbamate-modified glycidyl methacrylate starch (DMGS) with fast complexation of the metal ions [20]. The adsorption kinetics and equilibrium isotherm of heavy metal ions (Cu2+, Cd2+, Co2+, Zn2+, Ni2+ and Mn2+) on DMGS were investigated. The adsorption kinetics data showed a higher match between the pseudo-second-order equation and the experimental data. The metal ions adsorption rate constants for DMGS related to the substitution rates of hydrated metal ions in aqueous solutions, showing typical chemisorption. The equilibrium data fit well with Langmuir isotherm and capacities followed the sequence Cu2+ > Cd2+ > Co2+ > Zn2+ > Ni2+ > Mn2+. In such case, the ionic radius did not appear to reflect the adsorption capacities. A linear relationship can be found between the capacity and the solubility product (Ksp) of metal sulfide (Fig. 6). It indicated the adsorption mechanism based on chelating interaction caused by sulfur atoms. The dithiocarbamate-modified porous starch (DTCPS) was synthesized. It is an cheap sorbent with super adsorption ability for V(V) ions removal from aqueous solutions [21]. The DTCPS has many micropores, which favors the adsorption of V(V) ions. Adsorption results indicate that mechanism is predominately based on electrostatic attraction. The adsorption of V(V) ions on DTCPS was largely dependent on the pH value and the optimal pH was 3.0. In such solution, the decavanadate V10O26(OH)2

4− and V10O27(OH)5− are main species. They adsorbed to DTCPS following the pseudo-second-order equation and Langmuir isotherm.

10 15 20 25 30 350.10

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Fig. 6 Plots of maximum capacities qm versus the solubility product of metal sulfide Ksp. Reproduced from reference [20], copyright Elsevier 2013.

Starch-g-Poly-(N-methylacrylamide-co-acrylic acid) was synthesized by solution polymerization technique using potassium perdisulfate (K2S2O8) as the initiator at 90°C [22]. This synthetic graft copolymer as a adsorbent applied to


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remove Hg(II) from wastewater. Factors affecting the sorption process such as pH, sorbent concentration, treatment time, initial metal ion concentration and temperature were extensively investigated. The experimental data well fitted with the pseudo-second-order kinetic model and Langmuir isotherm. The adsorption mechanism based on the complexation by binding Hg(II) ions with the –COOH groups of the graft copolymer. The graft copolymer as a biodegradable material has been proved by enzymatic cleavage using a-amylase as the enzyme. A series of starch-g-poly(acrylic acid)/sodium humate (St-g-PAA/SH) hydrogels were used to adsorb Cu (II) from the aqueous solution [23]. The effects of ion strength and competitive ion on the adsorption capacity were also investigated. The St-g-PAA polymeric networks coated by 5% SH significantly improved adsorption rate and adsorption capacity and can be recycled. The adsorption data could be well described by the pseudo-second-order kinetic model and Langmuir isotherm model. The main adsorption mechanism based on complexation interaction.

Chang’ group reported the modification of porous starch by attached xanthate and carboxylate groups producing porous starch xanthate (PSX) and porous starch citrate (PSC), respectively [24]. The PSX and PSC as a adsorbent was used to remove Lead(II) in the subsequent adsorption process, respectively. The adsorption capacity was highly dependent on the carbon disulfide/starch and citric acid/starch mole ratios used during preparation. The adsorption kinetics data of lead(II) ion on PSX and PSC well fitted with the pseudo-second-order kinetic model and the Langmuir isotherm model, respectively. The maximum adsorption capacity of PSX and PSC was 109.1 and 57.6 mg g−1, respectively. The adsorption mechanism based on the chelation and electrostatic interactions between lead(II) and xanthate and carboxylate groups of porous starch, respectively. The synergetically acting new absorbent crosslinked starch-graft-polyacrylamide-co-sodium xanthate (CSAX) was synthesized by grafting copolymerization reaction of corn starch, acrylamide (AM), and sodium xanthate using epichlorohydrin (EPI) as cross-linking reagent and ceric ammonium nitrate (CAN) as initiator in aqueous solution [25]. The adsorption performance of CSAX was investigated in wastewater treatment. The adsorption capacity proved that CSAX was more effective than crosslinked starch xanthate (CSX) and much more effective than crosslinked starch-graft-polyacrylamide (CSA) for removing copper ions. The Cl- and SO4

2- have no effect on the removal of Cu (II) ions; however, the EDTA has significantly effect on the adsorption capacity of Cu (II) ions. The amine groups have higher affinities for heavy metal ions. The graft copolymer of cross-linked starch/acrylonitrile was prepared by mixing cross-linked starch and acrylonitrile and used cerium ammonium nitrate as initiator [26]. The fixed bed was used for the dynamic adsorption of the copper ions in water and the whole adsorption process can be controlled by adjusting the inlet flow rate, inlet ion concentration and the bed height. The adsorption performance was studied by investigating initial concentration of copper ions, the bed heights and the flow rates. The corresponding penetrating curve equations were obtained. Xiao et al. synthesized new cross-linked amino starch with porous structure (CPS) by reverse emulsion polymerization, using waxy corn starch after enzyme hydrolysis (ES) as raw material, N,N’-methylene-bis-acrylamide (MBAA) as cross-linking agent, and ceric ammonium nitrate as initiator [27]. The effects of the volume ratio of oil phase/aqueous phase, the content of emulsifiers, ES, and MBAA on the swelling, solubility property, chromium (VI) adsorption capacity, grafting ratio, and conversion ratio of CPS were investigated. The optimal synthesis conditions were Voil: VH2O 8: 1, emulsifier 9%, starch 2%, and MBAA 10%. The adsorption capacity reached 28.83 mg/g. The CPS also showed superior adsorption property to other heavy metal ions such as cadmium (II) and lead (II) (17.37 and 35.56 mg g−1). The novel copolymers were synthesized by reacting N, N-dimethyl acrylamide (DMA) and acryl amide (AM) with hydroxyethyl starch (HES), respectively, namely HES-g-PAM and HES-g-PDMA, respectively [28]. These grafted copolymers as adsorbents used to remove metal ions from wastewater. The different factors affecting metal ion absorption including pH, treatment time, temperature, polymer dose were investigated. The two grafted copolymers all showed high affinity to metal ions and adsorption capacity of followed the sequence Hg(II) > Cu(II) > Zn(II) > Ni(II) > Pb(II), respectively. The adsorption mechanism based on coordination interaction between metal ion and oxygen atom of acryl amide. The pH 5.5 was optimal for the removal of metal ions from aqueous solution. Shang’ group reported the synthesis of a novel amino modified starch and application for removal Cd(II) ions from aqueous solution [29]. Firstly, the graft copolymer of glycidyl methacrylate (GMA) onto cassava starch (St-g-GMA) has been synthesized via grafting polymerization and ring-opening reaction using cassava starch and glycidyl methacrylate (GMA) as raw materials. Subsequently, the St-g-GMA reacted with ethylenediamine (EDA) for 12 h at 90°C producing amino modified starch (AMS). The adsorption experiments were carried out as a function of pH, adsorption time, initial Cd(II) ions concentration and temperature. The pseudo-second-order kinetic model fits very well with the adsorption behavior of Cd(II) ions. The adsorption equilibrium data were correlated well with the Langmuir isotherm model. The adsorption was a spontaneous and endothermic process with increased entropy. The amino modified starch (AMS) adsorbent can be recycled over three cycles without changing adsorption capacity. The starch dialdehyde aminothiazole (DASAT) based on novel Schiff base was synthesized by the reaction of aminothiazole and dialdehyde starch (DAS) from periodate oxidized corn starch [30]. The adsorption of Cu2+ onto the dialdehyde aminothiazole starches (DASATs) depended on pH of the solution, the initial concentration of Cu (II) ions as well as the adsorption temperature. The adsorption isotherm well correlated with the Langmuir isotherm. The adsorption capacity increases with the increasing degree of substitute. The adsorption process of dialdehyde aminothiazole starches (DASATs) is endothermic, and higher temperature is favourable to the adsorption of Cu (II) ions. The amino starch was prepared by reacting ethylenediamine with synthesized dialdehyde starch in aqueous alkaline solution for removal


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Cu(II) and Cr(VI) from the wastewater [31]. Different factors affecting the preparation including of ethylenediamine concentration, ethylenediamine: dialdehyde starch molar ratio, pH, duration and temperature have been investigated. It found that optimization synthesis condition of amino starch was ethylenediamine:dialdehyde starch molar ratio 4:1, ethylenediamine concentration 0.6 mol/L, pH 5.5 at 35°C for 2h. The amino starch derivatives as adsorbents were studied. The adsorption kinetics data well correlated with first-order kinetics. Adsorption processes for Cu(II) and Cr(VI) on crosslinked amino starch fit a Langmuir isotherm, and adsorption for Cu(II) and Cr(VI) from aqueous solution was endothermic reactions. The adsorption capacity of Cu(II) and Cr(VI) was 29.4 mg/g and 12.5 mg/g, respectively. The amino starch as an adsorbent can be recycled. Novel magnetic nanocomposite hydrogel (m-CVP) beads were prepared by instantaneous gelation of carboxymethyl starch-g-polyvinyl imidazole (CMS-g-PVI), poly(vinyl alcohol) (PVA), and Fe3O4 mixture in boric acid solution followed by crosslinking by glutaraldehyde (GA) [32]. The resulting m-CVP beads as eco-friendly adsorbent was used to remove crystal violet (CV) and congo red (CR) dye and Pb(II), Cu(II) and Cd(II) from water. The m-CVP adsorbent showed high affinity to the heavy metals and dyes in water. The adsorption data well fitted with pseudo-second-order kinetics and proved chemical sorption as the rate determining step. The adsorption isotherms of Pb(II), Cu(II), Cd(II), CR and CV onto m-CVP beads were well described by Langmuir adsorption model at different ionic strengths, with maximum adsorption capacities of 65.00, 83.60, 53.20, 83.66 and 91.58 mg g−1, respectively. The adsorbent m-CVP can be recycled and adsorption capacity was not affected during four cycles.

Fig.7 Scheme for the synthesis route of AT-MDAS nano-composite. Reproduced from reference [33], copyright Elsevier 2015.

The novel monodisperse AT-MDAS nano-composite has been successfully synthesized without any toxic

crosslinking agent by covalently linking dialdehyde starch (DAS) and amine functionalized Fe3O4 (NH2-Fe3O4) nanoparticle, and modifying with aminothiourea functional group (AT) [33]. The synthesis route of AT-MDAS nano-composite was shown in Fig.7. The saturation magnetization of NH2-Fe3O4 is 79.13 emu g-1 and the AT-MDAS is 59.6 emu g-1. The effect of pH, contact time, initial concentration and the selective separation from multi-metal system was tested as the operation variables on the extent of adsorption. The AT-MDAS nano-composite showed a strong affinity for Hg(II) in mixed solution contain Zn(II), Cd(II), Mg(II), Ni(II) and Hg(II) as a environmentally acceptable and economical adsorbent. The removal efficiency of the obtained nano-composite reached 96% and the adsorption capacity only decreased 2.6% after 5 cycles of successive adsorption-desorption. The maximum adsorption capacity reached saturation when the initial concentration of Hg(II) increased more than 150 mg L−1. The kinetics data well fitted with pseudo-second-order model. The adsorption isotherm is well described by Langmuir model than Freundlich model at studied temperature.

Carboxymethyl sago starch-acid (CMSS-acid) hydrogel was prepared via irradiation technique to remove divalent metal ions (Pb, Cu and Cd) from their aqueous solution [34]. The CMSS-acid hydrogel was used to remove Pb (II), Cu (II) and Cd (II) ions from aqueous solution as an adsorbent. The effect factors including metal uptake, adsorption capacity, sorption kinetics and isotherm model of CMSS-acid hydrogel toward the studied metal ions were also investigated. The optimum amount of CMSS-acid hydrogel for Pb ions was 0.050 g, while for Cu and Cd ions were 0.150 g and 0.200 g with the amount of metal uptake was 94.0%, 87.8% and 84.4%, respectively. The kinetics data well fitted with pseudo-second order equation. The equilibrium isotherm study shows that the sorption between Pb(II) and CMSS-acid hydrogel fitted the Freundlich model, while the other two metal ions (Cu and Cd) fitted the Langmuir isotherm model.

The starch-humic acid composite hydrogel beads (ST-HA) was prepared via inverse suspension crosslinking method from starch (ST) and humic acid (HA) [35]. The ST-HA as novel biodegradable adsorbent was used to remove Pb(II) and methylene blue in single-component and their binary systems, respectively. The ST-HA exhibited high removal efficiency for Pb(II) and methylene blue. The adsorption of Pb(II) mainly occurred on anionic groups on HA while the adsorption of methylene blue took place on both anionic and aromatic groups, since it is an aromatic compound. The adsorption mechanism for Pb(II) and methylene blue based on coordination interaction and ion exchange and π-π interaction, respectively. The adsorption kinetics well fitted with pseudo-second order equation. The adsorption


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capacity of Pb(II) and methylene blue is 58.82 mg g−1 and 111.10 mg g−1, respectively. The adsorption process was driven by entropy increase. The isotherm behaviors of Pb(II) and methylene blue are described by Langmuir equations. The adsorbent ST-HA can be recycled use at least for five cycles.

Ionic composites (CS/AOX composites) based on cross-linked chitosan (CS) as matrix and poly(amidoxime) grafted on potato starch (AOX) as entrapped chelating resin were prepared as beads for removal of Cu2+ from wastewater [36]. The CS/AOX composites were synthesized by two strategies: (1) thorough mixing of previously prepared AOX in the CS solution followed by the bead formation; (2) thorough mixing of the potato starch-g-poly(acrylonitrile) (PS-g-PAN) copolymer in the initial CS solution, followed by bead formation, the amidoximation of the nitrile groups taking place inside the beads. The structure difference of two CS/AOX composites was confirmed by FT-IR spectroscopy and swelling ratio values. The CS/AOX composites prepared by the in situ amidoximation of PS-g-PAN showed higher sorption capacity and much faster settlement of the equilibrium sorption. The maximum adsorption was 133.15 mg Cu2+ for the CS/AOX composite beads prepared with the first strategy and 238.14 mg Cu2+ /g for the CS/AOX composite beads prepared with the second strategy, at the same AOX content. The adsorption kinetics well fitted with pseudo-second-order kinetic model. The adsorption mechanism based on chemisorption between the chelating composites and the Cu2+ ions. The CS/AOX composites as sorbents can be recycled for five sorption/desorption cycles without affecting sorption capacity of Cu2+.

The cross-linked potato di-starch phosphate polymer was prepared by using POCl3 as a cross-linking agent in basic medium [37]. The cross-linked polymeric potato starch as an adsorbent was used to remove heavy metal ions (Cu2+, Ni2+, Zn2+, and Pb2+) from aqueous solution, respectively. The removal efficiency depended on the polymeric starch content and concentration of heavy metal ion. The removal order was found to be Pb2+ (78.1%) > Cu2+ (58.5%) > Zn2+ (20.5%) > Ni2+ (17.3%) against the constant polymeric starch content at the concentrations of meal ions ~208 mg/L. The stabilization sequence of starch-metal followed Pb2+ > Cu2+ > Zn2+ > Ni2+ and confirmed by wavelength shifts. The adsorption mechanism based on coordination interaction and complexation.

The radiation grafted polyvinyl alcohol (PVA) and polyvinyl alcohol/polysaccharide (as blended materials) hydrogels were synthesized by a γ-ray irradiation technique and then characterized by FTIR and gravimetric methods [38]. The prepared PVA/ maize-starch and PVA/corn –starch hydrogels exhibited outstanding properties such as good gel fraction, high degree of swelling and excellent adsorption performances for As3+ and Mn2+, Cr3+, Fe3+, Ni2+, Cu2+ and Pb2+, and showed high sorption capacity in comparison with other adsorbents. The prepared PVA/corn starch hydrogels prefer Fe3+ with the maximum adsorption capacity of 37075 mg kg-1, while showed a low adsorption tendency toward Pb2+. The prepared PVA/corn starch hydrogels exhibited good As3+ removal performances and a maximum uptake of 22112 mg kg-1. The absorption mechanism based on the coordination interaction. These hydrogels as adsorbents can be used up to 3 times with a high desorption rate (~90%). It found that polysaccharide (maize starch, corn starch) analogues showed affinities toward the metal ions in the following order: Fe3+>Mn2+>Cu2+>Pb2+.

The influence of origin of native starch used to obtain cationic cross-linked starch (CCS) on the adsorption of Cr(VI) onto CCS has been investigated [39]. CCS granule size depended on the botanical source of starch used in the cationic modification. Potato, corn, type A and type B wheat starches have been used to obtain CCS. The adsorption behavior of Cr(VI) onto CCS was investigated by using the Langmuir, Freundlich, Dubinin-Radushkevich and Temkin models. The Langmuir, Dubinin-Radushkevich and Temkin models indicated the best fitting to the experimental data. The value of change of the Temkin adsorption energy ( △ET ) decreased and sorption capacity of CCS increased with the decrease of CCS granule size and with the increase of number of amorphous regions in CCS granules. The number of amorphous sites in CCS granule closely related to the type of catalyst used in cationization. Compared to using NaOH as catalyst, the number of amorphous sites in CCS increased by using organic base-benzyltrimethylammonium hydroxide (BTMAOH) as catalyst. The affinity of dichromate anions to CCS increased and the adsorption of Cr(VI) proceeded more spontaneously as indicated by the higher negative value of △G. The adsorption process was more exothermic as witnessed by higher negative value of △H. The CCS Cr(VI) could be regenerated by two methods: (1) boiling of CCS with adsorbed Cr(VI) in concentrated sulphuric acid; (2) incineration at 800 ◦C temperature.Water-insoluble starch phosphates (SPs) were prepared by using crosslinked starch, phosphoric acid, and urea as materials and used to remove heavy metal ions Zn(II) from aqueous solution [40]. Three samples with different contents of phosphate groups named SP1, SP2 and SP3, respectively. The adsorption capacities of Zn(II) on SPs were pH dependent and maximum value was attained around pH 4 . The maximum adsorption capacity was 2.14 mmol g−1. The adsorption kinetics well fitted with Langmuir isotherm model. The adsorbent SPs adsorbed by Zn(II) can be easily desorbed with 0.5 M HCl as a desorption solution. The adsorbent SPs can be used up to 3 times without significantly affecting adsorption capacity.

3. Conclusion

In this chapter, we summarized recent development of functionalized starch-based biomaterial as environmentally friendly adsorbents for removal of cationic and anionic dyes, heavy metal ions, mixing of dyes and metal ions from wastewater solution. The starch-based adsorbents attracted the interesting of scientific workers because starch is an abundant, inexpensive, renewable and fully biodegradable natural raw material. We systematically reviewed


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preparation, adsorption kinetics and adsorption isotherm and adsorption capacity and desorption behaviour of modified starch adsorbents. The effects of pH value of solution, initial concentration, temperature and adsorption time on the adsorption capacity were also investigated. This chapter concerns of different dyes and heavy metal ions including of SafranineT, Brilliant Cresyl Blue, acid orange, acid orange 10, acid red 18, acid black 1, acid green 25, methyl orange, methylene blue, butyl Rhodamine B, congo red, brilliant blue X-BR, and Cu(II), Ni(II), Cr(VI), Zn(II), Pb(II), Cd(II), Co(II), Zn(II), Mn(II), Hg(II) and so on. The starch-based adsorbents showed higher adsorbent capacity than native starch. Thus, starch-based biomaterial is suggested to be a promising alternative adsorbent for dyes and heavy metal ions removal from polluted water.

Acknowledgements The authors thank professor Yijiu Li, Bo Xiang, Qiangqiang Liao for careful instructions and useful discussions. The authors also thank peer workers for their contributions to the work cited. We are also grateful for financial support from the Chinese National Nature Science Foundation (21405115), and Technology project of Zhejiang Province Medical and Health Project (2015KYB254) are acknowledged.

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