Modification of porous starch for the adsorption of heavy metal ions from aqueous solution

Novel Porous Starch Granules Fabricated Using Controlled Lipase-Amylase Treatments: Application as Delivery Systems and Resistant Starches

Porous starch granules (PSGs) are promising biomaterials for the encapsulation, protection, and delivery of bioactive ingredients. In this study, a lipase treatment was first used to generate pores in native starch granules, and then α-amylase was used to enlarge these pores. Electron and fluorescence microscopy analysis showed that the lipase treatment exposed the starch molecules located below the lipid-rich regions on the starch granule surfaces, which increased the swelling of the granules in aqueous solutions. Moreover, lipase treatment caused the surrounding areas to become more loosely packed, which facilitated subsequent starch hydrolysis and the formation of large internal cavities. Fourier transform infrared spectroscopy, X-ray diffraction, and thermogravimetric analyses provided further insights, these methods showed that the short-range order, long-range order, and thermal stability of the PSGs was enhanced by the sequential lipase-amylase modification. PSGs were highly resistant to amylase digestion and had strong adsorption capacity to hydrophobic and hydrophilic substances. This study shows that a combined lipase-amylase treatment can be used to fabricate PSGs, which may have health benefits due to their low digestibility and ability to encapsulate bioactive agents. These PSGs may therefore be suitable for application in the functional food, supplement, personal care, and pharmaceutical industries.

Starch-based self-assembled three-dimensional network nanostructure materials for sustainable cascade adsorption

Toward the development of a sustainable utilization strategy for adsorption materials, a starch-based adsorbent starch-chitosan-tannic acid (St-CTS-TA) with a three-dimensional (3D) structure was fabricated in water via electrostatic and hydrogen bonding reactions between St, CTS, and TA without using toxic reducing agents or special instruments. St-CTS-TA demonstrated a high specific surface area of 37 m2/g as well as a mesoporous/macroporous distribution ranging from 30 to 80 nm, which enhanced the mass transfer of adsorbate and the exposure of catechol groups in TA. The Langmuir isotherm adsorption model revealed that the highest adsorption capacities of St-CTS-TA for Fe3+ and Co2+ were 1678.2 and 944.8 mg/g, respectively. Surprisingly, the specific surface area of St-CTS-TA increased from 37 to 87 and 42 m2/g after Fe3+ and Co2+ adsorption, respectively, and the resulting St-CTS-TA-Fe and St-CTS-TA-Co could continuously adsorb basic fuchsin (BF) and rhodamine B (RhB). The adsorption capacities of St-CTS-TA-Fe and St-CTS-TA-Co for BF/RhB were found to be 1854.79/401.19 mg/g and 2229.77/537.49 mg/g, respectively, based on the Langmuir isotherm adsorption model.

Removal of Pb (II) and Zn (II) in the mineral beneficiation wastewater by using cross-linked carboxymethyl starch-g-methacrylic acid as an effective flocculant

The cross-linked carboxymethyl starch-g-methacrylic acid (CCMS-g-MAA) was prepared by using grafting and micro-cross-linking in the one-pot preparation process. CCMS-g-MAA presented high removal capacity of Pb (II) of 57.13 mg/g at pH = 4 and high removal capacity of Zn (II) of 51.41 mg/g at pH = 5 by using a sample dosage of 0.68 g/L. Characterization results of FTIR, TG, and XRD illustrate that methacrylic acid and sodium tri-metaphosphate were successfully introduced into the structure of carboxymethyl starch. SEM characterization presented that the sample particles were amorphous aggregates with surface voids, which was favorable for the adsorption of heavy metal ions from wastewater. Adsorption isotherm results indicated that Freundlich equation could be better used to describe the adsorption process of metal ions on CCMS-g-MAA. The adsorption kinetic results indicated that the pseudo-second-order model is more suitable to describe this removal process. XPS results indicated that metal ions interacted with functional groups on the surface of flocculant, especially carboxyl groups. The removal process may be purposed that metal ions were adsorbed by porous material, and then combined with surface functional groups of the flocculant via electrostatic interaction, chelation or ion exchange. Subsequently, metal ions were separated from the wastewater with flocs precipitated in the bottom of solution via bridging and patching. The obtained results illustrated that CCMS-g-MAA was an effective material for the treatment of wastewater containing polymetallic ions besides mineral beneficiation wastewater supported by its excellent regeneration.

Expanded porous-starch matrix as an alternative to porous starch granule: Present status, challenges, and future prospects

Exposing the hydrated-soft-starch matrix of intact grain or reconstituted flour dough to a high-temperature-short-time (HTST) leads to rapid vapor generation that facilitates high-pressure build-up in its elastic matrix linked to large deformation and expansion. The expanded starch matrix at high temperatures dries up quickly by flash vaporization of water, which causes loss of its structural flexibility and imparts a porous and rigid structure of the expanded porous starch matrix (EPSM). EPSM, with abundant pores in its construction, offers adsorptive effectiveness, solubility, swelling ability, mechanical strength, and thermal stability. It can be a sustainable and easy-to-construct alternative to porous starch (PS) in food and pharmaceutical applications. This review is a comparative study of PS and EPSM on their preparation methods, structure, and physicochemical properties, finding compatibility and addressing challenges in recommending EPSM as an alternative to PS in adsorbing, dispersing, stabilizing, and delivering active ingredients in a controlled and efficient way.

Adsorption properties of corn starch modified by malt amylases and crosslinking agents: A comparison between sodium trimetaphosphate and organic acids

In order to investigate the effects of different crosslinking agents on physicochemical properties and adsorption properties of porous starch. Native corn starch was hydrolyzed by maltase and crosslinked with different crosslinking agents. Sodium trimetaphosphate crosslinked porous starch (STMP-MPS), malic acid cross-linked porous starch (MA-MPS) and citric acid cross-linked porous starch (CA-MPS) were prepared. After crosslinking, MA-MPS and CA-MPS showed a new CO stretching absorption peak at 1738 cm-1, and the crosslinking degree was much higher than that of STMP-MPS. The surface area of MA-MPS was 36 % higher than that of STMP-MPS. Compared with the average pore size of 12.43 nm of STMP-MPS, CA-MPS (14.02 nm) and MA-MPS (14.79 nm) were increased more significantly. The degradation temperature of MA-MPS and CA-MPS was increased by the introduction of ester bond, which indicates that the organic acid cross-linking strengthens the starch granules and hence more energy is required for disruption. Compared with STMP-MPS, the water absorption of MA-MPS and CA-MPS increased by 64 % and 32 %, respectively. Furthermore, the adsorption capacity of MA-MPS to essential oil was the strongest, about 4 times that of STMP-MPS. Overall, it is feasible to modify porous starch by crosslinking reaction to improve its heat resistance and adsorption properties.

Modified porous starch for enhanced properties: Synthesis, characterization and applications

Native starches have low water solubility at room temperature and poor stability, which demand modifications to overcome. Porous starch as a modified one shows enhanced adsorptive efficiency and solubility compared with its native starch. In contrast, some inherent disadvantages exist, such as weak mechanical strength and low thermal resistance. Fortunately, modified porous starches have been developed to perform well in adsorption capacity and stability. Modified porous starch can be prepared by esterification, crosslinking, oxidation and multiple modifications to the porous starch. The characterization of modified porous starch can be achieved through various analytical techniques. Modified porous starch can be utilized as highly efficient adsorbents and encapsulants for various compounds and applied in various fields. This review dealt with the progress in the preparation, structural characterization and application of modified porous starch. The objective is to provide a reference for its development, utilization, and future research directions.

Thermoplastic starch (TPS)-based composite films for wastewater treatment: synthesis and fundamental characterization

Modification of starch is a potential basic research aiming to improve its water barrier properties. The general purpose of this study is to manufacture cross-linked iodinated starch citrate (ISC) with a degree of substitution (DS) ≈ 0.1 by modifying native corn starch with citric acid in the presence of iodine as an oxidizing agent. Thermoplastic starch (TPS) was generated with urea as a plasticizer and blended with various concentrations of ISC of (2, 4, 6%) (wt/wt) to obtain (UTPS/ISC₂, UTPS/ISC₄, and UTPS/ISC₆). Nanocomposite film was formed from UTPS/ISC₂ in presence of stabilized iodinated cellulose nanocrystals UTPS/ISC₂/SICNCs via gelatinization at a temperature of 80ºC. Water solubility and water vapor release were studied amongst the water barrier features. The fabricated starch-based composite films were evaluated utilizing Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electronic Microscope analysis (SEM), surface area, and tensile measurements. The adsorption of crystal violet (CV) dye onto produced samples was examined in an aqueous solution. The findings revealed that the UTPS/ISC₂/ISCNCs has 83% crystal violet elimination effectiveness. Moreover, the adsorption isotherms were assessed and figured out to vary in the order of Langmuir > Temkin > Freundlich > Dubinin-Radushkevich.

Construction of 1, 10-phenanthroline functionalized magnetic starch as a lead (II) tagged surface imprinted biopolymer for highly selective targeting of toxic lead ions

In this research 1, 10 - phenanthroline functionalized CaFe₂O₄ - starch was employed as a magnetic ion-imprinted polymer (IIP) for highly selective targeting toxic Pb²⁺ ions from aqueous media. VSM analysis revealed that the sorbent has magnetic saturation of 10 emu g^-1 which is appropriate for magnetic separation. Moreover, TEM analysis confirmed that the adsorbent is composed of particles with a mean diameter of 10 nm. According to XPS analysis, lead coordination with phenanthroline is the main adsorption mechanism that is along with electrostatic interaction. A maximum adsorption capacity of 120 mg g^-1 was obtained within 10 min at a pH of 6 and an adsorbent dosage of 20 mg. Kinetic and isotherm studies showed that lead adsorption followed the pseudo-second-order and Freundlich models, respectively. The selectivity coefficient of Pb (II) relative to Cu(II), Co(II), Ni(II), Zn(II), Mn(II), and Cd(II) was 4.7, 14, 20, 36, 13 and 25, respectively. Moreover, the IIP represents the imprinting factor of 1.32. The sorbent showed good regeneration after five cycles of the sorption/desorption process with an efficiency of >93 %. Finally represented IIP was used for lead preconcentration from various matrices i.e., water, vegetable, and fish samples.

Batch adsorption of herbicides from aqueous solution onto diverse reusable materials and granulated activated carbon

This study reports the kinetics and isotherms of the adsorption of five herbicides, MCPA, mecoprop-P, 2,4-D, fluroxypyr and triclopyr, from aqueous solutions onto a range of raw and pyrolysed waste materials originating from an industrial setting. The raw waste materials investigated demonstrated little capability for any herbicide adsorption. Granulated activated carbon (GAC) was capable of the best removal of the herbicides, with >95% removal observed. A first order kinetic model fitted the data best for GAC adsorption of 2,4-D, while a pseudo-first order model fitted the data best for GAC adsorption of fluroxypyr and triclopyr, indicating that adsorption was via physisorption. A pseudo-second order kinetic model fitted the GAC adsorption of MCPA and mecoprop-P, which is indicative of chemisorption. The adsorption of the herbicides in all cases was best described by the Freundlich model, indicating that adsorption occurred onto heterogeneous surfaces.

Hydrogel Beads of Amidoximated Starch and Chitosan as Efficient Sorbents for Inorganic and Organic Compounds

The synthesis of hydrogel beads involving natural polymers is, nowadays, a leading research area. Among natural polymers, starch and chitosan represent two biomolecules with proof of efficiency and low economic impact in various utilization fields. Therefore, herein, the features of hydrogel beads obtained from chitosan and three sorts of starch (potato, wheat and rise starches), grafted with acrylonitrile and then amidoximated, were deeply investigated for their use as sorbents for heavy metal ions and dyes. The hydrogel beads were prepared by ionotropic gelation/covalent cross-linking of chitosan and functionalized starches. The chemical structure of the hydrogel beads was analyzed by FT-IR spectroscopy; their morphology was revealed by optical and scanning electron microscopies, while the influence of the starch functionalization strategies on the crystallinity changes was evaluated by X-ray diffraction. Molecular dynamics simulations were used to reveal the influence of the grafting reactions and grafted structure on the starch conformation in solution and their interactions with chitosan. The sorption capacity of the hydrogel beads was tested in batch experiments, as a function of the beads’ features (synthesis protocol, starch sort) and simulated polluted water, which included heavy metal ions (Cu²⁺, Co²⁺, Ni²⁺ and Zn²⁺) and small organic molecules (Direct Blue 15 and Congo red).

Native and Oxidized Starch for Adsorption of Nickel, Iron, and Manganese Ions from Water

The adsorption of heavy metal ions from surface water with ecologically safe and biodegradable biopolymers is increasingly becoming an appealing research challenge. Starch as a biopolymer is exceptionally attractive to solve this problem for its low cost and abundant availability in nature. To expel Ni2+, Fe2+/3+, and Mn2+ from water, we analyzed two native and two oxidized starches, namely potato and corn starch, as bio-adsorbers. The morphology and the surface property of the different starches were studied using SEM. To assess the effectiveness of adsorption onto the starches, we tested three realistic concentrations based on German drinking water ordinance values that were 10-fold, 100-fold, and 1000-fold the limits for Mn2+, Fe2+, and Ni2+, respectively. The concentration of the different ions was measured using the ICP-OES. Furthermore, from subsequent investigations of the adsorption isotherms, we evaluated the adsorption capacities and mechanisms. The adsorption isotherms were fitted using the Langmuir, Sips, and Dubinin–Radushkevich models, whereby Sips showed the highest correlation. Oxidized potato starch achieved viable adsorption capacities of 77 µmol Fe2+/g, 84 µmol Mn2+/g, and 118 µmol Ni2+/g. Investigating the influence of initial swelling in water on the adsorption performance, we found that especially the percentage removal with oxidized starches decreased significantly due to the formation of hydrogen bonds with water molecules at their binding sites with prior swelling.

New approach for starch dialdehyde preparation using microwave irradiation for removal of heavy metal ions from water

This work presents a new and simple approach to prepare Dialdehyde Starch (DAS) in one step under microwave irradiations and using, a mild and safer oxidizing agent, potassium iodate. Aldehyde content was evaluated to compare the synthesis results with DAS prepared using potassium periodate as an oxidizing agent for starch. To optimize the synthesis parameters of the new approach, the effect of the quantity of oxidizing agent and the effect of reaction time on the content of aldehyde in DAS were evaluated. According to the results, the optimized time was 10 min at the power of 300 W, and the number of moles of oxidizing agent was 0.014 mol per 2 g of starch. After that, DAS was used to prepare two Schiff bases by reaction with urea (DASU) and thiourea (DASTU), respectively. DAS, DASU and DASTU were characterized by FTIR, XRD, and SEM. Furthermore, DAS, DASU and DASTU were investigated for removing Cu(II), Pb(II), Hg(II), Cd(II), and Cr(III) ions from water. DAS showed the highest removal efficiency towards Pb(II) ions, whereas DASTU exhibited excellent ability for removing the Hg(II) ions. The removal efficiencies of DAS for Pb(II) ions and DASTU for Hg(II) ions are 95.25% and 89.45%, respectively from aqueous solutions containing 100 ppm of respective ions. Adsorption isotherm study suggests that adsorption follows Langmuir isotherm model, (correlation factors (R2) for Langmuir and Freundlich models for DAS/Pb are equal to 0.984 and 0.799, respectively, and for DASTU/Hg they are 0.995 and 0.813, respectively). The theoretical maximum adsorption capacity for DAS/Pb and DASTU/Hg are 245.09 and 180.83 mg/g, respectively.

Structure and Menthone Encapsulation of Corn Starch Modified by Octenyl Succinic Anhydride and Enzymatic Treatment

In order to improve the ability of starch to absorb menthone, corn starch was modified by enzymatic treatment (amyloglucosidase and α-amylase) combined with octenyl succinic anhydride (OSA) esterification. The oil absorption rate of starch modified by enzymatic treatment followed by OSA (P-OSA) reached 101.33%, whereas that of samples with reverse action sequences (OSA-P) was only 59.67%. The degree of substitution of OSA-P was also generally lower than that of P-OSA. At high OSA addition, OSA-P had a smaller specific surface area with fewer pores because octenyl succinic (OS) groups impeded the enzymatic treatment. Compared with OSA-P, the lamellar structure of P-OSA is sparser and less ordered. Owing to its pores, P-OSA was beneficial for the reaction to occur inside the granules, which was observed by Raman spectroscopy and laser confocal microscopy. At high OSA addition, the loading of P-OSA to menthone could reach 64.34 mg/g.

Dithiocarbamate modification of activated carbon for the efficient removal of Pb(ii), Cd(ii), and Cu(ii) from wastewater

Proposed adsorption mechanisms: ion exchange and chelation.

Synthesis, characterization, and flocculation performance of cationic starch nanoparticles

A series of cationic starches with different degrees of substitution were synthesized by etherification of potato starch with 3-chloro-2-hydroxypropyl trimethylammonium chloride (CTA). Cationic starch nanoparticles (CTA-StNPs) with different sizes were prepared by precipitation. Flocculation behaviors of the CTA-StNPs in simulated water sample containing kaolin were studied. The results showed that the dosage required to bring the simulated water sample containing kaolin to attain maximum transmittance at pH = 4 was significantly less than that at pH = 7. Both the size and degree of substitution of the CTA-StNPs affected their flocculation performance. The smaller the size and the higher the degree of substitution of CTA-StNPs, the better was the flocculation performance. Charge neutralization played a leading role in the flocculation process. The adsorption process of the CTA-StNPs onto kaolin could be divided into rapid adsorption, stable adsorption and equilibrium adsorption and followed pseudo second-order kinetic equation very well (R² > 0.99).

A highly efficient nanoscale tapioca starch prepared by high-speed jet for Cu2+ removal in simulated industrial effluent

BACKGROUND

Nanoscale tapioca starch (NTS) was successfully developed by high-speed jet in our previous study. In this study, the adsorption capacity of Cu²⁺ onto NTS was further discussed. The optimal adsorption conditions (pH, contact time, contact temperature, initial Cu²⁺ concentration, and adsorbent concentration), adsorption kinetics, isotherms, and thermodynamic were also evaluated.

RESULTS

The results showed that NTS exhibited excellent performance in adsorption of Cu²⁺ , with adsorption capacities of 122.31 mg g^-1 for Cu²⁺ (pH 7, 0.04 g L^-1 , 0.2 g L^-1 , 313.15 K and 10 min). The pseudo-second-order and Langmuir isotherms models could be used to explain the adsorption kinetics and adsorption equilibrium, respectively. The thermodynamic results showed that the adsorption process was spontaneous and endothermic with an increase in entropy. Cu²⁺ was adsorbed onto NTS, which was confirmed by energy dispersive spectrometry analysis.

CONCLUSION

These findings indicated that NTS might be an effective, environment-friendly and renewable bio-resource adsorbent for removing heavy metals in industrial effluent. © 2021 Society of Chemical Industry.

Probing the structure-antioxidant activity relationships of four cinnamic acids porous starch esters

For investigation of antioxidant capacity relationship, four cinnamic acids (CNAs), including cinnamic (CA), ferulic (FA), p-coumaric (p-CA) and sinapic (SA) acids, were selected to modify porous starch (PS) with different degrees of substitution by esterification, respectively. The ester linkage of CNAs modified PS was confirmed by ¹H NMR, ¹³C solid-state NMR and FT-IR. The porous structure was maintained after esterification. Three in vitro antioxidant assays were applied to measure antioxidant capacities. The order of antioxidant capacity was SA@PS > FA@PS > p-CA@PS > CA@PS, due to the presence of phenolic hydroxyl groups with hydrogen donating abilities. Besides electron-donating group on ortho or para positions the benzene ring further enhances the hydrogen donating ability and the stability of hydroxyl radical. This study not only investigated the antioxidant mechanism of CNA modified starch derivatives but probed the way for synthesis of biodegradable antioxidant materials for the food industries.

Design and characterization of PANI/starch/Fe2O3 bio composite for wastewater remediation

A new synthesized polyaniline/starch/hematite bio composite (PANI/S/Fe₂O₃ BC) has been studied as an effective material for on-site water remediation. PANI/S/Fe₂O₃ BC was developed by combining the techniques of co-precipitation and interfacial polymerization in the presence of aqueous starch solution in an acidic medium under ultrasonic irradiation. The nano-morphologies and structures of the designed PANI/S/Fe₂O₃ BC were evaluated by various techniques relative to PANI and Fe₂O₃ nanoparticles. In single and multiple systems, PANI/S/Fe₂O₃ BC was evaluated as a possible adsorbent for different heavy metals, including As³⁺, Zn²⁺, and Co²⁺, relative to PANI and Fe₂O₃ nanoparticles. In terms of pH value, operating temperature, initial heavy metal concentration, contact time, adsorbent dose and competitive ions in the solutions, the adsorption process was optimized. For 92% overall adsorption of Co²⁺ and 100% overall adsorption of both As³⁺ and Zn²⁺, the adsorption equilibrium was achieved within 60 and 120 min, respectively. In addition, adsorption thermodynamic analysis shows that the As³⁺ ions adsorption process was not random and the pseudo-second-order fitted with experimental results. Moreover, PANI/S/Fe₂O₃ BC was evaluated as an antibacterial agent against Gram-negative bacteria (Salmonella typhimurium) and Gram-positive bacteria (S. aureus, Methicillin-Resistant Staphylococcus, Aureus Clinical isolate and Bacillus subtilis). The reported performances indicated that the PANI/S/Fe₂O₃ BC is a potent candidate for industrial water bioremediation.

Xanthate-modified alginates for the removal of Pb(II) and Ni(II) from aqueous solutions: A brief analysis of alginate xanthation

Mining is the most common activity that introduces heavy metal ions into aquatic ecosystems, especially in low income-developing nations where governments are implementing stricter regulations for industrial wastewater. In this context, this work is focused on the application of xanthate-modified alginates for the removal of Pb(II) and Ni(II) from aqueous solutions. In order to confirm the presence of xanthate groups alongside alginate chains, characterization by second-derivative FT-IR was carried out and significance evidence attributed to xanthate groups was found at around 1062-1079 cm^-1, 829-845 cm^-1 and 620-602 cm^-1. In addition to this, thermogravimetric analysis and differential scanning calorimetry were employed to explore thermal properties of modified alginates. According to these results, enthalpy changes (∆H) characteristic of dehydration and collapse of biopolymeric structure were estimated as +11.41 J/g and -6.83 J/g, respectively. Furthermore, the presence of S element was confirmed by EDS mapping technique, whereas FESEM image showed a cracked and homogeneous surface distribution. On the other hand, the effect of important parameters such as pH, dosage, initial concentration as well as Langmuir and Freundlich isotherm were deeply discussed. Finally, rheological measurements were performed aiming to investigate the gel-like viscoelastic features associated to nickel xanthate compound.

Recent trends in the application of modified starch in the adsorption of heavy metals from water: A review

The presence of polyfunctional ligands on the bio-macromolecules acts as an efficient adsorbent for heavy metal ions. Starch is one of the most abundant, easily available and cheap biopolymer of plant origin. However, native starch exhibits significantly low adsorption capacity due to the absence of some essential functional groups like carboxyl, amino or ester groups and is thus modified using various reaction routes like grafting, cross-linking, esterification, oxidation and irradiation for addition of functional groups to increase its adsorption capacity. The present review provides a comprehensive discussion on the above mentioned modification schemes of starch over the last 10-15 years highlighting their preparation methods, physico-chemical characteristics along with their adsorption capacities and mechanisms of heavy metal ions from water.

Xanthation of alginate for heavy metal ions removal. Characterization of xanthate-modified alginates and its metal derivatives

Xanthates are widely used in mining industry as collectors for its high affinity towards metal sulfides and precious metal ores. The possibility of using alginate for xanthation has not been explored yet despite the feasibility by the presence of hydroxyl groups alongside the polymeric chains. Therefore, this work aims to evaluate the alginate as a matrix for xanthation and its application on heavy metal ions removal. In order to obtain green materials, important pararmeter were explored such as the effect of reaction time (4-12 h), type of base (NaOH/KOH) and amount of carbon disulfide (2-10%v/v). Xanthated alginates were analyzed by NMR techniques and evidence of β-elimination was detected at 5.45 ppm. Furthermore, the presence of S element was confirmed by EDS mapping technique, while XRD showed a semi-crystalline structure. On the other hand, the chemical shifts of δ(C=S) and ν(C=S) bands were found around 863-805 cm^-1 and 662-602 cm^-1 respectively. Also, a shoulder at 182 ppm is appreciated by NMR in solid state attributed to CS group. According to FESEM analyses, morphology of xanthated alginates is affected by interaction with heavy metal ions. Finally, suitable materials for the removal of heavy metal ions were established at optimum pH values.

Three-dimensional nanoporous starch-based material for fast and highly efficient removal of heavy metal ions from wastewater

The development of advanced adsorbents with fast adsorption rate, simple preparation, low cost, and high adsorption capacity is one of the most important topics for water purification. Herein, a novel and pollution-free adsorbent, three-dimensional nanoporous starch-based nanomaterial (3D-PSN), was prepared via sacrifice template method and functionalized for the first time in this work. Relevant characterization was performed through XRD, SEM, TGA, zeta potential analysis, FTIR, and XPS to confirm the formation of nanomaterials. Owing to its unique three-dimensional network nanostructure and abundant active sites, this adsorbent displayed outstanding adsorption properties for heavy metal ions removal, as high as 532.28 mg/g for Cd (II), 381.47 mg/g for Hg(II), 354.15 mg/g for Cu(II), 238.39 mg/g for Pb(II), completed within 30 min. In this process, the pseudo-second-order kinetic model appeared more consistent with the adsorption kinetic data, and the adsorption behavior complied with the Langmuir adsorption model. The adsorption mechanism mainly replied on the ion-exchange reaction, as well as chemical complexation formation. This adsorbent has remarkable recyclability, exhibiting strong application prospects for water purification and environmental remediation.

Crosslinked Carboxymethyl Sago Starch/Citric Acid Hydrogel for Sorption of Pb2+, Cu2+, Ni2+ and Zn2+ from Aqueous Solution

In the present study, CMSS (carboxymethyl sago starch)-based hydrogel was synthesized by crosslinking with citric acid via esterification and then applied as a metal sorbent to overcome excessive heavy metal pollution. The CMSS/CA (carboxymethyl sago starch/citric acid) hydrogel was characterized by Fourier Transform Infrared (FT-IR), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and X-ray diffraction (XRD). The absorption band at 1726 cm⁻¹ was observed in the FT-IR spectrum of CMSS/CA hydrogel and indicated ester bonds formed. Further findings show that the cross-linkages in the CMSS/CA hydrogel increased the thermal stability of CMSS and various sizes of pores were also shown in the SEM micrograph. Conversely, the removal of heavy metals was analyzed using Inductively Coupled Plasma-Optic Emission Spectra (ICP-OES). The effects of the pH of the metal solution, contact time, initial concentration of the metal ions and temperature on the sorption capacity were investigated. Under optimum condition, the sorption capacity of Pb²⁺, Cu²⁺, Ni²⁺ and Zn²⁺ onto CMSS/CA hydrogel were 64.48, 36.56, 16.21, 18.45 mg/g, respectively. The experiments demonstrated that CMSS/CA hydrogel has high selectivity towards Pb²⁺ in both non-competitive and competitive conditions. In conclusion, the CMSS/CA hydrogel as a natural based heavy metal sorption material exhibited a promising performance, especially in the sorption of Pb²⁺ for wastewater treatment.

129Xe NMR: A powerful tool for studying the adsorption mechanism between mesoporous corn starch and palladium

For the first time, ¹²⁹Xe NMR measurements are utilized to explore adsorption mechanism between porous structures of mesoporous corn starch and Palladium. Dithiocarbamate modified mesoporous corn starch (donated as DTC MS) was synthesized and applied for adsorption of Pd (II) ion successfully. The structural characterization of DTC MS was carried out by FT-IR, ¹³C solid-state NMR and XRD, respectively. To study the adsorption mechanism, variable temperature ¹²⁹Xe NMR was measured on samples of DTC MS and Pd adsorbed in DTC mesoporous starch (donated as Pd-DTC MS), respectively. It was found that Pd ions were mainly located inside pores and channels instead of the surface of mesoporous starch. The results not only demonstrate that ¹²⁹Xe NMR spectroscopy is a powerful tool to assess the porous structure of MS, but also pave the way for investigating the interaction between functional molecules and porous starch.

Production and Properties of Starch Citrates-Current Research

Starch modification by chemical reaction is widely used to improve the properties of native starch. Modified by citric acid, starch is characterized by specific properties resulting from the presence of citrate residues and as a result of cross-linking starch. The chemicals used for preparing starch citrates are safe for human health and the natural environment compared to the harsh chemicals used for conventional modifications. Starch citrates are traditionally produced by heating starch-citric acid mixtures in semi-dry conditions or by a heat moisture treatment. The conditions of the modification process (roasting temperature, heating time, citric acid dose) and the botanic source or genotype of starch determine the degree of substitution and the properties of the obtained preparations. Changes of starch properties occurring during esterification lead to reduced relative crystallinity, resulting in a decrease in the affinity for water, the gelatinization parameters, and the viscosity of starch citrate. However, one of the most important outcome of the modification is the formation of resistant starch (RS), which has increased resistance to the action of amylolytic enzymes. Currently, new methods for producing starch citrates with improved functional and rheological properties while maintaining the highest possible content of resistant starch are being sought. The article presents an overview of recent studies on the production, properties. And applicability of starch citrates with special attention paid to their role as preparations of resistant starch (RS). The use of citric acid for modification of starch is better for the technology process, while using cross-linking is better than simply using esterification.

Modification methods toward the production of porous starch: a review

Starch is a complex carbohydrate formed by the repeating units of glucose structure connected by the alpha-glycosidic linkages. Starch is classified according to their derivatives such as cereals, legumes, tubers, palms, fruits, and stems. For decades, native starch has been widely utilized in various applications such as a thickener, stabilizer, binder, and coating agent. However, starches need to be modified to enhance their properties and to make them more functional in a wide range of applications. Porous starch is a modified starch product which has attracted interest of late. It consists of abundant pores that are distributed on the granule surface without compromising the integrity of its granular structure. Porous starch can be produced either by enzymatic, chemical, and physical methods or a combination thereof. The type of starch and selection of the modification method highly influence the formation of pore structure. By carefully choosing a suitable starch and modification method, the desired morphology of porous starch can be produced and applied accordingly for its intended application. Innovations and technologies related to starch modification methods have evolved over the years in terms of the structure, properties and modification effects of different starch varieties. Therefore, this article reviews recent modification methods in developing porous starch from various origins.

Synthesis, adsorption and molecular simulation study of methylamine-modified hyper-cross-linked resins for efficient removal of citric acid from aqueous solution

A series of methylamine-modified hyper-cross-linked resins were fabricated from chloromethylated polystrene-co-divinylbenzene by two continuous reactions (Friedel-Crafts alkylation and amination). The BET surface area and pore volume of the as-prepared resins took a positive correlation to the reaction time and temperature during alkylation reaction while lessened during amination process. When running batch adsorption experiments for adsorption of citric acid, the methylamine-modified resin named HM-65-2 showed higher adsorption capacity of 136.3 mg/g and selectivity of 6.98 (citric/glucose) than the precursor resins. The pseudo-second-order rate model fitted better than the pseudo-first-order model, implying the adsorption sites distributed on the resins surface tended to be heterogeneous. Subsequently, the interactions between citric acid and the resin were investigated by means of molecular simulation. Simulation result showed the addition of nitrogen-containing groups significantly enhanced the adsorption performance of citric acid. Lastly, the dynamic column experiments were performed to obtain the suitable operating conditions for the citric acid adsorption.

The effects of carbon disulfide driven functionalization on graphene oxide for enhanced Pb(II) adsorption: Investigation of adsorption mechanism

The surface properties of graphene oxide (GO) have been identified as the key effects on the adsorption of Pb(II) from aqueous solutions in this study. This study reveals the effect of the surface reactivity of GO via Carbon Disulfide (CS₂) functionalization for Pb(II) adsorption. After successfully preparing CS₂ functionalized GO (GOCS), the specific techniques were applied to investigate Pb(II) adsorption onto GOCS. Results indicated that the new sulfur-containing functional groups incorporated onto GOCS significantly enhanced Pb(II) adsorption capacity on GOCS than that of GO, achieving an improvement of 31% in maximum adsorption capacity increasing from 292.8 to 383.4 mg g^-1. The equilibrium adsorption capacity for GOCS was 280.2 mg g^-1 having an improvement of 83.2% over that of 152.97 mg g^-1 for GO at the same initial concentration of 150 mg L^-1 under the optimal pH of 5.7. Moreover, the results of adsorption experiments showed an excellent fit to the Langmuir and Pseudo-Second-Order models indicating the monolayer and chemical adsorption, respectively. The mechanism for Pb(II) adsorption on GOCS was proposed as the coordination, electrostatic interactions, cation-pi interactions, and Lewis acid-base interactions. The regeneration study showed that GOCS had an appreciable reusability for Pb(II) adsorption with the adsorption capacity of 208.92 mg g^-1 after five regeneration cycles. In summary, GOCS has been proved to be a novel, useful, and potentially economic adsorbent for the high-efficiency removal of Pb(II) from aqueous solutions.

Potential of siltstone and its composites with biochar and magnetite nanoparticles for the removal of cadmium from contaminated aqueous solutions: Batch and column scale studies

The present study is the first attempt to evaluate the pilot and batch scale adsorption potential of siltstone (SS) and its nanocomposites with biochar (EDB/SS), magnetite nanoparticles (MNPs/SS) and MNPs/EDB/SS for Cd removal from contaminated water. The SS, EDB/SS, MNPs/SS and MNPs/EDB/SS were characterized with FTIR, XRD, BET, SEM, TEM, TGA and point of zero charge (PZC). The effects of adsorbent dosage, contact time, initial Cd concentration, pH and presence of competing ions were evaluated on the Cd removal and its adsorption. The order for Cd removal was: MNPs/EDB/SS > MNPs/SS > EDB/SS > SS (95.86-99.72% > 93.10-98.5% > 89.66.98-98.40% > 74.90-90%). Column scale experiments yielded maximum retention (95%) of Cd even after 2 h of injection at 100 mg Cd/L. The exhausted SS, EDB/SS, MNPs/SS and MNPs/EDB/SS were reused without losing significant adsorption potential. Similarly, maximum Cd adsorption (117.38 mg/g) was obtained with MNPs/EDB/SS at dose 1.0 g/L. The results revealed that coexisting cations reduced the Cd removal due to competition with Cd ions. The experimental results were better explained with Freundlich isotherm model and pseudo 2nd order kinetic models. The results revealed that SS and its composites can be used efficiently for the removal of Cd from contaminated water.

Enhanced and Selective Adsorption of Zn(II), Pb(II), Cd(II), and Hg(II) Ions by a Dumbbell- and Flower-Shaped Potato Starch Phosphate Polymer: A Combined Experimental and DFT Calculation Study

Microwave-ultrasound-assisted facile synthesis of a dumbbell- and flower-shaped potato starch phosphate (PSP) polymer, hereafter PSP, was carried out by cross-linking the hydroxyl groups of native potato starch (NPS) using phosphoryl chloride as a cross-linking agent. Structural and morphological analysis manifested the successful formation of the dumbbell- and flower-shaped PSP biosorbent with enhanced specific surface area and thermal stability. Viscoelastic behavior of NPS and PSP suggested increased rigidity in PSP, which helped the material to store more deformation energy in an elastic manner. The synthesized PSP biosorbent material was successfully tested for efficient and quick uptake of Zn(II), Pb(II), Cd(II), and Hg(II) ions from aqueous medium under competitive and noncompetitive batch conditions with q m values of 130.54, 106.25, 91.84, and 51.38 mg g-1, respectively. The adsorption selectivity was in consonance with Pearson's hard and soft acids and bases (HSAB) theory in addition to their order of hydrated radius. Adsorption of Zn(II), Pb(II), Cd(II), and Hg(II) followed a second-order kinetics and the adsorption data fitted well with the Langmuir isotherm model. Quantum computations using density functional theory (DFT) further supported the experimental adsorption selectivity, Zn(II) > Pb(II) > Cd(II) > Hg(II), in terms of metal-oxygen binding energy measurements. What was more intriguing about PSP was its reusability over multiple adsorption cycles by treating the metal(II)-complexed PSP with 0.1 M HCl without any appreciable loss of its adsorption capacity.

Nanoadsorbents preparing from oligoethylene glycol dendron and citric acid: Enhanced adsorption effect for the removal of heavy metal ions

Poly(methacrylate oligoethylene glycol dendron-co-citric acid) (PGCA) that is based on citric acid and oligoethylene glycol (OEG) dendrons is utilized as a nanomaterial for the removal of heavy metal ions from aqueous solution. PGCA shows excellent solubility in aqueous solution and realizes satisfactory removal efficacy for Pb²⁺ ions; the removal rate exceeds 95 %. In addition, PGCA can be utilized in Chinese herbal decoctions; the removal rate of Pb²⁺ ions in the ligusticum wallichii decoction exceeds 90 %, meanwhile the concentration of the active ingredient, namely, ferulic acid, is maintained. In this nanoadsorbent, citric acid provides the active site for the chelation of heavy metal ions, and OEG dendron serves as a protective layer that reduces the opportunity for carboxyl groups to be occupied by other ingredients. In summary, nanomaterial PGCA is designed and synthesized successfully that can be applied as a nanoadsorbent for the removal of Pb²⁺ ions from aqueous solution, especially in Chinese herbal decoctions that have acidic compounds as active ingredients.

Double encapsulation of fucoxanthin using porous starch through sequential coating modification with maltodextrin and gum Arabic

This study aims to assess the effect of gum Arabic (GA), maltodextrin (MD), or their combination as a coating agent at different ratios (1/3, 1/5, and 1/7 w/w) to encapsulate fucoxanthin. For this purpose, fucoxanthin was initially extracted and purified from Sargassum angustifolium brown seaweed and then loaded into porous starch (PS). The fucoxanthin-loaded PS samples were further contributed in another encapsulation process using the coating materials. All samples were evaluated in terms of encapsulation efficiency, Fourier-transform infrared (FTIR) spectroscopy and stability under light, dark and low or high temperature (4 and 50°C) exposure over a certain time period. Purification of fucoxanthin was verified through HPLC and NMR spectroscopy. It was shown that the subsequent coating with MD + GA (1/7 w/w) caused an enhanced encapsulation of fucoxanthin-loaded PS, reaching to about 96%. In addition, the stability of fucoxanthin-loaded PS was greatly influenced by light and high temperature exposure and decreased from 85% to 58% using the GA-coated material (1/3 w/w). First-order kinetic model was found to be fitted well on thermal degradation data of fucoxanthin. Interestingly, the mixture of MD + GA (1/7 w/w) exhibited the highest fucoxanthin prevention at the end of the storage period. Conclusively, the findings of this study can provide simple and facile protocol for food chemists in protecting the food ingredients using encapsulation process.

Construction of octenyl succinic anhydride modified porous starch for improving bioaccessibility of β-carotene in emulsions

Modified porous starch (PS), by introducing octenyl succinic anhydride (OSA) moieties, was synthesized successfully, which was applied as an emulsion of β-carotene for the first time. The pores and channels within porous starch provided more possibilities for OSA to modify starch. The ester linkage of OSA modified PS with different degrees of substitution (DS) were confirmed by both ¹³C solid-state NMR and Fourier transform-infrared spectroscopy (FT-IR). The hydrophobic octenyl succinic and hydrophilic hydroxyl groups of OSA modified PS showed the good emulsifying capability, which could be utilized to prepare β-carotene emulsions. And the bioaccessibility of β-carotene was also enhanced with increasing DS of OSA modified starch. This study not only paves a new way using porous starches for modification of starch, but also offers an attractive alternative for obtaining emulsion-based delivery systems for bioactive components.

The synthesis and application of OSA modified porous starch.

Biosorption of Pb(II) ions from aqueous solution using alginates extracted from Djiboutian seaweeds and deposited on silica particles

High-molecular alginates were extracted from Djiboutian brown seaweeds, Sargassum sp. (S) and Turbinaria (T) and isolated as sodium salts in 31.0 and 42.7% yield by weight. 1H NMR analysis of the uronic acid block-structure indicates mannuronic/guluronic M/G ratios of 0.49 and 3.0 for the alginates extracts, respectively. The resulting alginates were deposited onto native Aerosil 200 silica, amine-functionalized and carboxyl-functionalized silica particles to enhance the mechanical strength providing Alg.(T/S)+SiO2) Alg.(T/S)+SiO2NH2) and Alg.(T)+SiO2CO2H) composites. Taking Pb(II) as examples for toxic heavy metal ions, the effects of the pH, adsorption kinetics, and isotherms have been studied systematically. The best uptake achieved was 585 mg Pb2+ ion/g using Alg.S+SiO2NH2. Furthermore, the Pb(II) ions were successfully desorbed in several cycles from Alg.T+SiO2 using 0.5 M hydrochloric acid. Therefore, Alg.T+SiO2 may be considered as a low-cost biosorbent that quickly adsorbs and easily desorbs analyte lead ions. A comparison of the adsorption capacity of our biopolymer-coated particles with that of other adsorbents reported in the literature reveals that our materials are among the best performing for the adsorption of Pb(II).