Anionic Contaminants Research Articles

A novel organic-inorganic hybrid hollow polymer capsule with rich amino/imino groups for anionic contaminant removal in wastewater: Synthesis, performance and mechanism

Herein, we developed a new organic-inorganic hybrid polymer adsorbent, termed PECP, by one-step precipitation polycondensation between polyethyene polyamine and hexachlorocyclotriphosphazene. The morphology and microstructure of PECP were investigated by FTIR, SEM, TEM, XPS, XRD and N2 adsorption. Results show PECP owned a hollow capsule structure and lots of amino/imino groups. The adsorption capacity of PECP for anionic dye methyl orange (MO) was up to 1031.9 mg g-1. The adsorption process was very fast. After five cycles, the adsorption capacity of PECP for MO still remained at 89 % of the initial adsorption capacity. Meanwhile, PECP delivered a high adsorption capacity for other anionic contaminants like acid chrome blue K (1003.5 mg g-1), congo red (1152.2 mg g-1) and diclofenac sodium (914.2 mg g-1). In the binary systems contaminated with double dyes, the separation factors of MO for methylene blue, Rhodamine B and crystal violet were up to 450.8, 55.4 and 355.9, respectively. The experimental data unveiled that the MO removal by PECP was very consistent with the pseudo-second-order kinetic model and the Langmuir isotherm model. The removal process was spontaneous and endothermic. FTIR spectroscopy and XPS analysis confirmed the role of electrostatic force and hydrogen bond on the adsorption of MO on PECP.

Preloading Long-Chain Quaternary Ammonium Groups to Synthesize a High-Efficient Anion-Exchange Resin for Eliminating Bacterial Contaminants in Drinking Water.

Bacterial contamination in drinking water is a global health concern, necessitating the development of highly efficient treatment techniques. Anion-exchange resins (AERs) have long been employed for removing anionic contaminants from drinking water, but their performance for bacterial contamination is poor. Here, we develop a novel AER (AER6-1) with exceptional bactericidal effects and ultrafast adsorption rates of extracellular DNA (eDNA) (2.2- and 11.5-fold compared to other AERs) achieved through preloading quaternary ammonium groups (QAGs) with hexyl chain (-C6-N+-) on the resin exterior and successively grafting QAGs with a methyl chain (-C1-N+-) inside a resin pore. The AER6-1 outperforms other commercial AERs and ultraviolet disinfection, exhibiting superior elimination of total bacteria, potential pathogens (Escherichia coli and Pseudomonas aeruginosa), eDNA, and antibiotic resistance genes (mexF, mexB, and bacA) in actual drinking water, while maintaining a comparable anion exchange capacity with other commercial AERs. Theoretical calculations of density functional theory and xDLVO combined with XPS elucidate the crucial roles of hydrogen bonding and hydrophobic force provided by the resin skeleton and -C6-N+- in cleaving the bacterial cell membrane and increasing the adsorption kinetics on eDNA. This study broadens the scope of AERs and highlights an effective way of simultaneously removing bacterial and anionic contaminants from drinking water.

Aluminum-Crosslinked Nanocellulose Scaffolds for Fluoride Removal.

Anionic carboxylated cellulose nanofibers (CNF) are effective media to remove cationic contaminants from water. In this study, sustainable cationic CNF-based adsorbents capable of removing anionic contaminants were demonstrated using a simple approach. Specifically, the zero-waste nitro-oxidization process was used to produce carboxylated CNF (NOCNF), which was subsequently converted into a cationic scaffold by crosslinking with aluminum ions. The system, termed Al-CNF, is found to be effective for the removal of fluoride ions from water. Using the Langmuir isotherm model, the fluoride adsorption study indicates that Al-CNF has a maximum adsorption capacity of 43.3 mg/g, which is significantly higher than that of alumina-based adsorbents such as activated alumina (16.3 mg/g). The selectivity of fluoride adsorption in the presence of other anionic species (nitrate or sulfate) by Al-CNF at different pH values was also evaluated. The results indicate that Al-CNF can maintain a relatively high selectivity towards the adsorption of fluoride. Finally, the sequential applicability of using spent Al-CNF after the fluoride adsorption to further remove cationic contaminant such as Basic Red 2 dye was demonstrated. The low cost and relatively high adsorption capacity of Al-CNF make it suitable for practical applications in fluoride removal from water.

Record High Iodate Anion Capture by a Redox-Active Cationic Polymer Network.

As a critical radioactive anionic contaminant, traditional adsorbents primarily remove iodate (IO3 -) through ion exchange or hard acid-hard base interactions, but suffer from limited affinity and capacity. Herein, employing the synergistic effect of ion exchange and redox, we successfully synthesized a redox-active cationic polymer network (SCU-CPN-6, [C9H10O2N5 ⋅ Cl]n) by merging guanidino groups with ion-exchange capability and phenolic groups with redox ability via a Schiff base reaction. SCU-CPN-6 exhibits a groundbreaking adsorption capacity of 896 mg/g for IO3 -. The inferior adsorption capacities of polymeric networks containing only redox (~0 mg/g) or ion exchange (232 mg/g) fragments underscore the synergistic "1+1>2" effect of the two mechanisms. Besides, SCU-CPN-6 shows excellent uptake selectivity for IO3 - in the presence of high concentrations of SO4 2-, Cl-, and NO3 -. Meanwhile, a high distribution coefficient indicates its exemplary deep-removal performance for low IO3 - concentration. The synergic strategy not only presents a breakthrough solution for the efficient removal of IO3 - but also establishes a promising avenue for the design of advanced adsorbents for diverse applications.

Record High Iodate Anion Capture by a Redox‐Active Cationic Polymer Network

AbstractAs a critical radioactive anionic contaminant, traditional adsorbents primarily remove iodate (IO3−) through ion exchange or hard acid‐hard base interactions, but suffer from limited affinity and capacity. Herein, employing the synergistic effect of ion exchange and redox, we successfully synthesized a redox‐active cationic polymer network (SCU‐CPN‐6, [C9H10O2N5 ⋅ Cl]n) by merging guanidino groups with ion‐exchange capability and phenolic groups with redox ability via a Schiff base reaction. SCU‐CPN‐6 exhibits a groundbreaking adsorption capacity of 896 mg/g for IO3−. The inferior adsorption capacities of polymeric networks containing only redox (~0 mg/g) or ion exchange (232 mg/g) fragments underscore the synergistic “1+1>2” effect of the two mechanisms. Besides, SCU‐CPN‐6 shows excellent uptake selectivity for IO3− in the presence of high concentrations of SO42−, Cl−, and NO3−. Meanwhile, a high distribution coefficient indicates its exemplary deep‐removal performance for low IO3− concentration. The synergic strategy not only presents a breakthrough solution for the efficient removal of IO3− but also establishes a promising avenue for the design of advanced adsorbents for diverse applications.

Polyvinylamine as a wet-end additive: Effects of pH and anionic contamination

The effects of polyvinylamine (PVAm) on papermaking process attributes and handsheet quality were evaluated for a recycled copy paper furnish in a near neutral-to-alkaline pH range. The degree of protonation of primary amine groups, such as those in PVAm, is known to decrease with increasing pH. Streaming potential tests surprisingly showed that a high treatment level of PVAm on the copy paper furnish was able to maintain a net positive zeta potential up to pH of about 11, whereas charge demand titrations indicated that PVAm maintained its positive charge character up to about pH 10. Favorable dewatering was observed when the furnish had been pretreated with 1% polyacrylate dispersant prior to treatment with PVAm at the 0.5% level, and the mass of filtrate increased slightly with increasing pH. First-pass retention tests showed poor retention efficiency in systems where the furnish had been treated with the dispersant, then PVAm, in an unfavorable pH range of about 9 to 9.5. Higher retention was achieved both at pH 8.2 and at pH 10 or higher. Handsheets showed superior breaking length results in the systems where the stock had been pretreated with the dispersant, though strength decreased strongly with increasing pH. Differences in filler content, as indicated by ash analysis, were not large enough to account for the observed strength differences. Formation uniformity was substantially increased by the pretreatment with dispersant, even in the presence of PVAm and throughout the studied pH range.

Measurement of total amine site concentrations on bacterial cell surfaces using selective site-blocking and potentiometric titrations

Bacterial cell surface amine binding sites can form strong complexes with both toxic metal cations and anionic contaminants, thereby affecting the behavior of these contaminants in both natural and engineered systems. In this study, a novel approach was developed to measure the concentration of total amine sites on bacterial cell surfaces by combining selective site-blocking, potentiometric titrations and surface complexation modeling. Our controls show that the amine blocker sulfo-N-hydroxysulfosuccinimide acetate (SNHS) selectively reacts with primary and secondary amine sites but does not react with other binding sites on the bacterial cell surface. Amine site concentrations on bacterial cell surfaces, therefore, can be measured as the difference between the total site concentrations of un-blocked and SNHS-blocked bacterial samples. We measured amine site concentrations on Bacillus subtilis and Pseudomonas putida of 52 ± 5 and 78 ± 6 μmol/g, respectively, which account for 24% and 32% of the total binding sites on each bacterial surface. Our results suggest that amine sites can be present in relatively high concentrations on bacterial surfaces, and further studies that are focused on the role of cell surface amine sites on the transport and bioavailability of toxic metal cations and anionic contaminants are crucial.

Optimization of Photoelectrochemical Response on TiO2 Nanotube Arrays Treated by H3PO4 and Mechanism Analysis of the Slowing Down Effect during Preparation.

The process control of anodization has been a hot topic for a long time. In this study, the addition of phosphoric acid to the traditional electrolyte changed the ion distribution on the reaction interface and the composition of the anion contamination layer so as to achieve the slowing down effect on anodization, the mechanism and theoretical model of which are also given in this paper. TiO2 is a common material in photoelectrocatalysis, but there are few studies on the photoelectrochemical performance of TiO2 nanotube arrays. The stability and rapidity of the photoelectrochemical response of TiO2 nanotube arrays prepared in phosphoric acid containing an electrolyte were effectively optimized in this study.

Effects of carboxymethyl starch as a papermaking additive

Carboxymethyl starch (CMS) is a bio-based, anionic polymer that has potential as part of a dry-strength additive program for papermaking. Due to its negative charge, its effects can be expected to depend on its interactions with various cationic agents. In this work, the effects of CMS were observed following its sequential addition after one of three selected cationic strength agents at different dosage levels. In selected tests, the furnish was pretreated at the 1% level by a dispersant, sodium polyacrylate, which might represent a high level of anionic contaminants in a paper mill system. Laboratory tests were conducted to show the effects on dewatering, fine-particle retention, and flocculation. These tests were supplemented with measurements of charge demand, zeta potential, and handsheet properties. Sequential addition of cationic glyoxylated acrylamide copolymers (gPAM) and CMS were found to strongly promote dewatering. Two gPAM products and a poly(vinylamine) product in sequential addition with CMS were very effective for promoting fine-particle retention. These same sequential treatments of the stock contributed to moderate fiber flocculation, though severe flocculation was caused by further treatment of the furnish with colloidal silica. Handsheet strength results were mixed. In the default recycled copy paper furnish, the average breaking length for the sheets made with cationic additives followed by CMS was not greatly different from the blank condition. Superior strength resulted when the default furnish was treated with a dispersant alone. When the dispersant-contaminated furnish was treated with the same combinations of cationic additives and CMS, the strength returned to the baseline achieved in the absence of the dispersant. The results were discussed in terms of the charged character of the different additives and their interactions not only with the fiber surfaces but also with each other.

2D/3D MXene/NiFeMn-layered double hydroxide decorated gelatin for removal of Cr(VI) and Congo red: Performance and mechanism

The discharge of toxic heavy metals and dyes into water is considered a principal reason for ecosystem deterioration. Therefore, the development of versatile adsorbents that can treat this threat is an urgent issue. On this basis, we designed and characterized a novel Ti3C2TX/NiFeMn-LDH@Gel composite to aptly remove hazardous hexavalent chromium ions Cr(VI) and organic Congo red dye (CR). Ti3C2TX/NiFeMn-LDH@Gel composite was facilely synthesized by introducing NiFeMn-layered double hydroxide and Ti3C2TX MXene into gelatin via a cross-linking reaction. Experimental data revealed that raising Ti3C2TX amount to 10 % in the matrix has dramatically promoted the adsorption aptitude of Ti3C2TX/NiFeMn-LDH@Gel towards Cr(VI) and CR. Freundlich model best described Cr(VI) and CR adsorption, with qmax reaching 423.73 mg/g, and 588.24 mg/g, respectively. Additionally, the adsorption kinetics of Cr(VI) and CR were fitted to the pseudo-second order model accompanied with spontaneity, randomness, and endothermic behavior. In addition, stability, and selectivity of Ti3C2TX/NiFeMn-LDH@Gel were investigated. Effect of ionic strength and interfering ions were explored as well. Besides, the recyclability test inferred superb adsorption capacities towards Cr(VI) and CR till the 5th cycle, revealing the potentiality of Ti3C2TX/NiFeMn-LDH@Gel towards anionic contaminants removal.

SPECTRAL AND PHOTOPHYSICAL CHARACTERISTICS OF ASYMMETRIC POLYMETHINE DYES IN POLYURETHANE MATRICES

Here the composite polymer sorbent hydrogels were synthesized by in situ technique via free radical polymerization of acrylamide (AAm), 2-hydroxyethyl methacrylate (2HEMA) and N,N’-methylene-bis(acrylamide) crosslinker mixture in the presence of as-prepared dispersion of nickel-aluminum layered double hydroxide (NiAl-LDH). A content of active NiAl-LDH filler in the polymer matrix was varied in a range of 30 – 70 wt.%. It was found a high filler content suppresses a molecular mobility of copolymer matrix chains and reduces a beginning of glass transition temperature of the polymer constituent. The results of thermal analysis of polymer composites demonstrate a high hydrophilicity level of polymer matrix and high solvation energy of polar functionalities by Н2О molecules that was concluded from slow moisture elimination process while the temperature grows up to 200–210 оС. Additionally, a dehydration process and changes in a structure of thermally labile filler were also observed at the same temperature interval. At higher temperatures a thermal degradation of polymer poly(AAm-co-2HEMA) matrix is carried out. When a temperature overcomes 400 оС the partially changed filler demonstrates a chemical interaction with degraded organic constituents of the composites and defined catalytic activity as well. Studying sorption activity of the composites shown that introducing NiAl-LDH into hydrophilic polymer matrix provides anion-exchange activity to the composite sorbents and, correspondingly, the ability to eliminate the anionic contaminants from aqueous media while the polymer matrix doesn’t absorb these substances at such conditions. The highest sorption capacity of 11,40 μmol/g against model contaminant – methyl orange dye was determined for composite sorbent with filler content of 70 wt. %. At the same time sorption capacity of NiAl-LDH filler in composite sorbents reduces from 25,7 to 16,6 μmol/g while a filler content grows from 30 to 70 wt.% as a result of filler particles aggregation processes during composites formation stage. To evaluate the ability of the composite sorbents to reuse the experiment of materials recycling was performed. It was stated out the using of anion-exchange technique and aqueous Na2CO3 solution as an efficient and non-hazardous eluent provides 80 % recovering efficiency of the active filler in the composites. It can be concluded the composite sorbents demonstrate a high overall efficiency and are valuable materials for practical application for decontamination of waste water.

Synthesis of CuS/CNTs/gCN ternary nanocomposite for enhanced photocatalytic response of harmful organic effulents

To find such materials which assist to cope environmental pollution issues especially water contamination is thought-provoking task in the scientific era. Herein, we synthesized 2D CuS materials through hydrothermal method and their composite with a well-known carbonaceous material CNTs. The CuS/CNTs/gCN ternary nanocomposite was synthesized via ultrasonication with a metal free co-catalyst graphitic carbon nitride (gCN). The as-prepared CuS, CuS/CNTs binary nanocomposite, and CuS/CNTs/gCN ternary nanocomposite were efficiently utilized to study photocatalytic response of a cationic dye (Rhodamine B) and an anionic dye (Methyl orange). The CuS/CNTs/gCN photocatalyst divulges best photodegradation response of RhB and MO dyes by degrading them up to 95.3% and 93.2% under solar light respectively. Important photo active species involved in photocatalysis progression were trapped by using different trapping agent and found hydroxyl radicals are highly photoactive during photocatalytic mechanism. The graphitic carbon nitride (gCN) as a metal free co-catalyst meaningfully heightened the surface area of the ternary composite and delivers extra active sites for redox reaction. The consequences concludes that CuS/CNTs/gCN composite have potential to compete in water pollution applications for remediation of both cationic and anionic contaminants.

A single functionalized graphene nanocomposite in cross flow module for removal of multiple toxic anionic contaminants from drinking water.

Polyether sulfone (PES)-based thin-film nanofiltration (TFN) membranes embedded with ferric hydroxide (FeIII(OH)x) functionalized graphene oxide (GO) nanoparticles were fabricated through interfacial polymerization for a generalized application in removal of a plethora of anionic and toxic water contaminants. Following the most relevant characterization, the newly synthesized membranes were fitted in a novel flat sheet cross-flow module, for experimental investigation on purification of live contaminated groundwater collected from different affected areas. The separation performances of the membranes in the flat sheet cross-flow module demonstrated that GOF membranes had higher selectivity for monovalent and divalent salt rejections than pristine GO membranes. Furthermore, both membranes were tested for simultaneously removing widely occurring hazardous ions of heavy metals and metalloids in groundwater, such as arsenic, selenium, chromium, and fluoride. Compared to the pristine GO and the reported membranes in the literature, the GOF membrane exhibited remarkable performance in terms of rejection efficiency (Cr (VI): 97.2%, Se (IV): 96.6%, As(V): 96.3%, F- 88.4%) and sustained flux of 184 LMH (Lm-2h-1) at an optimum transmembrane pressure of 16bar. The investigated membrane module equipped with the GOF membrane proved to be a low-cost system with higher anionic rejection and sustained high flux at a comprehensive pH range, as evident over long hours of study vis-à-vis reported systems.

Sorption of Alizarin Red S and Methylene Blue on Halloysite from Single and Mixed Solutions

The extensive use of synthetic materials in modern society presents a great challenge to environmental and water quality. As such, numerous studies were dedicated to the removal of emerging contaminants from water using novel materials as sorbents or catalysts. With large reserves and low material costs, Earth material has also attracted great attention for contaminant removal. Halloysite is a 1:1 layered clay mineral with moderate cation exchange capacity that can be used for the removal of cationic contaminants. On the other hand, as it may bear positive charges on the aluminum hydroxyl sheets, it could be used to remove anionic contaminants. In this study, the removal of a cationic dye, methylene blue (MB), and an anionic dye, alizarin red S (ARS), from the water was evaluated from single and mixed solutions. The results suggested that from single solutions, MB removal was via cation exchange while ARS removal could have originated from anion exchange. From mixed solutions, their removal was mutually increased, which may be due to a synergistic effect in the presence of a type of charged dyes serving as counterions to enhance the sorption of dyes of opposite charges. This finding suggests that halloysite may serve as a sorbent for the removal of organic contaminants of different charges at the same time, which is a new perspective that needs further evaluation and expansion.

Practical approach of As(V) adsorption by fabricating biochar with low basicity from FeCl3 and lignin

One of the main challenges of biochar application for environmental cleanup is rise of pH in water or soil due to high ash and alkali metal contents in the biochar. While this intrinsic property of biochar is advantageous in alleviating soil and water acidity, it severely impairs the affinity of biochar toward anionic contaminants such as arsenic. This study explored a technical approach that can reduce the basicity of lignin-based biochar by utilizing FeCl3 during production of biochar. Three types of biochar were produced by co-pyrolyzing feedstock composed of different combinations of lignin, red mud (RM), and FeCl3, and the produced biochar samples were applied to adsorption of As(V). The biochar samples commonly possessed porous carbon structure embedded with magnetite (Fe3O4) particles. The addition of FeCl3 in the pyrolysis feedstock had a notable effect on reducing basicity of the biochar to yield significantly lower solution pH values than the biochar produced without FeCl3 addition. The extent of As(V) removal was also closely related to the final solution pH and the greatest As(V) removal (>77.6%) was observed for the biochar produced from co-pyrolysis of lignin, RM, and FeCl3. The results of adsorption kinetics and isotherm experiments, along with x-ray spectroscopy (XPS), strongly suggested adsorption of As(V) occurred via specific chemical reaction (chemisorption) between As(V) and Fe–O functional groups on magnetite. Thus, the overall results suggest the use of FeCl3 is a feasible practical approach to control the intrinsic pH of biochar and impart additional functionality that enables effective treatment of As(V).

Release regularity and cleaning measures of magnetic anion exchange resin during application

Anion exchange resin is responsible for removing harmful anionic contaminants in drinking water treatment, but it may become a significant source of precursors for disinfection byproducts (DBPs) by shedding material during application without proper pretreatment. Batch contact experiments were performed to investigate the dissolution of magnetic anion exchange resins and their contribution to organics and DBPs. Dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) released from the resin were highly correlated with the dissolution conditions (contact time and pH), in which 0.7 mg/L DOC and 0.18 mg/L DON were distributed at exposure time of 2 h and pH 7. The formation potential of four DBPs in the shedding fraction was also revealed that trichloromethane (TCM), dichloroacetonitrile (DCAN), nitrosodimethylamine (NDMA), and dichloroacetamide (DCAcAm) concentrations could reach 21.4, 5.1, 12.1 μg/L, and 69.6 ng/L, respectively. Furthermore, the hydrophobic DOC that preferred to detach from the resin mainly originated from the residues of crosslinkers (divinylbenzene) and porogenic agents (straight-chain alkanes) detected by LC-OCD and GC-MS. Nevertheless, pre-cleaning inhibited the leaching of the resin, among which acid-base and ethanol treatments significantly lowered the concentration of leached organics, and formation potential of DBPs (TCM, DCAN, and DCAcAm) below 5 μg/L and NDMA dropped to 10 ng/L.

Tuneable electrohydrodynamics of core-shell graphene oxide vortex rings

The vortex ring (VR) effect occurs when fluid droplets impact on another fluid, leading to toroidal flow within the impacting droplet due to viscous friction, resulting in a wide variety of flow-induced morphologies. When applied to dispersions of 2-dimensional materials, such as graphene oxide (GO) in water, the VR effect can be used to generate 3-dimensional assemblies of GO flakes. Here, we have taken advantage of the surface charge on GO flakes in water, interacting with cationic aqueous surfactant systems, to generate an electrohydrodynamic VR effect. This yields GO hydrogel and aerogel microparticles with complex axially symmetric shapes, with a core-shell structure featuring a shell of aligned GO flakes. Using high frame-rate optical imaging, we have captured the real-time self-assembly of GO core-shell hydrogel microparticles shaped like spheres, donuts and jellyfish. We describe, both qualitatively and quantitatively, the electrohydrodynamics that drive the formation of such shapes. We also demonstrate how the underlying processes can be tuned by varying parameters such as GO concentration, flake size and drop velocity, and surfactant chemistry and concentration to produce a wide variety of controllable exterior and interior morphologies. Indeed, we show that the formation regimes of the different shapes are determined by dimensionless Weber and Ohnesorge numbers. Lastly, we demonstrate how these microparticles can be used for the efficient adsorption and removal of anionic contaminants in water, with tuneable adsorption capacity.

Nitrogen-rich hierarchical porous polyphosphazene for rapid and efficient adsorption of anionic contaminants: Kinetics, isotherm, thermodynamics and mechanism

The rapid and highly-efficient uptake of waterbody contaminants by polymer-based adsorbent is still a challenge. Herein, a new nitrogen-rich hierarchical porous polymer (PCPM) was synthesized via a self-catalyzed polycondensation between hexachlorocyclotriphosphazene and melamine. The PCPM possessed hierarchical pore architecture with specific surface area of 321.1 m2/g and pore size distribution from 1.3 to 63.0 nm. Owing to the remarkable porous texture and nitrogen-rich active sites with high electron density, PCPM exhibited a high adsorption capacity of 187.5, 336.2, and 320.4 mg g−1 for Cr (VI), Congo red (CR), and diclofenac sodium (DCF), respectively. Moreover, the adsorption rate of these contaminants onto PCPM was very fast, reaching 90 % of adsorption equilibrium capacity for Cr (VI), CR and DCF within the first 7 min, 45 min and 30 min, respectively. Adsorption data revealed that the adsorption process conformed to pseudo-second-order kinetics and Langmuir isotherm model. The removal process was spontaneous, exothermic for Cr (VI) and endothermic for CR and DCF. FT-IR and XPS analysis demonstrated that electrostatic interaction and hydrogen bonding contributed to the adsorption of CR and DCF onto PCPM, while the removal mechanism of Cr (VI) by PCPM included redox reaction and chelation besides the above two interactions.

Acetylated corn and potato starches as an alternative to the toxic inorganic coagulants/flocculants for wastewater treatment

Inorganic coagulants/flocculants have been key in water treatments. However, last years, it has been reported the potential contamination that these give to the environment and serious risks to human health. For that reason, new eco-friendly alternatives have been the subject of exploration and research. This work focused on developing and elaborating a natural flocculant based on corn and potato starches, and its application in industrial wastewater treatments. Starches were isolated from corn and potato, and modified by acetylation method with the aim of improve its solubility. The morphological characterization using SEM identified the effects of acetylation process, the surface of acetylated corn and potato starches presented small erosions. The vibrational characterization via FTIR elucidated the physicochemical changes owing to acetylation. It found the replace of hydroxyl groups of α-glucose by the acetyl ones of amide I. A loss of the crystalline quality of corn starch were identified through structural characterization utilizing DRX. The partial replacement of hydroxyl by acetyl groups due to acetylation induced structural modifications corroborated employing the area under curve of the diffraction patterns. In the case of potato starch, its characteristic hexagonal crystalline structure was favored by the acetylation process, as it exhibited a more defined diffraction pattern. The thermal analysis by means of TGA found three thermal events for the acetylated potato starch and four for the acetylated corn starch. The fourth thermal event in the acetylated potato starch was associated with the ester presence of the added group. The thermal degradation occurred at lower temperatures as mass loss curves showed that acetylation weakened the polymer chains. The pH of zero point charge was 6.52 for the acetylated corn starch and 5.55 for the acetylated potato one, indicating that anionic contaminants be retained at a pH below 6.52 and 5.55 for each case, and the removal of cationic contaminants will favor at pH above these values. The efficiency determination of the modified starch-based flocculant was performed utilizing a jar test at different concentrations to find the optimal concentration of the coagulant/flocculant. Turbidity, color, pH, and electrical conductivity measurements were made before and after the water treatment. These results indicated that both corn and potato starches showed good performance as coagulants/flocculant. The kinetics for adsorption was study using the pseudo-first and pseudo-second order kinetic models, the intra-particle diffusion model, and the Elovich kinetic one. These analyzes identified that the absorption process is governed by chemisorption mechanisms since the pseudo-second order kinetic model was the most accurate for describing the absorption kinetic of both acetylated corn and potato starches according to the R2, SSE, MSE, and RMSE.

Adsorption Characteristics for Cu(II) and Phosphate in Chitosan Beads under Single and Mixed Conditions

Chitosan, a natural organic polymer, has shown bifunctional characteristics in the removal of cationic and anionic contaminants from water and wastewater treatment. In particular, cationic Cu(II) and anionic phosphate can simultaneously interact with chitosan owing to the presence of the amino group in the form of NH2 and NH3+ in chitosan. To gain greater insight into the bifunctional adsorption characteristics of chitosan, its adsorption capacity for Cu(II) and phosphate was tested under single and mixed (co-ion) conditions to investigate the interactions between four types of chitosan beads and NH2 and NH3+. In the single condition, Cu(II) uptake was reduced from 0.243 to 0.0197 mmol/g due to the crosslinking and drying processes, whereas no significant reduction in phosphate uptake was observed, indicating that the crosslinking agent only interacted with NH2 to decrease the number of available adsorption sites for Cu(II). Under the mixed condition, the simultaneous presence of the two ions clearly increased the uptake of each other, with the adsorption of phosphate being more influenced than that of Cu(II). The comparison of the rate constant, k1 or k2, using pseudo-first- and pseudo-second-order models confirmed that phosphate reached equilibrium faster than Cu(II), suggesting that electrostatic interaction was preferred over coordination. In addition, under mixed conditions, co-ion competition slowed down the adsorption kinetics for both Cu(II) and phosphate.