Synergistic Removal of Copper(II) and Tetracycline from Water Using an Environmentally Friendly Chitosan-Based Flocculant

Evaluating the performance of bridging-assembly chelating flocculant for heavy metals removal: Role of branched architectures

A novel chelating flocculant with branched architectures, polyacrylamide grafted maleoyl chitosan-mercaptoacetic acid (PAM-g-M(CS-MA)), was successfully fabricated using maleic anhydride as the "bridge" between chitosan and polyacrylamide. The functional groups and structural characteristic information of copolymers were obtained via characterization analysis. Flocculation performance was systematically investigated via purifying a series of simulated wastewater containing Cu or Cd. The properties of the flocs were studied to give in-depth evidences for the role of chelation groups and branched architectures in flocculation. Results indicated that PAM-g-M(CS-MA) showed excellent flocculation capacity for heavy metals in high concentrations and was superior to other chelating flocculants. The maximum flocculation efficiency of Cu (93.90%) and Cd (92.47%) was achieved by PAM-g-M(CS-MA) at pH 7, dosage of 100 mg L^-1 and stirring speed of 90 rpm. The flocculation mechanisms of PAM-g-M(CS-MA) were deeply explored through the analyses of floc properties. The strong synergistic chelation of mercapto, carboxyl, amide and hydroxyl groups predominated for the capturing of heavy metals; and the branched architectures facilitated the formation of large and stable flocs via adsorption and bridging-furl effect. This study provided a solid foundation for the fabrication of flocculants for heavy metal wastewater treatment.

A novel hydrogel for highly efficient adsorption of Cu(II): synthesis, characterization, and mechanisms

Among the Cu(II) removal methods, adsorption is a favorable technique and has attracted large attention because of its effectiveness and low cost. In quest of seeking for a favorable adsorbent with a high Cu(II) adsorption capacity and excellent reusability, researchers have paid much attention to hydrogels with three-dimensional networks. In this study, a novel hydrogel (P(AMPS-co-VDT) hydrogel) based on free-radical polymerization was synthesized with ionic monomer sodium 2-acrylamido-2-methylpropane sulfate (AMPS-Na⁺) and 2-vinyl-4, 6-diamino-1, 3, 5-triazine (VDT) and applied for Cu(II) adsorption in aqueous solutions. The hydrogel was characterized for swelling performance, surface morphology, functional groups, thermal gravimetric behavior, and elements. The maximum Cu(II) adsorption capacity (175.75 mg/g) was relatively high compared with other hydrogels. The P(AMPS-co-VDT) hydrogel also was found to have a relatively good Cu(II) desorption and reuse behavior. The adsorption mechanism could be chelation and ion exchange. This work provides a new hydrogel for effective Cu(II) removal in the future.

High-Performance Flocculants for Purification: Solving the Problem of Waste Incineration Bottom Ash and Unpurified Water

The silicon-aluminum-iron flocculant (PAFSi) combines the most abundant resources of waste incineration bottom ash and unpurified water, being regarded as one of the most promising approaches toward water purification. Herein, in this research, waste incineration bottom ash was employed to produce a cost-effective and highly efficient flocculant. PAFSi with a particle size of 214 nm and a zeta potential of 8.63 mV reached the optimum performance using a dosage of 2 mL/50 mL at pH from 8 to 11. The results with the copolymer exhibited the following: (1) a good flocculation efficiency over a wide pH range, (2) superior flocculation performance compared to those of polyaluminum chloride and polyferric sulfate, (3) three-dimensional branching structure of PAFSi micelles with a high aggregation degree, (4) charge neutralization and bridging as the main flocculation mechanism, and (5) recycling the floc. Thus, this work provides an attractive solution to the pressing global clean water shortage problem.

Simultaneous nitriles degradation and bioflocculant production by immobilized K. oxytoca strain in a continuous flow reactor

High cost is one of the limiting factors in the industrial production of bioflocculant. Simultaneous preparation of bioflocculant from the contaminants in wastewater was considered as a potential approach to reduce the production cost. In this study, butyronitrile and succinonitrile were verified as sole nitrogen sources for the growth of strain K. oxytoca GS-4-08 in batch experiments. Moreover, more than 90 % of the mixed nitriles could be degraded in a continuous flow reactor, and the bioflocculant could be prepared simultaneously in the effluent. All the as-prepared bioflocculants exhibited high flocculation efficiencies of over 90 % toward Kaolin solution. FTIR and XPS results further unveiled that, the bioflocculant samples with abundance of carboxyl, amine and hydroxyl groups may play an important role on adsorption of Pd²⁺. The adsorption process could be well simulated by Freundlich model, and the K_f values were as high as 452.8 mg^1-1/n l^1/n g^-1. The results obtained in this study not only confirm the technical feasibility for preparation of bioflocculant from various single nitrile and/or mixed nitriles, but also promise its economic feasibility.

Fabrication of magnetic trimetallic metal–organic frameworks for the rapid removal of tetracycline from water

The metal–organic framework (MOF-74) series has the most open metal sites.

Removal of sulfamethoxazole antibiotic from aqueous solutions by silver@reduced graphene oxide nanocomposite

In the present study, the synthesizing of silver@reduced graphene oxide nanocomposite, through a facile precipitation method, is reported. In this method, in the synthesizing step, reduced graphene oxide was applied as a support, silver acetate as a precursor of Ag⁰, and sodium hydroxide as a medium for reducing procedure. Then synthesized particles were characterized by using transmission electron microscopy analysis, Fourier-transform infrared spectroscopy, field emission scanning microscopy/energy dispersive X-ray, and X-ray diffraction. Adsorbent potentials of the prepared nanocomposite were evaluated for sulfamethoxazole removal from polluted aqueous solutions via two different experimental methods, namely, "one-at-a-time" and "central composite design". The given results from the one-at-a-time method confirms that 0.007 g of silver@reduced graphene oxide nanocomposite can remove 88% (188.57 mg/g) of sulfamethoxazole from a 0.05 dm³ solution (initial concentration 30 mg/dm³) at pH = 5 after 3600 s' contact time. However, in the central composite design method, the optimum condition was 95% (79.17 mg/g) uptake of this drug from 0.05 dm³ of polluted solution with initial concentration of 30 mg/dm³ and pH = 7.5, using 0.018 g of the adsorbent in 3600 s. The main mechanism for sulfamethoxazole removal can be suggested as a suitable interaction between S atoms in functional groups in the drug and Ag atoms on the surface of nanoparticles. The pseudo-second-order patterns and Freundlich model described the empirical data isotherm and kinetics for the adsorption processes, respectively. The maximum adsorption capacity by experimental and theoretical isotherm methods (Langmuir) obtained 250 and 357 mg/g, respectively. Efficiency of the adsorbent in treatment of SMX from real samples displayed less hardness and electrical conductance samples have the maximum uptake percent while existence of nitrate ions in the solutions did not induce any negative effect on the removal of the SMX. All obtained results indicated loading of Ag nanoparticles on rGO nanosheets is an effective strategy for SMX uptake with high proficiency and shows great promise as pollutant adsorbent for environmental applications.

Preparation of a bioflocculant by using acetonitrile as sole nitrogen source and its application in heavy metals removal

A novel bioflocculant, A-GS408, produced by Klebsiella oxytoca GS-4-08 cultured in acetonitrile (ACN) as sole nitrogen source was investigated in this study. A complete degradation of 1 g l^-1 of ACN was achieved in 350 h, and 4.6 g of crude A-GS408 can be obtained in one litter of synthetic medium. The as-prepared bioflocculant exhibits good flocculation efficiency (over 90%) toward Kaolin solution with the aid of Fe³⁺. Chemical analysis showed that the bioflocculant was mainly composed of polysaccharides (46.3%) and proteins (20.6%). FTIR and XPS results indicated the abundant carboxyl, amine and hydroxyl groups in A-GS408 s, which play an important role on Pd²⁺ and Cu²⁺ adsorption. The adsorption of heavy metals can be well stimulated by Freundlich isotherm equation, and the K_f was up to 439.2 mg^1-1/n l^1/n g^-1 and 112.2 mg^1-1/n l^1/n g^-1 for Pb²⁺ and Cu²⁺, respectively. The kinetic fitting results proved that the adsorption of heavy metals by A-GS408 was chemisorption. This study may provide a new method for preparation of bioflocculant, which can not only degrade toxic compound i.e., acetonitrile, but also can reuse considerable nitrogen source from nitrile-containing wastewater.

Preparation of Functionalized Magnetic Fe₃O₄@Au@polydopamine Nanocomposites and Their Application for Copper(II) Removal

Polydopamine (PDA) displays many striking properties of naturally occurring melanin in optics, electricity, and biocompatibility. Another valuable feature of polydopamine lies in its chemical structure that incorporates many functional groups such as amine, catechol and imine. In this study, a nanocomposite of magnetic Fe₃O₄@Au@polydopamine nanopaticles (Fe₃O₄@Au@ PDA MNPs) was synthesized. Carboxyl functionalized Fe₃O₄@Au nanoparticles (NPs) were successfully embedded in a layer of PDA through dopamine oxypolymerization in alkaline solution. Through the investigation of adsorption behavior to Cu(II), combined with high sensitive electrochemical detection, the as-prepared magnetic nanocomposites (MNPs) have been successfully applied in the separation and analysis of Cu(II). The experimental parameters of temperature, Cu(II) concentration and pH were optimized. Results showed that the as-prepared MNPs can reach saturation adsorption after adsorbing 2 h in neutral environment. Furthermore, the as-prepared MNPs can be easily regenerated by temperature control and exhibits a good selectivity compared to other metal ions. The prepared Fe₃O₄@Au@PDA MNPs are expected to act as a kind of adsorbent for Cu(II) deep removal from contaminated waters.

Amphoteric starch derivatives as reusable flocculant for heavy-metal removal

A pH-responsive amphoteric starch derivative (PRAS) bearing dual functional groups (amino and carboxyl groups) was prepared through etherification of starch with 2-chloro-4,6-diglycino-[1,3,5]-triazine. PRAS exhibits a reversible pH-response property in aqueous solution. The attractive property of PRAS is that it could be used as an effective flocculant for heavy metal-ion (e.g. Cu(ii) and Zn(ii)) removal from wastewater by changing pH. The transition of hydrophobicity–hydrophilicity would produce shrinkage of the polymer matrix, facilitating the release of heavy-metal ions from the saturated flocculant. As an ideal flocculant PRAS displayed outstanding stability and reproducibility, whose remove rate for Cu(ii) and Zn(ii) remained at 93% and 91% after three flocculation/regeneration cycles.

A pH-responsive starch-based flocculants containing both cationic and anionic functional groups has been developed. The saturated flocculant can be facilely regenerated and separated from the solution by applying an external pH stimulus.

Separation and Sequential Recovery of Tetracycline and Cu(II) from Water Using Reusable Thermoresponsive Chitosan-Based Flocculant

Coexistence of antibiotics and heavy metals is typically detected in water containing both organic and inorganic contaminants. In this work, a flocculation method using a reusable thermoresponsive chitosan-based flocculant (CS-g-PNNPAM) was applied for separation and sequential recovery of tetracycline (TC) and Cu(II) from water. High synergistic removal rates of both TC and Cu(II) from water (>90%) were reached. Interactive effects among targeted water temperature (T₁), stock solution temperature (T₂), and flocculant dosage on flocculation performance were assessed using response surface methodology. To optimize flocculation, operation strategies of adjusting T₂ and dosage according to T₁ based on the interactive effects were given through mathematical analyses. The flocculation mechanism as well as interfacial interactions among CS-g-PNNPAM, TC, and Cu(II) were studied through experimental investigations (floc size monitoring, X-ray photoelectron spectroscopy, and UV spectra) and theoretical calculations (density functional theory and molecular dynamics simulations). Coordination of Cu(II) with TC and the flocculant promoted flocculation; switchable interactions (H bonds and hydrophobic association) of the TC-flocculant at different temperatures were key factors affecting operation strategies. When these interactions were weakened step by step, TC and Cu(II) were sequentially recovered from flocs using certain solutions. Meanwhile, the flocculant in flocs was regenerated and found reusable with high flocculation efficiency.

A review on chitosan-based flocculants and their applications in water treatment

In recent years, the use of chitosan and its derivatives as flocculants in water treatment has received considerable attention due to their many advantages, including their widespread availability, environmental friendliness, biodegradability, and prominent structural features. However, it is a significant strategy for selection and design of the high-performance materials on the basis of their structure-activity relationships. Here we describe several of the chemical modification methods commonly used to prepare chitosan-based flocculants. These methods allow convenient control and adjustment of the structures of the obtained materials to meet the different practical requirements. The influence of structural elements of the chitosan-based flocculants on their flocculation properties are emphasized in this review by examining different flocculation mechanisms and their applications in the treatment of various wastewaters containing different pollutants (insoluble suspended colloids but also dissolved matters). Above all, the chitosan-based flocculants with proper structures by precise structure control bear great application potentials in water treatment.

Water soluble EDTA-linked chitosan as a zwitterionic flocculant for pH sensitive removal of Cu(ii) ion

Water soluble EDTA-linked chitosan was synthesized and applied to remove Cu(ii) utilizing its property of chelation and pH sensitive precipitation.

Hierarchical porous carbon materials derived from a waste paper towel with ultrafast and ultrahigh performance for adsorption of tetracycline

Hierarchical porous carbon materials were prepared using paper towels as the carbon precursor for removal of tetracycline antibiotics with ultrafast kinetics property.

Flocculation of copper(II) and tetracycline from water using a novel pH- and temperature-responsive flocculants

Insufficient research is available on flocculation of combined pollutants of heavy metals and antibiotics, which widely exist in livestock wastewaters. Aiming at solving difficulties in flocculation of this sort of combined pollution, a novel pH- and temperature-responsive biomass-based flocculant, carboxymethyl chitosan-graft-poly(N-isoproyl acrylamide-co-diallyl dimethyl ammonium chloride) (denoted as CND) with two responsive switches [lower critical solution temperature (LCST) and isoelectric point (IEP)], was designed and synthesized. Its flocculation performance at different temperatures and pHs was evaluated using copper(II) and tetracycline (TC) as model contaminants. CND exhibited high efficiency for coremoval of both contaminants, whereas two commercial flocculants (polyaluminum chloride and polyacrylamide) did not. Especially, flocculation performance of the dual-responsive flocculant under conditions of temperature>LCST and IEP(contaminants)<pH<IEP(CND) was much better than that under other conditions. Further investigation on flocculation mechanism via pH monitoring, zeta potential measurements, floc properties analyses and spectral characterization indicated that, pairwise interactions among CND, copper(II) and TC were present in bridging flocculation, including charge attraction, coordination and hydrophobic effect. Based on these pairwise interactions, copper(II) and TC exerted "aid" roles to each other's removal with the existence of CND, and preferable flocculation performance was thus achieved.