Fabricating a novel chitosan-based adsorbent with multifunctional synergistic effect for Cu(II) removal: Maleic anhydride as a connecting bridge

Performance and mechanism of amphiphilic polymeric chelator for enhanced removal of high concentrations of Cu(II) from wastewater

An amphiphilic polymeric chelator (APC16-g-SX) grafted with sodium xanthate (SX) groups was successfully prepared for the efficient removal of high concentrations of Cu(II) from wastewater. The ordinary polymeric chelator (PAM-g-SX) based on linear polyacrylamide (PAM) was also prepared for comparative studies. The polymeric chelators were characterized by Fourier transform infrared spectroscopy (FT-IR), solid-state nuclear magnetic resonance (13C-NMR), gel permeation chromatography (GPC), elemental analyzer, and scanning electron microscope (SEM). The chelating performance of these polymeric chelators was investigated, and the mechanism of APC16-g-SX for enhanced removal of Cu(II) from wastewater was proposed based on fluorescence spectroscopy, cryo-scanning electron microscope (Cryo-SEM), energy-dispersive spectrometer (EDS), and X-ray photoelectron spectroscopy (XPS) tests. The results show that as the initial Cu(II) concentration in the wastewater increases, APC16-g-SX shows more excellent chelating performance than ordinary PAM-g-SX. For the wastewater with an initial Cu(II) concentration of 200 mg/L, the removal rate of Cu(II) was 99.82% and 89.34% for both 500 mg/L APC16-g-SX and PAM-g-SX, respectively. The pH of the system has a very great influence on the chelating performance of the polymeric chelators, and the increase in pH of the system helps to improve the chelating performance. The results of EDS and XPS tests also show that N, O, and S atoms in APC16-g-SX were involved in the chelation of Cu(II). The mechanism of enhanced removal of Cu(II) by APC16-g-SX can be attributed to the spatial network structure constructed by the self-association of hydrophobic groups that enhances the utilization of chelation sites.

Insight into the purification of algael water by a novel flocculant with enhanced branched nanochitosan structure

For improving inadequate nanostructural stability and promote algal removal efficiency, a novel nanochitosan-grafted flocculant (PAD-g-MNC) with an enhanced branched nanostructure and high molecular weight (MW) was fabricated via maleic anhydride acylation polymerization. Characterization results verified the successful synthesis of the flocculant and the formation of an irregular particle nanostructure. PAD-g-MNC exhibited superior algal and extracellular organic matter (EOM) removal and obtained the turbidity and chlorophyll-a removal rates of 93.46%-95.39% and 95.10%-97.31%, respectively, at the dosage of 4-5 mg L^-1. The growth rate, strength factor, and recovery factor of algal flocs flocculated by PAD-g-MNC were 90.36, 0.63, and 0.27 (100 rpm), respectively, and were higher than other flocculants prepared through conventional methods. Results indicated that the high intrinsic viscosity and stability branched nanostructure promoted the formation of stable flocs and regeneration ability of flocs. MW distribution and three-dimensional fluorescence analyses revealed that the special structure of PAD-g-MNC was beneficial to the removal of tryptophan-like proteins in EOM. Strong adsorption-adhesion and bridging-netting effects of the nanostructure chain were the dominated mechanisms in the improvement of flocculation efficiency. This study provided theoretical and experimental guidance for the design of flocculants with superior performance and efficient algal water purification performance.

Chitosan grafted tetracarboxylic functionalized magnetic nanoparticles for removal of Pb(II) from an aqueous environment

In this study, the chitosan-grafted tetracarboxylic functionalized magnetic nanoparticle (Fe₃O₄@TCA@CS) was synthesized via in situ co-precipitation process and amidation reaction to improve efficiency of adsorption process and obtain cost-effective adsorbents for removal of toxic Pb(II) metal from aqueous environment. The Fe₃O₄@TCA@CS nanocomposite was analyzed by FTIR, TEM-EDX, TGA, XRD, BET, and Zeta potential. The performance of Fe₃O₄@TCA@CS for Pb(II) ions adsorption was achieved as a function of pH, dose, contact time, initial Pb(II) concentration, and temperature. The influence of coexisting ions such as Na⁺, Ca²⁺, Mg²⁺, and Cd²⁺on removal efficiency of Pb(II) was also investigated. The results revealed that the coexisting ions had little influence on Pb(II) removal efficiency. The pseudo-first-order and Freundlich models were better to describe the adsorption of Pb(II) onto Fe₃O₄@TCA@CS and the maximum adsorption capacity of Pb(II) was 204.92 mg/g at pH:5.5; adsorbent dose: 0.015 g; and temperature: 298 K. Thermodynamic studies revealed that the Pb(II) adsorption onto Fe₃O₄@TCA@CS was an exothermic process. In conclusion, the study provides a new, simple, low-cost, and effective chitosan-based magnetic nanocomposite as a promising adsorbent with excellent adsorption capacity, magnetic separation, and reusability for Pb(II) removal from an aqueous environment.

Superhydrophilic and Underwater Superoleophobic Cotton Fabric for Oil-Water Separation and Removal of Heavy-Metal Ion

Superhydrophilic and underwater superoleophobic cotton fabric (named CS-CF-PDA, or m-CF) was prepared by modifying the cotton fabric (CF) with dopamine (DA) and chitosan (CS). The oil-water separation and heavy-metal ion (e.g., Cu(II)) adsorption performances of m-CF were investigated, and m-CF was characterized by field emission scanning electron microscopy (FE-SEM), energy-dispersive spectroscopy (EDS), Fourier transform infrared (FT-IR), and thermogravimetric analysis (TGA). The results showed that the underwater oil contact angle (UWOCA) of m-CF was more than 156°. The m-CF was used to treat artificial oily wastewater containing Cu(II) under room temperature and atmospheric pressure and gravity, by which the separation efficiency, water flux, and Cu(II) removal rate could reach 99%, 17 400 L·m^-2·h^-1, and 89%, respectively. Additionally, in the process of continuous treatment of oily wastewater, the water flux slightly decreased; on the contrary, the Cu(II) removal rate decreased significantly to 67% within 120 s. Cu(II) was one of the reasons for the decrease of water flux. The m-CF of adsorbed Cu(II) could be leached with HCl (0.1 mol·L^-1) solution, and the Cu(II) desorption rate could reach over 95% within 120 s. After strong acid, strong alkali, high salt, and abrasion treatment, the UWOCAs of m-CF were still higher than 150°. In a word, in terms of oil-water separation, m-CF exhibited good acid, alkali, salt, and abrasion resistances. Also, it is an underwater superoleophobic material involving simple preparation, low cost, and environmental friendliness, which could remove the floating oil and heavy-metal ions from wastewater and has good industrial application prospects.

Xanthate-Modified Magnetic Fe3O4@SiO2-Based Polyvinyl Alcohol/Chitosan Composite Material for Efficient Removal of Heavy Metal Ions from Water

Chitosan has several shortcomings that limit its practical application for the adsorption of heavy metals: mechanical instability, a challenging separation and recovery process, and low equilibrium capacity. This study describes the synthesis of a magnetic xanthate-modified polyvinyl alcohol and chitosan composite (XMPC) for the efficient removal and recovery of heavy metal ions from aqueous solutions. The XMPC was synthesized from polyvinyl alcohol, chitosan, and magnetic Fe₃O₄@SiO₂ nanoparticles. The XMPC was characterized, and its adsorption performance in removing heavy metal ions was studied under different experimental conditions. The adsorption kinetics fit a pseudo-second-order kinetic model well. This showed that the adsorption of heavy metal ions by the XMPC is a chemical adsorption and is affected by intra-particle diffusion. The equilibrium adsorption isotherm was well described by the Langmuir and Freundlich equations. The XMPC reached adsorption equilibrium at 303 K after approximately 120 min, and the removal rate of Cd(II) ions was 307 mg/g. The composite material can be reused many times and is easily magnetically separated from the solution. This makes the XMPC a promising candidate for widespread application in sewage treatment systems for the removal of heavy metals.

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.

Assessment of a novel aminated magnetic adsorbent with excellent adsorption capacity for dyes and drugs

Dyes and drugs with high toxicity and low biodegradability pose risk to human health and ecological security, and should be purified efficiently from effluents before discharge. Traditional adsorbents are limited by the insufficient active adsorption sites and low stability. In this study, a novel aminated magnetic adsorbent (MCTs) was fabricated via two cross-linking steps using chitosan and triethylenetetramine to fill the gaps between current adsorbent and performance requirements. The morphological and physicochemical characteristics of the as-prepared MCTs were determined and identified with the aid of several characterization techniques. The adsorption performance of dyes and drugs was also investigated and represented by their adsorption capacities. In particular, the adsorption capacities of Congo Red, Chicago Sky Blue, Reactive Brilliant Red, and Ibuprofen were 583.11, 465.01, 403.12, and 291.71 mg/g, respectively. They also remained at around 80% after four reuse cycles. MCTs were adsorbed via a monolayer spontaneous chemical reaction, and hydrogen bonding and electrostatic interaction were the dominant adsorption mechanisms. These results demonstrated that the preparation of MCTs via two cross-linking steps enhanced the adsorbents' adsorption capacity, reusability, and stability. They provided a new perspective for the preparation of high-efficient adsorbents and the purification of dye- and drug-polluted wastewater.

Chitosan based macromolecular probes for the selective detection and removal of Fe3+ ion

Chitosan has been widely used due to its biodegradable, cost-effective and environmentally friendly properties. Modification of chitosan attracts much attention as promising methods to detect and remove organic and inorganic pollutants. In this work, chitosan-based macromolecular probes were designed and synthesized. The probes can detect Fe³⁺ in the presence of other metal ions. The detection mechanism is investigated as well. The probe's fluorescence quenching upon the addition of Fe³⁺ ion could be ascribed to the complexation between the electron-deficient ion Fe³⁺ and "C=N" (electron-rich group) of fluorescent chitosan probes. What's more, the obtained fluorescent macromolecular probes can be used for the removal of Fe³⁺ in solution. The probes could adsorb the Fe³⁺ in solution and the removal efficiency can reach as high as 62.0% while the removal efficiency of original chitosan is only 16.0%. The probes have good selective detection for Fe³⁺ and the detection limit reaches 1.2 μM.