Application of Geopolymers Modified with Chitosan as Novel Composites for Efficient Removal of Hg(II), Cd(II), and Pb(II) Ions from Aqueous Media

Efficient Adsorption and Removal of the Herbicide 2,4-Dichlorophenylacetic Acid from Aqueous Solutions Using MIL-88(Fe)-NH2

Metal-organic frameworks (MOFs), a material known for its multifunctionality, chemical stability, and high surface area, are now commonly utilized as an adsorbent for water treatment. The MOF (MIL-88(Fe)-NH2) was synthesized and used to remove the commonly used toxic herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) from water. The MIL-88(Fe)-NH2 MOF was fully characterized using multiple techniques. A systematic investigation was conducted to evaluate the key parameters that impact the adsorption process, which include coexisting anions, adsorbent dosage, and solution pH. The adsorption isotherm was fitted using the Langmuir model, while the kinetics were fitted using pseudo-second-order. The adsorption process was both chemisorption and endothermic. The capacity for adsorption increased with rising temperatures. The MIL-88(Fe)-NH2 adsorbent has a maximum adsorption capacity of 345.25 mg g-1 for removing 2,4-D, significantly higher than previous adsorbents used for this purpose. The adsorption mechanism could be ascribed to hydrogen bonding, pore filling, π-π conjugations between the 2,4-D molecules and the MIL-88(Fe)-NH2 adsorbent, and electrostatic interactions. Furthermore, the adsorption capacity of MIL-88(Fe)-NH2 adsorbent showed only a slight decrease after five successive recycles, and it could be easily regenerated through solvent washing. When used in environmental water samples, especially those containing electronic wastes, the MIL-88(Fe)-NH2 adsorbent demonstrated satisfactory adsorption capacity and reusability. The MIL-88(Fe)-NH2 adsorbent is more practical and reusable and has better adsorption capacity and shorter equilibrium time compared to previously reported adsorbents.

Effect of chitosan on the mechanical properties and acid resistance of metakaolin-blast furnance slag-based geopolymers

Adding organics in the process of geopolymer synthesis can combine the functional groups of organics with the three-dimensional structure of geopolymer, thus changing the properties of geopolymer such as compressive strength, flexural strength, and acid resistance. In this work, excellent mechanical properties and acid resistance of metakaolin-blast furnance slag (Mk-BFS)-based geopolymer were synthesized by the incorporation of chitosan. The formation of sodium-alumino-silicate-hydrate (N-A-S-H) gel and calium-alumino-silicate-hydrate (C-A-S-H) gel in geopolymerization were characterized by ²⁹Si nuclear magnetic resonance (NMR). At 5% of chitosan, the compressive strength of Mk-BFS-based geopolymer could reach to 33.7 MPa. The results could be ascribed to that chitosan reacts with geopolymer to generate new C-O-Si structure meanwhile adhesion produced by the combination of positively charged cations and negatively charged ions makes the structure of geopolymer denser. After 7 days of sulfuric acid immersion, the reduction of compressive strength is less than 3 MPa, demonstrating its great acid resistance. The acid resistance of Mk-BFS-based geopolymer could attribute to that the free amino groups in chitosan preferentially react with acid solution and weakened the erosion of sulfuric acid. This study optimizes the compressive strength and acid resistance of geopolymer by adding appropriate amount of chitosan.

Adsorption of dyestuff by nano copper oxide coated alkali metakaoline geopolymer in monolith and powder forms: Kinetics, isotherms and microstructural analysis

To remove contaminants and pollutants from wastewater systems, adsorbents are widely used. Geopolymers offer a convenient alternative as adsorbents in the wastewater treatment system as they are low-cost, environmentally friendly, and safer. A new adsorbent material prepared by coating nano copper oxide on the surface of alkali-activated metakaolin showed a higher ability to remove methylene blue (MB) dye from wastewater, thus making them attractive in dye removal applications. First, nano copper oxide was prepared by sol gel method and metakaolin geopolymer was produced using sodium silicate solution having a Ms value of 1.1 (M). Afterwards, nano copper oxide (MC) was coated on the surface of the geopolymer. The ability of MB dye to bind to both pristine (M^p, MC^p) and powder forms (M^pr, MC^pr) of the geopolymer was evaluated. X-ray diffraction revealed that the halo found at 27.40°-31.077° (2θvalue) in both samples related to amorphous gel's composition and the major peaks of copper oxide in MC^pr were sited at a 2θ value of 35.45° and 38.88°.The dye removal efficiency can be inferred from the increased adsorption capacity of 11.9 mg/g (M^p) and 14.4 mg/g (MC^p) for the monolith form and 81.43 mg/g (M^pr) and 87.82 mg/g (MC^pr) for the powder form. The adsorption of reused active sites was 73% for M^pr and 83% for MC^pr up to the fifth cycle after regeneration by heat treatment at 400 °C. The models that best suited the adsorption data were pseudo-second-order and Freundlich isotherms, which indicated possible chemisorption with intra-particle diffusion. Furthermore, the binding energy is shifted to lower value in XPS spectra due to dye adsorption arising from electrostatic attraction. A higher electron density is formed due to interaction with an equal contribution of silanol Si-O-H and Si-O-Na/Cu(O1s). The adsorbents are effective over a wide pH range and their improved recycling capability increases their applications for a wide range of uses.

Research progress in the removal of heavy metals by modified chitosan

Chitosan and its modifiers have been widely studied for their good biocompatibility and excellent adsorption properties for heavy metal ions. The synthesis and application of modified chitosan, the effects of process variables (such as pH, amount of adsorbent, temperature, contact time, etc.), adsorption kinetics, thermodynamics and the adsorption mechanism on the removal of heavy metal ions are reviewed. The purpose is to provide the latest information about chitosan as adsorbent and to promote the synthesis of modified chitosan and its application in the removal of heavy metals.

Recovery of Heavy Metal Ions Using Magnetic Glycine-Modified Chitosan—Application to Aqueous Solutions and Tailing Leachate

The necessity of decontaminating effluents for the dual purpose of environmental beneficiation and valorization of low-grade resources is driving the development of new sorbents. The functionalization of biopolymers is a promising strategy for improving sorption performance. Incorporating magnetic micro-particles offers an opportunity for the facilitated recovery of spent micron-size sorbent. Combining magnetic facilities and biopolymer functionalization represents a winning strategy. Magnetic glycine-grafted chitosan (G@MChs) was synthesized for the sorption of Ni(II), Zn(II), and Hg(II) before being applied to the removal of hazardous and strategic metals from tailing leachates. The sorbent was characterized using Fourier transform infrared spectroscopy and scanning electron microscopy, before and after metal sorption. The acid–base properties of functionalized sorbent were also determined (pHPZC). Uptake kinetics were studied in mono- and multi-component solutions using different equations for kinetic modeling at optimized pH (i.e., pH0: 5.5). Langmuir and Sips equations were applied to model sorption isotherms in single-component solutions. In addition, sorption isotherms in multi-component solutions were used to evaluate the preference for selected metals. Maximum sorption capacities were 0.35 mmol Hg g−1, 0.47 mmol Zn g−1, and 0.50 mmol Ni g−1. Acidified urea solution (pH 2.7) successfully desorbs metal ions from G@MChs (desorption > 90%). The sorbent was tested for the recovery of hazardous and strategic metal ions from acidic leachates of tailings. This study demonstrates the promising performance of G@MChs for the treatment of complex metal-bearing solutions.

Research progress of adsorption and removal of heavy metals by chitosan and its derivatives: A review

Chitosan has received widespread attention as an adsorbent for pollutants because of its low cost and great adsorption potentials. Chitosan has abundant hydroxyl and amino groups that can bind heavy metal ions. However, it has defects such as sensitivity to pH, low thermal stability, and low mechanical strength, which limit the application of chitosan in wastewater treatment. The functional groups of chitosan can be modified to improve its performance via crosslinking and graft modification. The porosity and specific surface area of chitosan in powder form are not ideal, therefore, physical modification has been attempted to generate chitosan nanoparticles and hydrogel. Chitosan has also been integrated with other materials (e.g. graphene, zeolite) resulting in composite materials with improved adsorption performance. This review mainly focuses on reports about the application of chitosan and its derivatives to remove different heavy metals. The preparation strategy, adsorption mechanism, and factors affecting the adsorption performance of adsorbents for each type of heavy metal are discussed in detail. Recent reports on important organic pollutants (dyes and phenol) removal by chitosan and its derivatives are also briefly discussed.

Green synthesis of SnO2-ZnO-eggshell nanocomposites and study of their application in removal of mercury (II) ions from aqueous solution

BACKGROUND

Mercury (Hg) in dental amalgam is the world's hidden source of mercury contamination. The development of more eco-friendly and cost-effective adsorbents to reduce mercury pollutants in wastewater is highly desirable and is still a major challenge. In this study, a novel nanocomposite was synthesized and used as an efficient adsorbent for the removal of Hg(II) ions from aqueous solution.

METHODS

A green and cost-effective method was described to the synthesis of SnO₂-ZnO-eggshell nanocomposites using teucrium polium extract as a renewable reductant and mild stabilizer. The biosynthesized nanocomposites were characterized by various techniques. The novel SnO₂-ZnO-eggshell nanocomposites were used as an effective adsorbent in the removal of mercury (II) ions. To achieve the maximum absorption efficiency of Hg(II) ions, the effect of operating factors such as pH value, the dose of catalyst, the initial metal concentration of Hg(II) ions, and catalyst type were evaluated.

RESULTS

The removal percentage and adsorption capacity of Hg(II) were obtained 99.15% and 396.6 mg.g^-1, respectively, under optimal conditions after 5 minutes. The selectivity of SnO₂-ZnO-eggshell nanocomposites for the adsorption of metal ions was studied, and the highest selectivity was obtained for adsorption of Hg (II) ions. Furthermore, the SnO₂- ZnO-eggshell nanocomposites could be recovered and reused at least three times without considerable loss of their efficiency.

CONCLUSIONS

The present approach has advantages such as rapidity, simplicity, selectivity, low cost and, most importantly, the use of nanocomposites containing a bio-waste material of eggshell for removal of Hg(II) ions from aqueous solution.