Synthesis of membrane-type graphene oxide immobilized manganese dioxide adsorbent and its adsorption behavior for lithium ion

Study of the Reaction Mechanism of the Excessive Adsorption of Mn2+ from Water by In Situ Synthesis of MnO2@SiO2 Colloid as an Adsorbent

An in situ-generated MnO2@SiO2 colloidal (ISMC) composite was used for the adsorption of Mn2+ ions in water. The adsorption capacity of ISMC at a concentration of 1 mg/L at 25 °C was as high as 3017.97 mg/g for the original concentration of 50 mg/L Mn2+ ions. Material characterization revealed that it is a porous sponge with a fibrous structure with a rough surface, many folds, and abundant pores, and these features provide many adsorption sites, which are conducive to the attachment of Mn2+ ions on its surface. ISMC has an isoelectric point of 3.5, indicating a negative surface charge that favors electrostatic attraction of Mn2⁺ ions. The surface hydroxyl groups provide additional active sites that allow for strong complexation with Mn2⁺ ions. Adsorption conformed to the Freundlich isotherm model (R2 > 0.98), suggesting multilayer adsorption, followed by pseudo-second-order kinetics (R2 > 0.98), with an optimum adsorption time of approximately 12 h. Low temperatures favor physical adsorption, whereas higher temperatures promote chemisorption via hydroxyl group complexation. The adsorption capacity increased with pH, which was attributed to the increased presence of surface hydroxyl groups. These findings highlight the significant potential of ISMCs for cation adsorption in water treatment applications.

Lithium-Ion-Sieve Hydrogel Based on Aluminum Doping with High Stretchability, Strong Adsorption Capacity and Low Dissolution Loss

In recent years, with the development of the new energy industry, lithium resources need to be supplied in large quantities. The lithium-ion sieve (LIS) is regarded as an ideal adsorbent for recovering lithium resources from brine because of its excellent lithium adsorption capacity and structural stability. However, because it is powdery after molding, and there will be problems such as dissolution loss of manganese, which limits its industrial development. In this study, in the process of preparing hydrogels of acrylic acid (AA), acrylamide (AM) and chitosan (CS), an LIS hydrogel with high mechanical properties, strong adsorption capacity and low dissolution loss was prepared by doping LIS and Al ions. Among them, the stress of the prepared chitosan-acrylic acid-acrylamide hydrogel (PASA-1) with an Al doping content of 1% reached 603 KPa, and the maximum strain reached 189%, which showed excellent damage resistance. In addition, the adsorption performance of PASA-1 reached 43.2 mg/g, which was excellent, which was attributed to the addition of Al ions, which inhibited the dissolution loss of manganese ions. This idea has great potential in the direction of lithium resource recovery and provides a new method for the use of hydrogel in the direction of lithium-ion sieves.

Granulation of Lithium-Ion Sieves Using Biopolymers: A Review

The high demand for lithium (Li) relates to clean, renewable storage devices and the advent of electric vehicles (EVs). The extraction of Li ions from aqueous media calls for efficient adsorbent materials with various characteristics, such as good adsorption capacity, good selectivity, easy isolation of the Li-loaded adsorbents, and good recovery of the adsorbed Li ions. The widespread use of metal-based adsorbent materials for Li ions extraction relates to various factors: (i) the ease of preparation via inexpensive and facile templation techniques, (ii) excellent selectivity for Li ions in a matrix, (iii) high recovery of the adsorbed ions, and (iv) good cycling performance of the adsorbents. However, the use of nano-sized metal-based Lithium-ion sieves (LISs) is limited due to challenges associated with isolating the loaded adsorbent material from the aqueous media. The adsorbent granulation process employing various binding agents (e.g., biopolymers, synthetic polymers, and inorganic materials) affords composite functional particles with modified morphological and surface properties that support easy isolation from the aqueous phase upon adsorption of Li ions. Biomaterials (e.g., chitosan, cellulose, alginate, and agar) are of particular interest because their structural diversity renders them amenable to coordination interactions with metal-based LISs to form three-dimensional bio-composite materials. The current review highlights recent progress in the use of biopolymer binding agents for the granulation of metal-based LISs, along with various crosslinking strategies employed to improve the mechanical stability of the granules. The study reviews the effects of granulation and crosslinking on adsorption capacity, selectivity, isolation, recovery, cycling performance, and the stability of the LISs. Adsorbent granulation using biopolymer binders has been reported to modify the uptake properties of the resulting composite materials to varying degrees in accordance with the surface and textural properties of the binding agent. The review further highlights the importance of granulation and crosslinking for improving the extraction process of Li ions from aqueous media. This review contributes to manifold areas related to industrial application of LISs, as follows: (1) to highlight recent progress in the granulation and crosslinking of metal-based adsorbents for Li ions recovery, (2) to highlight the advantages, challenges, and knowledge gaps of using biopolymer-based binders for granulation of LISs, and finally, (3) to catalyze further research interest into the use of biopolymer binders and various crosslinking strategies to engineer functional composite materials for application in Li extraction industry. Properly engineered extractants for Li ions are expected to offer various cost benefits in terms of capital expenditure, percent Li recovery, and reduced environmental footprint.

Birnessite-Type MnO2 Modified Sustainable Biomass Fiber toward Adsorption Removal Heavy Metal Ion from Actual River Aquatic Environment

In this work, a novel birnessite-type MnO2 modified corn husk sustainable biomass fiber (MnO2@CHF) adsorbent was fabricated for efficient cadmium (Cd) removal from aquatic environments. MnO2@CHF was designed from KMnO4 hydrothermally treated with corn husk fibers. Various characterization revealed that MnO2@CHF possessed the hierarchical structure nanosheets, large specific surface area, and multiple oxygen-containing functional groups. Batch adsorption experimental results indicated that the highest Cd (II) removal rate could be obtained at the optimal conditions of adsorbent amount of 0.200 g/L, adsorption time of 600 min, pH 6.00, and temperature of 40.0 °C. Adsorption isotherm and kinetics results showed that Cd (II) adsorption behavior on MnO2@CHF was a monolayer adsorption process and dominated by chemisorption and intraparticle diffusion. The optimum adsorption capacity (Langmuir model) of Cd (II) on MnO2@CHF was 23.0 mg/g, which was higher than those of other reported common biomass adsorbent materials. Further investigation indicated that the adsorption of Cd (II) on MnO2@CHF involved mainly ion exchange, surface complexation, redox reaction, and electrostatic attraction. Moreover, the maximum Cd (II) removal rate on MnO2@CHF from natural river samples (Xicheng Canal) could reach 59.2% during the first cycle test. This study showed that MnO2@CHF was an ideal candidate in Cd (II) practical application treatment, providing references for resource utilization of agricultural wastes for heavy metal removal.

Adsorption performance and mechanism of Li+ from brines using lithium/aluminum layered double hydroxides-SiO2 bauxite composite adsorbents

A combined method of solid-phase alkali activation and surface precipitation was used to prepare the lithium/aluminum layered double hydroxides-SiO2 loaded bauxite (LDH-Si-BX) and applied to adsorb Li+ in brines. In the study, various characterization techniques such as SEM, XRD, BET, Zeta potential, and x-ray photoelectron spectroscopy (XPS) were applied to characterize and analyze the adsorbents. The adsorption-desorption performance of LDH-Si-BX for Li+ in brines was systematically investigated, including adsorption temperature, adsorption time, Li+ concentration, and regeneration properties. The results indicated that the adsorption kinetics were better fitted by the pseudo-second-order model, whereas the Langmuir model could match the adsorption isotherm data and the maximum Li+ capacity of 1.70 mg/g at 298K. In addition, in the presence of coexisting ions (Na+, K+, Ca2+, and Mg2+), LDH-Si-BX showed good selective adsorption of Li+, and the pH studies demonstrated that the adsorbents had better Li+ adsorption capacity in neutral environments. In the adsorption process of real brines, LDH-Si-BX had a relatively stable adsorption capacity, and after 10 cycles of adsorption and regeneration, the adsorption capacity decreased by 16.8%. It could be seen that the LDH-Si-BX adsorbents prepared in this report have the potential for Li+ adsorption in brines.

Study on the Adsorption Mechanism of Cobalt and Nickel in Manganese Sulfate by δ-MnO2

Manganese has excellent performance in removing metal ions from aqueous solutions, but there are few studies on the adsorption and removal of heavy metal impurities in metal salt solutions. In this paper, the adsorption of cobalt and nickel ions in MnSO₄ solution by δ-MnO₂ prepared from two different manganese sources was studied. The optimum adsorption conditions were as follows: When the concentration of Mn²⁺ was 20 g/L, δ-MnO₂ addition was 10 g/L, Co²⁺ concentration was 80 mg/L, Ni²⁺ concentration was 80 mg/L, reaction time was 60 min, reaction temperature was 80 °C, and pH value was 7, the adsorption rate of Co²⁺ and Ni²⁺ reached more than 80%. The manganese dioxide adsorbed by heavy metals was analyzed and detected. The results showed that MnOOH appeared in the phases of both kinds of δ-MnO₂, and their morphologies were dense rod-like structures with different lengths and flake-like structures of fine particles. Co and Ni were distributed on the surface and gap of MnO₂ particles, and the atomic percentage of Co was slightly higher than that of Ni. The new vibration peaks appeared near wave numbers of 2668.32, 1401.00, and 2052.19 cm^-1, which were caused by the complexation of cations such as Co^2 + and Ni^2 + with hydroxyl groups. Some cobalt and nickel appeared on the surface of δ-MnO₂, and the surface oxygen increased after adsorption. The above characterization revealed that the adsorption of cobalt and nickel in manganese sulfate by δ-MnO₂ was realized by the reaction of its surface hydroxyl with metal ions (M) to form ≡SOMOH.

Recent Advances in the Lithium Recovery from Water Resources: From Passive to Electrochemical Methods

The ever-increasing amount of batteries used in today's society has led to an increase in the demand of lithium in the last few decades. While mining resources of this element have been steadily exploited and are rapidly depleting, water resources constitute an interesting reservoir just out of reach of current technologies. Several techniques are being explored and novel materials engineered. While evaporation is very time-consuming and has large footprints, ion sieves and supramolecular systems can be suitably tailored and even integrated into membrane and electrochemical techniques. This review gives a comprehensive overview of the available solutions to recover lithium from water resources both by passive and electrically enhanced techniques. Accordingly, this work aims to provide in a single document a rational comparison of outstanding strategies to remove lithium from aqueous sources. To this end, practical figures of merit of both main groups of techniques are provided. An absence of a common experimental protocol and the resulting variability of data and experimental methods are identified. The need for a shared methodology and a common agreement to report performance metrics are underlined.

Relationship between Surface Hydroxyl Complexation and Equi-Acidity Point pH of MnO2 and Its Adsorption for Co2+ and Ni2

MnO₂ has shown great potential in the field of adsorption and has a good adsorption effect on heavy metal ions in aqueous solution, but there have been problems in the adsorption of heavy metal ions in high-concentration metal salt solutions. In this paper, different crystal forms of MnO₂ (α-MnO₂, β-MnO₂, γ-MnO₂, δ₁-MnO₂, δ₂-MnO₂, and ε-MnO₂) were prepared and characterized by XRD, SEM, EDS, XPS, ZETA, and FT-IR. The reasons for the equi-acidity point pH change of MnO₂ and the complex mechanism of surface hydroxylation on metal ions were discussed. The results showed that the equi-acidity point pHs of different crystalline MnO₂ were different. The equi-acidity point pH decreased with the increase of reaction temperature and electrolyte concentration, but the reaction time had no effect on it. The equi-acidity point pHs of MnO₂ were essentially equal to the equilibrium pH values of adsorption and desorption between surface hydroxyl and metal ions on them. The change of equi-acidity points was mainly due to the complexation of surface hydroxyl, and the equi-acidity point pHs depended on the content of surface hydroxyl and the size of the complexation ability. According to the equi-acidity point pH characteristics of MnO₂, more hydroxyl groups could participate in the complexation reaction by repeatedly controlling the pH, so that MnO₂ could adsorb heavy metals Co²⁺ and Ni²⁺ in high-concentration MnSO₄ solution, and the adsorption rates of Co²⁺ and Ni²⁺ could reach 96.55 and 79.73%, respectively. The effects of MnO₂ dosage and Mn²⁺ concentration on the adsorption performance were further investigated, and the products after MnO₂ adsorption were analyzed by EDS and FT-IR. A new process for MnO₂ to adsorb heavy metals Co²⁺ and Ni²⁺ in high-concentration MnSO₄ solution was explored, which provided a reference for the deep purification of manganese sulfate solutions.

Proteinaceous porous nanofiber membrane-type adsorbent derived from amyloid lysozyme protofilaments for highly efficient lead(II) biologic scavenging

To overcome the technical bottleneck of fine amyloid lysozyme fibrils in environmental engineering, a novel co-operative strategy was identified to fabricate free-standing lysozyme complex nanofibers based membrane-type adsorbent (Lys-CNFs membrane) through a combination of vacuum filtration for lead remediation. The composition of the membrane integrated the linear amyloid protofilaments that were obtained by acid-heating fibrillation and polydopamine that adjusted the fibers' diameters and surface chemistry. As expected, the Lys-CNFs membrane not only showed nanofibrous morphology and layer stacking architecture but presented a hierarchical macro-mesoporous structure along with a high surface area of 220.4 m²/g. Besides, the thermal stability up to 200 ℃ and wetting nature of below 2 s endowed its further applicability. Adsorption experiments showed that Lys-CNFs membrane can effectively uptake Pb(II) ions with acceptable selectivity, high adsorption capacity of 270.3 mg/g, rapid equilibrium kinetic within only 10 mins, and good reusability that dropped by 14.9% efficiency even after five cycles, indicating that Lys-CNFs membrane can be as an affordable technology for alleviating the lead pollution issues.