Adsorption characteristics of Pb(II), Cd(II) and Cu(II) on carbon nanotube-hydroxyapatite

Magnetized bentonite modified rice straw biochar: Qualitative and quantitative analysis of Cd(II) adsorption mechanism

Industrialization has caused a significant global issue with cadmium (Cd) pollution. In this study, Biochar (Bc), generated through initial pyrolysis of rice straw, underwent thorough mixing with magnetized bentonite clay, followed by activation with KOH and subsequent pyrolysis. Consequently, a magnetized bentonite modified rice straw biochar (Fe3O4@B-Bc) was successfully synthesized for effective treatment and remediation of this problem. Fe3O4@B-Bc not only overcomes the challenges associated with the difficult separation of individual bentonite or biochar from water, but also exhibited a maximum adsorption capacity of Cd(II) up to 241.52 mg g-1. The characterization of Fe3O4@B-Bc revealed that its surface was rich in C, O and Fe functional groups, which enable efficient adsorption. The quantitative calculation of the contribution to the adsorption mechanism indicates that cation exchange and physical adsorption accounted for 65.87% of the total adsorption capacity. In conclusion, Fe3O4@B-Bc can be considered a low-cost and recyclable green adsorbent, with broad potential for treating cadmium-polluted water.

Adsorption of Cd (II) ions and methyl violet dye by using an agar-graphene oxide nano-biocomposite

In this work, an agar-graphene oxide hydrogel was prepared to adsorb Cd (II) and Methyl Violet (MV) from water. The hydrogel was synthesised and characterised through SEM and EDS. Kinetic, equilibrium and regeneration studies were carried out, in which Langmuir, Freundlich and Sips isotherm models were fitted to the equilibrium experimental data; and regarding the kinetics, studies were conducted by modelling experimental data considering both empirical and phenomenological models. SEM and EDS have shown the composite present a 3D-disordered porous microstructure and that it is mainly constituted of C and O. Sips model fitted well to Cd (II) (R2 = 0.968 and χ2 =  0.176) and MV (R2 = 0.993 and χ2 =  0.783). The qmax values for MV and Cd (II) were 76.65 and 11.70 mg.g-1, respectively. Pseudo-order models satisfactorily described Cd (II) and MV adsorption kinetics with R2 > 0.90. Regeneration experiments revealed an outstanding reuse capacity of the adsorbent after three cycles of adsorption-desorption for both Cd (II) and MV. This study evidences the possibility of a feasible adsorbent for Cd (II) and MV removal from water for successive cycles of use.

Resourcization of Argillaceous Limestone with Mn3O4 Modification for Efficient Adsorption of Lead, Copper, and Nickel

Argillaceous limestone (AL) is comprised of carbonate minerals and clay minerals and is widely distributed throughout the Earth's crust. However, owing to its low surface area and poorly active sites, AL has been largely neglected. Herein, manganic manganous oxide (Mn3O4) was used to modify AL by an in-situ deposition strategy through manganese chloride and alkali stepwise treatment to improve the surface area of AL and enable its utilization as an efficient adsorbent for heavy metals removal. The surface area and cation exchange capacity (CEC) were enhanced from 3.49 to 24.5 m2/g and 5.87 to 31.5 cmoL(+)/kg with modification, respectively. The maximum adsorption capacities of lead (Pb2+), copper (Cu2+), and nickel (Ni2+) ions on Mn3O4-modified argillaceous limestone (Mn3O4-AL) in mono-metal systems were 148.73, 41.30, and 60.87 mg/g, respectively. In addition, the adsorption selectivity in multi-metal systems was Pb2+ > Cu2+ > Ni2+ in order. The adsorption process conforms to the pseudo-second-order model. In the multi-metal system, the adsorption reaches equilibrium at about 360 min. The adsorption mechanisms may involve ion exchange, precipitation, electrostatic interaction, and complexation by hydroxyl groups. These results demonstrate that Mn3O4 modification realized argillaceous limestone resourcization as an ideal adsorbent. Mn3O4-modified argillaceous limestone was promising for heavy metal-polluted water and soil treatment.

Preparation and adsorption properties of magnetic chitosan/sludge biochar composites for removal of Cu2+ ions

The magnetic chitosan/sludge biochar composite adsorbent was prepared using chitosan, Fe3O4, and sludge biochar as raw materials. The composite adsorbent was able to achieve rapid solid-liquid separation under an applied magnetic field. The morphology and microstructure of the composite adsorbent were characterized by FTIR, XRD, SEM, VSM, and BET analysis. The adsorption performance of the composite adsorbent on Cu2+ was investigated through static adsorption experiments, and the effects of adsorbent dosage, initial concentration of Cu2+, initial pH of the solution, and adsorption temperature on the adsorption efficiency of Cu2+ were discussed. The results showed that chitosan and Fe3O4 were successfully loaded on sludge biochar. When the initial concentration of Cu2+ was 30 mg/L, the dosage of the magnetic chitosan/sludge biochar composite material was 0.05 g, the adsorption time was 180 min, pH was 5, and the temperature was room temperature, the maximum removal rate of Cu2+ reached 99.77%, and the maximum adsorption capacity was 55.16 mg/g. The adsorption kinetics and adsorption isotherm data fitted well with the pseudo-second-order kinetic model and Langmuir adsorption isotherm model, indicating that the adsorption process was chemisorption with monolayer coverage.

Green synthesized hydroxyapatite for efficient immobilization of cadmium in weakly alkaline environment

The development of cost-effective passivators for the remediation of heavy metal-contaminated soils has been a research hotspot and an unsolved challenge. Herein, a novel hydroxyapatite (GSCH) was synthesized by co-precipitating distiller effluent-derived Ca with (NH₄)₂HPO₄ using straw-derived dissolved organic matter (S-DOM) as the dispersant. Batch adsorption experiments and soil incubation tests were performed to assess the immobilization efficiency of GSCH for Cd in weakly alkaline environments. As a result, GSCH showed an excellent adsorption efficiency to Cd with a maximum adsorption amount of ∼222 mg g^-1, which was fairly competitive compared to other similar previously materials reported. The kinetic data indicated that the adsorption of Cd on GSCH was a chemical and irreversible process, while the thermodynamic data revealed a spontaneous (ΔG° < 0) and endothermic (ΔH° > 0) adsorption process. Based on mechanism analysis, both physisorption (e.g., electrostatic attraction and pore filling) and chemisorption (e.g., ion exchange and complexation) were responsible for Cd adsorption on GSCH. Particularly, the incorporated S-DOM and hydroxyapatite phase in GSCH acted synergistically in the adsorption process. The incubation results showed that GSCH application could significantly reduce the bioavailability, phytoavailability and bioaccessibility of Cd in soil by 48.4%-57.8%, 20.4%-28.6% and 12.6%-24.0%, respectively. Moreover, GSCH application also improved soil bacterial communities and enhanced soil nutrient availability. Overall, this is the first study to demonstrate the potential application value of GSCH in Cd immobilization, providing promising insights into the development of green and cost-effective hydroxyapatite-based passivators for the remediation of heavy metal-contaminated soils.

Highly efficient Cd(Ⅱ) removal using 3D N-doped carbon derived from MOFs: Performance and mechanisms

Cadmium (Cd) removal is imperative to ensure the safety of aquatic-ecosystem, yet its effective removal technology has remained elusive by far. To address this concern, three-dimensional N-doped carbon (NC) polyhedrons affording ample porosity is fabricated based upon the thermal carbonization and KOH activation of zeolitic imidazolate framework-8 (ZIF-8) precursor. Thus-derived activated NC (a-NC) adsorbent not only overcomes the inherent instability of ZIF-8 but also harvests a maximum Cd(Ⅱ) adsorption capacity of 370.2 mg g^-1, which evidently surpasses those of bare NC counterpart as well as previously reported adsorbents. Impressively, a-NC achieves ca. 100% removal of aqueous Cd(Ⅱ) in a broad working pH range (5-9), and particularly attains stable performances (81-92%) in various realistic water. Theoretical calculations in combination with experimental characterizations further offer mechanistic insight into the enhanced removal exerted by a-NC. Notably, owing to the increased specific surface area (3041 vs. 389 m² g^-1) and enhanced sp² carbon content (91.7 vs. 68.8%) of a-NC as compared to NC, advanced Cd(Ⅱ) adsorption via a-NC can be exhibited. Our designed a-NC material harnessing favorable recycling capability would be in particular attractive in the realm of practical Cd(Ⅱ) remediation.

Tobacco Waste Liquid-Based Organic Fertilizer Particle for Controlled-Release Fulvic Acid and Immobilization of Heavy Metals in Soil

Every year, a large amount of tobacco waste liquid (TWL) is discharged into the environment, resulting in serious pollution for the environment. In this work, a TWL-based particle (OACT) was fabricated by CaO, attapulgite (ATP), and TWL, and, then, OACT was coated by amino silicon oil (ASO) to form OACT@ASO. Therein, OACT@ASO had high controlled-release ability for fulvic acid (FA), because of the nanonetworks structure for ATP and the high content of FA in TWL. The release ratio (RR) of FA from OACT@ASO reached 94% at 75 h in deionized water, and 23% at 32 d in silica sand. Furthermore, the release mechanism of FA from OACT@ASO was consistent with the First-order law. Additionally, OACT@ASO also possessed high immobilization capacity for Cu(II), Cd(II), and Pb(II) (CCP) in soil. Notably, a pot experiment indicated that OACT@ASO could facilitate the growth of pakchoi seedlings and decrease the absorption of CCP by pakchoi seedlings. Thus, this study provides a new kind of organic fertilizer which could not only release FA, but also immobilize CCP in soil.

APTMS-BCAD modified magnetic iron oxide for magnetic solid-phase extraction of Cu(II) from aqueous solutions

Fe₃O₄@SiO₂-3-aminopropyltrimethoxysilane-1,8-bis (3-chloropropoxy) anthracene-9,10-dione was synthesized as a new, sustainable, and environmentally friendly adsorbent for magnetic solid-phase extraction of Cu(II) from aqueous solutions. The structure of the adsorbent was characterized by FTIR, XRD, SEM, EDX, and TEM analysis. Optimum conditions for Cu(II) adsorption were determined as adsorbent dose 0.04 g, pH 5.0, contact time 120 min, and beginning concentration of 30 mg/L in the adsorption process. The adsorption capacity for Cu(II) ions was 43.67 mg/g and the removal efficiency was 84.72 percent. The Langmuir isotherm and the pseudo-second-order model fit the experimental data better. Adsorption was a spontaneous and endothermic process based on the obtained thermodynamic properties such as ΔG°, ΔH°, and ΔS°. The results showed that the sorbent has good selectivity in the presence of competing ions. The method was determined to be accurate and effective using real water samples and CRM.

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Magnetic Fe₃O₄@SiO₂-3-aminopropyl-trimethoxysilane-1,8-bis(3-chloropro-poxy) anthracene-9,10-dione was synthesized as a new, sustainable, and environmentally friendly adsorbent for magnetic solid-phase extraction of Cu(II) from aqueous solutions.

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The results showed that the presence of competitor ions did not have a significant effect on the sorption of Cu(II) ion and the sorbent had good selectivity.

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Using real water samples and CRM, the method was found to be accurate and effective.

Recent Progress in the Application of Hydroxyapatite for the Adsorption of Heavy Metals from Water Matrices

Wastewater treatment remains a critical issue globally, despite various technological advancements and breakthroughs. The study of different materials and technologies gained new valences in the last years, in order to obtain cheap and efficient processes, to obtain a cleaner environment for future generations. In this context, the present review paper presents the new achievements in the materials domain with highlights on apatitic materials used for decontamination of water loaded with heavy metals. The main goal of this review is to present the adsorptive removal of heavy metals using hydroxyapatite-based adsorbents, offering a general overview regarding the recent progress in this particular area. Developing the current review, an attempt has been made to give appropriate recognition to the most recent data regarding the synthesis methods and targeted pollutants, including important information regarding the synthesis methods and precursors, morphological characteristics of the adsorbent materials and effectiveness of processes.