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The recovery of silver ions from wastewater is of great importance due to their adverse environmental impact and significant economic value. This paper introduces a novel adsorbent (CS-AHMT) that can be easily synthesized via a one-step functionalization of chitosan with 4-Amino-3-hydrazino-1,2,4-triazol-5-thiol to efficiently recover silver ions from actual wastewater. CS-AHMT demonstrated superior adsorption performance, achieving an adsorption capacity of 241.4 mg·g -1 at pH 5 and 318 K, and the adsorption equilibrium was rapidly attained within 60 to 120 min. Kinetic and isotherm studies indicate that the adsorption process conforms to the pseudo-nth-order (PNO) and Sips models, suggesting a monolayer adsorption that incorporates both physical and chemical processes, with internal mass transfer being the primary rate-limiting step. Electrostatic and coordination interactions are primarily involved in the adsorption mechanism of silver ions on CS-AHMT, as further validated by density functional theory (DFT) calculations. The selectivity and practical applicability of CS-AHMT were confirmed in real wastewater containing high concentrations of competing ions. The findings underscore the potential of CS-AHMT as an effective adsorbent for silver ion recovery in wastewater treatment applications., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

In this investigation, a composite material comprising Ti-MOF and chitosan, denoted as BD-MOF(Ti)@CS/Fe 3 O 4 , was successfully designed for the efficient adsorption of Pb(II) from aqueous solutions. A comprehensive array of characterization techniques, including SEM, XRD, BET, FT-IR, and XPS, were meticulously employed to scrutinize the structural attributes and morphological features of the Pb(II) adsorbent. Notably, the material exhibits adaptability to a broad pH range, with adsorption efficiency reaching 99 % between pH 3 and 6. Kinetic studies reveal that the adsorption process of Pb(II) by BD-MOF(Ti)@CS/Fe 3 O 4 adheres closely to a pseudo-second-order kinetic model. Impressively, within a short duration of 40 min, the adsorption efficiency can reach 85 %. Furthermore, the adsorption isotherm aligns with the Hill isotherm model, signifying cooperative adsorption. This observation underscores the synergistic interplay among the functional groups on the surface of BD-MOF(Ti)@CS/Fe 3 O 4 in capturing Pb(II). As per the Hill model, the theoretical maximum capacity was an impressive 944.9 mg/g. Thermodynamic assessments suggested that the adsorption process was spontaneous, entropy increasing and exothermic. Even in the presence of various interfering ions, BD-MOF(Ti)@CS/Fe 3 O 4 exhibited robust adsorption performance, thereby affirming its utility in complex environments. Moreover, the material demonstrates noteworthy reusability, sustaining effective Pb(II) removal across five consecutive cycles in aqueous solutions., Competing Interests: Declaration of competing interest No conflict of interest exits in the submission of this manuscript, and manuscript is approved by all authors for publication. I would like to declare on behalf of my co-authors that the work described was original research that has not been published previously, and not under consideration for publication elsewhere, in whole or in part. All the authors listed have approved the manuscript that is enclosed., (Copyright © 2024 Elsevier B.V. All rights reserved.)

An O-hydroxyphenyl thiourea-modified chitosan (OTCS) with excellent Pb(II) adsorption performance and selectivity was prepared as an adsorbent. The structure and morphology of the adsorbent were systematically investigated by SEM, BET, FTIR, EDX, zeta-potential measurements, XPS and XRD. The impacts of the initial Pb(II) concentration, reaction time, temperature, pH value, and coexisting ions were explored. At pH 7 and 303 K, the maximal adsorption capacity of OTCS for Pb(II) was 208.33 mg/g, which was greater than those of other adsorbing materials reported in the literature. The metal ion adsorption kinetics and isotherm models were found to obey pseudo-second-order kinetics and the Langmuir isothermal model, indicating that the adsorption process was monolayer chemisorption. The adsorption process could proceed spontaneously, and the thermodynamic results revealed that the adsorption mechanism was an endothermic reaction. The ion exchange and chelation between the sulfur, nitrogen and oxygen groups on the adsorbent and lead ions endowed the material with excellent adsorption properties. Significantly, OTCS showed excellent selectivity toward Pb(II). Therefore, the adsorbent OTCS is expected to promote the wider application of chitosan in the adsorption of Pb(II)., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

The recovery of gold from wastewater has always been a research hotspot. Here, a novel chitosan-based adsorbent (CS-DPDM) was successfully synthesized by functionalizing chitosan with (N, N-(2-aminoethyl))-2,6-pyridinedicarboxamide. The adsorbent was analyzed by fourier transform infrared spectroscopy (FT-IR), nuclear magnetic resonance spectroscopy ( 1 H NMR), scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and zeta potential method (Zeta). To investigate the adsorption performance of CS-DPDM for Au(III), the effects of pH, temperature, adsorption time and initial concentration were discussed. The maximum adsorption capacity of CS-DPDM for Au(III) at pH 5.0 is 659.02 mg/g at 318 K. The adsorption is a spontaneous endothermic behavior, and the adsorption process follows the quasi-second-order kinetic and Langmuir isotherm models, indicating that a single layer of chemical adsorption may have occurred on the surface of the adsorbent. The competitive adsorption and repetitive experiments show that CS-DPDM has considerable selectivity and reusability for Au(III). X-ray photoelectron spectroscopy (XPS) results show that N and O functional groups adsorb Au(III) on the surface of CS-DPDM through electrostatic, chelation and reduction. These results indicate that CS-DPDM has broad application prospects in recovering gold ions from aqueous solutions., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Pollution generated by heavy metals has become a global environmental issue with much public concern. Herein, a functionalized chitosan-based adsorbent (CS-PAR) was synthesized via a simple one-step method for the adsorption of copper ions in solutions. A series of characterization methods have shown that CS-PAR was successfully synthesized. The experimental results showed that the maximum adsorption capacity of CS-PAR for Cu(II) ions was 170.23 mg/g. The adsorption process of Cu(II) on CS-PAR conformed to Langmuir and pseudo second-order models and belonged to a single-layer chemical adsorption process on the surface of a homogeneous medium. The adsorption mechanism of the adsorbent to Cu(II) ions was the complexation between the N-containing functional groups existing on the surface of the adsorbent and Cu(II). These results also showed that the adsorbent was an efficient material for removing heavy metal copper in wastewater and had very important practical significance., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

A novel benzothiazole modified chitosan (BCS) with excellent Au(III) adsorption performance and selectivity was prepared as adsorbents. The structure and morphology of the adsorbents were characterized by FTIR, SEM, XRD and XPS. The adsorption property of the adsorbents for Au(III) were investigated under different reaction time, initial concentration of Au(III), temperature, pH and coexisting ions. The maximum adsorption capacity of BCS for Au(III) was 1072.22 mg/g at 298 K and optimal pH = 4, which was better than that of other adsorbents reported in literature. The adsorption kinetics and isotherm models fit the pseudo-second-order and Langmuir equations. This shows that the adsorption process of Au(III) is a monolayer chemical adsorption. The adsorption process can proceed spontaneously and belong to the endothermic reaction according to the thermodynamic results. The excellent adsorption performance is mainly attributed to the ion exchange and chelation of the nitrogen, sulfur and oxygen groups on the adsorbent with gold ions. Significantly, BCS has excellent selectivity toward Au(III) and remarkable recycle performance. With the high adsorption capacity, excellent selectivity and outstanding reusability, the BCS adsorbent could be a promising candidate to adsorb Au(III) from wastewater., (Copyright © 2021 Elsevier B.V. All rights reserved.)

A chitosan-based adsorbents (CS-Ninhydrin) was prepared by grafting ninhydrin for Pb(II) ions adsorption. SEM-EDS, XRD and FTIR analysis were used to characterize the synthesized CS-Ninhydrin. The static adsorption experiments showed that CS-Ninhydrin had a good removal rate for Pb(II) ions in a wide range of pH 3 to 7, quickly reached equilibrium (120 min) and had a higher adsorption capacity (196 mg/g). Pseudo second-order and Langmuir models showed that the adsorption process of Pb(II) by CS-Ninhydrin was a single-layer chemical adsorption. Temperature experiments showed that the reaction was a spontaneous exothermic process. In the wastewater experiment, CS-Ninhydrin showed an excellent selectivity to Pb(II) ions. The reusability of CS-Ninhydrin was perfect after five adsorption-desorption cycles. The main adsorption mechanism was the chelating and electrostatic action between N and O groups in CS-Ninhydrin and Pb(II) ions. Therefore, the new adsorbent CS-Ninhydrin was expected to promote the wide application of chitosan in Pb(II) adsorption., (Copyright © 2018 Elsevier B.V. All rights reserved.)

The recovery of gold from wastewater has received significant attention in the last years due to its high economic value and low availability. A novel chitosan-based adsorbent (CS-GTU) was successfully synthesized by using formaldehyde as a crosslinker between chitosan and guanylthiourea, and applied for selective adsorption of Au III from an aqueous medium. Through batch experiments, the maximum adsorption capacity of CS-GTU for Au III could reach up to 695.63 mg/g at pH 5.0, and the adsorption process followed the Pseudo-second-order kinetic and Langmuir isotherm models, indicating that the monolayer chemisorption possibly occurred on the adsorbent surfaces. The adsorption was an enthalpy driven and spontaneous chemical process based on thermodynamic analysis. Furthermore, the adsorbent has demonstrated outstanding selectivity toward Au III from multi-metallic solutions, and five cycled experiments of adsorption-desorption showed that CS-GTU could be efficiently regenerated. Experimental breakthrough curves were successfully simulated by using the Thomas model, which can fit the experimental data with the correlated curve (R 2  > 0.9) well. This improvement in adsorption was a consequence of the complexation and electrostatic attraction of gold ions with the abundant sulfur/nitrogen-containing groups. The CS-GTU beads can be considered as a suitable and efficient adsorbent for gold ions in aqueous solutions., Competing Interests: Declaration of competing interest The authors declare no competing financial interest., (Copyright © 2021 Elsevier B.V. All rights reserved.)

A novel magnetic chitosan adsorbent (CDF-CS) was synthesized by inserting magnetic particles into the crosslinked compound of chitosan (CS) and cystamine based on one-step method for selectively recovering Au(III) from aqueous solution. The characterization and adsorption mechanism of CDF-CS were studied by SEM-EDS, VSM, FT-IR and XPS, respectively. The experimental results show that the adsorption capacity of CDF-CS is still large in a wide range of pH values (from 1 to 7) and has a higher adsorption capacity for Au(III) than the raw chitosan, the maximum adsorption capacity of CDF-CS for Au(III) was 478.47 mg/g about 6 h at pH = 7.0. The adsorption behavior is most consistent with this pseudo-second-order kinetic model. The adsorption process of gold ions by CDF-CS follows the Langmuir adsorption isotherm. Furthermore, the thermodynamic parameter indicates that the adsorption reaction of gold ions by CDF-CS is an endothermic chemisorption. CDF-CS has great potential for removing gold ions from aqueous solutions due to the excellent repeatability and selectivity. Finally, the adsorption mechanism is that chelation reaction and ion exchange mainly occurred between CDF-CS and Au(III). Therefore, CDF-CS is very promising in recovery of Au(III) from aqueous solutions., (Copyright © 2019 Elsevier B.V. All rights reserved.)

The gold recovery from wastewater is not only beneficial to environmental protection, but also to alleviate the shortage of resources. Chitosan is considered as an excellent adsorption material, but its application in gold recovery is always some shortcomings including low adsorption capacity and selectivity. This work developed an efficient biosorbent (CS-ES) by functionalizing chitosan with poly(ethylene sulfide) for gold recovery from simulated wastewater. The properties and adsorption mechanism of CS-ES were investigated using SEM, EDS, XRD, FT-IR, BET and XPS. The results of experiments revealed that the adsorption efficiency of CS-ES for Au(III) reaches more than 90% in a wide pH range (2.0–6.0) and the highest adsorption efficiency about 99.07% was achieved at pH = 5.0. At 318 K, the highest adsorption ability of CS-ES for gold ions was 657.49 mg/g. The adsorption findings supported the Langmuir and pseudo-second-order models, suggesting that monolayer chemisorption is the dominant adsorption mechanism. The thermodynamic performance (ΔH° and ΔS° > 0, ΔG° <0) showed that gold ion adsorption by CS-ES is spontaneous exothermic reaction. CS-ES shows an excellent reproducibility after four adsorption-desorption cycles and selectivity against six metal ions. Moreover, a variety of physicochemical and spectroscopic tests demonstrate the extremely effective adsorption and in-situ reduction of gold by CS-ES are based on electrostatic attraction, chelation, and reduction between gold and nitrogen/sulfur groups. In this work, a novel adsorbent for recovering Au(III) from wastewater was devised with great efficiency, selectivity and repeatability. [Display omitted] • A novel chitosan-based adsorbent was prepared by a facile method for gold ions. • The maximum adsorption capacity of the adsorbent was 657.49 mg/g at 318 K. • The adsorbent can be effective over a wide pH range. • The adsorbent exhibits excellent selectivity and reusability for gold ions. • The adsorption mechanisms are electrostatic attraction, chelation and reduction. [ABSTRACT FROM AUTHOR]

• Different mass ratios chitosan/MoS 2 biosorbents used for the first time to recover gold ions from solution. • CS-MoS 2 complex exhibited ultrahigh sorption capacity up to 3108.79 mg/g only in 300 min. • The three biosorbents possess superior selectivity and reusability. • Adsorption mechanism of CS-MoS 2 -1, 2, 3 for Au(III) is electrostatic attraction and complexation. The design and synthesis of high-performance materials for the recovery of gold are of paramount importance to alleviate its high consumption and protect the environment. Herein, three different ratios biosorbents (CS-MoS 2 -1, 2, 3) were successfully synthesized by embeding MoS 2 into the crosslinking chitosan to recover gold ions from solution. These materials not only inherit the excellent properties of chitosan, but also possess the sulfur-rich surface of MoS 2 , making that the maximum adsorption capacity of CS-MoS 2 -1, 2 and 3 were 2012.46, 2611.32 and 3108.79 mg/g, respectively. Besides, these biosorbents show outstanding selectivity for gold ions in the presence of coexisting ions, and demonstrate attractive reusability after four cycles. Adsorption mechanism of the three biosorbents to Au(III) was mainly electrostatic attraction and coordination. With the easy synthesis, environmental-friendly and ultra-efficient performance, CS-MoS 2 -1, 2, 3 are expected to be a promising candidate for Au(III) adsorption from aqueous media. [ABSTRACT FROM AUTHOR]

[Display omitted] • A Novel Adsorbent Co-Al-LDH@CS/Fe 3 O 4 for Pb (II) and Cr (VI) Removal from Water. • The adsorption capacity of adsorbents for Pb (II) and Cr (VI) reached to 558.84 and 710.79 mg/g, respectively. • The adsorbent shows excellent reusability and selectivity for Pb (II) and Cr (VI). • Adsorption mechanism is chelation and electrostatic interaction based on XPS and DFT. A novel sorbent Co-Al-LDH@CS/Fe 3 O 4 was synthesized in this learning for the elimination of Pb (II) and Cr (VI) from water using Co-Al layered double hydroxides (LDHs) as precursors, combined with cross-linked compounds of magnetically interspersed chitosan (CS) and cystamine. The successful synthesis of the adsorbent Co-Al-LDH@CS/Fe 3 O 4 was demonstrated by SEM, FTIR, XRD and XPS characterization. The maximum adsorption capacities of Co-Al-LDH@CS/Fe 3 O 4 at 25 °C were 558.84 and 710.79 mg/g for Pb (II) (pH = 6) and Cr (VI) (pH = 4), respectively. The sorption kinetics prove that the sorption is chemisorption and the rate-limiting step is exterior dispersion. The adsorption isotherms indicate that the sorption process is an irreversible process with positive synergistic effects at multiple sites. Thermodynamic studies show that Pb (II)/Cr (VI) sorption is spontaneous and irreversible in the process. Further, Co-Al-LDH@CS/Fe 3 O 4 also possesses a good selectivity and reusability (5 cycles) for Pb (II) and Cr (VI). The DFT calculations revealed that -SH and –NH 2 on the adsorbent surface have a stronger affinity for Pb (II) and Cr (VI). [ABSTRACT FROM AUTHOR]

A pyridine-modified chitosan (PMCS) adsorbent with excellent adsorption performance and specific selectivity for Au(III) in wastewater was prepared. FTIR, SEM, XPS and XRD were used to study its adsorption performance, and various models were used to fit and analyze the experimental adsorption data. The maximum adsorption capacity of PMCS for Au(III) is 549.41 mg/g (298 K, pH = 4). The data analysis results prove that the PSO and Langmuir models best describe the adsorption process. Adsorption experiments in the presence of multiple ions proved that PMCS is selective for the adsorption of Au(III). The adsorption and desorption experiments showed that the adsorption rate of PMCS could still reach 94.77% after three cycles. In summary, PMCS was demonstrated to be a high-quality material for the adsorption of Au(III) from wastewater due to its excellent adsorption performance, specific selectivity and reusability. [Display omitted] • A novel pyridine-modified chitosan (PMCS) adsorbent was synthesized. • The maximum adsorption capacity of PMCS for Au(III) is 549.41 mg/g (298 K, pH = 4). • PMCS has excellent selectivity and recyclability. [ABSTRACT FROM AUTHOR]