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Recovering silver from wastewater not only significantly reduces environmental harm but also meets the growing demand for silver in modern industry. Here, a novel metal-organic framework adsorbent (MOF-RD) using rhodanine derivatives as linkers is introduced for the efficient and selective capture of silver ions in real wastewater. The adsorption of MOF-RD followed pseudo-second-order and Sips models, and thermodynamic investigations revealed the process to be endothermic. MOF-RD demonstrated a remarkable adsorption capacity of 707.2 mg·g -1 for Ag(I) at pH 5 and 318 K. The interaction between silver ions and MOF-RD was mainly electrostatic attraction and coordination, with coordination primarily occurring at the CO and CS sites within the rhodanine motif. The practical applicability of MOF-RD for selective adsorption of Ag(I) was validated in actual wastewater with high-concentration competing metal ions. Furthermore, after 10 adsorption-desorption cycle experiments, MOF-RD still retained a strong regenerative capability. The results reveal the good potential of MOF-RD as an adsorbent for selectively recovering Ag(I) from industrial wastewater. Additionally, the strategies and methods adopted in this article also provide new perspectives and technical paths for the separation and recovery of other metal ions in wastewater., 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.)

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.)

With the boom of modern industry, the demand for precious metals palladium (Pd) and gold (Au) is increasing. However, the discharge of Pd(II) and Au(III) wastewater has caused environmental pollution and shortage of resources. Here, a new metal-organic frameworks adsorbent (MOF-AFH) was synthesized to efficiently separate Pd(II) and Au(III) from the water. The adsorption behavior of Pd(II) and Au(III) was explored at the same time. When gold and palladium are adsorbed separately, the adsorption capacity of gold and palladium is 389.02 mg/g and 191.27 mg/g, respectively. The equilibration time is 3 h. When gold and palladium coexist, the adsorption capacities of Au(III) and Pd(II) are 238.71 and 115.02 mg/g, respectively. The experimental results show that the adsorption of Pd(II) and Au(III) on MOF-AFH is a single-layer chemical adsorption, which is an endothermic process. MOF-AFH has excellent selectivity and after MOF-AFH is repeatedly used 4 times, the removal effect can still reach more than 90%. The adsorption mechanisms include reduction reaction and chelation with N and O-containing functional groups on the adsorbent. There is also electrostatic interaction for Au(III) adsorption. The adsorbent can be used to efficiently recover gold and palladium from wastewater., (Copyright © 2022 Elsevier Inc. All rights reserved.)

Lead ions in water have notorious effects on humans and environment. It is important to design an adsorbent with high adsorption capacity and reproducibility for efficiently removing Pb (II)ions from polluted water. Here, a novel Ti-based MOFs material (BDB-MIL-125(Ti)@Fe 3 O 4 ) was prepared by modifying NH 2 -MIL-125(Ti) with sulfhydryl and amino groups. Due to the large number of active sites, the maximum Pb (II) adsorption capacity of BDB-MIL-125(Ti)@Fe 3 O 4 was 710.79 mg/g at 25 °C and pH = 6 within 120 min corresponding to a maximum removal rate of 95.68%. The adsorbent also has extremely high selectivity and good cycling adsorption performance. The adsorption isotherms and kinetics agree with the Langmuir and the pseudo-second-order models, indicating that the process was chemisorption. Thermodynamic studies prove that spontaneous processes enhance Pb (II) adsorption at higher temperatures. DFT and FMOs calculations were used to discuss the adsorption mechanism. The sulfhydryl groups on the surface of organic ligands have a stronger affinity for Pb (II)., (Copyright © 2022 Elsevier B.V. All rights reserved.)

A new zirconium-based adsorption material (UiO-66-AMP) was prepared by modifying UiO-66-NH 2 with 5-adenosine to effectively remove Pb(II) and Cr(VI) from wastewater. The SEM, EDS, XRS and FT-IR characterization confirmed the successful synthesis of UiO-66-AMP. We conducted a sets of experiments to test the adsorption effectiveness of UiO-66-AMP for Pb(II) and Cr(VI). The maximum adsorption capacity of UiO-66-AMP for Cr(VI) (pH=2) and Pb(II) (pH=4) are 196.60 and 189.69 mg/g, respectively. The adsorption process conforms to the pseudo-second-order and Langmuir models, which indicates that the adsorption is a single-layer chemical process. Gibbs free energy (∆G) indicates that the adsorption of Pb(II) is an exothermic reaction, while the adsorption of Cr(VI) is an endothermic reaction. At the same time, the adsorbent maintains excellent adsorption capacity at least after 4 cycles. The good adsorption performance of UiO-66-AMP towards the metal ions was attributed to the surface complexation and electrostatic interactions. Therefore, the new adsorbent has obvious application prospect to remove Pb(II) and Cr(VI) from wastewater., (Copyright © 2021 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.)

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 novel metal-organic framework (UiO-66-PTC) for efficient removal of Pb 2+ ions from wastewater has been prepared by using 4-phenyl-3-thiosemicarbazide as the modifier. Various characterizations showed that UiO-66-PTC was successfully synthesized. The absorption results showed that the maximum adsorption capacity of Pb(II) is 200.17 mg/g at 303 K and optimal pH 5. The adsorption kinetic follows the pseudo-second-order model and the adsorption isotherms fit the Langmuir model. This shows that Pb(II) is a single-layer adsorption on the surface of the adsorbent and the rate-controlling step is chemical adsorption. The thermodynamic results show that the adsorption process can proceed spontaneously, belong to the exothermic reaction. The adsorbent can selectively uptake lead ions from wastewater containing multiple interfering ions. After four adsorption and desorption cycles, the adsorption efficiency is still high. The adsorption mechanism of Pb(II) on the adsorbent is mainly through the chelation of Pb(II) with N and S atoms. These results indicate that UiO-66-PTC is an effective material for efficiently and selectivity removal of Pb(II) from solution, which is of practical significance., (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.)

A new MOFs adsorbent was prepared by post-functionalization of UiO-66-NH 2 with 2,5-Dimercapto-1,3,4-thiadiazole and utilized to remove the Hg(II) in water selectively. The UiO-66-types were detected by Fourier transform infrared spectroscopy (FTIR), field emission scanning electron microscope (FESEM), Brunauer-Emmett-Teller (BET) and zeta potential instruments. The adsorption properties of the new MOFs adsorbent were investigated by batch experiments. The actual maximum adsorption amount was 670.5 mg/g at the optimal pH of 3. Adsorption kinetic and isotherm models were exceedingly fitted to pseudo-second-order and Langmuir/Dubinin-Radushkevich, respectively. The adsorption process and mode were geared to monolayer and chemisorption, the removal rate was directly proportional to the square of mercury ions concentration. The UiO-66-DMTD adsorbent was easy to be regenerated and the removal rate decreased by only 13.5% after ten consecutive cycles. The results of FTIR, XRD and XPS suggested that the adsorption mechanism lay on the complexation reaction between Hg(II) and thiol/nitrogen-containing groups. Moreover, compared with other competitive metal ions, viz., Zn(II), Co(IV), Ni(II), Cd(II), Mg(II), Fe(III), Ca(II) and Cu(II), the UiO-66-DMTD demonstrated an outstanding selective adsorption for Hg(II). These results manifested that the UiO-66-DMTD was a latent adsorbent for the efficient and selective removal of Hg(II) in wastewater., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Waste carbonaceous catalyst (WCC) from vinyl chloride monomer (VCM) production is a potential environmental threat due to the mercury toxicity. Microwave heating (MWH) was used to decontaminate WCC. Treatment temperature had a stronger influence on mercury removal than that of treatment time while mercury removal was highly depended on treatment time at lower temperature. When WCC was treated at 350 °C for 60 min, 400 °C for 30 min and 450 °C or more for 10 min, leaching toxicity of mercury conformed to the US EPA standard. 99.98% of total mercury was removed and residual mercury concentration was only 4.5 mg kg -1 when treated at 500 °C for 30 min. Soluble and exchangeable Hg and Hg combined with labile organics were more easily to be removed than that of Hg bound to crystalline Fe/Al oxides, Hg combined with non-labile organics and HgS. The removal limit for different mercury species may be achieved at 500 °C. Evaporation removal of mercury followed exponential decay model. Activation energy for mercury removal was reduced due to the catalytic effect of MWH. Removal mechanisms of mercury included thermal evaporation, breakdown of molecular bonds, selective stripping of carbonaceous impurities., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Dielectric properties of spent adsorbent with zinc sulfate are investigated by cavity perturbation technique at 2450MHz from 20°C to approximately 1000°C. Two weight loss stages are observed for spent adsorbent by thermogravimetric-differential scanning calorimeter (TG-DSC) analysis, and zinc sulfate is decomposed to ZnO·2ZnSO 4 and ZnO at about 750°C and 860°C. Microwave absorption capability of ZnSO 4 increases with increasing temperature and declines after ZnO generation on account of the poor dielectric properties. Dielectric properties of spent adsorbent are dependent on apparent density and noticed an interestingly linearly relationship at room temperature. The three parameters increase gently from 20°C to 400°C, but a sharp increase both in real part and imaginary part are found subsequently due to the volatiles release and regeneration of carbon. And material conductivity is improved, which contributes to the π-electron conduction appearance. Relationship between penetration depth and temperature further elaborate spent adsorbent is an excellent microwave absorber and the microwave absorption capability order of zinc compounds is ZnO·2ZnSO 4 , ZnSO 4 and ZnO. Heating characteristics suggest that heating rate is related with dielectric properties of materials. The pore structures of spent adsorbent are improved significantly and the surface is smoother after microwave-regeneration., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Hyperbranched polyglycerols were grown from magnetic nanoparticles (MNPs) via surface-initiated anionic ring-opening polymerization of glycidol. The modified MNPs were characterized by using TEM, XPS, TGA and FTIR. Hyperbranched polyglycerols resist the nonspecific adsorption of proteins on magnetic nanoparticles. The capability of hyperbranched polyglycerols is comparable favorably with the performance of methyloxy poly(ethylene glycol) (a linear mPEG with a molecular weight of 750) in resisting the adsorption of proteins.