Rapid and selective recovery of Ag(I) from simulative electroplating effluents by sulfydryl-rich covalent organic framework (COF-SH) with high adsorption capacity

Effects of active silicon amendment on Pb(II)/Cd(II) adsorption: Performance evaluation and mechanism

In this study, a high-Si (Si) adsorbent (APR@Sam) was prepared by acid leaching slag (APR) from lead-zinc (Pb-Zn) tailings based on high-temperature alkali melting technology. The synthesized Si-based materials were applied to aqueous solutions contaminated with Pb and cadmium (Cd) to investigate the crucial role of active Si in sequestering heavy metals. The adsorption capacities of APR@Sam and the Si-depleted material (APR@Sam-NSi) were studied under different pH and temperature conditions. The results showed that as the pH increased from 3 to 7, the adsorption capacity increased, the active Si content in the solution increased by 63 %, and the maximum pH of the solution after adsorption was 7.12. After the removal of active Si, the Pb (II) and Cd (II) adsorption capacities of APR@Sam decreased by 45 % and 11.96 %, respectively. OH- promoted the release of Si into the solution, enhancing the material's adsorption efficiency. The reaction mechanism is mainly attributed to surface complexation guided by Si-O and Si-O-Si bonds, metal cation exchange, and bidentate coordination. The results indicated that the Si component is critical for the removal of Pb (II) and Cd (II) by APR@Sam and provide valuable insights into resource recovery strategies from leaching residues.

Covalent Organic Framework Nanoarchitectonics: Recent Advances for Precious Metal Recovery

The recovery of precious metals (PMs) from secondary resources has garnered significant attention due to environmental and economic considerations. Covalent organic frameworks (COFs) have emerged as promising adsorbents for this purpose, owing to their tunable pore size, facile functionalization, exceptional chemical stability, and large specific surface area. This review provides an overview of the latest research progress in utilizing COFs to recover PMs. Firstly, the design and synthesis strategies of chemically stable COF-based materials, including pristine COFs, functionalized COFs, and COF-based composites, are delineated. Furthermore, the application of COFs in the recovery of gold, silver, and platinum group elements is delved into, emphasizing their high adsorption capacity and selectivity as well as recycling ability. Additionally, various interaction mechanisms between COFs and PM ions are analyzed. Finally, the current challenges faced by COFs in the field of PM recovery are discussed, and potential directions for future development are proposed, including enhancing the recyclability and reusability of COF materials and realizing the high recovery of PMs from actual acidic wastewater. With the targeted development of COF-based materials, the recovery of PMs can be realized more economically and efficiently in the future.

Recovery of Ag(I) from Wastewater by Adsorption: Status and Challenges

Untreated or inadequately treated silver-containing wastewater may pose adverse effects on hu-man health and the ecological environment. Currently, significant progress has been made in the treatment of Ag(I) in wastewater using adsorption methods, with adsorbents playing a pivotal role in this process. This paper provides a systematic review of various adsorbents for the recovery and treatment of Ag(I) in wastewater, including MOFs, COFs, transition metal sulfides, metal oxides, biomass materials, and other polymeric materials. The adsorption mechanisms of these materials for Ag(I) are elaborated upon, along with the challenges currently faced. Furthermore, insights into optimizing adsorbents and developing novel adsorbents are proposed in this study.

Ferrocene crosslinked and functionalized chitosan microspheres towards bio-based Fenton-like system for the removal of organic pollutants

Dye-containing wastewater treatment has been a major long-term global challenge. For this purpose, a novel bio-based microspheres (CS-FC) with high specific surface area (63.24 m2·g-1) and nano-channels (17.95 nm) was prepared using chitosan as the framework and ferrocene as a crosslinking active group. CS-FC not only has the ability to rapidly enrich methyl orange (MO) through hydrogen-bonding and electrostatic attraction, but also almost completely degrades it in the presence of H2O2/K2S2O8 through a synergistic radical/non-radical mechanism under the activating effect of ferrocene. Without H2O2/K2S2O8, the maximum MO adsorption capacity of CS-FC is in the range 871-1050 mg·g-1, and conforms to a Langmuir isothermal model with pseudo-second-order kinetics. In the presence of H2O2/K2S2O8, the removal of MO dramatically increased from 32 % to nearly 100 % after incubation for 60 min, due to the simultaneous formation of highly reactive 1O2 and ·OH. The significant contribution from 1O2 endowed CS-FC/H2O2/K2S2O8 with high universality for degrading various organic pollutants (including azo dyes and antibiotics), a wide pH window (2-8), and low sensitivity to co-existing ions. Such cost-effective, recyclable porous bio-based microspheres are suitable for heterogeneous Fenton-like catalysis in organic wastewater treatment that rely on synergistic radical/non-radical reaction pathways.

Selective Adsorption and Recovery of Silver from Acidic Solution Using Biomass-Derived Sulfur-Doped Porous Carbon

It is vital to recycle precious metals effectively such as silver from waste sources because of limited natural reserves. Herein, passion fruit (Passiflora edulis Sims) shell-derived S-doped porous carbons (SPCs) were newly synthesized by hydrothermal carbonization and following with activation by KOH/(NH4)2SO4, and the adsorption of Ag+ on SPC under acidic solutions was investigated. It was found that the activator of (NH4)2SO4 can not only introduce the doping of S elements but also increase the proportion of mesopores in the as-prepared SPC. As the active site, the increasing S doping can improve the adsorption of Ag+ on SPC. The kinetic data of Ag+ adsorption by SPC was consistent with the pseudo-second-order kinetic model. The Langmuir isothermal model was used to well fit the Ag+ adsorption isotherms of SPC, and the maximum adsorption capacity of the optimized SPC-3 for Ag+ is up to 115 mg/g in 0.5 mol/L HNO3 solution. SPC-3 showed good selectivity toward Ag+ over diverse competing cations, which is mainly attributed to the strong bonding between Ag+ ions and the sulfur-containing functional groups on the surface of SPC-3 resulting in the formation of Ag2S nanoparticles. The adsorbed Ag could be recovered as an elemental form by a simple calcination. This study provides a new insight into the design of an environmentally friendly and efficient adsorbent for the selective recovery of silver from acidic aqueous media.

An Ethyl-Thioglycolate-Functionalized Fe3O4@ZnS Magnetic Fluorescent Nanoprobe for the Detection of Ag+ and Its Applications in Real Water Solutions

Ethyl-thioglycolate-modified Fe₃O₄@ZnS nanoparticles (Fe₃O₄@ZnS-SH) were successfully prepared using a simple chemical precipitation method. The introduction of ethyl thioglycolate better regulated the surface distribution of ZnS, which can act as a recognition group and can cause a considerable quenching of the fluorescence intensity of the magnetic fluorescent nanoprobe, Fe₃O₄@ZnS-SH. Benefiting from stable fluorescence emission, the magnetic fluorescent nanoprobe showed a highly selective fluorescent response to Ag+ in the range of 0-400 μM, with a low detection limit of 0.20 μM. The magnetic fluorescent nanoprobe was used to determine the content of Ag⁺ in real samples. A simple and environmentally friendly approach was proposed to simultaneously achieve the enrichment, detection, and separation of Ag⁺ and the magnetic fluorescent nanoprobe from an aqueous solution. These results may lead to a wider range of application prospects of Fe₃O₄ nanomaterials as base materials for fluorescence detection in the environment.

Qualitative and quantitative analysis of four benzimidazole residues in food by surface-enhanced Raman spectroscopy combined with chemometrics

In this study, surface-enhanced Raman spectroscopy (SERS) combined with chemometric methods were developed for qualitative and quantitative analysis of four benzimidazole (BMZs) residues in corn. Sulfhydryl functionalized Fe₃O₄@SiO₂@Ag-SH magnetic SERS substrates were prepared to obtain the SERS spectra of four BMZs for chemometric analysis. The partial least squares regression discrimination analysis (PLS-DA) model performed best, with a recall rate upwards 99.17%, and could successfully distinguish four BMZs. Under the support vector machine regression (SVR) model, the detection limits of carbendazim, benomyl, thiophanate-methyl and thiabendazole were 0.055 mg/L, 0.056 mg/L, 0.067 mg/L and 0.093 mg/L, respectively; the average recovery was in the range of 85.6%-107.5%. Furthermore, the method verified by HPLC, and the results showed that there was no significant difference between two methods (p > 0.05). Therefore, the strategy based on SERS coupling chemometrics can be served as a promising tool for rapid determination of BMZs residues in food.

Chirality-Controlled Mercapto-β-cyclodextrin Covalent Organic Frameworks for Selective Adsorption and Chromatographic Enantioseparation

Chiral covalent organic frameworks (CCOFs) benefit from superior stability, abundant chiral environment, and homogeneous pore configuration. In its constructive tactics, only the post-modification method allows for the integration of supramolecular chiral selectors into achiral COFs. Here, the finding utilizes 6-deoxy-6-mercapto-β-cyclodextrin (SH-β-CD) as chiral subunits and 2,5-dihydroxy-1,4-benzenedicarboxaldehyde (DVA) as the platform molecule to synthesize chiral functional monomers through thiol-ene click reactions and directly establish ternary "pendant-type" SH-β-CD COFs. The chiral site density on SH-β-CD COFs was regulated by changing the proportion of chiral monomers to obtain an optimal construction strategy and remarkably improve the ability of chiral separation. SH-β-CD COFs were coated on the inner wall of the capillary in a covalently bound manner. The prepared open tubular capillary was achieved for the separation of six chiral drugs. By combining the outcomes of selective adsorption and chromatographic separation, we observed the higher density of chiral sites in the CCOFs, and poorer results were achieved. From the perspective of spatial conformational distribution, we interpret the variation in the performance of these chirality-controlled CCOFs for selective adsorption and chiral separation.

Highly defective copper-based metal-organic frameworks for the efficient adsorption and detection of organophosphorus pesticides: An experimental and computational investigation

Organophosphorus pesticide (OP) residues pose a serious threat to human health, motivating the search for novel adsorbents and detection methods. Herein, defective copper-based metal organic frameworks (Cu-MOFs) were synthesized by the reaction of Cu²⁺ ions and 1,3,5-benzenetricarboxylate linkers in the presence of acetic acid. As the amount of acetic acid increased, the crystallization kinetics and morphology of the Cu-MOFs changed, leading to mesoporous Cu-MOFs with many large surface pores (defects). Adsorption studies of OPs revealed the defective Cu-MOFs showed faster pesticide adsorption kinetics and higher pesticide adsorption capacities. Density functional theory calculations showed that pesticide adsorption in the Cu-MOFs was mainly electrostatic. A dispersive solid phase extraction method was developed based on a defective Cu-MOF-6 for rapidly extracting pesticides from food samples. The method allowed pesticide detection over a wide linear concentration range, low limits of detection (0.0067-0.0164 µg L^-1) and good recoveries in pesticide-spiked samples (81.03-109.55%).

Feasible synthesis of bifunctional polysilsesquioxane microspheres for robust adsorption of Hg(II) and Ag(I): Behavior and mechanism

The pollution of Hg(II) and Ag(I) to water system exerts hazardous effect to aquatic ecosystem and public security. Simple strategy for constructing adsorbents to efficient remove them is greatly desired. Thus, a series of thiol and amino groups containing bifunctional polysilsesquioxanes (ASPSS) microspheres with adjustable porous structure and functional group content were synthesized by one-step feasible sol-gel process. The adsorption behavior and mechanism of ASPSS microspheres toward Hg(II) and Ag(I) was thoroughly determined. The maximum adsorption capacity of ASPSS for Hg(II) and Ag(I) are 4.32 and 3.86 mmol·g^-1 under 25 ℃. The as-prepared ASPSS microspheres can 100% selectively capture Hg(II) with the coexisting of Mn(II), Co(II), Pb(II), Cd(II), Cu(II), Fe(III). And they can 100% adsorb Ag(I) with the presence of Cd(II), Pb(II), Co(II), Ni(II), and Zn(II). Moreover, the ASPSS microspheres exhibit good removal efficiency for Hg(II) and Ag(I) from simulated industrial wastewater with the coexistence of multiple pollutants. Adsorption mechanism suggests the adsorption for Hg(II) and Ag(I) is the synergistic coordination effect of amino and thiol groups. The excellent adsorption selectivity for Hg(II) and Ag(I) is attributed to the super binding ability of these functional group. ASPSS microspheres also exhibit good regeneration ability and could be reused for removing Hg (II) and Ag(I) from aqueous solution with practical value.