A novel S,N-rich MOF for efficient recovery of Au(III): Performance and mechanism

Recovery of Au(III) from electronic waste using solid phase extraction based on a magnetic nanobiocomposite, OCBs@Fe3O4@UiO-66-SH

A zirconium-based MOF (UiO-66-NH2) with thiol groups attached to its magnetic corn surface was used for the adsorption and extraction of Au(III) from electronic waste. The composite was characterized using FTIR, XRD, FESEM, TGA, and BET techniques. The effects of the temperature, adsorption period, and pH on Au(III) adsorption were investigated. The optimal conditions to achieve the maximum adsorption of Au(III) on the adsorbent surface were pH 6.0, 50◦C, 40 min, and 10 mg of adsorbent. Moreover, oxidized magnetic corncobs functionalized with thiol (OCBs@Fe3O4@UiO-66-SH) showed a notable ability to adsorb Au(III), with a capacity of 1587 mg/g. With the mass ratios of Au(III) to competing ions (Mg, Mn, Cu, Zn, Co, Cd, and Ni) fixed at 1:1 or extended to 1:5, this adsorbent prefers Au(III) ions while showing negligible adsorption to other ions. This study validated a technique to extract Au (III) from various electronic waste samples, achieving high recoveries  (95.30% to 104.75%), demonstrating its effectiveness and lack of matrix interference. Examining various isotherm and kinetic models demonstrated that the Langmuir and pseudo-first-order models could effectively interpret the experimental and kinetic data. Thermodynamic calculations showed that the adsorption process is endothermic and occurs spontaneously. The optimal utilization of renewable waste as an adsorbent base, high adsorption capacity, recoverability, and reusability owing to its magnetic properties, high recovery rate of Au(III) from electronic matrices, and highly selective adsorption in the presence of competing ions are among the advantages of this adsorbent. Together, these features highlight the novelty of the present study.

Pt nanoparticles functionalized hydrogen-bonded organic frameworks: A three-in-one nanozyme for colorimetric detection of alkaline phosphatase

To meet the increasing demands for highly active and stable nanozymes for bioanalysis, Pt nanoparticles (NPs) were successfully supported on the surface of hydrogen-bonded organic frameworks (Pt/HOFs) to obtain a stable, multifunctional and highly active nanozyme for the colorimetric detection of alkaline phosphatase (ALP). Through a redox reaction, Pt precursors are reduced to ultrasmall Pt NPs that are loaded on HOFs. The Pt/HOFs nanozyme showed excellent oxidase-like, peroxidase-like and some catalase-like activity. To avoid the signal instability caused by H2O2 decomposition, the oxidase-like activity of Pt/HOFs was applied for the detection of ALP using 3,3', 5,5 '-tetramethylbenzidine (TMB) as a chromogenic substrate. When the substrate L-ascorbic acid 2-phosphate (AAP) is present, ALP can catalyze AAP to produce strongly reductive ascorbic acid (AA). AA can reduce the oxidation product of TMB. Therefore, a colorimetric sensing strategy for ALP detection was constructed. The linear range of the strategy was from 0.5 to 8 mU mL-1, and the detection limit was 0.46 mU mL-1. Finally, the strategy was successfully applied to the detection of ALP in human serum, which provided a reliable strategy for the colorimetric detection of clinical ALP. This study not only presents a simple approach to maintain the high activity of nanoparticle-based nanozymes, but also expands the application of multifunctional HOF-based materials for future applications.

Modulation of S and N Active Sites for Coordination Polymers to Achieve Enhanced Hg2+ Sensing Performances

It is challenging and vital to develop coordination polymers (CPs) with an outstanding sensing performance. In this work, CP-based sensors with active S and N sites are first exploited. Three new Cu-CPs [Cu(L)(SCN)2·2DMF]n (1), [Cu(L)(SCN)·2DMF]n (2), and [Cu(L)(CN)·2DMF]n (3) were successfully synthesized by 9,10-bis(di(pyrimidin-5-yl)methylene)-9,10-dihydroanthracene (L) and SCN-/CN- ligands. 1 demonstrates a 1D wavelike chain, fabricated by L bridges linking with Cu(SCN)2 units. 2 exhibits a 2D (3,3)-connected network fabricated by SCN-, 3-connected L, and Cu units. 3 exhibits a 3D framework, built by 4-connected Cu centers, CN-, and L bridges. 1-3 have good water, pH, and thermal stabilities. 1 and 2 have uncoordinated S and N active sites and can detect Hg2+ through the fluorescence enhancing ("turn-on") effect. Meanwhile, 3 only has uncoordinated N active sites and shows a negative Hg2+ sensing ability. 1 and 2 have ultrahigh Hg2+ sensing sensitivity and selectivity. The KSV and LOD of 1 toward Hg2+ are about 3 and 5 times superior to those of 2, separately. 1 and 2 represent the first S- and N-rich CP-based sensors and exhibit an excellent "turn-on" Hg2+ sensing capacity. Their "turn-on" Hg2+ sensing mechanism and difference sensing performances are discussed in detail.

Ultra-Efficient and Selective Gold Separation via Second-Sphere Coordination of Aurous Dihalide Using a Nonporous Amorphous Superadsorbent

The escalating demand for gold, coupled with dwindling terrestrial reserves, underscores the urgent need for innovative separation strategies, including e-waste recycling and seawater extraction. However, the development of ultra-efficient, highly selective adsorbents capable of recovering trace amounts of gold from complex aquatic matrices remains a formidable challenge. Herein, a covalent organic superphane cage is reported as a nonporous amorphous superadsorbent (NAS) for selective and efficient gold recovery via intermolecular second-sphere coordination of AuBr₂⁻ (or AuCl₂⁻) ions, subsequently converted to metallic gold through disproportionation. NAS demonstrates outstanding performance, including an exceptional gold uptake capacity of 2750 mg g⁻¹, ultrafast adsorption kinetics (40 s), broad pH tolerance (1-11, up to 6 M acids), and remarkable gold uptake even in 36 wt.% HCl solution (821 mg g⁻¹). NAS achieves over 99% selective gold recovery, even amidst excess competing ions, retaining efficacy across 30 regeneration cycles. Its versatile and scalable design enables applications in gold separation from gold-bearing e-waste, catalytic residues, gold ores, and seawater. A large-scale trial recovered 23.8 Karat gold from printed circuit board leachates, positioning NAS as a sustainable and eco-friendly solution for industrial and environmental gold recovery.

Anion-π Interactions on Functionalized Porous Aromatic Cages for Gold Recovery from Complex Aqueous with High Capacity

High capacity, selective recovery and separation of precious metals from complex aqueous solutions is essential but remains a challenge in practical applications. Here, we prepared a thiophene-modified aromatic porous organic cage (T-PAC) with high stability for precise recognition and recovery of gold. T-PAC exhibits an outstanding gold uptake capacity of up to 2260 mg/g with fast adsorption kinetics and high adsorption selectivity. It's also used to selectively recover gold from a variety of complex aqueous solutions in a stable and efficient manner. The theoretical calculations and dedicated experiments suggest that anion-π interactions between the [AuCl4]- and TFP fractions on T-PAC cooperated with S/N boning and redox effects play the decisive role in the highly efficient gold recovery performance.

Highly Selective Recovery of Gold by In Situ Magnetic Field-Assisted Fe/Co-MOF@PDA/NdFeB Double Network Gel

There are enormous economic benefits to conveniently increasing the selective recovery capacity of gold. Fe/Co-MOF@PDA/NdFeB double-network organogel (Fe/Co-MOF@PDA NH) is synthesized by aggregation assembly strategy. The package of PDA provides a large number of nitrogen-containing functional groups that can serve as adsorption sites for gold ions, resulting in a 21.8% increase in the ability of the material to recover gold. Fe/Co-MOF@PDA NH possesses high gold recovery capacity (1478.87 mg g-1) and excellent gold selectivity (Kd = 5.71 mL g-1). With the assistance of an in situ magnetic field, the gold recovery capacity of Fe/Co-MOF@PDA NH is increased from 1217.93 to 1478.87 mg g-1, and the recovery rate increased by 24.7%. The above excellent performance is attributed to the efficient reduction of gold by FDC/FC+, Co2+/Co3+ double reducing couple, and the optimization of the reduction reaction by the magnetic field. After the samples are calcined, high-purity gold (95.6%, 22K gold) is recovered by magnetic separation. This study proposes a forward-looking in situ energy field-assisted strategy to enhance precious metal recovery, which has a guiding role in the development of low-carbon industries.

Sulfur-Functionalized Single-Walled Carbon Nanotube Buckypaper/MTV-BioMetal-Organic Framework Nanocomposites for Gold Recovery

Developing sustainable, efficient, and selective gold recovery technology is essential to implement the valorization of complementary alternative sources for this precious metal, such as spent e-waste, and to preserve the environment. The main challenge in recovering gold from liquors obtained from leached waste electronics is the low concentration of this precious metal compared to impurities. Here, we report the preparation of a novel multivariate biological metal-organic framework (MTV-BioMOF) as a potential material for the selective recovery of gold metal ions from water, even in the presence of other interfering metals. Moreover, MTV-BioMOF can be incorporated within single-walled carbon nanotube buckypapers (SWCNT-BP) to yield an MTV-BioMOF@HS-SWCNT-BP composite, which combines enhanced mechanical properties and high chemical stability. The thiol-functionalized SWCNT-BP surface and the presence of thioether groups evenly decorating the MTV-BioMOF channels shape a task-specific functional environment that boosts the interactions with gold metal ions. The efficiency of gold recovery reaches values up to 99.5% when MTV-BioMOF@SWCNT-BP is used as an adsorbent for treating Au(III) in very diluted solutions (initial concentration of 5 ppm). This high recovery efficiency, with values as high as 98.0%, is maintained even in the presence of competing metal cations, also demonstrating a noticeable selectivity. This composite material represents a promising paradigm for the selective extraction, enrichment, and purification of gold.

Efficient recovery of gold from solution with a thiocyanate-modified Zr-MOF: adsorption properties and DFT calculations

The design and development of new large-capacity and selective materials for extracting rare precious metals via electronic waste is practically essential. In this paper, a new efficient UiO-66-NCS has been obtained as a consequence of the modification of the classical Zr-MOF (UiO-66-NH2), and its ability to recover gold has been investigated. These batch results adequately illustrated that UiO-66-NCS exhibited good adsorption capacity (675.5 mg g-1) and exceptional selectivity. In addition, UiO-66-NCS achieved faster adsorption equilibrium times of about 120 min. Adsorption kinetics and isotherms demonstrated that the pseudo-second-order adsorption scheme and a Langmuir-type procedure were shown by the adsorption of Au(III) on UiO-66-NCS. Characterized by pH effect experiments, TEM, XRD, and XPS, the adsorption of UiO-66-NCS with Au(III) relies on coordination, which further results in reduction, and the generated Au(0) is uniformly dispersed in the MOF. The adsorbent has considerable advantages for cyclic regeneration. Finally, DFT fitting results showed that the adsorption binding energy of UiO-66-NCS with [AuCl4]- was -8.63 kcal mol-1 for the adsorption process. UiO-66-NCS is likely to be an ideal substance for gold recovery.

An O/N/S-rich porous Fe-based metal-organic framework (MOF) for gold recovery from the aqueous phase with excellent performance

Recovering gold from wastewater has both economic and environmental benefits. However, how to effectively recover it is challenging. In this work, a novel Fe-based metal-organic framework (MOF) was synthesized and decorated with 2,5-thiophenedicarboxylic acid to have a well-developed porous architecture to effectively recover Au(III) from water. The maximum Au(III) sorption capacity by the finally-synthesized porous material MIL-101(Fe)-TDCA reached 2350 mg/g at pH = 6.00 ± 0.15, which is one of the highest among all literature-reported relevant materials including MOFs, and high sorption strength can be maintained within a wide pH range from 2.0 to 10.0. Besides, Au(III) sorption efficiency at low concentrations (i.e., 3.5 × 104 mg/mL) reached over 99%. Mechanically, outstanding Au(III) sorption by MIL-101(Fe)-TDCA resulted from the O/N/S-containing moieties on its surface, large surface area and porosity. The N- and S-containing functionalities (CS, CONH) served as electron donors to chelate Au(III). The O-containing (FeOFe, COFe, COOH, and coordinated H2O) and N-containing (CONH) moieties on MIL-101(Fe)-TDCA interacted with OH groups on the hydrolyzed species of Au(III) (AuCl3(OH)-, AuCl2(OH)2-, and AuCl(OH)3-) by hydrogen bond, which further increased Au(III) sorption. Furthermore, about 45.71% of Au(III) was reduced to gold nanoparticles by CS groups on the decorated 2,5-dithiophene dicarboxylic acid during sorption on MIL-101(Fe)-TDCA. Over 98.35% of Au(III) was selectively sorbed on MIL-101(Fe)-TDCA at pH 4.0, much higher than that of the coexisting heavy metal ions including Cu(II), Zn(II), Pb(II), and Ni(II) (< 5%), despite their same concentration at 0.01 mg/mL. Although sorption selectivity of a noble metal Pt(IV) by MIL-101(Fe)-TDCA is relatively poor (68.23%), it could be acceptable. Moreover, reusability of MIL-101(Fe)-TDCA is also excellent, since above 90.5% Au(III) still can be sorbed after two sorption-desorption cycles. Overall, excellent sorption performance and the roughly-calculated gold recycling benefits (26.30%) highlight that MIL-101(Fe)-TDCA is a promising porous material for gold recovery from the aqueous phase.

Efficient and selective capture of Au(III) from PCBs by pentaethylenehexamine-modified chloromethylated polystyrene beads

Recycling of gold promotes solving the problems of resource waste and environmental pollution. In this work, pentaethylenehexamine (PEHA)-modified chloromethylated polystyrene beads (PEHA-CMPS) was synthesized for the recovery of Au(III) from actual printed circuits boards (PCBs) leaching solution. PEHA-CMPS exhibited excellent adsorption efficiency at a wide pH range. It was discovered that the pseudo-second-order and Langmuir model provided a superior match for the Au(III) adsorption process. The maximum adsorption capacity for Au(III) was 1186 mg/g. Furthermore, PEHA-CMPS was able to selectively capture trace Au(III) with recovery efficiencies of above 80% from the actual PCBs leaching solution. In addition, the column separation approach was utilized to better assess the practical applications for PEHA-CMPS, proving that the prepared adsorbent exhibited great prospects in industrial applications. The adsorption efficiency still maintained 95% after five adsorption-desorption cycles. The FTIR, XRD, and XPS analyses demonstrated that Au(III) uptake on PEHA-CMPS was a collaborative process involving electrostatic interaction, chelation, and oxidation-reduction. The PEHA-CMPS provided a promising strategy in Au(III) recovery and environmental remediation.

MIL-161 Metal-Organic Framework for Efficient Au(III) Recovery from Secondary Resources: Performance, Mechanism, and DFT Calculations

The recovery of precious metals from secondary resources is significant economically and environmentally. However, their separation is still challenging because they often occur in complex metal ion mixtures. The poor selectivity of adsorbents for gold in complicated solutions prevents further application of adsorption technology. In this study, a Zr-based MOF adsorbent, MIL-161, was synthesized using s-tetrazine dicarboxylic acid (H₂STz) as an organic ligand. MIL-161 demonstrated a high adsorption capacity of up to 446.49 mg/g and outstanding selectivity for gold(III) in a simulated electronic waste solution as a result of the presence of sulfur- and nitrogen-containing groups. In addition, the MIL-161 adsorbents were characterized using Fourier transform infrared (FT-IR), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TG), Brunner-Emment-Teller (BET), and X-ray photoelectron spectroscopy (XPS). Additionally, the adsorption kinetics, isotherms, and thermodynamics of the MOF adsorbents were also thoroughly examined. More importantly, the experimental results and DFT calculations indicate that chelation and electrostatic interactions are the main adsorption mechanisms.