Fast and effective recovery of Au(III) from aqueous solution by a N-containing polymer

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.

One-pot Construction of Metal Nanoparticles Loaded COF Catalysts for Aqueous Hydrogenation Reactions

The catalysis performance of metal nanoparticles (NPs) will be significantly deteriorated because of their spontaneous agglomeration during practical applications. Covalent-organic frameworks (COFs) materials with functional groups and well-defined channels benefit for the dispersion and anchor of metal ions and the confined growth of metal NPs, working as an ideal platform to compose catalytic systems. In this article, we report a one-pot strategy for the preparation of metal NPs loaded COFs without the need of post-modification. During the polymerization process, the pre-added metal ions were stabilized by the rapidly formed COF oligomers and hardly disturb the construction of COFs. After reduction, metal NPs are uniformly anchored on the COF matrix. Eventually, a wide spectrum of metal NPs, including Au, Pd, Pt, AuPd, CuPd, CuPt and CuPdPt, loaded COFs are successfully prepared. The versatility and metal ions anchoring mechanism are verified with four different COF matrixes. Taking AuPd NPs as example, the resultant AuPd NPs loaded COF materials can selectively decompose ammonium formate and produce hydrogen in-situ, exhibiting over 99 % conversion of hydrodechlorination for chlorobenzenes and nitro-reduction reaction for nitroaromatic compounds under ambient temperature in aqueous solution.

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.

Formation and Growth of Atomic Scale Seeds of Au Nanoparticle in the Nanospace of an Organic Cage Molecule

Seed-mediated growth has been widely used to synthesize noble metal nanoparticles with controlled size and shape. Although it is becoming possible to directly observe the nucleation process of metal atoms at the single atom level by using transmission electron microscopy (TEM), it is challenging to control the formation and growth of seeds with only a few metal atoms in homogeneous solution systems. This work reports site-selective formation and growth of atomic scale seeds of the Au nanoparticle in a nanospace of an organic cage molecule. We synthesized a cage molecule with amines and phenols, which were found to both capture and reduce Au(III) ions to spontaneously form the atomic scale seeds containing Au(0) in the nanospace. The growth reaction of the atomic scale seeds afforded Au nanoparticles with an average diameter of 2.0±0.2 nm, which is in good agreement with the inner diameter of the cage molecule.

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

A novel S,N-rich MOF with adenine and 4,4'-thiodiphenol as organic ligands was synthesized via the one-step solvothermal method, and used for gold recovery. The pH impact, adsorption kinetics, isotherms, thermodynamics, selectivity, and reusability were investigated accordingly. The adsorption and desorption mechanism were also explored comprehensively. The electronic attraction, coordination, and in situ redox account for the Au(III) adsorption. The Au(III) adsorption is affected strongly by the pH of solutions, and best at pH of 2.57. The MOF exhibits exceptional adsorption capacity as high as 3680 mg/g at 55 °C, fast kinetics with 8 min for 9.6 mg/L Au(III), and excellent selectivity for gold ion in real e-waste leachates. The adsorption process of gold on the adsorbent is endothermic and spontaneous, and influenced visibly by temperature. The adsorption ratio still maintained 99% after seven adsorption-desorption cycles. The column adsorption experiments show that the MOF has outstanding selectivity for Au(III) with 100% of removal efficiency in a complex solution containing Au, Ni, Cu, Cd, Co, and Zn ions. A glorious adsorption with a breakthrough time of 532 mins was obtained for the breakthrough curve. This study not only provides an efficient adsorbent for gold recovery, but also guidance for designing new materials.

Porous Covalent Organic Framework Based Hydrogen-Bond Nanotrap for the Precise Recognition and Separation of Gold

Utilizing weak interactions to effectively recover and separate precious metals in solution is of great importance but the practice remains a challenge. Herein, we report a novel strategy to achieve precise recognition and separation of gold by regulating the hydrogen-bond (H-bond) nanotrap within the pore of covalent organic frameworks (COFs). It is found that both COF-HNU25 and COF-HNU26 can efficiently capture Au^III with fast kinetics, high selectivity, and uptake capacity. In particular, the COF-HNU25 with the high density of H-bond nanotraps exhibits an excellent gold uptake capacity of 1725 mg g^-1 , which is significantly higher than that (219 mg g^-1 ) of its isostructural COF (COF-42) without H-bond nanostrap in the pores. Importantly, the uptake capacity is strongly correlated to the number of H-bonds between phenolic OH in the COF and [AuCl₄ ]^- in water, and multiple H-bond interactions are the key driving force for the excellent gold recovery and reusability of the adsorbent.

Fabrication of 2D nanosheet sorbents through metastable emulsion droplets and subsequent two-step grafting polymerization for efficient blood lead removal in vitro

Hemoperfusion is a powerful and yet simple method for lead poisoning treatment, but creation of safe and effective sorbents with excellent selectivity remains a real challenge. To address this, we here construct 2D nanosheet sorbents (BM-SH) through metastable emulsion droplets and subsequent two-step grafting polymerization for efficient blood lead removal in vitro. Metastable emulsion droplets endow typical nanosized sheet-like structure (thickness of 30 nm) and relatively round shape. The consecutive two grafting processes using hydroxyethyl methacrylate (HEMA) and L-cysteine monomer (D-SH) provide BM-SH with a high density of accessible binding sites towards lead ions (Pb²⁺). A high adsorption capacity of 390.5 mg g^-1 and quick capture 97.35 % of Pb²⁺ within initial 10 min are obtained, surpassing most of the reported sorbents for lead removal. Besides, adsorption distribution coefficient (K_d) of BM-SH among four coexisting metal ions achieved 7792 mL g^-1, showing outstanding selectivity toward Pb²⁺. Importantly, a possible adsorption mechanism is recognized as coordination with carboxyl, sulfydryl and imino groups from L-cysteine, and mercapto ligand as the key chelating agent may be the reason for high Pb²⁺ affinity. And what's more, BM-SH displays good hemocompatibility and high efficiency of blood lead removal rate (above 86 % in vitro).

Synthesis of reusable cyclodextrin polymers for removal of naphthol and naphthylamine from water

As one group of important naphthalene derivatives, naphthol and naphthylamine are diffusely employed as dye intermediates. The presence of naphthol and naphthylamine in water systems may pose risks to the environment and public health due to their carcinogenicity. In this study, four mesoporous polymers prepared by β-cyclodextrin derivatives and tetrafluoroterephthalonitrile were obtained and applied to adsorbing 1-naphthylamine, 2-naphthylamine, 1-naphthol, and 2-naphthol from water. The impact of adsorption time, initial concentration of naphthol and naphthylamine, and temperature on the adsorption efficiency of the four polymers were explored separately. The four polymers present fast adsorption kinetics toward naphthol and naphthylamine, attaining 93 ~ 100% of adsorption equilibrium uptake for 1-naphthol, 1-naphthylamine, 2-naphthylamine in 15 min, and 87 ~ 90% of equilibrium uptake for 2-naphthol in 15 min. The kinetics could be depicted well by the pseudo-second-order kinetic model. The adsorption isotherms of the four polymers toward naphthol and naphthylamine accord with the Redlich-Peterson or Sips model. The maximum adsorption capacities of 1-naphthylamine, 2-naphthylamine, 1-naphthol, and 2-naphthol are 189.9 mg/g, 82.8 mg/g, 137.7 mg/g, and 88.7 mg/g, respectively. The adsorption ratio increases fast with reducing the initial concentration of naphthol and naphthylamine, and the adsorption ratio of naphthol and naphthylamine in 5 mg/L can achieve over 95% in 25 °C. In addition, the four polymers can be effortlessly regenerated by a gentle and simple washing procedure with little reduction in performance. The adsorption performance of the four polymers toward the four naphthalene derivatives can be improved by increasing the adsorption temperature. In conclusion, the prepared β-cyclodextrin polymers exhibit rapid water treatment in removing the four low-concentration naphthalene derivatives with convenient regeneration and good reusability.

Development of quaternized polyethylenimine-cellulose fibers for fast recovery of Au(CN)2- in alkaline wastewater: Kinetics, isotherm, and thermodynamic study

The purpose of this study was to fabricate quaternized polyethylenimine-cellulose fibers (QPCFs) for the fast recovery of Au(I) from alkaline e-waste leachate. QPCFs were prepared by quaternizing PEI-modified cellulose fibers using a (3-chloro-2-hydroxypropyl)trimethylammonium chloride solution. The maximum Au(I) adsorption capacity of QPCFs was estimated to be 109.87 ± 3.67 mg/g at pH 9.5 using the Langmuir model. The values of k₁ and k₂ calculated by the pseudo-first and pseudo-second-order models were 1.79 ± 0.15 min^-1 and 0.045 ± 0.003 g/mg min, respectively. Adsorption equilibrium was reached within 5 min. Thermodynamic studies revealed that the Au(I) adsorption process by the QPCFs was spontaneous (ΔG° < 0) and exothermic (ΔH° < 0). The characterization and adsorption mechanism of QPCFs were investigated by Fourier transform infrared spectroscopy, X-ray diffraction, and X-ray photoelectron spectrometry. Quaternary amine sites were well developed in the QPCFs. Oxidation or reduction of adsorbed Au(I) was not observed. When QPCFs were applied to the solution obtained by bioleaching of e-waste, the recovery efficiencies of Au and Cu were 61.7 ± 3.1% and 11.1 ± 2.9%, respectively, indicating that QPCFs have Au selectivity. Therefore, QPCFs are suitable for actual wastewater applications because of their high adsorption performance and fast adsorption rate.

Environmental footprint of voltammetric sensors based on screen-printed electrodes: An assessment towards "green" sensor manufacturing

Voltammetric sensors based on screen-printed electrodes (SPEs) await diverse applications in environmental monitoring, food, agricultural and biomedical analysis. However, due to the single-use and disposable characteristics of SPEs and the scale of measurements performed, their environmental impacts should be considered. A life cycle assessment was conducted to evaluate the environmental footprint of SPEs manufactured using various substrate materials (SMs: cotton textile, HDPE plastic, Kraft paper, graphic paper, glass, and ceramic) and electrode materials (EMs: platinum, gold, silver, copper, carbon black, and carbon nanotubes (CNTs)). The greatest environmental impact was observed when cotton textile was used as SM. HDPE plastic demonstrated the least impact (13 out of 19 categories), followed by ceramic, glass and paper. However, considering the end-of-life scenarios and release of microplastics into the environment, ceramic, glass or paper could be the most suitable options for SMs. Amongst the EMs, the replacement of metals, especially noble metals, by carbon-based EMs greatly reduces the environmental footprint of SPEs. Compared with other materials, carbon black was the least impactful on the environment. On the other hand, copper and waste-derived CNTs (WCNTs) showed low impacts except for terrestrial ecotoxicity and human toxicity (non-cancer) potentials. In comparison to commercial CNTs (CCNTs), WCNTs demonstrated lower environmental footprint and comparable voltammetric performance in heavy metal detections, justifying the substitution of CCNTs with WCNTs in commercial applications. In conclusion, a combination of carbon black or WCNTs EMs with ceramic, glass or paper SMs represents the most environmentally friendly SPE configurations for voltammetric sensor arrangement.

Cu-Zn bimetal ZIFs derived nanowhisker zero-valent copper decorated ZnO nanocomposites induced oxygen activation for high-efficiency iodide elimination

Studies on the elimination of iodide anions (I^-) by Cu-based adsorbents have been conducted for decades, however its unsatisfactory adsorption performance and its non-reusability are still the main obstacles for large-scale practical applications. Here, an efficient technique was proposed for the elimination of iodide using nanowhisker zero-valent copper (nwZVC) decorated ZnO nanocomposites obtained by two steps pyrolysis of Cu-Zn bimetal ZIFs precursors. The as-synthesized materials were extensively characterized and the results clearly revealed that nanoscale ZVC were well-dispersed in the ZnO matrix, and the morphology and the amount of nanoscale ZVC could be tuned by adjusting the molar ratio of Cu/Zn in ZIF precursors. The following batch adsorption experiments demonstrated that the resultant materials exhibited high adsorption capacity of 270.8 mg g^-1 under condition of adequate oxygen, as well as high selectivity, strong acidity resistance and an excellent reusability. The mechanism investigations revealed that the elimination of I^- by as-fabricated materials involved adsorption process coupled with oxidation, and the existence of nwZVC was responsible for this since nwZVC could activate molecular oxygen to generate H₂O₂ accompanied by the release of Cu⁺, thus leading to I^- adsorbed by the released Cu⁺ and oxidized by the H₂O₂.

Metal-organic frameworks for pesticidal persistent organic pollutants detection and adsorption - A mini review

The global population growth demands intensification of anthropogenic processes, thus leading to inter alia pollution of both land and aquatic environments with toxic organic compounds. Particularly harmful synthetic compounds are classified as persistent organic pollutants (POPs). Their relatively high chemical resistance resulted in a worldwide ban or strict control on the use of POPs. The majority of POPs were commonly used as pesticides, and unfortunately, some of them are still utilized as an aid in agricultural practices. Therefore, environmental monitoring in terms of reliable detection and quantification of pesticidal POPs is an ever-increasing need. Chemical sensors and adsorption materials crafted for specific pesticide operate on host-guest interactions should provide selectivity and sensitivity, thus leading to the detection of target molecule down to the nanomolar range. This could be achieved with materials exhibiting a very large active surface area, well-defined structure, and high stability. The novel materials studied in that context are metal-organic frameworks (MOFs). The structure of various MOFs can be functionalized to provide desired host-guest interactions. In this mini-review, we critically discuss the application of MOFs for the detection and adsorption of selected pesticides that are classified as POPs according to the Stockholm Convention.