Melamine-based adsorbent materials and methods of use for recovery of metals from aqueous sources

Abstract

Melamine-based porous aromatic framework adsorbents and their use in separating platinum-group metal ions from complex mixtures having the coexistence of rare earth ions and / or transition metal ions in solution. Melamine-based porous aromatic framework materials containing platinum-group metal ions adsorbed thereto.

Description

MELAMINE-BASED ADSORBENT MATERIALS AND METHODS OF USE FOR RECOVERY OF METALS FROM AQUEOUS SOURCESSTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT

[0001] N / ACROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present application claims the benefit under 35 USC § 119(e) of United States Provisional Patent Application No. 63 / 668,369, filed July 8, 2024. The entire contents of the above-referenced patent application(s) are hereby expressly incorporated herein by reference.BACKGROUND

[0003] The limited availability of precious metals and the ever-expanding demand for them across industries has necessitated recycling technologies effective to recover these metals from end-of-life materials and waste streams alongside traditional mineral extraction practices. Often, the precious metal content in standard waste electrical and electronic equipment, end- of-life industrial or automotive catalysts, fuel cells, and batteries is notably higher than that in mineral sources. The development of efficient and highly selective noble metal recovery technologies is essential for a circular economy of resources. It is to such recovery technologies that the present disclosure is directed.BRIEF DESCRIPTION OF THE DRAWINGS

[0004] Several embodiments of the present disclosure are hereby illustrated in the appended drawings. It is to be noted, however, that the appended drawings only illustrate several typical embodiments and are, therefore, not intended to be considered limiting of the scope of the inventive concepts disclosed herein. The patent or application file contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the Office upon request and payment of the necessary fee.

[0005] FIG. 1A shows the primary chemical reactants for forming PAF1, PAF2, and PAF3.

[0006] FIG. IB shows SEM images and corresponding size distributions of PAF1 nanoparticles (b,c), PAF2 nanoparticles (d,e), and PAF3 nanoparticles (f,g).

[0007] FIG. 2 shows examples of other ligands that can be conjugated to melamine to form PAF adsorbents that can be used in accordance with the present disclosure. The followingchemical structures are shown: a=Isophthalic acid, b=5 -Hydroxyisophthalic acid, c= 1,2, 4,5- Benzenetetracarboxylic acid, d=Biphenyl-4,4'-dicarboxylic acid, e=Biphenyl-3,4',5- tricarboxylic acid, f=2,6-Naphthalenedicarboxylic acid, g=3,3',5,5'- Tetracarboxydiphenylmethane, h=l ,3,5-Tris(4-carboxyphenyl)benzene, i=4,4',4"-s-Triazine- 2,4,6-triyl-tribenzoic acid, j=l,3,5-Triscarboxyphenylethynylbenzene, and k=l, 2,4,5- Tetrakis(4-carboxyphenyl)benzene.

[0008] FIG. 3A shows results of FT-IR analysis of PAF1 nanoparticles.

[0009] FIG. 3B shows results of FT-IR analysis of PAF2 nanoparticles.

[0010] FIG. 3C shows results of FT-IR analysis of PAF3 nanoparticles.

[0011] FIG. 3D shows results of PXRD analyses of PAF1 , PAF2, and PAF3 nanoparticles.

[0012] FIG. 3E shows results of BET surface area analyses of PAF1, PAF2, and PAF3 nanoparticles.

[0013] FIG. 3F shows results of zeta potential characterization of PAF1, PAF2, and PAF3 nanoparticles.

[0014] FIG. 4 shows a comparison of adsorption efficiencies of Ru, Pd, and Pt ions by PAF1, PAF2 and PAF3. Equimolar aqueous solutions of Ru, Pd and Pt ions, with initial concentration values of ~1 ppm (A) and ~10 ppm (B), were used.

[0015] FIG. 5 shows the effects of increasing acidity on the adsorption efficiency (a) and separation efficiency (b) of Ru, Pd, and Pt ions by PAF3 (mpAF3 =25 mg, Vions = 15 mL).

[0016] FIG. 6 shows the effects of an acidic environment on PAF3 adsorption / separation of ions of Ru, Pt, Pd, Nd, La, Ce, Ni, Cu, Co, and Mn: adsorption efficiency at (a) [H+] = 0 mM, and (b) [H+] = 2.7 mM. At a qualitative level, the term “soft” refers to large species with low charge states, a high polarizability, a low electronegativity (e.g., bases), a relatively high HOMO (energy of bases), and a relatively low LUMO (energy of acids), and the term “hard” refers to large species with high charge states, a low polarizability, a high electronegativity (e.g., acids), a relatively low HOMO (energy of bases), and a relatively high LUMO (energy of acids). “Borderline” refers to species which are intermediate between the “soft” category and “hard” category.

[0017] FIG. 7 shows a (a) schematic illustration of PAF3 bead production, (b) PAF3 bead product, (c) PAF3 bead before (left) and after (right) adsorption / separation of 10 ions from a solution containing Ru, Pt, Pd, Nd, La, Ce, Ni, Cu, Co, and Mn ions simultaneously, SEM images of PAF3 beads (d) before, and (e) after exposure to the solutions of the 10 ions, and (f) adsorption efficiency of the 10 ions in solution by PAF3 beads.

[0018] The following abbreviations are used herein:A: Angstrom,BET: Brunauer-Emmett-Teller,Cd: Cadmium,Ce: Cerium,Co: Cobalt,Cu: Copper,DMSO: dimethylsulfoxide,EDTA: Ethylenediamine tetraacetic acid,Eu: Europium,Fe: Iron,FT-IR: Fourier-transform infrared spectroscopy,Gd: Gadolinium,Hg: Mercury,ICP-OES: Inductively coupled plasma optical emission spectroscopy,Ir: Iridium,KOH: Potassium hydroxide,La: Lanthanum,Mn: Manganese,NaOH: Sodium hydroxide,Nd: Neodymium,Ni: Nickel,PAF1: porous aromatic framework 1,PAF2: porous aromatic framework 2,PAF3: porous aromatic framework 3,Pb: Lead,Pd: Paladium,Pr: Praseodymium,Pt: Platinum,PXRD: Powder X-Ray diffraction,Os: Osmium,Rh: Rhodium,Ru: Ruthenium,Sb: Antimony,SEM: scanning electron microscopy,Sn: Tin,Zn: Zinc,Zr: Zirconium.DETAILED DESCRIPTION

[0019] The present disclosure describes, in the first aspect, the novel utilization of melamine-based porous aromatic framework (PAF) adsorbents for the separation of precious metal ions. The second novel aspect of the present disclosure is the successful conversion of powder forms of these precious metal-selective PAF materials into beads and / or pellets effective for continuous engineering processes (e.g., in a fixed-bed adsorber) in which the selective functionality of the powder-form of the adsorbents is preserved. In non-limiting embodiments, the PAF adsorbent beads of the present disclosure are constructed of melamine ligands combined with formaldehyde, terephthalic acid, or trimesic acid. These melamine ligand-formaldehyde, melamine ligand-terephthalic acid, and melamine ligand-trimesic acid adsorbents are referred to herein as PAF1, PAF2, and PAF3, respectively. In one embodiment, the disclosed PAF adsorbents feature distinct selectivity toward precious metal ions (such as, but not limited to, Pd, Pt, and Ru) even at trace levels, which is often a challenge using other recovery techniques. For example, the presently disclosed PAF adsorbents exhibit excellent performance by capturing precious metal ions at concentration values as low as 1 ppm. For example, PAF3 demonstrates superior performance compared to PAF1 and PAF2, which may be attributed to its distinct surface area and porous structure.

[0020] Without being bound by theory, it is believed that the remarkable adsorption ability of the disclosed PAFs may be due to the abundant presence of N-containing groups within the PAF structure and its porous structure. Of note, the preferential binding of PAFs to platinum group metal ions (e.g., Ir , Pd, Pt, Os, Rh, Ru) in mixtures with rare-earth ions (e.g., La, Ce, Nd) and / or transition metal ions (e.g., Cu, Ni, Co, Mn) was activated in the presence of protons. Furthermore, demonstrated herein is the successful translation of the PAF nanoparticles into a robust and scalable bead platform in which the excellent adsorbent functionality of PAFs in discriminating and uptaking only precious metal ions from the complex mixtures is maintained. In particular, disclosed herein are melamine-based PAF adsorbent beads which have exceptional proficiency in separating precious ions, particularly Pd ions, from mixtures comprising precious metal ions (e.g., Ru, Pd, and / or Pt), rare-earth ions (e.g., La, Ce, and / or Nd), and transition metal ions (e.g., Cu, Ni, Co, and / or Mn).

[0021] Before further describing various embodiments of the present disclosure in more detail by way of exemplary description, examples, and results, it is to be understood that the compounds, compositions, and methods of present disclosure are not limited in application to the details of specific embodiments and examples as set forth in the following description. The description provided herein is intended for purposes of illustration only and is not intended to be construed in a limiting sense. As such, the language used herein is intended to be given the broadest possible scope and meaning, and the embodiments and examples are meant to be exemplary, not exhaustive. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description only and should not be regarded as limiting unless otherwise indicated as so. In the description below, numerous specific details are set forth in order to provide a more thorough understanding of the present disclosure. However, it will be apparent to a person having ordinary skill in the art that the present disclosure may be practiced without these specific details. In other instances, features which are well known to persons of ordinary skill in the art have not been described in detail to avoid unnecessary complication of the description. It is intended that all alternatives, substitutions, modifications, and equivalents apparent to those having ordinary skill in the art are included within the scope of the present disclosure. Thus, while the compounds, compositions, and methods of the present disclosure have been described in terms of particular embodiments, it will be apparent to those of skill in the art that variations may be applied to the compounds, compositions, and methods and in the steps or in the sequence of steps of the methods described herein without departing from the concept, spirit, and scope of the inventive concepts.

[0022] Each patent, published patent application, and non-patent publication referenced in any portion of this application is expressly incorporated herein by reference in its entirety to the same extent as if the individual patent, or published patent application, or non-patent publication was specifically and individually indicated to be incorporated by reference.

[0023] Unless otherwise defined herein, scientific and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those having ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

[0024] As utilized in accordance with the methods and compositions of the present disclosure, the following terms, unless otherwise indicated, shall be understood to have the following meanings:

[0025] The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and / or the specification may mean “one,” but it is also consistentwith the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and / or” unless explicitly indicated to refer to alternatives only or when the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and / or.” The use of the term “at least one” will be understood to include one as well as any quantity more than one, including but not limited to, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 100, or any integer inclusive therein. The term “at least one” may extend up to 100 or 1000 or more, depending on the term to which it is attached; in addition, the quantities of 100 / 1000 are not to be considered limiting, as higher limits may also produce satisfactory results. In addition, the use of the term “at least one of X, Y and Z” will be understood to include X alone, Y alone, and Z alone, as well as any combination of X, Y and Z. The term “plurality” refers to two or more items. Where used herein, the specific term “single” is limited to only “one,” and a “pair” means two.

[0026] As used herein, all numerical values or ranges include fractions of the values and integers within such ranges and fractions of the integers within such ranges unless the context clearly indicates otherwise. Thus, to illustrate, reference to a numerical range, such as 1-10 includes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, as well as 1.1, 1.2, 1.3, 1.4, 1.5, etc., and so forth. Reference to a range of 1-50 therefore includes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc., up to and including 50, as well as 1.1, 1.2, 1.3, 1.4, 1.5, etc., 2.1, 2.2, 2.3, 2.4, 2.5, etc., and so forth. Reference to a series of ranges includes ranges which combine the values of the boundaries of different ranges within the series. Thus, to illustrate reference to a series of ranges, for example, of 1-10, 10-20, 20-30, 30-40, 40-50, 50-60, 60-75, 75-100, 100-150, 150- 200, 200-250, 250-300, 300-400, 400-500, 500-750, 750-1,000, includes ranges of 1-20, 10- 50, 50-100, 100-500, and 500-1,000, for example.

[0027] As noted above, any numerical range listed or described herein is intended to include, implicitly or explicitly, any number or sub-range within the range, particularly all integers, including the end points, and is to be considered as having been so stated. For example, "a range from 1.0 to 10.0" is to be read as indicating each possible number, including integers and fractions, along the continuum between and including 1.0 and 10.0, that is, having a minimum value equal to or greater than 1.0 and a maximum value equal to or less than 10.0, such as, for example, 3.25 to 8.65. Any maximum numerical limitation recited herein is intended to include all lower numerical limitations subsumed therein, and any minimum numerical limitation recited in this specification is intended to include all higher numerical limitations subsumed therein. Accordingly, Applicant reserves the right to amend this specification, including the claims, to expressly recite any sub-range subsumed within theranges expressly recited herein. Thus, even if a particular data point within the range is not explicitly identified or specifically referred to, it is to be understood that any data points within the range are to be considered to have been specified, and that the inventor(s) possessed knowledge of the entire range and the points within the range.

[0028] As used in this specification and claims, the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

[0029] The term “or combinations thereof’ as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof’ is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AAB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

[0030] Throughout this application, the terms “about” or “approximately” are used to indicate that a value includes the inherent variation of error for the composition, the method used to administer the composition, or the variation that exists among the study subjects. As used herein the qualifiers “about” or “approximately” are intended to include not only the exact value, amount, degree, orientation, or other qualified characteristic or value, but are intended to include some slight variations due to measuring error, manufacturing tolerances, observer error, and combinations thereof, for example. The term “about” or “approximately”, where used herein when referring to a measurable value such as an amount, a temporal duration, and the like, is meant to encompass, for example, variations of ± 20% or ± 10%, or ± 5%, or ± 1%, or ± 0.1% from the specified value, as such variations are appropriate to perform the disclosed methods and as understood by persons having ordinary skill in the art. As used herein, the term “substantially” means that the subsequently described event or circumstance completely occurs or that the subsequently described event or circumstance occurs to a great extent or degree. For example, the term “substantially” means that the subsequently described event or circumstance occurs at least 80% of the time, at least 90% of the time, at least 91% of the time, at least 92% of the time, at least 93% of the time, at least 94% of the time, at least 95% of the time, at least

[0031] As used herein any reference to “one embodiment” or “an embodiment” means that a particular element, feature, composition, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

[0032] Where used herein, the terms “precious metals” or “platinum group metals” include, but are not limited to, Ir, Os, Pd, Pt, Rh, and Ru, the term “rare earth” includes, but is not limited to, La, Ce, Nd and other elements in the lanthanide group of elements, and the term “transition metal” includes, but is not limited to, Cu, Ni, Co, and Mn. Other rare earth or transition metal ions include, but are not limited to, Pr3+, Eu3+, Gd3+, Zr4+, Fe3+, Hg2+, Rh3+, RU3+, Cd2+, Pb2+, Sn2+, Sb3+.

[0033] Where used herein, the pronoun “we” is intended to refer to all persons involved in a particular aspect of the investigation disclosed herein and as such may include non-inventor laboratory assistants and non-inventor collaborators working under the supervision of the inventor(s).

[0034] The term “wt%” (a.k.a., “wt / wt%” and “%(w / w)”) when used in reference to a solute is a measure of the concentration of a solute in a solution in terms of the mass of the solute and the mass of the solvent in which the solute is dissolved. The solutemass + the solventmass = the solutionmass. Wt% is calculated by dividing the solutemass by the solutionmass, then multiplying the resulting quotient by 100.

[0035] Where reference is made herein to a step of “passing the aqueous solution across the porous aromatic framework (or PAF) adsorbent,” it is intended to refer to a step in which an aqueous solution is passed over a stationary or a moving substrate comprising the PAF adsorbent nanoparticles, or is passed across a surface having the PAF adsorbent acting as an active layer, or is passed through a packed-bed column or container holding the PAF adsorbent, or wherein a quantity of the PAF adsorbent is mixed with an aqueous solution then separated therefrom. Thus the step is not to be limited to passing an aqueous solution over or through a stationary (or moving) mass of the PAF adsorbent.

[0036] Certain novel embodiments of the present disclosure, having now been generally described, will be more readily understood by reference to the following examples, which are included merely for purposes of illustration of certain aspects and embodiments of the present disclosure, and are not intended to be limiting. The following examples are to be construed, as noted above, only as illustrative, and not as limiting of the present disclosure in any waywhatsoever. Those skilled in the art will promptly recognize appropriate variations from the various compositions, structures, components, procedures and methods.METHODS1. Fabrication of melamine-based PAF adsorbents a. Synthesis of PAF constructed from melamine and formaldehyde (PAF1)

[0037] PAF1 was synthesized by reacting melamine with formaldehyde (FIG. 1 A). We first dissolved paraformaldehyde (1.296 g, 43.2 mmol), and melamine (3.024 g, 24 mmol) in 30 mF of DMSO, while ensuring proper mixing with a magnetic stirrer. The resulting mixture was then carefully transferred into a 50 mF teflon-lined autoclave for a solvothermal reaction at 120°C for 1 hour. Subsequently, the teflon-lined autoclave was gently relocated to a magnetic plate for an additional hour of stirring, after which the temperature was increased to 170°C and maintained for 10 hours. Upon cooling down to ambient temperature, we collected the white PAF1 product by filtration and proceeded to wash it sequentially with DMSO, acetone, and tetrahydrofuran. The PAF1 product was then dried overnight under vacuum at 50°C. The PAF1 nanoparticles were then characterized as to shape and morphology (FIG. IB(b)) and size distribution (FIG. IB(c)). The PAF1 nanoparticles were further analyzed by FT-IR, (FIG. 3A), PXRD (FIG. 3D), BET surface area (FIG. 3E), and zeta potential characterization (FIG. 3F). b. Synthesis of PAF constructed from terephthalic acid and melamine (PAF2)

[0038] PAF2 was synthesized by reacting melamine with terephthalic acid (FIG. 1A). In a 100 mF one-necked round bottom flask, we dispersed melamine (21 mmol) with a 25 mF DMSO solution (previously sonicated for 5 minutes) and added terephthalic acid (7 mmol). The mixture was heated to 120°C and maintained at this temperature for 3 hours. Afterwards, an additional 15 mF of DMSO was introduced, and the temperature was further increased to 150°C, where it was kept for 72 hours. Then, the resulting precipitate was centrifuged before being washed with water, tetrahydrofuran, and methanol. Note that the list of solvents that could be used for this rinsing step is not necessarily limited to these three solvents. The PAF2 product was then dried overnight under vacuum at 50°C. The PAF2 nanoparticles were then characterized as to shape and morphology (FIG. IB(d)) and size distribution (FIG. IB(e)). The PAF2 nanoparticles were further analyzed by FT-IR, (FIG. 3B), PXRD (FIG. 3D), BET surface area (FIG. 3E), and zeta potential characterization (FIG. 3F).c. Synthesis of PAF constructed from trimesic acid and melamine (PAF3)

[0039] PAF3 was synthesized by reacting melamine with trimesic acid (FIG. 1A). In a 25 mL DMSO solution, melamine (21 mmol) and trimesic acid (7 mmol) were added. The reaction was carried out at 120°C for 3 hours. Then, an additional 15 mL of DMSO was added. The temperature was then elevated to 150°C, and the reaction was allowed to continue for 72 hours. Afterwards, the resulting precipitate was filtered and washed with hot water and methanol. The PAF3 product was then dried overnight under vacuum at 50°C. The PAF3 nanoparticles were then characterized as to shape and morphology (FIG. 1 B(f)) and size distribution (FIG. 1 B(g)). The PAF3 nanoparticles were further analyzed by FT-IR, (FIG. 3C), PXRD (FIG. 3D), BET surface area (FIG. 3E), and zeta potential characterization (FIG. 3F). d. Synthesis of PAF adsorbents constructed from melamine and alternate ligandsOther carboxylic acid ligands that can be reacted with melamine to form PAF adsorbents for use in accordance with the present disclosure include but are not limited to Isophthalic acid, 5- Hydroxyisophthalic acid, 1,2,4,5-Benzenetetracarboxylic acid, Biphenyl-4,4'-dicarboxylic acid, Biphenyl-3,4',5-tricarboxylic acid, 2,6-Naphthalenedicarboxylic acid, 3, 3', 5,5'- Tetracarboxydiphenylmethane, l,3,5-Tris(4-carboxyphenyl)benzene, 4,4',4"-s-Triazine-2,4,6- triyl-tribenzoic acid, 1,3,5-Triscarboxyphenylethynylbenzene, and 1,2,4,5-Tetrakis(4- carboxyphenyl)benzene, the chemical structures of which are shown in FIG. 2. Ethylenediamine tetraacetic acid (EDTA) could also be used as the ligand.2. Production of bead-type PAR adsorbents

[0040] We initially dispersed 75 mg of PAF3 adsorbent in 1 mL of an aqueous solution containing sodium alginate at a concentration of 20 mg / mL. Other materials such as gelatin, chitosan, polyvinyl alcohol (PVA), starch, or other dissovable natural polysaccharides could be used with or instead of sodium alginate. This mixture was stirred thoroughly. In the meantime, a curing solution was prepared by dissolving 188 mg of CaCh in 30 mL of an aqueous solution containing 0.675 g of polyacrylic acid. Subsequently, the sodium alginate suspension was carefully dropped into the curing solution using syringe, initiating the bead shaping process. The resulting PAF3 bead product was then collected and subjected to three washes with deionized water. Finally, the beads were stored in deionized water in a refrigerator at 4 °C.3. Selective adsorption experimental apparatus

[0041] To assess and compare the ability of the PAF-based adsorbent beads in adsorptive separating precious ions such as Ru, Pd, and Pt ions, we prepared equimolar solutions of three ions at ~1 ppm and ~10 ppm. A glass vial containing 25 mg of one type of adsorbent beads (PAF1, PAF2, or PAF3) was filled with a 15 mL aqueous solution of Ru, Pd, and Pt ions at a concentration of approximately 10 ppm. The mixture was further processed by subjecting it to vortexing and sonication. It was subsequently transferred to a roller shaker and left to agitate at 55 rpm for a duration of 24 hours at room temperature. Afterwards, the mixture was filtered through a 0.22 pm membrane filter to obtain a clear solution. Finally, the concentration of Ru, Pd, and Pt ions in the solution was measured using ICP-OES to evaluate the adsorption performance of the adsorbents (FIG. 4). PAF3 beads were the most efficient at removing the Ru, Pt, and Pd ions from solution at both concentration levels than PAF2, which were more efficient than PAF1 beads (FIG. 4(a-b)).

[0042] PAF3 adsorbent beads were then chosen to assess the influence of an acidic environment on the adsorption and separation of Ru, Pd, and Pt ions. The pH of the aqueous solution containing the Ru, Pd, and Pt ions was adjusted with a 0. 1 M HC1 solution. In certain non-limiting embodiments, the pH may be adjusted to a level in a range of 1.5 to 3.5, or 2.0 to 3.0, or 2.1 to 2.9, or 2.2 to 2.8, or 2.3 to 2.7, or 2.4 to 2.7, or 2.4 to 2.6, or 2.45 to 2.6, or 2.5 to 2.6, or 2.51 to 2.59, or 2.52 to 2.58, or 2.52 to 2.57, or 2.53 to 2.56, or 2.53 to 2.55, or to about 2.54. For the evaluation of adsorption and separation capabilities of PAF3 bead, 25 mg of PAF3 beads were dispersed in a 15 mL equimolar solution containing a mixture of ten ions, including Ru, Pd, Pt, Nd, La, Ce, Ni, Cu, Co, and Mn ions at a concentration of approximately 1 ppm for each ion. The mixture underwent vortexing and sonication before being placed on a roller shaker at 55 rpm for 24 hours. Subsequently, the mixture was filtered through a 0.22 pm membrane filter to obtain a clear solution. Finally, the concentrations of Ru, Pd, Pt, Nd, La, Ce, Ni, Cu, Co, and Mn ions in the post-separation solution were measured using ICP-OES to assess the adsorption performance of the adsorbents.RESULTS

[0043] The results of the separations using the PAF adsorbent beads are shown in FIGS. 4- 7. The removal of precious metal ions (e.g., Pt, Pd, Ru) from solutions at trace levels is a considerable challenge. However, as shown herein, the melamine-based PAFs of the present disclosure exhibit excellent adsorption performance by capturing these precious metal ions at concentrations as low as ~1 ppm (FIG. 4). While it is typical that the adsorbents will reducetheir adsorptive separation performance in diluted ion solutions, we envision that the minimum concentration that separation could still be effectively achieved is at about 100 ppb to about 200 ppb. Without wishing to be bound by theory, it is hypothesized that the remarkable adsorption ability of the disclosed PAFs might be attributed to the abundant presence of N- containing groups within the PAF structure and its porous structure. In terms of adsorption order, at the concentrations tested, PAF3 adsorbent beads demonstrated superior adsorption efficiency compared to PAF2 and PAF1 beads, which may be attributed to their distinct surface area and porous structure.

[0044] Under acidic conditions, the separation factors for Pd / Ru and Pd / Pt of PAF3 exhibit an increasing trend as the proton concentration enhances (i.e., as lower pH values). This increase in proton concentration results in a more efficient isolation of Pd ions from a solution containing Ru, Pt, and Pd ions (FIG. 5).

[0045] We tested PAF3 adsorption and separation capabilities in a challenging mixture that simultaneously containing ten different ions: Ru, Pt, Pd, Nd, La, Ce, Ni, Cu, Co, and Mn. Interestingly, under neutral conditions ([H+] = 0 mM), PAF3 demonstrated a strong affinity for precious metal ions (Ru, Pd, Pt) and rare-earth ions (La, Ce, Nd) as compared to transition metal ions (Cu, Ni, Co, Mn) (FIG. 6(a)). When protons were added ([H+] = 2.7 mM), the selectivity of the PAF3 adsorbent beads for precious metal ions (Ru, Pd, Pt) greatly surpassed that of rare-earth ions (La, Ce, Nd), and transition ions (Cu, Ni, Co, Mn) (FIG. 6(b)). PAF3 adsorbent maintains its excellent separation behavior whether in the nanoparticle form or bead form. It successfully separates precious metal ions, e.g., Pt, Pd, and Ru, from a mixture that includes precious metal ions (Ru, Pd, Pt), rare-earth ions (La, Ce, Nd), and transition metal ions (Cu, Ni, Co, Mn) (FIGS. 6(b), 7).

[0046] In at least certain embodiments, the present disclosure is directed to a method of isolating a platinum group metal ion from an aqueous solution, comprising (1) providing an aqueous solution comprising at least one platinum group metal ion and at least one additional ion selected from the group consisting of rare earth ions and transition metal ions, (2) providing a porous organic adsorbent material comprising nanoparticles, the nanoparticles comprising a ligand conjugated to melamine, and (3) exposing the aqueous solution to the porous organic adsorbent material, wherein the at least one platinum group metal ion is adsorbed preferentially onto the porous organic adsorbent material as compared to the at least one additional ion, thereby reducing the concentration of the platinum group metal ion in relation to the at least one additional ion in the aqueous solution. The porous organic adsorbent material may be, for example, bead-shaped or pellet- shaped. The porous organic adsorbent material may be adheredto or disposed on a solid support structure. The porous organic adsorbent material may be contained within a column or container. The aqueous solution may comprise at least one of wastewater, brine, and mine drainage. The aqueous solution may have a pH in a range of about 2.5 to about 7. The at least one platinum group metal ion may be selected from an ion of Ir, Os, Pd, Pt, Rh, and Ru. The at least one additional ion may be a rare earth ion. The rare earth ion may be an ion of a lanthanide element. The lanthanide element may be selected from La, Ce, and Nd. The at least one additional ion may be an ion of a transition metal. The transition metal may be selected from Cu, Ni, Co, and Mn.

[0047] In at least certain embodiments, the present disclosure is directed to a method of isolating a platinum group metal ion from an aqueous solution, comprising (1) providing an aqueous solution comprising at least one platinum group metal ion and at least one additional ion selected from the group consisting of rare earth ions and transition metal ions, (2) providing a porous organic adsorbent material comprising nanoparticles, the nanoparticles comprising a ligand conjugated to melamine, and (3) exposing the aqueous solution to the porous organic adsorbent material, wherein the at least one platinum group metal ion is adsorbed preferentially onto the porous organic adsorbent material as compared to the at least one additional ion, thereby reducing the concentration of the platinum group metal ion in relation to the at least one additional ion in the aqueous solution. The porous organic adsorbent material may be, for example, bead-shaped or pellet- shaped. The porous organic adsorbent material may be adhered to or disposed on a solid support structure. The porous organic adsorbent material may be contained within a column or container. The aqueous solution may comprise at least one of wastewater, brine, and mine drainage. The aqueous solution may have a pH in a range of about 2.5 to about 7. The at least one platinum group metal ion may be selected from an ion of Ir, Os, Pd, Pt, Rh, and Ru. The at least one additional ion may be a rare earth ion. The rare earth ion may be an ion of a lanthanide element. The lanthanide element may be selected from La, Ce, and Nd. The at least one additional ion may be an ion of a transition metal. The transition metal may be selected from Cu, Ni, Co, and Mn.

[0048] In at least certain embodiments, the present disclosure is directed to a metal-organic adsorbent complex, comprising (1) a porous organic adsorbent material, and (2) at least one platinum group metal ion complexed to the porous organic adsorbent material, wherein the porous organic adsorbent material comprises nanoparticles, the nanoparticles comprising a ligand conjugated to melamine. The ligand may be a carboxylic acid. The carboxylic acid may be selected from the group consisting of terephthalic acid, trimesic acid, Isophthalic acid, 5- Hydroxyisophthalic acid, 1,2,4,5-Benzenetetracarboxylic acid, Biphenyl-4,4'-dicarboxylicacid, Biphenyl-3,4',5-tricarboxylic acid, 2,6-Naphthalenedicarboxylic acid, 3, 3', 5,5'- Tetracarboxydiphenylmethane, 1 ,3,5-Tris(4-carboxyphenyl)benzene, 4,4',4"-s-Triazine-2,4,6- triyl-tribenzoic acid, 1,3,5-Triscarboxyphenylethynylbenzene, 1,2,4,5-Tetrakis(4- carboxyphenyl)benzene, and Ethylenediamine tetraacetic acid. The ligand may be formaldehyde. The at least one platinum group metal ion may be selected from an ion of fr, Os, Pd, Pt, Rh, and Ru. The metal-organic adsorbent complex may further comprise at least one rare earth ion complexed to the porous organic adsorbent material. The at least one rare earth ion may be an ion of a lanthanide element. The lanthanide element may be selected from La, Ce, and Nd. The metal-organic adsorbent complex may further comprise at least one ion of a transition metal. The transition metal may be selected from Cu, Ni, Co, and Mn. The porous organic adsorbent material may have a bead-shaped structure or a pellet-shaped structure. The porous organic adsorbent material may be adhered to or disposed on a solid support structure. The porous organic adsorbent material may be contained within a column or container.

[0049] While the present disclosure has been described herein in connection with certain embodiments so that aspects thereof may be more fully understood and appreciated, it is not intended that the present disclosure be limited to these particular embodiments. On the contrary, it is intended that all alternatives, modifications and equivalents are included within the scope of the present disclosure as defined herein. Thus the examples described above, which include particular embodiments, will serve to illustrate the practice of the inventive concepts of the present disclosure, it being understood that the particulars shown are by way of example and for purposes of illustrative discussion of particular embodiments only and are presented in the cause of providing what is believed to be the most useful and readily understood description of procedures as well as of the principles and conceptual aspects of the present disclosure. Changes may be made in the formulation of the various compositions described herein, the methods described herein or in the steps or the sequence of steps of the methods described herein without departing from the spirit and scope of the present disclosure. Further, while various embodiments of the present disclosure have been described in claims herein below, it is not intended that the present disclosure be limited to these particular claims.

Claims

What is claimed is:

1. A method of isolating a platinum group metal ion from an aqueous solution, comprising; providing an aqueous solution comprising at least one platinum group metal ion and at least one additional ion selected from the group consisting of rare earth ions and transition metal ions; providing a porous organic adsorbent material comprising nanoparticles, the nanoparticles comprising a ligand conjugated to melamine; and exposing the aqueous solution to the porous organic adsorbent material, wherein the at least one platinum group metal ion is adsorbed preferentially onto the porous organic adsorbent material as compared to the at least one additional ion, thereby reducing the concentration of the platinum group metal ion in relation to the at least one additional ion in the aqueous solution.

2. The method of claim 1, wherein the porous organic adsorbent material is bead-shaped or pellet-shaped.

3. The method of claim 1, wherein the porous organic adsorbent material is adhered to or disposed on a solid support structure.

4. The method of claim 1, wherein the porous organic adsorbent material is contained within a column or container.

5. The method of claim 1, wherein the aqueous solution comprises at least one of wastewater, brine, and mine drainage.

6. The method of claim 1, wherein the aqueous solution has a pH in a range of about 2.5 to about 7.

7. The method of claim 1, wherein the at least one platinum group metal ion is selected from an ion of Ir, Os, Pd, Pt, Rh, and Ru.

8. The method of claim 1, wherein the at least one additional ion is a rare earth ion.

9. The method of claim 8, wherein the rare earth ion is an ion of a lanthanide element.

10. The method of claim 9, wherein the lanthanide element is selected from La, Ce, and Nd.

11. The method of claim 1, wherein the at least one additional ion is an ion of a transition metal.

12. The method of claim 11, wherein the transition metal is selected from Cu, Ni, Co, and Mn.

13. A metal-organic adsorbent complex, comprising: a porous organic adsorbent material, and at least one platinum group metal ion complexed to the porous organic adsorbent material, wherein the porous organic adsorbent material comprises nanoparticles, the nanoparticles comprising a ligand conjugated to melamine.

14. The metal-organic adsorbent complex of claim 13, wherein the ligand is a carboxylic acid.

15. The metal-organic adsorbent complex of claim 14, wherein the carboxylic acid is selected from the group consisting of terephthalic acid, trimesic acid, Isophthalic acid, 5- Hydroxyisophthalic acid, 1,2,4,5-Benzenetetracarboxylic acid, Biphenyl-4,4'-dicarboxylic acid, Biphenyl-3,4',5-tricarboxylic acid, 2,6-Naphthalenedicarboxylic acid, 3, 3', 5,5'- Tetracarboxy diphenylmethane, l,3,5-Tris(4-carboxyphenyl)benzene, 4,4',4"-s-Triazine-2,4,6- triyl-tribenzoic acid, 1,3,5-Triscarboxyphenylethynylbenzene, 1,2,4,5-Tetrakis(4- carboxyphenyl Jbenzene, and Ethylenediamine tetraacetic acid.

16. The metal-organic adsorbent complex of claiml3, wherein the ligand is formaldehyde.

17. The metal-organic adsorbent complex of claim 13, wherein the at least one platinum group metal ion is selected from an ion of Ir, Os, Pd, Pt, Rh, and Ru.

18. The metal-organic adsorbent complex of claim 13, further comprising at least one rare earth ion complexed to the porous organic adsorbent material.

19. The metal-organic adsorbent complex of claim 18, wherein the at least one rare earth ion is an ion of a lanthanide element.

20. The metal-organic adsorbent complex of claim 19, wherein the lanthanide element is selected from La, Ce, and Nd.

21. The metal-organic adsorbent complex of claim 13, further comprising at least one ion of a transition metal.

22. The metal-organic adsorbent complex of claim 21, wherein the transition metal is selected from Cu, Ni, Co, and Mn.

23. The metal-organic adsorbent complex of claim 13, wherein the porous organic adsorbent material has a bead-shaped structure.

24. The metal-organic adsorbent complex of claim 13, wherein the porous organic adsorbent material is adhered to or disposed on a solid support structure.

25. The metal-organic adsorbent complex of claim 13, wherein the porous organic adsorbent material is contained within a column or container.

Images