Precious metal recovery from electronic waste by a porous porphyrin polymer

Y. Hong, D. Thirion, S. Subramanian, M. Yoo, H. Choi, H. Y. Kim, J. F. Stoddart*, C. T. Yavuz*
Proc. Natl. Acad. Sci., 117 (28), 16174-16180 (2020).
DOI: 10.1073/pnas.2000606117


Urban mining of precious metals from electronic waste, such as printed circuit boards (PCB), is not yet feasible because of the lengthy isolation process, health risks, and environmental impact. Although porous polymers are particularly effective toward the capture of metal contaminants, those with porphyrin linkers have not yet been considered for precious metal recovery, despite their potential. Here, we report a porous porphyrin polymer that captures precious metals quantitatively from PCB leachate even in the presence of 63 elements from the Periodic Table. The nanoporous polymer is synthesized in two steps from widely available monomers without the need for costly catalysts and can be scaled up without loss of activity. Through a reductive capture mechanism, gold is recovered with 10 times the theoretical limit, reaching a record 1.62 g/g. With 99% uptake taking place in the first 30 min, the metal adsorbed to the porous polymer can be desorbed rapidly and reused for repetitive batches. Density functional theory (DFT) calculations indicate that energetically favorable multinuclear-Au binding enhances adsorption as clusters, leading to rapid capture, while Pt capture remains predominantly at single porphyrin sites.

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Gold Recovery from E-Waste by Porous Porphyrin–Phenazine Network Polymers

T. S. Nguyen, Y. Hong, N. A. Dogan, C. T. Yavuz*
Chem. Mater., 32, 12, 5343–5349 (2020).
DOI: 10.1021/acs.chemmater.0c01734

Gold recovery from electronic waste could prevent excessive mining with toxic extractants and provide a sustainable path for recycling precious metals. Unfortunately, no viable recycling is practiced, except burning electronic circuit boards in underdeveloped countries, mainly because of the lack of chemical scavengers as adsorbents. Here, we report the synthesis of a family of porphyrin–phenazine-based polymers and their gold-capturing properties as well as application in gold recovery from actual e-waste. The polymers show high selectivity toward gold as well as other precious metals. The Au(III) adsorption isotherms were well-fitted to the Langmuir adsorption model and proportionality between porosity and uptake capacity was observed. Solution pH values and illumination conditions were shown to have influences on the performance of the adsorbents with the highest capacity of 1.354 g/g obtained in acidic pH and under continuous UV irradiation. Such a remarkable capacity of 7 times the theoretical estimate was achieved through photochemical adsorption–reduction mechanism supported by the observed suppressing effect of oxidant on gold-capturing ability. The adsorbents are robust and recyclable, a significant advantage over other emerging materials.

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Direct Z-Scheme Tannin–TiO2 Heterostructure for Photocatalytic Gold Ion Recovery from Electronic Waste

K. R. Kim, S. Choi, C. T. Yavuz, Y. S. Nam*
ACS Sustain. Chem. Eng., 8, 19, 7359–7370 (2020).
DOI: 10.1021/acsaem.0c00539

Precious-metal recovery from industrial wastewater has received considerable attention because of rapidly increasing amounts of electronic waste. Existing technologies have yet to be widely applied due to their high cost and low selectivity toward precious-metal ions. Herein, we report a direct Z-scheme tannin–TiO2 heterostructure for selective gold adsorption from electronic waste under solar irradiation. The tannin-coated TiO2 nanoparticles were prepared by a simple dipping method, and under light illumination, both tannin and TiO2 can serve as photosensitive components for the reduction of metal ions, with metal-to-ligand charge transfer from TiO2 to tannin extending the lifetime of the excited electrons. Moreover, no additional electron donors are required because the tannin layer scavenges the reactive oxygen species generated by the holes from the light-activated TiO2 surface. The heterostructure allows for the highly efficient photocatalytic recovery of gold ions, with 11 times higher adsorption capacity in the light compared to the dark. High selectivity toward gold ions was also demonstrated using a metal ion mixture including nine different metal ions that are commonly found in electronic waste. Our findings suggest that the Z-scheme heterostructure of polyphenol and semiconductor provides a promising photochemical pathway for efficient and selective metal ion recovery from electronic waste.

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Thiourea-Based Extraction and Deposition of Gold for Electroless Nickel Immersion Gold Process

J. Son, Y. Hong, C. T. Yavuz, J. Han*

Ind. Eng. Chem. Res., 59, 16, 8086-8092 (2020).
DOI: 10.1021/acs.iecr.0c00493


Gold electroless plating for surface finishing of electronic circuits, named electroless nickel immersion gold (ENIG), is widely practiced in the electronics packaging industry. Noncyanide substitutions of the current cyanide bath for immersion gold are being sought for environmental and safety reasons. Herein, as a promising option, a bath using a noncyanide gold complex, Au(I)–thiourea, was developed. The kinetics of gold deposition were estimated with respect to gold concentration, thiourea concentration, pH, and temperature; the transfer coefficient of gold concentration and activation energy were found to be 0.697 and 36.69 kJ·mol–1, respectively. In addition, the quality of gold coating in terms of corrosion resistance was verified by electrochemical analysis. The relationship between particle size and corrosion resistance of the coating was confirmed by morphology observation through scanning electron microscopy and Tafel plots. The corrosion potential of the gold layer with thiourea was found to be −62 mV, close to that of the layer using a thiosulfate–sulfite bath, with an advantage of faster deposition rate. The results suggest Au(I)–thiourea can serve as an eco-friendly and field-implementable option for the ENIG process, helping to realize a closed-loop process of gold: recovering the precious metal from electronic wastes and reusing it in new products.

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Gold recovery using porphyrin-based polymer from electronic wastes: Gold desorption and adsorbent regeneration

J. Son, Y. Hong, G. Han, T. S. Nguyen, C. T. Yavuz, J. Han*
Sci. Total Environ., 704, 135405 (2020).
DOI: 10.1016/j.scitotenv.2019.135405

Electronic wastes containing precious metals have great potential as a sustainable source of such metals. Separation and refining, however, remain complicated, and none of the existing technologies have yet experienced commercialization. A novel porphyrin-based porous polymer, named COP-180, was recently introduced as a powerful adsorbent option, especially for gold, and in this study, aspects of desorption and recovery of adsorbed gold and regeneration of the polymer were investigated. A hydrometallurgical method using non-cyanide leaching agents was developed, and an acid thiourea-based solution was found to be particularly suited for the method based on COP-180 with gold desorption efficiency of 97%. Fourier-transform infrared spectroscopy spectra demonstrated the unaffected structure of COP-180 after desorption, implying the potential of its reuse. This high desorption efficiency was achieved even without typical aiding agents by means of a formamidine disulfide-mediated route that prevented thiourea consumption, which is considered a major drawback of the otherwise promising reagent. Using this method, the polymer was able to maintain more than 94% desorption efficiency after five times of regeneration. The results suggest that acid thiourea can offer a workable means of recovering gold particularly from the excellent gold-adsorbent of COP-180, and that repeated regeneration is also possible.

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Photochemically-enhanced Selective Adsorption of Gold Ions on Tannin-coated Porous Polymer Microspheres

J. Kim, K. R. Kim, Y. Hong, S. Choi, C. T. Yavuz, J. W. Kim*, Y. S. Nam*
ACS Appl. Mater. Interfaces, 11, 24, 21915-21925 (2019).
DOI: 10.1021/acsami.9b05197

Metal recovery from electronic waste and industrial wastewater has attracted increasing attention to recycle precious metals and inhibit the emission of hazardous heavy metals. However, the selective recovery of precious metals with a large quantity is still very challenging because wastewater contains a variety of different cations while precious metal ions are relatively scarce. Here, we introduce a simple method to selectively increase the adsorption of gold ions using tannin-coated porous polymer microspheres through photochemical reduction. Mesoporous poly(ethylene glycol dimethacrylate-co-acrylonitrile) microspheres with an average pore diameter of 13.8 nm were synthesized and used as an adsorbent matrix. Tannic acid (TA) was deposited onto the internal pores of the polymer matrix by simple immersion in an aqueous milieu. TA coatings increased the maximum number of adsorbed gold ions by 1.3 times because of the well-known metal ion chelation of TA. Under light illumination, the maximum number of adsorbed gold ions dramatically increased by 6.1 times. We examined two distinct mechanisms presumably involved in the enhanced adsorption: the photooxidation of TA and plasmon-induced hot electrons. Moreover, TA-coated microspheres exhibited remarkable selectivity for gold ions among competing metal ions commonly found in waste resources. This work suggests that the photochemically activated TA can serve as an excellent adsorbent for the selective and efficient recovery of gold ions from wastewater.

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Radioactive Strontium Removal from Seawater by a MOF via Two-Step Ion Exchange

M. Garai, C. T. Yavuz*
Chem, 5 (4), 750-752 (2019). Preview 
DOI: 10.1016/j.chempr.2019.03.020

Radioactive waste, such as 90Sr, 134Cs, and 131I, from the Fukushima nuclear spill highlighted the need to find effective adsorbents for scrubbing radioactive ions from seawater. In this issue of Chem, Wang and colleagues report a remarkably 90Sr-selective metal-organic framework (SZ-4) that operates with a two-step ion-exchange mechanism and at a wide pH range while being active and intact when tested in actual seawater.

Link to the journal website

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Applicability of disulfide-polymer particles surface embedded on alginate beads for cadmium removal from airport derived stormwater

D. Ko, H. Kim, H. Lee, C. T. Yavuz, H. R. Andersen, Y. Hwang*
J. Environ. Chem. Eng., 6, 4124–4129 (2018).
DOI: 10.1016/j.jece.2018.06.007

Stormwater runoff derived from airports causes severe cadmium contamination in excess of the maximum limit level and is difficult to treat due to the irregular contamination levels from scattered rainfall. To overcome this and remove cadmium from runoff, a new reactive filtration column is introduced. Sulfur functionalized polymer particles were successfully embedded onto the surface of alginate bead (DiS-algi) and simulated a real stormwater treatment filtration column. The DiS-algi shows 22.3 mg/g of batch and 877 μg/g of continuous flow sorption capacity. Also, the results for the new sorption material show that within 6 mins half of the cadmium was removed with 31 L/mg of Langmuir sorption affinity, outperforming an activated carbon filter. From a breakthrough test the reactive column shows complete uptake of cadmium from a contaminated flow, lasting two hours until reaching the breakthrough point. Furthermore, regeneration tests of the column verified its reusability. DiS-algi appears to be a viable new cadmium sorption material for airport derived stormwater runoff filtration systems.

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Disulfide polymer grafted porous carbon composites for heavy metal removal from stormwater runoff

D. Ko*, P. D. Mines, M. H. Jakobsen, C. T. Yavuz, H. C. B. Hansen, H. R. Andersen
Chem. Eng. J., 348, 685–692 (2018).
DOI: 10.1016/j.cej.2018.04.192

The emerging concern of heavy metal pollution derived from stormwater runoff has triggered a demand for effective heavy metal sorbents. To be an effective sorbent, high affinity along with rapid sorption kinetics for environmental relevant concentrations of heavy metals is important. Herein, we have introduced a new composite suitable for trace metal concentration removal, which consists of cheap and common granular activated carbon covered with polymers containing soft bases, thiols, through acyl chlorination (DiS-AC). Material characterization demonstrated that the polymer was successfully grafted and grown onto the surface of the carbon substrate. The distribution coefficient for Cd2+ bonding was 89·103 L/kg at a solution concentration of 0.35 mg/L, which is notably higher than sorption affinities for Cd2+ seen in conventional sorbents. The sorption isotherm is well described by the Freundlich isotherm and within an hour, half of the initial trace (0.2 mg/L) concentration of Cd2+ was removed by the DiS-AC at a sorbent loading of 2 g/L. Therefore, the novel material DiS-AC promises to be an ideal candidate for filters treating stormwater runoff.

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Granular activated carbon with grafted nanoporous polymer enhances nanoscale zero-valent iron impregnation and water contaminant removal

P. D. Mines, B. Uthuppu, D. Thirion, M. H. Jakobsen, C. T. Yavuz, H. R. Andersen, Y. Hwang*
Chem. Eng. J., 339, 22-31 (2018).
DOI: 10.1016/j.cej.2018.01.102

Granular activated carbon was customized with a chemical grafting procedure of a nanoporous polymeric network for the purpose of nanoscale zero-valent iron impregnation and subsequent water contaminant remediation. Characterization of the prepared composite material revealed that not only was the polymer attachment and iron impregnation successful, but also that the polymeric shell acted as a protective barrier against the effects of oxidation from the surrounding environment, nearly 99% of total iron content was in the form of zero-valent iron. When applied towards the remediation of two common water contaminants, nitrobenzene and nitrate, the composite material exploited the qualities of both the activated carbon and the polymeric network to work together in a synergistic manner. In that the increased protection from oxidation allowed for increased reactivity of the nanoscale zero-valent iron, and that the adsorption abilities of both the carbon and the polymer achieved a higher amount of total removal of the contaminants.

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Reversible water capture by a charged metal-free porous polymer

J. Byun, H. A. Patel, D. Thirion, C. T. Yavuz*
Polymer, 126, 308-313, (2017).
Invited paper for the special issue on Porous Polymers
DOI: 10.1016/j.polymer.2017.05.071

Climate change and industrial pollution threatens the availability of clean water. Although established protocols of water treatment exist, water capture by porous materials has emerged as a viable alternative to energy intensive processes. Here we introduce a new charged porous polymer that is capable of capturing and releasing water by simple humidity or temperature swings. The quaternary amines on the framework structure attract water molecules and further solvate by coordination. The porosity of the network structure also provides enough void where water can diffuse throughout the solid. Water uptake capacity of the porous polymer surpasses common desiccants like silica gel and molecular sieves, and has the potential to act as an organic desiccant in applications like electronics or food packaging.

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Selective removal of cationic micro-pollutants using disulfide-linked network structures

M. S. Atas, S. Dursun, H. Akyildiz, M. Citir, C. T. Yavuz*, M. S. Yavuz*
RSC Adv., 7, 25969-25977, (2017). Open Access
DOI: 10.1039/C7RA04775D

Micropollutants are found in all water sources, even after thorough treatments that include membrane filtration. New ones emerge as complex molecules are continuously produced and discarded after used. Treatment methods and sorbent designs are mainly based on non-specific interactions and, therefore, have been elusive. Here, we developed swellable covalent organic polymers (COP) with great affinity towards micropollutants, such as textile industry dyes. Surprisingly, only cationic dyes in aqueous solution were selectively and completely removed. Studies of the COPs surfaces led to a gating capture, where negatively charged layer attracts cationic dyes and moves them inside the swollen gel through diffusive and hydrophobic interaction of the hydrocarbon fragments. Despite its larger molecular size, crystal violet has been taken the most, 13.4 mg g−1, surpassing all competing sorbents. The maximum adsorption capacity increased from 12.4 to 14.6 mg and from 8.9 to 11.4 mg when the temperature of dye solution was increased from 20 to 70 °C. The results indicated that disulfide-linked COPs are attractive candidates for selectively eliminating cationic dyes from industrial wastewater due to exceptional swelling behaviour, low-cost and easy synthesis.

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Selective removal of heavy metal ions by disulfide linked polymer networks

D. Ko, J. S. Lee, H. A. Patel, M. H. Jakobsen, Y. Hwang, C. T. Yavuz, H. C. B. Hansen, H. R. Andersen*
J. Hazard. Mater., 332, 140–148, (2017).
DOI: 10.1016/j.jhazmat.2017.03.007.

Heavy metal contaminated surface water is one of the oldest pollution problems, which is critical to ecosystems and human health. We devised disulfide linked polymer networks and employed as a sorbent for removing heavy metal ions from contaminated water. Although the polymer network material has a moderate surface area, it demonstrated cadmium removal efficiency equivalent to highly porous activated carbon while it showed 16 times faster sorption kinetics compared to activated carbon, owing to the high affinity of cadmium towards disulfide and thiol functionality in the polymer network. The metal sorption mechanism on polymer network was studied by sorption kinetics, effect of pH, and metal complexation. We observed that the metal ions–copper, cadmium, and zinc showed high binding affinity in polymer network, even in the presence of competing cations like calcium in water.

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Charge-specific size-dependent separation of water-soluble organic molecules by fluorinated nanoporous networks

J. Byun, H. A. Patel, D. Thirion, C. T. Yavuz*
Nature Commun., 7, 13377, (2016). OpenAccess
DOI: 10.1038/ncomms13377. ReadCube: rdcu.be/mw1d.
Highlighted in Chemical & Engineering News by Stephen K. Ritter

Molecular architecture in nanoscale spaces can lead to selective chemical interactions and separation of species with similar sizes and functionality. Substrate specific sorbent chemistry is well known through highly crystalline ordered structures such as zeolites, metal organic frameworks and widely available nanoporous carbons. Size and charge-dependent separation of aqueous molecular contaminants, on the contrary, have not been adequately developed. Here we report a charge-specific size-dependent separation of water-soluble molecules through an ultra-microporous polymeric network that features fluorines as the predominant surface functional groups. Treatment of similarly sized organic molecules with and without charges shows that fluorine interacts with charges favourably. Control experiments using similarly constructed frameworks with or without fluorines verify the fluorine-cation interactions. Lack of a σ-hole for fluorine atoms is suggested to be responsible for this distinct property, and future applications of this discovery, such as desalination and mixed matrix membranes, may be expected to follow.

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Covalent organic polymer functionalization of activated carbon surfaces through acyl chloride for environmental clean-up

P. D. Mines*, D. Thirion, B. Uthuppu, Y. Hwang, M. H. Jakobsen, H. R. Andersen, C. T. Yavuz* Chem. Eng. J., 309, 766-771, (2017). DOI: 10.1016/j.cej.2016.10.085.

Nanoporous networks of covalent organic polymers (COPs) are successfully grafted on the surfaces of activated carbons, through a series of surface modification techniques, including acyl chloride formation by thionyl chloride. Hybrid composites of activated carbon functionalized with COPs exhibit a core-shell formation of COP material grafted to the outer layers of activated carbon. This general method brings features of both COPs and porous carbons together for target-specific environmental remediation applications, which was corroborated with successful adsorption tests for organic dyes and metals.

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Engineered nanoparticles for water treatment application

J. Byun, C. T. Yavuz*
Chapter 2 in Engineered Nanoparticles and the Environment: Biophysicochemical Processes and Toxicity, Edited by B. Xing, C. D. Vecitis, N. Senesi.
WILEY-IUPAC Series in Biophysico-Chemical Processes in Environmental Systems
Published by John Wiley & Sons, Inc.
ISBN: 9781119275824
DOI: 10.1002/9781119275855.ch2

In this chapter, water treatment processes using nanoparticles and studies related to the removal of waterborne contaminants, such as anionic, cationic, and organic pollutants, will be reviewed.

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Rapid extraction of Uranium ions from seawater using novel porous polymeric adsorbents

Y. Sihn,§ J. Byun,§ H. A. Patel, W. Lee*, C. T. Yavuz*
RSC Adv., 6, 45968-45976, (2016). §: Equal contribution. DOI: 10.1039/C6RA06807C

Seawater contains uranium in surprisingly high quantities that can supply vast energy, if recovered economically. Attempts to design effective sorbents led to the identification of organic functional groups such as amidoximes. Here we report a porous polymer, a polymer of intrinsic microporosity (PIM) with permanent pores that feature amidoxime pendant groups, which is capable of removing more than 90% uranyl [U(VI)] from seawater collected from the Ulleung basin of the East Sea of the Republic of Korea. From this uptake, over 75% was collected in less than six hours, leading to highly feasible field applications. When the seawater was acidified by bubbling CO2 (pH = 5.4), the uptake increased dramatically. Regeneration studies showed full recovery of sorbents and no loss in capture capacity. Our results indicate that successful uranium recovery can be realized by scalable applications of porous polymeric networks and when low cost CO2 is co-administered, uptake can be significantly enhanced.

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Covalent organic polymer framework with C-C bonds as a fluorescent probe for selective iron detection

E. Ozdemir, D. Thirion, C. T. Yavuz*
RSC Adv., 5, 69010-69015, (2015). DOI: 10.1039/C5RA10697D.

A new carbon–carbon bonded nanoporous polymer network was synthesized via efficient and catalyst free Knoevenagel-like condensation polymerization in near quantitative yields. The obtained polymer network, Covalent Organic Polymer – COP-100 possesses strong fluorescent properties and designed solubility in polar aprotic solvents, which shows promise for use as a metal-sensing material in solution. COP-100 exhibited high selectivity towards Fe2+ and Fe3+ in the presence of other common metal cations (Al3+, Ag+, Cd2+, Co2+, Cr3+, Cu2+, Hg2+, Mg2+, Mn2+, Na+, Ni2+, Zn2+) as the fluorescence of the polymer was significantly quenched even at very low concentrations. In the range from 2.5 × 10−6 to 2 × 10−4 M, a linear fluorescence emission response with equipment limited detection minimum of 2.13 × 10−7 M and 2.45 × 10−7 M for Fe2+ and Fe3+, respectively, was observed. These results suggest that COP-100 is a promising material as a selective fluorescence sensor for iron ions.

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Magnetic BaFe12O19 nanofiber filter for effective separation of Fe3O4 nanoparticles and removal of arsenic

J. Byun, H. A. Patel, C. T. Yavuz*
J. Nanopart. Res., 16:2787 (2014). [DOI]

Magnetic nanoparticles are promising in applications where magnetic separation is intended, although material losses via leaching mechanisms are often inevitable. Magnetic separations with widely available permanent magnets can effectively trap particles, leading to a complete removal of used or waste particles. In this report, we first demonstrate the synthesis of the thinnest (112.7 ± 16.4 nm) and most magnetic (71.96 emu g−1) barium hexaferrite (BaFe₁₂O₁₉, BHF—fridge magnet) via an organic solvent-free electrospinning procedure. When the fibers are then packed into a column, they clearly remove 12 nm magnetite (Fe₃O₄) nanoparticles quantitatively. The same BHF cartridge also removes more than 99.9 % As-treated magnetite nanoparticles at capacities up to 70 times of its weight. As a result, one liter of 150 μg L−1 As-contaminated water can be purified rapidly at a material cost of less than 2 US cents.

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Exceptional organic solvent uptake by disulfide-linked polymeric networks

H. A. Patel, M. S. Yavuz, C. T. Yavuz*
RSC Adv., 4 (46), 24320 - 24323, (2014). [DOI] [pdf] [WOS]

Disulfide-linked covalent organic polymers (COPs) were prepared through catalyst-free oxidative coupling polymerization. Owing to the excellent swelling behavior, low cost, and efficient synthesis, these materials can be promising materials for removal of organics in concentrated streams. COPs show 1,4-dioxane uptake up to 1.8 g g⁻¹.

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