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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Triazatruxene-Based Ordered Porous Polymer: High Capacity CO2, CH4, and H2 Capture, Heterogeneous Suzuki–Miyaura Catalytic Coupling, and Thermoelectric Properties

A. E. Sadak*, E. Karakuş*, Y. Chumakov, N. A. Dogan, C. T. Yavuz 

ACS Appl. Energy Mater., 3, 5, 4983–4994 (2020). 

DOI: 10.1021/acsaem.0c00539

A hypercrosslinked ultramicroporous and ordered organic polymer network was synthesized from a planar trimer indole building block called triazatruxene (TAT) through anhydrous FeCl3 catalyzed Friedel–Crafts alkylation using methylal as a crosslinker. The polymer network is stable in a variety of chemicals and thermally durable. The hypercrosslinked network TATHCP shows a high BET (Brunauer–Emmet–Teller) specific surface area of 997 m2 g–1 with CO2 uptake capacity of 12.55 wt % at 273 K, 1.1 bar. Gas selectivities of 38.4 for CO2/N2, 7.8 for CO2/CH4, 40.6 for CO2/O2, and 32.1 for CO2/CO were achieved through IAST calculation. The PXRD analysis has revealed that TATHCP has a fully eclipsed structure in full agreement with Pawley refinement. The ordered 2D layers provide anisotropy that could be used in catalysis and thermoelectric measurements. After loading with Pd(II), TATHCP-Pd showed high catalytic activity in Suzuki–Miyaura cross coupling reaction with a wide range of reagents and excellent reaction yields of 90–98% with good recyclability. The structure of TATHCP-Pd was found to have two independent molecules of Pd(OAc)2 in the asymmetric unit cell which are arranged between two TATHCP layers. Thermoelectric properties of TATHCP showed a high Seebeck coefficient and ZT, a first and promising example in HCPs with applications in all-organic thermal energy recovery devices.

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Sustainable synthesis of superhydrophobic perfluorinated nanoporous networks for small molecule separation

S. Kim§, D. Thirion§, T. S. Nguyen, B. Kim, N. A. Dogan, C. T. Yavuz* 
Chem. Mater., 31, 14, 5206-5213, (2019). §: Equal contribution
DOI: 10.1021/acs.chemmater.9b01447

Nanoporous polymers offer great promise in chemical capture and separations because of their versatility, scalability, and robust nature. Here, we report a general methodology for one-pot, metal-free, and room-temperature synthesis of nanoporous polymers by highly stable carbon–carbon bond formation. Three new polymers, namely, COP-177, COP-178, and COP-179, are derived from widely available perfluoroarenes and found to be superhydrophobic, microporous, and highly stable against heat, acid, base, and organic solvents. Nitrile, amine, and ether functionalities were successfully installed by SNAr-type postfunctionalization and were shown to increase CO2 uptake twice and CO2/N2 selectivity 4-fold. Due to its inherent superhydrophobicity, COP-177 showed high organic solvent uptake both in liquid and vapor form. Furthermore, in a first of its kind, by combining microporosity and hydrophobicity, COP-177 separated two small molecules with the same boiling point in a continuous column setting.

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Inversion of dispersion: Colloidal stability of calixarene modified metal-organic framework nanoparticles in non-polar media

U. Jeong, N. A. Dogan, M. Garai, T. S. Nguyen, J. F. Stoddart, C. T. Yavuz* 
J. Am. Chem. Soc., accepted, (2019).
DOI: 10.1021/jacs.9b04198

Making metal-organic frameworks (MOFs) which are stabilized in non-polar media is not as straightforward as their inorganic nanoparticle counterparts, since surfactants penetrate through the porous structures or dissolve the secondary building units (SBUs) through ligand-exchange linker modulator mechanisms. Herein we report that calixarenes stabilize UIO-66 nanoparticles effectively by remaining outside the grains through size exclusion, without pores becoming blocked, all the while providing amphiphilicity that permits the formation of stable colloidal dispersions with much narrower size distributions. Using the UIO-66 dispersed solutions, we showed that smooth films from an otherwise immiscible polystyrene can be made feasibly.

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Sustainable porous polymer catalyst for size-selective cross-coupling reactions

S. Kim, B. Kim, N. A. Dogan, C. T. Yavuz*
ACS Sustain. Chem. Eng., 7, 10865-10872 (2019).
DOI: 10.1021/acssuschemeng.9b01729

A new, high surface area, nanoporous polymer (COP-220) was synthesized using sustainable building blocks, namely, a food coloring dye (erythrosine B) and a commercial alkyne. During the Sonogashira coupling, it is observed that Pd and Cu ions and triphenylphosphine ligands of the catalyst get trapped inside the pores. The remnant synthesis catalyst components were characterized in detail and were tested as a new catalyst for Suzuki–Miyaura coupling reactions. COP-220 showed conversion yields comparable to the commercial homogeneous catalyst Pd(PPh3)2Cl2 with an additional advantage of size-dependent catalytic activity when bulkier substrates were used. COP-220 was highly stable under thermal and chemical treatments and recyclable with no loss of activity. These findings show a clear need for extensive characterization of nanoporous polymers made through cross-coupling reactions and the potential of the trapped catalysts for new catalytic activity without additional loading.

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Nanoporous Polymer Microspheres with Nitrile and Amidoxime Functionalities for Gas Capture and Precious Metal Recovery from E-Waste

N. A. Dogan, Y. Hong, E. Ozdemir, C. T. Yavuz*
ACS Sustain. Chem. Eng., 7 (1), 123–128 (2019).
Invited paper for the special issue on advanced porous materials
DOI: 10.1021/acssuschemeng.8b05490 

Nanoporous materials could offer sustainable solutions to gas capture and precious metal recovery from electronic waste. Despite this potential, few reports combine target functionalities with physical properties such as morphology control. Here, we report a nanoporous polymer with microspherical morphology that could selectively capture gold from a mixture of 15 common transition metals. When its nitriles are converted into amidoxime, the capacity increases more than 20-fold. Amidoximes are also very effective in CO₂ binding and show a record high CO₂/CH₄ selectivity of 24 for potential use in natural gas sweetening. The polymer is successfully synthesized in 1 kg batches starting from sustainable inexpensive building blocks without the need for costly catalysts. Because the morphology is controlled from the beginning, the nanoporous materials studied in lab scale could easily be moved into respective industries.

Link to the journal webpage

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Direct access to primary amines and particle morphology control in nanoporous CO2 sorbents

N. A. Dogan§, E. Ozdemir§, C. T. Yavuz*
ChemSusChem, 10, 2130-2134, (2017). DOI: 10.1002/cssc.201700190. §: Equal contribution

Chemical tuning of nanoporous, solid sorbents for an ideal CO₂ binding requires unhindered amine functional groups on the pore walls. Although common for soluble organics, post-synthetic reduction of nitriles in porous networks often fail due to the insufficient and irreversible metal hydride penetration. Here, we synthesized a nanoporous network with pendant nitrile groups, microsphere morphology and in large scale. The hollow microspheres were easily decorated with primary amines through in situ reduction by widely available boranes. CO₂ capture capacity of the modified sorbent was increased up to an eight times of the starting nanoporous network with a high heat of adsorption (98 kJ/mol). Surface area can be easily tuned between 1 and 354 m²/g. Average particle size (~50 µm) is also quite suitable for CO₂ capture applications where processes like fluidized bed require spheres of micron sizes.

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