Fig. 1. Structure and concept of SRF. (a) Schematic illustration of fabricating PAN/PMMA fibers using a dry-jet wet spinning machine. The diameter of the PAN/PMMA fiber was readily controlled by regulating the injection rate and rolling speed. Information on the diameter of the fibers is summarized in table S1. Illustrations representing the physicochemical structure of (b) the PAN/PMMA fiber and (c) the SRF. (d) A series of courses for self-regeneration in which crystal layers are repetitively formed-detached on an SRF surface. The heavy metal ions and counter-anions induced nuclei for crystal growth, resulting in the formation of crystal layers. The crystal layers are self-detached from the SRF surfacevia collisions with each other, non-sticky surfaces, and the curvature of the fiber, and new crystals grow on the SRF surface in which the crystal layers are detached. (e) SEM image of the SRFs immersed in 1,000 ppm copper nitrate solution for 1 h. The three self-detachment aspects of the copper crystal layer, i.e., collision between the crystal layers, a non-sticky surface, and curvature of the SRF, were observed. Scale bar: 100 μm (f) Snapshot images show the course of self-detachment of crystal layers from an SRF via (g) non-sticky surface formation, (h) collision, and (i) surfacecurvatureduring an elapsed time of 55 min (Ci of 100 ppm and no pH adjustment). Scale bar: 200 μm.
Fig. 2. Analysis of the self-detachment of crystal layers on the SRF surface. (a) Defect regions, which are negligibly narrow compared to the size of the crystal layers, cause the non-sticky SRF surface. (b) It also accelerates the detachment of the crystal layers by an elastic restoring force against the curvature of the SRF. (c) The dominant detachment phenomenon of crystal layers around the critical defect area is a collision between the crystal layers, accompanied by divergence or convergence depending on their angle and position. (d) When the defect region is larger than the size of the crystal layers, the growth of the crystal layers is terminated. FEG-SEM images show the self-detaching phenomena of the copper crystal layers from the SRF surface. (e) Self-detachment by the non-sticky surface, (f) the curvature of fiber, (g) and the divergence (inset scale bar: 1 μm) and (h) the convergence of crystal layers. (i) Termination of crystal growth. The purple region expressed on the fiber to distinguish it from the heavy metal crystal layer formed on the SRF surface represents wide defect regions where the crystal layer is not formed. Commonly, new crystals grow on the SRF surface after the existing crystal layer is self-detached. Scale bar: 50 μm. (j) XRD pattern of the SRF including crystals grown from the adsorbed Cu2+. It is matched well with that of a Cu2(NO3)(OH)3 polycrystal (ICDD No.01-075-1779). (k) SEM image of the Cu2+ crystal layers separated from the SRF surface exhibits a form similar to the curved surface of SRF. Scalebar: 200μm. (l) HR-TEM image of the Cu2+ crystal layer displays d-spacing values that match well with the XRD pattern. Scalebar: 10nm.
Fig. 3. A heavy metal recovery module packed with the SRF. (a) Representative illustration of the module packed with the SRF for continuous recovery of heavy metals. The recovery module includes an upper part, in which the SRF is filled and is connected to the inlet and outlet pipes of the heavy metal solution, and a lower space, in which crystals of the heavy metal resources self-detached from the SRF surface can be concentrated by a density difference. (b) Actual photographs of the module packed with the SRF. (c) The heavy metal ions are crystallized on the surface of the SRF fiber. Scale bar: 500 μm. (d) Actual photographs of the module packed with the SRF during the injection of copper nitrate solution for 5h. (e) The heavy-metal crystal layers are self-detached and gathered at the bottom of the module. Scale bar: 200 μm. (f) A constant weight of crystal layers for heavy metals could be recovered during continuous injection of 100 L of copper nitrate solution with 100 ppm concentration into the module, packed with 5 g of SRF at a flow rate of 0.2 L/min. (g) Deconvoluted XPS peaks of N 1s on the SRF with different immersing times in the copper nitrate solution: 0, 1, 5, 10, 20, and 50 h.
Newswise — Technology to recover valuable metals from wastewater generated in various industries such as plating, semiconductors, automobiles, batteries, and renewable energy is important not only for environmental protection but also for economic reasons. In Korea, chemicals are mainly added to wastewater to precipitate heavy metal ions in the form of oxides, but accidents such as leakage of hazardous chemicals have occurred one after another, so it is necessary to develop more eco-friendly technologies.
Against this backdrop, the Korea Institute of Science and Technology (KIST) announced that Dr. Jae-Woo Choi's team at the Water Resource Cycle Research Center has developed a fiber-like metal recovery material that can recover metal ions in water by adsorbing and crystallizing the metal, and the recovered metal crystals can desorb and regenerate themselves.
KIST research team has developed a semi-permanent adsorption material by utilizing the phenomenon that metal ions in water crystallize when certain chemical functional groups are fixed on the surface of a fiber-like material and introducing a technology to remove the formed crystals. When tested with copper ions, the maximum adsorption amount of existing adsorbents is only about 1,060 mg/g, but by utilizing the developed material, near-infinite adsorption performance can be secured.
In addition, existing high-performance adsorbents are in the form of small granules with diameters ranging from a few nanometers to tens of micrometers, making it difficult to utilize them underwater, but the metal recovery material developed by the KIST research team is in the form of fibers, making it easy to control underwater, making it easy to apply to actual metal recovery processes.
“Since the developed material is based on acrylic fibers, it is not only possible to mass produce it through a wet spinning process, but also to utilize waste clothing,” said Dr. Jae-woo Choi of KIST. “The wastewater recycling technology will help reduce the industry's dependence on overseas sources of valuable metals that are in high demand.”
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KIST was established in 1966 as the first government-funded research institute in Korea. KIST now strives to solve national and social challenges and secure growth engines through leading and innovative research. For more information, please visit KIST’s website at https://eng.kist.re.kr/
The research, funded by the Ministry of Science and ICT (Minister Jong-ho Lee) through the Leading Project for Material Innovation (2020M3H4A3106366), Sejong Science Fellowship (RS-2023-00209565), and KIST Institutional Unique Project (2E32442), was published on October 16, 2023 in the international journal Advanced Fiber Materials.
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Credit: Figure 1. Structure and concept of SRF
Caption: Fig. 1. Structure and concept of SRF. (a) Schematic illustration of fabricating PAN/PMMA fibers using a dry-jet wet spinning machine. The diameter of the PAN/PMMA fiber was readily controlled by regulating the injection rate and rolling speed. Information on the diameter of the fibers is summarized in table S1. Illustrations representing the physicochemical structure of (b) the PAN/PMMA fiber and (c) the SRF. (d) A series of courses for self-regeneration in which crystal layers are repetitively formed-detached on an SRF surface. The heavy metal ions and counter-anions induced nuclei for crystal growth, resulting in the formation of crystal layers. The crystal layers are self-detached from the SRF surfacevia collisions with each other, non-sticky surfaces, and the curvature of the fiber, and new crystals grow on the SRF surface in which the crystal layers are detached. (e) SEM image of the SRFs immersed in 1,000 ppm copper nitrate solution for 1 h. The three self-detachment aspects of the copper crystal layer, i.e., collision between the crystal layers, a non-sticky surface, and curvature of the SRF, were observed. Scale bar: 100 μm (f) Snapshot images show the course of self-detachment of crystal layers from an SRF via (g) non-sticky surface formation, (h) collision, and (i) surfacecurvatureduring an elapsed time of 55 min (Ci of 100 ppm and no pH adjustment). Scale bar: 200 μm.
Credit: Korea Institute of Science and Technology(KIST)
Caption: Fig. 2. Analysis of the self-detachment of crystal layers on the SRF surface. (a) Defect regions, which are negligibly narrow compared to the size of the crystal layers, cause the non-sticky SRF surface. (b) It also accelerates the detachment of the crystal layers by an elastic restoring force against the curvature of the SRF. (c) The dominant detachment phenomenon of crystal layers around the critical defect area is a collision between the crystal layers, accompanied by divergence or convergence depending on their angle and position. (d) When the defect region is larger than the size of the crystal layers, the growth of the crystal layers is terminated. FEG-SEM images show the self-detaching phenomena of the copper crystal layers from the SRF surface. (e) Self-detachment by the non-sticky surface, (f) the curvature of fiber, (g) and the divergence (inset scale bar: 1 μm) and (h) the convergence of crystal layers. (i) Termination of crystal growth. The purple region expressed on the fiber to distinguish it from the heavy metal crystal layer formed on the SRF surface represents wide defect regions where the crystal layer is not formed. Commonly, new crystals grow on the SRF surface after the existing crystal layer is self-detached. Scale bar: 50 μm. (j) XRD pattern of the SRF including crystals grown from the adsorbed Cu2+. It is matched well with that of a Cu2(NO3)(OH)3 polycrystal (ICDD No.01-075-1779). (k) SEM image of the Cu2+ crystal layers separated from the SRF surface exhibits a form similar to the curved surface of SRF. Scalebar: 200μm. (l) HR-TEM image of the Cu2+ crystal layer displays d-spacing values that match well with the XRD pattern. Scalebar: 10nm.
Credit: Korea Institute of Science and Technology(KIST)
Caption: Fig. 3. A heavy metal recovery module packed with the SRF. (a) Representative illustration of the module packed with the SRF for continuous recovery of heavy metals. The recovery module includes an upper part, in which the SRF is filled and is connected to the inlet and outlet pipes of the heavy metal solution, and a lower space, in which crystals of the heavy metal resources self-detached from the SRF surface can be concentrated by a density difference. (b) Actual photographs of the module packed with the SRF. (c) The heavy metal ions are crystallized on the surface of the SRF fiber. Scale bar: 500 μm. (d) Actual photographs of the module packed with the SRF during the injection of copper nitrate solution for 5h. (e) The heavy-metal crystal layers are self-detached and gathered at the bottom of the module. Scale bar: 200 μm. (f) A constant weight of crystal layers for heavy metals could be recovered during continuous injection of 100 L of copper nitrate solution with 100 ppm concentration into the module, packed with 5 g of SRF at a flow rate of 0.2 L/min. (g) Deconvoluted XPS peaks of N 1s on the SRF with different immersing times in the copper nitrate solution: 0, 1, 5, 10, 20, and 50 h.
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