Hydroxyl radical (•OH) is a potent reactive oxygen species with the ability to degrade hazardous organic compounds, kill bacteria, and inactivate viruses. However, an off-the-shelf, portable, and easily activated biomaterial for generating •OH does not exist. Here, microgels were functionalized with catechol, an adhesive moiety found in mussel adhesive proteins, and hematin (HEM), a hydroxylated Fe3+ ion-containing porphyrin derivative. When the microgel was hydrated in an aqueous solution with physiological pH, molecular oxygen in the solution oxidized catechol to generate H2O2, which was further converted to •OH by HEM. The generated •OH was able to degrade organic dyes, including orange II and malachite green. Additionally, the generated •OH was antimicrobial against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus epidermidis) bacteria with the initial concentration of 106 to 107 cfu/mL. These microgels also reduced the infectivity of a nonenveloped porcine parvovirus and an enveloped bovine viral diarrhea virus by 3.5 and 4.5 log reduction values, respectively (99.97–99.997% reduction in infectivity). These microgels were also functionalized with positively charged [2-(methacryloyloxy)ethyl] trimethylammonium chloride, which significantly enhanced the antibacterial and antiviral activities through electrostatic interaction between the negatively charged pathogens and the microgel. These microgels can potentially serve as a lightweight and portable source of disinfectant for an on-demand generation of •OH with a wide range of applications.
Separation between two recycled electrode active materials from spent Li-ion batteries by a conventional froth flotation method has been challenging due to similarity in their surface hydrophobicity. In this study, a new coarse flake particle flotation technology has been developed to separate the electrode active materials from Li-ion batteries. The new process separates the recycled electrode flake particles effectively at a size range of 212−850 μm by taking advantage of a significant difference in densities between the anode flake materials and cathode flake materials. At a feed size of 212 μm or less, a fraction of recycled cathode particles is floated in the froth layers resulting in a loss of cathode materials in the sink product. At a feed size of 850 μm or above, a small fraction of anode flakes becomes non-floatable, resulting in a decrease in the grade of cathode materials in the sink product. The mechanism has been investigated by induction time measurements, bubble−flake detachment, contact angle measurements, and force analysis. The anode flakes are more hydrophobic than cathode flakes, which is consistent with the result obtained from induction time measurements. A force analysis reveals that the critical size for electrode flake particles being attached to air bubbles varies with advancing contact angle and density. Maintaining a desirable feed size is essential to achieve an optimum separation performance. In this regard, a flotation column is superior to mechanical flotation cells in minimizing size reduction during the flotation process. Lab-scale column flotation trials showed that a good separation between anode and cathode flake particles has been achieved by column flotation with 98−99% purity of cathode flake materials in the sink product at a recovery rate of 96−99%. The present study demonstrates a new process in separating two electrode flake materials from spent Li-ion batteries.
Direct recycling of Li-ion batteries is a promising and low-cost recycling technology since the process recovers values of active materials directly without converting active materials into metal elements. However, the process is challenging from a separation perspective due to purity requirement. Herein, a new physical separation system was developed to recycle and produce ultra-high purity of cathode active materials from EV Li-ion batteries. Results showed that the recycled cathode active material product contained 99% purity of active materials with less than 500 ppm of aluminum and copper. Both the stoichimetry and structure of the recycled cathode active materials remained the same compared with those collected manually from electrode sheets. Results obtained from electrochemical testing showed that the capacity of the recycled materials was comparable to that of pristine cathode active materials, despite there was a lithium loss associated with battery charging and discharging. The present result demonstrates a viable direct recycling process for electric vehicle Li-ion batteries.
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