Lactic acid plays an important role as a biochemical indicator for sports medicine and clinical diagnosis. The detection of lactic acid in sweat is a promising technique without any intrusive inconvenience or risk of infection. In this study, we present a selective nonenzymatic amperometric detection method for lactic acid in human sweat utilizing a multi-wall carbon nanotube (MWCNT)-polypyrrole core-shell nanowire. Because polypyrrole is a p-type conducting polymer, onto which anions are exclusively doped, leading to charge transfer, it offers selective detection for lactate anions at a specific potential, while being inert to the neutral and cationic species contained in human sweat. A chronoamperometric study reveals good sensing performance for lactic acid with a high sensitivity of 2.9 μA mM⁻¹ cm⁻² and detection limit of 51 μM. Furthermore, the MWCNT-polypyrrole nanowire exhibits excellent selectivity for lactic acid over interfering species, such as sodium chloride, glucose, urea, and riboflavin, which coexist with lactic acid in sweat. Finally, a nonenzymatic amperometric sensor for the selective detection of lactic acid in human sweat is demonstrated on commercial flexible electrodes. The results demonstrate the potential applications of the MWCNT-polypyrrole core-shell nanowire as a nonenzymatic amperometric lactate sensor.

A complete recycling process for the cathode material of spent lithium-ion batteries is demonstrated with a simple two-step process comprised of one-pot cobalt recovery to nanostructured materials and single step synthesis of LiCoO₂. For the facile and efficient recovery of cobalt, we employ malic acid as a leaching agent and oxalic acid as a precipitating agent, resulting in nanostructured cobalt oxalate. X-ray diffraction and Fourier transform infrared spectroscopy (FT-IR) analysis clearly show that cobalt species are simultaneously leached and precipitated as cobalt oxalate with a high yield of 99.28%, and this material can then be used as a reactant for the synthesis of LiCoO₂ for use as a cathode material. In addition to its advantages in simplifying the process, the proposed method allows for not only enhancing the efficiency of cobalt recovery, but also enabling reaction without a reducing agent, H₂O₂. Through successive single-step reaction of the obtained cobalt oxalate without any purification process, LiCoO₂ is also successfully synthesized. The effect of the annealing temperature during synthesis on the nanostructure and charge–discharge properties is also investigated. Half-cell tests with recycled LiCoO₂ exhibit a high discharge capacity (131 mA·h·g⁻¹) and 93% charge–discharge efficiency.