Optical and quantitative detection of cobalt ion using graphitic carbon nitride-based chemosensor for hydrometallurgy of waste lithium-ion batteries.

A hydrometallurgy is one of the most important techniques for recycling waste LIBs, where identifying the exact composition of the metal-leached solution is critical in controlling the metal extraction efficiency and the stoichiometry of the regenerated product. In this study, we report a simple and selective optical detection of high-concentrated Co2+ using a graphitic carbon nitride (g-CN)-based fluorescent chemosensor. g-CN is prepared by molten salt synthesis using dicyandiamide (DCDA) and LiI/KI. The mass ratio of LiI/KI to DCDA modifies the resulting g-CN (CNI) in terms of in-plane molecular distances of base sites including cyano functional groups (─CN) and fluorescent emission wavelength via nucleophilic substitution. The fluorescent sensing performance of CNIs is evaluated through photoluminescence (PL) emission spectroscopy in a broad Co2+ concentration range (10-4-100 M). The correlation between the surface exposure of hidden nitrogen pots (base sites) and PL intensity change is achieved where the linear relationship between the PL quenching and the logarithm of Co2+ concentration in the analyte solution is well established with the regression of 0.9959. This study will provide the design principle of the chemosensor suitable for the fast and accurate optical detection of Co2+ present in a broad concentration range for hydrometallurgy for the recycling of waste LIBs.

Macroscopic graphitic carbon nitride monolith for efficient hydrogen production by photocatalytic reforming of glucose under sunlight.

Large particulate photocatalysts allow efficient recovery or installation into the substrate, while limiting possible light-catalyst interaction or mass/charge-transfer. In this study, we developed monodisperse organic single-crystal monoliths with controllable dimensions in the range of 10-100 µm. These were prepared on a 10-g scale by a solution-processed molecular cooperative assembly between melamine (M) and trithiocyanuric acid (TCA) and then transformed into the corresponding g-CN (MTCA-CN) by thermal polycondensation. Molecular precursors that are tightly bound in the crystal undergo polycondensation without losing their macroscopic properties depending on the dimensions of MTCA, thereby changing the microstructure, electronic structure, and photocatalytic activity. Such dimensional tunability enables the fulfillment of various catalytic requirements such as particle size, light absorption, charge separation, band edge potential, and mass transfer. As a proof-of-concept, it was shown that MTCA-CN is tailored to have a high rate of evolution of hydrogen (3.19 µmol/h) from glucose via photoreforming under AM1.5G by using MTCA-100 crystals, leading to the formation of g-CN with the more positive highest occupied molecular orbital (HOMO) level. This study highlights the possibility of developing photocatalysts for practical use and obtaining value-added products (VAPs) without losing the photocatalytic activity relevant for wastewater treatment.

Hierarchical Porous, N-Containing Carbon Supports for High Loading Sulfur Cathodes.

The lithium-polysulfide (LiPS) dissolution from the cathode to the organic electrolyte is the main challenge for high-energy-density lithium-sulfur batteries (LSBs). Herein, we present a multi-functional porous carbon, melamine cyanurate (MCA)-glucose-derived carbon (MGC), with superior porosity, electrical conductivity, and polysulfide affinity as an efficient sulfur support to mitigate the shuttle effect. MGC is prepared via a reactive templating approach, wherein the organic MCA crystals are utilized as the pore-/micro-structure-directing agent and nitrogen source. The homogeneous coating of spherical MCA crystal particles with glucose followed by carbonization at 600 °C leads to the formation of hierarchical porous hollow carbon spheres with abundant pyridinic N-functional groups without losing their microstructural ordering. Moreover, MGC enables facile penetration and intensive anchoring of LiPS, especially under high loading sulfur conditions. Consequently, the MGC cathode exhibited a high areal capacity of 5.79 mAh cm-2 at 1 mA cm-2 and high loading sulfur of 6.0 mg cm-2 with a minor capacity decay rate of 0.18% per cycle for 100 cycles.