The use of sulfur as a cathode material for lithium−sulfur (Li−S) batteries has attracted significant attention due to its high theoretical specific capacity (1675 mA h g ⁻¹ ); however, practicality is hindered by a number of obstacles, including the shuttling effect of polysulfides and the low electrical conductivity of sulfur. Herein, ball milling sulfur with unzipped multiwalled carbon nanotubes (UMWNTs) was found to covalently immobilize sulfur nanoparticles to the UMWNTs and resulted in composites (designated as S@UMWNTs) with high electrical conductivity. The unzipping degree of MWNTs was first controlled to optimize the immobilization of sulfur nanoparticles to UMWNTs and the electrochemical performance of the resulting Li−S batteries. The presence of C−S covalent bonds between the UMWNTs and sulfur nanoparticles was verified using x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy, and the formation of C−S bonds was ascribed to the reactions between the mechanically-induced sulfur radicals and the functional groups of UMWNTs. As a result, when used as a cathode material for Li−S batteries, the S@UMWNTs exhibited excellent electrochemical performance, including a good long-term cycling stability and low capacity decay (e.g., ca. 0.09% per cycle over 500 charge/discharge cycles at 1 C) due to the suppression of the shuttling effect by the C−S covalent bonds.

Bioluminescence imaging assays have become a widely integrated technique to quantify effectiveness of cell-based therapies by monitoring fate and survival of transplanted cells. To date these assays are still largely qualitative and often erroneous due to the complexity and dynamics of local micro-environments (niches) in which the cells reside. Here, we report, using a combined experimental and computational approach, on oxygen that besides being a critical niche component responsible for cellular energy metabolism and cell-fate commitment, also serves a primary role in regulating bioluminescent light kinetics. We demonstrate the potential of an oxygen dependent Michaelis-Menten relation in quantifying intrinsic bioluminescence intensities by resolving cell-associated oxygen gradients from bioluminescent light that is emitted from three-dimensional (3D) cell-seeded hydrogels. Furthermore, the experimental and computational data indicate a strong causal relation of oxygen concentration with emitted bioluminescence intensities. Altogether our approach demonstrates the importance of oxygen to evolve towards quantitative bioluminescence and holds great potential for future microscale measurement of oxygen tension in an easily accessible manner.

Due to their high surface areas and large pore volumes, porous carbons (PCs) are valuable materials for use as electrodes in energy storage and conversion devices. Biomass is an ideal precursor for the preparation of PCs in part because it is sustainable and eco-friendly. Herein, new methodology for converting agarose, a naturally occurring type of biomass that forms robust hydrogels, into PCs with tunable pore structures and high electrochemical performance is described. The synthetic process is straightforward and entails heating a gel that is composed of agarose and potassium oxalate (K₂C₂O₄). Since the salt transforms into gaseous byproducts at elevated temperatures, the decomposition process was harnessed to create activated, open pores as the hydrogel underwent carbonization. For example, a PC with a surface area of 1754.9 m² g^–1 and a pore volume of 2.643 cm³ g^–1 was obtained by heating a mixture of agarose and K₂C₂O₄ in a 1:3 weight ratio at 700 °C. The material was subsequently used as the electrode material in a supercapacitor and found to display a specific capacitance of 166.0 F g^–1 at 0.125 A g^–1. Varying the quantity of added K₂C₂O₄ resulted in predictable changes in porosity and thus offered a means to tune the textural properties and the electrochemical performance of the PCs. For example, changing the feed ratio of agarose to K₂C₂O₄ to 1:6 afforded a PC that exhibited a high persistent specific capacitance (64.1 F g^–1 at 5 A g^–1 after 10,000 cycles) and a high-power density (20 kW kg^–1 at 10 A g^–1).