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Autocatalytic reactions commonly display reaction-diffusion behavior that can give rise to spatial patterns, oscillations, and wavefronts. Herein, we present experimental demonstrations and computational analyses of a new chemical traveling wave originating from the electrochemical S2O82–/C2O42– autocatalytic reaction. Following a brief electrochemical initiation step, the S2O82–/C2O42– chemical traveling wave propagates through the solution away from the electrode surface and is imaged using a colorimetric method based on a pH change induced by CO2 generation at the wavefront. Following mediated initiation using the Ru(NH3)63+/2+ redox couple, a chemical traveling wave with an initial velocity of ∼8 μm/s propagates through the solution. Finite element simulations based on a reaction-diffusion model demonstrate that the experimentally observed chemical traveling wave behavior originates from the autocatalytic reaction between S2O82– and C2O42–. However, the chemical traveling wave displays nonideal reaction-diffusion behavior as indicated by a decrease in wave velocity after ∼3 min and an approach to purely diffusional mass transfer within ∼10 min. Simulated concentration profiles are consistent with a declining SO4·– concentration with time due to quenching by Cl– and phenol red, resulting in a gradual dissipation of the chemical traveling wave. Lastly, the colorimetric method used to analyze the chemical traveling wave may be generally useful in monitoring the concentration distribution of dissolved CO2 in real time. 

Lithium is a critical mineral in a wide range of current technologies, and demand continues to grow with the transition to a green economy. Current lithium mining and extraction practices are often highly ecologically damaging, in part due to the large amount of water and energy they consume. Biomineralization is a natural process that transforms inorganic precursors to minerals. Microbial biomineralization has potential as an ecofriendly alternative to current lithium extraction techniques. This work demonstrates Lysinibacillus sphaericus biomineralization of lithium chloride to lithium hydroxide. Quantitative analysis of biomineralized lithium via the 2-(2-hydroxyphenyl)-benzoxazole fluorescence assay reveals significantly greater recovery with L. sphaericus than without. Furthermore, L. sphaericus biomineralization is specific to lithium over sodium. The nanoparticles produced were further characterized via Fourier transform infrared and transmission electron microscopy analysis as crystalline lithium hydroxide, which is an advanced functional material. Finally, ESI–LC/MS was used to identify several proteins involved in this microbial biomineralization process, including the S-layer protein. Through the isolation of L. sphaericus ghosts, this work shows that the S-layer protein alone plays a critical role in the biomineralization of crystalline lithium hydroxide nanoparticles. Through this study of microbial biomineralization of lithium with L. sphaericus, there is potential to develop innovative and environmentally friendly extraction techniques. 

We investigate switching of photoluminescence from PbS quantum dots crosslinked with photochromic diarylethene molecules with different degree of halogenation.