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We introduce the facile one-step biosynthesis of a bilayer structured hydrogel composite of reduced-graphene oxide (rGO) and bacterial nanocellulose (BNC) for multiple photothermal water treatment applications. One-step in situ biosynthesis of a bilayered hydrogel was achieved via modification of BNC growth medium supplemented with an optimized concentration of corn steep liquor as a growth enhancer. A two-stage, growth rate-controlled formation mechanism for the bilayer structure was revealed. The final cleaned and freeze-dried reduced-GO embedded BNC bilayer membrane enables versatile applications such as filtration (tested using gold nanoparticles, Escherichia coli cells, and plasmid DNA), photothermal disinfection of entrapped E. coli , and solar water evaporation. Comparable particle rejection (up to ≈4 nm) and water flux (146 L h −1 m −2 ) to ultrafiltration were observed. Entrapment and photothermal inactivation of E. coli cells were accomplished within 10 min of solar exposure (one sun). Such treatment can potentially suppress membrane biofouling. The steam generation capacity was 1.96 kg m −2 h −1 . Our simple and scalable approach opens a new path for biosynthesis of nanostructured materials for environmental and biomedical applications. 

4-Mercaptopyridine (4-Mpy) is a pH reporter molecule commonly used to functionalize nanoprobes for surface-enhanced Raman spectroscopy (SERS) based pH measurements. However, nanoprobes functionalized by 4-Mpy alone have low pH sensitivity and are subject to interference by halide ions in sample media. To improve nanoprobe pH sensitivity and reliability, we functionalized gold nanoparticles (AuNPs) with both 4-Mpy and bromide ion (Br − ). Br − electrostatically stabilizes protonated 4-Mpy, thus enabling sensitive SERS detection of the protonation state of 4-Mpy as a function of pH while also reducing variability caused by external halide ions. Through optimization of the functionalization parameters, including suspension pH, [4-Mpy], and [Br − ], the developed nanoprobes enable monitoring of pH from 2.1 to 10 with high SERS activity and minimal interference from halide ions within the sample matrix. As a proof of concept, we were able to track nanoprobe location and image the pH distribution inside individual cancer cells. This study provides a novel way to engineer reliable 4-Mpy-functionalized SERS nanoprobes for the sensitive analysis of spatially localized pH features in halide ion-containing microenvironments. 

Rapid adoption of lithium‐ion batteries for electronics and electric vehicles requires cost‐effective and efficient recycling of battery components especially the valuable cathode active materials. The direct recycling method transforms end‐of‐life (EOL) cathode materials into battery grade materials with minimal energy consumption and least environmental disruption. In direct recycling, the relithiation step to restore the lithium stoichiometry of the cathode materials is critical. In this work, a novel electrochemical relithiation approach in an aqueous electrolyte followed by a heat treatment for recycling cathode materials in EOL lithium‐ion batteries is demonstrated and analyzed. Using LiCoO₂as an example, it is shown that the recycled LiCoO₂materials show equivalent crystal structure, morphology, and electrochemical performance to the commercial LiCoO₂.