The study of transparent daytime radiative cooling with no additional energy consumption is a promising area of research. Its applications include solar cells and building and automobile windows that are prone to heating issues. Ubiquitous applications necessitate the development of metamaterials with high mechanical flexibility in a scalable manner while overcoming translucence. In this study, visibly clear and flexible radiative cooling metamaterials have been developed using a newly designed optical modulator filled into randomly distributed silica aerogel microparticles in a silicone elastomer. The optical modulator effectively suppresses visible light scattering, thus enabling higher loading of silica aerogel microparticles while securing visible clarity. The significant suppression of the rise in temperature by the metamaterial is verified using both indoor and outdoor experiments. The visibly clear metamaterials deployed in solar cells and windows can effectively suppress the rise in temperature under solar irradiation, thereby mitigating the performance degradation of solar cells by heating issues and suppressing the rise in temperature of indoor air.

Acetogenic bacteria use cellular redox energy to convert CO2 to acetate using the Wood–Ljungdahl (WL) pathway. Such redox energy can be derived from electrons generated from H2 as well as from inorganic materials, such as photoresponsive semiconductors. We have developed a nanoparticle-microbe hybrid system in which chemically synthesized cadmium sulfide nanoparticles (CdS-NPs) are displayed on the cell surface of the industrial acetogen Clostridium autoethanogenum. The hybrid system converts CO2 into acetate without the need for additional energy sources, such as H2, and uses only light-induced electrons from CdS-NPs. To elucidate the underlying mechanism by which C. autoethanogenum uses electrons generated from external energy sources to reduce CO2, we performed transcriptional analysis. Our results indicate that genes encoding the metal ion or flavin-binding proteins were highly up-regulated under CdS-driven autotrophic conditions along with the activation of genes associated with the WL pathway and energy conservation system. Furthermore, the addition of these cofactors increased the CO2 fixation rate under light-exposure conditions. Our results demonstrate the potential to improve the efficiency of artificial photosynthesis systems based on acetogenic bacteria integrated with photoresponsive nanoparticles.

A viable approach for methanol production under ambient physiological conditions is to use greenhouse gases, methane (CH4) and carbon dioxide (CO2), as feed for immobilized methanotrophs. In the present study, unique macroporous carbon particles with pore sizes in the range of ∼1–6 μm were synthesized and used as support for the immobilization of Methylocella tundrae. Immobilization was accomplished covalently on hierarchical macroporous carbon particles. Maximal cell loading of covalently immobilized M. tundrae was 205 mgDCM g–1 of particles. Among these particles, the cells immobilized on 3.6 μm pore size particles showed the highest reusability with the least leaching and were chosen for further study. After immobilization, M. tundrae showed up to 2.4-fold higher methanol production stability at various pH and temperature values because of higher stability and metabolic activity than free cells. After eight cycles of reuse, the immobilized cells retained 18.1-fold higher relative production stability compared to free cells. Free and immobilized cells exhibited cumulative methanol production of 5.2 and 9.5 μmol mgDCM –1 under repeated batch conditions using simulated biogas [CH4 and CO2, 4:1 (v/v)] as feed, respectively. The appropriate pore size of macroporous particles favors the efficient M. tundrae immobilization to retain better biocatalytic properties. This is the first report concerning the covalent immobilization of methanotrophs on the newly synthesized macroporous carbon particles and its subsequent application in repeated methanol production using simulated biogas as a feed.

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Eggshell membrane has selective permeability that enables gas or liquid molecules to pass through while effectively preventing migration of microbial species. Herein, inspired by the architecture of the eggshell membrane, we employ three-dimensional (3D) printing techniques to realize bioresponsive devices with excellent selective permeability for effective biochemical conversion. The fabricated devices show 3D conductive carbon nanofiber membranes in which precultured microbial cells are controllably deployed. The resulting outcome provides excellent selective permeability between chemical and biological species, which enables acquisition of target responses generated by biological species confined within the device upon input signals. In addition, electrically conductive carbon nanofiber networks provide a platform for real-time monitoring of metabolism of microbial cells in the device. The suggested platform represents an effort to broaden microbial applications by constructing biologically programmed devices for desired responses enabled by designated deployment of engineered cells in a securely confined manner within enclosed membranes using 3D printing methods.