researchers need to identify efficient routes toward solar fuels production. Solar fuels refer to fuels produced by action of sunlight, particularly H 2 produced from water and C 1 or C 1+ energized molecules (i.e., CO, CH 4 , CH 3 OH) produced from CO 2 . [1] The latter reaction, i.e., CO 2 photo reduction, is the focus of this study. Photo catalysis represents one route toward CO 2 photo reduction. In that case, the design and manufacturing of a costeffective, sustainable, efficient, and robust photo catalyst is of paramount importance and remains a highly challenging task com bining aspects of materials science, photo chemistry, and reactor design engineering.The most widely researched photocata lysts for CO 2 reduction are semiconduc tors. Of which, TiO 2 has inspired intense research since the first demonstration in 1972, [2] owing to its high stability, low cost, and nontoxic nature. These studies have shown that the TiO 2 morphology (e.g., 1D structures), crystalline form (e.g., anatase, rutile, brookite, and titanate), and com position (e.g., heterojunction, heterostuc ture formation) all are critical factors for improved photocatalytic activity. [3] Another example of semicon ductor, considered as a derivative of titania, is titanate. Titanate materials are photocatalytically active, with a crystalline struc ture similar to anatase TiO 2 and a 1D morpho logy. Compared to conventional TiO 2 , they exhibit attractive properties for photoca talysis such as a high surface area, a welldefined morphology, an improved photogenerated charge separation, and a small bandgap. [4] Titanates have been used for photocatalysis, [5] and in particular, we note two studies on CO 2 photoreduction. [6] Recent photocatalytic improvements routes using titanate-not limited to CO 2 photoreduction-include the formation of composite mate rials for improved charge separation [4b,5d,7] and the conversion to a mixed phase anatase/titanate material hydrothermally, while retaining the fiber morphology. [8] Specifically, mixed phase TiO 2 can enhance charge separation and catalytic activity. [9] Despite these improvements, the photocatalytic activity of TiO 2 remains below acceptable levels for large scale deployment due to its large bandgap, rapid photogenerated charge recombination, and low CO 2 adsorption capacity. [10] Metal-organic frameworks (MOFs) have also recently been explored as photocatalysts for CO 2 reduction, with their CO 2 photoreduction to C 1 /C 1+ energized molecules is a key reaction of solar fuel technologies. Building heterojunctions can enhance photocatalysts performance, by facilitating charge transfer between two heterojunction phases. The material parameters that control this charge transfer remain unclear. Here, it is hypothesized that governing factors for CO 2 photoreduction in gas phase are: i) a large porosity to accumulate CO 2 molecules close to catalytic sites and ii) a high number of "points of contact" between the heterojunction components to enhance charge transfer. The former requirement ca...

Over the past decades, functional hydrogels that respond to a variety of mechanical and chemical stimuli with a volume change of more than 100% have been developed. Despite this impressive behavior, practical applications of conventional hydrogels are limited by the need to transform their isotropic swelling/contraction into useful deformations, as well as their slow response times. Here, these challenges are addressed by combining poly(N‐isopropylacrylamide) (PNIPAM), a widely used temperature‐responsive polymer, with carbon nanotubes (CNTs). To ensure strong PNIPAM−CNT cohesion, the hydrogel is synthesized directly on the CNT surfaces using in situ redox polymerization. The anisotropy of vertically‐aligned CNT forests is used to transform the isotropic (de)swelling of PNIPAM into anisotropic motion. This material combination is particularly attractive because the high optical absorption and heat conductivity of carbon nanotubes converts light irradiation into PNIPAM actuation. A wide variety of CNT‐skeleton microstructures are tested to reveal a range of actuation behaviors. The authors demonstrate fast reversible movement, active switching from low to high light absorption states, lattice shape changes, and good cycling stability.

Natural carbons, such as coal and petroleum feedstocks, or the undesirable by-products of subsequent chemical processing of these feedstocks, such as tars, comprise a huge chemical phase space incorporating a wide range of chemical, optical, and

In article number https://doi.org/10.1002/smll.201805473, Camille Petit and co‐workers provide directions to design heterojunctions for solar fuel production. A heterojunction formed of TiO2 nanofibers is shown decorated with metal–organic framework particles. The controlled morphology, obtained via an in‐situ process, enhances charge transfer and CO2 photoreduction.