The Effect of Materials Architecture in TiO₂/MOF Composites on CO₂ Photoreduction and Charge Transfer

Abstract

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...

Near-infrared absorbing 2D/3D ZnIn2S4/N-doped graphene photocatalyst for highly efficient CO2 capture and photocatalytic reduction

“…To this end, sunlight-driven CO 2 conversion into value-added chemicals and/or fuels has shown great potential to solve the ongoing serious environmental issue [1][2][3][4][5][6][7][8][9]. Since the pioneer research by Halmann in 1978, diverse semiconductor-based photocatalysts have been developed for CO 2 reduction with water [10][11][12][13][14][15][16]. To date, the efficiencies of CO 2 conversion are well below the expected levels for practical applications, due to the fast recombination of the photogenerated charge carriers, the limited light absorption ability of the photocatalysts as well as the sluggish CO 2 adsorption and diffusion [17][18][19][20][21][22].…”

Highly Selective Photoreduction of CO2 with Suppressing H2 Evolution by Plasmonic Au/CdSe–Cu2O Hierarchical Nanostructures under Visible Light

“…[ 12 ] However, the disadvantages of nanocrystalline TiO 2 are also conspicuous; only UV light responsive activity results from the wide bandgap. [ 13 ] Plasmonic metal‐based metal/semiconductor hybrid nanostructure is another possible solution because the plasmonic nanoparticles (NPs) exhibit unique attributes in the light absorption benefit from their strong light–matter interaction. [ 14 ] In our previous work, photoinduced electron/hole separation and plasmon enhancement can be realized by plasmonic metal/semiconductor hybrid structure.…”

Photosensitive Hybrid Nanostructured Materials: The Big Challenges for Sunlight Capture

“…Cu(II)-porphyrin and TiO 2 nanoparticles into MOF structure (PCN-224(Cu)) leads to a marked improvement of light-harvesting features and promotes separation of photogenerated charges, reaching superior photocatalytic performance for CO 2 reduction [219,256]. Also, composites or heterostructures of titanium oxide or titanate fibers and MOFs, such as TiO 2 @NH 2 -MIL-88B(Fe), disclose high photocatalytic activity [257][258][259]. Recently, novel heterojunctions, based on bismuthoxyhalide-MOFs composites, were successfully produced by controlled growth of BiOX (X=Cl, Br) nanosheets on the surface of NH 2 -UiO-66 and NH 2 -MIL-125 (Ti).…”