Reticular Materials for Artificial Photoreduction of CO₂

Abstract

fatally affects the natural greenhouse. Therefore, seeking solutions that ameliorate fossil fuel dependency and CO 2 emission undoubtedly is of urgency. [4] The carbon cycle including selective CO 2 capture, [5] sequestration, [6] and conversion [7] has been used for years to deal with the issues mentioned above. Unlike the capture and sequestration, which have been successfully explored using a variety of porous materials, [8] CO 2 conversion, in which CO 2 is used as C1 starting material for the chemical transformation into other useful feedstocks, is in the early stage of development because there is a lack of effective catalysts and/or optimized conversion processes; therefore, the CO 2 reduction becomes one of the most important but challenging tasks. [9] To cope with this crucial challenge, it is necessary to briefly review the natural photosynthesis, [10] which plants, algae, and/or bacteria capture sunlight and use its photon energy to reduce CO 2 into oxygen (Scheme 1). Notably, in the oxygenic photosynthesis conducted by plants, O 2 and water molecules (six molecules of each) are formed as equivalent as CO 2 input (six molecules). This photosynthesis process not only reintroduces the breathable oxygen but also inspires researchers in imitating the natural photoreduction of CO 2 into clean-burning fuels. The reduction of CO 2 using catalysts activated by sunlight, the universal photon energy from Nature, termed photocatalysis is of great importance for renewable energy. In 1972, Fujishima and Honda discovered the application of TiO 2 as a semiconductor for water hydrolysis under ultraviolet irradiation. [11] This work has influentially underpinned scientists to artificially synthesize many kinds of photocatalytic materials for the transformation of CO 2 under ultraviolet or visible light irradiation, of which the latter is more applicable and important due to its environmental friendly attributes. [12-14] To date, semiconductors commonly used for photocatalysis are TiO 2 , metal alloys, nanowires, quantum dots, graphenebased composites, and to name but a few. [15-17] Among them, porous crystalline materials have been proven to be promising candidates for the CO 2 photoreduction into high value-added chemicals because of their large internal surface area and densely catalytically active sites. [18,19] Particularly, reticular chemistry of metal-organic frameworks (MOFs) possessing endless possibilities to precisely control crystal structures

Metal–Organic Frameworks Can Photocatalytically Split Water—Why Not?

“…[35] Many efforts to promote the chemistry of MOFs for photocatalytic applications are under urgent demand; especially at this stage, finding renewable energy has been centered by scientists worldwide and is of paramount importance. [40] It is not appropriate to compare the photocatalytic activity of MOFs with metal oxides (nitrides) [41,42] which is well-developed for water splitting for more than 50 years. [43] Nevertheless, from the author's point of view, it is stringent to prepare metal oxides (nitrides) or solid solutions of such kinds of materials (i.e., metal-oxide compositions), which requires high temperature and even inert conditions.…”

A Review on Removal of Carbon Dioxide (CO2) using Zeolitic Imidazolate Frameworks: Adsorption and Conversion via Catalysis

“…MOFs have advanced photoreduction of CO2 [284,[305][306][307][308][309][310][311][312][313][314][315][316][317][318][319][320][321][322] . The reaction requires a ZIF materials with good light absorption.…”

Metal–Organic Frameworks for Photocatalytic Water Splitting

“…[ 35–37 ] In addition, many MOF photocatalysts were reported to drive uphill photoreactions including water splitting and CO 2 reduction. [ 19,34 ]…”

“…In photochemistry, especially water splitting, similar to artificial photoreduction of CO 2 , [19] the semiconductor characteristic feature of the photocatalyst plays an essential role. [8,11] In particular, bandgap energy (E g ), the band width between the top level of VB highest occupied molecular orbital (HOMO) and the bottom level of CB lowest unoccupied molecular orbital (LUMO), is the most important factor, if not the first structural aspect of the photocatalyst that should be considered.…”

“…[35][36][37] In addition, many MOF photocatalysts were reported to drive uphill photoreactions including water splitting and CO 2 reduction. [19,34] At the same time, being modified down to the molecular level, either the backbone or the metal building units in MOFs can be functionalized to 1) engineer the bandgap energy, [38] which includes the energy level of either VB or CB, 2) improve the charge-carrier mobility, [39] and 3) facilitating the charge separation upon visible-light irradiation. [40] In addition, MOFs are highly crystalline materials that straightforwardly allow the study of crystal structures by advanced techniques (single-crystal X-ray diffraction or neutron diffraction) to reveal the role of catalytic active sites.…”