Increasing human consumption of fossil fuels continues to contribute to adversely high levels of atmospheric CO2 and a changing climate on the planet. Photosynthesis offers a blueprint to mitigating this global problem by converting intermittent light energy into electrical current for converting CO2 and H2O into sugars for sustainable energy storage.
Artificial photosynthesis (AP), which aims to mimic natural photosynthesis (NP) that utilizes sunlight, water, and carbon dioxide to produce storable/transportable fuels or desired chemicals, has been the ultimate goal of scientists for many years, due to its great potential to solve both global energy and environmental crises simultaneously [1].
Both NP and AP follow the same physical chemistry steps including 1) light absorption, 2) charge separation, 3) water splitting, and 4) chemical synthesis, although electron accepters and charge transfer processes are different in details [2]. More than 5,000 publications related to artificial photosynthesis, photocatalytic water splitting, and photoelectrochemical carbon dioxide reduction are available [1].
Figure 1 Schematic diagram of AP vs environment [3].
A research team from the IMDEA Energy Institute from Spain conducting many researches on AP, they are demonstrating AP impact in environment (Figure 1). They mentioned that “one of the most important and elusive challenges that Science faces today is the development of technologies capable of alleviating the effect of greenhouse gases (GHGs) as main actors of global warming. To face this challenge, FotoArt-CM proposes the development of a new technology called artificial photosynthesis based on sustainable energy sources, which allows to reduce and recover those emissions and leads to the valorization of abundant feedstocks (Co2,H2, N2 and biomass) to obtain products useful products for society such as fuels, drugs, plastics, fertilizers, etc…” [3].
Figure 2 Schematic representation of the preparation of COF-318-SCs via the condensation of COF-318 and semiconductor materials [4].
Very recently, Prof. Dr. Y-Q. Lan and his research team develop a strategy to fabricate crystalline covalent organic frameworks (COFs) coupled to inorganic oxide semiconductors through stable covalent bonds, forming organic–inorganic Z-scheme heterojunctions for artificial photosynthesis [4]. A series of COF–semiconductor Z-scheme photocatalysts combining water-oxidation semiconductors (TiO2, Bi2 WO6, and a-Fe2O3) with CO2 reduction COFs (COF-316/318) was synthesized and exhibited high photocatalytic CO2-to-CO conversion efficiencies (up to 69.67 mmolg-1h-1), with H2O as the electron donor in the gas– solid CO2 reduction, without additional photosensitizers and sacrificial agents (Figure 2). This is the first report of covalently bonded COF/inorganic-semiconductor systems utilizing the Z-scheme applied for artificial photosynthesis. This strategy represents a new insight for the future rational design of Z-scheme organic–inorganic heterojunctions for artificial photosynthesis.
This type of Z-scheme system has been widely used in water splitting, while only a few studies have been conducted in the field of the CO2RR because many vital aspects are difficult to solve simultaneously in most all-inorganic Z-scheme system:
i) efficient light absorption;
ii) fast CO2 adsorption and diffusion;
iii) suitable redox sites and band structure for simultaneous CO2 reduction and H2O oxidation;
iv) fast separation and migration of photo-generated electrons and holes to the adsorbed CO2 and H2O molecules, respectively, at the active sites [5].
As a result, the photocatalytic
efficiency of the CO2 reduction for all inorganic Z-scheme systems is still
difficult to improve presently. The combination of functionalized organic
components and inorganic semiconductors is an effective way to improve these
factors, but the connectivity between them suffers from instability and the
ineffectiveness of physical adsorption or the stacking force [5]. On the contrary, employing catalysts with
well-defined structures to further systematically study the reaction mechanisms
is of great significance [6].
The field of artificial photosynthesis aims to store renewable energy in chemical bonds spanning fuels, foods, medicines, and materials using light, water, and CO2 as the primary chemical feedstocks, with the added benefit of mitigating the accumulation of CO2 as a greenhouse gas in the atmosphere. Still, more research needs for to be use AP technique in commercial usage.
References
[1]. T. Butburee, P. Chakthranont, C. Phawa, K. Faungnawakij, ChemCatChem 2020, 12, 1873-1890.
[2]. a) R. J. Cogdell, T. H. Brotosudarmo, A. T. Gardiner, P. M. Sanchez, L. Cronin, Biofuels 2010, 1, 861; b) H. Zhou, R. Yan, D. Zhang, T. Fan, Chem. Eur. J. 2016, 22, 9870.
[4]. M. Zhang, M. Lu, Z-L. Lang, J. Liu, M. Liu, J-N. Chang, L-Y. Li, L-J. Shang, M. Wang, S-L. Li, Y-Q. Lan, Angew. Chem. Int. Ed. 2020, 59, 6500 –6506.
[5]. L. Wang, W. Chen, D. Zhang, Y. Du, R. Amal, S. Qiao, J. Wu, Z. Yin, Chem. Soc. Rev. 2019, 48, 5310–5349.
[6]. a) M. Lu, J. Liu, Q. Li, M. Zhang, M. Liu, J.-L. Wang, D.-Q. Yuan, Y.-Q. Lan, Angew. Chem. Int. Ed. 2019, 58, 12392–12397; Angew. Chem. 2019, 131, 12522–12527; b) Y.-Z. Zhang, B.-Q. Qia, J.-R. Ran, K. Davey, S.-Z. Qiao, Adv. Energy Mater. 2020, https://doi.org/10.1002/aenm.201903879.
Blog Written By
Dr. A. S. GANESHRAJA
National College
ReplyDeletez scheme is effective in water splitting
Yes, Z-Scheme is more effective in water splitting but need more research on commercial usage. Need to solve many issues on it.
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