Semiconductor/Covalent‐Organic‐Framework Z‐Scheme Heterojunctions for Artificial Photosynthesis

Abstract

A strategy to covalently connect crystalline covalent organic frameworks (COFs) with semiconductors to create stable organic–inorganic Z‐scheme heterojunctions for artificial photosynthesis is presented. A series of COF–semiconductor Z‐scheme photocatalysts combining water‐oxidation semiconductors (TiO2, Bi2WO6, and α‐Fe2O3) with CO2 reduction COFs (COF‐316/318) was synthesized and exhibited high photocatalytic CO2‐to‐CO conversion efficiencies (up to 69.67 μmol g−1 h−1), with H2O as the electron donor in the gas–solid CO2 reduction, without additional photosensitizers and sacrificial agents. This is the first report of covalently bonded COF/inorganic‐semiconductor systems utilizing the Z‐scheme applied for artificial photosynthesis. Experiments and calculations confirmed efficient semiconductor‐to‐COF electron transfer by covalent coupling, resulting in electron accumulation in the cyano/pyridine moieties of the COF for CO2 reduction and holes in the semiconductor for H2O oxidation, thus mimicking natural photosynthesis.

Porphyrin Conjugated Polymer Grafted onto BiVO4 Nanosheets for Efficient Z‐Scheme Overall Water Splitting via Cascade Charge Transfer and Single‐Atom Catalytic Sites

“…[ 33,34 ] More importantly, ZnPtP‐CP/BiVO 4 displays new IR band (≈1756 cm −1 ) and Raman scattering peak (≈677 cm −1 ), which are ascribable to the Zn–O asymmetric stretching vibration formed by central Zn 2+ ions of ZnPor units and O‐atoms in the (010) facets of BiVO 4 , demonstrating that ZnPtP‐CP NSs are grafted onto the BiVO 4 NSs via Zn–O–V bridging bonds. [ 3 ] Also, the composite shows the same 13 C NMR signals as the ZnPtP‐CP alone (Figure S14a, Supporting Information), indicating that ZnPtP‐CP NSs have grafted onto the BiVO 4 NSs through the in situ Sonogashira coupling process.…”

“…It is generally known that water photosplitting is one of potential approaches to tackle the current energy and environmental issues, [ 1–3 ] and constructing a suitable photosystem with matched energy band structures, adequate photon absorption and efficient charge separation is the essential goal for achieving superior water splitting performance. [ 4,5 ] In the past decades, artificial Z‐scheme photosystem with step‐wise charge transfer pathway has attracted extensive concerns because it cannot only favor the separation of photoexcited charge carriers, but also maintain the high redox ability of the two semiconductor constituents.…”

Conjugated Acetylenic Polymers Grafted Cuprous Oxide as an Efficient Z‐Scheme Heterojunction for Photoelectrochemical Water Reduction

“…The positive shift binding energy (≈0.1 eV) of Cu2p under UV‐light irradiation was due to the electron density reduction of Cu 2 O. [ 46–48 ] These results showed the photogenerated electrons migration from Cu 2 O to pDET, evidencing its Z‐scheme pathway (Figure S12, Supporting Information).…”

Reticular Materials for Artificial Photoreduction of CO2

“…This result exceeded the performance of COF‐316‐SCs, COF‐318‐SCs, and semiconductors (TiO 2 , Bi 2 WO 6 , and α‐Fe 2 O 3 ). [ 155 ] The intricate and comprehensive characterizations supported by DFT calculations underpinned the hypothesis of the authors: the covalent binding between COF and semiconductor facilitated the photoexcited charge separation and further stimulated the photogenerated electrons to straightforwardly transfer to the active catalytic sites to catalyze the CO 2 photoreduction. This work paved the way for designing the Z‐schematic photocatalytic systems that are based on MOF or COF heterojunctions.…”

“…Based on the exceptional activity of TTCOF‐Zn consisting of high conjugation linkers of donor‐acceptors, Lan and co‐workers have further attempted to synthesize COFs whose SBUs are based on the strong electronic conjugation of 2,3,6,7,10,11‐hexahydroxytriphenylene (HHTP) and tetrafluorophthalonitrile (TFPN) (COF‐316) or 2,3,5,6‐tetrafluoro‐4‐pyridinecarbonitrile (TFPC) (COF‐318). [ 155 ] With respect to exploiting the Z‐scheme strategy in the photocatalysis, the CO 2 photoreduction performance over Z‐schematic semiconductor/COF heterojunctions may be improved. Bearing this idea in mind, the authors synthesized a series of COF heterojunctions by combing two COFs (COF‐316 and COF‐318) and three kinds of semiconductors (TiO 2 , Bi 2 WO 6 , and α‐Fe 2 O 3 ).…”