Metal-Complex/Semiconductor Hybrid Photocatalysts and Photoelectrodes for CO2 Reduction Driven by Visible Light

Recent advances in the photothermocatalytic oxidation of formaldehyde in air

A synergistic combination of photocatalysis and thermocatalysis (photothermocatalysis) has been realized to harness the full solar spectrum with a particular focus on the infrared region to support sustainable oxidation reactions of carcinogenic oxygenated volatile organic compounds such as formaldehyde (FA). Here, recent advances in the oxidative removal of FA in air have been reviewed systematically. First, the fundamentals of the photothermocatalytic mechanism are introduced and discussed. Second, various aspects of the development and application of photothermocatalytic systems are described and reviewed. A specific focus is placed on the physicochemical characteristics of photothermocatalysts with respect to reaction conditions and oxidation performance using FA as a model compound. Third, the pathways and mechanisms of FA oxidation are elaborated and discussed in detail to provide insights into associated surface phenomena and surface chemistry at the molecular level. Finally, current shortcomings and future research directions are identified and discussed to help expand this research field further into the practical realm.

Multi-heterointerface charge transfer in amine-functionalized cadmium sulfide-copper sulfide@titanium dioxide hollow spheres with rich oxygen vacancies for carbon dioxide photoreduction

Photocatalytically reducing CO2 into high-value-added chemical materials has surfaced as a viable strategy for harnessing solar energy and mitigating the greenhouse effect. But the inadequate separation of the photogenerated electron-hole pair remains a major obstacle to CO2 photoreduction. Constructing heterostructure photocatalysts with efficient interface charge transfer is a promising approach to solving the above problems. Herein, a straightforward synthetic strategy is developed to fabricate amine-functionalized cadmium sulfide-copper sulfide@titanium dioxide (CdS-CuS@TiO2) hollow spheres with rich oxygen vacancies for CO2 photoreduction. The synthetic route involves successive steps of the coating of CdS nanolayer on the prepared SiO2 solid nanospheres, transformation of CdS into CdS-CuS through cation exchange reaction, the coating of amorphous TiO2 nanoparticle layer on the SiO2@CdS-CuS solid nanospheres, and the simultaneous transformations of solid nanospheres to hollow nanospheres and amorphous TiO2 nanoparticle layer to amine-functionalized anatase TiO2 nanosheets with rich oxygen vacancies via the hydrothermal reaction process in the presence of ethylenediamine. In the composite catalyst, the formed multi-heterointerfaces among the different components accelerate charge separation and transport. Moreover, the formed hollow spherical structure covered with amine-functionalized TiO2 ultrathin nanosheets with rich oxygen vacancies exposes a greater number of active sites for CO2 adsorption and increases incident light absorption and utilization. As anticipated, the optimal composite catalyst demonstrates much higher CO2 reduction properties with a considerable CO yield (115.66 μmol g-1 h-1), surpassing that of the control catalysts (single component and bicomponent). This research offers a versatile synthetic method to synthesize excellent catalysts aimed at the production of solar fuels.

Synergizing PIERS and photocatalysis effects in a photo-responsive Ag/TiO2 nanostructure for an ultrasensitive and renewable PI-PC SERS technique

Surface-enhanced Raman spectroscopy (SERS) is a renowned analytical technique for non-invasive molecular identification. Advancements in SERS technology pivot on designing nano-structured substrates to enhance sensitivity and reliability. A key emerging trend involves integrating pre-treatment and post-treatment techniques on these substrates, leveraging advanced nanostructures to bring unique features, such as ultrasensitivity or reusability, to bridge the gap between laboratory and real-world applications of the SERS technique. Despite these advances, the synergistic application of pre- and post-treatment techniques on a single SERS substrate to fully exploit unique physicochemical effects remains underexplored. To address this, we introduce photo-induced-photo-catalytic SERS (PI-PC SERS), a novel technique that synergistically combines photo-induced enhanced Raman scattering (PIERS) and photocatalysis using a single Ag/TiO2 nanocomposite structure. This method aims to deliver ultrasensitive sensing capabilities and reusability. The PI-PC SERS technique involves pre-irradiating the SERS substrate with UV light to amplify the Raman signal and post-irradiating to remove fouled analytes. Pre-irradiation enhances the SERS signal by several orders of magnitude compared to normal SERS, attributed to the PIERS effect. Consequently, the detection sensitivity for methylene blue (MB) using PI-PC SERS reaches 1.02 × 10-14 M, significantly better than the 3.04 × 10-11 M achieved with normal SERS. Similar enhancements are observed for thiram, with a limit of detection (LOD) of 1.02 × 10-11 M for PI-PC SERS compared to 2.19 × 10-9 M for normal SERS. Additionally, post-irradiation facilitates the removal of analyte molecules via photocatalysis, restoring the substrate to its pristine state, as the byproducts - water and CO2 gas - are easily managed. Our findings demonstrate that PI-PC SERS creates ultrasensitive sensors and ensures substrate cleanliness and longevity. This method shows great promise for ultrasensitive, sustainable, and cost-effective applications in chemical sensing and molecular diagnostics.

Recycling e-waste into gold-loaded covalent organic framework catalysts for terminal alkyne carboxylation

The rising demand for gold requires innovative methods for its recovery from e-waste. Here we present the synthesis of two tetrazine-based vinyl-linked covalent organic frameworks: TTF-COF and TPE-COF that adsorb gold ions and nanoparticles and catalyze the carboxylation of terminal alkynes. These covalent organic frameworks have low band gaps and high photocurrent responses. TTF-COF has an adsorption capacity toward aqueous Au(III) of 2440 mg g-1, and TPE-COF's Au(III) adsorption capacity is 1639 mg g-1. The gold source is metal flakes isolated from waste computer processing units. Of the gold present, > 99% is selectively captured by TTF-COF whereas only 5% of the Ni and 2% of the Cu in the solution is adsorbed. The Au-loaded covalent organic frameworks catalyze the carboxylation of terminal alkynes and are stable and reusable for six reuse cycles. Our covalent organic frameworks convert e-waste into a valuable catalyst for a useful green organic transformation.

Molecular Heterogeneous Photocatalysts for Visible-Light-Driven CO2 Reduction

Photoreduction of CO2 to high-value chemical fuels presents an effective strategy to reduce reliance on fossil fuels and mitigate climate change. The development of a photocatalyst characterized by superior activity, high selectivity, and good stability is a critical issue for PCR. Molecular heterogeneous photocatalytic systems integrate the advantages of both homogeneous and heterogeneous catalysts, creating a synergistic enhancement effect that increases photocatalytic performance. This review summarizes recent advancements in molecular heterogeneous photocatalysts for CO2 reduction. Much of the discussion focuses on the types of molecular heterogeneous photocatalysts, and their photocatalytic performance in CO2 reduction is summarized. The synthesis strategies for molecular heterogeneous photocatalysts are thoroughly discussed. Finally, the challenges and future prospects of molecular heterogeneous photocatalysts for PCR are addressed.

Engineering the electron localization of metal sites on nanosheets assembled periodic macropores for CO2 photoreduction

Photocatalytic conversion of CO2 into syngas is highly appealing, yet still suffers from the undesirable product yield due to the sluggish carrier transfer and the uncontrollable affinity between catalytic sites and intermediates. Here we report the fabrication of Co sites with tunable electron localization capability on two dimensional (2D) nanosheets assembled three dimensional (3D) ordered macroporous framework (3DOM-NS). The as-prepared Co-based 3DOM-NS catalysts exhibit attractive photocatalytic performances toward CO2 reduction, among which the cobalt sulfide one (3DOM Co-SNS) shows the highest syngas generation rate up to 347.3 μmol h-1 under the irradiation of visible light and delivers a remarkable catalytic activity (1150.7 μmol h-1) in a flow reaction system under natural sunlight. Mechanism studies reveal that the high electron localization of metal sites in 3DOM Co-SNS strengthens the interaction between Co and HCOO* via the orbital interactions of dyz/dxz-p and s-s, thus facilitating the cleaving process of C-O bond. Additionally, the ordered macroporous framework with nanosheet subunits elevates the transfer efficiency of photoexcited electrons, which contributes to its high activity.

Integration of Plasmonic Ag(I) Clusters and Fe(II) Porphyrinates into Metal-Organic Frameworks for Efficient Photocatalytic CO2 Reduction Coupling with Photosynthesis of Pure H2O2

Efficient photocatalytic CO2 reduction coupled with the photosynthesis of pure H2O2 is a challenging and significant task. Herein, using classical CO2 photoreduction site iron porphyrinate as the linker, Ag(I) clusters were spatially separated and evenly distributed within a new metal-organic framework (MOF), namely Ag27TPyP-Fe. With water as electron donors, Ag27TPyP-Fe exhibited remarkable performances in artificial photosynthetic overall reaction with CO yield of 36.5 μmol g-1 h-1 and ca. 100 % selectivity, as well as H2O2 evolution rate of 35.9 μmol g-1 h-1. Since H2O2 in the liquid phase can be more readily separated from the gaseous products of CO2 photoreduction, high-purity H2O2 with a concentration up to 0.1 mM was obtained. Confirmed by theoretical calculations and the established energy level diagram, the reductive iron(II) porphyrinates and oxidative Ag(I) clusters within an integrated framework functioned synergistically to achieve artificial photosynthesis. Furthermore, photoluminescence spectroscopy and photoelectrochemical measurements revealed that the robust connection of Ag(I) clusters and iron porphyrinate ligands facilitated efficient charge separation and rapid electron transfer, thereby enhancing the photocatalytic activity.

Incorporation of a Binuclear Cobalt Complex into MOFs for Photocatalytic CO2 Reduction with H2O as an Electron Donor

The development of molecular composite photocatalysts for cost-effective, sacrificial-reagent-free CO2 reduction is desirable but challenging. Herein, we employed an in situ encapsulation strategy to encapsulate the binuclear cobalt complex (Co2L) within NH2-MIL-125 and synthesized a range of MOF-based composites with varying cobalt content for photocatalytic CO2 reduction. The photocatalytic results showed that the catalytic performance increased with the increase in Co2L content, reaching a rapid CO generation rate of 27.95 μmol·g-1·h-1, over 5 times that of bare NH2-MIL-125, with water as the electron donor instead of any organic sacrificial agent. This composite catalyst effectively harnesses the advantages of both molecular catalysts and MOFs, leveraging the superior catalytic activity of molecular catalysts while also capitalizing on the light absorption and water oxidation capabilities of MOFs, resulting in a remarkable ability for photocatalytic CO2 reduction. The photocatalytic mechanism involving electron transfer and CO2 activation has been revealed by photoluminescence spectroscopy, in situ X-ray photoelectron spectroscopy, in situ diffuse reflectance infrared Fourier transform spectroscopy, and other control experiments.

Exploring the Impact of Water Content in Solvent Systems on Photochemical CO2 Reduction Catalyzed by Ruthenium Complexes

To achieve artificial photosynthesis, it is crucial to develop a catalytic system for CO2 reduction using water as the electron source. However, photochemical CO2 reduction by homogeneous molecular catalysts has predominantly been conducted in organic solvents. This study investigates the impact of water content on catalytic activity in photochemical CO2 reduction in N,N-dimethylacetamide (DMA), using [Ru(bpy)3]2+ (bpy: 2,2'-bipyridine) as a photosensitizer, 1-benzyl-1,4-dihydronicotinamide (BNAH) as an electron donor, and two ruthenium diimine carbonyl complexes, [Ru(bpy)2(CO)2]2+ and trans(Cl)-[Ru(Ac-5Bpy-NHMe)(CO)2Cl2] (5Bpy: 5'-amino-2,2'-bipyridine-5-carboxylic acid), as catalysts. Increasing water content significantly decreased CO and formic acid production. The similar rates of decrease for both catalysts suggest that water primarily affects the formation efficiency of free one-electron-reduced [Ru(bpy)3]2+, rather than the intrinsic catalytic activity. The reduction in cage-escape efficiency with higher water content underscores the challenges in replacing organic solvents with water in photochemical CO2 reduction.

Supra-ceramics: a molecule-driven frontier of inorganic materials

Discoveries and technological innovations over the past decade are transforming our understanding of the properties of ceramics, such as 'hard', 'brittle', and 'homogeneous'. For example, inorganic crystals containing molecular anions exhibit excellent secondary battery characteristics, and the fusion of inorganic solids and molecules results in innovative catalytic functions and physical properties. Different from the conventional ceramics such as metal oxides that are formed by monatomic cations and anions, unique properties and functions can be expected in molecular-incorporated inorganic solids, due to the asymmetric and dynamic properties brought about by the constituent molecular units. We name the molecular-incorporated inorganic materials that produce innovative properties and functions as supra-ceramics. In this article, we describe various kinds of supra-ceramics from the viewpoint of synthesis, analysis and physical properties/functions for a wide range of applications.

Noble Metal Plasmon-Molecular Catalyst Hybrids for Renewable Energy Relevant Small Molecule Activation

Significant endeavors have been dedicated to the advancement of materials for artificial photosynthesis, aimed at efficiently harvesting light and catalyzing reactions such as hydrogen production and CO2 conversion. The application of plasmonic nanomaterials emerges as a promising option for this purpose, owing to their excellent light absorption properties and ability to confine solar energy at the nanoscale. In this regard, coupling plasmonic particles with molecular catalysts offers a pathway to create high-performance hybrid catalysts. In this review, we discuss the plasmonic-molecular complex hybrid catalysts where the plasmonic nanoparticles serve as the light-harvesting unit and promote interfacial charge transfer in tandem with the molecular catalyst which drives chemical transformation. In the initial section, we provide a concise overview of plasmonic nanomaterials and their photophysical properties. We then explore recent breakthroughs, highlighting examples from literature reports involving plasmonic-molecular complex hybrids in various catalytic processes. The utilization of plasmonic materials in conjunction with molecular catalysts represents a relatively unexplored area with substantial potential yet to be realized. This review sets a strong basis and motivation to explore the plasmon-induced hot-electron mediated photelectrochemical small molecule activation reactions. Utilizing in situ spectroscopic investigations and ultrafast transient absorption spectroscopy, it presents a comprehensive template for scalable and sustainable antenna-reactor systems.

Charge Transport Approaches in Photocatalytic Supramolecular Systems Composing of Semiconductor and Molecular Metal Complex for CO2 Reduction

The design of photocatalytic supramolecular systems composing of semiconductors and molecular metal complexes for CO2 reduction has attracted increasing attention. The supramolecular system combines the structural merits of semiconductors and metal complexes, where the semiconductor harvests light and undertakes the oxidative site, while the metal complex provides activity for CO2 reduction. The intermolecular charge transfer plays crucial role in ensuring photocatalytic performance. Here, we review the progress of photocatalytic supramolecular systems in reduction of CO2 and highlight the interfacial charge transfer pathways, as well as their state-of-the-art characterization methods. The remaining challenges and prospects for further design of supramolecular photocatalysts are also presented.

Recent advances in heterogeneous catalysis of solar-driven carbon dioxide conversion

Solar-driven carbon dioxide (CO2) conversion including photocatalytic (PC), photoelectrochemical (PEC), photovoltaic plus electrochemical (PV/EC) systems, offers a renewable and scalable way to produce fuels and high-value chemicals for environment and energy sustainability. This review summarizes the basic fundament and the recent advances in the field of solar-driven CO2 conversion. Expanding the visible-light absorption is an important strategy to improve solar energy conversion efficiency. The separation and migration of photogenerated charges carriers to surface sites and the surface catalytic processes also determine the photocatalytic performance. Surface engineering including co-catalyst loading, defect engineering, morphology control, surface modification, surface phase junction, and Z-scheme photocatalytic system construction, have become fundamental strategies to obtain high-efficiency photocatalysts. Similar to photocatalysis, these strategies have been applied to improve the conversion efficiency and Faradaic efficiency of typical PEC systems. In PV/EC systems, the electrode surface structure and morphology, electrolyte effects, and mass transport conditions affect the activity and selectivity of electrochemical CO2 reduction. Finally, the challenges and prospects are addressed for the development of solar-driven CO2 conversion system with high energy conversion efficiency, high product selectivity and stability.

Unveiling photoinduced electron transfer in cobalt(iii)-R-pyridine complexes anchored to anatase nanocrystals: photoluminescence and magnetic studies

In this study, we synthesized mixed ligand complexes of the cis-[Co(tn)2(Rpy)Br]Br2 type using a novel mechanochemical approach. Characterization involved spectral measurements and single crystal X-ray diffraction analysis, confirming the structure of the cis-[Co(tn)2(4-Mepy)Br]Br2 complex. The single crystal refinement data revealed a monoclinic crystal system with a distorted octahedral geometry. The choice of the sixth ligand influenced the emission and magnetic properties, showing a ferromagnetic character in the Co(iii)-complex environment. We investigated efficient electron transfer to the cobalt(iii) center using TiO2 nanoparticles under UV-light irradiation. The adsorption characteristics of cis-[Co(tn)2(Rpy)Br]Br2 in aqueous 2-propanol varied, leading to surface compound formation. Under UV irradiation, the anatase surface exhibited remarkable adsorption capabilities, facilitating efficient electron transfer to the Co(iii) center and resulting in a high photoefficiency for Co(ii) formation. Our study has put forward a model for interfacial electron transfer (IET), taking into account the overlap between the TiO2 conduction band and the acceptor level of the Co center, as well as the electronic coupling between the donor level of the Ti center and the acceptor level of the Co center. This model sheds light on the accumulation of electrons for reducing the adhered complex ion. The IET process was corroborated by the conversion of 2-propanol into acetone, as verified by 1H NMR technique. Overall, our findings provide novel insights into the role of the Rpy moiety in modifying the structure of the TiO2-cobalt(iii)-Rpy compound and propose a mechanism for IET reactions, thus advancing the field.

Improved Carrier Separation and Recombination by Ferroelectric Polarization in the CuBiP2Se6/C2N Heterostructure: A Nonadiabatic Molecular Dynamics Study

The rapid recombination of photogenerated carriers heavily restricts the photocatalytic efficiency. Here, we propose a new strategy to improve catalytic efficiency based on the ferroelectric van der Waals heterostructure (CuBiP2Se6/C2N). Combining density functional theory and the nonadiabatic molecular dynamics (NAMD) method, we have systematically analyzed the ground-state properties and carrier dynamics images in the CuBiP2Se6/C2N heterostructure. Our calculations showed that the ferroelectric polarization of CuBiP2Se6 provides the internal driving force for the photogenerated carriers separation. NAMD results demonstrate that the excited-state carrier transfer and recombination processes in the CuBiP2Se6/C2N are consistent with a type II mechanism. Meanwhile, constructing the ferroelectric heterostructure can effectively prolong the carrier lifetime, from ∼65.98 to ∼124.54 ps. Moreover, the high quantum efficiency and tunable band edge positions mean that the CuBiP2Se6/C2N heterostructure is an excellent potential candidate material for photocatalytic water splitting.

Application of GaS nanotubes as efficient catalysts in photocatalytic hydrolysis: a first principles study

Photocatalytic hydrogen production is a promising and sustainable technology that converts solar energy into hydrogen energy with the assistance of semiconductor photocatalysts. Herein, we investigated the geometric structure and electronic and photocatalytic properties of single-walled GaS nanotubes under the framework of density functional theory with HSE06 as an exchange-correlation function. This paper presents the first study on the geometric structure, electron, and photocatalytic properties of single-walled GaS nanotubes. The results show that the strain energy and formation energy of GaS nanotubes decrease, while the structure is more stable, with increasing radius. Our study shows that after rolling from the slab, the nanotubes undergo a transition from an indirect band gap to a direct band gap and have appropriate band gaps for absorbing visible light. Moreover, it is speculated that the large disparity between the effective mass of electrons and holes can reduce charge carrier recombination. Among them, the nanotube with a diameter larger than (35, 0) showed promising band edge positions for photocatalytic hydrolysis redox potential with pH values between 0 and 7. Based on these properties, we believe that GaS nanotubes will be promising in photocatalytic hydrolysis.

Stable Photoelectrochemical Reactions at Solid/Solid Interfaces toward Solar Energy Conversion and Storage

Electrochemistry has extended from reactions at solid/liquid interfaces to those at solid/solid interfaces. However, photoelectrochemistry at solid/solid interfaces has been hardly reported. In this study, we achieve a stable photoelectrochemical reaction at the semiconductor-electrode/solid-electrolyte interface in a Nb-doped anatase-TiO2 (a-TiO2:Nb)/Li3PO4 (LPO)/Li all-solid-state cell. The oxidative currents of a-TiO2:Nb/LPO/Li increase upon light irradiation when a-TiO2:Nb is located at a potential that is more positive than its flat-band potential. This is because the photoexcited electrons migrate to the current collector due to the bending of the conduction band minimum toward the negative potential. The photoelectrochemical reaction at the semiconductor/solid-electrolyte interface is driven by the same principle as those at semiconductor/liquid-electrolyte interfaces. Moreover, oxidation under light irradiation exhibits reversibility with reduction in the dark. Thus, we extend photoelectrochemistry to all-solid-state systems composed of solid/solid interfaces. This extension would enable us to investigate photoelectrochemical phenomena uncleared at solid/liquid interfaces because of low stability and durability.

Solar CO2 reduction using a molecular Re(I) catalyst grafted on SiO2via amide and alkyl amine linkages

Heterogenized molecular catalysts have shown interesting activities in different chemical transformations. In our previous studies, a molecular catalyst, Re(bpy)(CO)3Cl where bpy is 2,2'-bipyridine, was covalently attached to silica surfaces via an amide linkage for use in photocatalytic CO2 reduction. Derivatizing the bpy ligand with electron-withdrawing amide groups led to detrimental effects on the catalytic activity of Re(bpy)(CO)3Cl. In this study, an alkyl amine linkage is utilized to attach Re(bpy)(CO)3Cl onto SiO2 in order to eliminate the detrimental effects of the amide linkage by breaking the conjugation between the bpy ligand and the amide group. However, the heterogenized Re(I) catalyst containing the alkyl amine linkage demonstrates even lower activity than the one containing the amide linkage in photocatalytic CO2 reduction. Infrared studies suggest that the presence of the basic amine group led to the formation of a photocatalytically inactive Re(I)-OH species on SiO2. Furthermore, the amine group likely contributes to the stabilization of a surface Re(I)-carboxylato species formed upon light irradiation, resulting in the low activity of the heterogenized Re(I) catalyst containing the alkyl amine linkage.

Elucidating protonation pathways in CO2 photoreduction using the kinetic isotope effect

The surge in anthropogenic CO2 emissions from fossil fuel dependence demands innovative solutions, such as artificial photosynthesis, to convert CO2 into value-added products. Unraveling the CO2 photoreduction mechanism at the molecular level is vital for developing high-performance photocatalysts. Here we show kinetic isotope effect evidence for the contested protonation pathway for CO2 photoreduction on TiO2 nanoparticles, which challenges the long-held assumption of electron-initiated activation. Employing isotopically labeled H2O/D2O and in-situ diffuse reflectance infrared Fourier transform spectroscopy, we observe H+/D+-protonated intermediates on TiO2 nanoparticles and capture their inverse decay kinetic isotope effect. Our findings significantly broaden our understanding of the CO2 uptake mechanism in semiconductor photocatalysts.

Progress and Perspectives on Promising Covalent-Organic Frameworks (COFs) Materials for Energy Storage Capacity

In recent years, a new class of highly crystalline advanced permeable materials covalent-organic frameworks (COFs) have garnered a great deal of attention thanks to their remarkable properties, such as their large surface area, highly ordered pores and channels, and controllable crystalline structures. The lower physical stability and electrical conductivity, however, prevent them from being widely used in applications like photocatalytic activities and innovative energy storage and conversion devices. For this reason, many studies have focused on finding ways to improve upon these interesting materials while also minimizing their drawbacks. This review article begins with a brief introduction to the history and major milestones of COFs development before moving on to a comprehensive exploration of the various synthesis methods and recent successes and signposts of their potential applications in carbon dioxide (CO2 ) sequestration, supercapacitors (SCs), lithium-ion batteries (LIBs), and hydrogen production (H2 -energy). In conclusion, the difficulties and potential of future developing with highly efficient COFs ideas for photocatalytic as well as electrochemical energy storage applications are highlighted.

Synergistic coupling of interface ohmic contact and LSPR effects over Au/Bi24O31Br10 nanosheets for visible-light-driven photocatalytic CO2 reduction to CO

The challenge of synergistically optimizing different mechanisms limits the further improvement of plasmon-mediated photocatalytic activities. In this work, an Au/Bi24O31Br10 composite, combining an interface ohmic contact and localized surface plasmon resonance (LSPR), is prepared by a thermal reduction method. The LSPR effect induces the local resonance energy transfer effect and the local electric field enhancement effect, while the interface ohmic contact forms a stronger interface electric field. The novel synergistic interaction between the interface ohmic contact and LSPR drives effective charge separation and provides more active sites for the adsorption and activation of CO2 with improved photocatalytic efficiency. The optimized 0.6 wt% Au (5.7 nm) over Bi24O31Br10 nanosheets showed an apparently improved photocatalytic activity without any sacrificial reagents, specifically CO and O2 yields of 44.92 and 17.83 μmol g-1 h-1, and demonstrated superior stability (only lost 6%) after continuous reaction for 48 h, nearly 5-fold enhanced compared to Bi24O31Br10 and a great advantage compared with other bismuth-based photocatalysts.

Morphology, Energy Level Alignment, and Charge Transfer at the Protoporphyrin IX-Semiconductor Interface

The combination of molecular catalysts and semiconductor substrates in hybrid heterogeneous photo- or electrocatalytic devices could yield synergistic effects that result in enhanced activity and long-term stability. The extent of synergy strongly depends on the electronic interactions and energy level alignment between the molecular states and the valence and conduction band of the substrate. These properties of hybrid interfaces are investigated for a model system composed of protoporphyrin IX (PPIX) as a stand-in for molecular catalysts and a variety of semiconductor substrates. Monolayers of PPIX are deposited using Langmuir-Blodgett deposition. Their morphology is studied in dependence of the deposition surface pressure to achieve a high-quality, dense coverage. By making use of ultraviolet-visible spectroscopy and ultraviolet photoelectron spectroscopy, the band alignment is determined by the vacuum level and incorporates an interface dipole of 0.4 eV independent of the substrate. The HOMO, LUMO, and LUMO+1 levels were determined to be at 5.6, 3.7, and 2.7 eV below the vacuum level, respectively. The quenching of PPIX photoluminescence in dependence of the potential gradient between excited state and electron affinity of the semiconductor substrates is overall in good agreement with electron transfer processes occurring at very fast time scales on the order of femtoseconds. Nevertheless, deviations from this model become apparent for narrower band gap semiconductors, which points to an additional relevance of other processes, such as energy transfer. These findings highlight the importance of matching the semiconductor to the molecular catalyst to prevent undesirable deactivation pathways.

Nanomaterials as catalysts for CO2 transformation into value-added products: A review

Carbon dioxide (CO₂₎ is the most important greenhouse gas (GHG), accounting for 76% of all GHG emissions. The atmospheric CO₂ concentration has increased from 280 ppm in the pre-industrial era to about 418 ppm, and is projected to reach 570 ppm by the end of the 21^st century. In addition to reducing CO₂ emissions from anthropogenic activities, strategies to adequately address climate change must include CO₂ capture. To promote circular economy, captured CO₂ should be converted to value-added materials such as fuels and other chemical feedstock. Due to their tunable chemistry (which allows them to be selective) and high surface area (which allows them to be efficient), engineered nanomaterials are promising for CO₂ capturing and/or transformation. This work critically reviewed the application of nanomaterials for the transformation of CO₂ into various fuels, like formic acid, carbon monoxide, methanol, and ethanol. We discussed the literature on the use of metal-based nanomaterials, inorganic/organic nanocomposites, as well as other routes suitable for CO₂ conversion such as the electrochemical, non-thermal plasma, and hydrogenation routes. The characteristics, steps, mechanisms, and challenges associated with the different transformation technologies were also discussed. Finally, we presented a section on the outlook of the field, which includes recommendations for how to continue to advance the use of nanotechnology for conversion of CO₂ to fuels.

Development of an Integrated System for Highly Selective Photoenzymatic Synthesis of Formic Acid from CO2

Herein, a Zr-based dual-ligand MOFs with pre-installed Rh complex was employed for NADH regeneration in situ and also used for immobilization of formic acid dehydrogenase (FDH) in order to realize a highly efficient CO₂ fixation system. Then, based on the detailed investigations into the photochemical and electrochemical properties, it is demonstrated that the introduction of the photosensitive meso-tetra(4-carboxyphenyl) porphin (TCPP) ligands increased the catalytic active sites and improved photoelectric properties. Furthermore, the electron mediator Rh complex, anchored on the zirconium-based dual-ligand MOFs, enhanced the efficiency of electron transfer efficiency and facilitated the separation of photogenerated electrons and holes. Compared with UiO-66-NH₂ , Rh-H₂ TCPP-UiO-66-NH₂ exhibits an optimized valence band structure and significantly improved photocatalytic activity for NAD⁺ reduction, resulting the synthesis of formic acid from CO₂ increased from 150 μg mL^-1 (UiO-66-NH₂ ) to 254 μg mL^-1 (Rh-H₂ TCPP-UiO-66-NH₂ ). Moreover, the assembled photocatalyst-enzyme coupled system also allows facile recycling of expensive electron mediator, enzyme, and photocatalyst.

Second Sphere Effects Promote Formic Acid Dehydrogenation by a Single-Atom Gold Catalyst Supported on Amino-Substituted Graphdiyne

Regulating the second sphere of homogeneous molecular catalysts is a common and effective method to boost their catalytic activities, while the second sphere effects have rarely been investigated for heterogeneous single-atom catalysts primarily due to the synthetic challenge for installing functional groups in their second spheres. Benefiting from the well-defined and readily tailorable structure of graphdiyne (GDY), an Au single-atom catalyst on amino-substituted GDY is constructed, where the amino group is located in the second sphere of the Au center. The Au atoms on amino-decorated GDY displayed superior activity for formic acid dehydrogenation compared with those on unfunctionalized GDY. The experimental studies, particularly the proton inventory studies, and theoretical calculations revealed that the amino groups adjacent to an Au atom could serve as proton relays and thus facilitate the protonation of an intermediate Au-H to generate H₂ . Our study paves the way to precisely constructing the functional second sphere on single-atom catalysts.

Near-infrared-featured broadband CO2 reduction with water to hydrocarbons by surface plasmon

Imitating the natural photosynthesis to synthesize hydrocarbon fuels represents a viable strategy for solar-to-chemical energy conversion, where utilizing low-energy photons, especially near-infrared photons, has been the ultimate yet challenging aim to further improving conversion efficiency. Plasmonic metals have proven their ability in absorbing low-energy photons, however, it remains an obstacle in effectively coupling this energy into reactant molecules. Here we report the broadband plasmon-induced CO₂ reduction reaction with water, which achieves a CH₄ production rate of 0.55 mmol g^-1 h^-1 with 100% selectivity to hydrocarbon products under 400 mW cm^-2 full-spectrum light illumination and an apparent quantum efficiency of 0.38% at 800 nm illumination. We find that the enhanced local electric field plays an irreplaceable role in efficient multiphoton absorption and selective energy transfer for such an excellent light-driven catalytic performance. This work paves the way to the technique for low-energy photon utilization.

Surface Immobilization of a Re(I) Tricarbonyl Phenanthroline Complex to Si(111) through Sonochemical Hydrosilylation

A sonochemical-based hydrosilylation method was employed to covalently attach a rhenium tricarbonyl phenanthroline complex to silicon(111). fac-Re(5-(p-Styrene)-phen)(CO)₃Cl (5-(p-styrene)-phen = 5-(4-vinylphenyl)-1,10-phenanthroline) was reacted with hydrogen-terminated silicon(111) in an ultrasonic bath to generate a hybrid photoelectrode. Subsequent reaction with 1-hexene enabled functionalization of remaining atop Si sites. Attenuated total reflectance-Fourier transform infrared spectroscopy confirms attachment of the organometallic complex to silicon without degradation of the organometallic core, supporting hydrosilylation as a strategy for installing coordination complexes that retain their molecular integrity. Detection of Re(I) and nitrogen by X-ray photoelectron spectroscopy (XPS) further support immobilization of fac-Re(5-(p-styrene)-phen)(CO)₃Cl. Cyclic voltammetry and electrochemical impedance spectroscopy under white light illumination indicate that fac-Re(5-(p-styrene)-phen)(CO)₃Cl undergoes two electron reductions. Mott-Schottky analysis indicates that the flat band potential is 239 mV more positive for p-Si(111) co-functionalized with both fac-Re(5-(p-styrene)-phen)(CO)₃Cl and 1-hexene than when functionalized with 1-hexene alone. XPS, ultraviolet photoelectron spectroscopy, and Mott-Schottky analysis show that functionalization with fac-Re(5-(p-styrene)-phen)(CO)₃Cl and 1-hexene introduces a negative interfacial dipole, facilitating reductive photoelectrochemistry.

Engineered 2D Metal Oxides for Photocatalysis as Environmental Remediation: A Theoretical Perspective

Modern-day society requires advanced technologies based on renewable and sustainable energy resources to meet environmental remediation challenges. Solar-inspired photocatalytic applications such as water splitting, hydrogen evolution reaction (HER), and carbon dioxide reduction reaction (CO2RR) are unique solutions based on green and efficient technologies. Considering the special electronic features and larger surface area, two-dimensional (2D) materials, especially metal oxides (MOs), have been broadly explored for the abovementioned applications in the past few years. However, their photocatalytic potential has not been optimized yet to the level required for practical and commercial applications. Among many strategies available, defect engineering, including cation and anion vacancy creations, can potentially boost the photocatalytic performance of 2D MOs. This mini-review covers recent advancements in 2D engineered materials for various photocatalysis applications such as H2O2 oxidation, HER, and CO2RR for environmental remediation from theoretical perspectives. By thoroughly addressing the fundamental aspects, recent developments, and associated challenges—the author’s recommendations in compliance with future challenges and prospects will pave the way for readers.

Advances in Biomimetic Photoelectrocatalytic Reduction of Carbon Dioxide

Emerging photoelectrocatalysis (PEC) systems synergize the advantages of electrocatalysis (EC) and photocatalysis (PC) and are considered a green and efficient approach to CO2 conversion. However, improving the selectivity and conversion rate remains a major challenge. Strategies mimicking natural photosynthesis provide a prospective way to convert CO2 with high efficiency. Herein, several typical strategies are described for constructing biomimetic photoelectric functional interfaces; such interfaces include metal cocatalysts/semiconductors, small molecules/semiconductors, molecular catalysts/semiconductors, MOFs/semiconductors, and microorganisms/semiconductors. The biomimetic PEC interface must have enhanced CO2 adsorption capacity, preferentially activate CO2 , and have an efficient conversion ability; with these properties, it can activate CO bonds effectively and promote electron transfer and CC coupling to convert CO2 to single-carbon or multicarbon products. Interfacial electron transfer and proton coupling on the biomimetic PEC interface are also discussed to clarify the mechanism of CO2 reduction. Finally, the existing challenges and perspectives for biomimetic photoelectrocatalytic CO2 reduction are presented.

Insight into the mechanism of deep NO photo-oxidation by bismuth tantalate with oxygen vacancies

Deeply photocatalytic oxidation of nitrogen oxides is still difficult to achieve, mainly limited by few intrinsic active sites and inefficient carrier separation of photocatalysts. Accordingly, we develop a simple room temperature tactic to introduce oxygen vacancies (OVs) into Bi₃TaO₇ (BTO). Based on solid experimental and DFT theoretical supports, we explore the mechanism of NO removal over OVs decorated BTO (OVs-BTO). OVs can not only alter the distribution of local electrons to result in the formation of a fast charge transfer channel between OVs and the adjacent Ta atoms, which improves the transport rate of photogenerated carriers; but also function as active sites to adsorb small molecules (NO, O₂ and H₂O), which being activated and positively drive the NO oxidation reaction. In order to investigate a possible reaction path, a combination of in-situ DRIFTS and simulated Gibbs free energy reveals that the intermediate products of OVs-BTO are helpful to promote the deep oxidation of NO to NO₃^-, while pristine BTO is more likely to produce NO₂ intermediate toxic by-products, which greatly hinders the deep photocatalytic oxidation of NO. This work provides insights into the role of OVs in photocatalysts, and also points out a guideline for the mechanism of semiconductor photocatalysts in eliminating gaseous pollutants.

Implanting CoOx Clusters on Ordered Macroporous ZnO Nanoreactors for Efficient CO2 Photoreduction

Despite suffering from slow charge-carrier mobility, photocatalysis is still an attractive and promising technology toward producing green fuels from solar energy. An effective approach is to design and fabricate advanced architectural materials as photocatalysts to enhance the performance of semiconductor-based photocatalytic systems. Herein, metal-organic-framework-derived hierarchically ordered porous nitrogen and carbon co-doped ZnO (N-C-ZnO) structures are developed as nanoreactors with decorated CoO_x nanoclusters for CO₂ -to-CO conversion driven by visible light. Introduction of hierarchical nanoarchitectures with highly ordered interconnected meso-macroporous channels shows beneficial properties for photocatalytic reduction reactions, including enhanced mobility of charge carriers throughout the highly accessible framework, maximized exposure of active sites, and inhibited recombination of photoinduced charge carriers. Density functional theory calculations further reveal the key role of CoO_x nanoclusters with high affinity to CO₂ molecules, and the CoO bonds formed on the surface of the composite exhibit stronger charge redistribution. As a result, the obtained CoO_x /N-C-ZnO demonstrates enhanced photocatalysis performance in terms of high CO yield and long-term stability.

The roles of gold and silver nanoparticles on ZnIn2S4/silver (gold)/tetra(4-carboxyphenyl)porphyrin iron(III) chloride hybrids in carbon dioxide photoreduction

The construction of hybrid catalysts composed of inorganic semiconductors and molecular catalysts shows great potential for achieving high photocatalytic carbon dioxide (CO₂) conversion efficiency. In this study, ZnIn₂S₄ was first synthesized via a solvothermal route. Gold (Au) and silver (Ag) nanoparticles were then deposited on ZnIn₂S₄ via the reduction of noble metal precursor by sulfur vacancy defects. The obtained composite was further combined with tetra(4-carboxyphenyl)porphyrin iron(III) chloride (FeTCPP) molecular catalyst for efficient photocatalytic CO₂ conversion. The roles of different noble metal nanoparticles in charge separation and interfacial electron transfer have been comprehensively studied. The photocatalytic performance and photoelectrochemical characterizations demonstrate that the introduction of Ag or Au nanoparticles is beneficial for charge separation. More importantly, the presence of Ag nanoparticles plays a crucial role in promoting the interfacial charge transfer between ZnIn₂S₄ and FeTCPP, whereas, Au nanoparticles function as active sites for the water reduction reaction.

Single-Atom Catalysts (SACs) for Photocatalytic CO2 Reduction with H2 O: Activity, Product Selectivity, Stability, and Surface Chemistry

In recent years, single-atom catalysts (SACs) have attracted the interest of researchers owing to their suitability for various catalytic applications. For instance, their optoelectronic features, site-specific activity, and cost-effectiveness make SACs ideal for photocatalytic CO₂ reduction. The activity, product selectivity, and photostability of SACs depend on various factors such as the nature of the metal/support material, the interaction between the metal atoms and support, light-harvesting ability, charge separation behavior, CO₂ adsorption ability, active sites, and defects. Consequently, it is necessary to investigate these factors in depth to elucidate the working principle(s) of SACs for catalytic applications. Herein, the recent progress in the development of SACs for photocatalytic CO₂ reduction with H₂ O is reviewed. First, a brief overview of CO₂ photoreduction and SACs for CO₂ conversion is provided. Several synthesis strategies and useful techniques for characterizing SACs employed in heterogeneous catalysis are then described. Next, the challenges of SACs for photocatalytic CO₂ reduction and related optimization strategies, in terms of activity, product selectivity, and stability, are explored. The progress in the development of noble metal- and transition metal-based SACs and dual-SACs for photocatalytic CO₂ reduction is discussed. Finally, the prospects of SACs for CO₂ reduction are considered.

Alumina-Supported Alpha-Iron(III) Oxyhydroxide as a Recyclable Solid Catalyst for CO2 Photoreduction under Visible Light

Photocatalytic conversion of CO2 into transportable fuels such as formic acid (HCOOH) under sunlight is an attractive solution to the shortage of energy and carbon resources as well as to the increase in Earth's atmospheric CO2 concentration. The use of abundant elements as the components of a photocatalytic CO2 reduction system is important, and a solid catalyst that is active, recyclable, nontoxic, and inexpensive is strongly demanded. Here, we show that a widespread soil mineral, alpha-iron(III) oxyhydroxide (α-FeOOH; goethite), loaded onto an Al2 O3 support, functions as a recyclable catalyst for a photocatalytic CO2 reduction system under visible light (λ>400 nm) in the presence of a RuII photosensitizer and an electron donor. This system gave HCOOH as the main product with 80-90 % selectivity and an apparent quantum yield of 4.3 % at 460 nm, as confirmed by isotope tracer experiments with 13 CO2 . The present work shows that the use of a proper support material is another method of catalyst activation toward the selective reduction of CO2 .

Coupling Ruthenium Bipyridyl and Cobalt Imidazolate Units in a Metal-Organic Framework for an Efficient Photosynthetic Overall Reaction in Diluted CO2

Artificial photocatalytic CO₂ reduction, using water as the reductant, is challenging mainly because it is difficult for multiple functional units to cooperate efficiently. Here, we show that the classic photosensitive and H₂O-oxidizing ruthenium bipyridyl units and CO₂-reducing cobalt imidazolate units can be incorporated into a metal-organic framework using a classic organic ligand, imidazo[4,5-f][1,10]phenanthroline. Under visible light without additional sacrificial agents and photosensitizers, the overall conversion of CO₂ and H₂O to CO and O₂ was achieved by the multifunctional photocatalyst in the CH₃CN/H₂O mixed solvent with a high CO production rate of 11.2 μmol g^-1 h^-1 and CO selectivity of ca. 100%. Thanks to its ultramicroporous structure with moderately strong CO₂ adsorption ability, the photocatalyst also exhibited high performances with CO/CH₄ production rates of 5.15/0.62 and 4.26/0.20 μmol g^-1 h^-1 in the gas phase with pure and even diluted CO₂, respectively. Photoluminescence emission spectroscopy and photoelectrochemical tests confirmed that the photosensitive and catalytic units cooperated well to give suitable photocatalytic redox potentials and fast electron-hole separation.

The Importance of the Macroscopic Geometry in Gas-Phase Photocatalysis

Photocatalysis has the potential to make a major technological contribution to solving pressing environmental and energy problems. There are many strategies for improving photocatalysts, such as tuning the composition to optimize visible light absorption, charge separation, and surface chemistry, ensuring high crystallinity, and controlling particle size and shape to increase overall surface area and exploit the reactivity of individual crystal facets. These processes mainly affect the nanoscale and are therefore summarized as nanostructuring. In comparison, microstructuring is performed on a larger size scale and is mainly concerned with particle assembly and thin film preparation. Interestingly, most structuring efforts stop at this point, and there are very few examples of geometry optimization on a millimeter or even centimeter scale. However, the recent work on nanoparticle-based aerogel monoliths has shown that this size range also offers great potential for improving the photocatalytic performance of materials, especially when the macroscopic geometry of the monolith is matched to the design of the photoreactor. This review article is dedicated to this aspect and addresses some issues and open questions that arise when working with macroscopically large photocatalysts. Guidelines are provided that could help develop novel and efficient photocatalysts with a truly 3D architecture.

CO2 Reduction Using Water as an Electron Donor over Heterogeneous Photocatalysts Aiming at Artificial Photosynthesis

Photocatalytic and photoelectrochemical CO₂ reduction of artificial photosynthesis is a promising chemical process to solve resource, energy, and environmental problems. An advantage of artificial photosynthesis is that solar energy is converted to chemical products using abundant water as electron and proton sources. It can be operated under ambient temperature and pressure. Especially, photocatalytic CO₂ reduction employing a powdered material would be a low-cost and scalable system for practical use because of simplicity of the total system and simple mass-production of a photocatalyst material.In this Account, single particulate photocatalysts, Z-scheme photocatalysts, and photoelectrodes are introduced for artificial photosynthetic CO₂ reduction. It is indispensable to use water as an electron donor (i.e., reasonable O₂ evolution) but not to use a sacrificial reagent of a strong electron donor, for achievement of the artificial photosynthetic CO₂ reduction accompanied by ΔG > 0. Confirmations of O₂ evolution, a ratio of reacted e^- to h⁺ estimated from obtained products, a turnover number, and a carbon source of a CO₂ reduction product are discussed as the key points for evaluation of photocatalytic and photoelectrochemical CO₂ reduction.Various metal oxide photocatalysts with wide band gaps have been developed for water splitting under UV light irradiation. However, these bare metal oxide photocatalysts without a cocatalyst do not show high photocatalytic CO₂ reduction activity in an aqueous solution. The issue comes from lack of a reaction site for CO₂ reduction and competitive reaction between water and CO₂ reduction. This raises a key issue to find a cocatalyst and optimize reaction conditions defining this research field. Loading a Ag cocatalyst as a CO₂ reduction site and NaHCO₃ addition for a smooth supply of hydrated CO₂ molecules as reactant are beneficial for efficient photocatalytic CO₂ reduction. Ag/BaLa₄Ti₄O₁₅ and Ag/NaTaO₃:Ba reduce CO₂ to CO as a main reduction reaction using water as an electron donor even in just water and an aqueous NaHCO₃ solution. A Rh-Ru cocatalyst on NaTaO₃:Sr gives CH₄ with 10% selectivity (Faradaic efficiency) based on the number of reacted electrons in the photocatalytic CO₂ reduction accompanied by O₂ evolution by water oxidation.Visible-light-responsive photocatalyst systems are indispensable for efficient sunlight utilization. Z-scheme systems using CuGaS₂, (CuGa)_1-xZn_2xS₂, CuGa_1-xIn_xS₂, and SrTiO₃:Rh as CO₂-reducing photocatalyst, BiVO₄ as O₂-evolving photocatalyst, and reduced graphene oxide (RGO) and Co-complex as electron mediator or without an electron mediator are active for CO₂ reduction using water as an electron donor under visible light irradiation. These metal sulfide photocatalysts have the potential to take part in Z-scheme systems for artificial photosynthetic CO₂ reduction, even though their ability to extract electrons from water is insufficient.A photoelectrochemical system using a photocathode is also attractive for CO₂ reduction under visible light irradiation. For example, p-type CuGaS₂, (CuGa)_1-xZn_2xS₂, Cu_1-xAg_xGaS₂, and SrTiO₃:Rh function as photocathodes for CO₂ reduction under visible light irradiation. Moreover, introducing a conducting polymer as a hole transporter and surface modification with Ag and ZnS improve photoelectrochemical performance.

Solar-Driven CO2 Reduction Using a Semiconductor/Molecule Hybrid Photosystem: From Photocatalysts to a Monolithic Artificial Leaf

The synthesis of organic chemicals from H₂O and CO₂ using solar energy is important for recycling CO₂ through cyclical use of chemical ingredients produced from CO₂ or molecular energy carriers based on CO₂. Similar to photosynthesis in plants, the CO₂ molecules are reduced by electrons and protons, which are extracted from H₂O molecules, to produce O₂. This reaction is uphill; therefore, the solar energy is stored as the chemical bonding energy in the organic molecules. This artificial photosynthetic technology mimicking green vegetation should be implemented as a self-standing system for on-site direct solar energy storage that supports CO₂ recycling in a circular economy. Herein, we explain our interdisciplinary fusion methodology to develop hybrid photocatalysts and photoelectrodes for an artificial photosynthetic system for the CO₂ reduction reaction (CO₂RR) in aqueous solutions. The key factor for the system is the integration of uniquely different functions of molecular transition-metal complexes and solid semiconductors. A metal complex catalyst and a semiconductor appropriate for a CO₂RR and visible-light absorption, respectively, are linked, and they function complementary way to catalyze CO₂RR under visible-light irradiation as a particulate photocatalyst dispersion in solution. It has also been proven that Ru complexes with bipyridine ligands can catalyze a CO₂RR as photocathodes when they are linked with various semiconductor surfaces, such as those of doped tantalum oxides, doped iron oxides, indium phosphides, copper-based sulfides, selenides, silicon, and others. These photocathodes can produce formate and carbon monoxide using electrons and protons extracted from water through potential-matched connections with photoanodes such as TiO₂ or SrTiO₃ for oxygen evolution reactions (OERs). Benefiting from the very low overpotential of an aqueous CO₂RR at metal complexes approaching the theoretical lower limit, the semiconductor/molecule hybrid system demonstrates a single tablet-formed monolithic electrode called "artificial leaf." This single electrode device can generate formate (HCOO^-) from H₂O and CO₂ in a water-filled single-compartment reactor without requiring a separation membrane under unassisted or bias-free conditions, either electrically or chemically. The reaction proceeds with a stoichiometric electron/hole ratio and stores solar energy with a solar-to-chemical energy conversion efficiency of 4.6%, which exceeds that of plants. In this Account, the key results that marked our milestones in technological progress of the semiconductor/molecule hybrid photosystem are concisely explained. These results include design, proof of the principle, and understanding of the phenomena by time-resolved spectroscopies, synchrotron radiation analyses, and DFT calculations. These results enable us to address challenges toward further scientific progress and the social implementation, including the use of earth-abundant elements and the scale-up of the solar-driven CO₂RR system.

Highly Efficient Photocatalytic Reduction of CO2 to CO by In Situ Formation of a Hybrid Catalytic System Based on Molecular Iron Quaterpyridine Covalently Linked to Carbon Nitride

Efficient and selective photocatalytic CO₂ reduction was obtained within a hybrid system that is formed in situ via a Schiff base condensation between a molecular iron quaterpyridine complex bearing an aldehyde function and carbon nitride. Irradiation (blue LED) of an CH₃ CN solution containing 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH), triethylamine (TEA), Feqpy-BA (qpy-BA=4-([2,2':6',2'':6'',2'''-quaterpyridin]-4-yl)benzaldehyde) and C₃ N₄ resulted in CO evolution with a turnover number of 2554 and 95 % selectivity. This hybrid catalytic system unlocks covalent linkage of molecular catalysts with semiconductor photosensitizers via Schiff base reaction for high-efficiency photocatalytic reduction of CO₂ , opening a pathway for diverse photocatalysis.