This tutorial review describes the physical–chemical aspects one must consider when building photocatalytic liposomes for solar fuel production.

Mechanistic understanding of electro-and photocatalytic CO2 reduction is crucial to develop strategies to overcome catalytic bottlenecks. In this regard, herein it is presented for a new CO2-to-CO reduction cobalt aminopyridine catalyst, a detailed experimental and theoretical mechanistic study toward the identification of bottlenecks and potential strategies to alleviate them. The combination of electrochemistry and in-situ spectroelectrochemistry together with spectroscopic techniques led us to identify elusive key electrocatalytic intermediates derived from complex [L N4 Co(OTf)2] (1) (L N4 =1-[2-pyridylmethyl]-4,7-dimethyl-1,4,7triazacyclononane) such as a highly reactive cobalt (I) (1 (I)) and cobalt (I) carbonyl (1 (I)-CO) species. The combination of spectroelectrochemical studies under CO2, 13 CO2 and CO with DFT disclosed that 1 (I) reacts with CO2 to form the pivotal 1 (I)-CO intermediate at the 1 (II/I) redox potential. However, at this reduction potential, the formation of 1 (I)-CO restricts the electrocatalysis due to the endergonicity of the CO release step. In agreement with the experimentally observed CO2-to-CO electrocatalysis at the Co I/0 redox potential, computational studies suggested that the electrocatalytic cycle involves striking metal carbonyls. In contrast, under photochemical conditions, the catalysis smoothly proceeds at the 1 (II/I) redox potential. Under the latter conditions, it is proposed that the electron transfer to form 1 (I)-CO from 1 (II)-CO is under diffusion control. Then, the CO release from 1 (II)-CO is kinetically favored, facilitating the catalysis. Finally, we have found that visible-light irradiation has a positive impact under electrocatalytic conditions. We envision that light-irradiation can serve as an effective strategy to circumvent the CO poisoning and improve the performance of CO2 reduction molecular catalysts. 1750 1950 2050 2150 Wavenumber (cm-1) Co I-CO Co 0-CO Co II-CO Theoretical 43 cm-1 Experimental under CO 2 Experimental under CO 1910 cm-1 44 cm-1 [L N4 Co I-CO] +

A dual catalytic system based on earth-abundant elements reduces aromatic ketones and aldehydes to alcohols in aqueous media under visible light. An unprecedented selectivity for the reduction of aromatic ketones versus aliphatic aldehydes is reported.

Ni‐deposited mesoporous graphitic carbon nitride (Ni‐mpg‐CNx) is introduced as an inexpensive, robust, easily synthesizable and recyclable material that functions as an integrated dual photocatalytic system. This material overcomes the need of expensive photosensitizers, organic ligands and additives as well as limitations of catalyst deactivation in the existing photo/Ni dual catalytic cross‐coupling reactions. The dual catalytic Ni‐mpg‐CNx is demonstrated for C–O coupling between aryl halides and aliphatic alcohols under mild condition. The reaction affords the ether product in good‐to‐excellent yields (60–92 %) with broad substrate scope, including heteroaryl and aryl halides bearing electron‐withdrawing, ‐donating and neutral groups. The heterogeneous Ni‐mpg‐CNx can be easily recovered from the reaction mixture and reused over multiple cycles without loss of activity. The findings highlight exciting opportunities for dual catalysis promoted by a fully heterogeneous system.

The nature of the oxidizing species in water oxidation reactions with chemical oxidants catalyzed by α-[Fe(OTf)2(mcp)] (mcp = N, N′-dimethyl-N,N′-bis(pyridin-2-ylmethyl)cyclohexane-1,2-diamine, OTf = trifluoromethanesulfonate anion), (1α) and β-[Fe(OTf)2(mcp)], (1β) has been investigated. Mössbauer spectroscopy provides definitive evidence that 1α and 1β generate oxoiron(IV) species as the resting state. Decomposition paths of the catalysts have been investigated by identifying and quantifying ligand fragments that form upon degradation. This analysis correlates the water oxidation activity of 1α and 1β with stability against oxidative damage of the ligand via aliphatic C-H oxidation. The site of degradation and the relative stability against oxidative degradation is shown to be dependent on the topology of the catalyst. Furthermore, the mechanisms of catalyst degradation have been rationalized by computational analyses, which also explain why the topology of the catalyst enforces different oxidation sensitive sites. This information has served for creating catalysts where sensitive C-H bonds have been replaced by C-D bonds. Deuterated analogs, D4-α-[Fe(OTf)2(mcp)] (D4-1α), D4-β-[Fe(OTf)2(mcp)] (D4-1β) and D6-β-[Fe(OTf)2(mcp)] (D6-1β) were prepared, and their catalytic activity has been studied. D4-1α proves to be an extraordinarily active and efficient catalyst (up to 91% of O2 yield); it exhibits initial reaction rates identical to its protio analogue, but it is substantially more robust towards oxidative degradation and yields more than 3400 TON (n(O2)/n(Fe)). Altogether evidence that the water oxidation catalytic activity is performed by a well-defined coordination complex and not by iron oxides formed after oxidative degradation of the ligands.

Chemical recycling of synthetic polymers represents a promising strategy to deconstruct plastic waste and make valuable products. Inspired by small-molecule C–H bond activation, a visible-light-driven reaction is developed to deconstruct polystyrene (PS) into ∼40% benzoic acid as well as ∼20% other monomeric aromatic products at 50 °C and ambient pressure. The practicality of this strategy is demonstrated by deconstruction of real-world PS foam on a gram scale. The reaction is proposed to proceed via a C–H bond oxidation pathway, which is supported by theoretical calculations and experimental results. Fluorescence quenching experiments also support efficient electron transfer between the photocatalyst and the polymer substrate, providing further evidence for the proposed mechanism. This study introduces concepts from small-molecule catalysis to polymer deconstruction and provides a promising method to tackle the global crisis of plastic pollution.

The synthesis of primary anilines via sustainable methods remains a challenge in organic synthesis. We report a photocatalytic protocol for the selective synthesis of primary anilines via cross‐coupling of a wide range of aryl/heteroaryl halides with sodium azide using a photocatalyst powder consisting of nickel(II) deposited on mesoporous carbon nitride (Ni‐mpg‐CNx). This heterogeneous photocatalyst contains a high surface area with a visible light‐absorbing and adaptive “built‐in” solid‐state ligand for the integrated catalytic Ni site. The method displays a high functional group tolerance, requires mild reaction conditions, and benefits from easy recovery and reuse of the photocatalyst powder. Thereby, it overcomes the need of complex ligand scaffolds required in homogeneous catalysis, precious metals and elevated temperatures/pressures in existing protocols of primary anilines synthesis. The reported heterogeneous Ni‐mpg‐CNx holds potential for applications in the academic and industrial synthesis of anilines and exploration of other photocatalytic transformations.

Semiartificial approaches to renewable fuel synthesis exploit the integration of enzymes with synthetic materials for kinetically efficient fuel production. Here, a CO 2 reductase, formate dehydrogenase (FDH) from Desulfovibrio vulgaris Hildenborough, is interfaced with carbon nanotubes (CNTs) and amorphous carbon dots ( a -CDs). Each carbon substrate, tailored for electro- and photocatalysis, is functionalized with positive (−NHMe 2 + ) and negative (−COO – ) chemical surface groups to understand and optimize the electrostatic effect of protein association and orientation on CO 2 reduction. Immobilization of FDH on positively charged CNT electrodes results in efficient and reversible electrochemical CO 2 reduction via direct electron transfer with >90% Faradaic efficiency and −250 μA cm –2 at −0.6 V vs SHE (pH 6.7 and 25 °C) for formate production. In contrast, negatively charged CNTs only result in marginal currents with immobilized FDH. Quartz crystal microbalance analysis and attenuated total reflection infrared spectroscopy confirm the high binding affinity of active FDH to CNTs. FDH has subsequently been coupled to a -CDs, where the benefits of the positive charge (−NHMe 2 + -terminated a -CDs) were translated to a functional CD-FDH hybrid photocatalyst. High rates of photocatalytic CO 2 reduction (turnover frequency: 3.5 × 10 3 h –1 ; AM 1.5G) with dl -dithiothreitol as the sacrificial electron donor were obtained after 6 h, providing benchmark rates for homogeneous photocatalytic CO 2 reduction with metal-free light absorbers. This work provides a rational basis to understand interfacial surface/enzyme interactions at electrodes and photosensitizers to guide improvements with catalytic biohybrid materials.