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Efficiently generating C1 building blocks from environmentally friendly carbon sources, such as through photocatalytic CO2 reduction, is essential for fostering a sustainable circular economy. The pursuit of mild catalytic activation methods has yielded powerful catalysts that can be synergistically employed alongside various reaction media to enhance overall performance. Herein, we elucidate the influence of diverse imidazolium‐based ionic liquids as additives for visible‐light‐driven CO2 reduction with ruthenium(II)‐ and rhenium(I)‐bipyridine complexes. Our investigation reveals that incorporating ionic liquids into traditional solvents at concentrations below 10 % can markedly boost CO production while suppressing H2 generation. The best results were obtained for the highly basic ionic liquid [C2mim][OAc], resulting in a substantial rise in CO formation from 0.3 μmol/h to 5.4 μmol/h and an increase in turnover number from 3 to 59. This study underscores the cooperative influence of imidazolium‐based ionic liquids on CO2 photoreduction while circumventing their use as primary solvents, thus offering a promising avenue for sustainable chemical synthesis. [ABSTRACT FROM AUTHOR]

Thermal treatments can have detrimental effects on the photocatalytic hydrogen (H2) evolution performance and impact the formation mechanism of the active state of surface‐supported co‐catalysts. In this work, a range of Ni‐based co‐catalysts is investigated immobilized on TiO2, evaluated their H2 evolution rates in situ over 21 h, and analyzed the samples at various stages with a comprehensive set of spectroscopic and microscopy techniques. It is found that achieving the optimal hydrogen evolution (HER) performance requires the right Ni0:Ni2+ ratio, rather than only Ni0, and that Ni needs to be weakly adsorbed on the TiO2 surface to create a dynamic state. Under these conditions, Ni can undergo an efficient redox shuttle, involving the transformation of Ni2+ to Ni0 and back after releasing the accumulated electrons for H+ reduction (i.e., Ni2+ ↔ Ni0). Yet, when the calcination temperature of the Ni/TiO2 photocatalysts increases, resulting in stronger coordination/adsorption of Ni on TiO2, this process is gradually inhibited, which ultimately leads to decreased HER performances. This work emphasizes the significance and influence of thermal treatments on the Ni active state formation – a process that can be relevant to other HER co‐catalysts. [ABSTRACT FROM AUTHOR]

Metal‐organic frameworks (MOFs) are promising materials for photocatalytic water splitting reactions, but examples of visible light‐responsive, catalytically active, and stable MOFs are still rare. A detailed investigation is conducted for COK‐47 – a recently described MOF comprising 2D Ti‐O6 secondary building units (SBUs) – toward a photocatalytic hydrogen evolution reaction (HER), showing how overall particle morphology, surface area, and missing ligand defects are central parameters governing the material's ultimate performance. The newly synthesized COK‐47ISO is among the most active MOFs to date, yielding HER‐rates of 8.6 µmol h−1, and an apparent quantum yield (AQY) of 0.5% under visible light illumination. Optoelectronic and photoluminescence investigations, supported by theoretical calculations, enable the unraveling of its electronic structure along with charge transfer and recombination kinetics. A wavelength‐dependent reaction mechanism is proposed involving ligand to metal charge transfer (LMCT) and the main challenges for visible or UV photoexcitation are identified, demonstrating that the unique 2D layered structure aids charge separation and is key to the high performance. This work introduces COK‐47 as a promising alternative to the well‐known MIL‐125 family and offers directions for future studies [ABSTRACT FROM AUTHOR]

Laterally large (≈3 µm), atomically thin 2D Bi2O2CO3 nanosheets (2D bismuth oxycarbonate, 2D bismutite) are fabricated via sonochemically assisted, template‐free synthesis. Keys to the synthesis of the freestanding, laterally large 2D Bi2O2CO3 nanosheets from bulk Bi powder are choice of suspension medium, controlled reaction temperatures, and several hours processing time. Lateral sizes of 2D Bi2O2CO3 can be controlled between µm‐sized nanosheets and tens of nm sized nanoflakes solely based on the choice of suspension medium. The here introduced 2D Bi2O2CO3 nano‐sheets/‐flakes are then hybridized by a simple mix‐and‐match approach with TiO2 nanoparticles for testing in suspension‐type photocatalytic hydrogen production via water splitting. This introduces the 2D Bi2O2CO3 as a prospective noble‐metal‐free catalyst component with TiO2 for photocatalytic hydrogen evolution, beyond Bi2O2CO3's current use as photocatalyst for organic pollutant degradation. These results enrich the fabrication toolbox of emerging 2D pnictogen oxycarbonates toward large 2D nanosheets and demonstrate the potential of 2D Bi2O2CO3 as a catalyst component for hydrogen evolution in photocatalytic water splitting. [ABSTRACT FROM AUTHOR]

Metal-organic frameworks (MOFs) are commended as photocatalysts for H2 evolution and CO2 reduction as they combine light-harvesting and catalytic functions with excellent reactant adsorption capabilities. For dynamic processes in liquid phase, the accessibility of active sites becomes a critical parameter as reactant diffusion is limited by the inherently small micropores. Our strategy is to introduce additional mesopores by selectively removing one ligand in mixed-ligand MOFs via thermolysis. Here we report photoactive MOFs of the MIL-125-Ti family with two distinct mesopore architectures resembling either large cavities or branching fractures. The ligand removal is highly selective and follows a 2-step process tunable by temperature and time. The introduction of mesopores and the associated formation of new active sites have improved the HER rates of the MOFs by up to 500%. We envision that this strategy will allow the purposeful engineering of hierarchical MOFs and advance their applicability in environmental and energy technologies. While metal organic frameworks offer highly tunable materials for photocatalytic applications, catalytic site accessibility is a crucial parameter. Here, authors demonstrate selective ligand removal to introduce new active sites and mesopores and to enhance photocatalytic H2 evolution. [ABSTRACT FROM AUTHOR]

Abstract: Nanocarbon–metal oxide hybrids are among the most promising functional materials in many cutting‐edge environmental and energy applications where efficient charge separation and extraction are keys to success. The next level of hybrid structures will be achieved once one learns how to control and tune charge/energy transfer processes at the interfaces. However, little is yet known about the nature and extent of these interfacial dynamics in nanocarbon hybrids. Here a model is designed in which ultrathin dielectric layers (Al2O3, ZrO2) between the hybrid's components (ZnO, TiO2) and carbon nanotubes allow for evaluating and tuning of interfacial charge transfer over an unusually long distance of at least 50 nm. Surprisingly, the transfer efficiency correlates linearly with the barrier layer thickness, indicating that electron conduction through the barrier layer constitutes the rate‐limiting step. It is also demonstrated that the charge transfer efficiency can be tuned by the type of interlayer and its degree of crystallinity, thus controlling the hybrid's performance in the photocatalytic production of hydrogen. It is believed that this model system will help to understand and decipher the fundamentals regarding interfacial charge and energy transfer in nanocarbon hybrids with the aim to further advance these hybrid structures for a wide range of energy applications. [ABSTRACT FROM AUTHOR]

Abstract: We investigate how residual catalyst from carbon nanotube (CNT) templates can be used to engineer novel functional nanomaterials. CNTs, produced via continuous flow chemical vapour deposition, typically contain catalyst residues in the form of encapsulated metal clusters or of iron oxide nanoparticles attached to the outside of the CNTs. These CNTs are used as sacrificial templates for TiO2 coatings using benzyl alcohol as a linking agent. Upon oxidation of the CNTs, the encapsulated iron particles dissolve into the TiO2 lattice and form iron-doped TiO2 nanotubes without the formation of secondary phases, while the iron oxide particles merely attach to the outer surface. The materials show extended light absorption into the visible range, a requirement for visible-light photocatalyst. [Copyright &y& Elsevier]

Single-crystalline sillenite-type bismuth titanate nanowires with photocatalytic properties have been synthesized viaa simple solution-phase synthesis route. [ABSTRACT FROM AUTHOR]

Pure and Nb‐doped TiO2 photocatalysts with highly ordered alternating gyroid architecture and well‐controllable mesopore size of 15 nm via co‐assembly of a poly(isoprene)‐block‐poly(styrene)‐block‐poly(ethylene oxide) block copolymer are synthesized. A combined effort by electron microscopy, X‐ray scattering, photoluminescence, X‐ray photoelectron spectroscopy, Raman spectroscopy, and density functional theory simulations reveals that the addition of small amounts of Nb results in the substitution of Ti4+ with isolated Nb5+ species that introduces inter‐bandgap states, while at high concentrations, Nb prefers to cluster forming shallow trap states within the conduction band minimum of TiO2. The gyroidal photocatalysts are remarkably active toward hydrogen evolution under UV and visible light due to the open 3D network, where large mesopores ensure efficient pore diffusion and high photon harvesting. The gyroids yield unprecedented high evolution rates beyond 1000 µmol h−1 (per 10 mg catalyst), outperforming even the benchmark P25‐TiO2 more than fivefold. Under UV light, the Nb‐doping reduces the activity due to the introduction of charge recombination centers, while the activity in the visible triple upon incorporation is owed to a more efficient absorption due to inter‐bandgap states. This unique pore architecture may further offer hitherto undiscovered optical benefits to photocatalysis, related to chiral and metamaterial‐like behavior, which will stimulate further studies focusing on novel light–matter interactions. Superior hydrogen evolution is achieved by using highly ordered mesoporous pure and Nb‐doped TiO2 with alternating gyroid architecture due to their large pores and 3D connectivity. The incorporation of Nb5+ has different effects on visible and UV‐based photocatalysis. [ABSTRACT FROM AUTHOR]

Recently, carbon spherogels have been introduced as a novel monolithic aerogel composed of hollow spheres. This material is conveniently obtained via polystyrene (PS) sphere templating. In the present study, we apply a water-soluble titania precursor (titanium(IV) bis(ammonium lactate) to the aqueous sol-gel synthesis based on resorcinol-formaldehyde (RF) to effectively encapsulate titania. In this way, a very high mass loading of up to 59 mass% of titania can be confined strictly to the inside of the hollow carbon spheres. In the final synthesis step, carbonization at 800 °C has three simultaneous effects: Transformation of the RF coating on PS into microporous carbon, PS template removal by decomposition, and formation of titania due to precursor dissociation. A deliberate tuning of the microporous carbon shell, accessibility of the titania, titania amount, and titania's polymorph is further demonstrated by thermal treatment under a carbon dioxide atmosphere. In contrast to non-tuned or TiC-containing carbon spherogels, CO 2 activation of the composites results in a three orders of magnitude rise of their photocatalytic activity towards hydrogen evolution reaction, which we evaluate using flow and batch reactors. We further show that this effect is related to the partial etching of the carbon shell, which renders the TiO 2 surface accessible to the reactants in the solution and allows for an efficient hole scavenging. Given the simplicity of the hybrid carbon spherogel (HCS) composite fabrication, the high degree of control of their morphological characteristics, and the striking effects of CO 2 -activation on performance, we believe that our results will contribute to the development of similar carbon-inorganic composites. [Display omitted] [ABSTRACT FROM AUTHOR]

We demonstrate a unique route towards hierarchical assemblies of mesoporous TiO 2 and CNT/TiO 2 photocatalysts by a combination of electrospinning and sol–gel methods. The resulting materials exhibit a mesoporous network of highly crystalline, well-connected inorganic nanocrystals with an order of magnitude higher photocatalytic activity than individualised TiO 2 nanoparticles. The in-situ combination of small amounts of MWCNTs with TiO 2 to form an electrospun CNT/TiO 2 hybrid further enhanced the oxide photoactivity considerably, reaching hydrogen evolution rates of 1218 μmol/h in water splitting in the presence of sacrificial reagents under UV irradiation. We also discuss the effect of oxygen vacancies on the oxide crystallisation and phase transformation. These vacancies lead to inter-bandgap states and a lower flat band potential that facilitates the photocatalytic process. [ABSTRACT FROM AUTHOR]

Abstract: Hybridizing carbon nanotubes with complex inorganic nanostructures provides a new route to designing next-generation photocatalysts. These hybrids utilize charge transfer processes through the interface, which reduce the electron–hole recombination rate in the photocatalyst. This work presents the first complex CNT hybrid, using titanium-silicate (TS-1), with dramatically improved photocatalytic activity for the degradation of organic compounds compared with the corresponding nanocomposite and the individual components. [ABSTRACT FROM AUTHOR]

• We unravelled the impact of ligand composition on photocatalytic hydrogen evolution over Ti-based MOFs. • MIL-125-Ti outperforms NH2-containing counterparts by up to 38 times in methanol • Photoluminescence spectroscopy shows effective hole scavenging by methanol in MIL-125-Ti. • Triethanolamine leads to corrosion of the MOFs within the first few hours through partial ligand exchange. • We propose three mechanisms for photocatalytic hydrogen evolution for both single-ligand and mixed-ligand MOFs. We synthesized a series of isostructural MIL-125-Ti with various terephthalic: amino-terephthalic acid ratios and evaluated their photostability and performance for photocatalytic hydrogen evolution in aqueous solutions with different hole scavengers. We demonstrate that the commonly used triethanolamine corroded the MOFs under photocatalytic conditions, in contrast to methanol. The combination of MIL-125-Ti and methanol outperformed the photocatalytic activity of NH 2 -MIL-125-Ti by 45 times under broad UV irradiation. Photoluminescence spectroscopy under simulated photocatalytic conditions and in solid-state as well as time-resolved emission studies reveal that the holes residing in the metal-oxo cluster can be effectively scavenged by methanol, leading to high HER activity, while the holes residing in the NH 2 -groups in the ligand favour charge recombination and are thus detrimental to the photocatalytic performance. The mixed-ligand MOFs follow a dual-excitation pathway, introducing new states and transitions. These results are expected to advance our understanding of MOF-based photocatalysis. [ABSTRACT FROM AUTHOR]