One of the alternatives to decrease CO2 emissions at the atmosphere is carbon capture and utilization. In this context, selective catalytic hydrogenation of CO2 is one of the possibilities being considered, since it is assumed that green hydrogen will be widely available, for instance, from water electrolysis. Among the various products that can be obtained in this process, long chain hydrocarbons and alcohols are the products with the highest economic value. While, reverse water gas shift can convert CO2 into CO and, in a second step, methanol synthesis or Fischer-Tropsch synthesis can produce alcohols through mature technologies, this is a two-step process that consumes considerable energy and it could be more advantageous the direct selective hydrogenation of CO2 to methanol.

Within this context, our group has been working on the photocatalytic CO2 hydrogenation using a variety of photocatalysts based on supported metal nanoparticles. Depending on the support, the process can be either photothermal, or it can be photocatalytic through a charge separated state or a combination of the two. However, all the cases the products formed are CH4 or CO. However, using certain photocatalysts and adjusting the reaction conditions it has been possible to obtain photocatalytically mixtures of methanol and formic acid. Their formation has been firmly confirmed by isotopic 13C label experiments recording 1H NMR spectroscopy, in which the singlets corresponding to the H-C bonds in both chemicals become splitting with a JC-H coupling constant in accordance with the C atomic hybridization. Figure 1 shows some of these 1H NMR spectra. The final goal is the use of natural sunlight to promote the photocatalytic CO2 reduction to methanol in a way that could be economically competitive with the thermo catalytic process.

The transformation of lignocellulosic biomass, an abundant, renewable, and underutilized resource, into energy-relevant molecules is a key objective in the pursuit of a sustainable energy transition. Among the promising routes, hydrogen emerges as a clean energy carrier with strong potential. Yet, most current hydrogen is still produced via fossil-fuel-based reforming, emitting CO₂ and requiring high energy input (~60 MJ/kg H₂), thus limiting its environmental benefits.

To overcome these challenges, research has turned toward catalytic hydrogen production involving water. However, water electrolysis remains energy-intensive (~50–55 MJ/kg) and economically uncompetitive. Integrating solar energy into hydrogen production is a promising strategy. Since the pioneering work of Fujishima and Honda using TiO₂ [1], solar-assisted water splitting has been extensively studied. Nevertheless, its widespread application remains constrained by the UV absorption limitation of most semiconductors and the sluggish kinetics of the four-electron water oxidation process, which suffers from fast charge recombination. These limitations can be alleviated through the use of sacrificial electron donors.

Carbohydrates, constituting 70–85% of plant biomass as cellulose and hemicellulose, are abundant and renewable substrates. Many saccharide-rich by-products from agro-industries remain unvalorized and represent promising feedstocks. We have previously demonstrated that mono- and oligosaccharides can serve as efficient sacrificial agents for photocatalytic hydrogen production using Au/SC materials under simulated solar illumination [2]. Their oxidation not only accelerates charge separation but also enables theoretical yields up to 12 mol H₂ per mole of glucose, surpassing conventional methane reforming. Moreover, this photocatalytic transformation of sugars can concurrently generate bio-based platform chemicals of high interest for various sectors such as cosmetics, detergents, and pharmaceuticals, thereby enhancing the overall economic and environmental value of the process.

In this work, we present the synthesis, structural and electronic characterization of Au/SC photocatalysts, and their performance in photo-reforming various carbohydrate substrates. The impact of key parameters (pH, substrate concentration, light intensity, catalyst composition) on H₂ evolution will be discussed. Finally, a mechanistic proposal based on experimental insights will be outlined, shedding light on the interplay between photocatalyst properties and reaction pathways.

Background and motivation

What lies beyond photocatalysis? Light-driven chemical reactions prompted by photogenerated carriers on semiconductors’ surfaces are extensively studied,[1,2] yet the role of photons in directly reshaping materials remains largely untapped. Therefore, increasing attention has been recently paid to understanding how photoinduced redox processes can lead to structural and compositional modifications of materials themselves. Such investigations not only open new pathways for mitigating photodegradation but also offer promising strategies for the light-triggered synthesis of composite materials under conditions “orthogonal” to their functional application. In this context, bismuth oxides have emerged as ideal candidates due to their tunable properties and rich redox chemistry, which favour the formation of diverse Bi-based composites.[3]

Here, we demonstrate that light can be harnessed to directly modify bismuth oxide (Bi₂O₃), yielding a complex composite that integrates (BiO)₂CO₃ nanosheets alongside PbO₂ nanoparticles. Furthermore, light also plays a pivotal role in triggering the composite’s reactivity, yielding intermediate non-hydroxyl radicals which can effectively degrade phenol.

Materials and methods

Bi₂O₃ microrods were obtained according to literature protocols.[3] These microrods were dispersed in bidistilled water, and the suspension was placed in a quartz reactor hosting a jacketed 450 W medium-pressure Hg lamp. The illumination in the presence of a continuous flow of 10 mL min^–1 of CO₂ yielded the composite Bi₂O₃/(BiO)₂CO₃ (“BBc”). PbO₂ was, in turn, photodeposited on the materials with or without (BiO)₂CO₃ by adding Pb(NO₃)₂ as precursor (yielding respectively the composites “BBcPb” and “BPb”) and keeping the suspension under oxygen-reduced conditions by Ar bubbling (20 mL min^–1). The sample “BBcBx” has also been synthesized for comparison by irradiating BBc under an inert atmosphere in the absence of Pb(NO₃)₂.
 

Results and discussion

A wide set of composite semiconductors was obtained through this light-mediated route. The formation of (BiO)₂CO₃ nanosheets was observed as a consequence of the intercalation of CO₂ into the photogenerated defective (BiO)₂²⁺ surface states. On the contrary, the presence of PbO₂ stimulated the epitaxial formation of Bi₂O_4–x nanoprisms, which contributed to increasing the surface area. These features have been confirmed through ex-situ high-resolution SEM and TEM images on the material sampled at precise time intervals.

Moreover, the Bi₂O₃ microrods functionalized with (BiO)₂CO₃ nanosheets and PbO₂ (“BBcPb”) exhibited the highest activity in the photocatalytic generation of ethanol-based radicals, which, in turn, attack and degrade phenol. Mechanistic investigations have been carried out to prove the importance of the presence of ethanol as radical mediator.

Thus, our findings highlight the transformative power of photons – not just as catalysts’ activators but as architects of functional materials.

The sustainable synthesis of fuels and chemicals using sunlight as driving force and simple readily available feedstock such as H₂O and waste CO₂ provides a potential feasible pathway to mitigate increasing CO₂ emissions and transitioning toward a greener chemical industry. In this context, natural photosynthesis is a source of inspiration and has led to the evolving and multidisciplinary field of artificial photosynthesis (AP).^[1-4]

In this regard, when designing bioinspired photocatalytic platforms for AP, the role of natural membranes -in the compartmentalization and separation of the redox half reactions involved in natural photosynthesis-, is sometimes overlooked. Our research group is currently working towards studying this key structural factor of natural photosynthesis.^[4] We are working in the development of polymeric microphotoreactors functionalized with (photo)catalysts to produce solar fuels and chemicals. Our ultimate goal is to drive the electrons from the oxidation of water to the reduction of CO₂-to-Carbon-based fuels and chemicals in aqueous media using solar energy as driving force.^[5] As such, we have developed a novel family of asymmetric porphyrin and phthalocyanine complexes bearing Co, Ni, and Fe as 1^st row transition metal centers for photocatalytic CO₂ reduction in combination with Ir-, Cu-based photosensitizers and organic dyes, under visible light irradiation (447 nm) in aqueous-organic mixtures in presence of a sacrificial electron donor.^[5-6] The Co and Fe phthalocyanine complexes show a remarkable photocatalytic activity and selectivity for photocatalytic CO₂ reduction to CO (up to 2600 TON CO with 88% selectivity) in homogeneous conditions, even with 10% of water. In contrast, the porphyrin complexes show remarkable activity and selectivity for methane production in organic mixtures. Moreover, to further explore the applicability and increase the stability of these systems, we have anchored them onto the membrane of polymeric vesicles, developing the first polymersome for compartmentalized photocatalytic CO₂ reduction.^[6] The effect of anchoring and the nature of the photosensitizer used allows to tune the selectivity of the photocatalytic reaction to obtain only CO₂ reduction derived products in water, suppressing the normally competing hydrogen evolution reaction. Mechanistic studies are ongoing to rationalize these differences in reactivity between homogeneous and heterogenized systems.

References

[1] Das Neves Gomes C., et al. Angew. Chem. Int. Ed. 2012, 51, 187-190.

[2] Boutin E., et al. Chem. Soc. Rev. 2020, 49, 5772-5809.

[3] Pannwitz A., et al. Chem. Soc. Rev. 2021, 50, 4833-4855.

[4] L. Velasco-Garcia, C. Casadevall. Commun. Chem. 2023, 6:263

[5] E. J. Espinoza-Suárez, A. Bekaliyev, A. Vital-Grappin, L. Velasco-Garcia, L. Subirats-Valls, C. Casadevall. Manuscript under revisions.                                                                            

[6] L. Velasco-Garcia, K. Nassif, A. Bekaliyev, E. J. Espinoza-Suarez, C. Casadevall. Manuscript in preparation.

Two-dimensional materials in the carbon nitride family have recently garnered attention for their ability
to function as photocatalysts under visible light. However, their application as thin films have been
limited due to poor coating homogeneity. We have developed an innovative chemical vapor deposition
(CVD) method that enables the deposition of carbon nitride thin films with tuneable thickness and high
uniformity.1 The conformal nature of these CVD-grown films allows integration into microfluidic
reactors, where they demonstrate superior performance in the photocatalytic oxidation of benzylic
alcohols under flow conditions.2 Furthermore, the homogeneity of the films facilitates the use of
advanced spectroscopic techniques—including NMR, XPS, and XAS—for in-operando analysis of
photocatalytic reaction mechanisms. Using in-operando XPS and XAS, we explored the mechanism of
photocatalytic water splitting, uncovering the crucial role of surface interactions, particularly the
formation of hydrogen bonds with water, in activating the carbon nitride surface. Upon illumination we
were able to confirm the evolution of hydrogen and oxygen while the spectroscopic features recorded
support the proton-coupled electron transfer (PCET) mechanism. These insights provide a fundamental
understanding of one of the most extensively studied reactions of the past decade, both experimentally
and theoretically. Although the use of thin films in energy conversion is still emerging, our work
highlights their potential to drive significant progress in photocatalysis, photoelectrocatalysis, and
beyond.
Keywords: carbon nitride, thin films, artificial photosynthesis, water splitting

Heterogeneous photocatalytic processes suffer from instability when operated for reasonable reaction times, under illumination, and significant deterioration in performance is usually observed. To circumvent some of the main issues causing this decline in activity, arising from reduced light absorption, dispersibility issues, and agglomeration, owing to temporal changes in the electrostatic interactions between individual photocatalyst particles, flow reactions over stable photocatalyst panels are developed. Importantly, to enable such configuration for practical applications, a stable connection between the photocatalyst and the substrate must remain intact under reaction conditions (illumination, flow, heat, in situ generated reactive species, and so forth). Most current methodologies use various forms of binders to maintain a stable attachment of the photocatalyst to the substrate. We have developed a simple method to enhance their photocatalytic stability significantly using a binder-free approach. This method is highly versatile in terms of the photocatalyst used and the plastic substrate nature (on the condition the plastic has a thermoplastic component). Generally, by means of physical adhesion on plastic panels. We embed the photocatalyst onto the surface of various plastics that serve as the support (substrate) via a partial melting process. As a demonstration, we use a variety of plastic supports, such as Polypropylene (PP), Ethylene vinyl-acetate (EVA), Poly (methyl methacrylate) (PMMA), Low-density Polyethylene (LDPE), and High-density polyethylene (HDPE), to deposit various photocatalysts (e.g., Bi2O3, ZnO, WO3, TiO2, and polymeric carbon nitride (CN)). In this work, we show CN|HDPE panels as a case study. CN materials are environmentally friendly1 and are active for ORR2, HER, and other organic conversions. With this method, we were able to achieve stable photocatalytic hydrogen evolution reaction (HER) activity with an average of ~4.18 mmol h^–1 m^–2 for more than 21 weeks on a single panel. This implies the possibility of significantly improving the stability of many heterogeneous photocatalytic processes with a simple method while using harmful plastic waste instead of disposing of the plastics by incineration or landfilling, which cause air and soil pollution, respectively.

A major challenge in solar fuels is to identify and control the multiple factors that determine the efficiency of the light-driven molecular transformation under realistic operating conditions. In semiconductor photoelectrodes such as hematite, recombination and trapping of photogenerated charge carriers compete with their transport to the electrode-electrolyte interface, thereby limiting overall conversion efficiency. While these processes have been studied at microscopic spatial scales [1] or ultrafast temporal timescales [2], their simultaneous investigation remains largely underexplored. In particular, direct characterization of carrier transport is missing. Despite carrier diffusion length being a critical parameter in the calculation of photo(electro)chemical efficiency, it is rarely known.

Transient reflectance microscopy [3, 4] has emerged as a powerful method to spatiotemporally resolve the lifetime, transport, and diffusion length of photogenerated charges in a wide range of photoactive materials. This presentation will describe the development of this method to study hematite photoelectrodes under water oxidation conditions. I will discuss recent results that quantify how these carrier transport metrics are affected under applied bias.

The conversion of solar energy into chemical energy through photoelectrochemical (PEC) water splitting is a promising approach to decarbonize the energy sector and mitigate the associated environmental and geopolitical problems, producing green hydrogen with zero carbon footprint. However, to ensure its commercial viability and industrial deployment, it is essential to achieve high solar-to-hydrogen (STH) conversion efficiency and long-term stability of tandem devices. Bismuth vanadate (BiVO₄) has been considered an excellent material as photoanode in this type of devices. Nonetheless, addressing issues related to its severe charge recombination is mandatory, and the incorporation of hole transport layers (HTL) for effective charge separation can mitigate this problem. Finding HTL materials with suitable band structures for BiVO₄ and uniform coating on the nanostructure represent a significant challenge.

In this context, our group has optimized the electrochemical deposition of a conjugated polycarbazole (p-CBZ) acting as HTL. The performance of these hybrid photoanodes for water splitting showed a two-fold increased photocurrent (from 0.87 to 1.91 mA·cm^-2 at 1.23 V vs. Reversible Hydrogen Electrode (RHE)) when the p-CBZ layer is deposited. Moreover, an outstanding six times improvement of the photocurrent density is achieved when a NiOOH co-catalyst is deposited,^[1] reaching 5.5 mA·cm^-2 at 1.23 V vs. RHE. Moreover, the stability of the photoanode was improved, demonstrating a near cero loss of photocurrent for more than 70 hours of operation under continuous illumination.

The direct coupling of light harvesting and charge storage in a single material opens new avenues to light storing devices. Here we demonstrate the decoupling of light and dark reactions in the two-dimensional layered niobium tungstate (TBA)⁺(NbWO₆)⁻ for on-demand hydrogen evolution and solar battery energy storage [1]. Light illumination drives Li⁺/H⁺ photointercalation into the (TBA)⁺(NbWO₆)⁻ photoanode, leading to small polaron formation assisted by structural distortions on the WO_x sublattice, along with a light-induced decrease in material resistance over 2 orders of magnitude compared to the dark. The photogenerated electrons can be extracted on demand to produce solar hydrogen upon the addition of a Pt catalyst. Alternatively, they can be stored for over 20 h under oxygen-free conditions after 365 nm UV illumination for only 10 min, thus featuring a solar battery anode with promising capacity and long-term stability. The optoionic effects described herein offer new insights to overcome the intermittency of solar irradiation, while inspiring applications at the interface of solar energy conversion and energy storage, including solar batteries, “dark” photocatalysis, solar battolyzers, and photomemory devices.

In a world that is running out of natural resources, there is a growing need to design and develop sustainable and green energy resources. In that respect, photo-electrocatalytically driven reactions for the production of alternative fuels (such as water splitting or CO₂ reduction) hold the potential to provide a route for future carbon neutral energy economy. Nevertheless, the slow kinetics of those catalytic reactions demands the development of efficient catalysts in order to drive it at lower overpotentials. Indeed, a variety of molecular catalysts based on metal complexes are capable of electrochemically reducing CO₂ and/or protons. Yet, despite the significant progress in this field, practical realization of molecular catalysts will have to involve a simple and robust way to assemble high concentration of these catalysts in an ordered, reactant-accessible fashion onto a conductive electrode. 

Our group utilizes Metal-Organic Frameworks (MOFs) based materials as a platform for heterogenizing molecular electrocatalysts. Their unique properties (porosity and flexible chemical functionality), enables us to use MOFs for integrating all the different functional elements needed for efficient catalysts: 1) immobilization of molecular catalysts, 2) electron transport elements, 3) mass transport channels, and 4) modulation of catalyst secondary environment. Thus, in essence, MOFs could possess all of the functional ingredients of a catalytic enzyme.  

In this talk, I will present our recent study on (photo)-electrocatalytically active MOFs incorporating molecular catalysts for solar fuel reactions.

The global challenges of climate change and energy availability demand urgent solutions to reduce our dependence on fossil fuels and promote clean, renewable energy alternatives. Among emerging technologies, (photo)electrocatalysis stands out as a promising pathway to produce sustainable fuels and chemicals with minimal environmental impact, supporting the shift toward a low-carbon future.[1]

This presentation focuses on our recent efforts on the development of bismuth vanadate (BiVO₄) as a photoanode material for solar-driven oxidation reactions. BiVO₄ offers multiple advantages—it is composed of relatively Earth-abundant elements, has chemical stability, favorable electronic properties for charge separation, and remains cost-effective. Nevertheless, its practical application is hindered by intrinsic limitations, including sluggish water oxidation kinetics, rapid charge recombination, low charge carrier mobility, and limited carrier diffusion lengths (~70 nm).[2]

To overcome these challenges, we introduce nanostructuring strategies that significantly enhance the material’s performance.[4-5] By integrating organic hole transport layers and catalytic coatings to form efficient heterostructures, we achieve improved activity and long-term stability. Importantly, these enhancements are compatible with scalable production methods: we demonstrate a continuous flow-synthesis approach for fabricating large-area photoelectrodes (up to 50 cm²) with competitive performance.[3] A central aspect of our research is gaining mechanistic insight. Using a suite of spectroscopic techniques, we probe charge carrier dynamics and interfacial processes, revealing the factors that govern device behavior and identifying pathways for further optimization.[6]

Direct solar conversion of abundant reactants in photoelectrochemical devices offers a promising pathway for producing clean fuels and chemicals. Achieving high efficiency and long-term stability in these systems demands innovative strategies that build on advances in mature fields such as photovoltaics and electrocatalysis. This presentation highlights recent progress in integrating halide perovskite- and organic bulk heterojunction-based photovoltaic devices with electrocatalytic sheets to develop high-performance photoelectrodes for solar fuel and chemical production. For example, we demonstrate CsPbBr₃-based photoanodes delivering stable photocurrents >6 mA cm⁻² at 1.23 V vs. RHE, and organic bulk heterojunction photoanodes (e.g., PM6/PTQ10 blends) achieving photocurrents of 25 mA cm^-2 or over 5% unassisted solar-to-hydrogen efficiency in tandem configurations. Electrocatalytic sheets composed of carbon allotropes (graphite, glassy carbon, boron-doped diamond) and Ni- or NiFeOOH-based catalysts enable efficient oxygen evolution, while confined Pt catalysts support hydrogen evolution at photocathodes. Minimizing voltage losses and optimizing charge injection into electrolytes are critical to drive solar fuel and chemical production. Our characterization studies underscore key strengths of these devices, including strong solar absorption and substantial photovoltage generation, pointing to new opportunities for unassisted solar chemical synthesis.

We present a photochemical oxidation strategy for the spatially controlled deposition of crystalline rhodium oxide (RhO_x) co-catalysts on CdSe@CdS nanorods (SRs). Mechanistic investigations reveal that key reaction parameters - including pH, excitation wavelength, and electron acceptor identity - critically govern the site-selective heterogeneous nucleation of RhO_x. Systematic tuning of these parameters during the photo-oxidative deposition process enables precise modulation of charge carrier dynamics within the semiconductor heterostructure. In particular, control over the directionality and density of photogenerated electron–hole pairs allow deterministic growth of Rh₃O₄ nanoparticles, yielding tunable co-catalyst architectures ranging from single-domain to multi-domain configurations. The refined synthetic protocol provides precise control over nanoparticle morphology, spatial positioning, and surface coverage, enabling the engineered formation of well-defined RhO_x-SR interfaces through selective surface oxidation. These tailored heterojunctions exhibit optimized interfacial charge transfer kinetics and represent a significant advancement toward the rational design of efficient photocatalysts for overall water splitting. Such precise interfacial control is crucial for maximizing photocatalytic activity, accelerating the development of next-generation solar-to-fuel conversion technologies.

A single photon in the UV-vis range of the electromagnetic spectrum carries 2–4 eV of energy. Upon absorption of such a photon, graphitic carbon nitride converts this energy into a potential difference that can drive the generation of a radical or radical ion from an organic molecule through one-electron reduction or oxidation, or hydrogen atom abstraction. Radicals and radical ions are more reactive than their parent organic molecules. Therefore, these species generally react without an energy barrier with suitable reactants. Based on ten years of research, this lecture covers two major aspects:

1) It provides an overview of the structural features of graphitic carbon nitrides that can be employed to design new organic reactions and improve the quantum yield of known ones.[1],[2]

2) It offers concise guidelines on how to choose the “right” organic precursors to synthesize target products.[3]

A speaker will also share his experience in popularization of photocatalysis through video gaming.

Nowadays, one of the main challenges our society is facing is the mitigation and reverse of climate change. For this purpose, we must use and store renewable energy to be used as fuels, electricity or to produce fine chemicals. One of the most attractive alternatives is the use of sunlight to drive these processes given that the energy coming from the sun to Earth in one hour, if fully harnessed, is enough to energetically sustain the whole planet for a full year. In this context, using sunlight to drive redox transformations is a promising technology to decarbonize transportation, heating and fine chemicals sectors.

Sunlight driven processes are complex since they involve several steps that need to take place simultaneously in a harmoniously and synchronized manner. Firstly, the light, with the right energy, is absorbed by promoting electrons from the highest occupied energetic level (valence band in semiconductors) to the lowest unoccupied one (conduction band in semiconductors), generating oxidative equivalents (holes). These charges are accumulated to the surface/electrolyte interface, and holes are used to oxidise a substrate and the electrons will either be used to reduce protons, CO₂ to generate carbon-based products or N₂ to generate NH₃. When the oxidative reaction is water oxidation, this is the bottleneck of the whole solar- driven process.[1] Some approaches consider the possibility of substituting this demanding process for an organic molecule oxidation, which can be energetically less demanding and potentially also producing added value compounds.[2–3]

In this talk I will present different photo(electro)chemical systems containing catalysts to carry out different catalytic oxidative transformations (water oxidation and glycerol oxidation). Through different system designs and study of the limiting factors, different key point for more efficient and active photo(electro)catalysts will be discussed.

Bismuth oxide (Bi₂O₃) represents a promising photocatalytic material owing to its favorable optical properties and exceptional chemical stability under operational conditions. Notably, Bi₂O₃ exhibits rich polymorphism with four distinct crystal phases, making it uniquely suited for materials design strategies. Selective control over Bi₂O₃ polymorphism provides a powerful materials design approach for tuning optical and electronic properties in photocatalytic applications. While the thermodynamically stable monoclinic α-phase (Eg = 2.8 eV) dominates under conventional conductive/convective heating (furnace annealing), the metastable tetragonal β-phase exhibits superior photocatalytic properties with its reduced bandgap of 2.4 eV, enabling enhanced visible light harvesting. However, accessing β-Bi₂O₃ through conventional thermal pathways (α→δ at ~730°C, δ→β upon cooling at 645-650°C) faces significant challenges for practical applications. These high-temperature requirements are incompatible with temperature-sensitive substrates, such as fluorine-doped tin oxide (FTO), which degrades above ~550°C, and may also be problematic for nanostructured materials and thin films, where the thermal behavior can differ significantly from that of bulk systems.

We demonstrate Flash Photonic Heating (FPH) as a transformative radiative heating technique that overcomes substrate thermal limitations while enabling the selective control of Bi₂O₃ polymorphs. FPH employs millisecond white light radiative pulses with ultra-rapid heating rates (10⁶-10⁷ °C/s) to induce the α-to-β phase transformation in Bi₂O₃ films deposited on FTO substrates, circumventing conventional thermal constraints. X-ray diffraction analysis confirmed successful β-phase formation, while optical absorption and surface photovoltage (SPV) spectroscopy revealed distinct characteristics consistent with the α-to-β transformation and the narrower bandgap of β-Bi₂O₃. Notably, the substrate integrity was maintained throughout the process, demonstrating the compatibility of this approach with device-relevant architectures.

This work establishes FPH as a rapid, substrate-compatible, and scalable method for accessing metastable semiconductor phases through radiative heating. The ability to selectively stabilize β-Bi₂O₃ demonstrates a broader paradigm for structural fine-tuning at the atomic level, where precise control over crystal phases can dramatically alter optoelectronic properties. This approach opens new avenues for developing high-performance photocatalytic materials with designer properties tailored for advanced catalytic materials design in light-driven chemical transformations.

Concerning levels of CO2 in the atmosphere have urged researchers to develop technologies that can not only reduce its atmospheric concentration, but also use CO2 as a feedstock for producing carbon-based fuels and value-added chemicals. Solar irradiation, a renewable and abundant source of energy, can be used to drive these chemical transformations in a process known as artificial photosynthesis [1]. Recently, porous materials, such as covalent organic frameworks (COFs), have been explored as photo-responsive supports for catalysts due to their remarkable physical and chemical stability, structural diversity and large surface areas [2]. Furthermore, through careful selection of building blocks, a wider photo-absorption window can be targeted, while also tuning the bandgap to extend the lifetime of electron-hole pair separation, thus establishing a thermodynamically favourable process [3].

The incorporation of metal catalysts, such as metal nanoparticles (MNPs), into these types of organic, photo-active supports creates a hybrid material which can facilitate redox reactions; electrons excited within the framework can be accepted by the MNP and subsequently used to carry out CO2 reduction. MNPs are widely used for catalysis due to their high surface energy and quantum size effects; particularly, gold nanoparticles (Au NPs) are highly selective towards CO2 reduction to CO. However, their aggregation can result in gradual loss of catalytic activity, therefore uniformly immobilising them on light-harvesting, porous supports is effective in extending their photocatalytic performance. Additionally, RuO2 NPs are impregnated into the remaining COF pores to help retain photogenerated holes and facilitating the oxidation of water; RuO2 NPs possess excellent affinity toward O2 gas with a favourable O2 binding energy, low overpotential, and high OER activity.

In this work, a photo-absorbing porphyrin-perylene COF has been decorated with Au NP and RuO2 NPs, thus creating a novel, robust material for the purpose of artificial photosynthesis. The COF was functionalised with thiol groups to assist in localisation and stabilisation of the Au NPs, resulting in the formation of well-distributed and locally separated NPs anchored into the COF network. The size of the Au NPs has been modulated by adjusting the concentration of gold salt precursor vs. the number of thiol ligands. Previously synthesised RuO2 nanoparticles were incorporated into the COF unoccupied pores to produce the final MNP-COF hybrid material. NPs size effect and metal loading concentration have been evaluated to enhance the material performance. Results of their photocatalytic efficiency for the simultaneous photocatalytic CO2 reduction and water oxidation under visible light irradiation will be presented.