Photocatalytic H₂ generation by water splitting is a promising alternative for producing renewable fuels. This work synthesized a new type of Ta₂O₅/SrZrO₃ heterostructure with Ru and Cu (RuO₂/Cu_xO/Ta₂O₅/SrZrO₃) using solid-state chemistry methods to achieve a high H₂ production of 5164 μmol g^-1 h^-1 under simulated solar light, 39 times higher than that produced using SrZrO₃. The heterostructure performance is compared with other Ta₂O₅/SrZrO₃ heterostructure compositions loaded with RuO₂, Cu_xO, or Pt. Cu_xO is used to showcase the usage of less costly cocatalysts to produce H₂. The photocatalytic activity toward H₂ by the RuO₂/Cu_xO/Ta₂O₅/SrZrO₃ heterostructure remains the highest, followed by RuO₂/Ta₂O₅/SrZrO₃ > Cu_xO/Ta₂O₅/SrZrO₃ > Pt/Ta₂O₅/SrZrO₃ > Ta₂O₅/SrZrO₃ > SrZrO₃. Band gap tunability and high optical absorbance in the visible region are more prominent for the heterostructures containing cocatalysts (RuO₂ or Cu_xO) and are even higher for the binary catalyst (RuO₂/Cu_xO). The presence of the binary catalyst is observed to impact the charge carrier transport in Ta₂O₅/SrZrO₃, improving the solar to hydrogen conversion efficiency. The results represent a valuable contribution to the design of SrZrO₃-based heterostructures for photocatalytic H₂ production by solar water splitting.

This work proposes a novel approach to immobilize the lead-free bismuth halide perovskite Cs₃Bi₂I₉ in mica and cellular porous concrete supports. The perovskites were evaluated as visible-light active photocatalysts in the CO₂ reduction to generate HCOOH with high energy conversion efficiencies. The approach ensured the material’s stability exposed to an aqueous medium under visible light irradiation. According to the results, the Cs₃Bi₂I₉ particles exhibited a different morphology depending on the support used; its growth on mica favored the formation of well-defined hexagonal particles. Meanwhile, the porous concrete favored the formation of needle-like particles. Also, the optical characterization indicated that when the Cs₃Bi₂I₉ particles grew as a thin film, their surface energy seemed higher, favoring the formation of layered structures related to the lattice defects. On the other hand, the concrete cellular offers a porous interconnected network, an excellent medium to encapsulate the Cs₃Bi₂I₉ particles. These properties favored the formation of 2,570 µmol of HCOOH in the steady state with an energy conversion efficiency of up to 24.3%, which is higher than the required value to scale up the process. The analysis of the perovskite after the reaction revealed that the sample maintains its properties, and it shows the growth of flake-like particles on top of hexagonal particles, which eventually participate in the photocatalytic reaction. Also, it was demonstrated that the approach implemented here favored high thermal stability of the Cs₃Bi₂I₉ perovskite.

Introduction: One of the main environmental problems is air pollution due to high CO ₂ emissions, a greenhouse gas that contributes to climate change because of the excessive use of fossil fuels. For this reason, CO ₂ reduction emerges as a promising solution by converting it into renewable fuels using sunlight and advanced semiconductor materials. Recently, hybrid systems based on artificial leaves composed of lead-free halide perovskites and porous support materials have been demonstrated to be highly efficient for CO ₂ reduction. In addition, the recycling and utilization of natural sources such as the brown algae, considered a plague in the Caribbean, represents an additional advantage for the pollution reduction, carbon sequestration, and social and economic impacts. Methods: This research proposes an innovative solution to address this environmental problem by demonstrating that hybrid systems based on bismuth halide perovskites (K ₃ Bi ₂ I ₉ ) and brown algae-functionalized clay biosupports are promising for the reduction of CO ₂ with high efficiencies for formic acid production (2.5 mmol h ^-1 ) under visible light. The content of the brown algae was investigated to find the best load that promotes higher and stable CO ₂ reduction efficiencies. Results: The presence of the brown algae enhanced light absorption by its chlorophyll, provided free electrons to the semiconductor and highly reactive species (•OH), that favored the formation of C1-C3 products, e.g., HCOOH, CH ₃ COOH, and CH ₃ (CH ₂ ) ₂ OH, with efficiencies in the order of >1 mmol. In addition, the stability of the hybrid systems was demonstrated after five hours of continuous visible light irradiation in liquid phase, which analysis of the medium showed a minimal leaching of potassium. Discussion: The addition of 5 wt.% brown algae in the clays promoted both high efficiency and stability of the hybrid system by preventing cracking, while promoting a porous framework that maintained effective CO ₂ adsorption. This enhanced effect was attributed to efficient perovskite encapsulation and the presence of chlorophyll (from algae) acting as an electron donor, enhancing light absorption and charge transfer. This synergistic effect enabled efficient CO ₂ conversions to C ₁ –C ₃ value-added products. In conclusion, this work demonstrated that the utilization of abundant natural materials such as clays and sargassum supports an ecological and scalable approach while addressing global and local environmental problems.