The Importance of the Macroscopic Geometry in Gas-Phase Photocatalysis

Construction of manganese ferrite/zinc ferrite anchored graphene-based hierarchical aerogel photocatalysts following Z-scheme electron transfer for visible-light-driven carbon dioxide reduction

Herein, atomic-level interfacial coupling between spinel-type MnFe2O4 (MFA) and ZnFe2O4 (ZFA) was achieved via a sol-gel method combined with phase separation. These composites were then anchored onto a three-dimensional graphene aerogel (GA) through ethylenediamine-assisted hydrothermal self-assembly, forming a hierarchically porous MFA/ZFA@GA with a high surface area (191.06 m2/g). The optimized MFA/ZFA@GA exhibited a CO production rate of 21.14 μmol·g-1·h-1 (96 % selectivity, 94 % stability) under visible light, a 3.87-fold enhancement over single-component systems. The in-situ MFA/ZFA heterojunction and graphene-enhanced electron transfer synergistically prolonged photogenerated electron lifetime by 10 times. The hierarchical pores also boosted CO2 adsorption (7.66 wt%), the appreciable saturation magnetization intensity (37.49 emu/g) enabled magnetic separation recovery, and *COOH monitoring confirmed rapid desorption kinetics for high CO selectivity. Experiments combined with theoretical calculations revealed a Z-scheme mechanism: MnFe2O4's reductive electrons (-0.79 V vs. NHE) drove CO2 reduction, while ZnFe2O4's oxidative holes (1.50 V vs. NHE) facilitated H2O oxidation. Strategic integration of heterostructures, carbon hybridization, and aerogel architectures offered an efficient pathway for monolithic photocatalyst design.

Mechanical and Light Activation of Materials for Chemical Production

Mechanical expansion and contraction of pores within photosynthetic organisms regulate a series of processes that are necessary to manage light absorption, control gas exchange, and regulate water loss. These pores, known as stoma, allow the plant to maximize photosynthetic output depending on environmental conditions such as light intensity, humidity, and temperature by actively changing the size of the stomal opening. Despite advances in artificial photosynthetic systems, little is known about the effect of such mechanical actuation in synthetic materials where chemical reactions occur. It is reported here on a hybrid hydrogel that combines light-activated supramolecular polymers for superoxide production with thermal mechanical actuation of a covalent polymer. Superoxide production is important in organic synthesis and environmental remediation, and is a potential precursor to hydrogen peroxide liquid fuel. It is shown that the closing of pores in the hybrid hydrogel results in a substantial decrease in photocatalysis, but cycles of swollen and contracted states enhance photocatalysis. The observations motivate the development of biomimetic photosynthetic materials that integrate large scale motion and chemical reactions.

Direct air capture of CO2 for solar fuel production in flow

Direct air capture is an emerging technology to decrease atmospheric CO2 levels, but it is currently costly and the long-term consequences of CO2 storage are uncertain. An alternative approach is to utilize atmospheric CO2 on-site to produce value-added renewable fuels, but current CO2 utilization technologies predominantly require a concentrated CO2 feed or high temperature. Here we report a gas-phase dual-bed direct air carbon capture and utilization flow reactor that produces syngas (CO + H2) through on-site utilization of air-captured CO2 using light without requiring high temperature or pressure. The reactor consists of a bed of solid silica-amine adsorbent to capture aerobic CO2 and produce CO2-free air; concentrated light is used to release the captured CO2 and convert it to syngas over a bed of a silica/alumina-titania-cobalt bis(terpyridine) molecular-semiconductor photocatalyst. We use the oxidation of depolymerized poly(ethylene terephthalate) plastics as the counter-reaction. We envision this technology to operate in a diurnal fashion where CO2 is captured during night-time and converted to syngas under concentrated sunlight during the day.

Crystal-Defect-Induced Longer Lifetime of Excited States in a Metal-Organic Framework Photocatalyst to Enhance Visible-Light-Mediated CO2 Reduction

We report the structural defects in Zr-metal-organic framework (MOFs) for achieving highly efficient CO2 reduction under visible light irradiation. A series of defective Zr-MOF-X (X = 160, 240, 320, or 400) are synthesized by acid-regulated defect engineering. Compared to pristine defect-free Zr-MOF (NNU-28), N2 uptake increases for Zr-MOF-X synthesized with the HAc modulator, producing a larger pore space and Brunauer-Emmett-Teller surface area. The pore size distribution demonstrates that defective Zr-MOF-X exhibits mesoporous structures. Electrochemistry tests show that defective Zr-MOF-X possesses a more negative reduction potential and a higher photocurrent responsive signal than that of pristine NNU-28. Consequently, the defective samples exhibit a significantly higher efficiency in the photoreduction of CO2 to formate. Transient absorption spectroscopies manifest that structural defects modulate the excited-state behivior of Zr-MOF-X and improve the photogenerated charge separation of Zr-MOF-X. Furthermore, electron paramagnetic resonance and in-suit X-ray photoelectron spectroscopy provide additional evidence of the high photocatalytic performance exhibited by defective Zr-MOF-X. Results demonstrate that structural defects in Zr-MOF-X also improve the charge transfer, producing abundant Zr(III) catalytically active sites, exhibiting a slower decay process than defect-free Zr-MOF. The long-lifetime Zr(III) species in defective Zr-MOF-X are fully exposed to a high-concentration CO2 atmosphere, thereby enhancing the photocatalytic efficiency of CO2 reduction.

A Versatile Synthesis Platform Based on Polymer Cubosomes for a Library of Highly Ordered Nanoporous Metal Oxides Particles

Polymer cubosomes (PCs) have well-defined inverse bicontinuous cubic mesophases formed by amphiphilic block copolymer bilayers. The open hydrophilic channels, large periods, and robust physical properties of PCs are advantageous to many host-guest interactions and yet not fully exploited, especially in the fields of functional nanomaterials. Here, the self-assembly of poly(ethylene oxide)-block-polystyrene block copolymers is systematically investigated and a series of robust PCs is developed via a cosolvent method. Ordered nanoporous metal oxide particles are obtained by selectively filling the hydrophilic channels of PCs via an impregnation strategy, followed by a two-step thermal treatment. Based on this versatile PC platform, the general synthesis of a library of ordered porous particles with different pore structures3 ¯ $\bar{3}$ 3 ¯ $\bar{3}$ , tunable large pore size (18-78 nm), high specific surface areas (up to 123.3 m2 g-1 for WO3) and diverse framework compositions, such as transition and non-transition metal oxides, rare earth chloride oxides, perovskite, pyrochlore, and high-entropy metal oxides is demonstrated. As typical materials obtained via this method, ordered porous WO3 particles have the advantages of open continuous structure and semiconducting properties, thus showing superior gas sensing performances toward hydrogen sulfide.

Unraveling the Impact of Curvature on Electrocatalytic Performance of Carbon Materials: A State-of-the-Art Review

Curvature of carbon materials has gained significant attention as catalysts due to their distinctive properties and potential applications. This review comprehensively summarizes how the bending of carbon materials can improve electrocatalytic performance, with special attention to the applications of various bent carbon materials (such as carbon nanotubes, graphene, and fullerene) in electrocatalysts and a large number of related density functional theory (DFT) theoretical calculations. Extensive mechanism research has provided a wealth of evidence indicating that the curvature of carbon materials has a profound impact on catalytic activity. This improvement in catalytic performance by curved carbon materials is attributed to factors like a larger active surface area, modulation of electronic structure, and better dispersal of catalytic active sites. A comprehensive understanding and utilization of these effects enable the design of highly efficient carbon-based catalysts for applications in energy conversion, environmental remediation, and chemical synthesis.

Leave No Photon Behind: Artificial Intelligence in Multiscale Physics of Photocatalyst and Photoreactor Design

Although solar fuels photocatalysis offers the promise of converting carbon dioxide directly with sunlight as commercially scalable solutions have remained elusive over the past few decades, despite significant advancements in photocatalysis band-gap engineering and atomic site activity. The primary challenge lies not in the discovery of new catalyst materials, which are abundant, but in overcoming the bottlenecks related to material-photoreactor synergy. These factors include achieving photogeneration and charge-carrier recombination at reactive sites, utilizing high mass transfer efficiency supports, maximizing solar collection, and achieving uniform light distribution within a reactor. Addressing this multi-dimensional problem necessitates harnessing machine learning techniques to analyze real-world data from photoreactors and material properties. In this perspective, the challenges are outlined associated with each bottleneck factor, review relevant data analysis studies, and assess the requirements for developing a comprehensive solution that can unlock the full potential of solar fuels photocatalysis technology. Physics-informed machine learning (or Physics Neural Networks) may be the key to advancing this important area from disparate data towards optimal reactor solutions.

Optimization of Mass and Light Transport in Nanoparticle-Based Titania Aerogels

Aerogels composed of preformed titania nanocrystals exhibit a large surface area, open porosity, and high crystallinity, making these materials appealing for applications in gas-phase photocatalysis. Recent studies on nanoparticle-based titania aerogels have mainly focused on optimizing their composition to improve photocatalytic performance. Little attention has been paid to modification at the microstructural level to control fundamental properties such as gas permeability and light transmittance, although these features are of fundamental importance, especially for photocatalysts of macroscopic size. In this study, we systematically control the porosity and transparency of titania gels and aerogels by adjusting the particle loading and nonsolvent fraction during the gelation step. Mass transport and light transport were assessed by gas permeability and light attenuation measurements, and the results were related to the microstructure determined by gas sorption analysis and scanning electron microscopy. Mass transport through the aerogel network was found to proceed primarily via Knudsen diffusion leading to relatively low permeabilities in the range of 10-5-10-6 m2/s, despite very high porosities of 96-99%. While permeability was found to depend mainly on particle loading, the optical properties are predominantly affected by the amount of nonsolvent during gelation, allowing independent tuning of mass and light transport.

Atomic Aerogel Materials (or Single-Atom Aerogels): An Interesting New Paradigm in Materials Science and Catalysis Science

The concept of "single-atom catalysis" is first proposed by Tao Zhang, Jun Li, and Jingyue Liu in 2011. Single-atom catalysts (SACs) have a very high catalytic activity and greatly improved atom utilization ratio. At present, SACs have become frontier materials in the field of catalysis. Aerogels are highly porous materials with extremely low density and extremely high porosity. These pores play a key role in determining their surface reactivity and mechanical stability. The alliance of SACs and aerogels can fully reflect their structural advantages and lead to new enhancement effects. Herein, a general concept of "atomic aerogel materials" (AAMs) (or single-atom aerogels (SAAs)) is proposed to describe this interesting new paradigm in both material and catalysis fields. Based on the basic units of "gel," the AAMs can be divided into two categories: carrier-level AAMs (with micro-, nano-, or sub-nanometer pore structures) and atomic-level AAMs (with atomic-defective or oxygen-bridged sub-nanopore structures). The basic unit of the former (i.e., single-atom-functionalized aerogels) is the carrier materials in nanostructures, and the latter (i.e., single-atom-built aerogels) is the single metal atoms in atomic structures. The atomic-defective or oxygen-bridged AAMs will be important development directions in versatile heterogeneous catalytic or noncatalytic fields. The design proposals, latent challenges, and coping strategies of this new "atomic nanosystem" in applications are pointed out as well.

Designing Highly Photoactive Hybrid Aerogels for In-Flow Photocatalytic Contaminant Removal Using Silica-Coated Bacterial Nanocellulose Supports

This study explores the use of silica-coated bacterial nanocellulose (BC) scaffolds with bulk macroscopic yet nanometric internal pores/structures as functional supports for high surface area titania aerogel photocatalysts to design flexible, self-standing, porous, and recyclable BC@SiO₂-TiO₂ hybrid organic-inorganic aerogel membranes for effective in-flow photo-assisted removal of organic pollutants. The hybrid aerogels were prepared by sequential sol-gel deposition of the SiO₂ layer over BC, followed by coating of the resulting BC@SiO₂ membranes with a porous titania aerogel overlayer of high surface area using epoxide-driven gelation, hydrothermal crystallization, and subsequent supercritical drying. The silica interlayer between the nanocellulose biopolymer scaffold and the titania photocatalyst was found to greatly influence the structure and composition, particularly the TiO₂ loading, of the prepared hybrid aerogel membranes, allowing the development of photochemically stable aerogel materials with increased surface area/pore volume and higher photocatalytic activity. The optimized BC@SiO₂-TiO₂ hybrid aerogel showed up to 12 times faster in-flow photocatalytic removal of methylene blue dye from aqueous solution in comparison with bare BC/TiO₂ aerogels and outperformed most of the supported-titania materials reported earlier. Moreover, the developed hybrid aerogels were successfully employed to remove sertraline drug, a model emergent contaminant, from aqueous solution, thus further demonstrating their potential for water purification.

Architected Metal Selenides via Sequential Cation and Anion Exchange on Self-Organizing Nanocomposites

Shape-preserving conversion reactions have the potential to unlock new routes for self-organization of complex three-dimensional (3D) nanomaterials with advanced functionalities. Specifically, developing such conversion routes toward shape-controlled metal selenides is of interest due to their photocatalytic properties and because these metal selenides can undergo further conversion reactions toward a wide range of other functional chemical compositions. Here, we present a strategy toward metal selenides with controllable 3D architectures using a two-step self-organization/conversion approach. First, we steer the coprecipitation of barium carbonate nanocrystals and silica into nanocomposites with controllable 3D shapes. Second, using a sequential exchange of cations and anions, we completely convert the chemical composition of the nanocrystals into cadmium selenide (CdSe) while preserving the initial shape of the nanocomposites. These architected CdSe structures can undergo further conversion reactions toward other metal selenides, which we demonstrate by developing a shape-preserving cation exchange toward silver selenide. Moreover, our conversion strategy can readily be extended to convert calcium carbonate biominerals into metal selenide semiconductors. Hence, the here-presented self-assembly/conversion strategy opens exciting possibilities toward customizable metal selenides with complex user-defined 3D shapes.

In-situelectrochemical fabrication of Ag@AgCl NW-PET film with superior photocatalytic bactericidal activity

Constructing a composite photocatalyst with efficient charge-transfer pathways is contribute to improving charge separation, which has attracted wide attention owing to its availability in photocatalysis applications. In this work, three-dimensional (3D) silver@silver chloride (Ag@AgCl) network structures are fabricated for photocatalytic inactivation ofEscherichia coli(E. coli) by thein situelectrochemical introducing AgCl shell on the surface of Ag nanowire (NW) networks that are coated on a polyethylene terephthalate (PET) substrate. The obtained Ag@AgCl NW-PET films exhibit good photocatalytic bactericidal activity againstE. coliunder simulated Sunlight irradiation, mainly due to their efficient charge-transport channel constructed by the Ag NWs network. It is worth noting that the content of converted AgCl shell is positively correlated with their photocatalytic bactericidal efficiency. The experimental results also demonstrate that the synergistic contribution of Ag⁺sustained release, rough surfaces and energy band structure optimization in photocatalytic sterilization. Besides, the prepared Ag@AgCl NW-PET film can be recycled, and the photocatalytic sterilization efficiency can still keep above 99% after three cycles. This work might provide new and more diverse opportunities for the development of excellent charge-transport, recyclable photocatalysts for photocatalytic sterilization.

The solvent-free mechano-chemical grinding of a bifunctional P25-graphene oxide adsorbent-photocatalyst and its configuration as porous beads

Owing to their use in water-cleaning technology, titanium-dioxide-based nanomaterials have dominated the photocatalysis scene, with so-called Degussa (P25) being the most promising under UV light. However, this is not the case under visible light, where it is necessary to combine titanium dioxide with other photosensitising nanomaterials. Unfortunately, most of the strategies aimed in this direction are chemically non-facile, energy-intensive, economically expensive, and not suitable for large-scale production. We herein describe a straightforward solvent-free approach for accessing visible-light-activated titanium-dioxide-based photocatalysts via the mechanochemical grinding of Degussa P25 with a second solid partner. Upon comparing several solid-material benchmarks, P25-graphene oxide is the best combination. The resulting material showed efficient performance for the adsorption and photodegradation of different dye pollutants, namely methylene blue, malachite green, Congo red, and methyl orange. The recorded performance was nearly comparable to that reached using sol-gel materials, with the ultimate advantage of being more sustainable and industrially scalable. The recyclability can be improved through a porous-bead configuration using biomass waste chitosan hydrogel, an approach that can further fulfill the requirement for more sustainable photocatalyst designs.