Hollow Multishelled Structured SrTiO3 with La/Rh Co-Doping for Enhanced Photocatalytic Water Splitting under Visible Light

Sight into a Rare-Earth-Based Catalyst with Spatial Confinement Effect from the Perspective of Electronic Structure

Rare-earth elements include 15 kinds of lanthanides as well as Sc and Y elements. Interestingly, the special electronic configuration of a lanthanide rare earth is [Xe]4fn5d0-16s2 (n = 0-14), which results in rare-earth materials' unique activity in such areas as thermal catalysis, electrocatalysis, photocatalysis, etc. It is worth noting that a class of materials with spatial confinement effects are playing an increasingly important role in the catalytic performance; especially, the construction of hollow multishelled structures (HoMSs) can further enhance the activity of rare-earth catalytic materials. In this review, we discuss in depth the important roles of the rare-earth 4f5d electronic structure. Subsequently, this review systematically summarizes the synthesis methods of rare-earth HoMSs and their research progress in the field of catalysis and specifically introduces the advanced characterization and analysis methods of rare-earth HoMSs. Finally, the research directions, application prospects, and challenges that need to be focused on in the future of rare-earth-based HoMSs are discussed and anticipated. We believe that this review will not only inspire more creativity in optimizing the local electronic structure and spatial confinement structure design of rare-earth-based catalysts but also provide valuable insights for designing other types of catalysts.

Simultaneous Structural and Electronic Engineering on Bi- and Rh-co-doped SrTiO3 for Promoting Photocatalytic Water Splitting

Activating metal ion-doped oxides as visible-light-responsive photocatalysts requires intricate structural and electronic engineering, a task with inherent challenges. In this study, we employed a solid (template)-molten (dopants) reaction to synthesize Bi- and Rh-codoped SrTiO3 (SrTiO3 : Bi,Rh) particles. Our investigation reveals that SrTiO3 : Bi,Rh manifests as single-crystalline particles in a core (undoped)/shell (doped) structure. Furthermore, it exhibits a well-stabilized Rh3+ energy state for visible-light response without introducing undesirable trapping states. This precisely engineered structure and electronic configuration promoted the generation of high-concentration and long-lived free electrons, as well as facilitated their transfer to cocatalysts for H2 evolution. Impressively, SrTiO3 : Bi,Rh achieved an exceptional apparent quantum yield (AQY) of 18.9 % at 420 nm, setting a new benchmark among Rh-doped-based SrTiO3 materials. Furthermore, when integrated into an all-solid-state Z-Scheme system with Mo-doped BiVO4 and reduced graphene oxide, SrTiO3 : Bi,Rh enabled water splitting with an AQY of 7.1 % at 420 nm. This work underscores the significance of simultaneous structural and electronic engineering and introduces the solid-molten reaction as a viable approach for this purpose.

Recent progress in doping engineering of perovskite oxides for photocatalytic green hydrogen production via water splitting

Given the immense potential for addressing energy and environmental issues, the utilization of solar energy for hydrogen production by water splitting (WS) has garnered widespread attention in the scientific community. Perovskite oxides (POs), with their compositional flexibility and structural stability, hold significant promise in the photocatalytic hydrogen evolution reaction (HER). Rational doping of POs is the key to enhancing the rate of the photocatalytic HER. In this review, with the aim of providing guidance for the enhancement of photocatalytic efficiency, the recent advancements in ion-doping engineering of PO-based photocatalysts are summarized. The principles of photocatalytic WS, the preparation methods of ion-doped POs, the types of dopants, and the effects of doping on the photocatalytic performance of the HER are systematically reviewed and discussed. Background and advances in practical applications are further elaborated. Ultimately, prospects and challenges of the doped POs for the photocatalytic HER are proposed. This review provides a good reference for making informed decisions regarding the selection of doped ions and a valuable suggestion for establishing high-stability photocatalytic systems toward large-scale applications.

Solar Fuel Synthesis Using a Semiartificial Colloidal Z-Scheme

The integration of enzymes with semiconductor light absorbers in semiartificial photosynthetic assemblies offers an emerging strategy for solar fuel production. However, such colloidal biohybrid systems rely currently on sacrificial reagents, and semiconductor-enzyme powder systems that couple fuel production to water oxidation are therefore needed to mimic an overall photosynthetic reaction. Here, we present a Z-scheme colloidal enzyme system that produces fuel with electrons sourced from water. This "closed-cycle" semiartificial approach utilizes particulate SrTiO3:La,Rh and BiVO4:Mo (light absorbers), hydrogenase or formate dehydrogenase (cocatalyst), and a molecular cobalt complex (a redox mediator). Under simulated solar irradiation, this system continuously generates molecular hydrogen or formate, while co-producing molecular oxygen for 10 h using only sunlight, water, and carbon dioxide as inputs. In-depth analysis using quartz crystal microbalance, photoelectrochemical impedance spectroscopy, transient photocurrent spectroscopy, and intensity-modulated photovoltage spectroscopy provides mechanistic understanding and characterization of the semiconductor-enzyme hybrid interface. This study provides a rational platform to assemble functional semiartificial colloidal Z-scheme systems for solar fuel synthesis.

Enhanced Ionic Power Generation via Light-Driven Active Ion Transport Across 2D Semiconductor Heterostructures

2D semiconductor heterostructures exhibit broad application prospects. However, regular nanochannels of heterostructures rarely caught the researcher's attention. Herein, a metal-organic framework (i.e., Cu3(HHTP)2) and transition metal dichalcogenides (i.e., MoS2)-based multilayer van der Waals heterostructure (i.e., Cu3(HHTP)2/MoS2) realized band alignment-dominated light-driven ion transport and further light-enhanced ionic energy generation. High-density channels of the heterostructure provide high-speed pathways for ion transmembrane transport. Upon light illumination, a net ionic flow occurs at a symmetric concentration, suggesting a directional cationic transport from Cu3(HHTP)2 to MoS2. This is because Cu3(HHTP)2/MoS2 heterostructures containing type-II band alignment can generate photovoltaic motive force through light-induced efficient charge separation to drive ion transport. After introducing into the ionic power generation system, the maximum power density under illumination can achieve notable improvement under different concentration differences. In addition to the photovoltaic motive force, type-II band alignment and material defect capture-induced surface charge increase also raise ion selectivity and flux, greatly facilitating ionic energy generation. This work demonstrates that 2D semiconductor heterostructures with rational band alignment can not only be a potential platform for optimizing light-enhanced ionic energy harvesting but also provide a new thought for biomimetic iontronic devices.

Pore walls as high-way for efficient bulk charge transfer in porous SrTiO3 single crystals boosting photocatalytic overall water splitting

Suppressing carrier recombination in bulk and facilitating carrier transfer to surface via rational structure design is of great significance to improve solar-to-H2 conversion efficiency. We demonstrate a facile hydrothermal method to synthesize porous SrTiO3 single crystals (SrTiO3-P) with exposed (001) facets by introducing carbon spheres as templates. The obviously increased surface photovoltage and photocurrent response indicate that the interconnected pore walls act as enormous charge transfer "highways", accelerating carrier transport from bulk to surface. Furthermore, the absence of grain boundaries and high crystallinity could also lower the carrier recombination rate. Thus, the SrTiO3-P photocatalyst loaded with Rh/Cr2O3 as cocatalyst exhibits 1.5 times higher overall water splitting activity than that of solid SrTiO3, with gas evolution rate of 19.99 μmol h-1 50 mg-1 for H2 and 11.37 μmol h-1 50 mg-1 for O2. Additionally, SrTiO3-P also shows superior stability without any decay during cycling testing. This work provides a new insight into designing efficient multicomponent photocatalysts with a single-crystal porous structure.

Enhanced Photocatalytic Water Splitting of SrTiO3 Perovskite through Cobalt Doping: Experimental and Theoretical DFT Understanding

Throughout extensive research endeavors, SrTiO3 has emerged as a promising photocatalytic material for utilizing solar energy and facilitating hydrogen production via water splitting. Yet, the pursuit of enhanced efficiency and amplified hydrogen generation has prompted researchers to delve into the realm of advanced doping strategies. In this work, using experimental characteristics and DFT calculations, we studied the effect of cobalt substitution on the structural, electronic, optical, and magnetic properties as well as the photocatalytic activity of SrTi1-xCoxO3-δ (x = 0, 0.125, 0.25, 0.375, and 0.5) perovskites. The samples were successfully prepared by using the solid-state reaction method. Based on X-ray diffraction and the Rietveld refinement method, the elaborated samples were shown to preserve the absorption range up to the visible region. Moreover, the position of band edge levels after cobalt doping becomes more appropriate for water splitting. Our findings report that all cobalt-doped compounds exhibit good photocatalytic activities and could be used as suitable photocatalyst materials for hydrogen production.

Defect-Enriched Hollow Porous Carbon Nanocages Enable Highly Efficient Chlorine Evolution Reaction

Metal-free carbon-based catalysts are crucial for the electrocatalytic chlorine evolution reaction (CER) to reduce the usage of noble metals and industrial cost. However, the corresponding catalytic activity of high overpotential and low durability hinders their wide application. Here, a hollow porous carbon (HPC) nanocage with a controlled oxygen electronic state around designed carbon defects for CER activity is reported. Alkali etching can bring defects in zeolite with a hollow structure. In a hard template strategy, the type of carbon defects is directly related to etching degree of the zeolite template. More importantly, the oxygen atoms can be "borrowed" from the zeolite framework by the defective carbon. The electron density around unsaturated O atoms can be decreased on the minor defects in carbon compared with that on large defects which is favorable for the adsorption of Cl^- . Consequently, the as-synthesized HPC nanocages with minor defects show excellent electrocatalytic performance for CER with a low overpotential of 94 mV at current density of 10 mA cm^-2 with good stability, which is superior to the commercial precious metal catalyst of dimensionally stable anode (DSA), and the best in the reported carbon materials. The designed carbon materials provide an option for metal-free industrial catalysts with significant CER activities.

The Construction of Phosphorus-Doped g-C3N4/Rh-Doped SrTiO3 with Type-II Band Alignment for Efficient Photocatalytic Hydrogen Evolution

It is of great importance to promote charge separation in photocatalysts for enhanced photocatalytic activity under visible light irradiation. In this work, a type-II heterostructured photocatalyst was constructed by compositing phosphorus-doped g-C₃N₄ (P-CN) and Rh-doped SrTiO₃ (Rh-STO) via a thermal calcination treatment. A series of characterizations were conducted to investigate the structure of heterostructured P-CN/Rh-STO. It was found that Rh-STO interacted with in situ generated P atoms from the decomposition of P-CN during the calcination process, thus leading to the formation of heterojunction of P-CN/Rh-STO. Compared with the single component, i.e., P-CN or Rh-STO, the obtained P-CN/Rh-STO showed superior photocatalytic activity to that of both P-CN and Rh-STO due to the effective charge separation across the heterojunction between P-CN and Rh-STO.

Synergistic Effect of Sr-O Divacancy and Exposing Facets in SrTiO3 Micro/Nano Particle: Accelerating Exciton Formation and Splitting, Highly Efficient Co2+ Photooxidation

As a typical perovskite-type crystal, polyhedral strontium titanate (SrTiO₃ ) has shown anisotropic charge transport behavior in recent studies, however, the carrier transportation and transition of which has not been explained very clearly. This work present the existence of Sr and O divacancies in the novel rhombicuboctahedron SrTiO₃ micro/nano particles (Sr_{1- x} TiO_{3- x} /TiO_{2- x} ) with exposing (100), (110) and (111) facets and the diameter of 300-700 nm synthesized via hydrothermal synthesis, and also summarizes the dissociation mechanism of self-trapped excitons (STEs) caused by the divacancy and facet effect. In addition, most importantly, the metastable STEs with ultra-low binding energy (E_b  < 3 meV) under illumination are discovered. Combining the model of S-scheme heterojunction, a conversion mechanism of photoinduced carriers is proposed. The photocatalytic reaction of Co²⁺ is used as the probe reaction, and the unique Sr_{1- x} TiO_{3- x} /TiO_{2- x} possesses a high photooxidation efficiency of Co²⁺ , by which 70.3% of Co²⁺ is oxidized to Co³⁺ (CoOOH) in 5 min. This finding may provide a guideline for an optimal design of the photocatalytic materials for the recovery and extraction of metal ions based on SrTiO₃ .

Density Functional Theory Study on the Enhancement Mechanism of the Photocatalytic Properties of the g-C3N4/BiOBr(001) Heterostructure

The van der Waals heterostructures fabricated in two semiconductors are currently attracting considerable attention in various research fields. Our study uses density functional theory calculations within the Heyd-Scuseria-Ernzerhof hybrid functional to analyze the geometric structure and electronic structure of the g-C₃N₄/BiOBr(001) heterojunction in order to gain a better understanding of its photocatalytic properties. The calculated band alignments show that g-C₃N₄/BiOBr can function as a type-II heterojunction. In this heterojunction, the electrons and holes can effectively be separated at the interface. Moreover, we find that the electronic structure and band alignment of g-C₃N₄/BiOBr(001) can be tuned using external electric fields. It is also noteworthy that the optical absorption peak in the visible region is enhanced under the action of the electric field. The electric field may even improve the optical properties of the g-C₃N₄/BiOBr(001) heterostructure. Given the results of our calculations, it seems that g-C₃N₄/BiOBr(001) may be significantly superior to visible light photocatalysis.

strong synergistic effect of the (110) and (100) facets of the SrTiO3 perovskite micro/nanocrystal: decreasing the binding energy of exciton and superb photooxidation capability for Co2

Crystal facet regulation is an effective method for preparing SrTiO₃ or other perovskite semiconductor materials with high photochemical catalysis performance. In general, the edge-truncated cube of SrTiO₃ micro-nano particles has been widely reported because of the multiple crystal facets exposed at the same time. However, the effect of the (110) facet and the interaction between the (100) and (110) facets on the properties of photo-induced carriers is still not very clear. In this article, we have designed and prepared two edge-truncated cube SrTiO₃-a small and large area proportion of the (110) facet, respectively. In addition to the morphological and structural characterization, high-resolution XPS and femtosecond multiphoton transient absorption (fs-TA) spectroscopy were used to detect the atomic vacancy and were applied to confirm the state of carrier transition. The results showed that the larger (110) facet led to two influences-more Sr vacancies and more self-trapping excitons (STEs) with an ultra-low binding energy (E_b = 2.13 meV), about 1.17 meV lower than that of the sample with the smaller (110) facet. In particular, the larger (110) facet also caused a much higher photooxidation performance for Co²⁺ to Co³⁺. This study not only enriches the arsenal of SrTiO₃ materials but also sheds new insights into the understanding of the synergistic effect essence of the (100) and (110) facets, which could promote the development of new perovskite photocatalytic materials, particularly in the recovery of heavy metals.

Effect of CuO Loading on the Photocatalytic Activity of SrTiO3 for Hydrogen Evolution

A CuO-loaded SrTiO3 catalyst showed highly photocatalytic activity for H2 evolution. This catalyst was prepared by an impregnation method and characterized by XRD, TEM, BET, XPS, Uv-vis DRS and PL techniques. Under optimum conditions, the best rate of H2 evolution of the CuO-loaded SrTiO3 catalyst is 5811 µmol h−1g−1, whereas it is a mere 34 µmol h−1g−1 for the pure SrTiO3. High efficiency, low cost and good stability are some of the merits that underline the promising potential of CuO-loaded SrTiO3 in the photocatalytic hydrogen.

Ru/Rh Cation Doping and Oxygen-Vacancy Engineering of FeOOH Nanoarrays@Ti3 C2 Tx MXene Heterojunction for Highly Efficient and Stable Electrocatalytic Oxygen Evolution

Oxyhydroxides hold promise as highly-efficient non-noble electrocatalysts for the oxygen evolution reaction (OER), but their poor conductivity and structural instability greatly impede their progress. Herein, the authors develop a cation-doping and oxygenvacancy engineering strategy to fabricate Ru/Rh-doped FeOOH nanoarrays with abundant oxygen-vacancies in situ grown on Ti₃ C₂ T_x MXene (Ru/Rh-FeOOH@Ti₃ C₂ T_x ) as highly-efficient OER electrocatalysts. Benefiting from Ru/Rh-cation regulation, oxygenvacancy engineering, and heterojunction synergy between MXene and modulated FeOOH, the optimized Rh/Ru-FeOOH@Ti₃ C₂ T_x electrocatalysts exhibit excellent OER activities and remarkable stabilities with 100 h. Particularly, 3%Rh-FeOOH@Ti₃ C₂ T_x electrocatalyst only needs a 223 mV overpotential at 10 mA cm^-2 and 306 mV to reach 100 mA cm^-2 , which is superior to commercial IrO₂ catalyst and most reported oxyhydroxide-based electrocatalysts. Further, systematically theoretical caculation, kinetics, thermodynamics, and microstructural analysis verify that the integration of Ru/Rh-cation doping and oxygen vacancy obviously enhances the intrinsic conductivity and lattice defects of FeOOH and expose more active sites, thereby decreasing the adsorption/desorption energy barrier and activation energy, and improving the specific activity and catalytic kinetics of electrocatalysts, whereas in situ hybridization with MXene strengthens the structural stability. This work clearly confirms that cationdoping and oxygen-vacancy engineering offers a joint strategy for the electronic structure modulation and design of highly-efficient inexpensive OER electrocatalysts.

Cubic structured SrTiO3 with Ce/Cr Co-doping for photoinduced catalytic oxidation of gaseous mercury

A cubic SrTiO₃ (STO) composite material co-doped with Ce and Cr ions was synthesized by solvothermal method. The fully characterized samples were employed as photocatalysts for the oxidation of Hg⁰. The co-doped samples afforded excellent catalytic removal efficiency of 98.99% using UV irradiation and 89.9% using visible light irradiation for Hg⁰ compared with the single-doped samples. It was found that co-doped samples had a lower electron-hole recombination rate, largest Brunauer-Emmett-Teller specific surface area, and reduced band gap. The electron spin resonance results revealed that ·O₂^- and ·OH were the main active species in the catalytic process. Moreover, the co-doped samples exhibited the best electron transfer rate and the highest photocurrent response intensity. The electron transfer between the elements in the co-doped sample enables it to achieve stable and efficient catalytic performance. In addition, even after five consecutive catalytic runs, the co-doped sample maintained high catalytic activity. This work highlights the potential of the perovskite-type STO materials in the photocatalytic oxidation of gaseous mercury.

Hollow Multishell-Structured TiO2/MAPbI3 Composite Improves Charge Utilization for Visible-Light Photocatalytic Hydrogen Evolution

Interfacial photogenerated charge separation and transport have demonstrated great influence on photocatalytic performance. Herein, the composite photocatalysts of methylammonium lead iodide perovskite (MAPbI₃) in TiO₂ with a hollow multishell structure (HoMS) are designed and synthesized. The results indicate that the heterogeneous interface within the MAPbI₃/Pt/TiO₂-HoMS can help enhance the separation of photogenerated charges. HoMSs assembled with multiple shells can not only support large surfaces available for building a heterogeneous interface and photocatalytic reactions but also improve the light absorption capability of photocatalysts. Besides, the thin shell structure can also reduce the transmission distance of carriers so as to hinder charge recombination and improve charge utilization. As a result, samples of MAPbI₃/Pt/triple-shelled TiO₂ hollow structure displayed a H₂ yield of 6856.2 μmol h^-1 g^-1 under visible light, which is greatly better than that of bare MAPbI₃ (268.6 μmol h^-1 g^-1).

An efficient strategy to enhance the photocatalytic activity of Ir-doped SrTiO3: a hybrid DFT approach

Present study revealed that the codoping of Al, Cr, and La not only stabilize Ir in preferred oxidation state, but also form charge compensated system, thereby ensuring improved photoconversion efficiency under visible light.