Fast Flux Reaction Approach for the Preparation of Sn<sub>2</sub>TiO<sub>4</sub>: Tuning Particle Sizes and Photocatalytic Properties

O’Donnell, Shaun; Hamilton, Adam M.; Maggard, Paul A.

doi:10.1149/2.0141905jes

Cited by 17 publications

(30 citation statements)

References 38 publications

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“…NaCl/KCl) has been shown to tailor the crystallinity and grain boundary structure in the resulting material as well as to limit the formation of defects. This molten salt synthesis has been used to obtain a number of photocatalysts with high degrees of crystallinity and fewer defects, such as SrTiO 3 , (La-doped) NaTaO 3 , , PbTiO 3 , Sn 2 TiO 4 , , La 2 Ti 2 O 7 , Ta 3 N 5 , Na 2 Ca 2 Nb 4 O 13 , and BaNb 1– x Ta x O 2 N . This is possible due to the ability of molten salts to accelerate the diffusion of constituent ions and to control the crystal growth process during the synthesis.…”

Section: Charge Separation and Transportmentioning

confidence: 99%

Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies

2019

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Solar-driven water splitting provides a leading approach to store the abundant yet intermittent solar energy and produce hydrogen as a clean and sustainable energy carrier. A straightforward route to light-driven water splitting is to apply self-supported particulate photocatalysts, which is expected to allow solar hydrogen to be competitive with fossil-fuel-derived hydrogen on a levelized cost basis. More importantly, the powder-based systems can lend themselves to making functional panels on a large scale while retaining the intrinsic activity of the photocatalyst. However, all attempts to generate hydrogen via powder-based solar water-splitting systems to date have unfortunately fallen short of the efficiency values required for practical applications. Photocatalysis on photocatalyst particles involves three sequential steps: (i) absorption of photons with higher energies than the bandgap of the photocatalysts, leading to the excitation of electron–hole pairs in the particles, (ii) charge separation and migration of these photoexcited carriers, and (iii) surface chemical reactions based on these carriers. In this review, we focus on the challenges of each step and summarize material design strategies to overcome the obstacles and limitations. This review illustrates that it is possible to employ the fundamental principles underlying photosynthesis and the tools of chemical and materials science to design and prepare photocatalysts for overall water splitting.

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Section: Charge Separation and Transportmentioning

confidence: 99%

Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies

2019

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“…As described below, crystalline semiconductors containing new combinations of these M/M′ cations have been prepared in my laboratory and others and investigated for their photoelectrochemical properties. − ,− Many representatives within these systems are listed in Table in order of increasing band gaps. Notably, a predominant fraction of ∼80% of these semiconductors has been found to occur as thermodynamically unstable phases, as denoted in the right-hand column.…”

Section: Mixed-metal Oxide (M′mo X ) Semiconductorsmentioning

confidence: 99%

“…In addition, the binary oxides may oxidize in air or decompose in vacuum; for example, both Ag 2 O and SnO disproportionate in vacuum at temperatures of only ∼250–300 °C. Molten salt reactions have been extensively used to synthesize metastable oxides, ,,,− ,− ,− as listed in Table and shown in the SEM images in Figure . In this technique, a salt mixture at a low-melting eutectic composition is used to dissolve and react the metal oxides at relatively low temperatures, as reviewed previously. , The salt mixture can be selected from among, for example, metal halides or metal sulfates such as NaCl/KCl or Na 2 SO 4 /K 2 SO 4 , among many possibilities.…”

Section: Mixed-metal Oxide (M′mo X ) Semiconductorsmentioning

confidence: 99%

“…The small band edge overpotentials likely lead to relatively lower photocatalytic rates for H 2 formation. In a follow up study, a fast flux reaction was used to attain nanoscale particles with larger bandgaps and overpotentials with higher rates (up to 2×) for H 2 production of up to 141 μmol·g –1 ·h –1 . After prolonged testing, no bulk decomposition was observable by X-ray diffraction.…”

Section: Mixed-metal Oxide (M′mo X ) Semiconductorsmentioning

confidence: 99%

“…This occurs for Sn 2 TiO 4 and in the double metal-cation solid solution (Ba 1−x Sn x )(Zr 1−y Ti y )O 3 . 1,3,28 Shown in Figure 9, the Sn 2 TiO 4 semiconductor exhibits photoanodic currents as a polycrystalline film, as well as photocatalytic activity for O 2 or H 2 generation without the need for a surface cocatalyst. The photocatalytic rates for O 2 evolution reach a peak of ∼325 μmol• g −1 •h −1 under only visible-light irradiation in a 0.05 M AgNO 3 solution.…”

Section: Photoelectrochemical Properties Of M′mo X Semiconductorsmentioning

confidence: 99%

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Capturing Metastable Oxide Semiconductors for Applications in Solar Energy Conversion

Maggard

2021

Acc. Chem. Res.

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Metrics & MoreArticle Recommendations CONSPECTUS: Many small bandgap semiconductors have been discovered or predicted to exist beyond the edges of stability, that is, accessible only as metastable solids that are thermodynamically unstable. In many cases, these metastable semiconductors have been revealed to have technologically promising properties for solar energy conversion, such as in photocatalysis or in photovoltaics. This Account presents a review of research results selected from my group and others in recent years on these semiconductors. Notably, these include the chemical systems of mixed-metal oxides (i.e., M′MO x ; M = Ti(IV), Nb(V), or Ta(V) cation; M′ = Ag(I), Cu(I), Sn(II), Pb(II), or Bi(III) cation), which have diverse structure types and compositions. High photocatalytic activities have been found for the light-driven reduction or oxidation of water as p-or n-type photoelectrodes, respectively, or as suspended powders in aqueous solutions. These have exhibited new combinations of favorable semiconductor properties, such as deep visible-light absorption, near-optimal band edge energies, defect tolerance, and functional carrier mobilities and charge separation. As described herein, this set of properties is inextricably linked to their metastable nature, that is, the crystalline structures and compositions needed for these characteristics lead naturally to thermodynamic instabilities. This Account focuses on current research efforts that have begun unlocking the potential of these semiconductors via new recent advances in (1) synthetic approaches that enable their preparation and (2) the understanding of structure−property relationships discovered at the precipices of stability that lead to the improved semiconductor properties. For example, low-temperature reactions have been developed to facilitate greater kinetic control, such as with the use of molten salts, and have been a key factor in preparing many of these semiconductors. As a result, a plethora of promising new mixed-metal oxide systems have been uncovered that exhibit band gaps spanning the range of photon energies from ∼1.3 to >3.0 eV. Especially relevant for visible-light applications are the Cu(I)-and Sn(II)-containing semiconductors. For example, n-type Sn(II)-titanates and p-type Cu(I)-niobates can be synthesized by flux methods and exhibit some of the smallest known visible-light band gaps that also maintain suitable conduction and valence band edges for driving the water-splitting half reactions. Kinetic stabilization of these metastable semiconductors against thermally driven phase segregation is increased with the formation of solid solutions for both the M and M′ cation sites, leading to effective strategies to more finely tune their band gaps, band edge energies, and photoelectrochemical properties. Many unique and useful relationships are emerging between the synthesis and structures of metastable semiconductors and their physical properties, leading to more efficient solar energy conversion.

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Switching Lead for Tin in PbHfO₃: Noncubic Structure of SnHfO₃**

Gabilondo,

Newell,

Broughton

et al. 2023

Angewandte Chemie

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The removal of lead from commercialized perovskite‐oxide‐based piezoceramics has been a recent major topic in materials research owing to legislation in many countries. In this regard, Sn(II)‐perovskite oxides have garnered keen interest due to their predicted large spontaneous electric polarizations and isoelectronic nature for substitution of Pb(II) cations. However, they have not been considered synthesizable owing to their high metastability. Herein, the perovskite lead hafnate, i.e., PbHfO3 in space group Pbam, is shown to react with SnClF at a low temperature of 300 °C, and resulting in the first complete Sn(II)‐for‐Pb(II) substitution, i.e. SnHfO3. During this topotactic transformation, a high purity and crystallinity is conserved with Pbam symmetry, as confirmed by X‐ray and electron diffraction, elemental analysis, and 119Sn Mössbauer spectroscopy. In situ diffraction shows SnHfO3 also possesses reversible phase transformations and is potentially polar between ≈130–200 °C. This so‐called ‘de‐leadification’ is thus shown to represent a highly useful strategy to fully remove lead from perovskite‐oxide‐based piezoceramics and opening the door to new explorations of polar and antipolar Sn(II)‐oxide materials.

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Fast Flux Reaction Approach for the Preparation of Sn₂TiO₄: Tuning Particle Sizes and Photocatalytic Properties

Cited by 17 publications

References 38 publications

Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies

Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies

Capturing Metastable Oxide Semiconductors for Applications in Solar Energy Conversion

Switching Lead for Tin in PbHfO₃: Noncubic Structure of SnHfO₃**

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Fast Flux Reaction Approach for the Preparation of Sn2TiO4: Tuning Particle Sizes and Photocatalytic Properties

Cited by 17 publications

References 38 publications

Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies

Particulate Photocatalysts for Light-Driven Water Splitting: Mechanisms, Challenges, and Design Strategies

Capturing Metastable Oxide Semiconductors for Applications in Solar Energy Conversion

Switching Lead for Tin in PbHfO3: Noncubic Structure of SnHfO3**

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Product

Resources

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Fast Flux Reaction Approach for the Preparation of Sn₂TiO₄: Tuning Particle Sizes and Photocatalytic Properties

Switching Lead for Tin in PbHfO₃: Noncubic Structure of SnHfO₃**