Materials
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2023
·Vol. 16
·期 14
·5195
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IF 3.4
Jun Yang,Jinbiao Pang,Xiaofang Luo,Laiyuan Ao,Qiang Xie,Xing Wang,Hongyu Yang,Xianzhong Tang
This work studied the phase constitution, bond characteristics, and microwave dielectric performances of Sr2TiO4ceramics. Based on XRD and Rietveld refinement analysis, pure tetragonal Ruddlesden–Popper type Sr2TiO4ceramic is synthesized at 1425~1525 °C. Meanwhile, the microstructure is dense and without porosity, indicating its high sinterability and densification. Great microwave dielectric performances can be obtained, namely anεrvalue of 39.41, and aQ × fvalue of 93,120 GHz, when sintered at 1475 °C. Under ideal sintering conditions, the extrinsic factors are minimized and can be ignored. Thus, the intrinsic factors are considered crucial in determining microwave dielectric performances. Based on the P–V–L complex chemical bond theory calculation, the largest bond ionicity, and proportions to the bond susceptibility from Sr–O bonds suggest that Sr–O bonds mainly determine the dielectric polarizability. However, the Ti–O bonds show lattice energy about three times larger than Sr–O bonds, emphasizing that the structural stability of Sr2TiO4ceramics is dominated by Ti–O bonds, and the Ti–O bonds are vital in determining the intrinsic dielectric loss. The thermal expansion coefficient value of the Sr2TiO4structure is also mainly decided by Ti–O bonds.Keywords:Sr2TiO4;microwave dielectric properties;P–V–L complex chemical bond theory
研究领域:
材料科学
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物理学
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产品关联
DOI
PubMed
高影响因子
Nature Communications
·
2025
·Vol. 16
·期 1
·1-10
·
IF 15.7
Yu Jinxing,Huang Jie,Li Ronghua,Li Yanbo,Liu Gang,Xu Xiaoxiang
Photocatalytic overall water splitting is a promising approach for a sustainable hydrogen provision using solar energy. For sufficient solar energy utilization, this reaction ought to be operated based on visible-light-active semiconductors, which is very challenging. In this work, an F-expedited nitridation strategy is applied to modify the wide-bandgap semiconductor Sr 2 TiO 4 for visible-light-driven photocatalytic overall water splitting. Compared to the conventional nitridation approach, F-expedited nitridation introduces the desirable integration of a high concentration of N dopant for strong visible light absorption and a low concentration of defects (i.e. Ti 3+ and oxygen vacancies) for effective separation of photocarriers. After being coated with Ti-oxyhydroxide protection layer and deposited with RhCrO y cocatalyst, the product from F-expedited nitridation can stably run photocatalytic overall water splitting with apparent quantum efficiency of 0.39% at 420 ± 20 nm and solar-to-hydrogen efficiency of 0.028%. These findings justify the effectiveness of F-expedited nitridation strategy and serve as a guidance to upgrade the photocatalytic activity of many other wide-bandgap semiconductors.
研究领域:
材料科学
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能源化学
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DOI
PubMed
高影响因子
INORGANIC CHEMISTRY
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2015
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IF 4.762
Xiaoqin Sun,Yinghao Xie,Fangfang Wu,Hongmei Chen,Meilin Lv,Shuang Ni,Gang Liu,Xiaoxiang Xu
Layered semiconductor photocatalysts have been found to exhibit promising performance levels, probably linked to their interlayer framework that facilitates separation of charge carriers and the reduction/oxidation reactions. Layered titanates, however, generally demonstrate activities under UV irradiation, and therein lies the strong desire to extend their activity into the visible light region. Here, we investigated a series of layered perovskite by doping Sr2TiO4 with Cr and/or La in the hope to improve their visible light responses. Their crystal structures and other physicochemical properties were systematically explored. Our results show that La and Cr can be successfully accommodated in the layered structure and Cr is an efficient dopant for the extension of visible light absorbance. Much enhanced photocatalytic hydrogen evolution was observed after doping and was found to be composition-dependent. The highest hydrogen production rate approaches 97.7 μmol/h for Sr2Ti0.95Cr0.05O4-δ under full range irradiation (λ ≥ 250 nm) and 17 μmol/h for Sr2Ti0.9Cr0.1O4-δ under visible light irradiation (λ ≥ 400 nm), corresponding to an apparent quantum efficiency of 0.16% and 0.05%, respectively. Theoretical calculation reveals that the improved optical and photocatalytic properties are owing to a newly formed spin-polarized valence band from Cr 3d orbitals. The decreased unit cell parameters, reduced band gaps as well as anisotropic properties of layered architectures are likely the reasons for a better activity. Nevertheless, instability of these compounds in the presence of moisture and CO2 was also noticed, suggesting that protective atmospheres are needed for the storage of these photocatalysts.
研究领域:
材料科学
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光催化
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能源材料
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半导体物理
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无机化学
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DOI
高影响因子
APPLIED CATALYSIS B-ENVIRONMENTAL
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2017
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IF 9.446
Xiaoqin Sun,Xiaoxiang Xu
Layered semiconductor compounds often exhibit intriguing properties for photocatalytic water splitting, probably correlated with their peculiar crystal structures that facilitate charge separations. In this work, we perform an investigation on the layered Ruddlesden-Popper compound Sr 2 TiO 4 and its La/Rh co-doped counterparts for photocatalytic hydrogen production from water. Their crystal structures, optical absorption and other physicochemical properties have been systematically explored. Our results suggest that La/Rh can be successfully incorporated into Sr 2 TiO 4 with layered crystal structure maintained. The use of polymerized-complex method for sample synthesis significantly reduces the calcination temperature as low as 900 °C. La/Rh serves as efficient dopants for extending the light absorbance of Sr 2 TiO 4 as far as 550 nm. Photocatalytic hydrogen productions are also considerably improved after La/Rh co-doping under both full range (λ ≥ 250 nm) and visible light irradiation (λ ≥ 420 nm). An optimal doping level is reached at 3% (Sr 1.97 La 0.03 Ti 0.97 Rh 0.03 O 4 ) which gives the highest average hydrogen production rate ∼100 μmol/h and ∼40 μmol/h under full range (λ ≥ 250 nm) and visible light irradiation (λ ≥ 420 nm), corresponding to apparent quantum efficiency ∼1.27% and ∼1.18%, respectively. Photoelectrochemical analysis reveals that charge separation and electron lifetime strongly depends on the level of La/Rh co-doping. Mott-Schottky analysis and theoretical calculations indicate that the improved light absorption of La/Rh co-doped Sr 2 TiO 4 stems from the formation of new valence band with Rh 4d character which uplifts the valence band edge of Sr 2 TiO 4 .
研究领域:
材料科学
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光催化
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能源材料
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半导体物理
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无机化学
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DOI
高影响因子
JOURNAL OF CATALYSIS
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2018
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IF 6.759
Hong Zhang,Shuang Ni,Yongli Mi,Xiaoxiang Xu
Doping techniques generally serve as effective means for tailoring the physicochemical properties of a target compound. In this work, we successfully co-doped La/Fe into Ruddlesden-Popper (RP) compound Sr 2 TiO 4 and performed a detailed investigation on the crystal structure, morphology, optical absorption and photocatalytic hydrogen production reactions after doping. Our findings suggest that La/Fe co-doping slightly expand the unit cell of Sr 2 TiO 4 while maintains the structure lamination. Incorporating La/Fe into Sr 2 TiO 4 efficiently reduces the band gap and the level of band gap reduction can be controlled by varying the amounts of dopants. La/Fe co-doping significantly improves the photocatalytic properties of Sr 2 TiO 4 under both full range (λ ≥ 250 nm) and visible light illumination (λ ≥ 420 nm). A fivefold enhancement in hydrogen production rate (∼106.2 μmol/h) is seen in sample Sr 1.9 La 0.1 Ti 0.9 Fe 0.1 O 4 (x = 0.1). Efficient photocatalytic hydrogen production under visible light illumination (λ ≥ 420 nm) is also achieved in sample Sr 1.7 La 0.3 Ti 0.7 Fe 0.3 O 4 (x = 0.3) with AQE as high as ∼1.18% at 420 nm. DFT calculations confirm the critical role of Fe in reducing the band gap of Sr 2 TiO 4 by forming additional spin-polarized bands (SPB). The anisotropic charge transportation in Sr 2 TiO 4 is also verified by our calculations as both conduction band minimum (CBM) and valence band maximum (VBM) are buried in TiO 6 octahedron layers. The 2D charge transportation properties are particularly useful for photocatalytic reactions since interlayer charge recombination is essentially prevented.
研究领域:
材料科学
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光催化
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能源材料
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固态化学
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DOI
高影响因子
ACS Catalysis
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2018
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IF 11.384
Xiaoqin Sun,Yongli Mi,Feng Jiao,Xiaoxiang Xu
Solar water splitting into H2 and O2 upon a particulate photocatalyst relies on significant advances in material engineering where a number of important properties such as optical absorption, charge transportation, defect level, etc. can be manipulated. In this work, we have gained control over these properties for the wide band gap semiconductor Sr2TiO4 and successfully actualized water splitting under visible light illumination. This has been realized by codoping La/N into the laminated perovskite structure of Sr2TiO4. Strong visible light absorption as far as 650 nm can be tailored by varying the La/N content in Sr2–xLaxTiO4–yNy (0 ≤ x ≤ 0.5). Optimal photocatalytic H2 and O2 production has been achieved at x = 0.2, 0.3 and outweighs that of a number of typical perovskite oxynitrides. These activities are a function of several important parameters for photogenerated charges (e.g., concentration, mobility, and lifetime) which are all linked to La/N codoping levels. More strikingly, overall water splitting has been achieved at x = 0.2 with Rh/Cr2O3 as a cocatalyst. Defects such as Ti3+ species play a negative role in the photocatalytic activity, as they strongly promote charge recombination and shorten the electron lifetime. Theoretical calculations reveal the crucial role of N in uplifting the valence band maximum of Sr2TiO4 by hybridization with O 2p orbitals. La, therefore, balances the charge discrepancies induced during N/O replacements which would otherwise be unfeasible for substantial doping. Our calculations also suggest that Sr2TiO4 has a 2D charge transportation character which is extremely useful for charge separations.
研究领域:
材料科学
·
化学
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产品关联
DOI
高影响因子
Journal of Energy Chemistry
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2020
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IF 7.216
Jinxing Yu,Xiaoxiang Xu
Cr doped Ruddlesden-Popper compound Sr 2 TiO 4 has been successfully modified by fluorine to form a new compound Sr 2 Ti 0.95 Cr 0.05 O 3 F 2 . Structure analysis suggests two types of fluorine in the structure of this new compound, i.e. intralayer and interlayer F, which induce strong built-in electric field within this layered compound. The electric field stems from uneven distribution of F atoms on the two sides of perovskite layers therefore leads to charge disproportionation . DFT calculations suggest that this unique structural feature is highly beneficial for charge dissociations as it breaks the coplanar settlement of conduction band minimum and valence band maximum whilst maintains the 2D charge transportation properties. This is clearly demonstrated by the superior photocatalytic activities of Sr 2 Ti 0.95 Cr 0.05 O 3 F 2 for hydrogen production from water. Apparent quantum efficiency (AQE) as high as 1.16% at 420 ± 20 nm has been achieved which stands as the highest AQE reported on Sr 2 TiO 4 to date. Photoelectrochemical (PEC) analysis confirms improved charge separation conditions and prolonged charge lifetime.
研究领域:
材料化学
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光催化
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能源化学
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物理化学
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无机功能材料
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太阳能转化
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环境科学
✓ 已验证
DOI
高影响因子
危险品化学品经营许可证（带存储）