CH3NH3PbBr3 perovskite nanocrystals (PNCs) of different sizes (ca. 2.5–100 nm) with high photoluminescence (PL) quantum yield (QY; ca. 15–55 %) and product yield have been synthesized using the ...branched molecules, APTES and NH2‐POSS, as capping ligands. These ligands are sterically hindered, resulting in a uniform size of PNCs. The different capping effects resulting from branched versus straight‐chain capping ligands were compared and a possible mechanism proposed to explain the dissolution–precipitation process, which affects the growth and aggregation of PNCs, and thereby their overall stability. Unlike conventional PNCs capped with straight‐chain ligands, APTES‐capped PNCs show high stability in protic solvents as a result of the strong steric hindrance and propensity for hydrolysis of APTES, which prevent such molecules from reaching and reacting with the core of PNCs.
Perovskite nanocrystals: Variously sized perovskite nanocrystals (PNCs) with high photoluminescence quantum yield and uniformity have been synthesized using branched ligands (APTES). APTES‐capped PNCs show high stability in protic solvents because the steric and hydrolysis properties of APTES prevent protic reactions with the core of PNCs.
Here we demonstrate that the photoactivity of Au-decorated TiO2 electrodes for photoelectrochemical water oxidation can be effectively enhanced in the entire UV–visible region from 300 to 800 nm by ...manipulating the shape of the decorated Au nanostructures. The samples were prepared by carefully depositing Au nanoparticles (NPs), Au nanorods (NRs), and a mixture of Au NPs and NRs on the surface of TiO2 nanowire arrays. As compared with bare TiO2, Au NP-decorated TiO2 nanowire electrodes exhibited significantly enhanced photoactivity in both the UV and visible regions. For Au NR-decorated TiO2 electrodes, the photoactivity enhancement was, however, observed in the visible region only, with the largest photocurrent generation achieved at 710 nm. Significantly, TiO2 nanowires deposited with a mixture of Au NPs and NRs showed enhanced photoactivity in the entire UV–visible region. Monochromatic incident photon-to-electron conversion efficiency measurements indicated that excitation of surface plasmon resonance of Au is responsible for the enhanced photoactivity of Au nanostructure-decorated TiO2 nanowires. Photovoltage experiment showed that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was attributable to the effective surface passivation of Au NPs. Furthermore, 3D finite-difference time domain simulation was performed to investigate the electrical field amplification at the interface between Au nanostructures and TiO2 upon SPR excitation. The results suggested that the enhanced photoactivity of Au NP-decorated TiO2 in the UV region was partially due to the increased optical absorption of TiO2 associated with SPR electrical field amplification. The current study could provide a new paradigm for designing plasmonic metal/semiconductor composite systems to effectively harvest the entire UV–visible light for solar fuel production.
We demonstrate the decoration of methylamine lead bromide (MAPbBr 3 , MA: CH 3 NH 3 + ) perovskite nanoparticles on protonated graphitic carbon nitride (p-g-C 3 N 4 ) sheets to form nanocomposites ...(NCs) for the first time. The intrinsic type II band structure of MAPbBr 3 /p-g-C 3 N 4 NCs resulted in significant charge separation properties, which were greatly beneficial for related applications in photoelectric conversion. The interfacial charge transfer behavior of MAPbBr 3 /p-g-C 3 N 4 NCs was analyzed via time-resolved photoluminescence (TRPL) spectroscopy and singular-value decomposition global fitting (SVD-GF), which revealed that photoexcited electrons in the conduction band (CB) and shallow-trap (ST) states of MAPbBr 3 could be transferred into the CB of g-C 3 N 4 . The fitting results for TRPL traces indicated that the control of the related compositions could modulate the interfacial charge carrier dynamics of MAPbBr 3 /g-C 3 N 4 NCs. An increase in the charge transfer rate constant ( k et ) for MAPbBr 3 /g-C 3 N 4 NCs was discovered when the constituent ratio of p-g-C 3 N 4 was enhanced. Furthermore, we utilized MAPbBr 3 /p-g-C 3 N 4 NCs as a photocatalyst to carry out the photocatalytic reduction of p -nitrophenol (PNP) under visible-light irradiation. A significant photoreduction rate ( k PNP ) of PNP was observed in the photocatalytic reaction, which indicated the great potential of MAPbBr 3 /p-g-C 3 N 4 NCs to convert solar energy into chemical energy. In particular, the present investigation opens a new field for organolead bromide perovskites in applications in photocatalysis, as well as related photoelectric conversion.
The interfacial charge carrier dynamics of the three-component semiconductor–semiconductor–metal heterojunction system were investigated and presented for the first time. The samples were prepared by ...selectively depositing Pt nanoparticles on the TiO2 surface of In2O3-decorated TiO2 nanobelts (In2O3–TiO2 nanobelts (NBs)) using the typical photodeposition method. For In2O3–TiO2 NBs, because of the difference in band structures between In2O3 and TiO2, the photoexcited electrons of In2O3 nanocrystals would preferentially transfer to TiO2 NBs to cause charge carrier separation. With the introduction of Pt on TiO2 surface, a fluent electron transfer from In2O3, through TiO2, and eventually to Pt was achieved, giving rise to the increasingly pronounced charge separation property for the as-prepared In2O3–TiO2–Pt NBs. The remarkable charge separation of the samples was revealed with the corresponding photocurrent measurements. Time-resolved photoluminescence spectra were measured to quantitatively analyze the electron transfer event between In2O3 and TiO2 for In2O3–TiO2 NBs and its dependence on Pt deposition. Upon the deposition of Pt, In2O3–TiO2 NBs showed an increased apparent electron-scavenging rate constant, fundamentally consistent with the result of their performance evaluation in photocatalysis. The current study provides a new paradigm for designing highly efficient three-component nanoheterojunction photocatalysts which can effectively produce chemical energy from absorbing light.
Core-shell CdS/TiO
2
structures are promising for solar-to-fuel conversion applications because their ideal type-II band alignment helps effective charge transfer to form the CdS
+
/TiO
2
−
system. A ...better understanding of the charge carrier dynamics is critical to provide guiding principles for designing photoelectrochemical (PEC) devices. Hence, TiO
2
shell-thickness dependent charge carrier dynamics and competition between electron relaxation in CdS (
e.g.
recombination and trapping) and electron transfer from CdS to TiO
2
were investigated using ultrafast transient absorption (TA) spectroscopy. The results indicate that the CdS/TiO
2
nanocomposite with a molar ratio of 2 : 1 exhibits the highest electron transfer rate constant of
k&cmb.macr;
ET
= 2.71 × 10
10
s
−1
, along with an electron relaxation rate of
k&cmb.macr;
CdS/TiO
2
= 3.43 × 10
10
s
−1
, resulting in an electron transfer quantum efficiency of
Q
ET
= 79%, which also corresponds to the best PEC hydrogen generation in the CdS/TiO
2
core-shell composites. However, the electron transfer rate decreases with increasing thickness of the TiO
2
shell consisting of aggregated nanoparticles. One possible explanation is that the CdS and TiO
2
form relatively larger, separate particles, or less conforming small particles, with poor interfaces with increasing TiO
2
, thereby reducing electron transfer from CdS to TiO
2
, which is supported by SEM, and TEM data and consistent with PEC results. The thickness and morphology dependence of electron transfer and relaxation provides new insight into the charge carrier dynamics in such composite structures, which is important for optimizing the efficiency of PEC for solar fuel generation applications.
Shell-thickness dependent charge carrier dynamics and enhanced photoelectrochemical performance were studied in uniform core-shell CdS/TiO
2
composites.
Organic–inorganic perovskite materials in the form of nanocrystals and thin films have received enormous attention recently because of their unique optoelectronic properties such as high absorption ...coefficient, narrow and tunable emission bandwidth, high photoluminescence quantum yield, long exciton lifetime, and balanced charge transport properties. These properties have found applications in a number of important fields, including photovoltaic solar cells, light-emitting diodes, photodetectors, sensors, and lasers. However, the stability of the materials and devices is strongly affected by several factors such as water moisture, light, oxygen, temperature, solvent, and other materials in contact such as metal oxides used in devices. Defects, particularly those related to surface states, play a critical role in the stability as well as the performance of the perovskites. Various surface modification and defect passivation strategies have been developed to enhance stability and improve performance. We review some recent progress in the development of synthetic approaches to produce high-quality nanostructured and bulk film perovskites with controlled properties and functionalities. We also highlight the degradation mechanism and surface passivation approaches to address the issue of instability. To help gain deeper fundamental insight into mechanisms behind degradation and surface passivation, relevant properties, including structural, optical, electronic, and dynamic, are discussed and illustrated with proposed models.
Summary
A novel Bi2WO6/rGO/3D‐GCN composite with 2D/2D/3D heterojunction is synthesized by a simple microwave‐assisted method and used as a visible‐light‐responsive photocatalyst in the CO2 ...reduction. The chemical properties and morphology of prepared photocatalysts are identified by a variety of analytic tools and spectroscopies. As a result, the heterojuncted Bi2WO6/3D‐GCN exhibits superior CO2 reduction performance as compared to the pristine 3D‐GCN, which may be caused by the intimate contact between Bi2WO6 and 3D‐GCN. The harvest of visible‐light absorption, reduced charge transfer resistance and suppressed recombination of electron‐hole pairs are accountable for surpassing performance of Bi2WO6/3D‐GCN. Upon further incorporation of rGO into Bi2WO6/3D‐GCN heterojunction, the photocatalytic production of CO can be notably boosted by ca. 7.9‐fold higher than 3D‐GCN, suggesting the key contribution of rGO in facilitating the interfacial charge transfer kinetics and increasing CO2 uptake. This work exemplifies a time and energy‐saving method to prepare the unique 3D GCN with laminated hexagonal structure which can serve as a shuttle for Bi2WO6 heterojunction and rGO incorporation. This Bi2WO6/rGO/3D‐GCN photocatalyst could offer the potential applications in the natural solar conversions of CO2.
A Bi2WO6/rGO/3D‐GCN with 2D/2D/3D heterojunction is prepared by using a microwave‐assisted route.
High visible‐light absorption, interfacial charge transfer kinetics and suppressed recombination of e‐h pairs result in the surpassing CO2 photoreduction.
The obtained results could offer the potential applications in the natural solar conversions of CO2.
Butein is a flavonoid isolated from various medicinal plants. It is known to have different biological activities including anti‐inflammation, anti‐adipogenesis, and anti‐angiogenesis. In the study, ...we demonstrated the anti‐proliferative effect of butein in human osteosarcoma U‐2 OS cells. Our data showed that butein significantly suppressed the viability and colony formation ability of U‐2 OS cells. Further experiments revealed butein exposure resulted in a cell cycle arrest at S and G2/M phase in U‐2 OS cells. Importantly, we found that butein activated the tumor suppressor p53, and trigged a p53‐dependent senescence in U‐2 OS cells. Knockdown of p53 suppressed the senescence and rescued the viability in butein‐treated U‐2 OS cells. Furthermore, we observed that butein exposure significantly enhanced reactive oxygen species (ROS) levels in U‐2 OS cells. Co‐administration of the ROS inhibitor NAC largely abolished the up‐regulated p53 protein level, and rescued the suppressed viability and colony formation ability in butein‐exposed U‐2 OS cells. Taken together, our data proposed the increased ROS by butein exposure activated p53, and the activated p53 was involved in the anti‐proliferative effect of butein via inducing senescence in U‐2 OS cells. This report suggests that butein is a promising candidate for cancer therapy against osteosarcoma.
It has recently been demonstrated that the photoelectrochemical performance of a number of metal oxides can be substantially improved by controllably increasing their carrier densities through ...controlled introduction of defects such as oxygen vacancies. The creation of defects can be achieved via different synthetic methods, including hydrogenation, thermal treatment in oxygen deficient environment, chemical reductions, ion bombardment and electrochemical reductions. Here we report a general strategy to prepare oxygen-deficient metal oxides, including WO 3 , TiO 2 (rutile and anatase), BiVO 4 , and ZnO, by electrochemically induced formation of low valent metal species. These electrochemically treated metal oxides show significantly enhanced photoactivity, as a result of improved charge injection and charge separation efficiency. The reported electrochemical method in this work represents a simple, rapid, highly scalable and safe approach to prepare high performance metal oxide photoanodes.
Photoelectrochemical (PEC) water splitting using solar energy has received widespread attention, and strong performance photocatalysts are highly desired. In this work, uniform carbon-coated CdS ...nanostructures have been fabricated using ascorbic acid as the carbon source by a facile hydrothermal method and characterized using transmission electron microscopy (TEM). The thickness of the carbon layer can be well controlled by the amount of ascorbic acid added during the reaction. Compared to pristine CdS, carbon-coated CdS nanostructures exhibit stronger light absorption and more efficient electron transfer as determined by absorption and photoluminescence (PL) spectroscopy. Ultrafast charge carrier dynamics in the composite CdS/C structures were studied using femtosecond transient absorption (TA) spectroscopy, which revealed direct evidence of effective charge transfer from CdS to the carbon layer. In addition, the CdS/C composites were employed as photoanodes for PEC hydrogen generation, which showed significant improvement in photoactivity over pristine CdS nanospheres. The photocurrent density (-1.0 V vs. Ag/AgCl) of one of the composite structures, CdS/7-C, exhibited similar to 20 times enhancement compared with that of pristine CdS. The enhanced PEC property can be attributed to increased light scattering and consequently the light harvesting throughout the whole spectral wavelength, and the effective electron transfer from CdS to the carbon layer. Such carbon-coated semiconductor composites based on a simple and low-cost synthesis method should be useful in PEC as well as other applications such as photovoltaics, detectors and sensors.
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