17 research outputs found
Epitaxial Growth of CsPbBr<sub>3</sub> Pyramids/CdS Nanobelt Heterostructures for High-Performance Photodetectors
Perovskites have great potential for optoelectronic applications
due to their high photoluminescence quantum yield, large absorption
coefficient, great defect tolerance, and adjustable band gap. Perovskite
heterostructures may further enhance the performance of optoelectronic
devices. So far, however, most of perovskite heterostructures are
fabricated by mechanical stacking or spin coating, which could introduce
a large number of defects or impurities at the heterointerface owing
to the random stacking process. Herein, we report the epitaxial growth
of CsPbBr3 pyramids/CdS nanobelt heterostructures via a
2-step vapor deposition route. The CsPbBr3 triangular pyramids
are well aligned on the surface of CdS nanobelts with the epitaxial
relationships of (0ā22)CsPbBr3||(1ā20)CdS and (ā211)CsPbBr3||(002)CdS. Time-resolved photoluminescence results reveal that effective
charge transfer occurred at the heterointerface, which can be attributed
to the type-II band arrangement. Theoretical simulations reveal that
the unique CsPbBr3 pyramids/CdS nanobelt structure facilitates
diminishing the reflection losses and enhancing the light absorption.
The photodetector based on these CsPbBr3 pyramids/CdS nanobelt
heterostructures exhibited an ultrahigh photoswitching ratio of 2.14
Ć 105, a high responsivity up to 4.07 Ć 104 A/W, a high detectivity reaching 1.36 Ć 1013 Jones, fast photoresponses (Ļrise = 472 Ī¼s
and Ļdecay = 894 Ī¼s), low dark current, and
suppressed hysteresis
Bioinspired Formation of 3D Hierarchical CoFe<sub>2</sub>O<sub>4</sub> Porous Microspheres for Magnetic-Controlled Drug Release
Bioinspired
by the morphology of dandelion pollen grains, we successfully prepared
a template-free solution-based method for the large-scale preparation
of three-dimensional (3D) hierarchical CoFe<sub>2</sub>O<sub>4</sub> porous microspheres. Besides, on the basis of the effect of the
reaction time on the morphology evolution of the precursor, we proposed
an in situ dissolutionārecrystallization growth mechanism with
morphology and phase change to understand the formation of dandelion
pollenlike microspheres. Doxorubicin hydrochloride, an anticancer
drug, is efficiently loaded into the CoFe<sub>2</sub>O<sub>4</sub> microspheres. The magnetic nanoparticles as field-controlled drug
carriers offer a unique power of magnetic guidance and field-triggered
drug-release behavior. Therefore, 3D hierarchical CoFe<sub>2</sub>O<sub>4</sub> porous microspheres demonstrate the great potential
for drug encapsulation and controlled drug-release applications
Three-Dimensional Porous Nickel Frameworks Anchored with Cross-Linked Ni(OH)<sub>2</sub> Nanosheets as a Highly Sensitive Nonenzymatic Glucose Sensor
A facile and scalable
in situ microelectrolysis nanofabrication technique is developed for
preparing cross-linked NiĀ(OH)<sub>2</sub> nanosheets on a novel three-dimensional
porous nickel template (NiĀ(OH)<sub>2</sub>@3DPN). For the constructed
template, the porogen of NaCl particles not only induces a self-limiting
surficial hot corrosion to claim the āstart engine stopā
mechanism but also serves as the primary battery electrolyte to greatly
accelerate the growth of NiĀ(OH)<sub>2</sub>. As far as we know, the
microelectrolysis nanofabrication is superior to the other reported
NiĀ(OH)<sub>2</sub> synthesis methods due to the mild condition (60
Ā°C, 6 h, NaCl solution, ambient environment) and without any
post-treatment. The integrated NiĀ(OH)<sub>2</sub>@3DPN electrode with
a highly suitable microstructure and a porous architecture implies
a potential application in electrochemistry. As a proof-of-concept
demonstration, the electrode was employed for nonenzymatic glucose
sensing, which exhibits an outstanding sensitivity of 2761.6 Ī¼A
mM<sup>ā1</sup> cm<sup>ā2</sup> ranging from 0.46 to
2100 Ī¼M, a fast response, and a low detection limit. The microelectrolysis
nanofabrication is a one-step, binder-free, entirely green, and therefore
it has a distinct advantage to improve clean production and reduce
energy consumption
Effective Formation of Oxygen Vacancies in Black TiO<sub>2</sub> Nanostructures with Efficient Solar-Driven Water Splitting
Black TiO<sub>2</sub> nanomaterials have attracted considerable
attention since they usually exhibit excellent photocatalytic activities.
Herein, we report the facile preparation of black TiO<sub>2</sub> nanostructures
with ultrathin hollow sphere morphology, high crystalline quality,
small grain size (ā¼8 nm), and ultrahigh surface area (168.8
m<sup>2</sup> g<sup>ā1</sup>) through Al reduction. Electron
paramagnetic resonance (EPR) spectra demonstrate the existence of
oxygen vacancies in black TiO<sub>2</sub> nanostructures, which could
increase the donor density and effectively promote the separation
and transportation of photogenerated electronāhole pairs. The
black TiO<sub>2</sub> nanostructures exhibit a high solar-driven hydrogen
generation rate (56.7 mmol h<sup>ā1</sup> g<sup>ā1</sup>) under the full spectrum of solar light, which is nearly 2.5 times
than that of pristine TiO<sub>2</sub> nanostructures and superior
to those kinds of black TiO<sub>2</sub> photocatalytic materials reported
previously
Effects of Organic Cation Length on Exciton Recombination in Two-Dimensional Layered Lead Iodide Hybrid Perovskite Crystals
In recent years, 2D layered organicāinorganic
lead halide
perovskites have attracted considerable attention due to the distinctive
quantum confinement effects as well as prominent excitonic luminescence.
Herein, we show that the recombination dynamics and photoluminescence
(PL) of the 2D layered perovskites can be tuned by the organic cation
length. 2D lead iodide perovskite crystals with increased length of
the organic chains reveal blue-shifted PL as well as enhanced relative
internal quantum efficiency. Furthermore, we provide experimental
evidence that the formation of face-sharing [PbI<sub>6</sub>]<sup>4ā</sup> octahedron in perovskites with long alkyls induces
additional confinement for the excitons, leading to 1D-like recombination.
As a result, the PL spectra show enhanced inhomogeneous broadening
at low temperature. Our work provides physical understanding of the
role of organic cation in the optical properties of 2D layered perovskites,
and would benefit the improvement of luminescence efficiency of such
materials
Porous CoO Nanostructure Arrays Converted from Rhombic Co(OH)F and Needle-like Co(CO<sub>3</sub>)<sub>0.5</sub>(OH)Ā·0.11H<sub>2</sub>O and Their Electrochemical Properties
Novel CoO nanostructure arrays on
nickel foam with needle-like
and rhombic morphologies have been prepared by using urea and hexamethylenetetramine
as hydrolysis agents through fluoride-assisted hydrothermal method,
respectively. The possible formation mechanism and effect factors
of the novel arrays were systematically investigated by X-ray diffraction,
scanning and transmission electron microscopies, N<sub>2</sub> sorption,
X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy.
The precursor CoĀ(CO<sub>3</sub>)<sub>0.5</sub>(OH)Ā·0.11H<sub>2</sub>O or CoĀ(OH)F plays a crucial role in the formation of needle-like
or rhombic arrays. As-prepared precursor arrays can be further converted
to corresponding CoO arrays by annealing at 450 Ā°C for 2 h without
signification alteration of one-dimensional (1D) morphology. When
tested as anodes for lithium ion batteries (LIBs) without the addition
of other ancillary materials (carbon black and binder), the synthesized
CoO arrays with needle-like and rhombic morphologies deliver ultrahigh
initial discharge capacities of 1973.3 and 1447.9 mAh g<sup>ā1</sup>, respectively. In addition, they also maintain high reversible capacities
of 710 and 719 mAh g<sup>ā1</sup> at 0.2 C after 50 cycles,
respectively
A H<sub>2</sub>O<sub>2</sub> Oxidation Approach to Ti<sub>3</sub>C<sub>2</sub>/TiO<sub>2</sub> for Efficient Photocatalytic Removal of Distinct Organic Pollutants in Water
To
develop versatile photocatalysts for efficient degradation of
distinct organic pollutants in water is a continuous pursuit in environment
remediation. Herein, we directly oxidize Ti3C2 MXene with hydrogen peroxide to produce C-doped anatase TiO2 nanowires with aggregates maintaining a layered architecture
of the MXene. The Ti3C2 MXene provides a titanium
source for TiO2, a carbon source for in situ C-doping,
and templates for nanowire aggregates. Under UV light illumination,
the optimized Ti3C2/TiO2 exhibits
a reaction rate constant 1.5 times that of the benchmark P25 TiO2 nanoparticles, toward photocatalytic degradations of trace
phenol in water. The mechanism study suggests that photogenerated
holes play key roles on the phenol degradation, either directly oxidizing
phenol molecules or in an indirect way through oxidizing first the
surface hydroxyl groups. The unreacted Ti3C2 MXene, although with trace amounts, is supposed to facilitate electron
transfer, which inhibits charge recombination. The unique nanostructure
of layered aggregates of nanowires, abundant surface oxygen vacancies
arising from the carbon doping, and probably the Ti3C2/TiO2 heterojunction guarantee the high photocatalytic
efficiency toward removals of organic pollutants in water. The photocatalyst
also exhibits an activity superior to, or at least comparable to,
the benchmark P25 TiO2 toward photodegradations for typical
persistent organic pollutants of phenol, dye molecule of rhodamine
B, antibiotic of tetracycline, pharmaceutical wastewater of ofloxacin,
and pesticide of N,N-dimethylformamide, when evaluated
in total organic carbon removal
Simple Approach to Improving the Amplified Spontaneous Emission Properties of Perovskite Films
Organo-lead halide
perovskite has emerged as a promising optical gain media. However,
continuous efforts are needed to improve the amplified spontaneous
emission (ASE) even lasing properties to evade the poor photostability
and thermal instability of the perovskites. Herein, we report that
simply through the coating of polymer layer, the CH<sub>3</sub>NH<sub>3</sub>PbBr<sub>3</sub> polycrystalline films prepared by a modified
sequential deposition process show remarkably enhanced photoluminescence
and prolonged decay lifetime. As a result, under nanosecond pulse
pumping, the ASE threshold of the perovskite films is significantly
reduced from 303 to 140 Ī¼J/cm<sup>2</sup>. Furthermore, the
light exposure stability is improved greatly after the polymer coating.
We confirmed that the polymer layer plays the roles of both surface
passivation and symmetric waveguides. Our results may shed light upon
the stable and sustained output of laser from perovskite materials
2D Behaviors of Excitons in Cesium Lead Halide Perovskite Nanoplatelets
Fundamental
to understanding and predicting the optoelectronic
properties of semiconductors is the basic parameters of excitons such
as oscillator strength and exciton binding energy. However, such knowledge
of CsPbBr<sub>3</sub> perovskite, a promising optoelectronic material,
is still unexplored. Here we demonstrate that quasi-two-dimensional
(quasi-2D) CsPbBr<sub>3</sub> nanoplatelets (NPLs) with 2D exciton
behaviors serve as an ideal system for the determination of these
parameters. It is found that the oscillator strength of CsPbBr<sub>3</sub> NPLs is up to 1.18 Ć 10<sup>4</sup>, higher than that
of colloidal IIāVI NPLs and epitaxial quantum wells. Furthermore,
the exciton binding energy is determined to be of ā¼120 meV
from either the optical absorption or the photoluminescence analysis,
comparable to that reported in colloidal IIāVI quantum wells.
Our work provides physical understanding of the observed excellent
optical properties of CsPbBr<sub>3</sub> nanocrystals and would benefit
the prediction of high-performance excitonic devices based on such
materials