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Hematite has been considered an important candidate for the development of an efficient photoelectrocatalytic water-splitting system. One of the most serious obstacles that limits the efficiency of hematite is low absorption capacity in visible light. Herein, we report the production of hematene nanoplatelets from hematite ore with yields of up to 60%, using a low-cost, sustainable method that is based on the ultrasonic treatment of hematite ore in a water solution of a series of organic aromatic compounds. We show that the chemisorption of molecules with increased aromaticity on the surface of hematene resulted in the significant improvement of its visible light absorptivity, with an increase of up to 200%. As a result, using a water solution of terephthalaldehyde as a liquid medium, hematite ore was exfoliated to hematene nanoplatelets with a yield of 40% and remarkable stability in water. Due to this, hematene was easily drop-casted on glass forming homogenous thin films with strong absorptivity in the visible region. [ABSTRACT FROM AUTHOR]

Atomically precise two-dimensional (2D) cadmium chalcogenide nanoplatelets (NPLs) have increased interest in optoelectronic applications. In this work, we highlight the influence of the reaction growth time on the structural and photophysical properties, carrier dynamics, and photodetection properties of NPLs. The coexistence of the wurtzite (WZ) and zinc blende (ZB) polymorphs in ∼5:3 ratio is found in CdSe/CdS core/shell (CS) NPLs from the Rietveld analysis of X-ray diffraction (XRD) patterns. The tuning of photoluminescence emission from green to red and 12 times enhancement of the decay time in CdSe/CdS CS NPLs have been achieved by increasing the growth time. Femtosecond transient absorption spectroscopic analysis reveals the increase in rise time from 500 to 900 fs, and the overall bleach recovery dynamics get slower with the growth time. In the CdSe/CdS CS NPLs-based photodetector device, the photo-to-dark current intensity ratio is ∼600 with a fast photoresponse time of ∼100 ms. The maximum photoresponsivity in the visible region is around ∼113 mA/W with a very high detectivity of ∼2.1 × 1013 Jones. Analysis reveals that these solution-processed CdSe/CdS CS NPLs-based photodetectors are promising for next-generation optoelectronic applications. [ABSTRACT FROM AUTHOR]

Improving the understanding of multiple exciton interactions and dynamics in semiconductor nanostructures is mandatory for their successful use as photoactive materials in light convertors such as electroluminescent diodes, lasers, or single-photon sources. Here high-fluence and high-energy excitation effects are investigated in strongly confined two-dimensional (2D) lead iodide perovskite nanoplatelets (NPLs) using time-resolved photoluminescence and femtosecond transient absorption spectroscopy. Nonradiative Auger recombination (AR) is the dominant pathway for multiexciton recombination. Its dynamics are found to be subquadratic with the exciton density. Indeed, because of the limited exciton wave-function delocalization length, AR is limited by exciton diffusion in the 2D plane at moderate excitation fluence and takes place in several hundreds of picoseconds, with typical recombination rates on the order of 10–2 cm2/s. At high excitation fluence leading to an average interexciton distance comparable with the exciton delocalization length, the measured "intrinsic" AR time is faster than 10 ps and independent of the NPL composition. The strong dependence of the AR rate on the interexciton distance allows us to identify the recombination resulting from multiple exciton generation, involving the reaction of "geminate biexcitons", upon excitation at low fluence with high-energy photons. [ABSTRACT FROM AUTHOR]

Colloidal nanocrystals are playing an increasing role for the development of low cost optoelectronics. Among these materials, 2D nanoplatelets (NPL) offer particularly well-controlled optical features and their integration into device such as transistor and photoconductor is here discussed. We present recent results obtained on the optoelectronic properties of CdSe/CdS and HgTe 2D nanoplatelets (NPL). The manuscript is organized along three main sections. The first part is an introduction to 2D NPLs and their structural and optical properties. The second part gets focused on CdSe/CdS NPL and their photoconductive properties. We in particular highlight the key role plays by the 2D geometries on the charge dissociation. Finally the last part of the paper discusses about the recent report of HgTe and HgSe NPL with optical features in the near infrared. Here we discuss how the surface chemistry can be used to tune the majority carrier and the photoconductive properties of the material. [ABSTRACT FROM AUTHOR]

2D semiconducting nanoplatelets (NPLs) are an emerging class of photoactive materials. They can be used as building blocks in optoelectronic devices thanks to their large absorption coefficient, high carrier mobility, and unique thickness-dependent optical transitions. The main drawback of NPLs is their large lateral size, which results in unfavorable band energy levels and low quantum yield (QY). Here, ultrasmall lead chalcogenide PbSe1- xS x NPLs are prepared, which exhibit an unprecedented QY of ≈60%, the highest ever reported for this structure. The NPLs are applied as light absorber in a photoelectrochemical system, leading to a saturated photocurrent density of ≈5.0 mA cm−2 (44 mL cm−2 d−1), which is a record for NPL-based photoelectrodes in solar-driven hydrogen generation. Ultrasmall NPLs hold the potential for breakthrough developments in the field of optically active nanomaterials. [ABSTRACT FROM AUTHOR]

We investigate the electronic and transport properties of HgTe 2D colloidal quantum wells. We demonstrate that the material can be made p- or n-type depending on the capping ligands. In addition to the control of majority carrier type, the surface chemistry also strongly affects the photoconductivity of the material. These transport measurements are correlated with the electronic structure determined by high resolution X-ray photoemission. We attribute the change of majority carriers to the strong hybridization of an n-doped HgS layer resulting from capping the HgTe nanoplatelets by S2– ions. We further investigate the gate and temperature dependence of the photoresponse and its dynamics. We show that the photocurrent rise and fall times can be tuned from 100 μs to 1 ms using the gate bias. Finally, we use time-resolved photoemission spectroscopy as a probe of the transport relaxation to determine if the observed dynamics are limited by a fundamental process such as trapping. These pump probe surface photovoltage measurements show an even faster relaxation in the 100–500 ns range, which suggests that the current performances are rather limited by geometrical factors. [ABSTRACT FROM AUTHOR]

Lead-based halide perovskite nanocrystals (NCs) are recognized as emerging emissive materials with superior photoluminescence (PL) properties. However, the toxicity of lead and the swift chemical decomposition under atmospheric moisture severely hinder their commercialization process. Herein, we report the first colloidal synthesis of lead-free Cs 4 CuIn 2 Cl 12 layered double perovskite NCs via a facile moisture-assisted hot-injection method stemming from relatively nontoxic precursors. Although moisture is typically detrimental to NC synthesis, we demonstrate that the presence of water molecules in Cs 4 CuIn 2 Cl 12 synthesis enhances the PL quantum yield (mainly in the near-UV range), induces a morphological transformation from 3D nanocubes to 2D nanoplatelets, and converts the dark transitions to radiative transitions for the observed self-trapped exciton relaxation. This work paves the way for further studies on the moisture-assisted synthesis of novel lead-free halide perovskite NCs for a wide range of applications.

Realization of suitable membrane-based technology for efficient CO 2 capture to mitigate climate change relies on the development of thin-film composite (TFC) membranes with superior separation performance. Graphene oxide (GO), due to its 2D morphology, intrinsic strength and chemical compatibility, was used as a nanofiller to enhance CO 2 separation performance and stability of a facilitated transport membrane. SHPAA (sterically hindered polyallylamine)-based blend matrix was selected as the polymeric matrix material in this work. The high aspect ratio of GO-based fillers, when coupled with optimized coating protocol, resulted in TFC membranes of ultrathin (200 nm) selective layers with the in-plane orientation of nanoplatelets, leading to enhanced separation properties that can be retained for long term. Porous graphene oxide (pGO) was also incorporated as nanofillers, resulting in significantly improved gas permeation at a very low filler loading of 0.2 wt%; A CO 2 permeance of up to 607 GPU with a CO 2 /N 2 separation factor of 36 in flat-sheet configuration was documented. Chemical modification of GO with PEG groups was found to further increase the selectivity of the membranes but reduces the CO 2 permeance, showing a CO 2 /N 2 separation factor of 90 with a CO 2 permeance of 205 GPU. The effect of various 2D nanoplatelets on CO 2 transport properties in the membranes of hydrophilic PVA (polyvinyl alcohol) matrix and facilitated transport SHPAA/PVA matrix was elucidated with respect to the nanofiller property and loading. Image 1 • GO-based 2D nanoplatelets were employed as nanofillers in polymeric membranes. • SHPAA and PVA were used as polymeric matrices to study facilitated transport effect. • Hybrid TFC membranes with defect-free selective layers (~200 nm) were fabricated. • In-plane orientated 2D nanoplatelets at very low loading influences transport properties. • CO 2 permeance increased due to enhanced sorption and water re-distribution resulted in by GO. [ABSTRACT FROM AUTHOR]