Quantum Dots Graphene Research Articles

Probing the Critical Role of Interfaces for Superior Performance in PbS Quantum Dot/Graphene Nanohybrid Broadband Photodetectors.

Colloidal quantum dots/graphene (QD/Gr) nanohybrids have been studied intensively for photodetection in a broadband spectrum including ultraviolet, visible, near-infrared, and shortwave infrared (UV-vis-NIR-SWIR). Since the optoelectronic process in the QD/Gr nanohybrid relies on the photogenerated charge carrier transfer from QDs to graphene, understanding the role of the QD-QD and QD-Gr interfaces is imperative to the QD/Gr nanohybrid photodetection. Herein, a systematic study is carried out to probe the effect of these interfaces on the noise, photoresponse, and specific detectivity in the UV-vis-NIR-SWIR spectrum. Interestingly, the photoresponse has been found to be negligible without a 3-mercaptopropionic acid (MPA) ligand exchange, moderate with a single ligand exchange after all QD layers are deposited on graphene, and maximum if it is performed after each QD layer deposition up to five layers of total QD thickness of 260-280 nm. Furthermore, exposure of graphene to C-band UV (UVC) for a short period of 4-5 min before QD deposition leads to improved photoresponse via removal of polar molecules at the QD/Gr interface. With the combination of the MPA ligand exchange and UVC exposure, optimal optoelectronic properties can be obtained on the PbS QD/Gr nanohybrids with high specific detectivity up to 2.6 × 1011, 1.5 × 1011, 5 × 1010, and 1.9 × 109 Jones at 400, 550, 1000, and 1700 nm, respectively, making the nanohybrids promising for broadband photodetection.

Erratum to: A DFT study of Ti3C2O2 MXenes quantum dots supported on single layer graphene: Electronic structure and hydrogen evolution performance

Heterojunction structure has been extensively employed for the design of novel catalysts. In the present study, density functional theory was utilized to investigate the electronic structure and hydrogen evolution performance of Ti3C2O2 MXene quantum dots/graphene (QDs/G) heterostructure. Results show that a slight distortion can be observed in graphene after hybriding with QDs, due to which the electronic structure of QDs have been changed. Associated with such QDs-graphene interaction, the catalytic activity of Ti3C2O2 QDs has been optimized, leading to excellent HER catalytic performance.

Stimulating Charge Transfer Over Quantum Dots via Ligand-Triggered Layer-by-Layer Assembly toward Multifarious Photoredox Organic Transformation

Semiconductor quantum dots (QDs) have garnered tremendous attention by virtue of their substantial light-harvesting and conversion efficiencies, large number of active sites, unique quantum size confinement, and multiple exciton generation effects. In this regard, recent years have witnessed their widespread applications in photocatalysis. Nonetheless, intrinsic disadvantages of QDs including unfavorable photostability, ultrafast charge recombination rate, and sluggish kinetic of charge carriers retard the construction of high-efficiency QDs-based photocatalysts for solar energy conversion. Thus far, in-depth investigation on the visible-light-driven photoredox organic transformation over QDs has not yet been exhaustively explored, and corresponding photocatalytic mechanisms remain elusive. In this work, selecting cadmium selenide (CdSe) as a quintessential category of semiconductor QDs, we demonstrated a facile, green, easily accessible, and rather efficient electrostatic self-assembly strategy to conspicuously boost the versatile photoredox performances of CdSe QDs toward selective organic transformation under visible light irradiation by intimately integrating with graphene (GR) via judicious surface charge tuning. In this scenario, intrinsically negatively charged CdSe QDs and surface-modified positively charged GRs were utilized as the building blocks for spontaneous electrostatic self-assembly buildup, which gives rise to well-defined CdSe QDs–GR ensembles. More intriguingly, ligands capped on the CdSe QDs surface enable the alternate layer-by-layer (LbL) assembly of CdSe QDs and GR forming three-dimensional spatially multilayered heterostructures. Furthermore, it was significant to unveil that such self-assembled CdSe QDs–GR nanocomposites exhibit remarkably enhanced and multifunctional photoredox performances toward selective oxidation of aromatic alcohols to corresponding aromatic aldehydes and selective reduction of nitroaromatics to amino compounds under visible light irradiation, which far exceeds the pristine CdSe QDs counterpart, which exhibits almost negligible photoactivities. This can be ascribed to the pivotal role of GR for conspicuously capturing and shuttling electrons from band-gap photoexcitation of CdSe QDs, intimate interfacial contact between the building blocks, and enlarged specific surface area stemming from seamless GR encapsulation and intercalation, along with the unique ligand-triggered LbL assembly integration mode between CdSe QDs and GR, hence synergistically reducing the recombination rate and prolonging the lifetime of charge carriers. Furthermore, photoredox mechanisms of the CdSe QDs–GR ensemble were elucidated. It is anticipated that our work would afford an efficacious avenue to finely modulate the charge transport over QDs for solar energy conversion.

Highly tunable doping in Ge quantum dots/graphene composite with distinct quantum dot growth evolution

Quantum dots/graphene (QDs/Gr) composites have become the research hotspot recently due to their unique synergistic effect as optical absorption material for next-generation electronic and optoelectronic devices. In this work, Ge QDs/Gr composite is prepared by a simple and effective ion-beam sputtering deposition technique. The intact growth evolution process is detailly investigated by means of the effect of Ge deposition amount, which will induce the enhanced crystallinity in QDs and the reduced defects in graphene. Moreover, a feasible and inspiring strategy to effectively tune doping in graphene by artificial control through changing the deposition amount of Ge atoms on graphene is demonstrated. In addition, charge transfer and interaction strength at the interface of Ge QD and graphene is influenced via the oxygen defect in the QD surface, which is consistent with field-effect transistor test and first-principle calculations. The p-doping characteristics of graphene decorated by Ge QDs may have significant application prospects in energy band engineering of graphene-based building blocks for graphene-based composite development and near-infrared detector applications.

Review of the Synthetic Techniques and Applications of the Quantum Dots/Graphene Composites

The Quantum Dots/Graphene (QDs/GR) composites have attracted numerous interests caused by its unique physical and chemical properties in past few decades. The shortages of the single QD and graphene materials could be remedied by the synergistic effects from QDs/GR composite materials; meanwhile, some unique phenomena and superior physical properties were also produced. The QDs/GR composites processed better photocatalytic activities, higher photon capture abilities and excellent optical responsibilities. Therefore, they were widely applied in various techniques. Here, we reviewed and discussed recent research progresses about the QDs/GR composites and focused on their industrial preparation and commercial applications. Among these synthetic methods, ion beam sputtering deposition (IBSD) and molecular beam epitaxy (MBE) were discussed in detail because they could be directly applied in commercial industry for preparing size-tunable quantum dots. In another part, the applications of the QDs/GR composites were also discussed, the advanced physical and chemical properties promoted these composites to have numerous potential for being applied in photodetectors, lithium ion batteries, solar cells, supercapacitors and other devices. The appropriate synthetic method for QDs/GR materials is highly dependent on the requirements of its applications. We firmly believe that the direct synthesis technique of ideal QDs/GR composite for specific applications is a challenge and research emphasis for scientist and engineers in future.

Recent progress in the preparation and application of quantum dots/graphene composite materials

Quantum dots/graphene (QDs/GR) composite materials show a distinct synergistic effect between the QDs and graphene, which has aroused vast attention toward their unique characteristics in the last few decades.

Facile one-step hydrothermal method to fabricate Fe3O4 quantum dots–graphene nanocomposites for extraction of dye from aqueous solution

Fe3O4 quantum dots (QDs)–graphene (GN) nanocomposites were successfully synthesized via a simple one-step hydrothermal method. The results showed that Fe3O4 QDs were well dispersed on the surface of graphene nanosheets, forming Fe3O4–GN nanocomposites. All of the samples exhibited superparamagnetic properties, the magnetic saturation value of the Fe3O4–GN nanocomposites was decreased as the initial mass ratio of the Fe3O4 QDs and GN decreased from 5:1 to 1:5. The Fe3O4–GN nanocomposites (Fe3O4:GN = 1:5) exhibited excellent adsorption ability in the removal of MB dyes, and all samples could achieve completely adsorption of MB within 12 min, suggesting their use as a promising adsorbent for water treatment.

Facile one-pot synthesis of MoS2 quantum dots-graphene-TiO2 composites for highly enhanced photocatalytic properties.

We reported a simple one-pot solvothermal approach to fabricate a MoS2 quantum dots (QDs)-graphene-TiO2 (MGT) composite photocatalyst with significantly improved photocatalysis properties, which is caused by the increased charge separation, visible-light absorbance, specific surface area and reaction sites upon the introduction of MoS2 QDs.

Intersubunit Electron Transfer (IET) in Quantum Dots/Graphene Complex: What Features Does IET Endow the Complex with?

First principles calculations of quantum dots (QDs)/graphene (QDs/GR) hybrid nanomaterials were performed to investigate the interfacial electron–hole separation process at the atomistic level for verifying the tentative mechanism and unveiling the functionalities endowed by the intersubunit electron transfer. Our calculated results unveil the intersubunit electron transfer mechanism of QDs/GR nanomaterials: upon visible light adsorption, the ground electron of CdS QD in nanomaterials is first promoted to the excitated state, which then injects into the conduction band of graphene and transports along graphene layer through π* orbitals to achieve interfacial electron–hole separation. Adiabatic and nonadiabatic methods are used to estimate the electron transfer time at the heterogeneous interface from CdS QD to graphene. Our findings suggest a new route to facilitate the design of QDs@GR based nanodevices.