This review summarizes recent progress in the design and applications of cadmium-free quantum dots (Cd-free QDs), with an emphasis on their role in biophotonics and nanomedicine. We first present the features of Cd-free QDs and describe the physics and emergent optical properties of various types of Cd-free QDs whose applications are discussed in subsequent sections. Selected specific QD systems are introduced, followed by the preparation of these Cd-free QDs in a form useful for biological applications, including recent advances in achieving high photoluminescence quantum yield (PL QY) and tunability of emission color. Next, we summarize biophotonic applications of Cd-free QDs in optical imaging, photoacoustic imaging, sensing, optical tracking, and photothermal therapy. Research advances in the use of Cd-free QDs for nanomedicine applications are discussed, including drug/gene delivery, protein/peptide delivery, image-guided surgery, diagnostics, and medical devices. The review then considers the pharma...

New Generation Cadmium-Free Quantum Dots for Biophotonics and Nanomedicine

Constructing 2D layered hybrid CdS nanosheets/MoS2 heterojunctions for enhanced visible-light photocatalytic H2 generation

Cadmium sulfide (CdS) has long time been one of the most promising inorganic photocatalysts for hydrogen production driven by visible light However, the photocorrosion of CdS is the most serious problem which constrains its development Here, we report the design and fabrication of a carbon dots-cadmium sulfide (CDs-CdS) nanocomposite, showing significant photocatalytic water splitting properties with impressive stability without requirement for any sacrificial agents or cocatalysts The highest hydrogen production rate was obtained for about 255 μmol h −1 , with an oxygen evolution rate for about 052 μmol h −1 , when the concentration of CDs in the sample is 003 g CDs /g catalyst  Even the produced H 2 and O 2 are not equal to the stoichiometric ratio of 2:1 (H 2 :O 2 ), the CDs-CdS nanocomposite shows greater stability (8-time repetitive catalytic experiments) than the CdS catalysts reported up to now (without sacrificial agents or cocatalysts) It is also inspiring that when we increased the concentration of CDs in the catalysts, the produced H 2 and O 2 were gradually adjusted to meet the stoichiometric ratio of 2:1 in spite of low hydrogen production rate (013 μmol h −1 )

Carbon dots enhance the stability of CdS for visible-light-driven overall water splitting

In the past decade, inorganic semiconductors have been successfully demonstrated as light absorbers in efficient solar water splitting to generate chemical fuels. Pseudobinary semiconductors Zn1–xCdxS (0 ≤ x ≤ 1) have exhibited a superior photocatalytic reactivity of H2 production from splitting of water by artificial solar irradiation without any metal catalysts. However, most studies had revealed that the extremely high efficiency with an optimal content of Zn1–xCdxS solid solution was determined as a result of elevating the conduction band minimum (CBM) and the width of bandgap. In addition to corresponding band structure and bandgap, the local crystal structure should be taken into account as well to determine its photocatalytic performance. Herein, we demonstrated the correlations between the photocatalytic activity and structural properties that were first studied through synchrotron X-ray diffraction and X-ray absorption spectroscopy. The crystal structure transformed from zinc blende to coexisted ...

Heterojunction of Zinc Blende/Wurtzite in Zn1-xCdxS Solid Solution for Efficient Solar Hydrogen Generation: X-ray Absorption/Diffraction Approaches

Construction of functional photocatalysts with ultrahigh photocatalytic hydrogen evolution using solar energy is still a serious challenge for scientific researchers. Here, recently, a facile chemical reduction method is developed to synthesize NixCo1-x/Zn0.75Cd0.25S nanohybrid photocatalysts, a kind of promising smart material with optimizing H2 evolution rate being 0.21 mol h−1 g−1 under simulated solar light irradiation with an apparent quantum efficiency (AQE) of 13.3% at 365 nm, an ultrahigh H2 evolution rate among almost all the semiconductor-based photocatalysts. More importantly, the NixCo1-x/Zn0.75Cd0.25S photocatalyst shows a sufficient stability property for >20 h. The pronounced synergistic effect between non-noble-metals of Ni and Co boosts the transfer and separation of photo-generated electron-hole pairs, and a synergistic catalytic mechanism has been proposed and studied in detail.

Synergistic effect based NixCo1-x architected Zn0.75Cd0.25S nanocrystals: An ultrahigh and stable photocatalysts for hydrogen evolution from water splitting

A new sulfur precursor with a highly reactive chemical nature was prepared with S powder and NaBH₄ at the high temperature of 180 °C in a closed autoclave and made it possible to carry out the synthesis of high quality metal sulfide nanocrystals (NCs) with diverse composition and structure Using this new sulfur source, we demonstrated aqueous synthesis of colloidal Cu-doped ZnCdS NCs (d-dots) with pure, color-tunable photoluminescence (PL) in a wide spectral range (from 517 to 650 nm) based on the 'co-nucleation doping' strategy The influences of the various experimental variables, including Cd/Zn ratio, Cu-doping concentration, pH value and amount of mercaptopropionic acid (MPA), on the optical properties of Cu-doped ZnCdS NCs were systematically investigated Furthermore, highly efficient and stable dopant emission from Cu:ZnCdS/ZnS core/shell d-dots with PL quantum yield as high as 40% was achieved by the deposition of a ZnS shell around the bare Cu:ZnCdS cores; this is the highest reported to date for aqueous doped NCs The optical properties and structure of the d-dots were characterized by UV-vis absorption spectra, PL spectra, x-ray photoelectron spectroscopy, powder x-ray diffraction, and transmission electron microscopy The experimental results indicated that this facile synthesis route would provide a versatile approach for the preparation of other water-soluble sulfide NCs

https://iopscience.iop.org/article/10.1088/0957-4484/25/13/135602/pdf

Aqueous synthesis of Cu-doped ZnCdS/ZnS core/shell nanocrystals with a new and highly reactive sulfur source

Water-soluble, highly emissive, color-tunable, and stable Cu:ZnSeS/ZnS core/shell doped nanocrystals (d-dots) with pure dopant emission have been synthesized through a simple aqueous synthetic route. The influence of various experimental variables, including introduction of chloride ions, amount of mercaptopropanoic acid (MPA), pH value and Cu-doping concentration, on the optical properties of Cu dopant emission have been systematically investigated. Through epitaxial growth of a ZnS shell on Cu:ZnSeS cores, the fabricated Cu:ZnSeS/ZnS d-dots exhibit a high PL QY of up to 40%, which is the highest ever reported for any type of water-soluble Cu-doped selenide-based II–VI semiconductor nanocrystals (NCs). Moreover, the serious photostability problem of Cu-based d-dots in the presence of air and light is solved and the quenching of the excitonic emission is suppressed as well. The stable testing of these highly luminescent d-dots shows that the Cu:ZnSeS/ZnS d-dots have better photostability and preserve more than ~90% of the initial intensity in the presence of air and light 30 days later. This new class of green emissive material shows their potential applications in biolabeling, bioimaging, and light emitting devices.

Water-soluble, highly emissive, color-tunable, and stable Cu-doped ZnSeS/ZnS core/shell nanocrystals

High-quality, pure, and color-tunable Ag:ZnCdS quantum dots (d-dots) are prepared by optimization of the experimental conditions including Ag-doping concentration and Zn/Cd precursor ratio. Highly emissive Ag:ZnCdS/ZnS core/shell d-dots with photoluminescence quantum yield (PL QY) as high as 58% are constructed in situ by the growth of a ZnS shell around the crude Ag:ZnCdS solution, which is the highest PL QY reported to date for Ag-based semiconductor d-dots. The emission color of a Ag:ZnCdS d-dot can be tuned toward a larger red region by simple Se treatment at high temperature (220–260 °C). With Se treatment, Ag:ZnCdS alloyed d-dots are transformed into Ag:ZnCdSSe alloyed d-dots, and the corresponding optical changes of d-dots in this process are investigated systematically. This strategy provides a versatile approach for the preparation of other multinary semiconductor nanocrystals.

Facile synthesis of Ag-doped ZnCdS nanocrystals and transformation into Ag-doped ZnCdSSe nanocrystals with Se treatment

Hydrothermal Synthesis of Mn-Doped ZnSe Quantum Dots and Effects of Surface Overcoating on Their Optical Properties

High-quality Mn:ZnS doped nanocrystals (d-dots) with photoluminescence (PL) quantum yield (QY) of 50-70% have been synthesized based on nucleation-doping strategy by choosing 1-dodecanethiol (DDT) as the capping ligand. Controlling the growth of small-sized MnS core nanoclusters was successfully achieved by changing the injection temperature of sulfur precursor, the growth time of MnS nuclei, and the amount of DDT. Furthermore, MnS/ZnS core/shell d-dots with a diffusion layer at the interface between the MnS core and the ZnS shell were fabricated through an overcoating of the ZnS shell layer on the presynthesized MnS core nanoclusters. The resulting monodisperse d-dots exhibited spherical shape with a zinc-blende crystal structure. The critical temperature for lattice diffusion of Mn ions in the ZnS host lattice was determined to be about 260 degrees C by annealing the presynthesized and purified Mn:ZnS d-dots.

Yunqiang Zhao

Papers

Aqueous synthesis of Cu-doped ZnCdS/ZnS core/shell nanocrystals with a new and highly reactive sulfur source

Water-soluble, highly emissive, color-tunable, and stable Cu-doped ZnSeS/ZnS core/shell nanocrystals

Facile synthesis of Ag-doped ZnCdS nanocrystals and transformation into Ag-doped ZnCdSSe nanocrystals with Se treatment

Hydrothermal Synthesis of Mn-Doped ZnSe Quantum Dots and Effects of Surface Overcoating on Their Optical Properties

Facile synthesis of Mn-doped ZnS nanocrystals and determination of critical temperature for lattice diffusion process.