Carbon quantum dots as novel sensitizers for photoelectrochemical solar hydrogen generation and their size-dependent effect

Maize starch derived boron doped carbon spheres via facile solvothermal route as the photoluminescence sensor for determination of pH and Cr(VI)

In this work, a kind of boron doped carbon spheres (B-CSs) was successfully synthesized utilizing maize starch as carbon source and boric acid as dopant via facile solvothermal method. The chemical structure of the prepared B-CSs was systemically investigated by TEM, FT-IR, XRD, XPS and EDS. The synthesized B-CSs feature spherical structure with average size of ∼254 nm and exhibit strong photoluminescence (PL) with maximum emission at a wavelength of ∼453 nm under irradiation at 350 nm, leading to a quantum yield of 6.2%. Furthermore, the aqueous pH and Cr(VI) has a significantly various impact on the PL intensity of B-CSs, which can be flexibly utilized as the PL sensor for detection aqueous pH and Cr(VI) in aqueous. Particularly, the B-CSs have a desirable sensitivity and selectivity for detection of Cr(VI) with a low detection limit of ∼0.34μmol l^-1. Conclusively, our work provides a novel and dual-functional fluorescent sensor for detection of the pH and toxic metal ions in water environment.

Band gap tuning and surface modification of carbon dots for sustainable environmental remediation and photocatalytic hydrogen production - A review

Energy and water are the two major issues facing the modern mankind. Providing freshwater requires energy and producing energy uses water. In the present-day scenario, both these routes face growing problems and limitations. Energy crisis has risen due to the depletion of fossil fuels that cause pollution to water bodies making the water unusable for human consumption. In this regard, semiconductor nanocrystals with luminescent properties or carbon quantum dots (CQDs) are the newly developed nanomaterials whose distinctive photo-physical characteristics are focusing to a new generation of robust materials and sensors for sustainable development. In this review, advances in surface and band gap modification of CQDs to improve the activity of nanomaterials will be discussed with special reference to some specific CQDs exhibiting special optical properties for water treatment/splitting applications. Recent advances on CQDs nanocomposites including their applications in photodegradation of organic pollutants, sensing of heavy metal ions in water and water splitting are discussed critically to narrate the future prospects in this field. Challenges and limitations for further improvement are covered to provide smart choices for creating sustainability of benign environment and economic benefits.

Preparation of Core-Shell CQD@PANI Nanoparticles and Their Electrochemical Properties

In recent years, carbon quantum dots (CQDs) have been extensively investigated in many fields because of their incomparable and unique properties. However, the application of CQDs in the electrochemical field meets a big challenge due to their low specific capacitance. It is very important to improve the electrochemical performance of CQDs. In this study, a facile synthesis method was developed to synthesize CQD@PANI nanoparticles. The CQD@PANI nanoparticles were prepared via a precise quantitative adsorption polymerization method. TEM results showed that the PANI shell thickness could be adjusted by controlling the additive amount of aniline. Cyclic voltammetry and galvanostatic charge/discharge results showed that the electrochemical properties of CQDs have been significantly improved by coating PANI.

Photocatalytic water reduction using a polymer coated carbon quantum dot sensitizer and a nickel nanoparticle catalyst

Hydrogen gas is produced photocatalytically using 470 nm light, PVP-coated carbon quantum dots (CQDs) as the photosensitizer, and nickel nanoparticles (NiNPs) as the catalyst. The effect of the amount of polyvinylpyrrolidone (PVP) on the ability of the CQD/NiNP composites to catalyze proton reduction was studied. A maximum of 330 mmols H₂/g CQD is produced using 68 μg ml^-1 of CQDs and 6 μg ml^-1 of NiNPs, with activity persisting for 4 h when 20 wt%-PVP-coated CQDs were used. The H₂ production quantum yield under these conditions is 6%. It was found that composites having higher weight percent PVP had decreased rates of H₂ production, but increased duration. Increasing the weight percent of PVP coating also increases the fluorescence quantum yield of CQDs. Fluorescence quenching titrations reveal that H₂ production could occur by either a reductive or oxidative quenching mechanism. The nanomaterials, prepared using simple methods, are used as the photosensitizer and catalyst in the proton reduction system that operates using visible light.

Green synthesis of carbon quantum dots embedded onto titanium dioxide nanowires for enhancing photocurrent

The green synthesis of nanowired photocatalyst composed of carbon quantum dots-titanium hybrid-semiconductors, CQDs/TiO₂, are reported. Where graphite-based CQDs with a size less than 5 nm are directly synthesized in pure water electrolyte by a one-step electrochemistry approach and subsequently electrodeposited onto as-prepared TiO₂ nanowires through a voltage-driven reduction process. Electron paramagnetic resonance studies show that the CQDs can generate singlet oxygen and/or oxygen radicals to decompose the kinetic H₂O₂ intermediate species upon UV light illumination. With the effect of peroxidase-like CQDs, photocurrent density of CQDs/TiO₂ is remarkably enhanced by a 6.4 factor when compared with that of as-prepared TiO₂.

Smart Utilization of Carbon Dots in Semiconductor Photocatalysis

Efficient capture of solar energy will be critical to meeting the energy needs of the future. Semiconductor photocatalysis is expected to make an important contribution in this regard, delivering both energy carriers (especially H₂ ) and valuable chemical feedstocks under direct sunlight. Over the past few years, carbon dots (CDs) have emerged as a promising new class of metal-free photocatalyst, displaying semiconductor-like photoelectric properties and showing excellent performance in a wide variety of photoelectrochemical and photocatalytic applications owing to their ease of synthesis, unique structure, adjustable composition, ease of surface functionalization, outstanding electron-transfer efficiency and tunable light-harvesting range (from deep UV to the near-infrared). Here, recent advances in the rational design of CDs-based photocatalysts are highlighted and their applications in photocatalytic environmental remediation, water splitting into hydrogen, CO₂ reduction, and organic synthesis are discussed.

Carbon quantum dots decorated Cu2S nanowire arrays for enhanced photoelectrochemical performance

The photoelectrochemical (PEC) performance of Cu2S nanowire arrays (NWAs) has been demonstrated to be greatly enhanced by dipping-assembly of carbon quantum dots (CQDs) on the surfaces of Cu2S NWAs. Experimental results show that the pristine Cu2S NWAs with higher aspect ratios exhibit better PEC performance due to the longer length scale for light absorption and the shorter length scale for minority carrier diffusion. Importantly, the CQDs decorated Cu2S NWAs exhibit remarkably enhanced photocurrent density, giving a photocurrent density of 1.05 mA cm(-2) at 0 V vs. NHE and an optimal photocathode efficiency of 0.148% under illumination of AM 1.5G (100 mW cm(-2)), which is 4 times higher than that of the pristine Cu2S NWAs. This can be attributed to the improved electron transfer and the energy-down-shift effect of CQDs. We believe that this inexpensive Cu2S/CQD photocathode with increased photocurrent density opens up new opportunities in PEC water splitting.

Light emitting diodes based on carbon dots derived from food, beverage, and combustion wastes

One important resource for material synthesis is waste. Utilization of waste as a resource for material synthesis is an environmentally responsible approach that reduces the need for virgin resources and subsequent processing. In this report a method to produce multicolored, luminescent carbon dots (CDs) and subsequent fabrication of light emitting diodes from food, beverage, and combustion wastes, is discussed. Apart from food and beverages, combustion exhaust was also utilized for CDs production. Optical characterization results suggest that CDs from waste food and beverages are more luminescent than those produced from combustion waste.

Carbon quantum dots and applications in photocatalytic energy conversion

Quantum dots (QDs) generally refer to nanoscale particles of conventional semiconductors that are subject to the quantum-confinement effect, though other nanomaterials of similar optical and redox properties are also named as QDs even in the absence of strictly defined quantum confinement. Among such nanomaterials that have attracted tremendous recent interest are carbon dots, which are small carbon nanoparticles with some form of surface passivation, and graphene quantum dots in various configurations. In this article, we highlight these carbon-based QDs by focusing on their syntheses, on their photoexcited state properties and redox processes, and on their applications as photocatalysts in visible-light carbon dioxide reduction and in water-splitting, as well as on their mechanistic similarities and differences.

Carbon quantum dots and their applications

This review covers the progress in the research and development of carbon quantum dots and their applications in chemical sensing, biosensing, bioimaging, nanomedicine, photocatalysis and electrocatalysis.

Label-free photoelectrochemical cytosensing via resonance energy transfer using gold nanoparticle-enhanced carbon dots

A universal and label-free photoelectrochemical biosensing platform for the direct detection of HeLa cells was developed based on carbon-dots–AuNPs–cysteamine conjugates.