Gas assisted method synthesis nitrogen-doped carbon quantum dots and Hg (II) sensing

One Pot Hydrothermal Synthesis and Application of Bright-yellow-emissive Carbon Quantum Dots in Hg2+ Detection

Carbon quantum dots (CQD) have drawn great interest worldwide for their extensive application as sensors due to their extraordinary physical and chemical characteristics, good biocompatibility, and high fluorescence in nature. Here, we demonstrate a technique for detecting mercury (Hg2+) ion using a fluorescent CQD probe. Ecology is concerned about the accumulation of heavy metal ions in water samples due to their harmful effects on human health. Sensitive identification and removal of metal ions from water samples are required to reduce heavy metals' risk. To find out Mercury in the water sample, carbon quantum dots were used and synthesized by 5-dimethyl amino methyl furfuryl alcohol and o-phenylene diamine through the hydrothermal technique. The synthesized CQD shows yellow emission when exposed to UV irradiation. Mercury ion was used to quench carbon quantum dots, and it was found that the detection limit was 5.2 nM with a linear range of 15-100 µM. The synthesized carbon quantum dots were demonstrated to efficiently detect Mercury ions in real water samples.

Preparation, Properties, and Application of Lignocellulosic-Based Fluorescent Carbon Dots

Carbon dots (CDs) are a relatively new type of fluorescent carbon material with excellent performance and widespread application. As the most readily available and widely distributed biomass resource, lignocellulosics are a renewable bioresource with great potential. Research into the preparation of CDs with lignocellulose (LC-CDs) has become the focus of numerous researchers. Compared with other carbon sources, lignocellulose is low cost, rich in structural variety, exhibits excellent biocompatibility,^[1] and the structures of CDs prepared by lignin, cellulose, and hemicellulose are similar. This Review summarized research progress in the preparation of CDs from lignocellulosics in recent years and reviewed traditional and new preparation methods, physical and chemical properties, optical properties, and applications of LC-CDs, providing guidance for the formation and improvement of LC-CDs. In addition, the challenges of synthesizing LC-CDs were also highlighted, including the interaction of different lignocellulose components on the formation of LC-CDs and the nucleation and growth mechanism of LC-CDs; from this, current trends and opportunities of LC-CDs were examined, and some research methods for future research were put forward.

Development of a surface-modified paper-based colorimetric sensor using synthesized Ag NPs-alginate composite

There has been an increase in the discovery and usage of sensors for the detection of chemical compounds in the field of analytical chemistry since the last several years. This has led to progressive research in nanotechnology for developing efficient nanomaterials for bio-chemical sensing applications. Thereby, a deft synthesis of silver nanoparticles (Ag NPs) under microwave irradiation was achieved using sodium alginate as a reducing and capping agent in a fast and cost-effective approach. As per the X-ray diffraction analysis, the average particle size of Ag NPs was found to be 10 nm. X-ray photoelectron spectroscpopy analysis showed characteristic peaks at binding energies of 368.10 and 374.11 eV indicating the formation of Ag NPs. The synthesized Ag NPs-alginate composite was further used to develop a paper-based sensor for the detection of H₂O₂. Detection of H₂O₂ is based on the discolouration of the Ag NPs-alginate composite modified paper sensor as a function of H₂O₂ concentration. The analysis of the decoloured paper strips was done by a smartphone camera and an RGB Colour Reader application (app) to measure colour intensity. The sensing characteristics were found in the range of 0.1-10 mM. The colour analysis revealed piecewise linear relationship of intensity of RGB to H₂O₂ concentration in the range of 0.1-1.5 and 2-10 mM with R² values of 0.97 and 0.9778, respectively. Owing to the high sensitivity, selectivity, and cost-effectiveness, the developed paper sensor can be a potential tool for real-time analysis of H₂O₂.

Synthesis of Fluorescent Carbon Dots and Their Application in Ascorbic Acid Detection

Water-soluble fluorescent carbon dots (CDs) were synthesized by a hydrothermal method using citric acid as the carbon source and ethylenediamine as the nitrogen source. The repeated and scale-up synthetic experiments were carried out to explore the feasibility of macroscopic preparation of CDs. The CDs/Fe3+ composite was prepared by the interaction of the CDs solution and Fe3+ solution. The optical properties, pH dependence and stability behavior of CDs or the CDs/Fe3+ composite were studied by ultraviolet spectroscopy and fluorescence spectroscopy. Following the principles of fluorescence quenching after the addition of Fe3+ and then the fluorescence recovery after the addition of asorbic acid, the fluorescence intensity of the carbon dots was measured at λex = 360 nm, λem = 460 nm. The content of ascorbic acid was calculated by quantitative analysis of the changing fluorescence intensity. The CDs/Fe3+ composite was applied to the determination of different active molecules, and it was found that the composite had specific recognition of ascorbic acid and showed an excellent linear relationship in 5.0-350.0 μmol·L-1. Moreover, the detection limit was 3.11 μmol·L-1. Satisfactory results were achieved when the method was applied to the ascorbic acid determination in jujube fruit. The fluorescent carbon dots composites prepared in this study may have broad application prospects in a rapid, sensitive and trace determination of ascorbic acid content during food processing.

A review on nanostructured carbon quantum dots and their applications in biotechnology, sensors, and chemiluminescence

Carbon quantum dots (CQDs) are a member of carbon nanostructures family which have received increasing attention for their photoluminescence (PL), physical and chemical stability and low toxicity. The classical semiconductor quantum dots (QDs) are semiconductor particles that are able to emit fluorescence by excitation. The CQDs is mainly referred to photoluminescent carbon nanoparticles less than 10 nm, with surface modification or functionalization. Contrary to other carbon nanostructures, CQDs can be synthesized and functionalized fast and easily. The fluorescence origin of the CQDs is a controversial issue which depends on carbon source, experimental conditions, and functional groups. However, PL emissions originated from conjugated π-domains and surface defects have been proposed for the PL emission mechanisms of the CQDs. These nanostructures have been used as nontoxic alternatives to the classical heavy metals containing semiconductor QDs in some applications such as in-vivo and in-vitro bio-imaging, drug delivery, photosensors, chemiluminescence (CL), and etc. This paper will introduce CQDs, their structure, and PL characteristics. Recent advances of the application of CQDs in biotechnology, sensors, and CL is comprehensively discussed.

CdSe quantum dots capped with p-nitrophenyldiazenylphenyloxadiazole: a nanosensor for Cd2+ ions in aqueous media

A nanosensor based on p-nitrophenyldiazenylphenyloxadiazole (NDPO) capped CdSe quantum dots (QDs) was developed for Cd2+ ions in aqueous solutions. The nanosensor exhibited a high selectivity for cadmium ions and showed linear correlation with Cd2+ ions concentration in the range of 0.05–1.0 mmol/L. The prepared NDPO capped CdSe QDs were characterized by TEM, SEM, EDX, and FTIR techniques.