Doped Dots Research Articles

Development of silver-doped carbon dots sensor derived from lignin for dual-mode fluorometric and spectrophotometric determination of valsartan in a bulk powder and a commercial product

Doping of carbon dots (CDs) with heteroatoms has garnered growing attention in recent years as a useful method of controlling their physicochemical properties. In this study, a new dual-mode sensor based on silver-doped CDs (AgCDs) derived from lignin was developed for fluorometric and spectrophotometric determination of valsartan (VAL). The analysis of AgCDs revealed a structure that closely resembled graphene oxide, with the successful doping of Ag. The mean particle size of AgCDs was 3.50 ± 0.89 nm and it exhibited a reasonable fluorescence quantum yield of 28.1%. The emission at 612 nm of AgCDs is quenched by VAL after being excited at 275 nm due to a combination of dynamic and static quenching mechanisms. The enhancement in the absorbance of AgCDs upon the addition of the medication was measured at 275 nm. The most favorable circumstances for the dual-mode sensing were achieved with a pH of 8 and a volume of 0.10 mL of AgCDs. The measurements were conducted using fluorometry after 3 min at 10°C, followed by spectrophotometry after 7 min at 20°C. The fluorometric data indicated a linear response within the range of 2.0-50.0 μg/mL, while the spectrophotometric results showed a dynamic range of 5.0-100.0 μg/mL. The limits of detection (LODs) were 0.57 and 1.38 μg/mL for the fluorometric and spectrophotometric methods, respectively. The limits of quantification (LOQs) were 1.72 and 4.19 μg/mL for the fluorometric and spectrophotometric methods, respectively. The nano sensor efficiently assessed the presence of VAL in pharmaceutical tablets and produced a favorable outcome with the mean of recovery of 98.91% and 99.76% with relative standard deviation (RSD%) of 0.79 and 0.78 for the fluorometric and spectrophotometric methods, respectively.

Effect of doping with carbon dots on the alignment and dielectric properties of nematic liquid crystal 4-cyano-4′-pentylbiphenyl in ITO sample cells without conventional alignment layers for low-cost display applications

The melding of nanomaterials with liquid crystalline materials is at the frontier of scientific research due to the transformative impact of nanoparticles on the functionalities of host liquid crystal materials. Here, we report the effect of doping of carbon dots (CDs) in the nematic liquid crystal (NLC), 5CB (4-cyano-4′-pentylbiphenyl) in indium tin oxide (ITO) sample cells without alignment layers (i.e., unaligned ITO (U-ITO) sample cells) using polarizing optical microscopy and dielectric spectroscopic techniques. Polarizing optical microscopy reveals largely dark optical textures under crossed polarizers confirming vertical alignment of Pure 5CB in U-ITO sample cells. However, defects present in the texture pose severe constraints on the use of induced vertical alignment in U-ITO sample cells for device applications. To improve the quality of vertical alignment, CDs of size 2.8 nm at concentrations of 0.03, 0.05 and 0.1 wt% are doped into 5CB. Optical texture studies show the quality of induced vertical alignment of the 0.03 wt% composite is better than pure 5CB and other composites. Frequency-temperature dependent dielectric studies verify the induced vertical alignment by observation of the short-axis molecular relaxation. The stability of the vertical alignment throughout the nematic phase of 5CB is confirmed through temperature dependent dielectric and optical texture studies. The induced vertical alignment of 5CB in U-ITO sample cells could be attributed to the stronger LC-LC interaction than the ITO-LC interaction. The improvement in the quality of vertical alignment of CDs-5CB composites could be due to the CDs influencing LC-LC and ITO-LC interactions. Finally, the effect of CDs on the increasing dc electrical conductivity of 5CB in U-ITO sample cells is investigated. Our results clearly indicate that CD-5CB composites would be useful in cost-effective display and other photonic devices devoid of alignment layers.

Lentils/urea as precursors for profound S and N doping of carbon dots for selective sequential determination of Hg(II) and S(II) in food and environmental samples

In this article, we described a new platform for probing toxic pollutants, namely Hg2+ and S2-, in aquatic environment by tracing the “on–off-on” fluorescence signals of quantum dots. To achieve this, red lentils and urea, as natural precursors, were utilized as sources of S and N doping, respectively, to fabricate blue fluorescent carbon quantum dots, namely, lentils/urea quantum dots (LUQDs) with good quantum yield and plentiful S-doping. In the present work, the quality-by-design (QbD) strategy was applied to control and select the optimum conditions for the microwave-aided synthesis of the carbon dots. LUQDs exhibit excitation-dependent emissions, where the maximum fluorescence emission was at 360 nm after excitation at 300 nm. During the detection step, the fluorescence of LUQDs is quenched by the incorporation of Hg2+ over the range of 0.50–70.0 μM. Next, S2- reacts with Hg2+, resulting in turning on the fluorescence emission of LUQDs in the range of 10.0–150.0 µM.The method was applied for the detection of both Hg2+ and S2- in tap, sewage, and river water samples with a recovery rate ranging between 98.96 % and 101.26 %; in addition, Hg2+ was detected in canned Tuna samples with a recovery of 98.70 %. Furthermore, the greenness of the developed method was confirmed through various greenness metrics.

Solvent-Free Synthesis of S,N-Doped Carbon Dots for Extended Visible-Light-Induced Oxidase-Mimicking Activities and Antimicrobial Applications.

Photo-oxidase nanozymes are emerging enzyme-mimicking materials that produce reactive oxygen species (ROS) upon light illumination and subsequently catalyze the oxidation of the substrate. Carbon dots are promising photo-oxidase nanozymes due to their biocompatibility and straightforward synthesis. Carbon dot-based photo-oxidase nanozymes become active for ROS generation under UV or blue light illumination. In this work, sulfur and nitrogen doped carbon dots (S,N-CDs) were synthesized by solvent-free, microwave assisted technique. We demonstrated that sulfur, nitrogen doping of carbon dots (band gap of 2.11 eV) has enabled photo-oxidation of 3,3,5,5'-tetramethylbenzidine (TMB) with extended visible light (up to 525 nm) excitation at pH 4. The photo-oxidase activities by S,N-CDs produce Michaelis-Menten constant (Km ) of 1.18 mM and the maximum initial velocity (Vmax ) as 4.66×10-8 Ms-1 , under 525 nm illumination. Furthermore, visible light illumination can also induce bactericidal activities with growth inhibition of Escherichia coli (E. coli). These results demonstrate that S,N-CDs can increase intracellular ROS in the presence of LED light illumination.

Halogen-doped phosphorescent carbon dots for grayscale patterning

Flexible organic materials that exhibit dynamic ultralong room temperature phosphorescence (DURTP) via photoactivation have attracted increasing research interest for their fascinating functions of reversibly writing-reading-erasing graphic information in the form of a long afterglow. However, due to the existence of a nonnegligible activation threshold for the initial exposure dose, the display mode of these materials has thus far been limited to binary patterns. By resorting to halogen element doping of carbon dots (CDs) to enhance intersystem crossing and reduce the activation threshold, we were able to produce, for the first time, a transparent, flexible, and fully programmable DURTP composite film with a reliable grayscale display capacity. Examples of promising applications in UV photography and highly confidential steganography were constructed, partially demonstrating the broad future applications of this material as a programmable platform with a high optical information density.

Deep blue photoluminescence and optical gain from sodium-doped carbon dots

The photoluminescence (PL) from carbon dots can be dramatically modified through the engineering of surface oxygen-containing functional groups. Despite the recent surge of interest in the non-metal doping of carbon dots, the photo-physical properties of metal-doped carbon dots remain unexplored. Here, we report the highly efficient deep blue PL and amplified spontaneous emission from sodium (Na)-ion-doped carbon dots. Based on the structure- and temperature-dependent PL and the temporal evolution of PL, we reveal that the introduction of Na ions into carbon dots not only passivate the electronegative oxygen related defects but also create new Na–O related defect centers in the band gap, leading to deep blue PL with dramatically reduced bandwidth and significantly enhanced quantum yield. We establish a luminescence model with four energy levels to interpret the PL dynamics of Na+-doped carbon dots. We demonstrate for the first time the ASE from such carbon dots, which exhibit a net optical gain coefficient of 47.8 cm−1 at 440 nm. Our results open new horizons for improving the PL of carbon dots and pave the way for realizing optoelectronic devices based on carbon dots.

Effects of Heteroatom Doping of Carbon Dots from Sugar on Optical Properties, Phenolic Content, Antioxidant Activity, Photostability, and Cytotoxicity

AbstractCarbon dots (CDs) are fascinating nanomaterials with technologically relevant properties; however, the effects of heteroatom doping on several properties of CDs have not been studied. In this work, a facile method for the synthesis and heteroatom doping of carbon dots from table sugar was developed using nitric acid, phosphoric acid, and sulfuric acid as simultaneous catalysts and dopants. The optical properties, phenolic content, antioxidant activity, photostability, and cytotoxicity of the CDs were measured and compared. L‐ascorbic acid, a well‐known antioxidant, and avobenzone and oxybenzone, common UV absorbers in sunscreens, were used for comparison. Interestingly, heteroatom doping has adverse effects on several properties of the CDs as the undoped CDs yielded the highest UV‐vis absorption, phenolic content, antioxidant activity, photostability, and biocompatibility. Only fluorescence quantum yields were improved by heteroatom doping. These findings will be crucial for choosing precursors for the synthesis of CDs because heteroatoms inherently present in precursors can have negative effects on the properties of the resulting CDs.

Exploration of highly photoluminescent first-row transition metals (manganese, iron, cobalt, nickel, copper and zinc) co-doped nano carbon dots as energy storage materials

Carbon nanodots have currently emerged as a unique and promising material focusing on advanced applications especially in the field of optoelectronic and energy storage devices. The preferential doping of nanocarbon dots with first row transition elements will enhance the photoluminescence characteristics and thereby, we can fine-tune its photophysical properties. In the present work, we have synthesized a series of first-row transition metal atoms (Mn2+, Fe2+, Co2+, Ni2+, Cu2+, and Zn2+) co-doped with nitrogen and nitrogen- sulfur carbon dots by a greener synthetic strategy. The formation of doped carbon dots were confirmed by its characteristic surface plasmon resonance absorptions using the Ultraviolet–visible spectroscopy. The presence of major elements and the functional group identification was done with the aid of EDS and FT-IR spectral analysis, the morphology and size were analyzed by high-resolution TEM analysis and photophysical characteristics were investigated from the fluorescence measurements. The photoluminescence studies reveal that by co-doping the transition metals with nitrogen or nitrogen- sulfur carbon dots, the emissions maxima of the nanodots can be tuned. The doped carbon dots were explored for their energy storage application and their super capacitance characteristics. The capacitance values of the carbon dots were found to be increased with the effect of co-doping with the first-row transition elements and the capacitance values were in the range of 2.6 µF/cm2 to 0.5 µF/cm2 and are in tune with the capacitance values for carbon-based materials including graphene and C-dots reported in the literature. Also the cyclic voltammetric loops were found to be sufficiently rectangular in shape, desirable for a supercapacitor, and the rectangular areas were found to be increased with increase in scan rate.

Green emitting N, P-doped carbon dots as efficient fluorescent nanoprobes for determination of Cr(VI) in water and soil samples

The doping of carbon dots (CDs) with non-metallic elements has been a strategy to improve their optical properties and application fields. In the present work, nitrogen and phosphorus-doped CDs (N, P-CDs) were prepared through one-pot hydrothermal synthesis using phytic acid (PA) and L-arginine (Arg) as precursors. The synthesized N, P-CDs were characterized using transmission electron microscopy, FTIR, Raman, UV–vis, and fluorescence spectroscopies. The N, P-CDs exhibited green fluorescence (λem = 515 nm) that can be quenched sensitively and selectively in the presence of Cr(VI), combining static quenching, electron transfer, and an inner filter effect. Consequently, a new fluorescence sensing method applied to Cr(VI) determination was developed using the presently synthesized fluorescent CDs. Under optimized conditions, a linear range from 0.05 to 3 µM in Cr(VI)) was obtained, with a limit of detection of 26 nM. Additionally, the N, P-CDs were selective toward Cr(VI) in the presence of Cr(III) and twenty other species, indicating its potential use to monitor Cr(VI) in environmental samples. Then, Cr(VI) was successfully determined, with recoveries from 85 to 107% in water and soil samples. The method, combining high sensitivity and selectivity, is easy to implement and promotes the use and valorization of eco-friendly materials.

Coal based carbon dots: Recent advances in synthesis, properties, and applications

AbstractCarbon dots are zero‐dimensional carbon nanomaterials with quantum confinement effects and edge effects, which have aroused great interests in many disciplines such as energy, chemistry, materials, and environmental applications. They can be prepared by chemical oxidation, electrochemical synthesis, hydrothermal preparation, arc discharge, microwave synthesis, template method, and many other methods. However, the raw materials' high cost, the complexity and environmental‐unfriendly fabrication process limit their large‐scale production and commercialization. Herein, we review the latest developments of coal‐based carbon dots about selecting coal‐derived energy resources (bituminous coal, anthracite, lignite, coal tar, coke, etc.) the developments of synthesis processes, surface modification, and doping of carbon dots. The coal‐based carbon dots exhibit the advantages of unique fluorescence, efficient catalysis, excellent water solubility, low toxicity, inexpensive, good biocompatibility, and other advantages, which hold the potentiality for a wide range of applications such as environmental pollutants sensing, catalyst preparation, chemical analysis, energy storage, and medical imaging technology. This review aims to provide a guidance of finding abundant and cost‐effective precursors, green, simple and sustainable production processes to prepare coal‐based carbon dots, and make further efforts to exploit the application of carbon dots in broader fields.

Facile defect engineering in ZnIn2S4 coupled with carbon dots for rapid diclofenac degradation

Semiconductor-mediated photocatalysis is a promising photochemical process for harvesting inexhaustible solar energy to address the energy crisis and environmental issues. However, the low solar-light response and poor carrier migration are severe drawbacks that limit its practical application. Herein, we propose a convenient pathway for improving electron-hole separation and solar energy utilisation by engineering defective ZnIn2S4 with doping of carbon dots. The optimum ZnIn2S4/CD200 nanosheet exhibited 100% diclofenac (DCF) degradation within 12 min under visible-light. The estimated photocatalytic efficiency under natural sunlight was 98.2%. Scavenging experiments and electron spin resonance (ESR) analysis indicated that the superoxide radical (O2−), photoelectron (e−), hole (h+) and hydroxyl radical (OH) were the predominant contributions in the ZnIn2S4/CD200/DCF/visible light system. Furthermore, ZnIn2S4/CD200 exhibited excellent reusability and stability after 4 times recycling. The photodegradation routes mainly involved hydroxylation, decarboxylation, CN bond cleavage, dechlorination, ring closure, and ring-opening. The ecological risk assessment and total organic carbon (TOC) tests exhibited desirable toxicity reduction and mineralization results. These observations not only offer a facile strategy for the construction of defective ZnIn2S4, but also pioneer the direct utilisation of natural light for highly efficient environmental remediation.

In Situ Chromophore Doping: A New Mechanism for the Long-Wavelength Emission of Carbon Dots

Doping of carbon dots (CDs) with heteroatoms (e.g., N, S, P, and B) is known as an efficient method to modulate the electronic and optical properties of these fluorescent carbonaceous nanomaterials...

Performance improvement of dye sensitized solar cells based on cadmium sulfide/S, N co doped carbon dots nanocomposites

In this paper, cadmium sulfide (CdS), sulfur and nitrogen co-doped carbon dots (S,N-CDs) and cadmium sulfide/sulfur and nitrogen co-doped carbon dots (CdS/S,N-CDs) were prepared via hydrothermal route. Cadmium acetate dihydrate, thiourea and citric acid were applied as a source of cadmium, sulfur and carbon respectively. Thiourea plays dual role as a dopant source for doping of carbon dots and sulfur source for the synthesis of cadmium sulfide. The influence of hydrothermal temperature on the morphology of CdS and CdS/S,N-CDs was determined in terms of structure, size and morphology through X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and Fourier-transform infrared spectroscopy (FTIR) analysis. Results showed that temperature has a significant effect on the morphology of cadmium sulfide. Homogenous flower like morphology of CdS in 160 °C was converted to non-homogenous worm-like particles at 200 °C. Moreover, the flower-like morphology of CdS was converted to the particle morphology during the preparation of CdS/S,N-CDs since the acidity of solution is changed for the presence of citric acid. After morphological and structural engineering, nitrogen and sulfur co-doped carbon dots and CdS/S,N-CDs were applied in dye sensitized solar cells. The JSC of S,N-CDs and CdS/S,N-CDs were measured 14.07 and 18.38 mA/cm2 respectively. Results showed that the VOC equal to 0.61 V for CDs while decreased to 0.59 V in CdS/S,N-CDs case. Although VOC decreased, hole PCE show improvement in CdS/S,N-CDs case, PCE enhanced from 3.44% to 5.7%.

Superior Oxygen Reduction Reaction on Phosphorus‐Doped Carbon Dot/Graphene Aerogel for All‐Solid‐State Flexible Al–Air Batteries

AbstractCarbon dots have been recognized as one of the most promising candidates for the oxygen reduction reaction (ORR) in alkaline media. However, the desired ORR performance in metal–air batteries is often limited by the moderate electrocatalytic activity and the lack of a method to realize good dispersion. To address these issues, herein a biomass‐deriving method is reported to achieve the in situ phosphorus doping (P‐doping) of carbon dots and their simultaneous decoration onto graphene matrix. The resultant product, namely P‐doped carbon dot/graphene (P‐CD/G) nanocomposites, can reach an ultrahigh P‐doping level for carbon nanomaterials. The P‐CD/G nanocomposites are found to exhibit excellent ORR activity, which is highly comparable to the commercial Pt/C catalysts. When used as the cathode materials for a primary liquid Al–air battery, the device shows an impressive power density of 157.3 mW cm−2 (comparing to 151.5 mW cm−2 of a similar Pt/C battery). Finally, an all‐solid‐state flexible Al–air battery is designed and fabricated based on our new nanocomposites. The device exhibits a stable discharge voltage of ≈1.2 V upon different bending states. This study introduces a unique biomass‐derived material system to replace the noble metal catalysts for future portable and wearable electronic devices.

Doping of Carbon Quantum Dots (CDs) in Calcium Phosphate Nanorods for Inducing Ectopic Chondrogenesis via Activation of the HIF-α/SOX-9 Pathway

Calcium phosphate (CaPs)-based nanostructures are mostly known to induce osteogenic differentiation of mesenchymal stem cells (MSCs). However, in the current study, doping of carbon quantum dots into calcium phosphate nanorods (C-CaPs) has been observed to affect the differentiation pathway and enhanced the expression of chondrogenic genes instead of osteogenic ones. Here, we report a microwave-assisted single-step synthesis and doping of carbon dot into calcium phosphate nanorods and their ectopic chondrogenicity in a rodent subcutaneous model. High-resolution transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy studies show that the doping of carbon dots results in p-type semiconductor-like structure formation at the phosphate site of the bioceramic nanostructure, whereas UV–vis absorption shows a drastic drop in band-gap energy, which enhances the molecular oxygen reduction reaction. The cytocompatibility, free radical scavenging property, and fluorescence mi...

Low-temperature rapid synthesis of nitrogen and phosphorus dual-doped carbon dots for multicolor cellular imaging and hemoglobin probing in human blood

Heteroatom doping of carbon dots (CDs) can efficiently tune the structure of electronic energy levels and modulate the photochemical properties of CDs. However, the reported synthesis routes of heteroatom-doped CDs are complicated and rigorous. Herein, a simple and rapid low-temperature heating strategy was applied to synthesize fluorescent nitrogen and phosphorus dual-doped CDs (N,P-CDs) using sucrose as carbon source, and 1,2-ethylenediamine (EDA) and phosphoric acid as dopants, respectively. These N,P-CDs exhibit excellent fluorescent stability over wide pH range solutions (4–11), ultrahigh ion strength (3 M KCl), and longtime UV light irradiation (3 h continuously), which makes these N,P-QDs promising good candidates for fluorescent probes. These N,P-CDs showed excellent biocompatibility, multicolor cellular imaging, and non-cytotoxicity to human hepatocellular carcinoma HepG2 cells even at 500 μg/mL levels for 48 h incubation. These N,P-CDs exhibited a strong blue emission and a sensitive response to hemoglobin. The N,P-CDs based fluorescent probe was then applied to sensitively determine hemoglobin with a detection limit of 0.29 nM. Notably, it was also applied for label-free detection of hemoglobin in human urine samples and human blood samples, which indicated its potential applications in clinical diagnosis and other biologically related study.

Efficiency Improvement of Inverted Organic Solar Cells via Introducing a Series of Polyfluorene Dots in Electron Transport Layer

This article describes a positive effect on improving the performance of organic solar cells (OSCs) by introducing a series of water-soluble polyfluorene (PF) dots. When poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-1-thiadiazole)] (PF1), poly(9,9-dioctylfluorenyl-2,7-diyl) (PF2), and poly(9,9-dioctylfluorene)-co-(4,7-di-2-thienyl -2,1,3-benzothiadiazole) (PF3) dots are mixed into the polyethylenimine (PEI) cathode buffer layer, active layer and PEI films show an enhancement on light absorption in comparison with control film, which leads to the realization of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl-C61-butyric acid methyl ester (PCBM) solar cells with power conversion efficiency (PCE) of 4.33% for PF1 doping, 4.49% for PF2 doping, and 4.72% for PF3 doping, accounting for 23.0%, 27.6%, and 34.1% enhancement, respectively. Simultaneously, doping of PF dots also contributes to the improvement of exciton dissociation, charge transport, and charge collection. PF dots could be used as a dual functional additive to enhance optical and electrical properties for OSCs.