Synthesis of highly fluorescent and water soluble graphene quantum dots for detection of heavy metal ions in aqueous media

Zero-Dimensional Carbon Nanomaterials for Fluorescent Sensing and Imaging

Advances in nanotechnology and nanomaterials have attracted considerable interest and play key roles in scientific innovations in diverse fields. In particular, increased attention has been focused on carbon-based nanomaterials exhibiting diverse extended structures and unique properties. Among these materials, zero-dimensional structures, including fullerenes, carbon nano-onions, carbon nanodiamonds, and carbon dots, possess excellent bioaffinities and superior fluorescence properties that make these structures suitable for application to environmental and biological sensing, imaging, and therapeutics. This review provides a systematic overview of the classification and structural properties, design principles and preparation methods, and optical properties and sensing applications of zero-dimensional carbon nanomaterials. Recent interesting breakthroughs in the sensitive and selective sensing and imaging of heavy metal pollutants, hazardous substances, and bioactive molecules as well as applications in information encryption, super-resolution and photoacoustic imaging, and phototherapy and nanomedicine delivery are the main focus of this review. Finally, future challenges and prospects of these materials are highlighted and envisaged. This review presents a comprehensive basis and directions for designing, developing, and applying fascinating fluorescent sensors fabricated based on zero-dimensional carbon nanomaterials for specific requirements in numerous research fields.

Preparation of multilayer strontium-doped TiO2/CDs with enhanced photocatalytic efficiency for enrofloxacin removal

Multilayer strontium-doped TiO₂/carbon dots (CDs) materials (TC) were produced via sol-gel-layered carbonization method. A thorough analysis of the fabricated composites via XRD, SEM, and XPS revealed that strontium ions, TiO₂ and CDs, were combined with each other to form layered structures. According to the UV-Vis diffuse reflectance spectrograms and (αhv)^1/2 vs. hv plots, the electron-donor property of strontium ions caused a more positive TC conduction band position than that in the pure TiO₂, thereby increasing the visible-light absorption range of TC. Based on the photocatalytic degradation data, the degradation rate of enrofloxacin was 84.7% at the dosage of 0.05 g·L^-1 and the concentration of 10 mg·L^-1. The capture experiments and ESR results showed that ·O₂^- and e^- played a major role in the degradation process of TC. The possible degradation mechanism of enrofloxacin was explained in terms of decarboxylation and defluorination, as was detected via ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) analysis.

Efficient removal of RR2 dye by electro- Ce(III) process with its elegant arts and attractive charm in performance, energy consumption and mechanism

Reactive red 2 (RR2) azo dye wastewater poses a serious hazard to the water environment health, so using a novel and efficient Electro- Ce(III) (E- Ce(III)) process takes on a critical significance in treating RR2 dye wastewater. In this study, the effects of a variety of single-factor conditions on RR2 removal efficiency were evaluated in depth. The results indicated that the optimal experimental conditions are as reaction temperature of 25 °C, Na₂SO₄ concentration of 25 mM, Ce(III) concentration of 0.3 mM, pH of 4.0, and current density of 40.0 mA/cm². When the RR2 dye wastewater was treated for 40 min under the optimal experimental conditions, a high removal rate of 99.8% for RR2 was obtained. It is suggested that the background ion PO₄^3- in the dye wastewater inhibits the E-Ce (III) process, whereas Cl- facilitates this process. Moreover, the yield of Ce(IV) increases with the increase of the current density. At the current density of 40.0 mA/cm², a reasonable energy consumption of 3.85 kW h/gTOC for the process was obtained after the 3-h treatment. The effects of different degradation processes (including Direct Electrooxidation (DEO), single Ce(III), and E-Ce (III)) on RR2 removal efficiency and TOC change were compared. The types of oxidizing substances in the E-Ce (III) process were detected, and the mechanism of RR2 oxidative degradation in the E-Ce (III) process was summarized. The result suggests that the E-Ce (III) process has low power consumption. Meanwhile, in the E-Ce (III) process, free reactive Ce(IV) with strong oxidation is continuously generated, RR2 can be efficiently degraded. And the continuous cycle transformation between Ce(III) and Ce(IV) maintains the strong oxidation of the process. The contribution of free reactive Ce(IV) and DEO to RR2 degradation was obtained as 58.8% and 39.8%, respectively. The combined effect of Ce(IV) and DEO played a major role in the E-Ce (III) process, while ·OH exhibited a relatively weak effect (nearly 1.4%). RR2 was comprised of 13 major intermediates, and the biodegradability of wastewater was improved significantly after treatment, thus facilitating the further mineralization and biodegradation of the products. The E- Ce(III) process is novel, efficient, and environment-friendly, and has a large market application space, suggesting that it can be applied as an efficient, economic, and sustainable water treatment process.

Development of Red-Emissive Porphyrin Graphene Quantum Dots (PGQDs) for Biological Cell-Labeling Applications

Red and near-infrared emission is a highly desirable feature for fluorescent nanoparticles in biological applications mainly due to longer wavelengths more easily being able to deeply penetrate tissues, organs, skin, and other organic components, while less autofluorescence interference would be produced. Additionally, graphene quantum dots (GQDs) that contain unique optical and electrical features have been targeted for their use in cell labeling applications as well as environmental analysis. Their most desirable features come in the form of low toxicity and biocompatibility; however, GQDs are frequently reported to have blue or green emission light and not the more advantageous red/NIR emission light. Furthermore, porphyrins are a subgroup of heterocyclic macrocycle organic compounds that are also naturally occurring pigments in nature that already contain the desired red-emission fluorescence. Therefore, porphyrins have been used previously to synthesize nanomaterials and for nanoparticle doping in order to incorporate the red/NIR emission light property into particles that otherwise do not contain the desired emission light. Meso-tetra(4-carboxyphenyl)porphine (TCPP) is one type of porphyrin with a large conjugated π-electron system and four carboxyl groups on its exterior benzene rings. These two key characteristics of TCPP make it ideal for incorporation into GQDs, as it would design and synthesize red-emissive material as well as give rise to excellent water solubility. In this work, TCPP is used in tangent with cis-cyclobutane-1,2-dicarboxylic acid (CBDA-2), a biomass derived organic molecule, to synthesize "green" porphyrin-based graphene quantum dots (PGQDs) with red-emission. The obtained PGQDs were characterized by various analytical methods. Utilizing TEM, HRTEM, and DLS the size distribution of the particles was determined to be 7.9 ± 4.1, well within the quantum dot range of 2-10 nm. FT-IR, XPS, and XRD depicted carbon, nitrogen, and oxygen as the main elemental components with carbon being in the form of graphene and the main porphyrin ring of TCPP remaining present in the final PGQDs product. Lastly, absorption and fluorescence spectroscopy determined the excitation wavelength at 420 nm and the emission at 650 nm which was successfully utilized in the imaging of HeLa cells using confocal microscopy.

Folic Acid-Functionalized Graphene Quantum Dots: Synthesis, Characterization, Radiolabeling with Radium-223 and Antiviral Effect against Zika Virus Infection

The use of graphene quantum dots as biomedical devices and drug delivery systems has been increasing. The nano-platform of pure carbon has shown unique properties and is approved to be safe for human use. In this study, we successfully produced and characterized folic acid-functionalized graphene quantum dots (GQD-FA) to evaluate their antiviral activity against Zika virus (ZIKV) infection in vitro, and for radiolabeling with the alpha-particle emitting radionuclide radium-223. The in vitro results exhibited the low cytotoxicity of the nanoprobe GQD-FA in Vero E6 cells and the antiviral effect against replication of the ZIKV infection. In addition, our findings demonstrated that functionalization with folic acid doesn't improve the antiviral effect of graphene quantum dots against ZIVK replication in vitro. On the other hand, the radiolabeled nanoprobe ²²³Ra@GQD-FA was also produced as confirmed by the Energy Dispersive X-Ray Spectroscopy analysis. ²²³Ra@GQD-FA might expand the application of alpha targeted therapy using radium-223 in folate receptor-overexpressing tumors.

Electrochemiluminescence biosensor for determination of lead(II) ions using signal amplification by Au@SiO2 and tripropylamine-endonuclease assisted cycling process

MXene@Au as the base and Au@SiO₂ as signal amplification factor were used for constructing an ultrasensitive "on-off" electrochemiluminescence (ECL) biosensor for the detection of Pb²⁺ in water. The use of MXene@Au composite provided a good interface environment for the loading of tris(2,2-bipyridyl)ruthenium(II) (Ru(bpy)₃²⁺) on the electrode. Based on resonance energy transfer, the Au (core) SiO₂ (shell) (Au@SiO₂) nanoparticles stimulate electron transport and promote tripropylamine (TPrA) oxidation. The luminescence effect of Au@SiO₂ was five times that of AuNPs and SiO₂ nanomaterials alone, and the ECL intensity was greatly improved. In addition, Pb²⁺ activated the aptamer to exert its endonuclease activity, which realized the signal cycle amplification in the process of Pb²⁺ detection. When Pb²⁺ was added, the ECL signal weakened, and the Pb²⁺ concentration was detected according to the decreased ECL intensity. Under optimized experimental conditions, this aptamer sensor for Pb²⁺ has a wide detection range (0.1 to 1 × 10⁶ ng L^-1) and a low detection limit (0.059 ng L^-1). The relative standard deviation (RSD) of the sensor is 0.39-0.99%, and the recovery of spiked standard is between 90.00 and 125.70%. The sensor shows good selectivity and high sensitivity in actual water sample analysis. This signal amplification strategy possibly provides a new method for the detection of other heavy metal ions and small molecules.

Alkaline n-gqds fluorescent probe for the ultrasensitive detection of creatinine

Creatinine (Crn) is an important excretory product of the human body. Medical laboratory technology has improved over years and brought many advancements in clinical diagnostics equipment, and testing techniques and made the tests more efficient. Yet, the quantitative analysis of Crn is still carried out by the classical Jaffe's reaction (using Picric acid (PA) with NaOH) method. Since PA is hazardous to human health, alternative solutions such as; nanoparticles and surface-modified nanoparticles can be used. Exploring the optoelectronic properties of carbon-based quantum dots for biomolecule sensing is of current interest among researchers. Nitrogen functionalized graphene quantum dots (Alk-NGQDs) measured featured Crn easier and reduced the time taken for the test carried out in laboratories. The synthesized Alk-NGQDs optical, structural, morphological properties, surface and compositions are studied through XPS, HRTEM, XRD, FTIR, and spectroscopic techniques. Alk-NGQDs at alkaline conditions (pH 9.5) form a stable complex with Crn through intermolecular charge transfer (ICT). The fluorescence titration method is used to sense Crn in commercial Crn samples and human blood serum. To understand the efficacy of sensing creatinine using Alk-NGQDs, working concentration, fluorescence quantum yield, the limit of detection, and quenching constant are calculated using the Stern-Volmer plot. The emission property of Alk-NGQDs is aimed to bring an alternative to the traditional colorimetric Jaffe's reaction.

Plastic Waste Precursor-Derived Fluorescent Carbon and Construction of Ternary FCs@CuO@TiO2 Hybrid Photocatalyst for Hydrogen Production and Sensing Application

A sustainable nexus between renewable energy production and plastic abatement is imperative for overall sustainable development. In this regard, this study aims to develop a cheaper and environmentally friendly nexus between plastic waste management, wastewater treatment, and renewable hydrogen production. Fluorescent carbon (FCs) were synthesized from commonly used LDPE (low-density polyethylene) by a facile hydrothermal approach. Optical absorption study revealed an absorption edge around 300 nm and two emission bands at 430 and 470 nm. The morphological analysis showed two different patterns of FCs, a thin sheet with 2D morphology and elongated particles. The sheet-shaped particles are 0.5 μm in size, while as for elongated structures, the size varies from 0.5 to 1 μm. The as-synthesized FCs were used for the detection of metal ions (reference as Cu2+ ions) in water. The fluorescence intensity of FCs versus Cu2+ ions depicts its upright analytical ability with a limit of detection (LOD) reaching 86.5 nM, which is considerably lesser than earlier reported fluorescence probes derived from waste. After the sensing of Cu2+, the as-obtained FCs@Cu2+ was mixed with TiO2 to form a ternary FCs@CuO@TiO2 composite. This ternary composite was utilized for photocatalytic hydrogen production from water under 1.5 AM solar light irradiation. The H2 evolution rate was found to be ~1800 μmolg−1, which is many folds compared to the bare FCs. Moreover, the optimized FCs@CuO@TiO2 ternary composite showed a photocurrent density of ~2.40 mA/cm2 at 1 V vs. Ag/AgCl, in 1 M Na2SO4 solution under the illumination of simulated solar light. The achieved photocurrent density corresponds to the solar-to-hydrogen (STH) efficiency of ~0.95%. The efficiency is due to the fluorescence nature of FCs and the synergistic effect of CuO embedded in TiO2, which enhances the optical absorption of the composite by reaching the bandgap of 2.44 eV, apparently reducing the recombination rate, which was confirmed by optoelectronic, structural, and spectroscopic characterizations.

Application of Nanotechnology in Analysis and Removal of Heavy Metals in Food and Water Resources

Toxic heavy metal contamination in food and water from environmental pollution is a significant public health issue. Heavy metals do not biodegrade easily yet can be enriched hundreds of times by biological magnification, where toxic substances move up the food chain and eventually enter the human body. Nanotechnology as an emerging field has provided significant improvement in heavy metal analysis and removal from complex matrices. Various techniques have been adapted based on nanomaterials for heavy metal analysis, such as electrochemical, colorimetric, fluorescent, and biosensing technology. Multiple categories of nanomaterials have been utilized for heavy metal removal, such as metal oxide nanoparticles, magnetic nanoparticles, graphene and derivatives, and carbon nanotubes. Nanotechnology-based heavy metal analysis and removal from food and water resources has the advantages of wide linear range, low detection and quantification limits, high sensitivity, and good selectivity. There is a need for easy and safe field application of nanomaterial-based approaches.

Quantum Dots Based Fluorescent Probe for the Selective Detection of Heavy Metal Ions

Heavy metal ions are one of the primary causes of environmental pollution. A marshal effect of heavy metal ions is a paramount ultimatum to humans, aquatic animals and other organisms present in nature. Multitude arrays of materials have been proclaimed for sensing of heavy metal ions and also many methodologies are applied for heavy metal ion sensing. Due to their toxicity and non-biodegradability, it is required to be perceived immediately prior to its manifestation of harmful effects. Quantum Dots (QDs) are zero-dimensional nanomaterial particles and owing to their distinctive optical and electronic properties, they are utilized as nanosensors. QDs have enriched fluorescence properties which includes broad excitation spectrum, narrow emission spectrum and photostability. QDs offer eclectic and sensitive detection of heavy metal ions due to presence of discrete capping agents and different functional groups present on the surface of the QDs. These capping layers and functional groups attune the sensing capability of the QDs, which leverages the interactions of QDs with various analytes by different mechanisms. This review, comprising of papers from 2011 to 2020,focuses on heavy metal ions sensing potential of various quantum dots and its applicability as a nanosensor for on field heavy metal ions detection in water. Quantum Dots (QDs) based Heavy Metal Detection.

Outstanding Graphene Quantum Dots from Carbon Source for Biomedical and Corrosion Inhibition Applications: A Review

Graphene quantum dots (GQD) is an efficient nanomaterial composed of one or more layers of graphene with unique properties that combine both graphene and carbon dots (CDs). It can be synthesized using carbon-rich materials as precursors, such as graphite, macromolecules polysaccharides, and fullerene. This contribution emphasizes the utilization of GQD-based materials in the fields of sensing, bioimaging, energy storage, and corrosion inhibitors. Inspired by these numerous applications, various synthetic approaches have been developed to design and fabricate GQD, particularly bottom-up and top-down processes. In this context, the prime goal of this review is to emphasize possible eco-friendly and sustainable methodologies that have been successfully employed in the fabrication of GQDs. Furthermore, the fundamental and experimental aspects associated with GQDs such as possible mechanisms, the impact of size, surface alteration, and doping with other elements, together with their technological and industrial applications have been envisaged. Till now, understanding simple photo luminance (PL) operations in GQDs is very critical as well as there are various methods derived from the optical properties of manufactured GQDs can differ. Lack of determining exact size and morphology is highly required without loss of their optical features. Finally, GQDs are promising candidates in the after-mentioned application fields.

Metal Nanostructures for Environmental Pollutant Detection Based on Fluorescence

Heavy metal ions and pesticides are extremely dangerous for human health and environment and an accurate detection is an essential step to monitor their levels in water. The standard and most used methods for detecting these pollutants are sophisticated and expensive analytical techniques. However, recent technological advancements have allowed the development of alternative techniques based on optical properties of noble metal nanomaterials, which provide many advantages such as ultrasensitive detection, fast turnover, simple protocols, in situ sampling, on-site capability and reduced cost. This paper provides a review of the most common photo-physical effects impact on the fluorescence of metal nanomaterials and how these processes can be exploited for the detection of pollutant species. The final aim is to provide readers with an updated guide on fluorescent metallic nano-systems used as optical sensors of heavy metal ions and pesticides in water.

Red-fluorescent graphene quantum dots from guava leaf as a turn-off probe for sensing aqueous Hg(ii)

In this work, we have prepared red-fluorescent graphene quantum dots and utilized as a highly selective and sensitive fluorescence turn-off probe for detection of the toxic metal ion Hg²⁺ from guava leaf extract.