Nitrogen-doped Graphene Quantum Dots Research Articles

Computational Studies on the Nitrogen-Doped Graphene Quantum Dots as Potential Sensor for Hazardous Gases

Computational Studies on the Nitrogen-Doped Graphene Quantum Dots as Potential Sensor for Hazardous Gases

Novel palladium nanoparticles/4-aminophenol functionalized nitrogen-doped graphene quantum dots-based nanocomposite electrochemical sensor: Synthesis, characterization, capacitance, and dopamine sensing

In this study, an ultrasensitive electrochemical sensor based on palladium nanoparticles/4-aminophenol functional nitrogen-doped graphene quantum dots (PdNPs/4AP N-GQDs) composite was fabricated to detect dopamine (DA). The sensor was characterized by FTIR, UV–Vis, TEM, EDX, and XRD methods. The electrochemical analysis of the nanocomposite modified glassy carbon electrode (GCE) was conducted by cyclic voltammetry (CV). HOMO-LUMO energy levels and band gap energy was calculated from cyclic voltammograms, and the band gap energy was found to be small at 0.06 eV. The electrode reaction properties of dopamine on this developed ultrasensitive electrode were investigated by CV and differential pulse voltammetry (DPV), which showed that the electrode had electrocatalytic activity for dopamine sensing. Moreover, the developed electrode exhibited good sensitivity and improved performance, and the linear calibration curve for dopamine was calculated to have a LOD (limit of detection) of 21 pM in the range of 250 pM to 10 nM. Finally, the selectivity of the GQDs nanocomposite modified GCE towards dopamine was studied in the presence of several bioactive compounds with inhibitory effects. In addition, the specific capacitance of the nanocomposite material at 5 mV s−1 was found to be as high as 0.777F g−1. Furthermore, the dopamine selectivity of the sensor among some organic and inorganic interfering bioanalytes was investigated and the sensor was found to have excellent DA selectivity despite the bioanalytes.

A self-assembled theranostic nanoplatform for efficient tumor sonodynamic-gas therapy

The powerful antioxidant system in tumor tissues limits the efficacy of sonodynamic therapy (SDT) by reducing the availability of the produced reactive oxygen species (ROS). To address this problem, a pH/ultrasound (US) responsive theranostic nanoplatform is elaborately constructed by self-assembly of nitrogen-doped graphene quantum dots (NGQDs), benzothiazole sulfinate (BTS), Gd3+ ions and poly(lactide-co-glycolide)-b-poly(ethylene glycol) (PLGA-PEG). The NGQD component with excellent sonodynamic activity wrapped in the resulting Gd-NGQDs/BTS@PLGA-PEG can efficaciously respond to ultrasonic irradiation and cause abundant ROS generation. Importantly, in response to acidic tumor microenvironment, the loaded BTS sustainably releases SO2, which induces the increase of intracellular •O2− level by inhibiting superoxide dismutase activity and further promotes the enrichment of ROS by reducing intracellular glutathione level and suppressing glutathione peroxidase 4 activity. The well-designed SO2 gas therapy-enhanced SDT strategy leads to high oxidative stress in tumor cells and effective inhibition of the growth of bilateral tumors with only a single intravenous injection of the nanomedicine and a subsequent single US irradiation. Gd-NGQDs/BTS@PLGA-PEG can also be employed as a good T1-weighted magnetic resonance imaging contrast agent to guide tumor therapy. This innovative therapeutic strategy developed in our contribution may provide a new paradigm for the exploration of deep tumor therapy.

Optoelectronic Properties of Nitrogen-Doped Hexagonal Graphene Quantum Dots: A First-Principles Study.

Graphene quantum dots have been widely studied owing to their unique optical, electrical, and optoelectrical properties for various applications in solar devices. Here, we investigate the optoelectronic properties of hexagonal and nitrogen-doped graphene quantum dots using the first-principles method. We find that doping nitrogen atoms to hexagonal graphene quantum dots results in a significant red shift toward the visible light range as compared to that of the pristine graphene quantum dots, and the doped nitrogen atoms also induce a clear signature of anisotropy of the frontier orbitals induced by the electron correlation between the doped nitrogen atoms and their adjacent carbon atoms. Moreover, time-dependent density functional theory calculations with the M06-2X functional and 6-311++G(d,p) basis set reproduce well the experimental absorption spectra reported recently. These results provide us with a novel approach for more systematic investigations on next-generation solar devices with assembled quantum dots to improve their light selectivity as well as efficiency.

Efficient decolorization performance of graphene quantum dots modulated nanofiltration membranes with tunable pore size for precise molecular sieving

The discharge of wastewater containing dyes not only causes serious environmental pollution but also poses a severe threat to human health. The selective separation of dyes and reuse of inorganic salts are vital in the textile industry. In this work, nitrogen-doped graphene quantum dots (N-GQDs) was successfully synthesized via the “one-step solvothermal method”, and the N-GQDs composite membranes were innovatively fabricated by constructing a thin selective layer top the modified multi-walled carbon nanotubes (MWCNTs) matrix membrane via interfacial polymerization process. The pore size of the N-GQDs membranes could be flexibly modulated by regulating the contents of the N-GQDs. The suitable N-GQDs membrane (M4, 0.35 wt% of N-GQDs) possessed over 96 % rejection rate for diverse charged dyes, which was higher than that of the piperazine polyamide (PA3) membrane. Notably, the rejection of the smaller molecular weight of Methylene Blue by the M4 membrane reached ∼98.93 %, which was higher than that reported in most literature, mainly owing to the relatively smaller average pore size and stronger electronegativity of the membrane. Especially compared with our previous work, the prepared M3 and M4 membranes exhibited an enhancement of ∼37.79 % and 39.48 % in rejection of Methylene Blue, ∼ 78 % and 19 % in pure water permeability, respectively. On account of the size sieving and charge effect, the N-GQDs membrane (M4) could maintain high rejection for dyes and exhibited efficient separation for dye/salt with a separation factor of 115 for the Congo Red/sodium chloride mixture after continuous cross-flow filtration for 24 h in the simulated wastewater condition. Furthermore, the N-GQDs membrane also exhibited favorable acid-base resistance and satisfactory anti-fouling performance. Importantly, the N-GQDs membranes presented excellent decolorization efficiency for the practical textile wastewater. These results revealed that the as-prepared N-GQDs membrane possessed great potential for actual textile wastewater advanced treatment and purification. This study also offers a new candidate to rationally manipulate the separation properties of nanofiltration membranes adopting new aqueous monomers.

Nitrogen-doped graphene quantum dots/ polyvinyl alcohol nanocomposite for photon management: Application in CIGS photovoltaic cells

The efficiency (η) of copper indium gallium selenide (CIGS) solar cells has been hampered by absorption losses that happen within the ZnO and CdS layers. A photon downconversion layer created from polyvinyl alcohol (PVA) and nitrogen-doped graphene quantum dots (NGQDs) composite (NGQDs/PVA) was implemented on the top of the cell to overcome this obstacle. Notably, the NGQDs/PVA layers, prepared at spin speeds of 3000, 4000, and 5000 rpm, exhibited optimal characteristics, demonstrating superior light absorption at low wavelengths along with elevated transmittance at longer wavelengths. The η was found to be highest for the layer prepared at 4000 rpm, accompanied by elevated values of short-circuit current (Jsc), open-circuit voltage (Voc), and fill factor (FF). Consequently, Cell #2 incorporating the champion NGQDs/PVA layer outperformed all other CIGS photovoltaic cells, showcasing an impressive enhancement of 8.96 % in Jsc, 1.62 % in Voc, 2.03 % in FF, and an overall η of 11.51 %. This champion cell significantly improves the performance of CIGS photovoltaics.

Highly sensitive fluorescent nitrobenzene gas sensing by nitrogen-doped graphene quantum dots embedded in ZIF-8 nanocomposite

This study introduces a straightforward and highly sensitive luminescence gas sensor designed for the detection of nitrobenzene in gaseous state. The sensor utilizes an innovative composite composed of nitrogen doped graphene quantum dots (nGQDs) as luminescent materials, successfully encapsulated within the stable porous carrier zeolitic imidazolate framework-8 (ZIF-8). The resulting nGQD@ZIF-8 nanocomposite showed highly sensitive luminescence sensing towards nitrobenzene gas, with a wide linear detection range from 8 to 320 ppm, and the detection limits of sensor as low as 0.44 ppm. Moreover, the nGQD@ZIF-8 sensor demonstrated enhanced ppm-level sensitivity and long-term stability for nitrobenzene detection at room temperature, while maintaining high stability under varying humidity levels and exposure to high temperatures. This enhancement is attributed to the increased contact area provided by ZIF-8 matrix, facilitating adsorption of nitrobenzene molecules on nGQDs. The nGQD@ZIF-8 exhibited good selectivity towards nitrobenzene gas (57 %) compared to other nitro volatile organic compound (VOC) vapors (nitromethane and nitropropane), and almost no significant responses were observed for the other tested VOC vapors (methanol, acetone, formaldehyde, benzene). This can be attributed to the strong interaction between the electron-deficient nitrobenzene and the nGQD@ZIF-8 nanocomposite. Overall, the proposed gas sensor in this study showed high potential for a simple, efficient, and reliable detection of nitrobenzene gas in environmental monitoring.

Electrochemical synthesis of nitrogen-doped graphene quantum dots and their photocatalytic hydrogen evolution application

A very simple electrochemical top-down procedure was employed to obtain pure graphene quantum dots (GQDs) in water and using only graphite as carbonaceous precursor. The graphitic structure of the GQDs has been clearly observed by high-resolution transmission electronic microscopy (HRTEM). Then, the synthesis of N-doped GQDs was allowed by the addition of ammonia in the solution. The nitrogen doping was plainly evidenced by X-ray photoelectron (XPS) and Raman spectroscopies. The role of the electrolytic solution employed during the synthesis has been also discussed. Finally, these N-doped and non-doped GQDs were further used to prepare hybrids by grafting them onto ZnO semi-conductors, and their photocatalytic properties towards water-splitting were investigated. Interestingly, a very important enhancement of the amount of dihydrogen produced was observed with N-doped GQDs, compared to ZnO alone or to hybrids prepared with non-doped GQDs.

Synthesis of Bone Meal-derived 4-Carboxyphenylboronic Acid Functionalized Sulfur and Nitrogen Co-doped Graphene Quantum Dots Nanoprobe for Sialic Acid Sensing

Detection of sialic acid using advanced sensors in milk-based products is essential in the food industry. Therefore, the present work reports the sulfur and nitrogen-doped graphene quantum dots from bone meal functionalized with boronic acid (Boro-S/N-dGQDs) nanoprobe for sialic acid sensing applications. Briefly, S/N-dGQDs were functionalized with 4-carboxyphenylboronic acid to improve performance of fluorescent sensors toward the detection of sialic acid. Here, boronic acid surface decoration on S/N-dGQD was confirmed by several spectral characterizations. The addition of different quantities of sialic acid results in a directly proportionate correlation to fluorescence quenching. It gives a broad linear range of 50 ng/mL to 1000 ng/mL and a limit of detection of 6.04 ng/mL. Also, it displayed remarkable selectivity, likely due to interaction of sialic acid-containing 1,2-diol with hydroxyl group of Boro-S/N-dGQDs nanoprobe. Designed sensor demonstrated good stability and reproducibility. Real-time analysis of sialic acid in different milk-based products confirmed practicability of Boro-S/N-dGQDs.

Electrochemical determination of ascorbic acid using palladium supported on N-doped graphene quantum dot modified electrode

To precise screening concentration of ascorbic acid (AA), a novel electrochemical sensor was prepared using palladium nanoparticles decorated on nitrogen-doped graphene quantum dot modified glassy carbon electrode (PdNPs@N-GQD/GCE). For this purpose, nitrogen doped GQD nanoparticles (N-GQD) were synthesized from a citric acid condensation reaction in the presence of ethylenediamine and subsequently modified by palladium nanoparticles (PdNPs). The electrochemical behavior of AA was investigated, in which the oxidation peak appeared at 0 V related to the AA oxidation. Considering the synergistic effect of Pd nanoparticles as an active electrocatalyst, and N-GQD as an electron transfer accelerator and electrocatalytic activity improving agent, PdNPs@N-GQD hybrid materials showed excellent activity in the direct oxidation of AA. In the optimal conditions, the voltammetric response was linear in the range from 30 to 700 nM and the detection limit was calculated to be 23 nM. The validity and the efficiency of the proposed sensor were successfully tested and confirmed by measuring AA in real samples of chewing tablets, and fruit juice.

Fluorescence/electrochemical dual-mode strategy for Golgi protein 73 detection based on molybdenum disulfide/ferrocene/palladium nanoparticles and nitrogen-doped graphene quantum dots.

Golgi protein 73 (GP73) is a new serum marker associated with early diagnosis and postoperative assessment of hepatocellular carcinoma (HCC). Herein, an electrochemical/fluorescence dual-signal biosensor was designed for determination of GP73 based on molybdenum disulfide/ferrocene/palladium nanoparticles (MoS2-Fc-PdNPs) and nitrogen-doped graphene quantum dots (NGQDs). GP73 aptamer (Apt) was labeled with NGQDs to form the NGQDs-Apt fluorescence probe. MoS2-Fc-PdNPs served not onlyas the fluorescence quencher but also as electrochemical enhancer. The sensing platform (NGQDs-Apt/MoS2-Fc-PdNPs) was formed based on the fluorescence resonance energy transfer (FRET) mechanism. In the presence of GP73, the specific binding of NGQDs-Apt to GP73 interrupted FRET, restoring the fluorescence of NGQDs-Apt at λex/em = 348/438nm and enhancing the oxidation current of Fc in MoS2-Fc-PdNPs at 0.04V through differential pulse voltammetry (DPV). Under the optimal conditions, the DPV current change and fluorescence recovery have a good linear relationship with GP73 concentration from 1.00 to 10.0ng/mL. The calibration equation for the fluorescence mode was Y1 = (0.0213 ± 0.00127)X + (0.0641 ± 0.00448) and LOD was 0.812ng/mL (S/N = 3). The calibration equation of the electrochemical mode was Y2 = (3.41 ± 0.111)X + (1.62 ± 0.731), and LOD of 0.0425ng/mL (S/N = 3). The RSDs of fluorescence mode and electrochemical mode after serum detection were 1.62 to 5.21% and 0.180 to 6.62%, respectively. By combining the electrochemical and fluorescence assay, more comprehensive and valuable information for GP73 was provided. Such dual-mode detection platform shows excellent reproducibility, stability, and selectivity and has great application potential.

Study on a novel Si3N4-based composite with the incorporation of N-GQDs produced from nano-lignin

In order to enhance the mechanical properties of ceramic materials and realize the high value utilization of lignin, the nano-lignin precursor was added into the silicon nitride matrix as the second phase to obtain a novel ceramic composite material with excellent mechanical performance in this study. During the preparation, the nano-lignin was transformed into nitrogen-doped graphene quantum dots(N-GQDs) in the ceramic matrix by the pyrolysis-hot pressing sintering coupling process. Aiming to reveal the pyrolysis conversion process of lignin, the segmented products at the different temperature gradient were prepared, and their phase composition and microstructure were deeply analyzed by various test methods. In addition, the continuous pyrolysis process of nano-lignin was further studied by simultaneous thermal analyzer. The results showed that, nano-lignin was transformed into solid products (amorphous carbon) in the temperature range of room temperature to 800 °C and produced a large number of volatiles. Subsequently, in the temperature range of 800∼1400 °C, part of amorphous carbon began to transform into N-GQDs, and part of α-Si3N4 also began to transform into β-Si3N4. When the temperature rose to the temperature of 1700 °C, all amorphous carbon was transformed into N-GQDs through carbon structure rearrangement and nitrogen doping, and meanwhile the most of α-Si3N4 was transformed into β-Si3N4. At the final stage, β-Si3N4 columnar grains were covered by an overlayer composed of N-GQDs, and a novel ceramic composite with a special “core-shell” microstructure was obtained and exhibited excellent mechanical performance. This study presents a promising approach for the preparation of high-performance ceramic materials, and can also intrigue great interests in lignin graphitization and lignin-derived carbon materials.

Palladium Metal Nanocomposites Based on PEI-Functionalized Nitrogen-Doped Graphene Quantum Dots: Synthesis, Characterization, Density Functional Theory Modeling, and Cell Cycle Arrest Effects on Human Ovarian Cancer Cells.

In this study, the synthesis, characterization, density functional theory calculations (DFT), and effect of polyethylenimine (PEI)-functionalized nitrogen-doped graphene quantum dots (PEI N-GQDs) and their palladium metal nanoparticles nanocomposites (PdNPs/PEI N-GQDs) on cancer cells were extensively investigated. The focus also includes investigating their cytotoxic and apoptotic effects on ovarian cancer cells, which pose a serious risk to women's health and have high death rates from delayed diagnosis, inadequate response to treatment, and decreased survival. Graphene quantum dots and their palladium nanocomposites were differentially effective against ovarian cancer cell lines. In particular, the smaller particle size and morphology of PdNPs/PEI N-GQDs nanocomposites compared with PEI N-GQDs probably enhance their activity through highly improved uptake by cells. These findings emphasize the importance of particle size in composite drugs for efficient cancer treatment. DFT results revealed that the Pd-containing nanocomposite, with a smaller highest occupied molecular orbital-lowest unoccupied molecular orbital gap, exhibited higher reactivity and anticancer effects in human ovarian cancer cell line, OVCAR-3. Significantly, the application of nanocomposites to ovarian cancer cells initiated apoptosis, offering valuable insights into the intricate interplay between nanomaterials and cancer biology.

Utilization of Nitrogen-Doped Graphene Quantum Dots to Neutralize ROS and Modulate Intracellular Antioxidant Pathways to Improve Dry Eye Disease Therapy.

Patients afflicted with dry eye disease (DED) experience significant discomfort. The underlying cause of DED is the excessive accumulation of ROS on the ocular surface. Here, we investigated the nitrogen doped-graphene quantum dots (NGQDs), known for their ROS-scavenging capabilities, as a treatment for DED. NGQDs were prepared by using citric acid and urea as precursors through hydrothermal method. The antioxidant abilities of NGQDs were evaluated through: scavenging the ROS both extracellular and intracellular, regulating the nuclear factor-erythroid 2-related factor (Nrf2) antioxidant pathway of human corneal epithelial cells (HCECs) and their transcription of inflammation related genes. Furthermore, NGQDs were modified by Arg-Gly-Asp-Ser (RGDS) peptides to obtain RGDS@NGQDs. In vivo, both the NGQDs and RGDS@NGQDs were suspended in 0.1% Pluronic F127 (w/v) and delivered as eye drops in the scopolamine hydrobromide-induced DED mouse model. Preclinical efficacy was compared to the healthy and DPBS treated DED mice. These NGQDs demonstrated pronounced antioxidant properties, efficiently neutralizing free radicals and activating the intracellular Nrf2 pathway. In vitro studies revealed that treatment of H2O2-exposed HCECs with NGQDs induced a preservation in cell viability. Additionally, there was a reduction in the transcription of inflammation-associated genes. To prolong the corneal residence time of NGQDs, they were further modified with RGDS peptides and suspended in 0.1% Pluronic F127 (w/v) to create RGDS@NGQDs F127 eye drops. RGDS@NGQDs exhibited superior intracellular antioxidant activity even at low concentrations (10 μg/mL). Subsequent in vivo studies revealed that RGDS@NGQDs F127 eye drops notably mitigated the symptoms of DED mouse model, primarily by reducing ocular ROS levels. Our findings underscore the enhanced antioxidant benefits achieved by modifying GQDs through nitrogen doping and RGDS peptide tethering. Importantly, in a mouse model, our novel eye drops formulation effectively ameliorated DED symptoms, thereby representing a novel therapeutic pathway for DED management.

Improving adsorption and visible light photocatalytic performance of TiO2 via synergistic effect of nitrogen-doped graphene quantum dots and reduced mildly oxidized graphene oxide for cationic dye pollutants removal

In this study, a new type of ternary composite for efficient removal of cationic dye pollutants, P25/nitrogen-doped graphene quantum dots/reduced mildly oxidized graphene oxide (P25/NGQDs/rmGO) was successfully prepared by a two-step hydrothermal process. P25/NGQDs/rmGO exhibited outstanding removal performance towards methylene blue (MB), crystal violet (CV) and Basic Red 46 (BR46) under visible light or solar light irradiation owing to the excellent adsorption-photocatalytic property resulting from the synergistic effect of NGQDs and rmGO. The negatively charged NGQDs significantly improved the adsorption capacity for positively charged dye based on the adsorption experiment results. The investigations of adsorption kinetics and isotherm for MB demonstrated that the adsorption process followed the pseudo-second-order kinetic model and Langmuir adsorption isotherm, respectively. Thermodynamics analysis indicated that the adsorption process was exothermic and spontaneous. Furthermore, NGQDs and rmGO could both extend photoresponse range and enhance charge separation and transportation based on UV–vis DRS, PL spectra, transient photocurrent and electrochemical impedance spectra results. The optimized P25/NGQDs/rmGO composite obtained the removal efficiencies of 96.6 %, 100 % and 82.4 % for MB, CV and BR46, respectively, after 30-min adsorption and 150-min photodegradation under visible light irradiation. In addition, solar light irradiation was more favorable for the removal of these cationic dye pollutants. The high adsorption and photocatalytic degradation performance of P25/NGQDs/rmGO make it an excellent candidate for removing cationic dye pollutants from the industrial effluents. This study also provided a new idea on the roles of NGQDs and rmGO in adsorption-photocatalysis systems and promoted the practical application of TiO2-based composites in environmental field.

Superparamagnetic properties of metal-free nitrogen-doped graphene quantum dots

This article reports the superparamagnetic behavior of metal-free nitrogen-doped graphene quantum dots (N-GQDs). The pulsed laser ablation (PLA) method was utilized to synthesize N-GQDs with an average diameter of 3.45 nm and a high doping level (N/C) of 1.4. Magnetic properties of as-synthesized N-GQDs were explored by performing magnetization vs magnetic field (M–H) and magnetization vs temperature (M–T) measurements. M–H plots measured in a temperature range of 2–300 K revealed the superparamagnetic behavior of N-GQDs. The value of saturation magnetization was found to be directly correlated to nitrogen concentration and a saturation magnetization up to 28.7 emu/g was obtained at room temperature (300 K). M–T measurements with zero-field-cooled (ZFC) and field-cooled (FC) conditions were employed to study anisotropy energy barriers and blocking temperature. A variation in the blocking temperature (TB) from 288 to 61 K was observed when the external magnetic field (H) was changed from 0.1 to 0.6 T. The origin of superparamagnetism was attributed to the presence of graphitic nitrogen bonding configuration and defect states. The observed superparamagnetic properties along with the optical properties of N-GQDs create an opportunity for developing materials for biomedical applications and data recording devices.

Tuning photovoltaic performance of co-doped graphene quantum dots

The photovoltaic performance of graphene quantum dots (GQDs) faces instability due to structural irregularities. To understand optoelectronic properties, this study employs density functional theory (DFT) to investigate nitrogen-doped GQDs (NGQDs) co-doped with sulfur (N,S) and phosphorous (N,P). Co-doping with N and S or N and P reduces electron-hole pair separation, increasing thermal loss in GQDs with graphitic N functionality. N,S co-doping heightens surface defect likelihood, while N,P co-doping diminishes it. The chemical reactivity of NGQDs is influenced by polar solvent choice, unlike excited-state properties of GQDs doped with other elements. NGQDs with graphitic and pyrrolic N functionalities outperform co-doped GQDs in photovoltaic performance due to enhanced parameters. This study guides rational design of electronic devices using GQD materials.

Multifunctional graphene quantum dots: A therapeutic strategy for neurodegenerative diseases by regulating calcium influx, crossing the blood-brain barrier and inhibiting Aβ-protein aggregation

Multifunctional nanoparticles could be the hallmark for the treatment of neurodegenerative diseases. Dissociation of protein aggregates causing neuronal damage and transfer of specific drugs which can downregulate neuronal excitotoxicity by inhibiting glutamatergic N-Methyl-d-Aspartate-receptors (NMDA) and then reducing calcium influx are among the main factors to consider for proper therapy. Here, we present a multiplatform based on nitrogen-doped graphene quantum dots (NGQDs) with such functionalities. The NGQDs were functionalized with Memantine, the clinically used drug, via covalent and non-covalent coupling, and we confirmed that the pharmaceutical activity was not altered. Apart from that, using xCELLigence technology and flow cytometric analysis of ABC transporter function, we uncovered that the ABC transporters of the blood-brain barrier (BBB) do not affect the ability of NGQD to cross BBB. Surprisingly, this study found that NGQDs have an inhibitory effect on NMDA receptors, thus supporting the action of Memantine. Moreover, NGQDs and their derivatives demonstrated the potential to dissociate β-amyloid aggregates while possessing features suitable for bioimaging in various cell lines.

The room temperature highly sensitive ammonia gas sensor based on polyaniline and nitrogen doped graphene quantum dot coated flower‐like tungsten oxide composite

AbstractIn this study, the newly synthesized polyaniline (PANI)/polyethylenimine modified nitrogen doped graphene quantum dot (PN‐GQD)/tungsten oxide (WO3) ternary composites were used as ammonia (NH3) gas sensor detected the NH3 at room temperature. Fourier transform infrared spectrometer, field‐emission scanning electron microscopy, transmission electron microscopy, and x‐ray photoelectron spectroscopy were applied to illustrate the chemical structure and morphology of the fabricated ternary composites. The NH3 gas‐sensing performances of PANI/PN‐GQD/WO3 composite sensor were determined in the concentration between 0.6 and 2.0 ppm at room temperature and the response value of the ternary composite sensor with an exposure of 1.0 ppm NH3 was 19.9, which was much better than those of PANI and PANI/WO3 sensors. Because their highly sensitive detection of NH3 ranging from the concentration between 0.6 and 2.0 ppm at room temperature, the PANI/PN‐GQD/WO3 composite sensor was confirmed to be extremely effective to detect the kidney or hepatic disease from the human breath. This ternary composite sensor with an exposure of 1.0 and 2.0 ppm NH3 also displayed extraordinary repeatability and selectivity at room temperature. According to these findings, this fabricated PANI/PN‐GQD/WO3 composite sensor will be an excellent gas‐sensing material to detect the kidney or hepatic disease from the human breath.

Removal of organic amino derivatives from wastewater by using fluorescent nitrogen-doped GQDs under visible light and fluorescence application under ultra violet light

Photocatalysis is one of the most popular organic waste degradation treatments because it can result in the total decomposition of organic pollutants under visible light illumination. Here, we present a metal-free visible-light active catalyst for the effective decomposition of organic aromatic amino derivatives Methylene blue (MB) and Rhodamine B (RB) as model-contaminated dye molecules. Through a one-pot hydrothermal process, blue colour emissive nitrogen-doped graphene quantum dots (N-GQDs) were synthesized from urea and malic acid. The physicochemical characteristic techniques were used to analyze the surface morphology, elemental analysis, surface functional groups, absorption, emission, and band gap of prepared N-GQDs. The effective light absorption properties, transfer of electrons, separation of photoinduced charge carriers, and excellent stability with a band gap of 2.69 eV of synthesized N-GQDs have enabled the degradation of Rh B and MB up to 90 % and 86 % respectively, within 120 min of visible light irradiation. Based on extensive active species trapping experiments, a probable photocatalytic dye degradation mechanism is proposed. These N-GQDs can also be used to make fluorescent ink for imaging and security purposes.