Eco-Friendly Sustainable Fluorescent Carbon Dots for the Adsorption of Heavy Metal Ions in Aqueous Environment

Nitrogen-doped carbon dots as fluorescent probes for sensitive and selective determination of Fe3

At present, the contamination of water resources by heavy metal ions has posed a significant threat to human survival. Therefore, it is particularly critical to develop low-cost, easy-to-use, and highly efficient heavy metal detection technologies. In this work, a fast and cost-effective fluorescent probe for nitrogen-doped carbon dots (N-CDs) was prepared using one-step hydrothermal method with citric acid (CA) as carbon source, and melamine as nitrogen source. The structural and optical characterizations of the resulting N-CDs were investigated in details. The results showed that the quantum yield of the prepared fluorescent probe was as high as 45 %, and an average fluorescence lifetime was about 7.80 ns. N-CDs have excellent water solubility and dispersibility, with an average size of 2.58 nm. N-CDs exhibited excellent specific responsiveness to Fe3+ and can be used as an effective method for detecting Fe3+ at low-concentrations (the concentrations of N-CDs as low as 0.24 μg/mL) using fluorescent probes. The linear response of the fluorescent probe N-CDs to Fe3+ was formed in the concentration range of 20-80 μM, and the detection limit was 3.18 μM. In addition, in the actual water samples analysis, the recovery rate reached 97.05-100.58 %. The prepared of N-CDs provide available Fe3+ fluorescent probes in the environment.

Enhancing the production of PHA in Scenedesmus sp. by the addition of green synthesized nitrogen, phosphorus, and nitrogen-phosphorus-doped carbon dots

Plastic consumption has increased globally, and environmental issues associated with it have only gotten more severe; as a result, the search for environmentally friendly alternatives has intensified. Polyhydroxyalkanoates (PHA), as biopolymers produced by microalgae, might be an excellent option; however, large-scale production is a relevant barrier that hinders their application. Recently, innovative materials such as carbon dots (CDs) have been explored to enhance PHA production sustainably. This study added green synthesized multi-doped CDs to Scenedesmus sp. microalgae cultures to improve PHA production. Prickly pear was selected as the carbon precursor for the hydrothermally synthesized CDs doped with nitrogen, phosphorous, and nitrogen-phosphorous elements. CDs were characterized by different techniques, such as FTIR, SEM, ζ potential, UV-Vis, and XRD. They exhibited a semi-crystalline structure with high concentrations of carboxylic groups on their surface and other elements, such as copper and phosphorus. A medium without nitrogen and phosphorous was used as a control to compare CDs-enriched mediums. Cultures regarding biomass growth, carbohydrates, lipids, proteins, and PHA content were analyzed. The obtained results demonstrated that CDs-enriched cultures produced higher content of biomass and PHA; CDs-enriched cultures presented an increase of 26.9% in PHA concentration and an increase of 32% in terms of cell growth compared to the standard cultures.

Reducing nitrogen loss from farmland by layered double hydroxide-supported carbon dots-enhanced ammonium immobilization

It remains a significant challenge to develop a kind of cost-effective and eco-friendly adsorbent with strong immobilization capabilities for ammonium in farmland. In this work, we employed Ca/Al layered double hydroxide-supported carbon dots (CDs@Ca/Al-LDHs) as a novel and efficient adsorbent for ammonium immobilization both in aqueous and soil environments. Such a composite could exhibit a high adsorption capacity towards ammonium in solution, which was four times higher than zeolite and three times higher than biochar under the same conditions. The mechanism investigations revealed that electrostatic interactions between the negatively charged CDs and the positively charged ammonium played a key role in the adsorption. In 30-day leaching experiments, the fabricated composite cumulatively reduced ammonium and nitrate by 6.3% and 9.7%, respectively at a dosage of 0.1% (w/w). Incubation experiments further confirmed that the developed composite could effectively inhibit ammonia volatilization and nitrification by immobilizing the ammonium within soil matrices. Our results demonstrated that CDs@Ca/Al-LDHs represented a promising candidate for cost-effective and eco-friendly immobilization of excess ammonium from over-fertilized farmland.

Enhanced photosynthetic efficiency by nitrogen-doped carbon dots via plastoquinone-involved electron transfer in apple

Artificially enhancing photosynthesis is critical for improving crop yields and fruit qualities. Nanomaterials have demonstrated great potential to enhance photosynthetic efficiency; however, the mechanisms underlying their effects are poorly understood. This study revealed that the electron transfer pathway participated in nitrogen-doped carbon dots (N-CDs)-induced photosynthetic efficiency enhancement (24.29%), resulting in the improvements of apple fruit qualities (soluble sugar content: 11.43%) in the orchard. We also found that N-CDs alleviated mterf5 mutant-modulated photosystem II (PSII) defects, but not psa3 mutant-modulated photosystem I (PSI) defects, suggesting that the N-CDs-targeting sites were located between PSII and PSI. Measurements of chlorophyll fluorescence parameters suggested that plastoquinone (PQ), the mobile electron carrier in the photosynthesis electron transfer chain (PETC), was the photosynthesis component that N-CDs targeted. In vitro experiments demonstrated that plastoquinone-9 (PQ-9) could accept electrons from light-excited N-CDs to produce the reduced plastoquinone 9 (PQH2-9). These findings suggested that N-CDs, as electron donors, offer a PQ-9-involved complement of PETC to improve photosynthesis and thereby fruit quality. Our study uncovered a mechanism by which nanomaterials enhanced plant photosynthesis and provided some insights that will be useful in the design of efficient nanomaterials for agricultural/horticultural applications.

Efficient Adsorptive Removal of Methylene Blue Dye from Aqueous Solution Using Eragrostis Teff Biomass-Derived Nitrogen and Phosphorus-Codoped Carbon Quantum Dots

Carbon quantum dots have a great application potential in environmental protection via adsorption technology due to their large specific surface area and negative zeta potential. In this work, nitrogen and phosphorus-codoped carbon quantum dots (NP-CQDs) with a large specific surface area and negative zeta potential were successfully synthesized by a single-step hydrothermal synthesis. Batch adsorption studies were utilized to assess the adsorbent's capacity to remove common methylene blue (MB) dye contaminants from an aqueous solution. The experiment showed that MB dye could be removed in 30 min under optimum experimental conditions, with a removal efficiency of 93.73%. The adsorbent's large surface area of 526.063 m2/g and negative zeta potential of -12.3 mV contribute to the high removal efficiency. The Freundlich isotherm model fits the adsorption process well at 298 K, with R2 and n values of 0.99678 and 4.564, respectively, indicating its applicability. A kinetic study demonstrated that the pseudo-second-order model, rather than the pseudo-first-order model, is more suited to represent the process of MB dye adsorption onto NP-CQDs. This research established a simple and cost-effective method for developing a highly efficient NP-CQD adsorbent for organic dye degradation by adsorption.

Synergistic Enhancement of Photocatalytic H2 Evolution over NH2-MIL-125 Modified with Dual Cocatalyst

The construction of efficient photocatalysts for water splitting to enable H2 evolution is pivotal to alleviate energy issues and environmental concerns. In this work, carbon dots (CDs) were prepared by employing "green solvent" ionic liquids as carbon sources and then combined with Pt/NH2-MIL-125, resulting in the emergence of a high-efficiency photocatalyst termed CDs-Pt/NH2-MIL-125 for the first time. This composite photocatalyst exhibited outstanding photocatalytic activity in H2 production under visible light irradiation. Notably, the H2 production rate of CDs100-Pt/NH2-MIL-125 reaches up to 951.4 μmol/g/h, which was 3.1 times that of Pt/NH2-MIL-125. The characterization results indicate that CDs and Pt uniformly dispersed on the surface of NH2-MIL-125 and fabricated a synergistic compact structure, providing a high BET surface area (985 m2 g-1) and a suitable band gap. Furthermore, the distinctive embeddable-dispersed CDs and Pt, as dual cocatalyst, can harvest light and facilitate the transfer of photogenerated electrons, thereby significantly augmenting the exploitation of visible light. The plausible mechanism of photocatalytic H2 evolution over the CDs-Pt/NH2-MIL-125 catalyst was also discussed. This work introduces a promising strategy for designing high-performance CDs-MOFs-based photocatalysts, an innovative step toward achieving efficient photocatalytic water splitting for H2 production.

Scaling-up of carbon dots hydrothermal synthesis from sugars in a continuous flow microreactor system for biomedical application as in vitro antimicrobial drug nanocarrier

Carbon dots (CDs) are a new class of nanomaterials exhibiting high biocompatibility, water solubility, functionality, and tunable fluorescence (FL) property. Due to the limitations of batch hydrothermal synthesis in terms of low CDs yield and long synthesis duration, this work aimed to increase its production capacity through a continuous flow reactor system. The influence of temperature and time was first studied in a batch reactor for glucose, xylose, sucrose and table sugar precursors. CDs synthesized from sucrose precursor exhibited the highest quantum yield (QY) (175.48%) and the average diameter less than 10 nm (~6.8 ± 1.1 nm) when synthesized at 220°C for 9 h. For a flow reactor system, the best condition for CDs production from sucrose was 1 mL min-1 flow rate at 280°C, and 0.2 MPa pressure yielding 53.03% QY and ~ 6.5 ± 0.6 nm average diameter (6.6 mg min-1 of CDs productivity). CDs were successfully used as ciprofloxacin (CP) nanocarrier for antimicrobial activity study. The cytotoxicity study showed that no effect of CDs on viability of L-929 fibroblast cells was detected until 1000 µg mL-1 CDs concentration. This finding demonstrates that CDs synthesized via a flow reactor system have a high zeta potential and suitable surface properties for nano-theranostic applications.

Carbon Dots-Types, Obtaining and Application in Biotechnology and Food Technology

Materials with a "nano" structure are increasingly used in medicine and biotechnology as drug delivery systems, bioimaging agents or biosensors in the monitoring of toxic substances, heavy metals and environmental variations. Furthermore, in the food industry, they have found applications as detectors of food adulteration, microbial contamination and even in packaging for monitoring product freshness. Carbon dots (CDs) as materials with broad as well as unprecedented possibilities could revolutionize the economy, if only their synthesis was based on low-cost natural sources. So far, a number of studies point to the positive possibilities of obtaining CDs from natural sources. This review describes the types of carbon dots and the most important methods of obtaining them. It also focuses on presenting the potential application of carbon dots in biotechnology and food technology.

Uncommon 2D diamond-like carbon nanodots derived from nanotubes: atomic structure, electronic states, and photonic properties

In this article, we report the results of a relatively facile fabrication of carbon nanodots from single-walled and multi-walled carbon nanotubes (SWCNTs and MWCNTs). The results of X-ray photoelectron spectroscopy (XPS) and Raman measurements show that the obtained carbon nanodots are quasi-two-dimensional objects with a diamond-like structure. Based on the characterization results, a theoretical model of the synthesized carbon nanodots was developed. The measured absorption spectra demonstrate the similarity in the local atomic structure of carbon nanodots synthesized from single-walled and multi-walled carbon nanotubes. However, the photoluminescence (PL) spectra of nanodots synthesized from both sources turned out to be completely different. Carbon dots fabricated from MWCNTs exhibit PL spectra similar to those of nanoscale carbon systems with sp³ hybridization and a valuable edge contribution. At the same time nanodots synthesized from SWCNTs exhibit PL spectra which are typical for quantum dots with an estimated size of ∼0.6-1.3 nm.

A sensitive fluorescence sensor based on a glutathione modified quantum dot for visual detection of copper ions in real samples

Copper (Cu²⁺), as a heavy metal, accumulates in the human body to a certain extent, which can induce various diseases and endanger human health. Rapid and sensitive detection of Cu²⁺ is highly desired. In present work, a glutathione modified quantum dot (GSH-CdTe QDs) was synthesized and applied in a "turn-off" fluorescence probe to detect Cu²⁺. The fluorescence of GSH-CdTe QDs could be rapidly quenched in the presence of Cu²⁺ through aggregation-caused quenching (ACQ), resulting from the interaction between the surface functional groups of GSH-CdTe QDs and Cu²⁺ and the electrostatic attraction. In the range of 20-1100 nM, the Cu²⁺ concentration showed a good linear relationship with the fluorescence decline of the sensor, and the LOD is 10.12 nM, which was lower than the U.S. Environmental Protection Agency (EPA) defined limit (20 μM). Moreover, aiming to attain visual analysis, colorimetric method was also used for rapidly detecting Cu²⁺ by capturing the change in fluorescence color. Interestingly, the proposed approach has successfully been applied for the detection of Cu²⁺ in real samples (i.e., environment water, food and traditional Chinese medicine) with satisfactory results, which provides a promising strategy for the detection of Cu²⁺ in practical application with the merits of being rapid, simple and sensitive.

Preparation of hydrogels based on poplar cellulose and their removal efficiency of Cd(II) from aqueous solutions

Industrial heavy metal-contaminated wastewater is one of the main water pollution problems. Adsorbents are a promising method for the removal of heavy metal contaminants. Herein, polyaspartic acid/carboxymethyl poplar sawdust hydrogels (PASP/CMPP) and ascorbic acid/carboxymethyl poplar sawdust hydrogels (VC/CMPP) were prepared by aqueous polymerization using alkalized poplar sawdust (CMPP) as the substrate and PASP and vitamin C (VC) as modifiers. The effective results, provided by the characterization analysis of SEM and BET, indicate that the surface of the PASP/CMPP hydrogel has a larger number of loose pores and a larger pore volume than the VC/CMPP hydrogel. The treatment effects of the two hydrogels on simulated wastewater containing Cd(II) were investigated by a batch of experiments. The results showed that PASP/CMPP had a better adsorption effect than VC/CMPP under the same adsorption conditions. Interestingly, the solid concentration effect was found in the process of sorption kinetics and sorption isotherms. The sorption kinetic curves of Cd(II) on PASP/CMPP were well-fitted by the quasi-second-order kinetics under different adsorbent concentrations. The adsorption conforms to Langmuir and Freundlich adsorption isotherm models. More importantly, PASP/CMPP composites are expected to be used as a new kind of environmental adsorbent for wastewater treatment.

Remediation of environmental toxicants using carbonaceous materials: opportunity and challenges

Adsorption and photocatalytic properties of carbonaceous materials, viz., carbon nanotubes (CNTs), fullerene, graphene, graphene oxide, carbon nanofiber nanospheres, and activated carbon, are the legitimate weapons for the remediation of emerging and persistent inorganic/organic contaminants, heavy metals, and radionucleotides from the environment. High surface area, low or non-toxic nature, ease of synthesis, regeneration, and chemical modification of carbonaceous material make them ideal for the removal of toxicants. The research techniques investigated during the last decade for the elimination of environmental toxicants using carbonaceous materials are reviewed to offer comprehensive insight into the mechanism, efficiency, applications, advantages, and shortcomings. Opportunities and challenges associated with carbon materials have been discussed to suggest future perspectives in the remediation of environmental toxicants.

Synthesis of Graphene Quantum Dot Magnesium Hydroxide Nanocomposites and Investigation of Their Antioxidant and Antimicrobial Activities

In this paper, we synthesized graphene quantum dots magnesium hydroxide nanocomposites (GQDs/Mg(OH)₂). The synthesized nanocomposites were characterized by UV-Vis spectroscopy, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Malvern Zetasizer. The antimicrobial and antioxidant properties of the obtained GQDs/Mg(OH)₂ nanocomposites were investigated. GQDs/Mg(OH)₂ nanocomposites have MIC values of 15.625 μg/mL against fungi (C. metapsilosis and C. parapsilosis) and 62.5 μg/mL against Gram (+) (S. pneumonia and E. faecalis) and Gram (-) (E. coli). The synthesized GQDs/Mg(OH)₂ nanocomposites showed moderate antioxidant activity. The results showed that at 100-µg/mL GQDs/Mg(OH)₂ nanocomposite concentration, the H₂O₂ scavenging activity was 62.18%.

Rambutan seed waste-derived nitrogen-doped carbon dots with l-aspartic acid for the sensing of Congo red dye

In this study, new nitrogen-doped carbon dots (N-CDs) were prepared by utilizing rambutan seed waste and l-aspartic acid as dual precursors (carbon and nitrogen sources) through a hydrothermal treatment method. The N-CDs showed blue emission in solution under UV light irradiation. Their optical and physicochemical properties were examined via UV-vis, TEM, FTIR spectroscopy, SEM, DSC, DTA, TGA, XRD, XPS, Raman spectroscopy, and zeta potential analyses. They showed a strong emission peak at 435 nm and excitation-dependent emission behavior with strong electronic transitions of C[double bond, length as m-dash]C/C[double bond, length as m-dash]O bonds. The N-CDs exhibited high water dispersibility and great optical properties in response to some environmental conditions such as heating temperature, light irradiation, ionic strength, and storage time. They have an average size of 3.07 nm and good thermal stability. Owing to their great properties, they have been used as a fluorescent sensor for Congo red dye. The N-CDs selectively and sensitively detected Congo red dye with a detection limit of 0.035 μM. Moreover, the N-CDs were utilized to detect Congo red in tap and lake water samples. Thus, rambutan seed waste was successfully converted into N-CDs and these functional nanomaterials are promising for use in important applications.

A comprehensive model of nitrogen-free ordered carbon quantum dots

We propose and demonstrate a novel range of models to accurately determine the optical properties of nitrogen-free carbon quantum dots (CQDs) with ordered graphene layered structures. We confirm the results of our models against the full range of experimental results for CQDs available from an extensive review of the literature. The models can be equally applied to CQDs with varied sizes and with different oxygen contents in the basal planes of the constituent graphenic sheets. We demonstrate that the experimentally observed blue fluorescent emission of nitrogen-free CQDs can be associated with either small oxidised areas on the periphery of the graphenic sheets, or with sub-nanometre non-functionalised islands of sp2-hybridised carbon with high symmetry confined in the centres of oxidised graphene sheets. Larger and/or less symmetric non-functionalised regions in the centre of functionalised graphene sheet are found to be sources of green and even red fluorescent emission from nitrogen-free CQDs. We also demonstrate an approach to simplify the modelling of the discussed sp2-islands by substitution with equivalent strained polycyclic aromatic hydrocarbons. Additionally, we show that the bandgaps (and photoluminescence) of CQDs are not dependent on either out-of-plane corrugation of the graphene sheet or the spacing between sp2-islands. Advantageously, our proposed models show that there is no need to involve light-emitting polycyclic aromatic molecules (nanographenes) with arbitrary structures grafted to the particle periphery to explain the plethora of optical phenomena observed for CQDs across the full range of experimental works.

Carbon dots as fluorescent nanoprobes for assay of some non-fluorophoric nitrogenous compounds of high pharmaceutical interest

Background

Carbon dots, CDs, have excellent photoluminescence properties, good biocompatibility, low toxicity and good light stability. The optical, magnetic and electronic properties of CDs make them a hugely relevant tool to be used in pharmaceutical analysis, bioimaging, drug delivery, and other fields. The fluorescence of carbon nanodots makes it suitable for assay of some nitrogenous compounds of high pharmaceutical interest. In this work, we develop simple, fast and green spectrophotometric methods for quantification of Azithromycin and Rasagiline mesilate using synthesized fluorescent CDs from garlic peels.

Results

The spectrometric methods depend on stoichiometric reactions of both drugs with fluorescent CDs. Carbon dots exhibit a declared absorption peak λmax at 238 nm and potent fluorimetric emission at λem 528 nm, upon excitation at λex 376 nm. Drugs' concentrations in ppm are efficiently calculated using Stern-Volmer Equation. Decrease in fluorescence (ΔF = F _o - F) and the F-ratio values are linearly correlated to molar concentration of each quencher (drug). A significant linear diminish in the dots' measured absorbance and fluorimetric emission values was observed. Validation of all the developed methods was according to the ICH guidelines.

Conclusions

In a new way, this work successfully indicates, spectrometric methods for rapid detection of two non-fluorophoric nitrogenous compounds using potent carbon nanodots. Consequently, these green developed methods offer several benefits as simplicity, ease of quantification, accuracy and precision that encourage the application of the developed methods in routine analysis of Azithromycin and Rasagiline mesilate in quality control laboratories as analytical tool.

Supplementary Information

The online version contains supplementary material available at 10.1186/s43088-023-00346-z.

Eco-friendly Synthesis of Carbon Quantum Dots as an Effective Adsorbent

Fluorescent carbon quantum dots (CQDs) were prepared by an economical, green, and single-step procedure with the assistance of microwave heating of urea with bagasse (SCB), cellulose (C), or carboxymethyl cellulose (CMC). The prepared CQDs were characterized using a series of spectroscopic techniques, and they had petite size, intense absorption in the UV, and excitation wavelength-dependent fluorescence. The prepared CQDs were used for Pb(II) adsorption from an aqueous solution. The removal efficiency percentages (R %) were 99.16, 96.36, and 98.48% for QCMC, QC, and QSCB, respectively. The findings validated the efficiency of CQDs synthesized from CMC, cellulose, and SCB as excellent materials for further utilization in the environmental fields of wastewater pollution detection, adsorption, and chemical sensing applications. The kinetics and isotherms studied found that all CQDs isotherms fit well with the Langmuir model than Freundlich and Temkin models. According to R², the pseudo-second-order fits the adsorption of QCMC, while the first-order one fits with QC and QSCB.

Nitrogen-Doped Carbon Quantum Dots for Biosensing Applications: The Effect of the Thermal Treatments on Electrochemical and Optical Properties

The knowledge of the ways in which post-synthesis treatments may influence the properties of carbon quantum dots (CDs) is of paramount importance for their employment in biosensors. It enables the definition of the mechanism of sensing, which is essential for the application of the suited design strategy of the device. In the present work, we studied the ways in which post-synthesis thermal treatments influence the optical and electrochemical properties of Nitrogen-doped CDs (N-CDs). Blue-emitting, N-CDs for application in biosensors were synthesized through the hydrothermal route, starting from citric acid and urea as bio-synthesizable and low-cost precursors. The CDs samples were thermally post-treated and then characterized through a combination of spectroscopic, structural, and electrochemical techniques. We observed that the post-synthesis thermal treatments show an oxidative effect on CDs graphitic N-atoms. They cause their partially oxidation with the formation of mixed valence state systems, [CDs]⁰⁺, which could be further oxidized into the graphitic N-oxide forms. We also observed that thermal treatments cause the decomposition of the CDs external ammonium ions into ammonia and protons, which protonate their pyridinic N-atoms. Photoluminescence (PL) emission is quenched.

A comprehensive review on multi-colored emissive carbon dots as fluorescent probes for the detection of pharmaceutical drugs in water

Exposure to constituent hazardous chemicals in medical products has become a threat to environmental health across the globe. Excessive medication and the mishandling of pharmaceutical drugs can lead to the increased presence of chemicals in the aquatic environment, causing water pollution. Only a few nanomaterials exist for the detection of these chemicals and they are limited in use due to their adverse toxicity, instability, cost, and low aqueous solubility. In contrast, carbon dots (C-dots), a member of the family of carbon-based nanomaterials, have various beneficial properties including excellent biocompatibility, strong photoluminescence, low photobleaching, tunable fluorescence, and easy surface modification. Herein, we summarize recent advancements in various synthetic strategies for high-quality tunable fluorescent C-dots. The root of fluorescence has been briefly explained via the quantum confinement effect, surface defects, and molecular fluorescence. The surface functional moieties of C-dots have been investigated in depth to recognize the various types of pharmaceutical drugs that are used for the treatment of patients. The modulation of C-dot fluorescence in the course of their interactions with these drugs has been carefully explained. Different types of interaction mechanisms behind the C-dot fluorescence alteration have been discussed. Finally, the challenges and future perspectives of C-dots have been proposed for the vibrant field development of C-dot-based drug sensors.

Evaluation of Antimicrobial and Antibiofilm Activity of Citrus medica Fruit Juice Based Carbon Dots against Pseudomonas aeruginosa

Pseudomonas aeruginosa (P. aeruginosa) is one of the common immortal pathogens that cause intense chronic infections in low-immunity patients, significantly evading the immune system and suppressing the respiratory system. This work reports on the synthesis of prominent members of the carbon family, carbon quantum dots (CQDs), from a natural carbon precursor, Citrus medica (C. medica) fruit, and their inhibiting property against P. aeruginosa. CQDs synthesized by the conventional hydrothermal method with an average particle size of 4.5 nm exhibit renowned antimicrobial properties. To enhance the properties of the CQDs, nitrogen was doped using ammonium hydroxide as a nitrogen source, and absorption and fluorescence studies and the elemental composition of CQDs were also reported. CQDs potentially inhibited the growth of bacteria at the lowest concentration level of 1.25% (v/v). Similarly, CQDs moderately inhibited biofilm formation at the concentration level of 0.07% (v/v) for both clinical and control strains of P. aeruginosa. A fluorescence microscopy study revealed that the treated strain shows a moderately reduced biofilm formation when compared to the control strain of P. aeruginosa PAO1.

Synthesis and adsorption performance of ultra-low silica-to-alumina ratio and hierarchical porous ZSM-5 zeolites prepared from coal gasification fine slag

Since the human consumption of coal is increasingly growing and coal-based solid wastes are discharged in large quantities, the resource utilization of coal-based solid wastes has been paid more attention. In the present work, for the first time, the coal gasification fine slag is subjected to prepare ZSM-5 zeolites with ultra-low n(SiO₂)/n(Al₂O₃) ratios (less than 20) and hierarchical pore structures. The increase in the concentration of the alkaline extract leads to the decrease of the crystallinity, the irregularity of the microscopic morphology, and the decrease of the specific surface area, resulting in the in-situ generation of mesopores within ZSM-5. Moreover, adsorption experiments demonstrate that ZSM-5-2M exhibits the best methylene blue adsorption performance at the pH of 9 with a removal rate of up to 82.07%, and it also has good adsorption performance in simulated real water samples. Furthermore, the adsorption performance of ZSM-5-2M on the malachite green, Rhodamine B, Congo red, and methyl orange has been investigated and it is found to be very effective for the adsorption of cationic dyes, and its adsorption performance for methylene blue and malachite green is reduced in the presence of anions.

Chlorophyll Detection by Localized Surface Plasmon Resonance Using Functionalized Carbon Quantum Dots Triangle Ag Nanoparticles

An optical sensor-based localized surface plasmon resonance (LSPR) sensor was demonstrated for sensitive and selective chlorophyll detection through the integration of amino-functionalized carbon quantum dots (NCQD) and triangle silver nanoparticles (AgNPs). The additions of amino groups to the CQD enhance the detection of chlorophyll through electrostatic interactions. AgNPs-NCQD composite was fabricated on the surface of the silanized glass slide using the self-assembly technique. The experimental results showed that the AgNPs-NCQD film-based LSPR sensor detects better than AgNPs and AgNPs-CQD films with a good correlation coefficient (R² = 0.9835). AgNPs-NCQD showed a high sensitivity response of 2.23 nm ppm^-1. The detection and quantification limits of AgNPs-NCQD are 1.03 ppm and 3.40 ppm, respectively, in the range of 0.05 to 6 ppm. Throughout this study, no significant interference was observed among the other ionic species (NO₂^-, PO₄^-, NH₄⁺, and Fe³⁺). This study demonstrates the applicability of the proposed sensor (AgNPs-NCQD) as a sensing material for chlorophyll detection in oceans.

Aerogel Assembled by Two Types of Carbon Nanoparticles for Efficient Removal of Heavy Metal Ions

Both sodium alginate and polyethyleneimine (PEI) have a good ability to adsorb heavy metal ions. PEI and sodium alginate were used as important precursors to synthesize positively charged carbon nanoparticles (p-CNDs) with hydroxyl and carboxyl, and negatively charged carbon nanoparticles (n-CNDs) with amino, respectively. The carbon nanoparticles (CNDs) aerogel with a large specific surface area and rich functional groups were constructed by self-assembled p-CNDs and n-CNDs via electrostatic attraction for adsorption of heavy metal ions in water. The results show that CNDs aerogel has good adsorption properties for Pb²⁺ (96%), Cu²⁺ (91%), Co²⁺ (86%), Ni²⁺ (82%), and Cd²⁺ (78%). Furthermore, the fluorescence emission intensity of CNDs aerogel will gradually decrease with the increase in the adsorption rate, indicating that it can detect the adsorption process synchronously. In addition, the cytotoxicity test reveals that CNDs have good biocompatibility and will not cause secondary damage to biological cells.

Direct and Sensitive Detection of Dopamine Using Carbon Quantum Dots Based Refractive Index Surface Plasmon Resonance Sensor

Abnormality of dopamine (DA), a vital neurotransmitter in the brain’s neuronal pathways, causes several neurological diseases. Rapid and sensitive sensors for DA detection are required for early diagnosis of such disorders. Herein, a carbon quantum dot (CQD)-based refractive index surface plasmon resonance (SPR) sensor was designed. The sensor performance was evaluated for various concentrations of DA. Increasing DA levels yielded blue-shifted SPR dips. The experimental findings revealed an excellent sensitivity response of 0.138°/pM in a linear range from 0.001 to 100 pM and a high binding affinity of 6.234 TM⁻¹. The effects of varied concentrations of DA on the optical characteristics of CQD thin film were further proved theoretically. Increased DA levels decreased the thickness and real part of the refractive index of CQD film, according to fitting results. Furthermore, the observed reduction in surface roughness using AFM demonstrated that DA was bound to the sensor layer. This, in turn, explained the blue shift in SPR reflectance curves. This optical sensor offers great potential as a trustworthy solution for direct measurement due to its simple construction, high sensitivity, and other sensing features.

What makes carbon nanoparticle a potent material for biological application?

Carbon materials are generally utilized in the form of carbon allotropes and their characteristics are exploited as such or for improving the thermal, electrical, optical, and mechanical properties of other biomaterials. This has now found a broader share in conventional biomaterial space with the generation of nanodiamond, carbon dot, carbon nanoparticles (CNPs), and so forth. With properties of better biocompatibility, intrinsic optical emission, aqueous suspendability, and easier surface conjugation possibilities made CNPs as one of the fore most choice for biological applications especially for use in intracellular spaces. There are various reports available presenting methods of preparing, characterizing, and using CNPs for various biological applications but a collection of information on what makes CNP a suitable biomaterial to achieve those biological activities is yet to be provided in a significant way. Herein, a series of correlations among synthesis, characterization, and mode of utilization of CNP have been incorporated along with the variations in its use as agent for sensing, imaging, and therapy of different diseases or conditions. It is ensembled that how simplified and optimized methods of synthesis is correlated with specific characteristics of CNPs which were found to be suitable in the specific biological applications. These comparisons and correlations among various CNPs, will surely provide a platform to generate new edition of this nanomaterial with improvised applications and newer methods of evaluating structural, physical, and functional properties. This may ensure the eventual use of CNPs for human being for specific need in near future. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Biosensing Diagnostic Tools > In Vitro Nanoparticle-Based Sensing Therapeutic Approaches and Drug Discovery > Emerging Technologies.

The Role of N and S Doping on Photoluminescent Characteristics of Carbon Dots from Palm Bunches for Fluorimetric Sensing of Fe3+ Ion

This work aims to enhance the value of palm empty fruit bunches (EFBs), an abundant residue from the palm oil industry, as a precursor for the synthesis of luminescent carbon dots (CDs). The mechanism of fIuorimetric sensing using carbon dots for either enhancing or quenching photoluminescence properties when binding with analytes is useful for the detection of ultra-low amounts of analytes. This study revealed that EFB-derived CDs via hydrothermal synthesis exceptionally exhibited luminescence properties. In addition, surface modification for specific binding to a target molecule substantially augmented their PL characteristics. Among the different nitrogen and sulfur (N and S) doping agents used, including urea (U), sulfate (S), p-phenylenediamine (P), and sodium thiosulfate (TS), the results showed that PTS-CDs from the co-doping of p-phenylenediamine and sodium thiosulfate exhibited the highest PL properties. From this study on the fluorimetric sensing of several metal ions, PTS-CDs could effectively detect Fe3+ with the highest selectivity by fluorescence quenching to 79.1% at a limit of detection (LOD) of 0.1 µmol L−1. The PL quenching of PTS-CDs was linearly correlated with the wide range of Fe3+ concentration, ranging from 5 to 400 µmol L−1 (R2 = 0.9933).

Dual Fluorescence in Glutathione-Derived Carbon Dots Revisited

Dual-fluorescence carbon dots have great potential as nanosensors in life and materials sciences. Such carbon dots can be obtained via a solvothermal synthesis route with glutathione and formamide. In this work, we show that the dual-fluorescence emission of the synthesis products does not originate from a single carbon dot emitter, but rather from a mixture of physically separate compounds. We characterized the synthesis products with UV-vis, Raman, infrared, and fluorescence spectroscopy, and identified blue-emissive carbon dots and red-emissive porphyrin. We demonstrate an easy way to separate the two compounds without the need for time-consuming dialysis. Understanding the nature of the system, we can now steer the synthesis toward the desired product, which paves the way for a cheap and environmentally friendly synthesis route toward carbon dots, water-soluble porphyrin, and mixed systems.

Synthesis, Purification, and Characterization of Carbon Dots from Non-Activated and Activated Pyrolytic Carbon Black

In this work, carbon dots were created from activated and non-activated pyrolytic carbon black obtained from waste tires, which were then chemically oxidized with HNO3. The effects caused to the carbon dot properties were analyzed in detail through characterization techniques such as ion chromatography; UV–visible, Fourier-transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy; ζ potential; transmission electron microscopy (TEM); and spectrofluorometry. The presence of functional groups on the surface of all carbon dots was revealed by UV–visible, FTIR, XPS, and Raman spectra. The higher oxidation degrees of carbon dots from activated precursors compared to those from nonactivated precursors resulted in differences in photoluminescence (PL) properties such as bathochromic shift, lower intensity, and excitation-dependent behavior. The results demonstrate that the use of an activating agent in the recovery of pyrolytic carbon black resulted in carbon dots with different PL properties. In addition, a dialysis methodology is proposed to overcome purification obstacles, finding that 360 h were required to obtain pure carbon dots synthesized by a chemical oxidation method.

Improved production of titanate nanotubes by hydrothermal method for adsorption of organic dyes

Background

Increasing the yield of nanomaterials using the same reactor size and fixing most of the reactants and conditions will greatly improve the production process by saving time, energy and efforts. Titanate nanotubes are mainly prepared by hydrothermal process, in which TiO2 powder reacts with NaOH at certain conditions to form the desired nanotubes. It was reported that it is a must to use high concentrations of NaOH (10 N) to enable the tubular form formation, and the amount of NaOH from the stoichiometry point of view is much higher than that of TiO2; this means excess amounts of NaOH are not used and washed off. This work was designed to improve the production yield by making use of this excess amount of NaOH.

Results

More than 60 g of sodium titanate nanotubes was prepared using simple hydrothermal method. The prepared nanotubes were characterized by X-ray powder diffraction, high-resolution transmission electron microscopy, Fourier-transform infrared spectroscopy and BET surface area analysis. The adsorption capacity of these nanotubes was tested against three commonly used dyes: methyl orange, crystal violet and thymol blue. The samples showed great affinity toward crystal violet and lower activity toward methyl orange and thymol blue, where they achieved more than 90% removal efficiency under different experimental conditions.

Conclusions

Sodium titanate nanotubes were prepared in large amounts using modified hydrothermal method. The obtained nanotubes efficiently removed crystal violet from water. This improved synthesis of titanate nanotubes will reduce the total cost of nanomaterials production, and subsequently the treatment process, since titanate nanotubes are used in adsorption and photocatalysis processes.

Sulfur-doped carbon dots synthesis under microwave irradiation as turn-off fluorescent sensor for Cr(III)

This study synthesized a facile and high sensitive fluorescent probe based on sulfur-doped carbon dots (S-CDs) using a one-step microwave irradiation method. The probe exhibited a strong blue emission and a high quantum yield (QY) of 36.40%. In the detection, the presence of trivalent chromium (Cr(III)) strongly quenched the PL intensity of S-CDs by the inner filter effect (IFE) quenching mechanism of Cr(III) on the S-CDs. The S-CDs exhibited good sensitivity to turn-off Cr(III) detection with a linear range concentration of 0–45 μM and a detection limit of 0.17 μM. Furthermore, the proposed method has been successfully applied for Cr(III) detection in natural water samples with the 93.68–106.20% recoveries.

Carbon Dots: Classification, Properties, Synthesis, Characterization, and Applications in Health Care-An Updated Review (2018-2021)

Carbon dots (CDs) are usually smaller than 10 nm in size, and are meticulously formulated and recently introduced nanomaterials, among the other types of carbon-based nanomaterials. They have gained significant attention and an incredible interest in the field of nanotechnology and biomedical science, which is merely due to their considerable and exclusive attributes; including their enhanced electron transferability, photobleaching and photo-blinking effects, high photoluminescent quantum yield, fluorescence property, resistance to photo-decomposition, increased electrocatalytic activity, good aqueous solubility, excellent biocompatibility, long-term chemical stability, cost-effectiveness, negligible toxicity, and acquaintance of large effective surface area-to-volume ratio. CDs can be readily functionalized owing to the abundant functional groups on their surfaces, and they also exhibit remarkable sensing features such as specific, selective, and multiplex detectability. In addition, the physico-chemical characteristics of CDs can be easily tunable based on their intended usage or application. In this comprehensive review article, we mainly discuss the classification of CDs, their ideal properties, their general synthesis approaches, and primary characterization techniques. More importantly, we update the readers about the recent trends of CDs in health care applications (viz., their substantial and prominent role in the area of electrochemical and optical biosensing, bioimaging, drug/gene delivery, as well as in photodynamic/photothermal therapy).

pH sensing and bioimaging using green synthesized carbon dots from black fungus

Biomass is regarded as an excellent candidate for the preparation of carbon nanomaterials. A pH sensor was established based on carbon dots synthesized from black fungus, and possesses good fluorescence response and reversibility for pH detection. Meanwhile, the CDs can also be applied to intra-cellular bioimaging, showing potential for bioimaging.

Carbon dots derived from black fungus were prepared and applied as a pH sensor for real water samples.

Combination therapy of biogenic C-dots and lysozyme for enhanced antibacterial and antibiofilm activity

Nearly 80% of human chronic infections are caused due to bacterial biofilm formation. The increased resistance against the conventional antimicrobial agents makes it difficult to treat the biofilm-related infections. The antibiotics resistance developed by planktonic cells has also become a major threat for human. Therefore, we have attempted here to develop an effective alternative strategy to overcome the issues of antibiotics resistance of bacteria. Upon synthesis, biogenic C-dots were combined with lysozymes which were further encapsulated into chitosan nanocarrier to form C-dots carrier (CDC). The as-synthesized C-dots were found irregular shaped and the average size of C-dots and CDC were 8 ± 2 nm and 450 ± 50 nm, respectively. To ensure secure and targeted delivery of C-dots and lysozyme we have employed chitosan, a biodegradable and natural biopolymer, as a delivery system. The study of time-dependent bacterial growth and flow cytometry analysis demonstrated that CDC can exhibit a synergistic bactericidal activity against the antibiotics resistant recombinant E. coli cells. Further, we have shown that the CDC could be a potent agent for both prevention of biofilm formation and eradication of preformed biofilm. In addition, we have observed that our drug delivery system is hemocompatible in nature making it suitable for in vivo applications. Therefore, we believe that the combination therapy of C-dots and lysozyme may be used as an excellent antibacterial and antibiofilm strategy.

N, S doped carbon quantum dots inside mesoporous silica for effective adsorption of methylene blue dye

This study aimed to develop non-metal elements for doping carbon quantum dots (CQDs) with nitrogen and sulfur (N, S-CQDs), which loaded inside hexagonal mesoporous silica (HMS) in order to effectively remove methylene blue dye (MB) from an aqueous solution. The histidine and cysteine amino acids were used as the source for synthesis N, S-CQDs through the hydrothermal method. Morphology and structure of the N, S-CQDs, and adsorbent (N, S-CQDs/HMS) were characterized by using different microscopic and spectroscopic techniques. The adsorption parameters such as adsorbent dosage (0.25–1 g/L), pH (2–10), contact time (15–75 min), and initial MB dye concentration (20–300 mg/L) were investigated. The maximum adsorption capacity and removal efficiency of MB were determined at 370.4 mg/g and 97%, respectively, under optimum conditions at 303 K. The adsorption isotherm studies were fitted with the Freundlich isotherm equation, and the dye removal kinetics of the adsorbent followed the pseudo-second-order model. Thermodynamic studies showed that the adsorption process had exothermic and spontaneous behavior. The removal of MB next to the Rhodamine B and Reactive Black 5 dyes indicated that the N, S-CQDs/HMS had excellent selective behavior for MB absorption. This prepared adsorbent could be well recycled with suitable activity after four repeated adsorption–desorption cycles. Results revealed that the porous characters, surface area, charge properties, reduction in the bandgap, and quantum yield of the N, S-CQDs/HMS were essential factors that affected dye adsorption.

Carbon Nanoparticles as Sources for a Cost-Effective Water Purification Method: A Comprehensive Review

As the global population grows, the demand for cost-effective and eco-friendly water purification methods is increasing, which presently is at its peak due to the increase of impurities in water and the increasing awareness of waterborne disease. Carbon-based materials, which includes activated carbon, carbon nanotubes (CNTs), graphene, graphene oxide (GO), reduced graphene oxide (rGO), fullerene, and carbon dots, are observed as potential candidates for water treatment. In the present review, developments related to water purification methods using carbon nanomaterials over the last decade are critically summarized, with an emphasis on their thermophysical properties. The fabrication techniques for activated carbon, CNTs, graphene, and graphene oxide are presented, with an emphasis on the properties of carbon materials that allow their usage for water purification. Then, an extensive review of 71 patents dedicated to water purification using carbon materials such as activated carbon and cotton fibers is performed. Subsequently, the more important research studies on water purification using carbon nanomaterials are discussed, showing that CNTs, GO, and rGO are widely used in water treatment processes. The present review critically discusses the recent developments and provides important information on water purification using carbon materials.

Characterization of Chemically Activated Pyrolytic Carbon Black Derived from Waste Tires as a Candidate for Nanomaterial Precursor

Pyrolysis is a feasible solution for environmental problems related to the inadequate disposal of waste tires, as it leads to the recovery of pyrolytic products such as carbon black, liquid fuels and gases. The characteristics of pyrolytic carbon black can be enhanced through chemical activation in order to produce the required properties for its application. In the search to make the waste tire pyrolysis process profitable, new applications of the pyrolytic solid products have been explored, such as for the fabrication of energy-storage devices and precursor in the synthesis of nanomaterials. In this study, waste tires powder was chemically activated using acid (H2SO4) and/or alkali (KOH) to recover pyrolytic carbon black with different characteristics. H2SO4 removed surface impurities more thoroughly, improving the carbon black's surface area, while KOH increased its oxygen content, which improved the carbon black's stability in water suspension. Pyrolytic carbon black was fully characterized by elemental analysis, inductively coupled plasma-optical emission spectrometry (ICP-OES), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), N2 adsorption/desorption, scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), dynamic light scattering (DLS), and ζ potential measurement. In addition, the pyrolytic carbon black was used to explore its feasibility as a precursor for the synthesis of carbon dots; synthesized carbon dots were analyzed preliminarily by SEM and with a fluorescence microplate reader, revealing differences in their morphology and fluorescence intensity. The results presented in this study demonstrate the effect of the activating agent on pyrolytic carbon black from waste tires and provide evidence of the feasibility of using waste tires for the synthesis of nanomaterials such as carbon dots.

Abdullah A, Ozoemena KI, Elzatahry A. Unveiling Fabrication and Environmental Remediation of MXene-Based Nanoarchitectures in Toxic Metals Removal from Wastewater: Strategy and Mechanism

Efficient approaches for toxic metal removal from wastewater have had transformative impacts to mitigating freshwater scarcity. Adsorption is among the most promising purification techniques due to its simplicity, low cost, and high removal efficiency at ambient conditions. MXene-based nanoarchitectures emerged as promising adsorbents in a plethora of toxic metal removal applications. This was due to the unique hydrophilicity, high surface area, activated metallic hydroxide sites, electron-richness, and massive adsorption capacity of MXene. Given the continual progress in the rational design of MXene nanostructures for water treatment, timely updates on this field are required that deeply emphasize toxic metal removal, including fabrication routes and characterization strategies of the merits, advantages, and limitations of MXenes for the adsorption of toxic metals (i.e., Pb, Cu, Zn, and Cr). This is in addition to the fundamentals and the adsorption mechanism tailored by the shape and composition of MXene based on some representative paradigms. Finally, the limitations of MXenes and their potential future research perspectives for wastewater treatment are also discussed. This review may trigger scientists to develop novel MXene-based nanoarchitectures with well-defined shapes, compositions, and physiochemical merits for efficient, practical removal of toxic metals from wastewater.