Electro-spinning of cellulose acetate nanofibers/Fe/carbon dot as photoluminescence sensor for mercury (II) and lead (II) ions

Synthesis and Properties of Nitrogen-Doped Carbon Quantum Dots Using Lactic Acid as Carbon Source

Nitrogen-doped carbon quantum dots (N-CQDs) were synthesized in a one-step hydrothermal technique utilizing L-lactic acid as that of the source of carbon and ethylenediamine as that of the source of nitrogen, and were characterized using dynamic light scattering, X-ray photoelectron spectroscopy ultraviolet-visible spectrum, Fourier-transformed infrared spectrum, high-resolution transmission electron microscopy, and fluorescence spectrum. The generated N-CQDs have a spherical structure and overall diameters ranging from 1-4 nm, and their surface comprises specific functional groups such as amino, carboxyl, and hydroxyl, resulting in greater water solubility and fluorescence. The quantum yield of N-CQDs (being 46%) is significantly higher than that of the CQDs synthesized from other biomass in literatures. Its fluorescence intensity is dependent on the excitation wavelength, and N-CQDs release blue light at 365 nm under ultraviolet light. The pH values may impact the protonation of N-CQDs surface functional groups and lead to significant fluorescence quenching of N-CQDs. Therefore, the fluorescence intensity of N-CQDs is the highest at pH 7.0, but it decreases with pH as pH values being either more than or less than pH 7.0. The N-CQDs exhibit high sensitivity to Fe³⁺ ions, for Fe³⁺ ions would decrease the fluorescence intensity of N-CQDs by 99.6%, and the influence of Fe³⁺ ions on N-CQDs fluorescence quenching is slightly affected by other metal ions. Moreover, the fluorescence quenching efficiency of Fe³⁺ ions displays an obvious linear relationship to Fe³⁺ concentrations in a wide range of concentrations (up to 200 µM) and with a detection limit of 1.89 µM. Therefore, the generated N-CQDs may be utilized as a robust fluorescence sensor for detecting pH and Fe³⁺ ions.

Recent progress in cellulose-based electrospun nanofibers as multifunctional materials

Cellulose, the most abundant natural polymer, has good biocompatibility, biodegradability, and non-toxicity, which make it and its derivatives promising candidates for the fabrication of multifunctional materials, while maintaining sustainability and environmental friendliness. The combination of electrospinning technology and cellulose (and its derivatives) provides a feasible approach to produce nanostructured porous materials with promising functionalities, flexibility, renewability and biodegradability. At the same time, it enables value-added applications of cellulose and its derivatives that are derived from nature or even biomass waste. This review summarizes and discusses the latest progress in cellulose-based electrospun nanofibers, including their construction methods and conditions, various available raw materials, and applications in multiple areas (water treatment, biomaterials, sensors, electro-conductive materials, active packaging, and so on), which are followed by the conclusion and prospects associated with future opportunities and challenges in this active research area.

Green sonochemistry assisted synthesis of hollow magnetic and photoluminescent MgFe2O4-carbon dot nanocomposite as a sensor for toxic Ni(ii), Cd(ii) and Hg(ii) ions and bacteria

The purpose of this study was synthesis of photoluminescent nanoparticles for detection of toxic metal ions. Also, these controllable magnetic nanocomposites were used for detection of Pseudomonas aeruginosa bacteria. Carbon nano-templates were formed by calcination and sonication of lemon extract as a bio-compatible precursor. Then MgFe₂O₄ nanoparticles were incorporated on the carbon nano-templates. The composite was calcinated to decompose carbon and obtain hollow structures. Finally, photoluminescent carbon dots were deposited on the porous magnesium ferrite core. Because of the hollow structure, carbon dots can diffuse to the Mg-ferrite core so magnetic and photoluminescence properties are available simultaneously. Photoluminescence intensity decreases with increasing Ni(ii), Cd(ii), Hg(ii) metal ions and Pseudomonas aeruginosa. Results show an effective nanostructure for identification of toxic metal ions and also bacteria.

The purpose of this study is synthesis of magnetic and photoluminescence nanoparticles at the same time for finding of bacteria that could be fatal and its detection are crucial for some illness prohibition.

Development and Characterization of Cellulose/Iron Acetate Nanofibers for Bone Tissue Engineering Applications

In tissue engineering, design of biomaterial with a micro/nano structure is an essential step to mimic extracellular matrix (ECM) and to enhance biomineralization as well as cell biocompatibility. Composite polymeric nanofiber with iron particles/ions has an important role in biomineralization and collagen synthesis for bone tissue engineering. Herein, we report development of polymeric cellulose acetate (CA) nanofibers (17 wt.%) and traces of iron acetates salt (0.5 wt.%) within a polymeric solution to form electrospinning nanofibers mats with iron nanoparticles for bone tissue engineering applications. The resulting mats were characterized using field emission scanning electron microscopy (FESEM), transmission electron microscope (TEM), Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The resulted morphology indicated that the average diameter of CA decreased after addition of iron from (395 ± 30) to (266 ± 19) nm and had dense fiber distributions that match those of native ECM. Moreover, addition of iron acetate to CA solution resulted in mats that are thermally stable. The initial decomposition temperature was 300 °C of CA/Fe mat > 270 °C of pure CA. Furthermore, a superior apatite formation resulted in a biomineralization test after 3 days of immersion in stimulated environmental condition. In vitro cell culture experiments demonstrated that the CA/Fe mat was biocompatible to human fetal-osteoblast cells (hFOB) with the ability to support the cell attachment and proliferation. These findings suggest that doping traces of iron acetate has a promising role in composite mats designed for bone tissue engineering as simple and economically nanoscale materials. Furthermore, these biomaterials can be used in a potential future application such as drug delivery, cancer treatment, and antibacterial materials.

Modulating transparency and colour of cellulose nanocrystal composite films by varying polymer molecular weight

HYPOTHESIS

Cellulose nanocrystals (CNC) can produce photonic composite films that selectively reflect light based on their periodic cholesteric structure. The hypothesis of this research is that by incorporating water-soluble polymer, photonic properties of CNC composite film can be designed by manipulating the polymer molecular weight.

EXPERIMENTAL

Flexible free-standing composite films of five different poly (ethylene glycol) (PEG) molecular weights were prepared via air drying under a controlled environment, and characterised by reflectance UV-vis spectrometer, atomic force microscopy (AFM) and scanning electron microscopy (SEM). Films with each molecular weight were investigated over a concentration range.

FINDINGS

The colour and transmission haze of the composite films was modified by varying both the PEG molecular weight and concentration. Depending on the molecular weight, the films were able to reflect light from the UV region (242 nm) across the visible spectrum to the near-infrared region (832 nm). Different trends in variation of the reflected light based on the molecular weight was found with increasing PEG concentration and was explained by weak depletion interactions occurring between CNC and PEG, which was reduced with increasing PEG molecular weight.

Hydrogen Bond Association to Prepare Flame Retardant Polyvinyl Alcohol Film with High Performance

It has always been the goal of flame retardant research to improve the flame retardancy of a polymer efficiently without compromising comprehensive properties such as mechanical properties. For polyvinyl alcohol (PVA), inspired by the multiple hydrogen bonding in spider silk, we design a new type of compound containing phosphorus and nitrogen with multiple hydrogen-bonding reaction sites (N,N',N''-tris(2-aminoethyl)phosphoric triamide (TE)) as it is flame retardant. The dynamic cross-linking structure is constructed, and the hyperdispersion of flame retardancy is achieved by the hydrogen bond self-assembly between TE and PVA, thus the high-performance flame retardant PVA is obtained. With only a 10 wt % addition of TE, the PVA film with a thickness of 0.15 mm can reach the UL94 VTM-0 level, and its tensile strength, ductility, and initial decomposition temperature can be increased by 33, 15, and 12 °C, respectively. In addition, the hydrogen-bonding effect and flame retardant mechanism are characterized and studied. This work overcomes the shortcomings of traditional flame retarding approaches and provides an effective strategy for the preparation of flame retardant polymers with an excellent performance.

A novel polyaniline/NiO nanocomposite as a UV and visible-light photocatalyst for complete degradation of the model dyes and the real textile wastewater

The textile processing industry utilizes enormous amounts of water. After the dying process, the wastewater discharged to the environment contains carcinogens, non-biodegradable, toxic, and colored organic materials. This study aimed to develop a nanocomposite material with improved photocatalytic activity to degrade textile dyes and without a need for a post-separation process after the use. For this, nickel oxide nanoparticles (NiO NPs) were synthesized by a simple method in aqueous media. Then, NiO-doped polyaniline (PANI/NiO) with efficient absorption in the visible region (optical band gap of 2.08 eV) synthesized on a stainless steel substrate with electropolymerization of aniline in the aqueous media. The photocatalytic activity of PANI/NiO film was also investigated by the degradation of model dyes. Under UV and visible light irradiation, the PANI/NiO film degraded methylene blue and rhodamine B dyes entirely in 30 min. Moreover, the PANI/NiO film was also utilized to degrade real textile wastewater (RTW) without applying any pre-process; it was entirely decomposed by the nanocomposite film in only 45 min under UV light irradiation. The photocatalytic reaction rate of the pure PANI film is increased as 2.5 and 1.5 times with the addition of NiO NPs under UV and visible light irradiations for degradation RTW, respectively. The photocatalytic efficiency was attributed to reduced electron-hole pair recombination on the photocatalyst surface. Furthermore, the photocatalytic stability is discussed based on re-use experiments. The photocatalytic performance remains nearly unchanged, and the degradation of dyes is kept 94% after five cycles.

Porous BMTTPA-CS-GO nanocomposite for the efficient removal of heavy metal ions from aqueous solutions

In this study, a stable, cost-effective and environmentally friendly porous 2,5-bis(methylthio)terephthalaldehyde–chitosan–grafted graphene oxide (BMTTPA–CS–GO) nanocomposite was synthesized by covalently grafting BMTTPA–CS onto the surfaces of graphene oxide and used for removing heavy metal ions from polluted water. According to well-established Hg²⁺–thioether coordination chemistry, the newly designed covalently linked stable porous BMTTPA–CS–GO nanocomposite with thioether units on the pore walls greatly increases the adsorption capacity of Hg²⁺ and does not cause secondary pollution to the environment. The results of sorption experiments and inductively coupled plasma mass spectrometry measurements demonstrate that the maximum adsorption capacity of Hg²⁺ on BMTTPA–CS–GO at pH 7 is 306.8 mg g⁻¹, indicating that BMTTPA–CS–GO has excellent adsorption performance for Hg²⁺. The experimental results show that this stable, environmentally friendly, cost-effective and excellent adsorption performance of BMTTPA–CS–GO makes it a potential nanocomposite for removing Hg²⁺ and other heavy metal ions from polluted water, and even drinking water. This study suggests that covalently linked crucial groups on the surface of carbon-based materials are essential for improving the adsorption capacity of adsorbents for heavy metal ions.

Novel porous BMTTPA–CS–GO nanocomposites are prepared by covalently grafting BMTTPA–CS onto GO surfaces, and used for efficient removal of heavy metal ions from polluted water.

Rapid synthesis of a hybrid of rGO/AuNPs/MWCNTs for sensitive sensing of 4-aminophenol and acetaminophen simultaneously

In this work, a hybrid of multiwalled carbon nanotubes, nanogold, and reduced graphene (rGO/AuNPs/MWCNTs) was synthesized rapidly with an easy method, and then combined with chitosan (CS), which was fixed on a glassy carbon electrode (GCE) to construct a new kind of electrochemical sensor to simultaneously determine 4-aminophenol (4-AP) and acetaminophen (AC). When detecting 4-AP and AC simultaneously, the linear range is 0.12~12 μM for acetaminophen and 0.05~25 μM for 4-aminophenol; the detection limit is 42 nM for acetaminophen and 2.95 nM for 4-aminophenol. Compared with previously related reports, the proposed sensor has an excellent electrocatalytic performance for the redox of 4-AP and AC, which can effectively determine 4-AP and AC simultaneously in actual samples and has potential application prospect. Graphical abstract.

Facile synthesis of carboxymethyl cellulose sulfur quantum dots for live cell imaging and sensitive detection of Cr(VI) and ascorbic acid

Nowadays the synthesis of stable fluorescent sulfur quantum dots (SQDs) remains a big challenge. Herein, the utilization of carboxymethyl cellulose (CMC) to synthesis of SQDs is reported. Benefiting from the unique composition and structure of CMC macromolecule, the resulted CMC-SQDs simultaneously show high aqueous dispersibility and stability, tunable emission, stable fluorescence and low cytotoxicity, which make them promising for working as a fluorescent probe. Fluorescence detection experiments suggested that the CMC-SQDs could serve as a fluorescence on-off-on switch to sensitive and selective detection of Cr(VI) and ascorbic acid (AA) based on the inner filter effect (IFE). The limit of detection towards Cr(VI) and AA can reach 0.024 and 0.18 μM with linear range of 0.5-225 and 1-300 μM, respectively, which compares favorably to other reported fluorescent probes. In addition, the employment of fluorescent CMC-SQDs for practical detection of Cr(VI) and AA was also studied.

Fabrication of Poly Vinyl Acetate (PVAc) Nanofibers Using DMAC Solvent: Effect of Molecular Weight, Optimization by Taguchi DoE

This study experimentally investigated the effect of different molecular weights of Poly vinyl acetate (PVAc) on electrospinning ability of PVAc/DMAC sol-gels. The influences of polymer solution concentration and electrospinning process parameters (needle tip to collector distance, flow rate, and applied voltage) on the mean diameters of electrospun PVAc nanofibers were examined by design of the experiments based on the Taguchi method. Three levels were considered for each process factor as inputs for the Taguchi DoE technique. To characterize and optimize the mentioned parameters, Taguchi's L9 orthogonal design (four parameters, three levels) was used. The “smaller-the-better” approach was used to utilize the optimum production conditions based on the signal-to-noise (S/N) ratios. The results indicated that the polymer solution concentration was the most important parameter on the mean diameter of the nanofibers. The minimum nanofiber diameter at the optimum conditions was measured about 52 nm. In conclusion, the Taguchi DoE method was identified as an efficient technique to characterize and optimize the electrospinning process parameters to increase the robustness of nanofiber fabrication.

Improvement of the Solubility and Evaluation of the Physical Properties of an Inclusion Complex Formed by a New Ferulic Acid Derivative and γ-Cyclodextrin

Ferulic acid derivative 012 (FAD012) is a ferulic acid (FA) derivative. The current study prepared a solid dispersion of FAD012 and γ-cyclodextrin (γCD) and ground it using a three-dimensional ball mill (3DGM) to prepare an inclusion complex. This study also assessed the physicochemical properties such as solubility of that complex. A Job's plot indicated that FAD012 and γCD formed an inclusion complex at a molar ratio of 1:1. Phase solubility diagrams revealed that FAD012 produced a B_S diagram. According to PXRD, FAD012 produced a diffraction peak at 2θ = 7.0° and γCD produced a diffraction peak at 2θ = 9.1°. Those two peaks were not produced by the 3DGM, but new peaks (2θ = 7.3 and 16.5°) were evident. DSC patterns revealed an endothermic peak due to the melting of FAD012 at 190 °C, but no endothermic peaks were evident with the 3DGM. NIR spectra of the 3DGM indicated that the methyl group of FAD012 produced a higher peak and that the OH groups of γCD produced a higher peak. ¹H-¹H ROESY NMR spectra (D₂O) revealed cross peaks for protons of the methyl group of FAD012 and a proton (H-3) in the cavity of γCD, so FAD012 presumably interacts with the wide opening of the γCD torus. A solubility test (25 °C) indicated that solubility improved about 5-fold for the 3DGM in comparison to the solubility of FAD012 alone (about 140 μg/mL). Based on these findings, an FAD012/γCD complex was formed by cogrinding, and its solubility improved. These observations are expected to expand the usefulness of cogrinding of FAD012 with γCD using a 3D ball mill.

Fibrous strips decorated with cleavable aggregation-induced emission probes for visual detection of Hg2

The widespread contamination and high poisonousness have created significant concerns and thus demands for facile, rapid and selective monitoring of trace Hg²⁺. Inspired from the unique aggregation-induced emission (AIE) feature, in the current study, novel tetraphenylethylene (TPE) derivatives are prepared containing sulfonic groups for water solubility modulation and carboxyl dithioacetals for Hg²⁺ sensing. The TPE derivatives are grafted on electrospun fiber as test papers to initiate the AIE activities, while the Hg²⁺-specific cleavage of dithioacetal groups leads to the release of TPE derivatives and fluorescence turn-off. The decrease in the fluorescence intensities of fibrous mats could be fitted with Hg²⁺ levels for quantitative analysis, and the fibrous mats turn from green to bluish-green and then to blue in the presence of different Hg²⁺ levels. The limit of detection (LOD) reaches as low as 20 nM Hg²⁺, satisfying the threshold detection in drinking water, and the Hg²⁺ sensing indicates negligible interference from other metal ions and pH variations. The detected Hg²⁺ levels in lake water are consistent with the added amount with a recovery rate of over 98 %. It demonstrates a feasible strategy to integrate Hg²⁺-cleavable AIE probes on fibrous strips for real-time, highly specific and naked-eye detection of trace Hg²⁺.

Carbon and graphene quantum dots: a review on syntheses, characterization, biological and sensing applications for neurotransmitter determination

Neuro-transmitters have been considered to be essential biochemical molecules, which monitor physiological and behavioral function in the peripheral and central nervous systems. Thus, it is of high pharmaceutical and biological significance to analyze neuro-transmitters in the biological samples. So far, researchers have devised a lot of techniques for assaying these samples. It has been found that electro-chemical sensors possess features of robustness, selectivity, and sensitivity as well as real-time measurement. Graphene quantum dots (GQDs) and carbon QDs (CQDs) are considered some of the most promising carbon-based nanomaterials at the forefront of this research area. This is due to their characteristics including lower toxicity, higher solubility in various solvents, great electronic features, strong chemical inertness, high specific surface areas, plenty of edge sites for functionalization, and versatility, in addition to their ability to be modified via absorbent surface chemicals and the addition of modifiers or nano-materials. Hence in the present review, the synthesis methods of GQDs and CQDs has been summarized and their characterization methods also been analyzed. The applications of carbon-based QDs (GQDs and CQDs) in biological and sensing areas, such as biological imaging, drug/gene delivery, antibacterial and antioxidant activity, photoluminescence sensors, electrochemiluminescence sensors and electrochemical sensors, have also been discussed. This study then covers sensing features of key neurotransmitters, including dopamine, tyrosine, epinephrine, norepinephrine, serotonin and acetylcholine. Hence, issues and challenges of the GQDs and CQDs were analyzed for their further development.

Carbon and graphene quantum dots for biological and sensing applications of neurotransmitters.