Poly(ether amine) (PEA)-based fluorescent polymer carbon dots (FPCDs) have been synthesized via a simple Schiff base reaction between poly(ether amine) (PEA) and formaldehyde followed by its hydrothermal treatment. The resulting water-soluble FPCDs are 2 nm in size and show excitation-dependent emission properties. Blue-emissive FPCDs exhibit the maximum intensity of fluorescence at 440 nm under 360 nm excitation and show a high quantum yield of ∼18%. FPCDs are used for selective Fe3+ metal ion sensing in aqueous media through the fluorescence quenching of FPCDs with a limit of detection of ∼162 nM. Nontoxic FPCDs have been used for cancer cell imaging and also for intracellular Fe3+ metal ion sensing in cancer cells. FPCDs have been used for Fe3+ ion sensing in industrial effluents, and they serve as sensors even in the presence of other competing metal ions. To determine the real application potential of FPCDs as a sensor, FPCDs are used to establish the Fe3+ metal ion content in samples of spiked blood serum with remarkable specificity, sensitivity, and accuracy. Moreover, we proposed a possible sensing mechanism wherein Fe3+ metal ions interacted with the functional groups present on the surface of FPCDs, and fluorescence quenching occurred via a static quenching mechanism along with an inner filter effect (IFE).
Herein, we have fabricated cadmium-sulfide (CdS)-doped glucose-derived carbon nanoflakes (CNF) via a simple two-step methodology. The as-prepared CdS-doped CNF (CdS-CNF) shows selective photocatalytic activity toward the degradation of organic dye named Indigo Carmine (IC) from the tested nine model organic dyes importantly under the influence of sunlight. The viability of sunlight-promoted photodegradation was supported via comparative half-life (t 1/2) values, which is ∼14 min–1 for sunlight compared to ∼125 min–1 for artificial bulb light. The photodegradation of IC follows pseudo-first-order kinetics, and the rate associated with the sunlight-promoted photodegradation is ∼8 times faster compared to the reaction under artificial bulb light. Based on the trap experiments, the photocatalytic degradation mechanism showed the involvement of superoxide radicals. The photodegradation results are supported via a comparative proton nuclear magnetic resonance and Fourier transform infrared spectroscopic analysis. Additionally, CdS-CNF is used to degrade IC dye from industrially spiked wastewater samples to demonstrate its potential as a photocatalyst for real-life applications.
Cadmium sulfide (CdS)-decorated, cross-linked melamine–formaldehyde polymer-based nanocomposite (MFP-CdS) has been synthesized. MFP-CdS is utilized here as a photoactive material for the photodegradation of six model organic dyes and their mixture in an aqueous medium in the presence of sunlight. The half-life values from the kinetic study of multiple dyes strongly support the importance of sunlight on the fast degradation of all six dyes compared to bulb light and control (dark) conditions. A comparative 1H NMR analysis of the dyes and their degraded products has been performed to support the breakdown of the aromatic framework of organic dyes using MFP-CdS in sunlight. The mechanisms involved in the photodegradation of dyes have been investigated based on radical trapping studies that support the significant involvement of superoxide radicals along with holes. Moreover, the dye removal efficiency using MFP-CdS from real industrial wastewater samples is evaluated via the external spiking of organic dyes and their mixture in unknown industrial effluents where they showed similar photodegradation results. Based on the high recyclability of MFP-CdS, these are used for multiple cycles.
Cellulose nanocrystals (CNCs) as a bio-based adsorbent material have been synthesized at mild temperature reaction conditions using acid hydrolysis of microcrystalline cellulose (MCC) by sulfuric acid. CNCs by a simple acid treatment become enriched with negatively charged surface functionalities and shows good adsorption capacity. The CNCs have been characterized by X-ray photoelectron spectroscopy, Fourier transform Infrared, X-ray diffraction spectroscopy, and thermogravimetric analysis for their chemical composition, functionality, crystallinity, and stability, respectively. Sulfated CNCs have been used to selectively remove the toxic Janus Green (JG) dye tested out of many other dyes via adsorption and showed a Langmuir adsorption capacity of ∼77 mg g. −1 The effects of pH, temperature, concentration, and loading capacity have also been explored. The adsorption kinetics follows the pseudo-second-order pathway and thermodynamic analysis of the system indicates that the process is exothermic and spontaneous. Moreover, for the practical applicability of the proposed method, the adsorption of JG was also analyzed in four spiked industrial samples collected from nearby textile industries, where they removed more than 80% of the dye from the complex industrial water system.
A two-step viable synthetic approach for quick and energy-efficient acid-based charring is described here to fabricate self-passivated fluorescent water-soluble CD (wsCD) from sustainable microcrystalline cellulose (MCC) materials. The aqueous solution of wsCD exhibits blue emission under UV-light illumination and shows a fluorescence quantum yield of ∼6%. The wsCD are used here for the selective sensing of ofloxacin (OFLX) from among the four tested antibiotics of the fluoroquinolone class, namely, ciprofloxacin (CPLX), ofloxacin (OFLX), levofloxacin (LVLX), and moxifloxacin (MXLX) based on the simpler fluorescence quenching experiment with a detection limit of ∼0.025 ppm. The plausible mechanism for the selective sensing of OFLX has been proposed based on a detailed analysis of absorbance and time-resolved photoluminescence spectroscopy which indicates the involvement of the inner-filter effect (IFE). Antimicrobial studies of wsCD were conducted on two bacterial strains (Escherichia coli and Staphylococcus aureus) and two fungal strains (Aspergillus niger and Penicillium chrysogenum), where wsCD did not show any toxic effects up to the concentration of 1 mg/mL, hence supporting their biocompatible behavior. Further, an antibiosis study involving the combination of the antibiotic and antifungal agents with wsCD against the growth of the same bacterial and fungal strains was conducted, where wsCD showed mild antifungal activity.
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