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The required treatment and monitoring of contaminants in wastewater reinforces the development of low-cost adsorbents/chemosensors, introducing advantages relative to the detection/removal of toxic metals and dyes. Herein, it is reported a two-step process of fabrication of fluorescent carbon dots via the hydrothermal treatment of amino acids for the following encapsulation in electrospun fibers. The prominent anionic behavior of electrospun fibers of Eudragit L100 was explored for adsorption of cationic dyes (methylene blue and crystal violet)—with the prevailing electrostatic interaction of parts being favored by the formation of monolayers on the surface of adsorbents. On the other hand, the controlled release of carbon dots (CDs) from fibers to the reactor can be explored for a second application: the nitrogen ligands from released glycine-based carbon dots can be explored to indicate the presence of metal ions in aqueous solution. Our experiment resulted in a quenching in the fluorescence of the CDs in order of 90% in the emission of particles in the response of the presence of Fe3+ ions, characterizing a promising perspective for this experimental system.

In this study, samples of pristine and chemically modified coconut shells are used as adsorbents for the removal of crystal violet from an aqueous solution. The modification based on NaOH treatment of coconut shell fibers was evaluated by scanning electron microscopy and Fourier transform infrared spectroscopy. The dye uptake efficiency was evaluated by determining the variation in dye concentration, pH, adsorbent mass, and reaction time. The equilibrium condition of the overall process was analyzed by standard methods (Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherms), while kinetics were evaluated using the pseudo-first-order/pseudo-second-order, Elovich, and intra-particle diffusion models.

The health benefits and sensing applications of curcumin-based systems depend on their prevailing photophysical and chemical properties at a specific environment—the characteristic low solubility of curcumin in water hinders high-dosage based applications. To circumvent this drawback, curcumin has been incorporated in hydrophobic environments in nanoscale. Herein, electrospun fibers of Eudragit L100 were loaded with curcumin and applied in fluorescence and antibacterial assays to evaluate prevailing physical and chemical properties in solid-state. The characteristic high loading degree of curcumin (250 mg/mL in Eudragit L100 solution) preserves not only the photophysical properties of molecules (such as the intrinsic fluorescence) but also the antibacterial activity of released molecules from electrospun fibers, characterizing an important strategy for improvement in the applicability potential of natural materials.

The green synthesis of silver nanoparticles represents an important strategy for production of alternative antibacterial agents. Herein, the reduction of silver nanoparticles is provided by the action of leaf extract of Ziziphus joazeiro. The as-synthesized material presented pH-dependent behavior that affects the kinetics of nanoparticles nucleation and the following aggregation. Alkaline and acidic environment favors the increasing polydispersity of nanoparticles providing the production of different distribution of particle size. At neutral condition (pH 7), particles with lower size and reduced aggregation degree are obtained and present antibacterial activity against S. aureus and E. coli. The number of viable cells for both systems (from initial culture containing 104 colonies) reached negligible counting after 5 h of interaction with silver nanoparticles prepared at neutral pH.

The development of environmentally friendly prototypes for use as antibacterial agents and as alternatives to antibiotics is a necessary step toward the control of infections. With this in mind, the production of hybrid composites based on natural and synthetic materials has been successfully explored. Herein, the chemical polymerization of polyaniline on natural fibers of Calotropis procera was used to explore the combined available surface area of fibers with the intrinsic properties of the conductive layer of PANI. What resulted was a coating of conducting polymer on natural fibers with strong antibacterial activity against Staphylococcus aureus and Escherichia coli. The characteristic time for the complete elimination of colonies (kill time) observed in assays was in the region of 3–4 h of treatment, with an inhibition halo of 20 mm (against E. coli) and 24 mm (against S. aureus). In addition to the antibacterial activity against S. aureus and E. coli, the modified fibers exhibited antibiofilm activity against S. aureus, which was evidenced in the reduction in the degree of bacterial adhesion to the surface applied in treatment (with a 39.96% biofilm inhibition). The proposed method represents a simple, low-cost, and one-step method for the modification of natural fibers with relevant applications in antibacterial agents.

Polymer electrospun fibers are potential candidates for use as ionic dye adsorbents, due to its low cost and massive production provided by a simple nanofabrication method. The optimization in the processing variables for development of more efficient adsorbents revealed a strong dependence between the fiber diameter and the adsorption capacity of fibers, which was measured as a function of dye concentration, pH, adsorbent amount and contact time. The available active sites on electrospun fibers favor the efficient dye removal and easy desorption, allowing the successive reuse of electrospun fibers, preserving typical adsorption capacity of 135.37 mg·g-1 in association with fast desorption at acidic condition, allowing successive reuses of adsorbents.

The performance of metal oxide-based devices for humidity impedimetric sensors depends on different conduction mechanisms during water molecules adsorption. As consequence, new strategies for development of hierarchical and doped structures of mixed metal oxides play a critical role in the production of more efficient humidity sensors. It is reported an alternative method for synthesis of hexagonal ZnO nanocrystals on TiO2-decorated electrospun fibers, allowing the production of ordered arrays of hierarchical TiO2/ZnO nanostructures. Polymeric matrix supporting fibers were removed after annealing (500 °C), providing nanostructures with promising application as low-cost humidity sensors. The structure of resulting materials was explored in addition to the influence of relative humidity (RH) (measured in the range 400 Hz–40 MHz) on complex impedance spectra.

The development of highly conductive, flexible, mechanical reinforced and chemically modified cotton yarns for electrodes of supercapacitors represents an important advance in the energy storage devices applied in wearable electronics. The production of carbon-based conductive layers as supports for chemical polymerization of active polymeric materials (such as polypyrrole) is an important strategy that associates the high electrical double-layer capacitance of the carbon derivatives (carbon nanotubes and graphene nanoplatelets) and the pseudocapacitance of the polypyrrole in truly flexible devices with improved electrochemical response—high capacitance. These properties are affected by relative concentration of graphene nanoplatelets in carbon complexes due to the variation in overall conductivity of electrodes (in consequence of low aggregation degree and available surface area) and the electrochemical properties of the resulting devices that reaches capacitance in order of 45.5 F g−1 with a capacitive retention of 70% after 2000 cycles of use. These promising results open possibilities for new systems in wearable electronics.

The development of nanostructures based on interaction of organic matrix and metal oxide particles (such as polypyrrole/zinc oxide composites) introduces interesting advantages due to synergistic/complementary photocatalytic activity of resulting material. Particularly, the available high surface area of resulting composite contributes with minimal aggregation of metal oxide nanoparticles and reduces the electron/hole pair recombination rate (if applied as a photocatalyst). Results indicate that superior performance is detected for composite of polypyrrole/zinc oxide applied in the photodegradation of rhodamine B and rhodamine 6G in comparison with degradation established by colloidal photocatalyst (surfactant/zinc oxide/dye). Progressive cleavage of organic dye molecule takes place in substitution to typical N-deethylation process.

Composites of metal oxide nanoparticles incorporated into poly(vinyl pyrrolidone) electrospun fibers can be considered potential and low cost bactericidal agents. Homogeneous distribution of nanoparticles in the core of fibers and minimal aggregation induced by strong interaction with polymeric template are factors that contribute with diffusion of metal oxide nanoparticles from bulk to the fiber surface and subsequent release of nanoparticles to bacterial culture. Hybrid electrospun fibers were successfully applied against bacteria as a result of reasonable degree of interaction between zinc oxide and fibers as detected from FTIR analysis, DSC curves and SEM images.

Nanocomposites of polypyrrole and titanium dioxide (TiO2) are potential candidates for applications involving photocatalytic devices and humidity/gas sensors, if considering that interaction of conducting polymer/titanium dioxide promotes the surface modification of semiconductor and subsequent reduction in the bandgap. We have analyzed the influence of different synthesis routes on the physical properties of nanocomposites (with special attention to the nakedness/coverage level of TiO2 nanoparticles) and the results indicate that the doping level induced by silver nitrate and strong interaction with titanium dioxide introduce key roles in the optimization of nanocomposite applied as a photocatalyst.