Characterization of pyomelanin secreted by Shewanella sp. and their application in metal recovery

Melanin is a biopolymer with versatile structural and functional properties and diverse applications in recovering toxic chemicals from water and wastewater, biomedical imaging, and as theragnostic agent. We report the structural characterization and biosynthetic pathway of an extracellular pyomelanin secreted by a sponge-associated bacterium, Shewanella sp. (Shewanella-melanin), and their potential application in metal recovery from liquid. Pyomelanin particles of > 50 µm size were found in the culture medium within 48 h of growth, which were formed through the self-polymerization of benzoquinone molecule produced through homogentisic acid pathway. The aspC and hppD genes involved in the biosynthetic pathway of pyomelanin were detected in the whole genome sequence of Shewanella sp. The FT-IR spectra of Shewanella-melanin, at ~ 3300-3420 cm^-1 corresponding to the stretching vibration of -NH and -OH, was in good agreement with that of Sepia melanin, while its elemental composition (C/N/H/S of 29.2:8.23:6.41:1.58) was unique. Shewanella-melanin showed ~ 300 and ~ 950 times increased chelation of manganese and iron from a liquid medium supplemented with 2 mM of MnSO₄ and FeSO₄, respectively, compared to a control. The FT-IR spectrum showed the binding of metal ions to the carboxylic acid, hydroxyl, and amine groups of Shewanella-melanin. The Shewanella-melanin, with its excellent metal biosorption, could be a potential candidate for removing toxic compounds from water, in turn contributing to the fulfillment of sustainable development goal (SDG) 6.

Stimuli-Responsive Electrospun Piezoelectric Mats of Ethylene-co-vinyl Acetate-Millable Polyurethane-Nanohydroxyapatite Composites

Piezoelectric materials have gained interest among materials scientists as body motion sensors and energy harvesters on account of their fast responsiveness and substantial output signals. In this work, piezoelectric polymer mats have been fabricated from ethylene-co-vinyl acetate-millable polyurethane/nanohydroxyapatite (EVA-MPU/nHA) composite systems by employing the electrospinning technique. The ferro-piezoelectric features of the samples were confirmed from the butterfly loops of electrostatic force microscopy (EFM) amplitude signals as well as through the hysteresis curves of the EFM phase recorded with the assistance of dynamic-contact EFM. Piezoelectric responses of the samples to random finger tapping were evaluated after fabricating a simple device prototype connected to an oscilloscope. The efficacy of the mats to generate a voltage in response to activities such as mechanical bending, movement of throat muscles while drinking, movement of elbow joints, air blowing, and so forth has also been investigated. The results suggest the promising possibility of fabricating user-friendly piezoelectric mats out of the EVA-MPU/nHA system for physiological motion-sensing applications.

Electrospun Poly(vinylidene fluoride-trifluoroethylene)-Based Polymer Nanocomposite Fibers for Piezoelectric Nanogenerators

The present work deals with the preparation, characterization, and application of self-poled nanofibers using piezoelectric polymer poly(vinylidene fluoride-trifluoroethylene), zinc oxide, and exfoliated graphene oxide by electrospinning process. The characterization of nanofiber is carried by different techniques such as field emission scanning electron microscopy, Fourier transform Infrared spectroscopy, X-ray diffraction techniques, and dynamic contact mode electrostatic force microscopy. The nanofiber based piezoelectric nanoenergy generator devices are fabricated for analyzing the energy generating efficiency. Piezoelectric hybrid nanofibers are exhibiting better energy generating efficiency and identified as potential material for energy harvesting applications.

Water-Chloroform Interface Assisted Microstructure Tuning of Polypyrrole-Silver Sheets

The liquid-liquid interface of two immiscible solvents remarkably controls the morphology of polymeric nanostructures as compared to the polymerization in single solvent systems. The polymerization of pyrrole in the water-chloroform medium using silver nitrate (AgNO₃) as oxidant yields polypyrrole/silver (PPy/Ag) sheets. The water-chloroform interface acts as a template for the growth of PPy/Ag hybrids into sheets by preventing the secondary growth of silver associated pyrrole oligomers in a three-dimensional (3-D) manner. On the contrary, the 3-D growth of pyrrole oligomers into spherical shapes at the water-chloroform interface is observed when ammonium persulfate (APS) is used as the oxidant. Transmission electron microscopic and scanning electron microscopic images reveal the sheetlike morphology of PPy/Ag with a relatively uniform distribution of Ag NPs (∼100 nm) on PPy sheets. The ratio of aqueous-organic bisolvent and the concentration/type of oxidant have a distinct effect on morphology, crystallinity, and electrical properties of PPy/Ag sheets. The dispersed PPy/Ag sheets are stable in moderately polar solvents up to 2 weeks. The electrochemical behavior of PPy/Ag sheets is confirmed by H₂O₂ sensing capability through cyclic voltammetry experiments. The antibacterial activity toward E. coli and S. aureus is quantitatively assessed using the minimum bactericidal concentration (MBC) determination.

The real time optical transmittance of swollen heterogeneous natural rubber/poly (ethylene-co-vinyl acetate) blends

This work demonstrates a novel simple method to study the accurate real time optical transparency of a crosslinked polymer blend during its swelling in good solvent. Heterogeneous natural rubber (NR) and poly (ethylene-co-vinyl acetate) (EVA) blends were used for this experiment. Aromatic solvents such as benzene, toluene and xylene were used as the probe molecules. Optical transparency of the samples increases with increase in EVA content in the blends during swelling. The penetrant solvent molecular size also affects the optical transparency of the blends. This new method can effectively measure the optical transparency of polymer gels during their swelling. Also, these blends can be a promising material for optical switching.

Fabrication of superhydrophobic polycaprolactone/beeswax electrospun membranes for high-efficiency oil/water separation

A novel superhydrophobic, superoleophilic electrospun nanofibrous membrane of beeswax and polycaprolactone has been fabricated.

Thermo-responsive poly(ethylene-co-vinyl alcohol) based asymmetric membranes

This paper reports surface modification of poly(ethylene-co-vinyl alcohol) microporous membranes, by surface-initiated atom transfer radical polymerization of N-isopropylacrylamide and its subsequent applications in thermo responsive permeation.