Application of in-situ casted ZnO-starch nanocomposite for packaging of strawberries (Fragaria x ananassa).

Nanomaterials have recently been used in packaging as antibacterial coatings because of their desirable antibacterial and antifungal properties. In this study, we describe the synthesis of zinc oxide nanoparticles (ZnO NPs) and evaluate potato peel starch based ZnO NPs nanocomposite paper (ZnO-starch NC paper) on microbiological activity, storage, and properties of strawberries (Fragaria x ananassa). The ZnO-starch NC paper was used to package the strawberries and then stored at 4 °C and 27 °C for 10 days, respectively, controls were incubated without the ZnO-starch NC paper. The ZnO NPs were synthesized and characterized, the formation of sizes ranging from 35 to 40 nm were confirmed by SEM and XRD. The SEM showed that the ZnO NPs were successfully embedded in the starch forming the ZnO-starch NC. The antimicrobial and antifungal analysis showed that the ZnO-starch NC paper was effective against the fungi, B. cinerea, gram positive bacteria, B. subtilis and S. aureus but not against the gram negative bacteria, E. coli and P. aeruginosa. Total phenolic compounds and Vitamin C content of both the ZnO-starch NC packaged and controls were found to be in the normal range of recommended quality parameters of strawberries as there was no change in intrinsic factors of the fruits during incubation. Application of the ZnO-starch NC in packaged strawberries resulted in the reduction of weight loss and microbial growth compared to the controls. The overall weight loss showed that the loss of moisture and nutrients was not statistically significant (p > 0.05). We conclude that the ZnO-starch NC packaging is a promising safe alternative to extend storage period and increase the shelf-life of strawberries.

Processing-properties-performance triad relationship in a Washingtonia robusta mesoporous carbon materials-based supercapacitor device.

Two-electrode electrochemical tests provide a close performance approximation to that of an actual supercapacitor device. This study presents mesoporous carbon materials successfully derived from Washingtonia robusta bark (Mexican fan palm) and their electrical performance in a 2-electrode supercapacitor device. The triad relationship among carbon materials "processing, properties, and performance" was comprehensively investigated. X-ray diffraction reveal that amorphousness increases with activating KOH ratio and decreases with both activation time and temperature. Raman spectroscopy shows an increase in structural defects and degree of graphitization with an increase in KOH ratio, temperature and time while transmission electron microscopy shows conversion of aggregated particles to materials with interconnected porosity and subsequent destruction of porosity with an increase in KOH ratio. A nitrogen-sorption study reveals varying trends between BET, micro and mesopore surface areas, however, pore size and volume and hysteresis loop size decreases with KOH ratio and temperature. Electrochemical studies on the other hand reveal that both the specific capacitance and charge-discharge time increase with KOH ratio, temperature and time while both charge transfer and Warburg resistances decrease and the phase angles increases towards the ideal -90° with an increase in KOH ratio, temperature and time. The device fabricated with the HHPB sample prepared at 700 °C, KOH ratio 3 for 60 min attained a specific capacitance of 179.3 and 169 F g-1 at a scan rate of 5 mV s-1 and current density of 0.5 A g-1, respectively, good cycling stability with 95% capacitance retention and 100% coulombic efficiency when cycled 5000 times at a current density of 2 A g-1. HHPB electrodes reveal perfect EDLC behavior with an energy density of 20 W h kg-1 and power density of 2000 W kg-1 when used in a symmetric coin supercapacitor cell with 6 M KOH solution. These findings show the potential of fan palm bark as electrode materials with good stability and high-rate capability for supercapacitor application.

Reduction of hazardous reactive oxygen species (ROS) production of ZnO through Mn inclusion for possible UV-radiation shielding application.

Mnx - ZnO(1-x) nanopowders were successfully synthesised through a simple sol-gel method. The samples were annealed at 300 °C to enhance their crystallinity. The lattice structure, morphology and optical properties of the prepared powdered samples were extensively studied using different characterization techniques, confirming the formation of Mnx - ZnO(1-x). The inclusion of Mn did not cause any change to the wurtzite structure of ZnO; however slight peak shifting and increase in lattice parameters were indicated. The normal absorption spectra pointed to a cut-off edge extending beyond the UV region and a Burstein- Moss type band gap broadening induced by the Mn doping. ZnO showed excellent photodegradation activity against methylene blue (MB) upon UV irradiation. Intensifying the dopant concentration resulted in further diminution of photoactivity against MB. This reduction of photocatalytic activity of ZnO upon doping can be drawn to be due to the presence of Mn in the ZnO lattice, which acted as recombination sites for the photogenerated charge carriers. The results demonstrated that doping ZnO with Mn can be used to suppress the oxidative stress induced by reduced oxygen species (ROS) through generation of recombination centres. The suppression of toxic ROS generation implies possible application in fabrics and ointments for UV shielding applications.

Extraction of nanocellulose and in-situ casting of ZnO/cellulose nanocomposite with enhanced photocatalytic and antibacterial activity.

Polymer hosted metallic nanostructures with diverse applications have become a prominent area of materials science, engineering and technology. In this study nanocellulose (NC) was synthesized from oil palm empty fruit bunches biomass via alkaline treatment and acid hydrolysis and characterized. The obtained NC was used as a host polymer for the synthesis of zinc oxide (ZnO) nanostructures through in-situ solution casting method. Alkaline treatment and acid hydrolysis increased the percentage crystalline index from 35.7% to 43.3% and 53.3% respectively. X-ray diffraction studies pointed to cellulose I, with a monoclinic structure. Zinc oxide/cellulose nanocomposite displayed more photocatalytic activity than pure ZnO nanostructures upon degradation of methylene blue, and also improved antibacterial activity against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli.