Adsorption-photocatalytic degradation abilities of γ-irradiated chitosan-ZnO-AgNP composite for organic dye removal and antibacterial activity.

We synthesized a γ-irradiated chitosan-ZnO-AgNPs (ICZA) composite by using a simple hydrogels method. We evaluated its adsorption/photocatalytic degradation abilities for the removal of an organic dye and its antibacterial activity. The XRD, SEM, TEM, EDS, and FTIR techniques were used to characterize the obtained samples. Based on the adsorption and degradation of methylene blue (MB) in the dark and under UV light irradiation, the adsorption and the photocatalytic activity of the as-obtained samples were evaluated. The optimum conditions for synthesizing the composite were as follows: contact time of 210 min, a dosage of 2 g/L, MB concentration of 40 mg/L, and a solution pH of 8.0. The ICZA had a high adsorption capacity, which was suitable for removing MB from the aqueous solutions; it showed a maximum adsorption capacity (qm) of 92.59 mg/g. The fit of the adsorption isotherms with the Langmuir model was satisfactory. The photocatalytic degradation ability of the composite was also better than that of other catalysts in the presence of UV light, with an apparent rate constant (kapp) of 3.08 × 10-2. The synthesized ICZA also showed good antibacterial activity against Staphylococcus aureus, with a minimum inhibitory concentration (MIC) and a minimum bactericidal concentration (MBC) of 12.5 g/mL and 50 g/mL under light-incubation and dark-incubation conditions. Finally, we discussed the hypothesized mechanism of the adsorption/photocatalytic activity and antibacterial activity of the ICZA composite in this study.

Effect of Na and Al doping on ZnO nanoparticles for potential application in sunscreens.

This study investigated the environment-friendly production and characterization of zinc oxide nanoparticles (ZnO NPs) doped with sodium (Na) and aluminum (Al) metals to decrease the photocatalytic activity of ZnO for use in sunscreen. The metal-doped zinc oxide (ZnO) materials were prepared by the microwave method using extracts of Averrhoa carambola, also known as star fruit, as a reducing agent. The effects of metal-ion doping on the crystal structure, morphology, and optical characteristics of ZnO were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM), and ultraviolet-visible (UV-Vis) spectroscopy. The sun protection factor (SPF) of the sunscreen formulations containing undoped ZnO, Na-doped ZnO (Na/ZnO), and Al-doped ZnO (Al/ZnO) NPs were found to be 10.10, 25.10, and 43.08, respectively. Therefore, Na/ZnO and Al/ZnO showed increased SPF. Additionally, the prepared nanomaterials and sunscreens were effective against Gram-positive and Gram-negative bacteria and showed antioxidant activities. The methylene blue (MB) degradation was used to evaluate the photocatalytic activities of the undoped ZnO, Na/ZnO, and Al/ZnO NPs, which were found to be 66%, 46%, and 38%, respectively. Therefore, due to the structural defects of ZnO NPs, their photocatalytic activity was decreased with Na- and Al- doping. Additionally, Al/ZnO is an ideal candidate as an ingredient in sunscreens.

Microwave-assisted synthesis of Ag/ZnO nanoparticles using Averrhoa carambola fruit extract as the reducing agent and their application in cotton fabrics with antibacterial and UV-protection properties.

This is the first time Averrhoa carambola fruit extract has been used as a reducing agent to synthesize Ag/ZnO composites for coating cotton to develop antibacterial activity and UV protection under domestic microwave irradiation. The effects of the molar concentration of silver nitrate solutions, applied power, reaction duration, and pH on the yield of nanoparticles were determined. The treated fabrics were subjected to the investigation of surface morphology and chemical structure using SEM and EDX techniques, respectively. The antibacterial activity of the ZnO NPs and the Ag/ZnO nanocomposite coated on cotton fabric was evaluated against E. coli and S. aureus using the agar well diffusion method. The results revealed good antibacterial activity in the cotton fabric treated with the Ag-doped ZnO composite. The stability of the Ag/ZnO nanocomposite coated fabrics was determined by a wash durability test, the results of which demonstrated that this fabric could retain good antibacterial activity even after 20 wash cycles. The UV-blocking capacity of the treated fabrics was evaluated based on the ultraviolet protection factor (UPF) value determined in the range of 280-400 nm. The UPF value determined for the Ag/ZnO-coated fabric was 69.67 ± 1.53, which indicated an excellent ability to block UV radiation. Collectively, these results demonstrated the Ag/ZnO nanocomposite prepared in the present study as a promising material for preparing textiles with good antibacterial activity and UV protection.

Enhanced Resistance to Leaf Fall Disease Caused by Phytophthora palmivora in Rubber Tree Seedling by Sargassum polycystum Extract.

The brown seaweed (Sargassum polycystum C. Agardh-Sargassaceae) extract was examined for its bioelicitor properties in the rubber tree seedling (Hevea brasiliensis (Willd. ex A.Juss.) Müll.Arg. - Euphorbiaceae) and its application to reduce the leaf fall disease caused by Phytophthora palmivora (Edwin John) Butler, 1917 (Peronosporaceae). The major purpose of this study was to apply this seaweed extract (SWE) to improve the disease resistance in rubber tree seedling compared to a chemical fungicide (1% metalaxyl). After foliar spraying of SWE solution, two antioxidant enzymes, catalase (CAT) and peroxidase (POD) and systemic acquired resistance (SAR)-triggered enzyme, ß-1,3-glucanase (GLU), were analyzed. Both secondary metabolites, a phytoalexin scopoletin (Scp) and a signaling molecule salicylic acid (SA) were measured by high performance liquid chromatography (HPLC). Both SWE- and metalaxyl-treated plants had a close disease index (DI)-score which were 16.90 ± 1.93 and 15.54 ± 1.25, respectively, while the positive control sprayed with P. palmivora showed DI-score of 29.27 ± 1.89 which was much higher than those treated with SWE or fungicide. CAT, POD, and GLU were increased in rubber tree leaves treated with SWE solution. Furthermore, Scp and SA were significantly increased in SWE-treated leaves. Enhanced systemic acquired resistance induction, 2.09 folds of SA accumulation, was observed in the distal area comparing to the local area of SWE application. In conclusion, the positive effects of SWE elicitation from these studies revealed that SWE could be used as an alternative biocontrol agent for foliar spraying to enhance the defense responses in rubber tree seedling against P. palmivora.

Salicylic Acid Induces Resistance in Rubber Tree against Phytophthora palmivora.

Induced resistance by elicitors is considered to be an eco-friendly strategy to stimulate plant defense against pathogen attack. In this study, we elucidated the effect of salicylic acid (SA) on induced resistance in rubber tree against Phytophthora palmivora and evaluated the possible defense mechanisms that were involved. For SA pretreatment, rubber tree exhibited a significant reduction in disease severity by 41%. Consistent with the occurrence of induced resistance, the pronounced increase in H2O2 level, catalase (CAT) and peroxidase (POD) activities were observed. For defense reactions, exogenous SA promoted the increases of H2O2, CAT, POD and phenylalanine ammonia lyase (PAL) activities, including lignin, endogenous SA and scopoletin (Scp) contents. However, SA had different effects on the activity of each CAT isoform in the particular rubber tree organs. Besides, three partial cDNAs encoding CAT (HbCAT1, HbCAT2 and HbCAT3) and a partial cDNA encoding PAL (HbPAL) were isolated from rubber tree. Moreover, the expressions of HbCAT1, HbPAL and HbPR1 were induced by SA. Our findings suggested that, upon SA priming, the elevated H2O2, CAT, POD and PAL activities, lignin, endogenous SA and Scp contents, including the up-regulated HbCAT1, HbPAL and HbPR1 expressions could potentiate the resistance in rubber tree against P. palmivora.