Synthesis of silver nanoparticles–chitosan composite particles sphere (AgNPs-chi-spheres) has been completed and its characterization was fulfilled by UV–vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and zetasizer nano. UV–vis spectroscopy characterization showed that AgNPs-chi-spheres gave optimum absorption at a wavelength of 410 nm. The XRD spectra showed that the structure of AgNPs-chi-spheres were crystalline and spherical. Characterization by SEM showed that AgNPs-chi-spheres, with the addition of 20% of NaOH, resulted in the lowest average particle sizes of 46.91 nm. EDX analysis also showed that AgNPs-chi-spheres, with the addition of a 20% NaOH concentration, produced particles with regular spheres, a smooth and relatively nonporous structure. The analysis using zetasizer nano showed that the zeta potential value and the polydispersity index value of the AgNPs-chi-sphere tended to increase with an increased NaOH concentration. The results of the microbial activity screening showed that the AgNP-chi-Spheres with highest concentration of NaOH, produced the highest inhibition zone diameters against S. aureus, E. coli, and C. albicans, with inhibition zone diameters of 19.5, 18.56, and 12.25 nm, respectively.

Herein, we report our success synthesizing silver nanoparticles (AgNPs) using aqueous extracts from the leaves and flowers of Calotropis gigantea growing in the geothermal manifestation Ie Seu-Um, Aceh Besar, Indonesia. C. gigantea aqueous extract can be used as a bio-reductant for Ag⁺→Ag⁰ conversion, obtained by 48h incubation of Ag⁺, and the extract mixture in a dark condition. UV–Vis characterization showed that the surface plasmon resonance (SPR) peaks of AgNPs-leaf C. gigantea (AgNPs-LCg) and AgNPs-flower C. gigantea (AgNPs-FCg) appeared in the wavelength range of 410–460 nm. Scanning electron microscopy energy-dispersive X-ray spectrometry (SEM-EDS) revealed the agglomeration and spherical shapes of AgNPs-LCg and AgNPs-FCg with diameters ranging from 87.85 to 256.7 nm. Zeta potentials were observed in the range of −41.8 to −25.1 mV. The Kirby-Bauer disc diffusion assay revealed AgNPs-FCg as the most potent antimicrobial agent with inhibition zones of 12.05 ± 0.58, 11.29 ± 0.45, and 9.02 ± 0.10 mm for Escherichia coli, Staphylococcus aureus, and Candida albicans, respectively. In conclusion, aqueous extract from the leaves or flowers of Calotropis gigantea may be used in the green synthesis of AgNPs with broad-spectrum antimicrobial activities.

The characteristics of MgH2 as a hydrogen storage material in this study were observed by varying the composition of the catalyst. The added catalyst was a dual catalyst, namely nickel and natural silica extracted from rice husk ash with a composition of MgH2 + 10 wt% SiO2 + 10 wt% Ni (Sample A),...

MgH2 is a very hopeful material for application as hydrogen storage material in the solid form. This is due to its reversibility and its ability to store large amounts of hydrogen, which is 7.6 wt%. However, this material still has weaknesses, namely high operating temperature and slow kinetic reactions. Various attempts have been made to overcome this weakness, including downsizing and adding catalyst. In this study, double catalyst was used, namely natural silica extracted from rice husk ash and nickel nano powder, with a composition of MgH2 + 10 wt% SiO2 + 5 wt% Ni. The purpose of this research was to study the effect of downsizing and using these catalysts to the thermodynamic and kinetic properties of the hydrogen storage material MgH2. Samples were prepared by using High Energy Ball Milling (HEBM), with variations in milling time of 1, 5, 10, and 15 hours. The X-ray Diffraction (XRD) pattern showed the presence of an impurity phase in the samples milled for 10 and 15 hours. It also showed a reduction in grain size with increasing milling time. However, agglomeration has occurred in the samples milled for 15 hours. From the Scanning Electron Microscope (SEM) results can be seen that the sample with longer milling time, were homogeneously distribute. Thermal investigation showed that the lowest desorption temperature was achieved in samples with milling time of 5 and 10 hours, namely 287 °C and 288 °C. This study shows that natural silica catalyst plays a role in improving the thermodynamic characteristics of MgH2, while Ni plays a role in improving the kinetic characteristics of MgH2. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0).

Recently, milling under reactive atmosphere was introduced in preparing the Mg-based hydrogen storage materials. Metal or metal oxides at the nanometer scale ha