RESUMO
Nickel (Ni) doped Mn3O4 nanoparticles (NPs) were synthesized by a quick and facile chemical precipitation technique to investigate their performance in the degradation of methylene blue (MB) in the absence of light. XRD, FESEM, TEM, AAS, XPS, and FT-IR were used for the investigation of the structural, surface morphological, and elemental composition of Ni doped Mn3O4 NPs. XRD confirms the formation of a tetragonal phase structure of pure Mn3O4 and 1% and 3% Ni doped Mn3O4 NPs. However, mixed phases were found in the case of 5 to 10% Ni doped Mn3O4 NPs. Well-defined spherical-shaped morphology was presented through FESEM. Particle sizes decreased linearly (58.50 to 23.68 nm) upon increasing the doping concentration from 0% (pure Mn3O4) to 7% respectively, and then increased (48.62 nm) in the case of 10% doping concentration. TEM further confirmed spherical shaped 32 nm nanoparticles for 7% Ni doped Mn3O4. The elemental composition and oxidation state of the prepared NPs were confirmed by using XPS spectra. Mixed valence Mn2+ and Mn4+ states were found in pure Mn3O4 and 1% and 3% Ni doped Mn3O4 NPs in the ratio of 2MnO-MnO2. In addition, three different oxidation states Mn2+, Mn3+, and Mn4+ were found in 5 to 10% Ni doped Mn3O4 NPs. Moreover, as a dopant Ni exists as Ni2+ and Ni3+ states in all Ni doped Mn3O4 NPs. The synthesized NPs were then applied as potent oxidants for the degradation of MB at pH 3. With the increase of doping concentration to 7%, the degree of degradation was increased to 79% in the first 10 min and finally, it became about 98%. The degradation of MB follows the pseudo-first-order linear kinetics with a degradation rate of 0.0342 min-1.
RESUMO
The COVID-19 (Coronavirus 2019) pandemic has proven to be the biggest global shock since World War II. That war resulted in 5.5 million deaths. The number of COVID-19-infected persons exceeded 13 million in the first 6 months of the pandemic and many more asymptomatic cases are undocumented. The global economy has been affected severely. The tension, the fear, the drastic measures to try to control the spread of the disease disrupted everyone's life from child to senior. The condition is worse in the global south, such as in Bangladesh, where the average population density is 7.5 times higher than that of China, where COVID-19 began and spread uncontrollably at the end of 2019. Lockdowns and social distancing were tried to stop the transmission of the disease but were often not observed faithfully or were less effective than thought to be. People need to trade and interact to earn money to survive but these activities could endanger others' lives if they do not maintain safety measures. Individual awareness is not only curtailing the spread of COVID-19 but also saves others' lives. This cross-sectional study used Ordinal and Binary logit models to predict the level of awareness through potential regressors of the citizen toward COVID-19 in Bangladesh. Findings of the study are that the level of awareness is dependent on the level of trauma; also, that household income is a statistically-significant predictor of awareness. Behavioral activities such as use of masks, outdoor activities, and stockpiling tendencies are found to be statistically significant predictors of awareness as well.
