Reproductive performance of freshwater snail, Helisoma duryi under the effect of bulk and nano zinc oxide.

Nanotechnology has been used to apply nanoparticle essential elements to enhance the ability of animals to absorb these elements and consequently improve their reproductive performance. High concentrations of nanoparticles (NPs) can directly harm a range of aquatic life forms, ultimately contributing to a decline in biodiversity. Helisoma duryi snails are a good model for studying the toxicological effects of bulk zinc oxide (ZnO-BPs) and nano zinc oxide (ZnO-NPs) on freshwater gastropods. This study aimed to compare the toxic effects of ZnO-BPs and ZnO-NPs on H. duryi snails and explore how waterborne and dietary exposure influenced the reproductive performance of this snail. ZnO-BPs and ZnO-NPs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray powder (XRD). This study revealed that the size of ZnO-BPs and ZnO-NPs were 154 nm and 11-31 nm, respectively. The results showed that exposure of adult snails to sub-lethal concentrations of both ZnO forms (bulk and nano) for 24 h/week for 4 weeks markedly changed their reproductive performance in a concentration-dependent manner, where fecundity was negatively affected by high concentrations. It was concluded that dietary exposure to the lowest tested concentration of ZnO-NPs (1 ppm) has a positive effect as the number of eggs and egg masses/snails increased and the incubation period decreased. Also, poly-vitelline eggs (The formation of twins) were observed. ZnO-NPs at low concentrations positively affect the reproductive performance of snails, especially after dietary exposure. The results revealed that 1 ppm ZnO-NPs could be supplementary provided to snails to improve their fertility, reduce the developmental time course, increase hatchability percentage, and produce poly-vitelline eggs.

Sonophotocatalytic degradation of malachite green in aqueous solution using six competitive metal oxides as a benchmark.

A comparison study examines six different metal oxides (CuO, ZnO, Fe3O4, Co3O4, NiO, and α-MnO2) for the degradation of malachite green dye using four distinct processes. These processes are as follows: sonocatalysis (US/metal oxide), sonocatalysis under ultra-violet irradiation (US/metal oxide/UV), sonocatalysis in the presence of hydrogen peroxide (US/metal oxide/H2O2), and a combination of all these processes (US/metal oxide/UV/H2O2). The effective operating parameters, such as the dosage of metal oxide nanoparticles (MONPs), the type of the process, and the metal oxides' efficiency order, were studied. At the same reaction conditions, the sonophotocatalytic is the best process for all six MOsNPs, CuO was the better metal oxide than other MOsNPs, and at the sonocatalysis process, ZnO was the best metal oxide in other processes. It was found that the metal oxide order for sonocatalytic process is CuO > α-MnO2 ≥ ZnO > NiO ≥ Fe3O4 ≥ Co3O4 within 15-45 min. The order of (US/metal oxide/UV) process is ZnO ≥ NiO ≥ α-MnO2 > Fe3O4 ≥ CuO ≥ Co3O4 within 5-40 min. The order of (US/ MOsNPs/ H2O2) process is ZnO ≥ CuO ≥ α-MnO2 ≥ NiO > Co3O4 > Fe3O4 within 5-20 min. The maximum removal efficiency order of the sonophotocatalytic process is ZnO ≥ CuO > α-MnO2 > NiO > Fe3O4 ≥ Co3O4 within 2-8 min. The four processes degradation efficiency was in the order US/MOsNPs ˂ US/MOsNPs/UV ˂ US/MOsNPs/H2O2 ˂ (UV/Ultrasonic/MOsNPs/H2O2). Complete degradation of MG was obtained at 0.05 g/L MONPs and 1 mM of H2O2 using 296 W/L ultrasonic power and 15 W ultra-violet lamp (UV-C) within a reaction time of 8 min according to the MOsNPs type at the same sonophotocatalytic/H2O2 reaction conditions. The US/metal oxide/UV/H2O2 process is inexpensive, highly reusable, and efficient for degrading dyes in colored wastewater.

Single-Doped and Multidoped Transition-Metal (Mn, Fe, Co, and Ni) ZnO and Their Electrocatalytic Activities for Oxygen Reduction Reaction.

The electrochemical oxygen reduction reaction (ORR) is the limiting half-reaction of fuel cells, which is mediated by using platinum-based catalysts. Hence, the development of low-cost, active ORR catalysts is highly required to make fuel cell technology commercially available. In this report, transition-metal (TM; Mn, Fe, Co, and Ni) single-doped and multidoped (MD) ZnO nanocrystals (ZNs) were prepared for use as ORR catalysts using a simple precipitation method. The effects of single doping and multidoping on the structure, morphology, and properties of the TM-doped ZNs were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence, X-ray photoelectron microscopy, electron paramagnetic resonance, and Raman and photoluminescence (PL) spectroscopies. The XRD results reveal that synthesized ZnO samples retained a pure hexagonal wurtzite crystal structure, even at high levels of multidoping (nominal 20%). SEM analyses show that the morphology of the prepared ZNs varies with the doping elements, doping mode, and amounts of doping. The observation of peak shifting and peak intensity changes in Raman studies confirms the presence of dopants in ZnO. The PL investigation reveals that the incorporation of dopants into the ZnO structure increases the oxygen vacancies within the materials. The highest oxygen vacancies were present in Mn-doped ZnO and 15% MD ZnO among the single-doped and MD samples, respectively. Linear-sweep voltammetry studies conclude that doped ZnO shows enhanced ORR activity compared to the undoped samples. The Mn-doped ZnO and 15% MD ZnO exhibited the highest ORR activity among the prepared single-doped and MD ZN samples, respectively. In comparison, single doping showed better ORR activity than the multidoping system. The enhanced ORR activity of the synthesized ZN materials correlates with the amount of oxygen vacancies present in the samples. The enhanced activity of TM-doped ZnO suggests that these materials can be used as potential, low-cost electrocatalysts for ORR in fuel cell technology.

Understanding the role of gold nanoparticles in enhancing the catalytic activity of manganese oxides in water oxidation reactions.

The Earth-abundant and inexpensive manganese oxides (MnOx) have emerged as an intriguing type of catalysts for the water oxidation reaction. However, the overall turnover frequencies of MnOx catalysts are still much lower than that of nanostructured IrO2 and RuO2 catalysts. Herein, we demonstrate that doping MnOx polymorphs with gold nanoparticles (AuNPs) can result in a strong enhancement of catalytic activity for the water oxidation reaction. It is observed that, for the first time, the catalytic activity of MnOx/AuNPs catalysts correlates strongly with the initial valence of the Mn centers. By promoting the formation of Mn(3+) species, a small amount of AuNPs (<5%) in α-MnO2/AuNP catalysts significantly improved the catalytic activity up to 8.2 times in the photochemical and 6 times in the electrochemical system, compared with the activity of pure α-MnO2.