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The presence of secondary metabolites in Moringa oleifera is the decisive factor for the green synthesis of silver nanoparticles (AgNPs). Among the metabolites involved in this process, phenols and flavonoids in the plant extract are the two most important groups, acting both as reducing and stabilizing agents. M. oleifera, a well-known herb from Indonesia, was used in this study due to its exceptional properties, such as antioxidant, antimicrobial, and anti-inflammatory among others. The total phenolic content and total flavonoid content in the aqueous extract of M. oleifera leaves were determined, and the values were 62.01 ± 2.05 mg/g and 71.97 ± 0.94 mg/g, respectively. The synthesis factors including pH, extract volume, and temperature for the synthesis of AgNPs were optimized using the onefactor- at-a-time approach. The synthesis experiment showed that a pH of 8.0, an extract volume of 0.3 mL, and a temperature of 80°C resulted in the highest intensity of localized surface plasmon resonance at a wavelength of 419 nm, which favored the synthesis after 24 h of reaction time. Due to the remarkable content of metabolites, M. oleifera can be used as a promising candidate for the effective synthesis of AgNPs.

Microplastics have aroused global concern due to their widespread environmental distribution and the possible danger they pose to humans, animals, and microbes. In response to this concern, photocatalytic degradation, a technique that utilizes semiconductor nanomaterials as the photocatalyst, is being explored to reduce microplastics into less harmful compounds, making it a game-changing strategy for addressing this environmental problem. Besides the superiority of titanium dioxide (TiO2) as a photocatalyst, zinc oxide (ZnO) nanoparticles are also one of the semiconductors that have been widely explored to date. Studies have proven its potential to degrade microplastics in either solid- or aqueous phases. In the photocatalytic degradation of microplastics, the reactive oxygen species (ROS), including hydroxyl (•OH) and superoxide ions (O2•-), play an essential role in the process, resulting in the breakdown of the polymeric chain and the generation of reaction intermediates. Therein, the primary focus of this review is limited to the photocatalytic degradation of microplastics using a ZnO-based photocatalyst and its mechanisms. The exploration and comparison of microplastic's solid- and aqueous-phase photocatalytic processes in terms of their experimental setup and performance were also discussed further. Furthermore, an insight into future research prospects is also suggested here, based on the restrictions of present photocatalytic degradation systems. [ABSTRACT FROM AUTHOR]