Microplastics (MPs) are generated from plastic and have negative impact to our environment due to high level of fragmentation. They can be originated from various sources in different forms such as fragment, fiber, foam and so on. For detection of MPs, many techniques have been developed with different functions such as microscopic observation, density separation, Raman and FTIR analysis. Besides, due to ingestion of MPs by wide range of marine species, research on the effect of this pollution on biota as well as human is vital. Therefore, we comprehensively reviewed the occurrence and distribution of MPs pollution in both marine and freshwater environments, including rivers, lakes and wastewater treatment plants (WWTPs). For future studies, we propose the development of new techniques for sampling MPs in aquatic environments and biota and recommend more research regarding MPs release by WWTPs.
The dehydration of ethanol into diethyl ether over a SO4/SiO2 catalyst was investigated. The SO4/SiO2 catalysts were prepared by the sulfation method using 1, 2, and 3 M of sulfuric acid (SS1, SS2, and SS3) via hydrothermal treatment. This study is focused on the synthesis of a SO4/SiO2 catalyst with high total acidity that can be subsequently utilized to convert ethanol into diethyl ether. The total acidity test revealed that the sulfation process increased the total acidity of SiO2. The SS2 catalyst (with 2 M sulfuric acid) displayed the highest total acidity of 7.77 mmol/g, whereas the SiO2 total acidity was only 0.11 mmol/g. Meanwhile, the SS3 catalyst (with 3 M sulfuric acid) has a lower total acidity of 7.09 mmol/g due to the distribution of sulfate groups on the surface having reached its optimum condition. The crystallinity and structure of the SS2 catalyst were not affected by the hydrothermal treatment or the sulfate process on silica. Furthermore, The SS2 catalyst characteristics in the presence of sulfate lead to a flaky surface in the morphology and non-uniform particle size. In addition, the surface area and pore volume of the SS2 catalyst decreased (482.56-172.26 m2/g) and (0.297-0.253 cc/g), respectively, because of the presence of sulfate on the silica surface. The SS2 catalyst's pore shape information explains the formation of non-uniform pore sizes and shapes. Finally, the activity and selectivity of SO4/SiO2 catalysts in the conversion of ethanol to diethyl ether yielded the highest ethanol conversion of 70.01% and diethyl ether product of 9.05% from the SS2 catalyst (the catalyst with the highest total acidity). Variations in temperature reaction conditions (175-225 °C) show an optimum reaction temperature to produce diethyl ether at 200 °C (11.36%).