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Using NIR irradiation and magnetic bismuth ferrite microparticles to accelerate the removal of polystyrene microparticles from the drinking water
Summary
Researchers used magnetic bismuth ferrite microparticles combined with near-infrared irradiation to remove polystyrene nano- and microplastics from drinking water, achieving effective removal through a magnetic separation mechanism. The method represents a novel approach to removing plastic particles from water supplies.
Magnetic bismuth ferrite (BiFO) microparticles were employed for the first time for the removal of polystyrene (PS) nano/microplastics from the drinking water. BiFO is formed by porous agglomerates with sizes of 5-11 μm, while the PS nano/microparticles have sizes in the range of 70-11000 nm. X-ray diffraction studies demonstrated that the BiFO microparticles are composed of BiFeO/BiFeO (the content of BiFeO is ≈ 8.6%). Drinking water was contaminated with PS nano/microparticles (1 g L) and BiFO microparticles were also added to the contaminated water. Later, the mixture of PS-particles + BiFO was irradiated with NIR light (980 nm). Consequently, PS nano/microparticles melted on the BiFO microparticles due to the excessive heating on their surface. At the same time, the NIR (near infrared) light generated oxidizing agents (∙OH and h), which degraded the by-products formed during the photocatalytic degradation of PS nano/microparticles. Subsequently, the NIR irradiation was stopped, and a Neodymium magnet was utilized to separate the BiFO microparticles from the water. This last procedure also permitted the removal of PS nano/microparticles by physical adsorption. Zeta potential measurements demonstrated that the BiFO surface was positively charged, allowing the removal of the negatively charged PS nano/microparticles by electrostatic attraction. The combination of the photocatalytic process and the physical adsorption permitted a complete removal of PS nano/microparticles after only 90 min as well as a high mineralization of by-products (≈95.5% as confirmed by the total organic carbon measurements). We estimate that ≈23.6% of the PS nano/microparticles were eliminated by photocatalysis and the rest of PS particles (≈76.4%) by physical adsorption. An outstanding adsorption capacity of 195.5 mg g was obtained after the magnetic separation of the BiFO microparticles from the water. Hence, the results of this research demonstrated that using photocatalysis + physical-adsorption is a feasible strategy to quickly remove microplastic contaminants from the water.