A density gradient centrifugation method for rapid separation of nanoTiO2 and TiO2 aggregates from microalgal cells in complex mixtures with mercury

The Encapsulation of Natural Organic Dyes on TiO2 for Photochromism Control

Titanium dioxide (TiO₂) plays a pivotal role in photocatalytic reactions and holds great promise for the cosmetic and paint industries due to its white color and high refractive index. However, the original color of TiO₂ changes gradually to blue or yellow with UV irradiation, which affects its color realization. We encapsulated TiO₂ with several natural organic dye compounds, including purpurin, curcumin, and safflower, to control its photochromism and realize a range of different colors. The chemical reaction between TiO₂ and dyes based on their functional group was investigated, and the light absorption was tested via FTIR and UV-Vis spectroscopy. The changes in morphology and size distribution additionally supported their successful encapsulation. The discoloration after UV irradiation was evaluated by measuring the color difference (ΔE) of control TiO₂ and dye encapsulated TiO₂. The unique structure utilized natural dyes to preserve photochromism based on the physical barrier and automatically controlled the electronic transition of core TiO₂. In particular, the color difference values of purpurin and curcumin were 4.05 and 3.76, which is lower than the 5.36 of the control TiO₂. Dye encapsulated TiO₂ was manipulated into lipstick to verify its color realization and retention.

Kinetic Aspects of the Interactions between TiO2 Nanoparticles, Mercury and the Green Alga Chlamydomonas reinhardtii

Aquatic organisms are exposed to mixtures of environmental pollutants, including engineered nanoparticles; however, the interactions underlying cocktails’ effects are poorly understood, in particular, the kinetic aspects. The present study explored the time course of the interactions between nano-sized titanium dioxide (nTiO2) with different primary particle sizes, algae and inorganic mercury (Hg) over 96 h under conditions that were representative of a highly contaminated environment. The results showed that nTiO2 with smaller primary particle size and higher concentrations rapidly reduced the adsorption and internalization of mercury by green alga Chlamydomonas reinhardtii. Such a mitigating effect on mercury bioavailability could be explained by the strong adsorbing capacity of nTiO2 for Hg and the aggregation and sedimentation of nTiO2 and bound Hg. The present study highlighted the key processes determining the bioavailability of mercury to the algae in mixture exposure under conditions representative of a highly contaminated environment, such as industrial wastewater effluents.