Natural melanin/TiO2 hybrids for simultaneous removal of dyes and heavy metal ions under visible light

Interactions of Melanin with Electromagnetic Radiation: From Fundamentals to Applications

Melanin, especially integumentary melanin, interacts in numerous ways with electromagnetic radiation, leading to a set of critical functions, including radiation protection, UV-protection, pigmentary and structural color productions, and thermoregulation. By harnessing these functions, melanin and melanin-like materials can be widely applied to diverse applications with extraordinary performance. Here we provide a unified overview of the melanin family (all melanin and melanin-like materials) and their interactions with the complete electromagnetic radiation spectrum (X-ray, Gamma-ray, UV, visible, near-infrared), which until now has been absent from the literature and is needed to establish a solid fundamental base to facilitate their future investigation and development. We begin by discussing the chemistries and morphologies of both natural and artificial melanin, then the fundamentals of melanin-radiation interactions, and finally the exciting new developments in high-performance melanin-based functional materials that exploit these interactions. This Review provides both a comprehensive overview and a discussion of future perspectives for each subfield of melanin that will help direct the future development of melanin from both fundamental and applied perspectives.

Effect of the Photoreduction Process on the Self-Cleaning and Antibacterial Activity of Au-Doped TiO2 Colloids on Cotton Fabric

This study aims at understanding the effect of the photoreduction process during the synthesis of gold (Au)-doped TiO2 colloids on the conferred functionalities on cotton fabrics. TiO2/Au and TiO2/Au/SiO2 colloids were synthesized through the sol-gel method with and without undergoing the photoreduction step based on different molar ratios of Au:Ti (0.001 and 0.01) and TiO2/SiO2 (1:1 and 1:2.3). The colloids were applied to cotton fabrics, and the obtained photocatalytic self-cleaning, wet photocatalytic activity, UV protection, and antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria were investigated. The obtained results demonstrated that the photoreduction of Au weakened the self-cleaning effect and reduced the photocatalytic activity of coated fabrics. Also, an excess amount of Au deteriorated the photocatalytic activity under both UV and visible light. The most efficient self-cleaning effect was obtained on fabrics coated with a ternary TiO2/Au/SiO2 colloid containing ionic Au, where it decomposed coffee and red-wine stains after 3 h of illumination. Adding silica (SiO2) made the fabrics superhydrophilic and led to greater methylene blue (MB) dye adsorption, a faster dye degradation pace, and more efficient stain removal. Moreover, the photoreduction process affected the size of Au nanoparticles (NPs), weakened the antibacterial activity of fabrics against both types of tested bacteria, and modestly increased the UV protection. In general, the photoactivity of Au-doped colloids was influenced by the synthesis method, the ionic and metallic states of the Au dopant, the concentration of the Au dopant, and the presence and concentration of silica.

Synthesis and application of titanium dioxide photocatalysis for energy, decontamination and viral disinfection: a review

Global pollution is calling for advanced methods to remove contaminants from water and wastewater, such as TiO₂-assisted photocatalysis.  The environmental applications of titanium dioxide have started after the initial TiO₂ application for water splitting by Fujishima and Honda in 1972. TiO₂ is now used for self-cleaning surfaces, air and water purification systems, microbial inactivation and selective organic conversion. The synthesis of titanium dioxide nanomaterials with high photocatalytic activity is actually a major challenge. Here we review titanium dioxide photocatalysis with focus on mechanims, synthesis, and applications. Synthetic methods include sol-gel, sonochemical, microwave, oxidation, deposition, hydro/solvothermal, and biological techniques. Applications comprise the production of energy, petroleum recovery, and the removal of microplastics, pharmaceuticals, metals, dyes, pesticides, and of viruses such as the severe acute respiratory syndrome coronavirus 2.

Detecting Pb2+by a 'turn-on' fluorescence sensor based on DNA functionalized magnetic nanocomposites

Sensitive and selective detection of the lead ion (Pb²⁺) plays an important role in terms of both human health and environmental protection, as the heavy metal is fairly ubiquitous and highly toxic. The highly stable fluorescence biosensor is composed of Fe₃O₄@TiO₂core-shell nanocomposites, functionalized with a carboxyl fluorescein labeled DNA. The morphology, physical and chemical properties of the sensing nanomaterials were studied by transmission electron microscopy, FT-IR spectroscopy (FT-IR), x-ray powder diffraction and vibrating sample magnetometer. UV-visible and fluorescence spectroscopy were used to characterize the fluorescein functionalized magnetic nanoparticles. The performance of Pb²⁺detection displayed an excellent linearity (R² = 0.995) in the range of 10^-10to 5 × 10^-9ppm with a detection limit of 10^-10ppm, based on the optimization of the fabrication process and aptamers' specification. The fluorescence biosensor has an accurate response, excellent recoveries and high adsorbent capacities. It was successfully applied for the determination of Pb²⁺in contaminated water and serum samples; the detection of limit in both media were 10^-10ppm. These features ensure the potential use of aptamer functionalized magnetic nanocomposites as a new class of non-toxic biocompatible sensors for biological and environmental applications.

Study on Simultaneous Removal of Dye and Heavy Metal Ions by NiAl-Layered Double Hydroxide Films

Herein, nickel-aluminum-layered double hydroxide (NiAl-LDH) films were prepared by the hydrothermal method. Based on the photoinduced reduction ability and degradation of LDHs on heavy metal ions and organic compounds, NiAl-LDH films displayed favorable simultaneous removal performance. Benefiting from the electron traps of heavy metals reduced from solution, the coexisting metal ions improved the photocatalytic activity of NiAl-LDH films on methyl orange. The higher the Fermi level of coexisting metal ion was, the higher the photocatalytic degradation rate of methyl orange obtained. Meanwhile, the removal rates of heavy metal ions (Ag⁺, Pb²⁺, and Cu²⁺) from wastewater were both enhanced and could reach 95%. NiAl-LDH films showed affinity toward Ag⁺. Furthermore, NiAl-LDH films are tightly coupled with the substrate, providing active sites and a simple method for the catalyst recovery. This study provides new insights into the simultaneous removal of heavy metal ions and organic pollutants using LDH films.

Advances in photocatalytic self-cleaning, superhydrophobic and electromagnetic interference shielding textile treatments

The use of nanomaterials in textiles provides many new opportunities and advantages for users and manufacturers; however, it comes with some of its downsides and challenges which need to be understood and overcome for enhancing the applicability of these products. This review article discusses the recent progress in developing self-cleaning and conductive textiles as two of the leading research fields of smart textiles. In particular, different aspects of fabricating nanocoatings for photocatalytic self-cleaning, superhydrophobic and electromagnetic interference (EMI) shielding effect will be brought to light. The theoretical concepts, mechanisms, latest fabrication methods along with their potential applications will be discussed. Moreover, the current drawbacks of these fields will be underlined and some recommendations for future research trajectories in terms of performance, current limitations, sustainability and safety will be proposed. This review article provides a comprehensive review on the state-of-the-art achievements in the field, which will be a valuable reference for researchers and decision makers.

Designing 2D–2D g-C3N4/Ag:ZnIn2S4 nanocomposites for the high-performance conversion of sunlight energy into hydrogen fuel and the meaningful reduction of pollution

The generation of hydrogen-based energy and environmental remediation using sunlight is an emerging topic of great significance for meeting the ever-growing global need. However, the actual photocatalytic performance is still far below expectations because of the relatively slack charge-carrier separation and migration as well as insufficient spectral absorption in semiconductors. Therefore, the rational construction of heterojunctions is considered as an effective approach to solving the above issues. In this context, we have, for the first time, designed and synthesized a two-dimensional 2D-on-2D heterostructure, based on 2D Ag-doped ZnIn₂S₄ nanoplates deposited on 2D g-C₃N₄ nanosheets (denoted as g-C₃N₄/Ag:ZnIn₂S₄). This construct benefits from improved visible-light absorption by unveiling a greater number of catalytically active sites, effectively enhancing charge-carrier separation and relocation. Detailed analysis has proved that under visible-light irradiation, the optimized g-C₃N₄/20 wt% Ag:ZnIn₂S₄ nanocomposite has substantially upgraded photocatalytic activity in hydrogen formation by water splitting (hydrogen evolution rate of up to 597.47 μmol h⁻¹ g⁻¹) and in residual dyestuff degradation (methyl orange, MO; degradation rate constant of 0.1406 min⁻¹). Noteworthily, these two exceptionally high values respectively represent 30.73 and 5.42 times enhancements vs. results obtained with bare g-C₃N₄. Another strong point of our g-C₃N₄/Ag:ZnIn₂S₄ is its impressive recyclability for 20 runs, with no relevant metal release in the aqueous solution following photocatalysis. This work introduces new, superior access to highly efficient photocatalysts founded on 2D/2D nanocomposites serving both the production of hydrogen as an energy carrier and environmental remediation.

The generation of hydrogen-based energy and environmental remediation using sunlight is an emerging topic of great significance for meeting the ever-growing global need.