Influence of a silica interlayer on the structural and magnetic properties of sol-gel TiO₂-coated magnetic nanoparticles

On the adsorption kinetics and mechanism of enhanced photocatalytic activity of Fe3 O4 -SiO2 -TiO2 core-multishell nanoparticles against E. coli

In the present study, a Fe₃ O₄ -TiO₂ (FT) core-shell and a core-multishell structure of Fe₃ O₄ -SiO₂ -TiO₂ (FST) were synthesized, and their bactericidal capability was investigated on Escherichia coli (E. coli). Scanning electron microscopy (SEM), ultraviolet-visible spectroscopy (UV-vis), X-ray diffraction, Brunauer-Emmett-Teller, zeta potential, and fluorimetry were carried out to characterize properties of synthesized nanoparticles. An efficiency of 98% adsorption and harsh bacterial damage was observed when E. coli was put in contact with FST. Weaker adsorption of bacteria in contact with FT demonstrated that heterojunction has destructive effects on nanostructure. Further investigation proved that more OH were produced on the surface of FST, which is a sign of its longer lifetime. Moreover, results revealed that the presence of SiO₂ in the structure caused enhanced coverage, surface area, and porosity in TiO₂ outer layer, all of which have positive effects on adsorption. However, UV-vis showed smaller band gap for FT. It suggests that although photoactivity of FST is less influenced by light absorption, it possesses more e/h lifetime for generation of reactive oxygen species. Results point to the importance of SiO₂ as an obstacle of heterojunction on both adsorption and photoactivity. It was also proposed that increasing band gap in FST can be attributed to the porosity of SiO₂ that causes suppression of TiO₂ nanocrystallite growth.

Synthesis of MgAC-Fe3O4/TiO2 hybrid nanocomposites via sol-gel chemistry for water treatment by photo-Fenton and photocatalytic reactions

MgAC-Fe₃O₄/TiO₂ hybrid nanocomposites were synthesized in different ratios of MgAC-Fe₃O₄ and TiO₂ precursor. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray fluorescence spectrometry (XRF), electron spin resonance spectrometry (ESR), Brunauer-Emmett-Teller (BET), photoluminescence (PL), and UV photoelectron spectroscopy (UPS) were used to characterize the nanocomposites. The increase of MgAC-Fe₃O₄, in the hybrid nanocomposites’ core-shell structure, led to the decrease of anatase TiO₂ peaks, thus reducing the photo-Fenton and photocatalytic activities. According to the obtained data, MgAC-Fe₃O₄ [0.05 g]/TiO₂ showed the best photo-Fenton and photocatalytic activities, having removed ~93% of MB (photo-Fenton reaction) and ~80% of phenol (photocatalytic reaction) after 20 and 80 mins, respectively. On the pilot scale (30 L), MgAC-Fe₃O₄ [0.05 g]/TiO₂ was completely removed after 27 and 30 hours by the photo-Fenton and photocatalytic activities, respectively. The synergistic effect gained from the combined photo-Fenton and photocatalytic activities of Fe₃O₄ and TiO₂, respectively, was credited for the performances of the MgAC-Fe₃O₄/TiO₂ hybrid nanocomposites.

Fabrication of methyl acrylate and tetraethylenepentamine grafted magnetic chitosan microparticles for capture of Cd(II) from aqueous solutions

MCS-MA-TEPA microparticles, with 251.22 mg g^-1 of adsorption capacity for Cd(II), higher than most of the counterparts, were first fabricated by chemical coprecipitation, spray drying, and Michael addition reaction, without any cross-linker participation. These Fe₃O₄-nanoparticle-embedded microparticles of 5.95 μm in size, derived from modifications by methyl acrylate (MA) and tetraethylenepentamine (TEPA) on magnetic chitosan (MCS) microparticles, were of plum-pudding-like and wrinkle-like topography portrayed by TEM and SEM. Such features were beneficial to adsorbent recycling and Cd(II) capture. BET examinations illustrated 6.084 m² g^-1 of specific surface area, 0.015 mL g^-1 of pore volume, and 6.536 nm of pore diameter. FTIR, VSM, XRD, TEM-SAED, TG, and DTG characterizations were indicative of successful synthesis, satisfactory magnetism, well-defined architecture, and good thermostability. Optimal adsorption parameters for Cd(II) were determined via batch experiments. Thermodynamic parameters and adsorption data fitting implied an exothermic, spontaneous, monolayer, and chemisorption process. XPS analyses confirmed a potential adsorption mechanism that N and O atoms on microparticles chelated with Cd(II) ions in solutions. Additionally, MCS-MA-TEPA-Cd(II) microparticles were magnetically separated easily and had outstanding reusability even after five-time recycling, with a slight adsorption capability loss (< 12%). Altogether, MCS-MA-TEPA microparticles might serve as a promising adsorbent for contaminated water scavenging.

Core-shell structured titanium dioxide nanomaterials for solar energy utilization

Because of its unmatched resource potential, solar energy utilization currently is one of the hottest research areas. Much effort has been devoted to developing advanced materials for converting solar energy into electricity, solar fuels, active chemicals, or heat. Among them, TiO2 nanomaterials have attracted much attention due to their unique properties such as low cost, nontoxicity, good stability and excellent optical and electrical properties. Great progress has been made, but research opportunities are still present for creating new nanostructured TiO2 materials. Core-shell structured nanomaterials are of great interest as they provide a platform to integrate multiple components into a functional system, showing improved or new physical and chemical properties, which are unavailable from the isolated components. Consequently, significant effort is underway to design, fabricate and evaluate core-shell structured TiO2 nanomaterials for solar energy utilization to overcome the remaining challenges, for example, insufficient light absorption and low quantum efficiency. This review strives to provide a comprehensive overview of major advances in the synthesis of core-shell structured TiO2 nanomaterials for solar energy utilization. This review starts from the general protocols to construct core-shell structured TiO2 nanomaterials, and then discusses their applications in photocatalysis, water splitting, photocatalytic CO2 reduction, solar cells and photothermal conversion. Finally, we conclude with an outlook section to offer some insights on the future directions and prospects of core-shell structured TiO2 nanomaterials and solar energy conversion.