Composite Photocatalyst of Nitrogen and Fluorine Codoped Titanium Oxide Nanotube Arrays with Dispersed Palladium Oxide Nanoparticles for Enhanced Visible Light Photocatalytic Performance

A novel composite photocatalyst of nitrogen (N) and fluorine (F) codoped titanium oxide (TiO2) nanotube arrays with dispersed palladium oxide (PdO) nanoparticles was developed by dispersing PdO nanoparticles into N and F codoped TiO2 nanotube array template created by anodization of titanium foil. These N and F codoped TiO2/PdO nanotube arrays demonstrated increased visible light absorption, fast superhydrophilicity conversion, and enhanced photocatalytic degradation of organic pollutants. The enhancement on the photocatalytic performance was explained by the optoelectronic coupling between dispersed PdO nanoparticles and N and F codoped TiO2 nanotube arrays under visible light illumination, which involves trapping of electrons by PdO nanoparticles, and subsequently decreases the electron/hole pair recombination. Various transition metal/metal oxide nanoparticles could be introduced into nanotube arrays by this simple approach, which could create novel properties for nanotube arrays and promise a wide range of technical applications

Self-Organized Nitrogen and Fluorine Co-doped Titanium Oxide Nanotube Arrays with Enhanced Visible Light Photocatalytic Performance

Self-organized nitrogen and fluorine co-doped titanium oxide (TiONF) nanotube arrays were created by anodizing titanium foil in a fluoride and ammoniate-based electrolyte, followed by calcination of the amorphous nanotube arrays under a nitrogen protective atmosphere for crystallization. TiONF nanotube arrays were found to have enhanced visible light absorption capability and photodegradation efficiency on methylene blue under visible light illumination over the TiO2 nanotube arrays. The enhancement was dependent on both the nanotube structural architecture and the nitrogen and fluorine co-doping effect. TiONF nanotube arrays promise a wide range of technical applications, especially for environmental applications and solar cell devices

As(III) Removal by Palladium-Modified Nitrogen-Doped Titanium Oxide Nanoparticle Photocatalyst

Removal of arsenic species from water by palladium-modified nitrogen-doped titanium oxide (TiON/PdO) nanoparticles was investigated with and without visible light. For the first time, a high degree of As(III) removal under visible light illumination was demonstrated on oxide photocatalysts. Over 2 orders of magnitude decrease of As(III) concentration in water was observed in 1 h as the As(III) concentration was reduced below the U.S. Environmental Protection Agency standard (10 μg/L) by TiON/PdO photocatalyst. Such an efficient removal of As(III) was shown to result from the combined effects of strong adsorption and photooxidation by TiON/PdO, where an enhanced photocatalytic activity under visible light illumination than nitrogen-doped titanium oxide (TiON) was derived from the strong optoelectronic coupling between PdO and TiON

As(III) and As(V) Adsorption by Hydrous Zirconium Oxide Nanoparticles Synthesized by a Hydrothermal Process Followed with Heat Treatment

Hydrous zirconium oxide (ZrO₂·<i>x</i>H₂O) were synthesized by a low-cost hydrothermal process followed with heat treatment. ZrO₂·<i>x</i>H₂O nanoparticles ranged from 6 nm to 10 nm and formed highly porous aggregates, resulting in a large surface area of 161.8 m² g^–1. The batch tests on the laboratory water samples demonstrated a very high degree of As(III) and As(V) removal by ZrO₂·<i>x</i>H₂O nanoparticles. The adsorption mechanism study demonstrated that both arsenic species form inner-sphere surface complexes on the surface of ZrO₂·<i>x</i>H₂O nanoparticles. Higher arsenic removal effect of these ZrO₂·<i>x</i>H₂O nanoparticles were demonstrated, compared with commercially available Al₂O₃ and TiO₂ nanoparticles. Ionic strength and competing ion effects on the arsenic adsorption of these ZrO₂·<i>x</i>H₂O nanoparticles were also studied. Testing with natural lake water confirmed the effectiveness of ZrO₂·<i>x</i>H₂O nanoparticles in removing arsenic species from natural water, and the immobilization of ZrO₂•xH₂O nanoparticles on glass fiber cloth minimized the dispersion of nanoparticles into the treated body of water. The high adsorption capacity of ZrO₂·<i>x</i>H₂O nanoparticles is shown to result from the strong inner-sphere surface complexing promoted by the high surface area, large pore volume, and surface hydroxyl groups of zirconium oxide nanoparticles

Visible-Light-Induced Bactericidal Activity of Titanium Dioxide Codoped with Nitrogen and Silver

Titanium dioxide nanoparticles codoped with nitrogen and silver (Ag2O/TiON) were synthesized by the sol−gel process and found to be an effective visible light driven photocatalyst. The catalyst showed strong bactericidal activity against Escherichia coli (E. coli) under visible light irradiation (λ > 400 nm). In X-ray photoelectron spectroscopy and X-ray diffraction characterization of the samples, the as-added Ag species mainly exist as Ag2O. Spin trapping EPR study showed Ag addition greatly enhanced the production of hydroxyl radicals (•OH) under visible light irradiation. The results indicate that the Ag2O species trapped eCB− in the process of Ag2O/TiON photocatalytic reaction, thus inhibiting the recombination of eCB− and hVB+ in agreement with the stronger photocatalytic bactericidal activity of Ag2O/TiON. The killing mechanism of Ag2O/TiON under visible light irradiation is shown to be related to oxidative damages in the forms of cell wall thinning and cell disconfiguration

Synthesis of Superparamagnetic Core–Shell Structure Supported Pd Nanocatalysts for Catalytic Nitrite Reduction with Enhanced Activity, No Detection of Undesirable Product of Ammonium, and Easy Magnetic Separation Capability

Superparamagnetic nanocatalysts could minimize both the external and internal mass transport limitations and neutralize OH^– produced in the reaction more effectively to enhance the catalytic nitrite reduction efficiency with the depressed product selectivity to undesirable ammonium, while possess an easy magnetic separation capability. However, commonly used qusi-monodispersed superparamagnetic Fe₃O₄ nanosphere is not suitable as catalyst support for nitrite reduction because it could reduce the catalytic reaction efficiency and the product selectivity to N₂, and the iron leakage could bring secondary contamination to the treated water. In this study, protective shells of SiO₂, polymethylacrylic acid, and carbon were introduced to synthesize Fe₃O₄@SiO₂/Pd, Fe₃O₄@PMAA/Pd, and Fe₃O₄@C/Pd catalysts for catalytic nitrite reduction. It was found that SiO₂ shell could provide the complete protection to Fe₃O₄ nanosphere core among these shells. Because of its good dispersion, dense structure, and complete protection to Fe₃O₄, the Fe₃O₄@SiO₂/Pd catalyst demonstrated the highest catalytic nitrite reduction activity without the detection of NH₄⁺ produced. Due to this unique structure, the activity of Fe₃O₄@SiO₂/Pd catalysts for nitrite reduction was found to be independent of the Pd nanoparticle size or shape, and their product selectivity was independent of the Pd nanoparticle size, shape, and content. Furthermore, their superparamagnetic nature and high saturation magnetization allowed their easy magnetic separation from treated water, and they also demonstrated a good stability during the subsequent recycling experiment

Synthesis of Cu₂O Nanospheres Decorated with TiO₂ Nanoislands, Their Enhanced Photoactivity and Stability under Visible Light Illumination, and Their Post-illumination Catalytic Memory

A novel Cu₂O/TiO₂ composite photocatalyst structure of Cu₂O nanospheres decorated with TiO₂ nanoislands were synthesized by a facile hydrolyzation reaction followed by a solvent-thermal process. In this Cu₂O/TiO₂ composite photocatalyst, Cu₂O served as the main visible light absorber, while TiO₂ nanoislands formed heterojunctions of good contact with Cu₂O, beneficial to the photoexcited electron transfer between them. Their band structure match and inner electrostatic field from the <i>p</i>–<i>n</i> heterojunction both favored the transfer of photoexcited electrons from Cu₂O to TiO₂, which effectively separated the electron–hole pairs. Photogenerated holes on Cu₂O could react with water or organic pollutants/microorganisms in water to avoid accumulation on Cu₂O because of the partial TiO₂ nanoislands coverage, which enhanced their stability during the photocatalysis process. Their superior photocatalytic performance under visible light illumination was demonstrated in both the degradation of methyl orange and the disinfection of <i>Escherichia coli</i> bacteria. An interesting post-illumination catalytic memory was also observed for this composite photocatalyst as demonstrated in the disinfection of <i>Escherichia coli</i> bacteria in the dark after the visible light was shut off, which could be attributed to the transfer of photoexcited electrons from Cu₂O to TiO₂ and their trapping on TiO₂ under visible light illumination, and their release in the dark after the visible light was shut off

Enhanced Visible-Light-Induced Photocatalytic Disinfection of <i>E. coli</i> by Carbon-Sensitized Nitrogen-Doped Titanium Oxide

Nitrogen-doped titanium oxide (TiON) nanoparticle photocatalysts were synthesized by a sol−gel process, for disinfection using E. coli as target bacteria. Our work shows that the calcination atmosphere has strong effects on the composition, structure, optical, and antimicrobial properties of TiON nanoparticles. Powders calcinated in a flow of N2 atmosphere (C−TiON) contain free carbon residue and demonstrate different structures and properties compared to the TiON powders calcinated in air. Disinfection experiments on Escherichia coli indicate that C−TiON composite photocatalyst has a much better photocatalytic activity than pure TiON photocatalyst under visible light illumination. The enhanced photocatalytic activity is related to stronger visible light absorption of the carbon-sensitized TiON

Synthesis of Mn₃O₄/CeO₂ Hybrid Nanotubes and Their Spontaneous Formation of a Paper-like, Free-Standing Membrane for the Removal of Arsenite from Water

One-dimensional nanomaterials may organize into macrostructures to have hierarchically porous structures, which could not only be easily adopted into various water treatment apparatus to solve the separation issue of nanomaterials from water but also take full advantage of their nanosize effect for enhanced water treatment performance. In this work, a novel template-based process was developed to create Mn₃O₄/CeO₂ hybrid nanotubes, in which a redox reaction happened between the OMS-2 nanowire template and Ce­(NO₃)₃ to create hybrid nanotubes without the template removal process. Both the Ce/Mn ratio and the precipitation agent were found to be critical in the formation of Mn₃O₄/CeO₂ hybrid nanotubes. Because of their relatively large specific surface area, porous structure, high pore volume, and proper surface properties, these Mn₃O₄/CeO₂ hybrid nanotubes demonstrated good As­(III) removal performances in water. These Mn₃O₄/CeO₂ hybrid nanotubes could form paper-like, free-standing membranes spontaneously by a self-assembly process without high temperature treatment, which kept the preferable properties of Mn₃O₄/CeO₂ hybrid nanotubes while avoiding the potential nanomaterial dispersion problem. Thus, they could be readily utilized in commonly used flow-through reactors for water treatment purposes. This approach could be further applied to other material systems to create various hybrid nanotubes for a broad range of technical applications

Photoirradiation-Induced Capacitance Enhancement in the <i>h</i>‑WO₃/Bi₂WO₆ Submicron Rod Heterostructure under Simulated Solar Illumination and Its Postillumination Capacitance Enhancement Retainment from a Photocatalytic Memory Effect

Recently, photoassisted charging has been demonstrated as a green and sustainable approach to successfully enhance the capacitance of supercapacitors with low cost and good efficiency. However, their light-induced capacitance enhancement is relatively low and is lost quickly when the illumination is off. In this work, a novel active material system is developed for supercapacitors with the photoassisted charging capability by the decoration of a small amount of Bi2WO6 nanoparticles on an h-WO3 submicron rod surface in situ, which forms a typical type II band alignment heterostructure with a close contact interface through the co-sharing of W atoms between h-WO3 submicron rods and Bi2WO6 nanoparticles. The photogenerated charge carrier separation and transfer are largely enhanced in the h-WO3/Bi2WO6 submicron rod electrode, which subsequently allows more charge carriers to participate in its photoassisted charging process to largely enhance its capacitance improvement under simulated solar illumination than that of the h-WO3 submicron rod electrode. Furthermore, the h-WO3/Bi2WO6 submicron rod electrode could retain its photoinduced capacitance enhancement in the dark for an extended period of time from the photocatalytic memory effect. Thus, our work provides a solution to the two major drawbacks of reported supercapacitors with the light-induced capacitance enhancement property, and supercapacitors based on active materials with the photocatalytic memory effect could be utilized in various technical fields