Innovative Ag–TiO2 Nanofibers with Excellent Photocatalytic and Antibacterial Actions

Ag–TiO2 nanostructures were prepared by electrospinning, followed by calcination at 400 °C, and their photocatalytic and antibacterial actions were studied. Morphological characterization revealed the presence of one-dimensional uniform Ag–TiO2 nanostructured nanofibers, with a diameter from 65 to 100 nm, depending on the Ag loading, composed of small crystals interconnected with each other. Structural characterization indicated that Ag was successfully integrated as small nanocrystals without affecting much of the TiO2 crystal lattice. Moreover, the presence of nano Ag was found to contribute to reducing the band gap energy, which enables the activation by the absorption of visible light, while, at the same time, it delays the electron–hole recombination. Tests of their photocatalytic activity in methylene blue, amaranth, Congo red and orange II degradation revealed an increase by more than 20% in color removal efficiency at an almost double rate for the case of 0.1% Ag–TiO2 nanofibers with respect to pure TiO2. Moreover, the minimum inhibitory concentration was found as low as 2.5 mg/mL for E. coli and 5 mg/mL against S. aureus for the 5% Ag–TiO2 nanofibers. In general, the Ag–TiO2 nanostructured nanofibers were found to exhibit excellent structure and physical properties and to be suitable for efficient photocatalytic and antibacterial uses. Therefore, these can be suitable for further integration in various important applications.

Solar-Powered Photodegradation of Pollutant Dyes Using Silver-Embedded Porous TiO2 Nanofibers

Titanium dioxide (TiO₂) nanomaterials have been ubiquitously investigated as a photocatalyst for organic contaminant treatment in wastewater due to their exemplary semiconductor properties. However, their huge band gap remains a barrier for visible light absorption, limiting their utility in practical applications. The incorporation of noble metals in the TiO₂ scaffold would help mitigate the problem via plasmonic resonance enhancements. Silver (Ag) is the chosen noble metal as it is relatively cheap and has great plasmonic effects. In this study, the use of electrospun Ag-embedded TiO₂ nanofibers as a photocatalyst is shown to be effective in decomposing rhodamine B and methyl orange dyes under a solar simulator in 3 h, which is more efficacious as opposed to pristine TiO₂ nanofibers. This showcases the potential of a simple and economic wastewater treatment system for the removal of organic pollutants.

Controllable growth of three-dimensional CdS nanoparticles on TiO2 nanotubes to enhance photocatalytic activity

Exploiting photocatalysts with characteristics of low cost, high reactivity and good recyclability is a great significance for environmental remediation and energy conversion. Herein, hollow TiO2 nanotubes were fabricated by a novel and efficient method via electrospinning and an impregnation calcination method. With the hydrothermal method, the CdS nanoparticles were modified on the surface and in walls of the TiO2 nanotubes. By changing the reaction conditions, the morphology of CdS nanoparticles presents a controllable three-dimensional (3D) structure. The morphology of the samples was characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The structure and components of samples were characterized by X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). The light absorption efficiency was detected using UV-vis diffuse reflectance spectroscopy (DRS) and photoluminescence (PL). The photocatalytic properties were evaluated by degradation of methyl orange (MO) and photocatalytic hydrogen evolution under visible light irradiation. From the results, the TiO2/CdS nanotubes exhibit better photocatalytic activity than the pure TiO2. The synthetic mechanism of TiO2/CdS heterostructures and a possible photocatalytic mechanism based on the experimental results were proposed.

Electrospun Ag-TiO2 Nanofibers for Photocatalytic Glucose Conversion to High-Value Chemicals

TiO₂ nanofibers were fabricated by combination of sol-gel and electrospinning techniques. Ag-doped TiO₂ nanofibers with different Ag contents were prepared by two different methods (in situ electrospinning or wetness impregnation of Ag on TiO₂ nanofibers) and heat treated at 500 °C for 2 h under an air or N₂ atmosphere. The obtained catalysts were characterized by field emission scanning electron microscopy, X-ray diffraction, photoluminescence, and N₂ adsorption analyzed by the Brunauer-Emmett-Teller (BET) method. Photocatalytic glucose conversions with electrospun TiO₂ and Ag-doped TiO₂ nanofibers for production of high-value products were carried out. From different doping methods, the results indicated that 1 wt % Ag-TiO₂ nanofibers prepared by an in situ method with calcination under N₂ achieved the highest glucose conversion (85.49%). From several Ag loading contents (i.e., 0, 1, 2, and 4 wt %) in Ag-doped TiO₂ nanofibers, the nanofibers exhibited different glucose conversions [in order of 2 wt % (99.65%) > 1 wt % (85.49%) > 4 wt % (77.72%) > 0 wt % (29.64%)]. Arabinose, xylitol, gluconic acid, and formic acid were found as the high-value chemicals with the photocatalytic reaction of TiO₂ and Ag-doped TiO₂ nanofibers under UVA irradiation. Product yields of each converted chemicals from different photocatalysts from different Ag loading contents showed relatively same trends with the glucose conversion. From all results, it can be concluded that the good characteristics of 2 wt % Ag-TiO₂ nanofibers such as the smallest anatase crystallite size (8.25 nm) and the highest specific surface area (S _BET = 53.69 m²/g) promoted the highest photocatalytic activity. Additionally, TiO₂ and Ag-doped TiO₂ nanofibers exhibited higher photocatalytic performance for glucose conversion than commercial TiO₂ (P25) and synthesized TiO₂ nanoparticles. Finally, Ag-doped TiO₂ nanofibers showed recycling ability with high photocatalytic glucose conversion after four-time use.

Bi-functional Ag-CuxO/g-C3N4 hybrid catalysts for the reduction of 4-nitrophenol and the electrochemical detection of dopamine

The immense need to build highly efficient catalysts has always been at the forefront of environmental remediation research. Herein, we have synthesized dual-phase copper oxide containing Cu2O and CuO originating from the same reaction using hexamethyltetramine (HMT). Simultaneously, we coupled it with g-C3N4 (g-CN), constructing a triple synergetic heterojunction, which is reported significantly less often in the literature. Hydrothermal reactions led to the formation of various catalysts, namely, Ag-Cu2O-CuO-gCN (ACCG), Ag-CuO-gCN (ACG), Ag-Cu2O-CuO (ACC) and Ag-CuO (AC), which were thoroughly characterized via XRD and FESEM to gain structural, crystallographic and morphological insights. We clearly observed the pure phase formation of the catalysts and the development of sheet-like CuO and truncated octahedrons of Cu2O fused together within the g-CN framework. Also, XPS studies revealed the presence of copper in two different oxidation states, namely, Cu2+ and Cu+. BET analysis was performed to analyze the surface area and pore volume of the catalysts, which play very significant roles in catalytic reduction. The catalytic efficiencies of the catalysts were evaluated via the reduction of 100 ppm 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) without using any light irradiation. The most efficient catalyst was ACCG, revealing the reduction of 4-NP in 4 minutes. Both Cu2O and g-CN played significant roles in reduction, following zero-order kinetics, unlike that which is often reported in the literature. We also evaluated the catalytic reduction with different concentrations of 4-NP and tuning the catalyst amount as well. A mechanism was postulated based on the XRD results of the post-catalytic reduction catalyst. The ACCG catalyst was also successfully tested as an effective dopamine sensor. The GC/ACCG electrode exhibited oxidation peak current density of 0.28 mA cm-2, which was much higher than those of the other catalysts. This unique combination of pure phase materials to form a composite as an effective catalyst as well as a sensor is an exclusive effort towards environmental remediation.

Rahman MY, Mat Salleh M, Oyama M. Two-Dimensional, Hierarchical Ag-Doped TiO2 Nanocatalysts: Effect of the Metal Oxidation State on the Photocatalytic Properties

This paper reports the synthesis of two-dimensional, hierarchical, porous, and (001)-faceted metal (Ag, Zn, and Al)-doped TiO₂ nanostructures (TNSs) and the study of their photocatalytic activity. Two-dimensional metal-doped TNSs were synthesized using the hydrolysis of ammonium hexafluorotitanate in the presence of hexamethylenetetramine and metal precursors. Typical morphology of metal-doped TNSs is a hierarchical nanosheet that is composed of randomly stacked nanocubes (dimensions of up to 5 μm and 200 nm in edge length and thickness, respectively) and has dominant (001) facets exposed. Raman analysis and X-ray photoelectron spectroscopy results indicated that the Ag doping, compared to Zn and Al, much improves the crystallinity degree and at the same time dramatically lowers the valence state binding energy of the TNS and provides an additional dopant oxidation state into the system for an enhanced electron-transfer process and surface reaction. These are assumed to enhance the photocatalytic of the TNS. In a model of photocatalytic reaction, that is, rhodamine B degradation, the AgTNS demonstrates a high photocatalytic activity by converting approximately 91% of rhodamine B within only 120 min, equivalent to a rate constant of 0.018 m^-1 and ToN and ToF of 94 and 1.57 min^-1, respectively, or 91.1 mmol mg^-1 W^-1 degradation when normalized to used light source intensity, which is approximately 2 times higher than the pristine TNS and several order higher when compared to Zn- and Al-doped TNSs. Improvement of the crystallinity degree, decrease in the defect density and the photogenerated electron and hole recombination, and increase of the oxygen vacancy in the AgTNS are found to be the key factors for the enhancement of the photocatalytic properties. This work provides a straightforward strategy for the preparation of high-energy (001) faceted, two-dimensional, hierarchical, and porous Ag-doped TNSs for potential use in photocatalysis and photoelectrochemical application.

Controllable synthesis of Ag@TiO2 heterostructures with enhanced photocatalytic activities under UV and visible excitation

The proposed mechanism of photo-generated charge separation and migration process in the Ag/TiO₂ nanoheterostructures under UV light.

A novel preparation for a PVA/l-histidine/AgNPs membrane and its antibacterial property

The process of preparation for PVA/l-histidine/AgNPs membrane.

Band edge movement in dye sensitized Sm-doped TiO2 solar cells: a study by variable temperature spectroelectrochemistry

Pure TiO₂ and 8 at% Sm-doped TiO₂ nanoparticles are prepared via a novel hydrolysis followed by a hydrothermal process at 473 K for 24 h and successfully used in the photoanode of dye sensitized solar cells (DSSCs).