Simple route to enhanced photocatalytic activity of p25 titanium dioxide nanoparticles by silica addition

Designing versatile heterogeneous catalysts based on Ag and Au nanoparticles decorated on chitosan functionalized graphene oxide

Herein we report the covalent grafting of chitosan on graphene oxide (GO) followed by a simple approach for anchoring silver (AgNPs) and gold (AuNPs) nanoparticles onto a chitosan grafted graphene oxide surface by a NaBH4 reduction method. Catalytic activity of prepared heterogeneous GO grafted chitosan stabilized silver and gold nanocatalysts (GO-Chit-Ag/AuNPs) was explored for the reduction of aromatic nitroarenes and degradation of hazardous azo dyes in the presence of NaBH4. Both catalysts were found to exhibit excellent catalytic activity towards the reduction of aromatic nitroarenes and azo dyes degradation. Furthermore, the nanocatalysts were found to be selective towards the reduction of nitro groups in halonitroarenes without any dehalogenation under mild conditions.

Investigation of the Photodegradation of Reactive Blue 19 on P-25 Titanium Dioxide: Effect of Experimental Parameters

The photocatalytic decolorization and degradation of an anthraquinone-based reactive dye, C.I. Reactive Blue 19, was carried out in laboratory-scale experiments with the systematic variation of several operational parameters, including electron acceptor (hydrogen peroxide) concentration, initial pH, use of buffer solution, aeration, and the specific chemical nature of the buffer solution. Photodegradation was performed under simulated natural light, and conditions were chosen to mimic those found in industry. Mineralization and decolorization were monitored by UV-vis spectroscopy and total organic carbon analysis, and kinetics were modelled using an in-series first-order combination mechanism. Reaction products were examined and monitored by high-resolution mass spectrometry. Under the conditions explored, the reaction rate was found to depend not only on pH and electron acceptor concentration, but also on the specific chemical nature of the buffer used.

Adenovirus inactivation by in situ photocatalytically and photoelectrocatalytically generated halogen viricides

This study investigates and compares the virucidal performances of photocatalytic (PC) and photoelectrocatalytic (PEC) treatments in the presence and absence of halides, such as Br^- and Cl^-, under comparable experimental conditions. The results confirm that the PC virucidal efficiency can be enhanced in the presence of low halide concentrations (e.g., X = Br^- or Cl^-) and further enhanced by applying potential bias onto the photoanode in a PEC system. The PEC treatment in the presence of 1.0 mM Br (PEC-Br) shows the highest virucidal efficiency, enabling complete inactivation of a ∼1000 TCID50 replication-deficient recombinant adenovirus (RDRADS) population within 31.7 s. The superior virucidal performances of PEC-X treatments can be attributed to the increased production of active oxygen species and additional viricides resulting from the PEC halide oxidation, as well as prolonged lifetime of photoholes (h⁺ ) for direct inactivation. The findings of this work confirm that new forms of active species generated in situ via a PC or PEC process are effective for viruses.

Facile synthesis of TiO2 hollow spheres composed of high percentage of reactive facets for enhanced photocatalytic activity

In this study, facile synthesis of hollow TiO₂ spheres composed of a high percentage of reactive facets (~85%) is successfully prepared with TiOSO₄ and HBF₄ by the hydrothermal method.

Silica decorated TiO2 for virus inactivation in drinking water--simple synthesis method and mechanisms of enhanced inactivation kinetics

A new method of modifying TiO2 photocatalysts with SiO2 is developed in which SiO2 nanoparticles are simply mixed with TiO2 in water under ambient conditions. This method does not require the use of toxic solvents or significant energy input. Although the SiO2 modification slightly reduces hydroxyl free radical production, the composite SiO2-TiO2 nanomaterials have markedly higher photocatalytic inactivation rates for a common surrogate virus, bacteriophage MS2 (up to 270% compared to the unmodified TiO2), due to the greatly improved adsorptive density and dark inactivation of MS2. The Langmuir isotherm describes the adsorption data well and shows that the TiO2 modified with 5% SiO2 has a maximum adsorption density qmax 37 times that of the unmodified TiO2. The Langmuir-Hinshelwood model fits the photocatalytic inactivation kinetic data well. The SiO2-TiO2 material produces a greater maximum initial inactivation rate yet a lower intrinsic surface reaction rate constant, consistent with the reduced hydroxyl radical production and enhanced adsorption. These results suggest that modifying photocatalyst surface to increase contaminant adsorption is an important strategy to improve photocatalytic reaction efficiency. Simple and cheap synthesis methods such as that used in this study bring photocatalysis closer to being a viable water treatment option.

Enabling antibacterial coating via bioinspired mineralization of nanostructured ZnO on fabrics under mild conditions

Herein, we present an environmentally benign method capable of mineralization and deposition of nanomaterials to introduce antibacterial functionalities into cotton fabrics under mild conditions. Similar to the way in which many naturally occurring biominerals evolve around the living organism under ambient conditions, this technique enables flexible substrates like the cotton fabric to be coated with inorganic-based functional materials. Specifically, our strategy involves the use of long-chain polyamines known to be responsible in certain biomineralization processes, to nucleate, organize, and deposit nanostructured ZnO on cotton bandage in an aqueous solution under mild conditions of room temperature and neutral pH. The ZnO-coated cotton bandages as characterized by SEM, confocal micro-Raman spectroscopy, XRD, UV-DRS, and fluorescence microscopy demonstrate the importance of polyamine in generating a stable and uniform coating of spindle-shaped ZnO particles on individual threads of the fabric. As the coating process requires only mild conditions, it avoids any adverse effect on the thermal and mechanical properties of the substrate. Furthermore, the ZnO particles on cotton fabric show efficient antibacterial activity against both gram-positive and gram-negetive bacteria. Therefore, the developed polyamine mediated bioinspired coating method provides not only a facile and "green" synthesis for coating on flexible substrate but also the fabrication of antibacterial enabled materials for healthcare applications.

Chlortetracycline degradation by photocatalytic ozonation in the aqueous phase: mineralization and the effects on biodegradability

Chlortetracycline (CTC) is a hazardous material in aquatic environments. This study was focused on optimization of photocatalytic ozonation processes for removal of CTC from wastewater at pH 2.2 and 7.0. In this study, the tested processes for CTC removal were arranged from the least efficient to the most efficient as: UV, UV/TiO2, O3, O3/UV and O3/UV/TiO2. Ozonation efficiency was due to ozone affinity for electron-rich sites on the CTC molecule. In the O3/UV and O3/UV/TiO2 processes, efficiency was increased by the photolysis of CTC and generation of *OH. At pH 7.0, all the processes were more efficient for CTC degradation than at pH 2.2 due to CTC speciation, ozone decay to *OH and the attractions between ionized CTC and TiO2 particles. UV/O3 at pH 7.0 showed an additive effect while other combination processes showed a synergistic effect that resulted in higher rates of reactions than the sums of individual reaction rates. The TOC removal ranged from 8% to 41% after one hour of reaction, with the above-mentioned order of efficiency. The biodegradability increased rapidly during the early minutes of the reaction. A reaction time of 10-15 min was sufficient for near maximum biodegradability, making these processes good pretreatments for the biological processes.

Recent Development on Titania Based Mixed Oxide Photocatalysts for Environmental Application under Visible Light

In the recent years most of the studies are confined to the mixing of ZrO2, SiO2, WO4 or ceria with titania in different composition so as to stabilize anatase phase, maintain high surface area and increase visible light absorption for better photocatalytic activity. Method of synthesis also helps in effective doping and enhancing surface area of the resultant materials. Nonmetal doping of oxide semiconductor materials facilitates the visible light application of photocatalysis. Based on the recent literature this review elaborately discuss on the development of titania based mixed oxide catalyst with or without different doping for visible light application. In addition this review deals with critical analysis of these materials towards photocatalytic oxidation of organics and reduction of pollutants like toxic metal ions and nitrates.

Mesoporous hollow sphere titanium dioxide photocatalysts through hydrothermal silica etching

Robust, monodisperse, mesoporous titanium dioxide (TiO₂) submicrometer hollow spheres were synthesized through a single step hydrothermal silica etching reaction under mild conditions. Efficient silica (SiO₂) removal was achieved without the use of toxic reagents, and a unique controllable silica redeposition mechanism was identified, imparting the hollow spheres with excellent structural integrity. The parameters of the hydrothermal reaction affecting the etching process, including pH, temperature, and silica concentration, were systematically investigated and optimized for the production of silica-templated hollow structures. The resulting processing conditions yielded TiO₂ hollow spheres with a surface area of ∼300 m² g⁻¹ and anatase phase crystallization, which exhibited high adsorption capacity for methylene blue dye and good photocatalytic activity without requiring high-temperature calcination.

A comparative study on aggregation/sedimentation of TiO2 nanoparticles in mono- and binary systems of fulvic acids and Fe(III)

The aggregation/sedimentation potentials of TiO(2) nanoparticles were studied in mono- and binary systems of Suwannee River fulvic acids (SRFA) and Fe(III) at different pH values. SRFA adsorption significantly enhanced the stability of TiO(2) nanoparticles at pH 4, 6 and 8, mainly due to the dramatic increase in negative surface charges. The presence of Fe(III) stabilized aggregation/sedimentation of TiO(2) nanoparticles at pH 4 due to the increasing positive charges after Fe(III) sorption, but destabilized aggregation/sedimentation at pH 6 and 8 attributed to the bridging effect of Fe(III)-hydroxy. The formation of COO-Fe(III) complex was found in binary system of SRFA and Fe(III). Thus, the positive charges that Fe(III) imparted to nanoparticles were neutralized by SRFA. Compared with those in mono-system of Fe(III), SRFA enhanced aggregation/sedimentation at pH 4, while stabilized TiO(2) nanoparticles at higher pH in binary system of SRFA and Fe(III). The sedimentation rates of TiO(2) nanoparticles showed relatively lower coefficient with zeta potentials (-0.883, P<0.01) than with hydrodynamic particle sizes (0.964, P<0.01), due to the steric hindrance of SRFA and the bridging effect of Fe(III)-hydroxy, which was confirmed by DLVO calculation. These results have important implications for prediction of the stability and fate of nanoparticles in natural water.