Effects of the amount of Au nanoparticles on the visible light response of TiO2 photocatalysts

Noble Metal Nanoparticle-Loaded Porphyrin Hexagonal Submicrowires Composites (M-HW): Photocatalytic Synthesis and Enhanced Photocatalytic Activity

Surface plasmon resonance (SPR) photocatalysts have attracted considerable attention because of their strong absorption capacity of visible light and enhanced photogenic carrier separation efficiency. However, the separate production of metal nanoparticles (NPs) and semiconductors limits the photogenic charge transfer. As one of the most promising organic photocatalysts, porphyrin self-assemblies with a long-range ordered structure-enhance electron transfer. In this study, plasmonic noble metal-based porphyrin hexagonal submicrowires composites (M-HW) loaded with platinum (Pt), silver (Ag), gold (Au), and palladium (Pd) NPs were synthesized through a simple in situ photocatalytic method. Homogeneous and uniformly distributed metal particles on the M-HW composites enhanced the catalytic or chemical properties of the organic functional nanostructures. Under the same loading of metal NPs, the methyl orange photocatalytic degradation efficiency of Ag-HW [k_Ag-HW (0.043 min^-1)] composite was three times higher than that of HW, followed by Pt-HW [k_Pt-HW (0.0417 min^-1)], Au-HW [k_Au-HW (0.0312 min^-1)], and Pd-HW [k_Pd-HW (0.0198 min^-1)]. However, the rhodamine B (RhB) and eosin B photocatalytic degradations of Pt-HW were 4 times and 2.6 times those of HW, respectively. Finally, the SPR-induced electron injection, trapping, and recombination processes of the M-HW system were investigated. These results showed that M-HW plasmonic photocatalysts exhibited excellent photocatalytic performances, making them promising materials for photodegrading organic pollutants.

Template-assisted synthesis of Ag/AgCl hollow microcubes and their composition-dependent photocatalytic activity for the degradation of phenol

Plasmonic photocatalysts with hollow structures and tunable composition exhibit significant advantages due to their high efficiency in light collection and effective charge transfer across the tight contact heterojunction interface. Herein, hollow Ag/AgCl microcubes were developed by treating nanosheet-assembled hollow Ag microcubes with FeCl3, where a part of Ag at the interface could be in situ transformed and oxidized into AgCl. Equally, by adjusting the concentration of Fe3+ ions, Ag/AgCl hollow microcubes with different compositions could be easily achieved. Electron transfer was favored by a lot of tiny Ag/AgCl heterojunctions induced by the in situ oxidation of the multicrystalline Ag hollow microcube template containing a number of grain boundaries. The designed hollow Ag/AgCl microcubes exhibited strong visible-light adsorption owing to the surface plasmon resonance effect of Ag nanoparticles, in addition to the multiple light-reflections inside the hollow structure. The as-obtained products were then used as visible-light photocatalysts, where the results indicated that 91.6% of phenol was degraded within 150 min under visible light by the as-obtained sample with a Ag to AgCl ratio of 1 : 3. The superior visible-light photocatalytic activity resulted from the enhancement of the visible light-harvesting and the efficient charge separation at the Ag and AgCl contact interfaces.

Impact of Titanium Dioxide (TiO2) Modification on Its Application to Pollution Treatment—A Review

A high-efficiency method to deal with pollutants must be found because environmental problems are becoming more serious. Photocatalytic oxidation technology as the environmentally-friendly treatment method can completely oxidate organic pollutants into pollution-free small-molecule inorganic substances without causing secondary pollution. As a widely used photocatalyst, titanium dioxide (TiO2) can greatly improve the degradation efficiency of pollutants, but several problems are noted in its practical application. TiO2 modified by different materials has received extensive attention in the field of photocatalysis because of its excellent physical and chemical properties compared with pure TiO2. In this review, we discuss the use of different materials for TiO2 modification, highlighting recent developments in the synthesis and application of TiO2 composites using different materials. Materials discussed in the article can be divided into nonmetallic and metallic. Mechanisms of how to improve catalytic performance of TiO2 after modification are discussed, and the future development of modified TiO2 is prospected.

Synthesis of Supported Metal Nanoparticles (Au/TiO2) by the Suspension Impregnation Method

This work reports a new technique called “Suspension Impregnation Method” (SiM) as an alternative to the “Incipient Impregnation Method” (IiM) for the synthesis of noble metal (Au) nanoparticles. The SiM was used to synthesize gold nanoparticles supported by titanium oxide and compared with those of IiM. The reactor for the SiM technique was based on the principles of mixing, heat, and mass transfer of the suspension reactors and the metal particle synthesis was processed in situ under the oxidation reduction potentials. Three different conditions were established to observe the effect of pH on the size of the metal particles: acid (HCl), neutral (water) and alkaline (urea). The samples were characterized by nitrogen adsorption, X-Ray Diffraction (XRD), Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES), Thermogravimetric Analysis (TGA)/Differential Thermal Analysis (DTA), Transmission Electron Microscopy (TEM) and CO2 adsorption. The surface area was slightly modified, and the average pore diameter was reduced in all materials. The structure of the titanium oxide was not altered. A deposit of organic material was detected in samples synthesized in alkaline medium for both methods. The pH influenced the formation of conglomerates in IiM and resulted in large particle sizes (3–9 nm). In contrast, an in situ reduction in the species in SiM resulted in smaller particle sizes than IiM (2–3 nm).