Isolated/interacting Au islands on TiO2 NTs for the switching photocatalytic/photoelectrocatalytic degradation of refractory organic pollutants in wastewater

Fundamentals and applications of photoelectrocatalysis as an efficient process to remove pollutants from water: A review

Water pollution is an environmental problem in constant raising because of population growing, industrial development, agricultural frontier expansion, and principally because of the lack of wastewater treatment technology to remove organic recalcitrant and toxic pollutants from industrial and domestic wastewater. Recalcitrant compounds are a serious environmental and health problem mainly due to their toxicity and potential hazardous effects on living organisms, including human beings. Conventional wastewater treatments have not been able to remove efficiently pollutants from water; however, electrochemical advanced oxidation processes (EAOPs) are able to solve this environmental concern. One of the most recent EAOPs technology is photoelectrocatalysis (PEC), it consists in applying an external bias potential to a semiconductor film placed over a conductive substrate to avoid the recombination of photogenerated electron-hole (e^-/h⁺) pairs, increasing h⁺ availability and hydroxyl radicals' formation, responsible for promoting the degradation/mineralization of organic pollutants in aqueous medium. This review summarizes the recent advances in PEC as a promising technology for wastewater treatment. It addresses the fundamentals and kinetic aspects of PEC. An analysis of photoanode materials and of the configuration of photoelectrochemical reactors is also presented, including an analysis of the influence of the main operational parameters on the treatment of contaminated water. Finally, the most recent applications of PEC are reviewed, and the challenges and perspectives of PEC in wastewater treatment are discussed.

Color Tuning of Electrochromic TiO2 Nanofibrous Layers Loaded with Metal and Metal Oxide Nanoparticles for Smart Colored Windows

Co-axial electrospinning was applied for the structuring of non-woven webs of TiO2 nanofibers loaded with Ag, Au, and CuO nanoparticles. The composite layers were tested in an electrochromic half-cell assembly. A clear correlation between the nanoparticle composition and electrochromic effect in the nanofibrous composite is observed: TiO2 loaded with Ag reveals a black-brown color, Au shows a dark-blue color, and CuO shows a dark-green color. For electrochromic applications, the Au/TiO2 layer is the most promising choice, with a color modulation time of 6 s, transmittance modulation of 40%, coloration efficiency of 20 cm2/C, areal capacitance of 300 F/cm2, and cyclic stability of over 1000 cycles in an 18 h period. In this study, an unexplored path for the rational design of TiO2-based electrochromic device is offered with unique color-switching and optical efficiency gained by the fibrous layer. It is also foreseen that co-axial electrospinning can be an alternative nanofabrication technique for smart colored windows.

Facile strategy for the fabrication of noble metal/ZnS composites with enhanced photocatalytic activities

The introduction of noble metal nanoparticles to photocatalysts can effectively improve the separation efficiency of the photogenerated electron-holes. Therefore, noble metal/ZnS composites were synthesized using a low-temperature solid-phase chemical method with sodium borohydride as the reducing agent. The characterization results showed that the noble metal/ZnS composites have been successfully obtained and that the noble metals were distributed on the surface of ZnS. The catalytic results suggested that the composites exhibited improved activity after introduction of noble metals, which can be attributed to the rapid migration of carriers and the enhancement of the light absorption, mainly owing to the tight combination between the ZnS and noble metals and the plasmon resonance effect of the noble metals. The catalytic mechanism was explored by using photoluminescence spectroscopy, photocurrent spectra, valence band X-ray photoelectron spectroscopy (XPS-VB) spectra and capture agent experiments, and a possible mechanism was proposed. This work provides a new strategy for the high-volume synthesis of noble metal-based composite photocatalysts, which could be helpful for sustainable development.

Photoelectrocatalytic oxidation of 3-pyridinemethanol to 3-pyridinemethanal and vitamin B3 by TiO2 nanotubes

In this paper, the first photoelectrocatalytic 3-pyridinemethanol oxidation to 3-pyridinemethanal and vitamin B₃ was investigated.

Effects of Ag0-modification and Fe3+-doping on the structural, optical and photocatalytic properties of TiO2

Pure TiO2, Ag0-modified TiO2, Fe3+-doped TiO2, and Ag0-modified/Fe3+-doped TiO2 photocatalysts were synthesized via sol-gel technology. The crystal structure, element composition and surface morphology of the obtained photocatalysts were characterized via XRD, XPS, SEM and TEM, respectively. The results indicate that Ag-TiO2 samples show higher photocatalytic activity than pure TiO2. Unexpectedly, the photocatalytic activities of Fe-TiO2 and 1% Ag/1% Fe-TiO2 are lower than pure TiO2. To analyze the main factors affecting photocatalytic performance, the samples were further investigated by PL, DRS and BET. The results prove that the additions of Ag and Fe are advantageous for inhibiting the recombination of photoinduced pairs and improving the utilization of light. Fe-TiO2 and 1% Ag/1% Fe-TiO2 exhibit smaller specific surface areas than pure TiO2, which is the primary reason for their reduced photocatalytic performances.

Vertically aligned Pt/TiO2 nanobelt films on Ti sheets for efficient degradation of a refractory ethyl thionocarbamate collector

Noble metal modified TiO2 nanostructures on a substrate featuring a two-dimensional (2D) morphology are of great interest in wastewater remediation due to high photocatalytic activity and avoidance of separating powder catalysts from water. In this work, vertically aligned Pt/TiO2 nanobelt films (Pt/TNFs) on Ti sheets were fabricated via a synthesis strategy including an alkaline hydrothermal treatment and electrostatic self-assembly. The Pt/TNFs had a BET specific surface area of 93.35 m2 g-1, showing high adsorption capacity in removing an ethyl thionocarbamate (ETC) flotation collector. After the deposition with Pt nanoparticles, the photocatalytic activity of the TNFs increased by 94.98% with the enhanced mineralization of the ETC collector. Moreover, the Pt/TNFs on Ti sheets exhibited strong substrate adhesion enabling superior photocatalytic stability in the cyclic degradation of ETC. The solid phase extraction and gas chromatography-mass spectrometry (SPE/GC-MS) analysis revealed that seven byproducts still remained even when 100% of ETC was degraded, showing the difficulty in the complete mineralization of the ETC collector. The Pt/TNF can serve as a promising photocatalyst to treat mineral flotation wastewaters containing organic reagents.

Multiplasmon modes for enhancing the photocatalytic activity of Au/Ag/Cu2O core-shell nanorods

One of the critical challenges for semiconductor photocatalysis is the high efficiency utilization of solar energy. For plasmonic metal-semiconductor photocatalysts, the photocatalytic activity over an extended wavelength range for a photoresponsive semiconductor could be significantly improved either via the direct electron transfer (DET) or via the plasmon-induced resonant energy transfer (PIRET). Still, the narrow spectral overlap of plasmon and the semiconductor band edge is a key factor in restricting the development of PIRET. Herein, we have introduced a simple and versatile strategy to realize a broad spectral overlap by creating multipolar plasmon resonances near the semiconductor band edge. Cu₂O coated Au/Ag nanorods (NRs) were prepared using a facile wet chemistry method. Transverse plasmon modes of Au/Ag/Cu₂O NRs can split into dipole and octupole plasmon modes. The core aspect ratio and shell thickness could be used to regulate these two modes for extending the spectral overlap of plasmon resonance and the Cu₂O band edge. Au/Ag/Cu₂O NRs were found to display enhanced visible light photocatalytic activity compared to spherical Au/Ag/Cu₂O nanoparticles. The enhancement mechanism was ascribed to both dipole and octupole plasmon modes boosting electron-hole separation in Cu₂O via PIRET as confirmed by transient absorption measurements.