Construction of graphene-WO3/TiO2 nanotube array photoelectrodes and its enhanced performance for photocatalytic degradation of dimethyl phthalate

In-situ electrodeposition synthesis of Z-scheme rGO/g-C3N4/TNAs photoelectrodes and its degradation mechanism for oxytetracycline in dual-chamber photoelectrocatalytic system

The dual-chamber photoelectrocatalytic (PEC) system possess advantages in the degradation efficiency and processing cost of organic contaminants. In this study, TiO₂ nanotube arrays modified by rGO and g-C₃N₄ (rGO/g-C₃N₄/TNAs) photoelectrodes were successfully prepared. The surface micromorphology, chemical structure, crystal structure, and basic element composition of rGO/g-C₃N₄/TNAs photoelectrodes were studied by SEM, FTIR, XRD, Raman, and XPS. UV-vis absorption, photoluminescence (PL) spectra, and photoelectrochemical (PECH) tests were used to explore the photoelectrochemical characteristics of rGO/g-C₃N₄/TNAs photoelectrodes. Under simulated sunlight illumination, the dual-chamber PEC system with external bias voltage was used to investigate the degradation of oxytetracycline (OTC) on rGO/g-C₃N₄/TNAs photoelectrodes. The results showed that rGO and g-C₃N₄ were successfully loaded on TNAs, and the separation efficiency of electrons and holes at rGO/g-C₃N₄/TNAs photoelectrodes was improved. The light absorption range of rGO/g-C₃N₄/TNAs photoelectrodes extends to the visible light region and has better light absorption performance. Compared with the photocatalytic process, when 1.2 V bias voltage was applied, the degradation efficiency of OTC in anode and cathode chambers in PEC were increased by 3.28% and 44.01% within 60 min, respectively. In addition, the anode and cathode chambers have different degradation effects on OTC. Both the external bias voltage and initial pH have significant effects in cathode chamber, but have little effect in photoanode chamber. The fluorescence excitation-emission matrix spectra and liquid chromatography-tandem mass spectrometry showed that there were different intermediates in the degradation process of OTC. This study indicated that for the dual-chamber PEC system, rGO/g-C₃N₄/TNAs photoelectrodes exhibited excellent photocatalytic performance and have potential application prospects in water environmental remediation.

Recent Achievements in Development of TiO2-Based Composite Photocatalytic Materials for Solar Driven Water Purification and Water Splitting

Clean water and the increased use of renewable energy are considered to be two of the main goals in the effort to achieve a sustainable living environment. The fulfillment of these goals may include the use of solar-driven photocatalytic processes that are found to be quite effective in water purification, as well as hydrogen generation. H2 production by water splitting and photocatalytic degradation of organic pollutants in water both rely on the formation of electron/hole (e-/h+) pairs at a semiconducting material upon its excitation by light with sufficient photon energy. Most of the photocatalytic studies involve the use of TiO2 and well-suited model compounds, either as sacrificial agents or pollutants. However, the wider application of this technology requires the harvesting of a broader spectrum of solar irradiation and the suppression of the recombination of photogenerated charge carriers. These limitations can be overcome by the use of different strategies, among which the focus is put on the creation of heterojunctions with another narrow bandgap semiconductor, which can provide high response in the visible light region. In this review paper, we report the most recent advances in the application of TiO2 based heterojunction (semiconductor-semiconductor) composites for photocatalytic water treatment and water splitting. This review article is subdivided into two major parts, namely Photocatalytic water treatment and Photocatalytic water splitting, to give a thorough examination of all achieved progress. The first part provides an overview on photocatalytic degradation mechanism principles, followed by the most recent applications for photocatalytic degradation and mineralization of contaminants of emerging concern (CEC), such as pharmaceuticals and pesticides with a critical insight into removal mechanism, while the second part focuses on fabrication of TiO2-based heterojunctions with carbon-based materials, transition metal oxides, transition metal chalcogenides, and multiple composites that were made of three or more semiconductor materials for photocatalytic water splitting.

WO3/p-Type-GR Layered Materials for Promoted Photocatalytic Antibiotic Degradation and Device for Mechanism Insight

Graphene enhanced WO₃ has recently become a promising material for various applications. The understanding of the transfer of charge carriers during the photocatalytic processes remains unclear because of their complexity. In this study, the characteristics of the deposited WO₃/graphene layered materials were investigated by Raman spectroscopy, UV-vis spectroscopy, and SEM. According to the results, p-graphene exhibits and enhances the characteristics of the WO₃/graphene film. The photocatalytic activities of WO₃/graphene layered materials were assessed by the photocatalytic degradation of oxytetracycline antibiotics as irradiated by UV light. Here, a higher current of cyclic voltammetry and a higher resistance of impedance spectra were obtained with the as-grown WO₃/graphene directly synthesized on Cu foils under UV light using an electrochemical method, which was different from traditional WO₃ catalysts. Thus, it is urgent to explore the underlying mechanism in depth. In this study, a large layered material WO₃/graphene was fabricated on a Si substrate using a modified CVD method, and a WO₃/graphene device was developed by depositing a gold electrode material and compared with a WO₃ device. Due to photo-induced doping effects, the current-voltage test suggested that the photo-resistance is larger than dark-resistance, and the photo-current is less than the dark current based on WO₃/graphene layered materials, which are significantly different from the characteristics of the WO₃ layered material. A new pathway was developed here to analyze the transfer properties of carriers in the photocatalytic process.

Noble metal-modified titania with visible-light activity for the decomposition of microorganisms

Commercial titania photocatalysts were modified with silver and gold by photodeposition, and characterized by diffuse reflectance spectroscopy (DRS), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning transmission electron microscopy (STEM). It was found that silver co-existed in zero valent (core) and oxidized (shell) forms, whereas gold was mainly zero valent. The obtained noble metal-modified samples were examined with regard to antibacterial (Escherichia coli (E. coli)) and antifungal (Aspergillus niger (A. niger), Aspergillus melleus (A. melleus), Penicillium chrysogenum (P. chrysogenum), Candida albicans (C. albicans)) activity under visible-light irradiation and in the dark using disk diffusion, suspension, colony growth ("poisoned food") and sporulation methods. It was found that silver-modified titania, besides remarkably high antibacterial activity (inhibition of bacterial proliferation), could also decompose bacterial cells under visible-light irradiation, possibly due to an enhanced generation of reactive oxygen species and the intrinsic properties of silver. Gold-modified samples were almost inactive against bacteria in the dark, whereas significant bactericidal effect under visible-light irradiation suggested that the mechanism of bacteria inactivation was initiated by plasmonic excitation of titania by localized surface plasmon resonance of gold. The antifungal activity tests showed efficient suppression of mycelium growth by bare titania, and suppression of mycotoxin generation and sporulation by gold-modified titania. Although, the growth of fungi was hardly inhibited through disc diffusion (inhibition zones around discs), it indicates that gold does not penetrate into the media, and thus, a good stability of plasmonic photocatalysts has been confirmed. In summary, it was found that silver-modified titania showed superior antibacterial activity, whereas gold-modified samples were very active against fungi, suggesting that bimetallic photocatalysts containing both gold and silver should exhibit excellent antimicrobial properties.