Highly efficient visible light induced photoelectrochemical anticorrosion for 304 SS by Ni-doped TiO2

Progress in semiconductor materials for photocathodic protection: Design strategies and applications in marine corrosion protection

Metal protection of offshore equipment is very complicated owing to the complex marine environment. Photocathodic protection (PCP) is one of the popular research topics in marine metal protection. The protection efficiency of photoanode depends largely on the photoelectric properties of semiconductor materials, viz. the process of charge separation, charge migration, and light absorption. In this article, the enhancement strategies, photoelectrochemical properties, and electron transfer mechanisms of different composites for PCP were reviewed and highlighted. Some photoanodes with unusual and striking properties were emphasized. In addition, the outlooks and challenges of the application of PCP and the design of photoanodes materials are proposed.

Direct Z-scheme MgIn2S4/TiO2heterojunction for enhanced photocathodic protection of metals under visible light

To improve the photocathodic protection performance of traditional TiO₂photoanodes for metals, constructing a Z-scheme heterojunction is one of the most promising and creative strategies. Herein, we fabricated a novel Z-scheme MgIn₂S₄nanosheets/TiO₂nanotube nanocomposite through anodization and hydrothermal method. The optimized Z-scheme MgIn₂S₄/TiO₂nanocomposites exhibited stronger visible light absorption, higher separation efficiency of photoelectrons and photocathodic protection performances in comparison to pure TiO₂. The theoretical analysis and experimental results show that the Z-scheme heterojunction and oxygen vacancies jointly improved the separation efficiency of photogenerated electron-hole pairs and visible light absorption capacity, thereby improving the photoelectric conversion performance of the MgIn₂S₄/TiO₂nanocomposites. Furthermore, the influence of the precursor solution concentration on the photocathodic protection performances of the composites was investigated. As a result, when the concentration of magnesium source in the precursor solution was 0.06 mmol, the prepared MgIn₂S₄/TiO₂-0.06 displayed the best photocathodic protection performance. In addition, the hydroxyl radicals (·OH) generated in the electron spin resonance (ESR) experiment verified the Z-scheme heterojunction mechanism of the MgIn₂S₄/TiO₂composite, and also demonstrated the excellent redox performance of the composite. This work provides valuable reference for the construction of high-performance Z-scheme heterojunctions for photocathode protection of metals.

Role of NiO Nanoparticles in Enhancing Structure Properties of TiO2 and Its Applications in Photodegradation and Hydrogen Evolution

Pure and modified mesoporous TiO2 nanoparticles with different loadings of NiO (3-20.0 wt %) were prepared through the surfactant-assisted sol-gel approach with the use of cetyltrimethylammonium bromide as a template. The optical and structural properties of different samples were examined using N2 adsorption-desorption analysis, energy-dispersive spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, UV-vis spectroscopy, Fourier transform infrared spectroscopy, and photoluminescence (PL) spectroscopy. X-ray diffraction results confirmed the insertion of Ni2+ into the lattice of TiO2, and the crystallite size reduced remarkably after the addition of NiO. The diffuse reflectance spectroscopy spectra displayed obvious red shift in the absorption edges, and new absorption bands appeared in the visible region when NiO was added, which indicates the formation of surface defects and oxygen vacancies. The optical band gap of TiO2 reduced sharply when the contents of NiO were increased. The increase in the surface defects as well as oxygen vacancies were examined using PL spectroscopy. The photocatalytic performance of the as-synthesized samples was investigated over photodegradation of brilliant green (BG) and phenol and hydrogen generation under visible light. 10% NiO/TiO2 exhibited the highest photocatalytic efficiency. The photocatalytic activity was improved due to the creation of a p-n junction at the interface of NiO/TiO2, which efficiently promotes the separation of photogenerated electron/hole pairs and consequently enhances its photodegradation activity. According to the photocatalytic activity results, NiO contents were considered one of the most important factors affecting the photodegradation of BG and phenol and H2 evolution. Also, we discussed the mechanism of photodegradation, mineralization (total organic carbon), and photocatalytic reaction kinetics of BG and phenol.

Facile and Green Synthesis of Silver Quantum Dots Immobilized onto a Polymeric CTS-PEO Blend for the Photocatalytic Degradation of p-Nitrophenol

Immobilization of inorganic metal quantum dots (especially, noble transition metals) onto organic polymers to synthesize nanometal-polymer composites (NMPCs) has attracted considerable attention because of their advanced optical, electrical, catalytic/photocatalytic, and biological properties. Herein, novel, highly efficient, stable, and visible light-active NMPC photocatalysts consisting of silver quantum dots (Ag QDs) immobilized onto polymeric chitosan-polyethylene oxide (CTS-PEO) blend sheets have been successfully prepared by an in situ self-assembly facile casting method as a facile and green approach. The CTS-PEO blend polymer acts as a reducing and a stabilizing agent for Ag QDs which does not generate any environmental chemical pollutant. The prepared x wt % Ag QDs/CTS-PEO composites were fully characterized through X-ray diffraction, Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis, and UV/visible spectroscopy. The characterization results indicated the successful synthesis of the Ag QDs/CTS-PEO composites by the interactions and complexation between x wt % Ag QDs and CTS-PEO blend sheets. TEM images revealed small granules randomly distributed onto the CTS-PEO blend sheets, indicating the immobilization of Ag QDs onto CTS-PEO composites. The presence of a surface plasmon resonance (SPR) band and the shifting of the absorption edge toward higher wavelengths in the UV/vis spectra indicated the formation of x wt % Ag QDs/CTS-PEO composites. The Ag QDs in the polymeric blend matrix led to remarkable enhancement in the optical, thermal, electrical, and photocatalytic properties of x wt % Ag QDs/CTS-PEO composites. The photocatalytic efficiency of the prepared composites was evaluated by the photodegradation of p-nitrophenol (PNP) under simulated sunlight. The maximum photocatalytic degradation reached 91.1% efficiency within 3 h for the 12.0 wt % Ag QDs/CTS-PEO photocatalyst. Generally, the Ag QDs immobilized onto CTS-PEO blend composites significantly enhance the SPR effect and the synergistic effect and reduce the band gap, leading to a high photocatalytic activity.

Preparation of FeS2/TiO2 nanocomposite films and study on the performance of photoelectrochemistry cathodic protection

FeS2/TiO2 nanotube array composite films with clean, high efficiency, low cost and low consumption were prepared by electrochemical anodization and hydrothermal methods. The modification of FeS2 nanoparticles on the surface of TiO2 nanotube array film not only broadens the light absorption range of TiO2, but also improves the utilization ratio of visible light and the separation rate of photogenerated electron-hole pairs, which greatly improves the photoelectrochemical cathodic protection performance of TiO2 for 304 stainless steel (304SS). Under visible light irradiation, the open circuit potential of 304SS coupled with the FeS2/TiO2 nanocomposite films decreased from - 170 to - 700 mV, and the electrode potential can still maintained at - 400 mV after the light was turned off. Compared with pure TiO2 nanotube array film, FeS2/TiO2 nanocomposite film has better photoelectrochemical cathodic protection effect on 304SS in 3.5 wt% NaCl corrosion medium.

Preparation of SnIn4S8/TiO2 Nanotube Photoanode and Its Photocathodic Protection for Q235 Carbon Steel Under Visible Light

TiO₂ is an attractive semiconductor suitable for photocathodic protection, but its weak absorption of visible light and low quantum yield limit its usage. Here, a new heterostructured SnIn₄S₈ nanosheet/TiO₂ nanotube photoanode was prepared and its photocathodic protection performance was analyzed. SnIn₄S₈ nanosheets were uniformly deposited on the surface of the TiO₂ nanotube via a solvothermal treatment. The SnIn₄S₈/TiO₂ composite exhibited better photocathodic protection performance compared with pure TiO₂ nanotubes, owing to its good visible-light response and photogenerated carrier separation efficiency. Moreover, the composite exhibited a maximum photocurrent density of 100 μA cm^-2 for a 6 h solvothermal reaction under visible light irradiation. The negative shift of the photoinduced potential of Q235 carbon steel connected to the composite could reach 0.45 V versus SCE. Therefore, the SnIn₄S₈/TiO₂ composite can offer efficient photocathodic protection for Q235 carbon steel against corrosion in 3.5 wt% NaCl solution. This work provides a new approach for the development of high-efficient photoanode materials for the photocathodic protection of metals.

Research progress of TiO2 photocathodic protection to metals in marine environment

Corrosion protection has become an important issue as the amount of infrastructure construction in marine environment increased. Photocathodic protection is a promising method to reduce the corrosion of metals, and titanium dioxide (TiO₂) is the most widely used photoanode. This review summarizes the progress in TiO₂ photogenerated protection in recent years. Different types of semiconductors, including sulfides, metals, metal oxides, polymers, and other materials, are used to design and modify TiO₂. The strategy to dramatically improve the efficiency of photoactivity is proposed, and the mechanism is investigated in detail. Characterization methods are also introduced, including morphology testing, light absorption, photoelectrochemistry, and protected metal observation. This review aims to provide a comprehensive overview of TiO₂ development and guide photocathodic protection.

Theoretical investigation on the photoelectrochemical anticorrosion mechanism of SnO2–TiO2nanotube

In this work, the calculated electron density difference, Bader charge analysis and the density of states (DOS) of SnO2–TiO2-nanotubes (NTs) indicate that the electrons are transferred from the Ti atoms of TiO2into the O atoms of (SnO[Formula: see text] in SnO2–TiO2-NTs and the supported (SnO[Formula: see text] cluster acts as the role of storage for photogenerated electrons excited from TiO2-NTs, which is in good agreement with experimental results that the SnO2–TiO2-NTs composite films have higher photocurrent density for photocathodic protection of 304 stainless steel (304SS). The theoretical investigations provide a plausible explanation for the photoelectrochemical anticorrosion mechanism of SnO2–TiO2-NTs using periodic density functional theory (DFT).

Reduced energy offset via substitutional doping for efficient organic/inorganic hybrid solar cells

Charge carrier transport in bulk heterojunction that is central to the device performance of solar cells is sensitively dependent on the energy level alignment of acceptor and donor. However, the effect of energy level regulation induced by nickel ions on the primary photoexcited electron transfer and the performance of P3HT/TiO₂ hybrid solar cells remains being poorly understood and rarely studied. Here we demonstrate that the introduction of the versatile nickel ions into TiO₂ nanocrystals can significantly elevate the conduction and valence band energy levels of the acceptor, thus resulting in a remarkable reduction of energy level offset between the conduction band of acceptor and lowest unoccupied molecular orbital of donor. By applying transient photoluminescence and femtosecond transient absorption spectroscopies, we demonstrate that the electron transfer becomes more competitive after incorporating nickel ions. In particular, the electron transfer life time is shortened from 30.2 to 16.7 ps, i.e., more than 44% faster than pure TiO₂ acceptor, thus leading to a notable increase of power conversion efficiency in organic/inorganic hybrid solar cells. This work underscores the promising virtue of engineering the reduction of 'excess' energy offset to accelerate electron transport and demonstrates the potential of nickel ions in applications of solar energy conversion and photon detectors.