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A BiVO4/TiO2 nanotube composite film was fabricated by anodization and low temperature solvothermal reaction for photocathodic protection. The results showed that after modifying the TiO2 nanotube film with BiVO4 nanoparticles, the light absorption of the BiVO4/TiO2 composite film was extended to the visible region. The photocurrent density of the composite film reached 271 μA cm−2, and was 8.5 times higher than that of the TiO2 film. Under white light irradiation, the composite film made the potential of the coupled 403 stainless steel in a 0.5 M NaCl solution drop by 520 mV, showing an effective photocathodic protection effect.

In order to obtain a TiO2 composite film with improved photoelectrochemical properties, a TiO2 nanotube array (NTA) film was constructed on a Ti substrate via anodization, then Ag nanoparticles (NPs) and carbon quantum dots (CQDs) were successively deposited on the TiO2 NTA film by pulse current deposition and hydrothermal treatment, respectively. After the sensitization by CQDs and Ag NPs, the light absorption of the TiO2 composite film was extended to the visible region. Under white light irradiation, the photocurrent density of the composite film in a 0.5 M Na2SO4 solution reached 110 μA cm−2, much higher than that (60 μA cm−2) of the single TiO2 film. The CQDs/Ag/TiO2 composite film as a photoanode showed an improved photocathodic protection effect, which made the potential of the coupled 403 stainless steel (403SS) in the 0.5 M NaCl solution drop by 400 mV relative to its corrosion potential.

In order to obtain a TiO2 nanocomposite film with enhanced photoelectrochemical properties for corrosion protection of metals, a TiO2 nanotube film was fabricated on a Ti substrate via anodization, then ZnIn2S4 nanosheets and CdSe nanoparticles were sequentially deposited on the TiO2 film by hydrothermal treatment and electrodeposition, respectively. The CdSe/ZnIn2S4 co-modified TiO2 heterostructured nanocomposite film showed remarkably enhanced visible light absorption and photoelectrochemical properties. Under white light irradiation, the photocurrent density of the nanocomposite film in the mixed solution with 0.1 M Na2S and 0.1 M Na2SO3 was 33 times higher than that of the TiO2 film. The nanocomposite could negatively shift the potential of the coupled 403 stainless steel immersed in a 0.5 M NaCl solution by 440 mV, showing efficient photoelectrochemical cathodic protection.

An ordered TiO2 nanotube array (NTA) film was first fabricated on a Ti substrate by anodization, β-Bi2O3 nanoparticles were then electrodeposited on the film for obtaining a heterostructured β-Bi2O3-TiO2 NTA composite film with enhanced photocathodic protection performances. Compared to the bare TiO2 NTA film, the composite film showed a wider light absorption region and higher charge carrier separation efficiency. Under white light illumination, the composite film as a photoanode made the potential of 403 stainless steel in a 0.5 M NaCl solution decrease by 450 mV relative to its corrosion potential, showing an effective photoelectrochemical cathodic protection effect.

A TiO2 nanotube film was fabricated on a Ti foil via anodization, SnO2 quantum dots were deposited on the film by hydrothermal treatment, and then Ag nanoparticles were formed on the SnO2/TiO2 film by pulse electrodeposition to obtain a Ag/SnO2 co-modified TiO2 composite photoanode with good photocathodic protection performance and charge storage ability. The properties of the composite film were investigated by surface analyses, UV–vis and fluorescence spectroscopies, and photoelectrochemical measurements. The results showed that the light absorption of the Ag/SnO2/TiO2 film was extended into the visible region compared with the TiO2 film. The photocurrent intensity of the composite film was two times as high as that of the TiO2 film. The composite photoanode under illumination by white light made the potential of the coupled 403 stainless steel (403SS) in a 0.5 M NaCl solution drop by 475 mV in contrast with its corrosion potential, showing an enhanced photocathodic protection effect. It is noteworthy that the 403SS potential was still 270 mV lower than the corrosion potential within 22.5 h after cutting off the illumination, demonstrating that the cathodic protection could be maintained through the charge storage ability of the composite photoanode.

Study on the corrosion behavior of reinforcing steel is one of the most significant research topics in the field of corrosion and protection of metals. The scanning microelectrode technique is a powerful tool to study localized corrosion behavior of reinforcing steel in a corrosive solution. In this work, the corrosion behavior of reinforcing steel in a simulated concrete pore solution with Cl- and the inhibition effect of a mixture of NaNO2 and Na2SiO3 on the steel were studied by the scanning microelectrode technique assisted by polarization curve measurements and surface analyses. Q235 reinforcing steel was used as the tested material. The cylindrical steel specimen with dimension of Æ1.14 cm ´ 0.50 cm was sealed in a PVC holder enveloped with epoxy resin, and only a cross section (1.00 cm2) of the steel served as the working surface. Before experiments, the steel specimen was sequentially polished by silicon carbide sandpaper up to 1500 grit and 0.3 µm Al2O3 powder, and then ultrasonically cleaned in deionized water and ethanol. A saturated Ca(OH)2 solution was used as the simulated concrete pore (SCP) solution. The simulated polluted concrete pore (SPCP) solution was prepared from SCP solution by adjusting its pH to 11.50 with deionized water and adding 0.05 M NaCl. NaNO2 and Na2SiO3 with different concentrations as corrosion inhibitors were added to the SPCP solution. The potential distribution on the reinforcing steel surface was measured by a home-built scanning microelectrode measurement system. Ag/AgCl electrodes were used as a scanning microprobe and a micro-reference electrode. Polarization curve measurements were carried out by an Autolab Potentiostat Galvanostat. A three–electrode cell was used with the steel specimen as the working electrode, a saturated calomel electrode (SCE) as the reference electrode and a platinum electrode as the counter electrode. All the measurements were performed at ambient temperature. The results showed that there were no stable large potential peaks on the steel surface in the pure Ca(OH)2 solution with pH 12.50 or 11.50, indicating that the steel surface was in a passive state and no corrosion took place. For the steel in the SPCP solution with 0.050 M NaCl and pH 11.50, a stable and large local potential peak occurred on its potential map after 20 min immersion. This result indicated that the steel was active and localized corrosion occurred resulting from the Cl- attack. For the SPCP solution with 0.004 M NaNO2 and 0.001 M Na2SiO3, there were no stable potential peaks on the potential map of the steel immersed in the solution for 8 h, indicating that no localized corrosion took place. Therefore, the mixture of NaNO2 with Na2SiO could protect the reinforcing steel from corrosion. The polarization curve measurements and surface analyses also confirmed the above results. This work was supported by the National Natural Science Foundation of China (Nos. 21073151, and 21173177).

A combined hydrothermal reaction and sequential chemical bath deposition method is developed for fabricating a Bi 2 S 3 modified single crystalline rutile TiO 2 nanorod array film on transparent conductive glass. The results indicate that the modification of Bi 2 S 3 nanoparticles extends the photoresponse of the Bi 2 S 3 /TiO 2 composite film into the visible light region, and enhances its photoactivity. The Bi 2 S 3 /TiO 2 film can serve as a photoanode in a photoelectrochemical cell and provide more effective photogenerated cathodic protection for 403 stainless steel in a corrosion cell with a 0.5 M NaCl solution under white or visible light illumination compared with the pure TiO 2 film.

An ordered TiO2 nanotube film was first fabricated by anodization on a Ti substrate. WO3 nanoparticles were then deposited on the film via potentiostatic electrodeposition with the aim of improving the photoelectrochemical properties of the film. In comparison with the plain TiO2 film, the photoresponse of the WO3/TiO2 nanotube composite film was shown to be enhanced in the visible region. When subjected to white light illumination, the WO3/TiO2 composite film reduced the potential of the coupled 403 stainless steel in a 0.5 M NaCl solution by 370 mV (relative to its corrosion potential), demonstrating a good photoelectrochemical anticorrosion effect. It was found that even after the illumination had been switched off the composite film could provide cathodic protection for 19 h due to its charge storage capability. Keywords: TiO2 nanotube film, WO3, Anodization, Electrodeposition, Photoelectrochemical anticorrosion, Stainless steel

Reinforcing steel in concrete is normally passivated against corrosion in the concrete pore solution with high alkalinity (often pH ≥ 12.5) resulting from the cement hydration. However, the carbonation of concrete and the presence of aggressive species may induce the breakdown of the passive film on the steel surface and the occurrence of steel corrosion. In some environments, such as marine and saline-alkali land environments, sulfate ions (SO4 2-) also is a key factor affecting the corrosion behavior of reinforcing steel in concrete. Researchers have studied the chloride and/or carbonation induced steel corrosion, explored some corrosion mechanisms, and developed many anticorrosion techniques. Additionally, it is necessary to study the corrosion behavior of reinforcing steel in the sulfate environment for the corrosion protection of the steel in concrete. In this work, the corrosion behavior of reinforcing steel in the simulated concrete pore solution containing sulfate was studied by electrochemical techniques (electrochemical impedance spectroscopy and potentiodynamic polarization measurements) and surface analyses. All corrosion test specimens (Ø 11.2 mm × 4 mm) were cut from a Q235 reinforcing steel bar. Before testing, the specimens with a working surface of 1.00 cm2 were polished down to 1500 grade SiC paper and rinsed with deionized water. A saturated calcium hydroxide solution served as the simulated concrete pore solution, and was used as the test solution after the solution pH was adjusted to 11.00 with a 0.8 M NaHCO3 solution and NaSO4 with different concentrations was added. Electrochemical measurements were carried out in the test solutions by an Autolab Potentiostat/Galvanostat. The steel specimen, a saturated calomel electrode, and a platinum sheet served as the working electrode, the reference electrode and the counter electrode, respectively. The surface topography and chemical composition of the steel specimen were characterized by SEM/EDS/Electron Micro-Probe Analyzer. The results indicated that the Na2SO4 concentration had an effect on the corrosion behavior of reinforcing steel. Based on the Nyquist plots of the steel in the test solution, when the Na2SO4 concentration was lower than 0.01 M, the impedance arc radius of the steel was large, and its charge transfer resistance (R ct) was about 300 kΩ cm2, which was similar to that in the solution without SO4 2-. This indicated that the steel might be in a passive state. However, when the Na2SO4 concentration reached 0.05 M or higher, the impedance arc radius of the steel became small, and its R ct value decreased to below 50.00 kΩ cm2, showing that the passive film of the steel might be destroyed and the steel corrosion occur in the solution with high Na2SO4 concentrations. The polarization curve measurements showed that when the Na2SO4 concentration was higher than 0.05 M, the corrosion potential of the steel decreased dramatically and no a stable passive region occurred in the curves, indicating that the corrosion activity of the steel occurred. Based on the electrochemical test results, the critical SO4 2- concentration for corrosion of the reinforcing steel in the simulated concrete pore solution with pH 11.0 was 0.05-0.10 M. The SEM observations showed that the general corrosion of the steel occurred after it was immersed in the test solution with 0.5 M Na2SO4 for 1 h.

A novel Bi2S3/reduced graphene oxide (rGO) co-modified TiO2 nanotube photoanode was fabricated on a Ti foil by anodization combined with cyclic voltammetric electrodeposition, and successive ionic layer adsorption and reaction. After modifying the TiO2 nanotube film with rGO sheets and Bi2S3 nanoparticles, the band gap of the Bi2S3/rGO/TiO2 composite film decreased, and its photoresponse was extended to the visible region. Under white light irradiation, the composite film in a 0.1 M Na2SO3 and 0.1 M Na2S solution exhibited 62.5 times higher photocurrent density than the TiO2 film. The composite film photoanode could make the potential of the coupled 403 stainless steel in a 0.5 M NaCl solution negatively shift by 490 mV, showing enhanced photoelectrochemical cathodic protection.

Reinforcing steel corrosion in concrete is a main reason for the deterioration of durability of reinforced concrete structures. The widespread corrosion of reinforcing steel caused by chloride ions is a common and serious problem all over the world. Obviously, corrosion protection of reinforcing steel in concrete has become an urgent and important task. The use of corrosion inhibitors is one of the promising protection methods for controlling steel corrosion in concrete because of their low cost and easy application. The development and application of surfactant corrosion inhibitors have drawn special attention. Many surfactants have inviting application prospects for the corrosion protection of metals. Cetyltrimethylammonium bromide (CTMAB), a cationic surface active agent, has been studied for metal corrosion protection due to its main advantages of non-toxicity and a popular price. Nevertheless, there is little information on CTMAB as a corrosion inhibitor for steel in concrete. In this work, the surfactant CTMAB was employed as a corrosion inhibitor and its inhibition performance against reinforcing steel corrosion in the simulated concrete pore solutions was studied by electrochemical measurements and surface analyses. The cylindrical specimens with Ø11.2 mm × 4 mm were cut from a Q235 reinforcing steel bar. The specimen mounted in epoxy resin was used as the working electrode with an exposed area of 1.00 cm2during electrochemical measurements, and a platinum sheet and a saturated calomel electrode (SEC) served as the auxiliary electrode and the reference electrode, respectively. The compositions of the specimens were analyzed by X-ray energy dispersive spectroscopy (EDS), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), and their morphologies were observed by scanning electron microscopy (SEM). A saturated Ca(OH)2 solution with pH about 12.50 was selected as a simulated concrete pore solution. After the solution was adjusted to pH 11.00 with a 0.8 mol/L NaHCO3solution and 0.5 M NaCl was added, it served as a simulated polluted concrete pore (SPCP) solution, namely a test solution. Then different concentrations of CTMAB were added to the SPCP solution to investigate the corrosion inhibition effect of CTMAB on the reinforcing steel. The EIS analysis of the steel in the SPCP solution showed the capacitive reactance arc size increased gradually while the CTMAB concentration was increased from 0 to 0.005 M, then decreased with the increasing of the CTMAB concentration from 0.005 to 0.1 M. When the CTMAB concentration was 0.005 M, the interfacial charge transfer resistance (R ct) of the steel reached a maximum of 41.17 kΩ cm2, and the inhibition efficiency of CTMAB was 79.9%. The inhibition efficiency of CTMAB determined from the polarization curve of the steel in the SPCP solution with 0.005 M CTMAB reached 87.6%, indicating that the CTMAB could inhibit corrosion of reinforcing steel effectively. For the SPCP solution without CTMAB there was not a passive region on the potentiodynamic anodic polarization curve of the steel, indicating that the steel corrosion took place. However, the steel was in a passive state for the solution with 0.005 M CTMAB. The SEM results also indicated that CTMAB could protect the steel from corrosion. XPS and Raman results proved that CTMAB was an adsorption type corrosion inhibitor. The adsorbed CTMAB resulted in the formation of a protective film on the steel surface to protect the steel from corrosion.