Semiconductor photocatalysis has been regarded as one of the most promising methods for treatment of Cr(VI)-containing wastewater, but the high recombination rate of photogenerated carriers and photocorrosion have limited severely its practical application. The objective of the current study was to employ a layered double hydroxide (LDH) to mitigate these problems by designing and constructing a multiple heterojunction system of g-C3N4/LDH/Ag3PO4 (CNLDHAP) through a two-step hydrothermal route. The structures, morphologies, chemical states, and optical properties of the products were investigated systematically. The CNLDHAP composite showed superior photocatalytic activity for Cr(VI) reduction than that of the individual components under visible-light irradiation. The composite exhibited high photocatalytic reduction stability after five recycles. The enhanced photocatalytic performance may originate from the very efficient separation of photogenerated carriers of the multiple heterojunction system. Possible photocatalytic mechanisms for the reduction of Cr(VI) over the CNLDHAP composite photocatalyst are proposed.

Since the photocatalytic effect of a single conventional photocatalyst is often not ideal, it is particularly important to design and construct an efficient and stable photocatalyst in a compound way. In this study, we exploited the sol–gel method to combine BiOCl and TiO2 and gave full play to their respective advantages to prepare BiOCl/TiO2 composite materials. Then, X-ray diffraction (XRD), scanning electron microscope (SEM), and transmission electron microscope (TEM) characterization techniques were utilized to study important indicators of composites—composition, morphology, and structure. In the photodegradation experiment of methyl orange (MO), it was found that the photocatalytic performance of 10BTO (the molar ratio of TiO2 to BiOCl is 10:1) was the best among all the composite photocatalysts, and almost complete degradation of MO was realized. Besides, repeated experiments and recyclability tests on composite materials display favorable stability. Through ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis DRS), photoluminescence (PL), transient photocurrent response, electrochemical impedance spectroscopy (EIS), and electron spin resonance (ESR), a possible degradation mechanism is proposed. Given that there are serious environmental pollution problems in our country, we sincerely hope this research will do its best to degrade organic pollutants in wastewater.

{001} facets dominant TiO2 nanosheets have attracted intensive attention in the photocatalytic field, due to their undercoordinated Ti5c centers, higher surface energy, and photocatalytic activity than those of any other low-energy facet. However, a fluorine-rich (001) surface is controversial to the photocatalytic activity of TiO2 nanocrystals. We have removed the surface F atoms bonding with Ti by hydrogenation method successfully, and found that {001} facets dominant TiO2 nanosheets without the terminated F atoms showed dramatic enhancement in the photocatalytic activity. Moreover, the clean (001) surface was more in favor of the deposition of PdO than the fluorine-rich surface, and the amorphous structure from the hydrogenation is beneficial to the reduction of PdCl42− to Pd nanoparticles. The PdO attached on {001} facets and the amorphous structure promoted the separation of charge carriers, and Pd nanoparticles transferred plasmonic-induced electrons to the conduction band of hydrogenated TiO2 under simulated solar irradiation. Thus, a significantly enhanced photocatalytic activity of Pd–H–TiO2 is achieved on degrading organic environmental pollution, due to the synergy of palladium species and hydrogenation on {001} facets exposed TiO2.

Visible-light responsive plasmonic Ag2O/Ag/g-C3N4 nanosheets (NS) were successfully prepared by a simple and green photodeposition method. The obtained composites were characterized by XRD, Fourier transform infrared, transmission electron microscopy, UV-vis, and the photoluminescence (PL) results indicated that the Ag2O/Ag/g-C3N4 NS composites showed better photoabsorption performance than g-C3N4 due to the surface plasmon resonance effect of Ag nanoparticles. Meanwhile, the composite exhibited excellent photocatalytic activities, which was ∼3.8 and ∼3.0 times higher than those of bulk g-C3N4 and pure g-C3N4 NS, respectively. Moreover, the as-prepared composites showed a high structural stability in the photodegradation of Rhodamine B. A possible photocatalytic and charge separation mechanism was suggested based on the PL spectra and the active species trapping experiment.

To obtain a floating and magnetically recyclable photocatalyst, nano-scaled Fe3O4 particles are first deposited on the surface of the KH-550 modified cenosphere under a hydrothermal condition. The Fe3O4 coated cenosphere is then loaded with a layer of globular-flower-like SiO2 particles by a precipitation method. The Fe3O4/SiO2 double-layer structured cenosphere is finally immobilized with TiO2 nanoparticles doped with rare earth element Eu3+ to enhance the photoactivity of TiO2 using titanium sulfate, urea, and polyvinylpyrrolidone by a hydrothermal treatment. The as-prepared cenosphere is systematically characterized by various characterization techniques. The properties of photocatalytic degradation of methylene blue dye are also investigated. Results show that after being doped with 0.1% Eu3+ ions in relation to Ti4+ ions, the photocatalytic degradation efficiency for the Fe3O4/SiO2/Eu-doped TiO2 coated cenosphere is significantly improved under both ultraviolet and visible light irradiations. The saturation magnetization of the Fe3O4/SiO2/Eu-doped TiO2 coated cenosphere increases to some degree.

There is high scientific and technological interest to develop photocatalytic coatings on stainless steels surface to remove fouling under light radiation. In this study, a novel method is described to prepare photocleanable stainless steel by anodization to form aligned nanopore arrays (NPAs) on the surface in ethylene glycol containing perchloric acid. Perchloric acid concentration, applied voltage and anodization time of anodization process were investigated. The NPAs are mainly composed of iron (III) oxide and chromium (III) oxide. This photocleanable stainless steel has remarkable visible-light photocatalytic activities, which show potential applications particularly for outdoor purpose. Moreover, the stainless steel surface remains highly polished and exhibits good corrosion resistance after anodization.