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Constructing a highly efficient and stable photocatalyst is a promising strategy to protect the environment. In this work, we creatively synthesized a novel CdS/Bi4NbO8Cl heterostructured photocatalyst by in situ hydrothermal method. By using ciprofloxacin as target antibiotic residue pollutant, it is found that the CdS/Bi4NbO8Cl shows improved photocatalytic efficiency compared to bare CdS or Bi4NbO8Cl, and the photocatalytic activity of CdS/Bi4NbO8Cl with the molar ratio of 0.3 is the highest, reaching about 90%. X-ray diffraction, scanning electron microscope, and transmission electron microscope were employed to study the composition, morphology, and structure of the composite photocatalysts, while UV–vis diffuse reflection (UV–vis DRS), photoluminescence, transient photocurrent response, electrochemical impedance spectroscopy, and Mott–Schottky plots together show that the significant improvement in photocatalytic activity is due to synergistic effects of enhanced light harvesting and separation of photo-induced charges carriers, caused by the intimate contact between CdS and Bi4NbO8Cl. It is expected that the facile, low-cost method and the excellent performance of the synthesized photocatalyst in this paper can contribute to the management of water pollution.

A strategy to improve its photocatalytic performance is still a challenge for the novel Sillen–Aurivillius perovskite type Bi4NbO8Br. Herein, novel Pt modified Bi4NbO8Br composites (Pt/BNB) with sufficient oxygen vacancies were successfully fabricated via a facile in situ chemical reduction method. For one thing, the deposition of Pt nanoparticles brings about a Mott–Schottky effect at the interface to accept photo-induced electrons, leading to an efficient charge separation. For another thing, the electronic metal–support interaction of Pt and Bi4NbO8Br decreases the formation energy of oxygen defects, which could serve as active sites for O2 activation. On account of the synergetic effect of Pt and oxygen vacancies, the dominant active species-photogenerated holes are accumulated on the surface of the photocatalysts, while the additional superoxide radicals are also involved. Hence, Pt/BNB performed with excellent photocatalytic activities in the degradation of wastewater contaminants, and the kinetic rate was 4.64, 10.21, 5.53, 9.80, 1.71 and 4.05 times, respectively, those of pristine Bi4NbO8Br towards methyl orange, rhodamine B, 2,4-dichlorophenol, p-nitrophenol, ciprofloxacin and tetracycline hydrochloride.

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.

The strategy to improve the photocatalytic removal efficiencies towards organic pollutants is still a challenge for the novel Sillen–Aurivillius perovskite type Bi4NbO8Cl. Herein, we report carbon-supported TiO2/Bi4NbO8Cl (C-TiO2/Bi4NbO8Cl) heterostructures with enhanced charge separation efficiency, which were fabricated via molten-salt flux process. The carbon-supported TiO2 particles were derived from MXene Ti3C2 precursors, and attached on plate-like Bi4NbO8Cl, acting as electron-traps to achieve supressed recombination of photo-induced charges. The improved charge separation confers C-TiO2/Bi4NbO8Cl heterostructures superior photocatalytic performance with 53% higher than pristine Bi4NbO8Cl, towards rhodamine B removal with the help of photo-induced holes. Moreover, the C-TiO2/Bi4NbO8Cl heterostructures can be expanded to deal with other water contaminants, such as methyl orange, ciprofloxacin and 2,4-dichlorophenol with 44, 25 and 13% promotion, respectively, and thus the study offers a series of efficient photocatalysts for water purification.

NiTiO3/Bi4NbO8Cl heterostructure photocatalysts were successfully synthesized by a mechanical mixing method. The crystal structure, morphology, optical properties and energy band structures of all samples were determined by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscope, transmission electron microscope, ultraviolet–visible diffuse reflection spectra (UV–Vis DRS), and Mott–Schottky tests. The NiTiO3/Bi4NbO8Cl composites were observed to possess an improved activity in the photocatalytic degradation of organic dye rhodamine B (RhB) under irradiation. In particular, Bi4NbO8Cl modified with NiTiO3 (10% in weight) exhibits the best photocatalytic performance. The enhanced photocatalytic performance can be ascribed to the formation of intimate interfacial contact and type-II band alignment between NiTiO3 and Bi4NbO8Cl. From the results of photoluminescence spectra (PL), time-resolved decay spectra (TR-PL), photocurrent and electrochemical impedance spectroscopy, the rapid separation and transportation of photoinduced charge carriers were proved. In addition, the proposed mechanism for the enhanced photocatalytic activities is proposed in this paper.

A strong interfacial contact of heterostructured photocatalysts plays a key role in charges migration, thus promoting photocatalytic performance. Benefiting from the unique two-dimensional (2D) morphology and abundant terminals, 2D/2D “face-to-face” WO3·H2O/g-C3N4 heterostructured self-assemblies were fabricated employing tungsten oxide hydrate (WO3·H2O) nanoplates and graphitic carbon nitride (g-C3N4) sheets as precursors. Compared to pristine WO3·H2O and g-C3N4, the binary WO3·H2O/g-C3N4 heterostructures exhibit excellent photocatalytic performance towards water decontamination, using organic dye rhodamine B/methyl orange as probes. It is found that WO3·H2O/g-C3N4 with 20 wt% mass ratio (WHC-20) possesses the best photocatalytic activities, with about 3.05 times higher than that of pristine g-C3N4. The remarkable increase performance is attributed to the enhanced evolution of superoxide radicals (·O2−) via photoreduction in adsorbed oxygen molecules (O2−), which are promoted by efficient Z-scheme charges separation and rapid electrons transfer at 2D/2D interface. Given the low-cost, facile synthetic procedure and recycling stability, the heterostructured WO3·H2O/g-C3N4 could be served as a promising photocatalyst to deal with water contamination.

Heterogeneous photocatalytic system are widely applied to degrade organic pollutants or converse into high value-added chemicals. Both environmental and energy aspects should be considered to improve these chemical processes, favoring reaction conditions that involve room temperature and ambient O2 pressure. In the present work, hollow titanium dioxide nanospheres were fabricated via template-free method. The prepared samples were characterized by X-ray diffraction, N2 adsorption–desorption isotherms, transmission electron microscopy, and X-ray photoelectron spectroscopy. The photocatalytic activity was evaluated by photocatalytic oxidation of benzyl alcohol to benzaldehyde with visible light under atmospheric pressure at room temperature. The designed hollow structure (2%Pt–TiO2–5) not only exhibited a very high surface area, but also promoted photonic behavior and multiple light scattering, which as an efficient photocatalyst performed moderate conversion (about 20%) and high selectivity (> 99%) for oxidation of benzyl alcohol to benzaldehyde at room temperature with visible light in solvent of toluene. This work suggests that both hollow structure and Pt nanoparticles have great potential for execution of oxidative transformations under visible light. Keywords: Titanium dioxide, Hollow nanospheres, Photocatalytic oxidation, Benzyl alcohol, Visible light

Utilizing more solar energy and suppressing recombination of photo-induced charges are primary issues for photocatalyst's design. In this work, BiOBr was introduced into CdTe/TiO2 to construct a novel ternary BiOBr/CdTe/TiO2 composite via a facile solvothermal method. The composition, morphologies, optical properties, specific area, and photocatalytic performances were all investigated in detail. The heterojunction among three-dimensional TiO2 particles, BiOBr and CdTe acts an interfacial channel to boost the charges migration. As a result, the ternary BiOBr/CdTe/TiO2 heterojunctions exhibited higher visible light photocatalytic activities on photo-decolorization of methyl orange (MO) than the pure TiO2 and the binary CdTe/TiO2 and BiOBr/TiO2. Furthermore, the ternary BiOBr/CdTe/TiO2 composites were converted into hollow structure, and showed the better photocatalytic performance, reaching 75% degradation towards MO in 120 min. This study provided an attractive thought to design highly efficient photocatalysts, which possessed a promising for wastewater purification.

Hollow and heterostructured architectures are recognized as an effective approach to improve photocatalytic performance. In this work, ternary TiO2/CdTe/BiOI with hollow structure was constructed via a step-by-step method. In addition, the effect of TiO2 structural regulation and the energy band alignment of BiOI and CdTe quantum dots (CdTe QDs) with TiO2 in TiO2/CdTe/BiOI on photocatalytic dye removal were also studied. The results reveal that the TiO2/CdTe/BiOI heterostructures with hollow substrates exhibit much higher photocatalytic activities than pure TiO2, P25, TiO2/CdTe, and TiO2/BiOI and ternary TiO2/CdTe/BiOI with solid substrates. For TiO2(H)/CdTe/BiOI, several synergistic factors may be responsible for the remarkable visible-light photodegradation performance, such as strong visible-light absorption by BiOI and larger specific surface area.

Constructing heterojunction is an effective strategy to enhance photocatalytic performance of photocatalysts. Herein, we fabricated ZnTiO3/Bi4NbO8Cl heterojunction with improved performance via a typical mechanical mixing method. The rhodamine (RhB) degradation rate over heterojunction is higher than that of individual ZnTiO3 or Bi4NbO8Cl under Xenon-arc lamp irradiation. Combining ZnTiO3 with Bi4NbO8Cl can inhibit the recombination of photo-excited carriers. The improved quantum efficiency was demonstrated by transient-photocurrent responses (PC), electrochemical impedance spectroscopy (EIS), photoluminescence (PL) spectra, and time-resolved PL (TRPL) spectra. This research may be valuable for photocatalysts in the industrial application.

A series of novel binary TiO2/BiOX (X = Cl, Br, I) and ternary TiO2/CQDs/BiOBr hybrid photocatalysts were prepared through a facile hydrothermal method. TiO2/BiOX heterostructures were fabricated by varying the halogen ions. The photocatalysts were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy, and X-ray photoelectron spectroscopy. Among the binary TiO2/BiOX, TiO2/BiOBr showed the most preferable photocatalytic activities due to suitable band gap alignment and photo stability, reaching almost 80% MO degradation during 180 min irradiation under simulated sunlight. Moreover, the effects of synthesis temperature, Ti/Bi ratio on the composition and structure were investigated, the results indicated TiO2/BiOBr with Bi/Ti = 10% prepared at 120 °C possessed the best photocatalytic performance. Carbon quantum dots were introduced to accelerate electrons transfer at interface or prevent charges recombination on the surface, resulting a much better photocatalytic performance for TiO2/CQDs/BiOBr hybrid photocatalysts.

BiVO4/TiO2 nanocomposites were fabricated by a facile wet-chemical process, followed by the synthesis of TiO2 hierarchical spheres via hydrothermal method. The BiVO4/TiO2 nanocomposites were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–Vis diffuse reflectance spectroscopy and X-ray photoelectron spectroscopy. The results showed that prepared TiO2 presented hierarchical spherical morphology self-assembled by nanoparticles and an anatase–brookite mixed crystal phase. The introduction of monoclinic BiVO4 components retained the hierarchical structures and expanded the light response to around 510 nm. Type II BiVO4/TiO2 heterostructured nanocomposites exhibited improved photocatalytic degradation towards methylene blue under visible-light irradiation, especially for the composite photocatalysts with atomic Ti/Bi = 10, which showed double degradation rate than that of pure BiVO4. The enhanced photocatalytic mechanism of the heterostructured BiVO4/TiO2 nanocomposites was discussed as well.

The development of a photocatalyst with high activity, large specific surface area and precise band gap adjustment is the focus of the field of photocatalysis in realizing energy conversion and improving environmental issues. In this paper, a simple synthesis process for co-doping of KCl and NH4Cl to precisely adjust the band gap of g-C3N4 was developed. Various characterization results show that doping with KCl and NH4Cl can reduce the band gap of the carbon nitride, increase its visible light absorption, improve its carrier separation efficiency, thus showing good photocatalytic activity. Cl and K enter the g-C3N4 layers via intercalation and form a dual-element charge transport channel between these layers, thereby facilitating the transport of electrons. The introduction of NH4Cl increases the specific surface area of the composite, thus providing abundant adsorption and reaction sites. The co-loaded photocatalyst CN-NH4Cl-0.05KCl was used to degrade rhodamine B (RhB) and tetracycline (TC) and showed excellent photocatalytic activity. A possible mechanism of photocatalytic degradation is proposed based on the analytic results.

Potassium and iodide codoped mesoporous titanium dioxide (TiO2) was synthesized via an improved sol–gel method using F127 and polyvinylpyrrolidone (PVP) as pore-forming agents. Due to the synergistic effect of codoped K and I, the light absorption of the catalyst is enhanced, and the separation efficiency of photogenerated charge is improved. KI doping also increases the specific surface area, improves the adsorption capacity of TiO2 to pollutants, and promotes active site exposure for organic pollutant degradation. The synthesized potassium and iodide codoped titanium dioxide shows excellent photocatalytic activity and stability under simulated sunlight and exhibits perfect acid and alkali resistance.

Bi4NbO8Cl is a novel bismuth-based catalyst with a 2D sheet structure for photodegradation under visible light irradiation. However, Bi4NbO8Cl semiconductor has low quantum efficiency, as well as the photogenerated electrons (e-) and holes (h+) tend to recombine in a single semiconductor, thereby decreasing their degradation efficiency. Hence, in this work, Bi2O3/Bi4NbO8Cl 0D/2D heterojunctions containing Bi2O3 quantum dots were prepared to enhance the photocatalytic performance, in which e- and h+ were separated and transferred to different semiconductors for oxidation and reduction, respectively. Compared to bare Bi4NbO8Cl, the photocatalytic activity of 0.5 Bi2O3/Bi4NbO8Cl increases by 2.6 times in the degradation of Rhodamine B since the formation of heterojunctions. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR) has confirmed the formation of heterojunction. The photoluminescence (PL), photocurrent, and electrochemical impedance spectra (EIS) tests indicate that the quantum efficiency has been improved. This research may be valuable for the industrial application of photocatalysts and provide a new idea for designing photocatalysts.

The strategy to improve the photocatalytic performance is still a challenge for the novel Sillen-Aurivillius perovskite type Bi4NbO8Cl. Herein, heterostructured Bi/Bi4NbO8Cl was fabricated via in-situ solvothermal method, without the additional introduction of Bi-sources. Simultaneously, the amount of oxygen vacancies (OVs) were increased, as the [Bi2O2] blocks released in the solvothermal process to serve as precursors for Bi particles. Due to the large work function of Bi, a Schottky barrier formed at the Bi/Bi4NbO8Cl interface, promoting photo-induced charge separation generated in the Bi4NbO8Cl semiconductor, supplying more holes for the organic compounds decomposition, which could be widely applied in water decontamination. Furthermore, the OVs facilitate the consumption of photo-induced electrons by assisting oxygen activation to produce superoxide radicals (·O2−), leaving more holes in the valence band of Bi4NbO8Cl, and thus result in the enhancement of Rhodamine B (RhB) degradation by 1.82 times over Bi/Bi4NbO8Cl photocatalysts. Through the synergistic effect of Bi and OVs, the Bi/Bi4NbO8Cl also exhibits enhanced photocatalytic performance towards various organic water-contaminants, such as methyl orange, acid orange 7, p-nitrophenol and tetracycline hydrochloride.

Altering the semiconductor composition and suitable energy levels to form a cascade structure is a feasible approach to achieve superior photocatalytic activity. In this study, Bi4NbO8Cl was prepared by a ball milling-calcination method. And one-pot hydrothermal process was developed as a new strategy to synthesize ternary Bi4NbO8Cl/BiOCl/Nb2O5 (BBN) composites, where ultrafine Nb2O5 nanoparticles and BiOCl were in-situ grown and loaded on the surface of Bi4NbO8Cl using NbCl5 as raw material. An enhanced photocatalytic performance towards RhB removal by Bi4NbO8Cl/BiOCl/Nb2O5 is assigned to the in-situ formation of intimated interfaces contacts among Bi4NbO8Cl, BiOCl and Nb2O5, and suitable conduction band (CB) alignments in the ternary hybrid. The staggered energy levels inhibit the recombination of photoinduced electron-hole pairs and increase the separation efficiency of charge carriers, subsequently enhances the photocatalytic efficiency.

Using (C16H36O4)Ti, Gd2O3 and HNO3 as raw materials, TiO2 and TiO2:Gd3+ hollow spheres with different Gd dopant concentrations of 0.25, 0.5, 1, 1.5 and 2 mol% were obtained with the assistance of the carbon sphere templates. The morphology, structure, specific surface area and photocatalytic properties of the prepared hollow spheres were studied by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Brunauer–Emmett–Teller and UV–Vis 2550 spectrophotometer, respectively. Several factors influencing the photocatalytic activities of the samples were studied, which include pH value of the solutions, Gd dopant concentrations, amount of the additive catalysts and types of the dyes. In this work, fabrication of TiO2:Gd3+ hollow spheres (b) was obtained with the assistance of the carbon sphere template (a). Characterization of the samples was also reported in this paper.

In this work, fabrication and characterization of ordered arrays of CNT/TiO2 nanotubes imbedded in porous anodic aluminum oxide (AAO) membranes were reported. The coaxial core–shell structures were exploited for the photocatalytic degradation of organic pollutants, such as methyl orange. The presence of the CNT greatly enhanced the efficiency of photocatalytic activity compared with the bare TiO2 nanotubes. The key achievement of this work is to fabricate ordered arrays of CNT/TiO2 composite nanotubes with coaxial core–shell structures by using a simple, convenient, and environmentally friendly process. Further application of this CNT/TiO2 hybrid material in many fields could be hopefully expected.

In this work, TiO2/MS (M = Pb, Zn) core–shell coaxial nanotube arrays were prepared by a simple method of liquid deposition using anodic aluminium oxide templates. The mechanism of the formation of TiO2/MS (M = Pb, Zn) coaxial nanotubes is discussed here. Compared to bare TiO2 nanotubes, TiO2/PbS and TiO2/ZnS composite nanotubes showed improved photocatalytic properties and analysis of such results was also conducted.

TiO2/WO3 composite nanotubes were synthesized in an anodic aluminum oxide (AAO) template by a sol–gel method. The prepared nanotubes were characterized by transmission electron microscopy, scanning electron microscopy, powder X-ray diffraction, and Brunauer–Emmett–Teller surface area. Using the nanotubes embedded in the AAO templates as catalysts, photocatalytic degradation of methyl orange aqueous solution was carried out under UV light irradiation. The results showed that the TiO2/WO3 composite nanotubes with the thickness about 50 nm could be successfully synthesized by this method. TiO2 showed anatase phase and WO3 displayed monoclinic phase. The composite nanotubes (TiO2/WO3) exhibited higher photocatalytic activity than the pure nanotubes (WO3 or TiO2). The possible reason for improving the photocatalytic activity was also discussed.

Layered perovskite oxyhalide Bi4NbO8Cl has been reported as a stable photocatalyst for the organic pollutant removal. In this work, Bi4NbO8Cl was synthesized using liquid-combustion approach, and an efficient Ag/Bi4NbO8Cl photocatalyst was prepared via photo-deposition method. Transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) display that metallic Ag nanoparticles (∼10 nm) are uniformly distributed on the surface of Bi4NbO8Cl. Owing to a shift of the valence and conduction band and band-gap narrowing, demonstrated by UV-vis diffuse reflection spectroscopy (UV-vis DRS) and Mott-Schottky results, the Ag/Bi4NbO8Cl show enhanced photocatalytic degradation of RhB with almost 100% within 3 h. Photogenerated holes (h+) are foremost active specie responsible for the degradation of RhB via the capture agent test. The improvement of photocatalytic performance of 3% Ag/Bi4NbO8Cl could be attributed to the synergetic effect of the surface plasmon resonance and electron sinkers by Ag nanoparticles, strengthening the visible-light absorption ability, as well as promoting the separation efficiency of charge carriers, which are beneficial for enhancing photocatalytic performance. The present work provides a promising insight into the design Bi-based photocatalysts to solve environmental pollution.

Heterostructured photocatalysts play a significant role in the removal of contaminants by decreasing the recombination of the photo-induced charges. Herein, we presented novel TiO2/C/BiVO4 ternary hybrids employing a 2D layered Ti3C2 MXene precursor, overcoming the lattice mismatching of TiO2/BiVO4 binary heterostructures simultaneously. Raman and XPS analyses proved the strong coupling effects of TiO2, carbon and BiVO4 components, and the heterostructures were identified from high-resolution transmission electron microscopy results. Moreover, the ternary TiO2/C/BiVO4 composites exhibit excellent photocatalytic performance of Rhodamine B degradation, which is about four times higher than pure BiVO4 and twice that of binary TiO2/BiVO4 heterostructures, reaching a reaction constant of 13.7 × 10-3 min-1 under visible-light irradiation (λ > 420 nm). In addition, for the possible mechanism for dye elimination it was proposed that RhB molecule be directly oxidized by photo-induced holes (h+) on the BiVO4 components and superoxide radical ([Formula: see text]) generated from conduction band electrons of the heterostructures. This work will provide possibilities for developing visible-light responsive nanomaterials for efficient solar utilization.

ZnO powders with different Co2+ doping concentrations (0, 0.5, 1, 3 and 5 mol%) were prepared by the hydrothermal method and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis diffuse reflectance spectrometer, and photochemical reaction instrument. The results show that the ZnO powders are hexagonal wurtzite structures and their crystallization decrease with the increase of Co2+ doping concentration. The products are spherical which have diameter of about 200 nm, and their absorption edge shift to longer wavelength with the increase of the Co2+ concentration. The photocatalytic activities of the powders are evaluated using a basic organic dye, methyl orange (MO). Compared with undoped ZnO, it is found that the photocatalytic properties of the Co-doped ZnO have been improved greatly. When the doping concentration is 3 mol%, the degradation ratio of MO can reach 78% after reacting for 240 min.

ZnO/Cu(2)O compound photocatalysts were prepared by "soak-deoxidize-air oxidation" with different concentrations of Cu(2+) (0.125, 0.25, 0.5, 1, 1.5 and 2 mol/L). The prepared ZnO/Cu(2)O samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), UV-vis diffuse reflectance spectrometer, and photochemical reaction instrument. The results show that ZnO was hexagonal wurtzite structure and the crystallinity had no change with the increase of Cu(2+) concentration. Cu(2)O belonged to cubic structure and the crystallinity increased with the increase of Cu(2+) concentration. ZnO were rods and bulks which had diameter of about 300-400 nm, some small round Cu(2)O particles which had a diameter of about 50 nm adhered to these rods and bulks. In the compounds the mole ratio of Cu(2)O to ZnO was 0.017, 0.025, 0.076, 0.137, 0.138, and 0.136, respectively. An absorbance in the visible light region between 400 and 610 nm was seen and the reflection rate became less with the mole ratio of Cu(2)O to ZnO increasing. The photocatalytic activities of ZnO/Cu(2)O compound were evaluated using a basic organic dye, methyl orange (MO). It was found that, compared with pure ZnO, the photocatalytic properties of ZnO/Cu(2)O compound were improved greatly and some compounds were better than pure Cu(2)O.