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In this study, TiO₂ coatings are deposited on Si(100) wafers by direct current pulsed magnetron sputtering technology. The crystal structure of TiO₂ coatings gradually transforms from the anatase phase to the amorphous phase when the sputtering power is decreased from 900W to 150W. Besides, the growth surface temperature of TiO₂ coatings decreases from 630${}^{\circ }$C to 241${}^{\circ }$C. The relationship between the growth behavior and growth surface temperature of TiO₂ coatings is investigated using the dynamic scaling theory. The results show that in the first stage, the growth behavior of TiO₂ coatings gradually transforms from the Frank–van der Merwe mode to the Volmer–Weber mode with decreasing sputtering power from 900W to 150W. In the second stage, the growth behavior of TiO₂ coatings gradually transforms from the Stranski–Krastanov mode to the Volmer–Weber mode. Transformation of the growth behavior of TiO₂ coatings in the second stage transforms the crystal structure of TiO₂ coatings from the anatase phase to the amorphous phase.

An anatase TiO₂ photoanode with a novel three-dimensional nest-like structure was prepared directly on a transparent conductive glass substrate through hydrothermal cycles by three times. First, an unidirectional banded structure film was prepared by a facile hydrothermal method. And then, with the time of hydrothermal cycle increased, part of nanobelts were ruptured into a lot of small polyhedrons, but they still maintained a trend of the previous connection, and some fine nanobelts were interweaved in small polyhedrons. Finally, we successfully prepared a film with a novel 3D nest-like structure, and it had all the characteristics of the hierarchitectures. It had better photoelectric properties than the film with fewer times of hydrothermal cycle. Its photoelectric conversion efficiency reached 3.81%, which is due to a large dye adsorption amount, rapid electronic transmission, and superior light scattering and more electrons transmission paths.

A new photocatalyst of sodium humate (HA–Na)/Nano-TiO₂ coating on the glass spheres for flue gas denitrification (DeNO_x) was prepared using the impregnation method. The HA–Na/TiO₂ is characterized by Brunauer–Emmett–Teller (BET), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and scanning electron microscope (SEM). The photocatalytic activity of HA–Na/TiO₂ on removing NO_x was investigated in a self-designed photocatalytic reactor. The synergistic mechanism of HA–Na and TiO₂ on DeNO_x is also proposed and demonstrated. The experimental results indicate that specific surface area and average pore size of HA–Na are improved owing to the mixed TiO₂ nanoparticles. The crystal structure of TiO₂ has little change after mixing with HA–Na. Due to high photocatalytic performance of TiO₂, NO was oxidized to NO₂ and HNO₃ eventually. On the other hand, HA–Na support can absorb and react with HNO₃, which accelerates 10% of the catalytic reaction of TiO₂ and the utilization of light source. The chemical and physiological activity of oxidized HA–Na are improved than the original humate. The HA–Na/TiO₂ photocatalysts show great property on eliminating NO_x because of the promoting effect between HA–Na and TiO₂, and the NO removal efficiency can reach to 80% at the optimum condition.

Different kinds of graphene (GN)/titania nanocomposites using graphene and P25 or Titanium (IV) n-butoxide (TBOT) as precursors were prepared with hydrothermal method. To investigate the differences of the photocatalytic properties of composites with various shapes of titanium dioxide (TiO${}_2)$, three types of TiO₂, including titanium nanotubes (TNT), titanium nanosheets (TNS) and titanium nanoparticles (TNP) were successfully prepared and combined with GN to form the composites. The prepared composites were confirmed by Ultraviolet-visible spectroscopy (UV-Vis), X-ray diffraction (XRD), Fourier transform infrared (FTIR), X-ray Photoelectron Spectroscopy (XPS), and transmission electron microscopy (TEM), etc. Photocatalytic activities of composites were carried out by the degradation of Reactive Black 5 (RBk5) and Norfloxacin (NFXC) under the radiation of UV lamp. Results indicate that the differences in the TiO₂ morphology of the composites greatly influence the catalytic properties. In addition, the heterojunction between graphene and TiO₂ also play an important role in the photocatalytic abilities of composites. In this study, it can be seen that the prepared composites exhibit higher photocatalytic activity including excellent adsorption capacity and photo-degradation ability than P25. The photocatalytic activity of GN–TNS is higher than that of GN–TiO₂ and GN–TNT.

A novel nanomaterial composed of copper and carbon nanofibers (CuCNFs) decorated with Ag-doped TiO₂ (Ag–TiO${}_2)$ nanoparticles was prepared through electrospinning, carbonization and solvothermal treatment. The composites were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS). The obtained composites were mixed with laccase and Nafion to construct novel hydroquinone biosensor. The electrochemical behavior of the novel biosensor was studied using cyclic voltammetry (CV) and chronoamperometry. The results demonstrated that the biosensor possessed a wide detection linear range (1.20–176.50$\mu$M), a good selectivity, repeatability, reproducibility and storage stability. This work provides a new material to design more efficient laccase (Lac) based biosensor for hydroquinone detection.

2,9,16,23-tetranitrophthalocyanine zinc (TNZnPc)/TiO₂ organic–inorganic heterostructures were successfully fabricated by a simple combination method of electrospinning technique and solvothermal processing. These photocatalysts were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, UV–Vis, energy dispersive X-ray and X-ray photoelectron spectroscopy. The photocatalytic studies revealed that the TNZnPc/TiO₂ organic–inorganic heterostructures exhibited enhanced photocatalytic efficiency of photodegradation of rhodamine B compared with pure TiO₂ nanofibers under visible-light irradiation. Further studies indicate that the photosynergistic effect of organic–inorganic heterostructures can remarkably enhance the photoinduced interfacial charge transfer, thereby increasing the charge separation during the photocatalytic reaction.

TiO₂ nanotube arrays (TiO₂NTs) were prepared by anodic oxidation, then soaked in thiourea solution, and finally transformed into modified anatase TiO₂ structure by heat treatment. Through the test results of SEM, TEM, XRD, XPS, UV-vis diffuse reflectance spectroscopy, photo-current and so on, finding that S replaces Ti${}^{4+}$ in the form of S${}^{6+}$, and part of the Ti${}^{4+}$ is reduced to Ti${}^{3+}$. Ladder type energy band structure, producing by the appearance of S${}^{6+}$ and Ti${}^{3+}$, makes the electron–hole more easily and increases the carrier transfer speed to a certain degree. The photo-current size has increased from 1.07mA/cm² to 2.13mA/cm². By simulating decolorization test of sample to methylthionine chloride under visible light, the degradation rate of the modified sample to methylene blue increases from 32% to 63%, and increased by 1.97 times.

In this study, the TiO₂/Bi₄V₂O${}_{11}$ nanocomposite photocatalysts were prepared by loading different amount of TiO₂ nanoparticles onto the surface of Bi₄V₂O${}_{11}$ nanospheres via a facile hydrothermal method. Afterwards, the as-synthesized samples were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), N₂ adsorption–desorption isotherms, X-ray photoelectron spectroscopy (XPS), UV-Vis diffuse reflectance spectroscopy (DRS) and photocurrent techniques. The optimal TiO₂/Bi₄V₂O${}_{11}$ composite with 20wt.% TiO₂ loading (TB2) exhibited the best photocatalytic activity, which could degrade almost RhB completely within 30min under visible light irradiation. The enhanced photocatalytic activity of TiO₂/Bi₄V₂O${}_{11}$ composites for RhB degradation could be mainly ascribed to the efficient charge separation over dye-induced sensitized and the increased specific surface area. Also, the photocatalytic activities of TiO₂/Bi₄V₂O${}_{11}$ for CIP degradation were tested. After five consecutive recycling experiments, the photocatalytic degradation activity of TB2 could still reach 99% which indicated that the catalysts had superior stability. Based on the experimental and bandgap calculations, a possible photocatalytic mechanism of TiO₂/Bi₄V₂O${}_{11}$ for RhB degradation was proposed.

The Bi₂S₃-TiO₂-RGO composites were synthesized by a facile one-step hydrothermal method and applied for the photocatalytic degradation of Rhodamine B (Rh B) under the visible light. The Bi₂S₃-TiO₂-RGO composites were characterized by transmission electron microscopy, X-ray diffraction, Raman and Fourier transform infrared spectrometer. The results indicated that the Bi₂S₃-TiO₂-RGO composites were successfully prepared, and Ti-O-C and S-C bonds were existing among Bi₂S₃, TiO₂ as well as RGO. Furthermore, the photocatalytic ability of Bi₂S₃-TiO₂-RGO composites was excellent under visible light due to its responding to the whole visible light region, low recombination rate of photogenerated electron–hole pairs and relatively negative conduction band. Rh B photocatalytic degradation rate was 99.5% after 50min and still could reach 98.4% after five cycles. Finally, a formation mechanism as well as a photocatalytic mechanism of Bi₂S₃-TiO₂-RGO composites were proposed based on the experimental results.

The CuInS₂ quantum dots sensitization of TiO₂ nanonails (NNs) array was successfully carried out by a successive ionic layer absorption and reaction (SILAR) method using CuCl₂ ⋅ 2H₂O, InCl₃ ⋅ 4H₂O and Na₂S ⋅ 9H₂O as precursors. The morphology, elemental composition and crystalline structure of the CuInS₂ quantum dots sensitized TiO₂ NNs array heterojunction nanostructures were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and X-ray-photoelectron spectroscopy (XPS). The above characterization results could unanimously reveal that the nanoparticles successfully loaded on the TiO₂ NNs array can be assigned as CuInS₂ quantum dots. UV-Vis absorption measurements indicated that the CuInS₂ quantum dots sensitization extended the visible light absorption. The largest short-circuit photocurrent density of 17.7mA/cm² was obtained, which indicated that the CuInS₂ was a promising material in activating visible light functionalities and enhancing photoelectrochemical performance.

Here, the lamellar-shaped Bi₂S₃ grown on a porous TiO₂ monolith was obtained by a two-step method including a sol–gel route and hydrothermal treatment. The photocatalytic activity of the as-synthesized Bi₂S₃/TiO₂ composites was evaluated for photodegradation of methylene blue (MB) dye in aqueous solution under the visible-light irradiation. Based on our experimental results, 5% (molar ratio of Bi₂S₃ to TiO${}_2)$ Bi₂S₃/TiO₂ photocatalysts exhibited a maximum photodegradation rate of MB up to 96.9% under visible-light irradiation for 120 min. Our findings indicated that the lamellar-shaped Bi₂S₃ can extend the light absorption up to visible areas, and porous TiO₂ can provide enhanced specific surface area and more mass transfer pathway to enhance the photodegradation efficiency. Furthermore, porous TiO₂ can accept the electrons from the Bi₂S₃ conduction band due to the relatively positive electrode potential to impede the photoproduced electron and hole combination to result in advanced photocatalytic performance.

To improve the high charge carrier recombination rate and low visible light absorption of {001} facets exposed TiO₂ [TiO₂(001)] nanosheets, few-layered MoS₂ nanoparticles were loaded on the surfaces of TiO₂(001) nanosheets by a simple photodeposition method. The photocatalytic activities towards Rhodamine B (RhB) were investigated. The results showed that the MoS₂–TiO₂(001) nanocomposites exhibited much enhanced photocatalytic activities compared with the pure TiO₂(001) nanosheets. At an optimal Mo/Ti molar ratio of 25%, the MoS₂–TiO₂(001) nanocomposites displayed the highest photocatalytic activity, which took only 30min to degrade 50mL of RhB (50mg/L). The active species in the degradation reaction were determined to be h${}^{+}$ and ${}^{•}$OH according to the free radical trapping experiments. The reduced charge carrier recombination rate, enhanced visible light utilization and increased surface areas contributed to the enhanced photocatalytic performances of the 25% MoS₂–TiO₂(001) nanocomposites.

In recent years, all inorganic bismuth lead-halide perovskite nanocrystals [CsPbX₃ (X$=$Cl, Br, I)] have received extensive attention due to their high performance in fluorescence quantum yield, narrow emission spectrum, and adjustable emission range. However, the disadvantages of high cost and poor stability have greatly limited the development prospects of the material. Here, in order to develop a perovskite quantum dot lasing cavity with high chemical stability, high quality factor and low fabrication cost, we have successfully fabricated a 3D random cavity device based on porous silicon/TiO₂ nanowires. A TiO₂ nanowire is grown on the porous silicon to form a 3D resonant cavity, and a perovskite quantum dot is spin-coated on the surface of the 3D resonant cavity to form a novel 3D complex film. The novel structure enhances the chemical stability and lasing quality factor of the resonant cavity while the fluorescence generated by the large quantum dots in the spatial interference structure constitutes the feedback loop, which will provide favorable support for the development of information optics.

Organic–inorganic hybrid perovskite solar cells have become one of the highly promising candidates for photovoltaic technologies because of their low processing cost, rapid-growing power conversion efficiency and easy preparation process. Electron transfer layer (ETL) plays an important role in exciton separation and charge transport for perovskite devices. A TiO₂–ZnO binary mixed nanoparticle (NP) ETL, which can be prepared in low-temperature hydrothermal method, was proposed. By analyzing the XRD and SEM, the incorporation of mixed NPs thin film improved the interfacial stability of ZnO/perovskite and prevented the perovskite layer from being decomposed as compared to the pure ZnO NPs thin film. Furthermore, UV spectrum and EIS results show that TiO₂–ZnO mixed NP ETL has high transmittance and maintains good electrical properties of pure ZnO NPs basically. Finally, the efficiency of perovskite device based on TiO₂–ZnO mixed NP ETL was improved to 15%. Our research provides a simple way for the application of ZnO in PCSs.

Developing nonmetal-doped mesoporous TiO₂ is highly attractive for preparing semiconductor visible photocatalyst with high activities. Here, we prepare N/F co-doped mesoporous TiO₂ with high vis-photocatalytic activities by a simple liquid phase deposition process followed by annealing in air using C${}_{16}$TAB as a bi-functional template (forming mesoporous and providing dopants). N₂ adsorption isotherms, low-angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicate the formation of wormhole-like mesoporous structure. Wide-angle XRD and high-resolution TEM demonstrate the presence of anatase TiO₂ mesopore wall. XPS analyses reveal that N is doped into TiO₂ lattice in the forms of substitutional and interstitial N species, and that F is doped into the TiO₂ lattice in the form of interstitial F. The mesopore-forming and doping mechanisms are thoroughly discussed based on the bi-function of C${}_{16}$TAB template. Mesoporous structure results in a high BET surface area of TiO₂. High-concentration nitrogen species in anatase lattice and mesoporous structure remarkably increase the visible absorption of TiO₂. As a result, the reaction rate constant of MB degradation catalyzed by N/F co-doped mesoporous TiO₂ photocatalysts is about 7 times that by P25.

Double element co-doped carbon quantum dots (CQDs) have unique electron properties and broad prospects in photocatalysis. In this paper, the phosphorus and nitrogen co-doped CQDs (PNCQDs) were loaded on TiO₂ nanosheets by in-situ synthesis method. Physical structure and chemical composition of samples were analyzed by XRD, FT-IR, XPS, SEM and TEM. UV–Vis spectra show the donor–acceptor coupling between PNCQDs and TiO₂ and enhanced strong UV light absorption. Photoluminescence spectra indicate that PNCQDs effectively promote charge separation, which is different from nitrogen doped CQDs. The sample 1-PNCT with the optimal phosphorus doping amount has the highest kinetic constant for photodegradation of Methylene Blue (MB), which is 3.4 times pure TiO₂. A possible Z-scheme photodegradation mechanism is proposed according to the active species scavenge experiment results in which PNCQDs can not only accept but also localize photogenerated electrons to dopant sites due to the quantum wells created by P and N doping energy barriers.

Nowadays, the treatment of refractory wastewater such as oil-field wastewater has become one of the most concerning environmental problems. Using nanometer photocatalyst to treat wastewater under visible light is an alternative solution. In this study, N and B co-doped TiO₂ particles with Ag surface modification (Ag/TNB) were prepared to improve the visible-light activity. The catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and UV–VisDRS. The decomposition of Rh.B, and hydrocarbons in the oil-field wastewater under visible light was studied. The results showed that the presence of N, B and Ag improved the photocatalytic activity of TiO₂. 98% of Rh.B was removed after 1 h photocatalysis at the conditions of pH 6 with the catalyst loading of 1 g/L. The COD value of oil-field wastewater was reduced by 54% after 2 h at the conditions of pH 8 with the catalyst loading of 2 g/L. The modified catalyst revealed its great potential in the practical application for environmental purification.

Constructing heterojunction photocatalyst is an effective method to enhance the separation of photogenerated electron and hole, which significantly improves ability of visible light response. In this study, calcination methods have been proposed to prepare highly efficient magnetic ternary photocatalyst g-C₃N₄/TiO₂-MnFe₂O₄ halloysite. It showed an enhanced photocatalytic degradation for dyes (crystal violet) and nonsteroidal anti-inflammatory drugs (acetaminophen) under vision light irradiation. Compared to pure g-C₃N₄, TiO₂, MnFe₂O₄ halloysite and binary g-C₃N₄-MnFe₂O₄ halloysite, the optimized ternary g-C₃N₄/TiO₂-MnFe₂O₄ halloysite displayed enhanced photodegradation efficiency with 91.1% removal of crystal violet (10ppm) in 90min under visible light irradiation, the optimized ternary g-C₃N₄/TiO₂-MnFe₂O₄ halloysite composite showed significantly enhanced photocatalytic activity with more than 79.1% removal of acetaminophen (10ppm) within 90min under visible light. The photocatalytic mechanism was identified through the free radical quenching experiment. The heterojunction photocatalyst could be easily recovered by an extra magnetic field and reused several times without any obvious deterioration in catalytic activity. Besides, the ternary heterojunction also exhibited antibacterial ability against Escherichia coli. The superior photocatalytic performance of composite should be mainly attributed to both the improvement of light harvesting as well as the enhanced separation and transfer efficiency. It is expected that this novel ternary visible-light responding composite would be a promising candidate material for organic pollutants degradation and bacteria inactivation.

The three-dimensional (3D) mesoporous titanium dioxide (TiO₂) was synthesized by microwave-assisted hydrothermal method, using titanium sulfate as titanium source and urea to adjust pH value. Its structure and photocatalytic oxidation properties were studied. The results show that the TiO₂ particles have a 3D mesoporous structure, uniform distribution and spherical shape, the average diameter is about 0.67$\mu$m. These properties provide strong light adsorption, high specific surface area, which increases the active site of the photocatalyst, porosity can also enhance the ability of the material to adsorb pollutants, thus has better stability. It was applied to photocatalytic degradation of 10mg/L rhodamine B (RhB) solution. After 80min of irradiation under 420nm ultraviolet (UV) light, the degradation rate of RhB reached more than 90%. In addition, it also provided an excellent photocatalytic efficiency of removing Hg⁰ in simulated flue gas. The removal efficiency could still reach over 86% after 40 h, which could be used in the treatment of heavy metal pollutants such as metallurgical flue gas.

The anatase phase titanium dioxide sols were prepared by hydrothermal method using titanium sulfate as the titanium source. Copper acetate monohydrate was used as the copper source, cubic phase Cu₂O with matched bandgap TiO₂ was introduced to synthesize hollow spherical nano-TiO₂/Cu₂O composites by precipitation method. The powder samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), transmission electron microscopy (TEM), specific surface area testing (BET), X-ray electron spectroscopy (XPS) and ultraviolet and visible spectrophotometry (UV–Vis) diffuse reflectance spectroscopy analysis using methyl orange (MO) solution as indicator. The results showed that the introduction of Cu₂O did not affect the physical phase of TiO₂. Titanium dioxide was a shuttle-shaped nanorod with an average particle size less than 20 nm, Cu₂O was a sphere with an average particle size greater than 400 nm. TiO₂ loading results in smaller particle size, larger specific surface area, thinner spherical walls, increased hollowness, and improved adsorption and photocatalytic properties of spherical Cu₂O. The optimum Ti content of TiO₂/Cu₂O nanocomposite was 4.0 wt.%, the maximum specific surface area of TiO₂/Cu₂O sample was 90.57 m²/g with particle size less than 150 nm. When TiO₂/Cu₂O sample with Ti content of 4.0 wt.% was used as photocatalyst, the adsorption effect was 66.2% under the dark reaction at 60 min, the degradation effect was 91.2% under visible light irradiation at 120 min. The adsorption and photocatalytic performance were excellent when the TiO₂/Cu₂O sample with Ti content of 4.0 wt.% was used as the photocatalyst. This work provides an effective method for photocatalytic treatment of waste liquids.