Preparation and characterization of Cu2O/TiO2 nano–nano heterostructure photocatalysts

Cu₂O/TiO₂ nano–nano heterostructures with different concentrations of Cu₂O were prepared by an alcohol-aqueous based chemical precipitation method, and were characterized by X-ray diffraction, transmission electron microscopy, scanning electron microscopy and UV–vis diffuse reflection absorption spectra. The photocatalytic efficiency of the Cu₂O/TiO₂ heterostructures was evaluated by degradation of Acid Orange II in water under UV–vis light and visible light irradiation. The results show that the heterostructures have dramatically improved photocatalytic activity comparing with pure TiO₂ (P25). The prepared Cu₂O/TiO₂ heterostructures with the Cu₂O concentrations of 30% and 70% have the best photocatalytic efficiencies, which are 6 times and 27 times higher than that of pure TiO₂ (P25) under UV–vis light and visible light irradiation, respectively.     

Preparation of multi-walled carbon nanotube supported TiO2 and its photocatalytic activity in the reduction of CO2 with H2O

Multi-walled carbon nanotube (MWCNT) supported TiO₂ composite catalysts were prepared by sol-gel and hydrothermal methods. X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy and N₂-adsorption analysis were carried out to characterize the composite catalysts. In using the sol-gel method, the MWCNTs were coated with anatase TiO₂ nanoparticles, and by the hydrothermal method, rutile TiO₂ nanorods were uniformly deposited on the MWCNTs. The photocatalytic activities of the composite catalysts were evaluated by the reduction of CO₂ with H₂O. The results indicate that the addition of an appropriate amount of MWCNTs as supports for TiO₂ could remarkably improve the efficiency of the photocatalytic reaction. The composite catalysts prepared by the sol-gel method lead to the main formation of C₂H₅OH, while HCOOH is found to be the major product on the sample prepared by the hydrothermal method.     

Cu2O/TiO2 heterostructure nanotube arrays prepared by an electrodeposition method exhibiting enhanced photocatalytic activity for CO2 reduction to methanol

Cu₂O/TiO₂ composite nanotube arrays demonstrating enhanced photocatalytic performance were synthesized using an electrodeposition method to impregnate the p-type Cu₂O into the n-type titanium dioxide nanotube arrays (TNTs). The morphological results confirmed that the TNTs are wrapped by the Cu₂O nanoparticles and the UV–Vis absorption spectra showed that the Cu₂O/TNTs display a better ability for visible light absorption compared to the pure TNTs. CO₂ photocatalytic reduction experiments carried out by using Cu₂O/TNT nanocomposites proved that Cu₂O/TNTs exhibit high photocatalytic activity in conversion of CO₂ to methanol, while pure TNT arrays were almost inactive. Furthermore, Cu₂O/TNTs also exhibited augmented activity in degradation of target organic pollutant like acid orange (AO) under visible light irradiation. The ultra enhanced photocatalytic activity noticed by using Cu₂O/TNTs in CO₂ reduction and degradation of organic pollutant could be attributed to the formation of Cu₂O/TiO₂ heterostructures with higher charge separation efficiency.     

Bismuth oxide cocatalyst and copper oxide sensitizer in Cu2O/TiO2/Bi2O3 ternary photocatalyst for efficient hydrogen production under solar light irradiation

A novel Cu₂O/TiO₂/Bi₂O₃ ternary nanocomposite was prepared, in which copper oxide improves the visible light absorption of TiO₂ and bismuth oxide improves electron–hole separation. The ternary composite exhibited extended absorption in the visible region, as determined by UV–Vis diffuse reflectance spectroscopy. High-resolution transmission electron microscopy images showed close contact among the individual semiconductor oxides in the ternary Cu₂O/TiO₂/Bi₂O₃ nanocomposite. Improved charge carrier separation and transport were observed in the Cu₂O/TiO₂/Bi₂O₃ ternary composite using electrochemical impedance spectroscopy and photocurrent analysis. TiO₂ modified with bismuth and copper oxides showed exceptional photocatalytic activity for hydrogen production under natural solar light. With optimum bismuth and copper oxide loadings, the Cu₂O/TiO₂/Bi₂O₃ ternary nanocomposite exhibited an H₂ production (3678 μmol/h) 35 times higher than that of bare TiO₂ (105?μmol/h). The synergistic effect of improved visible absorption and minimal recombination was responsible for the enhanced performance of the as-synthesized ternary nanocomposite.     

A unique Cu2O/TiO2 nanocomposite with enhanced photocatalytic performance under visible light irradiation

A unique Cu₂O/TiO₂ nanocomposite with high photocatalytic activity was synthesized via a two-step chemical solution method and used for the photocatalytic degradation of organic dye. The structure, morphology, composition, optical and photocatalytic properties of the as-prepared samples were investigated in detail. The results suggested that the Cu₂O/TiO₂ nanocomposite is composed of hierarchical TiO₂ hollow microstructure coated by a great many Cu₂O nanoparticles. The photocatalytic performance of Cu₂O/TiO₂ nanocomposite was evaluated by the photodegradation of methylene blue (MB) under visible light, and compared with those of the pure TiO₂ and Cu₂O photocatalysts synthesized by the identical synthetic route. Within 120 min of reaction time, nearly 100% decolorization efficiency of MB was achieved by Cu₂O/TiO₂ photocatalyst, which is much higher than that of pure TiO₂ (26%) or Cu₂O (32%). The outstanding photocatalytic efficiency was mainly ascribed to the unique architecture, the extended photoresponse range and efficient separation of the electron-hole pairs in the Cu₂O/TiO₂ heterojunction. In addition, the Cu₂O/TiO₂ nanocomposite also retains good cycling stability in the photodegradation of MB.     

Enhanced UV-light driven photocatalytic performances and recycling properties of TiO2/AlON composite photocatalyst

AlON has been reported to have photocatalytic capability under ultraviolet-light (UV-light), which can be improved by fabricating large-sized powder (~20?µm) having porous skeleton microstructure. To further enhance photocatalytic property of AlON, highly photocatalytic-efficient nanocrystalline TiO₂ was loaded onto both the outer and inner surface of porous AlON particles by hydrothermal method. In order to ensure easy recovery without secondary pollution, the obtained composite powder was filtered in deionized water three times to remove both small-sized AlON and free TiO₂ particles to produce a composite photocatalyst with particle size >10?µm. The proposed TiO₂/AlON showed excellent photocatalytic performance on Methylene blue (MB) and Methyl orange (MO) for 97.9% and 99.1% of pollutants (in 30?mg/L, 40?mL solution) being degraded by 50?mg as-synthesized composite photocatalyst in 120?min. Further test showed that the hydrothermal process can significantly improve the photocatalytic performance of TiO₂/AlON composite photocatalyst and its enhancement mechanism were discussed. In addition, the large-sized composite photocatalyst is easy to recover and stable to reuse with no regeneration needed.     

Effect of Pt loading and calcination temperature on the photocatalytic hydrogen production activity of TiO2 microspheres

TiO₂ microspheres were synthesized by hydrothermal reaction using Ti(OBu)₄ as the precursor. In order to enhance the efficiency of water splitting by the TiO₂ microspheres, Pt-modified TiO₂ microspheres were prepared by the impregnation-reduction method. The diameter of TiO₂ microspheres is around 5–10 μm. The photocatalytic performances of the catalysts were measured by hydrogen generation from a mixture of water and methanol under UV light irradiation. The photocatalytic activity of the TiO₂ microspheres was remarkably enhanced by loading Pt. The optimal Pt loading is 1.2 wt%. Pt/TiO₂ microspheres exhibit about 125 times greater H₂ production rate than the unmodified TiO₂ microspheres. The effect of calcination temperature on photocatalytic activity of the TiO₂ microspheres was also investigated.     

Facile in-situ Solvothermal Method to synthesize double shell ZnIn2S4 nanosheets/TiO2 hollow nanosphere with enhanced photocatalytic activities

The design and construction of efficient visible light responsive composite photocatalysts with intimate interfacial contacts in photocatalytic field have attracted huge interest. Herein, a double-shelled ZnIn₂S₄ nanosheets/TiO₂ hollow composite single nanosphere (ZIS/TiO₂) was first fabricated by a facile hydrothermal process, where 2D ZnIn₂S₄ nanosheets self-assembled on the external surface of TiO₂ hollow nanosphere to form the double-shelled hollow single sphere. The morphologies, structures, optical properties of as-prepared double-shelled ZIS/TiO₂ hollow nanospheres were characterized in detail. The photocatalytic activities of double-shelled ZIS/TiO₂ nanospheres for the photodegradations of Tetracycline hydrochloride, Levofloxacin and Rhodamine B under visible light irradiation have been investigated. Compared to pure TiO₂ and ZnIn₂S_4, the obtained ZIS/TiO₂ samples have significantly improved photocatalytic performances. The most optimal photocatalytic activity of ZIS/TiO₂-2 nanocomposite with 64 wt% ZnIn₂S₄ nanosheets coated is observed, and its degradation rate constant is 2.32 and 2.14 times as high as those of pure TiO₂ and ZnIn₂S₄. The superior photocatalytic performance of ZIS/TiO₂ nanocomposite can be ascribed to its unique double shell hollow structure and the synergistic effect between ZnIn₂S₄ and TiO₂. Our result provides some guidance for designing novel morphologies of composite photocatalyst with good photocatalytic performance.     

Experimental Study on Photocatalytic Activity of Cu2O/Cu Nanocomposites Under Visible Light

Cu₂O/Cu nanocomposites (NCs) are synthesized using a two-step hydrothermal method, their different phase compositions are obtained by adjusting the reaction time, and then, they are used as photocatalysts to degrade dye Procion Red MX-5B (PR), methylene blue (MB) and methyl orange (MO) under visible-light. Experimental results indicate Cu₂O/Cu NCs exhibit a much higher photocatalytic activity than pure Cu₂O, they remain almost unchanged in their phase compositions in the long photocatalytic reaction process, except for partial oxidation of particle surface. They still exhibit a high photocatalytic activity even at the end of four photocatalytic reaction cycles. It can therefore be concluded that Cu₂O/Cu nanocomposites are good candidates for processing of pollutant water.     

Formation of TiO2 nano fibers on a micro-channeled Al2O3-ZrO2/TiO2 porous composite membrane for photocatalytic filtration

In this study, needle-shape TiO₂ fibers were successfully fabricated inside a micro-channeled Al₂O₃-ZrO₂ composite porous membrane system using sol-gel method. The micro-channeled Al₂O₃-ZrO₂ composite was fabricated using the fibrous monolithic (FM) process. Pure anatase phase TiO₂ was crystallized from the as-coated amorphous phase during calcination at 510 °C. The TiO₂ fibers grew on the surface frame of the micro-channeled Al₂O₃-ZrO₂ composite membrane and fully covered the inside of the micro-channeled pores. The specific surface area of the TiO₂ coated membrane system was dramatically increased by over 100 fold compared to that of the non-coated system. The photocatalytic activity of the membrane was also assessed and was shown to very effectively convert organic materials. Thus, this novel membrane holds promise for use as an advanced filtration system.     

Synthesis of 3D CQDs/urchin-like and yolk-shell TiO2 hierarchical structure with enhanced photocatalytic properties

A novel CQDs/TiO₂ hierarchical structure with enhanced photocatalytic properties was achieved by uniformly decorating urchin-like and yolk-shell TiO₂ microspheres (UYTMs) with carbon quantum dots (CQDs) through an environmentally friendly hydrothermal process. The CQDs were firstly synthesized by the electrochemical method, and the TEM, Raman and PL characterizations strongly indicated that the as-prepared CQDs exhibited good dispersion, high crystallinity and unique up-conversion properties. The UYTMs synthesized by a NaOH-assisted hydrothermal process showed stable 3D hierarchical structure and large surface area, which was beneficial for light absorption and contacting with contamination. The good combination of CQDs and UYTMs was further successfully achieved during the hydrothermal process, and demonstrated by a series of tests. The photocatalytic experiments suggested that the CQDs/UYTMs exhibited better photocatalytic activities than the pure UYTMs and P25 under both visible and UV light irradiation. The CQDs/UYTMs combining with 6?wt% of CQDs showed the best photocatalytic efficiency, while excessive CQDs tended to inhibit the photocatalytic activity. According to the results and discussions, a possible mechanism in improving the photocatalytic efficiency of the CQDs/UYTMs is significantly proposed. The up-conversion property of CQDs can broaden the absorption spectrum of CQDs/UYTMs to the visible light. Moreover, the CQDs, as the electron reservoirs, are efficient to separate the electrons and holes, leading to an improved photocatalytic activity of CQDs/UYTMs.     

Graphene modified Nd/TiO2 photocatalyst for methyl orange degradation under visible light irradiation

A novel nanoscale GR–Nd/TiO₂ composite photocatalyst was synthesized by the hydrothermal method. Its crystal structure, surface morphology, chemical composition and optical properties were studied using XRD, TEM, and XPS, DRS and PL spectroscopy. It was found that graphene and neodymium modification shifts the absorption edge of TiO₂ to visible-light region. The results of photoluminescence (PL) emission spectra show that GR–Nd/TiO₂ composites possess better charge separation capability than do Nd/TiO₂ and pure TiO₂. The photocatalytic activity of prepared samples was investigated by degradation of methyl orange (MO) dye under visible light irradiation. The results show that the GR–Nd/TiO₂ composite can effectively photodegrade MO, showing an impressive photocatalytic activity enhancement over that of pure TiO₂. The enhanced photocatalytic activity of the composite catalyst might be attributed to the large adsorptivity of dyes, extended light absorption range and efficient charge separation due to Nd doping and graphene incorporation.     

Facile synthesis of Cu<Subscript>x</Subscript>O (x = 1, 2)/TiO<Subscript>2</Subscript> nanotube arrays as an efficient visible-light driven photocatalysts

TiO₂ nanotube arrays (TNTs) modified with Cu_xO (x = 1, 2) were prepared by a simple impregnation-calcinations method. The obtained samples were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy , UV–Vis diffuse reflectance spectroscopy and photocurrent tests. The photocatalytic ability of the as-prepared photocatalysts was evaluated using rhodamine B (RhB) as a target pollutant. Compared with pure TNTs, the Cu_xO/TNTs composite exhibited much higher photocatalytic activity under visible-light irradiation (λ > 420 nm). The photocatalytic activity of the composite was related to impregnation time of the copper nitrate solution, and an optimal time was 2 h. The activity of 2-Cu_xO/TNTs displayed 4.9 times as high as that of pure TNTs. The enhanced photocatalytic performance is mainly attributed to the synergistic effects of initiating visible-light absorption and the matched band edge positions of Cu₂O, CuO and TiO₂. Also, a possible mechanism on the Cu_xO/TNTs photocatalytic degradation of RhB is proposed. Overall, the inexpensive and environmentally friendly photocatalyst, as promising materials, could be used to remove some aquatic pollutants in the field of water purification.     

Preparation of hollow porous Cu2O microspheres and photocatalytic activity under visible light irradiation

Cu₂O p-type semiconductor hollow porous microspheres have been prepared by using a simple soft-template method at room temperature. The morphology of as-synthesized samples is hollow spherical structures with the diameter ranging from 200 to 500 nm, and the surfaces of the spheres are rough, porous and with lots of channels and folds. The photocatalytic activity of degradation of methyl orange (MO) under visible light irradiation was investigated by UV-visible spectroscopy. The results show that the hollow porous Cu₂O particles were uniform in diameters and have an excellent ability in visible light-induced degradation of MO. Meanwhile, the growth mechanism of the prepared Cu₂O was also analyzed. We find that sodium dodecyl sulfate acted the role of soft templates in the synthesis process. The hollow porous structure was not only sensitive to the soft template but also to the amount of reagents.     

Hydrothermal synthesis of graphene wrapped Fe-doped TiO2 nanospheres with high photocatalysis performance

In this study, graphene wrapped Fe-doped TiO₂ (G-TiO₂-Fe) spheres were prepared through a simple hydrothermal process. The structural, optical and photocatalytic properties of synthesized composite were characterized by field emission scanning electron microscope (FE-SEM), X-ray diffraction (XRD), Raman Microprobe (Raman), X-ray photoelectron spectroscopy (XPS) and UV–Vis diffuse reflectance spectrophotometer (DRS). The G-TiO₂-Fe composite showed a significant red-shift in light response edge as compared with TiO₂. Meanwhile, the band gap exhibited an obvious decline from 3.24 to 2.99 eV. The photocatalytic capacity of G-TiO₂-Fe was further evaluated by methylene blue (MB) degradation experiments, and the results indicated that the optimized G-TiO₂-Fe exhibited a remarkable increase in photocatalytic activity. The superior photocatalytic performance of the novel material could be ascribed to the synthetic effects of doped Fe and wrapped graphene shells. The unique geometrical configuration and constructive component which modified the TiO₂ electronic structure will largely improve the electron transporting efficiency and restrain the electron-hole recombination.     

Photocatalytic activity of TiO2 supported on multi-walled carbon nanotubes under simulated solar irradiation

TiO₂ particles supported on multi-walled carbon nanotubes (MWCNTs) were prepared using a sol–gel method to investigate their photocatalytic activity under simulated solar irradiation for the degradation of methyl orange (MO) in aqueous solution. The prepared composites were analyzed using XRD, SEM, EDS and UV–vis absorption spectroscopy. The results of this study indicated that there was little difference in the shape and structure of MWCNTs/TiO₂ composite and pure TiO₂ particles. The composite exhibited enhanced absorption properties in the visible light range compared to pure TiO₂. The degradation of MO by MWCNTs/TiO₂ composite photocatalysts was investigated under irradiation with simulated solar light. The results of this study indicated that MWCNTs played a significant role in improving photocatalytic performance. Different amounts of MWCNTs had different effects on photodegradation efficiency, and the most efficient MO photodegradation was observed for a 2% MWCNT/TiO₂ mass ratio. Photocatalytic reaction kinetics were described using the Langmuir–Hinshelwood (L–H) model. The photocatalyst was reused for eight cycles, and it retained over 95.2% photocatalytic degradation efficiency. Possible decomposition mechanisms were also discussed. The results of this study indicated that photocatalytic reactions with TiO₂ particles supported on MWCNTs under simulated solar light irradiation are feasible and effective for degrading organic dye pollutants.     

Ag@AgCl‐TiO2/organic rectorite/quaternized chitosan microspheres: An efficient and environmental photocatalyst

A plasmonic composite, Ag@AgCl‐TiO₂/OREC, was prepared by sol–gel combing calcination technique, precipitation, and photoreduction method. Then, Ag@AgCl‐TiO₂/OREC/QCS composite microspheres were fabricated by an emulsification/chemical crosslinking method using quaternized chitosan and Ag@AgCl‐TiO₂/OREC as scaffolds materials, potassium persulphate as initiator and N,N′‐methylenebisacrylamide as crosslinker. The resulting materials were characterized by Fourier transform infrared spectrometer (FTIR), X‐ray diffraction (XRD), UV‐visible diffused reflectance spectra (UV–vis DRS), and scanning electron microscopy (SEM). SEM showed that the Ag@AgCl‐TiO₂/OREC/QCS composite microspheres had loose, rough surface, and spherical shape, with an average diameter of 15–45 μm. The Ag@AgCl‐TiO₂/OREC/QCS composite microspheres present good adsorption–photocatalytic activities in the degradation of methylene orange (MO) and 92.1% MO was degraded after irradiation for 180 min. The high photocatalysis activity was attributed to the combined results of the relative high adsorption capacity, loose structure, and the surface plasmon resonance of silver nanoparticles formed on the surface of AgCl. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44601.     

Charge transfer properties and photoelectrocatalytic activity of TiO2/MWCNT hybrid

The vertically aligned multiwalled carbon nanotube (MWCNT) arrays on tantalum foils were successfully coated with TiO₂ nanoparticles by a hydrothermal process. The prepared TiO₂/MWCNT hybrid was characterized by scanning electron microscopy and transmission electron microscopy. The charge transfer properties and photocatalytic degradation of rhodamine B with and without bias potential under UV irradiation were investigated. The MWCNTs promoted the separation of photoinduced carriers in the TiO₂, thus enhanced photocatalytic activity. Applying bias potential on the photoanode further enhanced its catalytic activity. The efficient charge transportation and high photoelectrocatalytic activity towards degradation of rhodamine B made this hybrid material promising for photocatalyst and for the development of photoelectrical devices.     

Aerosol-assisted flow synthesis of B-doped, Ni-doped and B–Ni-codoped TiO2 solid and hollow microspheres for photocatalytic removal of NO

In this study, highly effective B-doped, Ni-doped and B–Ni-codoped TiO₂ microspheres photocatalysts were directly synthesized via an aerosol-assisted flow synthesis method. The resulting samples were characterized by XRD, SEM, TEM, UV–vis diffuse reflectance spectroscopy, nitrogen adsorption and XPS. The characterizations revealed hollow microspherical structure of the B-doped and B–Ni-codoped TiO₂ photocatalysts, while the Ni-doped and undoped TiO₂ products consisted of solid microspheres. It was found that the boron dopant was partially embedded into the interstitial TiO₂ structure, existing in the form of Ti–O–B structure. The band gap was enlarged after the boron doping. However, both Ni-doped and B–Ni-codoped TiO₂ samples showed obvious red shift in their absorption edges because of the Ni doping. The photocatalytic activities of these samples were evaluated on the photocatalytic removal of NO under simulated solar light irradiation. All the aerosol-assisted flow synthesized samples had much higher photocatalytic activities than P25 and the doped TiO₂ microspheres exhibited enhanced photocatalytic activity than the undoped counterparts. More interestingly, the B–Ni-codoped TiO₂ photocatalyst possessed superior photocatalytic activity to the as-prepared single doped TiO₂ products. The enhanced photocatalytic activity was explained and the formation mechanisms of hollow and solid microspheres were also proposed on the basis of characterizations. We think this general method may be easily scaled up for industrial production of highly active microspherical photocatalysts for efficient NO removal under simulated solar light irradiation.     

Preparation of transparent PVA/TiO2 nanocomposite films with enhanced visible-light photocatalytic activity

Polymer/semiconductor oxide nanocomposite films have been intensively investigated for various applications. In this work, we reported a simple hydrothermal method to fabricate highly transparent poly(vinyl alcohol)/titanium dioxide (PVA/TiO₂) nanocomposite films with enhanced visible-light photocatalytic activity. The as-prepared PVA/TiO₂ nanocomposite films showed high optical transparency in the visible region even at a high TiO₂ content (up to 40 wt.%). The determination of photocatalytic activity by photodegradation of methyl orange (MO) and colorless phenol showed that PVA/TiO₂ nanocomposite films exhibited enhanced visible-light photocatalytic activity and excellent recycle stability. This work provided new insights into fabrication of polymer/TiO₂ nanocomposites as high performance photocatalysts in waste water treatment.