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.     

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.     

Photocatalytic properties of mesoporous TiO2 nanocomposites modified with carbon nanotubes and copper

The photocatalytic activity of mesoporous TiO₂ modified by the addition of carbon nanotubes (CNTs) and Cu is reported. Nanocomposites of carbon nanotubes (CNTs) containing varying amounts of Cu were formed by treatment with Cu²⁺ then reduced to Cu⁰ using NaBH₄ as the reducing agent. The mesoporous TiO₂, synthesized by a sol-gel method from titanium isopropoxide, was combined with the CNT/Cu nanocomposites to form the photocatalysts which were characterized by XRD, SEM, TEM, FTIR, XPS and BET surface area analysis. The photocatalytic properties of the mesoporous TiO₂ composites were studied by measuring the degradation of methyl orange (MO) which was optimal in the sample containing 20 wt% of the Cu-CNT nanocomposite. The degradation efficiency for MO was a synergistic effect of photo-degradation of TiO₂ and may be due to improvement of the electrical conductivity of the system by the presence of the CNT/Cu networks, since the photodegradation of MO and the photocatalytic activity of the photoactive systems increased with increasing copper content.     

High-performance Cu2O-based photocatalysts enabled by self-curling nanocelluloses via a freeze-drying route

Enhancing the photocatalytic stability of Cu₂O in the degradation of tetracycline is a great challenge in combating environmental water pollution because it is prone to deactivation by photocorrosion in aqueous environment. In this study, Cu₂O/cellulose microfiber aerogel is synthesized through freeze-drying, utilizing the self-curling effect of cellulose and then calcined to produce Cu₂O/C composite aerogel. The derived Cu₂O/C composite aerogel features hollow carbon microfibers anchored with Cu₂O nanocubes. Due to the curling structure and conductivity of the carbon microfibers, the photodegradation efficiency of the obtained Cu₂O/C composite aerogel for tetracycline is drastically improved to 97.3% under 120 min of visible-light irradiation, and remains a cycling photodegradation rate of 84.3% after 10 cycles. The Cu₂O/C composite aerogel shows remarkable strategies for designing and constructing Cu₂O-based photocatalyst in the practical photodegradation of tetracycline under visible-light exposure.     

Construction of Au/TiO2 Heterojunction with high photocatalytic performances under UVA illumination

Anatase TiO₂ nanoparticles (NPs) were successfully prepared through a hydrothermal approach, and Au NPs at various Au (0.1–2 wt%) contents were photodeposited onto the TiO₂ NPs surface. The photocatalytic efficiency for the Au/TiO₂ NPs for resorcinol photodegradation throughout UVA illumination was assessed. The TEM images and XPS findings indicated that the Au NPs are highly distributed onto TiO₂ surface in the metallic state. The 0.1%Au/TiO₂ NPs exhibited the highest photocatalytic efficiency of about 95.34%; however, 72.36% is given by pure TiO₂ NPs. It was found that the photodegradation rate of 0.1% Au/TiO₂ NPs exhibited 1.5 times of magnitude higher than pure TiO₂ NPs. 0.1%Au/TiO₂ NPs was considered to be the outstanding photoactive due to the ultimate efficient charge-carriers separation through charge transfer between Au and TiO₂ NPs. The Au NPs sizes, its dispersity on TiO₂ surface and surface plasmon resonance (SPR) were believed the critical factors for the higher photocatalytic performance of 0.1% Au/TiO₂ NPs. The prepared photocatalysts are found to be the promising materials for toxic organic compounds remediation and solar conversion.     

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.     

A novel approach for the synthesis of highly active ZnO/TiO2/Ag2O nanocomposite and its photocatalytic applications

The present work is focused on the preparation of hybrid ZnO/TiO₂/Ag₂O nanocomposite for enhanced photocatalytic activity. The resultant samples are characterized by using XRD, SEM, EDX, HR-TEM, UV-DRS, BET and XPS techniques. X-ray diffraction analysis indicates the co-existence of wurtzite, anatase and cubic phases in ZnO/TiO₂/Ag₂O nanocomposite. The band gap energy value of the photocatalyst is 3.39 eV, which has been evidenced from UV–visible diffuse reflectance spectroscopy measurements. Photocatalytic degradation of methylene blue dye has been investigated by using UV–visible spectrophotometer. From the result, it has been concluded that ZnO/TiO₂/Ag₂O nanocomposite has proven to be an efficient photocatalyst under UV irradiation when compared to that of mono and binary oxide systems. Further, the possible photodegradation mechanism is proposed to support the enhancement of photocatalytic activity towards degradation of dyes.     

Preparation of TiO2/carbon nanotubes photocatalysts: The influence of the method of oxidation of the carbon nanotubes on the photocatalytic activity of the nanocomposites

A method for the preparation of efficient TiO₂/multi-wall carbon nanotubes nanocomposite photocatalysts by precipitation of anatase TiO₂ nanoparticles onto differently oxidized carbon nanotubes is presented. The precursor compound titanium(IV) bromide was hydrolyzed producing pure anatase phase TiO₂ nanoparticles decorated on the surface of the oxidized carbon nanotubes. The oxidative treatment of the carbon nanotubes influenced the type, quantity and distribution of oxygen-containing functional groups, which had a significant influence on the electron transfer properties, i.e., the photocatalytic activity of the synthesized nanocomposites. The results of C.I. Reactive Orange 16 photodegradation in the presence of all the synthesized nanocomposites showed their better photocatalytic activity in comparison to the commercial photocatalyst Degussa P-25.     

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.     

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.     

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.     

Photocatalysis of methylene blue on titanium dioxide nanoparticles synthesized by modified sol-hydrothermal process of TiCl4

Titanium dioxide nanoparticles were synthesized by the hydrolysis and condensation of TiCl₄, an economic titanium precursor, in a mixed solvent of iso-propyl alcohol and water. As-prepared powders were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FE-SEM), energy filtering transmission electron microscopy (EF-TEM). To examine the photocatalytic activity of the as-prepared TiO₂, the photodegradation of MB which is a typical dye resistant to biodegradation has been investigated on TiO₂ powders in aqueous heterogeneous suspensions. The photocatalytic activity of TiO₂ powders prepared by the hydrolysis of TiCl₄ in the mixed solutions of iso-PrOH/H₂O exceeded that of commercial TiO₂ powders. The apparent first order rate constants (k _app) for the photodegradation of methylene blue (MB) showed a good correlation with the absorbance area obtained by UV-VIS DRS on wavelength in the limits of used lamp emission 300∼420 nm.     

Cu2O-based binary and ternary photocatalysts for the degradation of organic dyes under visible light

As competitive photocatalysts, Cu₂O nanoparticles meet with severe photogenerated carries recombination and insufficient light absorption, leading to the poor photocatalytic performance. Herein, the truncated Cu₂O-Au (CA) binary and Cu₂O-Au-TiO₂ (CAT) ternary octahedra with Au nanoparticles (Au NPs), preferentially supported on the (110) and (100) planes of Cu₂O, are synthesized for efficient photocatalytic degradation reactions. The photodegradation rates of MO of CA1 (Cu₂O-Au containing 1 wt % Au) and CAT are as high as 95.61% and 96.5% under 60 min of visible light irradiation, respectively. On the one hand, the synergistic function of localized surface plasmon resonance (LSPR) of Au NPs and Schottky barrier accelerate the separation and transfer of photogenerated carriers. On the other hand, a Z-scheme electron transfer system is constructed in CAT to promote the photodegradation performance. According to the finite-difference-time-domain (FDTD) simulation result, there is a strong electric field enhancement at the contact sites between Au, Cu₂O and TiO₂, which accelerates the electron transfer to a large extent and separates the electron-hole pairs. Therefore, this work may provide an approach for the synthesis and applications of multiple heterostructure catalyst.     

Preparation of Cu2O/TiO2 composite porous carbon microspheres as efficient visible light-responsive photocatalysts

In this paper, Cu₂O/TiO₂ composite porous microspheres were prepared in the absence of templates and additives by a simple hydrothermal method using Cu(CH₃COO)₂·H₂O and (NH₄)₂TiF₆ as precursors. The photocatalytic activity of the samples was evaluated by the photo-degradation of methylene blue (MB) aqueous solution under the visible-light illumination. To the best of our knowledge, this is the first report on the preparation and photocatalytic activity of Cu₂O/TiO₂ composite porous microspheres with a template-free hydrothermal method. This work may provide new insights into preparing other inorganic porous microspheres.     

Synthesis and characterization of interpenetrating polymer network based on sodium alginate and methacrylic acid and potential application for immobilization of TiO2 nanoparticles

An interpenetrating polymer network (IPN) based on the sodium alginate (A) and partially neutralized poly(methacrylic acid) (MAA) was prepared by free radical polymerization followed by additional cross‐linking of sodium alginate with calcium ions. Obtained material (A/MAA IPN) was characterized by FTIR spectroscopy, thermogravimetric analysis, scanning electron microscopy, and rheological measurements. Swelling behavior of synthetized IPN has been also investigated. TiO₂ nanoparticles (TiO₂ NPs) were immobilized onto A/MAA IPN by dip‐coating method and obtained TiO₂/IPN nanocomposite was used for removal of the methylene blue (MB) from aqueous solution. The photodegradation (under illumination) and sorption (in the dark) processes for dye removal were monitored through decrease of dye concentration in the solution by UV/VIS spectrometer. The TiO₂/IPN nanocomposite sorbed approximately 93% of the MB from a 10 mg L^?1 MB solution in the dark, but no degradation occurred. Likewise, more than 93% of dye was removed after 8 h of illumination. However, after 24 h of illumination, the samples were discolored indicating that dye molecules were successfully degraded. Thus, the TiO₂/IPN nanocomposite could be utilized in the photodegradation–sorption process for the abatement of pollutants in water. POLYM. ENG. SCI., 55:2511–2518, 2015. © 2015 Society of Plastics Engineers     

Preparation of aerochitin‐TiO2 composite for efficient photocatalytic degradation of methylene blue

An aerochitin–titania (TiO₂) composite was successfully synthesized and characterized by Fourier transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, field emission scanning electron microscopy, and N₂ adsorption isotherms. The photocatalytic activity of the composite was investigated on the degradation of the model organic pollutant, methylene blue (MB) dye, under UV irradiation. The aerochitin–TiO₂ composite showed excellent adsorptive and photocatalytic activity with a degradation degree of 98% for MB. The first‐order rate constants for the photodegradation MB by TiO₂ nanoparticles and aerochitin–TiO₂ composite were found to be (3.49 ± 0.04) × 10^?3 and (1.82 ± 0.02) × 10^?2 min^?1. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45908.     

Photocatalytic activity enhancement by composition control of mechano-thermally synthesized BiVO4-Cu2O nanocomposite

In this paper, BiVO₄-Cu₂O nanocomposites have been synthesized by a mechano-thermal method with a controlled composition of Bi₂O₃, V₂O₅ and Cu₂O contents. The effects of milling time, heat treatment temperature and composition on the structure and microstructure of the prepared samples were studied. The optical properties and photocatalytic performance of the samples under visible light irradiation were studied by Diffuse reflectance spectroscopy (DRS), photoluminescence (PL) and dye degradation. The BiVO₄ and Cu₂O contents in the nanocomposite were changed and the effects on the structural stability and photocatalytic performance were studied. X-ray diffraction (XRD) patterns showed that both BiVO₄ and Cu₂O contents were effective on the synthesis and stability of the monoclinic phase of BiVO₄. Field emission scanning electron microscopy (FESEM) micrographs indicated semi-spherical nanocomposite particles with an average particle size of 100 nm. The heterostructure at the interface between Cu₂O and BiVO₄ was shown by Transmission electron microscopy (TEM) and proved by X-ray photoelectron spectroscopy (XPS) spectra. DRS results indicated the minimum band gap energy of 2.12 eV for BiVO₄-10 wt% of Cu₂O with a 10 wt% excessive V₂O₅ content. The PL result has shown the lowest rate of the recombination of electron-holes for this sample. Also, the maximum degradation of 97% has been obtained for methylene blue (MB) by this sample after 240 min of being irradiated in visible light region. The photocatalytic mechanism was determined using scavengers. The kinetics of MB and methyl orange (MO) degradations was compared to study the effect of pH on the photocatalytic performance.     

Novel CdIn2S4 nano-octahedra/TiO2 hollow hybrid heterostructure: In-situ synthesis,synergistic effect and enhanced dual-functional photocatalytic activities

The development of highly efficient and multifunctional composite photocatalysts for both energy conversion and environmental governance has obtained great concerns. Here, a novel CdIn₂S₄/TiO₂ (CIS/THS) hollow composite photocatalyst was firstly designed and synthesized via a facile in-situ growth process, where the CdIn₂S₄ nano-octahedra densely attached on the surface of TiO₂ hollow spheres to form the unique hybrid heterostructure. The as-synthesized CIS/THS heterojunctions exhibit much superior photocatalytic activities for hydrogen evolution and Methyl Orange (MO) decomposition in comparison to pure CdIn₂S₄ and TiO₂ hollow spheres. The experimental results display that the CIS/THS-3 sample with the 30 wt% of TiO₂ presents the optimal photocatalytic H₂ production efficiency and its generation rate is 3.38 and 2.56 times as high as those of pure TiO₂ and CdIn₂S₄. Besides, the as-synthesized CIS/THS-3 hybrid also possesses the best MO photodegradation performance and its rate constant is 11.43 and 8.34 times higher than those of pure TiO₂ and CdIn₂S₄. The enhanced photocatalytic activities can be assigned to the synergistic effect, optimized light-harvesting capacity and the formation of hybrid heterostructure for boosting interfacial charge transfer and separation. Furthermore, based on the trapping experiments and ESR analysis, the possible type-Ⅱ interface charge transport mechanism was also proposed. Our study may provide the direct guidance for constructing other hollow TiO₂-based composite photocatalysts with superior photocatalytic water splitting and degradation performances.     

Ag nanoparticles loaded TiO2/MWCNT ternary nanocomposite: A visible-light-driven photocatalyst with enhanced photocatalytic performance and stability

A visible light active photocatalyst, Ag/TiO₂/MWCNT was synthesized by loading of Ag nanoparticles onto TiO₂/MWCNT nanocomposite. The photocatalytic activity of Ag/TiO₂/MWCNT ternary nanocomposite was evaluated for the degradation of methylene blue dye under UV and visible light irradiation. Ag/TiO₂/MWCNT ternary nanocomposite exhibits (~9 times) higher photocatalytic activity than TiO₂/MWCNT and (~2 times) higher than Ag/TiO₂ binary nanocomposites under visible light irradiation. The enhancement in the photocatalytic activity is attributed to the synergistic effect between Ag nanoparticles and MWCNT, which enhance the charge separation efficiency by Schottky barrier formation at Ag/TiO₂ interface and role of MWCNT as an electron reservoir. Effect of different scavengers on the degradation of methylene blue dye in the presence of catalyst has been investigated to find the role of photogenerated electrons and holes. Simultaneously, the Ag/TiO₂/MWCNT shows excellent photocatalytic stability. This work highlights the importance of Ag/TiO₂/MWCNT ternary nanocomposite as highly efficient and stable visible-light-driven photocatalyst for the degradation of organic dyes.     

Degradation of chlorophenol by photocatalysts with various transition metals

In this research, the photocatalytic degradation of 4-chlorophenol (4-CP) in TiO₂ aqueous suspension was studied. TiO₂ photocatalysts were prepared by sol-gel method. The dominant anatase-structure on TiO₂ particles was observed after calcining the TiO₂ gel at 500 °C for 1 hr. Photocatalysts with various transition metals (Fe, Cu, Nd, Pd and Pt) loading were tested to evaluate the effect of transition metal impurities on photodegradation. The photocatalytic degradation in most cases follows first-order kinetics. The maximum photodegradation efficiency was obtained with TiO₂ dosage of 0.4 g/L, retention time of 1 min and air flow rate of 2,500 cc/min. The photodegradation efficiency with Pt-TiO₂ or Pd-TiO₂ is higher than pure TiO₂ powder. The optimal content value of Pt and Pd is 2 wt%. However, the photodegradation efficiency with Fe(1.0 wt%)-TiO₂ and Cu(1.0 wt%)-TiO₂ is lower than pure TiO₂ powder. This paper was prepared at the 2004 Korea/Japan/Taiwan Chemical Engineering Conference held at Busan, Korea between November 3 and 4, 2004.