Fabrication of Cu 2 O/TiO 2 nano-tube arrays photoelectrode and its enhanced photoelectrocatalytic performance for degradation of 2,4,6-trichlorophenol

Ti/TiO2 nanotubes sensitized PbS quantum dots as photoelectrodes applied for decomposition of anticancer drugs under simulated solar energy

One of the challenges in research into photoelectrocatalytic (PEC) degradation of pollutants is finding the appropriate photoanode material, which has a significant impact on the process efficiency. Among all others, photoelectrodes based on an ordered TiO₂ nanotube arrays are a promising material due to well-developed surface area and efficient charge separation. To increase the PEC activity of this material, the SILAR method was used to decorate Ti/TiO₂ nanotubes by PbS quantum dots (QD). The ifosfamide (IF) degradation rate constants was twice as higher for PbS-Ti/TiO₂ (0.0148 min^-1) than for Ti/TiO₂ (0.0072 min^-1). Our research showed the highest efficiency of PEC degradation of drugs using IIIPbS-Ti/TiO₂ made with 3 SILAR cycles (PbS QD size mainly 2-4 nm). The 4 and 6 of SILAR cycles resulted in the aggregation of PbS nanoparticles on the Ti/TiO₂ surface and decreased IF PEC degradation rate to 0.0043 and 0.0033 min^-1, respectively. Research on PEC mechanism has shown that the drugs are degraded mainly by the activity of photogenerated holes and hydroxyl radicals. In addition, the identified drug intermediates made possible to propose a degradation pathways of anticancer drugs and the ecotoxicity test show no inhibition of Lemna minor growth of treated solutions.

TiO2@Cu2O n-n Type Heterostructures for Photochemistry

A TiO2@Cu2O semiconductor heterostructure with better photochemical response compared to TiO2 was obtained using an electrochemical deposition method of Cu2O on the surface of TiO2 nanotubes. The choice of 1D nanotubes was motivated by the possibility of achieving fast charge transfer, which is considered best suited for photochemical applications. The morphology and structural properties of the obtained heterojunction were determined using standard methods -SEM and Raman spectroscopy. Analysis of photoelectrochemical properties showed that TiO2@Cu2O heterostructures exhibit better properties resulting from an interaction with sunlight than TiO2. A close relationship between the morphology of the heterostructures and their photoproperties was also demonstrated. Investigations representing a combination of photoelectrochemical cells for hydrogen production and photocatalysis-photoelectrocatalysis-were also carried out and confirmed the observations on the photoproperties of heterostructures. Analysis of the Mott-Schottky plots as well as photoelectrochemical measurements (Iph-V, Iph-t) showed that TiO2 as well as, unusually, Cu2O exhibit n-type conductivity. On this basis, a new energy diagram of the TiO2@Cu2O system was proposed. It was found that TiO2@Cu2O n-n type heterostructure prevents the processes of photocorrosion of copper(I) oxide contained in a TiO2-based heterostructure.

The application of FTO-Cu2O/Ag3PO4 heterojunction in the photoelectrochemical degradation of emerging pharmaceutical pollutant under visible light irradiation

We report the photoelectrochemical application of a visible light active FTO-Cu₂O/Ag₃PO₄ photoanode for the abatement of sulfamethoxazole in water. The as-synthesised photoanodes were characterised using XRD, field emission SEM, EDX, diffuse reflectance UV-vis, impedance spectroscopy and chronoamperometry. The results obtained confirmed a successful formation of p-n heterojunction at the Cu₂O/Ag₃PO₄ interface. The highest photocurrent response of 0.62 mAcm^-2 was obtained for the composite photoanode which was four times higher than pure Cu₂O and about three times higher than pristine Ag₃PO₄. The photoanode gave 67% removal efficiency within 2 h upon its photoelectrochemical application in the degradation of sulfamethoxazole with 1.5 V bias potential at pH 6.2. The FTO-Cu₂O/Ag₃PO₄ electrode was also applied in the treatment of a cocktail of synthetic organics containing sulfamethoxazole and orange II dye. The photogenerated holes was found to be the major oxidant and the photoanodes was stable and reusable.

Cu2O as an emerging semiconductor in photocatalytic and photoelectrocatalytic treatment of water contaminated with organic substances: a review

A wide range of semiconductor photocatalysts have been used over the years in water treatment to eliminate toxic organic substances from wastewater. The quest for visible or solar light driven photocatalysts with striking merits such as wide range of applications, ease of preparation, tailored architecture that gives rise to improved performance, ability of dual existence as both p type or n type semiconductor, among others, presents copper(i) oxide as a promising photocatalyst. This paper reviews the recent applications of Cu2O in photocatalytic and photoelectrocatalytic treatment of water laden with organic pollutants such as dyes and pharmaceuticals. It covers the various modes of synthesis, morphologies and composites or heterostructures of Cu2O as found in the literature. Concluding remarks and future perspectives on the application of Cu2O are presented.

Efficient removal of 2,2',4,4'-tetrabromodiphenyl ether with a Z-scheme Cu2O-(rGO-TiO2) photocatalyst under sunlight irradiation

Z-scheme Cu₂O-(rGO-TiO₂) photocatalyst was successfully synthesized via a simple three-step approach for 2,2',4,4'-tretrabromodiphenyl ether (BDE47) reductive removal under simulated solar irradiation. Unlike the traditional heterojunction, the addition of reduced graphene oxide (rGO) enhanced the redox ability of Cu₂O-TiO₂ by increasing charge transfer. When modifying Cu₂O films by adding 1% rGO and coating with 70% TiO₂, the resulting Cu₂O-(rGO-TiO₂) exhibited the best photocatalytic activity for BDE47 removal. The charge transfers of Cu₂O-(rGO-TiO₂) were proven to follow a Z-scheme pathway through the electron paramagnetic resonance analysis. The degradation pathways of BDE47 were elucidated by identifying intermediate products via gas chromatography-mass spectrometry (GC-MS) and gas chromatography (GC). Photo-electrons (e^-) generated from the conduction band of Cu₂O and hydrogen protons (H⁰) reduced from H⁺ in water were the main contributing elements for the removal of BDE47, which response to the ortho and para debromination. Ortho-Br of BDE47 was attacked by e^- and BDE28 was the dominant debromination product on the first stage. Then e^- and H⁰ attacked ortho-Br and para-Br of BDE28 to form BDE15 and BDE8, respectively. The concentration of BDE8 was higher than that of BDE15, suggesting that H⁰ played the most important role on the second debromination stage. An effective Cu₂O-(rGO-TiO₂)-based Z-scheme system for BDE47 debromination was proposed in this study, which may contribute to the development of novel green technologies.

Au-Mediated Charge Transfer Process of Ternary Cu2O/Au/TiO2-NAs Nanoheterostructures for Improved Photoelectrochemical Performance

Based on a facile three-step preparation method, Cu2O/Au/TiO2-NAs ternary heterojunction nanocomposites have been successfully synthesized by electrodepositing a Cu2O layer on the surface of Au nanoparticles (NPs) decorated highly ordered TiO2 nanotube arrays (NAs). The structure, surface morphology, chemical composition, and optical and intrinsic defects properties of the as-prepared samples are characterized by transmission and scanning electron microscopy (TEM and SEM), X-ray diffraction (XRD), UV-vis light absorbance spectra, Raman scattering, and X-ray photoelectron spectroscopy (XPS). Simultaneously, the Cu2O/Au/TiO2-NAs ternary nanohybrids exhibited progressively improved photoelectrocatalytic (PEC) performance compared with the dual Cu2O/TiO2-NAs type-II nanoheterojunctions, confirming by the photocurrent density versus testing time curve (amperometric I-t curve), open-circuit potential versus testing time curve (V oc-t curve), and electrochemical impedance spectroscopy (EIS) measurements, which were mainly ascribed to the synergistic effect of reduced interfacial charge transfer resistance and boosted energetic charge carriers generation associated with embedding Au NPs. Furthermore, the self-consistent charge transfer mechanism of Z-scheme and interband transitions mediated with Au NPs for Cu2O/Au/TiO2-NAs triple nanocomposites is proposed, which was evaluated by nanosecond time-resolved transient photoluminescence (NTRT-PL) spectra excited by 266 and 400 nm, respectively. Following this scheme, UV-vis light photocatalytic activities of Cu2O/Au/TiO2-NAs ternary nanohybrids were elaborated toward photodegradation of methyl orange (MO) in aqueous solution, and the photodegradation rate of optimum triple nanocomplex was found to be 90%.

Construction of H4x K2x Sn2-x S4+x /TiO2 nanocomposites with enhanced visible light-driven photocatalytic performance

In this paper, a new photocatalyst with TiO2 nanospheres decorated on ultrathin layered thiostannate H4x K2x Sn2-x S4+x (X = 0.5-0.6, HKTS) nanosheets was successfully synthesized by a facile solvothermal method combined with the hydrolysis of tetrabutyl titanate and it was denoted as HKTS/TiO2. By adjusting the content of tetrabutyl titanate, composites with different Sn/Ti molar ratios were prepared. The composites were applied for RhB degradation under visible light irradiation, and the optimum proportion of HKTS/TiO2 was obtained. The results of X-ray diffraction, Raman spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy confirmed that TiO2 was successfully decorated on HKTS nanosheets. The combination of TiO2 and HKTS extended the absorption wavelength of TiO2 from UV to visible light range, and the separation efficiency of photoexcited electron-hole pairs was also enhanced. The photocatalytic degradation rate of RhB over HKTS/TiO2-1.0 was almost 97.9% after 60 min illumination, which was higher than those of HKTS and pure TiO2. The photocatalyst exhibited excellent reusability and stability as the degradation rate of RhB was 95.7% even after three cycles. The photocatalytic mechanism experiment indicated that ·O2 - and h+ played a dominant role in the photocatalytic process. All these results indicate that the newly fabricated HKTS/TiO2 composites provide a high-performance photocatalyst for waste water treatment, and the application of thiostannate can be extended to the field of photocatalytic materials.

Advances in Template Prepared Nano-Oxides and their Applications: Polluted Water Treatment, Energy, Sensing and Biomedical Drug Delivery

The nano-oxide materials with special structures prepared by template methods have a good dispersion, regular structures and high specific surface areas. Therefore, in some areas, improved properties are observed than conventional bulk oxide materials. For example, in the treatment of dye wastewater, the treatment efficiency of adsorbents and catalytic materials prepared by template method was about 30 % or even higher than that of conventional samples. This review mainly focuses on the progress of inorganic, organic and biological templates in the preparation of micro- and nano- oxide materials with special morphologies, and the roles of the prepared materials as adsorbents and photocatalysts in dye wastewater treatment. The characteristics and advantages of inorganic, organic and biological template are also summarized. In addition, the applications of template method prepared oxides in the field of sensors, drug carrier, energy materials and other fields are briefly discussed with detailed examples.

Characterization of Cu2O/TiO2NTs nanomaterials using EDXRF, XRD and DRS for photocatalytic applications

TiO₂ nanotube arrays (TiO₂NTs) were decorated with Cu₂O nanoparticles by pulse electrochemical deposition. The Cu₂O nanoparticles were uniformly distributed onto TiO₂NTs surface and with diameter varying between 50 and 200 nm. The effects of the independent variables on the photocatalytic response were simultaneously assessed by a multivariate statistical design. Energy-Dispersive X-Ray Fluorescence, X-Ray Diffraction, FEG-SEM and Diffuse Reflectance Spectroscopy were employed to Cu₂O/TiO₂NTs characterization. The Cu₂O films obtained on TiO₂NTs surface were crystalline. DRS analysis confirmed that the modification of TiO₂NTs with Cu₂O nanoparticles improved the quantum efficiency of the material. The Cu₂O/TiO₂NTs photoelectrode shows an intense absorption peak in the visible region decreasing the band gap energy from 3.20eV for TiO₂NTs to 2.96 eV for Cu₂O/TiO₂NTs.

Heterostructure Cu2O/(001)TiO2 Effected on Photocatalytic Degradation of Ammonia of Livestock Houses

In this paper, a heterogeneous composite catalyst Cu2O/(001)TiO2 was prepared by the impregnation-reduction method. The crystal form, highly active facet content, morphology, optical properties, and the photogenerated electron-hole recombination rate of the as-prepared catalysts were investigated. The performance of Cu2O/(001)TiO2 was appraised by photocatalytic degradation of ammonia under sunlight and was compared with lone P25, Cu2O, and (001)TiO2 at the same reaction conditions. The results showed that 80% of the ammonia concentration (120 ± 3 ppm) was removed by Cu2O/(001)TiO2, which was a higher degradation rate than that of pure P25 (12%), Cu2O (12%), and (001)TiO2 (15%) during 120 min of reaction time. The reason may be due to the compound’s (Cu2O/(001)TiO2) highly active (001) facets content that increased by 8.2% and the band gap width decreasing by 1.02 eV. It was also found that the air flow impacts the photocatalytic degradation of ammonia. Therefore, learning how to maintain the degradation effect of Cu2O/(001)TiO2 with ammonia will be important in future practical applications.

Photocatalytic Degradation of Methylene Blue over TiO2 Pretreated with Varying Concentrations of NaOH

In this paper, different NaOH concentrations (2, 5, 10, and 15 M) were used to treat {001}TiO2. The effect of NaOH on the crystal structure, morphology, optical properties, light raw electronic-hole recombination, and degradation performance of {001}TiO2 on methylene blue were studied. The results demonstrate that rutile TiO2 appeared when the NaOH concentration was as high as 10 M, showing much better photolytic performance than others. As the concentration of sodium hydroxide increases, the morphology changes accordingly. The specific surface area increases and the optical electronic-hole recombination rate decreases. Radical scavenging tests showed that hydroxyl radical and hole are very important in photocatalysis.