Enhanced the photocatalytic activity of B–C–N–TiO2 under visible light:Synergistic effect of element doping and Z-scheme interface heterojunction constructed with Ag nanoparticles

In order to enhance the photocatalytic activity of TiO₂ under visible light, Ag nanoparticles were introduced into tridoped B–C–N–TiO₂ (TT) catalyst by photoreduction deposition. Ag/B–C–N–TiO₂ (ATT) catalysts with the functions of reducing band gap and carrier recombination were prepared. At the same time, the effect of the amount of Ag on the photocatalytic performance of ATT catalyst was investigated. Through XRD, XPS, PL and other characterization methods, the (211)/(101)/Ag interface heterojunction mechanism similar to the traditional Z-scheme heterojunction was proposed. The intervention of Ag nanoparticles changed the P–N interface heterojunction between (211)/(101) to the (211)/(101)/Ag Z-scheme interface heterojunction. The results show that ATT catalyst exhibits the highest photocatalytic activity when the molar amount of Ag is 0.005% with the MB degradation rate of the ATT catalyst (0.01707 min^?1), which is 14.59 times of TiO₂ (0.00117 min^?1) and 2.02 times of TT (0.00847 min^?1). In addition, the four cycles efficiencies of ATT for MB degradation were all above 94.00%.This study reveals the possibility of construction of Z-scheme heterojunctions between precious metal nanoparticles and different interfaces of TiO₂, and provides a reference for the construction of Z-scheme interface heterojunctions.     

Fabrication of TiO2‒Ag nanocomposite thin films via one-step gas-phase deposition

In this work, TiO₂‒Ag nanocomposite thin films were fabricated for the first time via simultaneous plasma-enhanced chemical vapor deposition and physical vapor deposition of TiO₂ and Ag nanoparticles in the gas-phase, respectively. The presence of Ag nanoparticles in the prepared nanocomposites has been confirmed using transmission electron microscopy and energy dispersive X-ray spectrometry techniques. The obtained electron microscopy images showed that the average size of TiO₂‒Ag nanoparticles was larger than that of pristine TiO₂. Moreover, the temperature of the anatase transformation into the rutile phase was decreased due to the presence of Ag nanoparticles in the TiO₂ matrix, while the photocatalytic activity of the produced nanocomposite (estimated by studying the degradation of methylene blue aqueous solution under UV irradiation) was 35% greater than that of pristine TiO₂. Therefore, the addition of Ag nanoparticles into the TiO₂ matrix significantly affected the morphology, phase transformation temperature, and photocatalytic performance of the fabricated material.     

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.     

A novel deposition precipitation method for preparation of Ag-loaded titanium dioxide

Ag/TiO₂ photocatalysts were prepared by a novel deposition precipitation method. Formation of Ag nanoparticles on the surface of TiO₂ was confirmed by XRD, HRTEM and XPS. The photocatalytic activity of Ag/TiO₂ was tested with the photocatalytic degradation of methyl orange and found effectively enhanced. The optimum content of Ag for photocatalytic activity is about 2.0 wt%.     

A multifunctional Ag/TiO2/reduced graphene oxide with optimal surface-enhanced Raman scattering and photocatalysis

A multifunctional Ag/TiO₂/reduced graphene oxide (rGO) ternary nanocomposite was prepared by a one-step photochemical reaction with TiO₂ and Ag nanoparticles successively deposited on reduced graphene oxide. The structure, morphology, composition, optical, and photoelectrochemical properties of Ag/TiO₂/rGO were investigated in detail. Meanwhile, the ternary nanocomposite possessed much higher adsorption capacity to organic dyes compared with bare TiO₂ and binary Ag/TiO₂, which would help to its use for surface-enhanced Raman scattering detection and photocatalytic degradation. Due to the charge transfer between rGO and organic dyes and enhanced electromagnetic mechanism of Ag, Ag/TiO₂/rGO nanocomposites as surface-enhanced Raman scattering substrates demonstrated dramatically improved sensitivity and good uniformity. The detection limit of rhodamine 6G (R6G) was as low as 10⁻⁹ mol/L, and the relative standard deviation values of the intensities remained below 5%. Most importantly, the synergistic coupling effect of three components extended the photoresponse range and accelerated separation of the electron-hole pairs, leading to greatly improved photocatalytic activity under simulated sunlight. The maximum rate constant (k, 0.06243 min⁻¹) of Ag/TiO₂/rGO was 50 and four times higher than that of TiO₂ and Ag/TiO₂, respectively.     

Solar photocatalytic decolorization of synthetic dye solution using pilot scale slurry type falling film reactor

Ag deposited TiO₂ was prepared by simple chemical reduction method and its photocatalytic efficiency was evaluated for the decolorization of methylene blue dye using pilot scale slurry type falling film reactors (FFR) under sunlight. The characterization of the prepared catalysts by XRD, TEM, EDAX, DRS and PL confirmed that silver, which acts as electron trap, was deposited over the TiO₂ surface. The operational parameters, such as catalyst loading, concentration of the dye solution, pH of the slurry, addition of oxidizing agents and effect of different substrates, were optimized. The photocatalytic efficiency of Ag deposited TiO₂ increased two-fold times than pure TiO₂ and the maximum decolorization of dye was observed under acidic conditions. The reaction rate significantly increased with the addition of oxidizing agent H₂O₂. The ceramic tile as well as double skin reactor have higher photocatalytic efficiency than glass as substrate. In addition, Ag-deposited TiO₂ photocatalyst could be easily recovered by simple sedimentation process and reused for repeated experimental cycles with more than 95% decolorization efficiency.     

Synthesis of TiO2−xNy/Ag‐PbMoO4 Composite and Their Photocatalytic Activity Under Simulated Solar Light Irradiation

TiO_2?xN_y/Ag‐PbMoO₄ composite were synthesized by sonochemical method. The results revealed that the band‐gap energy absorption edge of TiO_2?xN_y/Ag‐PbMoO₄ composite was shifted to a longer wavelength as compared to TiO₂, TiO_2?xN_y, PbMoO_4, and Ag‐PbMoO₄. The TiO_2?xN_y/Ag‐PbMoO₄ composite showed the enhanced photocatalytic activity for degradation of indigo carmine dye (ICD) under simulated solar light irradiation. The TiO_2?xN_y/Ag‐PbMoO₄ composite exhibited the highest percentage (95.4%) of degradation of ICD and the highest reaction rate constant (0.0244 min^?1) in 2 h. The results suggested that a good combination of Ag and TiO_2?xN_y nanoparticles has great influence on the photocatalytic behavior of PbMoO₄.     

Enhancement of the photocatalytic performance of Ag-modified TiO2 photocatalyst under visible light

A highly visible-light photocatalytic active Ag-modified TiO₂ (Ag–TiO₂) was prepared by a simple sol–gel process using TiOSO₄ as the starting material, AgNO₃ as a silver doping source, and hydrazine as a reducing agent. The prepared Ag–TiO₂ samples were characterized by several techniques such as X-ray powder diffraction (XRD), BET surface area measurement, scanning electron microscopy (SEM), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), energy dispersive X-ray spectrometry (EDX), X-ray absorption spectroscopy (XAS) and UV–vis diffuse reflectance spectroscopy (DRS). The Ag–TiO₂ photocatalyst, a mixture of amorphous and anatase phases, has a high surface area. The silver contents in the Ag–TiO₂ samples were determined by ICP measurements. The diffused reflectance UV–vis spectra indicated that the Ag–TiO₂ samples exhibited higher red shifts compared with the undoped TiO₂ sample. Indigo carmine degradation under visible irradiation indicated that the Ag–TiO₂ catalyst gave higher photocatalytic efficiency than those of commercial P25-TiO₂ and undoped-TiO₂ samples. The Ag–TiO₂ catalyst can be reused many times without any additional treatment.     

TiO2 nanofibers assembled on graphene-silver platform as a visible-light photo and bio-active nanostructure

The heterogeneous titanium oxide-reduced graphene oxide-silver (TiO₂/RGO/Ag) nanocomposites were successfully prepared by incorporation of two dimensional (2D) RGO nanosheets and spherical silver nanoparticles (NPs) into the 1D TiO₂ nanofibers. The novel TiO₂/RGO/Ag nanocomposites were synthesized by loading TiO₂ nanofibers, prepared via electrospinning technique, on the RGO/Ag platform. The resulting nanocomposites have been characterized using various techniques containing transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and ultra-violet-visible (UV–vis) spectroscopy. Microscopic studies clearly verified the existence of TiO₂ nanofibers with Ag NPs on the surface of RGO sheet and formation of TiO₂/RGO/Ag nanocomposites. Moreover, the results of UV–vis spectroscopy demonstrated that TiO₂/RGO/Ag nanocomposites extended the light absorption spectrum toward the visible region and significantly enhanced the visible-light photocatalytic performance of the prepared samples on degradation of rhodamine B (Rh. B) as a model dye. It was found that, incorporation of 50 µl RGO/Ag into the TiO₂ nanofibers lead to a maximum photocatalytic performance. Also, the improvement of the inactivation of Escherichia coli (E. coli) bacteria under visible-light irradiation was revealed by introduction of RGO/Ag into the TiO₂ matrix. The significant enhancement in the photo and bio-activity of TiO₂/RGO/Ag nanocomposites under visible-light irradiation can be ascribed to the RGO/Ag content by acting as electron traps in TiO₂ band gap.     

Photocatalytic activity of TiO2 nanotube layers coated with Ag and Pt

Abstract

Abstract

Thin films of anatase TiO₂ nanotube arrays (TiO₂ NTs) were prepared in this study. Pt and Ag were coated on the TiO₂ NTs films, which intend to increase the photocatalytic activity under ultraviolet-visible (UV-vis) irradiation. The phase and structure of the films were investigated by X-ray diffraction and scanning electron microscopy. Photocatalytic activity was tested by UV-vis absorption spectroscopy and showed that UV-vis light absorption of the films was remarkably improved by coated Ag and Pt by 72% and 183% respectively. The photocatalytic activities of the films towards degraded methyl orange and HCHO were compared and were all found to follow the sequence Pt/TiO₂ NTs>Ag/TiO₂ NTs>TiO₂ NTs. It was also found that the kinetics of HCHO photocatalytic degradation by the films fits the first order reaction model better and has higher efficiency than that of the methyl orange photocatalytic degradation by the same films.     

Visible light photocatalytic degradation of thiophene using Ag–TiO2/multi-walled carbon nanotubes nanocomposite

Ag–TiO₂ nanocatalyst, supported on multi-walled carbon nanotubes, was synthesized successfully via a modified sol–gel method, and the prepared photocatalyst was used to remediate aqueous thiophene environmentally by photocatalytic oxidation under visible light. The prepared Ag–TiO₂/multi-walled carbon nanotubes nanocomposite photocatalyst was characterized through X-ray diffraction, Brunauer–Emmett–Teller (BET), transmission electron microscopy, and UV–vis spectra (UV–vis). The results showed that both Ag and TiO₂ nanoparticles were well-dispersed over the MWCNTs and formed a uniform nanocomposite. Ag doping can eliminate the recombination of electron–hole pairs in the catalyst, and the presence of MWCNTs in the TiO₂ composite can change surface properties to achieve sensitivity to visible light. The optimum mass ratio of MWCNT:TiO₂:Ag was 0.02:1.0:0.05, which resulted in the photocatalyst's experimental performance in oxidizing about 100% of the thiophene in a 600 mg/L solution within 30 min and with 1.4 g L⁻¹ amount of catalyst used.     

Preparation of Ag nanoparticles loaded TiO2 nanoplate arrays on activated carbon fibers with enhanced photocatalytic activity

Ag loaded TiO₂ nanoplate array which grew on activated carbon fiber (ACF) was prepared in the present work. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV–Vis diffuse reflectance spectra (DRS). The photocatalytic degradation of methylene blue (MB) was used to investigate the activity of the synthesized samples. Under both UV and visible light irradiation, the Ag loaded samples showed enhanced photocatalytic activity. Besides, the effect of the deposition dosage of Ag nanoparticles on the photocatalytic activity was also investigated. Under UV light irradiation, the Ag nanoparticles acted as electron traps, which enhanced electron–hole separation efficiency of TiO₂. Under visible light irradiation, the Ag nanoparticles showed surface plasmon resonance, which induced the visible light responsive photocatalytic activity for the obtained samples.     

Synthesis and photocatalytic performance of PVA/TiO2/graphene‐MWCNT nanocomposites for dye removal

TiO₂/graphene‐MWCNT nanocomposite was prepared using solvothermal reaction for the effective distribution of TiO₂ nanoparticles on carbonaceous materials. TiO₂/graphene‐MWCNT nanocomposite was immobilized in poly(vinyl alcohol) (PVA) matrix for a convenient recovery after wastewater purification. MWCNT was incorporated in a nanocomposite not only to prevent the restacking of graphene but also to increase the electron transfer from TiO₂. The detailed characterization of the nanocomposite was performed using SEM, EDX, XRD, XPS, and FTIR. The photocatalytic performance of PVA/TiO₂/graphene‐MWCNT nanocomposite was investigated by UV spectroscopy on the basis of degradation of organic pollutants. PVA/TiO₂/graphene‐MWCNT nanocomposite showed improved photocatalytic decomposition of more than 70% of residual dye left in case of using PVA/TiO₂/graphene nanocomposite due to the improved electron transfer and the higher adsorption of organic pollutants. PVA/TiO₂/graphene‐MWCNT nanocomposite was suitable as a promising material for the recyclable photocatalytic wastewater purification system. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40715.     

Combination of sonochemical and freeze-drying methods for synthesis of graphene/Ag-doped TiO2 nanocomposite: A strategy to boost the photocatalytic performance via well distribution of nanoparticles between graphene sheets

Preparation of visible-light active photocatalysts for efficient degradation of pollutants from the industrial wastewater has received considerable attention in recent decades. The present study introduces a new sonochemical route for the preparation of graphene/TiO₂/Ag nanocomposite for visible-light photocatalytic degradation of X6G (C.I. Reactive Yellow 2), a commonly used textile azo-dye. The obtained graphene/TiO₂/Ag nanocomposite is extracted from the reaction solution by two drying methods: (1) conventional centrifuging and drying, and (2) freeze drying. Both of the dried samples are calcinated at 500 °C. The TEM images reveal that distribution of TiO₂/Ag nanoparticles within the graphene sheets in the freeze dried nanocomposite is better than the conventional dried sample. Furthermore, the freeze dried nanocomposite has higher photocatalytic activity than the other nanocomposite. In conventional centrifuging and drying method, some of the TiO₂/Ag nanoparticles are gradually pushed out from the graphene sheets during the drying process and graphene layers are stacked, therefore the dispersion effect of sonication is destroyed. However, in the freeze dried nanocomposite, because of the fast freezing of the sonicated sample by liquid N₂, the TiO₂/Ag nanoparticles are kept between the graphene sheets and calcination process attached and fixed them to the graphene, preserving the dispersion effect of sonication.     

Removal of persistent tartrazine dye by photodegradation on TiO2 nanoparticles enhanced by immobilized calcinated sewage sludge under visible light

TiO₂ nanoparticles on calcined sewage sludge (TiO₂/sludge) were prepared by the sol-gel method and were fully characterized. The photocatalytic efficiency of TiO₂/sludge was evaluated by tartrazine dye degradation by halide lamp. TiO₂/sludge exhibited a high photocatalytic oxidation efficiency (more than 90%) of tartrazine compared with naked TiO₂ (less than 20%) due to the synergy effect of sewage sludge. The optimization of experimental conditions was 0.5 g/l TiO₂/Sludge, pH 8 with 50 mg/l tartrazine dye. The addition of sewage sludge to TiO₂ improves the efficiency of dye mineralization. The prepared catalyst showed easier separation and effective reuse.     

Increasing of Photocatalytic Performance of TiO2 Nanotubes by Doping AgS and CdS

Highly ordered titanium nanotubes (TiO₂ NTs) photocatalyst was prepared by the anodic oxidation method, and AgS, CdS, and AgS/CdS nanoparticles were doped on the surface of TiO₂ NTs by the successive ion adsorption and reaction (SILAR) method. The photocatalysts were characterized by SEM, EDS, XRD, and potentiostat system. The SEM and EDS analyses respectively show that the average outer diameter of prepared photocatalysts is in the range of 50–120?nm, and the presence of Ti, O, Ag, and Cd is successfully proved. The photocatalytic properties of TiO₂ NTs and doped TiO₂ NTs were studied by measuring the degradation of Methylene Blue (MB) solution. The experimental results show that AgS/CdS/TiO₂ photocatalyst exhibited most efficient photocatalytic activity with 340?µA/cm² photocurrent value. AgS/CdS/TiO₂ NTs photocatalyst shows up to 22.20% higher than TiO₂ NTs, 16.42% higher than CdS/TiO₂ NTs, and 4.3% higher than AgS/TiO₂ NTs.     

Photoelectrocatalytic properties of Ag nanoparticles loaded TiO2 nanotube arrays prepared by pulse current deposition

A pulse current deposition technique was adopted to construct highly dispersed Ag nanoparticles on TiO₂ nanotube arrays which were prepared by the electrochemical anodization. The morphology, crystallinity, elemental composition, and UV-vis absorption of Ag/TiO₂ nanotube arrays were characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and diffuse reflectance spectra (DRS). In particular, the photoelectrochemical properties and photoelectrocatalytic activity under UV light irradiation and the photocatalytic activity under visible light irradiation for newly synthesized Ag/TiO₂ nanotube arrays were investigated. The maximum incident photon to charge carrier efficiency (IPCE) value of Ag/TiO₂ nanotube arrays was 51%, much higher than that of pure TiO₂ nanotube arrays. Ag/TiO₂ nanotube arrays exhibited higher photocatalytic activities than the pure TiO₂ nanotube arrays under both UV and visible light irradiation. The photoelectrocatalytic activity of Ag/TiO₂ nanotube arrays under UV light irradiation was 1.6-fold enhancement compared with pure TiO₂ nanotube arrays. This approach can be used in synthesizing various metal-loaded nanotube arrays materials.     

TiO<Subscript>2</Subscript> porous ceramic/Ag–AgCl composite for enhanced photocatalytic degradation of dyes under visible light irradiation

TiO₂ porous ceramic/Ag–AgCl composite was prepared by incorporating AgCl nanoparticles within the bulk of TiO₂ porous ceramic followed by reducing Ag⁺ in the AgCl particles to Ag⁰ species under visible light irradiation. The porous TiO₂ ceramic was physically robust and chemically durable, and the porous structure facilitated the implantation of AgCl NPs. Compared with the bare TiO₂ ceramic, TiO₂ porous ceramic/Ag–AgCl composite exhibited higher photocatalytic performance for the degradation of MO and RhB under visible light irradiation. The reaction rate constants k of MO and RhB degradation over TiO₂ porous ceramic/Ag–AgCl composite was respectively 6.25 times and 3.62 times higher than those recorded over the bare TiO₂ porous ceramic. The photocatalytic activity showed virtually no decline after four times cyclic experiments under visible light irradiation. Scanning electron microscopy, energy dispersive X-ray analysis, X-ray diffraction, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectra and X-ray photoelectron spectroscopy were used to characterize the TiO₂ porous ceramic/Ag–AgCl composite.     

Preparation of calcined hydrotalcite/TiO2-Ag composite and enhanced photocatalytic properties

A series of calcined hydrotalcite/TiO₂-Ag (HTC/TiO₂-Ag) composites with different silver (Ag) contents were successfully prepared and investigated as a catalyst for the photodegradation of phenol using UV–vis light (λ>300 nm). The Ag nanoparticles were deposited on the surface of TiO₂ (TiO₂-Ag) through photodeposition method. The TiO₂-Ag nanoparticles were supported on hydrotalcite (HT) by the co-precipitation method at variable pH (HT/TiO₂-Ag), and then calcined at 500 °C to obtain the HTC/TiO₂-Ag composites. The composites were characterized by inductively coupled plasma mass spectrometry (ICP-MS), N₂ adsorption/desorption (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), and diffuse reflectance spectra (DRS). Results show that there is an optimum silver ratio to obtain the highest photocatalytic performance in the HTC/TiO₂-Ag photocatalyst which is 2 wt%, and is assigned as HTC/TiO₂-Ag(2). The association of silver nanoparticles on TiO₂ enhanced photocatalytic activity of the bare semiconductor composite. Only 56% of phenol was photodegraded when photodegradation was performed with HTC/TiO₂, whereas ~100% was photodegraded using HTC/TiO₂-Ag(2). The data gathered from the photocatalytic degradation of phenol were successfully fitted to Langmuir-Hinshelwood model, and can be described by pseudo-first order kinetics. The results showed the HTC/TiO₂-Ag(2) as efficient photocatalyst, low cost, separable from solution by sedimentation, and reusable. The superior performance of HTC/TiO₂-Ag(2) composite photocatalyst may be attributed to the synergic catalytic effect between silver and TiO₂, dispersion of TiO₂-Ag(2) nanoparticles supported on calcined hydrotalcite, and the calcined hydrotalcite like photocatalyst.     

Investigation into Photocatalytic Degradation of Gaseous Benzene in a Circulated Photocatalytic Reactor (CPCR)

Due to the fact that suspended TiO₂ powder enjoys free contact with gaseous pollutant molecules in photocatalytic reactors, it can generally achieve better efficiency than immobilized TiO₂ catalysts. However, difficulties with the separation of this catalyst powder from treated pollutants and its re‐use often limit its application. Therefore, a circulated photocatalytic reactor (CPCR) was designed to enhance the performance of the photocatalytic degradation of gaseous benzene. TiO₂ film photocatalysts were prepared by the sol‐gel method at low temperatures and coated onto the inner wall of this reactor by a bonding agent composed of poly‐(2, 2‐dimethyl)‐acrylic ethylene ester emulsion in which TiO₂ powder was characterized by FTIR, TEM and SEM. In particular, the influences of initial concentration and gas flow rate of benzene on the degradation conversion, D_p, apparent reaction rate constants, k_r, initial degradation rate, r, and the deactivation and regeneration of catalyst in the CPCR, were investigated. The results indicated that the degradation conversion, apparent reaction rate constants and initial degradation rate were closely correlated to the initial concentration of benzene. To elucidate the factors governing the observations, the adsorption characteristics and kinetics of the photocatalytic degradation of benzene were analyzed using the Langmuir adsorption isotherm and Langmuir‐Hinshelwood kinetic model. It was found that the reaction kinetics were best described by a fixed pseudo‐first‐order kinetic equation of photocatalytic degradation of gaseous benzene in the CPCR.