Photocatalytic Composites Research Articles

Graphene-Based Photocatalysts for Hydrogen Generation.

Graphene-based photocatalysts have gained increasing interest as a viable alternate to increase photocatalytic H2 production performance in converting solar energy into chemical energy. The use of graphene to enhance the efficiency of photocatalysts has been proved due to its unique two-dimensional conjugated structure and electronic properties. In this Perspective, we have summarized the recent significant advances on the design and applications of graphene-based photocatalytic composites. The rational designs for high-performance photocatalysts using graphene-based materials are described. The applications of the new materials in photocatalytic hydrogen evolution are presented. Finally, the ongoing challenges and opportunities for the future development of graphene-based photocatalysts are also proposed.

Directed self-assembly of CdS quantum dots on bacteriophage P22 coat protein templates

The hierarchical organization of inorganic nanostructures has potential applications in diverse areas such as photocatalytic systems, composites, drug delivery and biomedicine. An attractive approach for this purpose is the use of biological organisms as templates since they often possess highly ordered arrays of protein molecules that can be genetically engineered for specific binding. Indeed, recent studies have shown that viruses can be used as versatile templates for the assembly of a variety of nanostructured materials because of their unique structural and chemical diversity. These highly ordered protein templates can be employed or adapted for specific binding interactions. Herein we report the directed self-assembly of independently synthesized 5 nm CdS nanocrystal quantum dots on ∼60 nm procapsid shells derived from wild-type P22 bacteriophage. The bacteriophage P22 shell is comprised of hexameric and pentameric clusters of subunits known as capsomeres. The pre-synthesized CdS QDs show the corresponding hexameric and pentameric patterns of assembly on these P22 shells, possibly by interacting with particular protein pockets.

A facile one-pot synthesis of Cu2O/RGO nanocomposite for removal of organic pollutant

Gathering the photocatalysis of semiconductors and the superduper electron transmittability of graphene, graphene-based semiconductor photocatalytic composites are attracting increasing interest of researchers. In this paper, a Cu2O/reduced-graphene-oxide (Cu2O/RGO) nanocomposite was prepared via a facile wet-reduction process, for removal of organic pollutants. The samples were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, transmission electron microscopy, and UV–vis spectrophotometry. The nanocomposite is composed of Cu2O nanoparticles with sizes of 100–500nm attached to the RGO sheets. For photodegradation of methylene blue (MB) under visible light, the Cu2O/RGO nanocomposites exhibited greatly enhanced photocatalytic efficiency compared to the pure Cu2O nanoparticles. The enhanced photocatalytic performance was mainly ascribed to the increased adsorptivity to organic dye as well as the efficient charge transportation and separation from Cu2O to RGO.

Novel Sm2Ti2O7/SmCrO3 heterojunction based composite photocatalyst for degradation of Rhodamine 6G dye

Efficiency of the photocatalytic reaction decreases due to the recombination of the photogenerated charge carriers. If both the charge carriers are diverted to different surfaces, then the efficiency can be improved further. This is possible with the heterojunction semiconductor photocatalyst with built in chemical potential differences that tend to separate the electron and hole into different region of the catalyst. In the quest to achieve low recombination; in this work, experimental methods and results are reported on the one-pot synthesis of Sm2Ti2O7/SmCrO3 composite semiconductor photocatalyst with heterojunction structure prepared by solid state combustion method. The prepared catalysts are characterized by XRD, DRUV–Vis spectrophotometer, HRTEM, FESEM, PL, XPS and BET surface area measurements. The activity of the prepared catalysts is tested towards the degradation of R6G dye under its natural pH. The rate of degradation of R6G dye by heterojunction photocatalysts is higher than that of single phase. The proposed mechanism for the enhanced visible-light photocatalytic activity composites was proven by photoluminescence (PL) spectroscopy and hydroxyl radicals trapping measurement.

Photo-catalytic degradation of Metanil Yellow dye using TiO2 immobilized into polyvinyl alcohol/acrylic acid microgels prepared by ionizing radiation

Polyvinyl alcohol (PVA) microgels were prepared using electron beam irradiation. To improve the PVA microgel functionality and gel fraction, chains of polyacrylic acid (PAA) were incorporated into PVA microgel by radiation grafting technique. The increase in the acrylic acid (AA) content as well as PVA Mwt is accompanied by a mutual increase in the gel fraction and a decrease in the swelling%. Immobilization of different TiO2 concentrations on the surface of the prepared PVA–AA microgel was carried out. The structural changes in the prepared PVA–AA microgel immobilized with TiO2/were investigated using FTIR, EDX and XRD. Photodegradation efficiency of TiO2/PVA–AA microgel against metnil yellow dyes was studied. TiO2/PVA–AA microgel activity increases with the increase of the amount of TiO2 and results in an increase in the rate of the photodegradation reaction. Easily recovery and reusability made TiO2/PVA/AA of great important in practice use as a photocatalytic degradation composite, for dye removal from wastewater.

Visible Light Activity of Photocatalytic Composites Composed of Metal Oxides

Visible Light Activity of Photocatalytic Composites Composed of Metal Oxides

Preparation of TiO2 nanotubes coated on polyurethane and study of their photocatalytic activity

TiO2 nanotubes have been synthesized by a hydrothermal method and their surface has been effectively modified with silane coupling agents. TiO2 nanotubes–polyurethane photocatalytic composites were then successfully synthesized through a series of activation reactions using polyurethane (PU) membrane as a solid carrier. All of these products have been characterized and identified by means of scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR). The results have shown that the TiO2 nanotubes treated by silicon alkylation could efficiently combine with the solid carrier (PU) and that the surface multilayer structure was very stable and compact. In addition, the new composite showed very good photocatalytic activity and was recyclable, which was demonstrated by the photocatalytic degradation of Rhodamine B.

Fabrication of photocatalytic composite of multi-walled carbon nanotubes/TiO 2 and its application for desulfurization of diesel

Composite of multi-walled carbon nanotubes (MWNTs) and titanium (IV) oxide (TiO 2) were prepared by a heterogeneous gelation method. The activities of the MWNTs/TiO 2 composites were evaluated by photocatalytic oxidative desulfurization using dibenzothiophene (DBT), 4,6-dimethyl dibenzothiophene (4,6-DMDBT), n-tetradecane, and commercial diesel under irradiation using a high-pressure Hg lamp. The microstructures of MWNTs/TiO 2 composites were characterized by N 2 adsorption, scanning electron microscopy, transmission electron microscope, and X-ray diffraction. It was found that more than 98% of sulfur compounds in commercial diesel were oxidized and removed by the use of the MWNTs/TiO 2 composite as a photocatalyst.

Graphene-based photocatalytic composites

The use of graphene to enhance the efficiency of photocatalysts has attracted much attention. This is because of the unique optical and electrical properties of the two-dimensional (2-D) material. This review is focused on the recent significant advances in the fabrication and applications of graphene-based hybrid photocatalysts. The synthetic strategies for the composite semiconductor photocatalysts are described. The applications of the new materials in the degradation of pollutants, photocatalytic hydrogen evolution and antibacterial systems are presented. The challenges and opportunities for the future development of graphene-based photocatalysts are also discussed.

Visible-light sensitive cobalt-doped BiVO4 (Co-BiVO4) photocatalytic composites for the degradation of methylene blue dye in dilute aqueous solutions

A series of visible-light sensitive Co-BiVO4 photocatalysts were synthesized by heteronuclear complexing method using diethylenetriamine pentaacetic acid (DTPA) as the chelating agent. The photocatalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM). UV-vis diffuse reflectance spectroscopy (DRS), and Raman spectroscopy. Results indicated that all Co-BiVO4 photocatalysts had a crystal structure of monoclinic scheelite. Loading BiVO4 with cobalt did not alter the crystal structure of the composites. Cobalt was present as oxides and was deposited on the surface of larger BiVO4 particles. The oxidation state of cobalt varied with its content in Co-BiVO4. The photocatalytic activity of Co-BiVO4 was studied by the decolorization of methylene blue (MB). BiVO4 containing 5% (molar wt) of cobalt exhibited the greatest photocatalytic activity with a 85% of MB removal versus 65% by pure BiVO4 in 5 h. Factors such as pH, initial MB concentration, electrolytes, and irradiation conditions that may affect the photodegradation of methylene blue were studied. High pH and low initial MB concentration resulted in fast photocatalytic reaction. Electrolytes, especially those capable of scavenging hydroxyls, can inhibit MB degradation. The stability of the photocatalysts was confirmed using reclaimed Co-BiVO4 in three successive runs. There was no loss of photocatalytic ability in three successive runs each of which lasted for 6h with BM removal remained high at >90%. Results demonstrated clearly that Co-BiVO4 was stable and resistant to photocorrosion during the photocatalytic oxidation of organic compounds such as methylene blue. (C) 2010 Elsevier B.V. All rights reserved.

Photocatalytic treatment of organic pollutants in textile effluent using hydrothermally prepared photocatalytic composite

The hydrothermal synthesis of TiO2 nanoparticles on the surface of calcium aluminosilicate beads of 0·5–1·0 mm in diameter has been carried out under mild hydrothermal conditions. The advantage of immobilisation of the TiO2 nanoparticles by coating on calcium aluminosilicate beads is the ease and efficiency to recover the photocatalyst. The experimental temperature was varied from 150 to 220°C and the experimental duration was 24 h with an autogenous pressure in 1M HCl as solvent. A systematic characterisation of TiO2 coated calcium aluminosilicate beads was carried out by employing analytical techniques like X-ray powder diffraction, SEM, FTIR spectroscopy and positron annihilation lifetime spectroscopy. The photocatalytic treatment of toxic organic pollutants in textile effluents was studied using hydrothermally prepared TiO2 coated calcium aluminosilicate beads. The photodegradation characteristics were studied under both sunlight and ultraviolet light source on the degradation of organic pollutants. Several parameters like concentration and dilution factors of effluents, light source and intensity, initial pH of medium, experimental duration and catalyst loaded into the aqueous medium of textile effluent were studied. The degradation reaction was optimised with respect to the experimental duration and catalytic loaded. The reduction in the chemical oxygen demand (COD) and %T revealed the minimisation of organic pollutants along with colour removal from the textile effluent.

High performance nano-titania photocatalytic paper composite. Part I: Experimental design study for TiO2 composite sheet using a natural zeolite microparticle system and its photocatalytic property

Nanosized titanium dioxide (TiO2) photocatalytic papers were successfully prepared using a natural zeolite microparticle retention aid in papermaking. Applying a factorial experimental design, natural zeolite has been demonstrated to be the most significant and interactive factor for increasing the TiO2 retention rate in paper stock. The photocatalysis of as-prepared sheets was evaluated with toluene as one of the representative volatile organic compounds (VOCs). Under UV irradiation, it was shown to be effective in removing gaseous toluene by photodecomposition, assisted by adsorption. It was revealed that natural zeolite plays an important role in both increasing retention rate of TiO2 nanoparticles and enhancing photocatalytic efficiency of the paper. The photocatalytic paper can be potentially applied for environmental purification.

High performance nano-titania photocatalytic paper composite. Part II: Preparation and characterization of natural zeolite-based nano-titania composite sheets and study of their photocatalytic activity

A novel paper composite with high photocatalytic performance was fabricated using natural zeolite (clinoptilolite)-based nanosized TiO 2. Photocatalytic materials, from sol–gel derived TiO 2 colloids to its coupling with zeolite, have been designed, prepared and characterized. As-prepared anatase TiO 2 on zeolite particles were readily used in photocatalytic paper, which revealed zeolite-TiO 2 particles dispersed on a dense network of fibers with microvoids. Natural zeolite-based TiO 2 composite sheets described here decomposed gaseous toluene very effectively after UV irradiation and its removal efficiency was higher than that accomplished by photocatalytic paper made with Degussa P25 TiO 2 or Ahlstrom commercial photocatalytic non-woven paper.

Highly Effective Silver/Semiconductor Photocatalytic Composites Prepared by a Silver Mirror Reaction

Nano silver particles loaded on micrometer-size TiO2, nanosize TiO2, and BiVO4 were prepared by a silver mirror reaction (SMR), which is an old and well-known method. Morphology of silver on the surface of semiconductor particles was characterized by energy dispersion spectrum, transmission electron microscopy, and electron backscatter diffraction. The photocatalytic activities of these photocatalysts were evaluated by the degradation of methyl orange and hydrogen production under UV and visible light irradiation, respectively. The experimental results indicated that the photocatalytic activities of Ag/TiO2 and Ag/BiVO4 composites prepared by the SMR were remarkably higher than those prepared by the photoinduced deposition method.

Synthesis and performance of a photocatalytic titania-hydroxyapatite composite

The photocatalytic degradation of methylene blue (MB) over a porous titania-hydroxyapatite (HAp) composite under ultraviolet radiation was studied. The catalyst was prepared by coating porous HAp with a titanium butoxide [Ti(OBu)4] sol at titania loadings of 17–49 wt%. Quantitative powder x-ray diffraction showed higher proportions of anatase as the calcination temperature increased from 500 to 800 °C due to crystallization of an amorphous precursor. The transformation of anatase to rutile was delayed until 900 °C, demonstrating the high thermal stability of the composite. Decomposition of HAp to α- and β- tricalcium phosphates takes place at 900 °C and is accompanied by the formation of perovskite at 1000 °C. A systematic study of the influence of calcination temperature and titania:HAp ratios demonstrated that for the optimal material, a surface area of 100 m2 g−1 was obtained at a titania loading of 49 wt% and calcination temperature of 600 °C. A highly dispersed suspension of finely ground titania-HAp enhanced the photodegradation of MB, allowed a high percentage recovery of catalyst, and was shown to be recyclable.

Design of fluidized bed photoreactors: Optical properties of photocatalytic composites of titania CVD-coated onto quartz sand

Volumetric optical properties (spectral absorption, scattering and extinction coefficients) of differently expanded narrow-path fluidized beds (FB) of a photocatalyst obtained by plasma-CVD deposition of titania onto quartz sand, relevant for photoreactor design purposes, are determined by using an unidirectional and unidimensional (1DD) model for the solution of the radiative transfer equation (RTE). Two simplified approaches are used: a Kubelka–Munk (KM) type of solution, by which the RTE is transformed into a pair of ordinary differential equations, and a discrete ordinate method (DOM) by which the complete RTE is transformed into an algebraic system that can be solved computationally. The second approach was validated by introducing the obtained optical parameters into a more elaborated bi-directional and two-dimensional (2DD) DOM model. Despite its simplicity, the KM method was able to yield fair order-of-magnitude estimates of the spectral optical properties of these FB.

Photocatalytic activity of TiO2 crystallite-activated carbon composites prepared in supercritical isopropanol for the decomposition of formaldehyde

An effort was made to develop photocatalytic TiO2 crystallite–activated carbon (TiO2-AC) composites from tetraisopropyl titanate (TPT)-soaked activated carbon in supercritical isopropanol. It was subsequently found that TPT in supercritical isopropanol could be effectively converted to the anatase form of the TiO2 crystallites. The prepared composites, composed of activated carbon as an adsorbent and the anatase form of TiO2 as a photocatalyst, were evaluated for their adsorption capacity and subsequent photocatalytic activity against formaldehyde, one of the harmful air pollutants in the environment. As a result, the supercritically treated TiO2–AC composites, particularly at 300°C and 350°C, had much higher formaldehyde-decomposing ability compared to a noncomposite comprising a simple mixture of activated carbon and TiO2 granules. This indicates that the supercritical treatment can be effective for preparing the photocatalytic composites that have a high synergetic effect of adsorption and photocatalytic decomposition of formaldehyde for environmental cleaning.

The preparation and properties study of photocatalytic nanocrystalline/nanoporous WO 3 thin films

In this paper, a r.f. magnetron reactive method is used to prepare photocatalytic nanocrystalline/nanoporous WO 3 thin films immobilized on glass plates. In order to investigate the effects of film structure and properties on photocatalytic reactivity, the structure, morphology, composition and bond of the thin films are studied with transmission electronic microscope (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The light transmission of the films is measured by an UV spectrophotometer. The microstructure, oxygen vacancies and photocatalytic reactivity of the WO 3 films have been proved as a function of deposition temperature. The structure of the films is converted from an amorphous state to a basically crystalline state with the increase of substrate temperature. The efficiency of photocatalytic degradation is improved as a result of increasing crystalline content and decreasing oxygen vacancies in the WO 3 thin films.

3,3,5-trimethylcyclohexyl ethyl ether

A protection of the skin from harmful UV rays is important in preventing the skin damage and skin aging when exposed to sunlight. Titanium dioxide composites are used as a UV filter in sunscreen products combined with organic compounds such as butyl methoxydibenzoyl methane (avobenzone) and octyl methoxycinnamate (OMC) to improve the function of the sunscreen. In this study, the photolysis of avobenzone and OMC caused by the photocatalytic TiO2 nano composites (NCs) is investigated. Three different types of oil/water (O/W) sunscreen formulations containing avobenzone and OMC were prepared. Each formulation contained one of three different types of surface modified TiO2 NCs, which were WP-S (small sized hydrophilic TiO2NCs, ~10 nm), OP-S (small sized hydrophobic TiO2NCs, ~15 nm), and OP-L (large sized hydrophobic TiO2NCs, ~200 nm). The physicochemical properties of the NCs were analyzed using biophysical tools. Addition of a different size of TiO2NCs into O/W sunscreen formulations significantly increased the photolysis of OMC. Effect of quercetin on degradation of avobenzone and OMC by the NCs was also studied for all three formulations. Although the OP-S NCs showed the lowest photocatalytic ability and the highest UV blocking capability, the NCs promoted the photolysis of OMC to the greatest extent. These results can be utilized to design more effective sunscreens, which could potentially ensure optimal photo-protection.