Photocatalytic Activity Of Photocatalysts Research Articles

Influence of heat treatment process on photocatalytic activity of photocatalyst TiO2/TiCxOy coatings during heat treatment in carbon powder

Photocatalyst TiO2/TiCxOy coatings on alumina (Al2O3) balls had been successfully fabricated by mechanical coating technique with titanium (Ti) powder and subsequent heat treatment in carbon powder. The influence of heat treatment conditions in carbon powder on the formed compounds, surface morphology and photocatalytic activity of photocatalyst TiO2/TiCxOy coatings was investigated. XRD results show that the compounds of TiCxOy and TiO2 were formed on the surface of Ti coatings during heat treatment in carbon powder. The relative amounts of TiCxOy and TiO2 remarkably varies with changing the heat treatment temperature and/or holding time. The formed nano-bump structure during heat treatment in carbon powder at 1073 or 1173 K, could increase the accessible surface area. The formation of Ti3+ and generated oxygen vacancies confirmed by XPS measurement, are in favor of narrowing band gap to enhance the visible-light photocatalytic activity of photocatalyst TiO2/TiCxOy coatings. The photocatalytic activity of the sample by heat treatment in carbon powder at 1173 K for 15 h shows highest. The fabrication strategy provides us a facile preparation procedure of visible-light responsive photocatalyst coatings.

Graphene-wrapped Ag3PO4/LaCO3OH heterostructures for water purification under visible light

We demonstrated a unique synthesis approach of graphene (GR)-wrapped Ag3PO4/LaCO3OH (APO/LCO) heterostructures by an in-situ wet chemical method. FESEM analysis reveals the formation of rhombic dodecahedrons of APO decorated with LCO and later wrapped with GR flakes. Optical studies shows two absorption edges corresponding to the band gap energies of APO (2.41 eV) and LCO (4.1 eV). Considering the absorption edge of the heterostructures in the visible region, the photocatalytic activities of photocatalysts containing different APO/LCO mass ratios were evaluated by the degradation of MB. GR-decorated composite with 20% LCO (APO/LCO20/GR) exhibited the highest photocatalytic activity for MB degradation, with a rate constant, k of 0.541 min−1. The photocatalytic activity of APO/LCO20/GR more greatly enhanced than those of the individual constituents (APO, LCO, APO/LCO20). The enhanced photocatalytic activity of the heterostructure can be attributed to the co-catalytic effect of LCO as well as intriguing physicochemical properties of GR. To understand the enhanced photocatalytic activity of the heterostructures the photocatalytic reaction mechanism is proposed in detail. The recyclability of the APO/LCO/GR composite photocatalyst is further evaluated by reusing the catalyst in replicate photocatalytic experiments which shows consistent photocatalytic activity thereby confirms the stability and reusability of heterostructure photocatalyst.

Photocatalytic performance of thermally prepared TiO 2 /C photocatalysts under artificial solar light

A simple method of preparation of artificial solar light-active TiO2 photocatalysts is presented. The new TiO2/C samples were obtained by thermal treatment (150, 250, 350 and 450 °C) of industrial titanium dioxide (TiO2-starting) in the presence of naphthalene vapours. The obtained nanomaterials were investigated by means of UV-vis/DR, Fourier transform infrared spectroscopy/diffuse reflectance infrared and X-ray powder diffraction methods. Brunauer–Emmett–Teller (BET) specific surface area and carbon content were also measured. The photocatalytic activity of the photocatalysts was investigated on the basis of phenol degradation under artificial solar light. TiO2/C photocatalysts show higher photocatalytic activity in comparison with TiO2-starting and commercial KRONOClean 7000 photocatalysts. It was noted that the highest decomposition and mineralisation degree of phenol and its degradation co-products were found for sample obtained at 450 °C and contained 0.19 wt.% of carbon. The carbon content, BET surface area and anatase crystallite size are the mean features, which strongly contribute the photocatalytic activity of new carbon-modified TiO2 photocatalysts under artificial solar light. Modification of TiO2 with naphthalene vapours is a promising method, especially taking the mineralisation of phenol and the co-products of its degradation into account.

Mechanism of NO Photocatalytic Oxidation on g-C3-N4 Was Changed by Pd-QDs Modification. [Corrected

Quantum dot (QD) sensitization can increase the light absorption and electronic transmission of photocatalysts. However, limited studies have been conducted on the photocatalytic activity of photocatalysts after modification by noble metal QDs. In this study, we developed a simple method for fabricating Pd-QD-modified g-C3N4. Results showed that the modification of Pd-QDs can improve the NO photocatalytic oxidation activity of g-C3N4. Moreover, Pd-QD modification changed the NO oxidation mechanism from the synergistic action of h+ and O2− to the single action of ·OH. We found that the main reason for the mechanism change was that Pd-QD modification changed the molecular oxygen activation pathway from single-electron reduction to two-electron reduction. This study can not only develop a novel strategy for modifying Pd-QDs on the surface of photocatalysts, but also provides insight into the relationship between Pd-QD modification and the NO photocatalytic oxidation activity of semiconductor photocatalysts.

Ag-AgBr nanoparticles loaded on TiO2 nanofibers as an efficient heterostructured photocatalyst driven by visible light

A novel photocatalyst Ag-AgBr/TiO2 heterostructured nanofibers was fabricated by means of combining solvothermal technique with photoreduction method based on the electrospun TO2 nanofibers support. And, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–vis spectrophotometer (UV–vis), and photoluminescence (PL) measurements were used to characterize the structure, morphology, and properties of the as-prepared photocatalysts. Further, the photocatalytic activity of photocatalysts was tested by degrading methylene blue dye under visible light. As a result, the photocatalytic activity of the Ag-AgBr/TiO2 heterostructured nanofibers is far superior to that of TiO2 nanofibers and Ag-AgBr power, which could be attributed to the surface plasmon resonance effect of Ag nanoparticles and the synergetic effect between the three components of Ag, AgBr and TiO2. Significantly, the stability and recycling of the photocatalyst was also investigated. The possible mechanism related to the photocatalytic performance of the Ag-AgBr/TiO2 heterostructured nanofibers was also gone deep into discuss.

Co-doped mesoporous titania photocatalysts prepared from a peroxo-titanium complex solution

In this study, nitrogen doped and nitrogen/silver co-doped TiO2 photocatalsysts were fabricated using a sol–gel method at room temperature. The obtained gels were neutralized, washed with pure water, and calcined at 400°C for 4h. The photocatalysts were characterized by scanning and transmission electron microscopy, X-ray diffraction, diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, and BET specific surface area. The results showed that spherical particles with anatase structure were produced after annealing at 400°C.N 1s (400eV) and Ag 3d (367.3eV) states indicated that nitrogen doping and silver co-doping were in the form of NO bonds and AgO, respectively. The photocatalytic activity of photocatalysts was investigated using a batch reactor system exposed to artificial solar irradiation. Both nitrogen and silver/nitrogen co-doped materials were effective in the photocatalytic degradation of hexamethyl pararosaniline chloride.

Enhanced Photocatalytic Performance of SnO<sub>2</sub> Doped with Fe<sub>2</sub>O<sub>3</sub>

In this paper, SnO2 andFe2O3 doped-SnO2 photocatalysts with different molar ratio of Fe/Sn were synthesized by a parallel flow coprecipitation method. The photocatalysts prepared were characterized by Brunauer-Emmett-Teller (BET) method, X-ray diffraction (XRD) and UV/Vis diffuse reflectance, respectively. The photocatalytic activity of photocatalysts prepared toward decolorization of methyl orange (MO) solution was evaluated. Of all of the photocatalysts prepared among the experimented compositions, Fe2O3 doped-SnO2 with 1.5%Fe possesses the best photocatalytic activity.

TiO2 supported on silica nanolayers derived from vermiculite for efficient photocatalysis

Various TiO2 composite photocatalysts were synthesized by immobilizing TiO2 nanoparticles onto the surface of silica nanolayers (SNLs) derived from vermiculite via a simple reaction between titanium hydrate and SNLs by varying Ti/SNLs ratios and using different acidic media (HCl, HNO3 and H2SO4). As-obtained composites were characterized by means of XRD, SEM and BET analytical techniques. The photocatalytic activities of photocatalysts were evaluated using methylene blue (MB) as a model pollutant in aqueous solution. It was found that the acidic media HCl and HNO3 favored the formation of tri-crystalline and flat spongy-like thin layers of TiO2 nanoparticles with large specific surface area giving excellent photocatalytic activity; while H2SO4 medium resulted in the single-phase of anatase TiO2 with ball-like aggregates on the TiO2 thin layer, giving relatively low photocatalytic activity. The excellent performance of the composites obtained using proper SNLs content and suitable acidic medium can be mainly ascribed to the mixed-phase structures with an optimum ratio and large specific surface area, as well as the facile immobilization of TiO2 on the support, which will be beneficial to their separation from water treatment system in practical application.

Photocatalytic mineralisation of humic acids using TiO2 modified by tungsten dioxide/ hydrogen peroxide

Photocatalytic mineralisation of humic acids using TiO2 modified by tungsten dioxide/ hydrogen peroxide TiO2 of anatase structure was modified by tungsten dioxide and H2O2 in order to obtain WO3-TiO2 photocatalyst with enhanced photocatalytic activity under both, UV and artificial solar light irradiations. WO2 was dissolved in 30% H2O2 and mixed with TiO2 in a vacuum evaporator at 70°C. Such modified TiO2 was dried and then calcinated at 400 and 600°C. The prepared samples and unmodified TiO2 were used for the photocatalytic decomposition of humic acids (Leonardite standard IHSS) in the aqueous solution under irradiations of both, UV and artificial solar light. Modification of TiO2 with tungsten dioxide and H2O2 improved separation of free carriers in TiO2 which resulted in the increase of OH radicals formation. Calcination caused an increase of anatase crystals and higher yield in OH radicals. The uncalcined samples showed high abilities for the adsorption of HA. Combination of adsorption abilities and photocatalytic activity of photocatalyst caused that the uncalcined TiO2 modified with WO2/H2O2 showed the shortest time of HA mineralisation. The mineralisation of HA under the artificial solar light was much lower than under the UV. It was proved that, although OH radicals are powerful in the decomposition of HA, adsorption can facilitate the contact of the adsorbed molecules with the photocatalyst surface and accelerate their photocatalytic decomposition.

Characterization and photocatalytic activity of Zn 2+–TiO 2/AC composite photocatalyst

Activated carbon (AC) supported Zn 2+–TiO 2 photocatalyst was prepared by sol–gel method. The prepared samples were characterized by X-ray diffraction, scanning electron micrograph, nitrogen absorption, diffuse reflectance UV/VIS and X-ray photoelectron spectroscopy. Using toluene as a pollution target, the photocatalytic activity of photocatalyst was evaluated. The results showed that prepared photocatalyst was obviously helpful for the removal of toluene in air. The photocatalytic degradation of toluene by Zn 2+–TiO 2/AC reached 100% for 40 min and remained 75% after 160 min, while degradation by TiO 2 was only 30%. It indicated that the photocatalytic activity of prepared photocatalyst was enhanced. It is due to Zn 2+-doping increased the oxidation and reduction of hole–electron pairs, which was the important factor in heterogeneous photocatalysis.

Novel photodegradable insecticide W/TiO2/Avermectin nanocomposites obtained by polyelectrolytes assembly

Stable and even microcrystals of Avermectin (AVM) were produced by recrystallization in presence of a stabilizer. Sequential layer growth was achieved by the layer-by-layer (LbL) self-assembly of biocompatible polyelectrolytes (PEs). The coated colloids were characterized using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The in vitro release of Avermectin from microcapsules was studied under the simulated insect midgut conditions. W-doped TiO2 photocatalysts were synthesized by a simple hydrothermal method, and characterized by Brunauer–Emmett–Teller (BET) surface area measurements and SEM. The photocatalytic activities of photocatalysts, which were undoped with TiO2 and W-doped TiO2, were evaluated by the photocatalytic oxidation degradation of AVM microcapsules in aqueous solution under UV illumination. The toxicity of the photodegradable insecticide was evaluated by the adult stage Martianus dermestoides. The results showed that AVM microcrystals which were obtained by association had a mean length of 13.8μm and a zeta potential of −34.7mV. The drug loading and encapsulation efficiency were 65.57±0.96% and 46.15±0.96%, respectively. The in vitro release experiments revealed that the polyelectrolytes prolonged the release time of the encapsulated AVM microcrystals. The sample which was prepared at 120°C with 4.0mol% W-doped amount had the highest photocatalytic activity. Toxicity of the novel photodegradable insecticide was higher in the adult stage compared to the 95% AVM as indicated by the lower LC50 value.

A novel photodegradable insecticide: Preparation, characterization and properties evaluation of nano-Imidacloprid

Imidacloprid (IMI) microcrystals were directly encapsulated with nature polysaccharides chitosan (CHI) and sodium alginate (ALG) through layer-by-layer (LbL) self-assembly. The coated colloids were characterized using confocal laser scanning microscopy (CLSM) and scanning electron microscopy (SEM). The in vitro controlled release pattern of IMI through the PE diffusion barrier was studied using a diffusion cell assembly at physiological pH of 7.4. Photocatalysts were characterized by Brunauer–Emmett–Teller (BET) surface area and SEM. The adsorption and photocatalytic activities of photocatalysts were evaluated by isothermal adsorption and IMI degradation under UV light and natural light illumination. The toxicity of the photodegradable insecticide was evaluated against the adult stage of Martianus dermestoides. The results showed that thermodynamically stable IMI microcrystals were obtained by association and had a mean length of 7 μm and a ζ-potential of −37.5. The drug loading and encapsulation efficiency were 56.15 ± 0.96% and 81.57 ± 0.96%, respectively. The polysaccharide capsules prolonged the release time of the encapsulated IMI crystals. Among the photocatalysts, SDS/Ag/TiO 2 had the highest photocatalytic activity. Toxicity of the novel 50% nano-SDS/Ag/TiO 2-IMI was higher in the adult stage compared to the 95% IMI as indicated by the lower LC 50 value.

A mesoporous structure for efficient photocatalysts: Anatase nanocrystals attached to leached clay layers

Increasing the content of anatase nanocrystals and improving the accessibility of these crystals to reactants (UV photons, organic contaminant molecules and oxygen molecules) will enhance photocatalytic performance. Thus we designed a synthesis approach to achieve such structures. The synthesis involves reaction of clay suspensions with TiOSO 4, which leads to formation of anatase nanocrystals attaching to leached clay layers through Ti–O–Si bonds. It is also discovered that the crystal size, the pore size and the specific surface area of the catalysts, can be tailored by manipulating the acidity, the ratio of Ti/clay and the hydrothermal temperature of the synthesis systems. Such a synthesis is different from the conventional approach of pillared intercalated layered clays. The activity of these catalysts for the degradation of phenol was investigated, and we find that the catalytic activity increases with the increasing volume of the pore larger than 3 nm because formation of mesoporous system and anatase nanocrystals leads to improvement in the photocatalytic activity of photocatalysts. This new structure is a more efficient photocatalyst structure for degradating organic pollutant in water, compared to the conventional titania pillared layered clay. The knowledge acquired in this study is useful for designing photocatalysts with high efficiency.

Effect of surface species on Cu-TiO 2 photocatalytic activity

The Cu-TiO 2 nanoparticles with different Cu dopant content were prepared by sol–gel method. The structure of the as-prepared catalysts and the surface species of Cu-TiO 2 were determined using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflection spectroscopy (DRS). The relationship between the photocatalytic activity and the surface species of Cu-TiO 2 was revealed via the measurement of surface photovoltage spectroscopy (SPS) as well as the degradation of the rhodamine B (RhB). The experimental results suggest that the Cu-TiO 2 photocatalysts with appropriate content of Cu (about 0.06 mol%) possess abundant electronic trap, which effectively inhibits the recombination of photoinduced charge carriers, improving the photocatalytic activity of TiO 2. While at high Cu dopant region (>0.06 mol%), the excessive oxygen vacancies and Cu species can become the recombination centers of photoinduced electrons and holes. Meanwhile, at heavy Cu doping concentration, excessive P-type Cu 2O can cover the surface of TiO 2, which leads to decrease in the photocatalytic activity of photocatalyst. The photocatalytic experimental results are in good agreement with the conclusions of SPS measurements, indicating that there is a close relationship between the photocatalytic activity and the intensity of SPS spectra.