Preparation and photocatalytic properties of macroporous honeycomb alumina ceramics used for water purification

In this work, porous alumina ceramics with highly ordered capillaries were successfully fabricated by ionotropic gelation process of alginate/alumina suspensions. By varying the initial solid loading (10–30 wt%) of slurries, the porosity of alumina ceramics ranged from 60.4% to 79.5% with controlled pore size (180–315 μm). Due to the well-crosslinked macroporous structure and large specific surface areas, the porous ceramics were utilized as the photocatalyst supports of TiO₂ catalysts whose photocatalytic activity was characterized by degrading methyl blue under UV irradiation. TiO₂ coatings prepared by sol–gel method demonstrated excellent adhesion to the substrates. When the solid loading of supports reached 15 wt%, the TiO₂ coatings showed the highest photocatalytic efficiency of 79.52%. Besides, TiO₂ films possessed nearly the same photocatalytic activity as titania/water suspension. Thus, the honeycomb ceramic prepared by self-organization process holds promise for use as photocatalyst supports in water purification without recycling process of powders.     

Influence of calcination temperature on the photocatalytic performance of the hierarchical TiO2 pinecone-like structure decorated with CdS nanoparticles

Herein, a novel hierarchical TiO₂ pinecone-like structure (TPS) has been successfully fabricated for the first time by self-assembling anodic oxidation methods on the Ti plate. Then it was constructed that a series of CdS-TPS nanocomposites with different cycles CdS modifying by a successive ionic layer adsorption and reaction (SILAR) after different temperature annealing in air. The structures and properties of the CdS-TPS were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Current-voltage (I-V), ultraviolet-visible (UV–vis/DRS). The results shown that the optical properties of the CdS-TPS could be rationally tailored by adjusting the CdS-modified cycles and annealing temperature, which significantly enhanced photocatalytic activity. To be used in photocatalytic organic pollutant removal after optimizing both the CdS modification cycles and annealing temperature. The 15-CdS-TPS-500?°C exhibited significantly improved photocatalytic activities of methyl orange (MO) degradation under simulated sunlight irradiation. With 180?min, 85% of the MO (0.05?mM/L, 5?mL) was photodegraded and its kinetic constant reached to 0.0104?min^?1, which is the 3.0 times and 3.6 times quicker than that of 5-CdS-TPS-500?°C and 15-CdS-TPS-0?°C, respectively. This could be ascribed to the result of the synergy effects of the suitable quantity of CdS nanoparticles modifier, the special surface structure, excellent crystallinity, higher electrical conductivity, and band structure matching. The possible photocatalytic mechanism of the CdS-TPS sample is investigated as well.     

Synthesis and Photocatalytic Activity of Anatase TiO2 Nanoparticles-coated Carbon Nanotubes

A simple and straightforward approach to prepare TiO₂-coated carbon nanotubes (CNTs) is presented. Anatase TiO₂ nanoparticles (NPs) with the average size ~8 nm were coated on CNTs from peroxo titanic acid (PTA) precursor even at low temperature of 100 °C. We demonstrate the effects of CNTs/TiO₂ molar ratio on the adsorption capability and photocatalytic efficiency under UV–visible irradiation. The samples showed not only good optical absorption in visible range, but also great adsorption capacity for methyl orange (MO) dye molecules. These properties facilitated the great enhancement of photocatalytic activity of TiO₂ NPs-coated CNTs photocatalysts. The TiO₂ NPs-coated CNTs exhibited 2.45 times higher photocatalytic activity for MO degradation than that of pure TiO₂.     

Enhanced UV-light driven photocatalytic performances and recycling properties of TiO2/AlON composite photocatalyst

AlON has been reported to have photocatalytic capability under ultraviolet-light (UV-light), which can be improved by fabricating large-sized powder (~20?µm) having porous skeleton microstructure. To further enhance photocatalytic property of AlON, highly photocatalytic-efficient nanocrystalline TiO₂ was loaded onto both the outer and inner surface of porous AlON particles by hydrothermal method. In order to ensure easy recovery without secondary pollution, the obtained composite powder was filtered in deionized water three times to remove both small-sized AlON and free TiO₂ particles to produce a composite photocatalyst with particle size >10?µm. The proposed TiO₂/AlON showed excellent photocatalytic performance on Methylene blue (MB) and Methyl orange (MO) for 97.9% and 99.1% of pollutants (in 30?mg/L, 40?mL solution) being degraded by 50?mg as-synthesized composite photocatalyst in 120?min. Further test showed that the hydrothermal process can significantly improve the photocatalytic performance of TiO₂/AlON composite photocatalyst and its enhancement mechanism were discussed. In addition, the large-sized composite photocatalyst is easy to recover and stable to reuse with no regeneration needed.     

Ag@AgCl‐TiO2/organic rectorite/quaternized chitosan microspheres: An efficient and environmental photocatalyst

A plasmonic composite, Ag@AgCl‐TiO₂/OREC, was prepared by sol–gel combing calcination technique, precipitation, and photoreduction method. Then, Ag@AgCl‐TiO₂/OREC/QCS composite microspheres were fabricated by an emulsification/chemical crosslinking method using quaternized chitosan and Ag@AgCl‐TiO₂/OREC as scaffolds materials, potassium persulphate as initiator and N,N′‐methylenebisacrylamide as crosslinker. The resulting materials were characterized by Fourier transform infrared spectrometer (FTIR), X‐ray diffraction (XRD), UV‐visible diffused reflectance spectra (UV–vis DRS), and scanning electron microscopy (SEM). SEM showed that the Ag@AgCl‐TiO₂/OREC/QCS composite microspheres had loose, rough surface, and spherical shape, with an average diameter of 15–45 μm. The Ag@AgCl‐TiO₂/OREC/QCS composite microspheres present good adsorption–photocatalytic activities in the degradation of methylene orange (MO) and 92.1% MO was degraded after irradiation for 180 min. The high photocatalysis activity was attributed to the combined results of the relative high adsorption capacity, loose structure, and the surface plasmon resonance of silver nanoparticles formed on the surface of AgCl. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44601.     

Selective photocatalytic degradation of organic pollutants by CuxS/ZnO/TiO2 heterostructures

Photoactive heterostructures containing Cu_xS/ZnO/TiO₂ have been obtained by spray pyrolysis deposition followed by post-deposition thermal treatment. The ZnO middle layer morphology was tailored by using chemical additives during the deposition. The samples have crystalline structure with average crystallite size around 80 Å for metal oxides and 90 Å for Cu_xS. The roughness varies from 27.5 nm for Cu_xS/dZnO/TiO₂ to 33.6 nm for Cu_xS/pZnO/TiO₂ samples. The wettability properties were tested based on the contact angle measurements. The highest surface energy value (106.4 mN/m) corresponding to Cu_xS/pZnO/TiO₂ with 30 min UV irradiation, with a predominant polar component of 85.3 mN/m. The photocatalytic efficiency under UV–Vis light irradiation was evaluated using methylene blue and phenol as pollutants. The highest photocatalytic values (93.4% for methylene blue and 72.3% for phenol) were obtained for Cu_xS/pZnO/TiO₂ heterostructure with successive 30 min UV irradiation at 2 h intervals. The mineralization efficiency was tested using total organic carbon analysis and the results are slightly lower compared with photocatalytic efficiency.     

Functionalizing slag wool fibers with photocatalytic activity by anatase TiO2 and CTAB modification

Anatase TiO₂ coatings prepared by solvothermal process in a neutral ethanol solution of isopropyl titanate at 160 °C have been grown on slag wool fibers (SWF) which were modified by hexadecyltrimethylammonium bromide (CTAB) in advance. X-ray diffraction patterns confirmed the coatings are of a nanocrystalline anatase structure, and scanning electron microscopy observations and energy-dispersive X-ray spectrum revealed a continuous coverage of TiO₂ formed on the fiber surfaces. The photocatalytic activity of the samples was tested by the photocatalytic degradation of methylene blue (MB) solution. The results show that CTAB modified slag wool fibers (CMSWF) are not a suitable adsorbent for MB due to their weaker negative surface charges. Anatase TiO₂ coated CMSWF display higher photocatalyst activity than anatase TiO₂ coated SWF without CTAB modification, and Anatase TiO₂ coated CMSWF are relatively stable under UV-light irradiation.     

Photocatalytic activities of electrospun tin oxide doped titanium dioxide nanofibers

SnO₂ doped TiO₂ electropsun nanofiber photocatalysts were successfully prepared by means of electrospinning process. The surface morphology, structure and optical properties of the resultant products were characterized by field-emission electron microscopy (FE-SEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), UV–vis spectroscopy, photoluminescence (PL) and cathodoluminescence (CL) techniques. The utilized physiochemical analyses indicated that the introduced SnO₂ doped TiO₂ nanofibers have a smooth surface and uniform diameters along their lengths. The photocatalytic performance of the composite nanofibers was tested for degradation of methylene blue (MB) and methyl orange (MO) dye solution under ultraviolet (UV) irradiation. Under the UV irradiation, the photocatalytic reaction rate in case of utilizing SnO₂-doped TiO₂ nanofibers was rapidly increased than that of the pristine TiO₂ nanofibers. Overall, this study demonstrates cheap, stable and effective material for photocatalytic degradation at room temperature.     

Role of phase content on the photocatalytic performance of TiO2 coatings deposited by suspension plasma spray

In this work, suspension plasma spraying (SPS) with different hydrogen (H₂) flow rates was employed to produce TiO₂ coatings with various phase contents, oxygen contents, and roughnesses. To eliminate the role of the morphology and oxygen content on the photocatalytic activity, all coatings were polished to reach the same roughness followed by heat-treatment at 550 °C in air for 48 h. Then coatings were analyzed by X-ray diffractometer (XRD), confocal laser microscope, scanning electron microscope (SEM), UV–visible spectrometer, Raman microscope, and thermogravimetric analyzer. The XRD data indicated that the percentage of anatase decreased as function of H₂ flow rates, and almost 46% of anatase transformed to rutile during SPS process at the highest H₂ flow rate. Moreover, the photocatalytic performance was evaluated by monitoring the degradation of methylene blue under visible light irradiation, and the results indicated that anatase phase positively enhances the photocatalytic activity of TiO₂ coatings.     

Photocatalytic degradation of azo dye using TiO2 supported on spherical activated carbon

TiO₂ supported on spherical activated carbon (TiO₂/SAC) was prepared through an ion-exchange method followed by a heat-treatment process. The adsorption characteristic of TiO₂/SAC was evaluated using azo dye methyl orange (MO) as a target substance, and the photocatalytic degradation of MO under UV irradiation was also discussed. A synergistic effect of both the adsorption capacity of activated carbon and the photoactivity of TiO₂ on the removal of MO from aqueous solution was observed. Experimental results revealed that the photocatalytic degradation of MO improved with increasing photocatalyst dosage and followed a pseudo-first order kinetic. After five-cycle runs, TiO₂/SAC still exhibited relatively high photocatalytic characteristic for the degradation of MO. Besides, the prepared TiO₂/SAC can be helpful in the easy separation of photocatalyst from solution after photocatalysis of MO. Furthermore, the use of liquid chromatography/mass spectrometry (LC/MS) technique, identified three intermediates as degradation products during the photocatalytic reaction of MO with TiO₂/SAC.     

Electrophoretic deposition of nanocrystalline hydroxyapatite on Ti6Al4V/TiO2 substrate

Hydroxyapatite is a bioactive material that is the main inorganic constituent of human hard tissue (Ca/P ratio of 1.67) whose coatings provide requisite surface bioactivity to the bone implants. In the current work, the characteristics of nanocrystalline hydroxyapatite (HA) coatings, electrophoretically deposited on Ti6Al4V substrate, have been investigated. To enhance the coating’s compatibility, a 0.75 μm thick TiO₂ layer was thermally grown as a diffusion barrier prior to electrophoretic deposition of HA. Subsequently, HA was electrophoretically deposited (EPD) at different deposition voltages (100–250 V) while keeping the deposition time as 10 s. Both anodic oxidation during EPD for 10 s and thermal oxidation during sintering at 1000°C for 2 h resulted in the growth of a TiO₂ layer thickness of more than 25 μm. Enhancement of voltage also has shown significant influence on the mechanism of the evolution of biphasic microstructures, attributed to the simultaneous growth of TiO₂ and HA phases. Optimized distribution of HA and TiO₂ phases was evidenced at 200 V, with explicit HA retention as observed via transmission electron microscopy. An empirical relationship is developed to relate the voltage with the suppression of cracking in the deposited coatings.     

Effect of TiO2 on sinterability and physical properties of pressureless sintered Ti3AlC2 ceramics

TiO₂ was selected as effective sintering aid for pressureless sintering of Ti₃AlC₂ ceramics in this study. The addition of only 5?wt% TiO₂ largely promotes the densification and nearly dense Ti₃AlC₂ ceramic was obtained by pressureless sintering at 1500?°C. Significant strengthening and toughening effects were observed with the addition of TiO₂. High Vickers hardness, flexural strength and fracture toughness of 3.22?GPa, 298?MPa and 6.2?MPa?m^?1/2, respectively, were achieved in specimen pressureless sintered with 10?wt% TiO₂. Additionally, the addition of 5?wt% TiO₂ had no deleterious effect on the excellent oxidation resistance of Ti₃AlC₂ ceramic under 1200?°C water vapor atmosphere, while addition of 10?wt% TiO₂ accelerates the oxidation rate by two orders of degree.     

Statistical optimization of process conditions for photocatalytic degradation of phenol with immobilization of nano TiO<Subscript>2</Subscript> on perlite granules

Response surface methodology (RSM) using D-optimal design was applied to optimization of photocatalytic degradation of phenol by new composite nano-catalyst (TiO₂/Perlite). Effects of seven factors (initial pH, initial phenol concentration, reaction temperature, UV irradiation time, UV light intensity, catalyst calcination temperature, and dosage of TiO₂/perlite) on phenol conversion efficiency were studied and optimized by using the statistical software MODDE 8.02. On statistical analysis of the results from the experimental studies, the optimum process conditions were as follows: initial pH, 10.7; initial phenol concentration, 0.5 mM; reaction temperature, 27 °C; UV irradiation time, 6.5 h; UV light intensity, 250 W; catalyst calcination temperature, 600 °C; and TiO₂/perlite dosage, 6 g/L. Analysis of variance (ANOVA) showed a high coefficient of determination (R²) of 91.8%.     

Fabrication of superhydrophilic self-cleaning SiO2–TiO2 coating and its photocatalytic performance

Generally, superhydrophilic self-cleaning coatings are prepared from semiconductors with photocatalytic properties. Organic pollutants attached to the coating surface can be degraded by its photocatalytic performance realizing a self-cleaning goal. Herein, SiO₂–TiO₂ composite particles were fabricated by the hydrolysis and precipitation of TiOSO₄, and SiO₂ microspheres were chosen as carriers, which are inexpensive and environmentally friendly. Then, superhydrophilic self-cleaning SiO₂–TiO₂ coatings were fabricated by spraying the composites on the surfaces of substrates. The morphology, structure and self-cleaning performance of the SiO₂–TiO₂ coating were characterized and tested. The results revealed that nano-TiO₂ was loaded on the surfaces of SiO₂ microspheres uniformly forming a hierarchical micro/nanostructure. The SiO₂–TiO₂ composite particles exhibited excellent photocatalytic degradation performance, and the degradation rate of methyl orange (10 ppm) was more than 98% under UV irradiation for 40 min. Furthermore, the coating prepared with the SiO₂–TiO₂ composite particles exhibited superhydrophilicity. A water droplet spreads completely on the coating surface in 0.35 s, and the contact angle reaches 0°. In addition, rhodamine B (RhB) and methylene blue (MB) on the coating surface can be degraded efficiently under sunlight irradiation. The SiO₂–TiO₂ composite particles can be sprayed directly on the surfaces of concrete, brick, wood, and glass slides. Therefore, the particles showed good adaptability to different substrates. The superhydrophilic property was due to the hydrophilicity of SiO₂ and TiO₂, the hierarchical micro/nanostructure of the SiO₂–TiO₂ composites, and the photoinduced superhydrophilicity of TiO₂. The above experimental results show that the as-prepared superhydrophilic self-cleaning SiO₂–TiO₂ coating has a large application potential.     

Photocatalytic degradation of methylene blue and acetaldehyde by TiO<Subscript>2</Subscript>/glaze coated porous red clay tile

Nanosized TiO₂ sol synthesized by sol-gel method was successfully coated on the porous red clay tile (PRC tile) with micrometer sized pores. PRC tile was first coated with a low-firing glaze (glaze-coated PRC tile) and then TiO₂ sol was coated on the glaze layer. A low-fired glaze was prepared at various blending ratios with frit and feldspar, and a blending ratio glazed at 700 °C was selected as an optimum condition. Then TiO₂ sol synthesized from TTIP was dip-coated on the glazed layer (TiO₂/glaze-coated PRC tile), and it was calcined again at 500 °C. Here, these optimum calcination temperatures were selected to derive a strong bonding by a partial sintering between TiO₂ sol particles and glaze layer. Photocatalytic activity on the TiO₂/glaze-coated PRC tile was evaluated by the extent of photocatalytic degradation of methylene blue and acetaldehyde. Methylene blue with the high concentration of 150 mg/l on the surface of TiO₂/glaze-coated PRC tile was almost photodegraded within 5 hours under the condition of average UV intensity of 0.275 mW/cm₂, while no photodegradation reaction of methylene blue occurred on the glaze-coated PRC tile without TiO₂. Another photocatalytic activity was also evaluated by measuring the extent of photocatalytic degradation of gaseous acetaldehyde. The photodegradation efficiency in TiO₂/glaze-coated PRC tile showed about 77% photocatalytic degradation of acetaldehyde from 45,480 mg/l to 10,536 mg/l after the UV irradiation of 14 hours, but only about 16% in the case of the glaze-coated PRC tile.     

Preparation and characterization of a novel activated carbon‐supported N‐doped visible light response photocatalyst (TiO2−xNy/AC)

A photocatalyst, TiO_2?xN_y/AC (activated carbon (AC) supported N‐doped TiO₂), highly active in both the Vis and UV range, was prepared by calcination of the TiO₂ precursor prepared by acid‐catalyzed hydrolysis in an ammonia atmosphere. The powders were characterized by diffuse reflectance spectroscopy, scanning electron microscopy, X‐ray diffraction, N₂ adsorption, Fourier transform infrared spectroscopy and phenol degradation. The doped N in the TiO₂ crystal lattice creates an electron‐occupied intra‐band gap allowing electron‐hole pair generation under Vis irradiation (500–560 nm). The TiO_2?xN_y/AC exhibited high levels of activity and the same activity trends for phenol degradation under both Vis and UV irradiation: TiO_2?xN_y/AC calcined at 500 °C for 4 h exhibited the highest activity. The band‐gap level newly formed by doped N can act as a center for the photo‐generated holes and is beneficial for the UV activity enhancement. The performance of the prepared TiO_2?xN_y/AC photocatalyst revealed its practical potential in the field of solar photocatalytic degradation of aqueous contaminants. Copyright © 2007 Society of Chemical Industry     

Preparation and antibacterial activity of Ag/TiO2-functionalized ceramic tiles

An Ag/TiO₂ coating was deposited onto glazed ceramic tiles by a sol-gel and spraying method at high temperatures. The coating was characterized by X-ray diffraction, scanning electron microscopy, and atomic force microscopy. The results showed that silver was present in rutile-TiO₂, and the temperature did not change the phase composition of the samples. The Ag/TiO₂ coating had a higher roughness than the TiO₂ coating. The tape test (D 3359–08) showed that the coatings prepared at 950 °C and 1000 °C had good adhesion to the ceramic tile substrate. The antibacterial activity of the coating was tested by photocatalytic sterilization experiments. The results showed that the Ag/TiO₂ coating had a higher antibacterial activity than the TiO₂ coating, and the sterilization efficiency of Escherichia coli, Staphylococcus aureus, Shigella, and Salmonella exceeded 99.655% under 2 h of visible light irradiation. This research provides a method to create Ag/TiO₂ coatings with good thermal resistance, adhesion, and antibacterial activity. This improves the low photocatalytic activity caused by the anatase-to-rutile transformation of TiO₂ at high temperatures and the poor adhesion at low temperatures.     

The effect of UV irradiation on the electrospun PCL/TiO2 composites fibers

The effect of UV irradiation and micro‐ and nano‐TiO₂ as well as titanate nanotubes (TiNT) on the phase morphology and thermal properties of the electrospun PCL composite fibers was investigated. Polycaprolactone (PCL)/TiO₂ (micro‐ and nano‐TiO₂ as well as titanate nanotubes) composite fibers were prepared by electrospinning a polymer solution. The PCL and PCL/TiO₂ composite fibers were exposed to UV light at irradiation times of 5 and 10 days. After UV irradiation the crystallinity of the electrospun PCL/TiNTcomposite fibers increased because of the large specific surface area of TiNT. The thermal stability of the PCL/TiNT electrospun composite fibers increased due to the formation of crosslinking structure after UV irradiation. The SEM analysis suggests that after UV radiation the fibers showed high degree of degradation due to the high number of fibers breakages and fibers surface voids. The results of FTIR spectroscopy confirmed that the TiO₂ particles enhance the degradation process because of their photocatalytic activity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43539.     

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.     

Photocatalytic H2 Production from Ethanol–Water Mixtures Over Pt/TiO2 and Au/TiO2 Photocatalysts: A Comparative Study

Pt/TiO₂ (Pt loadings 0–4 wt%) and Au/TiO₂ (Au loadings 0–4 wt%) photocatalysts were synthesized, characterized and tested for H₂ production from ethanol–water mixtures (80 vol% ethanol, 20 vol% H₂O) under UV excitation. Average metal nanoparticle sizes determined by TEM were 1–3 nm for Pt in the Pt/TiO₂ photocatalysts and 5–7 nm for Au in the Au/TiO₂ photocatalysts. Au/TiO₂ showed an intense localized surface plasmon resonance feature at ~570 nm, typical for metallic Au nanoparticles of diameter ~5 nm supported on TiO₂. X-ray photoelectron spectroscopy and X-ray diffraction analyses established that Pt and Au were present in metallic form on the TiO₂ support. X-ray fluorescence revealed close accord between nominal and actual Pt and Au loadings. The Au/TiO₂ and Pt/TiO₂ photocatalysts both displayed very high activities for H₂ production under UV irradiation, with the Au/TiO₂ samples affording slightly superior rates of H₂ production at most metal loadings. The 2 wt% Au/TiO₂ and 1 wt% Pt/TiO₂ photocatalysts showed the highest H₂ production rates (32–34 mmol g^?1 h^?1). Photoluminescence studies confirmed that Pt and Au nanoparticles positively enhance the photocatalytic properties of P25 TiO₂ for H₂ production by acting as electron acceptors and thereby suppressing electron–hole pair recombination in TiO₂.