Synthesis and characterization of highly dispersed TiO2 nanocrystal colloids by microwave-assisted hydrothermal method

Anatase TiO₂ nanocrystal colloids with high dispersion and photocatalytic activity were rapidly synthesized from peroxo-titanium-acid precursor by microwave-assisted hydrothermal method within 30?min at low temperature (120–180?°C). The transmission electron microscopy results indicate that the as-prepared TiO₂ have a narrow particle size distribution (25–29?nm) and high dispersion. The crystal structure of all these products are pure anatase phase (XRD, Raman), and they show good crystallinity and large surface area (N₂ adsorption–desorption measurements BET). The results of the UV–Visible absorbance and Fourier transform infrared spectra indicate that the surface peroxo group Ti(O₂) still remains in TiO₂ nanoparticles prepared by microwave-assisted hydrothermal method at 120?°C, and this surface peroxo group can be decomposed effectively by drying at 140?°C. The photocatalytic activity of the as-prepared TiO₂ were evaluated by the degradation of reactive brilliant red X-3B, it is found that the as-prepared TiO₂ exhibited good photocatalytic performance. Moreover, the existence of surface peroxo group greatly suppressed the photocatalytic activity of the TiO₂ nanoparticles.     

Microwave hydrothermal synthesis of AgInS2 with visible light photocatalytic activity

AgInS₂ nanoparticles with superior visible light photocatalytic activity were successfully synthesized by a microwave hydrothermal method. This method is a highly efficient and rapid route that involves no organic solvents, catalysts, or surfactants. The photocatalytic activity of AgInS₂ nanoparticles was investigated through the degradation of dyes under visible light irradiation. Compared with TiO_2−xN_x, AgInS₂ has exhibited a superior activity for photocatalytic degradation MO under the same condition. The experiment results showed that superoxide radicals (O₂⁻), hydrogen peroxides (H₂O₂) and holes (h⁺) were the mainly active species for the degradation of organic pollutants over AgInS₂. Through the determination of flat band potential, the energy band structure of the sample was obtained. A possible mechanism for the degradation of organic pollutant over AgInS₂ was proposed.     

Cu-BTC metal organic framework (MOF) derived Cu-doped TiO2 nanoparticles and their use as visible light active photocatalyst for the decomposition of ofloxacin (OFX) antibiotic and antibacterial activity

Herein, we report the ultrasonic-assisted precipitation technique for the fabrication of Cu-doped TiO₂ nanoparticles. The prepared sample showed high crystallinity, purity and nanoparticles like structure with the diameter in the range of 10–22 nm. The bandgap for Cu-doped TiO₂ nanoparticles was estimated to be 2.91 eV using Tauc plot, which is considerable for improving the light-harvesting capacity. Further, the prepared Cu-doped TiO₂ was used as photocatalyst for the eradication of ofloxacin (OFX), an antibiotic from an aqueous phase under visible illuminations. About 72% degradation of OFX (10 mg/L, pH 7) was achieved with Cu-doped TiO₂ nanoparticles after 180 min of visible illumination. The probable photocatalytic mechanism for the decomposition of OFX has been proposed based on reactive species trapping study. Moreover, the antibiotic efficiency of OFX was investigated against Escherichia coli and it was observed that its antimicrobial activity was significantly diminished after the photocatalytic decomposition of the OFX solution with synthesized nanoparticles.     

Mesocrystalline TiO<Subscript>2</Subscript>/sepiolite composites for the effective degradation of methyl orange and methylene blue

Mesocrystalline TiO₂/sepiolite (TiS) composites with the function of adsorption and degradation of liquid organic pollutants were successfully fabricated via a facile and low-cost solvothermal reaction. The prepared TiS composites were characterized by FESEM, HRTEM, XRD, XPS, N₂ adsorption-desorption, UV–vis DRS, and EPR. Results revealed the homogeneous dispersion of highly reactive TiO₂ mesocrystals on the sepiolite nanofibers. Thereinto each single–crystal–like TiO₂ mesocrystal comprised many [001]-oriented anatase nanoparticles about 10–20 nm in diameter. The photocatalytic activity was further evaluated by the degradation of anionic dye (methyl orange) and cationic dye (methylene blue) under the UV-vis light (350≤λ≤780 nm) irradiation. By selecting appropriate experimental conditions, we can easily manipulate the photocatalytic performance of TiS composites. The optimal TiS catalyst (the sepiolite content of 28.5 wt.%, and the reaction time of 24 h) could efficiently degrade methyl orange to 90.7% after 70 min, or methylene blue to 97.8% after 50 min, under UV-vis light irradiation. These results can be attributed to their synergistic effect of high crystallinity, large specific surface area, abundant hydroxyl radicals, and effective photogenerated charge separation.     

Unique and hierarchically structured novel Co<Subscript>3</Subscript>O<Subscript>4</Subscript>/NiO nanosponges with superior photocatalytic activity against organic contaminants

In the present study, novel Co₃O₄/NiO nanosponges designed for the photocatalytic degradation of organic contaminants were synthesized by a simple precipitation technique. The formation of sponge-like nanostructures was clearly evident through the TEM analysis. The photocatalytic efficiency was tested against rhodamine B (RhB) and congo red (CR) dye solutions. Co₃O₄/NiO nanosponges showed excellent and enhanced photocatalytic efficacy compared to those of Co₃O₄, NiO nanoparticles, and standards like TiO₂ and ZnO. The influence of paramount important operational parameters was explored and the conditions for the best photocatalytic efficiency were optimized. The trapping experiment revealed that the reactive oxygen species (ROS) identified was $OH radical. These findings certainly open up a new way for synthesizing a morphology dependent photocatalyst.     

Synthesis of nanostructured TiO2 particles in room temperature ionic liquid and its photocatalytic performance

Nanostructured TiO₂ particles were synthesized by sol-gel method with room temperature ionic liquid (RTIL) 1-n-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) as a reaction medium. The structure and morphology of TiO₂ nanoparticles were characterized with X-ray powder diffraction (XRD) and transmission electron microscopy (TEM). The as-prepared TiO₂ nanoparticles present anatase crystal phase even without being calcined at high temperature, and show better photocatalytic performance in the degradation of methyl orange. The photocatalytic efficiency increases evidently along with increasing the concentration of nanostructure TiO₂, and the degradation percent can reach 100% at the optimal catalyst concentration (2.0 g/L).     

Preparation of metal ion (Fe and Ni) doped TiO2 nanoparticles supported on ZSM-5 zeolite and investigation of its photocatalytic activity

Metal ion doped TiO₂ nanoparticles supported on ZSM-5 zeolite (M-TiO₂/ZSM-5 composites, M = Fe or Ni) were synthesized by hydrothermal method. The prepared composites were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activities of composites were evaluated by degradation of yellow GX aqueous solution under ambient condition. Fe-TiO₂/ZSM-5 composite showed to be more efficient catalyst for degradation of dye molecules as compared with Ni-TiO₂/ZSM-5 and TiO₂/ZSM-5. Its higher photocatalytic activity is attributed to the effective separation of charge carriers that will be discussed in this paper in detail.     

Facile synthesis of nano-TiO2/stellerite composite with efficient photocatalytic degradation of phenol

In this paper, we report a kind of nano-TiO₂/stellerite composite with enhanced photoactivity, which was synthesized by a typical homogeneous precipitation method followed by a calcination crystallization process using natural stellerite as support. The as-prepared composites were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), nitrogen adsorption-desorption, high resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The results showed that TiO₂ loading amounts and calcination temperatures had significant influence on the adsorption and photocatalytic degradation properties of phenol. Moreover, it was indicated that the TiO₂ nanoparticles (NPs) with smaller grain size (around 12.0?nm) and narrower size distributions were uniformly deposited on the surface of stellerite as a layer of film. Compared with commercial P25, the received composite exhibited more superior photocatalytic degradation performance towards phenol. The enhanced photocatalytic degradation performance should result from the better dispersibility of TiO₂ NPs and higher separation efficiency of photogenerated electron-hole pairs. This work may set foundation for the practical application of this new composite photocatalyst in the field of wastewater treatment.     

Preparation and characterization of Cu-doped TiO2 nanomaterials with anatase/rutile/brookite triphasic structure and their photocatalytic activity

Pure TiO₂ and Cu–doped TiO₂ containing different amounts of copper ions with anatase/rutile/brookite triphasic structure were successfully synthesized through a simple hydrothermal method. The obtained samples were characterized by X–ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), transmission electron microscope (TEM), X–ray photoelectron spectroscopy (XPS), UV?vis diffuse reflectance spectroscopy (UV-DRS), photoluminescence spectroscopy (PL) and Brunauer–Emmett–Teller surface area analyze (BET). Both pure and Cu–doped TiO₂ show relatively high photocatalytic activity owing to their considerable surface areas. Moreover, the three–phase coexisting structure and the conversion between Cu²⁺ and Cu⁺ ions facilitate the separation of photogenerated electrons and holes, which is favorable for photocatalytic performance. 1%Cu–TiO₂ exhibits the highest photocatalytic activity and the degradation degree of rhodamine B (RhB) reaches 93.5% after 30 min, which is higher than that of monophasic/biphasic 1%Cu–TiO₂. ·O₂^? radical is the main active species, and h⁺ and ·OH species are subsidiary in the degradation process.

     

Enhanced photoelectrochemical properties of TiO2 nanorod arrays decorated with CdS nanoparticles

TiO₂ nanorod arrays (TiO₂ NRAs) sensitized with CdS nanoparticles were fabricated via successive ion layer adsorption and reaction (SILAR), and TiO₂ NRAs were obtained by oxidizing Ti NRAs obtained through oblique angle deposition. The TiO₂ NRAs decorated with CdS nanoparticles exhibited excellent photoelectrochemical and photocatalytic properties under visible light, and the one decorated with 20 SILAR cycles CdS nanoparticles shows the best performance. This can be attributed to the enhanced separation of electrons and holes by forming heterojunctions of CdS nanoparticles and TiO₂ NRAs. This provides a promising way to fabricate the material for solar energy conversion and wastewater degradation.     

Photocatalytic performance of very thin TiO2/SnO2 stacked-film prepared by magnetron sputtering

TiO₂/SnO₂ stacked-layers are synthesized by reactive sputter deposition on the glass substrate. Very thin TiO₂/SnO₂ bilayer-photocatalysts exhibited a very high photocatalytic activity for a degradation of gaseous acetaldehyde. Both the control of an electronic structure of TiO₂ overlayer in the near-surface region and the interfacial separation of photogenerated electrons/holes in the TiO₂/SnO₂ stacked-layer are keys to improve the photocatalytic performance.     

One step synthesis of Bi@Bi2O3@carboxylate-rich carbon spheres with enhanced photocatalytic performance

Bi@Bi₂O₃@carboxylate-rich carbon core-shell nanosturctures (Bi@Bi₂O₃@CRCSs) have been synthesized via a one-step method. The core–shell nanosturctures of the as-prepared samples were confirmed by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and Raman spectroscopy. The formation of Bi@Bi₂O₃@CRCSs core–shell nanosturctures should attribute to the synergetic roles of different functional groups of sodium gluconate. Bi@Bi₂O₃@CRCSs exhibits significant enhanced photocatalytic activity under visible light irradiation (λ > 420 nm) and shows an O₂-dependent feature. According to trapping experiments of radicals and holes, hydroxyl radicals were not the main active oxidative species in the photocatalytic degradation of MB, but O₂⁻ are the main active oxidative species.     

Shifting mechanisms in the initial stage of dye photodegradation by hollow TiO2 nanospheres

Hollow TiO₂ (HT) sphere aggregates were prepared using carbon spheres as templates. The photocatalytic activity of HT was determined by degradation of two nitrogen-containing dyes, methylene blue (MB) and methyl orange (MO). The adsorption isotherms and the photocatalytic degradation kinetics of the two dyes were studied and compared using different concentrations of dyes for the pure, isopropanol-added, and KI-added systems. Isopropanol was used as a OH^? radical scavenger, while KI was added as a valance band hole scavenger. The results showed that the reaction mechanism of the photocatalytic process of MB was first governed by OH^? radicals, and then by valence band holes, whereas holes played a major role in the whole photodegradation process of MO. The photocatalytic adsorption constant K _V has a positive correlation with the reaction constant k _ov in all systems. The photodegradation efficiencies of the dyes were discussed considering the surface characteristics of HT and the structure of the dyes with different catalyst loads (0.25–2 g L^?1) and under different pH (3–10) conditions. Compared with solid TiO₂, HT exhibited enhanced performance in photocatalytic degradation of both MB and MO.     

Synthesis and characterization of Ag/TiO2-B nanosquares with high photocatalytic activity under visible light irradiation

Square-like B doped TiO₂ nanocrystals were first synthesized by a mild solvothermal method with H₃BO₄ and titanium isopropoxide as the precursors, and isopropyl alcohol as reaction medium. Then, Ag nanoparticles were deposited on TiO₂-B nanosquares by photo-deposition. The as-synthesized products have been investigated by photocatalytic reaction test and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (DRS). The results showed that boron was successfully doped into TiO₂ nanosquares under solvothermal condition. The obtained Ag/TiO₂-B composite showed high efficiency in degradation of acid orange II under visible light irradiation. The high photocatalytic performance could be attributed to the synergistic effect of B doping and the plasmon photocatalysis role of the deposited silver nanoparticles over TiO₂.     

Influence of lanthanum precursors on the heterogeneous La/SnO<Subscript>2</Subscript>–TiO<Subscript>2</Subscript> nanocatalyst with enhanced catalytic activity under visible light

Surfactant controlled synthesis of La/SnO₂–TiO₂ nanocomposite was studied by using anionic surfactant dioctyl sulfosuccinate sodium salt (DOSS) synthesized via sol–gel method followed by hydrothermal method by using different lanthanum precursors. The structural investigation, thermal degradation, kinetics, thermodynamics properties, crystallite size, morphology, surface and photocatalytic properties of synthesized samples were studied by using different characterization techniques i.e. Thermogravimetric analysis (TGA), Fourier transform-infrared spectroscopy (FTIR), Particle Size Analyzer (PSA), Powder X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), and Ultraviolet–Visible spectrophotometer (UV–VIS). Band gap calculations and optical properties of both SnO₂–TiO₂ and La/SnO₂–TiO₂ were studied by using UV–Visible spectroscopy. The performance of both SnO₂–TiO₂ and La/SnO₂–TiO₂ nanocomposites as a photocatalytic agent was also investigated for the degradation of methylene blue (MB) under the illumination of sunlight.     

Photocatalytic degradation of dyes and organic contaminants in water using nanocrystalline anatase and rutile TiO2

Nanocrystalline TiO₂ was synthesized by controlled hydrolysis of titanium tetraisopropoxide. The anatase phase was converted to rutile phase by thermal treatment at 1023 K for 11 h. The catalysts were characterized by X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier-transform infrared absorption spectrophotometry (FT-IR) and N₂ adsorption (BET) at 77 K. This study compare the photocatalytic activity of the anatase and rutile phases of nanocrystalline TiO₂ for the degradation of acetophenone, nitrobenzene, methylene blue and malachite green present in aqueous solutions. The initial rate of degradation was calculated to compare the photocatalytic activity of anatase and rutile nanocrystalline TiO₂ for the degradation of different substances under ultraviolet light irradiation. The higher photocatalytic activity was obtained in anatase phase TiO₂ for the degradation of all substances as compared with rutile phase. It is concluded that the higher photocatalytic activity in anatase TiO₂ is due to parameters like band-gap, number of hydroxyl groups, surface area and porosity of the catalyst.     

A novel protocol to design TiO2-Fe2O3 hybrids with effective charge separation efficiency for improved photocatalysis

TiO₂-based heterogeneous photocatalysis has been widely considered as a promising technique for decontamination of water. Herein the hybrid of TiO₂ nanocrystals decorated Fe₂O₃ nanoparticles was successfully synthesized via a mild hydrothermal method, derived from favorable titanium glycolate and water-soluble Fe^II salt precursors. The composition and structure of the as-synthesized TiO₂-Fe₂O₃ hybrids were characterized by Powder X-ray diffraction (XRD), EDX mapping, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The photocatalytic activity was evaluated by the decomposition of Rhodamine B in an aqueous solution under visible-light (λ > 420 nm). The results show that the TiO₂-Fe₂O₃ nanocomposite exhibits superior photocatalytic capability to the bare ones upon Rhodamine B degradation, owing to promoted photo-induced electrons and holes separation and migration on the basis of photoluminescence spectra, photocurrent measurements, and electrochemical impedance (EIS) spectroscopy.     

Enhanced Photocatalytic Performances of CeO2/TiO2 Nanobelt Heterostructures

CeO₂/TiO₂ nanobelt heterostructures are synthesized via a cost‐effective hydrothermal method. The as‐prepared nanocomposites consist of CeO₂ nanoparticles assembled on the rough surface of TiO₂ nanobelts. In comparison with P25 TiO₂ colloids, surface‐coarsened TiO₂ nanobelts, and CeO₂ nanoparticles, the CeO₂/TiO₂ nanobelt heterostructures exhibit a markedly enhanced photocatalytic activity in the degradation of organic pollutants such as methyl orange (MO) under either UV or visible light irradiation. The enhanced photocatalytic performance is attributed to a novel capture–photodegradation–release mechanism. During the photocatalytic process, MO molecules are captured by CeO₂ nanoparticles, degraded by photogenerated free radicals, and then released to the solution. With its high degradation efficiency, broad active light wavelength, and good stability, the CeO₂/TiO₂ nanobelt heterostructures represent a new effective photocatalyst that is low‐cost, recyclable, and will have wide application in photodegradation of various organic pollutants. The new capture–photodegradation–release mechanism for improved photocatalysis properties is of importance in the rational design and synthesis of new photocatalysts.     

Enhanced sorption and photodegradation of chlorophenol over fluoride-loaded TiO2

The presence of NaF in the aqueous suspension of TiO₂ can accelerate the photocatalytic degradation of organic pollutants. However, disposal of such a fluoride-containing wastewater is not allowed by environmental regulation. In the present work, we report on surface modification of TiO₂ with a hardly water soluble salt, fluorite and fluorapatite. The modified catalysts at low loading displayed a higher activity than bare TiO₂ for the sorption and photocatalytic degradation of phenol and 2,4-dichlorophenol in water. A kinetic study using butanol as hydroxyl radical scavenger revealed that the fluoride-modified catalysts produced more hydroxyl radicals than bare TiO₂. Five repeated experiments showed that the fluorapatite-modified TiO₂ was very stable, and could be re-used without significant loss in activity.     

Evaluation of magnetic nanoparticles performance as photocatalyst for the catalytic treatment of direct red 28 dye in synthetic and real water effluents

Integrated water resources management practice is gaining popularity as an alternative water source due to the limited supply of freshwater. The present study was carried out on the photocatalytic degradation of Direct red 28 (DR-28) dye using magnetic nanoparticles (MNPs; Fe₃O₄) as a photocatalyst. The study was conducted on the photocatalytic degradation of DR-28 dye in synthetic dye effluent water, to understand the effects of different photoreaction parameters on the degradation kinetics. The influence of different parameters such as time, amount of photocatalyst, concentration of H₂O₂ and pH was investigated. At the optimum dosage of MNPs (0.6?g/L) with 4?mmol/L of H₂O₂, significant photocatalytic degradation of DR-28 dye (93.2%) was observed. The kinetic study revealed that the photocatalytic degradation followed pseudo-first-order kinetics. The degradation performance of Fe₃O₄ nanoparticles as a photocatalyst for DR-28 dye was compared with titanium dioxide (TiO₂) and it was found that the performance of Fe₃O₄ as a photocatalyst is superior to TiO₂ photocatalyst. The real dye effluent was also degraded at optimum conditions and promising results were achieved.