Synthesis and photocatalytic performance of hollow sphere particles of SiO2-TiO2 composite of mesocellular foam walls

Hollow Microspheres of SiO₂-TiO₂ photocatalysts whose walls are made up of mesoporous cellular foams were synthesized with the aid of hexane as a swelling agent and P123 as a pore template by an emulsion templating method. Pore structure of materials and crystal phase of titanium oxide was tailored by hydrothermal and calcination temperature during synthesis of samples. The samples were characterized with field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), N₂ adsorption–desorption experiments, X-ray photoelectron spectroscopy (XPS) and X ray diffraction (XRD) techniques. The effect of pore structure and titania phase on photoactivity were evaluated by methylene blue (MB) degradation test under UV light as well. Results showed that hydrothermal temperature during synthesis process has a significant effect on pore and window sizes of mesostructured cellular foam. Interestingly, for the sample hydrothermally treated at higher temperature (130 °C), anatase to rutile transformation was avoided after calcination treatment as high as 800 °C. The highest photocatalytic activity was detected from the sample hydrothermally treated at 130 °C and calcined at 800 °C for which the highest degree of crystallinity and anatase phase as well as enhanced pore connectivity was obtained.     

Novel nitrogen-doped anatase TiO2 mesoporous bead photocatalysts for enhanced visible light response

This work reports the synthesis and characterization of a novel, high surface area N-doped anatase TiO₂ mesoporous bead as a photocatalyst for visible light photodegradation. The beads were prepared using a two-cycle microwave-assisted hydrothermal method using three different types of nitrogen dopants: diaminohexane, triethylamine, and urea. In the first cycle, TiO₂mesoporous beads with controlled structures were synthesized at 200 °C without further calcination. The obtained beads were then subjected to a second cycle of microwave -assisted hydrothermal process for nitrogen doping. The photocatalytic activity of the N-doped mesoporous TiO₂ beads was determined by measuring the decomposition of a methyl blue aqueous solution under UV and visible light. It was found that different precursors lead to different degrees of doping which enhances the light absorption primarily in the visible light region. We demonstrate that the photocatalytic activity or photodegradation is enhanced in the visible light region.     

Application of TiO2/perlite photocatalysis for degradation of ammonia in wastewater

The purpose of this study was removal of ammonia by a new photocatalytic process from synthetic wastewater under UV irradiation. TiO₂ was used as the photocatalyst and immobilized on perlite granules as a supporter. The prepared catalysts were characterized by SEM and FTIR analysis showed that TiO₂/perlite catalyst has mesoporous structures and uniform coating of TiO₂ on support. Also, the optimum efficiency of photocatalytical degradation of ammonia was obtained at pH 11 for UV intensity irradiation with 125 W lamp. About 68% degradation of ammonia in wastewater was achieved after 180 min of irradiation by using the optimized reaction conditions.     

Effect of calcination temperature on morphology of mesoporous YSZ

A nano-structured mesoporous yttria-stabilized zirconia (YSZ) powders were prepared for the first time using cetyltrimethylammonium bromide (CTAB) as the surfactant and urea as the hydrolyzing agent and using ZrO(NO₃)·6H₂O and Y(NO₃)₃·6H₂O as inorganic precursors. The Brunauer–Emmett–Teller (BET) surface area, Barrett–Joyner–Halender (BJH) pore size distribution and crystallite/particle size of mesoporous YSZ varied with calcine temperatures were studied. Characterizations revealed that the mesoporous YSZ powder calcined at 600 °C was weakly agglomerated and had a high surface area of 137 m²/g with an average grain size of ∼5.8 nm. It was demonstrated that the mesoporous structure remained up to 900 °C. The low-densified YSZ sample with porosity as high as 33% was prepared from mesoporous YSZ powder sintered at 1500 °C for 6 h.     

From AgI/TiO2 to Ag/TiO2: effects of the annealing temperature on the compositions,porous nanostructures,and visible-light photocatalytic properties

AgI/TiO₂ and Ag/TiO₂ porous nanostructures were synthesized using AgNO₃, KI, thioglycollic acid, and tetrabutyl orthotitanate as a precursor. AgI nanoparticles were used as seeds to initiate the nucleation of a precursor TiO₂ shell, and thioglycollic acid acted as a hydrolysis inhibitor and porosity promoter. The hybridized samples were annealed at different temperatures. Porous AgI/TiO₂ nanostructures were formed at low annealing temperatures (300 and 400 °C). At 600 °C, the porous Ag/TiO₂ nanostructures exhibited a plasmon resonance effect. The formation mechanism of the different porous nanostructures was also investigated. Methylene blue solutions were used as wastewater to evaluate the visible-light photocatalytic activity of the samples. The porous nanostructured photocatalyst exhibited substantially high visible-light-induced photocatalytic activity for the photodegradation of methylene blue compared with pristine AgI and TiO₂ nanoparticles.     

Evaluating the photocatalytic activity of Pt/TNT film catalyst

TiO₂ nanotubes (TNT) were prepared by a hydrothermal method from the commercially available TiO₂-P25. Five types of TNT were produced at different temperatures (120 °C, 130 °C, and 150 °C) and by using different reaction times (12 h, 24 h, and 30 h). The photocatalytic reactor that was used is a film catalytic reactor, in which the height of the catalyst is 1.0 mm. The BET and FESEM analysis results showed that TNT130-24 (130 °C, 24 h) and TNT150-12 (150 °C, 12 h) possessed well-formed tubular structures with a high specific surface area (282.9–316.7 m² g⁻¹) and large pore volumes (0.62–0.70 cm³ g⁻¹). However, TNT120-30 (120 °C, 30 h) presented the best photocatalytic activity upon CO removal due to the synergistic effect of TiO₂ nanotubes and TiO₂ particles. After the TNT catalysts were modified with Pt particles, the removal efficiency was in the order of Pt/TNT120-30>Pt/TNT130-24>Pt/P25. Pt/TNT120-30 showed 99% removal efficiency in a continuous photoreactor with a high space velocity of 1.79×10⁴ h⁻¹. The results of the TEM and DRS analyses confirmed that the Pt particles enhanced the photocatalytic reaction, which was attributed to the well-dispersed nature of the 1 nm nanoscaled Pt particles on the surfaces of the TNT catalysts, and narrowed the band gap from 3.22 eV to 3.01 eV.     

Selective catalytic reduction of NO by ammonia using mesoporous Fe-containing HZSM-5 and HZSM-12 zeolite catalysts: An option for automotive applications

Mesoporous and conventional Fe-containing ZSM-5 and ZSM-12 catalysts (0.5–8 wt% Fe) were prepared using a simple impregnation method and tested in the selective catalytic reduction (SCR) of NO with NH₃. It was found that for both Fe/HZSM-5 and Fe/HZSM-12 catalysts with similar Fe contents, the activity of the mesoporous samples in NO SCR with NH₃ is significantly higher than for conventional samples. Such a difference in the activity is probably related with the better diffusion of reactants and products in the mesopores and better dispersion of the iron particles in the mesoporous zeolite as was confirmed by SEM analysis. Moreover, the maximum activity for the mesoporous zeolites is found at higher Fe concentrations than for the conventional zeolites. This also illustrates that the mesoporous zeolites allow a better dispersion of the metal component than the conventional zeolites. Finally, the influence of different pretreatment conditions on the catalytic activity was studied and interestingly, it was found that it is possible to increase the SCR performance significantly by preactivation of the catalysts in a 1% NH₃/N₂ mixture at 500 °C for 5 h. After preactivation, the activity of mesoporous 6 wt% Fe/HZSM-5 and 6 wt% Fe/HZSM-12 catalyst is comparable with that of traditional 3 wt% V₂O₅/TiO₂ catalyst used as a reference at temperatures below 400 °C and even more active at higher temperatures.     

Investigation on textural and structural evolution of the novel crack-free equimolar Al2O3-SiO2-TiO2 ternary aerogel during thermal treatment

Crack-free mesoporous equimolar Al₂O₃-SiO₂-TiO₂ ternary nanocomposite aerogel has been synthesized using an ethanol supercritical drying technique. The effects of heat treatment temperatures on its textural and structural evolution during thermal treatment are investigated in this study. XRD results reveal that only anatase phase is detected in the as-dried ternary aerogel, whereas peaks corresponding to silica and alumina phase are not shown due to its much faster polymerization rate of titania precursor. Structural transition from boehmite to γ-Al₂O₃ begins to occur at 450 °C within the ternary aerogel, and this process is completed at nearly 615 °C. The needle-like reticulated γ-Al₂O₃ grows along the anatase backbone, however, it is not evident in the XRD patterns. The morphologies of the ternary aerogel become more homogeneous after the structural transition, as indicated by the SEM analysis, which is also consistent with the BET results. With the increase of heat temperature up to 1050 °C, the γ-Al₂O₃ phase disappears and no separate SiO₂ is detected. At the same time, the silica-alumina network originates in a structure of Al-O-Si, and the silicon atoms incorporate into the alumina phase in the γ-Al₂O₃ structure, disordering the alumina primary particles. When the heat treatment temperature increases to 1200 °C, mullitization begins to occur along the titania backbone, whereas silica crystallization happens at 1300 °C. The 600 °C calcinated ternary aerogel is typically mesoporous, showing high specific surface area (255.37 m²/g), suitable average pore diameter (22.83 nm) and large pore volume (1.34 cm³/g). Moreover, the ternary aerogels show high surface acid activity at temperatures below 1000 °C, which have future applications for ideal catalysts and catalyst supports at elevated temperatures.     

Synergy effect in the photocatalytic degradation of methylene blue on a suspended mixture of TiO2 and N-containing carbons

N-containing carbon materials were obtained from waste plum stones submitted to pyrolysis under Ar flow at 700 °C or to activation under steam at 800 °C and enriched with nitrogen by heating in a NH₃/air mixture at 270 °C or in NO at 300 °C. In situ mixtures of TiO₂ and carbons were prepared by the slurry method and methylene blue photodegradation was chosen as a model reaction to verify the influence of N-containing carbons on the photocatalytic activity of TiO₂ under artificial visible light irradiation. From the kinetics of methylene blue degradation an important synergy effect between both solids was detected with a remarkable increase up to a factor of 5.3 higher in the photocatalytic activity on TiO₂–C than that on TiO₂ alone. A mechanism for the photoassisting role of N-containing carbons upon the photoactivity of TiO₂ under visible light is discussed.     

Au anchored to (α-Fe2O3)-MCM-41-HS as a novel magnetic nanocatalyst for water-medium and solvent-free alkyne hydration

A novel catalytic system based on Au nanoparticle functionalized magnetic mesoporous silica was prepared as (α-Fe₂O₃)-MCM-41-HS-Au. This material was obtained through the reaction of ordered mesoporous silica-coated magnetic nanoparticles (α-Fe₂O₃)-MCM-41, (3-mercaptopropyl) trimethoxysilane (MPTMS) and HAuCl₄. This catalyst was extensively characterized by various techniques such as SEM, TEM, XRD, EDX, IR and N₂-sorption isotherm. Very uniform dispersion and ordered mesopores of (α-Fe₂O₃)-MCM-41-SH (about 2–3 nm) causes Au nanoparticles to be distributed very finely on the pore surfaces, resulting in a very useful and robust magnetically recyclable catalyst for water-medium and solvent-free alkyne hydration.     

Sol–gel preparation of titania multilayer membrane for photocatalytic applications

The main goal of the present study is to prepare a titania membrane with high permeability and photocatalytic activity for environmental applications. In this investigation a mesoporous titania multilayer membrane on alumina substrate is successfully fabricated via the sol–gel processing method. The prepared titania polymeric sol for the membrane top layer has an average particle size of 11.7 nm with a narrow distribution. The resulting TiO₂ multilayer membrane exhibits homogeneity with no cracks or pinholes, small pore size (4 nm), large specific surface area (83 m²/g), and small crystallite size (10.3 nm).The permeability and photocatalytic properties of the titania membrane were measured. The photoactivity of the titania membrane was examined to be 41.9% after 9 h UV irradiation based on methyl orange degradation. This measurement indicates high photocatalytic activity per unit mass of the catalyst. Through multilayer coating procedure, the photocatalytic activity of the membrane improved by 60% without sacrificing the membrane permeation. The prepared TiO₂ photocatalytic membrane has a great potential in developing high efficient water treatment and reuse systems due to its multifunctional capability such as decomposition of organic pollutants and physical separation of contaminants.     

Preparation of novel nanometer TiO2 catalyst doped with upconversion luminescence agent and investigation on degradation of acid red B dye using visible light

An unreported nanometer TiO₂ photocatalyst doped with upconversion luminescence agent (40CdF₂ · 60BaF₂ · 0.8Er₂O₃) utilizing visible light was prepared. Its photocatalytic activity was checked through the photocatalytic degradation of acid red B as a model compound under visible light irradiation. Results show that the upconversion luminescence agent prepared as dopant can effectively turn visible lights to ultraviolet lights, which can be absorbed by nanometer TiO₂ particles to produce the electron-cavity pairs. Therefore, the photocatalytic ability of this novel TiO₂ photocatalyst has greatly been enhanced compared with undoped and common TiO₂ photocatalyst.     

Self-assembly hydrothermal assisted synthesis of mesoporous anatase in the presence of ethylene glycol

Mesoporous nanocrystalline anatase was prepared hydrothermally employing P123 as structure-directing agent. Ethylene glycol was used as a key synthesis parameter to fine tune the morphology, crystal size and pore size of the resultant mesophases. The incorporation of EG in the synthesis gel resulted in the formation of 1–2 μm sphere-like shapes and led to an increase in the specific surface area from ∼95 to ∼170 m²/g, decrease in the average pore size from ∼11 to ∼4.8 nm, and decrease in the average crystallite size from ∼17 to ∼12 nm. These mesophases were used as photocatalysts for the UV degradation of methylene blue and methyl orange. The mesoporous anatase phases photodegraded MB ∼1.5–3× faster than commercially available P25 and showed limited photocatalytic behavior for methyl orange.     

Synthesizing carbon nanotubes and carbon nanofibers over supported-nickel oxide catalysts via catalytic decomposition of methane

Supported-NiO catalysts were tested in the synthesis of carbon nanotubes and carbon nanofibers by catalytic decomposition of methane at 550 °C and 700 °C. Catalytic activity was characterized by the conversion levels of methane and the amount of carbons accumulated on the catalysts. Selectivity of carbon nanotubes and carbon nanofiber formation were determined using transmission electron microscopy (TEM). The catalytic performance of the supported-NiO catalysts and the types of filamentous carbons produced were discussed based on the X-ray diffraction (XRD) results and the TEM images of the used catalysts. The experimental results show that the catalytic performance of supported-NiO catalysts decreased in the order of NiO/SiO₂ > NiO/HZSM-5 > NiO/CeO₂ > NiO/Al₂O₃ at both reaction temperatures. The structures of the carbons formed by decomposition of methane were dependent on the types of catalyst supports used and the reaction temperatures conducted. It was found that Al₂O₃ was crucial to the dispersion of smaller NiO crystallites, which gave rise to the formation of multi-walled carbon nanotubes at the reaction temperature of 550 °C and a mixture of multi-walled carbon nanotubes and single-walled carbon nanotubes at 700 °C. Other than NiO/Al₂O₃ catalyst, all the tested supported-NiO catalysts formed carbon nanofibers at 550 °C and multi-walled carbon nanotubes at 700 °C except for NiO/HZSM-5 catalyst, which grew carbon nanofibers at both 550 °C and 700 °C.     

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.     

Study on properties and synthesis of sulfonated coal supported nanostructure TiO2 photocatalysts

Nano-TiO₂ was synthesized with titanium sulfate by a simple economical microwave-assisted-hydrolysis method, and it was successfully coated on semi-organic-matter sulfonated coal (SC). SC as a semi-organic matter was first chosen as the substrate of nano-TiO₂. Their surface morphology and structure were investigated by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD). The hybrid nano-composite photocatalyst exhibited a good photocatalytic activity in degrading methylene blue (MB). Results revealed that under the assistance of microwave-process, the anatase TiO₂ can be synthesized at low temperature (around 100 °C), presents a strong crystalline and has a good photocatalytic performance.     

Re-formation of metastable ε-Fe2O3 in post-annealing of Fe2O3/SiO2 nanostructure: Synthesis,computational particle shape analysis in micrographs and magnetic properties

Several Fe₂O₃/SiO₂ nanostructures were synthesized by the combination of the microemulsion and a sol-gel methods. Based on X-ray powder diffraction (XRD) and magnetic measurements (giant coercivity ~2.13 T) we identified ε-Fe₂O₃ (hard magnet) as the dominant crystalline phase. TEM analysis showed a wide size distribution of iron oxide nanoparticles (from 4 to 50 nm) with various morphologies (spherical, ellipsoidal and rod-like). We quantitatively described (computational analysis, MATLAB code) morphological properties of nanoparticles using the ellipticity of the shapes. The as-synthesized hard magnetic material was subjected to a post-annealing treatment at different temperatures (200, 500, 750, 1000 and 1100 °C) in order to investigate stability, formation and transformation of the ε-Fe₂O₃ polymorph. We found decreasing coercivity in the thermally treated samples up to the temperature of 750 °C (H_c=1245 Oe), followed by an observation of a surprising jump in coercivity H_C~1.5 T after post-annealing at 1000 °C. We conclude that the re-formation of the ε-Fe₂O₃ structure during post-annealing at 1000 °C is the origin of the observed phenomena. The phase transformation ε-Fe₂O₃→α-Fe₂O₃ and crystallization of amorphous silica in quartz and cristobalite were observed in the sample treated at 1100 °C.     

Effect of pyrolysis temperature on the pore structure evolution of polysiloxane-derived ceramics

Homogeneous silicon oxycarbide (SiOC) ceramic powders were prepared by pyrolysis of cross-linked polysiloxane at different temperatures (1250–1500 °C) under vacuum. The effect of pyrolysis temperature on the pore structure evolution was investigated by means of N₂ adsorption, SEM, XRD, IR and element analysis (EA). Studies showed that predominate mesoporous ceramics with the average pore size in the range of 2–13 nm were obtained after pyrolysis in this temperature range. The pore structure transformation is strongly correlated with the thermolytic decomposition process of the used precursor, such as phase separation and carbothermal reduction. At relatively lower temperature (1250–1350 °C), the ceramics had a relative small specific surface areas (35 m²/g) owing to the low degree of carbothermal reduction. However, as the carbothermal degree had an obvious augment at relative higher temperature (1400–1450 °C), the specific surface areas and total pore volume increased and reached to the maximum of 66 m²/g and 0.214 cm³/g, respectively, and subsequently decreased rapidly after 1500 °C for the reason of partial sintering of the nano-sized SiC derived from polysiloxane.     

Decomposition of nonionic surfactant on a nitrogen-doped photocatalyst under visible-light irradiation

A visible-light-active N-containing TiO₂ photocatalysts were prepared from crude amorphous titanium dioxide by heating amorphous TiO₂ in gaseous NH₃ atmosphere. The calcination temperatures ranged from 200 to 1000 °C, respectively. UV–vis/DR spectra indicated that the N-doped catalysts prepared at temperatures <400 °C absorbed only UV light (E_g = 3.3 eV), whereas samples prepared at temperatures ≥400 °C absorbed both, UV (E_g = 3.10–3.31 eV) and vis (E_g = 2.54–2.66 eV) light. The chemical structure of the modified photocatalysts was investigated using FT-IR/DRS spectroscopy. All the spectra exhibited bands indicating nitrogen presence in the catalysts structure. The photocatalytic activity of the investigated catalysts was determined on a basis of a decomposition rate of nonionic surfactant (polyoxyethylenenonylphenol ether, Rokafenol N9). The most photoactive catalysts were those calcinated at 300, 500 and 600 °C. For the catalysts heated at temperatures of 500 and 600 °C Rokafenol N9 removal was equal to 61 and 60%, whereas TOC removal amounted to 40 and 35%, respectively. In case of the catalyst calcinated at 300 °C surfactant was degraded by 54% and TOC was removed by 35%. The phase composition of the most active photocatalysts was as follows: (a) catalyst calcinated at 300 °C—49.1% of amorphous TiO₂, 47.4% of anatase and 3.5% of rutile; (b) catalyst calcinated at 500 °C—7.1% of amorphous TiO₂, 89.4% of anatase and 3.5% of rutile; (c) catalyst calcinated at 600 °C—94.2% of anatase and 5.8% of rutile.     

Electrospun CdS–TiO2 doped carbon nanofibers for visible-light-induced photocatalytic hydrolysis of ammonia borane

CdS/TiO₂ NPs-decorated carbon nanofibers were introduced as a novel photocatalyst working under visible light radiation for the effective hydrolytic dehydrogenation of ammonia borane. Calcination of electrospun nanofiber mats composed of titanium tetraisopropoxide, poly (vinyl pyrrolidone) (PVP), and cadmium acetate dihydrate with a few drops of ammonium sulfide in argon atmosphere at 850 °C led to the production of CdS–TiO₂ decorated carbon nanofibers. As-synthesized nanocomposite exhibited a strong photocatalytic activity for catalytic hydrolysis of ammonia–borane. The favorable electrons-transfer properties, better dispersion, high surface area, and adsorption property are the main features of nanocomposites that exhibit high catalytic efficiency.