Sol-gel derived TiO2–carbon composites with adsorption-enhanced photocatalytic activity and gas sensing performance

We report the in-situ sol-gel synthesis of TiO₂–carbon composites (black TiO₂) by carbonization of the gel. With ultra-fine anatase TiO₂ nanoparticles dispersed homogeneously on amorphous carbon, the as-prepared black TiO₂ possesses a BET surface area as high as 145.4 m²/g. Due to the synergy effect of adsorption and photocatalysis, the as-synthesized black TiO₂ is demonstrated to exhibit enhanced photocatalytic activity. The gas sensing properties of black TiO₂ have been rigorously investigated with and without UV illumination at room temperature. It is found that increased adsorption of gas molecules can effectively improve the sensor response. The mechanism of the adsorption-enhanced gas sensing performance of black TiO₂ has been detailedly discussed.     

Uniform dispersion of CuO nanoparticles on mesoporous TiO2 networks promotes visible light photocatalysis

Here, we focus our efforts on synthesizing a uniform dispersion of CuO nanoparticles on mesoporous TiO₂ networks for the first time. H₂PtCl₆ was added through a photocatalytic reaction to produce 0.5% Pt/CuO–TiO₂ nanocomposites. XRD patterns confirmed that the prepared TiO₂ formed the anatase phase. TEM images showed close contacts between CuO and TiO₂ with 5–10 nm particle sizes. One of the advantages of the synthesized mesoporous CuO–TiO₂ nanocomposites was the high pore volume (0.540 cm³ g⁻¹) and large surface area (300 m² g⁻¹). The H₂ evolution over the mesoporous 3 wt% CuO–TiO₂ nanocomposites using a glucose hole scavenger [10 vol%] was determined to be ~13000 μmol/g, a value that was 1300 times greater than that of mesoporous TiO₂. The H₂ evolution rate was increased by up to 1300 and 20 times for 3 wt% CuO–TiO₂ and 0.1 wt% CuO–TiO₂ nanocomposites, respectively, compared with that of mesoporous TiO₂. The increase in H₂ evolution over mesoporous CuO–TiO₂ nanocomposites was explained by the increased light harvesting capacity, high glucose molecule diffusion and efficient charge carrier separation. Moreover, the construction of a heterostructure with a p–n CuO–TiO₂ heterojunction expedited the separation of charge carriers and promoted the evolution of H₂. In addition, H₂ evolution was substantially increased by the synergistic effects of Pt and CuO on the mesoporous TiO₂ networks. Photoelectrochemical and photoluminescence measurements were employed to prove the H₂ evolution mechanism over the CuO nanoparticles deposited on the mesoporous TiO₂ networks.     

Facile synthesis of mesoporous Ag-loaded TiO2 thin film and its photocatalytic properties

Ag nanoparticles highly dispersed into TiO₂ thin films are synthesized via a remarkably simple one-pot route in the presence of a P123 triblock copolymer as template directing and reducing agents, where the reduction of Ag⁺ to Ag⁰ by in situ heat-induced reduction through the oxidation of template at 400 °C and the controlled polymerization of TiO₂ take place simultaneously. The obtained mesoporous Ag/TiO₂ films deposited on soda-lime glass were optically transparent and crack-free. SEM and Kr adsorption clearly prove that Ag/TiO₂ films at different Ag contents are mesoporous with large surface area and regularly ordered mesopores and the thickness of the obtained films is ∼280 ± 20 nm. The pristine TiO₂ film exhibits a specific surface area of 63 cm²/cm² and specific pore volume of 0.013 mm³/cm² that it is decreased to 42 cm²/cm² and 0.010 mm³/cm² respectively as a result of Ag-loaded mesoporous TiO₂. The newly prepared photocatalysts Ag/TiO₂ films were evaluated for their photocatalytic degradation of 2-chlorophenol as a model reaction. It was found that the meso-ordered Ag/TiO₂ films are more photoactive 8 times than nonporous commercial photocatalysts Pilkington Glass Activ™. The recycling tests indicated that Ag/TiO₂ films was quite stable during that liquid-solid heterogeneous photocatalysis since no significant decrease in activity was observed even after being used repetitively for 10 times, showing a good potential in practical application. In general, the cubic mesoporous Ag/TiO₂ nanocomposites are stable and can be recycled without loss of their photochemical activity.     

Crystallization and final morphology of HDPE: Effect of the high energy ball milling and the presence of TiO2 nanoparticles

The influence of high energy ball milling process, HEBM, and the presence of TiO₂ nanoparticles on the non-isothermal crystallization and fusion behavior of the HDPE were investigated. HEBM was used to homogeneously disperse TiO₂ nanoparticles into a high density polyethylene, HDPE. Differential scanning calorimetry was used to analyze their non-isothermal crystallization and fusion behavior while, with X-ray diffraction the crystalline structures were determined. Atomic force microscopy was used to study the influence of the presence of nanoparticles on the final morphology of the polymer. It has been demonstrated that HEBM is a good method to prepare nanocomposites of well dispersed TiO₂ nanoparticles within an HDPE matrix. When nanoparticles are absent the HEBM induces reduction of crystallinity of the polymer although a double crystallization process was observed; however, when nanoparticles are present, in addition of being favored the appearance of a metastable monoclinic phase, the fraction of crystals increases as milling time increases. AFM clearly showed how well dispersed were the TiO₂ nanoparticles within the HDPE and how they are localized exactly between the lamellas. This result is the first clear visual evidence confirming that well dispersed nanoparticles actually do not act as nucleating agents in semicrystalline polymers. It was also shown that a 2% by weight of well dispersed TiO₂ nanoparticles within the HDPE matrix induces a more homogeneous crystallization leading to denser spherulites with thicker lamellae.     

Synthesis and Microscopic Characterization of Dendrimer-Derived Ru/Al2O3 Catalysts

Fourth generation poly(amidoamine) dendrimers have been used to template and stabilize Ru nanoparticles in solution. UV-visible spectroscopic results indicate that Ru³⁺ ions from a RuCl₃ precursor can complex with functional groups within the dendrimer structure. Subsequent reduction of the Ru³⁺ ions yields finely dispersed Ru nanoparticles with a narrow particle size distribution. These dendrimer-stabilized nanoparticles were deposited onto an alumina support and thermally activated to remove the dendrimer “shell”, as indicated by in situ Fourier transform infrared (FTIR) spectroscopic measurements. High resolution transmission electron microscopy (HRTEM) measurements indicate that the resulting Ru/Al₂O₃ catalyst has a smaller mean metal particle size and a narrower particle size distribution than a similar catalyst prepared by a traditional wet impregnation from the same RuCl₃ precursor.     

A Bimetallic Nanozyme with Cascade Effect for Synergistic Therapy of Cancer

Novel nanocomposites were constructed through encapsulation of Au nanoparticles and Ru nanoparticles into dendritic mesoporous silica (DMSN-Au-Ru NPs). These exhibit improved effects due to a cascade catalytic ability for the synergistic therapy of cancer. Au nanoparticles with glucose oxidase-like properties were found to catalyze the oxidation of glucose to produce H₂O₂, while Ru nanoparticles could decompose H₂O₂ and produce toxic ¹O₂ for improved photodynamic therapy (PDT). In addition, the nanocomposites were found to have good photothermal performance under irradiation by near-infrared (NIR) light. Both in vitro and in vivo experiments show that the nanocomposites have good therapeutic effects due to the cascade catalytic effect and synergistic effect. These findings provide an effective way to design a new generation of nanodrugs for highly efficient cancer treatment.     

One-pot synthesis of bifunctionalized TiO<Subscript>2</Subscript> mesoporous photocatalyst with visible light response

A series of Fe-doped SH/TiO₂ mesoporous photocatalysts have been firstly prepared by one-pot method using P123 as structure-directing agent. This bifunctionalized mesoporous TiO₂ possesses perfect anatase crystal structure and high surface area. The surface area of Fe-doped SH/TiO₂ mesoporous material is 4 times higher than that of P25. Based on the EPR results, it was found that trivalent Fe ions exist at low spin state and substitutes a part of Ti⁴⁺ ions into TiO₂ lattice. Fe-dropping in TiO₂ extends the adsorption band side of the resulting material to about 600 nm. Much high photocatalytic activity in the degradation of phenanthrene was obtained on the bifunctionalized mesoporous TiO₂ under visible light irradiation (λ > 420 nm), which is 6 times higher than that of pristine mesoporous TiO₂. The enhancement in the photocatalytic activity of bifunctionalized TiO₂ is ascribed to the extended absorption to visible light and strong interaction between SH-groups and PHE molecules.     

A simple aqueous solution based chemical methodology for synthesis of Ag nanoparticles dispersed on mesoporous silicate matrix

A simple chemical method has been developed for preparation of Ag nanoparticles dispersed on mesoporous silicate matrix, SBA-15. Ag nanoparticles were uniformly dispersed on SBA-15 matrix by using the reduction reaction of AgNO₃ with trisodium citrate. The synthesized materials were characterized by using room temperature powder XRD analysis, N₂ adsorption-desorption isotherm, high resolution TEM and SEM. It was observed that the synthesized SBA-15 and Ag-SBA-15 have a surface area of 778 and 151 m²/g respectively. The synthesized materials have long range ordering of pores with narrow pore size distribution centered at ∼ 7 nm. Pore structure of SBA-15 remains preserved even after deposition of Ag nanoparticle. This chemical route reported here offers a simple method for preparation of Ag-SBA-15, where unagglomerated Ag nanoparticles (∼ 20 nm) are uniformly dispersed on SBA-15.     

Anchoring Pt nanoparticles on hydrophobic ordered mesoporous carbon through solid-state reduction

Highly ordered mesoporous carbon-nickel nanocomposites have been prepared through solvent evaporation-induced self-assembly method using NiCl₂ as Ni precursor. The nanocomposites maintain uniform pore structure as C-FDU-15 type and include Ni nanoparticles after a carbothermal reduction. The water contact angle of the Ni-free mesoporous carbon reaches as large as 124°, which has little change with the modification of Ni. Therefore, a solid-state reduction method is developed to load Pt nanoparticles, wherein PtCl₆ ²⁻ with H₂PO₂ ⁻ ions could be adsorbed to the carbon support and then in situ reduced. Electrochemical performance in sulfuric acid by cyclic voltammetry has demonstrated that this strategy is efficient to anchor Pt nanoparticles on the hydrophobic surface.     

Synthesis and enhanced photocatalytic activity of Mn/TiO2 mesoporous materials using the impregnation method through CVC process

TiO₂ particles were prepared by chemical vapor condensation and used to synthesize MnO_x/TiO₂ mesoporous materials by impregnation. The Mn-doped TiO₂ particles were smaller (8.5?nm vs. 10.5?nm) and had greater surface areas (203.7?m²?g^?1 vs. 134.4?m²?g^?1) than undoped particles. They were also smaller and had a greater surface area than similarly doped commercial P25, indicating highly dispersed Mn species on the surfaces of the crystalline TiO₂. The resulting materials?? photocatalytic activities towards methylene blue decomposition were compared: the synthesized TiO₂ particles with MnO₂ showed higher photocatalytic activity than the similarly doped commercial P25.     

Effect of Functionalized TiO2 on Mechanical,Thermal and Swelling Properties of Chitosan-Based Nanocomposite Films

In this work, a novel type of biodegradable hybrids consisting of titanium dioxide (TiO₂) and chitosan has been fabricated. At first, the TiO₂ nanoparticles were modified with N-trimellitylimido-S-valine diacid to express biomateral moieties through available amino acid groups. The microscopy results demonstrated that the modified TiO₂ nanoparticles were dispersed homogeneously in the chitosan matrix at the nanometric scale, which could be assigned to covalent bonds as well as hydrogen bonding formed between chitosan and TiO₂-diacid. Among all of the prepared films, a nanocomposite film containing 15 wt.% TiO₂ exhibited the highest thermal and mechanical performance.     

Mesoporous polyaniline or polypyrrole/anatase TiO2 nanocomposite as anode materials for lithium-ion batteries

A functional composite as anode materials for lithium-ion batteries, which contains highly dispersed TiO₂ nanocrystals in polyaniline matrix and well-defined mesopores, is fabricated by employing a novel one-step approach. The as-prepared mesoporous polyaniline/anatase TiO₂ nanocomposite has a high specific surface area of 224 m² g⁻¹ and a predominant pore size of 3.6 nm. The electrochemical performance of the as-prepared composite as anode material is investigated by cyclic voltammograms and galvanostatic method. The results demonstrate that the polyaniline/anatase nanocomposite provides larger initial discharge capacity of 233 mAh g⁻¹ and good cycle stability at the high current density of 2000 mA g⁻¹. After 70th cycles, the discharge capacity is maintained at 140 mAh g⁻¹. The excellent electrochemical performance of the polyaniline/TiO₂ nanocomposite is mainly attributed to its special structure. Furthermore, it is accessible to extend the novel strategy to other polymer/TiO₂ composites, and the mesoporous polypyrrole/anatase TiO₂ is also successfully fabricated.     

Al-doped TiO<Subscript>2</Subscript> mesoporous materials: synthesis and photodegradation properties

Aluminium-doped TiO₂ mesoporous material was successfully fabricated by solid-state reaction with cetyltrimethylammonium bromide as a template agent and tetrabutyl orthotitanate as a precursor. The characteristic results from low-angle and wide-angle X-ray diffraction, high resolution transmission electron microscopy and energy dispersive spectroscopy, N₂ absorption–desorption, Fourier transform infrared spectroscopy, Raman spectroscopy, ultraviolet visible light spectroscopy and X-ray photoelectron spectroscopy (XPS) clearly showed that the mesoporous architecture of aluminium-doped TiO₂ was composed of crystal wall and micro-/mesopore formed gradually by the mesopore degradation of anatase TiO₂, and aluminium had been doped into the framework of anatase TiO₂. The mesoporous Al-doped TiO₂ material, not only possessed high thermal stability hexahedral mesostructure, large BET surface area and narrow distribution of pore size, but also showed excellent photodegradation behavior for Congo Red. Furthermore the medium UV–Vis absorption peak of mesoporous aluminium-doped TiO₂ in the range 210–370 nm was the absorption peak of aluminium oxide nanoparticles locating the extraframework of TiO₂. A small quantity of aluminium doped into anatase TiO₂ could obviously improve photodegradation activity, and the photodegradation activity of aluminium-doped TiO₂ was higher than that of pure TiO₂.     

Direct synthesis of nano titania on highly-ordered mesoporous SBA-15 framework for enhancing adsorption and photocatalytic activity

This paper reports the synthesis of TiO₂-containing mesoporous catalysts for effectively enhancing the adsorption and photocatalytic activity. The factors that affect the photocatalytic activity of catalyst composites, including types of silica support, TiO₂ content, calcination temperature, and catalyst mass, were examined in this study. The samples were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and surface area analysis. The experimental results showed that incorporating TiO₂ nanoparticles into silica gel or SBA-15 frameworks could enhance the photodegradation rate more effectively than pure TiO₂. The TiO₂/SBA-15 sample displayed much higher adsorption and photocatalytic activity levels than did TiO₂/silica-gel. The pore volume and pore size of TiO₂/SBA-15 were as high as 1.317 cm³/g and 7.51 nm, respectively, which exceeded those of TiO₂/silica-gel (0.437 cm³/g and 3.68 nm, respectively). The rate constants of photocatalysis were determined. The photodegradation rate of the catalyst increased with decreasing TiO₂ content and increasing calcination temperature. The proposed method of preparing mesoporous photocatalysts is simple and suitable for mass production.     

Poly(arylene sulfide sulfone) hybrid ultrafiltration membrane with TiO2‐g‐PAA nanoparticles: Preparation and antifouling performance

Poly(arylene sulfide sulfone) (PASS) is a kind of newly developed polymeric membrane material which has excellent mechanical strength, thermal stability, and solvent resistance. And, it would be a potential material for high temperature ultrafiltration and organic solvent filtration. In this article, PASS hybrid ultrafiltration membrane with improved antifouling property was prepared by mixing TiO₂ nanoparticles which were grafted with polyacrylic acid (PAA). These membranes were prepared by a phase inversion technique and their separation performance and antifouling property of the prepared membranes were investigated in detail by SEM, FTIR, EDS, contact angle goniometry, filtration experiments of water, and BSA solution. The results shown that the TiO₂‐g‐PAA nanoparticles dispersed well in membrane matrix, the hydrophilicity of the membranes prepared within TiO₂‐g‐PAA nanoparticles have been improved and these membranes exhibited excellent water flux and antifouling performance in separation than that of the pure PASS membranes and PASS membranes with TiO₂ nanoparticles. More specifically, among membrane sample M0, M1.5, and MP1.5, MP1.5 which contained 1.5 wt% TiO₂‐g‐PAA exhibited the highest water permeation (190.4 L/m² h at 100 kPa), flux recovery ratio, and the lowest BSA adsorption amount. POLYM. ENG. SCI., 55:2829–2837, 2015. © 2015 Society of Plastics Engineers     

Preparation and characterization of high-surface-area titanium dioxide by sol-gel process

One of the important ways to improve photocatalytic efficiency is to prepare catalyst with enhanced surface area. In this work, titanium dioxide (TiO₂) nanoparticles having enhanced surface area were synthesized under the interference of SiO₂. The mixed oxide, SiO₂-TiO₂ (10% mol% Si), was prepared by a sol-gel procedure using titanium tetra-n-butoxide as Ti-precursor. The commercial SiO₂ nanoparticles were added into the TiO₂ sols after hydrolysis. After condensation and calcination heat treatment, the SiO₂-TiO₂ nanoparticles were obtained. To achieve the purpose of obtaining the high-surface-area TiO₂, the SiO₂ was removed subsequently by aqueous NaOH solution. The TiO₂ products were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), electron spectroscopy for chemical analysis (ESCA), and by N₂ adsorption-desorption isotherm. A fine mesoporous structure was formed for as-prepared TiO₂ after calcination at 400^°C and the average pore diameter was about 7 nm. The porous TiO₂ products possess mixing phases of anatase and rutile. Phase transformation from anatase to rutile occurred when the samples were calcined. The phase transition temperature is sensitive to the silicon content. The particle size of ～43 nm remained constant upon calcinations from 500 to 700^°C. The specific surface area was increased up to 66% compared to regular TiO₂ samples that were prepared by the similar sol-gel procedure. The porous TiO₂ nanostructures exhibited enhanced photocatalytic performance to decompose methylene blue under UV irradiation.     

Hydrophobic composite coatings with photocatalytic self-cleaning properties by micro/nanoparticles mixed with fluorocarbon resin

A newly developed hydrophobic composite coating was fabricated by incorporating modified TiO₂ nanoparticles and hydrophobic material polytetrafluoroethylene (PTFE) micropowders dispersed in fluorocarbon resin. Moreover, the surface characteristics and self-cleaning properties of the newly developed composite material were examined. The material was found to exhibit sufficient hydrophobicity with a water contact angle of 133°. The surface free energy of the composite coating was 4.11 mJ/m². Scanning electron microscopy results revealed a micro/nanocomposite structure composed of PTFE micropowders and TiO₂ nanoparticles, which was verified by X-ray photoelectron spectroscopy results. Through ultraviolet irradiation the modified TiO₂-PTFE/FEVE composite coating successfully removed oleic acid absorbed on its surface. These results showed that the functional composite coating had a sufficiently hydrophobic surface with an efficient self-cleaning effect.     

Effects of templating surfactant concentrations on the mesostructure of ordered mesoporous anatase TiO2 by an evaporation-induced self-assembly method

We prepared ordered hexagonal mesoporous TiO₂ by an evaporation-induced self-assembly (EISA) method using Pluronic P123 and tetrabutyl orthotitanate (Ti(OBuⁿ)₄, TBOT) as the templating agent and the titanium source, respectively. The main purpose of this study was to elucidate the effects of surfactant concentrations on the pore arrangement, pore size, specific surface area and structure of mesoporous TiO₂ by the EISA method. The mesostructures of mesoporous TiO₂ were characterized with X-ray diffraction (XRD), nitrogen adsorption/desorption isotherms, and transmission electron microscopy (TEM). By varying the concentration of the block copolymer, mesoporous TiO₂ of various pore sizes and pore ordering were prepared. Because the mesostructure is governed by the concentration of P123 surfactant at gelation of the solution, a higher P123/TBOT mole ratio favored the formation of highly ordered mesoporous TiO₂ with a maximum pore volume of 0.26 cm³/g, a high specific surface area of 244 m²/g, and a BJH average pore size of 4.7 nm.     

Thermal properties of PMMA/TiO2 nanocomposites prepared by in-situ bulk polymerization

The surface of anatase TiO₂ nanoparticles, obtained by the controlled hydrolysis of titanium tetrachloride, was modified by 6-palmitate ascorbic acid. The surface modified TiO₂ nanoparticles were dispersed in methyl methacrylate and mixed with a appropriate amount of poly(methyl methacrylate) to obtain a syrup. The nanocomposite sheets were made by bulk polymerization of the syrup in a glass sandwich cell using 2,2′-azobisisobutyronitrile as initiator. The molar masses and molar mass distributions of synthesized poly(methyl methacrylate) samples were determined by gel permeation chromatography. The content of unreacted double bonds in synthesized samples was determined by ¹H NMR spectroscopy. The influence of TiO₂ nanoparticles on the thermal stability of the poly(methyl methacrylate) matrix was investigated using thermogravimetric analysis and differential scanning calorimetry. The synthesized samples of poly(methyl methacrylate) have different molar mass and polydispersity depending on the content of the surface modified TiO₂ nanoparticles. The values of glass transition temperature of so prepared nanocomposite samples were lower than for pure poly(methyl methacrylate), while the glass transition temperature of samples preheated in inert atmosphere was very similar to the glass transition temperature of pure poly(methyl methacrylate). The thermal stability of nanocomposite samples in nitrogen and air was different from thermal stability of pure poly(methyl methacrylate). POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Ignition performance of TiO2 coated boron particles using a shock tube

This study coated the surface of irregularly shaped 5-μm boron particles with TiO₂ nanoparticles to improve the ignition performance of the boron. A simple and inexpensive chemical method was used to coat the surface of boron with TiO₂. Five different samples of boron coated with TiO₂ nanoparticles were obtained by varying the concentration of Ti precursor. Surface structures were analyzed using different characterization techniques, which showed the formation of nanocrystalline TiO₂ nanoparticles over the boron surface. The nanoparticles of TiO₂ were well dispersed over the boron surface, and exhibited strong interfacial contact with the boron. The oxidation of boron and boron coated with TiO₂ was analyzed by thermogravimetric technique in an air atmosphere from room temperature to 1000 °C. Results revealed that the oxidation of boron started at a temperature approximately 162 °C lower after coating with TiO₂. The ignition behavior of the boron and boron coated with TiO₂ particles was studied using a shock tube. The results of the shock tube experiments demonstrated the TiO₂ coated boron had a shorter ignition delay time than the bare boron. An approximate 35% reduction was observed in the ignition delay time of boron after coating with TiO₂ nanoparticles, showing its potential value in high energy density fuels.