Evaluation of humic acid, chromium (VI) and TiO2 ternary system in relation to adsorptive interactions

Batch adsorption studies were carried out for the assessment of the adsorptive interactions of the system composed of humic acid, Cr(VI) and TiO₂. These were preceded by a thorough investigation of the effect of the chromium ion concentration on the adsorption of humic acid onto TiO₂. The adsorption equilibrium of total chromium, humic acid, and titanium dioxide in water were examined separately and in all combinations in order to distinguish the effects based on the interaction of the components. The adsorption data for the binary system as well as the ternary system were modeled with a simple Freundlich model and the model parameters were compared in terms of Cr(VI) and humic acid as expressed by Color₄₃₆ (color forming moieties) and UV₂₅₄ (UV absorbing centers) parameters.

In binary systems composed of Cr(VI) and TiO₂ no direct relationship could be assessed between adsorption capacity values (K_F) and changes in chromium ion concentration. Chromium ion and humic acid interactions were followed by UV-Vis spectra. A minor change irrespective of added chromium ion concentration was observed for Color₄₃₆ and UV₂₅₄ parameters of humic acid (<5%). However, a significant alteration was observed at 365 nm wavelength indicating the formation of chromate esters. In ternary systems comprising humic acid, Cr(VI) and TiO₂, increasing Cr(VI) concentration five-fold did not cause drastic changes in the adsorption capacity values in terms of Cr(VI) concentration. On the other hand, the adsorption capacity values for color forming moieties as well as for UV absorbing centers of humic acid exhibited a decreasing trend with respect to increasing chromium ion concentration.     

Preparation and characterizations of a new PS/TiO2 hybrid membranes by sol-gel process

New organic-inorganic hybrids based on PS/TiO₂ hybrid membranes were prepared by sol-gel and phase inversion process. The membranes were characterized in terms of morphology, structure, hydrophlicity, UF performance and thermal stability. The results showed that macrovoids were nearly suppressed with formation of a sponge like membrane structure. The TiO₂ particles were uniformly dispersed in membrane. The nanodispersed inorganic network formed after sol-gel process and the strong interaction between inorganic network and polymeric chains led to the improvement of porosity and thermal stability. In particular hydrophilicity and permeability increased drastically with the increasing of TiO₂ content in the range of 0-9.3 wt%, without changing retention properties of membrane. However, high-TiO₂ concentration induces nanoparticles aggregate, resulting in the decline of hydrophilicity and permeability. Thus, PS/TiO₂ hybrid membranes with proper TiO₂ content are desirable to meet some specific requirements in industrial separation.     

Morphological and optical behavior of thermoset matrix composites varying both polystyrene-block-poly(ethylene oxide) and TiO2 nanoparticle content

Novel inorganic/organic epoxy based materials were fabricated using both poly(styrene-b-ethylene oxide) (SEO) block copolymer and synthesized TiO₂ nanoparticles as modifier. The influence of the ratio between modifiers on the final morphology generated in the investigated epoxy systems was studied by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Results indicated that even for high nanoparticle content, TiO₂ nanoparticles synthesized via sol-gel were homogenously dispersed in the epoxy-rich phase. The morphology of the inorganic/organic epoxy based composites consisted of both well-dispersed TiO₂ nanoparticles and microphase separated PS block in the continuous PEO block/epoxy-rich phase since block copolymer acted as templating agent for selective location of TiO₂ nanoparticles. Differential scanning calorimetry (DSC) was used to study the curing behavior and the influence of the type and quantity of modifier on the glass transition temperature of epoxy matrix. Additionally, optical properties, transparency and UV-shielding efficiency of these new multiphase advanced thermosetting materials were also investigated.     

Photocatalytic activity of Cu2O/TiO2, Bi2O3/TiO2 and ZnMn2O4/TiO2 heterojunctions

Cu₂O/TiO₂, Bi₂O₃/TiO₂ and ZnMn₂O₄/TiO₂ heterojunctions were studied for potential applications in water decontamination technology and their capacity to induce an oxidation process under VIS light. UV–vis spectroscopy analysis showed that the junctions-based Cu₂O, Bi₂O₃ and ZnMn₂O₄ are able to absorb a large part of visible light (respectively, up to 650, 460 and 1000 nm). This fact was confirmed in the case of Cu₂O/TiO₂ and Bi₂O₃/TiO₂ by photocatalytic experiments performed under visible light. A part of the charge recombination that can take place when both semiconductors are excited was observed when a photocatalytic experiment was performed under UV–vis illumination. Orange II, 4-hydroxybenzoic and benzamide were used as pollutants in the experiment. Photoactivity of the junctions was found to be strongly dependent on the substrate. The different phenomena that were observed in each case are discussed.     

Comparative performance study of polyethersulfone and polysulfone membranes for trypsin isolation from goat pancreas using affinity ultrafiltration

The comparative performance of polysulfone and polyethersulfone membranes (of 30 kDa MWCO) in isolation of trypsin from goat pancreas by affinity ultrafiltration is examined using cross-linked soybean trypsin inhibitor (STI) as affinity ligand, 0.1 M Tris–HCl as wash buffer and 0.5 M KCl–HCl as elution buffer in an unstirred, dead-ended module at 392.28 kPa (4 kg/cm²) transmembrane pressure and room temperature (ca. 30 °C) with 1:1 (v/v) ratio of pancreatic extract and wash buffer. No active trypsin was found to be detectably present in the washing phase permeate in any of the experiments, indicating good binding efficiency of the target enzyme with the ligand employed. The total protein recovery obtained with the polyethersulfone membrane (70%) is 1.5 times higher than that with the polysulfone (46%). Yields of active trypsin for the two membranes are, however, similar (74% for polyethersulfone and 70% for polysulfone) although comparable with earlier reported trypsin yield (from porcine pancreas). In both the washing and elution phases of affinity ultrafiltration, the polyethersulfone membrane facilitates consistently and substantially higher volumetric flux as well as permeated protein throughput than the polysulfone.     

Preparation and photocatalysis of TiO2-fluoropolymer electrospun fiber nanocomposites

The preparation and photocatalytic properties of titanium dioxide (TiO₂)-fluoropolymer fiber nanocomposites were studied. The fluoropolymer nanofibers with carboxyl group were prepared by electrospinning. The complex was formed between carboxyl on fluoropolymer electrospun fiber surface and titanium ion, and then the TiO₂ nanoparticles were immobilized on the surface of fluoropolymer electrospun fibers through hydrothermal complex-precipitation. By controlling the reaction conditions, different sizes and numbers of TiO₂ nanocrystals can be obtained. The Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) results reveal that an interaction exists between TiO₂ and fluoropolymer fibers. The degradation of methylene blue solution is performed by TiO₂-fluoropolymer fiber nanocomposites under UV irradiation. There may be an adsorption-migration-photodegradation process during the degradation of methylene blue by using TiO₂-fluoropolymer fiber nanocomposites as photocatalyst. The experimental results show that the TiO₂-fluoropolymer fiber nanocomposites have good photocatalytic ability, recycling and stability for the potential applicability in an environmental remediation.     

Conversion of benzoic acid during TiO2-mediated photocatalytic degradation in water

The photocatalytic degradation of benzoic acid in water over Degussa P-25 TiO₂ suspensions was studied. UVA irradiation at 365 nm was supplied by a medium pressure mercury lamp providing 25 mW cm⁻² light intensity. Experiments were conducted at benzoic acid initial concentrations between 25 and 150 mg L⁻¹, catalyst loadings between 0.2 and 1 g L⁻¹ and initial solution pH values between 2 and 10.6. Conversion increased with increasing catalyst loading up to about 0.6 g L⁻¹ and it was favored at alkaline or neutral conditions but impeded at extremely acidic conditions. Increasing initial substrate concentration led to decreased benzoic acid conversion, which was found to follow a Langmuir–Hinshelwood kinetic expression. High performance liquid chromatography (HPLC) was employed to follow benzoic acid concentration profiles as well as to identify reaction by-products, while chemical oxygen demand (COD) and total organic carbon (TOC) analyses were carried out to assess the extent of mineralization. Benzoic acid hydroxylation by-products, namely 2-, 3- and 4-hydroxybenzoic acids as well as phenol were identified as reaction intermediates, although these contributed only a small fraction of the residual organic content. Although benzoic acid at 50 mg L⁻¹ was not ecotoxic to marine photobacteria Vibrio fischeri, its photodegraded solution exhibited substantial toxicity, which, however, proved not to be due to the identified intermediates.     

Photovoltaic performance improvement of dye-sensitized solar cells based on tantalum-doped TiO2 thin films

Dye-sensitized solar cells based on a tantalum (Ta)-doped TiO₂ thin film prepared by the hydrothermal method show a photovoltaic efficiency of 8.18%, which is higher than that of the undoped TiO₂ thin film (7.40%). The Mott-Schottky plot indicates that the Ta-doped TiO₂ photoanode shifts the flat band potential positively and increases the electron density. The positive shift of the flat band potential improves the driving force of injected electrons from the LUMO of the dye to the conduction band of TiO₂. Furthermore, the increased electron density caused by the Ta-doped TiO₂ improves the fill factor of the solar cell. The increased electron density accelerates the transfer rate of electrons in the Ta-doped TiO₂ thin films by comparison to undoped films, which is confirmed by intensity-modulated photocurrent spectroscopy measurements.     

EIS study of photo-induced modifications of nano-columnar TiO2 films

Long-lasting UV-induced physical and/or physico-chemical modifications of nano-structured TiO₂ (anatase) films are highlighted in this work by electrochemical methods. These changes occurring in TiO₂ film upon UV exposure are analysed through electrochemical impedance spectroscopy (EIS) measurements. Interfacial capacity measurements show significant and long-lasting modifications of the semiconducting and dielectric properties of TiO₂ due to UV exposure. Furthermore, UV exposure significantly modifies the energetic distribution of surface states in the gap of TiO₂. Based on Mott-Schottky analysis, the relative dielectric constant is found to increase (from 440 to 870) after UV exposure. An explanation for such an effect is that UV exposure enables hydrogen insertion into the nano-columnar TiO₂ film and thereby increases the dielectric constant of the film.     

Polyvinyl alcohol/polysulfone (PVA/PSF) hollow fiber composite membranes for pervaporation separation of ethanol/water solution

Polysulfone (PSF) hollow fiber membranes were spun by phase‐inversion method from 29 wt % solids of 29 : 65 : 6 PSF/NMP/glycerol and 29 : 64 : 7 PSF/DMAc/glycol using 93.5 : 6.5 NMP/water and 94.5 : 5.5 DMAc/water as bore fluids, respectively, while the external coagulant was water. Polyvinyl alcohol/polysulfone (PVA/PSF) hollow fiber composite membranes were prepared after PSF hollow fiber membranes were coated using different PVA aqueous solutions, which were composed of PVA, fatty alcohol polyoxyethylene ether (AEO₉), maleic acid (MAC), and water. Two coating methods (dip coating and vacuum coating) and different heat treatments were discussed. The effects of hollow fiber membrane treatment methods, membrane structures, ethanol solution temperatures, and MAC/PVA ratios on the pervaporation performance of 95 wt % ethanol/water solution were studied. Using the vacuum‐coating method, the suitable MAC/PVA ratio was 0.3 for the preparation of PVA/PSF hollow fiber composite membrane with the sponge‐like membrane structure. Its pervaporation performance was as follows: separation factor (α) was 185 while permeation flux (J) was 30g/m²·h at 50°C. Based on the experimental results, it was found that separation factor (α) of PVA/PSF composite membrane with single finger‐void membrane structure was higher than that with the sponge‐like membrane structure. Therefore, single finger‐void membrane structure as the supported membrane was more suitable than sponge‐like membrane structure for the preparation of PVA/PSF hollow fiber composite membrane. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 247–254, 2005     

A quantitative evalution of the photocatalytic performance of TiO2 slurries

This paper reports the results of a comparison between two TiO₂ photocatalysts that differ for particle size and absorption/scattering optical properties. The catalyst with larger particles and lower surface area performed better in the degradation of phenol than the specimen with smaller particles and larger surface area. Following carefully designed experiments, it is possible to assess the relative role of light absorption/scattering properties and catalyst-related efficiency by means of a basic kinetic model for the rate of photocatalytic reactions. Explicit relationships are derived in the framework of the steady-state approximation for the quantum yield as a function of one a-dimensional number collecting surface kinetic constants for charge carrier reactions at the interface, absorbed light and surface substrate concentrations. The dimensionality change to volume-defined quantities allows derivation of the explicit dependence of the quantum yield on substrate concentration and partition constants, catalyst concentration, and the rate of volumetric light absorption. Following this approach, the rate expression for slurry systems, valid in the absence of back reactions, is directly derived. Some further simplification of the rate equation for the case of low quantum yield regime leads to analytical relationships able to account for the dependence of the rate on catalyst concentration and absorbed light in the case of stirred and unstirred conditions. The reported properly designed experiments allow the estimation of catalyst-specific micro-kinetic constants.     

Nickel(II) ion-intercalated MXene membranes for enhanced H2/CO2 separation

Hydrogen fuel has been embraced as a potential long-term solution to the growing demand for clean energy. A membrane-assisted separation is promising in producing high-purity H₂. Molecular sieving membranes (MSMs) are endowed with high gas selectivity and permeability because their well-defined micropores can facilitate molecular exclusion, diffusion, and adsorption. In this work, MXene nanosheets intercalated with Ni²⁺ were assembled to form an MSM supported on Al₂O₃ hollow fiber via a vacuum-assisted filtration and drying process. The prepared membranes showed excellent H₂/CO₂ mixture separation performance at room temperature. Separation factor reached 615 with a hydrogen permeance of 8.35 × 10⁻⁸ mol·m⁻²·s⁻¹·Pa⁻¹. Compared with the original Ti₃C₂T_x/Al₂O₃ hollow fiber membranes, the permeation of hydrogen through the Ni²⁺-Ti₃C₂T_x/Al₂O₃ membrane was considerably increased, stemming from the strong interaction between the negatively charged MXene nanosheets and Ni²⁺. The interlayer spacing of MSMs was tuned by Ni²⁺. During 200-hour testing, the resultant membrane maintained an excellent gas separation without any substantial performance decline. Our results indicate that the Ni²⁺ tailored Ti₃C₂T_x/Al₂O₃ hollow fiber membranes can inspire promising industrial applications.     

Preparation of carbon-coated TiO2 nanostructures for lithium-ion batteries

Carbon-coated TiO₂ one-dimensional nanostructures are synthesized by hydrothermal reaction followed by post-calcination at various temperatures. Post-calcination induces crystallization of TiO₂ and the complete crystallization of anatase phase is observed at 600 °C of the calcination temperature. Carbon-coated TiO₂ nanostructures show relatively poor crystallinity as compared with the pristine counterparts, but their lithiation capacity and high rate capability are improved throughout all calcination temperatures. The coated carbon suppresses severe agglomeration of TiO₂ nanotubes which allows easy access of Li-ions and electrons to the whole surface of primary nanotubes, leading to the better lithiation performance. Higher calcination temperatures cause excessive growth of nanotube walls, leading to the collapse of tubular morphology and deterioration of lithiation performance. At 700 °C of the calcination temperature, the enhanced electronic conductivity from the graphitization of the coated carbon seems to be the main reason for the improved capacity of TiO₂ nanowires.     

Carbon nanotubes/titanium dioxide (CNTs/TiO2) nanocomposites prepared by conventional and novel surfactant wrapping sol–gel methods exhibiting enhanced photocatalytic activity

In this work, a conventional sol–gel method was used to prepare CNTs/TiO₂ nanocomposites with different carbon loading in the range up to 20% CNTs/TiO₂ by weight. The bare CNTs (multi-walled), and the composites were characterized by a range of analytical techniques including TEM, XRD, BET and TGA–DSC. The results show the successful covering of the CNTs with discrete clusters of TiO₂ and bare CNTs surfaces which after annealing at 500 °C led to mesoporous crystalline TiO₂ (anatase) clusters. The photocatalytic activities of the nanocomposites were monitored from the results of the photodegradation of methylene blue (MB). The optimum CNTs/TiO₂ ratio in the composites prepared by conventional sol–gel method was found to be in the range from 1.5% to 5% by weight under the experimental conditions investigated. The maximum increase in activity was found to be 12.8% compared to the pure TiO₂ sample.In contrast, the synthesis of CNTs/TiO₂ nanocomposites by a novel surfactant wrapping sol–gel method [B. Gao, C. Peng, G.Z. Chen, G. Li Puma, Appl. Catal. B: Environ. 85 (2008) 17.] led to a uniform and well-defined nanometer-scale titania layer on individual CNTs. The nanocomposites were found to enhance the initial oxidation rate of methylene blue by onefold compared to the pure TiO₂ sample. This larger degree of rate enhancement is attributed to the supporting role of the CNTs and surface properties prepared by this novel modified sol–gel method.     

Role of adsorption and diffusion pathways on the CO2/N2 separation performance of nanocomposite (B)-MFI-alumina membranes

This work reports a detailed study of CO₂ and N₂ adsorption and diffusion pathways on MFI-alumina hollow fibres and their role on both pure and mixture CO₂/N₂ permeation. The hollow fibres have been prepared by pore-plugging hydrothermal synthesis starting from a clear solution with molar composition 1 SiO₂: 0.45 TPAOH: 27·8H₂O: xB(OH)₃ (x=0–0.02), showing a final nanocomposite architecture. A comprehensive screening has been performed to select the most suitable model for describing CO₂ and N₂ adsorption and pure permeation in the (B)-MFI-alumina hollow fibres. The classical Ideal Adsorption Solution Theory (IAST) has been implemented to different permeation models to account for binary CO₂/N₂ permeation within the fibres.     

Tubular V-free and V-doped TiO2 derived from H2Ti12O25 hollow spheres: Vapour-thermal synthesis,morphology evolution,and photocatalytic performance

Vanadium (V)-free and V-doped H₂Ti₁₂O₂₅ hollow spheres (HTOHSs) were first synthesised via vapour-thermal method at 290?°C using common chemicals and solvents, over super-critical temperature (243?°C) of ethanol (vapour source). Then, they were annealed at 600?°C under different processing conditions to obtain titanium dioxide (TiO₂) photocatalysts. All catalysts were characterised by means of XRD, SEM, TEM, XPS, UV–vis DRS, FT-IR, N₂ adsorbtion-desorbtion and fluorescence lifetime. Results indicated that after the treatment in air, V-free HTOHSs were transformed into open-ended hollow tubes with uniform length of ~5?µm and diameter of ~1?µm, and walls of hollow tubes consisted of aggregated nanosheets. Furthermore, HTOHS crystallised into anatase TiO₂ (white) phase. The treatment in N₂ atmosphere led to the breaking of longer tubes into shorter ones. In contrast, after the treatment in N₂ atmosphere or by reduction using NaBH₄ as a reductant, V-doped HTOHS resulted in the formation of anatase TiO₂ (black) samples and consisted of fewer tubes and more deformed spheres. In this study, fluorescence lifetime (τ) of photo-generated carriers corresponded well with the ratio of oxygen vacancy, indicating that oxygen vacancy dominates the lifetime even though it is very sensitive to many factors. The evolution of structure and morphology and photocatalytic mechanism were analysed and discussed.     

Photocatalytic reduction of carbon dioxide into gaseous hydrocarbon using TiO2 pellets

It has been shown that CO₂ could be transformed into hydrocarbons when it is in contact with water vapour and catalysts under UV irradiation. This paper presents an experimental set-up to study the process employing a new approach of heterogeneous photocatalysis using pellet form of catalyst instead of immobilized catalysts on solid substrates. In the experiment, CO₂ mixed with water vapour in saturation state was discharged into a quartz reactor containing porous TiO₂ pellets and illuminated by various UV lamps of different wavelengths for 48 h continuously. The gaseous products extracted were identified using gas chromatography. The results confirmed that CO₂ could be reformed in the presence of water vapour and TiO₂ pellets into CH₄ under continuous UV irradiation at room conditions. It showed that when UVC (253.7 nm) light was used, total yield of methane was approximately 200 ppm which was a fairly good reduction yield as compared to those obtained from the processes using immobilized catalysts through thin-film technique and anchoring method. CO and H₂ were also detected. Switching from UVC to UVA (365 nm) resulted in significant decrease in the product yields. The pellet form of catalyst has been found to be attractive for use in further research on photocatalytic reduction of CO₂.     

Electrochemical response of a composite Pt/TiO2 layer formed potentiodynamically on titanium surfaces

By potentiodynamic polarization of mechanically polished titanium in a diluted aqueous solution of hexachloroplatinic acid, nearly spherical Pt microparticles were grown, embedded into the simultaneously formed TiO₂ film. The real surface of platinum may be easily controlled by the number of potentiodynamic cycles, and roughness factors exceeding 100 were obtained. Within the potential region of both hydrogen and oxygen underpotential deposition, in both acidic and alkaline solutions, the electrode displayed an excellent electrochemical response characteristic of smooth polycrystalline platinum, unlike to highly dispersed platinum electrodes produced by other methods. The preparation method applied in this work presents an easy way to obtain an electrode surface combining the behaviour of smooth polycrystalline platinum with the behaviour of microdisc arrays. Its high electrocatalytic effectiveness was demonstrated for oxygen reduction and bromide ion adsorption/oxidation.     

Effect of formate and methanol on photoreduction/removal of toxic cadmium ions using TiO2 semiconductor as photocatalyst

Photoreduction/removal of cadmium was studied at pH 7 using TiO₂ Degussa as photocatalyst, and either formate or methanol as hole scavengers. In the absence of organic additives, approximately 60% of cadmium was found to be removed from the solution by adsorption. Addition of formate resulted in the photoreduction of cadmium to its metallic form. No cadmium reduction was observed when methanol was added as the hole scavenger. Zeta potential measurements of the catalyst suspensions and studies on the extent of organic additive adsorption and mineralisation were used to prove the photoreduction process. It was found that the adsorption of both cadmium and the organic hole scavenger is crucial for the photoreduction of cadmium. It is postulated that to be an effective hole scavenger the organic additive needs to be easily photooxidised under an anoxic environment. In addition, the presence of formate radicals could be responsible for the Cd photoreduction.     

NiPd/TiO2催化剂的制备及其催化甲酸分解制氢性能

高效、清洁且无毒无害的催化剂是实现以甲酸(HCOOH)为化学储氢材料分解制氢的重点。本文采用水热法在453K的条件下制备TiO₂载体,再通过浸渍法向其中加入总量为0.1 mmol的NiCl₂.6H₂O和K₂PdCl₄金属溶液,将活性组分Ni、Pd负载到TiO₂载体上合成NiPd/TiO₂催化剂,并探究其对催化甲酸分解制氢的性能的影响。探究结果表明,在光照条件下,NiPd/TiO₂催化剂中,当金属Ni:Pd比例为2:8时,催化剂的反应转化频率(TOF)值最大,此时催化剂的 TOF 为3528 h_-1^,且该催化剂上甲酸分解的活化能(E_a)为53.9 kJ/mol。关键词：镍钯催化剂;甲酸;分解制氢;二氧化钛;光照中图分类号：TQ630 文献标识码： A 文章编号：