Bioinspired Hierarchical Nanotubular Titania Immobilized with Platinum Nanoparticles for Photocatalytic Hydrogen Production

A bioinspired nanocomposite composed of platinum nanoparticles and nanotubular titania was fabricated in which the titania matter was templated by natural cellulose substance. The composite possesses three‐ dimensional hierarchical structures, and ultrafine metallic platinum particles with sizes of ca. 2 nm were immobilized uniformly on the surfaces of the titania nanotubes. Such a nanocomposite with 1.06 wt % of platinum content shows the optimal photocatalytic hydrogen production activity from water splitting of 16.44 mmol h^?1 g^?1, and excessive loading of platinum results in poorer photocatalytic performance. The structural integrity of the nanocomposite upon cyclic water‐splitting processes results in its sufficient photocatalytic stability.     

Visible light-induced photocatalysis through surface plasmon excitation of platinum-metallized titania for photocatalytic bleaching of rhodamine B

Abstract  

Nanocomposites consisting of titania nanoparticles and metallic platinum were prepared via a soft chemical reduction method. The detailed structural, compositional, and optical characterization and physicochemical properties of the obtained products were analyzed by X-ray diffraction, nitrogen adsorption, Raman spectroscopy, UV–Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, and FT-IR spectroscopy techniques. Employing photodegradation of rhodamine B as the model reaction, we found that the as-prepared Pt/TiO₂ nanocomposite showed an excellent photocatalytic oxidation activity under visible light irradiation. On the basis of these results, the intrinsic mechanism of visible light-induced photocatalytic oxidation of organic compounds on the platinized titania is proposed and discussed. The superior visible light-driven photocatalytic efficiency of the Pt/TiO₂ nanocomposite photocatalyst can be ascribed to the high efficiency of charge-pair separation due to the presence of deposited Pt serving as electron sinks to retard the rapid e⁻–h⁺ couple recombination; the good photoabsorption capacity in the visible light region; and the higher concentration of surface hydroxyl groups, which are able to effectively scavenge photogenerated valence band holes. Accumulation of the holes at the catalyst surface increases the probability of the formation of OH· as a reactive species that readily oxidizes the organic dye molecule.     

The effect of Pt nanoparticles distribution on the removal of cyanide by TiO2 coated Al-MCM-41 in blue light exposure

With an aim to enhance the photocatalytic activity, Pt loaded TiO₂–Al-MCM-41 catalysts with high surface area were synthesized by a multistep route. The waste of the rice processing, rice husk (RH), was used as the precursor for the extraction of silica. The diffuse reflectance and photoluminescence spectroscopy revealed the extension of the absorption edge in the visible region and exciton trapping nature of the dispersed platinum. The structural analysis was carried out by XRD, whereas X-ray photoelectron spectroscopy identified the chemical states of the components of the synthesized powders. The BET surface area measurements revealed the reduction in the surface area and pore volume with the increasing platinum loading. TEM micrographs showed the uniform distribution of TiO₂ and Pt nanoparticles at the surface of Al-MCM-41. The photocatalytic efficiency of the synthesized powders as photocatalysts was obtained for the removal of 100 ppm CN⁻ from aqueous solution in fluorescent blue light exposure. Compared to unsupported TiO₂, the Pt-loaded catalysts exhibited substantially high activity for the removal of CN⁻. A plausible mechanism for the removal of cyanide ions was proposed. The catalysts showed excellent stability and reproducibility in the successive use.     

Preparation and characterization of titania/tetratitanate nanocomposites

Nanocomposite titania/tetratitanate particles were prepared by utilizing the electrostatic interaction of the colloidal tetratitanate nanosheets and TiO₂ powders through dispersing TiO₂ into tetratitanate solution at pH4. The samples were characterized by X-ray powder diffraction, transmission electron microscopy, chemical analysis, and photocatalytic activity measurement. The crystallites of Ti₄O₉^2? in the form of tetratitanate nanosheets have lateral size around 100 nm. The visible light responsive photocatalytic activity of rutile nanoparticles could be improved by forming nanocomposite with layered tetratitanate. The high specific surface area of this kind of composite and a certain amount of mesopores in nanocomposite powder could be responsible for better performance in the NO elimination.     

掺氮TiO2可见光降解有机污染物的比较研究

用溶胶-凝胶法制备了不同掺杂量的N/TiO₂复合纳米粉末, 采用X射线衍射(XRD)、扫描透镜(TEM)、紫外-可见反射吸收光谱(UV-vis)对催化剂进行了初步表征. 通过X射线光电子能谱(XPS)、元素分析仪(EA)测定其含氮量. XPS分析结果显示TiO₂晶格中的氧被氮原子取代, N/TiO₂表面存在Ti^3＋离子; 紫外-可见反射吸收光谱测得不同掺杂量的N/TiO₂的禁带宽度(E_g), 推测在TiO₂价带上方生成了由N诱导产生的中间带, 当氮、钛摩尔比为0.0880时N/TiO₂的E_g最小, 为2.50 eV. 在可见光下, 以酸性桃红(SRB)和无色小分子对氯苯酚(4-CP)作为可见光活性实验的探针反应, 确定了最佳掺杂比为n_N/n_Ti＝0.0880. 结果表明, 最佳掺杂量下N/TiO₂能显著降解SRB和4-CP, 通过测定ESR, IR, TOC, COD, 重点比较了TiO₂在掺杂N前后在降解SRB和4-CP时的差异, 包括氧化物种、矿化率、最终产物等, 证明在可见光下, N/TiO₂的降解机理为电子从独立的N 2p轨道激发到Ti 3d轨道, 产生羟基自由基等氧化物种, 达到降解有机物的目的.     

TiO<Subscript>2</Subscript>/TiO<Subscript>2−<Emphasis Type="Italic">x</Emphasis></Subscript>N<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> nanocomposite and its acetaldehyde photodecomposition ability

Nitrogen-doped titania was coupled with the commercial titania nanoparticles by mechanical milling in liquid medium. The as-prepared nanocomposites (TiO₂/TiO_2−x N _y ) were characterized by X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET) specific surface area, UV–Vis spectroscopy, chemiluminescence, and acetaldehyde decomposition activity techniques. When a small amount of nitrogen-doped titania was added into the commercial titania, higher intensity and longer lifetime of ¹O₂ was observed, and the photocatalytic activity was efficiently improved. The TiO_2−x N _y acts as the acceptor of photoinduced holes. The recombination of the electron-hole was effectively depressed by the heterogeneous electron transfer. This could be an effective way to obtain highly active photocatalysts.     

The effect of silver doping on photocatalytic properties of titania multilayer membranes

In this investigation an Ag doped titania multilayer membrane is successfully fabricated via the sol–gel processing method. The doped membrane is characterized via X-ray Diffraction and N₂-sorption techniques and the photocatalytic properties of the membrane are investigated via methyl orange degradation. The properties included high surface area (101 m²/g), small pore size (3.1 nm), and active anatase crystal phase. The prepared titania membrane has a high photocatalytic activity and decomposes methyl orange by 50% after 9 h of UV irradiation. The prepared membrane can be applied in the development of efficient photocatalytic systems for the treatment of water. Due to the high photoactivity of the prepared titania membrane, this study reveals the possibility of combining two processes for removal of organic pollutants: the photocatalytic process and the membrane separation process. In the combining process the lifetime of the membrane increases and the quality of water is enhanced.     

Effects of calcining temperature on photocatalytic activity of Fe-doped sulfated titania

Using industrial titanyl sulfate as a raw material, Fe‐doped sulfated titania (FST) photocatalysts were prepared by using the one‐step thermal hydrolysis method and characterized using XRD, SEM, TGA–DSC, FTIR, UV–Vis DRS and N₂ adsorption–desorption techniques. The effects of calcining temperature on the structure of the titania were investigated. The photocatalytic activity of the FST was evaluated using the photodegradation of methylene blue and photooxidation of phenol in aqueous solutions under UV and visible light irradiation, respectively. The results evinced that Ti⁴⁺ is substituted by Fe³⁺ in titania lattice and forms impurity level within the band gap of titania, which consequently induces the visible light absorption and visible‐light‐driven photocatalytic activity. The synergistic effects of Fe‐doping and sulfation are beneficial to the efficient separation of the photogenerated carriers and also improve the quantum efficiency of photocatalysis. In addition, Brönsted acidity arisen from the strong inductive effect of sulfate is also conducive to enhancing the photocatalytic performance of FST. However, when the calcining temperature is higher than 800°C, sulfur species and surface hydroxyl groups decompose and desorb from FST and the specific surface area decreases sharply. Moreover, severe sintering and rutile phase formation occur simultaneously. All these are detrimental to photocatalytic activity of FST.     

Effect of synthesis temperature on the preparation of titanium dioxides by the hydrothermal method. photocatalytic activity

Summary TiO₂ nanoparticles were prepared by the hydrolysis of titanium tetraisopropoxide (TTIP) using TMA (tetramethylamine) as a peptizer in the hydrothermal method. The photocatalytic degradation of Orange II has been studied in a batch reactor under UV light. The particle size was similar to that from hydrothermal treatment at 120-170^oC, but it increased to 23 nm at 200^oC. The titania particles prepared at 170^oC and calcined at 600^oC showed the highest activity in the photocatalytic decomposition ofOrange II.     

Demonstration of a novel,flexible, photocatalytic oxygen-scavenging polymer film

The preparation of a novel, flexible, photocatalytic, oxygen-scavenging polymer film is described. The film incorporates nanocrystalline titania particles in an ethyl cellulose polymer film, with or without an added sacrificial electron donor of triethanolamine. When coated on the inside of a glass vessel its UV-driven light-scavenging action is demonstrated by platinum octaethyl porphyrin coated glass beads sealed inside, since their luminescence increases with increasing UV-irradiation time. When used as a flexible film, work with an oxygen electrode shows that the film is able to scavenge oxygen at an average rate of 0.017 cm³ O₂ h⁻¹ cm⁻² over a 24 h period, which compares favourably to other, well-established oxygen-scavenger systems. The potential of using such as system for oxygen scavenging in packaging is discussed briefly.     

Modified,Amorphous Titania—A Hybrid Semiconductor for Detoxification and Current Generation by Visible Light

Amorphous, microporous TiO ₂ hybrid semiconductors modified with transition metals induce generation of a photocurrent and photocatalytic degradation of the water contaminant 4-chlorophenol through photoinduced charge separation (the postulated mechanism is shown in the picture, Ar=4-ClC₆H₄). In contrast to the previously known crystalline titania photocatalysts, which are active only when excited with UV light, the amorphous semiconductors modified with platinum, rhodium, and gold chloride enable both processes also with visible light.     

Effect of calcination atmosphere on the structure and photocatalytic properties of titania mesoporous powder

In the work presented here, mesoporous titania (MTO) powders are synthesised by the sol?Cgel method using amphiphilic triblock copolymer as a template in two different calcination atmospheres, N₂ and air. Various techniques such as sequential thermal analysis (STA), small-angle X-ray diffraction (SAXRD), wide-angle X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), ultraviolet (UV)?Cvisible spectroscopy, high-resolution transmission electron microscopy (HRTEM) and N₂-adsorption/desorption analysis were utilised to study the prepared samples. Furthermore, the photocatalytic activities of the prepared samples were evaluated from the photo-degradation analysis of methylene blue (MB). For the sample calcined at N₂, the formation of an ordered mesostructure with a high specific surface area (172?m²?g^?1), mesoporosity (48%) and enhanced photocatalytic activity were obtained compared to that of the sample calcined in air. The observed increased MB degradation for the latter is mainly attributed to the formation of higher specific surface area and mesoporosity. The availability of highly ordered open-pore channels could provide increased contacts between reactants in the solution and the active sites on the surface of titania mesoporous particles. Considering the photoactivities of the samples, it is revealed that the photocatalytic activity is enhanced, together with an increase in the surface defects in N₂ atmosphere.     

PtOxCly(OH)z(H2O)n Complexes under Oxidative and Reductive Conditions: Impact of the Level of Theory on Thermodynamic Stabilities

Platinum-based catalysts with Cl⁻, OH⁻, O²⁻ and H₂O ligands, are involved in many industrial processes. Their final chemical properties are impacted by calcination and reduction applied during the preparation and activation steps. We investigate their stability under these reactive conditions with density functional theory (DFT). We benchmark various functionals (PBE-dDsC, optPBE, B3LYP, HSE06, PBE0, TPSS, RTPSS and SCAN) against ACFDT-RPA. PBE-dDsC is well adapted, although hybrid functionals are more accurate for redox reactions. Thermodynamic phase diagrams are determined by computing the chemical potential of the species as a function of temperature and partial pressures of H₂O, HCl, O₂ and H₂. The stability and nature of the Pt species are highly sensitive to the activation conditions. Under O₂, high temperatures favour PtO₂ while under H₂, platinum is easily reduced to Pt(0). Chlorine modifies the coordination sphere of platinum during calcination by stabilizing PtCl₄ and shifts the reduction of platinum to higher temperatures under H₂.     

Photocatalytic disinfection of bacterial pollutants using suspended and immobilized TiO2 powders

The photocatalytic disinfection of Enterobacter cloacae and Enterobacter coli using microwave (MW), convection hydrothermal (HT) and Degussa P25 titania was investigated in suspension and immobilized reactors. In suspension reactors, MW‐treated TiO₂ was the most efficient catalyst (per unit weight of catalyst) for the disinfection of E. cloacae. However, HT‐treated TiO₂ was approximately 10 times more efficient than MW or P25 titania for the disinfection of E. coli suspensions in surface water using the immobilized reactor. In immobilized experiments, using surface water a significant amount of photolysis was observed using the MW‐ and HT‐treated films; however, disinfection on P25 films was primarily attributed to photocatalysis. Competitive action of inorganic ions and humic substances for hydroxyl radicals during photocatalytic experiments, as well as humic substances physically screening the cells from UV and hydroxyl radical attack resulted in low rates of disinfection. A decrease in colony size (from 1.5 to 0.3 mm) was noted during photocatalytic experiments. The smaller than average colonies were thought to occur during sublethal ^?OH and O₂^?? attack. Catalyst fouling was observed following experiments in surface water and the ability to regenerate the surface was demonstrated using photocatalytic degradation of oxalic acid as a model test system.     

Integration of [(Co(bpy)3]2+ Electron Mediator with Heterogeneous Photocatalysts for CO2 Conversion

An efficient chemical system for electron generation and transfer is constructed by the integration of an electron mediator ([Co(bpy)₃]²⁺; bpy=2,2′‐bipyridine) with semiconductor photocatalysts. The introduction of [Co(bpy)₃]²⁺ remarkably enhances the photocatalytic activity of pristine semiconductor photocatalysts for heterogeneous CO₂ conversion; this is attributable to the acceleration of charge separation. Of particular interest is that the excellent photocatalytic activity of heterogeneous catalysts can be developed as a universal photocatalytic CO₂ reduction system. The present findings clearly demonstrate that the integration of an electron mediator with semiconductors is a feasible process for the design and development of efficient photochemical systems for CO₂ conversion.     

Bimodal Heterogeneous Functionality in Redox-Active Conjugated Microporous Polymer toward Electrocatalytic Oxygen Reduction and Photocatalytic Hydrogen Evolution

The designing and development of heterogeneous catalysts for conversion of renewable energy to chemical energies by electrochemical as well as photochemical processes is at the forefront of energy research. In this work, two new donor–acceptor-based redox-active conjugated microporous polymers (CMPs) (TAPA-OPE-mix and TAPA-OPE-gly) are synthesized through Schiff base condensation reaction using a microwave synthesizer. Notably, the asymmetric and symmetric bola-amphiphilic nature of the OPE struts results in distinct nanostructuring and morphologies in the CMPs. Interestingly, both CMPs show impressive heterogeneous catalytic activity toward electrochemical O₂ reduction and photocatalytic H₂ evolution reactions, and therefore, act as bimodal electro- and photocatalytic porous organic materials. Furthermore, the redox-active property of the CMPs is exploited for in situ generation and stabilization of platinum nanoparticles (Pt), and these Pt@CMPs exhibit significantly enhanced photocatalytic activity.     

Fabrication of titania and titania–silica aerogels using rapid supercritical extraction

Titania (TiO₂) and titania–silica (TiSi) aerogels are suitable for photocatalytic oxidation of volatile organic compounds for pollution mitigation; however, methods for fabricating these aerogels can be complex. In this work we describe the use of a rapid supercritical extraction (RSCE) technique to prepare TiO₂ and TiSi aerogels in as little as 8 h. The RSCE technique uses a metal mold and a four-step hydraulic hot press procedure to bring the solvents in the sol–gel pores to a supercritical state and control the supercritical fluid release process. Resulting TiO₂ aerogels were powdery with BET surface areas of 130–180 m²/g, pore volumes ~0.5 cm³/g and skeletal densities of 3.6 g/mL. Monolithic TiSi aerogels were made using two different methods. An impregnation process, in which titania precursor was added to a silica sol–gel, took 4–8 days to complete with a 7-h RSCE and resulted in translucent aerogels with high surface area (560–650 m²/g) and pore volume (2.0–2.6 cm³/g), bulk densities ranging from 0.1 to 0.4 g/mL and skeletal densities of 2.3 g/mL. A co-precursor method for preparing TiSi aerogels took 8 h to complete. The precursor chemical mixture was poured directly into the mold and processed in a 7-h RSCE process. The resulting aerogels were opaque, with high surface areas (510–580 m²/g), low bulk density (0.03 g/mL), skeletal densities of 2 g/mL and pore volumes of 2.6–3.5 cm³/g. Preliminary solar simulator studies show that TiO₂ and TiSi aerogels are capable of photocatalytic degradation of methylene blue in aqueous solution.     

Visible-light-driven Oxygen Vacancy and Carbon Doping of C@TiO2-x Photocatalyst for Enhanced Pollutants Degradation Performance

Oxygen Vacancy (OVs) and carbon doping of the photocatalyst body will significantly enhance the photocatalytic efficiency. However, synchronous regulation of these two aspects is challenging. In this paper, a novel C@TiO_2-x photocatalyst was designed by coupling the surface defect and doping engineering of titania, which can effectively remove rhodamine B (RhB) and has a relatively high performance with wide pH range, high photocatalytic activity and good stability. Within 90 minutes, the photocatalytic degradation rate of RhB by C@TiO_2-x (94.1 % at 20 mg/L) is 28 times higher than that of pure TiO₂. Free radical trapping experiments and electron spin resonance techniques reveal that superoxide radicals (⋅O²⁻) and photogenerated holes (h⁺) play key roles in the photocatalytic degradation of RhB. This study demonstrates the possibility of regulating photocatalysts to degrade pollutants in wastewater based on an integrated strategy.     

Highly Dispersed Platinum Nanoparticles on TiO2 Prepared by Using the Microwave‐Assisted Deposition Method: An Efficient Photocatalyst for the Formation of H2 and N2 from Aqueous NH3

A simple and practical technique to synthesize nanosized platinum particles loaded on TiO₂ (Pt–TiO₂) by using a microwave (Mw)‐assisted deposition method has been exploited in the development of a highly efficient photocatalyst for the formation of H₂ and N₂ gases from harmful nitrogen‐containing chemical wastes, for example, aqueous ammonia (NH₃). Upon Mw irradiation, a platinum precursor can be deposited quickly on the TiO₂ surface from an aqueous solution of platinum and subsequent reduction with H₂ affords the nanosized platinum metal particles with a narrow size distribution (Mw‐Pt–TiO₂). Characterization by CO adsorption, platinum L_III‐edge X‐ray absorption fine structure analysis, and TEM analysis revealed that the size of the metal nanoparticles strongly depended on the preparation methods. Smaller platinum nanoparticles were obtained by the Mw heating method than those obtained by conventional preparation techniques, such as photoassisted deposition (PAD), impregnation (Imp), and equilibrium adsorption (EA) deposition by conventional convective heating. The H₂ and N₂ formation rates increased with increasing dispersity of platinum. Pt–TiO₂ prepared by the Mw heating method exhibited a specifically high H₂ formation activity in the photocatalytic decomposition of aqueous NH₃ in a nearly stoichiometric 3:1 (H₂/N₂) molar ratio under inert conditions. The present Mw heating method is applicable to a variety of anatase‐type TiO₂ species possessing different specific surface areas to provide small and highly dispersed platinum nanoparticles with a narrow size distribution.     

Pivotal Role of Holes in Photocatalytic CO2 Reduction on TiO2

Evidence is provided that in a gas-solid photocatalytic reaction the removal of photogenerated holes from a titania (TiO₂) photocatalyst is always detrimental for photocatalytic CO₂ reduction. The coupling of the reaction to a sacrificial oxidation reaction hinders or entirely prohibits the formation of CH₄ as a reduction product. This agrees with earlier work in which the detrimental effect of oxygen-evolving cocatalysts was demonstrated. Photocatalytic alcohol oxidation or even overall water splitting proceeds in these reaction systems, but carbon-containing products from CO₂ reduction are no longer observed. H₂ addition is also detrimental, either because it scavenges holes or because it is not an efficient proton donor on TiO₂. The results are discussed in light of previously suggested reaction mechanisms for photocatalytic CO₂ reduction. The formation of CH₄ from CO₂ is likely not a linear sequence of reduction steps but includes oxidative elementary steps. Furthermore, new hypotheses on the origin of the required protons are suggested.