Effect of sacrificial electron donors on hydrogen generation over visible light–irradiated nonmetal-doped TiO2 photocatalysts

Hydrogen generation over carbon-, nitrogen- and sulfur-doped TiO₂ semiconductor photocatalysts (represented as C–TiO₂, N–TiO₂ and S–TiO₂, respectively) under visible light irradiation has been achieved using various sacrificial electron donors, namely triethanolamine, diethanolamine, monoethanolamine, triethylamine, MeOH, EtOH, EDTA, l-ascorbic acid and phenol. The highest initial rate of H₂ production was found to be in the range 1,000–2,200 μmol/g/h at ambient conditions when triethanolamine was used as sacrificial electron donor. The efficacy of hydrogen production over these photocatalysts depends strongly on the nature of the sacrificial electron donor and decreases in the following order: C–TiO₂ > S–TiO₂ > N–TiO₂. The results of the present studies suggest that the rate of H₂ production is not simply governed by the reduction potential of the sacrificial electron donor but also by the kinetic barrier of the electron transfer process.     

A carbon–carbon hybrid – immobilizing carbon nanodots onto carbon nanotubes

The thrust of this work is to integrate small and uniformly sized carbon nanodots (CNDs) with single-walled carbon nanotubes (SWCNT) of different diameters as electron donors and electron acceptors, respectively, and to test their synergetic interactions in terms of optoelectronic devices. CNDs (denoted pCNDs, where p indicates pressure) were prepared by pressure-controlled microwave decomposition of citric acid and urea. pCNDs were immobilized on single-walled carbon nanotubes by wrapping the latter with poly(4-vinylbenzyl trimethylamine) (PVBTA), which features positively charged ammonium groups in the backbone. Negatively charged surface groups on the CNDs lead to attractive electrostatic interactions. Ground state interactions between the CNDs and SWCNTs were confirmed by a full-fledged photophysical investigation based on steady-state and time-resolved techniques. As a complement, charge injection into the SWCNTs upon photoexcitation was investigated by ultra-short time-resolved spectroscopy.     

Mesoporous Pt/TiO2-xNx nanoparticles with less than 10 nm and high specific surface area as visible light hydrogen evolution photocatalysts

Journal of Sol-Gel Science and Technology - Mesoporous TiO2-xNx nanoparticles were synthesized by selective dissolving of Si in N-doped Ti-Si binary oxides, which were nitridized at...     

Hydrothermal in situ preparation of phthalocyanine–TiO2 nanocomposites for photocatalytic activity under visible light irradiation

Research on Chemical Intermediates - In this study, phthalocyanine (Pc)–TiO2 nanocomposites were prepared via in situ hydrothermal method. The metal-free, zinc(II), cobalt(II), nickel(II) and...     

Facile synthesis of thin black TiO2 − x nanosheets with enhanced lithium-storage capacity and visible light photocatalytic hydrogen production

Journal of Solid State Electrochemistry - In combination of a facile and scalable solvothermal method and solid-phase reduction reactions, a novel two-dimensional black TiO2 − x...     

Photocatalytic degradation pathway of sulfadiazine over Ag–TiO2 under visible light irradiation

Research on Chemical Intermediates - In the past decades, TiO2-based photocatalysis has received much research attention as an effective strategy for decomposing the antibiotics in a water system....     

Cyclohexane photooxidation under visible light irradiation by WO3–TiO2 mixed catalysts

Research on Chemical Intermediates - Cyclohexane photocatalytic oxidation was performed over WO3 photocatalysts under visible light irradiation with molecular oxygen. Cyclohexanone and cyclohexanol...     

Enzyme mediated synthesis of Ag–TiO2 photocatalyst for visible light degradation of reactive dye from aqueous solution

The purpose of this study was to develop bio-inspired photocatalyst with solar light activity for textile dye degradation. Three TiO₂ samples namely TiO₂ (TiO₂-A), biotemplated TiO₂ (TiO₂-B), and enzyme mediated Ag–TiO₂ biotemplate (TiO₂-C), were developed. The presence of anatase phase of TiO₂ and silver in synthesized samples were confirmed using X-ray diffraction, field emission scanning electron microscopy, energy-dispersive spectroscopy, and UV–Vis–NIR spectroscopy. Photocatalytic efficiencies of these photocatalysts were evaluated by studying the oxidation of a commercial reactive dye (reactive black) under solar light irradiation in batch reactors. Photocatalytic efficiencies of the sample were compared using statistical tools like one-way ANOVA and Tukey test. The results confirmed that photocatalytic efficiency of TiO₂-C was 40 % higher than that of TiO₂-A under solar light irradiation.     

Photocatalytic bacteria inactivation by polyethylene glycol-assisted sol–gel synthesized Cd-doped TiO2 under visible light

Cd-doped TiO₂ nanoparticles have been obtained by polyethylene glycol-assisted sol–gel synthesis and characterized by powder X-ray diffraction, energy dispersive X-ray analysis, high-resolution scanning electron microscopy and UV–visible diffuse reflectance, photoluminescence and impedance spectroscopies. Use of polyethylene glycol as templating agent provides club-shaped particles. Doping TiO₂ with Cd decreases the average crystallite size and charge transfer resistance, increases the capacitance, and leads to blue emission. Cd-doping enhances the visible light photocatalytic disinfection of bacteria but not dye degradation.     

Porous carbon coupled with an interlaced MoP–MoS2 heterojunction hybrid for efficient hydrogen evolution reaction

The design and development of electrocatalysts composed of non-noble-metal catalysts with both large surface area and high electrical conductivities are crucial for the hydrogen evolution reaction(HER).Here,a xylose-based porous carbon is coupled with a MoS2-Mo P heterojunction(MoS2-Mo P/FPC)hybrid and used as a promising catalyst for HER.The hybrid is prepared by immobilizing petal-like MoS2 nanosheets on porous carbon(MoS2/FPC),followed by controlling the phosphidation in Ar/H2 to form MoS2-Mo P/FPC.Red phosphorus provides the P species that can induce the construction of the heterojunction under the reducing atmosphere,along with the generation of a Mo P phase and the splitting of the MoS2 phase.The as-prepared MoS2-Mo P/FPC catalyst offers a low overpotential of 144 mV at a current density of 10 m A cm^-2 and a small Tafel slope of 41 m V dec^-1 for the HER in acidic media,as well as remarkable stability.Apart from the active nature of the hybrid,its outstanding activity is attributed to the MoS2-Mo P heterojunction,and the good charge/mass-transfer ability of porous carbon.This strategy provides a new method to develop and design low-cost and high-performance catalysts for the HER.     

Highly Dispersible Hexagonal Carbon–MoS2–Carbon Nanoplates with Hollow Sandwich Structures for Supercapacitors

MoS₂, a typical layered transition-metal dichalcogenide, is promising as an electrode material in supercapacitors. However, its low electrical conductivity could lead to limited capacitance if applied in electrochemical devices. Herein, a new nanostructure composed of hollow carbon–MoS₂–carbon was successfully synthesized through an l -cysteine-assisted hydrothermal method by using gibbsite as a template and polydopamine as a carbon precursor. After calcination and etching of the gibbsite template, uniform hollow platelets, which were made of a sandwich-like assembly of partial graphitic carbon and two-dimensional layered MoS₂ flakes, were obtained. The platelets showed excellent dispersibility and stability in water, and good electrical conductivity due to carbon provided by the calcination of polydopamine coatings. The hollow nanoplate morphology of the material provided a high specific surface area of 543 m² g⁻¹, a total pore volume of 0.677 cm³ g⁻¹, and fairly small mesopores (≈5.3 nm). The material was applied in a symmetric supercapacitor and exhibited a specific capacitance of 248 F g⁻¹ (0.12 F cm⁻²) at a constant current density of 0.1 A g⁻¹; thus suggesting that hollow carbon–MoS₂–carbon nanoplates are promising candidate materials for supercapacitors.     

Characterization and activity of visible light–driven TiO<Subscript>2</Subscript> photocatalysts co<Emphasis Type="Bold">-</Emphasis>doped with nitrogen and lanthanum

Nitrogen and lanthanum co-doped titania photocatalysts were prepared by a modified sol–gel process with urea and lanthanum nitrate doping precursors and characterized by various techniques including XRD, FTIR, TEM, EDS, and UV–Vis DRS. The average crystallite size was ca. 12–15 nm as calculated from XRD patterns, and anatase was the dominant crystalline type in the as-prepared samples. The UV–Vis DRS of the samples revealed significant absorption within the range of 400–500 nm. The optimum composition of N(0.020)La(0.012)TiO₂ exhibited the highest photocatalytic activity for degradation of methyl orange (MO) aqueous solution under simulated sunlight. The percent degradation of MO was ca. 97% for N(0.020)La(0.012)TiO₂ under simulated sunlight irradiation for 9 h. The enhanced photocatalytic activity was ascribed to the synergistic effects of the nitrogen and lanthanum co-doping.     

NKT cell-dependent glycolipid–peptide vaccines with potent anti-tumour activity

It is known that T cells can eliminate tumour cells through recognition of unique or aberrantly expressed antigens presented as peptide epitopes by major histocompatibility complex (MHC) molecules on the tumour cell surface. With recent advances in defining tumour-associated antigens, it should now be possible to devise therapeutic vaccines that expand specific populations of anti-tumour T cells. However there remains a need to develop simpler efficacious synthetic vaccines that possess clinical utility. We present here the synthesis and analysis of vaccines based on conjugation of MHC-binding peptide epitopes to α-galactosylceramide, a glycolipid presented by the nonpolymorphic antigen-presenting molecule CD1d to provoke the stimulatory activity of type I natural killer T (NKT) cells. The chemical design incorporates an enzymatically cleavable linker that effects controlled release of the active components in vivo. Chemical and biological analysis of different linkages with different enzymatic targets enabled selection of a synthetic vaccine construct with potent therapeutic anti-tumour activity in mice, and marked in vitro activity in human blood.     

Sol–gel synthesized vanadium doped TiO2 photocatalyst: physicochemical properties and visible light photocatalytic studies

Vanadium doped titanium dioxide (V–TiO₂) photocatalyst was synthesized by the sol–gel method using ammonium vanadate as vanadium source. The prepared samples were characterized by XRD, N₂ adsorption–desorption method, UV–Vis DRS, Fourier transform infrared (FTIR), scanning electron microscope–energy dispersive X-ray and photoluminescence (PL) analysis. The results show that V⁵⁺ ions were successfully incorporated into the crystal lattice of TiO₂ as a consequence, not only an obvious decrease in the band gap and a red shift of the absorption threshold into the visible light region was recorded for the V modified TiO₂, but, also a decrease in photogenerated electrons and holes recombination rate was observed as demonstrated by PL analysis. FTIR study indicated that in undoped TiO₂ sample the acetate group favored a bidentate bridging mode of binding with titanium atoms, whereas a bidentate chelating mode of linkage was observed in V–TiO₂ powders. The crystallite size of the samples calcined at 300 and 500 °C were decreased beyond the molar ratio of 200:1 (V:Ti), this may be due to dopant presence in the grain boundaries hindering the crystal growth. The photocatalytic activities for both pure and vanadium doped TiO₂ powders were tested in the discoloration of a reactive dyestuff, methylene blue, under visible light. The 100:1 (V:Ti) doped photocatalyst, calcined at 300 °C showed enhanced photocatalytic activity under visible light with a rate constant (k_obs) of 5.024 × 10^?3 min^?1 which is nearly five times higher than that of pure TiO₂, as result of low band gap value, high specific surface area and a decrease in recombination rate.     

Graphene–DNAzyme junctions: a platform for direct metal ion detection with ultrahigh sensitivity

Many metal ions are present in biology and in the human body in trace amounts. Despite numerous efforts, metal sensors with ultrahigh sensitivity (<a few picomolar) are rarely achieved. Here, we describe a platform method that integrates a Cu²⁺-dependent DNAzyme into graphene–molecule junctions and its application for direct detection of paramagnetic Cu²⁺ with femtomolar sensitivity and high selectivity. Since DNAzymes specific for other metal ions can be obtained through in vitro selection, the method demonstrated here can be applied to the detection of a broad range of other metal ions.     

Three-phase junction for modulating electron–hole migration in anatase–rutile photocatalysts

The heterophase solid–solid junction as an important type of structure unit has wide applications for its special mechanics and electronic properties. Here we present a first three-phase atomic model for the anatase–rutile TiO₂ heterophase junction and determine its optical and electronic properties, which leads to resolution of the long-standing puzzles on the enhanced photocatalytic activity of anatase–rutile photocatalysts. By using a set of novel theoretical methods, including crystal phase transition pathway sampling, interfacial strain analysis and first principles thermodynamics evaluation of holes and electrons, we identify an unusual structurally ordered three-phase junction, a layer-by-layer “T-shaped” anatase/TiO₂-II/rutile junction, for linking anatase with rutile. The intermediate TiO₂-II phase, although predicted to be only a few atomic layers thick in contact with anatase, is critical to alleviate the interfacial strain and to modulate photoactivity. We demonstrate that the three-phase junction acts as a single-way valve allowing the photogenerated hole transfer from anatase to rutile but frustrating the photoelectron flow in the opposite direction, which otherwise cannot be achieved by an anatase–rutile direct junction. This new model clarifies the roles of anatase, rutile and the phase junction in achieving high photoactivity synergistically and provides the theoretical basis for the design of better photocatalysts by exploiting multi-phase junctions.     

Synthesis and visible light photocatalytic activity of Ag spot-coated TiO2–60 wt% SrO composite powders

Nano-sized TiO₂–60 wt% SrO composite powders were synthesized from titanium isopropoxide and Sr(OH)₂·8H₂O by use of a sol–gel method. Ag spot-coated TiO₂–60 wt% SrO composite powders containing 3, 5, or 7 wt% Ag were synthesized by hydrothermal-assisted attachment, by use of Ag hydrosol in a high-pressure bomb at 250 °C and 450 psi. Nano-sized Ag particles approximately 5–25 nm in diameter adhered to the TiO₂–60 wt% SrO₂ composite powders. The photocatalytic activity of Ag spot-coated TiO₂–SrO powders in the degradation of phenol showed that all were highly active when irradiated with UV light. TiO₂–60 wt% SrO composite powder spot-coated with 5 wt% Ag was more photocatalytically active under visible light than TiO₂–SrO composite powder.     

Novel sol–gel synthesis of N-doped TiO<Subscript>2</Subscript> hollow spheres with high photocatalytic activity under visible light

Novel ammonia and triethanolamine assisted sol–gel synthesis method was developed to fabricate the N-doped TiO₂ hollow spheres. The prepared hollow spheres were in submicron size and had good morphology and high specific surface area. Polystyrene (PS) latexes in size of 470 nm were used as the templates to fabricate PS/TiO₂ core–shell spheres. Here ammonia and triethanolamine was first employed together to control the sol–gel process. The N-doped TiO₂ hollow spheres were got after calcinations of the core–shell spheres by using triethanolamine as N source, and the amount of doped N could be easily adjusted by changing the amount of triethanolamine. The hollow spheres had distinct visible light response, and the optical response shifted more to the visible region as the amount of doped N increases. The photodegradation of methylene blue expressed the high photocatalytic activity of the N-doped TiO₂ hollow spheres under visible light.     

Turning it off! Disfavouring hydrogen evolution to enhance selectivity for CO production during homogeneous CO2 reduction by cobalt–terpyridine complexes

Understanding the activity and selectivity of molecular catalysts for CO₂ reduction to fuels is an important scientific endeavour in addressing the growing global energy demand. Cobalt–terpyridine compounds have been shown to be catalysts for CO₂ reduction to CO while simultaneously producing H₂ from the requisite proton source. To investigate the parameters governing the competition for H⁺ reduction versus CO₂ reduction, the cobalt bisterpyridine class of compounds is first evaluated as H⁺ reduction catalysts. We report that electronic tuning of the ancillary ligand sphere can result in a wide range of second-order rate constants for H⁺ reduction. When this class of compounds is next submitted to CO₂ reduction conditions, a trend is found in which the less active catalysts for H⁺ reduction are the more selective towards CO₂ reduction to CO. This represents the first report of the selectivity of a molecular system for CO₂ reduction being controlled through turning off one of the competing reactions. The activities of the series of catalysts are evaluated through foot-of-the-wave analysis and a catalytic Tafel plot is provided.     

Development of TiO2 pastes modified with Pechini sol–gel method for high efficiency dye-sensitized solar cell

A titanium oxide layer used for a dye-sensitized solar cell (DSSC) has to meet two opponent properties to assure a high efficiency DSSC: good connection between TiO₂ grains and a large inner surface area. Three different paste formulations based on commercial nanocrystalline TiO₂ powder (Degussa P25) are studied. Results confirm that modification of the TiO₂ paste with the Pechini sol–gel method increases the surface area of the TiO₂ layer while maintaining good connections between the nanocrystalline grains, consequently the efficiency of the DSSC increases from 1.8% to 5.3%. The structure and morphology of the TiO₂ layers are described by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HR-TEM) and X-ray diffraction (XRD).