Enhance photocatalytic properties of TiO2 using π-π* conjugate system

Abstract

A novel π-π* conjugate system photo-catalyst was successfully constructed using aniline, pyrrole and TiO₂. The structures of photo-catalyst were measured by XRD, SEM, BET, TEM, FT-IR, XPS and TGA in detail. The photocatalytic properties were investigated in rhodamine B and methyl orange solution, respectively. And the enhance mechanism of π-π* conjugate system was discussed in depth. The weight percentage of Ti weight about 47% in the compound and the π-π* conjugate system did not change the crystal structure of TiO₂. The photocatalytic degradation properties of the π-π* conjugate system photo-catalyst could get 99% for rhodamine B and methyl orange after 10 and 15?min, respectively. The introduction of the π-π* conjugate system into TiO₂ was beneficial to improve light harvest, photoelectric response and separation of electron-holes.     

Organometallic dithiolene complexes of benzenedithiolate analogues with π-coordinating and π-interacting Cp* ligand

Organometallic dithiolene complexes, which were formulated as [Cp*M(dcbdt)] and [Cp*M(dcdmp)] (M = Co, Rh, Ir; Cp* = η⁵-pentamethylcyclopentadienyl, dcbdt = 4,5-dicyanobenzene-1,2-dithiolate, dcdmp = 2,3-dicyano-5,6-dimercaptopyrazine) were prepared from a low valent Cp*Co^I or high valent Cp*M^III species (M^III = Co^III, Rh^III, Ir^III). The UV-Vis absorption spectral and electrochemical data of them were obtained. The lowest absorption (HOMO-LUMO) energies of them became redshift in order of the Co > Rh > Ir complexes. The reduction potentials suggested that the central metal modifies their LUMO levels. The molecular and crystal structures of [Cp*Co(dcbdt)] (3a), [Cp*Co(dcdmp)] (4a) and [Cp*Rh(dcdmp)] (4b) were determined by X-ray diffraction studies. The cobalt complexes 3a and 4a were monomeric, formally 16-electron complexes and have two-legged piano-stool geometries. The crystal structure of 3a indicated some plane-to-plane intermolecular interactions such as benzene?benzene interaction on the dcbdt ligand and two Cp*?benzene π-π stackings. 4a showed plane-to-plane interaction with a pseudo-4-fold-symmetry arrangement between the pyrazine moieties on the dcdmp ligand. The rhodium complex 4b was dimeric in the crystal to form a criss-cross arrangement and had a three-legged piano-stool geometry, but it was monomerized in solution. The dimer of 3b was observed in the oxidation process of the cyclic voltammogram.     

Redox properties of ruthenium(III/II)–edta complexes with o-phenylenediamine and o-benzoquinone diimine ligands

The reaction of [Ru^III(edta)(H₂O)]⁻ with o-phenylenediamine (opda) in water, under aerobic conditions, affords the diamagnetic [Ru^II(edta)(bqdi)]²⁻ product (where edta stands for the ethylenediaminetetraacetate co-ligand, and bqdi represents the non-innocent o-benzoquinone α,α^′-diimine ligand). In the current communication, the redox chemistry of this system in aqueous solution is described in details on the basis of electrochemical and spectroelectrochemical studies. The electrochemical behavior of “free” opda is rather complicated with further chemical reactions following the irreversible two-proton/two-electron oxidation (opda→bqdi+2e⁻+2H⁺), whereas its complex is electrochemically well-behaved with two chemically reversible redox processes: the monoelectronic couple associated with the metal ion (Ru^III/Ru^II) and another bielectronic step centered on the coordinated ligand (bqdi/opda). The set of UV–Vis electronic spectra were obtained by electrolytical generation, in situ, of all the redox species accessible in the CV working conditions (i.e., the starting [Ru^II(edta)(bqdi)]²⁻, the fully oxidized [Ru^III(edta)(bqdi)]⁻, and the fully reduced [Ru^II(edta)(opda)]²⁻ species), which are stable and totally interconvertible. The electrochemistry and absorption spectroscopy of these complexes in water were found to be comparable with the tetraammine counterparts. A remarkable difference in redox behavior between the diimine- and the analogous dioxolene-complexes was also revealed by comparison of the system reported herein with the one derived from catechol, and rationalized in terms of the quite efficient π-accepting electronic nature of the bqdi ligand.     

Formation of self-assembled monolayers of π-conjugated molecules on TiO2 surfaces by thermal grafting of aryl and benzyl halides

We demonstrate the formation of molecular monolayers of π-conjugated organic molecules on nanocrystalline TiO(2) surfaces through the thermal grafting of benzyl and aryl halides. X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy were used to characterize the reactivity of aryl and benzyl chlorides, bromides, and iodides with TiO(2) surfaces, along with controls consisting of nonhalogenated compounds. Our results show that benzyl and aryl halides follow a similar reactivity trend (I > Br > Cl > H). While the ability to graft benzyl halides is consistent with the well-known Williamson ether synthesis, the grafting of aryl halides has no similar precedent. The unique reactivity of the TiO(2) surface is demonstrated using nuclear magnetic resonance spectroscopy to compare the surface reactions with the liquid-phase interactions of benzyl and aryl iodides with tert-butanol and -butoxide anion. While the aryl iodides show no detectable reactivity with a tert-butanol/tert-butoxide mixture, they react with TiO(2) within 2 h at 50 °C. Atomic force microscopy studies show that grafting of 4-iodo-1-(trifluoromethyl)benzene onto the rutile TiO(2)(110) surface leads to a very uniform, homogeneous molecular layer with a thickness of ～0.45 nm, demonstrating formation of a self-terminating molecular monolayer. Thermal grafting of aryl iodides provides a facile route to link π-conjugated molecules to TiO(2) surfaces with the shortest possible linkage between the conjugated electron system and the TiO(2).     

Preconcentration of Ultra-trace Cadmium with Nanometer-size TiO2 Colloid and Determination by GFAAS with Slurry Sampling

Cadmium-a heavy metal used in coatings, batteries and plastics-can accumulate in human’s liver and kidney, causing osteoporosis and cancer1,2. The monitoring of its content is, therefore, of great importance. But the average concentration of cadmium in w…     

Formation of γ-Lactones by the Reaction of π-Allylnickel Complexes with Carbon Dioxide

Recently, considerable interest has been shown in the reaction of carbon dioxide with olefins or alkynes caused by transition metal complexes. Incorporation of CO₂ in oligomerizations of butadiene¹⁾ and 1-hexyne²⁾ has been performed to give lactone derivatives by Pd-Ph₂ PCH₂ CH₂ PPh₂ and Ni (COD)₂-Ph₂P(CH₂)₄PPh₂ (COD : 1,5-cyclooctadiene) systems, respectively. Very recently, Jolly et al. reported the reaction of CO₂ with π-allylnickel complexes which are the key intermediates of the oligomerization of diolefins.³⁾ For example, bis (η-methylallyl) nickel reacts with CO₂ in the presence of a phosphine ligand to give a nickel carboxylate complex:     

Synthesis and hydrophosphorylation of π-complexes of dibenzylideneacetone and cyclic conjugated dienones with homocarbonyl and carbonylcyclopentadienyl molybdenum compounds

Reactions of dibenzylideneacetone and cyclic cross-conjugated dienones with hexacarbonylmolybdenum(0) and bis[tricarbonyl(cyclopentadienyl)molybdenum(0)] afforded the corresponding complexes with η²-(C=C),η²-(C=O) coordination of the diketone to metal center, regardless of the ligand structure and initial molybdenum compound. The reactivity of the multidentate ligands may change as a result of coordination.     

Photogeneration of reactive oxygen species over ultrafine TiO2 particles functionalized with rutin–ligand induced sensitization and crystallization effects

Research on Chemical Intermediates - Interaction of amorphous and crystalline TiO2 ultrafine particles (2–6 nm) with rutin results in the formation of colored nanomaterials of an...     

Synthesis of azamacrocyclic compounds by cyclocondensation of aliphatic α,ω-diamines with acetone

Cyclocondensation of 1,4-diaminobutane and 1,6-diaminohexane with acetone afforded the corresponding 18- and 22-membered trans-azamacrocyclic Curtis compounds in high yield, which contain two azomethine and amine nitrogen atoms. A complex mixture of the products formed containing less than 25% of 16-membered azamacrocyclic cis- and trans-isomers when reacting 1,3-diaminopropane with acetone.     

Photocurrent of TiO2 Photoelectrode Enhanced by Nafion Modification

Introduction Since Gratzel‘s group^[1-5] first fabricated the dye-sensitized solar cell (DSSC) by using mesoporous TiO2 electrodes in 1991, as a possible alternative to P-N junction inorganic silicon cells, DSSCs have attracted more and more attention[6-11] The photo-to-electricity conversion of DSSCs is achieved by means of ultrafast electronin jection into the conduction band of TiO2 from an photoexcited dye, subsequent dye regeneration and hole transportation to the counter electrode.     

Photoelectrochemical Character of TiO2 Nanocrystalline Electrodes Sensitized by Aluminum Phthalocyanines Modified with Sulfonate Groups

IntroductionIn recent years, dye-sensitized solar cells(DSSCs) have attracted more and more attention be-cause of their low cost and simple fabrication[1—3].They are made of four parts: a photo-electrode, a dyesensitizer, an electrolyte and a counter-ele…     

Analysis of influence of substituents on electrochemical oxidation and reduction potentials of aromatic and heterocyclic compounds,on the basis of the dependence of electronic effects of the substituents in π-systems on the character of the π-molecular orbitals

The influence of substituents on the electrochemical potentials of aromatic and heterocyclic -systems has been analyzed from the standpoint of the relationship between the electronic effects of the substituents and the structure of the -molecular orbitals. The proposed calculational schemes and parametrization can be used for quantitative estimates of the magnitudes of the electrochemical oxidation and reduction potentials of substituted aromatic and heterocyclic compounds.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 31, No. 3, pp. 153–165, May–June, 1995.     

Enhanced Photocatalytic Efficiency of TiO2 by Combining the Modification of Ag Nanoparticles with the Application of Anodic Bias

Ag-TiO2/TTO film electrode was used as photoanode to investigate the feasibility of a hybrid technology of Ag nanoparticles combined with the application of anodic bias.The results showed that the deposited Ag and applied anodic bias have an apparent additive effect.     

Copper(I) π-complexes with allyl derivatives of heterocyclic compounds: structural survey of their crystal engineering

In this review an exhaustive crystallochemical analysis of copper(I) π-complexes with allyl derivatives of heterocyclic compounds has been performed. Structural genesis of inorganic constituents starting from the simplest units to the most complicated aggregates was considered taking into account the specific role of Cu-(C=C) interaction, the construction of the organic ligands, the basicity and nucleophilic activity of their heteroatoms, as well as olefin Cu(I) π-complex preparation route.      

Reactions of aminoguanidine with α-dicarbonyl compounds studied by electrospray ionization mass spectrometry

Aminoguanidine possesses extensive pharmacological properties. This drug is recognized as a powerful α-dicarbonyl scavenger. In order to better elucidate the reactivity of aminoguanidine with α-dicarbonyls, aminoguanidine was reacted with several aldehydic and diketonic α-dicarbonyls. Electrospray ionization mass spectrometry is a suitable technique to study chemical and biochemical processes, and was selected for the purpose. In aminoguanidine reactions, triazines were detected and, other compounds that have never been reported before were identified. Triazine precursor forms were detected, namely tetrahydrotriazines and singly dehydrated tetrahydrotriazines. Moreover, species with bicyclic ring structures, and dehydrated forms, were also identified in aminoguanidine reactions. These species appear to result from tetrahydrotriazines and triazines reactions with one dicarbonyl molecule. Experiments revealed that these bicyclic species, in particular the ones resulting from triazines reactivity, could exist in solution, since they were both identified in the reactions of aminoguanidine and of a selected triazine with the dicarbonyls studied. The results obtained, regarding aminoguanidine/triazines reactivities, appear to support the capability of triazines to condensate and form polycyclic ring structures, and also to support literature mechanistic data for dihydroimidazotriazines formation via dihydroxyimidazolidine-triazines. The data obtained in this study may prove to be valuable to complement solution information, concerning the reactivity of amines with α-dicarbonyls, in particular.     

A novel olefination of carbonyl compounds with α-bromoacetic ester mediated by tri-n-butylstibine

Tri-n-butylstibine has been found to mediate the olefinatlon of carbonyl compounds by α-bromoacetic ester to give corresponding olefins in good yields.     

Synthesis of derivatives of 2-aminoimidazole and 2-iminoimidazolidine by cyclization of 1-aryl-2-(4,6-dimethylpyrimidin-2-yl)guanidines with α-bromocarbonyl compounds

Cyclization of 1-aryl-2-(4,6-dimethylpyrimidin-2-yl)guanidines with α-bromoacetophenone and ethyl bromoacetate gave derivatives of 1,4-diphenyl-1H-imidazole-2-amine and 2-amino-1-phenylimidazolidin- 4-one respectively. The mechanism of the reaction was determined on the basis of quantum-chemical calculations, NOESY NMR spectroscopy, and X-ray crystallography.     

Effect of Chemical Treatment on TiO2 Particles by IMPS

The photodegradation reaction rate of CHCl3 in TiO2 particulate suspension was imperoved significantly by HCl-treatment.The effect of HCl-treatment on the photocatalytic activity of TiO2 was strdied in a PEC cell by using Intensity-Modulated Photocurrent Spectroscopy(IMPS).The magntude of photocurrent response and the characteristic frequencies of the upper and lower semicircles in the complex plane of IMPS response were analyzed,and the ccathodic and anodic reaction processes of photogenerated holes and electrons were discussed.The increases in the cathodic and anodic photocurrent response and in the time constants of both cathodic and anodic reaction processes of photogenerated holes and electrons were discussed.The increases in the cathodic and anodic photocurrent response and in the time constants of both cathodic and anodic reaction processes indicate that HCl-treatment leads to the improvement of the photocatalytic activity of TiO2 and a change of the photocatalytic kinetic mechanism.