Low band gap dyes based on 2-styryl-5-phenylazo-pyrrole: Synthesis and application for efficient dye-sensitized solar cells

A new series of low band gap dyes, C1, C2 and S, based on 2-styryl-5-phenylazo-pyrrole was synthesized. These dyes contain one carboxy, two carboxy and one sulfonic acid anchoring groups, respectively. They were soluble in common organic solvents, showed long-wavelength absorption maximum at ∼620 nm and optical band gap of 1.66-1.68 eV. The photophysical and electrochemical properties of these dyes were investigated and found to be suitable as photosensitizers for dye sensitized solar cells (DSSCs). The quasi solid state DSSCs with dye S showed a maximum monochromatic incident photon to current efficiency (IPCE) of 78% and an overall power conversion efficiency (PCE) of 4.17% under illumination intensity of 100 mW cm⁻² (1.5 AM), which is higher than the other dyes (3.26% for C2 and 2.59% for C1). Even though dye S contains one sulfonic acid anchoring group, the higher PCE for the DSSCs based on this dye has been attributed to the higher dye loading at the TiO₂ surface and enhanced electron lifetime in the device, as indicated by absorption spectra and electrochemical impedance spectra measurements. Finally, by increasing the molecular weight of poly(ethylene oxide) (PEO) in electrolyte, the PCE also increases up to 4.8% for the electrolyte with PEO molecular weight of 2.0 × 10⁶. This improvement has been attributed to the enhancement in iodide ions diffusion due to the increase in free volume of polymer gel electrolyte.     

Magnetic graphene oxide nanocomposites as the adsorbent for extraction and pre-concentration of azo dyes in different food samples followed by high-performance liquid chromatography analysis

ABSTRACT

This work presents a method of magnetic solid-phase extraction (MSPE) combined with high-performance liquid chromatography (HPLC) to analyse five synthetic azo dyes (tartrazine, amaranth, carmine, sunset yellow, allura red) in different food samples. The magnetic graphene oxide nanocomposite (GO@Fe₃O₄) was prepared by a one-step solvothermal method and used as the sorbent for extraction and pre-concentration of azo dyes in food samples. The as-prepared GO@Fe₃O₄ nanocomposite was characterised by transmission electron microscope, Fourier transform-infrared spectroscopy, X-ray diffraction, vibrating sample magnetometer, and Brunuer-Emmett-Teller analysis. The extraction and desorption parameters were investigated, including the material amount, extraction time, pH of the solution, desorption temperature, and desorption solvents. Under the optimised conditions, the limits of detection (LODs) were 1.14–2.23, 0.36–0.77 and 0.68–1.26 ng/g for candy, jelly, and plum candy, respectively. The limits of quantification (LOQs) were 4.02–7.73, 1.21–2.50 and 2.31–4.20 ng/g for candy, jelly, and plum candy, respectively. For the analysis of spiked jelly, recoveries were between 73.2% and 107.7%, with RSDs lower than 1.34 %. The developed method was successfully applied to the analysis of real samples including jelly, candy and plum candy.     

Removal of reactive red-120 and 4-(2-pyridylazo) resorcinol from aqueous samples by Fe3O4 magnetic nanoparticles using ionic liquid as modifier

The nanoparticles of Fe₃O₄ as well as the binary nanoparticles of ionic liquid and Fe₃O₄ (IL-Fe₃O₄) were synthesized for removal of reactive red 120 (RR-120) and 4-(2-pyridylazo) resorcinol (PAR) as model azo dyes from aqueous solutions. The mean size and the surface morphology of the nanoparticles were characterized by TEM, DLS, XRD, FTIR and TGA techniques. Adsorption of RR-120 and PAR was studied in a batch reactor at different experimental conditions such as nanoparticle dosage, dye concentration, pH of the solution, ionic strength, and contact time. Experimental results indicated that the IL-Fe₃O₄ nanoparticles had removed more than 98% of both dyes under the optimum operational conditions of a dosage of 60 mg, a pH of 2.5, and a contact time of 2 min when initial dyes concentrations of 10-200 mg L⁻¹ were used. The maximum adsorption capacity of IL-Fe₃O₄ was 166.67 and 49.26 mg g⁻¹ for RR-120 and PAR, respectively. The isotherm experiments revealed that the Langmuir model attained better fits to the equilibrium data than the Freundlich model. The Langmuir adsorption constants were 5.99 and 3.62 L mg⁻¹ for adsorptions of RR-120 and PAR, respectively. Both adsorption processes were endothermic and dyes could be desorbed from IL-Fe₃O₄ by using a mixed NaCl-acetone solution and adsorbent was reusable.     

Photodegradation of orange I in the heterogeneous iron oxide-oxalate complex system under UVA irradiation

To understand the photodegradation of azo dyes in natural aquatic environment, a novel photo-Fenton-like system, the heterogeneous iron oxide-oxalate complex system was set up with the existence of iron oxides and oxalate. Five iron oxides, including gamma-FeOOH, IO-250, IO-320, IO-420 and IO-520, were prepared and their adsorption capacity was investigated in the dark. The results showed that the saturated adsorption amount (gamma(max)) was ranked the order of IO-250 > IO-320 > gamma-FeOOH > IO-420 > IO-520 and the adsorption equilibrium constant (Ka) followed the order of IO-250 > IO-520 > gamma-FeOOH > IO-420 > IO-320. The effect of initial pH value, the initial concentrations of oxalate and orange I on the photodegradation of orange I were also investigated in different iron oxide-oxalate systems. The results showed that the photodegradation of orange I under UVA irradiation could be enhanced greatly in the presence of oxalate. And the optimal oxalate concentrations (C(ox)0) for gamma-FeOOH, IO-250, IO-320, IO-420 and IO-520 were 1.8, 1.6, 3.5, 3.0 and 0.8 mM, respectively. The photodegradation of orange I in the presence of optimal C(ox)0 was ranked as the order of gamma-FeOOH > IO-250 > IO-320 > IO-420 > IO-520. The optimal range of initial pH was at about 3-4. The first-order kinetic constant for the degradation of orange I decreased with the increase in the initial concentration of orange I. Furthermore, the variation of pH, the concentrations of Fe3+ and Fe2+ during the photoreaction were also strongly dependent on the C(ox)0 and iron oxides.     

二向色性染料偏振膜的研究

偏振片在液晶显示技术中占据着很重要的位置,改善偏振片的偏振性能是液晶显示技术中的关键问题。二向色性有机染料因具有优良的耐湿热性能,被用作液晶显示偏光材料的研究日渐活跃,现在普遍研究的有偶氮染料偏振片和聚环染料偏振片。     

Intercalation of cationic azobenzene derivatives in a synthetic mica and their photoresponse

Four types of cationic azobenzene derivatives (Azds) having quaternary ammonium functional group at the 4-position (“single-hand”) or at the 4 and 4′-positions (“double-hand”) were synthesized and intercalated in a synthetic mica, Li taeniolite (LiTN), by ion exchange to obtain photoresponsive complexes. Powder X-ray results suggested that the long axis of molecules was at an angle of 58–62° from the mica layer for the single-hand series and at about 24° for the double-hand series. Photoresponse by ultraviolet (UV) irradiation with λ=365 nm and visible light (VIS) with λ=436 nm was monitored by the change in d(001), the basal spacing. Each Azd/TN complex showed different types of behavior toward UV/VIS irradiation. Complexes of a double-hand azo derivative showed a basal-spacing contraction of 0.7% under UV irradiation, but recovered their initial length under VIS irradiation, or by standing in the dark. Another complex presented a nonreversible change in basal spacing of 4%. This contraction under UV irradiation was attributed to trans-to-cis isomerization of the azobenzene moiety in guests, although the complex interlayer-space environment may have caused a different response after contraction.     

Decolourization of Methyl Orange using Fenton-like mesoporous Fe(2)O(3)-SiO(2) composite

Rapid decolourization of Methyl Orange by Fenton-like mesoporous Fe(2)O(3)-SiO(2) catalyst has been reported. The effect of various parameters such as initial pH, initial H(2)O(2) concentration, Fe content in the catalyst and initial dye concentration on decolourization process were studied. The results show that 20mg of mesoporous Fe(2)O(3)/SiO(2) composite (with Si/Fe=10) was sufficient to decolourize 0.6 mg/ml of Methyl Orange in presence of 2 ml of H(2)O(2) at an initial pH of 2.93 within 20 min. The pH range for effective decolourization (≥90%) was found to be 1-3. Leaching tests indicated that the activity of the catalyst was almost unaffected up to three consecutive cycles although ≤0.2 ppm of Fe ion was leached into treated water in each run.     

Nanoparticles of organosilane-based nitrite ionic liquid immobilized on silica for the diazotization of aniline derivatives and subsequent synthesis of azo dyes

Imidazolium based nitrite ionic liquid containing trimethoxysilyl group was prepared from the reaction of N-methylimidazole and (3-chloropropyl) trimethoxysilane. This ionic liquid was immobilized on silica covalently to give nanoparticles with the imidazolium nitrite moiety remaining intact. The diazotization reaction was performed as a model reaction to examine the activity of these nanoparticles as a nitrosonium source. Excellent performance was exhibited in the diazotization reaction of various aniline derivatives in the presence of HCl under mild heterogeneous conditions (room temperature and short reaction time). In-situ coupling of diazonium salts to a range of tertiary anilines, phenols and naphthols afforded the requisite azo dyes in good yield, using standard experimental procedures.