Dyes and Pigments (v.69, #3)

Aggregation of Solophenyl red 3BL (C.I. Direct 80) polyazo dye in aqueous solution was investigated using UV–visible and infrared spectroscopy techniques. The results showed a J-aggregate feature in highly acidic aqueous solutions with a red shift compared to monomer in the UV–visible absorption spectra which is due to dimer molecules. Infrared spectra showed that the carbonyl functional group stretch band of the dye molecule was eliminated in highly acidic aqueous solutions which can be related to intermolecular H-bonding. Photocatalytic degradation of Solophenyl red 3BL in aqueous TiO2 suspension under UV light irradiation in different acidity conditions was also investigated, the results showed that the complete mineralization occurs in low acidic, neutral and basic aqueous solutions but in the highly acidic solutions incomplete photocatalytic degradation was observed which can be related to the aggregated form of 3BL dye molecule. Further studies showed that azo–hydrazone tautomerism did not have any significant effect on the photocatalytic degradation of Solophenyl red 3BL in aqueous solution.
Keywords: Photocatalytic degradation; Aggregation; Azo–hydrazone tautomerism; Solophenyl red 3BL (C.I. Direct 80); TiO2;

New unsymmetrical perylene diimides have been synthesized to investigate their potential for applications. The symmetrical derivatives of all the compounds have been synthesized for comparison. The compounds are characterized by UV–vis, IR, MS, DSC, TGA and CV measurements. The fluorescence lifetimes, quantum yields and singlet-state energies are presented. All the compounds have very similar fluorescence lifetimes. The LUMO energy values of all the compounds as determined by cyclic voltammetry, are nearly identical. N-substituents have little influence on the electrochemical behavior of all the compounds. The color, solubility, thermal stability, extinction coefficients, aggregation and fluorescence quantum yields are dependent on the nature of the N-substituents. They show different aggregation in solid state.
Keywords: Perylenes; Fluorescence dyes; Unsymmetrical pigments; Aggregation;

Capacity of activated carbon in the removal of acid dyes subsequent to its thermal treatment by Amina A. Attia; Wafaa E. Rashwan; Soheir A. Khedr (128-136).
A commercial activated carbon (Prolabo) was subjected to thermal treatment at 400 and 600 °C for 2 h. Characterization of the parent, and heated products, was carried out by determining the N2/77 K adsorption isotherms, FTIR spectra, acidic/basic sites, and adsorption of iodine, Acid Blue 74 (AB), Acid Red 73 (AR) and Acid Yellow 23 (AY) from aqueous solution. Thermal treatment resulted in some enhancement in the porosity characteristics (specific area and pore volume) particularly in micropores, although insignificant changes appear in the surface chemical properties. Two liquid-phase adsorption models are applied, the Langmuir and Dubinin–Radushkevich linear equations, which showed satisfactory fit to the adsorption data. Evaluated capacity and affinity parameters demonstrated that the uptake of the acid dyes decrease in the order of AB > AR >> AY, which may be ascribed to chemical structure differences in substituents and side chains leading to unavailable accessibility. Heated carbons exhibit a reduction in uptake of AB, and an increase in case of AY and AR dyes. Changes in surface chemical groups, under action of heat probably influence the adsorbate/adsorbent, adsorbate/liquid and adsorbent/liquid relationships leading to the apparent differences.
Keywords: Active carbon; Thermal activation; Dye removal; Adsorption isotherm;

Continuous surface treatment of PET and PTT fabrics was carried out to introduce nanoscale surface roughness using an electrodeless UV bulb for different periods of time. Reflectance of the irradiated fabrics decreased in the low wavelength regions of visible light, especially at 400 nm. The surface roughness of the irradiated fabrics was investigated to verify the scattering and destructive interference of visible light using SEM and AFM analyses. AFM images indicated that the treatment developed the nano-sized roughness on the polyester surfaces. The surface roughness increased by two-fold from 58 nm to 122 nm in terms of peak–valley roughness, which can interfere destructively the incident light of as high as 488 nm wavelength in the visible spectrum. The dyeability of the surface modified polyester fabrics to disperse dyes was similar to that of untreated fabrics. However, irradiation both after and before dyeing with black disperse dyes significantly decreased lightness of the dyed fabrics up to 8% with increasing treatment due to the enhanced surface roughness. Surprisingly color fastness of the dyed polyester fabrics was excellent because of surface-limited treatment of the polyester fabrics.
Keywords: PET; PTT; UV irradiation; Nano roughening; Disperse dyes; Color deepening;

Solar photocatalytic degradation of azo-dyes by photo-Fenton process by Juan Matías Chacón; Ma. Teresa Leal; Manuel Sánchez; Erick R. Bandala (144-150).
A solar photocatalytic degradation of the azo-dye acid orange 24 was carried out by means of a photo-Fenton reaction promoted by solar energy. The dye degradation was monitored during the experimental runs through UV/Vis absorption as well as COD and TOC concentration determination and toxicity reduction. In most cases, a discoloration higher than 85% was reached using 50 kJ/l of accumulated energy. In the case of the best reaction conditions, a discoloration of up to 95% and a toxicity reduction from 37 to 5 TU were accomplished with 50 kJ/l. In the same experiment, the removal of COD up to 88% and TOC up to 85% was reached after 105 kJ/l. Results consigned in this work are comparable to others reported in literature for different dyes. The reduction on toxicity values obtained by this methodology was most relevant and present dye degradation by the solar photo-Fenton process as an interesting alternative for coupling with biological processes.
Keywords: Solar photocatalytic degradation; Photo-Fenton process; Advanced oxidation technologies; Azo-dye; Discoloration; Compound parabolic concentrators;

Photo-oxidative fading of seven pyrazolinylazo dyes was examined by exposing the dyed cellulose films immersed in an aerobic aqueous Rose Bengal solution to a carbon arc. The ease with which the dye was photo-oxidised was determined as k 0, the second-order rate constant of the reaction of the dye with singlet oxygen, from the initial rate of the fading. Calculating standard enthalpies of formation for the dyes in the gas phase and water by the PM5 method determined the azo–hydrazone tautomerism (AHT) of the dyes. Four dyes existed as a hydrazone tautomer (HT) and one dye as an azo tautomer (AT) in both phases without exhibiting AHT, and two dyes as HT in the gas phase and as an azo/keto tautomer (A/KT) in water. According to frontier orbital theory, the reaction sites for the corresponding tautomer(s) of azo dyes on cellulose to molecular singlet oxygen and their reactivity were analysed. The reaction sites were primarily the double bonds (C=N) of the hydrazone structure and other double bonds in the pyrazoline ring and secondarily several double bonds around carbon atoms connected with substituents. The probable reaction modes are ene and [2 + 2] cycloaddition toward the double bonds. These reaction modes were confirmed to be consistent with the absorption spectra of decomposed products combined with cellulose. The k 0-values obtained had a close correlation with the sum of Fukui's electrophilic frontier densities, fr (E), at both atoms of the corresponding double bonds (i.e. a linear correlation between log  k 0 and the sum of fr (E)). The sum was demonstrated to be a molecular descriptor of the reactivity toward singlet oxygen of a molecule.
Keywords: Reactive dye; Reactivity toward singlet oxygen; Electrophilic frontier density; Ene reaction; [2 + 2] Cycloaddition; Molecular descriptor;

Dye–micelle aggregate formation for effective photobleaching by Subrata Kundu; Sudipa Panigrahi; Anjali Pal; Sujit Kumar Ghosh; Sudip Nath; Snigdhamayee Praharaj; Soumen Basu; Tarasankar Pal (177-184).
Incorporation of six different (three cationic: MB, CV, AO and three anionic: RB, E and Fl) dye molecules in three different micellar environments has been examined critically for photobleaching of the dye–micelle aggregates. Micellar media have been found to influence the rate of decolorization which has been explained considering electrostatic, hydrophobic and charge transfer interactions. Further rate enhancement of colour bleaching was observed with Se nanoparticles. In depth, kinetic studies have been carried out to realize the interaction of the dyes with micelles. Kinetic studies have revealed that the reaction is first order with respect to dye concentration.
Keywords: Micelle; Dye; Degradation; Colour; UV light; Kinetics;

Four different types of nylon 6,6 fabric (deep-dyeable, standard-dyeable, cationic-dyeable and acetylated variants) were dyed using solubilised sulphur dyes as well as sulphur dyes. The colour strength of the dyeings on the four different types of nylon 6,6 fabric was little influenced by either the AEG content of the fibre or the nature of the polymer from which the substrates had been made. The finding that the colour of dyeings on each of the four types of fibre was not dissimilar also implied that the interactions between both solubilised sulphur dyes as well as sulphur dyes and the different fabrics was little influenced by the nature of the polymer. It is postulated that the adsorption of both solubilised sulphur dyes and sulphur dyes onto nylon 6,6 is predominantly non-site-specific and, therefore, that dye–fibre substantivity occurs principally through H-bonding, dispersion forces and polar van der Waals' forces of interaction.
Keywords: Nylon 6,6; Sulphur dyes; Solubilised sulphur dyes; Dye–fibre substantivity;

The morphology and internal structure of mica particles coated with metal oxide, TiO2, produced by the hydrolysis method were investigated by transmission electron microscopy on thin sections prepared by means of a specially designed sample preparation technique. Cross-sectional TEM images clearly revealed the comparatively uniform thickness and composition of the TiO2 layer as a component of the particles. It was found that the TiO2 layer was composed of randomly oriented small particles about 50 nm in diameter with small variation of the diameter depending on the position in a mica particle, while near the surface of the mica particle a monolayer of TiO2 oxide was observed.
Keywords: TiO2/mica particle; Pigment; Thin section; Thickness; Internal structure; Transmission electron microscopy;

Evaluation of the performance of adsorption and coagulation processes for the maximum removal of reactive dyes by Jae-Wook Lee; Seung-Phil Choi; Ramesh Thiruvenkatachari; Wang-Geun Shim; Hee Moon (196-203).
Physicochemical processes of adsorption and coagulation were systematically evaluated for the removal of reactive dyes (Orange 16 and Black 5) in a laboratory scale experimental setup. The effectiveness of combined processes of adsorption and coagulation for complete removal of dyes was also investigated. The right sequence of operation was identified for the combined treatment system. A coconut-based powdered activated carbon (PAC) was used as an adsorbent and alum chloride was chosen as a coagulant. The results indicated that adsorption capacity of Orange 16 was much higher than that of Black 5. Also, adsorption capacity on PAC was highly dependent on the pH of solution. The dye removal efficiencies for 100 mg l−1 of Black 5 and Orange 16 by coagulation were almost 99% and 80% under the determined optimal conditions for Black 5 (250 mg l−1 coagulant dose and pH 6) and for Orange 16 (350 mg l−1 coagulant dose and pH 6). Coagulation followed by adsorption was found to be more efficient than having adsorption prior to coagulation. There was a significant increase in adsorption capacity of PAC for the combined process where coagulation was carried out prior to adsorption. The combined coagulation–adsorption process has the capability of complete dye removal and thus total decolourization, reduction in coagulant and adsorption amounts and thereby produce less amount of sludge.
Keywords: Coagulation; Adsorption; Reactive dyes; Combined treatment system; Aluminium chloride; Activated carbon;

The parameters such as quantum yield and molar absorption coefficients of the photoinitiator that are responsible for holographic sensitivity in photopolymer material are investigated with a single beam exposure experiment. The influence of exposure intensity, the concentrations of N-phenylglycine and dye on the photobleaching process of xanthenes dyes are presented. In addition, the effect of diphenyliodonium hexafluorophosphate salt on the quantum yield and molar absorption of xanthene dyes is studied.
Keywords: Photopolymer; Holographic recording; Quantum yield; Molar absorption;

In the study, bagasse fly ash (BFA) (generated as waste material from sugar mill), was used as an adsorbent for the removal of Orange-G (OG), and Methyl Violet (MV), from aqueous solution. Batch studies were performed to address various experimental parameters like pH, contact time, adsorbent dose and initial concentration for the removal of these dyes. Effective pH for OG and MV removal were 4 and 9, respectively. Greater percentage of dye was removed with decrease in the initial concentration of dyes, and increase in amount of adsorbent used. Kinetic study showed that the adsorption of dyes on BFA was a gradual process. Quasi-equilibrium reached in 4 h. Pseudo-first-order, pseudo-second-order, Bangham and intra-particle particle diffusion models were used to fit the experimental data. Pseudo-second-order rate equation was able to provide realistic description of adsorption kinetics. Equilibrium isotherms were analysed by Freundlich, Langmuir, Redlich–Peterson, Dubnin–Radushkevich, and Tempkin isotherm equations using correlation coefficients and five different error functions. Freundlich equation is found to best represent the equilibrium data for OG-BFA system while Redlich–Peterson equation better fits the data for MV-BFA system. Thermodynamic study showed that adsorption of MV on BFA (with a more negative Gibbs free energy value) is more favoured among the dyes studied. BFA which was used without any pretreatment showed high surface area, pore volume and pore size exhibiting its potential to be used as an adsorbent for the removal of OG and MV.
Keywords: Adsorption; Dye removal; Bagasse fly ash; Kinetic study; Error analyses;

The photocatalytic degradation of a mixture of two dyes: Crystal Violet (CV), also known as C.I. Basic Violet 3, which is a cationic triphenylmethane dye and Methyl Red (MR), which is an anionic azo dye was studied using untreated TiO2 and silver ion doped TiO2 under UV irradiation. To increase the photocatalytic efficiency of TiO2 and to make its separation from the treated effluent after degradation easier, it was doped with silver ion using liquid impregnation method. The degradation of the dyes in the mixture was measured spectrophotometrically at their respective λ max values. The degradation kinetics fitted well to the Langmuir–Hinselwood pseudo first order rate law. The effects of pH and different interfering substances like Cl, NO3 , SO4 2−, HPO4 2−, Ca2+, Fe2+, humic acid, O2 and electron acceptors like H2O2, (NH4)2S2O8 and KBrO3 on the degradation were also investigated. Several mixtures of these dyes prepared by mixing CV (5 × 10−5  mol dm−3) and MR (7.5 × 10−5  mol dm−3) in the V/V ratios of 1:1, 1:5 and 1:10 degraded by >99% on UV irradiation for 90 min in the presence of Ag+ doped TiO2 and about 70% under similar conditions in presence of TiO2. COD removal was measured at regular intervals to quantify the mineralization of the dye. Above 86% mineralization was observed using 90 min irradiation.
Keywords: Ag+ doped TiO2; Crystal violet; Dye degradation; Methyl red; Photocatalytic;

Dyeing properties of a series of alkali-clearable azohydroxypyridone disperse dyes containing a fluorosulfonyl group on poly(ethyleneterephthalate) have been investigated. The dyes showed reasonably good build-up properties and had a yellow shade on PET. The dyes exhibited excellent fastness properties on PET fabric, irrespective of the clearing method. Specially, the azohydroxypyridone dyes containing a nitro group in place of the fluorosulfonyl group in the para position to azo group were synthesised in order to compare their dyeing and fastness properties on poly(ethyleneterephthalate) with those of fluorosulfonyl-substituted analogues.
Keywords: Azohydroxypyridone disperse dyes; Poly(ethyleneterephthalate); Build-up properties; Fastness properties; Fluorosulfonyl group;

Spin-coated films of poly(bisphenol A carbonate) (PC) and poly(styrene-co-acrylonitrile) (SAN) doped by 4-(N,N-dimethylamino)-4′-nitrostilbene (DANS) were prepared, and their poling and depoling behaviors were investigated mainly by UV–visible absorption spectra and second-harmonic generation (SHG). The absorbance of DANS in the PC and SAN films proportionally increased with increasing its weight concentration up to 5 wt%, indicating homogeneous dissolution of DANS in the host polymers. However, above this concentration, heterogeneous structures due to DANS crystallites could be observed under a polarizing microscope. Poling of the films was performed using a triode corona discharging system. The maximum d coefficients were obtained at slightly lower poling temperature than the glass transition temperature of the corresponding dye-doped polymer. The KWW stretched exponential function could be fitted to the experimental temporal relaxation data of SHG for the SAN system. Relatively high long-term stability was observed for the PC system because of its relatively rigid backbone structure.
Keywords: PC; SAN; DANS; SHG; Dipole relaxation; Backbond and heterogeneous structure; Glass transition and temporal stability;

The fixed bed column study was undertaken for the removal of crystal violet (CV), also known as Basic Violet 3, a well-known cationic dye from wastewater using surfactant-modified alumina (SMA) as an adsorbing media. The SMA was found to be a very efficient media for the removal of dye from wastewater. The column with 2 cm diameter, different bed heights such as 10, 20 and 30 cm could treat 3.58 l, 7.94 l and 12.51 l, respectively, of CV bearing wastewater with CV concentration 200 mg/l and flow rate 8.5 ml/min. The adsorption bed was exhausted within a very short time (∼1.5 h) after the breakthrough occurred. This indicated that the adsorption zone was almost saturated at the time of exhaustion. Different column design parameters like depth of exchange zone, time required for exchange zone to move its own height, adsorption rate, adsorption capacity etc. were calculated. Effect of flow rate and initial concentration was studied. Theoretical breakthrough curve was drawn from the batch isotherm data and was compared with experimental breakthrough curve. Desorption of CV from the SMA surface was possible using 1 M sodium hydroxide solution, rectified spirit and acetone.
Keywords: Alumina; Sodium dodecyl sulfate; Surfactant-modified alumina; Crystal violet; Adsorption; Column study; Breakthrough curve;