Photocatalytic decolorization of rhodamine B by immobilized TiO2/UV in a fluidized-bed reactor

The photocatalytic oxidation of Rhodamine B (RhB) was studied by using a newly developed immobilized photocatalyst (TiO₂ immobilized by support consisting of a perlite and silicone sealant) and a fluidized-bed reactor. Three 8W germicidal lamps were used as the light source and the reactor volume was 2.8l. When this photocatalyst was employed in a batch process, a total decolorization of the RhB in reaction times lower than 60 min was observed. The optimum dosage of photocatalyst was 33.8 g/l. The initial RhB decolorization rate of the immobilized TiO₂ was higher than that of the suspended TiO₂ and this did not agree with pseudo first-order kinetics because of the adsorption onto the surface of the immobilized TiO₂. This result indicated that the adsorption capacity of the immobilized photocatalyst is very important in photocatalysis.     

A Study into the Influence of Paper Coatings on Paper Properties and Print Quality of Dye Sublimation Thermal Prints

The need for good quality paper for dye sublimation transfer printing has been reported previously as a principal requirement for the process. Pigmented coated papers have gained acceptance in the traditional paper printing industry, but, despite their importance, have inspired very few reports in literature about their application in heat transfer printing.

In the current work, we studied the influence of both clay and ground calcium carbonate (GCC) pigments and the incorporation of plastic pigment on the surface structure and mechanical properties of the coated paper used for transfer printing. The results showed that paper coating significantly reduced the surface roughness of the paper. The mechanical properties of the prepared coated paper, including tensile strength, stretch, tensile energy absorption (TEA), and burst index, were improved when coated compared to those of uncoated paper. The addition of plastic pigment to the coating mixture helped improve the paper's properties.

The optical density of the transfer-printed polyester fabric using the prepared coated paper was also compared with that of uncoated paper. It was shown that a slight increase in optical density was evident in the coated paper.

The possibility of producing a second polyester print from the exhaust paper was also investigated. Coated paper incorporating plastic pigment, in particular, showed higher optical density than did uncoated paper.

We found that coated paper based on clay, GCC, clay/plastic pigment, or GCC/plastic pigment consumed less dye paste than uncoated paper though producing printed fabric with higher optical density—especially in the second print.     

ADSORPTION OF A LEATHER DYE ON MESOPOROUS STRUVITE OBTAINED FROM SWINE WASTEWATER

Struvite powder obtained from swine wastewater was used as adsorbent to remove an azo leather dye from aqueous solution. The material was characterized by X-ray diffraction, surface area, and atomic force microscopy. The sample presented a single phase having a mesoporous structure and surface area of 35.63 m² g^?1. Langmuir and Freundlich isotherm models were fitted to the adsorption data and both satisfactorily represented the process. The maximum adsorption capacity was 38.14 mg g^?1. From the analysis of thermodynamic parameters such as free energy of adsorption (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) it was verified that the adsorption process is very fast, spontaneous, and exothermic in nature, with weak forces acting.     

On the measurement of critical micelle concentrations of pure and technical-grade nonionic surfactants

The critical micelle concentrations (CMC) of nine commercial nonionic surfactants (Tween 20, 22, 40, 60, and 80; Triton X-100; Brij 35, 58, and 78) and two pure nonionics [C₁₂(EO)₅ and C₁₂(EO)₈] were determined by surface tension and dye micellization methods. Commercially available nonionic surfactants (technical grade) usually contain impurities and have a broad molecular weight distribution owing to the degree of ethoxylation. It was shown that the surface tension method (Wilhelmy plate) is very sensitive to the presence of impurities. Much lower CMC values were obtained with the surface tension method than with the dye micellization method (up to 6.5 times for Tween 22). In the presence of highly surfaceactive impurities, the air/liquid interface is already saturated at concentrations well below the true CMC, leading to a wrong interpretation of the break in the curve of surface tension (γ) vs. concentration of nonionic surfactant (log C). The actual onset of micellization happens at higher concentrations, as measured by the dye micellization method. Furthermore, it was shown that when a commercial surfactant sample (Tween 20) is subjected to foam fractionation, thereby removing species with higher surface activity, the sample yields almost the same CMC values as measured by surface tension and dye micellization methods. It was found that for monodisperse pure nonionic surfactants, both CMC determination methods yield the same results. Therefore, this study indicates that precaution should be taken when determining the CMC of commercial nonionic surfactants by the surface tension method, as it indicates the surface concentration of all surface-active species at the surface only, whereas the dye method indicates the presence of micelles in the bulk solution.     

Dicationic bis-imidazolium molten salts for efficient dye sensitized solar cells: Synthesis and photovoltaic properties

New dicationic bis-imidazolium salts based ionic liquids were synthesized to develop new electrolytes to improve photovoltaic properties of dye sensitized solar cells. Various properties of electrolytes such as viscosities, ion diffusion coefficients, charge transfer resistances and photovoltaic properties were studied. Electrochemical impedance spectroscopy has been performed to investigate diffusion coefficients and charge transfer resistances. Influence of polarity and chain length on the photovoltaic performance, was investigated. A DSSC employing the K34 (butyl-1,4-bis(3-methyl imidazolium iodide) gives an open-circuit voltage of 0.64 V, a short-circuit current of 17.11 mA/cm² and conversion efficiency of 5.60% under light intensity of 100 mW/cm² while the DSSC based on 1-butyl-3-methyl imidazolium iodide which is a reference ionic liquid exhibited 5.64% efficiency due to the lowest viscosity, highest diffusion coefficient.     

Removal of cationic dyes from aqueous solutions by kaolin: Kinetic and equilibrium studies

Experimental investigations were carried out using commercially available kaolin to adsorb two different toxic cationic dyes namely crystal violet and brilliant green from aqueous medium. Kaolin was characterized by performing particle size distribution, BET surface area measurement and XRD analysis. The effects of initial dye concentration, contact time, adsorbent dose, stirring speed, pH, salt concentration and temperature were studied in batch mode. The extent of adsorption was strongly dependent on pH of solution. Free energy of adsorption (ΔG⁰), enthalpy (ΔH⁰) and entropy (ΔS⁰) changes were calculated. Adsorption kinetic was verified by pseudo-first-order, pseudo-second-order and intra-particle-diffusion models. The rate of adsorption of both crystal violet and brilliant green followed the pseudo-second-order model for the dye concentrations studied in the present case. The dye adsorption process was found to be external mass transfer controlled at earlier stage and intra-particle diffusion controlled at later stage. Calculated external mass transfer coefficient showed that crystal violet dye adsorbed faster than brilliant green on kaolin. Adsorption of crystal violet and brilliant green on kaolin followed the Langmuir adsorption isotherm.     

Chitosan intercalated montmorillonite: Preparation, characterization and cationic dye adsorption

Chitosan intercalated montmorillonite (Chi-MMT) was prepared by dispersing sodium montmorillonite (Na⁺-MMT) into chitosan solution at 60 °C for 24 h. The Chi-MMT was characterized by XRD, XRF and FT-IR. The intercalation was accomplished via the ion-exchange of Na⁺ ions with –NH₃⁺ of chitosan, resulting in the expansion of d₀₀₁ from 1.42 nm of Na⁺-MMT to 2.21 nm of Chi-MMT. The chitosan content in the Chi-MMT measured by TGA was about 17 mass%. The adsorption capacity of Chi-MMT was investigated in comparison with the starting Na⁺-MMT and chitosan using three different cationic dyes, i.e. basic blue 9 (BB9), basic blue 66 (BB66) and basic yellow 1 (BY1). The Chi-MMT showed the highest adsorption capacity in the range of 46–49 mg/g when the initial dye concentration was 500 mg/L, being equivalent to 92–99 wt.% of dye removal. The adsorption capacities of Chi-MMT for all basic dyes increased with an increase of initial dye concentration. An increase of adsorption capability of Chi-MMT was attributed to the existence of intercalate-chitosan. It could enlarge the pore structure of Chi-MMT, facilitating the penetration of macromolecular dyes, and also electrostatically interact with the applied dyes. These results indicated the competency of Chi-MMT adsorbent for basic dye adsorption.     

Degradation of an azo dye Orange II using a gas phase dielectric barrier discharge reactor submerged in water

A dielectric barrier discharge (DBD) system employing wastewater as one of the electrodes was applied to the degradation of an azo dye, Orange II. The main advantage of this system is that reactive species like ozone and ultraviolet (UV) light produced by the DBD can be utilized for the treatment of wastewater. This system was able to remove the chromaticity and destroy the benzene and naphthalene rings in the dye molecule effectively. The results obtained under several conditions revealed that the UV emission from the DBD reactor could enhance the degradation of the dye, particularly in the presence of titanium oxide photocatalyst. The products resulting from the destruction of the rings in the dye molecule were found to be highly recalcitrant against further oxidation to smaller molecules. The change in the initial dye concentration showed that the reaction order was around 0.8 with respect to the dye concentration. The reduction in the concentration of total organic carbon was much more efficient with oxygen than with air.     

Recycling of supported nanocomposites for hazardous industrial wastewater treatment via Solar photocatalytic process

Study of the photocatalytic activity of the synthesized polyvinylidene fluoride/multi-walled carbon nanotubes/titanium dioxide (PVDF/x%(MWCNTs/8%TiO2) nanocomposites using a simple modified solvent casting technique in decontamination of hazardous industrial wastewater and Reactive Yellow 145 dye as an industrial organic pollutant (local textile dye) were evaluated. Also, different MWCNTs/8%TiO₂ weight percentages in PVDF/x%(MWCNTs/8%TiO₂) nanocomposites were prepared and evaluated. The surface morphology and the structures of the synthesized samples were characterized using SEM, ATR-FTIR, DRS, XRD, and BET. The evaluated bandgap values for MWCNTs/xTiO₂ nanocomposites are from 2.38 to 2.69 based on the weight ratios (2%, 5%, and 8%). The results of the surface area of samples and the best optical behavior obtained at MWCNTs/8%TiO₂ are reported and its photodegradation rate raised to 10.22x10^?3S^?1. The photodegradation process of Reactive Yellow 145 dye by PVDF/x%(MWCNTs/8%TiO₂) nanocomposites was monitoring using chemical oxygen demand (COD). Also, the observed PL intensity for PVDF/MWCNTs/8%TiO₂ has high photonic efficiency and photocatalytic activity. The solar photocatalytic process efficiency for an Egyptian dying factory by repeating it 10 times using PVDF/10%(MWCNTs/8%TiO₂) nanocomposites as a supported photocatalyst for the industrial wastewater treatment was evaluated by the COD method and still under Egyptian environmental law allowed COD limit (1000 ppm).     

纳米二氧化钛粉体的制备及对染料脱色研究

以钛酸四丁酯为原料,采用溶胶-凝胶法、水热沉淀法、水解法制备了纳米二氧化钛粉体。经XRD对3种方法制得粉体进行了表征,讨论了3种方法的优缺点。以水解法制得二氯化钛粉体。利用太阳光对染料进行了脱色研究,结果表明其具有良好的光催化脱色性能。经8h光照,染料废水脱色效果好。