Preparation and application of α-Fe2O3@MIL-101(Cr)@TiO2 based on metal-organic framework for photocatalytic degradation of paraquat.

In this study, a new magnetic α-Fe2O3@MIL-101(Cr)@TiO2 photocatalyst was successfully synthesized. The material synthesized had been fully characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, vibrating sample magnetometry, transmission electron microscopy, and Brunauer-Emmett-Teller isotherm methods. The X-ray diffraction analysis corroborates that nanoparticles are polycrystalline with rhombohedral and tetragonal crystal structures for Fe2O3 and TiO2, respectively. In addition, the photocatalytic degradation of the herbicide paraquat in the presence of α-Fe2O3@MIL-101(Cr)@TiO2 under ultraviolet (UV) irradiation was studied. The effect of experimental parameters such as the initial concentration of catalyst, the pH, and the initial paraquat was investigated. The optimal conditions were achieved for concentration of catalyst 0.2 g L-1, pH 7, and concentration of paraquat 20 mg L-1. The photocatalytic degradation efficiency was 88.39% after 15 min with α-Fe2O3@MIL-101(Cr)@TiO2 under UV irradiation. The pseudo-second-order kinetic model for photocatalytic degradation of paraquat was obtained. The catalysts could be recovered and reused without any loss of efficiency for five times in the consequent reactions. To the best of our knowledge, this is the first report on the photocatalytic degradation of paraquat using new α-Fe2O3@MIL-101(Cr)@TiO2 photocatalyst under UV irradiation condition.

Evaluation of extracting titanium dioxide from water-based paint sludge in auto-manufacturing industries and its application in paint production.

Almost 2555-4380 tons of paint sludge are produced annually in an auto-manufacturing plant; recycling and reproduction of beneficial materials such as titanium dioxide (TiO2) and its application in paint production from paint sludge are evaluated in this article. The disposal of these sludge is environmentally important and is the main and most serious challenge for auto-manufacturing units. Today, these sludge are recognized as toxic wastes, whose disposal is much costly and constrained by environmental standards. Controlled disposal requires spaces, which are expensive and impermeable, because the sludge contains large amounts of hazardous materials such as heavy metals, solvents, and other materials polluting wells, springs, and other water resources. In this research, X-ray diffraction spectroscopy was carried out to determine the types of sludge combinations. Then, chemical digestion and centrifuge was used to extract TiO2, the extracted TiO2 reached 67.41% using these techniques. Next, a powder containing TiO2 in a certain percentage was used for paint production. Here, not only the amount of sludge decreased to as much as 70% but also the fresh paint required annually will be reduced by 21%. Furthermore, all heavy metals and toxic wastes will be removed as an environmental challenge.

Reduction of pollutants in painting operation and suggestion of an optimal technique for extracting titanium dioxide from paint sludge in car manufacturing industries--case study (SAIPA).

Paint sludge of car manufacturing industries are not disposed in landfills, since they contain hazardous materials with a high concentration of chromium, aluminum, titanium, barium, copper, Iron, magnesium, strontium, and so on. Thus, it is essential to find solutions in order to neutralize them or suggest cost-effective techniques, which are also environmentally acceptable. Because, this sludge contains considerable amounts of Ti pigments and unbaked resins, recycling these pigments--which could be used in a variety of industries such as paint factories--is an appropriate subject for further research. In this article, with the aim of identification of main pollutants in order to eliminate them and suggest a cost-effective solution to recover the sludge, a large number of tests including X-ray fluorescence spectroscopy, X ray diffraction spectroscopy, and diffusion thermal analysis are conducted to determine types and concentration of elements, and combinations of paint sludge in car manufacturing industries. As titanium dioxide (TiO2) is widely used as the main pigment of automobile paints, an optimal technique is suggested for extracting TiO2 with high purity percentage through adopting scientific methods such as membrane and electrolysis.

Determination of the effect of wind velocity and direction changes on turbidity removal in rectangular sedimentation tanks.

In the present study, a pilot-scale sedimentation tank was used to determine the effect of wind velocity and direction on the removal efficiency of particles. For this purpose, a 1:20 scale pilot simulated according to Frude law. First, the actual efficiency of total suspended solids (TSS) removal was calculated in no wind condition. Then, the wind was blown in the same and the opposite directions of water flow. At each direction TSS removal was calculated at three different velocities from 2.5 to 7 m/s. Results showed that when the wind was in the opposite direction of water flow, TSS removal efficiency initially increased with the increase of wind velocity from 0 to 2.5 m/s, then it decreased with the increase of velocity to 5 m/s. This mainly might happen because the opposite direction of wind can increase particles' retention time in the sedimentation tank. However, higher wind velocities (i.e. 3.5 and 5.5 m/s) could not increase TSS removal efficiency. Thus, if sedimentation tanks are appropriately exposed to the wind, TSS removal efficiency increases by approximately 6%. Therefore, energy consumption will be reduced by a proper site selection for sedimentation tank unit in water and waste water treatment plants.

Ozonation optimization and modeling for treating diesel-contaminated water.

The effect of ozonation on treatment of diesel-contaminated water was investigated on a laboratory scale. Factorial design and response surface methodology (RSM) were used to evaluate and optimize the effects of pH, ozone flow rate, and contact time on the treatment process. A Box-Behnken design was successfully applied for modeling and optimizing the removal of total petroleum hydrocarbons (TPHs). The results showed that ozonation is an efficient technique for removing diesel from aqueous solution. The determination coefficient (R(2)) was found to be 0.9437, indicating that the proposed model was capable of predicting the removal of TPHs by ozonation. The optimum values of experimental initial pH, degree of O3, and reaction time were 7.0, 1.5, and 35 min, respectively, which could contribute to approximately 60% of TPH removal. This result is in good agreement with the predicted value of 57.28%.

Decolorization of two synthetic dyes using the purified laccase of Paraconiothyrium variabile immobilized on porous silica beads.

BACKGROUND: Decolorization of hazardous synthetic dyes using laccases in both free and immobilized form has gained attention during the last decades. The present study was designed to prepare immobilized laccase (purified from Paraconiothyrium variabile) on porous silica beads followed by evaluation of both free and immobilized laccases for decolorization of two synthetic dyes of Acid Blue 25 and Acid Orange 7. Effects of laccase concentration, pH and temperature alteration, and presence of 1-hydroxybenzotriazole (HBT) as laccase mediator on decolorization pattern were also studied. In addition, the kinetic parameters (Km and Vmax) of the free and immobilized laccases for each synthetic dye were calculated. RESULTS: Immobilized laccase represented higher temperature and pH stability compare to free one. 39% and 35% of Acid Blue 25 and Acid Orange 7 was decolorized, respectively after 65 min incubation in presence of the free laccase. In the case of immobilized laccase decolorization percent was found to be 76% and 64% for Acid Blue 25 and Acid Orange 7, respectively at the same time. Increasing of laccase activity enhanced decolorization percent using free and immobilized laccases. Relative decolorization of both applied dyes was increased after treatment by laccase-HBT system. After nine cycles of decolorization by immobilized laccase, 26% and 31% of relative activity were lost in the case of Acid Blue 25 and Acid Orange 7, respectively. CONCLUSIONS: To sum up, the present investigation introduced the immobilized laccase of P. variabile on porous beads as an efficient biocatalyst for decolorization of synthetic dyes.