Synthesis and characterization of a novel composite of rice husk-derived graphene oxide with titania microspheres (GO-RH/TiO2) for effective treatment of cationic dye methylene blue in aqueous solutions

Graphene oxide (GO) was synthesized utilizing rice husk (RH) as the starting raw material via a modified Hummers' method. Ground pencil leads were used as a control powder of the starting raw material to monitor the consistency of the synthesis method. TiO₂ microspheres were synthesized via a precipitated method using the pluronic F127 solution as the pore template. GO derived from RH (GO-RH) was composited with TiO₂ microspheres as GO-RH/TiO₂ composites by an impregnation method with weight ratios of 3:1, 2:2, and 1:3. Characterized results revealed GO-RH formed a ternary phase material of graphene oxide, graphite oxide, and silica. A typical microstructure of the calcined TiO₂ microspheres was found as the agglomerated anatase nanoparticles. Furthermore, the composites belong to large surface areas and numerous oxygen-containing functionalities on their surfaces. Removal efficiencies of cationic dye methylene blue (MB) from aqueous solutions by the composites, GO-RH and TiO₂, were studied under UV illumination for 180 min. Due to the effective combination of adsorption and photodegradation for the MB removal, the composites provided the higher efficiencies (99-100%) faster than those of GO-RH and TiO₂ and could be reused at least 4 times. Finally, a mechanism of the MB removal by the composites was proposed.

Industrial performance, reusability and mechanical reliability of mesoporous gamma alumina packed bed fabricated through boehmite extrusion for removal of reactive dyes from textile wastewaters

The reusable γ-alumina packed bed was fabricated by extrusion of boehmite as rods for the removal of reactive dyes from the industrial textile wastewaters in a dynamic system. The appropriate calcination temperature, and time were determined to maximize the removal efficiency, ∼90%, in the acidic environments, pH 2-3. On the other hand, the current contribution addressed the estimation of failure probability which is a challenge for the reliable design of packed beds. Therefore, the normal, and Weibull distributions were used to evaluate the reliability of rods through Akaike information criterion (AIC), and Anderson-Darling test (ADT). The results revealed that the Weibull distribution possesses the higher accuracy in the analysis of compression strength scatter. The calcination of rods at 850 °C within 90 min not only led to fabricate a reliable packed bed with a mean strength about 860 kPa but also brought the better mesoporous structure, 8 nm, which is the main reason for the development of active sites. The thermal stability of rods provided an industrial potential for the regeneration of packed bed at 500 °C, without efficiently losing the adsorptive performance, even after reuse for ten times.

Couple of graphene oxide and functionalized carbon nanotubes for dye degradation enhancement of anatase under visible light and solar irradiation

Graphene oxide sheets (GO) were coupled with carbon nanotubes (CNTs) to enhance the photoactivity of anatase under visible and solar irradiation. The carbon nanotube surface was functionalized in the acidic reflux condition before coupling with GO and decoration of anatase by the sol-gel method. A modified kinetic model was appropriately applied to predict the breakthrough in the methylene blue degradation yield and determine the constant rate which was clearly affected by coupling architecture. The nanocomposite fabricated by the same proportions of GO and CNTs, 3.33%, exhibited the maximal degradation yield, 96.5%, in the dye solution with the initial concentration of 3.0 mg l-1. The characterizations based on X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and field emission scanning electron microscopy (FESEM) revealed that the functionalized CNTs could create the appropriate space between the graphene sheets for uniformly interconnection of anatase via oxygen-containing groups onto the material surfaces. This enhancement in the degradation efficiency could be ascribed to the unique architecture, leading to a decrease in bandgap energy, 2.2 eV, which facilitated the electron-hole separation. Besides of breakthrough in the photoreaction rate, the adequate architecture led to an efficient reduction in the content of carbon-based materials. Also, the performance of mentioned nanocomposite under sunlight photons was effectively higher than that under UV irradiation. The hybrid nanocomposite provided a large number of active sites for photoreactions to facilitate the treatment of wastewater under solar irradiation.

Solar treatment of sewage discharged from industrial estate for reduction of chemical oxygen demand over Degussa P-25 titania

The aim of current investigation was to demonstrate the effectiveness of Degussa P-25 titania in the photocatalytic treatment of sewage, discharged from industrial estate, as a combined process under solar irradiation. The study was aimed to understand the role of fundamental factors including, titania load, initial COD level, and pH on the photocatalytic degradation rate. The commercially produced TiO₂ represented a mesoporous structure, 2-30 nm, indicating the adequate activity in the COD reduction of sewages collected from the streams entreating anaerobic, aerobic, and sand filtration stages when 0.5 g L^-1 of photocatalyst was loaded. According to the obtained results, the degradation rate is accelerated with an increase in the initial COD level. Although the solar treatment of streams entering to the anaerobic, and aerobic stages indicated the higher rates, the separation of titania particles from the sludge is very difficult. Therefore, it seems that the downstream of recovery network is still the best position to assemble the photocatalytic system, as an auxiliary process to reduce COD below the standard level, and improve the recovery rate. The maximal removal efficiency, 87%, was achieved within 20 min by the solar treatment of sewage in the alkali condition with the control of pH around 8.

Application of solid waste of ductile cast iron industry for treatment of wastewater contaminated by reactive blue dye via appropriate nano-porous magnesium oxide

The solid waste of ductile iron industry, which contains at least 88.0% magnesium oxide, is one of the toxic materials, leading to land contamination. On the other hand, the removal of reactive dyes from wastewaters is difficult required effective adsorbent like nano-porous MgO. The novelty of present investigation is based on nano-porous magnesium oxide production by precipitation from the solid waste to treat the wastewaters contaminated by reactive dye which is abundantly used in the textile industry. In order to improve the adsorptive properties of extracted MgO powder, the combinations of surfactants, containing cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) and polyoxyethylene octyl phenyl ether (TX100) were applied based on the mixture design algorithm in the precipitation. The effects of processing factors such as surfactant composition, powder calcination temperature, surfactant dose and pH were evaluated on the removal efficiency. The results revolved that the combination of SDS and TX100, 1:1, plays an effective role in the production of particles with the appropriate average pore size, 16 nm. The adsorbent prepared in the optimum condition indicated a significant affinity for the removal of reactive dye which shows relatively pH-independent efficiency in the range of 3-9. The applied producer for fabrication of adsorbent eventually overcomes the pH-dependent problem for the toxic dye uptake, leading to produce the adsorbent with maximal adsorption capacity of 1000 mg g^-1.

Efficient photocatalytic methylene blue degradation by Fe3O4@TiO2 core/shell linked to graphene by aminopropyltrimethoxysilane

In the present article, Fe₃O₄@TiO₂ core/shell (FT) linked to graphene was fabricated by sol-gel technique as a photocatalyst and was employed for the solar degradation of cationic methylene blue (MB) in aqueous solution. The prepared core/shells were linked to graphene oxide (FTGO) and reduced graphene oxide (FTRGO) via embedding into 3-aminopropyltrimethoxysilane (APS). The structure of this magnetic composition was characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and BET surface area measurements. The significance of the composite structure in photocatalytic degradation was spectrophotometrically tested by blending the obtained powders with wastewater containing methylene blue under solar irradiation. The appropriate dosage of APS to link the Fe₃O₄@TiO₂ core/shell onto GO and RGO surfaces was determined to be 1 ml per gram of FT. The kinetic studies were performed to investigate the effects of different parameters, such as composition structure, APS dosage, and repeatability. Kinetic data are well fitted by a first-order model with a high correlation coefficient. Regardless of the prominent advantage of composites in magnetic powder separation, the Fe₃O₄@TiO₂ core/shell linked to graphene oxide is an efficient composite in comparison to FTRGO for the dye degradation without losing the original activity and stability.