Photodegradation of methylene blue with a titanium dioxide/polyacrylamide photocatalyst under sunlight

Hydrogels containing TiO₂ nanoparticles (NPs) have photocatalytic properties and degrade pollutants under light. In this study, a polyacrylamide (PAAm) hydrogel was synthesized with TiO₂ P25 NPs as the initiator, acrylamide as a monomer, and N,N′‐methylene bisacrylamide as a crosslinker in aqueous media under sunlight. Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and transmission electron microscopy were applied to characterize the TiO₂/PAAm hydrogel. The effects of different synthetic conditions, such as the initiator concentration, crosslinker, and dilution, on swelling were investigated. The maximum swelling of the TiO₂/PAAm hydrogel was 45 g/g in the hydrogel synthesized with optimum conditions by 0.2% TiO₂. The photocatalytic degradability of the hydrogel was investigated with methylene blue (MB) as the pollutant target. Also, the effects of the pH and MB concentration were studied. Under optimum conditions, 95.00% of the MB was degraded by the TiO₂/PAAm photocatalyst after 5 h of irradiation under sunlight. The comparison of the results with those of the TiO₂ P25 powder showed that the TiO₂ NPs had better activity than the hydrogel, but unlike the hydrogel, the activity of these NPs decreased in each recycling time because of the aggregation of NPs. Finally, the hydrogel was recycled seven times without a considerable reduction in the degradation efficiency. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43386.     

Environmental control of the dominant phytoplankton in Aras Reservoir (Iran): A multivariate approach

This study was undertaken to determine the phytoplankton structure and the environmental variables comprising the driving factors leading to cyanobacterial blooms in Aras Reservoir. Sampling was carried out seasonally at five sampling sites along the main body of the reservoir. Samples were collected for phytoplankton identification and enumeration, chemical analyses and chlorophyll‐a (Chl‐a) concentrations at each sampling site. Principal component analysis (PCA) and two‐way unweighted pair group method with arithmetic mean (UPGMA) were performed to determine the environmental variables affecting phytoplankton community dynamics. Seventy‐two species belonging to five divisions were determined during this study. Cyanobacteria contained the highest density (74%) during the study period, with Pseudanabaena limnetica being the most abundant species. The Shannon diversity index was low (0.44–1.87), indicating a high level of cyanobacteria dominance and eutrophic water status. Principal component analysis indicated that total phosphorus and temperature were significantly associated with cyanobacteria growth. Two‐way clustering by UPGMA indicated a close relationship among sampling sites during the same season from the perspective of the phytoplankton density. The findings of this study suggested Aras Reservoir could be highly affected by agricultural runoff and untreated sewage loadings. Thus, the proper use of fertilizers and sewage treatment should be taken into account in considering effective conservation and management plans.     

Design and analysis of mechanical face seals

An analytical study of the characteristics of mechanical face seals with misalignment is presented. The complete pressure equation was solved without using the narrow bearing assumption. Results are presented and it is concluded that simplified treatments overestimate the load and the moments particularly at touch. Design charts are given to calculate the separating force, the leakage rate, the moment and coefficient of friction for different tilt parameters ? and the ratio $\text{r}{}_{\mathrm{i}}\text{r}{}_{\mathrm{o}}$ of the inner radius to the outer radius.     

Design of tilted hydrostatic thrust bearings

Hydrostatic bearings are usually designed to operate under parallel conditions, but structural and thermal deformations cause tilting of the pad. A semianalytical solution of the pressure equation is used. It is shown that tilting of hydrostatic thrust bearings gives rise to negative pressures and that cavitation may occur depending on the tilt parameter. The characteristic values of the bearing are found to be strong functions of the tilt parameter and of the bearing number.