RESUMO

A new adsorbent composite has been developed based on low-density polyethylene and zeolite. This material was used to remove diesel as pollutant in an aqueous system. In the synthesis of the composite and diesel removal were combined these effects: capacity of the zeolite to degrade polyethylene, partial filling of the zeolite with the polyethylene degradation products, favorable thermodynamic interactions between composite-diesel and porosity of the composite (imbibition effect). The term composite is used in the sense that partially degraded-polyethylene oligomers (waxes) are introduced into the zeolite pores in intergranular positions, insuring a good cohesion of waxes and zeolite. The material was synthetized easily by mixing low-density polyethylene and zeolite (1:1) and degraded at 200 °C at three different times: 2, 4 and 6 h. Several techniques as Differential Scanning Calorimeter, Thermogravimetric analysis, Size Exclusion Chromatography and X-Ray Diffraction are combined to study the steps of synthesis and the mechanism of diesel adsorption. The molecular weight obtained at different degradation time varied between 8470 and 99,100, while the molecular weight of the original LDPE was 136,300 g/mol. Diesel removal capacity was determined by TGA through the difference of weight loss at diesel evaporation temperatures (115-275 °C). All the prepared materials presented buoyancy in water and swelling of diesel. Highlighting among them the material prepared at 2 h with a weight loss of 39%, meanwhile the materials prepared for 4 and 6 h presented a weight loss of 29% and 23% respectively, that corresponded to the diesel removed from the water.

Assuntos

RESUMO

In the title salt, C16H24N4 (2+)·2NO3 (-), both the cation and anion are placed in general positions, although the cation displays non-crystallographic inversion symmetry, with the aliphatic chain extended in an all-trans conformation. The benzene rings are almost parallel, with a dihedral angle between their mean planes of 3.3 (6)°. The nitrate ions are placed in the vicinity of the protonated amine groups, forming efficient N-H⋯O inter-ion hydrogen bonds. Each nitrate ion in the asymmetric unit bridges two symmetry-related cations, forming an R 4 (4)(18) ring, a common motif in organic ammonium nitrate salts. This results in the formation of chains along [010] with alternating cations and anions. The neutral amine groups are involved in slightly weaker N-H⋯O hydrogen bonds with the nitrate O atoms, and there are also a number of C-H⋯O hydrogen bonds present. The resulting supra-molecular structure is based on a two-dimensional network extending in the ab plane.

RESUMO

The prevalence of heavy metal pollution and mobility of both Pb and Cd was investigated in street dust samples from the Metropolitan Area of Monterrey (MAM) in northern Mexico. Street dust samples from 30 selected sites were analysed for their content of Zn, Cd, Pb, Cr and Ni after digestion according to U.S. EPA Method 3051. Multivariate analysis including correlation coefficient analysis, Principal Component Analysis and Cluster Analysis was used to analyse the data and identify possible sources of these heavy metals. Compared with background values, elevated concentrations of Pb (300 mg kg(-1)), Cd (7.6 mg kg(-1)) and Cr (78 mg kg(-1)) were observed in street dust of MAM. Based on multivariate statistical approaches, the studied elements were classified in three main sources: (1) Cr, Ni and Zn mainly derived from industrial activities; (2) Cd originating from traffic-related activities; and (3) Pb associated with vehicular emissions. A sequential extraction procedure using the Tessier method was applied to evaluate the mobility of Pb and Cd in street dust. The majority of Pb was associated with the residual fraction followed by the carbonate fraction. The majority of Cd was associated with the residual fraction. These results indicated that the mobility was higher in Pb (26%) compared with Cd (11%), posing a potential risk to the environment.

Assuntos