Classical chemical sciences
In this investigation, the removal of divalent heavy metals by two types of zeolites has been studied. The mechanism of cation exchange for Cu2+, Ni2+, Cd2+ and Pb2+ on NaX Faujasite and Linde type A (LTA) zeolites was studied. Both zeolites are very efficient in divalent heavy metals removal from water. Ion exchange isotherms were performed and the thermodynamic parameters were calculated as well. Kielland plots showed that the order of selectivity is not the same for both the zeolites. For NaX it followed the following order Pb2+ > Cu2+ > Cd2+ > Ni2+ while for LTA the order is Pb2+ > Cd2+ > Cu2+ > Ni2+. Exchange velocity (kw) and the radii of the hydrated metals ions are involved in determining this order of selectivity.
Keywords: NaX zeolite; LTA zeolite; exchange mechanism; heavy metals; selectivity
A highly efficient three-component one step system for the synthesis of 2-amino-4H-chromens is developed. Excellent yields were obtained simply by mixing malononitrile, aromatic aldehyde and α-napthol in lemon juice as a catalyst of natural origin and solvent, avoiding using hazardous organic solvents. The main advantages of this method are its green method character, short reaction time and simple workup procedures and the lack of using any metal containing catalysts.
Keywords: Green synthesis; benzaldehyde; malononitrile; catalyst of natural origin; ultrasound; 2-amino-4H-chromenes
Materials and environmental chemistry
In large urban centers, the major contributors to much of the degradation of air quality are motor vehicles on the road. In some cities, the levels of concentrations of air pollutants have reached levels that pose a risk to human health. Ozone (O3) is a secondary pollutant formed from photochemical reactions of nitrogen oxides (NOx). Numerous studies have found associations between daily levels of ozone with a number of health effects. In the state of South Mato Grosso (MS), there has been a growing increase of ozone levels in the atmosphere in recent years. Considering the above, this study aimed to identify the best estimator for the Weibull distribution, in analyzing the ozone concentration, for the city of Campo Grande-MS. For this, electronic data from the continuous air monitoring station located on the campus of the Federal University of South Mato Grosso (UFMS), Campo Grande was utilized. According to the results presented by the tests, it was verified that the LSRM method presented the poorest performance. The EPFM, MOM and MSDM are most efficient methods to adjust the Weibull distribution curves for the evaluation of ozone concentrations in the atmosphere.
Keywords: Ozone distribution of probability, air monitoring, Weibull distribution
Nanoenergetics has the potential to become the next generation of explosives and propellants. Nano-explosives often show better performances in terms of energy release, ignition and mechanical properties compared to their bulk counterparts. In addition to monomolecular explosives such as nano-TNT and nano-RDX, diverse energetic nanocomposites have been developed, including the nanometer-sized versions of conventional thermites (nanothermites) and those using carbon-based nanomaterials (e.g., fullerenes and carbon nanotubes). While the unique characteristics of nanomaterials allow groundbreaking applications, they also result in distinct environmental fate, transport and toxicity. The high surface to volume ratio and reactivity of nanomaterials make them highly dynamic in environmental systems. Once released in the environment, nanoenergetic chemicals will undergo transportation and transformation processes including dissolution, aggregation, adsorption, photolysis and biotransformation, which will also affect their persistence and bioavailability. This review was conducted to better understand the potential environmental fate and ecological impact of the use of nanoenergetics.
Keywords: Nanomaterial, nanothermite, environmental fate, nanotoxicity
The possibility of using of rice husk ash (RHA) in the mortar has been studied. The impact of physical properties and chemical composition of RHA on dry-shrinkage of mortar is a potential problem, especially in the context of the increased use of new generation solutions and the development of new materials to ensure sustainability. In this study, the effects of RHA content, RHA particles size (fineness) and silica structure have been evaluated. Comparisons are made over the full test period and at specific periods ranging from 3 days to 180 days. Incorporation of RHA provided lower dry shrinkage, where the amount of decrease in dry shrinkage increased with increase crystalline silica content and coarse particles size when compared to the control Ordinary Portland Cement (OPC) mixture, with finer RHA giving better improvement. Fine RHA exhibited the highest shrinkage value due to the effect of microfine particles which increases its shrinkage values considerably.
Keywords: Physical properties; chemical composition; fineness; drying shrinkage, crystalline silica; rice husk ash
Theoretical and computational chemistry
The aim of this study was to devise simple kinetic equations to describe ab initio initiated nonbranched-chain processes of addition of saturated free-radical to double bonds of unsaturated molecules in binary reaction systems of saturated and unsaturated components. In these processes the formation rate of the molecular addition products (1:1 adducts) as a function of concentration of the unsaturated component reaches a limiting value. Five reaction schemes are suggested for the addition processes. The proposed schemes include the reaction competing with chain propagation reactions through a reactive free radical. The chain evolution stage in these schemes involves three or four types of free radicals. One of them is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. Based on the suggested schemes, nine rate equations are deduced using quasi-steady-state treatment. These equations provide good fits for the non-monotonic (peaking) dependences of the formation rates of the molecular products (1:1 adducts) on the concentration of the unsaturated component in the binary systems. The unsaturated compound in these systems is both a reactant and an autoinhibitor generating low-reactive free radicals. A similar kinetic description is applicable to the nonbranched-chain process of the free-radical hydrogen oxidation, in which the oxygen with the increase of its concentration begins to act as an oxidation autoinhibitor (or an antioxidant). The energetics of the key radical-molecule reactions are considered.
Keywords: Low-reactive radical, autoinhibitor, competing reaction, nonbranched-chain addition, thermochemical data