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The present work synthesized two new materials of functionalized multi-walled carbon nanotubes (MWCNT-OH and MWCNT-COOH) impregnated with magnetite (Fe3O4) using solution precipitation methodology. The resulting MWCNT-OH-Mag and MWCNT-COOH-Mag materials were characterized by scanning electron microscopy coupled with energy dispersion X-ray spectroscopy, Fourier transform infrared, X-ray diffraction, atomic force microscopy, and electrical force microscopy. The characterization results indicate that the -OH functional groups in the MWCNT interact effectively with magnetite iron favoring impregnation and indicating the regular distribution of nanoparticles on the surface of the synthesized materials. The adsorption efficiency of the MWCNT-OH-Mag and MWCNT-COOH-Mag materials was tested using the pollutants 2,4-D and Atrazine. Over batch studies carried out under different pH ranges, it was found that the optimal condition for 2,4-D adsorption was at pH 2, while for Atrazine, it was found at pH 6. The rapid adsorption kinetics of 2,4-D and Atrazine reaches equilibrium within 30 min. The pseudo-first-order model described 2,4-D adsorption well. The General-order model described better atrazine adsorption. The magnetically doped adsorbent functionalized with -OH surface groups (MWCNT-OH-Mag) demonstrated superior adsorption performance and increased Fe-doped sites. The Sips model described the adsorption isotherms accurately. MWCNT-OH-Mag presented the greatest adsorption capacity at 51.4 and 47.7 mg g-1 for 2,4-D and Atrazine, respectively. Besides, electrostatic forces and complexation rule the molecular interactions between metals and pesticides. The leaching and regeneration tests of the synthesized materials indicate high stability in an aqueous solution. Furthermore, experiments with wastewater samples contaminated with the model pollutants indicate that the novel adsorbents are highly promising for enhancing water purification by adsorptive separation.

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RESUMO

Real hospital wastewater was effectively treated by a promising technology based on degradation reaction catalyzed by Fe0 under microwave irradiation in this work. Fe0 powders were synthesized and characterized by different techniques, resulting in a single-phase sample with spherical particles. Optimum experimental conditions were determined by a central composite rotatable design combined with a response surface methodology, resulting in 96.8% of chemical oxygen demand reduction and 100% organic carbon removal, after applying MW power of 780 W and Fe0 dosage of 0.36 g L-1 for 60 min. Amongst the several organic compounds identified in the wastewater sample, diclofenac and ibuprofen were present in higher concentrations; therefore, they were set as target pollutants. Both compounds were completely degraded in 35 min of reaction time. Their plausible degradation pathways were investigated and proposed. Overall, the method developed in this work effectively removed high concentrations of pharmaceuticals in hospital wastewater.

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RESUMO

Physical systems such as optical traps and microwave cavities are realistically modeled by billiards with soft walls. In order to investigate the influence of the wall softness on the billiard dynamics, we study numerically a smooth two-dimensional potential well that has the elliptical (hard-wall) billiard as a limiting case. Considering two parameters, the eccentricity of the elliptical equipotential curves and the wall hardness, which defines the steepness of the well, we show that (1) whereas the hard-wall limit is integrable and thus completely regular, the soft wall elliptical billiard exhibits chaos, (2) the chaotic fraction of the phase space depends nonmonotonically on the hardness of the wall, and (3) the effect of the hardness on the dynamics depends strongly on the eccentricity of the billiard. We further show that the limaçon billiard can exhibit enhanced chaos induced by wall softness, which suggests that our findings generalize to quasi-integrable systems.

RESUMO

Asthma is the commonest respiratory disease of the paediatric population and its prevalence is increasing in all parts of the world. Repeated readmission to hospital often leads to poorer school attendance, disruption of family life and increased cost to the state. Thus, global recommendations stress preventive strategies. Previous studies of readmissions of paediatric cases in developed countries have highlighted non-compliance with preventive medication and lack of parental and patient education as some of the factors that contribute to the re-admission. The purpose of this study was to determine the factors that contribute to the readmission of paediatric patients to hospitals in Trinidad. The method adopted was a descriptive survey using a questionnaire instrument. The study population consisted of 23 consecutive parents or guardians of children, aged 3-12 years, who had two or more admissions in the last year to the Emergency Room (ER) department at the Eric Williams Medical Sciences Complex for the treatment of acute bronchial asthma. The survey was conducted over a three-day period in May 2000. We found that 74 percent of the patients were less than 8 years of age with a male predominance (57 percent). Seventy-eight percent had at least four acute asthmatic attacks in the year prior to the survey and 74 percent had visited the ER at least three times during this period with 39 percent having to be warded for further management between attacks. This may have been due to a lack of education about the disease; 65 percent of parents/guardians had received no teaching about asthma. Seventy-seven of these children missed school at least once as a result of their illness in the two months prior to the survey. In a few instances, the patients' physical activities were being curtailed by parents who thought that this would prevent the child's asthma. The parents/guardians of paediatric asthma patients with frequent re-admissions to hospital have limited knowledge of their children's disorder, despite recurrent contact with healthcare professionals during their children's ER and ward admissions. Most of these children have not received adequate preventative care between attacks. Failure of the healthcare staff to follow-up these patients in clinic and educate parents and guardians about asthma may contribute to frequent hospital admissions and poor school attendance. (AU)

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