Rubi Romero

Carbon nanospheres: synthesis, physicochemical properties and applications

The discovery of carbon nanostructures, essentially carbon nanotubes (CNT) and carbon nanofibres (CNF) has led to a big effort devoted to their synthesis, characterization, surface modification and use. Indeed, these structures have encountered application in a wide range of technological fields, such as adsorption, catalysis, hydrogen storage or electronics. Apart from the filamentous arrange of graphene sheets conducting to CNT or CNF, carbon can bond in other different ways to create structures with dissimilar properties. The pairing of pentagonal and heptagonal carbon rings can result in the formation of carbon nanospheres (CNS). This novel nanostructure has only now started to attract significant research activity. In its spherical arrangement, the graphite sheets are not closed shells but rather waving flakes that follow the curvature of the sphere, creating many open edges at the surface. Contrary to the chemically inert C60, the unclosed graphitic flakes provide reactive “dangling bonds” that are proposed to enhance surface reactions, establishing CNS as good candidates for catalytic and adsorption applications. Despite the embryonic stage of the field and the existing data being too scattered, this work is aimed to provide a comprehensive review of the existing literature related to CNS, exploring the different preparation routes employed, the critical characterization results as well as the applications studied so far.

PREPARATION AND CHARACTERIZATION OF Fe-PILCS. INFLUENCE OF THE SYNTHESIS PARAMETERS

Iron-pillared clays (Fe-PILCs) were synthesized from hydrolyzed FeCl3 solutions added to NaOH solutions using different synthesis conditions. X-ray diffraction, N2 adsorption-desorption, chemical analysis, thermogravimetric analysis, differential thermal analysis, temperature-programmed desorption of ammonia and temperature-programmed reduction were used to characterize the resulting Fe-pillared clays (Fe-PILCs). A higher degree of pillaring was obtained when the Fe content was adjusted to 60 mmoles of Fe/g of clay. It was observed that higher values of this ratio led to worse acidity and textural characteristics, a consequence of the probable formation of Fe oxides that could not only deposit on the surface but also block the pores formed during the pillaring process. Likewise, it was found that the amount of Fe that can be introduced depended on the OH/Fe ratios. Total surface and micropore area decreased and Fe content increased with increasing pillaring solution concentrations. Finally, all pillared samples prepared here were thermally stable at temperatures up to 400°C.

Biodiesel Production by Using Heterogeneous Catalysts

In recent years, biodiesel has gained international attention as a source of alternative fuel due to characteristics like high degradability, no toxicity, low emission of carbon monoxide, particulate matter and unburned hydrocarbons (Al Zuhair, 2007; Vicente et al., 1998). Biodiesel is a mixture of alkyl esters and it can be used in conventional compression ignitions engines, which need almost no modification. As well, biodiesel can be used as heating oil and as fuel (Mushrush et al., 2001; Wardle, 2003). So far, this alternative fuel has been successfully produced by transesterification of vegetable oils and animal fats using homogeneous basic catalysts (mainly sodium or potassium hydroxide dissolved in methanol). Traditional homogeneous catalysts (basic or acid) possess advantages including high activity (complete conversion within 1 h) and mild reaction conditions (from 40 to 65 °C and atmospheric pressure). However, the use of homogeneous catalysts leads to soap production. Besides, in the homogeneous process the catalyst is consumed thus reducing the catalytic efficiency. This causes an increase in viscosity and the formation of gels. In addition, the method for the removal of the catalyst after reaction is technically difficult and a large amount of wastewater is produced in order to separate and clean the products, which increases the overall cost of the process. Thus, the total cost of the biodiesel production based on homogeneous catalysis, is not yet sufficiently competitive as compared to the cost of diesel production from petroleum. An alternative is the development of heterogeneous catalysts that could eliminate the additional running costs associated with the aforementioned stages of separation and purification. In addition, the use of heterogeneous catalysts does not produce soap through free fatty acid neutralization and triglyceride saponification. Therefore, development of efficient heterogeneous catalysts is important since opens up the possibility of another pathway for biodiesel production. The efficiency of the heterogeneous process depends, however, on several variables such as type of oil, molar ratio alcohol to oil, temperature and catalyst type. Thus, the objective of this chapter is to present a review of the effect of the aforesaid variables on important characteristics of biodiesel such as methyl esters content. Some characterization techniques for both, biodiesel and heterogeneous catalysts will also be addressed.

Ozonation of Indigo Carmine Catalyzed with Fe-Pillared Clay

The ozonation catalyzed by iron-pillared clays was studied. The degradation of dye indigo carmine (IC) was elected as test reaction. Fe-pillared clays were synthesized by employing hydrolyzed FeCl3 solutions and bentonite. The pillared structure was verified by XRD and by XPS the oxidation state of iron in the synthesized material was established to be

Biological hazard evaluation of a pharmaceutical effluent before and after a photo-Fenton treatment

The aim of this study was to evaluate the biological hazard of a pharmaceutical effluent before and after treatment. For the former, the determined 96h-LC50 value was 1.2%. The photo-Fenton treatment catalyzed with an iron-pillared clay reduced this parameter by 341.7%. Statistically significant increases with respect to the control group (P<0.05) were observed at 12, 24, 48 and 72h in HPC (50.2, 30.4, 66.9 and 43.3%), LPX (22, 83.2, 62.7 and 59.5%) and PCC (14.6, 23.6, 24.4 and 25.6%) and antioxidant enzymes SOD (29.4, 38.5, 32.7 and 49.5%) and CAT (48.4, 50.3, 38.8 and 46.1%) in Hyalella azteca before treatment. Also increases in damage index were observed before treatment of 53.1, 59.9, 66.6 and 72.1% at 12, 24, 48 and 72h, respectively. After treatment the same biomarkers of oxidative stress decreased with respect to before treatment being to HPC (29.3, 22.5, 41.6 and 31.7%); LPX (14.2, 43.1, 30.7 and 35.5%); PCC (12.6, 21.3, 24.2 and 23.9%); SOD (39.2, 33.9, 49.5 and 37.9%) and CAT (28.6, 35.8, 33.7 and 31.7) at 12, 24, 48 and 72h, respectively (P<0.05). The damage index were decreased at 12, 24, 48 and 72h in 48.9, 57.8, 67.3 and 72.1%, respectively. In conclusion, the obtained results demonstrate the need of performing bioassays in order to characterize an effluent before discharge and not base such a decision only upon current normativity. In addition, it was also concluded that the heterogeneous photo-Fenton process decreases the presence of PCT, oxidative stress, genotoxic damage and LC50 in Hyalella azteca.

Oxidation of 4-Chlorophenol by Mesoporous Titania: Effect of Surface Morphological Characteristics

Mesoporous nanocrystalline anatase was prepared via EISA employing CTAB as structure directing agent. The drying rate was used as a key synthesis parameter to increase the average pore diameter. The resultant mesoporous crystalline phases exhibited specific surface areas between 55 and 150 m2 g−1, average unimodal pore sizes of about 3.4 to 5.6 nm, and average crystallite size of around 7 to 13 nm. These mesophases were used as photocatalysts for the degradation of 4-chlorophenol (4CP) with UV light. Under the studied conditions, the mesoporous anatase degraded 100% 4CP. This was twice faster than Degussa P-25. 57% reduction of chemical oxygen demand (COD) value was achieved.

Kinetics of Transesterification of Safflower Oil to Obtain Biodiesel Using Heterogeneous Catalysis

Abstract The kinetics of the transesterification of safflower oil and methanol catalyzed by K2O/NaX was studied and modeled. The influence of the oil-methanol initial molar ratio and amount of catalyst were investigated to achieve a maximum triglycerides conversion (99 %) and a final methyl esters content of 94 % ±1. A kinetic model based on an Eley–Rideal mechanism was found to best fit the experimental data when assuming methanol adsorption as determining step. Other models derived from Langmuir – Hinshelwood – Hougen –Watson (LHHW) mechanisms were rejected based on statistical analysis, mechanistic considerations and physicochemical interpretation of the estimated parameters.

Biodiesel Production in Stirred Tank Chemical Reactors: A Numerical Simulation

The biodiesel production was performed in stirred tank chemical reactor by numerical simulation. The main results are that the percentage of conversion from triglyceride to biodiesel is approximately of 82 % when the molar flow ratio between triglyceride/alcohol is 1:5. This system displays only one equilibrium point. Since there are imaginary eigenvalues in the Jacobian matrix analysis, the equilibrium point is unstable. The biodiesel production in stirred tank chemical reactor is good because the settling time is short, and has higher conversion.

Advanced Oxidation Processes II: Removal of Pharmaceuticals by Photocatalysis

In this chapter, basic concepts of advanced oxidation processes (AOP) are cited, such as photolysis, photocatalysis, and semiconductors used as photocatalysts. This is important since the wastewater pollution with drugs, coming from domestic use, hospitals, and industry is not only an environmental problem but social too. Pharmaceutical case study is shown to exemplify the photocatalytic degradation of different drugs contained in wastewater taken directly from some currents in the pharmaceutical industry, such as diclofenac, acetaminophen, naproxen, and ibuprofen, using modified TiO2 catalysts with different tin contents.

Modelling and Simulation of the Radiant Field in an Annular Heterogeneous Photoreactor Using a Four-Flux Model

This work focuses on modeling and simulating the absorption and scattering of radiation in a photocatalytic annular reactor. To achieve so, a model based on four fluxes (FFM) of radiation in cylindrical coordinates to describe the radiant field is assessed. This model allows calculating the local volumetric rate energy absorption (LVREA) profiles when the reaction space of the reactors is not a thin film. The obtained results were compared to radiation experimental data from other authors and with the results obtained by discrete ordinate method (DOM) carried out with the Heat Transfer Module of Comsol Multiphysics® 4.4. The FFM showed a good agreement with the results of Monte Carlo method (MC) and the six-flux model (SFM). Through this model, the LVREA is obtained, which is an important parameter to establish the reaction rate equation. In this study, the photocatalytic oxidation of benzyl alcohol to benzaldehyde was carried out, and the kinetic equation for this process was obtained. To perform the simulation, the commercial software COMSOL Multiphysics v. 4.4 was employed.