R. Sánchez-Tovar

Influence of hydrodynamic conditions on growth and geometry of anodic TiO2 nanotubes and their use towards optimized DSSCs

In the present work we grow anodic TiO2 nanotube layers under defined hydrodynamic conditions using a rotating Ti anode. We show that hydrodynamic control can be beneficially used to achieve two main effects. First, under conditions where tube growth is controlled by diffusion (for low concentration of fluoride ions in the electrolyte), growth can significantly be accelerated (or even be enabled) by increasing flow rates in the electrolyte. Second, ill-defined nanotube top morphologies can be avoided – this is particularly important in view of designing optimum tube geometries for the use of TiO2 nanotube layers in photoelectrochemical applications such as DSSCs.

The effectiveness of the stabilization/solidification process on the leachability and toxicity of the tannery sludge chromium

A stabilization/solidification (S/S) process by using cement was applied to tannery sludge in order to find a safer way of landfilling this waste. The effects of three parameters on the process effectiveness were analysed in terms of leachate toxicity and chromium retention (%). The parameters studied were the relative amount of added water (30-50xa0wt.%), cement (10-60xa0wt.% in the solid components), and the use of three different types of cement (clinker with additions of limestone, with additions of limestone and fly ashes, and with additions of pozzolans). Statistical analysis performed by variance analysis and categorical multifactorial tests reveals that all the studied parameters significantly influence the effectiveness of the process. Results showed that chromium retention decreases as the relative amount of cement and water increases, probably due to additional chromium provided by cement and increased in the porosity of the mixtures. Leachate toxicity showed the same minimum value for mixtures with 30% or 40% cement, depending on the type of cement, showing that clinker is the main material responsible for the process effectiveness, and additives (pozzolans or fly ashes) do not improve it. The volume increase is lower as less sludge is replaced by cement and the relative amount of water decreases, and for the cement without additions of fly ashes or pozzolans. Therefore, the latter seems to be the most appropriate cement in spite of being more expensive. This is due to the fact that the minimum toxicity value is achieved with a lower amount of cement; and moreover, the volume increase in the mixtures is lower, minimizing the disposal cost to a landfill.

ZnO/ZnS heterostructures for hydrogen production by photoelectrochemical water splitting

This work studies the photoelectrochemical behavior of novel ZnO/ZnS heterostructures obtained by means of anodization in water and glycerol/water/NH4F electrolytes with different Na2S additions under controlled hydrodynamic conditions. For this purpose different techniques such as Field Emission Scanning Electronic Microscopy (FE-SEM) with EDX, Raman spectroscopy and photoelectrochemical water splitting tests under standard AM 1.5 conditions have been carried out. The obtained results showed that the hydrodynamic conditions promoted an ordered nanotubular morphology which facilitates electron–hole separation and consequently, the photoelectrochemical activity for water splitting is enhanced. Additionally, the effect of glycerol in the anodization solutions seems to be beneficial for increasing the dark current photostability.

Study of Passive Films Formed on AISI 316L Stainless Steel in Non-Polluted and Underwater-Volcano-Polluted Seawater

This work studies the semiconducting behavior of passive films formed on AISI 316L (UNS S31603) in two different sea-water solutions, non-polluted and polluted, collected from the volcano of El Hierro Island. Polarization measurements, potentiostatic passivation tests, electrochemical impedance spectroscopy, and capacitance measurements were performed. Results show that the polluted seawater worsens passivation kinetics. Additionally, passive films formed on AISI 316L stainless steel in polluted seawater have been found to be less protective than those formed in non-polluted seawater, showing a more defective structure, owing to the acidity of the polluted medium.

Influence of Temperature and Reynolds Number on the Galvanic Corrosion of the Copper/AISI 304 Stainless Steel Pair in Lithium Bromide Using a Zero-Resistance Ammeter

The effects of temperature and Reynolds number (Re) on the galvanic corrosion of the copper (UNS C15710)/AISI 304 (UNS S30400) stainless steel pair in a concentrated lithium bromide (LiBr) solution was investigated in a hydraulic circuit using a zero-resistance ammeter. Results show that copper is the anode and that galvanic current density decreases with time because of the formation of a protective film. Initially, galvanic current density increases with Re; however, with time, differences decrease and this tendency is even reversed. As Re increases, greater quantities of corrosion products are initially produced and a thicker film is formed. The galvanic current density increases with temperature, suggesting that the films formed at lower temperatures are less defective and more resistant; however, at the highest flow rate, with time, the galvanic current density is lower at 75°C than at 50°C. This behavior is attributed to the quick and large formation of corrosion products at the highest flow and tem...

Integrating Sustainable Development in Chemical Engineering Education: The Application of an Environmental Management System.

The principles of sustainable development have been integrated in chemical engineering education by means of an environmental management system. These principles have been introduced in the teaching laboratories where students perform their practical classes. In this paper, the implementation of the environmental management system, the problems arisen, the proposed solutions and the obtained results are discussed. The main problems are related to the chronological order of the courses in the chemical engineering degree, the commitment of students and the proper management of wastes. The suggested solutions are a combination of preliminary theoretical explanations, the supply of adequate documents to students and the evaluation of their work from the principles of sustainable development. Results show that after the implementation of the system, it is possible to reduce the consumption of raw materials and resources, and the generation of wastes. Results also suggest an improvement in the skills, attitudes and values of the students according to the sustainable-development principles.

The effect of Reynolds number on TiO2 nanosponges doped with Li+ cations

Anatase TiO2 nanosponges have been synthesized by anodization of Ti, and Li+ cations have been inserted in these nanostructures. The influence of hydrodynamic conditions (Reynolds number, Re = 0 to Re = 600) during anodization has been studied. Li-Doped TiO2 nanosponges were characterized by field emission scanning electron microscopy (FE-SEM), Raman confocal microscopy, electrochemical impedance spectroscopy (EIS) and Mott–Schottky analysis (M–S). The photoelectrochemical performance and resistance to photocorrosion were also measured. Li–TiO2 nanosponges proved to be better photocatalysts for water splitting than Li–TiO2 nanotubes. Moreover, the photoelectrochemical behavior of the Li-doped nanosponges improved as the Reynolds number increased.

Visible-light photoelectrodegradation of diuron on WO3 nanostructures

The degradation of pesticide diuron has been explored by photoelectrocatalysis (PEC) under visible light illumination using two different WO3 nanostructures, obtained by anodization of tungsten. The highest degradation efficiency (73%) was obtained for WO3 nanosheets synthesized in the presence of small amounts of hydrogen peroxide (0.05u202fM). For that nanostructure, the kinetic coefficient for diuron degradation was 133% higher than that for the other nanostructure (anodized in the presence of fluoride anions). These results have been explained by taking into account the different architecture and dimensions of the two WO3 nanostructures under study.

Effect of Volcano-Polluted Seawater on the Corrosion Behaviour of Different Alloys

During a subsea volcano eruption, gases and thermal water emissions are released. This might change the behaviour of the materials that are in contact with the seawater caused by the decrease of the pH value. For this reason, the materials for marine applications are selected to maintain the integrity of the structure and to be corrosion resistant. In spite of this, corrosion can cause great damage to marine steel infrastructures such as bridges, wharfs, platforms and pipeline systems. These corrosion problems could be aggravated if the medium is altered, due to volcano emissions, since the resistance of the surface film is influenced by the environmental conditions. Electrochemical techniques are useful to evaluate the corrosion behaviour of different metals and alloys. However, literature regarding the influence of underwater-volcanopolluted seawater on the passivation/corrosion behaviour of stainless steels is scarce. According to this, the objective of the chapter is the evaluation of the influence of an underwater volcano eruption on the corrosion behaviour of different materials that might be used in seawater environments. Electrochemical techniques are applied to evaluate the performance of the different materials when they are immersed in polluted volcano seawater. The results are relevant in the evaluation of natural hazard risk assessments involving critical infrastructures.

Effect of Temperature and Impurities on the AISI 316L/Microplasma Arc Welded AISI 316L Galvanic Pair in H3PO4 under Flowing Conditions

The authors would like to express their gratitude to the Spanish MAEC (PCI Mediterraneo C/8196/07, C/018046/08, D/023608/09, D/030177/10), to the FPU grant given to Rita Sanchez Tovar and to Dr. Asuncion Jaime for her translation assistance.