Effect of pH in the synthesis of organo-clays for rare earths removal

Two montmorillonitic clays were modified with N-(methoxy-polyethylene glycol) ethylene diamine and tested as sorbents for removal of Rare Earths (REs) from aqueous solutions. Lanthanum was chosen as representing element of REs family and adsorption tests were performed with the aim of selecting a system with good uptake efficiency for the pollutant abatement in wastewaters. The effects of pH were studied and the properties ofthe obtained final materials were evaluated with simple model systems of the final application. The modified clays were characterized before and after the intercalation, combining the results ofX-ray diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FT-IR), whereas the solutions were analysed by means of Chemical Oxygen Demand to quantify the amount of intercalated polymer and by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) to quantify the metal ions concentration. The results showed that the organo-clays have been efficiently prepared while the characterization techniques showed that the intercalation mechanism was strongly dependent on the pH ofthe preparation procedure, affecting the protonation ofthe amino groups

Use of Electrochemical Impedance Spectroscopy for the Evaluation of Performance of PEM Fuel Cells Based on Carbon Cloth Gas Diffusion Electrodes

Polymer electrolyte membrane fuel cells (PEMFCs) have attracted great attention in the last two decades as valuable alternative energy generators because of their high efficiencies and low or null pollutant emissions. In the present work, two gas diffusion electrodes (GDEs) for PEMFCs were prepared by using an ink containing carbon-supported platinum in the catalytic phase which was sprayed onto a carbon cloth substrate. Two aerograph nozzles, with different sizes, were used. The prepared GDEs were assembled into a fuel cell lab prototype with commercial electrolyte and bipolar plates and tested alternately as anode and cathode. Polarization measurements and electrochemical impedance spectroscopy (EIS) were performed on the running hydrogen-fed PEMFC from open circuit voltage to high current density. Experimental impedance spectra were fitted with an equivalent circuit model by using ZView software which allowed to get crucial parameters for the evaluation of fuel cell performance, such as ohmic resistance, charge transfer, and mass transfer resistance, whose trends have been studied as a function of the applied current density

Use of natural clays as sorbent materials for rare earth ions: materials characterization and set up of the operative parameters

Two mineral clays of the montmorillonite group were tested as sorbents for the removal of Rare Earths (REs) from liquid solutions. Lanthanum and neodymium model solutions were used to perform uptake tests in order to: (a) verify the clays sorption capability, (b) investigate the sorption mechanisms and (c) optimize the experimental parameters, such as contact time and pH. The desorption was also studied, in order to evaluate the feasibility of REs recovery from waters. The adsorption–desorption procedure with the optimized parameters was also tested on a leaching solution obtained by dissolution of a dismantled NdFeB magnet of a hard-disk. The clays were fully characterized after REs adsorption and desorption by means of X-ray powder diffraction (XRPD) and X-ray photoelectron spectroscopy (XPS); the liquid phase was characterized via Inductively Coupled Plasma–Optical Emission Spectroscopy (ICP–OES) analyses. The experimental results show that both clays are able to capture and release La and Nd ions, with an ion exchange mechanism. The best total efficiency (capture 50%, release 70%) is obtained when the uptake and release processes are performed at pH = 5 and pH = 1 respectively; in real leached scrap solutions, the uptake is around 40% but release efficiency is strongly decreased passing from a mono-ion system to a real system (from 80% to 5%). Furthermore, a strong matrix effect is found, with the matrix largely affecting both the uptake and the release of neodymium

Hempcrete from cradle to grave: the role of carbonatation in the material sustainability

The goal of reducing buildings impact to the environment is achieved by minimizing the energy consumption and through the employment of sustainable materials. However, the sustainability of building materials is assessed too many times considering a single phase of the material lifecycle (e.g. the use phase for good insulating materials). Even “LCA” studies focus sometimes on a single stage of the lifecycle, but this approach is particularly wrong for materials that improve or reduce their environmental performance during the operational phase or at the end of the building’s life. This is the case for materials containing lime, whose strength and sustainability increase theoretically along with the carbonatation process. An innovative building material containing lime is the hempcrete brick: a non-structural composite material obtained from a mixture of hemp shives (woody core of the hemp stalk) and a lime based binder; this material shows good thermal performances ( . m) and moisture buffering capacit. LCA studies about hempcrete materials either leave out the carbonatation process from the assessment or assume that lime is fully recarbonated in the use phase of the building. The goal of our study is to assess the real rate of carbonatation of hempcrete bricks in order to include the results in a thorough LCA study and to understand the weight this process can have in the overall sustainability of the material. The carbonatation rate has been evaluated on bricks produced by the Italian company Equilibrium Srl. The degree of carbonatation is evaluated through X-ray diffraction on samples extracted at regular intervals from the brick production up to 5 months. Carbonatation depth profiles are obtained too. Results show the importance of evaluating the behavior of a material in all the phases of the lifecycle and could be used for future LCA studies on hempcrete materials exposed to similar conditions

Properties of cement-lime mortars vs. cement mortars containing recycled concrete aggregates

Cement based materials have a very special presence amongst building and construction materials, and therefore their recycling is of capital importance. In this research, concrete wastes were used as replacement of natural aggregates in cement and cement-lime mortars. The mortars were cured for 28-days with an increasing substitution of fine natural aggregates with recycled aggregates and have been prepared as well as characterized. The results show that, as expected, cement mortars always have better mechanical properties than the corresponding cement-lime mortars. A worsening of mechanical properties is observed upon increasing the amount of recycled aggregates in the cement mortars; on the contrary, cement-lime mortars show an improvement in mechanical properties of up to 60% when increasing the amount of recycled aggregates. The experimental results suggest that this improvement could arise from a synergic effect of lime hydraulicity and the filler effect due to the fine fraction of recycled aggregates within the mix, that lead to better densification of the lime mortars by blocking the capillary pores

Comparison of Ten Metal-Doped LaFeO₃ Samples on Photocatalytic Degradation of Antibiotics in Water under Visible Light: Role of Surface Area and Aqueous Phosphate Ions

Doping semiconducting oxides, such as LaFeO3 (LF), with metallic elements is a good strategy to improve the performance of photocatalysts. In this study, LF and ten different nanopowders metal-doped at the La or Fe site of LaFeO3 were evaluated in the photocatalytic degradation of ciprofloxacin (CP) and oxytetracycline (OTC). The following metals were used in the doping (mol%) process of LF: Pd 3% and 5%; Cu 10%; Mg 5%, 10%, and 20%; Ga 10%; Y 10% and 20%; and Sr 20%. The doped samples were synthetized using a citrate auto-combustion technique. From the X-ray diffraction (XRD) data, only a single crystalline phase, namely an orthorhombic perovskite structure, was observed except for trace amounts of PdO in the sample with Pd 5%. The specific surface area (SSA) ranged from 9 m2 g−1 (Ga 10%) to 20 m2 g−1 (Mg 20%). SEM images show that all samples were constituted from agglomerates of particles whose sizes ranged from ca. 20 nm (Mg 20%) to ca. 100 nm (Pd 5%). Dilute aqueous solutions (5 × 10−6 M) prepared for both CP and OTC were irradiated for 240 min under visible-light and in the presence of H2O2 (10−2 M). The results indicate a 78% removal of OTC with Cu 10% doped LF in a phosphate buffer (pH = 5.0). The degradation of CP is affected by pH and phosphate ions, with 78% (in unbuffered solution) and 54% (in phosphate buffer, pH = 5.0) removal achieved with Mg 10% doped LF. The reactions follow a pseudo-first order kinetic. Overall, this study is expected to deepen the assessment of photocatalytic activity by using substrates with different absorption capacities on photocatalysts

A Review of Visible Light Responsive Photocatalysts for Arsenic Remediation in Water

This review summarizes the progress over the last fifteen years in visible light reactive photocatalysts for environmental arsenic remediation. The design and performance of several materials including (1) doped and surface functionalized TiO2, (2) binary composites combining TiO2 with another semiconductor that absorbs visible light radiation or a metal (Pt), (3) ternary composites incorporating TiO2, a conductive polymer that can retard electron-hole recombination and an excellent adsorbent material for the removal of As(V), (4) tungsten, zinc, and bismuth oxides, (5) g-C3N4 based catalysts, and (6) M@AgCl core–shell structures. These results show that long reaction time remains a major challenge in achieving high As(III) oxidation

DIFFUSION STUDIES BY EDS AND LA-ICP-MS ACROSS THE La0.8Sr0.2MnO3 /La0.83Sr0.17Ga0.83Mg0.17O2.83 INTERFACE,

Energy dispersive spectrometry (EDS) line scan and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) were applied to the study of chemical reactivity and elemental interdiffusion at the interface between La0.8Sr0.2MnO3 (LSM) and La0.83Sr0.17Ga0.83Mg0.17O2.83 (LSGM), which are typical materials for intermediate temperature – solid oxide fuel cells (IT-SOFC). LSM and LSGM were synthesized by solid state and co-precipitation routes, respectively, and their characterization was performed by X-ray diffraction (XRD). The study focused on the interface reactivity of pellet/film and film/film configuration interfaces. The samples were fired at 1300 °C for a few hours and the chemical interaction and cation interdiffusion was evaluated with the two above mentioned independent techniques. Both methods reveal moderate diffusion of Mn into the LSGM matrix and possibly a small counterdiffusion of Ga ions into the LSM matrix