Immobilization of nanobeads on a surface to control the size, shape and distribution of pores in electrochemically generated sol-gel films

Electrochemically assisted deposition of an ormosil film at a potential where hydrogen ion is generated as the catalyst yields insulating films on electrodes. When the base electrode is modified with 20-nm poly (styrene sulfonate), PSS, beads bound to the surface with 3-aminopropyltriethoxysilane (APTES), and using (CH3) 3SiOCH3 as the precursor, the resulting film of organically modified silica (ormosil) has cylindrical channels that reflect both the diameter of the PSS and the distribution of the APTES-PSS on the electrode. At an electrode modified by a 20-min immersion in 0.5 mmol dm−3 APTES followed by a 30-s immersion in PSS, a 20-min electrolysis at 1.5 V in acidified (CH3) 3SiOCH3 resulted in an ormosil film with 20-nm pores separated by 100 nm. Cyclic voltammetry of Ru (CN) 6 4− at scan rates above 5 mV s−1 yielded currents controlled primarily by linear diffusion. Below 5 mV s−1, convection rather than the expected factor, radial diffusion, apparently limited the current

Microstructural defects in nanocrystalline iron probed by x-ray-absorption spectroscopy

An EXAFS (extended x-ray-absorption fine structure) study of nanocrystalline iron prepared by high-energy ball milling is presented. Accurate data analysis has been performed using a recently developed ab initio multiple-scattering method (GNXAS). The crystalline iron EXAFS spectrum, taken as reference, has been analyzed taking proper account of the important multiple-scattering signal. Results of the data analysis are shown to be in good agreement with known structural values. The dramatic decrease of the first-neighbor coordination number found in nanocrystalline iron, as a function of the milling time, is shown to be related to the presence of a large defect density. The corresponding decrease of the coordination numbers of the second and further neighbors, as well as the significant decrease of the multiplicities of the three-atom configurations, confirms this interpretation. A simple model which takes into account the presence of atomic defects is shown to lead to marked reduction of coordination numbers and three-atom multiplicities in agreement with the experimental data. Selected models without lattice defects are shown to be unable to give a quantitative explanation of the intensity reduction of the EXAFS signal found in milled nanocrystalline iron. An in situ annealing of the sample (up to about 1100 °C) milled for the longer time (32 h) is shown to reduce considerably the density of the defects, as expected, although no complete recovering of the crystalline order is found. The transition from α iron to γ iron has been directly observed for such nanocrystalline material

Geopolymers for hazardous cations and anions inertization

Several waste liquors are classified as toxic or hazardous waste and represent a real burden for companies in terms of costs and treatment time. One of the most difficult to treat is the tannery waste water that represent a high pollution risk if not treated and collected properly. Geopolymeric matrix based on metakaolin has been used to treat tannery waste water without any post use treatment. The as received waste water containing tannins, chromium soluble salts, phenols, bicarbonates, and a mixture of organic compounds have been added to a geopolymeric formulation which was optimized for Cr+3 liquor [1]. Please click Additional Files below to see the full abstract

Sustainable Chromium Encapsulation: Alkali Activation Route

This article highlights recent experimental advances in the use of inorganic substances in the encapsulation of pollutants and, in particular, discusses the potential applicability and constraints of the geopolymerization process for the treatment of wastewater containing chromium. A great percentage of waste containing chromium salts is produced by the leather industry during the tannery process. Such industrial waste is in the form of liquor containing almost 40% of the initial chromium combined with many other pollutants. The stabilization/solidification (S/S) treatment of this type of waste must be combined with chromium encapsulation in an economic, environmentally friendly and efficient process to be industrially feasible. Here we present a novel process in which the wastewater is used as a component of the formulation together with a clay by-product and with the addition of NaOH pellets with the goal of a no-water plus no-waste technology approach. The final solidified “ceramic-like” material successfully immobilized the heavy metal cations as well as anions and macromolecules of surfactants, avoiding environmental damages to soil and groundwater. The article is completed by mentioning other S/S processes where wastewater has been treated and the resulting sludge encapsulated. The future of the S/S technologies in the tannery industry should progress in the direction of significantly reducing the amount of wastewater directed to the treatment plants, with associated reductions in transport and their CO2 emissions. This article intends to be a contribution in the direction of preventing waste, aligning circular economy and waste management objectives

XAS investigation on polyvalent cation intercalation in V2O5 aerogels.

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