Raffaele Molinari

Influence of Excitation Wavelength (UV or Visible Light) on the Photocatalytic Activity of Titania Containing Gold Nanoparticles for the Generation of Hydrogen or Oxygen from Water

Gold nanoparticles supported on P25 titania (Au/TiO(2)) exhibit photocatalytic activity for UV and visible light (532 nm laser or polychromatic light λ > 400 nm) water splitting. The efficiency and operating mechanism are different depending on whether excitation occurs on the titania semiconductor (gold acting as electron buffer and site for gas generation) or on the surface plasmon band of gold (photoinjection of electrons from gold onto the titania conduction band and less oxidizing electron hole potential of about -1.14 V). For the novel visible light photoactivity of Au/TiO(2), it has been determined that gold loading, particle size and calcination temperature play a role in the photocatalytic activity, the most active material (Φ(H2) = 7.5% and Φ(O2) = 5.0% at 560 nm) being the catalyst containing 0.2 wt % gold with 1.87 nm average particle size and calcined at 200 °C.

Efficient Visible-Light Photocatalytic Water Splitting by Minute Amounts of Gold Supported on Nanoparticulate CeO2 Obtained by a Biopolymer Templating Method

When irradiated with visible light (λ > 400 nm) 1 wt % gold-supported ceria nanoparticles generate oxygen from water (10.5 μmol·h(-1)) more efficiently than the standard WO(3) (1.7 μmol·h(-1)) even under UV irradiation (9.5 μmol·h(-1)). This remarkable photocatalytic activity arises from a novel preparation method to reduce the particle size of ceria (5 nm) by means of electrostatic binding of Ce(4+) to alginate gel, subsequent supercritical CO(2) drying, and calcination. The low loading of Au is crucial for the observed high catalytic activity.

Treatment of aqueous effluents of the leather industry by membrane processes: A review

Abstract A general overview on the potentiality of membrane processes in the treatment of aqueous solutions coming from the leather industry is reported. The wet operations of the leather cycle which can be combined with or modified by membrane processes, such as microfiltration, ultrafiltration (UF), nanofiltration (NF) and reverse osmosis, have been described on the basis of consolidated applications and experimental tests on laboratory and industrial pilot scale. Some new applications are also proposed. The membranes and modules employed for the treatment of the effluents, pretreatment of fluids, cleaning procedures and fluid dynamic conditions in experimental applications are reported and discussed. An outline of direct and indirect energy analysis of tanning operations and the results of a mathematical model applied to the degreasing step are also presented. The integrated membrane processes described permit to rationalize the tanning cycle realizing the recovery and the recycle of several chemicals utilized in the tanneries. A reduction of environmental impact, a simplification of cleaning-up processes of wastewaters, an easy re-use of sludges, a decrease of disposal costs, a saving of chemicals and water and of direct and indirect energy are some advantages coming from the described membrane operations. In the future a wider application of the more consolidated membrane processes in this field is expected in the plant innovation phase of a tanning factory.

Studies on various reactor configurations for coupling photocatalysis and membrane processes in water purification

General aspects and perspectives of heterogeneous photocatalysis for the treatment of polluted aqueous effluents are presented. Some experimental results obtained by using various configurations of photocatalytic membrane reactors (PMRs) are reported. The configurations studied were: (i) irradiation of the cell containing the membrane, with three sub-cases: (i1) catalyst deposited on the membrane; (i2) catalyst in suspension, confined by means of the membrane; (i3) entrapment of the photocatalyst in a PSF membrane; (ii) irradiation of the re-circulation tank and catalyst in suspension confined by means of the membrane. In the case “(i)”, a preliminary investigation of membrane stability under UV irradiation was carried out. PMR characterization in photodegradation tests was mainly carried out in a recycle batch membrane reactor and, in some cases, in a continuous membrane reactor. The comparison between the first set of results, where the membrane was used only as a support for the photocatalyst, and the newest ones, where the adsorption of the pollutant on the membrane and membrane rejection play an important role in the global reactor performance, showed interesting perspectives and synergy for coupling photocatalysis and membranes. Furthermore, the configuration where the re-circulation tank was irradiated and the catalyst was used in suspension, appeared to be the most interesting for industrial applications. For example, in reactor optimization, high irradiation efficiency, high membrane permeate flowrate and selectivity can be obtained by sizing separately the “photocatalytic system” and the “membrane system” and taking advantage of all the best research results for each system.

Metal ion separation and concentration with supported liquid membranes

Abstract An experimental study of metal ion separations by supported liquid membranes is described. The supported liquid membranes (SLMs) use the extraction reagents D2EHPA, LIX 64N, DNNSA and Aliquat 336 as carriers. SLMs with different geometries (plane and cylindrical) have been studied and the experimental results have been compared with the results obtained from mathematical models. The best experimental conditions to perform a Cu(II)Zn(II) separation and Cr(III) and Cr(VI) recovery have been identified.

Quality improvement of recycled chromium in the tanning operation by membrane processes

Abstract Use of pressure-driven membrane processes integrated with conventional precipitation/dissolution operations is described in order to reduce chromium content in waste water from the tanning process and simultaneously improve the quality of the recycled chromium by means of elimination/reduction of organic lipolytic components, metals and other impurities that accompany the chromium recovered by traditional processes. The results obtained in the identification of types of membranes and modules, chemical-physical parameters, pretreatment of fluids, cleaning procedures and fluid dynamic conditions are reported and discussed. According to the obtained results, it is possible to suggest a process scheme that, starting from the exhausted chromium solution, through a nanofiltration membrane purification/concentration permits to obtain solutions that can be reused in tanning and/or retanning operations. The concentrate solution seems to guarantee improved characteristics of tanned and retanned skins with respect the skins treated with the traditional techniques as showed by chemical and physical essays on leather samples. The process permits also the reuse of the permeate from the nanofiltration in the pickling phase, considering the high content of chlorides in the solution.

Removal of silver and copper ions from acidic thiourea solutions with a supported liquid membrane containing D2EHPA as carrier

Facilitated counter-transport of silver and copper ions, both in acidic thiourea medium, across a supported liquid membrane (SLM) by using di(2-ethylhexyl)phosphoric acid (D2EHPA) as carrier, dissolved in chloroform, has been investigated. The fundamental parameters influencing the transport of silver and copper ions have been determined. They are: thiourea concentration in the feed phase, pH of the strip solution, D2EHPA concentration in the membrane phase, silver and copper concentrations in the feed phase, pH of feed solution, temperature of the system, membrane support characteristics and the type of acid. Thiourea can form, with both ions, successive complexes, which are less mobile than the free metal cation. In fact, the mass transport flux of silver and copper ions decreases when the concentration of thiourea in the feed phase increases. The obtained results show that Ag(I) and Cu(II) species predominate at very low thiourea concentration (10−5–10−4 M) and they are substituted by complexes M(Tu)n+ (M=Ag, Cu with n=1–4 and Tu refers to thiourea) with increasing thiourea concentration. Transport fluxes of silver and copper ions from feed solutions of different anionic composition, in absence and presence of thiourea, followed the order: NO3−>Cl−>SO42−>PO43−. This means that preferentially nitric acid should be used in preparing leaching solutions of polymetallic ores that are then used as feed in the SLM system. It was possible to take advantage of the different fundamental parameters for the separation of Ag(I) and Cu(II) in presence of thiourea, indeed working in the optimal conditions, the selectivity of the transport (JAg(I)/JCu(II)) increased from 1.29 to 1.96 with increasing thiourea concentration from 0 to 0.1 M.

Recovery and reuse of chemicals in unhairing, degreasing and chromium tanning processes by membranes

Membrane operations such as ultrafiltration, nanofiltration and reverse osmosis, properly integrated among them and/or with other conventional separation processes, have proven to be clean chemical processes. The study of a tanning process showed that many operations can be improved integrating them with membrane operations. The steps studied in this work were: enzymatic skins unhairing, degreasing of pickled sheepskins and chromium tanning; furthermore, the recovery and reuse of salts contained in the solution coming from chromium (III) precipitation were studied. The obtained results realize a reduction in environmental impact, a simplification of depuration processes of waste water, an easy reuse of sludge, a decrease of disposal costs and a saving of chemicals and water.

Stability and Effect of Diluents in Supported Liquid Membranes for Cr(III), Cr(VI), and Cd(II) Recovery

Abstract Some results obtained with the aim of optimizing the permeation fluxes, separation factors, and stability of SLMs are described. A flat sheet polypropylene membrane was used in all the experiments. The ions on which the SLMs were tested were Cr(III), Cr(VI), and Cd(II). The carriers were dinonyl-naphthalene sulfonic acid (DNNSA), Aliquat 336, and Alamine 336. The diluents were o-xylene, kerosene, n-heptane, and their mixtures. Among the various mixtures tested for membrane impregnation, a maximum separation factor of 15.0 by using the SLM 50% v/v DNNSA + 25% v/v o-xylene + 25% v/v kerosene was obtained. The stability of this membrane was greater than 70 hours of continuous operation. The effect of temperature in the 25-35°C range was also investigated.

Comparison of polyethylenimine, polyacrylic acid and poly(dimethylamine-co-epichlorohydrin-co-ethylenediamme) in Cu2+ removal from wastewaters by polymer-assisted ultrafiltration☆

Some results on metal ions removal from wastewaters using water-soluble polymers such as polyethylenimine (PEI), polyacrylic acid (PAA), polyacrylic acid sodium salt (PAASS) and poly(dimethylamine-co-epichlorohydrin-co-ethylene-diamine) (PDEHED) as chelating agents and the Cu 2+ ion as the model in combination with a polymer-assisted ultrafiltration process (PAUF) are reported. In particular, the performances of these polymers in Cu 2+ removal from wastewaters were compared. Tests of bonding capacity and best operating conditions of the process showed that complexation conditions depend on pH; indeed, copper ions are complexed by PEI, PAA, PAASS and PDEHED at pHs higher than 6, 4.6, 4.6 and 8, respectively. The decomplexation reactions took place at pH <3. Bonding capacity was 0.333 mg Cu 2+ /mg polymer, meaning a ratio of polymer/Cu 2+ = 3 (w/w) for PEI, PAA and PAASS. For the chelating agent PDEHED, a ratio of PDEHED/Cu 2+ = 0.5 (w/w) was determined. UF tests, realised at two trans-membrane pressures (2 and 4 bar) by using five different flat-sheet membranes, showed that the PAA polymer and the PAN GKSS HV2/T membrane can be used when the objective of the purification process is to decrease methal concentration not lower than a certain value. The PDEHED polymer is useful if the objective of wastewater treatment is to obtain complete copper removal. Simple washings with tap water were enough for regeneration and reuse of the membranes.