Experimental and Theoretical Investigation of Ion Pairing in Gold(III) Catalysts

The ion pairing structure of the possible species present in solution during the gold(III)-catalyzed hydration of alkynes: [(ppy)Au(NHC)Y]X2 and [(ppy)Au(NHC)X]X [ppy = 2-phenylpyridine, NHC = NHCiPr = 1,3-bis(2,6-di-isopropylphenyl)-imidazol-2-ylidene; NHC = NHCmes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene X = Cl-, BF4-, OTf-; Y = H2O and 3-hexyne] are determined. The nuclear overhauser effect nuclear magnetic resonance (NMR) experimental measurements integrated with a theoretical description of the system (full optimization of different ion pairs and calculation of the Coulomb potential surface) indicate that the preferential position of the counterion is tunable through the choice of the ancillary ligands (NHCiPr, NHCmes, ppy, and Y) in [(ppy)Au(NHC)(3-hexyne)]X2 activated complexes that undergo nucleophilic attack. The counterion can approach near NHC, pyridine ring of ppy, and gold atom. From these positions, the anion can act as a template, holding water in the right position for the outer-sphere attack, as observed in gold(I) catalysts.

Abatement of the ecotoxicological risk of landfill leachate by heterogeneous Fenton-like oxidation

Landfill leachates are highly contaminated liquid waste, and their treatment and detoxification are a challenging task. The current system of ecotoxicological risk assessment is complex and time-consuming. It is of fundamental importance to develop simpler and faster tools for the evaluation of the treated liquid waste and for an easier preliminary screening of the most active catalytic formulation/reaction conditions of the Fenton-like process. Here, several analytical techniques have been used for the assessment of the reduction of toxicity of the landfill leachate after Fenton process over copper-zirconia catalyst (ZrCu). Ultraviolet-visible (UV-vis) spectroscopy and absorbable organic halogens (AOX) analysis have been coupled to achieve further insight into the degradation of contaminants. In addition, for the first time, the qualitative abatement of organic compounds is monitored through proton nuclear magnetic resonance (¹H NMR) analysis, providing a new method for evaluating the effectiveness of the treatment. Spectroscopic techniques reveal that the Fenton process induces a significant abatement of the aromatic and halogen compounds (51%) in the landfill leachate with a reduction of the toxicity that has been confirmed by ecotoxicological test with algae. These results validate the investigated tool for a simple rapid preliminary evaluation of the detoxification efficacy.

Plastic electrode decorated with polyhedral anion tetrabutylammonium octamolybdate [N(C4H9)4]4 Mo8O26 for nM phosphate electrochemical detection

Inorganic phosphorous (as phosphate (PO₄^3-), is one of the essential nutrients for all living forms, either terrestrial or marine. In oligotrophic seawaters, this macronutrient is limited (10^-9 M) and its ratio with other elements (nitrogen or carbon) is denoting the health state of the marine environment; a small variation of its concentration can produce eutrophication. The gold standard method used for PO₄^3- detection is based on colorimetric detection of phosphomolybdate. The colored complex is obtained by mixing water-soluble molybdenum salts (Mo(VI)) and reducing agents in acid media, along with the sample containing PO₄^3-. Moreover, the kinetic of complex formation is slow, about 1 h is generally required for color to develop, exposing the assay to the drawbacks of interferences as those from silica. The detection is preferably performed in a controlled environment (i.e. in a laboratory) because several chemicals and steps of preparations are required as well as the optical instrumentation is not intended for in-field use. Electrochemical sensors offer portability and simplicity making them a practical option for on-site detection applications. To gain an analytical alternative in measuring low quantities of PO₄^3- (10^-9 M), and overcome some of the drawbacks of the classical approaches, we optimised a new easy way to produce a plastic electrode decorated with an alkyl Mo-polyoxometalate (Mo₈O₂₆^4-), that is soluble in organic solvents. This tetra-butyl-ammonium octamolybdate powder, [N (C4H9)4]4 Mo8O26, purposely synthetized was identified with FTIR, Raman, MS methods, and the electroactivity and reactivity with PO₄^3- was confirmed in solution with cyclic voltammetry (CV). When the Mo-decorated electrode was in contact with PO₄^3-, an electroactive phosphomolybdate aggregate formed at the electrode surface that was electrochemically detectable with square wave voltammetry (SWV). A remarkably low detection limit of 6.1 nM, to PO₄^3-, as well as good stability and selectivity were obtained also in real samples. In fact, PO₄^3- was measured in saline simulated and real seawater samples at nM concentrations in less than 5 min. The present investigation provides a new alternative to the current standard colorimetric methods to detect low phosphate concentrations, showing the potential to be used for monitoring nutrients in oligotrophic seawater.

Combined ultrasound-ozone treatment for reutilization of primary effluent-a preliminary study

The present work is a preliminary study on the potential of low-frequency ultrasound irradiation coupled with O₃ process for the disinfection of a primary effluent from a municipal wastewater treatment plant preserving nutrient levels (in particular nitrogen and phosphorous), for its possible reuse in civil, industrial, and agricultural sectors. The treated water could be reused, after appropriate dilution, contributing to the circular economy perspective and reducing the need for both chemical fertilizer addition and freshwater supply. The effect of different specific ultrasonic energies and ozone doses was assessed on a bench-top system, composed of an ultrasonic reactor and a semi-batch ozonation vessel. The results showed that the combined US-O₃ process produces a good removal efficiency regarding soluble Chemical Oxygen Demand, sCOD (ca. 60%), anionic surfactants (ca. 50%), and formaldehyde (ca. 50%), and an optimal abatement for Methylene Blue Active Substances (MBAS, > 90%). The process also reached high disinfection performances, obtaining 4 logs for E. coli and 5 log abatement for Total Coliforms. The high removal efficiency is matched by an outstanding retention of nutrients (total nitrogen and orthophosphate) highlighting a high potential value for agricultural reuse of the treated primary effluent, with possible significant saving of chemical fertilizers. It was concluded that low-frequency ultrasound pre-treatment, combined with ozonation, could be a useful process for primary effluent recovery for several purposes. Further studies are expected to be planned and executed to evaluate system scale-up feasibility.

In situ environmental HRTEM discloses low temperature carbon soot oxidation by ceria–zirconia at the nanoscale

In situ environmental transmission electron microscopy discloses room temperature carbon soot oxidation by ceria–zirconia at the nanoscale.

(Eco)toxicological maps: A new risk assessment method integrating traditional and in silico tools and its application in the Ledra River (Italy)

Contaminants giving rise to emerging concern like pharmaceuticals, personal care products, pesticides and Endocrine Disrupting Chemicals (EDCs) have been detected in wastewaters, as reported in the literature, but little is known about their (eco)toxicological effects and consequent human health impact. The present study aimed at overcoming this lack of information through the use of in silico methods integrated with traditional toxicological risk analysis. This is part of a pilot project involving the management of wastewater treatment plants in the Ledra River basin (Italy). We obtained data to work up a global risk assessment method combining the evaluations of health risks to humans and ecological receptors from chemical contaminants found in this specific area. The (eco)toxicological risk is expressed by a single numerical value, permitting the comparison of different sampling sites and the evaluation of future environmental and technical interventions.

Efficient fluoride adsorption by mesoporous hierarchical alumina microspheres

Mesoporous Hierarchical Alumina Microspheres (HAM) with high efficiency for fluoride removal have been synthesized and characterized.

Ceria-Zirconia Particles Wrapped in a 2D Carbon Envelope: Improved Low-Temperature Oxygen Transfer and Oxidation Activity

Engineering the interface between different components of heterogeneous catalysts at nanometer level can radically alter their performances. This is particularly true for ceria-based catalysts where the interactions are critical for obtaining materials with enhanced properties. Here we show that mechanical contact achieved by high-energy milling of CeO2-ZrO2 powders and carbon soot results in the formation of a core of oxide particles wrapped in a thin carbon envelope. This 2D nanoscale carbon arrangement greatly increases the number and quality of contact points between the oxide and carbon. Consequently, the temperatures of activation and transfer of the oxygen in ceria are shifted to exceptionally low temperatures and the soot combustion rate is boosted. The study confirms the importance of the redox behavior of ceria-zirconia particles in the mechanism of soot oxidation and shows that the organization of contact points at the nanoscale can significantly modify the reactivity resulting in unexpected properties and functionalities.

BMP tests of source selected OFMSW to evaluate anaerobic codigestion with sewage sludge

The aim of this study is to characterize different types of source selected organic fraction of municipal solid waste (SS-OFMSW) in order to optimize the upgrade of a sewage sludge anaerobic digestion unit by codigestion. Various SS-OFMSW samples were collected from canteens, supermarkets, restaurants, households, fruit-vegetable markets and bakery shops. The substrates characterization was carried out getting traditional chemical-physical parameters, performing elemental analysis and measuring fundamental anaerobic digestion macromolecular compounds such as carbohydrates, proteins, lipids and volatile fatty acids. Biochemical methane potential (BMP) tests were conducted at mesophilic temperature both on single substrates and in codigestion regime with different substrates mixing ratios. The maximum methane yield was observed for restaurant (675 NmlCH4/gVS) and canteens organic wastes (571 and 645 NmlCH4/gVS). The best codigestion BMP test has highlighted an increase of 47% in methane production respect sewage sludge digestion.

Salt-assisted thermal desorption of mercury from contaminated dredging sludge

In this study, we tested a new procedure for the decontamination of mercury-polluted dredging sludge (Marano-Grado Lagoon, northeastern Italy) based on cationic exchange associated with thermal desorption at a low temperature. Four mercury-polluted sludge slurries were treated using thermal desorption at 393 K for 2h. Three different salts, NaCl (sodium chloride), (CH(3))(4)NCl (tetramethylammonium chloride) and (C(4)H(9))(4)NCl (tetrabutylammonium chloride) were used as exchangers. The selected salts have a monovalent cationic part that progressively increases in molecular weight. The results show that the association of cationic exchange with thermal treatment leads to a significant improvement in the removal of mercury from the contaminated material at a low temperature compared to samples that were not treated with salt. The highest levels of decontamination were attained were obtained when the slurries, which had mercury pollution ranging from 20 to 200 ppm, were treated with a 15% solution of (C(4)H(9))(4)NCl. The efficiency of the removal at 393 K (from 24% up to 60%) depended on the nature of the sample. When the samples were treated at a similar temperature without the salt, no remediation of mercury was detected. Our results show that the thermal decontamination temperature can be significantly lowered by this remediation approach, which is the first example based on cationic exchange of the pollutant with an appropriate salt.

Bench-scale tests on ultrasound-assisted acid washing and thermal desorption of mercury from dredging sludge and other solid matrices

A series of ultrasonic assisted acid washing and thermal desorption tests were performed on sludge and other solid matrices with the aim to assay these removal technologies and to determine if the application of low frequency ultrasound was effective to enhance mercury removal. Unpolluted dredging sludge, 820 K calcinated dredging sludge, silica and alumina were characterized, polluted with a known concentration of mercury and treated both by acid washing and thermal desorption with and without low frequency ultrasound application. The acid washing was carried out by a 4% HNO(3) acid solution and the thermal desorption was performed in a 370-620K range. X-ray semi-quantitative analysis of dredging sludge before and after acid washing and granulometric curves of the matrices after the ultrasonic treatment were considered in order to evidence chemical or physical changes during these treatments. Total residual mercury measurements were carried out before and after sonication. Results showed not measurable acid washing extraction from polluted dredging sludge, a little (3%) extraction from 820K heat-treated sludge and a significant (10-20%) extraction from alumina and silica within 120 min of treatment. The ultrasound application gave generally poor improvement of the mercury removal. On the contrary thermal desorption of mercury was somewhat effective for alumina, silica and heat-treated dredging sludge samples in which mercury removal was 30-40% at 370 K and 90-99% at 570 K. Likewise ultrasound application did not improve desorption. Instead, the thermal treatment of dredging sludge had a negligible amount of mercury desorption at 370 K but it reached 95% at 570 K. The application of ultrasound improved the thermal extraction of 25% in the 470-520 K range of temperature.

Fast firing of tiles containing paper mill sludge, glass cullet and clay

The paper describes results obtained in the development of a previous research. We study here, in fast firing, the sintering behaviour and measure some properties of tiles containing a mixture of 60 wt% of paper mill sludge and 40 wt% of glass cullet. The behaviour of this material is compared to those displayed by materials obtained by the same mixture added with 10, 20 and 30 wt% of a natural red clay. In parallel, the same properties are measured also on a reference blend, which is presently used to produce commercial tiles. We show that powders containing 60 wt% of paper sludge and 40 wt% of glass cullet to which 30 wt% of clay is added give rise to materials that display a stable sintering process and have good hardness and strength and therefore could be used for the industrial production of tiles.