Towards Light Driven Water Splitting

Electrochemsitry and electrocatalysis are useful techniques for energy conversion and energy storage applications. In this project, the electrocatalytic activation of small molecules, H₂O, methanol and ethanol, and CO₂, has been studied as potential methods for energy storage and conversion. A hexaniobate Lindqvist ion assisted Co and Ni nanostructure deposition method has been developed. Efficient catalytic activity towards water oxidation has been observed with high TOF values obtained in alkaline 1 M NaOH solution and even one cycle of potential for film deposition generating significant catalytic activity. CoIV and NiIV may be responsible for the high catalytic activities as results showed by FTAC voltammetry. Four cobalt phosphonate coordination polymers were also studied and showed catalytic activity for water oxidation in both phosphate buffer and water-saturated ionic liquid [BMIM][PF₆]. The catalytic activity shows a structural dependence and presumably due to the different intrinsic catalytic activities of these catalysts towards water oxidation reaction or/and their different rates of decomposition to form the well-known CoOx water oxidation catalysts. Voltammetric studies of the Ru-containing water oxidation molecular catalyst, [{Ru₄O₄(OH)₂(H₂O)₄}(-SiW₁₀O₃₆)₂]10- have been carried out in aqueous media over a wide range of pH (2 to 12) and ionic strength conditions. Well defined voltammograms in the buffered media are only obtained when Frumkin double layer effects are suppressed by the presence of a sufficient concentration of additional supporting electrolyte (LiNO3, NaNO3, KNO3, Ca(NO3)₂, Mg(NO3)₂, MgSO₄ or Na₂SO₄). Analysis of the reversible potentials reveals that (i) K+ has a significantly stronger interaction with the one-electron oxidized form 1(1) than the other cations investigated; (ii) proton transfer may not necessarily be coupled to all electron transfer steps to generate active water oxidation catalysts; (iii) the four-electron oxidized form, 1(4), is capable of oxidizing water under all conditions studied and (iv) under some conditions, the three-electron oxidized form, 1(3), also exhibits considerable activity. These electrochemical knowledge obtained for the molecular water oxidation catalyst [1(-SiW₁₀O₃₆)₂]10- have been also applied to the electrooxidation of methanol and ethanol. In both aqueous and alcohol media, the one-electron oxidized form 1(1) is able to catalyze methanol and ethanol under all conditions, and the 1(0) showed some catalytic activity especially for ethanol oxidation under some conditions. Methanol and ethanol were oxidized into aldehyde and acid through two- and four-electron transfer pathways, respectively, as shown by analysis of products after bulk electrolysis. One Cu and two Ni macrocyclic complexes have been studied for electrocatlytic CO₂ reduction. N,N´-ethylenebis(acetylacetoniminato) complexes of nickel(II) and copper(II) both showed catalytic activity for CO₂ reduction in organic and ionic solvents, and also for proton reductions. C₂O₄2- was formed after bulk electrolysis as shown by spectroelectrochemical data. A novel square-planar nickel(II) Schiff base complex, [Ni(L´)]PF6 (where L´ is 2,4,9,11,11-pentamethyl-2,3,4 triaza-1-one-4-amine), has been synthesized and shown with electrocatalytic activity for CO₂ reduction with oxalate and bicarbonate as the reduction products after bulk reductive electrolysis under a CO₂ atmosphere.

Fil: Galatro, Andrea Veronica. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Houssay. Instituto de Bioquimica y Medicina Molecular. Universidad de Buenos Aires. Facultad de Farmacia y Bioquimica. Instituto de Bioquimica y Medicina Molecular; Argentina

A wide range of gaseous and particulate phase pollutants are emitted into the atmosphere by routes like external or internal combustion,evaporation,eolian and others.Once released into the atmosphere,these primary emissions are dispersed,transported and,at the same time,transformed by various chemical processes that determine their ultimate environmental fate.The secondary products of these processes are more important ones concerning their effects on human health and the quality of the environment,which represent the critical property determining the establishment of certain air standards and regulatory policies.The prevalence of tropospheric photooxidants is of international concern because of their adverse effects on human health and environment.A lot of nitrogen oxides(NOx) and volatile organic compounds(VOCs) have been emitted from natural and factitious sources,and then transform into secondary photochemical oxidants by the atmospheric oxidation reactions,contributing to atmospheric oxidation capacity and climate change patterns.The formation of secondary photochemical oxidants including ozone(O3),gaseous nitric acid(HNO3),hydrogen peroxide(H2O2) and peroxy acetyl nitrate(PAN) is driven by hydroxyl radical(OH) during the daytime whose main sources are photolysis of O3 and nitrous acid(HONO).At night,the nitrite radical(NO3) substitutes OH radical and plays the most important role in the nighttime atmospheric chemical processes.However,the more complicated situation is that aerosol particles are ubiquitous in the Earth's atmosphere.As reactive surfaces they can take part in the heterogeneous reactions with secondary photochemical oxidants.It changes the tropospheric composition and the properties of the gaseous reactants,making the atmosphere pollution even more serious.It also alters the properties of aerosols like hygroscopicity and influences the radiation balance by the direct and indirect effects.Thus,many efforts have been made to this subject,which has become one of focuses of the atmospheric chemical research currently.In order to make clear the intricate coupling effect between secondary photochemical oxidants and aerosol particles,laboratory simulation is basic.Aerosol samples produced in the laboratory or collected in the atmosphere are selected and put into the reactor such as flow tube,Knudsen cell or aerosol chamber,which react with the secondary photochemical introduced.The kinetics processes and products can be detected by the equipment involving mass spectrometry(MS),Fourier transform infrared spectrometry(FTIR),diffuse reflectance infrared Fourier transform(DRIFTS) and aerosol mass spectrometry(AMS),which are connected to the reactors.Chromatography and surface characterization techniques also can be applied to detect the heterogeneous reaction as the off-line methods.Laboratory researches about heterogeneous kinetic and mechanism are of importance to understand this coupling effect,which could contribute to comprehending the field observed events and provide the basic parameters to model forecast.Research on heterogeneous reactions of secondary photochemical oxidants is challenging.However,there are some aspects that are not clear,and more studies are needed.First,the researches mainly concentrate on the O3 and HNO3 heterogeneous reactions,while less about others.The data must be enriched through the future studies.Second,the reaction system often has isolated secondary photochemical oxidant and individual particles,which is not consistent with real atmospheric composition.It leads certain error between the results from laboratory simulation and field observation.Last but not least,no commercial equipment is applicable to this area.Researchers must establish high-precision and sensitive apparatuses to detect the transformation of reactants under atmospheric conditions.In this review,the formation of secondary photochemical oxidants is introducesd and the recent international laboratory researches and state of the art with regard to this area are concluded.In the end the main scientific problems are put forward,and the prospect is made.

Micropollutants are emerging as a new challenge to the scientific community. The discharge of treated effluent from wastewater treatment plant (WWTP) is a major pathway for the introduction of emerging contaminants into surface water. Solar advanced oxidation processes can achieve high and consistent micropollutants' removal. This study deals with the destruction of trace organic contaminants in secondary treated effluents by (i) sulphate radical based (SO 4 -) homogeneous photo-Fenton using peroxymonosulphate as an oxidant, ferrous ion Fe(II) as catalyst, (ii) hydroxyl radical (○ OH) heterogeneous photocatalysis using suspended titanium dioxide (TiO 2) as catalyst, (iii) photolysis and solar irradiation as a light source. Solar advanced oxidation processes of wastewater was conducted in a panel solar pilot and the efficiency of this treatment was evaluated on the basis of micropollutants' disappearance, reduction of total organic matter content (TOC), and measurement of the final estrogenicity. The chemical analyses of the wastewater collected showed that several contaminants persisted at the end of its treatment in the WWTP. Contaminants elimination was followed by Liquid Chromatography/Quadrupole ion trap Mass Spectrometry analysis after a pre-concentration 100:1 by solid phase extraction. 74 target micropollutants were identified. Some of them were found at trace level also after the applied AOPs. The ecotoxicity of the effluent wastewater was evaluated using different commonly adopted bio-tests as Daphnia magna, Vibrio fischeri, Brachionus calyciflorus, Spirodela polyrhiza, Pseudokirchneriella subcapitata. These standard methods can give an idea about of quality of wastewater, but they are not able to respond also to the presence of estrogenic activity, that can be a crucial problem. For overtake this point, the treatment efficiency was provided by estrogenic activity measurements based on the use of bioluminescent HELN ERa cell line. The order of micropollutants elimination efficiency under the experimental condition evaluated was solar heterogeneous photocatalysis with TiO 2 > solar PMS/Fe (II) >solar photolysis.

The removal of M. aeruginosa from natural waters has been investigated by using a fixed bed cell with 3-dimensional electrodes in continuous mode. Steady state values of chlorophyll-a pigment, contained in the microalgae, were obtained, as well as concentrations of oxidizing species in the outlet stream of the system. In particular, attention was paid to two key parameters, flow rate and current density, to determine their influence on the removal of microalgae and on the concentration. Experiments were performed in a plastic cylindrical single pass cell, filled with glass spheres, connected to a hydraulic circuit. Grids of Titanium, arranged in stacks in-series, were employed as electrodes packing. The grids of the cathode packing were coated with platinum, while the grids of the anode packing were coated with Ir/Ru mixed oxides. The effect of the operative parameters on the possible mechanism of removal, namely electric field and electro-generated oxidants was investigated. The results show that the removal of M. aeruguinosa may be related to the synergistic effect of electro-generated oxidants produced from the chloride ions and electric field, although the main mechanism is the killing by long life oxidants electro-generated at the anode surface.

استحصال سریم اکسید از مخلوط عناصر نادر خاکی حاصل از کنسانتره فسفات اسفوردی

The chemical-mechanical polishing process (CMP) is an essential part of the production of integrated circuits. Metal to be polished in the CMP reacts with the oxidants from the aqueous suspension (slurry) and the passive film is formed on the metal surface. Suspended abrasive nano particles from the slurry cause detachment of the formed friable passive films. The CMP represents the tribocorrosion process where material deterioration results from the interaction of wear and corrosion which takes place in tribological contact exposed to an aggressive environment. Due to increasing number of the materials to be polished in the modern integrated circuits it is necessary to gather fundamental understanding of the removal mechanism of each material. The aim of this work is to elucidate the removal mechanisms of tungsten (W), as a typical microelectronic metal (chosen as a model system), under different oxidising conditions (represented by electrochemically imposed potential). Also, we want to evaluate the effect of the slurry composition (chelating agents lactic and phosphoric acid) on material removal. To achieve this electrochemical techniques (chrono amperometry, cyclic voltametry, passivation kinetics measurements under mass transport control), and tribocorrosion techniques (tests on tribometer with electrochemical cell with reciprocating sliding motion of alumina ball) were used. Surface analysis techniques (SEM, XPS, AES) were used to assess worn and unworn surfaces' morphology and chemistry. In addition, electrochemical tests and polishing tests on the CMP machine were performed with technical CMP slurries. The sliding action of the alumina ball on tungsten in the 0.01 M H2SO4 solution was found to cause three distinct wear responses depending on imposed electrode potential. Below the first threshold potential the wear is low due to negligible oxide film formation. In the following wear region, up to the second threshold potential, materials deterioration in the rubbed area proceeds by cyclic mechanical removal of the WO3 passive film followed by repassivation of tungsten. The amount of anodic oxidation corresponds to the overall removed metal volume. Beyond the second threshold potential a compact tribolayer of WO3 (more than 400 nm thick), probably formed by agglomeration of oxide particles detached from the metal surface, forms and covers the wear track. Similar tribocorrosion behavior of tungsten was also observed in the presence of 0.1 M H3PO4. The presence of chelating agents, lactic acid and phosphoric acid, in the 0.01 M H2SO4 solution does not change the volume of material wastage at potentials below the second threshold potential. Beyond this electrode potential, lactic acid promotes WO3 dissolution and thus impedes the third body formation and enhances wear. Electrochemical factors have a strong influence on the tungsten CMP removal rate. It was found that CMP removal rate increases with the open circuit potential (electrode potential) and with passivation charge density. A good correlation of tribocorrosion results and CMP practice was observed. Tribocorrosion models can be successfully applied to the tribocorrosion of tungsten and as well can be fairly used for modelling the material removal in CMP.

Atmospheric concentrations of carbon dioxide (CO2) are significantly increasing since the industrial revolution at an accelerating rate causing environmental impact such as global warming and climate change. Projections indicate that CO2 concentrations will continue to rise to unsustainable levels. This highlights the scale of the challenge our scientists are facing in order to reduce CO2 emissions and underpins the importance of promoting green process engineering for the utilisation of CO2 as a valuable commodity in the process industry. The transformation of CO2 to value-added chemicals such as organic carbonates provides a promising technological advancement aimed at reducing CO2 atmospheric concentrations to sustainable levels. Dimethyl carbonate (DMC) is a promising green compound that exhibits versatile and excellent chemical properties and therefore finds applications as an intermediate in the chemical and pharmaceutical industries. DMC has a high oxygen content and can be used as an oxygenate additive to gasoline to improve its performance and reduce exhaust emission. The conventional method for DMC synthesis involves the utilisation of phosgene as a toxic feedstock. Thus, greener and more sustainable synthetic processes for the synthesis of DMC are required. Recently, non-toxic synthetic routes have been explored; these include, oxidative carbonylation of carbon monoxide (CO), oxygen (O2) and MeOH, direct synthesis from MeOH and CO2 and the transesterification of cyclic carbonates and methanol (MeOH). The oxidative carbonylation route suffers from the use of expensive raw materials and corrosive reagents as well as being hazardous due to the explosive potential of CO. The direct production of DMC from MeOH and CO2 offers an attractive and green synthetic route for DMC synthesis. Also, the synthesis of DMC via the transesterification of cyclic carbonates and MeOH, where cyclic carbonates can be synthesised from their corresponding epoxides and CO2, makes the synthesis of DMC via transesterification route more environmentally friendly and desirable in terms of green chemistry and sustainable development. Therefore, in this research new greener catalytic processes for DMC synthesis via addition of MeOH to CO2 route and transesterification route have been explored. In this work, several commercially available heterogeneous catalysts such as ceria and lanthana doped zirconia (Ce–La–Zr–O), ceria doped zirconia (Ce–Zr– O), lanthana doped zirconia (La–Zr–O), lanthanum oxide (La–O) and zirconium oxide (Zr–O) have been extensively assessed for the synthesis of DMC. Strongly coupled graphene based inorganic nanocomposites represent an exciting and new class of functional materials and therefore the utilisation of graphene oxide (GO) as a suitable support for metal oxide catalysts has been explored. Ceria doped zirconia graphene nanocomposites (Ce–Zr/GO) have been synthesised using conventional wet impregnation methods. Samples of Ce–Zr/GO have been subjected to heat treatment at various temperatures (773 K, 873 K, 973 K and 1073 K) in an attempt to enhance their catalytic performance. As-prepared Ce– Zr/GO sample and the corresponding heat treated samples have been assessed for the direct synthesis for DMC from MeOH and CO2. Furthermore, a new innovative approach has been employed for synthesising advanced, highly efficient and active heterogeneous catalysts via utilisation of a continuous hydrothermal flow synthesis (CHFS) reactor. Tin doped zirconium oxide (Zr–Sn– O) and tin doped zirconia/graphene nanocomposite (Zr–Sn/GO) have been assessed as suitable heterogeneous catalysts for the synthesis of DMC via the transesterification route. The catalysts were characterised using various analytical techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and Brunauer-Emmett-Teller (BET) surface area measurement. A heterogeneous catalytic process for the synthesis of DMC has been investigated using a high pressure reactor. The effect of various reaction parameters such as the reactant molar ratio, catalyst loading, reaction temperature, CO2 pressure, reaction time and the use of a dehydrating agent was studied for the optimisation of DMC synthesis. Reusability studies were conducted to evaluate the long term stability of the heterogeneous catalysts by recycling and reusing the catalyst several times for the synthesis of DMC. Tin doped zirconia graphene oxide (Sn–Zr/GO) nanocomposite catalyst has been found to be the best performed catalyst for the synthesis of DMC as compared to other catalysts evaluated in this research work. This can be attributed to the phase composition and crystallinity of the catalyst along with the defects on the graphene sheet such as, holes, acid/basic groups and presence of residual which can provide additional active catalytic sites. Catalyst reusability studies evidently showed that Sn–Zr/GO nanocomposite can be easily recovered and reused without any significant reduction in the catalytic performance. Response Surface Methodology (RSM) has track record in helping researchers in modeling and optimisation of the experimental design for various applications in food industry, catalysis and chemical reaction engineering. Therefore, it has been employed to evaluate the relationship between multiple process variables in order to optimise a specified response (i.e. yield of DMC). RSM using Box-Behneken design (BBD) was carried out for process modeling and optimisation, with an aim to better understand the relationship between five operating variables (i.e. MeOH:PC molar ratio, catalyst loading (w/w), reaction temperature, reaction time and stirring speed) and their impact on the yield of DMC. A model for the synthesis of DMC by transesterification of PC and MeOH has been developed using BBD to compare the experimental data and the predicted results by the BBD model. Furthermore, regression analysis was applied to establish the optimum reaction conditions for a maximising DMC synthesis. The BBD model predicted values are in good agreement with the experimental results.

This work contributes to the generalization of the Non-faradaic Electrochemical Modification of Catalytic Activity effect, known under the acronym NEMCA. This effect is observed for the first time over an oxide catalyst, namely IrO2 supported on yttria-stabilized-zirconia. The activity of the IrO2 catalyst for the complete ethylene oxidation is remarkably and reversibly increased by polarizing the catalyst-solid electrolyte interface. The reaction rate in excess oxygen is enhanced by at least an order of magnitude, when the catalyst is polarized positively with respect to a reference electrode. The rate enhancement may be up to 1·104 times higher than the rate of O2- supply to the catalyst. The application of low negative potentials generally causes the rate to decrease. However, under a limited range of experimental conditions, namely temperatures above 370 °C and high overpotentials, the cathodic polarization induces a rate enhancement. The ethylene oxidation kinetics over an IrO2 catalyst exhibits a Langmuir-Hinshelwood behaviour with competitive adsorption of reactants. The rate dependence on the oxygen partial pressure indicates that the reaction may proceed via an intermediate. The electrochemical promotion of the catalyst is most effective in oxygen-rich gas phase compositions, where the rate is essentially limited by the ethylene adsorption. In-situ cyclic voltammetry is used to maintain the reaction rate at a higher value than under open-circuit conditions. This simple method of investigation has just entered in the world of catalysis and provides valuable information on the state of the catalyst surface. The redox processes involving very small amounts of electroactive species can only be studied in low oxygen pressures. The main finding of this work is the experimental evidence that the electrochemical promotion of the ethylene oxidation rate is linearly related to the electrical charge stored at the electrode-electrolyte interface, measured by cyclic voltammetry. The voltammetric analysis of the IrO2 catalyst in air shows that, upon positive polarization, the catalyst surface is oxidized to a higher oxide IrO2+δ which is responsible for the rate enhancement observed.

Water oxidation is a key reaction in natural photosynthesis and in many schemes for artificial photosynthesis. Inspired by energy challenges and the emerging understanding of photosystem II, the development of artificial molecular catalysts for water oxidation has become a highly active area of research in recent years. In this Focus Review, we describe recent achievements in the development of single-site ruthenium catalysts for water oxidation with a particular focus on the overpotential of water oxidation. First, we introduce the general scheme to access the high-valent ruthenium-oxo species, the key species of the water-oxidation reaction. Next, the mechanisms of the OO bond formation from the active ruthenium-oxo species are described. We then discuss strategies to decrease the onset potentials of the water-oxidation reaction. We hope this Focus Review will contribute to the further development of efficient catalysts toward sustainable energy-conversion systems.

F(R), FT-IR and Raman spectra included in the manuscript

Efficient catalysis of the oxygen-evolution half-reaction (OER) is a pivotal requirement for the development of practical solar-driven water splitting devices. Heterogeneous OER electrocatalysts containing first-row transition metal oxides and hydroxides have attracted considerable recent interest, owing in part to the high abundance and low cost of starting materials. Among the best performing OER electrocatalysts are mixed Fe/Ni layered double hydroxides (LDH). A review of the available experimental data leads to the conclusion that iron is the active site for [NiFe]-LDH-catalyzed alkaline water oxidation.

Fenton reaction is often used for the treatment of industrial wastewaters polluted by a toxic and difficult to remove compounds where other methods as emulsion breaking chemical precipitation, or advanced chemical processes fail. To this category belong phenols, polychlorinated aromatic hydrocarbons, amines, mercaptans, and stable chemical complexes containing heavy metals at different concentrations and sometimes even radioactive isotopes. These wastewaters can cause severe damage to the environment, so their removal has a high priority. The principle of Fenton’s reaction is based on radical oxidation of the difficult to remove compounds realised by the application of oxidising reagent catalysed by the addition of metallic cations as an oxidant is frequently used hydrogen peroxide, ozone, or chloride lime which allows production of the hydroxyl radicals. As a catalyst, Cu+, Ti3+ or Cr2+ can be successfully employed, but most commonly, Fe2+ cations are used. The contribution of this paper is an adding of Fe2+ ions by dissolution of the electrodes. The advantage of this method consists of indirect adding of Fe+2 from solid phase which eliminates the need of dosing of the Fe in the form of the solution (FeSO4, FeCl2, FeCl3, Fe2(SO4)3 …) causing secondary pollution and an increase of salinity. This technology avoids unnecessary salts addition essential in cases, with problems of high salinity of the wastewater. To realise this process in the industrial scale, profound knowledge of the electrocoagulation and/or electroflotation is indispensable, especially for scale-up. This paper brings knowledge about the electrochemical background and technological approach for successful design for required volume flow. Based on our results, some details of suitable reactor types and its scale-up is presented in brief overview revealing suitability for selected cases.

A pair of metal organic framework (MOF)-derived oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts for zinc-air batteries

The effect of acute nonbacterial dependent peritonitis on lung and liver oxidant stress and antioxidant activity.