Adsorption of MCPA pesticide by MgAl-layered double hydroxides

In the present study, the adsorption characteristics of the herbicide MCPA (4-chloro-2-methylphenoxyacetic acid) on layered double hydroxides (LDHs) were evaluated under laboratory conditions with particular attention to the effect of layer charge, original interlayer anion and morphology. The final objective is the use of LDHs and modified LDH materials as recyclable adsorbents and heterogeneous catalysts for the treatment of contaminated waste waters.The anionic clays tested were [Mg_1−xAl_x(OH)₂]^x+[X_x/m^m−·nH₂O] materials. The MCPA adsorption capacity was determined from adsorption isotherms and a kinetic study. We looked at the influence of the pH, the Mg²⁺/Al³⁺ ratio, i.e. the anion exchange capacity, the nature of the intercalated anion X (CO₃²⁻, NO₃⁻, Cl⁻) and the morphology of the adsorbent on the extent of adsorption. The adsorption isotherms, described by Freundlich model, are of S-type with tendency to L-type for high MCPA equilibrium concentration. Furthermore, the adsorption capacity increases with the layer charge density. Hence, MCPA adsorption on LDHs occurs by anion exchange in two steps, an external exchange followed by an interlayer exchange, which explain these changes of type within the same isotherm. Besides, the adsorption capacity depends on the nature of the starting anions, following the affinity order (NO₃⁻<Cl⁻<CO₃²⁻) proposed by Miyata and increases with the specific surface area.     

Kinetics of the catalytic destruction of cyanogen chloride

The catalytic destruction of cyanogen chloride (CNCI) in air has been investigated in a fixed-bed microreactor using a 2.15% Pt/α-alumina catalyst. If the feed stream contains water vapor, CNCl conversion as high as 98% can be achieved at 375°C and 170 000 cm³ h⁻¹ g⁻¹ space velocity. In contrast, the CNCl conversion in a dry inlet gas stream is 20% at 440°C and 46 000 cm³ h⁻¹ g⁻¹ space velocity. Water vapor in the feed stream significantly enhances the conversion of CNCl by providing an alternate hydrolysis pathway for destruction. It also promotes the complete conversion of CNCl to CO₂ and HCl with negligible selectivity to CO and Cl₂. The CNCl conversion decreases with increasing concentration in the feed stream. A kinetic model of the form r = kC_a/1(1 + K_pC_p) adequately represents the data in the presence of water vapor.     

Diamond-like carbon thin films by microwave surface-wave plasma CVD aimed for the application of photovoltaic solar cells

The nitrogen doped diamond-like carbon (DLC) thin films were deposited on quartz and silicon substrates by a newly developed microwave surface-wave plasma chemical vapor deposition, aiming the application of the films for photovoltaic solar cells. For film deposition, we used argon as carrier gas, nitrogen as dopant and hydrocarbon source gases, such as camphor (C₁₀H₁₆O) dissolved with ethyl alcohol (C₂H₅OH), methane (CH₄), ethylene (C₂H₄) and acetylene (C₂H₂). The optical and electrical properties of the films were studied using X-ray photoelectron spectroscopy, Nanopics 2100/NPX200 surface profiler, UV/VIS/NIR spectroscopy, atomic force microscope, electrical conductivity and solar simulator measurements. The optical band gap of the films has been lowered from 3.1 to 2.4 eV by nitrogen doping, and from 2.65 to 1.9 eV by experimenting with different hydrocarbon source gases. The nitrogen doped (flow rate: 5 sccm; atomic fraction: 5.16%) film shows semiconducting properties in dark (i.e. 8.1 × 10^{− 4} Ω^{− 1} cm^{− 1}) and under the light illumination (i.e. 9.9 × 10^{− 4} Ω^{− 1} cm^{− 1}). The surface morphology of the both undoped and nitrogen doped films are found to be very smooth (RMS roughness ≤ 0.5 nm). The preliminary investigation on photovoltaic properties of DLC (nitrogen doped)/p-Si structure show that open-circuit voltage of 223 mV and short-circuit current density of 8.3 × 10^{− 3} mA/cm². The power conversion efficiency and fill factor of this structure were found to be 3.6 × 10^{− 4}% and 17.9%, respectively. The use of DLC in photovoltaic solar cells is still in its infancy due to the complicated microstructure of carbon bondings, high defect density, low photoconductivity and difficulties in controlling conduction type. Our research work is in progress to realize cheap, reasonably high efficiency and environmental friendly DLC-based photovoltaic solar cells in the future.     

Factors influencing the hydration of layered double hydroxides (LDHs) and the appearance of an intermediate second staging phase

The hydration of layered double hydroxides (LDHs) was investigated by changing the interlayer anion species, the Mg/Al ratio of the LDH hosts and the relative humidity (RH). The anions were CO₃²⁻, Cl⁻, Br⁻, NO₃⁻, I⁻, SO₄²⁻, and ClO₄⁻ (listed in the order of ion size, small to large) and LDHs with Mg/Al = 1.90 (LDH2) and 2.91 (LDH3) were used. Their XRD profiles were measured by an XRD diffractometer while controlling the RH in the range 0–95% at 25 °C. Only I⁻, SO₄²⁻, and ClO₄⁻ LDH2s and SO₄²⁻ LDH3 showed a large step-wise basal-spacing expansion, 0.24–0.28 nm, under high RH conditions (> ca. 60%) probably due to the insertion of one water layer into the interlayer space. Such hydration occurred more favorably for the LDHs with larger anions and those with a higher layer charge (LDH2). Among them, I⁻ and ClO₄⁻ LDH2s exhibited the second staging – alternate stacking of hydrated (H) and non-hydrated (NH) interlayers – in the intermediate RH region.     

Changes in potassium exchangeability in heated lepidomelane

Changes in the K behavior of lepidomelane were induced by heating samples of the mica. These changes were related to concurrent alterations in the heated mineral to obtain information about the role of mineral properties in the exchangeability of interlayer K. The masking effects of small particles and fixable cations in the extractant were minimized by using 5–10 μm samples and NaCl---NaBPh₄ extracting solutions, respectively. The mica samples were heated in a muffle furnace for different periods at several temperatures between 300° and 950°C before they were characterized in terms of their K release to the NaCl---NaBPh₄ solutions. The effects of these thermal treatments on the Fe²⁺ content, d-spacing and weight of the mica samples were also recorded.The thermal treatments reduced the rate and degree of interlayer K exchange in the lepidomelane. Heat treatments at 300°C had relatively little effect, but the extraction of interlayer K required progressively longer periods when the temperature was increased incrementally to 950°C or the heating period at these higher temperatures was increased. Using the amounts of K extracted in 3 days as an index of the average rate of K release, a close relationship between the K release rate and Fe²⁺ oxidation in the heated mica was shown to exist. At the same time, however, reductions in the sample weight and basal spacing of the mineral occurred and were attributed to dehydroxylation in the heated mica. These changes in basal spacing probably had some effect on the rate with which all the K was released but had a more pronounced effect on the last 30% of interlayer K and finally made this part of the K nonexchangeable. The reduction in maximum extractable K indicates that a portion of the mica layers have a higher charge density. The processes of dehydroxylation and Fe²⁺ oxidation occurred independently in the heated mica and are reflected in the combined effects of basal spacing, layer charge and OH status of the mineral on interlayer K exchange.     

Deep desulphurization of diesel fuels on bifunctional monolithic nanostructured Pt-zeolite catalysts

The preparation of Pt-zeolite catalysts, including choice of the noble metal precursor and loading (1.0–1.8 wt.%), was optimized for maximizing the catalytic activity in thiophene hydrodesulphurization (HDS) and benzene hydrogenation (HYD). According to data obtained by HRTEM, XPS, EXAFS and FTIR spectroscopy of adsorbed CO, the catalysts contained finely dispersed Pt nanoparticles (2–5 nm) located on montmorillonite and zeolite surfaces as: Pt⁰ (main, ν_CO = 2070–2095 cm⁻¹), Pt^δ+ (ν_CO = 2128 cm⁻¹) and Pt²⁺ (ν_CO = 2149–2155 cm⁻¹). It was shown that the state of Pt depended on the Si/Al zeolite ratio, montmorillonite presence and Pt precursor. The use of H₂PtCl₆ as the precursor (impregnation) promoted stabilization of an oxidized Pt state, most likely Pt(OH)_xCl_y. When Pt(NH₃)₄Cl₂ (ion-exchange) was used, the Pt⁰ and hydroxo- or oxy-complexes Pt(OH)₆²⁻ or PtO₂ were formed. The addition of the Ca-montmorillonite favoured stabilization of Pt^+δ. The Cl⁻ ions inhibit reduction of oxidized Pt state to Pt particles. The Pt-zeolite catalyst demonstrated high efficiency in ultra-deep desulphurization of DLCO. The good catalyst performance in hydrogenation activity and sulphur resistance can be explained by the favourable pore space architecture and the location and the state of the Pt clusters. The bimodal texture of the developed zeolite substrates allows realizing a concept for design of sulphur-resistant noble metal hydrotreating catalyst proposed by Song [C. Song, Shape-Selective Catalysis, Chemicals Synthesis and Hydrocarbon Processing (ACS Symposium Series 738), Washington, 1999, p. 381; Chemtech 29(3) (1999) 26].     

Tribological properties of DLC films with different hydrogen contents in water environment

Diamond-like carbon (DLC) films were deposited on silicon wafers by thermal electron excited chemical vapor deposition (CVD). To change the hydrogen content in film, we used three types of carbon source gas (C₇H₈, CH₄, and a CH₄+H₂) and two substrate bias voltages. The hydrogen content in DLC films was analyzed using elastic recoil detection analysis (ERDA). Tribological tests were conducted using a ball-on-plate reciprocating friction tester. The friction surface morphology of DLC films and mating balls was observed using optical microscopy and laser Raman spectroscopy.Hydrogen content in DLC films ranged from 25 to 45 at.%. In a water environment, the friction coefficient and specific wear rate of DLC films were 0.07 and in the range of 10⁻⁸–10⁻⁹ mm³/Nm, respectively. The friction coefficient and specific wear rate of DLC film in water were hardly affected by hydrogen content. The specific wear rate of DLC film with higher hardness was lower than that of film with low hardness. Mating ball wear was negligible and the friction surface features on the mating ball differed clearly between water and air environments, i.e., the friction surface on mating balls in water was covered with more transferred material than that in air.     

Layered double hydroxides pillared by macropolyoxometalates

Pillared derivatives of Mg_1−xAl_x layered double hydroxides (LDHs) were prepared by anion exchange reaction of a synthetic meixnerite precursor, [Mg₃Al(OH)₂](OH), with macromolecular polyoxometalate ions. The intercalated polyoxometalates included the lacunary Dawson ion (α-P₂W₁₇O₆₁)¹⁰⁻, the Finke (Zn₄(H₂O)₂(AsW₉O₃₄)₂)¹⁰⁻ and (WZn₃(H₂O)₂(ZnW₉O₃₄)₂)¹²⁻ ions, the doubled Dawson (P₄W₃₀Zn₄(H₂O)₂O₁₁₂)¹⁶⁻ and the polyoxocryptates (NaSb₉W₂₁O₈₆)¹⁸⁻ and (NaP₅W₃₀O₁₁₀)¹⁴⁻. Anion exchange reaction of [Zn₂Al(OH)₂](NO₃⁻) with (NaP₅W₃₀O₁₁₀)¹⁴⁻ also resulted in a crystalline pillared product. The intercalates exhibited gallery heights up to 16.6 Å and thermal stabilities to 200°C. Nitrogen adsorption/desorption studies for the LDH intercalates showed that access to the gallery micropores was achieved upon POM intercalation. All of the intercalates contained a salt-like impurity phase, as indicated by XRD. The Zn₂Al–(NaP₅W₃₀O₁₁₀)¹⁴⁻ LDH was investigated as a catalyst for the peroxide oxidation of cyclohexene. A comparison of the reactivities of three samples containing different fractions of the salt-like impurity suggested that the impurity phase contributes significantly to the observed activity.     

Thermal and chemical stability of Cu–Zn–Cr-LDHs prepared by accelerated carbonation

Layered double hydroxides Cu_xZn_6 − xCr₂(OH)₁₆(CO₃)·4H₂O with different molar ratios of Cu/Zn/Cr were synthesized by accelerated carbonation. The products were characterized by XRD, SEM, FT-IR and TG-DTG-DSC-MS. The chemical stability was tested by the modified Toxicity Characteristic Leaching Procedure (TCLP). The results showed that the products were the mixture of Cu_xZn_6 − xCr₂(OH)₁₆(CO₃)·4H₂O and (CuZn)₂(CO₃)(OH)₂, with similar thermal behavior. All products were chemically stable with reduced leaching at pH > 6 (Cu²⁺, Zn²⁺) or > 5 (Cr³⁺).     

Mechanistic study of C12 evolution at Ti-supported Co3O4 anodes

Co₃O₄ layers were prepared by thermal decomposition of Co(NO₃)₂ at various temperatures in the range 200–500° C on a Ti support with and without an interlayer of RuO₂. Kinetic studies were carried out with and without dissolved Cl₂ at various partial pressures in NaCl solutions of concentration in the range 0.5–5 mol dm^–3. The effect of the solution pH was especially investigated. Kinetic measurements were carried out both close to and far from equilibrium. The following parameters were determined: transfer coefficient, Tafel slope, stoichiometric number, reaction orders with respect to Cl^–, H⁺ and surface sites, activation energy. The most intriguing feature observed was the retarding effect of acidity on the anodic Cl₂ reaction. This has been ascribed to the complex surface behaviour of oxides in solution. A detailed mechanistic scheme has been proposed and discussed. The stability of the oxide surface was monitored by measuring the voltammetric charge in alkaline solution after sets of experiments.Paper presented at the 34th Meeting of the International Society of Electrochemistry, Erlangen, 19–23 September, 1983.     

Oxidation of catechol and l-ascorbic acid by [Ru(tpy)(pic)(OH)] (tpy = 2,2′6′,2″-terpyridine; pic = picolinate): Kinetic and mechanistic studies

Kinetics of oxidation of catechol (H₂cat) to benzoquinone (BQ) and, ascorbate (HA⁻) to dehydroascorbic acid (A) by [Ru^III(tpy)(pic)(OH)]⁺ (1) (tpy = 2,2’6’,2”-terpyridine; pic⁻ = picolinate) have been studied as function of [H₂cat] (or [HA⁻]), ionic strength (0.01 − 0.25 M), temperature (10–30 °C) at a constant pH = 3.2, using stopped-flow and rapid-scan diode array spetrophotometric techniques. The rate of reaction of 1 with HA⁻ was found to be very fast as compared to that of with H₂cat. The kinetic data and activation parameters are interpreted in terms of an associative interchange mechanism. Analysis of spectral and kinetic data revealed that the reaction of 1 with catechol proceeds by a straightforward outer-sphere electron transfer pathway, whereas, reduction of 1 with HA⁻ involves ion-pair formation.     

Direct formation of H2O2 from H2 and O2 and decomposition/hydrogenation of H2O2 in aqueous acidic reaction medium over halide-containing Pd/SiO2 catalytic system

Formation of H₂O₂ from H₂ and O₂ and decomposition/hydrogenation of H₂O₂ have been studied in aqueous acidic medium over Pd/SiO₂ catalyst in presence of different halide ions (viz. F⁻, Cl⁻ and Br⁻). The halide ions were introduced in the catalytic system via incorporating them in the catalyst or by adding into the reaction medium. The nature of the halide ions present in the catalytic system showed profound influence on the H₂O₂ formation selectivity in the H₂ to H₂O₂ oxidation over the catalyst. The H₂O₂ destruction via catalytic decomposition and by hydrogenation (in presence of hydrogen) was also found to be strongly dependent upon the nature of the halide ions present in the catalytic system. Among the different halides, Br⁻ was found to selectivity promote the conversion of H₂ to H₂O₂ by significantly reducing the H₂O₂ decomposition and hydrogenation over the catalyst. The other halides, on the other hand, showed a negative influence on the H₂O₂ formation by promoting the H₂ combustion to water and/or by increasing the rate of decomposition/hydrogenation of H₂O₂ over the catalyst. An optimum concentration of Br⁻ ions in the reaction medium or in the catalyst was found to be crucial for obtaining the higher H₂O₂ yield in the direct synthesis.     

FTIR analyses of water in MX-80 bentonite compacted from high salinary salt solution systems

The effect of the exchangeable cations on the infrared (IR) spectra of water in MX-80 bentonite compacted from high salinary salt solution systems was studied using self-supporting film and attenuated total reflection (ATR) techniques. Na-bentonite MX-80 was saturated with homo-cationic (NaCl, KCl, CaCl₂ or MgCl₂) or hetero-cationic (mixtures of Na–, K–, Ca– and Mg–chlorides) solutions. The specimens for IR spectroscopy were prepared as self-supporting films (ssf) or compacted pastes. Differences in the wavenumbers and intensities of the structural OH group vibrations in relation to the type of the interlayer cation were found in the spectra of heated ssf. The most pronounced changes were observed for Mg-ssf, while only negligible changes occurred for K-ssf. The absorptions of water in heated Na- and K-ssf showed displacement of the stretching and bending bands to higher and lower wavenumbers, respectively, which indicates decreasing strength of H-bonding between water molecules. In contrast, for Mg-ssf the position of the stretching band of water substantially decreased on heating up to 90 °C followed by an increase upon further heating above 100 °C. The origin of these differences was discussed in terms of variations in the polarising ability of the interlayer cations influencing their hydration number. The ATR spectra of homo-cationic clay-pastes showed that the interlayer cations modify both the position and the intensity of the complex water band near 3400 cm⁻¹. The position decrease and the intensity increase followed the same order: K⁺, Na⁺, Ca²⁺, Mg²⁺. Good correlation between water band position and polarising power of the cations confirmed their influence on the strength of hydrogen bonds between water molecules. Similarly, a systematic shift of the H₂O-stretching band to lower frequencies with the increasing Mg²⁺ content in the samples was observed in the spectra of clay-pastes saturated with hetero-cationic chloride solutions. The intensity of the stretching band of water of both homo- and hetero-cationic pastes correlated very well with the water content obtained gravimetrically.     

Quantitative characterization of the solid acidity of montmorillonite using combined FTIR and TPD based on the NH3 adsorption system

The complete parameters of montmorillonite solid acidity, namely amount, strength, and types of acidity, were determined and the properties of the acid sites after heating were proposed by combining the temperature-programmed desorption (TPD) and Fourier transform infrared spectroscopy (FTIR) based on the NH₃ adsorption system. The total amount of montmorillonite acid sites was 1.15 mmol/g, which was higher than the value obtained by the Hammett indicator method because of the detection of solid acid sites in the montmorillonite interlayer space. These acid sites were composed of 1.00 mmol/g Brønsted and 0.15 mmol/g Lewis acid sites. The acidity of montmorillonite was primarily derived from the interlayer polarized water, Si–OH, H₃O⁺ adsorbed by negatively charged tetrahedral AlO₄, and unsaturated Al^3 + ions, all of which were attributed to the Brønsted acid sites with the exception of the unsaturated Al^3 + ions (Lewis acid sites). Heating led to an increase in the acid strength and the acid amount and altered the type of the partial acid sites. The interlayer polarized water provided more protons after heating at 120 °C and exhibited higher acid strength than that of raw montmorillonite. After heating at 400 °C, the interlayer polarized water acted as very strong acid sites. The H₃O⁺ adsorbed by tetrahedral AlO₄ was attributed to weak-strength acid sites and transformed into Si–O(H)–Al after dehydration, while displaying strong-strength acidity. The unsaturated Al^3 + ions showed medium-strength Lewis acidity, although a portion of these ions adsorbed water molecules and exhibited weak Brønsted acidity. After dehydroxylation at 600 °C, an abundance of unsaturated Al^3 + ions appeared and the amount of Lewis acid sites increased.     

Influence of degree of dehydroxylation on the pozzolanic activity of metakaolin

Three kaolins were heated between 500 and 850 °C. The samples were tested by X-ray diffraction (XRD), differential thermal analysis (DTA), and Infra-Red (IR) spectroscopy in order to determine their mineralogical composition and degrees of crystallinity and dehydroxylation. The reactivity of the heated samples was evaluated by the determination of the residual quantity of Ca(OH)₂ by differential thermal analysis (DTA) performed on hydrated mixtures of 50% metakaolin and 50% Ca(OH)₂. There was no direct relationship between the pozzolanic activity of metakaolin and the degree of dehydroxylation. Highest activity was obtained when the degree of dehydroxylation was > 95%.     

Oxidation-reduction mechanisms in iron-bearing phyllosilicates

Reviewed in this article are the effects of structural Fe oxidation states on the physicochemical properties of smectite clay minerals. Reducing agents selected were dithionite (S₂O₄²⁻), sulfide (S²⁻), thiosulfate (S₂O₃²⁻), hydrazine (N₂H₄), ascorbic acid (C₆H₈O₆), hydroquinone (C₆H₆O₂), and sodium oxalate (Na₂C₂H₂O₄). Clay samples were prepared as aqueous suspensions of < 2 μm particle-size fractions of Na-saturated, freeze-dried ferruginous smectite. The reductive strength of each reducing agent, as determined by measuring the resultant level of Fe(II) in the clay mineral crystal using either a photo-colorimetric method or Mössbauer spectroscopy, decreased in the order S₂O₄²⁻ > S²⁻ > C₆H₈O₆ > S₂O₃²⁻ > C₆H₆O₂ ≈ C₂H₂O₄. The heat of reaction of three of these reducing agents with the clay was measured, and decreased in the order S₂O₄²⁻ > S₂O₃²⁻ > S²⁻. Compared to the order of reductive strength, the heats of reaction with S₂O₃²⁻ and S²⁻ are reversed, suggesting that entropy changes are greater in the S²⁻ treatment. Electron spin resonance (ESR) revealed that free radicals may be responsible for the greatest levels of reductive potential, which provides an important attribute by which potential reducing agents can be screened. Measurements of rheological properties of oxidized and reduced clay suspensions indicated that structural Fe(II) increases the viscosity of clay suspensions as a result of greater attractive forces between clay particles. The type of bonding between particles has yet to be ascertained. Microbial reduction of the clay produces moderate to high levels of reduction and causes changes in physico-chemical properties similar to chemical reduction of the clay.     

Formation of an unusual copper(II) complex from the degradation of a novel tricopper(II) carbohydrazone complex

An unusual copper(II) complex [Cu(L^1a)₂Cl₂] CH₃OH·H₂O·H₃O⁺Cl⁻ (1a) was isolated from a solution of a novel tricopper(II) complex [Cu₃(HL¹)Cl₂]Cl₃·2H₂O (1) in methanol, where L^1a is 3-(2-pyridyl)triazolo[1,5-a]-pyridine, and characterized with single crystal X-ray diffraction study. The tricopper(II) complex of potential ligand 1,5-bis(di-2-pyridyl ketone) carbohydrazone (H₂L¹) was synthesized and physico-chemically characterized, while the formation of the complex 1a was followed by time-dependant monitoring of the UV–visible spectra, which reveals degradation of ligand backbone as intensity loss of bands corresponding to O → Cu(II) charge transfer.     

The effect of bentonite on the interaction of I with PbO

In the long-term disposal of nuclear fuel waste, the radioactive fission product ¹²⁹I requires special attention. This is because of its long half-life (1.7·10⁷ yr), and the fact that it exists in solution as an anion (I⁻ or IO₃⁻) and does not intereact strongly with most geological materials such as clays and rock. Mixtures of bentonite and sand are being evaluated as candidate buffer materials to surround nuclear fuel waste containers in an underground disposal vault in Canada. Since bentonite and sand sorb only minor amounts of I⁻, research is being conducted to identify materials that could be mixed with the buffer material to selectively ‘sorb’ ¹²⁹I⁻, and consequently retard its movement through the buffer after the waste containers are breached. PbO has been proposed as a potential buffer additive, since it has been found to be very effective in removing I⁻ from solution. However, when bentonite is present (≥75 wt% of the total solids) in the PbO/I⁻ system, the amount of I⁻ removed from a solution with an initial I⁻ concentration of 10⁻⁵ mol/l is significantly decreased. On the other hand, kaolinite has little effect. The same phenomenon occurs when bentonite is physically separated from the PbO by a semipermeable membrane. In the PbO/I⁻ system, X-ray diffraction analysis indicates that the Pb phases present are PbO, Pb₃(CO₃)₂(OH)₂, and 7PbO·PbI₂·2H₂O; however, when bentonite is present, 7PbO·PbI₂·2H₂O is not detectable. When bentonite is treated with NaOAc to remove carbonates and then added to the Pb/I⁻ system, the amount of I⁻ released into solution is much less than in the system containing untreated bentonite. Furthermore, the addition of CaCO₃ or a solution of NaHCO₃ to the Pb/I⁻ system causes a release of I⁻ into solution. The data indicate that bentonite affects the stability of 7PbO·PbI₂·2H₂O, shifting the equilibrium between it and Pb₃(CO₃)₂(OH)₂ by increasing the HCO₃⁻ activity in the system (the bentonite contains 0.29% carbonate-C). The results indicate that PbO would not be an effective additive to a buffer material in a nuclear fuel waste disposal vault for the selective removal of ¹²⁹I⁻ from solution.     

Effect of electrolyte addition on activity of (Ga1−xZnx)(N1−xOx) photocatalyst for overall water splitting under visible light

Effects of electrolyte addition on photocatalytic activity of (Ga_1−xZn_x)(N_1−xO_x) modified with either Rh_2−yCr_yO₃ or RuO₂ nanoparticles as cocatalysts for overall water splitting under visible light (λ > 400 nm) are investigated. The cocatalyst Rh_2−yCr_yO₃ is confirmed to selectively promote the photoreduction of H⁺, while RuO₂ functions as both H₂ evolution sites and as efficient O₂ evolution sites. The activity of Rh_2−yCr_yO₃-loaded (Ga_1−xZn_x)(N_1−xO_x) is found to be suppressed in the presence of Cl⁻, which undergoes oxidation by photogenerated holes in the valence band of (Ga_1−xZn_x)(N_1−xO_x). Alkaline- and alkaline earth-metal cations in the reactant solution compensate the negative effect of Cl⁻ to a certain extent depending on the metal cation employed. Among the electrolytes examined, the addition of an appropriate amount of NaCl or A₂SO₄ (A = Li, Na, or K) to the reactant solution without pH control is found to increase activity by up to 75% compared to the case without additives. Direct splitting of seawater to produce H₂ and O₂ is also demonstrated using Rh_2−yCr_yO₃-loaded (Ga_1−xZn_x)(N_1−xO_x) catalyst under visible light.     

Polymeric ternary metal thiols I. Products from reaction of Cu(II) with MoS4

The black, polymeric, product isolated from the reaction of Cu(II) salts with MoS₄²⁻ has been shown to have some unexpected and unusual properties, i.e. a stoichiometry of Cu_1.6MOS₄X_y (X = Cl⁻, Br⁻, y ≈ 1; X = SO₄²⁻, y ≈ 0.5), reduction of the metal centres to Cu(I) and Mo(V), the presence of S radical centres, and the absorption of ca. 2 mol O₂. EXAFS spectra have also been recorded. The W anion WS₄²⁻ behaves identically.