Formation of needle‐like lepidocrocite fine particles by oxidation of an aqueous suspension of ferrous hydroxide in a bubble column

Extremely fine particles of needle‐like lepidocrocite (γ‐FeOOH) were synthesized by the oxidation of aqueous suspensions of ferrous hydroxide using a bubble column with draft tube at a constant temperature of 30°C, and the effects of the reaction conditions or the oxidation rate were investigated in order to determine the parameters that control the particle size. When the concentration of oxygen in the feed stream was varied under a constant gas velocity, the mean size based on the major axis of a needle‐like particle decreased from 0.7 µm to 0.4 µm with increasing oxidation rate. By adding of NaH2PO4 to an aqueous Fe(OH)2 suspension, in concentrations up to 1.0 mol/m3 during the air oxidation, and up to 0.9 mol/m3 during the oxidation with 30% and 50% O2, the major axis could be reduced to ca. 0.3 µm with the minor axis and the oxidation rate remained almost unchanged.

This study addresses the bacterial inactivation mechanism by photo-Fenton process at near-neutral pH, focusing on iron-oxides and iron-citrate as photocatalysts for solar water disinfection and using E. coli as a bacteria model. Cell envelope damage during bacterial inactivation by photo-Fenton and TiO2 photocatalysis were investing providing evidence for lipid peroxidation and cell permeability. TiO2 photocatalysis induced significant cell membrane damage, in contrast to the photo-Fenton process, but the inactivation kinetics for both disinfection processes was similar. A higher efficiency of photo-generation of reactive oxygen species (ROS) in the presence of TiO2 photocatalyst compared with the photo-Fenton system was observed. The bactericidal effect of Fe3+/hv seems possible due to the adsorption of Fe3+ ions on the bacterial cell wall followed by photosensitization of iron-bacteria exciplexes oxidizing the cell membrane. In contrast, the effect of Fe2+/hv was associated with diffusion into the cell giving raise to intracellular dark Fenton?s reactions. We suggest that cell envelope damage might not necessarily be a unique pathway in bacterial inactivation by photo-Fenton treatment. In particular, the enhancement of an internal (photo)-Fenton process by the synergistic action of UVA and the external Fenton's reactants appears to be an important contribution to bacterial inactivation. Bacterial inactivation by the heterogeneous photo-Fenton process was carried out via iron (hydr)oxide particles, i.e. hematite, goethite, wustite and magnetite. We found that, the iron (hydr)oxides act as photocatalytic semiconductors and catalysts in the heterogeneous photo-Fenton process with the exception of magnetite, which needs H2O2 as electron acceptors. The Hydroxyl radical and superoxide radical were the principal ROS produced by iron (hydr)oxide particles under light in the absence or presence of H2O2. Natural organic matter (NOM) and inorganic substances did not interfere with the photocatalytic semiconducting action of hematite during bacterial inactivation, but enhanced bacterial inactivation mediated by hematite used as the photo-Fenton reagent. Our results demonstrated, for the first time, that low concentration of iron (hydr)oxides (0.6 mg/L) under sunlight, acting both as semiconductors or catalysts of the heterogeneous photo-Fenton process, may serve as a disinfection method for waterborne bacterial pathogens. Bacterial inactivation by the homogeneous photo-Fenton process was carried out using Fe?citrate complex as a source of iron. The efficiency of the homogeneous photo-Fenton process using Fe-citrate complex strongly improved bacterial inactivation as compared with the FeSO4 and goethite as sources of iron. The bacterial inactivation rate increased in the order of goethite < FeSO4 < Fe-citrate, which agreed with the ?OH radicals detected by ESR. Encouraging results were also obtained while applying this treatment for bacterial inactivation in natural water samples at pH 8.5. No bacterial reactivation and/or growth were observed showing that Fe-citrate-based photo-Fenton process efficiently inactivate bacteria using a low iron concentration of Fe-citrate, while avoiding precipitation of ferric hydroxides. The application of the photo-Fenton process at near-neutral pH is a promising technique for bacterial inactivation, due to its simplicity, the use of the sun, the low concentration of reagents and does not produce toxic waste.

Free radicals in atmosphere have played an important role in the atmospheric chemistry. The chloro-Criegee free radicals are produced easily in the decomposition of primary ozonide (POZ) of the trichloroethylene, and can react with O2, NO, NO2, SO2 and H2O subsequently. Then the inorganic salts, polar organic nitrogen and organic sulfur compounds, oxygen-containing heterocyclic intermediates and polyhydroxy compounds can be obtained. The heterogeneous nucleation of oxidation intermediates in the formation of fine particles is investigated using molecular dynamics simulation. The detailed nucleation processes are reported. According to molecular dynamics simulation, the nucleation with a diameter of 2 nm is formed in the Organic Compounds-(NH4)2SO4-H2O system. The spontaneous nucleation is an important process in the formation of fine particles in atmosphere. The model study gives a good example from volatile organic compounds to new fine particles.

Formation of fine drug particle by cogrinding with cyclodextrins: Part II. The influence of moisture condition during cogrinding process on fine particle formation

Behavior of chlorine and sulfur is critical on the formation of fine particles (here particles smaller than one micrometer, PM1.0) during combustion. In this investigation, we studied experimentally fine particle formation in a pilot-scale circulating fluidized bed reactor during combustion of bark and pulp and paper mill sludge. The effect of chlorine and sulfur on fine particle formation was investigated by adding HCl and SO2 into the reactor. Fine fly ash particles were formed from alkali species that were released from the fuel to the gas phase. In low-HCl conditions, alkali species reacted readily with silicates, and therefore, a large fraction of alkalis was retained in the bottom ash. Consequently, fine particle concentrations in the flue gas were relatively low. In this case, fine particles were both alkali metal chlorides and sulfates. HCl addition increased the concentration of fine particles considerably due to gas phase reactions between alkali metal species and HCl. Alkali metal chlorides that were formed condensed producing large mass concentrations of fine alkali metal chloride particles. Due to extensive alkali metal chloride formation, significantly less alkalis reacted with silicates and ended up in the bottom ash than when HCl concentration was low. Further SO2 addition transformed some of the chlorides into sulfates in the fine particle mode. At the same time, the total fine particle concentration decreased, possibly due to formation of coarse mixed K−Ca−sulfate ash particles.

To improve the micromeritical properties of pranlukast (PRK) hydrate, a cogrinding process with cyclodextrin was used, and the formation of fine drug particles was investigated. PRK crystals were ground with either beta-cyclodextrin (beta-CD) anhydrate or beta-CD hydrate crystals at a mixing molar ratio of 2:1 (beta-CD:PRK) to prepare the ground mixtures (GMs). Powder X-ray diffraction measurement and particle size analysis were performed. The two GMs differed from one another in appearance, wettability, and fine particle production. Quantitative determination demonstrated that when the beta-CD hydrate/PRK GM was dispersed in water, 96% of PRK loaded in GM became fine particles smaller than 0.8 microm. In contrast, only 1.4% of PRK in GM transformed to fine particles in the case of beta-CD anhydrate/PRK GM. The PRK fine particles were considered to be dispersed as small crystals. The stability of PRK particles in the aqueous solution was improved by the addition of a water-soluble polymer. Cogrinding with a beta-CD of higher water content can be an effective method to prepare fine drug particles at the submicron level.

In this study, models were used for the first time to investigate the fate and transport of rare earth elements (REE) in the presence of hydrous manganese and ferric oxides in groundwaters from the coastal Bohai Bay (China). Results showed that REE sorption is strongly dependent on pH, as well as hydrous manganese and ferric oxide content. Higher proportions of REE were sorbed by hydrous manganese oxide as compared to hydrous ferric oxides, for example in the presence of neodymium. In this case, a mean 28% of this element was sorbed by hydrous manganese oxide, whereas an average 7% sorption was observed with hydrous ferric oxides. A contrasting REE sorption behavior was observed with hydrous manganese and ferric oxide for all investigated groundwaters. Specifically, REE bound to hydrous manganese oxides showed decreasing sorption patterns with increasing atomic number. The opposite trend was observed in the presence of hydrous ferric oxides. In addition, these results suggested that light REE (from La to Sm) rather than heavy REE (from Eu to Lu) are preferentially scavenged by hydrous manganese oxide. However, the heavy REE showed a greater affinity for hydrous ferric oxides compared to light REE. Therefore, both hydrous manganese and ferric oxide are important scavengers of REE. This study shows the implication of hydrous manganese and ferric oxide sorption for the sink of REE in groundwater.

Reactions of monosilicic acid and boric acid with hydrous oxides of aluminum and iron were studied. Adsorption of B by hydrous iron oxides was satisfactorily described by the Langmuir equation over the range of equilibrium solution concentrations investigated (0–14m M ). Adsorption by hydrous aluminum oxides conformed to the Langmuir equation at equilibrium solution concentrations less than 6m M B. Maximum adsorption of boric acid by aluminum hydrous oxides was found to occur at approximately pH 7.5. Aging freshly precipitated hydrous aluminum and iron oxides up to 12 hours markedly reduced B adsorption; beyond 12 hours the effects of aging diminished. Successive treatments with 1.4m M solutions of Si(OH) 4 were applied to freshly precipitated aluminum‐ and ironhydrous oxides until an apparent saturation was attained. The adsorption of Si followed the Langmuir equation, with maximum adsorption of 2.96 and 2.67 millimoles of Si per gram of aluminum and iron hydrous oxide, respectively. Boric acid at concentrations of 1.85 and 18.5m M were applied to individual samples after each Si(OH) 4 treatment. Aluminum‐ and iron‐Si complexes retained less B as the amount of adsorbed Si on these hydrous oxides increased.

Major concerns about the effects of increasing fossil fuel consumption on the environment and energy security have prompted the development of sustainable and environmentally-friendly energy conversion and storage technologies based on electrochemical processes (e.g. water electrolysers, batteries and supercapacitors). Electrode materials are a key component of these technologies, and high-performance electrode systems are essential for the realization of a clean-energy-based economy. Numerous efforts have been made to develop advanced electrode materials for energy conversion and storage applications. However, current electrode synthesis methods are usually energy-intensive, not environmentally friendly, difficult to scale, or costly to produce. This thesis aims to utilize electrode structure engineering to develop highperformance electrodes based on earth-abundant materials via low-cost, energy-efficient and green synthesis strategies. Further, the applications of these electrodes in various energy conversion and storage applications are explored. Nickel-iron oxides or hydroxides are considered promising electrocatalysts for the oxygen evolution reaction, featuring a high activity and long cycling life in alkaline solution. A room temperature, electroless method has been developed here to grow nickel-iron hydroxides on a nickel foam current collector. The activity of nickel foam for the oxygen evolution reaction can be remarkably enhanced by simply immersing the nickel foam in a ferric nitrate solution at room temperature. During this process, the oxidation of the nickel foam surface by ferric nitrate ions increases the near-surface concentration of hydroxide ions, which results in the in situ deposition of a highly active, amorphous nickel-iron hydroxide layer. This phenomenon is described in Chapter 2 of this thesis. Carbon cloth is a widely-adopted current collector for the fabrication of electrodes. A facile, two-step method has been investigated here to turn commercial carbon cloth into a high-performance electrode for zinc-air batteries. Mild acid oxidation followed by air calcination directly activate carbon cloth to generate uniform, nanoporous and superhydrophilic surface structures with optimized, oxygen-rich functional groups and dramatically increased surface area. This two-step-activated carbon cloth exhibits superior bifunctional oxygen electrocatalytic activity and durability. A rechargeable, flexible zinc-air battery using the activated carbon cloth as a binder-free, flexible air electrode yields a remarkably high peak power density, high flexibility, and good cycling performance, with a small charge-discharge voltage gap. This work is elaborated in Chapter 3. Cost-effective synthesis of large-scale, uniform electrode materials with high activity and cycling stability is challenging. In Chapter 4, a reaction environment confinement strategy for scalable and reproducible production of nanostructured materials is proposed. Nickel foam is simply immersed in metal nitrate aqueous solution, with the volume of solution per unit area of nickel foam kept very low. A precisely designed reactor with a spiral tunnel ensures the same width of solution on each side of the nickel foam. The reaction environment is confined to ensure reproducible and uniform synthesis of nanostructured materials across the Ni foam. This approach has the largest REAVC (ratio of electrode area to precursor volume consumption) value reported so far, 2.0 cm2 mL-1. The synthesized nickel-iron hydroxides/nickel foam electrodes with uniformity in both microstructure and electrochemical properties exhibit remarkable activity for both the oxygen evolution reaction and hydrogen evolution reaction. Manganese oxides are a class of promising electrode materials for high performance supercapacitors. However, not all types of manganese oxides with different phases are electrochemically active, and their crystal structures have a considerable effect on their capacitance. In Chapter 5, a facile strategy is developed for the transformation of manganese oxide from the orthorhombic to birnessite crystal structure. The product exhibits significantly enhanced electrochemical performance as a supercapacitor electrode. This work opens up new possibilities for changing the crystal structure of manganese oxides towards optimized properties in electrochemical applications. This thesis makes significant contributions to our understanding of electrode structure engineering, materials science and electrochemical energy conversion and storage through: (i) designing novel nanostructured nickel-foam-based electrode systems with high electrocatalytic activity towards water oxidation via a simple immersion strategy at ambient temperature; (ii) developing facile activation procedures to endow commercially available, inactive carbon cloth with oxygen-rich functional groups and high oxygen electrocatalytic activity; (iii) controlling ion diffusion in a confined zone for uniform deposition of active materials over large-size electrodes, electrodes useful for various electrochemical applications; (iv) probing the phase transformation of manganese oxides from orthorhombic to birnessite, a material with enhanced electrochemical performance; (v) investigating the growth mechanisms of these advanced electrode materials to understand the origin of their exceptional activity.

Anodic oxidation of ferrous ion on passive iron

Adsorption onto hydrous iron oxide (HIO) was compared as a function of pH for a variety of organophosphorus compounds (OPs), including phosphate esters of ethanolamine, hydroxyamino acids and sugars, phosphonates with methyl and aminoethyl substituents, and nucleotides. The percentage adsorption versus pH curves could be classified into four types according to an empirical rule, viz., that the adsorptivity of OPs depended primarily on the number of unsubstituted P–O moieties in the tetrahedral structure around the P atom of the compound. The rule predicted that a large group of OPs containing more than three unsubstituted P–O moieties should be collected quantitatively by HIO from waters of pH 5.0–6.5. The OPs collected by adsorption onto HIO did not show appreciable degradation during storage for at least 2 weeks. In addition, they could be released from the HIO by using pentane-2,4-dione [acetylacetone (Hacac)] so that they entered a small-volume awueous phase which was derived from the HIO by the following reaction: Fe2O3·nH2O·(OPs)+ 6Hacac → 2Fe(acac)3+(n+ 3)H2O +(OPs). The whole procedure, involving adsorption of OPs onto HIO from a 1 l water sample, separation of the HIO from water by filtration and release of the OPs from the HIO into a 2.5 ml aqueous phase, realized a 400-fold concentration with efficiencies ranging from 45%(for adenosine-5′-triphosphate) to 92%(for 2-aminoethylphosphonate).

The major limitations of the Fenton process are the working pH range (2–5) and the high cost of H2O2. These limitations were unraveled using the Fe2+-air oxidation process, in which ferrous ions were used with continuous aeration without H2O2 at a higher pH (pH = 10). This paper studies the effect of the initial hydrous ferric oxide (HFO) concentration on the Fe2+-air process. The enhancement in degradation of the dye [Reactive Black 5 (RB5)] was observed using the Fe2+-air process in the presence of initial HFO, as compared to the Fe2+-air process in the absence of initial HFO. The enhancement is possibly attributable to the adsorption of ferrous ions, dye, and oxygen onto the HFO surface and leading to effective utilization of reactive oxidizing species. The oxidizing entities appear to be generated during oxidation of adsorbed ferrous ions under oxic conditions—probably on the surface of HFO. Furthermore, the Fe2+-air process in the presence of HFO reduces the concentration of ferrous ions requ...

The prevailing view for aqueous secondary aerosol formation is that it occurs in clouds and fogs, owing to the large liquid water content compared to minute levels in fine particles. Our research indicates that this view may need reevaluation due to enhancements in aqueous reactions in highly concentrated small particles. Here, we show that low temperature can play a role through a unique effect on particle pH that can substantially modulate secondary aerosol formation. Marked increases in hydroxymethanesulfonate observed under extreme cold in Fairbanks, Alaska, demonstrate the effect. These findings provide insight on aqueous chemistry in fine particles under cold conditions expanding possible regions of secondary aerosol formation that are pH dependent beyond conditions of high liquid water.

Bioenergetic challenges of microbial iron metabolisms

The available information regarding the pathways of processes leading to precipitation of iron (hydrous) oxides in aqueous salt solutions is reviewed. The importance of the early hydrolysis stages in determining the nature and the morphology of the solid phases is discussed. In the second part, the phase transformation between various oxides and oxohydroxides in aqueous suspensions is described with emphasis on mechanistic considerations. Such phase transformations may proceed under milder conditions (e.g., at lower temperatures) by a dissolution-recrystallization mechanism than in dry powders, which can also influence the morphology and the size of the resulting particles. A proper control of experimental parameters has resulted in a number of well defined colloidal iron (hydrous) oxides with respect to their composition, structure, morphology, and size.