The effect of free chlorine and monochloramine on lead in drinking water and epitaxial electrodeposition of tin sulfide

Electrochemical deposition is utilized in various electronic and photovoltaic applications and in the protective coating industries. This dissertation primarily addresses the environmental aspects of electrochemical deposition. In the first part of this study, Pb dissolution in drinking water was investigated in the presence of two disinfectants: free chlorine (in the form of HOCI/OCr) and monochloramine (NH₂Cl). In the second part of this study, epitaxial SnS nanodisks were electrodeposited onto a Au(100) substrate. Water utility systems use either free chlorine or monochloramine in their disinfection program. Whereas free chlorine reacts with natural organic matter in the water to produce halogenated organic byproducts that are suspected to be carcinogens, NH₂Cl, a weaker oxidant, may lead to elevated Pb levels in drinking water. Thermodynamically, NH₂Cl is capable of oxidizing Pb and Pb²⁺ species to PbO₂, which is a stable and insoluble oxide of Pb and should minimize the Pb dissolution. However, experimental results utilizing EQCM, XRD, and SEM show that NH₂Cl elevated Pb levels in water by oxidizing Pb or reducing PbO₂ films to soluble Pb²⁺ species. The solubility of PbO₂ in NH₂Cl increases if the concentration of NH₂Cl increases or the pH of the water decreases from pH 10 to pH 7. Epitaxial films of Δ-SnS were deposited electrochemically on single-crystal Au(100) surfaces from an acidic solution at 70°C. The films grew with [100] and [301] out-of-plane orientations and four equivalent in-plane orientations. For the SnS(100) orientation, the in-plane mismatch was 2.4% in the [010] direction and 6.1% in the [001] direction. For the (301) orientation, the in-plane mismatch was 2.4% in the [010] direction and 3.4% in the [103] direction. SEM images of the deposit show a disk-like morphology with a diameter of 300 nm and a thickness of 50 nm --Abstract, page iv

Geopolymer Development by Powders of Metakaolin and Wastes in Thailand

Geopolymer has been developed as an alternative material to Portland cement. Geopolymer is based on the polymerization of alkaline activation and oxide of silicon and aluminium. These oxides can be found in many pozzolanic materials such as metakaolin and the wastes from industries and agricultures in Thailand, e.g., fly ash, bagasse ash and rice husk ash. Pozzolanic materials were selected as source materials for making geopolymers into 4 different types. Sodium hydroxide concentration of 10 Molar (10MNaOH) and sodium silicate (Na2SiO3) solutions were used as alkaline activators by the mass ratio of Na2SiO3/NaOH at 1.5. The mixtures were cast in 25×25×25 mm. cubes. After casting, the geopolymers were cured at 80๐C for 24 hrs. in an oven and then at room temperature for 7 days. The pozzolanic materials effects, the Si/Al molar ratio and the Na/Al molar ratio were studied and characterized. An X-ray fluorescence (XRF) was chosen to determine the percentages of silica and alumina in order to verify the proper ratio of the fly ash, Rice husk ash, Bagasse ash and Metakaolin.The study also included the impact on mechanical and physical properties such as compressive strength, water absorption, density and porosity

Electrochemistry of Free Chlorine and Monochloramine and Its Relevance to the Presence of Pb in Drinking Water

The commonly used disinfectants in drinking water are free chlorine (in the form of HOCl/OCl-) and monochloramine (NH2Cl). While free chlorine reacts with natural organic matter in water to produce chlorinated hydrocarbon byproducts, there is also concern that NH2Cl may react with Pb to produce soluble Pb(II) productsleading to elevated Pb levels in drinking water. In this study, electrochemical methods are used to compare the thermodynamics and kinetics of the reduction of these two disinfectants. The standard reduction potential for NH2Cl/Cl- was estimated to be +1.45 V in acidic media and +0.74 V in alkaline media versus NHE using thermodynamic cycles. The kinetics of electroreduction of the two disinfectants was studied using an Au rotating disk electrode. The exchange current densities estimated from Koutecky−Levich plots were 8.2 × 10-5 and 4.1 × 10-5 A/cm2, and by low overpotential experiments were 7.5 ± 0.3 × 10-5 and 3.7 ± 0.4 × 10-5 A/cm2 for free chlorine and NH2Cl, respectively. The rate constant for the electrochemical reduction of free chlorine at equilibrium is approximately twice as large as that for the reduction of NH2Cl. Equilibrium potential measurements show that free chlorine will oxidize Pb to PbO2 above pH 1.7, whereas NH2Cl will oxidize Pb to PbO2 only above about pH 9.5, if the total dissolved inorganic carbon (DIC) is 18 ppm. Hence, NH2Cl is not capable of producing a passivating PbO2 layer on Pb, and could lead to elevated levels of dissolved Pb in drinking water

Epitaxial Electrodeposition of Tin(II) Sulfide Nanodisks on Single-crystal Au(100)

Epitaxial nanodisks of tin(II) sulfide (SnS) are deposited electrochemically on a [100]-oriented single-crystal Au substrate from an acidic solution at 70 °C. The SnS grows with two different out-of-plane orientations of [100] and [301], which each have four equivalent in-plane orientations. X-ray pole figures reveal the following epitaxial relationships: SnS(100)[010]//Au(100)[010], SnS(100)[010]//Au(100)[01̅0], SnS(100)[010]//Au(100)[001], SnS(100)[010]//Au(100)[001̅], SnS(301)[010]//Au(100)[010], SnS(301)[010]//Au(100)[01̅0], SnS(301)[010]//Au(100)[001], and SnS(301)[010]//Au(100)[001̅]. For the SnS[100] orientation, the in-plane mismatch is −2.4% in the [010] direction and 6.1% in the [001] direction. For the [301] orientation, the in-plane mismatch is −2.4% in the [010] direction and alternates between 3.4% and 6.7% in the [103̅] direction. The SnS deposits with a disklike morphology with a diameter of 300 nm and a thickness of 50 nm

Evidence That Monochloramine Disinfectant Could Lead to Elevated Pb Levels in Drinking Water

Many water districts have recently shifted from free chlorine (in the form of HOCl/OCl-) to monochloramine (NH2Cl) as a disinfectant for drinking water to lower the concentration of chlorinated hydrocarbon byproducts in the water. There is concern that the use of NH2Cl disinfectant may lead to higher Pb levels in drinking water. in this study, the electrochemical quartz crystal microbalance is used to compare the effects of these two disinfectants on the dissolution of Pb films. a 0.5 m thick Pb film nearly completely dissolves in a NH2Cl solution, but it is passivated in a HOCl/OCl- solution. X-ray diffraction analysis shows that the NH2Cl oxidizes Pb to Pb(II) species such as Pb3(OH)2(CO3)2, whereas the stronger oxidant, HOCl/OCl-, oxidizes Pb to Pb(IV) as an insoluble PbO2 conversion coating. Although NH2Cl may produce less halogenated organic byproducts than HOCl/OCl- when used as a disinfectant, it may lead to increased Pb levels in drinking water

Enantiospecific Electrodeposition of Chiral CuO Films from Copper(II) Complexes of Tartaric and Amino Acids on Single-Crystal Au(001)

Chiral films of CuO were electrochemically deposited onto achiral Au(001) using chiral precursors such as tartaric acid and the amino acids alanine and valine to complex the Cu(II). The chirality of the electrodeposited films was dictated by the chiral solution precursor. X-ray diffraction pole figures and azimuthal scans, in conjunction with stereographic projections, were used to determine the absolute configuration and enantiomeric excess of the chiral CuO films. CuO films grown from L-tartaric acid have a (1) orientation with an enantiomeric excess of 95%, while the films grown from D-tartaric acid have a (11) orientation with an enantiomeric excess of 93%. CuO films grown from chiral amino acids have two types of chiral orientations, each showing lower enantiomeric excess compared with the films deposited from tartaric acid. The films grown from L-alanine and L-valine solution have an excess of the (11) and () orientations, while the films grown from D-alanine and D-valine have an excess of (1) and (111). Films of CuO deposited from a solution of achiral glycine consist of a racemic mixture of the (11) and (1) orientations. Chiral CuO films deposited on both single-crystal Au(001) and polycrystalline Au films were shown to exhibit chiral recognition for the electrochemical oxidation of tartaric acid