Ivan S. Cole

Corrosion of zinc as a function of pH

Abstract Anodic and cathodic polarization of zinc was carried out in 0.1 M sodium chloride (NaCl) solution with pH ranging from 1 to 13. The electrochemical data was then contrast to thermodynamic ...

2D WS2/carbon dot hybrids with enhanced photocatalytic activity

Two-dimensional (2D) tungsten disulfide (WS2) nanoflakes were synthesised and hybridised with carbon dots (CDs) using a facile two-step method of exfoliation of bulk tungsten disulphide followed by microwave irradiation of nanoflakes in a solution of citric acid. Physicochemical characterisation indicated that the hybrid consists of graphitic carbon dots with diameters of approximately 2–5 nm, attached to monolayer tungsten disulphide via electrostatic attraction forces. This synthesised hybrid material was investigated for photocatalytic applications. We found that within one hour approximately 30% more of the model organic dye was photodegraded by the hybrid material compared with the pristine 2D WS2. This enhancement was associated to the affinity of the CDs to the organic dye rather than heterojunctioning. Comparisons of the photocatalytic efficacy of this hybrid material with those of recently reported 2D transition metal dichalcogenides and their hybrids showed a significantly higher turnover frequency. Additionally, the presented microwave based synthesis method for developing hybrids of 2D WS2 and CDs, without making significant changes to the base 2D crystal structure and its surface chemistry, has not been demonstrated before. Altogether, the hybrid 2D material provides great potential for photocatalysis applications.

What really controls the atmospheric corrosion of zinc? Effect of marine aerosols on atmospheric corrosion of zinc

Abstract This paper reviews the processes that control the production, transportation and deposition of aerosols and examines how these parameters affect the atmospheric corrosion of zinc on which the aerosols have deposited. The factors that influence the size and chemistry of aerosols are summarised. It is shown that marine aerosols may be acidified through the absorption of gases and strong acids, and that they may attain very low pH values. Aerosol transportation and deposition are size dependent, with aerosol deposition increasing with aerosol size and decreasing with transportation distance. Acidified marine aerosols may be transported to considerable distances from the sources of the acid precursor gases. The review examines the differences in the electrochemical phenomena on zinc surfaces under fine acidified marine or industrial aerosols and under large near neutral aqueous droplets, and shows that the low pH, fine size and high dissolved ionic salt content of the acidified marine aerosols leads to significant oxide dissolution and higher corrosion rates. Acidified marine aerosols disrupt protective oxide films and establish electrochemical cells in which anodic corrosion separation and resistance through the solution are small and oxygen depletion is unlikely. The authors’ analysis shows that the susceptibility of zinc to chloride containing environments may in part be associated with the effect of acidified marine aerosols.

Towards chromate-free corrosion inhibitors: structure–property models for organic alternatives

Progressive restrictions on the use of toxic chromate-based corrosion inhibitors present serious technical challenges. The most critical of these is the lack of non-toxic ‘green’ alternatives that offer comparable performance, particularly on corrosion-prone aluminium alloys such as the 2000 and 7000 series. In this study we used computational modelling methods to investigate the properties of a range of small organic, potentially safer inhibitors and their interactions with technologically relevant alloy surfaces. We have generated robust and predictive computational models of corrosion inhibition for a structurally related data set of organic compounds from the literature. Our studies have correlated molecular features of the inhibitor molecules with inhibition and identified those features that have the greatest impact on experimentally determined corrosion inhibition. This information can be used to drive guided decision making for in silico or experimental screening of molecules for their corrosion inhibition efficiency, while considering more carefully their environmental consequences.

Carbon dots functionalized by organosilane with double-sided anchoring for nanomolar Hg2+ detection

Surface functional groups on carbon dots (CDs) play a critical role in defining their photoluminescence properties and functionalities. A new kind of organosilane-functionalized CDs (OS-CDs) were formed by a low temperature (150°C) solvothermal synthesis of citric acid in N-(β-aminoethyl)-γ-aminopropylmethyl-dimethoxysilane (AEAPMS). Uniquely, the as-synthesized OS-CDs have dual long chain functional groups with both NH2 and Si(OCH3)3 as terminal moieties. Double sided anchoring of AEAPMS on CDs occurs, facilitated by the water produced (and confined at the interface between CDs and solvent) when citric acid condenses into the carbon core. The resultant OS-CDs are multi-solvent dispersible, and more significantly, they exhibit excellent selectivity and sensitivity to Hg(2+) with a linear detection range of 0-50 nM and detection limit of 1.35 nM. The sensitivity and selectivity to Hg(2+) is preserved in highly complex fluids with a detection limit of 1.7 nM in spiked 1 M NaCl solution and a detection limit of 50 nM in municipal wastewater effluent. The results show that the OS-CDs synthesised by the solvothermal method in AEAPMS may be used as an effective Hg(2+) sensor in practical situations.

Pitting Corrosion of Zn and Zn-Al Coated Steels in pH 2 to 12 NaCl Solutions

Corrosion behavior of hard zinc, Zn-5% Al (Galfan), and Zn-55% Al alloy (Zincalume or Galvalume) coated steels was studied using cyclic voltammetry and potential scan/hold technique in the presence of 0.10-0.90 mol L -1 NaCl over a pH range of 2 to 12. Influence of chloride concentration and electrolyte pH on pitting potential values of the above three types of specimens were examined. On the basis of the electrochemical, scanning electron microscopy with energy dispersive X-ray spectroscopy, and chemical equilibria data obtained from hard zinc, a pitting corrosion mechanism involving a series of processes from anion competitive adsorption to penetration to nucleation and growth was proposed.

Photoluminescence enhancement of carbon dots by gold nanoparticles conjugated via PAMAM dendrimers

Carbon dots (CDs) have many fascinating fluorescent properties, however, their low quantum yield limits their applications. In this study, the photoluminescence (PL) of CDs in the vicinity of gold nanoparticles (Au NPs) is enhanced significantly due to the surface plasmon resonance (SPR) of the Au NPs. This is achieved by conjugating Au NPs and CDs to dendrimers (PAMAM) through an amidation reaction, resulting in the formation of the Au-PAMAM-CD conjugates. The maximum 62-fold enhancement was obtained with an optimized molar ratio between Au NPs, PAMAM, and CDs. In this process, PAMAM, which serves as a spacer, can keep Au NPs and CDs at an appropriate distance for PL enhancement. The adjustment of the amount of Au NPs or CDs linked to PAMAM can induce the optimum PL enhancement. This strategy can be easily applied to different metal-space-fluorophore systems to enhance the fluorescence of fluorophores.

The toxicity of graphene quantum dots

Recently, there has been a rapidly expanding interest in a new nano material, graphene quantum dots, owing to its profound potential in various advanced applications. Despite its exciting application outlook, the toxicology of the material has to be well addressed before its practical use in the highly prospective areas – especially for bio-applications such as bio-sensing, bio-imaging and nanomedicine (e.g. drug delivery). This review provides a comprehensive account of the current research status regarding the toxicity of graphene quantum dots (GQDs), including raw GQDs, chemically doped GQDs and chemically functionalized GQDs. It summarises the existing tests on both in vivo and in vitro toxicity. Important topics including the uptake mechanism by cells and parameters governing the toxicity of GQDs (such as concentration, methods of synthesis, particle size, surface chemistry and chemical doping) are discussed. It also covers demonstrations on toxicity regulation of GQDs via chemical modification, as a toxicity mechanism via generation of reactive oxygen species (ROS) by some GQDs is also evident. Based on the evaluation of the current research status, possible future perspectives are also suggested.

Using Fourier transform Infrared analysis to detect corrosion products on the surface of metals exposed to atmospheric conditions

Abstract Fourier transform Infrared (FTIR) analysis was applied to characterize the surface of atmospherically exposed metal plates. Early stages of atmospheric corrosion result information of corrosion films. Corrosion films are made up of layers of corrosion products initially caused from chemical reactions between the metal substrate and adsorbed gases and then by reactions between corrosion products and adsorbed gases. A protocol was developed for analysis of corrosion films in situ on zinc-galvanized and 55% Al-Zn surfaces. Using a variable angle reflectance accessory, modeling, and cautious interpretation, functional groups were deduced from IR absorbance spectra. The fingerprint region of the mid-IR was interpreted to postulate the effect of orientation and structure of key functional groups that made up part of the corrosion product. Efforts were made to assign bands in the region of < 600 cm−1. Corrosion products based on a layer structure composed of metal hydroxides with metal chlorides or meta...

Aqueous Corrosion Testing and Neural Network Modeling to Simulate Corrosion of Supercritical CO2 Pipelines in the Carbon Capture and Storage Cycle

A database was constructed from tests in aqueous electrolytes simulating the damage that may occur to ferrous transport pipelines in the carbon capture and storage (CCS) process. Temperature and concentrations of carbonic acid (H2CO3), sulfuric acid (H2SO4), hydrochloric acid (HCl), nitric acid (HNO3), sodium nitrate (NaNO3), sodium sulfate (Na2SO4), and sodium chloride (NaCl) were varied; the potentiodynamic polarization response, along with physical damage from exposure, was measured. Sensitivity analysis was conducted via generation of fuzzy curves, and a neural network model also was developed. A correlation between corrosion current (icorr) and exposure tests (measured in the form of weight and thickness loss) was observed; however, the key outcome of the work is the presentation of a model that captures corrosion rate as a function of environments relevant to (CCS) pipeline, revealing the extent of the threat and the variables of interest.