Junshe Zhang

Adsorption of surfactants on two different hydrates.

The interaction between surfactants and hydrates provides insight into the role of surfactants in promoting hydrate formation. This work aims at understanding the adsorption behavior of sodium dodecyl sulfate (SDS) on cyclopentane (CP) hydrates and its derivative surfactant on tetrabutylammonium bromide (TBAB) hydrates. Cyclopentane (CP) is a hydrophobic former whereas tetrabutylammonium bromide (TBAB) is a salt that forms semiclathrate hydrates. The adsorption on these two hydrates was studied by zeta potential and pyrene fluorescence measurements. CP hydrates have a negative surface charge in the absence of SDS, and it decreases to a minimum as the SDS concentration increases from 0 to 0.17 mM. Then, it increases with further increased SDS concentration. The adsorption density of DS (-) on CP hydrates reaches a saturated value at 1.73 mM SDS. The micropolarity parameter of the TBAB hydrate/water interface starts to increase rapidly at 0.17 mM SDS and levels off at 1.73 mM SDS. The presence of Br (-) in TBAB hydrate suspensions could compete with TBADS (from association of DS (-) and TBA (+)) and DS (-) for the adsorption on the hydrate surface, but they have a much stronger affinity for the hydrates than does Br (-). From the fluorescence measurements, it was found that the micropolarity of the hydrate/water interface is mainly dependent on the polarity of hydrate formers.

Competitive adsorption between SDS and carbonate on tetrahydrofuran hydrates

Sodium dodecyl sulfate (SDS) has been well known as a promoter for the formation of hydrates. However, the use of SDS to enhance the formation of CO(2) hydrates has not been effective. This work will present an idea of competitive adsorption that will provide insights into the nonpromoting effect of SDS under high carbonate concentrations. The competitive adsorption is studied between DS(-) monomers and carbonate ions on tetrahydrofuran (THF) hydrates. The adsorption is qualitatively investigated by using pyrene fluorescence measurements. The SDS concentration at which hydrophobic domains occur on the hydrate surface increases with the increased carbonate concentration and this trend is less dependent on the order of addition of these two species. This concentration is 0.17 mM at carbonate concentrations less than 2 microM and it shifts to 3.47 mM at carbonate concentrations higher than 2.5 microM. Thus, using carbonate with its concentration higher than 2.5 microM would be enough to displace the hydrophobic domains formed by SDS up to the solubility limit.

Investigations of surfactant effects on gas hydrate formation via infrared spectroscopy

This infrared (IR) spectroscopic study addresses surfactant effects on cyclopentane (CP) hydrate-water interfaces by observing both ice-like (3100 cm(-1)) and water-like (3400 cm(-1)) bands in the bonded OH region together with free OH bands. IR spectroscopy of hydrates has not been actively employed due to the overwhelming signal saturation of the OH bonding. However, this work is able to utilize this large signal of the OH bonding to understand the water structure changes upon adding sodium dodecyl sulfate (SDS) to CP hydrate-water interfaces. The spectral data suggest a change to more ice like (3100 cm(-1)) features starting from 100 ppm to 750 ppm SDS, indicating favorable nucleation. At the same instance, water like (3400 cm(-1)) features are also shown in this range of SDS concentration, which suggests looser hydrogen bonding that is an indicator for facilitating hydrate growth. Additionally, this ATR-IR study firstly identifies both symmetric and anti-symmetric free OH bands of the hydrogen bond (HB) acceptors in the clathrate hydrate system. Relative area ratios of free and bonded OH bands provide important information about spatial arrangements of adsorbed SDS monomers.

Boron-doped carbon–iron nanocomposites as efficient oxygen reduction electrocatalysts derived from carbon dioxide

Developing cost-effective oxygen reduction reaction (ORR) catalysts is pivotal for development of fuel cells. While Fe-N-C catalysts were proposed for ORR, Fe-B-C catalysts have not been explored. This work introduces the B-doped carbon catalysts encapsulating iron cores using CO2 as a carbon source. The Fe-B-C catalysts show enhanced ORR activity and durability due to the iron core within the graphitic layers.

Boron-doped electrocatalysts derived from carbon dioxide

This work addresses the derivation of active electrocatalysts using carbon dioxide (CO2) as a carbon source. CO2 is converted to boron-doped porous carbon (B-PC) with sodium borohydride as a reduction agent at ambient pressure and 500 °C. Further activation of the BPC using the thermal treatment in the presence of NaBH4 greatly enhances its catalytic activity for oxygen reduction reaction (ORR). The treated B-PC has ORR activity comparable to a Pt-activated carbon (Pt-AC) catalyst but it shows better ORR selectivity. The improvement of electrocatalytic performance is not originated from the carbon morphology change but comes from the change of surface boron bonds with carbon atoms and the widened π state. The synthesis of B-PC from CO2 under mild conditions and the application of the derived B-PC to the fuel cell electrode might be one feasible way of numerous sustainable CO2 utilization practices.

Progress and prospects in thermolytic dehydrogenation of ammonia borane for mobile applications

Using hydrogen as a transportation fuel has been attracting considerable interest due to zero carbon emissions from vehicles. Storing hydrogen compactly, safely and affordably remains a major scientific and technological challenge in on-board applications. Over the past decade, significant efforts have been made in developing solid-state hydrogen storage techniques. Among the chemical storage materials, ammonia borane is one most promising candidate because it has a high hydrogen density of 19.6 wt% and it is a non-flammable and non-explosive crystalline compound at ambient conditions. Hydrogen can be extracted from ammonia borane via thermolysis, hydrolysis, hydrothermolysis, and methanolysis. This review covers various approaches and prospects of facilitating thermolysis, along with a brief discussion of the nature of ammonia borane and the regeneration of spent fuel.

Adsorption of sodium dodecyl sulfate onto clathrate hydrates in the presence of salt

This work presents the effect of NaCl on the adsorption of sodium dodecyl sulfate (SDS) at the cyclopentane (CP) hydrate-water interface. The adsorption isotherms and the SDS solubility in NaCl solutions are obtained using liquid-liquid titrations. The solubility data are determined at typical hydrate forming temperatures (274-287 K) to ensure that the adsorption isotherms are obtained within SDS solubility limits in NaCl solutions. The isotherms show L-S (Langmuir-Step) type behaviors with 1mM and 10mM NaCl solutions while L type isotherm is determined for 25 mM NaCl solutions due to the low SDS solubility in this salt concentration. Zeta potentials of CP hydrate particles in the aqueous solutions support the shape of the adsorption isotherm with the 1mM NaCl solution. The 1mM NaCl case shows the highest SDS adsorption amount among the cases with 0 mM, 10 mM, and 25 mM NaCl solutions. In this case, the competition for adsorption between Cl(-) and DS(-) is not as strong compared to the 10 and 25 mM NaCl cases and the presence of Na(+) ions may reduce the repulsion between DS(-) ions, which results in a higher adsorption of DS(-) ions and enhanced enclathration.