Bo Ram Lee

Precursor Effects of Citric Acid and Citrates on ZnO Crystal Formation

We have studied the precursor effects of citric acid and various citrates-including triethyl citrate, tripotassium citrate, trisodium citrate and triammonium citrate-on the formation of ZnO crystals in alkaline solution. These citrate-related chemicals could be divided into three groups (group A, triethyl citrate; group B, tripotassium citrate and trisodium citrate; and group C, citric acid and triammonium citrate) based on their activity for modifying the ZnO growth direction and solution pH dependency on their concentration. We could obtain ZnO structures with various distinct morphologies by simply changing the concentration of citric acid or citrate additive dissolved in the alkaline reaction solution. On the basis of the results, we propose the growth mechanisms underlying the formation of the various ZnO structures in the absence and presence of citric acid or citrate additives.

Hydrophobic amino acids as a new class of kinetic inhibitors for gas hydrate formation.

As the foundation of energy industry moves towards gas, flow assurance technology preventing pipelines from hydrate blockages becomes increasingly significant. However, the principle of hydrate inhibition is still poorly understood. Here, we examined natural hydrophobic amino acids as novel kinetic hydrate inhibitors (KHIs), and investigated hydrate inhibition phenomena by using them as a model system. Amino acids with lower hydrophobicity were found to be better KHIs to delay nucleation and retard growth, working by disrupting the water hydrogen bond network, while those with higher hydrophobicity strengthened the local water structure. It was found that perturbation of the water structure around KHIs plays a critical role in hydrate inhibition. This suggestion of a new class of KHIs will aid development of KHIs with enhanced biodegradability, and the present findings will accelerate the improved control of hydrate formation for natural gas exploitation and the utilization of hydrates as next-generation gas capture media.

Facile and Fast Synthesis of Single-Crystalline Fractal Zinc Structures through a Solution Phase Reaction and Their Conversion to Zinc Oxide

We report a novel method for the synthesis of fractal Zn structures through a solution phase reaction. An Al-film-deposited substrate was immersed in an aqueous ammonia solution containing Zn ions and maintained at 95 degrees C for 5 min. After the reaction, the Al-deposited side of the substrate was found to be covered with fractal Zn structures. These Zn structures are highly oriented, and the Zn(002) planes are parallel to the substrate. They are single-crystalline and the average thickness of the plates is approximately 50 nm. On the basis of our results, we propose a mechanism for the spontaneous growth of such fractal Zn structures. Single-crystalline fractal ZnO structures can also be obtained by calcination of the as-synthesized fractal Zn crystals at 500 degrees C for 5 h in air. These fractal ZnO structures are highly oriented and inherit their morphologies from the Zn structures.