This manuscript explains the effective determination of urea by redox cyclic voltammetric analysis, for which a modified polypyrrole-graphene oxide (PPY-GO, GO 20% w/w of PPY) nanocomposite electrode was developed. Cyclic voltammetry measurements revealed an effective electron transfer in 0.1 M KOH electrolytic solution in the potential window range of 0 to 0.6 V. This PPY-GO modified electrode exhibited a moderate electrocatalytic effect towards urea oxidation, thereby allowing its determination in an electrolytic solution. The linear dependence of the current vs. urea concentration was reached using square-wave voltammetry in the concentration range of urea between 0.5 to 3.0 μM with a relatively low limit of detection of 0.27 μM. The scanning electron microscopy was used to characterize the morphologies and properties of the nanocomposite layer, along with Fourier transform infrared spectroscopy. The results indicated that the nanocomposite film modified electrode exhibited a synergistic effect, including high conductivity, a fast electron-transfer rate, and an inherent catalytic ability.

This study is carried out to obtain basic data regarding oxidation and reduction reactions, originated on the recycling of waste tungsten hard scraps by oxidation and reduction processes. First, it is estimated that the theoretical Gibbs free energy for the formation reaction of WO2 and WO3 are calculated as ΔG1,000K= -407.335 kJ/mol and ΔG1,000K = -585.679 kJ/mol, from the thermodynamics data reported by Ihsan Barin. In the experiments, the oxidation of pure tungsten rod by oxygen is carried out over a temperature range of 700-1,000oC for 1 h, and it is possible to conclude that the oxidation reaction can be represented by a relatively linear relationship. Second, the reduction of WO2 and WO3 powder by hydrogen is also calculated from the same thermodynamics data, and it can be found that it was difficult for the reduction reaction to occur at 1,027oC, in the case of WO2, but it can happen for temperatures higher than 1127oC. On the other hand, WO3 reduction reaction occurs at the relatively low temperature of 827oC. Based on these results, the reduction experiments are carried out at a temperature range of 500-1,000oC for 15 min to 4 h, in the case of WO3 powder, and it is possible to conclude that the reduction at 900oC for 2h is needed for a perfect reduction reaction.

Catalytic reduction and oxidation of NO over polyacrylonitrile based activated carbon fibers (PAN-ACF) under various conditions were carried out to develop removal process of NO from the flue gas. The effect of temperature, oxygen concentration and the moisture content for the reduction of NO with ammonia as a reducing agent was investigated. The reduction of NO increased with the oxygen concentration, but decreased with the increased temperature. The moisture content in the flue gas affects the reduction of NO as the inhibition of the adsorption of the other components and the reaction on the surface of ACE For the oxidation of NO to NO2 over PAN-ACF without using a reducing gas, it showed the temperature and the oxygen concentration of the flue gas are the important factors for the NO conversion in which the conversion increased with oxygen concentration and decreased with the temperature increase and might be the alternative option for the selective catalytic reduction process.

In this study, the applicability of reduction-oxidation-linked treatment was evaluated for nitrobenzene and a by-product by analyzing the reaction kinetics. Nitrobenzene showed very low reactivity to persulfate that was activated using various methods. Nitrobenzene effectively reacted through the reduction process using Zero-Valent Iron (ZVI). However, aniline, a toxic substance, was produced as a by-product. Reduction-oxidation-linked treatment is a method that can allow the oxidative degradation of aniline after reducing nitrobenzene to aniline. The experimental results show improved reactivity and complete decomposition of the by-product. Improved reactivity and decomposition of the by-product were observed even under conditions in which the reduction-oxidation reaction was induced simultaneously. No activator was injected for persulfate activation in the process of reducing oxidant linkage, and the activation reaction was induced by ferrous iron eluted from the ZVI. This indicates that this method can be implemented relatively simply.

The re-emission of mercury (Hg), as a consequence of the formation and dissociation of the unstable complex HgSO3, is a problem encountered in flue gas desulphurization (FGD) treatment in coal-fired power plants. A model following a pseudo-second-order rate law for Hg2+ reduction was derived as a function of [SO32-], [H+] and temperature and fitted with experimentally obtained data to generate kinetic rate values of (0.120 ± 0.04, 0.847 ± 0.07, 1.35 ± 0.4) mM-1 for 40°, 60°, and 75℃, respectively. The reduction of Hg2+ increases with a temperature increase but shows an inverse relationship with proton concentration. Plotting the model-fitted kinetic rate constants yields ΔH = 61.7 ± 1.82 kJ mol-1, which is in good agreement with literature values for the formation of Hg0 by SO32-. The model could be used to better understand the overall Hg2+ re-emission by SO32- happening in aquatic systems such as FGD wastewaters.

This study examined the treatment characteristics of hard-to-degrade pollutants such as TCE which are found in organic solvent and cleaning wastewater by nZVI that have excellent oxidation and reduction characteristics. In addition, this study tried to find out the degradation characteristics of TCE by Fenton-like process, in which H2O2 is dosed additionally. In this study, different ratios of nZVI and H2O2, such as 1.0 mM : 0.5 mM, 1.0 mM : 1.0 mM, and 1.0 mM : 2.0 mM were used. When 1.0 mM of nZVI was dosed with 1.0 mM of H2O2, the removal efficiency of TOC was the highest and the first order rate constant was also the highest. When 1mM of nZVI was dosed with 0.5 mM of H2O2, the first order rate constant and removal efficiency were the lowest. The size of first order rate constant and removal efficiency was in the order of nZVI 1.0 mM : H2O2 1.0 mM ＞ nZVI 1.0 mM : H2O2 2.0 mM ＞ nZVI 1.0 mM : H2O2 0.5 mM ＞ H2O2 1.0 mM ＞ nZVI 1.0 mM. It is estimated that when 1.0 mM of nZVI is dosed with 1.0 mM of H2O2, Fe2+ ion generated by nZVI and H2O2 react in the stoichiometric molar ratio of 1:1, thus the first order rate constant and removal efficiency are the highest. And when 1.0 mM of nZVI is dosed with 2.0 mM of H2O2, excessive H2O2 work as a scavenger of OH radicals and excessive H2O2 reduce Fe3+ into Fe2+. As for the removal efficiency of TOC in TCE by simultaneous dose and sequential dose of nZVI and H2O2, sequential dose showed higher first order reaction rate and removal efficiency than simultaneous dose. It is estimated that when nZVI is dosed 30 minutes in advance, pre-treatment occurs and nanoscale Fe0 is oxidized to Fe2+ and TCE is pre-reduced and becomes easier to degrade. When H2O2 is dosed at this time, OH radicals are generated and degrade TCE actively.

토양 하부 및 지하수에 생존하고 있는 미생물들이 지하수의 산화/환원전위 변화에 관여하는 사실을 알아보기 위해 미생물들을 주입한 수용액의 시간별 Eh 변화량을 측정하였다. 황산염환원 미생물이 주입된 경우 수용액의 Eh값이 5일 만에 -120 mV에서 -500 mV까지 떨어졌으며, 실험 결과 디설프리칸스 세균이 불가리스 세균보다 수용액을 환원하는 능력이 상대적으로 좋았다. 철환원 미생물인 스와넬라 세균의 경우 Eh값이 황산염환원 세균보다 조금 높은 -400 mV를 보여 주었다. 금속환원미생물에 의해 수용액의 Eh값이 떨어지는 동안 용존 황산염 혹은 산화철이 환원되고 맥키나와이트(FeS)라는 황화광물이 형성되기 시작하였다. 이러한 실험 결과를 바탕으로 일반 지하수의 산화/환원전위는 그 지하수에 생존하고 있는 지하미생물들의 대사 활동에 많은 영향을 받고 있다는 사실과 극환원된 지하수 및 생기원 황화광물들이 풍부한 지하 환경은 산화 핵종들이 환원된 형태로 침전되어 핵종 이동이 억제될 가능성이 높은 곳으로 판단된다.