Flexible supercapacitors (FS) are ideal as power backups for upcoming stretchable electronics due to their high power density and good mechanical compliance. However, lacking technology for FS mass manufacturing is still a significant obstacle. The present study describes a novel method for preparing FS based on reduced graphene oxide (RGO) using the N+ plasma technique, in which N+ reduces graphene oxide on the surface of a cotton/polyester substrate. The effect of aloe vera (AV) as a natural reducing & capping agent and carbon nanotubes (CNT) as nanoconductors on the electrochemical performance of the electrodes is studied. FESEM and XPS were employed to investigate the electrodes' structural and chemical composition of electrodes. The galvanostatic charge–discharge curves of electrodes revealed the enhancement of the electrochemical activity of the as-prepared electrode upon additions of AV and CNT. The areal capacitance of the RGO, RGO/AV, and RGO/ AV/CNT supercapacitors at 5 mV/s was 511, 1244.5, and 1879 mF/cm2, respectively. The RGO electrode showed capacitive retention of 80.9% after 2000 cycles enhanced to 89.7% and 92% for RGO/AV and RGO/AV/CNT electrodes, respectively. The equivalent series resistance of the RGO electrode was 126.28 Ω, decreased to 56.62 and 40.06 Ω for RGO/AV and RGO/ AV/CNT electrodes, respectively.

Thermal reduction of graphite oxide (GO) is considered as a prospective method for the preparation of high-performance graphene-based materials. However, this method has certain limitations, and the major is that this exothermic process is difficult to control. In this research, we focused on the kinetic studies of the reduction of graphite oxide using non-isothermal differential calorimetry (DSC) method. Six GO nanocomposites with dyes were tested to study the shift in kinetic parameters. The apparent reaction order is determined to be ca 0.7 for the thermal decomposition of pure GO, while in the presence of dye molecules it increases sometimes reaching a value of 2.0 for higher dye concentrations. Decisively, the thermal decomposition of pure GO can be presented as an intermediate between a zero- and first-order reaction, while the introduction of dye molecules turns a certain part of the energy consumption via the bimolecular pathway. Our research revealed that the process of GO thermal decomposition can be operated and properties of the final product (reduced graphene oxide (rGO) and its derivatives) can be adjusted more precisely using additive molecules, which interact with GO sheets.

PURPOSES : The purpose of this study was to analyze the effect of reducing nitrogen oxide concentration in a photocatalyst (titanium dioxide) using statistical methods such as the Anderson-Darling test. METHODS : To compare and analyze the effect of reducing the nitrogen oxide concentrations in titanium dioxide, titanium dioxide was applied to the public road, and data acquisition in terms of nitrogen oxide concentration was conducted from roads with/without applying titanium dioxide (test section and reference section, respectively). Then, the probabilities of occurrence of nitrogen oxide concentrations in the test and reference sections were estimated and compared using the Anderson-Darling test. RESULTS : According to the comparison and analysis of probabilities in the nitrogen oxide concentration of the test and reference sections, the probabilities of nitrogen oxide concentration on December 4th were estimated as ‘High’ (17.5%, 37.9%), ‘Moderate’ (30.5%, 40.8%), and ‘Low’ (52.0%, 21.3%), respectively, and on December 5th, as ‘High’ (20.6%, 39.1%), ‘Moderate’ (26.2%, 33.0%), and ‘Low’ (53.2%, 27.9%), respectively. In addition, the probabilities of nitrogen oxide concentration in the test and reference sections were analyzed on December 6th as ‘High’ (16.5%, 36.8%), ‘Moderate’ (27.9%, 38.5%), and ‘Low’ (55.6%, 24.8%), respectively. CONCLUSIONS : Based on the results of this study, in the test section with application of titanium dioxide, the nitrogen oxide concentration was found to have a low probability, and in the reference section, the nitrogen oxide concentration was found to be higher than that in the test section. Therefore, it can be concluded that titanium dioxide applied to road facilities has a nitrogen oxide reduction effect.

PURPOSES : This study analyzes the characteristics of nitrogen oxide concentration by applying titanium dioxide to existing roads in urban areas, using correlation analysis and a generalized linear model. METHODS : To analyze the characteristics of nitrogen oxide concentration with/without applying titanium dioxide to the urban road segment, data acquisition was conducted for nitrogen oxide concentration, weather information, and traffic information, etc., and a correlation analysis was conducted for each factor, with/without applying titanium dioxide to the roads. In addition, nitrogen oxide concentration generation models with/without the application of titanium dioxide to the roads were estimated using a generalized linear model. RESULTS : The results demonstrate that relative humidity and temperature were found to be slightly correlated with the nitrogen oxide concentration, both with and without the application of titanium dioxide to the roads; however, wind speed, solar radiation, and traffic volume were found to have somewhat low correlation according to the results of a correlation analysis. Moreover, relative humidity, temperature, solar radiation, and traffic volume were significant when titanium dioxide was applied to the roads, based on the estimated model from a generalized linear model, and the wind speed, solar radiation, and traffic volume were significant for the absence of titanium dioxide on the roads. CONCLUSIONS : Analytical results indicated that the characteristics of nitrogen oxide concentration vary depending on the application of titanium dioxide to the roads. In particular, when titanium dioxide was applied to the roads, the relative humidity and temperature were analyzed; according to both analyses, i.e., correlation analysis and a generalized linear model, the nitrogen oxide concentration was affected.

PURPOSES : This study analyzes the characteristics of generated fine particulate matter (PM2.5) and nitrogen oxide (NOX) at roadsides using a statistical method, namely, a generalized linear model (GLM). The study also investigates the applicability and capability of a machine learning methods such as a generalized regression neural network (GRNN) for predicting PM2.5 and NOX generations. METHODS : To analyze the characteristics of PM2.5 and NOX generations at roadsides, data acquisition was conducted in a specific segment of roads, and PM2.5 and NOX prediction models were estimated using GLM. In addition, to investigate the applicability and capability of a machine learning methods, PM2.5 and NOX prediction models were estimated using a GRNN and were compared with models employing previously estimated GLMs using r-square, mean absolute deviation (MAD), mean absolute percentage error (MAPE), and root mean square error (RMSE) as parameters. RESULTS : Results revealed that relative humidity, wind speed, and traffic volume were significant for both PM2.5 and NOX prediction models based on estimated models from a GLM. In addition, to compare the applicability and capability of the GLM and GRNN models (i.e., PM2.5 and NOX prediction models), the GRNN model of PM2.5 and NOX prediction was found to yield better statistical significance for r-square, MAD, MAPE, and RMSE as compared with the same parameters used in the GLM. CONCLUSIONS : Analytical results indicated that a higher relative humidity and traffic volume could lead to higher PM2.5 and NOX concentrations. By contrast, lower wind speed could affect higher PM2.5 and NOX concentrations at roadsides. In addition, based on a comparison of two statistical methods (i.e., GLM and GRNN models used to estimate PM2.5 and NOX), GRNN model yielded better statistical significance as compared with GLM.

In this paper, nitrogen-doped reduced graphene oxide(rGO) is obtained by thermal annealing of nitrogen-containing compounds and graphene oxide (GO) manufactured by modified Hummers' method. We use melamine as a nitrogen-containing compound and treat GO thermally with melamine at over 800 ~ 1,000℃ and 1 ~ 3 hr under Ar atmosphere. The electrical conductivity of doped rGO is measured by 4-point probe method. As a result, nitrogen contents on rGO are found to be in the range of 2.5 to 12.5 at% depending on the doping conditions after thermal annealing. The main doping site on graphene oxide is changed from pyridinic-N and pyrrolinic N to the graphitic site as the heat treatment temperature increases. The electrical conductivity of doped rGO increases as the N doping content increases. As the thermal treatment time increases, the change of both total doping contents and doping sites is slight and the surface resistance is remarkably reduced, which is caused by healing effects of doped graphene oxide at high temperature.

대기오염물질 중 미세먼지는 심각한 사회적 환경문제로 인식되고 있다. 미세먼지의 원인 물질 중 하나인 질소산화물(NOx)은 석탄화력발전소의 연소공정에서 주로 발생하므로 효율적인 NOx 제거가 필요한 실정이다. 본 연구에서는 선택적 촉매 환원법(Selective Catalytic Reduction, SCR)을 이용한 NOx 제거에서 TiO2 광촉매의 NO 제거효율을 연구하였다. NO 제거효율을 평가하기 위해 발열제가 내장된 Al2O3 기판 표면에 TiO2 촉매와 인산염의 접착 바인더를 혼합하여 도포한 후 제조된 기판을 열처리하면서 실험을 수행하였다. 온도에 따른 촉매의 NO 제거효율을 평가하였고, 촉매의 물리화학적 특성을 위하여 XRD, SEM, TG-DTA, BET 분석을 수행하였다. NOx 제거 효율은 시간에 따른 온도변화(250℃∼500℃) 로 20분에서 제거효율은 58.7%∼65.9%이며, 30분에서 63.7%∼66.0%로 나타났다. 질소산화물 제거용 SCR로 사용되는 TiO2는 300℃가 제거효율이 가장 효율적인 것으로 판단된다.

울금(Curcuma longa L.)의 산화억제 및 질소산화물 소거활성 등 기능성 소재로서 활용 가능성을 검토한 결과, 프로안토시아니딘(proanthocyanidin) 함량은 69.000±2.737 mg catechin equivalents (CE)/g dry weight으로 확인되었으며, 증류수(distilled water, DW), 70% 에탄올 및 노르말 부탄올(n-butanol)의 3가지 용매를 사용한 추출 수율은 DW (17.11%), 70% 에탄올(15.26%), 노르말 부탄올(4.12%) 순으로 관찰되었다. 총 플라보노이드(total flavonoid) 함량은 DW, 70% 에탄올 및 노르말 부탄올에서 각각 0.032, 0.512 및 2.221 mg quercetin equivalents (QE)/g의 함량으로 나타났고, 노르말 부탄올에서는 유의적인 차이를 보이며 높게 관찰되었다(p<0.05). Nitric oxide (NO) 라디칼 소거 활성은 농도 별(0.2~0.8 mg/mL) DW에서 15.64~26.20%, 70% 에탄올 10.52~20.76%, 노르말 부탄올 에서 13.39~69.92%로 확인되었다. Nitrite (NO2) 소거활성은 DW 및 70% 에탄올과 비교하였을 때 노르말 부탄올에서 강한 NO2 소거활성을 보였다. β-carotene 탈색 저해활성은 DW에서 8.81~25.93%, 70% 에탄올 1.20~20.20%, 노르말 부탄올 12.08~43.93%로 나타났다. 지질과산화 저해활성은 DW, 70% 에탄올 및 노르말 부탄올에서 각각 5.60~27.54%, 37.78~50.79% 및 41.79~46.39%로 동정되었다. 이에, 천연 항산화제 등 기능성 소재로서의 활용 가능성이 있을 것으로 사료된다.

치자 껍질의 70% methanol, ethyl acetate (EA) 및 distilled water (DW)의 용매 별 추출물 의 total phenol 함량 및 질소 산화물 소거능, 환원력, β-carotene 탈색을 이용한 항산화력 및 지질과 산화 저해능 측정을 통하여 치자의 기능성 식품 소재로서의 가치를 검토한 결과, anthocyanin 함량은 3.519±0.635 mg/100 g DW로 나타났으며, 용매 별 추출 수율은 DW (39.87%), 70% methanol (36.26%), EA (2.88%) 로 관찰되었다. 추출 용매 별 항산화 활성은 농도(0.2, 0.4, 0.6 mg/mL)가 증가 할수록 유의적으로 증가하였으며 control로 사용된 ascorbic acid, BHA, trolox 보다는 낮은 활성이 확 인되었다. 치자 껍질의 total phenol 함량은 EA, 70% methanol, DW 추출물 순으로 EA 추출물에서 26.59±0.20 CAE (caffeic acid equivalents) mg/g으로 가장 높았으며, Nitric oxide (NO) radical 소거 능에서는 70% methanol (70.32~76.15%), DW (52.66~59.31%), EA (34.65~46.98%) 추출물 순으로 나타났다. Nitrite (NO2) 소거능은 70% methanol (34.57~39.33%), DW (32.53~38.47%), EA (27.59~32.62%) 순으로 관찰되었다. β-carotene 탈색 저해능은 DW (41.55~50.97%), 70% methanol (23.37~44.80%), EA (13.37~25.24%) 순으로 동정되었다. Reducing power (optical density)는 70% methanol (0.044~0.127), DW (0.033~0.099), EA (0.026~0.097) 순으로 확인되었다. 지질과산화 저해 능은 껍질 추출물 중 70% methanol (56.51~76.21%), EA (54.59~63.34%), DW (47.92~61.11%) 순 으로 관찰되었다(p<0.05). 이에, 치자 껍질은 기능성 식품 및 천연 항산화제로서의 가치가 매우 높을 것 으로 판단된다.

치자 씨 추출물이 항산화력 및 지질과산화 저해능에 미치는 영향을 알아 보고 치자의 기능성 식품 소재로서의 가치를 검토하기 위하여 실험을 수행한 결과, 치자 씨의 anthocyanin 함량을 측정한 결과 2.201±0.516 mg/100 g DW로 나타났으며, 치자 씨의 용매 별 추출 수율은 chloroform:methanol (CM, 2:1, v/v) 36.39%, 70% ethanol (27.32%), n-butanol (26.23%) 로 확인되었다. 추출 용매 별 항산화 활성은 농도(0.2, 0.4, 0.6 mg/mL)가 증가할수록 유의적으로 증가하였으며 positive control로 사 용된 ascorbic acid, BHA, trolox 보다는 낮은 활성이 관찰되었다. 치자 씨의 total phenol 함량(mg CAE/g)은 CM (32.50), 70% ethanol (30.09), n-butanol (11.07) 추출물 순으로 n-butanol 추출물에 서 가장 적은 함량을 보였으며, Nitric oxide (NO) radical 소거능에서는 CM (76.97~84.24%), 70% ethanol (74.10~79.99%), n-butanol (30.66~37.15%) 추출물 순으로 관찰되었다. Nitrite (NO2) 소거능 은 CM (33.53~43.23%), 70% ethanol (32.40~35.98%), n-butanol (24.72~28.14%) 순으로 관찰되었 다. β-carotene 탈색 저해능은 CM (23.73~44.70%), 70% ethanol (22.03~41.32%), n-butanol (16.00~27.87%) 순으로 확인되었다. Reducing power (optical density)는 70% ethanol (0.073~0.182), CM (0.057~0.154), n-butanol (0.028~0.079) 순으로 관찰되었다. 지질과산화 저해능은 씨 추출물 중 CM (53.26~76.56%), 70% ethanol (52.97~76.56%), n-butanol (38.54~53.33%) 순으로 나타났다. 이 에, 치자씨 추출물은 천연 항산화제로서 기능성 식품의 가치가 높을 것으로 판단된다.

We present an excellent detection for nitrogen monoxide (NO) gas using polycrystalline ZnO wire-like films synthesized via a simple method combined with sputtering of Zn metallic films and subsequent thermal oxidation of the sputtered Zn nanowire films in dry air. Structural and morphological characterization revealed that it would be possible to synthesize polycrystalline hexagonal wurtzite ZnO films of a wire-like nanostructure with widths of 100-150 nm and lengths of several microns by controlling the sputtering conditions. It was found from the gas sensing measurements that the ZnO wirelike thin film gas sensor showed a significantly high response, with a maximum value of 29.2 for 2 ppm NO at 200 oC, as well as a reversible fast response to NO with a very low detection limit of 50 ppb. In addition, the ZnO wire-like thin film gas sensor also displayed an NO-selective sensing response for NO, O2, H2, NH3, and CO gases. Our results illustrate that polycrystalline ZnO wire-like thin films are potential sensing materials for the fabrication of NO-sensitive high-performance gas sensors.

We present the detection characteristics of nitrogen monoxide(NO) gas using p-type copper oxide(CuO) thin film gas sensors. The CuO thin films were fabricated on glass substrates by a sol-gel spin coating method using copper acetate hydrate and diethanolamine as precursors. Structural characterizations revealed that we prepared the pure CuO thin films having a monoclinic crystalline structure without any obvious formation of secondary phase. It was found from the NO gas sensin measurements that the p-type CuO thin film gas sensors exhibited a maximum sensitivity to NO gas in dry air at an operating temperature as low as 100 oC. Additionally, these CuO thin film gas sensors were found to show reversible and reliable electrical response to NO gas in a range of operating temperatures from 60 oC to 200 oC. It is supposed from these results that the ptype oxide semiconductor CuO thin film could have significant potential for use in future gas sensors and other oxide electronics applications using oxide p-n heterojunction structures.

In this study, a micro gas sensor for NOx was fabricated using a microelectromechanical system (MEMS) technology and sol-gel process. The membrane and micro heater of the sensor platform were fabricated by a standard MEMS and CMOS technology with minor changes. The sensing electrode and micro heater were designed to have a co-planar structure with a Pt thin film layer. The size of the gas sensor device was about 2mm×2mm. Indium oxide as a sensing material for the NOx gas was synthesized by a sol-gel process. The particle size of synthesized In2O3 was identified as about 50 nm by field emission scanning electron microscopy (FE-SEM). The maximum gas sensitivity of indium oxide, as measured in terms of the relative resistance (Rs=Rgas/Rair), occurred at 300˚C with a value of 8.0 at 1 ppm NO2 gas. The response and recovery times were within 60 seconds and 2 min, respectively. The sensing properties of the NO2 gas showed good linear behavior with an increase of gas concentration. This study confirms that a MEMS-based gas sensor is a potential candidate as an automobile gas sensor with many advantages: small dimension, high sensitivity, short response time and low power consumption.

We report on the NO gas sensing properties of non-directional ZnO nanofibers synthesized using a typical electrospinning technique. These non-directional ZnO nanofibers were electrospun on an SiO2/Si substrate from a solution containing poly vinyl alcohol (PVA) and zinc nitrate hexahydrate dissolved in distilled water. Calcination processing of the ZnO/PVA composite nanofibers resulted in a random network of polycrystalline ZnO nanofibers of 50 nm to 100 nm in diameter. The diameter of the nanofibers was found to depend primarily on the solution viscosity; a proper viscosity was maintained by adding PVA to fabricate uniform ZnO nanofibers. Microstructural measurements using scanning electron microscopy revealed that our synthesized ZnO nanofibers after calcination had coarser surface morphology than those before calcination, indicating that the calcination processing was sufficient to remove organic contents. From the gas sensing response measurements for various NO gas concentrations in dry air at several working temperatures, it was found that gas sensors based on electrospun ZnO nanofibers showed quite good responses, exhibiting a maximum sensitivity to NO gas in dry air at an operating temperature of 200˚C. In particular, the non-directional electrospun ZnO nanofiber gas sensors were found to have a good NO gas detection limit of sub-ppm levels in dry air. These results illustrate that non-directional electrospun ZnO nanofibers are promising for use in low-cost, high-performance practical NO gas sensors.

Zinc oxide as an optoelectronic device material was studied to utilize its wide band gap of 3.37 eV and high exciton biding energy of 60 meV. Using anti-site nitrogen to generate p-type zinc oxide has shown a deep acceptor level and low solubility. To increase the nitrogen solubility in zinc oxide, group 13 elements (aluminum, gallium, and indium) was co-added to nitrogen. The effect of aluminum on nitrogen solubility in a 3×3×2 zinc oxide super cell containing 72 atoms was investigated using density functional theory with hybrid functionals of Heyd, Scuseria, and Ernzerhof (HSE). Aluminum and nitrogen were substituted for zinc and oxygen sites in the super cell, respectively. The band gap of the undoped super cell was calculated to be 3.36 eV from the density of states, and was in good agreement with the experimentally obtained value. Formation energies of a nitrogen molecule and nitric oxide in the zinc oxide super cell in zinc-rich conditions were lower than those in oxygen-rich conditions. When the number of nitrogen molecules near the aluminum increased from one to four in the super cell, their formation energies decreased to approach the valence band maximum to some degree. However, the acceptor level of nitrogen in zinc oxide with the co-incorporation of aluminum was still deep.