Achieving cost-effective and defect-free graphene sheets is highly desirable for sensor devices. Aiming this, few-layer graphene (~ 3) sheets are prepared by an electrochemical exfoliation with [NMP] [ HSO4] electrolyte (i.e., Bronsted acidic ionic liquid). A novel approach for the effective exfoliation of graphene sheets is demonstrated by (i) simultaneously applying a constant potential through an electrochemical cell (with different electrolyte concentrations) and (ii) together with sonication. The exfoliated graphene sheets are characterized through state-of-the-art techniques and sprayed on a glass substrate at optimum conditions. Thus, the transparent conducting sensor device is fabricated with a suitable contact electrode and used for ammonia vapor sensing and the sensor performances are highly dependent on the concentration of the ionic liquid used during the electrochemical exfoliation. The sensing response and limit of detection for the exfoliated graphene-based film were calculated as 3.56% and 432 ppb, respectively. Further studies indicated that the fabricated sensors are more selective towards ammonia molecules with quick response and recovery times.

Concentration of nitrogen, one of the major elements, and ratio of two nitrogen forms (NH4 + and NO3 –) in the nutrient solution affect the quality and food safety of fresh vegetable produce. This study was conducted to find an appropriate strength and NH4 +:NO3 – ratio of a nutrient solution for growth and development of a Romaine lettuce (Lactuca sativa L. var. longiflora) ‘Caesar Green’, a representative leafy vegetable, grown in a home hydroponic system. In the first experiment, plants were grown using three types of nutrient solution: A commercial nutrient solution (Peters) and two strengths (GNU1 and GNU2) of a multipurpose nutrient solution (GNU solution) developed in a Gyeongsang National University lab. Plants grown with the GNU1 and GNU2 had greater shoot length, leaf length and width, and biomass yield than Peters. On the other hand, the root hairs of plants grown with Peters were short and dark in color. Tissue NH4 + content in the Peters was higher than that of the GNU1 and GNU2. The higher contents of NH4 + in this solution may have caused ammonium toxicity. In the second experiment, eight treatment solutions, combining GNU1 and GNU2 solutions with four ratios of NO3 –:NH4 + named as 1, 2, 3 and 4 were used. Both experiments showed more growth in the GNU2 group, which had a relatively low ionic strength of the nutrient solution. The growth of Romaine lettuce showed the greatest fresh weight along with low tissue NO3 – content in the GNU2-2. This was more advantageous in terms of food safety in that it suppressed the accumulation of surplus NO3 – in tissues due to the low ionic strength of the GNU2 subgroup. In addition, this is preferable in that it can reduce the absolute amount of the input of inorganic nutrients to the nutrient solution.

This work describes the synthesis and characterization of a heterogeneous catalyst consisting of piperazine-functionalized reduced graphene oxide decorated with Fe3O4 nanoparticles ( Fe3O4@rGO-NH), and the study of its catalytic activity as a magnetic heterogeneous catalyst for the Pechmann synthesis of coumarins. Catalyst Fe3O4@ rGO-NH was fully characterized by various techniques, including IR, XRD, TEM, VSM, TGA, and elemental analysis. Then, the catalyst was used as an efficient and easy-separable heterogeneous catalyst for the solvent-free synthesis of some coumarins by Pechmann reaction. The reaction was optimized in terms of reaction time and temperature, catalyst dosage, and the presence/absence of the solvent. Finally, the reusability of the catalyst was studied.

In this study, UiO-66-NH2 was synthesized and incorporated with graphene aerosol (UiO-66-NH2/GA) and ethylenediamine functionalized graphene oxide (UiO-66-NH2/GO-NH2). These composites were characterized using infrared spectroscopy, powder X-ray diffraction, ultraviolet–visible light spectroscopy, scanning electron microscope, and energy-dispersive X-ray spectroscopy. UiO-66-NH2/GO-NH2 exhibited 93% adsorption of quinoline in 5 h, UiO-66-NH2 and UiO-66-NH2/GA presented 80.4% and 86.5%, respectively. The high adsorption observed on UiO-66-NH2/GO-NH2 was attributed to the unique electronic properties, and hydrogen bonding between the nitrogen atom of quinoline and NH2- phenyl fragment of UiO-66-NH2, and N–H of ethylenediamine. GO also offered combined strong π–π interactions on its surface, and the oxygen coverage (~ 50%) on GO within the structure is responsible for the formation of strong hydrogen bonds with quinoline. Theoretical calculation suggested that UiO-66-NH2/GO-NH2 presented a more favourable adsorption energy (− 18.584 kcal/ mol) compared to UiO-66-NH2 (− 16.549 kcal/mol) and UiO-66-NH2/GA (− 13.991 kcal/mol). These results indicate that nanocomposites have a potential application in quinoline capture technologies in the process of adsorptive denitrogenation.

For the selective catalytic reduction of NOx with ammonia (NH3-SCR), a V2O5WO3/TiO2 (VW/nTi) catalyst was prepared using V2O5 and WO3 on a nanodispersed TiO2 (nTi) support by simple impregnation process. The nTi support was dispersed for 0~3 hrs under controlled bead-milling in ethanol. The average particle size (D50) of nTi was reduced from 582 nm to 93 nm depending on the milling time. The NOx activity of these catalysts with maximum temperature shift was influenced by the dispersion of the TiO2. For the V0.5W2/nTi-0h catalyst, prepared with 582 nm nTi-0h before milling, the decomposition temperature with over 94 % NOx conversion had a narrow temperature window, within the range of 365-391 °C. Similarly, the V0.5W2/nTi-2h catalyst, prepared with 107 nm nTi-2h bead-milled for 2hrs, showed a broad temperature window in the range of 358~450 °C. However, the V0.5W2/Ti catalyst (D50 = 2.4 μm, aqueous, without milling) was observed at 325-385 °C. Our results could pave the way for the production of effective NOx decomposition catalysts with a higher temperature range. This approach is also better at facilitating the dispersion on the support material. NH3-TPD, H2-TPR, FT-IR, and XPS were used to investigate the role of nTi in the DeNOx catalyst.

Excess nitrogen (N) flowing from livestock manure to water systems poses a serious threat to the natural environment. Thus, livestock wastewater management has recently drawn attention to this related field. This study first attempted to obtain the optimal conditions for the further volatilization of NH3 gas generated from pig wastewater by adjusting the amount of injected magnesia (MgO). At 0.8 wt.% of MgO (by pig wastewater weight), the volatility rate of NH3 increased to 75.5% after a day of aeration compared to untreated samples (pig wastewater itself). This phenomenon was attributed to increases in the pH of pig wastewater as MgO dissolved in it, increasing the volatilization efficiency of NH3. The initial pH of pig wastewater was 8.4, and the pH was 9.2 when MgO was added up to 0.8 wt.%. Second, the residual ammonia nitrogen (NH4 +-N) in pig wastewater was removed by precipitation in the form of struvite (NH4MgPO4·6H2O) by adjusting the pH after adding MgO and H3PO4. Struvite produced in the pig wastewater was identified by field emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD) analysis. White precipitates began to form at pH 6, and the higher the pH, the lower the concentration of NH4 +-N in pig wastewater. Of the total 86.1% of NH4 +-N removed, 62.4% was achieved at pH 6, which was the highest removal rate. Furthermore, how struvite changes with pH was investigated. Under conditions of pH 11 or higher, the synthesized struvite was completely decomposed. The yield of struvite in the precipitate was determined to be between 68% and 84% through a variety of analyses.

전자 및 화학 산업의 초순수 생산 및 원자력 발전소의 부식 제어를 위해 이온교환 수지탑의 성능 파악이 필수적이다. 따라서 본 연구에서는 4종의 H 및 ETAH 형 양이온 교환수지가 채워진 양이온 및 혼상 이온교환수지탑에 미량의 NaCl를 포함하는 에탄올아민(ETA) 및 암모니아(NH3) 용액을 주입하여 양이온 파과특성을 조사하였다. 조사 결과, 주성분인 ETAH+ 및 NH4 +와 달리, 미량성분인 Na+는 (이론적교환용량의 3배 이상) 시험기간 동안 수지탑 출구에서 파과 및 오버슈팅 현상이 나타나지 않았다. H형 수지탑의 파과현상은 ETAH+ 및 NH4 +가 순서대로 일어났고, 오버슈팅은 NH4 +가 파과할때 ETAH+에 대해서 발생했다. 파과영역의 너비로 결정되는 상대적 선택도는 NH4 +가 ETAH+보다 최대 51.5 % 더 높았다. 유입수 Na+ 농도가 높을수록, 선택도는 감소하고 오버슈팅 현상은 증가하였다. 이온교환 수지의 고유 특성을 개선하여 감소시킬 수 있는 Na+ 누출은, ETAH형에서 높았고 4종의 양이온수지에 대해 동일하지 않은 것으로 조사되었다.

Cr thin films with O added are deposited on sapphire substrate by DC sputtering and are nitrided in NH3 atmosphere between 300 and 900 oC for various times. X-ray diffraction results show that nitridation begins at 500 oC, forming CrN and Cr2N. Cr oxides of Cr2O3 are formed at 600 oC. And, at temperatures higher than 900 oC, the intermediate materials of Cr2N and Cr2O3 disappear and CrN is dominant. The atomic concentration ratios of Cr and O are 77% and 23%, respectively, over the entire thickness of as-deposited Cr thin film. In the sample nitrided at 600 oC, a CrN layer in which O is substituted with N is formed from the surface to 90 nm, and the concentrations of Cr and N in the layer are 60% and 40%, respectively. For this reason, CrN and Cr2N are distributed in the CrN region, where O is substituted with N by nitridation, and Cr oxynitrides are formed in the region below this. The nitridation process is controlled by inter-diffusion of O and N and the parabolic growth law, with activation energy of 0.69 eV.

Bi2MoO6 (BMO) via the structure-directing role of CO(NH2)2 is successfully prepared via a facile solvothermal route. The structure, morphology, and photocatalytic performance of the nanoflake BMO are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fluorescence spectrum analysis (PL), UV-vis spectroscopy (UVvis) and electrochemical test. SEM images show that the size of nanoflake BMO is about 50 ~ 200 nm. PL and electrochemical analysis show that the nanoflake BMO has a lower recombination rate of photogenerated carriers than particle BMO. The photocatalytic degradation of tetracycline hydrochloride (TC) by nanoflake BMO under visible light is investigated. The results show that the nanoflake BMO-3 has the highest degradation efficiency under visible light, and the degradation efficiency reached 75 % within 120 min, attributed to the unique hierarchical structure, efficient carrier separation and sufficient free radicals to generate active center synergies. The photocatalytic reaction mechanism of TC degradation on the nanoflake BMO is proposed.

The objectives of this study were (i) to evaluate the effects of temperature and relative humidity on two electrochemical sensors measuring hydrogen sulfide and ammonia using a laboratory testing system for various sensors, and (ii) to propose a calibration method for those concentrations to collect more reliable monitoring data. The effect of temperature and relative humidity was tested under three different conditions, respectively. The linearities measured data under all different conditions for the relative humidity and temperature were excellent, indicating more than 0.99 of R2 for both odor sensors. Under the condition of zero concentration, baselines (intercepts) at zero increased with increasing relative humidity for both hydrogen sulfide and ammonia sensors. The rate of gas concentration according to ADC variation (slopes) increased with increasing relative humidity about only the hydrogen sulfide sensor. In this study, slope, and intercept are utilized for calibration of hydrogen sulfide and ammonia concentration, and the reliability of the data of hydrogen sulfide and ammonia sensors is further enhanced by the relational expression obtained by this paper.

We used three gas sensors to monitor hydrogen sulfide, ammonia, and volatile organic compounds (VOCs), which were frequently emitted from environmental facilities, such as municipal wastewater treatment, livestock manure treatment, and food waste composting facilities. Two electrochemical (EC) sensors for detecting hydrogen sulfide and ammonia, and a photoionization detector (PID) sensor for detecting VOCs were characterized in this study. The performance of their linearity by concentration levels, lower detection limit (LDL), repeatability, reproducibility, precision, and response time were tested under the laboratory condition. The linearity according to concentration levels were favorable for all three sensors with high correlation coefficients (R2 > 0.98). The ammonia sensor showed the highest LDL (18.6 ppb) and the hydrogen sulfide and VOC sensors showed 22.3 ppb and 26.7 ppb of LDL, respectively. The reproducibility and precision were favorable for all three sensors, indicating a lower relative standard deviation (RSD) than 0.9% in the reproducibility test and 7.2% in the precision test. The response times to reach target concentration were varied from 1 to 12 minutes. The ammonia sensor needed 12 minutes of response time at 1 ppm target the NH3 concentration and the hydrogen sulfide and VOC sensors needed less than 2 minutes of response time.