Anaerobic Digestion Treatment for the Mixture of Chinese cabbage Waste Juice and Swine Manure

( Gopi Krishna Kafle ),( Sang Hun Kim ),( Beom Soo Shin ) 한국농업기계학회 2012 바이오시스템공학 Vol.37 No.1

Purpose: The objective of this study was to investigate the feasibility of anaerobic digestion of Chinese cabbage waste juice (CCWJ) and swine manure(SM). Methods: The anaerobic digestion test was conducted under batch and continuous conditions at mesophilic temperature (36-38℃). The batch test was divided into Experiment I and II. In the Experiment I, biogas potential and production rate of CCWJ was evaluated. In Experiment II the effect of F/M ratio (2.0, 3.2, 4.9) at mixture ratio of 25:75(CCWJ: SM, % vol. basis) on biogas yield was studied. Results: CCWJ produced biogas and methane yield of 929 and 700 mL/g VS added respectively. The biogas yield from the mixture of CCWJ and SM was almost same at F/M ratio of 2.0 and 3.2 but dropped by 14% when F/M ratio increased from 3.2 to 4.9. In continuous test the mixture of CCWJ and SM (25:75, % vol. basis) produced biogas yield of 352 mL/g VS added which is around 11% higher compared to biogas yield from SM alone. Addition to biogas yield digester performance was also improved with co-digestion of CCWJ with SM. Conclusions: The results showed that the anaerobic digestion of CCWJ with SM could be promising for improving both the biogas yield and digester performance at mesophilic temperature.

Agri-environmental System Engineering and Energy : Original Article ; Emissions of Odor, Ammonia, Hydrogen Sulfide, and Volatile Organic Compounds from Shallow-Pit Pig Nursery Rooms

( Gopi Krishna Kafle ),( Lide Chen ) 한국농업기계학회 2014 바이오시스템공학 Vol.39 No.2

Purpose: The objective of this study was to measure emissions of gases (ammonia (NH3), hydrogen sulfide (H2S) and carbondioxide (CO2)), volatile organic compounds (VOC) and odor from two shallow pit pig nursery rooms. Gas and odor reductionpractices for swine operations based on the literature were also discussed. Methods: This study was conducted for 60 daysat a commercial swine nursery facility which consisted of four identical rooms with mechanical ventilations. Two rooms(room 1 (R1) and room 2 (R2)) with different pig numbers and ventilation rates were used in this study. The pig manurefrom both the R1 and R2 were characterized. Indoor/outdoor temperatures, ventilation rates/duration, NH3, H2S, CO2, andVOC concentrations of the ventilation air were measured periodically (3-5 times/week). Odor concentrations of theventilations were measured two times on two days. Three different types of gas and odor reduction practices (diet control,chemical method, and biological method) were discussed in this study. Results: The volatile solids to total solids ratio(VS/TS) and crude protein (CP) value of pig manure indicated the pig manure had high potential for gas and odor emissions. The NH3, H2S, CO2 and VOC concentrations were measured in the ranges of 1.0-13.3, 0.1-5.7, 1600-3000 and 0.0-1.83 ppm,respectively. The NH3 concentrations were found significantly higher than H2S concentrations for both rooms. The odorconcentrations were measured in the range of 2853-4432 OUE/m3. There was significant difference in odor concentrationsbetween the two rooms which was due to difference in pig numbers and ventilation duration. The literature studies showedthat simultaneous use of dietary control and biofiltration practices will be more effective and environmentally friendly forgas and odor reductions from pig barns. Conclusions: The gas and odor concentrations measured in the ventilation air fromthe pig rooms indicate an acute need for using gas and odor mitigation technologies. Adopting diet control and biofiltrationpractices simultaneously could be the best option for mitigating gas and odor emissions from pig barns.

ZnO nanorods decorated with metal sulfides as stable and efficient counter-electrode materials for high-efficiency quantum dot-sensitized solar cells

Gopi, C. V.,Venkata-Haritha, M.,Lee, Y. S.,Kim, H. J. Royal Society of Chemistry 2016 Journal of materials chemistry. A, Materials for e Vol.4 No.21

<P>As a promising type of new-generation solar cells, the electrocatalytic activity and stability of counter electrodes (CEs) play a key role in the performance of QDSSCs (quantum-dot-sensitized solar cells) at present. Here, a facile solution-processing method for fabricating metal sulfides (CoS, NiS, CuS and PbS) on vertically aligned ZnO nanorods (NRs) has been demonstrated and used to produce efficient CEs in polysulfide electrolyte-based QDSSCs. Compared with bare metal sulfide CEs (CoS, NiS, CuS and PbS), the ZnO NR framework presents a larger surface area for loading more metal sulfide catalysts and easy accessibility of the electrolyte. Additionally, the metal sulfide catalyst with high catalytic activity plays the main role in the reduction of the oxidized polysulfide, white the ZnO NRs offer an excellent electron pathway for shuttling electrons to highly catalytic metal sulfide sites and facilitate charge transport during catalysis. Cyclic voltammetry measurements indicate that the ZnO/PbS CEs still retain good cyclability after 50 cycles, demonstrating super-stability, while the ZnO/CoS, ZnO/NiS, ZnO/CuS, and Pt CEs show obvious fluctuations. Therefore, the ZnO/PbS CE exhibits much higher catalytic activity with the polysulfide electrolyte than ZnO/CoS, ZnO/NiS, ZnO/CuS and Pt CEs. As a result, a QDSSC based on the ZnO/PbS CE achieves a power conversion efficiency (eta) of 4.76%, which is attributed to the high fill factor (FF) of 0.566, and the eta is much higher than that based on ZnO/CoS (2.75%), ZnO/NiS (3.12%), ZnO/CuS (4.10%) and Pt (1.54%) CEs. The excellent catalytic performance along with the facile preparation of ZnO NRs decorated with metal sulfide CE materials make them a distinctive choice among the various CEs studied.</P>

Evaluation of the Biogas Productivity Potential of Fish Waste: A Lab Scale Batch Study

( Gopi Krishna Kafle ),( Sang Hun Kim ) 한국농업기계학회 2012 바이오시스템공학 Vol.37 No.5

Purpose: The biogas productivity potential of fish waste (FW) was evaluated. Methods: Batch trials were carried out in 1.3 L glass digesters kept in a temperature controlled chambers at 36.5˚C. The first order kinetic model and the modified Gompertz model were evaluated for biogas production. The Chen and Hashimoto model was used to determine the critical hydraulic retention time (HRT Critical) for FW under mesophilic conditions. The feasibility of co-digestion of FW with animal manure was studied. Results: The biogas and methane potential of FW was found to be 757 and 554 mL/g VS, respectively. The methane content in the biogas produced from FW was found to be 73% and VS removal was found to be 77%. There was smaller difference between measured and predicted biogas production when using the modified Gompertz model (16.5%) than using first order kinetic model (31%). The time period for 80%-90% of biogas production (T80-90) from FW was calculated to be 50.3-53.5 days. Similarly, the HRT Critical for FW was calculated to be 13 days under mesophilic conditions. The methane production from swine manure (SM) and cow manure (CM) digesters could be enhanced by 13%-115% and 17%-152% by mixing 10%-90% of FW with SM and CM, respectively. Conclusions: The FW was found to be highly potential substrate for anaerobic digestion for biogas production. The modified Gompertz model could be more appropriate in describing anaerobic digestion process of FW. It could be promising for co-digestion of FW with animal manure.

One-pot hydrothermal synthesis of tungsten diselenide/reduced graphene oxide composite as advanced electrode materials for supercapacitors

Gopi, Chandu V.V. Muralee,Reddy, Araveeti Eswar,Bak, Jin-Soo,Cho, In-Ho,Kim, Hee-Je Elsevier 2018 Materials letters Vol.223 No.-

<P><B>Abstract</B></P> <P>Nanosheet-like tungsten diselenide (WSe<SUB>2</SUB>)/reduced graphene oxide (rGO) hybrid has been developed for the first time by facile one-step hydrothermal route for supercapacitor applications. Electrochemical measurements show that the WSe<SUB>2</SUB>/rGO-based supercapacitor electrode exhibits a maximum specific capacitance of 389 F g<SUP>−1</SUP> at 1 A g<SUP>−1</SUP> with capacitance retention of 98.7% after 3000 charge/discharge cycles at a high current density of 7 A g<SUP>−1</SUP>, and delivered a energy density of 34.5 W h kg<SUP>−1</SUP> at 400 W kg<SUP>−1</SUP> and 22.4 W h kg<SUP>−1</SUP> at a high power density of 4000 W kg<SUP>−1</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel WSe<SUB>2</SUB>/rGO firstly synthesized for energy storage applications. </LI> <LI> WSe<SUB>2</SUB>/rGO shows large surface area and superior conductivity. </LI> <LI> WSe<SUB>2</SUB>/rGO composite exhibits high specific capacitance and outstanding cycling stability. </LI> </UL> </P>

A strategy to improve the energy conversion efficiency and stability of quantum dot-sensitized solar cells using manganese-doped cadmium sulfide quantum dots

Gopi, Chandu V. V. M.,Venkata-Haritha, M.,Kim, Soo-Kyoung,Kim, Hee-Je The Royal Society of Chemistry 2015 Dalton Transactions Vol.44 No.2

<P>This article describes the effect of manganese (Mn) doping in CdS to improve the photovoltaic performance of quantum dot sensitized solar cells (QDSSCs). The performances of the QDSSCs are examined in detail using a polysulfide electrolyte with a copper sulfide (CuS) counter electrode. Under the illumination of one sun (AM 1.5 G, 100 mW cm<SUP>−2</SUP>), 10 molar% Mn-doped CdS QDSSCs exhibit a power conversion efficiency (<I>η</I>) of 2.85%, which is higher than the value of 2.11% obtained with bare CdS. The improved photovoltaic performance is due to the impurities from Mn<SUP>2+</SUP> doping of CdS, which have an impact on the structure of the host material and decrease the surface roughness. The surface roughness and morphology of Mn-doped CdS nanoparticles can be characterised from atomic force microscopy images. Furthermore, the cell device based on the Mn-CdS electrode shows superior stability in the sulfide/polysulfide electrolyte in a working state for over 10 h, resulting in a highly reproducible performance, which is a serious challenge for the Mn-doped solar cell. Our finding provides an effective method for the fabrication of Mn-doped CdS QDs, which can pave the way to further improve the efficiency of future QDSSCs.</P> <P>Graphic Abstract</P><P>Better stability and higher performance of Mn-doped CdS QDSSCs (PCE = 2.85%) than those of CdS QDSSCs (PCE = 2.11%). <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4dt03063j'> </P>

Low-temperature easy-processed carbon nanotube contact for high-performance metal- and hole-transporting layer-free perovskite solar cells

Gopi, C.V.V.M.,Venkata-Haritha, M.,Prabakar, K.,Kim, H.J. Elsevier Sequoia 2017 Journal of photochemistry and photobiology. A, Che Vol.332 No.-

Expensive and energy-consuming vacuum process of metal deposition with ambient-unstable hole transporters are incompatible with large-scale and low-cost production of perovskite solar cells (PSCs) and thus hampers their commercialization. For the first time, we demonstrate cost-effective novel carbon nanotube (CNT) paste that was applied to FTO substrate by the facile doctor blade method and processed at low temperature (100<SUP>o</SUP>C). Herein we report a new method of cost-efficient perovskite solar cells with the use of conventional hole transporters by directly clamping a selective hole extraction electrode made of CNT and a TiO<SUB>2</SUB>/perovskite photoanode. Most importantly, under optimized conditions in the absence of an organic hole-transporting material and metal contact, CH<SUB>3</SUB>NH<SUB>3</SUB>PbI<SUB>3</SUB> and CNTs formed a solar cell with an efficiency of up to 7.83%. The PSC devices are fabricated in air without high-vacuum deposition which simplifies the processing and lowers the threshold of both scientific research and industrial production of PSCs. Electrochemical impedance spectroscopy demonstrates good charge transport characteristics of CEs on the photovoltaic performance of devices. The PSCs exhibited good stability over 50h. The abundance, low cost, and excellent properties of the CNT material offer wide prospects for further applications in PSCs.

FIXED POINTS OF SET-VALUED MAPPINGS IN RELATIONAL METRIC SPACES

( Gopi Prasad ),( Ramesh Chandra Dimri ),( Shivani Kukreti ) 한국수학교육학회 2021 純粹 및 應用數學 Vol.28 No.3

In this paper, we generalize the notion of comparable set-valued mappings by introducing two types of R-closed set-valued mappings and utilize these to obtain an analogue of celebrated Mizoguchi and Takahashi fixed point theorem in relational metric spaces. To annotate the claims and usefulness of such findings, we prove fixed point results for both set-valued and single-valued mappings and validate the assertions with the help of examples. In this way, these investigations extend, modify and generalize some prominent recent fixed point results obtained by Tiammee and Suantai [24], Amini-Harandi and Emami [4], Prasad and Dimri [19] and several others in the settings of relational metric spaces.

Monitoring and removal technologies of microplastics in the environment

Gopi Kalaiyarasan,Sung Chul Yi,Byoung-In Sang 한양대학교 청정에너지연구소 2022 Journal of Ceramic Processing Research Vol.23 No.6

Microplastic (MP) contamination of the environment is one of the major problems to human and other creatures' health. Inrecent decades, researchers hardly work to find alternate products for MPs sources, detection, and removal technologies ofMPs from various polluted environments. This review discusses the various sources of MPs, ways to minimize thecontamination, environmental health effects caused by MPs pollution, and the detection of MPs in various environmental andfood samples. Additionally, the sensing mechanism, efficiency, merits, demerits, and challenges in detection techniques forvarious samples like air, water, and soil samples are described along with suitable examples. Further, the microplastic removaland treatment technologies such as coagulation and flocculation, membrane, biological, filtration, advanced oxidation process,and adsorption technologies are deeply evaluated to gather the necessary knowledge to make a pollution-free environment. Inthe end, the complications in detection and removal technologies in the current situation and opportunities to overcome theMPs' pollution problem are addressed.

Highly effective nickel sulfide counter electrode catalyst prepared by optimal hydrothermal treatment for quantum dot-sensitized solar cells

Gopi, Chandu V.V.M.,Srinivasa Rao, S.,Kim, Soo-Kyoung,Punnoose, Dinah,Kim, Hee-Je Elsevier 2015 Journal of Power Sources Vol.275 No.-

<P><B>Abstract</B></P> <P>Nickel sulfide (NiS) thin film has been deposited on a fluorine-doped tin oxide substrate by a hydrothermal method using 3-mercaptopropionic acid and used as an efficient counter electrode (CE) for polysulfide redox reactions in quantum dot-sensitized solar cells (QDSSCs). NiS has low toxicity and environmental compatibility. In the present study, the size of the NiS nanoparticle increases with the hydrothermal deposition time. The performance of the QDSSCs is examined in detail using polysulfide electrolyte with the NiS CE. A TiO<SUB>2</SUB>/CdS/CdSe/ZnS-based QDSSC using the NiS CE shows enhanced photovoltaic performance with a power conversion efficiency (PCE) of 3.03%, which is superior to that of a cell with Pt CE (PCE 2.20%) under one sun illumination (AM 1.5, 100 mW cm<SUP>−2</SUP>). The improved photovoltaic performance of the NiS-based QDSSC may be attributed to a low charge transfer resistance (5.08 Ω) for the reduction of polysulfide on the CE, indicating greater electrocatalytic activity of the NiS. Electrochemical impedance spectroscopy, cyclic voltammetry, and Tafel-polarization measurements were used to investigate the electrocatalytic activity of the NiS and Pt CEs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nickel sulfide is used as counter electrode of quantum dots-sensitized solar cell. </LI> <LI> Nickel sulfide shows superior electro-catalytic activity than Pt. </LI> <LI> The content of sulfur in nickel sulfide thin film depends on the deposition time. </LI> <LI> The QDSSC using NiS CE yield a high PCE value of 3.03%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>