Effective charge separation in rGO/NiWO4@Au photocatalyst for efficient CO2 reduction under visible light

Jongmin Shin,Jun Neoung Heo,Jeong Yeon Do,Young-Il Kim,Seog Joon Yoon,Yang Soo Kim,Misook Kang 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.81 No.-

Catalyst performance can be improved by introducing an electron donor into both the valence band (VB)and conduction band (CB) to facilitate charge separation and suppress electron-hole recombination. Herein, Au nanoparticles served as CB electron donors in NiWO4 core particles which were evenlydispersed on a reduced graphene oxide (rGO) sheet that served as a VB electron donor. The resulting rGO/NiWO4@Au photocatalyst was applied to reducing CO2. The particles exhibited broadband absorbancefrom the ultraviolet to near-infrared, with a specific Au surface plasmon resonance (SPR) absorption peakat 600 nm. Moreover, the catalyst exhibited low photoluminescence (PL) and a high photocurrent density,indicating that photo-excited electron-hole recombination was suppressed and the charges effectivelyseparated. Photocatalytic reduction of CO2 on rGO/NiWO4@Au was significantly enhanced as evidencedby the total amounts of reduction products (CO and CH4), which were 15 times those for NiWO4 and sixtimes those for rGO/NiWO4 and NiWO4@Au. The expected electron-transfer mechanism on rGO/NiWO4@Au involves electron donation into the VB from the p-electron rich rGO, combined with photo-excited electrons from the NiWO4 and Au particles where electrons on the Au surfaces were amplified bythe SPR and then moved to the CB of NiWO4. Intensity-modulated photovoltage spectroscopy of rGO/NiWO4@Au indicated a significantly reduced electron-hole recombination rate.

Novel NiWO₄ nanoberries morphology effect on photoelectrochemical properties

Babu, Eadi Sunil,Rani, B. Jansi,Ravi, G.,Yuvakkumar, R.,Guduru, Ramesh K.,Ganesh, V.,Kim, Sungjin Elsevier 2018 Materials letters Vol.220 No.-

<P><B>Abstract</B></P> <P>We report a novel method to synthesis NiWO<SUB>4</SUB> nanoberries and their morphology dependent photoelectrochemical properties. XRD result revealed monoclinic wolframite NiWO<SUB>4</SUB> structure formation. FESEM and TEM showed average particle and nanoberries size of 4 and 50 nm respectively. Raman active stretching W–O vibration mode at 889 cm<SUP>−1</SUP>, PL blue green emission of intrinsic WO<SUB>6</SUB> <SUP>6−</SUP> complex with double emission center (3T<SUB>1u</SUB>-1A<SUB>1g</SUB>) and FTIR spectrum confirmed NiWO<SUB>4</SUB> formation with a calculated band gap of 2.86 eV. The much higher photocurrent of 0.03 mA/cm<SUP>2</SUP> was obtained at 0 V potential under visible light due to higher band gap (2.86 eV) of nanoberries morphology which led to efficient light absorption and increase in electron and hole separations.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel synthesis of NiWO<SUB>4</SUB> nanoberries morphology. </LI> <LI> Higher photocurrent of 0.03 mA/cm<SUP>2</SUP> due to higher band gap 2.86 eV. </LI> <LI> Nanoberries morphology led to absorption, increase electron hole separations. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Graphical abstract clearly shows the schematic representation of nanoberries formation which is evident that the effect of surfactant for the formation of a big berry contains number of small berries.</P> <P>[DISPLAY OMISSION]</P>

NiO/NiWO₄ Composite Yolk–Shell Spheres with Nanoscale NiO Outer Layer for Ultrasensitive and Selective Detection of Subppm-level <i>p</i>-Xylene

Kim, Tae-Hyung,Kwak, Chang-Hoon,Lee, Jong-Heun American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.37

<P>NiO/NiWO4 composite yolk shell spheres with a nanoscale NiO outer layer were prepared using one-pot ultrasonic spray pyrolysis and their gas sensing characteristics were studied. The NiO/NiWO4 yolk shell spheres exhibited an extremely high response to 5 ppm p-xylene (ratio of resistance to gas and air = 343.5) and negligible cross -responses to 5 ppm ethanol, ammonia, carbon monoxide, hydrogen, and benzene, whereas pure NiO yolk shell spheres showed very low responses and selectivity to all the analyte gases. The detection limit for p-xylene was as low as 22.7 ppb. This ultrasensitive and selective detection of p-xylene is attributed to a synergistic catalytic effect between NiO and NiWO4, high gas accessibility with large specific surface area, and increased chemiresistive variation due to the formation of a heterojunction. The NiO/NiWO4 yolk shell spheres with a thin NiO outer layer can be used to detect subppm-level p-xylene in a highly sensitive and selective manner for monitoring indoor air pollution.</P>

Evaluation of CO₂ methanation performance using rGO-NiWO₄@Au photocatalyst

신종민,강미숙 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

CO₂는 온실가스 전체 부피 중 76%를 차지하며 지구온난화로 인한 심각한 환경문제들을 야기하는데, 최근 CO₂ 감축과 동시에 에너지원으로 전환하는 기술(CCSU: Carbon Capturing Storage and Utility)이 전 세계적으로 많은 관심을 받고 있다. 이 중에서 태양에너지를 활용하는 CO₂의 광화학적 전환 기술이 최근 친환경적 미래 기술로써 많은 각광을 받고 있지만, 기술의 상용화를 위해서는 반응을 촉진시킬 수 있는 광촉매의 개발이 필수적이다. 따라서 본 연구에서는 메탄화 촉매로써 잘 알려진 Ni이 포함된 NiWO4를 이용하여 CO₂ 광환원 촉매로 사용하고자 하였다. 그리고 rGO에 NiWO4를 올려 촉매의 효율을 효과적으로 높이고자 했다. 이후 Au 나노 입자를 로딩해 SPR효과를 통한 효율상승을 확인하였다. 촉매의 물리 화학적 특성은 XRD, SEM/EDS, TEM을 통해 확인하였고, 광학적 특성은 PL, UV-Vis, XPS, Photo Current, IMVS, IMPS등을 이용해 확인하였다.

Morphology-controlled synthesis of 3D flower-like NiWO₄ microstructure via surfactant-free wet chemical method

Kumar, Mohit,Lee, Young Hun,Kim, Min Seob,Jeong, Dong In,Kang, Bong Kyun,Yoon, Dae Ho Elsevier 2018 JOURNAL OF ALLOYS AND COMPOUNDS Vol.753 No.-

<P><B>Abstract</B></P> <P>Three-dimensional (3D) flower-like controllable microstructures of nickel tungsten oxide (NiWO<SUB>4</SUB>) were synthesized by using a surfactant free wet chemical method at low temperature (60 °C). The uniform morphologies of NiWO<SUB>4</SUB> were molded by adjusting the temperature, stirring rate, and dosage of hydrazine in aqueous solution. We reported immediate precipitation of the 3D NiWO<SUB>4</SUB> microflowers (MFs) by introducing hydrazine monohydrate (N<SUB>2</SUB>H<SUB>4</SUB>·H<SUB>2</SUB>O). This approach resulted in a better yield and shortened the reaction time. In this work, we investigated the probable mechanism behind the formation of flower-like microstructures. Furthermore, the flower-like microstructure was assessed for its electrochemical properties towards non-enzymatic glucose sensing by addition of 50 μL of a glucose solution (50 μM) in an electrolyte (0.1 M NaOH) using glassy carbon electrode.</P> <P><B>Highlights</B></P> <P> <UL> <LI> 3D NiWO<SUB>4</SUB> MFs was successfully synthesized through a wet chemical method. </LI> <LI> 3D flower-like morphology was transformed by introducing hydrazine. </LI> <LI> 3D NiWO<SUB>4</SUB> MFs exhibits good electrochemical performance in terms of sensing glucose. </LI> </UL> </P>

Evaluation of CO₂ methanation performance using Ni_1-xLi₂xWO₄ photocatalyst

신종민,강미숙 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.0

최근 화석연료 사용의 증가로 대기 중 CO₂가 차지하는 부피가 커지며 지구온난화를 야기하고 있다. 이러한 환경문제를 야기하는 CO₂ 감축과 동시에 에너지원으로 전화하는 기술(CCSU: Carbon Capturing Storage and Utility)가 최근 많은 관심을 받으며 이를 위해서 광촉매의 개발은 필수적이다. 특히 본 연구에서는 메탄화 촉매로써 잘 알려진 Ni이 포함된 NiWO₄를 이용하여 CO₂ 광환원 촉매로 사용하고자 하였다. 하지만 촉매의 밴드갭이 빛에 의해 전자가 VB에서 CB로 들뜰 수 있도록 겹쳐져야 한다. 따라서 NiWO₄의 Energy Potential의 위치를 바꾸고자 비율에 따라 Ni을 Li로 치환 하였다. 이후 Li 비율에 따른 CO₂메탄화 효율을 비교해 최적의 비율을 찾고자 하였다. 촉매의 물리 화학적 특성은 XRD, TEM을 통해 확인하였고, 광학적 특성은 PL, UV-Vis, Photo Current등을 이용해 확인하였다.

Photocatalyst activities of rGO/NiWO₄@Au particles on carbon dioxide reduction under visible light

신종민,강미숙 한국공업화학회 2019 한국공업화학회 연구논문 초록집 Vol.2019 No.1

CO₂는 온실가스 전체 부피 중 76%를 차지하며 지구온난화로 인한 심각한 환경문제들을 야기하는데, 최근 CO₂ 저장과 에너지원으로 전환하는 기술(CCSU: Carbon Capturing Storage and Utility)이 전 세계적으로 많은 관심을 받고 있다. 이 중에서 태양에너지를 활용하는 CO₂의 광화학적 전환 기술이 최근 친환경적 미래 기술로써 많은 각광을 받고 있지만, 기술의 상용화를 위해서는 반응을 촉진시킬 수 있는 광촉매의 개발이 필요하다. 따라서 본 연구에서는 메탄화 촉매로써 잘 알려진 Ni이 포함된 NiWO₄를 이용하여 CO₂ 광환원 촉매로 사용하고자 하였다. 그리고 NiWO₄를 rGO에 올려 촉매의 효율을 효과적으로 높이고자 했다. 이후 Au 나노 입자를 로딩해 SPR효과의 영향을 보고자 했다. 그 결과 visible light 하에서 gas chromatography를 통해 CO₂ 메탄화 성능이 크게 향상되었다. 촉매의 물리 화학적 특성은 XRD, HR-TEM, TEM, Mass을 통해 확인하였고, 광학적 특성은 PL, UV-Vis, FT-IR, Raman, XPS, Photo Current, IMVS, IMPS등을 이용해 확인하였다.