Au@NiO core-shell nanoparticles as a p-type gas sensor: Novel synthesis, characterization, and their gas sensing properties with sensing mechanism

Majhi, Sanjit Manohar,Naik, Gautam Kumar,Lee, Hu-Jun,Song, Ho-Geun,Lee, Cheul-Ro,Lee, In-Hwan,Yu, Yeon-Tae Elsevier 2018 Sensors and actuators. B, Chemical Vol.268 No.-

<P><B>Abstract</B></P> <P>In this work, Au@NiO core-shell nanoparticles (C-S NPs) as a p-type gas sensing material was synthesized by a facile wet-chemical method, and evaluated their gas sensing properties as compared to the pristine NiO NPs gas sensors. Transmission electron microscope (TEM) results exhibited the well-dispersed formation of Au@NiO C-S NPs having the total size of 70–120 nm and NiO shells having 30–50 nm thickness. The C-S morphology as well as the overall particle sizes are unchanged even at 500 °C. The gas sensing result reveals that the response of Au@NiO C-S NPs gas sensor is higher than pristine NiO NPs gas sensor for 100 ppm of ethanol at 200 °C operating temperature. The baseline resistance in the air for Au@NiO C-S NPs sensor is lowered as compared to pristine NiO NPs, which is due to the increased number of holes as charge carriers in Au@NiO C-S NPs. The high response of Au@NiO core-shell NPs as compared to pristine NiO NPs is attributed to electronic and chemical sensitization effects of Au. In Au@NiO C-S structure, the contact between metal (Au) and semiconductor (NiO) formed a Schottky junction since Au metal acted as electron acceptor, a withdrawal of electrons from NiO by Au metal core leaved behind number of holes as charge carriers in Au@NiO C-S NPs. Therefore, the baseline resistance of Au@NiO C-S NPs greatly decreased than pristine NiO NPs, as a result the Au@NiO C-S NPs showed higher response. On the other hand, in chemical sensitization effect, Au NPs catalyzed to dissociate O<SUB>2</SUB> molecules into ionic species. This work will give some clue to the researchers for the further development of p-type based C-S NPs sensors.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Au@NiO core-shell nanoparticles (C-S NPs) maintained spherical morphology and showed porous structure after calcined at 500 °C. </LI> <LI> Au@NiO C-S NPs sensor showed higher ethanol response than pure NiO NPs. </LI> <LI> The baseline resistance of Au@NiO C-S NPs was lowered than pure NiO NPs. </LI> <LI> Au@NiO C-S NPs sensor showed good repeatability. </LI> <LI> The role of Au NPs for high response of Au@NiO C-S NPs was investigated. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Au@NiO core-shell nanoparticles (C-S NPs) as a p-type gas sensing material was synthesized by a facile wet-chemical method and shows higher gas sensing properties as compared to the pristine NiO NPs gas sensors.</P> <P>[DISPLAY OMISSION]</P>

A Comparative Study of Gas Sensing Properties of Au-loaded ZnO and Au@ZnO Core-shell Nanoparticles

Sanjit Manohar Majhi,Dung Van Dao,Hu-Jun Lee,유연태 한국센서학회 2018 센서학회지 Vol.27 No.2

Au@ZnO core-shell nanoparticles (NPs) were prepared by a simple method followed by heat-treatment for gas sensor applications. The advantage of the core-shell morphology was investigated by comparing the gas sensing performances of Au@ZnO core-shell NPs with pure ZnO NPs and different wt% of Au-loaded ZnO NPs. The crystal structures, shapes, sizes, and morphologies of all sensingmaterials were characterized by XRD, TEM, and HAADF-STEM. Au@ZnO core-shell NPs were nearly spherical in shape and Au NPswere encapsulated in the center with a 40–45 nm ZnO shell outside. The gas sensing operating temperature for Au@ZnO core-shellNPs was 300°C, whereas it was 350°C for pure ZnO NPs and Au-loaded ZnO NPs. The maximum response of Au@ZnO core-shell NPs to 1000 ppm CO at 300°C was 77.3, which was three-fold higher than that of 2 wt% Au-loaded ZnO NPs. Electronic and chemicaleffects were the primary reasons for the improved sensitivity of Au@ZnO core-shell NPs. It was confirmed that Au@ZnO core-shellNPs had better sensitivity and stability than Au-loaded ZnO NPs.

Effect of Au Nanorods on Potential Barrier Modulation in Morphologically Controlled Au@Cu₂O Core–Shell Nanoreactors for Gas Sensor Applications

Majhi, Sanjit Manohar,Rai, Prabhakar,Raj, Sudarsan,Chon, Bum-Soo,Park, Kyung-Kuen,Yu, Yeon-Tae American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.10

<P>In this work, Au@Cu<SUB>2</SUB>O core–shell nanoparticles (NPs) were synthesized by simple solution route and applied for CO sensing applications. Au@Cu<SUB>2</SUB>O core–shell NPs were formed by the deposition of 30–60 nm Cu<SUB>2</SUB>O shell layer on Au nanorods (NRs) having 10–15 nm width and 40–60 nm length. The morphology of Au@Cu<SUB>2</SUB>O core–shell NPs was tuned from brick to spherical shape by tuning the pH of the solution. In the absence of Au NRs, cubelike Cu<SUB>2</SUB>O NPs having ∼200 nm diameters were formed. The sensor having Au@Cu<SUB>2</SUB>O core–shell layer exhibited higher CO sensitivity compared to bare Cu<SUB>2</SUB>O NPs layer. Tuning of morphology of Au@Cu<SUB>2</SUB>O core–shell NPs from brick to spherical shape significantly lowered the air resistance. Transition from p- to n-type response was observed for all devices below 150 °C. It was demonstrated that performance of sensor depends not only on the electronic sensitization of Au NRs but also on the morphology of the Au@Cu<SUB>2</SUB>O core–shell NPs.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-10/am5008694/production/images/medium/am-2014-008694_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5008694'>ACS Electronic Supporting Info</A></P>

Facile Approach to Synthesize Au@ZnO Core–Shell Nanoparticles and Their Application for Highly Sensitive and Selective Gas Sensors

Majhi, Sanjit Manohar,Rai, Prabhakar,Yu, Yeon-Tae American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.18

<P>We successfully prepared Au@ZnO core-shell nanoparticles (CSNPs) by a facile low-temperature solution route and studied its gas-sensing properties. The obtained Au@ZnO CSNPs were carefully characterized by X-ray diffraction, transmission electron microscopy (TEM), high-resolution TEM, and UV-visible spectroscopy. Mostly spherical-shaped Au@ZnO CSNPs were formed by 10-15 nm Au NPs in the center and by 40-45 nm smooth ZnO shell outside. After the heat-treatment process at 500 degrees C, the crystallinity of ZnO shell was increased without any significant change in morphology of Au@ZnO CSNPs. The gas-sensing test of Au@ZnO CSNPs was examined at 300 degrees C for various gases including H-2 and compared with pure ZnO NPs. The sensor Au@ZnO CSNPs showed the high sensitivity and selectivity to H2 at 300 degrees C. The response values of Au@ZnO CSNPs and pure ZnO NPs sensors to 100 ppm of H-2 at 300 degrees C were 103.9 and 12.7, respectively. The improved response of Au@ZnO CSNPs was related to the electronic sensitization of Au NPs due to Schottky barrier formation. The high selectivity of Au@ZnO CSNPs sensor toward H2 gas might be due to the chemical as well as catalytic effect of Au NPs.</P>

Morphology controlled Ag@SiO2 core–shell nanoparticles by ascorbic acid reduction

Raj, Sudarsan,Rai, Prabhakar,Majhi, Sanjit Manohar,Yu, Yeon-Tae Springer-Verlag 2014 Journal of materials science Materials in electron Vol.25 No.3

Nitrogen doping on the core-shell structured Au@TiO₂ nanoparticles and its enhanced photocatalytic hydrogen evolution under visible light irradiation

Naik, Gautam Kumar,Majhi, Sanjit Manohar,Jeong, Kwang-Un,Lee, In-Hwan,Yu, Yeon Tae Elsevier 2019 JOURNAL OF ALLOYS AND COMPOUNDS Vol.771 No.-

<P><B>Abstract</B></P> <P>The current study concerns about the large band gap of TiO<SUB>2</SUB> for its use as photocatalysts. The photocatalytic activity of core-shell structured Au@TiO<SUB>2</SUB> nanoparticles were enhanced by the doping of nitrogen. The nitrogen doping has been done by simple hydrothermal method taking ethylenediamine as the precursor for nitrogen. The crystals structure of TiO<SUB>2</SUB> shell remained unaltered even with the introduction of nitrogen. The photocatalytic activity of the prepared samples were evaluated towards the hydrogen evolution from photocatalytic water splitting under solar light irradiation. It was found that nitrogen doped core-shell structured Au@TiO<SUB>2</SUB> nanoparticles (Au@N-TiO<SUB>2</SUB>) showed higher photocatalytic activity with an average H<SUB>2</SUB> evolution rate of 4880 μmol h<SUP>−1</SUP>g<SUP>−1</SUP>, which is 3.79 times more than that of bare TiO<SUB>2</SUB> in 4 h under xenon light irradiation. The relationship among the other samples was in order of Au@N-TiO<SUB>2</SUB> > Au@TiO<SUB>2</SUB> > N-TiO<SUB>2</SUB> > TiO<SUB>2</SUB>. This enhanced photocatalytic activity of Au@N-TiO<SUB>2</SUB> can be responsible for the formation of an plasmonic photocatalyst and the formation of an impurity band between the conduction band (CB) and the valence band (VB) of TiO<SUB>2</SUB>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nitrogen (N) was doped on the core-shell structured Au@TiO<SUB>2</SUB> nanoparticles. </LI> <LI> N was doped via a low temperature microwave assisted hydrothermal process. </LI> <LI> N doped Au@TiO<SUB>2</SUB> core-shell are highly absorbed in whole of the solar spectrum. </LI> <LI> There was no morphological distortion during N doping. </LI> <LI> Synthesized catalysts are highly efficient for photocatalytic hydrogen evolution. </LI> </UL> </P>

Au@Cu2O core-shell nanoparticles as chemiresistors for gas sensor applications: effect of potential barrier modulation on the sensing performance

Rai, Prabhakar,Khan, Rizwan,Raj, Sudarsan,Majhi, Sanjit Manohar,Park, Kyung-Kuen,Yu, Yeon-Tae,Lee, In-Hwan,Sekhar, Praveen Kumar The Royal Society of Chemistry 2014 Nanoscale Vol.6 No.1

Au@Cu2O core-shell nanoparticles (NPs) were synthesized by a solution method at room temperature and applied for gas sensor applications. Transmission electron microscopy (TEM) images showed the formation of Au@Cu2O core-shell NPs, where 12-15 nm Au NPs were covered with 60-30 nm Cu2O shell layers. The surface plasmon resonance (SPR) peak of Au NPs was red-shifted (520-598 nm) after Cu2O shell formation. The response of Au@Cu2O core-shell NPs was higher than that of bare Cu2O NPs to CO at different temperatures and concentrations. Similarly, the response of Au@Cu2O core-shell NPs was higher than that of bare Cu2O NPs for NO2 gas at low temperature. The improved performance of Au@Cu2O core-shell NPs was attributed to the pronounced electronic sensitization, high thermal stability and low screening effect of Au NPs.

Conducting Polymer Nanofibers based Sensors for Organic and Inorganic Gaseous Compounds

Mirzaei Ali,Kumar Vanish,Bonyani Maryam,Majhi Sanjit Manohar,Bang Jae Hoon,Kim Jin-Young,김현우,김상섭,김기현 한국대기환경학회 2020 Asian Journal of Atmospheric Environment (AJAE) Vol.14 No.2

Resistive-based gas sensors built through the combination of semiconducting metal oxides and conducting polymers (CPs) are widely used for the detection of diverse gaseous components. In light of the great potential of each of these components, electrospun CPs produced by a facile electrospinning method can offer unique opportunities for the fabrication of sensitive gas sensors for diverse gaseous compounds due to their large surface area and favorable nanomorphologies. This review focuses on the progress achieved in gas sensing technology based on electrospun CPs. We offer numerous examples of CPs as gas sensors and discuss the parameters affecting their sensitivity, selectivity, and sensing mechanism. This review paper is expected to offer useful insights into potential applications of CPs as gas sensing systems.