Synthesis of nitrogen-doped multilayer graphene from milk powder with melamine and their application to fuel cells

Zhao, H.,Hui, K.S.,Hui, K.N. Pergamon Press ; Elsevier Science Ltd 2014 Carbon Vol.76 No.-

We reported on the facile synthesis of N-doped multilayer graphene (N-MLG) from milk powder that uses melamine as a nitrogen-doping source with Fe<SUP>2+</SUP> ions as catalytic growth agents. We showed that milk powder could be used as a precursor for large-scale N-MLG synthesis through heat treatment at 1000<SUP>o</SUP>C under N<SUB>2</SUB> atmosphere for 45-120min. In addition, heating time has a remarkable effect on N content and type in N-MLG. The resulting N-MLG exhibited higher catalytic activity than undoped graphene and carbon nanotubes (CNTs), as well as comparable catalytic activity to commercial Pt/C catalyst toward oxygen reduction reaction (ORR). Furthermore, the catalytic activity was sensitive to N content and type, particularly the ratio of pyridinic-N to total N atoms. Results showed that Fe atoms in N-MLG were found to function not as synergetic catalysts for ORR but as catalytic growth agents for N-MLG formation, thereby promoting and stabilizing N atoms. The present method could lead to the synthesis of bulk amounts of N-MLG, which is promising for applications in electrochemical energy devices, such as fuel cells and metal-air batteries.

IDENTIFICATION CAMPAIGN OF SUPERNOVA REMNANT CANDIDATES IN THE MILKY WAY. I.<i>CHANDRA</i>OBSERVATION OF G308.3-1.4

Hui, C. Y.,Seo, K. A.,Huang, R. H. H.,Trepl, L.,Woo, Y. J.,Lu, T.-N.,Kong, A. K. H.,Walter, F. M. IOP Publishing 2012 The Astrophysical journal Vol.750 No.1

<P>ROSAT all-sky survey data have provided another window in which to search for supernova remnants (SNRs). In re-examining this data archive, a list of unidentified extended X-ray objects have been suggested as promising SNR candidates. However, most of these targets have not yet been fully explored by state-of-the-art X-ray observatories. To select a pilot target for a long-term identification campaign, we observed the brightest candidate, G308.3-1.4, with the Chandra X-ray Observatory. An incomplete shell-like X-ray structure that is well correlated with the radio shell emission at 843 MHz has been revealed. The X-ray spectrum suggests the presence of a shock-heated plasma. All these evidences confirm G308.3-1.4 as an SNR. The brightest X-ray point source detected in this field of view is also the one located closest to the geometrical center of G308.3-1.4, which has a soft spectrum. The intriguing temporal variability and the identification of the optical/infrared counterpart rule out the possibility of an isolated neutron star. On the other hand, the spectral energy distribution from the K-s band to the R band suggests a late-type star. Together with a putative periodicity of similar to 1.4 hr, the interesting excesses in the V and B bands and in H alpha suggest that this source is a promising candidate for a compact binary that survived a supernova explosion.</P>

Green synthesis of dimension-controlled silver nanoparticle-graphene oxide with in situ ultrasonication

Hui, K.S.,Hui, K.N.,Dinh, D.A.,Tsang, C.H.,Cho, Y.R.,Zhou, W.,Hong, X.,Chun, H.H. Elsevier Science 2014 Acta materialia Vol.64 No.-

A green chemical approach to control the dimensions of Ag nanoparticle-decorated graphene oxide (AgNP-GO) composites was proposed by in situ ultrasonication of a mixture of AgNO<SUB>3</SUB> and GO solution with the assistance of vitamin C acting as an environmentally friendly reducing agent at room temperature. The AgNP-GO composites were characterized by X-ray diffraction, transmission electron microscopy, energy-dispersive spectroscopy, Fourier transform infrared spectroscopy, Raman spectra and ultraviolet-visible absorption spectra. The results demonstrated that Ag nanoparticles with an average diameter of ~15nm were uniformly dispersed on the surface of GO nanosheets by in situ ultrasonication of 1min with vitamin C. Increasing the ultrasonication times resulted in Ag nanoparticles with tunable dimensions ranging from 15 to 55nm being formed on the surface of GO nanosheets. The amount of silver nitrate and the ultrasonication time play a key role in the control of the dimension of Ag nanoparticles on GO, and a formation mechanism of the as-prepared AgNP-GO composites is proposed. This study provides a guide to controlling the dimensions of AgNP-GO composites, which may hold promise as advanced materials for various analytical applications such as catalysis, sensors and microchips.

3D hierarchical transition-metal sulfides deposited on MXene as binder-free electrode for high-performance supercapacitors

Hui Li,Xin Chen,Erfan Zalnezhad,K.N. Hui,K.S. Hui,Min Jae Ko 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.82 No.-

MXene has been considered as a promising two-dimensional material for supercapacitors owing to itslarge surface area, high conductivity, and excellent cycling stability. However, its low specific capacitancerestricts its extensive applications. Therefore, to address the issue, we homogeneously deposited NiCo2S4nanoflakes on the surface of MXene on conductive nickel foam (denoted as MXene-NiCo2S4@NF), whichwas used as a composite binder-free electrode for supercapacitor applications. The NiCo2S4 nanoflakesincreased the surface area of the composite electrode, thereby increasing its specific capacity from106.34 C g 1 to 596.69 C g 1 at 1 A g 1. Compared to the pristine MXene, MXene-NiCo2S4@NF maintainedthe high retention rate of pristine MXene and exhibited excellent cycling stability with 80.4% of its initialspecific capacity after 3000 cycles. The composite electrode exhibited improved electrochemicalperformance for supercapacitors, owing to the combined merits of NiCo2S4 (high specific capacity) andMXene (high retention rate and good cycling stability. The fabricated asymmetric solid-statesupercapacitor using MXene-NiCo2S4 as a positive electrode and active carbon as a negative electrode,exhibited an energy density of 27.24 Wh kg 1 at 0.48 kW kg 1 of power density.

Synthesis of Co3O4 nanowire arrays supported on Ni foam for removal of volatile organic compounds.

Hui, K N,Yin, Cui-Lei,Hui, K S,Lee, J Y,Li, M,Lee, S K,Tsui, K L,Chao, C Y H,Kwong, C W American Scientific Publishers 2012 Journal of Nanoscience and Nanotechnology Vol.12 No.4

<P>Crystalline Co3O4 nanowire arrays freely supported on Ni foam are successfully synthesized using a template-free method. The effects of reaction time, concentration of reactants, and temperature on the morphology of the nanowires are studied. The results indicate that uniform Co3O4 nanowires could be synthesized at 90 degrees C, and a transformation of the samples' morphology from nanoparticles to nanowires to microrods is observed by controlling the concentration of the reactants. The well-ordered nanowires synthesized under the selected reaction conditions are composed of spinel Co3O4 with diameters of 500-580 nm and lengths of 6-8 microm. These nanowires show good catalytic activity for the ozone catalytic oxidation of toluene.</P>

Electroreduction of H2O2 by Co3O4 and NiCo2O4 nanowires and beta-Ni(OH)2 nanoplates grown on Ni foam.

Hui, K N,Yin, Cui-Lei,Hui, K S,Lee, J Y,Cao, Dianxue,Wang, Guiling American Scientific Publishers 2012 Journal of nanoscience and nanotechnology Vol.12 No.4

<P>Nanowires (Co3O4 and NiCo2O4) and nanoplates (beta-Ni(OH)2) grown on Ni foam are successfully prepared by a template-free method and used as cathode electrodes for the electroreduction of H2O2, in an alkaline medium. Catalytic performance is investigated via cyclic voltammetry and chronoamperometry. The Co3O4 and NiCo2O4 nanowire electrodes exhibit much better catalytic activity, stability, and mass transfer properties for H2O2 electroreduction than pressed Co3O4 and NiCo2O4 nanoparticle/carbon/PTFE electrodes. A current density of 101.8 mA cm(-2) and 122.7 mA cm(-2) are respectively achieved on Co3O4 and NiCo2O4 nanowire electrodes at -0.4 V in 0.4 mol/L H2O2, and 3.0 mol/L NaOH solution at room temperature.</P>

Synthesis of Co₃O₄ nanowires on nickel foam by a novel microwave-assisted template-free method

Hui, K.S.,Hui, K.N.,Yin, C.L.,Hong, X. North-Holland 2013 Materials letters Vol.97 No.-

Spinel cobalt oxide (Co<SUB>3</SUB>O<SUB>4</SUB>) nanowires grown on Ni foam are successfully synthesized using a novel microwave-assisted template-free method. The effect of reaction temperature, concentration of reactants, and reaction time on the morphology and crystalline structures of the prepared nanowires is studied. The present work has demonstrated that uniform Co<SUB>3</SUB>O<SUB>4</SUB> nanowires with diameters of 500-580nm and lengths of 6-8μm can be synthesized under proper reaction condition. Moreover, the proposed microwave-assisted template-free method can significantly reduce reaction time, increase reaction efficiency, and provide better control over the geometry of the nanostructures.

Enhancement of Quality in Early Childhood Education : Using the Early Childhood Environment Rating Scale- Extension (ECERS-E) and Revised (ECRES-R) as Formative Assessment Tools for Professional Development - An Experience from Hong Kong

Anna N. N. Hui,Maria L. W. Lee,Priscilla S. C. Yeung,Jannet H. Y. Chick,Adith K. Y. Ho,Carly K. Y. Ng 환태평양유아교육연구학회 2017 Asia-Pacific journal of research in early childhoo Vol.11 No.3

The current study examined the reliability and applicability of the Chinese translated versions of the Early Childhood Environment Rating Scale ?Revised (ECERS-R) and Early Childhood Environment Rating Scale ?Extension (ECERS-E) as formative tools for use by local practitioners to perform selfevaluations on the various aspects of the educational environments being provided to pre-school children in their own settings with the goal of helping to facilitate changes that may help to enhance the quality of educational experiences for young children. Five registered kindergartens were recruited and received trainings in the administration of the said tools by the PECERA-HK (ECERS) professional team. Three assessment trials were administered in three different phases. For each trial, teacher representatives from each kindergarten completed the assessment using the said tools together with the trainers. Discussions were also held with the trainers on their observations. Internal reliability for the tools was found to be quite robust. Qualitative findings also suggested that the ECERS-R and ECERS-E can serve to assist practitioners in identifying the respective strengths and weaknesses in the educational environment they were providing to children and in setting clear directions for making corresponding improvements.

A Prospective Study on the Prevalence, Extent of Disease and Outcome of Eosinophilic Gastroenteritis in Patients Presenting with Lower Abdominal Symptoms

( Chee K Hui ),( N Kit Hui ) 대한간학회 2018 Gut and Liver Vol.12 No.3

Background/Aims: The epidemiology of eosinophilic gastroenteritis remains unclear. We aim to determine the prevalence of eosinophilic gastroenteritis in patients with lower abdominal symptoms. Methods: In a prospective study, colonoscopy was performed on 2,469 consecutive patients. Biopsies were taken from the terminal ileum and ascending, transverse, descending and sigmoid colon in all patients. Results: Sixty-four of the 2,469 patients (2.6%) had eosinophilic gastroenteritis. Only five of the 64 patients (7.8%) with eosinophilic gastroenteritis had endoscopic mucosal abnormalities during colonoscopy. Six of these 64 patients (9.4%) had severe disease at presentation, and seven of these 64 patients (10.9%) required systemic steroid treatment. An elevated absolute peripheral eosinophil count was independently associated with severe disease at presentation (4/6 [66.7%] vs 3/58 [5.2%], p=0.005; odds ratio [OR], 25.320; 95% confidence interval [CI], 2.628 to 243.910), and severe disease at the time of presentation was independently associated with the use of systemic steroid treatment (6/7 [85.7%] vs 0/57 [0%], p=0.008; OR, 18.021; 95% CI, 2.163 to 150.152). Conclusions: The prevalence of eosinophilic gastroenteritis is common, and patients usually present normal- appearing mucosa on colonoscopy. Those with severe disease at presentation usually have a raised absolute peripheral eosinophil count and should be commenced on systemic steroids as an initial therapy. (Gut Liver 2018;12:288- 296)

Influence of Bi³⁺-doping on the magnetic and Mössbauer properties of spinel cobalt ferrite

Gore, Shyam K.,Mane, Rajaram S.,Naushad, Mu.,Jadhav, Santosh S.,Zate, Manohar K.,Alothman, Z. A.,Hui, Biz K. N. The Royal Society of Chemistry 2015 Dalton Transactions Vol.44 No.14

<P>The influence of Bi<SUP>3+</SUP>-doping on the magnetic and Mössbauer properties of cobalt ferrite (CoFe<SUB>2</SUB>O<SUB>4</SUB>), wherein the Fe<SUP>3+</SUP> ions are replaced by the Bi<SUP>3+</SUP> ions to form CoBi<SUB><I>x</I></SUB>Fe<SUB>2−<I>x</I></SUB>O<SUB>4</SUB> ferrites, where <I>x</I> = 0.0, 0.05, 0.1, 0.15 or 0.2, has been investigated. The structural and morphological properties of undoped and doped ferrites, synthesized chemically through a self-igniting sol–gel method, are initially screened using X-ray diffraction, scanning electron microscopy and Fourier transform infrared spectroscopy measurements. The changes in magnetic moment of ions, their coupling with neighboring ions and cation exchange interactions are confirmed from the Mössbauer spectroscopy analysis. The effect of Bi<SUP>3+</SUP>-doping on the magnetic properties of CoFe<SUB>2</SUB>O<SUB>4</SUB> ferrite is examined from the vibrating sample magnetometry spectra. Saturation magnetization and coercivity values are increased initially and then decreased, as result of Bi<SUP>3+</SUP>-doping. The obtained results with improved saturation magnetization (from 26.36 to 44.96 emu g<SUP>−1</SUP>), coercivity (from 1457 to 1863 Oe) and remanence magnetization (from 14.48 to 24.63 emu g<SUP>−1</SUP>) on 0.1–0.15 mol Bi<SUP>3+</SUP>-doping of CoBi<SUB><I>x</I></SUB>Fe<SUB>2−<I>x</I></SUB>O<SUB>4</SUB> demonstrate the usefulness for magnetic recording and memory devices.</P> <P>Graphic Abstract</P><P>Bi<SUP>3+</SUP>-doping improves the saturation magnetization, coercivity and the remanence magnetization, which can be applied for magnetic recording and memory devices, of CoFe<SUB>2</SUB>O<SUB>4</SUB> ferrite. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c5dt00156k'> </P>