Synthesis of Sea Urchin-Like NiCo2O4 via Charge-Driven Self-Assembly Strategy for High Performance Lithium-Ion Batteries

In this study, hydrothermal synthesis of sea urchin-like NiCo2O4 was successfully demonstrated by a versatile charge-driven self-assembly strategy using positively charged poly(diallydimethylammonium chloride) (PDDA) molecules. Physical characterizations implied that sea urchin-like microspheres of ~ 2.5 μm in size were formed by self-assembly of numerous nanoneedles with a typical dimension of ~ 100 nm in diameter. Electrochemical performance study confirmed that sea urchin-like NiCo2O4 exhibited high reversible capacity of 663 mAh g−1 after 100 cycles at current density of 100 mA g−1. Rate capability indicated that average capacities of 1085, 1048, 926, 642, 261, and 86 mAh g−1 could be achieved at 100, 200, 500, 1000, 2000, and 3000 mA g−1, respectively. The excellent electrochemical performances were ascribed to the unique micro/nanostructure of sea urchin-like NiCo2O4, tailored by positively charged PDDA molecules. The proposed strategy has great potentials in the development of binary transition metal oxides with micro/nanostructures for electrochemical energy storage applications

Sea-Urchin-Like ZnO Nanoparticle Film for Dye-Sensitized Solar Cells

We present novel sea-urchin-like ZnO nanoparticles synthesized using a chemical solution method. Solution approaches to synthesizing ZnO nanostructures have several advantages including low growth temperatures and high potential for scaling up. We investigated the influence of reaction times on the thickness and morphology of sea-urchin-like ZnO nanoparticles, and XRD patterns show strong intensity in every direction. Dye-sensitized solar cells (DSSCs) were developed using the synthesized ZnO nanostructures as photoanodes. The DSSCs comprised a fluorine-doped tin oxide (FTO) glass with dense ZnO nanostructures as the working electrode, a platinized FTO glass as the counter electrode, N719-based dye, and I-/I3-liquid electrolyte. The DSSC fabricated using such nanostructures yielded a high power conversion efficiency of 1.16% with an incident photo-to-current efficiency (IPCE) as high as 15.32%. Electrochemical impedance spectroscopy was applied to investigate the characteristics of DSSCs. An improvement in the electron transport in the ZnO photoanode was also observed

Laser spectroscopic technique for direct identification of a single virus I: FASTER CARS

From the famous 1918 H1N1 influenza to the present COVID-19 pandemic, the need for improved viral detection techniques is all too apparent. The aim of the present paper is to show that identification of individual virus particles in clinical sample materials quickly and reliably is near at hand. First of all, our team has developed techniques for identification of virions based on a modular atomic force microscopy (AFM). Furthermore, femtosecond adaptive spectroscopic techniques with enhanced resolution via coherent anti-Stokes Raman scattering (FASTER CARS) using tip-enhanced techniques markedly improves the sensitivity [M. O. Scully, et al, Proc. Natl. Acad. Sci. U.S.A. 99, 10994-11001 (2002)]

Synthetic BiOBr/Bi2S3/CdS Crystalline Material and Its Degradation of Dye under Visible Light

Constructing heterojunction has attracted widespread concerns in photocatalysis research. BiOBr/Bi2S3/CdS composite material with a sea urchin shape was directly obtained by first synthesizing BiOBr microspheres. The morphology, structure and composition of the composite material were characterized by XRD, EDX, SEM and XPS. Dye degradation experiments showed that 83.3% of methylene blue removal was achieved after 2 h of visible light irradiation. The reaction rate under optimal conditions was 0.014 min−1 and the photocatalytic degradation process follows a pseudo-first-order kinetic model. Based on the EPR test results, the main active species involved in the reaction were •O2− and h+. The conduction band and valence band edge potential calculations confirmed the key role of CdS in the production of •O2−

Cell-Penetrating Protein/Corrole Nanoparticles

Recent work has highlighted the potential of metallocorroles as versatile platforms for the development of drugs and imaging agents, since the bioavailability, physicochemical properties and therapeutic activity can be dramatically altered by metal ion substitution and/or functional group replacement. Significant advances in cancer treatment and imaging have been reported based on work with a water-soluble bis-sulfonated gallium corrole in both cellular and rodent-based models. We now show that cytotoxicities increase in the order Ga < Fe < Al < Mn < Sb < Au for bis-sulfonated corroles; and, importantly, that they correlate with metallocorrole affinities for very low density lipoprotein (VLDL), the main carrier of lipophilic drugs. As chemotherapeutic potential is predicted to be enhanced by increased lipophilicity, we have developed a novel method for the preparation of cell-penetrating lipophilic metallocorrole/serum-protein nanoparticles (NPs). Cryo-TEM revealed an average core metallocorrole particle size of 32 nm, with protein tendrils extending from the core (conjugate size is ~100 nm). Optical imaging of DU-145 prostate cancer cells treated with corrole NPs (≤100 nM) revealed fast cellular uptake, very slow release, and distribution into the endoplasmic reticulum (ER) and lysosomes. The physical properties of corrole NPs prepared in combination with transferrin and albumin were alike, but the former were internalized to a greater extent by the transferrin-receptor-rich DU-145 cells. Our method of preparation of corrole/protein NPs may be generalizable to many bioactive hydrophobic molecules to enhance their bioavailability and target affinity

금속-유기 골격체(MOF) 를 활용하여 합성된 구리-철-질화물과 철-몰리브덴-산 질화물의 수분해 활성 연구

학위논문(박사) -- 서울대학교대학원 : 융합과학기술대학원 융합과학부(나노융합전공), 2021.8. 박원철.지난 수십 년간 각국은 지구 온난화를 늦출 필요성을 지속적으로 공론화해왔다. 이러한 정치적 움직임에도 불구하고 대기의 온실 가스 양은 빠른 속도로 증가하여 기후 변화 문제는 심각한 난제에서 본격적인 비상사태로 급등하였다. 지구 온난화에 대처하는 가장 효과적인 방법 중 하나는 현재의 탄소 기반 에너지 시스템을 녹색 수소 기반 에너지 시스템으로 전환하는 것이다. 수소는 전기, 열에너지 등의 최종 에너지로 변환 될 수 있으며, 전기와 달리 대용량으로 장기간 저장될 수 있다. 현재 화석 연료를 기반으로 한 수소 생산 방법은 상당한 양의 이산화탄소를 배출하기 때문에 재생 에너지를 기반으로 한 녹색 수소 생산이 필요 된다. 녹색 수소는 재생 에너지로 구동되는 전해조를 사용하는 물 전기 분해를 통해 생산될 수 있다. 물 전기 분해는 음극에서의 수소 발생 반응 (HER)과 양극에서의 산소 발생 반응 (OER)으로 구성되는데 본질적으로 느린 촉매 동역학으로 인해 실제 사용시 낮은 전기 화학 효율을 초래한다. 따라서 고도로 활성화 된 첨단 전기화학 촉매의 개발이 필요 된다. 과거에 Pt, Ru 및 Ir과 같은 백금족 금속이 높은 촉매 활성으로 인해 처음 제안되었지만 높은 비용, 희소성 및 불안정한 안정성으로 인해 대규모 산업 응용 분야에서 제한적이다. 이러한 이유로, 전이 금속 산화물, 탄화물, 인화물, 황화물, 질화물 및 산 질화물과 같은 다양한 형태의 지구에 풍부한 전이 금속이 대체 전기 촉매로서 집중적으로 조사되고 있다. 그 중에서도 전이 금속 질화물 / 산 질화물은 그의 화학적 안정성과 전도도를 포함한 유리한 특성으로 인해 큰 관심을 받고 있다. 그간 Co, Ni 및 Fe와 같은 전이 금속은 다양한 조합으로 광범위하게 연구되었으며 전기 분해에 유망한 것으로 입증되었다. 그러나 귀금속 기반 촉매에 비해 상대적으로 촉매 효율이 부족하기 때문에 추가 연구를 위한 여지가 충분하다. 본 논문에서는 수전해를 위한 전이금속 질화물/산질화물 기반 고성능 전기화학 촉매의 두 가지 예시를 제시한다. 첫 번째 연구에서는 구리-철 질화물/탄소나노튜브 복합체의 합성과 그의 전기화학 촉매 효율을 소개한다. 구리-철 질화물/탄소나노튜브 복합체는 유기금속 골격체 (MOF)를 전구체로 사용하여 마이크로파-질화를 통해 빠르게 합성될 수 있다. 전구체 MOF의 형태와 조성은 용매 의존적 성장 역학과 구리와 철 염의 비율을 조정하여 쉽게 제어 할 수 있다. 수성 매체에서 얻은 절묘한 성게 모양의 구리-철-MOF의 질화를 통해 얻어진 구리-철 질화물/탄소나노튜브 복합체는 크게 향상된 OER 활성을 나타내며 420mV의 적용된 과전압에서 전류 밀도가 단 4.25mA에서 236.32mA로 증가하여 5460.47 % 로 큰 폭의 향상을 보인다. 두 번째 연구에서는 마이크로파 합성법으로 빠르게 만들어진 MOF에서 파생 된 철-몰리브덴 산질화물 촉매의 제작과 수전해 성능을 다루었다. 철-몰리브덴 산질화물 촉매는 전구체 MOF의 다공성 미세 구조에 갇힌 5-10 nm 나노 입자로 구성되어 전해질 및 가스 수송을위한 여러 활성 부위와 경로를 제공한다. 또한 최적의 비율로 Mo를 첨가할 시 느린 Volmer 단계를 조정하여 촉매 활성이 크게 향상되는 것이 확인되었다. 철-몰리브덴 산질화물 촉매로 구성된 알칼리수 전해조는 상용 Pt/CRuO2 전해조 (100mA cm-2의 전류 밀도에서 1.89V)를 능가하는 촉매 거동(100mA cm-2의 전류 밀도에서 1.81V)과 우수한 안정성을 확보하였다. 두 연구 모두에서 개질되지 않은 비교군과 비교하여 개질된 촉매의 과전합이 크게 감소하는 것으로 보아 구조적 제어, 이중 금속 도입 및 질화 전략이 촉매활성 향상에 상당한 관련이 있음을 확인하였다.Over the past several decades, nations have collectively acknowledged the necessity to slow global warming. Despite the political movements, the amount of greenhouse gases in the atmosphere increased at an alarming rate, elevating climate change from a serious issue to a full-blown emergency. One of the most effective ways to tackle global warming is to convert the current carbon-based energy system to green hydrogen-based energy system. Hydrogen can be transformed into final energy such as electricity and thermal energy, and unlike electricity, it can be stored for a long time with a large capacity. As the current hydrogen production methods based on fossil fuels emit a considerable amount of carbon dioxide, green hydrogen production based on renewable energy is crucial. Green hydrogen can be produced through water electrolysis using an electrolyzer powered by renewable energy. Water electrolysis consists of the hydrogen evolution reaction (HER) at the cathode and the oxygen evolution reaction (OER) at the anode. However, the intrinsically sluggish catalytic kinetics result in low electrochemical efficiency for practical use. It is therefore necessary to develop highly active advanced electrocatalysts. In quest of such feasible electrocatalyst, noble metal groups such as Pt, Ru and Ir were first proposed for their high catalytic activity toward electrolysis, but their high cost, scarcity, and unreliable stability limits them for large-scale industrial applications. For these reasons, earth-abundant transition-metals have been intensively investigated as alternative electrocatalysts, in various forms such as transition-metal oxides, carbides, phosphides, sulfides, nitrides, and oxynitrides. Among them, transition metal nitrides/oxynitrides (TMN/TMON) are of great interest owing to their advantageous properties including chemical stability and conductivity. Transition metals such as Co, Ni, and Fe have been and still are extensively researched in various combinations and proven promising for electrolysis. Still, the relative lack of catalytic efficiency compared to the noble metal-based catalysts leaves plenty of room for further research. In this thesis, two examples of transition metal-based electrocatalysts efficient water electrolysis are presented. The first study demonstrates an environmentally benign synthesis of CuFeN/CNT as efficient OER catalyst by structural and electrochemical manipulation of its precursor MOF. The morphology and the composition of the precursor MOF can be easily controlled by adjusting the solvent-dependent growth kinetics and the ratio of the transition metal salts. An exquisite urchin-shaped CuFe-MOF obtained in aqueous medium is then rapidly transformed into CuFeN via microwave-assisted nitridation. The final catalyst CuFeN/CNT exhibits a greatly enhanced OER activity compared to its unmodified counterparts, exhibiting current density increase from a mere 4.25 mA to 236.32 mA at an applied overpotential of 420 mV, marking a 5460.47 % increase. The second study introduces a simple and energy-efficient synthesis route for MOF-derived FeMoON bifunctional catalyst. The final FeMoON catalyst derived from the precursor MOF is composed of 5-10 nm nanoparticles confined in the initial porous microstructure, providing multiple active sites and pathway for electrolyte and gas transport. The incorporation of Mo in optimal ratio significantly enhances the catalytic activity by tuning the sluggish Volmer step. The optimized FeMoON alkaline water electrolyzer shows catalytic behavior surpassing that of the commercial Pt/CRuO2 electrolyzer (1.81 V and 1.89 V, respectively, for current density of 100 mA cm−2) and good stability as well. The impact of structural control, secondary metal introduction, and nitridation on the enhanced electrocatalytic performances of the catalysts in both studies were confirmed by significantly increased overpotentials of the comparisons prepared in the absence of each conditions.Chapter 1. Introduction 17 1.1 Introduction to water electrolysis 17 1.1.1 Hydrogen evolution reaction 24 1.1.2 Oxygen evolution reaction 25 1.1.3 Overall water electrolysis 26 1.2 Transition metal-based catalysts 28 1.2.1 Strategies for developing transition metal-based catalysts. 34 1.2.2 Metal organic framework derived transition metal based catalysts 36 1.3 Perspective and outlook 41 1.4 Dissertation overview 44 Chapter 2. Bimetallic transition metal nitride/oxynitride-based catalysts for water electrolysis 47 2.1 CuFeN/CNT composite derived from kinetically modulated urchin-shaped MOF for highly efficient OER catalysis 47 2.1.1 Motivation 47 2.1.2 Experimental section 51 2.1.2.1 Reagents 51 2.1.2.2 Apparatus 52 2.1.2.3 Preparation of Cu2O nanoparticles 52 2.1.2.4 Preparation of CuFeO nanoparticles 53 2.1.2.5 Preparation of CuMOF urchins 53 2.1.2.6 Preparation of CuFeMOF urchins 54 2.1.2.7 Preparation of CuMOF/CNT/NH4HCO3 sponge 54 2.1.2.8 Preparation of CuFeMOF/CNT/NH4HCO3 sponge 54 2.1.2.9 Preparation of CuN/CNT catalysts 54 2.1.2.10 Preparation of of CuFeN/CNT catalysts 55 2.1.2.11 Electrochemical measurements 55 2.1.3 Results and discussion 57 2.1.4 Conclusion 101 2.2 Transformation of microwave synthesized highly uniform FeMo-MIL-88B nanorod to oxynitride derivate for overall water splitting reaction 102 2.2.1 Motivation 102 2.2.2 Experimental section 106 2.2.2.1 Reagents 106 2.2.2.2 Apparatus 106 2.2.2.3 Preparation of Fe-MIL-88B 107 2.2.2.4 Preparation of FeMo-MIL-88B 107 2.2.2.5 Preparation of FeMoON 108 2.2.2.6 Electrochemical measurements 108 2.2.3 Results and discussion 110 2.2.4 Conclusion 154 2.2.5 References 156 Chapter 3. Conclusion 182 국문 초록 (Abstract in Korean) 185박

Structural, Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Nanocrystalline Materials: Synthesis, Characterization and Application

This book is a collection of the research articles and review article, published in special issue "Structural, Magnetic, Dielectric, Electrical, Optical and Thermal Properties of Nanocrystalline Materials: Synthesis, Characterization and Application"

The impact of structure on the electrical transport properties of nitrogen-doped carbon microspheres

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. April 2016.Chemical vapour deposition was used to synthesise four carbon microspheres (CMS) samples. Introduction of acetonitrile in different quantities produced spheres of differing nitrogen concentration. The structure of the spheres was investigated using Raman spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy techniques. The Raman investigation revealed a decrease in average graphitic flake size which forms the surface layers of the spheres with nitrogen incorporation. XPS showed that increased nitrogen doping caused a larger proportion of pyridinic nitrogen, which process likely restricts the growth of the crystallite flakes detected with the Raman technique. Microscopy revealed spheres with differing morphologies which did not correlated with the level of nitrogen doping. Electron paramagnetic resonance techniques were employed to investigate the impact of nitrogen doping on the spin system of the samples. Electrical transport and Hall effect data were collected with an automated experiment station purpose built for this work. Samples displayed semiconducting behaviour at low temperatures which was ascribed to fluctuation assisted tunnelling. At higher temperatures all four samples display a transition to metallic behaviour. Models for conduction, which were tested but ultimately rejected, include variable range hopping in all its dimensional forms, Efros-Shklovskii VRH and weak localisation. A comparison of the conduction results and the structural information showed the conductivity to be more closely affected by the structure of the spheres than the overall doping level. A case is made for the dominant conduction mechanism being determined by the intersphere rather than the intrasphere conduction. This research shows that creating carbon microspheres with specific electrical properties requires control of the structure induced during synthesis. Nitrogen doping alone does not determine the final physical and electrical transport properties.LG201