Feasibility Study of Synthesizing Graphene Quantum Dots From the Spent Resin in a Nuclear Power Plant

Seungbin Yoon,Woo Nyun Choi,Jaehoon Byun,Hee Reyoung Kim 한국방사성폐기물학회 2022 한국방사성폐기물학회 학술논문요약집 Vol.20 No.1

The feasibility study of synthesizing graphene quantum dots from spent resin, which is used in nuclear power plants to purify the liquid radioactive waste, was conducted. Owing to radiation safety and regulatory issues, an uncontaminated ion-exchange resin, IRN150 H/OH, prior to its use in a nuclear power plant, was used as the material of experiment on synthesis of graphene quantum dots. Since the major radionuclides in spent resin are treated by thermal decomposition, prior to conducting the experiment, carbonization of ion-exchange resin was performed. The experiment on synthesis of graphene quantum dots was conducted according to the general hydrothermal/solvothermal synthesis method as follows. The carbonized ion-exchange resin was added to a solution, which is a mixture of sulfuric acid and nitric acid in ratio of 3:1, and graphene quantum dots were synthesized at 115°C for 48 hours. After synthesizing, procedure, such as purifying, filtering, evaporating were conducted to remove residual acid from the graphene quantum dots. After freeze-drying which is the last procedure, the graphene quantum dots were obtained. The obtained graphene quantum dots were characterized using atomic force microscopy (AFM), Fourier-transform infrared (FT-IR) spectroscopy and Raman spectroscopy. The AFM image demonstrates the topographic morphology of obtained graphene quantum dots, the heights of which range from 0.4 to 3 nm, corresponding to 1–4 graphene layers, and the step height is approximately 2–2.5 nm. Using FT-IR, the functional groups in obtained graphene quantum dots were detected. The stretching vibrations of hydroxyl group at 3,420 cm?1, carboxylic acid (C=O) at 1,751 cm?1, C-OH at 1,445 cm?1, and C-O at 1,054 cm?1. The identified functional groups of obtained graphene quantum dots matched the functional groups which are present if it is a graphene quantum dot. In Raman spectrum, the D and G peaks, which are the characteristics of graphene quantum dots, were detected at wavenumbers of 1,380 cm?1 and 1,580 cm?1, respectively. Thus, it was verified that the graphene quantum dots could be successfully synthesized from the ionexchange resin.

Graphene transparent conductive electrodes doped with graphene quantum dots-mixed silver nanowires for highly-flexible organic solar cells

Shin, Dong Hee,Seo, Sang Woo,Kim, Jong Min,Lee, Ha Seung,Choi, Suk-Ho Elsevier 2018 Journal of alloys and compounds Vol.744 No.-

<P><B>Abstract</B></P> <P>Recent active studies on flexible photovoltaic cells strongly call for matchable flexible transparent electrodes. Graphene (GR) is one of the promising candidates as transparent conductive electrodes (TCEs) for flexible photovoltaic cells, but high sheet resistance of GR limits the efficiency of the cells. Here, we first fabricate GR TCEs doped with graphene quantum dots (GQDs)-mixed silver nanowires (Ag NWs) on polyethylene terephthalate substrates for highly-flexible organic solar cells (OSCs). With increasing doping concentration of GQDs to 0.03 g/L, the sheet resistance of the Ag NWs/GR TCE decreases to ∼92 Ω/sq whilst its work function increases to ∼4.53 eV, resulting in 3.66% power-conversion efficiency (PCE). In addition, the GQDs enhance the bending flexibility of the Ag NWs/GR TCEs, thereby maintaining the initial PCE of the OSCs over 90% even after 1000 bending cycles at a curvature radius of 4 mm.</P> <P><B>Highlights</B></P> <P> <UL> <LI> First use of graphene transparent conductive electrodes doped with graphene quantum dots-mixed silver nanowires. </LI> <LI> Graphene quantum dots make the doped graphene more suitable for anode electrodes of organic solar cells. </LI> <LI> Graphene quantum dots enhance the power-conversion efficiency of organic solar cells to 3.66%. </LI> <LI> Graphene quantum dots enhance the bending flexibility of organic solar cells. </LI> </UL> </P>

Fabrication of graphene quantum dot-decorated graphene sheets via chemical surface modification

유재훈,장정식 한국공업화학회 2015 한국공업화학회 연구논문 초록집 Vol.2015 No.1

A novel approach to link graphene quantum dots (GQDs) with graphene was explored via chemical surface modification of graphene using 1,5-diaminonapthalene (DAN). Interestingly, the population of GQDs increased with increasing the molar concentration of the DAN solution. The synthesized-GDGS was applied to photocatalyst for the degradation of methylene blue (MB) under visible light irradiation. The GDGS showed 1.6 times enhanced photocatalytic performance than pristine GQDs due to influences of graphene such as increase of visible light absorbance, charge separation, and adsorption on organic pollutants. This facile synthetic approach, which connects graphene to GQDs for the first time, is expected to promote the application of GQDs in photocatalyst and also in many other areas.

그래핀에 형성된 자기 양자점의 에너지 스펙트럼

명노준,임국형 한국물리학회 2017 새물리 Vol.67 No.10

우리는 그래핀 위에 불균일 자기장을 인가하여 형성된 자기 양자점의 고유에너지에 대해 연구를 수행하였다. 본 연구의 동기는 그래핀 위에 정전기 퍼텐셜을 이용하여 양자구조를 만드는데 존재하는 어려움들을 자기 퍼텐셜을 이용하면 극복할 수 있기 때문이다. 양자점에 강하게 국소 된 상태들이 양자홀 영역에서 발견되는데 이들은 양자점의 경계를 따라 시계 방향 또는 반시계 방향으로 도는 자기 끝머리 상태들로 이해할 수 있다. 고유 에너지 스펙트럼은 자기 양자점의 비균일한 자기장으로 말미암아 없어진 자기 선속 양자수에 크게 의존한다. 이러한 국소 상태들은 실험적으로 증명될 수 있는데 작은 그래핀 도체 위의 중앙에 자기 양자점을 형성하고 도체의 양 끝을 흐르는 두 단자 전기전도율을 측정하면 이들 국소 상태들을 통한 공명 후방산란 효과가 나타나게 된다. We investigate the eigen energies of a magnetic quantum dot formed in graphene by using the inhomogeneous distributions of magnetic fields. The motivation of our study is to overcome the existing difficulties in the formation of quantum structures in graphene via electrostatic confinements. Strongly localized states on the magnetic quantum dot are observed in the quantum Hall region and can be understood by using magnetic edge states circulating either clockwise or counterclockwise along the boundary of the dot. The eigen energy spectra are shown to depend critically on the number of missing flux quanta in the magnetic quantum dot. The existence of localized magnetic edge states can be proven experimentally by measuring the two-terminal conductance of a small graphene conductor with a magnetic quantum dot formed in its center, which reflects resonant backscattering via the magnetic edge states.

Live cell biosensing platforms using graphene-based hybrid nanomaterials

Kim, Tae-Hyung,Lee, Donghyun,Choi, Jeong-Woo Elsevier 2017 Biosensors & bioelectronics Vol.94 No.-

<P><B>Abstract</B></P> <P>A novel strategy to precisely detect or monitor various biomaterials in living cells poses paramount importance in understanding cellular processes. Graphene, a newly emerged two-dimensional carbon material, has been widely utilized for biosensors owing to its multifarious characteristics including mechanical, electrical, and optical properties (e.g. stability, conductivity, fluorescence quenching and photoluminescence). In addition, graphene derivatives and their innate characteristics, such as biocompatibility low cytotoxicity and water solubility have facilitated the use of graphene-based materials for live cell biosensing, wherein graphene is utilized as a core material by itself or in combination with other functional nanomaterials to load target-specific probes, fluorescent dyes, and other signaling molecules. Such graphene-based hybrid nanomaterials have been employed to detect various cellular entities in living cells, including ions, biomolecules, genetic molecules, proteins, enzymes, and even whole cells. The following review will discuss a number of previous studies in which graphene-based hybrid constructs were used for live cell biosensing, and their potential applications in cancer research and stem cell therapy.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Live-cell biosensing is highly important to understand major cellular activities. </LI> <LI> Graphene hybrid nanomaterials for live-cell biosensing were summarized. </LI> <LI> Graphene-modified substrates for live-cell biosensing were highlighted. </LI> </UL> </P>

Uniform Growth of High-Quality Oxide Thin Films on Graphene Using a CdSe Quantum Dot Array Seeding Layer

Kim, Yong-Tae,Lee, Seoung-Ki,Kim, Kwang-Seop,Kim, Yong Ho,Ahn, Jong-Hyun,Kwon, Young-Uk American Chemical Society 2014 ACS APPLIED MATERIALS & INTERFACES Vol.6 No.15

<P>Graphene displays outstanding properties as an electrode and a semiconducting channel material for transistors; however, the weak interfacial bond between graphene and an inorganic oxide material-based insulator presents a major constraint on these applications. Here, we report a new approach to improving the interface between the two materials using a CdSe quantum dot (QD)-based seeding layer in an inorganic material–graphene junction. CdSe QDs were electrochemically grown on graphene without degrading the properties of the graphene layer. The graphene structure was then used as the electrode in an oxide semiconductor by depositing a zinc oxide thin film onto the graphene coated with a QD seed layer (QD/G). The zinc oxide film adhered strongly to the graphene layer and provided a low contact resistance. A high-k dielectric layer in the form of an HfO<SUB>2</SUB> film, which is an essential element in the fabrication of high-performance graphene-based field effect transistors, was also uniformly formed on the QD/G sheet using atomic layer deposition. The resulting transistors provided a relatively good performance, yielding hole and electron mobilities of 2600 and 2000 cm<SUP>2</SUP>/V·s.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2014/aamick.2014.6.issue-15/am502922w/production/images/medium/am-2014-02922w_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am502922w'>ACS Electronic Supporting Info</A></P>

An alternative of NiCoSe doped graphene hybrid La₆W₂O₁₅ for renewable energy conversion used in dye-sensitized solar cells

Areerob, Yonrapach,Cho, Ju Yong,Jang, Won Kweon,Cho, Kwang Youn,Oh, Won-Chun Elsevier 2018 Solid state ionics Vol.327 No.-

<P><B>Abstract</B></P> <P>A cost effective and efficient alternative counter electrode (CE) to replace commercially existing platinum (Pt)-based CEs for dye-sensitized solar cells (DSSCs) is necessary to make DSSCs competitive. Herein, we report the model-controllable synthesis of Graphene-La<SUB>6</SUB>W<SUB>2</SUB>O<SUB>15</SUB> doped NiSe-CoSe quantum dot (GLW-NiCoSe) nanosheets with various NiCoSe content via simple hydrothermal method and used as CE for DSSC application. Electrochemical impedance spectroscopy (EIS) results confirmed that the as-synthesized GLW-NiCoSe nanosheets quantum dot exhibited good electrocatalytic properties and a low charge transfer resistance at the electrolyte-electrode interface. In addition, Thermal images and Photocurrent also demonstrate stability effect of material with more exposed edge sites and appropriate NiCoSe ratio. GLW-NiCoSe nanosheets performed rough surfaces, well-defined interior voids, large specific surface areas and outstanding catalytic actives. Finally, the mechanism of this material has been reported. All of these results showed a high energy conversion efficiency of up to 8%, which was comparable to the Pt CE (7%). The simple fabricated and good electrocatalytic properties of GLW-NiCoSe nanosheets make them as an alternative CE for DSSCs.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Novel Graphene-La<SUB>6</SUB>W<SUB>2</SUB>O<SUB>15</SUB>-NiSe-CoSe nanocomposites were successfully synthesized via simple hydrothermal method. </LI> <LI> DSSC based on Graphene-La<SUB>6</SUB>W<SUB>2</SUB>O<SUB>15</SUB>-NiSe-CoSe composite with different wt% of Graphene were fabricated using N719 dye as a sensitizer. </LI> <LI> La<SUB>6</SUB>W<SUB>2</SUB>O<SUB>15</SUB>-NiSe-CoSe can enhance short-circuit photocurrent and fill factor remarkably. </LI> <LI> Among all the structures, nanocomposites show the highest efficiency of 8.14%. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Graphene impregnated electrospun nanofiber sensing materials: a comprehensive overview on bridging laboratory set-up to industry

Al-Dhahebi Adel Mohammed,Gopinath Subash Chandra Bose,Saheed Mohamed Shuaib Mohamed 나노기술연구협의회 2020 Nano Convergence Vol.7 No.27

Owing to the unique structural characteristics as well as outstanding physio–chemical and electrical properties, gra‑ phene enables significant enhancement with the performance of electrospun nanofibers, leading to the generation of promising applications in electrospun-mediated sensor technologies. Electrospinning is a simple, cost-effective, and versatile technique relying on electrostatic repulsion between the surface charges to continuously synthesize various scalable assemblies from a wide array of raw materials with diameters down to few nanometers. Recently, electrospun nanocomposites have emerged as promising substrates with a great potential for constructing nanoscale biosensors due to their exceptional functional characteristics such as complex pore structures, high surface area, high catalytic and electron transfer, controllable surface conformation and modification, superior electric conductivity and unique mat structure. This review comprehends graphene-based nanomaterials (GNMs) (graphene, graphene oxide (GO), reduced GO and graphene quantum dots) impregnated electrospun polymer composites for the electro-device developments, which bridges the laboratory set-up to the industry. Different techniques in the base polymers (preprocessing methods) and surface modification methods (post-processing methods) to impregnate GNMs within elec‑ trospun polymer nanofibers are critically discussed. The performance and the usage as the electrochemical biosen‑ sors for the detection of wide range analytes are further elaborated. This overview catches a great interest and inspires various new opportunities across a wide range of disciplines and designs of miniaturized point-of-care devices.

Self-powered Ag-nanowires-doped graphene/Si quantum dots/Si heterojunction photodetectors

Shin, Dong Hee,Jang, Chan Wook,Kim, Jong Min,Choi, Suk-Ho Elsevier 2018 Journal of alloys and compounds Vol.758 No.-

<P><B>Abstract</B></P> <P>We report Ag-nanowires (Ag NWs)-doped graphene/p-type SiO<SUB>2</SUB>-embedded Si quantum dots (<I>p</I>-SQDs:SiO<SUB>2</SUB>)/n-Si heterojunction photodetectors (PDs). It is found that the p-n junctions show excellent PD characteristics including photocurrent/dark current (on/off) ratio of 10<SUP>5</SUP> at 0 V bias, meaning “self-powered”. The PDs optimized at an Ag NWs concentration of 0.1 wt % exhibit 0.32–0.65 AW<SUP>-1</SUP> responsivity (R), ∼85% external quantum efficiency (EQE), and ∼4.5 × 10<SUP>12</SUP> cm Hz<SUP>1/2</SUP>/W detectivity in the visible range of 500–900 nm. The linear dynamic range and response time of the PDs at 532 nm are ∼83 dB and ∼2 μs, respectively. The loss of the R is only 15% of its initial value while the PDs are kept for 700 h in air. In particular, the EQE of the self-powered PD is comparable to that of commercially-available Si PD and better than those of previously-reported graphene/Si PDs. These results suggest that the doped graphene/p-SQDs:SiO<SUB>2</SUB>/n-Si heterojunctions are promising for their applications in self-powered optoelectronic devices.</P> <P><B>Highlights</B></P> <P> <UL> <LI> First demonstration of self-power photodetector (PD) operation in graphene/Si quantum dots/Si heterojunctions. </LI> <LI> The PD parameters are comparable to those of commercial Si PDs and even better than those of graphene/Si PDs. </LI> <LI> The loss of the responsivity is only 15% of its initial value for 700 h in air. </LI> </UL> </P>

Highly-flexible and -stable deep-ultraviolet photodiodes made of graphene quantum dots sandwiched between graphene layers

Jang, Chan Wook,Shin, Dong Hee,Choi, Suk-Ho Elsevier 2019 Dyes and pigments Vol.163 No.-

<P><B>Abstract</B></P> <P>We first report highly-flexible and -stable deep-ultraviolet (DUV) photodiodes (PDs) by employing graphene (GR) quantum dots (GQDs) sandwiched between top/bottom GR layers on polyethylene terephthalates (PETs). Here, 3-aminopropyl triethoxysilane is inserted between the bottom GR and the PET substrate to enhance the bending stabilities without degradation or delamination by the chemical bonding. GQDs of ∼5 nm diameter are proved to be well formed on the bottom GR by various structural and optical analysis tools including high-resolution transmission electron microscopy, Raman scattering, and photoluminescence. The DUV PDs exhibit 10 photo-/dark-current ratio, 0.1 AW<SUP>-1</SUP> responsivity (R), and 1.1 × 10<SUP>13</SUP> cm Hz<SUP>1/2</SUP>/W detectivity at a wavelength of 254 nm. In addition, the R is reduced by only 13% even after 1000-times repeated bending tests at a bending curvature of 4 mm, and is almost consistent during the operations for 1000 h under ambient conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> First report of flexible deep UV photodiodes by employing graphene quantum dots. </LI> <LI> 0.1 AW<SUP>-1</SUP> responsivity and 1.1 × 10<SUP>13</SUP> cm Hz<SUP>1/2</SUP>/W detectivity is achieved. </LI> <LI> Stability maintaining ∼87% of initial responsivity after 1000 bending cycles. </LI> </UL> </P>