Multi-Functionality of Macroporous TiO₂ Spheres in Dye-Sensitized and Hybrid Heterojunction Solar Cells

Veerappan, Ganapathy,Jung, Dae-Woong,Kwon, Jeong,Choi, Jeong Mo,Heo, Nansra,Yi, Gi-Ra,Park, Jong Hyeok American Chemical Society 2014 Langmuir Vol.30 No.11

<P>Micron-sized macroporous TiO<SUB>2</SUB> spheres (MAC-TiO<SUB>2</SUB>) were synthesized using a colloidal templating process inside emulsions, which were then coated on a nanocrystalline TiO<SUB>2</SUB> light absorption film to prepare a bilayered photoanode for liquid-based dye-sensitized solar cells (DSSC) and hybrid heterojunction solid-state solar cells. MAC-TiO<SUB>2</SUB> layers can enhance light scattering as well as absorption, because their pore size and periodicity are comparable to light wavelength for unique multiple scattering and a porous surface can load dye more. Moreover, due to the bicontinuous nature of macropores and TiO<SUB>2</SUB> walls, electrolyte could be transported much faster in between the TiO<SUB>2</SUB> spheres rather than within the small TiO<SUB>2</SUB> nonporous architectures. Electron transport was also facilitated along the interconnected TiO<SUB>2</SUB> walls. In DSSCs with these MAC-TiO<SUB>2</SUB> scattering layers, efficiency was higher than conventional DSSCs incorporating a commercial scattering layer. The unique geometry of MAC-TiO<SUB>2</SUB> results in strong improvements in light scattering and infiltration of hole-transporting materials, thereby the MAC-TiO<SUB>2</SUB>-based solid-state device showed comparatively higher efficiency than the device with conventional nanocrystalline TiO<SUB>2</SUB>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/langd5/2014/langd5.2014.30.issue-11/la404841h/production/images/medium/la-2013-04841h_0007.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/la404841h'>ACS Electronic Supporting Info</A></P>

High-reversible capacity of Perovskite BaSnO₃/rGO composite for Lithium-Ion Battery Anodes

Veerappan, Ganapathy,SunyoungYoo, Ganapathy,Zhang, Kan,Ma, Ming,Kang, Byoungwoo,Park, Jong Hyeok Elsevier 2016 ELECTROCHIMICA ACTA Vol.214 No.-

<P><B>Abstract</B></P> <P>To the best of our knowledge, this is first report about composite of perovskite materials and reduced graphene oxide as anode material for high performance lithium ion battery (LIB). Here, we report outstanding specific capacities and cyclic stabilities of perovskite BaSnO<SUB>3</SUB> nanoparticles (NPs), decorated on 2D graphene sheets. Electrochemical measurements show that the composite BaSnO<SUB>3</SUB>/rGO20 (20wt.%rGO) delivered a highest capacity of 1200mAhg<SUP>−1</SUP> at a current rate of 0.5C (650mAg<SUP>−1</SUP>), which is comparatively much higher than individual pristine BaSnO<SUB>3</SUB> and graphene anodes. The BaSnO<SUB>3</SUB>/rGO composite anode exhibits a very high rate capability even at the 10C discharge rate (1059mAhg<SUP>−1</SUP>) and outstanding long-term stability. Notably, the composite anode material maintains its discharge capacity even after 100 cycles.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Sub-micrometer-sized Graphite As a Conducting and Catalytic Counter Electrode for Dye-sensitized Solar Cells

Veerappan, Ganapathy,Bojan, Karunagaran,Rhee, Shi-Woo American Chemical Society 2011 ACS APPLIED MATERIALS & INTERFACES Vol.3 No.3

<P>Sub-micrometer-sized colloidal graphite (CG) was tested as a conducting electrode to replace transparent conducting oxide (TCO) electrodes and as a catalytic material to replace platinum (Pt) for I<SUB>3</SUB><SUP>−</SUP> reduction in dye-sensitized solar cell (DSSC). CG paste was used to make a film via the doctor-blade process. The 9 μm thick CG film showed a lower resistivity (7 Ω/◻) than the widely used fluorine-doped tin oxide TCO (8−15 Ω/◻). The catalytic activity of this graphite film was measured and compared with the corresponding properties of Pt. Cyclic voltammetry and electrochemical impedance spectroscopy studies clearly showed a decrease in the charge transfer resistance with the increase in the thickness of the graphite layer from 3 to 9 μm. Under 1 sun illumination (100 mW cm<SUP>−2</SUP>, AM 1.5), DSSCs with submicrometer-sized graphite as a catalyst on fluorine-doped tin oxide TCO showed an energy conversion efficiency greater than 6.0%, comparable to the conversion efficiency of Pt. DSSCs with a graphite counter electrode (CE) on TCO-free bare glass showed an energy conversion efficiency greater than 5.0%, which demonstrated that the graphite layer could be used both as a conducting layer and as a catalytic layer.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2011/aamick.2011.3.issue-3/am101204f/production/images/medium/am-2010-01204f_0006.gif'></P>

Facile control of intra- and inter-particle porosity in template-free synthesis of size-controlled nanoporous titanium dioxides beads for efficient organic–inorganic heterojunction solar cells

Veerappan, Ganapathy,Yu, Sora,Wang, Dong Hwan,Lee, Wan In,Park, Jong Hyeok Elsevier 2015 Journal of Power Sources Vol.279 No.-

<P><B>Abstract</B></P> <P>In thin film solid-state heterojunction solar cells (HSCs), titanium-dioxide (TiO<SUB>2</SUB>) electrodes need to be optimized to have large specific surface area, controllable pore sizes, and superior light scattering properties. In this study, we synthesize hierarchical nanoporous TiO<SUB>2</SUB> beads with sub-micron diameters by a template-free, fast, and low-temperature synthetic scheme to satisfy the aforementioned requirements for HSCs. These nanoporous TiO<SUB>2</SUB> beads are composed of numerous TiO<SUB>2</SUB> nano crystallites that provide mesopores, and the inter-particle distances of size-controlled TiO<SUB>2</SUB> beads can provide additional controllable macropores. We report the first successful application of TiO<SUB>2</SUB> bead films (SP250, SP450) with controllable hierarchical nanostructure to be sensitized with Sb<SUB>2</SUB>S<SUB>3</SUB> for all-solid-state heterojunction solar cells (Sb-HSCs). The Sb-HSCs made using the controlled TiO<SUB>2</SUB> beads as photoanodes exhibit a superior light-to electricity conversion efficiency of 4.8%, yielding more than 15% enhancement in comparison with that (3.6%) of commercial TiO<SUB>2</SUB> nanoparticle (NP40) electrodes. The well-tailored photoanode with high surface area, fewer grain boundaries, multi-scale pore structure, and enhanced optical scattering results in much better infiltration of hole-conducting materials, decreased recombination with increased electron lifetime, and enhanced light scattering, which result in the enhanced photovoltaic properties.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Nanoporous TiO<SUB>2</SUB> beads with uniform sizes were synthesized by hydrothermal method. </LI> <LI> TiO<SUB>2</SUB> beads are composed of numerous TiO<SUB>2</SUB> nanoparticles that provides large surface area. </LI> <LI> TiO<SUB>2</SUB> beads big pores are favorable for uniform QD sensitization and HTM penetration. </LI> <LI> First successful application of TiO<SUB>2</SUB> beads (SP250, SP450) for Sb<SUB>2</SUB>S<SUB>3</SUB> sensitized all solid-state heterojunction solar cells. </LI> <LI> Devices made with TiO<SUB>2</SUB> beads showed superior light-to electricity conversion efficiency (4.8%). </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Identification and Molecular Characterization of CDPK Genes in Brassica oleracea

Karpagam Veerappan,Sathishkumar Natarajan,Harshavardhanan Vijayakumar,Jong-In Park,Ill-Sup Nou 한국원예학회 2016 한국원예학회 학술발표요지 Vol.2016 No.5

Sequence Variation in SlMYB12 is Associated with Fruit Peel Color in Pink Tomato Cultivars

Karpagam Veerappan,정희정,황인덕,고강희,정미영,노일섭 한국원예학회 2016 Horticulture, Environment, and Biotechnology Vol.57 No.3

The peel of pink-colored tomato is transparent due to the lack of accumulation of the flavonoid naringenin chalcone during ripening. A strong correlation was found between flavonoid expression and the function of SlMYB12, which is a transcriptional regulator of flavonoid biosynthesis. Thus, SlMYB12 is a strong candidate gene underlying the pink phenotype. Three allelic variants, a 603 bp deletion, a nucleotide substitution (C > T), and a 1 bp insertion (TG > TAG) in the SlMYB12 gene have been previously reported. We performed PCR genotyping based on these three allelic variations in 47 tomato cultivars displaying either a pink or red phenotype. However, the genotype did not match with the expected phenotype in one pink cultivar “Prime Alexander”. This cultivar was therefore self-pollinated to produce 20 progeny plants. To identify new mutations in SlMYB12, the sequence of genomic DNA and CDS were compared between the progeny 17 and the reference line, Heinz 1706. A novel G > T nucleotide substitution was found in the 2nd intron. This SNP leads to a deletion of 7 bp (GTAACAG) from the end of the 2nd exon, resulting in a premature stop codon. The presence of this SNP associates the pink phenotype with the genotype. This novel SNP will be useful as a genetic marker for marker-assisted breeding of pink tomato.

Preparation of gold nanoparticles using Salicornia brachiata plant extract and evaluation of catalytic and antibacterial activity

Ayaz Ahmed, K.B.,Subramanian, S.,Sivasubramanian, A.,Veerappan, G.,Veerappan, A. Pergamon 2014 Spectrochimica acta. Part A, Molecular and biomole Vol.130 No.-

The current study deals with the synthesis of gold nanoparticles (AuNPs) using Salicornia brachiata (Sb) and evaluation of their antibacterial and catalytic activity. The SbAuNPs showed purple color with a characteristic surface plasmon resonance peak at 532nm. Scanning electron microscopy and transmission electron microscopy revealed polydispersed AuNPs with the size range from 22 to 35nm. Energy dispersive X-ray and thin layer X-ray diffraction analysis clearly shows that SbAuNPs was pure and crystalline in nature. As prepared gold nanoparticles was used as a catalyst for the sodium borohydride reduction of 4-nitro phenol to 4-amino phenol and methylene blue to leucomethylene blue. The green synthesized nanoparticles exhibited potent antibacterial activity against the pathogenic bacteria, as evidenced by their zone of inhibition. In addition, we showed that the SbAuNPs in combination with the regular antibiotic, ofloxacin, exhibit superior antibacterial activity than the individual.

Ulmus macrocarpa Hance extract modulates intestinal microbiota in healthy adults: a randomized, placebo-controlled clinical trial

Kim Kwangmin,Veerappan Karpagam,Woo Nahyun,Park Bohyeon,Natarajan Sathishkumar,Chung Hoyong,김철민,Park Junhyung 한국미생물학회 2021 The journal of microbiology Vol.59 No.12

The stem and root bark of Ulmus macrocarpa Hance has been used as traditional pharmacological agent against inflammation related disorders. The objective of this study was to explore the impact of Ulmus macrocarpa Hance extract (UME) on human gut microbiota. A randomized placebo-controlled clinical study was conducted in healthy adults. The study subjects were given 500 mg/day of UME or placebo orally for 4 weeks. Eighty fecal samples were collected at baseline and 4 weeks of UME or placebo intervention. The gut microbiota variation was evaluated by 16S rRNA profiling. The microbial response was highly personalized, and no statistically significant differences was observed in both species richness and abundance. The number of bacterial species identified in study subjects ranged from 86 to 182 species. The analysis for taxonomical changes revealed an increase in Eubacterium ventriosum, Blautia faecis, Ruminococcus gnavus in the UME group. Functional enrichment of bacterial genes showed an increase in primary and secondary bile acid biosynthesis in UME group. Having known from previous studies Eubacterium regulated bile acid homeostasis in protecting gut microbial architecture and immunity, we suggest that UME supplementation might enhance host immunity by modulating gut microbiota. This is the first stage study and forthcoming clinical studies with larger participants are needed to confirm these findings.

Ramifi cations of Structural Deformations on Collapse Loads of Critically Cracked Pipe Bends Under In-Plane Bending and Internal Pressure

Sumesh Sasidharan,Veerappan Arunachalam,Shanmugam Subramaniam 한국원자력학회 2017 Nuclear Engineering and Technology Vol.49 No.1

Finite-element analysis based on elasticeperfectly plastic material was conducted to examine the influence of structural deformations on collapse loads of circumferential through-wall critically cracked 90˚ pipe bends undergoing in-plane closing bending and internal pressure. The critical crack is defined for a through-wall circumferential crack at the extrados with a subtended angle below which there is no weakening effect on collapse moment of elbows subjected to in-plane closing bending. Elliptical and semioval cross sections were postulated at the bend regions and compared. Twice-elastic-slope method was utilized to obtain the collapse loads. Structural deformations, namely, ovality and thinning, were each varied from 0% to 20% in steps of 5% and the normalized internal pressure was varied from 0.2 to 0.6. Results indicate that elliptic cross sections were suitable for pipe ratios 5 and 10, whereas for pipe ratio 20, semioval cross sections gave satisfactory solutions. The effect of ovality on collapse loads is significant, although it cancelled out at a certain value of applied internal pressure. Thinning had a negligible effect on collapse loads of bends with crack geometries considered.

Efficient Hole Extraction from Sb₂S₃ Heterojunction Solar Cells by the Solid Transfer of Preformed PEDOT:PSS Film

Kim, Jung Kyu,Veerappan, Ganapathy,Heo, Nansra,Wang, Dong Hwan,Park, Jong Hyeok American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.39

<P>Here, we report significant improvements of <I>V</I><SUB>oc</SUB> and FF in Sb<SUB>2</SUB>S<SUB>3</SUB> quantum dot (QD)-based, solid-state heterojunction solar cells prepared from the solid transfer of preformed PEDOT:PSS hole extraction layers. Despite the moderate optical properties of Sb<SUB>2</SUB>S<SUB>3</SUB> QDs, the solid state QD solar cells suffer from poor power conversion efficiency (PCE) resulting from the disappointing <I>V</I><SUB>oc</SUB> and the high series resistance since there is inefficient charge extraction from QDs to the metal top electrode. In order to improve the hole extraction performance, a significantly uniform PEDOT:PSS (poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)) layer was transferred on the hole transport layer (P3HT, poly(3-hexylthiophene-2,5-diyl)) by using a simple solid-transfer method. In contrast with conventional spin-cast methods, the hydrophilic PEDOT:PSS layer was uniformly coated on the hydrophobic P3HT layer without any significant detriment to P3HT film properties. Due to improved contact surface for the Au top electrode and hole conductance resulting in significantly improved charge extraction, the power conversion efficiency was dramatically enhanced. Furthermore, the thickness of the PEDOT:PSS film was precisely optimized by layer-by-layer solid transfer, and thereby the PCE of the PEDOT:PSS solid-transfer device (30 nm) was improved by 25.7% in comparison to the PEDOT:PSS spin-cast device and by 76% in comparison to the PEDOT:PSS free device.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-39/jp507652r/production/images/medium/jp-2014-07652r_0005.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/jp507652r'>ACS Electronic Supporting Info</A></P>