Heterogeneous modulation of exciton emission in triangular WS₂ monolayers by chemical treatment

Dhakal, Krishna P.,Roy, Shrawan,Yun, Seok Joon,Ghimire, Ganesh,Seo, Changwon,Kim, Jeongyong The Royal Society of Chemistry 2017 Journal of materials chemistry. C, Materials for o Vol.5 No.27

<▼1><P>Spatially heterogeneous effects of bis(trifluoromethane)sulfonimide (TFSI) and benzyl viologen (BV) treatment on the optical properties of triangular monolayer tungsten disulfides are investigated by nanoscale spectral imaging.</P></▼1><▼2><P>Chemical treatments were recently shown to be very effective in enhancing the exciton emission of monolayer transition metal dichalcogenides (1L-TMDs) by suppressing the exciton quenching caused by structural defects. However, the effects of these chemical treatments varied greatly depending on the synthesis method and the type of 1L-TMD; therefore, the exact origin of the emission enhancement is still elusive. Here we report the spatially heterogeneous effects of bis(trifluoromethane)sulfonimide (TFSI) and benzyl viologen (BV) treatment on the optical properties of triangular 1L-WS2 grown by chemical vapor deposition (CVD). Nanoscale photoluminescence (PL) and Raman spectral maps showed that TFSI had a minimal effect on the inner region of the triangular WS2 grain, whereas the PL of the edge region was enhanced up to 25 times; further, BV reduced the PL, also more strikingly in the edge region. Systematic variation of the spectral weights among neutral excitons, trions, and bi-excitons indicated that p-doping and n-doping with TFSI and BV, respectively, occurred in both the inner and edge regions; however, the PL enhancement was attributed mainly to the reduction of structural defects caused by TFSI treatment. Our observation of the spatially heterogeneous effects of chemical treatment suggests that the inner and edge regions of CVD-grown 1L-WS2 are populated with different types of structural defects and helps in clarifying the mechanism by which chemical treatment enhances the optical properties of 1L-TMDs.</P></▼2>

Optically active charge transfer in hybrids of Alq₃ nanoparticles and MoS₂ monolayer

Ghimire, Ganesh,Dhakal, Krishna P,Neupane, Guru P,Gi Jo, Seong,Kim, Hyun,Seo, Changwon,Hee Lee, Young,Joo, Jinsoo,Kim, Jeongyong IOP 2017 Nanotechnology Vol.28 No.18

<P>Organic/inorganic hybrid structures have been widely studied because of their enhanced physical and chemical properties. Monolayers of transition metal dichalcogenides (1L-TMDs) and organic nanoparticles can provide a hybridization configuration between zero- and two-dimensional systems with the advantages of convenient preparation and strong interface interaction. Here, we present such a hybrid system made by dispersing <I>π</I>-conjugated organic (tris (8-hydroxyquinoline) aluminum(III)) (Alq<SUB>3</SUB>) nanoparticles (NPs) on 1L-MoS<SUB>2</SUB>. Hybrids of Alq<SUB>3</SUB> NP/1L-MoS<SUB>2</SUB> exhibited a two-fold increase in the photoluminescence of Alq<SUB>3</SUB> NPs on 1L-MoS<SUB>2</SUB> and the n-doping effect of 1L-MoS<SUB>2</SUB>, and these spectral and electronic modifications were attributed to the charge transfer between Alq<SUB>3</SUB> NPs and 1L-MoS<SUB>2</SUB>. Our results suggested that a hybrid of organic NPs/1L-TMD can offer a convenient platform to study the interface interactions between organic and inorganic nano objects and to engineer optoelectronic devices with enhanced performance.</P>

Differential pulse voltammetric sensor for tetracycline using manganese tungstate nanowafers and functionalized carbon nanofiber modified electrode

라먀라므쿠마르,Ganesh Dhakal,심재진,김우경 한국화학공학회 2022 Korean Journal of Chemical Engineering Vol.39 No.8

A label-free approach was employed to selectively detect tetracycline using manganese tungstate (MnWO4)nanowafers and functionalized carbon nanofiber-modified glassy carbon electrode (GCE). MnWO4 nanowafers weresynthesized hydrothermally and characterized along with functionalized carbon nanofibers (f-CNFs). Cyclic voltammetryand differential pulse voltammetry were employed to detect tetracycline, and the sensor exhibited linear ranges ofdetection of 1.75‒109.25 M and 109.25‒409.25 M, respectively. The limit of detection was found to be 0.24 M (S/N=3) with a sensitivity of 9.91 A M1 cm2. Interference studies were carried out with ciprofloxacin (Cip), penicillin(Pen), and amoxicillin (Amox). The modified electrode (MnWO4/f-CNF/GCE) was found to provide sensitive andselective detection of tetracycline in the presence of interfering agents.

Sulfur Doping: Unique Strategy To Improve the Supercapacitive Performance of Carbon Nano-onions

Mohapatra, Debananda,Dhakal, Ganesh,Sayed, Mostafa Saad,Subramanya, Badrayyana,Shim, Jae-Jin,Parida, Smrutiranjan American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.8

<P>Recently, enhancement of the energy density of a supercapacitor is restricted by the inferior capacitance of negative electrodes, which impedes the commercial development of high-performance symmetric and asymmetric supercapacitors. This article introduces the in situ bulk-quantity synthesis of hydrophilic, porous, graphitic sulfur-doped carbon nano-onions (S-CNO) using a facile flame-pyrolysis technique and evaluated its potential applications as a high-performance supercapacitor electrode in a symmetric device configuration. The high-surface wettability in the as-prepared state enables the formation of highly suspended active conducting material S-CNO ink, which eliminates the routine use of binders for the electrode preparation. The as-prepared S-CNO displayed encouraging features for electrochemical energy storage applications with a high specific surface area (950 m<SUP>2</SUP> g<SUP>-1</SUP>), ordered mesoporous structure (∼3.9 nm), high S-content (∼3.6 at. %), and substantial electronic conductivity, as indicated by the ∼80% sp<SUP>2</SUP> graphitic carbon content. The in situ sulfur incorporation into the carbon framework of the CNO resulted in a high-polarized surface with well-distributed reversible pseudosites, increasing the electrode-electrolyte interaction and improving the overall conductivity. The S-CNOs showed a specific capacitance of 305 F g<SUP>-1</SUP>, an energy density of 10.6 W h kg<SUP>-1</SUP>, and a power density of 1004 W kg<SUP>-1</SUP> at an applied current density of 2 A g<SUP>-1</SUP> in a symmetrical two-electrode cell configuration, which is approximately three times higher than that of the pristine CNO-based device in a similar electrochemical testing environment. Even at 11 A g<SUP>-1</SUP>, the S-CNO||S-CNO device rendered an energy density (6.1 W h kg<SUP>-1</SUP>) at a deliverable power density of 5.5 kW kg<SUP>-1</SUP>, indicating a very good rate capability and power management during peak power delivery applications. Furthermore, it showed a high degree of electrochemical reversibility with excellent cycling stability, retaining ∼95% of its initial capacitance after more than 10 000 repetitive charge-discharge cycles at an applied current density of 5 A g<SUP>-1</SUP>.</P> [FIG OMISSION]</BR>

Solar light-active S-scheme TiO2/In2S3 heterojunction photocatalyst for organic pollutants degradation

Manjiri A. Mahadadalkar,Ganesh Dhakal,Sumanta Sahoo,Deivasigamani Ranjith Kumar,Marjorie Lara Baynosa,Van Quang Nguyen,Mostafa Saad Sayed,Abdelrahman M. Rabie,Woo Kyoung Kim,Jae-Jin Shim 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.124 No.-

Heterojunction TiO2/In2S3 composite photocatalyst was prepared using a simple low-temperature onestephydrothermal method. In2S3 nanosheets with a thickness of 1–5 nm were decorated with 20–30 nm TiO2 nanoparticles, forming a stable heterojunction. The electron transfer mechanism and bandalignment between TiO2 and In2S3 was studied using X-ray photoelectron spectroscopy and UV–visiblespectroscopy, which suggested the formation of an S-scheme heterojunction in TiO2/In2S3 composite. The TiO2/In2S3 composite with a 1:1 mole ratio showed 99.9% photocatalytic degradation ofRhodamine B within 20 minutes of solar light irradiation, which was better than the results for pristineTiO2, pristine In2S3, and their physical mixture, as well as any other previously reported materials of thesame kind. The as-prepared TiO2/In2S3 composite showed excellent stability (98% for Rhodamine B) evenafter five successive reuse cycles. This excellent performance of TiO2/In2S3 was attributed to the S-schemeheterojunction because of an internal electric field, columbic attraction, and band bending. A radical trappingstudy showed that superoxide radicals O2 contribute the most to the photocatalytic degradationof Rhodamine B followed by hydroxyl radicals (OH) and holes (hVB+ ). The use of a low synthesis temperatureand a simple, one-step formation method, with no secondary pollutants generated, makes this processan environmentally friendly and sustainable solution for cost-effective wastewater treatment,highlighting its future commercial applications.