Facile in-situ formation of rGO/ZnO nanocomposite: Photocatalytic remediation of organic pollutants under solar illumination

Shanmugasundaram, Arunkumar,Boppella, Ramireddy,Jeong, Yun-Jin,Park, Jongsung,Kim, Young-Bae,Choi, Byungchul,Park, Su Han,Jung, Seunghun,Lee, Dong-Weon Elsevier 2018 Materials chemistry and physics Vol.218 No.-

<P><B>Abstract</B></P> <P>Herein, we present a facile hydrothermal route for the preparation of hierarchical mesoporous zinc oxide (ZnO) and reduced graphene oxide-zinc oxide (ZnO<SUB>rGO</SUB>) composites for degradation of organic pollutants from natural water resources. Morphologies of the as-synthesized materials were carried out by electron microscopy in scanning and transmission modes. Thermal stability of the as-prepared products was characterised by thermogravimetric-differential thermal analysis. Crystal structure and phase purity of the materials was characterised by powder x-ray diffraction, micro-Raman, and X-ray photoelectron spectroscopy analysis. Optical properties of the as-prepared materials were investigated by ultra violet-diffused reflectance and photoluminescence spectroscopy analysis. Photocatalytic activity of the as-prepared materials was estimated by evaluating the degradation kinetics of methylene blue (MB) dye in aqueous solution under standard solar light illumination. The calculated rate constant of the Zn<SUB>rGO</SUB> is found to be ∼2.831 h<SUP>−1</SUP> which is ∼6.3 times higher than the estimated rate constant of the as-prepared pristine ZnO (0.455 h<SUP>−1</SUP>). The exceptional photocatalytic activity of the as-prepared Zn<SUB>rGO</SUB> composites is attributed to the account of their synergetic effect, porous structure, and effective separation of charge carriers. Finally, based on the obtained experimental results viable photocatalytic mechanism has been proposed.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new one-step approach yields ZnO/rGO hybrids with <I>in-situ</I> formation of heterojunctions. </LI> <LI> Ethanolamine used to mineralize the ZnO precursor and also facilitates the reduction GO <I>in-situ</I>. </LI> <LI> The ZnO/rGO heterojunctions show improved photo catalytic activity under solar light illumination. </LI> <LI> Plausible photo catalysis mechanism has been proposed. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Facile in situ Formation of CuO/ZnO p-n Heterojunction for Improved H₂S-sensing Applications

( Arunkumar Shanmugasundaram ),( Dong-su Kim ),( Tian Feng Hou ),( Dong Weon Lee ) 한국센서학회 2020 센서학회지 Vol.29 No.3

In this study, hierarchical mesoporous CuO spheres, ZnO flowers, and heterojunction CuO/ZnO nanostructures were fabricated via a facile hydrothermal method. The as-prepared materials were characterized in detail using various analytical methods such as powder X-ray diffraction, micro Raman spectroscopy, X-ray photoelectron spectroscopy, field-emission scanning electron microscopy, and transmission electron microscopy. The obtained results are consistent with each other. The H2S-sensing characteristics of the sensors fabricated based on the CuO spheres, ZnO flowers, and CuO/ZnO heterojunction were investigated at different temperatures and gas concentrations. The sensor based on ZnO flowers showed a maximum response of ~141 at 225 ℃. The sensor based on CuO spheres exhibited a maximum response of 218 at 175 ℃, whereas the sensor based on the CuO/ZnO nano-heterostructure composite showed a maximum response of 344 at 150 ℃. The detection limit (DL) of the sensor based on the CuO/ZnO heterojunction was ~120 ppb at 150 ℃. The CuO/ZnO sensor showed the maximum response to H₂S compared with other interfering gases such as ethanol, methanol, and CO, indicating its high selectivity.

ZnO/Cu₂O-decorated rGO: Heterojunction photoelectrode with improved solar water splitting performance

Hou, Tian-Feng,Shanmugasundaram, Arunkumar,Hassan, Mostafa Afifi,Johar, Muhammad Ali,Ryu, Sang-Wan,Lee, Dong-Weon Pergamon Press 2019 International journal of hydrogen energy Vol.44 No.35

<P><B>Abstract</B></P> <P>In present work, we report a facile fabrication process to improve the photoelectrochemical (PEC) performance of ZnO-based photoelectrodes. In order to achieve that, the Cu<SUB>2</SUB>O nanocubes are cathodic-deposited on the as-prepared ZnO nanorods. Then rGO nanosheets are electrodeposited on the ZnO/Cu<SUB>2</SUB>O heterostructures. The fabricated photoelectrodes are systematically studied in detail by different characterization techniques such as powder X-ray diffraction, micro-Raman, X-ray photoelectron spectroscopy, ultraviolet diffused reflectance spectroscopy and photoluminescence spectroscopy analysis. Morphologies of the fabricated photoelectrodes are investigated through electron microscopy in scanning and transmission mode. To evaluate the PEC performance of the fabricated photoelectrodes, the line scan voltammetry (LSV) measurement is performed using a three-electrode system in 0.5-M Na<SUB>2</SUB>SO<SUB>4</SUB> electrolyte solution under stimulated light illumination at 100 mW/cm<SUP>2</SUP> from a 300-W Xenon Arc lamp coupled with an AM 1.5G filter using a three-electrode system. The photocurrent measurement demonstrates that the photoelectrodes based on ZnO/Cu<SUB>2</SUB>O/rGO possess enhanced PEC performance compared to the pristine ZnO and ZnO/Cu<SUB>2</SUB>O photoelectrodes. The photocurrent density of ZnO/Cu<SUB>2</SUB>O/rGO-15 photoelectrode (10.11 mA/cm<SUP>2</SUP>) is ∼9 and ∼3 times higher than the photoelectrodes based on pristine ZnO (1.06 mA/cm<SUP>2</SUP>) and ZnO/Cu<SUB>2</SUB>O (3.22 mA/cm<SUP>2</SUP>). The enhanced PEC performance of ZnO/Cu<SUB>2</SUB>O/rGO photoelectrode is attributed to the excellent light absorption properties of Cu<SUB>2</SUB>O and excellent catalytic and charge transport properties of rGO. Experimental results reveal that the proposed functional nanomaterials have a great potential in water splitting applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> rGO-protected ZnO/Cu<SUB>2</SUB>O heterojunction photoelectrodes for water splitting. </LI> <LI> Thickness of rGO on heterostructure controlled by electrochemical reduction time. </LI> <LI> Cu<SUB>2</SUB>O significantly enhances the light absorption for ZnO/Cu<SUB>2</SUB>O heterojunction. </LI> <LI> Super catalytic and charge transport properties of rGO improved the PEC performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>The improved PEC performance of the ZnO/Cu<SUB>2</SUB>O/rGO hybrid photoelectrodes is attributed to (i) excellent crystalline nature of the as-prepared ZnO NRs and Cu<SUB>2</SUB>O nanocubes, (ii) large light absorption property of the Cu<SUB>2</SUB>O nanocubes, (iii) high electrical conduction effect and excellent charge transport property of the rGO nanosheets, (iv) electric effect induced by the heterojunction between the vertically aligned ZnO NRs, Cu<SUB>2</SUB>O nanocubes and rGO nanosheets (Scheme 2) and (v) excellent electron acceptor and passivation layer of rGO. All these factors coupled together contribute to the excellent PEC performance of ZnO/Cu<SUB>2</SUB>O/rGO hybrid based photoelectrodes.</P> <P>[DISPLAY OMISSION]</P>

Hierarchically self-assembled ZnO architectures: Establishing light trapping networks for effective photoelectrochemical water splitting

Hou, Tian-Feng,Boppella, Ramireddy,Shanmugasundaram, Arunkumar,Kim, Dong Ha,Lee, Dong-Weon Pergamon Press 2017 International journal of hydrogen energy Vol.42 No.22

<P><B>Abstract</B></P> <P>Here we develop photoanodes based on hierarchical zinc oxide (ZnO) nanostructures such as vertically aligned nanorods (NR), nanorods interconnected by thin nanosheets (NR@TN) and nanorods interconnected by dense nanosheets (NR@DN). The morphological variations were successfully controlled by secondary growth time and the plausible formation mechanisms of these hierarchical ZnO architectures were explained based on the experiment analysis. Under simulated light illumination (AM 1.5, 100 mW cm<SUP>−</SUP> <SUP>2</SUP>), NR@TN produced a photocurrent density of 0.62 mA/cm<SUP>2</SUP> at 1.23 V vs. reversible hydrogen electrode (vs. RHE). Importantly, 35% enrichment in photoconversion efficiency was observed for NR@TN at much lower bias potential (0.77 V vs. RHE) compared with NR (0.135%) and NR@DN (0.13% at 0.82 V vs. RHE). Key to the improved performance is believed to be synergetic effects of excellent light-trapping characteristics and the large surface-to-volume ratios due to the nanosheet structures. The nanorod connected with thin nanosheet structures improved the efficiency by means of improved charge transfer across the nanostructure/electrolyte interfaces, and efficient charge transport within the material. We believe that the hierarchical ZnO structures can be used in conjunction with doping and/or sensitization to promote the photoelectrochemical (PEC) performance. Further, the ZnO nanorod interconnected with nanosheets morphology presented in this article is extendable to other metal oxide semiconductors to establish a universal protocol for the development of high performance photoanodes in the field of PEC water splitting.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new approach yields ZnO photoanodes for water splitting application. </LI> <LI> Versatile nanostructure like nanorod and nanorod connected by nanosheet is prepared. </LI> <LI> The multi reflection in photoanodes increases capture rate of incident photons. </LI> <LI> Electron transfer from thin nanosheet to nanorod leads to effectively split e–h pair. </LI> <LI> Numerous light trapping network in NR@TN gives rise to the improved PEC performances. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Structured devices such as nanorods arrays (right) enable the orthogonalization of light absorption and carrier collection. Decoupling <I>L</I> <SUB>min</SUB> from <I>α</I> <SUP>+</SUP> reduces certain materials' quality constraints. In addition, the light can be transferred longer distance to enhance the light absorption due to the multi-reflection of the nanorod arrays and the high surface roughness property thin film on the top side of ZnO nanorods.</P> <P>[DISPLAY OMISSION]</P>

Polyurethane-acrylate-based hydrophobic film: Facile fabrication, characterization, and application

Park, Jongsung,Nguyen, Bui Quoc Huy,Kim, Ji-Kwan,Shanmugasundaram, Arunkumar,Lee, Dong-Weon Institute of Pure and Applied Physics 2018 Japanese Journal of Applied Physics Vol. No.

Wireless pressure sensor integrated with a 3D printed polymer stent for smart health monitoring

Park, Jongsung,Kim, Ji-Kwan,Kim, Dong-Su,Shanmugasundaram, Arunkumar,Park, Su A,Kang, Sohi,Kim, Sung-Ho,Jeong, Myung Ho,Lee, Dong-Weon Elsevier 2019 Sensors and actuators. B Chemical Vol.280 No.-

<P><B>Abstract</B></P> <P>The primary objective of this study was to deploy a promising wireless pressure sensor system capable of monitoring real-time biological signals in an experimental object. MEMS-based micromachining technology was used to fabricate the proposed SU-8 wireless pressure sensor. The sensor utilizes a capacitor-inductor resonant circuit that can operate the sensor without any external power supply. The variable capacitor in the pressure sensor is designed to change the resonance frequency (130, 183 MHz) in response to applied pressure. The fabricated wireless pressure sensor was integrated into a polymer-based smart stent to minimize the discomfort of medication administration and hospital visits. A 3D bio-printing-based manufacturing technique was employed for the production of a smart polymer stent with complicated shapes. The proposed method is considerably more comfortable than the conventional metal stents fabrication process. The polymer smart stent made of the biocompatible polycaprolactone (PCL) material which can be fully absorbed by the body after a medication period. After integrating the fabricated wireless pressure sensor with the polymer smart stent, various basic experiments such as the working distance of the sensor were performed using a simple experimental setup. The biocompatibility of the proposed polymer stent and the wireless pressure sensor was also successfully confirmed using an experimental animal. The preliminary investigation results indicate that the proposed wireless sensor can be used to obtain necessary information in various parts of the human body as well as the stent.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Fabrication of SU-8 based wireless pressure sensor for battery-less operation. </LI> <LI> Manufacturing of biodegradable polymer stent using 3D printing technique. </LI> <LI> Integration of wireless pressure sensor into polymer stent for real-time blood pressure monitoring. </LI> <LI> Verification of the biocompatibility of smart stent and its operation with experimental animals. </LI> <LI> Continuous measurement of blood pressure change in animals for more than 3 months. </LI> </UL> </P>