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>

Enhanced photoelectrochemical (PEC) and photocatalytic properties of visible-light reduced graphene-oxide/bismuth vanadate

Soltani, Teyyebah,Tayyebi, Ahmad,Lee, Byeong-Kyu Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.448 No.-

<P><B>Abstract</B></P> <P>A simple visible-light-assisted photocatalytic reduction of graphene oxide (GO) to reduced graphene oxide (rGO) using BiVO<SUB>4</SUB> (BVO) in BVO/GO was designed to remarkably improve the photocatalytic degradation and photoelectrochemical (PEC) water splitting efficiencies of BVO. The resulting smaller particle size and strong interfacial interaction on the graphene sheet of the prepared BVO/rGO nanocomposite (NC) enhanced the photocatalytic degradation of tetracycline (TC) and methylene blue (MB) from aqueous solution, and also PEC water splitting. The photocatalytic degradation of MB and TC from aqueous solution using BVO/rGO was enhanced almost 2-fold compared to using BVO with complete photodegradation being achieved in 60 and 55 min of visible-light irradiation, respectively. The photocurrent onset potential of BVO/rGO was negatively shifted by −0.2 V vs. Ag/AgCl. The photocurrent density of BVO/rGO was greatly improved to 133 µA cm<SUP>−2</SUP> at 0.8 V vs. Ag/AgCl, as compared to 21 µA cm<SUP>−2</SUP> with BVO. The charge recombination time was greatly increased from 5 s<SUP>−1</SUP> for BVO to 11 s<SUP>−1</SUP> for BVO/rGO. The BVO/rGO photoanode exhibited long-term operation stability by maintaining 90.2% of the initial photocurrent density after 2400 s, while BVO showed poor stability of 65.1%. The great improvement of photocatalytic (2.0-fold) and PEC water splitting activity (6.3-fold) in BVO/rGO was attributed to the longer electron lifetime (2.2-fold), enhanced carrier concentration (5.87-fold), reduced interfacial electron transfer resistance, excellent stability and reusability, reduced particle size, and extended photoresponse range, which were derived from the ultimate coverage of BVO by rGO.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Photocatalytic reduction of GO produced complete coverage of BVO by rGO sheets. </LI> <LI> Photodegradation of MB and TC was 2-fold greater than that using BVO. </LI> <LI> Photocurrent density of BVO/rGO (133 µA cm<SUP>−2</SUP>) was greatly increased compared to that of BVO (21 µA cm<SUP>−2</SUP>). </LI> <LI> BVO/rGO photoelectrode exhibited a very high stability of 90% even after 2400 s. </LI> <LI> Charge recombination time of BVO/rGO (11 s<SUP>−1</SUP>) was greatly increased compared to that of BVO (5 s<SUP>−1</SUP>). </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Purposive Assembling of Poly(3-hexylthiophene) onto Chemically Treated Multi-Wall Carbon Nanotube versus Reduced Graphene Oxide

Somaiyeh Charoughchi,Samira Agbolaghi,Raana Sarvari,Sahar Aghapour 한국고분자학회 2018 Macromolecular Research Vol.26 No.13

Surfaces of multi-walled carbon nanotubes (CNTs) and reduced graphene oxide (rGO) nanosheets were chemically modified to design distinct donor-acceptor nano-hybrids having different morphologies and orientations. In unmodified CNTs and their derivatives functionalized with 2-hydroxymethyl thiophene (CNT-f-COOTh) and grafted with poly(3-dodecylthiophene) (CNT-g-PDDT), double-fibrillar, shishkebab, and stem-leaf nanostructures were decorated. Furthermore, rGO nanosheets functionalized with 2-thiophene acetic acid (rGO-f-TAA) and grafted with poly(3- dodecylthiophene) (rGO-g-PDDT) were prepared to study differences in CNT and rGO supramolecules. Three types of orientations subsuming face-on, edge-on, and flat-on were detected in nano-hybrids based on CNT and rGO. Morphology (fibrillar) and orientation (face-on) of poly(3-hexylthiophene) (P3HT) assemblies were similar onto unmodified CNT and rGO nanostructures. Although patternings of P3HT chains were completely different onto functionalized CNT and rGO (shish-kebab versus nanocrystal decorated nanosheets), edge-on orientation was detected in CNT-f-COOTh/P3HT and rGO-f-TAA/P3HT nano-hybrids. In CNT-g-PDDT/P3HT and rGO-g-PDDT/P3HT systems, P3HT chains were extendedly assembled onto grafted carbonic materials; however, their different natures reflected stem-leaf and patched-like configurations, respectively. For unmodified, functionalized, and grafted CNT and rGO patterned with P3HT chains, a photoluminescence quenching was detected for a donor-acceptor nature. Owing to flat-on oriented P3HTs, the best photoluminescence quenching, thereby the best donating-accepting features were detected for CNT-g-PDDT/P3HT and rGO-g-PDDT/P3HT supramolecules.

Effect of Reduced Graphite Oxide as Substrate for Zinc Oxide to Hydrogen Sulfide Adsorption

Nu Ri Jeon,Hoon Sub Song,Moon Gyu Park,Soon Jin Kwon,Ho Jeong Ryu,Kwang Bok Yi 한국청정기술학회 2013 청정기술 Vol.19 No.3

ZnO(산화아연)와 rGO(환원 흑연산화물, reduced graphite oxide)로 구성된 복합체를 제조하여 중저온 영역(300-500 ℃)에서 H₂S(황화수소) 흡착실험을 수행하였다. rGO에 붙어있는 수산화기, 에폭시기, 그리고 카르복실기와 같은 산소를 포함하는 관능기들이 H₂S흡착에 미치는 영향을 조사하기 위해서 다양한 특성분석(TGA, XRD, FT-IR, SEM, 그리고 XPS)을 실시하였다. GO(흑연산화물, graphite oxide)를 rGO로 환원시키기 위해서 마이크로파 조사법을 사용하였다. 마이크로파 조사법에 의한 환원공정에서는 온화한 환원분위기를 조성하여 rGO 표면에 상당량의 산소 관능기들이 남아있는 것을 확인하였다. 이러한 관능기들은 나노 크기의 ZnO가 2D rGO 표면에 균일하게 부착되도록 유도하여 고온 영역에서도 ZnO의 응집 및 소결이 일어나는 것을 방지하는 효과가 있다. 이로 인해 ZnO/rGO 복합체는 순수한 ZnO와 비교하여 3.5배 정도의 흡착량을 보여주었다. Zinc oxide (ZnO) and reduced graphite oxide (rGO) composites were synthesized and tested as adsorbents for the hydrogen sulfide (H₂S) adsorption at mid-to-high (300 to 500 ℃) temperatures. In order to investigate the critical roles of oxygen containing functional groups, such as hydroxyl, epoxy and carboxyl groups, attached on rGO surface for the H₂S adsorption, various characterization methods (TGA, XRD, FT-IR, SEM and XPS) were conducted. For the reduction process for graphite oxide (GO) to rGO, a microwave irradiation method was used, and it provided a mild reduction environment which can remain substantial amount of oxygen functional groups on rGO surface. Those functional groups were anchoring and holding nano-sized ZnO onto the 2D rGO surface; and it prevented the aggregation effect on the ZnO particles even at high temperature ranges. Therefore, the H₂S adsorption capacity had been increased about 3.5 times than the pure ZnO.

p-Pheneylendiamine functionalized rGO/Si heterostructure Schottky junction for UV photodetectors

Chandrakalavathi, T.,Reddeppa, Maddaka,Revathi, T.,Basivi, Praveen Kumar,Viswanath, Sujaya Kumar,Murali, G.,Kim, Moon-Deock,Jeyalakshmi, R. Elsevier 2019 Diamond and related materials Vol.93 No.-

<P><B>Abstract</B></P> <P>In this work, we report on p-Phenylenediamine (PPD) functionalized reduced graphene oxide (rGO)/Si hybrid-structure designed for UV photodetector applications (PD). The hybrid-structure was characterized by using Fourier Transform-infrared spectroscopy, X-ray photoelectron spectroscopy to confirm the formation of nano-hybrid structure and the experimental results confirmed the covalent bond between rGO and PPD. The diode parameters such as barrier height, series resistance, and ideality factor were estimated for both PPD functionalized rGO (PrGO)/Si and rGO/Si heterostructure by using I-V characteristics. The time-resolved photocurrent spectroscopy used to examine the photoresponse properties of both PrGO/Si and rGO/Si samples with UV light (λ = 382 nm). The experimental results showed that PrGO/Si exhibited significant UV photoresponse than that of rGO/Si PD. The PrGO/Si heterostructure device exhibited photoresponsivity of 1.4 × 10<SUP>−3</SUP> A/W, which is 15 times higher than rGO/Si. The high photoresponse was attributed to the synergistic effects originated from the charge transfer between PPD and rGO. The results proved that PrGO is a promising material for high response photodetector applications.</P> <P><B>Highlights</B></P> <P> <UL> <LI> p-Pheneylendiamine covalently functionalized with rGO. </LI> <LI> PPD-rGO/Si hybrid structure practically applied for photodetector applications. </LI> <LI> The charge transfer between PPD and rGO could be enhanced the photoresponse of hybrid structure. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Electrochemical, Photocatalytic and Photoluminescence properties of BaWO4 and rGO-BaWO4 nano-composites: A Comparative study

Sridhar Ch,Neha,Seo Young-Soo,Rabani Iqra,Turpu G.R.,Tigga Salinta,Padmaja G. 한국물리학회 2024 Current Applied Physics Vol.58 No.-

The rGO-BaWO4 (rGO-BWO) nanocomposites were synthesized by employing the ultrasonic-assisted co-precipitation method. Nanocomposites formed with BWO nanoparticles anchored to layers of reduced graphene oxide through in situ reduction and a homogeneous distribution of BWO nanoparticles were confirmed by SEM images. The rGO-BWO nanocomposite showed improved photocatalytic activity for the visible light degradation of Methylene Blue (MB) dye with a rate constant of 27 × 10 3 min 1 compared to pristine BWO. The band gaps for BWO nanoparticles estimated using UV–Vis DRS are of the order of 3.25 eV–4.25 eV, while they were 2.78 eV–3 eV for rGO BWO nanocomposites. The delocalized surface charges induced by the interactions between the rGO and BWO nanoparticles in the composite material might be responsible for the observed reduction in the band gap. Photoluminescent investigations demonstrate that rGO-BWO nanocomposites have a lower peak intensity compared to pure BWO particles, indicating a reduced recombination rate and better photocatalytic activity. In particular, when used as supercapacitor electrodes, the produced nanocomposites outperform BWO. Because of its larger surface area, the rGO-BWO nanocomposites display two-fold higher outcomes including 586, 571, 406, 375 and 307 F/g compared to BWO 391, 352, 291, 214 and 174 F/g at each current density 1, 2, 3, 5 and 10 A/g and faster charge transfer owing to improved porosity in the surface of rGO-BWO.

Effect of Reduced Graphite Oxide as Substrate for Zinc Oxide to Hydrogen Sulfide Adsorption

Jeon, Nu Ri,Song, Hoon Sub,Park, Moon Gyu,Kwon, Soon Jin,Ryu, Ho Jeong,Yi, Kwang Bok The Korean Society of Clean Technology 2013 청정기술 Vol.19 No.3

Zinc oxide (ZnO) and reduced graphite oxide (rGO) composites were synthesized and tested as adsorbents for the hydrogen sulfide ($H_2S$) adsorption at mid-to-high (300 to $500^{\circ}C$) temperatures. In order to investigate the critical roles of oxygen containing functional groups, such as hydroxyl, epoxy and carboxyl groups, attached on rGO surface for the $H_2S$ adsorption, various characterization methods (TGA, XRD, FT-IR, SEM and XPS) were conducted. For the reduction process for graphite oxide (GO) to rGO, a microwave irradiation method was used, and it provided a mild reduction environment which can remain substantial amount of oxygen functional groups on rGO surface. Those functional groups were anchoring and holding nano-sized ZnO onto the 2D rGO surface; and it prevented the aggregation effect on the ZnO particles even at high temperature ranges. Therefore, the $H_2S$ adsorption capacity had been increased about 3.5 times than the pure ZnO. ZnO(산화아연)와 rGO(환원 흑연산화물, reduced graphite oxide)로 구성된 복합체를 제조하여 중저온 영역($300-500^{\circ}C$)에서 $H_2S$(황화수소) 흡착실험을 수행하였다. rGO에 붙어있는 수산화기, 에폭시기, 그리고 카르복실기와 같은 산소를 포함하는 관능기들이 $H_2S$흡착에 미치는 영향을 조사하기 위해서 다양한 특성분석(TGA, XRD, FT-IR, SEM, 그리고 XPS)을 실시하였다. GO(흑연산화물, graphite oxide)를 rGO로 환원시키기 위해서 마이크로파 조사법을 사용하였다. 마이크로파 조사법에 의한 환원공정에서는 온화한 환원분위기를 조성하여 rGO 표면에 상당량의 산소 관능기들이 남아있는 것을 확인하였다. 이러한 관능기들은 나노 크기의 ZnO가 2D rGO 표면에 균일하게 부착되도록 유도하여 고온 영역에서도 ZnO의 응집 및 소결이 일어나는 것을 방지하는 효과가 있다. 이로 인해 ZnO/rGO 복합체는 순수한 ZnO와 비교하여 3.5배 정도의 흡착량을 보여주었다.

A Comparative Study of the Effects of Different Methods for Preparing RGO/Metal-Oxide Nanocomposite Electrodes on Supercapacitor Performance

Jinpyo Hong,티루세 테카파우 멍에샤,홍석원,Hyung-Kook Kim,황윤회 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.76 No.3

We have synthesized binary reduced-graphene-oxide (RGO)/metal-oxide (Ni(OH)2, NiO, MnO2, and Fe3O4) nanocomposites by using a facile hydrothermal process. The morphology and the structure of the composite are confirmed by using x-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM), field-emission scanning electron microscopy (FESEM) and Raman spectroscopy. The electric capacitances that have been achieved for the nanocomposites at a current density of 1 A/g are 55, 140, 150 and 183 F/g for RGO/Fe3O4, RGO/Ni(OH)2, RGO/NiO and RGO/MnO2, respectively. Among them, RGO/MnO2 having the best electric capacity was used for preparing a current collector electrode by using various methods to attach the RGO/MnO2 nanocomposite to nickel foams. The supercapacitor performances of differently prepared current collector electrodes were tested, and the electric capacities found with the nanocomposites having a current density of 1 A/g are 28, 53, 112 and 212 F/g when the two-step drop method, the hydrothermal method, the doctor-blade method and the nanocomposite-drop method were used, respectively. Compared to a single metal-oxide, RGO/MnO2 nanocomposites show a superior electric conductivity, an electric capacity and a charge/discharge efficiency for supercapacitor performance, indicating that the RGO/metal-oxide nanocomposite is a promising material for supercapacitor applications.

Reduced graphene oxide as an efficient support for CdS-MoS₂ heterostructures for enhanced photocatalytic H₂ evolution

Ben Ali, Monaam,Jo, Wan-Kuen,Elhouichet, Habib,Boukherroub, Rabah Elsevier 2017 International journal of hydrogen energy Vol.42 No.26

<P><B>Abstract</B></P> <P>Cadmium sulphide nanorods-reduced graphene oxide-molybdenum sulphide(CdS-rGO-MoS<SUB>2</SUB>) composites were successfully synthesized using hydrothermal process for enhancing the interfacial contact between CdS nanorods and MoS<SUB>2</SUB> layer. The good contact between CdS and MoS<SUB>2</SUB> is important for improving the photocatalytic hydrogen (H<SUB>2</SUB>) evolution. The morphological and structural studies showed the production of highly pure CdS phase with nanorod-like structure dispersed on rGO-MoS<SUB>2</SUB> layer. X-ray photoelectron spectroscopy (XPS) and Raman results confirmed the reduction of graphene oxide (GO) into reduced graphene oxide (rGO). The higher photocurrent density of CdS-rGO-MoS<SUB>2</SUB> composites compared to CdS/MoS<SUB>2</SUB> and the fluorescence quenching observed for this composite provided some evidence for an inhibition of electron-hole recombination, which leads to a longer life time of the photogenerated carriers. Fast electron transfer can occur from CdS nanorods by the bidimensionnel rGO area to MoS<SUB>2</SUB> layer due to the intimate interfacial contact. Composite CdS-rGO-MoS<SUB>2</SUB> with 20 wt% rGO was found to be the most effective photocatalyst for H<SUB>2</SUB> evolution (7.1 mmol h<SUP>−1</SUP>g<SUP>−1</SUP>). The good photocatalytic performance arose from the positive synergistic effect between CdS, rGO and MoS<SUB>2</SUB> elements.</P> <P><B>Highlights</B></P> <P> <UL> <LI> CdS-rGO-MoS<SUB>2</SUB> composite was prepared by a hydrothermal technique. </LI> <LI> Reduced graphene oxide sheets led to a good adhesion between CdS and MoS<SUB>2</SUB>. </LI> <LI> Higher photocurrent density of CdS-rGO-MoS<SUB>2</SUB> composite is observed. </LI> <LI> The fluorescence of the nanocomposite was partially quenched. </LI> <LI> Good photocatalytic performance under visible light irradiation. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Effect of synthesis parameters on visible light photocatalytic activity of graphene-TiO₂ nanocomposites for industrial wastewater treatment

Kim, Seu-Run,Ali, Imran,Kim, Jong-Oh THE KOREAN SOCIETY OF INDUSTRIAL AND ENGINEERING 2018 JOURNAL OF INDUSTRIAL AND ENGINEERING CHEMISTRY -S Vol.66 No.-

<P><B>Abstract</B></P> <P>Reduced graphene oxide (RGO)-TiO<SUB>2</SUB> nanotubes (TNTs) were used for industrial wastewater treatment that was obtained from Banwol Sihwa Industrial Complex, Korea. RGO-TNT were fabricated using one-step and two-step anodization at different RGO concentrations, RGO deposition times, anodization voltages and anodization times. Synthesized catalysts were characterised using FESEM, XRD, TEM, EDS, XPS, UV–vis DRS, PL, Raman, and pH<SUB>PZC</SUB>. Compared with pure-TNTs, two-step and one-step RGO-TNT exhibited 2.7 and 3.3-times higher photocatalytic activities for industrial wastewater. Scavenger experiments identified that OH and e<SUP>−</SUP> are main species involved in photocatalytic degradation of MB and industrial wastewater. RGO-TNTs are suitable for industrial wastewater treatment.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The photocatalytic degradation of industrial wastewater was performed using RGO-TNT. </LI> <LI> RGO-TNT were synthesized by one-step and two-step anodization method. </LI> <LI> We checked effect of RGO concentration & deposition time, anodization volt & time. </LI> <LI> One-step RGO-TNT synthesis was more efficient and stable than two-step synthesis. </LI> <LI> Scavenger test identified that OH* & e<SUP>−</SUP> are main species for photocatalytic process. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>