Influence of surface modification of zinc oxide–based nanomaterials on the photocatalytic reduction of carbon dioxide

ZnO (Z-1), Co-doped ZnO (Z-2), and Co-doped ZnO/rGO (Z-3) nanocomposites are successfully synthesized using a solvothermal method and investigated toward the photoreduction of CO₂ to CH₃OH. The as-prepared ZnO (Z-1), Co-doped ZnO (Z-2), and Co-doped ZnO/rGO (Z-3) nanomaterials are characterized by a range of spectroscopic, imaging, and thermal techniques, including X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray analysis, thermogravimetry analysis-differential thermal calorimetry, UV–Vis diffuse reflectance spectroscopy, scanning electron microscopy, and transmission electron micrograph. It was found that Z-3 presented a higher CH₃OH rate of 30.1 μmol/g compared with Z-2 (27.3 μmol/g) and Z-1 (7.5 μmol/g). Enhanced catalytic activity of Z-3 over other samples was because of the combined effect of the amount of Co, reduced graphene (rGO), and surface area (10.62 m²/g). Theoretical calculation revealed that photocatalytic activity has some relationship with the E_LUMO = ?2.922 eV (doped ZnO). The results can not only provide an important indication about the influence of Co and rGO on the activity of CO₂ photoreduction over ZnO but also demonstrate a strategy for tuning the CO₂ photoreduction performance. Our work may lay the groundwork for directing the future design of efficient metal-modified ZnO photocatalysts for CO₂ reduction.     

Complementary combinative strategy of defect engineering and graphene coupling for efficient energy-functional materials

The synergetic combination of defect engineering and graphene coupling enables to develop an effective way of exploring efficient bifunctional electrocatalyst/electrode materials. Defect-engineered amorphous MoO₂-reduced graphene oxide (rGO) nanohybrid was synthesized by soft-chemical reduction of K₂MoO₄ in graphene oxide colloids. Mo K-edge X-ray absorption spectroscopy clearly demonstrates the rutile-type local atomic structure of amorphous MoO₂ with significant oxygen vacancies and intimate electronic coupling with rGO. The defect-introduced MoO₂-rGO nanohybrid shows excellent bifunctionality as electrocatalyst for hydrogen evolution reaction and electrode for sodium-ion batteries, which are superior to those of crystalline MoO₂-rGO homologue. The beneficial effect of simultaneous defect control and rGO coupling can be ascribed to the provision of oxygen vacancies acting as active sites, the increase of electrical conductivity, and the improvement of reaction kinetics.     

Magnetic ZnO Crystal Nanoparticle Growth on Reduced Graphene Oxide for Enhanced Photocatalytic Performance under Visible Light Irradiation

Magnetite zinc oxide (MZ) (Fe₃O₄/ZnO) with different ratios of reduced graphene oxide (rGO) was synthesized using the solid-state method. The structural and optical properties of the nanocomposites were analyzed using transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), ultraviolet–visible diffuse reflectance spectroscopy (UV–Vis/DRS), and photoluminescence (PL) spectrophotometry. In particular, the analyses show higher photocatalytic movement for crystalline nanocomposite (MZG) than MZ and ZnO nanoparticles. The photocatalytic degradation of methylene blue (MB) with crystalline ZnO for 1.5 h under visible light was 12%. By contrast, the photocatalytic activity for MZG was more than 98.5%. The superior photocatalytic activity of the crystalline nanocomposite was detected to be due to the synergistic effect between magnetite and zinc oxide in the presence of reduced graphene oxide. Moreover, the fabricated nanocomposite had high electron–hole stability. The crystalline nanocomposite was stable when the material was used several times.     

Green synthesis of reduced graphene oxide/Fe3O4/Ag ternary nanohybrid and its application as magnetically recoverable catalyst in the reduction of 4‐nitrophenol

Materials having both magnetic and catalytic properties have shown great potential for practical applications. Here, a reduced graphene oxide/iron oxide/silver nanohybrid (rGO/Fe₃O₄/Ag NH) ternary material was prepared by green synthesis of Ag on pre‐synthesized rGO/Fe₃O₄. The as‐prepared rGO/Fe₃O₄/Ag NH was characterized using Fourier transform infrared spectroscopy, X‐ray diffractometry, Raman spectroscopy, vibrating sample magnetometry, transmission electron microscopy and energy‐dispersive X‐ray spectroscopy. rGO sheets were covered with Fe₃O₄ (8–16 nm) and Ag (18–40 nm) nanoparticles at high densities. The mass percentages were 13.47% (rGO), 62.52% (Fe₃O₄) and 24.01% (Ag). rGO/Fe₃O₄/Ag NH exhibited superparamagnetic behavior with high saturated magnetization (29 emu g⁻¹ at 12 kOe), and efficiently catalyzed the reduction of 4‐nitrophenol (4‐NP) with a rate constant of 0.37 min⁻¹, comparable to those of Ag‐based nanocatalysts. The half‐life of 4‐NP in the presence of rGO/Fe₃O₄/Ag NH was ca 1.86 min. rGO/Fe₃O₄/Ag NH could be magnetically collected and reused, and retained a high conversion efficiency of 94.4% after the fourth cycle. rGO/Fe₃O₄/Ag NH could potentially be used as a magnetically recoverable catalyst in the reduction of 4‐NP and environmental remediation.     

水热合成部分还原氧化石墨烯-K2Mn4O8超级电容器纳米复合材料

通过控制水热反应温度以及氧化石墨烯(GO)与高锰酸钾的填料比, 合成了两组部分还原的GO-K₂Mn₄O₈纳米复合材料. X射线衍射(XRD)分析说明水热过程中合成了α-MnO₂和一种新的晶相K₂Mn₄O₈.通过X射线光电子能谱(XPS)分析了水热反应前后氧化石墨的含氧官能团的变化. 扫描电子显微镜(SEM)显示样品由片状还原的氧化石墨烯构成, 其表面附有许多小的纳米颗粒, 这种结构有利于储能时电子的传递. 通过这两组复合材料的结构分析, 更好地理解了材料的电化学性能的变化. 利用循环伏安法和恒流充放电测试比较了材料的电容性能. 用1 mol·L^-1的硫酸钠做电解液, 电位范围是0-1 V, 在1 A·g^-1的电流密度下, 测得的样品最佳比电容达到251 F·g^-1, 能量密度为32 Wh·kg^-1, 功率密度为18.2 kW·kg^-1. 并且在5 A·g^-1的电流密度下循环1000次后样品的比电容仍维持在初始比电容的88%.     

Concise,Single‐Step Synthesis of Sulfur‐Enriched Graphene: Immobilization of Molecular Clusters and Battery Applications

The concise synthesis of sulfur‐enriched graphene for battery applications is reported. The direct treatment of graphene oxide (GO) with the commercially available Lawesson's reagent produced sulfur‐enriched‐reduced GO (S‐rGO). Various techniques, such as X‐ray photoelectron spectroscopy (XPS), confirmed the occurrence of both sulfur functionalization and GO reduction. Also fabricated was a nanohybrid material by using S‐rGO with polyoxometalate (POM) as a cathode‐active material for a rechargeable battery. Transmission electron microscopy (TEM) revealed that POM clusters were individually immobilized on the S‐rGO surface. This battery, based on a POM/S‐rGO complex, exhibited greater cycling stability for the charge‐discharge process than a battery with nanohybrid materials positioned between the POM and nonenriched rGO. These results demonstrate that the use of sulfur‐containing groups on a graphene surface can be extended to applications such as the catalysis of electrochemical reactions and electrodes in other battery systems.     

Facile synthesis of nickel cobalt sulfide nano flowers for high performance supercapacitor applications

A facile synthesis of nickel cobalt sulfide (NCS) nanoflowers have been deposited successfully onto binder free 3D nickel foam electrodes using simple successive ionic layer adsorption and reaction (SILAR) method for supercapacitor applications. The obtained NCS nanoflowers manifest ultrahigh specific capacitance of 1899 F g^?1 at a scan rate of 5 mV s^?1. The NCS nanoflowers exhibit a prominent energy density of 55.16 Wh kg^?1 at power density of 495 W kg^?1 and superior cyclic stability of 94% after 10000 cycles. In addition, the asymmetric supercapacitor (ASC) device is fabricated using NCS nanoflower as positive and reduced graphene oxide (rGO) as negative electrodes, respectively. The ASC (NCS//rGO) delivered good capacity with excellent energy and power densities within 1.6 V wider potential window. Hence, NCS nanoflowers are an outstanding material for energy storage applications in near future.     

Comparison of photocatalytic and antibacterial activities of allotropes of graphene doped Sm2O3 nanocomposites: Optical,thermal, and structural studies

This study mainly focuses on the synthesis of two allotropes of graphene, graphene oxide (GO) and reduced graphene oxide (rGO), by the modified Hummers' method and chemical reduction method, respectively. Sm₂O₃/GO and Sm₂O₃/rGO nanocomposites were further synthesized in the presence of the cationic surfactant CTAB via the sol–gel method followed by the reflux method. Synthesized nanocomposites were subjected to characterization by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and UV–Visible spectroscopy to explore structural, thermal, optical, and photocatalytic properties. Characteristic FTIR peaks were observed in nanocomposites, and the bond length of the Sm-O bond was calculated. The Coats-Redfern method was employed to calculate the kinetics and thermodynamic parameters. Hexagonal crystallite shapes of Sm₂O₃/GO and Sm₂O₃/rGO nanocomposites with 11.8 and 13.13 nm crystallite sizes and 3.9 and 2.5 eV optical band gaps were observed. The photocatalytic efficiency of Sm₂O₃/GO and Sm₂O₃/rGO nanocomposites was assessed against the degradation of methylene blue in the presence of sunlight, and its degradation was confirmed through FTIR. The antimicrobial activities were also performed against the bacterial strains Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus.     

High solar-light photocatalytic activity of using Cu3Se2/rGO nanocomposites synthesized by a green co-precipitation method

Current work presents a facile, cost-effective, and green method to synthesize copper selenide nanostructures and copper selenide/graphene nanocomposites. The products were synthesized by a co-precipitation method by glycine amino acid as a green surfactant and graphene oxide (GO) sheets as a graphene source. X-ray diffraction patterns (XRD) of the products indicated that the products were Cu₂Se₃ with tetragonal phase. Fourier transform infrared (FTIR) spectroscopy and the XRD patterns indicated that the GO sheets were changed into reduced GO (rGO) during the synthesis process. Scanning and transmission electron microscopy (SEM and TEM) images showed the nanoparticles (NPs) that were decorated on rGO sheets had the significantly smaller size in compared to the pristine NPs. UV-vis results revealed that, the absorption peak of the products were in the visible region with a band-gap value between 1.85 eV and 1.95 eV. Finally, the products were applied as photocatalytic materials to remove Methylene Blue (MB) dye under solar-light and visible-light irradiation conditions. It was observed; the rGO had a significant role in enhancing the photocatalytic performance of the products and Cu₂Se₃/rGO (15%) could degrade more than 91% and 73% of MB only during 1 h under solar-light and visible-light sources, respectively.     

Magnetic Nanohybrids Loaded with Bimetal Core–Shell–Shell Nanorods for Bacteria Capture,Separation, and Near‐Infrared Photothermal Treatment

A novel antimicrobial nanohybrid based on near‐infrared (NIR) photothermal conversion is designed for bacteria capture, separation, and sterilization (killing). Positively charged magnetic reduced graphene oxide with modification by polyethylenimine (rGO–Fe₃O₄–PEI) is prepared and then loaded with core–shell–shell Au–Ag–Au nanorods to construct the nanohybrid rGO–Fe₃O₄–Au–Ag–Au. NIR laser irradiation melts the outer Au shell and exposes the inner Ag shell, which facilitates controlled release of the silver shell. The nanohybrids combine physical photothermal sterilization as a result of the outer Au shell with the antibacterial effect of the inner Ag shell. In addition, the nanohybrid exhibits high heat conductivity because of the rGO and rapid magnetic‐separation capability that is attributable to Fe₃O₄. The nanohybrid provides a significant improvement of bactericidal efficiency with respect to bare Au–Ag–Au nanorods and facilitates the isolation of bacteria from sample matrixes. A concentration of 25 μg mL^?1 of nanohybrid causes 100 % capture and separation of Escherichia coli O157:H7 (1×10⁸ cfu mL^?1) from an aqueous medium in 10 min. In addition, it causes a 22 °C temperature rise for the surrounding solution under NIR irradiation (785 nm, 50 mW cm^?2) for 10 min. With magnetic separation, 30 μg mL^?1 of nanohybrid results in a 100 % killing rate for E. coli O157:H7 cells. The facile bacteria separation and photothermal sterilization is potentially feasible for environmental and/or clinical treatment.     

Concise,Single-Step Synthesis of Sulfur-Enriched Graphene: Immobilization of Molecular Clusters and Battery Applications

The concise synthesis of sulfur-enriched graphene for battery applications is reported. The direct treatment of graphene oxide (GO) with the commercially available Lawesson's reagent produced sulfur-enriched-reduced GO (S-rGO). Various techniques, such as X-ray photoelectron spectroscopy (XPS), confirmed the occurrence of both sulfur functionalization and GO reduction. Also fabricated was a nanohybrid material by using S-rGO with polyoxometalate (POM) as a cathode-active material for a rechargeable battery. Transmission electron microscopy (TEM) revealed that POM clusters were individually immobilized on the S-rGO surface. This battery, based on a POM/S-rGO complex, exhibited greater cycling stability for the charge-discharge process than a battery with nanohybrid materials positioned between the POM and nonenriched rGO. These results demonstrate that the use of sulfur-containing groups on a graphene surface can be extended to applications such as the catalysis of electrochemical reactions and electrodes in other battery systems.     

Degradation of carbon tetrachloride using ultrasound‐assisted nanoscaled zero‐valent iron particles@sulfur/nitrogen dual‐doped reduced graphene oxide composite: Kinetics,activation energy,effects of reaction conditions and degradation mechanism

We report a study of the synthesis of nanoscale zero‐valent iron particles stabilized by sulfur/nitrogen dual‐doped reduced graphene oxide (i.e. nZVI@SN‐rGO) and their applications as major reactants for the dechlorination of carbon tetrachloride (CT) by combining sonolysis with consideration of several operation parameters such as pH, temperature, catalyst dosage, as well as in the presence of common inorganic anions. The experimental results showed that the modified technology could remain effective for up to 180 min of reaction time under optimal conditions. Especially, there was no significant reduction in the removal efficiency toward CT even after five cycles, which was indicative of good stability. A study of the effects of common inorganic anions revealed that the presence of Clˉ and HCO₃ˉ exhibited different positive effects in the following order: Clˉ > HCO₃ˉ; NO₃ˉ and SO₄²ˉ showed inhibition effects on CT removal. The structure and properties of nZVI@SN‐rGO were characterized using X‐ray diffraction, scanning electron microscopy, surface area analysis, Raman spectroscopy and X‐ray photoelectron spectroscopy. Additionally, the corresponding activation energy was approximately 31.04 kJ mol^?1, suggesting that the surface chemical reaction rather than diffusion was the rate‐limiting step in the CT decomposition process. More importantly, the possible reaction mechanism and dechlorination pathway of CT using the ultrasound‐assisted nZVI@SN‐rGO system were also investigated.     

中空分级结构Fe3O4@C/rGO复合材料的合成及其储锂性能

以氧化石墨烯(GO)为基底,Fe(NO_3)_3·9H_2O、异丙醇、甘油为原料,通过溶剂热法和后续热处理过程2步合成了Fe_3O_4@C/rGO复合材料,实现了碳包覆的Fe_3O_4纳米粒子自组装形成的分级结构空心球在氧化石墨烯片上的原位生长。采用X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和恒流充放电等手段分析了材料的物理化学性能与储锂性能。结果表明,该复合材料在5.0 A·g~(-1)的电流密度下,仍有437.7 mAh·g~(-1)的可逆容量,在1.0 A·g~(-1)下循环200圈后还有587.3 mAh·g~(-1)的放电比容量。这主要归因于还原态氧化石墨烯(rGO)对碳包覆Fe_3O_4分级空心球整体结构稳定性和导电性的提高。     

Cu2O/reduced graphene oxide/TiO2 nanomaterial: An effective photocatalyst for azide-alkyne cycloaddition with benzyl halides or epoxide derivatives under visible light irradiation

Cu₂O/reduced graphene oxide/TiO₂ (Cu₂O/rGO/TiO₂) photocatalyst was synthesized under ultrasonic irradiation. The nanomaterial was identified by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, UV–vis absorption, and inductively coupled plasma optical emission spectroscopy (ICP-OES). The Cu₂O/rGO/TiO₂ photocatalyst was utilized in “click” reaction for the preparation of 1,4-disubstituted 1,2,3-triazoles via one pot multicomponent reaction of benzyl halide or epoxide derivatives with alkynes in presence of NaN₃ and triethylamine under visible light irradiation. The “click” reaction was performed under mild conditions affording good to excellent yields of the triazole compounds using low catalyst loading in short reaction times. The nanocomposite was recovered and recycled for five successive runs without a major diminution in its catalytic performance.     

Electrochemical detection of selenium using glassy carbon electrode modified with reduced graphene oxide

In this work, a simple experimental procedure was reported for the electroanalytical determination of selenium (IV) using reduced graphene oxide (rGO) to modify glassy carbon electrode (GCE). The rGO was obtained by reduction of graphene oxide obtained via Hummer’s method. The synthesised rGO was characterised using X-ray diffraction, Raman spectroscopy, scanning electron microscope (SEM), energy-dispersive spectroscopy and transmission Electron microscopy (TEM). GCE was modified with rGO and the electrochemical properties of the bare and modified electrode were investigated using cyclic voltammetry and electrochemical impedance spectroscopy. The results obtained showed that the modified electrode exhibited more excellent electrochemical properties than the bare GCE. The optimum conditions for detection of selenium in water using square wave anodic stripping voltammetry were as follows: deposition potential ?500 mV, pH 1, pre-concentration time of 240 s and 0.1 M nitric acid was used as supporting electrolyte. The linear regression equation obtained was I (µA) = 0.8432C + 9.2359 and the detection limit was calculated to be 0.85 μg L^?1. However, Cu(II) and Cd(II) are the two cations that interfered in the analysis of selenium in water.

The sensor was also applied for real sample water analysis and the result obtained was affirmed with inductively coupled plasma optical emission spectroscopic method. It is believed that our proposed sensor hold promise for practical application.     

Silver nanowires-copper sulfide core/shell nanostructure for electrochemical supercapacitors

This paper reports the synthesis of a new hybrid core (silver nanowires (AgNWs))/shell (copper sulfide (Cu₂S)) nanostructure using simple and inexpensive drop casting and successive ionic layer adsorption and reaction (SILAR) methods. The effects of the thickness of the Cu₂S shell on the Ag NW core on the electrochemical properties of the nanocomposite were studied by varying the number of SILAR cycles from one to four. The structure and microstructure of the prepared composite nanostructure electrode materials were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. The AgNW/Cu₂S exhibited a high specific capacitance of 603 Fg^?1 (stainless steel substrate) and 707 Fg^?1 (Ni foam substrate) at a scan rate of 10 mVs^?1 with an energy density of 10.01 Whkg^?1 and 25.33 Whkg^?1 at an applied current of 0.2 mA. This study provides a simple and cost-effective strategy for the fabrication of nanostructured electrodes for supercapacitor applications.     

Applied bias photon-to-current conversion efficiency of ZnO enhanced by hybridization with reduced graphene oxide

The role of reduced graphene oxide(rGO) in the enhancement of photo-conversion efficiency of ZnO films for photoelectrochemical(PEC) water-splitting applications was analyzed. ZnO and rGO-hybridized ZnO(rGO/ZnO) films were prepared via a two-step electrochemical deposition method followed by annealing at 300 °C under argon gas flow. The physical, optical and electrochemical properties of the films were characterized to identify the effect of rGO-hybridization on the applied bias photon-to-current efficiency(ABPE) of ZnO. Scanning electron microscopy and X-ray diffraction indicated the formation of verticallyaligned, wurtzite-phase ZnO nanorods. Diffuse-reflectance UV–visible spectroscopy indicated that rGO-hybridization was able to increase the light absorption range of the rGO/ZnO film. UPS analysis showed that hybridization with rGO increased the band gap of ZnO(3.56 eV) to 3.63 eV for rGO/ZnO sample,which may be attributed to the Burstein–Moss effect. Photoluminescence(PL) spectra disclosed that rGOhybridization suppressed electron-hole recombination due to crystal defects. Linear sweep voltammetry of the prepared thin films showed photocurrent density of 1.0 and 1.8 m A/cm~2 for ZnO and rGO/ZnO at+0.7 V, which corresponded to an ABPE of 0.55% and 0.95%, respectively. Thus, this report highlighted the multi-faceted role of rGO-hybridization in the enhancement of ZnO photo-conversion efficiency.     

Microwave-Assisted Synthesis of ZnO–rGO Core–Shell Nanorod Hybrids with Photo- and Electro-Catalytic Activity

The unique two-dimensional structure and surface chemistry of reduced graphene oxide (rGO) along with its high electrical conductivity can be exploited to modify the electrochemical properties of ZnO nanoparticles (NPs). ZnO–rGO nanohybrids can be engineered in a simple new two-step synthesis, which is both fast and energy-efficient. The resulting hybrid materials show excellent electrocatalytic and photocatalytic activity. The structure and composition of the as-prepared bare ZnO nanorods (NRs) and the ZnO–rGO hybrids have been extensively characterised and the optical properties subsequently studied by UV/Vis spectroscopy and photoluminescence (PL) spectroscopy (including decay lifetime measurements). The photocatalytic degradation of Rhodamine B (RhB) dye is enhanced using the ZnO–rGO hybrids as compared to bare ZnO NRs. Furthermore, potentiometry comparing ZnO and ZnO–rGO electrodes reveals a featureless capacitive background for an Ar-saturated solution whereas for an O₂-saturated solution a well-defined redox peak was observed using both electrodes. The change in reduction potential and significant increase in current density demonstrates that the hybrid core–shell NRs possess remarkable electrocatalytic activity for the oxygen reduction reaction (ORR) as compared to NRs of ZnO alone.     

Preparation and electrochemical analysis of graphene/polyaniline composites prepared by aniline polymerization

Polyaniline (PANI)/graphene nanosheet (GNS) composites were prepared by a chemical oxidation polymerization. The morphology, structure, and crystallinity of the composites were examined by scanning electron microscopy, transition electron microscopy, and X-ray diffraction. Electrochemical properties were characterized by cyclic voltammetry in 1 M H₂SO₄ electrolyte. GNS are considered as supporting materials which can provide a large number of active sites. The PANI nanofibers with diameter of 50 nm were homogeneously coated on the surface of GNS. The PANI/GNS composites exhibited a better electrochemical performance than the pure individual components. The PANI/GNS composites showed the highest specific capacitance 923 Fg^?1 at 10 mVs^?1 compared to 465 Fg^?1 for pure PANI and 99 Fg^?1 for GNS.     

Low-cost reduced graphene oxide-based conductometric nitrogen dioxide-sensitive sensor on paper

The fabrication concept for a low-cost sensor device using reduced graphene oxide (rGO) as the sensing material on a porous paper substrate is presented. The sensors were characterized using conductivity and capacitance measurements, atomic force microscopy and X-ray photoelectron spectroscopy. The effects of different reducing agents, graphene oxide (GO) flake size and film thickness were studied. The sensor was sensitive to NO₂, and devices based on a thin (10-nm) hydrazine-reduced GO layer had the best sensitivity, reaching a 70 % reduction in resistance after 10 min of exposure to 10 ppm NO₂. The sensitivity was high enough for the detection of sub-parts per million levels of NO₂. Desorption of gas molecules, i.e. the recovery of the sensor, could be accelerated by UV irradiation. The structure and preparation of the sensor are simple and up-scalable, allowing their fabrication in bulk quantities, and the fabrication concept can be applied to other materials, too.