Photocatalysis performance enhancement of Ag2O/Al-doped ZnO heterojunction by introducing ZnO nanorod array

Fabric-based nano semiconductor photocatalysts have attracted much attention in recent years. In this study, polyester fibers were modified by Ag₂O/ZnO nanorod (NR)/Al-ZnO p-type/high resistivity/n-type (P-HR-N) heterojunction arrays. Al-doped ZnO (Al-ZnO) seed layer was reactively sputtered on polyester fibers. Al doping was used to change the work function (WF) of the ZnO film. The ZnO NR arrays were hydrothermally grown on the Al-ZnO seed layer and modified with Ag₂O film. The work functions (WFs) of Ag₂O and Al-ZnO layers were measured, resulting in $5.53$ and $4.81\mathrm{e}\mathrm{V}$, respectively. The WF difference between the two layers was $0.72\mathrm{e}\mathrm{V}$. The electron-hole separation of the P-HR-N heterojunction array was characterized by surface photovoltage (SPV) spectra. The photocatalytic activities of the prepared samples were investigated by removing Rhodamine B (RB) under UV irradiation. The P-HR-N heterojunction sample displayed a better photocatalytic performance than the Ag₂O/Al-doped ZnO PN heterojunction sample and ZnO NR/Al-ZnO array-coated sample. The enhanced photocatalytic performance of the P-HR-N heterojunction based sample was mainly attributed to the high and widened built-in electric field (BEF) in the multilayer film.     

Synthesis of In2O3/GNPs nanocomposites with integrated approaches to tune overall performance of electrochemical devices

The electroactive material with a porous structure, good electrical conductivity, hybrid composition, and a higher surface is considered more suitable for applications as an electrode in the energy storage device. Herein, we report the preparation of In₂O₃ nanoparticles via a simple chemical route and their nanocomposites with 10% (IOG-10), 30% (IOG-30), 50% (IOG-50), 70% (IOG-70), and 100% G-100 graphene nanoplatelets (GNPs) via ultra-sonication. The presence of GNPs in the nanocomposite samples was verified by powder X-ray diffraction (PXRD), Raman, and scanning electron microscopy (SEM) results. The prepared samples were loaded onto the porous 3D nickel foam (NF) substrate to manufacture the working electrode for electrochemical testing. The cyclic voltammetry (CV), as well as galvanostatic charge/discharge (GCD), results proposed the IOG-30@NF as a suitable electrode for electrochemical applications. More precisely, the IOG-30@NF electrode shows a specific capacitance of 1768 Fg^-1 at 1 Ag^-1, which is considerably higher than that of either G-100@NF or In₂O₃@NF electrodes. Besides, the IOG-30@NF electrode shows good cyclic stability of 92.2% after 4000 GCD tests completed at 12 Ag^-1. When increasing the current density value from 1 to 4, the IOG-30@NF electrode maintains a specific capability of 81%, ensuring its exceptional rate capability. The higher specific capacity, higher rate-performance, and better cyclic activity of the IOG-30@NF electrode can be ascribed to its hybrid-composition, nanoarchitecture In₂O₃, 3D but porous nickel foam substrate, appropriate graphene content, and interaction between In₂O₃ nanoparticles and GNPs nanosheets.     

ZnO nanorod array-coated mesh film for the separation of water and oil

Dense and vertically aligned ZnO nanorod arrays with a large area have been fabricated successfully on the stainless steel mesh by a simple chemical vapor deposition method. The coated mesh exhibited both superoleophilic and superhydrophobic properties, even if it was not modified by low surface energy materials. The separation efficiencies were more than 97% in the filtration of water and oil. Besides, the wettability of the coated mesh was still stable after it was soaked in the corrosive solutions for 1 h. A detailed investigation showed that the coated mesh has the best superhydrophobic property when the stainless steel mesh pore size was about 75 μm.     

Synthesis of well-aligned ZnO nanorod arrays from mixed sulfide-oxide lead and zinc ore

A novel process of recovery of zinc from mixed sulfide-oxide lead and zinc ore was presented in this paper. ZnO nanorod arrays (ZNRAs) on FTO substrate pre-coated with a layer of ZnO seeds was synthesized successfully from the mixed ore via the oxidative ammoniacal leaching process and a two-step process including precipitation and hydrothermal synthesis. The characterization results from the XRD, SEM and UV–vis spectrophotometer analysis showed that the as-prepared ZNRAs was well-aligned, large-scale, perpendicular to the FTO substrate and had a reduced band gap energy of 3.03 eV. XPS analysis indicated that the grown ZNRAs were doped by a small quantity of carbon and did not contain any other impurities particularly Fe and Pb. The total zinc extraction can reach 92.4% after the oxidative ammoniacal leaching process and the precipitation process. The elimination of conventional purification process in zinc production was achieved due to the efficient and selective oxidative ammoniacal leaching process.     

Anisotropy of functional properties of SiC composites with GNPs,GO and in-situ formed graphene

This paper reports on anisotropy of functional properties of different silicon carbide-graphene composites due to preferential orientation of graphene layers during sintering. Dense silicon carbide/graphene nanoplatelets (SiC/GNPs) and silicon carbide/graphene oxide (SiC/GO) composites were sintered in the presence of yttria (Y₂O₃) and alumina (Al₂O₃) sintering additives at 1800 °C in vacuum by the rapid hot pressing (RHP) technique. It is found that electrical conductivity of SiC/GNPs and SiC/GO composites increases significantly in the perpendicular direction to the RHP pressing axis, reached up to 1775 S/m in the case of SiC/GO (for 3.15 wt.% of rGO). Also, thermal diffusivity was found to increase slightly by the addition of GNPs in the SiC/GNPs composites in the perpendicular direction to the RHP pressing axis. But, in the parallel direction, the addition of GNPs showed a negative effect. The formation of graphene domains was observed in reference sample SiC-Y₂O₃-Al₂O₃ sintered by RHP, without any addition of graphene. Their presence was confirmed indirectly by increasing electrical conductivity about three orders of magnitude in comparison to the reference sample sintered by conventional hot press (HP). Raman, SEM and TEM analysis were used for direct evidence of presence of graphene domains in RHP reference sample.     

Controllable growth of ZnO nanorod arrays with different densities and their photo-electric properties

ABSTRACT: Since the photo-electric response and charge carriers transport can be influenced greatly by the density and spacing of the ZnO nanorod arrays, controlling of these geometric parameters precisely is highly desirable but rather challenging in practice. Here, we fabricated patterned ZnO nanorod arrays with different density and spacing distance on silicon (Si) substrate by electron beam lithography (EBL) method combined with the subsequent hydrothermal reaction process. By using the EBL method, patterned ZnO seed layers with different areas and spacing distances were obtained firstly. ZnO nanorod arrays with different density and various morphologies were obtained by the subsequent hydrothermal growth process. The combination of EBL and hydrothermal growth process was very attractive and made us could control the geometric parameters of ZnO nanorod arrays expediently. Finally, the vertical transport properties of the patterned ZnO nanorod arrays were investigated through the micro probe station equipment and the I-V measurement results indicated that back-to-back Schottky contacts with different barriers height were formed in dark conditions. Under UV light illumination, the patterned ZnO nanorod arrays showed a high UV light sensitivity, and the response ratio was about 104. The controllable fabrication of patterned ZnO nanorod arrays and understanding for their photo-electric transport properties were helpful to improve the performance of nanodevices based on them.     

Electrodeposition of flexible stainless steel mesh supported ZnO nanorod arrays with enhanced photocatalytic performance

Large scale well oriented ZnO nanorod arrays (ZNRAs) were electrodeposited on flexible stainless steel mesh (SSM) substrate pre-treated by Al doped ZnO (AZO) seed layers. The effects of substrate pre-treatment conditions such as Al doping and spin coating times of the colloid on the morphology characteristics and photocatalytic properties of as-prepared ZNRAs were systematically studied. The results showed that by introducing Al into ZnO colloid solution, well aligned ZNRAs with relatively higher specific surface area (higher growth density and smaller rod diameter) could be obtained on the premodified SSM substrate. In addition, increasing spin coating times of AZO colloid solution would decrease the average diameter of ZNRAs. Under the optimum preparing conditions, the formed flexible SSM supported ZNRAs exihibited enhanced photocatalytic performance of 93.42% and remarkable photocatalytic stability under the UV-lamp for degradation of Rhodamine B.     

Synthesis,optical and electrochemical properties of ZnO nanowires/graphene oxide heterostructures

Large-scale vertically aligned ZnO nanowires with high crystal qualities were fabricated on thin graphene oxide films via a low temperature hydrothermal method. Room temperature photoluminescence results show that the ultraviolet emission of nanowires grown on graphene oxide films was greatly enhanced and the defect-related visible emission was suppressed, which can be attributed to the improved crystal quality and possible electron transfer between ZnO and graphene oxide. Electrochemical property measurement results demonstrated that the ZnO nanowires/graphene oxide have large integral area of cyclic voltammetry loop, indicating that such heterostructure is promising for application in supercapacitors.     

ZnO纳米棒阵列的改进水热方法制备、银修饰及光催化活性研究

ZnO纳米棒阵列是近来研究较多的光催化剂,通过银等贵金属修饰可提高光催化活性。以硝酸锌和六亚甲基四胺为前驱物,通过优化水热合成参数（包括种子层和水热生长液浓度等）以及光化学还原沉积银制备高活性ZnO纳米棒阵列。利用扫描电子显微镜、X射线粉末衍射以及紫外-可见漫反射光谱对样品进行表征。结果表明,种子层和水热反应液浓度均对ZnO纳米棒阵列的活性产生影响。银修饰后,光吸收增强,吸收带边从紫外光区拓展到可见光区。光催化降解甲基橙溶液结果表明,银修饰的ZnO纳米棒阵列较纯ZnO纳米棒阵列降解甲基橙的活性提高30%。     

Synthesis and Characterization of ZnO Nanorods and Nanodisks from Zinc Chloride Aqueous Solution

ZnO nanorods and nanodisks were synthesized by solution process using zinc chloride as starting material. The morphology of ZnO crystal changed greatly depending on the concentrations of Zn²⁺ ion and ethylene glycohol (EG) additive in the solution. The effect of thermal treatment on the morphology was investigated. Photocatalytic activities of plate-like Zn₅(OH)₈Cl₂ · H₂O and rod-like ZnO were characterized. About 18% of 1 ppm NO could be continuously removed by ZnO particles under UV light irradiation.     

A close correlation between nucleation sites,growth and final properties of ZnO nanorod arrays: Sol-gel assisted chemical bath deposition process

Different ZnO seed layers are synthesized by changing sol-gel parameters, including precursor concentration, type of solvent, and type of additive in order to systematically investigate the importance of seed layer properties on the nucleation, growth, and final properties of zinc oxide (ZnO) nanorod (NR) arrays. The X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) show the importance of the seed layer on ZnO NRs properties. Results verify that the relative intensity (RI factor) of (002) polar planes in the XRD patterns of ZnO nanoparticles (NPs) together with the aspect ratio, density, and alignment of ZnO NRs control the structural characteristics of those arrays. For instance, the RI factor of ZnO NPs and NRs follow the same trend when changing precursor concentration in sol preparation step. However, the importance of other parameters, including aspect ratio, density, and alignment of NRs is confirmed by changing solvent and additive. In addition, FESEM images show that the density of ZnO NRs is proportional to NPs density and inversely proportional to the size of ZnO NPs in the seed layers. Besides, the significant role of wrinkled inter-layer on NRs properties, together with the formation mechanism of that inter-layer are profoundly investigated.     

Thermal conductivity and lap shear strength of GNP/epoxy nanocomposites adhesives

The addition of graphene nanoplatelets (GNPs) into the epoxy adhesives has been studied in order to increase their thermal conductivity. Thermally conductive adhesives are often used as thermal interface materials (TIMs). The incorporation of 8 and 10 wt% GNPs reinforcement caused a thermal conductivity enhancement of ~206 and ~306%, respectively. The wettability seems to decrease with low GNPs content (2–3 wt%) in comparison with the neat epoxy adhesive but the contact angle remains constant for higher GNPs contents. Lap shear strength remains constant for neat adhesives and resins doped with GNPs. The lack of enhancement of adhesive properties of doped resins is due to a weak interface reinforcement-matrix. In fact, the joint failure is in the adhesive except for high GNPs content (10 wt%) where a cohesive failure mode is observed.     

Structural and optical properties of ZnO nanorods by electrochemical growth using multi-walled carbon nanotube-composed seed layers

We reported the enhancement of the structural and optical properties of electrochemically synthesized zinc oxide [ZnO] nanorod arrays [NRAs] using the multi-walled carbon nanotube [MWCNT]-composed seed layers, which were formed by spin-coating the aqueous seed solution containing MWCNTs on the indium tin oxide-coated glass substrate. The MWCNT-composed seed layer served as the efficient nucleation surface as well as the film with better electrical conductivity, thus leading to a more uniform high-density ZnO NRAs with an improved crystal quality during the electrochemical deposition process. For ZnO NRAs grown on the seed layer containing MWCNTs (2 wt.%), the photoluminescence peak intensity of the near-band-edge emission at a wavelength of approximately 375 nm was enhanced by 2.8 times compared with that of the ZnO nanorods grown without the seed layer due to the high crystallinity of ZnO NRAs and the surface plasmon-meditated emission enhancement by MWCNTs. The effect of the MWCNT-composed seed layer on the surface wettability was also investigated.     

Synthesis, structure and photoelectrochemical performance of micro/nano-textured ZnO/eosin Y electrodes

Micro/nano-textured ZnO thick films were synthesized through deposition and pyrolysis of layered hydroxide zinc acetate (LHZA), Zn₅(OH)₈(CH₃COO)₂·2H₂O. LHZA films having a unique, rose-like morphology were initially deposited on conducting glass sheets in a chemical bath composed of methanol and zinc acetate dihydrate at 60 °C under neutral conditions. Pyrolysis of the LHZA films resulted in formation of ZnO without destroying the original morphology. Pyrolysis temperatures were found to greatly influence grain sizes and specific surface areas of the ZnO films. Photoelectrochemical performance of the films as ZnO/eosin Y electrodes was investigated in dye-sensitized solar cells using an I⁻/I₃⁻ redox electrolyte solution. The cell using the ZnO film pyrolyzed at 150 °C exhibited overall light to electricity conversion efficiencies of 2.0 and 3.3% under an AM-1.5 illumination at 100 and 10 mW cm⁻², respectively. While microscale pores in the electrodes facilitated mass transfer of fluid electrolytes in the depth direction, nanoscale pores contributed to an increase in the amount of adsorbed dye. The maximum incident photon-to-current conversion efficiency (IPCE) of the electrode reached 84.9% at a wavelength of 530 nm.     

Hydrogen treatment-improved uniform deposition of Ag nanoparticles on ZnO nanorod arrays and their visible-light photocatalytic and surface-enhanced Raman scattering properties

ZnO nanorod arrays were synthesized by chemical bath deposition. After heat treatment in hydrogen or air, Ag nanoparticles were deposited on ZnO nanorod arrays by photo-reduction method. The size of Ag nanoparticles as well as the surface morphology, structure, composition, and optical property of ZnO nanorod arrays before and after the deposition of Ag nanoparticles were characterized by SEM, XRD, EDS, and UV/VIS/NIR spectrophotometer. As compared to the samples with heat treatment in air or without heat treatment, the ZnO nanorod arrays after heat treatment in hydrogen allowed Ag nanoparticles to be deposited more uniformly, densely, and numerously. Also, they exhibited higher efficiency for the visible light-driven photocatalytic degradation of Rhodamine 6G (R6G) dye. The effects of the amount of Ag nanoparticles, initial dye concentration, and temperature on the photocatalytic degradation efficiency were investigated. Furthermore, they also exhibited better surface-enhanced Raman scattering property for the detection of R6G dyes.     

Innovative synthesis of a novel ZnO/ZnBi2O4/graphene ternary heterojunction nanocomposite photocatalyst in the presence of tragacanth mucilage as natural surfactant

Developing interfacial connections is one of the breakthrough strategies to improve the photocatalytic activity of graphene/p-n heterojunction systems. Herein, natural tragacanth mucilage, for the first time, was employed as cost-effective and ecofriendly surfactant to prepare highly efficient ZnO–ZnBi₂O₄/graphene hybrid photocatalyst. The results indicated that the methylene blue (MB) photocatalytic degradation efficiency of ZnO–ZnBi₂O₄/graphene-mucilage heterojunction, containing 10 wt% ZnBi₂O₄ and 1 wt% graphene, was ～1.2, 1.4, 3.1 and 8.3 times higher than that of ZnO–ZnBi₂O₄/graphene, ZnO–ZnBi₂O₄, ZnBi₂O₄ and ZnO samples, respectively. This significant improvement in the photocatalytic performance could be mainly ascribed to the desirable advantages of using natural mucilage as surfactant, including uniform distribution of ZnO–ZnBi₂O₄ nanoparticles on the surface of graphene sheets, increasing of the effective surface area, and improving of the charge carriers separation. Based on the trapping experiments, electron spin resonance and photoelectrochemical Mott-Schottky tests, direct Z-Scheme charge transfer mechanism with hydroxyl radicals as main active species was suggested for photocatalytic degradation of MB on the ZnO–ZnBi₂O₄/graphene-mucilage nanocomposite. This study provides a new insight to fabricate more homogeneous and close contact interfaces in graphene-based hybrid photocatalytic systems for environmental remediation.     

水热合成CuS/GO纳米复合材料及光催化降解有机污染物的研究

以醋酸铜 Cu(Ac)2 和硫化钠（Na2S）以及氧化石墨烯 (GO) 为原料，去离子水作溶剂，十六烷基三甲基溴化铵 (CTMAB) 为表面活性剂，在水热条件下合成CuS/GO纳米复合材料。并对其进行了XRD，FT-IR，XPS，SEM和 TEM 表征，发现具有10~20nm左右CuS纳米粒子均匀的负载在氧化石墨烯上。CuS/GO纳米复合材料在可见光照射下对有机物四环素(TC)和罗丹明B (Rh-B)表现优异的光催化活性，在可见光照射120分钟后分别对TC和Rh-B降解速率达到63%和85%。通过-ln(C/C0) 对反应时间呈现线性关系说明样品在降解TC和Rh-B过程遵循一级动力学原理。     

Eco-Friendly Synthesis of Graphene Oxide Reinforced Hydroxypropyl Methylcellulose/Polyvinyl Alcohol Blend Nanocomposites Filled with Zinc Oxide Nanoparticles for High-k Capacitor Applications

Polymer/inorganic nanocomposites comprising of hydroxypropyl methylcellulose and polyvinyl alcohol as a polymer matrix and unique combination of graphene oxide and zinc oxide nanoparticles as fillers have been prepared using colloidal processing technique and characterized using various analytical methods. The dielectric properties of the nanocomposites are investigated using impedance analyzer. The nanocomposites show improvement in the dielectric properties compared to hydroxypropyl methylcellulose/polyvinyl alcohol (50/50) blends, which results from the homogeneous dispersion of fillers into the polymer matrix. The results indicate that these nanocomposites have a potential to meet the technological demands of high-k dielectrics and/or embedded capacitors.     

Structural,optical, cytotoxicity,and antimicrobial properties of MgO,ZnO and MgO/ZnO nanocomposite for biomedical applications

In this study, MgO nanoparticles were successfully fabricated and incubated inside ZnO NPs to form MgO/ZnO nanocomposite for biomedical applications. The x-ray diffraction analysis of MgO, ZnO, and MgO/ZnO has shown the single-phase x-ray diffraction patterns through X'pert High score. The crystallite sizes were calculated as 18 nm, 42 nm, and 53 nm, respectively. The average particle size of MgO, ZnO, and MgO/ZnO nanopowders depicted from secondary electron images of field emission electron microscopy were 56 nm, 400 nm, and 450 nm, respectively. The presence of MgO NPs inside ZnO NPs was confirmed by transmission electron microscopy. The elemental dispersive spectroscopy of MgO, given the peaks of oxygen and magnesium, also showed only zinc and oxygen peaks in ZnO, which confirms no other impurities in MgO and ZnO powders. The elemental analysis of MgO/ZnO nanocomposite showed the peaks of Zinc and Oxygen, along with a tiny peak of Mg. The photoluminescence and UV–vis spectroscopy revealed the absorbance fluorescence limit of the nanomaterials. Fourier transform infrared spectroscopy confirmed the several groups present in the nanocomposite. The biocompatibility of MgO, ZnO, and MgO/ZnO was observed with human peripheral blood mononuclear cells. The cytotoxicity studies were also performed against human cancer (liver and breast) cell lines. The MgO, ZnO, and MgO/ZnO exhibited the antimicrobial properties against Escherichia coli and Staphylococcus aureus.     

Nanostructured conformal hybrid solar cells: a promising architecture towards complete charge collection and light absorption

We introduce hybrid solar cells with an architecture consisting of an electrodeposited ZnO nanorod array (NRA) coated with a conformal thin layer (<50 nm) of organic polymer-fullerene blend and a quasi-conformal Ag top contact (Thin/NR). We have compared the performance of Thin/NR cells to conventional hybrid cells in which the same NRAs are completely filled with organic blend (Thick/NR). The Thin/NR design absorbs at least as much light as Thick/NR cells, while charge extraction is significantly enhanced due to the proximity of the electrodes, resulting in a higher current density per unit volume of blend and improved power conversion efficiency. The NRAs need not be periodic or aligned and hence can be made very simply.