Studies of surface plasmon resonance of silver nanoparticles reduced by aqueous extract of shortleaf spikesedge and their catalytic activity.

This study describes the synthesis of silver nanoparticles (AgNPs) using shortleaf spikesedge extract (SSE) to reduce AgNO3. Visual observation, in addition to analyses of UV-vis, EDX, XRD, FTIR, and TEM was employed to monitor the formation of AgNPs. The effects of SSE concentration, AgNO3 concentration, reaction time, pH, and temperature on the synthesis of AgNPs were studied based on the surface plasmon resonance (SPR) band. From the TEM image, highly-scattered AgNPs of quasi-spherical shape with an average particle size of 17.64 nm, were observed. For the catalytic study, the reduction of methylene blue (MB) was evaluated using two systems. A detailed batch study of the removal efficiency (%RE) and kinetics was done at an ambient temperature, various MB initial concentrations, and varying reaction time. Employing the electron relay effect in System 2, the batch study clearly highlighted the significant role of AgNPs in boosting the catalytic activity for MB removal. At 30-100 mg/L initial concentrations, MB was reduced by 100% in a very short reaction time between 1.5 and 5.0 mins. The kinetic data best fitted the pseudo-first-order model with a maximum reaction rate of 2.5715 min-1. These findings suggest the promising application of AgNPs in dye wastewater treatment.The SSE-driven AgNPs were prepared using unwanted dried biomass of shortleaf spikesedge extract (SSE) as a reducing as well as stabilizing agent. Employing the electron relay effect, the batch study clearly highlighted the significant role of SSE-driven AgNPs in boosting the catalytic activity for MB removal. At 30-100 mg/L initial concentrations, MB was reduced by 100% in a very short reaction time between 1.5 and 5.0 mins. In this sense, SSE-driven AgNPs acted as an electron relay point that behaves alternatively as acceptor and donor of electrons. The findings revealed the good catalytic performance of SSE-driven AgNPS, proving their viability for dye wastewater treatment.

Enhanced photocatalytic and antimicrobial performance of a multifunctional Cu-loaded nanocomposite under UV light: theoretical and experimental study.

Due to modern industrialization and population growth, access to clean water has become a global challenge. In this study, a metal-semiconductor heterojunction was constructed between Cu NPs and the Co0.5Ni0.5Fe2O4/SiO2/TiO2 composite matrix for the photodegradation of potassium permanganate, hexavalent chromium Cr(VI) and p-nitroaniline (pNA) under UV light. In addition, the electronic and adsorption properties after Cu loading were evaluated using density functional theory (DFT) calculations. Moreover, the antimicrobial properties of the prepared samples toward pathogenic bacteria and unicellular fungi were investigated. Photocatalytic measurements show the outstanding efficiency of the Cu-loaded nanocomposite compared to that of bare Cu NPs and the composite matrix. Degradation efficiencies of 44% after 80 min, 100% after 60 min, and 65% after 90 min were obtained against potassium permanganate, Cr(VI), and pNA, respectively. Similarly, the antimicrobial evaluation showed high ZOI, lower MIC, higher protein leakage amount, and cell lysis of nearly all microbes treated with the Cu-loaded nanocomposite.

Photoreduction of Cr(VI) in wastewater by anodic nanoporous Nb2O5 formed at high anodizing voltage and electrolyte temperature.

In this study, nanoporous anodic film was produced by anodization of niobium, Nb in a fluoride ethylene glycol electrolyte. The effect of anodization voltage and electrolyte temperature was studied to find an optimum condition for circular, ordered, and uniform pore formation. The diameter of the pores was found to be larger when the applied voltage was increased from 20 to 80 V. The as-anodized porous film was also observed to comprise of nanocrystallites which formed due to high field-induced crystallization. The nanocrystallites grew into orthorhombic Nb2O5 after post-annealing treatment. The Cr(VI) photoreduction property of both the as-anodized and annealed Nb2O5 samples obtained using an optimized condition (anodization voltage: 60 V, electrolyte temperature: 70 °C) was compared. Interestingly, the as-anodized Nb2O5 film was found to display better photoreduction of Cr(VI) than annealed Nb2O5. However, in terms of stability, the annealed Nb2O5 presented high photocatalytic efficiency for each cycle whereas the as-anodized Nb2O5 showed degradation in photocatalytic performance when used continually.

Self-Assembled Iron Oxide Nanoparticle-Modified APTES-ITO Electrode for Simultaneous Stripping Analysis of Cd(II) and Pb(II) Ions.

Carboxyl (-COOH)-stabilized iron oxide nanoparticles (IONPs) synthesized through co-precipitation were used to modify an indium tin oxide (ITO) electrode, which was chemically functionalized with 3-aminopropyltriethoxysilane (APTES) for heavy metal detection. The effect of soaking time (30, 60, 90, and 120 min) of IONP-COOH self-assembled on an APTES-ITO electrode was studied. Cyclic voltammetry and scanning electron microscopy were applied to analyze the electrochemical properties and morphologies of IONP-COOH/APTES-ITO modified electrode. The modified electrodes were then employed for the simultaneous detection of Cd(II) and Pb(II) by using square wave anodic stripping voltammetry. At 90 min of soaking time, excellent electrochemical performance and larger effective surface area (A e) were obtained. The linear range for the simultaneous detection of Cd(II) and Pb(II) ions using the modified electrode was 10-100 ppb with limits of detection of 0.90 and 0.60 ppb, respectively. The interference study revealed a low interference effect from Cr(III), Hg(II), Zn(II), Cu(II), Mg(II), Na(I), and K(I) toward the simultaneous detection of Cd(II) and Pb(II). Finally, the IONP-COOH/APTES-ITO-modified electrode was applied to analyze seawater samples and was able to simultaneously detect Cd(II) and Pb(II) ions.

Formation of Dense and High-Aspect-Ratio Iron Oxide Nanowires by Water Vapor-Assisted Thermal Oxidation and Their Cr(VI) Adsorption Properties.

Coral-like and nanowire (NW) iron oxide nanostructures were produced at 700 and 800 °C, respectively, through thermal oxidation of iron foils in air- and water vapor-assisted conditions. Water vapor-assisted thermal oxidation at 800 °C for 2 h resulted in the formation of highly crystalline α-Fe2O3 NWs with good foil surface coverage, and we propose that their formation was due to a stress-driven surface diffusion mechanism. The Cr(VI) adsorption property of an aqueous solution on α-Fe2O3 NWs was also evaluated after a contact time of 90 min. The NWs had a removal efficiency of 97% in a 225 mg/L Cr(VI) solution (pH 2, 25 °C). The kinetic characteristic of the adsorption was fitted to a pseudo-second-order kinetic model, and isothermal studies indicated that the α-Fe2O3 NWs exhibited an adsorption capacity of 66.26 mg/g. We also investigated and postulated a mechanism of the Cr(VI) adsorption in an aqueous solution of α-Fe2O3 NWs.

Nanoporous anodic Nb2O5 with pore-in-pore structure formation and its application for the photoreduction of Cr(VI).

An anodic film with a nanoporous structure was formed by anodizing niobium at 60 V in fluorinated ethylene glycol (fluoride-EG). After 30 min of anodization, the anodic film exhibited a "pore-in-pore" structure; that is, there were smaller pores growing inside larger pores. The as-anodized film was weakly crystalline and became orthorhombic Nb2O5 after heat treatment. The energy band gap of the annealed nanoporous Nb2O5 film was 2.9 eV. A photocatalytic reduction experiment was performed on Cr(VI) under ultraviolet (UV) radiation by immersing the nanoporous Nb2O5 photocatalyst in a Cr(VI) solution at pH 2. The reduction process was observed to be very slow; hence, ethylenediaminetetraacetic acid (EDTA) was added as an organic hole scavenger, which resulted in 100% reduction after 45 min of irradiation. The photocatalytic reduction experiment was also performed under visible light, and findings showed that complete reduction achieved after 120 min of visible light exposure.

Nanomaterial Fabrication through the Modification of Sol-Gel Derived Coatings.

In materials processing, the sol-gel method is one of the techniques that has enabled large-scale production at low cost in the past few decades. The versatility of the method has been proven as the fabrication of various materials ranging from metallic, inorganic, organic, and hybrid has been reported. In this review, a brief introduction of the sol-gel technique is provided and followed by a discussion of the significance of this method for materials processing and development leading to the creation of novel materials through sol-gel derived coatings. The controlled modification of sol-gel derived coatings and their respective applications are also described. Finally, current development and the outlook of the sol-gel method for the design and fabrication of nanomaterials in various fields are described. The emphasis is on the significant potential of the sol-gel method for the development of new, emerging technologies.

Formation of grassy TiO2 nanotube thin film by anodisation in peroxide electrolyte for Cr(VI) removal under ultraviolet radiation.

Arrays of TiO2 nanotubes (TiO2 NTs) with grassy surfaces were observed on titanium foil anodised at 60 V in fluorinated ethylene glycol (EG) with added hydrogen peroxide (H2O2). The grassy surface was generated by the chemical etching and dissolution of the surface of the TiO2 NTs walls, which was accelerated by the temperature increase on the addition of H2O2 . Upon annealing at 600 °C, the grassy part of the TiO2 NTs was found to consist of mostly anatase TiO2 whereas the bottom part of the anodic oxide comprised a mixture of anatase and rutile TiO2. The TiO2 NTs were then used to reduce hexavalent chromium (Cr(VI)) under ultraviolet radiation. They exhibited a rather efficient photocatalytic effect, with 100% removal of Cr(VI) after 30 min of irradiation. The fast removal of Cr(VI) was due to the anatase dominance at the grassy part of the TiO2 NTs as well as the higher surface area the structure may have. This work provides a novel insight into the photocatalytic reduction of Cr(VI) on grassy anatase TiO2 NTs.

Facile Fabrication of Plasmonic Enhanced Noble-Metal-Decorated ZnO Nanowire Arrays for Dye-Sensitized Solar Cells.

Novel decoration of high aspect ratio zinc oxide nanowires (ZnO NWs) with noble metals such as Ag and Au nanoparticles (NPs) was demonstrated in this work. A facile method of chemical deposition with good controllability, as well as good homogeneity would be a huge advantage towards large scale fabrication. The highlight of this work is the feasibility of multiple component decoration such as a hybrid (co-exist) Ag-Au NPs decorated ZnO NWs formation that could be beneficial towards the development of nanoarchitectured materials with the most desired properties. The local surface plasmon effect (LSPR) of Ag and Au NPs were confirmed using extinction spectra and significant photoelectrochemical conversion efficiency (PCE) enhancement of dye-sensitized solar cells (DSSCs) was achieved. The Ag-NPs and hybrid Ag-Au NPs decorated ZnO NWs marked an impressive 125 and 240% efficiency improvement against pure ZnO NWs. The improved dye light extinction resulted from the LSPR effect that had enabled greater electron generation leading to improved PCE. As the complex design of oxides' nanoarchitectures have reached a point of saturation, this novel method would enable further enhancement in their photoelectrochemical properties through decoration with noble metals via a simple chemical deposition route.

Methylene blue dye removal on silver nanoparticles reduced by Kyllinga brevifolia.

Silver nanoparticles (AgNPs) were prepared by reacting Kyllinga brevifolia extract (KBE) with AgNO3 aqueous solution at room temperature (22 ± 3 °C). The phytochemical constituents in KBE responsible for the reduction process were identified as carbohydrate, protein, and plant sterols (stigmasterol and campesterol). KBE was also found to function as a capping agent for stabilization of AgNPs. The AgNPs were stable at room temperature and had a quasi-spherical shape with an average particle size 22.3 nm. The use of KBE offers not only eco-friendly and non-pathogenic path for AgNPs formation, it also induced rapid formation of the AgNPs. Methylene blue (MB) removal was then done on the AgNPs in the presence of either KBE or NaBH4. Ninety-three percent removal of MB was achieved with a rate of reaction 0.2663 min-1 in the solution with KBE+AgNPs (pH 2). However, in NaBH4+AgNPs system, 100% MB removal was achieved at pH 8-10. The reaction rate was 2.5715 min-1 indicating a fast removal rate of MB dye. The process of reduction occurs via electron relay effect whereas in KBE+AgNPs system, sedimentation occurred along with the reduction process. Nevertheless, the use of KBE+AgNPs system is preferred as the reducing agent is more benign to the environment.

Fabrication and Characterization of Glucose Biosensors by Using Hydrothermally Grown ZnO Nanorods.

Highly oriented ZnO nanorod (NR) arrays were fabricated on a seeded substrate through a hydrothermal route. The prepared ZnO nanorods were used as an amperometric enzyme electrode, in which glucose oxidase (GOx) was immobilised through physical adsorption. The modified electrode was designated as Nafion/GOx/ZnO NRs/ITO. The morphology and structural properties of the fabricated ZnO nanorods were analysed using field-emission scanning electron microscope and X-ray diffractometer. The electrochemical properties of the fabricated biosensor were studied by cyclic voltammetry and amperometry. Electrolyte pH, electrolyte temperature and enzyme concentration used for immobilisation were the examined parameters influencing enzyme activity and biosensor performance. The immobilised enzyme electrode showed good GOx retention activity. The amount of electroactive GOx was 7.82 × 10-8 mol/cm2, which was relatively higher than previously reported values. The Nafion/GOx/ZnO NRs/ITO electrode also displayed a linear response to glucose ranging from 0.05 mM to 1 mM, with a sensitivity of 48.75 µA/mM and a low Michaelis-Menten constant of 0.34 mM. Thus, the modified electrode can be used as a highly sensitive third-generation glucose biosensor with high resistance against interfering species, such as ascorbic acid, uric acid and L-cysteine. The applicability of the modified electrode was tested using human blood samples. Results were comparable with those obtained using a standard glucometer, indicating the excellent performance of the modified electrode.

Sunlight activated anodic freestanding ZrO2 nanotube arrays for Cr(VI) photoreduction.

Visible-light-active freestanding zirconia (ZrO2) nanotube (FSZNT) arrays were fabricated by a facile electrochemical anodization method in fluoride containing ethylene glycol electrolyte added to it was 1 vol% of potassium carbonate (K2CO3) at 60 V for 1 h. Poor adhesion at the metal∣oxide interface was induced by K2CO3 leading to the formation of FSZNT flakes. The effect of the crystal structures of the FSZNTs e.g., amorphous, amorphous/tetragonal, and tetragonal/monoclinic was investigated towards the photocatalytic reduction of 10 ppm hexavalent chromium, Cr(VI) at pH 2 under sunlight. The results demonstrate the amorphous FSZNTs exhibited the highest Cr(VI) removal efficiency than the crystalline FSZNTs (95% versus 33% after 5 h). The high photocatalytic activity of the amorphous FSZNTs can be attributed to enhanced Cr(VI) adsorption, high visible light absorption, and better charge carrier separation. The low photocatalytic activity of the crystalline FSZNTs annealed at 500 °C was mainly attributed to poor Cr(VI) adsorption, low visible light absorption, and less photoactive monoclinic-ZrO2.

Photocatalytic performance of freestanding tetragonal zirconia nanotubes formed in H2O2/NH4F/ethylene glycol electrolyte by anodisation of zirconium.

ZrO2 nanotubes (ZrNTs) were produced by anodisation of zirconium foil in H2O2/NH4F/ethylene glycol electrolyte. The as-anodised foils were then soaked in the anodising electrolyte for 12 h. Soaking weakens the adherence of the anodic layer from the substrate resulting in freestanding ZrNTs (FS-ZrNTs). Moreover, the presence of H2O2 in the electrolyte also aids in weakening the adhesion of the film from the foil, as foil anodised in electrolyte without H2O2 has good film adherence. The as-anodised FS-ZrNTs film was amorphous and crystallised to predominantly tetragonal phase upon annealing at >300 °C. Annealing must, however, be done at <500 °C to avoid monoclinic ZrO2 formation and nanotubes disintegration. FS-ZrNTs annealed at 450 °C exhibited the highest photocatalytic ability to degrade methyl orange (MO), whereby 82% MO degradation was observed after 5 h, whereas FS-ZrNTs with a mixture of monoclinic and tetragonal degraded 70% of MO after 5 h.

Anodic Ag/TiO2 nanotube array formation in NaOH/fluoride/ethylene glycol electrolyte as a photoanode for dye-sensitized solar cells.

Self-organized, 23 µm-thick anodic TiO2 nanotube (TNT) arrays were formed in sodium hydroxide/fluoride/ethylene glycol (EG) electrolyte at 60 V for 60 min. The presence of sodium hydroxide (NaOH) in the fluoride/EG electrolyte accelerates the formation of the TiO2 nanotube arrays. The anodic film was then decorated with silver nanoparticles (Ag NPs) by the photodeposition process and used as a photoanode in a rear-side-illuminated dye-sensitized solar cell. The Ag NPs decorated TNT arrays, with the former having diameters of 10-30 nm formed from 0.2 M of Ag-precursor solution and exhibiting the highest photoconversion efficiency (η) of 3.7% and a short-circuit current density of 12.2 mA cm(-2) compared to η = 3% and short-circuit current density of 9.1 mA cm(-2) for a sample without Ag NPs. The increase in η is thought to be due to the surface plasmon resonance and excess electrons from the nanoparticles.

Ag nanoparticle-deposited TiO2 nanotube arrays for electrodes of Dye-sensitized solar cells.

ABSTRACT: Dye-sensitized solar cells composed of a photoanode of Ag nanoparticle (NP)-deposited TiO2 nanotube (TNT) arrays were fabricated. The TNT arrays were prepared by anodizing Ti films on fluorine-doped tin oxide (FTO)-coated glass substrates. Efficient charge transportation through the ordered nanostructure of TNT arrays should be carried out compared to conventional particulate TiO2 electrodes. However, it has been a big challenge to grow TNT arrays on FTO glass substrates with the lengths needed for sufficient light-harvesting (tens of micrometers). In this work, we deposited Ag nanoparticles (NPs) on the wall of TNT arrays to enhance light-harvesting property. Dye-sensitized solar cells with these Ag NP-deposited TNT arrays yielded a higher power conversion efficiency (2.03 %) than those without Ag NPs (1.39 %). PACS CODES: 06.60.Ei Sample preparation, 81.05.Bx Metals, Semimetals, Alloys, 81.07.De Nanotubes.

Formation of two-dimensional ZnO nanosheets by rapid thermal oxidation in oxygenated environment.

Crystalline 2-D (dimensional) ZnO nanosheets were formed by rapid thermal oxidation of etched Zn foil in oxygen at 300 degrees C and 400 degrees C. Short oxidation time was varied from 10, 20 and 30 min. The morphologies and optical properties of the ZnO nanosheets evolved with the oxidation temperature and time. At 300 degrees C, ZnO nanosheets with thickness ranging from 32 nm to 80 nm were obtained while at 400 degrees C, the thickness of the nanosheets increased from 88 nm to approximately 200 nm after 10 and 30 min of oxidation, respectively. The surface roughness of the ZnO nanosheets and grain size increased with oxidation time and temperature. Photoluminescence of the oxidized samples shows ultraviolet (UV) and visible emissions indicating good crystallinity of ZnO which was further confirmed by high-resolution transmission electron microscope observation of ZnO wurtzite interplanar spacing. Photocatalytic activity of ZnO was also investigated by using degradation of methyl orange (MO) and all the samples exhibit photocatalytic activity. The sample oxidized at 400 degrees C for 10 min show better MO degradation after 2 h of exposure due to higher surface area and better crystallinity of the ZnO nanosheets obtained.

Growth of ZnO nanorods on stainless steel wire using chemical vapour deposition and their photocatalytic activity.

The photodegradation efficiency of ZnO nanoparticles in removal of organic pollutants deteriorates over time as a high percentage of the nanoparticles can be drained away by water during the wastewater treatment. This problem can be solved by growing the ZnO nanorods on stainless steel wire. In this work, ZnO nanorods were successfully grown on stainless steel wire by chemical vapour deposition. The SAED analysis indicates that ZnO nanorod is a single crystal and is preferentially grown in [0001] direction. The deconvoluted O 1s peak at 531.5 eV in XPS analysis is associated with oxygen deficient, revealing that the ZnO nanorods contain many oxygen vacancies. This observation is further supported by the finding of the small I(uv)/I(vis) ratio, that is, ~1 in the photoluminescence analysis. The growth of ZnO nanorods on stainless steel wire was governed by vapour-solid mechanism as there were no Fe particles observed at the tips of the nanorods. The photodegradation of Rhodamine B solution by ZnO nanorods followed the first-order kinetics.

Structural and morphology of ZnO nanorods synthesized using ZnO seeded growth hydrothermal method and its properties as UV sensing.

In this study, zinc oxide (ZnO) nanorod arrays were synthesized using a simple hydrothermal reaction on ZnO seeds/n-silicon substrate. Several parameters were studied, including the heat-treatment temperature to produce ZnO seeds, zinc nitrate concentration, pH of hydrothermal reaction solution, and hydrothermal reaction time. The optimum heat-treatment temperature to produce uniform nanosized ZnO seeds was 400°C. The nanorod dimensions depended on the hydrothermal reaction parameters. The optimum hydrothermal reaction parameters to produce blunt tip-like nanorods (770 nm long and 80 nm in top diameter) were 0.1 M zinc nitrate, pH 7, and 4 h of growth duration. Phase analysis studies showed that all ZnO nanorods exhibited a strong (002) peak. Thus, the ZnO nanorods grew in a c-axis preferred orientation. A strong ultraviolet (UV) emission peak was observed for ZnO nanorods grown under optimized parameters with a low, deep-level emission peak, which indicated high optical property and crystallinity of the nanorods. The produced ZnO nanorods were also tested for their UV-sensing properties. All samples responded to UV light but with different sensing characteristics. Such different responses could be attributed to the high surface-to-volume ratio of the nanorods that correlated with the final ZnO nanorods morphology formed at different synthesis parameters. The sample grown using optimum synthesis parameters showed the highest responsivity of 0.024 A/W for UV light at 375 nm under a 3 V bias.

Photoelectrochemical behaviour of uniform growth TiO2 nanotubes via bubble blowing synthesised in ethylene glycol with hydrogen peroxide.

Uniformly sized TiO2 nanotubes with high aspect ratios were synthesised on a large substrate (100 mm x 100 mm) via the bubbling system through anodisation of Ti in ethylene glycol containing 5 wt% NH4F and 5 wt% H2O2. The benefits of bubbling system in producing uniformly sized TiO2 nanotubes throughout the Ti foil are illustrated. Moreover, the effects of applied voltage and fluoride content on the resulting nanotubes were also considered. Such uniform sized TiO2 nanotubes are a key to produce hydrogen efficiently using PEC cell. The results show higher photocurrent responses for the high aspect ratio, uniform TiO2 nanotubes because of excellent interfacial electron transfer.

Fast-rate formation of TiO2 nanotube arrays in an organic bath and their applications in photocatalysis.

In this work, 18.5 microm titanium oxide (TiO(2)) nanotube arrays were formed by the anodization of titanium (Ti) foil in ethylene glycol containing 1 wt% water and 5 wt% fluoride for 60 min at 60 V. The fast growth rate of the nanotube arrays at 308 nm min(-1) was achieved due to the excess fluoride content and the limited amount of water in ethylene glycol used for anodization. Limited water content and excess fluoride in ethylene glycol inhibited the formation of a thick barrier layer by increasing the dissolution rate at the bottom of the nanotubes. This eased the transport of titanium, fluorine and oxygen ions, and allowed the nanotubes to grow deep into the titanium foil. At the same time, the neutral condition offered a protective environment along the tube wall and pore mouth, which minimized lateral and top dissolution. Results from x-ray photoelectron spectra revealed that the TiO(2) nanotubes prepared in ethylene glycol contained Ti, oxygen (O) and carbon (C) after annealing. The photocatalytic activity of the nanotube arrays produced was evaluated by monitoring the degradation of methyl orange. Results indicate that a nanotube with an average diameter of 140 nm and an optimal tube length of 18.5 microm with a thin tube wall (20 nm) is the optimum structure required to achieve high photocatalytic reaction. In addition, the existence of carbon, high degree of anatase crystallinity, smooth wall and absence of fluorine enhanced the photocatalytic activity of the sample.