Komposit Nanostrukturerade Material för Tillämpningar för Förnybar Energi

Diverse sources of energy are becoming increasingly significant in today's world. The most common source of energy today is fossil fuels, such as coal, oil, and gas. While this energy source has many advantages, it also comes with many problems. In order to meet this demand, environmentally friendly and sustainable alternatives to energy are urgently needed. Renewable energy such as hydro, wind, photovoltaics, biomass, and geothermal is an attractive and promising kind of energy. Solar energy is among the most efficient, cleanest, and cheapest sources of energy. In this thesis, two photo-processes are utilized to produce solar energy using nanostructured materials. One is photocatalysis, mainly photoelectrochemical (PEC) water splitting for hydrogen production and photodegradation of organic dyes, and another is a sunlight-powered photovoltaic cell.   In this thesis, we aim to demonstrate optimized low-cost sustainable electrodes based on nanostructured materials for solar energy applications. For PEC water splitting two materials namely ZnO NRs and CuO NLs are fabricated by hydrothermal methods followed by deposition of different materials such as Ag2WO4 and AgBr. These materials show relatively high PEC water splitting efficiency using sunlight. Similarly, for the photodegradation of organic dyes Ta2O5 is used with the addition of Ag/AgCl nanoparticles (Ag/AgCl NPs), which results in an effective plasmonic photocatalyst for the removal of water-soluble Congo red (CR) dye compounds. For high-efficiency solar cells two methods are applied. Firstly, a FDTD simulation method was applied to study the plasmon enhancement of light absorption from p-i-n junction GaAs nanowires. Secondly a study of anisotropic deformation of colloidal particles exposed to heavy ions irradiation. Finally, a novel low-cost template-assisted method was used in order to improve the alignment of ZnO NRs grown on Si substrates. Idag finns det ett ökat behov av olika energikällor. Den energikälla som i stor utsträckning används är fossilt bränsle, som till exempel kol, olja och gas. Emellertid finns det många kriser som associeras med denna energikälla. Därför är det bråttom att utveckla alternativa energikällor som är ekologiska och uthålliga. Förnybara energikällor som väte, vind, sol, biomassa och geotermisk energi är attraktiva. I denna avhandling demonstrerar vi två fotoprocesser som använder solenergi och är baserade på nanostrukturmaterial. Den första metoden som vi använder är fotokatalys: fotoelektrokemisk (PEC) vattensplittring för väteproduktion. Den andra metoden är fotodegradering av organiska färgämnen genom att använda solstrålning som inkommande energi. Dessutom undersöker vi hur nanotrådar kan användas som aktiva solceller.    Avsikten med avhandlingen är att demonstrera optimiserade, billiga och uthålliga elektroder baserade på nanostrukturer för solenergitillämpningar. För PEC baserad vattensplittring använder vi två material, ZnO och CuO, som tillverkas med hjälp av hydrotermisk metoder följt av att vi deponerar olika material som Ag2WO4, och AgBr. Dessa material visar relativt hög effektivitet för PEC baserade användande av synligt solljus. För fotodegradering av organiska färgämnen användes Ta2O3 följt av deponering av Ag/AgCl nanopartiklar, som resulterar i effektiv plasmonisk fotokatalys för borttagande av det vattenlösliga Congo röda färgämnet. För högeffektiva solceller tillämpas två metoder först, en FDTD-simuleringsmetod användes för att studera plasmonförstärkningen av ljusabsorption från’’p-i-n junction’’ GaAs nanotrådar. För det andra en studie av anisotrop deformation av kolloidala partiklar under kraftig jonbestrålning. Slutligen användes en ny, billig mallassisterad metod för att förbättra anpassningen av ZnO NRs odlade på Si substrat.

Anisotropic deformation of colloidal particles under 4 MeV Cu ions irradiation

Anisotropic deformation of colloidal particles was investigated under ion irradiation with 4 MeV Cu ions. In this study, 0.5 mu m-diameter colloidal silica particles, 0.5 mu m-diameter Au-silica core-shell particles, and 15 nm-diameter Au colloids embedding in a planar Si/SiO2 matrix were irradiated with 4 MeV Cu ions at room temperature and normal incidence. In colloidal silica particles, ion beam irradiation causes dramatic anisotropic deformation; silica expands perpendicular to the beam and contracts parallel, whereas Au cores elongate. Au colloids in a planar SiO2 matrix were anisotropically transformed from spherical colloids to elongated nanorods by irradiating them with 4 MeV Cu ions. The degree of anisotropy varied with ion flux. Upon irradiating the embedded Au colloids, dark-field light scattering experiments revealed a distinct color shift to yellow, which indicates a shift in surface plasmon resonance. A surface plasmon resonance measurement reveals the plasmon resonance bands are split along the arrays of Au colloids. Our measurements have revealed resonance shifts that extend into the near-infrared spectrum by as much as 50 nm.Funding Agencies|Ajman University Internal Research Grant, UAE [2021-IRG-HBS-14]</p

Outcomes of arteriovenous fistula for hemodialysis in Sudanese patients: Single-center experience

A well-functioning arteriovenous fistula (AVF) is essential for the maintenance of hemodialysis (HD) in patients with chronic renal failure. Our aim is to review our experience of creating AVF and to asses its success rate and common complication. A prospective, hospital-based study was conducted on 73 patients (48 males and 25 females) on chronic HD in Gezira Hospital for Renal Diseases and Surgery, from January to July 2007. Their mean age was 43.9 years (range from 18 to 72 years). Seventy-one (97.3%) of the study subjects had been dialyzed before creation of the AVF, 67 (91.8%) of them having undergone HD with temporary access. All patients (n=73) had a native AVF as the permanent vascular access (VA). A primary radiocephalic AVF was created in 78.1% of the patients, cubital fossa in 20.5% and one case had left snuff box AVF (1.4%). Percentage of AVF maturation was reported in 67.1% of the cases within the first six weeks and in 9.6% of the cases AVF never matured. Failure of AVF function occurred in 26% of the cases, due to thrombosis in 20.5% (n=15) and aneurysm in 5.5% of the cases. We conclude that an optimum outcome is likely when there is a multidisciplinary team approach, and early referral to vascular surgery is paramount

Plasmon-Enhanced Light Absorption in (p-i-n) Junction GaAs Nanowire Solar Cells : An FDTD Simulation Method Study

A finite-difference time-domain method is developed for studying the plasmon enhancement of light absorption from vertically aligned GaAs nanowire arrays decorated with Au nanoparticles. Vertically aligned GaAs nanowires with a length of 1 mu m, a diameter of 100 nm and a periodicity of 165-500 nm are functionalized with Au nanoparticles with a diameter between 30 and 60 nm decorated in the sidewall of the nanowires. The results show that the metal nanoparticles can improve the absorption efficiency through their plasmonic resonances, most significantly within the near-bandgap edge of GaAs. By optimizing the nanoparticle parameters, an absorption enhancement of almost 35% at 800 nm wavelength is achieved. The latter increases the chance of generating more electron-hole pairs, which leads to an increase in the overall efficiency of the solar cell. The proposed structure emerges as a promising material combination for high-efficiency solar cells

Nanopatterned rGO/ZnO:Al seed layer for vertical growth of single ZnO nanorods

In this work, we demonstrate a novel low-cost template-assisted route to synthesize vertical ZnO nanorod arrays on Si (100). The nanorods were grown on a patterned double seed layer comprised of reduced graphene oxide (rGO) and Al-doped ZnO nanoparticles. The seed layer was fabricated by spray-coating the substrate with graphene and then dip-coating it into a Al -doped ZnO sol-gel solution. The growth template was fabricated from a double-layer resist, spin-coated on top of the rGO/ZnO:Al seed layer, and patterned by colloidal lithography. The results show a successful chemical bath deposition of vertically aligned ZnO nanorods with controllable diameter and density in the nanoholes in the patterned resist mask. Our novel method can presumably be used to fabricate electronic devices on virtually any smooth substrate with a thermal budget of 1 min at 300 degrees C with the seed layer acting as a conductive strain-relieving back contact. The top contact can simply be made by depositing a suitable transparent conductive oxide or metal, depending on the specific application.Funding Agencies|AForsk Foundation [19-725]</p

Solar-Driven Photoelectrochemical Performance of Novel ZnO/Ag2WO4/AgBr Nanorods-Based Photoelectrodes

Highly efficient photoelectrochemical (PEC) water oxidation under solar visible light is crucial for water splitting to produce hydrogen as a source of sustainable energy. Particularly, silver-based nanomaterials are important for PEC performance due to their surface plasmon resonance which can enhance the photoelectrochemical efficiency. However, the PEC of ZnO/Ag2WO4/AgBr with enhanced visible-light water oxidation has not been studied so far. Herein, we present a novel photoelectrodes based on ZnO/Ag2WO4/AgBr nanorods (NRs) for PEC application, which is prepared by the low-temperature chemical growth method and then by successive ionic layer adsorption and reaction (SILAR) method. The synthesized photoelectrodes were investigated by several characterization techniques, emphasizing a successful synthesis of the ZnO/Ag2WO4/AgBr heterostructure NRs with excellent photocatalysis performance compared to pure ZnO NRs photoelectrode. The significantly enhanced PEC was due to improved photogeneration and transportation of electrons in the heterojunction due to the synergistic effect of the heterostructure. This study is significant for basic understanding of the photocatalytic mechanism of the heterojunction which can prompt further development of novel efficient photoelectrochemical-catalytic materials.Funding Agencies|Linkoping University, Sweden</p

Correction: Efficient Ni-Fe layered double hydroxides/ ZnO nanostructures for photochemical water splitting (vol 273, pg 186, 2019)

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Efficient CuO/Ag2WO4 photoelectrodes for photoelectrochemical water splitting using solar visible radiation

Water splitting energy production relies heavily on the development of high-performance photoelectrochemical cells (PECs). Among the most highly regarded semiconductor materials, cupric oxide (CuO) is an excellent photocathode material. Pristine CuO does not perform well as a photocathode due to its tendency to recombine electrons and holes rapidly. Photocathodes with high efficiency can be produced by developing CuO-based composite systems. The aim of our research is to develop an Ag2WO4/CuO composite by incorporating silver tungstate (Ag2WO4) nanoparticles onto hydrothermally grown CuO nanoleaves (NLs) by successive ionic layer adsorption and reaction (SILAR). To prepare CuO/Ag2WO4 composites, SILAR was used in conjunction with different Ag2WO4 nanoparticle deposition cycles. Physicochemical characterization reveals well-defined nanoleaves morphologies with tailored surface compositions. Composite CuO/Ag2WO4 crystal structures are governed by the monoclinic phase of CuO and the hexagonal phase of Ag2WO4. It has been demonstrated that the CuO/Ag2WO4 composite has outstanding performance in the PEC water splitting process when used with five cycles. In the CuO/Ag2WO4 photocathode, water splitting activity is observed at low overpotential and high photocurrent density, indicating that the reaction takes place at low energy barriers. Several factors contribute to PEC performance in composites. These factors include the high density of surface active sites, the high charge separation rate, the presence of favourable surface defects, and the synergy of CuO and Ag2WO4 photoreaction. By using SILAR, silver tungstate can be deposited onto semiconducting materials with strong visible absorption, enabling the development of energy-efficient photocathodes.Funding Agencies|department of Science and Technology (ITN), at Campus Norrkoping; Linkoping University, Sweden; Ajman University [2022-IRG-HBS-5, 2022-RTG-02]; National Research Infrastructure for Advanced Electron Microscopy (ARTEMI)</p

Social networking and fear of missing out (FOMO) among medical students at University of Khartoum, Sudan 2021

Abstract Background With students becoming more involved in the internet and social networking sites, they become more prone to their consequences. This study focuses on measuring the social networking intensity and the fear of missing out among the medical students of University of Khartoum, then examining the association between them. Methods Facility-based, descriptive, cross-sectional study was conducted at Faculty of Medicine, Khartoum University between January and March 2021. A total of 333 students were selected by simple random sampling. Data was collected from the participants using a structured self-administered questionnaire that involved the social networking intensity (SNI) scale and fear of missing out (FOMO) scale. The data was analyzed by the Statistical Package for Social Science (SPSS) software version 26. Results Moderate positive correlation between social networking intensity and fear of missing out was found (p-value < 0.01). Of the total participants; 51 participants (15.4%) experienced low SNI and low FOMO. Another 78 participants (23.6%) had moderate SNI and moderate FOMO and only 16 Participants (4.8%) showed high SNI and high FOMO. There were no significant differences in SNI or FOMO scores among the different socio-demographic variables, except for the SNI score which was positively correlated to the monthly income. Conclusion An association between SNI and FOMO was found. SNI was not affected by socio-demographic factors except for the monthly income

PdO@CoSe2 composites: efficient electrocatalysts for water oxidation in alkaline media

In this study, we have prepared cobalt selenide (CoSe2) due to its useful aspects from a catalysis point of view such as abundant active sites from Se edges, and significant stability in alkaline conditions. CoSe2, however, has yet to prove its functionality, so we doped palladium oxide (PdO) onto CoSe2 nanostructures using ultraviolet (UV) light, resulting in an efficient and stable water oxidation composite. The crystal arrays, morphology, and chemical composition of the surface were studied using a variety of characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) spectroscopy. It was also demonstrated that the composite systems were heterogeneous in their morphology, undergoing a shift in their diffraction patterns, suffering from a variety of metal oxidation states and surface defects. The water oxidation was verified by a low overpotential of 260 mV at a current density of 20 mA cm(-2) with a Tafel Slope value of 57 mV dec(-1). The presence of multi metal oxidation states, rich surface edges of Se and favorable charge transport played a leading role towards water oxidation with a low energy demand. Furthermore, 48 h of durability is associated with the composite system. With the use of PdO and CoSe2, new, low efficiency, simple electrocatalysts for water catalysis have been developed, enabling the development of practical energy conversion and storage systems. This is an excellent alternative approach for fostering growth in the field.Funding Agencies|Ajman University [2022-IRG-HBS-5]; National Natural Science Foundation of China [NSFC 51402065, 51603053]</p