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

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 °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

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

Photocatalytic properties for different metal-oxide nanomaterials

We here demonstrate the synthesis of different nanostructures, including nanoparticles, nanorods, core-shell structures,and compound metal oxide nanostructures all synthesized by a low temperature chemical process. We furtherinvestigated their photocatalytic properties for degradation of toxic waste and their photochemical efficiency for watersplitting. All the photocatalytic properties as well as the photochemical properties were utilized using sun radiation. Theresults presented indicate huge potential for the investigated processes with positive impact to energy consumption andbenefits for the environment.Funding agencies: Knut and Alice Wallenberg foundation (KAW), through a Wallenberg Scholar grant; China Scholarship CouncilChina Scholarship Council</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

An Anomaly Detection Algorithm Selection Service for IoT Stream Data Based on Tsfresh Tool and Genetic Algorithm

Anomaly detection algorithms (ADA) have been widely used as services in many maintenance monitoring platforms. However, there are numerous algorithms that could be applied to these fast changing stream data. Furthermore, in IoT stream data due to its dynamic nature, the phenomena of conception drift happened. Therefore, it is a challenging task to choose a suitable anomaly detection service (ADS) in real time. For accurate online anomalous data detection, this paper developed a service selection method to select and configure ADS at run-time. Initially, a time-series feature extractor (Tsfresh) and a genetic algorithm-based feature selection method are applied to swiftly extract dominant features which act as representation for the stream data patterns. Additionally, stream data and various efficient algorithms are collected as our historical data. A fast classification model based on XGBoost is trained to record stream data features to detect appropriate ADS dynamically at run-time. These methods help to choose suitable service and their respective configuration based on the patterns of stream data. The features used to describe and reflect time-series data’s intrinsic characteristics are the main success factor in our framework. Consequently, experiments are conducted to evaluate the effectiveness of features closed by genetic algorithm. Experimentations on both artificial and real datasets demonstrate that the accuracy of our proposed method outperforms various advanced approaches and can choose appropriate service in different scenarios efficiently

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

Malaria incidence among kidney-transplanted recipients in an endemic malaria area, Sudan

Malaria is endemic all over Sudan. The population are at risk of malaria infection to variable degrees. Kidney-transplanted patients on maintenance immunosuppressive therapy are known to be prone to infection, but there is not enough data in the medical literature as to whether they are more susceptible to malaria infection in endemic areas. This study was conducted in the Gezira Hospital for Renal Diseases and Surgery to assess the effect of maintenance immunosuppressive therapy in renal transplantation on malaria incidence. A total of 110 individuals were enrolled: 55 were renal-transplanted patients with end-stage renal disease who received kidney transplantation at least one year earlier and were on maintenance immunosuppressive medi-cations. The other 55 individuals were the compatible healthy group. Thorough follow-up was exercised for both groups for one year (January-December 2009). Following the World Health Organization criteria for malaria diagnosis, a total of 51 malarial attacks were reported in both the groups, 25 in the transplanted group and 26 in the controls. The incidence difference between both groups was statistically insignificant [0.76 (΁1.170) and 1.09 (΁1.917) P = 0.282 among transplanted group and control group, respectively]. Providing routine malaria prophylaxis is not required for renal transplant recipients on maintenance immunosuppressive