Sharif Digital Repository

Ease of solar hydrogen production using water splitting and its environmental benefits, distinct hydrogen from other energy carriers. Hydrogen is the most abundant material in the world that make up more than 90% of the world compounds. So applying this material as a clean fuel is the best way to prevent environmental problems caused by fossil fuels. For efficient hydrogen production from water, a suitable electrocatalyst with low overpotential, high mechanical strength and reasonable catalytic activity must be utilized. In this research, cobalt based electrocatalyst was used considering that electrodepositon conditions play an important role in its final efficiency. On the other hand,... 

Regarding increasing world population, air pollution and depletion of fossil fuels supplies, hydrogen production via photoelectrochemical water splitting is a promising approach for providing a clean and renewable source of energy. Hematite (α-Fe2O3), the most common natural form of iron oxide, with a suitable band gap, high stability, earth-abundant nature and low cost has been widely acknowledged as a photoanode. However, intrinsic drawbacks of hematite like low electrical conductivity, short hole diffusion length and high recombination rate of electron-hole pairs hinder its photoelectrochemical performance with high efficiency. In this research, hematite nanostructures were synthesized... 

Currently, fossil fuels are the primary source of energy in the world. The increasing human need for energy and the limited resources of fossil fuels and their environmental side effects necessitate the search for other sources of energy. Considering its abundance and eco-compatibility, using solar energy is one of the best candidates for future. One of the methods to use solar energy is to convert and store it as hydrogen fuel by photoelectrochemical cells. In recent years, the main challenge with the production of hydrogen fuel in photoelectrochemical is optimizing them to increase efficiency. For this purpose, various approaches have been proposed such as the fabrication and use of... 

Two-dimensional (2D) nanomaterials are ultrathin nanomaterials with a high degree of anisotropy and chemical functionality. Research on 2D nanomaterials is still in its infancy, with the majority of research focusing on elucidating unique material characteristics and few reports focusing on biomedical applications of 2D nanomaterials. Here we report the properties and application of 2Dnanomaterials in field of bio technology while used main material in our project is graphene oxide for investigating its antibacterial properties. Because the properties of graphene oxide (GO)-based materials strongly depend on the lateral size and size distribution of GO nanosheets; therefore, GO and its... 

Antibacterial resistance towards existing antibiotics has become a major problem in medicine and health in recent years. Therefor it has become a challenge for scientists in different fields to find new antibiotics. Graphene and its derivatives, specially Graphene Oxide has gained attention in this area due to their unique physical properties. Graphene Oxide is considered to be a promising 2D nanomaterial for biomedical applications, due to its ease of production, stability in water, unique chemical and mechanical properties and its biocompatibility compared to other nanomaterials. In this study, graphene Oxide was synthesized using modified Hummers’ method. In order to investigate the... 

One of the pillars of reaching a steady development is to utilize sustainable energies. In order to make use of these modern means of energy, appropriate energy storage devices are inevitable. One of the families of these devices is the supercapacitors. Moving toward the 4th industrial revolution, we are encountering modern technologies such as internet of things and wearable electronics. Therefore, designing and fabricating microsupercapacitors is of paramount importance in order to reduce the weight and size of these devices. Cobalt and nickel are considered as two important elements to be used in synthesizing supercapacitive materials and composites, because of their good electrochemical... 

The 21st century is facing two major obstacles on the way of accessing clean and renewable energies: first, the rapidly increasing need to the energy resources; and second, the limitations - as well as side-effects - of the conventional fossil fuels. Meanwhile, the production of the solar hydrogen, through water splitting, has been proposed as a promising solution to find a clean and effective source of energy. This process occurs in photo-electro-chemical systems with the activation energy that lies within the range of visible light. One approach that herewith comes to mind, is to start the process by utilizing semiconductors to absorb the sunlight. In order to overcome the overpotential... 

Hydrogen is known to be a renewable and clean source of energy, which produces water vapor and zero carbon dioxide as a result of its combustion. Photoelectrochemical water splitting (PEC) could be a promising approach in order to generate hydrogen by sunlight. Hematite (α-Fe2O3), as the most abundant naturally occurring form of iron oxide with suitable band gap, low cost, high stability and nontoxicity is considered to be an ideal photoanode. However, intrinsic drawbacks of hematite including low electrical conductivity, limited hole diffusion length, and high recombination rate of electron-hole pairs restrict its photoelectrochemical performance efficiency. In the present research,... 

In this study, one dimensional titanium dioxide nanostructures including nanotube and nanowire were synthesized by anodization and hydrothermal methods respectively and were used for PEC glucose sensing. Meanwhile various length of nanotubes was investigated toward glucose sensing. Finally, nanotubes with the length of 2.7 µm were selected as the optimum sample. Finally, to improve sensitivity toward glucose, TiO2 nanotubes were modified by graphene oxide nanosheets which caused several percent increase in PEC sensing performances. In the next stage branched TiO2 nanowires were grew on FTO substrate in various conditions. In spite of acceptable reproducibility of this structure,... 

Due to the increasing demand for clean energy, layered double hydroxides (LDHs) have gained attention as electrocatalytic materials for water splitting into hydrogen and oxygen. Nickel-cobalt-based LDHs are favored for their ease of production and environmental compatibility, but they face challenges such as a lack of active sites and structural instability. The use of a core-shell structure can enhance the specific surface area and electroactive sites while preventing structural degradation. Furthermore, this structure can improve electrochemical performance and facilitate the oxygen evolution reaction (OER). In this research, a core-shell structure based on nickel-cobalt was developed,... 

Due to imminent shortage of fossil fuels, environmental issues that occur from their intensive use, population growth and industrialization of societies moving towards renewable energy sources is inevitable. Sun is the most clean and abundant source of energy but it is needed to be accompanied with an energy storage system as it is intermittent and cannot supply our required energies on demand. Water splitting electrochemical cells are promising solutions to cope with this problem by producing hydrogen as a clean fuel. The overpotential imposed by anode is the bottleneck of the water splitting reaction. The anodes with sufficient efficiency that are used today are made from precious and... 

A global concern has arisen owing to rapid industrial development and population growth, resulting in energy scarcity and earth pollution. In this regard, developing green and sustainable methods for producing clean energy and solving environmental pollution problems have absorbed enormous attention. Among various auspicious strategies, semiconductor photocatalysis has been widely studied in recent years owing to its capabilities to obtain hydrogen as an energy carrier, to remove organic pollutants, and to reduce CO2 emission by converting solar energy into chemical energy. Recently, a metal-free semiconductor photocatalyst based on graphitic carbon nitride, g-C3N4, has received much... 

Fighting contagious microbial diseases is considered a serious health issue, which has attracted much attention in worldwide. Thus, development of new materials based on nanostructures as a new generation of antibiotics to address this challenge has been of interest to researchers in recent years. Nanostructures based on metallic oxide semiconductors such as oxides with light absorption, production of electron-hole pairs in needle like structures cause tearing bacterial membrane and eventually destroy the bacterium. To this end, we designed experiments to study mechanism and physics governing the process of bacterial degradation to determine the best conditions for inhibiting bacteria... 

Properties of biomaterials, especially in application as planting, can be controlled and optimized by alloying and hardening sedimentation. In recent years, the study on the simultaneous improvement of mechanical properties, toughness and corrosion behavior of magnesium composite by carbon nanotubes (CNTs) is very limited. In this study, the behavior of mechanical properties and corrosion of magnesium alloy composites with different percentages of CNTs have been investigated. The production of magnesium alloy composite by powder metallurgy and aging process have been used as effective methods for improving mechanical properties and increasing the corrosion resistance of magnesium alloys. For... 

The optimized geometry and structure of iron oxide(Fe2O3) nanorod arrays as the photoanodes of photoelectrochemical cells have been calculated. Using finite element method, different structures have been studied in order to maximize the photocurrent density generated by the photoanodes. Two main characteristics of nanorod arrays namely the aspect ratio of nanorod and the density of nanorods in array have been selected as the variables. The absorbance of the photoanode has been calculated using Electromagnetic Waves Physics in COMSOL Multiphysics software. In this study, nanorods with aspect ratio of 3.6 to 40 have been varied and compared. The results reveal that the current density has a... 

Solar cells can be a solution to the challenges of energy and the environment. Perovskite solar cells are currently very popular, with an efficiency of around 25%. Silver nanowires are being considered as the next generation of flexible transparent electrodes in solar cells. Their stability is the most important challenge. Perovskite cells were fabricated in the laboratory, and the best efficiency of 14.3% was achieved with a gold electrode. Silver nanowires were synthesized using the polyol method with an average diameter of approximately 65 nanometers and an average length of about 13 micrometers. The spray method was used to deposit nanowires at temperatures between 100 and 200°C. When... 

Growing demand on energy and limitation and consequence of fossil fuels have caused to utilize the clean and renewable energy sources. Hydrogen is a clean energy carrier which produced just water vapor during combustion. Today, methods which are usually used to produce this fuel are based on using fossil fuel compounds. Therefore, utilizing new production methods is unavoidable. One of these methods is using semiconductors such as TiO2 to spilt water and produce H2 by solar irradiation. Reducing the energy gap of these semiconductors to match the solar spectrum, specially in its visible range, modification of their structures, surfaces and stability are the main challenges in hydrogen...