Modification of single wall carbon nanotubes by electromagnetic radiation from the visible, infrared and microwave spectra

Резиме: Утицај електромагнетног зрачења на једнослојне угљеничне нанотубе је предмет интензивног проучавања. У оквиру ове докторске дисертације испитано је дејство електромагнетног зрачења из видљиве, инфрацрвене и микроталасне области на танке слојеве једнослојних угљеничних нанотуба депонованих вакуумском филтрацијом. У оквиру дисертације су коришћене нанотубе два произвођача, које су добијене методом хемијске депозиције из парне фазе али уз употребу различитог катализатора. Танки слојеви угљеничних нанотуба депоновани методом вакуумске филтрације су испитани раманском спектроскопијом помоћу три ексцитациона ласера: 532, 633 и 780 nm и микроскопијом атомских сила. Установљено је да 532 nm ласер испитује стање на површини узорка, док са друге стране ласер на 780 nm испитује целу запремину узорка. Последице озрачивања ОПО ласером различитих таласних дужина из области видљивог зрачења су декомпозиција, фотооксидација и издвајање из снопова. Издвајање из снопова и уклањање угљеничних нечистоћа се јављају након динамичке оксидације. Осим тога, приликом динамичке оксидације може доћи до сагоревања нанотуба мањих пречника. Изотермална оксидација има различит утицај на нанотубе коришћене у склопу ове дисертације, што је последица различитих катализатора коришћених за време синтезе. Озрачивање микроталасима изазива повећање температуре узорка током озрачивања, али не доводи до селективне деструкције једног типа нанотуба. Дејство микроталаса на структуру угљеничних нанотуба се махом манифестује у издвајању појединих нанотуба из снопова.The influence of electromagnetic waves upon single wall carbon nanotube is the subject of great scientific interest. In this PhD thesis a detailed study of the influence of electromаgnetic radiation from visible, infrared and microwave regions upon thin films of single wall carbon nanotubes prepared by vacuum filtration is presented. In this PhD thesis carbon nanotubes from two different suppliers were used; both were synthesized by chemical vapor deposition method but with different catalyst. Thin films of carbon nanotubes deposited by vacuum filtration method are characterized by Raman spectroscopy using three excitation lines: 532, 633 and 780 nm and by atomic force microscopy. It was established that the 532 nm excitation line probes the surface of nanotube films, while the 780 nm excitation line probes the bulk of films. The effects of OPO laser with radiation of different wavelengths upon thin films of carbon nanotubes are decomposition, photooxidation and debundling. Debundling and deffective carbon removal is the major effect of dynamic oxidation. Also, dynamic oxidation can cause the removal of small diameter nanotubes. Isothermal oxidation causes different effects on carbon nanotubes from different suppliers, which is the consequence of the catalysts used during synthesis. Microwave irradiation upon carbon nanotubes results in temperature increase of the samples during irradiation, but selective destruction of one type of SWCNT was not observed. Major effect of microwave irradiation was debundling

Measurement of EMI shielding perfomance of graphene oxide – silver nanoparticles composites

Silver nitrate has been exposed to low-dose (1–20 kGy) gamma irradiation in the presence of graphene-based material (graphene oxide or electrochemically exfoliated graphene) to form silver nanoparticles (Ag NPs). The successful nucleation and growth of Ag NPs, which produce the evenly covered graphene surface, are made possible by the vast surface area of those graphene-based materials as well as the presence of oxygen-containing functional groups on the surface. With a significant size distribution of 10–50 nm for graphene oxide and 10–100 nm for electrochemically exfoliated graphene, the produced Ag NPs were spherical. We also performed ElectroMagnetic Interference (EMI) shielding performance measurements of these materials. EMI shielding performance measurement revealed relatively good performance of the EEG material whereas GO material does not show EM shielding.Twenty-First Young Researchers’ Conference - Materials Science and Engineering: Program and the Book of Abstracts; November 29 – December 1, 2023, Belgrade, Serbi

Twinning for graphene-based composites in EMI shielding

In the era of intensive development of microelectronics, energy, and car industries along with Radio-Frequency (RF) telecommunications, the pollution caused by Electromagnetic Waves (EWs) is ever-present. EW interferences (Electromagnetic Interference-EMI) exhibit perturbation and negative impact on devices and systems including those used in everyday life as well as on the specialized, sensitive, and sophisticated instruments used in research laboratories. EMI could cause untrusted signals and RF noise. To prevent these issues, materials able to block or absorb the radiated EWs are urgently required. The GrInShield project is focused on developing new graphene-based shielding nano-materials and increasing researchers' expertise in EMI shielding measuring, protective materials, and possibilities to bring these new products to the market. INTRODUCTION: The GrInShield project uses graphene oxide (GO) obtained by Hummers' reaction and electrochemical exfoliation of graphite [1,2]. We have analysed the factors that affect the shielding efficiency of materials [3] and studied the reaction conditions that lead to obtaining graphene with different sizes and oxygen content [4]. RESULTS AND DISCUSSION: The GrInShield project aims to produce composites of GO with silver nanowires (AgNWs) to develop GO-AgNW composites for EMI shielding applications. To achieve these goals, the project gathers experts from the chemistry of nanomaterials, and polymer processing, along with specialists for near-field microscopy tools and radiofrequency (RF) characterization of materials. CONCLUSIONS: The GrInShield project is developing new nanomaterials for EMI shielding based on carbon nanomaterials, metallic nanomaterials, and polymers. The fabrication of low-cost, sustainable, eco-friendly, durable EMI shielding material should be achieved.Supplementary Issue - ExcellMater Conference 2024Innovative biomaterials for novel medical devices conference : AbstractsAvailable on-line at the Journal web address: [https://www.ache.org.rs/HI/

The Morphology of Pani/Graphene Composites Prepared Under Isothermal Conditions

This article investigates the morphology of polyaniline/electrochemically exfoliated graphene composites prepared by oxidative polymerization with ammonium persulfate at a constant temperature (15 °C). During the polymerization, the pH of the reaction mixture decreases, which was used to monitor the rate of the reaction. A granular morphology with the presence of large sheet-like structures is found to be predominant for the composite prepared without added acid, while rod-shaped and tubular morphology is characteristic for the composite prepared with the addition of glacial acetic acid. The nanotubular and nanorod morphology of the sample prepared with the addition of glacial acetic acid was also confirmed by the presence of prominent phenazine structural units in Raman spectra. The composite prepared with the addition of HCl has granular morphology with a small amount of rod-like structures

Nanosecond Laser-Assisted Nitrogen Doping of Graphene Oxide Dispersions

N-doped reduced graphene oxide (RGO) has been prepared in bulk form by laser irradiation of graphene oxide (GO) dispersed in an aqueous solution of ammonia. A pulsed Nd:YAG laser with emission wavelengths in the infrared (IR) 1064 nm, visible (Vis) 532 nm, and ultraviolet (UV) 266 nm spectral regions was employed for the preparation of the N-doped RGO samples. Regardless of the laser energy employed, the resulting material presents a higher fraction of pyrrolic nitrogen compared to nitrogen atoms in pyridinic and graphitic coordination. Noticeably, whereas increasing the laser fluence of UV and Vis wavelengths results in an increase in the total amount of nitrogen, up to 4.9 at. % (UV wavelength at 60 mJ cm fluence), the opposite trend is observed when the GO is irradiated in ammonia solution through IR processing. The proposed laser-based methodology allows the bulk synthesis of N-doped reduced graphene oxide in a simple, fast, and cost efficient manner

The Influence of Reaction Conditions on the Properties of Graphene Oxide

The present study focuses on correlations between three parameters: (1) graphite particle size, (2) the ratio of graphite to oxidizing agent (KMnO4 ), and (3) the ratio of graphite to acid (H2SO4 and H3PO4 ), with the reaction yield, structure, and properties of graphene oxide (GO). The correlations are a challenge, as these three parameters can hardly be separated from each other due to the variations in the viscosity of the system. The larger the graphite particles, the higher the viscosity of GO. Decreasing the ratio of graphite to KMnO4 from 1:4 to 1:6 generally leads to a higher degree of oxidation and a higher reaction yield. However, the differences are very small. Increasing the graphite-to-acid-volume ratio from 1 g/60 mL to 1 g/80 mL, except for the smallest particles, reduced the degree of oxidation and slightly reduced the reaction yield. However, the reaction yield mainly depends on the extent of purification of GO by water, not on the reaction conditions. The large differences in the thermal decomposition of GO are mainly due to the bulk particle size and less to other parameter

A review on graphene and graphene composites for application in electromagnetic shielding

As wireless solutions for communication, information, and sensing in modern society, electromagnetic waves (EMWs) have contributed considerably to the increase in the quality of people’s everyday lives. At the same time, EMWs produce electromagnetic pollution, issues with electromagnetic interference (EMI), and radio frequency (RF) signal leakage. These circumstances lead to high demand for efficient EMI shielding materials. To design an EMI shielding product, a compromise must be achieved between the electromagnetic shielding efficiency, the thickness of shielding materials, durability, mechanical strength, reduced volume and weight, and elasticity. Due to its ability to block EMWs, flexibility, lightweight, and chemical resistivity, graphene has been identified as a promising candidate material for efficient EMI shielding. Herein, we reviewed the studies that investigated various graphene-based composites as potential EMI shielding materials, with a focus on the composites based on graphene and silver nanowires due to their high EMI shielding efficiency, low production price, and favorable mechanical properties

Antioxidant and Prooxidant Features of N-CQD in Photocatalytic Testing of Aquatic Media

The modern age science is still searching for an effective photocatalytic material for the treatment of colored discharges from different industries which cause severe environmental issues. The excellent properties of nitrogen doped carbon quantum dots (N-CQD) enable their successful application as photocatalytic material in organic dye removal triggered under light absorption. With this in mind we first present a successfully performed microwave-assisted synthesis method, a green, simple and economically affordable method for N-CQD synthesis with high nitrogen percentage incorporated in the form of pyrrolic, pyridinic/NH2 and graphitic/NH3+ groups. The pro-oxidant and antioxidant features of the synthesized N-CQD were further presented, with high removal efficiency of synthesized N-CQD towards the methylene blue (MB) organic dye, as one of the leading water pollutants with a major risk to aquatic and human life

Ambient light induced antibacterial action of curcumin/graphene nanomesh hybrids

Curcumin and its derivates are well-known for their different biological activities including antibacterial. On the other hand there are controversial reports concerning the antibacterial potential of graphene and, in particular, graphene oxide. In this study we have reported for the first time the antibacterial activity of curcumin/graphene nanomesh hybrids under ambient light conditions. The graphene nanomesh was synthesized by electrochemical exfoliation of highly oriented pyrolytic graphite in 1 M solution of ammonium persulfate and further functionalized by curcumin. Identical values of minimum inhibitory concentration (1 mg mL(-1)) were determined for pure curcumin and curcumin/graphene nanomesh hybrids toward Staphylococcus aureus. All tested samples had more pronounced antibacterial activity against Gram positive bacteria, Staphylococcus aureus compared to Escherichia coli as a representative of Gram negative strains. The poor antibacterial potential of exfoliated graphene improves significantly by the functionalization with curcumin, which allows for its usage as a antibacterial coating

ANALIZA DIJELOVA I MODELIRANJE AUTOMATSKE STROJNICE PKT

U ovom završnom radu je opisana strojnica PK i PKT kroz povijest te se prikazala i objasnila namjena strojnice PKT. Napravljena je analiza sastavnih dijelova strojnice PKT kako tekstom tako i slikama računalnog modela prethodno napravljenog u programu SolidWorks. U ovom radu detaljno je opisan proces opaljenja, sastavljanje i rastavljanje strojnice PKT što je pokazano u animaciji koja je napravljena u programu SolidWorks. Navedene su i objašnjene vrste streljiva kao i mogući zastoji koje može imati strojnica PKT te je detaljno objašnjeno njezino čuvanje, održavanje i pregledi. Opisi su rađeni na način da se rad i uporaba strojnice PKT može što bolje razumjeti i primijeniti u praksi te tako olakša uporaba vojniku.This final paper describes the PK and PKT machine guns throughout history, and further presents and explains the purpose of the PKT machine gun itself. An analysis of the components of the PKT machine gun was made with both text and images of a computer model previously created in SolidWorks. This paper explains in detail the firing process, assembly and disassembly PKT machine guns which is shown in the animation made in the program SolidWorkd. The types of ammunition are listed and explained, as well as the delays that the PKT machine gun can have, and its storage, maintenance and inspections are explained in detail. The descriptions are made in such a way as to be as close as possible to the reader and that the work and use of the PKT machine gun can be better understood and that all of the above is easier to apply in practice and facilitate the use of each soldier