مجله مواد و فناوری های پیشرفته
سال هشتم شماره 4 (زمستان 1398)

In this research, carbon nitride nanosheets were synthesized from melamine precursor by both thermal and combined methods. Melamine first reached 550 °C for 75 minutes and remained at this temperature for 4 hours until g-C3N4 was obtained. In the heating method, the produced g-C3N4 reached 500 °C for 100 minutes and stored at this temperature for 3 hours to obtain nanosheet carbon nitride. In the combined approach, g-C3N4 was first sonicated for 130 minutes in a solution of water and ethanol and then the heating process was repeated for it. Sample characterization by X-ray diffraction (XRD), scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) surface area analysis were done. The photocatalytic performance of the samples was evaluated by measuring the degradation of the rhodamine b. It was found that both methods are capable of producing carbon nitride of nanosheet shape. In the combined approach, over the same period, nanosheets of about 30% less thickness than the heating method can be made. Samples that were made by the combined way showed better photocatalytic activity than thermal samples.

Zinc oxide (ZnO) is used widely in electrical and optical applications due to its wide band gap and also semiconductor properties. In the present study ZnO and Al doped (Al/Zn ratio equals to 6 wt.%) nanofibers (NFs) were synthesized by electrospinning method and post calcination at different temperatures 250, 300 and 400 ˚C. The effect of dopant on  microstructure, crystallography, functional molecule groups, and photoluminescence behavior of ZnO NFs were studied by means of scanning electron microscopy (SEM), X-ray diffraction pattern (XRD), Fourier-transform infrared spectroscopy (FTIR), and photoluminescence spectroscopy (PL), respectively. Results showed that the average diameter of ZnO NFs was increased from 131 to 468 nm after calcination. XRD analysis indicated that the hexagonal wurtzite ZnO was formed in both samples. Also it confirmed that the Al dopant was incorporated into ZnO NFs. Comparison of FTIR spectra showed that the Al doping caused to shift the Zn-O band to higher frequencies and also construct the stronger bonds inside the ZnO lattice. PL results also revealed that the Al doping enhanced the optical properties. It is because that the point defects issued by Al doping create lower energy levels for transferring the electrons from conduction band to valence band.

In this study, different amounts of amine-functionalized single-walled carbon nanotubes (SWCNTs-amine) with the 0, 0.1, 0.2 and 0.5 weight percentages (%wt) were added to polycaprolactone, to enhance biological and mechanical properties of scaffolds, then PCL-SWCNTs composite nanofibers were prepared by electrospinning method. The attachment, proliferation, differentiation and growth of rat bone marrow-derived mesenchymal stem cells (BMSCs) on the scaffolds were analyzed by scanning electron microscopy (SEM), MTT, live-dead and alkaline phosphatase activity assays. The morphology and mechanical properties of the scaffolds, using the SEM and tensile strength test, were characterized and the bioactivity of the scaffolds in simulated body fluid (SBF) was assessed. The results indicated that PCL-SWCNTs 0.2 wt. % had the highest tensile strength (about 10 MPa) and showed a significant increase as compared with the pure PCL. Moreover, no toxicity was reported after 1, 3 and 5 days after cell seeding on scaffolds. In addition, surveys carried out by SEM showed that the use of single-walled carbon nanotubes, had promoted cell attachment on the scaffold fibers. This increase was more considerable in PCL-SWCNTs 0.5 wt. %. Furthermore, alkaline phosphatase activity demonstrated enhanced proliferation and differentiation of cells on scaffolds containing nanoparticles in comparison with the pure PCL.

Powder metallurgy involves forming processing of metal powders into useful metallic parts. In fact this process is a unique method which can produce porous parts so that its porosities, distribution and pour size are controllable. Stainless steel filters are commonly made from steel or alloy powder via pressing and sintering. In this research, ST.ST.316L and ST.ST. 316Lt + 2%wt Sn powders have been used to from filter by using uniaxial press to forming powder and then sintered. When Tin powder added sinterability showed improved. Tin addition affected microstructure so that grain growth was obvious evidence, also pore size expansion occurred. Grain coarsing in the sintered tin added stainless steel samples may indicate that liquid tin accelerates atomic diffusion related processes occurring during heating of powder compacts. Also, some pores created by Tin particle disappearance, were observed in addition to those initiated by original voids in the green compacts. The remained porosity was between 46 to 38 %.

In this research, Zn/MWCNT porous nanocomposite and ZnO nanoparticles were prepared using Zn-based metal organic framework (MOF). Porous ZnO without MOF precursor was also synthesized. Structure, morphology and size of the films were analyzed by XRD and scanning electron microscope (SEM). Dye sensitized solar cells (DSSCs) were fabricated with ZnO/MWCNT nanocomposite and ZnO nanoparticles as photoanode. It was determined that ZnO based on MOF show higher surface area, more photon absorption and better short circuit current density compared with the reference ZnO without MOF precursor. Moreover, Effect of multiwall carbon nanotubes (MWCNT) on the porous structure of ZnO was studied and DSSC based on ZnO/MWCNT photoanode exhibited a short circuit current density of 23.89 mA cm-2, open circuit voltage of 0.68 V, and power conversion efficiency of 4.78%, which is almost 15% larger than that of the DSSC based on ZnO photoanode based on MOF (4.06%). The enhancement of efficiency in DSSCs made of ZnO/MWCNT nanocomposite can be attributed to the increase of the electrical conductivity of the photoanode, strong connection between conduction band of the anode with dye molecules and more contact surface of photoanode with electrolyte.

Cathode is the most important part of Li-ion batteries and it determines performance and behavior of these energy storage devices. LiFeSO4F as a cathode material with Tavvorite structure and C2/c space group is investigated by density functional theory (DFT) using Wine2k program package. Calculation were performed by different methods GGA, GGA+U and PBE-Fock-α (a Hybrid Functionals method, HF). Structural calculations were demonstrated structural stability after Lithium ion extraction. Theoretical voltage was evaluated, using total energy of the considered structures. The most agreeable calculated voltage in comparison with the experimental value (3.9 V) belongs to HF method. According to obtained Density of States (DOS) diagrams, lithiated structure is n-type semiconductor and delithiated structure is p-type semiconductor. This material had been suggested as a potentially high rate capable cathode due to its unclose structure and high diffusion coefficient of Li-ions in the structure; however, inversely-biased-diode phenomenon turns it as low rate capable in comparison with oxide cathode materials. For the first time, internist-like and extrinsic-like band gap were calculated and reported for the cathode material.

In this research, the gas sensing properties of cadmium metal oxide semiconductor fabricated using low frequency AC electrophoretic deposition toward pollutant gases such as NO2 and CO were investigated. For the electric field-assisted method, the parameters affecting the deposition pattern including frequency and the medium of deposition along with the dominant deposition mechanism in different frequency intervals in the range of 1 Hz to 10 kHz were studied using co-planar gold electrodes. SEM and Optical microscopy strongly show that the formation of CdO nanoparticles chains along with electrodes was the distinguished effect which was observed in the acetone suspension at frequency of 10 KHz. Gas sensing tests were performed on platinum-based comb-like electrodes towards different concentration of NO2 and CO gases using a normal dynamic gas sensing setup. The deposition of CdO nanoparticles was done at the frequency of 10 KHz, voltage of 30V and time duration of 5 min. The attained chain like structures of ceramic particles of CdO can be providing favorite sensing properties. All results indicated which fabricated sensor possesses a good response toward NO2 and CO gases.

In current investigation a novel radar absorbing coating was developed on nonwoven fabric based on a composite nanomaterial of BaFe12O19/ MWCNT which was synthesized by combustive sol-gel technique. The functional carboxylated carbon nanotubes was utilized in silicon matrix and printed on fabric surface to enhance the intensity and band width of wave absorption. The microscopic images of the fabric coated magnetic nanoparticles shows a homogenous layer of nanoparticles on fabric surface. The maximum reflection drop of nanoparticles was recorded about -7 dB on 9.5 GHz. Moreover, the maximum absorption in X band was close to -38.45 dB in 10.5 GHz for samples with thickness of 1.5 mm and band width of 2.6 GHz. Meanwhile, the absorption property measurement indicates the maximum value for a thickness of 1.5 mm compared to other sample thickness. Moreover in Ku band, the maximum absorption for BaFe12O19/ MWCNT sample with thickness of 1.5 mm was reported on -31.38 dBm which was recorded on 15.9 GHz with Band width of 3.2 GHz. Therefore, the composite samples enhanced with hollow structure carboxylated CNT (10%w/w) not only shows improved electrical properties, but also endorse a higher maximum absorption value and band width. Interestingly, the fabric coated with bare BaFe12O19 nanoparticle, a maximum absorption value of -3.5 dBin was observed on 9.7 GHZ. In the meantime, the fabric coated with BaFe12O19/ MWCNT nanoparticle in X band region shows significant increase for absorbption value to -17.8 dB on 9.8 GHZ with bandwidth of 1.8 GHZ. However, the coated fabric with BaFe12O19 nanoparticle in Ku band shows lower value of -2.4 dB compared to X band in 17.6 GHZ. In comparisons, for composite nanoparticle coated sample, however, a nearly similar maximum value of -17.6 dB was recorded on 16.7 GHz with band width of 2.2 GHz. Therefore , results indicate that the fabric samples coated with composite BaFe12O19/ MWCNT nanoparticle compared to neat BaFe12O19  represents appreciable maximum absorption value of more than 90%  in X and Ku bands which can be attributed to presence of carbon structure in composite material.