Sharif Digital Repository

We compare and contrast the physisorption behavior of imidazolium and butyltrimethylammonium based ionic liquids (ILs) on mono-vacant nitrogen and boron defective hexagonal boron nitride nanoflakes (h-BNNF) using M06-2X/cc-pVDZ level of theory. The presence of defects on the nanoflakes results in an increase in IL binding energy by ~ 1–27 kcal/mol partly due to the lowering of the energy band in the defective nanoflakes. Imidazolium based ILs adsorb energetically more favorably on h-BNNF-VB than on h-BNNF-VN while butyltrimethylammonium based ILs prefer to adsorb on h-BNNF-VN. Upon adsorption of imidazolium ILs on the nanoflakes, an increase in both HOMO and LUMO orbital energies is observed... 

Two-dimensional boron nitride quantum dots (2D BNQDs) with excellent chemical stability, high photoluminescence efficiency, and low toxicity are a new class of advanced materials for biosensing and bioimaging applications. To overcome the current challenge about the lack of facile, scalable, and reproducible synthesis approach of BNQDs, we introduce a green and facile approach based on mechanochemical exfoliation of bulk h-BN particles in ethanol. Few-layered hydroxylated-functionalized QDs with a thickness of 1-2 nm and a lateral dimension of 2-6 nm have been prepared. The synthesized nanocrystals exhibit a strong fluorescence emission at 407 and 425 nm with a quantum efficiency of ∼6.2%.... 

In this study, adsorption of important pollutant cations on the surface of graphitic carbon nitride (g-C3N4) was investigated by density functional theory. The calculations indicated that N6 cavity surrounded by triazine units is the most probable adsorption site on this surface. The structural optimizations also predicted a planar surface for Cr3+, and Ni2+/g-C3N4 systems while the structure of the surface for other systems indicated a considerable distortion with strong dependency on the cation size. Also, g-C3N4 surface exhibited the high adsorption energies for Cr3+, As3+, and Sb3+ ions in the gas phase. However, formation energies of the metal-aquo complexes of these cations indicated... 

In the present paper, phase and microstructural characterization of low carbon MgO-C refractories with addition of Fe-catalyzed phenolic resins as binder were investigated. Initially, phenolic resin was modified using various amounts of Fe particles as catalyst originated from iron nitrate ([Fe(NO3)3·9H2O]). The MgO-C matrix compositions were prepared by using 7% of modified phenolic resin, shaped and cured at 200 °C for 24 h. The cured samples were coked in the temperature range from 800 to 1400 °C and then characterized by XRD and FE-SEM techniques. Based on attained results, in-situ graphitic carbons, particularly in carbon nanotubes (CNTs) network were gradually formed from Fe-catalyzed... 

In this study, the fatigue behavior of Ti-6Al-4V alloy is tend to be improved by severe plastic deformation via shot peening and plasma nitriding. Shot peening with sub-branches: Conventional shot peening (A12-14), severe shot peening (A28–30 and A34-36) and repeening (N6-8) are exposed. Besides plasma nitriding is implemented at 500 °C, 550 °C and 600 °C with the durations of 4, 8 and 16 h. Due to utilization of shot peening as prior severe plastic deformation during diffusion of nitrogen, two methods are applied in sequence. Severe shot peening forms ultra-fine crystals and oriented grains by disintegrating of α and β phases just below the surface and increases surface roughness. Plasma... 

Highly porous nanocomposites of graphitic-carbon nitride and tin oxide (g-C3N4/SnO2) were prepared through simple pyrolysis of urea molecules under microwave irradiation. The initial amount of tin was varied in order to investigate the effect of SnO2 content on preparation and properties of the composites. The synthesized nanocomposites were well-characterized by XRD, FE-SEM, HR-TEM, BET, FTIR, XPS, DRS, and PL. A homogeneous distribution of SnO2 nanoparticles with the size of less than 10 nm on the porous C3N4 sheets could be obtained, suggesting that in-situ synthesis of SnO2 nanoparticles was responsible for the formation of g-C3N4. The process likely occurred by the aid of the large... 

Thermally stable cubic silver nanoparticles were grown by simply annealing a silver nano-thickness layer on a crystalline TiN buffer layer deposited on a Si(1 0 0) substrate. Formation of silver nanocubes was investigated by scanning electron microscopy, atomic force microscopy, x-ray diffractometry and UV-visible spectroscopy. The shapes of the silver nanoparticles were controlled by the thickness of the Ag layer. The silver nanocubes were self-ordered single crystals bounded mainly by {1 0 0} facets. It was found that a change in the shape of the nanoparticles from semi-spherical to cubic resulted in a substantial variation of their surface plasmon resonance absorption peak from 410 to 590... 

In this work, a GaN-based quantum well LED is theoretically analyzed in a multi-layer structure composed of a quantum well embedded in a waveguide core surrounded by photonic crystal slab and a sapphire substrate. The electromagnetic eigenmodes are obtained throughout above structure via revised plane wave-scattering matrix method. The omnidirectional transmission and reflection are investigated for both TE and TM polarizations from diffraction channels in Ewald construction. Then, we introduced angular power density and calculated radiative modes extraction efficiency. All structural parameters, such as lattice geometry, lattice constant, photonic crystal thickness and filling factor, are... 

Hydrogen-induced cracking (HIC) and sulfide stress cracking (SSC) susceptibility of the submerged arc welded API 5L-X70 pipeline steel with different amounts of titanium at two levels of manganese (1.4% and 2%) were studied. The centerline segregation region (CSR) observed in the X70 pipe steel played an important role in the HIC susceptibility. Increased acicular ferrite content in the microstructure improved HIC resistance and SSC resistance, while bainite and martensite/austenite constituents deteriorated the workability of the welded specimens in sour environments. The 2% Mn-series welds showed higher SSC susceptibility than the 1.4% Mn-series welds due to the higher hardness values of... 

Graphitic carbon nitride (g-C3N4) is promising as adsorbent for water remediation as its chemical structure allows a variety of mechanisms to interact with wastewater pollutants. However, several issues, such as low specific surface area and insufficient dispersibility in water, have to be tackled to achieve a competitive performance in such use. Previous attempts to improve the features of g-C3N4as an adsorbent have relied on carbon doping and exfoliation in the solid phase by thermal expansion. Here, we demonstrate that exfoliation in the liquid phase by a combination of oxidation and sonication allows preparing g–C3N4–based materials with improved dispersibility in water, increased... 

The reverse osmosis (RO) desalination capability of hydrogenated and hydroxylated graphene nanomesh membranes (GNMs) inspired by the morphology of carbon nitride (C2N) has been studied by using molecular dynamics simulation. As an advantage, water permeance of the GNMs is found to be several orders of magnitude higher than that of the available RO filters and comparable with highly strained C2N (S-C2N) as follows: 6,6-H,OH > 12-H > S-C2N > 5,5-H,OH > 10-H. The reverse order is found for salt rejection, regardless of S-C2N. The hydrophilic character of the incorporated -OH functional group is believed to be responsible for linking the water molecules in feed and permeate sides via the... 

Al-Si3N4 couples were heat-treated at 850-1150°C for 250 hours. The thickness of the interacted area was measured by scanning electron microscopy (SEM) and scanning/transmission electron microscopy (TEM/STEM). The interaction rate increases exponentially with inverse temperature, with an activation energy of 194.23 kJ/mol and diffusion pre-coefficient of 5 × 10−9 m2/s, indicating that the interaction is diffusion-dependent. As the results showed, the interfacial area is comprised of Al alloy channels, Si precipitates, and AlN grains. Al-Si transfer through the solid solution (Si3-xAlxN4-y) at the interface of Al alloy and β-Si3N4 grains controls the kinetic of the interaction. When... 

A novel binary BiOI/ZnFe2O4 (BZ) with p-n heterojunction based on the different metal-organic framework (MOF) MIL-88B(Fe) and graphite carbon nitride (g-C3N4) as substrates has been designed. As-prepared ternary nanocomposites have been first obtained via a simple hydrothermal system and subsequently deposited onto the MOF and g-C3N4 substrates. The photoactivity of the ternary nanocomposites was evaluated by organic pollutants degradation under LED light. These characterization results indicated that BiOI as a p-type semiconductor was well deposited on the surface of ZnFe2O4 (n-type semiconductors). The p-n heterojunction photocatalyst (BZ) improved the valence band potential of ZnFe2O4 and... 

This study involves the capability of severe shot peening (SSP) as a catalyst intake for plasma nitriding process and the probability of reducing the requirement of thermal energy individually on the diffusion of interstitial atoms. To this end, combination of mechanical-thermal energy is run with pure thermal plasma assisted energy. Therefore, SSP is exposed to AISI 304 austenitic stainless steel as a former treatment and gradient structured surface (nanograined zone, ultrafine grain martensite-twin intersections zone and twin densed zone) is created. Then, plasma nitriding at 400 0 C-4h and 475 0 C-2h temperature-duration conditions. The condition of 475 0 C-2h provides the requirements of... 

In the present paper, phase and microstructural characterization of low carbon MgO-C refractories with addition of Fe-catalyzed phenolic resins as binder were investigated. Initially, phenolic resin was modified using various amounts of Fe particles as catalyst originated from iron nitrate ([Fe(NO3)3·9H2O]). The MgO-C matrix compositions were prepared by using 7% of modified phenolic resin, shaped and cured at 200 °C for 24 h. The cured samples were coked in the temperature range from 800 to 1400 °C and then characterized by XRD and FE-SEM techniques. Based on attained results, in-situ graphitic carbons, particularly in carbon nanotubes (CNTs) network were gradually formed from Fe-catalyzed... 

Two-dimensional mesoporous carbon nitride and its highly efficient nanorod framework were prepared via hard-templating method. The obtained materials were fully characterized. The results showed that the samples structural ordering and morphology were similar to those of the parent silica templates; they had large pore volumes as well as high surface area structures. Carbon nitride carbocatalysts were used for H2S selective oxidation. The catalytic tests were carried out at 190, 210 and 230 °C in a fixed bed reactor. The obtained selectivity values for mesoporous carbon nitride rod and mesoporous carbon nitride toward elemental sulfur at 190 °C were 88.8% and 83%, respectively. Both samples... 

Recently, graphitic carbon nitride (g-C3N4) has attracted great interest for photo(electro)chemical applications such as sensing, solar energy exploitation, photocatalysis, and hydrogen generation. This paper presents the potential application and benefits of g-C3N4 nanolayers as a green and highly efficient electrode modifier for the detection of trace lead ions in drinking water and urban dust samples. Carbon nitride nanosheets with a thickness of ∼6 A° and lateral of 100–150 nm were prepared through high-temperature polymerization of melamine followed by sonication-assisted liquid exfoliation. A glassy carbon electrode (GCE) was modified by a thin layer of g-C3N4 through drop casting and... 

It has long been an aspirational goal to create artificial structures that allow fast permeation of water but reject even the smallest hydrated ions, replicating the feat achieved by nature in protein channels (e.g., aquaporins). Despite recent progress in creating nanoscale pores and capillaries, these structures still remain distinctly larger than protein channels. We report capillaries made by effectively extracting one atomic plane from bulk crystals, which leaves a two-dimensional slit of a few angstroms in height. Water moves through these capillaries with little resistance, whereas no permeation could be detected even for such small ions as Na + and Cl − . Only protons (H + ) can...