A computational study of adsorption H2S gas on the surface of the pristine,Al&P-doped armchair and zigzag BNNTs

Density function theory is used to study the H₂S adsorption on the surface of pristine, Al-, P- and Al&P- doped (4, 4) armchair and (8, 0) zigzag BNNTs. All considered different models for H₂S adsorption on the exterior and interior surface of nanotube are optimized by using B3LYP/6-31G (d, P) level of theory. The adsorption energy values (E_ads) of the B-I, B-II,C-I, D-I, D-II, F-I, F-II and H-II models are negative, while the E_ads values for the A-III, B-III, C-III, D-III, E-III, F-III, G-III and H-III models are positive. On the other hand, Al, P and Al&P doped in all models increase significantly the adsorption energy of H₂S on the surface of BNNTs, and so the selectivity of nanotube for adsorbing and making a sensor of H₂S increase significantly from original state. The positive values of the charge transfer parameters (ΔN) and more values of the electronic chemical potentials of H₂S gas for all studied models demonstrate that H₂S gas in this system has a donor electron effect on the nanotube. The MEP results display that a low charge transfer occurs from H₂S gas toward nanotube, resulting in a weak ionic bonding in the BNNTs’ surface.     

Application of carbon nanostructures toward SO2 and SO3 adsorption: a comparison between pristine graphene and N-doped graphene by DFT calculations

We studied the adsorption of SO_x (x?=?2,3) molecules on the surface of pristine graphene (PG) and N-doped graphene (NDG) by density functional theory (DFT) calculations at the B3LYP/6-31G(d) level. We used Mulliken and NBO charge analysis to calculate the net charge transfer of adsorbed SO_x on pristine and defected graphene systems. Our calculations reveal much higher adsorption energy and higher net charge transfer by using NDG instead of pristine graphene. Furthermore, the density of state (DOS) graphs point to major orbital hybridization between the SO_x and NDG, while there is no evidence of hybridization by using pristine graphene. Based on our results, it is found that SO₂ and SO₃ molecules can be adsorbed on the surface of NDG physically and chemically with adsorption energies (E_ads) of ?27.5 and 65.2?kJ?mol^?1 (19.6 and 51.4?kJ?mol^?1 BSSE), respectively, while low adsorption energies were calculated in the case of using pristine graphene. So we introduced NDG as a sensitive adsorbent/sensor for detection of SO₂ and SO₃.     

An ab initio study on properties of cationic chalcogen bonds in XF2Y+⋯NCZ (X═H,CN, F; Y═S,Se; Z═H,Cl, Br) complexes

The geometries, interaction energies, and bonding properties of cationic chalcogen bonds are studied in binary complexes XF₂Y⁺?NCZ (X═H, CN, F; Y═S, Se; Z═H, Cl, Br). The nature of these interactions is studied by a vast number of methods, including molecular electrostatic potential (MEP), Noncovalent Interaction Index (NCI), quantum theory of atoms in molecules (QTAIM), and natural bond orbital (NBO) analyses. The interaction energies of these complexes vary between ?20.94?kcal/mol in HF₂S⁺?NCH and ?33.72?kcal/mol in F₃Se⁺?NCBr. According to the QTAIM analysis, all these cationic chalcogen bonds are classified as a closed-shell interaction with a partial covalent character. Moreover, cooperative effects between cationic chalcogen bond and hydrogen or halogen bond interactions are studied in ternary XF₂Y⁺?NCZ?NH₃ complexes. These cooperative effects are analyzed in terms of the parameters derived from the QTAIM and NBO analyses, and electron density difference plots.     

Sorption of Cadmium from Aqueous Solution with a Highly Effective Sorbent – B-Doped g-C3N4

B-doped g-C₃N₄ was prepared in the laboratory via heating a mixture of melamine and boric acid. The synthesized material was characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR) analysis, which revealed the high specific surface area and large amount of active groups on the surface of B-doped g-C₃N₄. The sorption of cadmium from aqueous solutions by B-doped g-C₃N₄ was studied under equilibrium conditions in the concentration range of 0.01?5.0 mmol/L. The pH of the solution was varied over a range of 2?6. The sorption of cadmium on the material was determined to be pH-dependent, and the Lagergren-second-order kinetic model was suitable to simulate the sorption process. The maximum sorption capacity from the Langmuir model was determined to be 1.4162 mmol/g (about 159.2 mgCd/g). XPS and FTIR data suggest that cadmium ions were mainly attached to the N-H and O-H groups on the surface of B-doped g-C₃N₄.     

Boron- and nitrogen-doped multi-wall carbon nanotubes for gas detection

The response of pristine, nitrogen and boron doped carbon nanotube (CNT) sensors to NO₂, CO, C₂H₄ and H₂O at ppm concentrations was investigated at both room temperature and 150 °C. N-doped CNTs show the best sensitivity to nitrogen dioxide and carbon monoxide, while B-doped CNTs show the best sensitivity to ethylene. All tubes (including undoped) show strong humidity response. Sensing mechanisms are determined via comparison with density functional calculations of gas molecule absorption onto representative defect structures in N and B-doped graphene. N-CNTs show decreased sensitivity with temperature, and detection appears to occur via gas physisorption. B-CNTs appear to react chemically with many of the absorbed species as shown by their poor baseline recovery and increasing sensitivity with temperature. This limits their cyclability. Overall gas sensitivity is as good or better than post-growth functionalised nanotubes, and used in combination, CNTs, N-CNTs and B-CNTs appear highly promising candidates for cheap, low power, room temperature gas sensing applications.     

The intermolecular interaction studies in the complexes of isothiocyanic acid (HNCS) and its derivatives with H2S: a computational study

The computational investigations are carried out on the complexes of isothiocyanic acid (HNCS) and its derivatives with H₂S through MP2/aug-cc-PVTZ//MP2/aug-cc-PVDZ level. Five, four, three and four structures are located on the potential energy surface of the HNCS?H₂S, HSCN? H₂S, HCNS? H₂S and HSNC?H₂S heterodimers, respectively. The calculated results reveal that the most stable heterodimers among all heterodimers obtained for the HNCS?H₂S, HSCN?H₂S, HCNS?H₂S and HSNC?H₂S systems belong to HSCN?H₂S system. Therefore, HSCN?H₂S system has a key role in the atmosphere.     

Synthesis of boron and nitrogen-doped expanded graphite as efficient reinforcement for Al2O3-C refractories

Boron and nitrogen doped expanded graphite (B-doped EG & N-doped EG) were synthesized for the first time by annealing the mixtures, obtained from the suspensions of expanded graphite (EG) with boric acid and urea, respectively. Afterwards, the doped EG were introduced into Al₂O₃-C refractories by partially replacing the graphite flake. Synthesized materials were characterized using SEM-EDS, XPS, XRD, TG-DSC and Raman Spectroscopy. Also, evaluation of various mechanical properties and oxidation resistance tests were conducted. Boron (B) and Nitrogen (N) were successfully introduced into the C skeleton via different C-B bonds (B4C, B-sub-C and BC2O) and C-N bonds (pyridine-N, amino-N and graphitic-N) respectively, maintaining the hexagonal graphitic lattice and lower reactivity. Compared to as-received EG, the B-doped EG and N-doped EG remained relatively intact structure in Al₂O₃-C refractories at high temperature due to their less defects and lower reactivity. Addition of B-doped EG and N-doped EG into Al₂O₃-C refractories showed improved mechanical properties such as modulus of rupture (CMOR), force, displacement and thermal shock resistance. Besides, the Al₂O₃-C specimens containing B-doped EG and N-doped EG exhibited significantly better oxidation resistance, which further promote the reinforcement effect of doped EG in Al₂O₃-C refractories during actual service condition.     

Crystal structure,microstructure, thermal expansion and electrical conductivity of CeO2–ZrO2 solid solution

CeO₂–ZrO₂ solid solution was synthesised by mechanical activation solid-state chemical reaction method and characterised by X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal dilatometer, Hebb–Wagner method and DC van der Pauw method. The effects of CeO₂ content on the crystal structure, microstructure, thermal expansion coefficient (TEC), electronic conductivity and total conductivity were investigated. XRD analysis showed that (25 and 75?mol-%) CeO₂–ZrO₂ solid solutions corresponded to tetragonal and cubic phase, and 50?mol-% CeO₂–ZrO₂ belonged to the mixture of tetragonal and cubic phases. SEM analysis showed that doping CeO₂ was helpful to the sinterability of CeO₂–ZrO₂ samples. The TECs increased from 13.27?×?10^?6 to 14.72?×?10^?6?K^?1 with increasing CeO₂ content. The electronic and total conductivities of 75?mol-% CeO₂–ZrO₂ were largest, reaching 1.02?×?10^?4?S?cm^?1 and 1.02?×?10^?2?S?cm^?1 at 850°C, respectively.     

Anionic effect of chloride,fluoride, and sulfide ions on the viscosity of slag melt

The effect of the addition of CaX (X=Cl₂, F₂ and S) on the viscous behavior and structure of CaO–SiO₂–Al₂O₃–MgO–CaX slag was investigated by measuring its viscosity. The viscosity of the slag without CaX gradually decreased with an increase in the C/S ratio because of the depolymerization of the silicate groups in the slag. While the viscosity of the CaX‐bearing slag decreased with an increase in the CaX content, depolymerization was not observed in this case. Three distinct compositional regions for the activation energy of the viscous flow were observed because of the effect of the equilibrium of the polymeric silicate groups. The relaxation effect of the CaX groups on the activation energy was also observed. Raman spectroscopic analysis indicated that the relaxation in the viscosity and activation energy by CaX addition stemmed from the breaking of the NBO‐M²⁺‐NBO linkage to form NBO‐M²⁺‐F^?, NBO‐M²⁺‐Cl^?, or M²⁺‐S^2?. All these results are discussed in detail with the help of a viscous flow model based on the ionic interactions.     

Effects of annealing temperature on the photocatalytic activity of N-doped TiO2 thin films

The effects of annealing temperature on the photocatalytic activity of nitrogen-doped (N-doped) titanium oxide (TiO₂) thin films deposited on soda-lime-silica slide glass by radio frequency (RF) magnetron sputtering have been studied. Glancing incident X-ray diffraction (GIAXRD), Raman spectrum, scanning electron microscopy (SEM), atomic force microscopy (AFM) and UV-vis spectra were utilized to characterize the N-doped TiO₂ thin films with and without annealing treatment. GIAXRD and Raman results show as-deposited N-doped TiO₂ thin films to be nearly amorphous and that the rutile and anatase phases coexisted when the N-doped TiO₂ thin films were annealed at 623 and 823 K for 1 h, respectively. SEM microstructure shows uniformly close packed and nearly round particles with a size of about 10 nm which are on the slide glass surface for TiO₂ thin films annealed at 623 K for 1 h. AFM image shows the lowest surface roughness for the N-doped TiO₂ thin films annealed at 623 K for 1 h. The N-doped TiO₂ thin films annealed at 623 K for 1 h exhibit the best photocatalytic activity, with a rate constant (k_a) of about 0.0034 h⁻¹.     

A theoretical study of the tautomerism kinetics of 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one in the gas phase: NBO population and NICS analysis

The tautomerization reactions of the 4-amino-6-methyl-3-thioxo-3,4-dihydro-1,2,4-triazin-5(2H)-one studied by means of M06-2x and CBS-QB3 theoretical methods. The measured energy profiles are complemented with kinetic rate coefficients calculations using transition state theory (TST). In line with the optimized tautomers geometries using the CBS-QB3 method, the natural bond orbital (NBO) analysis reveals that the stabilization energies of non-bonding LP(e)_S8 to the σ*_N2–C3 antibonding orbitals increase from tautomers 1 to 2. Furthermore, the delocalization energies of LP(e)_S8→σ*_N2–C3 could explain the increase of LP(e)_S8 non-bonding orbitals occupancies in the tautomers 1 and 2 (2?>?1). The increase of LP(e)_S8→σ*_N2–C3 delocalizations could fairly explicate the kinetics of tautomeric pathways 1 and 2 (k_2?>?k₁). Moreover, the HOMO–LUMO energy gap is increased parallel with the decreasing of activation energy barriers. NBO results also show that the kinetics of these processes controlled using LP→σ* resonance energies. Furthermore, nucleus-independent chemical shift (NICS) indices show the calculated reaction and energy barriers are involved by changes in aromaticity characters as well as electron transfer from LP(e)_S8 to σ*_N2–C3 orbitals, thus these reactions are controlled from both thermodynamic and kinetic viewpoints by the changes aromaticity characters.     

Cyclic voltammetry studies of TiO2 nanotube arrays electrode: Conductivity and reactivity in the presence of H and aqueous redox systems

In this paper, we use cyclic voltammetry to investigate the effect of protons on the conductivity and reactivity of TiO₂ nanotube array (NTA) electrodes in an aqueous redox system. The H⁺ ion can change the TiO₂ nanotube (anatase phase) surface states for electrons transfer. It can also act as an intermediate state for electron transfer to the acceptor species in the electrolyte surrounding the TiO₂. The higher the concentration of H⁺ ions in the aqueous electrolyte, the easier it is for the electrons transfer from the TiO₂ to the electrolyte oxidized species. The reduction is facile, with a similar reduction potential for various acceptor species, but re-oxidation is not possible. It is apparently an electrochemical reduction involving a single-proton transfer and single-electron transfer. Based on this conclusion, an electrode (PB/Au/TiO₂ NTAs) was fabricated by means of electrodeposition. The electrode used to detect hydrogen peroxide. The sensitivity of the detector is high, and its the detection limit can be as low as 100 nM.     

Doped-SiCNT as a promising sensor for detection of CS2 molecule

In order to explore the novel sensors for detection of carbon disulfide (CS₂) molecule, the electronic sensitivity of Pd or Ni–SiCNT to CS₂ molecule is investigated using density functional theory and dispersion-corrected density functional theory methods. The adsorption energy, charge transfer, density of states and molecular frontier orbital of all systems are also analyzed. The adsorption energy values reveal that Pd_Si or Ni_Si–SiCNT weakly adsorbed the CS₂ molecule and their electronic properties do not change by adsorbing a gas molecule. While replacing C atom with Ni and Pd atoms can enhance the adsorption energy. Moreover, it is found that the electronic properties of Pd_C or Ni_C–SiCNT are changed upon exposure to the CS₂ molecule. And Ni_C–SiCNT has more sensitivity to CS₂ when compared to other considered nanotubes. Therefore, Ni_C–SiCNT is more suitable for detection and CS₂ adsorption than other investigated nanotubes. NBO analysis reveals that electrons transfer from the CS₂ molecule to the nanotube. ¹³C and ²⁹Si chemical shielding tensors are computed using the gauge-independent atomic orbital method. Nuclear magnetic resonance calculations reveal that the isotropy parameters at the sites of Si nuclei which are directly bonded to the impurity atoms undergo significant changes.     

Aerosol-assisted flow synthesis of B-doped, Ni-doped and B–Ni-codoped TiO2 solid and hollow microspheres for photocatalytic removal of NO

In this study, highly effective B-doped, Ni-doped and B–Ni-codoped TiO₂ microspheres photocatalysts were directly synthesized via an aerosol-assisted flow synthesis method. The resulting samples were characterized by XRD, SEM, TEM, UV–vis diffuse reflectance spectroscopy, nitrogen adsorption and XPS. The characterizations revealed hollow microspherical structure of the B-doped and B–Ni-codoped TiO₂ photocatalysts, while the Ni-doped and undoped TiO₂ products consisted of solid microspheres. It was found that the boron dopant was partially embedded into the interstitial TiO₂ structure, existing in the form of Ti–O–B structure. The band gap was enlarged after the boron doping. However, both Ni-doped and B–Ni-codoped TiO₂ samples showed obvious red shift in their absorption edges because of the Ni doping. The photocatalytic activities of these samples were evaluated on the photocatalytic removal of NO under simulated solar light irradiation. All the aerosol-assisted flow synthesized samples had much higher photocatalytic activities than P25 and the doped TiO₂ microspheres exhibited enhanced photocatalytic activity than the undoped counterparts. More interestingly, the B–Ni-codoped TiO₂ photocatalyst possessed superior photocatalytic activity to the as-prepared single doped TiO₂ products. The enhanced photocatalytic activity was explained and the formation mechanisms of hollow and solid microspheres were also proposed on the basis of characterizations. We think this general method may be easily scaled up for industrial production of highly active microspherical photocatalysts for efficient NO removal under simulated solar light irradiation.     

A hydrogen peroxide sensor based on a horseradish peroxidase/polyaniline/carboxy-functionalized multiwalled carbon nanotube modified gold electrode

We have developed a polyaniline/carboxy-functionalized multiwalled carbon nanotube (PAn/MWCNTCOOH) nanocomposite by blending the emeraldine base form of polyaniline (PAn) and carboxy-functionalized multiwalled carbon nanotubes (MWCNT) in dried dimethyl sulfoxide (DMSO) at room temperature. The conductivity of the resulting PAn/MWCNTCOOH was 3.6 × 10⁻³ S cm⁻¹, mainly as a result of the protonation of the PAn with the carboxyl group and the radical cations of the MWCNT fragments. Horseradish peroxidase (HRP) was immobilized within the PAn/MWCNTCOOH nanocomposite modified Au (PAn/MWCNTCOOH/Au) electrode to form HRP/PAn/MWCNTCOOH/Au for use as a hydrogen peroxide (H₂O₂) sensor. The adsorption between the negatively charged PAn/MWCNTCOOH nanocomposite and the positively charged HRP resulted in a very good sensitivity to H₂O₂ and an increased electrochemically catalytical current during cyclic voltammetry. The HRP/PAn/MWCNTCOOH/Au electrode exhibited a broad linear response range for H₂O₂ concentrations (86 μM–10 mM). This sensor exhibited good sensitivity (194.9 μA mM⁻¹ cm⁻²), a fast response time (2.9 s), and good reproducibility and stability at an applied potential of −0.35 V. The construction of the enzymatic sensor demonstrated the potential application of PAn/MWCNTCOOH nanocomposites for the detection of H₂O₂ with high performance and excellent stability.     

Surface modification of ABS by photocatalytic treatment for electroless copper plating

Surface roughness of acrylonitrile–butadiene–styrene (ABS) resin prior to metallization is treated generally with sulphuric/chromic acid system. However, the presence of chrominum (VI) ion imposes serious environmental problems. In this work, TiO₂ photocatalytic treatment was used to enhance the adhesion strength between the ABS surface and the electroless copper film. Effects of the TiO₂ content, irradiation time and UV power upon the surface topography, surface characterization and the adhesion strength were investigated. The results indicated that the surface hydrophilicity of ABS resin and the adhesion strength between the electroless copper film and ABS surface increased with an increase in the UV power and a prolongation in irradiation time, and did not increase linearly with an increase of TiO₂ content. Though the surface topography of ABS changed little, the adhesion strength reached 1.25?kN/m, which was higher than that in the optimal H₂SO₄–MnO₂ colloid. The surface chemistry results indicated that –COOH and –OH groups formed with the photocatalytic treatment and the absorption strengths increased with the UV power. XPS analysis results further demonstrated that the contents of C=O and –COOH reached 6.4 and 4.9% with the photocatalytic treatment, which was much higher than that of the H₂SO₄–MnO₂ colloid (3.9 and 3.1%). The high contents of C=O and –COOH groups enhanced the surface hydrophilicity of the ABS resin and improved the adhesion strength between the electroless copper film and ABS resin. The results indicated that the photocatalytic treatment was an environment-friendly and effective method to replace the commercial wet chemical process for ABS surface modification.     

Adsorption of binary CO2/CH4 mixtures using carbon nanotubes: Effects of confinement and surface functionalization

Effect of confinement and surface functionalization in carbon nanotubes (CNTs) on the competitive adsorption of a binary CO₂/CH₄ mixture has been investigated by grand canonical Monte Carlo simulations. Adsorption using CNTs with different functionalization arrangements, different diameters, different functionalization degrees, and different functional groups, such as –COOH, –CO, –OH, –CH₃, is investigated. Effects of (a) the pore textural properties, such as pore size and accessible surface area, and (b) the gas–adsorbent interaction, especially the electrostatic interaction, are discussed. From these results, we discuss the impact that variables such as confinement and surface functionalization have on the performance for CO₂ separation.     

A new strategy for hydrogen sulfide removal by amido-functionalized reduced graphene oxide as a novel metal-free and highly efficient nanoadsorbent

In this research, hydrogen sulfide is adsorbed on amido-functionalized reduced graphene oxide (AFRGO) as a nanoadsorbent. By the use of n-propylamine and allylamine, reduced graphene oxide (RGO) was amidated for the adsorption of hydrogen sulfide. The materials were characterized by adsorption of H₂S, potentiometric titration, scanning electron microscopy (SEM), Fourier-transform infrared (FT-IR) spectroscopy, and X-ray diffraction (XRD) analysis. The effect of the operational conditions of 4000–6000 h^?1 space velocities and 60,000?ppm H₂S feed concentrations were examined on adsorption capacity. The results show that H₂S feed concentration, space velocity, and functional groups of adsorbents have a major effect on H₂S adsorption. It was also found that the temperature in the range of 30–70°C had a significant effect on H₂S adsorption. The concentration of H₂S adsorbed in 3?h by AFRGO containing allyl substituent, AFRGO containing propyl substituent, graphene oxide (GO), and reduced graphene oxide (RGO) were reported as 59,710, 59,650, 59,600, and 59,500?ppm, respectively. Hydrogen sulfide adsorption analysis showed that nanoadsorbents increase adsorption capacity of H₂S.     

Effect of H2S on the hydrogenation of carbon dioxide over supported Rh catalysts

The hydrogenation of CO₂ was studied on supported noble metal catalysts in the presence of H₂S. In the reaction gas mixture containing 22 ppm H₂S the reaction rate increased on TiO₂ and on CeO₂ supported metals (Ru, Rh, Pd), but on all other supported catalysts or when the H₂S content was higher (116 ppm) the reaction was poisoned. FTIR measurements revealed that in the surface interaction of H₂ + CO₂ on Rh/TiO₂ Rh carbonyl hydride, surface formate, carbonates and surface formyl were formed. On the H₂S pretreated catalyst surface formyl species were missing. TPD measurements showed that adsorbed H₂S desorbed as SO₂, both from TiO₂-supported metals and from the support. IR, XP spectroscopy and TPD measurements demonstrated that the metal became apparently more positive when the catalysts were treated with H₂S and when the sulfur was built into the support. The promotion effect of H₂S was explained by the formation of new centers at the metal/support interface.     

Simple fabrication of N-doped mesoporous TiO2 nanorods with the enhanced visible light photocatalytic activity

N-doped mesoporous TiO₂ nanorods were fabricated by a modified and facile sol–gel approach without any templates. Ammonium nitrate was used as a raw source of N dopants, which could produce a lot of gasses such as N₂, NO₂, and H₂O in the process of heating samples. These gasses were proved to be vitally important to form the special mesoporous structure. The samples were characterized by the powder X-ray diffraction, X-ray photoelectron spectrometer, nitrogen adsorption isotherms, scanning electron microscopy, transmission electron microscopy, and UV-visible absorption spectra. The average length and the cross section diameter of the as-prepared samples were ca. 1.5 μm and ca. 80 nm, respectively. The photocatalytic activity was evaluated by photodegradation of methylene blue (MB) in aqueous solution. The N-doped mesoporous TiO₂ nanorods showed an excellent photocatalytic activity, which may be attributed to the enlarged surface area (106.4 m² g^-1) and the narrowed band gap (2.05 eV). Besides, the rod-like photocatalyst was found to be easy to recycle.