Mesoporous interstitial and substitutional nitrogen-containing titanium dioxide photocatalysts prepared by acid-assisted sol–gel procedure

Two different types of nitrogen-containing TiO₂ were synthesized via an acid-modified sol–gel method. Yellow-colored interstitial and white substitutional nitrogen-containing TiO₂ powders were characterized by means of X-ray diffraction, X-ray photoelectron spectroscopy, Brunauer–Emmett–Teller specific surface area and Barrett–Joyner–Halenda pore size distribution analyses, scanning electron microscopy, transmission electron microscopy and UV–vis absorption spectroscopy. The band gaps of interstitial and substitutional nitrogen-containing TiO₂ ceramics were estimated from UV–vis spectroscopy data to be 2.6 and 2.8 eV, respectively. Prepared substitutional nitrogen-containing TiO₂ featured steep light absorption edge with an approximately parallel characteristic to that in pure TiO₂. This fact is due to band-to-band visible light absorption ability of substitutional nitrogen-containing TiO₂. The photocatalytic properties of the produced nitrogen-containing TiO₂ samples were compared for the degradation of Direct Red 28 azo dye. Further studies were also devised to compare the catalytic efficiency of the nitrogen-containing TiO₂ powders with the pure TiO₂ synthesized via the similar sol–gel method. The produced nitrogen-containing TiO₂ samples revealed superior photocatalytic properties in comparison with pure TiO₂ due to their remarkable band gap narrowing, surface oxygen vacancies and much more surface defects. The results also revealed that the substitutional nitrogen-containing TiO₂ is the most effective photocatalyst under ultraviolet and visible light irradiation.     

Existence results to positive solutions of fractional BVP with $${\varvec{}}$$-derivatives

This paper investigates the existence and uniqueness of positive and nondecreasing solution for nonlinear boundary value problem with fractional q-derivative

$$\begin{aligned}&D_{q}^{\alpha }u(t)+f(t,u(t))=0, \quad {0<t<1, ~3<\alpha \le 4,} \\&u(0)= D_{q}u(0)=D_{q}^{2}u(0)=0, \quad D_{q}^{2}u(1)=\beta D_{q}^{2}u(\eta ), \end{aligned}$$

where \(D_{q}^{\alpha }\) denotes the Riemann–Liouville q-derivative of order \(\alpha \), \(0<\eta <1\) and \(1-\beta \eta ^{\alpha -3}>0\). Our analysis relies a fixed point theorem in partially ordered sets. An example to illustrate our results is given.

     

Numerical simulation of electronic structure,linear and third order nonlinear optical absorption coefficients in the polymeric nanoheterostructure using imaginary time propagation method

In the effective mass approximation, the charge density, the potential profile, the wavefunctions, and the corresponding energy states for zinc sulfide spherical quantum dot have been self-consistently solved, which is embedded in the polymeric media (PVP) by the imaginary time propagation method. Moreover, for the first time, the oscillator strength, linear, third order nonlinear, and total optical absorption coefficients for the transition between intersubbands 1s-1p, 1p-1d, 1d-1f, 1f-1g, 1g-1h, and 1h-1i are investigated with respect to photon energy and the saturation strength has been calculated for every transition too. Calculated result shows that the oscillator strength and the magnitude of optical absorption coefficients are enhanced for transition between intersubbands with higher energies. Also, calculations show that the total absorption coefficient depends on the strength of incident optical intensity and relaxation time.     

Turbulent heat transfer and fluid flow of alumina nanofluid inside three-lobed twisted tube

Turbulent flow characteristics and heat transfer applications of a twisted heat exchanger with 3-lobed cross section along with Y-tape insert are numerically studied. The working fluids for the simulations are pure water and water–Al₂O₃ nanofluid using two-phase mixture model. The study is carried out for various nanofluid volume fractions of 0.01, 0.02 and 0.03 with Reynolds number in the range of 5000–20,000. The effect of nanoparticles in heat transfer augmentation for smooth and lobed tubes is discussed based on presenting the highest thermal performance, which is a relation between heat transfer rate and pressure loss. Results show that implementing the twisted tube with Y-tape insert enhances the heat transfer more than the twisted tube. Relative Nusselt numbers for twisted tubes decrease with Reynolds number in comparison with the plain tube. Turbulent intensity, swirl number and tangential velocity of twisted tube with insert are higher than empty twisted tube indicating that inserting the Y-tape intensifies the turbulence and disturbs the fluid flow further. On the other hand, although the twisted tube increases the pressure drop more than plain tube, the case with Y-tape drastically increases the friction factor. So, the thermal performance of twisted tube with insert is lower than empty twisted tube. Adding nanoparticles to the base fluid has different influence on the investigated cases. It augments the relative Nusselt number inside plain tube and empty twisted tube with slight increment in friction factor. Increasing the nanoparticles concentration enhances the heat transfer rates for these cases while it does not increase the relative Nusselt number inside twisted tube with Y-tape insert at high Reynolds number and nanoparticle concentration. Moreover, it can be found that twisted tube with or without Y-tape insert is more efficient at low Reynolds number in comparison with the plain tube.

     

An NO+ reactant ion source for ion mobility spectrometry

The major reactant ion in conventional ion mobility spectrometry (IMS) is the hydronium ion, H₃O⁺ which is produced in the usual ionization sources such as corona discharge or radioactive sources. Using the hydronium reactant ion, mostly the analytes with proton affinity higher than that of water are ionized. A broader range of compounds can be detected by IMS if other alternative ionization channels, such as charge transfer from NO⁺, are employed. In this work we introduce a simple and novel method for producing NO⁺ as the major reactant ion in IMS. This was achieved by adding neutral NO to the corona discharge ionization source. The neutral NO was prepared via an additional discharge in an air stream, flowing into the corona discharge source. A curtain plate was mounted in front of the corona discharge to prevent the influence of the analyte on the production of NO⁺. Using this technique, the reactant ion could easily and quickly switch between the H₃O⁺ and NO⁺. The performance of the new source was evaluated by recording ion mobility spectra of test compounds with both H₃O⁺ and NO⁺ reactant ions.     

Simultaneous determination of vitamin B12 and its derivatives using some of multivariate calibration 1 (MVC1) techniques

Resolution of binary mixtures of vitamin B12, methylcobalamin and B12 coenzyme with minimum sample pre-treatment and without analyte separation has been successfully achieved by methods of partial least squares algorithm with one dependent variable (PLS1), orthogonal signal correction/partial least squares (OSC/PLS), principal component regression (PCR) and hybrid linear analysis (HLA). Data of analysis were obtained from UV-vis spectra. The UV-vis spectra of the vitamin B12, methylcobalamin and B12 coenzyme were recorded in the same spectral conditions. The method of central composite design was used in the ranges of 10-80mgL(-1) for vitamin B12 and methylcobalamin and 20-130mgL(-1) for B12 coenzyme. The models refinement procedure and validation were performed by cross-validation. The minimum root mean square error of prediction (RMSEP) was 2.26mgL(-1) for vitamin B12 with PLS1, 1.33mgL(-1) for methylcobalamin with OSC/PLS and 3.24mgL(-1) for B12 coenzyme with HLA techniques. Figures of merit such as selectivity, sensitivity, analytical sensitivity and LOD were determined for three compounds. The procedure was successfully applied to simultaneous determination of three compounds in synthetic mixtures and in a pharmaceutical formulation.     

Numerical study of melting inside concentric and eccentric horizontal annulus

This paper presents numerical investigations on melting of phase change material using N-eicosane inside a cylindrical container. Numerical simulations are performed for symmetric melting of phase change material between two cylinders in concentric and eccentric arrays using the FLUENT software which is sub-cooled initially to 1 °C. Inner cylindrical tube is considered hot wall while outer tube is insulated. Predicted result shows that melting rate is the same approximately for concentric and eccentric array before time of 15 min. After this time, melting rate decreases in concentric array. It is due to the pure conduction between hot tube and cold solid phase change material.     

Cyclic Alkyne Approach to Heteroatom‐Containing Polycyclic Aromatic Hydrocarbon Scaffolds

We report a modular synthetic strategy for accessing heteroatom‐containing polycyclic aromatic hydrocarbons (PAHs). Our approach relies on the controlled generation of transient heterocyclic alkynes and arynes. The strained intermediates undergo in situ trapping with readily accessible oxadiazinones. Four sequential pericyclic reactions occur, namely two Diels–Alder/retro‐Diels–Alder sequences, which can be performed in a stepwise or one‐pot fashion to assemble four new carbon–carbon (C?C) bonds. These studies underscore how the use of heterocyclic strained intermediates can be harnessed for the preparation of new organic materials.     

Outward melting of ice enhanced by Cu nanoparticles inside cylindrical horizontal annulus: Lattice Boltzmann approach

Heat transfer enhancement of water-(Ice) as a phase change material (PCM) through dispersion of Cu-nanoparticles is the centerpiece of this research study. The nanoparticle-enhanced phase change material (NEPCM) demonstrates increased thermal conductivity and decreased melting time in comparison with the conventional PCM. An enthalpy-based lattice Boltzmann method (LBM) with a double distribution function (DDF) model is implemented to trace phase change front in a cylindrical-horizontal annul. The subcooling case is neglected and Prandtl number, Stefan number and Rayleigh number are fixed to 6.2, 1 and 10⁵, respectively. In addition, the effects of varying the position of heated cylinder and nanoparticle volume fractions on the transient isotherms and liquid fractions are discussed.