Photocatalytic performance of Fe-substituted ZnAl2O4 powders under sunlight irradiation on degradation of industrial dyes

Using the sol–gel auto combustion method with diethanolamine (DEA) as fuel, a sequence of iron-substituted zinc aluminates, ZnFe_xAl_2-xO₄ powders, including variable Fe³⁺ ion concentrations (0 ≤ x ≤ 2) were effectively prepared. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), the Brunauer–Emmett–Teller (BET) method, UV–visible diffuse reflectance spectroscopy (UV-DRS), and vibrating sample magnetometer (VSM) were employed to examine the structures, chemical bonds, morphologies, composition, surface area, and optical properties as well as the magnetic behavior of the obtained samples. A single-phase spinel structure was obtained for the calcined aluminate powders with different interplanar spacing and crystallite sizes, as revealed by the classification results. The bandgap energy (E_g) of adapted aluminates was in the range of 2.04-3.14 eV, identified as being much lower compared to the pure sample (5.60 eV). Thus, Fe³⁺-substituted ZnAl₂O₄ samples could be successfully photoexcited using both ultraviolet and visible light, as suggested by the results. Examination of how the four main pollutant types decay when irradiated by sunlight was carried out to assess the samples and establish photocatalytic activity. These contaminants included rhodamine B (RhB), methylene blue (MB), methyl orange (MO), and methyl red (MR). The performance of photocatalytic degradation reached 98% after 150 min for all optimal samples of organic dyes. Besides, each of the altered photocatalysts could be recycled and displayed high stability. The S-shaped curve of ferrimagnetism can result in those samples as found by the magnetic measurements, though pure ZnAl₂O₄ displays diamagnetic characteristics. The adapted samples show intense improvement in the remanent magnetization (M_r) when compared to pure ZnAl₂O₄, signifying that magnetic photocatalyst recovery by applying an external magnetic field is easy. Thus, these results offer a convincing sign that ZnAl₂O₄ powders replaced by Fe³⁺ could provide the ability to aid in the ecologically friendly collection of solar energy.     

Nonlinear Factor-Augmented Predictive Regression Models with Functional Coefficients

This article introduces a new class of functional-coefficient predictive regression models, where the regressors consist of auto-regressors and latent factor regressors, and the coefficients vary with certain index variable. The unobservable factor regressors are estimated through imposing an approximate factor model on high dimensional exogenous variables and subsequently implementing the classical principal component analysis. With the estimated factor regressors, a local linear smoothing method is used to estimate the coefficient functions (with appropriate rotation) and obtain a one-step ahead nonlinear forecast of the response variable, and then a wild bootstrap procedure is introduced to construct the prediction interval. Under regularity conditions, the asymptotic properties of the proposed methods are derived, showing that the local linear estimator and the nonlinear forecast using the estimated factor regressors are asymptotically equivalent to those using the true latent factor regressors. The developed model and methodology are further generalized to the factor-augmented vector predictive regression with functional coefficients. Finally, some extensive simulation studies and an empirical application to forecast the UK inflation are given to examine the finite-sample performance of the proposed model and methodology.     

Junctions between a boron nitride nanotube and a boron nitride sheet

For future nanoelectromechanical signalling devices, it is vital to understand how to connect various nanostructures. Since boron nitride nanostructures are believed to be good electronic materials, in this paper we elucidate the classification of defect geometries for combining boron nitride structures. Specifically, we determine possible joining structures between a boron nitride nanotube and a flat sheet of hexagonal boron nitride. Firstly, we determine the appropriate defect configurations on which the tube can be connected, given that the energetically favourable rings for boron nitride structures are rings with an even number of sides. A new formula E = 6+2J relating the number of edges E and the number of joining positions J is established for each defect, and the number of possible distinct defects is related to the so-called necklace and bracelet problems of combinatorial theory. Two least squares approaches, which involve variation in bond length and variation in bond angle, are employed to determine the perpendicular connection of both zigzag and armchair boron nitride nanotubes with a boron nitride sheet. Here, three boron nitride tubes, which are (3, 3), (6, 0) and (9, 0) tubes, are joined with the sheet, and Euler's theorem is used to verify geometrically that the connected structures are sound, and their relationship with the bonded potential energy function approach is discussed. For zigzag tubes (n,0), it is proved that such connections investigated here are possible only for n divisible by 3.     

Degradation of Pb--EDTA complex by a H(2)O(2)/UV process

The degradation of PbEDTA in aqueous solution by a H(2)O(2)/UV process was studied. The effect of H(2)O(2) content, pH of the solution and the presence of nitrate were investigated. PbEDTA degradation by a H(2)O(2)/UV process was shown to be accompanied by simultaneous lead precipitation. PbEDTA was decomposed rapidly in acidic solutions while lead precipitation was achieved only when the pH of the solution was higher than 6. The presence of nitrate in significant amounts (0.04 M) inhibited remarkably the degradation of the complex and metal precipitation. The degradation of CdEDTA and ZnEDTA was also studied. It was found that the decomposition of metal-EDTA complex and metal removal by the H(2)O(2)/UV process depend greatly on the nature of the metal. CdEDTA and ZnEDTA were decomposed rapidly but metal precipitation was not achieved. The major by-products of the degradation of metal-EDTA complexes observed were nitrilotriacetic acid (NTA), iminodiacetic acid (IDA), oxalic acid and nitrate.     

First principles calculations of Hydrogen—Titanium vacancy complexes in SrTiO3

Hydrogen has been reported to serve exclusively as a donor in many oxides, including SrTiO₃. In a perfect crystal, a proton stays near an O atom, forming a strong O–H bond. In the presence of cation vacancies, i.e., Sr vacancy and Ti vacancy, protons prefer to electrically passivate the cation vacancies by forming strong bonds with the O atoms surrounding the vacancy. These result in the formation of nH–V_Sr and nH–V_Ti complexes. Based on first principles density functional calculations, local configurations and vibration signatures of nH–V_Sr complexes and their vibrational signatures have been previously reported [T-Thienprasert et al., Identification of hydrogen defects in SrTiO₃ by first-principles local vibration mode calculations, Physical Review B 85, 125205 (2012)]. Here, we report the computational results for nH–V_Ti complexes and compare the results with infrared measurements reported in the literatures.     

Development of magnetic recyclable spinel photocatalysts with enhanced sunlight-driven degradation of industrial dyes

Nanocrystalline nickel and copper-substituted zinc aluminate spinel powders (Ni_xZn_1−xAl₂O₄ and Cu_xZn_1−xAl₂O₄) with different additional ion concentrations (0 ≤ x ≤ 1) were successfully synthesized by the sol-gel auto combustion method using diethanolamine (DEA) as a fuel. The structures, chemical bonds, morphologies, composition, surface area, and optical properties including the magnetic behavior of the obtained samples were investigated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), the Brunauer-Emmett-Teller (BET) method, UV-visible diffuse reflectance spectroscopy (UV-DRS), and vibrating sample magnetometer (VSM). All characterization results confirmed that a single-phase spinel structure was obtained for all calcined aluminate powders with various crystallite sizes and lattice constants. The band gap energy (E_g) of all modified aluminates is in the range of 2.99-3.15 eV, which was found to be much lower than that of the pure sample (5.60 eV). These results indicate that the Ni²⁺ and Cu²⁺-substituted ZnAl₂O₄ samples could be effectively photoexcited by both the ultraviolet and visible light. Evaluation of the samples to determine the photocatalytic activity was carried out through investigation of the way the four main pollutant types decompose when irradiated by sunlight. These pollutants were rhodamine B (RhB), methylene blue (MB), methyl orange (MO), and methyl red (MR). For all optimum samples of organic dyes, the efficiency of photocatalytic degradation achieved 96% by the end of 150 min. Furthermore, each of the modified photocatalysts could be reused and showed a high degree of stability. According to magnetic measurements, the S-shaped curve of ferrimagnetism can arise in those samples with the optimum concentration, although pure ZnAl₂O₄ exhibits diamagnetic properties. In comparison to pure ZnAl₂O₄, the modified samples exhibit high enhancement in the remanent magnetization (M_r), which indicates that it is easy to recover those magnetic photocatalyst through the use of an external magnetic field application. These findings therefore serve as a strong indication that ZnAl₂O₄ powders substituted by both Ni²⁺ and Cu²⁺ may offer the capability to serve in environmentally beneficial harvesting of solar energy.     

Precisely controlled delivery of plant hormone using poly(vinyl alcohol)/zeolite A hydrofilm composite

Programmable release of a plant hormone, 1-naphthylacetic acid (NAA), could be achieved by using a novel zeolite–hydrofilm (ZHF) composite. The ZHF was prepared using poly(vinyl alcohol) and glutaraldehyde as a cross-linking agent with the addition of different amounts of zeolite A (0, 1.5, 2.0, 2.5, and 3.0 wt%). This reveals that ZHF was formed as a phase-separated microcomposite with chemical interactions between zeolite A and polymer matrix. We found that the composite film with 2.5 wt% zeolite A had the largest pore size, which exhibited the highest water absorbency and the longest water retention time of over 7 h with high thermal and mechanical stabilities. Release profile displayed rapid desorption of NAA from the film at the initial stage, followed by sustained release thereafter. This behavior was explained by the Korsmeyer–Peppas model with a predominant mechanism of simple Fickian diffusion. Additionally, ZHF with NAA could effectively enhance adventitious root formation of Ocimum basilicum Linn. (sweet basil) cuttings due to accurate releasing NAA and time duration for releasing plant hormone. Finally, the NAA released at the film surface could be in a controlled manner with less negative impact on plant and environment.     

Optical properties and versatile photocatalytic degradation ability of <Emphasis Type="Italic">M</Emphasis>Al<Subscript>2</Subscript>O<Subscript>4</Subscript> (<Emphasis Type="Italic">M</Emphasis> = Ni,Cu, Zn) aluminate spinel nanoparticles

Nanocrystalline NiAl₂O₄, CuAl₂O₄ and ZnAl₂O₄ aluminate spinels were successfully synthesized by the sol–gel auto combustion method using diethanolamine as a novel fuel. The structures, morphologies, particle sizes, and optical properties of these aluminate particles were investigated by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, and UV–Visible diffuse reflectance spectroscopy (UV-DRS). All characterization results confirmed that a single-phase spinel structure was obtained for all calcined aluminate powders with various crystallite sizes (40–60 nm) and distinct band gap energies, E _g (3.0–5.5 eV). The photocatalytic activity of NiAl₂O₄, CuAl₂O₄ and ZnAl₂O₄ nanoparticles were evaluated by the decomposition of four types of pollutants: phenol rhodamine B, heteropolyaromatic methylene blue, azoic methyl orange, and methyl red under ultraviolet irradiation. The photocatalytic degradation efficiencies of all organic dyes by aluminate spinels reach 80–95% within 100 min. These results suggested that NiAl₂O₄, CuAl₂O₄ and ZnAl₂O₄ can serve as photocatalysts for the degradation of a wide range of organic pollutants in environment.     

Two least squares analyses of bond lengths and bond angles for the joining of carbon nanotubes to graphenes

In order to transmit signals from future nanoelectromechanical graphene sheets to other materials, connections with carbon nanotubes need to be effected. Here, we examine three particular perpendicular connections of carbon nanotubes employing two simple distinct least squares approaches and using Euler’s theorem. Firstly, for (8, 0) and (4, 4) carbon nanotubes, we apply a least squares approach to the bond lengths. Sixteen distinct defects and two possible orientations for the armchair tube (4, 4) are identified. Assuming that only pentagons, hexagons, heptagons and occasionally octagons are accepted, the number of possibilities are greatly reduced. By excluding octagonal rings, the number of possible configurations may be further reduced to only one and two most likely configurations for the zigzag (8, 0) and the armchair (4, 4) tubes, respectively. Secondly, for (6, 0) and (8, 0) carbon nanotubes, we apply a least squares approach to bond angles, and for one particular (8, 0) junction, we show that the two least squares approaches produce similar structures in terms of atom locations.These purely geometric approaches can be formally related directly to certain numerical energy minimisation methods used by a number of authors.