Spinel nickel cobaltite nanoflakes anchored multiwalled carbon nanotubes driven photocatalyst for highly efficient degradation of organic pollutants using natural sunlight irradiation

Natural sun light driven photocatalytic materials have received remarkable attention due to their imminent applications in environmental remediation and energy conversions. In this study, natural sun light driven hierarchal spinel nickel cobaltite nanoflakes (NiCo₂O₄) anchored multiwalled carbon nanotubes (MWCNTs) nanocomposite was synthesized by using simple chemical route. The structural, morphological and functional group of as-prepared NiCo₂O₄ anchored MWCNTs was studied by using X-ray diffractometry, field emission scanning electron microscopy and Fourier transform infrared spectroscopy. The UV–vis diffusive reflectance spectroscopy results demonstrated decrease in optical bandgap from 1.32 to 1.16eV compared with pristine spinel NiCo₂O₄ nanoflakes. MWCNTs anchored NiCo₂O₄ showed extremely good photocatalytic behavior and we verified 98% degradation of MB in 35 min under natural sun light. NiCo₂O₄ anchored MWCNTs also confirmed its excellent stability and reusability by retaining 96% of photocatalytic efficiency after 7 cycles of operation. Improved photocatalytic behavior of NiCo₂O₄ anchored MWCNTs nanocomposite in comparison to NiCo₂O₄ nanoflakes is mainly attributed to excellent electron storage ability of MWCNTs which made catalyst a great acceptor. Moreover, porous structure of MWCNTs not only provides large surface area with more active sites but also increases conductivity and decreases agglomerations on the surface of material which render e^-/h⁺ pair recombination. Overall, this work shed new light for the synthesis of NiCo₂O₄ anchored MWCNTs with enhanced photocatalytic properties.     

Influencing parameters in the electrochemical anodization of TiO2 nanotubes: Systematic review and meta-analysis

Comprehensive control of processing techniques is primordial when fine-tuning the morphological features of titanium dioxide nanotube arrays (TNTs). This systematic review and meta-analysis compiled articles published from 2007 to date on the synthesis and growth mechanism of nanotubes fabricated via electrochemical anodization and evaluated the potential relationships between anodizing conditions and the resulting structures. Studies were gathered from the Science Direct online database, screened according to predefined criteria, and evaluated for their eligibility. Ninety-nine studies were assessed in the meta-analysis, 87 of them on tube length, 80 on tube diameter, and 33 on wall thickness. Multiple linear regression was performed to test if anodization parameters significantly predicted the resulting morphology of TiO₂ nanotubular structures. Overall regression for the three responses was statistically significant (length: R² = 0.487, p < 0.001; diameter: R² = 0.899, p < 0.001; wall thickness: R² = 0.792, p < 0.001). Applied potential was one of the main effects predicting all three responses (p < 0.001 in every model). Other important main predictors were anodizing time for tube length (p < 0.001), water percentage for tube diameter (p < 0.001) and ammonium fluoride (NH₄F) concentration for wall thickness (p < 0.001).     

Anatase TiO2 powder immobilized on reticulated Al2O3 ceramics as a photocatalyst for degradation of RO16 azo dye

The three-dimensional network of open-celled Al₂O₃ ceramic supports were first fabricated using a polymeric sponge replication technique. The polyurethane foams soaked with the highly loaded Al₂O₃ ceramic slurry were drained, slowly dried and sintered at 950 °C to complete the burn out process and to construct the ceramic preforms. They were then carefully soaked again with the moderately loaded Al₂O₃ slurry and sintered at 1500 °C to increase their strength. Finally, the photocatalyst ceramic powder covering the outer surfaces was placed layer by layer through dipping the rigid Al₂O₃ supports repeatedly in the slurry of TiO₂ powder. The dip-applied TiO₂ was sintered eventually at relatively low temperature of 700 °C to prevent phase transformation. The efficiencies of the TiO₂ coated Al₂O₃ samples were evaluated by the photocatalytic degradation of reactive orange 16 (RO16) azo dye molecules dissolved in water. Nearly complete color removals were achieved within 75 min under UVC irradiation.     

Non-uniform doping outperforms uniform doping for enhancing the photocatalytic efficiency of Au-doped TiO2 nanotubes in organic dye degradation

Uniform doping is usually recognized as an efficient method for enhancing photocatalysis of TiO₂, while non-uniform doping is generally supposed to be inefficient because of the inhomogeneous dispersion of dopants. However, in this study, we present the first example of non-uniform doping (with Au)-better enhanced photocatalysis of TiO₂ nanotubes, as compared to uniform doping, in terms of the photocatalytic organic dye degradation. The extent to which the non-uniform doping (achieved by liquid phase deposition (LPD)) can enhance photocatalysis is evaluated, along with a comparison with uniform doping. There exists an additional positive effect in the non-uniform doping system, that is, as generated interfaces between pure phase TiO₂ and Au-doped TiO₂, in contrast to the uniform doping system leading to a positive “platinum island” effect. Such double beneficial effects contribute to the highest performance in the photocatalytic organic dye degradation for the Au-non-uniformly doped TiO₂ nanotubes as compared to other samples involved in this study. Both the “platinum island” and interfacial separation effects are helpful to isolate the photo-generated electrons and holes, resulting in enhanced photocatalytic activities.     

Green synthesis of dysprosium stannate nanoparticles using Ficus carica extract as photocatalyst for the degradation of organic pollutants under visible irradiation

This paper describes a simple and environmentally friendly route to develop Dy₂Sn₂O₇ nanostructures with the aid of Ficus carica extract as naturally available fuel, for the first time. In this investigation, we found that shape, purity and dimension of Dy₂Sn₂O₇ could be controlled with varying the determinative factors, the quantity of Ficus carica extract and temperature. The varied techniques have been employed to denote the production of Dy₂Sn₂O₇ and examine its features. We applied diverse structures of Dy₂Sn₂O₇ (fabricated with Ficus carica extract) as visible-light-sensitive photocatalyst for destruction of Acid Violet 7 and crystal violet, for the first time. The fabricated Dy₂Sn₂O₇ with the aid of 2 ml of Ficus carica extract was capable of illustrating a great efficiency to destruct target pollutants. Our findings offer that the as-fabricated Dy₂Sn₂O₇ can be beneficially applied as novel kind of visible-light-sensitive photocatalyst for efficient removal and destruction of organic contaminants in water.     

An efficient method for the synthesis of 2-aminothiazoles using silica chloride as a heterogeneous catalyst

This article describes a facile and efficient synthesis of 2-aminothiazoles under mild reaction conditions with quantitative yields using silica chloride as an effective heterogeneous catalyst.     

Combination of photocatalytic and photoelectro-Fenton/citrate processes for dye degradation using immobilized N-doped TiO2 nanoparticles and a cathode with carbon nanotubes: Central composite design optimization

In this report, commercial TiO₂ nanoparticles were doped with nitrogen by a manual grinding method using urea. The prepared catalyst was characterized by X-ray diffraction (XRD), diffuse reflectance spectra (DRS), and transmission electron microscopy (TEM). N-doped TiO₂ was immobilized on ceramic plates by methyl tri-methoxy silane. Next, multi-walled carbon nanotubes (CNTs) were stabilized on carbon paper to fabricate the cathode. Scanning electron microscopy (SEM) was employed to confirm stabilization of the CNTs. The prepared cathode and immobilized catalyst were utilized for the degradation of C.I. Direct Red 23 (DR23) by the photoelectro-Fenton (PEF) process in the presence of citrate (Cit) combined with a photocatalytic process. The coupled PEF/Cit/N-TiO₂ process could be performed under visible light, not only due to the formation of iron–citrate complexes, but also because of the incorporation of nitrogen to the crystalline structure of TiO₂ and the generation of TiO₂ complexes with electrogenerated H₂O₂. Results demonstrated that the degradation efficiency of DR23 (20 mg/L) using the identical operational conditions, followed a decreasing order of: PEF/Cit/N-TiO₂ > PEF/Cit > PEF > EF > N-TiO₂. Eventually, a model was developed by the central composite design (CCD) method, describing the degradation efficiency as a function of the operational parameters.     

An efficient approach to control the morphology and the adhesion properties of anodized TiO2 nanotube arrays for improved photoconversion efficiency

We investigate an efficient approach to control the surface morphology and the geometrical parameter of TiO₂ nanotubes, while improving its adhesion to underlying titanium substrate, which is the key to successful fabrication of electro-optical devices. By controlling the water content and using the previously used electrolyte, nanotube arrays with surface morphology, geometrical parameters and adhesion properties relevant to required applications can be achieved. On the basis of these results, a mechanism of chemical dissolution rate is discussed in detail, in particular, with respect to the variation of nanotube length, presence of surface aggregation on the top surface, and the adhesion of nanotubes to underlying titanium substrate. It is found that the enhanced chemical dissolution rate can help to dissolve off the surface aggregation parts and reduce the internal stress at the barrier layer–metal interface. As a result this adhesion characteristic between the nanotubes and the underlying metal layer can be significantly improved. The contrastive photoelectrochemical experiments suggested that the photoconversion efficiency greatly depends on the geometric roughness factor of nanotubes and its adhesion to underlying metal layer. It shows that the 3.0% water content in previously used electrolytes has a combinative advantage to meet the optimal condition of photoconversion efficiency.     

An eco-friendly highly stable and efficient Ni-C-S codoped wurtzite ZnO nanoplate: a smart photocatalyst for the quick removal of food dye under solar light irradiation

In recent years, semiconductor photocatalysis has become more and more attractive and important since it has great potential to contribute to such environmental problems. This work investigates the photodegradation of tatrazine using Ni, C and S codoped ZnO (Ni-C-S/ZnO) nanoplates synthesized by the co-precipitation method. The synthesized photocatalyst was characterized by UV–visible-diffuse reflectance spectroscopy (UV–vis-DRS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) techniques. Ni-C-S/ZnO were found to be more photoactive than ZnO, Ni-ZnO and C-S/ZnO for the degradation of tatrazine under solar light irradiation. Ni, C and S, with a moderate amount (0.5:0.5:0.5:1) doped on ZnO, can act as electron traps and suppress the photogenerated electron–hole pair recombination and result in the improvement of photocatalytic performance samples. The optimum condition for 94% degradation was found to be 300 mL of 10 µM of dye solution along with 0.1 g/L of Ni-C-S/ZnO under solar light irradiation within 90 min. From this, the Ni-C-S/ZnO sample exhibited maximum photocatalytic efficiency for the degradation of tatrazine under solar light irradiation.     

Directly silica bonded analytical reagents: synthesis of 2-mercaptobenzothiazole–silica gel and its application as a new sorbent for preconcentration and determination of silver ion using solid-phase extraction method

A new and efficient method is described for the easy synthesis of directly bonded 2-mercaptobenzothiazole–silica gel. This new bonded analytical reagent is used as an effective sorbent for the solid-phase extraction of silver ion from aqueous solutions. Conditions for effective adsorption of trace levels of silver ion concentration are optimized with respect to different experimental parameters in column process. Sodium thiosulfate solution could efficiently elute the adsorbed silver ion from the surface of the sorbent which then was determined by atomic absorption spectroscopy (AAS). Common coexisting ions did not interfere with the separation and determination. The preconcentration factor is 300 (1 ml elution volume) for a 300 ml sample volume. The sorbent exhibited excellent stability and its sorption capacity under optimum conditions has been found to be 343 μg of silver per gram of sorbent. The relative standard deviation under optimum conditions is 2.04% (n=7). Accuracy of the method was estimated by using test samples of natural water spiked with different amounts of silver ion. The method is simple and inexpensive.