Typical Non–TiO2-Based Visible-Light Photocatalysts

Photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. However, the traditional photocatalyst, TiO2, cannot make use of visible light that accounts for 45% of solar spectrum because of a large bandgap (3.2 eV). Therefore, it is urgent to develop visible-light-driven photocatalysts. On the one hand, some modification technologies were explored to extend the light absorption of TiO2 to visible-light region, such as doping of metal and non-metal elements, dye sensitization, and so on. On the other hand, much effort has been directed toward the development of new visible-light photocatalysts. The good news is, some novel and efficient non-TiO2-based photocatalysts have been discovered, such as WO3, Ag3PO4, BiVO4, g-C3N4. In this chapter, these four typical visible light–driven semiconductor photocatalysts were highlighted. WO3 is a visible light–responsive photocatalyst that absorbs light up to ca. 480 nm. Besides that, WO3 has some advantages, such as low cost, harmlessness, and stability in acidic and oxidative conditions. Preparation of WO3 films with the deposition of noble metal is considered to be a promising approach for the photocatalytic applications. In addition, the characteristic morphology and improved photocatalytic performance of Ag3PO4-based and BiVO4-based have been raised up. New methods for fabrication Ag3PO4 with exposed high-energy facets and novel heterogeneous Ag3PO4 co-catalysts have been developed. Monoclinic BiVO4 is a promising photo-anode material for photocatalytic water splitting to produce hydrogen. Co-catalysts loaded on BiVO4 could improve the surface charge transfer efficiency. Furthermore, g-C3N4 is a promising visible-light photocatalyst due to its unique electronic structure. To date, g-C3N4-based photocatalysis has become a very hot research topic. The synthesis, bandgap engineering, and semiconductor composites of g-C3N4-based photocatalysts are highlighted

Non-monotonic compositional dependence of isothermal bulk modulus of the (Mg1–xMnx)Cr2O4 spinel solid solutions, and its origin and implication

AbstractThe compressibility of the spinel solid solutions, (Mg1−xMnx)Cr2O4 with x = 0.00 (0), 0.20 (0), 0.44 (2), 0.61 (2), 0.77 (2) and 1.00 (0), has been investigated by using a diamond-anvil cell coupled with synchrotron X-ray radiation up to ∼10 GPa (ambient T). The second-order Birch–Murnaghan equation of state was used to fit the PV data, yielding the following values for the isothermal bulk moduli (KT), 198.2 (36), 187.8 (87), 176.1 (32), 168.7 (52), 192.9 (61) and 199.2 (61) GPa, for the spinel solid solutions with x = 0.00 (0), 0.20 (0), 0.44 (2), 0.61 (2), 0.77 (2) and 1.00 (0), respectively (KT′ fixed as 4). The KT value of the MgCr2O4 spinel is in good agreement with existing experimental determinations and theoretical calculations. The correlation between the KT and x is not monotonic, with the KT values similar at both ends of the binary MgCr2O4MnCr2O4, but decreasing towards the middle. This non-monotonic correlation can be described by two equations, KT = −49.2 (11)x + 198.0 (4) (x ≤ ∼0.6) and KT = 92 (41)x + 115 (30) (x ≥ ∼0.6), and can be explained by the evolution of the average bond lengths of the tetrahedra and octahedra of the spinel solid solutions. Additionally, the relationship between the thermal expansion coefficient and composition is correspondingly reinterpreted, the continuous deformation of the oxygen array is demonstrated, and the evolution of the component polyhedra is discussed for this series of spinel solid solutions. Our results suggest that the correlation between the KT and composition of a solid solution series may be complicated, and great care should be paid while estimating the KT of some intermediate compositions from the KT of the end-members

Removal of the Pesticide Pymetrozine from Aqueous Solution by Biochar Produced from Brewer's Spent Grain at Different Pyrolytic Temperatures

Biochar (BC) produced from brewer's spent grain (BSG) via slow pyrolysis at 300, 400, 500, 600, and 700 °C was characterized and investigated as an adsorbent for the removal of the pesticide pymetrozine from aqueous solution. Batch BSG BCs adsorption experiments were carried out under various conditions (such as pH, pymetrozine concentration, and BC dosage) to adsorb the pymetrozine. The BSG BCs adsorption pymetrozine capacities were increased by 21.4% to 55.5% under pyrolysis temperatures of 300, 400, 500, and 600 °C compared to 700 °C with a pyrolysis time of 2 h and by 19.0% to 52.1% at 4 h. At solution pH values of 2, 4, 6, and 8, the adsorption capacities were increased by 9.6% to 39.5% compared with that at pH 10. A similar adsorption tendency was found for the different BCs dosage. In the first 60 min, BC absorbed 70% to 80% pymetrozine. The Langmuir and Freundlich model were highly correlated with BC adsorption. The magnitude of free energy decreased by 32.2% to 47.3% with increasing temperature. The value of the enthalpy change showed the adsorption to be endothermic. The BSG BC had high efficiency in adsorbing pymetrozine and had great potential to prevent the water pollution and reuse the waste of the beer factory

Template-Free Synthesis of Monoclinic BiVO4 with Porous Structure and Its High Photocatalytic Activity

Monoclinic BiVO4 photocatalysts with porous structures were synthesized by a two-step approach without assistance of any templates. The as-prepared samples were characterized by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET), ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy (DRS), photocurrent responses, and electrochemical impedance spectra (EIS). It is found that the as-prepared BiVO4 samples had a porous structure with aperture diameter of 50–300 nm. Moreover, the BET specific surface area of the porous BiVO4-200 °C sample reaches up to 5.69 m2/g, which is much higher than that of the sample of BiVO4 particles without porous structure. Furthermore, a possible formation mechanism of BiVO4 with porous structure was proposed. With methylene blue (MB) as a model compound, the photocatalytic oxidation of organic contaminants in aqueous solution was investigated under visible light irradiation. It is found that the porous BiVO4-200 °C sample exhibits the best photocatalytic activity, and the photocatalytic rate constant is about three times of that of the sample of BiVO4 particles without porous structure. In addition, the photocurrent responses and electrochemical impedance spectra strongly support this conclusion

Preparation of Al-Si composite from high-alumina coal fly ash by mechanical chemical synergistic activation

High-alumina coal fly ash (HAFA) is a special solid waste because it contains more than 45% alumina and 35% silica. This material can be applied to prepare Al Si series ceramics if the impurities can be removed and the Al/Si mass ratio can be elevated to a high level. In this work, a new mechanical chemical synergistic activation desilication process is proposed and optimized. During the synergistic activation, the morphology, ironic leaching ratios, efficient desilicated ratio (EDR), and mineral phases of different treatments are investigated. The reactivity of amorphous silica can be elevated to a high level (EDR &gt; 11%). After the desilication process, the contents of different impurities can be lowered up to less than 1%, and the Al/Si mass ratio can be elevated from 1.26 to 2.71. Mullite refractories are prepared from desilicated HAFA by forming and sintering process, and the bulk density and apparent porosity can reach to 2.85 g/cm(3) and 2.07%, respectively.</p

The environmental sustainability of synthetic wollastonite using waste from zirconium oxychloride production

A reasonable and economic process to achieve the comprehensive utilization of waste from production of zirconium oxychloride would benefit sustainable development of zirconium industries and reduce environmental pollution. In this paper, wollastonite was prepared from spent caustic liquor and zirconium-containing silicon slag at low temperature. The effects of CaO/SiO2 mole ratio, reaction temperature, reaction time, and rotation rate on the crystallization and morphology of wollastonite were systemically investigated. The optimal conditions for desilication were confirmed as a CaO/SiO2 mole ratio of 1.0, a reaction temperature of 90 degrees C, a desilication time of 60 min, and a rotation rate of 200 r/min. Wollastonite was subsequently prepared by calcination of the obtained calcium silicate hydrate at 1000 degrees C for 1.0 h. The developed process achieved good performance of wollastonite and alkali liquor with a low silicate content, which met the standard of an industrial-grade product. (C) 2017 Elsevier Ltd. All rights reserved

N-Doped K₃Ti₅NbO₁₄@TiO₂ Core-Shell Structure for Enhanced Visible-Light-Driven Photocatalytic Activity in Environmental Remediation

A novel N-doped K3Ti5NbO14@TiO2 (NTNT) core-shell heterojunction photocatalyst was synthesized by firstly mixing titanium isopropoxide and K3Ti5NbO14 nanobelt, and then calcinating at 500 &#176;C in air using urea as the nitrogen source. The samples were analyzed by X-ray diffraction pattern (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Vis absorption spectroscopy and X-ray photoelectron spectroscopic (XPS) spectra. Anatase TiO2 nanoparticles were closely deposited on the surface of K3Ti5NbO14 nanobelt to form a nanoscale heterojunction structure favorable for the separation of photogenerated charge carriers. Meanwhile, the nitrogen atoms were mainly doped in the crystal lattices of TiO2, resulting in the increased light harvesting ability to visible light region. The photocatalytic performance was evaluated by the degradation of methylene blue (MB) under visible light irradiation. The enhanced photocatalytic activity of NTNT was ascribed to the combined effects of morphology engineering, N doping and the formation of heterojunction. A possible photocatalytic mechanism was proposed based on the experimental results