Electronic and Band Structure Tuning of Ternary Semiconductor Photocatalysts by Self Doping: The Case of BiOI

Foreign nonmetal or metal element doping has been widely used to tailor the electronic and band structures of wide band gap binary oxide semiconductor photocatalysts, extending their absorption edges into the visible light range for better utilization of solar light. Besides doping with foreign elements, self-doping can also tune the electronic and band structures of semiconductor photocatalysts but only limited to binary metal oxides, such as oxygen-deficient TiOx (x 2 with discrete bands, confirming this is a novel electronic and band structure tuning method. This successful band structure tailoring example of ternary semiconductors suggests the self-doping strategy could be general to develop novel visible light driven ternary photocatalysts with enhanced performances

Efficient Visible Light Driven Photocatalytic Removal of RhB and NO with Low Temperature Synthesized In(OH)_<i>x</i>S_<i>y</i> Hollow Nanocubes: A Comparative Study

In this work, we report that RhB and NO could be effectively removed under visible light with hollow In(OH)xSy nanocubes fabricated at a low temperature of 80 °C. The photocatalytic experiments revealed that these low temperature synthesized hollow In(OH)xSy nanocubes were more efficient than P25 and In(OH)xSy counterpart hydrothermally synthesized at 180 °C (In(OH)xSy-180). The porous structures, larger surface area, and new valence band of low temperature synthesized hollow In(OH)xSy nanocubes were thought to account for their superior photocatalytic activity. Among all the In(OH)xSy samples, the one with original S/In ratio of 0.500 in synthetic solution exhibited the highest photocatalytic removal efficiencies of RhB, while the other with original S/In ratio of 1.000 removed NO most efficiently. We systematically studied the photocatalytic process of RhB on In(OH)xSy and analyzed their different photocatalytic performances on removing RhB and NO. This study reveals that these hollow In(OH)xSy nanocubes are promising for environmental remediation

Selective Nonaqueous Synthesis of C−Cl-Codoped TiO₂ with Visible-Light Photocatalytic Activity

We demonstrate a low-temperature, one-pot nonaqueous sol−gel method for the selective synthesis of C−Cl-codoped TiO2 with different crystal phases and morphologies, including anatase nanocrystals, rutile nanorods, and a mixed phase with anatase and rutile nanocrystals. The synthetic protocol employed titanium tetrachloride as the titanium precursor and the mixture of chloroform and ethanol as the solvent. The as-prepared C−Cl-codoped TiO2 powders were characterized in detail by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, high-resolution TEM, X-ray photoelectron spectroscopy, and UV−vis diffuse reflectance spectroscopy. We evaluated their photocatalytic performances by the degradation of rhodamine B (RhB) solution under visible-light irradiation. On the basis of the above measurements, the doping process and dopant origin of C−Cl-codoped TiO2 as well as the formation mechanism of different phases were analyzed. We concluded that the tuning of the chloroform volume in the reaction system could easily control the final TiO2 phase and realize the controllable C−Cl codoping. The chlorine dopant in C−Cl-codoped TiO2 might originate from TiCl4, not from the decomposition of chloroform. We also analyzed the C−Cl-codoping modes and their influence on the visible-light photocatalytic activity of the final C−Cl-codoped TiO2. This study provides a facile, nonaqueous approach to synthesize tunable C−Cl-codoped TiO2 with enhanced visible-light-driven photocatalytic activity

Synthesis and Enhanced Cr(VI) Photoreduction Property of Formate Anion Containing Graphitic Carbon Nitride

In this study, we report on the synthesis of formate anion containing graphitic carbon nitride and its dramatically enhanced activity and stability on Cr­(VI) photoreduction under visible light. We found that the incorporated formate anions could not only trap photogenerated holes to produce more photogenerated electrons, but also change two-step superoxide ions mediated indirect reduction to one-step direct photogenerated electron reduction of Cr­(VI) over graphitic carbon nitride under visible light through inhibiting surface dioxygen adsorption and thus enhance Cr­(VI) photoreduction. This study could not only develop a novel strategy to improve the Cr­(VI) photoreduction activity and stability of semiconductors but also shed light on the deep understanding of the relationship between intrinsic structure and Cr­(VI) photoreduction activity of semiconductor photocatalysts

Efficient Visible Light Photocatalytic Oxidation of NO on Aerosol Flow-Synthesized Nanocrystalline InVO₄ Hollow Microspheres

In this study, aerosol flow-synthesized (AFS) nanocrystalline InVO4 hollow microspheres (AFS-InVO4) were used to oxidize gaseous NO at indoor air level under visible light and compared with hydrothermally synthesized InVO4 counterpart powder. Results revealed that the AFS-InVO4 hollow spheres exhibited higher photocatalytic activity than the hydrothermally synthesized counterpart. The photocatalytic activity enhancement could be attributed to the large surface area and special hollow structures, which were favorable for the diffusion of intermediates and the deactivation inhibition of photocatalyst during the photocatalytic reaction. Fourier transform infrared spectroscopy results confirmed the generation of nitric acid on the AFS-InVO4 surface during the photocatalysis of NO in the gas phase, suggesting that the oxidation of NO molecules was the major process in this photocatalytic reaction. Multiple runs of the photocatalytic NO removal revealed that the AFS-InVO4 hollow spheres were very stable during photocatalysis. This study presents a promising approach for scaling up industrial production of InVO4 hollow spheres with improved photocatalytic activity for indoor air purification

Generalized Low-Temperature Synthesis of Nanocrystalline Rare-Earth Orthoferrites LnFeO₃ (Ln = La, Pr, Nd, Sm, Eu, Gd)

Rare-earth orthoferrite LnFeO3 nanocrystals were traditionally synthesized at temperatures higher than 700 °C. In this study, we developed a general nanosized heterobimetallic precursors approach for the synthesis of nanocrystalline rare-earth orthoferrite LnFeO3 (Ln = La, Pr, Nd, Sm, Eu, Gd) at 500 °C. The nanosized heterobimetallic precursors were obtained via the reaction between the Ln and Fe oleates synthesized from their corresponding metal nitrates and sodium oleate. Subsequently, the calcination of the nanosized heterobimetallic precursors at a relatively low temperature (500 °C) produced nanocrystalline rare-earth orthoferrites. The precursors and products were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), nitrogen adsorption, thermal analysis (TGA/DSC), and Fourier transform infrared absorption spectroscopy (FT-IR). On the basis of characterization results, we attributed the low temperature formation of nanocrystalline rare-earth orthoferrites to the reduced diffusion distance between the nanosized heterobimetallic precursors. We thought these heterobimetallic precursors ensured the desirable stoichiometry ratio of the orthoferrite products and avoided the formation of garnet. The magnetization features of the orthoferrites were evaluated at room temperature. The M-H curves revealed that EuFeO3 and GdFeO3 exhibit better weak ferromagnetic behavior, corresponding to the antisymmetric-exchange anisotropy. Our method may be extended to prepare other ternary metal oxides at relatively low temperatures

Enhanced Photocatalytic Removal of Sodium Pentachloro­phenate with Self-Doped Bi₂WO₆ under Visible Light by Generating More Superoxide Ions

In this study, we demonstrate that the photo­catalytic sodium penta­chloro­phenate removal efficiency of Bi₂WO₆ under visible light can be greatly enhanced by bismuth self-doping through a simple soft-chemical method. Density functional theory calculations and systematical characterization results revealed that bismuth self-doping did not change the redox power of photo­generated carriers but promoted the separation and transfer of photo­generated electron–hole pairs of Bi₂WO₆ to produce more super­oxide ions, which were confirmed by photocurrent generation and electron spin resonance spectra as well as super­oxide ion measurement results. We employed gas chromatography–mass spectrometry and total organic carbon analysis to probe the degradation and the mineralization processes. It was found that more super­oxide ions promoted the dechlori­nation process to favor the subsequent benzene ring cleavage and the final minerali­zation of sodium penta­chloro­phenate during bismuth self-doped Bi₂WO₆ photo­catalysis by producing easily decomposable quinone intermediates. This study provides new insight into the effects of photo­generated reactive species on the degradation of sodium penta­chloro­phenate and also sheds light on the design of highly efficient visible-light-driven photo­catalysts for chloro­phenol pollutant removal

Nonaqueous Sol−Gel Synthesized Hierarchical CeO₂ Nanocrystal Microspheres as Novel Adsorbents for Wastewater Treatment

Hierarchical CeO2 nanocrystal microspheres were synthesized with a nonaqueous sol−gel method at a low temperature of 120 °C. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and nitrogen sorption measurements. The adsorption performances of hierarchical CeO2 nanocrystal microspheres were tested with the batch removals of typical pollutants of Cr(VI) and rhodamine B from simulated wastewater. It was found that the nanostructured CeO2 could effectively remove Cr(VI) without pH preadjustment. The Freundlich adsorption isotherm was applicable to describe the removal processes. Kinetics of the Cr(VI) removal was found to follow pseudosecond-order rate equation. Furthermore, the as-prepared and Cr(VI)-adsorbed hierarchical CeO2 nanocrystal microspheres were carefully analyzed by X-ray photoelectron spectroscopy (XPS). On the basis of the XPS results, a possible mechanism of Cr(VI) removal with hierarchical CeO2 nanocrystal microspheres was proposed. Moreover, these nonaqueous sol−gel synthesized hierarchical CeO2 nanocrystal microspheres also exhibited remarkable ability to remove rhodamine B, suggesting they are promising absorbents for wastewater treatment

A Free-Radical Cascade Trifluoromethylation/Cyclization of <i>N</i>‑Arylmethacrylamides and Enynes with Sodium Trifluoromethanesulfinate and Iodine Pentoxide

An I2O5-promoted free-radical cascade trifluoromethylation/cyclization of a broad range of N-arylmethacrylamides and enynes with sodium trifluoromethanesulfinate in aqueous medium has been achieved. This strategy allows highly selective access to a variety of CF3-containing oxindoles and pyrrolidines. Electron spin resonance (ESR) studies indicate that atom-transfer processes are involved in this system

Efficient Removal of Heavy Metal Ions with Biopolymer Template Synthesized Mesoporous Titania Beads of Hundreds of Micrometers Size

We demonstrated that mesoporous titania beads of uniform size (about 450 μm) and high surface area could be synthesized via an alginate biopolymer template method. These mesoporous titania beads could efficiently remove Cr­(VI), Cd­(II), Cr­(III), Cu­(II), and Co­(II) ions from simulated wastewater with a facile subsequent solid–liquid separation because of their large sizes. We chose Cr­(VI) removal as the case study and found that each gram of these titania beads could remove 6.7 mg of Cr­(VI) from simulated wastewater containing 8.0 mg·L^–1 of Cr­(VI) at pH = 2.0. The Cr­(VI) removal process was found to obey the Langmuir adsorption model and its kinetics followed pseudo-second-order rate equation. The Cr­(VI) removal mechanism of titania beads might be attributed to the electrostatic adsorption of Cr­(VI) ions in the form of negatively charged HCrO₄^– by positively charged TiO₂ beads, accompanying partial reduction of Cr­(VI) to Cr­(III) by the reductive surface hydroxyl groups on the titania beads. The used titania beads could be recovered with 0.1 mol·L^–1 of NaOH solution. This study provides a promising micro/nanostructured adsorbent with easy solid–liquid separation property for heavy metal ions removal