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

Molecular Oxygen-Mediated Minisci-Type Radical Alkylation of Heteroarenes with Boronic Acids

The carbon–carbon bond formation via autoxidation of organoboronic acid using 1 atm of O₂ is achieved in a simple, clean, and green fashion. The approach allows a technically facile and environmentally benign access to structurally diverse heteroaromatics with medicinally privileged scaffolds. The strategy also displays its practicality and sustainability in the resynthesis of marketed drugs Crestor and pyrimethamine

Hydrothermal Carbon-Mediated Fenton-Like Reaction Mechanism in the Degradation of Alachlor: Direct Electron Transfer from Hydrothermal Carbon to Fe(III)

As Fenton systems suffer from the undesirable Fe­(III)/Fe­(II) cycle, great efforts were made to realize the effective reduction of Fe­(III) to Fe­(II). The effects of hydrothermal carbon (HTC) on the Fe­(III)/H₂O₂ Fenton-like reaction and the subsequent degradation of alachlor in water was systematically investigated, and the results indicated that HTC could enhance alachlor degradation in Fe­(III)/H₂O₂ by promoting the Fe­(III)/Fe­(II) cycle via electron transfer from HTC to Fe­(III) ions. The apparent alachlor degradation rate constant in the HTC-G/Fe­(III)/H₂O₂ system (7.02 × 10^–2 min^–1) was about 3 times higher than that in the Fe­(III)/H₂O₂ system (2.25 × 10^–2 min^–1). The electron spin resonance spectra analysis revealed that HTC consists of abundant carbon-centered persistent free radicals to act as the electron donor. Meanwhile, the hydroxyl groups on the surface of HTC also played an important role in the enhanced alachlor degradation because the decrease in the surface hydroxyl groups on HTC significantly decreased the degradation of alachlor. On the basis of these results, an Fe­(III) complex with surface hydroxyl groups on HTC was proposed to favor the electron transfer from the hydroxyl groups to Fe­(III), and then, the simultaneously produced Fe­(II) could accelerate the catalytic decomposition of H₂O₂ to facilitate alachlor degradation. These findings shed new light on the possible roles of carbon materials in a natural aquatic environment and provide a new pathway for environmental pollutant control and remediation of organic contaminants by HTC

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

Phosphate Shifted Oxygen Reduction Pathway on Fe@Fe₂O₃ Core–Shell Nanowires for Enhanced Reactive Oxygen Species Generation and Aerobic 4‑Chlorophenol Degradation

Phosphate ions widely exist in the environment. Previous studies revealed that the adsorption of phosphate ions on nanoscale zerovalent iron would generate a passivating oxide shell to block reactive sites and thus decrease the direct pollutant reduction reactivity of zerovalent iron. Given that molecular oxygen activation process is different from direct pollutant reduction with nanoscale zerovalent iron, it is still unclear how phosphate ions will affect molecular oxygen activation and reactive oxygen species generation with nanoscale zerovalent iron. In this study, we systematically studied the effect of phosphate ions on molecular oxygen activation with Fe@Fe₂O₃ nanowires, a special nanoscale zerovalent iron, taking advantages of rotating ring disk electrochemical analysis. It was interesting to find that the oxygen reduction pathway on Fe@Fe₂O₃ nanowires was gradually shifted from a four-electron reduction pathway to a sequential one-electron reduction one, along with increasing the phosphate ions concentration from 0 to 10 mmol·L^–1. This oxygen reduction pathway change greatly enhanced the molecular oxygen activation and reactive oxygen species generation performances of Fe@Fe₂O₃ nanowires, and thus increased their aerobic 4-chlorophenol degradation rate by 10 times. These findings shed insight into the possible roles of widely existed phosphate ions in molecular oxygen activation and organic pollutants degradation with nanoscale zerovalent iron

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

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

Efficient Visible Light-Driven Photocatalytic Degradation of Pentachlorophenol with Bi₂O₃/TiO_2–<i>x</i>B_<i>x</i>

In this study, a new TiO₂-based photocatalyst with both B doping and Bi₂O₃ coupling (Bi₂O₃/TiO_2–<i>x</i>B_<i>x</i>) was synthesized to degrade pentachlorophenol under visible light (λ > 420 nm) irradiation. The resulting Bi₂O₃/TiO_2–<i>x</i>B_<i>x</i> sample exhibited much higher photocatalytic performance than the counterparts with only B doping or Bi₂O₃ coupling or pure TiO₂. This is because B doping could result in more visible light absorption to produce more photogenerated electron–hole pairs, while Bi₂O₃ coupling could favor the separation and transfer of photoinduced charge carriers to inhibit their recombination. We interestingly found that the visible light-driven degradation of pentachlorophenol was mainly attributed to photogenerated holes and ·O₂^– other than ·OH as reported previously because the hybridization of B 2p orbital and O 2p orbital could elevate the VB edge of Bi₂O₃/TiO_2–<i>x</i>B_<i>x</i> as compared to that of pure TiO₂ and thus lower the oxidation ability of photogenerated holes, blocking the pathway of photogenerated holes induced oxidation of surface OH^– and water to generate ·OH. The intermediates during the PCP photodegradation were systematically analyzed, ruling out the existence of high toxic polychlorinated dibenzo-<i>p</i>-dioxins and polychlorinated dibenzofurans. These results reveal that the visible light-driven photocatalytic degradation of PCP over Bi₂O₃/TiO_2–<i>x</i>B_<i>x</i> is an effective and green method to remove highly toxic halogenated aromatic compounds

Design of a Highly Efficient and Wide pH Electro-Fenton Oxidation System with Molecular Oxygen Activated by Ferrous–Tetrapolyphosphate Complex

In this study, a novel electro-Fenton (EF) system was developed with iron wire, activated carbon fiber, and sodium tetrapolyphosphate (Na₆TPP) as the anode, cathode, and electrolyte, respectively. This Na₆TPP–EF system could efficiently degrade atrazine in a wide pH range of 4.0–10.2. The utilization of Na₆TPP instead of Na₂SO₄ as the electrolyte enhanced the atrazine degradation rate by 130 times at an initial pH of 8.0. This dramatic enhancement was attributed to the formation of ferrous–tetrapolyphosphate (Fe­(II)–TPP) complex from the electrochemical corrosion (ECC) and chemical corrosion (CC) of iron electrode in the presence of Na₆TPP. The Fe­(II)–TPP complex could provide an additional molecular oxygen activation pathway to produce more H₂O₂ and ^•OH via a series single-electron transfer processes, producing the Fe­(III)–TPP complex. The cycle of Fe­(II)/Fe­(III) was easily realized through the electrochemical reduction (ECR) process on the cathode. More interestingly, we found that the presence of Na₆TPP could prevent the iron electrode from excessive corrosion via phosphorization in the later stage of the Na₆TPP–EF process, avoiding the generation of iron sludge. Gas chromatograph-mass spectrometry, liquid chromatography-mass spectrometry, and ion chromatography were used to investigate the degradation intermediates to propose a possible atrazine oxidation pathway in the Na₆TPP–EF system. These interesting findings provide some new insight on the development of a low-cost and highly efficient EF system for wastewater treatment in a wide pH range

Dramatically Enhanced Aerobic Atrazine Degradation with Fe@Fe₂O₃ Core–Shell Nanowires by Tetrapolyphosphate

In this study, the effects of an inorganic ligand tetrapolyphosphate on the molecular oxygen activation and the subsequent aerobic atrazine degradation by Fe@Fe₂O₃ core–shell nanowires were investigated systematically at a circumneutral to alkaline pH range (pH 6.0–9.0). We interestingly found that the addition of tetrapolyphosphate could enhance the aerobic atrazine degradation rate 955 times, which was even 10 times that of the traditional organic ligand ethylenediamine tetraacetate. This tetrapolyphosphate induced dramatic aerobic atrazine degradation enhancement could be attributed to two factors. One was that the presence of tetrapolyphosphate strongly suppressed hydrogen evolution from the reduction of proton by Fe@Fe₂O₃ core–shell nanowires through proton confinement, leaving over more electrons for the reduction of Fe­(III) to Fe­(II) and the subsequent molecular oxygen activation. The other was that the complexation of tetrapolyphosphate with ferrous ions not only guaranteed enough soluble Fe­(II) for Fenton reaction, but also provided another route to produce more •OH in the solution via the single-electron molecular oxygen reduction pathway. We employed gas chromatography–mass spectrometry and liquid chromatography–mass spectrometry to identify the atrazine degradation intermediates and proposed a possible aerobic atrazine degradation pathway. This study not only sheds light on the promotion effects of ligands on the molecular oxygen activation by nanoscale zerovalent iron, but also offers a facile and green iron-based method for the oxidative atrazine removal