Trace Iron as single-electron shuttle for interdependent activation of peroxydisulfate and HSO3-/O2 enables accelerated generation of radicals.

The generation of reactive oxygen species generally requires initiators in various environmental remediation processes, which necessitates high dosage of activators and downstream treatment for eliminating the accumulation of deactivated catalysts. Herein, a coupled process was constructed using trace iron for simultaneously activating HSO3-/O2 system and peroxydisulfate (PDS) oxidation system, where the iron ions (2 mg/L) transferred single-electron from the former system to the latter due to the moderate redox potential (Fe3+/Fe2+, +0.77 V) between the potentials of SO3·-/HSO3- (+0.63 V) and PDS/SO4·- (+2.01 V). Hence, the phenol degradation quickly occurred at a first-order kinetic constant of k1=0.223 min-1 due to the accelerated generation of sulfate radical (SO4·-) and hydroxyl radical (·OH) in the process. The k1 value was almost 6-fold of that in the deoxygenated condition (0.040 min-1). Density function theory reveals that the single electron shuttle spatially separates the electron-donating activation of HSO3- and electron-accepting activation of PDS, while avoiding the "mutual-annihilation" of HSO3- and S2O82- via direct two-electron transfer. Finally, utilizing the in-situ generated electron-shuttle (dissolved iron from cast iron pipe), the HSO3-/PDS reagent could efficiently inactivate the chlorine-resistant pathogens and inhibits biofilm regrowth inside the distribution systems at regular intervals or infectious disease outbreak in a neighborhood.

Nitrogen and phosphorous recycling from human urine by household electrochemical fixed bed in sparsely populated regions.

Decentralized treatment of human urine in sparsely populated regions could avoid the problem of sewage collection in traditionally centralized treatment schemes and simultaneously utilize the recovered N/P fertilizer in-situ to nurture gardens. Herein, an integrated electrochemical fixed bed packed with divided magnesite and carbon zones was constructed for the pretreatment of human urine, followed by the recovery of 95.0% NH4+ and 85.8% PO43- via struvite precipitation and NH3 volatilization as well as the on-site employment of the produced struvite as fertilizer. In the process, the acid/base zones created by electrochemical water splitting dissolved the magnesite filler as the Mg2+ source of struvite, further creating an ideal pH environment for struvite precipitation and NH3 volatilization in the effluent. Without the need to control solution pH by chemical addition, the system can resist impacts from changes in water quality by adjustment of the current density and flow rate, indicating its great potential for automatic operation. Life cycle assessment indicated that the on-site employment of produced struvite avoids the long-distance fertilizer transportation required for fertilization, thus reducing carbon emission by a hundred million tons per year if the household facility is driven by clean electricity.

pH-Independent Production of Hydroxyl Radical from Atomic H*-Mediated Electrocatalytic H2O2 Reduction: A Green Fenton Process without Byproducts.

Hydroxyl radical (•OH) can hydroxylate or dehydrogenate organics without forming extra products and is thereby expediently applied in extensive domains. Although it can be efficiently produced through single-electron transfer from transition-metal-containing activators to hydrogen peroxide (H2O2), narrow applicable pH range, strict activator/H2O2 ratio requirement, and byproducts that are formed in the mixture with the background matrix necessitate the need for additional energy-intensive up/downstream treatments. Here, we show a green Fenton process in an electrochemical cell, where the electro-generated atomic H* on a Pd/graphite cathode enables the efficient conversion of H2O2 into •OH and subsequent degradation of organic pollutants (80% efficiency). Operando liquid time-of-fight secondary ion mass spectrometry verified that H2O2 activation takes place through a transition state of the Pd-H*-H2O2 adduct with a low reaction energy barrier of 0.92 eV, whereby the lone electron in atomic H* can readily cleave the peroxide bridge, with •OH and H2O as products (ΔGr = -1.344 eV). Using H+ or H2O as the resource, we demonstrate that the well-directed output of H* determines the pH-independent production of •OH for stable conversion of organic contaminants in wider pH ranges (3-12). The research pioneers a novel path for eliminating the restrictions that are historically challenging in the traditional Fenton process.

Oxidation of 2,4-dichlorophenol in saline water by unactivated peroxymonosulfate: Mechanism, kinetics and implication for in situ chemical oxidation.

Inorganic and organic pollutants present a hazard to surface and groundwater resources. Peroxymonosulfate (PMS, HSO5-) has received increasing attention for in situ chemical oxidation (ISCO) capable of remediating contaminated sites. Considering that saline waters occur widely in natural environments, it is desirable to evaluate the effect of Cl- on the PMS oxidation of organic compounds. In this study, 2,4-dichlorophenol (2,4-DCP) was used as a model pollutant. At a PMS concentration of 2.0 mM, Cl- concentration of 50 mM, and solution pH of 7.0, 2,4-DCP was completely degraded by PMS in the presence of Cl- (PMS/Cl- system), while PMS alone exhibited almost no reactivity with 2,4-DCP. The degradation of 2,4-DCP was optimized at a solution pH of 8.4 and high concentrations of PMS and Cl-. Quenching experiments and degradation pathway analyses indicated that HClO was responsible for 2,4-DCP oxidation, and HClO was mainly generated by the interaction of Cl- with HSO5-, rather than SO52-. Consequently, the transformation from HSO5- to HClO appeared under a solution pH of 10.0 and was favored in an acidic solution. Given the ambient pH and Cl- concentrations of saline waters, a considerable amount of HClO may be produced by the interaction of PMS with Cl- in the oxidant delivery stage of ISCO processes. Interestingly, H2O2 and peroxydisulfate did not exhibit reactions similar to those of PMS. This research indicated that caution must be exercised when choosing an oxidant for ISCO processes in saline waters.

Enhanced photoelectrocatalytic degradation of bisphenol a by BiVO4 photoanode coupling with peroxymonosulfate.

Peroxymonosulfate (PMS) was introduced into a photoelectrocatalytic (PEC) system with a bismuth vanadate (BiVO4) photoanode to enhance the PEC oxidation of bisphenol A (BPA). With the addition of 5 mM PMS, the degradation efficiency of 10 mg/L BPA was significantly improved from 24.2% to 100.0% within 120 min and the side reaction of O2 evolution was avoided at a potential as low as 0.25 V. The electron spin resonance and radicals quenching results suggested that photogenerated holes instead of SO4•- and OH were primarily responsible for the BPA degradation. To further explore the role of PMS, a photocatalytic fuel cell with the structure of BiVO4 (photoanode)|10 mg/L BPA|proton exchange membrane (separator)|5 mM PMS|Pt (cathode) was constructed and demonstrated that PMS played a key role as electrons acceptor instead of the precursor of SO4•-. The PEC tests including open-circuit potential, linear sweep voltammetry and electrochemical impedance spectroscopy indicated that a more efficient separation of photogenerated charges was achieved in the PEC process with the help of PMS, thus generating more photogenerated holes for enhanced BPA degradation. This work may provide a novel way to enhance the separation of photogenerated charges at the photoanode.

Mn assisted electrochemical generation of two-dimensional Fe-Mn layered double hydroxides for efficient Sb(V) removal.

In this work, MnSO4 was added into iron electrocoagulation (EC) system to enhance the removal efficiency of pentavalent antimony (Sb(V)) from wastewater. 99% of Sb(V) was removed after 10min in the presence of 0.5mM MnSO4, which was higher than that of without the addition of MnSO4 (72%). In addition, Mn2+ can be removed simultaneously and did not cause secondary pollution. The influencing factors such as MnSO4 concentration, initial pH and current density were investigated. It was found that high concentration of MnSO4, acid or neutral pH conditions and current density of 5-10mAcm-2 benefited the removal of Sb(V). The flocs generated in the EC process were analyzed by in-situ Raman, XRD and TEM. The results showed that 2-dimensional Fe-Mn layered double hydroxides (LDHs) were formed. Fe-Mn LDHs possess large internal surface areas with amphoteric surface hydroxyl groups, which are beneficial to the sorption of Sb(V). FT-IR and XPS results indicated that the removal of Sb(V) was mainly achieved through adsorption onto the surface of the Fe-Mn LDHs. The obtained results may provide meaningful insights into understanding the mechanisms of Fe coagulation and improving the efficiency of pollutants removal in Fe EC systems.

Cyanide oxidation by singlet oxygen generated via reaction between H2O2 from cathodic reduction and OCl(-) from anodic oxidation.

Cyanide is widely present in electroplating wastewater or metallurgical effluents. In the present study, the electrochemical destruction of cyanide with various anode and cathode compositions under alkaline conditions was investigated. The results indicated that the electrochemical system using RuO2/Ti as anode and activated carbon fiber (ACF) as cathode in the presence of sodium chloride was efficient for the cyanide removal. In this system, in situ generation of HClO by anodic oxidation of Cl(-) at RuO2/Ti anode occurred with the H2O2 generation by O2 reduction at ACF cathode. As confirmed by the electron spin resonance technique, the reaction between HClO and H2O2 led to the generation of singlet oxygen, which was responsible for the cyanide removal. Further experiment indicated that the cyanide removal efficiency increased with the increase of the current density or the sodium chloride concentration. Cyanate was identified as main product in the system. Besides, the system exhibited good stability for the cyanide removal, which was beneficial to its practical application.

Enhanced Photoelectrocatalytic Decomplexation of Cu-EDTA and Cu Recovery by Persulfate Activated by UV and Cathodic Reduction.

In order to enhance Cu-EDTA decomplexation and copper cathodic recovery via the photoelectrocatalytic (PEC) process, S2O8(2-) was introduced into the PEC system with a TiO2/Ti photoanode. At a current density of 0.2 mA/cm(2) and initial solution pH of 3.0, the decomplexation ratio of Cu complexes was increased from 47.5% in the PEC process to 98.4% with 5 mM S2O8(2-) addition into the PEC process (PEC/S2O8(2-)). Correspondently, recovery percentage of Cu was increased to 98.3% from 47.4% within 60 min. It was observed that nearly no copper recovery occurred within the initial reaction period of 10 min. Combined with the analysis of ESR and electrochemical LSV curves, it was concluded that activation of S2O8(2-) into SO4(·-) radicals by cathodic reduction occurred, which was prior to the reduction of liberated Cu(2+) ions. UV irradiation of S2O8(2-) also led to the production of SO4(·-). The generated SO4(·-) radicals enhanced the oxidation of Cu-EDTA. After the consumption of S2O8(2-), the Cu recovery via cathodic reduction proceeded quickly. Acidification induced by the transformation of SO4(·-) to OH· favored the copper cathodic recovery. The combined PEC/S2O8(2-) process was also efficient for the TOC removal from a real electroplating wastewater with the Cu recovery efficiency higher than 80%.

[Clinical application of micro-implant anchorage for treatment of scissors bite on one-side posterior teeth].

OBJECTIVE: To evaluate the efficiency of micro-implant anchorage (MIA) for posterior teeth intruded and the result of the treatment of scissors bite on one-side posterior teeth. METHODS: The study included 3 females and 1 male. All the overextruding upper posterior teeth were intruded by the MIA. The micro-implant screws were inserted into the buccal and lingual alveolar hone of the maxillary posterior teeth or the buccal alveolar hone of mandibular posterior teeth. About 0.833 N force was used to intrude the overgrowthing upper posterior teeth, and about 0.559 N force was used to draw buecally the low posterior teeth tilting lingually. RESULTS: The overextruding upper posterior teeth were intruded 2.0 mm on average, the low posterior teeth tilting lingually were upreared buccally. All the MIA screws kept stable during the treatment, but there was a slight inflammation around the implant screws. CONCLUSION: MIA could be used as an efficient method to correct scissors bite on one-side posterior teeth with intruding overgrowth upper posterior teeth, or uprearing buccally the tilting low posterior teeth.