Regulating iron center by defective MoS2 for superior Fenton-like catalysis in water purification: The key role of surface interaction and superoxide radical in accelerating metal redox-cycling.

Transition metals exhibit high reactivity for Fenton-like catalysis in environmental remediation, but how to save consumption and reduce pollution is of great interest. In this study, rationally designed defect-engineered Fe@MoS2 (Fe@D-MoS2) was prepared by incorporating reactive iron onto structural defects generated from the chemical acid-etching, aiming to improve the energetic consumption of the catalyst in Fenton-like applications. Morphological and structural properties were elucidated in details, the Fenton-like reactivity was evaluated with five phenolic contaminants for oxidant activation, radical generation and environmental remediation. Compared to Fe@MoS2, Fe@D-MoS2 exhibited a 18.9-fold increase in phenol degradation (0.09 versus 1.79 min-1). Quenching experiments, electron paramagnetic resonance tests and electrochemical measurements revealed the dominant sulfate and superoxide radicals. Rendered by strong metal-substrate surface and electronic interactions from regulated chemical environment and coordination structure, the inert ≡ Fe(III) was reduced to the reactive ≡ Fe(II) accompanied by the ≡ Mo(IV) oxidation to ≡ Mo(V) in MoS2 lattice, with adjacent sulfur serving as the key electron transfer bridge. Therefore, this work shows that the incorporation of reactive centers is able to boost two-dimensional sulfide materials for environmental catalysis applications.

Thermodynamic Analysis of n-Nonadecane (C19H40)/1-Octadecanol (C18H37OH) Blends.

The article delves into the intricate phase transitions of 1-Octadecanol and n-Nonadecane within a binary system, unveiling dynamic structural changes under varying conditions. Through Fourier transform infrared (FTIR) analysis, specific molecular vibrations were identified, shedding light on the molecular composition and interactions. The study highlights the challenges in detecting subtle phase transitions and emphasises the individuality of molecular behaviours in closely related compounds. The findings underscore the complexity of phase transitions in binary systems and advocate for a nuanced approach to studying molecular structures and behaviours.

Humic substances mediated superior photochemical pollutant conversion on defective TiO2 in environmentally relevant matrices: The key roles of oxygen vacancy in surface interactions, oxidant activation and radical generation.

Ubiquitous humic substances usually exhibit strong interfering effects on target pollutant removal in advanced water purification. This work aims to develop a photochemical conversion system on the nonstoichiometric TiO2 for pollutant removal in environmentally relevant matrices. In this synergistic reaction system, the redox-reactive humic substances and defective oxygen vacancies can serve as the organic electron transfer mediator and the key surface reactive sites, respectively. This system achieves a superior pollutant degradation in real surface water at low oxidant concentrations. Reactive oxygen vacancies on the TiO2 surface and sub-surface are of considerable interest for this photochemical reaction system. By engineering defective oxygen vacancies on high-energy {001} polar facet, the surface and electronic interactions between tailored TiO2 and humic substances are greatly strengthened for the promoted electron transfer and oxidant activation. Rendered by the strong surface affinity and molecular activation, defective oxygen vacancies thermodynamically and dynamically promote reactive chain reactions for free radical formation, including the selective O2 reduction to ·O2- and the H2O2 activation to ·OH. Our findings take new insights into environmental geochemistry, and provide an effective strategy to in-situ boost the humic substances-mediated water purification without secondary pollution. ENVIRONMENTAL IMPLICATION: Humic substances are widely distributed in aquatic environment, thus playing important roles in environmental geochemistry. For example, humic substances can achieve good surface adsorption through electrostatic adsorption, ligand exchange and electronic interactions with typical TiO2 to form reactive ligand-metal charge transfer complexes for pollutant degradation. Inspired by the unique properties of surface and sub-surface oxygen vacancies, the defective TiO2 was designed to refine the humic substances-mediated photochemical reactions. A superior reactivity was measured for pollutant degradation. Our findings provide an effective strategy to boost naturally photochemical decontamination in environmentally relevant matrices.

Impact of NOx and NH3 addition on toluene oxidation over MnOx-CeO2 catalyst.

An increasing number of industries remove toluene from flue gas by the existing NH3-selective catalytic reduction (NH3-SCR) units. A thorough probe into the impact of NOx and NH3 addition on toluene oxidation is imperative but still lacks a unified understanding. In this work, NH3-SCR reactants are found to inhibit the toluene oxidation process over the MnOx-CeO2 catalyst below 200 °C. The competitive adsorption between NH3-SCR reactants and toluene, the NO2 adsorption state, and carbon deposition are emphasized to play important roles in this deactivation. Within the NO2 adsorption states, only the adsorbed NO2 can enhance the toluene oxidation. The formed nitrate species (NO3-) on the surface is inactive. NO2 adsorption is the weakest among the reactants with the smallest adsorption energy of -0.42 eV, restricting its promotion on toluene oxidation. NO and N2O are both demonstrated to be inefficient to oxidize toluene. Meanwhile, MnOx-CeO2 catalyst suffers from serious acetonitrile and benzonitrile poisoning. The amount of nitrile species accounts for ~95% of total carbon deposition, while no simple substance carbon (C) can be generated from CO disproportionation. Special care should be considered towards the formation of environmentally hazardous benzamide in the off-gas from the simultaneous NOx and toluene removal process.

Pollution evaluation and children's multimedia exposure of atmospheric arsenic deposition in the Pearl River Delta, China.

The populous Pearl River Delta (PRD) region in China suffers from serious air arsenic (As) pollution. The objective of this study was to explore the pollution situation of atmospheric arsenic deposition in the PRD region, and to evaluate the associated multimedia daily intake in children. The average deposition flux was 3921.7 µg/m2/year during the 2016-2017, and the pollution situation was even worse than that in 2015. A continuously increasing trend of arsenic atmospheric deposition was found. The bioaccessibility of As in the settled dust was determined as about 22% by a physiologically based extraction test (PBET). After corrected with the bioaccessibilities of As in the settled dust and food items, the geometry means (GM) value of daily uptake through multimedia ingestion of produce (dust and diet) originated from arsenic atmospheric deposition was 0.23 µg/kg/day for 1- to 6-year-old children. The contribution of the non-dietary oral exposure (settled dust) was negligible and just accounted for only 0.01% of the daily uptake. This estimated value was much lower than those in the literatures, in which the bioaccessibility of As was not taken into account, concluding that the role of the settled dust in the total daily intake may have been overestimated previously. Milk, eggs and freshwater fish were the dominant pathways for children to intake the products derived from atmospheric arsenic deposition. There still be a concern about the high non-carcinogenic and carcinogenic risk by long-term multimedia ingestion. Special care should be considered toward the emission sources of air arsenic, including the coal combustion from industries and construction dust, etc., to reduce the negative effect of air arsenic in children.

N2O inhibition by toluene over Mn-Fe spinel SCR catalyst.

Co-removal of toluene in NH3-SCR unit over Mn based catalysts is desirable but still faces the big challenge of byproduct greenhouse gas N2O. In this work, the impacts of toluene on N2O formation mechanism was studied. The main N2O formation pathways in NH3-SCR over Mn-Fe spinel were NH3 oxidation and non-catalytic selective reduction (NSCR), in which NSCR dominated below 250 °C. The N2O from NSCR through both Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) mechanisms was confirmed. And the E-R mechanism was dominant at 200 °C. Toluene was effectively co-removed with NOx with the advantage of N2O inhibition. Toluene suppressed N2O generation from both NH3 oxidation and NSCR. NH3 oxidation by gaseous O2 and catalyst surface oxygen was all limited by toluene, resulting in less adsorbed NH that was further proved by the larger energy barriers of NH3*→NH2* and NH2*→NH* on toluene pre-adsorbed catalyst surface. NO oxidation was also limited, suppressing the generation of adsorbed NO3-. Due to the inhibition of NH3 and NO activation to key intermediates NH and NO3-, respectively, the N2O generation from E-R route was slightly decreased in the presence of toluene, while that from L-H route was completely prohibited at 200 °C.

Meteorological variations impeded the benefits of recent NOx mitigation in reducing atmospheric nitrate deposition in the Pearl River Delta region, Southeast China.

The trends and variability of atmospheric nitrogen deposition in the Pearl River Delta (PRD) region for the period 2008-2017 were investigated by integrating ground- and satellite-based observations and a chemical transport model, in order to gauge the effects of emission reductions and meteorological variability. We show that dry deposition observation of oxidized nitrogen decreased at the rate of 2.4% yr-1 for a moderate reduction in NOx emissions by 27% in the past decade, while reduced nitrogen presented an increase at the rate of 2.3% yr-1 despite no regulated interventions for NH3 emissions, which is likely related to changes in atmospheric gas-particle partitioning of NH3 as reductions in SO2 and NOx emissions. These results coincide with the trends in ground-level concentrations of oxidized and reduced nitrogen compounds in the atmosphere during 2008-2017. The changes in annual deposition fluxes of total oxidized and reduced nitrogen are not statistically significant trends and largely related with the inter-annual variability in their corresponding wet depositions, which reflects combined effects of variability in precipitation amount, and changes in atmospheric nitrogen compounds which dominates wet deposition of the oxidized and reduced forms. The meteorological conditions can mask 34% and 25% decrease in total oxidized and reduced nitrogen deposition on the decadal timescale, respectively. We conclude that meteorology-driven variability probably have masked the full response of oxidized nitrogen deposition to NOx emissions reduction. Our results also imply that persistent and integrated emission control strategies on NOx and NH3 are needed to effectively reduce total nitrogen deposition fluxes towards the critical limit in the PRD region.

Projections of long-term human multimedia exposure to metal(loid)s and the health risks derived from atmospheric deposition: A case study in the Pearl River Delta region, South China.

This is one of a limited number of studies that investigates multimedia exposure to metal(loid)s and the related human health risks caused by atmospheric deposition in China and Asia. The aggregate multimedia human exposure included the accidental ingestion and dermal adsorption of soil and surface water, as well as the intake of grains, fruits, vegetables, meats and eggs, milk and dairy products, and freshwater fish. The values and variabilities of atmospheric deposition and exposure factors were identified as two major uncertainty sources. The annual variations in wet and bulk deposition were propagated from the variabilities of particulate matter (PM) × precipitation and the linear regressed coefficients of flux~PM × precipitation, and the annual variation in dry deposition was propagated by subtracting the wet deposition from the bulk deposition. The variabilities in the exposure factors were updated based on the latest published regional data. Long-term atmospheric deposition was identified as a vital source of Cd contamination in surface soil and freshwater bodies and As accumulation in freshwater fish. The noncarcinogenic (NC) risk probabilities caused by Cd were the highest, followed by As. The overall uncertainties related to the NC risk probabilities were much lower for both adults and 6- to 17-year-old children/adolescents, while those related to the carcinogenic risk (CR) probabilities were much lower for 2- to 5-year-old children and 6- to 17-year-old children/adolescents. Our results could help infer the cobenefits due to the current regional air pollution control policy.

Wet and dry deposition fluxes of heavy metals in Pearl River Delta Region (China): Characteristics, ecological risk assessment, and source apportionment.

The atmospheric deposition of heavy metals poses serious risks to the ecological system and human health. To advance our knowledge of atmospheric dry/wet heavy metal deposition in the PRD region, monthly fluxes were examined based on soluble/insoluble fractions of five heavy metal elements (Cu, Pb, Cd, Cr and Zn) in samples collected from January 2014 to December 2015 at Guangzhou (urban) and Dinghushan (suburban) sites. The ratios of wet/dry deposition fluxes indicated that heavy metal deposition was governed by wet deposition rather than dry deposition in the PRD region. Affected by the shifting of the Asian monsoon, wet deposition fluxes exhibited significant seasonal variation between summer monsoon seasons (April to September) and winter monsoon seasons (October to February) in this region. Cd was classified as an extremely strong potential ecological risk based on solubility and the Hakanson ecological risk index. Source contributions to wet deposition were calculated by PMF, suggesting that dust, biomass burning, industries, vehicles, long-range transport and marine aerosol sources in Guangzhou, and Zn fertilizers, marine aerosol sources, agriculture, incense burning, biomass burning, vehicles and the ceramics industry in Dinghushan, were the potential sources of heavy metals.