Heterogeneous Photocatalytic Degradation Kinetic of Gaseous Ammonia Over Nano-TiO_2 Supported on Latex Paint Film

Objective To investigate the photocatalytic degradation of gaseous ammonia in static state by using nano-TiO2 as photoeatalyst supported on latex paint film under UV-irradiation. Methods Experiments were conducted to study the relationship between the initial concentration of ammonia and the degradation products competing to be adsorbed on catalyst surface. Degradation of ammonia and its products were detected by spectrophotometry and catalytic kinetic spectrophotometry, respectively. Results On the one hand, TiO2 catalyst was excellent for degradation of ammonia, and the crystal phase of TiO2, anatase or ruffle, had little effect on degradation of ammonia, but the conversion of ammonia grew with the increase of catalyst content. On the other hand, apparent rate constant and conversion of ammonia decreased with the increase of initial concentration of ammonia, and the photocatalytic degradation reaction followed a pseudo-first-order expression due to-the evidence of linear correlation between -lnC/C0 vs. irradiation time t, but the relationship between initial concentration and the degradation products was not linear in low initial concentration. Conclusion Whether the photocatalytic degradation of ammonia in static state follows a first-order reaction depends on the initial ammonia concentration due to competition in adsorption between reactant and the degradation products.

The magic of integration:Exploring the construction of dithienylethene-based infinite coordination polymers and their synergistic effect for gaseous ammonia probe applications

Infinite coordination polymers are recognized as excellent platform for functionalization.Dithienylethene motifs,which are one of the most attractive functional moieties,were incorporated into an infinite coordination polymer,to deliver a‘‘smart’’porous material that can response to external stimuli.The obtained dithienylethene-based infinite coordination polymers（named Cu-DTEDBA）share the advantages of both infinite coordination polymers（porosity and stability）and dithienylethene motifs（photochromism）.The physical and chemical properties of Cu-DTEDBA were characterized by FTIR,TEM,SEM,XRD,TGA,UV–vis,EDX and BET.Moreover,the combination of dithienylethene and infinite coordination polymers gives rise to a synergistic effect,which induces functional behaviors of ammonia sensor applications.Both open and closed forms of Cu-DTEDBA exhibit distinct colorimetric change upon exposure to gaseous ammonia,which is not observed in dithienylethene free molecules.

Low-temperature conversion of ammonia to nitrogen in water with ozone over composite metal oxide catalyst

As one of the most important water pollutants, ammonia nitrogen emissions have increased year by year, which has attracted people＇s attention. Catalytic ozonation technology, which involves production of ·OH radical with strong oxidation ability, is widely used in the treatment of organic-containing wastewater. In this work, MgO-Co3O4 composite metal oxide catalysts prepared with different fabrication conditions have been systematically evaluated and compared in the catalytic ozonation of ammonia（50 mg/L） in water. In terms of high catalytic activity in ammonia decomposition and high selectivity for gaseous nitrogen, the catalyst with MgO-Co3O4 molar ratio 8：2, calcined at 500°C for 3 hr, was the best one among the catalysts we tested, with an ammonia nitrogen removal rate of 85.2% and gaseous nitrogen selectivity of44.8%. In addition, the reaction mechanism of ozonation oxidative decomposition of ammonia nitrogen in water with the metal oxide catalysts was discussed. Moreover, the effect of coexisting anions on the degradation of ammonia was studied, finding that SO2-4 and HCO-3 could inhibit the catalytic activity while CO2-3 and Br-could promote it. The presence of coexisting cations had very little effect on the catalytic ozonation of ammonia nitrogen. After five successive reuses, the catalyst remained stable in the catalytic ozonation of ammonia.

δ^(15)N-stable isotope analysis of NH_(x): An overview on analytical measurements, source sampling and its source apportionment

Agricultural sources and non-agricultural emissions contribute to gaseous ammonia(NH_(3))that plays a vital role in severe haze formation.Qualitative and quantitative contributions of these sources to ambient PM_(2.5)(particulate matter with an aerodynamic equivalent diameter below 2.5µm)concentrations remains uncertain.Stable nitrogen isotopic composition(δ^(15)N)of NH_(3)and NH_(4)+(δ^(15)N(NH_(3))andδ^(15)N(NH_(4)+),respectively)can yield valuable information about its sources and associated processes.This review provides an overview of the recent progress in analytical techniques forδ^(15)N(NH_(3))andδ^(15)N(NH_(4)+)measurement,sampling of atmospheric NH_(3)and NH_(4)+in the ambient air and their sources signature(e.g.,agricultural vs.fossil fuel),and isotope-based source apportionment of NH_(3)in urban atmosphere.This study highlights that collecting sample that are fully representative of emission sources remains a challenge in fingerprintingδ^(15)N(NH_(3))values of NH_(3)emission sources.Furthermore,isotopic fractionation during NH_(3)gas-to-particle conversion under varying ambient field conditions(e.g.,relative humidity,particle pH,temperature)remains unclear,which indicates more field and laboratory studies to validate theoretically predicted isotopic fractionation are required.Thus,this study concludes that lack of refinedδ^(15)N(NH_(3))fingerprints and full understanding of isotopic fractionation during aerosol formation in a laboratory and field conditions is a limitation for isotope-based source apportionment of NH_(3).More experimental work(in chamber studies)and theoretical estimations in combinations of field verification are necessary in characterizing isotopic fractionation under various environmental and atmospheric neutralization conditions,which would help to better interpret isotopic data and our understanding on NH_(x)(NH_(3)+NH_(4)+)dynamics in the atmosphere.