Practical applications require hydrothermally stable metal−organic frameworks (MOFs). Achieving stable MOFs in the presence of water or humidity is challenging, especially for MOFs with open metals sites (OMSs) due to the high affinity of water molecules toward OMSs. A straightforward solution to tackling this problem is to protect OMSs in the porous structure of MOFs. A facile post-synthetic modification (PSM) method for the synthesis of molecular glycine-doped CuBTC MOF (BTC = benzene-1,3,5-tricarboxylic acid) was developed in this study. Developed materials, i.e., Gly-CuBTC MOFs, were characterized using various characterization techniques and evaluated using single-component gas (CO 2 and N 2) adsorption and dynamic water vapor adsorption experiments. The economical dopant of molecular glycine with amine and a carboxyl group was found to be able to saturate OMSs in the parent CuBTC MOF, leading to improved hydrothermal stability and CO 2 :N 2 selectivity. It was also found that the adsorption capacity, CO 2 :N 2 selectivity, and hydrothermal stability of Gly-CuBTC MOFs depend on the percentage of saturation of OMSs in the parent MOF.
Abstract. Hong Kong, as one of the densely populated metropolises in East Asia, has
been suffering from severe photochemical smog in the past decades, though
the observed nitrogen oxides (NOx) and total volatile organic compounds (TVOCs) were significantly reduced. This study, based on the observation
data in the autumns of 2007, 2013 and 2016, investigated the photochemical
ozone (O3) formation and radical chemistry during the three sampling
periods in Hong Kong with the aid of a photochemical box model incorporating
the Master Chemical Mechanism (PBM–MCM). While the simulated locally
produced O3 remained unchanged (p=0.73) from 2007 to 2013, the
observed O3 increased (p < 0.05) at a rate of 1.78 ppbv yr−1 driven
by the rise in regionally transported O3 (1.77±0.04 ppbv yr−1).
Both the observed and locally produced O3 decreased (p < 0.05)
from the VOC sampling days in 2013 to those in 2016 at a rate of
-5.31±0.07 and -5.52±0.05 ppbv yr−1, respectively.
However, a leveling-off (p=0.32) was simulated for the regionally
transported O3 during 2013–2016. The mitigation of autumn O3
pollution in this region was further confirmed by the continuous monitoring
data, which have never been reported. Benefiting from the
air pollution control measures taken in Hong Kong, the local O3
production rate decreased remarkably (p < 0.05) from 2007 to 2016,
along with the lowering of the recycling rate of the hydroxyl radical (OH).
Specifically, VOCs emitted from the source of liquefied petroleum gas (LPG)
usage and gasoline evaporation decreased in this decade at a rate of
-2.61±0.03 ppbv yr−1, leading to a reduction of the O3
production rate from 0.51±0.11 ppbv h−1 in 2007 to 0.10±0.02 ppbv h−1 in 2016. In addition, solvent usage made decreasing
contributions to both VOCs (rate =-2.29±0.03 ppbv yr−1) and
local O3 production rate (1.22±0.17 and 0.14±0.05 ppbv h−1 in 2007 and 2016, respectively) in the same period. All the rates
reported here were for the VOC sampling days in the three sampling
campaigns. It is noteworthy that meteorological changes also play important
roles in the inter-annual variations in the observed O3 and the
simulated O3 production rates. Evaluations with more data in longer
periods are therefore recommended. The analyses on the decadal changes of
the local and regional photochemistry in Hong Kong in this study may be a
reference for combating China's nationwide O3 pollution in near
future.
Amine‐functionalized bimetallic Fe/Ti‐based metal–organic frameworks (Fe/Ti‐MOF‐NH2) were synthesized via the solvothermal method and used as photocatalysts and activators for persulfate (PS)‐assisted visible light photocatalytic degradation of Orange II. Nearly 100% of Orange II was removed within 10 min in the Fe/Ti‐MOF‐NH2(3:1)/PS/Vis process, while only 10.7% and 70.9% of Orange II were removed in Fe/Ti‐MOF‐NH2(3:1)/Vis and Fe/Ti‐MOF‐NH2(3:1)/PS processes within 10 min, respectively. Therefore, the synergistic effect of PS activation and visible light photocatalysis was demonstrated by the Fe/Ti‐MOF‐NH2(3:1) composite. The enhanced photocatalytic activity of the photocatalyst can be attributed to the efficient electrons transfer by Fe3+/Fe2+ and Ti4+/Ti3+ redox cycles, activation of PS by photogenerated electrons to produce sulfate radicals (SO4•−), and increased formation of hydroxyl radicals (•OH). Concurrently, the Fe/Ti‐MOF‐NH2(3:1) photocatalyst also exhibited good reusability and stability in the photocatalytic reaction system.
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