Historically known as China's 'Netherlands', the lowlands of Lixiahe were and still are characterized by vast waterscapes. This paper introduces an island society fostered by this wet landscape, ...which thrived in premodern times and has undergone a transition into modernity. From a long-term perspective, there have been constant interactions between this island society and the water-land environments. This study details such socio-natural interactions and reconsiders the role of natural settings in the evolution of this island society in the modern context of intensifying human interventions. A comparative study is conducted in two periods of premodern and modern times, and a parallel examination is conducted into three levels of this island society to explore island relations. A boundary approach based on landscape ecology theories is employed to interpret the complex socio-natural interactions in both temporal and spatial dimensions. Through this historical exploration, the paper concludes with three links between resilience thinking and architecture/planning practice in wet landscapes and discusses contemporary issues connected with the socio-ecological resilience of these lowland islands.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, ODKLJ, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Peroxymonosulfate (PMS)-based advanced oxidation processes (AOPs) are emerging methods for VOC waste gas treatment, but the activation of PMS
via
heterogeneous metal catalysts is greatly limited by ...the low dispersion of active components. In this work, a highly dispersed Co-Fe bimetallic catalyst using uncalcined SBA-15 as the support (CFS) was successfully prepared by a simple one-step calcination method. The abundant Si-OH groups and nanoconfined space provided by uncalcined SBA-15 were responsible for the dispersion behavior of Co-Fe species. Simultaneously, the doping of Fe in CFS can greatly enhance the Co stability in the channels of SBA-15 and prevent Co ion leaching in reaction media. The prepared CFS can be stored for 3 months with almost no loss of activity. Compared with CFS, the Co-Fe catalyst derived from template free SBA-15 (CFCS) showed aggregated particles with much lower dispersion. CFS showed superior catalytic activity towards PMS activation and VOC degradation in a wet scrubber. The toluene removal efficiency over CFS was kept above 95% while it was only 62%, 30% and 42% over CFCS, Co/SBA-15 and Fe/SBA-15, respectively. The powerful hydroxyl (HO&z.rad;) and sulfate (SO
4
&z.rad;
−
) radicals were abundantly generated to oxidize toxic VOCs including toluene, styrene and chlorobenzene into soluble small molecules, which could be finally mineralized into CO
2
. The highly dispersed Co-Fe nanoparticles developed in this study not only show outstanding activity for PMS activation in AOPs, but also greatly reduce the environmental risk from Co leaching and emission of toxic VOCs and their by-products.
This work synthesized a highly dispersed Co-Fe bimetallic catalyst with uncalcined SBA-15 as the support, which was very efficient for PMS activation and gaseous toluene degradation in the wet scrubbing waste gas treatment system.
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•Gaseous toluene was efficiently removed over F-TiO2 in the WPCO process.•The photocatalytic activity of F-TiO2 has good stability and remained highly efficient after several ...runs.•Mobile HO was proposed to be reactive species responsible for enhanced toluene degradation over F-TiO2.•The F/Ti molar ratio (RF) greatly affected photocatalytic activity and RF = 1 is optimal.
The application of photocatalytic oxidation (PCO) of volatile organic compounds (VOCs) is strongly limited by catalyst deactivation, low mineralization ability and mass-transfer in gas-solid phase. Wet-scrubbing coupled with PCO (WPCO) provides a novel and efficient method for VOCs degradation. Fluorine-doped TiO2 (F-TiO2) photocatalyst was prepared and applied in this coupled process for toluene degradation. Toluene removal efficiency reached 80% over F-TiO2, while it was only 25% over TiO2 in the WPCO process. As for gas-solid PCO process, F-TiO2 had a low toluene removal efficiency of 10%. Furthermore, the mineralization capability of WPCO process over F-TiO2 also remarkably increased, achieving about 92 ppmv CO2 generated from toluene oxidation. Compared with TiO2, the surface fluorinated TiO2 significantly enhanced toluene degradation since it generated mobile hydroxyl radical (OH) in the WPCO process. The F/Ti molar ratio (RF) greatly affected photocatalytic activity towards toluene degradation, and the F-TiO2 with RF at 1 obtained the best performance. The photocatalytic activity of F-TiO2 had good stability and remained highly efficient after four runs.
We investigated the adsorption mechanisms for removing fluoride based on experimental and modeling studies. Lanthanum-aluminum perovskite was designed for treating wastewater contaminated by ...fluoride. A fluorine-species model was developed to calculate the concentrations of different species of fluorine: F−, HF, HF2−. Multiple kinetic models were examined and the pseudo-second order model was found the best to fit the experimental data, implying fast-chemisorption. The thermodynamic data were fitted by the Langmuir model and Freundlich model at different temperatures, indicating heterogeneous adsorption at low temperature and homogeneous adsorption at high temperature. The La2Al4O9 material had less influence from negative ions when adsorbing fluoride. The adsorption mechanisms were further studied using experiments and Density Functional Theory calculations. The adsorption experiments could be attributed to the lattice plane (1 2 1) and La, O, Al sites. More Al sites were required than La sites for the increase of fluoride concentration. By contrast, more La sites than Al sites were needed for increased pH.
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•The hollow Lanthanum-aluminum perovskite was first applied to remove fluoride.•The species of F−, HF, HF2− played a more important role at different pH.•The Lanthanum sites had more important effect than Aluminum at higher pH.•Ηigher concentrations of fluoride required more Aluminum than Lanthanum sites.
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•SO4•− was predominant in the initial oxidation of chlorobenzene (CB) in UV/PDS.•HO• played important role in the formation of CO2 during the oxidation of CB.•The synergetic effect of ...SO4•−, O2 and HO• led to efficient mineralization of CB.•Highly-toxic dimericproducts were produced in UV/PDS in the absence of O2.•The oxidation pathway was proposed based on the intermediates and DFT calculation.
Chlorobenzene is a typical chlorinated volatile organic compound (CVOC), and the degradation of chlorobenzene frequently produces high-toxic byproducts such as dioxins in the treatment process. To prevent this, complete oxidation of chlorobenzene into harmless CO2 is highly desirable. Wet scrubber coupled with advanced oxidation processes (AOPs) for gaseous VOCs treatment has been widely reported, but their mineralization capacity and mechanism are still poorly understood. Herein, this study developed an efficient technology for chlorobenzene oxidation via wet scrubbing process coupled with UV/peroxydisulfate (PDS), with UV/H2O2 as comparison. The mineralization efficiency of chlorobenzene was much higher in UV/PDS (75.4%) than that in UV/H2O2 (42.0%), although the removal efficiencies in both AOPs were similar at 90–97%. Sulfate radical (SO4•−) was predominant for the initial oxidation of chlorobenzene, forming the intermediates that were favorable for the mineralization process. Then, O2 and HO• played important roles on the formation of CO2 in the complete oxidation of chlorobenzene in UV/PDS. The role of O2 was further comfirmed by the result that high-toxic dimericproducts, rather than CO2, were generated in UV/PDS in the absence of O2. The possible pathway on chlorobenzene oxidation was proposed based on the evolution of intermediates and Density Functional Theory (DFT) calculation. Carbon cation radical was formed from the initial oxidation of chlorobenzene by SO4•−, followed by the ring-opening and more CO2 yields via the synergetic effect of SO4•−, O2 and HO•. This study not only provides an environment-friendly method to improve the VOC removal efficiency, but also gets a deep understanding of the different functions of SO4•−, HO• and O2 on the mineralization process.
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•Activated carbon supported monodispersed Co3O4 nanoparticles (Co3O4/AC) were prepared via a facile deposition method.•The presence of Co-OH+ on Co3O4/AC is highly efficient in PMS ...activation for gaseous toluene degradation.•SO4− play a dominant role for toluene degradation, HO derived from PMS activation can improve carbon mineralization.•Few gaseous intermediates were discharged during reaction process.
Gas-phase VOCs decomposition generally produces intermediates and causes secondary air pollution. To avoid this issue, we proposed a novel method for a typical gaseous VOC (toluene) degradation via catalytic activation of peroxymonosulfate (PMS) in the liquid phase. Herein, activated carbon supported monodispersed Co3O4 nanoparticles (Co3O4/AC) were prepared via a facile deposition method. It is highly efficient in PMS activation for toluene degradation due to the presence of Co-OH+ species and well dispersed Co3O4 on Co3O4/AC. A toluene removal efficiency of nearly 90% was maintained during the reaction, and few gaseous intermediates were discharged. Sulfate radical (SO4−) and hydroxyl radical (HO) derived from PMS activation played different roles during toluene oxidation and mineralization. Electron spin resonance (EPR) suggested that the generation of plentiful SO4− resulted in the superior toluene degradation, and the presence of HO can improve carbon mineralization. Radical quenching tests further confirmed that SO4− played a dominant role for toluene degradation, whereas the absence of HO inhibited the carbon mineralization. The toluene degradation pathway in the Co3O4/AC-PMS system was proposed based on the intermediates identified by GC–MS.
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•The gaseous VOCs were efficiently removed by WS + UV/PMS process.•The average VOCs absorption rates were enhanced in WS + UV/PMS process.•HO contributed to ethyl acetate degradation, ...while SO4− preferred toluene.•The solution can be reused with excellent oxidation performance via re-adding PMS.
In this study, wet scrubber coupled with UV/peroxymonosulfate (PMS) was used as a semi-batch process for removing gaseous VOCs. Both ethyl acetate and toluene could be removed efficiently using this coupled process due to the generation of SO4− and HO. The mass-transfer coefficients in this coupled process were larger than in wet scrubbing only process. The roles of SO4− and HO were investigated, in which SO4− acted as the predominant radical for toluene degradation while HO was major for ethyl acetate. This could be further confirmed by simultaneous degradation of ethyl and toluene. Moreover, the reaction solution reused at least four times still showed excellent performance for VOCs removal via re-adding PMS. A possible mechanism on toluene degradation was proposed based on the evolutions of intermediates during the process. This study clarified the roles of non-selective radical (i.e. HO) and selective radical (i.e. SO4− and Cl) in the removal of a continuous-flow gaseous VOCs by this coupled process.
Toluene is a representative and toxic contaminant in industry or indoor airs. In this work, a novel and facile method was developed to prepare mesoporous TiO2 for the photo-catalytic oxidation of ...toluene in a wet-scrubbing reactor. Interestingly, by changing the preparation parameters, including dosage of template material, hydrolysis rate, hydrothermal temperature and calcination temperature, the crystalline phase of catalyst could be partially adjusted among brookite, anatase and rutile. With 30 ppm toluene input, an enhanced toluene removal of 62% and CO2 production of 95 ppm were achieved, while no soluble or particulate byproduct was released. In contrast to traditional photo-catalysis, the UV adsorbing ability of catalyst, the cluster of mesoporous TiO2 and the corresponding structure in micrometer-scale were key to the UV utilization and toluene removal in wet-scrubbing reactor.
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•Combined process of wet-scrubbing and UV-catalysis for toluene removal.•A facile method was developed to prepare meso-TiO2 for enhanced removal.•Phase of TiO2 could be partially transformed among brookite, anatase and rutile.•Dispersion of TiO2 and toluene removal were improved by the addition of CTAB.•UV-catalytic performance determined by TiO2 clusters pile-ups and crystalline phase.
The elimination of volatile organic compounds (VOCs) via vacuum ultraviolet (VUV) photolysis is greatly limited by low removal efficiency and gaseous byproducts generation, while photocatalytic ...oxidation of VOCs suffers from catalytic deactivation. Herein, a coupled process of gaseous VUV photolysis with aqueous photocatalytic oxidation with P25 as the catalyst was firstly proposed for efficient aromatic VOCs removal (VUV/P25). The removal efficiency of toluene reached 86.2% in VUV/P25 process, but was only 33.6% and 58.1% in alone gaseous VUV photolysis and aqueous ultraviolet photocatalytic oxidation (UV/P25) process, respectively. Correspondingly, the outlet CO2 concentration in VUV/P25 process reached 132 ppmv. Toluene was firstly destructed by high-energy photons generated from gaseous VUV photolysis, resulting in its incomplete oxidation to form soluble intermediates including acids, aldehydes, esters. These soluble intermediates would be further degraded and mineralized into CO2 in subsequent aqueous UV/P25 process. Notably, the concentrations of intermediates in VUV/P25 were much lower than those in VUV photolysis, indicating the synergy effect of VUV photolysis and UV/P25 process. The stability tests proved that VUV/P25 process maintained an excellent toluene degradation performance and P25 did not suffer from catalytic deactivation. In addition to toluene, the VUV/P25 system also achieved the efficient and sustainable degradation of styrene and chlorobenzene, suggesting its good application prospect in industrial VOCs treatment. This study proposes an efficient and promising strategy for deep oxidation of multiple aromatic VOCs in industries.
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•The synergy effect of VUV photolysis and UV/P25 greatly promotes VOCs degradation.•Water-soluble byproducts in VUV photolysis are more likely to be attacked in UV/P25.•O2 plays an important role in deep oxidation of VOCs by generating abundant ROS.•VUV/P25 system is highly stable and greatly avoids catalytic deactivation.
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