Amine-grafted MSU-3 mesoporous silica samples were synthesized from pure and waste silica sources and their CO2 adsorption performances were evaluated. The obtained samples were characterized using X-ray diffraction (XRD), thermogravimetric analysis (TGA), N2 adsorption–desorption isotherm analysis, Fourier transform infrared (FTIR), and transmission electron microscopy (TEM). CO2 adsorption capacities of the samples at different temperatures were determined by TGA. The amine-modified MSU-3 synthesized from waste exhibited the highest CO2 adsorption capacity of 1.32 mmol/g at 25 °C and 1 bar, depending essentially on the porous texture and the amine content of the material. The CO2 adsorption isotherms of the synthesized samples were measured by a static volumetric method. Adsorption isotherm indicated that the amine-modified samples presented significantly higher CO2 adsorption capacity than the pure samples. The Avrami kinetic model fitted the experimental data well and suggested that complex reaction mechanism or the appearance of multiple reaction pathway occurred in the CO2 adsorption.
In this study, high surface area porous carbons were synthesized by chemical activation using petroleum coke as the precursor and KOH as the activation agent. The pore structure of the as-synthesized activated carbons was characterized by nitrogen adsorption, and their CO2 sorption capacities were measured by a magnetic suspension balance at 1 and 10 bar, respectively. The effects of activated carbon preparation parameters (preheating temperature, preheating time, activation time, heating rate during the pyrolysis, and particle size of the precursor) on porous texture, CO2 adsorption capacity, and CO2/N2 selectivity of the activated products were investigated. It has been found that at 1 bar, the CO2 adsorption capacity is determined by the micropore contribution, i.e., the ratio between micropore surface area and Brunauer–Emmett–Teller (BET) surface area of the sorbents, while at 10 bar, CO2 adsorption capacity is related to the BET surface area of the activated products. The maximum CO2 adsorption uptake of 15.1 wt% together with CO2/N2 selectivity of 9.4 at 1 bar were obtained for a sample activated at 700 °C indicating its high potential in the capture of CO2. 相似文献
Mesoporous silica with wormhole framework structure (HMS-OH) and its amine-functionalized material (HMS-NH2) were prepared through an electrically neutral assembly pathways, post-grafting process of 3-aminopropyltriethoxysilane (APTES), respectively. Their adsorption behaviors toward cationic dyes as well as heavy metal ions in aqueous system and the capture capacities for CO2 molecules all have been investigated. As-synthesized HMS-OH showed a high removal efficiency and rapid sorption rate to cationic dyes because of large surface area and versatile pore structure. HMS-NH2 exhibited better heavy metal ions and more CO2 gas sorption capacities due to the intrinsic property of amine groups grafted on the surface. The adsorption isotherms of methylene blue (MB) onto HMS-OH, Cu(II) onto HMS-NH2 were fitted with Langmuir model and kinetic processes followed well the pseudo-second order pattern. There results revealed that both HMS-OH and HMS-NH2 had a potential application in the treatment of cationic dyes, heavy metal ions, and greenhouse gas CO2. 相似文献
Modern light chestnut and chestnut soils and their analogues buried under steppe kurgans in the southeastern part of the Russian
Plain were studied in order to determine the rates of the CO2 production by these soils under the native (with the natural moisture content) and moistened (60% of the total water capacity)
conditions. It was found that the rates of the CO2 production by the soil samples in the native state are relatively close to one another and vary from 0.3 to 1.4 μg of C/100
g of soil/h. The rates of the CO2 production in the moistened state increased by two orders of magnitude for the modern surface soils and by an order of magnitude
for the buried soils. 相似文献
Determination of the C balance is of considerable importance when forecasting climate and environmental changes. Soil respiration
and biological productivity of ecosystems (net primary production; NPP) are the basic components of the terrestrial C cycle.
In this study, a previously made assessment of the annual CO2 flux from Russian soils was improved upon. CO2 emissions from Russian soils during the growing period were shown to represent, on average, 53–82% of the annual CO2 flux from Russian soils. The total annual CO2 flux from Russian soils was estimated at 4.50 Gt C (C source). The NPP of Russian ecosystems was estimated at 4.81 Gt C year–1 (C sink). Our calculations showed values of CO2 emissions and the C sink to be very close. This shows that, in general, terrestrial ecosystems are under steady state.
Received: 1 December 1997 相似文献
The results of quantitative assessment and modeling of carbon dioxide emission from urban pedolithosediments (cultural layer) in the central part of Velikii Novgorod are discussed. At the first stages after the exposure of the cultural layer to the surface in archaeological excavations, very high CO2 emission values reaching 10–15 g C/(m2 h) have been determined. These values exceed the normal equilibrium emission from the soil surface by two orders of magnitude. However, they should not be interpreted as indications of the high biological activity of the buried urban sediments. A model based on physical processes shows that the measured emission values can be reliably explained by degassing of the soil water and desorption of gases from the urban sediments. This model suggests the diffusion mechanism of the transfer of carbon dioxide from the cultural layer into the atmosphere; in addition, it includes the equations to describe nonequilibrium interphase interactions (sorption–desorption and dissolution–degassing of CO2) with the first-order kinetics. With the use of statistically reliable data on physical parameters—the effective diffusion coefficient as dependent on the aeration porosity, the effective solubility, the Henry constant for the CO2 sorption, and the kinetic constants of the CO2 desorption and degassing of the soil solution—this model reproduces the experimental data on the dynamics of CO2 emission from the surface of the exposed cultural layer obtained by the static chamber method. 相似文献
Three-month incubation of soils with K2CO3 raised the pH about the same as did an equivalent amount of CaCO3 but was substantially more effective in enhancing the water solubility of P (4–14-fold at the solution to soil ratio of 60:1). In the K2CO3-treated samples, the KCl added to achieve a 25% increase in ionic strength caused an 11–44% drop in the water-soluble P. However, if the water to soil ratio increased, the P desorption in the CaCO3 amended samples approached that in the K2CO3-treated soils, and the KCl-induced reduction in water-soluble P diminished. These responses to changes in the extraction ratio were taken to indicate that the cation species of the liming material and the ionic strength in the matrix solution affected the rate more so than the absolute quantity of P desorption. The significance of these factors under field conditions was discussed. 相似文献
Summary Information on the mineralization of inorganic phosphate (Pi) from organically bound P (Po) during decomposition of forest floor and soil organic matter is vital for understanding P
supply in forest ecosystems. Carbon (C) and phosphorus (P) fluxes were determined for forest floor samples from three Pinus radiata plots which had received no P (Control), 62.5 kg P ha–1 (Low P) and 125 kg P ha–1 (High P) 20 years before sampling. The P concentration of the forest floor samples had increased with fertilizer application,
and the C:P ratio ranged between 585 and 1465. During a 9-week laboratory incubation 8.2–19.0% of the forest floor C was evolved
as CO2-C. The amount of CO2 evolved from the forest floor of the Control plot was more than twice the amounts from the Low P and High P plots. There
was little change in net P mineralization in the Control and Low P treatments throughout the incubation, but it increased
slightly for the High P samples, suggesting a critical forest floor C:P ratio of 550 for net P mineralization. Changes in
the 32P-specific activities of the Pi and microbial P pools during incubation, and concurrent changes in microbial-32P and 32Pi, indicated internal P cycling between these pools. The rate of internal P cycling varied with forest floor quality, and was
highest in the High P forest floor. The High P samples had microbial C:P ratios of 22 : 1 which remained constant during the
incubation, suggesting the microorganisms had adequate P levels.
Received: 2 July 1997 相似文献
The regularities of the seasonal dynamics of the CO2 emission from the surface of a podzolic soil under a bilberry pine forest of the middle taiga were revealed. In mid-May, after the snow melt, the CO2 emission was 0.10–0.20 g of CO2/m2 per h. Then, the intensity of the CO2 emission increased, reached its maximum (1.0 to 1.5 g of CO2/m2 per h) in July–August, and decreased down to 0.04–0.10 g of CO2 g/m2 per h in mid-October. The correlation between the rate of the CO2 emission and the temperature and moisture of the soil was positive and negative: r = 0.34 to 0.91 and ?0.44 to ?0.86, respectively. According to the empirical model, 2.26–2.69 t of C-CO2/ha were emitted during the warm time of the year. 相似文献
The studies of recent soils and paleosols buried under kurgans created in the periods of long-term aridization (3000–2000 BC) and climatic optimum (13th–14th centuries AD) were performed in steppes of the southeastern part of the East European Plain (Privolzhskaya Upland and Caspian Lowland) in order to determine the rate of carbon dioxide production by the soil samples at the natural moisture and after moistening up to 60% of the total moisture capacity. The CO2 emission from the samples of paleosols corresponding to the period of climatic aridization in the Lower Volga River at their natural moisture status was lower than that from the samples of background surface soils, whereas the CO2 emission from the samples of paleosols buried under optimum climatic conditions was higher than that from the samples of background surface soils. After moistening of the samples, the increase in the CO2 emission from the paleosol samples depended on the actual humidity of the climate in the corresponding period. 相似文献
Fulvic acids (FA) were immobilized on alumina particles in order to evaluate their catalytic effect as solid-phase redox mediator
(RM) during the reductive dechlorination of carbon tetrachloride (CT) by anaerobic sludge. FA were extracted from three different
soil samples and two commercial composts. Electron carrying capacity (ECC) was determined in all FA samples in order to select
the appropriate source of redox-mediating compounds for CT dechlorination. TiO2, Al(OH)3, and γ-Al2O3 particles were tested as immobilizing materials for the extracted FA. FA extracted from a temperate pine forest soil showed
the highest ECC (291.72 μmol g−1). The highest adsorption capacity of FA, measured as total organic carbon (TOC), was achieved by alumina (γ-Al2O3) particles (12 mg TOC-FA g−1). Results suggest that the transfer of electrons rather than their microbial generation through glucose fermentation was
the rate-limiting factor during dechlorination of CT. Immobilized FA increase up to 10.4-fold the rate of CT dechlorination
as compared with the control lacking FA. Immobilization of FA on alumina particles was very stable, and spectrophotometric
screening did not detect any detachment of FA during dechlorination of CT, thus confirming that the enhanced dechlorination
achieved could exclusively be linked to the redox-mediating capacity of immobilized FA. The present study constitutes the
first demonstration that immobilized FA on alumina particles could serve as a solid-phase RM in dechlorination reactions. 相似文献
Seasonal drought in tropical agroecosystems may affect C and N mineralization of organic residues. To understand this effect,
C and N mineralization dynamics in three tropical soils (Af, An1, and An2) amended with haricot bean (HB; Phaseolus vulgaris L.) and pigeon pea (PP; Cajanus cajan L.) residues (each at 5 mg g−1 dry soil) at two contrasting soil moisture contents (pF2.5 and pF3.9) were investigated under laboratory incubation for 100–135 days.
The legume residues markedly enhanced the net cumulative CO2–C flux and its rate throughout the incubation period. The cumulative CO2–C fluxes and their rates were lower at pF3.9 than at pF2.5 with control soils and also relatively lower with HB-treated than
PP-treated soil samples. After 100 days of incubation, 32–42% of the amended C of residues was recovered as CO2–C. In one of the three soils (An1), the results revealed that the decomposition of the recalcitrant fraction was more inhibited by drought stress than easily
degradable fraction, suggesting further studies of moisture stress and litter quality interactions. Significantly (p < 0.05) greater NH4+–N and NO3−–N were produced with PP-treated (C/N ratio, 20.4) than HB-treated (C/N ratio, 40.6) soil samples. Greater net N mineralization
or lower immobilization was displayed at pF2.5 than at pF3.9 with all soil samples. Strikingly, N was immobilized equivocally
in both NH4+–N and NO3−–N forms, challenging the paradigm that ammonium is the preferred N source for microorganisms. The results strongly exhibited
altered C/N stoichiometry due to drought stress substantially affecting the active microbial functional groups, fungi being
dominant over bacteria. Interestingly, the results showed that legume residues can be potential fertilizer sources for nutrient-depleted
tropical soils. In addition, application of plant residue can help to counter the N loss caused by leaching. It can also synchronize
crop N uptake and N release from soil by utilizing microbes as an ephemeral nutrient pool during the early crop growth period. 相似文献
Wheat flour with 0.3% (w/w) thiamin was extruded on a twin‐screw laboratory‐scale extruder (19‐mm barrel) at lower temperatures and expanded using carbon dioxide (CO2) gas at 150 psi. Extrusion conditions were die temperature of 80°C and screw speed range of 300–400 rpm. Control samples were extruded at a die temperature of 150°C and screw speed range of 200–300 rpm. Dough moisture content was 22% in control samples and 22 and 25% in CO2 samples. Expansion ratio, bulk density, WAI, and %WSI were compared between control and treatment. CO2 injection did not significantly increase expansion ratio. Bulk densities in the CO2 extruded samples decreased when feed moisture decreased from 25 to 22%. The products using CO2 had lower WAI values than products puffed without CO2 at higher temperatures. The mean residence time was longer in CO2 screw configurations than in conventional screw configurations. Thiamin losses were 10–16% in the control samples. With CO2, thiamin losses were 3–11% at 22% feed moisture, compared with losses of 24–34% at 25% moisture. Unlike typical high‐temperature extrusion, thiamin loss in the low‐temperature samples decreased with increasing screw speed. Results indicate that thiamin loss at lower extrusion temperatures with CO2 injection is highly dependent on moisture content. 相似文献
Fungal and bacterial biomass were determined across a gradient from a forest to grassland in a sub-alpine region in central
Taiwan. The respiration-inhibition and ergosterol methods for the evaluation of the microbial biomass were compared. Soil
fungal and bacterial biomass both significantly decreased (P<0.05) with the shift of vegetation from forest to grassland. Fungal and bacterial respiration rates (evolved CO2) were, respectively, 89.1 μl CO2 g–1 soil h–1 and 55.1 μl CO2 g–1 soil h–1 in the forest and 36.7 μl CO2 g–1 soil h–1 and 35.7 μl CO2 g–1 soil h–1 in the grassland surface soils (0–10 cm). The fungal ergosterol content in the surface soil decreased from the forest zone
(108 μg g–1) to the grassland zone (15.9 μg g–1). A good correlation (R2=0.90) was exhibited between the soil fungal ergosterol content and soil fungal CO2 production (respiration) for all sampling sites. For the forest and grassland soil profiles, microbial biomass (respiration
and ergosterol) declined dramatically with depth, ten- to 100-fold from the surface organic horizon to the deepest mineral
horizon. With respect to fungal to bacterial ratios for the surface soil (0–10 cm), the forest zone had a significantly (P<0.05) higher ratio (1.65) than the grassland zone (1.05). However, there was no fungal to bacterial ratio trend from the surface
horizon to the deeper mineral horizons of the soil profiles.
Received: 30 March 2000 相似文献
Soil microbial biomass and the emission of CO2 from the soil surface were measured in yellow soils (Ultisols) of the karst areas of southwest China. The soils are relatively
weathered, leached and impoverished, and have a low input of plant residues. The measurements were made for a 1-year period
and show a reciprocal relationship between microbial biomass and surface CO2 efflux. The highest (42.6±2.8 mg CO2-C m–2 h–1) and lowest (15.6±0.6 mg CO2-C m–2 h–1) CO2 effluxes are found in the summer and winter, respectively. The cumulative CO2 efflux is 0.24 kg CO2-C m–2 year–1. There is also a marked seasonal variation in the amount of soil microbial biomass carbon, but with the highest (644±71 μg
C g–1 soil) and lowest (270±24 μg C g–1 soil) values occurring in the winter and summer, respectively. The cumulative loss of soil microbial biomass carbon in the
top 10 cm of the soil was 608 μg C g–1 year–1 soil over 17 sampling times. The mean residence time of microbial biomass is estimated at 105 days, suggesting that the carbon
in soil microbial biomass may act as a source of the CO2 released from soils.
Received: 13 July 1999 相似文献
This study aims to determine the effects of compost additions and high temperature on N2O and CO2 emissions from a Vietnamese agricultural soil. Soil samples amended with two compost types (commercial compost, SH and chicken compost, CC) at three rates of 1%, 2% and 4% w/w were aerobically incubated at 25°C, 30°C and 35°C for 28 days in the laboratory. N2O and CO2 emissions were determined on days 1, 3, 5, 7, 14, 21 and 28. Our results showed that N2O and CO2 emissions were significantly affected by temperature, compost additions, and their interactions. Greater N2O and CO2 emissions were seen in CC treatments than SH treatments. Higher application rates of CC led to greater N2O and CO2 emissions. In SH treatments, higher temperature lowered N2O emissions but did not affect CO2 emissions. N2O and CO2 emissions were enhanced with CC addition while they showed different responses to increasing temperature. 相似文献
Measurements made during 1982, 1983 and 1984 were used to study the CO2 budget of maize (Zea mays L.). Above-canopy CO2 flux density, which represents most of the CO2 absorption by crops, was monitored throughout each growing season using the eddy correlation technique. Intercepted solar radiation was calculated on an hourly basis using measurements of incident solar radiation, leaf area index and solar elevation. The observed relationships between above-canopy CO2 flux densities and intercepted solar radiation, for each growing season, were then used to estimate hourly above-canopy CO2 flux densities. Assimilation of soil-respired CO2 and nighttime losses of plant respiratory CO2 were also estimated, based on experimental data, and combined with above-canopy CO2 flux densities to determine net photosynthesis. Although clear short term relationships between above-canopy CO2 flux density and intercepted solar radiation have been observed for maize, a great variability in CO2 flux density as a function of estimated intercepted solar radiation is observed over the whole growing season. Comparison of estimated CO2 budget based on gaseous exchange estimates and destructive plant sampling are presented. For 1982 and 1983, both estimates agreed within ±1 standard error while for 1984 the estimates based on gaseous exchanges were consistently lower. The relative magnitudes of gross photosynthesis, soil and plant respiration are presented and techniques for improving our ability for closing the CO2 budget using gaseous exchanges estimates are discussed. 相似文献
