Dynamic and thermodynamic mechanisms of TFA adsorption by particulate matter

Preparation of 6-Amino-N-hydroxyhexanamide-Modified Porous Chelating Resin for Adsorption of Heavy Metal Ions

The pollution of water bodies by heavy metal ions has recently become a global concern. In this experiment, a novel chelating resin, D851-6-AHHA, was synthesized by grafting 6-amino-N-hydroxyhexanamide (6-AHHA) onto the (-CH2N-(CH2COOH)2) group of the D851 resin, which contained a hydroxamic acid group, amide group, and some carboxyl groups. This resin was developed for the purpose of removing heavy metal ions, such as Cr(III) and Pb(II), from water. The findings from static adsorption experiments demonstrated the remarkable adsorption effectiveness of D851-6-AHHA resin towards Cr(III) and Pb(II). Specifically, the maximum adsorption capacities for Cr(III) and Pb(II) were determined to be 91.50 mg/g and 611.92 mg/g, respectively. Furthermore, the adsorption kinetics of heavy metal ions by D851-6-AHHA resin followed the quasi-second-order kinetic model, while the adsorption isotherms followed the Langmuir model. These findings suggest that the adsorption process was characterized by monolayer chemisorption. The adsorption mechanism of D851-6-AHHA resin was comprehensively investigated through SEM, XRD, FT-IR, and XPS analyses, revealing a high efficiency of D851-6-AHHA resin in adsorbing Cr(III) and Pb(II). Specifically, the (-C(=O)NHOH) group exhibited a notable affinity for Cr(III) and Pb(II), forming stable multi-elemental ring structures with them. Additionally, dynamic adsorption experiments conducted using fixed-bed setups further validated the effectiveness of D851-6-AHHA resin in removing heavy metal ions from aqueous solutions. In conclusion, the experimental findings underscored the efficacy of D851-6-AHHA resin as a highly efficient adsorbent for remediating water bodies contaminated by heavy metal ions.

Simultaneously enhancing toluene adsorption and regeneration process by hierarchical pore in activated coke: a combined experimental and adsorption kinetic modeling study

Activated coke is a type of commonly used adsorbent for benzene series VOCs such as toluene, but traditional microporous activated coke usually faces the challenge of poor regeneration performance. Herein, based on self-made activated cokes with typical pore configuration, we found that adsorption and regeneration of toluene can be simultaneously enhanced by constructing hierarchical pore in activated coke. Correlations of pore configuration with toluene adsorption capacity and regeneration efficiency reveal that micropore contributes for strong toluene adsorption; meso-macropore provides mass transfer channel for toluene desorption and regeneration process. Hierarchical porous activated coke prepared from Zhundong subbituminous coal not only achieves the highest toluene adsorption capacity of 340.92 mg·g-1, but also can retain more than 90% of initial adsorption capacity after five adsorption-regeneration cycles. By contrast, micropore-dominant activated cokes can only retain 70% of initial adsorption capacity. Adsorption kinetic modelling on adsorption breakthrough curves shows that hierarchical porous activated coke prepared from Zhundong subbituminous coal exhibits high adsorption and diffusion rate constants of 14.39 and 33.45 min-1, respectively, much higher than those of micropore-dominant activated cokes. Due to the accelerated surface adsorption and diffusion processes induced by meso-macropore, toluene adsorption and regeneration behavior can be simultaneously improved. Results from this work validated the role of pore hierarchy in toluene adsorption-regeneration process, providing guidance for designing high-performance activated coke with synergistically improved toluene adsorption capacity and regeneration performance.

A novel method for production of nitrogen fertilizer with low energy consumption by efficiently adsorbing and separating waste ammonia

Recovering waste NH3 to be used as a source of nitrogen fertilizer or liquid fuel has recently attracted much attention. Current methods mainly utilize activated carbon or metal-organic frameworks to capture NH3, but are limited due to low NH3 adsorption capacity and high cost, respectively. In this study, novel porous materials that are low cost and easy to synthesize were prepared as NH3 adsorbents by precipitation polymerization with acid optimization. The results showed that adsorption sites (‒COOH, -OH, and lactone) which form chemical adsorption or hydrogen bonds with NH3 were successfully regulated by response surface methods. Correspondingly, the dynamic NH3 adsorption capacity increased from 5.45 mg g-1 to 129 mg g-1, which is higher than most known activated carbon and metal-organic frameworks. Separation performance tests showed that NH3 could also be separated from CO2 and CH4. The findings in this study will advance the industrialization of NH3 polymer adsorbents and provide technical support for the recycling of waste NH3.

Bifunctional Cu-incorporated carbon nanospheres via in-situ complexation strategy as efficient toluene adsorbents and antibacterial agents

Carbon adsorbents have been widely used to remove indoor volatile organic compounds (VOCs), however, the proliferation of bacteria on the carbon adsorbents may deteriorate the indoor air quality and thus pose a serious threat to human health. Herein, we report the synthesis of antibacterial porous carbon spheres (carbonized aminophenol-formaldehyde resin, CAF) with well-dispersed Cu species via an in situ incorporation of Cu2+ during the polymerization of 3-aminophenol-formaldehyde resin followed by a thermal carbonization and reduction process. Compared with CAF, the Cu/CAF-x nanocomposites with Cu loading show a much higher specific surface area (>700 m2 g-1vs. 569 m2 g-1 for CAF). In addition, the pore size of Cu/CAF-x is ranging from 0.7 to 1.68 nm, which is exactly conducive to adsorb the toluene molecules. As a result, the toluene adsorption capacity is improved from 123.50 mg g-1 for CAF to >170 mg g-1 for Cu/CAF-x. More importantly, such adsorbents possess excellent antibacterial performance, the Cu/CAF-10 (10 wt% of Cu loading) with a concentration of 50 μg mL-1 can completely kill the E. coli within 30 min. Our work paves the way to the development of bifunctional adsorbents with both efficient VOCs adsorption and excellent antibacterial performance.

Synthesis of a high-iron fly-ash-based Na-X molecular sieve and its application in the adsorption of low concentration of CO2

In addressing the environmental challenges posed by the accumulation of fly ash (FA), efforts have been geared towards its high-value utilization. By the use of high-iron FA as a raw material, a high-iron fly-ash-based Na-X molecular sieve was successfully synthesized by hydrothermal method. We combined pretreatment methods such as high-temperature calcination, acid leaching and alkali fusion activation. The as-synthesized product was used for the adsorption of a low concentration of CO2, and the adsorption data were fitted by a physical model. The changes in iron content in pretreatment and molecular sieve synthesis were revealed by SEM-mapping, UV-Raman and UV-Vis. The results showed that the pretreatment process reduces the iron content from 32.3% to 13.3%, and converts the inactive phases to active phases, with n (SiO2/Al2O3) = 4.94. The activated product was transformed further to a Na-X molecular sieve using a hydrothermal method. The product has a single crystal phase and octahedral crystal structure. Its specific surface area was 646.634 m2 g-1, and micropores were distributed between 0.46 nm and 0.71 nm, with a mesoporous phase of 4.6 nm. When used to adsorb a low concentration of CO2, the Na-X molecular sieve has a high adsorption capacity of 3.70 mmol g-1, which reaches 95.11% that of the commercial Na-X molecular sieve. The adsorption breakthrough time and adsorption capacity decreased with an increase in temperature. The adsorption kinetics were consistent with the Bangham model for surface pore adsorption and Weber-Morris model for internal diffusion. During the synthesis process, iron was converted from highly dispersed iron oxide to four-coordinated framework iron. Thus, this paper paves a path for the high-quality transformation and utilization of high-iron fly-ash.

Representativeness of the particulate matter pollution assessed by an official monitoring station of air quality in Santiago, Chile: projection to human health

Santiago, capital city of Chile, presents air pollution problems for decades mainly by particulate matter, which significantly affects population health, despite national authority efforts to improve air quality. Different properties of the particulate matter (PM₁₀, PM_2.5 and PM₁ fractions, particle surface and number) were measured with an optical spectrometer. The sampling was done during spring 2019 at different sites within the official representative area of Independencia monitoring station (ORMS-IS). The results of this study evidence large variations in PM mass concentration at small-scale areas within the ORMS-IS representative zone, which reports the same value for the total area. Results from PM properties such as PM₁, particle number and particle surface distribution show that these properties should be incorporated in regular monitoring in order to improve the understanding of the effects of these factors on human health. The use of urban-climate canopy-layer models in a portion of the sampled area around the monitoring station demonstrates the influence of street geometry, building densities and vegetation covers on wind velocity and direction. These factors, consequently, have an effect on the potential for air pollutants concentrations. The results of this study evidence the existence of hot spots of PM pollution within the area of representativeness of the ORMS-IS. This result is relevant from the point of view of human health and contributes to improve the effectiveness of emission reduction policies.

Adsorption of chloramphenicol from water using Carex meyeriana Kunth-derived hierarchical porous carbon with open channel arrays

A carbon material with both open macrochannel arrays and abundant micro/mesopores was prepared, characterized, and applied for removing chloramphenicol (CAP) from water. In the preparation process, Carex meyeriana Kunth (CM) with natural channel arrays was used as the precursor for producing the biochar, and NaOH was used for removing silicon and formatting micro- and mesopores of the porous carbon. The product (PCCM) exhibited the highest specific surface area (2700.24 m² g^-1) among the reported CM-derived porous carbons. The adsorption performances of PCCM were evaluated through batch adsorption experiments. The maximum adsorption capacity of PCCM toward CAP was 1659.43 mg g^-1. The adsorption mechanism was investigated with the aid of theoretical calculations. Moreover, PCCM exhibited better performance than other porous carbon adsorbents in fixed-bed experiments, which may be due to its structural advantages.

Effect of Physical Nature (Intact and Powder) of Coal on CO2 Adsorption at the Subcritical Pressure Range (up to 6.4 MPa at 298.15 K)

This study examines the influence of subcritical pressure and the physical nature (intact and powder) of coal samples on CO₂ adsorption capacity and kinetics in the context of CO₂ sequestration in shallow level coal seams. Manometric adsorption experiments were carried out on two anthracite and one bituminous coal samples. Isothermal adsorption experiments were carried out at 298.15 K in two pressure ranges: less than 6.1 MPa and up to 6.4 MPa relevant to gas/liquid adsorption. The adsorption isotherms of intact anthracite and bituminous samples were compared to that of the powdered samples. The powdered samples of the anthracitic samples had a higher adsorption than that of intact samples due to the exposed adsorption sites. The intact and powdered samples of bituminous coal, on the other hand, exhibited comparable adsorption capacities. The comparable adsorption capacity is attributed to the intact samples' channel-like pores and microfractures, where high density CO₂ adsorption occurs. The adsorption-desorption hysteresis patterns and the residual amount of CO₂ trapped in the pores reinforce the influence of the physical nature of the sample and pressure range on the CO₂ adsorption-desorption behavior. The intact 18 ft AB samples showed significantly different adsorption isotherm pattern to that of powdered samples for experiments conducted up to 6.4 MPa equilibrium pressure due to the high-density CO₂ adsorbed phase in the intact samples. The adsorption experimental data fit into the theoretical models showed that the BET model fit better than the Langmuir model. The experimental data fit into the pseudo first order, second order, and Bangham pore diffusion kinetic models showed that the rate-determining steps are bulk pore diffusion and surface interaction. Generally, the results obtained from the study demonstrated the significance of conducting experiments with large, intact core samples pertinent to CO₂ sequestration in shallow coal seams.

Experimental Study of Temperature Effect on Methane Adsorption Dynamic and Isotherm

Knowing the methane adsorption dynamic is of great importance for evaluating shale gas reserves and predicting gas well production. Many experiments have been carried out to explore the influence of many aspects on the adsorption dynamic of methane on shale rock. However, the temperature effect on the adsorption dynamic as a potential enhanced shale gas recovery has not been well addressed in the publications. To explore the temperature effect on the adsorption dynamic of methane on gas shale rock, we conducted experimental measurement by using the volumetric method. We characterized the adsorption dynamic of methane on gas shale powders and found that the curves of pressure response at different pressure steps and temperatures all have the same tendency to decrease fast at first, then slowly in the middle and remain stable at last, indicating the methane molecules are mainly adsorbed in the initial stage. Methane adsorption dynamic and isotherm can be well fitted by the Bangham model and the Freundlich model, respectively. The constant z of the Bangham model first decreases and then increases with equilibrium pressure increasing at each temperature, and it decreases with temperature increasing at the same pressure. The adsorption rate, constant k of the Bangham model, is linearly positively correlated with the natural log of the equilibrium pressure, and it decreases with temperature increasing at the same pressure. Constant K and n of the Freundlich model all decrease with temperature increasing, indicating that low temperatures are favorable for methane adsorption on shale powders, and high temperatures can obviously reduce constant K and n of the Freundlich model. Finally, we calculated isosteric enthalpy and found that isosteric enthalpy is linearly positively correlated with the adsorption amount. These results will be profoundly meaningful for understanding the mechanism of methane adsorption dynamic on shale powders and provide a potential pathway to enhance shale gas recovery.

Ethylene dimethacrylate used as an NH3 adsorbent with high adsorption capacity and selectivity

NH₃ molecularly imprinted polymers (NH₃-MIPs) were synthesized that could successfully separate and recover NH₃ during sludge aerobic composting; however, increased toluene usage during the adsorbent preparation incurred a high cost and severe environmental risks. The purpose of this study was to reduce toluene usage by optimizing the reagent composition of NH₃-MIPs, based on maintaining a high NH₃ adsorption capacity and selectivity. Five adsorbent groups, including NH₃-MIPs, and NH₃-Ethylene dimethacrylate adsorbents (NH₃-EGDMA) with 0%, 75%, 90%, and 100% toluene reduction efficiencies, were prepared and tested for their adsorption performance. The results showed that NH₃-EGDMA with 75% toluene reduction not only had a high NH₃ adsorption capacity (104.42 mg g^-1) but also had a high separation factor for NH₃/methyl sulfide (3121) and NH₃/dimethyl disulfide (4597). The adsorption mechanism was identified as a chemical force between NH₃ and NH₃-EGDMA with a 75% toluene reduction using the analysis of the kinetic model. This study significantly reduces NH₃ adsorbent cost as well as harm to the environment during the adsorbent preparation, which was beneficial to the popularization and application of this NH₃ adsorbent.

Disassembly of lignocellulose into cellulose, hemicellulose, and lignin for preparation of porous carbon materials with enhanced performances

Lignocellulose is the primary component of many biomasses, including corn straw. Herein, lignocellulose in corn straw was disassembled into the individual polymers, cellulose, hemicellulose, and lignin via a mild and facile method. Subsequently, three porous carbon materials were prepared by carbonization and chemical activation of cellulose (PCCC), hemicellulose (PCHC), and lignin (PCLC). The three materials showed higher specific surface areas (2565.7, 2996.1, and 2590.3 m² g^-1) and higher porosities (1.4261, 1.5876, and 1.2406 cm³ g^-1) than that of PCCS, a porous carbon material derived from raw corn straw (1993 m² g^-1 and 1.19 cm³ g^-1). Of note, PCCC and PCHC exhibited higher adsorption (1025.5 and 950.1 mg g^-1) of brilliant green (BG), than PCCS (876.7 mg g^-1). Besides, the BG adsorption capacities of the designed materials were higher than that of most adsorbents, and 2-2.5 times higher than that of graphite oxide (416.7 mg g^-1). These study results indicate that the disassembly of lignocellulosic biomass into cellulose, hemicellulose, and lignin is an effective strategy for preparing various porous carbon materials with enhanced performances.

CuO-modified activated carbon for the improvement of toluene removal in air

We used an impregnation method to prepare CuO/AC (activated carbon) composite materials of different CuO content and characterized them via scanning electron microscope (SEM), Brunauer-Emmett-Teller (BET), and Fourier transform infrared spectroscopy (FT-IR). The effect of CuO content on toluene adsorption/desorption was evaluated. We explored the reusability of AC and AC03 (CuO modified AC with CuO loading 0.3 wt.%) adsorbents via toluene adsorption/desorption cycle testing. We used quasi-first- and quasi-second-order models, the Bangham model, and the Weber-Morris model to fit the toluene adsorption data. The introduction of CuO species evidently improved the adsorption performance of activated carbon toward toluene. The CuO content markedly affected the specific surface area, CuO dispersal, the numbers of oxygen-containing functional groups on the surface, and adsorption performance of the prepared composite adsorbents. Low CuO content was not favorable for the formation of active adsorption sites, while high content greatly reduced the specific surface area, and even covered active adsorption sites. The toluene adsorption performance varied in the order AC03 > AC02 > AC05 > AC08 > AC01 (AC03, AC02, AC05, AC08 and AC01 are CuO modifying AC with CuO loading 0.3, 0.2, 0.5 0.8 and 0.1 wt.%, respectively). The breakthrough time and toluene adsorption capacity of the AC03 composite adsorbent were 94 min and 701.8 mg/g, respectively, and the recycling efficiency was 92.8% after thermal desorption at 200°C. The adsorption process was best described by the Bangham model and adsorption could be divided into three stages.

Deproteinization of four macroporous resins for rapeseed meal polysaccharides

In this study, the adsorption/desorption characteristics of rapeseed meal polysaccharides extract on four resins (HP-20, D3520, XAD-16, and AB-8) were evaluated. The results indicated that HP-20 resin had the best purification effect. Based on static adsorption test, the kinetics and isotherms of the four resins for protein and polysaccharide were investigated. The adsorption test showed that the pseudo-second-order kinetics model and the Freundlich isotherm model were more suitable for explanation of the adsorption process for protein and polysaccharide. Static desorption test showed that the highest protein desorption ratios of HP-20, D3520, and AB-8 resins could be obtained with 60% ethanol solution as eluate, and the highest protein desorption ratios of XAD-16 resin could be obtained with 40% ethanol solution as eluate. Dynamic adsorption/desorption tests of HP-20 resin showed that the deproteinization ratio was 91% and the polysaccharide recovery ratio was 62% when the treatment amount was 1.5 BV. Compared with three traditional methods, HP-20 resin adsorption method that the deproteinization ratio was 82% was more potent than the three traditional methods for purifying polysaccharides from rapeseed meal. In addition, UV/vis spectroscopy showed that most of the protein was absorbed by resins, and FT-IR spectroscopy indicated that the purity of the polysaccharide after purification was improved. Rapeseed meal polysaccharides could be effectively deproteinized using HP-20 resin, and it was suitable for purifying polysaccharides from rapeseed meal.

Distribution characteristics of trifluoroacetic acid in the environments surrounding fluorochemical production plants in Jinan, China

Trifluoroacetic acid (TFA) is a ubiquitous and extremely stable contaminant in the ambient environment and may be discharged during fluorochemical production processes. However, the impacts of fluorochemical production on surrounding areas have seldom been evaluated. We focused on Jinan, the capital of Shandong Province, China, and measured TFA levels in water, soil, and air samples. Our results showed that the average TFA concentrations in flowing water bodies were lower than those in landscape water bodies. The average TFA concentrations in soils were significantly higher than the background concentration. As for atmospheric TFA levels, the mean concentrations in the gas phase were higher than those in the particle phase, and average daytime levels were slightly higher than nighttime levels. In addition, the quotient method was used to assess the ecological risk of TFA in water in Jinan. The ratio of pollutant environmental concentration to predicted no-effect concentration (PEC/PNEC) for TFA was greater than 1, indicating that TFA does potentially damage the aquatic ecosystem of Jinan. Our findings suggest that TFA pollution around fluoride production plants is a serious problem and that actions are required to avoid exacerbating the local ecological and environmental risks of TFA.

Fully phosphorylated 3D graphene oxide foam for the significantly enhanced U(VI) sequestration

Efficient sequestration of U(VI) from complex aqueous solution is of vital importance for environmental remediation. In this work, the fully phosphorylated graphene oxide foam (phos-GOF) was synthesized via a facile hydrothermal method and the as-prepared 3D phos-GOF was served as an adsorbent to capture U(VI) from aqueous solution. The introduction of abundant phosphorus-containing groups via phytic acid endows phos-GOF good hydrophilia and excellent affinity for U(VI). The adsorption performance of phos-GOF for U(VI) was carefully evaluated under different environments. phos-GOF shows rapid and high efficiency for U(VI) adsorption. The maximum adsorption capacity of phos-GOF for U(VI) is ∼483 mg/g, which is much higher than that of pristine graphene oxide foam (GOF). In addition, the spent 3D phos-GOF can be easily regenerated by a simple and low-cost desorption process using 0.02 mol/L HNO₃. The interaction mechanism between phos-GOF and U(VI) is mainly attributed to the inner-sphere complexation between phosphoric functional groups and U(VI) based on a series of spectroscopic analyses. The 3D phos-GOF exhibits favorable sequestration performance towards U(VI) which can be used as a potential candidate in uranium-bearing wastewater treatment and disposal.

Multimedia Distribution and Transfer of Per- and Polyfluoroalkyl Substances (PFASs) Surrounding Two Fluorochemical Manufacturing Facilities in Fuxin, China

Industrial facilities can be point sources of per- and polyfluoroalkyl substances (PFASs) emission to the surrounding environment. In this study, 25 neutral and ionizable PFASs were analyzed in 94 multimedia samples including air, rain, outdoor settled dust, soil, plant leaves, river water, surface sediment, and shallow groundwater from two fluorochemical manufacturing parks (FMPs) in Fuxin, China, to elucidate the multimedia distribution and transfer pattern of PFASs from a point source. The concentrations of individual PFASs in air, outdoor settled dust, and surface river water decreased exponentially as the distance increases from the FMPs, whereas the concentrations of short-chain (C2-C4) perfluoroalkyl carboxylic acids (PFCAs) remained high (3000 ng/L) in the surface water 38 km away. At FMPs, air concentrations of fluorotelomer alcohols and iodides were found dominant with levels of up to 7900 pg/m³ and 920 pg/m³, respectively. Trifluoroacetic acid was directly released from FMPs and occurred in all the environmental matrices at levels 1-2 orders of magnitude higher than other PFCAs. Higher air-water concentration ratios of short-chain PFCAs (C2-C4) suggested their transfer tendency from air to water. Both short-chain (C2) and long-chain (>C6) PFCAs have greater sediment-water distribution coefficients and deposit dust-air coefficients, which have great influences on the long-range transport potential of different analogues.

Environmental effects of ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2017

The Environmental Effects Assessment Panel (EEAP) is one of three Panels of experts that inform the Parties to the Montreal Protocol. The EEAP focuses on the effects of UV radiation on human health, terrestrial and aquatic ecosystems, air quality, and materials, as well as on the interactive effects of UV radiation and global climate change. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than previously held. Because of the Montreal Protocol, there are now indications of the beginnings of a recovery of stratospheric ozone, although the time required to reach levels like those before the 1960s is still uncertain, particularly as the effects of stratospheric ozone on climate change and vice versa, are not yet fully understood. Some regions will likely receive enhanced levels of UV radiation, while other areas will likely experience a reduction in UV radiation as ozone- and climate-driven changes affect the amounts of UV radiation reaching the Earth's surface. Like the other Panels, the EEAP produces detailed Quadrennial Reports every four years; the most recent was published as a series of seven papers in 2015 (Photochem. Photobiol. Sci., 2015, 14, 1-184). In the years in between, the EEAP produces less detailed and shorter Update Reports of recent and relevant scientific findings. The most recent of these was for 2016 (Photochem. Photobiol. Sci., 2017, 16, 107-145). The present 2017 Update Report assesses some of the highlights and new insights about the interactive nature of the direct and indirect effects of UV radiation, atmospheric processes, and climate change. A full 2018 Quadrennial Assessment, will be made available in 2018/2019.