Biomass wastes are considered as cost-effective and sustainable precursors to prepare activated carbons for CO2 capture. In this study, two biomass-derived activated carbons were prepared using peanut shell and sunflower seed shell, and the optimal activated carbons were obtained at low KOH/carbon ratio of about 1. The peanut shell derived activated carbon (P-973-1.00) and sunflower seed shell derived activated carbon (S-973-1.25) exhibited CO2 uptake of 1.54 and 1.46 mmol/g, respectively, at 298 K and 0.15 bar, among the activated carbons with the highest CO2 adsorption. Although P-973-1.00 had much lower surface area and micropore volume than S-973-1.25, it possessed higher CO2 uptake at 298 K and 0.15 bar due to the higher volume of micropores in the range of 0.3–0.44 nm. The calculated higher isosteric heat values at lower CO2 uptake indicated the strong affinity of CO2 in these micropores. The ordered micro-sized pores in the activated carbons were favorable for CO2 diffusion into the porous materials and adsorption in the inner micropores. The activated carbons had moderate CO2 selectivity over N2 at 1 bar, but the selectivity was significantly enhanced at 0.15 bar. The spent activated carbons after vacuum regeneration exhibited stable CO2 adsorption in five cycles, showing the high reusability for CO2 capture.

Hydrophobic interaction has been considered to be responsible for adsorption of perfluorooctanesulfonate (PFOS) on the surface of hydrophobic adsorbents, but the long C–F chain in PFOS is not only hydrophobic but also oleophobic. In this study, for the first time we propose that air bubbles on the surface of hydrophobic carbonaceous adsorbents play an important role in the adsorption of PFOS. The level of adsorption of PFOS on carbon nanotubes (CNTs), graphite (GI), graphene (GE), and powdered activated carbon (PAC) decreases after vacuum degassing. Vacuum degassing time and pressure significantly affect the removal of PFOS by these adsorbents. After vacuum degassing at 0.01 atm for 36 h, the extent of removal of PFOS by the pristine CNTs and GI decreases 79% and 74%, respectively, indicating the main contribution of air bubbles to PFOS adsorption. When the degassed solution is recontacted with air during the adsorption process, the removal of PFOS recovers to the value obtained without vacuum degassing, further verifying the key role of air bubbles in PFOS adsorption. By theoretical calculation, the distribution of PFOS in air bubbles on the adsorbent surfaces is discussed, and a new schematic sorption model of PFOS on carbonaceous adsorbents in the presence of air bubbles is proposed. The accumulation of PFOS at the interface of air bubbles on the adsorbents is primarily responsible for its adsorption, providing a new mechanistic insight into the transport, fate, and removal of PFOS.

Polyethylenimine (PEI)-modified chitosan was prepared and used to remove clofibric acid (CA) from aqueous solution. PEI was chemically grafted on the porous chitosan through a crosslinking reaction, and the effects of PEI concentration and reaction time in the preparation on the adsorption of clofibric acid were optimized. Scanning electron microscopy (SEM) showed that PEI macromolecules were uniformly grafted on the porous chitosan, and the analysis of pore size distribution indicated that more mesopores were formed due to the crosslinking of PEI molecules in the macropores of chitosan. The PEI-modified chitosan had fast adsorption for CA within the initial 5 h, while this adsorbent exhibited an adsorption capacity of 349 mg·g−1 for CA at pH 5.0 according to the Langmuir fitting, higher than 213 mg·g−1 on the porous chitosan. The CA adsorption on the PEI-modified chitosan was pH-dependent, and the maximum adsorption was achieved at pH 4.0. Based on the surface charge analysis and comparison of different pharmaceuticals adsorption, electrostatic interaction dominated the sorption of CA on the PEI-modified chitosan. The PEI-modified chitosan has a potential application for the removal of some anionic micropollutants from water or wastewater.

Polyethylenimine (PEI)-impregnated resins with high CO2 adsorption capacity were successfully prepared in this study. The nonpolar resin HP20 was suitable for PEI loading to achieve high CO2 adsorption, and the optimal PEI loading was 50 wt %. On the basis of the pore-size distribution of the resin before and after PEI modification, it can be found that mesopores of <43 nm were mainly responsible for PEI loading and pores in the range of 43–68 nm were probably favorable for CO2 diffusion. The adsorbed amount of CO2 on HP20/PEI-50 decreased with increasing adsorption temperature because of the dominant role of exothermic reaction of CO2 adsorption. The adsorption of CO2 on the adsorbent was very fast, and sorption equilibrium was achieved within 6 min at 75 °C. HP20/PEI-50 almost kept a stable adsorption capacity for CO2 at concentrations of 15 vol % and 400 ppm in the consecutive adsorption–desorption cycles, and its adsorption capacity was 181 mg/g from pure CO2 and 99.3 mg/g from 400 ppm CO2 at 25 °C, higher than all PEI-modified materials reported. The high volume-based amount of CO2 adsorbed on HP20/PEI-50 (96.0 mg/cm3 at 25 °C and 84.5 mg/cm3 at 75 °C for pure CO2) is beneficial to reducing the required volume of the adsorption bed for CO2 capture. This spherical and stable HP20/PEI-50 adsorbent with high and fast CO2 adsorption exhibits a very promising application in CO2 capture from flue gas and ambient air.Keywords: amine-modified adsorbent; carbon capture; CO2 adsorption; polyethylenimine; resin;

Rapidly increasing concentration of CO2 in the atmosphere has drawn more and more attention in recent years, and adsorption has been considered as an effective technology for CO2 capture from the anthropogenic sources. In this paper, the attractive adsorbents including activated carbons and amine-modified materials were mainly reviewed and discussed with particular attention on progress in the adsorbent preparation and CO2 adsorption capacity. Carbon materials can be prepared from different precursors including fossil fuels, biomass and resins using the carbonization-activation or only activation process, and activated carbons prepared by KOH activation with high CO2 adsorbed amount were reviewed in the preparation, adsorption capacity as well as the relationship between the pore characteristics and CO2 adsorption. For the amine-modified materials, the physical impregnation and chemical graft of polyethylenimine (PEI) on the different porous materials were introduced in terms of preparation method and adsorption performance as well as their advantages and disadvantages for CO2 adsorption. In the last section, the issues and prospect of solid adsorbents for CO2 adsorption were summarized, and it is expected that this review will be helpful for the fundamental studies and industrial applications of activated carbons and amine-modified adsorbents for CO2 capture.

A novel Ni–Fe bimetal with high dechlorination activity for 4-chlorophenol (4-CP) was prepared by ball milling (BM) in this study. Increasing Ni content and milling time greatly enhanced the dechlorination activity, which was mainly attributed to the homogeneous distribution of Ni nanoparticles (50–100 nm) in bulk Fe visualized by scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) with image mapping. In comparison with the Ni–Fe bimetal prepared by a chemical solution deposition (CSD) process, the ball milled Ni–Fe bimetal possessed high dechlorination activity and stability before being used up. Dechlorination kinetics indicated that the dechlorination rates of 4-CP increased with increasing Ni–Fe dose but decreased with increasing solution pH. Solution pH had a significant effect on the dechlorination of 4-CP and the passivation of the Ni–Fe bimetal. The enhanced pH during the dechlorination process significantly accelerated the formation of passivating film on the bimetallic surface. The Ni–Fe bimetal at the dose of 60 g/L was reused 10 times without losing dechlorination activity for 4-CP at initial pH less than 6.0, but the gradual passivation was observed at initial pH above 7.0.

Three adsorbents including TiO2, Ti-Ce, and Ti-La hybrid oxides were prepared to remove fluoride from aqueous solution. The Ti-Ce and Ti-La hybrid adsorbents obtained by the hydrolysis-precipitation method had much higher sorption capacity for fluoride than the TiO2 adsorbent prepared through hydrolysis. Rare earth (Ce and La) oxides and TiO2 exhibited a synergistic effect in the hybrid adsorbents for fluoride sorption. The sorption equilibrium of fluoride on the three adsorbents was achieved within 4 h, and the pseudo-second-order model described the sorption kinetics well. The sorption isotherms fitted the Langmuir model well, and the adsorption capacities of fluoride on the Ti-Ce and Ti-La adsorbents were about 9.6 and 15.1 mg·g−1, respectively, at the equilibrium fluoride concentration of 1.0 mg·L−1, much higher than the 1.7 mg·g−1 on the TiO2. The sorption capacities of fluoride on the three adsorbents decreased significantly when the solution pH increased from 3 to 9.5. The electrostatic interaction played an important role in fluoride removal by the three adsorbents, and Fourier transform infrared (FTIR) analysis indicated that the hydroxyl groups on the adsorbent surface were involved in fluoride adsorption.

The concentration and size of suspended solids (SS) in the treated produced water beyond the criteria of injection water in Daqing oilfield have raised great concerns in recent years. The SS in produced water from water, polymer and alkali–surfactant–polymer (ASP) flooding were successfully separated and characterized using some analytical techniques in this study. X-ray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and heating method reveal that some organic compounds besides crude oil were present in the SS samples, and polyacrylamide was found in the SS from polymer and ASP flooding. X-ray diffraction (XRD) shows some crystal inorganic substances such as SiO2, Fe2O3, Fe3O4, and BaSO4 in the SS samples, and XPS analysis indicated that several iron compounds with different valences were present in the three SS samples. The mean diameters of three SS samples were 22.89, 11.28 and 17.61 μm, respectively. Most importantly, the aggregates formed by the SS and oil droplets as well as the small SS adsorbed on the surface of oil droplets were observed using a microscope, indicating that the SS can be removed with crude oil, and crude oil also contributes to the determination of the SS values.

Novel aminated polyacrylonitrile fibers (APANFs) were prepared through the reaction of polyacrylonitrile fibers (PANFs) with four multinitrogen-containing aminating reagents, and the best adsorbent was obtained after the optimization of preparation experiments. The APANFs were effective for arsenate removal from aqueous solution, and the sorption behaviors including kinetics, isotherms, effect of pH, and competitive anions were investigated. Experimental results show that the equilibrium of arsenate sorption on the fibers was achieved within 1 h, and Langmuir equation described the sorption isotherms well with a high sorption capacity of 256.1 mg/g obtained. The thermodynamic parameters calculated show that the sorption was spontaneous and exothermic under the condition applied. The zero point of ζ potential of the APANFs was at about pH = 8.2, in contrast with that of the PANFs at pH = 3.6. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) for the APANFs before and after arsenate adsorption revealed that the amine groups on the fiber surface played an important role in the removal of arsenate from water, attributed to the electrostatic interaction between the positive protonated amine groups and negative arsenate ions.

•PFOSF washing wastewater contains high concentrations of perfluorinated carboxylates.•Bamboo-derived activated carbon and resin IRA67 are suitable for PFCA removal.•PFOA is preferentially adsorbed on BAC and IRA67 among different PFCAs.•BAC exhibits stable removal of three PFCAs in the wide pH range.•IRA67 is successfully regenerated and exhibits stable removal in adsorption cycles.Perfluorooctanesulfonyl fluoride (PFOSF) washing wastewater contains high concentrations of perfluorinated carboxylates (PFCAs) including perfluorohexanoate (PFHxA, 0.10 mmol/L), perfluoroheptanoate (PFHpA, 0.11 mmol/L), and perfluorooctanoate (PFOA, 0.29 mmol/L). For the first time, we investigated the removal of these PFCAs from actual wastewater using the bamboo-derived activated carbon (BAC) and resin IRA67. Adsorption kinetics, effects of adsorbent dose, solution pH, and inorganic ions, as well as regeneration and reuse experiments were studied. The removal percents of three PFCAs by BAC and IRA67 followed the increasing order of PFHxA < PFHpA < PFOA, but the adsorption equilibrium time conformed to the reverse trend. PFCAs removal on IRA67 decreased with increasing pH, but BAC almost kept stable PFCAs removal at pH above 5.0. Among competitive adsorption of three PFCAs, PFOA was preferentially adsorbed on both BAC and IRA67. PFCAs removal from actual wastewater by BAC was higher than that in simulated solution, due to the presence of high concentration of inorganic ions in the wastewater. However, the co-existing organic compounds in wastewater significantly suppressed the adsorption of PFCAs. Both spent BAC and IRA67 were successfully regenerated by ethanol solution or NaCl/methanol mixture, and IRA67 showed the stable removal of PFCAs in five adsorption cycles.

•Granular bamboo-derived activated carbon is successfully prepared by KOH activation.•The micron and nano-sized pores are suitable for PFOS/PFOA diffusion and sorption.•The activated carbon has fast and high PFOS/PFOA adsorption.•Spent activated carbon can be regenerated in 50% methanol solution.A bamboo-derived granular activated carbon with large pores was successfully prepared by KOH activation, and used to remove perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) from aqueous solution. The granular activated carbon prepared at the KOH/C mass ratio of 4 and activation temperature of 900 °C had fast and high adsorption for PFOS and PFOA. Their adsorption equilibrium was achieved within 24 h, which was attributed to their fast diffusion in the micron-sized pores of activated carbon. This granular activated carbon exhibited the maximum adsorbed amount of 2.32 mmol/g for PFOS and 1.15 mmol/g for PFOA at pH 5.0, much higher than other granular and powdered activated carbons reported. The activated carbon prepared under the severe activation condition contained many enlarged pores, favorable for the adsorption of PFOS and PFOA. In addition, the spent activated carbon was hardly regenerated in NaOH/NaCl solution, while the regeneration efficiency was significantly enhanced in hot water and methanol/ethanol solution, indicating that hydrophobic interaction was mainly responsible for the adsorption. The regeneration percent was up to 98% using 50% ethanol solution at 45 °C.Download full-size image