•Orange peel-derived hydrochars are obtained by hydrothermal carbonization.•New adsorbents are developed by thermal and chemical activation of the hydrochars.•Adsorption of emerging contaminants ...depends on the adsorbents’ characteristics.•Kinetic studies are performed and adsorption isotherms are determined and modeled.
Activated hydrochars obtained from the hydrothermal carbonization of orange peels (Citrus sinensis) followed by various thermochemical processing were assessed as adsorbents for emerging contaminants in water. Thermal activation under flows of CO2 or air as well as chemical activation with phosphoric acid were applied to the hydrochars. Their characteristics were analyzed and related to their ability to uptake three pharmaceuticals (diclofenac sodium, salicylic acid and flurbiprofen) considered as emerging contaminants. The hydrothermal carbonization and subsequent activations promoted substantial chemical transformations which affected the surface properties of the activated hydrochars; they exhibited specific surface areas ranging from 300 to ∼620m2/g. Morphological characterization showed the development of coral-like microspheres dominating the surface of most hydrochars. Their ability to adsorb the three pharmaceuticals selected was found largely dependent on whether the molecules were ionized or in their neutral form and on the porosity developed by the new adsorbents.
Activated carbon cloths (ACC) were prepared from lyocell, a novel regenerated cellulose nanofibre fabric, by phosphoric acid activation in inert atmosphere at two different final thermal treatment ...temperatures (864 and 963
°C). Benzene, toluene and n-hexane isotherms at 298 and 273
K were measured in order to gain insight into the porous structure of the ACC and to evaluate their performance for the removal of volatile organic compounds (VOCs). The Dubinin–Radushkevich equation was employed to evaluate textural parameters of the ACC. The textural characteristics of the ACC were compared with those previously determined from nitrogen (77
K) and carbon dioxide (273
K) adsorption data. The samples were essentially microporous. The textural parameters calculated from the hydrocarbon isotherms were in good agreement with those evaluated from nitrogen isotherms for the ACC with the wider microporosity. Additionally, the Freundlich model provided a good description of the experimental isotherms for the three volatile organic compounds. The ACC obtained at the higher temperature exhibited a larger adsorption capacity. The ACC were also electrically conductive and showed potential for regeneration by the Joule effect, as determined from macroscopic electrical measurements before and after n-hexane adsorption.
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•Two pine cones species were explored as activated carbons novel precursors.•Effectiveness of the activated carbons in nitrate removal was examined.•Thermal and urea posttreatment ...were assayed to improve their adsorption performances.•Post-treated carbons showed greater ability in nitrate removal.•Uptake improvements were in line with enhanced N contents and basic functionalities.
Activated carbons from two species of pine cones (Pinus canariensis and Cupressus sempervirens) were prepared by phosphoric acid activation and tested for the removal of nitrate ions from aqueous solution. To investigate the feasibility of improving their nitrate adsorption capacity, two different post-treatments – a thermal treatment and a treatment with saturated urea solution – were also applied to the prepared activated carbons. Comparison of the treated and untreated activated carbons showed that both post-treatments improved the nitrate adsorption performance more than twice. The maximum adsorption capacity, as evaluated from determination of the adsorption isotherms for the P. canariensis based carbons, and their proper representation by the Langmuir model, demonstrated that the post-treatment with the urea solution led to activated carbons with increased nitrate removal effectiveness, even superior to other reported results. Enhancements in their adsorption capacity could be mainly ascribed to higher contents of nitrogen and basic functional groups, whereas porous structure of the activated carbons did not seem to play a key role in the nitrate uptake.
Three biomass, birch wood
Betula sp., marine brown alga
Fucus vesiculosus, and terrestrial moss
Pleurozium schreberi, have been compared as raw materials for preparation of biosorbents for removal of ...copper ions from diluted water solutions. Small sample doses (0.5
g/100
ml) of the biosorbents prepared from alga and moss enabled more than 90% removal of Cu(II) ions from diluted water solutions (5–20
mg/l). The sample from sawdust was less effective.
A pseudo-second-order rate model properly described the experimental kinetic data for the biosorbents. The maximum sorption capacities (
X
m) determined from the experimental equilibrium isotherms by applying the Langmuir model showed that the alga had the best copper-binding ability (
X
m
=
23.4
mg/g), followed by the moss (
X
m
=
11.1
mg/g), and the sawdust (
X
m
=
4.9
mg/g). No visible damages or performance losses were detected for the alga and moss after five sorption–desorption cycles using diluted HCl as eluent.
The feasibility of using cypress cone chips from
Cupressus sempervirens as a low-cost biosorbent for the removal of two representative basic dyes, methylene blue (MB) and rhodamine B (RhB), from ...aqueous solutions was investigated in batch and continuous modes. Dyes biosorption was strongly dependent on the solution’s pH. Sorption kinetics was determined and properly described by the pseudo-second-order rate model. Experimental equilibrium isotherms fitted the Langmuir model, showing maximum biosorption capacities of 0.62
mmol/g for MB and 0.24
mmol/g for RhB. Competitive experiments from a binary solution of the dyes demonstrated the preference of the cone chips for biosorbing MB. Very low desorption efficiencies were obtained for both dyes. Dynamic experiments showed that the breakthrough time was three times higher for MB biosorption than for RhB for the same conditions. Breakthrough curves were properly represented by a mathematical model.
Activated carbons were developed by phosphoric acid activation of sawdust from
Prosopis ruscifolia wood, an indigenous invasive species of degraded lands, at moderate conditions (acid/precursor ratio
...=
2, 450
°C, 0.5
h). For
in situ modification of their characteristics, either a self-generated atmosphere or flowing air was used. The activated carbons developed in the self-generated atmosphere showed higher BET surface area (2281
m
2/g) and total pore volume (1.7
cm
3/g) than those obtained under flowing air (1638
m
2/g and 1.3
cm
3/g). Conversely, the latter possessed a higher total amount of surface acidic/polar oxygen groups (2.2
meq/g) than the former (1.5
meq/g). To evaluate their metal sorption capability, adsorption isotherms of Cu(II) ion from model solutions were determined and properly described by the Langmuir model. Maximum sorption capacity (
X
m) for the air-derived carbons (
X
m
=
0.44
mmol/g) almost duplicated the value for those obtained in the self-generated atmosphere (
X
m
=
0.24
mmol/g), pointing to a predominant effect of the surface functionalities on metal sequestering behaviour. The air-derived carbons also demonstrated a superior effectiveness in removing Cd(II) ions as determined from additional assays in equilibrium conditions. Accordingly, effective phosphoric acid-activated carbons from
Prosopis wood for toxic metals removal from wastewater may be developed by
in situ modification of their characteristics operating under flowing air.
Development of activated carbons targeted at nitrate ion removal is investigated by chemical activation of sawdust from the invasive species Parkinsonia aculeata wood. Phosphoric acid and potassium ...hydroxide are comparatively used as activating agent. Its effect on main physico-chemical properties and on the effectiveness of the activated carbons in nitrate removal is compared with those determined for a commercial sample. Activated carbons developed with the base show the best effectiveness in nitrate removal, as determined from application of the Langmuir model to the experimental isotherms. The behavior is consistent with the development of surface basic groups and the more basic character of these carbons. Noticeable improvement in nitrate uptake for all the carbons is attained after treatment with a saturated urea solution, with removal levels of ∼80–90%, despite reductions in porous structures. Nitrate adsorption onto the urea-treated carbons is in direct correlation with their enhanced contents of elemental nitrogen.
► Chemically activated carbons from an unexplored biomass are developed with H3PO4 acid and KOH. ► Effectiveness of the carbons in nitrate removal is examined. ► KOH-derived carbons show greater ability in nitrate uptake. ► Urea post-treatment of the carbons improves nitrate uptake in line with enhanced contents of elemental N.
An industrial raw Kraft lignin was investigated to ascertain its potential use for removal of trace Ni(II) ion from wastewater by using dilute solutions (0.34–1.7
mM) as models. The effect of ...demineralisation on its metal sorption ability was examined by employing acid pre-treated samples. Under fixed pre-established equilibrium conditions, the raw lignin exhibited a lower effectiveness than the demineralised one, with the latter attaining an almost complete removal of Ni(II) ions. For both lignins, sorption kinetics was properly described by a pseudo-second order rate model. Equilibrium isotherms were also determined and adequately represented by conventional two-parameter models. The higher nickel sorption capacity for the demineralised lignin compared to the raw sample was consistent with enhancements in the negative magnitude of zeta potential, sodium sorption capacity, and content of phenolic hydroxyl groups occasioned by the acid pre-treatment. Accordingly, demineralisation appears as a readily convenient strategy to improve the behaviour of industrial Kraft lignin for potential use as a biosorbent of trace nickel from polluted water.
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