Sorption of perfluorinated compounds (PFCs) on carbon nanotubes (CNTs) is critical for understanding their subsequent transport and fate in aqueous environments, but the sorption mechanisms remain largely unknown. In this study, the sorption of six PFCs on CNTs increased with increasing C-F chain length when they had a same functional group, and the CNTs with hydroxyl and carboxyl groups had much lower adsorbed amount than the pristine CNTs, indicating that hydrophobic interaction dominated the sorption of PFCs on the CNTs. Electrostatic repulsion suppressed the sorption of PFCs on the CNTs, resulting in the lower sorption with increasing pH. Hydrogen bonding interaction was negligible. The hydrophobic C-F chains can be closely adsorbed on the CNTs surface in parallel to the axis or along the curvature, making it impossible to form micelles on the CNT surface, leading to the lower sorption than other adsorbents.

Complementary sorption of different chemicals was expected and investigating the relationship between the sorption inhibition of primary sorbate (ΔQᵖʳⁱ) and sorption of secondary sorbate (Qˢᵉᶜ) could provide a new angle to understand coadsorption of different chemicals. This study used bisphenol A (BPA) as the primary adsorbate, sulfamethoxazole (SMX) as the competitor, and carbon nanotubes as model adsorbents to study their complementary and competitive adsorption. At low BPA concentrations, the sorption of SMX (Qˢᵉᶜ) exceeded BPA sorption inhibition (ΔQᵖʳⁱ), indicating that these two chemicals complementarily adsorbed on their respectively preferred sorption sites. At high BPA concentrations, higher ΔQᵖʳⁱ was observed in comparison to Qˢᵉᶜ, which may be resulted from different packing efficiencies of the adsorbed SMX and BPA. This study emphasized that both competitive and complementary sorption should be discussed in binary sorption system.

The development of oil sorbents with high sorption capacity, low cost, scalable fabrication, and high selectivity is of great significance for water environmental protection, especially for oil spillage on seawater. In this work, we report nanoporous polystyrene (PS) fibers prepared via a one-step electrospinning process used as oil sorbents for oil spill cleanup. The oleophilic–hydrophobic PS oil sorbent with highly porous structures shows a motor oil sorption capacity of 113.87g/g, approximately 3–4times that of natural sorbents and nonwoven polypropylene fibrous mats. Additionally, the sorbents also exhibit a relatively high sorption capacity for edible oils, such as bean oil (111.80g/g) and sunflower seed oil (96.89g/g). The oil sorption mechanism of the PS sorbent and the sorption kinetics were investigated. Our nanoporous material has great potential for use in wastewater treatment, oil accident remediation and environmental protection.

In this study, the applications of mesoporous materials based on silica, and those with modifications, namely post-synthetic grafting, co-condensation, and pure SBA-15, were investigated for the removal of phosphate from sewage. The mesostructures were confirmed by X-ray diffraction, Brunauer–Emmett–Teller, Fourier transform infrared spectroscopy, and transmission electron microscopy. The absorption of phosphate by the mesoporous adsorbents was examined, using different adsorption models to describe the equilibrium and kinetic data. The maximum adsorption capacities of the mesostructured adsorbents were found to be 69.970, 59.890, and 2.018 mg/g for the co-condensation, post-synthetic grafting, and pure SBA-15, respectively. The kinetic data showed that the adsorption of phosphate onto three different mesostructures followed the pseudo-first-order kinetic model.

An effective adsorbent for the removal of heavy metals was manufactured by immobilization of jujube powder. The adsorptions of Cd, Zn and Cu from aqueous solutions by jujube complex beads (Type 1 and Type 2) were studied in a batch adsorption system. The adsorption data were fitted well with the Langmuir isotherm models. The adsorption capacities (β) for Cd, Zn and Cu were 4.23, 2.93 and 3.64 mg/g in Type 1 and 1.24, 0.70 and 1.35 mg/g in Type 2 beads. The removal efficiencies of the Type 2 beads, with a larger unit surface area, were lower than those of the Type 1 due to part of the casein or cyclic AMP being destroyed during the drying process of the Type 1. These values for Type 1 beads were higher than those of all other adsorbents for each heavy metal. A comparison of the kinetic models on the overall adsorption rate showed that the adsorption system was best described by pseudo-first-order kinetics. The removal efficiencies of Cd, Zn and Cu exhibited similar tendencies to those observed in the equilibrium tests. This indicates that the jujube complex beads developed in this study can be used as promising adsorbents for the removal of heavy metals from wastewater.

Three novel composite adsorbents, sulfate-coated zeolite (SCZ), hydrotalcite (SCH), and activated alumina (SCAA), were characterized and employed for the removal of phosphate from aqueous solution using equilibrium and kinetic batch experiments. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction spectrum were used to study the surface characteristics of the coated layer. Equilibrium tests showed that the adsorption of phosphate followed both Langmuir and Freundlich isotherms. The powder-type SCZ was better for phosphate removal (maximum binding energy, β = 111.49 mg g−1) compared to hydrotalcite and activated alumina. The adsorption of phosphate was considered to take place mainly by ion exchange. The kinetic data followed a pseudo-second-order kinetic model. The initial adsorption of phosphate onto the sulfate-coated adsorbents was fast, indicating that the sulfate-coated materials developed in this study can be used as promising adsorbents for the removal of phosphate from wastewater or sewage.

Arsenic mobility around mining districts is primarily controlled by distribution and abundance of iron minerals. Arsenite-rich mine waters although frequently reported, the interaction of which with schwertmannite is poorly understood despite its high toxicity and mobility. We examined three synthetic schwertmannite types distinguished by surface area (19.9–227.5 m2/g), Fe/S molar fractions (4.7–6.6), and saturation index (−1.6–0.8) towards arsenite retention through controlled batch equilibrium studies at 22 ± 2°C and 1 atmospheric pressure in oxic conditions. Sorption isotherms were investigated as a function of dissolved arsenite concentrations (0.13–1.33 mmol/L) at constant sediment load (10 g/L) and pH (3.0) in order to understand the role of synthesis pathway and physicochemical properties on arsenite immobilization. Multilayer surface coverage with more than one process governs arsenite uptake. X-ray diffractograms, infrared spectroscopy, and high resolution electron microscopic examination revealed new phase formation where schwertmannite underwent morphological and structural degradation. Ionic exchange between schwertmannite SO 4 2− and aqueous arsenite has resulted in an elevated aqueous SO 4 2− that varied according to dissolved arsenite concentrations. Stoichiometric calculations showed that 1 mol of dissolved arsenite can effectively replace 0.12–0.19 mol of schwertmannite SO 4 2− . This study implies that schwertmannites can be used as potential adsorbents for arsenite treatment where the total uptake will be strongly controlled by both ion exchange and surface precipitation.

The adsorption behavior of denim blue from aqueous solutions in column systems, using both carbonaceous material and Fe-zeolitic tuff (Fe-Z), was determined. The breakthrough data obtained for denim blue adsorption were fitted to the empty-bed contact time, Bohart–Adams, Thomas, and Yoon–Nelson models. The parameters such as breakthrough and saturation times, bed volumes, kinetic constants, adsorption capacities, and adsorbent usage rates (AUR) were determined. The results show that the breakthrough time increases proportionally with increasing bed height, but it decreases as the kinetic constant increases. The adsorption capacity for denim blue for carbonaceous material was higher than Fe-Z. AUR was lower for carbonaceous material than Fe-Z. The results indicated that the carbonaceous material from pyrolysis of sewage sludge is a good adsorbent for denim blue removal.

A batch sorption method was used to study the removal of few toxic metals onto the Late Cretaceous clays of Aleg formation (Coniacian–Lower Campanian system), Tunisia, in single, binary and multi-component systems. The collected clay samples were used as adsorbents for the removal of Pb(II), Cd(II), Cu(II) and Zn(II) from aqueous solutions. Results show that the natural clay samples were mainly composed of silica, alumina, iron and magnesium oxides. N2-adsorption measurements indicated mesoporous materials with modest specific surface area of <71 m2/g. Carbonate minerals were the most influencing parameters for heavy metal removal by natural clays in both single and multi-element systems. The affinity sequence was Pb(II)>Cu(II)>Zn(II)>Cd(II) due to the variable physical properties of the studied metals. The maximum adsorption capacity reached 131.58 mg/g in single systems, but decreased to <50.10 mg/g in mixed systems. In single, binary and muti-element systems, the studied clay samples removed substantial amounts of heavy metals, showing better effectiveness than the relevant previous studies. These results suggest that the studied clay samples of the Late Cretaceous clays from Tunisia can be effectively used as natural adsorbents for the removal of toxic heavy metals in aqueous systems.

The adsorption of As(III), As(V), Se(IV) and Se(VI) by seawater neutralized red mud and alum water treatment sludge was investigated and compared using the batch adsorption technique. For water treatment sludge, adsorption of As(V), Se(IV) and Se(VI), at equimolar concentrations of added metalloid, declined with increasing pH. The decline was rapid above pH 4.0 for Se(VI), above pH 5.0 for Se(IV) and above pH 6.0 for As(V). Adsorption of As(III) increased with increasing pH up to pH 9.0 and then declined. For red mud, adsorption of As(V), Se(IV) and Se(VI) showed a maximum at about pH 5.0 and for As(III) adsorption remained relatively constant over the pH range 2.0–10.0 after which it declined. Water treatment sludge removed 50 % or more of solution As(V) between pH 2.0 and 10.8, Se(IV) between 2.0 and 8.9, Se(VI) between 2.0 and 5.8 and As(III) between 8.4 and 10.9. By contrast, red mud showed less than 25 % adsorption of added Se(VI) and As(III) over the entire pH range tested (2.0–12.0) and reached 50 % or more for As(V) only over the pH range 4.0–6.9 and for Se(IV) between pH 4.3 and 5.6. At pH 5.0, adsorption of As(III) and Se(IV) was better described by the Langmuir than Freundlich equation but the reverse was the case for As(V) and Se(VI). Kinetic data for adsorption of all four oxyanions onto both adsorbents correlated well with a pseudo-second-order kinetic model suggesting the process involved was chemisorption. NaOH was more effective at removing adsorbed metals from both adsorbents than HNO₃. Water treatment sludge maintained its As(III) and Se(IV) adsorption capability at greater than 70 % of that added over eight successive cycles of adsorption/regeneration using 0.5 M NaOH as a regenerating agent. By contrast, for red mud, As(V) adsorption capacity declined very rapidly after three adsorption/desorption cycles and that for Se(IV) it decreased progressively with increasing numbers of cycles. It was concluded that water treatment sludge is a suitable material to develop as a low-cost adsorbent for removal of heavy metal oxyanions from wastewater streams.