The environmental risks of antibiotics have attracted lots of research attention, but their environmental behavior is not clear yet. Functionalized carbon nanotubes (CNTs) were used as model adsorbents and sulfamethoxazole (SMX) was used as a model antibiotic to investigate the effect of both cations (Ca²⁺, Cs⁺) and anions (phosphate) on antibiotics adsorption. Various mechanisms (such as electrostatic interaction, hydrophobic interaction, π–π and hydrogen bonds) play roles in SMX adsorption. Cations and anions could “wedge into” these mechanisms and thus alter SMX adsorption. This study emphasized that both increased and decreased SMX adsorption could be observed with the addition of cations/anions, depending on environmental conditions (such as pH in this current study). The net effect is the balance between the increased and decreased effects. The contribution of different mechanisms to the overall antibiotic adsorption on solid particles should be identified to accurately predict the apparent effect by cations and anions.

Increasing release of organic pollutants to the environment has caused one of the largest world crises for water resources. Volatile organic compounds are toxic monoaromatic pollutants of soil and water. In this research, natural zeolite nanoparticles were produced mechanically by means of a milling technique, modified using two cationic surfactants of hexadecyltrimethylammonium chloride and n-cetyl pyridinium bromide and formed as granules using a novel technique already developed by our group. The granulated adsorbents were used to uptake benzene, toluene, ethylbenzene, and xylenes (BTEX) from contaminated water. Two intra-particle diffusion models (i.e., Weber and Morris and Vermeulen models) and three surface reaction models (i.e., pseudo-first order, pseudo-second order, and Elovich) were applied to evaluate the kinetics of adsorption and the best fitted model was chosen. Results of the adsorption kinetic evaluations were shown that uptake of granulated nanozeolites are higher than natural zeolites (in the order of four). Kinetic results revealed that the adsorption follows a pseudo-second order indicating existence of chemisorption in the studied conditions. It was noticed that the intra-particle diffusion is prevailing in the first stage of adsorption for a relatively short time (i.e., first 25 min).

Petroleum monoaromatics including benzene, toluene, ethylbenzene, and xylenes (BTEX) are among the notorious volatile organic compounds that contaminate water and soil. In this study, a surfactant- modified natural zeolite and its relevant granulated nanozeolites were evaluated as potential adsorbents for removal of petroleum monoaromatics from aqueous solutions. All experiments performed in batch mode at constant temperature of 20°C and pH of 6.8 for 48 h. The results revealed that the amount of BTEX uptake on granulated zeolites nanoparticles were remarkably higher than the parent micron size natural zeolite (in the order of four times). The isotherms data were analyzed using five models namely, Langmuir, Fruendlich, Elovich, Temkin, and Dubinin–Radushkevich models. It was concluded that the Langmuir model fits the experimental data. The measured adsorption capacities were 3.89 and 4.08 mg of monoaromatics per gram of hexadecyltrimethylammonium-chloride and n-cetylpyridinium bromide (CPB)-modified granulated nanozeolite, respectively. Considering the type of surfactant, adsorbents modified with CPB showed greater tendency for the adsorption of the adsorbates.

The adsorption of lead onto date palm fibers (palm fibers) and leaf base of palm (petiole) has been examined in aqueous solution by considering the influence of various parameters such as contact time, solution pH, adsorbent dosage, particle sizes, ionic strength, and temperature. The adsorption of Pb(II) increased with an increase of contact time. The optimal range of pH for Pb(II) adsorption is 3.0-4.5. The linear Langmuir and Freundlich models were applied to describe the equilibrium isotherms, and both models fitted well. The monolayer adsorption capacity of Pb(II) on palm fibers and petiole was found as 18.622 and 20.040 mg/g, respectively, at pH 4.5 and 25°C. Dubinin-Radushkevich (D-R) isotherm model was also applied to equilibrium data. The mean free energy of adsorption (2.397 and 4.082 kJ/mol) onto palm fibers and petiole, respectively, may be carried out via physisorption mechanism. Pseudo-first-order rate equation and pseudo-second-order rate equation were applied to study the adsorption kinetics. In comparison to first-order kinetic model, pseudo-second-order model described well the adsorption kinetics of Pb(II) onto palm fibers and petiole from aqueous solution. From the results of the thermodynamic analysis, Gibbs free energy ΔG, enthalpy change ΔH, and entropy ΔS were determined. The positive value of ΔH suggests that interaction of Pb(II) adsorbed by palm fibers is endothermic. In contrast, the negative value of ΔH indicates that interaction of Pb(II) ions by petiole is exothermic. The negative value of ΔG indicates that the adsorption of Pb(II) ions on both palm fibers and petiole is a spontaneous process.

The adsorption capacity of seven inorganic solid wastes [air-cooled blast furnace (BF) slag, water-quenched BF slag, steel furnace slag, coal fly ash, coal bottom ash, water treatment (alum) sludge and seawater-neutralized red mud] for Cd2+, Cu2+, Pb2+, Zn2+ and Cr3+ was determined at two metal concentrations (10 and 100 mg L−1) and three equilibrium pH values (4.0, 6.0 and 8.0) in batch adsorption experiments. All materials had the ability to remove metal cations from aqueous solution (fly and bottom ash were the least effective), their relative abilities were partially pH dependant and adsorption increased greatly with increasing pH. At equimolar concentrations of added metal, the magnitude of sorption at pH 6.0 followed the general order: Cr3+ ≥ Pb2+ ≥ Cu2+ > Zn2+ = Cd2+. The amounts of previously sorbed Pb and Cd desorbed in 0.01 M NaNO3 electrolyte were very small, but those removed with 0.01 M HNO3, and more particularly 0.10 M HNO3, were substantial. Water treatment sludge was shown to maintain its Pb and Cd adsorption capability (pH 6.0) over eight successive cycles of adsorption/regeneration using 0.10 M HNO3 as a regenerating agent. By contrast, for BF slag and red mud, there was a very pronounced decline in adsorption of both Pb and Cd after only one regeneration cycle. A comparison of Pb and Cd adsorption isotherms at pH 6.0 for untreated and acid-pre-treated materials confirmed that for water treatment sludge acid pre-treatment had no significant effect, but for BF slag and red mud, adsorption was greatly reduced. This was explained in terms of residual surface alkalinity being the key factor contributing to the high adsorption capability of the latter two materials, and acid pre-treatment results in neutralization of much of this alkalinity. It was concluded that acid is not a suitable regenerating agent for slags and red mud and that further research and development with water treatment sludge as a metal adsorbent are warranted.

Purpose Adsorption of metals (Pb, Cd, Cu, Ni, Zn) to TiO₂ nanoparticles and bulk particles was examined for use as a contaminant removal substrate as a function of particle size, sorbent concentration, and exhaustion. Methods Adsorption experiments were conducted with 0.01, 0.1, and 0.5 g/L nanoparticles in a pH 8 solution and in spiked San Antonio tap water. Results When results were normalized by mass, nanoparticles adsorbed more than the bulk particles but when results were surface-area normalized, the opposite was observed. The adsorption data shows the ability of the TiO₂ nanoparticles to remove Pb, Cd, and Ni from solution with similar adsorption at 0.1 and 0.5 g/L. Adsorption kinetics for all metals tested was described by a modified first order rate equation with the nanoparticles having a faster rate of adsorption than the bulk particles. The nanoparticles were able to simultaneously removal multiple metals (Zn, Cd, Pb, Ni, Cu) from both pH 8 solution and spiked San Antonio tap water. Exhaustion experiments showed that both the nanoparticles and bulk particles were exhausted at pH 6 but at pH 8, exhaustion did not occur for the nanoparticles. Conclusion Comparison of K d, distribution coefficient, with other literature showed that the nanoparticles were better sorbents than other metal oxide nanoparticles and a commercial activated carbon.