Lead (Pb) is a priority pollutant, and the demand is growing for its cost-effective removal from water. A nanomaterial with Mn(II)-bearing Fe3O4 (Mn–Fe) as magnetic core and MnO2 as shell was synthesized, giving a specific surface area of 113.3 m2/g, particle size of 90–130 nm, cubic spinel magnetic phase, and saturation magnetization of 35.1 emu/g. It exhibited a strong propensity for adsorbing Pb(II), with a maximal adsorption capacity of 261.1 mg/g at pH 5.0. The process was rapid and pH dependent, but only slightly affected by ionic strength and coexisting cations, indicating the formation of the inner-sphere complexes. Used nanomaterial could be easily separated from solution by a magnet and readily regenerated with HCl. Its Pb(II) adsorption efficiency remained at about 80% of the original after the fourth regeneration. Thus, it has the potential for use as an effective adsorbent to remove Pb(II) from water.

To evaluate the contamination of organochlorine pesticides (OCPs) in marine organisms and their potential health risk on consumers in the northern Yellow Sea of China, mollusks, wild shrimps, and crabs were collected from the Yantai coast, and the OCP contents in the samples were analyzed and compared. The results indicate that all the samples have been contaminated by OCPs, and OCP concentrations varied in individual species and in sampling sites. Among the studied OCPs, ∑HCH and ∑DDT concentrations ranged from 0.91 to 13.92 ng g−1 and from 10.16 to 411.19 ng g−1, respectively. Meretrix was highly enriched with HCHs, while the highest DDT concentration was found in Crassostrea. For the OCP isomers, β-HCH was the predominant isomer of HCHs, and p,p′-DDE concentration was much higher than other isomers of DDTs. The concentrations of other OCPs (HCB, t-CHL, endrin, and mirex) were relatively low. For the shrimp and crab samples, Alpheus distinguendus samples accumulated a higher level of HCHs but lower DDTs than Oratosquilla aratoria and Carcinoplax vestitus in all sampling areas. HCHs in the samples of contrast area were not significantly lower than that of the sewage outfall area and port area, whereas DDTs in the samples of contrast area were relatively lower than that of the other two areas. Generally, all the OCP contents in the samples are in the range of the edible hygienic criteria except the total concentration of DDTs in Crassostrea.

Arsenate and arsenite typically co-exist in groundwater. Arsenite is more toxic than arsenate, while it is more difficult to be removed than arsenate. In order to effectively remove arsenate and arsenite simultaneously from water solution, a nanostructured zirconium–manganese binary hydrous oxide was successfully developed in this study. The amorphous sorbent was aggregate of nanoparticles with a high surface area of 213 m2 g−1. Our sorption experiments showed that the nano-scale particles could effectively oxidize As(III) to As(V) and greatly remove both As(V) and As(III). The maximal adsorption capacities of As(V) and As(III) were 80 and 104 mg g−1 at pH 5.0, respectively. As(V) uptake may be mainly achieved through replacement of hydroxyl groups and sulfate anions on the surface of the oxide and formation of inner complexes. The As(III) removal was essentially due to a sorption coupled with oxidation process; the MnO2 was mainly responsible for oxidization of As(III) to As(V) that was subsequently adsorbed onto ZrO2.Graphical abstractHighlights► The Zr–Mn binary hydrous oxide is effective for both As(V) and As(III) removal. ► As(III) could be effectively oxidized to As(V) by the hydrous oxide. ► As(V) removal is mainly achieved through sorption process. ► As(III) uptake is a sorption coupled with oxidation process.

To evaluate the contamination of polybrominated diphenyl ethers (PBDEs) in marine organisms of the northern Yellow Sea of China, mollusks, wild shrimps and crabs were collected from the Yantai coast and ten PBDE congeners levels in the samples were analyzed and compared. The results indicate all the samples have been contaminated by PBDEs and PBDEs concentrations varied in individual species and in sampling sites. The concentration range of ∑PBDEs in the samples was 0.23–10.56 ng/g d.w. below the national edible criteria 40 ng/g d.w.. Congener compositions were mainly dominated by BDE 209.

Arsenate retention, arsenite sorption and oxidation on the surfaces of Fe–Mn binary oxides may play an important role in the mobilization and transformation of arsenic, due to the common occurrence of these oxides in the environment. However, no sufficient information on the sorption behaviors of arsenic on Fe–Mn binary oxides is available. This study investigated the influences of Mn/Fe molar ratio, solution pH, coexisting calcium ions, and humic acids have on arsenic sorption by Fe–Mn binary oxides. To create Fe–Mn binary oxides, simultaneous oxidation and co-precipitation methods were employed. The Fe–Mn binary oxides exhibited a porous crystalline structure similar to 2-line ferrihydrite at Mn/Fe ratios 1:3 and below, whereas exhibited similar structures to δ-MnO2 at higher ratios. The As(V) sorption maximum was observed at a Mn/Fe ratio of 1:6, but As(III) uptake maximum was at Mn/Fe ratio 1:3. However, As(III) adsorption capacity was much higher than that of As(V) at each Mn/Fe ratio. As(V) sorption was found to decrease with increasing pH, while As(III) sorption edge was different, depending on the content of MnO2 in the binary oxides. The presence of Ca2+ enhanced the As(V) uptake under alkaline pH, but did not significantly influence the As(III) sorption by 1:9 Fe–Mn binary oxide; whereas the presence of humic acid slightly reduced both As(V) and As(III) uptake. These results indicate that As(III) is more easily immobilized than As(V) in the environment, where Fe–Mn binary oxides are available as sorbents and they represent attractive adsorbents for both As(V) and As(III) removal from water and groundwater.Graphical abstractAs(V) retention, As(III) oxidation and sorption were obviously affected by Mn/Fe molar ratio, and the Fe–Mn binary oxide has much higher sorption capacity toward As(III) than that of As(V) at each Mn/Fe molar ratio.Highlights► Arsenic uptake was obviously affected by Mn/Fe molar ratio of the binary oxide. ► The Fe–Mn binary oxides were more effective for As(III) removal than As(V). ► The MnO2 content in the Fe–Mn binary oxides can effectively oxidize As(III) to As(V). ► The presence of calcium ions enhanced arsenic sorption. ► The coexisting humic acids slightly decreased arsenic sorption.

In this study, MnFe2O4/activated carbon magnetic composites with mass ratio of 1:1, 1:1.5 and 1:2 were synthesized using a simple chemical coprecipitation procedure. A variety of techniques such as X-ray diffractometer, scanning electron microscope, magnetization measurements, BET surface area measurements were used to characterize the structure, morphology and magnetic performance of the prepared composite adsorbents. The results showed that the composites had good magnetic properties, which allowed their convenient magnetic separation from water. Spinel manganese ferrite was found to occur in the magnetic phase and the presence of magnetic particles of MnFe2O4 did not significantly affect the surface area and pore structure of the activated carbon. The magnetic composites were effective for tetracycline (TC) removal from water and the maximal adsorption capacity was 590.5 mmol kg−1 at pH 5.0. The TC adsorption followed pseudo-second-order kinetic model and its removal decreases gradually with an increase in pH value, whereas the removal rate was over 60% even at pH 9.0. The TC adsorption process is endothermic and the increase of temperature is favoring its removal. All these results indicated that the prepared composites had the potential to be used as adsorbents for the removal of TC from water or wastewater.Highlights► The MnFe2O4/activated carbon can be easily separated from water using a magnet. ► The MnFe2O4 did not significantly affect the sorption ability of activated carbon. ► The magnetic composite was effective for tetracycline removal from water.

Arsenate and arsenite may exist simultaneously in groundwater and have led to a greater risk to human health. In this study, an iron–zirconium (Fe–Zr) binary oxide adsorbent for both arsenate and arsenite removal was prepared by a coprecipitation method. The adsorbent was amorphous with a specific surface area of 339 m2/g. It was effective for both As(V) and As(III) removal; the maximum adsorption capacities were 46.1 and 120.0 mg/g at pH 7.0, respectively, much higher than for many reported adsorbents. Both As(V) and As(III) adsorption occurred rapidly and achieved equilibrium within 25 h, which were well fitted by the pseudo-second-order equation. Competitive anions hindered the sorption according to the sequence PO43->SiO32->CO32->SO42-. The ionic strength effect experiment, measurement of zeta potential, and FTIR study indicate that As(V) forms inner-sphere surface complexes, while As(III) forms both inner- and outer-sphere surface complexes at the water/Fe–Zr binary oxide interface. The high uptake capability and good stability of the Fe–Zr binary oxide make it a potentially attractive adsorbent for the removal of both As(V) and As(III) from water.Graphical abstractArsenate is removed by Fe–Zr binary oxide through formation of inner-sphere surface complexes, while As(III) is removed by formation of both inner- and outer-sphere surface complexes.Highlights► The Fe–Zr binary oxide has high adsorption capacity toward both As(V) and As(III). ► Co-existing anions did not significantly influence the arsenic adsorption. ► As(V) is adsorbed by formation of inner-sphere surface complexes. ► As(III) is adsorbed by formation of both inner- and outer-sphere surface complexes.

Phosphate removal is important in the control of eutrophication of water bodies and adsorption is one of the promising approaches for this purpose. A Fe–Mn binary oxide adsorbent with a Fe/Mn molar ratio of 6:1 for phosphate removal was synthesized by a simultaneous oxidation and coprecipitation process. Laboratory experiments were carried out to investigate adsorption kinetics and equilibrium, in batch mode. The effects of different experimental parameters, namely contact time, initial phosphate concentration, solution pH, and ionic strength on the phosphate adsorption were investigated. The adsorption data were analyzed by both Freundlich and Langmuir isotherm models and the data were well fit by the Freundlich isotherm model. Kinetic data correlated well with the pseudo-second-order kinetic model, suggesting that the adsorption process might be chemical sorption. The maximal adsorption capacity was 36 mg/g at pH 5.6. The phosphate adsorption was highly pH dependent. The effects of anions such as Cl-,SO42-, and CO32- on phosphate removal were also investigated. The results suggest that the presence of these ions had no significant effect on phosphate removal. The phosphate removal was mainly achieved by the replacement of surface hydroxyl groups by the phosphate species and formation of inner-sphere surface complexes at the water/oxide interface. In addition, the adsorbed phosphate ions can be effectively desorbed by dilute NaOH solutions. This adsorbent, with large adsorption capacity and high selectivity, is therefore a very promising adsorbent for the removal of phosphate ions from aqueous solutions.Adsorption isotherm of phosphate by Fe–Mn binary oxide adsorbent fitted with Langmuir and Freundlich models, which demonstrated a relatively high P adsorption capacity.