Adsorbent OxidationArsenite Removal a b s t r a c t Arsenite (As(III)) is more toxic and more difficult to remove from water than arsenate (As(V)).As there is no simple treatment for the efficient removal of As(III), an oxidation step is always necessary to achieve higher removal. However, this leads to a complicated operation and is not cost-effective. To overcome these disadvantage, a novel Fe-Mn binary oxide material which combined the oxidation property of manganese dioxide and the high adsorption features to As(V) of iron oxides, were developed from low cost materials using a simultaneous oxidation and coprecipitation method. The adsorbent was characterized by BET surface areas measurement, powder XRD, SEM, and XPS. The results showed that prepared Fe-Mn binary oxide with a high surface area ð265 m 2 g À1 Þ was amorphous. Iron and manganese existed mainly in the oxidation state þIII and IV, respectively. Laboratory experiments were carried out to investigate adsorption kinetics, adsorption capacity of the adsorbent and the effect of solution pH values on arsenic removal. Batch experimental results showed that the adsorbent could completely oxidize As(III) to As(V) and was effective for both As(V) and As(III) removal, particularly the As(III). The maximal adsorption capacities of As(V) and As(III) were 0:93 mmol g À1 and 1:77 mmol g À1 , respectively. The results compare favorably with those obtained using other adsorbent. The effects of anions such as SO 2À 4 , PO 3À 4 , SiO and humic acid (HA), which possibly exist in natural water, on As(III) removal were also investigated. The results indicated that phosphate was the greatest competitor with arsenic for adsorptive sites on the adsorbent. The presence of sulfate and HA had no significant effect on arsenic removal. The high uptake capability of the Fe-Mn binary oxide makes it potentially attractive adsorbent for the removal of As(III) from aqueous solution.

A novel Fe-Mn binary oxide adsorbent was developed for effective As(III) removal, which is more difficult to remove from drinking water and much more toxic to humans than As(V). The synthetic adsorbent showed a significantly higher As(III) uptake than As(V). The mechanism study is therefore necessary for interpreting such result and understanding the As(III) removal process. A control experiment was conducted to investigate the effect of Na2SO3-treatment on arsenic removal, which can provide useful information on As(III) removal mechanism. The adsorbent was first treated by Na2SO3, which can lower its oxidizing capacity by reductive dissolution of the Mn oxide and then reacted with As(V) or As(III). The results showed that the As(V) uptake was enhanced while the As(III) removal was inhibited after the pretreatment, indicating the important role of manganese dioxide during the As(III) removal. FTIR along with XPS was used to analyze the surface change of the original Fe-Mn adsorbent and the pretreated adsorbent before and after reaction with As(V) or As(III). Change in characteristic surface hydroxyl groups (Fe-OH, 1130, 1048, and 973 cm(-1)) was observed by the FTIR. The determination of arsenic oxidation state on the solid surface after reaction with As(III) revealed that the manganese dioxide instead of the iron oxide oxidized As(III) to As(V). The iron oxide was dominant for adsorbing the formed As(V). An oxidation and sorption mechanism for As(III) removal was developed. The relatively higher As(III) uptake may be attributed to the formation of fresh adsorption sites at the solid surface during As(III) oxidation.

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a b s t r a c tPhosphate 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 À ; SO 4 2À , and CO 3 2À 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.

CuFe 2 O 4 /activated carbon magnetic adsorbents, which combined the adsorption features of activated carbon with the magnetic and the excellent catalytic properties of powdered CuFe 2 O 4 , were developed using a simple chemical coprecipitation procedure. The prepared magnetic composites can be used to adsorb acid orange II (AO7) in water and subsequently, easily be separated from the medium by a magnetic technique. CuFe 2 O 4 /activated carbon magnetic adsorbents with mass ratio of 1:1, 1:1.5 and 1:2 were prepared. Magnetization measurements, BET surface area measurements, powder XRD and SEM were used to characterize the prepared adsorbents. The results indicate that the magnetic phase present is spinel copper ferrite and the presence of CuFe 2 O 4 did not significantly affect the surface area and pore structure of the activated carbon. The adsorption kinetics and adsorption isotherm of acid orange II (AO7) onto the composites at pH 5.2 also showed that the presence of CuFe 2 O 4 did not affect the adsorption capacity of the activated carbon. The thermal decomposition of AO7 adsorbed on the activated carbon and the composite was investigated by in situ FTIR, respectively. The results suggest that the composite has much higher catalytic activity than that of activated carbon, attributed to the presence of CuFe 2 O 4 . The variation of the adsorption capacity of the composites after several adsorption-regeneration cycles has also been studied.

a b s t r a c tArsenate 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 m 2 /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 PO 4 . 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.

Arsenate Arsenite Regeneration a b s t r a c tTo obtain a highly efficient and low-cost adsorbent for arsenic removal from water, a novel nanostructured FeeCu binary oxide was synthesized via a facile co-precipitation method.Various techniques including BET surface area measurement, powder XRD, SEM, and XPS were used to characterize the synthetic FeeCu binary oxide. It showed that the oxide was poorly crystalline, 2-line ferrihydrite-like and was aggregated with many nanosized particles. Laboratory experiments were performed to investigate adsorption kinetics, adsorption isotherms, pH adsorption edge and regeneration of spent adsorbent. The results indicated that the FeeCu binary oxide with a Cu: Fe molar ratio of 1:2 had excellent performance in removing both As(V) and As(III) from water, and the maximal adsorption capacities for As(V) and As(III) were 82.7 and 122.3 mg/g at pH 7.0, respectively. The values are favorable, compared to those reported in the literature using other adsorbents. The coexisting sulfate and carbonate had no significant effect on arsenic removal. However, the presence of phosphate obviously inhibited the arsenic removal, especially at high concentrations. Moreover, the FeeCu binary oxide could be readily regenerated using NaOH solution and be repeatedly used. The FeeCu binary oxide could be a promising adsorbent for both As(V) and As(III) removal because of its excellent performance, facile and low-cost synthesis process, and easy regeneration. ª 2013 Elsevier Ltd. All rights reserved. IntroductionArsenic, a ubiquitous element found in the environment, is well-known and extensively concerned with high toxicity and carcinogenicity. It is introduced into the water and groundwater through a combination of natural processes such as weathering reactions, dissolution of minerals and biological activity as well as through anthropogenic activities such as mining, agriculture and manufacturing (Cullen and Reimer, 1989;Smedley and Kinniburgh, 2002 Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate /wa tres w a t e r r e s e a r c h 4 7 ( 2 0 1 3 ) 4 0 2 2 e4 0 3 1 0043-1354/$ e see front matter ª

This paper investigates the consensus tracking problem of second-order nonlinear multiagent systems (MAS) with disturbance and actuator fault by the sliding mode control method. The communication topology of the MAS is directed and only part of the followers have access to the leader's information. First, a discontinuous sliding mode tracking protocol is studied for consensus tracking of the MAS. Second, to address the shortcoming of chattering and difficulty of setting the control gain in the discontinuous protocol, a continuous sliding mode tracking protocol with an adaptive mechanism is developed. The adaptive mechanism will adjust the gain of the control automatically and enable the tracking protocol to work well without prior knowledge of the MAS. Third, the performance of the adaptive sliding mode protocol for consensus tracking of the MAS in the presence of actuator faults of biased fault and partial loss of effectiveness fault is further investigated. Finally, numerical simulations are performed to illustrate the efficiency of the theoretical results.