•Bifunctional Zn-Fe mixed metal oxides were synthesized from LDH precursors and optimized.•Mutual effects of arsenic and ibuprofen on removal efficiency were investigated.•Pharmaceuticals and arsenic in actual water were removed simultaneously and efficiently.•Mechanisms involving photodegradation and oxidation/adsorption were fully elucidated.A series of ZnFe-MMOs were synthesized by in situ topotactic transformation of ZnFe-LDH precursors, and screened for obtaining an efficient functional material used in the simultaneous removal of pharmaceuticals and arsenic. In a mono-component system, the photodegradation efficiency of ibuprofen with optimal ZnFe-MMOs can reach 95.7% under simulated solar irradiation and the maximum adsorption capacity of arsenic was up to 176.3 mg·g−1. In the binary system of ibuprofen and arsenic, the degrading activity of ibuprofen inordinately decreased depending on both the arsenic species and concentrations, while the presence of ibuprofen had no significant impact on arsenic removal. The potential application of ZnFe-MMOs for the simultaneous removal of several pharmaceuticals (ibuprofen, acetaminophen and diclofenac) and arsenic in actual water matrix was also investigated. After 12 h, arsenic concentration decreased from 1000 to 1.61 μg·L−1 and no pharmaceutical was detected. Possible mechanisms were revealed, indicating that photogenerated h+ was primary reactive species for the photodegradation of ibuprofen, and arsenic species including As(III) and As(V) were removed by the combination of photocatalytic oxidation and surface complexation adsorption. Furthermore, ZnFe-MMOs exhibited good reusability after regeneration, rendering it a promising multi-functional material for the decontamination of polluted water with the coexistent pharmaceuticals and arsenic pollutants.Download high-res image (189KB)Download full-size image

Acetaminophen can increase the risk of arsenic-mediated hepatic oxidative damage; therefore, the decontamination of water polluted with coexisting acetaminophen and arsenic gives rise to new challenges for the purification of drinking water. In this work, a three-metal layered double hydroxide, namely, Cu–Zn–Fe-LDH, was synthesized and applied as a heterogeneous Fenton-like oxidation catalyst and adsorbent to simultaneously remove acetaminophen (Paracetamol, PR) and arsenic. The results showed that the degradation of acetaminophen was accelerated with decreasing pH or increasing H2O2 concentrations. Under the conditions of a catalyst dosage of 0.5 g·L–1 and a H2O2 concentration of 30 mmol·L–1, the acetaminophen in a water sample was completely degraded within 24 h by a Fenton-like reaction. The synthesized Cu–Zn–Fe-LDH also exhibited a high efficiency for arsenate removal from aqueous solutions, with a calculated maximum adsorption capacity of 126.13 mg·g–1. In the presence of hydrogen peroxide, the more toxic arsenite can be gradually oxidized into arsenate and adsorbed at the same time by Cu–Zn–Fe-LDH. For simulated water samples with coexisting arsenic and acetaminophen pollutants, after treatment with Cu–Zn–Fe-LDH and H2O2, the residual arsenic concentration in water was less than 10 μg·L–1, and acetaminophen was not detected in the solution. These results indicate that the obtained Cu–Zn–Fe-LDH is an efficient material for the decontamination of combined acetaminophen and arsenic pollution.Keywords: acetaminophen; adsorption; arsenic; heterogeneous catalysis; layered double hydroxides

•Novel Zn-Al-Ce-MMO composites were prepared by calcination of Ce-doped Zn-Al-LDH.•Zn-Al-Ce-MMO showed high photocatalytic activity for RhB and paracetamol.•Enhanced activity attributed to higher separation efficiency of electrons and holes.•Zn-Al-Ce-MMO displayed good stability and reusability.In this work, a series of novel Zn-Al-Ce multi-metal oxide (Zn-Al-Ce-MMO) photocatalysts with different Ce doping contents were prepared by calcination of Ce-doped Zn-Al layered double hydroxide (Zn-Al-Ce-LDH) precursors at various temperatures in air atmosphere. The synthesized Zn-Al-Ce-MMO materials were characterized by XRD, FTIR, TGA, BET, SEM, TEM, XPS and UV–vis DRS. The photocatalytic activities of the Zn-Al-Ce-MMO materials were evaluated by the photodegradation of rhodamine B (RhB) dye and paracetamol in aqueous solution under simulated solar light irradiation. The result of photodegradation of RhB showed that the Zn-Al-Ce-MMO samples exhibit much higher photocatalytic activity than that of Zn-Al-MMO, and the optimal Ce doping content is 5% of mole ratio (nCe/n(Zn+Al+Ce)). The enhanced photocatalytic activity of the Zn-Al-Ce-MMO was mainly attributed to the increasing in the separation efficiency of electrons and holes. The effect of calcination temperature was also studied. The photocatalytic activity of Zn-Al-Ce-MMO increased with increasing calcination temperature up to 750 °C, which can be ascribed to the formation of well-crystallized metal oxides during calcination. Under experimental conditions, 97.8% degradation efficiency of RhB and 98.9% degradation efficiency of paracetamol were achieved after 240 min. Active species trapping and EPR experiments suggested that hole (h+), superoxide radical (O2−) and hydroxyl radical (OH) played important roles during the RhB photocatalytic process. Moreover, the results indicated that the synthesized Zn-Al-Ce-MMO materials had good stability and reusability.

A novel composite adsorbent, hydroxyapatite/ manganese dioxide (HAp/MnO2), has been developed for the purpose of removing lead ions from aqueous solutions. The combination of HAp with MnO2 is meant to increase its adsorption capacity. Various factors that may affect the adsorption efficiency, including solution pH, coexistent substances such as humic acid and competing cations (Ca2+, Mg2+), initial solute concentration, and the duration of the reaction, have been investigated. Using this composite adsorbent, solution pH and coexistent calcium or magnesium cations were found to have no significant influence on the removal of lead ions under the experimental conditions. The adsorption equilibrium was described well by the Langmuir isotherm model, and the calculated maximum adsorption capacity was 769 mg·g−1. The sorption processes obeyed the pseudo-second-order kinetics model. The experimental results indicate that HAp/MnO2 composite may be an effective adsorbent for the removal of lead ions from aqueous solutions.

Inorganic arsenic occurs mainly in As(III) and As(V) states in water environment, but arsenite is more toxic and difficult to remove than arsenate by usual adsorption processes. To achieve the in situ oxidation of As(III) and simultaneous removal of both As(III) and As(V) in water, a novel-layered double hydroxide (Mg–Fe–S2O8–LDH) with the intercalation of persulfate has been designed and synthesized by a calcination-reconstruction method. The arsenic adsorption performances and removal mechanism with the Mg–Fe–S2O8–LDH material were studied. The experimental result showed that, since the strong oxidation ability of the exchangeable persulfate ions from the LDH, the As(III) species in water were almost completely oxidized to the As(V) state and simultaneously adsorbed onto the Mg–Fe–S2O8–LDH. It was found that the maximum adsorption capacity for As(III) and As(V) in single-pollutant system was 75.00 and 75.63 mg·g−1, respectively. When the adsorbent dosage was 0.5 g·L−1 for a mixed As(III) and As(V) solution, the batch experiment showed that the residual arsenic concentration can be reduced from 1 mg·L−1 to lower than the limit value of drinking water standard recommended by WHO. It indicated that the synthesized Mg–Fe–S2O8–LDH is a potential attractive adsorbent for simultaneous removal of As(III) and As(V) in water.

Recently, metal oxides with novel nanostructured architectures have been prepared by annealing the polyol-based metal alkoxides for water treatment. However, these materials often exhibit relatively low adsorption capacities possibly attributable to the decomposition of surface groups during the calcination process. In this work, we successfully synthesized a novel nanostructured hollow iron–cerium alkoxide (NH-ICA) with a high surface area and abundant surface functional groups through an ethylene glycol mediated solvothermal method. Cerium ion doping significantly influenced the morphologies, microstructures and adsorption performance of NH-ICAs. Interestingly, the synthesized NH-ICAs showed significantly higher affinity to As(III) than the iron alkoxide material without cerium doping. Moreover, a much higher adsorption capacity of the NH-ICAs for As(III) than As(V) was found. When the molar ratio of Fe to Ce was 5:1, the product with uniform nanostructured hollow architectures exhibited the best adsorption capacities for both As(V) and As(III) (206.6 and 266.0 mg g–1, respectively). The mechanistic study revealed that As(V) adsorption involved ion-exchange between the As(V) species and three types of negatively charged groups, including surface hydroxyl groups, CO32– and unidentate carbonate-like species. For As(III) adsorption, surface complexing was proposed. A broad adaptation pH range for both As(V) and As(III) adsorbed by the resulting product indicates its promising application perspective for decontamination of arsenic-polluted water.Keywords: adsorption; alkoxides; arsenic; hollow; iron−cerium; nanostructure

A novel ordered mesoporous cerium iron mixed oxide (OMCI) with high specific surface area and uniform and well-interconnected mesopores was synthesized through the nanocasting strategy using mesoporous silica (KIT-6) as a hard template. The obtained OMCI was used as an adsorbent to remove As(V) or Cr(VI) anions from aqueous solutions, and exhibited excellent performances with the maximum adsorption capacities of ∼106.2 and ∼75.36 mg g−1 for As(V) and Cr(VI), respectively. A mechanism study showed that both Fe and Ce compositions participated in the As(V) or Cr(VI) adsorption process, and complex interactions were involved, including electrostatic attraction and the replacement of hydroxyl groups to form anionic negatively charged inner-sphere surface complexes. The OMCI material could be easily regenerated and reused while maintaining high adsorption capacities for As(V) and Cr(VI). Owing to their integrated features including high specific surface area, uniform and well-interconnected mesopores and specific acid–base surface properties, the synthesized OMCI material is expected to have good potential for the decontamination of As(V) or Cr(VI) polluted waters.

•MIO–CNTs have been synthesized through a one-pot solid-phase route.•MIO–CNTs possess high SSA, good dispersibility, and desirable magnetic properties.•MIO–CNTs exhibited good arsenic adsorption capacities.•Oxygen-containing groups on MIO–CNTs play a crucial role in arsenic adsorption.Carbon nanotubes (CNTs) functionalized with magnetic nanoparticles are attractive for environmental remediation applications due to their high specific surface area conducive for adsorption of water contaminants and the possibility of recovering these nanohybrids after remediation using an external magnetic field. Most of existing methods for synthesizing magnetic iron oxide/CNTs (MIO–CNTs) composites are carried out in the liquid medium and are tedious, uneconomical, and environmentally unfriendly. Herein, we report a one-pot solid-phase route to synthesize MIO–CNTs composites based on pristine CNTs. MIO–CNTs possess a high specific surface area, good dispersibility, and desirable magnetic properties, making them promising as adsorbents for arsenic removal. The maximum arsenic adsorption capacities are 47.41 and 24.05 mg g−1 for As(V) and As(III), respectively. These values are among the highest for carbon-based materials. Oxygen-containing groups on the surface of MIO–CNTs play a crucial role in arsenic adsorption. This work is very important for the practical applications of pristine CNTs containing catalyst nanoparticles without the need of purifications.

A series of lanthanum-doped ferric-based layered double hydroxides with the carbonate intercalation (Mg–Fe–La–LDHs) of different M2+/M3+ molar ratio and their corresponding calcined products were successfully synthesized and characterized. In order to understand the effect of metal compositions in these materials on their adsorption performances for arsenate, various factors such as solution pH, contact time and initial arsenate concentrations were investigated. The results showed that the maximum adsorption capacity for Mg–Fe–La–LDHs decreased with the increment of the M2+/M3+ molar ratio, but the reversed trend occurred for the calcined products of Mg–Fe–La–CLDHs. This difference is closely related to the different adsorption mechanisms for layered double hydroxides (LDHs) and calcined layered double hydroxide (CLDHs). It was found that the adsorption isotherms can be well described by the Langmuir equation, and the adsorption kinetics followed the pseudo-second-order kinetic model. The results suggested that the obtained Mg–Fe–La–LDHs with lower molar ratio of M2+/M3+ in the materials were more suitable for removal of arsenate, while their calcined products Mg–Fe–La–CLDHs with higher molar ratio of M2+/M3+ were efficient adsorbents for arsenate. When the M2+/M3+ molar ratio in the material was 4.38, the maximum adsorption capacity of CLDH-3 was as high as 47.4 mg g−1.

In this study, a novel mixed Ce–Fe oxide decorated multiwalled carbon nanotubes (CF-CNTs) material was prepared through a surfactant assisted method. The CF-CNTs material was characterized by various methods, including BET surface area analysis, transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was found that the Ce–Fe oxide was uniformly dispersed on the surface of CNTs with a mean size of 7.0 nm. The obtained CF-CNTs material was used as an adsorbent to remove arsenic from aqueous solutions. The adsorption experimental results showed that this CF-CNTs material had an excellent adsorption performance for As(V) and As(III). The adsorption processes of As(V) and As(III) could be well described by the pseudo-second-order model. The mechanistic study showed that different interactions were involved in As(V) adsorption, including electrostatic attraction and surface complexation. For As(III) adsorption, partial As(III) was oxidized to As(V) followed by the simultaneous adsorption of As(V) and As(III). It was also found that intra-particle diffusion existed in the process of adsorption on CF-CNTs, but that it was not the only rate-limiting step. The resulting CF-CNTs material can be used in a broad pH range, which suggests its great potential for the decontamination of arsenic-polluted water.

Surfactant-modified natural zeolites (SMNZ) with different coverage types were prepared by loading hexadecyltrimethyl ammonium bromide (HTAB) onto the surface of a natural zeolite. The adsorption behavior of humic acid (HA) on SMNZ was investigated. Results indicate that the adsorbent SMNZ exhibited a higher affinity toward HA than the natural zeolite. HA removal efficiency by SMNZ increased with HTAB loading. Coexisting Ca2+ in solution favored HA adsorption onto SMNZ. Adsorption capacity decreased with an increasing solution pH. For typical SMNZ with bilayer HTAB coverage, HA adsorption process is well described by a pseudo-second-order kinetic model. The experimental isotherm data fitted well with the Langmuir model. Calculated maximum HA adsorption capacities for SMNZ with bilayer HTAB coverage at pH 5.5 and 7.5 were 63 and 41 mg·g−1, respectively. E2/E3 (absorbance at 250 nm to that at 365 nm) and E4/E6 (absorbance at 465 nm to that at 665 nm) ratios of the residual HA in solution were lower than that of the original HA solution. This indicates that the HA fractions with high polar functional groups, low molecular weight (MW), and aromaticity had a stronger tendency for adsorption onto SMNZ with bilayer HTAB coverage. Results show that HTAB-modified natural zeolite is a promising adsorbent for removal of HA from aqueous solution.

Microwave processing was used to stabilize copper ions in soil samples. Its effects on the stabilization efficiency were studied as a function of additive, microwave power, process time, and reaction atmosphere. The stabilization efficiency of the microwave process was evaluated based on the results of the toxicity characteristic leaching procedure (TCLP) test. The results showed that the optimal experimental condition contained a 700W microwave power, 20 min process time and 3 iron wires as the additive, and that the highest stabilization efficiency level was more than 70%. In addition, the different reaction atmospheres showed no apparent effect on the stabilization efficiency of copper in the artificially contaminated soil. According to the result of the Tessier sequential extraction, the partial species of copper in the contaminated soil was deduced to transform from unstable species to stable states after the microwave process.

AbstractPolyepoxysuccinic acid (PESA), as an environmental benign biodegradable chelant, was used to remove heavy metals from the sewage sludge of Shanghai Taopu Wastewater Treatment Plant. The extraction of cadmium (Cd) from sewage sludge using aqueous solution of PESA was studied. It was found that PESA was capable of extracting Cd from the sludge, and the extraction efficiency was dependent on both pH and the concentration of the chelating reagent. The extraction efficiency decreased gradually with increasing of pH, whereas the dependency on pH decreased as the concentration of PESA increased. In the case of the high PESA to total metal ratio, e.g., 10:1, the extraction efficiency reached above 70% within the pH range from 1 to 7. The highest extraction efficiency obtained in the experiment was 78%. By comparing the contents of the heavy metals in sewage sludge before and after the extraction, it was found that the extracted Cd came mainly from the four fractions: acid-soluble, reducible, oxidizable, and water-soluble fractions.

In this study, a novel mixed Ce–Fe oxide decorated multiwalled carbon nanotubes (CF-CNTs) material was prepared through a surfactant assisted method. The CF-CNTs material was characterized by various methods, including BET surface area analysis, transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). It was found that the Ce–Fe oxide was uniformly dispersed on the surface of CNTs with a mean size of 7.0 nm. The obtained CF-CNTs material was used as an adsorbent to remove arsenic from aqueous solutions. The adsorption experimental results showed that this CF-CNTs material had an excellent adsorption performance for As(V) and As(III). The adsorption processes of As(V) and As(III) could be well described by the pseudo-second-order model. The mechanistic study showed that different interactions were involved in As(V) adsorption, including electrostatic attraction and surface complexation. For As(III) adsorption, partial As(III) was oxidized to As(V) followed by the simultaneous adsorption of As(V) and As(III). It was also found that intra-particle diffusion existed in the process of adsorption on CF-CNTs, but that it was not the only rate-limiting step. The resulting CF-CNTs material can be used in a broad pH range, which suggests its great potential for the decontamination of arsenic-polluted water.

A novel ordered mesoporous cerium iron mixed oxide (OMCI) with high specific surface area and uniform and well-interconnected mesopores was synthesized through the nanocasting strategy using mesoporous silica (KIT-6) as a hard template. The obtained OMCI was used as an adsorbent to remove As(V) or Cr(VI) anions from aqueous solutions, and exhibited excellent performances with the maximum adsorption capacities of ∼106.2 and ∼75.36 mg g−1 for As(V) and Cr(VI), respectively. A mechanism study showed that both Fe and Ce compositions participated in the As(V) or Cr(VI) adsorption process, and complex interactions were involved, including electrostatic attraction and the replacement of hydroxyl groups to form anionic negatively charged inner-sphere surface complexes. The OMCI material could be easily regenerated and reused while maintaining high adsorption capacities for As(V) and Cr(VI). Owing to their integrated features including high specific surface area, uniform and well-interconnected mesopores and specific acid–base surface properties, the synthesized OMCI material is expected to have good potential for the decontamination of As(V) or Cr(VI) polluted waters.