Adsorption of Rhodamine B and Pb(II) from aqueous solution by MoS2 nanosheet modified biochar: Fabrication, performance, and mechanisms.

Mediated by polydopamine, MoS2 nanosheets were immobilized on the porous biochar derived from fungus residue, forming a novel biochar-based nanocomposite (MoS2-PDA@FRC) for the removal of Rhodamine B(RhB) and Pb(II) from water. Utilizing MoS2 nanosheets with abundant active adsorption sites, MoS2-PDA@FRC showed higher adsorption capacities than raw biochar, with 2.76 and 1.78 times higher capacities for RhB and Pb(II) respectively. MoS2-PDA@FRC also exhibited fast adsorption kinetics for RhB (120 min) and Pb (180 min) removal, as well as satisfactory adsorption selectivity in the presence of coexisting substances. The underlying removal mechanism was explored via Fourier transform infrared and X-ray photoelectron spectroscopies. Furthermore, during cyclic adsorption-regeneration and the fixed-bed adsorption experiments, the nanocomposite removed RhB and Pb(II) with high effectiveness and stability. Collectively, the results demonstrated the bright prospects of MoS2-PDA@FRC as a highly efficient decontamination agent of RhB and Pb(II) from water.

Renewable cellulose aerogel embedded with nano-HFO for preferable phosphate capture from aqueous solution.

Excess phosphate in water can cause eutrophication, which must be addressed. Despite many efforts devoted to the adsorptive removal of phosphate from water, the development of new adsorbents with high adsorption capacity is highly desirable. Herein, a novel nanocomposite was proposed for phosphate removal by confining hydrated ferric oxide (HFO) nanoparticles into a cellulose aerogel (CA) network named as HFO@CA. Benefiting from the characteristics of the low density and porous structure of CA, the internal surface of the nanocomposite is more accessible and thus improves the utilization of the HFO nanoparticles. Batch adsorption experiments were carried out to evaluate the phosphate uptake by the prepared adsorbent. The maximum adsorption capacity of HFO@CA occurs at near-acidic pH. With increasing temperature, the composite adsorbent is more favorable for phosphate adsorption. Moreover, the hybrid aerogel exhibited fast kinetic behavior for phosphate removal, which could be accurately depicted by pseudo-second-order model. HFO@CA shows excellent adsorption selectivity in solutions containing competitive anions at higher levels. In addition, five cycles of the phosphate adsorption experiments without obvious capacity loss indicated that HFO@CA has great regenerability. These results demonstrate that HFO@CA has a wide field of application with good prospects in phosphate removal from wastewater, which also provides a new strategy to prepare adsorbents with excellent performance using renewable cellulose resources.

Preferable phosphate sequestration using polymer-supported Mg/Al layered double hydroxide nanosheets.

The efficient removal of phosphate from waters is critical to mitigating eutrophication. Recently, layered double hydroxides (LDHs) have been believed to be promising adsorbents for phosphate removal. Nevertheless, the scaled-up application of LDHs is limited by the difficulties of separation, excessive pressure drops, and potential metal leaching. In this study, a millimeter-sized nanocomposite, MgAl-201, was fabricated by impregnating Mg/Al LDH nanosheets into a polystyrene anion exchanger D201. The resulting MgAl-201 combines the inherent affinity of Mg/Al LDH toward phosphate and the excellent hydrodynamic performance of the support material. Benefiting from the shielding effect from the cross-linked polymeric host, MgAl-201 exhibits satisfactory chemical stability in the range of pH 3-11 with a negligible metal release. Adsorption experiments show that MgAl-201 has superb applicability to neutral phosphate-contaminated waters. It reaches adsorption equilibrium within 270 min, and the maximum adsorption capacity calculated by the double Langmuir model is 52.0 mg/g. Meanwhile, MgAl-201 exhibits more preferable adsorption toward phosphate than D201 when coexisting anions are at relatively high levels. FTIR and XPS surveys revealed that two distinct adsorption interactions were involved in phosphate removal, that is, electrostatic interactions from the quaternary ammonium groups bonded on the host and the interlayer exchangeable anions in the encapsulated Mg/Al LDH, and specific inner-sphere complexation from the -OH groups in the Mg/Al LDH layers. For wastewater application, a satisfactory treatable volume of 580 BV was achieved to reduce the effluents from 2.0 mg/L to 0.5 mg/L, which was up to 8 times that of the traditional anion exchanger D201. Furthermore, MgAl-201 could be easily regenerated using the Na2CO3-NaCl binary solution and maintained good reusability without significant capacity loss after 5 adsorption-desorption cycles. The results suggest that MgAl-201 is of great application capability for preferable phosphate sequestration in advanced wastewater treatment.

Enhanced phosphate removal by using La-Zr binary metal oxide nanoparticles confined in millimeter-sized anion exchanger.

Phosphate removal plays a key role in alleviating the eutrophication of water bodies. Herein, a new bimetallic nanocomposite (La-Zr-D201) was prepared for enhanced phosphate removal by confining binary metal oxide (La-Zr) nanoparticles into the pores of a polymeric anion exchanger (D201). The encapsulated La-Zr oxides retain the specific sorption toward phosphate through ligand exchange. The host D201 provides satisfactory hydraulic properties and mechanical strength, and its macropores covalently bound positively charged ammonium groups could enhance nanoparticles dispersion and phosphate diffusion kinetics. Compared with the monometallic samples (La-D201, Zr-D201) and La-Zr loaded active carbon (La-Zr-AC), La-Zr-D201 possesses a higher adsorption capacity for its special structure and a stronger adsorption affinity toward phosphate. Phosphate removal on La-Zr-D201 was examined as a function of solution pH, reaction time, temperature, and competing anions, and the experiment results showed that the nanocomposite possessed superior phosphate adsorption capacity and selectivity. The underlying mechanism for the specific sorption and the stronger affinity of bimetallic adsorbents toward phosphate than monometallic ones were proved by XPS. Besides, column adsorption demonstrated 1350 BV of synthetic water (2 mg P-PO43-/L) could be treated efficiently by La-Zr-D201, while only 160 BV for the host D201. The binary NaOH-NaCl solution could effectively regenerate the spent adsorbents for repeated use. As a result, La-Zr-D201 possesses great potential in the application of enhanced phosphate removal from wastewater.

Preparation of molecular imprinted polymer based on attapulgite and evaluation of its performance for adsorption of benzoic acid in water.

In order to reduce the environmental impact of benzoic acid (BA), molecular imprinted polymers based on attapulgite were facilely prepared by molecular imprinted technique. The samples were characterized using scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermal gravimetric analysis. The adsorption performance, regeneration stability, and competitive selectivity of BA by benzoic acid-surface molecular imprinted polymers (BA-MIP) were systematically investigated by experiments. For this material, it has a high adsorption capacity of 41 mg/g and an equilibrium adsorption time of about 150 min. Compared with non-imprinted polymers, BA-MIP has a higher adsorption capacity for BA, and the dynamic adsorption behavior of BA by both of them conforms to the quasi-second-order kinetic model. The Langmuir adsorption isotherm equation was fitted the isothermal adsorption experiment. The thermodynamic analysis shows that the adsorption process is an exothermic reaction. The adsorption capacity of BA first increases and then decreases with an increase in pH, and the maximum adsorption capacity is reached at pH = 5. BA-MIP also has excellent selective adsorption capacity and regeneration stability for BA.

Synthesis and characterization of Ag-loaded p-type TiO2 for adsorption and photocatalytic degradation of tetrabromobisphenol A.

A p-type TiO2 with Ti vacancies (D-TiO2 ) was synthesized by a facile solvothermal treatment, and Ag/TiO2 with different Ag loading amount was prepared through a photo-reduction deposition method. The samples were characterized through scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The adsorption and photocatalytic characteristics of tetrabromobisphenol A (TBBPA) on D-TiO2 and Ag/TiO2 were investigated. The adsorption of TBBPA on Ag/TiO2 was significantly enhanced and was five times greater than that of pure TiO2 . The increase in pH significantly inhibited the adsorption of TBBPA. The 2%-Ag/TiO2 nearly completely degraded TBBPA in 10 min under UV-Vis light (λ > 360 nm), and the apparent reaction rate constant (kapp ) reached 0.63 min-1 . The significantly enhanced UV-Vis light catalytic properties of the Ag/TiO2 in comparison with that of TiO2 were attributed to the increased adsorption capacity and electron transfer ability of the Ag/TiO2 . Free radical trap experiments results showed that holes and superoxide radicals play a major role in the catalytic degradation of TBBPA by Ag/TiO2 . Moreover, the Ag/TiO2 catalyst exhibits high stability during TBBPA degradation even after three cycles. PRACTITIONER POINTS: Ti-defected TiO2 and Ag/TiO2 were synthesized using a solvothermal and photo-reduction deposition, respectively. Ag/TiO2 exhibited outstanding adsorption and photocatalytic activity for TBBPA removal under UV-Vis light. Holes and superoxide radicals play a major role in the photocatalytic degradation of TBBPA.

Selective and efficient sequestration of phosphate from waters using reusable nano-Zr(IV) oxide impregnated agricultural residue anion exchanger.

There is an urgent need to develop low-cost and effective adsorbents for enhanced removal of phosphate from contaminated waters. In this study, nanosized Zr(IV) oxide particles were immobilized on the amino modified corn staw (MCS) to fabricate a novel nanocomposite (Zr@MCS) with superior application capability. Compared with the widely used commercial anion exchangers in previous studies, the modified agricultural residue was empolyed as the host to avoid the high costs and secondary pollution in the preparation. Zr@MCS displayed remarkable selective removal of phosphate from water even in the presence of coexisting anions (Cl-, SO42-, NO3-) at high levels, as well as with a high adsorption capacity, fast adsorption kinetics and high availability in the wide range of pH 2-8 toward phosphate. The excellent adsorption performance of Zr@MCS is attributed to the synergistic effect of the electrostatic attraction of the quaternary ammonium groups fixed on the host skeleton and the specific adsorption of phosphate derived from the hydroxyl functional groups of Zr(IV) oxide. The exhausted Zr@MCS can be effectively regenerated by 5% NaOH-NaCl solution for sustainably utilized, and phosphorus in the desorption effluent could be recovered as high-quality struvite by a simple struvite recovery process. Furthermore, the considerable treatment volume for the synthetic solution and real wastewater in a fixed-bed flow system indicated that Zr@MCS is of great potential for phosphate removal in practice.

High adsorption performance for As(III) and As(V) onto novel aluminum-enriched biochar derived from abandoned Tetra Paks.

In order to develop promising sorbents for value-added application of solid wastes, low-cost aluminum-enriched biochar was prepared from abandoned Tetra Pak used to hold milks, a paper-polyethylence-Al foil laminated package box, after acid pretreatment and subsequent slow pyrolysis under an oxygen-limited environment at 600 °C. The basic physicochemical properties of the resultant biochar were characterized and the sorption performance of aqueous As(III) and As(V) was investigated via batch and column sorption experiments. Carbon (49.1%), Ca (7.41%) and Al (13.5%) were the most abundant elements in the resultant biochar; and the specific surface area and the pH value at the point of zero charge (pHPZC) were 174 m2 g-1 and 9.3, respectively. Batch sorption showed excellent sorption performance for both As(III) (24.2 mg g-1) and As(V) (33.2 mg g-1) and experimental data were fitted well with Langmuir model for the sorption isotherms and pseudo-second order kinetic model for the sorption kinetics. The residual concentrations of As(V) after sorption were below the limited value of arsenic in WHO Guidelines for Drinking water Quality (0.01 mg L-1) even if coexistence of PO43-. Column sorption confirmed the high sorption performance for As(III) and As(V). So the slow pyrolysis of abandoned Tetra Paks as low-cost and value-added sorbents is a sustainable strategy for solid waste disposal and wastewater treatment.

[Performance of Polymer-based Titanium and Zirconium Oxides Composite Adsorbent for Simultaneous Removal of Phosphorus and Fluorine from Water].

A novel composite adsorbent (Ti-Zr-D201) for simultaneous removal of phosphate and fluoride from water was prepared by loading nanosized titanium and zirconium oxides on the anion exchange resin named D201. Combining with the characterization of the adsorbent, adsorption isotherm experiments, effect of solution pH experiments, competitive tests, kinetic experiments and fixed bed column adsorption experiments were performed to explore the adsorption performance and mechanism. The maximum adsorption capacity of Ti-Zr-D201 for phosphorus and fluorine was 34.9mg·g-1 and 35.1mg·g-1 respectively, when the pH value was 5.8 and the temperature was 308K. Adsorption behavior was spontaneous, and higher temperature was favorable for phosphorus and fluoride adsorption. The effect of pH on the adsorption of fluoride was more significant compared with the adsorption of phosphorus. SO42-, NO3- and Cl- were selected as the competitive ions for competition experiments, and the results indicated that Ti-Zr-D201 exhibited favorable sorption selectivity for phosphorus and fluoride compared with the host material D201. The fitting results of the internal diffusion model showed that there were two different adsorption stages before the adsorption equilibrium of Ti-Zr-D201. Column adsorption experiments showed that Ti-Zr-D201 had a stable structure, excellent dynamic adsorption performance, and could be recycled, which showed the potential of practical application.

Antimony(V) removal from water by hydrated ferric oxides supported by calcite sand and polymeric anion exchanger.

We fabricated and characterized two hybrid adsorbents originated from hydrated ferric oxides (HFOs) using a polymeric anion exchanger D201 and calcite as host. The resultant adsorbents (denoted as HFO-201 and IOCCS) were employed for Sb(V) removal from water. Increasing solution pH from 3 to 9 apparently weakened Sb(V) removal by both composites, while increasing temperature from 293 to 313 K only improved Sb(V) uptake by IOCCS. HFO-201 exhibited much higher capacity for Sb(V) than for IOCCS in the absence of other anions in solution. Increasing ionic strength from 0.01 to 0.1 mol/L NaNO3 would result in a significant drop of the capacity of HFO-201 in the studied pH ranges; however, negligible effect was observed for IOCCS under similar conditions. Similarly, the competing chloride and sulfate pose more negative effect on Sb(V) adsorption by HFO-201 than by IOCCS, and the presence of silicate greatly decreased their adsorption simultaneously, while calcium ions were found to promote the adsorption of both adsorbents. XPS analysis further demonstrated that preferable Sb(V) adsorption by both hybrids was attributed to the inner sphere complexation of Sb(V) and HFO, and Ca(II) induced adsorption enhancement possibly resulted from the formation of HFO-Ca-Sb complexes. Column adsorption runs proved that Sb(V) in the synthetic water could be effectively removed from 30 microg/L to below 5 microg/L (the drinking water standard regulated by China), and the effective treatable volume of IOCCS was around 6 times as that of HFO-201, implying that HFO coatings onto calcite might be a more effective approach than immobilization inside D201.

New strategy to enhance phosphate removal from water by hydrous manganese oxide.

Hydrous manganese oxide (HMO) is generally negatively charged at circumneutral pH and cannot effectively remove anionic pollutants such as phosphate. Here we proposed a new strategy to enhance HMO-mediated phosphate removal by immobilizing nano-HMO within a polystyrene anion exchanger (NS). The resultant nanocomposite HMO@NS exhibited substantially enhanced phosphate removal in the presence of sulfate, chloride, and nitrate at greater levels. This is mainly attributed to the pHpzc shift from 6.2 for the bulky HMO to 10.5 for the capsulated HMO nanoparticles, where HMO nanoparticles are positively charged at neutral pH. The ammonium groups of NS also favor phosphate adsorption through the Donnan effect. Cyclic column adsorption experiment indicated that the fresh HMO@NS could treat 460 bed volumes (BV) of a synthetic influent (from the initial concentration of 2 mg P[PO4(3-)]/L to 0.5 mg P[PO4(3-)]/L), while only 80 BV for NS. After the first time of regeneration by NaOH-NaCl solution, the capacity of HMO@NS was lowered to ∼ 300 BV and then kept constant for the subsequent 5 runs, implying the presence of both the reversible and irreversible adsorption sites of nano-HMO. Additional column adsorption feeding with a real bioeffluent further validated great potential of HMO@NS in advanced wastewater treatment. This study may provide an alternative approach to expand the usability of other metal oxides in water treatment.

Adsorptive selenite removal from water using a nano-hydrated ferric oxides (HFOs)/polymer hybrid adsorbent.

Selenite (SeO(3)(2-)) is an oxyanion of environmental significance due to its toxicity when taken in excess. In the present study, a hybrid adsorbent (HFO-201) was prepared by irreversibly impregnating hydrated ferric oxide (HFO) nanoparticles within a commercial available anion-exchange resin (D-201), and its adsorption towards selenite from water was investigated in batch and column tests. HFO-201 exhibited improved sorption selectivity toward selenite as compared to the polymeric anion exchanger D-201. Two possible adsorption interactions were responsible for selenite removal by HFO-201, the electrostatic interaction from the ammonium groups bound to the D-201 matrix, and the formation of inner-sphere complexes between the loaded HFO nanoparticles and selenite. In a wide pH range (i.e., 3-8), increasing solution pH was found to result in a decrease of selenite removal on HFO-201. Adsorption isotherms fit the Freundlich model well, and selenite adsorption increased with increasing ambient temperature, indicating its endothermic nature. Column adsorption tests suggested that satisfactory removal of selenite from 2 mg/L to less than 0.01 mg/L could be achieved by HFO-201 even in the presence of the commonly encountered anionic competition at greater concentration, with the treatment capacity of approximately 1200 bed volume (BV) per run, while that for D-201 was only less than 30 BV under otherwise identical conditions. Furthermore, the exhausted HFO-201 was amenable to efficient in situ regeneration with a binary NaOH-NaCl solution.

Highly efficient removal of heavy metals by polymer-supported nanosized hydrated Fe(III) oxides: behavior and XPS study.

The present study developed a polymer-based hybrid sorbent (HFO-001) for highly efficient removal of heavy metals [e.g., Pb(II), Cd(II), and Cu(II)] by irreversibly impregnating hydrated Fe(III) oxide (HFO) nanoparticles within a cation-exchange resin D-001 (R-SO(3)Na), and revealed the underlying mechanism based on X-ray photoelectron spectroscopy (XPS) study. HFO-001 combines the excellent handling, flow characteristics, and attrition resistance of conventional cation-exchange resins with the specific affinity of HFOs toward heavy metal cations. As compared to D-001, sorption selectivity of HFO-001 toward Pb(II), Cu(II), and Cd(II) was greatly improved from the Ca(II) competition at greater concentration. Column sorption results indicated that the working capacity of HFO-001 was about 4-6 times more than D-001 with respect to removal of three heavy metals from simulated electroplating water (pH approximately 4.0). Also, HFO-001 is particularly effective in removing trace Pb(II) and Cd(II) from simulated natural waters to meet the drinking water standard, with treatment volume orders of magnitude higher than D-001. The superior performance of HFO-001 was attributed to the Donnan membrane effect exerted by the host D-001 as well as to the impregnated HFO nanoparticles of specific interaction toward heavy metal cations, as further confirmed by XPS study on lead sorption. More attractively, the exhausted HFO-001 beads can be effectively regenerated by HCl-NaCl solution (pH 3) for repeated use without any significant capacity loss.