•A novel HAP membrane with sandwich structure for removal of organic micropollutants.•Tunable hydrophilicity and hydrophobicity of HAP membrane.•Much higher adsorption capacity than other adsorbents.•Application of HAP membrane in both aqueous and organic solutions.A biocompatible and uniquely defined hydroxyapatite (HAP) adsorption membrane with a sandwich structure was developed for the removal of organic micropollutants for the first time. Both the adsorption and membrane technique were used for the removal of organic micropollutants. The hydrophilicity and hydrophobicity of the HAP adsorbent and membrane were tunable by controlling the surface structure of HAP. The adsorption of organic micropollutants on the HAP adsorbent was studied in batch experiments. The adsorption process was fit with the Freundlich model, while the adsorption kinetics followed the pseudo-second-order model. The HAP membrane could remove organic micropollutants effectively by dynamic adsorption in both aqueous and ethanol solutions. The removal efficiencies of organic micropollutants depended on the solution composition, membrane thickness and hydrophilicity, flow rate, and the initial concentration of organic micropollutants. The adsorption capacities of the HAP membrane with a sandwich structure (membrane thickness was 0.3 mm) were 6700, 6510, 6310, 5960, 5490, 5230, 4980 and 4360 L m−2 for 1-naphthyl amine, 2-naphthol, bisphenol S, propranolol hydrochloride, metolachlor, ethinyl oestradiol, 2,4-dichlorophenol and bisphenol A, respectively, when the initial concentration was 3.0 mg L−1. The biocompatible HAP adsorption membrane can be easily regenerated by methanol and was thus demonstrated to be a novel concept for the removal of organic micropollutants from both aqueous and organic solutions.Download high-res image (465KB)Download full-size image

A biocompatible and novelly-defined adsorption membrane for rapid removal of fluoride was prepared. Both adsorption and membrane techniques were used in this research. Al(OH)3 nanoparticles modified hydroxyapatite (Al-HAP) nanowires were developed and made into Al-HAP membrane. The adsorption data of Al-HAP adsorbent could be well described by Freundlich isotherm model while the adsorption kinetic followed pseudo-second-order model. The maximum of adsorption capacity was 93.84 mg/g when the fluoride concentration was 200 mg/L. The adsorption mechanism was anion exchanges and electrostatic interactions. The contribution rates of HAP nanowires and Al(OH)3 nanoparticles in fluoride removal were 36.70% and 63.30%, respectively. The fixed-bed column test demonstrate that the Al-HAP was biocompatible and in a good stability during the process of water treatment. The fluoride removal abilities of Al-HAP membrane with 0.3 mm thickness could reach 1568 L/m2 when fluoride concentrations were 5 mg/L. This study indicated that the Al-HAP membrane could be developed into a very viable technology for highly effective removal of fluoride from drinking water.Download high-res image (118KB)Download full-size image

•A high-surface-area and porous β-CD polymer adsorbent is prepared.•Rapid adsorption of Pb, Cu and Cd (5 min) is realized.•High adsorption capacities for Pb (196.4 mg/g), Cu (164.4 mg/g), Cd (136.4 mg/g) are obtained.•The order of removal efficiencies in multi-component adsorption is Pb>Cu>Cd.•H+ ions exchange and electrostatic interactions work together in the adsorption.Removing heavy metals from aqueous solutions has drawn more and more attentions these years because of their serious global health challenge to human society. To develop an adsorbent with low-cost and high-efficiency for removal of heavy metals (HMs), β-cyclodextrin (β-CD) polymers crosslinked with rigid aromatic groups were prepared and used for lead (Pb), copper (Cu) and cadmium (Cd) removal for the first time. The negatively charged β-CD polymers with large BET surface area were suitable to be used in HMs adsorption. The adsorption process completed in 5 min was well fit by Freundlich isotherm model and pseudo-second-order model. The intraparticle diffusion model was also appropriate to describe the adsorption of Pb, Cu and Cd on β-CD polymer. The maximum of adsorption capacities at 25 °C for Pb, Cu and Cd were 196.42, 164.43 and 136.43 mg/g when the initial concentration was 200 mg/L. The HMs adsorption process on the surface of β-CD polymer was an endothermic and spontaneous process. Both of the electrostatic interaction and distribution of Pb, Cu and Cd species influenced the adsorption process at different pH values. The order of removal efficiencies in multi-component adsorption for the three metal ions were Pb > Cu > Cd. The adsorption mechanisms were H+ ions on hydroxyl groups exchanged with heavy metal ions and electrostatic interactions. This study indicated that β-CD polymers could be developed into effective adsorbents for rapid removal of heavy metals.Download high-res image (119KB)Download full-size image

A novel adsorbent, hydroxyl aluminum oxalate (HAO), for the high efficient removal of fluoride from aqueous solution was successfully synthesized. The adsorbent was characterized and its performance in fluoride (F−) removal was evaluated for the first time. Kinetic data reveal that the F− adsorption is rapid in the beginning followed by a slower adsorption process; 75.9% adsorption can be achieved within 1 min and only 16% additional removal occurred in the following 239 min. The F− adsorption kinetics was well described by the pseudo second-order kinetic model. The calculated adsorption capacity of this adsorbent for F− by Langmuir model was 400 mg g−1 at pH 6.5, which is one of the highest capabilities of today’s materials. The thermodynamic parameters calculated from the temperature-dependent isotherms indicate that the adsorption reaction of F− on the HAO is a spontaneous process. The FT-IR spectra of HAO before and after adsorbing F− show adsorption mechanism should be hydroxyl and oxalate interchange with F−.

A novelly-defined adsorption membrane for rapid removal of fluoride from drinking water was prepared. Both zirconium metal-organic frameworks (Zr-MOFs) adsorbent and membrane with large specific surface area of 740.28 m2/g were used for fluoride removal for the first time. For adsorption technique, fluoride adsorption on Zr-MOFs was studied on a batch mode. The adsorption data could be well described by Langmuir isotherm model while the adsorption kinetic followed pseudo-second-order model. The maximum of adsorption capacity was 102.40 mg/g at pH 7.0 when the initial fluoride concentration was 200 mg/L. The FT-IR and XPS analyses of Zr-MOFs revealed that both surface hydroxyl groups and Zr(IV) active sites played important roles in fluoride adsorption process. The as-prepared Zr-MOFs adsorbent was suitable for practical treatment of drinking water and regeneration by sodium hydroxide solution (3 wt%). For membrane experiments, Zr-MOFs membrane supported on Alumina substrate could remove fluoride efficiently through dynamic filtration. The fluoride removal capability of Zr-MOFs membrane depended on flow rate and initial concentration of fluoride. The fluoride removal abilities of Zr-MOFs membrane with 20 μm thickness could reach 5510, 5173, and 4664 L/m2 when fluoride concentrations were 5, 8 and 10 mg/L, respectively. This study indicated that Zr-MOFs membrane could be developed into a very viable technology for highly effective removal of fluoride from drinking water.

A new uniform-sized CeCO3OH nanosphere adsorbent was developed, and tested to establish its efficiency, using kinetic and thermodynamic studies, for fluoride removal. The results demonstrated that the CeCO3OH nanospheres exhibited much high adsorption capacities for fluoride anions due to electrostatic interactions and exchange of the carbonate and hydroxyl groups on the adsorbent surface with fluoride anions. Adsorption kinetics was fitted well by the pseudo-second-order model as compared to a pseudo-first-order rate expression, and adsorption isotherm data were well described by Langmuir model with max adsorption capacity of 45 mg/g at pH 7.0. Thermodynamic examination demonstrated that fluoride adsorption on the CeCO3OH nanospheres was reasonably endothermic and spontaneous. Moreover, the CeCO3OH nanospheres have less influence on adsorption of F− by pH and co-exiting ions, such as SO42−, Cl−, HCO3−, CO32−, NO3− and PO43−, and the adsorption efficiency is very high at the low initial fluoride concentrations in the basis of the equilibrium adsorption capacities. This study indicated that the CeCO3OH nanospheres could be developed into a very viable technology for highly effective removal of fluoride from drinking water.

•Porous MgO nanoplates were synthesized through a facile precursor calcination method.•The adsorption capacity for fluoride is larger than 185.5 mg g−1.•The porous MgO nanoplates can efficiently removal fluoride at a wide pH rang of 2–10.•A novel hydroxyl and carbonate co-exchange mechanism was reported.•The porous MgO nanoplates is quite stable during the fluoride removal process.Porous MgO nanoplates were successfully synthesized through a facile and cost-effective precursor calcination method. The as-prepared porous MgO nanoplates were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Brunauer–Emmett–Teller measurements. The fluoride removal performance of the porous MgO nanoplates has been investigated. The fluoride adsorption rate of the absorbent was very fast, and the adsorption kinetics could be fitted into a pseudo-second-order model. The adsorption isotherm can be well fitted in Freundlich model, while the adsorption capacity was over 185.5 mg/g at pH 7. Furthermore, the porous MgO nanoplates can efficiently remove fluoride from water in a wide pH range of 2–10, which is favorable for practical application. The effect of co-existing anions on fluoride removal also has been investigated. The result indicated that the existence of carbonate, bicarbonate and phosphate can influenced the fluoride adsorption performance. Furthermore, the fluoride adsorption mechanism was investigated by the FTIR and XPS analysis. The results show that both the hydroxyl and surface carbonates can exchange with fluoride ions, revealing a hydroxyl and carbonate co-exchange mechanism. Moreover, the as-prepared porous MgO nanoplates is quite stable, only less than 0.18% of the absorbent was dissolved during the adsorption experiment. The results indicated that the as-prepared porous MgO nanoplates can be used as a potential suitable candidate for fluoride removal.

A novel environment friendly adsorbent, micro–nano hierarchical structured flower-like MgO/MgCO3 (MHS-MgO/MgCO3), was developed for fluoride removal from water. The adsorbent was characterized and its defluoridation properties were investigated. Adsorption kinetics fitted well the pseudo-second-order model. Kinetic data revealed that the fluoride adsorption was rapid, more than 83–90% of fluoride could be removed within 30 min, and the adsorption equilibrium was achieved in the following 4 h. The fluoride adsorption isotherm was well described by Freundlich model. The maximum adsorption capacity was about 300 mg/g at pH = 7. Moreover, this adsorbent possessed a very wide available pH range of 5–11, and the fluoride removal efficiencies even reached up to 86.2%, 83.2% and 76.5% at pH = 11 for initial fluoride concentrations of 10, 20 and 30 mg/L, respectively. The effects of co-existing anions indicated that the anions had less effect on adsorption of fluoride except phosphate. In addition, the adsorption mechanism analysis revealed that the wide available pH range toward fluoride was mainly resulted from the exchange of the carbonate and hydroxyl groups on the surface of the MHS-MgO/MgCO3 with fluoride anions.

•The method enhances 1–2 orders of magnitude the signals of analyte in comparison to the traditional method.•All of the successive spectra can reflect the dynamics process of this dynamic-SERS method.•The method shows much better correlations between concentration and intensity.•The natural samples tests show that this dynamic-SERS method is capable of quantitative analysis.We report the use of Polystyrene/Ag (PS/Ag) nanoparticles as dynamic surface-enhanced Raman spectroscopy (dynamic-SERS) substrates for sensitive detection of low levels of organophosphorus pesticides. The PS particles clearly observed using Raman microscopy provide the masterplate for in situ growth of Ag NPs, leading to multiple active sites for SERS measurements. Besides obtaining the fingerprints of target molecules and recording time-resolved Raman spectra, this dynamic-SERS method can be used as an ultra-sensitive analytical technique which can enhance 1–2 orders of magnitude the signals of analytes in comparison to that of the traditional methods. On the other hand, importantly, it shows much better correlations between concentration and intensity than does the conventional SERS technique so that it can build the foundation for quantitative analysis of analytes. The as-prepared individual PS/Ag nanoparticle has been demonstrated for the sensitive detection of organophosphorus paraoxon and sumithion. SERS spectra are acquired at different concentrations of each pesticide and linear calibration curves are obtained by monitoring the strongest intensity value of bands arising from stronger stretching mode as a function of analyte concentration. The limits of detection and limits of quantitation are reported for two pesticides. The limit of detection for paraoxon is 96 nM (0.026 ppm) and for sumithion is 34 nM (0.011 ppm). The limits of quantitation are 152 nM (0.042 ppm) and 57 nM (0.016 ppm) for paraoxon and sumithion, respectively. It can be seen that these two organophosphorus pesticides can be detected in the low nM range based on this dynamic-SERS analytical method. Also, in the real sample experiments of paraoxon and sumithion, the results confirm that this dynamic-SERS technique would have potential applicability for quantitative analysis with slight interference.

Gold nanoparticles (AuNPs)/reduced graphene oxide (rGO) heterojunctions were synthesized directly on SiO2/Si substrates via a seed-assisted growth process. The in situ chemical fabrication strategy has been proven to be quite simple and efficient for generating highly active surface-enhanced Raman scattering (SERS) substrates due to synergistic enhanced protocol from rGO and AuNPs. The SERS substrates with AuNPs/rGO heterojunctions have been utilized for trace analysis of mercury(II) ions via thymine–Hg2+–thymine coordination. Thereby, very low limits of detection, i.e., 0.1 nM or 20 ppt for Hg2+, can be achieved in contrast with some other SERS subsrtates, which suggests that the heterojunctions are appropriate as versatile surface-enhanced substrates applied in chemical sensing or biosensing.Keywords: gold nanoparticles; heterojunctions; reduced graphene oxide; sensor; SERS;

A new adsorbent, Fe3O4 sulfonated magnetic nanoparticle (Fe3O4-SO3H MNP), was developed for heavy metal ions removal from water, which could be effectively separated from the solution owing to the superparamagnetic property. The nanoparticles can be used to remove heavy metal ions due to the additional active site, “sulfo-group”, introduced by the AMPS branches grafted onto the iron oxide. The as-synthesized materials were characterized by SEM, TEM, FT-IR and BET. The FTIR, XPS and Zeta potential were used to describe the adsorption mechanism. The Fe3O4-SO3H MNPs showed rapid removal for Pb2+ and Cd2+ with maximum of adsorption capacity of 108. 93 and 80.9 mg/g at 25 °C, respectively. The adsorption isotherms for Pb2+ and Cd2+ fitted better with Langmuir than Freundlich models, indicated that the processes of the removal of Pb2+ and Cd2+ could follow a kind of similar adsorption manner. The adsorption kinetic was consistent with pseudo-second-order model. Furthermore, the reuse experiments results showed the adsorbent might have potential in treating heavy metal ions pollution in water.Figure optionsDownload full-size imageDownload high-quality image (59 K)Download as PowerPoint slide