Manganese oxides have been proven to be promising adsorbents to capture Pb(II) from wastewaters. In nature, MnO2 can be found in different crystalline structures, while the effect of crystal structure on their adsorption performance remains unclear. In this study, five manganese oxides with different crystallographic phases, α-, β-, γ-, δ-, and λ-MnO2 were prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), N2 adsorption–desorption, Fourier transform infrared (FT-IR) spectroscopy and zeta potential measurements. The adsorptive removal of aqueous Pb(II) was investigated using these manganese oxides as adsorbents. The results showed that the adsorption capacities of manganese oxides for Pb(II) varied with BET surface area and crystalline structure, following the order of δ-MnO2 > α-MnO2 > λ-MnO2 > γ-MnO2 > β-MnO2. δ-MnO2 displayed the highest capacity for Pb(II), and the adsorption was scarcely influenced by the presence of the coexisting Na+ cation. The surface complexation model was used to describe the Pb(II) adsorption on the MnO2 adsorbents. In a column adsorption test δ-MnO2 was capable of continuously treating 25 000 bed volumes synthetic wastewater stream with an influent concentration of 20 mg L−1 Pb(II) and an effluent concentration below 0.5 mg L−1. This work indicates that δ-MnO2 has great potential to be used as an effective adsorbent for Pb(II) removal.

•Functionalized magnetic core–shell composite (MFC) by ZrO2 (MFC@ZrO2) was prepared.•MFC@ZrO2 showed markedly enhanced phosphate adsorption compared to MFC.•Phosphate adsorption on MFC@ZrO2 increased with ZrO2 deposition level.•MFC@ZrO2 exhibits high stability in eight consecutive adsorption–desorption cycles.Adsorptive removal of phosphate has been considered as one of the most effective methods to eliminate phosphate pollution in water. In the present study, a magnetic core–shell composite with a Fe3O4 core and a carbon shell (denoted as MFC) was prepared using the hydrothermal method, and was further functionalized by ZrO2 at varied deposition levels (denoted as MFC@ZrO2). Phosphate adsorption onto the sorbents was tested. The magnetic sorbents with varied ZrO2 contents were characterized using X-ray diffraction, vibration sample magnetometer, transition electron microscopy, zeta potential measurement, N2 adsorption/desorption, and X-ray photoelectron spectroscopy. Characterization results indicated that MFC@ZrO2 consisted of a magnetite core with particle sizes of 500–700 nm, covered by carbon and ZrO2 shells with respective shell thickness of about 10 and 20 nm. The resultant MFC@ZrO2 sorbents could be readily separated and recovered under an external magnetic field. Negligible phosphate adsorption was observed on MFC, while ZrO2 functionalization led to markedly enhanced phosphate adsorption, and phosphate adsorption amount was found to be positively correlated to ZrO2 deposition level. Phosphate adsorption on the sorbents could be well described using the Freundlich adsorption model, and phosphate adsorption kinetics followed the pseudo-second-order kinetics. Increasing pH suppressed phosphate adsorption, and phosphate adsorption slightly increased with ionic strength. After 3 adsorption–desorption cycles, the adsorbent displayed stable adsorption behavior within 5 consecutive regeneration cycles.

A novel amino-functionalized Fe3O4@SiO2 magnetic nanomaterial with a core–shell structure was developed, aiming to remove heavy metal ions from aqueous media. The structural, surface, and magnetic characteristics of the nanosized adsorbent were investigated by elemental analysis, FTIR, N2 adsorption–desorption, transmission electron microscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, vibrating sample magnetometry, thermogravimetric analysis, and zeta-potential measurement. The amino-functionalized Fe3O4@SiO2 nanoadsorbent exhibited high adsorption affinity for aqueous Cu(II), Pb(II), and Cd(II) ions, resulting from complexation of the metal ions by surface amino groups. Moreover, the adsorption affinity for heavy metal ions was not much impacted by the presence of a cosolute of humic acid (10.6 mg/L) or alkali/earth metal ions (Na+, K+, Mg2+) (0.025–0.30 mmol/L). The metal-loaded Fe3O4@SiO2–NH2 nanoparticles could be recovered readily from aqueous solution by magnetic separation and regenerated easily by acid treatment. Findings of the present work highlight the potential for using amino-functionalized Fe3O4@SiO2 magnetic nanoparticles as an effective and recyclable adsorbent for the removal of heavy metal ions in water and wastewater treatment.High adsorption capacity, sufficient stability, easy separation, and regeneration properties make amino-functionalized Fe3O4@SiO2 magnetic nanoparticles superior adsorbents for removal of heavy metal ions.

Nitrate and benzene are commonly identified contaminants in groundwater. In this study, a series of TiO2 supported Pt–Cu bimetallic catalysts were prepared and photocatalytic nitrate reduction in the presence of benzene was investigated. The catalysts were characterized by XRD, N2 adsorption, TEM, X-ray photoelectron spectroscopy and IR spectroscopy of CO adsorption. The results showed that Pt–Cu alloy was formed in TiO2 supported bimetallic catalysts except for the bimetallic catalyst with TiO2 calcined at 700 °C as the support. In addition, higher alloy dispersion and smaller metal particle sizes could be obtained on TiO2 calcined at 300 °C compared to those calcined at 500 and 700 °C. For photocatalytic nitrate reduction in the presence of benzene, nitrate was mainly converted to ammonia or nitrite over Pt/TiO2 or Cu/TiO2, respectively, whereas TiO2 supported Pt–Cu bimetallic catalysts exhibited a considerable N2 selectivity for photocatalytic nitrate reduction. The catalytic activity and N2 selectivity of the supported bimetallic catalyst was strongly dependent on TiO2 calcination temperature, Pt/Cu ratio and metal loading amount. The bimetallic catalyst with TiO2 calcined at 300 °C as the support, Pt loading amount of 5 wt.% and Pt/Cu ratio of 4/1 displayed higher N2 selectivity compared with other bimetallic catalysts. The present results demonstrate the selective nitrate reduction over Pt–Cu/TiO2 catalysts with benzene as the hole scavenger, highlighting the validity of simultaneous removal of aqueous nitrate and benzene by photocatalysis.

In this study, solid phase extraction (SPE) and ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) were utilized to develop a rapid, sensitive and reliable method for trace analysis of 21 antibiotics belonging to 7 classes in influent and effluent of municipal wastewater treatment plant. Detection parameters for SPE preconcentration and UPLC-MS/MS analysis were optimized, including sample pH, eluant, mobile phase (solvent and formic acid concentration), column temperature, and flow rate. Under the optimal conditions, the recoveries for different antibiotics ranged from 60.5% to 109.7% and all analytes were detected within 10.0 min by UPLC-MS/MS. The validation study indicated that the method detection limits (MDLs) for the 21 antibiotics were from 0.3 to 60.0 ng L−1 for effluent, while higher MDLs (0.5–84.0 ng L−1) for influent. Accuracy and precision for both within-run (−11.6 to 14.3% and 0.2 to 15.6%) and between-run tests (−7.2 to 8.7% and 1.9 to 16.4%) were acceptable. The analysis of influent and effluent samples of two municipal wastewater treatment plants in Hong Kong revealed the presence of 11 antibiotics, including ampicillin, cefalexin, sulfamethoxazole, sulfadiazine, norfloxacin, ciprofloxacin, ofloxacin, tetracycline, roxithromycin, erythromycin-H2O, and trimethoprim. Their concentration ranged from 3.5 to 720.0 ng L−1 in influent and from 2.1 to 556.4 ng L−1 in effluent.

•Micro- and mesoporous covalent triazine-based framework were prepared and used as adsorbent.•CTFDCBP shows dramatically enhanced bulky antibiotic tylosin adsorption and fast adsorption kinetics.•Shaped, open and wide pore size distribution is responsible for the high adsorption affinity/capacity.The exposures of pharmaceutical antibiotics in water solution caused potential risks for ecological environment and human health. In the present study, porous covalent triazine frameworks (CTFs) were synthesized and the adsorption behavior of sulfamethoxazole (SMX) and tylosin (TL) was investigated. The CTFs were characterized by X-ray diffraction, transform infrared and N2 adsorption/desorption. Sulfamethoxazole displayed much stronger adsorption than tylosin on microporous CTF-1 adsorbent due to the pore-filling effect. While the adsorption of bulky tylosin on microporous CTF-1 was suppressed because of the size exclusion effect. Additionally, the porous CTFDCBP showed stronger adsorption affinity and faster adsorption kinetics than other porous adsorbents, which was attributed to wide pore size distribution and open pore structure. Findings in this study highlight the potential of using porous CTFs as a potential adsorbent to eliminate antibiotics from water, especially for selective adsorption of bulky molecular pollutant.Pore size distributions of adsorbents before and after adsorption of SMX and TL. Compare two figures, CTFDCBP shows high selective adsorption and adsorption affinity for major molecular antibiotic tylosin.Download high-res image (199KB)Download full-size image

•Al2O3-pillared layered MnO2 (p-MnO2) was prepared from δ-MnO2 precursor.•p-MnO2 showed markedly higher Pb(II) adsorption capacity than pristine δ-MnO2..•Pillaring of Al2O3 into the layer of δ-MnO2 enhanced the Pb(II) adsorption.In the present study, Al2O3-pillared layered MnO2 (p-MnO2) was synthesized using δ-MnO2 as precursor and Pb(II) adsorption on p-MnO2 and δ-MnO2 was investigated. To clarify the adsorption mechanism, Al2O3 was also prepared as an additional sorbent. The adsorbents were characterized by X-ray fluorescence analysis, powder X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy and N2 adsorption-desorption. Results showed that in comparison with pristine δ-MnO2, Al2O3 pillaring led to increased BET surface area of 166.3 m2 g−1 and enlarged basal spacing of 0.85 nm. Accordingly, p-MnO2 exhibited a higher adsorption capacity of Pb(II) than δ-MnO2. The adsorption isotherms of Pb(II) on δ-MnO2 and Al2O3 pillar fitted well to the Freundlich model, while the adsorption isotherm of Pb(II) on p-MnO2 could be well described using a dual-adsorption model, attributed to Pb(II) adsorption on both δ-MnO2 and Al2O3. Additionally, Pb(II) adsorption on δ-MnO2 and p-MnO2 followed the pseudo second-order kinetics, and a lower adsorption rate was observed on p-MnO2 than δ-MnO2. The Pb(II) adsorption capacity of p-MnO2 increased with solution pH and co-existing cation concentration, and the presence of dissolved humic acid (10.2 mg L−1) did not markedly impact Pb(II) adsorption. p-MnO2 also displayed good adsorption capacities for aqueous Cu(II) and Cd(II). Findings in this study indicate that p-MnO2 could be used as a highly effective adsorbent for heavy metal ions removal in water.