Treatment of lead contaminated water by a PVDF membrane that is modified by zirconium, phosphate and PVA

Adsorption performance and mechanisms of Pb(II), Cd(II), and Mn(II) removal by a β-cyclodextrin derivative

In this study, the novel adsorbent PVA-TA-βCD was synthesized via thermal cross-linking between polyvinyl alcohol and β-cyclodextrin. The characterization methods SEM-EDS, FTIR, and XPS were adopted to characterize the adsorbent. The effect of pH, contact time, initial concentrations, and temperature during the adsorption of Pb(II), Cd(II), and Mn(II) onto the PVA-TA-βCD was also investigated. In a single-component system, the data fitted well to pseudo-second-order, and film diffusion and intra-particle diffusion both played important roles in the adsorption process. As for isotherm study, it showed a heterogeneous adsorption capacity of 199.11, 116.52, and 90.28 mg g^-1 for the Pb(II), Cd(II), and Mn(II), respectively. Competition between the ions existed in a multi-component system; however, owing to the stronger affinity of the PVA-TA-βCD for Pb(II) relative to Cd(II) and Mn(II), the Pb(II) adsorption onto the PVA-TA-βCD was less affected by the addition of the other metals, which could be effectively explained by the hard and soft acid and base theory (HSAB). Furthermore, PVA-TA-βCD showed good reusability throughout regeneration experiments.

Facile synthesis of ZrO2 coated BiOCl0.5I0.5 for photocatalytic oxidation-adsorption of As(III) under visible light irradiation

ZrO₂ modified BiOCl_0.5I_0.5 composites (ZBCI), synthesized via a facile precipitation method at room temperature, were utilized to photocatalytically oxidize and adsorb arsenite from water under visible light irradiation. The composites were well characterized by using various techniques. With visible light irradiation, 5 mg L^-1 of As(III) could be completely removed by ZBCI (0.25 g L^-1) in 90 min. Particularly, we found that ZBCI composites not only could oxidize As(III) into As(V) with visible light irradiation, but also could effectively capture the generated As(V), leading to the negligible residual As(III) or As(V) in aqueous solutions after 90 min treatment. In the fabricated composites, ZrO₂ acted as the main adsorption sites while BiOCl_0.5I_0.5 served as the primary photocatalysis center. Because of the heterostructure of ZBCI, e^- generated by BiOCl_0.5I_0.5 would be transferred to ZrO₂ and inhibited e^--h⁺ recombination rate, contributing to the improved photocatalytic efficiency. ZBCI could effectively remove As(III) over a broad range of pH from 3 to 11. Chloride and nitrate did not obviously affect the photocatalytic As(III) removal, while sulfate and phosphate yet reduced the capture of As(III). Moreover, ZBCI composites exhibited high photocatalytic As(III) removal efficiency during the fourth reused cycles. The facile synthesized ZBCI could be employed to capture and oxidize As(III) from water.

Efficient removal of nickel(II) from high salinity wastewater by a novel PAA/ZIF-8/PVDF hybrid ultrafiltration membrane

Enhanced removal of trace toxic metals (ppm level) from high-salinity wastewater is crucial to ensure water safety but still a challenging task. In this study, we fabricated a new hybrid ultrafiltration membrane (PAA/ZIF-8/PVDF) by immobilizing zeolitic imidazolate framework-8 (ZIF-8) particles onto the surface of trimesoyl chloride (TMC)-modified polyvinylidene fluoride (PVDF) membrane under protection of polyacrylic acid (PAA) layer. The resultant PAA/ZIF-8/PVDF membrane exhibited relatively high water flux of 460 L·m^-2 h^-1 and outstanding nickel ion (Ni(II)) capacity (219.09 mg/g) from a synthetic high-salinity ([Na⁺] = 15000 mg/L) wastewater. X-ray photoelectron spectroscopic studies revealed that preferable Ni(II) uptake was mainly attributed to the specific interaction between Ni(II) and hydroxyl groups on ZIF-8 frameworks and carboxyl groups in PAA layer as well. Compared to PAA, ZIF-8 could selectively bind Ni(II) with negligible effect exerted by concentrated sodium ion. The filtration study showed that the 12.56-cm² membrane could effectively treat 5.76 L high-salinity wastewater ([Ni(II)₀ = 2 mg/L, [Na⁺]₀ = 15000 mg/L) to conspicuously reduce Ni(II) below the maximum contaminant level of China, 0.1 mg/L. Moreover, the hybrid membrane could be regenerated by HCl-NaCl solution (pH = 5.5) for repeated use under direct current electric field. Generally speaking, the newly developed ZIF-8 hybrid ultrafiltration membrane showed a very promising potential in enhanced removal of toxic metals from high-salinity wastewater treatment.

Novel Cu(II)-EDTA Decomplexation by Discharge Plasma Oxidation and Coupled Cu Removal by Alkaline Precipitation: Underneath Mechanisms

Strong complexation between heavy metals and organic complexing agents makes the heavy metals difficult to be removed by classical chemical precipitation. In this study, a novel decomplexation method was developed using discharge plasma oxidation, which was followed by alkaline precipitation to treat water containing heavy metal-organic complex, that is, Cu-ethylenediaminetetraacetic acid (Cu-EDTA). The decomplexation efficiency of Cu complex reached up to nearly 100% after 60 min's oxidation by discharge plasma, which was accompanied by 82.1% of total organic carbon removal and energy efficiency of 0.62 g kWh^-1. Presence of free Cu²⁺ favored Cu-EDTA decomplexation, whereas the presence of excessive EDTA depressed this process. Cu-EDTA decomplexation was mainly driven by the produced ¹O₂, O₂^•-, O₃, and •OH by discharge plasma. Cu-EDTA decomplexation process was characterized by UV-vis, ATR-FTIR, total organic carbon, and three-dimensional fluorescence diagnosis. The main intermediates including Cu-EDDA, Cu-IDA, Cu-NTA, small organic acids, NH₄⁺, and NO₃^- were identified, accompanied by Cu²⁺ releasing. The followed precipitation process removed 78.1% of Cu²⁺, and Cu-associated precipitates included CuCO₃, Cu₂CO₃(OH)₂, CuO, and Cu(OH)₂. A possible pathway of Cu complex decomplexation and Cu²⁺ removal in such a system was proposed.

Dynamic filtration and static adsorption of lead ions in aqueous solution by use of blended polysulfone membranes with nano size MCM-41 particles coated by polyaniline

MCM-41 mesopore was prepared by hydrothermal method and used for synthesis of polyaniline/MCM-41 nanocomposite via in situ polymerization. The nanocomposite was blended with polysulfone to prepare mixed matrix membrane in different content of nanocomposite by phase inversion method. Structural and surface properties of the samples were characterized by SEM, XRD, FTIR, AFM, TGA, BET, and zeta potential measurements. Effect of the nanocomposite content on the hydrophilicity, porosity, and permeability of the membrane was determined. Membrane performance was evaluated for removal of lead ions in dynamic filtration and static adsorption. The membranes were found as effective adsorptive filters for removal of lead ions via interactions between active sites of nanocomposite in membrane structure and lead ions during filtration. Results of batch experiments proved adsorptive mechanism of membranes for removal of lead ions with the maximum adsorption capacity of 19.6 mg/g.

Progress and prospect of adsorptive removal of heavy metal ions from aqueous solution using metal-organic frameworks: A review of studies from the last decade

The efficient removal of heavy metals (HMs) from the environment has become an important issue from both biological and environmental perspectives. Recently, porous metal-organic frameworks (MOFs), combining central metals and organic ligands, have been proposed as promising materials in the capture of various toxic substances, including HMs, due to their unique characteristics. Here we review recent progress in the field of water remediation from the perspective of primary HMs (including divalent metals and variable-valent metals) in water pollution and the corresponding MOFs (including virgin and modified MOFs, magnetic MOFs composites and so on) that can remove these metals from water. The reported values of various MOFs for adsorption of heavy metal ions were 8.40-313 mg Pb(II) g^-1, 0.65-2173 mg Hg(II) g^-1, 3.63-145 mg Cd(II) g^-1, 14.0-127 mg Cr(III) g^-1, 15.4-145 mg Cr(VI) g^-1, 49.5-123 mg As(III) g^-1, and 12.3-303 mg As(V) g^-1. The main adsorption mechanisms associated with these processes are chemical (including coordination interaction, chemical bonding and acid-base interactions) and physical (including electrostatic interaction, diffusion and van der Waals force) adsorption, which were discussed in detailed. Further efforts should be made towards expanding the repertoire of MOFs that effectively remove multiple targeted HMs, as well as exploring possible applications of MOFs in the removal of HMs from non-aqueous environments.

Preparation and characterization of a novel hybrid chelating material for effective adsorption of Cu(II) and Pb(II)

The discharge of heavy metal ions such as Cu²⁺ and Pb²⁺ poses a severe threat to public health and the environment owing to their extreme toxicity and bioaccumulation through food chains. Herein, we report a novel organic-inorganic hybrid adsorbent, Al(OH)₃-poly(acrylamide-dimethyldiallylammonium chloride)-graft-dithiocarbamate (APD), for rapid and effective removal of Cu²⁺ and Pb²⁺. In this adsorbent, the "star-like" structure of Al(OH)₃-poly(acrylamide-dimethyldiallylammonium chloride) served as the support of dithiocarbamate (DTC) functional groups for easy access of heavy metal ions and assisted development of large and compact floccules. The synthesized adsorbent was characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and thermogravimetric analysis (TGA). APD was demonstrated to have rapid adsorption kinetics with an initial rate of 267.379 and 2569.373mg/(g·min) as well as superior adsorption capacities of 317.777 and 586.699mg/g for Cu²⁺ and Pb²⁺ respectively. The adsorption process was spontaneous and endothermic, involving intraparticle diffusion and chemical interaction between heavy metal ions and the functional groups of APD. To assess its versatility and wide applicability, APD was also used in turbid heavy metal wastewater, and performed well in removing suspended particles and heavy metal ions simultaneously through flocculation and chelation. The rapid, convenient and effective adsorption of Cu²⁺ and Pb²⁺ gives APD great potential for heavy metal decontamination in industrial applications.

A novel method for the sequential removal and separation of multiple heavy metals from wastewater

A novel method was developed and applied for the treatment of simulated wastewater containing multiple heavy metals. A sorbent of ZnS nanocrystals (NCs) was synthesized and showed extraordinary performance for the removal of Hg²⁺, Cu²⁺, Pb²⁺ and Cd²⁺. The removal efficiencies of Hg²⁺, Cu²⁺, Pb²⁺ and Cd²⁺ were 99.9%, 99.9%, 90.8% and 66.3%, respectively. Meanwhile, it was determined that solubility product (K_sp) of heavy metal sulfides was closely related to adsorption selectivity of various heavy metals on the sorbent. The removal efficiency of Hg²⁺ was higher than that of Cd²⁺, while the K_sp of HgS was lower than that of CdS. It indicated that preferential adsorption of heavy metals occurred when the K_sp of the heavy metal sulfide was lower. In addition, the differences in the K_sp of heavy metal sulfides allowed for the exchange of heavy metals, indicating the potential application for the sequential removal and separation of heavy metals from wastewater. According to the cumulative adsorption experimental results, multiple heavy metals were sequentially adsorbed and separated from the simulated wastewater in the order of the K_sp of their sulfides. This method holds the promise of sequentially removing and separating multiple heavy metals from wastewater.

Enhanced conversion and stability of biosynthetic selenium nanoparticles using fetal bovine serum

This study aimed to optimize biosynthetic selenium nanoparticles (BioSeNPs) synthesis using fetal bovine serum (FBS) as part of the culture medium to enhance the conversion efficiency and stability of BioSeNPs.