Preparation sulfhydryl functionalized paramagnetic Ni0.25Zn0.75Fe2O4 microspheres for separating Pb(II) and Hg(II) ions from aqueous solution

Synthesis of functional poly(amidoamine) dendrimer decorated apple residue cellulose for efficient removal of aqueous Hg(II)

Water pollution caused by Hg(II) exerts hazardous effect to the environment and public health. The design and fabrication of eco-friendly bioadsorbents for efficient removal of Hg(II) from aqueous solution is a promising strategy. Herein, a series of bioadsorbents were synthesized by the decoration of apple residue cellulose with different generation (G) Schiff base functionalized poly(amidoamine) (PAMAM) dendrimers (SA-G0/CE, SA-G1.0/CE and SA-G2.0/CE). The structures of SA-G0/CE, SA-G1.0/CE and SA-G2.0/CE were characterized and their adsorption performances were determined comprehensively by considering various factors. The maximum adsorption capacity of SA-G0/CE, SA-G1.0/CE and SA-G2.0/CE for Hg(II) are 1.18, 1.73 and 1.88 mmol·g^-1, respectively. The as-prepared bioadsorbents exhibit competitive adsorption capacity as compared with other reported adsorbents. Moreover, they exhibit remarkable adsorption selectivity toward Hg(II) with the coexistence of Ni(II), Cd(II), Mn(II), or Pb(II). The bioadsorbents display satisfactory adsorption performance in real water sample and can be reused with good regeneration property. Adsorption mechanism reveals that the functional groups of OH, -CONH-, CN and NC take part in the adsorption for Hg(II). The work not only opens a pathway to realize the reuse of apple residue, but also provides a promising strategy to construct efficient bioadsorbents for the decontamination of Hg(II) from aqueous solution.

Enhanced heavy metal removal from an aqueous environment using an eco-friendly and sustainable adsorbent

Thiol-lignocellulose sodium bentonite (TLSB) nanocomposites can effectively remove heavy metals from aqueous solutions. TLSB was formed by using -SH group-modified lignocellulose as a raw material, which was intercalated into the interlayers of hierarchical sodium bentonite. Characterization of TLSB was then performed with BET, FTIR, XRD, TGA, PZC, SEM, and TEM analyses. The results indicated that thiol-lignocellulose molecules may have different influences on the physicochemical properties of sodium bentonite, and an intercalated-exfoliated structure was successfully formed. The TLSB nanocomposite was subsequently investigated to validate its adsorption and desorption capacities for the zinc subgroup ions Zn(II), Cd(II) and Hg(II). The optimum adsorption parameters were determined based on the TLSB nanocomposite dosage, concentration of zinc subgroup ions, solution pH, adsorption temperature and adsorption time. The results revealed that the maximum adsorption capacity onto TLSB was 357.29 mg/g for Zn(II), 458.32 mg/g for Cd(II) and 208.12 mg/g for Hg(II). The adsorption kinetics were explained by the pseudo-second-order model, and the adsorption isotherm conformed to the Langmuir model, implying that the dominant chemical adsorption mechanism on TLSB is monolayer coverage. Thermodynamic studies suggested that the adsorption is spontaneous and endothermic. Desorption and regeneration experiments revealed that TLSB could be desorbed with HCl to recover Zn(II) and Cd(II) and with HNO3 to recover Hg(II) after several consecutive adsorption/desorption cycles. The adsorption mechanism was investigated through FTIR, EDX and SEM, which demonstrated that the introduction of thiol groups improved the adsorption capacity. All of these results suggested that TLSB is an eco-friendly and sustainable adsorbent for the extraction of Zn(II), Cd(II) and Hg(II) ions in aqueous media.

Surface functionalization of recycled polyacrylonitrile fibers with ethylenediamine for highly effective adsorption of Hg(II) from contaminated waters

In this research, recycled polyacrylonitrile fibers (PANFs) acquired from the textile recycling process were amino-functionalized in one simple step by means of ethylenediamine (EDA). The amino-functionalized polyacrylonitrile fibers (AF-PANFs) were utilized for adsorption of Hg(II) ions from aquatic media. Temperature and contact time during the synthesis were optimized by the Central Composite Design (CCD) method. FE-SEM, EDS, BET, and FT-IR analysis, and pH_ZPC measurement were conducted to characterize the features of the AF-PANFs. The average diameter of raw fiber was 20 μm, which increased 20 percent after functionalizing. The impact of independent parameters on the adsorption process was investigated using the Box-Behnken Design (BBD) method during the batch experiments. The column tests were conducted in a semi-continuous system with the removal efficiency of over 99% for various initial concentrations after specific cycles. Freundlich, Langmuir, UT, Redlich-Peterson, and Temkin isotherm models were employed to analyze the relation between the final concentration of Hg(II) (C_o) and the equilibrium adsorption capacity (q_e) of the AF-PANFs. According to the isotherm models and experimental results, the maximum q_e of the AF-PANFs was 1116 mg g^-1 at initial Hg(II) concentration of 850 mg L^-1, contact time of 120 min, solution pH of 6, and at 40 °C. Kinetic and thermodynamic studies illustrated the approximate equilibrium time and endothermicity or exothermicity of the process. Regeneration of the AF-PANFs was accomplished for seven times without efficiency drop. The superb performance of the AF-PANFs in the presence of co-existing ions did not decline.

Microwave-Assisted Rapid Synthesis of Reduced Graphene Oxide-Based Gum Tragacanth Hydrogel Nanocomposite for Heavy Metal Ions Adsorption

Reduced graphene oxide (RGO) was synthesized in this research via Tour's method for the use of filler in the hydrogel matrix. The copolymerization of N,N-dimethylacrylamide (DMA) onto the gum tragacanth (GT) was carried out to develop gum tragacanth-cl-N,N-dimethylacrylamide (GT-cl-poly(DMA)) hydrogel using N,N'-methylenebisacrylamide (NMBA) and potassium persulfate (KPS) as cross-linker and initiator correspondingly. The various GT-cl-poly(DMA) hydrogel synthesis parameters were optimized to achieve maximum swelling of GT-cl-poly(DMA) hydrogel. The optimized GT-cl-poly(DMA) hydrogel was then filled with RGO to form reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide (GT-cl-poly(DMA)/RGO) hydrogel composite. The synthesized samples were used for competent adsorption of Hg²⁺ and Cr⁶⁺ ions. Fourier transform infrared, X-ray powder diffraction, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy were used to characterize the gum tragacanth-cl-N,N-dimethylacrylamide hydrogel and reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide hydrogel composite. The experiments of adsorption-desorption cycles for Hg²⁺ and Cr⁶⁺ ions were carried out to perform the reusability of gum tragacanth-cl-N,N-dimethylacrylamide hydrogel and reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide hydrogel composite. From these two samples, reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide exhibited high adsorption ability. The Hg²⁺ and Cr⁶⁺ ions adsorption by gum tragacanth-cl-N,N-dimethylacrylamide and reduced graphene oxide incorporated gum tragacanth-cl-N,N-dimethylacrylamide were best suited for pseudo-second-order kinetics and Langmuir isotherm. The reported maximum Hg²⁺ and Cr⁶⁺ ions adsorption capacities were 666.6 mg g^-1 and 473.9 mg g^-1 respectively.