Kinetic and thermodynamic studies on adsorption of Cu2+, Pb2+, methylene blue and malachite green from aqueous solution using AMPS-modified hazelnut shell powder

Fe3O4-lignin@Pd-NPs: A highly active, stable and broad-spectrum nanocomposite for water treatment

In this work, we report an environmentally friendly renewable nanocomposite magnetic lignin-based palladium nanoparticles (Fe3O4-lignin@Pd-NPs) for efficient wastewater treatment by decorating palladium nanoparticles without using any toxic reducing agents on the magnetic lignin abstracted from Poplar. The structure of composite Fe3O4-lignin@Pd-NPs was unambiguously confirmed by XRD, SEM, TEM, EDS, FTIR, and Zeta potential. After systematic evaluation of the use and efficiency of the composite to remove toxic organic dyes in wastewater, some promising results were observed as follows: Fe3O4-lignin@Pd-NPs exhibits highly active and efficient performance in the removal of toxic methylene blue (MB) (up to 99.8 %) wastewater in 2 min at different concentrations of MB and different pH values. Moreover, except for toxic MB, the other organic dyes including Rhodamine B (RhB), Rhodamine 6G (Rh6G), and Methyl Orange (MO) can also be removed efficiently by the composite. Finally, the easily recovered composite Fe3O4-lignin@Pd-NPs exhibits well stability and reusability, and catalytic efficiency is maintained well after ten cycles. In conclusion, the lignin-based magnetism Pd composite exhibits powerful potential practical application in industrial wastewater treatment.

Designed synthesis of multifunctional lignin-based adsorbent for efficient heavy metal ions removal and electromagnetic wave absorption

Multifunctional lignin-based adsorbents, which have shown great application prospect, have attracted widespread attention. Herein, a series of multifunctional lignin-based magnetic recyclable adsorbents were prepared from carboxymethylated lignin (CL), which was rich in carboxyl group (-COOH). After optimizing the mass ratio of CL to Fe₃O₄, the prepared CL/Fe₃O₄ (3:1) adsorbent showed efficient adsorption capacities for heavy metal ions. The kinetic and isotherm nonlinear fitting studies revealed that the adsorption process followed the second-order kinetic and Langmuir models, and the maximum adsorption capacities (Q_max) of CL/Fe₃O₄ (3:1) magnetic recyclable adsorbent for Pb²⁺, Cu²⁺ and Ni²⁺ ions reached 189.85, 124.43 and 106.97 mg/g, respectively. Meanwhile, after 6 cycles, the adsorption capacities of CL/Fe₃O₄ (3:1) for Pb²⁺, Cu²⁺ and Ni²⁺ ions could keep at 87.4 %, 83.4 % and 82.3 %, respectively. In addition, CL/Fe₃O₄ (3:1) also exhibited excellent electromagnetic wave absorption (EMWA) performance with a reflection loss (RL) of -28.65 dB at 6.96 GHz under the thickness of 4.5 mm, and its effective absorption bandwidth (EAB) achieved 2.24 GHz (6.08-8.32 GHz). In short, the prepared multifunctional CL/Fe₃O₄ (3:1) magnetic recyclable adsorbent with outstanding adsorption capacity for heavy metal ions and superior EMWA capability opens a new avenue for the diversified utilization of lignin and lignin-based adsorbent.

Application of diatomite for sorption of Pb, Cu, Cd and Zn from aqueous solutions: kinetic, thermodynamic studies and application of response surface methodology (RSM)

Contamination of water and soil with toxic metals is a serious environmental issue. To study the Pb, Cu, Cd, and Zn sorption behavior by diatomite, batch experiments were carried out with increasing levels of initial concentration (0-200 mg/L) under different contact times (0-360 min) and temperatures (283, 293, 303, and 313 K). The effects of concentration (0-200 mg/L), pH (3-6), and ionic strength (0.01-0.06 mol/L) on the sorption were modeled using response surface methodology (RSM). Results showed that adsorption data were well-fitted by the Langmuir equation. The sorption of metals intensified by increasing initial concentration and pH but ionic strength had inverse effect. High value for R² (0.99) and adjusted R² (0.99) showed that the removal of ions can be described by response surface method. One-way ANOVA showed (p-value < 0.0001) that quadratic model is the best model for determining the interaction of variables. The values of the sorption energy parameter from Dubinin-Radushkevich model (E < 8 kJ K^-1  mol^-1 ) and negative values of ∆G showed that the sorption of the metals was physical and spontaneous. The positive values of enthalpy (ΔH) indicated that the sorption reaction of metals was endothermic at 283-313 K. PRACTITIONER POINTS: Applications of diatomite increased the sorption of Pb, Cd, Zn, and Cu from aqueous solutions. Diatomite, as low-cost adsorbent, had significant potential to sorption of ions. The sorption of heavy metals by adsorbent intensified by increasing initial concentration and pH but ionic strength had inverse effect. High value for R² (0.99) and adj-R² (0.99) showed that removal of metals can be described by response surface method (RSM) and the initial concentration of metal was the most significant factor.

Design of magnetic nanoparticles with high magnetic separation efficiencies and durability for Cu2+ adsorption

Fe3O4@SiO2 core-shell structured nanoparticles are promising candidates for adsorption of heavy metal ions from waste water due to their high adsorption capacities and feasible recycling process. However, their practical applications have been hindered by the trade-off between the magnetic separation efficiency and durability. In this study, we demonstrate the preparation of amino-functionalized Fe3O4@SiO2 absorbents with both high magnetic separation efficiencies and durability in strong acidic environment. Our key strategy was to use a thin but highly protective silica layer by manipulating the sol-gel chemistry. With the protection of a thin but poorly permeable silica shell, the durability of the Fe3O4 in strong acid solution was significantly enhanced while its magnetic separation efficiency was maintained. We also demonstrated the adsorption of Cu2+ from aqueous solution corresponded well with the pseudo-second-order kinetic model and the Langmuir adsorption isotherm. The adsorption capacity can be further improved by coating an additional layer of mesoporous SiO2 outside Fe3O4@SiO2. The design of highly durable magnetic absorbents without sacrificing the magnetic separation efficiency greatly facilitates the practical applications of magnetic nanoparticles in adsorption of heavy metal ions.

Adsorption of Pb2+ from Aqueous Solutions Using Novel Functionalized Corncobs via Atom Transfer Radical Polymerization

The present study developed novel functionalized corncobs introducing brushes with dense and active carboxyl groups (-COOH), named MC-g-PAA, for the highly efficient adsorption of Pb2+ from aqueous solutions. MC-g-PAA were synthesized via atom transfer radical polymerization (ATRP) and characterized by Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The amount of Pb2+ adsorbed on MC-g-PAA by hydrolysis with t-BuOK was 2.28 times greater than that with NaOH, attributed to the larger steric effect of t-BuOK, which reduced the hydrolysis of the bromo-ester groups. The influence of different parameters including the solid/liquid ratio, working solution pH, sorption temperature, and initial concentration and sorption time on the adsorption of Pb2+ were investigated in detail in batch experiments. Thermodynamic studies have shown that the adsorption process was spontaneous, endothermic, and accompanied by an increase in randomness. A better fit for the isotherm data was obtained using the Langmuir model than for the other four models and the maximum amount ( q max ) of Pb2+ adsorbed on MC-g-PAA was 342.47 mg/g, which is 21.11 times greater when compared with that of pristine corncobs (16.22 mg/g). The adsorption of Pb2+ on MC-g-PAA was very fast and followed the pseudo-second-order kinetic equation with a correlation coefficient of 0.99999. This monolayer adsorption process was dominated by chemical adsorption, and may proceed according to complexation and electrostatic interactions between Pb2+ and the carboxylate groups. This study indicated that MC-g-PAA could be successfully used as an adsorbent for the removal of Pb2+ from aqueous solutions due to its excellent efficiency.